5 Must-Have Features in a RIELLO Ultra-Low Nitrogen Burners

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• 2. FORCED DRAUGHT BURNER HANDBOOK S e p t e m b e r 2 0 0 1 First Edition RIELLO S.p.A. Legnago - Italy Boilersinfo.com
• 3. © RIELLO S.p.A. - LEGNAGO Rights for translation, electronic memorization, reproduction and total or partial adaptment with every mean (included photostatic copies or microfilms) are reserved. First edition: September Boilersinfo.com
• 4. 1 FUNDAMENTAL COMBUSTION PRINCIPLES 13 1.1. Basic reactions 13 1.2. The combustion supporter 13 1.3. The combustion supporter 14 1.3.1. Gaseous fuels and their combustion 16 1.3.2. Liquid fuels and their combustion 21 1.4. Pollutant combustion emissions 21 1.4.1. Sulphur oxides 22 1.4.2. Nitric oxides 22 1.4.2.1. Reduction of the NOx in gaseous fuel combustion 23 1.4.2.2. Reduction of the NOx in liquid fuel combustion 25 1.4.3. Carbon monoxide (CO) 25 1.4.4. Total suspended particles 26 1.4.5. Comments on the emission of CO2 27 1.5. Combustion control 27 1.5.1. Combustion efficiency 29 1.5.2. Measurement units for combustion emissions 29 2 THE FORCED DRAUGHT BURNER 31 2.1 Foreword 31 2.2 The firing range of a burner 32 2.3 Typical system layout diagrams 35 2.3.1 System engineering diagrams for fired burners 36 2.3.2 System engineering diagrams for burners using low viscosity (< 6 cSt) liquid fuels - diesel oil / kerosene 36 2.3.3 System engineering diagrams for burners using high viscosity (> 6 cSt) liquid fuels 37 2.3.4 Diagrams for the calibration of single-stage burners 38 2.3.5 Diagrams for the calibration of multi-stage burners 39 2.3.6 Diagrams for the calibration of modulating burners 39 2.3.7 Diagram of burner with measurement and regulation of the percentage of O2 in the flue gases 40 2.3.8 Diagram of burner with pre-heating of the combustion supporter air 40 2.3.9 Diagram of burner with inverter controlled motors 41 2.3.10 Layout of the Burner Management -System 41 2.4 The Combustion head 42 2.4.1 Pressure drop air side 43 2.4.2 Pressure drop fuel side 43 2.5 The Fan 44 2.5.1 Regulating combustion air 46 SUMMARY Boilersinfo.com
• 5. 2.6 Fuel supply 48 2.6.1 Gas supply 48 2.6.1.1 Calculating the fuel gas supply pipelines 50 2.6.1.2 Choosing the gas train 52 2.6.1.3 The feeding of liquid petroleum gases (LPG) 53 2.6.2 Feeding diesel oil and kerosene 55 2.6.2.1 Drop-type system with supply from bottom / drop-type system with supply from summit / intake type system; 56 2.6.2.2 Systems with pressurised ring 57 2.6.3 Feeding of heavy oil (fuel oil) 61 2.6.3.1 Ring-type systems for multi-stage burners with or without service tanks (type 1-3) 62 2.6.3.2 Ring-type systems for modulating burners with or without service tanks 66 2.6.3.3 Heating the pipelines 67 2.6.3.4 Heating the storage tanks 70 2.7 Electrical supply and burner control 71 2.8 Noise levels in forced draught burners 74 2.8.1 Deadening noise made by forced draught burners 77 2.9 Optimising combustion with forced draught burners 78 2.9.1 Regulating the O2 78 2.9.2 Pre-heating the combustion supporter air 80 2.9.3 Regulating the fan speed 80 2.9.4 The Burner Management System 81 3 SELECTION OF A FORCED DRAUGHT BURNER 83 3.1 General criteria 83 3.1.1 Thermal capacity at the heat generator furnace 83 3.1.2 Back pressure in the combustion chamber 85 3.1.3 Type of heat generator 85 3.1.4 Fuel 86 3.1.5 Burner operation mode 86 3.1.6 Minimum feed pressure of gaseous fuel 86 3.1.7 Installation altitude and average combustion air temperature 86 3.1.8 Special installation features 87 3.2 Selection of a monobloc burner - numeric example 87 3.2.1 Selection of the burner model 87 3.2.2 Selection of the combustion head length 91 3.2.3 Verifying the flame length 91 3.2.4 Selection of the gas train 92 3.2.5 Selection of the components for the diesel oil feed circuit 93 3.3 Selection of a DUALBLOC burner - numeric example 94 3.3.1 Selection of the burner model 94 3.3.2 Selection of the burner model 96 3.3.3 Selection of the gas train 100 3.3.4 Selection of the thrust unit for liquid fuel and the nozzles 102 3.3.5 Selection of the components in the liquid fuel feed circuit 104 SUMMARY Boilersinfo.com
• 6. 3.3.5.1 Transfer pump between the storage tank and the service tank 105 3.3.5.2 Service tank 105 3.3.5.3 Pump in the main ring 105 3.3.5.4 Dimensioning the main ring pipelines 106 3.3.6 Selection of the electrical control panel 107 4 MEASURING COMBUSTION EFFICIENCY 109 4.1 Instruments 109 4.2 Preliminary operations 109 4.2.1 Systems fired by liquid fuel 109 4.2.2 Systems fired by gaseous fuel 109 4.3 Measurement conditions and operating methods 110 4.4 Calculating the combustion efficiency 111 4.4.1 Example for calculating combustion efficiency 111 5 READY-USE TABLES AND DIAGRAMS 115 5.1 Measuring units and conversion factors 115 5.2 Tables and diagrams about fuel viscosity 129 5.3 Tables and diagrams for circuits dimensioning 134 5.4 Tables and diagrams about combustion 156 SUMMARY Boilersinfo.com
• 7. SUMMARY OF DIAGRAMS 1 FUNDAMENTAL COMBUSTION PRINCIPLES 13 Diagram 1 - Elementary representation of a flame 13 Diagram 2 - Temperature and altitude influence on effective air delivery 14 Diagram 3 - Example of a viscosimeter 16 Diagram 4 - Formation process of acid rain 22 Diagram 5 - Type of NOx in certain fuels 23 Diagram 6 - Functional layout of combustion process for a gas burner - Blue flame type 24 Diagram 7 - Monobloc burner (light oil - Low NOx) of BGK series 25 Diagram 8 - Effects of carbon monoxide 25 Diagram 9 - Penetration of the particles in the respiratory system 26 Diagram 10 - Combustion triangle for methane gas 28 2 THE FORCED DRAUGHT BURNER 31 Diagram 11 - Gas fired monobloc burner 31 Diagram 12 - Burners operating chances: a) one-stage, b) two-stage, c) progressive two-stage, d) modulating 32 Diagram 13 - Layout of two monobloc (RL and RS series) burners and dual bloc (TI) burner 33 Diagram 14 - Firing ranges of Riello RLS series dual fuel burners 34 Diagram 15 - Test combustion chamber for burners 34 Diagram 16 - Firing range of Riello RLS100- two stage gas/light oil burner 35 Diagram 17 - Firing range for Riello TI Series Burner combustion heads 35 Diagram 18 - Gas supply - low pressure circuit 36 Diagram 19 - Gas supply - high pressure circuit 36 Diagram 20 - A=Drop-type plant with fedding from top; B=air intake system 36 Diagram 21 - Drop-type plant with feeding from bottom 36 Diagram 22 - System with ring under pressure 37 Diagram 23 - Ring-type system for multi-stage and modulating burners with service tank 37 Diagram 24 - Ring-type system for multi-stage and modulating burners without service tank 38 Diagram 25 - Layout of regulation components for a single-stage burner 38 Diagram 26 - Layout of regulation components for a two-stage burner 39 Diagram 27 - Layout of regulation components for a modulating burner 39 Diagram 28 - Layout of O2 regulation system 40 Diagram 29 - Layout of a system with pre-heating of comburent air 40 Diagram 30 - Layout of the fan speed rotation regulation with inverter 41 Diagram 31 - Layout of integrated management for supervising a combustion system 41 Diagram 32 - Nozzles: full cone and empty cone distribution; definition of spray angle 42 Diagram 33 - Drawing of composition of combustion head for gas/light oil Riello RLS 100 burner 42 Diagram 34 - Pressure drop air side in combustion head - dualbloc TI 10 burner 43 Diagram 35 - Pressure drop gas side in combustion head - dualbloc TI 10 burner 43 Diagram 36 - Feed pressure of liquid fuel 44 Diagram 37 - Fan of a dualbloc burner 44 Diagram 38 - Output absorbed from different types of fan varying delivery 44 Diagram 39 - Typical performance graphs of a centrifugal fan 45 Diagram 40 - Fan performance graphs on varying motor speed rotation 45 Diagram 41 - Performance graph of fan and resistant circuit with working point 45 Diagram 42 - Moody's abacus 47 Diagram 43 - Adimensional loss factors for air pipelines 47 Diagram 44 - Change of delivery by varying pressure drops of the circuit 48 Boilersinfo.com
• 8. Diagram 45 - Example of delivery changing by motor speed variation 48 Diagram 46 - Functional layout of the gas train 49 Diagram 47 - Gas filter 49 Diagram 48 - Pressure Regulator 49 Diagram 49 - Shut-off and safety valves 50 Diagram 50 - Gas pressure switch 50 Diagram 51 - Seal control system 50 Diagram 52 - Connection adaptor 50 Diagram 53 - Absolute viscosity of certain gases 51 Diagram 54 - LPG tank 53 Diagram 55 - Graph for the detrmination of the gas train 53 Diagram 56 - Shut-off solenoid valve on output circuit - close postition 55 Diagram 57 - Gear pump for liquid fule monobloc burner 55 Diagram 58 - Light oil burner feeding 56 Diagram 59 - Moody's abacus 60 Diagram 60 - Pressure regulating valve 60 Diagram 61 - Heavy oil preheating unit 61 Diagram 62 - Pumps for fuel oil 62 Diagram 63 - Service tank 63 Diagram 64 - Ring pressure - advised values 67 Diagram 65 - Self-regulating heating band 69 Diagram 66 - Turns' step for heating bands 69 Diagram 67 - Electrical layout of a monobloc burner with single-phase electrical power supply 71 Diagram 68 - Electrical layout of a monobloc burner with three phase power supply 71 Diagram 69 - Firing sequence of a methane gas burner 72 Diagram 70 - Diagram of the main components required for combustion control and regulation 72 Diagram 71 - Programming of the regulation temperatures for a two-stage burner 73 Diagram 72 - Electrical layout of a modulating burner with control devices 74 Diagram 73 - Isophonic curves 75 Diagram 74 - Weighted curves 76 Diagram 75 - Blimp for air blown burners 78 Diagram 76 - Reference values of the oxygen content in flue gases for a gas burner 79 Diagram 77 - Loss of the flue gases for different % of O2 80 Diagram 78 - Diagram for the evaluation of the energy saving by means of the inverter 81 Diagram 79 - Conceptual representation of a Burner Management System 82 Diagram 80 - Electrical power absorption with O2 regulation and inverter 82 3 SELECTION OF A FORCED DRAUGHT BURNER 83 Diagram 81 - Combustion chamber backpressure in relation to thermal output 85 Diagram 82 - Reverse flame boiler 85 Diagram 83 - Serpentine boiler 85 Diagram 84 - Fixing of the blast tube to the boiler port 86 Diagram 85 - Dual fuel (light oil-gas) burner of RLS series 88 Diagram 86 - Combustion head 91 Diagram 87 - Hot water boiler constructive layout 91 Diagram 88 - Lenght and diameter of the flame in relation to burner output 92 Diagram 89 - Diagram for selection of gas trains 93 Diagram 90 - Layout of a light oil feeding circuit 94 Diagram 91 - Dualbloc burner of TI series 94 SUMMARY OF DIAGRAMS Boilersinfo.com
• 9. Diagram 92 - Firing ranges for Riello TI Series of burner combustion heads 97 Diagram 93 - Combustion head pressure drops for TI series - air side 98 Diagram 94 - Pressure drops in circular pipelines 99 Diagram 95 - Performence graphs of GBJ fan series 100 Diagram 96 - Combustion head and butterfly valve pressure drops for TI series - gas side 101 Diagram 97 - Pressure drops in DMV safety valves 101 Diagram 98 - Nozzles delivery for modulating burners 103 Diagram 99 - Layout of a heavy oil feeding circuit 104 4 MEASURING COMBUSTION EFFICIENCY 109 Diagram 100 - Example of analyzer for measuring combustion efficiency 109 Diagram 101 - Gas flow characteristics measuring points 110 SUMMARY OF DIAGRAMS Boilersinfo.com
• 10. 1 FUNDAMENTAL COMBUSTION PRINCIPLES 13 Table 1 - Principal fuels classification 14 Table 2 - Characteistics of gaseous fuels 18 Table 3 - Names of liquid fuels in the main countries of use 19 Table 4 - Characteistics of liquid fuels 20 Table 5 - Maximum reccomended values of CO2 for the various fuels 28 Table 6 - Factors for calculation of the combustion efficiency 29 Table 7 - Mass equivalence of ppm of the main pollutant emissions 29 Table 8 - Maximum values of CO2 at 0% and at 3% of O2 for different fuels 30 2 THE FORCED DRAUGHT BURNER 31 Table 9 - Characteristic values of the absolute texture of different pipelines types 46 Table 10 - Maximum pressure drops of gas pipelines 51 Table 11 - Values of the equivalent lenghts of special pieces 52 Table 12 - Example for the tabular calculation of the diameter of the gas pipelines 52 Table 13 - Summary of liquid fuels 56 Table 14 - Schedule for the tabular scaling of the light oil feed pipelines 57 Table 15 - Absolute texture of the pipelines 59 Table 16 - Summary of liquid fuels 61 Table 17 - Typical values of sound power 74 Table 18 - Average values of sound pressure 75 Table 19 - Octave frequency band spectrum 76 Table 20 - Absorption factors of certain materials 77 3 SELECTION OF A FORCED DRAUGHT BURNER 83 Table 21 - Chart of the data required for a combustion system selection 84 Table 22 - F - correction factor of discharge head and delivery in relation to temperature and altitude 88 Table 23 - Example of backpressure reduction for a burner 88 Table 24 - Chart of the data required for a combustion system selection - example 89 Table 25 - Technical data of RLS series of monoblock burners 90 Table 26 - Iterative process table 90 Table 27 - Schedule for the tabular scaling of the light oil feed pipelines 94 Table 28 - Chart of the data required for a combustion system selection - example 95 Table 29 - Technical data of TI series 96 Table 30 - Kc - correction factor of discharge head and delivery in relation to temperature and altitude 98 Table 31 - Fans selection table 99 Table 32 - Nominal output declassing factor in relation to temperature and altitude 100 Table 33 - High pressure regulating/reducing units selection table 102 Table 34 - Pumping unit skids selection table 102 Table 35 - Nozzles selection table 103 Table 36 - Control panels selection table 107 4 MEASURING COMBUSTION EFFICIENCY 109 Table 37 - Coefficients for calculation of combustion efficiency 111 SUMMARY OF TABLES Boilersinfo.com
• 11. 11 PREFACE With these pages, there has been the intention of collecting, in an only volume, formulas, data and information useful for who faces problems whom solution involves understanding of combustion and systems which use forced draught burners for heating production. The text is divided up into five sections, arranged in logical sequence that permits the reader to first of all achieve the theoretical fundamentals of the chemistry-physics of combustion and the manufacturing technique of burners and systems which are closely linked, such as fuel feeding circuits. Proceeding through the manual, the reader will find examples for the selection and dimensioning of different types of burners and procedures for measuring the combustion efficiency. The last section is dedicated to a collection of ready-use tables and diagrams concerning the specific themes of combustion. The single chapters can be consulted separately in order to gain knowledge of the specific procedures and information required for the activities to be performed. The topics dealt underlie, before legislation, technical-scientific laws; for this reason, legislation is quoted only in cases of strict necessity. Each reader must therefore check the consistency of the information contained herein with current legislation in his own country. With this handbook, Riello wishes to make available an instrument practical and useful, without claiming to have completely dealt theoretical and installation apsects related to the argument of combustion systems. Published from: RIELLO S.p.A. Legnago - Italy Boilersinfo.com
• 12. 13 1.1 BASIC REACTIONS Combustion is the rapid oxidation of a fuel. The reaction is accompanied by that visible physical phenomenon which is called “flame” and by the generation of energy that is known as “heat”. Carbon combines with oxygen to form carbon dioxide, a non-toxic gas, and releases heat according to the following formula: C + O2 → CO2 + Heat Likewise, hydrogen combines with oxygen to form water vapour, with the consequent production of heat, according to the following formula: 2H2 + O2 → 2H2 O + Heat It is important to note that fuel and oxygen combine in well-defined and specific proportions. The quantities of oxygen and fuels in the mixture are in perfect or “stoichiometric” proportion, when they enable complete oxidation of the fuel without any oxygen residue. If there were excess fuel or insufficient oxygen, we would say the mixture was rich and the flame was reducing. This type of combustion is defined as incomplete because, although certain fuel particles are completely oxidised by the oxygen, others do not receive enough oxygen and consequently their combustion is only partial. As the following reaction formula indicates, partial or incomplete carbon combustion is accompanied by the formation of carbon monoxide, a highly toxic gas: 2C + O2 → 2CO + Heat The amount of heat produced here is lower than that which accompanies perfect combustion. Incomplete or reducing combustion is sometimes required in special industrial, thermal treatments, but these conditions must be avoided under any other circumstances. If, on the other hand, excessive oxygen is supplied to the mixture, we say the mixture is weak and combustion is oxidative. Besides carbon dioxide and water vapour, other compounds are produced during combustion in smaller amounts, such as sulphur oxides, nitric oxides, carbon monoxide and metallic oxides, which are dealt with further on. 1.2 THE COMBUSTION SUPPORTER The oxidative gas normally used is air, which is a gas mixture mainly made up of oxygen and nitrogen. If we know the exact chemical composition of the fuel we can calculate the stoichiometric amount of oxygen and consequently the combustion supporter air required for combustion purposes. The expression that provides the amount of stoichiometric air is as follows: Wa = 11,51·C + 34,28·H + 4,31·S – 4,32·O [kgair/kgfuel]; oppure: Wa = 8,88·C + 26,44·H + 3,33·S – 3,33·O [Nm3 air/kgfuel]; where C, H, S and O are respectively the mass percentages of carbon, hydrogen, sulphur and oxygen pertaining to the fuel composition. In tables 2 and 3, the stoichiometric air amounts are illustrated of several fuels. When “excess air” is used, i.e. an amount of oxygen higher than the stoichiometric amount, all the nitrogen and the portion of oxygen FUNDAMENTAL COMBUSTION PRINCIPLES 1 Diagram 1 Elementary representation of a flame Boilersinfo.com
• 13. 14 which does not combine with the fuel, do not participate in the oxidation reaction. Naturally, they absorb a certain amount of the heat produced during combustion, therefore the effective calorific energy is distributed over a greater volume of gas and the thermal level is lower (lower flame temperature). The amount of oxygen contained in the air is around 21% in volume and approximately 23% in mass. However, these values are not fixed but vary in relation to altitude and temperature. The variations in oxygen concentrations in the air are due to the fact that heating the combustion supporter air and an increase in altitude produce the same effect, i.e. a reduction in air density. A decrease in air density corresponds to a decrease in the amount of oxygen. At 1,000 metres above sea level, air density is nearly 10% lower than at 0 metres above sea level. The change in air density and, consequently, in the amount of oxygen, due to a considerable change in altitude or temperature with respect to normal conditions (height equal to 100 metres above sea level and a combustion supporter air temperature of 15°C), is a parameter which should not be overlooked, as is better illustrated in section 2 in the paragraph relating to the examples for choosing the burner. In certain conditions, for example when machinery is being used or other sources that create large amounts of humidity and steam, the amount of oxygen in the air could change, generally decreasing as relative humidity increases. The presence of dust, fibres in the intake combustion supporter air could also create problems with the combustion system. 1.3 THE FUELS A fuel is a substance which reacts with the oxygen in the air and gives rise to a chemical reaction with the consequent development of thermal energy and a small amount of electromagnetic energy (light), mechanical energy (noise) and electrical energy (ions and free electrons). Fuels can be classified on the basis of the physical state in which they are commonly found (solid, liquid or gaseous) and their nature (they are defined as natural or artificial fuels or derivatives). The most commonly used fuels are classified in table 1 according to the above two criteria. Natural fuels are concentrated in underground deposits from where they are extracted for Phase Provenance Natural Artificial (derivates) SOLID Wood, fossil carbons (pit coal) Coke, charcoal LIQUID Oil Petrol, kerosene, gasolio, feul oil GASEOUS Natural gas Methane, propane, butane, LPG, propane-air mix, town gas, bio-gas Diagram 2 Temperature and altitude influence on effective air delivery Table 1 Principal fuels classification m a.s.l. 5°C Qair = 10,67 mc/h 0 m a.s.l. 5°C Qair = 9,49 mc/h m a.s.l. 20°C Qair = 11,28 mc/h 0 m a.s.l. 20°C Qair = 10 mc/h Boilersinfo.com
• 14. 15 extracted from the flue gases produced by combustion, using a user machine that condenses the discharge gases. On the other hand, NCV indicates the maximum theoretical amount of heat that can be extracted from the flue gases produced by combustion using a user machine that does not condense the discharge gases. • Theoretical value This is the minimum quantity of combustion supporting air theoretically required to achieve ideal perfect stoichiometric combustion. This is measured in Nm3 /Nm3 for gaseous fuels or Nm3 /kg for liquid fuels. The following principle physical characteristics are also important for gaseous fuels: • Air/relative density ratio This is the ratio of equal volume masses of dry air and gas measured under the same temperature and pressure conditions. • Dew point The water vapour in the flue gases condenses at this temperature. This temperature may vary considerably from the standard value of 100°C, as water vapour is mixed with other gases and is dependent on the flue gas acidity. It is measured in degrees centigrade (°C). • Air explosive mixture This is the gas concentration range, expressed as a percentage, where the gas and air mixture is explosive. • Wobbe Index A parameter to define the heat released by a gas, obtained from the relationship between the gross caloric value and the square root of the density of the gas with respect to the air. This index is extremely useful to evaluate the interchangeability of two different gaseous fuels: when a certain gas, even if it has different thermotechnical features from the basic gas, gives similar values to the Wobbe index, it can be used correctly in systems that had been originally designed to work with basic gas. W = d P.C.I. processing; in fact, natural fuels are not directly utilisable as their composition is extremely variable and it is impossible to guarantee the safety and efficiency of the fuel beforehand. Typical processing methods tend to transform natural fuels into artificial ones. Charcoal is obtained from wood through slow and partial combustion inside a charcoal pit covered with earth. Distilling low-grade fatty anthracite at a medium heat produces Coke. Artificial gaseous fuels can be obtained from coal through synthesis processes such as dry distillation, partial oxidisation or reaction with water vapour. All artificial liquid and gaseous fuels can be obtained by distilling oil. Before natural gas can be used, the extremely pollutant fraction of H2S must be removed, through desulphurisation, together with the inert fraction of CO2. All these processes are aimed at making the chemical composition of the fuels uniform, making them easier to use and more profitable. In particular, liquid and gas fuels are easily transportable and can be finely proportioned to guarantee combustion efficiency. For these reasons, they are preferred in forced draught burners. The characteristics that distinguish the fuels are: • Calorific value The definition of the calorific value of a fuel is the amount of heat developed during total combustion of the fuel mass unit. The calorific value is measured in kJ/ Nm3 (1) for gas and in kJ/kg for liquids and solids. There are two calorific values: - superior or gross calorific value (GCV) when all the water present at the end of combustion is in a liquid state; - inferior or net calorific value (NCV) when all the water present at the end of conclusion is in a gaseous state. The relationship that ties GCV to NCV is the following: GCV=NCV+latent evaporation heat of the water produced by combustion GCV therefore indicates the maximum theoretical amount of heat that can be (1) A normal cubic meter (1 Nm3 ) corresponds to a cubic meter of gas at atmospheric pressure (1,013 mbar) and a temperature of 0°C. Boilersinfo.com
• 15. 16 The parameter is also useful to calculate pressure drops (for gas train selection) when a different gas is used, included among those allowed as given in the instruction manual for the burner. Gas pressure drops can be expressed with the following formula: For liquid fuels, the following main physical features are also important: • Viscosity This is the intermolecular internal friction of a fluid, and therefore the macroscopic dimension that describes the level of resistance with which the fluid moves. Dynamic viscosity (or absolute viscosity) is the tangential force per unit area of two parallel planes at unit distance apart when the space between them is filed with a fluid and one plane moves with unit velocity in its own plane relative to the other. The SI unit of measure of dynamic or absolute viscosity is N·s/m2 . In practice, kinematic viscosity is used, defined by the absolute viscosity of a fluid divided by its density. In the SI the kinematic viscosity is measured in m2 /s; in the technical system it is measured in cm2 /s; the unit is called "stoke" (St). Often, instead of the stoke its hundredth part is used, called centistoke (cSt) equal to mm2 /s. To measure the liquid viscosity, various instruments have been perfected, called viscometers, which have induced numerous ( )∆P2 = ∆P1 . W1 W2 2 units of measure depending on the type of viscometer and measuring technique. In Europe, the most common unit of measure besides the centistoke is the Engler degree (°E). The Engler viscometer is fundamentally a thermostatic container with a gauged hole, from which 200 cm3 of the tested liquid flows out and the flow time is measured. The relationship between this time and the time for 200 cm3 of water to flow out gives the °E viscosity. Due to the large number of measuring instruments and units of measure that are available, it is difficult to convert the viscosity levels. Therefore, nomographs and approximate conversion tables are given in chapter 5. • Inflammability flash point This is the lowest temperature at which a mixture of air and vapours given off by a liquid fuel, in the specific conditions established by legislation and using an adequate primer, is inflammable. It is measured in degrees centigrade °C. • Self-igniting temperature This is the minimum temperature at which a mixture of fuel and combustion supporter spontaneously ignites without using a primer. It is measured in degrees centigrade °C. 1.3.1 Gaseous fuels and their combustion As we have seen in the opening paragraphs concerning combustion, in order to burn, a fuel it must be mixed with oxygen: the burners provide fuel gas and combustion supporter air in the right proportions, they mix them and give rise to their controlled combustion in a combustion chamber. Gas burners can be classified according to two criteria. The first depends on the type of combustion supporter airflow into the burner and is classified as follows: • Natural draught burners; • Induced drauht burners; • Forced draught burners. Natural draught burners use the fuel gas supply pressure to pull the air through a Venturi system (normally performed by the nozzle) so that it is mixed with the fuel gas. As Diagram 3 Example of a viscometer Boilersinfo.com
• 16. 17 a rule, with natural draught burners, the air flow rate generated by the Venturi effect on the gas flow (primary air) does not reach more than 50% of that required for perfect combustion, therefore a further airflow is required (secondary air) into the combustion chamber. These burners can be extremely sensitive to combustion chamber depression (draught): greater is the depression, greater is the amount of air sucked in and mixed with the gaseous fuel, while, by contrast, a too low depression causes combustion without air, giving off extremely dangerous pollutants such as CO. In order to guarantee consistent hygienically safe combustion, gas burning in induction burners usually takes place with high levels of excess air (100% and over). In order to stabilise the operating conditions and be able to obtain combustion with lower excesses of air, induced draught burners are used, with a fan fitted up-stream (on the air side) or down-stream (to extract the combustion products) from the combustion chamber: in these conditions, primary air can reach 100% of that required for perfect combustion. In forced draught burners, the air flow rate is guaranteed by elevated head pressure fans which make the draught operating conditions more or less independent of the burner operation. These can achieve high modulation ranges and can be combined with high-yield, and therefore “pressurised” heat generators, achieving optimum fuel and combustion air mixtures, making it possible to operate with low excesses of air and, therefore, increased combustion efficiency. In this case, the fuel gas flows together in the air flow down-stream from the fan through several nozzles and usually requires greater delivery pressures than atmospheric burners, both due to the pressure drop by the nozzles and the need to control the air pressure. A second criteria to classify burners depends on the percentage mixture of combustion air with respect to the fuel taken before stabilising the flame. The pre-mixing percentages can be classified as follows: • Partial pre-mixed gas burners; (e.g. "premix" = 50%); • Total pre-mixed gas burners ("premix" = 100%); • Diffusion-flame burners. In the first two cases, fuel-air mixing takes place partially or completely, before the mixture passes onto the combustion chamber: induction burners are therefore also pre-mix burners. The pre-mixing allows rapid fuel oxidation reactions and therefore short flames; a consistent air-fuel mixture ratio also gives quieter combustion. In diffusion-flame burners, the fuel-air mixing stage and the combustion stage are more or less simultaneous: to guarantee hygienically safe combustion with low excesses of air, increased turbulence is therefore necessary, thus also, producing high pressure drops on the air side. Forced draught burners can be both pre-mixed or diffusion flame types. Gaseous fuels can form explosive mixtures (2) with air. This happens when the fuel gas concentration is within a specific range and is variable for each individual fuel. To avoid any accumulation in the combustion chamber and in the flue pipe, legislation requires a minimum air only pre-purge time through the combustion chamber for induced draught burners. Table 2 indicates the main gaseous fuels with their related thermo-technical characteristics. (2) The explosion is nothing more than rapid combustion with a violent increase of pressure. Boilersinfo.com
• 20. 21 1.3.2 Liquid fuels and their combustion Liquid fuels are made up of various types of hydrocarbons, i.e. molecules formed by carbon and hydrogen atoms. Unlike gaseous fuels, liquid fuels contain molecules of extremely long-chain hydrocarbons giving oils a liquid physical state. Liquid fuels cannot be directly mixed with the oxygen in the air, but must be atomised in extremely small droplets that have a considerable reaction surface. Inside the generator combustion chamber, the droplets of atomised liquid fuel heat up and evaporate releasing hydrocarbon vapours that ensure spontaneous fuel combustion. For combustion to be perfect, the drops of liquid fuel must be oxidised within the body of the flame; if not, the drops form particles of particulate, as more fully illustrated in the next paragraph on pollutants. Atomisation of liquid fuel is one of the main tasks performed by a burner. There are several atomisation methods for liquid fuels. The main ones are listed below: • Mechanical atomisation; • Pneumatic atomisation; • Centrifugal atomisation; The most common method is “mechanical atomisation” where liquid fuel atomisation is the result of the mechanical pressure exerted on the liquid, when it reaches the atomising nozzle, against the walls made up of small run channels and helicoidal holes in the nozzle. With this method, the fuel oil is split into a great deal of extremely small droplets due to brusque flow variations and impact against the walls due to high pressure (10-30 bar). The size of the droplets depends on the exerted pressure, the type of nozzle and the viscosity. Another system is the “pneumatic system” where the droplets of liquid fuel are further atomised by a second high-pressure fluid (compressed air or vapour) when they come out from the mechanical nozzle. This system guarantees excellent fuel atomisation levels for dense fuel oils, but at the same time more complicated construction, with auxiliary liquid being present (working pressure 5-9 bar) and consequently higher installation cost compared to the classic mechanical method. In rotary atomisation, the drops of fuel are formed by applying a centrifugal force to the liquid fuel with the aid of a rotating cup; this method is used for certain industrial-type burners. On today's market, systems are available aimed at improving the mechanical-type atomisation system using modified fuels; basically, fuel oil and water emulsions are used. The individual drops of fuel oil are emulsified into water droplets that, within the body of the flame, become water vapour causing the fuel oil drops to explode. Therefore more efficient fuel atomisation results. Independently from the type used for achieving a satisfactory atomisation degree, the liquid fuel must have a sufficiently low viscosity. The viscosity of liquid fuel is strictly linked to the temperature; when the temperature increases the viscosity decreases. Therefore, certain liquid fuels must be pre-heated to achieve the desired viscosity. As a rule, fuel oil viscosity required for achieving satisfactory atomisation is much lower than that requested by pumping systems, consequently a much higher temperature is required to achieve adequate atomisation than that requested for pumping the fluid. All these aspects translate into specific plant engineering choices that are fully covered in the section dedicated to plant engineering. The viscosity required for obtaining sufficient fuel oil atomisation varies according to the type of burner and type of nozzle used. Generally, the nozzles require oil viscosity between 1.5 and 5 °E at 50°C in relation to the type of fuel. This viscosity value also determines the pre-heating temperature value. For example: supposing we use a fuel oil with viscosity of 22°E at 50°C to obtain a value of 3°E needed by the nozzle to obtain the right atomisation, the fuel must be pre-heated to a temperature between 90 and 100°C. Table 3 gives the names used for liquid fuels in the main countries, while Table 4 shows the related thermotechnical characteristics. 1.4 POLLUTANT COMBUSTION EMISSIONS The leading polluting agents to be considered in the combustion phenomenon are: • sulphur oxides, generally indicated by SOx and mainly made up of sulphur dioxide SO2 and sulphur trioxide SO3; • nitric oxides, generally indicated by NOx Boilersinfo.com
• 21. 22 and mainly made up of nitric oxide NO and nitrogen dioxide NO2; • carbon monoxide CO; • total suspended particles indicated by TSP (PST). There are essentially three systems that can be adopted to reduce the pollutants: • preventive systems, by acting on the fuel before subjecting it to combustion, trying to reduce the amount of polluting agents. A typical case is represented by liquid fuels (light oil and naphtha) where the sulphur content tends to be reduced; • primary systems, by acting on the process and combustion equipment (burner), so that combustion takes place under the best conditions thus reducing the formation of pollutants; • secondary system, by acting on the combustion gases, to break down the polluting components before they are expelled into the atmosphere. During the design and the construction of civil engineering combustion plants, the first two systems should be used to reduce pollutants, therefore using “clean” fuels, gas, LPG, light oil and naphtha with a low sulphur (BTZ oil) and nitrogen content, and using special burners to minimise the polluting emissions of nitric oxides (Low-NOx burners); The third system is recommended for use only in large industrial and thermoelectric plants, which mainly work with naphtha, where the large amount of burnt fuel and, consequently, emitted combusted gases justify the creation of specific breakdown plants. 1.4.1 Sulphur oxides Sulphur oxides are considered toxic for man; especially sulphur dioxide SO2 causes irritation of the eyes and lachrymation when the concentration exceeds 300 mg/Nm3 . The danger threshold is estimated at around 500 mg/Nm3 . Moderate temperatures favour the formation of sulphur oxides. Under normal conditions of high combustion flame temperature and excess air around 20%, nearly all the sulphur present in the fuel oxidises into sulphur dioxide (SO2). Sulphur dioxide is a colourless gas with a density equal to nearly two and a half that of air, therefore it tends to stratify towards the ground in closed environments. The percentage of sulphur trioxide SO3 may become important for low combustion temperatures (400°C), for example in start-up phases of installations, or when the excess air is extremely high or even when pure oxygen is used. Sulphur trioxide SO3 reacts with water vapour, generating sulphuric acid H2SO4 that is corrosive even in the vaporous phase, thus damaging for heat generators, which are usually metallic. Measures for controlling sulphur dioxide SO2 and sulphur trioxide SO3 emissions are first of all based on preventive action on fuels during their production, by using catalytic desulphurisation processes. In large heavy oil-operated plants, the breakdown of nitric oxides is mainly by absorption using water-based solutions, which can achieve yields of around 90%. 1.4.2 Nitric oxides Nitric monoxide NO is a colourless, odourless gas which is insoluble in water. It represents more than 90% of all nitric oxides formed during high-temperature combustion processes; it is not particularly toxic when its concentration ranges between 10 and 50 ppm. and it is non-irritant. Nitrogen dioxide NO2 is a visible gas even in low concentrations, with a browny-reddish colour and a particularly acrid smell; it is highly corrosive and an irritant to the nasal membranes and eyes when concentrated at 10 ppm, while causing bronchitis at concentrations of 150 ppm and pulmonary Diagram 4 Acid rain formation process Sun- light Oxidation Dissolution Dry deposition Wet deposition Source of emission Dry deposition of gas, dust and aereosol Natural ammonia Humid deposition of dissolved acids Boilersinfo.com
• 22. 23 oedema at 500 ppm, even if exposure lasts just a few minutes. The nitric monoxide NO present in our city air can transform itself into nitrogen dioxide NO2 by means of photochemical oxidation. Three models of nitric oxide formation exist, which lead to the formation of different types of nitric oxide (different by type of origin but not by chemical composition); respectively they are: • thermal nitric oxides (thermal NOx); • prompt nitric oxides (prompt NOx); • fuel nitric oxides (fuel NOx); Thermal nitric oxides are formed by the oxidation of atmospheric nitrogen (contained in combustion supporter air) under high temperature (T> K) and high oxygen concentration conditions, and represent the majority of nitric oxides in the case of gaseous fuels (methane and LPG) and in general in fuels which do not contain nitrogenous compounds. Prompt nitric oxides are formed by means of the fixation of atmospheric nitrogen by hydrocarbon fragments (radicals) present in the flame area; this method of forming oxides is extremely rapid thus giving rise to the name prompt. Their formation essentially depends on the concentration of radicals in the first stage of the flame; for oxidative flames (combustion with excess of oxygen), their contribution is negligible, while in the case of rich mixtures and for low-temperature combustion, their contribution may reach 25% of the full nitric oxides total. Nitric oxides from fuel form by means of oxidation of the nitrogenous compounds contained in the fuel within the flame area, and their production is significant when the fuel’s nitrogen content exceeds 0.1% in weight, essentially only for liquid and solid fuels. Diagram 5 shows the contribution for each type of NOx depending on the type of fuel (under conditions of standard combustion): The portion of prompt nitric oxides remains more or less constant, whereas the portion of fuel nitric oxides grows and the portion of thermal nitric oxides decreases as we gradually pass to fuels with a higher molecular weight. 1.4.2.1 Reduction of the NOx in gaseous fuel combustion The thermal nitric oxides in gaseous fuels represent up to 80% of total emissions; a drop in the combustion temperature achieves inhibition of the formation of these compounds. The temperature drop may be carried out in various ways. - specific thermal load reduction An initial method involves decreasing the output burnt per unit of volume of the combustion chamber, resorting in fact to a “de-rating” of the boiler and thereby decreasing its nominal thermal capacity (if it is an existing boiler) or over-sizing the combustion chamber for new projects. - combustion chamber architecture Another solution that can be adopted involves the use of heat generators, which have combustion chamber architecture with three flue passes, in other words without inversion of the flame. In flame-inversion boilers, the combustion products re-ascend the combustion chamber during the flow inversion stage, confining the actual flame within an effectively smaller volume than that of the combustion chamber; a portion of the radiant energy possessed is also reflected towards the flame itself. These conditions lead to a flame temperature increase, with a consequent increase in the thermal nitric oxides. The same situation occurs in applications where the chamber wall temperatures are high, i.e. in furnaces or in boilers with fluid at high temperatures. - air and gas pre-mixing Under normal conditions the combustion systems are calibrated so that they can operate with excess air; this excess air establishes a lower effective combustion temperature than the adiabatic temperature and sometimes one that is lower than the limit which enables activation of the nitric oxide formation mechanism ( K). Since the flame is a typically turbulent domain fed by two reactants that are difficult to mix perfectly, it is normal that zones with differentDiagram 5 Type of NOx for certain fuels gas light oil heavy oil carbon Fuel Prompt Thermal N2 “fuel” (mass %) Total(%) Boilersinfo.com
• 23. 24 stoichiometry are formed therein. These will inevitably include zones with stoichiometric conditions or approximate to stoichiometric conditions: the temperatures in these regions will, without doubt, be so high that they will give rise to conditions suitable for thermal NOx formation. These observations suggest action which could impede, or at least reduce, such situations: pre-mix the air and gas accurately before combustion and develop the latter without excessive turbulence, in such a way as to come close to the stoichiometric conditions which would result in the required excess air (and therefore come close to the theoretical combustion temperature which can be derived from the stoichiometric one) whatever the region effected by combustion. An additional, positive contribution may be provided by uniform flame distribution- better still if this distribution covers wide surface areas - which also prevents the presence of small tongues of flame, inside which the temperatures would certainly be higher. Examples of these techniques are represented by porous surface areas (in metallic or ceramic materials) or those comprising masses of fibres or characterised by the presence of tiny microscopic holes: up-stream from these surfaces, attempts are made to create an accurate as possible pre-mixing, while on the external surfaces the objective is to obtain a region of flame which is fairly uniformly extended and distributed. This technique appears the most promising in absolute terms for Low NOx gas solutions, even if for now the high costs involved and certain constructive restrictions hinder its use, especially in the field of higher outputs. - staged combustion The nitric oxide formation speed is greater when in proximity to a ratio of fuel to combustion supporter, which is equal to the stoichiometric ratio. In order to obtain low nitric oxide formation speeds, it is possible to operate with a combustion system which on average operates with realistic excess air, but which presents internal zones with ratios between fuel and combustion supporter which are extremely different from the stoichiometric one, thereby resorting to a segregation of the fuel. As far as application is concerned, the aerodynamics of the flame and the fuel distribution can be adjusted, creating zones high in excess of air alternated with zones without, thus maintaining the global stoichiometry under correct operating conditions. - combustion products blow-by By diluting a portion of the burnt gases in the combustion supporter air, a decrease in the combustion supporter oxygen concentration is obtained together with a reduction of the flame temperature since part of the energy developed by combustion is immediately transferred to the inerts present in the fuel gas. The breakdowns achievable by means of this technique are extremely high in the case of gaseous fuels, because of ensuring a sufficient mixing between the blown-by combustion products and the combustion supporter/fuel mixture. It is relatively easy to active a blow-by of the combustion products in the flame directly within the chamber in the case of thermal generators, and therefore burners, with low outputs by resorting again to particular aerodynamics induced by the burner combustion head, As a rule these internal blow-bys are extremely high (around 50 %) because the fuel/combustion supporter reactants mixing is less effective and the flue gas temperature is relatively high (900 ÷ K). Sometimes, it is preferable to resort to an external blow-by of the combustion products for machines with a greater output due to the difficulties in obtaining this mixing, which only add to the aggravation of other problems (for example: the elevated combustion head load Diagram 6 Functional layout of combustion process for a gas burner - Blue flame type. 1 Comburent air - 2 Fuel gas intake - 3 Fuel gas jets- 4 Flame stabilization zone (combustion under stoichiometrics) - 5 Recirculed combustion products - 6 Over stoichiometrics combustion - mixture of fuel air, gas and recirculed combustion products - 7 “Cold” zone of the flame. Boilersinfo.com
• 24. 25 losses). By means of an auxiliary fan, or by utilising the burner fan itself, a portion of the combustion products is withdrawn at the heat generator outlet and is re-conveyed up-stream from the combustion head, so as to pre-mix it with the combustion supporter air. Even if in certain situations, a blow-by inside the combustion chamber may not be enough for extremely low NOx emission values (and this is the case now mentioned regarding high output burners), this technique may be applied in association with the staged combustion technique illustrated previously. 1.4.2.2 Reduction of the NOx in liquid fuel combustion The substantial difference - within certain limits of the nitric oxides argument - between the combustion of gas and the combustion of liquid fuels, is the presence in the latter of nitrogen under the guise of nitrogenous compounds; this is at the origin of NOx production from fuels which, dependent on the nitrogen content in the oil, may also represent a significant portion of the total NOx. As far as thermal and prompt nitric oxides are concerned, the same observations expressed in the case of gaseous fuels (discussed previously) apply. With regard to nitric oxides from fuels, it has been observed that in reducing environments the nitrogen contained in the fuel may not produce the undesired NOx, but simple and harmless molecular nitrogen N2. The combustion chamber is an environment devoted to the oxidation of fuel; however, it is possible to create zones rich in fuel in certain regions of the flame and therefore form reducing situations for the purpose of producing molecular nitrogen N2 in the place of nitric oxides. For example, steps could be taken to supply the initial combustion region with 80 % of the total combustion supporter air together with 100 % of the fuel and, further on, supply the remaining 20 % of the combustion supporter air (over firing air). These applications are still considered to be in the experimental stages for burners used in the sectors of standard heating systems. By contrast, these techniques are already a consolidated asset in the industrial systems of thermoelectric power stations. 1.4.3 Carbon monoxide (CO) Carbon monoxide is a colourless, odourless and tasteless gas. Its relative density compared to air is 0.96, therefore it does not Monobloc burner (light oil - Low NOx) of BGK series Diagram 7 Effects of carbon monoxideDiagram 8 Hours of exposure Death Danger of death Cefhalea, nausea Slight ailments Insignificant effects VolumepercentageofCO2intheair Boilersinfo.com
• 25. 26 disperse with ease. Carbon monoxide is a toxic gas which, if inhaled, reacts extremely rapidly with the haemoglobin in the blood, preventing the regular oxygenation of the blood and, as a consequence, of the entire organism. The physiological effects on the organism are the result of the concentration of the carbon monoxide in the air and the length of exposure of the person to said concentration. The diagram 8 illustrates the effects of carbon monoxide in relation to the two previously mentioned parameters. Carbon monoxide is present in combustion gas as the result of the partial oxidation of the carbon present in the fuel. Its presence in burnt gases is an indication of low combustion efficiency, because the carbon not perfectly oxidised to CO2 corresponds to heat not produced. Carbon monoxide is present in burnt gases when combustion is carried out with too little air than is required stoichiometrically and therefore the oxygen is insufficient for the purposes of completing the carbon oxidation reactions. Heating systems are responsible to a minimum extent for the presence of carbon monoxide in the atmosphere, since the combustion processes are usually conducted with excess air higher than the stoichiometric requirements. 1.4.4 Total suspended particles This category of polluting substances includes those emissions comprising particulates, inert solid substances and metallic components. The size of these particles varies from a minimum of 0.01 microns up to a maximum of 500 microns. The particulate may be of an organic or inorganic nature; in more detail, three categories can be identified: • Ashes, comprising inorganic, incombustible substances (metals, etc..), drawn into the combustion gases; • Gas black, made up of the fuel residues which have evaporated but not oxidised; • Cenopheres, comprising fuel residues that have been partially oxidised since they have been burnt before vaporising. The finest portion of the particulate is called soot. The danger of the particles is inversely proportionate to the size. Damage caused is mainly to the respiratory tracts and pulmonary system. The diagram 9 indicates the depth these particles can penetrate the human body according to their size. Furthermore, in the pulmonary alveolus the particulate acts as the vehicle transporting the metallic oxides (vanadium, nickel etc..) which may be produced during combustion and which are absorbed by the particles of the particulate. Only the particles with an equivalent diameter smaller than 10 microns are sufficiently light to remain suspended in the air for several hours and therefore represent real danger of being inhaled by man. Metal oxide emissions depend on the concentration of the respective metals in the fuel, therefore for civil installations the best solution for reducing emission essentially involves the utilisation of fuels with low heavy metals concentrations. Gas black is usually produced in particular areas of the flame where there are insufficient oxygen or low temperature conditions; therefore, in order to avoid the formation of gas black it is necessary to guarantee the combustion process an adequate temperature, a sufficient quantity of oxygen and considerable turbulence in order to obtain a satisfactory mix between the fuel and the oxygen. Cenospheres form when the nebulisation and volatilisation process of the liquid fuels in the combustion chamber is irregular or hindered by the elevated viscosity and low volatility of the fuel. In order to reduce the production of these components, it is necessary to increase the Penetration of the particles in the respiratory system Diagram 9 Nose Pharynx Primary bronchus Secondary Bronchus Terminal bronchus Alveolus Boilersinfo.com
• 26. 27 period spent in the combustion chamber and guarantee the fuel an adequate excess of oxygen. The maximum concentration of the pollutants in the flue gases deriving from combustion, is a value fixed by national legislation and in certain cases differs in relation to particularly sensitive regions and/or metropolitan areas. 1.4.5 Comments on the emission of CO2 Carbon dioxide CO2 was purposefully not included among the other pollutants mentioned since, together with water vapour, it is one of the main products of any hydrocarbon combustion process. The accumulation of carbon dioxide in the atmosphere is the main culprit of the phenomenon known as the “greenhouse effect”. Accumulated carbon dioxide absorbs part of the infrared radiation emitted by the earth towards the atmosphere, thus retaining the heat. The outcome of this phenomenon is the progressive increase in the Earth’s average temperature with disastrous resulting consequences. The absolute carbon dioxide quantity produced by combustion depends solely on the quantity of carbon C present originally in the burnt fuel. The greater the C/H ratio of the fuel, the greater the quantity of carbon dioxide produced will be. As a rule, all energy produced being equal, liquid fuels produce more carbon dioxide than gaseous fuels. As we will see in the next section concerning the control of combustion, the percentage of CO2 in the flue gases must be as high as possible to achieve greater output. All energy produced being equal, a lower CO2 percentage in the combustion flue gases leads to the system being less efficient and, as a consequence, more fuel being oxidised. This fact should not mislead the reader however, since even if we vary the percentage of CO2 in the flue gases in relation to the dilution of the flue gases, the total quantity of CO2 remains more or less unchanged. 1.5 COMBUSTION CONTROL For combustion to be perfect, a quantity of air must be used greater than the theoretical quantity of air anticipated by the chemical reactions (stoichiometric air). This increase is due to the need to oxidise all the available fuel, avoiding the possibility that fuel particles are only partially oxidised or completely unburnt. The difference between the quantity of real air and stoichiometric air is defined as excess air. As a rule, excess air varies between 5% and 50%, in excess of stoichiometric depending on the type of fuel and burner. Generally, the more difficult the fuel is to oxidise, the greater the amount of excess air required to achieve perfect combustion. The excess air cannot be too high because it influences combustion efficiency; an extremely large delivery of combustion supporter air dilutes the flue gases, which lowers the temperature and increases the thermal loss from the generator. In addition, beyond certain limits of excess air, the flame cools excessively with the consequent formation of CO and unburnt materials. Vice versa, an insufficient amount of air causes incomplete combustion with the previously mentioned problems. Therefore, the excess air must be correctly calibrated to guarantee perfect fuel combustion and ensure elevated combustion efficiency. Complete and perfect combustion is verified by analysing the carbon monoxide CO in the burnt flue gases. If there is no CO, combustion is complete. The excess air level can be indirectly obtained by measuring the uncombined oxygen O2 or the carbon dioxide CO2 present in the combustion flue gases. The excess air will be equal to around 5 times the percentage, in terms of volume, of the oxygen measured. When measuring CO2, the amount present in the combustion flue gases depends solely on the carbon in the fuel and not on the excess air; it will be constant in absolute quantity and variable in volumetric percentage according to the greater or lesser dilution of the flue gases in the excess air. Without excess air, the volumetric percentage of CO2 is maximum, with rising excess air, the volumetric percentage of CO2 in the combustion flue gases decreases. Taking lower excesses of air, higher quantities of CO2 correspond and vice versa, therefore combustion is more efficient when the quantity of CO2 is near to the maximum CO2. The composition of the burnt gases can be represented in simple graphic form using the Boilersinfo.com
• 27. 28 “combustion triangle” or Ostwald triangle, diversified according to the fuel type. Using this graph, (which is also included in chapter 5), we can obtain the CO content and the value of the excess air noting the percentages of CO2 and O2. By way of example, the combustion triangle for methane gas is presented below. The X-axis shows the percentage content of O2, the ordinate axis shows the percentage content of CO2. The hypotenuse is traced between point A corresponding to the maximum percentage of CO2 (dependent on the fuel) with zero amount of O2 and point B corresponding to zero values of CO2 and maximum values of O2 (21%). Point A represents the stoichiometric combustion conditions, point B the absence of combustion. The hypotenuse is the position of the points representing perfect combustion without CO. The straight lines corresponding to the various CO percentages are parallel to the hypotenuse. Let us suppose that we have a system powered by methane gas whose measurements of burnt gas have given readings of 10% CO2 and 3% O2; from the triangle relating to methane gas we can obtain the CO value equal to 0 and an excess air value of 15%. Table 5 shows the maximum CO2 values achievable for the different types of fuel and those advised in practice in order to achieve perfect combustion. We should note that when the maximum levels are obtained in the central column, a control system must be provided for the emissions as described in chapter 4. For liquid fuel powered systems, the flue gas index must also be measured, using the measurement method devised by Bacharach industries. The method involves sucking a specific volume of burnt gas with a small pump, and passing it through a filter of absorbent paper. The side of the filter fouled by the gas turns light grey-to-black in colour depending on the amount of soot present. The colour can be compared with a sample scale, made up of 10 shaded disks varying from 0 (white) to 9 (black). The sample scale number corresponding to the filter used determines the Bacharach number. The limit value of this number is established by national anti-pollution legislation and depends on the type of liquid fuel. To determine the particulate material contained in the combustion flue gases, there are two basic measurement concepts: • graviometric; • reflectometry. Using the graviometric method, the particulate material suspended in the burnt flue gases is collected on special filters and subsequently weighed, to give the weight difference of the filter before and after the experiment was carried out. The reflectometry principle determines a conventional index (equivalent black smoke) on the basis of the light absorption capacity, measured by reflectometry, of the particulate material collected on a filter after carrying out the experiment. Table 5 Maximum recommended CO2 values for the various fuels FUEL METHANE L.P.G. TOWN GAS LIGHT OIL HEAVY OIL CO2 max in vol [%] 11,65 13,74 10,03 15,25 15,6 CO2 advised[%] 9,8 - 11 11,5 - 12,8 8,2 - 9 12 - 14 11,8 - 13 Air excess [%] 20 - 8 20 - 10 20 - 10 30 - 12 35 - 20 Combustion triangle for methane gasDiagram 10 Boilersinfo.com
• 28. 29 1.5.1 Combustion efficiency Combustion efficiency is defined as the ratio between thermal energy supplied by combustion and the primary energy used for combustion Primary energy is equal to the amount of fuel used for its calorific value; in paragraph 1.3 two calorific values have been defined: the superior value and the inferior value, therefore when we define the combustion efficiency, we must specify which of the two we are referring to. The difference between the primary energy used and the energy supplied by combustion is equal to the thermal energy contained in the flue gases produced by combustion; the η combustion efficiency of a generator can therefore be calculated using the following formula: η = 100 – Ps [%] where: η = efficiency of the heat generator; Ps = thermal output lost through the flue pipe; The conventional formulas used for determining losses through the flue pipe are: if the concentration of available oxygen in the combustion flue gases is known, or: Ps = . (Tf - Ta) ( )A1 21 - O2 + B Ps = . (Tf - Ta) ( )A2 CO2 + B η = energy supplied by combustion · 100 (%) primary energy used if the concentration of carbon dioxide in the combustion flue gases is known. where: Ps = thermal output lost through the flue pipe [%]; Tf = flue gas temperature (°C); Ta = combustion supporter air temperature (°C); O2 = oxygen concentration in the dry flue gases [%]; CO2 = carbon dioxide concentration in the dry flue gases [%]; A1, A2 and B are empirical factors whose values, with reference to the N.C.V., are shown in table 6. 1.5.2 Measurement units for combustion emissions Legislation issued by various countries establishes certain limits expressed in various units of measurement, generally using ppm (parts per million), mg/Nm3 or mg/kWh with reference to 0% or to 3% of available oxygen present in combustion products. The transformation from ppm to mg/Nm3 can be done using the equation of the perfect gases correctly modified: where: p = pressure = 1 atm under normal conditions; R = gas constant = 0.082; T = temperature = 273 K under normal conditions; PM = molecular weight; The application of the previous equations for certain pollutants provides the following values: 1ppm = . (PM) [mg/Nm3] p R T. Factors for calculation of the combustion efficiency Table 6 FUEL METHANE L.P.G. LIGHT OIL HEAVY OIL A1 0,66 0,63 0,68 0,68 A2 0,38 0,42 0,50 0,52 B 0,010 0,008 0,007 0,007 Equivalence in weight of ppm in the main polluting emissions Table 7 COMPONENT CO NO NO2 (NOX) SO2 ppm 1 1 1 1 mg/Nm 3 1,25 1,34 2,05 2,86 Boilersinfo.com
• 29. 30 If the percentage of available oxygen in the flue gases differs from the usual reference values of 0% and 3%, the value of the E measured emissions can be converted - whatever their measurement unit is - to the equivalent referring to the reference percentages in the following ratios: If the CO2 percentage of the burnt flue gases is known, the following ratios can be used: where the maximum concentration percentages of CO2 are valid for the various fuels: Therefore, from an operational point of view, having analysed the combustion products, we can proceed with converting the value measured from ppm to mg/Nm3 and then relate this value to that referring to 0% or to 3% of oxygen. The conversion from ppm to mg/kWh relates to the type of fuel used, with reasonably good E3%O2 = .Emeasured %CO2 max at 0% O2 %CO2 flue gases E0%O2 = .Emeasured %CO2 max at 0% O2 %CO2 flue gases E3%O2 = .Emeasured 18 21 - %O2 flue gases E0%O2 = .Emeasured 21 21 - %O2 flue gases approximation, the following equivalents can be used: methane (G20 100% CH4): NOx : ppm3%O2 = 2.052 mg/kWh CO : 1 ppm3%O2 = 1.248 mg/kWh light oil (PCI= 11.86 kWh/kg): NOx : 1 ppm3%O2 = 2.116 mg/kWh CO : 1 ppm3%O2 = 1.286 mg/kWh Maximum values of CO2 at 0% and at 3% of O2 for the various fuels Table 8 FUEL METHANE L.P.G. TOWN GAS LIGHT OIL HEAVY OIL CO2 max at 0% of O2 [%] 11,65 13,74 10,03 15,25 15,6 CO2 max at 3% of O2 [%] 10 11,77 8,6 13,07 13,37 Boilersinfo.com
• 30. 31 2.1 FOREWORD The term “burners” describes a series of equipment for burning various types of fuel under suitable conditions for perfect combustion. The burner operates by sucking in the fuel and the combustion supporter air, mixes them thoroughly together and safely ignites them inside the heat generator furnace. The following are the parts that make up the burner and are analysed individually in the following paragraphs. • The combustion head which mixes the fuel and the combustion supporter, and generates an optimum form of flame; • The combustion air supply, comprising of the fan and any pipes for taking the air to the combustion head; • Fuel supply, comprising components used for regulating the fuel flow and guaranteeing the safety of the combustion system; • The electrical and control components required for firing the flame, the electricity supply to the motors and thermal output regulation developed by the burner. Forced draught burners can control the combustion of all gaseous fuels (methane, LPG, town gas) and liquid fuels (diesel oil, heavy oil). Burners exist which use only one family of fuel (liquid or gaseous) and others that can use both called “DUAL FUEL” (double fuel) burners. Thus, three classes of burner are obtained: • burners of gas fuels which use only gas fuels; • burners of liquid fuels which use only liquid fuels; • burners of liquid and gas fuels (DUAL FUEL) which use both gas and liquid fuels. Forced draught burners can also be classified according to the type of construction, specifically: • monobloc burners; • separate fired burners or DUALBLOC. In monobloc burners, the fan and pump are an integral part of the burner forming a single body. In DUALBLOC burners, the fan, pump and/or other fundamental parts of the burner are separate from the main body (head). Monobloc burners are those most commonly used in output ranges varying from tens of kWs to several Mw output. For higher outputs, or for special industrial processes, DUALBLOC burners are used. Depending on output delivery type, we can classify forced draught burners according to the following distinctions: • single-stage burners; • multi-stage burners; • modulating burners; Single-stage burners operate with single-state delivery, fuel delivery is invariable and the burner can be switched on or off (ON-OFF). Multi-stage burners, usually two-stage or three-stage, are set for running at one or more reduced output speeds or at maximum output (OFF-LOW-HIGH or OFF-LOW-MID-HIGH); switchover from one stage to another can be automatic or manual. Two-stage burners also include versions called progressive two-stage, where changeover from one stage to another is through a gradual increase in output and not with sudden step increases. THE FORCED DRAUGHT BURNER 2 Gas fired monobloc burnerDiagram 11 Boilersinfo.com
• 31. 32 In modulating burners, the delivered output is automatically varied continuously between a minimum and maximum value, for optimum delivery of the thermal output in relation to system requirements. Diagram 12 below shows the types of output delivery. Forced draught burners now available on the market can function coupled with generators with a pressurised or unpressurised furnace or those with a slight negative draught condition. The diagrams represent, respectively, an outline configuration of a monobloc two-stage diesel-fired burner, a monobloc modulating methane gas-fired burner and a DUALBLOC dual-fuel (gas and fuel oil) fired burner. It is clear that in DUALBLOC burners, the fan and certain parts dedicated to treating the fuel are separate from the main body of the burner, but their function does not change. Therefore, in this manual, monobloc burners and those with separate fans are dealt with on an equivalent basis, except for certain technical characteristic aspects. 2.2 THE FIRING RANGE OF A BURNER The firing range of an Forced draught burner is a representation in the Cartesian plan of an area, showing the pressure of the combustion chamber on the Y axis and the thermal output on the X axis; this area indicates working conditions under which the burner guarantees combustion corresponding to the thermo- technical requirements. The firing range is obtained referring to data gained from experimental trials, which are correct in a prudent sense. Diagram 14 shows the representation of the firing range of a series of diesel oil-fired burners. Quite often, the firing range of just one burner is not illustrated, but rather a whole series, as in the diagram above. The output can be expressed in kW or in kg/h of fuel burnt, while the pressure is expressed in either mbars or in Pa. The firing range is obtained in special test boilers according to methods established by European legislation, in particular: • EN 267 standard for liquid fuel burners; • EN 676 standard for gaseous fuel burners; These standards establish the dimensions that the test combustion chamber must have. Diagram 15 shows the graph indicating the dimensions of the test furnace for forced draught burners powered by liquid or fuel gas. The graph represents the average dimensions of commercial boilers; if a burner is to operate in a combustion chamber with distinctly different dimensions, preliminary tests are advisable. The firing range is determined experimentally under particular atmospheric pressure and combustion supporter air temperature test conditions. All the graphs showing the firing range for a forced draught burner must be accompanied by pressure and temperature indications, generally corresponding to a pressure of (3) mbar (100 m above sea level) and combustion supporter air temperature of 20°C. If running conditions are considerably different from the test conditions, certain corrections must be made, as shown in chapter 3 of this manual. Burners operating chances: a) one- stage, b) two-stage, c) progressive two-stage, d) modulating Diagram 12 (3) Normal pressure at 100 m above sea level. Start up Start up 1st stage Start up 1st stage Start up Stop Start up 2nd stage Start up 2nd stage Start up 2nd stage Start up 2nd stage Stop 2nd stage Stop 2nd stage Stop 2nd stage Stop 2nd stage Stop Stop 2nd stage Start upStop Stop Boilersinfo.com
• 32. 33 Layout of two monobloc (RL and RS series) burners and dual bloc (TI) burnerDiagram 13 RS series TI series RL series FR P.E. cell GF Gas filter BP Pilot burner V1,V2 Delivery oil valves PA Air pressure switch C2 Oil modulating cam PV Nozzzle holder PC Leak detection control device C3 Gas modulating cam AD Air damper C Anti-vibrant joint D Gas distributor M Air fan and pump motor PCV Gas pressure governor LPG Low pressure gas governor P Pump with oil filter and PG Minimum gas pressure switch MM Oil delivery gauge pressure regulator MT Two-stage hydraulic ram PGM Maximum gas pressure switch MR Oil return gauge V Supply air fan RG Gas flow regulator (butterfly valve) POMaximum oil pressure switch VS Gas safety valve C1 Air moudulating cam SI Ionisation probe VTR Combustion head SM Cam’s servomotor VP Pilot vaves regulation screw U,U1,U2 Nozzles VR Gas regulation valve VU Nozzle’s safety valve Boilersinfo.com
• 33. 34 The burner should be chosen so that maximum required load falls within the burner's firing range. The firing point is found by tracing a vertical line in correspondence with the required output value and a horizontal line in correspondence with the pressure in the combustion chamber; the intersection point between the two lines is the system firing point, including the burner and the heat generator. As far as the choice of single-stage burners is concerned, the firing point can be in any point of the burner's firing range. For two-stage burners the firing range is ideally divided into two areas, left (zone A) and right (zone B) of the vertical line traced for the point corresponding to the maximum head available, as indicated in Diagram 16. The firing point corresponding to the maximum output and, consequently, to operate in the 2nd stage, must be chosen within zone B. Zone B provides the maximum output of the burner in relation to the combustion chamber pressure. The 1st stage output should be chosen within the minimum/maximum declared formula and normally falls within zone A. The absolute lower limit corresponds to the minimum value of zone A. However, in certain cases, for example where the use of two-stage burners is required in domestic hot water boilers, it is advisable not to go below 60-65% of maximum output in the first stage, and, due to condensation problems, to maintain flue temperature around 170-180°C at maximum load and at 140°C at 65% of load. As far as progressive or modulating two-stage burners are concerned, the burner should be chosen in a similar manner to two-stage burners. In modulating burners, the nearer the firing point is to the maximum output values of the firing range, the higher the modulating formula of the burner. The modulating formula is defined as the turn down ratio between the maximum output and the minimum output expressed in proportion (e.g. 3:1 or 5:1). 0 1 2 3 4 5 6 7 50 100 150 200 250 300 350 400 450 500 550 600 kW Combustionchamberpressure(mbar) RLS 50 RLS 38 RLS 28 Firing ranges of Riello RLS series dual fuel burners Diagram 14 Test combustion chamber for burnersDiagram 15 d = diameter of the flame tube Heat output (kW) X Lenghtoftheflametube(m) Flametubefiring intensity(kW/m3 ) Boilersinfo.com
• 34. 35 The firing range in cartesian format can only be determined for monobloc forced draught burners, where the coupling of the combustion head with the fan is defined by the burner manufacturer. The situation changes for dual bloc burners, as the combination of the combustion head and the fan is delegated to the design engineer. In this case, the firing range is characteristic only for the combustion head and determined in relation to the maximum and minimum fuel output allowed to the head itself. For example Diagram 17 shows the firing ranges for combustion heads in the Riello TI Series Burners, where the darker area represents the range of optimum choice recommended by the manufacturer. The choice regarding the size of the combustion heads should be made solely in relation to the output and the temperature of the combustion supporter air. 2.3 TYPICAL SYSTEM LAYOUT DIAGRAMS The burner is just one of the components of a larger and more complex system for generating heat. Before passing on to the description of the individual parts of a combustion system, the following pages show the plant engineering diagrams for the various types of fuel, regulation of the thermal load and systems for optimising fuel control. By overlapping the diagrams of each of these layout classes, the entire combustion system can be designed. 0 0 kW0 Campo utile per la scelta del bruciatore Campo di modulazione Temperaturaaria°C Mcal/h TI 14 TI 13 TI 12 TI 11 TI 10 50°C 150°C 50°C 150°C 50°C 150°C 50°C 150°C 50°C 150°C Firing range of Riello RLS100- two stage gas/light oil burner Diagram 16 Firing range for Riello TI Series Burner combustion headsDiagram 17 Useful working field for choosing the burner Modulation range Airtemperature°C Boilersinfo.com
• 35. 36 2.3.2 System engineering diagrams for burners using low viscosity (< 6 cSt) liquid fuels - diesel oil / kerosene Gas supply - low pressure circuitDiagram 18 Gas supply - high pressure circuitDiagram 19 A = Drop-type plant with fedding from top; B = air intake system Diagram 20 Drop-type plant with feeding from bottom Diagram 21 Servomotor Burner air fan Anti-vibrating joint Gas filter Gas governor Min gas pressure switch Gas safety valve Leak proving system Gas regulation valve Gas flow regulator Max gas pressure switch Air pressure switch Servomotor Burner air damper Burner air fan Air pressure switch Light-oil tank Light oil filter Burner pump Nozzle holder lance Oil safety valve Servomotor Burner air damper Burner air fan Air pressure switch Light-oil tank Light oil filter Burner pump Nozzle holder lance Oil safety valve Servomotor Burner air damper Anti-vibrating joint Burner air fan Gas filter Second stage gas reduction Min gas pressure switch Gas safety valve Leak proving system Gas regulation valve Gas flow regulator Max gas pressure switch Air pressure switch Ambient air Ambient air Hmax (general10m) Ambient air Ambient air 2.3.1 System engineering diagrams for gas fired burners Gas pressure reduction Gas train Hmax (general10m) Boilersinfo.com
• 36. 37 2.3.3 System engineering diagrams for burners using high viscosity (> 6 cSt) liquid fuels System with ring under pressureDiagram 22 Ring-type system for multi-stage and modulating burners with service tankDiagram 23 BR Dualbloc burner BR1 Monoblock burner B Gas separator bottle r Oil filter 300 microns degree MM Oil delivery gauge P(MP) Pumping group – transfer ring P1(MP) Pumping group – burner circuit with filter and pressure regulator P2(MP) Pumping group – main circuit with filter PS Electrical oil preheater RS1 Pump heater resistance RS2 Oil tank heater resistance SB Main oil tank SB2 Service oil tank T Thermometer TC Temperature switch regulation Servomotor Burner air damper Burner air fan Air pressure switch Light-oil tank Light oil filter Burner pump Nozzle holder lance Oil safety valve Light-oil ring pump Oil pressure gauge Ambient air Tr Flexible oil line Tr1 Flexible oil line pressure 25-30bar TP Temperature probe TM Max oil pressure switch VC Vent valve VG Supply air fan VR1 Oil pressure regulator valve of the oil burner ring VR2 Oil pressure regulator valve of the oil main ring VS Preheater safety valve VG7 Safety valve VG Double valves Heavy oil pipe with electrical preheater cable Two stage burner Modulating burner Modulating burner Boilersinfo.com
• 37. 38 2.3.4 Diagrams for the calibration of single-stage burners Ring-type system for multi-stage and modulating burners without service tank Diagram 24 BR Dualbloc burner BR1 Monoblock burner B Oil burners gas separator F Oil filter 300 microns degree MM Oil delivery gauge P(MP) Pumping group - main circuit with filter P1(MP) Pumping group - burner circuit with filter and pressure regulator PS Electrical oil preheater RS1 Pump heater resistance RS2 Oil tank heater resistance SB Main oil tank T Thermometer TE Temperature switch regulation TF Flexible oil line TP Temperature probe TM Max oil temperature switch VC Control valve (3 way) VE Supply air fan VR1 Oil pressure regulator valve of the oil burner ring VR2 Oil pressure regulator valve of the oil main ring VS Preheater safety valve VGZ Safety valve VG Double valves Heavy oil pipe with electrical preheater cable SER1 Burner air damper VT Burner air fan C Anti-vibrating joint GF Gas filter PCV Gas governor PG Min gas pressure switch VS Gas safety valve PC Leak proving system VR Gas regulation valve RG Gas flow regulator PGM Max gas pressure switch T1 Thermostat QRP Burner control panel LA Nozzle holder lance VS Oil safety valve Layout of regulation components for a single-stage burnerDiagram 25 Two stage burner Modulating burner Modulating burner Ambient air Boilersinfo.com
• 38. 39 2.3.5 Diagrams for the calibration of multi-stage burners 2.3.6 Diagrams for the calibration of modulating burners Layout of regulation components for a two-stage burnerDiagram 26 Layout of regulation components for a modulating burnerDiagram 27 SMn Servomotor SER1 Burner air damper VT Burner air fan C Anti-vibrating joint GF Gas filter PCV Gas governor PG Min gas pressure switch VS Gas safety valve PC Leak proving system VR Gas regulation valve RG Gas flow regulator PGM Max gas pressure switch T1 Thermostato/Pressure switch 1st stage QRP Burner control panel LA Nozzle holder lance VS Oil safety valve T2 Thermostato/Pressure switch 2nd stage SMn Servomotor SER1 Burner air damper VT Burner air fan C Anti-vibrating joint GF Gas filter PCV Gas governor PG Min gas pressure switch VS Gas safety valve PC Leak proving system VR Gas regulation valve RG Gas flow regulator PGM Max gas pressure switch T1 Temperature / pressure probe QRP Burner control panel LA Nozzle holder lance MD Modulation device Ambient air Ambient air Boilersinfo.com
• 39. 40 2.3.7 Diagram of burner with measurement and regulation of the percentage of O2 in the flue gases 2.3.8 Diagram of burner with pre-heating of the combustion supporter air Layout of O2 regulation systemDiagram 28 Layout of a system with pre-heating of comburent air Diagram 29 SMn Servomotor SER1 Burner air damper V1 Burner air fan QRP Burner control panel LA Nozzle holder lance VS Oil safety valve EGA Exhaust gas analyzer FRV Fuel regulator valve (gas/oil) SO Exhaust gas probe SC Exhaust gas/air heat exchanger VT Fan VS Air damper Ambient air Ambient air Fuel pipe Heavy oil Boilersinfo.com
• 40. 41 2.3.10 Layout of the Burner Management -System Layout of the fan speed rotation regulation with inverterDiagram 30 Layout of integrated management for supervising a combustion systemDiagram 31 2.3.9 Diagram of burner with inverter controlled motors SMn Servomotor SER1 Burner air damper V1 Burner air fan QRP Burner control panel LA Nozzle holder lance VS Oil safety valve IV Inverter FRV Fuel regulator valve (gas/oil) M Three phase induction motor SMn Servomotor SER1 Burner air damper V1 Burner air fan QRP Burner control panel (i.e. micro modulation Autoflame) LA Nozzle holder lance VS Oil safety valve IV Inverter FRV Fuel regulator valve (gas/oil) EGA Exhaust gas analyzer SO Exhaust gas probe DTI Data transfer interface LPC Local computer MDM Modem RPC Remote computer Ambient air Heavy oil Heavy oil Heavy oil Ambient air Ambient air Boilersinfo.com
• 41. 42 2.4 THE COMBUSTION HEAD The combustion head is the part of the burner that mixes the combustion supporting air with the fuel and stabilises the flame that is generated. The combustion head essentially comprises the following components: • The fuel metering device: nozzles for liquid fuels and orifices and distributors for gaseous fuels; oil nozzles are characterised by three parameters: output, spray angle and type of spray distribution (pattern). • The turbulator diffuser disk, which mixes the fuel and the combustion air, and stabilises the flame to avoid it blowing back into the burner; • The flame ignition system, uses electric arcs produced by high-voltage powered electrodes directly igniting the flame or coupled with a pilot burner; • A flame sensor for motoring the flame; • The flame tube comprising made of profiled metal cylinder which defines the output speed range. The flame tube and the diffuser disk essentially determine the geometry of the flame developed by the burner. Especially the latter determines the rotational features of the fuel and combustion supporter mixture flow and, consequently, the flame dimensions. The rotational characteristic of the mixture flow is expressed in mathematical terms by the number of swirls defined as: S = Gf / (GxR) where: S = the number of swirls; Gf = the angular momentum of the flow; Gx = the axial force; R = the radius of the nozzle outlet; As a rule, an increase in the number of swirls causes an increase in the flame diameter and a decrease in the flame length. Drawing of composition of combustion head for gas/light oil Riello RLS100 burnerDiagram 33 FLAME TUBE FLAME FIRING ELECTRODES REGULATION CYLINDER GAS DISTRIBUTOR SWIRLER DISK DIFFUSER OIL NOZZLELIQUID FUEL SECONDARY AIR GAS NOZZLE Nozzles: full cone and empty cone distribution; definition of spray angle Diagram 32 Boilersinfo.com
• 42. 43 The section between the sleeve and the diffuser disk determines the amount of secondary air available for the flame. This amount is zero when the disk is closer and in contact with sleeve. In certain burners it is possible to adjust the space between the disk and the turbulator diffuser changes the secondary air by changing the position of the disk itself. Combustion heads can be classified according to the following layout: • Non-adjustable fixed head, where the position of the combustion head is fixed by the manufacturer and cannot be changed; • Adjustable head, where the position of the combustion head can be adjusted by the burner installer during commissioning; • Variable-geometry head, where the position of the combustion head can be varied during the modulating burner operation. Non-adjustable fixed head burners are generally burners used for industrial processes and dedicated to the generators they must be coupled to. For adjustable head burners, regulation is pre- set in correspondence with the maximum output of the burner for the specific application. For easier start-up and configuration operations, a graph is provided for each burner indicating the position of the regulation mechanisms in relation to the required thermal output. This construction type makes the burner suitable for different requirements, which is why monobloc Forced draught burners with a low to medium output are predominantly adjustable head types. Variable-geometry burners are generally high- output modulating burners. The geometry of the head is also extremely important in reducing polluting emissions, especially Nox, as described in paragraph 1.4.2. 2.4.1 Pressure drop air side The firing ranges of monobloc burners already take into account the air pressure drop of the combustion head. When choosing a dual bloc burner, for the purpose of choosing the correct fan, the pressure drop on the air side must be known in relation to the delivery; for easier reading, this information refers to a standard temperature and is supplied in relation to the thermal output developed. 2.4.2 Pressure drop fuel side To correctly select the fuel feed pipe for both monobloc and dual bloc burners, certain working information is required about the related circuits inside the combustion head. In the case of gaseous fuels, tables or diagrams are provided, such as those presented in diagram 35, which provide the overall pressure drop of the gas pipe in the head, in relation to the thermal output developed. For liquid fuels, the pressure value required by the nozzle for spill back nozzles (modulating), and the diagram of the minimum pressure to be guaranteed on the nozzle return pipe when the fuel delivery varies, are provided. TI 10 head pressure drop side air referred to backpressure 0 - air damper not included Air suction temperature 15°C 0 50 100 150 200 250 0 1 2 3 4 5 MW StaticPressure[mmw.c.] TI 10 P/NM TI 10 P/M Pressure drop air side in combustion head - dualbloc TI 10 burner Diagram 34 Natural gas G20 - Net calorific value 9,94 kcal/Nmc 0°C mbar 0 10 20 30 40 50 60 0 Output Power (MW) Pressureloss(mbar) Pressure drop gas side in combustion head - dualbloc TI 10 burner Diagram 35 Boilersinfo.com
• 43. 44 2.5 THE FAN Fans are machines capable of supplying energy to a fluid, by increasing pressure or speed, using a rotating element. Depending on the air-flow direction the following types of fan can be used: • centrifugal; • axial; • tangential. In centrifugal fans, the air enters along the direction of the rotation axis and exits tangentially to the fan wheel. In axial fans, the air direction is parallel to the axis of the fan wheel. In tangential fans, the air enters and exists tangentially to the fan wheel. The fans installed on monobloc burners and those used separately for dual bloc burners are generally centrifugal, such as that shown in the Diagram. Centrifugal fans are made up of a box that contains a keyed fan wheel on a shaft supported by bearings. The shaft can be connected directly to the electric motor using joints or, indirectly, using belts and pulleys. The fan wheel positioned inside the box may have differing blade orientations/profiles and specifically: • fan wheel with wing-shaped blades; • fan wheel with reverse curved blades, • fan wheel with radial blades; • fan wheel with forward curved blades; Diagram 37 shows the variation in absorbed output when fan delivery varies; the fan wheel with wing-shaped blades behaves similarly to the fan wheel with reverse curved blades. The working characteristics of a fan, similar to those for pumps, are described by the characteristic curve. The characteristic curve of a fan is represented in a Cartesian plan where the Y axis shows the pressure and the X axis shows the volumetric delivery (see Diagram 38). The characteristic curves can be accompanied by other curves such as performance or yield curves and the absorbed output curve of the electric motor (see Diagram 39). The number of characteristic curves for each fan depends on the number of rotation speeds, as shown in Diagram 40. When a fan operates in a circuit, which also Feed pressure of liquid fuelDiagram 36 Fan of a dualbloc burnerDiagram 37 Output absorbed from different types of fan varying delivery Diagram 38 delivery (%) curved forward blade radial fan axial fan reverse curve blades powerabsorbed(%) Nozzledelivery(kg/h) Return pressure (bar) Boilersinfo.com
• 44. 45 has a characteristic curve, delivery is supplied when total pressure developed is equal to the circuit pressure. This situation is represented by the intersection point between the characteristic fan curve and the characteristic circuit curve, as indicated in Diagram 41. In the case of forced draught burners, the system characteristic curve varies in relation to the setting of the combustion head and opening degree of the air damper. To correctly choose the fan, the circuit curve must correspond to the load used. Therefore, in order to discover the delivery and the head of a fan, we need sufficiently precise information regarding the pressure drop induced by the circuit, including the air intake pipes, burner head feeding pipes and the accessories. As already mentioned, circuit pressure drops have a parabolic flow with respect to fluid speed and, consequently, delivery. Pressure drops in an areaulic system are determined by two components: • concentrated pressure drops; • distributed pressure drops. Among the concentrated pressure drops, account must be taken of those introduced by the combustion head, where the air transits using a complex geometric route; furthermore, an air damper is fitted inside the burner for calibrating the delivery of combustion supporter air. Burner manufacturers provide graphs that represent the trend of pressure drops in relation to air delivery, or, for easier consultation, in relation to the thermal output delivered by the burner. Distributed pressure drops can be estimated by using the Darcy-Weisbach formula: eq 2.5-1 where: ∆pf = pressure drop due to friction [m]; f = friction factor; ∆pf = .f .L D v2 2 . g Typical performance graphs of a centrifugal fan Diagram 39 Fan performance graphs on varying motor speed rotation Diagram 40 Performance graph of fan and resistant circuit with working point Diagram 41 rpm density 1,2 kg/m3 Lpa = Sound pressure level in dBA at 1,5 m distance Delivery rpm Totalpressure Discharge air velocity dinamic pressure Lpa Maximum fan pressure Resistant circuit performance graph Fan performance graph Nominal delivery Nominalpressure Boilersinfo.com
• 45. 46 L = pipeline length [m]; D = pipeline diameter [m]; v = air speed inside the pipeline [m/s]; g = gravity acceleration 9.81 [m/s2 ]; The term v2 /2g is called dynamic pressure. The friction factor f can be determined using the MOODY abacus (Diagram 42) if the Reynolds number and related texture is known. The Reynolds number is defined by the following formula: eq 2.5-2 where: NRe = Reynolds number; d = internal pipeline diameter [m]; V = air speed [m/s]; g = kinematic air viscosity equal to 16.0 ·10-6 m2 /s; The related texture e/D is the formula between the absolute texture and the diameter of the pipeline both expressed in mm. Table 9 shows the absolute texture value of certain typical ducts. For easier calculation, a series of abacuses exist to determine linear pressure drops, shown in section 5. The formulas introduced always refer to certain circular sections, while in constructive practice rectangular pipelines are often used. To use the same formulas, an equivalent diameter De must be used, defined as: eq 2.5-3 De = 2 . a . b a + b NRe = d . V γ where: De = equivalent diameter [m]; a, b = side dimensions of the rectangular pipeline [m]; Localised pressure drops, due to the presence of dampers, grids and any heat exchangers, must be calculated for the effective value of the drop introduced, which must be provided by the manufacturer of the mentioned devices. Localised pressure drops, due to the presence of circuit peculiarities, such as curves, direction and section variations, can be calculated using the following equation: eq 2.5-4 where: ∆pw = pressure drop [Pa]; ξ = non-dimensional drop factor; ρ = volume mass [kg/m3 ]; v = average speed in the pipeline [m/s]; A series of tables exist in the technical literature, similar to those in Diagram 43 which show the ξ value for the various special pieces, some of which are illustrated in section 5 READY-TO-USE TABLES AND DIAGRAMS. 2.5.1 Regulating combustion air As already mentioned, the delivery of combustion supporter air is proportionate to the delivery of fuel burnt, which in turn is proportionate to the required output. For multi- stage and modulating burners, air provided by the fan must be changed in order to vary the delivery. In Forced draught burners, delivery can be varied in two principal manners: ∆pw = .ξ .ρ v2 2 Pipeline material Absolut texture (mm) Smooth iron plate duct 0,05 PVC duct 0,01 – 0,05 Aluminium plate duct 0,04 – 0,06 Galvanized sheet-iron duct with cross joints (1,2m step) 0,05 – 0,1 Galvanized sheet-iron circular duct, spiraliform with cross joints (3m step) 0,06 – 0,12 Galvanized sheet-iron duct with cross joints (0,8m step) 0,15 Glass fiber duct 0,09 Glass fiber (internal covering) duct 1,5 Protected glasswool (internal covering) duct 4,5 Flexible metal pipe 1,2 - 2,1 Flexible non-metal pipe 1 – 4,6 Cement duct 1,3 - 3 Non-dimensional drop factors for air pipelines Table 9 Boilersinfo.com
• 46. 47 • Varying the fan firing point; • Varying the number of fan revolutions; In the first regulation method, the fan firing point is moved, which remember can only be done along the characteristic curve, by varying the pressure drop of the areaulic circuit by introducing a servo-controlled damper (see Diagram 44). Depending on the opening degree of the damper, the various system curves are obtained. In our case, the regulation damper closing determines the variation of the characteristic system curve from curve 1 to curve 2; consequently, the fan firing point moves from A to B, with the consequent increase of the fan head from P1 to P2’ and the decrease of the delivery from Q1 to Q2. The opening degree of the damper introduces the various characteristic system curves thus determining differing delivery values. This system is rather effective, above all in centrifugal fans with forward curved blades, where a delivery drop corresponds to a drop in absorbed output. In centrifugal fans with reverse curved blades, the output curve has a virtually flat trend and therefore it is not possible to obtain optimum operating performances. The variation of the number of fan revolutions is obtained by using specific electronic devices called “inverters”. These devices vary the frequency of the power supply voltage to the electric motor connected to the fan wheel. The number of electric motor revolutions is linked to the power supply frequency according to the following equation: where: n = number of motor r.p.m.; f = power supply voltage frequency [Hz]; p = number of poles; By regulating the number of revolutions, maximum performance operating can be n = .120 f p Moody's abacusDiagram 42 Adimensional loss factors for air pipelines Diagram 43 f Reynolds number Re = ρ Vd / µ Transition flow Laminarflow Turbolent flow Boilersinfo.com
• 47. 48 obtained under the various working conditions, as the characteristic curve is translated until it coincides with the nominal firing point. Diagram 45 shows the fan behaviour when the number of motor revs is varied. branched (gas supply network). Inside the pipelines, the gas is at a pressure, which is variable by several tens of bars for main supply pipelines, and by several tens of mbars in final delivery pipelines of the gas to the user. The main problem in distribution networks of gaseous fuels is the variation in feed pressure. Any pressure instability within the distribution network causes the burner to work incorrectly. In order to avoid such problems, fuel gas feed pressure to the combustion head must be: • Greater than a minimum value which can overcome the pressure drop due to the combustion head (see paragraph 2.4.2) and the back pressure in the heat generator combustion chamber; • Lower than the permitted maximum pressure value declared by the manufacturer; • Stable and repetitive with respect to the settings. To guarantee these conditions, fuel gas supply to the burner is through a series of safety and control equipment that globally are called the “gas train”. Diagram 45 shows the functional layout of a gas train. The connection module comprises a manual shut off valve and an anti-vibration connection joint so that any vibrations produced by the burner are not transmitted to the entire feed network of the fuel gas. The filter is used to guarantee filtration of any particles that may be present in the gaseous fuel, particles that might damage the seal of the safety and shut off valve. The task of the pressure reducer is to reduce the pressure of the mains gas and maintain constant the outgoing pressure, independently from the incoming pressure and delivery. Pressure reduction and stabilising is made through use of a membrane-type system loaded by a spring that controls the shutter opening using levers. The high pressure unit includes the lock out, safety and discharge valves as well as several gauges upstream and downstream for visually controlling pressure levels. The pressure reducer has a maximum incoming pressure and a series of outgoing Change of delivery by varying pressure drops of the circuit Diagram 44 Example of delivery changing by motor speed variation Diagram 45 Functional layout of the gas trainDiagram 46 Connection modulus Filter Pressure reducer Pressure reducer Safety and delivery valves Burner Gas pipeline 2.6 FUEL SUPPLY 2.6.1 Gas supply Gaseous fuel is usually transported from the point of storage/drawing to the user by a series of pipelines, which may be more or less Boilersinfo.com
• 48. 49 pressure values that can be selected in relation to the spring and the effective rating. The pressure reducer and safety devices are necessary if network fuel gas pressure is greater than the maximum value established by the manufacturer for the downstream devices. (In this case, the function of stabiliser is included in the reducer). If the gas network delivery pressure is lower than the maximum value permitted by the manufacturer, as a rule between 300 and 500 mbar, a pressure reducer is not needed, just the stabiliser. The solenoid valve unit comprises a safety valve, a progressively opening regulating valve and a minimum pressure switch. For burners with outputs greater than 1,200 kW, the EN676 standard establishes that the valve unit must be also equipped with a seal control device for the safety and regulation valve; this device is available and can also be used on burners with lower outputs. The devices mentioned can be grouped into a single body, which incorporates the functions of stabiliser, and safety shut off. The valve units can be grouped into two categories, depending on the fuel shut off method: • single flow; • double flows. The application of one of these two types depends on the thermal load regulation devices installed on the burner. To attach the gas train to the burner, a connection adapter could be required. Furthermore, a series of taps must be fitted in the gas train for measuring the pressure upstream from the filter, upstream from the Gas filterDiagram 47 Pressure RegulatorDiagram 48 Gas differential pressure switch Shut-off and safety valvesDiagram 49 Gas pressure switchDiagram 50 Boilersinfo.com
• 49. 50 valve unit and in correspondence with the combustion head. As already said, if the pressure upstream from the manual shut off valve is lower than a certain value established by the manufacturer, the pressure reducer is not required. In this case, the gas train supplied with the burner can be monobloc, i.e. with the filter, stabiliser and valve unit included inside a single component or else comprising individual components joined in series. For domestic uses where the EEC 90/396 Gas Directive makes it compulsory for the manufacturer to type approve the whole system including the burners and the feed system, the complete gas train must be provided by the manufacturer and type approved together with the rest of the devices. The choice of the gas train depends on the minimum pressure to be guaranteed to the burner head and, consequently, the maximum pressure drop determined by the latter, as illustrated in the subsequent paragraph and in the example in section 3. A series of components are fitted to the burner, which have a very important role during setting and regulating the entire system. In particular, gas or dual fuel burners have a butterfly valve to regulate fuel delivery, driven by a variable profile mechanical cam servomotor, or in the more sophisticated systems, controlled by the Burner management system (electronic cam). Generally, there is a maximum gas pressure switch to shut off burner functions if pressure is too high along the fuel supply line. 2.6.1.1 Calculating the fuel gas supply pipelines The following formula is used for dimensioning the fuel gas supply pipelines: Eq. 2.6.1-1 where: ∆PA-B = pressure drop between point A and point B [Pa]; l = friction factor; V = the average gas speed [m/s]; r = the gas volume mass [kg/m3] referring to 15°C and 1,013 mbar; LTOT = total pipeline length [m]; Di = internal pipeline diameter [m]; The average gas speed inside the pipeline can be calculated using the following formula: Eq. 2.6.1-2 where: Q = fuel gas delivery [m3 /h]; Di = internal pipeline diameter [m]; The fuel gas delivery must be established using the following formula: Eq. 2.6.1-3 where: Q = fuel gas delivery [m3 /h]; m = maximum burner output [kW]; Hi = inferior calorific value of the fuel gas [kWh/m3 ]; Remember that 1 kWh = 3,600 kJ. The friction factor λ can be calculated using the following formula: Q = m Hi V = Q A = [m/s] Q . Di 2 ∆PA-B = . LTOT λ . V2 . ρ 2 . Di Seal control systemDiagram 51 Connection adaptorDiagram 52 ø2 ø1 Boilersinfo.com
• 50. 51 Eq. 2.6.1-4 where: Di = internal pipeline diameter [m]; Re = the Reynolds number which can be determined by using the following equation: Eq. 2.6.1-5 where: Di = internal pipeline diameter of the [m]; g = fuel gas kinematic viscosity [m2 /s]; Q = fuel gas delivery [m3 /h]; The viscosity of the gaseous fuel can be taken from the graph illustrated in diagram 53. The graph shows the absolute viscosity expressed in micropoises. Remember that the kinematic viscosity is linked to the dynamic viscosity by the formula: Eq. 2.6.1-6 where: γabsolute= dynamic or absolute viscosity [kg/m·s]; γ = fuel gas kinematic viscosity [m2 /s]; ρ = the volume mass of the gas [kg/m3 ] referring to 15°C and 1,013 mbar; In technical practice, the absolute viscosity is measured in Poises (P) equating to: γabsolute = γ ρ Re = .354 Q Di . γ . 10-6 λ = +0, + 2,9 . 10-5 . Re 0,109 Di 0,612 Re 0,35 The pressure drops in feed pipelines between the fuel gas delivery point and the burner gas train must be kept within limits that guarantee correct functioning of any reducer units present. For low pressure systems (p ≤ 40 mbar), the pressure drops must be kept within the following values: The pressure drops in the pipelines are the sum of those distributed along the pipeline and those concentrated due to joints and hydraulic accessories (filters, valves, etc..). The concentrated losses due to hydraulic accessories are calculated using the equivalent length method, in other words a concentrated loss is assimilated to a stretch of pipeline equal to the length of the related loss. To correctly dimension the pipelines, we can define the following sizes: LEFF = effective pipeline length [m]; LEQUIV = the sum of the equivalent lengths relating to concentrated pressure drops as a result of joints and hydraulic accessories[m]; LTOT = total pipeline length, sum of the effective length and the equivalent length [m]: LTOT = LEFF + LEQUIV Eq. 2.6.1-7 The equivalents lengths relating to the concentrated resistances of the components can be determined using the schedule shown in Table 11, which shows the reference equivalent lengths of the main concentrated resistances. To determine the equivalent length, we must presume an initial pipeline diameter imposing a maximum fuel gas flow speed of approximately 1 m/s, taking care to correct the value of the equivalent lengths if a different 1poise = 1 = Kg m . s g cm . s 0,1 Absolute viscosity of certain gasesDiagram 53 °C Pasx106 Maximum pressure drops of gas pipelines Table 10 Gas Town gas Natural gas and air mixtures Natural gas Natural gas replacements L.P.G. and air mixtures Liquid Petroleum Gas (G.P.L.) Pressure drop [mbar] 0,5 1,0 2,0 Boilersinfo.com
• 51. 52 diameter should emerge from the calculation carried out using equation 2.6.1-1. Section 5 contains some tables illustrating permissible gas delivery values in relation to the internal pipeline diameters and total lengths in steel and copper, for the gases in the first, second and third series; note that the total length and gas delivery is therefore essential to choose the pipeline diameter. 2.6.1.2 Choosing the gas train For using burners in domestic and commercial spheres, the EEC 90/396 Gas Directive obliges burner manufacturers to provide the burner with a gas train complete with all the components. The EEC 90/396 Gas Directive defines the essential requisites of the equipment that burns gaseous fuels. Self-certification of conformity by the manufacturer is not enough for all the aforementioned equipment, but certification is required which declares the compliance of the equipment with the provisions of the Gas Directive, issued by an Informed Body. The gas train should be chosen from the manufacturer's catalogue, exclusively in relation to the pressure drop introduced by the same train. To correctly choose the gas train to be combined with the burner, the sum of all the pressure drops suffered by the flow of the gaseous fuel from the delivery point up to the burner, must not exceed the available pressure at the delivery point. Starting downstream, the drops to be considered are as follows: H1: back pressure in the combustion chamber; H2: the combustion head H3: the gas train; H4: the feeding system up to the delivery point, calculated as described in the previous section. If we call H, the minimum pressure available at the delivery point for the gaseous fuel, the following conditions must be checked: Di (mm) 90° curve T Connection cross Sharp bend Cock Natural gas - CH4/air mixtures – Cracking gas <= 22,3 0,2 0,8 1,5 1 0,3 from 22,3 to 53,9 0,5 2 4 1,5 0,8 from 53,9 to 81,7 0,8 4 8 3 1,5 => 81,7 1,5 6,5 13 4,5 2 Liquid Petroleum Gas – L.P.G. mixtures <= 22,3 0,2 1 2 1 0,3 from 22,3 to 53,9 0,5 2,5 5 2 0,8 from 53,9 to 81,7 0,8 4,5 9 3 1,5 => 81,7 1,5 7,5 15 5 2 Maximum pressure drops of gas pipelines Table 11 Example for the tabular calculation of the diameter of the gas pipelinesTable 12 Thread Thickness mm Delivery Boilersinfo.com
• 52. 53 H ≥ H1 + H2 + H3 + H4 For ease of calculation, certain manufacturers provide diagrams of the pressure drops in the gas trains as the sum of the gas train pressure drop and the combustion head (H2+H3). Therefore, the choice of gas train must be satisfy the following equation: Noting the maximum allowable value of H2+H3, using diagrams similar to those in Diagram 47, we can choose the gas train. As shown in the diagram, the graph of the gas train characteristic curve is often accompanied by a graph showing the burner firing range to facilitate the choice. 2.6.1.3 The feeding of liquid petroleum gases (LPG) Liquid petroleum gases are gases in a liquid state obtained by distilling crude oil or taken from natural gas and residual gases from refinery process. The composition of LPG is somewhat variable but generally comprises mixtures of propane and butane, which are generally considered fuels with a high level of purity. LPG is produced and conserved in a liquid state, for storage and transporting large amounts in an economically viable manner. The volume formula between the gaseous stage and the liquid stage is variable and generally equates to 250 Nm3 /m3 ; this means that during the transition from the gaseous state to the liquid state the mixture reduces its volume by over 250 times, so that even with tanks of limited dimensions it is possible to store considerable amounts of the fuel. Therefore, to obtain a cubic metre of LPG in gaseous state, 4 litres of LPG in liquid state are needed. The vapour tension of LPG is low making it possible to liquefy the gas with a pressure around 3 ÷ 5 bars. LPG can be distributed to an individual user or to a series of users. In the first case, the individual user can be guaranteed a sufficient stock of fuel using a series of cylinders weighing several tens of kilograms connected in series or by small tanks usually with a capacity of less than 5 m3 . In the second case, a medium or low pressure distribution network linked to a single large 0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 460 480 500 520 540 560 580 600 620 640 660 680 700 720 740 760 780 800 820 Output (kW) Pressureloss(mbar) Combustion head MB 15/2 + combustion head MB 20/2 + combustion head Graph for the detrmination of the gas trainDiagram 55 LPG tankDiagram 54 Boilersinfo.com
• 53. 54 storage tank guarantees the supply to the individual user. The first solution is adopted to guarantee the gas supply to individual isolated users or those who have particular requirements, while the adoption of a distribution network is convenient for small communities or populated areas. With respect to the use of individual cylinders, installed in private property, the centralised system offers considerable advantages in terms of safety and continuity of running. The LPG contained in a tank comprises a liquid state in the lower part and a gaseous state in the upper part. The tank cannot be filled completely in the liquid state, because should the temperature rise, the liquid, which cannot be compressed and is under pressure, would not be able to expand, with the consequent danger of the tank exploding. Therefore, a portion of volume free from the liquid state must be guaranteed, equal to at least 20% of the total volume. LPG is used in burners and other equipment nearly always when the fuel is in a gaseous state. LPG can be bled from the tank directly in its gaseous state from the top of the tank or can be drawn off in the liquid state from the bottom of the tank to then be transformed into gas in a special vaporiser. When drawing off in the gaseous state, the delivery from the top of the tank causes a pressure drop inside the tank, thus modifying the balance between the liquid and the gaseous state, causing part of the liquid to evaporate in order to restore the initial pressure. LPG evaporation is an exothermic transformation, in other words it takes place by absorbing heat, subtracting it from the liquid mass of the LPG. The cooling of the liquid mass is proportionate to the amount of LPG drawn off in the gaseous state and determines a further pressure drop in the tank. If it is drawn off at a constant speed and within a certain limit, a balance will be established in which the heat required for transforming the state of the LPG is guaranteed by the heat exchange with the surrounding environment. It must be remembered that the heat exchange between the tank and the surrounding environment takes place exclusively through the portion of the external surface dampened by the liquid LPG. If the gas is drawn off at a speed greater than the limit allowed, the temperature of the tank will fall considerably to the extent that a layer of ice forms on the surface of the tank, further decreasing the heat exchange with the surrounding environment until the fuel transformation is blocked, making drawing off impossible. From the description of the process, we can see that the amount of gas that can be delivered from the tank depends on the heat transmission characteristics between the tank and the environment, which depend on the form, material and colour of the tank, as well as on the environmental conditions where the tank is installed. The tank manufacturers provide the maximum delivery capacity for the tank under standard working conditions, usually expressed in kg/h. This capacity may vary from 0.5 kg/h for small cylinders up to nearly 20 kg/h for tanks with a capacity of 5 m3 . We should also remember that the delivery capacity of a tank depends on the filling level, decreasing as the fuel level decreases, due to the decrease in pressure and the heat exchange surface area. This means that not all the contents of the tank can be used, in order to guarantee a sufficient feed pressure. This minimum filling level, after which it should be topped up, is established by the tank manufacturer and is equal to around 25% of the tank's volume. Therefore, the portion of the tank's volume that can be effectively used is equal to approximately 55% of the geometric volume of the tank. To calculate the thermal capacity stored, we can use the following equations: Es = 0,55 · VG · d · PCILPG Where: ES = energy stored by the tank [MJ]; VG = the geometric volume of the tank [m3 ]; d = LPG density equal to 0.52 kg/l [kg/l]; PCILPG = inferior calorific value of the LPG and equal to approximately 46 MJ/kg [MJ/kg]; The number of estimated annual refills is: n = ES / EU where: n = number of annual refills; ES = energy stored by the tank [MJ]; EU = energy consumed by the users [MJ]; Furthermore, we must always check that the total output installed does not exceed the maximum delivery capacity of the tank, in particular: mtank > musers = PU / PCILPG Boilersinfo.com
• 54. 55 where: mtank= maximum delivery capacity of the tank [kg/h]; musers = maximum fuel delivery required by the users [kg/h]; PU = output installed by the users [kW]; PCILPG = inferior calorific value of the LPG and equal to approximately 12.78 kWh/kg [kWh/kg] When the delivery requested by the users exceeds the maximum delivery capacity of the available tanks, it must be drawn of in the liquid state. It is drawn off from the bottom of the tank with the fuel in a liquid state, and then cause the liquid to vaporise using a heat exchanger (vaporiser). This system guarantees the complete vaporisation of the LPG and permits the eventual pre-heating of the latter to avoid the formation of condensation on the pipeline. It is usually used where the cost of vaporisation is justified by the complexity of the system and is virtually compulsory if, for reasons of safety and space, the tanks are underground, as in this case the heat exchange between the tank and the outside environment is poor. The pressure reduction from that inside the storage tank, (generally around 5 bars), to the working pressure (e.g. for small users around 30 mbars), is usually by a double-stage system. The first reducer reduces the pressure to 1.5 bars, while the second reducer reduces the pressure to 30 mbar (150 mbar for supplying industrial burners). LPG in the gaseous form has a density more than 50% higher than that of air, and therefore in case of accidental leakage it tends to stratify low down and stagnate in pockets on the floor. In order to expel it, aeration is not always enough but the physical removal using appropriate means is often required. Any detectors and permanent aeration vents should be positioned flush with the floor. 2.6.2 Feeding diesel oil and kerosene Hydraulic circuits on board liquid fuel burners or mixed burners, have different features and complexity, depending on the type of fuel, supplied output, load regulation logic (single- stage, multi-stage or modulating) and special standards in force. Generally the burners are fitted with a geared pump and a single or double fuel shut off solenoid system. Modulating burners also have shut off valves on the return circuit and a pressure regulator for varying output. The fan motor drives the pump, or it is run independently, it can have special features for using kerosene. The following diagram shows the section of a typical geared pump fitted to the RL 190/M model, for example, on monobloc diesel oil burners (RL series). In modulating burners, the modulating pressure regulator is activated in combination with the air damper, using mechanical lever systems or electronic systems that point by point supply fuel and combustion air in the correct proportions to obtain the required output. For adaptation to specific standards, pressure control devices can be fitted, such as minimum and maximum oil pressure switches. The table below shows the commercial Shut-off solenoid valve on output circuit - close postition Diagram 56 Gear pump for liquid fule monobloc burner Diagram 57 Suction Return To the nozzle Boilersinfo.com
• 55. 56 wording for the various liquid fuels, highlighting the typical plant engineering types for diesel oil and kerosene. The diesel oil feed systems covered in this section are a "bi-pipeline" type and namely those comprising a delivery pipeline from the tank to the burners and a return pipeline from the burner to the tank. Systems also exist with single diesel oil feeding pipelines, without a return line to the storage tank, where re-circulation of the unburned diesel oil takes place in proximity to the burner itself using specific accessory components. By varying the tank position with respect to the burner position, we have the following plant engineering examples: 1. drop-type systems with supply from bottom; 2. drop-type systems with supply from summit; 3. in-take type systems; 4. systems with ring under pressure. The first three plant engineering types do not require the use of an additional pump, but entrust diesel oil circulation to the pump installed on the burner. In the system with the ring under pressure, an additional pump is required with the task of guaranteeing the fuel flow in the main ring. Due to the long distance between storage tank and burner, the burner pump normally has to guarantee the feed pressure. The minimum temperature that diesel oil can reach in underground or insulated pipelines, can be assumed as +2°C. The first three plant engineering types are discussed together as they are subject to the same criticality. 2.6.2.1 Drop-type system with supply from bottom / drop-type system with supply from summit / intake type system As already mentioned, these three plant engineering types are related by the fact that the burner pump must guarantee fuel transport from the storage tank to the burner nozzles. Viscosity - + I Kerosene Gasolio Olio combustibi le fluido Olio combustibile semidenso Olio combustibile denso Catrami UK kerosene Gas oil Light fuel oil Medium fuel oil Heavy fuel oil Tars D Heizol EL Heizol M Heizol S Heizol S F kerosene Domestique Lourd n°1 Lourd n°2 Bitume USA 6 Air intake system yes yes no no no Drop-type system yes yes yes (unwary) no no Ring under pressure yes yes yes yes yes Pipelines heating no no optional advised yes Incombustible NameFeedingcircuit Light oil burner feedingDiagram 58 Summary of liquid fuelsTable 13 Teer Boilersinfo.com
• 56. 57 In drop-type systems with supply from the bottom (Diagram 21) the difference in height between the maximum level reachable in the storage tank and the centre of gravity of the pump must be lower than the value established by the burner manufacturer (generally between 4 and 10 meters) so as not to over-stress the pump seal mechanism. For drop-type systems with supply from the summit (Diagram 20A), it is advisable that the height P, vertical distance between the centre of gravity of the burner pump and the highest point in the circuit, does not exceed a certain value established by the burner manufacturer (generally between 4 and 10 meters) so as not to over-stress the pump seal mechanism. Furthermore, to allow self-priming the pump, the height V must be no greater than 4 meters. In the intake-type system (Diagram 20B), a pump depression of 50,000 Pa (0.50 bar) must not be exceeded, so that gas is not released from the fuel, sending the pump into cavitation. These pipelines can be dimensioned using the ready-to-use tables supplied by the burner manufacturer, where on the basis of the plant engineering type, the difference in height between the intake mouth and the pump's centre of gravity, and the pipeline diameter, the maximum realisable distance from the system is provided. This distance should be taken as the total length of the delivery pipeline. One of these tables is presented below by way of example: If we require an analytical calculation of the pipelines, we can use the procedure indicated in the following paragraph for systems with pressurised ring. Whatever the plant engineering type chosen, a diesel oil filter must be fitted on the delivery pipeline for separating water and impurities present in the fuel, and a standard valve at the end of the delivery pipeline in the fuel storage tank. The diesel oil storage tank must also be equipped with all the devices required by current local legislation (breather pipes, shut off valves, etc..). 2.6.2.2 Systems with pressurised ring If the burner pump cannot self-feed because the distance and/or the difference in height of the tank are greater than the values supplied by the burner manufacturer, a pressurised ring circuit must be adopted. The ring-type circuit comprises a pipeline, which departs from and returns to the storage tank, with an auxiliary pump to make the fuel flow under pressure. Pumping unit P (main ring) This pumping unit must have a delivery equal to at least twice the sum of the maximum drawing capacities of the burners and comprise a couple of pumps and filters with the possibility of switchover in by-pass: Qp2 = 2 · (∑Mi) eq 2.6.2-1 where Mi is the pump delivery of the individual burner. This over-dimensioning is necessary to guarantee stable pressure in the ring independently from the possible burner functioning combinations. This pumping unit must have a line filter with a metal net cartridge for diesel oil, to separate the impurities and water that may be present in the fuel. The pumping unit head should be calculated on the basis of the residual pressure which must be guaranteed to the ring and the pipeline pressure drops calculated as specified below. In the absence of certain information from the burner manufacturer concerning the pump delivery on the machine, the following typical values can be used: • for multi-stage burners: M = 1.3÷1.5 ·m • for modulating burners: M = 2.0÷2.5 ·m where m is the delivery of fuel equivalent to the maximum output of the burner. Schedule for the tabular scaling of the light oil feed pipelines Table 14 Pipeline length (m) Boilersinfo.com
• 57. 58 Pipelines The pipelines are dimensioned considering the flow inside the pipes under turbulent conditions, as diesel oil has low viscosity. The pipeline pressure drops are the sum of those distributed along the pipeline and those concentrated due to connecting elements and hydraulic accessories (filters, valves, etc..). The concentrated drops due to hydraulic accessories are reckoned using the equivalent lengths method, i.e. a concentrated loss is assimilated to a section of pipeline equivalent to the length of the related loss. To correctly dimension the pipelines the following sizes are defined: LEFF = effective length of the pipeline [m]; LEQUIV = sum of equivalent lengths relative to concentrated pressure drops as a result of connecting elements and hydraulic accessories [m]; LTOT = total length of the pipeline, sum of the effective and equivalent lengths [m]: LTOT = LEFF + LEQUIV [m] Eq 2.6.2 -2 The equivalent lengths relative to the concentrated resistances of the components must be taken from the technical specifications supplied by the manufacturer. If these values are not available, some tables exist, shown in section 5, which contain the equivalent lengths referring to the main concentrated resistances. Any filters must be calculated using the effective pressure drop procured by their presence provided by the manufacturer. If the exact pressure drop value is not available, the filter can be assimilated to an open valve. The calculation delivery is, obviously, equal to that of the pumping unit on the main ring. As far as the delivery pipeline is concerned, the diameter should be chosen in relation to the maximum permitted speed equating to 1÷2 m/s using the following equation: eq 2.6.2 -3 where: d = internal pipeline diameter [m]; Q = delivery in terms of liquid fuel volume [m3 /s] equal to m/ρ where ρ is the diesel oil volume mass as calculated below and m is the delivery in terms of diesel oil mass; V = liquid fuel flow speed equal to 1.5 m/s; A = π . = d⇒ √Q V d2 4 4 . Q π . V ⇒ Q V = The chosen pipeline corresponds to the commercially available diameter immediately above that determined using the equation 2.6.2-3. After establishing the pipeline diameter, the exact fluid speed inside the pipeline must be calculated using the equation 2.6.2-3 to establish the effective hydraulic status of the system, calculating the Reynolds Number using the following formula: Eq 2.6.2 -4 where: NRe = Reynolds Number; d = internal pipeline diameter [m]; V = liquid fuel flow speed; γ = kinematic viscosity at the transfer temperature of the liquid fuel [m2 /s]; If NRe > 2,320, the flow is defined as turbulent; otherwise we have a laminar flow. The intake pipeline, i.e. the length upstream from the pump, between the pump itself and the storage tank, must be dimensioned in relation to the maximum permissible project- related drop. The maximum project-related pressure drop is equal to: ∆Pprog = ∆Pamn - ∆hasp - ∆Pacc [Pa] Eq 2.6.2 -5 where: ∆Pamn= the absolute pressure allowed at intake (NPSH) indicated by the pump manufacturer; otherwise, this pressure must not be less than 50,660 Pa (0.5 bar); ∆hasp = intake height [Pa]; ∆Pacc = head loss due to the presence of hydraulic accessories not calculated in determining the equivalent lengths on the intake pipeline (filters, etc..) [Pa] The intake height is equal to: ∆hasp = ∆hgeom . ρ . 9,81 [Pa] eq 2.6.2 -6 where: ∆hgeom = the difference in height between the fuel test point in the tank and the centre of the delivery pump [m]; ρ = diesel oil volume mass [kg/m3 ]; The value of ∆hgeom is positive if the tank test point is lower than the centre of the pump, negative if the tank test point is higher than the centre of the pump. NRe = d . V γ Boilersinfo.com
• 58. 59 The liquid fuel volume mass depends on the temperature according to the following formula: eq 2.6.2 -7 where: ρ = liquid fuel volume mass [kg/m3 ]; ρ15 = liquid fuel volume mass at the reference temperature of 15°C equal to 865 kg/m3 ; t = transfer temperature of the diesel oil equal to 2°C [°C]; β = expansion formula equal to 0.°C-1; If the flow is laminar, the pipelines should be dimensioned according to the following formula: eq 2.6.2 -8 where: d = internal pipeline diameter [m]; γ = kinematic viscosity of the liquid fuel transfer temperature [m2 /s]; LTOT = total pipeline length, sum of the effective and equivalent lengths [m]; m = mass-related delivery of the pumping unit [kg/s]; ∆Pprog = maximum project-related pressure drop (depression) [Pa]; In technical practice the kinematic viscosity is expressed either in cSt or in a unit of measure depending on the type of viscometer used to measure the viscosity (Engler, Saybolt universal, Redwood degrees, etc…); therefore, before using the previous formula the d = 42 . γ . LTOT .m ∆Pprog√ ρ = ρ15 1 + β . (t - 15) kinematic viscosity must be transformed into cSt using the tables and alignment charts indicated in section 5, remembering that: 1 cSt = 1 mm2 /s = 10-6 m2 /s; eq. 2.6.2 -9 If the flow is turbulent, the pipelines should be dimensioned according to the following formula: where: d = internal pipeline diameter [m]; γ = the friction factor to be estimated in the diagram shown below in relation to the NRe and the relative texture e/D, where e represents the absolute texture in mm; LTOT = the total pipeline length, sum of the effective and equivalent lengths [m]; m = mass-related delivery of the pumping unit [kg/s]; ∆Pprog = maximum project-related pressure drop (depression) [Pa]; The table 15 shows the value of the absolute texture of certain types of pipelines: The graph 59 shows the friction factor value f in relation to the Reynolds Number NRe and the relative texture e/D. The diameter calculated in this manner must not, in any case, be less than 6 mm. Once the above-mentioned diameter has been calculated, it is necessary to check that the speed is not lower than 0.15 m/s using the equation (2.6.2-3), specifically: d = 0, . √ 5 γ . LTOT .m 2 ∆Pprog Material Wall status Absolute texture (mm) Wire-drawing pipes, new (copper, brass, bronze, light alloy) Synthetic material pipes, new technically smooth 0,001 3 ÷ 0,001 5 rolled film 0,02 ÷ 0,06 pickled 0,03 ÷ 0,04Non-welded pipes, new zinc-plated 0,07 ÷ 0,16 rolled film 0,04 ÷ 0,1 tarred 0,01 ÷ 0,05Longitudinal welded pipes, new galvanized 0,008 moderately rusted or lightly encrusted 0,15 ÷ 0,2 Stell pipes after long employ heavily encrusted up to 3 Absolute texture of the pipelinesTable 15 Boilersinfo.com
• 59. 60 Moody's abacusDiagram 59 Pressure regulating valveDiagram 60 [m/s] eq. 2.6.2 -10 where: d = internal pipeline diameter [m]; Q = liquid fuel delivery in volume [m3 /s]; If the transfer speed is less than the limit value of 0.15 m/s, proceed as follows: • the pipeline diameter that guarantees this minimum speed should be chosen using the formula: eq. 2.6.2 -11 • the total maximum pipeline length (effective + equivalent) connecting the tank and the pump is determined so as not to exceed the project-related pressure drop using the following formula: for the laminar flow eq. 2.6.2 -12LTOT = d4 . ∆Pprog 42 . γ . m A = π . = d⇒ Q V d2 4 ⇒ Q V = √ 4 . Q π . 0,15 V = Q A π . d2 4 = Q for the turbulent flow eq. 2.6.2 -13 The pump is situated at a distance from the tank, which should not exceed LTOT, considered as the sum of the effective and equivalent lengths. If the resulting diameter were less than 6 mm, a pipeline with an internal diameter of 6 mm should be chosen taking care to up-rate the delivery of the pump so that the fluid speed is greater than 0.15 m/s. Pressure regulating valves The pressure regulating valves are required to maintain the pressure in specific parts of the circuit and therefore the desired delivery. They LTOT = d5 . ∆Pprog 0, . γ . m f Reynolds number Re = ρ Vd / µ Laminarflow Boilersinfo.com
• 60. 61 are installed in the main ring, normally between the intake and return pipelines from the burner pump and essentially comprise a valve body in cast iron with hydraulic couplings for high and low pressure and a by-pass regulator piston with a related spring and rating organ. Their function is such that, even under a large delivery variation, the established pressure is maintained within a certain tolerance range. These valves are chosen on the basis of the following project data: • delivery equal to that of the pumping unit in the related circuit; • pressure range typically between 100,000 and 400,000 Pa (1÷4 bar). 2.6.3 Feeding of heavy oil (fuel oil) For the hydraulic circuits on board these burners, the same is valid as for diesel oil and kerosene, the only difference being a pre- heater is fitted (electric or fluid) for the fuel oil, like the one shown in the following figure. The basic characteristic of heavy oil or fuel oil that determines the plant engineering typology, is its viscosity. The viscosity of a liquid depends on its temperature Table 16 gives the commercial names of the various fuel oils together with the related plant engineering implications determined by viscosity. The supply systems in burners powered by high viscosity liquid fuel can be divided into two types: • drop-type systems; • pressurised ring systems. The first plant engineering type, applicable solely for multi-stage burners and not for modulating burners, is advisable only for extremely fluid fuel oil (viscosity < 3°E to 50°C) and usable only if the burner pump is guaranteed an adequate hydraulic head under all running conditions. These are used very little at present. This paragraph analyses the second plant engineering type, with pressurised ring, which offers a greater guarantee of satisfactory running. Basically, this supply system comprises two ring circuits plus a transfer circuit; the main one for circulating the heavy oil from the service tank, the secondary one for circulating the oil from the primary circuit to the burner Heavy oil preheating unitDiagram 61 Viscosity - + I Kerosene Gasolio Olio combustibile fluido Olio combustibile semidenso Olio combustibile denso Catrami UK kerosene Gas oil Light fuel oil Medium fuel oil Heavy fuel oil Tars D Heizol EL Heizol M Heizol S Heizol S Teer F kerosene Domestique Lourd n°1 Lourd n°2 Bitume USA 6 Air intake system yes yes no no no Drop-type system yes yes yes (unwary) no no Ring under pressure yes yes yes yes yes Pipelines heating no no optional advised yes Incombustible NameFeedingcircuit Summary of liquid fuelsTable 16 Boilersinfo.com
• 61. 62 Pumps for fuel oilDiagram 62and the transfer one for transferring the fuel oil from the storage tank to the service tank. All the circuits are controlled by their own pump; the pump for the primary and transfer circuits should be chosen by the design engineer, while those for the secondary circuit are provided as standard fittings with the burner. The possible variants depend on whether the burner is multi-stage or modulating. In summary, the plant engineering diagrams under analysis are the following: 1. ring-type system for multi-stage burners with service tank; 2. ring-type system for modulating burners with service tank; 3. ring-type system for multi-stage burners without service tank; 4. ring-type system for modulating burners without service tank; 2.6.3.1 Ring-type systems for multi- stage burners with or without service tanks ( type 1-3) The functional layout is illustrated in Diagrams 23 and 24. In this paragraph, we will analyse the dimensioning of the main circuit components. Storage tank The storage volume should be determined in relation to the fuel oil delivery method and derives from a compromise between the supply transport cost, delivery guarantee and installation cost for the tank. As a general indication, the following minimum types can be considered: • two tanks of 45,000 kg; • three tanks of 25,000 kg; Pumping unit P1 (transfer ring) This component is only present in plant engineering types with service tanks. This pumping unit, denominated transfer, must have a capacity equal to 1.2-1.5 times the peak maximum consumption, and comprise a pair of pumps and filters with the possibility of switchover in by-pass. They are : m i = maximum fuel consumption of the Nth burner; Mi = pump delivery of the Nth burner; The pumping unit delivery is equal to: Qp1 = 1,2÷1,5 · (∑mi) eq. 2.6.2 -14 This pumping unit must have a self-cleaning blade filter or similar, equipped with a heater, with meshes with a dimension between 400 and 600 µm. Fuel oil pumps can be monobloc or with separate gear or screw motors. The number of revs is normally low (900÷1,400 g/1’), and as a rule the more viscous the oil, the lower the number of revs must be. Pumping units already complete with filter, pumps, pressure regulating valve, gauge, check valve and shut off valve are available on the market. The head ensured by these pumps normally ranges between 100.00÷600,000 Pa (1÷6 bar). Service tank S This component is only present in plant engineering types with service tank. The service tank acts as a communication element between the transfer section and the ring section for final fuel oil pre-heating. This allows accumulating a certain amount of liquid fuel between the cistern and the burner. The tank must have the following characteristics: • tank capacity equal to 2-3 times the sum of the maximum hourly drawing capacities of the burners: VS = 2÷3 · (Mi) · 1 [kg] eq. 2.6.2 -15 • entry of the fuel oil from the end plate; • double fluid/electrical pre-heater; the fluid pre-heater (warm water or vapour) to be positioned immediately above the arrival point for the liquid fuel; the electrical pre-heater above the fluid pre-heater with integration and emergency functions; • drawing off the liquid fuel above the pre- heaters. The tank must be equipped with the following devices: Boilersinfo.com
• 62. 63 • end plate outlet for water and sediment; • level control with minimum and maximum alarm equipped with self-checking systems; • atmosphere breather pipe; • "over full" device with return line to storage tank; Pumping unit P2 (main ring) This pumping unit must have a delivery equal to at least 3 times the sum of the maximum drawing capacities of the burners and comprise a couple of pumps and filters with the possibility of switchover in by-pass: Qp2 = 3 · (Mi) eq. 2.6.2 -16 This over-dimensioning is due to the need to maintain a stable pressure independently from the possible combinations of the various burner running stages. This pumping unit must have a self-cleaning blade filter or similar, equipped with heater and with meshes measuring between 200 and 300 µm. The head of the pumping unit should be calculated on the basis of the ring pressure to be guaranteed, as a rule greater than 100,000 Pa (1 bar), and the pipeline pressure drops calculated as specified below. Remember that in the absence of definite information from the burner manufacturer concerning the pump delivery on board the machine, the following characteristic values can be used: • for multi-stage burners: M = 1.3÷1.5 ·m • for modulating burners: M = 2.0÷2.5 ·m Pressure regulating valves The pressure regulating valves are required to maintain the pressure in specific parts of the circuit and therefore the delivery desired. They are installed on the main ring and essentially comprise a valve body in cast iron with hydraulic couplings for high and low pressure and a by-pass regulator piston with a related spring and rating organ. Their function is such that, even under large delivery variations, the required pressure is maintained within a certain tolerance range. The choice of these valves is made on the basis of project data: • delivery equal to that of the pumping unit in the related circuit; • pressure range between 50,000 Pa (0.5 bar) and 500,000 Pa (5 bar), typically between 100,000 and 400,000 Pa (1÷4 bar). Calculating the pipelines The pressure drops in the pipelines are the sum of those distributed along the pipeline and those concentrated due to connecting elements and hydraulic accessories (filters, valves, etc…). To correctly dimension the pipelines the following sizes are defined: LEFF = effective pipeline length [m]; LEQUIV = sum of the equivalent lengths relative to concentrated pressure drops as a result of the connecting elements and hydraulic accessories [m]; LTOT = total pipeline length, sum of the effective and equivalent lengths [m]: LTOT = LEFF + LEQUIV [m] eq. 2.6.2 -17 The equivalent lengths relative to the concentrated elements of the components must be gained from the manufacturer's technical specifications. If these values are not available, some tables exist, as illustrated in section 5, which contain the equivalent lengths referring to the main concentrated resistances. Any filters must be calculated with the effective head loss procured by their presence. If the exact pressure drop value is not available, it is possible to assimilate the filter to an open valve. The following procedure can be used both for Service tankDiagram 63 A – oil from reservoir B – return oil from the burner D – tank drainage L – tank gage M – oil to the burner R – electrical heater V – steam heater S – overflow discharge Boilersinfo.com
• 63. 64 the transfer and the primary circuits. To correctly dimension the pipelines, the system must be divided into two parts: • intake pipelines; • delivery pipelines. This division is justified by the fact that while the pump performances on the delivery pipeline do not create any problems given the high heads that can be achieved, in the range of 300,000÷500,000 Pa (3÷5 bar), on the intake pipeline there are some maximum depression limits which must not be exceeded to avoid gasification problems with the fuel oil with consequent problems of pump cavitation. This value (NPSH) is supplied by the pump manufacturer and in any case cannot be any lower than 50,000 Pa (0.5 bar). The intake pipeline is dimensioned in relation to the following parameters: • maximum project-related pressure drop (depression) ∆Pprog [Pa]; • minimum speed Vmin equal to 0.15 m/s; • minimum internal diameter Dmin no less than 0.008 m The maximum project-related pressure drop is equal to: ∆Pprog = ∆Pamn - ∆hasp - ∆Pacc [Pa] eq. 2.6.2 -18 where: ∆Pamn = the absolute pressure allowed at intake (NPSH) indicated by the pump manufacturer; otherwise, this pressure must not be less than 50,660 Pa (0.5 bar); ∆hasp = intake height; ∆Pacc = head loss due to the presence of any hydraulic accessories not calculated in the determining the equivalent lengths present on the intake pipeline (filters, etc…) The intake height is equal to: ∆hasp = ∆hgeom . ρ . 9,81 [Pa] eq. 2.6.2 -19 where: ∆hgeom = the difference in height between the fuel test point in the tank and the centre of the delivery pump [m]; ρ = heavy fuel oil volume mass [kg/m3 ]; The value of ∆hgeom is positive if the tank test point is lower than the centre of the pump, negative if the tank test point is higher than the centre of the pump. The liquid fuel volume mass depends on the temperature according to the following formula: eq. 2.6.2 -20 where: ρ = liquid fuel volume mass [kg/m3 ]; ρ15 = liquid fuel volume mass at the reference temperature of 15°C equal to 990 kg/m3 ; t = liquid fuel transfer temperature [°C]; β = expansion formula equal to 0.°C-1; The liquid fuel transfer temperature is determined with reference to the constructive limits of the pumping unit, which in fact determine the maximum viscosity of the liquid that can be pumped and its temperature. As a general rule, the viscosity limit ranges between 30°E and 50 °E (228÷380 cSt) which determines a liquid fuel transfer temperature around 50÷60°C. There are some pumping units capable of pumping liquids with a viscosity greater than 100°E. In any event, it is good practice to keep the viscosity values below 50°E. The pipelines are dimensioned according to the following formula: eq. 2.6.2 -21 where: d = internal pipeline diameter [m]; γ = kinematic viscosity of the liquid fuel transfer temperature [m2 /s]; LTOT = total pipeline length, sum of the effective and equivalent lengths [m]; m = mass-related delivery of the pumping unit [kg/s]; ∆Pprog = maximum project-related pressure drop (depression) [Pa]; It should be pointed out that, in technical practice kinematic viscosity is expressed either in cSt or in a unit of measure depending on the type of viscometer used to measure the viscosity (Engler, Saybolt universal, Redwood, etc…); therefore, before using the previous formula the kinematic viscosity must be transformed into cSt using the tables and alignment charts indicated in section 5, remembering that: 1 cSt = 1 mm2/s = 10-6 m2/s eq. 2.6.2 -22 To determine the minimum internal diameter of the pipeline, the total length of the pipeline d = 42 . γ . LTOT .m ∆Pprog√ ρ = ρ15 1 + β . (t - 15) Boilersinfo.com
• 64. 65 must be determined and consequently the equivalent length that, in turn, depends on the internal diameter of the pipeline. We must therefore presume an initial provisional diameter for estimating the equivalent lengths. An initial diameter estimate can be made by presuming a liquid fuel flow speed, pre- determining the diameter with the following formula: eq. 2.6.2 -23 where: d = internal pipeline diameter [m]; Q = liquid fuel delivery in volume [m3 /s]; V = liquid fuel flow speed as equal to 0.15÷0.20 m/s; Once the equivalent length and, consequently, the total length have been determined, it is possible to use the equation (2.6.2-21) to determine the minimum internal diameter of the pipeline. If the diameter calculated in this manner is significantly different to that presumed for calculating the equivalent lengths, the equivalent lengths must be re-calculated with the new diameter using the equation (2.6.2-23) and subsequently repeat the diameter calculation using the equation 2.6.2-21. The pipeline will correspond to the commercially available diameter immediately above that determined using the equation (2.6.2-21). At this point, the speed in the pipeline must be checked using the following formula: [m/s] eq. 2.6.2 -24 where: d = internal pipeline diameter [m]; Q = liquid fuel delivery in volume [m3 /s]; If the transfer speed is lower than the limit value of 0.15 m/s, proceed as follows: • the pipeline diameter that guarantees this certain minimum speed should be chosen using the formula: eq. 2.6.2 -25 • the total maximum pipeline length (effective + equivalent) connecting the tank and the pump is determined so as not to A = π . = d⇒ Q V d2 4 ⇒ Q V = √ 4 . Q π . 0,15 V = Q A π . d2 4 = Q A = π . = d⇒ √Q V d2 4 4 . Q π . V ⇒ Q V = exceed the project pressure drop using the following formula: eq. 2.6.2 -26 The pump will be connected at a distance from the tank, which should not exceed LTOT considered as the sum of the effective and equivalent lengths. If the resulting diameter were less than 0.008 m, a pipeline with an internal diameter of 0.008 m should be chosen taking care to up-rate the pump delivery so that the fluid speed is greater than 0.15 m/s. As far as the delivery pipeline is concerned, the diameter should be chosen in relation to the maximum allowed speed equating to 0.6 m/s using the equation (2.6.2-23), more precisely: eq. 2.6.2 -27 where: d = internal pipeline diameter [m]; Q = liquid fuel delivery in terms of volume [m3 /s]; V = liquid fuel flow speed equal to 0.6 m/s; The pipeline will correspond to the commercially available diameter immediately above that is determined using the equation (2.6.2-23). After which, proceed calculating the pressure drop of the entire circuit (transfer or primary ring) using the following equation: eq. 2.6.2 -28 where: d = internal pipeline diameter [m]; γ = kinematic viscosity at the liquid fuel transfer temperature [m2 /s]; LTOT = total pipeline length, sum of the effective and equivalent lengths [m]; m = mass-related delivery of the pumping unit [kg/s]; ∆Pprog = calculation pressure drop [Pa]; The calculation pressure drop must be added to the loss due to any hydraulic accessories (filters, etc…) present on the delivery pipeline, the loss present on the delivery pipeline and ∆Pprog = 42 . γ . LTOT . m d4 A = π . = d⇒ √Q V d2 4 4 . Q π . V ⇒ Q V = LTOT = d4 . ∆Pprog 42 . γ . m Boilersinfo.com
• 65. 66 the difference in height between the intake pipeline and the delivery pipeline: eq. 2.6.2 -29 where: ∆Ptot = total pressure drop [Pa]; ∆Pcalc = calculation pressure drop of the delivery pipeline [Pa]; ∆Pacc = head loss due to the presence of any hydraulic accessories not calculated in determining the equivalent length, present on the delivery pipeline (filters, etc…) [Pa]; ∆Hpipelines = difference in height between the intake pipeline and the delivery pipeline [m]; ρ = liquid fuel volume mass [kg/m3 ]; The value calculated in this manner added to the residual head that must be guaranteed the ring, must be inferior to the head guaranteed by the pump; specifically: Ppump ≥ Pring + ∆Ptot [Pa] eq. 2.6.2 -30 where: Ppump = the head guaranteed by the pumping unit [Pa]; Pring = the pressure to be guaranteed the ring >100,000 Pa (>1 bar) [Pa]; ∆Ptot = total pressure drop in the pipelines [Pa]; In case of negative results, one of the following actions can be taken: • decrease the delivery pipeline length so as to reduce the pressure drops; • increase the delivery pipeline diameter so as to reduce the pressure drops; • choose a different pumping unit to guarantee the required head. The pipelines are mainly made in steel without welding. 2.6.3.2 Ring-type systems for modulating burners with or without service tanks Diagrams 23 and 24 illustrate the reference plant engineering layout for modulating burners. The system is similar to the previous one, except for the connection of the secondary burner circuit to the primary feed circuit. This connection be made via an outgas tank. This ∆Pcalc + ∆Pacc + 9,81 + ∆Hpipelines ρ ∆Ptot = [Pa] device is necessary to recover the heat discharged by the modulating burner when it is running at minimum. In fact, while in multi-stage burners the excess pump delivery is discharged by the pump control device, and therefore is not a burden for the heater, this does not happen in modulating burners, since practically the entire delivery of the burner pump passes through the heater and the return flow is more or less the atomisation temperature for the liquid fuel. Note that this temperature depends on the viscosity of the liquid fuel and may also be considerably higher than 100°C, therefore much higher than the fuel oil transfer temperature equal to approximately 50-60°C. During the modulation phase, the majority of the fuel oil delivery is discharged on the return line and this, first of all, represents a useless waste of energy and, in addition, a burden for the burner as the pre-heater may not be adequate for heating all the delivery, thus causing a consequent drop in temperature and deterioration of the atomisation, possibly extinguishing the flame. For these motives, correct connection of the modulating burner is achieved using the outgas tank which, thanks to its particular construction, enables almost total recovery of the heat contained in the return line, whilst also allowing the gases to be discharged. This outgas tank can also be conveniently used with multi-stage burners, as in this pre-heating phase there is a complete blow-by in the burner heater. To dimension the pipelines and system components, please refer to references illustrated previously for multi-stage burners. In this paragraph, attention is focused on just the pumping unit and the gas separator bottle. Pumping unit P2 (main ring) This pumping unit must have a delivery at least 3 times the sum of the maximum burner drawing capacities and comprise a couple of pumps and filters with the possibility of switchover in by-pass: Qp2 = 3 (∑Mi) eq. 2.6.2 -31 This over-dimensioning is required to maintain a stable pressure independently from the possible combinations of the various burner running stages. This pumping unit must have a self-cleaning blade filter or similar, equipped with heater and with meshes measuring between 200 e 300 µm. Boilersinfo.com
• 66. 67 The ring pressure to the regulator should be chosen with reference to the fuel oil temperature in the outgas device and, for reasons of safety, be equal to the atomisation temperature, to prevent the development of gas from the hot oil and ensure the burner pump runs correctly without the danger of pump cavitation. The ring pressure Pring, which the pumping unit must guarantee, should be calculated referring to the following graph: Gas separator bottle This device essentially comprises a vertical barrel divided horizontally by a circular sector. The oil circulating in the ring delivery pipeline runs through the upper portion. Two overlapping couplings are present in the lower portion for connecting the burner hoses; the upper of the two is the return line, while the lower one should be connected to the intake; the coupling of the return line is extended nearly as far as the opposite wall, to prevent the by-pass of hot oil to the upper chamber through the split made in the dividing sector. In this manner, the intake pipeline recovers nearly all the hot oil from the return pipeline and, because of the low descent speed of the oil taken in by the pump, it is possible the development and separation of gas bubbles which may have formed. The lower bottom of the tank must be equipped with an outlet and threaded coupling for inserting the electrical heating element. A breather pipe must be positioned in the upper part for discharging the gases that may have accumulated in the tank. 2.6.3.3 Heating the pipelines For all the plant engineering variations mentioned, the pipelines must be marked for heating the fuel oil. The following is the dimensioning method: The heat to be supplied to the transport pipelines takes into account two factors: • initial pipeline heating and normal setting; • compensation of the heat loss when running; To calculate the energy required for normal setting, the following formula can be used, which takes into account the oil mass to be heated and that of the steel pipeline under ideal conditions with no heat loss. The formula is as follows: e1 = (q . ρ . ce + M . cf ) . ∆T eq. 2.6.2 -32 where: e1 = specific energy per metre of length to supply to the pipeline [kJ/m]; q = oil content per metre of pipe [m3 /m]; ρ = fuel oil volume mass [kg/m3 ]; ce = fuel oil specific heat (equal to approximately 1.88 kJ/kg°C) [kJ/kg°C]; M = weight of the steel pipelines per linear metre of pipeline [kg/m]; cf = specific heat of the steel (equal to approximately 0.46 kJ/kg°C) [kJ/kg°C]; ∆T = thermal head of the pipeline and the fuel oil between the system stand-by status and steady running status (approximately 50°C) [°C]; The total energy to be supplied is given by: E1 = e1 . L eq. 2.6.2 -33 where: E1 = total energy to be supplied to the pipelines [kJ]; e1 =specific energy per metre of length to be supplied to the pipelines [kJ/m]; L = effective length of the pipeline [m]; The total power required to guarantee the energy depends on the time taken to achieve the steady running state: eq. 2.6.2 -34 where: E1 = energy to be supplied to the pipelines [kJ]; P1 = system power for obtaining steady running state in the pipelines [kW]; t = time taken to obtain steady running state conditions [hours]; The specific power per unit of length is: P1 = E1 t . Ring pressure - advised valuesDiagram 64 Boilersinfo.com
• 67. 68 eq. 2.6.2 -35 where: p1 = the specific power per unit of length for reaching the steady running state of the pipelines [W/m]; P1 = system power for reaching the steady running state of the pipelines [kW]; L = effective length of the pipeline [m]; To calculate the energy that needs to be supplied to compensate the heat loss during steady running state, the following simplified formula can be used which only takes into account the resistance of the pipeline's insulation without taking into account the scant resistance provided by the metal pipeline: eq. 2.6.2 -36 where: p2 = specific power per unit of length for heat losses from the pipelines [W/m]; λ = thermal conductivity of the pipeline insulation [W/m°C]; De = external diameter of the steel pipeline [mm]; Dtot = total diameter equal to De +2·s where s is the thickness of the insulation [mm]; ∆T = thermal head between the pipeline and fuel oil temperatures and the external temperature [°C]; The total power to be installed will be equal to: eq. 2.6.2 -37 where: P2 = total system power for heat losses from the pipelines [kW]; p2 = specific power per unit of length for heat losses from the pipelines [W/m]; L = effective length of the pipeline [m]; The heating system for heating the pipelines must be dimensioned to overcome the heat losses and provide the pre-heating heat. While heat losses are always present, pre-heating during start-up is only necessary when the system is primed or after long periods in stand- by, for example, for maintenance work. Increasing the thickness of the insulation can reduce heat loss, while the pre-heating heat may be deferred over time but not eliminated. P2 = p2 . L p2 = 2 . π . λ . ∆T ln ( )Dtot Dest p1 = . 100 P1 L If we presume rather short times for achieving steady running status (0.5÷1 hour), the load level due to heat loss is only a small fraction of the total which is nearly all absorbed by the pre-heating power. Given the high cost for heating the pipelines and the desultory nature of the operations for achieving steady running status, it is advisable to adopt fairly long pre-heating times, around 4 to 5 hours, so as to rationally make the best of the power employed, provided it is compatible with the type of system and its running requirements. To calculate the total power to be installed, the commitment required to satisfy the heat losses of the pipeline at steady running state is calculated by half: eq. 2.6.2 -38 where: Ptot = total system power for reaching steady running state and for the heat loss from the pipelines [kW]; P1 = system power for the reaching steady running state for the pipelines [kW]; P2 = system power for the heat loss from the pipelines [kW]; The pipelines can be heated in two different ways: • using electrical heating element; • using warm or overheated water; • using vapour In this manual we only touch upon electrical- type heating which permits simple and fast marking that can be easily modified if required. The pipes can be electrically heated by thermal bands or heating wires. The thermal bands are flexible polyester bands, which contain electrical elements insulated individually by PVC sheaths supplied either in rolls of a pre-cut length or in reels that must be cut by the user. The efficiency of the electrical heating systems is always less than 100% both because of imperfect contact with the pipe, and due to the inevitable heat loss outwards despite the insulation. Generally, the efficiency yields can reach the following value: • thermal bands and thermal covers η = 85%; • heating wires η = 70%; The total power to be supplied is equal to: Ptot = P2 2 P1 + Boilersinfo.com
• 68. 69 where: Peff = the total power which the electrical heating system must provide [kW]; Ptot = total system power for reaching steady running state and for the heat loss from the pipelines [kW]; The choice of the heating bands should be made according to the maximum temperature achievable by the pipeline (for example 65°C). The heating bands can be self-regulating, where the power issued decreases with the increase in temperature until it stops at a certain value (60÷80°C), or else non-self- regulating in which case a limit thermostat must be provided to control the temperature. The non-self-regulating heating bands have a constant power emitting ability which is independent from the temperature and they should be chosen according to the power required as calculated using the above procedures, in particular: where: peff = specific power per pipeline length which the electrical system must supply [W/m]; Peff = total power which the electrical heating system must supply [kW]; L = effective pipeline length [m]; If Pband is the specific heating power of the non-self-regulating band; we will obtain the length of the heating band per meter of pipeline as: peff = Peff L . Peff = Ptot η where: lband = the length of the heating band per metre of pipeline; peff = specific power per length of pipeline which the electrical system must provide [W/m]; pband = specific heating power per metre of band [W/m]; The specific power outputs of the bands can be varied by a few W/m units to several hundreds of W/m; as a rule this can be done using heating bands with a specific power between 20 and 40 W/m. Once the length of the belt has been obtained, the pitch of the turns can be obtained using which the oil fuel pipeline will coil, using the diagrams provided by the band manufacturers, such as those shown in diagram 66. The X axis shows the length of the heating band per metre of pipeline; the Y axis shows the pitch of the turn. This diagram should be used in the following manner: • from the point corresponding to the value lband on the X axis, trace a vertical line until you meet the curve corresponding to the diameter of the pipeline; • in relation to the point found, read the value of the turns required to obtain the power desired. lband = peff pband Self-regulating heating bandDiagram 65 Turns' step for heating bandsDiagram 66 band length (m) Boilersinfo.com
• 69. 70 If the number of the turns obtained in this manner is too high, it can be reduced by increasing the specific power of the heating band. In the event that self-regulating heating bands are chosen, their specific power Pband must be chosen in relation to a reference temperature, which is equivalent to the minimum achievable by the fuel oil, normally equal to 10°C; then the procedure is similar to that developed for non-self-regulating heating bands. Heating wires comprise a coated multi-wired conductor. When the heating wire is powered it produces heat using the “Joule” effect. The power dissipated depends on the conductor strength and the power supply potential. As a rule, manufacturers give the strength of the wire as the benchmark; the specific power should be calculated according to the law of Joule expressed for constant voltages: where: pwire = specific heating power per metre of heating wire [W/m]; V = power supply voltage of the heating wire [V]; rwire = specific strength per length of the heating wire [Ω/m]; Lwire = heating wire length [m]; The heating wire should have a specific power between 20÷40 w/m2 . The power supply pipeline can be marked with a copper tube with a small diameter, through which the heating wire can be passed for making installation and/or replacement easier. To connect the main ring and the secondary ring of the burner pump, there are several flexible heated and insulated pipes equipped with a specific thermostat. These pipes are shown as accessories in the burner-related catalogues, and they are equipped with a very powerful fixed element, to minimise waiting times for pre-heating the pipe after the burner has been in stand-by. 2.6.3.4 Heating the storage tanks As already mentioned, heavy oil at room temperature is usually solid and therefore not pwire = V2 rwire . L2 wire suitable for pumping purposes. To obtain viscosity values that are suitable for pumping, the oil must be pre-heated in the tanks. The heating system must be able to compensate the inevitable heat loss from the tank and provide the heat requirements for the oil being used. The heat loss takes place through the outside surface area of the tank and is due to the difference in temperature between the fuel contained in the tank and the environment. The calculation of the heat loss from a tank should be made according to the methods and the hypothesis of heat transmission, which is not always rapid or immediate as in the case of underground tanks. Section 5 contains a diagram for pre- dimensioning heating systems for full and completely heated tanks. The status of the tank completely full with hot oil is an ideal condition which rarely occurs, as the heating area is limited to the portion of volume involved in pumping, therefore the part of the tank heated is extremely small and thus an output equal to 1/3 of the nominal one found using the graph can be considered adequate. The heat requirement for pumped oil is calculated using the following equation: where: Q = power for heating the pumped oil [kW]; mc = correct fuel oil delivery [kg/h]; ce = specific fuel oil heat (equal to approximately 1.88 kJ/kg°C) [kJ/kg°C]; ∆T = the difference between the temperature of the delivery oil and the external temperature (50÷60°C) [°C]; For safety reasons, a corrected delivery value is used rather than the real value. If the transfer pump works non-stop with a ring equipped with a return line to the tank, the correct delivery will be equal to 1.5 times the burnt delivery. If the transfer pump feeds a service tank without a return line, running will be intermittent and regulated by the level switch in the service tank; in this case, the correct delivery will be equal to that of the transfer pump. The tanks can be heated by: • electrical systems; • warm or over-heated water systems; • vapour systems; Q = mc . ce . ∆T Boilersinfo.com
• 70. 71 In this section, we will analyse the electrical type of heating. The tanks can be electrically heated either by band-type heaters outside the surface area or by internal heaters. For heating with bands, the reader should refer to previous chapters for this type of heater, bearing in mind however that in this case the overall heat loss of the tank should be considered. The internal heater can essentially be classified in two types: • for upright tanks; • for horizontal tanks; Those for upright tanks are similar to water/vapour tube nest heaters and comprise an element battery welded to a tube plate. The specific thermal load must be as low as possible, at the most 2 W/m2 and possibly around 0.8 w/m2 , in order to reduce the formation of cracking products to a minimum. To exploit the features of these heaters to the utmost, they should not be attached directly to the tank, but rather equipped with a series of devices to make them work as out and out rapid exchangers. The heaters for horizontal tanks comprise a submersed bell-shaped container that contains the heating elements; the bell is laid vertically on the bottom of the tank and held up by a spacer. The great advantage of these heaters is the ease with which they can be installed, permitting rapid maintenance by extracting the heater via the manhole without having to empty the tank. However, the heaters are limited to a practical output value no greater than 36 kW. 2.7 ELECTRICAL SUPPLY AND BURNER CONTROL As we have seen in the previous paragraphs, components are installed on the burner which require an electricity power supply: • Fan; • Liquid fuel pre-heater; • Liquid fuel suction pump. As well as other components which require a low voltage power supply: • Auxiliary systems for regulating and controlling combustion. For small monobloc burners powered by single-phase current, the two classes of users are electrically powered with a single line. In the case of monobloc burners with an average to high output and separately powered burners, the power supply is separate from the auxiliary supply; in the case of monobloc burners, the electrical equipment is generally mounted on the machine, while for dualbloc burners, the electrical panels are separate from the frame of the combustion head. For monobloc burners, the electricity power supply data is clearly shown in the technical charts for the burner. The definition of the electrical energy requirement for a dualbloc burner, on the other hand, requires the design of the whole combustion system as certain components are separate from the combustion head and should be chosen in relation to the performance required from the system. Combustion regulation and control requires an electricity power supply to perform the Electrical layout of a monobloc burner with three phase power supply Diagram 68 B4 S3 T2 N L1T1 F Spina 7 poli TSSB TR N L PE h1 ~50Hz 230V C Presa 7 poli Electrical layout of a monobloc burner with single-phase electrical power supply Diagram 67 TR Regulating thermostat TS Safety thermostat (manual reset) h1 Single stage hour meter SB Lock out led C Fuse F Lead section L Capacitor PE Protection earth 7 pin plug 7 pin socket MB Regulating thermostat IN Safety thermostat (manual reset) TL Fuse 6A TR Fuse T6A Lead section F Burner terminal board L Manual switch TS Limit control thermostat Boilersinfo.com
• 71. 72 following functions: • Handling of the firing and flame safety sequence; • Regulating the thermal load. Observance of the safety instructions requires the use of special devices for supervising the burners. Legislation establishes, with reference to the type of burner, the control measures that must be adopted. However, the following principles are always valid: 1. The flame must be present within a limited period of time from when the fuel is made available to the nozzle and subsequently it must burn uninterruptedly; 2. Depending on the type of burner, the maximum margin of time must be indicated during which the fuel can be discharged without the flame forming. This period of time, which is sufficiently short, is called safety time; 3. In absence of flame detection within safety time, a system lock-out takes place and fuel flow is stopped; 4. For oil burners, if during working flame goes out due to a temporary problem, it may be re-established by a new firing; 5. Failure of burner devices that compromise safety, control and formation of the flame, must automatically interrupt the burner operations. This lock out, called a safety lock out, is indicated by a warning light and can only be released manually. The equipment required to perform these functions is as follows: 1. An on/off fuel system, for example an electromagnetic valve; 2. An electrical firing device; 3. A flame detection system which ascertains with safety the presence or absence of the flame and determines the corresponding control orders. For gas burners, the detection sensor is generally an ionisation type, while for liquid fuel or mixed fuel burners the sensor is usually a photocell type; 4. A timing circuit which establishes the safety time; 5. A lock out circuit in case of failure. Firing sequence of a methane gas burner Diagram 69 Diagram of the main components required for combustion control and regulationDiagram 70 Burner panel 1 - Burner select 2 - Fuel select 3 - Auto/manual 4 - Modulate down 5 - Modulate up 6 - Alarm mute 7 - Burner lock-out 8 - Stand-by Fault indication Alarm 1 2 543 6 7 8 Boiler temperature sensor Boiler pressure sensor Burner motor contactor Air pressure switch Air/fuel servomotor Ionisation probe Ultra-violet (UV) probe Photocell Main valve 1 Pilot valve Gas pressure sensor Ignition transformer Main valve 2 Modulation control Burner fan control Fuel/air ratio control Flame detection Fuel control and monitoring Boilersinfo.com
• 72. 73 Diagram 69 illustrates the firing sequence of a methane gas burner, while figure 70 shows the layout of the main components required for controlling the flame and regulating the load. According to the size, the fuel type and the requirements linked to the application, the air and fuel can be regulated as follows (see section 2.1): • Single-stage • Multi-stage (two-stage or three-stage) • Progressive two-stage • Modulating In the case of single-stage regulation, in order to start-up or stop the burner all that is needed is a device that activates the heat regulation handling system. As a rule, it is represented by the contact of a thermostat with two settings, which regulates, for example, the water temperature of a boiler. When the temperature decreases with respect to the value prescribed, the thermostat requests heat, therefore it closes the contact and starts up the burner; vice versa for an increase in temperature the contact opens and the burner is stopped. The control panel, which differs in relation to the output and the type of burner, having received the heat request signal, establishes the running sequence of the various devices. If, during the programme, firing does not occur during the safety time, the continuation of the programme is interrupted and the problem is signalled (safety lock out). If it becomes necessary to supply the thermal output on two levels, one can use a two-stage type regulation. In this case, two separate thermostats called first flame and second flame control the firings. Each of the two thermostats behaves like the single thermostat in the single-stage burner, activating/deactivating the release devices of the fuel and combustion supporter air. The two thermostats function at different temperature levels. The thermostat that controls the first stage must be calibrated to a higher temperature than that of the second thermostat. As the differentials of the two thermostats are not always immediately available, as given in diagram 60, this type of regulation can be done more accurately and effectively using double threshold thermostats (with fixed differential). Furthermore, for domestic boilers, which for a certain period of the year are only used to supply hot water, there is the so-called summer deactivation of the second threshold, where the second stage functions are cut off. Regulating the thermal load in the single-stage and two-stage type is defined as “rapid”, as the activating devices are instantaneous. For some applications, where a more gradual thermal load variation is required, progressive and modulating stage regulations are used. In progressive two-stage starting up, the fuel Time Measured temperature Second stage thermostat differential First stage thermostat differential 1°-2° stage ON 1°-2° stage ON 1° stage ON- 2°stage OFF 1° stage ON- 2°stage OFF 1° stage ON- 2°stage OFF 1°-2° stage OFF 1°-2° stage OFF Programming of the regulation temperatures for a two-stage burnerDiagram 71 Boilersinfo.com
• 73. 74 regulator is taken to the firing load position. The servomotor for the combined fuel/combustion supporter regulation with slow opening, varies the delivery up to maximum load. The servomotor then controls the capacity of the burner at maximum or at minimum load values. The difference between this mode and the modulating mode is the possibility of the latter to take intermediate regulation positions between maximum and minimum. To obtain satisfactory modulation, the servomotor can have slower stroke than the progressive two- stage burner; furthermore, an out and out electronic regulator must be provided with PI or PID regulation action complete with temperature probes or pressure probes. For monobloc burners, this device can usually be applied directly to the burner. 2.8 NOISE LEVELS IN FORCED DRAUGHT BURNERS Noise is defined as an undesired sound which, within the range of audible frequencies between 20 and 20,000 Hz, disturbs, provokes irritation and/or damages health. Sound is a collection of particle oscillations within a flexible medium. The emission of a sound by a source implies the emission of energy which, referring to a unit of time, represents the sonorous power measured in watts. The level of sonorous power is defined by the following equation: Lw= 10 log (W/W0) (dB) eq. 2.8 -1 where W0 is the reference power equal to 10-12 W. Furthermore, the difference between pressure in the presence of sound and pressure in a point in space in the absence of sound is defined as sonorous pressure in the same point in space; this is measured in Pascals. The level of sonorous pressure is expressed using the following equation: Lp= 20 log (P/P0) (dB) eq. 2.8 -2 where P is the reference pressure equal to 20·10-6 Pa, which represents the minimum pressure perceivable by the human ear. For ease of calculation, power and pressure levels have been introduced which are expressed in decibels (dB); the decibel reflects the logarithmic response of the ear to the variations in sonorous intensity. The table below shows some of the power values of certain sources and some sonorous pressure values in certain environments. Typical values of sound powerTable 17 Sound power [W] 25÷40 106 105 103 10 1 10 -1 10 -2 10 -3 10 -4 10 -9 Sound power level [dB] 195 170 150 130 120 110 100 90 80 30 Source type Lead missile Turbojet engine Commercial aircraft Large orchestra Pneumatic hammer m3 /h centrifugal fan Motor vehicle on motrorway m3 /h axial fan Conversation Whisper BT a b c d ~ M 3~50Hz 230V3 3N 50Hz 400/230V~ L1 L2 L3 N LMB 1 2 L PE L1 L2 L3 T6A N L TS S IN ~50Hz 230V 3 4 F ϑ P Q13 Q14QG-N L1 G+G1+U1 HW1B1 W2 CM AL1QU RWF 40 Y1Y2M1I1 TE ALN B3B4 Electrical layout of a modulating burner with control devices Diagram 72 MB Safety thermostat TS Fuse 6A S Fuse IN Lead section BT Burner terminal board T6A Manual switch F External lockout signal L Temperature probe RWF40 Power controller (modulating) Boilersinfo.com
• 74. 75 It is necessary to completely understand the difference between sonorous power and sonorous pressure; the power is an absolute magnitude referring to the emitting source. The pressure is a measurement relating to a point in space and consequently the emission of a sound by a source. The pressure measured in a point in space depends both on the sonorous source, the distance of the measurement point of the source and the conditions surrounding the system. Therefore, the sonorous pressure data is always accompanied by test conditions: distance of the measurement point and type of room in which the test was carried out. The sonorous power cannot be measured directly but is calculated using the measurements of sonorous pressure, in particular acoustic measuring laboratories. By virtue of the definition of the level using the equations indicated above, we can conclude that a doubling of the sonorous power is equivalent to an increase of 3 dB of the level of power, while a doubling of the sonorous pressure is equivalent to an increase of 6 dB of the level of pressure. In order to add or subtract different levels of pressure, it is possible to use the following equation: Lptot = 10 . log [ ∑10( 0,1Li ) ] [dB] eq. 2.8 -3 bearing in mind that in case of level differences, the summation must be carried out with relative values. Each noise comprises a collection of sounds with different frequencies. The sounds that can be heard by the human ear are those with a frequency ranging between 20 Hz and 20,000 Hz. However, the human ear does not assign the same sensitivity to sounds with different frequencies. Therefore, on an experimental basis, several isophonic curves were created, in other words curves of equal loudness measured in “phons” The number of phons is equal to the level of sonorous Average values of sound pressureTable 18 Isophonic curvesDiagram 73 Sound pressure [Pa] 200 63 20 6.3 0.63 0.2 0.002 Sound pressure level [dB] 140 130 120 110 90 80 60 Condition Aircraft taking off at 30 m Pneumatic machine operator Large thermal power plant Automatic press operator Lathe operator Heavy truck at 6 m distance Roadside with big traffic Restaurant Audibility threshold Frequency (Hz) Boilersinfo.com
• 75. 76 pressure corresponding to the reference frequency of Hz. The Diagram shows these curves in which the X axis shows the frequencies in Hz and the Y axis the level of sonorous pressure in dB; from an analysis of these curves, we can conclude how sounds of different frequencies produce the same loudness (same value of phons) despite having different values of sonorous pressure. is measured in dB; if, on the other hand, the measurement is made using the “A” weighted scale, the level is expressed in dB(A). When, for a determinate noise, the level divided into the various frequencies is known (for example: in octave band), the overall noise level is obtained by making the summation using the equation (2.6.3). In particular, for the following spectrum in octave band: Weighted curvesDiagram 74 Octave frequency band spectrumTable 19 Central band frequency [Hz] Level [dB] 63 72 125 80 250 67 500 60 62 55 51 45 Frequency (Hz) Relativesoundlevel(dB) (linearvaluecorrection) By examining the curves, we can see that the lower the frequency, the higher the level of sonorous pressure can be, loudness being equal. Therefore, if we wish to obtain measurements that are, as far as possible, in accordance with the auditory sensations of the ear, a damping of the lowest frequencies is necessary in order to gain a weighted measurement. Various weighted curves have been normalised, the most commonly used is called the “A” curve; these curves are shown in Diagram 74. The instruments for measuring sonorous pressure, called sound-level meters or phonometers, already have the possibility to carry out measurements using the weighted curve “A” within them. If the measurement is made using a linear weighted scale, the level of sonorous pressure the level of overall pressure will be equal to: As already estimated, it is not possible to directly measure the sonorous power of a machine, but it is necessary to read off the sonorous pressure in a given point in order to then arrive at the power. In free field, i.e. where the sound waves move away from the source in all directions, the equation that ties the level of sonorous power to the level of sonorous pressure is: Lw = LP + 20 · log( r ) + 11 [dB] eq. 2.8 -4 This equation is also used for the measurements made in the “free-field” chambers of the acoustic measurement laboratories. The free-field chambers are special measurement chambers, where the walls that enclose the physical space are made of material with an elevated absorption factor, in order to simulate ideal open field conditions. The above equation reveals, as already mentioned, that the level of sonorous pressure decreases as it moves away from the emitting source; this decrease is equal to 6 dB for each doubling of the distance between the measurement point and the source of emission. If you wish to determine the theoretical level of sonorous pressure within a room in which a machine is placed, such as a burner within a power station, the following equation should Lp = 10 . log [107.2 + 108.0 + 106.7 + 106.0 + 106.2 + 105.5 + 105.1 + 104.5 ] = 80.9 Boilersinfo.com
• 76. 77 be applied: eq. 2.8 -5 where: Lp = the level of sonorous pressure in dB; Lw = the level of sonorous power in dB; r = the distance from the source [m]; Q = the directional factors of the source equal to: = 1 for sources near the centre of the room; = 2 if the source is at the centre of a wall or floor; = 4 if the source of noise is positioned at the intersection of two walls. R = the constant of the room [m2 ]; The constant of the room can be determined using the following equation: eq. 2.8 -6 where: S = the total surface area of the walls of the room; αm = the average absorption factor of the room equal to: eq. 2.8 -7 where: Si = the surface area of the Nth wall; αi = the absorption factor of the Nth wall; αm = ∑i Si . αi S [m2 ] R = S . αm ( 1 - αm ) [m2 ] Lp = Lw + 10 . log [dB] ( )+ 4 R + 0,5 Q 2 . π . r2 The absorption factor varies in relation to the wave frequency of the incident sound, therefore the analysis using the equation 2.8.5 should be carried out for frequencies to then calculate the total value using the method previously described. Table 20 shows the absorption factors of certain materials. When measuring noise in an environment, it is necessary to remember that besides the noise produced by the machine, noise deriving from other sources is always present. The collection of extraneous signals is defined as background noise. The measurements made must therefore be cleansed of this value. The valuation of the cleansing is made by measuring the sonorous pressure level when the machine is on and when it is off, to measure the level of background noise. By then applying the equation (2.8.3.), the pressure value due only to the machine when running can be reached. We can presume, for example, that we have taken the measurement under the two conditions indicated with the following values: machine on Lp = 80 dB; machine off Lp = 76 dB; the sonorous pressure value corresponding to the machine alone will be equal to: 2.8.1 Deadening noise made by forced draught burners The noise produced by the burner essentially Materials Central band frequency 125 250 500 Crude wall 0,02 0,02 0,03 0,04 0,05 0,07 Finished wall 0,01 0,01 0,02 0,02 0,02 0,02 Plaster 0,02 0,03 0,03 0,04 0,02 0,03 Pine wood 0,01 0,01 0,01 0,09 0,1 0,12 Glass 0,03 0,03 0,03 0,03 0,02 0,02 Strained velvet tent situated at 20cm 0,08 0,289 0,44 0,5 0,4 0,35 Non-strained velvet tent situated at 20cm 0,14 0,35 0,55 0,75 0,7 0,6 Felt 0,09 0,14 0,29 0,5 0,62 0,56 Rock-wool (thick.=2,5cm) 0,26 0,45 0,61 0,72 0,75 0,85 Rock-wool (thick.=5cm) 0,38 0,54 0,65 0,76 0,78 0,86 Glasswool (thick 2,5 cm) 0,16 0,43 0,87 0,99 0,93 0,86 PU1 0,09 0,1 0,11 0,21 0,35 0,45 PU2 0,1 0,2 0,35 0,55 0,45 0,53 PU3 0,25 0,35 0,6 0,55 0,51 0,7 PU4 0,19 0,3 0,43 0,45 0,52 0,58 PU5 0,19 0,45 0,57 0,43 0,42 0,65 Absorption factors of certain materialsTable 20 Legend: PU means flexible expanded polyurethane with 30kg/m3 density. PU1: thickenss 10mm; PU2: thickness 30mm; PU3: thickness 50mm; PU4: thickness 70mm of which 20mm basic and 50mm pyramids; PU4: thickness 50mm of which 30mm basic and 20mm ashlar. Boilersinfo.com
• 77. 78 derives from these three sources: • Pumps in the pumping groups; • Fan; • Flame In order to limit the noise level, soundproofing devices can be fitted which should be installed on the burners and mount any pumps outside the burner on flexible supports. The blimps are articles that are available as optionals in burner manufacturers' catalogues and are made in sound-absorbent material (light materials tend to absorb high frequence noises, while heavy materials absorb better low frequence noises). They can reduce the noise level made by the fan, the pump installed on the machine and, in part, that made by the flame. Diagram 75 shows a blimp. In dual bloc burners, where the fan is outside the machine, the primary source of noise is still the fan, but the pressure waves which it produces are transmitted via the air in-take pipelines and the combustion head delivery pipelines. In order to reduce the noise emitted by external fans, it is necessary to choose those offer high performances at low speed, and with a running point positioned in the stable section of its characteristic curve. The installation of the machine must take place using anti-vibration supports. The connection of the fan with the pipelines must be made with anti-vibration joints. The connection pipelines must have a possible variation of the section, near to the fan, made with an inclination angle no greater than 15°; furthermore, any accessories must be installed at a distance of at least 3 equivalent diameters from the fan. In cases where a heavy noise reduction of the aeraulic system is required, special silencers can be installed comprising baffle plates in sound-absorbing material inside the intake pipeline section. The introduction of these silencers determines an increase in the pressure drops of the aeraulic system and therefore they should only be inserted in cases of effective need. Another technical solution used in order to limit the sound emissions, involves the installation of fans closed in special soundproofing devices. When one of the above mentioned systems is installed in an Forced draught burner (blimp, silencer or box) to dampen noise, the correct functions of the system should be tested with these devices fitted, to check that any head drops caused by them fall within acceptable levels. In certain countries legislation exists which fixes the limits for sound emission within the various application fields. 2.9 OPTIMISING COMBUSTION WITH FORCED DRAUGHT BURNERS In this section, we will analyse certain technologies capable of forcibly optimising the combustion process developed using an Forced draught burner. As can be seen, these techniques require the application of plant engineering subsystems, which allow accurate combustion monitoring and regulation, such as: • Systems for regulating combustion O2; • Pre-heating combustion supporter air; • Regulating the number of fan revolutions. • Burner Management System. 2.9.1 Regulating the O2 As anticipated in section 1, to avoid the presence of unburned combustion particles in the flue gases and therefore obtain total fuel oxidation, a degree of air in excess with respect to the stoichiometric value must be present, which cannot however be too high or the efficiency will suffer. The excess air is determined and established when the burner is set in relation to the average running parameters for the burner, and measured in relation to the amount of oxygen or carbon dioxide present in the discharge flue gases. The optimum value of the excess air however is variable when the burner is running, in relation to the amount of Blimp for air blown burnersDiagram 75 Boilersinfo.com
• 78. 79 oxygen required for perfect fuel oxidation. Therefore the exact amount of air to be supplied to the burner depends on the oxygen content in the air and the characteristics of the fuel; in particular, the parameters that have most influence on the amount of air required are: • Combustion supporter air temperature: an increase of 10°C in the combustion supporter air temperature corresponds to a decrease in air density of around 3% with the consequent decrease of the oxygen in the air by approximately 0.6%; • Barometric air pressure: a decrease in the barometric pressure of 10 mbars causes a drop in the air density by approximately 1% with a consequent decrease in the oxygen present in the air of around 0.2%; • Calorific value of the fuel: an increase of 5% in the calorific value of the fuel corresponds to an increase in the oxygen requirement of 1%; • Fuel delivery, temperature and pressure; • Draught of the flue and back pressure of the furnace; All the variables mentioned above influence combustion thus determining the amount of oxygen required and, consequently, the excess air. For the best control of the combustion process, the amount of air must be continually modified so that the amount of oxygen in the flue gases emerges as optimum. This system denominated “regulation of O2 in flue gases” involves a probe for measuring the oxygen in the flue gases, which is installed in the flue gas pipe in the generator, and an electronic control unit. The probe is linked to the electronic control unit and reads the oxygen value present in the combustion flue gases. The probes used are generally zircon (ZrO2) in type or electrochemical, as they are reliable, accurate and equipped with a more or less instantaneous response. The control unit determines the change between the oxygen value measured by the probe and the nominal value set, to determine the exact amount of air to feed to the burner. By positioning/correction of the burner air regulation damper, controlled by a servomotor, the control unit can guarantee the right contribution of combustion supporter air, and therefore of oxygen, in relation to the output supplied by the burner. The control of the oxygen in the combustion flue gases makes it possible to set the excess air to the value corresponding to the maximum technical combustion efficiency. In fact, while without the control of the O2 excesses of air must be guaranteed that are greater than the optimum ones for safety reasons, in order to take into account the variable working conditions, with the O2 regulation system, it is possible to set minimum oxygen values in the flue gases, to determine the minimum excess of air to obtain complete fuel oxidation without the need for increasing safety. In this way, NOx emissions are reduced, due to the smaller amount of oxygen present during combustion. Minimisation of excess air involves a decrease in the delivery of the burnt gases and, consequently, their temperature. The result is 0 1 2 3 4 5 6 7 8 9 10 100 150 200 250 300 350 400 450 500 Load (kg/h) O2influegases(%) Without oxygen regulation With oxygen regulation Reference values of the oxygen content in flue gases for a gas burnerDiagram 76 O2influegases(%) Boilersinfo.com
• 79. 80 a further increase in technical combustion efficiency. Diagram 77 clearly shows, for a given temperature of the flue gases, variation in efficiency by varying the percentage of oxygen. An additional advantage deriving from applying this system is the continual fuel monitoring, making it possible to immediately highlight any malfunctions which can be compensated until an allowed threshold is reached, beyond which it is possible, if necessary, to shut the system down. 2.9.2 Pre-heating the combustion supporter air This technical solution is adopted to recover the heat contained in the flue gases. The sphere of application is limited to high- temperature heat producing systems, such as diathermic oil systems. In such cases, in fact, the exchange fluid must be heated to a temperature of more than 300°C and, consequently, the flue gases exit the boiler at a high temperature. Generally, the pre-heating temperature of the combustion supporter air that is achieved is around 150°C. Heat recovery is achieved using an air/flue gas heat exchanger installed inside the flue gases discharge pipe. The amount of heat recovered is proportionate to the mass-related delivery of the air for the temperature change caused by the passage through the exchanger. On average, this technique makes it possible to obtain an improvement in efficiency up to 8 %. It is good practice to install the combustion supporter air thrust fan upstream from the heat exchanger. When calculating the pressure drops, the real conditions of air use must be taken into account, using the application of the correction factors shown in table 23. 2.9.3 Regulating the fan speed In section 2.5.1 concerning the fans, we saw how combustion supporter air regulation can be done using a variation in the system characteristic curve or using the fan characteristic curve: the first can be done using the variation in pressure drop introduced by a servo-controlled damper, while the second can be done varying the rotation frequency of the fan motor. The fan rotation frequency is changed using particular frequency and tension converters called inverters, capable of regulating the fan rotation speed and, consequently, the delivery of the combustion supporter air. The following advantages can be obtained with this: • reduction in electrical power absorbed by the fan; 0 2,5 5 7,5 10 12,5 15 17,5 20 22,5 25 27,5 30 0 0,5 1 1,5 2 2,5 3 3,5 4 4,5 5 5,5 6 6,5 7 7,5 8 8,5 9 9,5 10 Oxygen (%) Ps(%) 400°C 50°C 100°C 150°C 200°C 250°C 300°C 350°C Loss of the flue gases for different % of O2Diagram 77 Boilersinfo.com
• 80. 81 combustion efficiency, as well as guarantee an efficient supervision of the combustion system, the system can be supplemented by a burner supervision system called Burner Management System, a concept layout of which is shown in Diagram 79. Using this system, it is possible to unite and supervise all burner regulations and exploit them simultaneously. For example, it is possible to integrate oxygen regulation with the fan rotation speed, thus obtaining a saving in terms of electrical power absorbed as described in the following diagram, or handle the functioning of several burners at the same time. • reduction in noise levels; The electrical power absorbed by the fan is directly proportionate to the number of revs, therefore a decrease in the number of revs corresponds to a decrease in the power absorbed. The reduction in the noise level is obtained both at fan level and with regard to any dampers that are passed by an air flow that has a lower speed. For these advantages to be effective, the frequency converter (inverter) must guarantee the exact observance of the descent and ascent ramps. This is necessary to maintain the correct fuel/air formula; to obtain the latter the motor must precisely follow the value of the number of nominal revs programmed without any delays. The saving which can be obtained by introducing the rev converter is equal to approximately 40% of the electrical energy absorbed by the fan. A precise evaluation of the energy saving can be calculated using the graph in Diagram 78. 2.9.4 The Burner Management System To achieve an improvement in technical Output absorption saving with inverter employ 0 0,5 1 1,5 2 2,5 3 3,5 4 4,5 5 5,5 6 6,5 7 7,5 8 8,5 9 9,5 10 10,5 11 11,5 12 12,5 13 13,5 14 14,5 15 15,5 0% 5% 10% 15% 20% 25% 30% 35% 40% 45% 50% 55% 60% 65% 70% 75% 80% 85% 90% 95% 100% Fan delivery Outputabsorption(kW) Absorption without inverter Absorption with inverter Output saving Diagram for the evaluation of the energy saving by means of the inverterDiagram 78 Boilersinfo.com
• 81. 82 MODEM MODEM REMOTE MONITORING & SERVICE SUPPORT CUSTOMER BUILDING MANAGEMENT SYSTEM NETWORK NODE RS 232 RS 232 (MODBUS PROTOCOL) RS 232 (MODBUS PROTOCOL) RS 422 (MODBUS PROTOCOL) RS 422 (MODBUS AND OTHERS PROTOCOL OR OR INFRARED PORT LAP TOP FOR COMMISSIONING/SERVICE ANALOG I/O UNIT DIGITAL I/O UNIT SAMPLING PROBE LOAD SENSOR PRESSURE CUSTOMER BUILDING MANAGEMENT SYSTEM BOILER ROOM CONTROLS AND ALARMS LOAD SENSOR TEMPERATURE AIR SERVOMOTOR FUEL SERVOMOTOR CUSTOMER BUILDING MANAGEMENT SYSTEM STEAM HOT WATER EXHAUST GAS RS 232 (MODBUS PROTOCOL) NETWORK NODE LOCAL AREA NETWORK LOCAL AREA NETWORK CUSTOMER BUILDING MANAGEMENT SYSTEM 0% 5% 10% 15% 20% 25% 30% 35% 40% 45% 50% 55% 60% 65% 70% 75% 80% 85% 90% 95% 100% 0% 5% 10% 15% 20% 25% 30% 35% 40% 45% 50% 55% 60% 65% 70% 75% 80% 85% 90% 95% 100% Burner Output (%) Outputabsorption(%) Without O2 regulation With O2 regulation Electrical power absorption with O2 regulation and inverterDiagram 80 Conceptual representation of a Burner Management SystemDiagram 79 Boilersinfo.com
• 82. 83 For pressurised boilers, this efficiency is generally between 90% and 93% and it can be calculated by considerating the fuel efficiency (described in section 1.5.1) and the loss through the shell (which generally are 1÷2%). Preliminarily, if we only have the effective capacity of the boiler, the capacity at the boiler furnace can be calculated by dividing the effective capacity by 0.9: If the only data available is the delivery of vapour produced, generally expressed in kg-h or t/h, the furnace thermal output can be calculate using the following equation Qfurnace=[ Gv CP (Tvapour – Twater) + Gv CLAT VAP] / η Where: Gv = mass-related vapour delivery [kg/s] Cp = specific heat at constant pressure [kW/kg °C] Tvapour = vapour temperature [°C] Twater = water temperature entering the boiler [°C] CLAT VAP = latent vaporisation heat [kW/kg] η = efficiency of the vapour generator. Qfurnace = Quseful 0.90 η100% = Quseful Qfurnace 3.1 GENERAL CRITERIA In order to choose the correct burner, certain characteristic data must be known; a list of the main points is illustrated as follows: 1. thermal capacity at the furnace of the heat generator or thermal discharge Pfoc [kW]; 2. back pressure in the combustion chamber, or flue gas side pressure drop DP [Pa]; 3. type of boiler; 4. fuel; 5. regulation method for the installed power capacity; 6. minimum feed pressure of methane gas; 7. altitude of the system [m above sea level] and average air temperature; 8. special installation characteristics. The first three parameters are characteristic data of the boiler and must be supplied by the manufacturer; parameters 4 and 5 are technical choices that the design engineer must make, while parameters 6, 7 and 8 are a constraint of the heat generation system. For an organised and complete collation of the data required for correctly choosing a burner, a checklist can be used similar to Table 21. 3.1.1 Thermal capacity at the heat generator furnace The thermal capacity at the heat generator furnace constitutes the characteristic data of the generator and represents the energy that must be supplied to the generator by burning the fuel in the burner to obtain the effective boiler output, which must be no lower than hat required by the system. Sometimes this value is called the boiler thermal discharge and is expressed in either kW or in kcal/h. The difference between the value of the furnace thermal capacity and the effective output constitutes the portion of energy which will be lost, mainly via the flue gases and the boiler shell. Their ratio represents the effective boiler efficiency at maximum capacity: SELECTION OF A FORCED DRAUGHT BURNER 3 Boilersinfo.com
• 83. 84 CHART OF THE DATA REQUIRED FOR A COMBUSTION SYSTEM SELECTION Boiler model Manufacturer Year of prod. Fluid type Max firing pressure [bar] Max firing temp. [°C] Vapour prod. [kg/h] Flue gas pipes Boiler type Water pipes Nominal boiler output [KW] [Kcal/h] Boiler efficiency % Boiler furnace output [KW] [Kcal/h] Existing burner type (trademark): Combustion chamber data Backpressure / Furnace depression [mbar] [mm W.C.] Length [mm] Height [mm] Projection of burner headDiameter [mm] Breadth [mm] bruciatore [mm] Fuel Gas supply data Net calor. value [kWh/Nmc] [Kcal/Nmc ] Delivery pressure [mbar] [bar] [mm W.C.] Oil supply data Gas oil Light fuel oil Medium fuel oil Heavy fuel oil Viscosity Net calorific value [kJ/Kg] [kWh/Kg] [kcal/Kg] Installation place Country (abroad) Town Company Altitude [m a.s.l.] Tmin/max [°C] Electrical data 3-phase voltage supply/Control voltage/frequency Burner control options Dual block burner pumpibg unit (options) Pump/Filter Preheater Gas train Other requirments (norms, spcs, notes) Diathermic oilHot water Superheated water Superheated vapourHigh pressure vapour Hot air (indirect exch.) 3-turns Flame inversion Low pressure vapour Light oil Heavy oil LPGMethane gas Biogas Indoor Outdoor 400/230/50 400/110/50 210/120//220/60 / / Continuos self-checking Oxygen regulation Pre-mounted Single pump Double combustion chamber Coiled/rapid Kerosene City gas 6 cSt at 20°C 20°E at 50°C3°E at 50°C 50°E at 50°C Double pump Single filter Double filter Electrical Steam Doble (steam/electrical) Train regulation Safety train Leakage control Gas delivery measure D-shape Oil delivery measure Modulating regulation Only components Hot air (direct exchange) Vertical Absorption factors of certain materialsTable 21 Reverse flame chamber head Boilersinfo.com
• 84. 85 3.1.2 Back pressure in the combustion chamber Depending on the backpressure in the combustion chamber, the heat generators can be divided in two large families: 1. Boilers in slight depression; 2. Pressurised boilers; In depression-type boilers, the flow of combustion supporter air and combustion products depends on the draught effect of the flue, which is established as a result of the difference in temperature between the flue gases and external air, and/or the presence of balanced-draught systems. In both types of boiler, combustion supporter air is taken in by force by the fan, which in monobloc burners is incorporated in the burner itself. The thermal yield of the boiler is heavily influenced by the pressure value which is created in the combustion chamber by the turbulence of the flue gases; theoretically, by increasing the pressure drops on the flue gas side, the boiler heat exchange efficiency can be increased. Currently, boiler manufacturers have achieved a standardisation level of backpressure with values proportionate to the thermal discharge from the boiler. If the manufacturer does not supply precise information, an indicative value can be obtained from the graph below: The data presented is valid for recently produced boilers and for Western countries. It is therefore possible that, for older boilers or those manufactured in countries using methods greatly different from western technological culture, these values will also be considerably different. 3.1.3 Type of heat generator The boiler construction type is extremely important when choosing the burner, especially regarding the length of the combustion head. In fact, the various boilers mentioned above have combustion chambers and, consequently, flame form requirements that vary somewhat from one another. The combustion chambers can be divided in two categories: • with direct route of flue gases (e.g. boilers with three flue gas turns or serpentine boilers) • with inversion route of the flue gases in the chamber (e.g. boilers with two flue gas turns) for both types, the manufacturer must supply the length of the blast tube required by the burner, to create optimum combustion conditions; this value is determined on an experimental basis by laboratory tests. In the absence of such data, it is possible to form hypothesis and general considerations, which help in choosing the most appropriate length of blast tube; in detail: For cast iron component boilers and those in Combustion chamber backpressure - indicative values 100 200 300 400 500 600 700 800 900 Output (kW) Backpressure(Pa) Combustion chamber backpressure in relation to thermal output Diagram 81 Reverse flame boilerDiagram 82 Serpentine boilerDiagram 83 Boilersinfo.com
• 85. 86 steel with three flue gas turns, the blast tube can jut out only from the internal edge of the front door; for boilers with two flue gas turns and flame inversion, the blast tube must penetrate the combustion chamber beyond the second flue gas turn entry, to avoid any by- pass of burnt gas directly into the second turn. The head penetration inside the combustion chamber can be modified by adjusting one of the mobile flanges or by adopting of an extension and/or spacer placed between the burner connection plate and the front of the boiler. The complete definition of flue route is greatly influenced by the type of flue pipe and the hot or cold running setting. For burners with three flue gas turns or flame inversion chambers, protective heatproof insulating material (11 in the following diagram) should be fitted between the boiler refractory and the blast tube, and the flange should be fixed to the boiler plate with a gasket placed in- between (8 in the diagram 84). For boilers with combustion chambers in refractory walls, besides the above considerations regarding flue gas routes, the irradiation effect must also be considered directly on the combustion head, which is thermally stressed due to the elevated wall temperature. Precautional measures have to be evaluated singularly consulting boiler manufacturer. 3.1.4 Fuel The type of fuel is usually a system limit and is rarely a choice that the design engineer may make in relation to the cheapness of the fuel, yield and complexity of the fuel feed system. 3.1.5 Burner operation mode The operation mode of the mono-stage, two or three-stage or modulating burner is a choice made by the system design engineer, in relation to the variability of the system thermal load and the generator heat inertia characteristics. 3.1.6 Minimum feed pressure of gaseous fuel The minimum feed pressure value of gaseous fuel is required to choose the gas train. The value is provided and guaranteed with reasonable certainty by the fuel supply board and completes the supply contract. For independent installations with storage tanks, the data is represented by the pressure guaranteed by such equipment. 3.1.7 Installation altitude and average combustion air temperature The burner firing range refers to certain standardised barometric pressure values equating to mbar (average atmospheric pressure value at an altitude of 100 m above sea level) and combustion supporter air temperature values equating to 20°C, subject to different indication shown at the bottom of the firing ranges. If the burner has to function at a different altitude and/or at a combustion supporter air temperature that is different to the standard values, the performance variations must be taken into account both in terms of power/output and head guaranteed by the fan. These variations are due to the fact that heating the combustion supporter air and increasing altitude produce the same effect, i.e. a reduction in air density. A decrease in air density is matched by a decrease in the amount of oxygen and, consequently, a decrease in the maximum amount of fuel burnable with variations of the maximum output that can be achieved by the burner. Furthermore, the total head developed by the fan also undergoes a reduction which is directly proportionate to the decrease in density; in particular, by the law of fans, if the specific air weight varies following changes in its temperature and/or its pressure, all fans Fixing of the blast tube to the boiler port Diagram 84 11 8 Boilersinfo.com
• 86. 87 achieve the maximum pressure available; The pressure drops are a quadratic function of the flue gas delivery, equivalent to fuel delivery and consequently burner output. The equation that links the two magnitudes is as follows: In correspondence to every value of Qreduced, the above verification procedure should be repeated until the maximum correct head available is greater than the back pressure reduced in the combustion chamber. The procedure is indicated in the following example, where the F factor value can be taken from table 22. Tables exist, such as 30, showing the F inverse value. 3.1.8 Special installation features If the burner is to be fitted to the heat generator with special limits, such as installation direction, extreme temperatures or other factors, the manufacturer must be consulted to verify in each single case, if the family of burners chosen for the application is correct. 3.2 SELECTION OF A MONOBLOC BURNER - NUMERIC EXAMPLE Various information is required to correctly choose a burner. For this reason, the first step suggested is a correct and complete collation of the data, which can be drawn up on the basis of schedule 24. It is also necessary to outline the complete fuel feeding combustion system. 3.2.1 Selection of the burner model The series of double-powered burners (dual fuel) which satisfies the fuel requirement to be used (gas G20 + diesel oil) is the RLS with two-stage operating. The choice must be made with an identified virtual firing range starting from the correct output value at the furnace in relation to the height. ( )Preduced = Pfurnace . Qreduced Qfurnace 2 being equal, the fan volumetric delivery will not vary, but the pressure developed and the output absorbed vary according to the following law: where: P1= total pressure developed with a fluid density of δ1; P2= total pressure developed with a fluid density of δ2; N1= output absorbed with a fluid density of δ1; N2= output absorbed with a fluid density of δ2; To choose the burner, it is necessary to check that the system firing point remains inside the burner firing range, even under different temperature and altitude conditions. Therefore, to choose a burner for a system to be installed at an altitude and/or temperature which is different from the standard burner test values, we must create a virtual firing point, which has an increased output value with respect to the real firing point. The increase is made by dividing the effective output by factor F function of the temperature and the barometric pressure. This output value corresponds to a maximum head value of the burner fan Pmax which can be obtained from the firing range as the intersection between the curve of the firing range and the vertical line traced for the value Qburner. As mentioned previously, this value should be taken as valid for standard burner test conditions and must therefore be correct in relation to the variations in fan performances, in particular: If the head Pburner is greater than the backpressure to be overcome in the combustion chamber, the burner can satisfy the system requirements. If not, there are two possible actions: • choose the burner from the next class up and repeat the verification procedure described above; • reduce the burner fuel delivery, and consequently, the output, so as to reduce the pressure drops in the combustion chamber, to Pburner = Pmax . F Qburner = Qfoc F N1 = N2 . δ1 δ2 P1 = P2 . δ1 δ2 Boilersinfo.com
• 87. 88 Using table 22, for a height of 1,000 m and a temperature of 20°C, an F factor value is obtained equal to 0.898; the correct output will be equal to: The burner models that satisfy the parameter Qburner equal to 501.1 kW, taking the data from the tables in the catalogue or from the choice index. From table 25, we can see that there are two burners that satisfy the required capacity: the RLS 50 and the RLS 70. The choice between these two models of burner should be made in relation to the backpressure within the combustion chamber. This verification must be carried out with the help of the firing ranges. On the diagram of the chosen burners, a vertical line should be traced in correspondence to the maximum output Qburner = = = 501,1 kW Qfoc F 450 0,898 required of 501.1 kW, and thus the maximum back pressure value which can be overcome, supplied by the burner fan, is gained. We can obtain the following maximum heads m mbar 0 5 10 15 20 25 30 40 0 1,087 1,068 1,049 1,030 1,013 0,996 0,979 0,948 100 1,073 1,054 1,035 1,017 1,000 0,983 0,967 0,936 200 989 1,061 1,042 1,024 1,006 0,989 0,972 0,956 0,926 300 978 1,049 1,031 1,012 0,995 0,978 0,961 0,946 0,915 400 966 1,037 1,018 1,000 0,983 0,966 0,950 0,934 0,904 500 955 1,025 1,006 0,989 0,971 0,955 0,939 0,923 0,894 600 944 1,013 0,995 0,977 0,960 0,944 0,928 0,913 0,884 700 932 1,000 0,982 0,965 0,948 0,932 0,916 0,901 0,872 800 921 0,988 0,971 0,953 0,937 0,921 0,905 0,891 0,862 900 910 0,977 0,959 0,942 0,926 0,910 0,895 0,880 0,852 898 0,964 0,946 0,930 0,913 0,898 0,883 0,868 0,841 878 0,942 0,925 0,909 0,893 0,878 0,863 0,849 0,822 856 0,919 0,902 0,886 0,871 0,856 0,842 0,828 0,801 836 0,897 0,881 0,865 0,850 0,836 0,822 0,808 0,783 815 0,875 0,859 0,844 0,829 0,815 0,801 0,788 0,763 794 0,852 0,837 0,822 0,808 0,794 0,781 0,768 0,743 s. l. m. 0 d. m. a. d. n. m. a. s. l. Atmospheric pressure / Pressione atmosferica F ARIA / LUFT / AIR / AIR °C Example of backpressure reduction for a burnerTable 23 F - correction factor of discharge head and delivery in relation to temperature and altitudeTable 22 Dual fuel (light oil-gas) burner of RLS series Diagram 85 H1 – Required backpressure H2 – Backpressure in normal conditions H3 – Backpressure in particular installation conditions (temperature and altitude) Boilersinfo.com
• 88. 89 CHART OF THE DATA REQUIRED FOR A COMBUSTION SYSTEM SELECTION Boiler model Manufacturer Year of prod. Fluid type Max firing pressure [bar] Max firing temp. [°C] Vapour prod. [kg/h] Flue gas pipes Boiler type Water pipes Nominal boiler output [KW] [Kcal/h] Boiler efficiency % Boiler furnace output [KW] [Kcal/h] Existing burner type (trademark): Combustion chamber data Backpressure / Furnace depression [mbar] [mm W.C.] Length [mm] Height [mm] Projection of burner headDiameter [mm] Breadth [mm] bruciatore [mm] Fuel Gas supply data Net calor. value [kWh/Nmc] [Kcal/Nmc ] Delivery pressure [mbar] [bar] [mm W.C.] Oil supply data Gas oil Light fuel oil Medium fuel oil Heavy fuel oil Viscosity Net calorific value [kJ/Kg] [kWh/Kg] [kcal/Kg] Installation place Country (abroad) Town Company Altitude [m a.s.l.] Tmin/max [°C] Electrical data 3-phase voltage supply/Control voltage/frequency Burner control options Dual block burner pumpibg unit (options) Pump/Filter Preheater Gas train Other requirments (norms, spcs, notes) Diathermic oilHot water Superheated water Superheated vapourHigh pressure vapour Hot air (indirect exch.) 3-turns Flame inversion Low pressure vapour Light oil Heavy oil LPGMethane gas Biogas Indoor Outdoor 400/230/50 400/110/50 210/120//220/60 / / Continuos self-checking Oxygen regulation Pre-mounted Single pump Double combustion chamber Coiled/rapid Kerosene City gas 6 cSt at 20°C 20°E at 50°C3°E at 50°C 50°E at 50°C Double pump Single filter Double filter Electrical Steam Doble (steam/electrical) Train regulation Safety train Leakage control Gas delivery measure D-shape Oil delivery measure Modulating regulation Only components Hot air (direct exchange) Vertical 5 95 450 510 10 28 11,86 ITALIA 4,5 15/25 Chart of the data required for a combustion system selection - exampleTable 24 Reverse flame chamber head Boilersinfo.com
• 89. effective head of the burner overcomes the back pressure in the combustion chamber: The values in the columns have the following meaning: (1) original furnace output Qfurnace; (2) reduction percentage of furnace output r; (3) reduced furnace output Qreduced= r · Qfurnace (4) boiler head at reduced output; (5) required output at the burner Qburner = Qreduced /F; (6) maximum head available corresponding to Qburner Pmax; (7) effective burner head Pburner = Pmax · F A 6% reduction of output is required so that the fan head is greater than the backpressure in the combustion chamber of the boiler. If the system can cope with a 6% reduction of ( )Preduced = Pfurnace . Qreduced Qfurnace 2 90 Qfurnace [kW] (1) R [%] (2) Qreduced [kW] (3) Preduced [mbar] (4) Qburner [kW] (5) Pmax [mbar] (6) Pburner [mbar] (7) 450 1% 446 4,41 496 4,1 3,68 450 2 % 441 4,32 491 4,2 3,77 450 3 % 437 4,23 486 4,3 3,86 450 4 % 432 4,15 481 4,4 3,95 450 5 % 428 4,06 476 4,5 4,04 450 6 % 423 3,98 471 4,6 4,13 450 7 % 419 3,89 466 4,7 4,22 Iterative process tableTable 26 from the firing ranges: • RLS 50. Pmax = 4 mbar • RLS 70. Pmax = 9 mbar The maximum head taken from the graph must be corrected in relation to the installation height by using the F factor, obtaining the following values: for the RLS 50 burner: Pburner = Pmax . F = 4 . 0,898 = 3,6 mbar for the RLS 70 burner: Pburner = Pmax . F = 9 . 0,898 = 8,1 mbar The backpressure in the combustion chamber is equal to 4.5 mbar (450 Pa), greater than that which can be supplied by the RLS 50 series and lower than that which can be supplied by the RLS 70 series. Two solutions can be adopted: 1. the RLS 50 can be used, with a consequent reduction in the maximum output that can be supplied in relation to the maximum head available; 2. the RLS 70 burner can be used; In the first case, we can calculate the reduction in thermal output by using the iterative procedure summarised in the table below. The maximum output which can be supplied can be taken from the following table and is that corresponding to the line in which the RLS 28 RLS 38 RLS 50 RLS 70 RLS 100 RLS 130 kW 163-325 232-442 290-581 465-814 698- 930- Mcal/h 192-378 270-513 337-676 541-947 812- - Fuel delivery (2nd stage) kg/h 13,7-27,4 19,6-37,3 24,5-49 39-69 59-98 78-118 kW 100 116 145 232 349 465 Mcal/h 116 135 169 270 406 541 Fuel delivery (min. 1st stage) kg/h 8,5 9,8 12,3 19 29,5 39 Gas pressure at maximum delivery: G20/G25/G31 mbar 11/16,2/9,5 13/19,2/12 14/20,8/10,5 6,2/7,5/7,8 10/13/12 11,5/14,4/15 Ambient temperature °C Max combustion air temperature °C ELECTRICAL SUPPLY Phase - Hz - V ELECTRICAL MOTORS rpm Fan motor W 250 420 650 A 2,1 2,9 3-1,7 4,8-2,8 5,9-3,4 8,8-5,1 Pump motor W A PUMP delivery (at 12 bar) kg/h pressure range bar max fuel temperature °C ELECTRICAL POWER CONSUMPTION W max 530 760 910 ELECTRICAL PROTECTION APPROVAL CE DIN NOISE LEVELS (**) dBA 68 70 72 74 77,5 80 CONFORMITY TO EEC DIRECTIVES HEAT OUTPUT(*) (min. 1st stage) HEAT OUTPUT(*) (2nd stage) 1 - 50 -230 0,8 FUELS Light oil, viscosity at 20°C: 6mm2 /s max (1,5°E - 6cst) Natural gas: G20 (methane) - G21 - G22 - G23 - G25 GPL - G30 (propane) - G31 (butane) 2,4 4-18 10-20 3 N - 50 - 400/230 90 370 IP44 ASAR 67 164 Model (*) Reference conditions: Ambient temperature 20°C - Barometric pressure mbar - Altitude m a.s.l. (**) Sound pressure measured in manufacturer's combustion laboratory, with burner operating on test boiler and at maximum rated output. 0-40 60 5G835/97M- 90/396 - 89/336 - 73/23 - 92/42 90/396 - 89/336 - 73/24 60 Technical data of RLS series of monoblock burnersTable 25 Boilersinfo.com
• 90. 91 the maximum output, the RLS 50 series burner can be used. In the diagram representing the firing ranges, the burner firing point (indicated in yellow) has also been indicated in the event that installation is carried out at a height corresponding to the burner test value (100 m above sea level and 20°C), and thus with no need to correct the chosen parameters. As can be seen in this last hypothetical example, the maximum output required is possible with the inferior RLS 50 series, without a reduction in output. This demonstrates the importance of evaluating the geodetic installation height and of its weighting in reference to the output and pressure parameters. Continuing the example, we can hypothesise using the RLS70 burner. 3.2.2 Selection of the combustion head length The combustion head of the RLS 70 series burner is 250 mm long. The boiler in question is a flue gas pipe-type boiler with flame inversion. The constructive diagram of the boiler is shown in the illustration below. For this boiler, the distance C between the burner fastening plate and the entrance of the second flue gas turn after flame inversion is equal to approximately 200 mm. Considering the indications given previously, optimum conditions could be the protrusion of the combustion head beyond this section of at least 20-25% with respect to the distance between the fastening plate and the second flue gas turn entrance. The combustion head penetrates by around 50 mm into the combustion chamber. For the RLS70 series burner, the length of the combustion head is in fact equal to 250 mm, optimum value for the use in question. If this length were much greater than that requested, certain accessories would be needed to decrease the penetration inside the combustion chamber; these accessories are called spacers and are positioned between the burner coupling flange and the boiler shell. If the head were shorter, extensions would be used. In certain cases, the length of the burner combustion head is clearly declared by the boiler manufacturer. 3.2.3 Verifying the flame length Before choosing the fuel feed, the dimensions of the combustion chamber must be checked, which is to be combined with the chosen burner, to ensure they are similar to those of the test boiler used to test the burners. For this check, the diagram below should be used, in which by entering the thermal output or the fuel delivery on the X axis, we can read off the diameter of the combustion chamber on the upper axis and the length of the chamber on the Y axis. The choice is confirmed if the boiler the burner will be coupled to, falls within the tolerance range. In our case, the combustion chamber has aCombustion headDiagram 86 Hot water boiler constructive layoutDiagram 87 Boilersinfo.com
• 91. 92 diameter of 700 mm and a length of 1,600 mm, therefore the combination with the RLS 70 burner is confirmed. If the dimensions were very different to those of the test boiler, we could obtain a flame geometry (length and width) which is not optimised for the application; when the combustion chamber is too short, physical damage may be caused to the body of the boiler due to heat stress caused by the contact of the flame with the bottom wall. 3.2.4 Selection of the gas train The choice of the gas train to combine with the burner must be made, bearing in mind that the sum of all the pressure drops suffered by the gaseous fuel must not exceed the available pressure. Starting downstream, the following drops must be taken into consideration: 1. H1: back pressure in the combustion chamber; 2. H2: combustion head; 3. H3: gas train; 4. H4: feed system up to the delivery point delivery; The minimum pressure available at the delivery point for the gaseous fuel being H, the following condition must be verified: H ≥ H1 + H2 + H3 + H4 For ease of calculation, the graphs of gas train pressure drops have been estimated and represented graphically under the form of graphs and tables already inclusive of the portion lost due to the combustion head (H2+H3). However, to give complete information, these graphs also illustrate the pressure drop of the combustion head alone (H2). In order to obtain the pressure drop of just the gas train (H3), just calculate the difference between the two values. Therefore, the choice of the gas train must be made to satisfy the following equation: H2 + H3 ≤ H - (H1 + H4) In the case, the values are as follows: H=2,800 Pa (28 mbar); H1=450 Pa (4.5 mbar); H4=1.000 Pa (10 mbar) The pressure drop of the gas train and the combustion head must not exceed the following value: H2 + H3 ≤ 2.800 - (450 + ) = 1.350 Pa = 13,5 mbar 0 1 2 3 4 5 6 7 0 500 Thermal output (kW) Lenghtoftheflame(m) 0 0,5 1 1,5 2 2,5 3 3,5 4 Diameteroftheflame(m) LMAX LMIN DMAX DMIN Lenght and diameter of the flame in relation to burner outputDiagram 88 Boilersinfo.com
• 92. 93 The fluid pressure drops in a pressurised system are proportionate to the delivery of the fluid itself. In the case of methane gas, delivery can be calculated by using the following formula: where: Qfur= boiler output at the furnace [kW]; I.C.V. = inferior fuel calorific value [kWh/m3 ]; In the case, the delivery of gaseous fuel is equal to: The delivery used for choosing the gas train is the effective delivery at the boiler furnace. The choice of the gas train should be made using the graphs provided for two-stage gas flow trains. Specifically a vertical line should be drawn corresponding to the output at the furnace or corresponding to the fuel delivery according to the graph; the intersection of this line with the specific curves for each train provides the respective pressure drop inclusive of the portion due to the combustion head. The pressure losses for the various gas trains that can be used are as follows: combustion head + train MB15/2: m = = 45,0 450 10,0 [ ]Nm3 h m = Qfur I.C.V. [ ]Nm3 h Pa (16.5 mbar); combustion head + train MB 20/2: Pa (12.50 mbar); pressure drop for combustion head: 600 Pa (6 mbar); The gas train that satisfies the maximum pressure drop requirement that can be supported by our system is therefore the MB 20/2 model. In this case, the train does not require any adapter for connection to the burner, but as a rule, the appropriate accessories for correct coupling must be chosen. 3.2.5 Selection of the components for the diesel oil feed circuit The diesel oil feed circuit considered is that which involves direct intake from a tank installed at a height of 3 metres below the burner. The pipes are dimensioned using the following table supplied by the manufacturer, where the length of the pipelines is the extension to be taken as a sum of the total length of the pipes and the equivalent lengths of the devices introduced into the circuit. The circuit is 25 m long, and contains the 0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 460 480 500 520 540 560 580 600 620 640 660 680 700 720 740 760 780 800 820 Output (kW) Pressureloss(mbar) Combustion head MB 15/2 + combustion head MB 20/2 + combustion head Diagram for selection of gas trainsDiagram 89 Boilersinfo.com
• 93. 94 following components that correspond to the equivalent lengths; the following diagram was used for the calculation, presuming an internal pipeline diameter of 14 mm - 4 curves of 90° Leq curve = 0.1 m - 1 filter Leq filter = Leq valve (open) = 0.045 m - 2 shut-off valves. Leq valve (open) = 0.045 m The total equivalent length is therefore: Ltot eq = Lthere+back + ∑ Leq = 25 + 4x0.1 + 0.045 + 2x0.045 = 25.535 m Entering the table in the line relating to H = -3, a 26 metres length of pipeline corresponds to an internal diameter of the pipeline equal to 14 mm. Therefore, the hypothesis initially made for determining the equivalent lengths is correct; if the difference in height between the burner and the tank had been – 4 m, a pipeline with an internal diameter of 16 mm would have been used, and in this case the equivalent lengths of the curves, the valves and the filter would have to be recalculated. 3.3 SELECTION OF A DUALBLOC BURNER - NUMERIC EXAMPLE The previous paragraph shows the numerousness of the information required to make a pondered choice of the possible combustion system. It is also indispensable to gather all the data using the same method for separately powered burners. The DUALBLOC burner that we choose using this process must satisfy the following project-related data: The diagram below shows the plant- engineering layout of this application. The following diagram shows and industrial TI series burner. 3.3.1 Selection of the burner model The combustion requirement with pre-heated air, typical of diathermic oil generators, makes it necessary to adopt a separate ventilation burner. Layout of a light oil feeding circuitDiagram 90 Schedule for the tabular scaling of the light oil feed pipelines Table 27 SB Light oil tank FG Filter P Pump LA Nozzle holder VS Safety valve SMn Servomotor SER1 Air damper VT Fan AP Air pressure switch Dualbloc burner of TI seriesDiagram 91 Pipeline length (m) Boilersinfo.com
• 94. 95 The Riello Burners TI series of DUALBLOC burners satisfies the requirement of the double fuel to be used (gas + fuel oil), which has a characteristic regulation of the modulating thermal output. The burner must be chosen in relation to the requested furnace output: as a rule, this is indicated on the name plate of heat generator for existing installations and can be found in the manufacturer's catalogue for new installations. In this case, taking the nominal or effective output as the only data available, the thermal output at the furnace can be gained by using the simplified formula indicated in section 3.1.1. The installation height equating to 50 metres does not require any correction to this output value, therefore from the following technical data table we can learn that the first model to satisfy said requirements is the TI11. Qfurnace = = = kW Qeffective 0,90 0,9 CHART OF THE DATA REQUIRED FOR A COMBUSTION SYSTEM SELECTION Boiler model Manufacturer Year of prod. Fluid type Max firing pressure [bar] Max firing temp. [°C] Vapour prod. [kg/h] Flue gas pipes Boiler type Water pipes Nominal boiler output [KW] [Kcal/h] Boiler efficiency % Boiler furnace output [KW] [Kcal/h] Existing burner type (trademark): Combustion chamber data Backpressure / Furnace depression [mbar] [mm W.C.] Length [mm] Height [mm] Projection of burner headDiameter [mm] Breadth [mm] bruciatore [mm] Fuel Gas supply data Net calor. value [kWh/Nmc] [Kcal/Nmc ] Delivery pressure [mbar] [bar] [mm W.C.] Oil supply data Gas oil Light fuel oil Medium fuel oil Heavy fuel oil Viscosity Net calorific value [kJ/Kg] [kWh/Kg] [kcal/Kg] Installation place Country (abroad) Town Company Altitude [m a.s.l.] Tmin/max [°C] Electrical data 3-phase voltage supply/Control voltage/frequency Burner control options Dual block burner pumpibg unit (options) Pump/Filter Preheater Gas train Other requirments (norms, spcs, notes) Diathermic oilHot water Superheated water Superheated vapourHigh pressure vapour Hot air (indirect exch.) 3-turns Flame inversion Low pressure vapour Light oil Heavy oil LPGMethane gas Biogas Indoor Outdoor 400/230/50 400/110/50 210/120//220/60 / / Continuos self-checking Oxygen regulation Pre-mounted Single pump Double combustion chamber Coiled/rapid Kerosene City gas 6 cSt at 20°C 20°E at 50°C3°E at 50°C 50°E at 50°C Double pump Single filter Double filter Electrical Steam Doble (steam/electrical) Train regulation Safety train Leakage control Gas delivery measure D-shape Oil delivery measure Modulating regulation Only components Hot air (direct exchange) Vertical 10 300 15 90 10 2 11,86 10,67 ITALIA 15/25 Chart of the data required for a combustion system selection - exampleTable 28 Reverse flame chamber head Boilersinfo.com
• 95. 96 Fuel/AirDataElectricalDataEmissionsApproval Intermittent (at least one stop every 24 h) - Continuos (at least one stop every 72 h) TI 10 1 : 6 1 : 5 1 : 4 1 : 3 870/÷ 748/÷ /÷ 894/÷ /÷ /÷ /÷ /÷ 111/253÷438 152/268÷464 87/300÷520 101/349÷605 40/116÷202 Servo- motor natural gas LPG light oil heavy oil s kW Mcal/h kW Mcal/h kW Mcal/h kW Mcal/h °C min./max. kWh/kg Kcal/kg mm2 /s (cSt) Kg/h °C kWh/kg Kcal/kg mm2 /s (cSt) Kg/h °C bar kWh/Nmc kg/Nmc Nmc/h kWh/Nmc kg/Nmc Nmc/h kWh/Nmc kg/Nmc Nmc/h type °C max. Ph/Hz/V type VA A IP V1 - V2 I1 - I2 dBA W mg/kWh N° Bach. mg/kWh mg/kWh N° Bach. mg/kWh mg/kWh mg/kWh modulating SQM10 42 -15/60 11,8 4 ÷ 6 50 11,1÷11,3 ÷ 500 140 25÷28 10 0,71 8,6 0,78 25,8 2,02 Centrifugal with reverse curve blades 150 1/50-60/230 - (1/50-60/110 on request) LFL 1.333 - LFL 1.335 (Intermittent working) - LGK 16 (Continuos working) 630 2,7 - 5,7 54 230 V - 1x8 KV 1,4A - 30 mA -- -- < 110 < 1 < 250 Depending on the fuel amount Depending on the fuel amount Depending on the fuel amount < 100 < 170 89/336 - 73/23 - 98/37 - 90/396 CEE EN 267 - EN 676 -- TI 12 1 : 6 1 : 5 1 : 4 1 : 3 /÷ /÷ /÷ /÷ /÷ /÷ /÷ /÷ 183/506÷734 259/536÷777 145/600÷870 169/698÷ 67/233÷337 natural gas LPG light oil heavy oil TI 14 1 : 5 1 : 4 1 : 3,5 1 : 3 /÷ /÷ /÷ /÷ /÷ /÷ /÷ /÷ 287/717÷ 357/759÷ 240/850÷ 279/988÷ 116/329÷465 TI 11 1 : 6 1 : 5 1 : 4 1 : 3 /÷ 998/÷ /÷ /÷ /÷ /÷ /÷ /÷ 148/354÷590 208/375÷625 116/420÷700 135/488÷814 54/163÷271 TI 13 1 : 6 1 : 5 1 : 4 1 : 3 /÷ /÷ /÷ /÷ /÷ /÷ /÷ /÷ 232/658÷927 326/696÷982 183/780÷ 213/907÷ 85/302÷426 Heat Output Light oil Heavy oil G20 G25 LPG Light oil Heavy oil G20 Model Setting type Modulation ratio at max output type run time Working temperature net calorific value viscosity at 20°C Output max temperature net calorific value viscosity at 20°C Output max temperature Atomised pressure net calorific value Density Output net calorific value Density Output net calorific value Density Output Fan Air temperature Electrical supply Control box Auxiliary electrical power Total current Protection level Ignition transformer Operation Sound pressure Sound output CO emission Grade of smoke indicator NOx emission CO emission Grade of smoke indicator NOx emission CO emission NOx emission Reference directive Reference norms Certifications Reference conditions: Temperature: 20°C - Pressure: .5 mbar - Altitude: 100 meters a.s.l. - Noise measured at a distance of 1 meter. Chart of the data required for a combustion system selection - exampleTable 29 After this preliminary choice, a check must be made on the firing range. The firing range for separately powered burners is represented by a histogram that identifies the minimum and maximum outputs that can be developed by the burner. The TI firing ranges are shown below both for methane gas and fuel oil (naphtha) feeding. These diagrams illustrate the firing ranges relating to the two usual temperature values. 50°C in the case of combustion supporter air not reheated and 150 °C for processes where the combustion supporter air is pre-heated. Looking at the diagrams with furnace output equal to 6,460 kW, it is evident how the TI11 model, which develops a thermal output of 7 MW with combustion supporter air at 50 °C is not applicable with pre-heated air at a temperature of 150 °C. The choice therefore falls on the TI12 model. 3.3.2 Selection of the fan The information required to choose the fan includes air delivery and the head required to guarantee that the combustion supporter air participates correctly in the combustion process. Boilersinfo.com
• 96. 97 Calculating the combustion supporter air delivery The combustion supporter air delivery is proportionate to the delivery of burnt fuel, therefore The fan must therefore satisfy the additional air delivery from among those requested by the various fuels, in this case it is therefore Gair = mc/h. Since the installation is at a height of 1,000 metres above sea level and at a temperature of 40 °C, to guarantee an equal number of moles of oxygen, this delivery must be corrected using the F factor obtaining: If the manufacturer provides the characteristic data and curves of the fans already corrected to the intake temperature, the correction must be realised solely in function of the height obtaining: Gair = = = kW corrected (H,T) 0,898 Gair F Gair = = = kW corretta (H,T) 0,841 Gair F Gair = x gtheoretical air x eG 20 = x x 9,56 x 1,20 = mc/h Qfoc PCIG 20 G 20 G 20 10,0 Gair = x gtheoretical air x efuel oil = x 10,37 x 1,25 = mc/h fuel oil fuel oilQfoc PCIfuel oil 10,67 Calculating the fan head The fan head is the sum of the head at combustion head exit and the induced pressure drops in the air pipelines and from the combustion head. Called Hfan, the effective head of the fan, the following conditions must be checked: Hfan ≥ H1 + H2 + H3 + H4 where, H1 = back pressure in the combustion chamber; H2 = pressure drop in the combustion head; H3 = pressure drop in the air pipelines; H4 = pressure drop in the heat exchangers; The pressure drops must all refer to the effective air temperature and heights. Combustion chamber The backpressure in the combustion chamber is project-related data and is equal to H1 = 1,500 Pa. Combustion head The pressure drop in the combustion head is taken from the diagrams supplied by the burner manufacturer. For burners with a movable head, we must consider the characteristic curve obtained in the laboratory for the same layout of the head set for actual functioning . In this case, the drop in the burner head is therefore equal to H2 = 27 mbar = 2,700 Pa. This value refers to a test temperature equal to Test conditions conforming EN 267; EN 676: Temperature: 20°C - Pressure: .5 mbar - Altitude: 100 m.s.l. 0 0 kW0 0 0 kW0 Useful working field for choosing the burner Modulation range GAS OIL Airtemperature°C Airtemperature°C Mcal/h TI 14 TI 13 TI 12 TI 11 TI 10 50°C 150°C 50°C 150°C 50°C 150°C 50°C 150°C 50°C 150°C Mcal/h TI 14 TI 13 TI 12 TI 11 TI 10 50°C 150°C 50°C 150°C 50°C 150°C 50°C 150°C 50°C 150°C Firing ranges for Riello TI Series of burner combustion headsDiagram 92 Boilersinfo.com
• 97. 98 20°C, therefore the value obtained will be corrected with the following Kc (4) factor relating to a temperature of 150 °C, taken from the law of perfect gases (see section 2.5). The correct pressure drop will therefore be equal to H2 = 27 x 1.44 = 38,8 mbar = Pa The air which arrives at the head is taken in at a height greater than the standard laboratory test height; for this reason, the pressure drop must be further corrected by dividing H2 by the F factor relating to a height of 1,000 metres above sea level. The effective pressure drop of the head will therefore be equal to H2 = 38.98 x 1,114 = 43.43 mbar = Pa The distribution ducts The calculations of the dimensions of the air delivery duct section must satisfy various requirements: • limit the head requested at the fan; • limit the internal air speed; • respect the available dimensions. In this case, since there are no dimension limits, a maximum speed of 20 m/s is fixed and at the end of the calculation we will check that the loss induced by the duct does not exceed the value of 500 Pa. From the following diagram, for a speed of 20 m/s and a delivery of 2,586 l/s (9,331 mc/h) the diameter of the section of the ducts is equal to 450 mm. Again on the diagram, we can read the related distributed pressure drop equating to e = 9 Pa/m. The duct also presents two gentle 90° curves, which have a non-dimensional loss factor equal to ξ = 1, thus we can calculate the related pressure drops with the known formula with a hypothetical duct length of 20 m, the H3 pressure drop is therefore H3= ε . L + 2 . ∆pw= 9 . 20 + 2 . 220 =620 Pa. The air in the ducts or pipelines is however taken in under temperature and height conditions that are different from standard ones; this leads to a variation in air density and therefore a variation in the pressure drops. The value of H3 obtained as above must therefore be corrected by using the Kc = 1,19 factor relating to the intake conditions (5) of the fan (40 °C, 1,000 metres above sea level). ∆pw = = 1 . 1,1 . 202 / 2 = 220 Pa.ξ .ρ v2 2 mbar 10 40 20 30 50 kW 0 Mcal/h ∆P Perditadicarico 60 TI 14 TI 10 TI 11 TI12 TI 13 Combustion head pressure drops for TI series - air side Diagram 93 m 0 20 30 40 50 60 70 80 90 100 120 140 150 0 0,920 0,987 1,021 1,055 1,088 1,122 1,156 1,189 1,223 1,257 1,324 1,391 1,425 100 0,932 1,000 1,034 1,068 1,102 1,136 1,171 1,205 1,239 1,273 1,341 1,409 1,443 500 0,976 1,047 1,083 1,119 1,154 1,190 1,226 1,261 1,297 1,333 1,404 1,476 1,511 750 1,006 1,079 1,116 1,153 1,190 1,227 1,263 1,300 1,337 1,374 1,448 1,521 1,558 1,038 1,114 1,152 1,190 1,228 1,266 1,304 1,342 1,379 1,417 1,493 1,569 1,607 1,067 1,145 1,184 1,223 1,262 1,301 1,340 1,379 1,418 1,457 1,535 1,613 1,653 1,101 1,182 1,222 1,263 1,303 1,343 1,384 1,424 1,464 1,505 1,585 1,666 1,706 1,136 1,220 1,261 1,303 1,344 1,386 1,428 1,469 1,511 1,552 1,636 1,719 1,760 1,174 1,259 1,302 1,345 1,388 1,431 1,474 1,517 1,560 1,603 1,689 1,775 1,818 1,206 1,294 1,339 1,383 1,427 1,471 1,515 1,559 1,604 1,648 1,736 1,824 1,869 1,251 1,342 1,388 1,434 1,480 1,525 1,571 1,617 1,663 1,709 1,800 1,892 1,938 1,284 1,378 1,425 1,472 1,519 1,566 1,613 1,660 1,707 1,755 1,849 1,943 1,990 1,321 1,417 1,466 1,514 1,562 1,611 1,659 1,708 1,756 1,804 1,901 1,998 2,046 s. l. m. 0 d. m. a. d. n. m. a. s. l. Kc ARIA / LUFT / AIR / AIR °C Kc - correction factor of discharge head and delivery in relation to temperature and altitudeTable 30 Kc (4) The Kc correction factor is the inverse of the F correction factor. (5) The increase transformation of the temperature which takes place in the exchanger is isochor (volume=constant) therefore the density remains constant and the specific pressure drops do not change. Pressuredrop Boilersinfo.com
• 98. 99 H3 = Kc . H3 = 1,19 . 620 = 737.8 Pa The heat exchanger The heat exchanger should be chosen in relation to the air, the nominal flue gas delivery and the related increase in temperature of the combustion supporter air. Two effects cause the pressure variation in the heat exchanger: • the isochor transformation (at constant volume), where the flue gases release heat into the air; • the mechanical resistor of the tube nest. Heat exchanger manufacturers supply the characteristic curve for each heat exchanger taken from given input and output height and temperature conditions. This value must be corrected as a result of the different input/output temperatures and the various installation heights. The exchanger introduced into this system has a pressure drop, corresponding to the delivery of mc/h and a temperature increase of 110 °C (from 40°C to 150 °C), equal to H4 = 500 Pa The exchanger is however installed at 1,000 metres above sea level, therefore this drop must be corrected by using the parameter Kc, thereby obtaining H4 = 500 · 1.114 = 557 Pa The effective fan head The effective head that the fan must provide is therefore equal to Hfan = H1 + H2 + H3 + H4 = 1.000 + 4.343 + 620 + 300 = 6,320 Pa = 63,20 mbar From the tables provided by the manufacturer, similar to those below, we can choose the model of fan. In this case, the manufacturer provides the characteristic running values with air at 40 °C, therefore entering the table relating to effective heads of around 600 mm ( Pa) with a value of the corrected air delivery Gcorrected(H) of mc/h, we can obtain the fan model: GBJI, for which we must also indicate the orientation of the pressure Pressure drops in circular pipelinesDiagram 94 Fan model GBJH 600 550 500 450 400 300 GBJI 650 625 600 550 525 500 GBJH 710 700 675 650 600 550 GBJH 760 710 680 640 GBJI 700 675 650 630 GBJI 650 600 575 535 490 450 390 330 GBJI 740 700 660 625 590 550 500 450 400 GBJH 840 810 790 750 700 650 600 GBJI 830 875 850 825 800 770 740 GBJH 940 910 880 850 800 750 700 625 560 490 410 GBJI 810 780 755 725 695 650 610 585 530 490 425 390 330 GBJI 895 875 850 820 790 750 720 690 640 585 545 495 440 GBJIA 990 875 845 910 885 855 815 790 750 Delivery (m 3 /h) Static air pressure (mmH 2 O) Fans selection tableTable 31 Pressure drop (mm H2O) for 1 m length Airdelivery(m3 /h) Airdelivery(m3 /h) Boilersinfo.com
• 99. 100 ALTITUDE (m a.s.l.) Temperature (°C) 0- 0 1,98 1,2 1,3 1,3 10 1 1,1 1,2 1,3 20 0,9 1 1,1 1,2 30 0,8 0,9 1 1,1 40 0,7 0,8 0,9 1 50 0,6 0,7 0,8 0,9 60 0,5 0,6 0,7 0,8 Nominal output declassing factor in relation to temperature and altitude Table 32 inlet in relation to the intake inlet. The effective firing point of the fan must be verified on the real characteristic curve. As we can see from the diagram, the firing point falls halfway through the characteristic curve of the fan, which is thus verified. A further check can be carried out, when working at high altitudes, by declassing the motor, which gives a reduction in nominal output as the temperature and altitude increase. From graphs and tables similar to the following, supplied by the electric motor or fan manufacturers, the reduction factor is obtained for the motor nominal output; this must always be greater than the power absorbed by the fan at the effective working output. It is important to remember that the absorbed power by the fan is reduced by the F correction factor previously used for elevated altitudes and temperatures. 3.3.3 Selection of the gas train Generally, the gas train comprises two groups of components: • The safety and regulating valves; • The pressure reduction unit. The safety unit is chosen in relation to the combustion head pressure drops on the gas side; for the Riello Burner the characteristic curves from the gas side of the TI burner series for G20 natural gas are shown below. For a furnace output of 6,410 kW, the sum of the drops of the gas butterfly valve and the head is equal to 24+6=30 mbar (3,000 Pa). Using the diagram 97, we can choose the size of the safety value unit (6) DMV100/1, which has pressure drops equal to approximately 30 mbar (3,000 Pa). The sum of the pressure drops in the head and the valve unit is therefore: Hgas = (Hhead + Hbutterfly) + Hvalve = 30+30 = = 60 mbar The feed pressure of the gas is equal to 2 bar, therefore a reducer unit is necessary to guarantee an outgoing pressure equal to 60 mbar and a gas delivery equal to Ggas = Qfoc / PCIgas = 6,410 / 10 = 641 Nm3 / h Static air pressure GBJ series 250 350 450 550 650 750 850 950 mc/h mmw.c. GBJ H 15kW GBJ H 11kW GBJ I 18,5 kW GBJ H 30kW GBJ H 37kW GBJ I 15kW GBJ I 18,5kW GBJ I 22kW GBJ I 37 kW GBJ I 37kW GBJ I 45kW GBJ IA 55kW GBJ H 22kW Performence graphs of GBJ fan seriesDiagram 95 (6) The safety and regulating value unit comprises: a double automatic shut off valve and a low point pressure switch. Boilersinfo.com
• 100. 101 Pressuredrop Butterfly valve losses Combustion head losses G25 0 20 10 8 6 4 2 12 14 16 18 mbar 10 40 20 30 50 kW 0 Mcal/h G20 ∆P Pressuredrop 60 70 TI 14 TI10 TI11 TI12 TI13 ∆P mbar DN 100 DN 80 TI 10 TI 11 TI 12 TI 13 TI 14 Mcal/h kW G25 0 20 40 50 30 10 60 70 80 90 2 8 4 6 10 0 12 14 16 G20 Reference conditions: Temperature: 15°C Pressure: .5 mbar Reference conditions: Temperature: 15°C Pressure: .5 mbar Combustion head and butterfly valve pressure drops for TI series - gas sideDiagram 96 Pressure drops in DMV safety valvesDiagram 97 Boilersinfo.com
• 101. 102 From the table of pressure reducers for high pressure Riello Burners (>500 mbar - max 4 bar) we can choose the reducer unit (7) HPRT 750 with the BP type spring, which guarantees outgoing pressure regulation ranging from 60 to 110 mbar. 3.3.4 Selection of the thrust unit for liquid fuel and the nozzles In separate feed burners, the pre-heating and liquid fuel thrust components are separate from the burner body mounted on the heat generator. To complete the burner, a suitable thrust unit must therefore be chosen, both with regards type and nominal running characteristics. First, the functioning philosophy must be determined, which in this case we can presume is the type with a single pumping unit with electrical pre-heating. We must then take the pressure values of the combustion head fuel oil Phead and fuel oil delivery mpumping. The first can be gained from the technical data table for the TI12 burner Phead = 25 ÷ 28 bar. The delivery of the pumping unit must be approximately double the nominal delivery required for combustion: taking the fuel oil density as d =0.97 kg/l we obtain: mpumping / δ = .8 / 0.97 = .2 l/h mpumping = 2 . mburner = = 2 . = ,8 kg / h Qfoc PCIfuel oil 10,67 3/400/50 3/440/60 Version Heating type PH/V/HZ Port size Delivery [l/h] @15 bar Delivery [l/h] @30 bar Motor power [KW] - 50 Hz Max output kg/h Heating power KW 250 EP 3/400/50 3/440/60 1/2" 580 540 1,1 265 14 320 EP 3/400/50 3/440/60 3/4" 950 700 1,5 350 20 400 EP 3/400/50 3/440/60 3/4" 2,2 540 28 500 EP 3/400/50 3/440/60 3/4" 2,2 590 40 650 EP 3/400/50 3/440/60 3/4" 3 775 40 800 EP 3/400/50 3/440/60 3/4" 3 835 42 EP 3/400/50 3/440/60 1" 5,5 60 EP 3/400/50 3/440/60 1" 7,5 80SN 4EP20 SN 3EP14 SN 3EP20 SN 2EP20 SN 2EP20 SN 1EP20 SN 2EP14 Model type Electrical heaters Heavy oil electrical heating/pumping unit skid - single pumping unit SN 1EP14 Pumping unit skids selection tableTable 34 DN in Reg Valve DN out Max Press. [bar] Inlet Press. [bar] Max delivery G 20 [Nmc/h] Max delivery LPG [Nmc/h] 1"1/2 D 50 1"1/2 4 1,5 70 45 1"1/2 D 100 2" 4 1,5 140 90 2" D 160/32 65 4 1,5 225 144 65 D 250/40 65 4 1,5 422 270 80 D 250/50 80 4 1,5 765 490 100 N 50 100 4 1,5 736 100 N 65 100 4 1,5 864 125 N80 125 4 1,5 150220 HPRT 750 100200 HPRT 150220 HPRT 155230 HPRT HPRT 250 65120 HPRT 500 100200 HPRT 80 2760 HPRT 160 2760 Model type Version High pressure regulating train ( Pi > 500 mbar - max 4 bar ) Outlet pressure High pressure regulating/reducing units selection tableTable 33 (7) The reduction unit comprises: a manual shut off valve, a filter, a pressure regulator with safety valve, an anti-vibration joint and two pressure probes. Boilersinfo.com
• 102. 103 Model type Note Spry angle Max capacity [kg/h] Part.n° B5-45-AA TI 10 - TI 11 - TI12 - TI 13 45 250 B5-45-AA TI 10 - TI 11 - TI12 - TI 13 45 275 B5-45-AA TI 10 - TI 11 - TI12 - TI 13 45 300 B5-45-AA TI 10 - TI 11 - TI12 - TI 13 45 325 B5-45-AA TI 10 - TI 11 - TI12 - TI 13 45 350 B5-45-AA TI 10 - TI 11 - TI12 - TI 13 45 375 B5-45-AA TI 10 - TI 11 - TI12 - TI 13 45 400 B5-45-AA TI 10 - TI 11 - TI12 - TI 13 45 425 B5-45-AA TI 10 - TI 11 - TI12 - TI 13 45 450 B5-45-AA TI 10 - TI 11 - TI12 - TI 13 45 475 B5-45-AA TI 11 - TI 12 - TI 13 45 500 B5-45-AA TI 11 - TI 12 - TI 13 45 525 B5-45-AA TI 11 - TI 12 - TI 13 45 550 B5-45-AA TI 11 - TI 12 - TI 13 45 575 B5-45-AA TI 11 - TI 12 - TI 13 45 600 B5-45-AA TI 11 - TI 12 - TI 13 45 650 B5-45-AA TI 12 - TI 13 45 700 B5-45-AA TI 12 - TI 13 45 750 B5-45-AA TI 12 - TI 13 45 800 B5-45-AA TI 13 45 850 B5-45-AA TI 13 45 900 B5-45-AA TI 13 45 950 Spill back nozzles for mechanical atomizing 2-Stages - Progressive modulating Modulating nozzle delivery 100 200 300 400 500 600 700 800 900 0 5 10 15 20 25 30 Return pressure (atm) Delivery(kg/h) Ppump=30atm Ppump=25atm Ppump=20atm Pumping unit skids selection tableTable 35 Nozzles delivery for modulating burnersDiagram 98 Boilersinfo.com
• 103. 104 Looking at the fuel oil delivery column at a pressure of 30 bar, from the table for choosing the electrical pre-heating and thrust units with single pumping unit in Riello Burners, we can obtain the thrust unit model, which is the SN500 Selection the nozzles The nozzles must be chosen in relation to the type of fuel atomisation, the thermal load regulation type and the combustion chamber dimensions. In this case, atomisation is mechanical, load regulation is modulating and the combustion chamber has a standard length/diameter ratio. Looking at the maximum delivery column of the mechanical atomisation nozzles with a spray angle of 45° , we can choose the nozzle which has a nominal fuel delivery slightly greater than the theoretical one requested by the burner. The correct nozzle is therefore the B3-45-AA 650 kg/h code No. . Verification of the correct load modulating ratio requested of 1:5 must be made on the diagram provided by the nozzle manufacturer, in relation to the maximum and minimum fuel pressure in the return circuit. In this case, we have 650/130=5 mad therefore the requested modulating ratio is possible. mburner = = = 605,4 kg / hQfoc PCIfuel oil 10,67 3.3.5 Selection of the components in the liquid fuel feed circuit The liquid fuel feed circuit taken into consideration is the following: The circuit shown in the diagram is the most appropriate when using heavy oil with a viscosity between 7°E and 65 °E measured at 50°C. This feed system comprises two ring circuits plus a transfer circuit; the principal one for circulating the heavy oil from the service tank, the secondary one for circulating the oil from the primary circuit to the burner and the transfer one for transferring fuel oil from the storage tank to the service tank. All the circuits are controlled by their own pump, those for the primary circuit and transfer circuit should be chosen by the design engineer, while those for the secondary circuit are provided as standard fittings with the burner. As far as the primary ring and transfer ring are concerned, the viscosity pumping limit is usually around 70°E at 50°C. Therefore, for these circuits a temperature of 50-60°C can be considered as more than sufficient to avoid blocking the pipelines. The heavy oil must therefore be taken to a certain temperature for it to be adequately atomised and subsequently burnt in the combustion chamber. To obtain an adequate Layout of a heavy oil feeding circuitDiagram 99 BR Dualbloc burner B Gas separator bottle F Oil filter 300 microns degree MM Oil delivery gauge P(MP) Pumping group – transfer ring P1(MP) Pumping group – burner circuit with filter and pressure regulator P2(MP) Pumping group - main circuit with filter PS Electrical oil preheater RS1 Pump heater resistance RS2 Oil tank heater resistance SB Main oil tank SB2 Service oil tank T Thermometer TE Temperature switch regulation TF Flexible oil line TF1 Flexible oil line pressure 25-30bar TP Temperature probe TM Max oil pressure switch VC Vent valve VG Supply air fan VR1 Oil pressure regulator valve of the oil burner ring VR2 Oil pressure regulator valve of the oil main ring VS Preheater safety valve VG7 Safety valve VG Double valves Heavy oil pipe with electrical preheater cable modulating burner Boilersinfo.com
• 104. 105 atomisation of the fluid oil, the range of viscosity goes from 2°E to 5°E at 50°C. To obtain this viscosity value, the heaviest fuel oils must be pre-heated up to 130°C. Naphtha burners in the Riello Burners range are equipped with electrical modulating pre- heaters regulated by a series of regulating and safety thermostats capable of reaching the temperatures required for atomising the fuel. Furthermore, for the heaviest fuel oil special kits for heavy oil must be used, comprising a series of electrical elements for the secondary feed circuit pump. For dimensioning the circuit equipment, the following initial data is take for reference purposes: Effective length of intake pipelines Leff= 15 m; Equivalent length of intake pipelines Lequiv=10 m; Effective length of delivery pipeline Leff= 30 m; Equivalent length of delivery pipeline Lequiv=20 m; pump tank height difference ∆hgeom = 1 m; project-related temperature t = 60°C; volume mass of heavy fuel oil at the reference temperature (15°C) = 990 kg/m3 ; viscosity γ at 50°C = 50°E (approx.. 400·10-6 m2 /s); viscosity γ at 60°C = 40°E (approx. 200·10-6 m2 /s); fuel oil thrust unit delivery 1,200 kg/h = 20.7 l/min. 3.3.5.1 Transfer pump between the storage tank and the service tank The transfer circuit pumping plant must comprise a couple of pumps equipped with their own filters and with the possibility of switchover in by-pass. Both the pumps, suitable for heavy fuel oil (with gears), must be chosen with a delivery equal to 1.2-1.5 times the maximum peak consumption of the system, in this case: mpump1 = (1,2 → 1,5) . mpumping = (1,2 → 1,5) . = kg / h These pumps must be equipped with a self- cleaning blade filter (comb-type) with mesh dimension ranging between 400 and 600 mm and pre-heated to 50-60°C. It is well to the remember that to avoid problems on the intake pipelines, the pumping plant should be positioned as near as possible to the storage tank. 3.3.5.2 Service tank The service tank, which also acts as an outgas device, is a hydraulic disconnection element between the transfer stretch and that of the main ring. This tank must have the following characteristics: • fuel oil entry from the base; • double pre-heater, one fluid heater (water or vapour) to be positioned immediately above the arrival point of the heavy fuel oil and an electrical pre-heater above the fluid pre-heater with integration and emergency functions; • drawing of the heavy fuel oil above the two pre-heaters; • tank capacity equal to at least 2-3 times the sum of the maximum hourly drawing capacities of the burners; In this case, the tank has a capacity equal to: V = (2 → 3 ) .mpumping = (2 → 3) . 20,74 l /min . 60 min = → l This volume should be taken as effective, entirely occupied by the heavy fuel oil; a quota must be calculated equal to 10% of additional volume for the gases and vapours emitted by the oil. In addition, the service tank must be equipped with the following devices: • end plate outlet for water and sediment; • level control with minimum and maximum alarm equipped with self-checking systems; • atmosphere breather pipe; • "over full" device with return line to storage tank; 3.3.5.3 Pump in the main ring The pumping plant in the main ring must comprise a couple of pumps with their own filters and the possibility of switchover in by- pass. Both the pumps in the main ring should be chosen on the basis of the fluid delivery and viscosity at the temperature of the circulation fluid. The pumps in the main rings must be dimensioned for a minimum delivery equal to Boilersinfo.com
• 105. 106 at least 3-5 times the sum of the maximum drawing capacities of the burners. mpump = (3 → 5 ) .mpumping = (3 → 5) . = → kg / h These pumps must be equipped with a self- cleaning blade filter (comb-type) with mesh dimension ranging between 200 and 300 mm and pre-heated to 50-60°C, the pumping plant should be positioned as near as possible to the storage tank. We can presume using a pump with the following characteristics: Q = 4,000 kg/h (1,11 kg/s); H = 30 m approx. and a self-cleaning filter with meshes of 250 mm which, for delivery of approximately 4,000 kg/h introduces a pressure drop of 3,000 Pa. The ring circuit must be equipped with a pressure-regulating valve, with a regulating interval ranging between 1 and 4 bar and with a nominal delivery greater than that of the circuit corresponding to a pump delivery. 3.3.5.4 Dimensioning the main ring pipelines The pipelines must be made from black steel tubes without welding joints. The pipelines must be marked using an electrical heating wire with an output between 20 and 40 W/m or using heating fluid. For easier installation and maintenance operations, the pipeline can be marked with a copper tube (diameter 12x1- 20x1) within which the heating wire can run. The pipelines must be insulated in closed-cell foam. The diameter of the circuit pipeline must be dimensioned on the basis of the following considerations: minimum speed in the intake pipelines (upstream from the pumps): 0.15 m/s; maximum speed in the delivery pipelines (downstream from the pumps): 0.6 m/s; The heavy fuel oil volume mass at a temperature of 60°C is equal to: The intake pipeline must be dimensioned so ρ = = = 963 [kg/m3] ρ15 1 + β . (t - 15) 990 1 + 0, . (60 - 15) that the pressure drop in that stretch does not exceed the following value: ∆Pprog = ∆Pamn - ∆hasp - ∆Pacc [Pa] where: ∆Pamn = absolute pressure allowed at intake (NPSH) indicated by the pump manufacturer; otherwise, this pressure must not be less than 50,660 Pa (0.5 ata); ∆hasp = intake height; ∆Pacc = head loss due to the presence of accessories (filters, etc…) The intake height is equal to: ∆hasp = ∆hgeom .ρ .9,81 [Pa] where: ∆hgeom= difference in height between the fuel test point in the tank and the centre of the feed pump [m]; ρ = volume mass of the heavy fuel oil [kg/m3 ]; The value is positive if the tank is lower than the burner, and negative if the tank is higher. In this case, we have the following values: ∆hasp = ∆hgeom .ρ .9,81 = 1 . 963 . 9,81 = 9.447 [Pa] therefore, the maximum pressure drop allowed along the pipeline will be equal to: ∆Pprog = ∆Pamn - ∆hasp - ∆Pacc = 50.660 - 9.447 - 3.000 = 38.213 [Pa] The minimum internal diameter of the pipeline is obtained using the following formula: If we presume using an iron DN100 (4”) pipeline with an internal diameter of 101.6 m, the transfer speed is equal to: which is greater than the minimum allowed safety value of 0.15 m/s. If the transfer speed is lower than the limit value of 0.15 m/s, we should proceed as follows: V = Q A = = = 0,356 m/s π . d2 4 Q 0, 0,278 963 d = =42 . γ . LTOT .m ∆Pprog√ 4 42 . 200 . 10-6 . 25 .1,11 39.713√ 4 = 0,276 m Boilersinfo.com
• 106. 107 choose the pipeline diameter that guarantees the minimum speed using the formula: the total maximum length (effective + equivalent) of the connection pipeline between the tanks and the pump is determined, so as not to exceed the project-related pressure drops using the following formula: In the pressurised stretches, i.e. the pipeline downstream from the pump, the fluid speed can reach 0.6 m/s, which in our case gives a pipeline with the following diameter: therefore, we will choose a DN25 (1”) iron pipeline that has an internal diameter equal to 0. metres. The pressure drops distributed along the pipeline will be equal to: This value added to the concentrated pressure drops introduced by the special components (filters, valves, etc.) not calculated in the equivalent lengths, must be less than the head supplied by the pumping system. 3.3.6 Selection of the electrical control panel The types of electrical power supply and control signals for a DUALBLOC burner depend on the size of the components that make up the combustion system and the type of regulation of the thermal load. The manufacturers have tables for choosing the electrical power supply and control panels in relation to the type of burner, its maximum developed output and the type of regulation. In this case, the electrical panel will be chosen from the table relating to TI dual-fuel (heavy oil ∆Pprog = = = = 195.486 Pa (≅20 m approximately) 42.200 . 10-6 .50 .0,278 0, 42.γ . LTOT .m d4 √ √ π . 0,6 4 . Q π . 0,15 d = = = 0, m 0,278 . LTOT = d4 . ∆Pprog 42 . γ . m A = π . = d⇒ Q V d2 4 ⇒ Q V = √ 4 . Q π . 0,15 and natural gas) burners looking at the developed output column, in correspondence with the maximum value of 7,800 kW for a TI12 burner, we can read the initials of the electrical panel required QA12 NM and the related absorbed electrical output, corresponding to an electrical power supply with three-phase current. This latter information must be provided by the design engineer of the heating plant electrical systems where the heavy oil generator in question will be installed. Model type Burner output [kW] Fan Absorbed Power [KW] Heating Absorbed power [KW] Pump Absorbed power [KW] Heating type QA 10 PNM - 1A TI 10 max 11 20 1,5 EP QA 10 PNM - 1B TI 10 max 11 15 1,5 EV QA 10 PNM - 2A TI 10 max 11 28 2,2 EP QA 10 PNM - 2B TI 10 max 11 15 2,2 EV QA 11 PNM - 1A TI 11 max 15 28 2,2 EP QA 11 PNM - 1B TI 11 max 15 15 2,2 EV QA 11 PNM - 2A TI 11 max 15 40 2,2 EP QA 11 PNM - 2B TI 11 max 15 20 2,2 EV QA 11 PNM - 3A TI 11 max 22 40 3 EP QA 11 PNM - 3B TI 11 max 22 25 3 EV QA 12 PNM - 1A TI 12 max 22 40 3 EP QA 12 PNM - 1B TI 12 max 22 25 3 EV QA 12 PNM - 2A TI 12 max 30 42 3 EP QA 12 PNM -2B TI 12 max 30 30 3 EV QA 13 PNM - 1A TI 13 max 30 42 3 EP QA 13 PNM - 1B TI 13 max 30 30 3 EV QA 13 PNM - 2A TI 13 max 37 60 5,5 EP QA 13 PNM - 2B TI 13 max 37 40 5,5 EV QA 14 PNM - 1A TI 14 max 55 60 5,5 EP QA 14 PNM - 1B TI 14 max 55 40 5,5 EV QA 14 PNM - 2A TI 14 max 55 80 7,5 EP QA 14 PNM - 2B TI 14 max 55 50 7,5 EV Heavy oil/Natural gas dualbloc burners control panel Nozzles selection tableTable 36 Boilersinfo.com
• 107. 109 4.1 INSTRUMENTS The following instruments are required to correctly measure combustion efficiency: 1. Carbon dioxide CO2 analyser / or Oxygen O2 analyser; 2. Carbon monoxide CO analyser (gas only); 3. Measuring instruments for the “Bacharach” smoke grade index (liquid fuels only); 4. Thermometer for measuring combustion supporter air temperature; 5. Thermometer for measuring the temperature of combustion products; 6. Thermometer for measuring the temperature of the boiler fluid; 7. Chronometer. The instruments listed in points 1, 2, 3, 4 and 5 can be replaced by a single multi-function device similar to that illustrated in diagram 87; 4.2 PRELIMINARY OPERATIONS Before proceeding with calculating combustion efficiency, the effective capacity at the furnace where the measurement will be taken must be gauged; this can be determined by measuring the fuel delivery and multiplying it by the related inferior calorific value. Since it is not possible to determine the fuel delivery effectively burnt using the following methods; we will take the value declared by the manufacturer as the reference thermal output. The reference capacity at the furnace must be equal to or lower than the maximum output at the furnace. The measurement methods for both liquid and gaseous fuels, of the delivery of fuel burnt are illustrated as follows. 4.2.1 Systems fired by liquid fuel We proceed with the weighing method, with a tank filled with a known volume of fuel which is sucked in by the burner for a determinate period. The volume of fuel consumed divided by the test time provides the fuel delivery value. A simplified method, with an error margin up to 10%, involves verifying the size of the nozzle(s), and taking the atomisation pressure of the nozzle; referring to the tables of the nozzles mounted on the burner we can obtain the fuel delivery value (usually expressed in kg/h). This data should be multiplied by the corresponding inferior calorific value, thus obtaining the capacity effectively burnt. Ready-to-use tables exist, which in relation to the nozzle delivery and the pump pressure provide the delivery of the liquid fuel. 4.2.2 Systems fired by gaseous fuel In systems powered by mains gas, fuel delivery is taken by reading the meter; to calculate the output effectively burnt, the above methods are valid. We recommend paying great attention when reading the meter in that, if it is placed on a high pressure gas feed line, account must be taken of the gas compressibility; in fact by MEASURING COMBUSTION EFFICIENCY 4 Example of analyzer for measuring combustion efficiency Diagram 100 Boilersinfo.com
• 108. 110 compressing a gas, its is reduced volume but the number of molecules remains constant, i.e. density increases following the subsequent law. In this case, the reading, which is volumetric, will be lower than the effective mass-related delivery, Where: P1= gas pressure at a density of δ1; P2= gas pressure at a density of δ2; A simplified formula (valid only for meter pressure greater than 40 mbar) for correcting the delivery values read in relation to the pressure, is illustrated as follows: Where Vvc = correct delivery of gas [Nm3 /h] Vvi= measured delivery in terms of volume [Nm3 /h] P = gas pressure at the meter [mbar] Another simple method for calculating the effective gas delivery is represented by using the correction factors in the table, in relation to the pressure and the temperature read off the meter. Several of these tables are illustrated in section 5 of this manual. In systems without meters, a calibrated diaphragm must be fitted to the feed pipeline, or alternatively, the combustion head pressure can be used as an indication. Vvc = + P Vvi P1 = P2 . δ1 δ2 Gas flow characteristics measuring pointsDiagram 101 4.3 MEASUREMENT CONDITIONS AND OPERATING METHODS The measurements must be carried out when the heat generator is in a steady running state (for example: at around 70 ° C for hot water generators) and at the maximum output at the furnace for such measurements. To correctly take these measurements, the following must be performed: 1. Make a hole with a sufficient diameter for inserting the probes used for the measurements (approximately 10 mm.), in the flue gas connector, boiler/flue, two diameters in distance from the generator outlet, if available, use the specific hole provided by the heat generator manufacturer; 2. Ensure that there is no seepage of air prior to the hole for drawing off the combustion products (seal any holes, slits, etc…), because secondary air would alter the measured values, thereby discrediting the test; 3. Bring the heat generator to steady running state (for example: around 70° C for hot water heat generators); 4. For each single parameter take at least three measurements, at equal intervals during the test period deemed necessary by the operator, and each time at least 120 seconds after beginning the sample; 5. Seal the hole made for the measurements; 6. Transcribe the measured data, where the value measured of each individual parameter is obtained from the arithmetic mean of the first three significant measurements (any anomalous measurements must not be taken into account). Boilersinfo.com
• 109. 111 4.4 CALCULATING THE COMBUSTION EFFICIENCY The fuel efficiency _ of a generator can be calculated by using the following formula, with the drop at the generator shell considered as nil. η = 100 - Ps ± 2% Where: η heat generator efficiency; Ps is the thermal output lost via the flue; and ±2% is the tolerance linked to uncertainties relating to the measuring instruments and the reading of the parameters measured. As has already been seen in paragraph 1.5.1, the conventional formulas used for determining losses via the flue are: if the concentration of oxygen free in the combustion flue gases is known, or: if the concentration of carbon dioxide in the combustion flue gases is known. where: Ps = thermal output lost via the flue [%]; Tf = temperature of the flue gases (°C); Ta = temperature of the combustion supporter air (°C); O2 = concentration of oxygen in the dry flue gases [%]; CO2 = concentration of carbon dioxide in the dry flue gases [%]; A1, A2 and B are some empirical factors whose values are shown in the table below. Ps = . (Tf - Ta) ( )A2 CO2 + B Ps = . (Tf - Ta) ( )A1 21 - O2 + B Leaving aside the measured value of fuel efficiency, to consider combustion satisfactory the concentration of CO must be checked referred to the condition of dry combustion products and without air at lower than 0.1% ( ppm). The concentration of CO dry flue gases without air is provided by the equation: where: COm is the amount of carbon monoxide measured CO2theoretical is the theoretical CO2 CO2measured is the measured CO2 The values of CO2 theoretical are illustrated in Table 5 of section 1 - Maximum and recommended CO2 levels for various fuels. The same can be said, for heat generators powered by liquid fuel, if the smoke grade index referred to the Bacharach (8) scale, is greater than 2 for diesel oil and greater than 6 for fuel oil. 4.1.1 Example for calculating combustion efficiency Let us examine the following measured values: Fuel: natural gas Measurement of CO2: 9.6% Temperature of flue gases Tf: 170 ° C Temperature of combustion supporter air Ta: 30°C Measurement of CO: 80 ppm Theoretical CO2: 11,7% Since we know the value of CO2 present in the flue gases, we can obtain the following thermal output value lost at the flue: The fuel efficiency of the generator referred to the thermal output of the furnace for which the measurement was carried out, is given by: η = 100 - 6,94 = 993,06 ±2% To conclude, the concentration of CO must be checked referred to the condition of dry combustion products without air: equal to 0. % < 0.1 % COdry flue gases without air = 88 x = 107,25 ppm11,7 9,6 Ps = + 0,010 . (170 - 30) = 6,94( )0,38 9,6 COdry flue gases without air = COm x CO2 theoretical CO2 measured Fuel METHANE L.P.G. LIGHT OIL HEAVY OIL A1 0,66 0,63 0,68 0,68 A2 0,38 0,42 0,50 0,52 B 0,010 0,008 0,007 0,007 Coefficients for calculation of combustion efficiency Table 37 (8) The Bacharach measurement method has already been described in section 1. Boilersinfo.com
• 110. 112 5.1 MEASURING UNITS AND CONVERSION FACTORS 115 1.1 Units of International system SI and main conversion factors 115 1.2 Units used for heat transfer calculations 116 1.3 Conversion factors among the units of measurment 117 1.3.1 Lenght 117 1.3.2 Area 117 1.3.3 Volume 118 1.3.4 Mass 119 1.3.5 Pressure 119 1.3.6 Work, energy, heat, enthalpy 120 1.3.7 Power (mechanical, electric and thermal) 120 1.3.8 Velocity 121 1.3.9 Flow rate in volume 121 1.3.10 Other conversion factors for non SI units 122 1.4 Conversion of inches and fractions of inch in millimetres 123 1.5 Temperature conversion tables 124 1.6 Standard voltages and frequencies in different countries 126 1.7 Personal units of measurment and conversion factors 128 5.2 TABLES AND DIAGRAMS ABOUT FUEL VISCOSITY 129 1.8 Approximated equivalence table between viscosity measurements at the same temperature 129 1.9 Nomograph for viscosity units conversions 130 1.10 Viscosity variations in relation to temperature for different fuels 131 1.11 Gas dynamic viscosity 132 5.3 TABLES AND DIAGRAMS FOR CIRCUITS DIMENSIONING 134 1.12 Distributed pressure drops in air circular ducts 134 1.13 Equivalence between circular and rectangulare sections of air ducts 135 1.14 Air ducts dimensioning: loss coefficients for special pieces in circular and rectangular pieces 136 1.15 Distributed pressure drops in air pipelines for liquid and gaseous fuels 138 1.16 Liquid fuel feeding circuit dimensioning: equivalent lenght of main concentrated resistances 140 Boilersinfo.com
• 111. 113 1.17 Dispersion of heavy oil tanks 141 1.18 Compensation of thermal dispersions in steady condition 142 1.19 Calculation of total needed output 143 1.20 Diagram for passing from energy to output 144 1.21 Diagram for pipelines tracing with heating bands 145 1.22 Nozzle delivery with liquid fuels 146 1.23 Commercial features of steel and copper pipelines 150 1.24 Correction factors for lecture of gas delivery from gas meters 152 1.25 Graphical method for determining energy saving by use of inverter 155 5.4 TABLES AND DIAGRAMS ABOUT COMBUSTION 156 1.26 Combustion triangle for natural gas and light/heavy oil 156 1.27 Combustion air and gas burnt quantities in relation to air excess for different fuels: G20, LPG, light oil and heavy oil 157 1.28 Increase of temperature in exhausted gas in relation to soot thickness 161 1.29 Lenght and diameter of the flame in relation to burner output 162 1.30 SO2 emissions (mg/m3 e mg/kWh) in oil combustion in relation of S content (%) in the fuel at 3% of O2 163 1.31 NOx emissions in relation to the different parameters of influence 164 1.32 Efficiency loss in exhausted gasses in relation to O2 content for different fuels 166 1.33 Efficiency loss in exhausted gasses in relation to CO2 content for different fuels 168 1.34 Conversion factors for pollutant emissions 170 Boilersinfo.com
• 112. Boilersinfo.com
• 113. 115 READY-TO-USE TABLES AND DIAGRAMS 5 5.1 MEASURING UNITS AND CONVERSION FACTORS 1.1 Units of International system SI and main conversion factors Boilersinfo.com
• 114. 116 1.2 Units used for heat transfer calculations Boilersinfo.com
• 115. 117 1.3 Conversion factors among the units of measurment 1.3.1 Lenght 1.3.2 Area Boilersinfo.com
• 118. 120 1.3.6 Work, energy, heat, enthalpy 1.3.7 Power (mechanical, electric and thermal) Boilersinfo.com
• 119. 121 1.3.8 Velocity 1.3.9 Flow rate in volume Boilersinfo.com
• 120. 122 1.3.10 Other conversion factors for non SI units Boilersinfo.com
• 121. 123 1.4 Conversion of inches and fractions of inch in millimetres Boilersinfo.com
• 122. 124 1.5 Temperature conversion tables Boilersinfo.com
• 124. 126 1.6 Standard voltages and frequencies in different countries Country Frequency (Hz) Voltage/s (V) Country Frequency (Hz) Voltage/s (V) Afghanistan 50 220/380 Dominican republic 60 110/220 Algeria 50 127/220 Ecuador 60 120/208 50 220/380 60 127/220 American samoa 60 240/480 60 120/240 Angola 50 220/380 Egypt 50 220/380 Antigua 60 230/400 El salvador 60 115/230 Argentina 50 220/380 England (and Wales) 50 240/480 Australia (East zone) 50 240/415 50 240/415 (West zone) 50 254/440 Equatorial guyana 50 220 Austria 50 220/380 Ethiopia 50 220/380 Azorse 50 220/380 ex - U.S.S.R. 50 220/380 Bahamas 60 120/208 ex-Yugoslavia 50 220/380 60 115/200 Far Oer 50 220/380 60 120/240 Fiji 50 240/415 Bahrain 50 230/400 Finland 50 220/380 60 230/400 France 50 220/380 Bangladesh 50 220/380 50 110/220 50 230/400 50 115/230 Barbados 50 110/190 50 127/220 50 120/208 50 500 50 115/200 French guyana 50 220/380 50 115/230 Gabon 50 220/380 Belgium 50 127/220 Gambia 50 220/380 50 220/380 Germany 50 220/380 50 220 Ghana 50 220/380 Belize 60 110/220 Gibraltar 50 240/415 60 220/440 Greece 50 220/380 Benin 50 220/380 Grenada 50 Bermuda 60 120/240 Guadeloupe 50 220/380 60 120/208 Guam 60 120/208 Bolivia 50 110/220 60 110/220 50 220/380 Guatemala 60 120/240 50 115/230 60 120/208 60 220/380 Guinea 50 220/380 Botswana 50 220/380 Guinea bissau 50 220/380 Brazil 60 110/220 Guyana 50 110/220 60 220/440 60 110/220 60 127/220 Haiti 50 220/380 60 220/380 60 110/220 60 115/220 Honduras 60 110/220 60 125/216 Honk kong 50 200/346 60 230/400 Iceland 50 220/380 50 220/440 India 50 220/380 Bulgaria 50 220/380 50 230/400 Burundi 50 220/380 Indonesia 50 220/380 Cambodia 50 220/380 50 127/220 50 120/208 Iran 50 220/380 Camerun 50 127/220 Iraq 50 220/380 50 220/360 Ireland 50 220/380 50 230/400 Isle of Man 50 240/415 Canada 60 120/240 Israel 50 230/400 60 575 Italy 50 220/380 Canarie 50 127/220 50 127/220 50 220/380 Ivory coast 50 220/380 Cape Verde 50 220/380 Jamaica 50 110/220 Cayman Islands 50 220/380 Japan 50 100/200 Central african republic 50 220/380 60 100/200 Chile 50 220/380 Jerusalem 50 220/380 China 50 220/380 Jordan 50 220/380 Ciad 50 220/380 Kenya 50 240/415 Colombia 60 110/220 Korea 60 100/200 60 150/260 0 220/380 60 440 Kuwait 50 240/415 Congo 50 220/380 Laos 50 220/380 Costarica 60 120/240 Lebanon 50 110/190 Cuba 60 120/240 50 220/380 Cyprus 50 240/415 Lesotho 50 220/380 Czech republic 50 220/380 Denmark 50 220/380 Boilersinfo.com
• 125. 127 Country Frequency (Hz) Voltage/s (V) Country Frequency (Hz) Voltage/s (V) Liberia 60 120/208 Sri Lanka 50 230/400 60 120/240 St. Kitts & Nevis 60 230/400 Libya 50 127/220 St. Lucia 50 240/416 50 220/380 St. Vincent 50 230/400 Luxembourg 50 220/380 Sudan 50 240/415 50 120/208 Suriname 60 115/230 Macao 50 220/380 50 127/220 Madagascar 50 220/380 Swatziland 50 230/400 50 127/220 Sweden 50 220/380 Majorca 50 220/380 Switzerland 50 220/380 50 127/220 Syria 50 220/380 Malawi 50 220/380 Tahiland 50 220/380 Malaysia 50 240/415 Tahiti 60 127/220 Maldives 50 230/400 Taiwan 60 110/220 Mali 50 220/380 Tanzania 50 230/400 Malta 50 220/380 Togo 50 127/220 Martinique 50 220/380 50 220/380 Mauritius 50 240/415 Tonga 50 240/415 Mexico 60 127/220 Trinidad & Tobago 60 115/230 Monaco 50 220/380 60 230/400 50 127/220 Tunisia 50 127/220 Monzambique 50 220/380 50 220/380 Morocco 50 127/220 Turkey 50 220/380 60 220/380 Uganda 50 240/415 Nepal 50 220/440 United Arab Emirates 50 220/380 Netherland antilles 60 220/380 Uruguay 50 220 60 115/230 USA 60 600 50 120/208 60 120/240 50 127/220 60 460 Netherlands 60 220/380 60 575 New Zeland 50 230/400 Venezuela 60 120/208 Niacaragua 60 120/240 Vietnam 50 120/208 Niger 50 220/380 50 127/220 Nigeria 50 240/415 50 220/380 Northern Ireland 50 230/400 Virgin islands 60 120/240 50 230 Yemen 50 220/380 Norway 60 220/380 50 230/400 Oman 50 220/380 Zaire 50 220/380 Pakistan 50 220/380 Zambia 50 220/380 50 230/400 Zimbawe 50 220/380 Panama 60 110/220 60 115/230 60 120/208 Papua Nuova Guinea 50 240/415 Paraguay 50 220/380 Perù 60 110/220 50 220 Philippines 60 110/220 Poland 50 220/380 Portorico 60 120/208 Portugal 50 220/380 Qatar 50 240/415 Romania 50 220/380 Ruanda 50 220/380 Saudi Arabia 60 127/220 50 220/380 Scotland 50 240/415 Senegal 50 127/220 Seychelles 50 240 Sierra Leone 50 220/380 Singapore 50 230/400 Slovakia 50 220/380 Somalia 50 110/220 50 220/440 50 220/380 South Africa 50 220/380 Spain 50 220/380 50 127/220 In case the higher value is double than lower, there is a single phase system with three conductors with two main conductors and an intermediate conductor. In case the higher value is 1,73 times more then lower, there is a three phase system with 4 conductors with 3 main conductors and a conductor connected to the star-centre.220/380V voltage are being replaced from 230/400V. In case of a single value, there is a three phase system with three main conductors. Boilersinfo.com
• 126. 128 1.7 Personal units of measurment and conversion factors Boilersinfo.com
• 127. 129 5.2 TABLES AND DIAGRAMS ABOUT FUEL VISCOSITY 1.8 Approximated equivalence table between viscosity measurements at the same temperature Boilersinfo.com
• 128. 130 1.9 Nomograph for viscosity units conversions Cinematic viscosity, Centistokes Cinematic viscosity, Centistokes Saybolt universla seconds Redwood I seconds Engler degrees Saybolt furol seconds Redwood II seconds Boilersinfo.com
• 129. 131 1.10 Viscosity variations in relation to temperature for different fuels Viscosity(mm2 /s) Temperature (°C) Viscosity(°E) A – MAX and MIN limits of Gas oil (D) range B – light fuel oil (E) range D – medium fuel oil (F) range E – adviced limits of nozzle viscosity F – economical limit value for pumpability of fuel oil Boilersinfo.com
• 130. 132 1.11 Gas dynamic viscosity Boilersinfo.com
• 132. 134 5.3 TABLES AND DIAGRAMS FOR CIRCUITS DIMENSIONING 1.12 Distributed pressure drops in air circular ducts Airdelivery(m3 /h) Airdelivery(m3 /h) Pressure drop (mmH2O) for 1 m lenght Boilersinfo.com
• 133. 135 1.13 Equivalence between circular and rectangulare sections of air ducts SMALLER SIDE D U C T D IA M ETER d. BIGGERSIDE Boilersinfo.com
• 134. 136 1.14 Air ducts dimensioning: loss coefficients for special pieces in circular and rectangular pieces Plane curve Plenum Obstruction Obstruction Obstruction Boilersinfo.com
• 135. 137 Cuve Guiding fin without fins diafphragm with fins Bifurcation Jumber tube Free intake Divergence Narrowing Drilled metal sheets free section in % w is referred to the total section for net grilles ζ values are about a half ζ for w = 0,5 m/s Boilersinfo.com
• 136. 138 1.15 Distributed pressure drops in air pipelines for liquid and gaseous fuels PROCEDURE 1) Individuate on the horizontal axis at the top of square “1” fuel oil delivery required 2) Go down vertically until intersecating in square “2” the oblique line corresponding to oil viscosity at ref. temperature: two scales, in cSt and °E, are reported. 3) From intersection point proceed horizontally in the left direction until intersecating in square “3” the oblique line corresponding to pipeline lenght 4) From intersection point proceed upwards until intersecating in square “4” the oblique lines corresponding to different pressure drops in m c. H2O 5) At this point it is possible to procced in two ways: or it is prefixed max. pressure drop; then from intersection point with oblique line proceed horizontally in the right direction and on vertical axis of square “1” read pipeline diameter (mm and inches are reported). Otherwise from pipeline diameter, pressure drops are obtained with opposite procedure. Speed (m/s) Boilersinfo.com
• 137. 139 0,10,20,30,40,50,60,70, 3 6 9 12 15 22 30 V PERDITEDICARICO:mbar DIAMETROTUBO:Rp 1,4 LUNGHEZZATUBO:metri 1/2 3/4 1" 1" 1/2 6" 1" 1/4 4" 3" 2" 1/2 2" 15,34 = Portata gas Nm3/h f 1 - G20 = 0,62 - G25 1,18 - G31{ f V Gas delivery PIPELINELENGTH (m) PRESSUREDROP:mbar PIPELINEDIAMETER:Rp Boilersinfo.com
• 138. 140 1.16 Liquid fuel feeding circuit dimensioning: equivalent lenght of main concentrated resistances Boilersinfo.com
• 139. 141 1.17 Dispersion of heavy oil tanks PROCEDURE 1) Individuated on the left horizontal axis project ∆T (difference between heavy oil temperature and min. external), trace a vertical line until intersecating line relative to the specific tank. Zone 1 correspond to non isolated vertical tanks, line 2 is relative to horizontal grounded tanks and line 3 to vertical isolated tanks, 2) From intersection point proceed horizontally in the right direction and individuate on vertical axis the dispersion for m2 of tank external surface; 3) Evaluated external surface of tank, individuate the value on right horizontal axis; if this value is missing, make use of bottom axis where volume of vertical and horizontal tanks is reported (typical commercial values); 4) Trace vertical until intersecating previous horizontal line relative to dispersion for m2 of tank; 5) The line correspondant to intersection point represents dispersions of tank when it is completely full of preheated heavy oil. External vertical tank non isolated Grounded tank External vertical tank isolated Boilersinfo.com
• 140. 142 PROCEDURE 1) Individuate on the left horizontal axis pipeline diameter, 2) Trace vertical until intersecating oblique line correspondant to project ∆T between heavy oil and external temperature; 3) Trace from intersection point an horizontal line in the right direction and evaluate on vertical axis dispersion for 1 m of pipeline; 4) Extend horizontal line until intersecating oblique line relative to pipeline lenght; 5) Trace vertical and read on the right horizontal axis the total output required. 1.18 Compensation of thermal dispersions in steady condition Boilersinfo.com
• 141. 143 1.19 Calculation of total needed output NOTE: The diagram at the bottom, similar to the previous one from a functional point of view, allows to calculate the energy required from a system with oil preheating to reach the steady state. Boilersinfo.com
• 142. 144 1.20 Diagram for passing from energy to output NOTE: The diagram allows, once knew energy to reach steady state, to calculate output, which depends from warm-up time (represented in hours from oblique lines). Boilersinfo.com
• 143. 145 1.21 Diagram for pipelines tracing with heating bands PROCEDURE 1) Individuate on the left horizontal axis necessary output for 1 m of pipekine 2) Trace a vertical line until intersecating oblique line relative to linear output dispersed from the band; 3) From intersection point proceed horizontally in the right direction and individuate on vertical axis the band lenght for 1 m of pipeline; 4) Extend horizontal line until intersecating oblique line relative to pipeline diameter; 5) Trace vertical and on the right horizontal axis read approximatively the number of turns for 1 m of pipeline. Boilersinfo.com
• 144. 146 1.22 Nozzle delivery with liquid fuels Nozzle nominal delivery (GPH) 10 11 12 13 14 15 0,4 1,41 1,48 1,55 1,62 1,69 1,75 0,5 1,76 1,85 1,94 2,02 2,11 2,19 0,55 1,93 2,03 2,13 2,23 2,32 2,41 0,6 2,11 2,22 2,33 2,43 2,53 2,62 0,65 2,28 2,40 2,52 2,63 2,74 2,84 0,75 2,64 2,77 2,91 3,04 3,16 3,28 0,85 2,99 3,14 3,30 3,44 3,58 3,72 1 3,51 3,70 3,88 4,05 4,21 4,37 1,1 3,87 4,07 4,27 4,45 4,64 4,81 1,25 4,39 4,62 4,85 5,06 5,27 5,47 1,35 4,74 4,99 5,24 5,47 5,69 5,91 1,5 5,27 5,55 5,82 6,07 6,32 6,56 1,65 5,80 6,10 6,40 6,68 6,95 7,22 1,75 6,15 6,47 6,79 7,09 7,38 7,66 2 7,03 7,40 7,76 8,10 8,43 8,75 2,25 7,91 8,32 8,73 9,11 9,48 9,84 2,5 8,79 9,25 9,69 10,12 10,54 10,94 2,75 9,66 10,17 10,66 11,14 11,59 12,03 3 10,54 11,10 11,63 12,15 12,64 13,12 3,25 11,42 12,02 12,60 13,16 13,70 14,22 3,5 12,30 12,95 13,57 14,17 14,75 15,31 4 14,06 14,80 15,51 16,20 16,86 17,50 4,5 15,81 16,65 17,45 18,22 18,96 19,68 5 17,57 18,50 19,39 20,25 21,07 21,87 5,5 19,33 20,35 21,33 22,27 23,18 24,06 6 21,09 22,20 23,27 24,29 25,29 26,25 6,5 22,84 24,05 25,21 26,32 27,39 28,43 7 24,60 25,90 27,14 28,34 29,50 30,62 7,5 26,36 27,75 29,08 30,37 31,61 32,81 8 28,11 29,60 31,02 32,39 33,72 35,00 8,5 29,87 31,45 32,96 34,42 35,82 37,18 9 31,63 33,30 34,90 36,44 37,93 39,37 9,5 33,39 35,15 36,84 38,47 40,04 41,56 10 35,14 37,00 38,78 40,49 42,14 43,74 10,5 36,90 38,85 40,72 42,52 44,25 45,93 11 38,66 40,70 42,66 44,54 46,36 48,12 11,5 40,41 42,55 44,59 46,56 48,47 50,31 12 42,17 44,40 46,53 48,59 50,57 52,49 13 45,68 48,10 50,41 52,64 54,79 56,87 13,5 47,44 49,95 52,35 54,66 56,89 59,05 14 49,20 51,80 54,29 56,69 59,00 61,24 15 52,71 55,50 58,17 60,74 63,22 65,62 15,5 54,47 57,35 60,11 62,76 65,32 67,80 16 56,23 59,20 62,05 64,79 67,43 69,99 17 59,74 62,90 65,92 68,83 71,65 74,36 17,5 61,50 64,75 67,86 70,86 73,75 76,55 18 63,26 66,60 69,80 72,88 75,86 78,74 19 66,77 70,30 73,68 76,93 80,07 83,11 19,5 68,53 72,15 75,62 78,96 82,18 85,30 20 70,28 74,00 77,56 80,98 84,29 87,49 21,5 75,56 79,55 83,37 87,06 90,61 94,05 22 77,31 81,40 85,31 89,08 92,72 96,24 24 84,34 88,80 93,07 97,18 101,15 104,99 26 91,37 96,20 100,82 105,28 109,58 113,73 28 98,40 103,60 108,58 113,37 118,00 122,48 30 105,43 110,99 116,33 121,47 126,43 131,23 32 112,46 118,39 124,09 129,57 134,86 139,98 33 115,97 122,09 127,97 133,62 139,08 144,36 35 123,00 129,49 135,72 141,72 147,50 153,10 36 126,51 133,19 139,60 145,77 151,72 157,48 40 140,57 147,99 155,11 161,96 168,58 174,98 45 158,14 166,49 174,50 182,21 189,65 196,85 50 175,71 184,99 193,89 202,46 210,72 218,72 Effective delivery (kg/h) of nozzles for light oil at 25°C Fuel atomization pressure (bar) Boilersinfo.com
• 145. 147 Nozzle nominal delivery (GPH) 18 19,5 21 22,5 24 25,5 0,4 1,99 2,08 2,17 2,25 2,33 2,41 0,5 2,49 2,60 2,71 2,81 2,91 3,01 0,55 2,74 2,86 2,98 3,09 3,20 3,31 0,6 2,99 3,12 3,25 3,37 3,49 3,61 0,65 3,24 3,38 3,52 3,65 3,78 3,91 0,75 3,74 3,90 4,06 4,22 4,37 4,51 0,85 4,24 4,42 4,60 4,78 4,95 5,11 1 4,98 5,20 5,42 5,62 5,82 6,02 1,1 5,48 5,73 5,96 6,19 6,40 6,62 1,25 6,23 6,51 6,77 7,03 7,28 7,52 1,35 6,73 7,03 7,31 7,59 7,86 8,12 1,5 7,48 7,81 8,13 8,43 8,73 9,02 1,65 8,22 8,59 8,94 9,28 9,61 9,93 1,75 8,72 9,11 9,48 9,84 10,19 10,53 2 9,97 10,41 10,83 11,25 11,64 12,03 2,25 11,22 11,71 12,19 12,65 13,10 13,54 2,5 12,46 13,01 13,54 14,06 14,56 15,04 2,75 13,71 14,31 14,90 15,46 16,01 16,54 3 14,95 15,61 16,25 16,87 17,47 18,05 3,25 16,20 16,92 17,61 18,27 18,92 19,55 3,5 17,45 18,22 18,96 19,68 20,38 21,06 4 19,94 20,82 21,67 22,49 23,29 24,06 4,5 22,43 23,42 24,38 25,30 26,20 27,07 5 24,92 26,02 27,09 28,11 29,11 30,08 5,5 27,42 28,63 29,80 30,93 32,02 33,09 6 29,91 31,23 32,50 33,74 34,93 36,10 6,5 32,40 33,83 35,21 36,55 37,85 39,11 7 34,89 36,43 37,92 39,36 40,76 42,11 7,5 37,38 39,04 40,63 42,17 43,67 45,12 8 39,88 41,64 43,34 44,98 46,58 48,13 8,5 42,37 44,24 46,05 47,80 49,49 51,14 9 44,86 46,84 48,76 50,61 52,40 54,15 9,5 47,35 49,45 51,46 53,42 55,31 57,15 10 49,85 52,05 54,17 56,23 58,22 60,16 10,5 52,34 54,65 56,88 59,04 61,14 63,17 11 54,83 57,25 59,59 61,85 64,05 66,18 11,5 57,32 59,86 62,30 64,66 66,96 69,19 12 59,82 62,46 65,01 67,48 69,87 72,19 13 64,80 67,66 70,43 73,10 75,69 78,21 13,5 67,29 70,27 73,13 75,91 78,60 81,22 14 69,79 72,87 75,84 78,72 81,51 84,23 15 74,77 78,07 81,26 84,34 87,34 90,24 15,5 77,26 80,67 83,97 87,16 90,25 93,25 16 79,75 83,28 86,68 89,97 93,16 96,26 17 84,74 88,48 92,09 95,59 98,98 102,27 17,5 87,23 91,08 94,80 98,40 101,89 105,28 18 89,72 93,69 97,51 101,21 104,80 108,29 19 94,71 98,89 102,93 106,84 110,63 114,31 19,5 97,20 101,49 105,64 109,65 113,54 117,32 20 99,69 104,10 108,35 112,46 116,45 120,32 21,5 107,17 111,90 116,47 120,89 125,18 129,35 22 109,66 114,51 119,18 123,71 128,09 132,36 24 119,63 124,92 130,02 134,95 139,74 144,39 26 129,60 135,33 140,85 146,20 151,38 156,42 28 139,57 145,74 151,69 157,44 163,03 168,45 30 149,54 156,14 162,52 168,69 174,67 180,48 32 159,51 166,55 173,35 179,94 186,32 192,52 33 164,49 171,76 178,77 185,56 192,14 198,53 35 174,46 182,17 189,61 196,80 203,78 210,57 36 179,45 187,37 195,02 202,43 209,61 216,58 40 199,39 208,19 216,69 224,92 232,90 240,65 45 224,31 234,22 243,78 253,03 262,01 270,73 50 249,23 260,24 270,87 281,15 291,12 300,81 Effective delivery (kg/h) of nozzles for Heavy oil (3-5°E at 50°C) at 120°C Fuel atomization pressure (bar) Boilersinfo.com
• 146. 148 Nozzle nominal delivery (GPH) 8 9 10 11 12 0,4 1,17 1,25 1,32 1,39 1,46 0,5 1,46 1,56 1,65 1,74 1,82 0,55 1,61 1,71 1,81 1,91 2,00 0,6 1,75 1,87 1,98 2,08 2,18 0,65 1,90 2,03 2,14 2,26 2,37 0,75 2,19 2,34 2,47 2,61 2,73 0,85 2,49 2,65 2,80 2,95 3,09 1 2,92 3,12 3,30 3,47 3,64 1,1 3,22 3,43 3,63 3,82 4,00 1,25 3,66 3,90 4,12 4,34 4,55 1,35 3,95 4,21 4,45 4,69 4,91 1,5 4,39 4,68 4,95 5,21 5,46 1,65 4,83 5,14 5,44 5,73 6,01 1,75 5,12 5,45 5,77 6,08 6,37 2 5,85 6,23 6,60 6,95 7,28 2,25 6,58 7,01 7,42 7,82 8,19 2,5 7,31 7,79 8,25 8,68 9,10 2,75 8,04 8,57 9,07 9,55 10,01 3 8,77 9,35 9,90 10,42 10,92 3,25 9,51 10,13 10,72 11,29 11,83 3,5 10,24 10,91 11,55 12,16 12,74 4 11,70 12,47 13,20 13,89 14,56 4,5 13,16 14,03 14,85 15,63 16,38 5 14,62 15,58 16,50 17,37 18,20 5,5 16,09 17,14 18,15 19,10 20,02 6 17,55 18,70 19,80 20,84 21,84 6,5 19,01 20,26 21,44 22,58 23,66 7 20,47 21,82 23,09 24,31 25,48 7,5 21,94 23,38 24,74 26,05 27,30 8 23,40 24,93 26,39 27,79 29,12 8,5 24,86 26,49 28,04 29,52 30,94 9 26,32 28,05 29,69 31,26 32,77 9,5 27,78 29,61 31,34 33,00 34,59 10 29,25 31,17 32,99 34,73 36,41 10,5 30,71 32,73 34,64 36,47 38,23 11 32,17 34,28 36,29 38,21 40,05 11,5 33,63 35,84 37,94 39,94 41,87 12 35,10 37,40 39,59 41,68 43,69 13 38,02 40,52 42,89 45,15 47,33 13,5 39,48 42,08 44,54 46,89 49,15 14 40,95 43,63 46,19 48,63 50,97 15 43,87 46,75 49,49 52,10 54,61 15,5 45,33 48,31 51,14 53,84 56,43 16 46,79 49,87 52,79 55,58 58,25 17 49,72 52,98 56,09 59,05 61,89 17,5 51,18 54,54 57,74 60,79 63,71 18 52,64 56,10 59,39 62,52 65,53 19 55,57 59,22 62,69 66,00 69,17 19,5 57,03 60,78 64,33 67,73 70,99 20 58,49 62,33 65,98 69,47 72,81 21,5 62,88 67,01 70,93 74,68 78,27 22 64,34 68,57 72,58 76,42 80,09 24 70,19 74,80 79,18 83,36 87,37 26 76,04 81,04 85,78 90,31 94,65 28 81,89 87,27 92,38 97,26 101,94 30 87,74 93,50 98,98 104,20 109,22 32 93,59 99,74 105,57 111,15 116,50 33 96,51 102,85 108,87 114,62 120,14 35 102,36 109,09 115,47 121,57 127,42 36 105,29 112,20 118,77 125,04 131,06 40 116,99 124,67 131,97 138,94 145,62 45 131,61 140,25 148,46 156,31 163,83 50 146,23 155,84 164,96 173,67 182,03 Effective delivery (kg/h) of nozzles for kerosene at 25°C Fuel atomization pressure (bar) Boilersinfo.com
• 147. 149 Nozzle nominal delivery (GPH) 10 11 12 13 14 15 0,4 1,58 1,66 1,74 1,82 1,89 1,97 0,5 1,97 2,08 2,18 2,27 2,37 2,46 0,55 2,17 2,29 2,40 2,50 2,60 2,70 0,6 2,37 2,49 2,61 2,73 2,84 2,95 0,65 2,57 2,70 2,83 2,96 3,08 3,19 0,75 2,96 3,12 3,27 3,41 3,55 3,69 0,85 3,36 3,53 3,70 3,87 4,02 4,18 1 3,95 4,16 4,36 4,55 4,73 4,91 1,1 4,34 4,57 4,79 5,00 5,21 5,40 1,25 4,93 5,19 5,44 5,69 5,92 6,14 1,35 5,33 5,61 5,88 6,14 6,39 6,63 1,5 5,92 6,23 6,53 6,82 7,10 7,37 1,65 6,51 6,86 7,19 7,50 7,81 8,11 1,75 6,91 7,27 7,62 7,96 8,28 8,60 2 7,89 8,31 8,71 9,10 9,47 9,83 2,25 8,88 9,35 9,80 10,23 10,65 11,06 2,5 9,87 10,39 10,89 11,37 11,83 12,28 2,75 10,86 11,43 11,98 12,51 13,02 13,51 3 11,84 12,47 13,07 13,64 14,20 14,74 3,25 12,83 13,51 14,16 14,78 15,39 15,97 3,5 13,82 14,55 15,25 15,92 16,57 17,20 4 15,79 16,62 17,42 18,19 18,94 19,65 4,5 17,76 18,70 19,60 20,47 21,30 22,11 5 19,74 20,78 21,78 22,74 23,67 24,57 5,5 21,71 22,86 23,96 25,01 26,04 27,02 6 23,68 24,94 26,13 27,29 28,40 29,48 6,5 25,66 27,01 28,31 29,56 30,77 31,94 7 27,63 29,09 30,49 31,84 33,14 34,40 7,5 29,61 31,17 32,67 34,11 35,50 36,85 8 31,58 33,25 34,85 36,39 37,87 39,31 8,5 33,55 35,32 37,02 38,66 40,24 41,77 9 35,53 37,40 39,20 40,93 42,60 44,22 9,5 37,50 39,48 41,38 43,21 44,97 46,68 10 39,47 41,56 43,56 45,48 47,34 49,14 10,5 41,45 43,64 45,74 47,76 49,71 51,59 11 43,42 45,71 47,91 50,03 52,07 54,05 11,5 45,39 47,79 50,09 52,30 54,44 56,51 12 47,37 49,87 52,27 54,58 56,81 58,96 13 51,32 54,03 56,63 59,13 61,54 63,88 13,5 53,29 56,10 58,80 61,40 63,91 66,33 14 55,26 58,18 60,98 63,67 66,27 68,79 15 59,21 62,34 65,34 68,22 71,01 73,70 15,5 61,18 64,42 67,51 70,50 73,38 76,16 16 63,16 66,49 69,69 72,77 75,74 78,62 17 67,11 70,65 74,05 77,32 80,48 83,53 17,5 69,08 72,73 76,23 79,59 82,84 85,99 18 71,05 74,81 78,40 81,87 85,21 88,44 19 75,00 78,96 82,76 86,42 89,94 93,36 19,5 76,97 81,04 84,94 88,69 92,31 95,81 20 78,95 83,12 87,12 90,96 94,68 98,27 21,5 84,87 89,35 93,65 97,79 101,78 105,64 22 86,84 91,43 95,83 100,06 104,15 108,10 24 94,74 99,74 104,54 109,16 113,61 117,93 26 102,63 108,05 113,25 118,25 123,08 127,75 28 110,53 116,36 121,96 127,35 132,55 137,58 30 118,42 124,68 130,67 136,45 142,02 147,41 32 126,32 132,99 139,38 145,54 151,48 157,23 33 130,26 137,14 143,74 150,09 156,22 162,15 35 138,16 145,45 152,45 159,19 165,69 171,98 36 142,11 149,61 156,81 163,73 170,42 176,89 40 157,89 166,23 174,23 181,93 189,36 196,54 45 177,63 187,01 196,01 204,67 213,02 221,11 50 197,37 207,79 217,79 227,41 236,69 245,68 Effective delivery (kg/h) of nozzles for BioDiesel at 25°C Fuel atomization pressure (bar) Boilersinfo.com
• 148. 150 1.23 Commercial features of steel and copper pipelines SECTION (cm2 ) Weight Weight Vol. ext. Length for Length for Boilersinfo.com
• 149. 151 External Ø internal Normal thickness Non-welded pipelines Welded pipes Fretz Moon Welded pipes ERW (normal series) Weight Weight Weight Flow section Thickness Thickness Conventional designation Internal nominal Ø External nominal Ø Thickness Non- threaded black Flow section Execution type Threaded with sleeve Conventional weights Black Zinc-plated Boilersinfo.com
• 150. 152 1.24 Correction factors for lecture of gas delivery from gas meters Pgas (*) 0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 0 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 10 1, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 20 1, 1, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 30 1, 1, 1, 1, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 40 1, 1, 1, 1, 1, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 50 1, 1, 1, 1, 1, 1, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 60 1, 1, 1, 1, 1, 1, 1, 1, 1, 0, 0, 0, 0, 0, 0, 0, 70 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 0, 0, 0, 0, 0, 0, 80 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 0, 0, 0, 0, 0, 90 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 0, 0, 0, 100 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 0, 0, 110 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 0, 120 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 130 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 140 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 150 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 160 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 170 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 180 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 190 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 200 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 210 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 220 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 230 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 240 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 250 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 260 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 270 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 280 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 290 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 300 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 310 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 320 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 330 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 340 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 350 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 360 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 370 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 380 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 390 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 400 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 410 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 420 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 430 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 440 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 450 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 460 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 470 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 480 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 490 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 500 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 510 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 520 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 530 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 540 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 550 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 560 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 570 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 580 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 590 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 600 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 610 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 620 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 630 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 640 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 650 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, Corrective factor for lecture of gas delivery from gas meter (barometric pressure mbar) Gas temperature (°C) (*) Gas is read in mbar and it is relative to the atmospheric one Boilersinfo.com
• 151. 153 Pgas (*) 0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 650 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 660 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 670 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 680 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 690 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 700 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 710 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 720 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 730 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 740 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 750 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 760 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 770 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 780 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 790 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 800 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 810 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 820 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 830 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 840 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 850 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 860 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 870 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 880 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 890 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 900 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 910 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 920 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 930 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 940 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 950 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 960 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 970 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 980 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 990 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 2, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 2, 2, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 2, 2, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 2, 2, 2, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 2, 2, 2, 2, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 2, 2, 2, 2, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 2, 2, 2, 2, 2, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 2, 2, 2, 2, 2, 2, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 2, 2, 2, 2, 2, 2, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 2, 2, 2, 2, 2, 2, 2, 1, 1, 1, 1, 1, 1, 1, 1, 1, 2, 2, 2, 2, 2, 2, 2, 2, 1, 1, 1, 1, 1, 1, 1, 1, 2, 2, 2, 2, 2, 2, 2, 2, 1, 1, 1, 1, 1, 1, 1, 1, 2, 2, 2, 2, 2, 2, 2, 2, 2, 1, 1, 1, 1, 1, 1, 1, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 1, 1, 1, 1, 1, 1, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 1, 1, 1, 1, 1, 1, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 1, 1, 1, 1, 1, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 1, 1, 1, 1, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 1, 1, 1, 1, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 1, 1, 1, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 1, 1, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 1, 1, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 1, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, Corrective factor for lecture of gas delivery from gas meter (barometric pressure mbar) Gas temperature (°C) (*) Gas is read in mbar and it is relative to the atmospheric one Boilersinfo.com
• 152. 154 Pgas (*) 0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, Corrective factor for lecture of gas delivery from gas meter (barometric pressure mbar) Gas temperature (°C) (*) Gas is read in mbar and it is relative to the atmospheric one Boilersinfo.com
• 153. 155 1.25 Graphical method for determining energy saving by use of inverter PROCEDURE 7- On horizontal axis of the 1st diagram at the top from left individuate fan output (as percentage of max. output). 8- Trace vertical upwards and intersecate line representing saved electrical ouput. 9- From intersection point trace horizontal in the right direction until intersecating, on the 2nd diagram at the top from left, line representing the hours of working per day. 10- From intersection point trace vertical downwards until intersecating, on the 2nd diagram at the bottom from left, line representing the days of working per year. 11- From intersection point trace horizontal in the left direction until intersecating, on the 1st diagram at the bottom from left, line representing 1 kWh cost in euro. 12- From intersection point trace vertical downwards until reading on horizontal axis the money saved in a year by using an inverter. electricaloutputabsorptionatrpmfixed electricaloutputabsorptionatrpmvariable savedelectricaloutput working hours perday working daysper year d d d d d d d fanoutput kW/hcost electrical output absorbed (kW) Boilersinfo.com
• 154. 156 5.4 TABLES AND DIAGRAMS ABOUT COMBUSTION 1.26 Combustion triangle for natural gas and light/heavy oil Light/Heavy oil Natural gas Boilersinfo.com
• 155. 157 1.27 Combustion air and gas burnt quantities in relation to air excess for different fuels: G20, LPG, light oil and heavy oilgasmethane(G20)combustion O2andCO2volume%,amountofthecombustionair,dryandhumidexhaustedgas infunctionoftheairexcess 0,00 0,50 1,00 1,50 2,00 2,50 3,00 3,50 4,00 4,50 5,00 5,50 6,00 6,50 7,00 7,50 8,00 8,50 9,00 9,50 10,00 10,50 11,00 11,50 12,00 12,50 13,00 13,50 14,00 11,051,11,151,21,251,31,351,41,451,51,551,61,651,71,751,81,851,91,952 airexcessλ λ=ε+1 CO2 and O2 volume % 7,00 8,00 9,00 10,00 11,00 12,00 13,00 14,00 15,00 16,00 17,00 18,00 19,00 20,00 21,00 combustion air Va, humid exhausted gases Vegh, dry exhausted gases Vdeg [Nm3/Nm3gas] C02 02 Va Vegh Vdeg Boilersinfo.com
• 156. 158 LPGcombustion(LPG:70%propane30%butane) O2andCO2volume%,amountofthecombustionair,dryandhumidexhaustedgas infunctionoftheairexcess 0,00 0,50 1,00 1,50 2,00 2,50 3,00 3,50 4,00 4,50 5,00 5,50 6,00 6,50 7,00 7,50 8,00 8,50 9,00 9,50 10,00 10,50 11,00 11,50 12,00 12,50 13,00 13,50 14,00 14,50 15,00 15,50 16,00 11,051,11,151,21,251,31,351,41,451,51,551,61,651,71,751,81,851,91,952 airexcessλ λ=ε+1 CO2 and O2 volume % 24,00 25,00 26,00 27,00 28,00 29,00 30,00 31,00 32,00 33,00 34,00 35,00 36,00 37,00 38,00 39,00 40,00 41,00 42,00 43,00 44,00 45,00 46,00 47,00 48,00 49,00 50,00 51,00 52,00 53,00 54,00 55,00 56,00 combustion air Va, humid exhausted gases Vegh, dry exhausted gases Vdeg [Nm3/Nm3gas] C02 02 Va Vegh Vdeg Boilersinfo.com
• 159. 161 1.28 Increase of temperature in exhausted gas in relation to soot thickness %lossinfluegassesat13%ofCO2 Soot thickness (mm) Increaseinfluegassestemperature(∆T-°C) Boilersinfo.com
• 160. 162 1.29 Lenght and diameter of the flame in relation to burner output Range up to 1 MW 0 0,25 0,5 0,75 1 1,25 1,5 1,75 2 2,25 2,5 0 50 100 150 200 250 300 350 400 450 500 550 600 650 700 750 800 850 900 950 Thermal output (kW) Lenghtoftheflame(m) 0 0,2 0,4 0,6 0,8 1 1,2 1,4 1,6 1,8 Diameteroftheflame(m) Lmax Lmin Dmax Dmin Range 1-10 MW 0 1 2 3 4 5 6 7 Thermal output (kW) Lenghtoftheflame(m) 0 0,5 1 1,5 2 2,5 3 3,5 4 Diameteroftheflame(m) Lmax Lmin Dmax Dmin Boilersinfo.com
• 161. 163 1.30 SO2 emissions (mg/m3 e mg/kWh) in oil combustion in relation of S content (%) in the fuel at 3% of O2solforosaanhydride(SO2)inexaustedgasto3%ofoxygen infunctionofthefuelsulfur(S)concentration 0 250 500 750 00,10,20,30,40,50,60,70,80,911,11,21,31,41,51,61,71,81,92 sulfurmass%inthefuel SO2 to 3% of O2 [mg/m3] 0 250 500 750 SO2to3%ofO2[mg/kWh] Boilersinfo.com
• 162. 164 Influence of Fuel N on NOx emission level (*) 0 20 40 60 80 100 120 140 160 180 200 0 0,05 0,1 0,15 0,2 0,25 0,3 0,35 0,4 Fuel N (wt%) FuelNOx(ppm,at3%O2) (*) The range of values shows the dispersion due to different burners 1.31 NOx emissions in relation to the different parameters of influence Influence of furnace temperature on NOx emission level 1,4 1,45 1,5 1,55 1,6 1,65 1,7 1,75 1,8 600 700 800 900 Furnace temperature (°C) NOxemissionlevelrate(referment80°Cfurnace temperature) Boilersinfo.com
• 163. 165 Influence of combustion air temperature on NOx emission level 0 0,5 1 1,5 2 2,5 3 3,5 4 4,5 0 50 100 150 200 250 300 350 400 Preheated air temperature (°C) NOx-rateofemissionlevelwith/withoutpreheating ofair Load-ING Grafico 1 Pagina 1 Influence of thermal load on NOx emisison level Burner: T.I. 11 P/M Proof tube: ISO 0 100 200 300 400 500 600 700 0 0,5 1 1,5 2 2,5 Thermal specific load [ MW / m3 ] NOx[mg/kWh] Heavy oil Natural gas Boilersinfo.com
• 164. 166 Methane combustion (G20) Efficiency loss through exhaust gasses Ps [%] 2,00 3,00 4,00 5,00 6,00 7,00 8,00 9,00 10,00 11,00 12,00 13,00 14,00 15,00 16,00 17,00 18,00 19,00 20,00 21,00 22,00 23,00 24,00 25,00 26,00 27,00 28,00 29,00 30,00 31,00 32,00 33,00 34,00 35,00 60 70 80 90 100 110 120 130 140 150 160 170 180 190 200 210 220 230 240 250 260 270 280 290 300 310 320 330 340 350 360 370 380 390 400 Temperature difference between exhaust gasses and comburent air Tf-Ta Ps[%] O2 in volume 0% 1% 2% 3% 4% 5% 6% 7% 8% 9% 10% 11% 12% LPG combustion (70% propane 30% butane) Efficiency loss through exhaust gasses Ps [%] 2,00 3,00 4,00 5,00 6,00 7,00 8,00 9,00 10,00 11,00 12,00 13,00 14,00 15,00 16,00 17,00 18,00 19,00 20,00 21,00 22,00 23,00 24,00 25,00 26,00 27,00 28,00 29,00 30,00 31,00 32,00 33,00 34,00 35,00 60 70 80 90 100 110 120 130 140 150 160 170 180 190 200 210 220 230 240 250 260 270 280 290 300 310 320 330 340 350 360 370 380 390 400 Temperature difference between exhaust gasses and comburent air Tf-Ta Ps[%] O2 in volume 0% 2% 3% 5% 6% 7% 8% 9% 10% 11% 12% 1% 4% 1.32 Efficiency loss in exhausted gasses in relation to O2 content for different fuels Boilersinfo.com
• 165. 167 Light oil combustion Efficiency loss through exhaust gasses Ps [%] 2,00 3,00 4,00 5,00 6,00 7,00 8,00 9,00 10,00 11,00 12,00 13,00 14,00 15,00 16,00 17,00 18,00 19,00 20,00 21,00 22,00 23,00 24,00 25,00 26,00 27,00 28,00 29,00 30,00 31,00 32,00 33,00 34,00 35,00 60 70 80 90 100 110 120 130 140 150 160 170 180 190 200 210 220 230 240 250 260 270 280 290 300 310 320 330 340 350 360 370 380 390 400 Temperature difference between exhaust gasses and comburent air Tf-Ta Ps[%] O2 in volume 0% 2% 3% 5% 6% 7% 8% 9% 10% 11% 12% 1% 4% Heavy oil combustion (20°E a 50°C) Efficiency loss through exhaust gasses Ps [%] 2,00 3,00 4,00 5,00 6,00 7,00 8,00 9,00 10,00 11,00 12,00 13,00 14,00 15,00 16,00 17,00 18,00 19,00 20,00 21,00 22,00 23,00 24,00 25,00 26,00 27,00 28,00 29,00 30,00 31,00 32,00 33,00 34,00 35,00 60 70 80 90 100 110 120 130 140 150 160 170 180 190 200 210 220 230 240 250 260 270 280 290 300 310 320 330 340 350 360 370 380 390 400 Temperature difference between exhaust gasses and comburent air Tf-Ta Ps[%] O2 in volume 2% 5% 6% 8% 10% 11% 12% 3% 7% 9% 1% 4% 0% Boilersinfo.com
• 166. 168 gas methane combustion (G20) efficiency loss through exhausted gas Ps [%] 2,00 3,00 4,00 5,00 6,00 7,00 8,00 9,00 10,00 11,00 12,00 13,00 14,00 15,00 16,00 17,00 18,00 19,00 20,00 21,00 22,00 23,00 24,00 25,00 26,00 27,00 28,00 29,00 30,00 31,00 32,00 33,00 60 70 80 90 100 110 120 130 140 150 160 170 180 190 200 210 220 230 240 250 260 270 280 290 300 310 320 330 340 350 360 370 380 390 400 difference of temperature between exhausted gases and the combustion air Tf-Ta Ps[%] CO2 in volume CO2 max 11,65% 7% 8% 9% 10% 11% 11,65% LPG combustion (LPG: 70% propane 30% butane) efficiency loss through exhausted gas Ps [%] 2,00 3,00 4,00 5,00 6,00 7,00 8,00 9,00 10,00 11,00 12,00 13,00 14,00 15,00 16,00 17,00 18,00 19,00 20,00 21,00 22,00 23,00 24,00 25,00 26,00 27,00 28,00 29,00 30,00 31,00 32,00 33,00 60 70 80 90 100 110 120 130 140 150 160 170 180 190 200 210 220 230 240 250 260 270 280 290 300 310 320 330 340 350 360 370 380 390 400 difference of temperature between exhausted gases and the combustion air Tf-Ta Ps[%] CO2 in volume CO2 max 13,74% 7% 8% 9% 10% 11% 12% 13% 13,74% 1.33 Efficiency loss in exhausted gasses in relation to CO2 content for different fuels Boilersinfo.com
• 167. 169 Light oil combustion efficiency loss through exhausted gas Ps [%] 2,00 3,00 4,00 5,00 6,00 7,00 8,00 9,00 10,00 11,00 12,00 13,00 14,00 15,00 16,00 17,00 18,00 19,00 20,00 21,00 22,00 23,00 24,00 25,00 26,00 27,00 28,00 29,00 30,00 31,00 32,00 33,00 60 70 80 90 100 110 120 130 140 150 160 170 180 190 200 210 220 230 240 250 260 270 280 290 300 310 320 330 340 350 360 370 380 390 400 difference of temperature between exhausted gases and the combustion air Tf-Ta Ps[%] CO2 in volume CO2 max 15,25% 7% 8% 9% 10% 11% 12% 13% 14% 15,25% Heavy oil combustion (20°E a 50°C) efficiency loss through exhausted gas Ps [%] 2,00 3,00 4,00 5,00 6,00 7,00 8,00 9,00 10,00 11,00 12,00 13,00 14,00 15,00 16,00 17,00 18,00 19,00 20,00 21,00 22,00 23,00 24,00 25,00 26,00 27,00 28,00 29,00 30,00 31,00 32,00 33,00 60 70 80 90 100 110 120 130 140 150 160 170 180 190 200 210 220 230 240 250 260 270 280 290 300 310 320 330 340 350 360 370 380 390 400 difference of temperature between exhausted gases and the combustion air Tf-Ta Ps[%] CO2 in volume CO2 max 15,80% 7% 8% 9% 10% 11% 12% 13% 14% 15% 15,8% Boilersinfo.com
• 168. 170 1.34 Conversion factors for pollutant emissions Conversion from ppm to mg/Nm3 and from mg/Nm3 to ppm Gas CO 1 ppm = 1,25 mg/Nm3 1 mg/Nm3 = 0,8 ppm NO 1 ppm = 1,34 mg/Nm3 1 mg/Nm3 = 0,746 ppm NOx 1 ppm = 2,05 mg/Nm3 1 mg/Nm3 = 0,488 ppm SO2 1 ppm = 2,86 mg/Nm3 1 mg/Nm3 = 0,35 ppm C3H8 1 ppm = 1,98 mg/Nm3 1 mg/Nm3 = 0,505 ppm Conversion from ppm to mg/kWh and from mg/Nm3 to mg/kWh at 3% of O2 Metane G20 NOx 1 ppm = 2,052 mg/kWh NOx 1 mg/Nm3 = 1,032 mg/kWh CO 1 ppm = 1,248 mg/kWh CO 1 mg/Nm3 = 0,99 mg/kWh Light oil NOx 1 ppm = 2,116 mg/kWh NOx 1 mg/Nm3 = 1,032 mg/kWh CO 1 ppm = 1,286 mg/kWh CO 1 mg/Nm3 = 1, mg/kWh Boilersinfo.com

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The document provides information about forced draught burners including fundamental combustion principles, typical system layout diagrams, burner components, fuel supply, electrical supply and control, noise levels, and optimizing combustion. It also covers selection of forced draught burners and measuring combustion efficiency with tables, diagrams, and examples.

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