Fuel Combustion Fundamentals
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This document discusses different types of fuels used for combustion. It defines fuels as substances containing carbon that produce heat when burned. There are three main types of fuels - solid fuels like coal and wood, liquid fuels like petroleum products, and gaseous fuels like natural gas. The document discusses the characteristics, properties, advantages and disadvantages of each fuel type. It also covers topics like fuel classification, combustion principles, fuel analysis and different combustion technologies.
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Fuel Combustion Fundamentals
- 1. FUEL COMBUSTION Dept. Of Processing And Food Engineering Presented by : Potdar Pratik Pandit
- 2. What are fuels ? β’ Fuel is a substance , containing carbon as a main constituent which, when burnt produces heat β’ To utilize the energy of fuel in most usable form, it is required to transform the fuel from its one state to another Availability Cost Storage & Handling Pollution
- 3. Requirements of a Good Fuel o High calorific value o Moderate velocity of combustion o Moderate ignition temperature o Low contents of non-combustible matters o Low moisture content o Easy to transport and readily available at low cost o Combustion should be controllable o Free from objectionable and harmful gases like CO, SO2, H2S
- 4. β’ Principle of Combustion:- Rapid oxidation of fuel accompanied by the production of heat, or heat and light. β’ Aim: get maximum heat from a fuel in the shortest time β’ The fuel must be brought above its ignition temperature to start the combustion. β’ CxHy + x + π 4 π2 + 3.8 x + π 4 π2 xCO2 + π 2 π»2π + 3.8 x + π 4 π2 What is combustion?
- 5. 0 Rate of combustion depends on many factors like: #Nature of the fuel #Temperature #Concentration of the fuel and air 0 Combustion rate can be increased by - Preheating the fuel and air - Increasing the surface area of the fuel - Increasing the pressure of air 0The minimum ignition temperatures in atmospheric air are: Gasoline 260Β°C Carbon 400Β°C Hydrogen 580Β°C Carbon monoxide 610Β°C Methane 630Β°C
- 6. Classification of Fuel Fuels may broadly be classified in two ways, i.e. β’ According to the physical state in which they exist in nature β solid, liquid and gaseous. β’ According to the mode of their procurement β natural and manufactured.
- 7. 3Tβs of Combustion β’ Temperature high enough to ignite and maintain ignition of the fuel β’ Turbulence or intimate mixing of the fuel and oxygen β’ Time sufficient for complete combustion
- 8. Examples of the classified fuels
- 9. Solid Fuels andTheir Characteristics β’ Characteristics of Solid Fuels: - High ash content - Low thermal efficiency - Low calorific value - Require large excess air - Cost of handling is high - Cannot be used in IC engines
- 10. β’ Advantages β’ Ease of transport β’ convenient to store without any risk of spontaneous explosion β’ Low production cost β’ Possess moderate ignition temperature
- 11. β’ Disadvantages β’ High ash content β’ Large proportion of heat is wasted β’ Burn with clinker formation β’ combustion cannot be controlled easily
- 12. 1. Woods and their Characteristics β’ Most commonly used and easily obtainable in nature β’ It consists of mainly cellular tissue and lignin and lesser parts of fat and tar, as well as sugar β’ The cellular tissue has a definite chemical composition and thus has stable constituents β’ Density: 400-800 kg/m3 β’ The main kinds of woods are: - Beech wood - Pine wood - Birch wood - Fir wood
- 13. Combustion Characteristics of woood β’ The lighter the wood, the more intensely it burns with a long flame β’ Calorific value = 4730 cal/kg β’ If the wood is heavy, the penetration of air is difficult and a concentrated flame results with the development of more heat at the point of burning
- 14. οΌIntermediate stage between coal and wood. οΌImmature coal οΌForms in lakes and ponds οΌMoisture content = 60 to 90% οΌThickness varies from 2 m to 15 m. οΌ3 types of peat: i) Fibrous peat ii) Earthy peat iii) Mature peat 14 2. Peat
- 15. 3. COAL - It is a mineral substance of vegetable origin - Coal is classified on the basis of its rank - The rank of coal denotes its degree of maturity Wood Peat Lignite Sub- bituminous coal Bituminous coal Anthracite
- 16. Calorific Compo sition value k.cals/kg % Peat Highly 4000 - C = 57 Domestic fibrous light 5400 H = 06 fuel, power brown in O = 35 Generation colour Lignite Fibrous, 6500 - C = 67 Manufacture brown 7100 H = 05 of producer coloured coal O = 26 gas & steam Sub- Black 7000 - C = 77 Manufacture bituminous coloured, 7500 H = 05 of gaseous coal homogenious O = 16 fuels smooth mass, Bituminous Black, brittle, 8000 - C = 83 Power coal burns with 8500 H = 05 generation, yellow O = 10 coke making, smoky flame domestic fuel Anthracite Hard & most 8500 - C = 93 Boiler matured coal, 8700 H = 03 heating, burns without O = 03 metallurgical smoke furnace
- 17. Miscellaneous Fuels 1. Charcoal 2. Briquettes 3. Bagasse 4. Molasses 5. Straw 17
- 18. Analysis of Coal 1) PROXIMATE ANALYSIS :- β’ Gives good indication about heating and burning properties of coal β’ finding out percentage of moisture, volatile matter, fixed carbon and ash in coal β’ It is useful in deciding its utilization for a particular industrial use Analysis of coal is done for its burning properties. For this purpose, two commonly used tests are performed i.e. Proximate analysis and Ultimate analysis of coal. Moisture content Volatile Matter Ash content 1 gm of coal sample at 104Β°C to 110Β°C for 1 hour in an oven and finding the loss in weight 1 gm of coal sample in a covered crucible at 950oC for 7 minutes and determining loss in weight Completely burning the sample of coal in a muffled furnace at 700oC to 750oC and weighing the residue
- 19. - Finding out the weight percentage of C, H, N, O and S of the pure coal free from moisture and inorganic constituents - It is useful for designing of coal burning equipments and auxiliaries a) Carbon : % of C in coal = 12 π₯ π 44 π₯ π x 100 where, X = the weight of coal sample taken Y = the increase in the weight of KOH tube b) Hydrogen : % of hydrogen in coal = 2π₯π 18π₯π x 100 where, Z = the increase in the weight of CaCl2 tube c) Nitrogen: % of Nitrogen = 1.4π₯ ππππ’ππ ππ ππππ ππππ π’ππππ₯ ππππππππ‘π¦ ππππβπ‘ ππ ππππ π πππππ(π) π₯100 d) Sulphur : ππππ΄ πππππΏ ππππ Where, X = weight of coal sample taken M = weight of BaSO4 precipitate formed% of sulphur in coal =
- 20. 2) ULTIMATE ANALYSIS β’ Weight Percentage of Specific elements (C,H, N, O & S) β’ Useful for design of coal burning equipments and auxiliaries 1) Carbon : % of C in coal = 12 π₯ π 44 π₯ π x 100 where, X = the weight of coal sample taken Y = the increase in the weight of KOH tube
- 21. 2) Hydrogen : % of hydrogen in coal = 2π₯π 18π₯π x 100 where, Z = the increase in the weight of CaCl2 tube 3) Nitrogen: % of Nitrogen = 1.4π₯ ππππ’ππ ππ ππππ ππππ π’ππππ₯ ππππππππ‘π¦ ππππβπ‘ ππ ππππ π πππππ(π) π₯100
- 22. 4) Sulphur : % of sulphur in coal = ππππ΄ πππππΏ π₯100 Where, X = weight of coal sample M = weight of BaSO4 precipitate formed
- 23. Relationsip between proximate and ultimate analysis %C = 0.97C+ 0.7(VM - 0.1A) - M(0.6-0.01M) %H = 0.036C + 0.086 (VM -0.1xA) - 0.0035M2 (1-0.02M) %N2 = 2.10 -0.020VM where C = % of fixed carbon A = % of ash VM = % of volatile matter M = % of moisture
- 24. Significance of Ultimate Analysis C & H β’ Calorific value β’ Chamber size N β’ No calorific value S β’ Corrosion effect O β’ Moisture holding capacity
- 25. 1) Fixed Bed Combustion 2) Fluidized-Bed Combustion 3) Oxy-Fuel Combustion 4) Hand fired boilers 5) Stoker fired boilers Combustion of Solid Fuels Coal Combustion Technologies
- 26. β’ Higher calorific value per unit mass β’ Burn without dust, ash, clinkers, etc. β’ Easy firing and extinguishing β’ Easy to transport through pipes β’ Loss of heat in chimney is very low due to greater cleanliness. β’ Require less furnace space for combustion β’ Can be stored indefinitely without any loss. β’ Clean in use and economic to handle β’ Advantages Liquid Fuels andTheir Characteristics
- 27. β’ Disadvantages β’ Higher cost than solid fuels β’ Costly special storage tanks are required for storage β’ There is a greater risk of fire hazards β’ Specially constructed burners and spraying apparatus are required for efficient burning
- 28. Properties of Liquid Fuels 1. Flash Point :- The lowest temperature at which the fuel can be heated so that the vapour gives off flashes momentarily when an open flame is passed over it 2. Pour Point:- Lowest temperature at which it will pour or flow when cooled under prescribed conditions 3. Specific Heat:-The amount of heat needed to raise the temperature of 1 kg of oil by 1oC.The unit of specific heat is kcal/kgoC
- 29. 4. CalorificValue:- Measurement of heat or energy produced, and is measured either as gross calorific value or net calorific value * GCV (Gross CalorificValue):Quantity of heat produced by combustion when the water produced by combustion is allowed to return to the liquid state * NCV (Net CalorificValue) : Quantity of heat produced by combustion when the water produced by combustion remains gaseous
- 30. Fuel Oil Gross CalorificValue (kCal/kg) Kerosene 11,100 Diesel Oil 10,800 L.D.O 10,700 Furnace Oil 10,500 LSHS 10,600
- 31. CONSTITUENTS OF LIQUID FUELS Sulphur β’ 2-4 % in F.O. β’ Risk of corrosion by sulphuric acid Ash Content β’ 0.03-0.07 % β’ Fouling deposits Carbon Residue β’ 1% in residual oil β’ Tendency to deposit residue
- 32. Typical Specification of Fuel Oils Properties Fuel Oils Furnace Oil LS.H.S. L.D.O. Density (Approx. g/cc at 150C) 0.89-0.95 0.88-0.98 0.85-0.87 Flash Point (0C) 66 93 66 Pour Point (0C) 20 72 18 G.C.V. (Kcal/kg) 10,500 10,600 10,700 Sediment, % Wt. Max. 0.25 0.25 0.1 SulphurTotal, % Wt. Max. Upto 4.0 Upto 0.5 Upto 1.8 Water Content, %Vol. Max. 1.0 1.0 0.25 Ash % Wt. Max. 0.1 0.1 0.02
- 33. Gaseous Fuels andTheir Characteristics β’ Disadvantages - Very large storage tanks are needed - Highly inflammable, so chances of fire hazards in their use is high o Gaseous fuels occur in nature, besides being manufactured from solid and liquid fuels o The calorific value of gaseous fuel is expressed in Kilocalories per newton cubic meter (KCal/Nm3) β’ Burn without any smoke and ashes . β’ Combustion can readily be controlled for change in demand β’ Can be pre-heated by the heat of hot waste gases β’ Can be conveyed easily through pipelines and eliminate labour β’ Advantages
- 34. GASEOUS FUELS
- 35. 1) Natural Gas: - β’ Found always above the oil in the oil wells β’ Also called Marsh gas β’ Its calorific value varies from 12,000 to 14,000 kcal/m3 β’ If natural gas contains lower hydrocarbons like methane and ethane it is called lean or dry gas β’ The average composition of natural gas is as follows : Constituents Percentage(%) Methane 88.5 Ethane 5.5 Propane 4 Butane 1.5 Pentane 0.5 β’ Uses:- β’ Domestic and industrial fuel. β’ Raw material for the manufacturing of carbon black β’ Generation of electricity with help of fuel cells.
- 36. 2. WATER GAS (or) BLUE GAS β’ Its CalorificValue is 2800 kcals/m3. β’ It has high CalorificValue & burns with non- luminous flame. β’ Its flame is short but very hot. β’ Composition: The average composition is H2 = 48 % CO = 44 % O2, N2 and CH4 = rest β’ Uses:- - Carbureted water gas (water gas + oil gas) is used for lighting and heating purposes -Also used for welding purposes. - Used for the manufacturing of Methyl alcohol. Synthetic petrol Ammonia
- 37. 3. Producer Gas β’ It is prepared by passing air mixed with a little steam over a coke bed maintained at above 1100Β° C in a special reactor called ββ Gas Producerββ β’ It is a poisonous gas. β’ Insoluble in water. β’ Heavier than air. β’ Its Calorific Value is 1800 kcals/m3 . β’ Composition:- β’ Its average composition is N2 = 50 % CO = 30 % H2 = 10 % CO2 and CH4 = res Uses -It is used as fuel for heating open - earth furnaces ( steel and glass manufacturing), muffle furnaces (coal gas and coke manufacturing). - It provides reducing atmosphere in certain metallurgical operations
- 38. β’ Evaporates to produce about 250 times volume of gas. β’ Obtained as one of the top fractions in the fractional distillation of petroleum β’ Its CalorificValue is 27,000 kcals/m3 β’ Composition β’ n-Butane = 70 % Iso-butane = 17 % n-Propane = 11 % Butylene Ethane = rest 4. Liquified Petroleum Gas (LPG) β’ Uses:- - Heating industrial furnaces. - Used as an alternate for Gasoline in automobiles. - It is used as a fuel for domestic cooking.
- 39. β’ Gas Burners : - - If the fuel and gas are premixed before passing through the burner nozzle it is called premixed type. - In diffusion type, a small quantity of air is mixed in the flow of gas and there will be diffusion between them - Industrial burners for gaseous fuel are diffusion type - In diffusion burner air and gaseous fuel are supplied separately in the furnace - In the atmospheric type burner, the gas pressure varies from 2 to 12 of water gauge - In the high-pressure type, 0.5 to 40 psi gas pressure is used with a large combustion chamber Combustion of Gaseous Fuels
- 40. Combustion Apparatus Physical state of fuels Nature of medium Nature of the flame Mixing of fuel Nature of the fuel air mixture a) Gas burners b) Oil burners c) Powdered solid fuel burners d) Grates for burning solid fuel in lumps a) Normal / constant pressure burners b) Submerged combustion burners c) Constant volume apparatuses a) Ordinary non β luminous flame b) Incandescent or reducing flame c) Neutral flame a) Injection burners b) Diffusion burners a) Mixture prepared preliminarily b) Mixture obtained during the combustion itself
- 41. β’ The basic combustion theory and laws are applied for the design of burning equipment depending on the type of fuels, such as gaseous or liquid fuels β’ There are different liquid fuel and gaseous fuel burners β’ There are some similarities in their design but it depends on the type and properties of fuel in addition to their type of applications β’ Although many designs are available, but they are common in one aspect of requiring proper mixing of air and fuel prior to their combustion β’ These oil or gas burners are used in furnaces. Combustion Burners
- 42. β’ Usually classified based on their operating gas pressure β’ Operated both atmospheric and high-pressure conditions β’ Gases are supplied in different ways depending on the pressure β’ In low pressure burner, the gas pressure varies from 1 to 4 kPa β’ Whereas, high pressure burners the pressure varies from 7 to 70 kPa Gas Burners
- 43. β’ The oldest burning process of fuel oil is the pot type burner in which the oil is first vaporized by applying heat β’ After vaporization, the oil vapors are mixed with excess air and then burned β’ As oil is vaporized at a slower rate than the rate of combustion reaction, the process is modified by using atomizer to form tiny droplets of oil before its ignition β’ The nozzles are designed in such a way so that, it can be used to atomize oil at an elevated oil pressure at about 100 psi β’ The process can produce oil droplets in the range from 0.0002 inch to 0.010 inch. Oil Burners
- 44. Combustion of Liquid Fuels Swirl Oil Burner β’ The liquid oil is first pressurized at about 100-150 psi by a pump β’ Pressurized liquid fuel enters tangentially through the slots at a high velocity in the oil swirl chamber β’ It flows in the form of a vortex and escapes through a nozzle at the other end of the chamber β’ The centrifugal force is exerted on to the oil and it moves forward in the shape of a hollow tube β’ Air enters to the annular space and moves forward. Then the fine droplets emerge at the exit of the chamber in the form of a spray.
- 45. β’ Used in industry as well as for domestic purpose β’ The device consists of a rotating cup and a fan β’ Cup and the fan are rotated by an electric motor with a shaft β’ Oil is fed to the oil distributer to throw at the inner surface of the cup β’ The cup is rotated at a speed of about 3600 rpm β’ Oil flows in a swirling motion and is thrown as fine droplets at the other end. Rotary Cup Burner
- 46. β’ Air for combustion is supplied in the furnace chamber β’ Small portion of air is mixed with fuel as primary air and the rest amount, known as secondary air, is supplied above the burner port β’ Some fraction of total air is mixed with the fuel and this air supplied with the fuel is called the primary air β’ The secondary air is further added in the combustion point in the furnace β’ Mixing and combustion take place simultaneously β’ A free jet is produced in the downstream side of the burner during the discharge of fuel Gas Burners
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