1. Fuels and Combustion

2. Recommended Books Fuels and Combustion; M.L. Smith & K.W. Stinson
Fuels and Fuel Technology ; W. Francis & M.C. Peters
Fuel – Solid , Liquid and Gaseous; J.S.S. Brame & J.G. King
Hydrocarbon Fuels; E.M. Goodger
Coal Conversion Processes; Stanley & Lee
Fuel Testing: Laboratory Methods in Fuel Technology; G.W. Himus
Methods of Analysis of Fuels and Oils; J.R. Campbell

3. Fuel
A substance which produce heat either by combustion or by nuclear fission / fusion

4. Classification of Fuels
Fuels can be classified as solid, liquid and gaseous fuels.
Solid fuels         : wood, coal, charcoal and coke Liquid fuels        : petrol, kerosene, diesel, alcohol etc Gaseous fuels   : methane, propane, butane, hydrogen, coal gas, gobar gas etc

5. Classification of Fuels
Primary Fuels: Naturally occuing e.g. coal, wood, natural gas
Secondary Fuels: Which are derived from primary fuels e.g. kerosene, coke etc
Naturally occurring
Artificially prepared

6. Combustion
Combustion is the conversion of a substance called a fuel into chemical compounds known as products of combustion by combination with an oxidizer.
The combustion process is an exothermic chemical reaction, i.e., a reaction that releases energy ???

7. Combustion
Combustion or burning is a complex sequence of exothermic chemical reactions between a fuel (usually a hydrocarbon) and an oxidant accompanied by the production of heat or both heat and light

8. Combustion Fuel ? Oxidizer ? Products of Combustion ?
Fuel + Oxidizer => Products of combustion + Energy
Fuel ?
Oxidizer ?
Products of Combustion ?
Incomplete Combustion ?

9. Fundamental Definitions
Basic Flame types
Premixed: Fuel and oxidizer are mixed first and burned later
Non-premixed: Combustion and mixing occur simultaneously

10. Combustion Air-Fuel Ratio; A/F Oxygen-Fuel Ratio; O/F
Stoichiometric or Theoretical A/F
Excess Air
% excess air = 100[(A/F)actual - (A/F)theo ]/(A/F)theo
120% of theoretical air ?
Fuel- Rich flame: If there is an excess of fuel
Fuel - lean flame : if there is an excess of oxygen

11. Combustion 1 kg of C needs ? kg of O2 1 kg of H2 needs ? Kg of O2
1 kg of Sulphur needs ? kg of O2

12. Combustion
Problem:
A fuel contains by mass 88 % carbon, 8 % H2, 1% S and 3% ash. Calculate the stoichiometric air/fuel ratio.
Ans: ?

13. Fundamental Definitions
Calorific value
Amount of heat librated by the combustion of unit quantity of fuel. kcal/ kg , kcal / m3
Gross Calorific Value (G.C.V) or HCV
heating value measurement in which the product water vapour is allowed to condense
Net Calorific Value (N.C.V) or LCV
heating value in which the water remains a vapor and does not yield its heat of vaporization
HHV = LHV + (mwater /mfuel)ʎwater

14. Fundamental Definitions
Flash Point
The lowest temperature at which a liquid fuel gives enough vapours in air which produce a momentary flash when exposed to a flame
Firepoint
The lowest temperature at which a liquid fuel vapours in air produces a continuous flame when exposed to a flame

15. Fundamental Definitions
Density
Specific gravity
Viscosity
Pour Point
Carbon Residue

16. Fundamental Definitions
Theoretical Flame Temperature:
It is the temperature attained by the products of combustion of fuel when there is no loss of heat to the surroundings
Flue Gas: It is the gaseous product of combustion of fuel

17. Coal
Origin of Coal
Coal has been formed by the partial decay of plant materials accumulated million of years ago and further altered by the action of heat and pressure
In situ Theory: coal occupies the same site where the orignal palnts grew
Drift Theory: plants were uprooted and drifted by rivers to get deposited

18. Coal classification Peat : Lignite: soft coal and the youngest
sub-bituminous
Bituminous:
semi-bituminous:
Anthracite: hard and geologically the oldest composed mainly of carbon

19. Coal Analysis Proximate analysis of coal Ultimate analysis of coal
Determines only fixed carbon, volatile matter, moisture and ash
Useful to find out heating value (GCV)‏
Simple analysis equipment
Ultimate analysis of coal
Determines all coal component elements: carbon, hydrogen, oxygen, sulphur, etc
Useful for furnace design (e.g flame temperature, flue duct design)‏
Laboratory analysis

20. Proximate analysis Moisture Content :
Moisture in coal must be transported, handled and stored
Since it replaces combustible matter, it decreases the heat content per kg of coal
Aids radiation heat transfer
1-2 gm 72 mesh coal at C till constant weight

21. Proximate analysis Volatile Matter:
Consist of CH4, hydrocarbons, H2 and CO, and incombustible gases like CO2 and N2
Proportionately increases flame length, and helps in easier ignition of coal
Sets minimum limit on the furnace height and volume
72 mesh coal C for 7 minutes

22. Proximate analysis Ash Content : Ash is an impurity that will not burn
Reduces handling and burning capacity.
Increases handling costs.
Affects combustion efficiency and boiler efficiency
Causes clinkering
1-2 gm 72 mesh 800 C (burned)

23. Proximate analysis Fixed carbon:
Solid fuel left in the furnace after volatile matter is removed
consists mostly of carbon
may contains some H2, O2, S and N2
gives a rough estimate of heating value of coal