1. Analysis of FUEL UTILIZATION
P M V Subbarao
Professor
Mechanical Engineering Department
An Unending Journey of being Quasi-static while Destroying the Permanent Entropy Vehicles…..

2. Science always has its origin in the adaptation of thought to some definite field of experience.
Sir Ernst Mach

3. Fuel Model

4. Hydro carbon Chemistry of Crude Oils
Components of Crude Oils.
Paraffins (CnH(2n+2))
Olefins
Aromatics
Ultimate Analysis
C : % ; H : % ; O : % ; N : % ; S : %

5. Important Fuel Derivatives from Crude Oil

6. Boiling range, and molecule size for typical refinery
BOILING RATE # CARBON ATOMS
Refinery Gas <25oC
Gasoline oC
Naptha oC
Kerosene oC
Diesel Fuel oC
Residual Oil >400oC >25

7. Major Components of Gasoline (Petrol)

8. Major Components of Gasoline (Petrol)

9. Gaseous Fuels
Can be easily piped into furnace -- no physical handling is required.
Natural Gas -- True Fossil fuel
Odorless and colorless
Mainly CH4 + heavier HCs
Manufactured Gases
LPG -- light distillates of petroleum. -- Heavier than air!!!
Stored and transported under pressure ( Mpa).
SNG : Produced from coal by Hydrogenation -- cheap and clean..
Pressurized Hydrogen at 9000C is combined with coal to produce a number of light HCs.
Producer gas, Bio-gas, Water gas, Coke-oven gas etc….

10. Energy Content of A Fuel
Standard heat of combustion:
The energy liberated when a substance X undergoes complete combustion, with excess of oxygen at standard conditions (25°C and 1 bar).
The heat of combustion is utilised to quantify the performance of a fuel in a combustion system such as furnaces, motors and power generation turbines.
In industrial terminology it is identified as the Gross Heating(calorific) Value or Higher Heating (calorific) value.
In a general design calculations, only Net Heating(calorific) Value or Lower Heating (calorific) value is used.

11. Measurement of Calorific Value : Bomb Calorimeter

12. The Bomb & Fuel

13. Temperature of Water in Jacket

14. Energy Balance & Estimation of HHV

15. Gas Calorimeter

16. Heat Values of Various Fuels
Heat value
Hydrogen (H2)
MJ/kg
Methane (CH4)
50-55 MJ/kg
Petrol/gasoline
44-46 MJ/kg
Diesel fuel
45 MJ/kg
Liquefied Petroleum Gas (LPG)
49 MJ/kg
Natural gas
38-39 MJ/m3
Sub-bituminous coal
MJ/kg
Lignite/brown coal (IEA definition)
<17.4 MJ/kg
Firewood (dry)
16 MJ/kg

17. Sustainable Thermal Processing of Fuel
On heating, any solid/liquid fuel undergoes the following processes:
Drying (<150oC)
Pyrolysis ( oC)
Flaming Combustion
Glowing Combustion
Final products: CO2, H2O (complete combustion)
Advanced Thermal Treatment

18. Method of Solid Fuel Combustion ? Using just Commonsense…..

19. Fuel Bed Combustion O2+CO2+N2+H2O Secondary Air Flame Green Coal
Primary Air
Secondary Air
Flame
Green Coal
Incandescent coke
Grate
CO+CO2+N2+H2
VM+CO+CO2+N2+H2
O2+CO2+N2+H2O
ASH

20. Salient Features of Stokers
The grate heat release rate is < 1340 kW/sq.m.
Size of coal 19 mm to 38 mm.
Only suitable for non caking or free burning coal.
Max. ash allowed is 20%.
Largest capacity possible : 155MW.
Maximum steaming rate: 50kg/s.
Huge pressure drop
m U (1- e) rg U2 (1 – e)
Dp =
(fdp)2e fdpe3
How to make large Capacity Combustion Systems ?

21. 1920 : A Need for Break Through for Thermal Power Generation
The first limit on grate firing is that of scale.
A practical engineering limit seems to be reached when the length and width of the grate are about 9 m with grate area 80 m2.
At 2 MW/m2, the steam capacity at 85% efficiency would be 150 MW or 270 tons per hour.
In practice stokers have rarely exceeded a capacity of 135 tons/hour.
The limitation is partly grate area and partly firing density.
The limitation on firing density exist due to:
The rate of movement of the reaction plane could not match the opposed rate of fuel flow leading to blow-off.
The experience with grate combustion led to development of many requirements for further development.

22. Duties of A Furnace Dixon’s Theory:
Generate an environment of excited fuel and oxygen molecules.
All the fuel molecules should be surrounded by oxygen molecules.
Facilitate frequent collisions among excited fuel molecules and excited fuel molecules.
A successful collision can lead to combustion.
Many possible technologies are available to realize above conditions with varying levels of success and expenditure.
These are called Three Ts and one S technologies.

23. Five Requisites for Good Combustion
Fuel
MATtr Theory:
M : Proper mixing of the reactants.
A: Sufficient air.
T: Conducive temperature
t: Sufficient time
r: Satisfactory density of reactant.
Fourth DF systems contains various auxiliaries to satisfy MATtr theory as completely as possible.

24. Realization of MATtr Theory
Mixing: Fuel preparation systems.
Air: Draught systems.
T : Preheating of fuel.
t : Dimensions of combustion chamber.
r: Turbulence generation systems.

25. Combustion
performance
Thermal
Performance
Slagging.
Fouling &Erosion
Operational Issues
Fuel Handling
system
Fuel Preparation
Combustion
System
Thermal structures
Design Issues
Fuel & Air

26. Most Important Step in Design of Fuel Combustion System
Sufficient Supply of Air Flow

27. Fuel Model & Ideal Combustion
Ultimate Analysis of dry (moisture free) fuel: Gravimetric
Percentage of carbon : x --- Number of moles, X = x/12
Percentage of hydrogen : y --- Number of atomic moles, Y = y/1
Percentage of oxygen: k --- Number of atomic moles, K = k/16
Percentage of sulfur: z – Number of atomic moles, Z = z/32
Equivalent chemical formula : CXHYSZOK
Equivalent Molecular weight : 100 kgs.
Ideal combustion
CXHYSZOK (X+Y/4+Z-K/2) AIR → P CO2 +Q H2O + R N2 + G SO2
Ideal Air- Fuel Ratio: 6