1. FUEL
COMBUSTION
Dept. Of Processing And Food Engineering
Presented by :
Potdar Pratik Pandit

2. What are fuels ?
• Fuel is a substance , containing carbon as a main constituent which, when burnt produces heat
• 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. • Principle of Combustion:- Rapid oxidation of fuel accompanied by the production of heat, or heat
and light.
• Aim: get maximum heat from a fuel in the shortest time
• The fuel must be brought above its ignition temperature to start the combustion.
• CxHy + x +
𝑌
4
𝑂2 + 3.8 x +
𝑌
4
𝑁2 xCO2 +
𝑌
2
𝐻2𝑂 + 3.8 x +
𝑌
4
𝑁2
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 260°C
Carbon 400°C
Hydrogen 580°C
Carbon monoxide 610°C
Methane 630°C

6. Classification of Fuel
Fuels may broadly be classified in two ways, i.e.
• According to the physical state in which they exist in nature – solid, liquid and gaseous.
• According to the mode of their procurement – natural and manufactured.

7. 3T’s of Combustion
• Temperature high enough to ignite and
maintain ignition of the fuel
• Turbulence or intimate mixing of the fuel and
oxygen
• Time sufficient for complete combustion

8. Examples of the classified fuels

9. Solid Fuels andTheir Characteristics
• 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. • Advantages
• Ease of transport
• convenient to store without any risk of
spontaneous explosion
• Low production cost
• Possess moderate ignition temperature

11. • Disadvantages
• High ash content
• Large proportion of heat is wasted
• Burn with clinker formation
• combustion cannot be controlled easily

12. 1. Woods and their Characteristics
• Most commonly used and easily obtainable in
nature
• It consists of mainly cellular tissue and lignin
and lesser parts of fat and tar, as well as sugar
• The cellular tissue has a definite chemical
composition and thus has stable constituents
• Density: 400-800 kg/m3
• The main kinds of woods are:
- Beech wood
- Pine wood
- Birch wood
- Fir wood

13. Combustion Characteristics of woood
• The lighter the wood, the more intensely it
burns with a long flame
• Calorific value = 4730 cal/kg
• 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. Intermediate stage between coal and wood.
Immature coal
Forms in lakes and ponds
Moisture content = 60 to 90%
Thickness varies from 2 m to 15 m.
3 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 :-
• Gives good indication about heating and burning properties of coal
• finding out percentage of moisture, volatile matter, fixed carbon and ash in coal
• 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 104°C to 110°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 𝑥 𝑌
44 𝑥 𝑋
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 =
2𝑥𝑍
18𝑥𝑋
x 100 where,
Z = the increase in the weight of CaCl2 tube
c) Nitrogen: % of Nitrogen =
1.4𝑥 𝑉𝑜𝑙𝑢𝑚𝑒 𝑜𝑓 𝑎𝑐𝑖𝑑 𝑐𝑜𝑛𝑠𝑢𝑚𝑒𝑑𝑥 𝑁𝑜𝑟𝑚𝑎𝑙𝑖𝑡𝑦
𝑊𝑒𝑖𝑔ℎ𝑡 𝑜𝑓 𝑐𝑜𝑎𝑙 𝑠𝑎𝑚𝑝𝑙𝑒(𝑋)
𝑥100
d) Sulphur :
𝟑𝟐𝒙𝑴
𝟐𝟑𝟑𝒙𝑿
𝒙𝟏𝟎𝟎 Where, X = weight of coal sample taken
M = weight of BaSO4 precipitate formed% of sulphur in coal =

20. 2) ULTIMATE ANALYSIS
• Weight Percentage of Specific elements (C,H, N, O & S)
• Useful for design of coal burning equipments and auxiliaries
1) Carbon : % of C in coal =
12 𝑥 𝑌
44 𝑥 𝑋
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 =
2𝑥𝑍
18𝑥𝑋
x 100
where,
Z = the increase in the weight of CaCl2 tube
3) Nitrogen: % of Nitrogen =
1.4𝑥 𝑉𝑜𝑙𝑢𝑚𝑒 𝑜𝑓 𝑎𝑐𝑖𝑑 𝑐𝑜𝑛𝑠𝑢𝑚𝑒𝑑𝑥 𝑁𝑜𝑟𝑚𝑎𝑙𝑖𝑡𝑦
𝑊𝑒𝑖𝑔ℎ𝑡 𝑜𝑓 𝑐𝑜𝑎𝑙 𝑠𝑎𝑚𝑝𝑙𝑒(𝑋)
𝑥100

22. 4) Sulphur : % of sulphur in coal =
𝟑𝟐𝒙𝑴
𝟐𝟑𝟑𝒙𝑿
𝑥100 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
• Calorific
value
• Chamber
size
N
• No
calorific
value
S
• Corrosion
effect
O
• 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. • Higher calorific value per unit mass
• Burn without dust, ash, clinkers, etc.
• Easy firing and extinguishing
• Easy to transport through pipes
• Loss of heat in chimney is very low due to greater cleanliness.
• Require less furnace space for combustion
• Can be stored indefinitely without any loss.
• Clean in use and economic to handle
• Advantages
Liquid Fuels andTheir Characteristics

27. • Disadvantages
• Higher cost than solid fuels
• Costly special storage tanks are required for storage
• There is a greater risk of fire hazards
• 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
• 2-4 % in F.O.
• Risk of
corrosion by
sulphuric acid
Ash Content
• 0.03-0.07 %
• Fouling
deposits
Carbon Residue
• 1% in residual
oil
• 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
• 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)
• Burn without any smoke and
ashes .
• Combustion can readily be
controlled for change in demand
• Can be pre-heated by the heat of
hot waste gases
• Can be conveyed easily through
pipelines and eliminate labour
• Advantages

34. GASEOUS FUELS

35. 1) Natural Gas: -
• Found always above the oil in the oil wells
• Also called Marsh gas
• Its calorific value varies from 12,000 to 14,000
kcal/m3
• If natural gas contains lower hydrocarbons like
methane and ethane it is called lean or dry gas
• 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
• Uses:-
• Domestic and industrial fuel.
• Raw material for the manufacturing of carbon black
• Generation of electricity with help of fuel cells.

36. 2. WATER GAS (or) BLUE GAS
• Its CalorificValue is 2800 kcals/m3.
• It has high CalorificValue & burns with non-
luminous flame.
• Its flame is short but very hot.
• Composition:
The average composition is
H2 = 48 %
CO = 44 %
O2, N2 and CH4 = rest
• 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
• It is prepared by passing air mixed with a little steam over a coke
bed maintained at above 1100° C in a special reactor called ‘‘ Gas
Producer’’
• It is a poisonous gas.
• Insoluble in water.
• Heavier than air.
• Its Calorific Value is 1800 kcals/m3 .
• Composition:-
• 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. • Evaporates to produce about 250 times volume
of gas.
• Obtained as one of the top fractions in the
fractional distillation of petroleum
• Its CalorificValue is 27,000 kcals/m3
• Composition
• n-Butane = 70 %
Iso-butane = 17 %
n-Propane = 11 % Butylene
Ethane = rest
4. Liquified Petroleum Gas (LPG)
• Uses:-
- Heating industrial furnaces.
- Used as an alternate for Gasoline in automobiles.
- It is used as a fuel for domestic cooking.

39. • 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 –
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. • 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
• There are different liquid fuel and gaseous fuel burners
• There are some similarities in their design but it depends on the type and properties of fuel in
addition to their type of applications
• Although many designs are available, but they are common in one aspect of requiring proper mixing
of air and fuel prior to their combustion
• These oil or gas burners are used in furnaces.
Combustion Burners

42. • Usually classified based on their operating gas pressure
• Operated both atmospheric and high-pressure conditions
• Gases are supplied in different ways depending on the pressure
• In low pressure burner, the gas pressure varies from 1 to 4 kPa
• Whereas, high pressure burners the pressure varies from 7 to 70 kPa
Gas Burners

43. • The oldest burning process of fuel oil is the pot type burner in which the oil is first vaporized by
applying heat
• After vaporization, the oil vapors are mixed with excess air and then burned
• 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
• 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
• 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
• The liquid oil is first pressurized at about 100-150 psi
by a pump
• Pressurized liquid fuel enters tangentially through
the slots at a high velocity in the oil swirl chamber
• It flows in the form of a vortex and escapes through
a nozzle at the other end of the chamber
• The centrifugal force is exerted on to the oil and it
moves forward in the shape of a hollow tube
• 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. • Used in industry as well as for domestic purpose
• The device consists of a rotating cup and a fan
• Cup and the fan are rotated by an electric motor
with a shaft
• Oil is fed to the oil distributer to throw at the
inner surface of the cup
• The cup is rotated at a speed of about 3600 rpm
• Oil flows in a swirling motion and is thrown as
fine droplets at the other end.
Rotary Cup Burner

46. • Air for combustion is supplied in the
furnace chamber
• 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
• Some fraction of total air is mixed with
the fuel and this air supplied with the fuel
is called the primary air
• The secondary air is further added in the
combustion point in the furnace
• Mixing and combustion take place
simultaneously
• A free jet is produced in the downstream
side of the burner during the discharge of
fuel
Gas Burners

47. 47