Combustion Basics
Definition of combustion
Fuel
Oxygen
Combustion
Definition of combustion
complete combustion
All fuel
Minimum air
All FuelBurning
Air
Definition of combustion
fuelHeat O2
The combustion occur when the elements in a
fuel combine with oxygen to produce heat
Hydrocarbons
C H H
H
Others
C C
S
H
There are four Requirements for complete
combustion or MATT
• M ----- Proper mixture of air and fuel is
required
• A ----- Proper atomization of liquid fuel is
required .
• T ----- Proper temperature of air ,fuel and zone
temperature must be maintained to
achieve complete combustion .
• T ----- Proper time must be provided to
complete the combustion process before
the gases of the combustion come in
What is the function of the burner
1- Provide heat to the boiler .
2- Control the outlet temperature or
pressure of the boiler .
3- Provide a high turndown so that it
doesn’t shutoff over the full range of
boiler load demands .
4- Burn the fuel in the most efficient way
possible to keep fuel consumption low
Products of combustion
When the hydrogen and oxygen combine
intense heat and water vapor is formed .
H2
Intense heat O
Products of combustion
When carbon and oxygen combine intense heat and the
compounds of carbon dioxide or carbon monoxide are
formed .
O
OC
O C C
O O
Products of combustion
When sulfur and oxygen combine ,sulfur
dioxide and heat are formed .
O
S
O
Fuels
But we cant achieve 100% efficient combustion , So all fuels
contain some moisture and non combustible:
20
18
16
14
12
% 10
8
6
4
2
0
Top quality Residual oil Natural gas
coal
Fuel
TYPES OF
COMBUSTION
Perfect
Complete
Incomplete
1- Perfect combustion :-
All the fuel is burned using only the theoretical
amount of air ,
x
perfect combustion
cannot be
achieved in aboiler
2- Complete combustion :-
All the fuel is burned using the minimal amount of
air above the theoretical amount of air needed to
burn the fuel .
highest combustion efficiency
complete
combustion
low pollution
3- Incomplete combustion :-
All the fuel is not burned completely , which
results in the formation of soot and smoke .
Fuel
Air Requirements
Oxygen combustion is obtained from the atmosphere
air by weight 77
23
air by volume 79
21
0 20 40 60 80 100 120
Oxygen other gases
Air Requirements
Sea level , 80%
efficiency
One Gallon Air 2000 ft3
Fuel oil
Air Requirements
Air Air
Air Air
Air
Natural
15 ft3 of air
1 ft natural gas
3
gas sea level
75% Air
Air Air Air
Air
Air
Air Air Air Air
Classification of Air required in combustion
Primary air
Controls the
rate of
combustion ,w Secondary air
hich Controls
determines Excess air
combustion
the amount of efficiency by Is the air
fuel that can controlling supplied to the
be burned how burner that
completely the exceeds the
fuel is burned theoretical
amount needed to
burn the fuel
Forced / Natural Draft
Air requirements
For combustion
Remove the
products of
combustion.
Forced Draft
Blower
+ Pressure
Combustion products
Air Combustion
Chamber
Induced Draft
- Pressure Suction
Fan
Air Combustion products
Combustion
Chamber
Natural Draft
Combustion products
Combustion
Chamber
Air Air
- ve
Pressure
Combustion principles
1- Combustion of carbon in any fuel
C + O2 CO2
Knowing that the molar masses of the above species
are :
C: 12g O2: 32g CO2: 44g
2- Combustion of hydrogen mole in any fuel
2H2 + O2 2H2O
Knowing that the molar masses of the above species
are :
H2: 4g O2: 32g H2O: 36g
Combustion principles
3- for incomplete combustion, it is not possible to
convert all the carbon to carbon dioxide instead
carbon monoxide which is partially produced
2C + O2 2CO + heat (9,300 KJ / Kg)
As more air is added some carbon monoxide is
converted to carbon dioxide with more heat
release :
CO + O2
CO2 + heat (23,500 KJ / Kg)
EXAMPLE
Find the required amount of oxygen to burn propane C3H8
C + O2 CO2
H + O2 H2O
C3H8 + aO2 3 CO2 + 4H2O
3 +2 = a a=5
C3H8 + 5O2 3 CO2 + 4 H2O
( 3x 12 +(8x1)) kg propane +(5x 32) kg oxygen
3( 12+ 32) kg Carbon dioxide+ 4 ( 2+16) kg water
Therefore the oxygen required for combustion of propane =
(5x 32)/(3x12 +8) = 3.636Kg
Constructional Parts of Burners
The Burner Gun
• This is a tube through which the fuel is
supplied to the center of the burner.
• In case of liquid fuel the gun is provided
with atomizing nozzle or orifices at the
delivery end.
The Air Register
• Its task is to introduce the combustion air in such
a way into the combustion space that it is
intensively mixed with the fuel.
• The air register of a burner usually consists of a
cylindrical, flat, box type construction, normally
provided with vanes along the cylindrical part.
• Air registers are divided into primary and
secondary registers, each with its own openings.
The Burner Throat
• The opening in the boiler, through which
the flame and combustion products enter
the combustion space, is lined with
suitably shaped heat resistant material.
• Its first task is to reflect radiant heat from
the flame back to the origin of the flame in
order to create a hot zone around the
atomizer, consequently improving the
ignition.
• A second task is to complete the mixing of
fuel and combustion air.
BURNERS
COMBINED
OIL BURNERS BURNERS GAS BURNERS
Mechanical
Atomized
Premix Flame
Steam Atomized
Diffusion Flame
Air Atomized
