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combustion problems
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Combustion
Source of energy
We know that, in most of the world today, wood is not the main source of
fuel.
We generally use natural gas or oil in our homes.
We mainly use oil and coal to heat the water to produce the steam to drive the
turbines for our huge power generation
systems.
Coal, oil, and natural gas are often referred to as fossil fuels.
3 Requirements:
Combustible Material
Substance that supports combustion ( oxygen)
Kindling Temperature
Combustion Reactions:
C + O2 CO2
C + O2 CO
H2 + O2 H2O
S + O2 SO2S + O2 SO3
Types of Fuel:
Gaseous Fuel
The most environment friendly
Liquid Fuel
Solid Fuel
Methane, ethane, propane, etc.
Gasoline, kerosene, bunker
fuel, fuel oil, etc.
Coal, wood, etc.
combustion
chamberfuel
C, H, O, N, S,
ash
air/oxygen
Stack /flue
gas
Unburnt fuel, ash
combustion
chamberfuel
C, H, O, N
air/oxygen
Stack /flue
gas
Gaseous/
Liquid Fuel
Balance:
Unburnt fuel
CO2CO
O2N2
H2O
C in fuel
H in fuel =
O2in fuel
N2in fuel + N2 in air = N2 in unburnt fuel + free N2
+ C in CO= C in unburnt fuel + C in CO2
+ H in H2OH in unburnt fuel
O2 in unburnt fuel+ O2 in air = + O2 in H2O+ free O2
Analysis of Flue Gas
means to determine the
efficiency of the boiler
Complete or Wet Analysis
water is reported and is part of
the % composition
Dry or Orsat Analysis
water is not reported and is not part of
the % composition
mole Wet Analysis Orsat( Dry)
Analysis
CO2 30 30% 33.33%
CO 10 10% 11.11%
O2 5 5% 5.56%
N2 45 45% 50.00%
H2O 10 10%
total 100
1. Ethane is burned with 50%
excess air. The percentage
conversion of ethane is 90%; Of
the ethane burned, 25% reacts to
form CO and the balance reacts to
form CO2. Calculate the molar
composition of the stack gas on a
dry basis and the mole ratio of
water to dry stack gas.
3. A mixture of 75% mole propane and 25% mole
hydrogen is burned with 25% excess air.
Fractional conversion of 90% of the propane and
85% of the hydrogen are achieved. Of the
propane that reacts, 95% reacts to form CO2 and
the balance reacts to form CO. (a) Calculate the
concentration of CO (in ppm) in the stack gas
3. A mixture of 75% mole propane and 25% mole
hydrogen is burned with 25% excess air.
Fractional conversion of 90% of the propane and
85% of the hydrogen are achieved. Of the
propane that reacts, 95% reacts to form CO2 and
the balance reacts to form CO. (a) Calculate the
concentration of CO (in ppm) in the stack gas
A gas with the following composition is burnedwith 50% excess air in a furnace: 60% CH4, 20%C2H6, 5% CO, 5% O2 and 10% N2. What is thecomposition of the flue gas by percent assumingcomplete combustion? B. If 85% of thecarbons burns to form CO2 and the rest to CO,what is the Orsat analysis of the flue gas?
2. Pure carbon is burned inoxygen. The flue gas analysisis: 75% (n) CO2, 14% CO and11% O2. What was the %excess oxygen used
1. A hydrocarbon fuel is burned with
excess air. The Orsat analysis of the flue
gas shows 10.2% CO2, 1% CO, 8.4% O2 and
80.4% N2. Determine (a) atomic ratio of H
to C in the fuel (b) % excess air used.
4. The analysis of a flue gas from a fuel gas
containing no nitrogen is 4.62% CO2, 3.08%
CO, 8.91% O2 and 83.39% N2. Calculate a.
% excess air used b. If the fuel gas is a
mixture of methane and ethane, what is the
% of ethane in the fuel?