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?