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Flue gas emissions from fossil fuel combustion

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Flue gas emissions from fossil fuel combustion refers to the combustion product gas resulting from the burning of fossil fuels. Most fossil fuels are combusted with ambient air (as differentiated from combustion with pure oxygen).

Combustion productsEdit

Since ambient air contains about 79 volume percent gaseous nitrogen (N2), which is essentially non-combustible, the largest part of the flue gas from most fossil fuel combustion is unburnt nitrogen. The next largest part of the flue gas is carbon dioxide (CO2) which can be as much as 10 to 15 volume percent or more of the flue gas.

A typical flue gas from the combustion of fossil fuels will also contain some very small amounts of nitrogen oxides (NOx), sulfur dioxide (SO2) and particulate matter. The nitrogen oxides are derived from the nitrogen in the ambient air as well as from any nitrogen-containing compounds in the fossil fuel.

The sulfur dioxide is derived from any sulfur-containing compounds in the fuels. The particulate matter is composed of very small particles of solid materials and very small liquid droplets which give flue gases their black, smoky appearance.

Usage in power plantsEdit

The steam generators in large power plants and the process furnaces in large refineries and petrochemical plants burn very considerable amounts of fossil fuels and therefore emit large amounts of flue gas to the ambient atmosphere. The table below presents the total amounts of flue gas typically generated by the burning of fossil fuels such as natural gas, fuel oil and coal. The data in the table were obtained by stoichiometric calculations.

Comparitive generation of flue gasEdit

It is of interest to note that the total amount of flue gas generated by coal combustion is only 10 percent higher than the flue gas generated by natural gas combustion.

Flue gas generation dataEdit

EXHAUST FLUE GAS GENERATED BY COMBUSTION OF FOSSIL FUELS
(In SI metric units and in USA customary units)

Combustion Data Fuel Gas Fuel Oil Coal
Fuel properties:

Gross caloric value, MJ / Nm³
Gross heating value, Btu / scf
Gross caloric value, MJ / kg
Gross heating value, Btu / gallon
Gross caloric value, MJ / kg
Gross heating value, Btu / pound

Molecular weight
Specific gravity
Gravity, °API
Carbon / hydrogen ratio by weight

weight % carbon
weight % hydrogen
weight % oxygen
weight % sulfur
weight % nitrogen
weight % ash
weight % moisture

Combustion air:
Excess combustion air, %

Wet exhaust flue gas:
Amount of wet exhaust gas, Nm³/ GJ of fuel
Amount of wet exhaust gas, scf / 106 Btu of fuel
CO2 in wet exhaust gas, volume %
O2 in wet exhaust gas, volume %
Molecular weight of wet exhaust gas

Dry exhaust flue gas:
Amount of dry exhaust gas, Nm³/GJ of fuel
Amount of dry exhaust gas, scf / 106 Btu of fuel
CO2 in dry exhaust gas, volume %
O2 in dry exhaust gas, volume %
Molecular weight of dry exhaust gas

 

43.01
1,093
 
 
 
 

18
 
 
 

 
 
 
 
 
 
 

 
12

 
294.8
11,600
8.8
2.0
27.7

 
241.6
9,510
10.8
2.5
29.9

 

 
 
43.50
150,000
 
 

 
0.9626
15.5
8.1

 
 
 
 
 
 
 

 
15

 
303.1
11,930
12.4
2.6
29.0

 
269.3
10,600
14.0
2.9
30.4

 

 
 
 
 
25.92
11,150

 
 
 
 

61.2
4.3
7.4
3.9
1.2
12.0
10.0

 
20

 
323.1
12,714
13.7
3.4
29.5

 
293.6
11,554
15.0
3.7
30.7

Note:  Nm³ at 0 °C and 101.325 kPa, and scf at 60 °F and 14.696 psia.
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