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Flue Gas Emissions From Fossil Fuel Combustion




Flue gas emissions from fossil fuel combustion refers to the ). Since ambient air contains about 79 volume percent gaseous Nitrogen (N2)1, which is essentially non-combustible, the largest part of the Flue Gas from most fossil fuel combustion is uncombusted 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. This is closely followed in volume by water vapor (H20) created by the combustion of the hydrogen in the fuel with atmospheric oxygen. Much of the 'smoke' seen pouring from Flue Gas Stack s is this water vapor forming a cloud as it contacts cool air.

A typical flue gas from the combustion of fossil fuels will also contain some very small amounts of Nitrogen Oxide s (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 smoky appearance.

The steam generators in large Power Plant s and the process Furnace s in large Refineries , Petrochemical and Chemical Plant s, and Incinerator s 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 2
calculations. Air Dispersion Modeling Conversions and Formulas

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.

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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