Flue gas emissions from fossil fuel combustion


Flue gas emissions from fossil fuel combustion

Flue gas emissions from fossil fuel combustion refers to the combustion product gas resulting from the burning of fossil fuels [http://www.epa.gov/ttn/chief/ap42/index.html Compilation of Air Pollutant Emission Factors] ] . Most fossil fuels are combusted with ambient air (as differentiated from combustion with pure oxygen). Since ambient air contains about 79 volume percent gaseous nitrogen (N2) [cite book|author=Perry, R.H. and Green, D.W. (Editors)|title=Perry's Chemical Engineers' Handbook|edition=7th Edition|publisher=McGraw Hill|year=1997|id=ISBN ISBN 0-07-049841-5] , 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 (H2O) created by the combustion of the hydrogen in the fuel with atmospheric oxygen. Much of the 'smoke' seen pouring from flue gas stacks 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 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 smoky appearance.

The steam generators in large power plants and the process furnaces in large refineries, petrochemical and chemical plants, and incinerators 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 [cite book|author=Zumdahl, Steven S.|title=Chemical Principles|edition=5th Edition|publisher=Houghton Mifflin College Division|year=2005|id=ISBN 0-618-37206-7] calculations. [ [http://www.air-dispersion.com/formulas.html#combustion 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 DataFuel GasFuel OilCoal
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.

ee also

*AP 42 Compilation of Air Pollutant Emission Factors
*Emission standard
*Flue gas stacks
*Flue gas
*Flue gas desulfurization
*Gas stoichiometry
*Stoichiometry

References


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