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Flue gas emissions from fossil fuel combustion

Flue gas emissions from fossil fuel combustion

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Flue-gas emissions from fossil-fuel combustion refers to the combustion
Combustion
Combustion or burning is the sequence of exothermic chemical reactions between a fuel and an oxidant accompanied by the production of heat and conversion of chemical species. The release of heat can result in the production of light in the form of either glowing or a flame...

 product gas resulting from the much as 10 to 25 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 stack
Flue gas stack
A flue-gas stack is a type of chimney, a vertical pipe, channel or similar structure through which combustion product gases called flue gases are exhausted to the outside air. Flue gases are produced when coal, oil, natural gas, wood or any other fuel is combusted in an industrial furnace, a power...

s may in fact be water vapor forming a cloud as it contacts cool air.

A typical flue gas from the combustion of fossil fuels also contains nitrogen oxide
Nitrogen oxide
Nitrogen oxide can refer to a binary compound of oxygen and nitrogen, or a mixture of such compounds:* Nitric oxide, also known as nitrogen monoxide, , nitrogen oxide* Nitrogen dioxide , nitrogen oxide...

s (NOx), sulfur dioxide
Sulfur dioxide
Sulfur dioxide is the chemical compound with the formula . It is released by volcanoes and in various industrial processes. Since coal and petroleum often contain sulfur compounds, their combustion generates sulfur dioxide unless the sulfur compounds are removed before burning the fuel...

 (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
Sulfur
Sulfur or sulphur is the chemical element with atomic number 16. In the periodic table it is represented by the symbol S. It is an abundant, multivalent non-metal. Under normal conditions, sulfur atoms form cyclic octatomic molecules with chemical formula S8. Elemental sulfur is a bright yellow...

-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
Oil refinery
An oil refinery or petroleum refinery is an industrial process plant where crude oil is processed and refined into more useful petroleum products, such as gasoline, diesel fuel, asphalt base, heating oil, kerosene, and liquefied petroleum gas...

, petrochemical
Petrochemical
Petrochemicals are chemical products derived from petroleum. Some chemical compounds made from petroleum are also obtained from other fossil fuels, such as coal or natural gas, or renewable sources such as corn or sugar cane....

 and chemical plant
Chemical plant
A chemical plant is an industrial process plant that manufactures chemicals, usually on a large scale. The general objective of a chemical plant is to create new material wealth via the chemical or biological transformation and or separation of materials. Chemical plants use special equipment,...

s, and incinerators burn large amounts of fossil fuels and therefore emit large amounts of flue gas to the 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. Data in the table were obtained by stoichiometric
calculations.

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/m³ 43.01
Gross heating value, Btu/scf 1,093
Gross caloric value, MJ/kg 43.50
Gross heating value, Btu/gal 150,000
Gross caloric value, MJ/kg 25.92
Gross heating value, Btu/lb 11,150
Molecular weight
Molecular mass
The molecular mass of a substance is the mass of one molecule of that substance, in unified atomic mass unit u...

18
Specific gravity
Relative density
Relative density, or specific gravity, is the ratio of the density of a substance to the density of a given reference material. Specific gravity usually means relative density with respect to water...

 
0.9626
Gravity
API gravity
The American Petroleum Institute gravity, or API gravity, is a measure of how heavy or light a petroleum liquid is compared to water. If its API gravity is greater than 10, it is lighter and floats on water; if less than 10, it is heavier and sinks...

, °API
15.5
Carbon
Carbon
Carbon is the chemical element with symbol C and atomic number 6. As a member of group 14 on the periodic table, it is nonmetallic and tetravalent—making four electrons available to form covalent chemical bonds...

/hydrogen
Hydrogen
Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...

 ratio by weight
8.1
weight % carbon 61.2
weight % hydrogen 4.3
weight % oxygen
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...

 
7.4
weight % sulfur 3.9
weight % nitrogen 1.2
weight % ash  12.0
weight % moisture  10.0
Combustion air:
Excess combustion air, % 12 15 20
Wet exhaust flue gas:
Amount of wet exhaust gas, m³/GJ of fuel 294.8 303.1 323.1
Amount of wet exhaust gas, scf/106 Btu of fuel 11,600 11,930 12,714
CO2 in wet exhaust gas, volume % 8.8 12.4 13.7
O2 in wet exhaust gas, volume % 2.0 2.6 3.4
Molecular weight of wet exhaust gas 27.7 29.0 29.5
Dry exhaust flue gas:
Amount of dry exhaust gas, m³/GJ of fuel 241.6 269.3 293.6
Amount of dry exhaust gas, scf/106 Btu of fuel 9,510 10,600 11,554
CO2 in dry exhaust gas, volume % 10.8 14.0 15.0
O2 in dry exhaust gas, volume % 2.5 2.9 3.7
Molecular weight of dry exhaust gas 29.9 30.4 30.7
Note:  m³ are standard cubic meters at 0 °C and 101.325 kPa, and scf is standard cubic feet at 60 °F and 14.696 psia.

See also

  • AP 42 Compilation of Air Pollutant Emission Factors
    AP 42 Compilation of Air Pollutant Emission Factors
    The AP 42 Compilation of Air Pollutant Emission Factors, was first published by the U.S. Public Health Service in 1968. In 1972, it was revised and issued as the second edition by the U.S. Environmental Protection Agency . In 1985, the subsequent fourth edition was split into two volumes...

  • Emission standard
    Emission standard
    Emission standards are requirements that set specific limits to the amount of pollutants that can be released into the environment. Many emissions standards focus on regulating pollutants released by automobiles and other powered vehicles but they can also regulate emissions from industry, power...

  • Flue gas stacks
  • Flue gas
    Flue gas
    Flue gas is the gas exiting to the atmosphere via a flue, which is a pipe or channel for conveying exhaust gases from a fireplace, oven, furnace, boiler or steam generator. Quite often, the flue gas refers to the combustion exhaust gas produced at power plants...

  • Flue gas desulfurization
    Flue gas desulfurization
    Sulfur dioxide is one of the elements forming acid rain. Tall flue-gas stacks disperse emissions by diluting the pollutants in ambient air and transporting them to other regions....

  • Gas stoichiometry
  • Stoichiometry
    Stoichiometry
    Stoichiometry is a branch of chemistry that deals with the relative quantities of reactants and products in chemical reactions. In a balanced chemical reaction, the relations among quantities of reactants and products typically form a ratio of whole numbers...


External links

  • Article on Flue Gas Treatment including desulfurization and the removal of hydrogen chloride, sulphur trioxide, and other heavy metal particles such as mercury.