User:Milton Beychok/Sandbox
Flue gas is gas that exits to the atmosphere via a flue, which is a pipe, channel or chimney for conveying combustion product gases from a fireplace, oven, furnace, boiler or steam generator.
Flue gases are produced when coal, fuel oil, natural gas, wood or any other fuel is combusted in an industrial furnace or boiler, a steam-generator in a fossil fuel power plant or other large combustion source.
Flue gas composition
Flue gas is usually composed of carbon dioxide (CO2) and water vapor as well as nitrogen and excess oxygen remaining from the intake combustion air. It also contains a small percentage of pollutants such as particulate matter, carbon monoxide, nitrogen oxides and sulfur oxides. Typically, more than two-thirds of the flue gas is nitrogen.
| Combustion data | Fuel gas | Fuel oil | Coal |
|---|---|---|---|
| Fuel properties: | |||
| Gross heating value, MJ/m³ | 43.01 | ||
| Gross heating value, MJ/kg | 43.50 | 25.92 | |
| Molecular mass | 18 | ||
| Specific gravity | 0.9626 | ||
| Carbon/hydrogen ratio by weight | 8.1 | ||
| weight % carbon | 61.2 | ||
| weight % hydrogen | 4.3 | ||
| weight % oxygen | 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 combustion flue gas: | |||
| Wet combustion flue gas, m³/GJ of fuel | 294.8 | 303.1 | 323.1 |
| Molecular mass of wet combustion gas | 27.7 | 29.0 | 29.5 |
| Dry combustion flue gas: | |||
| Dry combustion flue gas, m³/GJ of fuel | 241.6 | 269.3 | 293.6 |
| Molecular mass of dry combustion gas | 29.9 | 30.4 | 30.7 |
| Notes: (1) Gas amounts (m³) are at 0 °C and 1 atm (2) Heating value = caloric value |
Flue gas treatment
At power plants, flue gas is often treated with a series of chemical processes and scrubbers, which remove pollutants. Electrostatic precipitators or fabric filters remove particulate matter and flue gas desulfurization captures the sulfur dioxide produced by burning fossil fuels, particularly coal.
Nitrogen oxides emissions are reduced either by modifications to the combustion process to prevent their formation, or by catalytic reaction with ammonia or urea. In either case, the aim is to produce nitrogen gas, rather than nitrogen oxides.
In the United States, there is also a rapid deployment of technologies to remove mercury from flue gas - typically by adsorption on sorbents or by capture in inert solids as part of the flue gas desulfurization product.
Technologies for the removal and capture of carbon dioxide from flue gases are now under active research and development as a means of reducing the emissions of so-called greenhouse gas.
See also
- Combustion
- Emission standard
- Exhaust gas
- Flue gas emissions from fossil fuel combustion
- Flue gas stacks
- Flue gas desulfurization (often referred to as FGD)
- Integrated Gasification Combined Cycle (often referred to as IGCC)
- Nitrogen oxides emission (often referred to as NOx)