Читать книгу Encyclopedia of Renewable Energy - James Speight G., James G. Speight - Страница 47

Flue gas desulfurization (FGD) is the technology used for removing sulfur dioxide (SO₂) from the exhaust flue gases in power plants that burn coal to produce steam for the steam turbines which, in turn, drive the electricity generators. Sulfur dioxide is responsible for acid rain formation. Tall flue gas stacks disperse the emissions by diluting the pollutants in ambient air and transporting them to other regions. However, such practices do not always remove the pollutants.

Advanced flue-gas desulfurization processes remove acid gas from combustion systems burning coal without expensive scrubbers. Emissions are piped into an absorber, where the acid gases react with an absorbing solution (such as a mixture of lime, water, and oxygen). In the process, the gas is usually passed through a particulate removal unit (such as an electrostatic precipitator) after which the flue gas is increased in pressure and then cooled from approximately 130°C (265°F) to 80°C (175°F). It enters the lowest part of the absorber and is further cooled by water used to wash the inlet duct to prevent a buildup of solids.

The main sulfur dioxide absorption process occurs as the gas is scrubbed by a recirculating limestone slurry. This is taken from the bottom of the absorber and is sprayed downwards from nozzles arranged at five separate levels in the absorber tower. As a result of the process chemistry, the recirculating slurry becomes predominantly gypsum (CaSO₄) and a portion is continuously pumped away for gypsum separation and the removal of water using a hydrocyclone system. A wastewater treatment plant ensures that any water from the flue gas desulfurization process returned to the environment meets quality standards set by the regulatory authority.

See also: Flue Gas, Gas Cleaning, Gas Processing, Gas Treating.