4 sump pit

Flue gas desulphurisation system

Flue gas desulphurisation system

In a flue gas desulphurisation system (FGD), sulphur compounds are removed from the exhaust emissions of fossil-fuelled power stations. This is done by means of an industrial process through the addition of absorbents. This can remove up to 95 % of the sulphur dioxide from the flue gas, since the current threshold value for SO 2 in the EU is 200 mg/Nm 3 (Nm 3 = normal cubic metre).

The wet process has become the main method of flue gas desulphurisation in large, fossil-fuelled power plants. In this method, the flue gases are steam-saturated with the absorbent in aqueous solution. Substances such as ammonia or sodium sulphite are used as absorbents; however the use of lime or limestone slurry (wet limestone scrubbing) is also widespread. The uncleaned flue gas is sprayed in a scrubber tower (absorber tower) with a mixture of water and limestone (scrubbing slurry), whereby most of the sulphur dioxide is bonded by chemical reaction.

After a number of chemical reactions, gypsum is finally produced in a suspension. After dewatering, this leaves gypsum with up to 10 % residual moisture, which provides a valuable product for the construction material industry.

The pumps used in the individual process stages are absorber circulating pumps (scrubber pumps, which - because of the high solids content and the aggressiveness of the fluid handled - are designed as non-clogging impeller pumps with special lining) and FGD auxiliary pumps (for lime and gypsum slurries in duplex materials).