What is Flue Gas De-sulphurisation (FGD)?

About Flue Gas De-sulphurisation (FGD)

• It is a technology to eliminate sulfur dioxide (SO2) from exhaust emissions.
• Where does Sulfur Dioxide come from?
  • Fossil fuels such as coal and oil often contain high amounts of sulfur, and when these fuels are burned, around 95% or more of the sulfur is converted to sulfur dioxide (SO2), which is emitted as flue gas.
  • Sulfur dioxide in itself is a major air pollutant which impacts all life. It is also a precursor of acid rain, which has significant adverse impacts on forests, freshwaters, and soils, in turn killing insect and aquatic life forms, causing paint to peel, corrosion of steel structures such as bridges, and weathering of stone buildings and statues.
  • The removal of sulfur dioxide is critical to establishing a safe and clean environment where toxic emissions are kept to a safe level.
• FGD Process:
  • FGD is done through the addition of absorbents, which can remove up to 95% of the sulphur dioxide from the flue gas.
  • 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.

Q1) What is limestone?

Limestone is a sedimentary rock primarily composed of calcium carbonate (CaCO3) in the form of mineral calcite or aragonite. It is one of the most common and widely distributed rocks on Earth, with a wide range of uses in various industries and natural settings.

Source: Installation of Flue Gas De-sulphurisation (FGD) equipment in thermal power plants