Flue Gas Desulphurisation
Also called: FGD · Topic: Geographical Issues: Pollution, Urban Waste, Slums and Land Degradation · NCERT: Beyond NCERT
Meaning
Flue Gas Desulphurisation (FGD) is a scrubber unit fitted to coal power plants. It removes sulphur dioxide (SO₂) from flue gas, the hot smoke that goes up the chimney. In the common type, the gas passes through a spray of wet limestone. The limestone reacts with the SO₂, which is taken out as gypsum before the smoke leaves the plant. This matters because SO₂ turns into acid in the air and falls as acid rain (rain with pH below about 5.6), which damages soils, lakes, forests and monuments. An FGD costs money to build and to run but makes no extra electricity. That cost can push up power tariffs (electricity prices), which is why plants keep asking for more time to fit one.
Example
India's environment ministry notified SO₂ limits for coal power plants in December 2015 and gave them until December 2017 to comply. The deadline has since been pushed back four times. The Ministry of Power has asked for a 20-year extension for 398 thermal plants. Fewer than 8% of India's coal power plants have fitted the recommended SO₂ control technology.
Don't confuse with
- Electrostatic precipitator (ESP): it uses electric charge to catch fly ash and other particles in chimney gas. It does not remove SO₂, which is a gas.
- Catalytic converter: it cleans exhaust gases from vehicles, not chimney smoke from power plants.