Flue gas desulphurisation units

Prelims: Current events of National and International Importance

Why in News?

The committee of experts has recommended that India do away with a decade-long policy of mandating Flue Gas Desulphurisation (FGD) units in all coal-fired thermal power plants (TPPs).

• Flue Gas - Flue gas is emitted as a byproduct of combustion of fossil fuels.
• It mainly contains pollutants such as carbon dioxide (CO2), sulphur dioxide (SO2), nitrogen oxides, particulate matter, etc.
• FGD units specifically target the SO2 emissions in flue gas.
• SO2 is an acidic gas, and is usually treated with a basic compound in the FGD unit to neutralise the pollutant.
• Types of FDGs - Dry sorbent injection, wet limestone treatment, and using seawater to remove SO2.
• The dry sorbent injection method involves adding a powdered sorbent like limestone to the flue gas, where it reacts with SO2.
• The resultant compound can be removed by using an electrostatic precipitator, or a fabric filter.
• The wet limestone treatment method also uses limestone to remove SO2, but instead of using it in a powdered form, it uses a limestone slurry.
• Passing SO2 through this slurry results in the formation of gypsum, which is a stable compound and has wide applications in industries like construction.
• This is the commonly used technology, and has very high efficiency.
• Sea water treatment is used in plants located near coastal areas.
• Sea water first absorbs SO2 from flue gas, and then the water is treated to make it suitable to be discharged back into the sea.

• Status of FGD units in India - In 2015, the Union Environment Ministry issued a policy that mandated all 537 coal-fired TPPs in India to install FGD units to reduce SO2 emissions.
• Further, it has extended to 2027, 2028, and 2029, respectively, depending on the category of the thermal power plant. It takes around 2 years to install an FGD unit.
• Alternative to FGD - There is no alternative to FGDs itself to remove SO2 that is released from the burning of coal.
• Washing of coal does not remove the sulphur that is embedded within the physical structure of the coal.

Reference

The Hindu | What are flue gas desulphurisation units?