Flue Gas Desulphurisation

19 Apr 2025

Flue Gas Desulphurisation

A recent National Institute of Advanced Studies (NIAS) study urges rollback of India’s 2015 mandate requiring all coal-fired plants to install Flue Gas Desulphurisation (FGD) units.

Rationale behind rolling back of the mandate

  • Low Sulphur Coal Usage: 92% of Indian coal has low sulphur (0.3%–0.5%), making universal FGD installation unnecessary, as per NIAS and IIT-Delhi data.
  • Environmental Trade-offs: FGDs would raise power and freshwater use, adding 69 million tonnes CO₂ (2025–30) while only cutting 17 million tonnes SO₂, worsening climate impact.
  • Cost-effective Alternatives Exist: Electrostatic precipitators by BHEL cost ₹25 lakh/MW (vs ₹1.2 crore/MW for FGD) and reduce particulate matter by 99%, offering better pollution control.

About Flue Gas Desulphurisation (FGD)

  • FGD : It  is a scrubbing method that utilizes an alkaline reagent, typically sodium- or calcium-based, to remove sulfur dioxide (SO₂) from the flue gas emissions of  coal-fired power plants.
  • Effectiveness: FGD can remove up to 95% of sulfur dioxide from flue gas, significantly reducing SO₂ emissions.
  • Flue Gas Composition: Also known as exhaust or stack gas, flue gas originates from combustion plants and contains a mix of pollutants, including particulate matter (dust), sulfur oxides, nitrogen oxides, and carbon monoxide.
  • It may contain pollutants such as particulates, sulfur dioxide, mercury, and carbon dioxide, but most flue gas consists of nitrogen oxides.
  • Untreated flue gas from power plants, industrial facilities, and other sources can significantly impact local and regional air quality.
  • Process Overview: In the scrubber or absorber tower, uncleaned flue gas is sprayed with a mixture of water and limestone (scrubbing slurry), which reacts with sulfur dioxide and binds it, preventing its release into the atmosphere.

Impact of Sulphur Dioxide in the Environment

  • Major Air Pollutant: Sulphur dioxide is a severe environmental pollutant, harmful to human, animal, and plant health.
  • Acid Rain Precursor: SO₂ contributes to acid rain, which harms forests, freshwaters, and soils.
    • Acid rain disrupts ecosystems by killing insects and aquatic life forms, damaging vegetation, and reducing biodiversity.
    • It causes damage to infrastructure and materials causing paint to peel and corrodes steel structures such as bridges.
    • Accelerates the weathering of stone buildings and statues, eroding cultural and historic landmarks

Electrostatic Precipitators vs FGD

Aspect Electrostatic Precipitators Flue Gas Desulphurisation (FGD)
Primary Purpose Electrostatic precipitators are designed to remove particulate matter (PM) from flue gases. Flue Gas Desulphurisation systems are used to remove sulphur dioxide (SO₂) from emissions.
Cost of Installation They cost approximately ₹25 lakh per megawatt (MW) to install. They are significantly more expensive, costing around ₹1.2 crore per megawatt (MW).
Efficiency of Pollution Control These systems can remove up to 99% of PM emissions, making them highly effective. FGDs reduce SO₂ emissions but have limited impact on other pollutants like PM.
Resource Consumption Electrostatic precipitators require less water and energy, making them more sustainable. FGDs consume more water and electricity, increasing overall environmental and operational load.
Relevance to Indian Coal They are highly relevant due to the high ash content of Indian coal. Their effectiveness is limited, as 92% of Indian coal has low sulphur content.

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