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What are flue gas desulphurisation units?

Introduction:

  • FGDs are pollution control devices used in coal-fired thermal power plants (TPPs) to remove sulphur dioxide (SO) from flue gas.
  • SO₂ is produced during the combustion of sulphur-rich fossil fuels like coal.
  • FGD units neutralise acidic SO₂ using basic compounds like limestone.

Relevance : GS 3(Environment and Ecology)

Common Types of FGD Technologies

  1. Dry Sorbent Injection:
    1. Uses powdered limestone or other sorbents.
    2. Reacts with SO₂ in flue gas and is filtered out using fabric filters or electrostatic precipitators.
  • Wet Limestone Scrubbing (most common):
    • Uses limestone slurry to absorb SO₂, forming gypsum as a byproduct.
    • High efficiency; gypsum has commercial uses.
  • Seawater FGD:
    • Used in coastal plants.
    • SO₂ is absorbed by seawater, which is then treated before being discharged.

Why are SO₂ Emissions Harmful?

  • Greenhouse gas contributing to global warming.
  • Causes respiratory illnesses and worsens air quality.
  • Converts into secondary PM2.5, a major pollutant.
    • ~15% of India’s ambient PM2.5 is from coal combustion.
    • Of that, 80% is from SO₂-derived secondary particles.

Status of FGD Compliance in India

  • 2015: Government mandated FGDs in all 537 coal-fired TPPs.
  • Deadlines were repeatedly postponed (2018 → 2027–29).
  • As of April 2025, only 39 out of 537 plants had installed FGDs.
  • December 2024: Deadline further extended by three years.
  • April 2025: Committee led by PSA Ajay Sood recommended rollback of the FGD mandate.

Why is FGD Implementation Contentious?

  • High capital cost: ₹1.2 crore/MW → ₹97,000 crore for planned 97,000 MW addition.
  • Potential tariff hike of ₹0.72 per kWh (mostly fixed costs).
  • Government concerns: balancing health, affordability, and energy expansion.

Expert Opinions on FGD Rollback

  • Critics warn that skipping FGD:
    • Compromises clean air goals.
    • Undermines public health.
  • FGDs are essential for reducing SO₂ and indirectly PM2.5.
  • Tariff impact is manageable and largely predictable.

Is There Any Alternative to FGDs?

  • No effective alternative exists for SO₂ removal from flue gases.
  • Dr. Ganesan: FGDs are urgent and unavoidable for compliance.

Conclusion

  • FGDs are technically essential but financially challenging.
  • India must weigh short-term costs against long-term health and environmental gains.
  • Delay in FGD installation risks worsening air pollution, especially from coal-based power generation.

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