Flue Gas Desulphurization (FGD)

• The Ministry of Environment, Forest and Climate Change (MoEFCC) has mandated the installation of Flue Gas Desulphurization (FGD) units in all coal-based Thermal Power Plants (TPPs) across India.
• The move aims to control Sulphur Dioxide (SO₂) emissions from power plants, which are a significant source of air pollution and acid rain.

What is FGD?

• Flue Gas Desulphurization (FGD) is a technology used to remove Sulphur Dioxide (SO₂) from exhaust flue gases of fossil-fuel power plants, especially coal-fired ones.
• It is part of air pollution control measures aimed at reducing harmful gas emissions and meeting environmental standards.

Efficiency:

• FGD systems can remove up to 90–95% of SO₂ emissions, thereby significantly reducing environmental and health risks.

Types of FGD Systems

Dry Sorbent Injection (DSI)

• How it works: A dry alkaline material, usually limestone or lime, is injected into the flue gas.
• Reaction: The sorbent reacts with SO₂ to form a solid by-product (calcium sulphate or sulphite).
• Used in: Smaller plants or retrofits due to lower cost and space requirements.

Wet Limestone-Based FGD

• How it works: Flue gas is passed through a slurry of limestone and water in an absorber tower.
• Chemical reaction: SO₂ reacts with calcium carbonate (CaCO₃) to form gypsum (CaSO₄·2H₂O).
• By-product utility: Gypsum produced can be used in the cement and construction industry.
• Most widely used FGD system globally.

Sea Water-Based FGD

• How it works: Flue gas is brought in contact with alkaline seawater, which absorbs SO₂.
• Neutralization: The acidic solution is naturally neutralized by carbonate ions in seawater.
• Used in: Coastal power plants due to proximity to seawater.
• Advantage: No need for limestone or other chemical reagents.

What is Sulphur Dioxide (SO₂)?

• SO₂ is a colourless, pungent-smelling gas, and a key air pollutant released mainly by coal combustion, industrial processes, and volcanic eruptions.
• It is a precursor to other sulphur oxides (SOₓ), which cause respiratory issues and environmental degradation.

Environmental & Health Impacts of SO₂

Health Hazards

• Short-term exposure can cause:
  • Irritation of the eyes, nose, throat, and lungs.
  • Breathing difficulties, especially in people with asthma or heart conditions.
• Long-term exposure may lead to:
  • Respiratory diseases, including bronchitis and reduced lung function.
  • Premature deaths in vulnerable populations (elderly, children).

Acid Rain

• SO₂ reacts with atmospheric water vapour to form sulphuric acid (H₂SO₄).
• This comes down as acid rain, damaging:
  • Soil fertility
  • Aquatic life in lakes and rivers
  • Buildings and heritage structures (especially those made of marble and limestone, e.g., Taj Mahal)

Particulate Matter (PM2.5)

• SO₂ contributes to the formation of secondary particulate matter (sulphates).
• These particles are fine enough to enter the bloodstream and cause severe health complications.

SO₂ Emissions in India – A Concern

• India is among the largest emitters of SO₂ globally, primarily due to coal-fired thermal power plants.
• Despite being essential for power generation, these plants significantly contribute to:
  • Urban air pollution
  • Smog
  • Public health crises in major cities

Why FGD is Crucial Now?

Compliance with Environment Norms

• In 2015, India notified stricter emission norms for thermal plants, including SO₂ limits.
• FGD is essential to meet these standards and avoid penalties.

Health Protection

• Reducing SO₂ reduces disease burden related to pollution.

Environmental Sustainability

• Reduces acid rain and ecosystem degradation.

International Commitments

• Supports India’s National Clean Air Programme (NCAP) and climate goals under the Paris Agreement.

Challenges in Implementation

• High Capital Cost: Installation and operation of FGD units are expensive.
• Technology Gap: Not all plants are technically equipped for retrofitting.
• Timeline Extensions: Deadlines have been pushed due to industry demands and COVID-19 disruptions.