Pollution Board to decide on future of FGD units: Minister

• This follows an April 2025 recommendation by a panel led by Principal Scientific Adviser Ajay Sood to do away with mandatory FGD installations.
• Currently, 92% of India’s 600 TPPs lack FGDs. If the recommendation is accepted, around 80% could be exempt from installing them.
• FGDs are used to reduce sulphur dioxide (SO₂) emissions, which contribute to air pollution and respiratory issues but also form sulphate aerosols that may slightly offset global warming.
• cited studies by CSIR and IIT Delhi, stating SO₂ emissions from Indian TPPs contribute less than 5% to human health impacts, suggesting some atmospheric sulphates may be beneficial in climate moderation.
• The government has extended deadlines for FGD compliance three times since 2017, most recently to 2027–2030.

Flue Gas and Flue Gas Desulphurisation (FGD)

(Relevant for UPSC Prelims and Mains – Environment, Pollution Control Technologies, Energy)

What is Flue Gas?

• Flue gas (exhaust or stack gas) is the by-product of fossil fuel combustion in industrial plants and power stations.
• It is expelled through chimneys or ducts (flues) and typically contains:
• Carbon dioxide (CO₂)
• Carbon monoxide (CO)
• Sulphur dioxide (SO₂)
• Nitrogen oxides (NO & NO₂)
• Water vapour, particulate matter, and trace pollutants
• The exact composition varies with fuel type and combustion conditions.

Importance of Flue Gas Analysis:

• Helps optimize air-to-fuel ratio for energy efficiency.
• Enhances burner efficiency, reducing fuel consumption.
• Essential for monitoring pollutant levels (SO₂, NOx) to comply with environmental standards.
• Prevents corrosion and protects equipment by tracking acid-forming emissions.

What is Flue Gas Desulphurisation (FGD)?

• FGD is a pollution control technology used to remove sulphur dioxide (SO₂) from flue gases.
• Primary goal: Reduce acid rain, improve air quality, and meet emission regulations.
• FGD can remove up to 90–95% of SO₂ emissions in coal-fired power plants.

FGD Process:

• Involves spraying uncleaned flue gas with an absorbent slurry (usually lime or limestone with water) in a scrubber tower.
• Chemical reaction bonds SO₂ with the slurry, removing up to 95% of the gas.
• Other absorbents like ammonia or sodium sulphite may also be used.

FGD Methods:

1. Wet scrubbing:
• Uses limestone or lime slurry (or seawater) in scrubber towers to chemically react with and remove SO₂.
2. Spray-dry scrubbing:
• Similar to wet scrubbing but uses atomised sorbent slurries sprayed into a hot flue gas stream.
3. Dry sorbent injection:
• Involves injecting powdered hydrated lime or other sorbents into exhaust ducts to capture SO₂ and SO₃.
4. Wet sulfuric acid process:
• Recovers sulphur as commercial-grade sulfuric acid.
5. SNOX process:
• Simultaneously removes sulphur dioxide, nitrogen oxides, and particulates from flue gas without using absorbents.

FAQs:

• Q1: What is flue gas?
  → Gas emitted from combustion of fossil fuels in power or industrial plants.
• Q2: Why is flue gas analysis important?
  → For improving combustion efficiency and meeting emission regulations.
• Q3: Why is it called 'flue' gas?
  → Because it exits through ‘flues’—industrial ducts or chimneys.