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Source: The Hindu

Context

A panel of specialists, led by Principal Scientific Advisor Ajay Sood, has proposed that India repeal the 10-year-old law requiring all coal-fired thermal power plants to install Flue Gas Desulphurisation (FGD) units.

What is flue gas desulphurization (FGD)?

• It is a method that removes sulfur compounds from exhaust fumes.
• FGD uses absorbents to remove up to 95% of sulphur dioxide from flue gases.
• Absorbents include ammonia and sodium sulphite. Lime or limestone slurry (wet limestone washing) is also commonly employed.
• The dirty flue gas is sprayed in a scrubber tower (absorber tower) with a mixture of water and limestone (scrubbing slurry), which binds most of the sulphur dioxide by chemical reaction.

What is Flue Gas?

• Flue gas, often known as exhaust gas or stack gas, is the gas discharged from combustion plants. This is a byproduct of burning fossil fuels.
• Flue gas is a mixture of gases, including carbon monoxide (CO), carbon dioxide (CO2), water vapor, nitrogen oxides (NO & NO2), sulfur dioxide (SO2), trace contaminants, and sometimes particulate debris.
• This mixture can escape through lengthy pipes, chimneys, and ducts known as 'flues', resulting in the word 'flue gas'.
• The composition of flue gas varies based on fuel type and combustion conditions.
• Pollutants need to be eliminated before being released into the atmosphere.

Why should India cancel the 10-year-old rule (the 2015 FGD mandate)?

• High Installation Cost Burden: Installing FGD units costs approximately ₹1.2 crore per MW and can drastically increase power generation costs and energy bills. For example, adding 97,000 MW of capacity will cost around ₹97,000 crore, making power less affordable.
• Delayed and Poor Implementation: Despite the 2015 requirement, compliance has been poor—only 39 of 537 plants had FGDs installed by 2025.  Repeated deadline extensions (up to 2029) demonstrate a lack of feasibility and institutional capacity.
• Limited Local Air Quality Impact in Some Areas: In some areas, SO₂ emissions from TPPs have no impact on PM2.5 levels.  For example, in Delhi, the majority of air pollution is caused by other sources such as cars and construction; therefore, FGDs at distant facilities may provide no help.

Rationale Behind the Rolling Back of the Mandate

• The NIAS and IIT-Delhi data show that 92% of Indian coal has low sulphur (0.3%-0.5%), eliminating the need for ubiquitous FGD installation.
• Environmental trade-offs: FGDs will increase power and freshwater use, adding 69 million tonnes CO₂ (2025-30) while only reducing 17 million tonnes SO₂, exacerbating the climate impact.
• Cost-effective alternatives Exist: BHEL's electrostatic precipitators cost ₹25 lakh/MW, compared to ₹1.2 crore/MW for FGD. They eliminate particulate matter by 99%, providing greater pollution management.

Flue Gas Desulphurisation (FGD) in Thermal Power Plants

How FGD Reduces SO₂ Emissions

Chemical Neutralisation Reaction:

• FGD units deploy alkaline substances like limestone or lime to neutralize acidic SO₂ in flue gases.
  
  
• Example: In wet limestone FGD, SO₂ reacts with limestone slurry to form gypsum (CaSO₄·2H₂O), a non-toxic industrial byproduct.
  

Efficient Scrubbing Techniques:

• Techniques such as wet scrubbers and dry sorbent injection are used to physically remove SO₂ before it enters the atmosphere.
  
  
• Example: In dry sorbent injection, powdered lime is sprayed into the flue gas stream, binding with SO₂, and the residue is captured using filters.
  

Controlled Emission Discharge:

• FGD ensures that treated flue gas released from power plants contains significantly lower SO₂ levels, aligning with environmental regulations.
  
  
• Example: Sea water FGD is used in coastal power plants, where sea water absorbs SO₂ and is later treated before discharge.

Status of FGD Installation in India (as of 2025)

Low Overall Commissioning

• Out of 537 thermal power units, only 39 units (about 19,430 MW capacity) have commissioned FGD systems.
  
  
• This represents only ~11% of the total required capacity.
  
  
• Example: In Delhi NCR, just 13 out of 35 units within 300 km have installed FGDs, despite being in a high-pollution zone.
  

Stalled Projects and Delays

• Contracts awarded: For 238 units (~105,200 MW capacity).
  
  
• Tendering stage: About 139 units (~42,847 MW) are still pending.
  
  
• Several projects are stalled due to regulatory and logistical challenges.
  
  
• Example: Some plants near Delhi may take up to 36 months for completion due to various administrative bottlenecks.
  

Repeated Deadline Extensions

• Original compliance deadline: 2017, now extended to 2024, and further to 2026–2029, based on plant location and category.
  
  
• Example: The Ministry of Environment has extended deadlines for Delhi NCR plants without strict justification, raising concerns over enforcement and accountability.

Practice Question: Q. Discuss global warming and mention its effects on the global climate. Explain the control measures to bring down the level of greenhouse gases which cause global warming, in the light of the Kyoto Protocol, 1997.