India’s push to curb air pollution is entering a critical new phase. At its center: Flue Gas Desulphurisation (FGD) technology—a process designed to slash sulphur dioxide (SO₂) emissions from coal-fired power plants. While FGD offers the promise of bluer skies and healthier communities, it comes with a new challenge: millions of tonnes of synthetic gypsum byproduct. To reap the benefits without spinning up fresh problems, India needs a policy rooted in environmental science, practical economics, and resource circularity.
Let’s break down the science, policy evolution, and what it means for India’s clean energy future.
Why SO₂ Control Matters
Sulphur dioxide is a harmful pollutant emitted primarily from coal combustion. High SO₂ levels:
- Contribute to acid rain, damaging crops and water bodies.
- Worsen fine particulate pollution (PM2.5), driving up rates of asthma, respiratory and cardiac illness.
- Harm infrastructure, soil, and public health.
A strong, enforceable SO₂ policy has the potential for profound societal health benefits.
How Does FGD Work? The Basics
FGD systems scrub SO₂ from flue gases before they enter the atmosphere. The most common technology in India:
Wet limestone scrubbing: Flue gases mix with a limestone slurry, which reacts with SO₂ to create calcium sulfite. Oxidation produces gypsum (CaSO₄·2H₂O) as a byproduct.
Other tech variants include dry sorbent injection, seawater FGD (for coastal plants), and lime/ammonia-based systems.
India’s SO₂ Standards and Evolving Policy
2015: Strict New Norms
MoEFCC introduced stringent SO₂ caps for coal plants—requiring universal FGD installation by 2017.
Norms: 100–600 mg/Nm³, depending on plant age and capacity. Goal: Remove 90–95% of SO₂ from flue gases. powerline
The Struggles and Realities
Reasons: high capital and operating costs, equipment shortages, inconsistencies in coal quality, and pandemic-related delays. powerline
Updated 2025 policy: Only plants near polluted cities or populations >1 million (Category A/B) must install FGDs by 2027/28. Many rural/smaller plants are exempt if ambient SO₂ is within limits. infra.economictimes
Analysis: India’s move mirrors global trends—avoiding “one-size-fits-all” mandates and focusing resources where health impacts are most acute.
The Byproduct Challenge: Managing FGD Gypsum
FGD tech transforms SO₂ into synthetic gypsum. While gypsum is valuable for cement and soil reclamation, the sheer scale from Indian plants poses unique management concerns:
Each large plant can generate thousands of tonnes of FGD gypsum annually. nature
Markets (e.g., cement, soil amendment) may not absorb all the output—raising questions about storage, safe disposal, and environmental risk.
Proper characterization and handling guidelines are needed to ensure heavy metals or contaminants do not leach into the environment.
Circular Opportunity: Industry and agriculture can use FGD gypsum to reclaim sodic soils—supporting sustainability and India’s land restoration targets. cpcb
Environmental Trade-offs and Cost-Benefit Realities
Pros:
Drastic SO₂ reduction where it matters most, improving air and health outcomes.
Gypsum reuse can advance circular economy goals.
Cons:
High installation costs—anywhere from Rs. 3.9 million to Rs. 14 million per MW—translate into higher electricity tariffs for consumers.
FGDs themselves consume energy and water (~14.4 mt more CO₂ nationally), offsetting some climate benefits.
Without robust gypsum markets, plants may face storage/disposal costs and land footprint concerns.
A blanket mandate could impose unnecessary cost, carbon, and infrastructure burdens for limited health gain in less-polluted regions.
What Does the Science Say?
Recent air quality research suggests:
Not all regions require uniform FGD rollout. Local air SO₂ readings determine risk, making targeted pollution control the scientifically sound policy.
Policy flexibility is crucial—in line with US, EU, and China, which have moved to targeted, rather than nationwide, mandates.
Guidelines for FGD gypsum use, monitoring, and disposal are evolving, aiming to minimize risks while maximizing resource recovery.
- Policy Recommendations: Science Meets Pragmatism
Targeted SO₂ Controls: Prioritize FGDs in densely populated, polluted, or sensitive regions.
Gypsum Circularity: Strengthen cement and agro-industrial uptake of FGD gypsum, backed by quality standards and environmental monitoring.
Economic Sensibility: Align timelines and investment with plant age, expected lifespan, and actual pollution risk.
Adaptive Regulation: Regularly review guidelines based on technological advances and market shifts.
Public Transparency: Clear reporting of emissions, gypsum output, and reuse/disposal data.
Takeaway: Getting SO₂ Policy Right Means Science—and Practicality
India’s approach to FGD and SO₂ emission control is evolving: from one-size-fits-all to targeted, impact-based regulation. The goal must remain crystal clear—cleaner air, sustainable industry, and affordable energy. Getting there requires not only deploying the right technology but also managing byproducts, supporting circular solutions, and crafting adaptive, locally intelligent policy. That’s the kind of green transition India deserves.
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