Recently, the Environment Ministry has exempted the majority of India’s thermal power plants from installing Flue Gas Desulphurisation (FGD) systems, which are designed to cut sulphur dioxide (SO2) emissions.

• The decision impacts approximately 180 thermal power plants and 600 units across India.
  • SO2 is a by-product of coal combustion in power plants and contributes to air pollution by creating secondary particulate matter.
• 2015 Policy Mandates: The Indian Environment Ministry mandated FGD installation in all coal-fired plants by 2018, with multiple deadline extensions.
  • Categories of Thermal Power Plants (TPPs):
    • Category A (11% of units): Located within a 10 km radius of the National Capital Region (NCR) or cities with a population of over 1 million.
      1. FGD installation deadline: December 30, 2027.
    • Category B (11% of units): Located near critically polluted areas (CPA) or non-attainment cities (NAC) (those not meeting National Ambient Air Quality Standards (NAAQS) for five years).
      1. Decision on FGD installation will depend on the Expert Appraisal Committee (EAC).
      2. FGD installation deadline: December 30, 2028.
    • Category C (78% of units): Exempted from installing FGD systems.

Rationale for exemption

• Low Sulfur Content of Indian Coal: Indian coal has a low sulfur content (0.3%-0.5%). 
• Minimal Impact on Public Health: SO₂ levels are below permissible limits in most areas. 
• High Costs: Installing FGDs is expensive (~₹1.2 crore per MW). 
  • Total cost for installing FGDs in 97,000 MW of new capacity could reach ₹116,400 crore.
• Electricity Tariff: FGDs can add up to ₹0.72 per kWh to electricity tariffs.
  • Over 80% of this increase in tariffs is due to the FGD technology’s fixed costs, and variable cost increase is in all cases less than ₹0.1 per kWh.
• Limited Vendor Capacity: There are few vendors in India able to install FGDs. 
  • This has caused delays in meeting previous deadlines.
• Alternative Pollution Control Focus: The government is focusing on particulate matter (PM). 
  • Electrostatic precipitators (ESPs) are cheaper and more effective for controlling PM.
• CO₂ Emissions and Climate Concerns: FGDs could lead to an increase in CO₂ emissions (69 million tons by 2030). 
  • This may worsen global warming, despite reducing SO₂ emissions.
• Exemption for Majority of Plants: 80% of plants are exempt, especially those away from major population centers. 
  • The focus is on high-risk areas like large cities and polluted zones.

What is Flue Gas Desulphurisation (FGD)?

• Flue gas is emitted as a byproduct from the combustion of fossil fuels like coal.
  • FGD units target the reduction of sulphur dioxide (SO2), an acidic gas that is harmful to both public health and the environment.

• • SO2 reacts with basic compounds in FGD systems to neutralize and remove it from the flue gas.
• How it Works: FGD systems typically involve chemical processes where absorbents such as limestone are used to react with SO₂ in the flue gas. 
  • The SO₂ is neutralized and removed from the exhaust.
• Effectiveness: FGD systems can remove up to 95% of SO₂ from flue gas, making them highly effective in controlling SO₂ emissions.

Types of FGD Systems

• Dry Sorbent Injection: A powdered sorbent (like limestone) is added to the flue gas, which reacts with SO2. The resulting compound is removed by electrostatic precipitators or fabric filters.
• Wet Limestone Treatment: A limestone slurry is used to absorb SO2, forming gypsum, which has industrial applications (e.g., construction).
• Sea Water Treatment: Used in coastal plants, where sea water absorbs SO2, and is then treated before being returned to the sea.

Impact of SO₂ Emissions on Global Warming

• Cooling Effect on the Atmosphere: Sulphur dioxide (SO₂) has a cooling effect on the atmosphere. When released into the air, SO₂ can react with water vapor and other compounds to form sulphate aerosols.
  • These aerosols reflect sunlight back into space, reducing the amount of solar radiation reaching the Earth’s surface, which can temporarily lower temperatures.
• Short-Lived Pollutant: SO₂ is a short-lived pollutant in the atmosphere. 
  • The cooling effect it causes lasts only for a short time, typically a few days to weeks, as sulphate aerosols fall out of the atmosphere relatively quickly.
  • Despite its temporary cooling effect, SO₂ does not offer a long-term solution to global warming, as it is eventually removed from the atmosphere.
• Contribution to Climate Change: While SO₂ helps cool the planet in the short term, its long-term effects are problematic. 
  • The overall goal of controlling global warming requires reducing greenhouse gas emissions, primarily CO₂, which have a far longer atmospheric lifetime.
  • The CO₂ released from the burning of fossil fuels continues to warm the planet for decades, even centuries, after emission, while the cooling effect of SO₂ diminishes rapidly.
• Trade-Off with CO₂ Emissions: The installation of Flue Gas Desulphurisation (FGD) systems to reduce SO₂ emissions can result in increased CO₂ emissions. 
  • FGDs consume energy, which may lead to higher carbon emissions from the additional fuel needed to run the systems.
  • According to expert committees, installing FGDs in all power plants could add 69 million tons of CO₂ between 2025-2030. 
• Impact on Climate Models: SO₂’s cooling effect is often considered in climate models, but its short lifespan makes it an unreliable solution for mitigating long-term climate change.
  • Reducing SO₂ emissions without a corresponding reduction in CO₂ emissions could lead to an overall net warming effect, as the temporary cooling influence of SO₂ is overshadowed by the persistent warming caused by CO₂.
• Policy Implications: The global warming effect of SO₂ emissions underscores the need for a balanced approach in climate policies. 
  • While reducing SO₂ is crucial for improving air quality and public health, it must be done in a way that does not inadvertently worsen climate change through higher CO₂ emissions.

Impact of Sulphur Dioxide (SO₂) on the Environment and Health

Environmental Impact

• Acid Rain: SO₂ reacts with water vapor in the atmosphere to form sulfuric acid, a major component of acid rain. Acid rain severely impacts ecosystems by:
  • Acidifying aquatic ecosystems like lakes, rivers, and wetlands, which harms aquatic life and reduces biodiversity.
  • Damaging vegetation and forests by weakening plant structures and depleting soil nutrients like calcium and magnesium.
  • Corroding buildings and infrastructure, leading to increased maintenance costs.
• Particulate Matter Formation: SO₂ can react with other atmospheric compounds to form sulphates. 
  • Secondary pollutants from coal combustion contribute to 15% of India’s ambient PM2.5 pollution, a significant public health concern.
• Reduced Visibility: The formation of sulphates from SO₂ contributes to haze in the atmosphere, reducing visibility, especially in urban areas with high pollution levels.

Health Impact

• Respiratory Issues: SO₂ is a strong irritant to the respiratory system. Short-term exposure can cause:
  • Coughing, wheezing, and shortness of breath.
  • Exacerbation of asthma and chronic bronchitis.
  • Increased risk of lung infections and other respiratory diseases, especially in children and elderly individuals.
• Cardiovascular Problems: Long-term exposure to elevated SO₂ levels can increase the risk of cardiovascular diseases, leading to more frequent hospitalizations and potentially higher mortality rates.
• Vulnerable Groups: People with existing lung diseases, children, and elderly individuals are more susceptible to SO₂ exposure and its harmful effects.

Alternatives to FGD

• Electrostatic Precipitators (ESPs): Primarily used to control particulate matter (PM) emissions by collecting fine particles from flue gases.
  • Cost-effective and widely used for PM2.5 control. They can be used alongside other technologies to reduce overall pollution.
• Low-Sulfur Fuels: Instead of burning high-sulfur coal, plants can switch to low-sulfur coal or natural gas. This reduces SO₂ emissions at the source.
  • Reduces the need for extensive pollution control equipment like FGDs.
• Fluidized Bed Combustion: A combustion process where limestone is mixed with coal in the combustion chamber. This reacts with SO₂ to form gypsum.
  • Pre-combustion method for SO₂ removal, which can reduce the amount of SO₂ released in the first place.
• Ammonia Scrubbing: Involves the use of ammonia to absorb and neutralize SO₂ from flue gases.
  • This system can be effective in smaller or older plants, where installing a large-scale FGD may be economically unfeasible.
• Advanced Sorbent Injection: Powdered sorbents such as limestone or sodium-based compounds are injected into the flue gas stream to absorb SO₂.
  • This method is less expensive compared to full-scale FGD systems and can be used to target specific emissions.
• Wet Scrubbing with Other Absorbents: Apart from limestone, other chemical absorbents like ammonium hydroxide or sodium hydroxide can be used in wet scrubbers to capture SO₂.
  • More flexible and potentially cheaper compared to traditional wet limestone scrubbing.
• Oxy-fuel Combustion: This technology involves burning coal in pure oxygen rather than air, which results in higher CO₂ concentrations and simplifies the separation of SO₂.
  • Potential for better carbon capture alongside reduced SO₂ emissions.
• Renewable Energy Transition: A longer-term solution is transitioning from coal to renewable energy sources such as solar, wind, and hydropower.
  • This would reduce SO₂ emissions entirely, as renewables do not produce any sulfur-based pollutants.
• Carbon Capture and Storage (CCS): While primarily aimed at CO₂, CCS can also help in reducing sulfur compound emissions when integrated with flue gas treatment systems.
  • Could address both SO₂ and CO₂ emissions in coal plants, improving overall environmental performance.

Electrostatic Precipitators vs FGD

Government Initiatives to Control Sulphur Dioxide (SO₂)

• The Air (Prevention and Control of Pollution) Act, 1981: This act empowers the Central Pollution Control Board (CPCB) and State Pollution Control Boards (SPCBs) to monitor and regulate the emission of pollutants, including SO₂, from industries and power plants.
• Environment (Protection) Act, 1986: Under this act, the government sets SO₂ emission limits for industries like power plants, refineries, and cement factories, ensuring compliance with national standards.
• National Ambient Air Quality Standards (NAAQS): The Ministry of Environment, Forest and Climate Change (MoEFCC) has developed the NAAQS, which specify the permissible concentration levels of SO₂ in ambient air to safeguard public health and the environment.
• BS-VI Fuel Standards: The Bharat Stage VI (BS-VI) standards, implemented for vehicles, regulate the sulfur content in fuels, thus reducing SO₂ emissions from automobiles.
• National Clean Air Programme (NCAP), 2019: Launched by the MoEFCC, the NCAP aims to improve air quality across cities, with specific measures to control SO₂ emissions, focusing on urban areas with high pollution levels.
• SAMEER App and Social Media Initiatives: The CPCB has developed the SAMEER App and uses social media platforms (e.g., Facebook and Twitter) to track and report the progress of SO₂ pollution control initiatives, improving transparency and accountability.
• Flue Gas Desulphurization (FGD) Mandate: The government has mandated the installation of FGD systems in coal-fired power plants to remove SO₂ from flue gases. This aims to reduce the harmful impact of SO₂ on air quality and public health.

Way Forward 

• Focus on PM Control: Prioritize Electrostatic Precipitators (ESPs) for effective PM2.5 control, as they are cost-effective and reduce respiratory diseases.
• Transition to Cleaner Fuels: Shift from high-sulfur coal to low-sulfur coal or natural gas to reduce SO₂ emissions at the source.
• Adopt Renewable Energy: Accelerate the transition to solar, wind, and hydropower. This will eliminate SO₂ emissions and support long-term sustainability.

• Hybrid Pollution Control: Use a combination of technologies such as ESP and advanced sorbent injection for targeted SO₂ and PM control, reducing pollution.
• Strengthen Regulations in Critical Areas: Ensure FGD installation in high-risk areas, such as cities with dense populations and high pollution levels, to safeguard public health.
• Address Technological Barriers: Support incentives for FGD installation and increase vendor capacity to meet deadlines and ensure proper maintenance.
• Collaborate Globally: Learn from international best practices to improve SO₂ and PM control technologies in India’s power sector.
• Policy Implications: The global warming effect of SO₂ emissions underscores the need for a balanced approach in climate policies. 
  • While reducing SO₂ is crucial for improving air quality and public health, it must be done in a way that does not inadvertently worsen climate change through higher CO₂ emissions.

Conclusion

The recent decision to exempt the majority of coal-fired power plants from mandatory Flue Gas Desulphurisation (FGD) installation reflects a balance between economic feasibility and environmental concerns. However, prioritizing particulate matter (PM) control and transitioning to cleaner fuels and renewable energy are critical for long-term public health and environmental sustainability.

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