It is no secret that coal combustion produces high levels of sulfur dioxide (SO₂) emissions. Because these emissions negatively impact health, the environment, and air quality, effective solutions are needed to control this pollution.
One of the most widely used technologies for reducing SO₂ emissions is Flue Gas Desulfurization (FGD).
This technology has become the new standard for air pollution control in modern coal-fired power plants. However, behind its benefits, FGD also hides a darker side that deserves serious attention.
What Is Flue Gas Desulfurization (FGD)?
Flue Gas Desulfurization (FGD) is an emission control technology designed to remove sulfur dioxide (SO₂) from flue gas produced by burning fossil fuels, especially coal.
This technology has long been used in coal-fired power plants and other large industrial facilities to comply with air quality standards.
The adoption of FGD is driven by clean air regulations that require industries to control SO₂ pollution before flue gases are released into the atmosphere.
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Why Is FGD Needed in the Energy Industry?
Implementing FGD is essential in the energy sector because sulfur dioxide (SO₂) from coal combustion can cause serious environmental and health impacts.
When SO₂ reacts in the atmosphere, it forms sulfuric acid, which falls as acid rain. This phenomenon can damage aquatic ecosystems, soil, forests, and accelerate corrosion in buildings and infrastructure.
To prevent these impacts, FGD is used as an emission control technology to reduce SO₂ levels before flue gases are released into the air.
This technology has become standard in modern coal power plants worldwide to comply with increasingly strict air quality regulations.
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How Does Flue Gas Desulfurization Work?
The most common type of FGD, wet limestone FGD, works by utilizing a chemical reaction between SO₂-containing flue gas and an alkaline sorbent.
In general, the process works as follows:
- Hot flue gas from the boiler is directed into the FGD unit.
- The flue gas is then brought into contact with a limestone slurry (CaCO₃) or quicklime (CaO).
- SO₂ reacts with the sorbent and oxygen, forming calcium sulfite, which then oxidizes into gypsum (CaSO₄·2H₂O).
- The gypsum by-product is separated for further processing, while the cleaned gas is released through the stack.
This process effectively reduces SO₂ content in the flue gas, ensuring emissions released into the atmosphere meet environmental standards.
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What Are the Types of FGD Systems?
FGD systems are developed in various types to match operational needs, efficiency levels, and available resources.
The three most widely used FGD systems are:
- Wet FGD: Uses limestone slurry; offers high efficiency and can remove more than 90% of SO₂.
- Dry & Semi-dry FGD: Uses dry or semi-dry sorbents; suitable for small–medium facilities or water-scarce regions.
- Seawater FGD: Utilizes natural alkalinity from seawater without chemicals; ideal for coastal power plants.
How Effective Is FGD in Reducing Emissions?
Flue Gas Desulfurization, especially wet FGD, is proven highly effective in lowering SO₂ emissions.
According to the U.S. Environmental Protection Agency (EPA), wet FGD systems typically achieve 90–99% emission reduction, making them the top choice for fossil-fueled power plants.
Meanwhile, dry and semi-dry systems offer advantages in capital cost and water requirements but have slightly lower efficiency compared to wet FGD.
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What Are the Positive Impacts of FGD on the Environment and Industry?
FGD provides several key benefits to both the environment and industry, especially in controlling sulfur emissions from fossil-fueled power plants.
Its three main positive impacts include:
- Reducing air pollution: FGD lowers SO₂ emissions, reducing the risk of acid rain and improving air quality.
- Supporting environmental compliance: Helps industries meet emission standards and strengthen responsible operational practices.
- Producing valuable by-products: FGD generates gypsum that can be reused in the cement or construction industries.
What Is the Dark Side of Flue Gas Desulfurization?
Despite its importance in reducing emissions, FGD also leaves behind several challenges that require serious attention.
High Investment and Operational Costs
FGD systems require significant capital investment. Operational and maintenance costs are also substantial.
Wet FGD systems can consume around 1–5% of the total power generated, creating a financial burden for small-scale power plants or companies in developing countries.
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Waste Production and Secondary Impacts
The FGD process generates waste such as slurry, gypsum, and sorbent residues, classified as Coal Combustion Residuals (CCR). While some gypsum can be reused, unused materials must be managed with strict controls.
FGD waste can pose contamination risks if mishandled, as it may contain chlorides, heavy metals, and suspended solids.
Water and Energy Consumption
Wet FGD systems require large amounts of water to produce slurry and facilitate SO₂ absorption, making them unsuitable for water-limited regions.
FGD also adds to the plant’s energy load (parasitic load), especially wet systems that rely on pumps, agitators, and other auxiliary equipment. This reduces the net electrical efficiency.
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What Is the Future of FGD in the Energy Transition Era?
The future of FGD will likely shift as the world transitions from coal toward cleaner energy or gas.
With increasing adoption of natural gas, including LNG (Liquefied Natural Gas), the need for FGD to control sulfur pollution from coal combustion may decline.
LNG produces significantly lower sulfur emissions, particulates, and other air pollutants compared to coal, meaning gas-based power plants do not require FGD.
However, FGD will not disappear globally anytime soon. Many coal plants continue to operate, making FGD relevant as a local pollution control technology to maintain air quality.
In many regions, environmental regulations and air quality requirements make FGD an essential part of modern coal operations.
Thus, FGD and LNG represent two different phases in the energy transition: FGD as an end-of-pipe solution in the coal era, and LNG as a bridge toward a low-carbon energy future.
References:
- ScienceDirect. Accessed 2025. Flue Gas Desulfurization
- ScienceDirect. Accessed 2025. Influence of Gas Components on SO₂ Removal in Semidry FGD Processes
- EPA. Accessed 2025. Air Pollution Control Technology Fact Sheet
- Kementerian ESDM. Accessed 20255. Kurangi Emisi, PLTU Sumsel 8 Gunakan Teknologi Flue Gas Desulphurization
