1. What is Flue Gas Desulfurization (FGD)?

Flue Gas Desulfurization (FGD) is a widely used air pollution control technology designed to remove sulfur dioxide (SO₂) from flue gas generated by industrial combustion processes. It is commonly applied in coal-fired power plants, coke oven gas treatment systems, and various heavy industries.

SO₂ emissions are a major source of acid rain and atmospheric pollution. As global environmental regulations become stricter, FGD systems have become essential for ensuring compliance and maintaining sustainable plant operations.

2. Why FGD Systems Are Important

FGD systems play a critical role beyond environmental protection:

• Regulatory Compliance: Meet strict SO₂ emission limits in modern industrial standards
• Equipment Protection: Reduce corrosion caused by acidic gases in downstream systems
• Operational Stability: Improve flue gas consistency for better performance of SCR and dust collection systems

Without an effective FGD system, most industrial facilities cannot meet emission requirements or maintain long-term operational reliability.

3. Main Types of FGD Systems

3.1 Wet FGD System

The wet FGD system, typically based on the limestone-gypsum process, is the most widely used technology.

• Working Principle: SO₂ reacts with limestone slurry and is converted into gypsum
• Efficiency: Up to 95% or higher
• Advantages: High efficiency and proven reliability
• Limitations: Higher investment and more complex operation

3.2 Dry FGD System

Dry FGD uses powdered or hydrated lime injected directly into the flue gas.

• Advantages: Simple system, no wastewater
• Applications: Small to medium-sized boilers
• Limitations: Lower efficiency (typically 80–90%)

3.3 Semi-Dry FGD System

Semi-dry systems use atomized lime slurry in a spray dryer absorber.

• Efficiency: Around 90–95%
• Advantages: No liquid discharge, moderate cost
• Limitations: Sensitive to operating conditions

4. Key Components of an FGD System

A typical FGD system includes:

• Absorber or reactor
• Reagent preparation unit
• Flue gas distribution system
• By-product handling system (gypsum or dry solids)
• Auxiliary systems such as pumps, blowers, and demisters

5. Engineering Considerations

Material Selection

FGD systems operate in highly corrosive environments. Common materials include rubber-lined steel, FRP, duplex stainless steel, and high-alloy materials.

Temperature and Heat Recovery

FGD reduces flue gas temperature significantly, creating opportunities for integrating heat recovery systems such as gas-gas heaters or economizers.

Fouling and Maintenance

Scaling and nozzle blockage are common in wet systems, requiring optimized design and easy maintenance access.

6. Industrial Applications

FGD systems are widely used in:

• Power generation plants
• Coke oven gas treatment
• Steel and metallurgical industries
• Cement plants
• Petrochemical facilities

7. Conclusion

Flue Gas Desulfurization (FGD) is a key technology for modern industrial plants, ensuring environmental compliance, protecting equipment, and improving operational efficiency.

Selecting the right FGD system depends on emission standards, plant size, and operating conditions. A well-designed system should balance efficiency, durability, and cost-effectiveness to achieve long-term performance.