10.FLUE GAS DESULPHURISATION UNIT & CORROSION PROTECTION

What is Flue Gas Desulphurisation (FGD)?

Flue Gas Desulphurisation (FGD) is a pollution control process used to remove sulphur dioxide (SO₂) from industrial exhaust gases before they are released into the atmosphere. Sulphur dioxide is generated during the combustion of fossil fuels and various industrial operations, including power generation, oil refining, cement manufacturing, steel production, paper mills, glass plants, and metal processing industries.

Since SO₂ emissions are a major contributor to acid rain, environmental pollution, and equipment degradation, governments worldwide have made Flue Gas Desulphurisation systems mandatory for many industries to reduce harmful emissions and meet environmental regulations.

Why Are FGD Systems Important?

FGD units play a crucial role in:

• Reducing sulphur dioxide (SO₂) emissions
• Preventing acid rain formation
• Ensuring compliance with environmental regulations
• Improving air quality
• Supporting sustainable industrial operations
• Reducing environmental impact on surrounding communities

As industries continue to focus on emission control, FGD systems have become an essential component of modern power plants and manufacturing facilities.

Common Flue Gas Desulphurisation (FGD) Technologies

Several technologies are used to remove sulphur dioxide from flue gases:

1. Wet Scrubbing

The most widely used FGD technology, wet scrubbing uses an alkaline slurry such as limestone, lime, or seawater to absorb and neutralize sulphur dioxide.

2. Spray Dry Scrubbing

This process involves spraying alkaline sorbent slurries into hot flue gases, where the moisture evaporates and reacts with SO₂.

3. Wet Sulphuric Acid Process

This method recovers sulphur dioxide and converts it into commercial-grade sulphuric acid.

4. SNOX Process

A specialized technology that simultaneously removes sulphur dioxide, nitrogen oxides (NOx), and particulate matter from flue gases.

5. Dry Sorbent Injection

Dry alkaline materials are injected directly into the flue gas stream to neutralize sulphur dioxide.

Corrosion Challenges in FGD Units

Among all FGD technologies, wet scrubbing systems are the most commonly used. In these systems, flue gases pass through fly ash removal equipment and then enter the SO₂ absorber.

After treatment, the exhaust gases remain saturated with moisture and may still contain traces of sulphur dioxide, sulphurous acid, sulphuric acid mist, chlorides, and other corrosive compounds. These conditions create an extremely aggressive environment that can severely damage downstream equipment.

Without proper corrosion protection, equipment can experience:

• Premature failure
• Increased maintenance costs
• Unplanned shutdowns
• Reduced plant efficiency
• Higher operational expenses

Equipment Vulnerable to Corrosion in FGD Systems

The following components are commonly exposed to severe corrosion in wet FGD units:

Equipments	Corrosion Conditions
Inlet piping, cooling tower	SO₂,vapor,etc.
Circulation Tank	H₂SO₃, H₂SO₄, fog, etc., Aspirating agent, soot, reaction products
Feed pipe, discharge pipe	SO₂, H₂SO₃, H₂SO₄, fog
Absorber	SO₂, H₂SO₃, fog of H₂SO₄, pH=3~12
Circulating Tower, Oxidation Tower	pH=3~14
Acid Mist Separator	Vapor of SO₂, H₂SO₃, fog of H₂SO₄
Concentrator	pH=3~12
Duct	≤100°C
Tank	Room temperature

Effective Corrosion Protection for FGD Units

To ensure long-term reliability and asset protection, industries require advanced corrosion-resistant lining systems capable of withstanding:

• Continuous immersion
• Acidic condensates
• Sulphur dioxide exposure
• Sulphuric acid attack
• Chloride contamination
• High temperatures
• Abrasion and erosion

Vinyl Ester Glass Flake Linings

Vinyl Ester Glass Flake Linings are widely recognized as one of the most effective corrosion protection solutions for FGD systems. These advanced linings provide:

• Exceptional chemical resistance
• Superior barrier protection
• Resistance to sulphuric acid and acidic condensates
• Excellent abrasion resistance
• High-temperature performance
• Long service life
• Reduced maintenance requirements

The unique glass flake structure creates a highly impermeable barrier that significantly slows the penetration of corrosive media, making it ideal for absorbers, ducts, chimneys, tanks, and wet scrubber components.

Benefits of Corrosion Protection in FGD Units

Implementing the right corrosion protection system offers several advantages:

• Extended equipment life
• Reduced downtime
• Lower maintenance costs
• Improved plant reliability
• Enhanced operational efficiency
• Better return on investment
• Compliance with environmental and safety standards

Conclusion

Flue Gas Desulphurisation (FGD) systems are critical for controlling sulphur dioxide emissions and meeting environmental regulations. However, the aggressive operating conditions inside wet FGD units create severe corrosion challenges for critical equipment.

By utilizing advanced solutions such as Vinyl Ester Glass Flake Linings, industries can effectively protect their assets from corrosion, abrasion, and chemical attack while improving plant reliability and reducing lifecycle costs.

For industries operating power plants, cement plants, refineries, steel plants, and other process industries, investing in proper FGD corrosion protection is essential for maximizing equipment life and ensuring uninterrupted operations.

Frequently Asked Questions (FAQs)

What is the purpose of an FGD unit?

An FGD unit removes sulphur dioxide (SO₂) from industrial flue gases, helping industries comply with environmental regulations and reduce air pollution.

Why are FGD systems prone to corrosion?

FGD systems operate in highly acidic and moisture-rich environments containing sulphur dioxide, sulphurous acid, sulphuric acid, and chlorides, which accelerate corrosion.

What is the most common FGD technology?

Wet scrubbing using limestone or lime slurry is the most widely used Flue Gas Desulphurisation technology worldwide.

Which equipment is most affected by corrosion in FGD units?

Absorbers, ducts, tanks, circulation towers, oxidation towers, piping systems, and mist eliminators are among the most corrosion-prone components.

What is the best lining system for FGD corrosion protection?

Vinyl Ester Glass Flake Linings are considered one of the most effective solutions due to their excellent resistance to chemicals, moisture, abrasion, and high temperatures.

How do Glass Flake Linings improve equipment life?

The glass flakes create a tortuous path that significantly reduces the penetration of corrosive chemicals, protecting the substrate and extending service life.

Which industries use Flue Gas Desulphurisation systems?

FGD systems are commonly used in thermal power plants, cement plants, steel plants, refineries, paper mills, glass manufacturing units, and metal processing industries.