Complete Guide To Flue Gas Desulfurization (FGD) And DeNOx Systems

Step 1 – Flue Gas Collection

The treatment process begins with collecting flue gas generated by industrial combustion processes.

Typical pollutants include:

• Sulfur dioxide (SO₂)
• Nitrogen oxides (NOx)
• Fly ash
• Dust particles

The exhaust gas is transported through ductwork into the desulfurization tower.

Step 2 – Wet Flue Gas Desulfurization (FGD)

Inside the wet desulfurization tower, limestone slurry is sprayed over the incoming flue gas.

As the gas flows upward, sulfur dioxide reacts with the alkaline slurry and is absorbed efficiently.

The primary chemical reaction is:

SO₂ + CaCO₃ → CaSO₄·2H₂O (Gypsum)

The treated gas leaves the absorber with most sulfur dioxide removed.

Step 3 – Gypsum Formation and Slurry Recycling

The absorbed sulfur compounds react with limestone slurry to produce gypsum.

 in industries such as:

• Cement manufacturing
• Construction materials
• Gypsum board production

Meanwhile, the remaining slurry is recycled back into the absorption tower, minimizing operating costs.

Step 4 – Selective Catalytic Reduction (SCR)

After desulfurization, the flue gas enters the denitrification reactor.

Ammonia (NH₃) or urea is injected into the gas stream before passing through catalyst layers.

Inside the catalyst reactor, nitrogen oxides are converted into harmless nitrogen and water.

Typical reaction:

4NO + 4NH₃ + O₂ → 4N₂ + 6H₂O

This process achieves NOx removal efficiencies above 90%.

Step 5 – Clean Gas Emission

After completing desulfurization and denitrification, the treated gas is discharged through the stack.

The final emissions contain dramatically reduced concentrations of:

• SO₂
• NOx
• Dust

allowing factories to comply with local and international environmental regulations.