Flue Gas Desulphurisation (FGD)

Flue Gas Desulphurisation (FGD)

Flue Gas Desulphurisation (FGD) is a set of technologies used to remove sulphur dioxide (SO2) from exhaust gases of fossil fuel burning power stations and other similar sulphur dioxide gas omitting processes

Flue Gas Desulphurisation 1
Flue Gas Desulphurisation 2
Flue Gas Desulphurisation 3

Flue Gas Desulphurisation (FGD) facilities remove sulphur dioxide from the flue gas before it is released into the atmosphere and hence reduces the impact on the environment. This allows coal fired power stations and other fossil fuel burning organisations to continue using high sulphur content coal, safe in the knowledge that they are no longer polluting the atmosphere.

The FGD technology is based on a chemical reaction that occurs when the warm exhaust gases from the coal-fired boiler come into contact with limestone. This reaction removes +90% of the sulphur dioxide from the flue gas and converts the limestone into calcium sulphite.

In practical terms, the flue gas is drawn from the boiler into the FGD diverter ducting and forced into a large vertical absorber tower by a booster fan. Once inside the absorber tower, the gas comes into contact with a limestone slurry mixture. The slurry is sprayed from banks of nozzles situated towards the top of the tower.

When the warm gas comes into contact with the limestone slurry a chemical reaction occurs between the sulphur dioxide (SO2) in the gas and the limestone. This reaction removes the SO2 from the flue gases and converts the limestone into calcium sulphite. This calcium sulphite and limestone slurry then precipitates to the base of the absorber where it is injected with compressed air. The compressed air oxidises the calcium sulphite and converts it to calcium sulphate – commonly known as gypsum.

This gypsum suspension, after passing through a bank of cyclone thickeners, becomes the feed stock for the FGD Vertical Batch Basket Filtration Centrifuge(s).

These designs can offer the following key features;

  • Specifically designed for the recovery of Calcium Sulphate (Gypsum)
  • Produce high quality gypsum for plaster wallboards
  • Generally heavier, more robust than conventional vertical filtration basket centrifuges
  • Efficient removal of unwanted salts to <50 ppm

If its low residual moisture content gypsum that is required , with less than 50 ppm chloride content, then FGD Vertical Batch Basket Filtration Centrifuges are the perfect solution. Several centrifuges can be programmed together that essentially turns the batch operation of the centrifuges into a fully continuous process.


NCD Separation Solutions Ltd. is a unique company that can offer a complete range of centrifuge consultancy and centrifuge engineering services.