FGD Power Plant


Since stringent environmental regulations limiting SO2 emissions have been enacted in many countries, SO2 is being removed from flue gases using a variety of methods. For a typical coal-fired power station, flue-gas desulfurization (FGD) may remove 90 percent or more of the SO2 from the flue gases.


Flue gas originates from the combustion of coal in power plants. Combustion of fossil fuels for energy production generates by-products like bottom ash and fly ash, as well as flue gas emissions to the atmosphere. The primary gases resulting from combustion of coal are sulphur oxides and nitrates.

When burned, sulphur that is present in coal is converted for 95% to sulphur dioxide (SO2). In recent years, due to stringent legal limits for effluent discharge, emissions from sulphur oxide emitting processes are increasingly being reduced across the globe.

Recently, air pollution legislations such as Europe’s Clean Air Quality Package, the Clean Air Act in the USA and India’s National Clean Air Programme have come into effect to reduce the amount of air pollution that is increasing worldwide. This type of legislation addresses numerous air quality problems.

One of the problems is acid rain caused by sulphur dioxide and nitrogen oxide emissions from fossil-fuelled power plants and other industrial and transportation sources. Sulphur oxides and nitrogen oxides (NOx) are recognized as harmful pollutants and great efforts are underway to remove these toxic gases. Under emission regulatory requirements and legislation to reduce the emission of these air pollutants, power plants in particular have installed Flue Gas Desulfurization (FGD) systems, otherwise known as scrubbers.

FGD Power Plant - Image


In a flue gas desulfurization (FGD) system, sulphur compounds are removed from the exhaust emissions of fossil-fuelled power stations. This is done by means of an industrial process through the addition of absorbents. Flue gas desulfurization can remove up to 95 % of the sulphur dioxide from the flue gas. Typical processes for removing SO2 are wet scrubbing and dry scrubbing.

In dry scrubbing systems, also known as dry injection or spray drying systems, the SO2 first reacts with limestone before removing particulates from the flue gas.


Wet flue gas desulfurization or scrubber systems are the most frequently used technology in large, fossil-fuelled power plants. They provide an excellent method for reducing the sulphur dioxide emissions caused by coal combustion boilers. In wet scrubbing systems, the fly ash is removed first by an electrostatic precipitator (ESP), and then the flue gas discharged from the boiler is fed into the SO2 absorber.

In the absorber, the flue gas is steam-saturated with an absorbent and water. Substances such as ammonia or sodium sulphite can be used as absorbents; however the use of lime or pulverized limestone slurry (wet limestone scrubbing) is also widespread.

The uncleaned flue gas is sprayed into a scrubber tower (absorber tower) with a mixture of water and limestone (scrubbing slurry), whereby most of the sulphur dioxide is bonded by chemical reaction.

The limestone slurry absorbs the sulphur dioxide (SO2) contained in the flue gas, reducing the emission of sulphur. The limestone reacts with the SO2 to produce calcium sulphite, which in turn reacts with oxygen and is then finally removed as gypsum. Both the limestone slurry and gypsum slurry are very abrasive. Dewatering the gypsum slurry leaves gypsum with up to 10 % residual moisture, which provides a valuable product for the construction material industry.

Flue gas exiting the absorber is highly corrosive, as it is saturated with water and still containing SO2. This highly corrosive flue gas can cause damage to any downstream equipment like fans, ducts and stacks. Reheating the gasses above dew point or using corrosion-resistant materials minimize corrosion.


  • High SO2 removal efficiency, up to 90%
  • Retrofit of existing equipment is not difficult (moderate to low)
  • Used reagents are inexpensive and readily available
  • Re-usable products of reaction