Flue Gas Desulphurization (FGD) System

Flue Gas Desulfurization (FGD) System is a crucial technology employed in various industries to mitigate the environmental impact of Sulphur Dioxide (SO2) emissions, particularly from combustion processes.

1.)   Desulfurization Process

 

·       FGD systems primarily work by removing Sulphur Dioxide (SO2) from the flue gas stream before it is discharged into the atmosphere.

·       The most common method of FGD is wet scrubbing, where the flue gas is brought into contact with a liquid sorbent in a scrubber vessel.

·       The liquid sorbent, often a slurry of limestone (Calcium Carbonate – CaCO3) or lime (Calcium Oxide – CaO or Hydroxide) in water, reacts with Sulphur Dioxide in the flue gas to form calcium sulphite (CaSO3) or calcium sulphate (CaSO4).

·       The chemical reaction occurs as follows:

o   SO2 + CaCO3 (or CaO/Ca(OH)2) + H2O = CaSO3 (or CaSO4) + CO2 (or H2O)

·       The resulting calcium sulphite or sulphate is typically collected as a slurry, which can be further processed to recover or dispose of the captured sulphur compounds (Gypsum).

·       Depending on the quality of the limestone, the by product gypsum can be re-used as a gypsum board.

 

2.)   Types of FGD Systems

 

·       Wet Scrubbers: In wet scrubbing systems, the flue gas is contacted with a liquid sorbent in a scrubber vessel. The sorbent absorbs sulphur dioxide, forming a slurry that is collected and treated to recover or dispose of the captured sulphur compounds.

·       Dry Scrubbers: Dry scrubbing systems use a dry sorbent material (such as hydrated lime or sodium bicarbonate) injected into the flue gas stream to react with Sulphur Dioxide. The reaction products are typically collected using fabric filters or electrostatic precipitators.

·       Spray Dryer Absorbers (SDA) and Circulating Dry Scrubbers (CDS): These are variations of dry scrubbing systems that involve spraying a lime slurry into the flue gas stream to neutralize sulphur dioxide.

 

3.)   Significance of FGD

 

·       Environmental Protection: FGD plays a crucial role in reducing emissions of sulphur dioxide, a major air pollutant responsible for acid rain formation, environmental degradation, and adverse health effects.

·       Public Health: Sulphur Dioxide emissions can exacerbate respiratory problems, cardiovascular issues, and other health conditions. FGD helps to mitigate these health risks by reducing sulphur dioxide emissions from industrial sources.

·       Regulatory Compliance: Many countries have established stringent emissions standards and regulations for sulphur dioxide and other air pollutants. FGD Systems enable industries to comply with these regulations and obtain operating permits by reducing their emissions to permissible levels.

·       Acid Rain Mitigation: Sulphur Dioxide emissions can react with atmospheric moisture to form sulphuric acid, contributing to acid rain formation. FGD helps to mitigate the environmental impacts of acid rain by reducing the release of sulphur compounds into the atmosphere.

In summary, Flue Gas Desulphurization is a vital pollution control technology used to remove sulphur dioxide emissions from industrial flue gases. By reducing air pollution, protecting public health, and mitigating environmental impacts such as acid rain formation, FGD systems play a critical role in promoting sustainable and responsible industrial operations.