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Flue gas desulfurization is commonly known as FGD and is the technology used for removing sulfur dioxide (SO2) from the exhaust combustion flue gases of power plants that burn coal or oil to produce steam for the turbines that drive their electricity generators. The most common types of FGD contact the flue gases with an alkaline sorbent such as lime or limestone. As sulfur dioxide is responsible for acid rain formation, stringent environmental protection regulations have been enacted in many countries to limit the amount of sulfur dioxide emissions from power plants and other industrial facilities. Prior to the advent of strict environmental protection regulations, tall flue gas stacks (i.e., chimneys) were built to disperse rather than remove the sulfur dioxide emissions. However, that only led to the transport of the emissions to other regions. For that reason, a number of countries also have regulations limiting the height of flue gas stacks. For a typical conventional coal-fired power plant, FGD technology will remove up to 99 percent of the SO2in the flue gases. FGD Chemistry SO2 is an acidic gas. Therefore, the most common large-scale FGD systems use an alkaline sorbent such as lime or limestone to neutralize and remove the SO2 from the flue gas. Since lime and limestone are not soluble in water, they are used either in the form of an aqueous slurry or in a dry, powdered form. When using an aqueous slurry of sorbent, the FGD system is referred to as a wet scrubber. When using a dry, powdered sorbent, the system is referred to as a dry system. An intermediate or semi-dry system is referred to as a spray-dry system. Types of FGD systems The major types of large-scale, power plant FGD systems include spray towers, spray dryers and dry sorbent injection systems. 1.Spray towers There are various types of wet scrubbers. For example, spray towers, venturi scrubbers, packed towers and trayed towers. Slurries would cause serious erosion problems in a venturi scrubber because of the high speeds at the throat of the venturi section. Packed towers or trayed towers would plug up if handling slurries. For handling slurries, the spray tower is a good choice and it is in fact a commonly used choice in large-scale FGD systems. 2. Spray-dryer Spray-dryers are used upstream of the particulate removal equipment (electrical precipitator or filter bag house) where the flue gas contains the combustion fly ash. In a spray-dryer system, the alkaline sorbent is usually lime slurry. 3. Venturi Scrubber Venturi Scrubbers are high performance system which can reduce the contamination level of flue gas up to 99%. They can remove both particulate matter and gaseous pollutants. It can be used when the percentage of dust is more. 4. Packed Bed Scrubber A Packed Bed Scrubber is a wet type scrubber that removes soluble chemicals, fumes,and odors. The packing maximizes the surface area for absorption of gases and vapors. It can be used when the concentration of sulphur dioxide is veryhigh and particulate matter is low. 5. Dry sorbent injection The dry FGD system simply injects powdered lime or limestone sorbent directly into the flue gas. Web Site: http://www.shimiresearch.in/ This article about flue gas desulfurization is a product of the Venturi Scrubber, Packed Bed Scrubber
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