Mg(OH) 2 (solid) + SO 2 (gas) ⇒ MgSO 3 (solid) + H 2O (liquid) When wet scrubbing with a Mg(OH) 2 ( magnesium hydroxide) slurry, the reaction produces MgSO 3 ( magnesium sulfite) and can be expressed as: When wet scrubbing with a Ca(OH) 2 (lime) slurry, the reaction also produces CaSO 3 (calcium sulfite) and can be expressed as:Ĭa(OH) 2 (solid) + SO 2 (gas) ⇒ CaSO 3 (solid) + H 2O ( liquid) The reaction taking place in wet scrubbing usingĪ CaCO 3 (limestone) slurry produces CaSO 3 ( calcium sulfite) and can be expressed as:ĬaCO 3 (solid) + SO 2 (gas) ⇒ CaSO 3 (solid) + CO 2 (gas) An intermediate or semi-dry system is referred to as a spray-dry system. When using a dry, powdered sorbent, the system is referred to as a dry system. When using an aqueous slurry of sorbent, the FGD system is referred to as a wet scrubber. 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. Therefore, the most common large-scale FGD systems use an alkaline sorbent such as lime or limestone to neutralize and remove the SO 2 from the flue gas. About 18% (or 25 gigawatts) utilized spray-dry scrubbers or dry sorbent injection systems. Approximately 79% of the units, representing about 199 gigawatts of capacity, were using lime or limestone wet scrubbing. About 45% of that FGD capacity was in the United States, 24% in Germany, 11% in Japan and 20% in various other countries. Īs of about 1999-2000, there were 678 FGD units operating worldwide (in 27 countries) producing a total of about 229 gigawatts. As of June 1973, there were 42 FGD units, ranging in size from 5 to 250 megawatts, in operation: 36 in Japan and 6 in the United States. Large-scale FGD units did not reappear in commercial operation until the 1970s, and most of the activity occurred in the United States and Japan. All three installations were abandoned during World War II. The third one was installed in 1938 at the Fulham Power Station. In 1935, the second one went into service at the Swansea Power Station. The first one began operation at the Battersea Station in London in 1931. ĭuring this period, major FGD installations went into operation in England at three power plants. This led to the imposition of SO 2 controls on all such power plants. Shortly thereafter a press campaign was launched against the erection of power plants within the confines of London. The problem did not receive much attention until 1929, when the British government upheld the claim of a landowner against the Barton Electricity Works for damages to his land resulting from SO 2 emissions. With the construction of large-scale power plants in England in the 1920s, the problems associated with large volumes of SO 2 emissions began to concern the public. Early concepts useful for flue gas desulfurization appear to have germinated in 1850 in England. Methods for removing sulfur dioxide from flues gases have been studied for over 150 years.
However, that only led to the transport of the emissions to other regions. 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. Īs 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. The most common types of FGD contact the flue gases with an alkaline sorbent such as lime or limestone. (CC) Photo: Organization for Economic Co-operation and Developmentįlue gas desulfurization is commonly known as FGD and is the technology used for removing sulfur dioxide (SO 2) from the exhaust flue gases of power plants that burn coal or oil to produce steam for the turbines that drive their electricity generators.