Flue-gas desulfurization

The flue gas desulfurization ( FGD also ) is a process for removing sulfur compounds ( SO2 and SO3) from the flue gases (eg, power plants, waste incineration plants or large engines ). The sulfur compounds are produced by the burning of sulfur-containing fossil fuels. Systems for flue gas desulfurization are abbreviated with FGD ( flue gas desulfurization system ).

Application

The process was invented in 1879 by the Robert Sodafabrikanten Hasenclever. Today, it is particularly used for power plants on the basis of coal and heavy fuel oil, in which the sulfur content is greater than one percent. In the combustion of gas, and light fuel oil is generally a desulfurization required.

Since 1974, the flue gas desulfurization is prescribed in Germany for new coal-fired power plants and large combustion Regulation in June 1983 also called for the retrofit or retirement of old plants. In lignite power plants in the early 1980s, a reduction of sulfur dioxide emissions was initially provided by the addition of lime to the raw lignite (also called dry additive process ), which would have been much more cost effective than the conventional FGD. As of June 1983 also lignite power plants in Germany had to carry the flue gas desulfurization, including any transitional periods.

Types of procedure

In power plants, in principle, it is possible to remove more than 95 percent by technical measures sulfur dioxide from the flue gas. There are more than hundred different procedures; they provide as a final product gypsum or ammonium sulfate.

A distinction is made for the desulfurization between regenerative and non-regenerative process.

  • For non- regenerative process, there is the lime washing, the world has enforced the most. Here, the addition of lime ( both limestone and as quicklime ) gypsum is produced. This usually happens in a countercurrent scrubber, the absorber. While the flue gas from below flows through the tank top, the sulfur compounds react with the washing suspension. This will, in finely divided form by spray planes that are mounted in the upper portion of the absorber and trickles down into a drip pan ( sump ). The container bottom is the reaction product of the sulfur dioxide ( calcium sulphite ) by the addition of oxygen (air) to form calcium sulfate (gypsum) is oxidised:
  • The regenerative process include the Wellman - Lord process, which finds application especially in refineries. Other methods (such as adsorption on activated carbon) have acquired any practical significance.

Waste Treatment

From a year in Germany approximately 7 million tonnes of accumulating FGD gypsum recycled building materials industry in 1995 about 3 million tonnes, so that about 4 million tons are spent annually in landfills. Compared to natural gypsum FGD gypsum has to be present the disadvantage of a higher residual moisture and as a dihydrate.

In the wet process for flue gas desulfurization (this includes all methods except the SDA and the dry sorption ) falls wastewater is mainly the soluble constituents - including from the fuel and from the absorbent - among other halogen compounds (chlorides, etc.) and heavy metal compounds. This wastewater must be purified prior to receiving water discharge.

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