Mercury capture boosts chemical requirement

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However, due to the many regulatory, technical and competitive factors, the annual U.S. market over the next ten years could vary significantly. There is also uncertainty relative to the markets in other countries. This is the conclusion reached by the McIlvaine Company in its Mercury Air Reduction Markets report.McIlvaine adds that the two main chemicals which are and will be employed are activated carbon and halogen compounds. Activated carbon in a powdered form is injected already into most waste-to-energy plants around the world. This market will grow at a steady pace at close to 7% per year. Activated carbon is also the chemical used as the basis for the U.S. EPA analysis justifying its new regulations for the utilities, cement plants and industrial boilers.Two halogen compounds are being utilised. One is hydrogen chloride and the other is calcium bromide. Chlorine already appears in varying contents in most coals. The plastic waste in-waste-to-energy plants is also high in chlorine content. This halogen compound reacts with elemental mercury to form mercury chloride. This compound is soluble in water and is captured in the same scrubber which removes the SO2.The other halogen compound is calcium bromide which is added as slurry with the coal. Bromine is orders of magnitude more effective in creating soluble compounds than is chlorine. Oxidation rates in excess of 95% can be achieved with bromine compounds.Activated carbon can also be brominated in order to reduce the amount of carbon consumed or to raise the mercury capture efficiency. This raises the cost per pound by 50-75%, but can cut the consumption in half thereby reducing total cost. A further use of activated carbon is to prevent re-emission of elemental mercury when used in the recirculating scrubber slurry. The additional advantage of this application is that the carbon with the mercury can be separated from the rest of the scrubber sludge in a hydrocyclone. This eliminates the need to dispose of the sludge in a hazardous waste landfill.The annual consumption of chemicals is forecast to range between $1.5-3 billion/year over the next decade based on a number of variables. These include: the continued use of coal as a fuel in the U.S. and Europe; the specific regulatory initiatives in various countries; the use of wet scrubbers for acid gas removal in power plants, industrial boilers; future technical advances; and the share for the less expensive halogen compounds versus the more expensive activated carbon.