Flue gas desulfurization and acid gas removal by spray dryer absorption (SDA) has developed from a novel to a mature technology over the past fifteen years. Today, SDA's treat flue gas from over 17,000 MW (1) of coal fired boilers and several hundred municipal solid waste (MSW) and hazardous waste incinerators (2). Activated carbon, in conjunction with spray dryers, has been used to enhance the removal of air toxics from incinerator flue gases for several years. This technology is now being applied to numerous MSW plants throughout Europe and the United States. This paper describes recent development work in applying the activated carbon technology to coal fired boilers. Results of studies characterizing the inherent mercury removal efficiency of full scale dry scrubbers in Europe and the United States is presented, as well as results of activated carbon testing at a full scale installation. The paper also reports the results of several recent pilot plant research projects. These include the results of numerous mercury removal tests with and without activated carbon injection on SDA slipstream pilot plants equipped with both electrostatic precipitators and fabric filters. Parameters and conditions significant for achieving high mercury removal in dry FGD systems are identified. Results to alter the speciation of mercury by adding compounds to coal in a pilot coal combustor are also presented. Conclusions from these pilot test programs provide insight into available alternatives for controlling mercury emissions from power plants burning both eastern and western U.S. coal.
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