Activated carbon injection in spray dryer/ESP/FF for mercury and toxics control

Abstract

In the last decade, dry scrubbing by spray dryer absorption (SDA) has been applied to more than 17 000 MW of coal-fired boilers, and several hundred municipal solid waste (MSW) and hazardous waste plants. In the MSW application, process development for air toxic control has advanced to a point where a spray dryer absorber, followed by a fabric filter, has been determined to be the best available control technology (BACT) in several countries throughout the world. Extremely high removal of dioxins and furans, as well as mercury and other trace toxics, is now state of the art in this application. The paper describes the recent development in the air toxics removal capability of dry scrubbing for coal-fired utility plants. Results of a study characterizing the inherent mercury removal efficiency of full-scale dry scrubbers in Europe and the United States are presented, as well as results of activated carbon injection tests performed at one full-scale installation. The paper further reports results of two pilot plant research programs. One pilot plant was equipped with an electrostatic precipitator, the other pilot plant with a baghouse. The paper reports results of activated carbon injection and identifies the parameters and conditions important for achieving high mercury removal in a dry FGD system. Options for control of mercury on eastern and western US coals are suggested. Results of mercury speciation are also given. Removal results of other vapor phase toxic trace metals, such as boron and selenium, are presented. Finally, the paper makes reference to the results of two mercury revolatilization studies.