ENVIRONMENTAL CONTROL OF TOXIC METAL AIR EMISSIONS FROM THE COMBUSTION OF COAL AND WASTES

The emission of toxic metals from combustion of fossil fuels and wastes is an important global environmental issue. Toxic metals, such as arsenic, selenium, mercury, chromium, lead and cadmium are present in coals and in many municipal and industrial wastes. This paper is concerned with the partitioning of these metals during combustion, and with the mitigation of their effect on the environment using high temperature sorbents. The paper is divided into three parts. First, the partitioning of arsenic and selenium during coal combustion in a 17kW laboratory down-fired furnace is discussed and appropriate mechanisms identified. Second, the speciation of mercury and chromium during combustion is addressed, through special experiments on a 73kW refractory lined combustor. Third, experimental results on the sorption of individual and multiple metals on sorbents are presented. These sorbents were kaolinite and lime, and were injected directly into flue gas containing lead and cadmium metals, which had vaporized in the main flame. Results suggest that toxic metals from coal and waste combustion can be associated with lime or kaolinite sorbents, and that for some multiple metal mixtures, designer sorbents containing calcium, aluminum, and silicon might be useful to capture them and render them environmentally benign.