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Show ABSTRACT Title III of the 1990 Clean Air Act Amendments classifies 189 species as "Air Toxics." Of these, eleven are heavy metals found in coal and are therefore of potential concern for electric utilities. The emission of these species is directly related to their volatility and the associated enrichment in either the vapor or submicron-sized particle phases. To minimize emissions, a utility must therefore minimize the vaporization of these elements, minimize their association with submicron particles, and maximize the capture of the smallest ash particles, either through combustion process modifications or the use of sorbents. In this paper, we present an overview of the results of our prior studies describing the partitioning of the inorganic air toxics species as a function of ash particle size during coal combustion. The results of this work suggest that species such as arsenic, selenium, and occasionally chromium may partially volatilize during combustion. W e also present new data indicating that during entrained gasification of an Illinois #6 coal, arsenic, selenium, antimony, and mercury were the only air toxics metals exhibiting measurable volatility. To address the minimization of air toxics emissions, a controlled bench-scale study emphasizing arsenic and chromium was conducted. Vaporization experiments with pure compounds suggested that the oxide forms of these elements would dominate, and would be amenable to capture by selected sorbents. BACKGROUND In 1990, a set of Amendments to the Clean Air Act were signed into law by President Bush. These Amendments are divided into several titles, each addressing a different aspect of air quality. One of these titles - Title III - identifies 189 hazardous air pollutants (HAPs) whose emissions will be regulated by the Environmental Protection Agency (EPA). A wide variety of stationary sources, including industrial and institutional combustion sources, are included in the list of affected sources. Sources are classified as major sources - those that emit more than 10 tons per year of any individual H A P or an aggregate of at least 25 tons per year - and "area" or minor sources. Specifically exempted from Title III regulation at present are coal-fired electricity-generating utility power plants. Pending the results of an E P A study of power plant emissions, however, utility boilers may be regulated. Eleven of the 189 HAPs listed in Title III are heavy metals, all of which can be found in coal. Concentrations of these elements are typically 0.5 - 50 p p m by weight as shown in Table 1(1). Principally because of the volume of coal burned worldwide, total combustion-derived emissions are significant for a few elements (2). This is shown in Table 2. The emissions of any specific element from a coal combustion or gasification system depends significantly upon its high temperature volatility. For example, mercury is highly volatile. It will remain in the vapor phase throughout much of a coal conversion system, will not be efficiently removed by air pollution control equipment, and will escape with the stack 1 11-14 |