HAPs-RX(TM)

Abstract

Coal cleaning is a technology that can solve a broad array of environmental problems associated with older, state-of-the-art, and future electric generating stations. Coal cleaning provides many environmental benefits. It reduces the concentration of inorganic minerals and elements found in association with coal, some of which are potentially toxic even though they are found in coal in only trace amounts. Currently, more sulfur and related S0{sub 2}, is removed by coal cleaning than by all post-combustion technologies combined. By increasing thermal efficiency and reducing parasitic power requirements, coal cleaning reduces all power plant emissions per unit of electricity produced, including S0{sub 2}, NO{sub x} C0{sub 2}, and hazardous air pollutant precursors (HAPs). While coal cleaning is a mature technology, in the past coal cleaning has only been used for the comparatively simple purposes of removing ash-forming and sulfur-bearing minerals. The application of this technology to H APs control will require a more sophisticated approach, based on a fundamental understanding of the mechanisms of trace element removal. The trace elements named as HAPs in the 1990 Amendments to the Clean Air Act can occur in coal in numerous forms. For example, antimony is believed to be present in pyrite, accessory sulfides such as stibnite, and organically-bound; arsenic may be primarily associated with late-stage (epigenetic) pyrite; cadmium is found with sphalerite and other sulfides; chromium may be associated with clays; mercury may occur predominately in epigenetic pyrite; and selenium may be organically-bound or associated with pyrite or accessory minerals such as clausthalite. In addition to a range of modes of occurrence, the range of concentration of trace elements in coals varies remarkably. For example, the United States Geological Survey (USGS) has reported the following range of concentrations for these elements: antimony - ND (not detected) to 35 ppm, arsenic - ND to 2,200 ppm, cadmium - ND to 170 ppm, chromium - ND to 250 ppm, mercury - ND to 5 ppm, and selenium - ND to 150 ppm.