18 Experimental study of toxic metal-sorbent reactions in a bench scale combustor

摘要

Toxic metals may enter a combustion chamber in many physical or chemical forms, for example, as a consitituent of a hazardous or municipal solid waste to be incincerated or as a trace quantity in coal. Control of toxic metal emissions from combustors is currently being stipulated by the U.S.EPA in the form of maximum achievable control technologies (MACT) for 11 metals (As, Be, Cd, Co, Cr, Hg, Mn, Ni, Pb, Sb, and Se) and their compounds under Tile III of the 1990 Clean Air Amendments. However, this is a problematic proposition for volatile metals such as mercury, lead, and cadmium. Volatile metals introduced into a combustion device may enter the gas phase at combustor temperatures, and then as the temperature decreases downstream of the combustor, undergo nucleation to form a submicrometer sized aerosol that is not easily captured by conventional air pollution control equipment.~(1-3) Several researchers have proposed using builk solid sorbents in several geometries (packed bed, fluidized bed, and dry sorbent injection) and have demonstrated the potential to effectively remove metals from an air stream by means of chemisorption.~(4-8) Chemisorption is preferred over physisorption because the metals may become environmentally immobile when chemistored by certain materials.~7 Equuilibrium calculations have been performed for a number of toic metals reacting with sorbents to establishe the relative effectivess of various sorbents.~9