Flue gas effects on a carbon-based mercury sorbent

Coal is now the primary source of anthropogenic mercury emissions in the United States, accounting for 46%, or 72 tons/year, of the total U.S. Environmental Protection Agency (EPA) estimated 158 tons/year [U.S. Environmental Protection Agency, Mercury Study Report to Congress, EPA/600/P-94/002Aa, External Review Draft, Jan. 1995.]. Development of cost-effective mercury control for coal-fired boilers is a primary research need identified in the EPA Mercury Study Report to Congress [U.S. Environmental Protection Agency, Mercury Study Report to Congress, EPA/600/P-94/002Aa, External Review Draft, Jan. 1995.]. During combustion of mercury-containing fuels such as coal, the mercury is completely volatilized and is not controlled by conventional particulate control devices unless the solid material effectively traps the mercury through sorption mechanisms. Typically, this does not occur naturally to a significant degree by the collected ash material. However, a promising approach for mercury control is the injection of an effective sorbent upstream of the particulate control device. Since the amount of mercury in the gas stream from coal combustion is usually in the range of 5 to 10 mu g/m(3) (about 1 ppbv), only very small amounts of a sorbent may be necessary. A requirement is that the mercury be tightly bound in the sorbent, not desorbing upon exposure to ambient air or leaching under wet disposal conditions. On a worldwide basis, the projected increase in coal usage over the next two decades in China, India, and Indonesia will dwarf the current U.S. coal consumption of 1 billion tons/year [International Energy Outlook, U.S. Department of Energy, Energy Information Administration, Office of Integrated Analysis and Forecasting, Washington, DC, April 1998, DOE/EIA-0484(98).]. Therefore, in the United States, coal will be the dominant source of mercury emissions, and worldwide, coal may be the cause of significantly increased mercury emissions unless an effective control strategy is implemented. However, there is much uncertainty over the most technically sound and cost-effective approach for reducing mercury emissions from coal-fired boilers. (C) 2000 Elsevier Science B.V. All rights reserved.