STATE-OF-THE-ART OF MERCURY CONTINUOUS EMISSION MONITORS FOR COAL-FIRED SYSTEMS

摘要

With the decrease in mercury emissions from other sources, recent attention has focused on mercury emissions from coal-fired utility boilers. Although there are several wet-chemistry methods validated for measuring mercury in combustion flue gases, these methods are difficult to perform, costly, time-consuming, and labor-intensive. Also, the results typically are not available for several days. Therefore, development of a continuous emission monitor (CEM) requiring minimal operator input to provide near-real-time mercury emission data that could be used as feedback control for mercury control systems is attractive. A number of on-line analyzers have been developed primarily for measuring mercury emissions from waste incinerators. However, application of these mercury CEMs to the flue gas from coal-fired boilers presents significant challenges. Typically, the flue gas mercury concentration is less than 10 mg/Nm~3 and contains fine paniculate that must be removed prior to mercury measurement. Also, the presence of acid gases including HC1, SO_2, and NO_x may interfere with the analyzers, requiring some form of pretreatment or conversion. To evaluate the accuracy and reliability of mercury CEMs, several test programs have either been completed or will be completed during the next year. These include a formal test sponsored by the U.S. Environmental Protection Agency (EPA) Office of Solid Waste and the U.S. Department of Energy in 1997 as well as tests conducted by the European certification agency TUeV Rheinland. In October 2000, Battelle, under its Environmental Technology Verification Program (funded by EPA), will be evaluating up to eight different CEMs at EPA's pilot-scale facility in Research Triangle Park. In addition, the Energy & Environmental Research Center (EERC) has conducted pilot- and full-scale projects that utilized several mercury CEMs. The results of the EERC tests have shown that the Sick Instruments MERCEM, PS Analytical Sir Galahad, and Semtech Hg 2010 had the capability of measuring total vapor-phase mercury in coal combustion flue gas within 20% of the wet-chemistry methods.