Measurement and Modeling of Air Toxics Emissions from Large-Scale Coal Combustion Equipment

The U.S. EPA is required by the 1990 Clean Air Act Amendments to evaluate the emissions of 189 hazardous air pollutants (including trace metals) from electric utilities and determine the levels of control achievable by flue gas scrubbing devices. Sampling and analysis efforts, supported largely by EPRI and DOE, have indicated that for most metals, high removal efficiencies can be achieved by facilities equipped with particulate control devices. Emissions of hazardous organic compounds may likewise be negligible from a health risk perspective. However, certain metals such as mercury, selenium, boron and some radionuclides are not as well controlled with particulate matter control. This paper compares the results of a modeling effort to predict metals behavior in coal-fired boilers with measured data from several sources. The results provide insight into the mechanisms responsible for fugitive volatile metals release, and in some cases the options the boiler operator may have to consider for mitigation of toxic metals emissions. This approach can serve as a guide to help planners, engineers, and facility owners/operators predict the levels of metals emissions from their facilities and to gain insight on the impact of coal characteristics,operating conditions and APCD design on metals emissions.