A model for the air emissions of trace metallic elements from coal combustors equipped with electrostatic precipitators

Trace element air emissions from pulverized coal combustion facilities are strongly element-dependent. Relatively non-volatile elements such as chromium and manganese are captured with efficiencies comparable to overall particulate capture, whereas more volatile elements such as selenium and arsenic are captured less efficiently than the ash particulate. Such element-specific behavior is a consequence of the partitioning of individual trace elements within the combustion and post-combustion environment, resulting in enrichment of the more volatile compounds in the smallest ash particles, coupled to size-dependent particulate penetration through air pollution control devices. In this paper, a model of trace element emissions that incorporates fundamental laboratory results on trace element partitioning as well as recent field emissions data is developed. Model results and comparison to field data indicate that while the emissions of non-volatile elements such as chromium are currently well predicted by existing database-referenced empirical models, predictions of the emitted concentrations of volatile compounds such as arsenic and selenium can be improved by more than 25% through incorporation of element and size-dependent partitioning and penetration.