Trace elements in two pulverized coal-fired power stations.

Abstract

Beside major pollutants (particulates, carbon, sulfur, and nitrogen oxides), coal combustion generates emissions of potentially toxic trace elements. The current work focuses on predicting the fate of eight trace elements (As, Cd, Hg, Ni, Pb, Se, V, and Zn) in power stations that fire pulverized coal and are equipped with flue gas scrubbers. The core of the study is global equilibrium analysis carried out with the aid of three extensive databases. The first set of equilibrium constants describes conditions prevailing in the furnace and the flue gas duct, while the second set describes reactions in the flue gas scrubber. Melting behavior of ash and solubility of trace elements within the slag are described as a third set of data. To test the modeling approach taken in this paper, the predicted overall partitioning of trace elements is compared with measured data from two full-scale facilities. The results of the study indicate that As, Cd, Ni, Pb, V, and Zn are captured in the fly ash, and that the fate of these element correlates with the overall particle capture of the power plants. Calculations for the flue gas scrubber facilities show that nonvolatile trace elements are likely to dissolve in the scrubber solution, and that capture of these elements likewise is correlated with the overall particulate behavior. Theoretical predictions of the melting behavior indicate that As, Ni, Zn, and to some extent Pb are likely to dissolve in the molten ash.