Possible interactions between As, Se, and Hg during coal combustion

A thermodynamic analysis has determined in detail the speciation of Hg, Se, and As, which are the most volatile trace elements in the flue gas from bu rning bituminous coal, depending on the temperature (400-1800 K), the atmos phere (reducing or oxidizing conditions), and the chlorine content. The amo unt of chlorine in the system greatly affects the identity of stable specie s; the relative affinities of the three elements to chlorine are in the ord er: Se > As > Hg under oxidizing conditions at both high (1100 K) and low ( 600 K) temperatures. Interactions between the three elements are investigat ed; AsSe(g) and HgSe(g) are found to be possibly present as the major speci es in the local CO-enriched zone in a boiler. The competing reactions of th ese three elements for oxygen, hydrogen, and chlorine are also discussed, ( C) 1999 by The Combustion Institute.