2-STAGE SIMULATION OF THE MAJOR HEAVY-METAL SPECIES UNDER VARIOUS INCINERATION CONDITIONS

A thermodynamic equilibrium model was used to determine the major spec ies of chromium, lead, cadmium, copper, and zinc formed under various incineration conditions. The effects of temperature and oxygen, chlori ne, sulfur, and hydrogen content on the speciation were established by the minimum Gibbs free energy method. Sixty-seven compounds of five m etallic species were determined in this study. The simulation conditio ns included: 1) single metal with oxygen, chlorine, and sulfur system; 2) different chlorine and hydrogen content; and 3) comparisons of a s ingle combustion chamber and a two-stage combustion chamber. The simul ation results indicated that the oxides were the dominant forms in a s ingle metal-oxygen system, while the metallic chlorides were the major species in a metal-chlorine-oxygen system. When sulfur was present, i n the case of all metals other than Pb, the metallic sulfates were the major species at temperatures below 1000 K, and metallic oxides were the dominant species above 1000 K. Increasing the temperatures caused a decrease of lead chloride, but increased the formation of other meta llic chlorides. The concentrations of metallic chlorides decreased sig nificantly as the hydrogen moles were 2 similar to 3 orders higher tha n those of chlorine. The level of difference between one-stage and two -stage simulations depends on the species formed in the one-stage simu lation. (C) 1998 Elsevier Science Ltd.