Trace elements from combustion and gasification of coal—An equilibrium approach

Abstract The fate of several trace elements in the thermal conversion of coal has been investigated, assuming global equilibrium and using an in-house database and a Fortran-77 computer code for the calculations. The format and content of the database DGFDBASE, containing reduced data on ΔG°fi(T) for approximately 800 chemical species of the elements Al, As, B, Be, Br, C, Ca, Cd, Cl, Co, Cr, F, Fe, Ga, Ge, H, Hg, K, Mg, N, Na, Ni, O, P, Pb, S, Sb, Se, Si, Sn, Ti, V and Zn are described. Results of thermodynamic equilibrium calculations performed using ‘the total Gibbs free energy minimization’ program MINGTSYS on simple systems containing one of the trace elements As, B, Be, Cd, Co, Cr, Ga, Ge, Hg, Ni, P, Pb, Sb, Se, Sn, Ti, V and Zn are presented and compared with results from the literature. Combustion as well as gasification conditions have been considered. At oxidizing conditions all the trace elements considered form at least one stable condensed phase in the temperature range from 300–2000 K. Regarding the condensed phase being stable at the lowest temperatures, the trace elements can be divided into two groups, the first of sulfate forming elements (this group includes the elements Be, Cd, Co, Cr, Hg, Ni, Pb, Sb, Sn, V, and Zn) and the latter of oxide-hydroxide forming elements (this group includes the elements: As, B, Ga, Ge, P, Se and Ti). At reducing conditions, the behavior of the trace elements considered is complex, and no simple classification of the elements is possible.