Prediction of the distribution of trace elements between the product streams of the Prenflo gasifier and comparison with reported data

The equilibrium distribution of the major, minor and trace elements in Pittsburgh No. 8 coal has been predicted for gasification under the conditions of the Prenflo gasifier using the FACT and MTDATA suites of predictive programs. The databases normally available with these programs have been supplemented with the MIRO-NPL oxide melt representation, a model of oxide melts from the field of geochemical modelling and representation of trace element solution in oxide melts based on the IMCC model. The results have been compared with observations at the Hirstenhausen Prenflo plant available in the literature. The gasifier is modelled as two regions: in the first the temperature is high (1400-2300 K) and the reacting mixture consists of the coal, carrier gas, added steam and oxygen. In the second region the equilibrium mixture from the first is quenched by addition of an equal amount of the cooled, dried product gas, then cooled in 10 K steps from 1073 to 473 K. The observed and predicted distributions of the elements are in general agreement. The elements may be grouped into those which are virtually immobile (Cr, Ni, Ba, Mn, V), somewhat mobile (Mo, Cu, Be), mobile (Sb, B) and almost totally mobilised (As, Cd, Pb, Tl, Sn, Zn) according to predictions, and this grouping is consistent with the experimental mobility as deduced from the relative abundances in slag, fly ash and filter cake. On cooling, arsenic is found to persist in the gas at 473 K at the highest fraction of the input level of any of the trace elements, which is consistent with observations. (C) 2001 Elsevier Science Ltd. All rights reserved.