Thermodynamic equilibrium study of trace element mobilisation under air blown gasification conditions

Thermodynamic equilibria have been examined for several trace elements at levels found in coal that might be used in the air blown gasifier air (ABG). The results obtained with the FACTWIN suite of programs were used to test the degree to which predictions are consistent with observed partitioning. Conditions of lime-free gasification, gasification with the design limestone addition and limestone addition at a higher fuel-lime ratio have been examined for 20 atm. pressure over a range of temperatures. The effects of varied sulphur and chlorine levels have also been examined. Curtailment of the ABG program means that the range of experimental data does not allow deep comparison of predictions with observations but in general there is broad agreement. It is concluded that the results form the basis of a method of representing the potential for mobilisation (low to standard limestone) from coal particles followed by reincorporation into condensed phases (standard to high limestone) during the in-bed processes. Simulation of cooling of the equilibrium gas phase at 1273 K in isolation by 10 K steps predicts incorporation of a range of elements into a matte, and others into an alkali-based chloride melt. (C) 2001 Published by Elsevier Science Ltd.