Influence of gas environment on reactions between sodium and silicon minerals during gasification of low-rank coal

Thermodynamic equilibrium calculations were performed to determine the possible compositions and conditions for formation of potential liquid phases responsible for fluidised bed agglomeration during gasification of a high-sulphur low-rank coal from South Australia. The coals from this region of Australia are typically characterised by containing high levels of sodium, silica and sulphur. The transformation behaviour of the form of sodium present in coal, as either a carboxylate forming part of the coal organic matter or as soluble salt (NaCl) and its reaction with silicon compounds (silica or kaolin) is presented. The influence of temperature and gas atmosphere on equilibrium composition was evaluated. Thermodynamic equilibrium calculations show that the distribution of sodium among the produced species will depend on the form of sodium in the coal, the gas atmosphere and the forms in which silicon is present in the coal. Steam was found to have the most significant effect causing a lowering of the sodium carbonate melting point temperature.