Thermodynamic equilibrium study of trace element mobilisation under pulverised fuel combustion conditions

The thermodynamic equilibrium distributions of the trace elements lead, arsenic, zinc, copper, nickel, chromium, manganese and boron have been examined using the factwin computational software and associated databases. It is found that the facility for simulation of these elements in a comprehensive model of the oxide melt formed by the major coal mineral elements and (in the early stages of combustion) in an extended sulphide melt model enhances the value of the predictions over those for earlier restricted fact melt models. This is emphasised by comparison with the limitations of predictions for strontium, barium and vanadium, for which no solution models are available in factwin. The influence of sulphur and chlorine concentration variations on the mobilities of the elements varies, and can differ markedly between oxidising and reducing conditions. The predictions are extensively compared with published partitioning results calculated from experimental observations on large combustors. Given the uncertainties involved in both observations and predictions, the degree of agreement is considered satisfactory. The condensation sequence from the equilibrium gas phase at 1300 K has been predicted on cooling, in isolation, by 10 K steps. An alkali sulphate-based melt is predicted to form, and the majority of the other elements are predicted to form sulphates, implying development of a complex sulphate melt, which cannot at present be modelled.