The prediction of char combustion kinetics at high temperature

The optimisation of numerical methods applied to the description of char combustion behaviour is required in order to achieve a good prediction of the amount of unburned carbon in fly ash from pulverised coal fired boilers. A question that arises is whether it is necessary to take into account the distribution of the coal properties and reactivity and how to describe them in such a simplified way in order to be handled in a simulation code. The reliability of a simple model for char heterogeneous oxidation describing the burning of single char particles has been assessed through the use of available experimental data for a high volatile bituminous coal in a pilot plant, under single stage and staged combustion conditions. Experiments in an electrodynamic chamber effected on the char particles collected in the pilot plant, showed the heterogeneity of particles properties, evaluated by fitting the temperature-time histories of single burning particles. The model was later used to predict kinetics data at high heating rate to be used in comprehensive code: the results of the prediction provide a reactivity distribution expressed in the form of a pre-exponential factor as a function of particle size. (C) 2000 Elsevier Science Inc. All rights reserved