EVALUATION OF CHAR REACTIVITY DATA BY DIFFERENT SHRINKING-CORE MODELS

Carbon reactivity was measured in two entrained flow reactors, two dro p tube furnaces and one fluidized bed. The results were interpreted by using three shrinking-core models. A number of minor differences betw een the models were identified and the resulting deviations could most ly be ascribed to non-measurable parameters such as particle specific heat capacity as a function of temperature, boundary layer gas composi tion and Nusselt and Sherwood numbers, together with bulk flow equatio ns and numerical procedure. Using all experimental data, the calculati ons gave different overall activation energies ranging from 107 to 130 kJ mol(-1). The differences between the model calculations with respe ct to overall kinetics were small but significant under realistic cond itions for combustion and for the experiments performed. A comparison between individual experiments showed that for experiments performed w ith small coal particles, long residence times or preheated particles, good agreement between model results was obtained. This was not so fo r larger particles, short residence time and no preheating, since data taken under transient conditions impair the results. Guidelines are g iven for experimental design for making reactivity measurements on sol id fuels in experimental reactors. Copyright (C) 1996 Elsevier Science Ltd.