An extended coal combustion model

Current coal combustion models are a useful tool in research but they use simplified coal particle devolatilisation and combustion steps in order to meet computational limitations. The availability of more advanced computers enables the use of more detailed steps for devolatilisation and the use of more realistic char combustion processes. In the present work the devolatilisation rates were calculated using the coal devolatilisation model FG-DVC. In this way devolatilisation rates and the yields of char and volatile were obtained. A drop tube reactor was operated at 1623 K to collect char samples, from Thoresby coal, at different sampling positions or residence times, and proximate and ultimate analysis were conducted on these char samples to confirm the results. The detailed char combustion sub-models being developed for CFD codes require char properties such as densities, surface areas and pore size distributions but a simplified model was used here. In this case the use of a simple global char oxidation model together with an empirical derived 'volatile' and FG-DVC predicted devolatilisation rate data seem to give good agreement with the experimental results available for the char burnout. However, there still remains considerable uncertainty in the use of char burnout models including the one used here is not sufficiently accurate in predicting carbon burnout in all conditions. (C) 1999 Elsevier Science Ltd. All rights reserved.