General modeling and numerical simulation of the burning characteristics of porous chars

The modeling and numerical simulation of char burning rate within the temperature range of 1273-1700 K, which is the normal range in most boilers and furnaces, were carried out in this paper. Considering the differences in pore structure between char and non-porous carbon, several key issues were studied and discussed, including fresh char reactivity and its change during the burning process, and the effects of internal oxygen diffusion on the char burning rate. In the section of modeling, dozens of model equations were given and then implanted into the computational code. In the section of numerical simulation, the predicted values were compared with the experimental data gained from the entrained flow reactor including carbon conversion and apparent diameter change of coal char along the tube length, and good agreement was obtained. Additionally, the numerical simulation for biomass char burning was also done and the applicability of the developed model was discussed. The developed char burning model needs few empirical parameters, which can be used conveniently in the numerical simulation of actual combustion process. (C) 2012 The Combustion Institute. Published by Elsevier Inc. All rights reserved