Variation of Apparent Reaction Order in Char Combustion and Its Effect on a Fractal Char Combustion Model

The variation of the apparent reaction order, , during char combustion is studied by simulating the combustion process inside the char particle pores. An expression for is obtained as a function of the particle temperature, the O2 partial pressure, and the pore structural parameters. A modulus, , is shown to represent the pore diffusion resistance, with a sufficient condition for given based on . becomes lower as the particle temperature and the O2 partial pressure increase and the pore structure has higher diffusion resistance. The expression for is used to improve the accuracy of a previous fractal char combustion model. The effect of on the char combustion rate and the regularity of how changes in the char combustion process are also studied.