The combustion of char particles including the effects of external mass transfer, surface reaction, pore diffusion, and pore growth is analyzed theoretically. A random pore model is used to relate pore surface area, pore volume and effective diffusivity to the local burnoff. The equations for oxygen concentration and burnoff as functions of time and position are solved analytically for the limiting case of strong diffusional limitations (high temperature or particle size) and numerically for the general case. The results include the variation of particle size and density with burnoff under conditions pertinent to pulverized and fluidized combustion. The analysis is compared with previous analyses from the literature.
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