Incomplete pore diffusion effect on internal burning of carbon

Abstract

The internal burning of carbon, e.g. graphite or coke, controlled simultaneously by the counterdiffusion of CO 2 and CO in the pores and the chemical reaction on the pore walls, is investigated through mathematical analysis. Because of the strong poisoning effect of CO on the rate of oxidation of carbon, incomplete pore diffusion markedly reduces the depth of internal burning. The effects of particle size, temperature and pressure on the rate of oxidation of graphite and coke in CO 2-CO mixtures derived from the mathematical analysis are found to be in reasonable accord with present and previous experimental observations. At the limiting case of incomplete internal burning, i.e. pore diffusion control, the rate per particle is found (1) to be proportional to the external geometrical surface area, (2) to be independent of pressure, and (3) to have an apparent heat of activation half of that for complete internal burning (chemical reaction control).