Diffusion effects burning within particle

The calculated profiles of O2 concentration and carbon load within a single particle during regeneration are shown in Figure 6.9.11 for two typical burn-off temperatures (450 and 550 °C). The initial effectiveness factor r/o (calculated with the initial Thiele modulus 4>o for ic = Ic,o) as a measure for the magnitude of the pore diffusion resistance is also given. 

In reality, CO is always formed in the initial reaction stages. The CO subsequently diffuses outward and reacts with oxygen. However, if CO bums within the boundary layer, the effective surface product is carbon dioxide, and the first stoichiometry is used. On the other hand, if CO burns outside the boundary layer, the effective surface product is CO and the second stoichiometry is utilized. Carbon dioxide can diffuse back to the char particle and react ... 

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