Abstract: The gas-solid reaction aA(g)+bB(s)=cC(g)+dD(s) taking place in packed bed is studied.Convection reaction-diffusion equations for gaseous reactant and gas product are presented and solved analytically.Case computation shows that the radius of pellet affects concentration of gases considerably, and the effect can be measured by Thiele module.Since Thiele module is proportional to L² and Peclet module is proportional to L, the length of reactor itself is an important factor to affect the reaction and conversion.The overall rate of REV has greater influence on the reaction and conversion that take place in packed bed than that of convection.Therefore it is important to give the exact reaction term.

Key words: convection-reaction-diffusion-analytical solution, multi-phase gas gas-solid reaction, Thiele number, Peclet number