A model of sulphur retention by limestone in presence of inerts has been developed

which blaze the following new trails:（1）the effect of sorbent chemical composition on the process of SOZ capture is stressed and the amount of inerts in limstone is taken as an palameter:（2）mass equations in transient nature for modelling SOZ diffusion into a lime particle is established and errors caused by traditional Pseudosteady assumption are eliminated;（3）the influence on gas difffusion in the process exerted by pore structure variations of the particle is taken into consideration. By scattering a series of partial differential equations in the model

a numerical method called limited Wegstein with the merits of quick convergence and high precision has been achieved.The calculation results have revealed that the presence of inerts benefits slowing down the pore blocking process

so the calcine utilization in calcine is improved

however

if the fraction of inerts in calcine is too large the overall rate and capacity of calium sulphation may be very low.The concept of the optimal amount of inerts in calcium for sulphation and the criteria for selecting limestone used as desulphurizer in fluidized beds have been proposed here which will find practical applications.