EFFECT OF CAS PRODUCT LAYER SINTERING ON LIMESTONE-H2S REACTION

Properties of the CaS produced from sulfidation of limestone and its e ffect on sulfidation rate were investigated by using TG, BET and SEM t echniques. CaS produced from limestone had an initial specific surface area of about 6.1x10(3) m(2).kg(-1) with grain size about 0.25 mu m, but fell to 0.6x10(3) m(2).kg(-1) after sulfidation of 40 minutes due to CaS sintering. The CaS sintering led the product layer to shrink an d lose porosity, and in turn to affect H2S gas diffusion in to the rea ction surface. Conversion of 5 mu m sizes particle only reached about 45% at sulfidation of 25 minutes. An unsteady state product layer diff usion model was developed for describing a gas-solid reaction with a s hrinking product layer. In the product layer, the effective diffusion coefficient, D-es(r) was varied with radius r and also with time t. Th e D-es(r) was determined by porosity changes of the product layer. Goo d agreement was noticed between calculation and experiment results. Ac cording to this model, conversion of 100% is possible obtained by sulf idating limestone particle smaller than 5 mu m.