In this study, dynamic analysis of diffusion and convective flows in the pores of calcined limestone pellets, which are used for the removal of acidic gases from flue gases, has been studied using the single pellet moment technique. Experiments have been conducted in a diffusion cell by using nitrogen gas (carrier) flowing through both faces of the pellet. Prior to the diffusion experiments limestone powders were calcined in an atmosphere of N-2 at 800 degrees C. Effective diffusivity of helium has been determined by giving a pulse of helium to the upper face of the calcined limestone pellet and by comparing the response peak on the lower face of the pellet with theoretical expressions. The values of effective diffusivities increased with increasing temperature and pellet porosity. Convective flow contributionto the diffusion flux was found to increase with the increase of pressure drop across the pellet.