Diffusion and convective flow in the pores of pellets formed by compressing mixtures of calcined limestone and CaSO4/CaCl2 powders have been studied experimentally by using the single pellet moment technique. The experiments were conducted in a diffusion cell by flowing nitrogen gas (carrier) through both faces of the pellet. Limestone powder was calcined in an atmosphere of N-2 at 800degreesC and mixed with CaSO4/CaCl2 for diffusion experiments. Effective diffusivity of helium has been estimated by exposing the upper face of the pellet to a pulse of and matching the response peak on the lower face of the pellet with theoretical expressions. The values of the effective diffusivities increased with temperature, but decreased with increasing CaSO4/CaCl2 content in the pellet. The convective flow contribution to the diffusion flux was found to increase with increasing pressure drop across the pellet.