The low cost CaSO4based oxygen carrier has been proposed as an alternative oxygen carrier for chemical-looping combustion of coal.The reduction of CaSO4to CaS is an important step for the cyclic process of reduction/oxidation in chemical-looping combustion of coal with CaSO4based oxygen carrier.Thermodynamic analysis of CaSO4oxygen carrier with CO based on the principle of the Gibbs free energy minimization showed that the main products of reduction were CO2

while the solid products were CaS instead of CaO.The reduction kinetics of a CaSO4based oxygen carrier with CO was investigated in a differential fixed bed reactor.The effects of gas partial pressure(20%-70%)and temperature(880-950℃)on the reduction were investigated.The reduction was described with shrinking unreacted core model.Experimental results of CO partial pressure on the solid conversion showed that the chemical reactions were of first order with respect to the CO and H2partial pressure for the fresh oxygen carriers.Both chemical reaction control and product layer diffusion control determined the reduction rate.The dependences of reaction rate constant and effective diffusivity with temperature were both obtained.The kinetic equation well predicted the experimental data.The kinetic study provided important information for the future use of CaSO4oxygen carrier in CLC of solid fuels and the design criteria of a CLC system.