Investigation into sulfur release in reductive decomposition of calcium sulfate oxygen carrier by hydrogen and carbon monoxide

Chemical looping combustion (CLC) is a promising technology with the inherent property of separating CO 2 from flue gas. For calcium sulfate (CaSO 4) oxygen carrier, the inhibition of the produced sulfurous gases in the reduction of CaSO 4, including sulfur dioxide (SO 2), hydrogen sulfide (H 2S) and carbonyl sulfide (COS), is the key for a CLC system. In this paper, the sensitivities of reacting temperature, oxygen ratio number (defined in this paper) and the mole fraction of both carbon monoxide (CO) and hydrogen(H 2) in the syngas to the sum of the amounts of released SO 2, H 2S and COS are discussed respectively. Thermo-gravimetric analysis (TGA) tests demonstrated that the amount of the produced sulfurous gases is greatly dependent on the partial pressure of H 2 or CO in the reduction of CaSO 4. When the partial pressure of H 2 or CO is higher than 40 kPa, the production of sulfurous gases, indicating the deterioration of the recyclability of CaSO 4, can be prevented completely even if the reacting temperature is as high as 1000 °C. A new kind of CaSO 4/CaCO 3 oxygen carrier is prepared using a mechanical mixing method. The addition of CaCO 3 nanoparticles largely improves the recyclability of the oxygen carrier in comparison with the fresh CaSO 4 oxygen carrier, without CaCO 3 nanoparticles, in a multi-cycle TGA test.