Sulfur Transformation Behavior of Inorganic Sulfur-Containing Compounds in Chemical Looping Combustion

Chemical looping combustion (CLC) is a promising technology for fuel conversion with inherent carbon capture. Because sulfur is an integral part of coal, the existence of sulfur contaminants in coal may degrade the purity of CO₂ and deteriorate the performance of the oxygen carrier in the CLC process. To uncouple the complex behavior of inorganic sulfur in coal, sulfur release of three inorganic sulfur-containing compounds (FeS₂, FeSO₄, and CaSO₄) mixed with activated carbon during the temperature-programmed process and the CLC process using iron ore as an oxygen carrier were investigated in a batch fluidized bed reactor at 950 °C. The results showed that, in the temperature-programmed process, the initial decomposition temperatures of FeS₂, FeSO₄, and CaSO₄ were about 400, 500, and 650 °C, respectively. During the reduction and oxidation stages of CLC, SO₂ was the main sulfur-containing gaseous compound. The sulfur stability of CaSO₄ was higher than those of FeS₂ and FeSO₄. The fractions of sulfur converted to gaseous species in the reduction stage (XS,g,ᵣₑd) of FeS₂ and FeSO₄ reached 90.38 and 87.42%, respectively, within 20.5 min, while the corresponding value was 53.97% for CaSO₄. During 5 cyclic redox experiments at 950 °C, the fraction of sulfur converted to gas species was almost maintained stable, while the energy-dispersive X-ray spectroscopy analysis showed the accumulation of sulfur after the cyclic reaction.