Release and fate of pyritic sulfur in chemical looping combustion

Chemical-looping combustion (CLC) technology is an attractive solution for efficient fuel conversion with inherent separation of the greenhouse gas CO2. Sulfur is a major consideration in coal utilization, and pyrite is the major inorganic sulfur contaminant in most coals, therefore the release and fate of pyritic sulfur in the CLC process was investigated. A natural iron ore, and two synthetic materials (CuO/SiO2 and NiO/Al2O3) produced by the impregnation method were selected as oxygen carriers to investigate the effect of oxygen carrier on the sulfur distribution. Results showed that SO2 was the major sulfurous gas released, and a small amount of H2S and CS2 was escaped from the reactor in the reduction stage. The fractions of sulfur converted to gaseous substances in this stage were 90.38%, 82.22%, and 78.00% when using iron ore, CuO/SiO2, and NiO/Al2O3 respectively. Part of sulfur was stored in the oxygen carrier, and the presence of metal sulfides was confirmed by X-ray diffractometer (XRD). In the reoxidation stage, SO2 was produced by the oxidation of metal sulfides. The fraction of sulfur converted to gaseous species in this stage reached 2.26%, 11.84%, and 15.42% for iron ore, CuO/SiO2, and NiO/Al2O3 respectively. The accumulation of sulfur on the surfaces of three oxygen carriers was all detected by the Energy dispersive X-ray spectroscopy (EDX).