Chemical looping gasification with a CuFe2O4-enhanced phosphogypsum oxygen carrier during reduction in a fluidized bed reactor

Abstract Aiming to solve the H2S releasing and reduce the temperature of reaction system from a Phosphogypsum (PG) Oxygen carrier (OC) during Chemical looping gasification (CLG), a new CuFe2O4-enhanced PG-CuFe2O4 OC for reducing lignite in the CLG process was explored. In this study, using lignite as a fuel, X-ray fluorescence spectrometer (XRF), Scanning electron microscope-Energy dispersive spectrometer (SEM-EDS), X-ray diffractometer (XRD), X-ray photoelectron spectrometer (XPS) were used to characterize the reduction process of PG-CuFe2O4. Thermodynamics and kinetics analyses of CuFe2O4-enhanced PG OC in a fluidized bed during reduction with lignite were conducted to better understand H2S capture and syngas production. The experimental results and mechanism analysis were as follows. In the fluidized bed reactor, to produce syngas with the highest possible proportions of CO and H2, the optimum reaction conditions were: reaction temperature should not exceed 1123 K, but 1073 K is recommended; the water vapor content R = 0.2; and PG-CuFe2O4 OC and lignite oxygen carbon ratio X = 0.6. During the reduction reaction, S6+ was reduced to S2− and Cu2+ was reduced to Cu1+ and Cu0. In addition, Fe3+ was reduced to Fe3/8+ and a small amount of Fe3/8+ was reduced to Fe2+. The mechanisms of oxygen release by OC during the reduction process followed the priority order: CaSO4 ˃ CuO ˃ Cu2O ˃ Fe2O3 ˃ Fe3O4 ˃ FeO. The PG-CuFe2O4 had an excellent H2S capture ability and the reduction intermediate products of Fe3O4, Cu, and FeS played important roles in the capture of H2S during the reaction. Using Kissinger and Flynn-Wall-Ozaw methods, the mechanism model of PG-CuFe2O4 OC during reduction process was confirmed, and the reaction kinetics model was dX dt = 1.98 × 10 18 exp - 215.02 × 10 3 RT × 3 2 ⊢ X 1 / 3 - 1 - 1 .