Investigation of reactivities of bimetallic Cu-Fe oxygen carriers with coal in high temperature in-situ gasification chemical-looping combustion (iG-CLC) and chemical-looping with oxygen uncoupling (CLOU) using a fixed bed reactor

Abstract

Bimetallic Fe-Cu oxygen carriers (OCs) with SiO2 as a support are attractive materials for coal chemical-looping combustion (CLC) based on their availability from naturally occurring, low cost materials. The objectives of this study are to investigate reduction reactivities and CO2 conversion efficiency of synthesized Fe-Cu-Si OCs for both in-situ gasification CLC (iG-CLC) and Chemical-Looping with Oxygen Uncoupling (CLOU) at high temperatures (950 to 1100 °C) with varying ratios of OC to coal char (ϕ) using a fixed bed reactor-quadrupole mass spectrometer system. Two Cu-Fe-Si OCs with high iron content (40% Fe2O3 + 20%CuO by wt.) (Fe40Cu20) and high copper content (Fe20Cu40) were prepared using a pressure pelletizing method. Oxygen uncoupling efficiency and rate for the Fe40Cu20 OC were lower than the Fe20Cu40 OC due to their CuFe2O4 and CuO composition difference from XRD analysis. For Fe40Cu20 OC with ϕ = 80 in iG-CLC, the carbon conversion rate increased 37% from 950 °C to 1000 °C but only increased 5.4% from 1000 °C to 1100 °C. As the ratios ϕ dropped (80, 40 and 24), the CO2 conversion efficiencies decreased and the content of metallic Cu in the reduced OC residues increased. So, the optimum ratio ϕ is important to avoid agglomeration caused by Cu at high temperature. The Fe20Cu40 OC with ϕ = 67 in CLOU had higher the carbon conversion rate (dXc/dt = 0.0083 s−1) and CO2 conversion efficiency (Sco2 = 0.96) compared to the Fe40Cu20 OC with ϕ = 80 in iG-CLC (dXc/dt = 0.0037 s−1 and Sco2 = 0.88).