The reactivity of CuO oxygen carrier and coal in Chemical-Looping with Oxygen Uncoupled (CLOU) and In-situ Gasification Chemical-Looping Combustion (iG-CLC)

Abstract

Chemical-looping combustion (CLC) has the primary advantage of the generation of a CO2 enriched flue gas, which greatly benefits CO2 capture. Many researchers have been particularly interested in developing combined or mixed oxygen carriers (OC) to enhance and improve single metal OC properties. To advance the development of mixed OC, this study first focused on the conditions that impact the chemical reactions taking place in both In-situ Gasification Chemical-Looping Combustion (iG-CLC) and Chemical-Looping with Oxygen Uncoupled (CLOU) for single metal Cu based OC with coal and the gas product distributions. The Cu compounds present during CuO reduction (CuO→Cu2O→Cu) were also investigated using X-ray diffraction (XRD) as a function of carbon conversion during the reaction. In this study, the reactivity of char with CuO was tested at two different ratios of CuO to coal char (ϕ = 26 and 8) at 850 °C and 950 °C in Ar and Ar + H2O. Char conversion rates were greater at higher reaction temperatures (950 °C vs 850 °C) for all rests. At a high ratio of oxygen carrier to char (ϕ = 26), char was fully converted by reacting with O2 released from CuO at both 950 °C and 850 °C in Ar. CuO was reduced to Cu2O resulting from the thermal release of gaseous oxygen. At a low ratio of oxygen carrier to char under Ar + H2O (ϕ = 8), char was fully converted at both 950 °C and 850 °C by char combustion with O2 from the OC and syngas CLC from char-H2O gasification. Additionally, CuO was reduced to metallic Cu. IG-CLC had a lower CO2 capture efficiency with CO in the product gas and a lower carbon conversion rate compared to CLOU. From a reactivity view point, CLOU is a promising process for coal chemical-looping combustion.