Chemical looping with oxygen uncoupling of high-sulfur coal using copper ore as oxygen carrier

Abstract

Chemical looping with oxygen uncoupling (CLOU) has been viewed as a promising candidate for solid fuel combustion with inherent CO2 separation at considerably low energy penalty. This work aimed to investigate the sulfur evolution behavior and performance of copper ore oxygen carrier (OC) within the CLOU process using a typical high-sulfur content coal in Sichuan (SC), China as fuel. Experiments at different temperatures and oxygen to fuel ratios were conducted in a laboratory-scale fluidized bed reactor and comparisons have been made between SC coal and Gaoping (GP) anthracite with low sulfur content. It was found that both the increase of temperature and decrease of oxygen to fuel ratio can enhance the generation of sulfurous gases. There were two SO2 peaks during the CLOU process of both SC and GP coals, due to the two relatively independent stages of coal combustion process: volatiles combustion and coal char combustion. The second peak was generally more sensitive to temperature, and a higher temperature would contribute to much more SO2 generation. Cyclic redox experimental results of SC coal in fluidized bed reactor showed stable sulfur evolution trend and moderate reactivity of copper ore OC. Moreover, calcium oxide (CaO) was introduced as desulfurizing agent to remove the sulfurous gases generated in the CLOU process of SC coal and the desulfurization efficiency was achieved as high as 98%. XRD and XPS analyses showed that no metallic sulfide was detected on the surface of the reduced OC samples and ESEM images indicated that no serious sintering problem occurred to the used particles.