Investigation of low-cost oxygen carriers for chemical looping combustion at high temperature

Chemical looping combustion (CLC) allows combustion with less complex effluent than typical atmospheric combustion. CLC, which oxidizes the fuel with a regenerable solid oxygen carrier (OC), typically requires a step to separate unburned carbon and ash from the OC using a separation unit. This study investigated the use of high temperature combustion (1100 degrees C) and low-cost OCs prepared using readily available natural and industrial waste materials to potentially reduce the need for the separation step. Two OC materials consisting of 1) iron-impregnated FCC, a spent fluid cracking catalyst and 2) red mud, the main waste product from the extraction of alumina from bauxite, were compared to a benchmark natural hematite. The high temperature conditions led to sintering and attrition of the hematite. Red mud was found to also suffer apparent sintering and attrition. Iron-impregnated FCC showed little morphology change or attrition when the fuel was limited to the amount that could be oxidized without reducing the iron beyond Fe3O4. The most promising candidate proved to be FCC loaded with a moderate amount of iron, and optimization may further improve the stability and performance.