Behaviour of a bauxite waste material as oxygen carrier in a 500 Wth CLC unit with coal

Abstract

This paper is focused on the Chemical Looping Combustion (CLC) of coal. Under this configuration, coal is fed directly into the fuel reactor where coal is gasified and the gaseous products react with the oxygen carrier. In CLC of coal it is especially interesting to consider low cost oxygen carriers as some losses of solid material may occur during the ashes drainage. The performance as oxygen carrier of a Fe-enriched sand fraction (Fe-ESF) generated in the alumina production from bauxite is evaluated in this work. The experiments were carried out in a continuous 500Wth unit using a bituminous coal. Different variables affecting the process were analyzed, such as the temperature in the fuel reactor, coal feeding rate, solid circulation flow and composition of the gasifying gas. High combustion efficiencies in the fuel reactor (around 90%) were obtained at all the temperatures tested. Low oxygen demand (<5%) values were also obtained in the temperature interval tested (880–930°C). Higher temperatures or the use of a carbon separation system would be needed to have high carbon capture efficiencies. Regarding OC performance, good results were found. During 40h of continuous operation, the attrition rate was adequate and no agglomeration problems were detected. The reactivity of the oxygen carrier slightly increased as well as the porosity. Compared to ilmenite, the most tested oxygen carrier material so far for this process, the Fe-ESF material provided lower oxygen demand at the fuel reactor outlet and higher oxygen transfer rates in similar experimental conditions, which makes Fe-ESF an interesting alternative for CLC processes with coal.