Chemical looping combustion of coal in a 5 kWth interconnected fluidized bed reactor using hematite as oxygen carrier

Abstract

A hematite, which has been operated in CH4-fuelled Chemical Looping Combustion (CLC) for more than 200h, was used as oxygen carriers for in-situ gasification chemical looping combustion (iG-CLC) of Chinese Bituminous coal in this study. The thermal power was varied between 2.0 and 6.0kWth. The total operation time was more than 100h in the hot mode. Hematite displayed high reactivity with this bituminous coal attaining up to 96.33% of combustion efficiency. The carbon capture efficiency ranged from 72.84% to 89.36% as only CO2 was used as coal gasification agent gas in the fuel reactor during the first tests. The CO2 yield in the fuel reactor was up to 92.82% under the operational temperature was 1000°C and the average coal feeding rate corresponding to the 2kWth of thermal power. The effect of operational parameters, such as the fuel reactor temperature, thermal power and the mass flow rates of the fluidization gas agent on three factors – combustion efficiency, carbon capture efficiency and CO2 yield – were investigated. The results illustrated that higher operating temperature and bed inventory per unit of thermal power in the fuel reactor were found to positively affect all the three factors. Upon completion of the experiment, the used samples were collected and analysed using electron microscopy, X-ray diffraction and surface area analysis. The results showed no appreciable sintering and agglomeration in the used sample. It was found that the reactivity of fresh and used samples did not differ significantly.