Cement bonded fine hematite and copper ore particles as oxygen carrier in chemical looping combustion

In this work, bimetallic oxygen carriers (OCs) were prepared from waste fine particles (<0.1 mm) of natural copper ore and hematite for possible application in chemical looping combustion (CLC) processes. The mixtures with different mass ratios of copper ore to hematite were physically bonded by 20 wt% of calcium aluminate cement to obtain OC particles with relatively high disperse structure and good mechanical strength. Cyclic isothermal redox tests were first conducted in a thermogravimetric analyzer (TGA) to optimize the copper ore to hematite mixing ratio in the bimetallic OC. Synergistic effect between copper ore and hematite was observed, and the copper ore to hematite mixing ratio was optimized at 20:80 (namely Cu20Fe80@C) based on a comprehensive consideration of OC reactivity, economic cost and auto-thermal balance in fuel reactor. Subsequently, performance of Cu20Fe80@C and Fe100@C (cement bonded pure hematite) were further evaluated in a batch fluidized bed reactor, using coal as fuel. The Cu20Fe80@C was found to be more reactive towards coal gasification products than that of Fe100@C, which is mainly attributed to the synergistic effect attained by the coexistence of copper ore and hematite in the Cu20Fe80@C OC. Moreover, the effects of steam concentration, oxygen to fuel ratio and coal type on the performance of Cu20Fe80@C were investigated. It was found that both the increase of steam concentration and oxygen to fuel ratio can facilitate the coal conversion, but they are not the higher the better and should be balanced between coal conversion and operational cost when turning to industrial application. Lignite was more suitable to be converted by Cu20Fe80@C OC in iG-CLC process due to its better gasification reactivity than anthracite. 30 cyclic redox tests with lignite showed that Cu20Fe80@C exhibited superior redox reactivity, nice fluidization behavior and good anti-sintering property in fluidized bed tests. This work demonstrated that cement bonded fine particles of hematite and copper ore could be a promising and competitive OC candidate for industrial application in iG-CLC processes.