Cement/CaO-modified iron ore as oxygen carrier for chemical looping combustion of coal

Chemical looping combustion (CLC) of solid fuels is considered as a potential technology to reduce the energy penalty and the cost for CO2 capture. However, the low efficiency of carbon conversion and gasification products conversion is a big concern for the in-situ gasification chemical looping combustion (IG-CLC) process with the low-cost natural iron ore as an oxygen carrier. This paper evaluates the enhanced fuel conversion with a new CaO-modified iron ore as oxygen carrier during the continuous coal CLC in a 1 kWth reactor. Both CaO-mixed iron ore and cement/CaO-combined iron ore were tested. The effect of oxygen carrier on the gaseous products was evaluated in the fuel reactor temperature range of 880-980 °C. The samples of oxygen carrier were characterized using BET, SEM-EDX and XRD. The results indicate that compared with the pure iron ore oxygen carrier, the utilization of both CaO-mixed iron ore and the cement/CaO-combined iron ore could efficiently enhance coal conversion and gaseous conversion in the fuel reactor. However, when the CaO-mixed iron ore was used, some CaO powder due to the attrition during continuous operation adhered to the particle surface of iron ore. The Ca-containing compounds, i.e., potential eutectic of a low melting point caused sintering on the particle surface of iron ore. As a result, it caused the reactivity deterioration of oxygen carrier at a high fuel reactor temperature. To avoid the occurrence of sintering on the particle surface of the oxygen carrier, an improvement of cement/CaO-combined iron ore as oxygen carrier was proposed. A stable structure of Ca2Al2SiO7 was formed during the calcination process of the cement/CaO-combined iron ore. The sintering resistance of the iron ore was improved and the oxygen carrier after experiments maintained the porous structure. Reactivity deterioration of the combined oxygen carrier did not occur during the 5 h continuous operation even at the fuel reactor temperature of 980 °C. Overall, the Cement/CaO-combined iron ore is a competitive oxygen carrier in the coal CLC process.