Iron ore as oxygen carrier improved with potassium for chemical looping combustion of anthracite coal

Chemical looping combustion (CLC) is an innovative combustion technology with inherent separation of CO2 without energy penalty. When solid fuel is applied in CLC, the gasification of solid fuel is the rate-limiting process for in situ gasification of coal and reduction of oxygen carrier. The K2CO3-decorated iron ore after calcinations was used as oxygen carrier in CLC of anthracite coal, and potassium ferrites were formed during the calcinations process. The experiments were performed in a laboratory fluidized bed reactor with steam as a gasification medium. Effects of reaction temperature, K2CO3 loading in iron ore and cycle on the gas concentration, carbon conversion, gasification rate and yields of carbonaceous gases were investigated. The carbon gasification was accelerated during the fast reaction stage between 860 °C and 920 °C, and the water-gas shift reaction was significantly enhanced in a wider temperature range of 800 °C to 920 °C. With the K2CO3 loading in iron ore increasing from 0% to 20% at 920 °C, the carbon conversion was accelerated in the fast reaction stage, and the fast reaction stage became shorter. The yield of CO2 reached a maximum of 94.4% and the yield of CO reached a minimum of 3.4% when use the iron ore loaded with 6% K2CO3. SEM analysis showed that the K2CO3-decorating in iron ore would cause a sintering on the particle surface of oxygen carrier, and the K2CO3 loading in iron ore should not be too high. Cycle experiments indicate that the K2CO3-decorated iron ore has a relative stable catalytic effect in the CLC process.