Effects of coal ash on iron-based oxygen carrier in chemical-looping combustion using three different rank coals as fuel

The combustion characteristics vary with coal rank changes, and coal ash has a significant effect on chemical looping combustion. In this work, combustion experiments of three coals and their acid-washing samples were carried out in a bench-scale fluidized bed reactor. The results showed that low-rank coal had higher reactivity and shorter reduction time. On account of high volatility and low density, combustion efficiency of high volatile coal was lower than high-rank coal resulting in lower CO2 concentration. CO2 concentration in combustion products of GY was up to 99.95%, but it was 91.2% for SF. The composition and content of coal ash had a great influence on the activity of the iron-based oxygen carrier. Reactivity of the oxygen carrier was significantly increased after burning high Ca content coal, and ash shortened reduction time from 46 to 35 min. The coal with high Si content had negative effect on the reactivity of oxygen carriers. The coal ash mainly affected the oxygen carrier at the later stage of the reduction.