Chemical looping combustion of low-ash and high-ash low rank coals using different metal oxides – A thermogravimetric analyser study

Multiple redox experiments have been performed in a thermogravimetric analyser with well characterised iron and nickel oxide to assess their reactivity with low-ash Victorian brown coal as fuel, and nitrogen, air, CO2 and steam as combustion and gasification atmosphere. In addition, a high-ash lignite was used as fuel to compare its performance with the Victorian brown coal. The results show good performance of iron oxide as oxygen carrier over multiple cycles. However, NiO, a good oxygen carrier for gaseous fuel, shows progressively less reactivity over the multiple cycles. It has been observed that both the metal oxides can initiate the reduction reaction as low as 400 °C under different experimental condition. Five reductions and oxidations (Re-dox) cyclic experiments reveal 87% combustion of Fe2O3 and coal mixture under CO2 atmosphere at the end of the 5th cycle. However, the same for NiO is 67%. Metal oxide and coal solid mixture mass during re-dox experiments have been compared with thermodynamic predictions in similar experimental conditions. A continuous mass loss trend for NiO has been observed different from the thermodynamic predictions.