Interaction of coal ashes with potassium-decorated Fe2O3/Al2O3 oxygen carrier in coal-direct chemical looping hydrogen generation (CLHG)

Abstract

Coal-direct CLHG is a novel hydrogen production technology with inherent CO2 capture. Potassium-decorated Fe2O3/Al2O3 oxygen carrier (OC) has been proved to be a potential OC for the technology. However, the ash in the coal could influence the OC performance. In this work, the effect of ash addition on the reactivity, the morphology structure and phase composition of OC, and the potassium migration in the reduction stage were investigated. Furthermore, the effect of OC on the ash fusion temperature was discussed. Results indicated that the OC reactivity had no significant change when SM (Shenmu) ash addition was less than 1% in the reduction stage and decreased when the addition was more than 2%. In the steam oxidation stage, the H2 yield varied between 5.80–5.57 mmol/g when the SM ash addition was less than 10% and decreased to 4.31 mmol/g when the addition was 40%. FeO could react with SiO2 deriving from coal ash to form Fe2SiO4, which could cause the loss of Fe and the OC sintering; K2CO3 could react with silicon-aluminum minerals which could cause the potassium loss. The ash with high CaO content had a less negative effect on the OC reactivity. With the increase of SM ash addition, the potassium in OC decreased, the potassium in char increased and the volatile potassium decreased after the reduction stage. After the OC addition, the deformation temperature decreased from 1242 °C to 1114 °C in the weak reduction atmosphere while increased from 1162 °C to 1300 °C in the air atmosphere.