Coal direct chemical looping hydrogen production with K-Fe-Al composite oxygen carrier

Hydrogen production by coal direct chemical looping (CDCL) process with iron-based oxygen carrier is an attractive option to produce H2 with sequestration-ready CO2. However, low reduction rate and high endothermicity are the two main difficulties of this process. In this work, the reduction rate of K-Fe-Al composite oxygen carrier by coal char, and the effect of Al2O3 on the endothermic property and sintering of oxygen carrier during reduction were investigated by thermogravimetric analyzer (TGA), differential scanning calorimetry (DSC), X-ray diffractometer (XRD), and scanning electron microscopy (SEM). The feasibility of this process was preliminary analyzed using a fixed-bed reactor by simulating different reaction steps. It was found that the reduction rate of composite oxygen carrier increased remarkably with higher potassium amount, but decreased with increasing Al2O3 amount. However, the addition of Al2O3 into oxygen carrier could not only mitigate the sintering, but also alleviated the endothermicity of reduction by the exothermic formation of FeAl2O4. This preliminary feasibility analysis suggests that it is possible to produce H2 using CDCL with the K-Fe-Al composite oxygen carrier