Research of coal-direct chemical looping hydrogen generation with iron-based oxygen carrier modified by potassium

Coal-direct chemical looping hydrogen generation (CLHG) is a promising process for hydrogen production with high coal conversion efficiency and low carbon footprint. In this work, experiments on coal-direct CLHG process were carried out using K2CO3 modified Fe2O3/ZrO2 as oxygen carrier (OC) and Shenmu (SM) char as fuel in a fixed-bed reactor. The effect of char/OC mass ratio on CO2/CO volume ratio, H2 production and phase transformation was investigated. Multicycle tests with SM char and deashed SM char were conducted to investigate the activity stability of OC and the reason for the deactivation of OC. The results confirm the feasibility of coal-direct CLHG process. Higher char/OC mass ratio could enhance the H2 production and decrease the CO2/CO volume ratio and oxidation state of iron oxides in OC. In the multicycle tests with SM char, carbon conversion and H2 production remained almost constant during the first 2 redox cycles and then decreased abruptly in the 3rd cycle. During the 3 cycles, the phases of OC residues remained unchanged and no detectable surface sintering was observed. Furthermore, the K contents of residues decreased slightly. In the multicycle tests with deashed SM char, the carbon conversion and accumulation H2 production were stable during the first 10 cycles and then decreased slowly. Some morphology features changes appeared during the 11 cycles, but no obvious surface sintering was observed. The K contents of residues declined by 2/3 after the 10th cycle.