Parameter optimization and thermodynamic analysis of COG direct chemical looping hydrogen processes

Coke-oven gas (COG) is largely by-produced in coking plants, being most burnt and resulting in serious energy waste and air pollutant emissions. Producing high-value hydrogen from COG is therefore promising, however, the traditional processes via steam methane reforming still suffer from high energy consumption and CO2 emissions. In this work, we propose efficient COG-to-hydrogen processes by chemical looping hydrogen technology. Parameter optimization of the proposed systems without and with support has also been conducted for the optimum COG utilization and maximum hydrogen production. The optimum molar ratios for the oxygen carrier/COG, steam/oxygen carrier, and air/oxygen carrier were found to be 2.0, 1.2, and 0.81, respectively, for the process without support. In the supported system, due to the presence of the high-temperature support, the optimum molar ratio of the oxygen carrier/COG is decreased to 1.1, while the steam/oxygen carrier ratio is increased to 3.9. The exergy efficiency, and CO2 capture efficiency, and hydrogen purity of the system with support are 63.8%, 73.3%, and 99.4 mol.%, respectively. It was found that the process including an intercooling between fuel reactor and steam reactor, and oxygen-enriched combustion in the heating air reactor provides a further improved exergy efficiency of 66.2% and CO2 capture efficiency of about 100%.