Thermodynamic analysis of chemical looping coupling process for coproducing syngas and hydrogen with in situ CO2 utilization

Abstract

This study proposed a novel chemical looping coupling system for coproducing syngas and hydrogen with in situ CO2 utilization. It integrates chemical looping combustion, chemical looping reforming, CO2-H2O co-splitting, hydrogen production and air oxidation using CH4 as fuel and iron oxide as oxygen carrier. In this process, syngas and H2 purification, in addition to CO2 capture and storage are no longer necessary. It not only produces high-purity hydrogen and syngas without pollutants and greenhouse gas emissions, but realizes the sufficient utilization of feed and oxygen carriers. A detailed thermodynamic analysis of the proposed chemical looping coupling process was conducted by Aspen Plus. The effects of key parameters, such as feed ratio, temperature, and pressure in each reactor on the process performance were investigated in terms of the utilization of CH4, the yield and purity of syngas and hydrogen, and the oxygen carrier coupling. In addition, the energy balance was analyzed for the coupling system with heat exchanger network. Based on the established process model, we concluded that the preferable feed ratios in combustion, reforming, co-splitting, steam and air reactors were 4, 1, 0.4, 1.1 and 1.5, respectively. The preferable temperatures in the five reactors mentioned above were 900, 900, 850, 500 and 500 °C in sequence, and the preferable pressure was 1 atm in each reactor. Under these conditions, high-purity hydrogen (100%) and syngas (99% and 93% purity) with ideal H2/CO ratio (~2) could be obtained. The energy efficiency and exergy efficiency of this coupling system reached up to 90.54% and 72.04%, respectively.