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Thermodynamic analysis on the parametric optimization of a novel chemical looping methane reforming in the separated productions of H2 and CO

Di, Zichen, Cao, Yan, Yang, Fengling, Zhang, Kai, Cheng, Fangqin
Energy conversion and management 2019 v.192 pp. 171-179
air, carbon dioxide, carbon monoxide, combustion, exergy, greenhouse gas emissions, heat, hydrogen, methane, natural gas, oxygen, pollutants, temperature
The large-scale natural gas reforming is currently the lowest cost method for hydrogen (H2) production. However, the mixture of H2 and CO2 in the produced gas inevitably includes CO2 and necessitates the costly CO2 separation. In this work, a novel chemical looping combustion-assisted chemical looping methane reforming technology (CLC-CLRHC) was proposed to enhance the separated production of H2 and CO in high purities in the absence of CO2. This novel reforming process not only produces high purity CO, H2, and even N2 without pollutants and/or GHG emissions, but realizes the energy coupling. The aim of this study is to thermodynamically analyze the operational parameters of the proposed new system, involving the optimized utilization of CH4, maximization of energy coupling and productivity yields and purity. Studies revealed that the optimal molar ratios for the Fe3O4/CH4, CaO/CH4 and H2O/CH4 in the chemical looping methane reforming process (CLRHC) were found to be 1.7, 1.0, 1.9, respectively. The molar ratio of the required additional CO2 from the chemical looping combustion to oxygen carriers should be 0.29. The heat balance between the CLRHC and the CLC was achieved via temperature settings of the air preheating prior to the air reactor of the CLC above 306 °C. Under the optimal conditions, the H2 purity, H2 yield, CO purity, CO yield and CH4 conversion were 98.55%, 2.26 mol/mol, 96.18%, 1.7 mol/mol and 99.24% respectively. The exergy efficiency of the system is about 70.60% and the CO2 utilization efficiency up to 94.62%.