A Novel 2-Reactor Chemical Looping System for Hydrogen Production with Biogas as the Feedstock: Process Simulation and Comparison with Conventional Reforming Processes

With increasing environmental concerns because of greenhouse gas (GHG) emissions from conventional sources of energy, a tremendous shift in momentum is observed toward clean combustion sources and carbon-neutral feedstocks. Hydrogen (H2) as a fuel negates carbon emissions during energy generation and hence is gaining attention as a valuable source of energy. The existing processes for producing H2 use non-renewable fossil fuels as feedstock. Biogas derived from the decomposition of waste organic matter is a renewable and carbon-neutral feedstock that can be utilized for fossil-free H2 generation. In this study, a novel 2-reactor chemical looping water-splitting process (CLWS-2R) is introduced, simulated, and analyzed for the production of H2 from biogas. Process simulations are carried out for the CLWS-2R system to achieve optimized process parameters for the desired system operating conditions. The process evaluation parameters of this scheme are compared with three established processes for H2 production from biogas, including the 3-reactor chemical looping water-splitting (CLWS-3R), the steam reforming (SR), and the mixed reforming (MR) process. The simulation results from this study indicate that for a biogas feedstock composition of 25% CO2 by volume, the CLWS-2R system can achieve the highest cold gas efficiency (CGE: 75%) and the highest effective thermal efficiency (ETE: 71%). The sensitivity analysis on biogas composition indicates that CLWS-2R achieves its highest ETE for biogas with a low CO2 content (25–30 vol %), which is almost equivalent to the ETE obtained using MR. For all the remaining biogas compositions with high CO2 content, MR achieves the highest ETE.