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 (H-2) 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 H-2 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 H-2 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 H-2 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. [GRAPHICS]