The growing impetus to reduce greenhouse gas emissions has garnered attention towards technologies that can decarbonize the state-of-the-art processes to manufacture commodity chemicals. Chemical looping systems utilizing the moving bed configuration have demonstrated the potential to be a technically feasible and economically attractive alternative for the production of commodity chemicals like hydrogen (H2) and syngas while enabling complete carbon capture. Our previous works have indicated that chemical looping H2 generation technology facilitated by iron oxide-based mixed-metal oxide carrier (MMOC) can enable higher energy efficiencies and a levelized cost of H2 of ~$1.4/kg, which presents a significant improvement over state-of-the-art processes like steam methane reforming (SMR) and autothermal reforming (ATR). While competent, certain challenges like solid attrition necessitating frequent MMOC make-up and the requirement of downstream compressors, hinder the commercial deployment of the moving bed technology at a commercial scale. Fixed bed chemical looping process, operating at high pressure to produce H2 from natural gas, facilitating no solid attrition, presents an appealing method to enable successful deployment of the technology. However, the dynamic nature of the fixed bed operation results in changing outlet gas compositions, which challenges the goal of producing capture-ready carbon dioxide (CO2) and achieving continuous operation of the system. In this work, we propose a novel reactor configuration that can enable continuous operation of the high-pressure fixed bed system to co-generate high-purity H2 and sequestration-ready CO2. The proposed configuration utilizes a set of four reactors working in unison to facilitate simultaneous reduction, steam oxidation, and air regeneration. The operating gas hourly space velocities, feed composition, solid conversions of MMOC, and cycle time of each step are identified to achieve continuous operation by simple gas switching. The following set of operating parameters are identified for a range of system pressures and temperatures to account for a robust operation. Simultaneously, the rate expressions and the rate constants were determined for the MMOC particle through extensive parametric study of varying feed composition, operating temperature, and pressure. By accounting for the mass transfer limitations in the fixed bed setup, the experimental data generated for the obtained set of operating conditions is integrated with the information obtained through the kinetic study of the MMOC particle to conceptualize a fixed bed model to predict the dynamic gas compositions and solid conversion profiles accurately. Preliminary techno-economic evaluation indicates a levelized cost of H2 in a similar range as that of the moving bed system. The predictive model is further used to identify operational strategies to maximize solid utilization and optimize the reactor design to achieve lower capital and operating costs. These efforts would enable de-risking the scale-up of the high-pressure fixed bed chemical looping system and may help achieve the U.S. Department of Energy’s Hydrogen Energy Earthshot initiative.
