Thermodynamic Evaluation of the Cross-Current Moving-Bed Chemical Looping Configuration for Efficient Conversion of Biomass to Syngas

The rising chemical demand and its associated concern of climate change have put an impetus on converting diverse domestic sources to valuable products in a decarbonized manner. Lignocellulosic biomass, a viable feedstock, is garnering significant attention as a sustainable alternative to fossil fuels. However, challenges in handling biomass feed variability and effectively processing its char and tar contents have hampered its commercial deployment. However, the chemical looping-based biomass-to-syngas (BTS) technology being developed by The Ohio State University is among the most promising technologies for industrial biomass reforming. It utilizes proprietary iron oxide particles in a cocurrent moving-bed reactor, leveraging the flow dynamics to transform biomass to syngas, and has been proven to be more efficient than conventional processes. However, this cocurrent system suffers from a thermodynamic barrier, inhibiting the syngas yield. To overcome this barrier, a novel chemical looping cross-current system is developed and investigated through detailed thermodynamic ASPEN studies after accounting for practical constraints. The barrier in the cocurrent system can be attributed to the equilibrium between exiting syngas and solid streams, which limits the oxidation of oxygen carriers. The cross-current reactor system overcomes this issue by shifting the exit of the syngas stream to the middle of the reactor, thus not allowing the exiting syngas and solid streams to be in equilibrium and creating a cocurrent section above the syngas exit and a countercurrent section below it. Thermodynamic simulations conducted under autothermal conditions reveal that the cocurrent and cross-current systems perform similarly with steam and CO2 co-injection. However, under an isothermal condition, which is now feasible with cheaper and sustainable heating methods, the cross-current system achieves similar to 34% higher syngas yield over the cocurrent system (similar to 0.074 in cross-current compared to similar to 0.055 in cocurrent) for both steam and CO2 co-injection. The findings from this study justify the scale-up of the cross-current system and provide system-level insights into biomass valorization.