(569fc) Multiple Chemical Looping Reforming (CLR) Reactors for Blue Hydrogen and Nitrogen Production

The production of low-emission hydrogen from fossil fuels – known as blue hydrogen – is crucial for reaching the Net Zero Emissions (NZE) scenario. Projections indicate that around 8 million tons (Mt) of blue hydrogen could be generated by 2030 [1]. However, to meet the 2050 target of 80Mt of blue hydrogen, a significant increase in production capacity is necessary. Moreover, using conventional steam-methane reforming (SMR) for blue hydrogen production faces a challenge in achieving CO₂ capture rates higher than 90% [2]. This difficulty primarily arises from the flue gas generated during the SMR process, where the CO₂ is substantially diluted with N₂, thereby complicating the CO₂ capture process.

Chemical looping Reforming (CLR) has emerged as a viable alternative for blue hydrogen production. This process feeds air and fuel into separate reactors or stages, preventing the mixing of N₂ and CO₂. Consequently, CLR yields three distinct product streams: one N₂-rich, another with a high syngas concentration, and a third consisting of CO₂ and steam. The process utilizes oxygen carriers, which serve as oxygen transfer materials and catalysts for the reforming reactions. In a previous study, a model-based design of CLR fixed bed reactor was developed, simulated, and optimized for blue H₂ and N₂ production [3]. Under optimized conditions, this reactor yielded a product stream with a high hydrogen concentration (~66%) during reforming step (REF), achieving a 62% efficiency without further H₂ purification. Furthermore, it generated high purity N₂ (>98%) during the oxidation step (OX), paving the way for ammonia synthesis [4] – a potential hydrogen carrier. However, the fixed-bed reactor resulted in discontinuities in the downstream. Therefore, to achieve continuous production of H₂ and N₂, adopting a system comprising multiple reactors is considered here.

The investigation involves multi-reactor systems optimized at two different cycle times (OX-RED-REF): 150-135-200 sec and 200-200-200 sec. A key requirement for each system is to ensure a continuous supply of H₂ and N₂ with a minimum production rate of 300 kgH₂/day. Under this constraint, the system with a 150-135-200 sec cycle time requires four reactors, allowing for potential overlap in each CLR stage. Meanwhile, the system with a 200-200-200 cycle time requires three reactors without CLR stages overlap. Both configurations are designed to generate three output streams: an N₂ stream, a CO₂ stream, and an H₂ stream. Simulation results indicate that the three-reactor system achieves a smoother output flow and temperature across all three product streams compared to the four-reactor system. However, the three-reactor system exhibits a lower production rate (380-456 kgH₂/day) than the four-reactor system (380-912 kgH₂/day). The H₂/N₂ ratio in the three-reactor system has a small fluctuation around 1.0, whereas it fluctuates between 0.6 and 1.5 in the four-reactor system. Notably, both systems generate high-temperature product streams (925-950°C), presenting an opportunity for heat recovery, particularly in gas preheating and steam generation.

Acknowledgments

This work was supported by a DIKTI-funded Fulbright Fellowship and the Pratt & Whitney Institute of Advanced Systems Engineering (P&W-IASE) of the University of Connecticut. Any opinions expressed herein are those of the author and do not represent those of the sponsor.

References

[1] US National Clean Hydrogen Strategy and Roadmap. 2023.

[2] International Energy Agency, “Global Hydrogen Review 2023”, 2023.

[3] A. R. Irhamna and G. M. Bollas, “Process intensification in a fixed bed reactor for a small-scale process in the stranded assets,” in 33rd European Symposium on Computer Aided Process Engineering, 2023, pp. 3043–3048.

[4] L. Burrows, P. X. Gao, and G. M. Bollas, “Thermodynamic feasibility analysis of distributed chemical looping ammonia synthesis,” Chem. Eng. J., vol. 426, no. May, p. 131421, 2021, doi: 10.1016/j.cej.2021.131421.