Study on high hydrogen yield for large-scale hydrogen fuel storage and transportation based on liquid organic hydrogen carrier reactor

Large-scale hydrogen fuel storage and transportation are one of the main bottlenecks in the hydrogen-supported future energy system. In this study, a symmetrical two-dimension model of large-scale liquid organic hydrogen carrier reactor using N-ethylcarbazole (NEC) hydrogen carrier as a case is developed to explore the dehydrogenation behavior. The influences of operating parameters including heating temperature, thermal conductivity, and LOHC mass flow rate and geometry parameter reactor length on the dehydrogenation are investigated for performance optimization. The flow field distribution of N-ethyl-tetrahydro-carbazole (4H-NEC) intermediate product shows that the peak position of 4H-NEC mass fraction is turning point of the competition between the reactions of N-ethyl-dodecahydro-carbazole(12H-NEC) to 4H-NEC and 4H-NEC to 0H-NEC. It is significant to obtain large conversion of 12H-NEC to 4H-NEC within the tube pass as short as possible. In comparison, the dehydrogenation reaction of 4H-NEC to 0H-NEC with the slow kinetics is the rate-determining step of whole dehydrogenation process. Based on the dehydrogenation mechanism, the optimal operating and geometry parameters are suggested to be 520 K for operating temperature, 83 W/(m∙K) for thermal conductivity, 24 mL/min for 12H-NEC mass flow rate, and 3 m for reactor length. In such case, the proposed reactor could achieve high hydrogen yield of 90.58% and fast reaction kinetics of 1.43 h for reaction duration in large scale.