Design And Simulation Of A Hydrogen Liquefaction Cycle Based On Liquid Nitrogen Precooling

Hydrogen, a well-accepted ideal energy carrier, can be obtained in various ways. It is one of the important bridges between fossil energy and renewable energy, and will definitely bring a revolution to the clean utilization of energy. For further widespread use, a set of problems such as production, storage, and application of hydrogen must be solved. The way of storage and transportation is always the key to the hydrogen utilization. Considering the facors of mass, volumetric hydrogen storage density, and temperature, liquid hydrogen would be the preferred option for bulk transportation once the efficiency of liquefaction processes is greatly improved.Up to now, nearly all the large-scale hydrogen liquefaction plants in use are performing with an exergy efficiency of only20-30%. Dozens of researchers have been studying to improve the efficiency of hydrogen liquefaction processes for decades. Modifications have been investigated based on the Claude cycle, and innovative schemes also have been proposed. However, almost all the improvements make the innovation and high performance of equipments as the precondition. Based on the comparison investigation on the existing processes, a hydrogen liquefaction process which is refrigerated by helium with liquid nitrogen pre-cooling is proposed in this study. The final expansion stage in this porcess is accomplished with J-T valve, in which the flash gas is condensed by helium directly. Theliquefaction process presented can be realized with available technologies and equipments. Since the traditional softwares, such as Aapen Plus, Pro/Ⅱ, HYSYS, and ChemCAD etc., is unable to provide equilibrium hydrogen properties, a program based on Matlab software is developed to simulate the process proposed. The program of Refprop is introduced to solve the problem with the balanced hydrogen’s properties. The simulation result shows that the exergy efficiency of the prososed process is approximately equal to that of the process using liquid-phase expander. For a large scale plant with the output of50000ton per day, the proposed process with J-T valve offers an exergy efficiency of38.52%, while the process with liquid expander offers an exergy efficiency of40.17%. Moreover, the U·A of heat exchanger is calculated, and the temperature distribution of fluid along the heat exchanger is simulated. Finally, a hydrogen liquefaction process pre-cooled by LNG was simulated, and the effects of various parameters such as the equipments’efficiency, the temperature difference of heat exchanger, and the pressure of hydrogen on the process was investigated.