Dynamic simulations of medium-sized hydrogen liquefiers have been performed using process simulation software EcosimPro. Two hydrogen liquefier process flows have been simulated. One process flow is a helium refrigerator with one helium turbine providing cooling power for hydrogen liquefier, the other one is a helium refrigerator with two helium turbines providing cooling power for hydrogen liquefier. Control logics and control strategies for these two hydrogen liquefiers have been proposed. The cooling down simulations have been performed separately. One turbine hydrogen liquefier, pressure ratio is 2/16 bara, helium mass flow rate is 111 g/s, hydrogen mass flow rate is 4.3 g/s, the liquefaction rate of hydrogen is about 191 L/h. Two turbines hydrogen liquefier, pressure ratio is 1/14 bara, helium mass flow rate is 110 g/s, hydrogen mass flow rate is 5.2 g/s, the liquefaction rate of hydrogen is about 184 L/h. Comparison and discussion have been proposed.

Abstract.Research on optimization of helium liquefier is limited at home and abroad, and most of the optimization is single-objective based on Collins cycle. In this paper, a multi-objective optimization is conducted using genetic algorithm (GA) on the 40 L/h helium liquefier developed by Technical Institute of Physics and Chemistry of the Chinese Academy of Science (TIPC,CAS), steady solutions are obtained in the end. In addition, the exergy loss of the optimized system is studied in the case of with and without liquid nitrogen pre-cooling. The results have guiding significance for the future design of large helium liquefier. 1.IntroductionIt's known that for a refrigeration cycle, the power needed increases sharply with lowering of the refrigeration temperature. Ideally, 70.43 W power is needed to be done on the refrigeration system to get 1W cooling capacity at 4.2 K. Certainly more power is expected to get liquid helium, so an optimization design means a lot for reducing energy consumption. Some optimization studies have already been carried out on helium liquefier and most of them are in theory. Rijo Jacob Thomas et al [1] have conducted an exergy analysis on Collins cycle, results show that the first and the last heat exchanger should be taken seriously for their low exergy efficiency. In addition, the optimal mass flow into expanders is found to be 80% of the total mass flow. Rijo Jacob Thomas et al [2] also analyzed the effect of the number of the Brayton cooling stage in a helium liquefier. It is found that the optimal number of Brayton cooling stage is four to achieve the highest exergy efficiency. There is 1 ICECICMC IOP Publishing

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