Thermodynamic design of hydrogen liquefaction systems with helium or neon Brayton refrigerator

Abstract

A thermodynamic study is carried out for the design of hydrogen liquefaction systems cooled by a helium or neon Brayton refrigerator. This effort is motivated by our immediate plan to develop a 100 L/h liquefier for domestic use in Korea. After an extensive review on different thermodynamic cycles to liquefy hydrogen, two specific systems are identified as feasible options, taking into account the economic and practical factors. The first system is to employ a helium Brayton refrigerator whose lowest temperature is below 20 K. The refrigerator is in direct thermal contact with the hydrogen flow at atmospheric pressure from room temperature gas down to cryogenic liquid. The standard and two modified versions (called two-stage and dual-turbine) of Brayton refrigerators are considered in the system. The second is the Brayton refrigerator pre-cooled JT system, where the JT circuit is pre-cooled down to 30~40 K with a neon Brayton refrigerator. This system can take advantage of recently developed neon turbo-Brayton technology and relatively low pressure operation of hydrogen cycle. Full cycle analysis is performed to determine the design parameters with real properties of fluids and performance model for key components. The temperature pinch problem and ortho-to-para converters are rigorously included in the analysis. The details of the optimized systems are presented and discussed towards the construction of a prototype.