Precooling systems in modern hydrogen liquefaction

This study presents recommendations for selecting a circuit design for low-capacity hydrogen liquefaction plants with production rate up to 20 kg/h or 0.48 tpd (ton per day). Main design criteria considered are specific energy cost, as well as capital costs and overall characteristics of the system. Theoretical and real hydrogen liquefaction cycles are reviewed. Mathematical models of different circuits are built considering real parameters of the typical equipment. The advantages and disadvantages associated with certain solutions are identified, and the hydrogen-liquefaction energy efficiency trends are analysed. According to the results, the main of the circuits for low-capacity hydrogen liquefaction plants are selected as per the obtained results.

AIMS: Theoretical and real hydrogen liquefaction cycles are reviewed, and circuit design is mathematically modeled considering the typical equipment’s real parameters.

MATERIALS AND METHODS: Hydrogen-liquefaction cycles are modeled using Aspen HYSYS. Further optimization and parameter selection are conducted using the MATLAB module “Global Optimization Toolbox.”

RESULTS: Advantages and disadvantages associated with certain technological solutions are identified, and the hydrogen-liquefaction energy efficiency trends are analyzed.

CONCLUSIONS: This study compares energy consumptions for liquefaction of various gases, showing the feasibility of energy consumption reduction for hydrogen liquefaction. The importance of continuous ortho–para conversion or increase in number of conversion stages via energy consumption reduction is presented. The main features of refrigerant cycles are described, and a precooling cycle using a mixed refrigerant is selected. Mixed-refrigerant precooling cycle and liquid nitrogen precooling are compared in terms of economic efficiency. The main issues of refrigerant selection are described, and the basic principles of modeling and parameter selection for a small-capacity hydrogen-liquefaction cycle are presented. A low-temperature helium cycle is modeled with the precooling circuit based on a mixed-refrigerant cycle. We reveal an optimum range of precooling temperatures for decrease in overall specific power consumption using a mixed refrigerant in a small-capacity hydrogen liquefaction plant of 80K–100K.