For small capacity liquefaction plants up to 3 tpd, a closed helium circuit supplies the refrigeration necessary to cool the hydrogen. Pure hydrogen gas at approx. 20 bar is fed into the vacuum-insulated cold box and, after a certain degree of subcooling at the end of the refrigeration process, it expands through a Joule-Thomson valve into the storage tank. The helium refrigeration cycle and hydrogen liquefaction are completely separated. The main components of the system are the helium compressor with oil purification, the cold box with heat exchangers and helium expansion turbines, the liquid hydrogen tank and filling stations for transportable containers.
For liquefaction capacities over 3 tpd, the necessary refrigeration for cooling and ortho-para conversion of the hydrogen is attained by means of a hydrogen Claude process, i.e. at the cold end of the process the H2 feed gas can be combined with the H2 of the refrigeration process.