The heart of every liquefaction plant is the cold box. Inside the cold box, the hydrogen feed gas is gradually cooled until it changes from gaseous to liquid.
The recycle gas stream is used to cool the hydrogen feed stream. For systems smaller than 5 tpd, the cooling circuit consists of a closed helium circuit. For systems larger than 5 tpd a Claude cooling cycle running on hydrogen is used.
The shelf life of the liquid hydrogen is ensured by an effective ortho-para conversion.