SMALL-SCALE LIQUEFACTION OF HYDROGEN

Hydrogen may be stored compactly as a cryogenic liquid at low pressure and temperature, i.e. 20 K at atmospheric pressure. Gaseous hydrogen at normal temperature may be liquefied on a small scale using a cryogenic refrigerator (cryocooler). Stirling refrigerators are well suited to this duty. These machines operate on a closed thermodynamic regenerative cycle with compression and expansion of the working fluid (helium) at different temperature levels. Very low temperature Stirling refrigerators have several stages of expansion, typically two or three for a hydrogen liquefier. A concept for an electrically driven Stirling hydrogen liquefier of low capacity is described. Stirling machines can also be used as power systems converting heat to work. A second concept is described for a combustion heated Stirling-Stirling hydrogen liquefier. Conceptual design studies for both units have been carried out including computer simulation of the power system and cryocooler systems. These indicate the net energy flow and principal dimensional parameters permitting first order estimates of costs for prototype manufacture and the unit costs in series production.