Hydrogen liquefaction

For a very long time, liquid hydrogen remained a niche market for space programs, industrial companies needing a high-purity product, or emergency storage. But with the growth of the hydrogen market in view of the energy transition (from 95 Mt/year in 2023 to an estimated 621 Mt/year in 2050), demand is diversifying and requires massive investment to meet the need.

Hydrogen liquefaction enables lighter logistics and greater storage volume. Depending on the application, the logistics chain based on liquid hydrogen can be less expensive than the gaseous version. What's more, for heavy-duty mobility (trucks, boats and planes), the required autonomy will necessitate carrying liquid hydrogen on board.

Market forecasts also predict hydrogen importing and exporting countries, depending on energy costs and the availability of renewable energies. To transport this hydrogen over long distances, several scenarios are possible: combining it with other molecules to produce synthetic fuels or ammonia, or liquefying it. As this sector is still in its infancy, it is difficult to predict the technological distribution of hydrogen over long distances.

Liquefaction technology, known and used since the 1960s, is now enjoying renewed interest. Indeed, to meet the growing needs of hydrogen mobility, the capacity of hydrogen liquefaction units needs to be increased (from a few t/d to over 100 t/d), opening up new avenues for process configuration and optimization to reduce unit production costs.

Like all gas liquefaction processes, the hydrogen process is based on compression/expansion cycles. The structure of these cycles is highly varied, depending on processing capacity, upstream hydrogen production method and downstream use. However, the very nature of hydrogen adds new issues to liquefaction technology, issues not present in more "conventional" gas liquefaction technologies (nitrogen, CO ₂ , methane).

The first notable difference with hydrogen is its liquefaction temperature (20.4 K at atmospheric pressure). This very low temperature calls for special measures to guarantee the unit's performance and safety. The insulation required to limit thermal ingress is much more extensive, and the entire process below the liquefaction temperature of the air must be carried out in a vacuum box. This very low liquefaction temperature necessitates a major purification step to prevent the solidification of impurities present in the hydrogen.

The second important difference is linked to an intrinsic property of hydrogen. In reality, "hydrogen" is a mixture of two spin isomers: the ortho-form and the para-hydrogen form. The distribution between these two...