Comparison criteria for large-scale hydrogen liquefaction processes

In a hydrogen liquefier the pre-compression of feed gas has generally higher stand-alone exergy efficiency than the cooling and liquefaction sub-process. Direct comparison of liquefiers based on overall exergy efficiency and specific power consumption will favour those with a higher portion of pre-compression. A methodology for comparing hydrogen liquefaction processes that compensates for non-uniformity in feed specifications has been developed and applied to three different hydrogen liquefiers. The processes in consideration have been modified to have equal hydrogen feed pressure, resulting in a more consistent comparison. Decreased feed pressure results in generally higher power consumption but also higher exergy efficiency, and vice versa. This approach can be adapted to the boundary conditions that the liquefaction process will be subject to in a real energy system.