Sammendrag
This paper elaborates a concept for designing efficient large scale hydrogen liquefaction plants, based on dividing the process into 4 independent stages and finding the optimum solution for each stage. The main focus is put on the precooling stage. Not because of its power consumption, but because it is the stage with the most degrees of freedom in design. Several processes have been discussed, mentioning some of the main advantages and disadvantages. One of the main challenges in efficient hydrogen liquefaction is light gas compression. This is unavoidable, since only light gases can provide cooling at the required temperature levels, but should be minimized by using heavier fluids where possible. Due to the higher exergy efficiency of compression compared to refrigeration, the hydrogen feed pressure should be as high as possible, as long as the pressure reduction in the liquefaction stage is performed by expansion machines instead of throttling.