On the importance of liquid hydrogen exergy utilisation for an energetically efficient hydrogen energy economy
Magnus Lenger, Steffen Heinke, Wilhelm Tegethoff, Jürgen Köhler
Abstract
The energy consumption of hydrogen liquefaction is often quantified as being approximately 40 % of hydrogen’s lower heating value (LHV), making hydrogen liquefaction energy-intensive. Boundary conditions for energy consumption values in the literature are, however, often unclear, rendering these values questionable. Two methods can nevertheless significantly decrease energy consumption: (1) implementing improved liquefiers; and (2) utilising liquid hydrogen exergy – the reversible liquefaction work – stored in the liquid. Liquid hydrogen exergy equals 11.5 % LHV. And in comparison: per energy content, liquid hydrogen exergy is 5.5 times liquefied natural gas exergy. To estimate the energy savings potential of combining liquefier improvements and exergy utilisation, the exergy efficiency of improved liquefiers is calculated (44 %) and used as a quality measure. The same efficiency is assumed for exergy utilisation processes. The net energy consumption for the liquefaction - regasification chain is thereby reduced to 13-26 % LHV, depending on boundary conditions. • The H 2 liquefaction-regasification chain is evaluated by exergy analyses. • LH 2 exergy is 11.5 % of H 2 ’s lower heating value ( LHV H 2 ), LNG exergy is 2.1 % of LHV CH 4 . • Improved H 2 liquefiers achieve 44 % exergy efficiency. • LH 2 exergy recovery during regasification estimated with liquefier exergy efficiency. • Energy consumption of H 2 liquefaction-regasification chain reducible to 13-26 % LHV H 2 .