Thermodynamic comparison of hydrogen production processes

The results are reported of comparisons based on energy and exergy analyses of a wide range of hydrogen production processes, including processes which are hydrocarbon-based (steam-methane reforming and coal gasification), non-hydrocarbon-based (water electrolysis and thermochemical water decomposition) and integrated (steam-methane reforming linked to the non-hydrocarbon-based processes). A version of the Aspen Plus process-simulation computer code, previously enhanced by the author for exergy analysis, is used in the analyses. Overall efficiencies are determined to range widely, from 21 to 86% for energy efficiencies, and from 19 to 83% for exergy efficiencies. The losses in all processes are found to exhibit many common factors. Energy losses associated with emissions account for 100% of the total energy losses, while exergy losses associated with emissions account for 4-10% of the total exergy losses. The remaining exergy losses are associated with internal consumptions. It is anticipated that the results will prove useful to those involved in the improvement of existing and design of future hydrogen production processes. Copyright (C) 1996 International Association for Hydrogen Energy.