ENERGY AND EXERGY ANALYSES OF ELECTROLYTIC HYDROGEN-PRODUCTION

The thermodynamic performance is investigated of a water-electrolysis process for producing hydrogen, based on current-technology equipment. Both energy and exergy analyses are used. Three cases are considered in which the principal driving energy inputs are (i) electricity, (ii) the high-temperature heat used to generate the electricity, and (iii) the heat source used to produce the high-temperature heat. The nature of the heat source (e.g. fossil fuel, nuclear fuel, solar energy, etc .) is left as general as possible. The analyses indicate that, when th e main driving input is the hypothetical heat source, the principal th ermodynamic losses are associated with water splitting, electricity ge neration and heat production; the losses are mainly due to the irrever sibilities associated with converting a heat source to heat, and heat transfer across large temperature differences. The losses associated w ith the waste heat in used cooling water, because of its low quality, are not as significant as energy analysis indicates.