HIGH-TEMPERATURE STEAM ELECTROLYSIS: TECHNICAL AND ECONOMIC EVALUATION OF ALTERNATIVE PROCESS DESIGNS.

A high-temperature water-vapor electrolysis (HTE) unit operating at an average temperature of 1000 degree C was integrated into a preliminary process design using electrical and thermal energy derived from coal. Process variations with either steam or water feeds under isothermal or nonisothermal HTE operation were considered. Operating and capital costs were estimated for each process flowsheet, with the lowest costs being obtained for operation with high steam conversions in the electrolyzer. Estimated hydrogen production costs were compared with estimates obtained from the literature for other hydrogen production processes. The estimated HTE hydrogen production costs ranged from 0. 17 to 0. 22 per standard cubic meter of hydrogen produced (13 to 17/GJ, using the higher heating value), assuming 1. 90/GJ for thermal energy and 13. 90/GJ for electrical energy.