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°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 H₂ production costs were compared with estimates obtained from the literature for other H₂ production processes. The estimated HTE H₂ production costs ranged from $0.17 to $0.22 standard m^-3 H₂ produced ($13-17 GJ^-1, using the higher heating value), assuming $1.90 GJ^-1 for thermal energy and $13.90 GJ^-1 for electrical energy.