Geothermal energy for high temperature hydrogen production with Solid Oxide Electrolysis: A thermodynamic analysis of SOE feed streams

Abstract

In this study SOE inlet and outlet streams are analyzed from a thermodynamic point of view to optimize energy usage in high temperature hydrogen production with thermal energy integration. Thermodynamic models were developed in Aspen Hysys to analyze locations in the feed stream with potential for increased thermal energy integration and determine fluid properties. CoolProp was used to model and optimize heat pumps for the feed stream locations identified in Aspen. In total three locations were identified with varying effects on the total electricity use of the system. The first location has the potential to reduce the thermal energy demand by 57.3 kWth and the required source temperature to 127°C. The second location can reduce the total electrical energy demand of the feed system by 4.8-6.3%, equivalent to 0.18-0.24% of the total electrical energy used for hydrogen production. Results at location 2 are theoretical as the compressor outlet temperature exceeds the maximum discharge temperatures of commercially available compressors. The third location identified has the highest potential for energy savings but is evaluated as unfeasible for the foreseeable future and was not studied further. The possibility of lowering the required thermal energy source temperature for steam generation was also considered. Results indicate that it is possible to achieve steam generation for an SOE feed with source temperatures as low as 90-100°C with a two-stage heat pump at a very similar cost to direct geothermal utilization with 163°C source temperatures.