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Hydrogen Production Using High-Temperature Steam Electrolysis Supported by Advanced Gas Reactors with Supercritical CO2 Cycles

Bilge Yildiz, Katherine J. Hohnholt, Mujid S. Kazimi

Nuclear Technology / Volume 155 / Number 1 / July 2006 / Pages 1-21

Technical Paper / Fission Reactors /

Hydrogen production using high-temperature steam electrolysis (HTSE) supported by a supercritical CO2 (SCO2) recompression Brayton cycle that is directly coupled to an advanced gas-cooled reactor (AGR) is proposed in this paper. The system features and efficiency are analyzed in a parametric fashion. The analysis includes the influence of the major components' performance and the component integration in a proposed plant layout. The configuration, HTSE-SCO2-AGR, with thermal recuperation from the product gas streams and an intermediate heat exchanger between the turbine exit and the feedwater stream is found to offer excellent thermal efficiency, operational flexibility, and expected cost. The HTSE average process temperature is 900°C, and the hydrogen pipeline delivery pressure is assumed to be 7 MPa for the evaluation of the plant performance. The reactor exit temperature and the SCO2 cycle turbine inlet temperature are the same as those for the SCO2 recompression cycle design: 550 to 700°C. The 900°C at the HTSE unit, which is higher than the reactor exit temperature, is achieved with recuperative and electrical heating. HTSE is assumed to operate within 80 to 90% voltage efficiency at 1 atm to 7 MPa of pressure. A parametric analysis of these operating conditions shows that the system can achieve 38.6 to 48.2% low heating value of net hydrogen production energy efficiency. The extensive experience from commercial AGRs, the compactness of the SCO2 power conversion system, and the progress in the electrolysis cell materials field can help the economical development of a future recuperative HTSE-SCO2-AGR. The major research and development needs for this plant concept are materials processing for the durability and efficiency of the HTSE system, the design update of the AGR with advanced materials to resist high-pressure CO2 coolant, thermal hydraulics of CO2 at supercritical pressures, and detailed component design for system integration.

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