Design Study of a Pilot Test Plant for Hydrogen Production by a Hybrid Thermochemical Process

Mass production of hydrogen is a major issue for the coming decades, particularly for greenhouse gas lowering purpose. Thanks to fourth-generation nuclear reactors development, providing high-temperature energy, hydrogen production processes are currently revisited worldwide. In France, the CEA is particularly investigating the Westinghouse hybrid sulfur cycle. This cycle, which combines an electrolysis step (oxidization of SO₂ to H₂SO₄ from a liquid-phase anode stream) and a thermochemical step (decomposition of H₂SO₄), was developed in the 1970s by Westinghouse Electric Corporation. Its production capacity was demonstrated at a scale of 150 NL·h⁻¹ of hydrogen and a conceptual plant, designed to produce 90 Nm³·s⁻¹, was developed in 1977. This plant was however never built, probably for both economic and technological reasons. Since 2000, the Westinghouse process is the subject of renewed interest. Indeed, the decomposition of sulfuric acid has been investigated in detail (many thermochemical cycles are based on sulfur) and it is now optimized from a thermodynamic standpoint. Moreover, the substantial research efforts devoted to fuel cells have led to the development of new materials and structures that are expected to yield significant performance improvements when applied to classical electrochemical processes. Therefore, the CEA has decided to build a pilot electrolysis facility with an hydrogen capacity of 100 NL·h⁻¹, allowing implementation of the most promising material technologies.