Development of a prototype of helium-heated sulfuric acid decomposer for sulfur-family thermochemical water splitting process

Abstract

The thermochemical iodine-sulfur (IS) and hybrid sulfur (HyS) cycles are among the most promising methods for large-scale hydrogen production, utilizing heat from high-temperature gas-cooled reactors (HTGRs) to achieve high efficiency and zero carbon dioxide emissions. The decomposition of sulfuric acid is a pivotal reaction in both IS and HyS technologies, occurring at the highest temperature and requiring the most heat input. The sulfuric acid decomposer (SAD) is a critical component that utilizes nuclear heat to facilitate sulfuric acid decomposition while simultaneously functioning as a process heat exchanger. In this study, the material balance of SAD as well as the flow rate and temperature distribution in the reactor were estimated through simulation, and a shell-and-tube SAD prototype was designed and manufactured based on the simulation data. A high-temperature helium heating circuit was established to investigate the thermohydraulic properties of the SAD prototype. Temperature distribution data for the interior and critical areas of the prototype were obtained when using helium as the heat source. The research results indicated that the heat exchanger efficiency of the decomposer can reach approximately 60 %. The sulfuric acid decomposition process was successfully validated at reaction temperature of higher than 800 °C. An oxygen production rate of 1.1 Nm³/h (corresponding to a hydrogen production rate of 2.2 Nm³/h of IS and HyS cycles) was achieved, and the decomposition reaction efficiency is about 70 %. These results confirmed the prototype's integrity, sealing performance, heat transfer efficiency, and chemical reaction capabilities under real conditions. The SAD prototype developed in this study represents the first reported instance of a decomposer constructed from engineering materials and heated by helium, and provides a significant reference for IS and HyS cycle water splitting technologies that utilize heat from HTGRs.