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The iodine–sulfur thermochemical water splitting process (I–S process) is considered to be one of the most promising clean and large-scale hydrogen production approaches. In the I–S process, the HI distillation step is considerably energy intensive, the heat of which largely affects the overall efficiency of hydrogen production. The present study explored the efficient operating parameters of the distillation column by process simulation assuming the feed solution of hyper-pseudoazeotropic composition which was obtainable by electro–electrodialysis. The Environmental Simulation Program (ESP), the chemical simulation software, was used for the simulation. At first, the vapor–liquid equilibrium database was validated using experimental data reported so far. Then, sensitivity analyses of the operating parameters were carried out, comprised of the HI mole fraction in the distillate, number of stages, feed location of the column, operating pressure, and feed composition. On the basis of the results of the sensitivity analyses, the optimum operation conditions were discussed.

SUMMARYThe iodine sulfur (IS) thermochemical water-splitting process, which has various merits, is considered as one of the most promising nuclear hydrogen production methods and has been intensively studied by many institutions. At the Institute of Nuclear and New Energy Technology of Tsinghua University in China, a proof-of-concept closed IS facility was built, and a closed-cycle experiment was conducted. Currently, as a prospective research item of the high-temperature gas-cooled reactor demonstration plant project, an integrated laboratory-scale IS facility (IS-100) that aims to achieve long-term stable operation of IS cycle is being developed, and the design and optimization of the flowsheet for the IS cycle are conducted. The specifications of the facility are presented along with simulation models. Mass balance and compositions of the streams in the Bunsen, sulfuric acid, and HI sections are calculated using Aspen Plus software with OLI database and embedded self-made models. Based on the comparison between mass of recycled streams and heat requirements as well as sensitivity analysis, the optimized flowsheet and the operational parameters are proposed. In addition, the preliminary closed cycle experiment results on IS-100 were presented, and the efficiency of the IS process and the R&D efforts to improve its efficiency are discussed.