Development of a novel flowsheet for sulfur-iodine cycle based on the electrochemical Bunsen reaction for hydrogen production

The sulfur-iodine (SI) cycle is one of the promising methods for large-scale hydrogen production. A new flowsheet of SI cycle assembled with electrochemical Bunsen reaction was devised and modeled in this work. Adoption of electrochemical Bunsen reaction simplifies the flowsheet. The high concentrations of H2SO4 and HI, especially the over-azeotropic HI solution, successfully generated in the separated compartments of electrochemical cell without requiring further separation and purification. The enriched HI gas evaporates through flash, eliminating the extra concentration process, and then decomposes into 1 mol/s of H2 in hydrogen perm-selective membrane reactor. A HI separator is employed to maximize the recycle of undecomposed HI. The concentrated H2SO4 after flash decomposes into 0.5 mol/s of O2. The mass and energy balances of the SI cycle were evaluated. The cascade utilization of energy was carried out through internal heat exchange between hot and cold streams in the flowsheet. The surplus waste heat was recovered as electric power to improve the energy utilization efficiency. The overall thermal efficiency of the flowsheet was estimated to be 42-50% and was sensitive to heat recovery ratio. The simplified and energy-efficient flowsheet is competitive to the previous traditional flowsheets and will provide a reference for the industrial utilization of SI cycle.