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The iodine-sulfur (I-S) cycle is one of the most promising thermochemical cycles to produce carbon-free hydrogen on a large scale. The employment of an efficient internal heat exchange network is very essential for the efficiency improvement of the I-S cycle, however, detailed research on this topic is seldomly reported. To enrich the existing research content, an I-S cycle-based hydrogen production system with an internal heat exchange network is proposed in this paper using Aspen Plus. The internal heat exchange network is designed by following the energy cascade utilization principle, and three sets of different heat transfer constraints corresponding to different temperature zones are imposed in the design process. The simulation results show that for the proposed I-S system, more than half of the system energy consumption is used by the distillation processes of two acid solutions, and more than 40% of the system energy consumption is used by the HI concentration and distillation process. Using the internal heat exchange network, about 422 kJ of waste heat (for 1 mol of hydrogen production) can be recovered and the system thermal efficiency is improved by about 4.9%. In addition, an efficiency improvement of about 11.8% can be achieved when the waste heat from the condensers of two distillation columns is completely recovered. In general, the thermal efficiency of the proposed I-S system is estimated to be in the range of 15.8% to 49.8%, and after adopting several common waste heat recovery measures, the system can achieve a promising thermal efficiency of approximately 36.7%.

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