Structural Design and Simulation Study of the Hydrogen Iodide Decomposition Reactor in the Thermochemical Iodine–Sulfur Cycle for Hydrogen Production

Abstract

Hydrogen, as a zero-carbon energy carrier, plays a pivotal role in global decarbonization efforts. The iodine–sulfur (I–S) thermochemical cycle stands out for its high efficiency and scalability in water-splitting hydrogen production, with the hydrogen iodide (HI) decomposition reaction being the critical step governing overall hydrogen yield. Existing HI decomposition reactors often rely on energy-intensive electric heating, which compromises system efficiency and economic viability. To address this limitation, this study proposes a novel shell-and-tube heat exchanger reactor utilizing high-temperature helium gas as a sustainable heat source, integrated with a catalytic reaction zone employing activated carbon. The reactor combines a preheating section and a catalytic decomposition section to optimize heat transfer and reaction kinetics. Using Ansys Fluent–based computational fluid dynamics (CFD) simulations, the impacts of structural parameters (reactor length, tube diameter, and residence time) and operational conditions (helium flow rate) on HI conversion efficiency were systematically investigated. Results demonstrate that increasing helium flow rate (up to 60 kg/h), reactor length (1450 mm), and tube diameter (38 mm) significantly enhances HI decomposition rates, achieving a 27.28% conversion efficiency and 1.364 Nm³/h hydrogen output. Notably, tube diameter emerged as the most influential design parameter due to its dual role in heat transfer area and residence time modulation. This work provides actionable insights for scaling energy-efficient HI decomposition reactors, advancing the industrial implementation of the I–S cycle for sustainable hydrogen production.