An improved sulfur iodine cycle for sour gas purification and hydrogen fuel production for better environment

The conventional sulfur-iodine (S-I) thermochemical cycle developed for sour gas purification and hydrogen production from H2S stoichiometrically produces 2 moles of H2. The present work aims to develop an improved sulfur-iodine cycle, here called the five-step sulfur-iodine cycle, that replaces direct sulfur oxidation with a reaction between metallic oxygen carrier (OC) and elemental S to produce hydrogen. This new cycle does not only produce more H2, but also produces extra H2SO4. The process is followed by a hydrolysis reaction to regenerate OC and produce additional hydrogen. Hydrogen sulfide from the flue gas is considered the major feedstock for the developed system. The stoichiometry of the cycle is also studied to ensure that all the reactants follow the cyclic pathways. The cycle is then modeled in the Aspen Plus process simulation software under steady-state conditions, and a comprehensive thermodynamic analysis of the entire system is conducted using energy and exergy methods, evaluating energy and exergy efficiencies, as well as the exergy destruction rates of major components. Furthermore, several parameters are thoroughly examined to better investigate the system peformance. The proposed cycle demonstrates a significant improvement in hydrogen yield, and produces 4 moles of H2 per mole of H2S. This represents a 100 % increase in hydrogen production efficiency compared to the conventional S-I cycle, which either produces 1 mole of H2 or 2 moles of H2 per mole of H2S. The hydrolysis and Claus reactors exhibit the highest exergy destruction rates accounting for 33.19 % and 16.69 % of the total exergy destruction rates, respectively. The energy and exergy efficiencies of the CBD section are found to be 72.89 % and 48.54 % respectively. The overall energy and exergy efficiencies of the new cycle configuration are found to be 74.72 % and 62.46 % respectively.