A new approach to improve the hydrogen yield for HIx system of I-S process

Iodine-Sulfur (I-S) closed loop cycle for water splitting integrated with high temperature nuclear reactors is one of the futuristic cycles for commercially viable production of hydrogen. I-S process consists of three steps namely Bunsen reaction, H2SO4 decomposition and HI reactive distillation. Efficient operation of reactive distillation of HIX system will improve the overall economics of hydrogen production. In the absence of conclusive simulation data and definite thermodynamic models, fresh approach for generating independent process scheme and design data based on proper material and energy balance, using NRTL thermodynamic model is presented. Various conceptual flow schemes are tried to improve equilibrium as well as kinetic yield of hydrogen production. Effect of total number of theoretical plates, various streams qualities and their locations on hydrogen yield was estimated. Present proposal advocates a fresh approach to a new scheme, completely different from previously published schemes. In this scheme no side stream is withdrawn from the column. Reasonably good reflux is experienced by whole column. It is observed that there exists a proper combination of HI and water composition in the column at which yield of hydrogen is significantly increased. Increased reflux in the column helps in in situ flushing of iodine generated by HI decomposition which in-turn improves the yield. It is to be noted that iodine enrichment for higher hydrogen yield scheme will be lower as compared to lower hydrogen yield schemes. Nevertheless, gain in yield will be more desirable to highly enriched iodine requirement, which is limited to the requirement of the boost reaction only. Due to lack of experimental data available in the literature, we feel, absolute value of hydrogen yield may vary from the reported. However, relative gain in various schemes can't be ignored. (author)