Process optimization and safety assessment on a pilot-scale Bunsen process in sulfur–iodine cycle

Abstract

This study investigates Bunsen reaction in the sulfur-iodine (SI) cycle for optimal conditions and specification of equipment in terms of the maximum HI yield and the least impurities in HIx (mixture of HI, I2 and H2O), the reaction safety, and dispersion of SO2 gas and HIX solution for leakage accident. The pilot-scale Bunsen process was simulated and validated. The optimization of the Bunsen reactor, 3-phase separator, and HIX purifier have been investigated in order to parameterize the operating conditions and equipment specification for three cases: (1) Maximize the HI yield for the final product (2) Minimize the H2SO4 impurities (3) Multi-objective case of both maximum HI production and minimum impurities. The gas reactivity safety was investigated on HI, H2SO4, I2, SO2, H2O, and O2. Also, the SO2 gas dispersion distance for 30 ppm, 0.75 ppm, and 0.2 ppm and HI dispersion distance for 120 ppm, 25 ppm, and 1 ppm was investigated for targeted unit operators at each optimization scenario. The deviation between pilot-scale experiment and simulation case falls within 1–3% for Bunsen reactor, 6~8% for 3-phase separator, and 2~4% for HIX purifier. The maximized HI production was increased by 17% for the maximum HI yield case from the designed case. The size and temperature of the Bunsen reactor was increased to enhance the reaction. However, the HIX purifier size was reduced since reverse Bunsen reaction causes loss in HI product. The H2SO4 impurities in the minimize H2SO4 impurities case were reduced by 71% from the designed case. The size of the Bunsen reactor remained the same as design case, but the HIX purifier size was increased to enhance the reverse Bunsen reaction. For multi-objective case, the HI productivity was increased by 16% and the H2SO4 impurities were reduced by 67% simultaneously. According Chemical Reactivity Worksheet (CRW) result, O2 should therefore not be stored with any components except iodine. For SO2 and HIX dispersion assessment, the maximum HI yield case reveals the maximum dispersion of SO2 gas and HIX solution from the Bunsen reactor. The dispersion from 3-phase separator was almost the same for all the cases. For HIX purifier, the minimum H2SO4 case exhibited the longest distance of SO2 gas and HI solution dispersion. At 3 bar and 140 °C, the maximum SO2 and HIX dispersion distance were occurred.