An optimal operating window for the Bunsen process in the I-S thermochemical cycle

摘要

We searched for the optimal compromised operating conditions for the Bunsen reaction of IS thermochemical water splitting, considering the key concerns of the IS cycle: the liquid-liquid equilibrium (LLE) phase separation performance, the characteristics of water distribution between the sulfuric acid (SA) phase and the poly-hydroiodic acid (HI_x) phase, side reaction occurrence, and the effect on operating costs. Experimental data available from a literature survey were combined, and common trends were examined through a series of parametric studies. Based on the results, the optimal operating point and allowable operating window for the Bunsen reaction have been proposed: the optimal point is represented by 4 mol of excess iodine and 11 mol of excess water in the stoichiometry at temperature of 330 K, while the allowable window ranges over 4-6 mol for the excess iodine, 11-13 mol for the excess water, and 330-350 K for the temperature. After the Bunsen reaction and LLE phase separation, 5 mol of the excess water is distributed to the SA phase and 6-8 mol to the HI_x phase. Operating within this window makes it possible to avoid the side reaction and iodine solidification, to increase the HI concentration well above the azeotropic point in the HI_x section, and to minimize operating costs arising from excess iodine and water.