Effects of Process Parameters of the IS Process on Total Thermal Efficiency to Produce Hydrogen from Water.

Thermal efficiency of the IS (sulfur-iodine) thermochemical hydrogen production cycle process was investigated. The heat and mass balance of the process were calculated with various operating conditions, and the effects of these conditions on the thermal efficiency were evaluated. The flowsheet of the H2SO4 decomposition designed by Knoche et al. (1984) was used. An electro-electrodialysis (EED) cell for the concentration of HI and a hydrogen permselective membrane reactor for decomposition of HI were applied to the process. Sensitivities of four operating conditions (the HI conversion ratio at the HI decomposition reactor, the reflux ratio at the HI distillation column, the pressure in the HI distillation column, and the concentration of HI after the EED cell) were investigated. The concentration of HI had the most significant effect on thermal efficiency. The difference of the efficiency was 13.3%. Other conditions had little effects within 2% of the efficiency. Effects of nonideality of the process (electric energy loss in the EED cell, loss at heat exchangers and loss of the waste heat recovery as electric energy) were evaluated. The difference of the efficiencies by the loss in the EED cell was 11.4%. The efficiency decreased by 5.7% by the loss at heat exchangers. The loss of the waste heat recovery lowered the efficiency by 6.3%. The result shows that the development of the EED cell, heat exchangers and electric recovery is effective in improving thermal efficiency. The operating conditions such as the HI concentration after the EED cell should be optimized to obtain the maximum thermal efficiency after the developments of the apparatuses. Change of the state of nonideality needs the optimization of the concentration. The thermal efficiency of the total process was 56.8% with ideal operating conditions of the EED cell, heat exchangers and high performance waste heat recovery.