Implementation of a Semi-Empirical Model for a Low-Temperature Alkaline Electrolyzer in Aspen HYSYS®

Water electrolysis performed by renewables allows to produce green Hydrogen: this process can boost the penetration of clean energy sources into electric grids. This work presents a model developed in Aspen HYSYS® aiming at evaluating the performance of a low-temperature alkaline (ALK) electrolyzer while varying the main operating conditions (e.g., power supply, temperature, and pressure). A Semi-empirical model published in the scientific literature, which describes the physic-chemical processes at the system level, has been implemented in Aspen HYSYS® and used for resembling the operational behaviour of an ALK electrolyzer. The model consists of common system-level blocks with a customized spreadsheet: semi-empirical correlations, which have been calibrated via multiple non-linear regression fittings of experimental data from the scientific literature, allowed to implement the main electro- and thermochemical-equations of the electrolysis process. Simulated results showed a good agreement with respect to the experimental ones for all the studied operating conditions in terms of Normal Root Mean Square Error (NRMSE). Regarding the Hydrogen flow rate, the comparison between the model and the experimental results showed NRMSE values ranging between 4.208e-05 and 6.415e-05, where the former is the lowest threshold value obtained in this analysis. On the other hand, as far as the Hydrogen-to-Oxygen (HTO) is concerned, NRSME values vary between 2.486e-04 and 5.519e-04, where the latter is the highest threshold value obtained in this analysis. Finally, this model can be considered a good starting point for creating a Hydrogen-integrated system through the connection of the electrolyzer with a Hydrogen storage system and a fuel cell.