Research on oxygen purity based on industrial scale alkaline water electrolysis system with 50Nm3 H2/h

In this paper an alkaline electrolysis water system with 50Nm3H2/h is established, and the electrolyzer is equipped with PPS (Polyphenylene sulfide) diaphragm. The characteristics of oxygen purity are investigated in this study. The oxygen purity is characterized by HTO (Hydrogen to Oxygen). Three different types of experiments are carried out to determine the stability, safe operation boundary, and dynamic response characteristics of oxygen purity. Experimental study reveals that the lowest load limit is just 40% rated load under maximum pressure. The change of HTO has the 3 min delay and dynamic change time of HTO from minute to hour levels after the step of operating conditions. A completed oxygen purity prediction model for this industrial-scale alkaline water electrolysis system is proposed. The steady-state, time-delay, and inertia of HTO are considered in the model, which effectively predicts the steady-state HTO of all operating points and the variation of HTO after the step of operating conditions with minimal error. The model is used to quantitatively analyze the hydrogen crossover driven by concentration difference, which exceeds 90% of the total hydrogen crossover. And the model reveals the reason for the poor gas purity at low current.