Electrostatic characteristics analysis and risk assessments of liquid hydrogen storage system

Electrostatic safety is a critical and significant issue in the transportation and storage of liquid hydrogen. The generation and accumulation of excess electrical charges in the transmission pipeline and storage tank can lead to the formation of an internal static electric field, potentially resulting in hazardous situations. To ensure the safety of liquid hydrogen systems, it is essential to analyze the electrostatic characteristics within the tank and conduct risk assessments based on safety boundaries. This study establishes a theoretical model to describe the distribution of electrical potential and the dynamic development of charge density, considering the effects of relaxation and dissipation. Through an extensive series of simulations, several critical conclusions have been drawn. Regarding static electrostatic characteristics, it is observed that the electrical potential within the storage tank exhibits a non-isotropic distribution. Increasing the charge density, scale factor, and diameter-height ratio intensifies the electrical potential and enhances the electrostatic risk. However, there exists an optimal filling fraction that yields the highest surface electrical potential. In terms of transient characteristics during the filling process, a peak electrical potential is observed when charged liquid hydrogen is injected into the tank. Elevating the charge density and filling flux significantly increases the electrical potential and escalates the electrostatic risk. Conversely, increasing the initial filling fraction beyond 30 % slightly reduces the risk. Taking a reference critical potential of 30 kV, a charge density of 1 x 10-5 C/m3 is identified as the critical value for static conditions within the tank. For dynamic filling processes, a charge density of 0.019 C/m3 in the transmission pipeline serves as another critical value, acting as the safety boundary. In conclusion, this work provides a comprehensive and in-depth understanding of the electrostatic characteristics of liquid hydrogen storage tanks. Furthermore, it conducts well-founded risk assessments for liquid hydrogen systems, thereby significantly contributing to the safety of transportation and storage practices involving liquid hydrogen.