Safety Issues of a Hydrogen Refueling Station and a Prediction for an Overpressure Reduction by a Barrier Using OpenFOAM Software for an SRI Explosion Test in an Open Space

Abstract

Safety issues arising from a hydrogen explosion accident in Korea are discussed herein. In order to increase the safety of hydrogen refueling stations (HRSs), the Korea Gas Safety Corporation (KGS) decided to install a damage-mitigation wall, also referred to as a barrier, around the storage tanks at the HRSs after evaluating the consequences of hypothetical hydrogen explosion accidents based on the characteristics of each HRS. To propose a new regulation related to the barrier installation at the HRSs, which can ensure a proper separation distance between the HRS and its surrounding protected facilities in a complex city, KGS planned to test various barrier models under hypothetical hydrogen explosion accidents to develop a standard model of the barrier. A numerical simulation to investigate the effect of the recommended barrier during hypothetical hydrogen explosion accidents in the HRS will be performed before installing the barrier at the HRSs. A computational fluid dynamic (CFD) code based on the open-source software OpenFOAM will be developed for the numerical simulation of various accident scenarios. As the first step in the development of the CFD code, we conducted a hydrogen vapor cloud explosion test with a barrier in an open space, which was conducted by the Stanford Research Institute (SRI), using the modified XiFoam solver in OpenFOAM-v1912. A vapor cloud explosion (VCE) accident may occur due to the leakage of gaseous hydrogen or liquefied hydrogen owing to a failure of piping connected to the storage tank in an HRS. The analysis results using the modified XiFoam predicted the peak overpressure variation from the near field to the far field of the explosion site through the barrier with an error range of approximately ±30% if a proper analysis methodology including the proper mesh distribution in the grid model is chosen. In addition, we applied the proposed analysis methodology using the modified XiFoam to barrier shapes that varied from that used in the test to investigate its applicability to predict peak overpressure variations with various barrier shapes. Through the application analysis, we concluded that the proposed analysis methodology is sufficient for evaluating the safety effect of the barrier, which will be recommended through experimental research, during VCE accidents at the HRSs.

A Database Extension for a Safety Evaluation of a Hydrogen Refueling Station with a Barrier Using a CFD Analysis and a Machine Learning Method

“…Thus, we did not include pressure sensor P8, located 41 m from the ignition point in the grid model, to reduce the computational time. We also decreased the width of the grid model to 5 m from the distance of 10 m used in a previous analysis [36] to ensure effective sensitivity calculations of the various barrier heights during a suitable computational time. A total of 2,569,440 hexahedral cells with an approximate cell length of 1.5 cm around the tent region and 15 to 25 cm at the far field region from the tent were generated in the grid model to resolve the rapid flame acceleration due to the spark ignition and the propagation of the pressure wave in the air environment.…”

“…A total of 2,569,440 hexahedral cells with an approximate cell length of 1.5 cm around the tent region and 15 to 25 cm at the far field region from the tent were generated in the grid model to resolve the rapid flame acceleration due to the spark ignition and the propagation of the pressure wave in the air environment. The cell length sizes in the grid model were determined based on previous mesh sensitivity calculation results [36]. The boundary conditions for the grid model are shown in Figure 3a.…”

“…The boundary conditions for the grid model are shown in Figure 3a. The opening condition allows for the inflow and outflow of air through the applied surfaces and simultaneously uses a wave transmissive outflow condition that can be expressed by Equations ( 8) and ( 9) [19,36]. In Equation ( 9), W p is the patch wave speed, φ p is the patch face flux, S f is the patch face area vector, ϕ p is the patch compressibility, and γ is the ratio of specific heat.…”