Numerical Study on the Diffusion Characteristics and Ventilation under Hydrogen Leakage in the Underground Hydrogen Facilities

Abstract

Hydrogen storage and supply system such as a hydrogen charging station needs to sufficient safety distance which are constructed on the ground space, but considering the use of domestic land space in Korea, it is already difficult to secure ground space due to high density development including the urban planning. Various studies are being conducted on the undergroundization of the hydrogen system to solve this problem, but the risk of explosion and fire should be considered when the gaseous hydrogen leaks including the concentration of hydrogen reaches more than 4% (Limit Flammability Level, LFL). Preventing these problems, the concentration of leakage hydrogen should be diluted using the proper ventilation methods in underground space. According to the NFPA, ventilation performance need to allow dilution below 25% of the LFL (1% hydrogen concentration). In this study, we investigated the diffusion phenomena of leakage hydrogen and ventilation performance when gaseous hydrogen leaks from underground facilities numerically, and suggested to reduce the hydrogen volume fraction in it. The flow rate at exhaust port, the number of exhaust port and inlet port were considered the design parameters in this study. The flow characteristics of leaking gaseous hydrogen was set based on the volume average concentration, the ventilation performance according to the variables was quantitatively checked, and the ventilation performance was analyzed through the stagnation region and residual hydrogen volume fraction in underground space.