1. Introduction
In recent years, people have been facing increasingly serious environmental pollution problems and energy crises, and the call for using clean and renewable energy to replace traditional fossil energy sources is becoming louder [
1,
2]. Hydrogen, as a new type of energy carrier, possesses the merits of high efficiency, low carbon emissions and wide distribution in nature, which paves a feasible path for energy transition [
3,
4,
5]. As a result, hydrogen energy is gradually receiving close attention from countries around the world, and its areas of application are being developed more and more widely [
6,
7]. Benefiting from continuous breakthroughs in hydrogen production, storage, and transportation technologies, the market scale of the hydrogen fuel cell vehicle industry has expanded [
8,
9]. Against this background, the number of hydrogen production stations and HRS has been increasing rapidly, and the primary type of hydrogen storage in the stations is currently high-pressure gaseous hydrogen storage [
10,
11,
12]. However, due to compact storage space and high storage pressures, ensuring the safety of the storage and transportation of hydrogen is very challenging [
13,
14]. Hydrogen is characterized by easy leakage, the hydrogen embrittlement reaction of metals, low ignition energy and a wide combustion range [
15,
16,
17]. Once a leakage accident occurs, the FHC formed by the leakage may be ignited, and it may lead to fires and explosions, which seriously threaten the personnel in the station and the inner building of the station [
18]. Therefore, to ensure the safe and stable operation of a hydrogen production and refueling station, it is necessary to study the process of accidental hydrogen leakage and to analyze the characteristics of the leakage and diffusion of hydrogen in the station.
Some scholars have carried out experimental studies on the leakage and diffusion of hydrogen. Kobayashi et al. [
19] conducted cryogenic compressed hydrogen leakage diffusion experiments, which showed that both the leakage flow rate and concentration of hydrogen increased with a decreasing supply temperature. An experimental study on hydrogen leakage at different initial pressures, nozzle diameters and ignition positions was carried out [
20]. The hysteresis parameters and flame propagation characteristics of hydrogen leakage were quantitatively analyzed, and a prediction model for the hysteresis parameters of hydrogen leakage was developed on the basis of the van der Waals equation. Xin et al. [
21] focused on the leakage behavior of an underground parking facility and built a scale-down model, and they obtained various data on different environmental conditions through experiments. Xu et al. [
22] experimentally studied the hydrogen leakage and diffusion characteristics in a space with a large aspect ratio, and the results showed that the higher the initial leakage rate, the stronger the initial intensity of turbulence, which is more favorable to the mixing of hydrogen and air. Shu et al. [
23] created a high-accuracy model of hydrogen leakage so that they obtained experimental data with a relatively low bias. Tanaka et al. [
24] performed a hydrogen leaking test in a storage room. The results showed that the leakage diameter, the amount of hydrogen released and the indoor ventilation characteristics had a significant effect on the hydrogen concentration.
A number of scholars have focused on computational methods for analyzing the behavior and characteristics of hydrogen leakage. Vanlaere et al. [
25] mainly investigated the distribution characteristics of hydrogen after it leaked in a confined space by means of a nilpotent analysis method. They proposed a risk reduction strategy with practical applications. Chang et al. [
26] analyzed potential leakage accidents in a hydrogen production facility based on the Dynamic Bayesian Network method. They successfully predicted the probability of the system collapse and the logic of the accidents. He et al. [
27] creatively utilized the ConvLSTM-based surrogate model to predict leakage in HRS accurately, which spent computing power more evenly on calculation. Rostamzadeh et al. [
28] created a new method named MACB to apply to the convergence problem to calculations of hydrogen leakage so that they optimized the traditional scheme and sped up calculation in specific situations.
Many scholars have utilized the computational fluid dynamics (CFD) method to study hydrogen leakage numerically. Choi et al. [
29] simulated the hydrogen leakage diffusion process of fuel cell vehicles in an underground car park. They found that the volume of the flammable region did not increase linearly in the initial stage but increased rapidly after a latent period. Shentsov et al. [
30] modeled the release and dispersion of a high-pressure hydrogen storage tank in a parking lot by CFD, investigated the effects of the release angle, canopy height and ventilation rate on the hydrogen diffusion, and proposed a safety strategy based on the results. Wang et al. [
31] used FLACS software to simulate hydrogen leakage in a confined room and considered various restrictions, including the side walls and corners. Patel et al. [
32] simulated the stratification characteristics of hydrogen after leakage in a semi-enclosed space with ANSYS FLUENT. They investigated the effect of the arrangement of the number and location of the vents on the reduction in the hydrogen concentration to derive an optimal ventilation scheme. Malakhov et al. [
33] used STAR CCM+ to simulate the distribution of hydrogen leakage in a semi-enclosed space with different initial leakage pressures and different leak opening sizes. They investigated ways to improve the efficiency of forced ventilation to guide hydrogen safety issues. Tian et al. [
34] simulated the pattern of leakage from a high-pressure hydrogen storage tank in a variety of scenarios using CFD methods. They analyzed the safety distances as well as the variation of the hydrogen concentration in the overall space. Thomas et al. [
35] studied hydrogen leakage accidents using numerical simulations and found that larger leakage rates were more likely to form an FHC in open space. Kikukawa et al. [
36] simulated the leakage of a hydrogen dispenser in an HRS using FLUENT software (version 6.2). They verified the possibility of constructing an HRS near a gas station by the distance of the diffusion of hydrogen. Qian et al. [
37] analyzed diverse scenarios, including various locations of leakage in hydrogen storage tanks and wind effects in an HRS. They found that the presence of obstacles greatly affected the shape and diffusion distance of the FHC, and the closer the leakage location was to the obstacle, the larger the contour of the FHC and the more irregular the shape. Patel et al. [
38] conducted a parametric study of the diffusion and explosion of hydrogen in an HRS by means of FLACS software, analyzed the range of acceptable safety distances for various scenarios and assessed the risk of accidental leakage and explosion in an HRS. Wang et al. [
39] modeled a hydrogen leakage accident from a heavy truck in an HRS with a large canopy structure by CFD methods. They performed a deterministic assessment of the accident risk. Gao et al. [
40] conducted a leakage model based on hydrogen storage tanks in a nuclear station. They obtained diffusion contours on account of a variety of factors. Han et al. [
41] investigated the diffusion law of hydrogen leakage for leakage holes with different diameters and different leakage pressures by numerical simulation and explored the evolution of the FHC. Xiao et al. [
42] studied the leakage and diffusion behavior of hydrogen using CFD methods and predicted the diffusion distance of the FHC via artificial neural networks. Cui et al. [
43] concentrated on the HRS in Ningbo Harbor. The impact of wind, the roof shape and the air humidity on the diffusion of hydrogen leakage was investigated. They found that headwinds significantly increased the volume of the FHC, sloping roofs could promote the diffusion of hydrogen, and the air humidity had a negligible effect.
The above studies focused on the diffusion characteristics of high-pressure hydrogen during the leakage process. However, there are fewer studies on the dissipation characteristics of hydrogen during the dissipation process when the leakage is over. In addition, most of the studies on hydrogen leakage are based on scenarios with small spaces or simplified building layouts. However, there are fewer studies on actual hydrogen-related scenarios with large spaces and complex building layouts. In this study, the leakage characteristics of high-pressure hydrogen in an integrated station were investigated, as well as the dissipation characteristics of hydrogen after the leakage stopped. Furthermore, the purpose of this study was to guide the construction of an IHPRS in Weifang, China, which is of great practical significance. The integrated station is characterized by a large space and a complex building layout, and the factors influencing the hydrogen leakage and dissipation in this scenario were investigated, including the leakage aperture, the leakage direction, and the ambient wind direction and speed.