A method for reducing the severity of liquid hydrogen leak and diffusion accidents using gas barriers

Abstract

This invention discloses a method for reducing the severity of liquid hydrogen leaks and diffusion accidents using a gas barrier, relating to the fields of liquid hydrogen storage, transportation, and safety applications. The method includes a gas supply unit, ductwork, air outlets, solenoid valves, and a control system. In the event of a liquid hydrogen leak and diffusion accident, the invention opens the air outlets upwind of the liquid hydrogen unit, vertically supplying air upwards to form a gas barrier. This suppresses the carrying effect of the incoming airflow from the ground on the flammable and explosive hydrogen cloud, promotes mixing of the hydrogen cloud with the surrounding air, reduces the separation distance between the hydrogen cloud and the ground, promotes the diffusion of the hydrogen cloud upwards, and reduces the hydrogen concentration in the downstream area of ​​the liquid hydrogen unit. This reduces the severity of the liquid hydrogen leak and diffusion accident, effectively ensuring the safety of surrounding personnel and equipment.

Description

Technical Field

[0001] This invention relates to the field of liquid hydrogen storage, transportation and safety applications, and in particular to a method for reducing the severity of liquid hydrogen leakage and diffusion accidents by utilizing gas barriers. Background Technology

[0002] Liquid hydrogen effectively increases the energy density per unit volume of hydrogen and is one of the main methods for storing and transporting hydrogen energy. Currently, liquid hydrogen is widely used as a new generation of cryogenic propellant for aerospace, and liquid hydrogen refueling stations and liquid hydrogen vehicles are receiving increasing attention. During the storage, transportation, and use of liquid hydrogen, operational errors, material failures, malfunctions of key components, and external collisions and impacts can all lead to the rupture and failure of storage tanks, pipelines, or valves, causing liquid hydrogen leakage and diffusion. Liquid hydrogen has extremely low temperatures; contact with it can cause frostbite and material denaturation. The evaporated cryogenic hydrogen gas mixes with the surrounding air to form flammable and explosive hydrogen clouds, seriously threatening the safety of surrounding personnel and equipment.

[0003] Current research largely focuses on the diffusion mechanisms of liquid hydrogen leaks and the influence of different operating parameters, with less attention paid to proactive intervention measures to reduce the hazards of liquid hydrogen leaks and diffusion. Whether to build dikes around liquid hydrogen installations remains controversial. For example, NASA recommends against building dikes and instead allowing the flammable and explosive hydrogen cloud to mix thoroughly with the surrounding air for rapid dilution. Existing research also indicates that although dikes significantly reduce the separation distance between the flammable and explosive hydrogen cloud and the ground, a flammable and explosive hydrogen cloud will remain inside the dike after the leak stops. If the dike size is improperly designed, the dilution time of the hydrogen cloud will be extended several times. Furthermore, dikes are generally suitable for stationary liquid hydrogen installations, but not for mobile liquid hydrogen installations such as hydrogen-powered vehicles and liquid hydrogen tank trucks.

[0004] Against this backdrop, this invention proposes a method for reducing the severity of liquid hydrogen leaks and diffusion accidents using a gas barrier. The aim is to reduce the separation distance between the flammable and explosive hydrogen cloud and the ground, promote the diffusion of the hydrogen cloud upwards, and reduce the hydrogen concentration in the downstream area of ​​the liquid hydrogen device, thereby reducing the severity of the leak and diffusion accident and effectively ensuring the safety of surrounding personnel and equipment. This method is easy to implement, applicable to both fixed and mobile liquid hydrogen devices, and ensures that flammable and explosive hydrogen clouds do not remain in the vicinity of the liquid hydrogen device for an extended period after the leak is terminated. Summary of the Invention

[0005] The purpose of this invention is to provide a method for reducing the severity of liquid hydrogen leak and diffusion accidents using a gas barrier. This method is easy to deploy and implement, applicable to both fixed and mobile liquid hydrogen installations, and can effectively reduce the severity of liquid hydrogen leak and diffusion accidents.

[0006] To achieve the above objectives, the present invention provides the following solution: The present invention provides a method for reducing the severity of liquid hydrogen leakage and diffusion accidents by utilizing a gas barrier. The device for forming the gas barrier includes a gas supply unit, a duct, an air outlet, a solenoid valve, and a control system. The duct includes a main duct and branch ducts. Multiple branch ducts are connected to the main duct, and solenoid valves are respectively installed on the main duct and the branch ducts. The solenoid valves are connected to the control system. The gas supply unit and the air outlet are connected through the main duct and the branch ducts. The air outlet includes four sets or one set of air outlets. When a liquid hydrogen leakage and diffusion accident occurs, the air outlet in the upwind direction of the liquid hydrogen device is opened, and air is supplied vertically upward to form a gas barrier. By suppressing the carrying effect of the incoming airflow from the ground area on the flammable and explosive hydrogen cloud, the hydrogen cloud is promoted to mix with the surrounding air, thereby reducing the separation distance between the hydrogen cloud and the ground, promoting the diffusion of the hydrogen cloud upward, reducing the hydrogen concentration in the downstream area of ​​the liquid hydrogen device, and thus reducing the severity of the liquid hydrogen leakage and diffusion accident.

[0007] Furthermore, for stationary liquid hydrogen facilities such as liquid hydrogen refueling stations, the gas supply department prioritizes the use of inert nitrogen gas and pre-positions high-pressure nitrogen cylinders around the liquid hydrogen facility or buries them underground; for mobile liquid hydrogen facilities such as hydrogen-powered vehicles and liquid hydrogen tank trucks, nitrogen gas or a blower can be used to transport surrounding air depending on the situation at the accident site.

[0008] Furthermore, the gas supply unit and the air outlet are connected by ductwork. The ductwork includes a main pipe connected to the gas supply unit and branch pipes connecting the main pipe and the air outlet. Solenoid valves are installed on both the main pipe and the branch pipes.

[0009] Furthermore, four sets of air supply outlets are pre-arranged on the ground around the liquid hydrogen unit, parallel and perpendicular to the local prevailing wind direction, respectively. For accident sites where pre-arrangement is not feasible, the operation can be simplified, with only one set of air supply outlets arranged upwind of the liquid hydrogen unit. The air supply outlets can adopt elongated, square, or circular structures. Each set of air supply outlets preferably uses a single elongated outlet, but multiple square or circular outlets can also be used at intervals. The air supply direction is vertically upward.

[0010] Furthermore, after a liquid hydrogen leak and diffusion accident occurs, the control system controls the operation of the gas supply unit, opens the solenoid valves on the main and branch pipes, and sends air vertically upward through the air outlets in the upwind direction of the liquid hydrogen unit to form a gas barrier. This suppresses the carrying effect of the incoming airflow from the ground area on the flammable and explosive hydrogen cloud, promotes the mixing of the hydrogen cloud with the surrounding air, thereby reducing the separation distance between the hydrogen cloud and the ground, promoting the diffusion of the hydrogen cloud upward, and reducing the hydrogen concentration in the downstream area of ​​the liquid hydrogen unit.

[0011] The present invention achieves the following technical effects compared to the prior art:

[0012] Proactive measures are taken to intervene in the liquid hydrogen leak and diffusion process. This involves vertically directing airflow upwards through the upwind air outlets of the liquid hydrogen device to form a gas barrier. This alters the wind speed and turbulence distribution in the near-ground area of ​​the device, suppressing the carrying effect of incoming winds on the flammable and explosive hydrogen cloud, and promoting mixing of the hydrogen cloud with the surrounding air, thereby reducing the severity of the liquid hydrogen leak and diffusion accident. Compared to constructing physical dikes, this method is easier to implement and applicable to mobile liquid hydrogen devices. After the leak is terminated, the area near the liquid hydrogen device will not retain a flammable and explosive hydrogen cloud for an extended period.

[0013] Furthermore, compared to simultaneously opening four sets of air outlets or forming a continuous, uninterrupted air supply around the liquid hydrogen device, this invention only opens the air outlets in the upwind direction of the liquid hydrogen device and forms a gas barrier. This reduces gas consumption and facilitates implementation. On the other hand, the gas barriers in the crosswind and downwind directions have limited effect on reducing the diffusion range of flammable and explosive hydrogen clouds. Figure 5 The downwind gas barrier not only increases the hydrogen concentration near the liquid hydrogen device but also extends the duration of the hydrogen cloud in the downstream area. This effectively confines the high-concentration hydrogen cloud to the vicinity of the liquid hydrogen device, thus inhibiting the hydrogen cloud dilution process. Figure 6 ). Attached Figure Description

[0014] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0015] Figure 1 This is a schematic diagram of the overall structure of the method for reducing the severity of liquid hydrogen leakage and diffusion accidents using a gas barrier in this invention.

[0016] Figure 2 A schematic diagram showing the layout of a long, narrow air outlet;

[0017] Figure 3 Schematic diagram of a square air outlet layout;

[0018] Figure 4 This is a schematic diagram of the liquid hydrogen leakage and diffusion process;

[0019] Figure 5 The simulation results show the separation distance between the flammable and explosive hydrogen cloud and the ground when the air supply outlets in different directions are opened;

[0020] Figure 6 The simulation results show the variation of hydrogen concentration in the downstream region of the liquid hydrogen unit when the air supply outlets in different directions are opened.

[0021] The components are as follows: 1. Liquid hydrogen unit; 2. Gas supply unit; 3. Main duct; 4. Main duct solenoid valve; 5. Branch duct connected to the upwind air outlet; 6. First branch duct solenoid valve; 7. Upwind air outlet; 8. Branch duct connected to the downwind air outlet; 9. Second branch duct solenoid valve; 10. Downwind air outlet; 11. Branch duct connected to the front crosswind air outlet; 12. Third branch duct solenoid valve; 13. Front crosswind air outlet; 14. Branch duct connected to the rear crosswind air outlet; 15. Fourth branch duct solenoid valve; 16. Rear crosswind air outlet; 17. Liquid pool; 18. Flammable and explosive hydrogen cloud; 19. Point where the flammable and explosive hydrogen cloud separates from the ground. Detailed Implementation

[0022] The purpose of this invention is to provide a method for reducing the severity of liquid hydrogen leaks and diffusion accidents by utilizing a gas barrier. This method aims to reduce the separation distance between the flammable and explosive hydrogen cloud and the ground, promote the diffusion of the hydrogen cloud upwards, reduce the hydrogen concentration in the downstream area of ​​the liquid hydrogen device, and effectively ensure the safety of surrounding personnel and equipment. Compared with methods such as building physical dikes, this method is easier to implement and applicable to mobile liquid hydrogen devices. After the leak is terminated, flammable and explosive hydrogen clouds will not remain in the vicinity of the liquid hydrogen device for a long time.

[0023] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0024] Example 1

[0025] like Figure 1As shown, this embodiment provides a method for reducing the severity of liquid hydrogen leak and diffusion accidents using a gas barrier. The device for forming the gas barrier includes a gas supply unit 2, a main duct 3, branch ducts (5, 8, 11, 14), air outlets (7, 10, 13, 16), a main duct solenoid valve 4, branch duct solenoid valves (6, 9, 12, 15), air outlets (7, 10, 13, 16), and a control system. The branch ducts include branch 5 connected to an upwind air outlet, branch 8 connected to a downwind air outlet, branch 11 connected to a front crosswind air outlet, and branch 14 connected to a rear crosswind air outlet. The air outlets include an upwind air outlet 7, a downwind air outlet 10, a front crosswind air outlet 13, and a rear crosswind air outlet 16. The branch solenoid valves include a first branch solenoid valve 6, a second branch solenoid valve 9, a third branch solenoid valve 12, and a fourth branch solenoid valve 15. The gas supply unit 2 connects to the main duct 3, which is equipped with a main solenoid valve 4. The pipeline after the main solenoid valve 4 splits into four paths: the first path connects sequentially to a branch duct 5 connected to an upwind air outlet and an upwind air outlet 7; the second path connects sequentially to a branch duct 8 connected to a downwind air outlet and a downwind air outlet 10; the third path connects sequentially to a branch duct 11 connected to a front crosswind air outlet and a front crosswind air outlet 13; and the fourth path connects sequentially to a branch duct 14 connected to a rear crosswind air outlet and a rear crosswind air outlet 16. The first branch solenoid valve 6 is installed on the branch duct 5 connected to the upwind air outlet. A second branch solenoid valve 9 is installed on the duct branch 8 connected to the downwind air outlet. A third branch solenoid valve 12 is installed on the duct branch 11 connected to the front crosswind air outlet. A fourth branch solenoid valve 15 is installed on the duct branch 14 connected to the rear crosswind air outlet.

[0026] For stationary liquid hydrogen devices such as liquid hydrogen refueling stations, the gas supply department 2 prioritizes the use of inert gas nitrogen, and pre-positions high-pressure nitrogen cylinders around the liquid hydrogen device 1 or buries them underground, with the high-pressure nitrogen cylinders containing nitrogen; for mobile liquid hydrogen devices such as hydrogen-powered vehicles, nitrogen or a blower can be used to transport surrounding air depending on the situation at the accident site.

[0027] The gas supply unit 2 is connected to the air outlet via the main duct 3 and duct branches. The upwind air outlet 7 is connected to the main duct 3 via the duct branch 5 connected to the upwind air outlet. The downwind air outlet 10 is connected to the main duct 3 via the duct branch 8 connected to the downwind air outlet. The front crosswind air outlet 13 is connected to the main duct 3 via the duct branch 11 connected to the front crosswind air outlet. The rear crosswind air outlet 16 is connected to the main duct 3 via the duct branch 14 connected to the rear crosswind air outlet.

[0028] Solenoid valves are installed on both the main and branch ducts: the main duct 3 is equipped with a main solenoid valve 4; the branch duct 5 connected to the upwind air outlet is equipped with a first branch solenoid valve 6; the branch duct 8 connected to the downwind air outlet is equipped with a second branch solenoid valve 9; the branch duct 11 connected to the front crosswind air outlet is equipped with a third branch solenoid valve 12; and the branch duct 14 connected to the rear crosswind air outlet is equipped with a fourth branch solenoid valve 15.

[0029] Air outlet arrangement as follows Figure 2 and Figure 3 As shown. Four sets of air supply outlets, namely, upwind air supply outlet 7, downwind air supply outlet 10, front crosswind air supply outlet 13, and rear crosswind air supply outlet 16, are pre-arranged on the ground around the liquid hydrogen unit 1, parallel and perpendicular to the local prevailing wind direction, respectively. For accident sites where pre-arrangement is not feasible, the operation can be simplified, with only one set of air supply outlets, namely upwind air supply outlet 7, arranged upwind of the liquid hydrogen unit 1. The air supply outlets adopt elongated, square, and circular structures. Each set of air supply outlets preferably uses a single elongated air supply outlet (…). Figure 2 Alternatively, multiple square or round air vents can be arranged at intervals. Figure 3 The air supply direction is vertically upward.

[0030] When a leak occurs in liquid hydrogen unit 1, the liquid hydrogen leakage and diffusion process is as follows: Figure 4 As shown. After liquid hydrogen leaks from device 1, it first accumulates on the ground to form a liquid pool 17. The liquid pool 17 evaporates and mixes with the surrounding air to form a flammable and explosive hydrogen cloud 18. Under the influence of the wind, it diffuses downstream of the liquid hydrogen device 1 and separates from the ground at a certain distance 19. According to the local wind direction (shown from right to left in the diagram), the control system controls the operation of the gas supply unit 2, opening the main solenoid valve 4 on the main duct 3 and the first branch solenoid valve 6 on the branch duct 5 connected to the upwind air outlet. Gas is blown vertically upward through the upwind air outlet 7 of the liquid hydrogen device, forming a gas barrier. This suppresses the carrying effect of the incoming wind on the flammable and explosive hydrogen cloud from the ground, promotes the mixing of the hydrogen cloud with the surrounding air, reduces the separation distance between the flammable and explosive hydrogen cloud and the ground, promotes the diffusion of the hydrogen cloud upward, and reduces the hydrogen concentration in the downstream area of ​​the liquid hydrogen device.

[0031] Any adaptive changes made according to actual needs are within the scope of protection of this invention.

[0032] Example 2

[0033] To more clearly and intuitively demonstrate the effect of this invention in reducing the severity of liquid hydrogen leakage and diffusion accidents using a gas barrier, the liquid hydrogen leakage and diffusion process was simulated in the CFD software ANSYS Fluent using the gas barrier described in Example 1, based on the Mixture multiphase flow model, the Realizable k-ε model, the component transport equation, and the Lee model. The liquid hydrogen leakage rate was 7.08 kg / s, the local wind speed was 2 m / s, and the wind direction was from right to left. The air outlets, namely the upwind air outlet 7, the downwind air outlet 10, the front crosswind air outlet 13, and the rear crosswind air outlet 16, were all located 3 m from the center of the liquid hydrogen device 1, and when opened, they all blow air vertically upwards at a speed of 5 m / s.

[0034] Figure 5 The simulation results show the separation distance between the flammable and explosive hydrogen cloud and the ground when the air supply outlets in different directions are opened. Compared with no intervention, opening the upwind air supply outlet 7 reduced the separation distance between the flammable and explosive hydrogen cloud and the ground by 30.5%; while opening the downwind air supply outlet 10 and the crosswind air supply outlets (i.e., the front crosswind air supply outlet 13 and the rear crosswind air supply outlet 16) had no significant effect on the separation distance between the flammable and explosive hydrogen cloud and the ground.

[0035] A monitoring point 15m downstream of the liquid hydrogen unit and 1.5m above it was selected. The simulation results of the hydrogen concentration change at the monitoring point when the air supply outlets in different directions were opened are as follows: Figure 6 As shown. Compared to taking no intervention measures, opening the upwind air outlet 7 significantly reduced the hydrogen concentration at the observation point downstream of the liquid hydrogen unit, and shortened the time it took for the hydrogen cloud to diffuse out of the flammable zone after the leak stopped. However, opening the downwind air outlet 10 slightly reduced the hydrogen concentration at the observation point downstream of the liquid hydrogen unit, but prolonged the time it took for the hydrogen cloud to diffuse out of the flammable zone after the leak stopped.

[0036] Numerical simulation results verify the effectiveness of opening the upwind air outlet of the liquid hydrogen device and forming a gas barrier in reducing the severity of liquid hydrogen leakage and diffusion accidents. It also shows that the gas barriers in the crosswind and downwind directions of the liquid hydrogen device have limited effect on reducing the separation distance between the flammable and explosive hydrogen cloud and the ground, and that the downwind gas barrier inhibits the dilution process of the hydrogen cloud to some extent.

[0037] The parts of this invention not described in detail are well-known to those skilled in the art. The embodiments described above are merely preferred embodiments of the invention, and do not exhaustively describe all details, nor do they limit the invention to the specific implementations described. Various modifications and improvements to the technical solutions of this invention made by those skilled in the art without departing from the spirit of the invention should fall within the protection scope defined by the claims of this invention.

Claims

1. A method for reducing the severity of liquid hydrogen leak and diffusion accidents using a gas barrier, characterized in that, The device for forming a gas barrier includes a gas supply unit, ductwork, air outlets, solenoid valves, and a control system. The ductwork includes a main duct and branch ducts. Multiple branch ducts are connected to the main duct, and solenoid valves are installed on both the main duct and branch ducts. The solenoid valves are connected to the control system. The gas supply unit and the air outlets are connected through the main duct and branch ducts. The air outlets have four sets of outlets. In the event of a liquid hydrogen leak and diffusion accident, the air outlets in the upwind direction of the liquid hydrogen device are opened to deliver air vertically upwards and form a gas barrier. This barrier suppresses the carrying effect of the incoming airflow from the ground area on the flammable and explosive hydrogen cloud, promotes the mixing of the hydrogen cloud with the surrounding air, reduces the separation distance between the hydrogen cloud and the ground, promotes the diffusion of the hydrogen cloud upwards, and reduces the hydrogen concentration in the downstream area of ​​the liquid hydrogen device, thereby reducing the severity of the liquid hydrogen leak and diffusion accident. The gas supply department uses either nitrogen or air; Four sets of air outlets are pre-arranged on the ground around the liquid hydrogen unit, parallel and perpendicular to the local prevailing wind direction. The two sets of air outlets parallel to the local prevailing wind direction are divided into air outlets in the upwind direction and air outlets in the downwind direction, and the two sets of air outlets perpendicular to the local prevailing wind direction are divided into air outlets in the front crosswind direction and air outlets in the rear crosswind direction. The air supply outlets are elongated, square, or circular in shape; each group of air supply outlets uses a single elongated outlet, or multiple square or circular outlets arranged at intervals, with the air supply direction being vertically upward; for fixed liquid hydrogen devices, the gas supply unit uses inert nitrogen gas, and high-pressure nitrogen cylinders are pre-positioned around the liquid hydrogen device or buried underground; for mobile liquid hydrogen devices, nitrogen gas or a blower is used to supply surrounding air depending on the accident site conditions.

2. The method according to claim 1, characterized in that, When a leak occurs, liquid hydrogen leaks from the liquid hydrogen unit and first accumulates on the ground to form a liquid pool. The liquid pool evaporates and mixes with the surrounding air to form a flammable and explosive hydrogen cloud. Carried by the incoming wind, it diffuses downstream of the liquid hydrogen unit and separates from the ground in the downstream area. The control system controls the gas supply unit to open the main solenoid valve on the main duct and the solenoid valve on the branch duct connected to the upwind air outlet. Gas is then blown vertically upward through the upwind air outlet of the liquid hydrogen unit, forming a gas barrier. This inhibits the carrying effect of the incoming wind on the flammable and explosive hydrogen cloud from the ground, promotes the mixing of the hydrogen cloud with the surrounding air, reduces the separation distance between the hydrogen cloud and the ground, promotes the diffusion of the hydrogen cloud upward, and reduces the hydrogen concentration in the downstream area of ​​the liquid hydrogen unit.

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