Pressure reducing device that enables the use of polymer piping for thermal pressure relief in hydrogen vehicles

Abstract

The present invention relates to a pressure reducing system for a high pressure tank (10), in particular a high pressure tank (10) of a motor vehicle, in which a fluid is stored under positive pressure, the high pressure tank (10) having an outlet (9) for relieving the pressure, the high pressure tank (10) being fluidly connected via the outlet (9) to a thermal pressure relief device (20) through which the fluid flows in a flow direction (x) when pressure is relieved. According to the present invention, the thermal pressure relief device (20) is provided with a pressure reducing device (1) for reducing the pressure when relieving the pressure of the high pressure tank (10).

Description

[Technical field]

[0001] The invention relates to a pressure reducing device for a high-pressure tank according to the preamble of claim 1. [Background technology]

[0002] For example, in vehicles fuelled by hydrogen or natural gas, high-pressure tanks are used to store the fuel, in which pressures of several hundred bar are typical, for example 700 bar in the passenger car sector.

[0003] For safety reasons, high pressure tanks are equipped with a thermal pressure relief device, which is usually a piping system, or relief pipe, that empties the high pressure tank in the event of a vehicle fire.

[0004] Relief pipes or thermal pressure relief devices that are directly connected to the hydrogen high pressure tank are already known from the prior art. These are usually stainless steel pipes that have a relatively high mechanical strength and, as a result, can withstand the high pressure conditions during fuel spills. Depending on the design of the system, when the thermal pressure relief device is activated, hydrogen flows from the high pressure tank into the pipe, and the pressure in the pipe reaches about 80 to 95% of the tank pressure.

[0005] Here, the disadvantage is that stainless steel piping is relatively heavy and expensive to manufacture.

[0006] The object of the present invention is to overcome these and other drawbacks of the prior art and to realize an improved pressure reduction system for high-pressure tanks of hydrogen vehicles, which can be constructed in a cost-effective manner using simple means and which at the same time has a low self-weight. Summary of the Invention

[0007] The main features of the invention are set forth in the characterizing part of claim 1. Design embodiments are the subject of claims 2 to 10.

[0008] A pressure reducing system for a high pressure tank, particularly a high pressure tank for an automobile, in which a fluid is stored under positive pressure, the high pressure tank has an outlet for relieving pressure, the high pressure tank is fluidly connected via the outlet to a thermal pressure relief device through which the fluid flows in a flow direction when pressure is relieved, and according to the present invention, the thermal pressure relief device is provided with a pressure reducing device for reducing pressure when pressure in the high pressure tank is relieved.

[0009] The present invention achieves this object in a surprisingly simple manner by using an additional pressure reducing device in the thermal pressure relief device, which reduces the pressure in the thermal pressure relief device, so that the thermal pressure relief device can be manufactured from extremely cost-effective and lightweight plastic materials, in particular polymeric materials. In this way, the present invention provides an exhaust system for a high-pressure tank, which guarantees a low pressure in the piping during pressure relief.

[0010] 2 The pressure reducing device is preferably a throttle valve, which has a throttle opening. By means of the throttle valve, the pressure at the outlet of the high-pressure tank and in the thermal pressure relief device is effectively reduced downstream in the flow direction or in the flow direction, respectively. It is particularly preferred here that the throttle valve is designed as an annular throttle valve. This represents a cost-effective construction variant and thus further reduces the overall manufacturing costs. Alternatively, other throttle shapes that are cost-effective to manufacture, such as, for example, a simple perforated sheet metal plate, are also conceivable.

[0011] The restrictor opening is preferably designed to be smaller in diameter than the outlet and the thermal pressure relief device, so that an effective reduction in the total pressure or increase in entropy in the system is achieved. At the same time, the restrictor reduces the static pressure downstream or in the flow direction within the thermal pressure relief device.

[0012] According to another variant of the embodiment of the invention, the throttle valve is arranged indirectly in the outlet of the high-pressure tank and in the thermal pressure relief device, the distance between the outlet and the throttle advantageously ensuring that during the draining operation, no excessively high pressure peaks arise in the area of ​​the outlet or at the piping inlet of the thermal pressure relief device.

[0013] According to a preferred embodiment, the invention provides that the thermal pressure relief device is designed as a relief pipe, the outlet of which has a diameter corresponding to the pipe diameter of the thermal pressure relief device. When flowing through the relief pipe, a uniform flow rate of the mass is ensured. Due to the throttle valve, the density of the fuel is reduced when flowing through the relief pipe. In order to compensate for the reduction in density, the diameter of the outlet or relief pipe is in principle dimensioned larger than in the known solutions from the prior art, so that, despite the throttling, a sufficient mass flow rate is achieved.

[0014] According to a further preferred embodiment variant, the thermal pressure relief device is designed as a polymer piping, which is particularly inexpensive to manufacture and at the same time very lightweight compared to stainless steel piping, the polymer piping here can be manufactured, for example, by simple injection molding methods.

[0015] According to an important embodiment, the invention provides that the pressure reducing device accelerates the flow to supersonic speed at the outlet. Acceleration of the fluid, or fuel, into the supersonic range can achieve an effective pressure reduction downstream or in the flow direction, respectively, in the thermal pressure relief device.

[0016] The pressure reducing device in this specification is preferably a Laval nozzle, which has a convergent section and a divergent section. The Laval nozzle is preferably arranged between the outlet and the thermal pressure relief device, with the convergent section of the Laval nozzle arranged directly and immediately after the outlet of the high pressure tank. The arrangement of the Laval nozzle allows the static pressure to be reduced without reducing the total pressure in the system. By installing a Laval nozzle at the outlet of the high pressure tank or at the inlet of the piping of the thermal pressure relief device, the outflowing fuel is accelerated to supersonic speed. In the divergent section of the Laval nozzle, the fuel can be further accelerated to supersonic flow, i.e. to Mach values ​​> 1. Since the static pressure decreases with increasing Mach value, the pressure in the thermal pressure relief device decreases significantly for a constant total pressure. Due to this interaction, the diameter of the thermal pressure relief device or the relief piping, respectively, can be dimensioned smaller than the throttling structure. The flow rate through the relief piping is preferably maintained in the supersonic range, even if it is reduced by friction forces.

[0017] In a preferred embodiment, the Laval nozzle has a reduced neck diameter, and the convergent section of the Laval nozzle transitions directly into a divergent section after reaching the neck diameter, or the convergent section of the Laval nozzle can transition steadily into a divergent section and have a slight axial widening in the region of the neck diameter.

[0018] In the Laval nozzle design, the outlet preferably has a diameter designed to be smaller than the tube diameter of the thermal pressure relief device. The Laval nozzle herein preferably has a circular or elliptical cross section over its entire length. The narrowest cross section of the Laval nozzle preferably corresponds to the neck diameter, where the flow reaches sonic speed and is accelerated to the supersonic range in the diverging section. [Brief description of the drawings]

[0019] Further features, details and advantages of the invention emerge from the claims and the following description of exemplary embodiments with reference to the drawings. [Figure 1a] FIG. 1 is a schematic diagram of a high pressure tank having thermal pressure relief piping according to the prior art. [Figure 1b] 1 is a schematic diagram of a pressure reduction system according to the present invention; [Figure 1c] FIG. 4 is a schematic diagram showing another embodiment of a pressure reduction system according to the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] Fig. 1a shows a high-pressure tank 10 in which hydrogen can be stored under high pressure. The high-pressure tank 10 is connected on the outlet side to a thermal pressure relief device 20, which is here designed as a relief pipe and has a pipe diameter D. When the pressure in the high-pressure tank 10 is relieved, the fuel flows in a flow direction (x) into the thermal pressure relief device 20. This arrangement corresponds to the prior art.

[0021] Figure 1b is a schematic diagram of a pressure reduction system for a hydrogen vehicle having at least one high pressure tank 10 in which fuel is stored under positive pressure. The high pressure tank 10 is provided with an outlet 9 for relieving pressure, and the high pressure tank 10 is fluidly connected by the outlet 9 to a thermal pressure relief device 20.

[0022] The thermal pressure relief device 20 is designed as a relief pipe. When pressure is relieved, the fuel flows through the relief pipe in a flow direction x, where the outlet 9 has a diameter D1 which corresponds to the pipe diameter of the thermal pressure relief device 20 or the relief pipe, respectively.

[0023] The pressure reducing device 1 is arranged in the relief line at an outlet 9. The pressure reducing device 1 in the illustrated embodiment is designed as a throttle valve 7 and has a throttle opening 8. This is in particular an annular throttle valve.

[0024] Figure 1c shows a schematic diagram of another embodiment of the invention, in which a Laval nozzle 5 is arranged instead of the throttle valve 7 of Figure 1b, and in this embodiment the thermal pressure relief device is also designed as a relief line.

[0025] Here, the Laval nozzle 5 has a converging section 2 and a diverging section 6. The Laval nozzle 5 is placed between the outlet 9 and the thermal pressure relief device 20 or in a section of relief piping with a constant profile, respectively. The converging section 2 of the Laval nozzle 5 is placed directly and immediately after the outlet 9 of the high pressure tank 10.

[0026] The Laval nozzle 5 further has a neck diameter 3, and the convergent section 2 of the Laval nozzle 5 transitions into a divergent section 6 immediately after reaching the neck diameter 3. The outlet 9 has a diameter D2 designed to be smaller than the pipe diameter D3 of the relief pipe, or thermal pressure relief device 20, respectively. The neck diameter 3 here has the smallest cross section, i.e., diameter, of the Laval nozzle 5.

[0027] The pressure reduction system according to the invention relates generally to high pressure vessels and thermal pressure relief devices. The invention particularly relates to hydrogen vehicles, which usually have a high pressure tank filled with hydrogen under positive pressure. The invention is particularly used for venting such high pressure tanks, due to the increased risk of explosion and fire in the event of an accident etc. However, in principle the pressure reduction system can also be implemented for stationary high pressure vessels equipped with a thermal pressure relief device.

[0028] All the features and advantages derived from the claims, the specification and the drawings, including the structural details, the spatial arrangement and the method steps, can be essential to the invention not only individually but also in the most diverse combinations. [Explanation of symbols]

[0029] D diameter (standard) D1 Diameter (aperture) D2 diameter (Laval nozzle) D3 diameter (Laval nozzle) x Flow direction 1 Pressure reducing device 2 Convergence section 3 Neck diameter 5 Laval nozzle 6 Diffusion section 7. Throttle valve 8 Aperture 9 exit 10. High Pressure Tank 20 Thermal Pressure Relief Device

Claims

1. A pressure reduction system for a high pressure tank (10), in particular for a high pressure tank (10) of a motor vehicle, in which a fluid is stored under positive pressure, the high pressure tank (10) having an outlet (9) for relieving pressure, the high pressure tank (10) being fluidly connected via the outlet (9) to a thermal pressure relief device (20) through which the fluid flows in a flow direction (x) when the pressure is relieved, the thermal pressure relief device (20) being provided with a pressure reduction device (1) for reducing the pressure in the high pressure tank (10) when the pressure is relieved.

2. 2. The pressure reduction system according to claim 1, wherein the pressure reduction device (1) is a throttle valve (7) having a throttle opening (8) and is designed in particular as an annular throttle.

3. 3. The pressure reduction system according to claim 2, wherein the thermal pressure relief device (20) is designed as a relief pipe and the outlet (9) has a diameter (D1) corresponding to the pipe diameter of the thermal pressure relief device (20).

4. 4. A pressure reduction system according to claim 2 or claim 3, wherein the throttle opening (8) is designed to be smaller in diameter than the outlet (9) and the thermal pressure relief device (20).

5. 3. The pressure reduction system according to claim 2, wherein the throttle valve (7) is arranged indirectly in the outlet (9) of the high pressure tank (10) and in a thermal pressure relief device (20).

6. 2. The reduced pressure system of claim 1, wherein the pressure reduction device (1) accelerates the flow to supersonic speed.

7. 7. The pressure reduction system according to claim 6, wherein the pressure reduction device (1) is a Laval nozzle (5), the Laval nozzle (5) having a converging section (2) and a diverging section (6).

8. 8. The pressure reduction system according to claim 7, wherein the Laval nozzle (5) is arranged between the outlet (9) and the thermal pressure relief device (20), the convergent portion (2) of the Laval nozzle (5) being arranged directly and immediately after the outlet (9) of the high pressure tank (10).

9. 8. The pressure reduction system according to claim 7, wherein the Laval nozzle (5) has a neck diameter (3) and the convergent section (2) of the Laval nozzle (5) transitions directly into the divergent section (6) after reaching the neck diameter (3).

10. 8. The pressure reduction system according to claim 7, wherein the thermal pressure relief device (20) is designed as a relief pipe and the outlet (9) has a diameter (D2) designed smaller than a pipe diameter (D3) of the thermal pressure relief device (20).

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