Equipment and automobiles for storing cryogenic hydrogen

Abstract

The present invention relates to a device (1) for storing cryogenic hydrogen, which has at least one container (2) in an apparatus and an automobile for storing cryogenic hydrogen. The device (1) according to the present invention is characterized in that the inner surface of the container (2) is provided with projections (4) that protrude at least partially into the interior of the container, and / or an element (5) with a rough surface or a rough surface, thereby preventing overheating due to the roughness of the surface.

Description

Technical Field

[0001] The present invention relates to an apparatus for storing cryogenic hydrogen having at least one container. The present invention further relates to a motor vehicle equipped with such an apparatus.

Background Art

[0002] For example, the storage of liquid hydrogen for use in motor vehicles is known from the prior art. The problem here is always that since liquid hydrogen is extremely cold, the storage container needs to be extremely well insulated. Nevertheless, the warming of hydrogen over time is inevitable, and then the hydrogen needs to be released when it reaches its gas phase and exceeds the predetermined maximum pressure of the container. In that case, this so-called boil-off gas is usually converted by a catalyst to prevent the emission of hydrogen into the environment. Nevertheless, this gas has become unusable for the desired applications. In addition, due to the unavoidable heating in the container for storing cryogenic hydrogen, the holding period of such a hydrogen storage system is relatively short. Conventional tanks can become empty or mostly empty within just a few days, leaving the hydrogen stored in the tank unusable in the desired manner.

[0003] To address this problem, for example, it is known from Patent Document 1 to create a storage container without temperature stratification for cryogenic liquids such as hydrogen. In that case, the storage container is divided into two storage regions, a main chamber and a secondary chamber. Liquid hydrogen from the main chamber is supplied to the secondary chamber and distributed from there via nozzles over the surface of the hydrogen in the main chamber, and a gas cushion accumulates above the hydrogen. This causes cooling, and thus ultimately the holding period becomes longer. However, in that case, the configuration is relatively complex and additional energy is required to supply the liquid hydrogen from the main chamber to the secondary chamber.

Prior Art Documents

Patent Documents

[0004] [Patent Document 1] German Patent No. 104342210 (C2) [Overview of the project] [Problems that the invention aims to solve]

[0005] The objective of this invention is, in this case, to create an improved apparatus for storing cryogenic hydrogen that enables a longer retention period with a simpler configuration. [Means for solving the problem]

[0006] According to the present invention, the problem is solved by an apparatus having the features of claim 1, and more specifically by an apparatus having the features described in the feature section of claim 1. Advantageous embodiments and variations will become apparent from the dependent claims. Automobiles, particularly commercial vehicles, equipped with such a device for storing cryogenic hydrogen also solve the problem.

[0007] According to the present invention, cryogenic hydrogen is stored in a container having protrusions on its inner surface that project inward, and / or a container having a rough surface or an element with a rough surface on its inner surface, with the aim of preventing overheating (Siedeverzug) by the roughness of the surface.

[0008] In the apparatus according to the present invention, the inner surface of the container has, at least partially, protrusions and / or a rough surface or an element having a rough surface. This achieves the most uniform heating possible of the liquid phase of the stored cryogenic hydrogen by utilizing two different mechanisms identified by the inventors. If more heat can be absorbed through the liquid phase, the pressure rise will be slower. As a result, the retention period of the hydrogen stored in the container will be longer.

[0009] The protrusions projecting into the interior of the container may be formed in particular as ribs or pins, and in typical container sizes such as those used for storing cryogenic hydrogen in commercial vehicles, they may protrude into the container by a range of a few millimeters to a few centimeters, producing three positive effects. The protrusions increase the surface area of ​​the inner wall of the container, thereby reducing the heat flow per unit area transferred from the outside to the inside of the container. The protrusions transport heat flow that cannot be completely avoided at the surface of the container across the boundary layer between the container surface and the cryogenic hydrogen, relatively further into the liquid hydrogen. This heats not only the boundary layer but also the hydrogen in areas somewhat away from the container wall. As a result, the heating of the cryogenic hydrogen becomes more uniform overall, and as already mentioned above, the storage period is extended. On the other hand, especially when the protrusions are formed as ribs, the protrusions obstruct the flow in the boundary layer region between the container wall and the cryogenic hydrogen. When the ribs are formed perpendicular to gravity in a suitable use, it is particularly advantageous because it can prevent the upward flow of warmer hydrogen, thereby reducing the flow in the boundary layer and, at the same time, the heat transfer between the liquid hydrogen and the container wall.

[0010] In addition to or instead of such protrusions, a rough surface or an element having a rough surface may be used. Such an element has a surface roughness that prevents overheating. The element may consist, for example, a sintered porous metal element, particularly a metal layer, or so-called zeolite, which is commonly known and used as a laboratory material.

[0011] The surface roughness is measured according to the version of the relevant standard valid on the filing date, in this case DIN EN ISO 4287, and is in the range of greater than 0.3 μm and up to 0.5 μm.

[0012] Regardless of whether elements such as zeolites are incorporated, or whether appropriate surface coatings or surface treatments are used on the inner walls of the container, or on any protrusions, this corresponding rough surface has the advantage of providing numerous nucleation sites for vapor bubble formation. The rough surface allows for the formation of a very large number of small vapor bubbles, rather than a few large ones, which can be dispersed to various locations within the container. Since only a relatively small amount of overheating (Uberhitzung) is required for these vapor bubbles to form, the incoming heat is absorbed very quickly by these vapor bubbles. The vapor bubbles then rise in the direction of gravity through the residual liquid, resulting in very effective mixing of the liquids and achieving very homogeneous and uniform heating of the liquid portion of hydrogen in the container. This also contributes to maximizing the retention period, as the entire liquid hydrogen is heated uniformly and evaporates in the outer regions along the container walls, while the liquid hydrogen itself remains at a much lower temperature inside the container. As a result, the pressure rise in the gas phase inside the container is not so significant, and there is no need to release boil-off gas as frequently.

[0013] A further highly advantageous embodiment of the apparatus according to the present invention is intended to include a tank heater positioned within the vessel for extracting hydrogen. In this case, the surface of the tank heater and the surface of the vessel in the area of ​​the tank heater have a lower surface roughness than the area of ​​the vessel surrounding the tank heater. The idea of ​​increasing the surface roughness to generate numerous small bubbles and avoid overheating in any case has been modified here so that in the area of ​​the tank heater, the surface has a very low roughness, i.e., is formed particularly smoothly. This intentionally prevents nucleation sites for vapor bubble formation, which is undesirable in other areas of the vessel, in order to achieve precisely in the area of ​​the tank heater. That is, overheating would occur in the area of ​​the tank heater. The tank heater is always operated only when hydrogen is to be extracted. In this case, overheating is advantageous because the overheated hydrogen quickly forms large vapor bubbles. This causes a rapid increase in the pressure of the gas phase, which is desirable when extracting hydrogen. On the other hand, superheating significantly limits the heating of the liquid hydrogen surrounding the very large bubbles generated by the superheating; that is, in this case, despite the heating required for hydrogen extraction, the adverse effect on the retention period can be reduced. This procedure results in only the hydrogen in the area immediately adjacent to the tank heater evaporating, with very little heat flowing into the surrounding area of ​​the liquid hydrogen.

[0014] Such tank heaters can be ideally utilized, in particular, by combining the morphology of the tank surface with heat conduction protrusions on the tank surface, and especially with the protrusions having a correspondingly high surface roughness to provide numerous nucleation sites. Such a configuration ensures that the heat entering the container through the insulation and storage is distributed as uniformly as possible, both during operation, i.e., during hydrogen extraction and during the stopped phase when no hydrogen is extracted. All of this has a positive effect on retaining cryogenic hydrogen in the apparatus according to the present invention for as long as possible.

[0015] In that case, according to a very advantageous embodiment of the apparatus according to the present invention, the tank heater itself may be positioned downward in the direction of gravity during use that is suitable for the purpose of the container, so that the tank heater is in contact with the liquid in any case, even if the container is already relatively empty.

[0016] As already mentioned above, the protrusions are preferably formed as ribs or pins, in which case the sintered metal elements or zeolites can be attached anywhere in the container, preferably where there is no tank heater. As already mentioned above, the protrusions exert their special effect when in the liquid phase, so the protrusions are also preferably positioned downward in the direction of gravity when the container is used in a suitable manner, according to a very advantageous embodiment of the apparatus according to the present invention. The zeolites or small sintered metal elements are, in principle, simply "thrown" into the tank and then gather downward in the direction of gravity, resulting in the formation of nucleation sites. If the zeolites or elements should be distributed and placed over a wider area of ​​the tank, they may be fixed to a net, for example, and held in the surface area. On the other hand, the rough or porous layer can also be realized as a surface treatment or surface coating. This applies not only to the inner wall of the container but also to the protrusions present therein, if applicable. These protrusions may also be formed in the shape of sintered metal ribs, for example, attached to the inside of the tank surface, for example, by welding or bonding.

[0017] In principle, this device for storing cryogenic hydrogen can be used not only in a stationary manner but also in a mobile manner. However, especially when used in a vehicle such as a commercial vehicle, for example, a long holding period plays an important role. Further, in this case, due to installation space and weight limitations, the options for insulating the device are usually more restricted than for stationary applications. Therefore, the innovative embodiments of the device of the present invention exhibit special advantages in this case. That is, the vehicle that solves the above problems is equipped with the aforementioned device according to the present invention in one of the described embodiments for storing liquid hydrogen. The vehicle itself may, in principle, use liquid hydrogen not only to operate a fuel cell but also to drive an internal combustion engine or the like, or may, in principle, simply be transported as a "tank truck".

[0018] Further advantageous configurations of the device according to the present invention will also become apparent from the examples described in detail below with reference to the drawings.

Brief Description of the Drawings

[0019] [Figure 1] It is a schematic cross-sectional view of the inner container of the device for storing liquid hydrogen in a first possible embodiment according to the present invention. [Figure 2] It is a schematic cross-sectional view of the inner container of the device for storing liquid hydrogen in a second possible embodiment according to the present invention. [Figure 3] It is a schematic longitudinal cross-sectional view of the inner container of the device for storing liquid hydrogen in a third possible embodiment according to the present invention.

Modes for Carrying Out the Invention

[0020] In the illustration of FIG. 1, a schematic cross-sectional view of the container 2 of the apparatus 1 for storing cryogenic hydrogen can be seen. This container 2 is usually insulated from the environment via a vacuum and / or other insulation mechanisms. Since the container 2 is inside the apparatus 1, it is thus also referred to as the inner container. Inside this container 2, at this time, hydrogen exists on the one hand as a liquid phase fl and on the other hand as a gas phase g. Furthermore, in a part of the volume, hydrogen may be in a supercritical state. The liquid phase fl is separated from the gas phase g according to the gravity F g shown below. In a use that conforms to the purpose of the apparatus 1, the liquid phase fl is located in the region shown below, and the gas phase g is located above it.

[0021] In reality, there is inevitably heat in the outer region of the container 2. It should be understood that the heat in this case is everything that exceeds the temperature of the hydrogen in the liquid phase fl with respect to its temperature. In order to introduce this heat into the hydrogen, especially the liquid phase fl, as uniformly as possible at this time and at the same time prevent the boundary layer flow between the liquid hydrogen and the inner side of the container wall 2, protrusions 4 in the shape of ribs or rods are distributively arranged on the inner surface of the container 2. The protrusions 4 can be distributively arranged over the entire circumference of the container 2, but their special effect is exerted especially in the region of the liquid phase fl of the hydrogen. Therefore, in a use that conforms to the purpose, they should be arranged in the particularly lower region in the direction of the gravity F g of the container 2.

[0022] These ribs or rods 4 protrude into the interior of the container 2 by several millimeters to several centimeters. Therefore, the ribs or rods 4 increase the surface area of the inner wall of the container 2, thereby reducing the heat flow per unit area from the outside of the container to the inside of the container, and thus substantially to the liquid hydrogen. Furthermore, the ribs or rods not only guide the heat flow to the boundary layer between the hydrogen in the liquid phase fl and the inner wall of the container 2, but also into the liquid phase fl of the hydrogen. As a result, not only the boundary layer is heated, but the hydrogen is also heated more uniformly. As a whole, this reduces the temperature stratification inside the hydrogen in the container 2 and lengthens the holding period in the container 2 or the apparatus 1. With an appropriate geometric arrangement of the ribs, for example, as shown in this figure, the ribs are extended horizontally along the container 2, from bottom to top in the direction of the gravity Fg By blocking flow in the direction of and opposite to the flow direction, the ribs can reduce boundary layer flow based on heat conduction into the liquid further, and in addition, they can also purely mechanically block such boundary layer flow.

[0023] Figure 2 illustrates a further modification of the container 2 for improvement. In this figure, the gaseous phase g and liquid phase fl of hydrogen can also be seen. Here, instead of the ribs 4, a surface or element 5 with high surface roughness is provided in the region of the inner wall of the container 2. As an example, this figure shows the corresponding element 5 along the surface. This element 5 is, for example, a sintered metal layer or a porous metal layer, or a surface roughness increased by machining. Alternatively or additionally, porous or coarse zeolites may be attached to the tank as element 5, for example, by holding them along the surface using a net. Here again, gravity F is present in the container 2. g Arrangements of use that are suitable for the purpose below in that direction are particularly useful, and for this reason, for example, it may be conceivable to simply loosely attach the zeolite inside the container.

[0024] The corresponding roughened surface or porous / rough surface of the zeolite prevents superheating, thus providing numerous nucleation sites for vapor bubbles. This, in turn, generates numerous corresponding vapor bubbles, which form anywhere in the porous or rough surface region, contributing to very uniform heating. The vapor bubbles schematically shown in this figure within the liquid phase fl, some of which are labeled reference numeral 6, further contribute to the mixing of hydrogen within the liquid phase fl, thus achieving a very uniform temperature distribution within the hydrogen. The numerous small vapor bubbles simultaneously reduce the pressure rise in the gas phase compared to, for example, the large vapor bubbles that would occur during superheating, i.e., when there are no or too few nucleation sites. This minimizes the need to release hydrogen when the maximum pressure of container 2 or apparatus 1 is reached. The retention period of hydrogen in apparatus 1 can also be extended by increasing the surface roughness or by attaching zeolite or other similarly acting elements 5.

[0025] Although the two mechanisms are shown separately in Figures 1 and 2, they can, of course, also be used in combination. Therefore, for example, a suitable coating can be provided not only on the inner wall of the container 2 but also on the projection 4, or the projection 4 can be made directly from a suitable porous material, such as a sintered metal element.

[0026] These means may preferably be distributed and arranged throughout the entire inner surface of the container, or they may be optionally combined with each other. As already mentioned above, it is advantageous to use them appropriately, especially in the region of the liquid phase fl, and therefore they are preferably used in a way that is suitable for the purpose of apparatus 1, with respect to gravity F g It is located in the lower region in that direction. In this case, the lower region refers to the region that is normally covered by the liquid phase fl after the apparatus 1 is filled with liquid hydrogen, and this region may also occupy most of the volume of the container 2.

[0027] Hydrogen is typically extracted from such a device 1 in gaseous form. For this purpose, a gas cushion of gaseous phase g, which forms on top of the liquid phase fl due to inevitable heating, can be used. However, this is generally insufficient to provide the required amount of hydrogen and the required pressure, for example, an operating pressure of 4-6 bar, to the fuel cell system. Therefore, to extract hydrogen, a tank heater 7 is provided, as is also common in the prior art, which evaporates the hydrogen, increases the pressure of gaseous phase g, and thus provides the possibility of extracting hydrogen as a gas from the device 1 at the desired pressure.

[0028] In the illustration in Figure 3, a longitudinal cross-section of the container 2 can be seen. In the illustration in Figure 2, the tank heater 7 is schematically shown on the left side, and the tank heater 7, in a suitable use, remains in the liquid phase fl region even when the container 2 is already largely empty, under gravity F gIt is positioned at the bottom in that direction. In the region surrounding the tank heater 7, protrusions 4 are preferably arranged, and in particular the surface roughness is correspondingly high, or, as described above, zeolite or another element 5 is used, whereas here in the region of the tank heater 7, the surface is made to a very low roughness, particularly less than 0.3 μm. Thus, for example, the heating coil and its surrounding region, which are heated electrically or by a correspondingly preheated medium, may be made by polishing. The very low surface roughness of the region of the tank heater 7 ensures that what must be prevented in other parts of the container 2 is precisely achieved here in the tank heater 7. In this case, because there are no or very few nucleation sites for forming vapor bubbles, superheating usually occurs in the region of the tank heater 7 based on the low surface roughness, and as a result the liquid hydrogen in this region is overheated, and then a sudden very large vapor bubble is formed. This is desirable in the region of the tank heater 7 in the embodiment of the apparatus 1. Unlike other regions, heat is introduced here, and vaporized or gaseous hydrogen is produced under high pressure. This is achieved by bubbling accompanied by superheating, with only a few large vapor bubbles 8 rising. This is illustrated in Figure 3 by comparing the large vapor bubbles 8 in the upper region of the tank heater 7 with the smaller vapor bubbles 6 similar to those in Figure 2. This raises the pressure of the gas phase g to the desired value, and thus hydrogen can be extracted from the container 2 or apparatus 1. At the same time, the heat input to the liquid phase fl through the large vapor bubbles 9 formed by superheating is very small because most of the heat remains within these bubbles, not heating or overheating the surrounding area.

[0029] In other words, a tank heater 7 with very low surface roughness on the one hand and a container 2 with high surface roughness and / or heat-conductive protrusions 4 such as ribs or pins on the other hand can extend the retention period not only during operation but also when hydrogen is not being extracted from the device 1. In this case, all the configurations are easy to implement and passively produce the desired effect, i.e., without requiring additional energy input, cooling circuits, etc. This is very simple, efficient, and energy-saving.

Claims

1. A device (1) for storing cryogenic hydrogen, having at least one container (2), The inner surface of the container (2) has, at least partially, a projection (4) that protrudes into the interior of the container, and / or An apparatus (1) is provided with a rough surface or an element (4) having a rough surface, characterized in that overheating is prevented by the roughness of the surface.

2. The apparatus (1) according to claim 1, comprising a tank heater (7) disposed within the container (2) for hydrogen extraction, wherein the surface of the container (2) and the surface of the tank heater (7) in the area of ​​the tank heater (7) have a lower surface roughness than the area of ​​the container (2) surrounding the tank heater (7).

3. The tank heater (7) is used in a manner suitable for the purpose of the container (2) and is resistant to gravity (F ｇ The apparatus (1) according to claim 2, characterized in that it is positioned downward in the direction of ).

4. The apparatus (1) according to claim 1, 2, or 3, characterized in that the rough surface is produced by coating or machining the surface.

5. The apparatus (1) according to any one of claims 1 to 4, characterized in that the projection (4) is formed in the shape of a rib or a pin.

6. The apparatus (1) according to any one of claims 1 to 5, characterized in that the element (5) is formed from a sintered metal and / or as a zeolite.

7. The apparatus (1) according to claim 6, characterized in that the element (5) is held in the region of the surface of the container (2) via a net.

8. The apparatus (1) according to any one of claims 1 to 7, characterized in that the projection (4) is formed as a sintered metal element having a rough surface.

9. The projection (4), the element (5), and / or the rough surface are such that, in use suitable for the purpose of the container (2), gravity (F ｇ The apparatus (1) according to any one of claims 1 to 8, characterized in that it is positioned downward in the direction of ).

10. An automobile comprising an apparatus (1) according to any one of claims 1 to 9, particularly for storing hydrogen for a fuel cell drive system.

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