Cryocontainer with boil-off valve

Abstract

The invention relates to a system (1) comprising a cryogenic container (2) for storing cryofluid and a connecting line (4) leading into the cryogenic container (2) for extracting cryofluid from the cryogenic container (2), wherein the connecting line (4) has a fitting inside the cryogenic container (2), wherein an opening cross-section (q1) of the fitting is at least 10 times, preferably 100 times or 1000 times, smaller than the inner cross-section (q2) of the connecting line (4) between the fitting and the connection point (7) on the cryogenic container (4), and wherein the connecting line (4) is guided between the fitting and the connection point (7) on the cryogenic container (2) with a predetermined length (L), which is preferably longer than 50 cm.

Description

[0001] The invention relates to a system comprising a cryogenic container for storing cryogenic fluid and a connecting line led into the cryogenic container for removing cryogenic fluid from the cryogenic container.

[0002] According to the current state of the art, liquefied gases can be stored in containers ("cryogenic containers") to serve as fuel for engines, for example. Cryogenic containers store gases in a cryogenically liquefied form. Gases such as methane or hydrogen, in their liquefied form, have a density 600 to 800 times higher than in their standard state (ambient temperature and pressure). This increase in density is the benefit of liquefaction and, at the same time, a risk in the protection of cryogenic containers, because the complete heating of a fully filled cryogenic container and thus the evaporation of the liquefied gas would lead to pressures well over 1,000 bar, up to 2,000 bar. Such pressures would, in any case, far exceed the mechanical load-bearing capacity of the pressure container.

[0003] Pressure control in the cryogenic vessel is therefore of particular importance in this technical field. On the one hand, it is known to connect a pressure relief valve to the cryogenic vessel to release gaseous cryogenic fluid from the vessel if the pressure exceeds a permissible maximum pressure when the system is at a standstill (see, for example, WO 2022 / 204745 A1). However, it is clear that the problem still exists that releasing cryogenic fluid into the environment represents an energy loss on the one hand and also impacts the environment on the other.

[0004] The pressure in the cryogenic vessel can also be regulated by withdrawing cryogenic fluid either in the gaseous or liquid state during operation of the system. So-called economizers are used for this purpose; see, for example, WO 2022 / 067362 A1.

[0005] In both of the aforementioned embodiments, pressure control is achieved by removing gaseous cryogenic fluid from the cryogenic vessel, i.e., the volume of cryogenic fluid in the cryogenic vessel is reduced while the temperature remains constant. Another theoretical possibility for reducing the pressure would be to cool the cryogenic fluid in the cryogenic vessel using external means such as a heat exchanger, but this is too complex and therefore hardly feasible in many areas, such as automotive engineering.

[0006] It is the object of the present invention to further develop the above-mentioned systems in such a way that the existing possibilities for pressure reduction in the cryogenic container are optimized.

[0007] This object is achieved by a system comprising a cryogenic container for storing cryogenic fluid and a connecting line led into the cryogenic container for withdrawing cryogenic fluid from the cryogenic container, wherein the connecting line has a fitting within the cryogenic container, wherein an opening cross-section of the fitting is permanently or in at least one operating position at least 100 times, preferably 10,000 times or 1,000,000 times smaller than the internal cross-section of the connecting line downstream of the fitting in the withdrawal direction (e.g. between the fitting and the connection point to the cryogenic container; alternatively, the throttle cross-section could also be led to the outside, although a short throttle section is usually desired), wherein the connecting line is led between the fitting and the connection point to the cryogenic container with a predetermined length, which is preferably longer than 50 cm.

[0008] The fitting according to the invention has the advantage that the cryofluid removed from the cryogenic vessel is already expanded inside the cryogenic vessel. This expansion leads to a reduction in the temperature of the expanded cryogenic fluid. This can be exploited to cool the cryogenic fluid in the cryogenic vessel, which is why the connecting line inside the cryogenic vessel is of a predetermined length to enable sufficient heat transfer between the expanded cryogenic fluid inside the connecting line and the cryogenic fluid outside the connecting line. The temperature reduction of the cryogenic fluid during expansion and the associated pressure reduction can, depending on the design of the fitting, be regarded as an isenthalpic or isentropic process. An ideal throttle would, for example, be referred to as an isenthalpic process, in which case the temperature reduction is known as the Joule-Thomson effect.While using a generator as a valve wouldn't result in a temperature reduction, the generated energy could be used differently. For example, if a generator were used in addition to or on its own as a valve, it could extract additional energy from the escaping fluid, thus leading to further cooling. The extracted energy could be transported outside the cryogenic vessel, for example, as electrical energy, using cables.

[0009] The invention utilizes the cooling effect of pressure relief by releasing pressure within the cryogenic vessel itself. The pressure relief is achieved through the small diameter of the valve. Upstream of the valve, the pressure is essentially the vessel pressure, while downstream, the pressure is as close as possible to atmospheric ambient pressure, into which the medium flows, in order to achieve the greatest possible cooling effect through the greatest possible pressure drop.

[0010] To achieve the expansion of the cryogenic fluid, the fitting has the smallest possible opening cross-section. For the purposes of the present invention, the opening cross-section of the fitting can be assumed to be at least 100 times, preferably 10,000 times or 1,000,000 times, smaller than the internal cross-section of the connecting line between the fitting and the connection point to the cryogenic container. For example, the fitting can have an opening cross-section of 1 µm 2< to 9 mm 2<, particularly preferably of 25 µm 2< to 1 mm 2<, or of 900 µm 2< to 40,000 µm 2<. These measures are particularly advantageous, but deviations from them are also possible. The absolute values ​​of the opening cross-section may depend in particular on the application, whereby in the vehicle sector or other mobile applications opening cross-sections in the 1 / 100 mm 2< range are common and in the petrol station sector or other static applications opening cross-sections in the mm 2< range could be provided.However, the exact dimensioning of the opening cross-section usually also takes into account the container size, type of cryogenic fluid, pressure ratio, quality of the container insulation and other parameters.

[0011] The length of the connecting cable can also depend on the application and can be, for example, 30 cm to 3 m or 1 m to 2 m long between the fitting and the connection point to the cryogenic vessel.

[0012] To achieve the most efficient heat transfer possible between the cryogenic fluid inside the connecting line and outside the connecting line, the connecting line can be routed in a meandering pattern within the cryogenic vessel, allowing a longer line length to be accommodated within the cryogenic vessel. Furthermore, the connecting line within the cryogenic vessel can also have surface-enlarging structures, in particular cooling fins, allowing the line length to be shortened. Surface-enlarging structures also mean that the connecting line could be designed, at least in sections, as a bellows tube. The connecting line is generally made of metal, preferably of the same material as the inner tank.

[0013] The fitting could, for example, be a throttle, an orifice, a nozzle, in particular a Laval nozzle, a valve, or a turbine. If the fitting is designed as a throttle, an orifice, or nozzle, it permanently has the same inner contour and thus also permanently has the same opening cross-section. The valve has a variable opening cross-section, so that the valve can be moved from at least one first operating position to a second operating position. A turbine has at least one movable element to convert kinetic energy into another form of energy during the passage of the cryogenic fluid.

[0014] The fitting is preferably a throttle with a throttle length of preferably at least 1 mm, wherein the throttle is formed by a bore through a pipe wall of the connecting line. Such throttles have the advantage that they can be manufactured particularly easily, even with a particularly small diameter. However, the bore through the usually cylindrical pipe wall is only optional and could, for example, also run through a plug such as an end cap of the connecting line.

[0015] The throttle is preferably dimensioned such that at a predetermined pressure (e.g. a maximum vessel pressure, which can be in a range between 15 bar and 20 bar, for example), just enough flows out to prevent the pressure in the cryogenic vessel from increasing any further. The mass flow removed through the throttle is essentially dependent on the density of the fluid upstream of the valve (and thus on the state of the fluid in the tank) and is limited by the critical velocity (i.e. the speed of sound) and therefore cannot be increased any further. The mass flow cannot therefore be actively influenced without further measures. However, it has been found that the mass flow can be adjusted sufficiently precisely for an application (e.g. boil-off) by suitably dimensioning the valve.

[0016] As an alternative to a throttle, the valve could also be designed as a nozzle, particularly a Laval nozzle. A nozzle allows the outflowing mass flow to reach a velocity greater than the speed of sound.

[0017] It should be noted here that a valve with a permanently small opening cross-section is not always advantageous, as it offers high flow resistance. However, it has been found that flow resistance is not relevant, especially for so-called boil-off lines, i.e., connecting lines that are only intended to release cryogenic fluid to the environment to reduce the pressure in the cryogenic vessel and not to supply the cryogenic fluid to a consumer. In general, however, the valve can also be used for extraction lines, for example, if the obstacle of flow resistance is less important than the additional cooling provided by expansion, or if additional measures are taken to reduce flow resistance.

[0018] In a further variant, however, the fitting could also be a valve with a variable opening cross-section, wherein the valve can be moved from the first operating position, in which it has the first-mentioned opening cross-section, which is at least 100 times, preferably 10,000 times or 1,000,000 times smaller than the internal cross-section of the connecting line between the valve and the connection point to the cryogenic container, into a second operating position, in which the valve has a second opening cross-section that is at least 100 times, preferably 10,000 times or 1,000,000 times larger than the first-mentioned opening cross-section. Particularly preferably, the second opening cross-section is the same size as the internal cross-section of the connecting line. This is particularly advantageous in the case in which the connecting line is connected to a consumer.This allows the flow resistance to be reduced during withdrawal by setting the valve to the second state. If no cryogenic fluid is actively being withdrawn from the cryogenic vessel, the valve can be set to the first state so that, for example, cryogenic fluid can be released back into the environment via a pressure relief valve connected to the connecting line or another outlet valve. A continuously variable cross-section from "as small as possible" (ideally closed with 0 mm²<, or the aforementioned 1 µm²< to 9 mm²<) to "as large as possible" (ideally the same size as the subsequent connecting line) would also be possible. In this case, the mass flow could be adapted to the requirements (e.g., the required mass flow for a consumer).

[0019] In the aforementioned embodiment with a valve, it is further preferred if the valve is connected to a control unit that receives pressure measurements from a pressure measuring unit arranged in the cryogenic container and is designed to control the opening cross-section of the valve such that the pressure in the cryogenic container remains substantially constant, e.g., constantly corresponds to a target boil-off pressure. The control unit can, for example, open the valve just enough to keep the container pressure constant. In this variant, no additional outlet valve is necessary.

[0020] Typically, the system also includes an outlet valve located outside the cryogenic vessel in the connecting line. In this variant, the valve, particularly the throttle, is located inside the cryogenic vessel, and the outlet valve is located outside the vessel. As long as no cryogenic fluid is escaping—during the hold time—the vessel pressure in the connecting line up to the outlet valve will essentially be the same. When the outlet valve opens, the ambient pressure downstream of the valve will essentially be the same. The outlet valve typically exhibits only low flow resistance.

[0021] In a first preferred embodiment, the outlet valve is a pressure relief valve designed to open when a predetermined pressure or pressure difference is present, releasing cryogenic fluid from the cryogenic vessel to the environment. As explained above, the flow resistance is typically negligible for this embodiment, so the combination of a valve in the cryogenic vessel and a pressure relief valve is particularly advantageous, especially if the valve is a rigid valve with a fixed opening cross-section.

[0022] Pressure relief valves located outside the cryogenic vessel can stutter because, once the pressure relief valve is opened, ambient pressure will be present on both sides. This is because the valve does not allow for immediate pressure equalization. If, for example, the pressure relief valve opens and closes due to a pressure difference upstream and downstream of the pressure relief valve, the pressure relief valve will only be open for a very short time and close again immediately. After a certain amount of time, after the pressure present in the cryogenic vessel has also returned to the connecting line, it will open again and then close again shortly afterwards, which is referred to as stuttering.

[0023] To prevent stuttering, the outlet valve can be designed as a controlled outlet valve, which receives pressure readings from a pressure measuring unit located in the cryogenic vessel and opens and / or closes based on the received pressure readings. The "reference pressure" on the basis of which the outlet valve is controlled is therefore not the pressure present directly at the outlet valve, but rather the pressure of the cryogenic fluid in the cryogenic vessel, i.e., upstream of the valve in the withdrawal direction. In other words, the pressure measuring unit measures the pressure in the cryogenic vessel upstream of the valve in the withdrawal direction.

[0024] In a further advantageous variant, the exhaust valve could receive temperature measurement values ​​from a temperature measuring unit, which preferably measures the temperature of a heat shield, wherein the exhaust valve opens and / or closes on the basis of the obtained temperature measurement values, ie the exhaust valve could, for example, remain open until an element such as a heat shield is sufficiently cooled, thereby simultaneously preventing stuttering of the exhaust valve.

[0025] In a further variant, the outlet valve could be equipped with a timer and configured to close again only after a predetermined period of time after opening. The period could, for example, be specified by a user or a control unit and selected such that a predetermined pressure reduction occurs in the cryogenic container over the period, e.g., to achieve a certain hold time, after which the outlet valve opens again.

[0026] The outlet valve could also be a purely mechanical valve, in particular a needle valve, which is preferably connected to the cryogenic container upstream of the fitting via a line. The line preferably runs directly through the fitting and opens and / or closes when a threshold pressure is exceeded. In this case, no control unit is required; instead, the outlet valve can be controlled purely mechanically, e.g., by manually actuating the outlet valve or by analog signals on the line.

[0027] At this point, however, it should also be noted that the valve could be designed as a pressure relief valve within the cryogenic vessel. However, installation would be more complicated, and replacement, for example, in the event of a pressure relief valve failure, would involve greater effort. In this case, an additional outlet valve outside the cryogenic vessel is optional.

[0028] As already explained above, the connecting line can be designed as a dedicated boil-off line, i.e. it can have a pressure relief valve or other outlet valve and is not connected to a consumer. The boil-off line can be led downstream of the outlet valve to a boil-off management system that burns the escaping fuel to reduce the danger potential when it escapes into the atmosphere, e.g. hydrogen is oxidized to water or methane to CO2 and water. Alternatively, the connecting line can also be connected to a consumer outside the cryogenic container, e.g. to an engine or a fuel cell. A T-piece can be provided in the connecting line 4, on the one hand to provide a pressure relief valve in the connecting line 4 and on the other hand to connect the connecting line to a consumer.

[0029] The invention can be used in particular in vehicles, so that the vehicle can also comprise a system in one of the aforementioned embodiments, wherein the cryogenic container is preferably mounted on a vehicle frame of the vehicle. The invention is particularly advantageous for use in vehicles because the more efficient pressure reduction can reduce boil-off losses. Further measures can extend the downtime until such a boil-off event occurs, the so-called "hold time." Both lead to a reduction in fuel losses.

[0030] In a further aspect, the invention relates to the use of a system in one of the aforementioned embodiments with a cryofluid of a predetermined composition in a predetermined thermodynamic state stored in the cryogenic container, wherein the opening cross-section of the fitting is selected such that the cryofluid expands upon withdrawal from the fitting, and preferably the length of the connecting line between the fitting and the connection point is selected such that the temperature of the cryofluid in the connecting line at the connection point substantially corresponds to the temperature of the cryofluid outside the connecting line. The selection of the opening cross-section and the length can be made, in particular, by a person skilled in the art using a phase diagram for the cryofluid of the predetermined composition.After the temperature of the cryogenic fluid after expansion has been determined, the length can also be determined using the heat transfer properties of the connecting line.

[0031] These and other advantageous embodiments of the system according to the invention are explained in more detail below with reference to the figures. Figure 1 shows a system according to the invention with a cryogenic container and a connecting line which has a throttle within the cryogenic container. Figure 2 shows the system of Figure 1 in a schematic view with the pressure relief valve closed. Figure 3 shows the system of Figure 1 in a schematic view with the pressure relief valve open. Figure 4 shows a variant of the system according to the invention, in which the outlet valve receives measurement data from measuring units. Figure 5 shows a possible variant for the implementation of the throttle. Figure 6shows a variant of the system according to the invention with a nozzle. Figure 7 shows a further variant of the system according to the invention, in which a pressure relief valve is arranged within the cryogenic container.

[0032] The Figures 8a and 8b show another variant with a valve in a first state ( Figure 8a ) and a second state ( Figure 8b ).

[0033] Figure 1shows a system 1 comprising a cryogenic container 2, in which cryogenic fluid is stored in the gaseous state and / or liquid state. The cryogenic fluid can be, for example, hydrogen, so that the cryogenic container 2 is a hydrogen container, or the cryogenic fluid can be LNG (liquefied natural gas), so that the cryogenic container 2 is an LNG container. Depending on the cryogenic fluid, the cryogenic container 2 is thus designed to store cryogenic fluid at temperatures of, for example, below 150 Kelvin, in the case of hydrogen even below 50 Kelvin or below 30 Kelvin or essentially 20 Kelvin. Depending on the application, the cryogenic container 2 could, for example, be designed to store sLH2 (subcooled liquid hydrogen) or CcH2 (cryo-compressed hydrogen) and thus also be designed for correspondingly high pressures and temporarily even higher temperatures, e.g. for maximum pressures between 5 bar and 350 bar.

[0034] The cryogenic container 2 described herein can be used, for example, as a fuel tank for a vehicle (not shown in detail) and can be mounted, for example, on the vehicle frame for this purpose. The cryogenic fluid stored in the cryogenic container 2 can, for example, be supplied as fuel to a consumer of the vehicle, such as an engine or a fuel cell. However, the cryogenic container 2 could also be used in other applications, e.g., at a gas station or another static system for storing liquefied nitrogen. The cryogenic container 2 can therefore also be installed stationary in the environment.

[0035] To remove cryogenic fluid from the cryogenic vessel 2, either to supply it to a consumer or to release it to the environment for pressure reduction, a connecting line 4 is routed into the cryogenic vessel and thereby passes through it. The connecting line 4 described herein is therefore expressly intended to be a withdrawal line and not a filling line, i.e., for example, there is no check valve in the section of the connecting line 4 between the throttle 9 explained below and the outlet valve or the consumer, since the check valve would prevent the removal of cryogenic fluid from the cryogenic vessel 2.

[0036] Conventional cryogenic containers 2 comprise an inner tank 5 and an outer container 6 that is vacuum-insulated from the inner tank 5, so that the connecting line 4 can pass through both the inner tank 5 and the outer container 6. The connection point 7 is referred to herein as the point at which the connecting line 4 passes through the cryogenic container 2, or through the inner tank 5, if present.

[0037] At the beginning, we will discuss the case where the connecting line 4 is intended to release cryogenic fluid into the environment when the pressure in the cryogenic container 2 is too high. In this case, the connecting line 4 can also be colloquially referred to as a "boil-off line" and does not need to be connected to a consumer. In this case, a first end of the connecting line 4 is provided inside the cryogenic container 2 and a second end is provided outside the cryogenic container 2. A pressure relief valve 8 is provided at the second end, which is triggered at a predetermined pressure in the cryogenic container 2, thus opening the connecting line 4.

[0038] The aforementioned pressure relief valve 8 thus blocks fluid flow when the pressure in the cryogenic container 2 is below a threshold value and opens when the pressure in the cryogenic container 2 exceeds the aforementioned or another threshold value. The pressure relief valve 8 thus assumes a critical safety role, as it prevents the pressure in the cryogenic container 2 from becoming too high and thereby damaging the cryogenic container 2. The aforementioned threshold value of the pressure relief valve 8, at which cryogenic fluid is to be released to the environment, is, for example, a so-called maximum allowable working pressure (MAWP) of the cryogenic container 2 and depends on the properties of the cryogenic container 2. This maximum allowable working pressure is, for example, 16 bar, so the pressure relief valve 8 can be designed to open from a pressure of 16 bar. However, the threshold value of the pressure relief valve 8 can generally be selected arbitrarily and can, for example,depend on the external circumstances or the intended use.

[0039] Conventional connecting lines with a pressure relief valve 8 only allow the cryofluid to be transferred from the interior of the cryocontainer 2 to the exterior, i.e., the volume of cryofluid in the cryocontainer 2 is reduced, while the temperature in the cryocontainer 2 remains essentially constant. However, due to the design of the connecting line 4 according to the invention described below, the removed cryofluid is also used to cool the cryofluid in the cryocontainer 2, i.e., both the volume and the temperature of the cryofluid in the cryocontainer are to be reduced.

[0040] This is achieved by providing the connecting line 4 with a throttle 9 at the end located in the cryogenic container 2, at which throttle the cryogenic fluid can expand. As the cryogenic fluid expands, its temperature drops, allowing the connecting line 4 and consequently the cryogenic fluid located in the cryogenic container 2 to cool. To achieve almost ideal expansion, the throttle 9 should have the smallest possible opening cross-section q1. Initial tests have shown that an opening cross-section q1 of substantially 2500 µm 2< has proven advantageous. Generally, an opening cross-section q1 of 1 µm 2< to 9 mm 2< is preferred; particularly, an opening cross-section q1 of 5 µm 2< to 1 mm 2< is preferred. However, the opening cross-section q1 can also be specified as a function of the internal cross-section q2 of the connecting line 4, wherein the opening cross-section q1 of the throttle 9 is, for example, at least 100 times, preferably 10,000 times or 1,000.000 times, is smaller than the internal cross-section q2 of the connecting line 4 between the throttle 9 and the connection point 7 to the cryogenic vessel 2. If the connecting line 4 has a variable diameter, the smallest internal cross-section q2 of the connecting line 4 between the throttle 9 and the connection point 7 to the cryogenic vessel 2 can be assumed as the internal cross-section q2.

[0041] It should be noted that we are referring here to opening cross-sections or internal cross-sections, whereby the throttle cross-sections or pipe cross-sections are usually circular. However, the shapes of the cross-sectional areas could also be different, e.g., oval or rectangular.

[0042] In order to provide a sufficient heat transfer path, the connecting line 4 between the throttle 9 and the connection point 7 should also have a predetermined length L, e.g., more than 10 cm, more than 30 cm, more than 50 cm, or more than 100 cm. The choice of the length L of the connecting line 4 between the throttle 9 and the connection point 7 can also be optimized, e.g., by determining a temperature gradient and choosing the said length L such that the expanded cryogenic fluid at the connection point 7 has essentially the same temperature as the cryogenic fluid stored in the cryogenic container 2. If the predetermined length L is chosen to be shorter, the maximum possible heat transfer is not fully utilized (which, however, could also be implemented according to the invention, in which case at least a certain amount of heat exchange still takes place). This can be used, in particular, for cooling a heat shield 21 which is located in Figure 4is shown). If the predetermined length L is chosen to be longer, the overall weight of the system is unnecessarily increased, which can be disadvantageous, particularly in the case of cryogenic containers 2 for vehicles.

[0043] To achieve advantageous heat transfer, the connecting line 4 can also be specially designed over the predetermined length L to increase the surface area in this region. For example, the connecting line 4 can be designed over the predetermined length L with ribs or other surface-enlarging structures on the inside and / or outside of the connecting line 4. As shown in Figure 1 As shown, the connecting line 4 can also be guided in a meandering manner, ie not in a straight line, within the cryogenic container, so that the predetermined length L can easily be accommodated in the cryogenic container 2.

[0044] The inventive concept of additional heat transfer after expansion through the throttle 9 will now be explained below with reference to the Figures 2 and 3 explained in more detail.

[0045] Figure 2 shows a state in which the pressure relief valve 8 was closed for an extended period of time, so that equilibrium has been established in the system. In this case, cryofluid with a temperature T1 is present in the cryogenic vessel 2. Due to the equilibrium state, cryofluid with a temperature T1 is also present within the connecting line 4. Therefore, there is no heat transfer between the cryogenic fluid inside the connecting line 4 and outside the connecting line 4. Furthermore, the same pressure p1 exists inside and outside the connecting line 4. However, outside the cryogenic vessel 2 and outside the connecting line 4, i.e. in the environment, there is an ambient pressure p2 (usually an air pressure of approximately 1 bar) which is lower than the pressure p1 in the cryogenic vessel 2.

[0046] Figure 3 shows the condition immediately or a short period after the pressure relief valve 8 was triggered, e.g., because the pressure p2 in the cryogenic container 2 became too high, causing the pressure relief valve 8 to open. Due to the relatively small volume within the connecting line 4, the cryogenic fluid present in the connecting line 4 is discharged to the environment in a very short time. However, the throttle 9 prevents a rapid flow of cryogenic fluid into the connecting line 4, so that the ambient pressure p2 will now essentially prevail within the connecting line 4.

[0047] Due to the aforementioned change of state, a large pressure gradient occurs at the throttle 9, since a pressure p1 (e.g., 16 bar) will be present upstream at the throttle 9 and a pressure p2 (e.g., 1 bar) will be present downstream of the throttle 9. The terms "upstream" and "downstream" refer to the direction in which the cryogenic fluid is withdrawn. This causes the cryogenic fluid to expand as it flows through the throttle 9. At the same time, the expansion leads to a reduction in temperature. In other words, the cryogenic fluid upstream of the throttle 9 will have a temperature T1, which the cryogenic fluid will also have at all other points around the connecting line 4. After the expansion, the fluid downstream of the throttle 9 will have a temperature T2 that is lower than temperature T1.The exact, absolute value of the temperature T2 that the cryogenic fluid will exhibit after expansion depends on various factors, such as the pressure difference p1-p2 and the cryogenic fluid (e.g., the temperature change may be different for hydrogen than for LNG). If an exact calculation of the temperature T2 is required, the expert can use a phase diagram.

[0048] In theory, the aforementioned effect is known as the Joule-Thomson effect for an ideal throttle 9, which in turn falls under the category of isenthalpic processes. However, it should be noted that other processes may also be incorporated into the invention, particularly since the gases present are not ideal gases and changes of state and flow processes may also occur, particularly when liquid cryogenic fluid is present upstream of the throttle 9. The use of the connecting line 4 or the throttle 9 can be limited to states of the cryogenic fluid in the cryogenic container 2 from which a pressure drop causes the expanded fluid to cool, e.g., due to the Joule-Thomson effect.

[0049] If the cryogenic fluid is present downstream of the throttle 9 at temperature T2, due to the thermal gradient T2 <T1 an dieser Stelle der Anschlussleitung 4 zu einem Wärmeübergang. In anderen Worten kann das nun expandierte Kryofluid das im Kryobehälter 2 vorliegende Kryofluid weiter kühlen, wodurch der Druck im Kryobehälter 2 nicht nur durch die Volumensreduktion, sondern auch durch eine zusätzliche Wärmeabfuhr gesenkt werden kann. Durch die Drossel 9 wird das Überdruckventil 8 früher schließen als bei einem vergleichbaren System ohne Drossel 9, da der Druck mit einer geringeren Volumensentnahme gesenkt werden kann. Es wird daher in Summe auch weniger Kryofluid an die Umwelt abgegeben.

[0050] It is understood that the expanded cryogenic fluid now present in the connecting line 4 is heated again by the heat transfer, so that after a certain distance Li it will have a temperature Ti which lies between the temperature T2 immediately after the expansion and the temperature T1 of the cryogenic fluid in the cryogenic container 2, ie T2 <Ti<T1. Nach einer weiteren Wegstrecke Lx wird die Temperatur Ti des Kryofluids in der Anschlussleitung 4 im Wesentlichen der Temperatur T1 des Kryofluids im Kryobehälter 2 entsprechen. Diese Wegstrecke Lx, nach der die Temperatur Ti des Kryofluids in der Anschlussleitung 4 zum ersten Mal im Wesentlichen der Temperatur T1 des Kryofluids im Kryobehälter 2 entspricht, wäre eine optimale Länge für die vorbestimmte Länge. Es ist ersichtlich, dass es nach der Länge Lx zu keiner weiteren Wärmeübertragung kommt, da kein Temperaturgradient vorliegen wird. Bevorzugt entspricht die Länge L daher der optimalen Länge Lx.

[0051] The pressure relief valve 8 described above can be implemented in a variety of ways. If the pressure relief valve is a purely mechanical pressure relief valve with a spring-loaded closure body, the pressure relief valve 8 will, for example, trigger when a pressure difference on both sides of the pressure relief valve 8 exceeds a threshold value S and close again when the pressure difference on both sides of the pressure relief valve 8 falls below the aforementioned threshold value S. However, with such a "simple" pressure relief valve 8, stuttering can occur, so that in a first variant, it could be considered that there is an upper threshold value S1 and a lower threshold value S2, where S1>S2. This "improved" pressure relief valve 8 can trigger (i.e.open) when a pressure difference on both sides of the pressure relief valve 8 exceeds the upper threshold S1 and only close again when the pressure difference on both sides of the pressure relief valve 8 falls below the lower threshold S2. Such solutions are quite effective for regular pressure relief valves 8 (without throttle 9), since the actual pressure of the cryogenic fluid in the cryogenic container 2 will usually be present on the inside of the pressure relief valve 8.

[0052] However, in combination with the solution according to the invention, even the aforementioned improved pressure relief valve 8 with two threshold values ​​S1, S2 may experience stuttering, since the throttle 9 on both sides of the pressure relief valve 8 will, after a short time, essentially equal the ambient pressure p2. It is difficult to set the lower threshold value S2 precisely to enable proper operation of the pressure relief valve 8 without stuttering.

[0053] Figure 4 shows that instead of a classic mechanical pressure relief valve 8 as in the Figures 2 and 3 A sensor-controlled outlet valve 8' could also be used, which can effectively prevent stuttering in the inventive solution. In yet other embodiments, the outlet valve could also be manually operable. All of these variants allow the fluid flow of cryogenic fluid from the cryogenic container 2 to be regulated; this is generally referred to as an outlet valve, regardless of whether it is a pressure relief valve 8, a sensor-controlled outlet valve 8', or a manually operable outlet valve.

[0054] In the illustrated variant, the outlet valve 8' receives measured values ​​from a pressure measuring unit 10 designed to measure the pressure of the cryogenic fluid in the cryogenic container 2 (i.e., the pressure of the cryogenic fluid upstream of the throttle 9). For example, the outlet valve 8 can open when the pressure in the cryogenic container 2 measured by the pressure measuring unit 10 exceeds an upper threshold value S1 and only close again when the pressure in the cryogenic container 2 measured by the pressure measuring unit 10 falls below a lower threshold value S2.

[0055] If desired, the ambient pressure can be measured using a dedicated pressure measuring unit 11, and the aforementioned opening and closing can be based on a pressure difference between the measured internal pressure and the measured ambient pressure. However, as previously explained, this is not necessary, since the opening and closing of the outlet valve 8' can also be based on the absolute values ​​of the aforementioned pressure measuring unit 10. Furthermore, for safety reasons, the pressure relief valve could still be triggered mechanically, i.e., based on a pressure difference directly present at the outlet valve 8'.

[0056] Figure 4further shows an embodiment in which a temperature measuring unit 20 is used alternatively or in addition to the pressure measuring unit 10, 11. The temperature measuring unit 20 can, for example, measure the temperature of a heat shield 21, which is arranged, for example, in the vacuum-insulated space between the inner tank 5 and the outer container 18. The outlet valve 8' can receive the measurement data from the temperature measuring unit 20 and initiate the opening and / or closing of the outlet valve 8' based on the received measured values ​​from the temperature measuring unit 20. An exemplary control can be implemented as follows. The outlet valve 8' opens when the pressure in the cryogenic container 2 reaches a predefined threshold value (which, as described above, can be determined by a pressure difference directly applied to the outlet valve 8' or by the pressure measuring unit 20).Closing only occurs when the temperature of the heat shield 21 reaches a predefined threshold value, which can, for example, essentially correspond to the temperature of the cryogenic fluid in the cryogenic container 2. For the sake of completeness, it should be noted that such heat shields are known per se, e.g., from EP 2 981 756 A1. In further embodiments, the temperature measuring unit 20 could also measure the temperature at a different location, e.g., on the connecting line 4 between the inner tank 5 and the outer container 6, or outside the cryogenic container 2 at a predetermined distance from the outer container 6.

[0057] A further embodiment of the outlet valve 8`, which functions without stuttering in combination with the throttle 9 according to the invention, is possible with the aid of a timer device 22. In this case, the outlet valve 8` is triggered when a pressure difference on the two sides of the outlet valve 8` exceeds a threshold value S, i.e. the outlet valve 8` can be designed as standard for differential pressure measurement and no pressure measuring unit 10 is required to measure the pressure of the cryogenic fluid in the cryogenic container, although this could also be provided. The outlet valve 8` is not closed when the pressure falls below the threshold value, but after a predetermined period of time, which can be set, for example, on the timer device 22. For example, the outlet valve 8` closes between 5 seconds and 5 minutes after opening.The time period after which a sufficient pressure reduction has occurred can be determined by experiments or analytically.

[0058] At this point, it should be noted that the outlet valve 8' can be purely mechanical (e.g., with a spring-loaded closure element) or electromechanical, particularly if the outlet valve 8' receives measurement data from one or more measuring units. In this context, the outlet valve 8' can also comprise a control unit or be connected to a control unit.

[0059] Furthermore, it should be noted that the variants mentioned can be provided individually or combined, e.g. by connecting a single outlet valve 8' to one or more of the following components: a first pressure measuring unit 10 for measuring the pressure in the cryogenic container 2, a second pressure measuring unit 11 for measuring the ambient pressure, a temperature measuring unit 20 and / or a timer device 22. It could also be provided that two or more outlet valves are provided parallel to one another on the connecting line 4, so that at least one of the outlet valves can trigger if other outlet valves fail.For example, a T-piece could be connected to the connecting line 4 and a first controlled outlet valve 8' with pressure measuring unit 10 is connected to a first outlet of the T-piece and a second purely mechanical pressure relief valve 8, which is triggered due to a pressure difference present thereat, is connected to a second outlet of the T-piece.

[0060] As in Figure 5 As shown, the throttle 9 could, for example, be formed by providing a bore in the outer wall of the connecting line 4. In this case, the wall thickness of the connecting line 4 forms the throttle length. In this variant, a plug 4' is usually provided in the connecting line 4, which closes it flush. Alternatively, the bore could also be located in the plug 4' and not in the connecting line 4.

[0061] Although it has been discussed so far that the inventive effect of additional heat transfer through the expanded cryogenic fluid is achieved by a throttle 9, other fittings could also be provided to achieve this effect. For example, Figure 6 that a nozzle such as a Laval nozzle could also be used. A Laval nozzle is particularly advantageous because it can achieve mass flows at supersonic speeds. From the comparison of the detailed views from the Figures 1 and 6The difference between a throttle 9 and a nozzle 9' is also clearly visible. A throttle 9 has a constant contour in the longitudinal direction and thus only a single opening cross-section. A nozzle 9', on the other hand, has a contour that is variable in the longitudinal direction (but constant over time), with the narrowest area being regarded as the opening cross-section, particularly with regard to the dimensions described here. The fitting could, for example, also be an orifice plate, which is understood to mean a throttle 9 with a throttle length of, for example, < 0.5 mm. The throttle described here could, for example, have a throttle length of 0.5 mm to 3 cm or even be longer. In a further variant, the fitting could also be a turbine. In all of the aforementioned embodiments, the throttle 9 could also be replaced by another fitting such as an orifice plate, a nozzle, a valve (in particular a pressure relief valve) or a turbine.

[0062] Figure 7 shows a further variant of the invention in which no stuttering occurs. The pressure relief valve 8 is not used as in the embodiments of Figures 1 to 4As shown, the pressure relief valve 8 is not provided outside the cryogenic container 2, but rather inside the cryogenic container 2 ("inside" and "outside" refer to the connection point 7). The pressure relief valve 8 can itself form a valve with a variable cross-section and assume a first state in which it closes the connecting line 4 and a second state in which it opens the connecting line 4, but only with a small size corresponding to the aforementioned opening cross-section. The pressure relief valve 8 can be designed with one or two threshold values, as explained above. The advantage is that no additional measures for the pressure relief valve 8, such as a timer device 22 or additional measuring units, are required. The disadvantage, however, is that such a pressure relief valve 8 is difficult to install inside the cryogenic container 2 and can only be replaced with considerable effort.

[0063] However, the invention is not limited to boil-off lines, where cryogenic fluid is to be released into the environment so that a maximum pressure is not exceeded. As already mentioned above, the connecting line 4 can also be part of a withdrawal line leading to a consumer. In this case, too, a rigid throttle 9 could be used, as shown in the Figures 1 to 4 However, it is preferred if a 9" valve with variable cross-section is used as the fitting, as shown in the Figures 8a and 8b It should be emphasized that the Figures 8a and 8b The valve 9" shown is only shown schematically and the actual structure may look different.

[0064] Figure 8a shows the valve 9" with variable cross-section, wherein the valve 9" is in a state (ie in a first operating position) in which it has a first opening cross-section q1. In Figure 8bthe valve 9" is shown in a second state (ie in a second operating position) in which it has a second opening cross-section qx. The first opening cross-section q1 is so small that an expansion of the cryogenic fluid as described above for the rigid throttle 9 of the Figures 1 to 4 explained. The second opening cross-section qx is, for example, at least 10 times, preferably 100 times or 1000 times, larger than the first opening cross-section q1 and has the aim of minimizing the flow resistance. The valve 9" can, for example, be connected by means of a control line 12 (or wirelessly) to a control unit 13, which can control the valve 9" in order to move it from the first state to the second state or from the second state to the first state. Instead of a control unit 13, the valve 9" could also be adjusted manually, e.g. by means of a manually operable switch.

[0065] In this embodiment, the first opening cross-section q1 is set when the aforementioned throttling effect is to be achieved. In this state, essentially the same function as explained above can be achieved if, for example, a pressure relief valve 8 is arranged in the withdrawal path by means of a T-piece 14, which can release cryogenic fluid to the environment. The valve 9" can, for example, be set to the first state when no cryogenic fluid is to be actively withdrawn from the cryogenic container 2.

[0066] However, for an active withdrawal of cryogenic fluid from the cryogenic container 2, i.e. when cryogenic fluid is to flow towards the consumer V, the connecting line 4 should have the lowest possible flow resistance, so that the valve 9" should be set to the second state during an active withdrawal. In the second state, the valve 9" is therefore preferably opened to its maximum so that it can also completely release the cross-section of the connecting line 4.

[0067] Advantageous compared to the variants of Figures 1 to 4 is that no separate piping is required for withdrawal into cryogenic container 2, thus eliminating one thermal bridge. However, the disadvantage is that valve 9" should be controlled to reduce flow resistance.

[0068] In addition to the conditions in the Figures 8a and 8b The valve 9" can also optionally be placed in a third state in which the valve 9" is completely closed. Alternatively, however, a valve could also be provided in the connecting line 4, which is located outside the cryogenic container 2 in the connecting line 4 in order to shut off fluid flow.

[0069] It is understood that the valve 9" can also assume all states between the first and the second state, ie it is continuously adjustable.

[0070] The aforementioned valve 9" could, for example, also be formed by connecting a throttle with the aforementioned opening cross-section q1 and an on / off valve in parallel. When the on / off valve is closed, the entire mass flow flows through the throttle, thereby achieving the aforementioned expansion and the associated temperature reduction of the withdrawn cryogenic fluid. However, when the on / off valve is opened, essentially the entire mass flow of cryogenic fluid will flow through the on / off valve, since this has a lower flow resistance than the throttle.

[0071] The previously described control unit 13 could also be connected to the valve 9", optionally in combination with one of the previously described controls via a measured pressure, temperature or time. In this case, the control unit 13 can also be connected to the previously described outlet valve 8, although this is not mandatory. The control unit 13 can, for example, receive the pressure from the cryogenic container 2 and control the valve 9" such that the pressure in the cryogenic container 2 remains essentially constant. For example, the valve 9" can remain closed until the pressure in the cryogenic container corresponds to a desired boil-off pressure and then open. After opening, the opening cross-section q1 of the valve 9" is, for example, between 1 µm 2< to 9 mm 2< . Now the control unit 13 can regulate the opening cross-section q1 within the range 1 µm 2< to 9 mm 2< (or a sub-range thereof) so that the pressure in the cryogenic container remains constant.Alternatively or additionally, the control unit 13 can also control the valve 9" in a different way, e.g. to continuously reduce the container pressure and / or to cool a cooling shield to a desired temperature, after which the valve 9" can be closed again.

[0072] In all of the aforementioned embodiments, the connecting line 4 can be provided for the withdrawal of either liquid cryofluid or gaseous cryofluid. For the withdrawal of liquid cryofluid, the end of the connecting line 4 located in the cryocontainer 2 is typically arranged in the lower half, in particular in the lower quarter, of the cryocontainer 2. For the withdrawal of gaseous cryofluid, the end of the connecting line 4 located in the cryocontainer 2 is typically arranged in the upper half, in particular in the upper quarter, of the cryocontainer 2.

[0073] It should be noted that several connecting lines 4 could also be routed into the cryogenic container 2, each of which has a throttle 9 or another corresponding fitting. For example, two connecting lines 4 could be provided, each of which has one of the aforementioned fittings, one for withdrawing liquid cryogenic fluid and one for withdrawing gaseous cryogenic fluid.

Claims

1. System (1) comprising a cryogenic container (2) for storing cryogenic fluid and a connecting line (4) guided into the cryogenic container (2) for removing cryogenic fluid from the cryogenic container (2), characterized in that the connecting line (4) within the cryogenic container (2) has a fitting, in particular a throttle (9), an orifice, a nozzle (9'), a valve (9") or a turbine, wherein the fitting has an opening cross-section (q1) permanently or in at least one operating position which is at least 100 times, preferably 10,000 times or 1,000,000 times, smaller than an internal cross-section (q2) of the connecting line (4) downstream of the fitting in the withdrawal direction, wherein the connecting line (4) is guided between the fitting and the connection point (7) on the cryogenic container (2) with a predetermined length (L), which is preferably longer than 50 cm.

2. System according to claim 1, wherein said opening cross-section (q1) has a size of 1 µm 2 up to 9 mm 2, particularly preferably 25 µm 2 up to 1 mm 2 , has.

3. System according to claim 1 or 2, wherein the connecting line (4) is guided between the fitting and the connection point (7) to the cryogenic container (2) with a length of 1 m to 3 m.

4. System according to one of claims 1 to 3, wherein the connecting line (4) is guided in a meandering manner within the cryogenic container (2) and / or wherein the connecting line (4) has surface-enlarging structures, in particular cooling fins, within the cryogenic container (2).

5. System according to one of claims 1 to 4, wherein the fitting is a throttle (9) with a throttle length of preferably at least 1 mm and is formed by a bore through a pipe wall of the connecting line (4).

6. System according to one of claims 1 to 4, wherein the fitting is a nozzle (9') which is designed as a Laval nozzle.

7. System according to one of claims 1 to 4, wherein the fitting is a valve (9") which has a variable opening cross-section (q1, qx), wherein the valve (9") can be moved from the first operating position, in which it has the first-mentioned opening cross-section (q1), which is at least 100 times, preferably 10,000 times or 1,000,000 times smaller than the internal cross-section (q2) of the connecting line (4) between the valve (9") and the connection point (7) to the cryogenic container (2), into a second operating position, in which the valve (9") has a second opening cross-section (qx) which is at least 100 times, preferably 10,000 times or 1,000.000 times, is larger than the first-mentioned opening cross-section (q1), wherein the system preferably comprises a control unit (13) connected to the valve (9"), which receives pressure measurement values ​​from a pressure measuring unit (10) arranged in the cryogenic container (2) and is designed to control the opening cross-section of the valve (9") such that the pressure in the cryogenic container remains substantially constant.

8. System according to one of claims 1 to 7, further comprising an outlet valve (8, 8') which is provided outside the cryogenic container (2) in the connecting line (4).

9. System according to claim 8, wherein the outlet valve (8) is a pressure relief valve which is designed to open when a predetermined pressure or a predetermined pressure difference is present in order to release cryogenic fluid from the cryogenic container (2) to the environment.

10. System according to claim 8 or 9, wherein the outlet valve (8) is a mechanical valve, in particular a needle valve, which is connected via a line to the cryogenic container upstream of the fitting, wherein the line is preferably led directly through the fitting, and opens and / or closes when a threshold value of the pressure applied there is exceeded.

11. System according to one of claims 8 to 10, wherein the outlet valve (8') receives pressure measurement values ​​from a pressure measuring unit (10) arranged in the cryogenic container (2) and opens and / or closes on the basis of the pressure measurement values ​​received, or wherein the outlet valve (8') receives temperature measurement values ​​from a temperature measuring unit (20), which preferably measures the temperature of a heat shield (21), wherein the outlet valve (8') opens and / or closes on the basis of the temperature measurement values ​​received.

12. System according to one of claims 8 to 11, wherein the outlet valve (8') is equipped with a timer device (22) and is designed to close again after opening only after a predetermined period of time.

13. System according to one of claims 1 to 12, wherein the connecting line (4) is connected to a consumer outside the cryogenic container (2).

14. A vehicle comprising a system (1) according to any one of claims 1 to 13, wherein the cryogenic container (2) is preferably mounted on a vehicle frame of the vehicle.

15. Use of a system (1) according to one of claims 1 to 13 with a cryogenic fluid of a predetermined composition in a predetermined thermodynamic state stored in the cryogenic container (2), wherein the opening cross-section (q1) of the fitting is selected such that the cryogenic fluid expands when removed from the fitting and preferably the length of the connecting line (4) between the fitting and the connection point (7) is selected such that the temperature of the cryogenic fluid in the connecting line (4) at the connection point (4) substantially corresponds to the temperature of the cryogenic fluid in the cryogenic container (2) outside the connecting line (4).

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