Apparatus for sensing the temperature of a medium in a cryogenic tank

Abstract

The invention relates to an apparatus for sensing the temperature of a medium in a cryogenic tank (1) comprising an inner container (2) for the cryogenic medium and comprising an outer container (3) surrounding the inner container, the inner container (2) being mounted in the evacuated outer container (3) by means of a fixed bearing (4) and at least one floating bearing (5), the apparatus comprising a measuring device (7) for sensing a length change (Δl) of the inner container (2) in the region of the floating bearing (5). The apparatus according to the invention is characterized in that a passive magnetic, inductive and / or capacitive indicating element (10) is disposed on a part (8) of the floating bearing (5) that is connected to the inner container (2), the corresponding sensing element (11) of a sensor (12) of the measuring device (7) for sensing the distance between the indicating element (10) and the sensing element (11) being disposed on the outer surface of the outer container (3), and the measuring device (7) comprising evaluation electronics (13) which are designed to infer a length change (Δl) of the inner container (2) and thus an associated temperature change from the distance between the indicating element (10) and the sensing element (11).

Description

[0001] Device for measuring the media temperature in a cryogenic tank

[0002] The invention relates to a device for detecting the media temperature in a cryogenic tank according to the type defined in the preamble of claim 1. Furthermore, the invention relates to a method for safeguarding the operation of a cryogenic tank with such a device.

[0003] The need to measure the temperature in cryogenic tanks with an inner and an outer container is known from the prior art. This arises in particular when it is necessary to prevent a warm cryogenic tank from being incorrectly filled with cryogenic liquid, in particular liquid hydrogen. This can lead to unacceptable pressure increases in the cryogenic tank due to sudden evaporation of the cryogenic liquid. Typically, temperature sensors are installed inside the inner container of such a cryogenic tank to measure the temperature of the stored medium, for example the temperature of liquid hydrogen. The routing of the cables to the temperature sensors is problematic here, as they must penetrate both the inner and outer containers, thus forming a thermal bridge through the vacuum insulation between the inner and outer containers.

[0004] Alternatively, temperature sensors can also be connected to the outer surface of the inner container. This also poses the problem that the measured values ​​must be transmitted through the vacuum and the outer container. Regarding such an arrangement of temperature sensors, reference is made purely to document US 2003 / 0029224 A1, which uses temperature and pressure to determine the mass of stored hydrogen. An alternative method for measuring the mass of stored hydrogen, in this case in a cryogenic pressure tank with pressures of up to 150 bar, is described in DE 10 2013214 004 A1. The method described therein utilizes the fact that the inner container is typically mounted relative to the outer container with a fixed bearing and at least one loose bearing.In practice, the temperature and, in the case of a cryogenic pressure tank, especially the pressure change, cause linear expansion of the inner container, which is recorded by a measuring device. From these recorded values, the mass of the stored medium contained in the inner container can then be determined.

[0005] The object of the present invention is to provide an improved device for detecting the media temperature in a cryogenic tank and a method for safeguarding the operation of such a cryogenic tank.

[0006] According to the invention, this object is achieved by a device having the features of claim 1, and in particular in the characterizing part of claim 1. Advantageous embodiments and refinements emerge from the dependent subclaims. Furthermore, a method for safeguarding the operation of such a cryogenic tank using such a device solves the problem. Here, too, an advantageous embodiment emerges from the dependent subclaim.

[0007] The device according to the invention is based on the prior art mentioned above, but does not relate to a cryogenic pressure tank as in that case, but rather to a standard cryogenic tank, which, according to a particularly advantageous development of the device according to the invention, is operated at a maximum pressure of up to 25 bar, typically at a pressure in the range of 6-20 bar. If the pressure exceeds this limit of, for example, 20 bar, vaporized hydrogen is released; in this context, this is referred to as a boil-off.

[0008] In the device according to the invention, the measuring device for detecting the change in length can be used to detect the medium temperature, since a pressure-induced change in length can easily be taken into account due to the linear relationship with the pressure. According to the invention, a passive magnetic, inductive and / or capacitive sensor is arranged on a part of the floating bearing connected to the inner container, wherein the corresponding pickup of a sensor of the measuring device for detecting the distance between the sensor and the pickup is arranged on the outer surface of the outer container. The measuring device further comprises evaluation electronics which is designed to infer the change in length of the inner container and an associated temperature change from the distance between the sensor and the pickup.

[0009] The change in length of the inner container is therefore converted into a change in its temperature. The high vacuum between the inner and outer containers ensures very good insulation. The liquid cryogenic medium, in particular liquid hydrogen, in the inner container, on the other hand, has good thermal conductivity with the inner container. The temperature of the inner container will therefore essentially correspond to the temperature of the medium in the inner container. The thermal expansion of the inner container then leads to the corresponding change in length. This is preferably measured along the longest axis of the inner container, with at least one of the floating bearings, usually a fixed bearing and exactly one floating bearing, typically being arranged along this axis anyway. The sensor itself is passive and can be, for example, a permanent magnet, a passive coil, or the like.It moves accordingly when the inner container changes length. The sensor detects this movement to determine the distance between the transmitter and the sensor. The sensor is located on the outer surface of the outer container and can be easily and efficiently mounted and wired there without compromising the insulation created by the vacuum between the inner and outer containers. With ideal insulation and avoiding a thermal bridge created by the sensor connection, the temperature of the medium in the inner container can be determined in this way.

[0010] According to a very advantageous embodiment, a calibration curve of the absolute length of the inner container versus temperature can be stored in the evaluation electronics, so that the temperature of the inner container and thus the temperature of the medium can be determined directly from the measured length. Temperature detection using the device according to the invention is particularly robust and reliable and is hardly subject to interference.

[0011] Various sensors can be used, as already explained above. A combination of different sensors, for example the use of a capacitive sensor together with a magnetic sensor or the like, is also conceivable. However, in a particularly advantageous form, the sensor can be designed as a permanent magnet. Such a permanent magnet can be positioned simply and efficiently in the area of ​​the loose bearing of the inner container, and its movement can be detected from the outside. For this purpose, the sensor can preferably be designed as an inductive sensor, which detects the position of the permanent magnet as a sensor relative to the sensor and can thus determine the distance of the sensor from the sensor.Together with the known length of the inner container, the wall thickness of the outer container and any parts of the loose bearing involved, the absolute length of the inner container can be determined, from which the temperature can be determined, for example, using the stored calibration curve mentioned above.

[0012] Preferably, a magnetic sensor is combined with an inductive sensor, as this combination offers decisive advantages. It is particularly suitable for a wide variety of materials for the outer container wall and delivers reliable results, even if the material of the outer container or the bearing journal itself is not ferromagnetic, for example, aluminum or stainless steel.

[0013] A particularly advantageous embodiment of the device according to the invention can further provide that the movable bearing comprises a movable bearing journal connected to the inner container, which carries the sensor. The movable bearing can therefore comprise the movable bearing journal in the region of the inner container, which is then mounted in corresponding receptacles of the movable bearing, which are connected to the outer container. Such a movable bearing journal can, for example, move in one spatial direction in an annular receptacle which is part of the outer container. The annular receptacle could also be replaced by individual bearing points which are distributed around the circumference of the movable bearing journal, for example three at an angular distance of 120° each. According to a particularly advantageous embodiment, the sensor can be arranged on the surface of the movable bearing journal facing the outer container.For example, a permanent magnet can be screwed to the loose bearing journal or glued to it, whereby in any case a gap remains between the outer container and the loose bearing journal, which gap is measured by the sensor together with the thickness of the material of the outer container in order to determine the length of the inner container and thus the media temperature in the inner container.

[0014] The method according to the invention serves to safeguard the operation of such a cryogenic tank and uses the device according to the invention for detecting the media temperature. The media temperature plays a decisive role, particularly during withdrawal, but above all during refueling of the cryogenic tank. According to a very advantageous embodiment of the method according to the invention, it is therefore provided that the cryogenic tank, which has at least one refueling line with a valve device, is controlled via the temperature detected by the device in such a way that the valve device remains closed above a limit temperature in order to prevent refueling. The predetermined limit temperature therefore determines the temperature up to which the medium stored in the inner container of the cryogenic tank can be refueled. If the temperature is higher, the corresponding valve device is closed.This means that potentially unsafe refueling of a warm inner container with a liquid cryogenic medium, such as liquid hydrogen, is no longer possible, thus ensuring safety.

[0015] Further advantageous embodiments of the device also emerge from the exemplary embodiment, which is described in more detail below with reference to the figures.

[0016] Showing:

[0017] Fig. 1 shows a schematic cross-section through a cryogenic tank with a movable bearing and a fixed bearing; and

[0018] Fig. 2 is an enlarged view of area II in Fig. 1 with a device designed according to the invention. In the illustration in Figure 1, a cryogenic tank 1 is schematically indicated. The cryogenic tank 1 serves to store a cryogenic liquid medium, here for example for storing liquid hydrogen LH2. The liquid hydrogen LH2 is stored in an inner container designated by 2. This inner container 2 is arranged in an outer container designated by 3. It is mounted in the outer container 3 via a fixed bearing 4, which is indicated here as an example on the left side, and a loose bearing 5, which is correspondingly indicated schematically on the right. The outer container 3 is evacuated in the intermediate space 6 formed between the outer container 3 and the inner container 2. A high vacuum preferably prevails here in order to enable the best possible thermal insulation of the inner container 2.Furthermore, the outer container 3 can of course be covered on its outer surface by an additional insulating layer, for example with a foamed plastic or the like.

[0019] For many operating conditions of such a cryogenic tank 1, but especially for refueling with fresh liquid hydrogen LH2, it is crucial that the temperature of the liquid hydrogen LH2, i.e., the medium in the inner container 2, is known. During refueling, a valve device in a refueling line (both not shown) could be closed for safety reasons to reliably prevent refueling that could lead to a safety-critical temperature and / or pressure increase.

[0020] In order to robustly and reliably measure the temperature of the medium in the inner container 2 without creating an unnecessary thermal bridge through the evacuated gap 6, a measuring device 7, as indicated in the illustration in Figure 2, can be provided. This is arranged in the area of ​​the floating bearing 5. The floating bearing 5 can for this purpose comprise a floating bearing journal 8, which is arranged in a receptacle 9. The design in the illustration in Figure 2 is to be understood purely as an example; a real structure will attempt to minimize the cross-sections for heat transfer accordingly. However, this is not further relevant for the measuring device 7 presented here. The selected schematic representation is sufficient for explanation.

[0021] As the temperature increases, the floating bearing journal 8 will move to the right, as indicated by the double arrow shown, and to the left, as the temperature decreases. This movement results from a change in length AI of the inner container 2, as indicated by the double arrow. The floating bearing journal 8 now has a sensor, designated 10, in particular a permanent magnet. This sensor 10 includes a pickup 11 within a sensor 12. This pickup 11 can be designed, in particular, as an inductive pickup 11. The sensor 12, together with the pickup 11 and the sensor 10, thus forms a device for detecting the distance between the sensor 10 and the pickup 11.They are part of the measuring device 7, which also includes evaluation electronics 13, which converts the measured distance between the sensor 10 and the transducer 11 into a current length of the inner container 2, taking into account the known initial length of the inner container 2 and the floating bearing journal 8 as well as the wall thickness of the outer container 3. This corresponds directly to the temperature of the inner container 2 and thus to the temperature of the cryogenic medium stored in the inner container 2, in this case liquid hydrogen LH2. Without the need for line elements, sensors, or the like to be passed through the gap 6 as primary insulation for the inner container 2, the change in length AI and thus the temperature or temperature change of the stored medium can be measured robustly and reliably without contact.

Claims

Patent claims 1. Device for detecting the medium temperature in a cryogenic tank (1), which comprises an inner container (2) for the cryogenic medium and an outer container (3) enclosing the latter, wherein the inner container (2) is mounted in the vacuum-sealed outer container (3) via a fixed bearing (4) and at least one movable bearing (5), with a measuring device (7) for detecting a change in length (AI) of the inner container (2) in the region of the movable bearing (5), characterized in that a passive magnetic, inductive and / or capacitive sensor (10) is arranged on a part (8) of the movable bearing (5) connected to the inner container (2), wherein the corresponding sensor (11) of a sensor (12) of the measuring device (7) for detecting the distance between the sensor (10) and the sensor (11) is arranged on the outer surface of the outer container (3), and wherein the measuring device (7) comprises evaluation electronics (13) which are used for is set up,to infer from the distance between the sensor (10) and the transducer (11) a change in length (AI) of the inner container (2) and an associated change in temperature., 2. Device according to claim 1, characterized in that a calibration curve of the absolute length of the inner container (2) versus the temperature is stored in the evaluation electronics (13).

3. Device according to claim 1 or 2, characterized in that the sensor (10) is designed as a permanent magnet.

4. Device according to one of claims 1 to 3, characterized in that the sensor (11) is designed as an inductive sensor (11).

5. Device according to one of claims 1 to 4, characterized in that the movable bearing (5) comprises a movable bearing pin (8) connected to the inner container (2) and carrying the sensor (10).

6. Device according to claim 5, characterized in that the sensor (10) is arranged on the surface of the loose bearing pin (8) facing the outer container (3).

7. Device according to one of claims 1 to 6, characterized in that the inner container (2) is designed for a maximum pressure of less than 25 bar.

8. Device according to claim 7, characterized in that the inner container (2) is designed for a maximum pressure of approximately 20 bar.

9. A method for safeguarding the operation of a cryogenic tank which comprises an inner container (2) for the cryogenic medium and an outer container (3) enclosing the inner container, the inner container (2) being mounted in the vacuumed outer container (3) via a fixed bearing (4) and at least one loose bearing (5), and which has at least one refueling line with a valve device, characterized in that the medium temperature of the cryogenic medium is determined using a device according to one of claims 1 to 8.

10. Method according to claim 9, characterized in that the detected medium temperature is compared with a limit temperature, wherein the Valve device in the refueling line is closed when the media temperature exceeds the specified limit temperature.

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