Patent Application
20210131908
This application claims the benefit of priority from European Patent Application No. 19 306 326.0, filed on Oct. 10, 2019, the entirety of which is incorporated by reference.
The invention relates to a monitoring device for monitoring the leak-tightness of a vacuum-insulated system. The monitoring system is, for example, configured to monitor the vacuum of a vacuum-insulated transfer line or of a superconductive cable system. The invention also relates to a tubular coupling for connecting two vacuum-insulated systems, which may for example be a section of a transfer line or of a superconductive cable. The invention also relates to a vacuum-insulated system having a monitoring device, and/or having a tubular coupling, according to the invention. Finally, the invention also relates to a method for retrofitting a vacuum-insulated system with a monitoring device.
A vacuum-insulated system involves for example a pipe or a pipeline for conducting a cooled medium, for example a cryogenic liquefied gas, around which pipe or pipeline a vacuum insulation which is closed off outwardly by a metallic pipe and which is subjected to operation in a vacuum is present. Another frequent application for a vacuum-insulated system is a cryostat for a superconductive cable. The vacuum-insulated system normally has an outer pipe and an inner pipe, which are separated by an evacuated space that provides for the thermal insulation of an inner pipe. The evacuated space of a vacuum-insulated system is normally closed off in a hermetically sealed manner by a metallic wall. The evacuated space or “vacuum space” may in principle be any hermetically sealed space in which the intention is to maintain a vacuum of greater or lesser strength. The further embodiments, representing all the other possible uses, relate to such a vacuum insulation.
In order to identify a leakage—referred to below for short as “leak”—in the sealed “casing” of a vacuum space, a response threshold of several kPa is sufficient. Pressures in the region of 10−3 Pa are normal for a vacuum insulation. The vacuum insulation largely loses its effectiveness in the region of 0.1 Pa. In the event of the occurrence of a leak in the outer pipe delimiting the vacuum insulation, a pressure of approximately 105 Pa is attained after a short time, whereas in the event of a leak in the inner pipe, a pressure, corresponding to the operating pressure, of for example up to 2 MPa can occur after a short time.
For the purpose of monitoring the vacuum, it is proposed in EP 1 953 517 A1 to connect a metallic corrugated bellows to the vacuum space in a hermetically sealed manner. If a leak occurs in the vacuum space, then the corrugated bellows extends and actuates a proximity switch which generates a signal which indicates a leak.
The corrugated bellows of the known monitoring device is welded onto the outer pipe of the vacuum-insulated system. The proximity switch is connected to a power supply, which provides the electrical energy required for the operation.
Taking this as a starting point, the object of the present invention is to provide a monitoring device for monitoring the leak-tightness of a vacuum-insulated system that is easier to attach and/or that increases the operational reliability of the vacuum-insulated system.
To achieve said object, the invention proposes, according to a first aspect, a monitoring device for monitoring the leak-tightness of a vacuum-insulated system. The monitoring device has a corrugated bellows which is connected in terms of flow to an evacuated space of the vacuum-insulated system in such a way that, in the event of an increase in pressure in the evacuated space, the length of the corrugated bellows is adjusted beyond a threshold value. A position detector connected to an energy store responds to the change in length of the corrugated bellows and outputs a signal.
The monitoring device of the vacuum-insulated system is independent of the operational control unit for the system, which is generally present anyway. The monitoring system thus constitutes a redundant safeguarding system which functions independently of an operational control unit. The energy store, which may for example be a battery or a pressure store for a fluid, supplies energy to the position detector. The energy store also gives the monitoring device the characteristic of functioning independently of the public electricity supply. In this way, a high degree of operational reliability is advantageously achieved for the vacuum-insulated system.
According to one embodiment, the monitoring device is arranged on a cover which is able to be mounted onto a flange of the vacuum-insulated system. This embodiment of the monitoring device is able to be retrofitted easily in that, for example, a blind cover of the vacuum-insulated system is replaced by a cover having the monitoring device arranged thereon.
In an expedient refinement of the monitoring device, the position detector is connected to a display device, which receives the signal of the position detector and indicates a leak in the vacuum-insulated system.
The display device may be situated for example in a control station, so that operating personnel can react to the indication of a leak with countermeasures or protective measures, for example activate additional vacuum pumps.
Advantageously, in one exemplary embodiment, the position detector is connected to a safeguarding device, which receives the signal of the position detector and initiates a measure for safeguarding the vacuum-insulated system. The advantage of this exemplary embodiment is that, even without the active intervention of operating personnel, protective measures can be initiated, automatically.
The position detector advantageously outputs the signal to the display device if the increase in pressure exceeds a first threshold value, and outputs a further signal to the safeguarding device if the increase in pressure exceeds a second threshold value.
In this embodiment, operating personnel can keep a small leak under control, for example by activating one or more additional vacuum pumps. Protective measures are initiated automatically, for example in that a pressure-relief valve is opened, only if the increase in pressure exceeds a second threshold value.
According to a second aspect of the invention, a tubular coupling having a monitoring device according to the first aspect of the invention which is arranged in an outer wall of the tubular coupling is proposed. The tubular coupling has the advantage that, with this, it is possible for vacuum-insulated systems to be retrofitted in a simple manner with the monitoring device.
According to a third aspect of the invention, a vacuum-insulated system having a monitoring device according to the first aspect and/or having a tubular coupling according to the second aspect of the invention is proposed.
Finally, according to a fourth aspect of the invention, a method for retrofitting a superconductive cable system with a monitoring device for monitoring the leak-tightness of a vacuum-insulated system is proposed. The method comprises
The invention will be discussed in more detail below by way of example on the basis of exemplary embodiments and with reference to the accompanying figures. All the figures are purely schematic and not to scale. In the figures:
Identical or similar elements are provided with identical or similar reference signs in the figures.
The outer pipe 101 has an opening 107. The opening 107 is closed off in a hermetically sealed manner by a metallic corrugated bellows 108. A first end of the corrugated bellows 108 is closed off in a vacuum-tight manner by a closure 109, while a second end of the corrugated bellows 108 is open and is welded on over the opening 107 of the outer pipe 101. In principle, other types of connection are also possible. It is only necessary that the connections are vacuum-tight. An inner space 111 of the corrugated bellows 108 is thus connected in terms of flow to the evacuated space 104. The corrugated bellows 108 consists of metal, for example of high-grade steel with a wall thickness of for example 0.1 mm to 0.4 mm. However, other materials, for example copper or a fibre-reinforced plastic, may also be considered for the corrugated bellows 108. Arranged around the corrugated bellows 108 is a protective pipe 112, which, for example, is welded on the outer pipe 101 and surrounds the corrugated bellows 108 with a radial spacing. A proximity switch 113 is arranged on that end of the protective pipe 112 opposite the corrugated bellows 108 and is sealed off with respect to an inner side of the protective pipe 112 by a sealing element 114. The corrugated bellows 108 and the proximity switch 113 are surrounded in a substantially sealed manner by the protective pipe 112 and, in this way, effectively protected from environmental influences. Nevertheless, approximately atmospheric pressure prevails in the inside space of the protective pipe 112.
The length of the protective pipe 112 is dimensioned such that the corrugated bellows 108, in the relaxed state, approaches the proximity switch 113 but does not make contact with it. The relaxed state of the corrugated bellows 108 is established if atmospheric pressure prevails in the normally evacuated space 104. In
If, in the event of an operational fault of the vacuum-insulated pipeline 100, a positive pressure is formed in the evacuated space 104, then the closure 109 of the corrugated bellows 108 comes into contact with an end side 110 of the proximity switch 113 and supports the corrugated bellows 108. This prevents the corrugated bellows 108 from being damaged in a positive pressure situation. The monitoring system 101 formed in this manner is an extremely robust system.
The proximity switch 113 is connected to an energy store 115. The energy store 115 is an electric battery in one exemplary embodiment. Furthermore, the proximity switch may also be connected to an electrical supply network. The proximity switch 113 is, in signal terms, also connected to an evaluation and display device 116 and to a safeguarding device 117. The safeguarding device 117 is for example a relief valve or the like. The proximity switch is preferably of a two-stage design, that is to say, in the event of increasing pressure in the evacuated space, upon exceedance of a first threshold value, firstly only a signal is output to the display device 116, and, if the pressure continues to increase and exceeds a second threshold value, then a signal is also output to the safeguarding device 117, with the result that the safeguarding device 117 responds.
The components welded onto the outer pipe 101 form, in cooperation with the proximity switch 113, a monitoring device, denoted overall by the reference sign 118, which monitors the vacuum in the evacuated space 104 of the pipeline 100.
In other exemplary embodiments (not illustrated), the monitoring device 118 comprises no energy store 115 and/or no safeguarding device 117.
If existing pipelines 100 are intended to be retrofitted with a monitoring device 118 described in
Using the example of a superconductive cable system, the intention is to describe an alternative embodiment of the monitoring device that is able to be retrofitted without welding tasks.
For the purpose of explanation,
The superconductive cable 201 is constructed in a two-part manner from a first superconductive cable 211 and a second superconductive cable 212, which are connected to one another by a connecting tubular coupling 213. The connecting tubular coupling 213 establishes a superconductive connection between the individual superconductors in the cables 211 and 212.
A vacuum pump 214 is moreover connected to the connecting tubular coupling, in order to maintain the vacuum in the evacuated space of the superconductive cable 201. Moreover, a monitoring device 301, illustrated in
The lid 306 has an opening 307. The opening 307 is closed off in a hermetically sealed manner by a corrugated bellows 108 and establishes a connection in terms of flow to the insulating vacuum. Furthermore, the monitoring device 301 is constructed in the same way as the monitoring device 118.
That embodiment of the monitoring device 301 which is described in
The monitoring devices 118 and 301 function in the same manner, which is described as follows:
During operation, the pipeline 100 or the superconductive cable system 300, including the inside space 111 of the corrugated bellows 108, is in an evacuated state. Below, for the sake of brevity, reference is made to a vacuum-insulated system, which may be both a pipeline 100 and a superconductive cable system 300. The difference in pressure between the inside space 111 and the space outside the corrugated bellows 108 leads to the corrugated bellow 108 being compressed in its longitudinal direction. The compressed state of the corrugated bellows 108 is illustrated in
If the pressure continues to increase and exceeds a second threshold value, then the closure 109 approaches the proximity switch 113 up to a second spacing, which is smaller than the first spacing. The proximity switch 113 then also outputs a signal to the safeguarding device 117. The safeguarding device 117 is for example a relief valve which opens, when addressed by signals, so as to prevent, in the event of a leak of the inner pipe, formation of a positive pressure in the vacuum-insulated system due to evaporation of the cryogenic medium, which positive pressure could lead to damage. One particular advantage of the monitoring device is that it still functions even if a power failure in the general supply network is present, because the energy store 115 supplies it with the is energy required for the operation. In this way, increased operational reliability of the vacuum-insulated system is achieved.
In other exemplary embodiments, the proximity switch 113 is only of a single-stage design. In these exemplary embodiments, the response of the proximity switch 113 either initiates only a corresponding indication on the display device 116 or initiates the actuation of the safeguarding device 117. In a further exemplary embodiment, both actions are realized one after the other or at the same time.
In a modified exemplary embodiment, the energy store 115 is a pressure store which contains a pressurized fluid, such as for example compressed air, and the proximity switch 113 is designed as a fluid switch which is mechanically coupled to the corrugated bellows 108. The mechanical coupling is not illustrated in
In principle, the monitoring device 118, 301, with a pressure switch, functions in the same way as in the above-described exemplary embodiments. If a first threshold value of the pressure in the evacuated space is attained, the proximity switch connects the pressure store 115 in terms of flow to the display device 116 on which the occurrence of a leak in the vacuum-insulated system is indicated. If the second threshold value is exceeded, then the proximity switch connects the pressure store 115 in terms of flow to the safeguarding device 117, so that for example a relief valve is hydraulically actuated. In another exemplary embodiment, the proximity switch is only of a single-stage design.
For existing vacuum-insulated systems, it may be the case that no unused connection pipe of the same type as the connection pipe 303 is available. In such cases, it is necessary to provide such a connection first of all, this being associated with complex welding tasks.
Alternatively, the present invention proposes to arrange the safeguarding device in an intermediate tubular coupling, which may for example be arranged at the place where a vacuum pump is installed in the vacuum-insulated system.
| Number | Date | Country | Kind |
|---|---|---|---|
| 19 306 326.0 | Oct 2019 | EP | regional |
