Fill-level radar device and liquid-gas tank

Abstract

A fill-level radar device designed for process automation in an industrial environment, comprising a flexible wave guide that can be wound up and a first end of which is connected to an electronic circuit of the fill-level radar device via a first interface.

Description

[0001] Level radar and LPG tank

[0002] Reference to related applications

[0003] This application claims priority from German patent application No. 10 2023 205 428.0, filed on June 12, 2023, which is incorporated in its entirety by reference into this document.

[0004] Technical area

[0005] The present disclosure relates to level measurement technology. In particular, the present disclosure relates to a level radar device configured for process automation in an industrial environment, the use of a flexible, windable waveguide for determining the level in the liquefied gas tank, and a liquefied gas tank with such a flexible, windable waveguide.

[0006] background

[0007] Liquefied gas tanks often have to be transported over long distances, for example by sea. Level gauges can be used to obtain an overview of the current tank contents. One example is pressure gauges installed in the tank that measure the pressure at the bottom of the container, which can then be converted into a fill level.

[0008] Since the liquefied gas in the tanks has a significantly lower temperature than the ambient temperature, effective insulation of the tank is advantageous. When using measuring devices in the tank, this insulation aspect should not be forgotten to minimize losses. Summary

[0009] Against this background, it is an object of the present disclosure to provide an alternative level determination in containers and in particular in liquid gas tanks, which enables simple installation and good thermal insulation of the tank.

[0010] This object is achieved by the features of the independent patent claims. Further developments of the invention emerge from the subclaims and the following description of embodiments.

[0011] A first aspect of the present disclosure relates to a level radar device configured for process automation in an industrial or private environment. The term "process automation in an industrial environment" also includes level measurement during the transport of liquefied gas tanks.

[0012] The level measuring device has a flexible, windable waveguide which is connected to an electronic circuit or a measuring device housing of the level radar device via a first interface located at a first end of the waveguide.

[0013] The electronic circuit of the level radar device is typically located outside the liquid gas tank or the process vessel in which the filling material is located.

[0014] It can be provided that the first interface has temperature insulation.

[0015] Flexible, coilable waveguides can be provided in sufficient length on a roll during installation or construction of the vessel, making it easy to equip the vessel.

[0016] This reduces the costs of otherwise very expensive level measurements in containers, especially in liquefied gas tanks. The installation of expensive rigid standpipes for level measurement is also no longer necessary. The term "process automation in industrial environments" can be understood as a branch of technology that includes measures for operating machines and systems without human intervention. One goal of process automation is to automate the interaction of individual components of a plant in the chemical, food, pharmaceutical, petroleum, paper, cement, shipping, or mining industries. A variety of sensors can be used for this purpose, which are specifically adapted to the specific requirements of the process industry, such as mechanical stability, insensitivity to contamination, extreme temperatures, and extreme pressures.Measured values ​​from these sensors are usually transmitted to a control room, where process parameters such as fill level, limit level, flow, pressure or density can be monitored and settings for the entire plant can be changed manually or automatically.

[0017] A sub-area of ​​process automation in the industrial environment concerns the logistics automation of plants and the logistics automation of supply chains. With the help of distance and angle sensors, processes inside or outside a building, or within a single logistics facility, are automated in the field of logistics automation. Typical applications for logistics automation systems include baggage and freight handling at airports, traffic monitoring (toll systems), retail, parcel distribution, and building security (access control). What the aforementioned examples have in common is that the respective application requires presence detection in combination with precise measurement of the size and location of an object.For this purpose, sensors based on optical measuring methods using lasers, LEDs, 2D cameras or 3D cameras that measure distances according to the time of flight (ToF) principle can be used.

[0018] Another sub-area of ​​process automation in the industrial environment concerns factory-to-production automation. Applications for this can be found in a wide variety of industries, such as automotive manufacturing, food production, the pharmaceutical industry, and packaging in general. The goal of factory automation is to automate the production of goods using machines, production lines, and / or robots, i.e., to run the process without human intervention. The sensors used here and the specific requirements regarding measurement accuracy for detecting the position and size of an object are comparable to those in the previous example of logistics automation.

[0019] The terms used in the claims should be construed to give them the broadest possible reasonable interpretation consistent with the foregoing description. For example, the use of the article "a" or "the" in introducing an element should not be construed to exclude a plurality of elements. Likewise, the mention of "or" should be construed to include a plurality of elements, so that the mention of "A or B" does not exclude "A and B" unless it is clear from the context or the preceding description that only one of A and B is intended.Furthermore, the phrase "at least one of A, B, and C" should be understood as one or more elements from a group of elements consisting of A, B, and C, and should not be interpreted as requiring at least one of each of the listed elements A, B, and C, whether A, B, and C are related as categories or otherwise. Furthermore, the reference to "A, B, and / or C" or "at least one of A, B, or C" should be interpreted to include each individual unit of the listed elements, e.g., A, each subset of the listed elements, e.g., A and B, or the entire list of elements A, B, and C.

[0020] According to this aspect of the present disclosure, the waveguide is designed as a (flexible) standpipe with an opening at the lower end for the entry of liquid gas and with one or more vent holes for pressure equalization.

[0021] According to a further embodiment of the present disclosure, the level radar device comprises an antenna connected to the waveguide via a second interface at a second end of the waveguide opposite the first end.

[0022] It can be provided that the second interface has temperature insulation. A "second line of defense" can also be provided in the area of ​​the second interface, which serves to seal the tank when the electronic circuit is removed. For example, a glass window with a thickness dependent on the dielectric constant and the relevant regulations for explosion protection is dimensioned precisely so that reflections at the glass window are minimal. The glass window consists of a metal sleeve that is filled with the glass in a melting process. The glass window is inserted axially into the waveguide and welded to the metal sleeve so that the waveguide is sealed pressure-tight. This prevents, for example, flammable gases or liquids from penetrating the waveguide into the area of ​​the electronics, igniting there and, in the worst case, triggering an explosion.

[0023] According to a further embodiment of the present disclosure, the waveguide is made of or comprises temperature-insulating material.

[0024] Suitable plastics are preferably used here. These should be flexible and low-damping at the intended operating frequency.

[0025] According to another embodiment of the present disclosure, the waveguide has an inner diameter of less than 6.5 mm.

[0026] The diameter depends on the operating frequency used. If the diameter is chosen too small, it will exhibit excessive attenuation. If it is chosen too large, higher-order modes will form, which will interfere with the desired signal and thus limit the measurement accuracy. An inner diameter of 6.5 mm is suitable for an operating frequency of 80 GHz.

[0027] According to a further embodiment of the present disclosure, the waveguide is designed as a hollow guide.

[0028] A further aspect of the present disclosure relates to the use of a flexible, windable waveguide for determining the fill level in a liquefied gas tank. The waveguide is connectable to an electronic circuit of a fill level radar device via a first interface at a first end of the waveguide and is provided for at least partial installation in the wall of the liquefied gas tank. The electronic circuit of the fill level radar device can thus be connected to it outside the liquefied gas tank. A further aspect of the present disclosure relates to a liquefied gas tank comprising a flexible, windable waveguide that is connectable to an electronic circuit of a fill level radar device via a first interface at a first end of the waveguide and is located at least partially in the wall of a liquefied gas tank, so that the electronic circuit of the fill level radar device can be connected to it outside the liquefied gas tank.

[0029] Embodiments of the present disclosure are described below with reference to the figures. Where the same reference numerals are used in the following description of the figures, they denote identical or similar elements. The representations in the figures are schematic and not to scale.

[0030] Short description of the characters

[0031] Fig. 1 shows a cross-sectional view of a liquefied gas tank with a

[0032] Level radar device according to an embodiment of the present disclosure.

[0033] Fig. 2 shows a cross-sectional view of a liquefied gas tank with a

[0034] Level radar device according to another embodiment of the present disclosure.

[0035] Fig. 3 shows a cross-sectional view of a liquefied gas tank with a level radar device according to another embodiment of the present disclosure.

[0036] Detailed description of embodiments

[0037] Fig. 1 shows a cross-sectional view of a liquefied gas tank 105 with a radar level detector 100 installed therein. When measuring levels in containers, especially gas tanks, installing standpipes for level measurement has proven to be very complex and costly. These must be arranged in a row, and the connection points must be free of any mechanical protrusions, as these can cause reflections.

[0038] In liquefied natural gas (LPG) tanks, liquefied natural gas is stored in highly insulated tanks. A standpipe that runs a short distance through the insulation weakens the insulation. The liquefied natural gas is transported at a low overpressure (a membrane tank, for example, has a maximum of 230 mbar) and a temperature of -164°C to -161°C. Liquid hydrogen, on the other hand, is transported at -253°C. Good insulation is very important because a reliquefaction plant is not provided for transport by ship, as this is not economically viable.

[0039] This places considerable demands on the use and manufacture of custom standpipes. Their arrangement must be carefully planned and comes pre-configured from the sensor manufacturer. This is complex and can be simplified as described below.

[0040] It is proposed to use a level radar device 100 whose electronic circuit 106 is arranged outside the liquefied gas tank 105. An antenna 103 is arranged inside the liquefied gas tank 105 and can be attached to the inner wall of the container 105. A flexible, windable waveguide 101 is provided between the antenna 103 and the electronic circuit 106. The waveguide has a first interface 102 at an upper end of the waveguide 101, to which the electronic circuit 106 of the level radar device 100 is connected.

[0041] At the opposite end of the waveguide 101 there is a second interface 104 to which the antenna 103 is connected.

[0042] It should be noted at this point that the flexible, windable waveguide 101 can also be a rigid waveguide.

[0043] The electronic circuit 106 of the level radar device 100 is removable. Typically, the flexible, coilable waveguide 101 and the antenna 103 are installed during the manufacturing process of the liquefied gas tank 105. Once the tank has been moved onto the ship, the electronic circuit 106 of the level radar device 100 can then be connected.

[0044] The level radar device can have an operating frequency of 60 GHz or more and be designed for measurement in a temperature range of -150°C or below. In particular, so-called explosion protection can be provided to prevent the risk of fire or explosion. The level radar device 100 of Fig. 1 measures non-contact, so that the antenna 103 can be mounted on the top of the inner container and is thus located at a distance from the surface of the liquefied gas 107.

[0045] The radar antenna 103 is mounted inside the insulated, double-walled container 105. The sensor electronics are mounted inside the container, either outside or through a maintenance hatch. Between the antenna 103 and the sensor electronics 106, the waveguide or hollow guide 101 connects the two units 103, 106. Appropriate interfaces 102, 104 are used for these connections. These interfaces 102, 104 meet the necessary requirements regarding length compensation and angle adjustment and exhibit excellent high-frequency properties.

[0046] In most cases, it's not desirable to install openings in the upper part of LPG tanks. These gas tanks are only provided with openings on the side, if necessary.

[0047] To transmit the radar signals toward the ground, it is possible to use a deflection unit, for example, in the form of metallic radar mirrors, to redirect the radar signals toward the bottom of the container. These mirrors can be attached to the antenna or to the container itself (not shown in the figures).

[0048] Fig. 2 shows a cross-sectional view of a liquefied gas tank 105 with a level radar device 100 according to another embodiment of the present disclosure. The waveguide 101, which may be embodied as a hollow waveguide, is also flexible and "off the reel," allowing it to be installed on-site.

[0049] To avoid thermally short-circuiting the insulation of the LPG tank 105, it is possible to manufacture the waveguide 101 from a material that is as thermally insulating as possible. The length of the waveguide 101 in the tank's insulation layer can also be increased (as shown in Fig. 2) to increase the temperature resistance across the length of the waveguide within the insulation.

[0050] This makes it possible to use a tube with a high-precision inner diameter as a waveguide, which also has good high-frequency properties. This flexible waveguide or hollow guide can be used in the setup described above.

[0051] A waveguide places very high demands on the surface inside the waveguide. The required surface roughness in waveguides is not directly related to the wavelength, but rather to the penetration depth of the field into the wall. This, in turn, depends on the specific resistance of the material used and the frequency.

[0052] As soon as the roughness reaches approximately the same order of magnitude as the penetration depth of the electromagnetic wave into the material, this begins to have an increasing effect through reflections and attenuation.

[0053] The following formula applies:

[0054] Penetration depth = 503 x p-.F, where p = specific resistance in Ohm x meter, F = frequency in Hertz.

[0055] At a penetration depth of 5 times, approximately 99% of the high-frequency current is captured.

[0056] When using stainless steel waveguides and frequencies of 80 GHz, a penetration depth of approximately 0.15 pm is achieved.

[0057] The corresponding requirements for other waveguides are less stringent.

[0058] Fig. 3 shows a liquid gas tank 105 with a fill level radar device according to another embodiment of the present disclosure. The fill level radar device has an electronic circuit 106 connected to a waveguide in the form of a standpipe. The standpipe runs from the electronic circuit 106, initially horizontally through the container wall and then bends vertically downwards to the container bottom or just before the container bottom. It is loosely attached to the container wall and threaded through, for example, using appropriate suspensions or clamps. It is important that the attachment has sufficient play so that the standpipe can contract or expand depending on the temperature. A "tube off the roll" can be used for the flexible, windable waveguide 101 in order to be attached on site with a corresponding interface to the electronic circuit 106 of the fill level radar device.The actual level measurement takes place in this tube. To allow the liquid to rise, one or more openings must be provided to allow pressure equalization. This pressure equalization can also be installed in the interface to prevent unwanted reflections elsewhere.

[0059] Typically, a standpipe is fed via a suitable antenna, which radiates the measurement signal into the standpipe. For a 26 GHz and an 80 GHz level radar, the standpipe has a diameter of approximately 48 to 50 mm.

[0060] In pulse radar devices, the pulsed measurement signal is transmitted directly from the electronics into the pipe. At 26 GHz, pipe diameters of 20 mm are often used.

[0061] For a pulse radar device operating at 80 GHz, the tube's inner diameter is approximately 6.5 mm, and correspondingly less at higher frequencies. To improve the tube's measurement properties, the number and size of the vent holes, as well as the number and thickness of the bends, must be selected appropriately. A single vent hole can be provided at the very top of the tube (but still inside the container) if the tube is open at the bottom.

Claims

Patent claims 1. A level radar device (100) configured for process automation in an industrial environment, comprising: a flexible, windable waveguide (101) connected to an electronic circuit (106) of the level radar device via a first interface (102) at a first end of the waveguide; wherein the waveguide (101) is designed as a standpipe with an opening at the lower end for the entry of liquefied gas and with one or more vent holes for pressure equalization.

2. Level radar device (100) according to claim 1, wherein the waveguide (101) consists of or comprises temperature-insulating material.

3. Level radar device (100) according to one of the preceding claims, wherein the waveguide (101) has an inner diameter of less than 6.5 mm.

4. Level radar device (100) according to one of the preceding claims, wherein the waveguide (101) is designed as a hollow guide.

5. Use of a flexible, windable waveguide (101) which can be connected to an electronic circuit of a level radar device via a first interface (102) at a first end of the flexible, windable waveguide, for at least partial installation in the wall of a liquid gas tank, so that the electronic circuit of the level radar device can be connected thereto outside the liquid gas tank, for determining the level in the liquid gas tank (105).

6. Liquid gas tank (105), comprising a flexible, windable waveguide (101) which is connected via a first interface (102) at a first end of the flexible, windable waveguide to an electronic circuit of a level radar device (100) and is at least partially located in the wall of a liquid gas tanks, so that the electronic circuit (106) of the level radar device can be connected to it outside the liquid gas tank.

7. The liquefied gas tank (105) according to claim 6, further comprising: an antenna (103) connected to a second end of the flexible, windable waveguide (101) is connected to the waveguide.

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