Containers for pressurized liquid gases, and level measuring systems

Abstract

According to the invention, there is provided a container (1) for pressurized liquid gas such as LPG or LNG, having an opening (2) leading from the outside to the inside of the container (1), and a microwave liquid level sensor (4) mounted on the outside of the container (1) above the opening (2) and configured to radiate a microwave beam towards the inside of the container (1) and to receive the microwave beam reflected from the surface of the liquid in the container (1). Between the microwave liquid level sensor (4) and the inside of the container (1) there is a lid (3) closing the opening (2), the lid (3) being made of a plastic material that is at least partially transparent to the microwave beam.

Description

[Technical field]

[0001] The present invention relates generally to the field of containers for storing liquid products and to a measuring device for determining and monitoring the filling level of a product stored in the container by a microwave transit time measurement method. More specifically, the subject or object of the invention is a container for pressurized liquid gas, for example LPG (liquefied petroleum gas) or LNG (liquefied natural gas), comprising a microwave fluid level sensor. The invention also relates to a liquid level measuring system. [Background technology]

[0002] Various devices are currently known for monitoring and measuring the fill level of liquid media in containers: these are, for example, mechanical float level indicators, magnetostrictive probes, ultrasonic sensors, and radar (microwave) tank gauges.

[0003] Each of these known devices has several drawbacks: some of them have mechanical moving parts that can clog or do not operate correctly at low liquid levels, others are difficult to install or replace on the vessel, require venting of the tank, or are expensive.

[0004] Known radar tank gauges work on the principle of microwave transit time measurement to determine the liquid level in a container: the filling level of the medium in the container is determined based on the transit time of a measurement signal, which is the distance between a microwave transmitted via an antenna towards the surface of the medium and the microwave reflected on the surface of the medium and received by a transceiver.

[0005] These known measuring devices or elements thereof are exposed to high pressures since some elements have to be mounted inside the container / tank or at least the tank needs to have through holes for mounting the sensors.

[0006] To protect the measurement electronics and microwave signal coupling in the transmitter from high pressure and aggressive chemicals, as well as to keep the radiation characteristics of the antenna constant, the multiple sensor elements or multiple sensitive elements of the antenna are sealed outside the container (tank).

[0007] WO 2003 / 046491 discloses a level measuring antenna which is protected from aggressive chemical media and high temperatures by being at least partially filled with a dielectric or dielectric material or a disk-shaped dielectric element.

[0008] WO 01 / 88488 discloses a filling level measuring device having an antenna, a hollow conductor and a hollow conductor connection in the form of a circuit board and a conductive body attached thereto, protruding into the hollow conductor. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] International Publication No. 2003 / 046491 [Patent Document 2] WO 01 / 88488 DISCLOSURE OF THEINVENTION

[0010] Summary of the Invention The object of the present invention is to achieve a simple and cost-effective solution for measuring the filling level of a liquid medium in a closed container, which overcomes the above-mentioned drawbacks.

[0011] According to a first aspect of the present invention, a container for pressurized liquid gas, e.g. LPG or LNG, is provided, the container having an opening leading from the outside to the inside of the container, on the outside of the container, for mounting a microwave liquid level sensor over the opening, configured to radiate a microwave beam towards the inside of the container and to receive a microwave beam reflected by a surface of the liquid in the container, the container further comprising a lid closing the opening, the lid being made of a plastic material that is transparent to at least a portion of said microwave beam.

[0012] Throughout this disclosure, "a lid formed of a material that is transparent to at least a portion of a microwave beam" means that the lid is formed of a material such that at least a portion of the microwave beam emitted from the sensor can pass through the lid and into the container, and at least a portion of the microwave beam reflected from the surface of the liquid in the container can pass through the lid and return to the sensor.

[0013] In one embodiment, the opening is provided with a flange for mounting a level sensor, and the lid described above is mounted onto this flange, preferably to the top (upper) part of the container.

[0014] In another embodiment, the lid is hermetically sealed (hermetically sealed).

[0015] In another embodiment, the lid is formed from a thermoformable plastic, resin, or polymer-based composite material (mixture) reinforced with inorganic (mineral) or synthetic materials.

[0016] In another embodiment, the lid is formed from a plastic material that has a similar coefficient of thermal expansion as the container in the operating temperature range of the LPG or LNG.

[0017] In another embodiment, the lid is formed from a modified polyamide.

[0018] In another embodiment, the lid is formed from polyaryletherketone, preferably polyetheretherketone.

[0019] In another embodiment, the lid is partially made of metal.

[0020] In another embodiment, the lid has a flat bottom or a convex spherical bottom.

[0021] In another embodiment, the container further includes a microwave level sensor mounted on the outside of the container over the opening and configured to emit a microwave beam toward the inside of the container and receive a microwave beam reflected by the surface of the liquid in the container, and mounting means configured for assembling and disassembling the microwave level sensor from the container without removing a lid, the lid closing the opening in the container and being positioned between the fluid level sensor and the inside of the container.

[0022] In another embodiment, the microwave liquid level sensor is configured to analyze the received microwave beam using an algorithm, preferably an adaptive algorithm.

[0023] According to a second aspect of the present invention, there is provided a liquid level measurement system including the container disclosed above and further including a data logging device.

[0024] In one embodiment, the system further includes a display, preferably an LCD display or an ePaper display.

[0025] In another embodiment, the system further includes a power source, preferably a battery or a photovoltaic cell.

[0026] In yet another embodiment, the photovoltaic cell is a silicon-based cell or a perovskite-based cell.

[0027] The invention will now be explained in more detail with reference to the drawings. [Brief description of the drawings]

[0028] [Figure 1] FIG. 1 is an exploded view of a liquid level measurement system according to a preferred embodiment of the present invention. [Diagram 2] FIG. 2 is a bottom view (perspective view) of the lid. [Diagram 3] FIG. 3 is an obstacle detection chart measured by the liquid level measurement system. [Figure 4] FIG. 4 is an exploded side view (perspective view) of the liquid-level measurement system excluding the container. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0029] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Tanks for storing liquids, such as petroleum (gasoline) and other flammable products, are generally metal containers that are hermetically sealed to prevent any vapors from escaping the container and to prevent any substances from entering the container. Some flammable products are stored under pressure, i.e. the pressure inside the container is higher than the pressure outside the container.

[0030] FIG. 1 shows in an exploded view a liquid level measuring system according to a preferred embodiment of the invention. The vessel 1 (only a partial view is shown) is a metal tank for storing pressurized liquid gas, e.g. LPG (liquefied petroleum gas) or LNG (liquefied natural gas). Since gas is valuable, information about the amount of stored liquid is of great importance during the life of the vessel. A sudden drop in the gas level may indicate a gas leak in the storage or supply system. For this reason the vessel 1 has an opening 2 (a through hole in the tank wall) leading from the outside to the inside of the vessel 1. A microwave level sensor 4 is mounted on the outside of the vessel 1 above this opening 2. The microwave level sensor 4 emits a microwave beam towards the inside of the vessel 1 and receives back the signal reflected by the surface of the liquid. Part of the emitted microwave beam passes through the lid, while the rest is reflected or scattered by the lid 3. A portion of the transmitted beam continues toward the surface of the liquid, a portion of the beam reflected from the surface passes through the lid 3 again and returns to the sensor 4, and the other portion penetrates the liquid and travels toward the bottom of the container 1. After reaching the bottom, a portion of the microwave beam reflected from the bottom also travels back toward the sensor 4.

[0031] By calculating the time or frequency difference (difference) between the emitted microwave beam and the microwave beam reflected from the surface of the liquid in the container 1 and received by the microwave level sensor 4, the liquid level or the level of the liquid can be estimated. Based on this estimation, the filling level of the liquid can be determined or measured. The microwave level sensor 4 may be configured and programmed to perform such an estimation.

[0032] In a preferred embodiment, the microwave liquid level sensor 4 can receive all reflected beams (i.e., beams reflected by various surfaces, including the gas surface) and select only the beams reflected by the surface of the liquid stored in the container 1 to measure the liquid level. An algorithm for selecting the appropriate beam based on a signal analysis algorithm such as FFT (Fast Fourier Transform) and / or an adaptive algorithm based on machine learning algorithms can be used. Figure 3 is a chart showing two reflected beams received and analyzed. The first beam with the larger amplitude is the beam reflected by the lid 3 itself. The second beam with the smaller amplitude is the beam reflected by the gas surface. The more reflections and refractions of the beam are possible (the more possible), the more complex the received beam chart can become.

[0033] As mentioned at the beginning, the liquid stored in the container is flammable and chemically aggressive. Direct contact with the microwave liquid level sensor 4 could damage the sensor or its elements. In the worst case, the vapours could even ignite due to an electric spark generated by the sensor's electronics. Therefore, the container 1 is provided with a lid 3 that closes the opening 2 and seals the container 1.

[0034] The lid 3 is made of a plastic that is at least partially transparent to microwaves. Preferably, the plastic is a synthetic polymer, a thermoplastic polymer, such as polyaryletherketone (PAEK) or polyetheretherketone (PEEK), or a resin-based polymer. In some preferred embodiments, the lid 3 is made of a polymer-based composite material reinforced with inorganic or synthetic materials. The lid 3 must be as strong as the container 1 and must withstand the harsh conditions of the stored gas inside the container 1. It must also withstand the harsh weather conditions outside the container. The container 1 contracts and expands while being filled, discharged (emptied), and heated (e.g. by sunlight during outdoor storage) or cooled (e.g. during depressurization of the pressurized gas stored inside). The main function of the lid 3 is to seal the container and withstand mechanical stresses in the same manner as the container 1, while being at least partially transparent (semi-transparent) to microwaves. Partially transparent (semi-transparent) means that at least a part of a microwave beam directed at the lid 3 can pass through it.

[0035] The lid 3 is securely (rigidly) and airtightly attached to the container 1, preferably by screws, bolts, rivets, adhesive or a press fit. The attachment needs to be strong enough to hold the pressure and temperature of the stored liquid.

[0036] In one preferred embodiment of the invention, a container 1 suitable for pressurized liquid gas, for example LPG or LNG, is realized. The container 1 has an opening 2 leading from the outside to the inside of the container 1, suitable for mounting a microwave liquid level sensor 4 on the outside of the container 1 over (covering) the opening 2. The container 1 further comprises a lid 3 closing the opening 2, said lid 3 being made of a plastic material that is at least partially transparent and / or translucent, meaning that at least a part of the microwave beam directed at the lid 3 can pass through, when the microwave beam is directed at the lid 3. The lid 3 is attached to the container 11. In a preferred embodiment, the container 1 has a flange around the opening 2. The flange is part of the wall of the container 1, the part of the wall having a thickness around the opening 2 that is thicker (greater) than the thickness of the remaining part of the wall of the container 1. The flange has a flat surface on the upper side parallel to the ground, suitable for mounting any kind of level sensor (mechanical, acoustic, microwave) or lid 3. In a preferred embodiment, the lid 3 is mounted on the flange to allow good leveling of the level sensor 4 when mounted on the lid 3. The flange is placed on the top of the vessel 1 for more accurate measurements. The flange for mounting the lid 3 and / or the level sensor 4 can be placed in various positions. Also, the angle of the flat surface of the flange could be varied.

[0037] The lid 3 is hermetically sealed using a sealing element 6, such as a rubber O-ring, or any other method, such as gluing, press-fitting, or hermetically screwing in. The lid 3 is preferably made of a plastic material that has the ability to deform under high pressure and conform to surfaces to seal the connection.

[0038] The lid 3 is preferably made of a thermoformable plastic material to facilitate the manufacturing process using injection molding or 3D printing techniques, but it can also be made of a resin or polymer-based composite material reinforced with inorganic (mineral) or synthetic materials.

[0039] In some embodiments, the lid 3 is partially made of metal with a small portion of plastic material forming a window-like structure in the middle, which reinforces the lid 3 in its outer portion or on its edges.

[0040] In one embodiment, the liquid level measurement system includes a microwave focusing element on the side of the lid 3 facing the inside of the container 1, preferably on the bottom side. The focusing element of the lid constitutes a bottom surface of a specific shape suitable for shaping the microwaves generated by the sensor into a beam of a certain shape. Containers of different shapes and with different liquids may require beams of different shapes to obtain better measurement accuracy. The microwave beam propagating in the metal container may be reflected, focused or scattered in a complex manner that makes it difficult to detect the reflected beam. As a result, the measurement accuracy is very low. In a preferred embodiment, the focusing element has a central convex spherical shape. A convex spherical shape is preferred for cylindrical shaped metal containers filled with liquid gas, for example LPG or CNG.

[0041] In another preferred embodiment, the lid 3 has a flat bottom surface. A flat surface makes it less likely that condensed gas or water droplets will accumulate in one specific location. This makes the measurement more accurate.

[0042] In a preferred embodiment, the container 1 further comprises a microwave level sensor 4 mounted on the outside of the container 1 above (covering) the opening 2. The microwave level sensor 4 is configured to emit a microwave beam towards the inside of the container 1 and to receive the beam reflected at the liquid surface. The microwave level sensor 4 also comprises mounting means configured to mount (assemble) and remove (disassemble) the microwave level sensor 4 from the container 1 without removing the lid 3. The microwave level sensor 4 is configured to receive all reflected and / or scattered beams and to select the beam reflected at the liquid surface.

[0043] The microwave liquid level sensor 4 may be attached to the lid 3 using screws, threads, a bayonet mount, press fit, magnets, adhesive, or other means suitable for easily separating the microwave liquid level sensor 4 from the lid 3.

[0044] A cover 5 is preferably used to protect the microwave liquid level sensor 4 from the outside world.

[0045] In yet another embodiment of the invention, the liquid level measurement system includes a data logging device, which typically consists of a microprocessor unit with data storage elements and a CPU unit programmed for level calculations, information storage and / or communication. In a preferred embodiment, the microwave liquid level sensor 4 is communicatively connected to another data processing unit via wireless communication means or cable connection. This includes Internet communication via cable infrastructure or wireless, e.g. WI-FI, GSM, Bluetooth, etc.

[0046] In some embodiments, the liquid level measurement system further includes a display, preferably an LCD display or an ePaper display suitable for presenting information regarding at least the liquid level in the container.

[0047] The liquid level measurement system may include a power source, preferably a battery or a photovoltaic cell, which may be a silicon-based cell or a perovskite-based cell.

[0048] In another preferred embodiment, the liquid level measurement system is configured to process information about the received signal relative to / from the interior of the vessel. The signal is processed using advanced signal processing methods such as Fast Fourier Transform (FFT) etc. to measure other liquid parameters such as composition, purity, temperature, density, rheology etc. In another embodiment, the liquid level measurement system is configured to measure the above mentioned parameters of the vapor above the liquid surface.

[0049] The microwave liquid level sensor 4 according to the invention uses a tank liquid level measurement method based on radar technology. The radar system offers high accuracy, low power solution and quick and easy installation in the tank without interfering with the tank structure. It offers radio band operation without interference (jamming) from noise, dust, color, direct or indirect light. The sensor operates at 60 GHz and offers an accuracy of a few mm at distances up to 5 m.

[0050] Radar measurement technology can penetrate plastic obstacles, which allows accurate liquid level measurement with a sensor positioned outside the tank. The sensor must be positioned at the top of the tank. Examples of sensor response and detection of possible obstacles and liquid level are provided.

Claims

1. A container for pressurized liquid gas, An opening in the container that extends from the outside to the inside, the outside of the container having an opening above the opening for mounting a microwave liquid level sensor configured to emit a microwave beam toward the inside of the container and to receive the microwave beam reflected by the surface of the liquid inside the container, Furthermore, the lid for closing the opening is made of a plastic material capable of transmitting at least a portion of the microwave beam, container.

2. The container according to claim 1, wherein a flange for attaching a liquid level sensor is provided in the opening, and the lid is attached on the flange.

3. The container according to claim 2, wherein the flange constitutes a part of the wall of the container that is thicker than the rest of the container.

4. The container according to claim 1, wherein the lid is airtight.

5. The container according to claim 1, wherein the lid is formed of a thermoformable plastic, resin, or polymer-based composite material reinforced with inorganic or synthetic materials.

6. The container according to claim 1, wherein the lid is made of a plastic material having the same coefficient of thermal expansion as the container in the operating temperature range of LPG or LNG.

7. The container according to claim 1, wherein the lid is made of modified polyamide.

8. The container according to claim 1, wherein the lid is made of polyaryletherketone (PAEK).

9. The container according to claim 8, wherein the metal portion of the lid is located on the outer part of the lid, and the plastic material forms a window-like structure in the center of the lid.

10. The container according to claim 1, wherein the lid is partially made of metal.

11. The container according to claim 1, wherein the lid has a flat bottom surface or a convex spherical bottom surface.

12. Furthermore, the container includes a microwave liquid level sensor mounted on the outside of the container above the opening and configured to emit a microwave beam toward the inside of the container and to receive the microwave beam reflected by the surface of the liquid inside the container, and mounting means configured to attach or detach the microwave liquid level sensor from the container without removing the lid, The lid closes the opening in the container and is positioned between the liquid level sensor and the inside of the container. The container according to claim 1.

13. The container according to claim 12, wherein the microwave liquid level sensor is configured to analyze the received microwave beam using an adaptive algorithm.

14. The container according to claim 1, wherein the lid includes a central portion having a groove, and a sealing element is disposed in the groove surrounding the opening to seal the space between the lid and the opening of the container.

15. The container according to claim 1, wherein the pressurized liquefied gas is either liquefied petroleum gas (LPG) or liquefied natural gas (LNG).

16. The container according to claim 1, wherein the lid is made of polyetheretherketone (PEEK).

17. A container for pressurized liquid gas containing LPG or LNG, the container having an opening that extends from the outside to the inside, the opening on the outside of the container above the opening for mounting a microwave liquid level sensor configured to emit a microwave beam toward the inside of the container and to receive the microwave beam reflected by the surface of the liquid inside the container, and further comprising a lid that closes the opening, the lid being made of a plastic material that can transmit at least a portion of the microwave beam, Data logging device, A liquid level measurement system including a liquid level measurement system.

18. Furthermore, the system according to claim 17, further comprising a display.

19. Furthermore, the system according to claim 17, including a power supply.

20. The system according to claim 19, wherein the power source is a photocell.

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