Magnetostatic extension liquid level measuring device for urea tower

Abstract

This invention discloses a magnetostrictive liquid level measuring device for urea towers. The technical solution includes a probe equipped with a magnetostrictive waveguide wire. The upper end of the probe is connected to a sensor and a data processing unit. A protective sleeve is fitted over the probe, and a float with a magnet inside is fitted through a flange at the lower end of the protective sleeve. A primary protective sleeve for the probe root is fitted over the protective sleeve below the flange, and the upper end of this primary protective sleeve is fixed to the flange, with a length equal to the vertical distance from the bottom of the flange to the highest allowable liquid level in the tower. This invention features a simple structure, ease of manufacture, and low cost. It possesses high precision, high reliability, and high stability, effectively resisting lateral liquid fluctuations caused by large impacts, and can operate stably for extended periods in high-temperature, high-pressure, and corrosive environments.

Description

Technical Field

[0001] This invention relates to a liquid level measuring device in the chemical industry, specifically a magnetostrictive liquid level measuring device for a urea tower. Background Technology

[0002] In the urea production process, the liquid level inside the urea tower is a critical parameter. Accurate measurement of the liquid level is essential for controlling the progress of the urea synthesis reaction, ensuring product quality, and guaranteeing production safety. The medium in the total condensation reactor of the urea plant is urea solution, with a design temperature of 198℃ and a design pressure of 16.2 MPa(g). The medium is characterized by high temperature, high pressure, strong corrosiveness, and easy crystallization. The use of various level measurement devices, such as glass tube level gauges and differential pressure level gauges, is greatly limited. Currently, two types of level gauges are widely used in urea towers: one is a radioactive level gauge with a Cs-137 radiation source, which emits radiation and requires 24-hour uninterrupted video monitoring. It incurs high annual maintenance costs and requires regular replacement of the rod source to achieve high measurement accuracy. The other type is the VEGA radar level gauge, which is patented by Carbon and is not sold separately.

[0003] A magnetostrictive level gauge is a high-precision measuring instrument capable of continuous liquid level and interface measurement, providing analog signal output for monitoring and control. It mainly consists of a probe equipped with a magnetostrictive waveguide wire, a float equipped with a permanent magnet, and a data processing unit (also known as a circuit unit). During measurement, the circuit unit generates a current pulse, which propagates downwards along the magnetostrictive waveguide wire, generating a circular magnetic field. When the current magnetic field meets the float's magnetic field, a "twisting" pulse, or "return pulse," is generated. The time difference between the "return" pulse and the current pulse is converted into a pulse signal, thereby calculating the actual position of the float and measuring the liquid level.

[0004] Magnetostrictive level gauges are commonly used for liquid level measurement in tanks, offering advantages such as high accuracy, high explosion-proof performance, and safe operation, making them suitable for measuring chemical raw materials and flammable liquids. However, in some special operating conditions, such as the environment inside a urea tower, the medium exhibits characteristics of high temperature, high pressure, strong corrosiveness, and easy crystallization, with impurities posing a risk of float jamming. Furthermore, the tower experiences significant lateral liquid fluctuations with strong impact forces, affecting not only accurate level measurement but also, because the probe of the magnetostrictive level gauge extends considerably downwards from the top of the tower, even with an added protective sleeve to increase rigidity, it is easily bent under lateral impact forces, leading to equipment deformation and other problems. Publication No. 212621016U discloses a magnetostrictive level gauge, including a liquid storage system and a magnetostrictive level gauge installed outside the liquid storage tank via a connecting pipe. External placement of the magnetostrictive level gauge can reduce the impact of liquid medium disturbance in the reaction tank on the level gauge and improve its service life. However, since it does not take into account the pressure-bearing capacity of the float under high pressure and the easy crystallization of liquid in the urea tower, there are problems such as float damage or float jamming.

[0005] Publication No. CN 216899146 U discloses a device for preventing float jamming in a magnetostrictive level gauge. The specific structure includes a magnetostrictive level gauge with a measuring rod fixedly connected to its lower end. A float is mounted on the measuring rod. The magnetostrictive level gauge is installed on the top flange of a storage tank. The measuring rod and float extend into the tank. This design includes a main venting pipe above the tank, extending into the tank and located on one side of the measuring rod. When impurities are present in the gap between the measuring rod and the float, the gap can be purged through the vent of the main venting pipe, cleaning the impurities and allowing the float to move normally, thus solving the problem of float jamming and inability to measure. However, this solution requires the introduction of a gas pipeline and purging of the medium, making it unsuitable for the high temperature, high pressure, highly corrosive, and easily crystallizing conditions of urea towers.

[0006] Therefore, we hope to develop a new type of magnetostrictive level gauge that is suitable for high temperature, high pressure and corrosive environments. Summary of the Invention

[0007] The purpose of this invention is to solve the above-mentioned technical problems and provide a magnetostrictive liquid level measuring device for urea towers that is simple in structure, easy to manufacture, low in cost, and has the characteristics of high precision, high reliability, and high stability. It can effectively resist the lateral fluctuation of liquid under large impact forces and can operate stably for a long time in high temperature, high pressure, and corrosive environments.

[0008] This invention relates to a magnetostrictive liquid level measuring device for urea towers, comprising a probe rod equipped with a magnetostrictive waveguide wire, the upper end of which is connected to a data processing unit, a probe rod protective sleeve being integrally fitted over the probe rod, and a float fitted through a flange at the lower section of the protective sleeve, the float containing a magnet; a primary protective sleeve for the probe rod root is fitted over the protective sleeve below the flange, the upper end of which is fixed to the flange, and its length is the vertical distance from the bottom surface of the flange to the highest allowable liquid level in the tower.

[0009] Preferably, a secondary protective sleeve is fitted over the primary protective sleeve at the root of the probe rod, and the upper end of the secondary protective sleeve is fixed to the flange, with a length of 1 / 2 of the total length of the primary protective sleeve at the root of the probe rod.

[0010] Preferably, the lower end of the probe protective sleeve is a sealed end, and the upper opening is sealed and locked to the probe by a retainer.

[0011] Preferably, the lower end of the probe protective sleeve is provided with a limiting member.

[0012] Preferably, a top buffer is installed on the probe protective sleeve below the probe root primary protective sleeve, and the upper end of the top buffer is fixed to the lower end of the probe root primary protective sleeve.

[0013] Preferably, a bottom buffer is installed above the limiting member at the lower end of the probe protective sleeve, and the lower end of the bottom buffer is fixed on the limiting member.

[0014] Preferably, the float is a hollow structure integrally formed with an inner tube, wherein the inner tube is fitted onto the probe protective sleeve, the middle section of the inner tube is a straight section protruding inward, and the upper and lower sections are inclined sections sloping outward.

[0015] Preferably, the length of the straight segment is 10%-12% of the total length of the inner tube.

[0016] Preferably, the wall thickness of the inner tube gradually increases from both ends toward the middle section.

[0017] Preferably, the float is filled with inert gas and has a pressure-resistant support.

[0018] Preferably, the inert gas is helium.

[0019] Preferably, the float has a top magnet for liquid level measurement at the top and a bottom magnet for self-calibration at the bottom.

[0020] Preferably, the self-calibration method is as follows: the distance between the top magnet and the bottom magnet inside the float is obtained as a fixed distance, denoted as L1; the time difference between the top magnet signal and the bottom magnet signal collected by the data processing unit at the current temperature is calculated and denoted as t1; the propagation speed v1 of the mechanical wave at the current temperature is calculated according to the formula v1=L1 / t1; and the liquid level value L in the urea tower at the current temperature is calculated as L=v1*t.

[0021] To address the problems in the background art, the inventors have made the following improvements: 1) The magnetostrictive level measuring device of this invention is directly installed on the urea tower and inserted into the medium for measurement, which is more accurate than the method of setting it outside the tower. Furthermore, to be applicable to the high-pressure environment of the urea tower, a protective sleeve is installed around the probe rod to form a double probe structure, greatly improving the pressure resistance and a certain degree of impact resistance. When used for level measurement inside the urea tower, the magnetostrictive level gauge needs to be installed at the top of the urea tower, and the probe rod protective sleeve needs to extend downwards into the tower by 4.5m or even longer. Under high pressure, the lateral fluctuation of the liquid inside the urea tower has a large impact force, and there is still a possibility of deformation. In-depth analysis revealed that this deformation stress is mainly concentrated at the root position below the flange. Therefore, this invention installs a primary protective sleeve at the probe root outside the probe rod protective sleeve below the flange. Further analysis shows that part of the probe rod protective sleeve extends below the liquid surface, while the impact force of the lateral fluctuation of the liquid is mainly concentrated at the liquid surface. Also, considering that… This design influences the float's range of motion, ensuring measurement reliability. The upper end of the primary protective sleeve at the probe root is fixed to the flange, with its overall length being the vertical distance from the flange bottom to the highest permissible liquid level in the tower. This means the lower end of the primary protective sleeve is located at the height of the highest permissible liquid level, increasing the rigidity of the probe protective sleeve above the highest permissible liquid level and improving the probe's resistance to lateral impact forces from the liquid surface. More preferably, considering the mechanical calculations of lateral forces, a secondary protective sleeve is fitted outside the primary protective sleeve, with its length limited to half the total length of the primary protective sleeve. This two-stage design lowers the actual fixing point of the probe protective sleeve, significantly limiting the swaying deformation of the protective sleeve caused by lateral impacts from the high-pressure liquid in the tower, thus enhancing the device's resistance to lateral impact forces.

[0022] 2) In response to the problem that pressure fluctuations and instantaneous pressure peaks may occur during the pressurization process in the urea tower, causing the float to move rapidly up or down on the probe rod protective sleeve, not only is a limiting component installed at the lower end of the probe rod protective sleeve, but also a top buffer component and a bottom buffer component are installed to prevent the float from falling off or being damaged by impact under pressure fluctuations.

[0023] 3) The inner tube of the float, fitted onto the protective sleeve of the probe rod, has been improved. The middle section of the inner tube wall forms an inwardly protruding straight section, while the upper and lower sections are outwardly inclined sloped sections. This invention utilizes the protruding straight section to ensure sufficient sliding contact with the protective sleeve of the probe rod with a smaller gap, forming an effective guide. This reduces the vibration and friction between the inner tube and the probe rod protective sleeve caused by gaps and external impacts when the entire inner tube of the float slides on the protective sleeve, thus improving the service life of the float. At the same time, the upper and lower sections are designed as outwardly inclined sloped sections, forming a structure with large openings at both ends. Compared with the traditional full sliding contact between the inner tube wall of the float and the probe rod, this reduces the contact area between the inner tube of the float and the protective sleeve of the probe rod, effectively reducing the risk of the float getting stuck due to the presence of impurities in the medium. Even if a small amount of impurities or crystals enter the gap between the inner tube of the float and the protective sleeve of the probe rod, the large openings on both sides make it easier to remove them when the float slides up and down along the protective sleeve of the probe rod. Preferably, the length of the straight section is 10%-12% of the total length of the inner tube. Too long a section increases the risk of the float getting stuck, while too short a section affects the guiding effect. Furthermore, considering the primary frictional relationship between the straight section and the probe protective sleeve, its inward convex shape can be cleverly utilized to design the inner tube's wall thickness to gradually increase from both ends towards the middle. That is, the straight section, where friction is greatest, has the thickest wall, while the wall thickness of the inclined sections on both sides gradually decreases towards the ends as the probability of friction decreases. This transforms the previous design of a uniform inner tube wall thickness into a gradually varying wall thickness design, thus significantly improving the wear resistance of the float's inner wall without increasing the float's weight. This special design of the float's inner wall combines guiding, anti-jamming, and wear-resistant properties, effectively improving the float's service life and reliability, demonstrating significant technical benefits.

[0024] 4) When measuring liquid level, the magnetostrictive level gauge calculates the level by multiplying the propagation speed of the mechanical wave by time. However, the propagation speed of the mechanical wave is usually assumed to be at room temperature. But the urea tower is a high-temperature environment with temperature variations. Due to these temperature differences, the propagation speed of the mechanical wave changes slightly. If the influence of temperature on the propagation speed is ignored, the detection accuracy will be low. To improve detection accuracy, this invention further improves the float structure by installing a top magnet for liquid level measurement at the top of the float and a bottom magnet for self-calibration at the bottom. The self-calibration method can calculate the liquid level L in the urea tower at the current temperature, thereby greatly improving detection accuracy and reliability.

[0025] Beneficial effects: This invention features a simple structure, ease of manufacture, low cost, high precision, high reliability, and high stability. It can effectively resist the lateral fluctuations of liquids under large impact forces and can operate stably for a long time in high temperature, high pressure, and corrosive environments, thus having broad market application prospects. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of the structure of the present invention.

[0027] Figure 2 This is a schematic diagram of the float's structure.

[0028] Figure 3 This is a simulation diagram of the buoy's compressive strength.

[0029] Among them, 1-Secondary protective sleeve at the root of the probe, 2-Primary protective sleeve at the root of the probe, 3-Top buffer, 4-Probe, 5-Probe protective sleeve, 6-Inner tube, 7-Float, 701-Sloping section, 702-Straight section, 703-Top magnet, 704-Compression support, 705-Bottom magnet, 8-Bottom buffer, 9-Limiting component, 10-Data processing unit, 11-Flange, 12-Flange. Detailed Implementation

[0030] The present invention will be further explained below with reference to the accompanying drawings: See Figure 1 The system includes a probe 4 equipped with a magnetostrictive waveguide wire. The upper end of the probe 4 is connected to a data processing unit 10. The magnetostrictive waveguide wire, as the core sensing component, generates a ring-shaped magnetic field through current pulses. This magnetic field interacts with the magnetic field of the float 7, triggering a magnetostrictive effect and generating a strain wave signal. The data processing unit 10 receives the excitation pulse signal and drives the magnetostrictive waveguide wire to generate the ring-shaped magnetic field. Simultaneously, it detects the strain wave signal induced by the magnetic field coupling of the float 7, converts the time difference into liquid level data, and ultimately obtains a recognizable liquid level display value, or further converts it into a remotely transmittable analog signal value. (The measurement principle of the magnetostrictive liquid level gauge is existing technology and will not be described in detail.)

[0031] The probe rod 4 is entirely fitted with a probe rod protective sleeve 5. Preferably, the lower end of the probe rod protective sleeve 5 is a sealed end, and the upper opening is sealed to the probe rod 4 by rigid compression. Preferably, it is sealed and locked by a clamping sleeve 11 with a pressure resistance of not less than 25 MPa. This ensures that even if the probe rod protective sleeve 5 is damaged under extreme conditions inside the tower, the liquid inside the urea tower will not overflow outside the urea tower through the gap between the probe rod 4 and the probe rod protective sleeve 5. The lower section of the probe rod protective sleeve 5 passes through the flange 12 (the probe rod protective sleeve 5 and the flange 12 are sealed and welded) and is fitted with a float 7. The float 7 contains a magnet.

[0032] This invention uses a flange 12 to fix the probe to the top of the urea tower. Below the flange 12, a primary protective sleeve 2 for the probe root is fitted over the probe rod protective sleeve 5. The upper end of the primary protective sleeve 2 is fixed to the bottom surface of the flange 12, and its length is the vertical distance from the bottom surface of the flange 12 to the highest allowable liquid level inside the urea tower. This improves the probe rod protective sleeve 5's resistance to lateral impact forces from the liquid surface area. A secondary protective sleeve 1 for the probe root is fitted over the primary protective sleeve 2. The upper end of the secondary protective sleeve 1 is fixed to the bottom surface of the flange 12, and its length is half the total length of the primary protective sleeve 2. This further strengthens the root pressure-bearing capacity of the probe rod protective sleeve 5, preventing local bending deformation. The combined effect of the primary and secondary protective sleeves lowers the fixing point of the probe rod protective sleeve 5, improves the level gauge's pressure resistance, impact resistance, and vibration resistance, making it possible to directly install the magnetostrictive level gauge inside the tower and ensuring the long-term stability of the equipment.

[0033] The lower end of the probe protective sleeve 5 is provided with a limiting member 9 to prevent the float 7 from falling out. A bottom buffer member 8 is installed on the probe protective sleeve 5 above the limiting member 9, and a top buffer member 3 is installed on the probe protective sleeve 5 below the first-level protective sleeve 2 at the root of the probe. Preferably, the upper end of the top buffer member 3 is fixed to the lower end of the first-level protective sleeve 2 at the root of the probe, and the lower end of the bottom buffer member 8 is fixed to the limiting member 5. When the float 7 is impacted and floats violently on the probe protective sleeve 5, the top buffer member 3 and the bottom buffer member 8 can provide cushioning, preventing damage to the float 7 and improving its service life. The top buffer member 3 and the bottom buffer member 8 can be buffer springs or other types of buffer components.

[0034] See Figure 2 The float 7 is a hollow structure integrally formed with an inner tube 6. The inner tube 6 is fitted onto the probe protective sleeve 5. The middle section of the inner tube 6 is an inwardly protruding straight section 702, and the upper and lower sections are outwardly inclined slope sections 701. The slope section 701 can be an outwardly inclined straight line or an arc. The angle between the slope section 701 and the axis is preferably 15-30 degrees, so that the entire inner tube 6 forms a cross-section with a narrowed middle section and an expanded upper and lower section. The length of the straight section 702 is 10% to 12% of the total length of the inner tube 6, and its inner diameter matches the outer diameter of the probe protective sleeve 5 to fulfill the guiding function. The straight section 702 moves along the axial direction of the probe protective sleeve 5, with a small contact area, reducing the risk of the float getting stuck due to the presence of media impurities. The inner diameter of the slope section 701 gradually expands outward, increasing the gap with the probe protective sleeve 5, increasing the probability of impurities or crystals entering the inner tube 6 flowing out, and avoiding local stagnation and jamming.

[0035] Furthermore, the wall thickness of the inner tube 6 gradually increases from both ends towards the middle, intentionally increasing the wall thickness of the straight section 702 that rubs most against the probe protective sleeve 5, while making the walls of the inclined sections 701 on both sides gradually thinner. This significantly improves the wear resistance of the inner wall of the float without increasing the weight of the float 7. The float 7 has a skeletal structure with a pressure-resistant support 704, which is equivalent to adding a skeleton inside a balloon. This not only effectively improves the pressure-bearing capacity of the float but also increases its self-balancing ability. Since the pressure-resistant support 704 itself has a limited weight, the added weight can be balanced by existing design. Preferably, the float 7 is filled with an inert gas, preferably helium. This type of inert gas has very stable properties, is non-flammable and does not support combustion, and can protect metal from oxidation at high temperatures. It can effectively balance the pressure inside the urea tower, thus reducing the external pressure on the float and the required float wall thickness, thereby reducing the weight of the float.

[0036] In this embodiment, the design pressure inside the urea tower is 16.2 MPa. To ensure the system operates safely and reliably under normal conditions and various possible operating conditions, a safety margin of 1.1 times is reserved. Therefore, the final design pressure of the urea tower level measuring device is 18 MPa. The probe protective sleeve 5, the tube wall of the probe 4, the primary protective sleeve 2 at the probe root, the secondary protective sleeve 1 at the probe root, and the support component 704 inside the float can all be made of HC-276 alloy material to improve pressure resistance and corrosion resistance, enabling them to withstand a pressure of 18 MPa. The selected clamping sleeve 11 also has a pressure-bearing capacity exceeding 18 MPa, ensuring the reliability of the measurement. Furthermore, the probe protective sleeve 5, the primary protective sleeve 2 at the probe root, the secondary protective sleeve 1 at the probe root, and the tube wall of the probe 4 are all subjected to antimagnetic treatment to improve the accuracy and stability of the measurement. Furthermore, to prevent the float 7 from generating static electricity through friction with the probe protective sleeve 5 during movement, a PTFE coating can be applied to the outer wall of the probe protective sleeve 5 to provide anti-static protection.

[0037] A high-pressure simulation experiment was conducted on float 7 of this embodiment, and the experimental results are as follows: 1.1 Analysis Types A pressure analysis was performed on the float to calculate its pressure resistance at 18 MPa.

[0038] 1.2 Material Properties The float material is HC-276 (elastic modulus: 210GPa, Poisson's ratio approximately 0.3, yield strength Rp0.2: 363MPa), and the compressive support material is aluminum alloy 7075-T6 (elastic modulus: 71.7GPa, Poisson's ratio approximately 0.33, yield strength Rp0.2: 503MPa). 1.3 Analytical Conclusions When the float is subjected to a pressure of 18 MPa, the calculated stress cloud diagram shows that the maximum stress point of the float is the middle part of the two supports of the outer shell and the pressure-resistant support; the maximum stress is 317 MPa.

[0039] in conclusion: The float sphere is made of HC276, with a yield strength of 363 MPa at Rp0.2 and a maximum stress of 317 MPa. The maximum stress is less than the yield strength of the material, which meets the design requirements. The compressive support is made of aluminum alloy 7075-T6, with a yield strength of 480 MPa at Rp0.2. The maximum stress is less than the yield strength of the material, which also meets the design requirements.

[0040] To conserve computational resources, the float was removed, and only 1 / 8 of it was calculated. The calculation result is essentially the same as that of the entire float. Simulation conclusions can be found in [link to simulation results]. Figure 3 The float can operate stably in a high temperature and high pressure environment of 260℃ and 18MPa.

[0041] In another embodiment: the top of the float 7 is equipped with a top magnet 703 for liquid level measurement, and the bottom is equipped with a bottom magnet 705 for self-calibration. The self-calibration method is as follows: the distance between the top magnet 703 and the bottom magnet 705 inside the float 7 is obtained as a fixed distance, denoted as L1; the time difference between the signal of the top magnet 703 and the signal of the bottom magnet 705 collected by the data processing unit at the current temperature is calculated and denoted as t1; the propagation speed v1 of the mechanical wave at the current temperature is calculated according to the formula v1=L1 / t1; and finally, the liquid level value L in the urea tower at the current temperature is calculated as L=v1*t.

[0042] Taking the actual operating conditions inside a urea tower as an example, the temperature inside the urea tower is 198℃. The wave velocity of the measuring device at room temperature is 2782 m / s, while at 198℃, the wave velocity changes slightly to 2796 m / s. Assuming the time difference in the level reading measured by the magnetostrictive level measuring device is 0.9 ms, the level calculated based on the wave velocity at room temperature is 2503.8 mm, while the level calculated based on the wave velocity at 198℃ is 2516.4 mm. The difference is 2516.4 - 2503.8 = 12.6 mm.

[0043] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Those skilled in the art can readily implement the present invention based on the accompanying drawings and the above description. However, any modifications, alterations, or variations made by those skilled in the art without departing from the scope of the present invention, utilizing the disclosed technical content, are equivalent embodiments of the present invention. Furthermore, any modifications, alterations, or variations made to the above embodiments based on the essential technology of the present invention are still within the protection scope of the present invention.

Claims

1. A magnetostrictive liquid level measuring device for a urea tower, comprising a probe equipped with a magnetostrictive waveguide wire, wherein the upper end of the probe is connected to a sensor and a data processing unit, characterized in that, The probe is fully encased in a probe protective sleeve. The lower section of the probe protective sleeve passes through the flange and is fitted with a float, which contains a magnet. Below the flange, the probe protective sleeve is encased in a primary protective sleeve at the probe root. The upper end of the primary protective sleeve at the probe root is fixed to the flange, and its length is the vertical distance from the bottom of the flange to the highest allowable liquid level in the tower.

2. The magnetostrictive liquid level measuring device for urea tower as described in claim 1, characterized in that, The probe root primary protective sleeve is fitted with a probe root secondary protective sleeve. The upper end of the probe root secondary protective sleeve is fixed to the flange, and its length is 1 / 2 of the total length of the probe root primary protective sleeve.

3. The magnetostrictive liquid level measuring device for urea tower as described in claim 1, characterized in that, The lower end of the probe protective sleeve is a sealed end, and the upper opening is sealed and locked to the probe by a retainer.

4. The magnetostrictive liquid level measuring device for urea tower as described in claim 1, characterized in that, The lower end of the probe protective sleeve is provided with a limiting component.

5. The magnetostrictive liquid level measuring device for urea tower as described in claim 4, characterized in that, A top buffer is installed on the probe protective sleeve below the probe root primary protective sleeve, and the upper end of the top buffer is fixed to the lower end of the probe root primary protective sleeve.

6. The magnetostrictive liquid level measuring device for urea tower as described in claim 5, characterized in that, The lower end of the probe protective sleeve is equipped with a bottom buffer, and the lower end of the bottom buffer is fixed to the limiting member.

7. The magnetostrictive liquid level measuring device for urea towers as described in any one of claims 1-6, characterized in that, The float is a hollow structure integrally formed with an inner tube. The inner tube is fitted onto the probe protective sleeve. The middle section of the inner tube is a straight section that protrudes inward, and the upper and lower sections are inclined sections that slope outward.

8. The magnetostrictive liquid level measuring device for urea tower as described in claim 7, characterized in that, The length of the straight segment is 10%–12% of the total length of the float's inner tube.

9. The magnetostrictive liquid level measuring device for urea tower as described in claim 7, characterized in that, The wall thickness of the inner tube gradually increases from both ends toward the middle section.

10. The magnetostrictive liquid level measuring device for urea tower as described in claim 1, characterized in that, The float is filled with inert gas and has a pressure-resistant support.

11. The magnetostrictive liquid level measuring device for urea tower as described in claim 10, characterized in that, The inert gas is helium.

12. The magnetostrictive liquid level measuring device for urea tower as described in any one of claims 1 or 8-11, characterized in that, The float has a top magnet for liquid level measurement at the top and a bottom magnet for self-calibration at the bottom.

13. The magnetostrictive liquid level measuring device for urea tower as described in claim 12, characterized in that, The self-calibration method is as follows: the distance between the top magnet and the bottom magnet inside the float is obtained as a fixed distance, denoted as L1; the time difference between the top magnet signal and the bottom magnet signal collected by the data processing unit at the current temperature is calculated and denoted as t1; the propagation speed v1 of the mechanical wave at the current temperature is calculated according to the formula v1=L1 / t1; and the liquid level value L in the urea tower at the current temperature is calculated as L=v1*t.

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