Float structure of magnetostrictive liquid level meter for urea tower

Abstract

The application discloses a float structure of a magnetostrictive liquid level meter for a urea tower, and has the technical scheme that the hollow structure is integrally processed and formed with an inner tube, a magnet for liquid level measurement is arranged, and the middle section of the inner tube is a linear section protruding inward, and the upper and lower sections are inclined surface sections obliquely outward. The application has the advantages that the structure is simple, the manufacture is easy, the cost is low, liquid transverse fluctuation against great impact force can be effectively resisted, the measurement precision, reliability and stability are improved, and long-term stable operation can be realized in a high-temperature, high-pressure and corrosive environment.

Description

Technical Field

[0001] This invention relates to a liquid level measuring device in the chemical industry, specifically a float structure for a magnetostrictive liquid level gauge used in 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, using Cs-137 as the radiation source. This requires 24-hour continuous video monitoring, incurs high annual maintenance costs, and necessitates regular replacement of the rod source to achieve high measurement accuracy. The other type is the VEGA radar level gauge, which is patented with Carbon and is not sold separately.

[0003] A magnetostrictive level gauge is a high-precision measuring instrument capable of continuous 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 "torsion" 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 such as high temperature, high pressure, strong corrosiveness, and easy crystallization, with impurities posing a risk of float jamming. Furthermore, the tower environment experiences significant lateral liquid fluctuations with strong impact forces, affecting not only accurate level measurement but also, because the magnetostrictive level gauge's probe extends considerably downwards from the tower top, even with an added protective sleeve to increase rigidity, it is easily bent under lateral impact forces, leading to equipment deformation and other problems.

[0005] Publication No. CN 216899146U 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. A main venting pipe is installed 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. This solution requires the introduction of a gas pipeline and purging of the medium, making it completely unsuitable for the high temperature, high pressure, highly corrosive, and easily crystallizing conditions of urea towers.

[0006] Therefore, the developers hope to improve the float structure to make the magnetostrictive level gauge more suitable for high temperature, high pressure, and corrosive environments, and further improve the accuracy, reliability, and stability of the measurement. Summary of the Invention

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

[0008] The float structure of the magnetostrictive level gauge for urea tower of the present invention is a hollow structure integrally formed with an inner tube, and is equipped with a magnet for level measurement. The middle section of the inner tube is a straight section protruding inward, and the upper and lower sections are inclined sections sloping outward.

[0009] Preferably, the angle between the inclined section and the axis is 15-30 degrees.

[0010] Preferably, the length of the straight segment is 10%-12% of the total length of the inner tube.

[0011] Preferably, the wall thickness of the inner tube gradually increases from both ends toward the middle section.

[0012] Preferably, the float is filled with inert gas and has a pressure-resistant support.

[0013] Preferably, the inert gas is helium.

[0014] Preferably, the float has a top magnet for liquid level measurement at the top and a bottom magnet for self-calibration at the bottom.

[0015] 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.

[0016] To address the problems in the background art, the inventors have made the following improvements: 1) 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 design of the upper and lower sections as outwardly inclined sloped sections forms 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 previously uniform inner tube wall thickness into a gradually varying wall thickness, 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.

[0017] 2) 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.

[0018] Beneficial effects: This invention has an extremely simple structure, is easy to manufacture, and has low cost. It can effectively resist the lateral fluctuations of liquid under large impact forces, improve the accuracy, reliability, and stability of the level gauge, 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

[0019] Figure 1 This is a schematic diagram of a magnetostrictive level gauge.

[0020] Figure 2 This is a schematic diagram of the structure of the float of the present invention.

[0021] Figure 3 This is a simulation diagram showing the compressive strength of the float of the present invention.

[0022] 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

[0023] The present invention will be further explained below with reference to the accompanying drawings: See Figure 1The float 7 described in this invention is an important component of a magnetostrictive level gauge. The magnetostrictive level gauge 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 level data, and ultimately obtains a recognizable level display value, or further converts it into a remotely transmittable analog signal value. (The measurement principle of the magnetostrictive level gauge is prior art and will not be detailed.) Those skilled in the art can choose various suitable probe structures that meet the above measurement principles for use in conjunction with the float structure of this invention.

[0024] In a preferred embodiment, 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.

[0025] The magnetostrictive level gauge is fixed to the top of the urea tower via the flange 12. A primary protective sleeve 2 for the probe root is fitted over the probe rod protective sleeve 5 below the flange 12. 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 enhances 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 and prevents local bending deformation. The primary protective sleeve 2 and the secondary protective sleeve 1 at the root of the probe work together to reduce the height of the fixing point of the probe protective sleeve 5, improve the pressure resistance, impact resistance and vibration resistance of the level gauge, make it possible to directly install the magnetostrictive level gauge inside the tower, and ensure the long-term stability of the equipment.

[0026] 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 primary protective sleeve 2 at the probe root. Preferably, the upper end of the top buffer member 3 is fixed to the lower end of the primary protective sleeve 2 at the probe root, 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.

[0027] See Figure 2 In this embodiment, 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-sectional state 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 meet 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.

[0028] 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.

[0029] The float 7 is not only applicable to Figure 1 The magnetostrictive level gauge shown is also applicable to other magnetostrictive level gauges with probe structures.

[0030] 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.

[0031] 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.

[0032] 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.

[0033] 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.

[0034] 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 3The float can operate stably in a high temperature and high pressure environment of 260℃ and 18MPa.

[0035] 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.

[0036] 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.

[0037] 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 float structure for a magnetostrictive level gauge used in a urea tower, comprising an integrally machined hollow structure with an inner tube, and equipped with a magnet for level measurement, characterized in that... The middle section of the inner tube is a straight section that protrudes inward, while the upper and lower sections are inclined sections that slope outward.

2. The float structure of the magnetostrictive level gauge for urea tower as described in claim 1, characterized in that, The angle between the inclined section and the axis is 15-30 degrees.

3. The float structure of the magnetostrictive level gauge for urea tower as described in claim 1, characterized in that, The length of the straight segment is 10%-12% of the total length of the inner tube of the float.

4. The float structure of the magnetostrictive level gauge for urea tower as described in any one of claims 1, characterized in that, The wall thickness of the inner tube gradually increases from both ends toward the middle section.

5. The float structure of the magnetostrictive level gauge for urea tower as described in claim 1, characterized in that, The float is filled with inert gas and has a pressure-resistant support.

6. The float structure of the magnetostrictive level gauge for urea tower as described in claim 5, characterized in that, The inert gas is helium.

7. The float structure of the magnetostrictive level gauge for urea tower as described in any one of claims 1-6, 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.

8. The float structure of the magnetostrictive level gauge for urea tower as described in claim 7, 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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