Floater structure of magnetostriction liquid level meter for urea tower

Abstract

According to the technical scheme, the floater structure of the magnetostriction liquid level meter for the urea tower is of an integrally-formed hollow structure provided with an inner pipe and is provided with a magnet used for liquid level measurement, the middle section of the inner pipe is a linear section protruding inwards, and the upper section and the lower section of the inner pipe are inclined plane sections inclining outwards. The device is simple in structure, easy to manufacture, low in cost and capable of effectively resisting liquid transverse fluctuation with large impact force, measuring precision, reliability and stability are improved, and the device can stably operate for a long time in high-temperature, high-pressure and corrosive environments.

Description

Technical Field

[0001] The present invention relates to a liquid level measuring device in the chemical industry field, specifically to a float structure of a magnetostrictive liquid level gauge for a urea tower. Background Art

[0002] In the production process of urea, the liquid level in the urea tower is a key parameter. Accurately measuring the liquid level in the tower is crucial for controlling the process of urea synthesis reaction, ensuring product quality, and ensuring production safety. The medium in the total condensation reactor of the urea plant is urea solution, with a designed temperature of 198 °C and a designed pressure of 16.2 MPa (g). The medium has the characteristics of high temperature, high pressure, strong corrosiveness, and easy crystallization. The use of various liquid level measuring devices such as glass tube liquid level gauges and differential pressure liquid level gauges is greatly restricted. Currently, there are two types of liquid level gauges widely used in urea towers. One is a radioactive liquid level gauge with a radiation source of Cs-137, which requires 24-hour continuous video monitoring due to radiation, and has a relatively high annual maintenance cost. The rod source needs to be replaced regularly to obtain higher measurement accuracy. The other is the radar liquid level gauge of VEGA that forms a patent binding with Carbone. This liquid level gauge is bound to Carbone's urea patent and is not sold separately.

[0003] A magnetostrictive liquid level gauge is a high-precision measuring instrument that can perform continuous liquid level and interface measurements and provide analog signal outputs for monitoring and control. It mainly includes a probe rod equipped with magnetostrictive waveguide wires, a float equipped with a permanent magnet, and a data processing unit (also known as a circuit unit). During measurement, the circuit unit generates an electric current pulse, which travels downward along the magnetostrictive waveguide wire and generates a circular magnetic field. When the electric current magnetic field meets the float magnetic field, a "twist" pulse, or a "return" pulse, is generated. The time difference between the "return" pulse and the electric current pulse is converted into a pulse signal, thereby calculating the actual position of the float and measuring the liquid level.

[0004] Magnetostrictive liquid level gauges are usually used for liquid level measurement in tanks, and have the advantages of high accuracy, high explosion-proof performance, and safe use, and are suitable for measuring chemical raw materials and flammable liquids. However, for some special working conditions, such as the environment inside the urea tower, on the one hand, the medium has the characteristics of high temperature, high pressure, strong corrosiveness, and easy crystallization, and the presence of medium impurities poses a risk of jamming the float; on the other hand, there is also a large lateral fluctuation of the liquid with a great impact force inside the tower, which not only affects the correct measurement of the liquid level, but also, since the probe rod of the magnetostrictive liquid level gauge extends downward from the top of the tower for a long distance, even if a protective sleeve is added outside the probe rod to increase its rigidity, it is very easy to bend under the action of the lateral impact force, resulting in problems such as equipment deformation.

[0005] Publication number CN 216899146 U discloses a device for preventing the float of a magnetostrictive level gauge from getting stuck. The specific structure is as follows: It includes a magnetostrictive level gauge. A measuring rod is fixedly connected to the lower end of the magnetostrictive level gauge. A float is arranged on the measuring rod. The magnetostrictive level gauge is installed on the top flange of the storage tank. The measuring rod and the float extend into the storage tank. In this solution, a main ventilation pipe is arranged above the storage tank, and the main ventilation pipe extends into the storage tank and is located on one side of the measuring rod. When there are impurities in the gap between the measuring rod and the float, the gap between the measuring rod and the float can be purged through the air outlet of the main ventilation pipe, and the impurities can be cleaned up, enabling the float to move normally and solving the problem that the float gets stuck and cannot be measured. This solution requires the introduction of a gas pipeline and gas purging into the medium, and is completely unsuitable for the high-temperature, high-pressure, strong corrosive and easy-to-crystallize working conditions of the urea tower.

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

[0007] The purpose of the present invention is to solve the above technical problems, and provide a float structure for a magnetostrictive level gauge used in a urea tower, which has a simple structure, is easy to manufacture, has a low cost, can effectively resist large impact forces of liquid lateral fluctuations, 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 the urea tower of the present invention is a hollow structure integrally formed with an inner tube, and is provided with a magnet for liquid level measurement. The middle section of the inner tube is a straight section protruding inward, and the upper and lower sections are inclined sections inclined outward.

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

[0010] Preferably, the length of the straight section 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 to the middle section.

[0012] Preferably, the float is filled with an inert gas and has a compressive support member.

[0013] Preferably, the inert gas is helium.

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

[0015] Preferably, the self-calibration method is as follows: obtain the distance between the top magnet and the bottom magnet inside the float as a fixed distance, denoted as L1, calculate the time difference between the top magnet signal and the bottom magnet signal collected by the data processing unit at the current temperature, denoted as t1, calculate the propagation speed v1 of the mechanical wave at the current temperature according to the formula v1 = L1 / t1, and calculate the liquid level value L in the urea tower at the current temperature as L = v1*t.

[0016] In response to the problems in the background art, the inventor has made the following improvements:

[0017] 1) The inner tube of the float sleeved on the probe protection sleeve is improved, so that a straight section protruding inward is formed in the middle section of the inner tube wall, and the upper and lower sections are inclined sections inclined outward. The present invention uses the protruding straight section to ensure sliding contact with the probe protection sleeve with a sufficient area and a smaller gap, forming an effective guide, reducing the vibration friction between the two caused by the gap and external impact when the traditional inner tube of the float slides on the probe protection sleeve as a whole, and improving the service life of the float; at the same time, the upper and lower sections are designed as inclined sections inclined outward, forming a structure with large openings at both ends. Compared with the full sliding contact between the inner wall of the traditional float and the probe, the contact area between the inner tube of the float and the probe protection sleeve is reduced, effectively reducing the risk of jamming the float caused by the presence of medium impurities. Even if a small amount of impurities or crystals enter the gap between the inner tube of the float and the probe protection sleeve, due to the large openings on both sides, it can be more easily carried out when the float slides up and down along the probe protection sleeve. Preferably, the length of the straight section is 10%-12% of the total length of the inner tube. If it is too long, the risk of jamming the float will increase, and if it is too short, the guiding effect will be affected. Further, considering that there is a main friction relationship between the straight section and the probe protection sleeve, the inward protruding shape can be cleverly used to design the wall thickness of the inner tube to gradually increase from both ends to the middle section, that is, the wall thickness of the straight section with the most friction is the largest, and the wall thickness of the inclined sections on both sides gradually decreases towards the two ends as the friction probability decreases. In this way, the uniform wall thickness of the past inner tube is changed to a gradually changing wall thickness. Therefore, the wear resistance of the inner wall of the float can be greatly improved almost without increasing the weight of the float. This special design of the inner wall of the float takes into account the dual performance of guiding, anti-jamming and wear resistance, effectively improving the service life and reliability of the float, and the technical effect is remarkable.

[0018] 2) When the magnetostrictive level gauge measures the liquid level, it calculates by multiplying the propagation speed of the mechanical wave by the time. The propagation speed of the mechanical wave is usually defaulted to the speed under normal temperature environment. However, the inside of the urea tower is a high-temperature environment and there are temperature changes. Due to different temperatures, the propagation speed of the mechanical wave will change slightly. If the influence of temperature on the propagation speed of the mechanical wave is ignored, there will be a problem of low detection accuracy. In order to improve the detection accuracy, the present invention further improves the float structure, installs a top magnet for liquid level measurement at the top of the float, and installs a bottom magnet for self-calibration at the bottom. Through the self-calibration method, the liquid level value L inside the urea tower at the current temperature can be calculated, thus greatly improving the detection accuracy and reliability better.

[0019] Beneficial effects:

[0020] The structure of the present invention is extremely simple, easy to manufacture, and low in cost. It can effectively resist the lateral fluctuation of the liquid with large impact force, 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, having a broad market application prospect. Description of the drawings

[0021] Figure 1 It is a schematic structural diagram of the magnetostrictive level gauge.

[0022] Figure 2 It is a schematic structural diagram of the float of the present invention.

[0023] Figure 3 It is a compressive resistance simulation effect diagram of the float of the present invention.

[0024] Among them, 1 - secondary protection sleeve at the root of the probe rod, 2 - primary protection sleeve at the root of the probe rod, 3 - top buffer, 4 - probe rod, 5 - probe rod protection sleeve, 6 - inner tube, 7 - float, 701 - inclined section, 702 - straight section, 703 - top magnet, 704 - compressive resistance support, 705 - bottom magnet, 8 - bottom buffer, 9 - limiting part, 10 - data processing unit, 11 - ferrule, 12 - flange. Specific implementation manners

[0025] The present invention will be further explained below in conjunction with the drawings:

[0026] See Figure 1, the float 7 of the present invention is an important component of the magnetostrictive liquid level gauge. The magnetostrictive liquid level gauge includes a probe rod 4 equipped with a magnetostrictive waveguide wire. The upper end of the probe rod 4 is connected to a data processing unit 10. Among them, the magnetostrictive waveguide wire, as the core sensing component, generates a circular magnetic field through an electric current pulse and interacts with the magnetic field of the float 7 to trigger the magnetostrictive effect and generate a strain wave signal. The data processing unit 10 is used to receive the excitation pulse signal and drive the magnetostrictive waveguide wire to generate a circular magnetic field, and at the same time detect the strain wave signal caused by the magnetic field coupling of the float 7, convert the time difference into liquid level data, and finally obtain an identifiable liquid level display value, or further convert it into an analog signal value that can be remotely transmitted. (The measurement principle of the magnetostrictive liquid level gauge is prior art and will not be elaborated). Those skilled in the art can select various probe rod structures that meet the above measurement principle and are suitable for use in combination with the float structure of the present invention.

[0027] As a preferred embodiment, the outer part of the probe rod 4 is integrally sleeved 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 end opening is sealed with the probe rod 4 by rigid crimping. Preferably, it is sealed and locked by a ferrule 11 with a pressure resistance of not less than 25 MPa, which can ensure that even if the probe rod protective sleeve 5 is damaged under extreme conditions in the tower, the liquid in the urea tower will not overflow to the outside of 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 a flange 12 (the probe rod protective sleeve 5 and the flange 12 are sealed and welded) and is sleeved with a float 7.

[0028] The magnetostrictive liquid level gauge is fixed on the top of the urea tower through the flange 12. An outer sleeve of the probe rod root first-level protective sleeve 2 is installed outside the probe rod protective sleeve 5 below the flange 12. The upper end of the probe rod root first-level protective sleeve 2 is fixed on 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 in the urea tower, so as to improve the ability of the probe rod protective sleeve 5 to resist the lateral impact force from the liquid level range. An outer sleeve of the probe rod root second-level protective sleeve 1 is installed outside the probe rod root first-level protective sleeve 2. The upper end of the probe rod root second-level protective sleeve 1 is fixed on the bottom surface of the flange 12, and its length is 1 / 2 of the total length of the probe rod root first-level protective sleeve 2, so as to further enhance the pressure-bearing capacity of the root of the probe rod protective sleeve 5 and avoid the occurrence of local bending deformation problems. The probe rod root first-level protective sleeve 2 and the probe rod root second-level protective sleeve 1 work together to lower the fixed point of the probe rod protective sleeve 5, improve the pressure resistance, impact resistance and vibration resistance performance of the liquid level gauge, make it possible to directly install the magnetostrictive liquid level gauge in the tower, and ensure the long-term stability of the equipment.

[0029] A limiting member 9 for preventing the float 7 from disengaging is provided at the lower end of the probe rod protective sleeve 5. A bottom buffer member 8 is installed on the probe rod protective sleeve 5 above the limiting member 9. A top buffer member 3 is installed on the probe rod protective sleeve 5 below the first-stage protective sleeve 2 at the root of the probe rod. Preferably, the upper end of the top buffer member 3 is fixed to the lower end of the first-stage protective sleeve 2 at the root of the probe rod, 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 rod protective sleeve 5, the top buffer member 3 and the bottom buffer member 8 can play a buffering role, avoiding damage to the float 7 and improving the service life of the float. The top buffer member 3 and the bottom buffer member 8 can be buffer springs or buffer components of other structures.

[0030] See Figure 2 , the float 7 of this embodiment is a hollow structure integrally formed with an inner tube 6, wherein the inner tube 6 is sleeved on the probe rod protective sleeve 5. The middle section of the inner tube 6 is a straight section 702 protruding inwards, and the upper and lower sections are inclined sections 701 inclined outwards. The inclined section 701 can be a straight line or an arc inclined outwards. The included angle between the inclined section 701 and the axis is preferably 15-30 degrees, so that the entire inner tube 6 forms a cross-sectional state with a reduced diameter in the middle section and an enlarged diameter in the upper and lower sections. The length of the straight section 702 is 10% - 12% of the total length of the inner tube 6, and its inner diameter matches the outer diameter of the probe rod protective sleeve 5, meeting the guiding function. The straight section 702 moves along the axis of the probe rod protective sleeve 5, with a small contact area, reducing the risk of jamming the float due to the presence of medium impurities; while the inner diameter of the inclined section 701 gradually expands outwards, increasing the gap with the probe rod protective sleeve 5 and improving the probability of impurities or crystals entering the inner tube 6 flowing out, avoiding local retention and jamming.

[0031] Furthermore, the wall thickness of the inner tube 6 gradually increases from both ends to the middle section, deliberately increasing the wall thickness of the straight section 702 that has the most friction with the probe rod protective sleeve 5, while making the wall thickness of the two side inclined sections 701 gradually thinner. Without increasing the weight of the float 7, the wear resistance of the inner wall of the float is greatly improved. The float 7 has a compressive support member 704 with a skeleton structure inside, which is equivalent to adding a skeleton inside a balloon, not only effectively improving the pressure-bearing capacity of the float but also increasing the self-balancing ability of the float. And the weight of the compressive support member 704 itself is limited, and the increased weight can be balanced through the existing design. Preferably, the float 7 is filled with an inert gas, preferably helium. This kind of inert gas has very stable properties, does not burn or support combustion, and can protect metals from oxidation at high temperatures. It can well balance the partial pressure inside the urea tower, so that the external pressure borne by the float is relatively reduced, and the requirement for the wall thickness of the float is relatively reduced, thereby reducing the weight of the float.

[0032] The float 7 is not only applicable to Figure 1 the magnetostrictive liquid level gauge shown, but also applicable to other magnetostrictive liquid level gauges with a probe rod structure.

[0033] In this embodiment, the design pressure inside the urea tower is 16.2 MPa. To ensure that the system can operate safely and reliably under normal operating conditions and various possible working conditions, a safety margin of 1.1 times is reserved. Finally, the design pressure of the urea tower liquid level measuring device is 18 MPa. The probe protection sleeve 5, the tube wall of the probe 4, the first-stage protection sleeve 2 at the root of the probe, the second-stage protection sleeve 1 at the root of the probe, and the support member 704 inside the float can all be made of alloy material with the material of HC-276 to improve the pressure resistance and corrosion resistance, and can withstand a pressure of 18 MPa. The selected ferrule 11 also has a pressure-bearing capacity exceeding 18 MPa to ensure the reliability of the measurement. Further, the probe protection sleeve 5, the first-stage protection sleeve 2 at the root of the probe, the second-stage protection sleeve 1 at the root of the probe, and the wall tube of the probe 4, etc. are all subjected to anti-magnetization treatment to improve the measurement accuracy and stability. Further, in order to prevent static electricity from being generated by friction between the float 7 and the probe protection sleeve 5 during movement, a PTFE coating can also be covered on the outer wall of the probe protection sleeve 5 to play an anti-static role.

[0034] A high-pressure simulation experiment was carried out on the float 7 of this embodiment, and the experimental results are as follows:

[0035] 1.1 Analysis type

[0036] Perform a pressure-bearing analysis on the float to calculate the pressure-bearing situation of the float under a pressure of 18 MPa.

[0037] 1.2 Material properties

[0038] The float material is HC-276 (elastic modulus: 210 GPa, Poisson's ratio is about 0.3, yield strength Rp0.2: 363 MPa), and the compressive support member material is aluminum alloy 7075-T6 (elastic modulus: 71.7 GPa, Poisson's ratio is about 0.33, yield strength Rp0.2: 503 MPa)

[0039] 1.3. Analysis conclusion

[0040] When the float is under a pressure of 18 MPa, from the calculated stress nephogram, it can be known that the maximum stress points of the floating ball are the middle parts between the two supports of the spherical shell and the compressive support member; the maximum stress is 317 MPa.

[0041] Conclusion:

[0042] The float sphere material is HC276, the material Rp0.2 yield limit is 363 MPa, the maximum stress value is 317 MPa, and the maximum stress value is less than the yield limit of the material, meeting the design requirements; the compressive support member material is aluminum alloy 7075-T6, the material Rp0.2 yield strength is 480 Mpa, and the maximum stress value is less than the yield limit of the material, meeting the design requirements.

[0043] To save computing resources, the floating ball is cut off, and only 1 / 8 part is calculated. The calculation result is basically the same as that of the whole ball. For the simulation conclusion, see Figure 3 , the float can operate stably in a high-temperature and high-pressure environment of 260 °C and 18 MPa.

[0044] As another embodiment: a top magnet 703 for liquid level measurement is installed at the top of the float 7, and a bottom magnet 705 for self-calibration is installed at the bottom. The self-calibration method is as follows: obtain the distance between the top magnet 703 and the bottom magnet 705 in the float 7 as a fixed distance, denoted as L1, calculate 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, denoted as t1, calculate the propagation speed v1 of the mechanical wave at the current temperature according to the formula v1 = L1 / t1, and finally calculate the liquid level value L in the urea tower at the current temperature as L = v1 * t.

[0045] Taking the actual working conditions in the urea tower as an example, the temperature in the urea tower is 198 °C. The wave speed of the measuring device at normal temperature is 2782 m / s. When the temperature is 198 °C, the wave speed changes slightly to 2796 m / s. Assume that the liquid level time difference measured by the magnetostrictive liquid level measuring device is 0.9 ms. Then, the liquid level value calculated according to the wave speed at normal temperature is: 2503.8 mm, and the liquid level value calculated according to the wave speed at 198 °C is: 2516.4 mm. The difference between the two is 2516.4 - 2503.8 = 12.6 mm.

[0046] As mentioned above, it is only the preferred embodiment of the present invention, and there is no any form of restriction on the present invention; any ordinary technician in the industry can smoothly implement the present invention according to the instructions in the attached drawings and the above description; however, any slight changes, modifications and evolutions made by those skilled in the art within the scope of the technical solution of the present invention by using the technical content disclosed above are equivalent embodiments of the present invention; at the same time, any equivalent changes, modifications and evolutions made to the above embodiments based on the essential technology of the present invention still fall within the protection scope of the technical solution of the present invention.

Claims

1. The float structure of a magnetostrictive liquid level gauge for a urea tower is a hollow structure integrally formed with an inner tube, and is provided with a magnet for liquid level measurement, characterized in that, The middle section of the inner tube is a straight section protruding inward, and the upper and lower sections are inclined sections sloping outward.

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

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

4. The float structure of the magnetostrictive liquid level gauge for urea towers according to any one of claims 1, characterized in that The wall thickness of the inner tube gradually increases from both ends to the middle section.

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

6. The float structure of the magnetostrictive liquid level gauge for urea towers according to claim 5, characterized in that, The inert gas is helium.

7. The float structure of the magnetostrictive liquid level gauge for urea tower according to any one of claims 1-6, characterized in that, A top magnet for liquid level measurement is installed at the top inside the float, and a bottom magnet for self-calibration is installed at the bottom.

8. The float structure of the magnetostrictive liquid level gauge for urea tower according to claim 7, characterized in that, The self-calibration method is as follows: Obtain the distance between the top magnet and the bottom magnet inside the float as a fixed distance, denoted as L1, calculate the time difference between the signal of the top magnet and the signal of the bottom magnet collected by the data processing unit at the current temperature, denoted as t1, calculate the propagation speed v1 of the mechanical wave at the current temperature according to the formula v1 = L1 / t1, and calculate the liquid level value L in the urea tower at the current temperature as L = v1 * t.

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