Active vibration wave liquid level measuring method of pressure vessel for aluminum oxide industry

Abstract

The invention discloses an active vibration wave liquid level measuring method for a pressure vessel used in the alumina industry, a vibration source and a sound sensing element are arranged at the bottom of the pressure vessel, the sound wave characteristic of the vibration source is different from that of the production process environment sound wave in the alumina industry, and according to the change of the sound wave frequency generated by the contact of the sound wave of the vibration source and a medium in the vessel, the sound sensing element can detect the liquid level. Conversion is carried out according to the sound wave frequency-liquid level height characteristic curve relation, and non-intrusive liquid level real-time monitoring of the pressure vessel under environmental interference is achieved during production and operation. The problem that the liquid level of the pressure vessel is difficult to measure under severe working conditions such as high temperature, high pressure, strong acid and strong alkali in the aluminum oxide production process is solved, the influence of the working environment on liquid level measurement is greatly reduced, the liquid level measurement cost can be remarkably reduced, operation is easy, use is convenient, no additional energy consumption exists in the operation process, and the application range is wide. Therefore, the liquid level measurement of the pressure vessel for the aluminum oxide industry is more efficient, reliable, energy-saving and safe.

Description

Technical Field

[0001] The invention relates to a liquid level measurement method, in particular to an active vibration wave liquid level measurement method for a pressure vessel used in the alumina industry. Background Art

[0002] Pressure vessels in the alumina industry are often used in important processes of alumina production such as dissolution, evaporation, and sedimentation. They need to have high strength and high chemical stability. The working media they carry are relatively complex, including high temperature, high pressure, and high alkali concentration gas, liquid, or liquid-solid mixed media. During the operation of pressure vessels in the alumina industry, other working equipment around the pressure vessels (such as centrifugal pumps, vacuum pumps, and air compressors, etc.) will generate certain noise, which will affect the control or measurement elements measured by sound wave frequency. At the same time, because the internal environment of the pressure vessel is harsh: high temperature, high pressure, strong acid, strong alkali, etc., when the liquid level measuring instrument is in direct contact with the medium in the container, there is not only a risk of being corroded by the medium in the container, but also affects the measurement accuracy and reliability, and the material requirements for the liquid level measuring instrument are relatively high. Therefore, the liquid level measurement of pressure vessels in the alumina industry is more suitable for a non-intrusive measurement method that is resistant to environmental interference to avoid pollution and reduced accuracy caused by direct contact with the measured liquid. At present, the commonly used non-intrusive liquid level measurement methods for pressure vessels mainly use various principles such as rays, electromagnetic waves, and light to indirectly obtain the liquid level value in the container, such as radar level measurement method, ultrasonic level measurement method, nuclear radiation level measurement method, etc. Among them, the radar level measurement method uses microwave radar technology for measurement, and the nuclear radiation level measurement method uses the principle that the intensity of nuclear radiation passing through the material varies with the thickness of the material layer. These two level measurement methods have high accuracy, but the measurement cost is relatively expensive, and the nuclear radiation level measurement method has certain safety hazards; while the ultrasonic level measurement method uses the propagation characteristics of ultrasonic waves for measurement. Although this method is easy to implement and has moderate cost, it is easy to produce errors when measuring volatile and foam-prone liquids.

[0003] The team of this invention has previously developed a method for measuring the liquid level of pressure vessels used in the alumina industry and applied for relevant patents. This technology discloses a method for measuring the liquid level of pressure vessels used in the alumina industry: according to the relationship between the sound waves generated by the medium in the pressure vessel used in the alumina industry during the flow process and the liquid level characteristics of the medium in the container, a sound sensing element is set at the bottom of the pressure vessel, and the sound wave echo received by the element is converted with the obtained sound wave frequency-liquid level height standard characteristic relationship to obtain the liquid level. This method can well solve the problem of liquid level measurement of pressure vessels, but when this method is used in a noisy environment or when the flow speed of the medium in the container is slow, the measurement results still have certain deviations. Summary of the invention

[0004] The purpose of the present invention is to provide an active vibration wave liquid level measurement method for pressure vessels used in the alumina industry. The principle of this method is based on the physical characteristics of sound wave reflection, and according to the characteristic relationship between the echo frequency change generated by the vibration source in the medium in the container and the liquid level height in the container, non-intrusive real-time monitoring of the pressure vessel liquid level is achieved.

[0005] The technical solution of the present invention is: an active vibration wave liquid level measurement method for pressure vessels used in the alumina industry, wherein a vibration source and a sound sensing element are arranged at the bottom of the pressure vessel, the sound wave characteristics of the vibration source are very different from the sound waves in the production process environment of the alumina industry, and the sound wave frequency generated by the contact between the vibration source sound wave and the medium in the container is converted by comparing the sound wave frequency-liquid level height characteristic curve relationship, thereby realizing non-intrusive real-time liquid level monitoring of the pressure vessel under environmental interference during production operation.

[0006] In the aforementioned active vibration wave level measurement method for a pressure vessel used in the alumina industry, the specific steps are as follows:

[0007] (1) A vibration source and a sound sensor element that are very different from the environmental sound waves of the alumina industry are set at the bottom of the pressure vessel. The distance from the horizontal plane where the vibration source and the sound sensor element are located to the liquid surface of the medium in the container is the liquid surface height H to be measured;

[0008] (2) The vibration source outputs vibration within a fixed frequency band P0 = [a, b]. The vibration wave beam propagates in the container medium and is reflected back from the liquid surface. The reflected echo is received by the sound sensing element and transmitted to the liquid level measurement data background for processing. The sound wave frequency-liquid level height characteristic curve relationship is used to convert the measured liquid level height H.

[0009] In the above-mentioned active vibration wave level measurement method for pressure vessels used in the aluminum oxide industry, the echo P received by the acoustic element r Extract the maximum peak segment {P r (x), x=a,...,b}, filter out the clutter and retain the valid data.

[0010] In the above-mentioned active vibration wave liquid level measurement method for pressure vessels used in the alumina industry, the relationship between the acoustic wave frequency and liquid level height characteristic curve can be expressed by the formula Indicates that It is related to the medium in the container and the thickness of the container wall, and the average value is taken. As the final liquid level value, in the above formula, H-the height of the liquid level to be measured; T-the temperature of the liquid to be measured; K-the correction coefficient, the value is 0.01~2.5; X-the sampling array; P r -The total amount of attenuated audio amplitude received by the sound sensor; P0-the frequency amplitude of the original sound wave generated by the flow; Z m-Acoustic impedance of the medium container; w-attenuation coefficient.

[0011] In the aforementioned active vibration wave level measurement method for pressure vessels used in the alumina industry, the correction coefficient K is related to the factors affecting the sound wave: the internal pressure of the vessel, the medium temperature, and the impurity deposition; Where P i is the internal pressure of the container, P s is the standard atmospheric pressure, △T is the difference between the actual temperature and the temperature under standard conditions. When the container contains gas, liquid, and slurry respectively, A is 0.5, 1, and 2 respectively.

[0012] In the aforementioned active vibration wave liquid level measurement method for a pressure vessel used in the alumina industry, the vibration source and the sound sensing element are arranged inside the soundproof cover.

[0013] In the aforementioned active vibration wave level measurement method for pressure vessels used in the alumina industry, the reflected echo is received by the sound sensing element and transmitted to the level measurement data background for processing through the sensor, thereby obtaining the measured liquid level height H, which is displayed through the on-site liquid level display screen.

[0014] Beneficial effects of the present invention: Compared with the prior art, the present invention has the following advantages due to the adoption of the above technical solution:

[0015] ① Non-intrusive liquid level measurement has a wider range of applications and no special requirements for the medium itself, and is suitable for alumina production processes;

[0016] ② It has low dependence on environmental noise and the flow rate and pressure of the medium in the pressure vessel. The introduction of active vibration brings higher measurement accuracy and a larger liquid level measurement range;

[0017] ③The principle is simple, the components used are common and universal, and the cost is low;

[0018] ④ There is no high additional energy consumption such as radar, sonar, electromagnetic, radiation, etc. during the liquid level measurement process, with low cost and high safety performance;

[0019] ⑤ By utilizing the characteristic relationship between the sound waves generated by the vibration source set at the bottom of the pressure vessel and the liquid level of the medium in the container, real-time monitoring with high accuracy can be achieved.

[0020] In summary, the present invention realizes real-time monitoring of the liquid level based on the characteristic relationship between the sound wave echo generated when the bottom of the pressure vessel vibrates and the liquid level of the medium in the container. It has a simple principle, is easy to use, and significantly reduces the cost of liquid level measurement. It has low cost and low additional energy consumption during operation, making the liquid level measurement of the pressure vessel used in the alumina production process more efficient, reliable, energy-saving, and safe, and the measurement results are more accurate. The error range can be controlled within 1% to 2%, which is smaller than the error standard of most level meter measurement methods on the market. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is a schematic diagram of the present invention.

[0022] Figure numerals: 1-vibration source, 2-sound sensing element, 3-soundproof cover, 4-sensor, 5-liquid level measurement data background, 6-on-site liquid level display screen. DETAILED DESCRIPTION

[0023] The present invention is further described below in conjunction with the accompanying drawings and embodiments, but they are not intended to limit the present invention.

[0024] An embodiment of the present invention: An active vibration wave liquid level measurement method for a pressure vessel for the alumina industry, wherein a vibration source 1 and a sound sensing element 2 are arranged at the bottom of the pressure vessel, and a soundproof cover 3 is arranged outside the two. The vibration source 1 vibrates at a fixed frequency and intensity, and the sound wave characteristics of the vibration source 1 are very different from the sound waves in the production process environment of the alumina industry. The sound waves emitted by the vibration source 1 within a fixed frequency band are propagated to the liquid surface through the container wall, reflected at the medium liquid surface and formed into echoes, which are collected by the sound sensing element 2 and converted into electrical signals of different amplitudes. The sensor 4 transmits the sound wave electrical signal generated by the medium in the pressure vessel during the vibration process received by the sound sensing element 2 to the liquid level measurement data background 5, and the liquid level measurement data background 5 automatically processes data according to the echo frequency-liquid level height standard characteristic relationship, and realizes non-intrusive real-time monitoring of the liquid level of the pressure vessel under environmental interference during production operation, obtains the liquid level height H to be measured, and returns the liquid level height H to be measured in digital form to the on-site liquid level display screen 6 and the control center.

[0025] The specific steps are as follows:

[0026] (1) A vibration source 1 and a sound sensor 2 which are very different from the environmental sound waves of the alumina industry are arranged at the bottom of the pressure vessel. The distance from the horizontal plane where the vibration source 1 and the sound sensor 2 are located to the liquid surface of the medium in the container is the liquid surface height H to be measured;

[0027] (2) The vibration source 1 outputs vibration within a fixed frequency band P0 = [a, b]. The vibration wave beam propagates in the container medium and is reflected back from the liquid surface. The reflected echo is received by the sound sensing element 2 and transmitted to the liquid level measurement data background 5 through the sensor 4 for processing. The liquid level measurement data background 5 uses the sound wave frequency-liquid level height characteristic curve relationship to convert and obtain the measured liquid level height H.

[0028] The echo P received by the sound sensor 2 r Extract the maximum peak segment {P r (x), x = a, ..., b}, the level measurement data needs to be processed by the background 5 to filter out the clutter and retain the valid data.

[0029] The relationship between the acoustic wave frequency and liquid level height characteristic curve can be expressed by the formula Indicates that It is related to the medium in the container and the thickness of the container wall, and the average value is taken. As the final liquid level value, in the above formula, H-the height of the liquid level to be measured; T-the temperature of the liquid to be measured; K-the correction coefficient, the value is 0.01~2.5; X-sampling array, for example, there are a sampling results, all the results are gathered into an array X, and the average value of this array is taken, which is the average acoustic wave result; P r -The total amount of attenuated audio amplitude received by the sound sensor; P0-the frequency amplitude of the original sound wave generated by the flow; Z m -Acoustic impedance of the medium container; w-attenuation coefficient.

[0030] The key technology of the above method lies in the frequency detection and data processing of vibration wave echo. The established sound wave frequency-liquid level height standard characteristic curve relationship formula is derived from the mean of multiple experimental measurements and the results of linear fitting statistical analysis. It reduces the measurement error caused by medium precipitation and temperature change in the container to a certain extent, and controls the error range to 1% to 2%, which is smaller than the error standard of most liquid level meter measurement methods on the market.

[0031] When the vibration wave propagates in the pressure vessel, it may be affected by factors such as aluminum oxide impurity deposition, alkali solution bubbles, and container wall thickness. Therefore, the vibration wave and the reflected echo do not always propagate vertically. The attenuation effect produced during the beam propagation process is represented by the correction coefficient K, thereby reducing the measurement error caused by uncertainty factors. The correction coefficient K is related to the factors affecting the sound wave: container internal pressure, medium temperature, and impurity deposition; Where P i is the internal pressure of the container, P s is the standard atmospheric pressure, △T is the difference between the actual temperature and the temperature under standard conditions. When the container contains gas, liquid, and slurry respectively, A is 0.5, 1, and 2 respectively.

[0032] When impurities are deposited at the bottom of the container, the sound wave frequency at the critical point between the impurities and the medium to be measured is weakened. At this time, it is necessary to continuously move the sound sensing element on the outer wall of the pressure vessel to observe the change of the sound wave signal, and perform multiple tests to roughly locate the solid-liquid interface where the impurities are deposited in the container (below the critical position of deposition below the liquid level, the sound wave frequency is relatively stable and no longer changes). Instead of directly measuring the liquid level value, after obtaining the estimated value of the deposition interface height, continue to measure and calculate the liquid level to be measured in the container. 液-固 The value is 1.8 to 2.5 according to the deposition height.

[0033] The vibration source and the sound sensing element are arranged inside the soundproof cover to avoid being affected by external environmental noise.

[0034] Take the evaporator in the evaporation workshop of the Bayer alumina plant as an example. The evaporator is a split tubular falling film evaporator with an elliptical head and a conical bottom structure, a diameter of 5m, a straight section height of 5m, a working pressure of 0.5Mpa, a working temperature of 158℃, and a medium in the tank of sodium aluminate solution and steam. Usually, a nuclear radiation level meter is used for measurement, which is expensive. At the same time, due to the presence of nuclear radiation, a nuclear source needs to be set up. In order to ensure safety, the operation is complicated and the approval procedures are cumbersome. After setting up the level meter using this method, the real-time liquid level measurement function can be realized, the measurement accuracy reaches ±5%, and it is low in price, easy to operate and safe.

Claims

1. An active vibration wave liquid level measurement method for pressure vessels used in the alumina industry, characterized in that: A vibration source and an acoustic element are arranged at the bottom of the pressure vessel. The acoustic wave characteristics of the vibration source are very different from the acoustic waves in the production process environment of the alumina industry. According to the change in the acoustic wave frequency generated by the contact between the acoustic wave of the vibration source and the medium in the container, the acoustic wave frequency-liquid level height characteristic curve is used for conversion, thereby realizing non-intrusive real-time liquid level monitoring of the pressure vessel under environmental interference during production operation.

2. The active vibration wave liquid level measurement method for a pressure vessel for the alumina industry according to claim 1, characterized in that: The specific steps are as follows: (1) A vibration source and a sound sensor element that are very different from the environmental sound waves of the alumina industry are set at the bottom of the pressure vessel. The distance from the horizontal plane where the vibration source and the sound sensor element are located to the liquid surface of the medium in the container is the liquid surface height H to be measured; (2) The vibration source outputs vibration within a fixed frequency band P0 = [a, b]. The vibration wave beam propagates in the container medium and is reflected back from the liquid surface. The reflected echo is received by the sound sensing element and transmitted to the liquid level measurement data background for processing. The sound wave frequency-liquid level height characteristic curve relationship is used to convert the measured liquid level height H.

3. The active vibration wave liquid level measurement method for a pressure vessel for the aluminum oxide industry according to claim 2, characterized in that: The echo P received by the sound sensor r Extract the maximum peak segment {P r (x), x=a,...,b}, filter out the clutter and retain the valid data.

4. The active vibration wave liquid level measurement method for a pressure vessel for the aluminum oxide industry according to claim 2, characterized in that: The relationship between the acoustic wave frequency and liquid level height characteristic curve can be expressed by the formula Indicates that It is related to the medium in the container and the thickness of the container wall, and the average value is taken. As the final liquid level value, in the above formula, H-the height of the liquid level to be measured; T-the temperature of the liquid to be measured; K-the correction coefficient, the value is 0.01~2.5; X-the sampling array; P r -The total amount of attenuated audio amplitude received by the audio sensor; P0-the frequency amplitude of the original sound wave generated by the flow; Z m -Acoustic impedance of the medium container; w-attenuation coefficient.

5. The method for measuring the liquid level of a pressure vessel for the aluminum oxide industry according to claim 4, characterized in that: The correction coefficient K is related to the factors affecting the sound wave: the internal pressure of the container, the medium temperature, and the impurity deposition; Where P i is the internal pressure of the container, P s is the standard atmospheric pressure, △T is the difference between the actual temperature and the temperature under standard conditions. When the container contains gas, liquid, and slurry respectively, A is 0.5, 1, and 2 respectively.

6. The method for measuring the liquid level of a pressure vessel for the aluminum oxide industry according to claim 1, characterized in that: The vibration source and the sound sensing element are arranged inside the soundproof cover.

7. The method for measuring the liquid level of a pressure vessel for the aluminum oxide industry according to claim 2, characterized in that: The reflected echo is received by the sound sensing element and transmitted to the liquid level measurement data background through the sensor for processing, thereby obtaining the liquid level height H to be measured, and the liquid level height H to be measured is displayed through the on-site liquid level display screen.

Images