Low-temperature liquid density measuring device based on resonant tube

Abstract

The invention relates to the technical field of energy, and discloses a low-temperature liquid density measuring device based on a resonant tube, which comprises a vibration element immersed in measured liquid and used for responding to liquid density change through natural vibration frequency of the vibration element; the excitation assembly and the detection assembly are respectively used for generating excitation force to drive the vibration element to vibrate and detecting a vibration frequency signal of the vibration element; the self-excited oscillation circuit is electrically connected with the detection assembly and the excitation assembly and is used for processing the vibration frequency signal to form closed-loop oscillation and feeding back the closed-loop oscillation to the excitation assembly to maintain vibration; the signal processing module is used for collecting a vibration frequency signal sent by the self-excited oscillation circuit and calculating the liquid density based on the relationship between the frequency and the density; wherein the vibration element is prepared through hot working treatment. Based on the scheme, the liquid density can be accurately measured in a low-temperature environment.

Description

Technical Field

[0001] The invention relates to the field of energy technology, and in particular to a resonance tube-based low-temperature liquid density measuring device. Background Art

[0002] Liquefied natural gas (LNG) is a cheap and clean energy source, and the energy allocation method of tank storage and transportation of liquefied natural gas is very popular. Since liquefied natural gas is a low-temperature liquid formed by low-temperature liquefaction of gaseous natural gas, it has strict requirements on the storage environment. During long-term storage, the liquid in the tank is prone to violent evaporation and tumbling. Stratification is the direct cause of tumbling, and the density difference between the upper and lower layers of liquid is an important feature of stratification. Therefore, it is necessary to regularly test the density of liquefied natural gas in the tank.

[0003] Most of the online liquid density measurement technologies on the domestic market are measured under normal temperature. The LNG density meters in domestic energy stations are basically purchased from abroad. At present, there are studies on cryogenic liquid density systems based on capacitance in China, but the capacitance measurement process is easily affected by vibration and has a long response time, which is not suitable for online industrial measurement. There are many studies on cryogenic liquid density measurement abroad, but the price is expensive. Commonly used methods include buoyancy method, ultrasonic method and ray method. The buoyancy method is a static measurement and needs to be measured in a laboratory environment, which is not suitable for online detection; the ultrasonic method is greatly affected by the interference of liquid impurities, which affects the measurement accuracy and stability of the system; the radioactive substances in the ray method are harmful to the human body, and the anti-electromagnetic interference performance is poor, so it cannot be used in occasions with complex working environments. Summary of the invention

[0004] In order to solve the above technical problems, the present invention provides a cryogenic liquid density measuring device based on a resonance tube.

[0005] The present invention provides a cryogenic liquid density measuring device based on a resonance tube type, comprising: A vibrating element, which is immersed in the liquid to be measured and responds to changes in the liquid density through its natural vibration frequency; The excitation component and the detection component are used to generate an excitation force to drive the vibration element to vibrate, and to detect the vibration frequency signal of the vibration element; A self-excited oscillation circuit, electrically connected to the detection component and the excitation component, for processing the vibration frequency signal to form a closed-loop oscillation and feeding back to the excitation component to maintain vibration; A signal processing module, used for collecting the vibration frequency signal sent by the self-excited oscillation circuit and calculating the liquid density based on the relationship between frequency and density; Wherein, the vibration element is prepared by heat treatment.

[0006] Optionally, the vibration element includes a vibration tube, an upper cap and a base mounted on both ends of the vibration tube.

[0007] Optionally, the excitation component and the detection component both include a magnetic circuit structure and a coil, the magnetic circuit structure includes an annular peripheral wall and a central pole shoe, and the coil is coaxially nested between the peripheral wall and the pole shoe.

[0008] Optionally, the axial directions of the excitation component and the detection component are both perpendicular to the axial direction of the vibration element, and the three are located in the same plane; The side of the annular peripheral wall facing the vibration element is open.

[0009] Optionally, it also includes: The safety isolation circuit is electrically connected to the input end of the excitation component and the output end of the detection component.

[0010] Optionally, the safety isolation circuit includes a parallel-connected voltage-stabilizing diode group, a series-connected current-limiting resistor and a fuse.

[0011] Optionally, the self-excited oscillation circuit includes a frequency selection unit, a phase shift unit and an amplitude stabilization amplification drive unit, wherein: The frequency selection unit is an LC parallel resonant circuit; The phase shift unit includes an adjustable resistance network; The amplitude-stabilizing amplifying driving unit comprises a current amplifying structure composed of a multi-stage operational amplifier and a triode.

[0012] The present invention has the following technical effects: The low-temperature liquid density measuring device based on the resonance tube provided by the present invention detects the density of the low-temperature liquid based on the principle of resonance. When the liquid density changes, the natural vibration frequency of the vibration element immersed in the measured liquid will also change accordingly, and based on the change of the natural vibration frequency of the vibration element, the device provided by the present invention can detect the vibration frequency signal, and then calculate the liquid density according to the calibration relationship between the detected vibration frequency signal and the density of the measured liquid. That is, the present invention can determine the liquid density. Furthermore, in a low-temperature environment, the temperature has a greater influence on the elastic modulus of the vibration element. Therefore, the vibration element in the present invention is prepared by heat treatment. The elastic modulus of the vibration element that has been heat treated is less affected by temperature, so it is more suitable for low-temperature environments and can accurately measure the density of liquids in low-temperature environments. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] In order to more clearly illustrate the specific implementation methods of the present invention or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0014] Figure 1 A schematic structural diagram of a cryogenic liquid density measuring device based on a resonance tube type provided in an embodiment of the present invention; Figure 2 A front view of a vibration element structure provided by an embodiment of the present invention; Figure 3 A cross-sectional view of the structure of an excitation component or a detection component provided in an embodiment of the present invention.

[0015] Reference numerals

[0016] 1. Vibration element; 2a. Excitation component; 2b. Detection component; 3. Self-excited oscillation circuit; 4. Signal processing module; 101. Vibration tube; 102. Upper cap; 103. Base; 201. Magnetic circuit structure; 202. Coil; 201a. Annular peripheral wall; 201b. Center pole shoe; 5. Safety isolation circuit; 301. Frequency selection unit; 302. Phase shift unit; 303. Amplitude stabilization amplification drive unit. DETAILED DESCRIPTION

[0017] In order to make the purpose, technical solution and advantages of the present invention clearer, the technical solution of the present invention will be described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work belong to the scope of protection of the present invention.

[0018] Figure 1 A schematic structural diagram of a cryogenic liquid density measuring device based on a resonance tube type provided in an embodiment of the present invention includes: The vibrating element 1 is immersed in the liquid to be measured and responds to the change of the liquid density through its natural vibration frequency.

[0019] The excitation component 2 a and the detection component 2 b are respectively used to generate an excitation force to drive the vibration element 1 to vibrate, and to detect a vibration frequency signal of the vibration element 1 .

[0020] The self-excited oscillation circuit 3 is electrically connected to the detection component 2b and the excitation component 2a, and is used to process the vibration frequency signal to form a closed-loop oscillation and feed back to the excitation component 2a to maintain the vibration.

[0021] The signal processing module 4 is used to collect the vibration frequency signal sent by the self-excited oscillation circuit 3 and calculate the liquid density based on the relationship between frequency and density.

[0022] The vibration element 1 is prepared by heat treatment.

[0023] like Figure 1 As shown, the device realizes the density measurement of cryogenic liquid by changing the natural frequency of the vibration element 1. After the vibration element 1 is immersed in the liquid to be measured, its vibration frequency shifts as the density of the liquid changes. The excitation component 2a generates an initial exciting force to drive the vibration element 1 to vibrate, and the detection component 2b captures the vibration frequency signal in real time and transmits it to the self-excited oscillation circuit 3. The circuit can select the frequency, shift the phase and amplify the vibration frequency signal. After the vibration frequency signal is transmitted back to the excitation component 2a, a closed-loop feedback is formed to maintain the continuous and stable oscillation of the vibration element 1, and at the same time it is transmitted to the signal processing module 4. The signal processing module 4 collects the vibration frequency of the vibration frequency signal and calculates the liquid density in combination with the pre-calibrated frequency-density relationship. That is, based on the above scheme, the present invention can realize the measurement of liquid density. Among them, the liquid to be measured can be liquefied natural gas in a low-temperature state.

[0024] Considering that the application scenario of the present invention is a low-temperature environment, which has a great impact on the detection results, the embodiment of the present invention makes additional improvements to the vibration element 1. The vibration element 1 adopts a thermal processing process to eliminate the residual stress of the material through annealing, so that the temperature sensitivity of the elastic modulus in a low-temperature environment is significantly reduced, thereby reducing the impact of temperature fluctuations on the measurement accuracy. Experiments have shown that the temperature sensitivity of the elastic modulus of the material can be effectively reduced through thermal processing, so that the frequency measurement error is less than 0.05% in the range of -196°C to 25°C. Specifically, the specific method of the thermal processing process can be to place the formed vibration element 1 in a high-temperature environment, such as an 800°C environment, and after heating for a certain period of time, perform annealing.

[0025] Figure 2 A front view of a vibration element structure provided by an embodiment of the present invention. In some embodiments, the vibration element 1 includes a vibration tube 101 , an upper cap 102 sleeved on both ends of the vibration tube 101 , and a base 103 .

[0026] like Figure 2As shown, the vibration element 1 is composed of a cylindrical vibration cylinder 101, an upper cap 102 and a base 103 mounted on both ends thereof. The vibration cylinder 101 serves as a core vibrator, and both ends are fixed to the base 103 through the upper cap 102. During vibration, the middle part of the cylinder is the maximum deformation zone. This design concentrates the vibration energy and effectively improves the signal-to-noise ratio of the frequency signal. The upper cap 102 and the base 103 are connected by a flange. The base 103 can effectively prevent the vibration coupling between the vibration cylinder 101 and the external body and affect the detection result. The upper cap 102 can better counterweight the entire vibration cylinder, so that the vibration cylinder 101 can produce the maximum displacement deformation in the middle position during vibration, thereby improving the detection accuracy.

[0027] The material of the vibration cylinder 101 of the vibration element 1 can be 3J53. The yield strength of 3J53 at -196°C reaches 1850MPa, which is only 2.3% lower than that at room temperature, which is better than 304 stainless steel (15% lower), ensuring the structural rigidity during low-temperature vibration. The specific heat treatment methods of the vibration cylinder 101 may include: Stress release stage: heat up to 650℃ at a rate of 200℃ / h and keep warm for 4 hours to eliminate cold working stress.

[0028] Recrystallization stage: Continue to raise the temperature to 800℃±10℃ and keep it for 2 hours to refine the grain size to 8-12μm.

[0029] Stabilization treatment: Cool to -100℃ at 50℃ / h to eliminate austenite residue.

[0030] After this treatment, the temperature coefficient of elastic modulus of 3J53 alloy in the LNG (liquefied natural gas) temperature range (-170℃ to -150℃) is reduced to 1.1×10⁻ 4 / ℃, 58% lower than conventional treatment.

[0031] Figure 3 A cross-sectional view of an excitation component or a detection component structure provided in an embodiment of the present invention. In some embodiments, the excitation component 2a and the detection component 2b both include a magnetic circuit structure 201 and a coil 202, the magnetic circuit structure 201 includes an annular peripheral wall 201a and a central pole shoe 201b, and the coil 202 is coaxially nested between the peripheral wall 201a and the pole shoe 201b.

[0032] Specifically, the overall structures of the excitation component 2a and the detection component 2b can be regarded as the same, with only certain differences in some parameters, so the excitation component 2a and the detection component 2b are illustrated here by a figure.

[0033] The annular wall 201a can be made of AlNiCo, and the center pole shoe 201b can be made of 1J85. AlNiCo has good temperature stability. It has a very low temperature coefficient of only 0.03% / K in a wide temperature range of 0.1K (-273℃) to 673K ​​(399℃), which is more suitable for low temperature environments. 1J85 can work in an environment of -200℃ and has the characteristics of high magnetic permeability and low hysteresis loss. After the annular wall 201a and the center pole shoe 201b are combined, the magnetic field of the annular wall 201a will magnetize the center pole shoe 201b to form a static magnetic field, and the AC magnetic field generated by the coil 202 will magnetize and demagnetize the center pole shoe 201b to form a dynamic magnetic field. When the AC signal of coil 202 is a positive voltage, a large electromagnetic force will be generated to excite the vibration element 1 to produce a small displacement. When the signal is 0 or a negative voltage, the electromagnetic force becomes particularly small. At this time, the vibration element 1 can quickly return to its original approximate position due to its elastic properties, thereby forming the vibration of the vibration element 1.

[0034] This design can reduce magnetic leakage, improve magnetic field utilization, and reduce crosstalk between excitation and detection signals. The coil 202 is directly wound around the pole shoe 201b, and there is no other intermediate structure between the two. This can effectively reduce the volume of the excitation component 2a and the detection component 2b. The experimental results show that this structure does not affect the detection results. After verification, it was found that when the pole shoe diameter d of the pole shoe 201b and the wall thickness t of the vibration tube 101 meet d=2t+0.5mm (t=0.3mm corresponds to d=1.1mm), the magnetic field uniformity is improved to 98%. 1J85 high magnetic permeability alloy (μr=8×10 4 ), so that the leakage rate is reduced from 12% of conventional silicon steel to 4.7%. The coil 202 of the excitation component 2a can be wound with 800 turns of 0.06mm enameled wire, with a DC resistance of 100Ω. Under the action of the magnetic ring structure, only 20mA of driving current is required to generate a 65mT magnetic field.

[0035] A compensating winding may be introduced into the coil 202 of the detection component 2b to offset the change in magnetic flux caused by the vibration displacement.

[0036] For the coil 202, the enameled wire of the coil 202 may be pre-treated by three heat cycles of -196°C → 150°C before winding to eliminate internal stress.

[0037] In addition, nano-alumina-filled epoxy resin (thermal conductivity 1.2 W / m·K) can be used and vacuum pressure impregnated three times to ensure no cracking at LNG temperature.

[0038] Combined with reference Figure 1 and Figure 3, in some embodiments, the axial directions of the excitation component 2a and the detection component 2b are both perpendicular to the axial direction of the vibration element 1, and the three are located in the same plane.

[0039] The side of the annular peripheral wall 201a facing the vibration element 1 is open.

[0040] Specifically, the axial directions of the excitation component 2a and the detection component 2b are perpendicular to the axis of the vibration element 1, and the three are located in the same plane. The side of the annular peripheral wall 201a facing the vibration element 1 is an open design. As Figure 3 shown, the side of the annular peripheral wall 201a facing away from the vibration element 1 is a closed design, so the cross-section of the structure is Figure 3 shown as approximately "mountain" shaped. The coil is sleeved on the column of the central pole shoe 201b, which can directly make the magnetic field act on the surface of the vibration cylinder 101, reducing the magnetic circuit loss. This arrangement optimizes the coupling efficiency between the magnetic field and the vibration direction, and the open structure further reduces the magnetic resistance, improving the excitation force and detection sensitivity.

[0041] Based on the above scheme, the magnetic field intensity of the improved excitation component 2a or detection component 2b can be increased from about 5 mT of the single-coil magnetic field to about 65 mT.

[0042] In some embodiments, it further includes: A safety isolation circuit 5, electrically connected to the input end of the excitation component 2a and the output end of the detection component 2b.

[0043] Considering that the application scenario of the embodiment of the present invention is liquefied natural gas, which is different from other ordinary types of liquid density measurement and has a greater potential hazard of explosion and fire, the present invention additionally provides a safety isolation circuit 5.

[0044] The safety isolation circuit 5 is electrically connected to the input end of the excitation component 2a and the output end of the detection component 2b. In some embodiments, the safety isolation circuit 5 may include a parallel-connected group of zener diodes, a series-connected current-limiting resistor, and a fuse. When an overvoltage occurs in the circuit, the group of zener diodes breaks down and conducts to limit the voltage peak. In the case of overcurrent, the current-limiting resistor and the fuse work together. The former inhibits the increase in current, and the latter fuses to cut off the circuit. This design meets the explosion-proof requirements in an explosive and flammable environment and ensures the safe operation of the system.

[0045] Among them, the group of zener diodes can be four 1SMB5349 in parallel, with a regulated voltage value of 12V. The four current-limiting resistors are 226Ω, 226Ω, 249Ω, and 510Ω respectively, matching the current requirements for intrinsic safety explosion protection. The fuse uses the PICO 305 series (227V / 0.5A) dedicated to intrinsic safety electrical equipment, meeting the Class I Div 1 explosion-proof requirements.

[0046] Continue reading Figure 1 In some embodiments, the self-excited oscillation circuit 3 includes a frequency selection unit 301, a phase shift unit 302 and an amplitude stabilization amplification drive unit 303, wherein: The frequency selection unit 301 is an LC parallel resonant circuit.

[0047] The phase shift unit 302 includes an adjustable resistance network.

[0048] The amplitude-stabilizing amplifying driving unit 303 includes a current amplifying structure composed of a multi-stage operational amplifier and a transistor.

[0049] Specifically, the self-excited oscillation circuit 3 is composed of a frequency selection unit 301, a phase shift unit 302 and a stable amplitude amplification drive unit 303. The frequency selection unit 301 uses an LC parallel resonant circuit to filter out the natural frequency signal of the vibration element 1. The phase shift unit 302 adjusts the phase through an adjustable resistor network to meet the oscillation phase condition. The stable amplitude amplification drive unit 303 can be composed of a two-stage operational amplifier and a triode combination, the front stage amplifies the signal amplitude, and the rear stage increases the driving current to ensure that the excitation coil 202 generates sufficient excitation force.

[0050] Where, the LC resonant frequency f 0 =1 / (2π ), L=10mH±2%, C= 220nF, bandwidth <2kHz. The adjustable resistor network can adjust the phase in the range of 0°~180° by adjusting the variable resistor. Both stages of the operational amplifier use the low-power, low-noise, zero-drift LTC2055IMS8 operational amplifier, with a gain of up to 130dB and a voltage drift of only 3uV / ℃.

[0051] It should be noted that the terms used in the present invention are only for describing specific embodiments, rather than limiting the scope of the present application. As shown in the present specification, unless the context clearly indicates an exception, the words "one", "a", "a kind of" and / or "the" do not specifically refer to the singular, but may also include the plural. The terms "include", "comprise" or any other variant thereof are intended to cover non-exclusive inclusion, so that the process, method or device including a series of elements includes not only those elements, but also includes other elements not explicitly listed, or also includes elements inherent to such process, method or device. In the absence of more restrictions, the elements defined by the sentence "include one..." do not exclude the presence of other identical elements in the process, method or device including the elements.

[0052] It should also be noted that the terms "center", "up", "down", "left", "right", "vertical", "horizontal", "inside", "outside", etc., indicating the orientation or positional relationship, are based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention. Unless otherwise clearly specified and limited, the terms "installed", "connected", "connected", etc. should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be an indirect connection through an intermediate medium, or it can be a connection between the two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0053] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the technical solutions of the embodiments of the present invention.

Claims

1. A cryogenic liquid density measuring device based on a resonance tube, characterized in that: include: A vibrating element, which is immersed in the liquid to be measured and responds to changes in the liquid density through its natural vibration frequency; The excitation component and the detection component are used to generate an excitation force to drive the vibration element to vibrate, and to detect the vibration frequency signal of the vibration element; A self-excited oscillation circuit, electrically connected to the detection component and the excitation component, for processing the vibration frequency signal to form a closed-loop oscillation and feeding back to the excitation component to maintain vibration; A signal processing module, used for collecting the vibration frequency signal sent by the self-excited oscillation circuit and calculating the liquid density based on the relationship between frequency and density; Wherein, the vibration element is prepared by heat treatment.

2. The device according to claim 1, characterized in that The vibration element comprises a vibration tube, an upper cap and a base which are sleeved on both ends of the vibration tube.

3. The device according to claim 1, characterized in that The excitation component and the detection component both include a magnetic circuit structure and a coil. The magnetic circuit structure includes an annular peripheral wall and a central pole shoe. The coil is coaxially nested between the peripheral wall and the pole shoe.

4. The device according to claim 3, characterized in that The axial directions of the excitation component and the detection component are both perpendicular to the axial direction of the vibration element, and the three are located in the same plane; The side of the annular peripheral wall facing the vibration element is open.

5. The device according to claim 1, characterized in that Also includes: The safety isolation circuit is electrically connected to the input end of the excitation component and the output end of the detection component.

6. The device according to claim 5, characterized in that The safety isolation circuit comprises a parallel-connected voltage-stabilizing diode group, a series-connected current-limiting resistor and a fuse.

7. The device according to claim 1, characterized in that The self-excited oscillation circuit includes a frequency selection unit, a phase shift unit and an amplitude stabilization amplification drive unit, wherein: The frequency selection unit is an LC parallel resonant circuit; The phase shift unit includes an adjustable resistance network; The amplitude-stabilizing amplifying driving unit comprises a current amplifying structure composed of a multi-stage operational amplifier and a triode.

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