Vortex wet gas phase separation flow measurement method based on liquid film-based film thickness modeling

Abstract

The present application relates to a kind of vortex wet gas phase flow measurement method based on liquid film base film thickness modeling, the measurement system used includes two liquid film thickness sensors, pressure sensor, vortex flowmeter and temperature sensor, the vortex wet gas phase flow measurement method includes the following steps: collecting two-phase flow related data, including collecting two-phase pressure, two-phase temperature, vortex flowmeter time sequence signal and the two liquid film thickness sequence output by two liquid film thickness sensors;Calculate gas density, liquid density, extract vortex signal frequency f VS And base film thickness value δ b , calculate the wave frequency f DW Of coherent disturbance wave, and obtain the wave speed V DW Of coherent disturbance wave;Solving gas phase flow Q g , solving liquid phase flow Q l .

Description

Technical Field

[0001] The invention belongs to the field of wet gas phase separation flow measurement and relates to a vortex street wet gas phase separation flow measurement method based on liquid film base film thickness modeling. Background Art

[0002] Wet gas two-phase flow is widely used in engineering applications such as chemical engineering, nuclear physics, and aerospace. Therefore, it is of great significance to study the method that can measure the flow online[5] and ensure the accuracy of the measurement results.

[0003] In order to measure two-phase flow online, traditional single-phase flowmeters have been widely used in wet gas flow measurement. Vortex flowmeters have been widely used due to their advantages such as low pressure loss, stable operation, no moving parts, and resistance to high temperature and high pressure. They are increasingly used in online measurement of wet gas flow. However, the loading of the liquid phase will produce a positive error in the gas flow, namely the instrument overreading (OR) [1] problem. The maximum OR value can reach 1.14%, which will result in a measurement error of 14% for wet gas. In order to improve the measurement accuracy of vortex flowmeters in wet gas phase separation measurement, overreading compensation is required. Many researchers have developed various overreading models with inlet parameters by fitting experimental data, such as the OR-liquid volume fraction correlation model proposed by Jia [2] and the OR-Lock-Martinelli parameter correlation model proposed by Stewart [3]. However, due to the complex dynamic phase flow conditions (flow direction, material, carrier gas pressure, etc.), it is impossible to derive a general formula, which limits its prediction accuracy and application range. Reference [4], based on the theory of droplet deposition and entrainment in annular flow, comprehensively considered factors such as velocity slip, entrainment rate and droplet diameter to deduce the overreading correction factor and provided a theoretical calculation formula. However, due to the difficulty of real-time measurement of droplet parameters (such as entrainment rate, droplet diameter and velocity) in practice, these formulas are difficult to directly apply to the online monitoring of wet air flow.

[0004] Liquid film parameters are also important parameters for characterizing the internal characteristics of two-phase flow and will also affect the vortex street moisture measurement characteristics. Reference [6] established a correlation formula for the average liquid film thickness and solved it together with the vortex street overreading equation to achieve vortex street overreading compensation. It can be seen that overreading compensation can be achieved using liquid film parameters.

[0005] Liquid film parameters have a variety of measurement methods. Currently, for the measurement of key droplet parameters such as droplet loading and droplet diameter, widely used methods include electrical conductivity measurement, ultrasonic detection and optical monitoring. However, these methods have limitations, not only are the equipment complex, but also the cost is high, making it difficult to popularize in practical applications, especially in realizing real-time online measurement. Patent CN201910134650.8 proposes a new method for measuring liquid film thickness in a humid environment in real time, making online measurement feasible. This patent uses a direct measurement method, which has the advantages of no iterative divergence, lower code implementation cost, faster calculation speed, etc. compared to iterative methods.

[0006] By combining the measurement method of liquid film parameters with the vortex shedding flow study, the compensation of vortex shedding flow can be effectively realized, and the gas phase flow in the wet gas can be measured online, thereby improving the accuracy and reliability of the measurement.

[0007] REFERENCES

[0008] [1] Lu Jia, Shi Yunxiao, Zheng Yonghui. Use vortex flowmeter to measure the mass flow of steam [J]. Petroleum and chemical industry automation, 2006 (4): 79-80.

[0009] [2] Y. F. Jia and D. R. Kong, "A study on measurement uncertainty of a vortex flow meter in discrete liquid

[0010] phase," AMR, vol. 346, pp. 593-599, Sep. 2011.

[0011] [3] D. Stewart, "The evaluation of dry gas meters in wet gas conditions," National Engineering Laboratory,

[0012] London, vol. 33, pp. 58, 2002.

[0013] [4] Zhang Jinjing. Study on the characteristics of vortex flowmeter in gas-liquid two-phase flow [D]. Tianjin: Tianjin University, 2015.

[0014] [5] Li Yongguang, Cai Zuhui, Li Meiling, et al. Research on the method of measuring gas-liquid two-phase flow and composition using vortex characteristics [J]. Instrumentation and analysis, 2015 (1): 1-4.

[0015] Journal, 1998, 19(2): 185-188.

[0016] [6]H.Sun, T.Yang, H.Ding, J.Li, and W.Zhang, “Online measurement of gasand liquid flow rates in wet gas

[0017] using vortex flowmeter coupled with conductance ring sensor," EEETrans.Lnstrum.Meas,vol.33,pp.58,2022 Summary of the Invention

[0018] This invention utilizes a liquid film sensor and a vortex flowmeter to establish a model containing the vortex overread coefficient and the basement membrane liquid film thickness, thereby achieving wet gas phase flow measurement. This invention is not only more accurate, but also provides real-time wet gas phase flow measurement. The technical solution is as follows:

[0019] A vortex wet gas phase flow measurement method based on liquid film base film thickness modeling, the measurement system used includes two liquid film thickness sensors, a pressure sensor, a vortex flowmeter and a temperature sensor, and the vortex wet gas phase flow measurement method includes the following steps:

[0020] (1) Collecting two-phase flow related data, including collecting two-phase pressure, two-phase temperature, vortex flow time sequence signal and two liquid film thickness sequences output by two liquid film thickness sensors;

[0021] (2) Calculate gas density and liquid density and extract vortex signal frequency f VS and base film thickness δ b , calculate the frequency f of the interfering vibration wave DW , and the wave velocity V of the interfering wave is obtained DW ;

[0022] (3) Solve for the gas phase flow rate Q g , the method is:

[0023] 1) Calculate the apparent gas volume flow rate Q according to formula (1): g,apparent

[0024]

[0025] Among them, K v is the instrument factor of the vortex flowmeter in single-phase gas;

[0026] 2) Calculate the vortex over-reading coefficient OR according to formula (2)

[0027]

[0028] Where D is the pipe diameter; k1 is the constant coefficient;

[0029] 3) Calculate the gas phase flow rate Q by formula (3) g ;

[0030]

[0031] (4) Solve for the liquid phase flow rate Q l , the method is:

[0032] 1) Combined with the frequency f of the interfering vibration wave DW , base film thickness δ b , the wave velocity V of the interfering wave DW Modeling and calculation of liquid superficial velocity U sl As shown in formula (4);

[0033]

[0034] Where k2 is a constant coefficient, n1, n2, n3, and n4 are constant power exponents obtained by fitting;

[0035] 2) Solve the liquid phase flow rate Q by formula (5) l ;

[0036]

[0037] Furthermore, in step (1), the collected two-phase flow related data are: two-phase pressure P, two-phase temperature T, vortex flow time sequence signal s(t) and two liquid film thickness sequences δ1(t) and δ2(t) output by two liquid film thickness sensors; in step (2), the gas density ρ is calculated respectively by the collected two-phase pressure P and two-phase temperature T. g and liquid density ρ l ; Perform fast Fourier transform on the time series signal s(t) of the vortex flowmeter to extract the frequency f of the vortex signal VS .

[0038] Furthermore, in step (2), the liquid film thickness sequence signal is processed to generate a probability density distribution curve of the liquid film thickness, and the liquid film thickness corresponding to the maximum value of the probability density distribution is taken as the base film thickness δ b The value of .

[0039] Furthermore, in step (2), the frequency of the liquid film thickness series δ1(t) and δ2(t) is averaged by fast Fourier transform (FFT) to obtain the wave frequency f of the interfering vibration wave. DW .

[0040] Further, in step (2), the correlation estimation is performed using the liquid film thickness sequences δ1(t) and δ2(t) to obtain the wave velocity V of the coherent disturbance wave DW .

[0041] According to the above method, the wet gas separated phase flow measurement is finally realized. And the method has the following advantages:

[0042] (1) Wet gas separated phase flow measurement can be realized

[0043] The method establishes the correlation between the over-reading coefficient OR and the base film liquid film thickness δ b , which can compensate for the over-reading of the uncorrected gas phase flow and realize accurate measurement of the gas phase flow. The model between the liquid film base film thickness δ b , the wave frequency f DW of the coherent disturbance wave, and the wave velocity V DW of the coherent disturbance wave is established to solve the liquid phase flow, and finally realize the wet gas separated phase flow measurement.

[0044] (2) Simple and direct measurement, non-iterative

[0045] This method has low algorithm complexity and low hardware requirement, and can realize wet gas separated phase flow measurement without iteration.

[0046] (3) High prediction accuracy

[0047] Using this method, the relative error of gas phase flow prediction is within ±1.5%; the relative error of liquid phase volume flow prediction is within ±10% in the full range. BRIEF DESCRIPTION OF DRAWINGS

[0048] Figure 1 : overall schematic diagram of the measurement device

[0049] Figure 2 : signal acquisition flowchart

[0050] Figure 3 : wet gas separated phase flow measurement implementation flowchart based on liquid film base film thickness

[0051] Figure 4 : over-reading coefficient OR and dimensionless base film relationship diagram

[0052] Figure 5 : gas phase flow prediction error schematic diagram

[0053] Figure 6 : relationship diagram between actual liquid phase flow diagram and predicted liquid phase flow diagram

[0054] Figure 7 : liquid phase volume flow prediction error schematic diagram DETAILED DESCRIPTION

[0055] The present invention will now be further described with reference to the accompanying drawings and embodiments.

[0056] The overall layout of the measurement system is shown in the attached Figure 1 The system includes a liquid film thickness sensor 1 and a liquid film thickness sensor 2, a pressure sensor 3, a vortex flowmeter 4, and a temperature sensor 5. This example is a vortex wet gas phase flow measurement method based on liquid film base film thickness modeling. The following are specific application details in wet gas flow measurement. Using the multi-parameter adjustable mist flow experimental system in patent 201810644726.7, the wet gas working pressure range is set to 150kPa ~ 350kPa, and the gas phase flow rate is between 12m 3 / h~24m 3 / h, and the liquid flow rate was between 0.55mL / s and 4.5mL / s. Furthermore, the experimental conditions included a fixed pipe diameter D of D = 15mm and a constant liquid surface tension σ, set at σ = 0.072N / m.

[0057] The signal acquisition flow chart is as attached Figure 2 As shown in the figure, the sampling frequency of s(t) is set to 100kHz, and the sampling time for each data set is 10s. The sampling frequency of δ(t) is set to 32MHz. Under the excitation of a sinusoidal signal (500kHz), 64 samples are taken per cycle. After 8 sampling cycles, the data is processed by the host computer. P is obtained from the pressure sensor, T is obtained from the temperature sensor, s(t) is obtained from the vortex flowmeter, and δ1(t) and δ2(t) are obtained from the liquid film sensor.

[0058] The gas density ρ is calculated by collecting the two-phase P and T. g and liquid density ρ l ; Perform fast Fourier transform on the time series signal s(t) of the vortex flowmeter to extract the frequency f of the vortex signal VS ; Process the liquid film signal to generate a probability density distribution curve of the liquid film thickness, and take the liquid film thickness corresponding to the maximum value of the probability density distribution as the base film thickness δ b The frequency of the interfering wave f is obtained by averaging the frequencies of δ1(t) and δ2(t) through the fast Fourier transform (FFT). DW ; The velocity V of the interfering vibration wave is obtained by cross-correlation estimation of the liquid time series membrane signals δ1(t) and δ2(t) DW .

[0059] In the wet gas flow scenario, due to the mixing of trace liquid phase, when the vortex flowmeter is used to measure the wet gas, the measured gas phase apparent volume flow rate Q g,apparent Compared with the actual gas flow Q gThis phenomenon is called "over-reading" (OR). g,apparent and the actual gas flow Q g The following relationship exists:

[0060]

[0061] Among them, the gas phase apparent volume flow rate Q g,apparent (m 3 / h) by the vortex shedding frequency f VS Calculated

[0062]

[0063] where K v It is known that the instrument coefficient of the vortex flowmeter in single-phase gas (m -3 ).

[0064] In order to improve the measurement accuracy of gas phase flow, it is necessary to correct the meteorological apparent volume flow. Since the liquid film basement membrane parameters are strongly correlated with the gas phase flow and the liquid film basement membrane parameters are easy to obtain, the liquid film basement membrane thickness δ b Establish the vortex street over-reading coefficient OR prediction model:

[0065]

[0066] Among them, δ b is the base film thickness, and D is the inner diameter of the pipeline.

[0067] The least square method is used to fit the liquid film thickness and OR, and k1 = 2.642 is obtained. Figure 4 As shown. So the OR prediction model:

[0068]

[0069] Considering the different pipe diameters under different experimental conditions, this patent specifies the liquid phase apparent flow velocity U sl After modeling, the liquid phase volume flow rate can be obtained by:

[0070]

[0071] Liquid superficial velocity U sl The frequency f of the interfering wave DW , tube diameter D, base film thickness δ b and the disturbance wave velocity V DW The liquid superficial velocity U is calculated by nonlinear regression. sl Modeling yields:

[0072]

[0073] Under the working conditions of this experiment, the experimental data were fitted by the least squares method, and k2 = 536.7, n1 = 0.214, n2 = 2.034, n3 = 0.655, n4 = 2.090 were obtained, and the equation was obtained as follows:

[0074] U sl =536.7f DW 0.214 D 2.034 δ b 0.655 V DW 2.090 (b7)

[0075] Based on the above modeling and calibration results, the wet gas phase flow measurement is carried out. The implementation process is as shown in the attached Figure 3 As shown, the method is as follows:

[0076] 1. Data Collection

[0077] 1) Collect the two-phase pressure P, two-phase temperature T, vortex flow time sequence signal s(t), and the liquid film thickness sequence δ1(t) and δ2(t) output by the liquid film sensor;

[0078] 2) Calculate the gas density ρ by collecting the two phases P and T g and liquid density ρ l ; Perform fast Fourier transform on the time series signal s(t) of the vortex flowmeter to extract the frequency f of the vortex signal VS ; Process the liquid film signal to generate a probability density distribution curve of the liquid film thickness, and take the liquid film thickness corresponding to the maximum value of the probability density distribution as the base film thickness δ b The value of

[0079] 3) The frequency of the interfering wave is obtained by averaging the frequencies of δ1(t) and δ2(t) through fast Fourier transform (FFT). DW ; The velocity V of the interfering vibration wave is obtained by cross-correlation estimation of the liquid time series membrane signals δ1(t) and δ2(t) DW .

[0080] 2. Solve for the gas phase flow rate Q g :

[0081] 1) Calculate the apparent gas volume flow rate Q by formula (b1) g,apparent

[0082] 2) Calculate the vortex over-reading coefficient OR according to formula (b4)

[0083] 3) Calculate the actual gas phase flow rate Q by formula (b1) g ;

[0084] 3. Solving liquid phase flow rate Q l ;

[0085] 1) Calculate liquid phase superficial velocity U from equation (b7) sl ;

[0086] 2) Calculate flow rate Q from equation (b5) l ;

[0087] According to the method proposed in the patent, the wet gas separated phase flow rate measurement is finally realized. In order to verify the feasibility of the above method, the liquid film base film thickness is used to predict the two-phase flow, and the gas phase flow prediction is shown in the attached Figure 5 , the relative error is within ±1.5%, and the liquid phase volume flow prediction is shown in the attached Figure 7 , the full range relative error is within ±10%.

[0088] The present application constructs a model based on the wet gas liquid film base film thickness and the vortex flowmeter over-reading coefficient, and further proposes a new vortex wet gas separated phase flow measurement method. The essential feature of the method is that the required parameters are easy to measure, the algorithm involved is simple without iteration, and the prediction accuracy is high.

Claims

1. A vortex wet gas phase flow measurement method based on liquid film basement film thickness modeling, wherein the measurement system used includes two liquid film thickness sensors, a pressure sensor, a vortex flowmeter, and a temperature sensor. The vortex wet gas phase flow measurement method includes the following steps: (1) Collecting two-phase flow related data, including collecting two-phase pressure, two-phase temperature, vortex flow time sequence signal and two liquid film thickness sequences output by two liquid film thickness sensors; (2) Calculate gas density and liquid density and extract vortex signal frequency f VS and base film thickness δ b , calculate the frequency f of the interfering vibration wave DW , and the wave velocity V of the interfering wave is obtained DW ; (3) Solve for the gas phase flow rate Q g , the method is: 1) Calculate the apparent gas volume flow rate Q according to formula (1): g,apparent in, K v is the instrument factor of the vortex flowmeter in single-phase gas; 2) Calculate the vortex over-reading coefficient OR according to formula (2) Where D is the pipe diameter; k1 is the constant coefficient; 3) Calculate the gas phase flow rate Q by formula (3) g ; (4) Solve for the liquid phase flow rate Q l , the method is: 1) Combined with the frequency f of the interfering vibration wave DW , base film thickness δ b , the wave velocity V of the interfering wave DW Modeling and calculation of liquid superficial velocity U sl As shown in formula (4); Where k2 is a constant coefficient, n1, n2, n3, and n4 are constant power exponents obtained by fitting; 2) Solve the liquid phase flow rate Q by formula (5) l ; 。 2. The vortex wet gas phase separation flow measurement method according to claim 1, characterized in that: Assume that the collected two-phase flow related data in step (1) are: two-phase pressure P, two-phase temperature T, vortex flow time sequence signal s(t) and two liquid film thickness sequences δ1(t) and δ2(t) output by two liquid film thickness sensors; in step (2), the gas density ρ is calculated respectively by the collected two-phase pressure P and two-phase temperature T. g and liquid density ρ l ; Perform fast Fourier transform on the time series signal s(t) of the vortex flowmeter to extract the frequency f of the vortex signal VS .

3. The vortex wet gas phase separation flow measurement method according to claim 2, characterized in that: In step (2), the liquid film thickness sequence signal is processed to generate a probability density distribution curve of the liquid film thickness, and the liquid film thickness corresponding to the maximum value of the probability density distribution is taken as the base film thickness δ b value.

4. The vortex wet gas phase separation flow measurement method according to claim 2, characterized in that: In step (2), the frequency of the liquid film thickness series δ1(t) and δ2(t) is averaged by fast Fourier transform (FFT) to obtain the wave frequency f of the interfering vibration wave. DW .

5. The vortex wet gas phase separation flow measurement method according to claim 2, characterized in that: In step (2), the cross-correlation estimation is performed using the liquid film thickness series δ1(t) and δ2(t) to obtain the wave velocity V of the interfering vibration wave. DW .

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