Moisture flow measurement method based on vortex street frequency-disturbance wave frequency dual-mode detection

Abstract

The invention discloses a moisture flow measuring method based on vortex street frequency-disturbance wave frequency dual-mode detection, an adopted measuring device comprises an annular electrode pair, a pressure sensor, a temperature sensor and a vortex street flowmeter, and the annular electrode pair is used for obtaining a liquid film thickness sequence; the pressure sensor is used for collecting working condition pressure, the temperature sensor is used for collecting working condition temperature, and the vortex shedding flowmeter is used for collecting vortex shedding signals; the measurement method comprises the following steps: (1) establishing a moisture measurement model; (2) a Newton iteration format with the actual value of the gas phase flow in the moisture as a parameter is obtained; and (3) iteratively solving the gas volume flow.

Description

Technical Field

[0001] The invention belongs to the field of gas-liquid two-phase flow measurement, and relates to a wet gas flow measurement method based on vortex street frequency-disturbance wave frequency dual-mode detection. Background Art

[0002] Wet gas two-phase flow is widely present in industrial processes, such as condensate natural gas carrying a small amount of liquid, wet steam injected into oil wells in heavy oil thermal recovery, etc. It usually refers to gas-liquid two-phase flow with a gas phase volume content greater than 95% or a Lockheed Martin parameter less than 0.3. [1] Annular mist flow is a common fluid form and occupies a core position in many industrial scenarios. Accurate measurement of wet gas two-phase flow is an indispensable part of energy extraction, safe production, transportation and trade, and energy protection. [2] .

[0003] When the gas velocity is high, the annular mist flow is the main wet gas flow pattern, in which the liquid phase exists in the form of entrained droplets and wall liquid film. A small amount of liquid phase in the wet gas will cause the gas phase measurement to be high, resulting in over-reading. To correct the vortex over-reading, it is necessary to obtain the liquid phase content information. The vortex over-reading correction methods can be divided into three categories.

[0004] The first method is to directly measure the liquid content, and then perform over-reading correction by establishing a correlation between vortex over-reading and liquid content. However, for small liquid flow rates, the measurement accuracy is difficult to guarantee, which is likely to cause over-reading correction and lead to greater measurement errors. [3] The second method is to use the additional information of the vortex flowmeter for over-reading correction, but it has high hardware requirements and is difficult to ensure real-time performance. [4] . The third method is to use other two-phase flow information for over-reading correction, which has simple modeling and high measurement reliability. Usually, information such as liquid film thickness and liquid film fluctuation frequency is used for correction. For liquid film thickness, its prediction accuracy depends on the calibration result of liquid film thickness, has high requirements on medium conductivity, and has limited application occasions. Patent CN202310242114.6 [5] It is proposed to use the liquid film fluctuation frequency (disturbance wave frequency) to establish a correction for vortex street overreading. The disturbance wave frequency formula is combined with the vortex street overreading and disturbance wave frequency formulas and then solved. This method can measure the gas and liquid phase flow rates at the same time, but there are many coefficients to be calibrated and the scalability of the model may be limited.

[0005] In wet gas measurement, the main requirement is to ensure the accuracy of gas phase flow measurement, while liquid phase measurement is mainly to ensure low uncertainty in gas phase measurement. Therefore, this patent proposes a wet gas flow measurement method that combines vortex frequency and disturbance wave frequency for gas phase flow measurement in wet gas.

[0006] References

[0007] [1]International Organization for Standardization Report:ISO / TR 11583[S].Measurement of wet gas flow by means of pressure differential devicesinserted in circular cross-section conduits,2012.

[0008] [2]Wet Gas Flowmetering Guideline.document ASME MFC-19G-2008[S].NewYork,USA,2008.

[0009] [3]Hall A, Steven RA discussion on vortex meter technologies with wetgas flows[C].Proceedings of 7th South East Asia Hydrocarbon Flow MeasurementWorkshop,2008:1-20.

[0010] [4] LI JX, WANG C, DING HB, et al. Online measurement of wet gas by modeling frequency and amplitude characteristics of a vortex flowmeter[J]. IEEE Transactions on Instrumentation and Measurement, 2019, 69(6): 3666-3678.

[0011] [5] Li Jinxia, ​​Xiao Zhili. Vortex frequency extraction and wet gas phase flow measurement method combined with disturbance wave frequency characteristics[P]. CN202310242114.6,2023. Summary of the invention

[0012] The present invention belongs to the field of gas-liquid two-phase flow measurement, and relates to a wet gas flow measurement method based on vortex frequency-disturbance wave frequency dual-mode detection. The technical solution of the present invention is as follows:

[0013] A wet gas flow measurement method based on vortex frequency-disturbance wave frequency dual-mode detection, the measurement device used includes an annular electrode pair, a pressure sensor, a temperature sensor and a vortex flowmeter, the annular electrode pair is used to obtain a liquid film thickness sequence d(t); the pressure sensor is used to collect the working pressure P, the temperature sensor is used to collect the working temperature T, and the vortex flowmeter is used to collect a vortex signal s(t), and s(t) and d(t) are respectively subjected to fast Fourier transform to obtain a vortex shedding frequency f vs and the disturbance wave frequency f w ; The measurement method is as follows:

[0014] (1) Establish a moisture measurement model by:

[0015] Actual value of gas phase flow Q g And the gas flow measurement value Q g,apparent There is a relationship as shown in formula (1), where OR is the overread coefficient

[0016]

[0017] Gas flow measurement value Q g,apparent (m 3 / h) is calculated by formula (2)

[0018]

[0019] Among them, f vs is the vortex shedding frequency, K v is the instrument factor of the vortex flowmeter in single-phase dry gas (m -3 );

[0020] The gas phase Weber number We g and the perturbation Post-Trauhal number St LF As a parameter, the vortex street over-reading is fitted using the power exponential form to establish a moisture measurement model, and the formula (3) is obtained:

[0021] OR=a+bSt LF α We g β (3)

[0022] in:

[0023] Perturbed Postrouhal number St LF The definition of is as follows:

[0024]

[0025] Where D is the pipe diameter, U sg is the gas phase superficial velocity;

[0026] Gas phase Weber number We g The definition of is as follows:

[0027]

[0028] Where σ is the surface tension coefficient of the liquid phase, ρ l is the liquid density, ρ g is the gas phase density, which is calculated based on the two-phase operating pressure P and operating temperature T; D is the pipe diameter, U sg is the gas phase superficial velocity, a and b are constant coefficients, α and β are power exponents, and are obtained by least squares regression;

[0029] (2) Obtain the actual value of the gas phase flow rate Q in wet gas g is the Newton iteration format of the parameters;

[0030] (3) Iterative solution of gas volume flow rate Q g .

[0031] Furthermore, the method of step (2) is:

[0032] The actual gas phase volume flow rate Q in wet gas g As parameters, the equation f(Q g )=0, as shown in formula (6):

[0033]

[0034] In the formula, n1=1-α+2β, C1=(f w DA D ) α , Pipe cross-sectional area A D =πD 2 / 4; parameter K is a parameter related to the working conditions.

[0035] The Newton iteration algorithm is used to solve equation (6). The Newton iteration format is:

[0036]

[0037] in,

[0038] Furthermore, the method of step (3) is:

[0039] 1) Collect working parameters, including pressure P, temperature T, vortex signal s(t) and liquid film signal d(t);

[0040] 2) Extract and calculate the operating parameters, including the vortex shedding frequency f vs , disturbance wave frequency f w, gas phase density r g , liquid density r l , liquid surface tension and instrument factor K v ;

[0041] 3) According to formula (2), calculate the gas flow measurement value Q in the two phases g,apparent ;

[0042] 4) Q g,apparent As the initial value of the iteration of gas volume flow rate: Q g,0 =Q g,apparent ;

[0043] 5) Substitute into Newton iteration format formula (7) and solve to obtain the next iteration result Q g,n+1 ;

[0044] 6) Set the threshold w (w = 0.1%), when the convergence condition is met, g,n+1 -Q g,n | / Q g,n When <w is less than, the iteration process ends; otherwise, let n=n+1 and continue back to step 5) until the iteration converges, and the last iteration result is used as the gas volume flow rate Q g .

[0045] and patent CN202310242114.6 [5] The difference is that the present invention directly establishes a correlation formula between vortex street overreading and disturbance wave frequency, which greatly simplifies the model form, reduces the unknown coefficients, and improves the robustness of the model, thereby facilitating the online accurate measurement of wet air flow. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 :Overall diagram of the measuring device

[0047] Figure 2 :Signal acquisition flow chart

[0048] Figure 3 :Flowchart of gas flow measurement implementation based on Newton iteration

[0049] Figure 4 : Vortex over-reading modeling results

[0050] Figure 5 :Comparison chart of predicted value and actual value of gas phase flow in wet gas

[0051] Figure 6 :Distribution diagram of gas phase volume flow prediction error in wet gas

[0052] The markings are as follows:

[0053] 1 Ring electrode 2 Pressure sensor 3 Vortex flowmeter 4 Temperature sensor DETAILED DESCRIPTION

[0054] This embodiment is a specific implementation of the wet gas flow measurement method based on vortex frequency-disturbance wave frequency dual-mode detection in wet gas measurement. The medium in this embodiment is air and water, the flow direction is vertical downward, the wet gas working pressure P = 150 ~ 350kPa, the gas phase volume flow Q g =12~24m 3 / h, liquid volume flow rate Q l =0.55~4.50ml / s.

[0055] like Figure 1 As shown, the measuring device consists of an annular electrode 1, a pressure sensor 2, a vortex flowmeter 3 and a temperature sensor 4. Through the two annular electrodes 1 arranged on the inner side of the pipe wall, the liquid film thickness sequence d(t) is obtained by using the conductivity characteristics of the liquid film. The pressure sensor 2 and the temperature sensor 4 collect the operating pressure P and the operating temperature T. The vortex flowmeter 3 collects the vortex signal s(t), and the piezoelectric probe converts the flow signal into an electrical signal. The hardware circuit amplifies the charge and voltage of the original signal, and the NI-USB6353 acquisition card performs data acquisition, which is displayed and saved in Labview. The sampling frequency is 20kHz and the sampling time is 5s, thereby obtaining the vortex signal s(t). Fast Fourier transform is performed on s(t) and d(t) to obtain the vortex shedding frequency f vs and the disturbance wave frequency f w， like Figure 2 shown.

[0056] According to formula (1), the gas volume flow measurement value can be obtained

[0057]

[0058] Among them, K v is the instrument factor of the vortex flowmeter in single-phase gas (m -3 ), according to the calibration results, in the Reynolds number range of 5.3×10 4 ~1.08×10 5 (Q g =10~25m 3 / h) within K v =336574.54m -3 , the calibration accuracy is ±1% and the linearity is 0.848%.

[0059] The obtained Q g,apparent As the initial value of the iteration of the gas phase volume flow rate, that is, Q g,0 =Q g,apparent .

[0060] According to the Karman vortex street principle, for dry gas flow, within a certain Reynolds number range, the vortex street frequency f is proportional to the average flow velocity U of the incoming flow. In the annular mist wet gas two-phase flow, due to the addition of the liquid phase, the two-phase Strouhal number St = f vs d / U sg It is greater than the Strouhal number St0 in the single phase, which causes the gas phase volume flow rate prediction to be too high in wet gas measurement, thus leading to the over-reading problem of the vortex flowmeter. The over-reading factor OR is as shown in formula (2):

[0061]

[0062] In the formula, Q g and Q g,apparent are the actual value and apparent value of gas phase volume flow in wet gas, St 0,mean It represents the average Strouhal number within the linear Reynolds number range of the instrument under dry gas conditions, and St is the two-phase Strouhal number.

[0063] Vortex overreading and disturbance wave frequency characteristics With the increase of liquid phase flow rate, the vortex overreading factor OR shows an increasing trend, and the higher the carrier gas pressure, the smaller the curve growth rate. LF As the liquid phase flow rate changes, the gas phase apparent velocity has an effect on the disturbance wave frequency f w The influence of gas phase superficial velocity U sg It is dimensionless, as shown in formula (3):

[0064]

[0065] Where D is the pipe diameter, St LF is the perturbation Post-Trauhal number, U sg is the gas phase superficial velocity.

[0066] According to research, OR is positively correlated with droplet loading. High gas velocity and high gas pressure both promote gas-liquid mass transfer, resulting in an increase in droplet entrainment, but at the same time, the carrier gas mass flow rate also increases, ultimately resulting in a decrease in droplet loading. This gas-liquid interface mass transfer is closely related to inertial force and surface tension, and the ratio of the two can be characterized by the modified gas phase Weber number, as shown in formula (4):

[0067]

[0068] Where σ is the surface tension coefficient of the liquid phase, ρ l is the liquid density, ρ g is the gas phase density, D is the pipe diameter, U sg is the gas phase superficial velocity.

[0069] Vortex overread OR with St LF It shows a nonlinear growth trend, and the gas phase Weber number Weg The larger the OR-St LF The smaller the growth rate of the curve, that is, OR and the perturbation Post-Strauhal number St LF Positively correlated with the gas phase Weber number We g Negatively correlated. LF and gas phase Weber number We g As a parameter, the vortex street overreading is fitted using the power exponential form, as shown in formula (5):

[0070] OR=a+bSt LF α We g β (5)

[0071] Among them, a and b are constant coefficients, and α and β are power exponents. The least squares regression method is used to fit equation (5), and we get a = 0.769, b = 2.15, α = 0.115, β = -0.179,

[0072] The fitting results are as follows Figure 4 As shown, the prediction accuracy is within ±1.5%, and the regression determination coefficient R 2 It can reach 0.93, and the relative root mean square error rRMSE = 0.68%, indicating that the regression effect of vortex over-reading coefficient OR using formula (5) is good.

[0073] The wet gas measurement model is established based on formula (5). In formula (5), except for the gas phase flow rate Q g and the gas phase superficial velocity U sg is an unknown quantity, and the other parameters are directly measured parameters or constants. To solve the established wet gas measurement model, the actual gas phase volume flow rate Q in the wet gas is g As parameters, the equation f(Q g )=0, as shown in formula (6):

[0074]

[0075] In the formula, n1=1-α+2β, C1=(f w DA D ) α , Pipe cross-sectional area A D =πD 2 / 4; parameter K is a parameter related to the working conditions.

[0076] To solve equation (6), the Newton iteration algorithm with fast convergence speed and simple calculation is used. The Newton iteration format is:

[0077]

[0078] in,

[0079] Based on the above modeling and calibration results, the wet gas flow measurement based on vortex frequency-disturbance wave frequency dual-mode detection is carried out as follows:

[0080] The technical solution of the present invention is as follows:

[0081] 1) Collect working parameters, including pressure P, temperature T, vortex signal s(t) and liquid film signal d(t);

[0082] 2) Extract and calculate the operating parameters, including the vortex shedding frequency f vs , disturbance wave frequency f w , gas phase density r g , liquid density r l , liquid surface tension and instrument factor K v ; Using the ideal gas equation, the gas phase density ρ is calculated based on the two-phase operating pressure P and operating temperature T g .

[0083] 3) According to formula (1), calculate the indication Q of the two-phase vortex flowmeter g,apparent ;

[0084] 4) Combine formulas (1), (2), and (3) to construct g Equation (6) with Q as the parameter g,apparent As the initial value of the iteration of gas volume flow rate: Q g,0 =Q g,apparent ;

[0085] 5) Substitute into Newton iteration format formula (7) and solve to obtain the next iteration result Q g,n+1 ;

[0086] 6) When the convergence condition is met, |Q g,n+1 -Q g,n | / Q g,n When the value is less than 0.1%, the iteration process ends. Otherwise, set n = n + 1 and return to step 5 until the iteration converges. The result of the last iteration is used as the gas volume flow rate Q. g .

[0087] In order to verify the wet gas flow measurement method based on vortex frequency-disturbance wave frequency dual-mode detection proposed above, Figure 5 The gas flow rate in wet gas is plotted against the liquid volume fraction (LVF) and the gas-liquid ratio r g / r l Comparison between the actual and predicted gas phase flow rates. Figure 6The distribution of percentage error (PE) of gas flow rate relative to liquid volume fraction (LVF) in wet gas is plotted. Gas flow PE at 97.5% flow point Qg The error range is within ±1.5%, and the uncertainty is 0.75%. The measurement accuracy is significantly improved compared with the maximum error of 12.1% before correction, basically reaching the accuracy level of dry gas measurement.

[0088] In order to improve the measurement accuracy of vortex wet gas, the present invention proposes a wet gas flow measurement model based on vortex-disturbance wave frequency dual-mode detection. The liquid film fluctuation frequency (disturbance wave frequency) is used to perform vortex over-reading correction, and there is no need to calibrate the liquid film thickness. The requirements for medium conductivity are low. By directly establishing the correlation formula between vortex over-reading and disturbance wave frequency, the wet gas measurement model is obtained. The form is greatly simplified, the coefficients to be determined are reduced, and the robustness and scalability of the model are greatly improved.

Claims

1. A wet gas flow measurement method based on vortex frequency-disturbance wave frequency dual-mode detection, the measurement device used includes an annular electrode pair, a pressure sensor, a temperature sensor and a vortex flowmeter, the annular electrode pair is used to obtain a liquid film thickness sequence d(t); the pressure sensor is used to collect the working pressure P, the temperature sensor is used to collect the working temperature T, and the vortex flowmeter is used to collect the vortex signal s(t), and s(t) and d(t) are respectively subjected to fast Fourier transform to obtain the vortex shedding frequency f vs and the disturbance wave frequency f w ; The measurement method is as follows: (1) Establish a moisture measurement model by: Actual value of gas phase flow Q g And the gas flow measurement value Q g,apparent There is a relationship as shown in formula (1), where OR is the overread coefficient Gas flow measurement value Q g,apparent (m 3 / h) is calculated by formula (2) in, f vs is the vortex shedding frequency, K v is the instrument factor of the vortex flowmeter in single-phase dry gas (m -3 ); The gas phase Weber number We g and the perturbation Post-Trauhal number St LF As a parameter, the vortex street over-reading is fitted using the power exponential form to establish a moisture measurement model, and the formula (3) is obtained: OR=a+bSt LF α We g β (3) in: Perturbed Postrouhal number St LF The definition of is as follows: Where D is the pipe diameter, U sg is the gas phase superficial velocity; Gas phase Weber number We g The definition of is as follows: Where σ is the surface tension coefficient of the liquid phase, ρ l is the liquid density, ρ g is the gas phase density, which is calculated based on the two-phase operating pressure P and operating temperature T; D is the pipe diameter, U sg is the gas phase superficial velocity, a and b are constant coefficients, α and β are power exponents, and are obtained by least squares regression; (2) Obtain the actual value of the gas phase flow rate Q in wet gas g is the Newton iteration format of the parameters; (3) Iterative solution of gas volume flow rate Q g .

2. The wet gas flow measurement method based on vortex frequency-disturbance wave frequency dual-mode detection according to claim 1 is characterized in that: The method of step (2) is: The actual gas phase volume flow rate Q in wet gas g As parameters, the equation f(Q g )=0, as shown in formula (6): In the formula, n1=1-α+2β, C1=(f w DA D ) α , Pipe cross-sectional area A D =πD 2 / 4; parameter K is a parameter related to the working conditions. The Newton iteration algorithm is used to solve equation (6). The Newton iteration format is: in, 3. The wet gas flow measurement method based on vortex frequency-disturbance wave frequency dual-mode detection according to claim 2 is characterized in that: The method of step (3) is: 1) Collect operating parameters, including pressure P, temperature T, vortex signal s(t) and liquid film signal d(t); 2) Extract and calculate the operating parameters, including the vortex shedding frequency f vs , disturbance wave frequency f w , gas phase density r g , liquid density r l , liquid surface tension and instrument factor K v ; 3) According to formula (2), calculate the gas flow measurement value Q in the two phases g,apparent ; 4) Q g,apparent As the initial value of the iteration of gas volume flow rate: Q g,0 =Q g,apparent ; 5) Substitute into Newton iteration format formula (7) and solve to obtain the next iteration result Q g,n+1 ; 6) Set the threshold w, when the convergence condition is met |Q g,n+1 -Q g,n | / Q g,n When <w is less than, the iteration process ends; otherwise, let n=n+1 and continue back to step 5) until the iteration converges, and the last iteration result is used as the gas volume flow rate Q g .

4. The wet gas flow measurement method based on vortex frequency-disturbance wave frequency dual-mode detection according to claim 3 is characterized in that: w＝0.1％。

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