Gas-liquid two-phase mass flow metering device based on critical flow

Abstract

A gas-liquid two-phase mass flow metering device based on critical flow mainly comprises an inlet straight pipe, a reducing pipe, a throat pipe, an expansion pipe, an outlet straight pipe, a temperature sensor, a pressure sensor, a differential pressure sensor, an ultrasonic transmitting probe, an ultrasonic receiving probe and the like. A swirler is arranged in the inlet straight pipe and used for adjusting the flow pattern, and the throat part is used for accelerating gas and liquid to form gas-liquid two-phase critical flow. The flow velocity of the gas-liquid mixture in the throat pipe is ingeniously obtained by measuring ultrasonic propagation, and then simultaneous measurement of the gas flow and the liquid flow is achieved in combination with a throttling equation. The method is not affected by factors such as pipeline gas-liquid phase flow patterns, radioactive measurement methods such as gamma rays are not adopted, and the method has the advantages of being low in operation cost, convenient to operate, high in measurement precision and the like.

Description

Technical Field

[0001] This invention belongs to the field of fluid metering, specifically relating to a multiphase metering device for measuring the flow rates of the gas and liquid phases in a gas-liquid two-phase mixture. Background Technology

[0002] In the petroleum industry, oil well produced materials are typically gas-liquid mixtures, and oil and gas production requires real-time monitoring of wellhead gas and liquid production. Multiphase flow measurement methods can be divided into two categories: separate metering and non-separate online metering.

[0003] Multiphase flow metering using separation methods involves using separation equipment to separate a gas-liquid mixture into single-phase gas and single-phase liquid, which are then measured using a standard single-phase flow meter. This transforms the measurement of two-phase flow into single-phase flow measurement, offering advantages such as reliable operation, high measurement accuracy, wide measurement range, and insensitivity to changes in the flow pattern of the gas and liquid phases. The biggest drawback of complete separation methods is the large size and high cost of the separation equipment, requiring a dedicated metering station and testing pipelines, which significantly increases metering costs.

[0004] The non-separation method involves placing the measuring instrument directly in a two-phase fluid environment, typically using a combination of throttling elements such as Venturi gauges and gamma-ray phase fractionators. Its disadvantages include the sensor operating directly in a two-phase flow environment. Compared to single-phase flow, a significant characteristic of two-phase flow is its strong fluctuation; the distribution of the gas and liquid phases across the pipe cross-section, i.e., the flow pattern, changes continuously with the flow rates of the gas and liquid phases, exhibiting patterns such as stratified flow, wavy flow, annular flow, and slug flow. Therefore, instruments operating directly in a two-phase fluid are greatly affected by the fluctuations in the two-phase flow, resulting in low measurement accuracy and a small measurement range. Furthermore, gamma rays are radioactive and pose a potential health risk.

[0005] To overcome the shortcomings of existing technologies, this invention utilizes the low sound velocity characteristics of gas-liquid two-phase flow to promote the accelerated flow of gas and liquid in the throat, reaching the critical flow of sound velocity. At this point, the propagation speed of ultrasound is equal to the flow velocity of gas and liquid in the throat, thus cleverly realizing the acquisition of the flow velocity of the gas-liquid mixture in the throat by measuring the propagation of ultrasound, and then combining the throttling equation to realize the simultaneous measurement of gas and liquid flow rates. Summary of the Invention

[0006] This invention relates to a gas-liquid two-phase mass flow metering device based on critical flow, which mainly includes an inlet straight pipe, a converging pipe, a throat, an expander, an outlet straight pipe, a cyclone separator, a pressure sensor, a differential pressure sensor, an ultrasonic generator probe, an ultrasonic receiver probe, and a temperature sensor, etc.

[0007] The inlet straight pipe, converging pipe, throat, expander pipe, and outlet straight pipe are connected in sequence. The hydrocyclone is located inside the inlet straight pipe near the inlet. The outer edge of the hydrocyclone's swirling blades is in close contact with the inner wall of the fluid inlet straight pipe. An upstream pressure tap is provided on the downstream inlet straight pipe of the hydrocyclone. An ultrasonic transmitting probe is provided on one side of the top of the throat and an ultrasonic receiving probe is provided on one side of the bottom of the throat. The two are distributed along the diameter direction of the throat. A downstream pressure tap is provided at the outlet of the throat. The upstream pressure tap is connected to a pressure sensor. The high-pressure end of the differential pressure sensor is connected to the upstream pressure tap, and the low-pressure end is connected to the downstream pressure tap. A temperature sensor is provided on the inlet straight pipe section between the upstream pressure tap and the converging pipe.

[0008] The converging tube inlet has the same diameter as the inlet straight pipe section, and its outlet section has the same diameter as the throat pipe; the throat pipe is a straight pipe of equal diameter, with a diameter d that is 0.25-0.5 times the diameter D of the inlet straight pipe, and its length is 1-2 times the diameter of the throat pipe; the expansion tube inlet diameter is the same as the throat pipe, its outlet diameter is the same as the outlet straight pipe, and the outlet straight pipe diameter is the same as the inlet straight pipe.

[0009] The bottom of both the upstream and downstream pressure taps penetrates the inner wall of the inlet straight pipe, and the bottom edge is flush with the inner wall of the inlet straight pipe.

[0010] Both the ultrasonic transmitting probe and the ultrasonic receiving probe penetrate the inner wall of the larynx, and the bottom edge of the probe is flush with the inner wall of the larynx.

[0011] The implementation steps of this invention are as follows:

[0012] (1) Measure the fluid pressure P at the inlet of the inlet straight pipe using a pressure sensor, and measure the throttling differential pressure between the inlet straight pipe and the throat using a differential pressure sensor. The inlet fluid temperature T of the inlet straight pipe is measured by a temperature sensor, and the time difference between the propagation of the ultrasonic pulse emitted by the ultrasonic transmitting probe and the ultrasonic receiving probe is applied. ;

[0013] (2) Based on the physical property equation, calculate the gas phase density of the fluid before the inlet of the converging tube using the measured fluid pressure P and temperature T. and liquid phase density ;

[0014] (3) Combined formula and formula Calculate the total mass flow rate M of the gas-liquid mixture. m And the mass gas content x, where A and B in the formula are constant coefficients that depend on the structure of the Venturi tube device and are determined through experimental calibration;

[0015] (4) According to the formula Calculate the gas phase mass flow rate M in a gas-liquid mixture. g According to the formula Calculate the liquid phase mass flow rate M in a gas-liquid mixture. l .

[0016] Compared with the prior art, the present invention has the following advantages:

[0017] (1) Under the action of the hydrocyclone, the wavy flow, stratified flow and non-uniform annular flow can be transformed into annular flow with uniform liquid film thickness, effectively eliminating the influence of two-phase flow pattern fluctuation on the measurement.

[0018] (2) The gas-liquid two-phase flow mixture has the characteristic of low sound speed. The gas and liquid accelerate in the throat and easily reach the speed of sound to form a critical flow. At this time, the propagation speed of ultrasound is equal to the flow speed of gas and liquid in the throat. The axial flow velocity of the gas-liquid mixture in the throat can be cleverly obtained by measuring the propagation of ultrasound.

[0019] (3) By combining the gas-liquid throttling differential pressure formula and the sound velocity formula, the two unknowns of gas-liquid mass flow rate and dryness fraction can be obtained by solving the two equations, and then the gas-liquid phase flow rate can be obtained;

[0020] (4) This invention has no moving parts, a simple structure, and does not use radioactive pioneer rate measurement technology such as gamma rays. It has the characteristics of low operating cost, safe and convenient operation, and high measurement accuracy. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the components of the present invention;

[0022] Figure 2 This is a schematic diagram illustrating the working principle of the present invention;

[0023] Figure 3 This is a schematic diagram illustrating the principle of sound velocity measurement in gas-liquid two-phase flow.

[0024] Figure 4 Relationship between acoustic velocity and gas content in gas-liquid two-phase flow;

[0025] Figure 5 Relationship between differential pressure and gas content in gas-liquid two-phase flow.

[0026] Wherein: 1-Inlet straight pipe; 2-Converging pipe; 3-Throat; 4-Expanding pipe; 5-Outlet straight pipe; 6-Hydrocyclone; 7-Pressure sensor; 8-Differential pressure sensor; 9-Ultrasonic transmitting probe; 10-Ultrasonic receiving probe; 11-Temperature sensor; 12-Upstream pressure tapping pipe; 13-Downstream pressure tapping pipe. Detailed Implementation

[0027] like Figure 1As shown, it mainly includes: an inlet straight pipe 1, a converging pipe 2, a throat 3, an expansion pipe 4, an outlet straight pipe 5, a hydrocyclone 6, a pressure sensor 7, a differential pressure sensor 8, an ultrasonic generating probe 9, an ultrasonic receiving probe 10, and a temperature sensor 11, etc. The inlet straight pipe 1, the converging pipe 2, the throat 3, the expansion pipe 4, and the outlet straight pipe 5 are connected in sequence. The hydrocyclone 6 is located inside the inlet straight pipe 1 near the inlet. The outer edge of the swirling blades of the hydrocyclone 6 is in close contact with the inner wall surface of the fluid inlet straight pipe 1. Downstream of the hydrocyclone 6... An upstream pressure tapping pipe 12 is provided on the inlet straight pipe 1. An ultrasonic transmitting probe 9 is provided on one side of the top of the throat pipe 3, and an ultrasonic receiving probe 10 is provided on one side of the bottom of the throat pipe 3. The two are distributed along the diameter direction of the throat pipe 3. A downstream pressure tapping pipe 13 is provided at the outlet of the throat pipe 3. The upstream pressure tapping pipe 12 is connected to the pressure sensor 7. The high-pressure end of the differential pressure sensor 8 is connected to the upstream pressure tapping pipe 12, and the low-pressure end is connected to the downstream pressure tapping pipe 13. A temperature sensor 11 is provided on the inlet straight pipe section 1 between the upstream pressure tapping pipe 12 and the converging pipe 2.

[0028] The converging tube 2 has the same inlet diameter as the inlet straight pipe 1, and its outlet section has the same diameter as the throat 3. The throat 3 is a straight pipe of equal diameter, with a diameter d that is 0.25-0.5 times the diameter D of the inlet straight pipe, and a length that is 1-2 times the diameter of the throat 3. The expansion tube 4 has the same inlet diameter as the throat 3, and its outlet diameter is the same as the outlet straight pipe 5. The outlet straight pipe 5 has the same diameter as the inlet straight pipe 1.

[0029] The bottom of both the upstream pressure tapping pipe 12 and the downstream pressure tapping pipe penetrates the inner wall of the inlet straight pipe 1, and the bottom edge is flush with the inner wall of the inlet straight pipe 1.

[0030] Both the ultrasonic transmitting probe 9 and the ultrasonic receiving probe 10 penetrate the inner wall of the larynx 3, with the bottom edge of the probe flush with the inner wall of the larynx 3.

[0031] The working principle of this invention is explained as follows:

[0032] like Figure 2 As shown, the swirling blades of the hydrocyclone 6 are in close contact with the inner wall of the fluid inlet straight pipe 1. After the gas-liquid two-phase fluid enters the fluid inlet straight pipe 1, it is forced to flow within the channel formed by the swirling blades and the wall of the inlet straight pipe 1 after passing through the hydrocyclone 6. Since the liquid phase density is much greater than the gas phase density, the liquid phase is thrown to the outermost side under the action of centrifugal force, forming a liquid film that adheres tightly to the wall of the fluid inlet straight pipe 1, while the gas phase flows in the center of the fluid inlet straight pipe 1. At this time, the flow pattern is a uniform annular flow. For horizontal pipes without a swirling device, under the action of gravity, the gas-liquid two-phase distribution in the pipe cross-section shows obvious asymmetry, with more liquid phase at the bottom and gas phase mainly concentrated in the upper part of the pipe. After passing through the hydrocyclone 6, the flow patterns such as stratified flow, wavy flow, semi-annular flow, and asymmetric annular flow are all adjusted to a uniform annular flow pattern with a liquid film evenly distributed along the pipe circumference, thereby improving the flow pattern distribution entering the throat 3 and making the gas-liquid cross-section distribution in the throat 3 more uniform.

[0033] When the gas-liquid two-phase flow passes through the throat 3, the cross-sectional area of ​​the fluid flow decreases and the flow velocity increases. Under strong shearing action, the annular liquid film is torn and broken into liquid, forming a diffuse flow with uniform gas-liquid phase distribution in the throat 3.

[0034] like Figure 3 As shown, an ultrasonic transmitting probe 9 and an ultrasonic receiving probe 10 are installed in the throat tube 3. The ultrasonic transmitting probe 9 emits ultrasonic pulses, which are received by the ultrasonic receiving probe 10, thereby allowing the measurement of the time difference between transmission and reception. , that is, the propagation time of the ultrasonic pulse in the larynx 3. Since the distance between the ultrasonic transmitting probe 9 and the ultrasonic receiving probe 10 is equal to the diameter d of the larynx 3, the propagation speed C of the ultrasonic wave in the larynx 3 is... m The following formula can be used for calculation:

[0035] (1)

[0036] like Figure 4 As shown, the sound velocity in a two-phase gas-liquid flow is much lower than that in a single-phase gas or single-phase liquid. Since the diameter of the throat 3 is only 0.25-0.5 times the diameter of the inlet straight pipe 1, under high inlet gas-liquid flow rates, the throat 3 easily reaches the sound velocity, i.e., reaches the critical flow. According to the pressure disturbance propagation theory, the ultrasonic velocity measured by the ultrasonic transmitting probe 9 and the ultrasonic receiving probe 10 at this time is related to the axial velocity V of the throat 3. m Maintaining consistency, that is:

[0037] (2)

[0038] Therefore, the volumetric mass flow rate of a gas-liquid two-phase flow can be calculated using the following formula:

[0039] (3)

[0040] In the above formula, The flow rate of the gas-liquid mixture in throat 3 is related to the mass gas content and can be calculated using the following formula:

[0041] (4)

[0042] From formulas (3) and (4), the mass flow rate formula can be obtained:

[0043] (5)

[0044] In the formula, For gas phase density, Let be the liquid density, and be a function of temperature and pressure. A pressure sensor 7 and a temperature sensor 11 are installed on the inlet straight pipe 1, thereby allowing the determination of ______. and value.

[0045] like Figure 5 As shown, the throttling differential pressure of the gas-liquid two-phase flow Total mass flow rate M of gas-liquid mixture m The relationship between the gas content (x) and the mass gas content (x) is specific and can be expressed by the following equation:

[0046] (6)

[0047] Where A and B are coefficients, which can be determined through calibration. The incoming gas-liquid flow rate is changed, and the mass flow rate M of the gas-liquid mixture is measured at multiple operating points. m Dryness x and corresponding differential pressure Through experiments, the coefficients A and B in equation (6) can be determined by using the least squares method.

[0048] (5) and (6) simultaneously contain the total mass flow rate M of the gas-liquid mixture. m The two unknown parameters, namely the mass gas content x, can be solved by solving a set of equations.

[0049] Obtain mass flow rate M m After determining the mass gas content x, the gas phase flow rate can be calculated using the following formula:

[0050] (7)

[0051] The liquid flow rate can be calculated using the following formula:

[0052] (8)

[0053] In summary, the implementation steps of this invention are as follows:

[0054] (1) The inlet fluid pressure P is measured by pressure sensor 7, and the throttling differential pressure between the inlet straight pipe 1 and the throat pipe 3 is measured by differential pressure sensor 8. The inlet fluid temperature T is measured by temperature sensor 11, and the time difference between the propagation of the ultrasonic pulse emitted by ultrasonic transmitting probe 9 and the ultrasonic receiving probe 10 is used. ;

[0055] (2) Calculate the gas phase density using the measured inlet fluid pressure P and temperature T based on the physical property equation. and liquid phase density ;

[0056] (3) Combined formula and formula Calculate the total mass flow rate M of the gas-liquid mixture. m and gas content x;

[0057] (4) According to the formula Calculate the gas phase mass flow rate in a gas-liquid mixture using the formula... Calculate the mass flow rate of the liquid phase in a gas-liquid mixture.

[0058] The formula in step (3) A and B in the equation are constant coefficients that depend on the structure of the apparatus and are determined through experimental calibration.

[0059] This invention employs a combined "ultrasound + throttling" design approach, proposing a novel method for measuring gas-liquid two-phase flow. A cyclone separator is used at the inlet to adjust the flow pattern, eliminating the influence of gas-liquid flow pattern fluctuations on the measurement. Utilizing the characteristic that the throat of a gas-liquid mixture easily reaches the critical velocity, ultrasonic measurement is used to measure the axial sound velocity at the throat. Combined with the throttling characteristic equation of gas-liquid two-phase flow, simultaneous measurement of the gas and liquid two-phase flows in the mixture is achieved. Compared with existing technologies, this invention has no moving parts, a simple structure, is unaffected by factors such as the gas-liquid flow pattern and velocity in the pipeline, and does not employ radioactive measurement methods such as gamma rays. It features low operating costs, convenient operation, and high measurement accuracy.

Claims

1. A critical flow based gas-liquid two-phase mass flow metering device, characterized by: The application relates to a flowmeter, which comprises an inlet straight pipe (1), a taper pipe (2), a throat pipe (3), an expansion pipe (4), an outlet straight pipe (5), a cyclone (6), a pressure sensor (7), a differential pressure sensor (8), an ultrasonic emission probe (9), an ultrasonic receiving probe (10) and a temperature sensor (11), wherein the inlet straight pipe (1), the taper pipe (2), the throat pipe (3), the expansion pipe (4) and the outlet straight pipe (5) are sequentially connected, the cyclone (6) is arranged in the inlet straight pipe (1) and close to an inlet, the outer edge of a cyclone blade of the cyclone (6) is tightly attached to the inner wall of the inlet straight pipe (1), an upstream pressure guide pipe (12) is arranged on the inlet straight pipe (1) downstream of the cyclone (6), the ultrasonic emission probe (9) is arranged on one side of the top of the throat pipe (3), the ultrasonic receiving probe (10) is arranged on one side of the bottom of the throat pipe (3), the two probes are distributed along the diameter direction of the throat pipe (3), and a downstream pressure guide pipe (13) is arranged at the outlet of the throat pipe (3); the upstream pressure guide pipe (12) is connected with the pressure sensor (7), the high-pressure end of the differential pressure sensor (8) is connected with the upstream pressure guide pipe (12), and the low-pressure end is connected with the downstream pressure guide pipe (13); the temperature sensor (11) is arranged on the inlet straight pipe (1) between the upstream pressure guide pipe (12) and the taper pipe (2).

2. A critical flow based gas-liquid two-phase mass flow metering device according to claim 1, characterized in that: The taper pipe (2) is connected with the inlet straight pipe (1) and has the same diameter, the outlet section of the taper pipe (2) has the same diameter as the throat pipe (3), the throat pipe (3) is a straight pipe with the same diameter, the diameter d of the throat pipe (3) is 0.25-0.5 times the diameter D of the inlet straight pipe (1), and the length of the throat pipe (3) is 1-2 times the diameter of the throat pipe (3); the expansion pipe (4) has the same diameter as the throat pipe (3) at the inlet, has the same diameter as the outlet straight pipe (5) at the outlet, and has the same diameter as the inlet straight pipe (1).

3. A critical flow based gas-liquid two-phase mass flow metering device as claimed in claim 1, wherein: The bottom of the upstream pressure guide pipe (12) and the bottom of the downstream pressure guide pipe (13) penetrate the inner wall of the inlet straight pipe (1), and the bottom edges are flush with the inner wall of the inlet straight pipe (1).

4. A critical flow based gas-liquid two-phase mass flow metering device as claimed in claim 1, wherein: The ultrasonic emission probe (9) and the ultrasonic receiving probe (10) penetrate the inner wall of the throat pipe (3), and the bottom edges are flush with the inner wall of the throat pipe (3).

5. A critical flow based gas-liquid two-phase mass flow metering device as claimed in claim 1, wherein: The flowmetering is realized through the following steps: (1) measuring the inlet fluid pressure P in the inlet straight pipe (1) by means of a pressure sensor (7) and the throttling differential pressure between the inlet straight pipe (1) and the throat (3) by means of a differential pressure sensor (8) , measuring the inlet fluid temperature T in the inlet straight pipe (1) by means of a temperature sensor (11) and the time difference of the ultrasonic pulses emitted by the ultrasonic transmitting probe (9) to the ultrasonic receiving probe (10) ; (2) The gas and liquid densities of the fluid before the inlet of the tapered pipe (2) are calculated according to the equation of state, using the measured fluid pressure P and temperature T before the inlet of the tapered pipe (2) and liquid densities ; (3) Combined formula and formula Calculate the total mass flow M of the gas-liquid mixture m and the mass gas content x, where A and B are constant coefficients in the formula, which depend on the structure of the Venturi device and are determined by experiments. (4) According to the formula Calculate the gas phase mass flow rate M in a gas-liquid mixture. g According to the formula Calculate the liquid phase mass flow rate M in a gas-liquid mixture. l .

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