Moisture two-phase flow measurement method

Abstract

The invention relates to a moisture two-phase flow measurement method, which comprises the following steps of: building a measurement system: sequentially arranging a differential pressure transmitter and an ultrasonic transducer along a flowing direction; building a pulse transceiving circuit; the ultrasonic signals of the differential pressure transmitter and the conditioned ultrasonic signals are collected respectively; aiming at the obtained conditioned ultrasonic signal, based on an ultrasonic pulse echo thickness measurement principle, obtaining the thickness of a liquid film at the bottom of the pipeline, and obtaining the wave velocity of a disturbance wave of the liquid film at the bottom; flow pressure drop is calculated according to the differential pressure average value and the distance between the two pressure taps; carrying out moisture experiments under different gas and liquid flows, measuring the three parameters corresponding to each working condition, and respectively establishing function relationships between the three parameters and the gas phase apparent velocity and between the three parameters and the liquid phase apparent velocity; and performing moisture two-phase flow measurement on line, and solving by adopting a Newton iteration method according to the established function relationship to obtain the gas phase apparent velocity and the liquid phase apparent velocity under the current working condition.

Description

Technical Field

[0001] The invention belongs to the technical field of flow measurement and relates to a wet gas two-phase flow measurement method. Background Art

[0002] In the process of natural gas extraction, the natural gas produced from the wellhead is not processed and mostly has a high liquid content. It shows obvious gas-liquid two-phase flow characteristics during transportation, which is usually called wet gas. As a special flow form of gas-liquid two-phase flow, wet gas is widely present in many fields such as petroleum, chemical industry, and electricity. The accurate measurement of wet gas flow is of great significance to industrial production and energy conservation. At present, there are two main methods for measuring wet gas: separation measurement and non-separation measurement. Among them, the separation measurement is to separate the gas phase and liquid phase in the wet gas by using a separation device, and then use the traditional single-phase flowmeter to measure the gas and liquid flow respectively. At present, the separation method has been widely used in industrial processes, but the separation device is usually expensive and bulky, which greatly limits its application in the measurement site. As a direct measurement method, the non-separation method has the advantages of easy installation and good real-time performance, and can realize dynamic monitoring of the measurement process, so it has received widespread attention. The combined measurement method with throttling flowmeter as the core is widely used at home and abroad, including the double differential pressure combination of Venturi tube and microwave moisture meter, Venturi tube and gamma ray, Venturi tube and ultrasonic flowmeter, Venturi tube and inner cone flowmeter, etc. Summary of the invention

[0003] The present invention proposes a non-throttling, non-invasive wet gas measurement method, which uses the upstream and downstream differential pressure of a straight pipe and an external ultrasonic transducer to measure the two-phase flow of wet gas. Compared with the traditional throttling flowmeter method, the pressure loss is small and the reliability is high. The technical solution of the present invention is as follows:

[0004] A method for measuring wet gas two-phase flow rate comprises the following steps:

[0005] 1) Build a measurement system: along the flow direction, arrange the differential pressure transmitter and ultrasonic transducer in sequence. The differential pressure transmitter is used to measure the differential pressure information at the top of the pipeline at a certain distance; the ultrasonic transducer includes two external ultrasonic transducers, which are used to measure the liquid film thickness and disturbance wave velocity information at the bottom of the pipeline;

[0006] 2) Build a pulse transceiver circuit to excite the ultrasonic transducer and condition the received ultrasonic signal;

[0007] 3) Collect the differential pressure transmitter and the conditioned ultrasonic signal respectively;

[0008] 4) Based on the ultrasonic pulse echo thickness measurement principle, the thickness of the liquid film at the bottom of the pipeline is obtained for the conditioned ultrasonic signal. The liquid film thickness time series over a period of time is collected and averaged to obtain the average thickness of the bottom liquid film. The delay time τ is obtained by cross-correlating the liquid film thickness time series obtained by the two ultrasonic transducers upstream and downstream; the bottom liquid film disturbance wave velocity u is obtained based on the distance between the two ultrasonic transducers. w ;

[0009] 5) Collect the differential pressure value of the differential pressure transmitter over a period of time and calculate its average value; calculate the flow pressure drop dp / dx based on the average differential pressure value and the distance between the two pressure tapping ports;

[0010] 6) Carry out wet gas experiments under different gas and liquid flow rates, and measure the average thickness of the bottom liquid film corresponding to each working condition Bottom liquid film disturbance wave velocity u w and flow pressure drop dp / dx results, and their relationship with gas phase superficial velocity v are established for these three parameters. sg and the liquid superficial velocity v sl Functional relationship of

[0011] 7) Online measurement of wet gas two-phase flow rate, based on the real-time acquisition of differential pressure transmitter and conditioned ultrasonic signal, the average thickness of the bottom liquid film corresponding to the current working conditions is measured Bottom liquid film disturbance wave velocity u w and flow pressure drop dp / dx; according to the functional relationship established in step 6), the Newton iteration method is used to solve the gas phase apparent velocity v under the current working conditions sg and the liquid superficial velocity v sl .

[0012] Furthermore, the average thickness of the bottom liquid film The general relationship is:

[0013]

[0014] Among them, Fr g and Fr. l are the Froude numbers of gas and liquid phases, respectively, and D is the pipe diameter; parameters c1, c2 and n1, n2, n3, n4 are obtained by the least squares nonlinear fitting method;

[0015] Furthermore, the bottom liquid film disturbance wave velocity u w The general relationship is:

[0016]

[0017]

[0018] Among them, ρg and ρ l are the gas and liquid phase densities, Re g and Re l are the gas and liquid phase Reynolds numbers, respectively, and the parameters c3, n5, and n6 are obtained by least squares nonlinear fitting;

[0019] Furthermore, the general relationship between the flow pressure drop dp / dx is:

[0020]

[0021]

[0022] Where X is the Loma parameter, and the parameters c4, c5, c6 and n7 are obtained by least squares nonlinear fitting.

[0023] Furthermore, according to the gas phase superficial velocity v under the current working conditions sg and the liquid superficial velocity v sl , and then multiply by the cross-sectional area of ​​the pipeline to obtain the gas and liquid flow values ​​Q g and Q l . BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 :Measurement system diagram

[0025] Figure 2 :Schematic diagram of pulse transceiver circuit

[0026] Figure 3 :Ultrasonic echo signal diagram DETAILED DESCRIPTION

[0027] The present invention will now be further described with reference to the accompanying drawings and embodiments.

[0028] 1) Measurement system such as Figure 1 As shown, the pipe diameter is 50mm, and the wet gas flows in from the right side of the pipe and out from the left side. It passes through the differential pressure transmitter measuring pipe section and the ultrasonic transducer measuring pipe section in turn. Among them, the distance between the upstream and downstream pressure holes of the differential pressure transmitter is 550mm, and the pressure is taken at the top of the pipe. The differential pressure transmitter model is 3051 series, produced by Rosemount, with a range of 0-6.216kPa and a measurement accuracy of 0.04%. The two ultrasonic transducers use SIUI's 5Z6N model piezoelectric ultrasonic transducers with a center frequency of 5MHz. They are externally mounted at the bottom of the pipe, and the distance between the two transducers is 100mm.

[0029] 2) Pulse transceiver circuit such as Figure 2As shown, the functions of the circuit include synchronous timing control, excitation signal generation and receiving signal preprocessing, which are mainly realized through power supply circuit, FPGA circuit, transmitting circuit, transceiver isolation circuit and receiving circuit. Among them, FPGA adopts Xilinx's Spartan-6 series XC6SLX9-2TQG144I, and the main frequency is set to 50MHz; the transmitting circuit adopts a dedicated high-voltage digital pulse generating chip MAX4940 to generate the excitation signal; the transceiver isolation circuit adopts a diode active bridge limiter circuit; the receiving circuit mainly amplifies and filters the ultrasonic echo signal, which is realized based on the operational amplifier.

[0030] 3) The data acquisition system consists of two AD data acquisition cards and a computer. The 4mA-20mA current signal output by the differential pressure transmitter is first converted into a 1V-5V voltage signal by connecting a 250Ω precision resistor in series, and then sampled by NI's USB-6009 data acquisition card with a sampling rate of 2kHz and a continuous acquisition time of 60s. The echo signals received by the two ultrasonic transducers are collected using Altai's PCI8512B data acquisition card. The two channels are synchronously triggered for sampling with a sampling rate of 80MHz, a trigger interval of 10ms, and an acquisition time of 60s. The two data acquisition cards are synchronized to start the acquisition by an external clock signal to ensure that the differential pressure transmitter and ultrasonic transducer collect data in the same time period and save them to the computer.

[0031] 4) For an ultrasonic transducer, the collected echo signal is as follows Figure 3 As shown. UE1 is the echo signal of the interface between the liquid phase and the inner wall of the tube, and UE2 is the echo signal of the interface between the liquid phase and the gas phase of the bottom liquid film. By analyzing the signal, the time difference ΔTOF between the two echo signals can be obtained. The thickness h of the bottom liquid film is calculated according to formula (6), where c is the speed of sound.

[0032]

[0033] By performing the above processing on 6000 echo signals collected in 60 seconds, 6000 liquid film thickness values ​​can be obtained, and the average liquid film thickness is obtained by averaging them, as shown in formula (7).

[0034]

[0035] For the two upstream and downstream ultrasonic transducers, the liquid film thickness time series within 60s are cross-correlated and the delay time τ of the two series can be obtained. According to the transducer spacing of 100mm, the bottom liquid film disturbance wave velocity u can be calculated by formula (8): w .

[0036] u w =0.1 / τ (8)

[0037] 5) The differential pressure signals collected within 60 s are averaged, and the flow pressure drop dp / dx is calculated by formula (9) based on the distance between the two pressure ports of 550 mm.

[0038]

[0039] 6) Carry out wet gas flow experiments under different gas and liquid flow rates according to the above method, where the gas phase superficial velocity v sg Range 8m / s-25m / s, liquid surface velocity v sl The range is 0.015m / s-0.3m / s, the experimental system pressure is 0.101MPa, and the temperature is 22℃. 121 working points were measured to obtain the average thickness of the bottom liquid film corresponding to each working condition. Bottom liquid film disturbance wave velocity u w and flow pressure drop dp / dx. The least squares nonlinear fitting method is used to model these three parameters respectively. Equation (10) is the average thickness of the bottom liquid film The measurement model.

[0040]

[0041] Formula (11) is the bottom liquid film disturbance wave velocity u w The measurement model.

[0042]

[0043]

[0044] Formula (12) is the flow pressure drop dp / dx measurement model.

[0045]

[0046]

[0047] 7) The Newton iteration method is used to solve the simultaneous equations (10), (11), and (12) to obtain the corresponding gas phase superficial velocity v under 121 working conditions: sg and the liquid superficial velocity v sl , multiplied by the cross-sectional area of ​​the pipeline to obtain the gas and liquid flow rates Q g and Q l .

[0048] The mean absolute error (MAPE) is introduced to evaluate the prediction error of gas and liquid flow, as shown in formula (13).

[0049]

[0050] where y irepresents the true value of the parameter, given by the standard table of the experimental device, The model-predicted values ​​of the representative parameters are obtained from the previous simultaneous equations.

[0051] Finally, the prediction errors MAPE of gas phase and liquid phase flow are 6.40% and 14.08% respectively, which verifies the effectiveness of the method of the present invention.

Claims

1. A method for measuring wet gas two-phase flow rate, comprising the following steps: 1) Build the measurement system: along the flow direction, arrange the differential pressure transmitter and ultrasonic transducer in sequence, where: The differential pressure transmitter is used to measure the differential pressure information at the top of the pipeline at a certain distance; the ultrasonic transducer includes two external ultrasonic transducers, which are used to measure the liquid film thickness and disturbance wave velocity information at the bottom of the pipeline; 2) Build a pulse transceiver circuit to excite the ultrasonic transducer and condition the received ultrasonic signal; 3) Collect the differential pressure transmitter and the conditioned ultrasonic signal respectively; 4) Based on the ultrasonic pulse echo thickness measurement principle, the thickness of the liquid film at the bottom of the pipeline is obtained for the conditioned ultrasonic signal. The liquid film thickness time series over a period of time is collected and averaged to obtain the average thickness of the bottom liquid film. The delay time τ is obtained by cross-correlating the liquid film thickness time series obtained by the two ultrasonic transducers upstream and downstream; the bottom liquid film disturbance wave velocity u is obtained based on the distance between the two ultrasonic transducers. w ; 5) Collect the differential pressure value of the differential pressure transmitter over a period of time and calculate its average value; calculate the flow pressure drop dp / dx based on the average differential pressure value and the distance between the two pressure tapping ports; 6) Carry out wet gas experiments under different gas and liquid flow rates, and measure the average thickness of the bottom liquid film corresponding to each working condition Bottom liquid film disturbance wave velocity u w and flow pressure drop dp / dx results, and their relationship with gas phase superficial velocity v are established for these three parameters. sg and the liquid superficial velocity v sl Functional relationship of 7) Online measurement of wet gas two-phase flow rate, based on the real-time acquisition of differential pressure transmitter and conditioned ultrasonic signal, the average thickness of the bottom liquid film corresponding to the current working conditions is measured Bottom liquid film disturbance wave velocity u w and flow pressure drop dp / dx; according to the functional relationship established in step 6), the Newton iteration method is used to solve the gas phase apparent velocity v under the current working conditions sg and the liquid superficial velocity v sl .

2. The wet gas two-phase flow measurement method according to claim 1, characterized in that: Average thickness of bottom liquid film The general relationship is: Among them, Fr g and Fr. l are the Froude numbers of gas and liquid phases respectively, D is the pipe diameter; the parameters c1, c2 and n1, n2, n3, n4 are obtained by the least squares nonlinear fitting method.

3. The wet gas two-phase flow measurement method according to claim 1, characterized in that: Bottom liquid film disturbance wave velocity u w The general relationship is: Among them, ρ g and ρ l are the gas and liquid phase densities, Re g and Re l are the gas and liquid phase Reynolds numbers respectively. Parameters c3, n5, and n6 are obtained by least squares nonlinear fitting.

4. The wet gas two-phase flow measurement method according to claim 1, characterized in that: The general relationship between flow pressure drop dp / dx is: Where X is the Loma parameter, and the parameters c4, c5, c6 and n7 are obtained by least squares nonlinear fitting.

5. The wet gas two-phase flow measurement method according to any one of claims 1 to 4, characterized in that: According to the gas phase apparent velocity v under the current working conditions sg and the liquid superficial velocity v sl , and then multiply by the cross-sectional area of ​​the pipeline to obtain the gas and liquid flow values ​​Q g and Q l .

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