A method for measuring wet gas two-phase flow

Abstract

The present invention relates to a method for measuring wet gas two-phase flow, comprising the following steps: building a measurement system: arranging a differential pressure transmitter and an ultrasonic transducer in sequence along a flow direction; building a pulse transceiver circuit; respectively collecting the differential pressure transmitter and conditioned ultrasonic signals; obtaining the thickness of a liquid film at the bottom of a pipeline and the velocity of a disturbance wave of the bottom liquid film based on the obtained conditioned ultrasonic signal based on the ultrasonic pulse echo thickness measurement principle; calculating the flow pressure drop according to an average differential pressure value and a distance between two pressure tapping ports; conducting wet gas experiments under different gas and liquid flow rates, measuring the above three parameters corresponding to each working condition, and establishing functional relationships between the three parameters and the gas phase apparent flow velocity and the liquid phase apparent flow velocity; performing wet gas two-phase flow measurement online, and solving the established functional relationships using the Newton iteration method to obtain the gas phase apparent flow velocity and the liquid phase apparent flow 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] During natural gas extraction, unprocessed natural gas produced from the wellhead often has a high liquid content. During transportation, it exhibits distinct gas-liquid two-phase flow characteristics, commonly referred to as wet gas. As a special form of gas-liquid two-phase flow, wet gas is widely present in numerous industries, including the petroleum, chemical, and power industries. Accurately measuring wet gas flow is crucial for industrial production and energy conservation. Currently, there are two main methods for measuring wet gas: separation-based and non-separation-based. Separation-based measurement utilizes a separation device to separate the gas and liquid phases in the wet gas. Traditional single-phase flow meters then measure the gas and liquid flow rates separately. While the separation-based method is widely used in industrial processes, the separation device is typically expensive and bulky, significantly limiting its application at the measurement site. Non-separation-based methods, on the other hand, offer advantages such as ease of installation and real-time performance, enabling dynamic monitoring of the measurement process, and therefore have attracted considerable attention. The combined measurement method with throttling flowmeter as the core is widely used at home and abroad, including the dual differential pressure combination of Venturi tube and microwave moisture meter, Venturi tube and gamma ray, Venturi tube and ultrasonic flowmeter, and Venturi tube and inner cone flowmeter. Summary of the Invention

[0003] This invention proposes a non-throttling, non-invasive wet gas measurement method that utilizes 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 to traditional methods based on throttling flowmeters, this method offers lower pressure drop and higher reliability. The technical solution of this invention is as follows:

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

[0005] 1) Build the measurement system: A differential pressure transmitter and ultrasonic transducer are arranged in sequence along the flow direction. The differential pressure transmitter measures the differential pressure at the top of the pipe at a certain distance. The ultrasonic transducer, consisting of two external ultrasonic transducers, measures the liquid film thickness and disturbance wave velocity at the bottom of the pipe.

[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 obtained conditioned ultrasonic signal, the thickness h of the liquid film at the bottom of the pipeline is obtained based on the ultrasonic pulse echo thickness measurement principle. The time series of the liquid film thickness 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 performing cross-correlation calculation on the liquid film thickness time series obtained by the two ultrasonic transducers at the upstream and downstream ends. 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 values ​​of the differential pressure transmitter over a period of time and calculate their 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 establish their relationship with gas phase superficial velocity v for these three parameters. sg and 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 corresponding average thickness of the bottom liquid film under 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 flow velocity v under the current working conditions sg and 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; the 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 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 apparent velocity v under the current working conditions sg and liquid superficial velocity v sl , and then multiply by the cross-sectional area of ​​the pipe to get 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 :Ultrasound 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 has a diameter of 50 mm. Moisture enters from the right side and exits from the left side. It passes through the differential pressure transmitter and ultrasonic transducer measurement sections, respectively. The upstream and downstream pressure tappings of the differential pressure transmitter are spaced 550 mm apart, and pressure is taken from the top of the pipe. The differential pressure transmitter is a 3051 series, manufactured by Rosemount, with a range of 0-6.216 kPa and an accuracy of 0.04%. The two ultrasonic transducers are SIUI 5Z6N piezoelectric ultrasonic transducers with a center frequency of 5 MHz. They are externally mounted on the bottom of the pipe, 100 mm apart.

[0029] 2) Pulse transceiver circuit such as Figure 2As shown in the figure, the circuit's functions include synchronous timing control, excitation signal generation, and receive signal preprocessing. These functions are primarily achieved through a power supply circuit, FPGA circuit, transmitter circuit, transceiver isolation circuit, and receiver circuit. The FPGA uses the Xilinx Spartan-6 series XC6SLX9-2TQG144I, with a main frequency of 50MHz. The transmitter circuit uses a dedicated high-voltage digital pulse generator chip, the MAX4940, to generate the excitation signal. The transceiver isolation circuit uses a diode active bridge limiter circuit. The receiver circuit, which primarily amplifies and filters the ultrasonic echo signal, is implemented using an op amp.

[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. This signal is then sampled using a National Instruments 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 an Altai PCI8512B data acquisition card. 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 by an external clock signal to ensure that the differential pressure transmitter and ultrasonic transducer collect data in the same time period and save it to the computer.

[0031] 4) For an ultrasonic transducer, the echo signal collected is as follows Figure 3 As shown in Figure 1, UE1 is the echo signal from the interface between the liquid phase and the inner wall of the tube, and UE2 is the echo signal from the interface between the liquid phase and the gas phase of the bottom liquid film. By analyzing these signals, the time difference ΔTOF between the two echo signals can be obtained. The bottom liquid film thickness h is calculated according to Equation (6), where c is the speed of sound.

[0032]

[0033] By performing the above processing on the 6000 echo signals collected in 60 seconds, 6000 liquid film thickness values ​​can be obtained. The average of these values ​​is obtained to obtain the average liquid film thickness, as shown in formula (7).

[0034]

[0035] For the two ultrasonic transducers upstream and downstream, 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 based on the distance between the two pressure ports of 550 mm, the flow pressure drop dp / dx is calculated using formula (9).

[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 phase apparent 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. Equation (10) is the average thickness of the bottom liquid film The measurement model.

[0040]

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

[0042]

[0043]

[0044] Equation (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), and the corresponding gas phase superficial velocity v under 121 working conditions can be obtained. sg and liquid superficial velocity v sl , multiplied by the cross-sectional area of ​​the pipe 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 iThe true value of the representative parameter is given by the standard table of the experimental device, The model-predicted values ​​of the representative parameters are obtained from the aforementioned simultaneous equations.

[0051] Finally, the prediction errors MAPE of gas phase and liquid phase flow were 6.40% and 14.08%, respectively, which verified the effectiveness of the proposed method.

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 obtained conditioned ultrasonic signal, the thickness of the liquid film at the bottom of the pipeline is obtained based on the ultrasonic pulse echo thickness measurement principle. , collect the time series of liquid film thickness for a period of time and average it to get the average thickness of the bottom liquid film ; Use the time series of liquid film thickness obtained by the upstream and downstream ultrasonic transducers to perform cross-correlation calculation to obtain the delay time ; Based on the distance between the two ultrasonic transducers, the velocity of the bottom liquid film disturbance wave is obtained ; 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 based on the average differential pressure value and the distance between the two pressure 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 and flow pressure drop As a result, the three parameters were respectively established to determine their relationship with the gas superficial velocity. and liquid superficial velocity The functional relationship of , where: Average thickness of bottom liquid film The general relationship is: ； in and are the Froude numbers of the gas and liquid phases, is the pipe diameter; parameter , and , , , Obtained by the least squares nonlinear fitting method; Bottom liquid film disturbance wave velocity The general relationship is: ； ； in, and are the gas and liquid phase densities, and are the gas and liquid phase Reynolds numbers, respectively, and the parameters and , Obtained by least squares nonlinear fitting; Flow pressure drop The general relationship is: ； ； in is the Loma parameter, parameter , , and Obtained by least squares nonlinear fitting; 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 corresponding average thickness of the bottom liquid film under the current working conditions is measured , bottom liquid film disturbance wave velocity and flow pressure drop According to the functional relationship established in step 6), the Newton iteration method is used to solve the gas phase apparent velocity under the current working conditions. and liquid superficial velocity .

2. The wet gas two-phase flow measurement method according to claim 1, characterized in that: According to the gas phase apparent velocity under the current working conditions and liquid superficial velocity , and then multiply by the cross-sectional area of ​​the pipe to get the gas and liquid flow values and .

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