CN1414382A - Detector of gas liquid two phase flow split-phase content based on resistance chromatographic imaging and method - Google Patents

Abstract

The microcomputer of the present invention is sequentially connected with photoelectric isolation, bus, excitation electrode selection analog switch, electrode drive, and input pole of the sensor; the sensor is connected with electrode drive, detection electrode selection analog switch, band-pass filter unit A, differential amplification unit, phase sensitive The demodulation unit, low-pass filter unit, analog-to-digital conversion module, and bus are sequentially connected; the bus is sequentially connected with the sine wave generator, voltage-controlled current source, and excitation electrode selection analog switch, and the bus is also connected with the differential amplifier unit and detection electrode selection respectively. The analog switch is connected, the sine wave generator is connected with the phase-sensitive demodulation unit, and the band-pass filter unit B is respectively connected with the detection electrode selection analog switch and the differential amplifier unit. The methods are as follows: 1. Calculate the _VR value from the data collected by the sensor at intervals by the computer, and judge whether it is stratified flow or bubbly flow; 2. Calculate the gas-liquid two-phase flow by calculating the _VR value of the stratified flow Phase separation holdup; 3. For bubbly flow, calculate the phase separation holdup of gas-liquid two-phase from the _VR value.

Description

Detector and method for phase holdup of gas-liquid two-phase flow separation based on electrical resistance tomography

Technical field

The invention belongs to the measurement category, and in particular relates to a measurement device and a measurement method for gas-liquid two-phase flow.

Background technique

The currently known electrical resistance tomography (ERT) technique is a simplified case of electrical impedance tomography (EIT), ie only the real part (information about the electrical resistance) is utilized. The physical basis of ERT technology is that different media have different conductivity, and the distribution of the medium in the object field can be known by judging the conductivity distribution of the sensitive field. The current working mode is current excitation (sine wave AC signal) and voltage measurement. When the conductivity distribution in the object field changes, the distribution of the current field will change accordingly, resulting in a change in the potential distribution in the field, so that the measured voltage on the field boundary will change. Using the measured voltage on the boundary, through certain imaging calculations, the conductivity distribution in the field can be reconstructed to realize visual measurement.

However, in the past, the ERT technology was used to estimate the phase containment based on the pixel distribution of the reconstructed image to estimate the phase containment. Due to the inhomogeneity of field distribution and boundary effects, large errors often occur in the estimation of phase holdup.

Contents of Invention

The purpose of the present invention is to provide a gas-liquid two-phase phase holdup detector and method based on electrical resistance tomography, to solve the above problems, to meet the needs of improving measurement accuracy, reducing measurement steps and calculations.

The object of the present invention is achieved like this: a kind of detector based on electric resistance tomography gas-liquid two-phase flow separation phase holdup, its microcomputer and photoelectric isolation, bus, excitation electrode selection analog switch, one end of electrode drive, The input poles of the sensor are connected in sequence; the output pole of the sensor is connected to the other end of the electrode drive, the detection electrode selection analog switch, the band-pass filter unit A, the differential amplifier unit, the phase-sensitive demodulation unit, the low-pass filter unit, the analog-to-digital conversion module, The bus is sequentially connected; the bus is sequentially connected to the other end of the sine wave generator, voltage-controlled current source, and excitation electrode selection analog switch, and the bus is also connected to the other end of the differential amplifier unit and the other end of the detection electrode selection analog switch. The other end of the wave generator is connected to the other end of the phase-sensitive demodulation unit, and the band-pass filter unit B is respectively connected to the detection electrode selection analog switch and the differential amplification unit.

The detector method of the gas-liquid two-phase flow separation phase holdup based on electrical resistance tomography comprises the following steps:

1. Inject the measured gas-liquid two-phase flow into the flow pipeline;

2. The gas-liquid two-phase flow separation phase holdup detector excites the sensor set in the gas-liquid two-phase flow pipeline with a certain time interval of sensitive field, and collects the detection signal of the induced boundary voltage;

3. The microcomputer calculates the detection signal data of the induction boundary voltage collected at regular intervals to obtain the characteristic voltage value V _R value of the frame data, and judges that the detected two-phase flow is stratified flow, or bubbly flow;

4. For stratified flow, the characteristic voltage value V _R value is calculated by the microcomputer, and the characteristic value related to the stratified flow phase holdup is used to calculate the phase separation content of the gas-liquid two-phase of the stratified flow. Rate;

5. For the bubbly flow, the microcomputer calculates the characteristic voltage value V _R value, and uses the eigenvalues related to the bubbly flow phase separation holdup to calculate, and the gas-liquid two-phase separation phase holdup of the bubbly flow can be obtained. Rate.

Since the present invention adopts the above technical scheme, it has the following advantages:

1. Using a multi-electrode sensor array, the two-dimensional/three-dimensional measurement information of the pipeline cross-sectional distribution can be obtained.

2. Using the method of feature extraction of the measured boundary voltage data, the information of the pipeline section and the information related to the phase holdup can be summarized and extracted, and the measurement accuracy and speed can be improved with less symmetrical data volume.

3. Calculate according to the eigenvalue, which can realize the rapid measurement and calculation of online phase holdup.

Description of drawings

Fig. 1 is a kind of circuit block diagram of the present invention;

Fig. 2 is a schematic diagram of the shape and structure of a sensor in the present invention;

Fig. 3 is a schematic diagram of a detector method for phase holdup of gas-liquid two-phase fluid separation based on electrical resistance tomography in the present invention.

In the picture:

1. Sine wave generator 2. Voltage-controlled current source 3. Electrode drive

4. Analog switch for excitation electrode selection 5. Analog switch for detection electrode selection 6. Band-pass filter unit A

7. Band-pass filter unit B 8. Differential amplification unit 9. Phase-sensitive demodulation unit

10. Low-pass filter unit 11. Analog-to-digital conversion module 12. Bus

13. Optical isolation 14. Microcomputer 15. Sensor

16. Excitation current signal 17. Detection voltage signal 18. Pipeline section

19. Inner wall of the pipeline 20. Outer wall of the pipeline 21. Electrode outlet

22. Electrode 23. Sensitive field excitation unit 24. Tested signal conversion unit

25. Data acquisition and processing unit 26. Image reconstruction and object field parameter extraction unit 27. Display

28. Measurement parameter output terminal

Detailed ways

Below in conjunction with accompanying drawing, the implementation of the present invention is described in detail as follows:

In Fig. 1, the detector of gas-liquid two-phase phase holdup based on electrical resistance tomography technology, its microcomputer 14 is connected with photoelectric isolation 13, bus 12, excitation electrode selection analog switch 4, one end of electrode driver 3, The input poles of the sensor 15 are connected sequentially; the output poles of the sensor 15 are connected to the other end of the electrode driver 3, the detection electrode selection analog switch 5, the band-pass filter unit A6, the differential amplifier unit 8, the phase-sensitive demodulation unit 9, and the low-pass filter The unit 10, the analog-to-digital conversion module 11, and the bus 12 are sequentially connected; the bus 12 is sequentially connected with the other end of the sine wave generator 1, the voltage-controlled current source 2, and the excitation electrode selection analog switch 4, and the bus 12 is also respectively connected with the differential amplifier unit The other end of 8 is connected to the other end of the detection electrode selection analog switch 5, the other end of the sine wave generator 1 is connected to the other end of the phase-sensitive demodulation unit 9, and the band-pass filter unit B7 is respectively connected to the detection electrode selection analog switch 5, The differential amplifier unit 8 is connected. in,

The sine wave generator 1 is used to generate the excitation sine wave to be detected by the electrical resistance tomography system under the control of the microcomputer 14, which can use a digital waveform generator EPROM2764.

The voltage-controlled current source 2 is used to convert the voltage signal output by the sine wave generator into a current signal. The input of the voltage-controlled current source 2 is a voltage sine wave signal, and the output is a current sine wave signal (excitation signal). The frequency of the excitation signal is 5.86KHz, 11.72KHz, 23.44KHz, 46.88KHz, 93.75KHz, and there are five levels of operating frequency; the amplitude of the output current of the excitation source is between 0-10mA 256 levels are optional; the phase is adjustable between 0°-180° or 0°--180°; it can be composed of double operational amplifier LF411 positive feedback.

The electrode driver 3 is used to apply the excitation current to the sensor 15 and output the induced voltage on the sensor 15 as a detection signal; it can use an operational amplifier LF411.

The excitation electrode selection analog switch 4 is used to select the excitation electrode (two adjacent excitations are selected each time); the analog switch used can select two 16-to-1 multi-way switch MAX306 chips, and the common terminal of U1 is connected to the excitation electrode. Current, the public end of U2 is connected to the analog ground. The address selection signal of MAX306 is generated by computer 14 through flip-flop 74LS374. Each time U1 and U2 gate one electrode (and these two electrodes are adjacent to form adjacent excitation), the excitation current signal flows from the common terminal of U1 to the excitation electrode selected by U1, and the induced current The electrodes selected by U2 flow out to ground through the common end of U2, thus forming an excitation loop.

Detection electrode selects the analog switch 5, which is used to select the detection electrode (two adjacent detections are selected at a time); the analog switch that it adopts can select two multi-way switches with 16 selections, such as the MAX306 chip, and the common terminal is the detection voltage output terminal V1, and the common terminal of U4 is another detection voltage output terminal V2, which is generated by the computer 14 through the flip-flop 74LS374.

The band-pass filter unit A6 and the band-pass filter unit B7 are used to filter waveforms of other noise frequencies; they can be composed of two 8-to-8 multi-way switches MAX307, one 8-to-1 multi-way switch MAX308 and an operational amplifier LF411. Since the system can work at five different frequencies, the band-pass filter is to pass the detected voltage waveform to filter out other noises. And the frequency of the detected voltage waveform is the same as the frequency of the excitation current, so the center frequency of the waveform that can be passed by the band-pass filter is exactly the frequency of the excitation current. Because the present invention can work at five frequencies, the center frequencies of the band-pass filter should correspond to five. By changing the RC value of the bandpass filter, its center frequency can be changed, and their control signal is the frequency selection signal. The input signal of the band-pass filter unit is the detected voltage signal V ₁ , V ₂ ; the output is the filtered voltage signal V ₁ ′, V ₂ ′.

The differential amplification unit 8 is used to complete the differential mode amplification of the signal without an external circuit (the amplification factor can be 100, 200, etc.). The input signal of the differential amplifier unit is V ₁ ′, V ₂ ′; the output signal is V=n*(V ₁ ′−V ₂ ′), where V is the output signal and n is the amplification factor. The differential amplifier unit is composed of precision instrumentation amplifier AD624.

The phase-sensitive demodulation unit 9 is used to convert the sine wave signal into a half-wave signal; the present invention adopts a switch demodulation mode, which can use MAX301 as the demodulation switch, and the highest address bit signal of the counter CD4024 as the demodulation signal control The switch of MAX301, the input signal of the demodulation part is V, and the output signal is half waveform.

The low-pass filter unit 10 is used to convert the demodulated half-wave signal into a DC signal output through a fourth-order Butterworth low-pass filter; it can use an operational amplifier LF411.

The analog-to-digital conversion module 11 is used to convert the analog DC signal output by the low-pass filter unit 10 into a digital signal output by the 12-bit analog-to-digital converter AD1674; AD1674 can be used.

The bus 12 is used for transmitting data signals, address signals and control signals.

Photoelectric isolation 13 is used to isolate the power supply of the system from that of the computer; a fast photoelectric isolation device 6N137 can be selected.

The microcomputer 14 is used to control signal generation, data processing, image reconstruction and calculation of characteristic parameters; it can be an ordinary microcomputer.

The sensor 15 is used to collect three pieces of data of the same flow pattern at regular intervals to characterize the three-dimensional information data signal of the flow pattern, and transmit the collected data signals to the electrode driver 3 .

In FIG. 2 , the sensor 15 is composed of an excitation current signal 16 , a detection voltage signal 17 , a pipe inner wall 19 , a pipe outer wall 20 , an electrode lead-out 21 , an electrode 22 and the like. The inner wall 19 of the pipeline is provided with 16 electrodes 22 uniformly distributed, and the outer wall 20 of the pipeline is connected with corresponding electrode leads 21 , and the electrode lead ends 21 are respectively connected to the electrode driver 3 by wires.

In the present invention, the method of exciting the sensitive field and inducing boundary voltage is used to sample the gas-liquid two-phase flow pipeline. First, the pipeline is excited and voltage sampled by means of adjacent current excitation and adjacent voltage detection. Then two adjacent electrodes are selected each time as the inflow and outflow electrodes of the excitation current, and the voltage values induced by the remaining 14 electrodes adjacent to each other are measured at the same time. Then change the excitation angle (a total of 16 excitation angles); and so on, finally will get 16 × 13 (total 208) sampling signals of 1 frame data of the measured voltage value, and send to the electrode driver 3, so as to obtain the timing interval time Collect three pieces of data of the same flow pattern to characterize the three-dimensional information data of the flow pattern.

In Figure 3,

The sensitive field excitation unit 23 is composed of a sine wave generator 1 and a voltage-controlled current source 2, and is used to generate an excitation signal.

The measured signal conversion unit 24 is composed of an electrode driver 3 , an analog switch 4 for selecting an excitation electrode, and an analog switch 5 for selecting an electrode for detection, and is used for excitation and detection signals.

The data acquisition and processing unit 25 is composed of a band-pass filter unit A6, a band-pass filter unit B7, a differential mode amplification unit 8, a phase-sensitive demodulation unit 9, a low-pass filter unit 10 and an analog-to-digital conversion module 11, and is used to detect The useful information in the signal is converted into digital quantities.

The image reconstruction and object field parameter extraction unit 26 is composed of the microcomputer 14 and corresponding calculation methods, and is used for data feature extraction and image reconstruction.

The display 27 is used for displaying the detection signal output by the microcomputer 14 in an image form and the measurement result.

The measurement parameter output terminal 28 is composed of a display or a printer, and is used to display or output measurement and calculation results, and any display or printer can be used. (When the measurement parameter output terminal 28 adopts a display, it can omit the above-mentioned display 27).

When the present invention is used in actual measurement, its detector method based on electrical resistance tomography gas-liquid two-phase flow separation phase holdup comprises the following steps:

1. Inject the measured gas-liquid two-phase flow into the flow pipeline.

2. The gas-liquid two-phase flow phase separation detector is used to generate an excitation signal for the sensor 15 provided in the gas-liquid two-phase flow pipeline by the sensitive field excitation unit 23 (sine wave generator 1 and voltage-controlled current source 2) , and the excitation of the sensitive field is carried out at a certain time interval through the excitation electrode selection analog switch 4, and the detection electrode selection analog switch 5 strobes two adjacent electrodes (except the excitation electrode) to collect the measurement signal of the induced boundary voltage.

3, the boundary voltage detection signal passes through the band-pass filter unit A6, band-pass filter unit B7, differential mode amplification unit 8, phase-sensitive demodulation unit 9, low-pass filter unit 10 and analog-to-digital conversion in the data acquisition and processing unit 25 ( module 11 conversion), the digital signal is delivered to microcomputer 14, and the detection signal data of the induction boundary voltage that collects during timing interval is calculated by microcomputer 14, obtains the characteristic voltage value V _R value of this frame data, and according to boundary measurement The voltage is combined with flow pattern recognition to judge whether the detected two-phase flow is stratified flow or bubbly flow.

4. For stratified flow, the microcomputer 14 calculates the characteristic voltage value V _R value, and uses the characteristic value related to the fractional phase holdup of stratified flow to calculate according to the empirical formula to obtain the gas-liquid ratio of stratified flow phase fraction.

empirical formula $\mathrm{\&alpha;}=a_5{V}_R^5+a_4{V}_R^4+a_3{\mathrm{<figure-callout\; id="3"\; label="V\; R"\; filenames="A0212906200081.png"\; state="\{\{state\}\}">V</figure-callout>}}_R^{}+a_2{\mathrm{<figure-callout\; id="2"\; label="V\; R"\; filenames="A0212906200081.png"\; state="\{\{state\}\}">V</figure-callout>}}_R^{}+a_1{V}_R+a_0,$ where _VR is the obtained characteristic voltage value,

a is the holdup of the gas phase, and a ₀ -- _{a 5} are undetermined coefficients, which can be calibrated according to different media and pipe diameters. 5. For the bubbly flow, the microcomputer 14 calculates the characteristic voltage value V _R value, and uses the eigenvalues related to the bubbly flow phase separation holdup to calculate according to the empirical formula to obtain the gas-liquid two-phase ratio of the bubbly flow. Phase holdup.

empirical formula $\mathrm{\&alpha;}=a_3{\mathrm{<figure-callout\; id="3"\; label="V\; R"\; filenames="A0212906200081.png"\; state="\{\{state\}\}">V</figure-callout>}}_R^{}+a_2{\mathrm{<figure-callout\; id="2"\; label="V\; R"\; filenames="A0212906200081.png"\; state="\{\{state\}\}">V</figure-callout>}}_R^{}+a_1{V}_R+a_0,$ where _VR is the obtained characteristic voltage value,

a is the holdup of the gas phase, and a ₀ -- _{a 3} are undetermined coefficients, which can be calibrated according to different media and pipe diameters. From the above, the present invention obtains the value related to the phase holdup after extracting the detected boundary features, so as to obtain the precise phase holdup of the gas-liquid two-phase flow.

The invention can be applied to the measurement of phase separation holdup of gas/liquid and liquid/liquid two-phase flow in industrial process. For example, multiphase flow transportation in the chemical industry, application in fluidized beds, flow measurement in the petroleum industry, environmental monitoring, energy, metallurgy, pharmaceuticals and other fields have broad application prospects. At the same time, since the phase separation holdup of two-phase flow is the basic parameter of fluid, the above-mentioned industries involve the research of thermodynamics, reaction kinetics, fluid mechanics and other aspects of two-phase flow, as well as the flow parameter measurement in industrial production process. , the detector and method of the present invention can be used to measure the phase separation holdup.

Claims (3)

1. A detector based on electrical resistance tomography gas-liquid two-phase flow separation phase holdup, characterized in that, microcomputer and photoelectric isolation, bus, excitation electrode selection analog switch, one end of electrode drive, the input pole of sensor Sequential connection; the output pole of the sensor is connected with the other end of the electrode drive, the detection electrode selection analog switch, the band-pass filter unit A, the differential amplifier unit, the phase-sensitive demodulation unit, the low-pass filter unit, the analog-to-digital conversion module, and the bus; The bus is sequentially connected to the other end of the sine wave generator, voltage-controlled current source, and excitation electrode selection analog switch. The bus is also connected to the other end of the differential amplifier unit and the other end of the detection electrode selection analog switch. The sine wave generator The other end is connected to the other end of the phase-sensitive demodulation unit, and the band-pass filter unit B is respectively connected to the detection electrode selection analog switch and the differential amplifier unit. 2. The detector of a gas-liquid two-phase flow phase holdup based on electrical resistance tomography according to claim 1, wherein the sensor is provided with 16 electrodes uniformly distributed, and the outer wall of the pipeline is provided with a connection The matched electrode terminals are respectively connected to the electrode driver. 3. a detector method of gas-liquid two-phase flow separation phase holdup based on electrical resistance tomography according to claim 1, comprising the following steps: 1) Inject the measured gas-liquid two-phase flow into the flow pipeline; 2) The gas-liquid two-phase flow separation phase holdup detector is used to excite the sensor set in the gas-liquid two-phase flow pipeline for a certain time interval to the sensitive field, and collect the detection signal of the induced boundary voltage; 3) The microcomputer calculates the detection signal data of the induced boundary voltage collected at regular intervals to obtain the characteristic voltage value V _R value of the frame data, and judges the detected two-phase flow according to the boundary measurement voltage combined with flow pattern identification Is stratified flow, or bubbly flow; 4) For stratified flow, the characteristic voltage value V _R value is calculated by the microcomputer, and the characteristic value related to the stratified flow phase holdup is used to calculate the phase separation holdup of the gas-liquid two-phase of the stratified flow. Rate; 5) For bubbly flow, the microcomputer calculates the characteristic voltage value V _R value, and uses the eigenvalues related to the bubbly flow phase separation holdup to calculate, and the gas-liquid two-phase separation phase holdup of the bubbly flow can be obtained. Rate.

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