CN102435641A - Coaxial conductivity sensor, measurement system and measurement method for oil content of oil-water two-phase flow - Google Patents

Abstract

The invention belongs to the technical field of oil-water two-phase flow measurement, and relates to a coaxial conductance sensor used for oil-water two-phase flow detection, comprising a coaxial annular outer electrode, an inner electrode and two protective electrodes; two protective electrodes The two ends of the inner electrode are respectively fixed, an insulating gasket is arranged between them and the inner electrode, and the radius of the two protective electrodes and the inner electrode are equal. The present invention also provides a measurement system using the above-mentioned coaxial conductance sensor, and provides a measurement method realized by using the measurement system. The measurement system includes: an excitation module, a coaxial conductance sensor, a measurement module, a demodulation module, an acquisition module and a calculation unit. The sensor and measuring system of the present invention improve the measurement accuracy, especially the measurement accuracy under high water content is improved.

Description

Coaxial conductivity sensor, oil-water two-phase flow oil content measurement system and measurement method

technical field

The invention relates to a coaxial conductance sensor and a measuring system thereof, which can realize on-line precise measurement of oil content in oil-water two-phase flow.

Background technique

In the process of crude oil extraction and transportation, the online accurate measurement of the holdup of oil-water two-phase fluid is of great value. The conductivity method has the advantages of simple structure and principle, fast response, low price and no radiation, and is widely used in the measurement and research of multiphase flow. The conductometric method is a method of measuring according to the different conductivity of oil and water. Many researchers have done a lot of research on the relationship between the phase separation ratio and the conductivity of the mixture. Among them, Maxwell model ^{[1, 12, 13]} and Bruggeman model ^{[2, 14, 15]} are widely used.

In order to obtain better measurement results, researchers have designed many forms of conductivity sensors. Conductivity probes ^{[3, 4, 5]} are mainly used for the measurement of phase holdup distribution; parallel plate ^{[6, 7]} structures have electric field distribution The advantages of uniformity, due to its structural limitations, are mainly used in the measurement of square pipes; arc electrodes ^[8] , in order to be suitable for the measurement of circular pipes, change the parallel plate electrode into a semicircular structure, although it can be applied to the measurement of circular pipes, However, the cross-sectional electric field distribution is not uniform; the cross-sectional multi-electrode structure ^{[9, 10]} is mainly used for electrical resistance tomography (ERT) and longitudinal ring multi-electrode ^[11] . In addition to the parallel plate structure of the traditional conductivity sensor, the uneven electric field distribution of other sensors affects the measurement accuracy of the holdup. Although the parallel plate electrode has the advantage of uniform electric field distribution, it is limited to the measurement of square pipes, and the actual application pipes are mostly round. shaped pipes, which limits its wide application. In the design of the conductivity sensor, improving the uniformity of the electric field in the conductivity sensor is the key to improving the online measurement accuracy of the holdup.

references

[1] Maxwell J C, Treatise on Electricity and Magnetism. UK: Oxford University Press; 1873.

[2] Bruggeman D A G, Berechnung verschiedener physikalischer Konstanten vonheterogenen Substanzen. Annalen der Physik 1935; 24:636-641.

[3] Vigneaux P, Chenais P, Hulin JP, Liquid-liquid flows in an inclined pipe, AIChEJ, 1988, 34(5): 781～789.

[4] Angeli P and Hewitt G F, Flow structure in horizontal oil-water flow, International Journal of Multiphase Flow, 2000, 26(7): 1117～1140.

[5] Zhao D, Guo L, Hu X, Zhang X, Wang X, Experimental study on local characteristics of oil-water dispersed flow in a vertical pipe, Interpretation of Multiphase Flows, 2006; 32(10-11): 1254～1268.

[6] Coney M W E, The theory and application of conductance probes for the measurement of liquid film thickness in two-phase flow, J.Phys.E: Sci.Instrum., 1973, 6:903～910.

[7] Dykesteen E, Hallanger A, Hammer E etc., Non-intrusive three-component ratiomeasurement using an impedance sensor, J.Phys.E: Sci.Instrum., 1985, 18:540～544.

[8] Costigan G, Whalley P B, Slug flow regime identification from dynamic voidfraction measurements in vertical air-water flows, Interpretation of MultiphaseFlows, 1997, 23(2): 263～282.

[9]Wang M, Dorwood A, Vlaev D, Mann R, Measurements of gas-liquid mixing in astirred vessel using electrical resistance tomography, Chem.Eng.Sci., 2000, 77:93～98.

[10] Dong F, Liu X P, Deng X, et al, Identification of two-phase flow regimes horizontal, inclined and vertical pipes, Measurement Science and Technology, 2001, 12(8): 1069～1075.

[11]Jin N D, Zhao X, Wang J et al, Design and geometry optimization of a conductiveprobe with a vertical multiple electrode array for measuring volume fraction and axial velocity of two-phase flow, Multiphase Science and Technology 08, 9( ), 045403.

[12] Yang H C, Kim D K, Kim M H, Void fraction measurement using impedance method, Flow Measurement and Instrumentation, 2003(14), 151-160.

[13] Dai Xuefei, Liu Xingbin. Simulation of full borehole conductance sensor and research on static experimental characteristics [J], Logging Technology, 2008, 32(1), 5-8.

[14] Devia F, Fossa M, Design and optimization of impedance probes for voidfraction measurements, Flow Measurement and Instrumentation, 2003(14), 139-149.

[15] Zhang Bo, Liu Runhua. Design of water content tester for crude oil based on capacitive conductivity method [J]. Instrument Technology and Sensors, 2009(7), 39-44.

Contents of the invention

The object of the present invention overcomes the above-mentioned deficiencies of the prior art, provides a kind of electric field distribution more evenly, detects more accurate conductance sensor, and provides a kind of measurement system and measurement method that adopts this kind of conductance sensor, improves oil-water two-phase with this Accuracy of holdup measurement.

A coaxial conductance sensor for oil-water two-phase flow detection, comprising a coaxial annular outer electrode, an inner electrode and two guard electrodes; the two guard electrodes are respectively fixed at both ends of the inner electrode, and they are An insulating spacer is arranged between the electrodes, and the radius of the two guard electrodes is equal to that of the inner electrode.

As a preferred embodiment, the coaxial conductivity sensor for oil-water two-phase flow detection includes an internal electrode assembly with a coaxial structure composed of an internal electrode, two guard electrodes, and two insulating gaskets. The internal electrode assembly The axial length is equal to the axial length of the external electrode; the coaxial conductance sensor, when in use, is fixed on a vertically ascending or vertically descending pipeline.

The present invention provides an oil-water two-phase flow oil content measurement system using the above-mentioned conductivity sensor, which includes a sensor, an excitation module, a measurement module, an acquisition module, a demodulation module and a calculation unit. The sensor is a coaxial conductivity sensor, including a coaxial Shaft annular outer electrode, inner electrode and two protective electrodes; the two protective electrodes are respectively fixed at both ends of the inner electrode, and an insulating gasket is arranged between them and the inner electrode, and the radius of the two protective electrodes is equal to that of the inner electrode and With the same potential, the excitation module generates a sinusoidal excitation signal and two reference signals with a phase difference of 90°, the two reference signals are sent to the demodulation module, and the excitation signal is loaded on the inner electrode or outer electrode as the excitation electrode, as The output signal of the inner electrode of the detection electrode passes through the measurement module and the demodulation module in turn to obtain the real part signal, and then is sent to the calculation unit through the acquisition module, and the calculation unit calculates the oil content of the oil-water two-phase flow according to the collected real part signal.

As a preferred embodiment, the calculation unit calculates the parallel resistance value of the measured oil-water two-phase flow equivalent resistance-capacitance parallel circuit according to the real part signal output by the demodulation module of the measurement system, and then uses the Maxwell model to calculate the oil content of the oil-water two-phase flow , if the measured oil content is greater than 50%, the oil content is calculated using the Bruggeman model, and the average value of the calculation results of the two models is used for correction to obtain the measured value when the oil content of the oil-water two-phase flow is greater than 50%.

The present invention also provides a measurement method implemented by the above-mentioned oil-water two-phase flow oil content measurement system, comprising the following steps:

(1) A sinusoidal excitation signal and two reference signals with a phase difference of 90° are generated by the excitation module;

(2) Apply a sinusoidal excitation signal to the excitation electrode, and send the two reference signals into the demodulation module;

(3) The output signal of the detection electrode is demodulated with the reference signal after the measurement module to obtain the real part signal;

(4) Calculate the oil content of oil-water two-phase flow according to the real part signal.

Wherein step (4), specifically may comprise the following steps:

(1) Calculate the resistance value of the measured oil-water two-phase flow, and then obtain its conductivity;

(2) Using the Maxwell model to calculate the oil content of oil-water two-phase flow;

(3) If the calculated oil content is greater than 50%, the oil content is calculated using the Bruggeman model, and the average value of the calculation results of the two models is used to correct the measured value when the oil content of the oil-water two-phase flow is greater than 50%.

In the present invention, the inner electrode and the outer electrode adopt a coaxial structure, and the electric field distribution therebetween is more uniform. At the same time, protective electrodes are added at both ends of the inner electrode to further reduce the influence of the edge effect. By adopting the sensor and measuring system of the present invention, the measurement accuracy can be improved, especially the measurement accuracy under high water content is improved: when the oil content is less than 50%, the measurement error of the sensor for measuring the oil content is within 2%; The measurement error is larger when the oil content is greater than 50%, and the maximum measurement error is 5% when the oil content is 70%. The device has important practical significance in the measurement of oil-water two-phase flow.

Description of drawings

Fig. 1 is the system structural diagram of device of the present invention;

Fig. 2 is the sensor structural diagram of device of the present invention;

Fig. 3 is a schematic diagram of the connection mode between the sensor and the measuring circuit of the device of the present invention, (a) and (b) are each a connection mode.

In the picture:

1. PC machine 2. Incentive module

3. Coaxial conductivity sensor 4. Measurement module

5. Demodulation module 6. Acquisition module

7. Fixed steps 8. Protective electrodes

9. Insulation gasket 10. Inner electrode

11. External electrode 12. Organic glass rod

13. Sensor tube wall 14. Fixing ring

Detailed ways

The coaxial conductance sensor and its measurement system for oil-water two-phase flow measurement of the present invention will be described below in conjunction with example drawings and embodiments.

The system structure of the present invention is shown in Figure 1, including: a coaxial conductance sensor 3, an excitation module 2, a measurement module 4, a data acquisition module 6, a demodulation module 5 and a PC (computing unit) 1 . The coaxial conductivity sensor is mainly composed of an inner electrode 10, an outer electrode 11, two protective electrodes 8, a fixed step 7, and a fixed ring 14. As shown in Figure 2, both ends of the sensor in this embodiment can be installed on a vertical on the straight pipe. The outer electrode 11 is a cylindrical structure, fixed on the inner wall of the pipe of the sensor section, and insulated from the pipe wall 13; the inner electrode 10 is also a cylindrical structure, placed in the pipe and coaxial with the outer electrode; Connect a guard electrode 8 that is coaxial and of the same radius as the inner electrode. In this embodiment, the radius of the outer electrode 11 is the same as the inner wall of the pipeline, which is 25mm, the radius of the inner electrode 10 is 15mm, and the length is 100mm. The length of each protective electrode 8 is 25mm, and each is connected to the inner electrode through an insulating pad 9. A plexiglass rod 12 is respectively connected between each protective electrode and the sensor end; The combination of steps and fixing rings, two upper and lower fixing rings and two plexiglass rods fix the inner electrode and two protective electrodes in the sensor, the inner electrode 10, two protective electrodes 8, two insulating pads 9 and two plexiglass The fixed connections between the rods 12 all adopt threaded connections. The axial length of the inner electrode 10, two insulating gaskets 9 and two protective electrodes 8 is the same as that of the outer electrode 11. This coaxial structure can make the electric field distribution in the sensor more uniform, and is more suitable for holdup measurement. The excitation module can generate one sinusoidal excitation signal and two reference signals (0°, 90°) at the same time, and the reference signal is applied to the demodulation module; the measurement module mainly converts the impedance signal measured by the sensor into a voltage signal, and then sends it to the demodulation module Perform demodulation to obtain the real part voltage value and imaginary part voltage value, and obtain the impedance signal of the measured object. The demodulation methods include switch demodulation, multiplication demodulation and digital demodulation. After the demodulated signal is collected by the acquisition module, it is sent to the PC for content calculation. The results of multiple experiments show that: for the application conditions with an oil content below 50%, the Maxwell model ^{[1, 12, 13]} is used to calculate the oil content; for the application conditions with an oil content above 50%, the Maxwell model and the Bruggeman model ^{[ 2, 14, 15]} The average value of calculated oil content is used as the final calculation result of oil content.

Among them, there are two ways of cooperation between the measurement system and the electrodes: 1. Use external electrodes to excite, the protection electrodes are grounded, and the internal electrodes are connected to the measurement module, whose potential is the same as the protection electrodes (as shown in Figure 3(a)); 2. Use external electrodes The grounding and internal electrodes are both used as excitation electrodes and detection electrodes at the same time, and the protection electrodes are kept at the same potential as the internal electrodes (as shown in Figure 3(b)).

(R_f为测量模块上的反馈电阻)。V_ol及激励模块两路参考信号(0°、90°)接解调信模块5。解调信模块5对V_ol及参考信号进行乘法解调，得到信号的实部电压值V_re。解调模块5的输出信号V_re接采集模块6。采集模块6将采集信号送入PC机1。PC机1对采集值进行计算可获得被测对象的电阻信号R，计算式为

将获得的被测对象电阻信号(电导率的倒数)带入Maxwell模型

(σ_m为油水混合物的电导率，σ_w为水单相的电导率，a为含水率)与Bruggeman模型σ_m＝a^3/2σ_w可得含水率进而可得含油率。代入计算模型的水的电导率σ_w是实验前由该传感器测量的单相水的电导率。通过实验装置上油路及水路的单相测量仪表获得流过测量管路的油水体积流量及含油率α_o，再对比本发明系统所得出的含油率，结果表明当含油率小于50％时，利用Maxwell模型获得的含率，误差均在2％以内。当含油率大于50％后，误差变大，利用Maxwell模型与Bruggeman模型测量含油率的平均值作为最终含油率值优于使用单一的模型，含油率70％时使用该组合模型最大误差为5％。在实际测量时，可以首先利用Maxwell模型计算含油率，如果测得的含油率大于50％，再利用Bruggeman模型计算含油率，利用两个模型的计算结果平均值进行修正得到含油率大于50％时的测量值。The experiment is carried out on the oil-water two-phase flow experimental device, the pipeline of DN50 is selected, and the sensor 3 is installed vertically on the experimental pipeline, which can avoid the influence of oil-water layer on the measurement results. The mode of cooperation between the sensor 3 and the measurement circuit is to select the external electrode excitation, the protective electrode is grounded, and the internal electrode is connected to the measurement module 4 (as shown in Figure 3(a)). The external electric level AC excitation signal V _i is provided by the excitation module 2. The measurement module 4 converts the oil-water impedance signal (equivalent to a parallel circuit of a capacitor C and a resistor R) flowing through the sensor 3 into a voltage signal V _ol for output, and the calculation formula is

(R _f is the feedback resistor on the measurement module). V _ol and two reference signals (0°, 90°) of the excitation module are connected to the demodulation module 5 . The demodulation module 5 multiplies and demodulates V _ol and the reference signal to obtain the real voltage value V _re of the signal. The output signal V _re of the demodulation module 5 is connected to the acquisition module 6 . The acquisition module 6 sends the acquisition signal to the PC 1 . PC 1 calculates the collected value to obtain the resistance signal R of the measured object, and the calculation formula is

Bring the obtained measured object resistance signal (reciprocal of conductivity) into the Maxwell model

(σ _m is the electrical conductivity of the oil-water mixture, σ _w is the electrical conductivity of the single-phase water, and a is the water content) and the Bruggeman model σ _m = a ^3/2 σ _w can obtain the water content and then the oil content. The conductivity _σw of water substituted into the calculation model is the conductivity of single-phase water measured by the sensor before the experiment. Obtain the oil-water volume flow rate and oil content α _o flowing through the measurement pipeline through the single-phase measuring instrument of the oil circuit and water circuit on the experimental device, and then compare the oil content obtained by the system of the present invention. The result shows that when the oil content is less than 50%, The error of the holdup obtained by Maxwell model is within 2%. When the oil content is greater than 50%, the error becomes larger. Using the average value of the Maxwell model and the Bruggeman model to measure the oil content as the final oil content value is better than using a single model. When the oil content is 70%, the maximum error of using the combined model is 5%. . In actual measurement, you can first use the Maxwell model to calculate the oil content, if the measured oil content is greater than 50%, then use the Bruggeman model to calculate the oil content, and use the average value of the calculation results of the two models to correct the oil content when the oil content is greater than 50%. measured value.

Claims (10)

1. one kind is used for the coaxial electrical derivative sensor that the oil-water two-phase flow oil content detects, and comprises the annular external electrode that is coaxial, interior electrode and two guard electrodes; The two ends of electrode in two guard electrodes are separately fixed at, they with interior electrode between be provided with insulation spacer, the radius of two guard electrodes and interior electrode is equal.

2. the coaxial electrical derivative sensor that is used for the detection of oil-water two-phase flow oil content according to claim 1; Constitute the internal electrode assembly of coaxial configuration by interior electrode, two guard electrodes and two insulation spacers, the axial length of this internal electrode assembly equates with the axial length of external electrode.

3. according to right 1 or 2 described sensors, described coaxial electrical derivative sensor in use, is fixed on vertical uplift or the pipeline that vertically descends.

4. oil-water two-phase flow oil content measuring system; Comprise sensor, stimulating module, measurement module, acquisition module, demodulation module and computing unit is characterized in that; Described sensor is the coaxial electrical derivative sensor, comprises coaxial annular external electrode, interior electrode and two guard electrodes; The two ends of electrode in two guard electrodes are separately fixed at; Be provided with insulation spacer between they and the interior electrode, two guard electrodes equate and electromotive force same with it with the radius of interior electrode, and it is 90 ° reference signal that stimulating module generates sinusoidal excitation signal and two phase differential; Two reference signals are admitted to demodulation module; Pumping signal is loaded on the interior electrode or external electrode as exciting electrode, pass through measurement module and demodulation module successively as the output signal of the interior electrode of detecting electrode after, obtain solid part signal; Be admitted to computing unit through acquisition module again, calculate the oil-water two-phase flow oil content according to the solid part signal of gathering by computing unit.

5. according to claim 4 an oil-water two-phase flow oil content measuring system; It is characterized in that; Described sensor constitutes the internal electrode assembly of coaxial configuration by interior electrode, two guard electrodes and two insulation spacers, and the axial length of this internal electrode assembly equates with the axial length of external electrode.

6. measuring system according to claim 4 is characterized in that, described external electrode is as exciting electrode, two guard electrode ground connection, and interior electrode is as detecting electrode.

7. measuring system according to claim 4 is characterized in that, external electrode ground connection, and two guard electrodes connect pumping signal, and interior electrode is both as exciting electrode, also simultaneously as detecting electrode.

8. measuring system according to claim 4; It is characterized in that; Computing unit calculates the parallel resistance value of tested oil-water two-phase flow equivalence RC parallel circuit according to the solid part signal of the demodulation module output of this measuring system, utilizes Maxwell Model Calculation oil-water two-phase flow oil content then; If the oil content that records is greater than 50%; Utilize Bruggeman Model Calculation oil content again, utilize the result of calculation mean value of two models to revise, obtain the oil-water two-phase flow oil content greater than 50% o'clock measured value.

9. a measuring method that adopts the described oil-water two-phase flow oil content of claim 4 measuring system to realize comprises the following steps:

(1) generating sinusoidal excitation signal and two phase differential by stimulating module is 90 ° reference signal;

(2) exciting electrode is applied sinusoidal excitation signal, the two-way reference signal is sent into demodulation module;

(3) the output signal of detecting electrode is carried out demodulation with reference signal behind measurement module and obtain solid part signal;

(4) calculate the oil-water two-phase flow oil content according to solid part signal.

10. measuring method according to claim 9 is characterized in that step 4 comprises:

(1) utilizes the solid part signal that measures to calculate the resistance value of tested oil-water two-phase flow, and then obtain its conductivity;

(2) utilize Maxwell Model Calculation oil-water two-phase flow oil content;

(3) if the oil content that calculates greater than 50%, utilizes Bruggeman Model Calculation oil content again, utilize the result of calculation mean value of two models to revise, obtain the oil-water two-phase flow oil content greater than 50% o'clock measured value.

Images