Preliminary Study On Measurement Method And System Design Of Physical Parameters Of Oil-Water Two-phase Flow Based On Dual-Frequency Digital Demodulation Technology

With Electric dehydration of crude oil has become an indispensable important link in crude oil treatment process because of its high efficiency and green environmental protection.with the popularization of tertiary oil recovery technology and the application of various chemical reagents,the composition of crude oil emulsion is complicated.the electrical conductivity of crude oil produced fluid increases,and the traditional electric dehydration can not dynamically monitor the physical parameters of the produced liquid with high emulsification and high electrical conductivity.It leads to the increase of electric field collapse frequency of electric dehydration equipment,which not only greatly reduces the crude oil recovery efficiency,but also brings hidden dangers to the safe production of crude oil.Because the two parameters of electrical conductivity and water content and their relationship are the key to the establishment of effective dehydration electric field in the process of electric dehydration,in this paper,the synchronous measurement method and system of electrical conductivity and water content are studied by dual-frequency digital demodulation technology.In order to verify the feasibility and means of measuring physical parameters of oil-water two-phase flow,the feasibility of simultaneous measurement of water content and conductivity of oil-water two-phase flow based on measuring displacement current and conductance current is verified by combining dielectric measurement theory with equivalent resistance-capacity model of two-phase flow in theoretical analysis and numerical simulation.Through the circuit simulation analysis and optimization of the traditional single-frequency analog demodulation and dual-frequency digital demodulation technology,it is concluded that the dual-frequency digital demodulation technology can better solve the problem of the mismatch between equivalent impedance and capacitance under a single fixed frequency and the inherent DC bias of analog demodulation technology.In order to solve the problem of poor fitting ability of linear fitting method to multi-factor variables,a measurement method based on BP neural network is proposed,and the nonlinear fitting data processing method is used to correct the error of the measurement results to improve the measurement accuracy.The structure and electric field distribution characteristics of the coaxial cylindrical electrode sensor are analyzed by COMSOL,and the geometric size of the coaxial cylindrical non-insulating layer sensor with the best sensitivity is obtained.In the measurement system,the modular design idea is used to realize the design of hardware circuit and software processing part,such as dual-frequency excitation signal generation,signal acquisition,data processing and so on.The hardware part includes:DAC module,ADC module,Ibeat V conversion module and temperature compensation module.The software part includes: DDS module based on ZYNQ system,DMA module,multiplier module,CIC filter module,gear switching program,resistance-capacitance matching program,upper computer interface based on QT and BP neural network algorithm for data error correction.Finally,the construction of the measurement system and the measurement experiments of water cut and electrical conductivity of oil-water two-phase flow were completed in the laboratory.The experimental results show that the resistance measurement error of the measurement system is less than 3%,and the capacitance measurement error is less than 2%.In static measurement,the conductivity measurement error is less than 5% and the moisture content measurement error is less than 2%.In dynamic measurement,the errors of moisture content and electrical conductivity are less than 7.5%.