Flow Measurement Of Gas-liquid Two-phase Flow By Time Difference Method Based On FPGA

The gas-liquid two-phase flow is one of the common flow forms in the production of oil and gas wells.Because of the compressibility of gas and the variability of gas-liquid interface,the flow measurement of gas-liquid two-phase flow rate is always a difficulty.The accurate measurement of gas-liquid two-phase flow is an important basis for evaluating the productivity of oil and gas wells.Ultrasonic flowmeter based on time difference method has been widely used in flow measurement of gas-liquid two-phase flow due to its wide measuring range,strong anti-interference ability and accurate measurement.The time difference method ultrasonic flowmeter is used to measure the flow rate by measuring the time difference of ultrasonic wave propagation in the fluid.At present,the time difference method of ultrasonic flowmeter is not high because of the calculation accuracy of the time difference of transmission,which leads to a large measurement error.Therefore,in order to improve the accuracy of gas-liquid two-phase flow measurement,an time difference method ultrasonic flow measurement system is designed based on the digital circuit of high-speed counter inside FPGA.This article first aimed at the key factors in the ultrasonic gas-liquid two-phase flow detection model,using COMSOL Multiphysics simulation software to establish the corresponding simulation model.The propagation characteristics of ultrasonic wave at different flow rates,different pipe diameters,different transmission frequencies and installation angles of ultrasonic transducer and different gas comparisons are analyzed.The simulation results provide theoretical basis for the selection and installation of ultrasonic transducer.The hardware circuit and software program of the ultrasonic time difference method gas-liquid two-phase flow measurement system based on FPGA are designed.The hardware circuit mainly includes the time difference detection circuit,the power circuit and the main control circuit composed of the transducer driving circuit,the switch switching circuit,the receiving signal conditioning circuit and the voltage comparison circuit.Finally,indoor simulation experiments were carried out to adjust the change of fluid velocity by adjusting the tap position of the pump,and to analyze the size of fluid flow under different gas-liquid ratios,so as to verify the reliability of the time difference measurement method designed in this article The experimental results show that the relative error of flow measurement decreases with the increase of gas phase proportion,but the overall measurement error is large.Through the analysis of the influencing factors of the flow measurement accuracy,the flow correction formula is given,and the error compensation of the measurement results is made by using Matlab.Compared with the error correction effect,the relative error of flow measurement after correction is less than 8%.