Development And Application Of Electrostatic Velocity Sensor Based On Gas Ionization

Under the background of the increasing demand for total energy for national economic development and the gradual strengthening of environmental protection,the control requirements of flue gas pollutant emission from coal-fired units are becoming more and more strict.As an important part of pollutant discharge control,the accuracy of flue gas flow parameters monitoring is directly related to whether the discharge of relevant pollutants can be truly reflected.This topic uses the principle of gas ionization,combined with the electrostatic cross-correlation velocity measurement technology,developed a convenient electrostatic velocity measurement system based on gas ionization,to achieve real-time and accurate measurement of high temperature,dust/low dust smoke gas,to provide reliable monitoring data for pollution gas emission control.The main work of this project is as follows:(1)The structure design of electrostatic velocity sensor(excitation sensor)based on gas ionization,which is suitable for the measurement of flue gas velocity in large cross-section flue,is studied.The discharge and induction characteristics of the excitation sensor are studied by COMSOL multiphysics software.The simulation results show that the discharge effect of the tip electrode is related to the included angle and length of the electrode.When the included angle is 40 ° and the length is 5mm,the density of charged particles in the space reaches the maximum;The relationship between the induced signal amplitude and the electrode length and the electrode angle increases first and then decreases.When the included angle is 40 ° and the electrode length is about 5mm,the signal amplitude reaches the maximum;The signal induction enhancement efficiency and signal induction intensity decrease with the increase of the distance between discharge electrode and induction electrode.If the distance between electrodes is smaller,the signal induction enhancement efficiency of the induction electrode is higher and the signal induction intensity of the induction electrode is greater;The amplitude of the induced current and the signal enhancement efficiency of the induced electrode increase with the increase of wind speed,but the increase decreases gradually.In addition,combined with the results of simulation research,some parameters of the excitation sensor structure are selected,and the corresponding research and analysis are carried out for the unselected structural parameters,including discharge voltage and inter electrode distance,which lays a foundation for the design of the excitation sensor.(2)Laboratory integration of excitation velocity measurement system is carried out.According to the inductive signal characteristics,functional requirements and portability of the excitation sensor,the software and hardware systems suitable for its signal processing and data display are selected,including cross-correlation calculator,signal conditioning circuit,signal acquisition circuit,display panel,etc.,and finally integrated into an equipment box.The wind-speed experiment platform is built to study the high voltage used by the excitation sensor and the distance between the discharge electrode and the induction electrode.Finally,it is determined that the discharge voltage is – 8kV and the distance between electrodes is 40 mm.The error of the excitation speed measurement system is corrected by using the built wind-speed experiment platform,and the reference speed and the speed calculated by cross-correlation are linearly fitted.After fitting,the correlation coefficient is high and the residual square is small,indicating that there is a good linear relationship between the measured value of the excitation speed measurement system and the reference speed;The accuracy test results of the excitation speed measurement system show that the measurement relative error of the corrected speed measurement system is less than 5% and the relative standard deviation is less than1%,indicating that the system has good accuracy and precision.(3)The application research of excitation speed measurement system in flue gas is carried out.Median filter and mean filter is adopted to eliminate the noise interference in the field environment,so as to improve the performance of excitation sensor;The engineering application results show that the velocity measurement fluctuation of the excitation velocity measurement system is small,the relative standard deviation of velocity measurement is no more than 3%,and the measurement precision is high;The speed measurement results of the speed measurement system and pitot tube are basically the same,and the maximum absolute error of the two speed measurement results is0.26m/s,which meets the measurement requirements of flue gas flow rate in industrial site.