Study On The Detection Method Of Pulverized Coal Concentration And Velocity Based On Ultrasonic

The mixed flow of air and pulverized coal in primary air duct of coal-fired boiler in thermal power station has complex gas-solid two-phase flow characteristics.The detection of the concentration and velocity of solid particles in gas-solid two-phase flow is the premise of ensuring the safe and efficient operation of the boiler.Because of the influence of the layout of the coal conveying pipeline and the performance of the coal pulverizer,and the instability of the gas-solid two-phase flow,the detection of the concentration and velocity of the pulverized coal particles is a big problem faced by enterprises and researchers.Ultrasonic has a good performance in penetration,reliability and other aspects.In recent years,it is a hot topic to use it to measure the concentration and velocity of gas-solid two-phase flow.In this paper,the concentration and velocity of gas-solid two-phase flow based on ultrasonic detection are studied and discussed in detail as follows:Firstly,the propagation mechanism of ultrasonic wave in two-phase flow is studied deeply.It is found that the main factors of ultrasonic wave attenuation in gas-solid two-phase flow pipe with fixed diameter are solid particle concentration,temperature,ultrasonic frequency and solid particle size.The research scheme of calculating the concentration of gas-solid two-phase flow by measuring the ultrasonic attenuation coefficient and the velocity of two-phase flow by measuring the ultrasonic time difference is determined.Secondly,the propagation of ultrasonic wave in gas-solid two-phase flow is simulated,and the influence of different frequency,concentration,temperature and particle size on ultrasonic attenuation coefficient is analyzed.It is found that when the signal frequency and solid particle size are fixed,the concentration of gas-solid two-phase flow has a linear relationship with the ultrasonic attenuation coefficient.The formula is verified in the finite element software,which proves the feasibility and correctness of ultrasonic measurement of gas-solid two-phase flow concentration.Then,the flow velocity of gas-solid two-phase flow measured by ultrasonic method is simulated.After studying the measurement principle,the velocity calculation formula is given.The time difference between the upstream and downstream of two-phase flow is calculated by using the difference of ultrasonic propagation velocity The calculated velocity is basically equal to the average velocity of gas-solid two-phase flow in the pipeline,which proves the feasibility of measuring the velocity of gas-solid two-phase flow by ultrasonic time difference method.Then,the factors that may affect the measurement error of velocity are studied.The influence of velocity on the measurement of gas-solid two-phase flow by ultrasonic method is very small,and the influence of temperature and pipeline diameter on the measurement error is also found Small,negligible.Finally,the ultrasonic method is used to measure the concentration of gas-solid twophase flow.In the experiment,gravity is used to provide transport power for solid particles,and five groups of solid particles with different concentrations are tested.The relationship between solid concentration and ultrasonic attenuation coefficient of gas-solid two-phase flow is obtained by analyzing the measured data,and the concentration calculation formula is given according to the relationship.Then,three kinds of solid particles with different concentrations are randomly selected for experiments.The experimental results show that there is a certain error between the actual concentration and the two-phase flow concentration calculated by measurement,but it can meet the initial measurement requirements.