Measurement Of Particles Flow Characteristics In The Fluidized Bed Using Electrostatic Sensor Arrays

Fluidized bed is widely used in many industrial applications because of its good heat and mass transfer efficiency and the ability to deal with a large number of particles.The velocity and concentration of particles in fluidized bed are the key factors,which influence the efficiency of the process.Therefore,through real-time measurement and monitoring of some key parameters in the production process,it is possible to realize the optimization of process control.In addition,it also has a very positive significance to improve production efficiency,help to reduce environmental pollution and other issues.Electrostatic method is a new method for detecting the movement of particles in the particulate process.Due to the advantages of simple structure,low cost,stable performance,high sensitivity and suitable for harsh industrial production environments,it has been widely used in the measurement of the pneumatic conveying process.In this paper,based on the principle of electrostatic measurement,wire-mesh electrostatic sensors which have a higher and more uniform sensitivity distribution are applied to measure the flow dynamics of solid particles,and some experimental results are obtained.The major findings are given in the following:1.In order to verify the measurement performance of the wire-mesh electrostatic sensor,an experimental study was carried out at the elbow of a lab scale pneumatic conveying pipe.By cross correlating the electrostatic signals from the corresponding electrodes in the upstream and downstream planes the velocity profile of the particles in the bend is obtained.From the velocity profile,it can be found that the velocity profile from the left to the right is relatively uniform in the elbow.Due to the effect of the centrifugal force,the particle velocity near the outer wall of the elbow is higher.The relative concentration distribution of solid particles in the elbow can be reconstructed by using the RMS values of the electrostatic signals from the wire-mesh electrodes.It is found from the reconstruction result that the relative concentration distribution can reflect the rope flow pattern of the solid particles in the outer wall region of the elbow.2.The wire-mesh electrostatic sensors are installed at a lab scale bubbling fluidized bed to measure the velocity profile and the charge distribution of the solid particles in the bed.The velocity profile of solid particles is obtained by cross-correlation calculation of the electrostatic signals at the corresponding positions of the upstream and downstream planes.In addition,the relationship between the cross-correlation coefficient and the fluidization air flow rate is analyzed.In order to increase the reliability of the measurement,the weighted average velocity is used to characterize the flow dynamics of the solid particles.The induced charges on the wire-mesh electrodes can be estimated by the RMS values of the electrostatic signals.According to the charge distribution reconstruction algorithm,the charge distribution of the solid particles in the cross section can be reconstructed by using the induced charges from all the electrodes.Due to the influence of particle velocity profile in the fluidized bed,induced charge on the electrode in the center of the bed is higher than that on the electrode near the bed wall.The charge distribution in the cross section is relatively uniform,and the maximum deviation with respect to the average value is less than 24%.In addition,based on the knowledge of the particle movement in the bubbling fluidized bed,the measurement of falling particles near the wall is studied.The experimental results show that most of the falling particles in the bubbling fluidized bed are near the bed wall.In conclusion,the particle velocity profile and charge distribution can be measured by the wire-mesh electrostatic sensors,which can be used to monitor the running state of the fluidized bed and improve the operation efficiency and product quality.