Mass Flow Rate Measurement Of Particles Based On Electrostatic Sensors

The transportation of solid particles in pneumatic conveying pipelines has been widely used in many industries, such as power generation, chemical, metallurgy, pharmaceutical, etc. Accurate and reliable on-line measurement of dynamic parameters about pneumatically conveyed particles will result in improved production efficiency and reduced energy consumption. The electrostatic sensors have been widely used in the mass flow rate and particles velocity measurement of gas-solid two-phase flow due to its advantages of simple structure, reliable performance and robustness. This study focuses on the main factors that affect mass flow measurement of pneumatically conveyed particles base on the electrostatic method. The main achievement and contributions of the research are as follows.A set of ring-shaped electrostatic sensors with 2 mm,4 mm,6 mm and 10 mm axial widths is designed and implemented through analyzing the induced mechanism of electrostatic sensors. The particle velocity is obtained based on cross-correlation. A signal acquisition system and a 74 mm bore gas-solid two-phase flow test rig, which can continuously adjust the air velocity and the feeding rate of solid particles, are also designed and implemented.Experimental tests were conducted on the rig under various velocity, mass flow rate and moisture content conditions. Glass beads with the mean equivalent diameter between 150μm and 200 μm were used as test material. Both root mean square (RMS) and power spectrum density (PSD) of electrostatic signals, which measured by the electrodes with different axial widths, were used to analyze the effects of the particle velocity, mass flow rate, moisture content and other factors on the characteristics of measured electrostatic signals. The peak frequency of the signal becomes higher when the particle velocity increases, the mass flow rate reduces or the width of electrodes reduces. The RMS and the area of PSD curve of electrostatic signals increase with the particles velocity, mass flow rate and width of electrodes increasing. Narrow electrode is more suitable for measuring the particle velocity, while the wide one is appropriate to measure the mass flow rate. The overall relative error of mass flow rate measurement is within ±10% under various test condition. In order to compare the effect of moisture content of solid and porous particles on electrostatic signals, glass beads and activated carbon were tested. The RMS and PSD of measured signals demonstrate that the higher moisture content, the lower the electrostatic charge and the worse fluidity.