ESMD Analysis Of Electrostatic Signal And Particle Velocity Measurement In Dense Phase Pneumatic Conveying System

Dense phase pneumatic conveying of pulverized fuel particles is one of the key techniques in the large scale entrained flow coal gasification, which is a potential approach to realize the highly-efficient and clean utilization of coal resource. The real time and continuous velocity measurement of dense phase pneumatically conveyed particles is of great significance for the in-depth understanding of particle flow dynamic behaviors, energy saving and the optimized design of the conveying system. Electrostatic techniques based on the particle electrification have gained worldwide attention due to their advantages of simple structure, high sensitivity, low cost, good performance and being suitable for harsh industrial environments. In this thesis, the electrostatic signal is analyzed based on extreme-point symmetric mode decomposition method (ESMD) for the particle velocity measurement and the further investigtion of the flow characteristics.A real time and continuous velocity measurement system is developed based on electrostatic sensors in combination with cross-correlation technique. The system mainly includes electrostatic sensors, electrostatic to voltage conversion circuit, data acquisition card and computer. The electrostatic signals are sampled by the data acquisition card and used to calculate the particle velocity by the computer. Experiments have been carried out on the V-belt pulley rig and a dense phase pneumatic conveyor to estimate the stability and accuracy of the particle velocity measurement system.The basic principle of ESMD is introduced in detail. Electrostatic signals from the ring and arc shape electrostatic sensors are analyzed based on ESMD. The energy and frequency information of the electrostatic signals in different decomposed modes is extracted and analyzed under various opertion cnditions of the pneumatic conveying system. The energy information of the electrostatic signal from the ring shape electrode can be used to identify the stability of conveying system during the process of startup and shut down, while those from the arc shape electrode array can be used to discern the distribution of solids inside the pipe.Based on the relationship between the freuency and the velocity, a new method to measure the particle velocity is proposed. Meanwhile, the experimental results from the V-belt pulley rig and the dense phase pneumatic conveyor are compared with those from spatial filtering method in the respects of stability and accuracy. Experimental results showed that the relative standard deviation of the correction factor in the new method is obviously lower, indicating that the new method is a stable and effective way to measure the particle velocity in dense phase pneumatic conveying system.