基于静电传感器阵列的流化床内颗粒动态特性的测量

发布时间：2018-05-20 23:10

本文选题：网状静电传感器 + 流化床　；参考：《华北电力大学(北京)》2017年硕士论文

【摘要】：流化床因为其出色的传热和传质效率与处理大量颗粒的能力而被广泛应用于很多工业场合。流化床中颗粒的速度与浓度等运行参数是保障其正常运行的关键性因素。通过对这些运行参数进行实时测量与监测,可实现工业过程的优化控制,提高生产效率并且有助于降低环境污染等问题。静电法是针对颗粒运动特征参数的一种新型测量方法,且该方法具有成本低、性能稳定、灵敏度高、测量装置简单和适用于恶劣的工业生产环境等优点,现己被用于气力输送的过程中。本论文基于静电测量原理,采用一种灵敏度更高且分布更加均匀的网状静电传感器,对固体颗粒动态参数的测量进行了相关的理论和实验研究,并得出了一定的实验结果,主要结论如下:1.为了验证网状静电传感器的测量性能,在实验室规模气力输送管道的弯管处进行了实验研究。通过对气力输送管道弯管附近上下游平面对应位置不同网状电极所得静电信号进行互相关计算,得出颗粒在弯管处的流速分布。从流速分布可以看出弯管径向方向从左到右的速度廓型是相对均匀的。由于颗粒在经过弯管的过程中,会受到离心力的作用,从而使得沿着弯管外壁附近运动的颗粒速度更高。利用网状电极一个平面上静电信号的RMS值可以重建出弯管处固体颗粒的相对浓度分布。重建结果表明,重建后的相对浓度分布可以反映出固体颗粒通过弯管时在弯管外壁处的绳状流流型。2.网状静电传感器被安装在实验室规模鼓泡流化床上,用于测量流化床中固体颗粒的速度廓形和电荷分布。网状静电传感器上下游对应位置的电极上静电信号作互相关计算可以得到固体颗粒的速度廓形,并分析了随着气体流量的变化,沿着径向方向的互相关系数的变化情况。加权平均速度可以在一定程度上表征流体的流动状态,因此在本文中被用来增加测量的可靠性。静电信号的RMS值被用于估算所有电极上的感应电荷量,并利用所得结果重建出电荷在截面处的分布情况。由于流化床内颗粒速度廓形的影响,中心处电极上的感应电荷量大于管壁附近电极上的感应电荷量。并且截面处电荷分布相对均匀,相对于平均值的最大偏差小于24%。除此之外,还结合鼓泡床中颗粒的运动特性,对管壁附近下落颗粒的测量作了一定的研究。数据表明鼓泡流化床中大部分的下落颗粒都在管壁附近。利用传感器获得的颗粒速度廓形和电荷分布,可以对流化床的运行状态进行监测,提高运行效率和产品质量。
[Abstract]:Fluidized bed is widely used in many industrial fields because of its excellent heat and mass transfer efficiency and its ability to deal with a large number of particles. The operation parameters such as velocity and concentration of particles in fluidized bed are the key factors to ensure their normal operation. Through the real-time measurement and monitoring of these operating parameters, the optimization control of industrial process can be realized, the production efficiency can be improved and the environmental pollution can be reduced. Electrostatic method is a new method for measuring the characteristic parameters of particle motion. The method has the advantages of low cost, stable performance, high sensitivity, simple measuring device and suitable for bad industrial production environment. It has been used in the process of pneumatic transportation. Based on the principle of electrostatic measurement, a network electrostatic sensor with higher sensitivity and more uniform distribution is adopted in this paper. The measurement of dynamic parameters of solid particles is studied theoretically and experimentally, and some experimental results are obtained. The main conclusions are as follows: 1. In order to verify the measurement performance of the network electrostatic sensor, an experimental study was carried out at the bend of the pneumatic conveying pipeline in laboratory. Based on the cross-correlation calculation of the electrostatic signals obtained from different grid electrodes near the upper and lower plane of the curved pipe in the pneumatic conveying pipeline, the velocity distribution of the particles in the bend pipe is obtained. From the velocity distribution, it can be seen that the velocity profile is relatively uniform in radial direction from left to right. Because the particle is subjected to centrifugal force in the process of passing through the pipe, the velocity of particles moving along the outer wall of the bend pipe is higher. The relative concentration distribution of solid particles in the curved tube can be reconstructed by using the RMS value of a plane electrostatic signal of the grid electrode. The reconstruction results show that the relative concentration distribution after reconstruction can reflect the flow pattern of rope flow at the outer wall of the bend pipe when the solid particles pass through the bend pipe. A netted electrostatic sensor is installed on a laboratory scale bubbling fluidized bed to measure the velocity profile and charge distribution of solid particles in the fluidized bed. The velocity profile of solid particles can be obtained by cross-correlation calculation of electrostatic signals on the electrode corresponding to the upstream and downstream position of the network electrostatic sensor. The variation of the cross-relation number along the radial direction with the change of gas flow rate is analyzed. The weighted average velocity can represent the flow state of the fluid to a certain extent, so it is used in this paper to increase the reliability of the measurement. The RMS value of the electrostatic signal is used to estimate the inductive charge on all electrodes and to reconstruct the distribution of the charge at the cross section using the obtained results. Because of the influence of particle velocity profile in fluidized bed, the inductive charge at the center electrode is larger than that on the electrode near the tube wall. The charge distribution at the cross section is relatively uniform, and the maximum deviation from the average value is less than 24. In addition, the measurement of falling particles near the tube wall is also studied in combination with the motion characteristics of the particles in the bubbling bed. Data show that most of the falling particles in the bubbling fluidized bed are near the tube wall. The particle velocity profile and charge distribution obtained by the sensor can be used to monitor the operating state of the fluidized bed and to improve the operation efficiency and product quality.
【学位授予单位】：华北电力大学(北京)
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TP212.9

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