静电场-外加电场耦合作用下的减阻悬浮输送技术理论研究

The presence of charged particles in the pneumatic conveying process increases the pressure drop, causes blockage, even leads to dusty explosion. Therefore, it is of vital importance to develop methods to use the electrostatics and then solve the related electrostatic problems. This project proposes to combine the electrostatic charges on particles and external electric fields, and develop a new environment for particles conveyed in which particles are suspended on the wall under influences of electric field forces. On the basis of this new conveying environment, particle-wall contacts are suppressed and the consequent energy loss and material loss are decreased. In order to realize above objects, this project will firstly trace trajectories of particles in the pipeline by sliding high-seed shooting, investigate the single effect of Coulomb force and Polarization force on particle motions by eliminating electrostatics on particles and conducting experiments under proper lower electric fields, and then reveal the effect mechanism of electric field forces on particles conveyed based on force analysis. Moreover, this project will study the effect of external electric field on contact charging by measuring the variation of charges on particle with the conveying length, and demonstrate the effect of electrostatic field on suspension effects of external electric fields by simulation. Based on this, the interaction between electrostatic fields and external electric fields will be figured out. In the end, a demonstration electric-field enhanced suspension conveying system will be established and the decrease of pressure drop and particle attrition will be evaluated quantitatively. This project will provide valuable guidance for application of electrostatics on particles, as well as the enhancement of the economy and stability of pneumatic conveying process.

气力输送过程中粉体荷电导致输送压降增大、管道堵塞、粉尘爆炸等诸多问题。如何利用气力输送过程的静电，“化害为利”，具有重要的研究价值。本申请创新性地将静电与外加电场深度耦合，利用荷电颗粒在外加电场中受到的电场作用力，期望构建荷电颗粒电悬浮输送环境，减少颗粒壁面接触，降低输送压降和能耗，减缓管道特别是弯头的磨损速率。本申请拟采用滑动高速摄像跟踪颗粒运动，分别在消除静电和低场强下研究库仑力和极化力对荷电颗粒运动行为的单因素作用，并通过力平衡分析揭示外加电场力对输送颗粒的作用机制；拟检测外加电场中颗粒荷电量随输送距离的动态波动、模拟计算静电场对电悬浮效果的反馈效应，厘清外加电场与静电场的交互关系；最后，搭建电场悬浮输送的示范装置，定量考评外加电场在降低输送压降和减小物料磨损两方面的作用效果，为利用外加电场解决静电问题，提高输送过程的经济性和稳定性提供指导。

气力输送过程将不可避免地导致输送粉体荷电，进而诱发管道堵塞、粉尘爆炸等诸多问题。如何利用气力输送过程的静电，“化害为利”，具有重要的研究价值。本项目提出了利用外加电场调控荷电颗粒的运动行为，以减少静电危害的电悬浮输送思想，并以此为核心开展了系列研究。项目首先建立了以滑动高速摄像和声发射检测技术为主要特征的外加电场悬浮输送示范装置，其中滑动高速摄像用于实时跟踪颗粒运动行为，声发射检测技术用于测量颗粒与管道壁面的相互作用并判别颗粒输送流型；以颗粒声信号为基础，借鉴聚合分子量分布指数的概念，构建识别颗粒输送流型的波动分布指数FI，可实现基于单一数值的颗粒流型识别。进一步，耦合高速摄像和声发射检测研究不同外加电场力对输送颗粒运动行为及颗粒流型的影响机制，揭示了直流电场作用下库仑力对颗粒径向运动的间断性促进作用以及极化力对颗粒输送速度的持续促进作用；研究静电场-外加电场-流场的耦合机制，揭示了输送管中颗粒-壁面接触主导的单极荷电机制及颗粒流场对静电场的主导作用，并以此为基础建立了分布式输入的多场耦合模拟新方法。最后，通过对气力输送的压降进行理论分解，明确了外加电场悬浮输送过程中降低输送压降的核心为降低颗粒悬浮能和颗粒-壁面摩擦损失，由此确定了直流电场作用下减阻操作的最优区间为中等电场强度的极化力与库仑力耦合作用区。在上述成果之外，项目还拓展开发了基于声信号的Janssen系数（压降定量计算的最关键参数）检测方法和AI+机理的输送流量智能预测方法，为输送过程的定量化描述和控制建立了良好基础。本项目的部分研究成果有力支撑了天津中沙45万吨/年Spherizone工艺聚丙烯装置共聚反应器的长周期稳定运行，使得共聚反应器的运行时间由半年延长至1年以上。