气液固三相流化床中云雾区及其特性研究

In the three-phase fluidized bed reactors with gas phase as the continuous phase, the existence form, evolution characteristics and control mechanism of liquid phase are always lack of clear definitions and quantitative description. By analogy with the atmospheric clouds, the present application proposes a research proposition for the existence of a cloudy-zone flow regime in a gas-liquid-solid three-phase fluidized bed, and a condensed-mode ethylene polymerization reactor is taken as an example to study the cloudy zone and its characteristics. This application intends to take the advantage of the rapid and reversible temperature-induced color change behaviors of polyethylene/iron powder/reversible thermo-sensitive coating composite microspheres, combine the techniques of particle image velocimetry and infrared camera, to establish a method for measuring the dynamic cloudy zone distribution, as well as the liquid phase distribution in it, based on the different imaging features of the liquid droplets and dry/wet particles. The dynamic and reversible distribution of the cloudy zone and the ‘phase diagram’ of the operation domain evolution will be explored. In addition, the flow transport model of the cloudy zone will be built to quantitatively characterize its characteristic parameters of the internal structures. By controlling the pressure and temperature to change the dew point of the reaction atmosphere to make continuous precipitation of the liquid phase, ethylene cloudy polymerization experiments with controllable particle wetting states are designed. In combination of the operation domain characteristics and the cloudy-zone model, the function mechanism of the cloudy zone on the polymerization performance will be studied. This application is expected to provide guidance for the operational optimization and process amplification of the ethylene cloudy polymerization process, and provide a new theoretical support for the innovative application of the three-phase fluidization reaction engineering.

在气相为连续相的三相流化床反应器中，液相的存在形式、演变规律及控制机制一直缺乏清晰定义和量化描述，成为三相流态化研究领域的持续性空白。本申请通过类比大气云雾，提出气液固三相流化床存在云雾区流型区间的研究命题，并以冷凝态乙烯聚合反应器为例研究云雾区及其特性。利用聚乙烯/铁粉/可逆热敏涂料复合微球随温度变化而快速可逆变色的特性，联用粒子成像测速仪和红外热像仪，基于液滴群、干/持液颗粒群的不同成像特征，建立包含液相分配特性的云雾区动态测量方法，获得云雾区动态可逆分布规律及操作域演化“相图”；建立云雾区流动传递模型，量化表征云雾区内部特征参数；基于压力、温度等控制反应气氛露点使液相连续析出的方法，设计颗粒持液状态可控乙烯云雾聚合实验，结合操作域特征和云雾区模型，研究云雾区对聚合特性的作用机制。本申请期望为乙烯云雾聚合工艺的操作优化和过程放大提供指导，为三相流态化反应工程的创新应用提供新的理论支撑。

本项目以流化床乙烯云雾聚合工艺为背景，建立了包含高速摄像、红外热成像、温敏可逆变色颗粒示踪等手段的云雾区表征方法，实现了云雾区、持液颗粒液膜区、液滴区的同步可视化。研究发现，云雾区分布范围的波动主要受气泡上升的影响；随着喷液流率的增加，云雾区中液膜占比升高，液滴占比下降。提出主导云雾区动态分布和液相分配特性的两对竞争协调机制，获得系统稳定性条件的数学表达式，结合流体力学、热量守恒、质量守恒等方程建立了云雾区模型。模型得到实验结果的验证并应用于喷液气固流化床的CFD模拟。建立了基于团聚形态、寿命、温度等特征参数的湿颗粒团聚识别方法，发现湿颗粒团聚具有三种典型的演化模式；颗粒粒径越小，形成的湿团聚数量越多，尺寸越大；喷液流率增大，湿团聚由中心分布向单侧集中分布转变。构建了温度、浓度差异化的气相聚合环境（非云雾区）与持液颗粒聚合环境（云雾区）交变的反应模式，发现反应环境的时间配比和切换频率显著影响聚合活性、产品支化度和结晶度。部分研究结果应用于天津石化12万吨/年乙烯云雾聚合工业装置，支撑了新产品的开发。