基于流场-静电场耦合的荷电气固流动电容层析成像

Gasifying coal is an important development direction of clean and efficient utilisation of coal. The current bottle-neck of coal-gasifying is the control of particle concentration. Online monitoring of particle concentration is a very important and difficult task to maintain high gasifying efficiency. As a non-intrusive and non-invasive technique, electrical capacitance tomography (ECT) can be used to measure particle concentration distribution in coal gasification process at high temperature and high pressure. However, the effect of electrostatic on the ECT system and measurement results is a scientific problem to be solved urgently. This project aims to develop an innovative method by combining fluid field and electrostatic field to address the above problem. On one hand, a coupling simulation model of fluid field and electrostatic field will be established to explore the influence mechanism of particle electrification on the measuring of complex gas-solid flow parameters using ECT, to attain the correspondence between permittivity and particle concentration distribution, and to establish an image reconstruction method using limited capacitance data. On the other hand, the continuous monitoring of concentration of gas-solid flow will be achieved by using the proposed method and combining with pressure measurement and advanced signal processing technology. Furthermore, the multi-scale characteristics of gas-solid flow will be quantitatively analysed. The success of the proposed work will provide an on-line measurement technology and theoretical basis for the optimisation of coal gasification process.

煤粉直接气化燃烧是煤炭清洁高效利用的重要发展方向，其关键是控制颗粒浓度分布，以准确获取气相和固相之间的传热传质规律，提高煤气的热值和碳转化率。电容层析成像（ECT）作为一种非接触式测量手段，可以在高温高压条件下对煤气化过程颗粒浓度分布进行在线测量。但是固体颗粒携带以及气固流动过程产生的静电对ECT测量系统及测量结果的影响机理是亟待解决的科学问题。本项目将流场与静电场有机融合来解决上述科学问题。一方面，建立流场与静电场耦合仿真模型，以此为基础探索颗粒带电对利用ECT测量复杂气固流动参数的影响机制，获取介电常数与颗粒浓度分布之间的对应关系，建立缺失数据ECT图像重构方法，为利用ECT对荷电气固流动分布参数进行测量奠定理论基础。另一方面，利用上述建立的方法，结合压力测量及先进信号处理技术，分析煤气化过程多尺度流动特性，实现对颗粒浓度分布的在线连续测量，为煤气化过程优化提供在线测量技术和基础数据。

复杂多相流动电学层析成像受到成像软场特性及流动复杂性的影响，其定量测量一直是本领域的难点。本项目的主要研究内容是以应用于流态化过程的电学层析成像传感器为研究对象，基于流场-静电场的多物理场耦合仿真平台，实现了复杂流动条件下电容层析成像传感器空间分辨率的定量研究。引入了低秩矩阵的方法，实现了利用电容层析成像含噪声数据图像的高精度动态重建。对电压激励电阻层析成像和电容层析成像的性能进行了对比研究，获取了两种电学层析成像技术在不同湿度气固分布条件下测量的特性规律。研究了感应电荷特征值的计算方法，为荷电气固流动中电荷静态信息的表征及成像测量提供有力的理论基础。提出了基于等效磁路的固相含率估计方法，为流态化过程固相含率的计算提供了理论模型。上述研究工作的开展最终实现了基于流场-静电场耦合的多相流动电学层析成像。