Abstract

Particle drying in fluidized beds is a common and important process in food and pharmaceutical industry. However, the fluidization characteristic is complex due to the moisture content change in the process and it is a challenge to monitor the flow characteristics by conventional measurement approach, likes pressure and thermal probes. In this research, process tomography including capacitance and microwave tomographic systems are used to investigate the flow characteristics in a fluidized bed dryer with high-moisture content particles. Static tests were firstly carried out to investigate the image characteristics based on microwave tomography (MWT) and electrical capacitance tomography (ECT). The imaging ability was compared between MWT and ECT. In the dynamic tests, the drying process for particles with high-moisture content was monitored on-line by MWT and ECT separately. The static test results show that the high calibration for ECT is critical and particles with low moisture content should be used for high calibration of an ECT system to achieve high quality images for the dynamic tests. For the high calibration of ECT, there is an upper limit for the moisture content. With a fixed calibration background, the moisture content of particles should not exceed this upper limit value. MWT basically has no limitation on the moisture content both for high calibration and measurement. Dynamic test results illustrate that MWT is a good option to monitor high-moisture content particles drying in a fluidized bed and it is possible to combine ECT together to identify the gas–solids flow regime transit and to determine the moisture content by MWT in a fluidized bed drying process.

摘要

流化床中的颗粒干燥是食品和制药工业中常见且重要的过程。然而，由于过程中水分含量的变化，流化特性很复杂，通过压力和热探头等传统测量方法监测流动特性是一项挑战。在这项研究中，包括电容和微波断层扫描系统在内的过程层析成像系统用于研究具有高水分含量颗粒的流化床干燥器中的流动特性。首先进行静态测试以研究基于微波断层扫描（MWT）和电容断层扫描（ECT）的图像特性。比较MWT和ECT的成像能力。在动态测试中，高水分颗粒的干燥过程由MWT和ECT分别在线监测。静态测试结果表明，ECT 的高校准至关重要，应使用低水分含量的颗粒对 ECT 系统进行高校准，以获得动态测试的高质量图像。对于 ECT 的高校准，水分含量有一个上限。在固定的校准背景下，颗粒的水分含量不应超过此上限值。MWT对高校准和测量的水分含量基本没有限制。