Abstract

The work attempts to investigate the dielectric properties and microwave drying characteristics of Yunnan lignite, so as to upgrade it. The effect of drying temperature, moisture content and microwave heating frequency on dielectric properties was measured using resonant cavity method. Results indicate that both the values of ε′ and ε″ presented two stage at the investigated temperatures. Bulk water was found to be the main factor contributing to an increase in the ε′ and ε″. Microwave drying kinetics of lignite were carried out. The Page model was the best model reflecting the drying kinetics, and the effective diffusion coefficient and active energy at different drying stages were obtained. In addition, the microwave drying mechanism has been proposed based on the study of dielectric and drying properties of lignite. The SEM images indicated that microchannels were formed within the lignite particle by the microwave pumping effect. FT-IR spectra showed that the oxygen-containing functional groups and hydrogen bonds between them were break by microwave drying. Based on the achieved results, the microwave treatment at 150 °C is helpful to upgrade the lignite.

摘要

本工作试图研究云南褐煤的介电特性和微波干燥特性，以对其进行升级。采用谐振腔法测量了干燥温度、水分含量和微波加热频率对介电性能的影响。结果表明，这两个值ε '和ε “提出了两个阶段在所研究的温度。发现大量水是导致ε ′ 和ε增加的主要因素”。进行了褐煤的微波干燥动力学。Page模型是反映干燥动力学的最佳模型，得到了不同干燥阶段的有效扩散系数和活性能。此外，基于褐煤介电和干燥特性的研究，提出了微波干燥机理。SEM图像表明通过微波泵浦效应在褐煤颗粒内形成微通道。FT-IR 光谱表明微波干燥破坏了含氧官能团和它们之间的氢键。根据取得的成果，150℃的微波处理有助于褐煤的提质。