Microwave drying performance of single-particle coal slime and energy consumption analyses

The drying of coal slime with high moisture is an essential step for the majority of its industrial applications. Microwave radiation could serve as an alternative way of efficient drying, owing to its unique heating properties. In this study, the weight loss and temperature distribution of spherical single-particle coal slime were measured by using a microwave thermogravimetric analysis (MTGA) device, which was designed for this study, equipped with an accurate electronic balance and fiber optic thermometers. In addition, the effects of microwave power (320, 480, 640, and 800 W) and particle size (30, 40, 50, and 60 mm) on the drying performances were studied. The microwave drying process of coal slime comprises three stages: an incubation period, whereby a rapid increase in temperature occurs, a constant-rate drying stage, during which a rapid moisture loss occurs at about 100 degrees C, and a falling-rate drying period, during which a significant increase in temperature is observed again. Weight loss rates increased with increasing power output of the microwave oven or with decreasing particle size. The energy consumption and the energy efficiency during the drying process were also analyzed. The results demonstrated that the specific energy consumption declined with the overall increase in power and particle size, while the efficiency of microwave output increased with increasing particle size. Furthermore, the diffusion kinetics of moisture in coal slime were examined. The effective diffusion coefficients of moisture increased with both increasing particle size and microwave power, whereas the activation energy of the diffusion process decreased with increasing particle size. (C) 2015 Elsevier B.V. All rights reserved.

高水分煤泥的干燥对于其大多数工业应用来说是必不可少的步骤。由于微波辐射具有独特的加热特性，它可作为一种高效干燥的替代方法。在本研究中，使用为本研究设计的微波热重分析（MTGA）装置测量了球形单颗粒煤泥的失重和温度分布，该装置配备了精确的电子天平以及光纤温度计。此外，还研究了微波功率（320瓦、480瓦、640瓦和800瓦）和颗粒尺寸（30毫米、40毫米、50毫米和60毫米）对干燥性能的影响。煤泥的微波干燥过程包括三个阶段：潜伏期，在此期间温度快速上升；恒速干燥阶段，在此期间约100℃时水分快速流失；降速干燥阶段，在此期间再次观察到温度显著上升。失重率随着微波炉功率输出的增加或颗粒尺寸的减小而增加。还分析了干燥过程中的能耗和能效。结果表明，单位能耗随着功率和颗粒尺寸的总体增加而降低，而微波输出效率随着颗粒尺寸的增加而提高。此外，还研究了煤泥中水分的扩散动力学。水分的有效扩散系数随着颗粒尺寸和微波功率的增加而增加，而扩散过程的活化能随着颗粒尺寸的增加而降低。（C）2015爱思唯尔有限公司保留所有权利。