ABSTRACT

Dewatering is considered as extremely significant and primary step to enhance the quality of lignite. A great number of research focus on conventional fluidized-bed drying technology or dynamics. In this paper, the microwave deep drying kinetics of Zhaotong lignite under different power levels and with different sample thicknesses were investigated. The drying kinetics of microwave deep drying was fitted by 13 different drying models given in the literature. Experimental results indicated that the microwave deep drying process exists three segments: increasing-rate, falling-rate and brief constant-rate segment. The drying time decreased and drying rate increased with microwave output power level increase, while the microwave penetration depth in lignite was affected by sample thickness, hence there is an irregular relationship between lignite sample thickness and microwave drying time or drying rate. Based on non-linear regression analysis, the Page model was considered adequate to describe the microwave deep drying behavior of Zhaotong lignite under various conditions, and the model could be used for residual moisture water content prediction at any time during the microwave deep drying process. Effective diffusion coefficient increased along with microwave output power level increase. The activation energy of the moisture emission from the lignite under different power levels was estimated at 10.2202 W/g using modified Arrhenius equation. The pore structure damage was observed in the lignite samples after microwave deep drying by SEM analysis. The surface of upgraded lignite had visible cracks, defects and small fragments compared with the samples by conventional drying.

摘要

脱水被认为是提高褐煤质量的极其重要和首要的步骤。大量研究集中在常规流化床干燥技术或动力学上。本文研究了昭通褐煤在不同功率水平和不同样品厚度下的微波深度干燥动力学。微波深度干燥的干燥动力学通过文献中给出的13种不同的干燥模型进行拟合。实验结果表明，微波深度干燥过程存在三个阶段：升速段、降速段和短暂的恒速段。随着微波输出功率水平的增加，干燥时间减少，干燥速率增加，而褐煤中的微波穿透深度受样品厚度的影响，因此，褐煤样品厚度与微波干燥时间或干燥速率之间存在不规则关系。基于非线性回归分析，认为Page模型足以描述昭通褐煤在不同条件下的微波深度干燥行为，该模型可用于微波深度干燥过程中任意时刻的残余水分含水率预测。有效扩散系数随着微波输出功率水平的增加而增加。使用修正的 Arrhenius 方程估计不同功率水平下褐煤水分排放的活化能为 10.2202 W/g。通过扫描电镜分析观察到微波深度干燥后的褐煤样品孔隙结构发生破坏。提质褐煤表面有明显裂纹，