微波对褐煤介电特性及干燥的影响

Effect of Microwave on the Dielectric Properties and Drying of Lignite

为研究微波干燥褐煤的可行性,选取云南昭通褐煤进行试验研究,采用微波介电特性变温测试系统研究褐煤介电特性及微波穿透深度随表观密度的变化。结果表明,褐煤介电特性与表观密度成正相关,穿透深度与表观密度成负相关,同时拟合得到褐煤表观密度与介电特性、微波穿透深度的关系式。采用微波干燥系统对不同功率和质量下的褐煤升温特性进行研究。结果表明,微波可以在1min内将褐煤升温至100℃,最大干燥速率为0.198(g/g db)·min-1,微波加热过程中,温度变化表现出3个阶段:快速升温阶段、恒温阶段、减速升温阶段。褐煤升温至100℃前,物料的质量和功率对升温速率影响不大,100℃之后,褐煤的升温速率随着功率的增加而增大,随物料质量增加而减小;通过微波干燥与常规干燥对比,发现当褐煤完全干燥时,微波干燥用时17min,常规干燥用时320min,微波干燥明显优于常规干燥。

To study the feasibility of microwave drying of lignite,Yunnan Zhaotong lignite were selected and the microwave dielectric properties of temperature testing system was adopted to study the lignite dielectric properties and microwave penetration depth with apparent density change.The results showed that the dielectric properties of lignite were positively correlated with the apparent density,and the penetration depth was negatively correlated with the apparent density,and the relationship between the apparent density and the dielectric properties and the microwave penetration depth was obtained.The heating characteristics of lignite under different power and quality were studied by microwave drying system.The results showed that the microwave could reach 100 ℃in 1 min,the maximum drying rate was 0.198（g/g db）·min-1,in the process of microwave heating,the temperature change showed three stages,namely the stage of rapid warming,constant temperature stage,slow heating stage.Before the lignite was heated to 100 ℃,the quality of materials and power has little effect on the heating rate,after 100 ℃,lignite heating rate increased with the increase of power,and decreased with the increase of material quality.Comparing microwave drying and conventional drying of contrast,it was found that when lignite was completely dried,microwave drying cost 17 min,conventional drying cost 320 min,microwave drying is superior to conventional drying.