在气固并流下行床中烟丝的快速干燥动力学分析

Kinetic Analysis of Rapid Drying of Cut Tobacco in Gas-solid Cocurrent Downflow Bed

为了研究在下行床中烟丝的快速干燥动力学行为,利用冷态下行床烟丝运动特性检测装置和热态下行床快速干燥处理装置,在一定的风速条件下,考察在下行床中烟丝的运动规律和热风温度（180～300℃）对烟丝快速干燥过程的影响,并对烟丝快速干燥动力学进行分析.结果表明：①在下行床中烟丝的下落是一个先加速后匀速的过程,加速段的距离小于1.2 m,匀速运动时烟丝的速度与含水率呈现线性关系,烟丝含水率与下落高度的关系可用指数关系描述;②在考察温度范围内烟丝的快速干燥过程为降速干燥过程,菲克第二定律可以较好地表征在下行床中烟丝的快速干燥动力学行为,该过程中,烟丝干燥过程有效扩散系数介于6.448x10-9～2.624x10-8 m2/s之间,表观活化能为5.23 k J/mol.

To study the kinetic behavior of rapid drying of cut tobacco in a downflow bed, the movement of cut tobacco and the effects of hot air temperature （180-300 ℃） on the drying process of tobacco at a constant air velocity were investigated in a downflow bed under cold and hot states respectively, the kinetic analysis of tobacco drying was conducted as well. The results showed that： 1） The downward movement of tobacco in the downflow bed comprised an accelerated velocity stage followed by a uniform velocity stage, and the displacement at the acceleration stage was less than 1.2 m. The velocity of tobacco in acceleration stage linearly correlated to the moisture content in tobacco, and the relationship between moisture content in tobacco and falling height of tobacco could be described by an exponential relationship. 2） Tobacco was in a deceleration drying process in the testing temperature range, the process could be characterized by the Fick＇s second law, the effective diffusion coefficient in the process of tobacco drying ranged from 6.448x 10-9 to 2.624x 10-8 m2/s with the apparent activation energy of 5.23 kJ/mol.