Abstract: In order to understand the operating characteristics of fixed bed reversing ventilation drying of peanut and provide suitable parameters for the box type reversing ventilation drying equipment, a series of partial differential equations was established based on the heat and mass transfer between peanut and air. On this basis, the finite difference method was used to simulate the drying process. The effects of the length of ventilation drying time from bottom to top in the left and right drying chambers, the reversing time in the reversing drying stage, and the ventilation volume per unit volume on the drying behavior were analyzed. The optimal ventilation and drying parameters were determined by uniform design and comprehensive weighted scoring method. The results showed that in the bottomup ventilation stage, the heat was mainly used to heat peanut materials and rapidly evaporate the water in peanut pod surfaces. The drying and heating rate of the lower, middle, and upper materials was different, and it was easy to form a large moisture gradient. In the reversing ventilation drying stage, the material temperature fluctuated like a wave, which could effectively control the drying uniformity of the whole bed. Shortening the ventilation time from bottom to top was helpful to reduce energy consumption and moisture difference, but it had little impact on drying time and productivity. In addition, the change of reversing time had little influence on time consumption, productivity, energy consumption, and moisture content difference. The increase of ventilation volume would help to reduce drying time, water difference, and productivity, but energy consumption would also increase rapidly. Uniform design and synthetical weighted marks were used for solving optimal ventilation parameters. The results showed that the comprehensive effect of batch drying was the best when the ventilation volume was 1 394 m3/(m3h) with moisture content greater than 25%, 838 m3/(m3h) with moisture content between 15%-25%, and 1 760 m3/(m3h) with water content less than 15%. Finally, the accuracy of the model simulation was verified by the verification experiment. The results showed that the correlation coefficient between the simulation results and the experimental results was more than 0.98, which reflected that the simulation could accurately describe the changes in material temperature and moisture content in the drying process. This study provided a reference for the improvement of peanut reversing ventilation drying equipment and process optimization.

Key words:  box drying, peanut, reversing ventilation, mathematical simulation

摘要： 为了解固定床花生换向通风干燥作业特性,为已研发的箱式换向通风干燥设备提供合适的花生干燥通风参数,以花生与空气间的传热传质为基础,建立干燥状态偏微分方程组,并以此为基础采用有限差分法对干燥过程进行数学模拟,分析左右干燥室同时从下向上通风干燥时长、换向干燥阶段换向时间、单位体积通风量对干燥行为的影响,并采用均匀设计和综合加权评分法确定最优通风干燥参数。结果表明:从下向上通风阶段,热量主要用于花生加热和表层水分快速蒸发,下、中、上层物料干燥升温速度差明显,易形成较大水分梯度;换向通风干燥阶段,物料温度呈类波浪状波动,有效控制整床物料干燥均匀性。缩短从下向上通风时间,有助于降低耗能和水分差,但对干燥耗时和生产率影响较小;换向时间的改变对耗时、生产率、耗能、水分差影响较小;单位体积通风量的增加有助于干燥耗时、水分差的降低及生产率的提高,但耗能亦将快速增加。均匀设计和综合加权评分表明,含水率>25%阶段通风量1 394 m~3/(m~3h),含水率15%～25%阶段通风量838 m~3/(m~3h),含水率0.98,模拟仿真可准确描述干燥过程物料温度和含水率变化。为花生换向通风干燥设备改进和工艺优化提供参考。

关键词: 箱式干燥, 花生, 换向通风, 数学模拟