Experiments of wheat drying by bin-ventilation dryer

Abstract: In recent years, the current sun-drying facilities in Chinese rural area are far from being able to meet the requirements of post-harvest drying of major grain crops because of the rapid development of harvesting mechanization, and grain dryers are widely demanded to reduce post-harvest losses of rural grain crops. As an economical and practical grain dryer, bin-ventilation dryer is considerably fitting for Chinese rural production practice.In order to understand the wheat ventilation drying characteristics in flat bed，experimental studies of post-harvest wheat drying were performed on SKS-480 type of bin-ventilation dryer, which involved in testing and analysis of the air field distribution upon the no-load aperture plate, the moisture distribution of materials, the temperature distribution of dry bed and the energy dissipation. The wheat dry bed was 15cm in depth, and the total drying time was set as 6 h, with air temperatures 50℃ during the first three hours and air temperature 60℃ during the latter three hours. For testing temperature and moisture content of the wheat dry bed, the drying region area on horizontal plane was evenly divided into 25 unit areas, and the 15 cm-deep dry bed on vertical plane was evenly divided into upper, middle and bottom layers, respectively.It was concluded that there was evident drying speed difference among the horizontal plane and vertical plane of the dry bed, which was caused by the uneven wind field distribution and the dry bed depth. After 6 h of drying, there was very significant difference (p<0.01) among the materials temperatures of upper, middle and bottom layer of wheat bed. And average moisture content of bottom layer was significantly higher than that of upper and middle layers (p<0.01), while there was smaller difference (p>0.01) between the average moisture content of upper and middle layers. And the maximal difference of moisture content among the whole dry bed was more than 3%, which failed to meet the relevant industry standards and the national standards, affecting the drying efficiency and drying cost of the entire batch of materials. After 5 h of drying, average moisture content of the whole dry bed was 11.5% (w.b.) and achieved the requirements of wheat storage. The energy cost for removing 5% moisture content of 1 kg wheat on this dryer was ￥0.09, while that of large-scale wheat dryers was ￥0.04. For wheat drying, this dryer had no advantage in terms of operation energy costs against the large-scale one. Consequently, there was a lot of room for the improvement of the drying performance on this kind of dryer.Based on the experimental results, some improvement measures of drying uniformity of this dryer were put forward, including setting wind-guide grids in the air inlet and rounding four corners of the drying bin to improve the uniformity of air field distribution in the material bed, and adopting airflow-reverse device and alternate-reverse ventilation drying process to reduce the difference of drying rate along the dry-bed depth. The study can provide a reference for the improvement of the similar dryers.