Design and experimental study of 5HP-25 type grain dryer

This study aims to enhance the operating efficiency and annual utilization rate in the mechanized drying of grains. Meanwhile, their versatility and reliability need to be improved. In order to strengthen the drying process, it is necessary to increase the dynamic coefficient, rather than the processing power only. A systematic investigation was made on the relationship between the geometric structural parameters and the motion parameters, in order to increase the drying dynamic coefficient for the non-destructive drying. The effects of geometric factors on grain flow characteristics were revealed using the combined geometric structure factors and motion parameters. Since the downward flow of grains depended mainly on the gravity of grains, the geometric structural parameters were used to express the natural flow state in the drying chamber. In addition, the flow speed of grain at a certain position was proportional to the speed of grain discharge. In the continuous flow process, there was an equal amount of absolutely dry matter flowing through any cross section in the drying chamber at any time, where the velocity ratio was equal to the inverse area ratio. A general-purpose grain dryer was developed, where the induced air was used to reduce pressure, while the partial flash evaporation was used to decrease the grain temperature, and a self-adaptive differential reciprocating grain discharging device was designed to strengthen the heat and mass transfer in the drying section. The dryer was widely used for many kinds of granular grains and seeds, which achieved high-quality, high-efficiency, and low-temperature drying. The heat and mass transfer were strengthened, because the grain changed the flow state spontaneously and rotated continuously during the continuous flow in the dryer. The drying uniformity was improved, further to avoid local overheating damage caused by single-side heating during the grain drying process. The variable cross-section angle box with the angle of 6° could increas the drying dynamic coefficient by 2-4 times, compared with the traditional cross flow. The temperature of grain was below 35℃, indicating lower than the glass transition temperature of grain. The dried rice seeds remained intact with high activity. The increased rate of crack and the moisture unevenness both were less than 1%. The germination potential increased by 76% than before, and the germination rate was close to 95%. The drying quality was significantly improved, compared with the concurrent flow drying. A dislocated and differential reciprocating mechanism was designed to achieve the adaptive and non-destructive grain discharge, indicating an effective bridging and blocking operation to avoid mechanical damage of grains. In the application of designed 5HP-25 type grain dryer, an optimal combination of parameters was obtained, where the average drying intensity of grain was 1.37%/h-2.70%/h, and the per-unit heat consumption of drying was 2 900-4 300 kJ/kg. Compared with the national standard 7 400 kJ/kg, the effect of energy saving was remarkable. The finding can provide a sound reference to design a high quality, high-efficiency, and energy-saving equipment for the grain drying process.