Abstract
Abstract: As the internationally competitive oil crop and cash crop, peanuts have attracted great attention in China, and become an important export commodity and the key to the agricultural structure adjustment. Transportation equipment has directly affected the peanut quality after harvest and the degree of automation. Nowadays, people are increasingly concerned about food safety, and the quality risk of peanut pods during the process of conveying, such as dehiscence and break, has drawn more attention. Due to various factors, the peanut pods are easy to break in the process of conveying, which not only affects the later production, but also increases the risk of aflatoxin in the process of transportation and storage. Pneumatic conveying has great advantages for granular materials because of its simple structure, flexible operation and stable production efficiency and so on, which is widely used in the areas of agricultural product processing. Aiming at the problems of power loss, peanut pod's dehiscence and break, crushing rate and unstable production efficiency, the structure and parameters of the existing pneumatic conveying equipment were improved and optimized. Besides, the experiments were conducted in main production areas of peanut. Through analyzing, the pod's damage elements, including pod physical characteristics, fan speed, pod moisture content and air lock structure, were determined respectively. In the process of conveying, the impact of various forces on peanut pods would cause damage easily. To avoid these damages, the silicone buffer plate was installed on the wall of separate cylinder, which reduced the force between the material and the separate cylinder effectively. In order to adjust airflow velocity, the frequency conversion governor was installed on the conveyor equipment to control the fan speed, which could reduce the impact force to achieve the best conveying effect without the decrease of production efficiency and the break of peanut pods, when materials entered the equipment. By using WDW-200 type computer-controlled electronic universal testing machine, the compression capabilities of different peanut varieties were contrasted, and we selected white sand peanuts as the test materials, whose shells are coarse and thin. Then, we measured the moisture content of this kind of peanut in different drying periods. Afterwards, the rotate plank type air lock was designed to replace the original rotation type air lock, which would remain to be closed until the weight of peanut pods reached the set value. This kind of air lock could not only reduce the shear force to the pods when the gravity plate was opening and closing, but also avoid the squeezing action to the peanuts. At the same time, when the conveyed material quantity was unstable, the gravity door of the air lock could adjust the conveying quantity, which avoided the reduction of gas material mix proportion and the increase of peanut pod's acceleration, and thus avoided the second break by relieving the strike of peanut pods in the unloader. According to the contrast test, the rotate plank type air lock caused a minor injury compared with the rotation type air lock. On this basis, pneumatic conveying orthogonal optimization test was conducted with the improved equipment. The influences of silicone buffer plate thickness, fan speed and peanut pod moisture content on productivity, dehiscence rate and broken rate were considered respectively. According to the comprehensively weighted evaluation and variance analysis, the results showed that the silicone buffer plate thickness had the most obvious influence, followed by the fan speed and peanut pod moisture content. When the thickness of silicone buffer plate was 5 mm, the fan speed was 2 700 r/min and the moisture content of peanut was 10%, the dehiscence and broken rate of peanut pods reached the minimum, which achieved the best conveying effect. This study can provide reliable evidence for structure optimization of pneumatic conveying equipment of peanuts.
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