| In order to meet the demand of straw comprehensive utilization, which from the scattered, smal-sized farm and individual contracted fields of South Jiangsu Area, some scholars have put forward the treatment by miniaturizing Smashing-Fermentation-Returning at field. It was achieved by the small pulverizer through the efficient and energy-saving cycle smashing technology. During the process of practice, it’s found that the straw particles generaly is in a long strip shape and contains certain humidity(according to the kinds of straw and freshness, humidity general between 20%- 50%). The qualified rate is higher when using the way of vibration screening, but with low yield and large vibration, which can hardly meet the capacity needs and miniaturization requirements of cycle smarshing. To improve the yield and get high sieving efficiency, this thesis combines advantages of high yield when screw conveying and low energy consumption of fixed screen, and put forward Straw Sifter Based on Screw Conveyor(SSSC).The SSSC has the advantages of high yield, compact volume, good sealing property and small vibration operation. However, the movement of straw particles in the screw screening process is complex, and the direction will influence the projection area of the screen surface and then influence the probability of sieving. Therefore, this thesis carries out theoretical study and sieving performance research on SSSC, so as to reveal mechanism of straw particles and the sieving performance through the screen.It provides theoretical guidance for the development of high performance and low power consumption of SSSC, thus exerting very important theoretical significance and engineering application value.This thesis takes smashed tomato straw as the screening object(the length mainly distributed in 25 mm, which 12 mm below for qualified straw), and SSSC device as the research object. It respectively carries out force and kinematics analysis of sieving process, the analysis of probability of crossing the screen. It also focus on SSSC performance by the EDEM discrete element simulation analysis and experimental verification work, so as to figure out the impact of straw traits and mechanical properties, mechanical structure and operating parameters of SSSC on the screening performance. The specific contents are as follows:Firstly, this thesis studies the dynamic characteristics of SSSC. Taking the single particle and particle group as the object, this thesis carries out force and kinematics analysis of SSSC process. The theoretical research showed that under the effect of different force, straw particles performs forward movement by . Meanwhile with increasing, straw particles in SSSC will roll and throw up so as to improve the straw particles hybrid hierarchical performance.Secondly, based on dynamic analysis, it figures out the conditional probability expression of SSSC and the analysis show that: the total through probability of straw particles is directly related to the straw particles original qualified rate, and mesh size is also directly related.Meanwhile, due to the shape of straw particles, the particles with a length greater than d while projection length less than 2d, can still cross the mesh hole. Therefore, the error sieving can not be avoided.Subsequently, it simulated and analyzed the effect of different factors on the performance of SSSC by EDEM software. The results showed that:(1) the sieving size greatly influences the qualified rate and yield increase of mesh size, mesh size can improve the screening rate and yield, but it has lower qualified rate;(2) by improving the stirring speed, the performance of hybrid layered straw particles, sieving rate and yield can be increased, but it has no obvious influence on the qualified rate;(3) by reducing the fil ing rate of the charging speed, it can reduce the straw particles in the screw sieving device so as to improve the performance of mixed layered straw particles, which can improve the screening rate, the qualified rate was less affected. Because the number of straw particles decrease, the yield will be decreased;(4) raw material components of the original qualified rate is increased, the final straw screw screening pass rate has significantly been improved, but the sieving rate is less affected. Meanwhile, the original yield and raw material is in direct proportion. The results of simulation are consistent with the theoretical analysis.Finally, a SSSC testing system was set up to verify the simulation. The empirical test results and simulation results are basically the same, thus getting an ideal screening effect when rotating speed 180 rpm, with sieving size of 8mm, charging speed 5kg/min: the screening rate was 23.56%, the qualified rate was 93.42%, and the yield was 133.4kg/h. |
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