Rice Hulling Mechanism And Parameter Optimization In Centrifugal Rice Huller

Rice hulling is the process of separating brown rice from rice husks and is a major component of the rice processing process.Centrifugal rice huller has the advantage of low processing cost and high quality of the hulled brown rice,which has become one of the important hulling methods for rice.At present,centrifugal rice hullers still suffer from low hulling ratio and high breakage ratio,which is one of the main reasons limiting their advantages and wide application.However,the impact hulling principle is still unclear,and the impact velocity and impact angle on the hulling pattern and impact behavior are yet to be clarified.Therefore,clarifying the impact hulling mechanism of rice can provide a theoretical basis for the design and parameter optimisation of huller,which has important engineering significance for improving the hulling performance of centrifugal rice huller.At the same time,it can also provide reference and learn from other agricultural materials impact hulling research,which is of great scientific value.This paper intends to study the influence of impact parameters on the hulling and breakage ratios,using DEM simulation(Discrete element method)to simulate the rice impact process,analyze the movement pattern and force characteristics of rice under different impact angles,reveal the mechanism of rice impact hulling by combining rice impact behavior and hulling patterns,and apply the comprehensive weighted scoring method to obtain the optimal impact velocity and impact angle.Based on the optimum impact parameters,DEM simulation is used to simulate the centrifugal rice huller,analyze the proportional distribution of impact velocity and angle of rice in the acceleration region,elucidate the influence of the existing impeller blade structure on impact velocity and angle,and optimize the blade structure on this basis.Based on the new blade structure,a quadratic orthogonal rotational combination test is applied to obtain the optimal combination of parameters to achieve the best possible impact velocity and angle for all the rice,thus fundamentally improving the hulling performance of the centrifugal rice huller.Finally,the hulling performance of the centrifugal rice huller is verified by actual hulling tests.The main conclusions are as follows.(1)Rice impact hulling is the formation of a velocity difference between the rice husk and the brown rice after impact,and the brown rice comes out of the husk under the action of inertia force.As the velocity of rice impact increases it helps to improve the hulling performance of the centrifugal rice huller,the improvement in hulling performance also depends on the angle of rice impact.The combined effect of impact and friction is the key to increasing the velocity difference to improve hulling performance.The results of the single seed rice impact test showed that the optimum hulling performance was achieved with a combination of impact velocity of 35-40 m/s and an impact angle of 60°,with a hulling ratio of 92% and a breakage ratio of 4%.(2)The way the impeller blades collide with the rice grain affects the impact velocity of the rice grain,and the way the upper and lower impeller baffles and contacts affect the impact angle of the rice grain.Reducing the number of rice bounces after collision with the impeller blades enables all the rice to reach the optimum impact velocity.Increasing the upper and lower baffles to support the rice can adjust the impact angle of the rice,so that the rice reaches the best impact angle possible.In combination with the above features,the "concave" blade is designed.Compared to the original impeller blades,the new blades allow the rice to reach the best possible impact velocity and angle,thus improving the hulling performance of the centrifugal rice huller.(3)Based on the new blade structure,the optimum combination of parameters for the practical production of centrifugal rice huller was determined,with the number of blades at 12,the blade placement angle at 30° and the impeller speed at 1800 rpm.The new impeller structure enables the optimum velocity to be achieved for all rice grains and the optimum angle to be achieved for 97.7%of the rice grains.The results of the validation tests show that the improved impeller structure can significantly improve the hulling performance of the centrifugal rice huller.The centrifugal rice huller had 93% ± 1.56% hulling ratio and 4% ± 0.34% breakage ratio.Compared to the original centrifugal rice huller,the centrifugal rice huller has an 8% ± 0.23% higher hulling ratio and a significantly lower breakage ratio of 7.33% ± 0.43%,meeting the requirements of the national standard for rice huller process performance.