Analysis of Flow, Breakage and Coating of Corn Seeds in a Mixer

In the seed processing industry, rotary batch seed coaters are widely used for providing a protective coating layer to the seeds consisting of various ingredients including fertilisers and crop protection chemicals. Seed motion and mixing are important in ensuring uniform coating; hence the focus of this work is to address the mixing efficiency and coating uniformity of corn seeds in a rotary batch seed mixer. In the present study, the Discrete Element Method (DEM) is used to analyse the motion and coating uniformity of the seeds. A comprehensive study has been carried out addressing the influence of the shape of corn seeds for accurately simulating their flow in the mixer using two commonly used techniques: (i) manipulation of coefficient of rolling friction of spherical particles, and (ii) clumping multiple spheres. Both methods were successful in simulating the flow of seeds in the mixer, however the former method is found to be an empirical approach rather than predictive. A coating model is used for predicting the coating uniformity of corn seeds in the mixer. Effect of various process parameters on variation of coating mass among the seeds is investigated. For the seed mixer, the baffle clearance gap, baffle geometry and position of the atomiser disc were found to be the key influential process parameters affecting the coating uniformity of corn seeds. Other process parameters such as the base rotational speed, baffle angle, width and curvature had less effects on coating variability. A study has also been carried out on tailoring the existing methods of measuring the extent of breakage of particles for seeds. Four breakage criteria were proposed and assessed for consideration of mass of broken seeds, and the most suitable methods are suggested. The simulations developed here are generic and can be applied to a wide range of coating processes, such as particle and tablet coating. The proposed methodology for measuring the extent of breakage of corn seeds can also be used for other types of seeds.