Research on screening mechanism and parameters optimization of equal thickness screen with variable amplitude based on DEM simulation

Screening technology has been widely applied for the classification of granular materials. The equal thickness screen with advantages of high-capacity and effective screening has been widely used in various industries, as a unit operation for separation of particles according to their size. In this work, a novel equal thickness screen was numerically simulated to evaluate its screening mechanism based on EDEM. The velocity of material flow, the variation of layer thickness and the distribution characteristics of particle population on the sieve plate were considered to comparatively analyze the migration regularity of overall feed group under the conditions of equal amplitude and variable amplitude. The influence of various factors including central amplitude (CA), amplitude gradient (AG), ejection angle (β) and inclination angle (α) on screening performance of variable amplitude equal thickness vibrating screening (VAETVS) was studied. Based on Box-Behnken response surface method (BBRSM), the mathematical model of screening efficiency was established. Significance analysis was performed for the effects from both single factors and factor combinations. In addition, parametric majorization and further experimental verification were conducted. The results showed that, compared with equal amplitude vibrating screening (EAVS), the overall speed of granules flow in the process of VAETVS is higher at the feed end and lower at the discharge end, which means that speed of particles decreased gradually along the flow. It can be concluded that both the degree of dispersion and conveying capacity of VAETVS are better. Accordingly, layer thickness on the sieve plate is approximately the same and distribution of coarse and fine particles is more uniform. Therefore, the processing capacity and screening effect of each screen section are better compared to EAVS. There were similar effects from every single factor on the screening performance, and all of them followed the trend of initial increase followed by decrease. The better efficiency η was obtained when the CA was 2.65 mm–2.85 mm, AG was 0.1 mm–0.3 mm, β was 45°–75°, and α was 8°–12°, respectively. The combination factors such as CA×AG, CA×β, AG×α, AG×β and α × β significantly affected the coal screening performance and the degree of influence of various factors on η followed the order: β > α > AG > CA. An actual screening efficiency of 84.01% was achieved when the operating conditions were CA = 2.74 mm, AG = 0.21