Coupled gas-particulate discharge from a bucket elevator

Abstract The vertical conveying of bulk materials is often performed using bucket elevators. Such devices use conveyor belts to drag a series of buckets in a circuit, up, around and then down within an enclosure. They are typically used for upward transport of fine granular materials. The speed at which these buckets travel can displace a large volume of air. Interaction between this air and the bucket contents can modify the discharge dynamics of the granular load. A coupled gas-particulate numerical model is presented using Finite Differences to solve for the gas flow with an Immersed Boundary Method (IBM) to represent the complex bucket and enclosure geometry in the model. The Discrete Element Method (DEM) is used for particulate flow. The combined method is used to investigate the effect of gas flow on particulate behavior, particularly at the time of discharge from the buckets. The bucket elevator design used is based on an existing installation with known operational issues. The presence of gas flow is shown to alter the preferential ejection of particles from the bucket, influence the shape of the trajectory of the ejected particle stream, and reduce the efficiency of particles exiting the elevator by 10–14%. These effects are also shown to be strongly size dependent with finer particles being much more susceptible to drag forces from the air flow. The retention of material inside the machine was found to consist of roughly 50% of material centrifugally ejected from near the bucket tip and roughly 70% of material located closer to the conveyor belt side of the bucket that spills off the splitter during the final stage of emptying and falls back down to the boot.