The transfer chute is an important engineering component that is designed to deliver bulk material from one conveyor belt to another. In cases of high tonnages where the material transported per hour is considerable, there are two risks, namely spillage and dust generation. While spillage refers to the escape of the material from the intended route, dust generation occurs through the aerosolization of particles caused by high impact and air currents (Turkevich et al., 2024). Designing an appropriate transfer chute is an important measure in minimizing such inefficiencies.
The design of the transfer chute involves determining the necessary size that can handle the highest volumetric flow rate of material to be handled. The transfer chute should offer enough clearance to avoid clogging but should still be designed in such a way that the material flows in a streamline manner. It is important for engineers to carefully evaluate the vertical height of the discharge pulley and the receiving belt. Minimizing this vertical distance is important because it reduces the amount of kinetic energy that the descending material possesses, thus reducing its impact.
Aside from volumetric requirements, designing the transfer chute also involves controlling the material trajectory to avoid spillage. In avoiding spillage, it is important to match the speed of the material coming out of the transfer chute to the speed and direction of the receiving belt. Failure to do so results in abrupt impact, which makes material bounce off the edges of the belt. Modern high-capacity chutes use “hood and spoon” design in directing the material.
The dust generation at high tonnage loading is driven primarily by the induced air entrainment effect. The bulk material moving downwards induces air, thus creating areas of high pressure inside the chute. Such dusty air impacting the receiving belt causes escape of the air through holes. In order to avoid such an effect, the chute design must include large enough stilling zones – the expanded sections where air velocity decreases and dust settles down. Additionally, a strong sealing system, including correctly adjusted skirtboards and dust curtains, must be implemented in order to confine the high-pressure air.
Since traditional equations for sizing are not applicable for complex high tonnage streams, the use of the Discrete Element Method (DEM) is very common in practice. The DEM is a mathematical tool for modeling bulk material movement in order to optimize chute geometry. This allows gaining valuable information about trajectories, impact forces and possible blockages, and consequently, allowing iterative optimization of internal dimensions of the chute (Scheffler & Coetzee, 2023). The combination of DEM analysis with air flow simulation allows the designer to reliably size the chute, avoiding dust generation and material spillage before implementation.
In conclusion, proper chute sizing in order to avoid spillage and dust generation requires careful geometry-based engineering work. Since defining the flow dynamics and controlling such factors as drop height and velocities as well as air entrainment allows ensuring the required performance, implementing curved chutes and expanding the stilling zones allows for complete material containment. Finally, employing DEM simulations ensures that the chosen dimensions will allow working with high tonnage.
References
Scheffler, O. C., & Coetzee, C. J. (2023). Discrete Element Modelling of a Bulk Cohesive Material Discharging from a Conveyor Belt onto an Impact Plate. Minerals, 13, 1501. https://doi.org/10.3390/min13121501
Turkevich, L. A., Chen, H., & Jog, M. A. (2024). Dust resuspension from the splash of a falling powder: A numerical aerodynamic simulation of a pellet falling onto a powder monolayer. Aerosol Science and Technology, 59, 49–65. https://doi.org/10.1080/02786826.2024.2417976
Walker, P., Doroszuk, B., & Król, R. (2020). Analysis of ore flow through longitudinal belt conveyor transfer point. Eksploatacja i Niezawodność – Maintenance and Reliability, 22, 536–543. https://doi.org/10.17531/ein.2020.3.17
