The use of DEM in the design and analysis of WEARBACK transfer chutes

1. Introduction
The design of transfer chutes is an important area in the mineral processing industry, with the main purpose of a transfer chute being to direct material from one conveyor to another. More specifically, when designing a transfer chute other objectives to consider are ensuring there are no blockages, minimising dust creation, minimising spillage and to minimise wear on the receiving conveyor belt and/or transfer chute liner. A designer has a number of tools available to them, with the two most common methods of analysis being the predominantly 2D Continuum method [1] and more recently the use of DEM, which allows 3D flow to be analysed. Previous work has been undertaken comparing the Continuum method with DEM in the area of transfer chutes and, as such, the reader is referred to [2] for detailed information on
this topic.

The Continuum method is generally applied in the design and analysis of straight on and 90° type transfer configurations, which are characterised by thin stream, rapid flow conditions where the material stream depth is typically smaller than the chute width. The theory is based on calculating the cross sectional material stream parameters at specific locations or areas of interest within the chute configuration. In contrast, DEM considers each individual particle, with the basic premise being to monitor each particle’s motion and the forces experienced by each particle to calculate its displacement per time step according to Newton’s laws of motion.

While the Continuum method has been in use for a number of years, the use of DEM in solving industrial problems has become more prevalent in recent times due to the rapid increase in computing power, as well as the increase in availability of commercial DEM codes. In this particular study, TBS provided an independent analysis of a rock-box type transfer chute by making use of both the Continuum method and DEM.

A DEM simulation was undertaken on a proposed transfer chute design to study the structure and mode of flow as the bulk solid material flow interacts with transfer chute geometry. The transfer chute studied was a WAMS WEARBACK liner-less design and was to be installed in an underground mine inclined conveyor system. The throughput of the proposed transfer is 4400tph
with incoming and outgoing conveyors travelling at 5.5m/s. The vertical loading height between the head pulley of the incoming belt and the impact point of the outgoing belt was approximately 6 metres. The material that was being handled was gold ore and, due to the typically hard rock nature of the gold ore, the selection of a rock-box type transfer over a hood and spoon design has the advantage of reducing maintenance costs, particularly related to chute lining.

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