Speaking about transfer chute design at last October?s IQA national conference in Perth, I was asked a seemingly simple question: ?Are modern design tools like DEM (discreet element modelling) and parametric modelling relevant to transfer chutes in the quarrying industry??
A ?good? transfer chute is characterised by:
? Minimal spillage.
? Minimal damage to conveyor belting.
? Very little noise and dust.
? Ease of maintenance and component interchangeability.
This has been achieved successfully where material has uniform properties, but in any typical quarry, material may vary from large rock to fines and everything in between with variable moisture contents.
DEM and other new technology has not benefitted owners of smaller conveyor operations to any significant extent. Often when conveyor equipment is procured from an Engineering Project Construction Management (EPCM) company, the parameters of how the transfer chute is to perform are rarely specified. Designers might simply enclose the transfer point with a ?box? (see Figure 2). It is the cheapest design option and the transfer chute will never choke or plug. This may be the designer?s primary objective. What is not taken into account is that:
? Material falling from two metres will have a velocity of seven metres per second. This impacting on a belt moving at three or four metres per second in the horizontal causes tremendous damage to the conveyor belt.
? If the belt is not loaded centrally, then tracking problems occur with inevitable edge and even structural damage.
? Spillage results in higher clean up costs.
? People interact with the system during clean up, creating a safety hazard.
Bad conveyor transfers create safety hazards and cost owners money.
DISCREET ELEMENT MODELING (DEM)
DEM is a family of numerical modelling techniques and equations designed to solve problems in engineering and applied science that exhibit gross discontinuous mechanical behaviour such as bulk material flow. DEM models the dynamic motion and mechanical interactions of each body or particle through a simulation and provides a detailed description of the positions, velocities and forces acting on each body and/or particle at discreet points in time during the analysis.
By studying the predicted behaviour of these particles through various chute geometry – velocities, build up, pressures and impact points – we can make changes to the geometry to achieve the design objectives.
DEM is a tool that designers can use to improve the chances of getting the best possible design in a transfer chute.
Using DEM with parametric modelling
To optimise the geometry of a transfer chute using DEM it is essential that the geometry of the transfer chute can be easily changed.
Certain parametric modelling packages now have DEM available as add-ins to the software. Chute geometry can be changed quickly. Studying material interactions is not only simplified but quicker and accurate.
IMPLICATIONS FOR QUARRyOWNERS AND OPERATORS
So, back to the question: ?Can DEM and its interaction with 3D parametric models benefit the quarry operator?? There are three interconnected answers:
1. The principles and techniques can be applied to all transfers and the performance (in relation to dust, noise, spillage and loading) and belt damage can be improved.
2. Great care must be taken to avoid plugging. Designs which limit velocity and try to maintain flow cross sectional areas (hood and spoon designs) may result in choking if material conditions change.
3. Wear of the liner material may increase and interchangeability needs to be considered in the design.
These tools used by the right designer with knowledge of specific plant conditions can greatly reduce operating costs and reduce risk on the conveying circuit.
Additionally, there are a number of skilled and experienced designers in Australia using these tools, so engaging an expensive EPCM may not be necessary.
Glenn Segers is the director of Eimquip Services, Wangara, Western Australia.
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