Onyx Projects has used Rocky DEM, a high-fidelity particle simulation program, to design and troubleshoot transfer chutes for key clients in the mining sector.
Bulk handlers that routinely handle ‘sticky’ iron-ore fines often find these materials build-up, requiring frequent hosing to avoid blocked chutes, non-central loading or spillage which leads to delays and lost production.
Perth-based Onyx Projects is a project management and engineering company that develops and delivers projects for the resources and infrastructure sectors. In an effort to definitively predict iron-ore fines’ flow behaviour the company turned to Rocky DEM discrete element modelling (DEM) software, supplied by local partners LEAP Australia.
In collaboration with the software’s developers, Onyx has created calibration/validation methodology for sticky fines to conduct representative material flow simulations that produce accurate results for one of the most challenging, and important, parts of DEM modelling.
The team determined that the process would entail three steps:
- The test should demonstrate the desired flow behaviour.
- The simulation procedure should match the test procedure.
- Calibration should entail simulating a real-life experiment and adjusting simulation input parameters to match the results of simulation to real-world test.
Quantifying sticky fines flow behaviour
Cohesive bulk solids (such as sticky iron-ore fines) can develop sufficient strength to form a stable arch, a phenomenon commonly associated with bins and hoppers, and less often with transfer chutes, that handle wet, sticky iron-ore fines. Fines flow properties are routinely tested in shear cells, measuring the stress at which the material yields (flows) over a range of consolidation pressures. To perform the final step of calibration/validation, contact parameters (friction coefficient, rolling resistance, adhesion) are adjusted to achieve a match to bench-tested flow properties.
Related stories:
In general, shear cell testing produces measurements that describe handleability of different bulk materials. The tests identify the interface between reliable flow and possible limiting or no-flow conditions. From this data, a wide variety of parameters can be obtained, including the yield locus representing the shear stress to
normal stress relationship at incipient flow, angle of internal friction, unconfined yield strength, cohesion, and a variety of related parameters such as flow function.
For cohesive materials, the yield locus is dependent on the normal stress applied during pre-shear. Typically, three or more normal stresses are tested to produce a family of instantaneous yield loci.
For transfer chute applications, the normal bulk material loads are typically much lower than for storage bins or stockpiles. When reviewing lab shear cell test results, low consolidation (below 10 kilopascals) flow properties are particularly relevant.
Typical flow properties test reports do not contain details of the pre-consolidation stage, the normal load applied, and the number of twisting cycles performed.
For dry materials, the pre-consolidation load is typically the same as the pre-shear normal load. However, for cohesive materials to achieve ‘critical consolidation’, it is often necessary to use a pre-consolidation load many times greater than the normal load used during pre-shear.
To achieve critical consolidation during the DEM simulation of cohesive materials, the shear cell is filled without adhesion between particles, with adhesion then applied before the twisting consolidation stage.
Richard Elliott, Principal Mechanical Engineer at Onyx Projects says the company’s client work relies on the advanced capabilities of Rocky DEM software and the speed of its GPU-powered solver.
“Engineers calibrate material flow behaviour through simulating lab-based flow property tests. Material model behaviour is then carefully validated with full-scale chute simulations that we directly compare to site observations of flow and wear patterns.”
By using the accurate DEM simulations with Rocky to capture real flow behaviour and real flow problems, Onyx can thoroughly test and validate its own engineering solutions, providing its clients with optimised products.
Clients processing sticky iron-ore fines can expect fewer problems in transfer chutes, reducing material build-up, blocked chutes, belt run-off/drift delays, material boiling on impact plates, and spillage.
If you would like more information on this topic, please visit leapaust.com.au/dem-calibration/ to watch a 30 minute on-demand webinar that explores materials calibration within Rocky DEM with real-world examples presented by Peter Rizkalla, Rocky DEM Product Manager, LEAP Australia and Dr Richard Elliot, Principal Mechanical Engineer, Onyx Projects.