TUNRA Bulk Solids worked with Roy Hill to solve a number of materials handling challenges by using the discrete element method, site experience and extensive knowledge on bulk behaviour.
The bulk materials handling supply chain consists of multiple transportation and storage operations for receiving, unloading, stocking, and transporting raw and processed materials.
Transfer chutes are a key component in the efficient operation of this handling chain, though they too frequently become bottlenecks that limit performance.
Common issues arising in poorly-designed transfer chutes include blockage, spillage and wear, and it is often the case that these do not receive the necessary attention during the design stage, leading to downtime and requiring remedial actions to optimise flow.
The application of the discrete element method (DEM) has become more prevalent as a solution to such industrial problems in an attempt to address the limitations of traditional methods based on material trajectories.
Modern analysis methods, especially DEM, have been applied to improve operating conditions across Australia and worldwide. This case-study, which was presented at the 13th International Conference on Bulk Materials Storage, Handling & Transportation, focuses on how TUNRA Bulk Solids has worked with Roy Hill in the solution of various materials handling challenges through the application of design principles with the use of DEM, coupled with site experience and extensive knowledge of bulk materials behaviour.
A number of issues were addressed as part of this scope, including material build-up, liner and belt wear, and central loading of the receiving conveyor. The successes seen in this study significantly contributed to the first ever week of 100 per cent equipment availability for process plant inflow system at the Roy Hill mine.
Application 1:
Background
Roy Hill commissioned an engineering company to design modifications for two chutes, CVR123/023 and CVR223/023. Ore had been building up in the chutes which lead to unscheduled downtime and impact idler failure was occurring on the receiving conveyor due to the unfavourable loading conditions.
This particular project was approached in two phases. TUNRA Bulk Solids was first engaged for a third-party review of the new design, which was already in the process of being implemented. Upon completion of Phase 1, a need for further improvements became apparent, and TUNRA was engaged to propose modifications to the installed insert.
The challenges
The proposed new design transitions from a rock-box chute to a sliding chute, so as to account for changes in the material being handled (Figure 1). TUNRA Bulk Solids conducted DEM simulations with a selection of parameters based on a combination of tools such as flow property data, experience, and feedback from site. Appropriate calibration is of utmost importance to adequately represent material flow, and TUNRA often works in conjunction with site experts to adjust the simulation parameters accordingly.
The independent review showed that the new proposed design for the lower insert demonstrated less total build-up, but also revealed the wall inclination angle in the lower part was too shallow for this specific material. This would be likely to lead to build-up in that region, which would require further maintenance actions to maintain reliability. This would also have consequences with regards to attempting a ‘softer’ loading onto the receiving conveyor when handling sticky materials.
Due to the advanced timeline of the project, this third-party review was conducted concurrently with the implementation of the proposed modifications, which meant that the findings could only be used as a risk-mitigation measure at that stage. Phase 1, therefore, resulted in recommendations for further improvement of the chute, which would become the focus of Phase 2.
The solution
After Phase 2, improved reliability was achieved through the following main modifications:
- Selection of a more appropriate rear wall slope angle to ensure flow and limit build-up
- Greater convergence of the insert side walls along with loading higher on the insert to likely improve control over the discharge of ore flow
- Extension of the lower insert to attempt to improve the soft loading effect and loading symmetry (as the gap between the bottom of the insert and the top of the receiving conveyor was shown to be too high).
For the purpose of illustrating these changes, Figure 2 shows the three chutes (initial design followed by the first proposed redesign and the improvements proposed in Phase 2).
The outcomes
Improved performance was subsequently verified on site, as shown in the diagram and graph below.
Application 2:
Background / Challenge
One of the critical pieces of equipment at Roy Hill’s plant is the lump stacker. Upon project commencement the plant required a 12-week shutdown cycle, with the receiving conveyor belt in the lump stacker being replaced every shutdown. TUNRA Bulk Solids was commissioned to conduct an investigation to reduce belt wear and assess the possibility of extending the maintenance interval to two cycles (24 weeks). Such an ambitious target would likely require a thicker belt cover in addition to the design modifications to the chute for improved flow.
The approach
Further to learnings of the previous project, the following steps were taken in the investigation:
a) Roy Hill engaged multiple vendors for submissions on the refurbishment of the lower feed chute to improve flow and reduce receiving conveyor wear
b) TUNRA conducted an independent review of all of the vendor proposals, providing a high-level assessment of the advantages and disadvantages of each option
c) Roy Hill completed their own evaluation based on a number of factors (including the TUNRA review), and awarded the contract to the successful vendor
d) TUNRA performed a complete review on the new proposed lower feed chute and offered further recommendations for improved flow outcomes.
The solution
The key modification was to make the angle of the chute shallower, which increases the wear inside the chute but decreases the wear on the receiving belt.
Given that the specific focus of the project was to decrease belt wear, this was an acceptable compromise. However, attention should be given to the fact that it may be the case where a modification to ‘improve’ a certain aspect may worsen another aspect, and all aspects shall be taken into account when proposing a design. A potential solution to this new issue (chute wear) is to ensure the selection of liners that are able to reach the set maintenance periods, thus meeting operational requirements.
The outcomes
Once again, improved performance was subsequently verified on site, through comparisons between site photos and the DEM wear profiles.
When installing the new proposed chute on site, at first with the same original belt, a 12 per cent wear reduction was observed. The same comparison in the DEM model yielded a reduction of 15 per cent. This difference can be explained by the complex nature of wear mechanisms and assumptions made in the DEM model, and is considered acceptable by industry standards.
Another observation from site was that the new chute completely eliminated failure of impact rollers, which had previously been observed as one to two rollers needing replacement in each maintenance shutdown.
After this initial assessment, in the next shutdown, the belt was replaced by a new one with a thicker top cover. So far, feedback from Roy Hill is that the new belt has exceeded expectations in terms of performance and the initial objective of reaching 24 weeks has been reached.
Concluding remarks
DEM is a powerful tool which can deliver a range of successful outcomes. However, as with any numerical modelling tool, the inputs are of critical importance. In these two case studies, such inputs were established through careful consideration of a range of factors, including experience with modelling technique and laboratory test data, but perhaps of most importance was the site validation and feedback.
By working closely together with its clients, TUNRA Bulk Solids delivers customised solutions to complex industry problems in all aspects related to the design of reliable materials handling and storage facilities. These services range from the characterisation of bulk materials under various operating conditions, to advanced calibration techniques, to the application of DEM simulations and verification with site observations. TUNRA’s expertise also include acting as a third-party independent reviewer, as well as independent testing of conveyor components such as belts and idlers.
Authored by Tim Donohue (TUNRA Bulk Solids), Nat Williams (Roy Hill), Shaun Reid, Bin Chen and Jens Plinke (TUNRA Bulk Solids).
For more information on projects like this and how TUNRA Bulk Solids can help your business, contact the authors through shaun.reid@newcastle.edu.au