A hands-on collaborative approach to D&C equipment supply drove the best end result for reliability, operability, maintainability and safety on the East Intercourse Island train positioner replacement project.
In 2010, Rio Tinto commissioned the replacement of the train positioner servicing the rail car dumper at its East Intercourse Island (Ell) port facility, located at Dampier, in the Pilbara. Aurecon and MIE Enterprises designed and engineered the new system.
The train positioner (or indexer) endured 40 years of operation, since 1972, and had reached the end of its service life. Intensive maintenance had become necessary to keep the machine in service and the car dumper operational. This maintenance included works to address extensive metal fatigue in the main frame and servicing of mechanical components, which resulted in significant down times.
The EII car dumper handles all ore delivered to the port. As such, the train positioner is a critical component with no redundancy in the mine to port supply chain. Over a 12 month period the train positioner performs about 200,000 indexer cycles to process 47mt of ore through the car dumper for transport to the port stockyard.
Aurecon provided the design and commissioning services to MIE Enterprises in their role as D&C Contractor to Rio Tinto.
Replacement of the train positioner provided the opportunity to increase the rate of inloading through the car dumper by reducing cycle times and improving machine availability and reliability. Rio Tinto also sought to focus and drive improvements in maintainability and operability and augment safety for people working in and around the machine.
The key design challenge was addressing the requirements of high duty, improved operability and maintainability, while working in the existing spatial envelope of this brownfield site.
Although the project framework for replacement of the train positioner was a traditional D&C contract, Rio Tinto cultivated a collaborative approach that both M.I.E and Aurecon adopted.
As well as performance im
provements the focus was to design for maintainability and enhanced safety.
At project commencement, Aurecon established consultation between the team and key operations and maintenance people who are in daily contact with the train positioner, and specialist project personnel on site.
Safety in design requires consideration of safety at concept stage. At this initial stage, the design is flexible enough to identify, develop and adopt design solutions that reduce risks to health and safety throughout the life of the machine being designed.
Early in the design, through consultation with key personnel, it was possible to identify and clarify hazards and discuss and develop ideas on the prevention or elimination of these through design implementation.
Following the full development of concepts, an iterative review process between fabricator, site personnel and design commenced and continued through to detailed design. This flexible and interactive approach helped mitigate risks throughout the project development process and provided the delivery of robust solutions while staying in schedule and budget commitments.
Operational issues and challenges
The key operational issues identified with the existing train positioner were:
Dating from the original installation, the machine duty had escalated substantially, with a 50 per cent increase in the number of cycles per day and an almost doubling in the tow load due to longer length of modern rakes and larger ore wagon payloads.
An overarching constraint to the design was the requirement to fit the new machine in the spatial envelope of this brownfield site, while achieving a 25 year life at the higher specified duty.
Design solutions and features
Aurecon implemented the following principles to address the identified operational issues and achieve budget:
3D drafting, utilised to develop the redesign of the train positioner, provided an effective tool for communicating concept ideas for both detail design of components and general machine layouts, and the rationale of the practical maintenance of these components.
Team members throughout the three stakeholder organisations received snapshots of design concepts taken from the 3D model. These provided an effective platform for feedback on developing design concepts.
A description of particular design solutions and features incorporated to achieve improvements in the key areas of maintainability, operability and safety follows.
Main frame fatigue
Fatigue of the main frame is a key issue with the design of wagon positioners.
Finite element analysis of the existing main frame at the specified duty for a 25 year life revealed that at least half the plates of the fully welded rectangular boxed girder structure would require more than a doubling in thickness. This would result in a significant increase in both weld size and cost and machine mass.
The specification of weld toe grinding as a post-weld improvement technique that produces a substantially increased fatigue life allowed utilisation of thinner plates resulting in reduced material costs and a lower overall weight for the steel structure.
The existing load wheel was a captured assembly where removal of the wheel assembly required extraction of the axle through the structure of the main frame. Maintenance of this wheel assembly often required extensive site based maintenance that included hot work procedures.
The new load wheel mount, developed by Aurecon, incorporated a split boss with a bolted clamp fixing arrangement. It is now possible to quickly remove the entire wheel assembly and replace it with a spare unit resulting in reduced machine downtime and a diminished requirement for site based maintenance. The performance of all maintenance work to the load wheel, including all hot work, can now take place in the workshop.
The original thrust wheel arrangement required a crane, four maintainers and three to four hours down time to adjust the positioning of the wheels.
Aurecon's new thrust wheel arrangement utilises an eccentrically located lateral restraint wheel mounted on a fixed vertical shaft, extending to the deck level of the train positioner.
At deck level the shaft terminates in a flange, held by a bolted clamp arrangement to preserve the rotated position of the thrust wheel assembly. Upper and lower split clamps secure the thrust wheel assembly to the train positioner's chassis. Bronze bushings inside the clamps provide a low friction low corrosion interface between the thrust wheel shaft and fixing.
Adjustment of the new eccentric thrust wheel assembly requires one person with a spanner and takes about 15 minutes. There has been great simplification of change out of a thrust wheel assembly with a reduction in unit change out time and enhancement of procedure safety.
Drive frame module mount
Mounted to the main chassis are six dual drive modules which provide long travel drive force of the train positioner. A bolted connection mounts the frame of the drive modules to the chassis of the train positioner and enables maintenance and replacement of the modules.
Recurrent failure of the existing connection which utilised an embedded thread incarcerated in the main frame structure necessitated hot work to the main frame to repair a stripped thread.
Aurecon's new design utilised a preloaded high strength bolted connection to address recurrent connection failure and an arrangement that incorporates an insertable nut to allow replacement of this item without welding or oxy-fuel work.
First car find and long travel overrun
Despite automated cycling of the train positioner, the process of finding the first wagon set at the start of the cycle was a manual process, requiring the operator to board the train positioner and operate it at the on-board local control station. Additionally manual intervention was required for the case when the train positioner travelled past the long travel limits.
The new positioner includes first car find automation, which utilises field devices to provide feedback to the control system and further automation to correct long travel overrun.
With the successful installation of first car find and over travel correction, automation of the train positioner operation is complete. It positions the control of wagon dumping processes by the new Remote Operations Centre (ROC) 1,300km away in Perth to achieve Rio Tinto's goal of automated mine-to-port Pilbara iron ore operations.
Successfully commissioned in May 2012, the new Ell Train Positioner is reliably operating at reduced cycle time and has an utilisation of 97 per cent.
Along with improved cycle times and reliability this machine requires significantly reduced onsite maintenance, reduced requirements for personnel to work in the vicinity of the travelling machine, and streamlined machine adjustment procedures.
Importantly all the design enhancements implemented to achieve these gains have resulted in a safer working environment for operations and maintenance personnel.
Enhanced automation upgrades to the train positioner have provided key building blocks in Rio Tinto's mine of the future programme for automated mine to port Pilbara iron ore operations.
Safety should be a key aspect driving optimal concept design. The commitment of the three-party project team to the collaborative process on the train positioner replacement project resulted in the prioritisation and achievement of safety in design.
This hands-on collaborative approach to D&C equipment supply drove the best end result for reliability, operability, maintainability and safety.
You can contact John Leech at email@example.com to find out more about our expertise in bulk material handling.
This article first appeared in the Australian Bulk Handling Review.