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Scales keep trains on track

Othe last few years Rio Tinto has made several efficiency improvements to its Pilbara rail network. A key contributor to this success was the optimisation of train loading operations at Yandicoogina.

An essential part of their integrated iron ore production process, Rio Tinto’s rail system directly affects the company’s capacity to blend ore to customer specifications. Linking 12 mines with three shipping terminals, this piece of infrastructure is the largest privately owned heavy freight rail network in Australia. Spanning some 1,400 km of track, it is responsible for moving 220 million tonnes of ore from Rio’s Pilbara mine sites through some of the harshest and remote country on the planet to their port facilities in Dampier and Cape Lambert.

Each train is operated by a single driver, and comprises up to 234 ore cars. A fully loaded train weighs in at around 29,500 tonnes and is about 2.4 km in length. On average, the network’s cycle time is 28 hours with a train movement every 25 minutes along the line. Due to the weight and length of each train, three locomotives are used to pull the load at the front and two to push at the end of the train.

With such an arrangement, the correct loading of the cars is critical. While consistently loading each car with as much iron ore as possible yields optimum network efficiency, it’s important not to exceed the car’s maximum load capacity. Overloading places stress on critical components, causing failures that can lead to train derailments. On the other hand, under loaded cars represent wasted capacity and poor network efficiency. Lightly loaded cars sandwiched between fully loaded cars can be lifted off the rails also leading to derailments.

Train derailments have a cata strophic effect on mining operations because they damage the tracks and depending on where they occur, can halt rail traffic from multiple mine sites to port. Repairing the line after such an incident and getting the train back on track can take days. If in the meanwhile, sites can’t load and dispatch their final product, their stock piles reach maximum capacity forcing them to shut down their processing plants and mine production.

Mine to port logistics operations are of such importance to Rio Tinto that in 2008 they launched a major project called ‘Drumbeat’ to optimise the efficiency of their entire supply chain. As part of this strategic project, mine sites were encouraged to improve the speed and accuracy of their train loading operations.

Responding to challenge

The team at Yandicoogina decided to target a long standing issue responsible for heated debate between the site and port operations. The issue related to a discrepancy between car load weights measured and estimated during train loading operations at the mine site and those measured at the port. The mine operates two train loaders, one had a weighing system with a 2% accuracy, which introduced a variability of around 2.3 tonnes per car. The other relied on a weightometer that provided the weight of ore loaded on each train. This data was then divided by the number of cars to obtain an average weight per car. The port operations on the other hand have a facility to weigh each car individually giving a better indication of the ore weight per car.

Unfortunately, by the time the train reached the port was weighed and the data fed back to the mine, 24 hours had passed during which another five or six trains had potentially been loaded incorrectly. The end result was that while the site was targeting 116 tonnes of ore per car, they were actu ally loading anywhere between 110 and 120 tonnes per car and were seldom achieving their target weight. The team realised that the only way to improve their loading accuracy was by weighing the wagons accurately at the point of loading rather than at the port.

A project team was assembled to tackle the problem and identified a number of ways of improving Yandicoogina’s train loading perform ance. The key was their ability to accu rately measure the weight of each car before and after loading and to provide the operator with rapid feedback as to how well he was loading the cars. Because loading speed was also an important consideration to operational efficiency, weighing had to be accom plished dynamically while the cars were moving through the loader.

Working with an external engi neering firm, the project team identified two of their existing suppliers that were capable of implementing such a system. Proposals from both companies were evaluated. The key selection criteria for the system were; accuracy and ease of integration into the existing train loader’s automation system. The team gained management approval for the project’s capital expenditure based on an average gain of one extra tonne of ore per car. Having received the green light from management, the project was handed over to Sang Nguyen, the site’s planning & engineering superintendant and his team of mechanical, electrical, condition monitoring & process control engineers, for execution.

Implementing the system

Nguyen, an electrical engineer with experience in automation and control systems said: “I took the project on myself due to its size, complexity and automation intensive nature.” Reflecting on the choice of Schenck Process as the system supplier, he notes: “In choosing our supplier, we were looking for a ‘one stop shop’. We needed a partner that could not only supply a weighing system to match our needs, but one that could also provide seamless integration into our existing PLC & Citect SCADA system. Schenck Process was a good choice because they were the OEM that had originally supplied the train load out and associated weighing and automation systems.”

“The fact that MultiRail was already being used successfully in many European ‘Legal – for – Trade’ applications with an accuracy of 0.5% also made the system appealing to us,” he adds.

System benefits

Gerry West, Yandicoogina’s Fixed Plant production superintendant is responsible for the day to day running and effi ciency of the mine site’s equipment and processes. West first arrived on site just as the new train scales were being installed and commissioned. He says: “The MultiRail track scale implementa tion was a very successful part of the Drumbeat project because it delivered on its promises. It has enabled us to control our loading within much tighter limits allowing us to increase the average load per car by two to three tonnes.”

With respect to integration into the overall control system, he says: “I would be surprised if some of our operators can even tell you where the scales are, the integration is so neat.”

West and his team use the new system to collect valuable statistical information that allows them to analyse the site’s loading performance and compare it to data measured by the port operations. Before the system was installed, data provided from the port indicated that 13% of their cars were being overloaded. Since the MultiRail scales have been installed that number has dropped down to less than 5%. Statistics fed back from the port also show that the standard deviation of tonnes per car have improved dramatically.

Project outcomes

Rio Tinto’s management discovered that instead of the projected one extra tonne per car, Yandi were able to achieve between two and three extra tonnes per car. This shortened the system payback period to just a few months.

The discrepancies between the esti mated tonnes per car loaded at the site and those reported from the port were a major concern for Mark Rodgers, Rio Tinto’s general manager at Yandicoogina. The last thing that he wanted was for his site to be responsible for a derailment — an event considered on par with the impact of a tropical cyclone.

Commenting on the impact of the project Mark says: “We’re always trying to squeeze out as many tonnes as we can and this system has helped us to achieve that objective.”

[Peter Newfield is Marketing & Technical Support Manager, Schenck Process Australia.]

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