Twin-cell tandem train unloader boosts Fortescue Metals Group’s export capabilities

Fortescue Metals Group recently upgraded its bulk material handling facilities at Port Hedland that will enable the company to reach its target export capacity of 155 million tonnes per annum (mtpa).

From modest beginnings in 2003 Fortescue has grown into the world’s fourth-largest iron ore producer. Its first mining operations started at the Cloudbreak mine in August 2007 with the construction of all mine, rail and port infrastructure reaching completion in 2008.

Fortescue’s railway is the heaviest haul line in the world, with a 40 tonne axle load capacity. The company’s rail infrastructure operates 24 hours-a-day, seven days-a-week. Each train is around 2.7km long and carries up to 32,800 tonnes of iron ore in 240 freight cars.

A critical part of the port infrastructure was the company’s train unloader, which was put into operation in April 2008 when Fortescue unloaded its first train at the Herb Elliott Port, near Port Hedland in North Western Australia.

Since then, the company has fast-tracked its growth by steadily increasing production from its Cloudbreak mine and then bringing the Christmas Creek mine on-line in 2009.

Recalling that time, Fortescue’s General Manager – Port, Gerhard Veldsman said, “At that stage, the mines were running at about 70-75mtpa; car dumper one was running really well, matching the capacity of our mines.

“Even now, I don’t think that anyone in the Pilbara is able to unload at that rate. The problem was that we had more mining capacity and shipping capacity than dumping capacity,” he said.

In 2010, Fortescue approved an ambitious expansion to triple production to 155mtpa. The US$9 billion project not only includes an expansion of mining operations at the Chichester Hub and a greenfield development at Solomon but an expansion of the company’s port, train unloading capacity and main rail network as well as a new line to Solomon.

Over the last few years Fortescue Port Shutdowns Supervisor, Brad Stillman has been involved in all aspects of the company’s first train unloader’s maintenance.

This has ranged from basic weekly inspections to major change outs. During that time, he has worked closely with Metso’s Service team on the procurement of spare parts, equipment enhancements and services.

Tippler ready to clamp a wagon in each cell prior to unloading.

Tippler ready to clamp a wagon in each cell prior to unloading.

For Stillman, TU601 is truly at home in the harsh conditions of the Pilbara due to its sturdy construction and reliability.

“We’re not in a pharmaceutical lab – it’s a really rugged environment out here. But even so, the unloader is like a Swiss watch – everything just works. That’s why it’s my favourite piece of the plant. It is a big, heavy, powerful piece of gear that needs to be treated with respect,” he said.

On the back of the performance of their first Metso twin cell, tandem train unloader commissioned in 2008, Fortescue awarded Metso Mining and Construction a contract to supply two more identical systems.

The first of the two new unloaders (TU602) was commissioned ahead of schedule in mid-September and the second (TU603) in November 2012.

Veldsman says it was crucial that TU602 was delivered on or ahead of schedule and that the ramp up had to go well, because the business was experiencing a “real bottleneck” when it came to unloading trains.

“It was delivered two weeks early, which was fantastic. The original ramp-up schedule was meant to be eight weeks, but we shortened that to six and we did it in four,” he said.

The early delivery of the second train unloader resulted in Fortescue being able to dump 580,000 tonnes of unbudgeted ore in September, said Veldsman.

According to Operational Readiness and Commissioning Manager, Mark Shirley, the company is benefitting from the additional capacity of TU602. Even though it is not yet needed for full time use, TU603 is already playing an important role.

As well as catering for future expansion of the company’s production capacity, TU603 provides overall system redundancy in case of any problems occurring with the other unloaders.

“Train unloader two is hugely important to the business, taking us to between 110 and 115 million tonnes capacity. TU603 is also one of the critical parts in our supply chain; if you’ve only got two train unloaders and you lose one, you’ve lost 50% of your capability,” said Shirley.

Veldsman agrees, adding that the installation of the two new train unloaders represents a significant part of the company’s move to expand their Herb Elliott Port facility.

Operators use a SCADA interface to monitor and control the process.

Operators use a SCADA interface to monitor and control the process. 

Trains arriving from the mine sites are moved through one of the unloaders. During unloading, two wagons are simultaneously unloaded every 90 seconds.

The unloader clamps and then inverts the wagons, rotating them through 150 degrees. This is done without uncoupling the wagons as each pair of wagons has a swivel coupling at either end.

Prior to each operation, the wheels of the train are locked in place to prevent the train moving during the rotation cycle.

The contents of the wagons are dumped into a chute that feeds an apron feeder which transports the ore onto a conveyor feeding one of the facility’s stackers. The stackers create the port’s stock piles which are later consumed by reclaimers that feed the company’s ship loaders.

Unloader composition and functionality

Each unloader consists of three main parts; the indexer, the tippler and the train holding devices. 

The indexer is a rail-mounted vehicle which is dedicated to advancing the train through the unloader, two wagons at a time.

This heavy-duty work-horse moves back and forth along a short, straight rail track, located at the entry to the unloader. It is moved by 13 vertically-mounted drive units, each powered by a 90kW, three-phase motor that turns a pinion via a gearbox.

These pinions engage in the indexer’s rack which is mounted down the middle of the rail section along which the indexer moves. Each pinion is around 400mm in diameter and over 200mm in height.

The indexer also incorporates a retractable hydraulic arm that is inserted between the wagons. The arm pushes the train along by two wagons for each cycle, and is retracted at the end of the indexer’s forward travel.

Train unloader automation is run on Ethernet, adding flexibility.Train unloader automation is run on Ethernet, adding flexibility. 

Photoelectric laser sensors are used to locate the gap between wagons, allowing the indexer arm to be precisely positioned before it is extended.

The position of the indexer is monitored by a rotary encoder as well as inductive proximity travel limit sensors.

This is backed-up by mechanical over travel limit switches which trigger an indexer ‘fast stop’ in case the travel limit sensors fail. The indexer’s drive motors are controlled by variable speed drives that deliver an amazing combined power of 1.1MW to move the train.

The tippler or freight car tipping and emptying device is a rotary machine which is made up of two unloading cells. Each cell comprises the main cell structure, a drive unit and support roller assemblies, as well as a braking and lubrication system. The tipplers are located in an enclosure which is part of a pressurisation and dust extraction system.

Each cell is equipped with train rail sections and on-board hydraulic clamps that hold the wagon in place as the cell rotates during the unloading cycle.

The clamping system consists of four hooked arms that have three positions: fully raised to allow a locomotive to pass; intermediate position allowing wagons to pass; and engaged position where the wagons are held.

The intermediate position is the normal retracted position during unloading, allowing a gap of just 20mm between an ore car and the bottom of the clamp, greatly reducing engagement/retraction time compared to the fully-raised position, thus allowing for optimal unloading times.

Each tippler cell has its own drive unit to rotate it. When the train unloader is tipping, the drive units of both cells are connected together via a cardan shaft to make sure that they are perfectly co-ordinated. The position of each cell is also monitored by its own encoder and fed back to the system’s PLC.

Both drive units comprise a three-phase 200kW electric motor which drives a pinion in either direction via a gearbox. The pinions act on geared drive racks that are mounted on the outer diameter of the cell end rings.

Gerhard Veldsman points to an impressive ramp-up schedule.

Gerhard Veldsman points to the impressive ramp-up schedule. 

The motors are controlled via variable-voltage variable-frequency (VVVF) drive units that incorporate closed-loop speed control, ensuring smooth and efficient operation.

Finally, each cell drive has a disc brake with two pairs of brake callipers. Each calliper has a dedicated hydraulic power pack to operate it independently of the other, providing redundancy in case of brake failure.

Hydraulically-powered train holding devices are located at both the inbound and outbound sections of the unloader.

Four sets of wheel locks are located before the tippler entry and six sets of wheel grippers are located after the tippler exit to prevent movement of the two ore cars being unloaded. Each set of holding devices is powered by its own hydraulic power pack.

According to Shirley, the system provides lots of flexibility, along with failsafe measures to protect staff as well as guarding against downtime and production loss.

“It’s certainly very easy to utilise the redundancy that’s provided by the new train unloaders by simply switching from one to another. Each train unloader is able to link with at least two stackers, providing operational flexibility. This is one advantage of having the three up and running,” he said.

“What we want to do is keep train unloader three in a ready state so that within 24 hours we can fire up and run it if we need to. So certainly the arrangement that we have provides a lot of flexibility.”

Safety is a top priority for Fortescue, and the team has worked with Metso to ensure maintenance personnel are kept out of harm’s way.

“Our scheduled shut-down happens every 12 weeks where we’ll go in and do work, which is mainly driven around the conveyor belt maintenance and chutes,” said Mr Shirley.

“We have trialled a new idea with TU602 & 3 where we’ve located the hydraulic power units off-board – on TU601 they’re actually on the tippler cell itself which creates a few maintenance issues. So we’ve taken the power packs off the tipplers and we’ve just got hoses running to them now.

“This means the maintenance technicians no longer have to go on the tippler itself, meaning a couple of the major hazards we had identified in our business are completely removed. With safety our number-one priority, the associated safety benefits are significant.”

System automation and control

Co-ordinating the three parts of the train unloader with their myriad of sensors, motors and hydraulics has been accomplished through the use of a GE Fanuc RX3i PLC. The motor starters, VVVF equipment and associated I/O are located in the switch room.

The field I/O located around the plant is connected back to the PLC by Profibus fibre optic. A GE Fanuc Cimplicity SCADA terminal in the unloader’s control room provides SCADA displays of plant status.

While the automation of each train unloader is rather complex and is managed by a standalone system, each train unloader also has to co-ordinate with the control of the other port equipment such as apron feeders, conveyors and stackers.

“Our process has to be highly automated because we run very lean structures. The more we can automate the better. We’re certainly on the bleeding edge of that technology.

The automation platform is GE and it’s all Ethernet connected, so there’s massive capability there; we can set-up remote condition monitoring at these locations and have it all reporting to a central data centre,” said Shirley.

{^image|(width)580|(height)222|(url)~/getmedia/60ac0281-7560-46dc-af09-1e7616afd638/Fortescue4.aspx?width=580&height=222|(hspace)10|(originalwidth)620|(align)middle|(behavior)hover|(originalheight)238|(sizetourl)True|(alt)A helicopter view of the train unloading system showing its key components.|(mouseoverheight)238|(mouseoverwidth)620|(vspace)5|(ext).jpg^}

A helicopter view of the train unloading system showing its key components.

On-site, Fortescue employs a process control team resourced with a lead, process control engineers, and on-shift technicians. One operator and one electrician together run an entire train unloader asset, while the train circuit itself is controlled from an integrated operations centre in Perth.

Two operators are responsible for inload and outload duties at the operations centre in Perth; this includes managing the activities of the on-site operators, such as directing who attends issues as they arise on the circuit.

“Two operators and two electrical technicians are on-site on a 24-hour basis. But essentially the system is all controlled out of Perth, so the role of our site staff is to do inspections and to provide rapid response if there is an issue. We can direct them very quickly and they can attend to the issue and get it resolved in the shortest possible time,” said Shirley.

Fortescue Director Development Peter Meurs said the commissioning of TU602 was a major milestone for the company as it continues its expansion to 155mtpa.

“The second train unloader takes our unloading capacity to 120mtpa, which gives us the capacity to reach a run rate of 115mtpa by the end of the March 2013 quarter, comprised of 95mtpa from the Chichester mines and 20mtpa from Firetail,” Meurs said.

“The third train unloader will give us inloading capacity well in excess of the 155mtpa we need for our current expansion project.”

Commenting on the successful deployment thus far, Metso Minerals Vice President of Capital Equipment, Max Wijasuriya, said; “We are delighted to play such a pivotal role in Fortescue Metals Group growth plans.”

“Not only do we supply our clients with a broad range of high quality capital equipment, we can also provide an extensive program of services post commissioning to ensure that our customers enjoy peak performance, as well as many years of trouble free service from their machines.”