The second installment of a piece on how innovation in bulk materials handling is helping Fortescue to reach its planned 155 mtpa goals. To read the first part of the article, click here.
Delivering ore from mine to Port
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.
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.
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.
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.
This is the end of part two of the three part series on Metso installation of train unloaders for Fortescue Metals Group, to read the conclusion to this article, click here.