Competitive logistics

In the aggregate industry, the key to competitiveness is in logistics. No one needs reminding about skyrocketing diesel fuel prices and the high operating costs of loaders and haul trucks. As such, everyone is inspecting their loading, hauling and transportation methods. Where possible, producers are tapping into lower-cost ship, barge or rail transport methods over long-distance trucking. But to maximise the cost efficiency of these alternatives, one must streamline the materials handling processes within the quarry. In other words, if you rely upon a fleet of loaders and haul trucks to load, unload, stockpile or transfer materials on-site, the big benefits of more affordable transportation methods are clearly compromised.

Obviously, as economies of scale in transportation rise, costs-per-tonne-mile decrease. Consider that producers can ship 18 tonnes via truck, 900 tonnes per rail car, 1630 tonnes per barge, and 40,820 tonnes per ship. Compared to the cost-per-tonne-mile using truck transport, the rail mode cost-per-tonne-mile is often only a third of trucking costs, barge transport is less than a sixth and ship transport is less than a tenth. However, rail and waterway transport requires a facility cost and specialised equipment, so your production volume must be high enough to be profitable in these alternative shipment methods.

It can be concluded then that where rail or water transport is appropriate – and is combined with the proper on-site material handling systems – the return on investment can be significant. Many operations are ensuring the profitability of rail and water transport modes by utilising customised loading and unloading systems.

The following examples involve customised equipment engineered by Superior Industries, a Minnesota-based manufacturer of conveyor systems and components. These case studies show how equipment like programmable telescoping radial stacking conveyors, automated truck unloaders and flexible tripper conveyor systems aid in maximising payback.

Unit train distribution centres
Note the case of a rail-based aggregate distribution centre managing two highway projects requiring over 1.8 million tonnes of aggregate. If transported by truck, it would have taken nearly 87,000 truckloads of material to service the projects.

The distribution centre is supplied by a dedicated 50- to 60-car unit train. The unloading of single-size tonnes from the entire unit train (4500 to 5500 tonnes) can be completed in six hours. The operation consulted with Superior Industries about unloading and stockpiling systems, which would be designed to eliminate loader use, while preventing material segregation.

Each railcar is a bottom-discharge unit which unloads into a surge pit, with material fed to a 73m overland conveyor, which feeds a Superior TeleStacker conveyor, an automated telescoping radial stacking conveyor that is fully programmable to build partially or fully desegregated stockpiles. It also meets the distribution centre?s need for multiple, high-volume stockpiles.

Notably, a stockpile built by a telescoping radial stacking conveyor will be 30 per cent higher in volume than a conventional conveyor, as the axle on a telescoping conveyor is closer to the feed point. Because the stinger conveyor retracts, the operator can stockpile back to the axle. The unit can be programmed to create stockpiles of different shapes, sizes and configurations, while allowing the operator to switch from one stockpile to another.

The operation realised savings in unloading 50 to 60 cars once a week versus the 10-car- per-day service typically available at older facilities. And, with the telescoping conveyor, the site eliminated multiple material handling, accelerated loader wear and the cost of maintaining staff for daily unloading and stockpiling.

Importantly, by combining effective rail transportation with customised material handling technology, this company meets its production goals while getting material to its projects more cost-effectively. After the highway projects are completed, the distribution centre will serve additional projects, allowing the company to expand market share in the region.

Another southern US-based rail distribution centre operates a 100-car unit train that delivers to a Florida terminal and splits into five different tracks. A locomotive backs in and hooks onto one of the sections at a time, and pulls each car over the tunnel conveyor where its load is conveyed to the telescoping radial stacking conveyor, which builds up to eight product stockpiles on the main part of the site. The telescoping conveyor is remotely adjusted to feed its load onto a 91m overland conveyor that transfers material to an additional yard that accommodates another eight high-volume stockpiles. The entire 9000-tonne shipment takes 10 hours to unload and stockpile, all without the use of a loader or truck.

Along with reducing costly loader use and getting more stockpile volume on a limited footprint, the operation cites safety and loss prevention as an important reason for replacing conventional stackers with telescoping radial stackers. Greater safety lies in the ability to adjust the telescoping stacker in bad weather. Once the stinger conveyor is retracted, the unit is converted into a low profile unit.

At another site, Superior operates a coal and petcoke operation blending coal products with ash and sulphur content to meet customer specifications. Coal is trucked into the site and unloaded by two Superior RazorTail truck unloaders to streamline the process. The unloading systems can quickly transfer material from belly dump trucks or end dump trucks onto a conveyor. An infrared eye is installed so that when the nose of the truck runs across the grate and dumps into the hopper, it breaks in front of that eye, which automatically kicks the conveyors on. Equipped with a timer so that the belts will cut off after material transfer is finished, the system does not require a dedicated operator.

The operation stresses the importance of the automated truck unloader being equipped with its own low-profile ramp. Any other type of unloader would require the operation to pour a concrete tunnel and install a conveyor within it. Superior has since combined the truck unloader with a telescoping conveyor to gain an even greater payback in product quality control and costs-per-tonne savings.

Inland waterway barge transport
When an Oregon-based aggregate producer acquired some Columbia River properties, Superior decided to harness the power of the waterway for cost-efficient barge transport. The operation built a new processing plant and a state-of-the-art loading facility to allow barge transport of 60 per cent of its material into the Portland Metro area, about 30 miles upriver.

The company estimates that shipping by barge, not truck, reduced transportation costs by over $1 million during its first seven months of operation.

A major hurdle was finding the right conveyor system for the barge loading application. The operation consulted with Superior Industries engineers who designed an automated telescoping radial stacking conveyor that would feed material onto any size barge. The manufacturer custom-built the conveyor, eliminating the normal undercarriage of a land-based unit, so that it could be mounted on a dock structure 110m out into the river where there is adequate water depth.

The loading operation had to raise and lower the conveyor to adjust to different stages of the river throughout the year. They also had to adjust the discharge height as the weight of the load causes the barge to drop by as much as 4m in the water. Thus, the unit was outfitted with a programmable logic controller and a wireless remote control package. The operators can raise and lower the telescoping conveyor while keeping the load centered on the barge. If the barge lists left or right, immediate adjustments can be made. The barge is loaded at 1800 tonnes per hour and is ready to travel in four hours. Up to three 7250-tonne-capacity barges are loaded per day. As a result of this one barge loading operation, more than 11,000 truckloads are spared annually.

Marine handling systems
In 2005, a new port facility was created in the US Gulf Coast for sulphur gathering, processing and distribution. At the site, molten sulphur is processed into pellets or prills at 1800 tonnes per day. This vast output means the prills must be properly stockpiled and stored at the facility until loaded onto ships or barges. Automated material handling via telescoping radial stacking conveyors, tripper conveyor systems and mechanical ship loaders has allowed the site to stockpile and distribute ?sulphur prills? – the only acceptable sulphur form for overseas shipments.

The challenge for Superior Industries was to integrate the stockpiling and conveying systems with a new mechanical ship loader. The sulphur material handling process begins with a telescoping radial stacker that is operated via touch-screen programming. The unit cost-effectively and safely stores and stockpiles large volumes of material in a defined area, until it is time to load it onto the large marine conveying system. Its biggest advantage is the automation, as it eliminates the need for an operator.

When it is time to reclaim the prills for shipping, material is loaded into hoppers and conveyed on portable conveyors to a large marine belt conveyor where it is transferred to Superior?s custom-designed tripper system, which works in conjunction with the mechanical ship loader.

Essentially, trippers (consisting of a frame supporting two idling pulleys, one above and forward of the other) are used to discharge materials from a belt conveyor at points upstream from the head pulley. The material on the belt is discharged to a chute as the belt wraps around the upper pulley. The chute can be arranged to catch and divert the discharged material in any direction. Augmented by moveable gates, material can be discharged to either or both sides of the belt conveyor.

The tripper system (with its tripper car) is connected to the mechanical ship loader. The ship loader ?drags? the tripper car with it from hatch to hatch within the ship. The tripper car allows the product to discharge from the tripper conveyor into each hatch.

The system loads 5000 to 10,000 tonnes into each hatch. Every ship is different, and the system automatically adjusts to each one. Typically, there are between five and seven hatches on a ship, so the facility loads 30,000 to 60,000 tonnes per ship. The site averages one ship per month, with material transported to almost any international market, from South America to South East Asia.

The supply chain
From the mine to market to construction site, competitive logistics involve rapid, timely delivery. Profitability lies in maximising stockpiling capacities to meet demand, and then getting materials from point A to point B at the lowest costs per tonne. By utilising customised loading, unloading, conveying and stockpiling systems, producers can truly cash in on the cost efficiencies of rail and waterborne transport.

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