Published in March 2009 Australian Longwall Magazine

“The reduction in rolling resistance due to new rubber compounds is the single biggest recent improvement in overland conveyor design, and this has led to other improvements across the range as we probe for better outcomes to suit new demands from owners,” he said.

“Less friction means reduced power consumption and lighter belts which are able to travel longer distances with lower wear rates due to better and fewer load stations.

“The advances in control systems and variable speed drives have been essential to turning the mechanical designs into reality, and the ability to accurately model the designs for all load cases is central to these developments.

“There are further improvements that have yet to be taken up due to restrictive specifications, but as clients become more aware of the benefits we expect these restrictions will be lifted by the use of performance specifications in lieu of prescriptive specifications as it is realised that overland conveyor design is a very specialised field.”

Gerard also identified other elements of conveyor design that could evolve down the road.

“Acceptance of reduced belt safety factors by adopting a safety factor on the splice, not the belt, is possible right now when detailed analysis is available.

“I see idlers as an area where improvements can be made, particularly in economical noise reduction, which is currently impacting a number of projects.”

Noise reduction is a key trade-off area in conveyor design, with Gerard saying noise emission from idler rollers is mainly due to the steel tube used being seam welded and not perfectly round.

“Extruded poly rollers are round but cannot withstand the loads from the wide idler spacing required for overland conveyors. Aluminium shells with poly end disc roll designs do help considerably with noise emissions but at a premium.”

As better rubber compounds become available, Gerard said improvements will eventuate and the key was the temperature range in which the belt operates.

“Different rubber compounds are better or worse at different temperatures. Extending the applicable temperature range of any one compound will generate savings and promote wider use.”

As weaker commodities markets linger on, mining companies will be looking at methods to not only cut costs but also to improve productivity, with upgrading an existing overland conveyor a possible option.

While much of Laing O’Rourke lies in building new conveyors, the company performs upgrades. It recently performed a study investigating the redesign of a series of old conveyors into a modern continuous overland one to achieve higher tonnage for a client.

“Certainly opportunities exist to economically upgrade older plant and also to replace truck haulage with more economical conveyor systems,” Gerard said.

For companies looking at either new conveyors or upgrades, he emphasised the importance of not overlooking overall design requirements in favour of capital cost.

“Clients only consider specialist overland designers when the conveyor is outside the comfort zone of the traditional delivery method. Often critical decisions about suppliers and components are made purely on commercial grounds with no understanding of the impact on the design.

“We know of cases where alternate belt suppliers have been used, resulting in conveyors not achieving their required performance.

“In one recent instance, an upgrade of an existing conveyor including a new belt, faster belt speed and more power actually resulted in significantly reduced capacity.

“Additional drives required to overcome this problem will result in reduced safety factors throughout the system – putting the entire plant operation at risk.”

Depending on the scope of the project, a well-designed overland conveyor can also provide valuable storage capacity, as seen at Wesfarmers’ Curragh North coal mine in Queensland.

Developed by Laing O’Rourke and Conveyor Dynamics International, the mine has the world’s longest single flight conventional conveyor and can store 1850 tonnes of coal on the belt at any of its operating speeds, even when stationary.

Aside from operational benefits, mining companies may also reconsider their conveyor designs as government greenhouse emission tax penalties materialise, with Gerard saying advanced conveyor design will have tax benefits in manufacture and operation over more traditional transport mediums.

Laing O’Rourke is continuing its conveyor project at Port Kembla in New South Wales while a new conveyor project for Centennial Coal’s upcoming Airly underground coal mine is getting underway.