Keeping it moving
Intelligentadvances in belt conveyor technology over the years have led many mines to reconsider whether traditional truck haulage is always the best option for transporting materials.
For more than a century, belt conveyor systems have helped minimize human labour in industrial applications ranging from automotive to agricultural.
While belt conveyor systems have been widely used to continuously transport ore in some mines, truck haulage has traditionally been the industry favourite.
But as mines go deeper and trucking distances and associated costs continue to climb, conveyors are proving an attractive alternative for many operators, says Craig Wheeler, associate professor in the School of Engineering at the University of Newcastle in Australia.
“The scales of new mining operations are resulting in unprecedented demands for greater haulage lengths, lifts and, of course, capacity,” says Wheeler, who began a career with BHP Billiton in 1989 as a cadet mechanical engineer and earned extensive belt conveying experience working in maintenance, operations and design positions at BHP’s Newcastle steelworks for more than a decade.
The wide world of conveyors
Sandvik is credited with engineering the first steel belt conveyors in 1902. Today Sandvik designs, manufactures and installs complete conveyor systems in mining operations around the globe.
“Sooner or later, every mine, every crushing plant, every processing plant will involve conveyors if it doesn’t already,” says Thomas Jabs, vice president product lines, Sandvik Mining Systems.
Long overland conveyors in Australia form the backbone of many mining operations and cooperate with the natural lie of the land, while shorter in-plant systems across Europe and South America feature large capacities and can include belt feeders, high-angle conveyors and totally closed conveyors.
“Many mines investigate how quickly they can introduce conveyors to replace some of their expensive trucks,” Jabs says. “We have a mine planning group to help operators determine at what point it becomes feasible to make the investment to replace trucks with conveyors.”
Important factors to consider include mine life, geology and deposit shape, scheduled material tonnage rates and the price of diesel fuel versus electricity.
“Every mass mining operation will eventually ask those questions, especially new mines,” Jabs says.
In addition to popular overland and in-plant systems, Sandvik offers innovative mine conveyors, compact-type conveyors, apron feeders and special conveyors that overcome differences in elevation.
“Our internal factories produce all conveyor components, including rollers, pulleys and other integral parts of conveyor systems,” Jabs says.
Solutions for opencast mines also include semi-mobile, shiftable and fully mobile track-mounted systems tailored to operator needs. Sandvik is now answering more demands for underground conveyor applications, which frequently involve extreme operating conditions.
“We’ve long served the global mining industry with conveyors for surface mining and materials handling applications, but we’re transforming into a major player in underground conveyor haulage too,” Jabs says.
He also notes the ever-increasing popularity of in-pit crushing and conveying (IPCC).
“It’s an efficient way to move part of the processing plant into the mine, bringing it closer to the shovel, to the face, so that trucks don’t have to travel a long distance to a processing plant outside a mine,” Jabs says. “Conveyors are an integral part of each IPCC system, and they’re the crucial link between primary crushers and spreaders.”
As bulk materials handling by roller-supported rubber belts has become more articulate and mobile over the years, conveyors have started to replace an increasing percentage of road truck haulage.
Today, conveyors work closer to the face behind blast and load operations than ever before. In many underground coal mines, conveyors are employed practically from the moment the coal is liberated from the face.
While early mining industry applications were primarily short in-plant conveyors, single flight conveyors tens of kilometres long can today move up to 20,000 tonnes per hour at speeds of more than 9 metres per second.
Conveyor technology, from components to capabilities, has developed continuously since the first systems were employed in the mining sector in the early 1900s.
Today’s intelligent conveyor designs drastically reduce friction and rolling energy losses. Optimized trough shapes and pronounced curvatures are now common. In-plant and underground conveyors have become more adaptable and are able to negotiate tighter corners. Higher-quality materials have improved operability and increased the life expectancies of today’s overland conveyors to more than 30 years in some cases, reducing capital and operating costs even further in new mines.
Wheeler says conveyor systems offer distinct advantages over truck haulage in efficiency and environment.
“Belt conveyors being continuous, rather than a batch transportation system, are used wherever they are technically and economically feasible,” says Wheeler, who undertook his doctoral studies in belt conveying. “With the demand for more and more automated mining operations, belt conveyors have clear operational advantages.”
Overland conveyors can be routed more directly than haulage roads and can effectively traverse grades of up to 20 degrees, while haulage road systems are often limited to less than 5 degrees. Conveyors carry more material per hour over longer distances and at higher speeds, increasing efficiency and reducing operating costs.
Conveyors also offer distinct environmental advantages over trucks. A conveyor belt in the average mine uses one-fifth as much energy as a heavy truck, reducing carbon dioxide emissions. Trucks burn diesel on empty return hauls, while conveyors haul material continuously.
Conveyors are also quieter, generate less dust and consume less land.
Each mine’s operational needs are unique, and Wheeler says different factors should be analyzed to determine whether ore might best be transported using belt conveyors, trucks or a combination of the two.
Conveyors carry a high cost per metre, and many operations that lack fixed haulage distances will always require the mobility of trucks, he says. Some mines have learned to combine the flexibility of trucks conducting level haulage with the lower operating costs of conveyors for primary haul out of a pit.
“Choosing the appropriate bulk handling system depends on transportation distance, throughput and terrain, among other things,” Wheeler says. “Research has shown belt conveyors are generally more cost-effective on a life-cycle cost basis than both road and rail transport for throughputs up to 5 million tonnes per annum over horizontal conveying distances up to 40 kilometres.”