The use of high speeds (for example, above 6 m/s), low energy rubbers and intermediate drives will allow longer and higher capacity conveyors. There are barriers emerging that will challenge this trend. These include noise, dust emissions, belt pressures on idler rolls, and lubricant loss. Conveyor systems, mines and populated areas are moving closer together, and environmental standards are changing and becoming more rigorous. There are direct relationships between belt speed, belt and idler roll surface geometry, noise, and dust levels. Technology may allow, say, a 9 m/s belt, but night-time noise restrictions at nearby homes may limit the speed to approximately half this value.
The use of the tripper drive concept is an extension of the underground mine intermediate drive arrangements that have been used for many years. These intermediate power injection designs have included piggyback booster belts, powered rollers, and tripper drives. Torsten (1982) described the mathematics of intermediate drive systems and how they could be used to minimise the tensions around horizontal curves. Weigel (1982) described a similar system used in a limestone mine. A more unusual idea, called the Ozomin drive, used the return belt to drive a section of the carry belt. This allowed the drive station to remain at the end of the conveyor. Some of the power from the drive would be shifted to a point along the carry belt, via the return belt.
The long-term trend for belt conveyors continues to be longer, faster, and higher capacity. The highest capacity conveyors include the 40 000 tph × 3200 mm wide belts on the Rheinbraun bucket-wheel excavators. The longest single flight conventional troughed conveyors include the 17 000 m long 1000 tph conveyor for transporting limestone that crosses the border between India and Bangladesh. More recently, an Australian company, Wesfarmers, commissioned a 20.3 kM 2500 tph × 1200 mm wide × 7.5 m/s coal conveyor at Curragh North Queensland mine. This was designed by Conveyor Dynamics Incorporated. The installed power is 4250 kW (4 × 1000 kW and 1 × 250 kW). There are 2 × 1000 kW tripper drives located at the mid position.
In this context, non-conventional means non-troughed. An emerging technology in belt conveying is the Doppelmayr Ropecon system. This system has applications in rough terrain regions and environmentally sensitive zones. The conveyor can pass over these regions at a high level, as the conveyor is supported by cables between pylons like a suspended cable bridge. The span between the pylons can be up to 1500 m. The conveyor is a box-type flat belt with flexible vertical concertina side walls. The belt is supported by axles and wheels that travel on the suspended cables. That means the items that require maintenance, i.e. the wheels and bearings, travel around the system and back to a convenient point where the work can be safely done. The longest length to date is approx. 3500 m, and highest capacity approx. 3500 tph.
Other non-conventional conveyors include High Angle Conveyor (HAC), Cable Belt, Pipe-types, Rail conveyor, Aerial ropeways, Sicon and Aerobelt.
The HAC system uses an additional conveyor belt to create a sandwich. The upper belt applies pressure to hold the material in place as it moves up the steep incline.
Cable Belt conveyors use a cross-reinforced belt supported by cables on each side. The belt is almost flat, with a slight curve, so the supporting belt is separated from the tension member. (A conventional trough conveyor has the tension member within the belt.) The cables are supported by wheels spaced out several metres apart. The longest length is 31 kM + 20 kM and capacities around 4000 tph are located at a bauxite mine, Worsley Alumina Pty Ltd Western Australia.
Pipe conveyors are similar to a conventional trough conveyor, except the belt is wider so that it can wrap up into a circular or pipe shape. The idler rollers, say six in a hexagonal pattern, hold the belt in the pipe shape. Pipe conveyors can bend around smaller vertical and horizontal curves than conventional troughed belt conveyors. Pipe conveyors are good for dusty materials and conveying in and around process plants. The longest lengths are > 8 kM with capacities near 4000 tph.
The Rail conveyor is being developed at the University of Newcastle, Australia. The system has a troughed belt, support carriages with wheels that run on a railway track.
Aerial ropeways come in a couple of forms. There is the classic bucket hanging from a rope (like the chairs on a ski lift). The bucket would hold several cubic metres of material. Doppelmayr and others supply this type of machine for low volumes over difficult or complex routes. Aerobelt conveyors are like conventional troughed belt conveyors, except the belt is supported by a cushion of air instead of idlers. There is an air plenum in the shape of a trough with many holes to allow the air to leak out and form the cushion. The longest length is near 800 m, and the speeds range up to 7 m/s. The maximum capacity is near 400 tph.
The Sicon conveyor has the belt hanging like a teardrop-shaped pouch, with the tension cables on the edge. These conveyors are good for dusty materials and conveying in and around process plants. The highest capacity is around 1000 tph and longest length 2.5 km.