4. Horizontal transportation
4.7 Conveyor belts
4.7.2 Evaluation of conveyor belt system
Feed and discharge arrangements
The feed and discharge arrangements for this type of conveyor will be similar to those of a conventional conveyor with a maximum permitted lump size of 125 mm.
This would require some primary crushing arrangement and in the case of the smaller diameter conveyor, secondary crushing may also be necessary.
Conveyor maintenance
The reduction of spillage, belt damage and belt cleaning requirements are major features of this type of design. Damage of the belt due to foreign objects could cause tearing of the belt or damage to the conveyor structure and thus all the necessary precautions would be required to prevent foreign objects from entering the belt.
Installation considerations
This type of conveyor system is able to negotiate reasonably sharp turns with radii of between 100 and 300 pipe diameters, depending upon the belt tension. Severe changes in direction could onlybeachieved using multiple conveyors.
. The conveyor cross section is smaller than for a conventional and although the support structure is lightweight it requires to be fixed firmly and rigidly. Thus, adjustments for ground movement may be difficult to achieve.
Compatibility with other systems
This system is not capable of carrying personnel or equipment.
Second, conveyors require straight runs, or slow and constant curvatures. These are difficult to achieve in ultra deep gold mines, except over short distances or in areas where the rock mass is particularly stable, such as in shaft pillar areas.
Third, conveyors are susceptible to high rates of mechanical wear, particularly when conveying very abrasive rock such as quartzite. Fourth, conveyor systems are prone to spillage, which would be very detrimental in ultra deep mines due to the number of working areas. Finally, conveyor belts, although flame resistant remain a major fire hazard.
Considering the above issues, it is unlikely that conveyor systems will be the most desirable method of transporting rock over long distances in ultra deep gold mines. This is further negated as additional transportation systems will be reqUired for material and most likely, personnel.
4.7.2.1 Size
In the case of personnel riding belts, minimum dimensions are legislated for the widths and clearances of both the belts and the boarding and alighting platforms.
A minimum belt width of 750 mm is allowed, a minimum clearance of 900 mm from the belt to any other belt or structure. Considering clearances and infrastructure requirements, a minimum tunnel height of 2,4 m and a minimum tunnel width of 1,8 m is required for the installation of a personnel riding belt.
Where pump columns and other services are required to make use of the· same tunnel as the personnel riding belt, the tunnel dimensions will have to be increased accordingly to ensure that the minimum clearances are maintained.
At boarding and alighting stations, minimum tunnel heights have to be increased to 4 m to allow for the legislated increased clearances of 1600 mm at the platforms. Minimum widths too would need to be increased to the order of 2,5 m to allow for the minimum required boarding and alighting platform widths.
4.7.2.2 Flexibility
Straight tunnel sections are required for the installation of conveyors. No bends within a single conveyor are possible although long radius curves can be accommodated. Any changes in horizontal alignment require the installation of a new section of belt.
Vertical changes in alignment can be accommodated, but the maximum recommended gradient for a conveyor is 15°. Personnel riding conveyors are primarily rock conveyors adapted to allow personnel riding. Therefore, they can be used both for the conveyance of personnel and rock. Materials on the other hand cannot be carried on the conveyor, thus an additional transportation system, such as rail or monorail would be required to convey material.
4.7.2.3 Environmental compatibility
The use of electric motors for the conveyor means that heat and pollution emissions are minimal. Electric motors are reasonably qUiet and unless there is damage to the belt or rollers, belt operation is quiet except for a slight hum.
Legislation requires that the belt material be flame resistant, so that in the event of a fire minimal toxic smoke is produced. As the rock being transported is wet, dust should not be an area of concern. In cases where the ore is dry, water sprays can be used to suppress the dust.
4.7.2.4 Control and automation
. An operator at the drive unit can control a single conveyor system, however, for two or more conveyors, remote control operation is desirable. A central control station over the entire system can co-ordinate the start up and shut down procedures for the system. Feeding chutes can also be remotely controlled to ensure an even discharge of rock from secondary conveyors onto the main conveyor, thus preventing overloading and spillage. .
Sensors can be installed onto the rollers or in the belt itself in order to detect the presence of rock or persons on the conveyor. Similarly, ID tags can be utilised in cap lamps to monitor the presence of workers. Linked to a control system, rock loading or personnel riding can be prioritised to ensure the smooth operation of the system.
At boarding stations, automatic-signalling systems can be installed in order to ensure the correct spacing between personnel riding on the conveyor.
Emergency stop pull wires allow the safe stopping of the conveyor in the case of an emergency such as a person falling off the conveyor, or a tear in the belt.
4.7.2.5 Cost implications
An approximate installation cost for a single personnel riding belt of ± 1 800 m in length would be in the order of R9 000 000. This cost includes the cost of all steelwork, head drives, tail and take-up pulleys and all safety devices associated with personnel riding needs. This cost breaks down into a cost of R5 000 per running metre for the belt, supports, emergency stop and communication systems, and lighting and warning signs. The additional costs over a standard rock carrying belt due to personnel riding safety requirements, boarding and alighting platforms, control cubicle, brakes and safety devices are R2 000 000.