TRENDS IN MINE HAULAGE

The Capsule pipeline

Truck Haulage

Conveyor

End Point

The transportation of minerals from the loading point to the disposal point has always been a critical activity and one of the most vital cost components of mining operations. Indeed, mine haulage has been observed to be as high as 60% of the entire pit’s mouth cost.

Over the years, significant technology and system improvements have been undertaken to optimize mining haulage by balancing costs and performance. Systems depend on various considerations including the geological occurrence and topography and cannot be standardized across the board. Truck haulage and conveyors are systems that have successfully stood the test of time. Even as they gear up to meet the ever present need for increased capacities, it appears that another system - the transfer by pipeline - is also making rapid strides.

This article looks at some of the successful mine haulage systems in use today, highlighting the latest developments.

The capsule pipeline

Sumitomo’s announcement that it has successfully tested transportation of limestone in solid form by capsule pipeline is path-breaking news. While transportation of slurry has been in place and pipelines handling crude over several thousands of kilometers across countries are in existence, the capsule transportation of aggregates is a milestone in mine transportation history.

The system runs trains of wheeled capsules with limestone in a pipeline using low air pressure. The entire system is centrally computer controlled and needs minimum attention and personnel. Since the pipeline is maintenance free and also tamper proof, many of the problems associated with other systems like trucks and conveyors are eliminated. A major advantage of the system is its immunity to climatic conditions. It is important to note that this system is very eco-friendly.

Details of the Limestone Capsule Pipeline (which has been in operation since April 1983) are given below:

The Limestone Capsule Pipeline: A gist
Location
Tochigi, Japan
Material Transported
Limestone
Travel distance
3,200 m

Annual Volume of Freight
2,000,000 tones
Annual Working Hour
6,000 H
Pipeline Diameter
998 mm
Capsule
Live Load 1.6 tons; 5 x 2 wheels; Launching Interval of a Train 50 sec (a train is composed of 3 capsules)
Energy Consumption
0.7 KWH/tone.km

Sumitomo is not alone when it comes to research on capsule pipelines. Capsule Pipeline Research Center (CPRC) has also been carrying out basic and applied research on both hydraulic and pneumatic capsule pipelines. The center had been conducting research on the development of systems for transportation of solids as well as hazardous wastes.

A brief review of the established systems of truck and conveyor haulage also indicates considerable advancements in the capacities and technology. Let us briefly look at each of these in turn.

Truck haulage

The Caterpillar company whose trucks are used for haulage all over the world including the super pit at Kalgoorlie open pit (Model 793C payload of 226 tones) is in the process of releasing their 797 truck with a payload of 326 metric tones. This is said to be the largest truck ever constructed. You may want to download the picture of the truck as your wallpaper!

While such super trucks are becoming commonplace it is also true that the size and numbers depend on the deposit being worked and the crusher mouth or disposal site acceptability. Whatever be the size of the truck certain factors go into their cycle time:

Activity
Fixed cycle time
Haul cycle time
Action Time

Case I Case II

Loading (A)
Lost time in acceleration (B)
Load (E)
Dump, turn and acceleration (C)
Empty (F)

D1=A1+B1+C1    D2=A2+B2+C2    G=E+F

Total cycle time = Average of (D1 AND D2) Plus (G)

The various parameters described above determine the operational probability, investment requirements, requirements for paving the road and cost of tires. The maintenance and the number of employees are directly proportional to the number of trucks.

Haulage performance therefore not only depends upon the selection of truck but on several other factors including maintenance of infrastructure and equipment, optimal working conditions, the loading and unloading sequence. The level of planning and monitoring required for ensuring minimal slippage is therefore very high in the case of trucks and conventional loading.

Conveyor

In-pit crushing working in tandem with a system of conveyors serves very well. The investment on the system is higher initially but compare favorably against rehabilitation and replacement required in the case of trucks.

Conveyors are more amenable for shifting the crusher to the pit itself. This does call for a proper design of “moving fronts” and a system of transfer feeders and conveyers. However, the restriction on the grade for haul roads becomes flexible and the actual conveying is limited to sized material instead of run of the mine.

Improvements are taking place in several areas including belt manufacture, drive designs, support devices, prevention against surge and controls. Developments over the years have rendered distances, high angles, curves, a non-issue. However the maintenance of the moving parts, checks against belt damage and operational speed do need attention. Continuous improvements in this sector are taking place. Powderandbulk.com provides a detailed list of manufacturers.

Cable belt systems claim further advantage over belt conveyors. Cables can handle steep grades, are smoother, contours of the belt allow better troughing and the inline pulleys result in positive tracking, eliminating/ reducing substantially the spillage and belt wear. Ckit has come out with a handbook for those in need of information on conveying belts.



End point

These developments in the transportation systems are in tune with the industry’s requirement but with such diversity in the operating conditions, there is always a float time between the actual requirement and the availability. Consequent upon these advancements, it is to be noted that the mines of all sizes and conditions require systems best suitable to local conditions.

The “Capsule Pipeline” therefore assumes importance as the size could match the requirements of most of the operations. The fact that such a system has had a successful run over a period of 10 years and has conveyed 2 million metric tonnes annually augers well for the industry’s future.