TRENDS IN MINE HAULAGE
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
pipelines 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
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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 |
50sec. a train is composed of
six 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.
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