conveyor system and a three‑flight
17 km overland conveyor system. At
the time, this was the single biggest
project awarded to Sandvik Mining. On
this project, Sandvik Mining Systems
recorded its most significant safety
achievement to date, with zero lost time
injuries (LTIs) after nearly
1.5 million man hr.
The project
The Shondoni lump sum turnkey
contract, awarded in November 2012,
encompasses a complete materials
handling system, effectively supplying
the underground and surface materials
handling systems at the new mine. This
includes the project’s engineering
design, procurement and
civil/structural construction.
“Drawing on the success of the
highly complex Thubelisha project, we
are on track to deliver another high-tech
solution in the materials handling
arena,” said Willem Niemandt,
Engineering Manager at Sandvik
Mining Systems. “Sandvik is recognised
worldwide for our capabilities in long
overland conveyors with both
horizontal and vertical curves.
Accommodating the natural lie of the
land, our long-distance systems provide
cost‑effective and more eco‑friendly
alternatives to hauling bulk materials by
truck. Together with our innovative
solutions for reducing noise and dust
emissions, they point toward a cleaner,
brighter future. Only a small pool of
companies are capable of executing this
type of design and we have successfully
installed multiple overland conveyor
systems all over Africa the past decade.”
According to Niemandt, although
Sasol Mining’s initial tender documents
for the Shondoni project called for a
series of two conveyors to cover the
20.5 km route, his team optimised the
design and included in its bid an
innovative alternative that combined
the two conveyors into a single flight
conveyor without any intermediate
drive stations systems. This design
achieved an optimised system by
eliminating the infrastructure required
at the intersection point of the two
conveyors, including power
reticulation. By removing an entire
transfer point, the single conveyor
design also reduced the risk to the
operations at Shondoni.
The scope of the project includes one
decline shaft conveyor, with an
1800 mm wide belt and a design
capacity of 3600 tph of coal, going into
the shaft to transport coal from the
mine’s coal seam to the surface. This
conveyor draws power from three
1 MW installed variable speed drives to
deposit the coal onto a surface level
bunker conveyor, with the same
capacity as the previous conveyor,
which feeds the tripper conveyor.
The tripper conveyor spans 160 m
with a 6 m lift and uses a special split
way chute to provide even distribution
of materials across the surface area and
minimise drop forces to prevent
degradation of the material. A tripper
car is situated on top of a 15 000 t
concrete precast surface bunker with a
throw-out stockpile facility also of
15 000 t.
Underneath is a reclaim conveyor
situated in a tunnel, being fed by
14 luffing chutes. The reclaim conveyor
feeds the 20.5 km overland conveyor,
which ties the mining operation to the
process plant operation situated in
Sasol’s main operations complex.
Power for the main conveyor drives
from five 1 MW of installed drives, four
at the head and a single drive at the tail.
The overland conveyor feeds both
the moving head conveyor and the
reclaim conveyor at the Sasol Coal
Supply (SCS) plant. The SCS moving
head conveyor feeds a 4000 t precast
concrete bunker, which is identical to
the big bunker, only a shortened
version. This bunker, using the same
method, also feeds a reclaim conveyor
that feeds the transfer conveyor, which
ties into the existing SCS infrastructure.
“The specifications for these systems
were technically demanding,
exacerbated by topography of the
project area, which prevented the
overland conveyor from running in a
straight line,” said Niemandt. “The
route passes two informal settlements,
several slimes dams, roads and other
existing infrastructure and crosses
about 56 different types of servitudes,
such as power lines and gas lines.”
“We also worked closely with the
client to design and optimise the
guided flow chutes to avoid any coal
degradation. The resulting optimised
chute design caters to both surge
capacity and optimal flow to meet the
specifications,” continued Niemandt.
Safety, maintainability and
environmental impact
Much emphasis was placed on the
operational safety and maintainability
of the overland conveyor. Sandvik’s
design includes an intelligent pull key
system that facilitates an emergency
stop at any point along the route of the
conveyor – a system that is unique
over this distance. Switches are
installed every 100 m and, in between
each switch, is a pull cable facilitating
an emergency stop. The intelligent
aspect of the system is that, once the
pull cable is tripped, an operator can
pinpoint the exact location of the trip,
enabling the rapid deployment of
personnel to assist and ultimately reset
the system. This is a requirement of
South African health and safety
legislation.
The overland conveyor design
allows for ease of maintenance, both
during preventative maintenance
activities and shutdowns. For example,
it has specific belt pulling points along
its complete length, to ensure isolation
of the belt at any particular point. A lot
of R&D also went into other
maintainability components, such as
belt clamps and a dual take-up system,
which is used as an additional belt
storage facility.
As part of the optimised design, a
low rolling resistant compound was
used on the bottom cover of the belt,
allowing the design team to use the
required belt class the client had
requested, while having an overall
saving on energy consumption when
compared to conventional rubber
covers.
A critical part of the conveyor
design was the correct selection of the
idlers. The selection becomes more
important on overland conveyors,
where not only the functional
selection, but the economic impact of
the selection becomes dominant. For
this conveyor, an oversized roll
diameter of 178 mm was selected to
keep the idler rotation speed within
28
|
World Coal
|
July 2015
