Cradle to grave
Finding the optimal design and delivery solution for a large
thickener at a remote gold mine in the West African state of
Mauritania meant considering a complex range of technical,
transportation, and assembly options. According to Ricus
van Reenen, senior account manager at FLSmidth, the cost
of transporting all the components for the 50m-diameter
thickener was a key factor affecting the design. He highlights
that transportation of components to remote sites can comprise
a substantial portion of costs, and that break-bulk shipping costs
are significantly higher than containerised transport.
“Given that the thickener components needed to be shipped
by sea as well as by road, containers were considered the most
economical mode solution,” says Van Reenen. “This requires
that the plate sections be cut and rolled in dimensions that can
be packed into containers for shipping to site. The structural
support sections like the I-beams will be fabricated to final stage
at our facility and just bolted on site, but the plates will need to
then be welded by expert welders,” he adds.
While bolted thickeners are often more economical to
construct, as they obviate the need for extensive on-site welding,
this option cannot easily be applied to thickeners larger than
50m in diameter.
For these larger designs, the support structure is erected on
site, followed by the welding together of the plate sections from
one end to the other. After the plate sections have been welded
to the structure, the welds are sandblasted, primed, and applied
with a final paint coating over the welded areas.
Certain cost-saving strategies can still be employed in
these situations; for instance, the plates can be painted before
shipping, with the weld strips left clean to facilitate on-site
welding.
Van Reenen emphasises the importance of the documented
assembly procedure — according to FLSmidth’s global best
practice — that is applied when erecting these large thickeners.
“When supplying a thickener, part of our engineering
deliverables includes an installation methodology for the site
contractor to follow, to make sure that they implement each
stage correctly,” he says. “FLSmidth also provides a technical
installation expert from the most suitable of our global offices,
who visits the site at appropriate intervals to advise and inspect.”
He further emphasises that the forces demanded within large
thickeners also makes the choice of gearbox drive much more
important.
“Smaller thickeners can usually be designed with planetary
gearbox drives, available from a number of OEMs,” he says.
“With really large drives requiring higher torque, however, we
prefer to use our own ring-gear Dorr Oliver drives, which can
reach much higher torque values than planetary drives. The
ring-gear drives are also able to handle axial and radial loadings
on the rakes.”
AUGUST 2018 MINING MIRROR
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The tough task of
transporting thickeners
A high-rate thickener installation.