Bolted benefits
FLSmidth explains how bolted thickeners help to reduce
project construction risk and duration
he concept of bolted thickeners is growing
in popularity. According to FLSmidth
Senior Account Manager, Ricus van
Reenen, this is a fit-for-purpose, high quality
dewatering solution with reduced project
construction risk and duration. These benefits
resulted in FLSmidth securing an order in July
2017 for a 24 m diameter high-rate thickener
from a South African iron ore mining company.
“Although this concept has been around for
at least a decade, it is becoming more
commonly used,” says van Reenen. “With a
bolted tank, the whole thickener is constructed
inside a purpose-designed fabrication facility
with all welding, sandblasting and painting
taking place under controlled conditions. This
guarantees that everything fits as it should so
there are no unexpected delays on site.”
Thickeners have traditionally been
constructed on site; all rolled and bent plates
are transported to the required location where
they are welded onto the prefabricated support
T
A bolted gold tailings thickener
The rake mechanism of a gold pre-leach thickener
P10 International Mining | MARCH 2018 Supplement
structure and radial beams. “This process can
take weeks to complete, as there are kilometres
of welding runs required,” he says. “Moreover,
the considerable weight of the material in the
finished tank – several thousand tonnes –
means that the weld quality needs to be high
and coded welders must conduct the work.”
These welders often have to be
accommodated on site for extended periods of
time, which adds to the cost; cross-border work
often involves the added burden of obtaining
work permits and special visas for these
workers. Sandblasting of the welding runs is
then necessary, as well as a final coat of paint.
The underflow system of a tailings thickener
In addition to the extra costs, the work is highly
weather dependent and delays can be caused
by rain or excessive dust.
“Weather related delays can cause time over-
runs for the contractor, which can then lead to
penalty costs,” he says. “This sort of project risk
is one of the main reasons why contractors are
choosing bolted thickeners. As a contractor,
your time on site is where your most significant
risk will lie.”
After the construction of a bolted thickener in
a workshop, the whole tank can be transported
to site where the bulk of the on-site work can be
undertaken by a mechanical supervisor, who
oversees the lifting and placement with the
support of a rigger and a crane driver. Local
labour can be used to fit the necessary bolts
into the structure, and a technical specialist can
come in to torque the bolts.
“Once in place, only touch-up painting is
required, so poor weather won’t be a serious risk
factor,” says van Reenen. “Ensuring that
deadlines are met means on-time commissioning,
which aligns well with FLSmidth’s role as
productivity partner to mining projects.”
He notes that FLSmidth has supplied at least
20 projects globally with bolted thickener tanks,
putting close to 40 of these units into the
market in recent years. The largest unit was a 45
m diameter high-rate thickener, while the more
specialised deep cone thickeners have also
been built in this way up to a size of 35 m in
diameter.