Why and how to avoid underground paste pumps
Robert Bradley of Golder Associates Ltd describes the
potential problems of underground booster paste pumps –
and advocates mine designs that avoid the need for pumps
ne of the biggest challenges in
underground paste backfill is ensuring
that the paste arrives at the point of
deposition at the right strength, consistency,
quality and quantity. To do this, most mines rely
on a surface pump to move the paste from the
plant to a borehole, where force of gravity adds
energy that helps move the paste along the
stope to where it is needed.
If the available pump pressure and gravity are
not enough to do the job, some additional
motive force must be used – generally, an
underground booster pump. While using these
pumps may sometimes be unavoidable, it’s
important to understand the difficulties that
they cause:
n Paste pumping is expensive, in part because
positive displacement pumps are needed,
and these have high capital and operating
costs – capital expenditures may rise by 12%
to 15%, and operating expenses increase by
10% for the overall paste delivery system
n A large excavation is needed for the pumps
and power packs – and factors including
excavation span and ground support must be
considered
n Compressed air is needed to help flush the
delivery pipes, requiring additional
compressed air and receiver capacity
n The pumps often need more than 1
MW of power, a significant load
for any underground
operation, and the pump is
often located deep inside the
mine, calling for lengthy
cabling
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P12 International Mining | JUNE 2017 Supplement
n The heat generated by the pumps and
compressors must be dissipated
n Additional skilled labour is needed for pump
operation and maintenance
n Process control and instrumentation is critical
to ensure that there are no stoppages, which
could cause overflows at the booster station
and production delays affecting the whole
mine.
For these reasons, and because of the critical
importance of paste backfill to today’s mining
operations, it is increasingly important to design
mines in a way that paste can be deposited
without relying on underground pumps. Here
are some success factors for making that happen:
n Mine designers should work closely with
pastefill practitioners to design mines that
are efficient and effective for ore extraction,
as well as for paste backfill. Ideally, the paste
can be fed into a borehole or pipe on surface,
and the force of gravity alone will be enough
to ensure that the paste gets to where it is
needed.
n The paste reticulation system should be
designed to cascade through the mine,
increasing the pressure gradient at the base of an
internal borehole, and that kinetic energy moves
the paste along the horizontal section.
n Be careful to ensure a good balance between
the pipe diameter and the flow velocity, to
ensure that high velocities do not increase
the pressure gradient, while also delivering
the required paste quantity.
n Paste systems should be designed for the
shortest route from the surface to the stope.
n Use boreholes where possible, and avoid
running pipelines along ramps, because the
long pipe lengths often negate the gradient
advantage. Also, the high pressures in paste
pipelines mean that ruptures caused by
vehicles can have serious consequences.
Where it is not possible to eliminate the need
for booster pumps through improved mine a nd
reticulation design, rheology modifiers may be
able to improve the flow regime. Although they
can be expensive, they can be added on surface
to the paste in order to reach especially
problematic stope locations.
In short, while underground booster pumps
can increase the reticulation capability in a
mine, it may be better to take steps to avoid
their use. IM
llustration of an underground
booster station layout