and is fitted with a Perspex ® cylinder directing
the hydrated polymer into the first dissolution
tank of the polymer train.
In regions where water sources contain high
fractions of colloids or solvents an additional
spray bar is installed in the first two chambers
of the dissolution tank to suppress any foaming,
which could potentially lead to spillages and
polymer wastage.
Polymer off-loading facility Polymer dissolution
propriety wetting apparatus which initiates the
hydration and dissolution process of the polymer.
The JWH is located in the initial compartments
of the dissolution trains. The correct operation of
the wetting apparatus is key to the operation of
the plant and can only be achieved with tight
control of the flow rate and pressure of water Each compartment in the dissolution tank is
equipped with a low shear agitator specifically
designed to effectively mix the concentrated
polymer avoiding shearing of the polymer
chains. The agitators in the first two
compartments are designed to not only
accelerate the dissolution of the polymer in
solution but also to mitigate any foam formation
produced during the hydration stage in the JWH.
Furthermore, the agitators are designed in such
a manner as to degas the solution. Gas pockets
in long transfer lines need to be avoided as they
can upset the dosing control and application of
the polymer into the slurry to be t reated.
The tank compartments are all arranged in a
horizontal under/over flow arrangement, ensuring
that the most aged dissolved polymer is first
removed from the tank. Furthermore, this type of
flow arrangement ensures that the hydrated
polymer powder is drawn into solution, without by-
passing further downstream. Square tanks were
chosen mainly for their modularisation ability with
the tanks having the capability to be fully drained
for winterisation purposes, if required.
Polymer wetting system
Polymer viscosity
feeding the unit. The water to powder dosing
ratio is under strict process control to optimally
run the plant, with the metered water flow
directing the screw feeder rate to meet the
polymer concentration set point.
The JWH units ensure that polymer powder is
properly hydrated and avoids the formation of
un-wetted polymer and in turn the presence of
fisheyes in solution. The JWH consists of an
arrangement of specially designed nozzles to
provide an effective spray that can handle
process or contaminated water containing
particulate matter of up to 5 mm. The unit is of
static operation and therefore low maintenance
Typical screw feeder calibration graph
Another important component of the process is
knowing the polymer design viscosity which
impacts the hydraulic profile in the dissolution
tank. This needs to be considered for plant
control purposes as significant time delays can
be experienced from when a change is initiated
to when the change is realised.
There are several factors that influence the
viscosity of a polymer solution including
molecular weight, concentration, temperature,
and the nature of the process water. For this
reason, as part of the design process for the
polymer plant it is important to run a series of
laboratory tests on selected polymer samples
exposed to differing conditions, allowing a
viscosity profile to be prepared.
Using such information, we can define an
optimal operating range for viscosity, however,
with the variable day to day conditions
experienced in plant processes, it is always a
requirement to build in a good safety factor,
and therefore in this case with the plant
having multiple agitators across the chambers,
these can be turned on and off as required.
Typical viscosity profile of various polymer
solutions
Based on a standard design of 2.0 Pa-s,
polymer concentrations can be increased to
meet the viscosity target, ultimately reducing
the hydration water requirement and flow
requirement when compared with lower polymer
concentrations. Where batch units are considered,
polymer viscosity can also hamper transfer times
from hydration tank to storage tank, adding an
additional 10-15 min onto cycle times while relying
on a single critical component ie transfer pump.
Polymer solution dosing
Progressive cavity dosing pumps fitted with
pressure relief valves and accurate flow
measurement are the preferred and selected
method to dose the polymer solution to the
field. When designing for the selected pump,
the operator will provide the appropriate data
and information allowing for the pump
calculations to be completed in-house and then
reviewed and confirmed by the pump manufacturer.
The pump skids are designed as a duty/
stand-by system that are easy to change over
and strip out for repair or replacement. The
selected pumps are low shear to avoid polymer
chain breakage and can be available to meet
high flow rates (<150 m 3 /hr) and high discharge
pressure (<3,000 kPa).
For applications where low environmental
temperatures prevail all pipes can be fully drained
for winterisation and an allowance can be made
for a system to displace the polymer solution in
the pumps with a low freezing point fluid.
Ancillary system components
The modular polymer plant has many other
components which complete the design and
processing system.
Typical modular plant polymer dosing pump
system
JUNE 2017 Supplement | International Mining P5