The size of the floccules is shown in both size
and colour. The increase in velocity seemed to
have a greater effect on the open-with-shelf
feedwell than on the closed feedwell. The
floccule size distribution inside either of these
two general feedwell types has wide
distribution with large and small floccules’. The
floccules size distribution exiting the closed
feedwell has a lack of larger floccules. The
open-with-shelf feedwell shows large floccules
generally only under the shelf. The study
confirms the importance of proper mixing for
floccules generation and that the mixing is
supplied by the feed velocity. It also shows that
there can be too much of a good thing, in that
shear will break the floccules with excess feed
velocity.
A new type of feedwell design
The patented WesTech EvenFlo™ design uses
an inner feedwell that communicates with an
outer feedwell through ports that direct the feed
flow radially out towards the outer feedwell
wall. This simple addition to an open-with-shelf
feedwell has been shown to provide great
benefits in correcting the shortcomings
discussed.
The feed flow energy is dissipated and
converted to radial flow out of the inner
feedwell. The inner feedwell ports are sized to
have the design exit velocity for the range of
feed volumetric flow rate experienced at the
thickener. The fact that the feed into the outer
feedwell is directed radially provides a large
volume with optimal mixing within the feedwell.
The exit velocity from the inner feedwell is
designed to be at the 1.0 - 2.5 m/s range.
AMIRA conducted a CFD study of this two
stage feedwell, similar to that reported in their
P266 project. The design tested was for a 14.5 m
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Minerals
Two stage feedwell floccule generation over range of feed velocity
feedwell in a 100 m high rate
thickener. The inner feedwell
diameter is about 8.5 m. The flow
rate was varied from 9,000 to 17,000
m 3 /h. The study included
determining the solids distribution,
the vertical element of the flow
velocity