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Diagram of a hydrocyclone:
1. the liquid-solid mixture enters, 2. heavy solids leave, 3. cleaned liquid leaves. |
A hydrocyclone is
a device to classify, separate or sort particles in a liquid suspension based
on the densities of the particles.
A hydrocyclone may
be used to separate solids from liquids or to separate liquids of different
density.
A hydrocyclone
will normally have a cylindrical section at the top where liquid is being fed tangentially, and a conical base.
The angle, and
hence length of the conical section, plays a role in determining operating
characteristics.
Design
A hydrocyclone has
two exits on the axis: the smaller on the bottom (underflow or reject) and a larger at the top (overflow or accept).
The underflow is
generally the denser or thicker fraction, while the overflow is the lighter or
more fluid fraction.
Internally,
centrifugal force is countered by the resistance of the liquid, with the effect
that larger or denser particles are transported to the wall for eventual exit
at the reject side with a limited amount of liquid.
The finer, or less
dense particles, remain in the liquid and exit at the overflow side through a
tube extending slightly into the body of the cyclone at the center.
Forward
hydrocyclones remove particles that are denser than the surrounding fluid.
Reverse
hydrocyclones remove particles that are less dense than the surrounding fluid. In
a reverse hydrocyclone, the overflow is at the apex and the underflow at the
base.
There are also
parallel-flow hydrocyclones where both the accept and reject are removed at the apex. Parallel-flow hydrocyclones remove particles
that are lighter than the surround fluid.
Hydrocyclones can
be made of metal (mostly steel), ceramic
or plastic (such as polyurethane, polypropylene, or other types).
Metal or ceramic
hydrocyclones are used for situations requiring more strength, or durability in
terms of heat or pressure.
When there is an
occurrence of much abrasion (such
as occurs with sand particles) polyurethane performs
better than metals or ceramics.
Metal lined with
polyurethane is used in cases of combined abrasion and high pressure.
In a suspension of
particles with the same density, a relatively sharp cut can be made. The size
at which the particles separate is a function of cyclone diameter, exit
dimensions, feed pressure and the relative characteristics of the particles and
the liquid.
Efficiency of
separation is a function of the solids' concentration: the higher the
concentration, the lower the efficiency of separation.
There is also a
significant difference in suspension density between the base exit (fines) and
the apex exit, where there is little liquid flow.
If the size range
of the particles is limited, but there are differences in density between types
of particles, the denser particles will exit preferentially at the apex.
The device is
therefore a means of selective concentration of, for example, minerals.
This device is
also related to the centrifuge; both of them are intended to separate
heavies and lights in liquid by application of centrifugal force.
Uses
A hydrocyclone is
most often used to separate "heavies" from a liquid mixture
originating at a centrifugal pump or some other continuous source of
pressurized liquid.
A hydrocyclone is
most likely to be the right choice for processes where "lights" are
the greater part of the mixture and where the "heavies" settle fairly
easily.
Generally,
hydrocyclones are used in continuous flow systems so that the instantaneous
liquid inflow to the hydrocyclone is equal to the total instantaneous outflow
of "lights" plus "heavies".
In cases where
"heavies" are a very small part of the whole liquid, it is sometimes
advantageous to accumulate them in the bottom of the hydrocyclone for batchwise
removal.
Applications include:
§ In pulp and paper mills to
remove sand, staples, plastic particles and other contaminants.
§ In the drilling industry to
separate sand from the expensive clay that is used for lubrication during the
drilling.
§ In industry to separate oil
from water or vice versa.
§ In metal working to
separate metal particles from cooling liquid.
§ In potato processing plants
to recover starch from waste water.
§ In the mining industry to
separate coarse tailings from the fine fraction to obtain good material
for tailings dam construction.
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| GS Series Submersible Pump |
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| Desander & desilter hydrocyclone |
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