AN IMPROVED FEED WELL AND METHOD FOR HANDLING OF FINES IN A
CLARIFIER
FIELD OF INVENTION
The present invention deals with an improved clarifier feed well for use in fine handling
clarification / thickening units in coal washeries. More particularly the present invention
deals with a modified design of the clarifier feedwell and the method of settling of fines in
the clarifier introduced through the said feed well which includes reducing apparent
horizontal velocity and hindered settling through proper flow distribution.
BACKGROUND ART
It is known to crush, classify and sort raw coal mine products in order to impart properties
rendering the products suitable for use or further processing. In coal mining, the raw
extracted material is usually sorted by gravity, at different densities into pure coal,
intermediate material and dirt. This is followed by further preparation and sorting,
particularly for the fine-grain particles of the material, by flotation or else by suitable
combinations of gravity sorting and floatation. Coal mining products which undergo
commercial application comprise particles with a size tip to about 0.75mm. The finer
material, regardless of its composition, is conveyed as washery water containing solids
for wastewater clarification. At this later stage the solids undergo sedimentation in
clarification tanks or other suitable units in order to recover the water-, while a certain
proportion of the washery water is returned to the water circuit after the sedimentation of
the fine particles the tank residues so far presented poses serious problem owing to the
impossibility of utilizing them. With residual water content, these slurries or slimes with
their still considerable proportion of combustible constituents minerally have to be
deposited and special processes are then required to render them stable. On large
dumps or so-called spoil banks special basins are provided in which the flotation waste
and similar fine-grained material from the earlier treatment can be deposited. These

dumps then have to be covered over, and in order to ensure the required stability such
spoil banks and dumps basins of this kind have to be situated a sufficient distance apart.
It is well known that the washing of coal involves the production of aqueous effluents
containing unwanted mineral particles in suspension. These particles must be removed
before the aqueous medium in which they are suspended can be re-used or even
discarded into sewers or water courses; it has been customary to remove these particles
by settling and decantation since much of the unwanted mineral matter in suspension is
of a clay-like character, such settling is slow. In recent years it has been customary to
accelerate the settling by adding to the effluent substances which will bring about
coagulation of the finely divided mineral particles. Various substances have been used
or proposed for use in this way including alginates, salts of polyvalent metals, polyacrylic
acid and polyacrylic acid derivatives.
Captive coal washery of Durgapur Steel Plant was installed to supply washed cleans for
coke making as per Blast Furnace (BF) requirements. Since most of the coking coal was
being imported, the washery had started treating mostly non-coking coal at the time of
study. This had changed the nature of the feed and consequently the load on fine coal
circuit had increased from about 10% earlier (design parameter of the unit for treating
domestic coking coal) to more than 25%. Desired level of suspended solids ( microfines )
in clarifier overflow is 100 mg/l for recycling of water. Overloading of fines circuit
adversely affected efficiency of the clarifier resulting in high level of suspended solids
content in the overflow, which was consistently more than 2500 mg/l and was often more
than 5000 mg/l at the time of study. Laboratory scale experiments in simulated process
conditions and plant scale trials were conducted to study the effect of physical and
chemical processes and parameters and their combinations in reducing suspended solids
in clarifier overflow. Plant data and laboratory test at various dilution level showed that
the slurry showed linear settling characteristics. At lower solid fraction level, particles
settle faster; however at higher solid fraction level hindered settling takes place. A
number of flocculent were tried and it was concluded that it is not possible to significantly
improve system efficiency by using more / better flocculants.

Based on experimental results and theoretical considerations, design modifications were
made in the feed distribution plate and horizontal distribution pipes of feed well. A new
dosing regime was also introduced in the entry zone of clarifier feedwell. This had
resulted in reduction in Total Suspended Solids (TSS) content from more than 2000 mg/l
to upto 200 mg/l in clarifier overflow.
SUMMARY OF THE INVENTION
Therefore such as herein described there is provided an improved feed well for use in a
clarifier/ thickener comprising of: an inlet feed pipe configured for easy entrance of the
feed material in the feed well; a feed distribution plate designed for inducing a plurality of
vertical settling zones; modified horizontal distribution pipes through which the flocculated
feed is removed by physico-mechanical transference followed by non-reactive solid-liquid
separation principles from the feed well; a plurality of compartments / settling zones into
which the flocculated feed is delivered and in compartments the flocculated feed is
frothed or mixed with other matter and from which zone the slurry is removed by
mechanical transference to a point outside the feed well, provided that solid product of
separation is collected and removed and that the feed well is so arranged and
constructed that it has constant liquid level, and the liquid product of separation is
removed either as filtrate or partially clarified overflow or both.
In addition there is also disclosed a method of treating fines in the feed well of a clarifier/
thickener wherein the incoming feed is separated into liquid and solid products in an
feedwell comprising the steps of:- catching of the incoming feed; slowing down the
momentum of the incoming feed by restricting the feed distribution angle; distributing the
incoming feed evenly across the settling tank evenly; flocculating the incoming feed
chemically which aids settling; removing the settled solids from the plurality of
compartments / settling zones provided by mechanical transference to a point outside the
feed well and providing a constant liquid level wherein the liquid product of separation is
removed as clarified overflow.

A general object of the invention is to provide an improved process for treatment of fines
in a clarifier that reduces floatation wastage and reduce suspended solids in the clarifier .
As per an exemplary embodiment of the present invention, the feed distribution angles of
the feedwell were set at 45° to reduce the apparent horizontal velocity.
Another exemplary embodiment of the present invention is to provide multiple settling
zones, which were induced through uniformly distributed circular openings in feed
distribution plate to reduce hindered settling of particles and improve particle distribution.
Still other advantages, however, are obtained by the construction of the feedwell, which is
made simple and cheap, the power consumption is nil, the reliability is high, moving parts
are not present, few workmen are required for supervision, the control may he effected
automatically Furthermore there is an enormous saving in space by the application of the
improved design in order to obtain the improved output.
Yet another exemplary embodiment of the present invention is introduction of a chemical
dosing circuit wherein i) the energy consumption was reduced by changing the flow
requirement of dosing liquid from bottom-up to top down ii) introduction of multi-point
dosing for improved homogenization / mixing and iii) introduction of system for efficient
mixing and variability of flocculent concentration based on variability of inlet feed
strength.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Fig 1 illustrates existing system of feed distribution through feed well in accordance with
the present invention.
Fig 2 illustrates the modified system of feed distribution through feed well in accordance
with the present invention

Fig 3 illustrates the modified system (exploded bottom view) of feed distribution through
feed well in accordance with the present invention
Fig 4 illustrates a graph showing suspended solids in overflow in the modified system of
feed distribution through feed well in accordance with the present invention.
DETAILED DESCRIPTION
Therefore in order to enhance the effects of the basic functions of the clarifier feedwell,
there is an urgent need for modification of the basic design of the feed well as shown in
Fig 1 (prior art).The process is carried out with an installation of the disclosed improved
feed well with a feed pipe leading into the solids entry is provided for pre-treatment. The
structure of the feed well is redesigned for the efficient use of each of the corners and the
drawbacks as discussed in the prior art. The feed well comprises of a plurality of settling
zones, induced in the feed distribution plate. The multiple settling zones are configured to
reduce the effect of hindered settling caused due to continuous feed entry from the inlet
feed pipe. This installation according to the invention thus subdivides the treatment
product between multiple treatments stages which are nevertheless recombined later.
The flotation wastage concerned here and suspended solids level in clarifier overflow is
minimum.
The primary function of thickening is to increase the concentration of suspended solids in
a feed stream, while that of clarification is to remove a relatively small quantity of
suspended particles and produce a clear effluent. These two functions are similar and
occur simultaneously. The terminology merely makes a distinction between primary
process results desired. Generally thickener mechanisms are designed for a heavier duty
requirements imposed by a large quantity of relatively concentrated pulp, while clarifiers
usually include features that ensure essentially complete suspended solids removal (as in
the present case), such as greater depth, special provision for coagulation or flocculation
of the feed suspension and greater overflow weir length.

A larger area may be desirable to minimize removal of fine particles that escape the
settling suspension. In the thickening region, both solids and some of the liquid moves
towards the underflow. Since the solids in the underflow contain less water than in the
settling zone above, the liquid velocity is less than solids velocity. The solids settle past
the water at a differential rate that is sufficient to bring them from the feed concentration
to the underflow concentration. The solids handling capacity of a continuous clarifier
generally passes through a minimum at some point between the feed and underflow
concentration. If the settling rate of solids relative to fluid is not large enough to transmit
the solids reaching the limiting zone, then the solids will build up and overflow. The
thickening capacity is controlled by the area needed to pass the solids through the
limiting zone.
A clarifier feedwell has maximum six functions to fulfill depending on process conditions
which are to dissipate the energy of the incoming feed, introduce dilution water to achieve
the optimal density in the feed well for flocculation of the solids, deaerate the incoming
feed, mix the flocculent into the incoming feed, retain feed in the feedwell whilst dilution
and flocculation occur, and distribute the flocculated material evenly over the clarifier
diameter. Optimising these tasks in a single chamber is at times difficult.
For complete or almost complete recyclability of the clarifier feedwell overflow the
invention provides that the clarifier incoporates a redesigned feed distribution plate, so
that the end product then accordingly provided is largely devoid of fines. The water loss is
thus reduced to a minimum. The time for which the product remains in the clarifier is also
reduced to such an extent that evaporation losses in self-contained clarifiers are kept
within limits.
The disclosed feedwell is modified herein for the functions of dissipation of energy of the
incoming feed, achieving of optimal density for distribution of feed, distribution of feed
material evenly over clarifier. Therefore the design modifications have been made in the
feed distribution plate and feed well with the objective of reducing apparent horizontal
velocity as well as reduce hindered settling through proper flow distribution. This has

been done with the scientific objective of reducing hindered settling regimes through
introduction of zones of normal settling regions within the hindered settling regimes as
shown in Fig 2 and 3.
Conventional clarifier feed well could not handle high solid fraction slurry. The disclosure
leads to performance improvement within the same physical space without any need of
retrofitting or additional capital investment. The improved design has been based on
analytical / semi-quantitative application of physico-chemical principles. The improved
design has lead to more than 500% efficiency improvement of the clarifier. The
innovation provides flexibility of clarifier/thickener application.
Referring now to FIG. 3, and further as per one of the embodiment of the present
invention which includes introduction of a chemical dosing circuit wherein a flocculent is
first introduced into a partially water-filled mixing chamber having stationary flow dividing
and mixing elements. Other apparatus such as homogenizing valves or mechanical
mixers may be used as well. The flocculent stream is then introduced to feed well for
futher mixing with a waste water stream containing coal particles and inorganic mineral
constituents in suspension. In addition the energy consumption was reduced by
changing the flow requirement of dosing liquid from bottom-up to top down and further
the introduction of multi-point dosing for improved homogenization / mixing and the
introduction of system for efficient mixing and variability of flocculent concentration based
on variability of inlet feed strength.
Consequently, coal particles are agglomerated into larger masses and treated slurry is
then passed to feed distribution plate wherein agglomerated coal particles are removed
from the other slurry constituents since_an important part of the clarifier feedwell is always
destined for the separation or concentration (thickening) of suspensions.
Other methods of dealing with tailings exist, in particular the use of "deep-cones", in
which the underflow from the froth cells, i.e., the tailings suspension, is thickened in
batteries of tall narrow conical vessels. These use poly-electrolyte flocculants to provide

very rapid "knock-down" of the suspended fine particles. The thickened tailings are
continuously extracted from the base of the cones, while clean water is continuously
spilled over the tops for return to the washery plant. The moisture content of the
thickened tailings produced is about 45% on a total weight basis and they are usually too
wet to be disposed of to tip along with the coarse discard unless further treatment is
given to them, for example stabilisation by the addition of a small proportion of Ordinary
Portland Cement.
Although the foregoing description of the present invention has been shown and
described with reference to particular embodiments and applications thereof, it has
been presented for purposes of illustration and description and is not intended to be
exhaustive or to limit the invention to the particular embodiments and applications
disclosed. It will be apparent to those having ordinary skill in the art that a number of
changes, modifications, variations, or alterations to the invention as described herein
may be made, none of which depart from the spirit or scope of the present invention.
The particular embodiments and applications were chosen and described to provide the
best illustration of the principles of the invention and its practical application to thereby
enable one of ordinary skill in the art to utilize the invention in various embodiments and
with various modifications as are suited to the particular use contemplated. All such
changes, modifications, variations, and alterations should therefore be seen as being
within the scope of the present invention as determined by the appended claims when
interpreted in accordance with the breadth to which they are fairly, legally, and equitably
entitled.

We Claim:
1. A feed well for use in clarifiers whereby the input feed is separated into liquid and
solid products comprising of:-
an inlet feed pipe configured for easy entrance of the feed material in the feed
well;
a feed distribution plate designed for inducing a plurality of vertical settling zones;
modified horizontal distribution pipes through which the flocculated feed is
removed by physico-mechanical transference followed by non-reactive solid-liquid
separation principles from the feed well.
a plurality of compartments / settling zones into which the flocculated feed is
delivered and in compartments the flocculated feed is frothed or mixed with other
matter and from which zone the slurry is removed by mechanical transference to a
point outside the feed well, provided that solid product of separation is collected
and removed and that the feed well is so arranged and constructed that it has
constant liquid level, and the liquid product of separation is removed either as
filtrate or partially clarified overflow or both.
2. A feed well for use in clarifiers as claimed in claim 1, wherein the feed distribution
angles were set at 45° to reduce the apparent horizontal velocity.
3. A feed well for use in clarifiers as claimed in claim 1, wherein the multiple settling
zones were induced in feed distribution plate to reduce hindered settling of
particles and improve particle distribution.
5. A feed well for use in clarifiers as claimed in claim 1, wherein the feedwell further
comprises of a horizontal, but angled, vanes, which creates two zones within the
feedwell, one for momentum dissipation and the other for maximizing vertical
settling rate.

6. A method of handing fines in a feed well for use in a clarifier wherein the incoming
feed is separated into liquid and solid products comprising the steps of:-
catching of the incoming feed;
slowing down the momentum of the incoming feed by restricting the feed
distribution angle;
distributing the incoming feed evenly across the settling tank evenly;
flocculating the incoming feed chemically which aids settling;
removing the settled solids from the plurality of compartments / setlling zones
provided by mechanical transference to a point outside the feed well;
7. A method of handling of fines in feed well of a clarifier as claimed in claim 6
wherein the feed distribution angles were set at 45° to reduce the apparent
horizontal velocity.
8. A method of handling of fines in feed well of a clarifier as claimed in claim 6
wherein the multiple settling zones were induced in feed distribution plate to
reduce hindered settling of particles and improve particle distribution.
9. A method of introducing flocculating chemicals in inlet stream of feedwell wherein
the incoming feed is separated into liquid and solid products comprising the steps
of:-
reducing the energy consumption by changing the flow requirement of dosing
liquid from bottom-up to top down
multi-point dosing for improved homozenisation / mixing and
mixing efficiently through variation of flocculent concentration based on variability
of inlet feed strength.

The present invention relates to A feed well for use in clarifiers whereby the input
feed is separated into liquid and solid products comprising of an inlet feed pipe
configured for easy entrance of the feed material in the feed well; a feed
distribution plate designed for inducing a plurality of vertical settling zones;
modified horizontal distribution pipes through which the flocculated feed is
removed by physico-mechanical transference followed by non-reactive solid-liquid
separation principles from the feed well; a plurality of compartments / settling
zones into which the flocculated feed is delivered and in compartments the
flocculated feed is frothed or mixed with other matter and from which zone the
slurry is removed by mechanical transference to a point outside the feed well,
provided that solid product of separation is collected and removed and that the
feed well is so arranged and constructed that it has constant liquid level, and the
liquid product of separation is removed either as filtrate or partially clarified
overflow or both, and a method of handing fines in a feed well for use in a clarifier.