Note: Descriptions are shown in the official language in which they were submitted.
CA 02607372 2011-02-03
THICKENER/CLARIFIER FEEDWELL ASSEMBLY WITH FROTH DISSIPATION
BACKGROUND OF THE INVENTION
This invention relates to thickener/clarifier tanks used to separate liquid
and solids
components of an influent feed slurry and specifically relates to feedwell
apparatus employed in
such thickener/clarifiers to enhance the clarification process.
Thickener/clarifier tanks are used in a wide variety of industries to separate
influent feed
slurry comprising a solids- or particulate-containing fluid to produce a
"clarified" liquid phase
having a lower concentration of solids than the influent feed slurry and an
underflow stream
having a higher concentration of solids than the influent feed slurry.
Thickener/clarifier tanks
conventionally comprise a tank having a floor and a continuous wall, which
define a volume
within which the clarification process takes place. Thickener/clarifier tanks
also include an
influent feed pipe for delivering influent feed to the tank, an underflow
outlet for removing
settled solids from the tank and a fluid discharge outlet for directing
clarified liquid away from
the tank. Thickener/clarifier tanks may also include a rake assembly having
rake arms for
sweeping along the floor of the tank, and may include an overflow launder or
bustle pipe for
collecting clarified liquid near the top of the tank.
Thickener/clarifier tanks of the type described operate by introducing an
influent feed
stream into the volume of the tank where the influent is retained for a period
long enough to
permit the solids to settle out by gravity from the fluid. The solids that
settle to the bottom of the
tank produce a sludge bed near the bottom of the tank, which is removed
through the underflow
outlet. Clarified liquid is formed at or near the top of the
thickener/clarifier tank and is directed
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away from the tank for further processing or disposal. Settling of solids may
be enhanced in
some applications by the addition of a flocculent or polymer that forms
agglomerates that settle
more readily. In many applications, an objective of fluid clarification is to
enhance the settling
process to achieve a high throughput of solids, and thereby enhance solids
recovery.
Many thickener/clarifier tanks are constructed with a feedwell, usually
centrally located
within the tank, into which the influent feed stream is delivered. The
feedwell generally serves
the purpose of reducing the fluid velocity of the incoming influent feed
stream so that the energy
in the stream may be dissipated to some degree before entering the tank.
Dissipation of energy
in the influent feed stream lessens the disruptive effect that the incoming
influent feed has on the
settling rate of the solids in the tank. In other words, introduction into a
thickener/clarifier of an
influent feed stream under high fluid velocity tends to cause turbulence in
the tank and
compromises the settling rate of solids. A feedwell maybe structured in a
variety of ways,
therefore, to create or enhance dissipation of energy in the influent feed.
For example, the
feedwell and influent feed pipe may be structured to introduce influent feed
to the feedwell at
two opposing directions and into an annular space, such as is disclosed in
U.S. Pat. No.
4,278,541 to Eis, et al.
Froth and/or air in a thickener/clarifier feed stream in existing methods of
feedwell entry
unavoidably contacts the flocculent and results in air being locked into the
flocculated solids
structure. This material then is slow to settle and is more persistent on the
tank surface with
resultant loss of solids to overflow and poor settling efficiency.
OBJECTS OF THE INVENTION
It is an object of the present invention to provide an improved feedwell
assembly for
thickener/clarifiers.
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A more specific object of the present invention is to provide a feedwell
assembly wherein
the incidence of froth or air in a thickener/clarifier feed stream is reduced.
An even more specific object of the present invention is to provide a feedwell
assembly
wherein the incidence of froth or air in a thickener/clarifier feed stream is
reduced prior to
contact of the feed stream with a flocculent.
Yet another object of the present invention is to provide such a feedwell
assembly
wherein froth and air reduction is accomplished inexpensively and simply.
These and other objects of the present invention will be apparent from the
drawings and
description herein. Although every object of the invention is believed to be
attained by at least
one embodiment of the invention, there is not necessarily any one embodiment
of the invention
that achieves all of the objects of the invention.
SUMMARY OF THE INVENTION
A feedwell assembly for a thickener/clarifier comprises, in accordance with
the present
invention, a feedwell body, at least one feed channel connected at a
downstream end to the body,
and a plate member disposed in the feed channel for separating froth from an
incoming slurry
stream. Optionally a liquid spray directed onto the plate member may dissipate
the separated
froth.
The plate member may be one flat, substantially horizontal or inclined plate
section or
take the particular form of a plurality of planar plate sections. The plate
member may include an
upstream portion that may incline upwardly from an upstream end of the plate
member and may
further include a downstream portion inclined downwardly from a downstream end
of the
upstream portion. The plate member has a leading edge that is disposed at a
froth-liquid
interface.
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In one embodiment of the present invention, the upstream portion and the
downstream
portion of the plate member meet along an elongate joint. At least one spray
nozzle may be
disposed so as to direct a liquid spray onto at least a portion of the plate
member in a region
about the joint.
A feedwell assembly for a thickener/clarifier more particularly comprises, in
accordance
with the present invention, (i) a feedwell body, (ii) a pair of infeed pipes
connected at
downstream ends to the body at locations spaced longitudinally and
circumferentially along the
body, (iii) a launder header, the infeed pipes being connected at upstream
ends to the header, and
(iv) a plate member disposed in the header so that an upstream end of the
plate member is
disposed approximately at a froth-liquid interface.
Optionally, at least a portion of the plate member is disposed above the
liquid level. In
that case, the plate member may have an upstream portion that is upwardly
inclined from the
froth-liquid interface, proceeding in a downstream direction. The inclined
upstream portion may
be a planar plate section. A second plate section, exemplarily planar, may
extend from a
downstream end or edge of the inclined upstream portion. The second plate
section may extend
downwardly.
The separated froth on the plate member naturally dissipates or collapses on
its own.
However, at least one spray nozzle may be disposed for directing a liquid
spray onto at least a
portion of the plate member to knock down or further dissipate froth thereon.
Where the plate member includes an upstream plate section inclined upwardly
from the
upstream end of the plate member and a downstream plate section inclined
downwardly from a
downstream end of the upstream portion, the plate sections meet along an
elongate joint, with the
at least one spray nozzle being disposed so as to direct a liquid spray onto
at least a portion of the
plate member in a region about the joint. The feedwell body may include a
lower portion and an
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upper portion, where the upper portion has a larger transverse dimension
(e.g., diameter) that the
lower portion. In that case the infeed pipes are connected to the lower
portion, while the plate
member extends to the upper portion.
A method for reducing froth and air fed to a feedwell in a thickener/clarifier
comprises, in
accordance with the present invention, (a) disposing, in a feed channel or
launder header, a plate
member in a position and orientation for separating froth from an incoming
slurry stream, (b)
attaching the plate member in the position to the feed channel or launder
header, and (c)
diverting froth from along an upper surface of the slurry onto the plate
member, while feeding
the slurry separated from the froth through the feedwell feed pipe.
The method may further comprise disposing at least one spray nozzle above the
plate
member, and ejecting a spray from the nozzle onto the froth on at least a
portion of the plate
member, thereby collapsing the froth into solids and liquid components and
releasing air
entrapped in the froth. The separated and collapsed froth may be guided to a
feedwell body.
Where the feedwell body includes a lower portion and an upper portion, the
feed pipe may
extend to the lower portion, while the plate member extends to the upper
portion. The disposing
of the plate member may include positioning the plate member so that an
upstream end of the
plate member is disposed at or below an operational liquid level in the feed
channel or launder
header and so that at least a portion of the plate member is disposed above
the liquid level.
The disposing of the plate member may further include positioning the plate
member so
that an upstream portion is inclined upwardly from the upstream end of the
plate member and a
downstream portion of the plate member is inclined downwardly from a
downstream end of the
upstream portion.
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Where the upstream portion and the downstream portion of the plate member meet
along
an elongate joint, the disposing of the spray nozzle may includes positioning
the spray nozzle so
as to enable a directing a liquid spray onto the plate member in a region
about the joint.
BRIEF DESCRIPTION OF THE DRAWING
FIG. 1 is a partial top plan view of a feedwell for a thickener/clarifier, in
accordance with
the present invention.
FIG. 2 is a side elevational view of the feedwell of FIG. 1.
FIG. 3 is a partial top plan view of another feedwell for a
thickener/clarifier, in
accordance with the present invention.
FIG. 4 is an elevational view taken from one side of the feedwell of FIG. 3,
in the
direction of arrow IV.
FIG. 5 is an elevational view taken from an opposite side of the feedwell of
FIG. 3, in the
direction of arrow V.
DETAILED DESCRIPTION
As shown in FIGS. I and 2, a feedwell assembly 12 for a thickener/clarifier
comprises a
cylindrical feedwell body 14, a pair of feed pipes 16 and 18 each connected at
a downstream end
to the body, the feed pipes extending from a feed launder or channel 20, and a
plate member 22
disposed at least partially upstream of the feed pipes 16 and 18 for
separating froth from an
incoming slurry stream guided along feed launder or channel 20. A liquid spray
directed onto
the plate member by one or more spray nozzles 26 disposed generally above the
plate member
can dissipate the froth separated by plate member 22.
Feed pipes 16 and 18 each include an angled upstream inlet portion 28 and 30
connected
to launder or channel 20 in a region about plate member 22. Feed pipes 16 and
18 each further
include a substantially horizontal inlet portion 32 and 34 connected to the
respective upstream
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portion 28 and 30 and extending to feedwell body 14. Horizontal inlet portions
32 and 34 are
connected to feedwell body 14 on opposite sides thereof and at staggered
elevations, so that
slurry enters the feedwell body 14 from feed pipes 16 and 18 traveling in
opposed
circumferential directions in vertically spaced planes P 1 and P2.
Feedwell assembly 12 further includes a triumvirate of flocculent feed pipes
36, 38, 40
extending from a vertical manifold pipe 42 inwardly to feedwell body 14 along
a common plane
P3 sandwiched between slurry infeed planes P 1 and P2.
Plate member 22 includes an upstream portion 44 inclined upwardly from an
upstream
end of the plate member and further includes a downstream portion 46 inclined
downwardly
from an elongate linear joint 48 at a downstream end of upstream portion 44.
Upstream portion
44 and downstream portion 46 take the particular form of planar plate
sections. Spray nozzles 26
are disposed so as to direct liquid spray onto plate member 22 in a region
about joint 48.
Accordingly, infeed pipes 16 and 18 are connected at downstream ends to
feedwell body
14 at locations spaced longitudinally and circumferentially along the body.
Plate member 22 is
more particularly located in a launder header 50, the infeed pipes 16 and 18
being connected at
upstream ends to the header. Plate member 22 is disposed in header 50 so that
an upstream end
of the plate member is disposed at or below an operational liquid level 52 in
the header and so
that at least a portion of the plate member is disposed above the liquid
level. Spray nozzles 26
are disposed for directing a liquid spray onto that portion of plate member 22
above the liquid
level 52 to knock down or dissipate froth thereon.
Feedwell body 14 includes a lower portion 66 and an upper portion 68. Upper
portion 68
has a transverse dimension or diameter that is larger than the corresponding
transverse dimension
or diameter of lower portion 66, with an annular inclined shelf 70 being
provided between an
outer wall (not separately designated) of upper portion 68 and an outer wall
(not separately
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designated) of lower portion 66. This allows volume for the froth to
accumulate in the feedwell
14 so as to allow time for the froth to dissipate naturally or with sprays so
as to keep the froth
from escaping to the overflow. The expanded area of upper portion 68 provides
a containment
area (size can be designed based on perception of the problem) where froth can
be accumulated
and knocked down as required. The froth solids that leave this zone pass
through the floc
addition zone where they have an opportunity to be flocculated to further
enhance their settling.
This expanded zone with or without sprays is optional.
Infeed pipe sections 32 and 34 are connected to lower feedwell body portion
66, while
downstream portion 46 of plate member 22 extends to upper feedwell body
portion 68.
A related method for reducing froth and air fed to a feedwell in a
thickener/clarifier
comprises providing plate member 22 and disposing the plate member in feed
launder or channel
or launder header 50 at least partially upstream of one or more feedwell feed
pipes 16 and 18
in a position and orientation for separating froth from an incoming slurry
stream. Plate member
22 is attached in that position to feed launder or channel 20 or launder
header 50, spray nozzle(s)
15 26 being positioned above the plate member, particularly in an exposed
region of the plate
member. During operation of the feedwell assembly 12 (and the associated
thickener/clarifier),
slurry is directed into feed launder or channel 20 and, optionally, launder
header 50 so that froth
along an upper surface of the slurry is guided onto plate member 22. A spray
is ejected from
nozzle(s) 26 onto the froth on plate member 22, thereby collapsing the froth
into solids and
20 liquid components and releasing air entrapped in the froth. The slurry is
fed in together with the
solids and liquid components of the collapsed froth through the one or more
feedwell feed pipes
16 and 18.
Plate member 22 is positioned so that an upstream end of the plate member is
disposed at
or below an operational liquid level 52 in the feed launder or channel 20 or
launder header 50
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and so that at least a portion of the plate member is disposed above the
liquid level. Plate
member 22 is preferably positioned so that upstream portion 44 is inclined
upwardly from the
upstream end of the plate member and a downstream portion 46 of the plate
member is inclined
downwardly from a downstream end of the upstream portion.
Where upstream portion 44 and downstream portion 46 of plate member 22 meet
along
elongate joint 48, spray nozzle(s) 26 may be positioned so as to enable a
directing a liquid spray
onto the plate member in a region about the joint.
Launder or channel 20 is connected to header 50 along a joint 54 by a
plurality of bolts
and nuts 56. Launder or channel 20 is suspended from bridge girders 58 and 60
by cross support
angles 62 and threaded rods 64.
As depicted in FIGS. 3-5, another feedwell assembly 72 for a
thickener/clarifier
comprises a cylindrical feedwell body 74 and a pair of eductor feed channels
76 and 78 each
connected at a downstream end to the feedwell body. Feed channels 76 and 78
include open-top
inlet port sections 80 and 82 having converging walls (not separately
designated), open-top
middle sections 84 and 86 of reduced and uniform transverse cross-sectional
area, and outlet or
discharge sections 88 and 90 of diverging walls (not separately designated)
and concomitantly
increasing cross-sectional area.
Directional nozzles 92 and 94 of thickener feed pipes 96 and 98 are disposed
at least
partially within inlet port sections 80 and 82 of eductor feed channels 76 and
78. Feed channels
76 and 78 are located below the liquid level of the clarifier tank (not shown)
so that liquid at the
top of the clarifier tank is entrained to flow with the thickener feed stream
through eductor feed
channels 76 and 78 into feedwell body 74. As described in U.S. Patent No.
5,389,250, eductor
feed channels 76 and 78 function as jet pumps to educt previously clarified
liquor from the
clarifier tank of settling basin to dilute the influent feed stream.
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As depicted in FIGS. 4 and 5, middle sections 84 and 86 of eductor feed
channels 76 and
78 are oriented substantially horizontally, whereas outlet or discharge
sections 88 and 90 are
downwardly inclined and are provided at their downstream ends with
horizontally oriented end
portions 100 and 102 that are coupled to feedwell body 74 and serve as inlets
thereto. Inlet
portions 100 and 102 are connected to feedwell body 74 at staggered
elevations, inlet portion 102
being located below inlet portion 100, so that slurry enters the feedwell body
74 from feed
channels 76 and 78 traveling in opposed circumferential directions in
vertically spaced planes P4
and P5. In accommodating the different vertical heights of eductor end
portions 100 and 102,
middle section 84 of eductor feed channel 76 is longer than middle section 86
of eductor feed
channel 78, and discharge section 90 is longer than discharge section 88.
Eductor feed channels 76 and 78 are provided with respective froth-separation
plates 104
and 106 disposed at least partially upstream of inclined discharge sections 88
and 90 for
separating froth from incoming slurry (diluted thickener) streams guided along
middle sections
84 and 86 of the eductor feed channels. Nozzles (not shown) may direct liquid
spray onto plates
104 and 106 for dissipating the froth separated from the slurry streams by the
plate members.
Froth separation plates 104 and 106 each include a respective upwardly
inclined upstream
section 108 and 110 and a respective downwardly inclined downstream section
112 and 114.
Spray nozzles (not shown) may be provided in zones generally above linear
joints 116 and 118
between upwardly inclined upstream plate sections 108 and 110, on the one
side, and
downwardly inclined downstream plate sections 112 and 114, on the other side.
Downwardly
inclined downstream plate sections 112 and 114 extend to respective froth
inlets 120 and 122 to
feedwell body 74.
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At points below upwardly inclined upstream plate sections 108 and 110
discharge
sections 88 and 90 of eductor feed channels 76 and 78 have closed upper ends
so as to deflect the
slurry or diluted thickener streams downwardly towards inlet portions 100 and
102.
Feedwell assembly 72 further includes (A) a first flocculent feed pipe 124
extending to
inlet port sections 80 and 82 of eductor feed channels 76 and 78, (B) a second
flocculent feed
pipe 126 extending to middle sections 84 and 86 of eductor feed channels 76
and 78, (C) a third
flocculent feed pipe 128 extending to feedwell body 74, and (D) a fourth
flocculent feed pipe
130 extending to a clarifier feed pipe 132. As shown in FIG. 4, clarifier feed
pipe 132 extends to
a clarifier inlet port 134 on feedwell body 74.
Eductor feed channels 76 and 78 are connected at downstream ends to feedwell
body 74
at locations spaced longitudinally and circumferentially along the body. Froth
separation plates
104 and 106 are disposed in feed channels 76 and 78 so that upstream edges of
the plates are
disposed at or below operational liquid levels (slurry-froth interfaces) in
the feed channels and so
that at least a portion of each plate member 104 and 106 is disposed above the
respective liquid
level.
A method related to the apparatus of FIGS. 3-5 for reducing froth and air fed
to feedwell
72 in a thickener/clarifier (not shown) comprises providing plates 104 and 106
and disposing the
plates in feed channels 76 and 78 in positions and orientations for separating
froth from
incoming slurry streams. Plate 104 and 106 are attached in that position to
channels 76 and 78,
spray nozzles being positioned above the plates, particularly in exposed
regions of plates.
During operation of the feedwell assembly 72 (and the associated
thickener/clarifier), thickener
is introduced into inlet ports 80 and 82 from feed pipes 96 and 98 and
accelerated along middle
channel sections 84 and 86 so that froth along upper surface of the slurry
streams is guided onto
plates 104 and 106. A spray is ejected from nozzles (not shown) onto the froth
on plates 104 and
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106, thereby collapsing the froth into solids and liquid components and
releasing air entrapped in
the froth. The slurry is fed in together with the solids and liquid components
of the collapsed
froth through the discharge sections 88 and 90 of feed channels 76 and 78.
It is to be noted that a froth separation and dissipation plate member as
disclosed herein
may be horizontal, multi-angled, and/or variously inclined upwardly or
downwardly at any
number of different angles relative to the horizontal. In addition, the plate
member may be
adjustably mounted both to enable variation in the angle of inclination, as
well as variation in the
height or vertical location of the leading edge of the plate member, for
instance, to enable
positioning of the leading edge precisely at the froth-liquid interface.
Although the invention has been described in terms of particular embodiments
and
applications, one of ordinary skill in the art, in light of this teaching, can
generate additional
embodiments and modifications without departing from the spirit of or
exceeding the scope of
the claimed invention. Accordingly, it is to be understood that the drawings
and descriptions
herein are proffered by way of example to facilitate comprehension of the
invention and should
not be construed to limit the scope thereof.
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