Note: Descriptions are shown in the official language in which they were submitted.
CA 02378330 2005-10-13
WO 01/10530 PCT/US001Z0334
DEEP BED THICKENERICLARIFIERS WITH ENHANCED
LIQUID REMOVAL
BACKGROUND OF THE INVENTION
This invention relates to clarifiers and thickeners of the deep bed
type. This invention also relates to an associated method for separating
liquid and solid particles in a suspension of slurry in thickness and
clarifiers.
Deep bed thickeners and cLarifiers (or so-called thickener/clarifier
devices) are shown and described, for example, in U.S. Patent Nos.
5,433,862, 5,549,827 and 5,800,715..
The device described in U.S. Patent No. 5,433.862 comprises a
vessel receiving a slurry of liquid and solid particles suspended on the
Liquid. The vessel defines a hindered settling zone in which the liquid and
solids of the slurry tend to separate, with the solids settling down into a
compaction zone below the hindered settling zone. Tn the compaction zone,
the solids concentration tends to increase, while the liquid phase rises to a
clarification zone above the hindered settling zone. An overflow launder,
adjacent the upper end of the vessel, receives the overflow phase of the
slurry separated in the vessel. An underflow discharge port toward the
bottom of the vessel receives the thickened or underflow phase of the slurry
separated in the vessel. One or more so-called separating members are
provided in the vessel extending upwardly from a lower end in the hindered
settling or compaction zones to an upper end in a clarification zone.
Preferably. this member includes cones or other downwardly inclined
surfaces that facilitate both the settling of solids down to the compaction
zone and the upward flow of free liquid from the hindered settling and/or
compaction zone to the clarification zone.
1
CA 02378330 2002-02-04
WO 01/10530 PCT/iJS00/20334
The deep bed thickener or clarifier device described in U.S. Patent
No. 5,800,71 is similar to that disclosed in U.S. Patent No. 5,433,862, but
further has a fluid flow barrier between the overflow clarification zone and
the other zones of the vessel, and one or more clarifying conduits extending
~ through the barrier. Each such conduit carnes a suspended floc bed of
particulate solids that filters and further clarifies the liquid flowing up
from
the hindered settling zone to the clarification zone. This further filtering
removes solid particles that would otherwise be carried along the "clarified"
liquid to the overflow launder. These clarification conduits thus serve a
significantly different purpose than do the separating members and function
independently thereof.
Deep bed thickener/clarifiers offer certain design and operational
advantages over the conventional thickeners and clarifiers while providing
clarity of overflow and solids concentration of underflow comparable to that
1~ of conventional thickener/clarifiers. Such thickeners and clarifiers are
typically of low-profile design (i.e., shorter in height but of much greater
diameter than deep bed thickeners). but like deep bed thickeners have
generally central feedwells and underflow underflow discharge ports.
Conventional low profile thickeners rely on the radial ehpanse of the
horizontal settling zones to effect settling of the slurry throughout the
thickener. To achieve this settling action, the influent feed is typically
dispersed radially outwardly from the central feedwell and rotating rake
arms, having generally plow shaped blades, gather and laterally direct the
settled solids along the thickener/clarifier bottom to the central discharge
2~ opening in the bottom of the thickener/clarifier tank. These rake blades
are
located closely adjacent the tank bottom and are designed to move the solids
across the tank bottom with minimal disruption in the downward (or
settling) flow pattern of the slury though the hindered settling and
CA 02378330 2005-10-13
WO 01/10530 PCT/tIS00/Z0334
compaction zones. Consistent with this purpose, the rakes are rotated at a
very slow speed, for example, less than 1 revolution per minute. U.S. Patent
Nos. 4,082,671, 4,217,916 and 4,271,027, for example, describe and
illustrate rake assemblies that perform this function of moving settled solids
across the tank bottom of conventional low-profile thickeners for discharge
at a central underflow outlet. Indeed, some of the rake assemblies are
intended to scrape the settled solids from the tank bottom, see U.S. Patent
No. 4,247,400.
In contrast, ''deep bed" thick~er/cla,rifiers rely on the height of the
hindered settling to cause separation of the slurry into its clarified liquid
and
settled solids phases. Deep bed thick~ers/clarifiers further have a deep,
high angle conical bottom for directing the settled solids toward the
discharge opening. Thus there is no need for rotating rakes to move the
solids within the thickener/clarifier to effect removal of the solids_ Indeed,
rakes would serve little purpose in moving the solid, but rather would add
expense and operating complexity.
Basically, deep bed thickeners rely on a conical tank bottom having
a sidewall extending an angle from horizontal generally greater than the
angle of repose of the settled solids to direct the solids to move by gravit5~
alone along the tank bottom to the discharge opening. This eliminates the
need for a rotating rake and thereby simplifies the operation and
construction of the thickener/clarifier as well as reduces the cost of the
thickener/clarii;ier compared to conventional thickeners/clarifiers. This cost
reduction takes the form of the elimination of a capital expenditure for the
2~ rake assemblies, as well as the elimination of the associated torque
driveheads and motors {often in excess of 1,000,000 foot pounds torque)
and high strength bridges spanning the tank top to support the drive.
CA 02378330 2002-02-04
WO 01/10530 PCT/US00/20334
In contrast. conventional low profile thickener/clarifiers have tank
bottoms that are flat or inclined at angles generally below the angle of
repose of the settled solids and thus require rake assemblies and the
associated drive and bridge (or column) structures to remove the settled
solids from the thickener/clarifier.
SUMMARY OF THE INVENTION
The present invention enhances liquid-solids separation in a deep
bed thickener/clarifier and thus produces an underflow product or sludge
which is thickened relative to that of existing deep bed
thickeners/clarifiers.
More particularly, the deep bed thickener/clarifier of this invention
provides for the release and removal of free or interstitial liquid (typically
water) trapped in the settled solids in the hindered settling zone and/or the
compaction zone. This release of liquid is effected without increasing the
size of the thickener/clarifier, disturbing the settling processes or the
naturally occurring movement of the solids along the conical tank bottom.
The deep bed thickener/clarifier of the present invention comprises a
vessel with an overflow launder and an underflow discharge port. The
vessel has an inlet for receiving a slurry of a liquid and solid particles
suspended in the liquid. In an upper portion of the vessel, a free settling
zone has a low concentration of solid slurry particles, while in a lower
portion of the vessel, a compaction zone has a high concentration of solid
slurry particles. The overflow launder is attached to the vessel adjacent an
upper end thereof for discharge of an overflow phase of the slurry that has
been separated in the vessel. The underflow discharge port is adjacent to a
bottom thereof for discharge of a thickened, underflow phase of the slurp-
that has been separated in the vessel.
An upper portion of the vessel holds the free settling zone and a
lower portion of the vessel holds the compaction zone. A hindered settling
4
CA 02378330 2002-02-04
WO 01/10530 PCT/US00/20334
zone extends between the free settling and compaction zones, with the
hindered settling zone and compaction zone constituting lower settling
zones. A deliquifying member is positioned in the vessel extending up from
adjacent the lower portion of the vessel to adjacent the upper portion of the
vessel for flow of liquid from at least one of the lower zones to the free
settling zone. The deliquifying member further serves to isolate this flow of
liquid from the flow of slurry down in the lower settling zones. A rake
assembly is mounted for rotation in the lower portion of the vessel, with the
rake assembly forming channels in the slurry held in the lower portion of the
I O vessel for releasing liquid in at least one of said lower settling zones
to flow
to the deliquifying member and on to the free settling zone.
The method of this invention for operating a deep bed
thickener/clarifier comprises, in accordance with the present invention.
feeding, into a vessel, a slurry of a liquid and solid particles suspended in
I ~ the liquid and separating the slurry by graviy into different zones having
respective degrees of liquid-solids separation including, at an upper portion
of the vessel, a free settling zone having a low concentration of solid slurry
particles and further including, at a lower portion of the vessel, a
compaction zone having a high concentration of solid slurry particles. A
20 hindered settling zone is positioned between these zones. The method also
comprises discharging, into an overflow launder attached to the vessel
proximately to an upper end thereof, an overflow phase of the slurry that has
been separated in the clarification zone and discharging, via an underflow
discharge port fixed to the vessel at least proximately to a bottom thereof a
2~ thickened. underflow phase of the slum- that has been separated in the
vessel. Liquid is directed from at least one of the lower settling zones to
the
free settling zone via a flow path which is isolated from the flow of slurw
down in the vessel in the lower settling zones. In accordance with this
i
CA 02378330 2002-02-04
WO 01/10530 PCT/US00/20334
invention, upwardly extending channels are formed in the slurry held in the
lower portion of the vessel to release liquid in at least one of the lower
settling zones to flow to the isolated flow path and then to the free settling
zone.
Other objects of the invention will be in part apparent and in part
described and shown in the following description of the drawings and
preferred embodiments.
BRIEF DESCRIPTION OF THE DRAWINGS
For detailed understanding of the present invention, reference should
be made to the following detailed description of the preferred embodiments,
taken in conjunction with the accompanying drawings, in which like
elements have been given like numerals and wherein:
FIG. 1 illustrates a vertical section of the thickener/clarifier of this
invention and its various components including the deliquifying member
and a rake assembly:
FIG. 2 illustrates a vertical section of a second thickener/clarifier of
this invention with the rake shaft passing through the inside of the
deliquifying member; and
FIG. 3 illustrates the enlarged detail of a rake picket in the slurry for
forming a water flow channel in the slurry.
DESCRIPT10N OF THE PREFERRED EMBODIMENTS
As illustrated in FIG. 1, a deep bed thickener/clarifier of this
invention, generally indicated at 10, comprises a vessel 11 having an inlet
12 receiving a slurry comprising liquid and solid particles suspended in the
liquid. The slurred components are separated in vessel 11 into a relatively
light-weight overflow phase (i.e., a primarily clarified liquid) and a
relatively heave underflow phase (i.e., a primarily high solid concentration).
Vessel 11 includes a downwardly tapering frusto-conical bottom 14 having
G
CA 02378330 2002-02-04
WO 01/10530 PCT/US00/20334
an apex (not designated) connected to an underflow discharge port 16 for
the discharge of the thickened, underflow phase of the slurry that has been
separated in vessel 11. A variable speed pump and motor 18 communicate
via a valve 65 with discharge port 16 for the controlled removal of the
underflow from vessel 11. Alternatively, a remotely actuated valve (not
shown) may be provided as a mechanical end use device at discharge port
16 to control the removal of the underflow.
The thickener/clarifier 10 further includes an overflow weir or
launder 20 for removal of the overflow phase separated from the slurry in
vessel 11. An upper lip (not designated) of launder 20 defines the upper
level of the clarified liquid. A cylindrical wall 26 in vessel 11 forms an
annular chamber 27 and defines a fluid barrier between the annular chamber
and the remainder of the vessel interior. Projecting through a lower wall or
panel 28 of annular chamber 27 is one or more elongate conduits 30 having
generally vertically extending sidewalk which support fluidized floc beds
32 of the particulate material suspended in the different conduits, as
described in greater detail in U.S. Patent No. 5,800,715. Two such conduits
30 are shown in FIG. 1. However, other vessel designs may have only one
such conduit or more than two conduits. Conduits 30 are shown to be of
square or circular shape in section, but may be of any shape in section.
To facilitate flocculation in vessel 11, a settling agent such as a
polyelectrolyrte may be delivered as an additive to the slurry or as shown in
FIG. 1 preferably to the free settling liquid in the vessel. As shown in FIG.
1. a source of settling agent such as a storage tank 36 is in fluid flow
2~ communication with the vessel 11. A fluid flow control device, such as a
remotely actuated valve 40. regulates the dosage of settling aid delivered to
the slurn~ and thus control the extent of floc formation within vessel 11.
7
CA 02378330 2002-02-04
WO 01/10530 PCT/US00/20334
The slurry received and held in vessel 11 separates by gravity into a
hindered settling zone 42 which is located above a compaction zone 44 and
below an interior free settling clarification zone 46 and an overflow
clarification zone 47 in annular chamber 27. Within hindered settling zone
42, the liquid and solid particles tend to separate with the solid particles
tending to flow downwardly to the compaction zone 44 and with the
clarified liquid flowing up to clarification zone 47. Within compaction zone
44 the solids concentration increases to the highest level of concentration at
discharge port or outlet 16 at the vessel bottom.
As described in U.S. Patent No. 5.433,862, a deliquifying member
48 extends up within vessel 11 from generally adjacent the compaction zone
44. Deliquifying member 48 is of generally tubular configuration and
receives free liquid released from compaction zone 44 and delivers the
liquid to the upper end of the deliquifying member 48 which is preferably
positioned at the interior free settling clarification zone 46. At its upper
end.
deliquifying member 48 is provided with openings 52 for feeding expressed
liquid to the free settling clarification zone 46. In the thickener/clarifier
of
FIG. 1, the deliquifying member 48 also serves as part of a rotary drive
member or rake shaft as described more fully hereinafter.
The vessel comprises an upper portion, indicated generally at 81,
holding at least a portion of the free settling zone 46 and a lower portion,
indicated generally at 83, holding at least a portion of the compaction zone
44. The hindered settling zone 42 may extend into either the upper or lower
portion of the vessel. The compaction zone 44 and hindered settling zone
2~ 42 constitute lower settling zones. The deliquifying member 48 in the
vessel extends up from the lower portion 83 of the vessel to the upper
portion 81 of the vessel for flow of liquid from at least one of the lower
settling zones to the free settling zone while isolating the flow of liquid
from
8
CA 02378330 2002-02-04
WO 01/10530 PCT/US00/20334
the flow of slurry down into the lower settling zone. A rake assembly 63 is
mounted for rotation as indicated at 60 in the lower portion 83 of the vessel
and has a plurality of generally vertical pickets 62 . As shown in FIG. 3, as
the rake assembly rotates, the pickets 62 travel through the slurry, see arrow
80, and form temporary channels 76 in the slurry held in the lower portion
of the vessel. These channels release free or interstitial liquid in pockets
75
in at least one of the lower settling zones to flow along generally vertical
paths 72 to the deliquifying member 48. From there, the liquid is free to
flow on to the free settling zone 46. The deliquifying member 48 supports
and rotates the rake assembly 63. At its upper end, deliquifying member 48
is operatively connected to a motor 70 via a drivehead 61. The motor 70
may be of fixed or variable speed, and use any suitable motive power, such
as an electric or hydraulic motor or a combustion engine.
Accordingly, the deliquifying member 48 facilitates removal of free
liquid from at least one of the lower zones to enable solids in the
compaction zone to increase to a higher concentration level and to do so
more rapidly than would otherwise be possible. The deliquifying member
48 is open to hindered settling zone 42 to facilitate release of free liquid
from that zone. To that end. deliquifying member 48 is provided with one
or more suitable inclined members such as upwardly tapering conical
deliquif~~ing baffles 56 shown, for example, in FIG. 1 as being ganged in a
sequence. Each conical deliquifying baffle 56 is open at a lower end 50 and
guides released liquid upwardly along an inner surface (not shown) to a
respective opening or aperture 54 provided in deliquifying member 48.
2~ Settling solids particles are directed along the outer surfaces of conical
deliquifving baffles 56 towards the bottom of vessel 11. Thus the
deliquifying member 48 isolates the upward flow of liquid from the
dow~mvard flow of the slurr<~.
c)
CA 02378330 2002-02-04
WO 01/10530 PCT/US00/20334
Deliquifying member 48 provides a conduit for the flow of free
liquid thus released from hindered settling zone 42 and compaction zone 44.
This channeling of the released liquid in those zones influences the solids
settling rate therein. Deliquifying member 48 is shown to be a tube of
circular or square cross-section. However, deliquifying member 48 may be
of other shapes as described and shown in U.S. Patent No. 5,433,862. The
word "tubular" is used herein to mean a hollow profile of any suitable cross-
sectional shape.
In operation, deliquifying member 48 is rotated at a slow rate during
the graviy settling process. The consequent movement of the pickets 62
through the thickened slurrv_ or sludge in the lower zones releases otherwise
trapped interstitial liquid 71. This freed liquid 71 generally escapes from
compaction zone 44 in laminar flow paths along pickets 62, as illustrated in
FIG. 3. The overall process of thickening or clarification in apparatus 10 is
controlled by adjusting the underflow withdrawal and overflow discharge
rates relative to the inlet. Thickener/clarifier 10 as provided with a
rotatable
rake assembly 63 provides for higher underflow solids concentration,
improved overflow clarity. increased rate of influent feed, reduced settling
aid usage or any combination of these advantages or results than would be
possible in treating slurries in conventional deep bed or low-profile, large
diameter thickener/clarifiers.
Thickener/clarifier 10 includes a cover plate or upper panel 74 which
carries drivehead 61 and motor 70. An outlet port 75 is provided at the
upper end of vessel 11 for discharging the clarified liquid phase which spills
2~ over weir or launder 20. The deliquif~zng member 48 is rotatably
suspended from cover plate or upper panel 74.
FIG. 2 depicts a second embodiment of the thickener/clarifier 110
which includes certain modifications with respect to the apparatus of FIG.
CA 02378330 2002-02-04
WO 01/10530 PCT/US00/20334
1. Like structures in FIGS. 1 and 2 are designated with the same reference
numerals.
In FIG. 2, the deliquifying member 148, unlike the deliquifying
member 48 in FIG. 1, does not serve to rotate the rake assembly and may be
rigidly fixed to cover or upper panel 74. The deliquifying member 148 is
also shown to terminate at an upper end of a lowermost conical deliquifying
baffle 56.
Thickener/clarifier 110 includes a rotatable rake 163 having a
plurality of generally parallel vertically extending pickets 162. Rake 163
ser<~es to augment or accelerate the deliquifying of the lower zones. Rake
163 is rotated by a drive shaft 166 which is generally coaxially and
longitudinally disposed in deliquifying member 148. Drive shaft 166 is
rotatably joumaled in cover plate or upper panel 74 and is operatively
connected to drivehead 61 and motor 70.
The upper three conical deliquifying baffles 56 communicate with a
lumen or interior (not designated) of fluid flow member 148 via openings or
apertures 154 provided in tubular fluid flow member 148. As discussed
above. settling solids particles are directed along the outer surfaces of
conical deliquifying baffles 56 towards the bottom of vessel 11.
The embodiment of FIG. 2 also differs from that of FIG. 1 in not
incorporating clarification tubes (such as tubes 30) and in directing
flocculant to the free settling zone at the exterior of the deliquifying
member
148.
Although the invention has been described in terms of its preferred
2~ embodiments. those skilled in the art will recognize that numerous
modifications and changes may be made while remaining within the scope
and spirit of the invention. For example, pickets 62 and 162 of rakes 63 and
163. respectively, extend parallel to one another vertically through
11
CA 02378330 2002-02-04
WO 01/10530 PCT/IJS00/20334
compaction zone 44 and into hindered settling zone 42. Pickets 62 and 162
may be alternatively inclined at an angle to the vertical. In addition,
conical
deliquifying baffles 56 may be greater or fewer in number than four. The
conical deliquifying baffles located below chamber 27 may be larger. In
addition, the pickets may be positioned and be of sufficient length to extend
into both the compaction zone 44 and hindered settling zone 42. The
deliquifying member 48, 148 may be open only adjacent its lower end to
receive liquid from one of the lower zones and adjacent its upper end to
discharge liquid conveyed by the member. Alternatively, the member may
be open at a plurality of locations as well as for a substantial portion of
its
length.
Accordingly, it is to be understood that the drawings and description
herein be offered by way of example to facilitate comprehension of the
invention and should not be construed to limit the scope thereof.
12
