Note: Descriptions are shown in the official language in which they were submitted.
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TITLE OF THE INVENTION
SOLIDS RECOVERY USING CROSS-FLOW MICROFILTER AND
AUTOMATIC PISTON DISCHARGE CENTRIFUGE
CROSS REFERENCE TO RELATED APPLICATIONS
This application is a continuation-in-part of co-pending
U.S. Application No. 11/218,280, filed September 1, 2005 and a
continuation-in-part of . International Application No.
PCT/IB2006/002411 filed August 25, 2006. This application
claims the priority of U.S. Provisional Application No_*60/742,558
filed December 5, 2005 and U.S. Provisional Application No.
60/756,381 filed January 4, 2006. Each of the foregoing related
applications is hereby incorporated by reference.
BACKGROUND OF THE INVENTION
Many different types of centrifugal separators are-known for
separating heterogeneous mixtures into components based on
specific gravity. Typically, a heterogeneous mixture, which may
also be referred to as feed material or liquid, is injected into a
rotating bowl of a centrifugal separator. The rotating bowl spins
at high speeds and forces components of the mixture that have a
high specific gravity to separate therefrom by sedimentation. As
a result, dense solids compress as a cake tightly against an inner
surface or wall of the bowl and clarified liquid forms radially
inward from the cake. The bowl may spin at speeds sufficient to
produce forces 20,000 times greater than gravity so as to separate
the solids from the centrate.
As solids accumulate along the wall of the bowl, the
clarified liquid exits from the bowl and leaves the separator as
"centrate." Once it is determined that a desired amount of solids
has accumulated, the separator is placed in a discharge mode in
which the solids are removed from the separator. Often, for
example, an internal scraper is engaged to scrape the solids from
the walls of the bowl.
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Conventional separators have many shortcomings when
discharging particular kinds of solids and liquids. For example,
some separators may not be capable of completely discharging
solids that are sticky, which can result in poor yields. A poor
yield can be especially problematic for high-value solids such as
those encountered in pharmaceutical processes. Traditional
separators also subject a feed material to-very high shear forces
when accelerating the material to the rotational speed of the
bowl, which can damage, for example, sensitive chemical or
biological substances such as intact cells.
Still, other separators do not provide a convenient means by
which to handle and recover sensitive solids. For example, an
operator is commonly used to assist with solids discharge and
recovery. Separators that require such operator intervention
often suffer from contamination problems. Furthermore, some
separators employ numerous mechanical components to facilitate
solids recovery, which can affect separator durability. Such
components are usually external to the separator or in the form of
add-on equipment that poses both size and compatibility issues.
Conventional separators also tend to be difficult to -clean or
sterilize without significantly increasing maintenance costs.
It would be desirable to have a centrifugal separator that
can be effectively used with solids of the type described above,
namely, those that result in sticky accumulations or are sensitive
to shear forces generated during centrifugation. It would also be
useful to have a separator that can easily recover such solids
without the possibility of external contamination or additional
mechanical equipment. Such a separator should also be able to be
conveniently cleaned or sterilized-in-place.
Furthermore, typical cross-flow microfiltration systems
employ pretreatment of feed liquid to ensure the solids
concentration is sufficiently below a threshold at which the
filter membrane would become fouled. Backwashing is often
necessary to reduce the concentration of accumulated solids on the
filter membrane, causing delays in processing. In addition, some
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mechanism must be provided to extract accumulated solids, such as
from a retentate tank. Such mechanisms previously have resulted
in removed solids wetted by a relatively significant amount of
retentate. The provision of pretreatment liquid and such a solids
removal mechanism result in increased processing time, complexity,
and cost while providing suboptimal solids drying performance.
SUMPsRY OF THE INVENTION
To alleviate the problems associated with previous
microfiltration systems, the presently disclosed system employs an
automatic piston discharge (APD) centrifuge in conjunction with a
microfiltration system. As solids concentration in the retentate,
as detected by turbidity or density measurements, reaches a
threshold, the retentate is directed to the centrifuge where
highly efficient separation occurs. Alternatively or in addition,
the pressure of the clear filtrate can be idonitored, as an
indication of the accumulation of solids and the need for solids
removal using the centrifuge. The dry solids are removed through
the solids discharge cycle of the centrifuge, and the removed
centrate is analyzed for suspended solids. If present, the
centrate is returned to the process'path. Otherwise, the clear
centrate is removed from the system.
Since solids build-up on the filter membrane is avoided, a
higher throughput through the microfilter is achieved. The solids
removed by the centrifuge are significantly drier as compared to
prior art methods. Since the feed stream is concentrated, a
relatively small centrifuge can be employed. With such dynamic
control over the retentate solids concentration, there is less
need for a large retentate tank, further contributing to cost
savings.
In accordance with the present invention, a system is
provided for the isolation and recovery of solid and/or liquid
components from a solids-containing suspension by combined
microfiltration and centrifugation. The system comprises a
microfiltration subsystem and a centrifugation subsystem.
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The microfiltration subsystem comprises a cross-flow
microfilter, a retentate tank, a retentate pump, a first valve,
and a first sensor. The microfilter has a feed input for
introduction of the suspension to the system, a filtrate output
for diverting filtrate from the system, and a retentate output.
The. retentate tank is fed from the retentate output of the
microfilter. The retentate pump is fed from an output of the
retentate tank. The first valve is fluidly connected to the
output of the retentate pump. The first sensor senses the solids
concentration in the retentate and controls the first valve.
Below a first preset solids concentration, the first valve returns
the retentate to the feed input of the microfilter. Above the
first preset solids concentration, the first valve diverts the
retentate to the centrifugation subsystem.
The centrifugation subsystem comprises an automatic piston
discharge centrifuge having a feed input, a solids discharge
output for diverting solids from the system, and a centrate
output. The centrifugation subsystem further comprises a second
valve that is fluidly connected to the centrate output, and a
second sensor capable of sensing the solids concentration in the
centrate output and controlling the second valve. Above a second
preset solids concentration, the second valve returns the centrate
to the retentate tank. Below the second preset solids
concentration, the second valve diverts the centrate from the
system.
Another aspect of the invention is a method of recovering a
solid component or a liquid component from a solids-containing
suspension by combined microfiltration and centrifugation. The
method comprises the steps of providing a system comprising a
microfiltration subsystem and a centrifugation subsystem as
described above, adding the solids-containing suspension to the
retentate tank, pumping the suspension through the microfilter
with the retentate purnp; sensing the solids concentration in the
retentate with the first sensor, sensing the solids concentration
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in the centrate with the second sensor, collecting filtrate from
the microfilter, collecting centrate from the centrifuge, and
collecting solids from the centrifuge. If the solids concentration
in the retentate is below a first preset solids concentration, the
5 first valve is adjusted to return the retentate to the feed input
of the microfilter. If the solids concentration of the retentate
is above the first preset solids concentration, the first valve is
adjusted to divert the retentate to the centrifugation subsystem.
If the solids concentration of the centrate is above a second
preset solids concentration, the second valve returns the centrate
to the retentate tank. if the solids concentration of the
centrate is below the second preset solids concentration, the
second valve is adjusted to divert the centrate for collection..
In yet another aspect, the present invention provides an
automatic piston discharge centrifuge, comprising a bowl, a solids
discharge assembly, a microfilter, a diaphragm, and a solids
discharge valve. The cylindrical bowl has a lower end with an
opening and is operative during a feed mode of operation to rotate
at a high speed to separate solids from feed liquid; solids
accumulate along an inner surface of the bowl. The solids
discharge assembly comprises a cylindrical outer piston movably
disposed against the inner surface of the bowl, and an inner
piston disposed at the end of a shaft which extends along the axis
of the bowl. The inner piston has a substantially cylindrical
portion and a substantially conical portion. The microfilter is
cylindrically disposed about the axis of the bowl and retains
solids in an outer gap between an outer surface of the microfilter
and the inner surface of the bowl. The microfilter allows a
filtered centrate to exit the bowl through an .inner gap adjacent
to an inner surface of the microfilter. The outer diameter of the
microfilter is less than the .inner diameter of the outer piston.
The diaphragm is cylindrically disposed about the axis of the bowl
and is adjacent to the inner gap.
Further in accordance with the present invention, a
centrifugal separator is disclosed that performs well with sticky
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solids and exhibits low-shear acceleration of feed material. The
separator can be particularly useful for sensitive solids such as
chemical or biological substances. A separator of the invention
can recover sensitive solids, liquids, materials or combinations
thereof without operator intervention or additional mechanical
equipment. The separator can also be conveniently cleaned or
sterilized-in-place.
The separator can include a cylindrical bowl having a conical
lower end with an opening through which feed material or liquid is
injected during a feed mode of operation. As the bowl spins or
rotates at a high speed, the injected feed liquid encounters a
sloped surface of the conical lower end of the bowl. Rotational
acceleration forces are imparted relatively gradually as the
liquid continues its movement radially outward. Solids then
separate from the feed liquid and accumulate along the inner
surface of the bowl, for example, as a cake.
Additionally, the separator can include a piston assembly
disposed within the bowl in tight-fitting relationship with an
inner surface thereof. The piston features an upper portion and a
lower conical portion that are contacted by pneumatic or hydraulic
pressure during different modes of separator operation. For
example, in a solids discharge mode, fluid such as compressed gas
or hydraulic liquid acts against the upper portion of the piston
urging it axially downward to force* accumulated solids from the
bowl via the opening in the conical lower end thereof. Exemplary
types of compressed gas for moving the piston include nitrogen and,
argon. Similarly, an exemplary hydraulic liquid for moving the
piston in the bowl can include distilled water. In one
embodiment, the lower end of the bowl and lower portion of the
piston have complementary shapes to promote relatively complete
discharge of solids. For example, the lower end of the bowl and
lower portion of the piston can feature substantially
frustoconical shapes.
For a separator of the invention, the piston can be held in
an uppermost position during a feed mode of operation by hydraulic
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pressure from the feed liquid as well as frictional forces between
one or more piston seals and the inner surface or wall of the
bowl. Such seals can be disposed about the piston and adjacent to
the inner surface of the bowl. The piston includes a centrate
valve that can be urged open during.the feed mode to permit the
feed liquid, after solids have been separated therefrom, to flow
out of the bowl as clarified liquid and into a centrate case
having a passage leading to a centrate outlet port. As the piston
is urged downward by fluid acting against the upper portion
thereof during solids discharge, the centrate valve automatically
closes to prevent accumulated solids from passing into the
centrate case.
With the piston held in its uppermost position, it is
permitted to rotate with the bowl as high speed rotational
separation of the solids from the feed liquid is performed.
During the feed mode and solids separation, clarified liquid exits
the bowl and enters the centrate case. The centrate case can also
include an isolation valve that may be urged open or closed by
pneumatic or hydraulic pressure. For example, the isolation valve
is open in the feed mode to allow clarified liquid to flow through
the centrate outlet port and an open centrate outlet port valve to
exit the separator as centrate. As the feed mode concludes,
hydraulic pressure from the feed liquid is reduced such that the
piston is held substantially in its uppermost position by
frictional forces between one or more piston seals and the inner
wall of the bowl as well as any solids accumulated within the
bowl. When the feed mode of operation is complete, the bowl stops
rotating and remaining or residual liquid in the separator flows
by gravity through the opening in the conical lower end thereof.
The separator can also feature a divert assembly including a
solids divert valve movably located below a rotatable residual
divert valve when the residual divert valve is at the opening in
the conical lower end of the bowl. As residual liquid drains from
the bowl, the residual divert valve is in a closed position to
permit the liquid to flow from the bowl and into a residual liquid
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drain passage. The liquid drain passage leads into a drain port,
where residual liquid exits the separator. The solids discharge
mode of operation can, for example, begin after the residual
liquid has substantially drained from the separator bowl.
= In the solids discharge mode, a residual divert valve
actuator rotates the residual divert valve to an open position
such that the solids divert valve can be urged upward, by a solids
divert piston, into communication with the opening in the bowl.
The centrate outlet port valve is then closed and a solids outlet
port valve for the divert assembly is opened. The isolation valve
is also urged closed by fluid such as compressed gas or hydraulic
,
liquid acting against an annular member associated with the
isolation valve, which controls its actuation and movement. In
addition, as described above, the piston is urged downward along a
vertical axis during solids discharge by fluid acting against the
upper portion thereof. The piston subsequently pushes or "pumps"
accumulated solids from the bowl into a solids passage leading to
a solids outlet port that features the open solids outlet port
valve.
In one embodiment, a solids discharge assembly for the
separator features the piston movably disposed against the inner
surface of the bowl. The piston can comprise an upper portion and
a lower portion. The solids discharge assembly can also feature a
driving port operative for introducing fluid into the bowl above
the upper portion of the piston. When fluid pressure in the bowl
above the upper portion of the piston is increased relative to
that below the lower portion of the piston, the piston moves
within the bowl. For example, during solids discharge,
introduction of fluid into the bowl above the upper portion of the
piston can move the piston axially downward. Preferably, the
piston is urged axially downward with respect to the bowl. As
described above, during the solids discharge mode of operation,
introduction of fluid into the bowl above its upper portion causes
the piston to push solids accumulated along the inner surface of
the bowl.
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The solids discharge assembly can also comprise a port
operative for introducing fluid into the bowl below the lower
portion of the piston. When fluid pressure in the bowl below the
lower portion of the piston is increased relative to that above
the upper portion of the piston, the piston moves within the bowl.
For example, introduction of fluid into the bowl below the lower
portion of the piston can cause the piston to move toward an upper
end of the bowl. Tn another embodiment, the separator can also
comprise a valve in an upper end region thereof, which is operable
to enable pressurization of the bowl above the upper portion of
the piston. Such a valve can be actuated in response to fluid
pressure applied against an annular member operably associated
therewith.
In another embodiment, the separator of the invention can
comprise a cylindrical bowl having a lower end with an opening.
During the feed mode of operation, the bowl is operative to rotate
at a high speed to separate solids from feed liquid. As described
above, the solids accumulate along the inner surface of the bowl.
The separator can also feature a solids discharge assembly and
first valve member, which defines a drain passage. The drain
passage is operative to permit liquid to drain from the opening in
the bowl when the first valve member is in a closed position.
Preferably, the opening in the bowl and the drain passage are
configurable to enable liquid to drain by gravity from the bowl
into the passage.
The first valve member can also def,ine a feed passage that
cooperates with or is proximate to the opening in the bowl during
the feed mode of operation. The feed passage permits feed liquid
to be injected into the bowl. The first valve member can also be
operatively coupleable to a valve actuator for rotating the member
about a rotational axis. In one embodiment, the separator can
also comprise a second valve member that cooperates with a lower
surface of the first valve member when the first valve member is
in a closed position. Moreover, the separator can feature a valve
piston having an uppermost end at which the second valve member is
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proximately disposed. The valve piston can be operative to move
the second valve member with respect to the bowl. For example,
during solids discharge, the valve piston can move the second
valve member upward along a vertical axis to cooperate with the
5 opening in the bowl. Similarly, during the feed mode of
operation, the first valve member is in the closed position and
defines the feed passage, which, as describe above, can cooperate
with the opening in the bowl to permit feed liquid to be injected
therein.
10 In one embodiment, the separator of the invention can
comprise a first passage partially disposed within the valve
piston. For example, the first passage can cooperate with the
second valve member at the uppermost end of the valve piston. The
opening in the separator bowl and the first passage can also be
configurable to enable solids from the bowl to pass through the
first passage during solids discharge. The first passage can also
cooperate with a second passage that is partially disposed in the
valve piston such that fluid introduced through a port for the
second passage may enter the first passage so as to contact solids
therein. Preferably, fluid introduced through the port for the
second passage enters the first passage to contact solids therein
when a valve member of the first passage is open. The valve
piston of the separator can also feature an annular flange
disposed thereabout such that the valve piston moves in response
to fluid pressure applied against the annular flange.
In one embodiment, the separator also comprises a first
passage partially disposed within the valve piston. The first
passage can cooperate with the second valve member, for example,
at the uppermost end of the valve piston, and a second passage
partially disposed within the valve piston. Preferably, when a
valve member of the first passage is closed, fluid introduced
through a port for the second passage enters the bowl below the
lower portion of the piston. Fluid introduced through the port
increases fluid pressure in the bowl below the lower portion of
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the piston relative to that above the upper portion thereof so as
to cause the piston to move toward an upper end of the bowl.
The invention also provides a method for discharging solids
from a centrifugal separator. In one embodiment, the method
comprises providing the separator and/or solids discharge assembly
described above and introducing fluid through the driving port to
increase fluid pressure in the bowl above the upper portion of the
piston relative to that below the lower portion thereof so as to
cause the piston to move within the bowl. The method can also
comprise discharging solids accumulated along the inner surface of
the bowl. Additionally, the method features injecting feed liquid
into the bowl for solids separation by high speed rotation of the
bowl. Preferably, the feed liquid is injected into the bowl prior
to introducing fluid through the driving port. A method of the
invention also includes returning the piston substantially to an
uppermost position. The piston can be returned substantially to
its uppermost position by introducing fluid into the bowl below
the lower portion of the piston so as to increase fluid pressure
in the bowl below the lower portion of the piston relative to that
above the upper portion thereof. The piston is preferably
returned substantially to its uppermost position after discharging
solids accumulated along the inner surface of the bowl. The
invention also contemplates carrying out the above method in any
particular order or manner.
DESCRIPTION OF THE DRAWINGS
Other features and advantages of the present invention will
be apparent from the following detailed description of the
invention, taken in conjunction with the accompanying drawings of
which:
Figure 1 is a section view of a centrifugal separator
embodiment in accordance with the invention;
Figure 2 is a section view of a centrifugal separator
embodiment in accordance with the invention;
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Figure 3 is a section view of the separator in Fig. 2
featuring a laser sensor assembly;
Figure 4 is a section view of the separator in Fig. 1
illustrating operation in a feed mode;
Figure 5 is a detailed section view including the piston and
bowl of the separator in Fig. 1 illustrating operation in the feed
mode;
Figure 6 is a section view of the separator in Fig. 1
illustrating operation when residual liquid drains from the bowl;
Figure 7 is a section view of the separator in Fig. 1
illustrating operation in a solids discharge mode;
Figure 8 is a section of the centrifuge in Fig. 1
illustrating operation after the solids discharge mode when the
piston is returned substantially to its uppertnost position;
Figure 9 is a detailed section view of a lower end region of
the separator of Fig. 1 when a solids passage is cleaned;
Figure 10 is a detailed section view of an upper portion of
the separator of Fig. 1 in the feed mode;
Figure 11 is a detailed section view of an upper portion of
the separator of Fig. 1 in a solids discharge mode;
Figure 12 illustrates an embodiment of a system for
combined microfiltration and centrifugation according to the
invention.
Figure 13 is a section view of a centrifuge embodiment
according to the invention. This embodiment has a peripheral
outer piston and an inner piston, as well as a microfiltration
membrane and diaphragm;
Figure 14 is a section view of the centrifuge embodiment of
Fig. 13 in the feed mode;
Figure 15 is a section view of the centrifuge embodiment of
Fig. 13 in the-discharge mode;
Figure 16 is a section view of the centrifuge embodiment of
Fig. 13 in the discharge mode;
Figure 17 is a section view of the centrifuge embodiment of
Fig. 13 in the retract mode;
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Figure 18 shows is a section view of the centrifuge
embodiment of Fig. 13 and depicts the passage of solids across
the microfiltration membrane;
Figure 19 shows is a section view of the centrifuge
embodiment of Fig. 13 and depicts the passage of solids across
the microfiltration membrane; and
Figure 20 shows is a section view of the centrifuge
embodiment of Fig. 13 and depicts the passage of solids across
the microfiltration membrane.
DETAILED DESCRIPTION OF THE INVENTION
Figure 1 shows a centrifugal separator in vertical section,
with a middle portion removed so as to illustrate a horizontal
section as well. The centrifugal separator includes a cylindrical
separator bowl 10 mounted in a central region 11 of a separator
housing 13. Preferably, the separator bowl can be of a length
that is greater than a diameter thereof. By having the length of
the bowl longer than its diameter, "end effects"in the bowl can
be minimized with respect to the bowl's internal volume_ In
general, end effects can be caused by fluid eddies along any of
the angled portions within the interior of the bowl and,
particularly, near the ends thereof. In one embodiment, the
separator bowl 10 can be a cylindrical type bowl having a
relatively small diameter D and a length L such that the ratio of
L/D is approximately 5/1 or greater. Such a ratio of L/D tends to
prevent axial waves from developing within the bowl as such waves
substantially dissipate as they travel the length of the bowl. By
employing an L/D ratio of approximately 5/1 or greater, a
separator of the invention can also avoid the need for baffles
within the bowl, which are used in conventional separators to
minimize axial waves.
The separator in Fig. 1 also includes a piston assembly
comprising a piston 12. As shown, the piston 12 can have a lower
conical portion that matches the shape of a coizical lower end 17
of the bowl 10. The conical lower end 17 acts as a rotational
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accelerator of the feed liquid during a feed mode of operation for
the separator. The separator can also feature, in an upper
portion 19, a centrate case 30 having an isolation valve 26 that
is urged open or closed by pneumatic or hydraulic pressure.
A variable speed drive motor 16 can also be connected by a
drive belt 5 to a drive pulley 18 of a mounted bearing and spindle
assembly 23 located at a collar-like extension 22 of the upper end
for the separator housing 13. A separator of the invention can
also be operated using other conventional motor and drive systems.
Preferably, the bearing and spindle assembly 23 can comprise a
semi-spherical portion 1 and a short cylindrical spindle portion
20, although other suitable assembly configurations could be used
in accordance with the invention. in one embodiment, the semi-
spherical portion comprises an upper semi-hemispherical portion
and a lower semi-hemispherical portion. Optionally, the semi-
spherical portion 1 can rest against mating surfaces of one or
more seats. For example, Fig. 1 shows seats 24 and 25 in
compressive contact with the upper and lower semi-hemispherical
portion, respectively, of the semi-spherical portion 1. An
exemplary semi-spherical portion that can be employed in a
separator of the invention has been described by U.S. Application
No. 10/874,150, which is hereby incorporated by reference herein.
Exemplary seats 24 and 25 can comprise low friction
components such as polytetrafluoroethylene (PTFE) or TEFLON-based
(E. I. du Pont de Nemours and Company, 1007 Market Street,
Wilmington, Delaware 19898) materials such that they allow some
extent of=shif ting of the semi-spherical portion 1 about a central
vertical axis 41 of the separator. Seats 24 and 25 tend to
prevent the semi-spherical portion 1 from processing radially
outward and axially upward or downward. Moreover, seats 24 and 25
can limit the amount of vertical and horizontal swiveling of the
spindle portion 20 as it rotates about the central vertical axis
41 of the separator at high speed during operation. Swiveling of
the spindle portion 20 may also be dampened by an optional swing
resistant ring 21 made, for example, of rubber. By preventing
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such radial or axial processing and limiting the amount of
swiveling, vibration associated with the natural frequency of the
rotating bowl 10 can be reduced. Seats 24 and 25 can also, for
example, be arched seating elements that substantially prevent
5 translation such asrotational translation of the assembly 23 or
housing thereof. Generally, preventing such translation can
operatively stabilize the semi-spherical portion 1.
In one embodiment, seats 24 and 25 can be formed as
continuous ring members, discrete stabilizing members or any
10 combination of such members. Seats 24 and 25 can also be
adjustable such that their compressive contact with the semi-
spherical portion 1 can be modified depending, for example, on
particular process requirements for the separator. Such
adjustability of seats 24 and 25 can be facilitated by, for
15 example, the use of one or more adjustment members associated
therewith. As described above, the invention also contemplates
employing an individual seat that may be in compressive contact
with the upper and/or lower semi-hemispherical portion of the
semi-spherical portion 1.
Rotation of the mounted bearing and spindle assembly 23 can
also be prevented by, for example, a positioning member such as an
anti-rotation pin 29. For example, Fig. 1 shows pin 29 positioned
so as to extend through an enlarged opening in the assembly 23.
in one embodiment, such a positioning member can cooperate with a
mounting region for the bearing and spindle assembly 23 to
substantially prevent translation, for example, rotational
translation, of the assembly 23 or housing thereof. As shown, the
anti-rotation pin 29 can move within the opening in the assembly
23 so that it does not interfere with the swiveling of the spindle
portion 20. The extent of rotation and swiveling experienced by
the separator can relate to the speed at which high speed
separation occurs. The drive motor 16 can also be controllably
operated to rotate the separator bowl 10 at desired speeds for
separation of the feed liquid.
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Also shown in Fig. 1 are the centrate case 30, a centrate
outlet port 32, a centrate outlet port valve 33 and a centrate
valve 34, all of which are, during operation, involved in removing
clarified liquid from the bowl 10 and centrate from the separator.
As described in greater detail below, the centrate case 30
includes an isolation valve 26 that is open as the feed liquid
enters the bowl 10 in the feed mode. The isolation valve 26 can
comprise an annular member 9, preferably, disposed thereabout.
During the feed mode, the centrate outlet port valve 33 is also
maintained open. In contrast, the isolation 26 and centrate
outlet port valves 33 both close when solids are pumped from the
separator. The isolation valve is described in greater detail
below with reference to Fig. 10, which shows the upper portion 19
of the separator during the feed mode. The centrate outlet port
valve 33 can be closed manually or via a conventional automatic
valve control assembly. The separator further comprises a lower
end region 39 of the separator housing 13.
Figure 1 also illustrates an embodiment of the separator
having, for example, a solids divert valve 90 movably located in
the lower end region 39 of the separator housing 13, below a lower
surface of a rotatable residual divert valve 92. Optionally, the
lower surface of -the residual divert valve 92 can have a feature
that partially extends within the solids divert valve 90. The
residual divert valve 92 located at an opening 76 in the conical
lower end 17 of the bowl 10 is shown in a closed position, which
is maintained during the feed mode. When closed, the valve 92
defines a feed liquid passage 94 in communication with a feed
liquid port 96, as well as a residual drain passage 98 in
communication with a residual liquid drain port 100. The residual
divert valve 92 can also be disposed to communicate within valve
receiving member 120, which may be provided integrally with the
lower end 39 of the separator housing 13. The valve 92 can also
be rotated from its closed position about axis 6 such that the
solids divert valve 90 can be urged upward into communication with
the opening 76 to the bowl.
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The separator of the invention can also comprise, as shown in
Fig_ 1, a solids passage 104, preferably, disposed axially within
a solids divert piston 102 and extending beyond the divert piston
102 at a lowermost end to incorporate a solids outlet port 106 and
a solids outlet port valve 107. The passage 104, piston 102, port
106 and valve 107 are each involved in removing accumulated solids
from the centrifugal separator during the solids discharge mode of
operation. While solids are pumped from the separator bowl 10,
the solids outlet port valve 107 can be open to, for example,
allow solids to pass from the solids passage 104 through the
solids outlet port 106 to exit the separator.
The solids outlet port valve 107 may be opened manually or
via a conventional automatic valve control assembly. The.solids
discharge mode generally pumps and recovers sensitive solids, such
as, for example, intact cells, and can, for example, pass these
solids onto another process or a storage vessel without further
handling. Without the solids being handled by an operator, they
are less likely to be damaged or contaminated. A separator of the
invention such as, for example, the separator of Fig. 1 can also
feature any configuration or arrangement of passages, valves,
pistons, actuators, assemblies, ports, members and so forth, as
described above, that would be suitable for a particular
application.
A cleaning passage 108 can also be disposed within the solids
divert piston 102, preferably, parallel to the solids passage 104
and, optionally, extending beyond the piston 102 at a lowermost
end to incorporate a cleaning port 111. At an uppermost end, the
cleaning passage 108 may be in communication with the solids
passage 104. The cleaning port ill and passage 108 together can
aid in the recovery of any solids remaining in the passage 104
following the solids discharge mode, as well as in cleaning or
sterilizing the separator. The cleaning port 111 and passage 108
can also operate to urge the piston 12 axially upward once the
solids discharge mode is complete.
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18
In particular, after solids are pumped from the separator,
the solids outlet port valve 107 can be closed such that fluid,
for example, compressed gas or hydraulic liquid, introduced
through the cleaning port 111 and passage 108 contacts the lower
conical portion of the piston 12 and urges the piston upward until
it is returned substantially to an uppermost position for the next
feed mode of operation. Exemplary types of compressed gas for
moving the piston 12 include nitrogen and argon. Similarly, an
exemplary hydraulic liquid that can be used to move the piston 12
within the bowl 10 can include distilled water.
In another embodiment, a separator of the invention can
feature, for example, a pinch or ball type valve assembly to
facilitate solids discharge. A conventional pinch type valve
assembly may be preferable for a separator encountering paste-like
solids during operation. An exemplary ball type valve assembly
can comprise a half-ball shaped discharge valve disposed in the
lower end region of the separator housing. The discharge valve of
a ball type valve assembly can also include passages for the feed
liquid and residual liquid being drained from the separator bowl.
For example, the discharge valve can rotate between a closed and
an open position during, respectively, the feed mode and solids
discharge mode of operation.
During the feed mode, the separator housing can be closed
except for the feed and residual liquid passages of the ball type
valve assembly, which may communicate with, for example, the
opening in the conical lower end of bowl. A ball type valve
assembly can also include, for example, one or more ports for
piston retraction and cleaning or sterilizing the separator. An
exemplary ball type valve assembly that can be employed in a
separator of the invention has been described by U.S. Patent No.
6,776,752, which is hereby incorporated by reference herein.
.Figure 2 shows one embodiment of a separator of the invention
comprising ball type valve assembly 40 disposed in the lower end
region 39 of the separator housing 13. Preferably, the ball type
valve assembly 40 features, as shown, a discharge valve 42. For
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19
example, the discharge valve 42 can be mounted below an inward-
facing flange 43. In one embodiment, the discharge valve 42 can
incorporate a feed liquid passage 44 in communication with a feed
liquid port 45, as well as a residual liquid drain passage 46 in
communicat.ion with a residual liquid drain port 47. A valve seal
48 can also be disposed on a lower surface of the flange 43.
During the feed mode, the separator of Fig. 2 features the
discharge valve 42 in a closed position in which its outer upper
surface rests against the valve seal 48. The valve seal 48 can be
inflated by fluid such as, for example, compressed gas or
hydraulic liquid introduced through a valve actuator 49.
Preferably, the valve seal 48 remains inflated throughout the feed
mode. Figure 2 shows that solids-bearing feed liquid can be
introduced through the feed liquid port 45. The feed liquid can
flow from the feed liquid port 45 into the feed liquid passage 44.
Preferably, the feed liquid passage 44 communicates with a main
passage 50, which can be axially disposed within a piston retract
actuator 52. An upper end of the main passage 50 incorporates a
jet port 154 for, during the feed mode, injecting feed liquid into
the opening 76 in the conical lower end 17 of the bowl 10.
The feed mode of operation for a separator of the invention
is described in greater detail below with reference to Fig. 4,
which shows an embodiment of the separator featuring the solids
divert valve movably located in the lower end region 39 of the
separator housing 13, below a lower surface of the rotatable
residual divert valve. With regard to Fig. 2, the feed mode can,
for example, be further characterized by having the piston retract
actuator 52 in contact with the conical lower end 17 of the
separator bowl 10. As shown, the piston retract actuator 52 can
move axially upward and downward in response to fluid such as, for
example, compressed gas or hydraulic liquid.
After solids have been separated from the feed liquid; the
piston remains in contact with the separator bowl 10 as residual
liquid in the bowl drains through the opening 76 onto a shaped
surface of the discharge valve 42, which also remains, as
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described above, in a closed position. As shown in Fig. 2,
residual liquid can then be channeled by the shaped surface of the
discharge valve 42 so as to pass through the residual liquid drain
passage 46. The residual liquid passes through the drain passage
5 46 and eventually exits the separator through the residual liquid
drain port 47.
In one embodiment, fluid pressure introduced at a fluid port
58 acts against a lower surface of an annular actuator flange 57
disposed about the piston retract actuator 52 to urge the retract
10 actuator 52 upward. The axial movement of the piston retract
actuator 52 may also be controlled by fluid introduced through an
actuator control port 54. For example, the actuator control port
54 can be provided in the lower end region 39 of the separator
housing 13 such that fluid enters the port 54 and contacts an
15 upper surface of the annular actuator flange 57 disposed about the
piston retract actuator 52.
The actuator control 54 and fluid port 58 can also act in
concert to actuate and move the piston retract actuator 52 by
concomitantly contacting the upper and lower surfaces of the
20 annular actuator flange 57 fluid. For example, the piston retract
actuator 52 can be urged upward when pressure acting against the
upper surface of the annular actuator flange 57 is less than that
acting against the lower surface thereof. During the feed mode,
the piston retract actuator 52 can be urged axially upward and
held in gas-tight communication with the opening 76 of the bowl
10. The interface of the piston retract actuator 52 and the bowl
opening 76 can also be sealed by, for example, PTFE or TEFLON-
based (E. I. du Pont de Nemours and Company, 1007 Market Street,
Wilmington, Delaware 19898) elastomeric seals disposed
therebetween.
Preferably, the piston retract actuator 52 is also in gas-
tight communication with the opening 76 of the bowl 10 while the
piston 12 is being returned substantially to its uppermost
position, which generally follows the solids discharge mode. As
described above, such gas-tight communication can be achieved via
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fluid pressure introduced through the fluid port 58, which acts
against the lower surface of the annular actuator flange 57
disposed about the piston retract actuator 52. Although fluid may
also enter the separator at the actuator control port 54, the
pressure exerted on the upper surface of the flange 57 would be
less than that acting against its lower surface to maintain the
gas-tight communication. It could also be preferable for the
actuator control port 54 not to introduce fluid to the upper
surface of the flange 57 such that the fluid port 58 would
entirely control the movement of the piston retract actuator 52.
To return the piston 12 substantially to its uppermost
position, fluid contacts the lower conical portion of the piston
12 after entering the separator bowl 10 via the feed liquid port
45 after fluid pressure urges the piston retract actuator 52
upward along the vertical axis 41 to communicate with the bowl
opening 76. When the piston is returned substantially to its
uppermost position, fluid introduced through the feed liquid port
45 can be discontinued. The piston 12 is then held substantially
in its uppermost position by frictional forces between one or more
piston seals adjacent the inner wall of the bowl 10. As shown in
Fig. 2, an annular piston seal 59 is disposed about the piston 12
and interfaces with the inner wall of the bowl 10. The seal 59
can comprise components such as, for example, PTFE or TEFLON-based
(E. I. du Pont de Nemours and Company, 1007 Market Street,
Wilmington, Delaware 19898) elastomeric materials.
Prior to returning the piston 12 substant'ially to its
uppermost position, the separator is typically operated in the
solids discharge mode in which solids are pumped from the bowl 10.
In the separator of the invention shown in Fig. 2, the solids
discharge mode is characterized by the discharge valve 42 rotated
about a rotational axis 6 to an open position such that solids can
leave the separator as the piston 12 travels axially downward.
The separator can also be readily cleaned or sterilized-in-place,
preferably, after the solids discharge mode, with the discharge
valve 42 rotated into an open position.
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For example, in order to rotate the discharge valve 42 from a
closed position, during the feed mode, to an open position, during
the solids discharge mode, the valve seal 48 can be deflated. The
valve seal can be deflated by, for example, discontinuing the
introduction of fluid at the valve actuator 49. An upper offset
portion of the discharge valve 42, which can include the piston
retract actuator 52, is then preferably rotated 900 about the
rotational axis 6, away from the opening defined by the inner edge
of the flange 43. In one embodiment, prior to rotating the
discharge valve 42 to an open position for the solids discharge
mode, the piston retract actuator 52 is removed from gas-tight
communication with the opening 76 of the bowl 10. The actuator 52
can move axially downward away from the bowl 10, for example, as
described above.
With the piston retract actuator 52 removed from gas-tight
communication with the bowl opening 76 and the discharge valve 42
rotated to an open position, solids can be pumped- from the
separator through the conical lower end 17 of the bowl 10.
Preferably, solids are pumped from the separator bowl as the
piston 12 travels axially downward. In general, the solids
discharge mode begins in the upper portion 19 of the separator
such as described in greater detail below with reference to the
separator in Fig. 7. As shown in Fig. 2, the piston 12 can also
feature a knife-edge 62, which may aid in the separation of
exceptionally paste-like solids that stick near the conical lower
end 17 or at the opening 76 of the separator bowl 10.
Figure 3 is a section view of the separator of Fig. 2
featuring a laser sensor assembly 122. For example, the assembly
122 can be mounted within or external to the separator housing 13
by any suitable means. in general, optical elements such as, for
example, focusing and reflecting members can be used to facilitate
.any suitable mounting options, configurations or arrangements for
the assembly 122. As shown, the laser sensor assembly can be
disposed above or at the upper portion 19 of the separator.
Preferably, the assembly 122 is disposed above the collar-like
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23
extension 22 of the upper end for the separator housing 13. The
laser sensor assembly 122 can be used to monitor the axial
movement of the piston 12 within the separator bowl 10. In one
embodiment, the separator can, for example, be any conventional
type of laser light emitting device.
For example, the laser sensor assembly 122 of Fig. 3 can
monitor the axial movement of the piston 12 by emitting a pulsed
laser light 124. As will be appreciated by those of ordinary
skill within the art, the assembly 122, by emitting then detecting
the pulsed laser light 124, can provide a time-to-travel
measurement from which the location of the piston 12 within the
bowl 10 can be determined. In one embodiment, a reflective
surface or member associated with the piston 12, and, preferably,
optically aligned with the laser sensor assembly 122 such as via
an optical path within the hub 60 of the bowl 10, can reflect the
laser light back to the assembly 122. Moreover, such a time-to-
travel measurement can also provide an operator with input
regarding the axial distance that the piston 12 has traveled. The
laser sensor assembly 122 in Fig. 3 can be used to monitor the
piston 12 within the bowl as the piston travels axially upward or
downward as, for example, a.function of pressure employed to move
the piston 12 within the bowl 10. The invention also contemplates
using other such conventional assemblies or devices based on, for
example, ultrasonic, infrared or radiation energy emitting means
to monitor the movement of the piston 12.
Figure 4 illustrates a separator of the invention operating
during the feed mode in which the bowl 10 and the piston 12 are
rotating together at high speed. For example, the solids-bearing
feed liquid is injected into the bowl and flows in a path 64 up
the inner surface of the conical lower end 17 of the bowl.
Preferably, the piston 12 is held at its uppermost position by
hydraulic pressure from the clarified liquid 72 such that it is
urged against the hub 60 of the bowl, maintaining the centrate
valve 34 in the open position. in one embodiment, the centrate
valve 34 is urged open by pins 67 extending from the hub 60 and
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24
into the piston 12 to push the valve 34 downward along the
vertical axis 41. The centrate valve 34 can close during the
solids discharge mode as, for example, springs 66 are urged
upward, which is described in greater detail below.
The centrate valve 34 and piston 12 can, for example, also
include one or more seals. Preferably, one or more seals can be
employed with the centrate valve to prevent clarified liquid from
returning to the interior of the separator bowl 10 after exiting
therefrom. Such seals can also be used so as to prevent solids
from entering the centrate case 30 during the downward movement of
the piston 12 in the solids discharge mode. Moreover, such seals
can allow a portion of the separator bowl 10 above the piston 12
to become and remain pressurized such that the piston can be
efficiently urged downward by fluid pressure during the solids
discharge mode. Seals associated with the centrate valve 34 and
piston 12 may also prevent clarified liquid from flowing between
the interior surface of the bowl 10 and piston 12. The invention
also contemplates employing one or more seals in association with
any one of or all of the passages, valves, pistons, actuators,
assemblies, ports, members and the like described herein.
Exemplary seals of the centrate valve 34 and piston 12 can
comprise components such as, for example, PTFE or TEFLON-based (E.
I. du Pont de Nemours and Company, 1007 Market Street, Wilmington,
Delaware 19898) elastomeric materials. For example, such seals
are described in greater detail below with reference to the
separator shown in Fig. 10. As shown in Fig. 4, the piston 12 can
also be held substantially in its uppermost position by frictional
forces between piston seals 56 adjacent the inner wall of the bowl
10. Preferably, these seals 56 are disposed about the piston 12
and interface with the inner wall of the bowl 10. In one
embodiment, the seals 56 can be separated from each other by a
linear portion on the piston 12. The seals 56 can, for example,
prevent misalignment of the piston during its axial movement and
provide for uniform communication with the interior surface of the
bowl such that the bowl may be efficiently pressurized either
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above or below the piston 12. In another embodiment, the piston
12 can feature a plurality of seals disposed thereabout and
interfaced wi.th= the inner wall of the bowl 10. Moreover, in lieu
of the seals 56, a single seal 59 such as, for example, shown in
5 Fig. 2 can be disposed about the piston 12.
In one embodiment, the interior of the bowl 10 of a separator
of the invention can feature a scratch resistant type coating_
For example, such a coating can be disposed along a portion or the
entire interior surface of the bowl 10. Exemplary coatings for
10 the interior of a separator bowl can include hard chromium, boron-
nitride, titanium or combinations thereof. Preferably, a scratch
resistant type coating can prevent abrasions to the bowl. Such
abrasions can lead to the feed liquid shearing, which may hinder
efficient solids separation and recovery. A scratch resistant
15 type coating within the bowl can also provide for uniform
communication between the interior surface thereof and one or more
seals disposed about the piston 12. Uniform communication between
the interior surface of the bowl and one or more seals disposed
about the piston 12 can aid in the efficient pressurization of the
20 bowl such as described above and in the efficient recovery of
accumulated solids.
Under the separation forces generated by high speed rotation
of the bowl 10, Fig. 4 shows the feed liquid separated into
accumulated solids 70 and clarified liquid 72. The clarified
25 liquid 72 continues upward along the path 64, through the centrate
valve 34 and exits the bowl at the centrate discharge aperture 74.
In one embodiment, the centrate discharge aperture 74 can be
disposed at or substantially at an upper end of the separator bowl
10. Preferably, the discharge aperture 74 leads into the centrate
case 30 that can feature the isolation valve 26, which is, for
example, open during the feed mode of operation. The isolation
valve 26 can be maintained open by fluid such as compressed gas or
hydraulic liquid acting against an annular member 9 disposed about
the valve 26.
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26
For example, in the feed mode, fluid can be introduced to a
lower surface of the annular member 9 through a lower port 4. The
clarified liquid 72 can then pass from the centrate case 30 into
the centrate outlet port 32, which features the centrate outlet
port valve 33. Preferably, the centrate outlet port valve 33 is
open during the feed mode to allow the clarified liquid 72 to exit
the separator as centrate 73.
A separator of the invention can also be employed in
applications in which there is a need to preserve the quality of
the centrate 73 that exits therefrom. For example, a sensitive
organic polymer that exits the separator as centrate may be the
only desired yield from a given separation. Indeed, the invention
also contemplates an application in which both the centrate and
solids are desired yields. In an application in which it is
important to preserve the quality of centrate exiting the
separator, the separator of the invention can be used to reduce
overall shearing of clarified liquid and centrate resulting
therefrom. Typically, such shearing can, for exattiple, degrade the
quality of sensitive centrate.
In one embodiment, a separator of the invention can employ,
for example, a separation and/or solids recovery means in addition
to or in lieu of a rotating bowl. One example of a separation
means is a conventional pairing-disc assembly. A separator of the
invention can comprise a pairing-disc assembly to, for example,
reduce the overall shearing of clarified liquid and centrate
resulting therefrom. For example, a pairing-disc assembly can be
used in an application for a separator of the invention in which
it is desired to preserve the quality of the centrate. As will be
appreciated by those of ordinary skill within the art, a pairing-
disc assembly can perform generally continuous separation of
solids from feed liquid with minimal overall shearing of, for
example, desired centrate.
A separator of the invention can also comprise one or more
features such as, for example, fastening and mounting means, by
which the bowl 10 can be decoupled from the separator housing 13.
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27
Preferably, with the bowl 10 decoupled, the piston 12 and its
associated assemblies can be substituted with a separation and/or
solids recovery means such as the pairing-disc assembly described
above. A separator bowl suitable for use with the substituting
separation and/or solids recovery means could subsequently be
coupled to the separator of the invention via one or more
features. The separator of the invention is then able to be used
for a specific application. The ability to modify the
configuration of a separator of the invention for a given solids
separation application permits use of such separation and/or
solids recovery means as an axial scraper or a piston-extrusion
assembly described by U.S. Patent Nos. 6,776,752, which is hereby
incorporated by reference herein.
As shown in the separator of Fig. 4, in the feed mode of
operation, the solids divert valve 90 can be held upwardly against
a lower surface of the residual divert valve 92 in gas-tight
agreement. In one embodiment, the solids divert valve 90 can
feature one or more seals such as, for example, disposed thereon.
For example, such seals can be used to enable pressurization of
the separator housing 13 and bowl 10, preferably, above the upper
portion of the piston 12 to provide for movement of the piston 12.
Such seals can comprise components such as, for example, PTFE or
TEFLON-based (E. I. du Pont de Nemours and Company, 1007 Market
Street, Wilmington, Delaware 19898) elastomeric materials. With
such seals enabling pressurization of the separator housing 13 and
the bowl 10, preferably, above the upper portion of the piston 12,
the isolation valve 26 can remain open during, for example, the
solids discharge mode. A configuration in which the isolation
valve 26 of the separator in Fig. 4 remains open during, for
example, the solids discharge mode of operation can be
advantageous for a particular application.
Preferably, the separator shown in Fig. 4 features the solids
divert valve 90 with one or more seals. Such seals can provide
for efficient pressurization of the separator bowl 10, preferably,
above the upper portion of the piston 12 when, for example, the
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28
isolation valve 26 is in a closed position such as during the
solids discharge mode. For example, by having the isolation valve
26 closed during a solids discharge mode of operation, the volume
pressurized to move the piston within the bowl and the time
required for pressurization can be reduced. The separator of the
invention as described above with reference to Fig. 2 preferably
features the isolation valve 26 in the closed position when it is
desirous to pressurize the separator bowl 10, for example, above
the upper portion of the piston 12 in order to axially move the
piston such as during the solids discharge mode of operation.
With the isolation valve closed, the volume between the housing 13
and the bowl 10 need not be pressurized, and the housing also need
not be constructed so as to be capable of maintaining such
pressurization.
Seals comprising components such as, for example, PTFE or
TEFLON-based (E. I. du Pont de Nemours and Company, 1007 Market
Street, Wilmington, Delaware 19898) elastomeric materials can
also, for example, be disposed on or associated with the residual
divert valve 92 to, preferably, seal the interface between the
valve 92 and the solids divert valve 90. In one embodiment, the
solids divert valve 90 can be urged upward by the solids divert
piston 102 on which the valve 90 is disposed at an uppermost end
in communication with the solids passage 104 of the piston 102.
As shown in Fig. 4, pneumatic or hydraulic pressure introduced at
an actuator port 112 acts against a lower surface of an annular
flange 110 disposed about the solids divert piston to urge the
piston 102 upward.
The solids divert piston 102 moves axially upward and
downward in response to pneumatic or hydraulic pressure. The
axial movement of the divert piston 102 may also be controlled by
compressed gas or hydraulic fluid introduced through a control
port 113. The control port 113 is provided in the lower end
region 39 of the separator such that compressed gas or hydraulic
fluid enters the port 113 and contacts an upper surface of the
annular flange 110 disposed about the solids divert piston 102.
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The control 113 and actuator port 112 can also act in concert to
actuate and move the divert piston by concomitantly contacting the
upper and lower surfaces of the annular flange 110 with compressed
gas or hydraulic fluid.
Also shown in Fig. 4 is the residual divert valve 92 in a
closed position located at the opening 76 in the bottom of the
bowl 10. The valve 92 defines the feed liquid passage 94 in
communication with the feed liquid port 96 such that the feed
liquid can be injected into the bowl 10 along the path 64. The
feed liquid is injected into the bowl 10 across a gap such that
the residual divert valve 92 need not contact the bowl 10 as it
rotates, preventing mechanical wear of the valve 92 and the bowl
10. Operatively coupled to the valve 92 is a residual divert
valve actuator 114. The actuator 114, which can be a pneumatic or
hydraulic cylinder, rotates the residual divert valve 92 from its
closed position about axis 6. While feed liquid is fed through
the feed liquid passage 94 and into the bottom of the bowl 10, the
solids outlet port 106 of the solids divert piston 102 features
the solids outlet port valve 107 in a closed position.
In one embodiment, a separator of the invention can reduce
the extent of overall shearing of the clarified liquid 72 as it
passes upward along path 64, through the centrate valve 34 and
exits the bowl 10 at the centrate discharge aperture 74. For
example, the extent of overall shearing of the clarified liquid 72
can be reduced by the movement of the clarified liquid 72 such as
shown in Fig. 5. Figure 5 shows that a separator of the invention
and, in particular, the centrate valve 34 can, by design, cause an
underflow effect of the clarified liquid along underflow path 129.
The underflow path shown in Fig. 5 is submerged below the
external boundary 130 of the clarified liquid 72 by the
configuration and/or arrangement of, for example, the bowl 10 and
centrate valve 34 during the feed mode. Preferably, by having the
underflow path 130 submerged beneath the external boundary 130,
air currents, surface waves, any non-concentric effects of the
bowl 10 and so forth generally tend not to disturb the movement of
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the clarified li.quid. For example, by not disturbing the movement
of the clarified liquid, the extent of overall shearing thereof
can be minimized using a separator of the invention.
As shown in Fig. 5, the underflow path 129 also tends to
5 avoid contact with the solids 70 accumulated along the interior
surface of the bowl 10, thereby avoiding any shearing of the
clarified liquid that could result from such contact. Generally,
in a conventional separator, the flow of clarified liquid is along
a surface boundary such as, for example, the boundary at the
10 accumulated solids or at the surface interior to the separator
bowl. in particular, coriolis acceleration effects within a
conventional separator tend to cause clarified liquid to flow
along the surface boundary at the interior of the bowl, exposing
the liquid to any potential shearing forces in the bowl. The
15 underflow path 129 of clarified liquid 72 in a separator of the.
invention avoids any such surface boundaries so as to limit the
extent of overall shearing.
Figure 6 illustrates the separator with the residual divert
valve 92 closed to permit the residual liquid 132 to drain out of
20 the bowl 10 and into the residual liquid drain passage-98. The
drain passage 98 leads into the residual liquid drain port 100,
where the residual liquid 132 eventually drains from the
separator. In one embodiment; the residual liquid 132 can also
be, for example, provided back to a feed tank associated with the
25 separator. The feed tank can then provide the separator with the
residual liquid, for example, in the feed liquid for further
solids separation. The liquid 132 is typically drained from the
separator by gravity after the feed mode is completed and the high
speed rotational separation has been performed. The feed liquid
30 port 96 is also closed or under sufficient back pressure to
prevent liquid 132 from exiting the separator through the feed
liquid passage 94. Although the bowl 10 and the piston 12 are no
longer rotating, accumulated solids 70 remain compressed tightly
against the inner surface of the separator bowl 10. The
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31
accumulated solids 70 can be recovered from the bowl 10 during the
solids discharge mode of operation.
As the residual liquid 132 drains from the bowl 10, the
piston 12 is also held substantially in its uppermost position
predominately by frictional forces between the piston seal or
seals 56 adjacent the inner wall of the bowl 10. In Fig. 6, the
separator is also shown with the solids outlet port valve 107
closed and the centrate outlet port valve 33 open. The isolation
valve 26 of the centrate case 30 is also maintained open.as it was
throughout the feed mode of operation. Also shown is the solids
divert piston 102 and the annular flange 110 disposed about the
piston 102. The lower surface of the annular flange 110 is
contacted by fluid such as, for example, compressed gas or
hydraulic liquid introduced through actuator port 112 such that
the solids divert piston 102 holds the solids divert valve 90
upward in gas-tight agreement with the residual divert valve 92.
The agreement between the solids divert valve 90 and the residual
divert valve 92 permits residual liquid 132 to drain out of the
bowl 10 and into the residual liquid drain passage 98, where the
liquid exits the separator.
After the residual liquid 132 has substantially drained from
the bowl 10, the separator is prepared for pumping of the
accumulated solids 70 in the solids discharge mode. The centrate
outlet port valve 33 and the isolation valve 26 are closed prior
to solids pumping. As described above, the centrate outlet port
valve 33 may be closed manually or via an automatic valve control
assembly. The isolation valve 26 is closed by discontinuing fluid
introduced through the lower port 4 of the separator. The fluid
had acted on a lower surface of the annular member 9 disposed
about the isolation valve 26 to maintain it open. For the solids
discharge mode, as shown in Fig. 7, fluid such as, for example,
compressed gas or hydraulic liquid instead contacts an upper
surface of the annular member 9 to actuate and close the isolation
valve 26. The fluid is introduced through an upper port 61 during
solids discharge and contacts the annular member 9 to urge the
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32
isolation valve 26 against the f lange 51 disposed in the upper
portion 19 of the separator.
Figure 7 illustrates the separator operating in the solids
discharge mode of operation. Figure 7 is split lengthwise to show
two separate positions of the piston 12. On the left, the piston
is partway through its downward travel, and on the right, the
piston is at the lowermost point of its stroke completing the
discharge operation, with its lower conical portion resting
against the inner surface of the conical lower end 17 of the bowl
10. As shown, the piston is urged downward along the vertical
axis 41 by, for example, fluid such as compressed gas or hydraulic
liquid acting against the upper portion of the piston 12. Also
shown is the centrate valve 34 in a closed position, under the
upward urging force of the springs 66. The springs 66 are urged
upward by interaction between the accumulated solids 70 and the
lower conical portion of the piston 12 during its downward travel.
With the piston 12 traveling down.ward, the accumulated solids 70
are pressed out of the opening 76 at the bottom of the bowl 10.
The lower conical portion of the piston 12 and the inner
surface of the conical lower end 17 of the bowl 10 are. machined
for precise fit to efficiently remove as much of the accumulated
solids 70 as possible. The movement of the piston 12 along the
vertical axis 41 is primarily caused by fluid introduced through a
driving port 2 in the upper portion 19 of the separator. Fluid
pressure introduced at the driving port 2 eventually contacts the
upper portion of the piston 12, when the centrate case 30 and the
section of the bowl 10 above the upper portion of the piston 12
disposed therein are completely sealed and pressurized. The
centrate case 30 and the section of the bowl 10 above the upper
portion of the piston 12 can be sealed and pressurized when the
isolation valve 26 is closed.
Moreover, the isolation valve 26 closes as it is urged
downward against the flange 51 by compressed gas or hydraulic
fluid introduced through the upper port 61. The compressed gas or
hydraulic fluid eventually contacts the upper surface of the
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annular member 9, which actuates the isolation valve 26. The.
centrate outlet port valve 33 for the centrate outlet port 32 is
also closed manually or by an automatic valve control assembly
during solids discharge mode. The isolation valve 26 is described
in greater detail, below with reference to Fig. 11, which shows the
upper portion 19 of the separator during the solids discharge
mode.
The solids discharge mode begins in the upper portion 19 of
the separator when the piston 12 is urged axially downward. At
the separator lower end region 39, the pumping mode begins as the
residual divert valve 92 is rotated from its closed position by
the residual divert valve actuator 114. The valve actuator 114
rotates the residual divert valve about axis 6 in response to, for
example, fluid pressure. After the solids divert piston 90 has
been lowered along the vertical axis 41 from contact with the
residual divert valve 92, the valve 92 is preferably rotated 900
from its closed position. The solids divert piston 90 is then
urged upward along the vertical axis 41 as fluid such as, for
example, compressed gas or hydraulic liquid is applied through the
actuator port 112 to act on a lower surface of the annular flange
110. Movement of the solids divert piston 102 may also be
controlled by fluid pressure introduced through the control port
113, which can act in concert with the actuator port 112. The
control port 113 allows fluid to contact the upper surface of the
annular flange 110. The solids divert piston 102 is then urged
upward when pressure acting against the upper surface of the
annular flange 110 is less than that acting against its lower
surface.
As shown, the solids divert piston 102 is urged axially
upward such that the solids divert valve 90 is held in gas-tight
communication with the opening 76 at the bottom of the separator
bowl 10. The interface of the solids divert valve 90 and the bowl
opening 76 can also be sealed by seals disposed therebetween
comprising components such as, for example, PTFE or TEFLON-based
(E. I. du Pont de Nemours and Company, 1007 Market Street,
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Wilmington, Delaware 19898) elastomeric materials such that any
solids pumped from the bowl 10 will not become contaminated by
contact with the surrounding environment. A sealed interface also
prevents accumulated solids 70 from being lost during recovery.
Accumulated solids 70 pushed through the opening 76 in the
bottom of the bowl 10 pass into the solids passage 104 disposed
partially within the solids divert piston 102 below the solids
divert valve 90. The solids passage 104 extends beyond the
lowermost end of the piston 102 leading into the solids outlet
port 106. As described above, the solids outlet port valve 107
for outlet port 106 is opened prior to discharge such that the
pumped solids can pass through the outlet port and valve 106, 107
to exit the separator. The solids outlet port and valve 106, 107
can also be configured so that the pumped solids may be passed
onto another process or a storage vessel without further handling
by an operator, which reduces the likelihood of or opportunity for
contamination.
Solids discharge is complete when the piston 12 reaches the
lowermost point of its downward stroke and rests against the inner
surface of the conical lower end 17 for the bowl 10 _ After the
accumulated solids 70 have been discharged from the bowl 10, the
piston 12 is returned substantially to its uppermost position by
fluid acting against the lower conical portion of the piston 12,
as shown in Fig_ 8. Fluid such as, for example, compressed gas or
hydraulic liquid introduced at the driving port 2 in the upper
portion 19 of the separator, which had acted on the upper portion
of the piston 12, is discontinued before the piston can be urged
upward along the vertical axis 41. Also shown in Fig. 8 is fluid
contacting the lower conical portion of the piston 12 after
entering the separator through the cleaning passage 108 from the
cleaning port 111. When the solids outlet port valve 107 is
closed, the fluid introduced at the cleaning port 111 eventually
passes through the bowl opening 76 to urge the piston 12 upward.
The separator bowl 10 may also be cleaned or sterilized-in-place
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while the piston 12 is moved upward or after it has substantially
reached its uppermost position.
The solids outlet port valve 107 transitions from an open to
a closed position after the accumulated solids are substantially
5 pumped from the separator. The outlet port valve 107 remains in a
closed positiori while the piston 12 is urged upward'and throughout
the next feed cycle of operation. Figure 8 further shows that
before the lower conical portion of the piston 12 is contacted by,
for example, compressed gas or hydraulic liquid, the isolation
10 valve 26 for the centrate case 30 and the centrate outlet port
valve 33 are opened. Fluid is also no longer introduced through
upper port 61 in the upper portion 19 of the separator. Instead,
fluid such as, for example, compressed gas or hydraulic liquid
enters the separator through the lower port 4 to eventually
15 contact a lower surface of the annular member 9 di'sposed about the
isolation valve 26 so as to open the valve 26. After the upward
stroke of the piston 12 is complete, the piston is held
substantially at an uppermost position by frictional forces
between piston seals 56 adjacent the inner wall of the bowl 10.
20 The solids divert piston 102 remains in gas-tight
communication with the opening 76 at the bottom of the bowl 10
.while the piston 12 is urged upward. The gas-tight communication
is achieved by fluid pressure introduced through the actuator port
112, which acts against the lower surface of the annular flange
25 110 disposed about the solids divert piston 102. Although fluid
such as, for example, compressed gas or hydraulic liquid may also
enter the separator at control port 113, the pressure exerted on
the upper surface of the annular flange 110 would be less than
that acting against its lower surface to maintain the gas-tight
30 communication. It could also be preferable for the control port
113 to not introduce fluid to the upper surface of the annular
flange 110 such that the actuator port 112 would entirely control
the movement of the solid divert piston 102.
When the piston 12 substantially reaches its uppermost
35 position, the solids divert valve 90 is drawn downward along the
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vertical axis 41 in response to movement by the solids divert
piston 102 such that the residual divert valve 92 can be rotated
to its closed position about the rotational axis 6. The residual
divert valve 92 is rotated closed by the residual divert valve
actuator 114. The solids- divert piston 102 can be lowered by
discontinuing or reducing the fluid pressure previously applied at
actuator port 112. Movement of the solids divert piston 102 may
also be controlled by fluid pressure introduced through the
control port 113, which can act in concert with the actuator port
112. The control port 113 allows fluid such as, for example,
compressed gas or hydraulic liquid to contact the upper surface of
the annular flange 110. The solids divert piston 102 is then
urged downward when pressure acting against the upper surface of
the annular flange 110 is greater than that acting against its
lower surface.
Figure 9 illustrates the lower end region 39 of the separator
in greater detail with the residual divert valve 92 returned to
its closed position. Although not shown, the piston has been
returned substantially to its uppermost position within the bowl.
As described above, the piston can be held in an uppermost
position by frictional forces between the piston seals adjacent
the inner wall of the bowl. In Fig. 9, the solids divert valve 90
is held upward against the lower surface of the residual divert
valve 92 by the solids divert piston 102. As shown, fluid such
as, for example, compressed gas or hydraulic liquid introduced at
the actuator port 112 acts against a lower surface of the annular
flange 110 disposed about the divert piston 102 to urge it upward
along a vertical axis 41. Although the solids discharge mode has
been completed, solids can remain in the solids passage 104 of the
piston 102. To remove the remaining solids, fluid such as, for
example, compressed gas or.hydraulic liquid is introduced through
the cleaning port 111 of the cleaning passage 108, while the
solids outlet port valve 107 is open.
The cleaning passage 108 and port 111 extend beyond the
lowermost end of the solids divert piston 102, with the cleaning
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passage partially disposed within the piston 102. The cleaning
passage 108 is also in communication at its uppermost end with the
solids passage 104 of the piston 102. This communication permits
fluid introduced at the cleaning port 111 to pass through the
cleaning passage 108 and into the solids passage 104. The fluid
pushes the remaining solids in the passage 104 toward the solids
outlet port 106, when the solids outlet port valve 107 is open.
As described above, when the solids outlet port valve 107 is
closed, the cleaning passage 108 and port 108 operate to urge the
piston 12 axially upward and return it substantially to an
uppermost position for the next feed cycle of operation.
As shown, the solids passage 104 is in communication with the
solids outlet port 106 such that any remaining solids in the
passage 104 can exit the separator by passing through the solids
outlet port valve 107. The solids outlet port 106 may pass the
recovered solids onto another process or a storage vessel without
further handling such as, for example, by an operator. The
cleaning passage 108 and port 111 can also be used to clean or
sterilize the solids passage 104 and solids outlet port 106 and
valve 107. Such clean-in-place or sterilize-in-place processes
are convenient for preparing the centrifugal separator for the
next cycle of operation. These processes also increase the solids
recovery yield and can reduce the likelihood of or opportunity for
contamination.
Figure 10 illustrates the upper portion 19 of the separator
in greater detail during the feed mode of operation with the
isolation valve 26 in an open position. In the feed mode, as
described above, the piston 12 is held at its uppermost position
by fluid pressure from the feed liquid as well as frictional
forces between piston seals 56 adjacent the inner wall of the bowl
10. As shown, the isolation valve 26 can be urged open or closed
by movement upward or downward, respectively, along the vertical
axis 41. The isolation valve 26 is urged upward by, for example,
compressed gas or hydraulic liquid acting against the lower
surface of the annular member 9 disposed about the valve 26. The
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compressed gas or hydraulic liquid is provided to the lower
surface of the annular member 9 through the lower port 4.
Figure 10 also shows optional seals 140 for the centrate
valve 34 and seals 145 for the piston 12. Preferably, the seals
145 can prevent clarified liquid from flowing between the piston
12 and the interior surface of the separator bowl 10. As
described above, seals 140 can be used so as to prevent solids
from entering the centrate case 30 during the downward movement of
the piston 12 in the solids discharge mode. Seals 145 can allow
the bowl 10 above the piston 12 to become and remain pressurized
such that the piston can be efficiently urged downward by fluid
pressure during the solids discharge mode. The invention also
contemplates additional seals that can be used in any one of the
embodiments of the invention.
7.5 Also shown in Fig. 10 is the isolation valve 26 separated
from flange 51 such that the piston 12 and bowl 10 can freely
rotate without significant mechanical wear. With the isolation
valve in an open position, the centrate 70 is allowed to enter the
centrate case 30 by passing through the centrate discharge opening
74. The centrate 70 eventually exits the separator after it
passes through the centrate outlet port 32 and the centrate outlet
port valve 33, which is also maintained in an open position in the
feed mode. The centrate outlet port valve 33 may be opened
manually or by an automated valve control.
Figure 11 illustrates the upper portion 19 of the separator
in greater detail during the solids discharge mode of operation.
As shown, the isolation valve 26 can be urged open or closed by
movement upward or downward, respectively, along the vertical axis
41. The isolation valve 26 is urged downward by fluid such as,
for example, compressed gas or hydraulic.liquid acting against the
upper surface of the annular member 9 disposed about the valve 26.
The fluid is provided to the upper surface of the annular member 9
through upper port 61. Prior to the solids discharge mode, fluid
introduced to the lower surface of the annular member 9,
maintaining the isolation valve 26 open, is preferably
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discontinued. The bowl 10 and piston 12 are also no longer
rotating such that the isolation valve 26 can then rest against
the flange 51.
With the isolation valve 26 in contact with the flange 51
and, as described above, the centrate outlet port valve 33 closed,
the centrate case 30 and the section of the bowl 10 above the
upper portion of the piston 12 disposed therein can be
pressurized. Pressurization of the centrate case 30 and the
section of the bowl 10 above the upper portion of the piston 12
occurs as fluid such as, for example, compressed gas or hydraulic
liquid is introduced to the separator at the driving port 2. The
fluid does not exit the centrate case 30 or the bowl 10 due to the
gas-tight agreement between the valve 26 and flange 51. A seal
made of components such as, for example, PTFE or TEFLON-based (E.
I. du Pont de Nemours and Company, 1007 Market Street, Wilmington,
Delaware 19898) elastomeric materials can also be disposed on the
valve 26 to seal its interface with the flange 51. For example,
in one embodiment, such as the seal associated with the valve 26
can prevent clarified liquid from passing into the separator
housing 13.
As the centrate case 30 and the section of the bowl 10 above
the piston 12 pressurizes, the isolation valve 26 is maintained
closed against the flange 51. Pressurization of the centrate case
and the section of the bowl 10 above the upper portion of the
25 piston 12 eventually provides a greater pressure above the piston
12 than below its lower conical portion. The difference in
pressure causes the piston 12 to be urged downward along the
vertical axis 41 as fluid contacts the upper portion of the
piston. The downward axial movement of the piston 12, as
30 described above and shown in Fig. 7, pushes any accumulated solids
72 along the inner wall of the bowl 10 through an opening 76 in
its conical lower end 17.
The following table is presented to more fully characterize
and describe the modes of operation for the various embodiments of
the invention described above. TABLE I provides, by way of
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example only, the position or configuration of the isolation valve
26, centrate valve 34, centrate outlet port valve 33, solids
outlet port valve 107,. solids divert valve 90 and residual divert
valve 92 during the feed and the solids discharge mode of
5 operation for the separator of Fig. 1. TABLE I also provides, by
way of example only, the position or configuration of each valve
of the separator in Fig. 1 when centrate drains from'the bowl, the
piston is returned substantially to an uppermost position
following solids discharge and when the separator of Fig. 1 is
10 cleaned or sterilized-in-place. The valves 26, 34, 33, 107, 90,
92 are each shown in the separator illustrated by Fig. 1. TABLE I
is not intended in any way to otherwise limit the scope of the
disclosure or any particular embodiment of the invention.
15 TABLE I
Mode Of Isolation Centrate Centrate Solids Solids Residual
Operation Valve Valve Outlet Outlet Divert Divert
Port Port Valve Valve
Valve Valve
Feed open Open Open Closed - Closed
Discharge Closed Closed Closed Open Upward Rotated
Drain Open Open Open Closed - Closed
Piston Open - Open Closed Upward Rotated
Clean - - - Open - Closed
Combined APD Centrifugation and Cross-flow Microfiltration Systems
When operating as a stand alone system, a cross-flow
20 mi.crofilter continuously concentrates the solids in the retentate
flow until the concentration of solids becomes so high that the
filter membrane is fouled, and the filtrate flow decreases. With
the addition of an APD centrifuge, solids are continuously removed
from the retentate flow in a highly concentrated state, and the
25 retentate solids concentration is kept low enough such that the
filtrate flow is not reduced.
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A schematic of one embodiment of a system for combined
microfiltration and APD centrifugation is shown in Fig. 12. A
solids-containing suspension 207 is feed into a tank 202 and then
pumped 203 to a microporous membrane filter. Solids concentration
in the retentate flow can be controlled by direct sensing using a
turbidity meter or density meter 204 used to control a retentate
pump 203, or can be deduced from the filtrate output pressure 205
or flow. This information can be used, for example, to decide
whether to return the retentate 236 to the microfilter 201 or to
divert the retentate by means of a valve 235 as feed 230 to an APD
centrifuge 210. This information can also be used to control the
feed rate through a positive displacement variable speed pump 234,
which results in a controlled solids removal. A turbidity or
density meter 220 also can be installed on the centrate output of
the APD centrifuge 210 to indicate when the APD bowl is full of
solids, and signal a need to cause solids discharge 104. The
turbidity or density of the centrate also can be used to control a
centrate pump 222 and to decide whether to return 224 the centrate
to the retentate tank 202 by means of a valve 223 or to discharge
228 the centrate from the system.
There are several advantages of using a system combining APD
centrifugation and microfiltration. The microfilter operates under
optimal conditions because there is no over-concentration of
solids in the retentate line. There is lower solids fouling, and
the flux rate across the filter can remain relatively constant.
The APD centrifuge can be sized smaller than if no microfiltration
is used, because the feed stream is more concentrated. The APD
centrifuge will deliver a drier solids discharge than other
devices that could be used for solids removal during
microfiltration. Thus, both pieces of equipment run optimally, and
capital costs are reduced. Continuous solids removal by the APD
results in continuous operation of the combined system. Less
smearing-up of solids will occur in the retentate flow due to the
lower solids concentration in the retentate. Finally, the
retentate/feed tank can be smaller by about ten-fold compared to a
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microfiltration system operated without an APD centrifuge for
solids removal.
The APD centrifuge for use in combination with
microfiltration is preferably of the type described in pending
U.S. Pat. Appl. No. 11/218,280, filed Sept. 1,.2005 and entitled
GAS DRIVEN SOLIDS DISCHARGE AND PUMPING PISTON FOR A CENTRIFUGAL
SEPARATOR. Other centrifuge systems may also be employed,
including systems described in the following patents and patent
applications: U.S. Pat. No. 6,632,166 entitled CENTRIFUGE
HAVING AXIALLY MOVABLE SCRAPING ASSEMBLY FOR AUTOMATIC REMOVAL
OF SOLIDS; U.S. Pat. No. 6,776,752 entitled AUTOMATIC TUBE-BOWL
CENTRIFUGE FOR CENTRIFUGAL SEPARATION OF LIQUIDS AND SOLIDS WITH
SOLIDS DISCHARGE USING A SCRAPER OR PISTON; U.S. Pat. Appi. No.
10/874,150 entitled CENTRIFUGE FOR SEPARATION OF LIQUIDS AND
SOLIDS WITH SOLIDS DISCHARGE USING A PISTON OR SCRAPER; U.S.
Pat. Appl. No. 10/823,844 entitled CONICAL PISTON SOLIDS
DISCHARGE CENTRIFUGAL SEPARATOR; and U.S. Pat. Appl. No.
10/973,949 entitled CONICAL PISTON SOLIDS DISCHARGE AND PUMPING
CENTRIFUGAL SEPARATOR. All of the foregoing, are incorporated
herein by reference.
In the 1280 application, a cylindrical bowl centrifuge is
shown having a one-piece gas driven piston. The piston head is
located at the upper end of the cylinder during feed liquid
introduction and centrifugal separation. After separation and
cessation of bowl rotation, gas pressure is used to translate the
piston head down through the bowl, pushing the accumulated solids
ahead of it and out of the bowl.
A system for APD centrifugation and microfiltration can be
combined in a single housing. For example, a microfilter can be
incorporated into the bowl of an APD centrifuge, such that piston
extrusion accommodates the presence of a microfiltration membrane.
For this embodiment, the single piston of the 1280 application can
be replaced with a peripheral outer piston and an inner piston.
Fig. 13 depicts an embodiment of an APD centrifuge incorporating a
microfilter. The apparatus is shown at the beginning of a solids
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discharge cycle. The cylindrical bowl 10 slows as the drive motor
16 brakes to a stop. Solids 70 have accumulated on the inner wall
of the bowl. The feed port 96 is closed, and residual liquid 132
drains from the bowl through residual liquid port 100. A
cylindrical microporous membrane 180 is positioned within the
bowl. Within the membrane is a cylindrical rubber diaphragm 190.
The outer piston 12a, also referred to as an outer solids
discharge piston, is cylindrical and has a lower face with a down
and inward slope. The inner piston 12b is disposed at the end of
a hollow shaft 12c which extends along the axis of symmetry of the
cylindrical bowl. The inner piston is a compound structure
comprised of a cylindrical portion and a substantially conical
portion. The lower end of the inner piston has a downwardly
facing concave depression.
At the upper end of the inner piston shaft, an outwardly
projecting circular flange has a lower surface adapted for
interfering with a spring disposed about the upper end of the
shaft, just below the flange. The shaft upper end is also
provided with an upwardly projecting cylindrical member having a
circular seal disposed thereabout. The upwardly projecting
cylindrical member has a hollow interior in communication with the
hollow interior of the shaft. The shaft is adapted for limited
vertical translation, as will be discussed below.
Above the vertical shaft is a vertically translatable
pressure coupling that is dimensioned to selectively mate, in a
fluid-tight relationship, with the upwardly projecting cylindrical
member of the shaft. A conduit formed in the coupling mates with
that of the cylindrical member once the coupling is driven down
against the shaft. A port at an upper end of the coupling enables
connection to a source of pressurized gas. A peripheral flange
provided on the coupling is disposed within the system housing
whereby introduction of pressurized gas above or below the
coupling flange drives the coupling down or up, respectively.
About a lower portion of the coupling there is provided an
inner piston actuator. Like the coupling, the actuator is
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provided with a peripheral flange, disposed in a respective
housing, having ports for introduction of pressurized gas above or
below the actuator flange, thereby driving the actuator down or
up, respectively. When driven down, the actuator presses upon an
upper end of the shaft, thereby driving the inner pi'ston down
towards and ultimately against a lower end of the cylindrical
bowl, which is also referred to as a low shear conical feed
accelerator. A lower end of the spring, located at the upper end
of the shaft, presses against a shoulder portion of the bowl
housing, thereby biasing the shaft in an upper position. The
lower face of the inner piston and the conical feed accelerator
have complimentary shapes, such that solids disposed therebetween
are squeezed out a lower exit port when the inner piston is driven
downward.
Within the cylindrical bowl, adjacent the shaft, is a. tubular
rubber diaphragm 190. Upper and lower ends of the diaphragm are
affixed to the bowl. Ports formed in the shaft enable pressurized
gas introduced at the port in the coupling to inflate the
diaphragm, which will be discussed subsequently.
A cylindrical microfiltration membrane 180, e.g., formed of
ceramic or sintered metal, is disposed about the rubber diaphragm
and affixed at upper and lower ends to the cylindrical bowl. A
cylindrical inner air gap exists between the membrane and the
diaphragm when the diaphragm is not inflated by pressurized gas.
A cylindrical outer air gap is formed between the outer
surface of the membrane and the inner surface of the cylindrical
bowl. It is in this outer air gap that the outer piston travels
following solids deposition. The lower end of the cylindrical
bowl defining the bottom of the outer air gap has the same shape
as the inwardly canted lower surface of the outer piston, thereby
enabling complete extrusion of solids accumulated in the outer air
gap once the outer piston is driven downwards, discussed below.
Plural conduits are formed between the inner and outer air
gaps, below the membrane and above the inner piston, to enable
draining of residual liquid from the bowl after separation.
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Similarly, plural conduits are f ormed between the outer air gap
and the area above the low shear conical feed accelerator to
enable liquid to pass into the outer air gap during feed liquid
introduction, to enable residual liquid to drain out after
5 separation, to enable solids to be forced out of the bowl by the
outer piston, and to enable pressurized gas introduced at the
lower end of the bowl to drive the outer piston to its upper
position.
An upper end of the cylindrical bowl is provided with two
10 sets of circularly arranged conduits. Proximate to and radially
outward from the outermost set of conduits is a centrate case
isolation valve. This valve has a peripheral flange on either
side of which can be created a pressure differential for moving
the centrate valve between open and closed positions. Open, in
15 this context, means there is no barrier between the centrate or
clarified liquid case above the cylindrical bowl and the air gap
between the housing and the cylindrical bowl outer surface. In
the closed position, the centrate valve creates a gas-tight
barrier between these regions. During bowl rotation, the centrate
20 valve is maintained in the open position to avoid interference
between the valve and the bowl. Movement between the open and
closed positions is accomplished by selectively introducing
pressurized gas into isolation piston control ports formed on the
outside of the housing.
25 Conduits are also formed through the centrate case isolation
valve itself. Depending upon bowl orientation, at least one of
these conduits is aligned with a solids discharge piston gas
supply port formed on the housing exterior surface. When the
centrate case isolation valve is closed, pressurized gas applied
30 to the solids discharge piston gas supply port passes through the
centrate case isolation valve conduits and the bowl upper end
outermost conduits to force the outer piston downward.
The innermost set of conduits formed in the bowl upper end
connect the inner air gap between the tubular rubber diaphragm and
35 the microfiltration membrane with the clarified liquid or centrate
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case. As discussed below, during initial separation, these
innermost conduits enable clarified liquid to process up and out
of the cylindrical bowl, into the centrate case, and out of the
centrate port.
At the lower end of the cylindrical bowl, a solids valve 91
is provided. The solids valve has open and closed' positions,
depending upon its orientation about an axis of rotation which is
orthogonal to the axis of rotation of the cylindrical bowl. Figs.
13-14 and 17 illustrate the solids valve in the closed position,
while Figs. 15-16 illustrate the solids valve rotated 90 degrees
about the axis of rotation (away from the viewer) to the open
position-. A solids valve actuator 95 and associated linkage
control the positioning of this valve. The actuator may be
pneumatic or hydraulic.
Disposed within the solids valve is a piston having a piston
retract actuator 52 which selectively places the solids valve
piston in mechanical communication with the bowl lower extent. A
peripherally disposed flange enables a differential in gas
pressure on opposite sides of the flange to control the piston
position. Two air ports formed on the solids valve enable the
formation of these pressure differentials. To seal the lower end
of the cylindrical bowl housing to the solids valve, a circular,
inflatable solids valve seal 93 is provided. A port formed on the
housing exterior connects a source of pressurized gas 195 to this
seal for selective inflation.
Also formed within the solids valve is a feed liquid conduit.
This conduit has a port 155 on the outside the -solids valve and
terminates below the lower extent of the solids valve piston. The
hollow interior of the piston and the concave lower extent of the
inner solids discharge piston are shaped to form a feed inlet pool
of radius R1, shown in Fig. 14 as 184.
Opposite the piston actuator control paths and the feed
liquid conduit in the solids valve is a residual liquid drain
(shown in Fig. 13 as 100) which may be connected to waste or to a
system for recycling or recovering the drained liquid.
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Fig. 14 illustrates the embodiment of Fig. 13 in feed mode.
The inner piston 12b is maintained in its upper position due to
spring biasing. The outer piston 12a is maintained in its upper
position through friction and pressure applied by the introduced
feed liquid to be separated. The centrate case isolation piston
194 is raised to its open position, and centrate 73 flows out
under gravity. The solids valve 91 is closed and the solids valve
seal 93 is inf lated . Within the solids valve, the piston retract
actuator 52 is driven down away from the lower extent of the bowl.
The motor 16 is driven at high speed, thus resulting in rapid
rotation of the bow]. 10.
Feed liquid 155 introduced through the solids valve 91 forms
a jet 154 as it exits the solids valve piston. The jet strikes
the concave lower surface of the inner piston and forms an inlet
pool of radius Rl 184 against the conical surface 17 of the low
shear feed accelerator. The feed liquid then passes through
conduits to the outer air gap. Solids 70 collect against the bowl
inner wall. Filtered centrate 182 passes through the membrane and
towards the bowl inner diameter. Air or hydraulic pressure 195
keeps the piston retract actuator 52 down and the solids valve
seal inflated 93.
While the tubular rubber diaphragm 190 is forced outward by
centrifugal action, the filtered centrate 182 pushes it away from
the membrane since the centrate exit port radius R2 185 is greater
than the feed pool radius R1 184.
Following the feed mode, a drain mode is initiated. Here,
bowl rotation ceases, allowing residual liquid to drain from the
inner and outer air gaps, through the bowl lower extent, into the
area above the sealed solids valve, and through the residual
liquid drain port. Feed liquid pressure is preferably maintained
to avoid residual liquid from passing into the solids valve piston
and the feed liquid path. Collected solids remain against the
bowl outer wall.
Discharge mode is shown in Figs. 15 and 16. In Fig. 15, air
or hydraulic pressure 195 is used to drive the vertically
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48
translatable pressure coupling down into gas-tight communication
with the cylindrical member atop the inner piston shaft.
Pressurized gas 195 is also used to close the centrate case
isolation valve. The solids discharge valve seal 93 is deflated,
the solids discharge valve piston is retracted, and the solids
discharge valve 91 itself is rotated to its open position.
Pressurized gas applied to the pressure coupling results in
pressurization within the shaft and the inner air gap between the
rubber diaphragm and the shaft, forcing the diaphragm 190 into
contact with the membrane inner surface. This then seals off the
membrane, preventing solids from migrating into the membrane as
they are scraped by the outer piston 12a. The latter occurs as
pressurized gas is introduced to the outer solids piston pressure
supply port on the housing surface. The gas flows through the
isolation valve conduits, through the outermost set, of conduits
formed in the cylindrical bowl upper end, and thereby into the
outer air gap above the outer piston. This pressure drives the
outer piston down, resulting in accumulated solids being scraped
from the membrane outer surface and the cylindrical bowl inner
surface, through the conduits connecting the outer air gap and the
area below the inner piston, and extruded 71 through an opening in
the bowl.
In Fig. 16, all solids beneath the outer piston 12a have been
forced either out of the bowl or into the area beneath the inner
piston 12b. The diameter of the conduits between the outer air
gap and the area beneath the inner piston is minimized to minimize
waste. Gas pressure 195 is used to move the inner piston actuator
within the vertically translatable pressure coupling. This gas
pressure overcomes the spring bias and the resistance of solids
accumulated in the area beneath the inner piston. As the inner
piston is driven downward, the remaining solids are driven from
the bowl. The perimeter of the concave region formed on the lower
extent of the inner piston is dimensioned to enable the remaining
extruded solids 71 to be cut off from the bowl opening.
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49
As shown in Fig. 17, the solids divert valve 91 is closed,
the solids valve seal 93 is inflated, and the solids discharge
valve piston 52 is raised after solids discharge. Gas pressure
195 is used to return the inner piston actuator to its upper
position, thereby retracting the inner piston 12b. Gas pressure
is also introduced to the feed port in the solids divert valve.
This also forces the inner piston up, as well as forcing the outer
piston 12a up. Gas pressure 195 continues to be applied to the
pressure coupling in order to keep the rubber diaphragm inflated
against the inner surface of the membrane.
As shown in Figs. 18, 19, and 20, fouling of the membrane can
occur as feed liquid migrates through membrane pores 183 on the
path towards the feed liquid exits (i.e. the innermost set of
conduits in the cylindrical bowl upper end). The fouling may
result from soli.ds, carried by the feed liquid to the membrane
outer surface, that form particulate 181 or whole or slime-like
70a deposits on the membrane. Due to the high rotation speeds,
both the particulate and slime-like deposits eventually have
sufficient mass to be forced away from the membrane outer surface
by centrifugal action.
Various resilient and non-reactive seals are illustrated in
the figures and are not discussed in detail, here. The benef its
associated with the semicircular bearing and bearing housing are
discussed in a related patent application. Materials preferred
for use in the system as shown are as described in the '280
application. The microfiltration membrane is preferably provided
as sintered metal or ceramic.
While the present invention has been described in conjunction
with a preferred embodiment, one of ordinary skill in the art,
after reading the foregoing specification, will be able to effect
various changes, substitutions of equivalents and other
alterations to the compositions, articles, methods and apparatuses
set forth herein. For example, fluid pressure may be replaced in
other embodiments by, without limitation, an electromechanical
force. Similarly, the lower portion and end of the piston and
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bowl, respectively, may not be conical in shape, although it is
preferable for solids recovery that their shapes be complimentary.
Moreover, the invention also contemplates that the various
passages, valves, pistons, actuators, assemblies, ports, members
5 and the like described herein can be in any configuration or
arrangement that would be suitable for operation of a centrifugal
separator. The embodiments described above may also each include
or incorporate any of the variations of all other embodiments.
For example, the laser sensor assembly described herein can be
10 used in conjunction with any or all of the embodiments of the
present invention. it is therefore intended that the protection
granted by Letter Patent hereon be limited only by the definitions
contained in the appended claims and equivalents thereof.
