Note: Descriptions are shown in the official language in which they were submitted.
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There are a number of circumstances in the treatment of
slurries in which it is desirable to transfer particles oE the
slurry from a first liquid, to a second liquid. This is
particularly so in the pulp and paper art in which slurries of
comminuted cellulosic fibrous material are present in a first
treatment liquid, and it is desired to transfer the slurry
particles to a second treatment liquid.
The present invention provides a screening assembly for
separating out particles contained in a Eirst liquid slurry and
introducing them into a second liquid flow, while maintaining the
particles and liquid under superatmospheric pressure, comprising:
a liquid tight pressure resistant vessel defining an open
interior; partition means for dividing said vessel open interior
into first and second distinct chambers so that the chambers are
isolated from each other except for means defining a slit in a mid
portion thereof; an inlet for the first liquid slurry, and an
outlet for the first liquid, operatively connected to said :Eirst
chamber; an inlet :Eor the second liquid, and an outlet for the
second liquid with entrained particles, operatively connected to
said second chamber; screening disk means for screening particles
from the first liquid slurry i.n the .Eirst chamber, and allowing
the particles to be entrained by the second liquid flow in the
second chamber; means Eor mounting said disk means so that it
essentially fills said slit, with portions thereof disposed in
each of said first and second chambers, and so that it extends
generally transverse to said partition means, and is rotatable
about an axis generally parallel to said partition means; and
means for rotating said disk means so that points spaced from the
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axis thereof move from one chamber to the other during rotation.
Not only is the apparatus according to the invention simple and
easy to construct and use, the general concepts thereof allow
great flexibility so that the concentration of particles in the
slurry can be greatly changed during transfer of the particles
from the first to the second liquid, allowing the slurry to be
; thickened or diluted.
In operation, the slurry of first liquid and particles
is caused to flow in a first direction. Particles from the slurry
are captured as it flows in the first direction, to separate the
particles from the flow. A flow of the second liquid is
established in a direction generally opposite to the first
direction; and the captured particles are moved into operative
association with the flow of the second liquid so that the
captured particles are entrained in the second liquid. As
mentioned above, the method has particular application to the
handling of slurries of comminuted cellulosic fibrous material
(paper pulp), and in particular switching the slurry particles
from one treatment liquid to another, distinct treatment licluid,
although the process can also be applied to transferring the
particles to a higher or lower pressure flow of the same liquid,
or merely as a way of effecting thickening or dilution of the
slurry. Alternatively thickening or dilution of the slurry can be
accomplished at the same time as the particles are transferred
from one treatment liquid to a second distinct treatment liquid.
The screening disk preferably comprises a generally
circular screen sandwiched between first and second circular disk
plates having through-extending openings therein, with the
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openings in the Eirst plate, and the screen, defining pockets in
which the particles are captured. The disk is rotated so that
points spaced from the axis thereof move from one chamber to the
other during rotation. Flanges associated with the partition in
the vessel, and the shape of the pockets and the disk (and the
solid areas between the pockets), are designed so that a pocket
does not communicate with both chambers at the same time, and
little liquid moves from one chamber to the other.
Features of the invention will become clear from an
inspection of the detailed description of the invention and from
the appended claims.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a side cross-sectional view of an exemplary
assembly according to the present invention;
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FIGURE 2 is a cross-sectional view taken along
lines 2-2 of FIGURE l;
FIGURE 3 is a detail cross-sectional view taker,
along lines 3-3 of FIGURE 2; and
FIGURE 4 is a view like that of FIGURE 2 only
showing a second embodiment of the assembly.
DETAILED DESCRIPTION 0~ T~E~ DRAWINGS
The screening assembly 10 exemplarly
illustrated in FIGURES 1 through 3, includes a
liguid tight pressure resistant vessel 11 defining
an open interior. The vessel is preferably formed
in two sections 12, 13, each having a peripheral lip
14, 15, respectively with an annular gasket 16
clamped between the lip~ 14, 15. Bolts, clamps, or
any other suitable conventional means can be
utilized to hold the vessel halfs 12, 13 together at
the lips 14, 15 80 that the vessel is liquid tight.
While the shape of the vessel 11 is not
particularly ~ignificant, since #uperatmospher1c
pressure will be applied, and ~ince the pres~ure may
be on the order of 10 bar, the vessel 11 preferably
takes the shape of a flattened spherical or
ellipsoidal shell (as illustrated in FIGURE 1) #o
that it has sufficient strength.
The assembly 10 al#o includes partition means
for dividing the vessel open interior into first and
second distinct chambers. The partition means
preferably take the form of the partition wall 18
located in the vessel half 12, and the partition
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wall 19 located in the vessel half 13. These walls
18, 19 extend the entire width of the vessel
portions 12, 13, respectively and separate the
interior into distinct chambers that are isolated
S from each other except at a slit between the
partition wall3 18, 19. Associated with the walls
18, 19 preferably are flanges 20, 21, respectively,
while the interior periphery of the vessel portion~
12, 13 preferably also include annular flanges 22,
23. The first chamber of the vessel 11 is denoted
by reference numeral 24 in FIGURE 1, while the
second chamber is denoted by reference numeral 25.
The assembly 10 further comprises an inlet 26
for a first liquid slurry, and an outlet 27 for the
first liquid, the inlet and outlet 26, 27 being
connected to the first chamber 24. Operatively
connected to the second chamber 25 are an inlet 28
for the second liquid, and an outlet 29 for the
second liquid with entrained particles. Inlet 26
and outlet 29 typically are in a common vertical
plane, as are outlet 27 and inlet 28.
The assembly 10 further comprises a screening
disk means, ~3hown generally by reference numeral 32,
for screenin~ particles from the first liquid slurry
in the first chamber 24, and allowing the particles
to be entrained by the second liquid flow in the
second chamber 25. While the screening disk means
may take a variety of forms, preferably it is formed
as illustrated in the drawings in which a generally
circular screen 36 (such as screen cloth of woven
metal wire) is sandwiched between generally circular
first and second disk plates 34, 35, respectively.
The disk plates 34, 35 are solid, except at the
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portions 38, 39 (see FIGURE 3) thereof which define
through-extending openings. The walls of the disk
plate 34 defining the openings 38, and the screen
36, define pockets 40 in the face of the disk means
32 closest to the inlet 26 and outlet 29, the
pockets 40 adapted to capture particles that have
been screened out of the first liquid flow through
the screen 36. The openings 38, 39 are aligned with
each other.
The pockets 40 preferably have a smaller width
adjacent the center of the ~creening disk means 32
than closer to the periphery thereof; that is they
have a generally sector-shape as illustrated in
FIGURE 2. The pockets 40 are preferably spaced
evenly along the entire disk means 32, with solid
portions 41 of the disk plate 34 disposed between
the pockets, with the portions 41 having dimensions
that are at least as large as the dimensions of the
pockets. The disk means 32 is also solid at the
portions thereof most closely adjacent to the center
of the partition walls 18, 19, and at the peripheral
interior flanges 22, 23, of the vessel portions 12,
13.
The disk means 32 are mounted by mounting means
so that the disk means essentially fills the slit
between the partition walls 18, 19 (see FIGURE 1)
with portions of the disk 32 disposed in each of the
chambers 24, 25, and so that the disk means 32
extends generally transverse to the partition walls
18, 19, and so that the disk means 32 is rotatable
about an axis 43 defined by shaft 42, which axis is
generally parallel to the partition means 18, 19.
The flanges 20 through 23 comprise means for
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mounting the disk means, engaging both of the disk
plates 34, 35 and essentially preventing the passage
of liquid between chambers 24, 25. To further
facilitate this function, the flanges 20, 21 are
formed to have dimensions greater than tha
dimensions of the pockets 40, and are shaped in
essentially the same way a~ the pockets 40 (i.e.
sector-shaped), as can be seen for the flanges 20 in
FIGURE 2. Note particularly at the top of FIGURE 2
wherein a flange 20 is illustrated having a sector
shape and having dimensions larger than a pocket 40,
which is shown in dotted line therebelow. In this
case, each pocket 40 i8 completely covered by a
flange 20 90 that it does not communicate with both
15 chambers 24, 25 at the same time (the flanges 20, 21
thus comprising means associated with the partitions
18, 19 so as to prevent such communication).
The assembly 10 also comprises means for
rotating the disk means 32 so that points spaced
from the axis thereof (e.g. pockets 40) move from
one chamber to the other during rotation. The
rotating mean~ are connected to the ~haft 42, and
may compri~e any conventional motor. In normal
operation, the motor rotating the shaft 42, and thus
the disk 32 connected thereto, would continuously
rotate the disk 32, and at substantially the ~ame
~peed during any given treatment operation.
While different arrangements and orientation 5
may be provided, as shown in FIGURES 1 and 2, the
shaft 42 may be mounted so that it is received
within the partition walls 18, 19, being surrounded
by the partition wall 18 throughout the length
thereof within the vessel portion 20, and having a
free end thereof journalled at 44 in the partition
wall 19. It will be seen that the disk 32 (and thus
the disk plate~ 34, 35 forming it) has a diameter
slightly greater than the radial distance between
opposite portions of the flanges ~2, 23, so that the
disk 32 is engaged thereby during rotation. There
will be ~ome clearance between the disk 32 and the
flanges 20 through 23 so that they do not retard the
rotation of the disk 32, 80 that a minor amount of
leakage will occur, but such minor leakage is not
significant. For example, if the liquid slurry 51
consists of a liquor having a fiber content of 200
ppm, and if the pockets 40 run filled with 10~ fiber
and 90% liguor, then the transfer of liquid will
amount merely to about 0.2% of the liquor flow.
It is further desirable to dimension the
pockets 40, and also taking into account the other
parameters, so that the pockets 40 are filled with
particle,s when they pass from chamber 24 to chamber
25 so that a minimum amount of liquid will be
transferred between them. This is particularly
significant where the first and second liquids are
entirely different types of treatment liquids, for
example in the case of the treatment of pulp, where
one liquid i~ a digesting liquid and the other i8 a
washing liquid. The inlets and outlets 26 through
2~ may be connected up to any desired conventional
equipment, for example the inlet 26 could be
connected up to the discharge from the continuous
digester while the outlet 27 is connected to an
evaporator, while the inlet 28 is connected up to a
source of wash liquid, while the outlet 29 is
connected up to a pressure diffuser or like
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treatment vessel.
In the embodiment illustrated in FIGURES 1
through 3, the chambers 24, 25 are substantially the
same size. That means that during treatment with
the assem~fly lO, if the flows of the first and
second liquids are essentially the same and the
shaft 42 rotates continuously at approximately the
same speed, the consistency of the slurry exiting
the outlet 29 will be substantially the same a~ the
consistency of the slurry entering the inlet 26
(e.g. about 6-15%). However according to the
present invention by makin~ simple modifications to
the a~sembly 10, or the flow rates, it is possible
to have a differential consistency between the
slurries. That is the slurry 53 (see FIGURE 1) of
particles in the second liquid, can be made to have
a different consistency (either greater than or less
than, but preferably greater than) the consistency
of the ~lurry 50, during operation of the a~sembly
lO in which the first liquid flow 51 after particle
6eparation i8 through the outlet 27, and the second
liquid flow 52 i8 through the inlet 28.
One simple way to accomplish differential
con~i~tencies between the ~lurry inlet and outlet
flows i~ to utilize the assembly 110 illustrated in
FIGURE 4. In FIGURE 4 components comparable to
those in the FIGURES 1 through 3 embodiment are
illustrated by the ~ame reference numeral only
preceded by a "1".
In the assembly llO, essentially all of the
elements are the same as in the FIGURES 1 through 3
embodiment, except for the partition wall means 118,
118' (and comparable partition walls corresponding
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to the partition wall 19 in the FI~URE 1 embodiment,
and not shown in FIGURE 4). In this embodiment, the
walls 118, 118' are disposed at an angle 55 of less
than 180 (as in the FIGURE~ 1 through 3
embodiment), 80 that one of the chambers is much
larger than the other. For the particular
relationship between components illustrated in
FIGURE 4, it will be seen that the first chamber 124
is much larger than the chamber 125, the angle 55
being approximately 36, so that the chamber 125 is
about 10% of the interior volume of the vessel
section 112, while the chamber 124 is approximately
90% of the lnterior volume. Of course any desired
ratio between the volumes 124, 125 can be provided
in order to accomplish any desired result.
Typically, the flows 50, 51 will be at
substantially the same pressure as the flows 52, 53,
and at ~ubstantially the same rate. However in
order to ensure that any leakage of liquid that
takes place is in a desired direction, a small
pressure difference may be maintained between the
chambers, or in some circumstances if it is desired
to enhance or reduce the pressure of the slurry a
pressure differentiation between the flows 50, 51 on
the one hand and 52, 53 on the other may be
provided. Minor pressure differences typically
result from the flow resistance of the screen 36,
but do not typically adversely affect the desired
results.
Method
In an exemplary method according to the
present invention, a slurry of a first liquid and
particles 50 passes through inlet 26 into first
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chamber 24 in a first direction, defined by the
continuous flow path between the inlet 26 and outlet
27. Particles in the slurry 50 are captured as it
flows in the first direction, in the pockets 40, to
separate the particle~ from the flow. The second
liquid 52 is caused to flow in a second direction,
defined by the inlet 28 and outlet 29, which second
direction is generally opposite to the first
direction. The captured particles are moved (by
rotating the disk 32) into operative a~sociation
with the second liquid flow 52, 80 tha-t the captured
particles are entrained in the second liquid and
define the cecond slurry 53. ~y controlling the
rate of the flow 50, 51 with respect to the rate of
the flow 52, 53, and/or by providing a differential
dimension between the chambers (e.g. chambers 124,
125), it i8 possible to either thicken or dilute the
slurry; for example, when the assembly llO is
utilized and the disk 132 is rotated continuously at
approximately the same speed, and the flow rates are
the same, the slurry 53 will have a significantly
greater consistency than the slurry SO, the relative
consistency being precisely calculatable based upon
the relative chamber dimen~ions, flow rates, and the
like (e.g. approximately a lO fold increase when the
apparatus llO i8 utilized with matching flow~).
The method is particularly desirable for
replacing one treatment liquid which entrains
comminuted ~ellulosic fibrous material (e.g. at a
consistency o about 6-15%) with a second, distinct,
treatment liquid, such as replacing a digesting
liquid with a wash liquid, or a wash liquid with a
bleaching liquid.
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Normally, the assembly 10 will be dispos~d so
that the flows 50 through 53 are vertical, with the
flows 50, 51 downward and the flows 52, 53 upward.
However a wide variety of other orientations may
S also be utilized, such as by making all of the flows
horizontal, or tilting the assembly 10 so that the
flows are inclined, and by switching positions of
inlets and outlets a~sociated with a particular
chamber, etc.
While the invention has been herein shown and
described in what is presently conceived to be the
most practical and preferred embodiment thereof, it
will be apparent to those of ordinary skill in the
art that many modifications may be made thereof
within the scope of the invention. For example, the
vessel 11 may be cylindrical in shape with dome
shaped tops and bottoms, and abutments provided to
prevent deformation of the screen disk. The screen
36 could be formed -- instead of by woven metallic
wire cloth -- from thin perforated or slitted
metallic plates. Further, the interior of the
ve~sel may be divided into more than two chambers,
such a~ four chamber~, so that the flows are
alternately directed upwardly and downwardly 90 that
the pre~ure upon the disk 32 is distributed over
the circumference and is mutually compensated.
These and other modification~ are intended to be
within the scope and ~pirit of the intended claims.
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