Note: Descriptions are shown in the official language in which they were submitted.
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LIQUID DISTRIBUTOR FOR A WASHING APPARATUS,
AND WASHING APPARATUS
TECHNICAL FIELD
The invention relates to a liquid distributor for a washing apparatus.
BACKGROUND
Pulp wash* is a key operation in the pulping line. There are many different
types of
washing apparatuses available, some of which are based on press washing and
comprise
means for pressing the pulp to remove liquid. After pressing, the pulp can, if
suitable,
be diluted to a desired consistency.
A well-known washing machine is a twin-roll press of the general type
disclosed in
US 3,980,518, for example. It has two counter-rotating rolls with perforated
outer
surfaces. A web of pulp is formed on the respective rolls and is transported
in the
direction of rotation in a vat partially surrounding the rolls, to the so-
called press nip
between the rolls. The liquid removed from the pulp, i.e. the filtrate, passes
through the
perforated roll surface in a radial inwards direction and is, by means of
axial filtrate
channels, led to the ends of the press roll, where it is output. Washing
liquid or other
treatment liquid may be supplied to the pulp web through inlets in the vat.
Another known washing equipment is a drum washer, as in e.g. US 5,046,338 or
SE 502815, where the cellulose-containing pulp is deposited and dewatered on a
single
rotating filter drum with a permeable outer surface, after the addition of
washing liquid,
which displaces the liquid remaining on the pulp web after the preceding
process step,
for example a cooking step or bleaching step. The static pressure causes the
contaminated liquid, called filtrate, to pass through the outer surface
permeable to liquid.
A further development of the original drum washer is the pressurized
displacement
washer, where the filtrate, under overpressure, is forced to pass through the
permeable
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outer surface. In these examples washing liquid is fed through a nozzle and is
then output
through a slot in a baffle.
A problem with directing the washing liquid perpendicular to the pulp web is
that it passes
right through the pulp web with high velocity and with the smallest possible
contact route
with the fibres. This gives longitudinal tracks in the fibre web and the
washing is ineffective,
since the washing liquid is mixed with the filtrate.
In SE 448524 a liquid distributor is shown with an output perpendicular to the
input and
where the output channel is enlarging towards the output. The purpose is to
slow down the
washing liquid, by having a conical nozzle. Since the cross section area is
continuously
increasing towards the outlet. the washing liquid will slow down. A problem is
that a cone
needs to be long in order to have effect and thus takes a lot of place and
will thus not be
efficient enough for this purpose.
The inlet to the conical nozzle is tangential to the cone which redirects the
flow. The cross
section area right after the flow redirection is the same as before the flow
redirection and the
flow redirection will therefore not in itself cause any decrease in velocity.
Instead, the purpose
to cause whirls.
SUMMARY
An object of the invention is to provide an improved liquid distributor for an
apparatus for
washing and/or dewatering of cellulose pulp.
According to an aspect of the present invention, there is provided a liquid
distributor for an
apparatus for washing of cellulose pulp, where pulp is arranged to be
transported in a vat
comprising a vat wall and a vat chamber, said liquid distributor comprising an
inlet arranged
to receive liquid in a first direction, a first flow redirecting wall arranged
to redirect the liquid
in a second direction, an outlet arranged to output the liquid into the vat
chamber, and a
channel with a first channel section, which first channel section has a first
channel cross
section area and is placed between the inlet and the first flow redirecting
wall, and with a
second channel section, which second channel section has a second channel
cross section area
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and is placed between the first flow redirecting wall and the outlet, wherein
the second
channel cross section area is everywhere larger than the first channel cross
section area; the
liquid distributor further comprises a second flow redirecting wall after the
first flow
redirecting wall; the channel comprises a third channel section with a third
channel cross
section area being placed between the second flow redirecting wall and the
outlet; the second
flow redirecting wall is arranged to redirect the liquid in a third direction;
and the third
channel cross section area is everywhere larger than the second channel cross
section area.
According to another aspect of the present invention, there is provided a
liquid distributor for
an apparatus for washing of cellulose pulp, where pulp is arranged to be
transported in a vat
comprising a vat wall and a vat chamber, said liquid distributor comprising an
inlet arranged
to receive liquid in a first direction, a first flow redirecting wall arranged
to redirect the liquid
in a second direction, an outlet arranged to output the liquid into the vat
chamber, and a
channel with a first channel section having a first channel wall and which
first channel section
is placed between the inlet and the first flow redirecting wall, and with a
second channel
section having a second channel wall that interconnects the flow redirecting
wall and the first
channel wall and which second channel section is placed between the first flow
redirecting
wall and the outlet, wherein the second channel section is an open channel
section which is
everywhere wider than the first channel section; the liquid distributor
further comprises a
second flow redirecting wall after the first flow redirecting wall; the
channel comprises a third
channel section being placed between the second flow redirecting wall and the
outlet; the
second flow redirecting wall is arranged to redirect the liquid in a third
direction; and the third
channel section is everywhere wider than the second channel section.
The invention builds on the insight that a tangential inlet to a nozzle or
other liquid distributor
where the incoming washing liquid is redirected by a flow redirecting wall,
does not slow
down the washing liquid, unless also the cross section area in the channel
after the flow
redirecting wall is everywhere larger than before the flow redirecting wall.
Otherwise the only
effect is to case whirls, which will have a limited effect to improve the
washing.
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The invention also teaches to further reduce the energy and momentum of the
washing
liquid by slowing it down.by means of a second flow redirecting wall. The
cross section
area in the channel after the second flow redirecting wall is everywhere
larger than before
the second flow redirecting wall. According to a particular advantageous
embodiment the
liquid distributor is arranged such that a part of the flow hits the second
flow redirecting
wall, whereas another part goes above.
An advantage is that the washing liquid can be provided with a high pressure,
which makes
the distribution to a number of nozzles or other liquid distributors easier,
without having to
have a separate valve to each nozzle. At the same time the velocity of the
washing liquid
will not be too high when it meets the pulp. This causes the washing liquid to
make a layer
on the outside of the pulp, instead of going right through the pulp at
isolated points. This
also minimises mixing of the filtrate preqsed from the pulp, which is not
desired. The
washing liquid is both calmed down and spread, which makes the washing of the
pulp
more effective. Since the solution is compact it does not take much place.
BRIEF DESCRIPTION OF THE DRAWINGS
Examples of embodiments of
the invention, together with further objects and advantages thereof, may best
be understood
by reference to the following description and appended drawings, in which:
Fig. I 'is a schematic cross-sectional view illustrating a washinedewatering
apparatus with
a liquid distributor according to an embodiment of the invention.
Fig. 2 is a schematic cross-sectional view of a first embodiment of a liquid
distributor
according to the invention.
Fig. 3 is a schematic cross-sectional view of a second embodiment of a liquid
distributor
according to the invention.
Fig. 4 is a schematic cross-sectional view of a third embodiment of a liquid
distributor
according to the invention.
Fig. 5a, b is a schematic cross-sectional view and a side view of a fourth
embodiment of a
liquid distributor according to the invention.
Fig. 6a, b, c is a schematic cross-sectional view of a fifth embodiment of a
liquid
distributor according to the invention with variants.
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Fig. 7 is a schematic cross-sectional view of a sixth embodiment of a liquid
distributor
according to the invention.
Fig. 8 is a schematic cross-sectional view of a seventh embodiment of a liquid
distributor
according to the invention.
DETAILED DESCRIPTION
In the drawings, similar or corresponding elements are denoted by the same
reference
numbers.
In this disclosure, a channel refers to a space where the washing liquid flows
in the liquid
distributor, when the apparatus for washing cellulose pulp is in operation.
Fig. 1 illustrates an example apparatus 100 for washing of cellulose pulp. A
twin roll press
100 comprising two co-operating cylindrical press rolls/drums 2 is shown. The
press
rolls 2 are arranged to rotate in opposite directions R, R' during operation
and each has a
permeable outer surface 4, such as a perforated metal sheet. The press rolls 2
are partially
enclosed by a vat 5 comprising a vat wall 5 and a vat chamber 8, which vat 5
is arranged
at a distance from the permeable outer surfaces 4 so as to partially enclose
the press rolls 2
in the circumferential direction.
During operation, pulp enters a pulp distribution device 1 of the respective
press roll 2.
The input consistency of the pulp is typically in the range of 2-13%. A pulp
web is formed
on the permeable roll surface 4. The pulp web is transported, guided by the
vat 5, in the
direction of rotation R, R' to be pressed in a nip 3 where the distance
between the press
rolls 2 is smallest. The press rolls 2 comprise axial filtrate channels 6,
which receive
filtrate from the pulp web. The filtrate passes through the permeable roll
surface 4 and is
transported towards the ends of the press rolls 2, where it is output. Washing
liquid is
supplied to the pulp web in the vat chamber 8 through liquid distributors 10.
The pulp is
output by means of a discharge screw 7.
In Fig. 2 a liquid distributor 10 is shown for the supply of washing liquid,
according to a
first embodiment of the invention. The liquid distributor 10 comprises an
inlet 12, an outlet
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13, a first flow redirecting wall 14 that redirects the liquid, a second flow
redirecting wall
after the first flow redirecting wall 14, and a channel 11 with a first
channel section
11a, a second channel section 1 lb and a third channel section 11c. In this
example, the
second channel section 1lb is also the penultimate channel section lib and the
third
5 channel section lie is also the last channel section 11c.
The first channel section ha has a first channel cross section area Al and is
placed
between the inlet 12 and the first flow redirecting wall 14. The second
channel section 1 lb
has a second channel cross section area A21 +A22, which is larger than the
first channel
cross section area Al, and is placed between the first flow redirecting wall
14 and the
10 outlet 13. More specifically, the second channel section 1 lb is placed
between the first
flow redirecting wall 14 and the second flow redirecting wall 15. The third
channel section
lie has a third channel cross section A3, A3', which is larger than the second
channel
cross section area A21+ A22, and is placed between the second flow redirecting
wall 15
and the outlet 13.
15 In this embodiment the second and penultimate channel section 1lb is
divided into two
parallel penultimate subchannels after the first flow redirecting wall 14,
which penultimate
subchannels have the second channel cross section areas A21 and A22. Thus, the
penultimate channel section 11 has a total second channel cross section area
A21 +A22.
Of course, also other areas than the second channel cross section area may he
divided into
a number of areas in a similar way. In each case it is the total flow area
that counts. There
are, however, special advantages with having subchannels in the penultimate
channel
section 11b, since this improves the spreading of the liquid onto the pulp
web. It may
sometimes be appropriate to have more than two penultimate subchannels in the
penultimate channel section 1 lb, e.g. four subchannels, because the more
subchannels the
less it matters how the subchannels are directed, when the nozzle 20 is
mounted. It is,
however, of course also possible in this embodiment to have a second channel
section 11b,
which is not divided into subchannels.
The second channel cross section area A21+A22 in the second channel section 1
lb is
everywhere larger than the first channel cross section area Al in the first
channel section
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ha. In Fig. 2 the second channel cross section area is constant from the first
flow
redirecting wall 14 to the outlet of the nozzle 20. The second channel cross
section area is,
according to an alternative embodiment (not shown), continuously increasing.
The second
channel cross section area may also be partly constant and partly increasing.
The second
channel cross section area is, however, preferably not decreasing, since that
would again
increase the velocity.
The inlet 12 receives the liquid in a first direction vi at a first velocity
vi with a first
pressure P1 in the first channel section 1 la. The first flow redirecting wall
14 redirects the
liquid in a second direction v2 at a second velocity v2 with a second pressure
P2 in the
second channel section 11b. The second flow redirecting wall 15 redirects the
liquid in a
third direction v3 at a third velocity v3 with a third pressure P3. Since the
second channel
cross section area A21 +A22 after the first flow redirecting wall 14 is larger
than the first
channel cross section area Al before the first flow redirecting wall 14, the
second velocity
v2 will be lower than the first velocity vi. Correspondingly, the third
velocity v3 will be
lower than the second velocity v2. By reducing the velocity of the washing
liquid, its
momentum is reduced, resulting in an improved spreading.
The combination of having a flow redirecting wall and an area increase makes
it possible
to have a high pressure on the washing liquid from the start, so that it
spreads well to all
the liquid distributors. The liquid distributors will then both spread the
washing liquid and
calm it down. This means that the washing liquid will be applied on one side
of the pulp
web and does not mix unnecessarily with the filtrate, which gives a more
efficient washing.
The second flow redirecting wall 15 results in an even more improved spreading
of the
washing liquid as compared to cases with only the first redirecting wall 14.
The
momentum of the liquid hitting two redirecting walls is considerably reduced,
i.e. the
washing liquid is calmed down. The washing liquid forms a layer on the outside
of the
pulp, instead of going right through the pulp at isolated points.
Laboratory studies with colored washing liquid show that a surprisingly good
washing
result is achieved when one portion of the flow is redirected by the second
flow redirection
wall 15 and another portion of the flow goes above the second flow redirecting
wall 15.
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The latter will not have its velocity reduced due to contact with the second
flow redirecting
wall 15, but forms an inclined jet spreading the washing liquid over a larger
area. This
flow portion has a small vertical force component, which means that it does
not go straight
through the pulp but forms a layer on the outside of the pulp. Hence, the
combination of
one subflow hitting the wall and another subflow shooting above provides
excellent
application of the washing liquid which forms a wide-spread layer propagating
through the
pulp.
Thus, according to a preferred embodiment, the liquid distributor 10 is
arranged such that
a first part of the flow of liquid is redirected by the second flow
redirecting wall 15,
whereas a second part of the flow of liquid goes above the second flow
redirecting wall 15
and directly into the vat chamber 8. Referring to Fig. 2, this may be achieved
by
arranging the nozzle 20 of the liquid distributor 10 at appropriate height and
appropriate
distance to the second flow redirecting wall 15. Preferably the nozzle 20 (or
corresponding part of the liquid distributor 10) is essentially in line with
the surface of
the vat wall 5 facing the vat chamber 8 (as illustrated in Fig. 4). The
advantageous
combination of one subflow being redirected a second time and another subflow
shooting
directly into the vat chamber 8 is then achieved while disturbing the pulp as
little as
possible, since the liquid distributor 10 essentially does not extend from the
vat wall 5.
The third channel cross section area A3, A3' in the third channel section 11c
is everywhere
larger than the second channel cross section area A21 +A22 in the second
channel section
11b. In Fig. 2 the third cross section area A3, A3' comprises two parts with
different
constant areas A3, A3' from the second flow redirecting wall 15 to the outlet
13, since the
nozzle 20 does not go all the way to the surface of the vat wall 5. But the
third cross
section area A3, A3' may of course also be constant all the way or be
continuously
increasing (e.g. in two parts as in Fig. 3) from the second flow redirecting
wall 15 to the
outlet 13 or be partly constant and partly increasing from the second flow
redirecting wall
15 to the outlet 13. The third cross section area A3, A3' is, however,
preferably not
decreasing from the second flow redirecting wall 15 to the outlet 13, since
that would again
increase the velocity and the pressure.
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Preferably, the third cross section area A3 is at least twice the second cross
section area
A21 +A22. Preferably, also the second cross section area A21 +A22 is at least
twice the
first cross section area Al.
In the embodiment in Fig. 2, the liquid distributor 10 comprises a nozzle 20
which
comprises the first channel section 11a, the second channel section 11b, the
inlet 12 and
the first flow redirecting wall 14. The third channel section 11c and the
second flow
redirecting wall 15 are provided in the vat wall 5. This solution makes it
possible to
exchange prior art nozzles having only a straight inlet with the new improved
nozzle 20.
An alternative is that the complete liquid distributor 10 is a nozzle 20. Any
combination of
what is made in the vat wall 5 and/or a nozzle 20 is possible. This applies to
all
embodiments. However, the first flow redirecting wall 14 will wear more than
any
subsequent flow redirecting walls, since the liquid meets the first flow
redirecting wall 14
with higher velocity than any subsequent flow redirecting walls. Therefore a
cheap solution
is to have the first flow redirecting wall 14 in a wear part that is easily
replaceable.
In Fig. 2 the liquid distributor 10 has an outlet 13, which is perpendicular
to the vat wall 5.
This is preferable, because the washing liquid will be distributed better in
that way.
Embodiments which instead has an outlet which is essentially parallel to the
vat wall 5 are
also possible. Also the following embodiments may be arranged with an outlet
essentially
parallel to the wall or at any angle there between.
Fig. 4 shows a liquid distributor which has a cut-off portion 17 (or cavity)
in the area
around the second channel section 11b outlet. The cut-off portion 17 results
in a
comparatively wide plume of washing liquid and an improved spreading of the
washing
liquid. A larger portion of the flow will go above the second flow redirecting
wall 15.
The cut-off portion 17 of Fig. 4 has a circular shape. This provides for
efficient spreading
of the liquid both in the vertical and the horizontal plane. The latter means
that, seen from
above, the nozzle 20 of Fig. 4 spreads the liquid over a larger sector than,
for example, the
nozzle of Fig.2. This reduces or eliminates the need for special means for
arranging the
nozzle 20 in the correct orientation.
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Other shapes than circular are of course possible, for example elliptical cut
off portions,
cut off portions with straight edges, etc.
An advantage of having two subchannels in the second (or penultimate) channel
section
11b, like in the embodiments of Fig. 2, 3, 4, 7, is that the cross section
area of each
subchannel can be larger than as compared with, for example, the embodiment
with four
subchannels. A larger cross section area means more widely spread washing
liquid.
Thus, a preferred embodiment has two subchannels in the penultimate channel
section 1 lb
and the cross section area of each subchtumel is, at the outlet portion, large
enough to
obtain an oblique jet of washing liquid. The liquid distributor 10 may have a
cut-off portion
at each subchannel, such as in Fig. 4, to further improve the spreading of the
washing
liquid.
Another advantage of having two penultimate subchannels is that there is less
risk of
plugging as compared to the case with a larger number of subchannels, e.g.
four
penultimate subchannels. With a plurality of subchannels, there may sometimes
be
plugging in the area where different subchannels meet, in particular when the
washing
liquid contains a high amount of cellulose fiber.
Fig. 5a, b illustrate another advantageous liquid distributor 10 in accordance
with the
invention. (Fig. 5b being a side view, turned 90 degrees as compared to Fig.
5a.) The
channel 11 comprises a first channel section ha, a second channel section I
lb', and a
third channel section 11c. The first channel section 1.1a has a first channel
wall 16a and is
placed between the inlet 12 and the first flow redirecting wall 14. The second
channel
section 1 lb' has a second channel wall 16b and is placed between the first
flow redirecting
wall 14 and the outlet 13. The second channel wall 16b interconnects the flow
redirecting
wall 14 and the first channel wall 16a. The second channel section 1 lb' is an
open channel
section which is everywhere wider than the first channel section 11a. The
third channel
section 11c is placed between the second flow redirecting wall 15 and the
outlet 13 and is
everywhere wider than the second channel section 1 lb'.
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The second channel section lib' provides a less restricted flow space than the
first channel
section 11a, such that the velocity v2 of the liquid after the first flow
redirecting wall 14 is
smaller than the velocity vi of the liquid before the first flow redirecting
wall 14.
The embodiment of Fig. 5 results in a wide plume of washing liquid both as
seen from
5 above and from the side. Due to the open second channel section 1 lb',
there is also a
minimum risk of plugging.
The second channel wall 16b is preferably arranged such that a flow space
covering a
sector of about 180 degrees is provided in the second channel section 11 b'
(as seen from
above, i.e. in a horizontal plane in the drawings).
10 In the illustrated example of Fig. 5, the first channel section 1 la is
a cylindrical space
defined by the first channel wall 16a and the second channel wall 16b is
curved, e.g.
shaped as half a cylinder. Other shapes are possible.
In Fig. 6a-c is shown a liquid distributor 10 with another way of spreading
out the washing
liquid on the pulp web. The same nozzle 20 as in Figs. 2 and 3 is used, but as
an example
having four penultimate subcharmels in the second and penultimate channel
section 1lb in
each nozzle 20. The number of penultimate subchannels may of course be any
number also
in this embodiment.
The liquid distributor 10 is here arranged to comprise a number of nozzles 20.
For
simplicity, Fig. 6b and c only shows three nozzles 20, but preferably there
are nozzles 20
all the way along the press rolls 2 in Fig. 1 in a direction perpendicular to
the view in Fig.
1. This may be seen as one large liquid distributor 10, where both the first
channel section
11a and the penultimate channel section 1 lb are divided into subchannels. The
total cross
section area of the first channel section 11 a then becomes All + Al2 +A13.
This means that the third and last channel section 11c becomes very large,
which both
slows down the washing liquid considerably and spreads the washing liquid in a
large area.
This may be further improved with an increasing third channel cross section
area as in Fig.
3.
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There may, however, still be flow concentrations of liquid in the case where
the
penultimate channel sections 1 lb from different nozzles face each other like
in Fig. 6b.
When the flows from two different nozzles 20 meet, there will be a
concentrated flow
upwards towards the pulp web. This is more pronounced the fewer the
penultimate
subchannels are in each nozzle 20. A similar flow concentration will occur
where the
distance from the outlet of the penultimate channel section llb is close to
the second flow
redirecting wall 15. Said flow concentrations are, however, not the fraction
as hard as what
is known in prior art and most of the liquid will still be put in a layer of
the pulp web,
without going right through the pulp web in concentrated beams as in prior
art.
But the spreading out of the liquid onto the pulp web may be improved by
mounting the
nozzles 20 so that the penultimate channel sections lib from different nozzles
20 does not
face each other, see Fig. 6c.
In Fig. 6c is also shown that the last channel section I lc may have enlarged
end parts 21 in
order to increase the distance from the outlet of the penultimate channel
section 1 lb to the
second flow redirecting wall 15.
In Fig. 7 is shown an embodiment with a single nozzle 20 having a penultimate
channel
section 1 lb with two penultimate subchannels pointing towards two enlarged
end parts 21.
Fig. 8 illustrates another embodiment, which like Fig. 7 has a single nozzle
20 arranged to
output washing liquid into a large third (and last) channel section 11c. The
nozzle 20
comprises a second channel section 11 b without subchannels and the washing
liquid is
output in a direction towards the center of the third channel section 11c. In
the third
channel section 11c, the washing liquid slows down and spreads over a large
area, whereby
practically the entire third channel section tic is filled with washing liquid
from the nozzle
20. Means to arrange the nozzle 20 in the correct orientation in the third
channel section
11c should preferably be provided.
The embodiments disclose two flow redirecting walls and redirections with
accompanying
area increases, but three or more flow redirecting walls and redirections with
accompanying area increases are also possible and are especially very good in
case of large
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velocity decreases, which otherwise would be very space consuming. If there
for example
are four channel sections, then the fourth channel section will be the last
channel section
and the third channel section will be the penultimate channel section. This
applies in a
corresponding way also when there are even more channel sections.
A further advantage, particularly with the embodiment in Fig. 6a-c, is that
larger and/or
fewer nozzles may be used than in prior art, which makes a cheaper solution.
In. Fig. 2-8 the liquid distributor 10 is arranged in the vat wall 5, without
extending into
the vat chamber 8. This is preferable in order to decrease the mixing of the
washing liquid
with the filtrate and to decrease the disturbance of the pulp web
transportation.
The cross section of the subchannels in the liquid distributor channel 11 may
with
advantage be circular.The invention is of course not restricted to the shown
embodiments,
but may be varied within the scope of the claims.
