Note: Descriptions are shown in the official language in which they were submitted.
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My prior Canadian Patent application Serial No. 245,
456, filed February 10, 1976, relates to a device for dewatering
sludge or similar substances, more particularly sludge yielded
in water purification plants or the like by filtration, wherein
one or more preliminary dewatering units are disposed in front
of a drum filter press and/or one or more high-pressure dewater-
ing units are disposed thereafter.
The present invention relates to a further develop-
ment and a specially preferred embodiment of the prior applica-
tion, and its aim is to provide a devic~ for dewatering
sludge or similar substances, which is very compact but has
high dewatering efficiency. In solving this problem, the
invention is based on the idea of subjecting the sludge or
similar substances to very uniform dewatering by gravity
while the substances are in the comparatively liquid phase,
more particularly after a first preliminary dewatering in
the rotating filter pockets, which form a preliminary de-
watering facility according to the prior application. In
this manner, according to the present invention, the drum press
~0 forming the medium-pressure stage and, if required, the platen
band press according to the prior application, which forms the
high-pressure dewatering stage, can be constructed much more
simply and therefore more economically.
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Starting from a device for dewatering sludge or
similar substances, more particularly sludge yielded in water
purification plants or the like by filtration, wherein,
according to the prior application, one or more preliminary
dewatering units are disposed in front of a medium-pressure
stage formed by a drum filter press and/or one or more high-
pressure dewatering stages are disposed downstream and,
furthermore, a preliminary dewatering unit is provided with
rotating filter pockets, the problem is solved substantially
in that one or more horizontal dewatering zones are provided
between the preliminary dewatering unit and the medium-
pressure stage, the zones being formed by the filter belts,
which extend horizontally at this place, and the zones being
disposed one abQve another and below the filter pockets.
In this and siMilar manner, the main advantages
of the device according to the invention are that ~a~ the
available dewatering zone is lengthened, so that a com-
paratively high content of dry substance is obtained even
during preliminary dewatering and (b) the substances for
de~atering are ~ot conveyed upwards before they reach the
required degree of solidity.
Accoxding to another advantageous feature, the
filter belt moving at the bottom is slideably disposed,
without interposition of rollers or the like, in the de-
watering zone on a flat surface permeable to fluid.
In a preferred embodiment of the invention, the
flat surface is constructed as a screen member which has
skimming edges extending transversely to the conveying
direction, for the liquid leaving the rear side of the filter
belt. In a specially preferred embodiment of the device
according to the invention, each top filter belt cooperates
with the corresponding bottom filter belt to form a wedge-
shaped compartment which tapers in the conveying direction
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in the dewatering zones. In this connection in accordance
with a 2articularly advantageous feature, a screen member
is disposed on the rear side of each top filter belt,
bears on its surface and has skimming edges which extend at
an angle to the conveying direction and remove the fluid
leaving the rear side of the filter belt.
Advantageously the screen members are made of
plastic, thus advantageously achieving low friction with the
filter belts.
In order to obtain higher stripping pressures, in
accordance with a variant, pressure rollers are disposed on
the rear side of each top filter belt, the rollers extending
at an angle to the conveying direction and laterally
deflecting the liquid emerging at the rear side.
According to another advantageous feature, a seal
is provided in the dewatering zone at the side edges between
the t-o~ and bottom filter belt, the seal being resiliently
deformable in accordance with the wedge shape.
Accordinq to a particularly preferred feature, the
top screen members are resiliently suspended or are spring
biased to form pressure grids and are made adjustable in
accordance with the wedge-shape.
The aforementioned embodiments follow the develop- ~
ment of the prior application, constructing a device of the ~-
aforementioned kind which can be described as a continuously
operating chamber press. The completely flat dewatering
zones disposed between the pocket dewatering unit and the
medium-pressure stage have the advantages, in conjunction with
the skimming edges, that (a) sludge on the filter belts is
not unnecessarily moved by being guided over rollers or the
like (this is particularly important to ensure a high degree
of dewatering) and (b) the water leaving the filter belts at
the rear is removed rapidly and efficiently. Since the
d~atering zones now extend in absolutely straight lines,
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comparatively uncomplicated seals of the previously-mentioned
kind can be provided at the side, thus substantially
approaching the aim of a continu~us}y operating chamber filter
press. In addition, as one skilled in the art can easily
see from the description and drawings of the embodiments
descri~ed hereinafter, the aforementioned dewatering zones
can be repeated as often as required at comparatively low
constructional cost, depending on the desired conte~t of
dry substance.
Additional embodiments illustrate simplification
of the medium-pressure stage or the adjacent high-pressure
stage which can be achieved by inserting the previously- ~rJ
described dewatering zones.
In accordance with one aspect of the present invention,
there is provided a device for dewatering sludge comprising:
means for supplying sludge to be dewatered, a first gravity
pressure dewatering stage having a plurality of endlessly
rotating perforated filter pockets for receiving sludge from
said means for supplying and for straining water therethrough,
a second dewatering stage located below and coupled to the
output of said first dewatering stage, said second stage
including a plurality of sequentially arranged horizontal
dewatering zones and a pair of perforated horizontal filter
belts each associated with a respective horizontal dewatering
zone, the output of one horizontal zone feeding the input of
another for further straining water from sludge exiting from
said first stage, said horizontal dewatering zones being pro-
vided one above another with a first such horizontal dewatering
zone receiving output sludge from said first stage, each of
sai~ horizontal filter be~ts sliding across a respective hori-
zontal dewatering zone on a flat surface permeable to fluid
and cooperating with the other filter belt to form a wedge
shaped compartment in each horizontal zone which tapers in
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the direction of sludge movement throu~h the associated hori-
zontal dewatering zone, said wedge shaped compartment applying
greater than gravity pressure to the sludge as it passes there-
throu~h; a third dewatering stage located below said first
and second dewatering stages and coupled to receive the output
sludge of said second dewatering stage, said third stage receiv-
ing said pair of horizontal filter belts from the last horizontal
dewatering zone of said second dewatering stage and including
at least two drums against which said pair of filter belts is
pressed, the pressure applied to sludge by the pressing con-
tact of said pair of filter belts with said drums being
higher than pressure applied to sludge by said pair of filter
belts defining said wedge shaped compartment; and, a fourth
dewatering stage for receiving said pair of filter belts from
said third stage and applying pressure to sludge greater than
that applied by said third dewatering stage and for discharging
dewatered sludge, said fourth stage comprising two endless
rotating platen belts pressurized towards one another, said
pair of filter belts passing through the nip defined by said
platen belts.
The invention will now be descri~ed in greater
detail with re~erence to embodiments shown by way of example
in the drawings, wherein:
Fig. 1 is a partly cut-away side view of a first
embodiment of the invention;
Fig. 2 is a sectional view of the device according
to Fig. l;
Fig. 2a shows details of the high-pressure stage D;
Fig. 3 is a sectional view of Fig. 2 along line
III-III;
Fig. 4 is a sectional view of Fig. 1 along line IV-IV;
Fig. 5 is a sectional view of a ~irst embodiment
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of one of the bottom screen bodies in the device according
to Figs. 1-4,
Fig. 6 is a plan view of the screen member in Fig~ 5,
Fig. 7 is a sectional view of a first embodiment
without the top screen member in the device according to
Figs. 1-4,
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Fig. 8 ls a plan view of the screen member in Fig.
7;
Fig. 9 is a plan view of a modified embodiment
of a screen memberi
Fig. 10 is a plan view of another embodiment of a
screen member;
Fig. 11 is a plan view of the surface of the platen
belt of the high-pressure stage;
Fig. 12 is a sectional view of Fig. 11;
Fig. 13 is a plan view of the surface of the
platen band of the high-pressure stage, showing a pattern
produced by combining a number of plates;
Fig. 14 is a sectLonal side view of a modified
embodiment of the device according to the invention;
Fig. 15'shows another modified embodiment of the
device according to the invention;
Fig. 15a is a sectional s;de view of the high-
pressure stage according to Fig. 15, and
Fig. 16 shows another embodiment of the device
according to the invention, which is particularly simple and
compact.
The embodiment of the invention shown in the drawings,
in contrast to the prior application, has an extensible stage
; which can be regarded as adapted for four-stage operation.
In the embodiment'of the invention described here', the various
~ dewatering phases are as follows: a pressureless pocket
; ~ dewatering stage A, an intermediate stage B in which the
pressure is raised from zero to a low value, a medium-pressure
stage C and a high~pressure stage D (see Fig. 1).
In all the embodiments, the pressureless preliminary
dewatering stage A comprlses a rotating belt pocket filter
which, depending on the effective filter area, is adapted for
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highcr filter ca~acity or a highcr degree of separation in
the final sludge. The belt ~ocket filter, which bears the
genera] reference numeral 1, is similar in construction to the
belt filter pocket according to the prior application, but
is longer, due to the construction of the medium-pressure
stage C (described in greater detail hereinafter~ and forms a
compact unit which can be placed on the rest of the device.
Filter 1 comprises an endless conveyor 2 disposed
in a housing (not shown) and having screen pockets 3 havin~
walls made of a suitable screen material 4 or perforated
sheet-metal, conveyor 2 being guided at both ends around
bucket wheels 5 and 6, one of which is driven.
Flocculated sludge is introduced through an inlet
7 into the individual pockets 3 of the band pocket filter 1,
as indicated by arrow 8 in Fig. 1, and is dewatered during its
travel through the zone from the bucket wheel 6 to the bucket
wheel S in Fig. 1, in the direction of arrow 9. The
water leaving through the filter pockets is connected in
a drip pan and removed at the side.
The pressureless pre-dewatered sludge from filter
pockets 3 travels at 10 to the first preliminary dewatering
zone of the interposed preliminary dewatering stage B.
In the embodiments in Figs. 1, 2, 14 and 15 stage
B, which can also be regarded as an extended feed zone on the
medium-pressure stage C, comprises three dewatering zones
11, 12 and 13.
After preliminary dewatering in filter 1, therefore,
3 sludge travels at 10 to the first filter belt 14, which
extends at the top from the high-pressure stage D, is deflected
over rollers 16, 16a and then extends horizontally into
the preliminary dewatering zone 11. The second filter
belt is labeled 15.
In the preliminary dewatering zone, filter belt
14 is completely flat and, without interposition of guide
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rollers or the li~e, slides on an additional screen member 16a
described in detail hereina~ter, SG that the conveyed sludge
is subjected to further pressureless preliminary dewatering
in a gentle manner, without vibrations, whereupon the water
emerging by gravity from the rear side of the first filter
belt 14 is stripped therefrom by the walls or ribs i8 of
screen member 17 r which extend at right angles to the convey-
ing direction, ie. the water cannot be pumped back into the
sludge. The stripped water is collected in a trough 19
under me~ber 7 and removed at the side.
At the end of the dewatering zone 11, belt 14 is
deflected over a roller 20 and a tension roller 21, so that the
sludge, after being deflected, is conveyed to the second
preliminary dewatering zone 12 or 22 on to the second filter
belt 15, which is conveyed backwards from beneath via rollers
23, 24, and 25.
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The second dewatering zone 12 is constructed as a
wedge-shaped first feed compartment 26, bounded by the filter
belts 14 and 15. In the wedge-shaped fee~ compartment, a
second filter belt, like the first, slides in a completely
horizontal manner on a screen member 27; as before, the
emerging water is stripped, collected in a trough 28, and
removed at the side. The top of the first filter belt 14,
which bounds the to~ of the wedge-shaped feed compartment 26,
bears on a screen member 29 which is pressed by springs 30
against belt 14 and is adjustable in height and has walls or
ribs 31 which are V-shaped or extend at an angle to the
conveying direction and laterally remove the water leaving
from the top side of belt 14. Screen member 29 exerts a
pressure, facilitating dewatering, on the sludge in the wedge-
shaped compartment 26.
At the end of the second dewatering zone 12, thesecond filter belt is deflected towards around a roller 32
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and a tension roller 33, whereas the first filter belt 14
is guided downwardson the outside right, over rollers 34
and 35, so that at 36 the sludge makes another turn and is
delivered to the first conveyor-belt 14, which in this
case enters the third dewatering zone.
The third dewatering zone 13 is likewise constructed
as a wedge-shaped feed compartment 37 for the medium-pressure
stage C and is constructed in similar manner to the second
dewatering zone 12. In the present case, belt 14 slides on
a screen member 38, which is constructed in similar manner
to screen members 17 and 27, and the stripped water, as
before, is collected in a trough 39 and removed at the side.
At the top, the wedge-shaped feed compartment 37 is bounded
by another spring-biased, adjustable screen member 40, which
in the present case bears on the top side of belt 15 and has
the same action and construction as screen member 29.
To obtain higher stripping pressures,the top
screen members ~ay be re~laced by pressure rollers (not
shown) which likewise preferably ex~end at an angle to the
conveying direction.
Belts 14 and 15 are made of fine-mesh wire, gauze,
the mesh width being chosen in accordance with the applied
pressure. Preferably, however, the filter belts are made of
plastic fabric, since this ensures the most advantageous
adaption of the friction with regard to the screen members,
which are preferably made of plastic.
After leaving the wedge-shaped feed compartment 37
at the end of the dewatering zone 13, belts 14 and 15,
holding -the sludge cake between them, travel around a first
drum 41, which for~s the beginning of the medium-pressure
stage C. Beyond drum 41, belts 14 and 15, alternately above
and below, extend around a number of adjacent and parallel
drums 42, 43, 44, 45 and 46, which together form the medium
pressure stage in the illustrated embodiment. ~'he advantaye
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here, as compared with the prior application, is a still
more compact construction and a considerable reduction in
manufacturing cost, since a single large drum, as in the prior
application, has to be specially manufactured in each case.
Since the ~edium-pressure stage is made up of a number
of drums, around which the sludge is conveyed in an undulating
path between the filter belts, liquid removal is carried out
alternately from each side of the sludge layer. This
results in considerably improved removal of filtrate.
As sho~n more particularly in Fig. 2, the drums at
which the filtrate arrives at the top, i.e. drums 41, 42,
44 and 46, are perforated ~7hereas the drums at which the
f;ltrate arrives at the botto~, ~e. d^ums ~ and 45, are
smooth and unperforated. This again considerably improves
the removal of filtrate. A water stripper or wiper 47, 48,
~9, 50, 51, 52 respectively lS disposed on the outside of each
respective drum and wipes off the filtrate emerging from the
rear side of belt 14 or; 15 and thus further intensifies the -~
removal of water.
To o~tain higher pressures, the wipers shown can be replaced
by pressure-rollers (not shown) for removing the emerging
filtrate.
In the first drum 41, which is yiven a somewhat
laryer diameter than the remaining drums of the mediu~-
pressure stage, there is also a drip pan 53, which collects
filtrate falling through the holes into the interior of drum
41 and removes it at the side. The other drums in the
medium-pressure stage do not need any drip pans, since the
filtrate can fall freely through gravity.
After leaving the last drum 46 of the mediu~-
pressure stage, the two filter belts 14 and 15, holding the
sludge cake between them, travel upwards to a high-pressure
stage. The high-pressure stage D has a dewatering zone of
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approximately the same length as in the parent patent
but is not divided; this greatly simplifies the construction
and reduces the manufacturing cost.
As in the parent patent, the high-pressure stage D
is a platen belt press, has substantially the same mechanical
construction and, in order to ohtain a maximum content of
dry substance, must exert a very high and steady pressure on
the sludge whic~ already, after leaving the medium-pressure
dewatering unit, has a com.paratively high solids content and
is in a fairly solid general condition. As shown more
particularly in Figs. 1 and 2j filter belts 14, 15 travel
into the nip between the belts, via a comparatively large
bcttom deflecting wheel 34, which is also the bottom reversal
point of one out of two platen belts described in detail
hereinafter. Wheel 54, compared with the platen press in the
prior application, is given a relatively large diameter,
substantially equal to the diameter of the row of drums 42-46.
This prevents the filter cake, which is relatively brittle
at this time, from breaking and falling out between belts 14
and 15 before they reach the nip. ~ -
The platen belt press or high-pressure stage D
proper has two substantially similar platen belts 55 and 56
whichj by mea~s of a drive, (not shown) travel round corres-
~` ponding chain drums 57, 58, 59 and the previously mentioned 54.
Apart fro~ details, which are described with reference to
Figs. 11-13, platen belts 55 and 56 are constructed as in the
high-pressure stage in the prior application. An additional
water stripper 60 is provided at wheel 54.
In the simplified emhodiment according to the
present invention, only one platen belt has to be biased
in the direction of the other platen belt, but additional
interacting biasing devices can be provided as shown in ~igs.
.
1 and 2.
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The biasing can ~e produced by stacks of springs
exerting a desired pressure of, if required, by hydraulic
(not shown).
Filter bands 14 and 15 are so guided according to
the invention that the dischargefor the dewatered sludge is at an
elevated position, as shown at 61,i.e. the sludgecan be discharged
directly into troughs or suitable vehicles.
After the discharge 61, belt 15 travels on the out-
side downards over the platen belt to the right in the
drawing, is deflected round a roller 62 and is conveyed on
rollers 63, 64 below the medium-pressure stage back to the
aorementioned roller 23 and thence to the preliminary
dewatering zone 12 ~elt 14 comes from the top from the nip
between platen belts 55,56 back to the afore~entioned rollers
16 and 17 and thence to the first preliminary dewatering
zone 11.
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Fig. 3 in sectional view, is a diagram of some
mechanical details of the hish-pressure stage D.
Figs. 5 and 6 show a first embodiment of the bottom
screen members 17, 27, and 38, on which the filter belts 14,
15 slide in the interposed dewatering æones 11, 12 and 13.
As shown in the sectionalview in Fig. 5, walls 65 of the
preferably plastic screen member extend at right angles to
the conveying direction and form the skimming edges 1~,
which strip the fluid emerging from the back of each filter
belt and convey it downwards through the rectangular apextures
67 left between the transverse walls 65 and the longitudinal
walls 66 of a screen member.
Figs. 7, ~, show an embodi~.ent of the top screen
members 29 and 40 which are biased in the direction of the two
wedge-shaped feed compartments. Since the fluid emerging at
the top side of filter belts 14, 15 must be removed very
quickly at the side without flowing back to the dewatered
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sludge, in the present embodiment of the screen members
the longitudinal walls 68, which cooperate with the transverse
walls 70 to bound the flow apertures 69, are constructed so
that the skim~ling edges 31 can, without hindrance, convey
the emerging filtrate to the side. To this end, in the
illustrated embodiment, the transverse walls 70 are made
V-shaped and the longitudinal walls 68 are somewhat lower
than walls 70, so that the skimming edge 31 has a continuous
shape, without being interrupted by longitudinal walls.
Fig. 9 illustrates a modified form of one of the
lower screen members, which advantageously ensures smoother
operation.
Fig. 1~ shows another means of disposing the flow
apertures in a screen member of the ~ind in question.
Figs. 11-13 show details of a specially preferred
embodiment of the platen belts 55, 56 of the high-pressure
stage D. The same embodiment is used to convey the filtrate
along a particularly advantageous path when it leaves the rear
side of filter belts 14 and 15.
To this end, each plate of each platen belt is
given the required rigidity by a steel core 71 surrounded by
a plastic layer 72. On the side facing the filter belts,
the platen-belt plate has grooves 73 extending diagonally
~' or forming a V, as in the illustrated embodiment. Grooves
73 are about 8 ~m deep and are integral with the plastic
coating 72. As Fig. 13 shows, when a number of plates are
placed together, grooves 73 form continuous flow ~aths 7~
which rapidly remove the emerging filtrate, so that when the
filter belts are unloaded at the discharge 61 the filtrate
~ cannot be pumped back into the dried sludge.
Before describing the embodiments in Figs. 14-16,
we shall briefly give a more detailed description of an
important detail illustrated in Fig. 4.
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As Fi~. 4 shows, the interposed dewatering zones
12 and 13 are constructed so that each lateral gap between
filter bel-ts 14 and 15 is closed ~y seals 75 so that the
sludge, which is still comparatively liquid at this stage,
can be exposed to pressure by screen ~ember 29 or 40 ~ithout
escaping laterally between belts 14 and 15. The seals are
preferably resilient elongated hollow members matching the
wed~e shape on both_siaes of a wedge shaped eed zone _
The result, if the friction between t`ne fil-ter belts and the
se~l is adjusted by choosing the materials thereof, is a
particularly simple construction ensuring that the seals
75 are laterally suspended and remain stationary and do not
share anv of the motion of the filter belts.
~part from the guidance of filter belts 14, 15
- and the fact that the high-pressure stage D comprises filter
belts 76, 77 separate from the belts 14 and 15, the
embodiment shown in Fig. 14 is identical with the embodiment
in Figs. 1 and 2, i.e. there is no need to repeat the
description of mechanical details.
In contrast to the embodiment in Figs. 1 and 2,
after filter belt 15 runs over the last perforated drum 46
of the medi~m-pressure stage C it is guided upwards over a
reversal roller 78 and an additional reversal roller 79
to the previously-mentioned guide rollers 63, 64 and back to
the second dewatering zone 12. The second filter belt 14,
after travelling over the last perforated drum 46 of the
medium-pressure stage C, is conveyed by suitable reversal
rollers directly upwards to the first interposed dewatering
zone 11.
~ith regard to the reversal roller 7~, the dried
sludge cake is transferred at 80 to the filter belt 77 of
the high-pressure stage D and is conveyed upwards between
belt 77 and belt 76 into the nip o~ the platen press. The
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advantage of tl~is e~bodiment is that the mesh wid-th of belts
76, 77 can be chosen in accordance with the much firmer
general state of the sludye and in addition the speed of the
high-pressure stage D can be controlled in~le?endently, in
accordance with the reduced volume of sludge.
Fig. 15 shows another modified e~bodiment'of the
invention, in which the previously-described construction
of the high-~ressure stage is replaced hy a se~arate high-
pressure platen press-, which is connected downstream as in
the prior a~plication. The structural details are s~own in
Fig. 15a and need not be described in detail here. Eowever,
in order to convey the sludge downwards into the high-pressure
platen ~ress according to the Prior a~plication, which here
bears the seneral reference 81, the filter belts 14, 16
bearing the sludge cake between them a-re conveyed, after
leaving the ~erforated drum 46 of the medium-pressure
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stage, around a perforated drum 82 provided with a drip pan
83 and u~wards around a large-diameter reversal roller 84.
Consequently, the filter cake between.belts 14 and 15 is
conveyed to tne top region of pla'en press ~1, where it is
conveyed over corresponding reversing rollers and dis-
charged from belt 15 into the nip, after which the belt
is returned by suitable reversal rollers to the second
dewatering zone 12.
~ ig. 16 shows an embodiment o~ the device
according to the invention which o-~erates in similar
~anner to the embodiment in Figs. 1 and 2 but is ~uch
simpler and shorter than the last-mentioned embodiment,
but is adequate for many cases where the sludge is
comparatively eas~ to dewater.
The main differences are that the three interposed
dewatering zones are replaced by only two dewatering zones
11 and 12, be~,~ond which the filter belts 14 and 15, with the
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sludge cake between them, are conveyed around the per-
forated drum 41. In the shortened version of the device
according to the invention, the five alternately verforated
and smooth dru~.ls in the first embodiment are replaced by a
single perforated drum 85 having a diameter slightly greater
than that of the alternatin~ drums in the first enbodiment.
On leaving the drums, the filter belts arç conveyed through
the high-pressure stage D in the previously-described manner.
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