Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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This invention relates to a device for dewatering sludge and also
compacting the dewatered sludge.
This application is a clivisional of our copending application Serial
No 202,3113 filed June 12~ 19740
There are known devices for dewatering sludge of the general type
above referred to in which cakes formed of sludge to be processed are guided
between two filter bands about the circumferential wall of a drum. As a result~ -
a certain percentage of the water contained in the cakes is removed as the
cakes are guided about the drum.
A method using this mode of dewatering sludge and also a device for
carrying out the method is described~ for instance~ in German DTAS
1~960~7870 This patent describes a dewatering press in which filter bands are
guided partly about the circumference of a single drum, the sludge to be pro
cessed being carried between two filter bands. It has been found that such an
arrangement does not result in an economically acceptable dewatering efficiency.
There are also known devices for the purpose from United States
Patent 2,111,7~0 and German Patent 689~090~ in which guidance of filter bands
used for causing dewatering of the sludge is similarly Imfavorable with
respect to efficiency.
Tests have shown that the shortcomings of dewatering devices as
previously described are caused primarily by an insufficient break-up of the
sludge during the dewatering operation itselfO
According to the invention there is provided a device for dewatering
sludge in the form of cakes~ said device comprising in combination: a first
rotary dewatering drum having a porous circumferential wall and a second ro-
tary dewatering drum also having a porous circumferential wall disposed side- -
by-side of said first clrumg said drums being rotatable in opposite directions;
two parallel spaced apart filter bands for supporting and conveying sludge
cakes placed therebetween~ said filter bands being guided about part of the
circumferen~l wall of the first drum for conveying the bands in the rotational
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direction of the first drum and also being guided about part of the circum-
ferential wall of the second drum for conveying the bands in the rotational
direction of the second drum and thus in opposition to the moving direction
of the bands while being conveyed about the first drum, and said filter
bands being guided about and by said drums so as to define an approximately
S-shape disposed in an upright plane; pressure rolls disposed at the walls
of the drums for pressing the filter bands against the circumferential wall
of at least one of the drums; said filter bands being guided to constitute
a straining and preliminary pressure zone for causing partial dewatering
of sludge cakes upstream of said first rotary drum; and guide rolls provided
at the inlet end of said straining and preliminary pressure zone for guiding
the filter band into said zone.
Thus, the invention combines a high dewatering efficiency with
minimal space requirements. These advantages of high dewa*ering efficiency
and minimal space requirements are obtained by increasing the active length
of the filter bands in relation to the total length of the filter bands which,
in all dewatering devices as heretofore known, was well below 50%. Modern
demands with respect to the quality of processing sewage water discharges
require much higher efficiency for environmental reasons coupled with econ-
omically acceptable costs.
The circumferential walls of the drums may be made either of
corrugated or perforated sheet metal such as steel, or they may be composed
of tubes extending lengthwise of the axes of the drums. The latter arrange-
ment assures that the filtrate as it is extracted from passing sludge will be
discharged into the interior of the drums from which it can be conveniently
removed.
The dewatering drums define within the range of their circumferen-
tial walls about which the filter bands are guided several pressure zones
within which an S-shaped guidance of the filter bands causes pulling, knead-
ing and deforming action upon the generally cake-shaped sludge portions placed
between the filter bands. As a result, the internal consistency of the
cake is loosened thereby facilitating extraction of water therefrom.
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In this connection, it may be mentioned ~hat the concept of the
invention is not limited to two drums, but in some instances it may be
preferable to provide more than two drums in side-by-side arrangement and to
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guide the filter bands accordingly over the circumferential walls of the
drums.
According to another embodiment of the inventiong sludge in the
form of sludge cakes of inhomogenous consistency~ after having been guided
through one or more straining and/or pre~;minary dewatering zones (-n)
supported on a filter band~ is guided to a further filter band while being
simultaneously mixed~ if desired~ assisted by gravitational force. mere-
upon the sludge cakes are guided between the two filter bands which are
disposed in parallel relationship and preferably along a linear path through
a preliminary pressure zone. A* the end of this 30ne the sludge is guided
over the first one of the afore_referred to dewatering drums, At the same
time~ the sludge cakes may be subjected to vibratory pressure and continuing
shear forcesO After having been subjected to the action of this composite
force resulting in a thorough loosening of the sludge cakes~ the filter bands
and thus also the sludge cakes therebetween are deflected after leaving the
first dewatering drum into the opposite direction and then guided upon the
second dewatering drum~ that is~ the sludge cakes are now subjected to a
pressure ~one curved in opposition to the curvature on the first drum since~ ~ -
as previously stated~ the two drums being driven in opposite direction.
~0The afore-referred to pulsing or vibrating pressure is obtained
by guiding the filter bands and thus also the sludge cakes between pressure
rolls and the circumferential wall of the dewatering drum l/nO The just-
described aspect of the invention may also provide that the pressure force
applied to the sludge cakes via the filter bands~ and more specifically
by the outer filter band~ is increasing in the driving direction of the bandsO
In a preferred embodiment of the invention~ the envelopment angle
of ~he filter bands on the drums which obviously controls the length of the
pressure zones is larger than 180 ~ It is further advantageous that the
pressure or planet rolls be provided at least along the circumferential range
of the drum as determined by the afore-mentioned angle of more than 180o
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As it is evident~ the longer the pressure zone is~ the more
intensive is the action of the shear forces upon the sludge cake as these
shear forces are generated when and while the filter bands envelope the
circumferential walls of the dewatering drumsO 0bviOuslyg the outer filter
band must travel a longer distance than the inner filter band as they are
driven by the rotation of the drums~ Accordingly~ assuming equal driving
speed for both bands3 the outer band will be retarded relative to the inner
band by a distance which is equal to the product of the radial differential~
that is~ the radial thickness of the cakes bet~een the two bands times the
angle of envelopmentO This retarding of the outer filter band causes
displacement or deformations within the cakes~ As a result there is a change
in the consistency of the cakes, and particularly a loosening thereof~ so
that liquid can be more readily driven out of the cakes. Moreover~ the
already described reversal of the direction of stresses due to the opposite
rotational directions materially increases the dewatering effect.
The invention also allows the pressure of the planet rolls~ both
for individual rolls and for a group thereof~ can be controlledO Such control
can be effected in a particularly simple manner by means of a tension member
such as a ropeO This tension member is in contact with lever arms provided
according to the invention~ which in turn are linked to a stand or frame
structure for the drums or to another suitable supportO
The rope or other tensioning member which is tensioned along
the circumferential outline of the dewatering drums may coact for example
with adjustable noses or dogs on the lever arms or other pivotal elements
can be usedO By tensioning of the rope the component of force composed of
the force of the rope in a direction normal to the lever arms is enlarged
As a result~ the pressure exerted by the planet roll or rolls toward the :
respective dewatering drum and thus the filter bands increases corresponding
to the effective length of each lever arm between its pivot point or the
setting of the nose or dogO .
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The pressure rolls can also be in the form of parts of contin-
uously rotating pressure bands~ etcO These parts may be coupled by chain
linksO In actual practice, it depends on the specific conditions under which
a particular device is operated whether the pressure bands are directly
driven or driven indirectly by being placed in driving contact with the filter
bands.
It is also possible to arrange pressure bands or similar members
so that they in turn will drive the filter bands without special drive for
the filter bandsO me control of the bands can be effected in an efficient
manner by means of deflection rolls, or as it is described in the present
invention, by means of the dewatering drumsO
In a preferred device of the invention, one of the filter bands
is extended to the location of a feed chute or hopper~ and it extends from
the point of feed about horizontally to a deflection rollO This distance
between the feed point and the deflection roll may be utilized as a straining
or pre-dewatering zoneO After passing the deflection rolla the aforementioned
extended filter band now jointly with the second filter band which is only
in tangential relationship with the deflection roll~ is thus moving in
opposition to its initial direction of movement through the preliminary
pressure zonesO At the end of the movement in this opposite direction~ both
filter bands are jointly guided upon the first one of the dewatering drumsO
This drum is enveloped by the two filter bands with an envelopment angle which
according to the embodiment is between 220 to 240~
After having passed about the first dewatering drum~ the two
filter bands are guided to a further dewatering drum which is disposed side-
by-side and approximately horizontally of the first drumO The envelopment
angle of the filter bands about the second drum is preferably larger than .
the envelopment angle for the first drumO :
After leaving the second dewatering drumJ or if there are more
than two drums after leaving the last drum, the now fully processed or worked
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sludge cake is discharged and each filter band is separately guided back to
the straining and/or preliminary pressure zoneO While moving toward these
zones, the filter bands are preferably guided into contact with at least some
of the pressure rolls on the sides thereof distant from the respective drum
thus increasing the effective pressure e~erted by these rollsO
A dewatering device according to the invention with two de-
watering drums having a drum diameter of 1 meter provide about 16 meters of
active band length and the total length of the devioe is not more than 2.5
meters. The thus obtained space utilization rationis more than 70%9 and this
is very much in excess over the utilization ration as can be obtained with
dewatering devices as heretofore knownO
In the accompanying drawing~ several embodiments of the inven-
tion are shown by way of illustration and not by way of limitationO
Figure 1 is a diagrammatic elevational section of a dewatering
device according to the invention including two substantially side-by-side
disposed dewatering drums;
Figure 2 is a detail view of Figure 1 on an enlarged scale;
Figure 3 is a view of a modified detail of the device according
to Figure 1 on an enlarged scale;
Figure 4 is an elevational sectional view of a modification of
a dewatering device according to-the invention, and
Figure 5 is a detail view of Figure 4 on an enlarged scale~ ~ :
Referring now to the figures in greater detailt and first to
Figure 1, this figure shows an exemplification of a dewatering device ~ ~
which includes two large dewatering drums 1 and 20 Two filter bands 4 and 5 :
which are disposed for part of their length in parallel spaced apart relation_
ship~ envelop the two drums for part of the circumferential walls thereof~
More specifically7 the envelopment angle for drum 1 is m (for instance 235)3 ~
and n (for instance 285)~ whereby the two filter bands approximately define
an upright S-shape
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A cake Q formed of sludge to be processed is fed in the direc-
tion t upon first filter band 4 in the conveying direction io This band
guides the cakes Q by means of support ro:Lls 6 through straining zone D
to effect preliminary dewatering of the cakesO Water extracted from the
cakes is removed through the mesh openings or holes in the pulling side 40
of band 4 and drops into a catch trough 70
Each preliminarily dewatered cake Q falls at a deflection roll
8 for filter band 4 upon the pulling side 500f filter band 5 which is disposed
approximately tangentially with respect to the lower side of deflection roll
80 As a result~ the cakes are successively turned around and also mixed~
Betveen the idling side 4u of the first filter band 4 and the pulling side
50 of the second filter band 5 the sludge cakes are guided through a pre-
liminary press zone D30 In this zone pressure rolls 9 which are disposed
staggered on both sides of filter band sides 4u and 50 process the sludge
cakesO Both rows of pressure rolls 9 are via pressure plates P pressed
against each band side 4 and 50 by means of power sources 10 coacting with
pressure plates P0
The deformation such as bends introduced by pressure rolls 9 in
the filter bands are ignored in the drawing to simplify the illustrationO
After leaving the preliminary pressure zone D3 the two filter
bands 4 and 5 with sludge cakes Q therebetween are guided upon the circum- ::
ferential vall of dewatering drum 1 in the rotational direction i~ within
the range of the envelopment angle m. mis angle controls the effective
length of the main pressure zone D5 in which the filter bands 4 and 5 are
guided between the circumferen*ial wall 11 of the drum on one hand and
planet rolls 40 disposed in juxtaposition to the outer side of the circum-
ferential wall of the drumO :
The drum wall 11 consists either of grooved or perforated metal
sheets such as steel sheets3 or according to Figure 2~ out of tubes 41 which
are disposed parallel to the rotational axis of the drum, me filtrate which
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is pressed out of cakes flows between the tubes into the interior J of the
drum. The tubes 41 are bored at their ends (not shown) so that any filtrate
accumulating in the lower part of the space U within the drum ~lows first
into the space within the tubes and can t'hen be removed from the tu~es at
the ends thereof.
The planet or pressure rolls 40 are biased by the action of
power supplies 42 toward the outside wall 11 of the drum. Such bias may
be obtained either for each one of the planet rolls 40 or for groups of
these rolls. Each roll 40 is pivotally supported by means of a li~c 44
hinged to a pivot 46 as it is schematically indicated by supports 45 or
similar means~ These pivokal links 44 mount dogs or noses 47 for placing
thereupon a pull rope 49. The p~ ;ng force exerted by this rope can be
adjusted by the power supply 42 shown as a rotary pulleyO
The aforedescribed pressure means (42 to 48) permit by utili- '-
zation of the leverage to effect individual regulation of the pressure for
each one of the planet rollsO By tensioning rope 48 the component of force '
as produced by the rope pnll in a direction normal to the pivotal linlc 44
is increased~ whereas the pressure of the planet roll 40 toward drum wall
11 varies the respective lever arm between the pivot point 46 of li~c 44
and the respective nose for supporting the pull rope 480
me pressure of the planet rolls toward the respective drum ' ~
wall is further enlarged by the tension of,the returning filter band portions ~ ,
4 and 5e within each range C in which the planet rolls 40 in toto or in-
dividual planet rolls 40zare utilized for effecting the deflecting of the ~,
filter bands~ The point at which the filter bands 4 and 5 leave drum l and
thus the pressure zone D5 is controlled by the lower leg of the envelopment
angle m.
At this stage of processing each sludge cake Q which was bent
to a curvature somewhat less than corresponding to the radius r of dewatering ---
drum l~ is suddenly flattened between filter bands 49 50 As a result~ the -
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previously inner parts of the cake are stretched ~nd the previously outside
lying cake parts are pushed together whereby the structural consistency
of the cake is correspondingly loosened and prepared for further pressing
operations.
As is now apparent, the action upon the sludge cakes is similar
to the one to which the cakes have been subjected in the straining zone Dl
and the preliminary pressure zone D3 due to the action of the gravitational
force.
When the outer wall surface 11 of the second dewatering drum
2 is reached at the end of the comparatively pressure-free zone F the
sludge cakes Q which are now loosened as described are again bent but now in
the opposite direction i3. As a result~ the effect due to the simultaneous
action of the pressure due to the tension of the filter bands and due to
the first planet rolls 40a, is further considerably increased. ~ue to such
preparation~ it is possible to extract from the sludge cakes~ which have now
a totally different structural consistency~ considerable quantities of liquid
as they are guided about the dewatering drum 2. Such further extraction of
water would not be possible without the aforedescribed relocation of the
sludge particles forming the cakeS The continuous shear action as it is
obtained by the more rapidly moving inner filter band 4 further substantially
assists the dewatering operation.
The dewatering drums 1 and 2 can be driven with synchronous
speed or with at least a minimum differential of circumferential speedO For
this purpose~ a power drive with gearings which have different transmission
ratios as hereinafter described can be usedO ~ -
Filter bands 4~ 5~ after leaving dewatering drum 2 and the range
of rolls 40z together with the dewatered sludge cakes now designated by O are
guided over a diverter roll 50 conmlon to both filter bands to small individual
rolls 520 The roll 50 is disposed àt the apex of an imaginary triangle.
This triangle is defined by line L which extends through the axes of the drums~
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as it is shown in Figure 1 and legs defining an angle v of about 35 0 The
roll 50 is associated with planet rolls 51; in addition, some of the planet
rolls 40 associated with the adjacent dewatering drum 1 touch part of the
filter band sides ~e and 5 0
me two individual rolls 52 are mounted spaced apart from each
other and define a discharge gap 53 between filter bands 4~ 5 for ejecting
dewatered sludge cakes 00 The return of pulling band portions 4e and 5
respectively, extend from discharge gap 53 first over the planet rolls 40
(range C)~ then via the upper deflector rolls 55~ back to the straining zone
Dl and to the preliminary pressure zones D3~ respectively. Band flushing
means 56 are interposed between the deflector rolls 55 and zones Dl and D30
Figure 3 shows another exemplification of the preliminary
pressure 7ones D3. According to this exemplification~ pressure rolls 9u
are disposed underneath band sides 4u and 50 and also rolls 90 over which
via roller bearings 60, engaged by chain links 61 are joined to form endless
pull;ng band portions 620 and 62U in the direction of arrow SO Accordingly~
a structure is formed which is similar to the flexible cage of~ for instance~
a needle bearingO
Driving of each pressure roll 9 is effected by frictional driving ~-
of filter bands 4~ 50 The pressure rolls 9 are pressed within the pressure
zones D3 upon the inner side of filter bands 4 and 5. Diametrically
opposite to pressure rolls 9 there is disposed a pressure plate Pl and P2,
respectivelyO Nhen now the chain links 61 are guided over the sprocket -
teeth 63, 64 in the driving direction i of the filter bands 4 and 5~ the
pressure rolls 9 are rol ;ng off on the stationary pressure plates PO
The rotational speed on the opposite side is now twice as high
as the running speed o-f the chains formed by links 610 This has the advantage
that by means of relatively thin-~alled and light pressure rolls 9~ high
pressures can be transmitted. mis is due to the fact that there is no
strain due to the absence of bending forces normal to the axis of the rollsO
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The bending forces are compensated by pressure plates P overlying the rollsO
The pressure plates P are sp:ring tensioned at 65 so that no
forces need to be transmitted by an external support structure~
In particular, if the bands are fairly light, the sprockets 63,
64 for the chain links can be driven and then in turn drive th~ filter bands
4 and 5 in the direction i via the pulling band sides 629 that isg the drive
of filter bands 4 and 5 is effected no longer by one of the de~lection rolls
8~ 50~ 55 or the dewatering drums 1 and 2 which would cause heavy strains
within the range of the transmission of force upon the respective filter band
4 or 5~ which must be pulled by a multitude of gaps between rollsO Instead
of this transmission of force there is obtained at each of the gaps between
the rolls a transmission of force corresponding to the prevailing pressure~
and this transmission of force is uniformly distributed over a large surfaceO
By selecting different diameters d and at axial spacings f
for the upper and lower pressure rollers 9 substantially more or less pro-
nounced sine-shaped deflectors can be obtained at the surfaces of the filter
bands between which sludge cakes Q are placedO Moreover, relative movement
can be superimposed by differential speeds of the upper and lower pulling
sides 620 and 62U of the bandsO
According to the exemplification shown in Figure 4~ the device
does not include the straining zone Dl~ but the sludge cakes Q drop immed-
iately into preliminary pressure zones D3 which is disposed below dewatering
drums 1 and 2. Pressure rolls 9 are loaded by means of pressure plates PO
mese plates in turn are swingingly supported on catch trough 7O
The sludge cakes Q are guided from the preliminary pressure ~one
D3 to the first one of the dewatering drumsO After leaving this drum~ cakes
Q are guided through pressure zone D5 and subsequently to pressure zone D
After having passed through the last-mentioned zone~ filter band 4 guides
the now dewatered cake 0 to deflection roll 90 which is continued by a dis
charge chute 91o Filter band 4 after having been guided over roll 90 passes
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through cleaning zone 56 and a subsequent catch trough 93. mis catch trough
is formed by two rolls 92 on band 4 itselfO Finally~ band 4 is guided by
deflection rolls 5S and 8 back to preliminary pressure zone D
The second filter band 5 is guided over and between the de-
watering drums l and 2 by the lower band 4 and it is also lifted by this band
above the drums and either immediately at planet rolls 40 or o~er further
deflection rolls and cleaning station 56 back to preliminary pressure zone
D3. Cleaning station 56 includes discharge elements 94 which accun~ate
the cleaning water and discharge the same via pipes 95.
If it is desired to effect preliminary dewatering also with the
exemplification ~, filters may be provided ahead of the feed-in points (not
shown).
Referring now to Figure 5~ according to this figure a further
belt 3 formed by filter bands 4 and 5 is guided over dewatering drum l in
the driving direction iO Sludge cakes Q are again placed between the filter
bands. The two filter bands 4 and 5 are passed about the circumferential
wa71 surface 11 of drum l within an enveloping angle m of about 235 ~ said
angle being the sum total of the so-called roller angles ml. me filter bands -
leave dewatering drum l which rotates in the direction il at the lower branch -
50 of enveloping angle m-0
A plurality of planet rolls 40 press the outer or upper Mlter -
band 4 toward the circumferential surface wall of drum l within pressure
zones D5 which in turn is controlled by the envelopment angle m~
The axle 70 of each planet or pressure roll 40 is journalled at
both ends by radially disposed bars 710 The end of these bars which faces
the drum shaft F mounts a lock nut 72~ A coil spring 74 which is positioned
to expand in radial direction is disposed between nut 72 and abutment pla~es
73 which in turn are supported by diagrammatically indicated drum holders
450 Each of these springs biases the respective pressure roll 40 toward the
circumferential wall ll of the drum.
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The axles 70 of the rolls are staggered in circumferential
direction by pull links 75. me axle 70a which is the first one in the
driving direction i is suspended by means of radially disposed guide bars
76 on a cross bar 77 on the drum support 45.
The effective length c of the guide parts 76 can be adjusted
by setting an adjustment nut 78-~ Similar:Ly3 the effective length of radially
disposed bars 71 can be adjusted by means of nuts 720
A dewatering device as exempLified~ that is, a device which
includes two dewatering drums 1 and 2~ provides that with a drum diameter
of 1 meter about 16 meters of effective filter band length are available.
Yet the total length of the device is not more than 205 meters. The result-
ing utilization of the filter bands is more than 70%~ and such high effic-
iency factor is far above the efficiency factor of any dewatering device of
the kind herein-referred to as now known.
While the invention has been described in detail with respect
to certain now preferred examples and embodiments of the invention~ it will
be understood by those sh-Lled in the art~ after understanding`the invention9
that various changes and modifications may be made without departing from
the spirit and scope of the invention, and it is intended~ therefore~ to
cover all such changes and modifications in the appended claimsO
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