Note: Descriptions are shown in the official language in which they were submitted.
10~i9378
With the ever increasing awareness of pollution prob-
lems in contemporary society, and with the ever increasing volume
of waste products which forms a natural byproduct of growth in the
industrialized world, there have been ever increasing demands
placed upon the requirements of new sewage treatment plants, and
also demands for improvement of existing systems. In my patents
U.S. 3,743,100, dated July 3, 1973, entitled FILTER PRESS, MORE
PARTICULARLY FOR DEWATERING SLUDGE IN SEWAGE TREATMENT PLANTS, and
U.S. 3,896,030, dated July 22, 1975, entitled identically to the
first-mentioned patent, I have described certain filter press
systems to be advantageously used for the facilitation of sludge
treatment. In the latter patent, 030, I have also discussed a
dewatering system which has been based on the principle of simply
straining sludge through the action of gravity. It was pointed
out in the 030 patent that various known filter presses possess a
preliminary dewatering section, which is essentially a straining
system, while in other cases the material on the filter belt is
first squeezed between pressure rollers, prior to treatment on a
rotary dr~m system. The filter press dewatering means described
in this prior art in the 030 patent have the disadvantage that
filtering efficiency is comparatively low, the construction ,
relatively complex, and the space occupied by the machine is
relatively great. In my 030 patent there is described a new
dewatering means which has a pretreatment system, whereby the
sludge, prior to reaching the rotary belt is pressed between two
filter belts, with a filter belt acting as a strainer. Thus,
through the action of gravity an appreciable amount of the water
is removed, thus reducing the total water content of the sludge
prior to entering the rotary drum system.
~ o6s378
Sludges may also be dewatered through the use of tower
presses, in which two filter belts are pressed vertically, one
against the other, both belts being used in this filtering process.
It should be noted that a totally satisfactory result is not
attained through this alternative method to the filter press
methods which have been described in the prior art, and referred
to in said copending application.
With respect to the evolution of drum filter press
techniques, although there have been efforts made in this area,
it has been found that when only one filter belt is used for all
the phases of dewatering, that the mesh size of such belt must be
designed for the highest pressure which is used in the process,
otherwise, the filtrate which is the result of this process is
heavily soiled. To be sure, the general condition of sludge alters
as it goes through such a press in accordance with the quantity of
the water which is removed from the sludge. Corresponding to the
overall condition of the sludge, one would better choose at each
point in time during the overall process optimum conditions of the
filter size, the pressure and pressing time, and other parameters
related to the general condition of the sludge. It can be seen
that such control is desirable as the applicant has seen that witX
typical drum filter presses the water is first expelled but then is
sucked back into the sludge when the pressure is cut off, leading
to the conclusion that the practically feasible end product solids
contents is not achieved. The failure to be able to regulate such
parameters as time and pressure at the individual steps in tne
t - 2 -
~ ,
lQ6937B
in the chang-S o~ the sluc~e condition in the dewatering processes
is thus detrimental to achieving an optimum result.
In its generic aspect, the present invention provides
both a method and apparatus for dewatering sludge, which comprises
consecutive dewatering steps which are independent of each other,
particularly providing for different speeds of the sludge througn
the systems, e.g., where the separate systems of the present
invention are used in combination they treat the sludge at varying
speeds, and the relative pressure on the slud3e is increased in
consecutive stages. While the pressure is increased as the stages
go by, the speed of passage of the sludge is decreased sta~ewise,
In accordance with a preferred method of the present r
invention, three stages were used, with the first stage being a
pressure-free dewatering stage, the dewatering depending on the
force of gravity to force the aqueous portion of the sludge
through a filter system, the second stage being of a relatively
greater pressuFe, and the`third stage being of a still higher
pressure.
In accordance with the invention in yet another pre-
ferred embodiment, a method and apparatus are provided by which
the sludge is dewatered in two stages, a first pressureless stage
and a second high pressure stage.
In accordance with yet another preferred embodiment
of the invention, a method and apparatus are provided by which the
sludge is dewatered in two stages, a first medium pressure stage
and a second high pressure stage.
In accordance with another preferred aspect of the
invention, there is a method and apparatus provided for the three
stage dewatering process, at ever increasing pressures and ever
decreasing time periods for each stage.
It should be noted that although the generic aspect in
o~ way relates to the new combination of successive application of
dewatering treatments, there are individual elements and sub-
-- 3 --
937~
combinations herein which form an invention in their own right.
For example, it was heretofore necessary in the treatment
ol sludge to use a drum filter press of a relatively complex
construction, when one wanted to use a drum filter press for
sludge treatment. Now, with the added benefit of the combination,
it is possible to use a much simpler and therefore less expensive
drum filter press in the combined process,
The high pressure stage utilizing at least two endless
rotating platen belts which are pressurized towards engagement
with each other, and having two endlessly rotating filter belts
extending throughbetween these platen belts, in accordance with
the description which follows, also represents a new system in
itself.
In the art of drum filter press techniques, the applicant
has discovered yet another advantageous refinement in this art,
the incorporation of the flocculant-sludge mixing chamber within
the drum itself.
~ From a broad aspect, the present invention provides a
process for dewatering sludge in the purification of water in a
filtration plant wherein said sludge is passed through consecutive
stages of dewatering, each stage being independent and at each ;
successive stage the pressure applied to the sludge is increased
and the relative speed of tne sludge being passed through each
stage is decreased stagewise, the water being separately removed
at each stage.
From a further broad aspect, the present invention also
provides an apparatus for dewatering sl~dge which comprises at
least two dewatering stages operating at successively higher
pressure and at successively lower dwell times, wherein one of
said dewatering stage means is a drum filter press.
A preferred embodiment of the invention wiil now be
described with reference to the accompanying drawings in which:
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lC169378
FIGURE 1 is a diagrammatic sectioned side elevation
of one embodiment in accordance with the
invention in a three-stage extensible stage'
FIGURE lA is a more detailed view of the high pressure
stage of Figure 1,
FIGURE lB shows a middle pressure stage of the ^
embodiment of Figure 1,
FIGURE 2 is a plan view of the apparatus shown in
Figure 1,
FIGURE 2A is a high pressure stage of
Figure 2,
FIGURE 2B is an aspect of the drive means of the high
pressure stage of Figure 2;
FIGURE 2C is a top view of the middle pressure stage
of Figure 2,
FIGURE 3 is a sectioned view of the apparatus shown
in Figure 1 on the line III-III;
FIGURE 3A is a top view of Figure 3, partially drawn
; in section,
FIGURE 4 is a sectioned view of the apparatus of
Figure 1 on the line IV-IV,
FIGURE 5 is a sectioned side elevation of a first
form of the drum of a drum filter press
provided as a medium pressure stage,
FIGURE 6 shows a second form of the drum as an
; alternative to Figure 5,
FIGURE 7 is a partly fragmented sectioned view of the :
drum of Figure 6,
FIGURE ~ is a sectioned view of the line VIII-VIII
of Figure 1,
FIGURE 8A shows details of the drive of the view shown
in Figure 8,
FIGURE 8B is a séction in a different plane corres-
- - - . : .
1069378
ponding to Figure 8,
FIGIJRE ~ is a side elevation of a preferred embodiment
of the drum filter press forming the medium
pressure stage,
FIGURE 10 is a depiction of the drum filter press
according to Figure 9 together with a first
embodiment of a pressureless preliminary
dewatering facility, -
FIGURE 11 is a view similar to Figure 10, with a
second form of the pressureless preliminary
dewatering stage, and
FIGUR~ 12 shows an extensible stage of the apparatus
according to the invention, such stage
comprising high-pressure dewatering and
medium-pressure dewatering. -
A particular advantage provided by the invention is that
each of the independent dewatering phases cooperating with one ano-
ther represents an independent and independently operating and con-
trollable dewatering unit which can adapt properly to the existing
overall condition of the sludge. For instance, the pressureless
stage can have filtering specially designed for this stage - i.e.,
in the case of pressureless dewatering the filter will have a very
large mesh. The filter used in the medium-pressure dewatering phase
embodied by the drum filter press will have a correspondingly
smaller mesh, while the filter belt of the high-pressure stage will
have the smallest mesh size.
Another advantage provided by the process and apparatus
according to the invention is that the feature of using a special
dewatering unit or stage having a special filter belt makes it
possible for the first time to have the optimum belt speed in
each individual stage, the optimum belt speed depends upon the
quantity which still remains to be dewatered - i~e~, belt speeds
-- 6 --
1069378
can be differentiated to suit the respsctive total quantities of
sludge remaining in each stage after the respective dewatering.
Also, each individual stage can have pressing means, such as rollers
; or plates or platens or the like, which are particularly suitable
for the overall condition of the sludge in such stage, to ensure
the best form of pressing in such stage. Another advantage provided
by the invention is that separating the dewatering stages means that
the sludge in each individual stage can be adjusted to any required
optimum layer thickness by variation of the belt speed in such
; 10 stage. Also, in the case of-a three-stage process, three such
stages can be combined as required, the stages being associated with
one another in accordance with the kind of sludge and with require-
ments. For instance, a readily dewaterable sludge having a high
solids content will require only the medium pressure dewatering
using the drum filter press, alternatively, such dewatering can be
combined in such a case with a simplified form of pressureless -
preliminary dewatering. A readily dewaterable sludge having low
solids contents will always be dewatered by pressureless preliminary
dewatering combined with drum dewatering. A difficulty dewaterable
sludge which has a high solids content in the as-supplied state
; and which it is required to deliver with a very high end solids con-
tent is treated by a co~bination of drum dewatering and high-
; pressure dewatering. A sludge which has a low solids content and
which is required to be discharged after extensive dewatering will
be dewatered, for instance, by a three-stage treatment. Also, the
high pressure dewatering stage construction forming the feature of
various sub-claims can, in accordance with available investment
finance, be expanded as required as a final stage if a delivered
sludge having very high solid contents is required, in such a case
a number of such high-pressure stages can be provided in series.
Such a step increases the uniform pressing time given in the final
stage, and so the extent of dewatering is affected correspondingly.
-- 7 --
~069378
The high-pressure plate or platen dewatering to be described in
detail hereinafter can provide substantially the same effect as
can at present be provided by the known intermittently operated
chamber filter presses, which are very expensive and very
complicated dewatering facilities. In the lig~t of the solids
contents obtainable, the high-pressure stage proposed in accordance
with the invention could be called a continuously operating
chamber filter press' a disadvantage of the known chamber filter
press is the fact that it is an intermittently operating device.
Of course, chamber filter presses are costly devices only ~ecause
they have to take over a low solids contents sludge right in the
initial phase, whereafter the sludge has to be given the various ;~
phases of dewatering treatment, its overall condition altering
: correspondingly, in a single unit. However, when the sludge
entering such a press is already in an overall condition such that
it has ceased to be flowable, as is the case e.g. when it has
from approximately 30 to 35% solids content, complicated sealing
of a high pressure pressing zone becomes unnecessary. According
to this invention, the sludge is so treated in the first two
stages, e~g. of pressureless pocket dewatering and of medium- ~
pressure drum dewatering that its overall condition at entry into
the high-pressure dewatering stage enables it to be pressed at
high pressure without difficulties arising as regards sealing.
Another advantage of the invention is that the filtrate
expressed from the sludge is yielded separately in the various
stages. Clearly, the dry-substance content of the filtrates
varies in the various stages' the pressureless pocket dewatering
phase yields a substantially solids-free filtrate, the medium
pressure dr~ treatment yields a poorer filtrate having a higher
solids content, and the worst filtrate is yielded by the high-
pressure plate or platen dewatering stage. To take a practical
example, the quantities of filtrate may be approximately 10 m3/
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~06s37s
hour, the individual yields being approximately 7.35 m3/
hour in the pocket dewatering stage, about 1.35 m3/hour in the
drum dewatering stage and approximately 0.3 m3/hour in the high-
pressure plate dewatering stage. Since these quantitie9 of
filtrate are yielded separately, it is very advantageous to
recycle the small quantities of low-quality filtrate from the
high-pressure dewatering zone and even ~rom the medium-pressure
dewatering zone, with the extra advantage that the filtrate rnay
also contain flocculant, so that the quantity of flocculant added
to the feed sludge can be reduced.
The advantageousness of the process according to the
invention will be further described briefly with reference to a
practical example. The starting material is a sludge having
approximately 4% solids content and the throughput assumed is
10 m /hour. In a particularly preferred embodiment of the
invention, pressureless pocket dewatering is given in the first
stage, practical experiments have shown that an input of 10 m /
hour of sludge having a 4% solids content is converted by the
pocket dewatering treatment into a sludge having an approximately
15% solids content, approximately 7.35 m3 of water being removed.
At discharge from pocket dewatering - i.e., at entry into the
medium-pressure drum dewatering - the feed quantity of sludge is
only 2.65 m3/hour and its solids content is 15%. The medium-
pressure dewatering can therefore be performed relatively slowly
in accordance with the invention and practical experiments have
shown that a dewatering to approximately 30 to 40% dry substance
can be expected. On the basis of the worst figure of 30%, only
about 1.3 ~3/hour of sludge, which has a 30% solids content, are
yielded at the exit from the medium-pressure treatment facility.
The quantity of filtrate yielded in the medium-pressure stage is
therefore approximately 1.35 m3/hour. Given careful estimation,
therefore, a minimum solids content of 50% is likely at the dis-
charge from the subsequent high-pressure dewatering zone, the
_ g _
, . ...
~C~6~337t~
-, .
yields being only approximately 0.80 m3/hour of sludge and
approximately 0.5 m /hour of filtrate. The decrease in total
quantities which is apparent from~the example just given shows
clearly that the time for which the pressing means act on the
sludge can be varied within wide limits, despite a large through-
put, precisely in those of the dewatering stages where such
variation is important.
In the following discussion, reference to Figures is
to the Figures of the present case, and not to my said copending
ap~lication:
Referring now to the embodiment of the apparatus ~ ;
according to the invention which is designated as Figure 1, there
can be seen an extensible stage designed for a three-stage process.
In this form of the invention the three independently operating
dewatering phases take the form of a pressureless pocket dewater-
ing stage A, a medium-pressure drum dewatering stage B and a high-
pressure plate or platen dewatering stage C, in Figure 1 the
integers A, B and C are shown separated from one another by
chain-dotted lines.
Also visible in Figure 1 in diagrammatic form is a conical
mixing hopper or the like 1 for the raw sludge which is mixed
therein with a flocculant; further details of the hopper 1 will
be given hereinafter. The mixture of raw sludge and flocculant
proceeds after~flocculation, through a line indicated by an arrow
-- 10 --
A
1069378
2, to a pressureless preliminary dewatering facility 3 which
takes the form in Fig. 1 of a rotating pocket filter and which
will be described in greater detail hereinafter. From filter
3 the pre-dewatered sludge goes to an outer filter belt 4 of a
drum filter press. Filter belt 4 initially runs substantially
horizontally over rollers 5, 5', an optional additional item
is a vibrator for imparting adjustable oscilIations or vibra-
tions to belt 4. The vibrator can be of any known kind. There
is therefore further pressureless pre-dewatering on the path
between the rollers 5 and 5'.
After the roller 5' begins a wedge-shaped entry or
feed chamber bounded at the bottom by the outer filter belt 4
and at the top by a second filter belt 6 which, in its passage
through a cleaning facility 7, passes around a spring-biased
roller 8. The sludge fed to belt 4 from the pocket dewatering
phase is therefore received between the two filter belts 4 and
6.
The outer be~t 4 and inner belt 6 take the form of a
fine-mesh wire fabric, corresponding to the increased pressure
operative in drum dewatering, the mesh size of the wire fabric
is smaller than the filter width of the pressureless dewatering
phase. Also, of course, the drum dewatering stage can have
backing belts which are designed for the higher pressure and
take the form e.g. of warp wires woven into steel cross bars.
Tensioners 9, 10 are provided for filter belt 6 and
tensioners 11, 12 are provided for belt 4.
The wedge-shaped feed chamber terminates at the place
where the belts 4, 6 start to run around a rotating drum 13,
in the embodiment shown the drum 13 has a smooth outer generated
surface and can be rotated by a motor 15 driving by way of a
drive shaft 15 and a gearbox or the like. Extending approximately
1069378
around one-half of the drum periphery which follows on from the
wedge-shaped feed chamber are pressing-roller pairs 16 which
adjustable springs 17 bias towards the centre of the drum 13.
Only two such pairs 16 are shown completely in Fig. 1, the re-
mainder being indicated only in dia~rammatic form. The sludge
taken up between the filter belts is therefore given a milling
pressurizing between the pairs 16 of pressing rollers and the
outer periphery of the drum 13.
Disposed in the direction of rotation and around that
part of the drum outer periphery which follows on from the pairs
16 of pressing rollers are further pressing-roller groups 18 in
the form of groups each consisting of three rollers. Those
roller pairs of the groups 18 which are relatively near the drum
13 operate similarly to the roller pairs 16 and are also biased
towards the centre of the drum 13 by adjustable springs 19. The
extra roller 20, which is so disposed above the other pair as
to bound an equilateral triangle, is biased towards the drum
centre through the agency of a separately adjustable spring 21.
As can be seen, the two sludge-receiving belts 4, 6
run through around the periphery of the drum 13 below the roller
pairs 16 and roller groups 18, and after passing over as much of
the drum periphery as possible the belts 4, 6 are deflected by
a roller 22 which also serves as jockey, whereafter the two
belts 4, Ç move, in the opposite direction to drum rotation,
between the extra rollers 20 and the roller pair therebelow,
the sludge therefore being given further milling. The further
milling is substantially the termination of the medium-pressure
dewatering treatment. After leaving the final nip below a roller
20 the inner belt 6 passes around a deflecting roller 24 and over
the tops of the extra rollers 20 to return to the beginning of
the wedge-shaped feed chamber. To ensure that the belt 6 does
- 12 -
~0693~78
not entrain sludge at the roller 24 when reversing, a doctor or
scraper device 23 is also provided. The outer filter belt 4 has
a deflecting roller 26 which also has a doctor or scraping device
25 and which in the view in Fig. 1 is displaced to the right,
since the roller 26 is also the place at which the sludge leaves
the medium-pressure facility, embodied by the drum filter press,
for transfer to the high-pressure dewatering stage. The outer
belt 4 then goes around another spring-biased deflecting roller
24 and the outsides of the pressure roller pairs 16, in the
opposite direction to the direction of rotation of drum 13 and
via a cleaning facility 28, to return to the roller 5 which has
the belt-tensioning facility 11.
Before a detailed description is given of the high-
pressure stage C, further details will be given about the embodi-
ment of the pressureless pocket preliminary dewatering facility
as shown in Fig. 1.
As can be seen in Fig. 1, the pressureless preliminary
dewatering stage 3 takes the form of a rotating belt pocket
filter designed, according to its active filter area, either for
high filtering capacity or for high end product dry contents.
Disposed in casing 29 of filter 3 is a rotating conveying belt
30 having filter pockets 31 whose walls are made of a filter
material 32 or of perforate metal sheet, belt 30 runs at both
ends around sprocket wheels 33 and 33a, the latter wheel driven
by a driving motor 35 via a drive 34.
As will be described in greater detail hereinafter,
flocculated sludge enters the various pockets of the filter, for
dewatering, through an inlet 37 in casing 29 and as indicated
by an arrow 36, in the view shown in Fig. 1, the pocket belt
moves from left to right. The water leaving the filter pockets
is collected by a plate 36 and removed laterally. At the lowest
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..... . ..
1016937~
point of the wheel 33a, which is on the right in Fig. 1, the
dewatered sludge starts to be placed on filter belt 4.
The left-lland wheel 33 need not be a sprocket wheel
like the right-hand wheel 33a but can be devised like a cage
whose bars engage between the various pockets 31 as the belt
passes around the wheel 33. Near the left-hand wheel 33 is a
sprayer 38 for washing out the filter walls of the pockets 31,
conveniently, the sprayer 38 is secured to the underside of
plate 36a. The resulting washing space is isolated by a wall 39
from the transfer zone between the preliminary facility 3 and the
filter belt 4.
The filter apertures in the walls of the pockets 31
are coarser than the apertures in the belts 4, 6. Also, the
conveying speed of the facility 3 can be varied independently
and steplessly through the agency of the variable-speed motor
35 so that the process according to the invention may be carried
into effect advantageously.
The high-pressure stage of the process according to
the invention and of the apparatus shown, such stage having the
general reference C in Fig. 1, is conveniently embodied in the
present case by a facility 40 which can be called a plate or
platen belt press.
For the sake of maximum end-product dry content, the
press 40 representing the high-pressure stage of the process
according to the invention in its three-stage embodiment is
required to apply a very high and steady pressure to the sludge
which as early as its departure from the medium-pressure stage
of the treatment has a comparatively high solids content and
which is yielded to the final high-pressure stage in a fairly
solid general condition. The sludge transferred at the scraper
or doctor 25 from the medium-pressure stage to the high-pressure
- 14 -
lC~6937~3
stage C is fed into the press 40 downwardly between an outer
filter belt 41 and an inner filter belt 42. In adaptation to
the altered overall condition of the sludge, the mesh size or
perforation of the belts 41, 42 is smaller than that of the
belts 4, 6 of the preceding medium-pressure treatment stage.
The outer belt 41 runs over a deflecting roller 43 and
enters the first nip downwardly between two of three plate or
platen belts 44, 45, 46 which will be described in greater
detail hereinafter, the outer belt 41 then runs over a combined
deflecting roller and tensioner 47, then moves upwards through
the next nip between the belts ~5 and 46. At the top reversal
point of the belt 46 the belt 41 runs over an outwardly dis-
placed deflecting roller 48 which also has a scraper or doctor
49 and which represents the discharge point of the end-product
dewatered sludge. Preferably,: in the embodiment shown the dis-
charge point or place is high up, viz., very close to the top
end of the apparatus, with the advantage that the discharged
dry sludge can be transferred directly into containers or trucks,
so that the apparatus according to the invention need not be dis-
posed on raised foundations and can readily be accommodatedin existing works buildings.
If a relatively high solids content is required, the
high-pressure stage 40 can be amplified as required, however,
merely to retain the advantage of the discharge place being
positioned high up, it is preferable to add two extra plate or
platen belts, with appropriate guidance of the filter belts, with
each extension stage. Another possibility is for complete high-
pressure stages constructed as shown to be provided consecutively
on the unit construction principle, so that the discharge place
shown in Fig. 1 is also the place of transfer to an identical
high-pressure plate press.
~06!337~
From roller 48 the belt 41 descends over another de-
flecting roller 50 having a tensioner 51, then enters a washer
52 where there is another deflecting roller 53 with its tensioner
54, whence the belt 41 returns upwards to the roller 43.
The "inner" filter belt 42 also descends into the first
nip between the belts 44 and 45, runs down around the roller 47
and then up through the second nip between the belts 45 and 46.
At the place of discharge a deflecting roller 55 which also has
a scraper or doctor 56 is provided above the deflecting roller
; 10 48 of the outer filter belt 41. From roller 55 the belt 42
rises into a washer 57 where there are two more deflecting
rollers 58, 59 with their respective tensioners 60, 61. The exit
of the filter belt 42 from the washer 47 is disposed substantial-
ly above the entry into the first nip.
Further details of a high-pressure stage embodied as
a belt press of the kind described can best be gathered from
Figs. 1, 2 and 8.
In the embodiment shown, the facility applying the
highest and steady pressure to the filter belts 41, 42 receiving
the sludge between them takes the form of three rotating plate
or platen belts 44, 45, 46, since each such belt is of sub-
stantially identical construction, just one of them will be des-
cxibed with reference more particularly to Fig. 8. A plate or
platen belt of the kind outlined comprises pivoted-together
plates 62 rotating around two spindles 63, 64. For constructional
reasons the plates can be further subdivided in the peripheral
direction so that the total width of the resulting press is formed
by a number of rotating relatively thin plate belts, as can be
seen in Fig. 8. In the embodiment shown, sprockets 65 each en-
gaging in a chain 66 and provided to a number corresponding tothe discrete elements 62 are secured to the spindles 63, 64. The
- 16 -
1016937~
plates 67 of each plate belt 62 are secured to the links of the
chains 66 and are preferably in the form of perforate sheet
metal elements or elements made of similar materials. Also, on
one or both sides the links of each chain have rollers 68 which,
on the pressing side of such a plate belt - i.e., on the side
near the pressing nip between two plate belts - run along a
pressing plate 69 provided in this region. The plate 69 can
have separate guides or rail-like thickenings 70 for the rollers
of each chain. The pressing plate 69 is biased by pressure
towards the associated nip through the agency of cross-bearers
71 disposed at intervals in the space between the reversing
stations embodied by the sprocXets 65.
The pressurizing can be provided through the agency of
either hydraulic or pneumatic pressure cushions or through the
agency of reciprocating hydraulic actuators or the like. How-
ever, for the sake of simplicity and construction, the pressurizing
in the embodiment shown is provided by compression springs 72
which are adjustable to allow for possible sagging or the like.
In the embodiment shown in Fig. 1, the two outer belts 44, 46
are biased towards the central and substantially fixedly mounted
belt 45, the compression springs 72 being disposed on both sides
of the two outer belts 44 and 46 on thrGugh-bolts or the like 73
extendlng through the cross-bearers 71.
As can be gathered more particularly from Fig. 2, the
plate belts 44 - 46 are driven by a common drive in the form
of a driving motor 74 and associated gearbox 75, motor speed
also being steplessly variable. The gearbox drive shaft 76
drives the central and substantially stationary plate belt 45
directly, the drives for the two outer belts 44 and 46 are pre-
ferably by way of chain drives 77, 78 driven off a sprocket 79
on the drive shaft 76 to make allowance for the movements of the
- 17 -
1069378
belts 44 and 46.
To complete the description, additional backing belts
which correspond to the pressure requirement can be provided for
all the filter belts 4, 6 and 41, 42. It may also be necessary
to,provide additional drives for the filter belts or the backing
belts.
- Fig. 2 also shows a driving motor 80 for the drum 13
of the drum filter press of the medium-pressure stage B.
As can be gathered from Figs. 1 and 8, the filtrate'
yielded in the high-pressure stage C is collected in casing
81, between the roller 47 and the bottom reversal point of the
belt 45 there is an extra collecting trough or channel 82 which
serves, by virtue of its downward inclination in both directions, ~;
to combine the filtrate yielded in this region with the rest of
the filtrate collected and whiçh prevents the filtrate from re-
turning on the roller 47 into the expressed sludge.
Details of the pressureless filter pocket dewatering
facility hereinbefore mentioned can be gathered from Fig. 4 in
association with Fig. 1, while Fig. 10 shows a second embodiment
of thé facility. As can be gathered more particularly from
Fig. 4, the filter pockets 31 having walls made of a filter
material or of perforate sheet metal are suspended, also pre-
ferably in the form of a conveyor belt or plate belt, on endless-
ly rotating side chains 83, 84 which reverse around sprockets
33, 33a. The filter pockets 31 are so secured to the chain by
means of bars 85 or the like as to be in cross-section substan-
" tially triangular. This filter pocket belt construction leads
more particularly to a very simple kind of constructi-on for
guiding and mounting. Preferably, the links of the two chains
83, 84 have on both sides rollers 86 which, in the section between
the reversing sprockets 33 and 33a run in guides 87 in the top run
and in guides 88 in the bottom run, taking the full weight in
the top run of the sludge-filled pockets.
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As can be gathered from Fig. 4, the collecting plate
36a in cross-section resembles a pitched roof, so that the
filtrate accumulating is removed laterally.
The embodiment of pressureless filter pocket dewatering
as shown in Fig. 10 is a simplified embodiment which is of
reduced overall size and which may be of use in cases in which
either a sludge having a relatively high solids content is pre-
sent or requirements as regards end-product solids content are
not particularly severe. The -embodiment which is shown here
and which will subsequently be referred to separately in combin-
ation with the drum filter press is embodied by a bucket wheel
or drum or the like 91 which is enclosed in a casing 90 and
which is driven anticlockwise by way of shaft 92, conveniently,
the same is embodied after the fashion of a hollow shaft on
whlch walls 93 of the cells or;buckets are secured. Disposed in
the wedge-shaped spaces bounded by the walls 93 are filter
pockets 94 which are also of wedge-shaped cross-section and
which take the form of filters or filter belts or perforate
sheet metal members of coarser mesh than the filter belts 4, 6
and which can be axially bounded at their side walls by the same
filter material. In the diagrammatic view of Fig. 10 the filters
have the reference 95.
As in the embodiment shown in Figs. 1, 2 and 4, the
- effective length of the drum 91 corresponds to the width of the
filter belts 4, 6 and the drum 91 is driven by a separate motor
which is not shown and whose speed is preferably steplessly
variable. The wheel or drum 91 is completely enclosed in the
casing 90 and, as in the case of the embodiment shown in Fig. 1,
the discharge point 96 of the drum 91 is disposed above the
filter belt 4, the same rises slightly in this zone to facilitate
discharge of the filtrate yielded during the additional preliminary
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~ol69378
dewatering occurring between the rollers 5 and 5'.
Figs. 3 and 5 to 7 show a particularly preferred
embodiment of the drum filter press forming the medium-pressure
stage. The special feature of the embodiments shown in Figs.
3 and 5 to 7 is that the interior of the drum 13 is devised as
an additional reaction chamber for sludge and flocculant. Since
there are of course basically two kinds of flocculant, the
difference between them being their reaction times with the
sludge - i.e., fast reacting and slow reacting flocculants -
according to the invention, so that both kinds of flocculant
may be used the drum interior ~is embodied as an after-reaction
chamber, since the drum interior is available without additional
expense and has to be driven anyway.
Accordingly, drum 13 has an interior 99 closed by side
walls 97, 98, extending in the interior 99 over the whole
width thereof are transverse walls 100 which are inclined forwards
in the direction of drum rotation and thus bound circula*ing~or
conveying pockets 101.
The drum 13 is also of double-skinned construction,
20 an inner skin 102 bounding the reaction chamber 99 while an
outer skin 103 extending around the inner skin 102 is made of
perforate sheet metal or the like and can thus receive the fil-
trate yielded during the medium-pressure dewatering treatment.
To remove the filtrate which penetrates between the two skins r
103 and 102 during the dewatering treatment, the cylindrical
space bounded by the two skins 102, 103 is subdivided at regular
intervals around the periphery by transverse walls 104 disposed
at an inclination to the direction of rotation, thus also ensur-
ing that the filtrate yie]ded is removed from one side of the
cylindrical space (Cf. Fig. 7).
The embodiment of a drum shown in Figs. 3, 6 and 7 has
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~ : ~
106937~
a plain outer skin 103, but the embodiment shown in Fig. 5 also
has on the outer skin 103 a roller cage 105 over which the
filter belts 4, 6 run, corresponding outer pressing rollers
being provided as in Fig. 1. With this feature the drum can be
driven in the opposite direction to the direction of movement of
the belts 4, 6 to provide, should the special nature of the
sludge to be dewatered so require it, a very intensive milling
action due to the rollers, which are in contact with one another
by way of the filter belts and of the layer of sludge there-
between, performing an undulating motion.
As can be gathered from Fig. 3, raw sludge for treat-
ment which is delivered from a sludge-dispensing pump (not
shown), is introduced into the conical mixir~g hopper 1 at a place
106, disposed in hopper 1 is an agitator 107 which is driven
by a hollow shaft 10~3. A flocculant is supplied therethrough
into hopper 1 to be mixed with the raw sludge, and the mixture
of sludge and flocculant rises in the hopper 1 and at the top
thereof enters a reaction charnber 109 which in the embodiment
shown is embodied by the top end of the hopper 1. The mi~ture
of sludge and flocculant goes from charn~er 109 through hollow
shaft 110 of drum 13 and through a line 111 into reaction chamber
99, with the result that, since the drum 13 normally rotates
slowly, extra time becomes available for an after-reaction
between the sludge and the flocculant. Through the agency of
the pockets 101 bounded by the transverse walls 100, the sludge
is then raised to the highest part of the drum 13 and collected
by a collecting trough 112 disposed near the drum central axis.
- Trough 112 discharges into a line 13 which extends through hollow
shaft 110 of the drum 13 and from which the mixture of flocculant
and reacted sludge is removed on the opposite side of the drum 13
at a place 114. The sludge then goes, in the embodiment shown
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` ~C969378
in Fig. 1, to the pressureless filter pocket dewatering stage.
On the basis of the embodiments hereinbefore described
of a possible extension stage of the apparatus according to the
invention, there are in this case three independently operating
dewatering phases provided by the sections A, B and C. Each
of these independently operated phases - the pressureless pocket
dewatering A, the medium-pressure drum dewatering B and the
high-pressure plate dewatering C - makes it possible to use the
best filter size to suit the overall condition of the sludge.
Also, and as already stated in the example ~ust given, since the
total quantity to be treated decreases continuously, if there
is a high throughput of sludge to start with, the time for
which the sludge is given pressure treatment, together with the
pressure itself, can increase from one stage to the next without
any reduction in throughput, since most of the reduction in bulk
- occurs during the pocket dewatering stage. This feature is of
special importance precisely in the case of the steady pressure
in the high-pressure plate dewatering stage. Consequently,
treatment can be given in each of the dewatering stages with a
special filter belt running at the optimum speed for the particu-
lar stage concerned in the light of the quantity still to be de-
watered, optimum pressure conditions can also be provided.
Another factor which is considered to be of importance
for the invention, although not shown in the drawings for the
sake of simplicity, is for the filtrate to be yielded separately
in the various stages, so that fairly heavily soiled filtrates
can be returned to the process and, since they contain surplus
flocculants, can even help to improve process economy. Because
of the pressureless preliminary pocket dewatering, the resulting
slight increase in the total quantity to be dewatered is virtually
negligible. Another feature which is not shown in the drawings
106937t3
is that e.g. the very clean filtrate yielded by the pressureless
pocket dewatering stage can be used as a cleaning agent for all
the cleaning facilities. The lines and pumps needed for cleaning
are not shown in the drawings.
Also, and more particularly in the case of the three-
stage embodiment shown in Fig. 1, since each of the units used
can operate completely independently of the others, further ad-
vantages arise from the fact that such units can be used in a
very wide variety of combinations or because, depending upon re-
quirements, additional similar units can be used before or afterthe units shown. Figs. 9 and 12 show various possible combinations
of such a kind, starting from an extension stage of the kind
shown in Fig. l; however, in the embodiment shown in Fig. 1, a
second pressureless pocket preliminary dewatering facility of
even more adapted filter size and speed can be provided before
the units shown, and one or more high-pressure stages having
appropriately adapted filter belts and speeds can be provided
after the high-pressure unit shown.
In Fig. 9 only the medium-pressure stage B is shown,
for cases where the sludges being treated are very simple to
dewater and requirements as to end-products solids contents are
fairly easy, in Fig. 9 such stage, similarly to the embodiment
shown in Fig. 1, has its discharge place 115 high up. For
further constructional details reference should be made to the
description of the embodiment shown in Figs. 1, 2, 3 and 5 to 7.
The combination shown in Fig. 10 is preceded by the
small model pocket preliminary dewatering facility hereinbefore
described, so that most of the water present in the sludge is in
this case removed in the pocket dewatering phase and the drum
filter press can be operated at optimum speed and filter belt
mesh size.
1069378
Fig. 11 shows a combination similar to Fig. 1 except
that, in accordance with the sludge for treatment and with end-
product solids contents, no high-pressure stage is provided.
Fig. 12 shows another possible alternative combination
in which there is no preliminary dewatering and a medium-pressure
stage B is followed by a high-pressure stage C.
As will be apparent from the foregoing, the invention
makes it possible for the first time to make allowance for
changes in the overall condition of the sludge during its dewater-
ing treatment.
It is considered to be of great importance for theinvention to combine pressureless pocket d~watering with high-
pressure plate dewatering in accordance with the stages A and
C described, since it then becomes possible for the prior art -;~
intermittently operating chamber filter press to be completely
replaced by a very low cost continuously operating plant.
It should be noted that the method and apparatus may
also be used by substituting for the instant system of filter
pockets in the pressure free stage a filter pocket system where
the filter pockets are compressed. In addition, yet a further
refinement of the overall invention disclosed in the present
case relates to embodiments which incorporate improvements in the
present system, particularly including the use of the variable
pockets.
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