Rotary filter

A multi-disk rotary filter in which a plurality of disks on a common shaft are partly immersed in a trough containing the suspension to be filtered and each of the filter disks is formed with a plurality of filter sectors or cells each connected to a control disk through which the filtrate is evacuated. According to the invention, each disk is formed with a cell carrier with a radial passage communicating with each sector and merging into an axial passage. The axially extending passages of at least some of the disks are formed at least in part by straight tube sections outwardly of the shaft.

FIELD OF THE INVENTION 
The present invention relates to a multi-disk rotary filter and, more 
particularly, to a rotary filter in which a plurality of filter disks are 
mounted upon a rotatable shaft in axially spaced relation to carry the 
filter surface formed on each disk into a trough containing the suspension 
to be filtered and the filtrate is evacuated from the respective filter 
cells, formed as sectors of the disk. 
BACKGROUND OF THE INVENTION 
Rotary disk filters of the afore-described type are, of course, known in 
the art and have the advantage that they are relatively compact and 
provide in a comparatively small space a large filter area which can 
enable withdrawal of filtrate from the individual filter cells in the 
suspension, to deposit solids on the filter surface (e.g. filter cloth) 
and to draw adherent filtrate from the solids when the latter are swung 
into a drying zone out of the trough. 
Rinsing can be effected along the portion of the disk out of the suspension 
and, indeed, the solids can be treated on the filter disks with other 
liquids as well (see the commonly assigned, copending application Ser. No. 
870,614 filed Jan. 19, 1978). 
A filter which functions in this manner is also described in the brochure 
Scheibenfilter SSF published by Krauss-Maffei A.G. In this filter system, 
each sectoral filter cell is connected by a separate filtrate tube or 
suction tube to the control disk at which the respective tubes are 
connected to the respective liquid displacement or aspiration ducts by 
separate tubes or conduits extending through the interior of the shaft 
which is hollow. 
The control head or disk, with which these conduits communicate, is a 
distribution valve subdivided into a washing zone, a drying suction zone 
and a cake-discharge zone at which, respectively, filtrate is pumped from 
the sector whose conduit registers with the first of these zones, residual 
fluid is aspirated by a suction pump in the second of these zones to draw 
air through the cake for drying purposes, and fluid under pressure is fed 
through the conduit aligned with the third of these zones to dislodge the 
filter cake from the filter material (cloth) of the disk. 
With the prior-art arrangement just described, the filtrate can readily be 
pumped out of the sectors of the lower quadrants of the disk while air can 
be drawn through a sector in an upper quadrant and compressed air can be 
blown into a sector of an upper quadrant for the dislodgment of the filter 
cake. 
A disadvantage of this arrangement is, however, that the provision of a 
large number of filter disks and a relatively large number of sectors 
within each disk requires an extremely large number of tubes or conduits 
which must pass through the shaft. The relatively dense tube bundle makes 
repair or replacement of the components and conduits difficult and 
expensive. 
The problem is especially pronounced when the tubes or conduits are 
subjected to wear as is the case when abrasive solids are to be filtered 
from the suspension and/or solids are to be filtered from corrosive media. 
In practice it has been found that the tubes connected to each sector last 
only for a brief period, e.g. several months, whereupon they must be 
replaced at considerable cost and by complex maintenance and repair 
procedures. Naturally during the replacement period, the apparatus is out 
of service. 
Investigations have already been made to attempt to reduce the cost of such 
apparatus and the maintenance and repair thereof by leading the filtrate 
from the individual cells of adjacent or successive disks in common 
through the filter shaft. While this is not usually a problem for the 
extraction of the filtrate from the sectors immersed in the trough, it 
does pose a problem when compressed air is to be fed to the sector after 
drying for dislodging the filter cake. In practice it has been found that 
the compressed air of systems of the latter type is not distributed 
uniformly to the filter disks. 
The compressed air takes the path of least resistance and is thus 
concentrated at the disks proximal to the control head and frequently the 
pressure pulse at more distal disks is insufficient to dislodge the filter 
cake. 
When the filter is not fully dislodged from some of the disks, it is 
rotated again into the suspension so that additional solids build up to 
form a thicker filter cake in the regions more remote from the control 
head. 
Eventually these thicker portions of the filter cake retain more moisture, 
are subject to less drying and, in general, interfere with the uniform 
operation of the system. The eventual removal of this moist filter cake 
can even create obstructions in the ducts which carry the filter cake away 
from the filter. 
OBJECTS OF THE INVENTION 
It is the principal object of the present invention to provide a rotary 
disk-type filter having a plurality of disks of the type described which 
avoids the disadvantages of earlier systems as described above. 
Another object of this invention is to provide an improved rotary disk 
filter which ensures a more uniform distribution of fluid to and from the 
filter sector than has been possible heretofore. 
A further object of our invention is to provide a rotary filter which can 
be used effectively even for the filtering of abrasive or corrosive 
suspensions with reduced problems with respect to maintenance and 
replacement of parts. 
Still another object of this invention is to provide a rotary filter which 
can be easily assembled and disassembled and in which replacement of the 
filter tubes can be effected at relatively low cost. 
SUMMARY OF THE INVENTION 
These objects and others which will become apparent hereinafter, are 
attained in accordance with the invention in a disk filter of the 
afore-described type which comprises a shaft on which are mounted at least 
two filter disks with respective cell carriers and a control disk or head 
whereby communication with the respective sectoral cells is established. 
According to the invention, each of the cell carriers has for each sectoral 
cell a passage which runs radially to the cell and then passes through a 
curved transition into a substantially axially extending passage which, 
between the curved transition or elbow and the control disk, is in the 
form of a straight tube section lying externally of the filter shaft. 
Advantageously, the elbow or bend transition portion is formed integrally 
with the cell carrier, i.e. unitary therewith, while the cell carrier 
itself is constituted as a case body. The wall of the filtrate passage in 
the region of the elbow or curved transition has a substantially greater 
thickeness than the wall of the passage elsewhere along its length and it 
has been found to be desirable to form the elbow such that its axis and 
indeed the elbow itself lie along a circular arc. 
In the latter case, the radius of curvature of the filtrate passage in the 
region of the elbow or transition is greater than the diameter of the 
filtrate passage and preferably is about twice this diameter. 
According to another feature of the invention, the cell carrier can be 
disk-shaped and the filtrate passage communicating with each cell can be 
formed by two substantially perpendicular bores, one of this is generally 
radial while the other is axial, the bores meeting within the disk-shaped 
carrier at a curved transition or elbow as described. 
In the latter embodiment it has been found to be advantageous to provide a 
rounded fluid deflection plate along the outer arc of the transition 
region, this plate being concave inwardly and composed of a low-wear 
material, e.g. a metal carbide. This deflection plate can be removable 
from the disk-shaped carrier and can be replaceable therein, e.g. by being 
received in a seat recessed in the carrier. 
In accordance with another aspect of the invention, the tube section of 
each filter disk more distal from the control disk or head lies radially 
inwardly of the tube sections of the filter disks closer to the control 
head. In accordance with this aspect of the invention it is advantageous 
to pass the tube section of each disk more removed from the control head 
through the sector or cell carrier of a disk closer to the control head. 
The tube sections of disk carrier more remote from the control can pass 
completely through the carrier proximal to this control head and can 
terminate in a member interposed between the control head and this 
proximal carrier itself. The ends of the tube sections may be removably 
held in the carriers or carrier in which they terminate, sealing being 
effected by O-rings. The tube sections can, alternatively, be threaded 
into the cell carriers, cemented therein, rolled into engagement with the 
cell carrier or sintered or fused therein. 
The bodies of the cell carriers can have feel which are releasably mounted 
upon the filter shaft which can be formed with pedestals to which the feet 
are connected, the outer diameter of each pedestal and the inner diameter 
of the corresponding cell carrier being increased stepwise from a disk 
proximal to the control head to a disk distal therefrom. 
Finally, in this connection, the tube sections can be oriented such that 
there is a downward flow from the cell in the drying quadrant. In this 
case, each of the straight tube sections is inclined relatively to the 
filter shaft axis in a sense of a twist to provide this downward path. 
The principal advantage of the system of the present invention is that the 
downtime of the unit is minimized and the useful life is increased because 
replacement of the tube sections need not be as frequent as has heretofore 
been the case. When, however, replacement of the tube sections is 
required, this replacement is relatively rapid and at low cost since only 
the straight tube sections need be replaced with any frequency even when 
abrasive suspensions are encountered. 
This is because the tube sections themselves do not carry the elbows or 
transition regions. Since tube sections lie wholly externally of the 
filter shaft, no disassembly of the latter is required and the tube 
sections are readily accessible and easily tested as to their integrity. 
While the greatest wear occurs in the region of the deflection of the 
filtrate from the radial to the axial portions of the passage, especially 
when abrasive media are provided, the longer paths in the axial direction 
cause damage to the tube sections which are more readily replaced. The 
elbow or transition regions are, because of the greater thickness, 
replaceability or choice of material, more able to withstand wear. 
According to the invention, the filtrate tube may have a relatively large 
cross section so that it also possesses a larger specific suction cross 
section than has heretofore been the case, thereby reducing flow 
resistance and increasing the uniformity of evacuation of the cells or the 
pressurization thereof. 
Naturally, where a disk carrier lies directly against the control head, the 
straight tube section can be eliminated since the elbow in this case can 
run directly to the control disk or head or can communicate therewith via 
a sealing disk.

SPECIFIC DESCRIPTION 
The present invention is applicable to multiple-disk filters of the type 
described in the aforementioned copending application and especially in 
the brochure entitled "Scheibenfilter SSF" published by Krauss-Maffei AG 
mentioned previously. Although two filter disks have been shown in various 
Figures and two filter carriers have been illustrated to carry the filter 
disks, it will be understood that the principles are also applicable to 
systems in which a larger number of filter disks are provided. 
As can be seen from FIGS. 1 and 2, a filter shaft 5, rotatable about the 
filter shaft axis 8 by means not shown, carries a pair of axially spaced 
cell carriers 1 and 1'. Thus FIGS. 1 and 2 are only intended to illustrate 
the principles of the invention while details of the attachment of the two 
sections to be described below will be apparent from FIGS. 5a-7b, the 
orientation of the tube sections form FIG. 8, and the means for attachment 
of the cell carriers 1 and 1' from FIG. 4. 
The cell carrier 1, which is cast in a single piece, has a foot shown to be 
welded to the periphery of the shaft 5 and carriers a filter disk which is 
subdivided into sectors each of which forms a filter cell 6. During the 
suction phases, at least one of which takes place while the filter cell is 
immersed in a suspension in a trough as shown in FIG. 8, the filtrate is 
exhausted along a filter passage in the direction of the arrow 27 through 
the elbow or transition devices 7, 7' of the cell carriers 1, 1', i.e. 
from a radial portion of the passage through a curved transition portion 
to an axial portion of the passage. 
The filtrate is withdrawn through a sealing disk 3 and further through a 
control disk 4 forming part of a control head functioning as a 
distribution valve in a manner known per se. 
The filtrate passes, as can be seen from the left-hand side of FIG. 1, from 
the cell carrier 1 directly into the sealing disk 3 and then into the 
control head 4 during evacuation of the cell. Naturally, as the cell is 
rotated out of the suspension, it continues to be subject to suction to 
draw air through the filter cake and thereby dry the latter, and then to a 
pressure pulse in which compressed air is momentarily introduced into the 
cell to cause the filter cake to be dislodged from the filter cloth on the 
opposite faces of the cell. The successive fluid flow from and to the cell 
is controlled by the distribution valve function of the control head 4. 
The elbow or transition regions 7 of the cell carriers 1 and 1' have a 
relatively large arc, i.e. correspond to circular arcs bent to a radius of 
curvature R which is approximately twice the diameter of the filtrate 
passage. 
When the cell carriers are, as shown in FIGS. 1 and 2, cast unitarily of a 
wear-resistant material, they have an especially long useful life, which 
is augmented by forming the outer arc portion of each elbow of greater 
thickness than the remaining wall thickness of the passage. This has been 
found to permit the system to withstand extremely long oscillating periods 
even with exceptionally abrasive suspensions. 
The filtrate from the cell carrier 1' in FIGS. 1 and 2, after leaving the 
respective elbow or transition member 7, 7', passes into a removable tube 
section 2 which traverses the cell carrier 1 and terminates in the 
left-hand portion of this cell carrier (FIG. 1) or directly in the sealing 
disk 3 (FIG. 2), the various methods by which the straight tube section 2 
of each cell carrier are affixed and sealed being illustrated in FIGS. 
5a-7b. 
The arrangement of FIG. 2 thus differs from that of FIG. 1 only in that the 
straight tube sections 2 of FIG. 2 extends completely through the cell 
carrier 1 and is fixed in the sealing disk 3 by one of the techniques 
shown in FIGS. 5a-7b. 
In order to replace the straight tube sections 2 of the system, it is only 
necessary to withdraw the tube section through the control and sealing 
disks to the left and to insert a new tube section. 
Since the straight tube sections 2 lie externally of the filter shaft 5, 
they are readily acceptable and can be free from any curves or bends which 
prevent ready replacement or increase the wear. Replacement can then be 
effected rapidly in a short time so that the filter will have a minimum 
down time during such maintenance. 
While the elbow portions 7 and 7' of FIGS. 1 and 2 have each been shown to 
the the same radius of curvature R for the respective elbow, it has been 
found to be advantageous in some instances to impart a greater radius of 
curvature for the elbow 7' more distal from the control head 4. This 
permits the filtrate passage of each more distal cell carrier to be 
located closer to the shaft 5. 
While FIGS. 1 and 2 have, for the sake of simplicity of illustration, shown 
only two filter disks, it will be readily apparent that the device is not 
limited to two such disks and further disks may be provided in axially 
spaced relationship along the shaft with each more distal carrier having 
its filtrate passages lying inwardly of the filter carriers more proximal 
to the control head 4. In this case, each additional filter carrier will 
have straight tubes which pass through all of the preceding filter 
carriers before terminating in the sealing disk 3 or the first or proximal 
carrier 1. 
The tubes are thus of progressively greater length. 
FIG. 3 illustrates an embodiment which is an alternative to that of FIGS. 1 
and 2 and in which the cell carriers 11, 11' are generally of disk shape 
and carry the filter disks in their respective cell as previously 
described. In this embodiment, however, each filtrate passage forms a 
respective sectoral filter cell comprises a radial bore which merges with 
an axial bore at an elbow or transition region 17, 17', the two bores 
being substantially perpendicular to one another. 
The flow deflection between the radial bore and the axial bore is effected 
at the elbow or transition region at which, along the outer arc of the 
elbow, a deflection plate 16 or 16' is provided. Each of these inwardly 
concave deflection plates is removably seated in a recess formed in the 
respective cell carrier 11, 11'. 
These deflection plates 16 and 16' perform a dual function in that they 
provide a smooth direction change of the filtrate flow and, in addition, 
can be replaced. The deflection plates 16 and 16' are formed from a 
low-wear material, such as tungsten carbide, with the filter plate being 
removable and replaceable together with or at different intervals from the 
removal and replacement of the straight tube sections 12 which function in 
the same manner as the tube sections 2 described previously. 
FIG. 4 shows that the filter shaft 5, which is rotatable about the shaft 
axis 8, can be provided with a pedestal 22 for the cell carrier foot 23 of 
the cell carrier proximal to the control head. A corresponding pedestal 
22' of greater outer diameter can be provided for the more distal cell 
carrier whose foot is shown at 23'. 
According to the invention, the cell carriers are held in place upon the 
pedestals 22, 22' by screws 23a and 23a' threaded into the heels of the 
seat 23, 23', respectively. 
Naturally, the mounting system of FIG. 4 can be used with the embodiments 
of FIGS. 1, 2 and 3 as well. 
In all cases, the outer diameter of the pedestal 22 is smaller than the 
inner diameter of the cell carrier foot 23' so that the more distal cell 
carriers can be simply slid over the preceding pedestals from left to 
right along the shaft. Naturally, when a three-disk filter is employed, a 
third pedestal is provided in axially spaced relationship to the right of 
pedestal 22' and its cell carrier has an inner diameter greater than the 
outer diameter of cell carrier 22. 
FIGS. 5a-7b show various methods of fastening the straight tube section 2 
in the cell carrier 1 or in the sealing disk 3. 
For example, in FIG. 5a, an O-ring 20 is recessed in an inwardly open 
groove in the cell carrier 1 and frictionally grips and seals the tube 
section 2. 
FIG. 5b shows that a similar system applies when the O-ring 21 is lodged in 
an outwardly open annular groove in the tube section 2 to engage a 
smooth-surfaced wall of a bore of the carrier 1 into which the tube 
section 2 is inserted. 
FIG. 6a illustrates an arrangement in which the tube section 2 is cemented 
into the cell carrier 1, e.g. by a layer of cement 50. FIG. 6b indicates 
that a swaging technique can be used by rolling an annular bulge 24 in the 
tube section 2 which is forced into the material of the cell carrier 1 to 
anchor the tube 2 therein. 
Another swaging technique has been shown in FIG. 7a in which an outward 
flange 25 is formed on the end of the tube section 2 and engages in a 
corresponding recess countersunk in the cell carrier 1. In the embodiment 
of FIG. 7b, the tube section 2 is externally threaded and is screwed into 
the internal thread in the cell carrier 1. 
The fastening and sealing systems of FIGS. 5a-7b can be used individually 
or in combination in accordance with the applications of the system. 
While the Figures of the drawing which have been discussed previously 
indicate that straight tube sections which are substantially parallel to 
the filter shaft axis 8 are provided, the filtrate runoff during the 
suction phase can be increased by inclining the straight tube sections 
relative to the filtrate shaft axis 8 to form a flow gradient. Such an 
arrangement has been illustrated in FIG. 8 in which the incline of the 
tube sections 2' has been illustrated. In this case, the bore of the 
carrier 1 in which the tube section 2' is received can be similarly 
inclined so that withdrawal of the straight tube sections 2' is as simple 
as in the embodiments previously discussed.