AU764854B2

AU764854B2 - Disk filter

Info

Publication number: AU764854B2
Application number: AU19456/00A
Authority: AU
Inventors: Ing Reinhard Dr. Bott; Ing Thomas Dr. Langeloh
Original assignee: Bokela Ingenieurgesellschaft fuer Mechanische Verfahrenstechnik mbH
Current assignee: Bokela Ingenieurgesellschaft fuer Mechanische Verfahrenstechnik mbH
Priority date: 1999-02-26
Filing date: 2000-02-25
Publication date: 2003-09-04
Anticipated expiration: 2020-02-25
Also published as: DE29903511U1; AU1945600A

Description

Regulation 3.2

AUSTRALIA

PATENTS ACT 1990 COMPLETE SPECIFICATION FOR A STANDARD PATENT

ORIGINAL

0 0 0 0 0 0..0 0000 0 0.

0 00 0 00 *0* 0 Name of Applicant: Actual Inventors: Address for Service: Invention title: BOKELA Ingenieurgesellschaft fuer mechanische Verfahrenstechnik mbH DR.-ING REINHARD BOTT DR.-ING THOMAS LANGELOH MADDERNS, 1st Floor, 64 Hindmarsh Square, Adelaide, South Australia, Australia DISK FILTER Details of Convention Application No: Based on German Patent Appln No 29903511.5 dated 26t February 1999 The following statement is a full description of this invention, including the best method of performing it known to us.

2 DISK FILTER The invention relates to a disk filter with a suspension trough for receiving a suspension to be filtered, a filter shaft mounted in rotary manner and constructed for rhe discharge of a filtrate, at least one filter disk fixed to the filter shaft and at least partly immersed in the suspension to be filtered and on whose lateral faces are provided filter areas and a pressure producing device for producing a differential pressure between an outside facing the suspension and an inside remote from the suspension of the filter areas, the filter disk comprising several filter disk segments, which in each case have a segment foot and are fixed by means of said segment foot in each case in separately detachable manner to the filter shaft, which also have a supporting framework and a filter medium located thereon and comprising a cavity bounded by the lateral surfaces entered by the filtrate after passing through the filter medium and from which the filtrate passes for discharge by means of the filter shaft.

Disk filters of the aforementioned type are known and are used for cakeforming filtration. It is also known to use drum filters. They have a substantially cylindrical shape and filter cake formation takes place on the cylinder jacket, which is partly immersed in the suspension to be filtered.

Compared with these drum filters in the case of the disk filters according to the preamble there is an improved relationship between the effective filter surface and the total surface. Disk filters also offer advantages with 21 regards to maintenance and repairs of the installation, because individual filter disk segments can be removed and replaced, without it being necessary .oee to render the complete installation inoperative for an undesirably long period of time. This is particularly important, because maintenance of the installation must take place at regular intervals. In particular, when Q necessary the filter medium must be replaced.

*.00 •e For high filter performances normally use is made of very large disk filters with diameters of up to 5 metres. As a result of the geometrical circumstances, such as the space required for fixing the segments to the shaft, the Smaximum possible number of filter disk segments is limited to 24 to 30 per 0. filter disk. In order to withstand the considerable forces arising in operation, the filter disk segments must be given an adequate stability. Thus, the segments have a typical mass of 28 to 35 kg. This high mass is disadvantageous in connection with the manipulatabiity of the filter disk segments. It would admittedly be possible for reducing the mass to decrease the size, i.e. the external radius of the segment. However, this would be disadvantageous for the filter performance. It must also be borne in mind that design changes to the supporting framework are only possible to a limited extent, because there must be a completely satisfactory flow behaviour within the filter disk segments.

The object of the invention is to address the problem arising from the weight and 10 stability requirements.

Therefore, the invention accordingly provides a disk filter having a suspension trough for receiving a suspension to be filtered, a filter shaft mounted in rotary S. manner and constructed for the discharge of a filtrate, at least one filter disk fixed to the filter shaft and at least partly immersed in the suspension to be filtered and on whose lateral faces are provided filter areas, and a pressure producing device for producing a differential pressure between an outside facing the suspension and an inside remote from the suspension of the filter areas, in which the filter disk 20 includes several filter disk segments, which in each case have a segment foot and !20 are fixed via said segment foot in each case in a separate detachable manner to the filter shaft, also having a supporting framework and a filter medium placed thereon, and including a cavity defined by the lateral faces and which is entered by the filtrate after passing through the filter medium and from which the filtrate passes for discharge via the filter shaft, characterised in that, a filter disk segment °25 has a critical mass of a maximum of 13.5 kg/m 2 related to the effective filter surface, and the reduction in the geometrical moment of inertia of the filter disk segment associated with the dropping below the critical mass is compensated by a S.corresponding increase in the internal spacing of the lateral faces defining the cavity.

3a Building up on the disk filter according to the preamble, according to the invention a filter disk segment has a critical mass of a maximum of 13.5 kg/m 2 relative to the effective filter surface and the reduction of the geometrical moment of inertia of the filter disk segment associated with the dropping below the critical mass is compensated by a corresponding increase in the internal spacing of the lateral surfaces defining the cavity. As a result of this measure it is on the one hand possible to satisfy the requirement of making available sufficiently lightweight filter disk segments, so that anyone is able to remove or replace them. On the other hand the stability loss linked with the mass reduction is compensated in that the 10 design of the supporting framework is appropriately modified. The specific change, i.e. the increase in the internal spacing of the lateral surfaces bounding the cavity, leads in simple manner to the desired result.

0 It is particularly advantageous of account is taken in the describes supporting framework design of the fact that the cross-sectional surface of the cavity is the centre-next filter area is smaller or equal to the flow cross-sections following in the direction of the filter shaft. A reduction of the flow cross-section in the direction of the filter shaft would inhibit filtrate discharge and consequently impair the filter performance.

A particularly favourable design of the participating flow cross-sections can be achieved if for the ratio of the external radius rl of the filter disk o *o o -4 to the radius r 2 in which the filter segments are fixed to the filter shaft r /r 2 a 3.8 applies. This ratio takes account of the fact that an increase in the radius r and therefore an increase in the space available for the flow cross-section is only possible within narrow limits. The reason for this is that only through a large ratio of the external radius r to the radius r 2 can it be ensured that a large filter surface and therefore an efficient operation of the installation is ensured.

It is also advantageous if in the case of a filter disk segment in the vicinity of its segment foot at a point of maximum load in operation, the geometricl mmen o inrti J4 4 rical moment of inertia Je exceeds 3.59 x 10 mm As a result of such a ges geometrical moment of inertia an adequate stability of the filter disk segments is ensured, so that even with high speeds 6 there is an adequate mechanical loading capacity.

Preferably the side walls of. the filter disk segments in the filter area have perforated plates with a thickness of 1.5 to 1.6 mm, the openings in said perforated plates representing at least 350 of the total surface of the perforated plates. Through the use of such perforated plates it is on the one hand possible to obtain an additional weight reduction and on the other the openings of the perforated plates provide passage areas for the filtrate passing out of the filter medium. The mutual spacing of the perforated S plates is preferably between 20 and 50 mm.

Preferably, in the filter area, perforated plates are provided, which at the external radius of the filter disk segments are zonally or continuously given a marginal profile or are zonally welded together or connected by means of a marginal bar. As a function of the stability requirements and intended use said measures are able to meet the existing quality requirements.

It is also advantageous to provide in the filter area perforated plates and for supporting the latter against the action of the differential pressure between the side of the filter areas facing the suspension and the side of the filter areas remote from the suspension installation takes place of perforated profiles as supports. Since during filtering there is a lower pressure within a filter disk segment than outside the same, the side walls tend to curve into the cavity or even buckle. This impairs the originally optimum design of the filter disk segment, with a particularly great influence on rhe outflow behaviour of the filtrate. This effect is counteracted by the supporting profiles. The profiles are once again Perforated in order to bring about the weight reduction sought by the invention.

The filter disk segments according to the invention are Particularly advantageous if they are covered with bag-like filter cloths as the filter medium.

Thus, following the disassembly of a filter disk segment it is possible to rapidly replace the filter medium, which merely involves the removal of the old bag and the attachment of a new bag. In order to further speed up the replacement of the filter disk segments, it is conceivable to keep in stock filter disk segments already equipped with new filter cloths.

In conjunction with the rapid replacement requirement, it is also useful for the filter disk segments to be fixed by means of quick fastenings in the form of stud bolts, a bayonet catch or a lever fastening to the filter shaft.

For example, in the case of a bayonet catch, a filter disk segment can be removed with a single manipulation and the new segment can equally easily be placed on the filter shaft.

The filter cake formed on the disk filter according to the invention is advantageously removed from the filter disk segments by means of a scraper.

This is a particularly easy design measure for filter cake removal.

However, it can also be advantageous to provide a compressed air supply for removing the filter cake. The compressed air is introduced into the interior of the filter disk segments and then the filter medium curves outwards and finally the filter cake is removed. As a result of this variant of the apparatus it is possible to bring about an almost complete removal of the filter cake, which shortens the maintenance intervals or the intervals S between individual filter medium replacement.

It is particularly useful for each of the filter disk segments to be subject to compressed air action. This leads to the advantage that for each filter disk segment the filter cake can be removed at the optimum time from the process engineering standpoint. It is pointed out in connection with the described removal by compressed air action, that this procedure represents a limiting condition regarding the maximum volume within the filter disk segments. If the volume is chosen too large, then the pressure building up in the filter disk segment is inadequate to ensure a satisfactory and reliable filter cake removal. It is also important in this connection that starting from the filter area no further flow cross-section reduction takes place in the direction of the filter shaft because, as described, this not only impedes filtrate outflow, but would also lead to the compressed air inflow being impeded.

The invention is based on the surprising finding that the stability loss of the filter disk segments can be compensated by a special design of the supporting framework of the individual filter disk segments and that it is simultaneously possible to choose a design conducive to a good flow behaviour.

The stability of the filter disk segments is particularly important with a view to the absolute weight loading through the dead weight and the filter cake and in view of the vibrations occurring during the filtering process.

A low weight improves the manipulatability of the installation, particularly during the generally regularly necessary maintenance activities. Moreover, S even physically less strong operators are consequently in a position to independently operate the disk filter installation according to the invention. The total mass of a filter disk segment is limited to a maximum of 25 kg and is preferably between 18 and 22 kg.

S• The specific values given in the present description, such as e.g. the critical mass of the filter disk segments, relate to a construction made solely from steel. When other materials are used, e.g. aluminium, values are .oee obtained which are adapted to the different mass densities and different material stabilities.

SThe invention is described in greater detail hereinafter relative to a 0 preferred embodiment and the attached drawings, wherein show: Fig. 1 A filter disk segment for a disk filter according to the invention.

7 Fig. 2 Possible marginal structures of the supporting framework of the filter disk segment of fig. 1.

Fig. 3 A side view of a disk filter according to the invention.

Fig. 4 A side view of the disk filter according to the invention in the viewing direction A in fig. 3.

Fig. 5 A side view of a detail of a filter disk segment system.

Fig. 6 Part of an individual filter disk segment.

Fig. 7 A cross-section through the filter disk segment of fig. 6.

Fig. 1 shows a filter disk segment 2 used in the disk filter according to the invention. The filter disk segment 2, shown in part sectional form, comprises a supporting frame having perforated plates 4. These perforated plates form the side walls of the filter disk segments 2. Profile 6 are provided for supporting the perforated plates 4. Such a support is particularly advantageous due to the differential pressure between the inner area and outer area of the filter disk segments 2 occurring during operation.

The filter area of the filter disk segments 2 issues on one side into a segment foot 8. At the transition point the cavity of the filter disk segment 2 has a cross-section

A

1 The segment foot 8 terminates in a quick fastening, which in the present case is constructed as a bayonet catch The bayonet catch 10 fixes the filter disk segment 2 to the not shown filter shaft. The terminal flow cross-section of the filter disk segment is A 2 In general, the indicated cross-sections A and A must satisfy the condition 2 s 2! A 1 so that the filtrate can flow in unhindered manner from the filter area to the filter shaft. In addition, said size ratio of the flow crosssection is useful if the filter cake results from the supply of compressed Sair via the cross-section A2, because in this way the originally supplied 20 pressure is not reduced in function-restricting manner by an unduly increased cross-section A2 On its external radius the filter disk segment 2 is provided with a marginal profile -8- Fig. 2 shows two exemplified possibilities of the marginal connection of the perforated plates 4. In the example of the first part of the drawing the perforated plates 4 are brought together at the edge and joined by a weld 12.

In the second part of the drawing the connection is brought about in that a marginal bar 14 engages positively in the perforated plates 4 to be connected.

Fig. 3 is a side view of a disk filter. It is possible to see the individual filter disk segments 2, which together form the filter disk 16. The filter disk segments 2 are mounted in rotary manner on the centrally positioned filter shaft 18. The filter disk 16 is partly immersed in a filter trough which has on one side a filter overflow 22. During operation the suspension to be filtered is located in the filter trough 20. In the filter shaft 18 is provided a discharge tube 24 for the cake forming filtrate, a discharge tube 26 for the drying filtrate and a compressed air line 26 for the supply of compressed air during filter cake discharge. A rinsing liquid 28 also passes through the filter shaft 18. The rotation direction of the filter disk 16 is indicated by the arrow B.

Fig. 4 shows the disk filter of fig. 3 in a different viewing direction and which is indicated as A in fig. 3. There are two filter disks 16, which are mounted in rotary manner on a common filter shaft 18 and which are immersed in a suspension in the filter trough 20. The suspension is introduced into the filter trough 20 by the suspension feeds 30. A draining device 32 is *25 provided in the lower area of the trough. There is also a paddle agitator 34 e*o.4o in the lower area of the trough 20. In the vicinity of the filter shaft 18 is provided on one side a control head 36 by means of which is controlled the rotation of the filter shaft 18.

30 To improve the understanding of the physical conditions which must be satisfied by a disk filter, further details are shown in figs. 5, 6 and 7.

Fig. 5 shows a part of a filter disk 16 with partly shown filter disk segments 2. The filter disk 16 has an external radius r The filter disk segments 2 are fixed by their segment feet 8 to the filter shaft with a radius r 2 It is also possible to see at what points of the filter disk -9 segments 2 the critical flow radii A 1 and A 2 occur and which, as stated hereinbefore, must satisfy the condition A 2 A Fig. 6 again shows on a larger scale an end portion of a filter disk segment 2 with perforated plate 4, segment foot 8 and bayonet catch 10. The line 38 indicates the cross-section of the maximum specific loading of a filter disk segment 2.

Along the line 38 of fig. 6, fig. 7 shows a cross-sectional representation.

Besides the perforated plates 4 marginally connected by means of welds 12 it is possible to see inside-supporting profiles 6. The Roman numerals indicate the areas with different mechanical characteristics, which in all represent the overall characteristics of the mechanical stability. This mechanical stability is determined by the geometrical moment of inertia J, which is formed from the individual contribution of the areas I, II and III, giving: ges I

III

The geometrical moment of inertia is dominated by the term J III so that in a good approximation the following applies: (b/12) (H 3 h 3 ges III It is possible to gather b, H and h from fig. 7. As a high geometrical '25 moment of inertia means a high stability, by means of the last equation it is possible to see the physical context on which the invention is based. For a given thickness of the perforated plates 4, i.e. for a given value of H-h, S the higher the absolute values of H or h the higher the geometrical moment of inertia. Thus, the stability decrease brought about by the mass reduction can be compensated by a corresponding geometrical change. This is utilized within the framework of the other limitations with respect to the geometry of the arrangement in the present invention. The other limitations are in particular that the cavity codetermined by the spacing h must have a correspondingly small volume, so that on applying compressed air there is a maximum momentum for the effective expanding of the filter cloth and therefore for the quasi-complete discharge of the filter cake. Moreover, when choosing the parameter h, account must be taken of its influence on the flow cross-section A 1 so that overall the condition A 2

A

1 can be fulfilled. This takes place within the scope of choosing the preferred ratio between the external radius rI and the radius r2 at which the filter disk segments 2 are fixed to the filter shaft 18, said radii fulfilling the relation rl/r2 3.8.

It will be understood that the term "comprise" and any of its derivatives (eg.

comprises, comprising) as used in this specification is to be taken to be inclusive of features to which it refers, and is not meant to exclude the presence of any 10 additional features unless otherwise stated or implied.

oo °*Although a preferred embodiment of the apparatus of the present invention has been illustrated in the foregoing detailed description, it will be understood that the invention is not limited to the embodiment disclosed, but is capable of numerous rearrangements, modifications and substitutions without departing from the scope of the invention as set forth and defined by the following claims.

*o go.

o 0 y,°

Claims

1. Disk filter having: a suspension trough for receiving a suspension to be filtered; a filter shaft mounted in rotary manner and constructed for the discharge of a filtrate; at least one filter disk fixed to the filter shaft and at least partly immersed in the suspension to be filtered and on whose lateral faces are provided filter areas; and a pressure producing device for producing a differential pressure between an outside facing the suspension and an inside remote from the suspension of the filter areas; *0 in which the filter disk includes several filter disk segments; •which in each case have a segment foot and are fixed via said segment foot in each case in a separate detachable manner to the filter shaft; also having a supporting framework and a filter medium placed thereon; and including a cavity defined by the lateral faces and which is entered by the filtrate after passing through the filter medium and from which the filtrate passes 20 for discharge via the filter shaft, characterised in that; a filter disk segment has a critical mass of a maximum of 13.5 kg/m 2 related to the effective filter surface; and the reduction in the geometrical moment of inertia of the filter disk segment associated with the dropping below the critical mass is compensated by a 25 corresponding increase in the internal spacing of the lateral faces defining the 0 cavity.

2. Disk filter according to claim 1, characterised in that the cross-sectional :"surface A 1 of the cavity in the centre-next filter area is smaller or equal to the flow cross-sections A 2 following in the direction of the filter shaft. -12-

3. Disk filter according to claim 1 or 2, characterised in that for the ratio of the external radius ri of the filter disk to the radius r2, in which the filter disk segments are fixed to the filter shaft rl r2 3.8 applies.

4. Disk filter according to any one of the preceding claims, characterised in that for a filter disk segment in the vicinity of the segment foot at a point of maximum loading in operation the geometrical moment of inertia Jges is higher than 3.59 x 104 mm 4 10

5. Disk filter according to any one of the preceding claims, characterised in that the side walls of the filter disk segments in the filter area have perforated plates with a thickness of 1.5 to 1.6 mm and that the openings in the perforated plates represent at least 35% of the total surface of the perforated plates.

6. Disk filter according to any one of the preceding claims, characterised in that in the filter area are provided perforated plates, which at the outer radius of the filter disk segments are zonally or continuously provided with a marginal profile or are zonally welded together or are connected by means of a marginal bar. o5o0 20

7. Disk filter according to any one of the preceding claims, characterised in that in the filter area perforated plates are provided and for supporting the perforated plates against the action of the differential pressure between the side of the filter areas facing the suspension and the side of the filter areas remote from the suspension perforated profiles are incorporated as supports. S. to.

8. Disk filter according to any one of the preceding claims, characterised in that the filter disk segments are covered with bag-like filter cloths as the filter medium. o S.. •o -13-

9. Disk filter according to any one of the preceding claims, characterised in that the filter disk segments are fixed by means of a quick fastening in the form of stud bolts, a bayonet catch or a lever fastening to the filter shaft.

10. Disk filter according to any one of the preceding claims, characterised in that scrapers are provided for removing a filter cake.

11. Disk filter according to any one of the preceding claims, characterised in that a compressed air supply is provided for removing a filter cake. 9 So

12. Disk filter according to claim 11, characterised in that each of the filter disk C segments is subject to compressed air action. 0 0 *0 000.

13. Disk filter substantially as herein described with reference to any one of the Oee* embodiments of the invention illustrated in the accompanying drawings. Dated this 9 th day of July, 2003. S C 000* 0 BOKELA INGENIEURGESELLSCHAFT FUER MECHANISCHE "20 VERFAHRENSTECHNIK MBH By its Patent Attorneys MADDERNS e.g: 0 "0 o 900 ^t e*.