AU626282B2 - Method for pressure filtering and device for carrying out same - Google Patents

Description

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I OPI DATE 01/08/89 w AOJP DATE 31/08/89 APPLN* ID 29230 89

PCT

PCT NUMBER PCT/SE88/00676 lvftww INTERNATIONAL APPLICATION PUBLISHED UNDER THE PATENT COOPERATION TREATY (PCT) (51) International Patent ssi io 9 International Publication Number: WO 89/ 06155 B01D 25/34 IV 2 8 l nternational Publication Date: 13 July 1989 (13.07.89) (21) International Application Number: PCT/SE88/00676 (81) Designated States: AT, AT (European patent), AU, BB, BE (European patent), BG, BJ (OAPI patent), BR, (22) International Filing Date: 13 December 1988 (13.12.88) CF (OAPI patent), CG (OAPI patent), CH, CH (European patent), CM (OAPI patent), DE, DE (European patent), DK, Fl, FR (European patent), GA (31) Priority Application Number: 8800039-3 (OAPI patent), GB, GB (European patent), HU, IT (European patent), JP, KP, KR, LK, LU, LU (Euro- (32) Priority Date: 8 January 1988 (08.01.88) pean patent), MC, MG, ML (OAPI patent), MR (OA- PI patent), MW, NL, NL (European patent), NO, (33) Priority Country: SE RO, SD, SE, SE (European patent), SN (OAPI patent), SU, TD (OAPI patent), TG (OAPI patenlt), US.

(71) Applicant (for all designated States except US): SALA INTERNATIONAL AB [SE/SE]; Box 302, S-733 00 Published Sala With international search report.

(72) Inventors; and Inventors/Applicants (for US only) CARLSSON, Mats [SE/SEI; Vikingavagen 13, S-740 41 MorgongAva JONSON, Torbj6rn [SE/SE]; V Tulegatan ID, S-733 00 Sala (SE).

(74) Agent: SIEBMANNS, Hubertus; Gotalands PatentbyrA AB, Box 154, S-561 22 Huskvarna (SE).

(54)Title: METHOD FOR PRESSURE FILTERING AND DEVICE FOR CARRYING OUT SAME (57) Abstract The present invention relates to a method of pressure filtering, the pressure filter used comprising pressure plates 4, 5, which can be pressed against each other. Pressure chambers are formed between the pressure plates and in each one of the pressure chambers two substantially vertical filter cloths are mounted. In order to loosen the filter cakes (32) from the filter cloths means are used to produce sudden acceleration forces, e.g. directly or indirectly acting blow devices (34, 36, 38) or blow devices or lifting means, cooperating with stop surfaces, which devices and means are designed to drop the guide rails (12) from a lifted position.

I J 0 A 1 METHOD FOR PRESSURE FILTERING AND DEVICE FOR CARRYING OUT SAME The present invention relates to a method and device for pressure filtering.

The invention relates particularly to solutions of problems of loosening and discharging the filter cake from such pressure filters. For this purpose it has already been suggested that the filter cloths be subjected to vibrations. DE-C 3,341,636 and 600 DE-A 3,527,735 describe already known pressure filters, in which the filter cloths are suspended from slewing brackets and springs which are raised on the pressure eeplates. The pressure chambers are opened up one at a time and the filter cake is loosened by means of a movable vibration device, which directly influences the suspension rod of the respective filter cloths. However, these constructions have a drawback. The discharge is very time-consuming, since the filter chambers are ooooo emptied one at a time.

0000 In order to empty all the filter chambers simultaneously it has been suggested that the suspension oo00o0 rods of the filter cloths be movably suspended in a horizontal direction in the longitudinal direction of the pressure filter on two flexibly or elastically suspended S.guide rails, which are provided with vibration devices in order to vibrate all of the suspension rods and the corresponding filter cloths at the same time. The positions of the suspension rods when the pressure plates are brought apart are obtained by means of flexible and/or pivotable distance means fastened to the ends of the suspension rods, which distance means connect the suspension rods to each other and to the movable gable plates of the pressure filter. Such a pressure filter allows a very fast loosening of the filter cakes from the filter cloths and

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WO 89/06155 PCT/SE88/00676 2 consequently short filtering cycle times.

This already known pressure filter functions very satisfactorily for most types of materials, with an excellent cake loosening effect. However, as far ascertain quite adhering or in other ways difficult to loosen types of materials are concerned vibrations of filter cloths produced in this already known pressure filter are not adequate, since they do not always result in a reliable and complete discharge of the filter cakes. Consequently, portions of or even entire filter cakes may remain in one or several of the filter chambers after 1 terminated filter cake discharge. Such remaining filter cake portions are particularly found in the upper parts of the filter chambers.

This results in an inferior filtering capacity, because during the next filtering cycle portions of the available filter chamber space already are occupied by the remaining filter cake residues. Such remaining filter cake residues usually will remain also during the subsequent filtering cycles and increasingly stick to the walls of the filter chamber, i.e. the filter cloths. Thus, the deterioration of the filtering capacity of the pressure filter will be permanent.

Said remaining filter cake residues can at least be partly removed by spraying a rinsing fluid onto the filter cloths, at least during certain filtering cycles. The filter cake residues will then be brought back to a container or the like for a liquid suspension of filter materials. The filter cake residues which have been loosened by washing will then form a circulating load on the pressure filter, which worsens the filtering capacity of the system. Also, large loosened and washed away filter cake residues may lead to shutdowns and/or other disturbances in the rinsing liquid circulation system.

3 Due to the above-mentioned drawbacks of already known pressure filters the purpose of the present invention is to suggest a method of efficiently and completely loosening the filter cakes from the filter cloths in the filter chambers during the cake discharge period. An additional purpose of the invention is to suggest a device to carry out said method.

Accordingly, in a first aspect, the present invention provides a method of using a pressure filter having pressure plates in pairs forming at least one pressure chamber in which two substantially vertical filter cloths are carried by suspension rods movable in a horizontal direction on flexibly or elastically supported guide rails, and means to feed a suspension of solid particles in a liquid under pressure into the pressure chamber and force the liquid through the filter cloths, the solid particles remaining between the filter cloths forming a filter cake, said method including the steps of: taking apart the pressure plates; mechanically agitating the suspension means to loosen the filter cakes from the filter cloths; and te subjecting the cloths to shearing forces by moving :the lower part of the filter cloths laterally in the plane direction of the filter cloths.

25 In a second aspect of the method of the invention, there is provided a method of using a pressure filter having pressure plates in pairs forming at least one pressure chamber in which two substantially vertical 30 filter cloths are carried by suspension rods movable in a horizontal direction on flexibly or elastically supported guide rails and means to feed a suspension of solid particles in a liquid under pressure into the pressure chamber and force the liquid through the filter cloths, the solid particles remaining between the filter cloths forming a filter cake including the steps of: moving apart the pressure plates; mechanically agitating the suspension rods to 4 loosen the filter cakes from the filter cloths; and subjecting the cloths to sudden acceleration forces by lifting the guide rails which carry the filter cloths and dropping the rails against stationary stops.

In a further aspect, the invention provides a pressure filter comprising a frame, pressure plates, means to press the plates against each other and to separate the plates from each other in pairs to form at least one pressure chamber capable of being closed and opened, and two substantially vertical filter cloths for forming filter cakes between the cloths in said chamber, suspension means suspending said cloths and movable in a horizontal direction on flexibly or elastically supported guide rails, and vibrating means to subject the suspension means to a mechanical agitation when the chamber is opened in order to loosen the filter cakes from the filter cloths said pressure filter including additional means to subject the filter cloths and the filter cakes to shearing forces by moving the lower part of the filter cloths laterally in the plane direction of the filter cloths.

a further aspect of the invention, there is provided a pressure filter having a frame, pressure plates, means to press the plates against each other and 25 to separate the plates from each other in pairs to form at least one pressure chamber capable of being closed and opened, and two substantially vertical filter cloths for forming filter cakes between the cloths in each chamber, said cloths suspended from suspension means movable in a i 30 horizontal direction on flexibly or elastically supported guide rails, and vibrating means to subject the e* suspension means to a mechanical agitation when the chamber is opened in order to loosen the filter cakes from the filter cloths, said pressure filter including further means to subject the filter cloths and the filter cakes to sudden acceleration forces.

In accordance with a preferred embodiment of the invention the suspension means of the filter cloths are i A4 subjected to blows, preferable in an upward direction, r 1 e.g. by means of a blow device and/or a drop hammer, acting directly or indirectly. These blow devices produce an effect, which resembles a lifting and a falling of the guide rails.

Preferably also, the presence of possibly remaining filter cakes is detected by means of load sensors, which 1-ransmit a signal to a process control unit. The process control unit may be designed, in case remaining filter cake residues are present, to transmit a control signal to start one or several of the above-mentioned cake loosening processes and/or to transmit a warning signal :..oand/or interrupt the filtration process in favor of a manual cleaning. If such a load sensor is used, one may S"confine oneself to using said above-mentioned cake loosening at those occasions when there really are S: remaining cake residues present. In this way the mechanical stresses on the suspension means of the filter cloths are reduced.

The invention will now be described in more detail by means of a few embodiments, reference being made to the attached, partly schematic drawings, in which: Fig. 1 shows a pressure filter according to the invention, provided with blow devices; Fig. 2 a schematic cross section of a pressure filter in a closed position; Fig. 3 a section which corresponds to Fig. 2 but showing an open position and also showing remaining filter cake residues; Fig. 4a and 4b a detail of an embodiment showing eccentric lifting devices and stationary stop surfaces; Fig. 5 a cross section of a filter according to the invention showing means for moving the lower part of the filter cloths; Fig. 6 a detail of the above-mentioned moving means; and Fig. 7 a cross section of a guide rail and a blow device fastened to the guide rail.

"S 2 7/t iPss 5a Fig. 1 shows a known pressure filter 1, as described in W088/00495. The pressure filter comprises mainly a frame 2, which supports a fixed gable plte 3, a movable gable plate 4 and pressure plates 5, 6 arranged between said gable plates. The pressure plates can be pressed against each other and brought apart from each other by means e* o** :e T~ ~t

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i- pl~ WO 89/06155 PCT/SE88/00676 6 i hydraulic cylinders 7. Pressure plates 3,4,5,6 form in 4 pairs between each other pressure chambers 8, in each of which two filter cloths 9 are placed.

The filter cloths are supported by suspension rods which are movable in a horizontal direction on two flexibly or elasticly supported guide rails 12. The rails are at their two ends supported by flexible or elastic supporting elements 14, e.g. rubber blocks or helical springs. Elements 14 are carried by supports 16, which can comprise separate posts fixed to the floor or a portion of frame 2 or consoles projecting from the frame. Guide rails 12 are connected to each othLr at their ends by means of transversal yokes 18, which support vibrators 20. The pressure filter is also provided with an inlet conduit A for material and outlet conduits B,C,D,E for filtrate as well as an inlet conduit F for a pressure fluid.

Fig. 2 and 3 show the pressure plates and the filter cloths in detail. Hollow suspension rods 10 are connected to rinsing water inlets G and are provided with upwardly directed positioning ribs 22 and rinsing nozzles 24. The filter cloths are provided with a divisible inlet sleeve 26 and rods 28 inserted in the lower hems. The rods on the respective sides of each pressure plate 5,6 are connected at their ends by rubber bands 30. Fig. 3 illustrates also how residues of filter cake 32 stick to filter cloths 9 in various manners, when the pressure filter is in an open position.

In order to loosen such residues of filter cakes 32, which could not be loosened solely by vibrations, sudden acceleration forces are produced by means of drop hammers 34,36, which fall from an elevated position onto pivotally mounted arms 38. Arms 38 abut yokes 18 of guide rails 12 with their opposite ends. However, it is also possible to, in other ways, subjec' suspension means 10,12 of filter cloths 9 to WO 89/06155 PCT/SE88/00676 7 preferably upwardly directed blows by means of drop hammers or other types of hammers.

Fig. 4 shows a detail of one end of the guide rails according to another embodiment of the invention, which includes eccentric lifting means 40 and stop surfaces, onto which the guide rails can drop. In this case supports 16 carry a cross bar 42 on top of elastic support elements 14, which cross bar is designed to carry the guide rails when they are in a not lifted position. A vibrator 20 (not shown) suitably is fastened to the center of the lower side of the cross bar and consequently is protected from blow stresses. Four guide rods 44 project upwardly fron cross bars 42 or supports 16 and °un through guide sleeves 46 fastened to the guide rails. Between support elements 14 and supports 16 load sensors, e.g. pressure transmitters, are mounted, which are connected to the process control anit (not shown) of the pressure filter.

Eccentric lifting means 40 are mounted in pairs o:'i shafts and designed to abut the projecting ends of guide rails 12 or yokes 18 which connect them. They are mouy.ted in an arbitrary way on supports 52 (not shown in detail), e.g.

posts erected on the floor. Shafts 50 are designed to be rotated jointly with one or several driving mieans (not shown in detail), e.g. by means of chain driving or gear motors. Eccentric means 40 are provided with an elevated part 54, from which matching guide rail 12 or yoke part 18 is to drop onto a semi-elevated part 56, which functions as an anvil or stop surface. The lowest part of eccentric lifting means 40 is designed to normally be directed upwardly and then does not abut guide rails 12. The latter are carried by cross bars 42 during the filtration period and during the vibration. When filter cakes are discharged the eccentric lifting means are rotated one revolution, the guide rails being lifted and then dropping. This lifting WO 89/06155 PCT/SE88/00676 8 cycle possibly can be repeated, in case load sensors 48 detect remaining residues of filter cakes 32. In case there are no filter cake residues from the start, the process control unit can transmit a signal that a lifting is not to take place.

Fig. 4 b shows an alternative embodiment, in which the ends of the guide rails or the tranversal yokes are designed to fall onto separate movable anvils 60, which are designed to be moved to a position below the ends of the guide rails or the yokes in a lifted position. This can e.g. be accomplished by means of pull .ods 62, the other end of which is mounted on eccentric discs 64 on shafts Eccentric discs 64 preferably are placed outside corresponding eccentric lifting means 40 in order not to interfere with them.

Fig. 5 and 6 show a device designed to loosen residues of filter cakes 32 by agitating the filter cloths and in this way produce shearing forces. This device comprises two longitudinal bars 66 and fingers 68, which project therefrom and are positioned just opposite every second pair of rods 28 in the lower hem of filter cloths 9. Said fingers can be pushed towards the ends of the rods by means of e.g. hydraulic cylinders 70 and thus every second cloth pair will be pushed to the right and every second to the left in the figure. Additional control means possibly can be used to move the bars in a longitudinal direction in order to move the lower part of the cloths in an opposite direction. The means which are used to control the ends of rods 28 can according to the invention also be controlled in another way, e.g. manually. This can be done when an alarm signal has been transmitted by load sensors 48 due to remaining filter cake residues in the filter. This device, designed to control the ends of rods 28, advantageously can be combined with the rest of the methods WO 89/06155 PCT/SE88/00676 9 for filter cake loosening described above.

Fig. 7 shows a device according to the invention designed to produce sudden acceleration forces. In this device guide rails 20 are below provided with a transversal reinforcement flange 72. A few blow devices, so called "rappers", are attached to this flange and designed to jointly produce blows directed upwards against the guide rails. Such blow devices are already known and are used i.a. to loosen adhering material from arched screens and slanting, inoperative screens and in this way to prevent a clogging of the screens.

The present invention is not limited to the illustrated embodiments, but it is possible to combine, in an arbitrary manner, various characterizing features of the invention, as the latter is set forth in the description and the attached drawings and as it is defined in the following patent claims.

Claims (9)

1. 2. A meuhod according to claim i, further including the step of: .to subjecting the suspension rods of the filter cloths to blows.
2. 3. A method according to claim 1, further including the step of: sensing the presence of filter cake residues °..remaining on the cloths by load sensors responsive to the weight of the cloths. o A method according to claim 1, wherein all of the filter cloths are vibrated while moving the lower parts of the cloths during the loosening of the filter cakes. A pressure filter comprising a frame, pressure plates, means to press the plates against each other and to separate the plates from each other in pairs to form at least one pressure chamber capable of being closed and opened, and two substantially vertical filter cloths for forming filter cakes between the cloths in said chamber, suspension means suspending said cloths and movable in a horizontal direction on flexibly or elastically supported I 1 7 11 guide rails, and vibrating means to subject the suspension means to a mechanical agitation when the chamber is opened in order to loosen the filter cakes from the filter cloths said pressure filter including additional means to subject the filter cloths and the filter cakes to shearing forces by moving the lower parts of the filter cloths laterally in the plane direction of the filter cloths.
3. 6. A pressure filter according to claim 5, wherein the additional means comprises rods in the lower parts of the filter cloths, and elements to push the lower parts of the filter cloths laterally respectively in opposite directions in the plane of the filter cloths.
4. 7. A pressure filter according to claim 5, including further means to subject the filter cloths and the filter cakes to sudden acceleration forces.
5. 8. A pressure filter according to claim 5, including load sensors detecting any filter cake residues remaining ooee on the cloths.
6. 9. A method of using a pressure filter having pressure •plates in pairs forming at least one pressure chamber in S' which two substantially vertical filter cloths are carried by suspension rods movable in a horizontal direction on flexibly or elastically supported guide oo* rails and means to feed a suspension of solid particles in a liquid under pressure into the pressure chamber and S.force the liquid through the filter clothL, the solid particles remaining between the filter cloths forming a filter cake including the steps of: moving apart the pressure plates; mechanically agitating the suspension rods to loosen the filter cakes from the filter cloths; and subjecting the cloths to sudden accelration forces by lifting the guide rails which carry the filter cloths and dropping the rails against stationary stops. A method according to claim 2 wherein said blows are upwardly directed.
7. 12- 11. A pressure filter according to claim 7, wherein said further means comprise blow devices positioned to act on the suspension means to produce sudden acceleration forces. 12. A pressure filter according to claim 11, wherein said blow devices comprise drop hammers acting indirectly on said suspension means.
8. 13. A pressure filter according to claim 11, wherein said blow devices comprise drop hammers acting directly on said suspension means.
9. 14. A pressure filter according to claim 11, wherein said blow devices comprise stop surfaces and lifting means operable to lift the suspension means and the .ilter cloths and to drop the suspension means against the stop surfaces to produce said sudden acceleration forces. A pressure filter having a frame, pressure plates, means to press the plates against each other and to o o 09°. separate the plates from each other in pairs to form at .least one pressure chamber capable of being closed and o opened, and two substantially vertical filter cloths for o forming filter cakes between the cloths in each chamber, said cloths suspended from suspension means movable in a horizontal direction on flexibly or elastically supported guide rails, and vibrating means to subject the :suspension means to a mechanical agitation when the chamber is opened in order to loosen the filter cakes o from the filter cloths, said pressure filter including further means to subject the filter cloths and the filter cakes to sudden acceleration forces. DATED this llth day of MAY, 1992 SALA INTERNATIONAL AB Attorney: LEON K. ALLEN Fellow Institute of Patent Attorneys of Australia of SHELSTON WATERS U S iA rt