FI118253B - Method and apparatus for cleaning the filter plate - Google Patents

Description

'' 1 1 8253 METHOD AND APPARATUS FOR CLEANING THE FILTER PLATE

Technical field

The invention relates to a disk filter apparatus in which the filter discs consist of discrete sector-shaped filter plates. The invention relates in particular to the cleaning of the filter plate.

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Technology background

The disk filter device comprises filter discs mounted on a rotor, the inner part of which is connected by means of radial suction tubes through the shaft to the suction device. The discs are rotated in a tank containing the sludge to be filtered so that part of the disc is always in the sludge and part above it. Suction forms a cake on the surface of the disc, which is scraped off before re-circulating in the slurry. The scraper has an inwardly extending drop shaft at the edge of the basin, through which the scraped-off cake falls down for transport.

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In a capillary-operated disc filter device, the filter disk is continuously impregnated with liquid. The principle of such a device is described, for example, in FI-C-77161. Commercially, too, these have been made ... (eg Outokumpu Oyj's Ceramec® filtration equipment). This type of filter disc is made of a suitable ceramic or plastic material.

A: The filter disc consists of several truncated sector shapes. * · * Filter plates mounted on the drum.

• · In use, the pores of the filter plate gradually become clogged. Lifetime of tiles ···. 30 different tile cleaning methods have been or are suggested to be used to lengthen. One way is to introduce the cleaning fluid at high pressure through the suction tube during or immediately after the scraping step. The filtrate from the apparatus can be used for this purpose. In addition, cleaning brushes can be used.

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One common method of cleaning is to drain the sludge from time to time and conduct. ! *. 35 replacements with cleaning fluid. In addition, an ultrasonic cleaning device located in the basin, as disclosed in FI-C-76705, may be used.

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In some cases, the tiles can become very clogged and the pool must be emptied at short intervals. Of course, this will reduce correspondingly more capacity. FI-C-82388 also proposes the use of continuously operating ultrasonic vibrators positioned on the sides of filter discs. These vibrators are placed immediately after the scratches, so that they are located at the very top of the slurry layer. Here the sludge is so dilute that it works well as an ultrasonic cleaning medium. US-6,217,782 proposes an arrangement in which a seal is formed by means of seals through which a plate is guided. Water is passed through the chamber and, in addition, there is an ultrasonic vibrator on each side of the slab 10.

SUMMARY OF THE INVENTION A method for cleaning a filter plate according to claim 1 has now been found. Certain preferred embodiments of the invention are set forth in the other claims.

According to the invention, the filter plates are cleaned in a sludge-containing basin, after the cake drop shafts in the 20 basins, by means of ultrasonic vibrators placed on the sides of the filter plates and simultaneously introducing reverse rinsing fluid, preferably filtrate, into the plates. Cleaning is carried out whenever necessary, for example every 3 minutes to 2 hours. When the pool is not separately emptied for cleaning, filled with 25 cleaning media and refilled with sludge, cleaning is quick.

* ·· A: The cleaning time is typically 1 to 2 minutes. Thus, the capacity of the device *: · is only slightly reduced due to cleaning. An additional advantage is that the amount of sludge in the basin during ultrasonic cleaning can be well below the maximum.

3o * · '··· 1 The distance between the vibrator and the plate should be such that the cake formed during the filtration step can pass between the vibrator and the plate. The distance can be ·· • 1 ·· eg 1 - 40 mm. The distance can also be adjustable. The power of the vibrator shall be: 1 'i so large that, at the required distance in the sludge in question, the desired cleaning power is achieved at t \ 35. A suitable power is, for example, 0.1 to 10 W / cm 2, such as about 1 **: 1 W / cm 2.

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During the ultrasonic treatment, pressure is preferably applied to the plate. The excess pressure may be, for example, from 0.2 to 3 bar, such as about 0.5 bar.

According to one embodiment of the invention, the apparatus has an overpressure line through which, under normal filtering conditions, after the scraping of the cake, the plate is momentarily pressurized through the suction pipe, for example 2-3 bar. There is a separate suction line for the plate at the ultrasonic vibrator, which can be closed to the vacuum source. The overpressure line must close the side line to this suction line. In the purification situation, the connection of this suction line to the vacuum source is closed and the connection via the side line to the vacuum line is opened. Thus, the overpressure is applied both to the plate after the scraping stage and to the plate at the vibrator. At this point, the overpressure can be lowered if necessary, thereby reducing the amount of liquid that returns to the slurry through the slab.

The invention can be used in particular in capillary-operated disc filter devices. DRAWINGS 20 The accompanying drawings are part of the detailed description of some embodiments which follow.

Fig. 1 schematically shows a capillary action disk filter device viewed from the end of the drum.

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Figure 2 is an enlarged view of the device of Figure 1 at the manifold valve.

DETAILED DESCRIPTION OF SOME EMBODIMENTS OF THE INVENTION 30

The filter apparatus of Figure 1 has a drum 1 and has filter discs, · * · *: each consisting of a plurality of sector-shaped filter plates 2. The plates are »», · * ·. mounted on hubs attached to the drum. * · * Radial suction pipe 3 is connected to the inside of the tiles 3. The respective suction pipes of the respective disks 35 are connected to their own central suction pipe in the center of the drum, which can *; · *: pressurize 4 or 5 or 6 overpressure through line 7.

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The discs are arranged to be rotated in a tank 8. to which the slurry to be dried is fed from line 9. The filter plates 2 in the slurry are subjected to a vacuum from line 4 or 5, whereby liquid is absorbed through the slab and 5 solids and liquid are formed on the slab surfaces. As the disc rises from the sludge, vacuum is maintained through line 6, whereupon more liquid is absorbed and the cake dries. After the cake has been formed, it may, if desired, be sprayed with a washing liquid prior to the final drying of the cake. Before the slab and cake re-descend into the slurry, the formed cake is removed by scraper 10. The detached dry cake 10 drops onto conveyor 12. There is an inward recess at each scraper on the basin wall to form a drop shaft 35 through which the removed cake can fall. During the cake removal step, the plates are momentarily pressurized through line 7 to clean the plates. The medium may be a filtrate and possibly other liquid. After the cleaning step, the plates 15 are re-pressurized to form a new cake. Figure 1 shows the various steps on the outside of the device as follows: cake forming step 13, cake washing step 14, drying step 15, cake removing and tile cleaning step 16.

The sub-palm lines 4, 5 and 6 are connected to a filtrate tank 17, where a negative pressure 18 is formed by means of a vacuum pump 18. The filtrate is removed from the tank via a filtration line 19 via an outlet pump 20 via a valve 24. The filtrate is led to the washing liquid through a valve 21 via a pump 20 and a pressure control valve 23 to the washing line. The detergent line may also be pumped with 25 detergent solutions from the reservoir 25 via the pump 22 via valve 28 or the process: external liquid to the washing fluid through the line 30.

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The vacuum line 4 has a vacuum valve 31 and is branched so that the first ♦ ·. ·. the branch forms the suction branch 33 of the tile • m 30 leading to the suction pipes 3 of the first cake forming step and the second branch leads to the overpressure 7 via the inlet valve • f * ··· 1 32. In the filtration stage the inlet valve is closed.

• · • 1 ·· To keep the slurry in the tank 8 homogeneous, there is a mixer 26 on the bottom. The pool can be emptied through the bottom valve 27.

35 «· · * ;;; 1 From time to time the tiles 2 need to be thoroughly cleaned. For this, there is an ultrasonic vibrator in the pool • · * ··· 'between the tiles and outside the outer tiles 29.

5 1 1 8253 The vibrator has a vibrating film perpendicular to the surface of the slab. The oscillator may be particularly so-called. a bar oscillator with oscillating crystals in one row. The oscillators between the tiles have a vibrating diaphragm on either side or there are two oscillators between the tiles having only 5 oscillating diaphragms on one side. The length of the vibration surface in the radial direction of the slab is substantially the same as that of the slab, whereby the vibration is directly applied to the entire surface of the slab. During the cleaning, the vacuum line 5, which leads to the plates in the second cake-forming step, is further depressurized, whereby the cake-forming at this point continues. Also, the drying vacuum line 6 operates normally during cleaning 10.

When the plates 2 are to be cleaned, the vacuum in the suction line 4 is removed by closing the vacuum valve 31 and opening the inlet valve 32, whereby the plates at the vibrators 29 are subjected to excess pressure through the suction branch 33, and the vibrators are actuated. The purification takes at least one cycle, for example about 1-2 minutes, and is carried out at intervals of about 1-2 hours as needed. A suitable overpressure is typically about 0.5 bar. The tile must not be exposed to ultrasound and vacuum at the same time. When the cleaning has been completed, the non-return valve 32 is closed and the vacuum valve 31 is opened, whereby the cake formation on the plates at the vibrators also continues.

The distance of the vibrators 29 from the plates 4 should be so large that the cake formed during the filtration step can pass between the vibrator and the plate. The distance can be: "[· * for example 20 - 40 mm. The distance can also be adjustable. A suitable power of the vibrators 25 28 is for example about 1 W / cm 2. The vibration frequency is for example 10 - 300 kHz.

* * * * ... Figure 2 shows even more in detail how the vacuum and pressure are applied to the tiles at different stages by means of the joiner 34.

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Claims (11)

6, 118253 A method for cleaning a filter plate in a disk filter device having filter discs (1) formed of separate filter plates (2) having their inner parts connected by radial suction tubes (3) to a manifold valve (34) and rotating the sludge containing filter sludge (5). (8) such that some of the slabs are always in the slurry and some are above it, thereby forming a cake on the slab surface, which is scraped off before being re-circulated into the slurry and dropped through an inwardly extending slit (35); ultrasonic vibration (29), characterized in that, 10 downstream of the manhole (35), the V filter plate (2) in the slurry is subjected, through the suction tube (3), to a back pressure equal to at least ambient pressure and towards a ultrasonic vibration (29). Method according to Claim 1, characterized in that the filter plate (2) is subjected to an overpressure, such as an overpressure of 0.2 to 3 bar, preferably about 0.5 bar. Process according to claim 1 or 2, characterized in that the purification is carried out every 3 minutes to 2 hours. Method according to one of the preceding claims, characterized in that after the scraping 20, the filter plate (2) is subjected to an overpressure from the overpressure line (7) through the suction line (3) and that the ultrasonic vibration cleanable filter plate is subjected to overpressure from this same overpressure line. »• · · ♦ A method according to claim 4, characterized in that during the ultrasonic cleaning, the overpressure of the overpressure line (7) is reduced, such as from 2-3 bar to 25 bar to 0.1 bar to 1 bar. • · · • · • 1 • · · A method according to claim 4 or 5, characterized in that the slabs other than the slurry to be cleaned are subjected to the cleaning step: 3; vacuum (5). • · · * * 1 7, Apparatus for cleaning the filter plate in capillary operation • · · 30 disk filter units with separate filter plates (2) · 1 · 1 · 2 M1 • 1 · · 3 ··· 7 118253 filter discs having internal plates connected by radial suction tubes (3) to the suction device (17, 18) via a manifold valve (34) and rotating the discs in a sludge tank (8) to be filtered so that part of the slabs is always in slurry and part above it, being scraped off before being re-circulated into the slurry and dropped through an inwardly extending manhole (35) at the edge of the basin and having an ultrasonic vibrator (29) for applying vibration to the filter plate, characterized in that the ultrasonic vibrator (29) is disposed in rotation ( 35) directly to its surface and that the apparatus has means for applying excess pressure to the filter plate through the suction tube (3) while ultrasonic vibration is applied to the surface of the filter plate. Apparatus according to claim 7, characterized in that the ultrasonic vibrator (29) has a power of 0.1 to 10 W / cm 2, such as about 1 W / cm 2. Apparatus according to claim 7 or 8, characterized in that the distance between the ultrasonic vibrator (29) and the surface of the filter plate (2) is 1 to 40 mm. Apparatus according to any one of claims 7 to 9, characterized in that the disc filter device has an overpressure line (7) for applying excess pressure to the post-scraping filter plate and the cleaning device having means 20 (32, 4) for applying overpressure from this overpressure line to the filter. * ·· • «• · ··· 11. Apparatus according to claim 10, characterized in that the filter device comprises ··. a vacuum line (4) with a valve (31) for applying vacuum to the filter plates in the slurry «·· * and that a line (7) with a valve (32) has a · · 25 line to this vacuum line. * * • * ♦ · 4 «· * I * * · · * •« • M * * · · * * »*« · · • · ♦ • · · · · · · · · ··· · • · ♦ ·· ♦ · • * «• · * •« β 118253