Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D33/00—Filters with filtering elements which move during the filtering operation
  • B01D33/44—Regenerating the filter material in the filter
  • B01D33/52—Regenerating the filter material in the filter by forces created by movement of the filter element
  • B01D33/54—Regenerating the filter material in the filter by forces created by movement of the filter element involving vibrations
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D33/00—Filters with filtering elements which move during the filtering operation
  • B01D33/15—Filters with filtering elements which move during the filtering operation with rotary plane filtering surfaces
  • B01D33/21—Filters with filtering elements which move during the filtering operation with rotary plane filtering surfaces with hollow filtering discs transversely mounted on a hollow rotary shaft
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D33/00—Filters with filtering elements which move during the filtering operation
  • B01D33/44—Regenerating the filter material in the filter
  • B01D33/46—Regenerating the filter material in the filter by scrapers, brushes nozzles or the like acting on the cake-side of the filtering element
  • B01D33/466—Regenerating the filter material in the filter by scrapers, brushes nozzles or the like acting on the cake-side of the filtering element scrapers
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D33/00—Filters with filtering elements which move during the filtering operation
  • B01D33/44—Regenerating the filter material in the filter
  • B01D33/48—Regenerating the filter material in the filter by flushing, e.g. counter-current air-bumps

Definitions

• the present invention relates to a vacuum disc filter wherein the each one of the filter disc is comprised of planar segmentally-shaped filter sectors. More specifically, the invention relates to the cleaning of such a segmental filter disc.
• a vacuum disc filter comprises a set of filter discs mounted on a rotor shaft and having their inner periphery connected by radial suction pipes via the shaft center to a vacuum source.
• the filter discs are rotated in a tank containing a slurry to be filtered, whereby a portion of each disc is at all times submerged in the slurry and the other portion of the disc is above the top level of the slurry.
• onto the disc surface is formed a cake that is scraped away before it will again become immersed into the slurry.
• the tank edge is provided with a downwardly directed cake discharge chute through which the cake pieces scraped off can fall onto a conveyor for transporting them away.
• a capillary disc filter In a capillary disc filter, the filter disc remains continuously immersed in a liquid.
• the operating principle of such a filter is described in patent publica- tion FI-C-77161 , for instance. Also commercial versions of these filters have been manufactured (e.g., filters made by Outokumpu Oyj (pic) under trade mark Ceramec ® ).
• the filter disc is fabricated from a suitable ceramic or polymeric material.
• the disc is comprised of plural filter elements shaped as truncated sectors that are mounted on a center barrel.
• One technique comprises passing a cleaning liquid at a head via the suction pipe onto the sector either at the scraping step or immediately thereafter.
• the filtrate passed away from the filter can be used for this purpose.
• Scraping brushes may be used additional- ly.
• One conventional cleaning method is to empty the tank at times free from the slurry and then fill the volume with a cleaning liquid.
• the tank can be equipped with an ultrasonic cleaning system as described in patent publication FI-C-76705.
• the present invention relates to a novel method disclosed in claim 1 for cleaning a filter disc sector. Certain preferred applications of the invention are described in other claims.
• filter disc sectors are cleaned in a tank containing a slurry after a sector has rotated off from the discharge chute zone with the help of ultrasonic transducers placed aside the filter discs while at the same time to the interior space of the sectors is passed at a head of at least 1 bar a reverse-flow cleaning liquid, most advantageously the filtrate.
• Cleaning is carried out on demand, e.g., at 3 min to 2 h intervals.
• the novel cleaning method functions rapidly.
• a typical cycle time of cleaning is 1-2 minutes. Hence, the cleaning cycle reduces the filter equipment capacity only fractionally.
• An additional benefit is that the amount of slurry in the tank during ultrasonic cleaning can be held substantially below the maximum level if so desired.
• the distance of the ultrasonic transducer from the filter disc sector must be set so wide that the cake formed in the filtration step can pass through the gap between the transducer and the sector.
• the offset distance can be set to 1-40 mm, for instance.
• the offset distance may be arranged to be adjustable.
• the ultrasonic output power of the transducer must be so high that a sufficient cleaning effect can be attained at the selected distance in the slurry being filtered.
• the emitted power level may appropriately be in the range of, e.g., 0.1-10 W/cm 2 , typically about 1 W/cm 2 .
• the cleaning liquid head can be, e.g., 0.2-3 bar, typically about 0.5 bar.
• the cleaning system incorporates a pressure line via which in a normal filtration situation the filter disc sector after the cake is scraped off is subjected via the suction pipe to a temporary pressure snap at a pressure of, e.g., 2-3 bar.
• a separate suction line whose connection to the vacuum source can be shut off.
• the pressure line has a valve-controlled shunt line connected to the suction line.
• the suction line is disconnected from the vacuum source and a connection is opened via the shunt line to the pressure line.
• the head is applied on both the sector already rotated off from the scraping step and the sector just facing the ultrasonic transducer. At this instant, the head may be lowered if so desired in order to reduce the volumetric flow of cleaning liquid passing through the sector back to the slurry.
• the invention is particularly suited for use in capillary disc filters.
• FIG. 1 is a schematic illustration of a capillary disc filter as seen from the center barrel end side;
• FIG. 2 is an enlarged detail view of the filter of FIG. 1 as seen at the pressure-switching valve.
• the filter shown therein comprises a center barrel 1 with filter discs mounted thereon, each one of the discs being assembled from a plurality of filter sectors 2.
• the sectors are mounted on circular frames supported on the center barrel.
• To the interior space of the sectors is con- nected a radial suction pipe 3.
• the suction pipes of mutually respective sectors of the in-line discs are connected to each other at respective central suction lines running through the bore of the center barrel, whereby each one of the suction lines during the cake form-and-dry steps can be taken to a negative pressure with the help of pressure-switching valve applied via vacuum line 4, 5 or 6 or, alternatively, during the sector cleaning step to a positive pressure applied via a line 7.
• the discs are adapted rotatable in a tank 8 whereto a slurry to be dried is passed via a line 9.
• the filter disc sectors 2 submerged in the slurry are internally subjected to a vacuum applied via line 4 or 5, whereby the liquid portion permeates through the filter sector and a cake is formed on the sector surfaces from the slurry solids wetted with the liquid.
• the vacuum is continuously kept switched on via line 6 thus allowing more liquid to be sucked from the cake whereby it is dried.
• washing liquid may additionally be sprayed thereon if so desired.
• the vacuum lines 4, 5 and 6 are connected to a filtrate tank 17 taken to a reduced pressure by a vacuum pump 18.
• the filtrate is removed from the tank via a filtrate line 19 via a valve 24 with the help of a discharge pump 20.
• a portion of the filtrate flow is utilized as a cleaning liquid by passing the same to the cleaning liquid line after pump 20 via a valve 21 and a pressure- control valve 23.
• a cleaning solution may be pumped to the cleaning liquid line from a container 25 by a pump 22 via a valve 28 or a liquid suitable for use as a cleaning liquid can be taken via a line 30 from a source external to the process.
• the vacuum line 4 is equipped with a vacuum check valve 31 and the line is branched such that the first branch forms a suction branch 33 connected to the suction pipes 3 of those sectors that are performing the first cake formation step while the other branch is connected via a pressure-switching valve 32 to the pressure line 7. During filtration, the pressure-switching valve is kept closed.
• an agitator 26 On the bottom of the tank is placed an agitator 26.
• the tank can be emptied via a bottom valve 27.
• an ultrasonic transducer 29 is placed both between the disc sectors and aside the outer discs.
• the transducer is protected by a vibration-transmitting membrane oriented perpendicular toward the sector surface.
• the transducer is a so-called stack transducer having the vibrating crystals mounted in a single-row array.
• the transducers mounted in the disc gaps have the vibration-transmitting membranes on both sides or, alternatively, two transducers are placed in each of the disc gaps, whereby the transducers have the vibration-transmitting membrane on one side only.
• the width dimen- sion of the membrane along the disc radius is substantially equal to the width of the disc sector thus allowing the emitted wavefront to impinge on the entire area of the sector surface.
• the vacuum line 5 that is switched to the sectors performing the second step of cake formation is conti- nuously maintaining a vacuum thereby promoting continuous cake formation in this step.
• the drying vacuum line 6 operates normally during cleaning.
• the vacuum of suction line 4 is removed by closing the vacuum check valve 31 and opening the pressure-switching valve 32, whereupon the sectors facing the transducers 29 are internally subjected to an above-atmosphere pressure via suction line branch 33 and the transducers are powered.
• the cleaning operation is maintained for at least one full rotation taking, e.g., about 1-2 minutes and the cleaning cycle is repeated as necessary at about 1-2 hour intervals.
• the applied pressure is typically about 0.5 bar above the atmosphere.
• the sector shall not be subjected to ultrasonic vibrations and vacuum acting simultaneously.
• the pressure-switching valve 32 is closed and the vacuum check valve 31 is opened, whereby cake formation also at the sectors facing the transducers is continued.
• the distance of the ultrasonic transducers 29 from the sectors 4 must be set so wide that the cake formed in the filtration step can pass through the gap between the transducer and the sector.
• the offset distance can be set to 20- 40 mm, for instance. Furthermore, the offset distance may be arranged to be adjustable.
• a suitable emitted power level of the transducers is, e.g., about ' 1 W/cm 2 .
• the operating frequency is, e.g., 10-300 kHz.
• FIG. 2 illustrates in more detail the alternating application by the distribution valve 34 of a positive and respectively a negative pressure on the sectors in their different operating steps.

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• Chemical & Material Sciences (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Filtration Of Liquid (AREA)
• Treatment Of Sludge (AREA)

Applications Claiming Priority (2)

Publications (1)

Family

ID=29225937

Family Applications (1)

Country Status (3)

Cited By (4)

Citations (3)

• 2003
  • 2003-10-13 FI FI20031490A patent/FI118253B/sv active IP Right Grant
• 2004
  • 2004-10-13 WO PCT/FI2004/000607 patent/WO2005035096A1/en active Application Filing
  • 2004-12-10 PE PE2004001235A patent/PE20060702A1/es active IP Right Grant

Patent Citations (3)

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