WO2018186795A1 - Filtre à disque sous pression pour liqueurs de caustification contenant de la boue de chaux - Google Patents

Filtre à disque sous pression pour liqueurs de caustification contenant de la boue de chaux Download PDF

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Publication number
WO2018186795A1
WO2018186795A1 PCT/SE2018/050354 SE2018050354W WO2018186795A1 WO 2018186795 A1 WO2018186795 A1 WO 2018186795A1 SE 2018050354 W SE2018050354 W SE 2018050354W WO 2018186795 A1 WO2018186795 A1 WO 2018186795A1
Authority
WO
WIPO (PCT)
Prior art keywords
filter
lime mud
causticization
pressurized
filter media
Prior art date
Application number
PCT/SE2018/050354
Other languages
English (en)
Inventor
Roger JANSSON
Jerk SÖDERMAN
Patrik BJÖRNVALL
Henrik RANSJÖ
Patrik LÖWNERTZ
Original Assignee
Valmet Ab
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Valmet Ab filed Critical Valmet Ab
Priority to CN201880023050.8A priority Critical patent/CN110475596A/zh
Priority to BR112019019801A priority patent/BR112019019801A2/pt
Priority to EP18780721.9A priority patent/EP3606636A4/fr
Publication of WO2018186795A1 publication Critical patent/WO2018186795A1/fr

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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
    • B01D33/15—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
    • B01D33/80—Accessories
    • B01D33/804—Accessories integrally combined with devices for controlling the filtration
    • B01D33/807—Accessories integrally combined with devices for controlling the filtration by level measuring
    • 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
    • B01D33/80—Accessories
    • B01D33/804—Accessories integrally combined with devices for controlling the filtration
    • B01D33/808—Accessories integrally combined with devices for controlling the filtration by pressure measuring
    • 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
    • B01D33/80—Accessories
    • B01D33/82—Means for pressure distribution
    • D—TEXTILES; PAPER
    • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
    • D21C—PRODUCTION OF CELLULOSE BY REMOVING NON-CELLULOSE SUBSTANCES FROM CELLULOSE-CONTAINING MATERIALS; REGENERATION OF PULPING LIQUORS; APPARATUS THEREFOR
    • D21C11/00—Regeneration of pulp liquors or effluent waste waters
    • D—TEXTILES; PAPER
    • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
    • D21C—PRODUCTION OF CELLULOSE BY REMOVING NON-CELLULOSE SUBSTANCES FROM CELLULOSE-CONTAINING MATERIALS; REGENERATION OF PULPING LIQUORS; APPARATUS THEREFOR
    • D21C11/00—Regeneration of pulp liquors or effluent waste waters
    • D21C11/04—Regeneration of pulp liquors or effluent waste waters of alkali lye

Definitions

  • the invention relates to an improved method for operating a pressurized disc filter for the filtering of causticization liquors containing lime mud particles, and relates also to the pressure disc filter as such.
  • Atmospheric disc filters using drop legs for application of a small differential pressure over the filter surface have been used, and are disclosed in, for example, US 6,258,282 and US 4,676,901, where a liquid level in the vat is above the rotating filter shaft.
  • Kvaemer, now Valmet developed pressurized disc filters for the causticization area in the 90- ies (and these were patented in, e.g., US 4,929,355), which provided a major production increase in effective filtering area per foot print area of the filter.
  • a precoat-filtering technique was applied, where a precoat of lime mud was built up on the filter media, typically a filter cloth with a dense web.
  • pressurized causticization disc filters with liquid level below a rotating filter shaft can be found in, e.g., US 7,005,067 (GL&V, 2006), which comprises lime mud chute designs; US 8,518,273 (Kvaemer 2013, now Vaimet), which uses white liquor for SquirtTM operations; and US 2007/0221345 (Kvaemer 2013, now Vaimet), which discloses the addition of oxygen to a filter compressor.
  • pulp production levels may regularly exceed 8000 adt/day, also the pressurized disc filters become colossal in size and the operating costs for a pressurized disc filter reaches considerable part of operating costs.
  • the term "causticization liquors” includes all kinds of alkaline liquors handled in the recovery area of a pulp mill, said causticization liquors being alkaline in varying degree from weak alkaline liquors to strong alkaline liquors, all having a content of varying degree of lime mud particles.
  • a causticization liquor can thus be: a) a green liquor that is slightly alkaline and obtained from dissolving tanks where melt from the recovery boiler is mixed with weak liquor and/or alkaline process water; b) a causticized green liquor from the causticizing train, from which liquor strong white liquor is filtered out, and c) a lime mud washing after white liquor extraction, where said lime mud is reslurried in weak liquors and/or in alkaline process water.
  • alkaline process water is meant any process filtrate obtained in a pulp mill, and can include wash filtrate from alkaline wash stages after cooking or alkaline bleaching stages. In all these filtering positions lime mud particles are present, either as a filter media for green liquor filtering or as a particle content in the slurry to be filtered.
  • the invention relates to a method for operating a pressurized disc filter for causticization liquors containing lime mud particles and comprises the following steps:
  • a precoat of lime mud on said filter media by arranging a distance between the edge of the doctor blade and the surface of the filter media, and is characterized in that a level of causticization liquor containing lime mud particles is established in the vat of the pressure vessel and said level located above the upper surface of the rotating hollow shaft and below the doctor blades, and in that the level of causticization liquor is established such that less than 40 %, but more than 10 %, of the total surface of the filter media is exposed to the pressurized gas phase in the pressure vessel.
  • a smaller compressor can be used, as the pressure losses through the exposed precoat surface are reduced in proportion to reduction of precoat surface exposed to the pressurized gas phase.
  • a pressure in the gas phase of the pressure vessel is established in the pressure range of 1.5-5 bar. This larger pressure range will partly compensate for the reduction of precoat surface exposed to the gas phase, and ensures similar production capacity as of filtered alkaline filtrate. Further, more preferably a pressure in the gas phase of the pressure vessel is established in the pressure range of 2.0-3.5 bar. This is higher than the pressure established in old filters with drop leg, where a pressure differential of about 1 bar is established with a drop leg of 10 meter, and also higher than the pressure established in conventional pressurized disc filters for causticization liquors.
  • a pressure drop in the range of 0.3- 2 bar is established over the filter media and associated precoat; and more preferably a pressure drop in the range of 0.5-1.8 bar is established over the filter media and associated precoat.
  • the level of causticization liquor can be established, such that less than 35 % of the total surface of the filter media is exposed to the gas phase in the pressurized vessel, and in an extreme implementation the level of causticization liquor is established such that less than 30 % of the total surface of the filter media is exposed to the gas phase in the pressurized vessel.
  • the pressurized disc filter comprises a pressure vessel fed with causticization liquor containing lime mud particles; a rotating hollow shaft with filter discs arranged on a rotating shaft having a filter media on said filter discs and a hollow interior of said discs in communication with the rotating hollow shaft via filter disc outlets; a storage tank connected to the interior of the hollow shaft receiving alkaline filtrate; a compressor for pressurizing the interior of the pressure vessel, lime mud chutes for collecting lime mud being scraped off by doctor blades from said filter media; and wherein a precoat of lime mud is established on said filter media by arranging a distance between the edge of the doctor blade and the surface of the filter media, and is characterized in that the pressurized disc filter includes means for establishing a level of causticization liquor containing lime mud particles above the upper surface of the rotating hollow shaft and below the doctor
  • Fig. la shows a cross-sectional side view of a conventional disc filter
  • Fig. lb shows a cross-sectional end view of the disc filter as seen in section A-A in Fig. l a, with conventional components identified;
  • Fig. lc illustrates how the doctor blade scrapes off a part of the lime mud layer, thereby leaving a precoat
  • Fig. 2a shows a cross-sectional side view of a disc filter according to the invention
  • Fig, 2b shows a cross-sectional end view of the disc filter as seen in section A-A in Fig. 2a; and Fig. 3a shows a cross-sectional side view of a disc filter according to the invention with an alternative liquor level control.
  • Fig. la conventional pressurized disc filter is disclosed, also seen through the section A-A in Fig. lb; and in Fig. l c is a detail of a doctor blade shown.
  • the disc filter is used to filter out fine lime particles in a causticization liquor.
  • the disc filter comprises a pressure vessel 1, which is fed with causticization liquor CL containing lime mud particles; a rotating hollow shaft 1 1 with filter discs 12 arranged on said rotating hollow shaft 11 and having a filter media on said filter discs and a hollow interior of said filter discs 12 in communication with the rotating hollow shaft 11 via filter disc outlets 13; a storage tank 40 connected to the interior of the rotating hollow shaft 1 1 and receiving alkaline filtrate Four; a compressor 50 for pressurizing the interior of the pressure vessel 1 ; lime mud chutes 28 for collecting lime mud being scraped off by doctor blades 30 from said filter media; and wherein a precoat of lime mud PC is established on said filter media by arranging a distance between the edge of the doctor blade 30 and the surface of the filter media.
  • a lower portion of the pressure vessel 1 constitutes a vat or vessel 31.
  • the causticization liquor CL can be fed to the vessel or vat 31 by a multitude of nozzles located one between each pair of filter discs. These nozzles can be of a so called mammoth-pump type, that includes an ejector that sucks up particles on the bottom of the vessel or vat 31 as the added causticization liquor CL is injected.
  • the nozzles may also be arranged for improved agitation in the vat, such as the nozzle arrangement shown in WO2017007417.
  • the disc filter 1 includes at least one disc 12.
  • the disc 12 is similar to those described in the prior art in that lime mud particles are removed from the causticization liquor by forcing the liquid through filtering discs 12 when the discs 12 are in the lower part of the vat 31, while the lime mud particles accumulate on the filter media.
  • the liquid is forced through the discs 12 by creating a pressure differential between the interior of the fi lter housing 10 and the outlet.
  • the pressurization is obtained by a compressor 30.
  • the filter media on the discs 12 can be a perforated material, such as metal, and covered with a fine mesh cloth, such as a polypropylene cloth.
  • the filter material is generally referred to as the filter cloth.
  • Each disc 12 is divided into disc sectors (not shown), which are individually covered with a filter cloth.
  • the discs 12 are positioned within the housing 10 that holds the caustici ation liquor in the bottom part, i.e. in the vat 31, at a certain liquid level LiqL and the discs are mounted firmly to the rotation shaft 11.
  • the level of the causticization liquor can vary, but is typically approximately close to or below the center of the rotation shaft 11.
  • each sector As the discs 12 rotate (the direction of rotation being indicated with ROT) each sector fully enters the slurry and an amount of lime mud particles are deposited on the surface of each disc sector. The lime mud particles are then removed from each sector, to separate the lime mud particles from the causticization liquor, thereby obtaining a clear alkaline filtrate on the inside of the filter sectors.
  • the filter cloth When filtering green or white liquor slurries in the recovery island of a pulp mill, the filter cloth itself is not sufficient to reach a low particle content in the filtrate.
  • the cloth is rather used to enable and facilitate the forming of a precoat layer of fine particles on the cloth, and after establishment of a precoat with sufficient thickness, effective filtration can begin, thereby obtaining a filtrate with low particle content.
  • a scraper mechanism is used to remove the particles accumulated.
  • the scraper mechanism comprises a doctor blade 30 that removes the cake layer from the precoat PC layer, as shown in Fig. l c. As each disc sector passes through the slurry and emerges from the slurry, additional solid material is deposited on the surface of the disc sector. As the disc sectors pass the doctor blade 30, the cake layer formed on top of the precoat layer is removed. The removed solid material falls by action of gravity into a chute 28 arranged immediately below the doctor blade 30,
  • a precoat is established with a starting thickness of about 1 ,0-3,0 cm, and thereafter additional layers of lime mud particles on top of the precoat are scraped off by the doctor blade.
  • the outermost layer of the precoat will be blinded by smaller lime mud particles, which is seen as a reduction of clear filtrate flow, and then the doctor blade is advanced towards the filter cloth at a small incremental adjustment being a fraction of the starting precoat thickness. This advancement can be in the order of 1-3 mm and will scrape off the outer layer of the precoat that has become blocked or blinded.
  • an entirely new precoat is formed with a starting thickness of about 1.0-3.0 cm.
  • the disc filter can also include wash showers and a precoat renewal high pressure jet system, for example the SQUIRTTM system sold by Valine!
  • a SQUIRTTM system can include a high-pressure nozzle 80, which slowly can be moved radially on a rail 81, and this high-pressure jet can dislodge a strip of precoat from the filter media as well as provide for a thorough filter cloth cleaning.
  • the advantage with this SQUIRTTM system is that the entire precoat can be renewed, as it becomes blocked over time, and the filtering process does not need to be halted for precoat renewal.
  • Fig. 2a pressurized disc filter 1 according to the present invention is illustrated, with same basic design as the filter shown in Fig.
  • the disc filter 1 is used to filter out fine lime particles in a causticization liquor.
  • the liquor level LiqL is raised to a level well above the rotating shaft 11, and secondly, as a consequence, also the inlet of the lime mud chute 28 is raised to a position above the liquor level LiqL, and includes also a third difference in a liquor level control.
  • the liquor level LiqL is controlled and maintained at the desired height in the vat 31 by a level sensor 70s, emitting a control signal X depending upon the current liquor level.
  • the control signal X can then control the degree of opening of an inlet valve 70v, which supplies causticization liquor to be filtered.
  • an alternative level control is disclosed with a passive overflow pipe 70d, having a funnel with an inlet arranged at the maximum allowable height of the liquor level I. qL.
  • the flow from the overflow pipe 70d can be led to the feeding pipe for new causticization liquor.
  • This solution can also include a sensor in the overflow pipe 70d, which similarly control the degree of opening of an inlet valve 70v, which supplies causticization liquor to be filtered.
  • Fig. 2b discloses a complementary design difference in the squirt function that may be considered in order to reduce pressure losses through the precoat.
  • a squirt rail 81 is located above the liquor level LiqL, but the high-pressure nozzle 80 is located on a swan neck protruding down into the liquor volume in the vat.
  • the high-pressure jet may dislodge a strip of precoat from the filter media as well as provide for a thorough filter cloth cleaning below the liquor level.
  • the advantage here is that the dislodged strip quickly becomes refilled, at least in part by new unblocked lime mud particles before this strip ascends into the pressurized gas phase.
  • the advantage with this alternative squirt system is that the entire precoat may be renewed, as it becomes blocked over time, and the filtering process does not need to be halted for precoat renewal.
  • the present invention has been described by way of illustration and not limitation.
  • the invention may be modified in a number of ways, such as implementation in a first stage of a two-stage pressurized white liquor disc filter, implementation in a pressurized lime mud disc filter of one or two stage design, where residual alkali is washed out from lime mud obtained from white liquor filters preceding the lime mud wash, and located ahead of the lime kiln; and/or implementation in pressurized green liquor disc filter, where typically the first precoat is built up using causticizat on liquor, because the precoat from lime mud particles obtains a far better fiiterabiiity compared to building up a precoat of green liquor grits.

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

Abstract

L'invention concerne une amélioration apportée à des filtres à disque sous pression utilisés pour le filtrage de liqueurs de caustification contenant des particules de boue de chaux. Selon le procédé et la conception de l'invention, le niveau de liqueur dans la cuve du filtre à disque est élevé au-dessus de l'arbre rotatif du filtre à disque, ce qui permet de réduire la puissance nominale dans des compresseurs utilisés pour mettre sous pression le filtre. En appliquant une pression de fonctionnement qui est de 1 à 2 bar supérieure à celle des filtres à disque sous pression classiques utilisés dans le domaine de la caustification, une siccité suffisante de la boue de chaux peut encore être obtenue, et les pertes de pression à travers la précouche sont sensiblement réduites.
PCT/SE2018/050354 2017-04-07 2018-04-04 Filtre à disque sous pression pour liqueurs de caustification contenant de la boue de chaux WO2018186795A1 (fr)

Priority Applications (3)

Application Number Priority Date Filing Date Title
CN201880023050.8A CN110475596A (zh) 2017-04-07 2018-04-04 用于含白泥的苛化液的加压盘式过滤器
BR112019019801A BR112019019801A2 (pt) 2017-04-07 2018-04-04 método para operar um filtro de disco pressurizado, e, filtro de disco pressurizado
EP18780721.9A EP3606636A4 (fr) 2017-04-07 2018-04-04 Filtre à disque sous pression pour liqueurs de caustification contenant de la boue de chaux

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
SE1750424A SE540553C2 (en) 2017-04-07 2017-04-07 Pressurized disc filter for causticization liquors containing lime mud
SE1750424-2 2017-04-07

Publications (1)

Publication Number Publication Date
WO2018186795A1 true WO2018186795A1 (fr) 2018-10-11

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ID=63580878

Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/SE2018/050354 WO2018186795A1 (fr) 2017-04-07 2018-04-04 Filtre à disque sous pression pour liqueurs de caustification contenant de la boue de chaux

Country Status (6)

Country Link
EP (1) EP3606636A4 (fr)
CN (1) CN110475596A (fr)
BR (1) BR112019019801A2 (fr)
CL (1) CL2019002845A1 (fr)
SE (1) SE540553C2 (fr)
WO (1) WO2018186795A1 (fr)

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4695381A (en) * 1985-05-02 1987-09-22 Ab Hedemora Verkstader Filter for continuous filtering of a suspension under pressure
EP0473722B1 (fr) * 1989-06-14 1994-11-09 Caustec Aktiebolag Filtre de filtration continue
WO2014011089A1 (fr) * 2012-07-09 2014-01-16 Metso Paper Sweden Ab Procédé et appareil permettant d'obtenir une liqueur blanche forte et de la boue de chaux à faible teneur résiduelle en alcalins

Family Cites Families (10)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
SE445655B (sv) * 1984-11-23 1986-07-07 Hedemora Ab Roterande skivfilter
SE463771C (sv) * 1985-05-02 1998-09-30 Caustec Ab Anordning och förfarande för separering av vitlut, mesa och eventuellt slam varvid användes ett roterande skivfilter
AU4909097A (en) * 1996-10-15 1998-05-11 Baker Hughes Incorporated Agitator for use with a disc filter
SE510603C2 (sv) * 1997-08-21 1999-06-07 Kvaerner Pulping Asa Roterande filter med förfiltrering i två steg, förfarande för filtrering samt användning av filtret för avvattning av cellulosafibersuspensioner
SE516246C2 (sv) * 2001-02-07 2001-12-10 Kvaerner Pulping Tech Rörsystem för mottagning och transport av mesa från ett vitlutsfilter
SE526706C2 (sv) * 2004-04-16 2005-10-25 Kvaerner Pulping Tech Förfarande och anordning för tvätt av mesa
SE0401358L (sv) * 2004-05-26 2005-02-22 Kvaerner Pulping Tech Förfarande och anordning för rengöring av filter
SE530768C2 (sv) * 2007-12-06 2008-09-09 Metso Fiber Karlstad Ab System för mottagning och transport av mesa från ett vitlutsfilter
WO2011078749A1 (fr) * 2009-12-23 2011-06-30 Metso Paper Sweden Ab Procédé et système de lavage de boue de chaux
SE538959C2 (en) * 2015-07-09 2017-03-07 Valmet Oy Agitator system for a disc filter

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4695381A (en) * 1985-05-02 1987-09-22 Ab Hedemora Verkstader Filter for continuous filtering of a suspension under pressure
EP0473722B1 (fr) * 1989-06-14 1994-11-09 Caustec Aktiebolag Filtre de filtration continue
WO2014011089A1 (fr) * 2012-07-09 2014-01-16 Metso Paper Sweden Ab Procédé et appareil permettant d'obtenir une liqueur blanche forte et de la boue de chaux à faible teneur résiduelle en alcalins

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
See also references of EP3606636A4 *

Also Published As

Publication number Publication date
EP3606636A4 (fr) 2021-01-06
SE1750424A1 (en) 2018-09-25
SE540553C2 (en) 2018-09-25
CN110475596A (zh) 2019-11-19
CL2019002845A1 (es) 2019-12-27
BR112019019801A2 (pt) 2020-04-22
EP3606636A1 (fr) 2020-02-12

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