US3599449A - Cellulose bleach tower with means for spreading a bleaching agent therein - Google Patents

Cellulose bleach tower with means for spreading a bleaching agent therein Download PDF

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Publication number
US3599449A
US3599449A US773385A US3599449DA US3599449A US 3599449 A US3599449 A US 3599449A US 773385 A US773385 A US 773385A US 3599449D A US3599449D A US 3599449DA US 3599449 A US3599449 A US 3599449A
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pulp
tower
bleaching
scraper blades
arms
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US773385A
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English (en)
Inventor
Johan C F C Richter
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Metso Fiber Karlstad AB
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Kamyr AB
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    • 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
    • D21C9/00—After-treatment of cellulose pulp, e.g. of wood pulp, or cotton linters ; Treatment of dilute or dewatered pulp or process improvement taking place after obtaining the raw cellulosic material and not provided for elsewhere
    • D21C9/10—Bleaching ; Apparatus therefor

Definitions

  • the concentration of the bleaching chemical is equalized over the cross section of the tower by means of rotating scrapers which in a short zone of the tower displace the pulp back and forth in the transverse direction of the tower, whereas the pulp else flows truly axially of the tower.
  • the invention relates to an upright cellulose bleach tower of the kind in which there is added to pulp flowing axially through the tower a bleaching agent which is spread in the pulp and distributed over concentric cylindrical faces situated at the same level as a series of concentric screening faces for screening off at least part of the liquid content of the pulp, spreading nozzles being arranged upon hollow arms attached to and supplying the bleaching agent from a tubular rotating shaft extending centrally in the tower.
  • the bleaching agent displaces the previous liquid content of the pulp, so that the consistency of the pulp is maintained substantially constant, but the distribution of the bleaching agent is uneven. This is of no great importance when the said spreading nozzles and screening faces are located close to the outlet end of a tower, from which the pulp is transferred to another tower wherein the treatment with the added bleaching agent takes place, because the transfer of pulp to said tower is almost unavoidably connected with stirring movements whereby the concentration of the bleaching agent within the pulp is equalized.
  • the invention relates to the case in which the treatment of the pulp with the bleaching agent supplied to the tower takes place in a zone of said same tower, and the object of the invention is to equalize the differences of concentration of the chemicals in the moving pulp column evolved from the concentric arrangement of the spreading faces and the screening faces.
  • said object is reached by providing said shaft with scrapers or similar means adapted for moving pulp inwardly towards the axis of the tower as well as outwardly towards its shell in order to distribute the bleaching agent evenly over the entire cross section of the tower in a layer of the pulp which, related to the axial direction of flow of the pulp, is situated closely after said concentric screening faces and before a zone of the tower wherein the main treatment by the bleaching agent takes place.
  • the pulp moves as a plug, i.e. with a movement in the longitudinal direction of the tower which is uniform over its cross section, but according to the invention there is interposed between said two zones a zone or a layer of a restricted axial extension, wherein the pulp is caused to move with a superimposed horizontal component, i.e. transversely to the general feed direction of the pulp.
  • a superimposed horizontal component i.e. transversely to the general feed direction of the pulp.
  • the pulp will not be fed more rapidly in certain parts of the tower cross section, e.g. along the tower shell, as would be the case if all scrapers were made to move the pulp away from the axis of the tower.
  • the inwardly operating scrapers are located at another level than the outwardly operating scrapers, so that the mixing zone is composed of a layer with predominantly outward radial pulp movement and a layer of predominantly inward radial movement. This involves good equalization over the entire cross section of the tower and not merely locally restricted whirling movements,
  • FIG. 1 diagrammatically shows a bleaching plant in which five bleaching steps are performed in two bleach towers designed according to the invention.
  • FIG. 2 is a vertical sectional view at a larger scale, of a middle part of one of the towers, and
  • FIG. 3 is a corresponding sectional view of the upper end part of the same tower.
  • the bleach plant shown in FIG. 1 mainly consists of two upright cylindrical towers 11 and 13 through which cellulosic pulp is continuously passed while being bleached in a series of different bleach steps performed with different chemicals, during different treating time periods and possibly at different pulp consistencies.
  • pulp is introduced into the bottom end of the first tower 111, during the upward movement of the pulp a first treatment with chlorine takes place in zone C, then alkali extraction takes place in zone E thereafter treatment with chlorine dioxide follows in zone D and finally the first part of an alkali extraction step takes place in zone IE at the top of the tower.
  • the pulp is fed through a conduit 15 to the top of the second tower 13 with downward pulp flow, wherein first the main part of the alkali extraction step E takes place, then treatment with chlorine dioxide is perfonned in zone D and finally the pulp is discharged at the bottom of the tower.
  • the treatment dura tions of the various steps may be: for C, 1 hour, E l/2 hour, D,, 3 hours, E 1/2 hour and D 4 hours.
  • the consistency of the pulp is maintained comparatively high in order to save tower space and secure plug flow.
  • the pulp may contain 8 to 10 percent dry fiber, whereas in the following steps there is preferably maintained a constant consistency of approximately 10 percent.
  • Pulp supplied through a conduit 17 is pumped by a pump 19 through a flowmeter 21 and a mixer 23 into the center of the conical bottom 25 of the tower 11. Chlorine obtained from the conduit 27 is mixed into the pulp in the mixer 23.
  • a central tube 29 which is rotary journaled at its ends and is turned by a motor 31 with a gear 33. Said central tube encloses a number of conduits and serves to turn various means attached thereto as will be more closely described hereinbelow.
  • a screening device Attached to the central tube approximately at the level of the joint between the conical bottom 25 and the cylindrical shell of the tower is a screening device consisting of three sector-shaped plates 35 leaving between them sector-shaped apertures for the passage of the pulp.
  • the cavity between perforated upper and lower walls of said plates communicates through the central tube 29 with an outlet 37. Liquid screened off the pulp by said screening device and departing through the outlet 37 is recirculated.
  • the details of the screening device may correspond to the embodiment shown in the US. Pat. No. 3,298,900.
  • the admixture of chlorine may take place in the manner described in said patent specification.
  • the pulp is concentrated to a dry content of about 8 to 10 percent on account of the described removal of part of its liquid content when it moves past the screening plates 35. Therefore, the main part of the chlorine bleaching operation takes place at said consistency while the pulp moves up through zone C.
  • Said device Inserted between the zones C and E is a device for withdrawal from the pulp of the reaction products formed during the chlorine treatment and for spreading therein of new chemicals, viz alkali.
  • Said device generally designated by reference numeral 39 and shown at an enlarged scale in FIG. 2, comprises a set of screens which is axially somewhat displaceable, and a rotary liquid spreader.
  • the screen set consists of concentric cylindrical screen rings 41 attached to radial carrying arms 43 which extend through the tower shell and are attached to an exterior hydraulic operating device 45 by means of which the screen set, which during the screening operation follows the pulp upwardly in its axial movement, is periodically returned to a lower limit.
  • the screen rings 41 and the arms 43 have inner cavities through which liquid screened offthe pulp flows to an exterior discharge conduit 47.
  • the rotary liquid spreader comprises horizontally and radi ally extending arms 49 carried by the central tube 29 and located at the same level immediately above the uppermost part of the screen set.
  • Vertical arms 51 extend downwardly from said first-mentioned arms 49. When moved said arms 51 describe concentric cylindrical faces situated outside of and between the screen rings 41.
  • Spreading nozzles are provided also in the wall of the central tube.
  • the nozzles 57, 59, 61 which are situated at the same level communicate each through a separate conduit with a pertaining compartment 63 in the tank 55 (see FIG.
  • the liquid supplied by conduit 79 and spread by the upper nozzles consists of a solution of NaOI-I, and the liquid supplied by conduit 65 and spread by the lower nozzles may consist of water or an alkalic effluent.
  • the liquids ejected from the spreading nozzles move in essentially radial directions and displace the previous liquid content of the pulp, which contains chlorine and reaction products, so as to discharge the same through the screen rings 41 and the outlet 47.
  • the pulp reaches the level of the upper edges of the screen rings, the liquid therein has been completely replaced and now consists of alkali solution.
  • any considerable amount of alkali should not escape through the outlet 47 and therefore the liquid spread through the upper nozzles is so proportioned that it does not reach the opposite screen faces. Consequently, at the level immediately above the screen set, pulp having passed adjacent to the screen faces will contain such weaker liquid as has been supplied through the lower spreading nozzles.
  • the pulp column will show a concentric pattern somewhat like the annual rings of a tree trunk.
  • concentration differences would remain in the entire zone E and cause uneven chemical treatment; however, in order to eliminate said drawback, according to the invention the described impregnation with chemicals by displacement is combined with mechanical equalization caused by radial pulp movements in a layer situated close to the screen set but not so close as to disturb the displacement operation which requires a truly axial movement of the pulp.
  • the known method of mixing chemicals into pulp by agitation e.g. in a mixer, it is easy to get a good equalization of the concentration but the pulp is diluted.
  • the consistency of the pulp may remain essentially unchanged, approximately as much liquid being screened off as is supplied through the rotary nozzles, and a high degree of equalization of the chemicals in the pulp is obtained by moderate agitating movements inthe pulp on account of the chemicals being distributed in the pulp already by the displacement, so that the agitation merely serves to effect a final higher degree of even distribution of the chemicals.
  • the displacement operation it is possible by the displacement operation to remove from the pulp its previous content of chemicals simultaneously with new chemicals being spread in the pulp.
  • the radial equalization movements of the pulp are caused by scraper blades attached to the horizontal arms 49.
  • the scraper blades are set obliquely to the radius in order to displace the pulp substantially radially when the arms 49 are turned, although a certain simultaneous movement of the pulp in the peripheral direction usually takes place, too.
  • Some of the scraper blades are adapted to move the pulp radially inwards towards the center and other blades are adapted to move the pulp outwards towards the shell of the tower.
  • Each arm 49 carries a plurality of scraper blades, viz lower scraper blades 81 and upper scraper blades 83.
  • the lower scraper blades 81 are set obliquely at the same angle
  • the upper scraper blades are also set obliquely at the same angle to the arm, but to the other side thereof.
  • the scraper blades are placed at different radial distances and with even intervals. Upon each arm the scraper blades are located alternately on the upper and the lower side. When the arms 49 are turned, the lower scraper blades will move the pulp outwardly towards the shell of the tower, whereas the upper scraper blades will return pulp in the direction towards the center of the tower, as indicated by arrows. In the short axial zone of the tower where the scraper blades are active, the slowly and continuously upward rising pulp therefore is subjected to a superimposed movement with horizontal components.
  • a device 85 for screening off the reaction products obtained by the alkali treatment and for supplying chlorine dioxide to the pulp is identical to the device 39.
  • the liquid screened off departs through the outlet 87, and washing liquid and bleaching chemicals are supplied from a distributor tank 89 on top of the tower.
  • a third screening and spreading device 91 is located at the top of the tower l1 and serves to screen off and convey to the outlet 93 such reaction products as are obtained during the chlorine dioxide treatment and to introduce into the pulp, alkali supplied from a distributor tank 95.
  • the main part of the treatment step E takes place in the top of the second tower l3, and therefore the device 91 differs from the devices 39 and 85 in that the horizontal spreader arms 97 carry merely a single series of equally set scraper blades 99, the object of which is to discharge pulp into the peripheral flume 101 and the connected conduit 15.
  • the spreader device proper is located in the top of the tower 13 and comprises two series of scraper blades acting in opposite radial directions.
  • arms 103 carried by the rotary central tube 107 in the tower 13, which tube is turned by a motor 105, and are located at such a level that they operate in the pulp closely below its surface at the top of the tower 13, which surface is maintained constant by level control.
  • a device 109 of the same construction as the above described device 39 Inserted in the tower 13 between the zones E and D is a device 109 of the same construction as the above described device 39, but turned upside down compared thereto, in order to adapt the same to the flow direction of the pulp which in the tower 13 is downward and opposite to the flow direction of the pulp in the tower 11. Liquid carrying reaction products of the alkali treatments is withdrawn from the fibers by means of the screens 11] and is discharged through the conduit 113.
  • Wash water and a new bleaching agent are supplied through the conduits IIS and 117, respectively, and are distributed in the container 119 between conduits extending through the central tube 107 and through cavities in the radial arms 121 and the vertical arms 123, to nozzles upon the latter through which the wash water and the bleaching agent are spread in the pulp at the level of the screens 111.
  • the arms 121 which carry upper and lower scraper blades 125, 127, are in this case placed at a level situated somewhat below the lowermost parts of'the screens I l l.
  • a bleach tower according to claim 1 characterized in that a first set of scraper blades attached to said arms obliquely thereto so as to move pulp radially inwards, is located at another level than a second set of scraper blades also attached to said arms obliquely thereto but in the opposite sense so as to move pulp radially outwards.
  • a bleach tower according to claim 2 characterized in that each horizontal arm carries upper scraper blades as well as lower scraper blades, the scraper blades taken in a radial order being alternately upper and lower scraper blades.
  • a bleach tower according to claim 3 characterized in that one and the same tubular shaft extending through the entire length of the tower carries a plurality of sets of horizontal arms, each set located at a separate level and the arms thereof carrying upper and lower scraper blades,

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  • Life Sciences & Earth Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Wood Science & Technology (AREA)
  • Paper (AREA)
US773385A 1967-11-06 1968-11-05 Cellulose bleach tower with means for spreading a bleaching agent therein Expired - Lifetime US3599449A (en)

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Application Number Priority Date Filing Date Title
SE15150/67A SE340216B (sv) 1967-11-06 1967-11-06

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US3599449A true US3599449A (en) 1971-08-17

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US (1) US3599449A (sv)
BR (1) BR6803770D0 (sv)
DE (1) DE1807345A1 (sv)
FI (1) FI48619C (sv)
FR (1) FR1590820A (sv)
NO (1) NO119663B (sv)
SE (1) SE340216B (sv)

Cited By (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3815386A (en) * 1971-02-02 1974-06-11 Kamyr Ab Device for bleaching of cellulosic pulp
US3976538A (en) * 1971-02-02 1976-08-24 Kamyr Aktiebolag Method for bleaching of cellulosic pulp
US4172037A (en) * 1975-10-10 1979-10-23 Kamyr Inc. Continuous process diffuser
US4222818A (en) * 1976-04-28 1980-09-16 A. Ahlstroom Osakeyhtio Method for treatment of lignocellulosic material with chlorine
US4556494A (en) * 1980-12-04 1985-12-03 Kamyr Aktiebolag Method of diffusion washing or thickening of pulp
WO1995020067A1 (en) * 1994-01-24 1995-07-27 Kvaerner Pulping Technologies Ab Diffuser
US5836181A (en) * 1994-04-18 1998-11-17 Kvaerner Pulping Ab Diffuser
US20020129911A1 (en) * 2000-10-16 2002-09-19 Marcoccia Bruno S. Process and configuration for providing external upflow/internal downflow in a continuous digester

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5560229A (en) * 1994-01-24 1996-10-01 Kvaerner Pulping Technologies Ab Diffuser

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2431478A (en) * 1942-07-25 1947-11-25 Raymond P Hill Bleaching fibrous material
US3298209A (en) * 1963-12-23 1967-01-17 Kamyr Ab Washing container
US3348390A (en) * 1965-03-25 1967-10-24 Kamyr Ab Cellulosic material process vessel liquid distribution device
US3398412A (en) * 1964-12-17 1968-08-27 Aremaa Toivo Ensio Method for precipitation or washing of materials containing cellulose

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2431478A (en) * 1942-07-25 1947-11-25 Raymond P Hill Bleaching fibrous material
US3298209A (en) * 1963-12-23 1967-01-17 Kamyr Ab Washing container
US3398412A (en) * 1964-12-17 1968-08-27 Aremaa Toivo Ensio Method for precipitation or washing of materials containing cellulose
US3348390A (en) * 1965-03-25 1967-10-24 Kamyr Ab Cellulosic material process vessel liquid distribution device

Cited By (9)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3815386A (en) * 1971-02-02 1974-06-11 Kamyr Ab Device for bleaching of cellulosic pulp
US3976538A (en) * 1971-02-02 1976-08-24 Kamyr Aktiebolag Method for bleaching of cellulosic pulp
US4172037A (en) * 1975-10-10 1979-10-23 Kamyr Inc. Continuous process diffuser
US4222818A (en) * 1976-04-28 1980-09-16 A. Ahlstroom Osakeyhtio Method for treatment of lignocellulosic material with chlorine
US4556494A (en) * 1980-12-04 1985-12-03 Kamyr Aktiebolag Method of diffusion washing or thickening of pulp
WO1995020067A1 (en) * 1994-01-24 1995-07-27 Kvaerner Pulping Technologies Ab Diffuser
CN1070960C (zh) * 1994-01-24 2001-09-12 卡瓦尔纳制浆技术公司 扩散器
US5836181A (en) * 1994-04-18 1998-11-17 Kvaerner Pulping Ab Diffuser
US20020129911A1 (en) * 2000-10-16 2002-09-19 Marcoccia Bruno S. Process and configuration for providing external upflow/internal downflow in a continuous digester

Also Published As

Publication number Publication date
BR6803770D0 (pt) 1973-01-16
FI48619B (sv) 1974-07-31
FI48619C (sv) 1974-11-11
NO119663B (sv) 1970-06-15
FR1590820A (sv) 1970-04-20
DE1807345A1 (de) 1969-10-30
SE340216B (sv) 1971-11-08

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