US3313678A - Bleaching of cellulose pulp in towers in completely filled and closed system - Google Patents

Bleaching of cellulose pulp in towers in completely filled and closed system Download PDF

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Publication number
US3313678A
US3313678A US258322A US25832263A US3313678A US 3313678 A US3313678 A US 3313678A US 258322 A US258322 A US 258322A US 25832263 A US25832263 A US 25832263A US 3313678 A US3313678 A US 3313678A
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stock
tower
bleaching
towers
consistency
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Expired - Lifetime
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US258322A
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English (en)
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Sten O Rydin
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Svenska Cellulosa AB
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Svenska Cellulosa 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
    • D21C9/1026—Other features in bleaching processes

Definitions

  • the present invention relates to continuous treatment, substantially bleaching, of cellulouse pulp in towers.
  • Towers used for this purpose are constructed, on the one hand, for operation with upward flow of the stock and, on the other hand, for operation with downward flow of the stock. Distinction is made between towers, operating with low stock consistencies in the range of l-%, medium high consistencies in the range of 58% and high consistencies in the range of 820%.
  • the invention has ref erence to towers, in which the contents are caused to flow either upwards or downwards, and in both cases they operate with stock of medium high and high consistencies.
  • the early towers adapted for high stock consistencies were of a construction in which the stock was caused to move from the top end portion of the tower towards the bottom end portion thereof. Thickened stock, delivered, for example, from a rotary thickener, was supplied at the top end portion of the tower and at the bottom end portion of the tower there was flushing means, diluted stock being discharged through a duct at the bottom end portion of the tower and supplied to a centrifugal pump and hence to a washer. Towers of this type either were open at the top or also they were covered with a roof, so that a space filled with air, or other gas, was formed above the stock.
  • An example of a tower, open at its top is disclosed in the Swedish patent specification No. 140,977.
  • a second fundamental type of bleaching towers that has been developed is one in which the stock is caused to flow from below and upwards.
  • building towers of this kind assistance was rendered by the development of pumps, so that at present it is possible to pump stock having a consistency of up to 15 to 20%.
  • bleaching in towers of this kind it is customary either to remove the pulp at the top end portion of the tower by scraping it out into a collecting channel, concentrically surrounding the top end portion of the tower, and diluting the pulp in said channel with liquid to a consistency in which it can be pumped by means of a centrifugal pump, for example, in the way shown in FIGURES 1 and 2 of the Swedish patent specification No.
  • Such way of discharging the pulp from the tower involves, inter alia, the drawback of bubbles of air, or of other gas, becoming intermixed with the pulp while the latter is being diluted in the channel or at the top end portion of the tower, which will, in turn, impair the capacity and the washing by the filter g device on which the pulp, customarily, is dewatered and washed after the treatment in the tower.
  • the intermixin-g of air occurs because of the relatively great differences between the speed of the stock and the speed of the diluting liquid which exist in the channel surrounding the top of the tower, when the pulp flows down into the channel or when a jet of diluting liquid is introduced into the top end portion of the tower.
  • the dilution In towers of the kind in which the pulp is diluted at the top end portion of the tower to such an extent that it will flow over the edge of the tower and down into the surrounding collecting channel, the dilution must be carried out to a low consistency, usually of the order 1 /z-3 If in that case the tower is built for operation with stock of a relatively high consistency, say 820%, the diluting liqaid will penetrate deep down into the tower by which the volume of the tower cannot be utilized in an effective way.
  • the present invention relates to a method by which the aforementioned drawbacks will be overcome, the advantages connected with high-density bleaching being maintained at the same time.
  • the invention is based upon the use of entirely closed bleaching towers and upon always keeping the towers filled, or substantially filled, with stock and also upon operating with high stock consistencies. Closed bleaching towers, operating while completely filled, previously have been used in connection with low stock consistencies, such as 25%, but then the low stock consistencies necessitate the use of large tower volumes and also result in the heat consumptionarising because of the necessity of raising the temperature of the stock in ceratin towers up to, for instance, 4080 C.becoming very great. Such towers are used mainly in conneetion with the chlorination of stock, and chlorination, as a rule, is carried out at low stock consistencies, such as from 25 for instance at 3.5%
  • the possibility of operating with an entirely closed and permanently filled tower at high stock consistencies and with a downward flow of the stock within the tower is based on the provision of a counterpressure at the stock discharge end of the tower, said counterpressure balancing the column of stock within the tower and preventing the formation of a vacuum at the top end portion of the tower.
  • FIGURE 1 shows a bleaching tower, in which cellulose stock of a high consistency is caused to move from the top of the tower to the bottom thereof.
  • the stock which for example is of a consistency of about 14% is supplied to a thick stock pump 1, which through a pipe line 2 pumps stock into the top end portion of the tower 3, said tower being provided with an air exhaust valve (not shown).
  • On top of the tower there is provided combined means 4 for distributing stock within the tower and for intermixing chemicals with the stock, said means being connected to a pipe line 13 through which the chemicals are supplied.
  • means for flushing away stock, said means, in the embodiment shown, comprising a number of flushing spouts 5 provided around the lower part of the tower and positioned some distance above the bottom of the tower.
  • a stirring propeller 7 At the bottom end portion of the tower there is a recess 6, above which there is provided a stirring propeller 7 and an inlet 8 for liquid.
  • the consistency may now, at will, be between about 1 and 5%, for example between 2 to 4%
  • the discharge duct 10 leads up to a washer 11, which is positioned at about the same level as, or somewhat higher than, the top of the tower.
  • a washer 11 which is positioned at about the same level as, or somewhat higher than, the top of the tower.
  • the discharge duct 10 extends up to such a high level that at the outlet 9 of the tower such a strong counterpressure is formed that no vacuum can arise within the top end portion of the tower.
  • the tower will always be filled with stock as long as a sufficient amount of stock is being supplied at the top end portion of the tower.
  • the stock feeding pump 1 continuously supplying the tower with stock, a uniform downward flow of stock will be obtained within the tower. Consequently, the above described mode of operation makes it possible always to maintain the same volume of stock within the tower, and furthermore that the tower will always deliver the same amount of pulp as the amount of stock supplied through the pump 1 and, finally, that the stock will thereby always stay within the tower for the same length of time.
  • the previously mentioned drawbacks of varying bleaching times are elimi nated and, furthermore, there is obtained the advantage of not having to make the tower any larger than what will answer the most preferred time of treatment and the desired consistency of the stock.
  • the tower is sealed by the stock within the pipe line 2, due to which gases cannot escape from the tower.
  • a further advantage is that the pump 1, feeding the stock into the tower, also is able to cause the stock to move on from the tower to the wash 1]., which is at the same level as, or higher up than, the top of the tower. Consequently, the pump provides for the entire transportation of stock from the feeding-in thereof into the tower and all the way to the feeding-in of the stock at the intake end of the wash, due to which there will be no need of a lifting pump, arranged after the tower.
  • FIGURE 2 shows a bleaching tower, in which cellulose stock of a high consistency, for example, about 14% is to be fed from the bottom of the tower and upwards within the same.
  • the thick stock pump 1 feeds the stock, which has been thickened by means of a filtering device or some other suitable apparatus, through the pipe line 2 to the; tower 3, which is provided with an air exhaust valve (not shown).
  • combined means 4 for distributing the stock within the tower and for intermixing hrnicals with the stock.
  • Chemicals for example, hypochlor'ite', caustic soda, or chlorine dioxide water, are dosed through the pipe line 13 to the intermixing means 4.
  • the tower tapers towards the discharge opening 9.
  • the supply of diluting liquid takes place along the periphery of the tower through tangentially die rected spouts 14 and stirring means 15 provided centrally within the top end portion of the tower, said stirring means being provided with spouts 16 for supplying diluting liquid at the center.
  • the stock leaving the tower is to be conveyed to a wash and therefore has to be further diluted, which preferably is done within the discharge duct 10 by supplying diluting liquid from a pipe line 17.
  • the stock, thus further diluted to a consistency of about 1 to 2% is then led to the filtering device (not shown).
  • the hereinbefore described arrangement makes it possible to operate with an entirely closed and a completely filled system at high stock consistencies.

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  • Life Sciences & Earth Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Wood Science & Technology (AREA)
  • Organic Low-Molecular-Weight Compounds And Preparation Thereof (AREA)
  • Paper (AREA)
US258322A 1962-02-14 1963-02-13 Bleaching of cellulose pulp in towers in completely filled and closed system Expired - Lifetime US3313678A (en)

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SE160062 1962-02-14

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US3313678A true US3313678A (en) 1967-04-11

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NO (1) NO117673B (en, 2012)

Cited By (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3668063A (en) * 1967-11-10 1972-06-06 Sunds Ab Removal of entrained air from cellulose pulp before bleaching of the pulp
US3884752A (en) * 1973-09-17 1975-05-20 Int Paper Co Single vessel wood pulp bleaching with chlorine dioxide followed by sodium hypochlorite or alkaline extraction
EP0018287A1 (fr) * 1979-04-17 1980-10-29 La Cellulose Des Ardennes Procédé de délignification de pâte à papier chimique écrue
FR2479295A2 (fr) * 1980-03-31 1981-10-02 Europeen Cellulose Procede de delignification de pate a papier chimique ecrue
EP0155928A1 (en) * 1984-03-05 1985-09-25 Kamyr, Inc. Mechanical pulp hydrosulfite bleaching
US5372679A (en) * 1992-06-08 1994-12-13 Air Products And Chemicals, Inc. Reactor system for treating cellulosic pulp at a constant upward flow velocity
US5589036A (en) * 1992-05-18 1996-12-31 Champion International Corporation Controlling pulp flow in an upflow pulp treatment tower

Citations (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US1643566A (en) * 1925-10-16 1927-09-27 Thorne Carl Busch Process for bleaching and the like purposes
US2089992A (en) * 1932-03-14 1937-08-17 Int Paper Co Continuous bleaching process and apparatus
US2474862A (en) * 1942-10-15 1949-07-05 Kamyr Ab Process and apparatus for continuous digestion of fibrous materials
US2662821A (en) * 1949-05-03 1953-12-15 Celotex Corp Fiber preparation device
US2711359A (en) * 1953-10-19 1955-06-21 Kamyr Ab Bleaching plant and method of bleaching cellulose pulp
US2769710A (en) * 1954-01-12 1956-11-06 Cellulose Dev Corp Ltd Process for the continuous treatment of vegetable fibers
US2876098A (en) * 1956-01-11 1959-03-03 Hans Werner Meyer Process of and apparatus for the continuous manufacture of cellulose or hemicellulose from cellulosic fibrous materials
US3007839A (en) * 1958-07-09 1961-11-07 Kamyr Ab Method and plant for continuous cellulose digestion

Patent Citations (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US1643566A (en) * 1925-10-16 1927-09-27 Thorne Carl Busch Process for bleaching and the like purposes
US2089992A (en) * 1932-03-14 1937-08-17 Int Paper Co Continuous bleaching process and apparatus
US2474862A (en) * 1942-10-15 1949-07-05 Kamyr Ab Process and apparatus for continuous digestion of fibrous materials
US2662821A (en) * 1949-05-03 1953-12-15 Celotex Corp Fiber preparation device
US2711359A (en) * 1953-10-19 1955-06-21 Kamyr Ab Bleaching plant and method of bleaching cellulose pulp
US2769710A (en) * 1954-01-12 1956-11-06 Cellulose Dev Corp Ltd Process for the continuous treatment of vegetable fibers
US2876098A (en) * 1956-01-11 1959-03-03 Hans Werner Meyer Process of and apparatus for the continuous manufacture of cellulose or hemicellulose from cellulosic fibrous materials
US3007839A (en) * 1958-07-09 1961-11-07 Kamyr Ab Method and plant for continuous cellulose digestion

Cited By (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3668063A (en) * 1967-11-10 1972-06-06 Sunds Ab Removal of entrained air from cellulose pulp before bleaching of the pulp
US3884752A (en) * 1973-09-17 1975-05-20 Int Paper Co Single vessel wood pulp bleaching with chlorine dioxide followed by sodium hypochlorite or alkaline extraction
EP0018287A1 (fr) * 1979-04-17 1980-10-29 La Cellulose Des Ardennes Procédé de délignification de pâte à papier chimique écrue
FR2479295A2 (fr) * 1980-03-31 1981-10-02 Europeen Cellulose Procede de delignification de pate a papier chimique ecrue
EP0155928A1 (en) * 1984-03-05 1985-09-25 Kamyr, Inc. Mechanical pulp hydrosulfite bleaching
US5589036A (en) * 1992-05-18 1996-12-31 Champion International Corporation Controlling pulp flow in an upflow pulp treatment tower
US5372679A (en) * 1992-06-08 1994-12-13 Air Products And Chemicals, Inc. Reactor system for treating cellulosic pulp at a constant upward flow velocity
US5397434A (en) * 1992-06-08 1995-03-14 Air Products And Chemicals, Inc. Method for distributing cellulosic pulp through a reactor at a constant upward velocity

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Publication number Publication date
NO117673B (en, 2012) 1969-09-08

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