Classifications

• • 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
• • 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
  • D21C9/02—Washing ; Displacing cooking or pulp-treating liquors contained in the pulp by fluids, e.g. wash water or other pulp-treating agents
• • 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
  • D21C9/1036—Use of compounds accelerating or improving the efficiency of the processes
• • 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
  • D21C9/1042—Use of chelating agents
• • 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
  • D21C9/1057—Multistage, with compounds cited in more than one sub-group D21C9/10, D21C9/12, D21C9/16
• • 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
  • D21C9/147—Bleaching ; Apparatus therefor with oxygen or its allotropic modifications
• • 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
  • D21C9/147—Bleaching ; Apparatus therefor with oxygen or its allotropic modifications
  • D21C9/153—Bleaching ; Apparatus therefor with oxygen or its allotropic modifications with ozone
• • 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
  • D21C9/16—Bleaching ; Apparatus therefor with per compounds
  • D21C9/163—Bleaching ; Apparatus therefor with per compounds with peroxides

Definitions

• the present invention relates to a new kind of a bleaching method for pulp by using chlorine-free chemicals.
• the invention is especially related to ozone bleaching of pulp without preceding removal of heavy metals.
• Typical bleaching sequences by which pulp has earlier been bleached are, for example, OOAZEZPZ, OAZEZPZ, OOAZEZP and OAZEZP. These sequences thus include one or more oxygen bleaching stages (O) , an A-stage (acid washing), an ozone stage (Z), an extraction stage (E), a second ozone stage (Z) and a peroxide stage (P), and possibly a third ozone stage (Z).
• the extraction stage (E) may be an oxidizing peroxide extraction stage or a conventional oxidizing extraction stage.
• the ozone bleaching stages are preferably carried out with pulp having the consistency of about 5-18%.
• washing stages in other words bleaching stages alternate with washing stages, i.e. washers, by which the chemicals separated from the fibers as reaction products or otherwise in each bleaching stage are removed from the suspension. Since the washers form a considerable part of the investment costs in a bleaching plant, the number of the washers should, of course, be limited as much as possible, if it is only possible without risking the quality of the final product.
• a conventional bleaching + screening plant has thus included four or five bleaching stages and one screening and/or vortex cleaning stage, which the washing stage separates from each other.
• the present invention compresses these five to six stages into three stages and thus almost halves the investment costs of a bleaching plant and a screening plant.
• pulp is bleached with a sequence beginning with ozone and without the removal of heavy metals preceding the ozone stage.
• pulp is bleached with a three-stage sequence (ZT) (EOP) (ZP) without the removal of heavy metals preceding the sequence, in which
• ZT refers to a bleaching stage with ozone, which also includes treatment of heavy metals and which stage is followed by washing and/or thickening
• EOP refers to a bleaching stage with peroxide or oxygen and peroxide in alkali conditions and the stage is followed by washing and/or thickening
• ZP refers to bleaching stage with ozone and peroxide without a between stage washing and which stage is followed by washing and/or thickening.
• FIG. 1 schematically illustrates a bleaching sequence in accordance with a first exemplary embodiment of the invention
• FIG. 2 schematically illustrates a bleaching sequence in accordance with a second embodiment of the invention
• FIG. 3 schematically illustrates the later part of a bleaching sequence in accordance with a third embodiment of the invention
• Fig. 4 schematically illustrates another bleaching sequence in accordance with the present invention, and especially portions thereof where acid and/or alkali may be added;
• FIG. 5 schematically illustrates a recirculation method for washing filtrates in accordance with another embodiment of the invention
• FIG. 6 schematically illustrates a recirculation method for washing filtrates in accordance with the second embodiment of the invention illustrated in FIGURE 2; and Fig. 7 schematically illustrates results of a research carried out with a DRUM DISPLACERTM washer.
• a bleaching sequence is provided using a high consistency pulp tower 10, from which pulp is discharged and fed, for example, with an MC® (i.e. fluidizing) pump 12 into an ozone reactor 14, from which pulp is preferably discharged by means of a gas separator 16 into a first reaction tower 18.
• Pulp is preferably discharged from tower 18 into a washer 22 by means of an MC® pump 20.
• the washer may be a conventional DRUM DISPLACERTM washer or a conventional pressure diffuser. Pulp is preferably pumped from washer 22 by an MC® pump 24 into an oxygen reactor 26, and from reactor 26 into a second reaction tower 28.
• a second washer 32 preferably a DRUM DISPLACERTM
• ozone in a carrier gas
• oxygen may be mixed prior to the oxygen reactor 26 with mixer 62 and the mixture of ozone and carrier gas prior to the second ozone reactor 36.
• the mixers 60, 62 are preferably AHLMIXERTM type fluidizing mixers, which are able to mix very large amounts of gas into fiber suspensions, including medium consistency suspensions.
• Fig. 1 teaches how, in order to adjust the pH value of the pulp for the first ozone stage and the removal of heavy metals subsequent thereto, acid may be supplied into the pulp, for example, in the pump 12.
• complex formers such as EDTA, and/or alkali may be added to the pulp. If too much magnesium is removed from the pulp by washer 22, it may be added, for example, with the alkali either in pump 24 and/or in the discharge from the oxygen reactor 26, or in any other appropriate way.
• Another possibility to adjust the pH of the pulp for the second ozone treatment is to feed acid subsequent to the second washer 32 in pump 34 or in some other suitable way.
• peroxide and/or magnesium may be added into the pulp, as illustrated in Fig. 1.
• All the reaction towers 18, 28 and 40 in Fig. 1 are shown as of the down flow type. Alternatively, they may be of the up flow type, as is shown in Fig. 2.
• the only significant difference between Figs. 1 and 2 is the flow direction of the reaction towers.
• components functionally equivalent to or the same as the components in the Fig. 1 embodiment are illustrated by the same reference numeral, only preceded by a "1".
• pumps 20, 30 and 42 of Fig. 1 are replaced by pumps 120', 130' and 142', because they have been relocated at the other side of the reaction tower, in other words instead of feeding washers 22, 32 and 44 as illustrated in Fig. 1 they feed pulp to the reaction towers 118, 128 and 140 in the embodiments of Fig. 2.
• pulp is cooked, for example with a continuous EMCC digester, sold by Kamyr Inc., of Glens Falls, New York, to a low kappa number, whereafter the kappa number is further decreased by oxygen bleaching to a value of about 14 or below.
• a continuous EMCC digester sold by Kamyr Inc., of Glens Falls, New York
• oxygen bleaching to a value of about 14 or below.
• hot alkali extraction and oxygen bleaching a kappa range of 14 - 5 is obtained both with soft wood and birch.
• a kappa number of 14 is sufficient in order to carry our the final bleaching with chlorine-free bleaching chemicals and yet reach a full brightness defined by ISO 86 (preferably ISO 88).
• ISO 86 preferably ISO 88
• the kraft pulp is bleached subsequent to the pulp washing and according to the invention without a separate removal of heavy metals, for example, with a sequence in accordance with Fig. 1, which is described more in detail below.
• Pulp may be treated, if so required, with enzymes prior to the sequence in accordance with the present invention.
• Pulp is brought from the high consistency pulp tower 10 to the first bleaching stage, which is a (ZT) stage.
• the first bleaching stage which is a (ZT) stage.
• pulp is bleached with ozone, the dosing being about 2-10 kg/adt, pH about 2- 7, and temperature about 40-70°C.
• the pH value of pulp is adjusted by adding acid to the bottom of the high consistency tower 10, pump 12 (or the discharge to pump 12 as seen in Fig. 1), or chemical mixer 60.
• the ozone having reacted, the residual gas is removed from the pulp preferably in a gas separator 16 and the treatment of heavy metals begins in the first reaction tower 18 in the T portion
• the T portion of the (ZT) stage may be carried out, for example, in the following ways.
• the first alternative is to allow the pH value of the pulp to decrease to the range of 2 - 4, whereby the majority of the heavy metals are dissolved into the filtrate phase and may be washed off in the thickener or washer 22 following that stage.
• the disadvantage here is that the majority of the magnesium (Mg) is also discharged, so that it is possible that magnesium must be added to the pulp, mostly in the form of magnesium sulphate, for the oxygen and/or peroxide stages following later on in the sequence.
• T portion of the (ZT) stage Another way to carry out the T portion of the (ZT) stage is to use complex formers, for example, EDTA.
• the T portion of the (ZT) stage is then carried out in the pH range of about 4-7 and it is advantageous also to have the pH of Z portion of the (ZT) stage preceding T portion above 4.
• manganese which is harmful in the oxygen stages
• Filtrate S. of the washer 22 subsequent to the (ZT) stage may be brought to pulp washing prior to the (ZT) stage, or passed to the sewer or to the recovery of cooking chemicals.
• the (ZT) stage is followed in Fig. 1 by an (EOP) stage.
• the oxygen dose is about 2-6 kg/adt and the peroxide dose about 10-20 kg/adt. In some special cases it is possible to run the process completely without oxygen.
• Temperature in the (EOP) stage is about 60-95°C, pH about 9-12, and the duration is about 2-8 hours. If required, magnesium may be added as a protective chemical.
• the (EOP) stage is followed by washing, which gives filtrate S 2 .
• the filtrate S 2 may be taken to pulp washing prior to or subsequent to the (ZT) stage, sewer, or recovery of chemicals.
• the (EOP) stage is followed in Fig. 1 by a second ozone bleaching stage, i.e. an (ZP) stage.
• the ozone portion of the (ZP) stage is normally carried out in the processes in accordance with the prior art in cold, acid conditions in order to have the ozone react properly.
• the P portion of the (ZP) stage is carried out according to the teachings of the prior art in hot, alkali conditions in order to have the peroxide react properly.
• the combination thereof in an economically advantageous way according to the present concepts is conventionally considered impossible.
• the (ZP) stage the following conditions may be utilized:
• the temperature in the ozone stage may be 50-80°C, preferably, for example, 60-70°C.
• the pH is 4-10, preferably about 6- 10.
• the dose in the P portion of the (ZP) stage is also small, usually less than 10 kg/adt. Normally about 3-7 kg/adt is sufficient.
• the temperature in the peroxide stage may be dropped to the range of 60-80°C, preferably to 70-80°C.
• the pH is 9-11, preferably about 10.
• the duration is about 1-6 hours.
• the pulp is washed and a filtrate S 3 is obtained.
• the filtrate S 3 may be used for the washing of pulp in connection with the earlier bleaching stages, discharged to the sewer, or led to the recovery of cooking chemicals.
• a vortex cleaner 66 and/or a screening plant may be added according to Fig. 3 to the last stage of the bleaching plant to precede the thickener/washer 68, which in this case does not have to be an MC® washer, as in the earlier embodiments.
• Pulp is diluted to the consistency range of about 0.5-1.5 % after the P-tower 140, when vortex cleaning or screening with a slotted screen is used.
• a dilution to about 2-4% is usually sufficient.
• FIG. 5 illustrates an oxygen delignification stage 80, which is followed by a two-stage washing 82. Pulp is transferred from the washing stage to the (ZT) stage 83, and from there via washing 84 to (EOP) stage 85, and from there via washing 86 to the (ZP) stage 87, which is followed by a washing stage 88.
• the amount of effluent, which is brought to the effluent clarification, discharge channel 90, is 0-5 m3/adt. Part of the effluent may alternatively be transferred to the manufacture of cooking chemicals, via discharge channel 92, to be used instead of fresh water. Thus the amount of effluent that must be treated is minimized.
• Fig. 5 may further be intensified by dividing the filtrates from the washer into two fractions with different pH according to Fig. 6.
• Fig. 6 utilizes the reference numbers of Fig. 5 with a preceding "1".
• the washers used in Fig. 6 are manufactured and marketed by A. Ahlstrom Corporation, and known as DRUM DISPLACERTM washers.
• the pulp for the last washer 188 comes from the alkali (ZP) stage.
• ZP alkali
• the first outwashed filtrate 1881 is clearly alkaline and the filtrate 1882 coming out later is less alkaline or even neutral, because water 1880 flowing to the last washer 188 is generally neutral or slightly acid.
• the pH of the filtrates may also be adjusted by adding acid or alkali to them before they are used again. In some cases it may, for example, be necessary to add alkali to the filtrates prior to their being brought to the brown stock washing or it may be necessary to add acid in order to maintain the pH low during the removal of the metals in the (ZT) stage (point 1840). It is possible that heavy metals are thickened again and attach to the fibers, if the pH increases during washing. Thus heavy metals are entrained to the P portion of the (ZP) stage following the Z portion and disturb the peroxide stage. Preferably the pH value is maintained less than 4, or at least maintained at 4, during the removal of heavy metals.
• the pH values of the filtrates are close to the pH values of the entering and exiting pulp, preferably closer to these than to each other.
• the present invention also includes a new method of arranging the screening subsequent to the pulp bleaching in such a way that a separate washing between the last washing stage and screening/vortex cleaning is unnecessary, but only dilution to screening/cleaning consistency. While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiment, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.

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• 1993
  • 1993-03-03 FI FI930954A patent/FI93232C/fi active
  • 1993-05-25 ES ES93910051T patent/ES2130260T3/es not_active Expired - Lifetime
  • 1993-05-25 BR BR9307858A patent/BR9307858A/pt not_active IP Right Cessation
  • 1993-05-25 RU RU95122814A patent/RU2126471C1/ru active
  • 1993-05-25 JP JP51962394A patent/JP3276083B2/ja not_active Expired - Fee Related
  • 1993-05-25 AU AU53705/94A patent/AU5370594A/en not_active Abandoned
  • 1993-05-25 WO PCT/FI1993/000222 patent/WO1994020673A1/en active IP Right Grant
  • 1993-05-25 EP EP93910051A patent/EP0687321B1/de not_active Expired - Lifetime
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  • 1993-05-25 EP EP98113684A patent/EP0884415B1/de not_active Expired - Lifetime
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  • 1993-05-25 AT AT93910051T patent/ATE176808T1/de not_active IP Right Cessation
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• 1995
  • 1995-08-30 FI FI954093A patent/FI954093A/fi not_active IP Right Cessation
  • 1995-09-01 NO NO953444A patent/NO953444L/no unknown

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