EP1244840A1 - Bleaching pulp with high-pressure o 2? - Google Patents
Bleaching pulp with high-pressure o 2?Info
- Publication number
- EP1244840A1 EP1244840A1 EP00938089A EP00938089A EP1244840A1 EP 1244840 A1 EP1244840 A1 EP 1244840A1 EP 00938089 A EP00938089 A EP 00938089A EP 00938089 A EP00938089 A EP 00938089A EP 1244840 A1 EP1244840 A1 EP 1244840A1
- Authority
- EP
- European Patent Office
- Prior art keywords
- pulp
- reactor
- oxygen
- stage
- pump
- Prior art date
- Legal status (The legal status 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 status listed.)
- Withdrawn
Links
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
- D21C9/1057—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
- D21C9/1005—Pretreatment of the pulp, e.g. degassing the pulp
-
- 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
Definitions
- This invention relates to bleaching wood pulp, in kraft and other wood pulping processes, to be manufactured into paper products (including paper, tissue, paper board, bleached pulp bales, wet laps, rolls, and slush to be de-inked).
- Steps in the standard kraft process include: (a) alkali and sulfur treatment of the wood pulp to produce treated wood pulp suitable for further delignif ⁇ cation; and (b) bleaching the treated wood pulp.
- step (a), above are processed by a chemical recovery cycle which includes an unbleached stock wash and screening, evaporation, the use of a chemical recovery boiler, and recausitcizing.
- a chemical recovery cycle which includes an unbleached stock wash and screening, evaporation, the use of a chemical recovery boiler, and recausitcizing.
- an O 2 delignif ⁇ cation step is used as part of step (a) (before the bleaching step), the filtrate from this delignification step being sent to the chemical recovery system.
- Wood pulp to be manufactured into paper products can be treated in a number of ways other than kraft processes, including various sulf ⁇ te processes, alcohol-based processes, various sulphite processes, MgO processes, and waste paper de-inking processes. Any of these processes typically produces a pulp that has a lignin content of from 0-6%. No matter which way the pulp is treated, it typically must be bleached before it can enter a paper mill and be made into a product suitable for white printing paper, tissue and white packing paper.
- wood pulp having a kappa number of between 10 and 30 is treated at low (e.g., between 2.0 and 6.0%) consistency and pH between 2.0 and 4.0 (preferably pH 2.0-3.0), at 110-185EF for 15 to 60 minutes.
- Pulp treated by this step is clean, well washed, and suitable for oxygen bleaching to a lower kappa number without excessive degradation of cellulose.
- a powerful oxygen bleaching step is then performed.
- the filtrate from this bleaching step is not processed by any chemical recovery system(s) that may be used to recover chemicals used in the pulp pre- treatment.
- the pretreatment can be essentially any process which results in wood pulp with the specified lignin content and is otherwise suitable for bleaching.
- One important example is, of course, a traditional kraft process as described above, in which the wood is converted to pulp suitable for manufacturing a paper or tissue product with kraft steps (a) and (b) described in the background above.
- the invention focuses on step (b), which includes an acidification step in which wood pulp having a kappa number of between 10 and 30 from kraft step (a) is bleached under the conditions described above. This step removes at least 10% of the hexeneuronic acids in the treated pulp, some metals, some bound sodium, and soluble organics.
- Pulp treated by this step is clean, well washed, and suitable for oxygen bleaching to a lower kappa number without excessive degradation of cellulose.
- the powerful oxygen bleaching step is then performed, and filtrate from this bleaching step is not processed by the chemical recovery system used in the kraft treatment.
- Such pulp has improved bleachability in subsequent stages, due in part to lower metals content and controlled conditions in the reactors to remove a significant portion of wood resins without cellulose fiber damage.
- the invention also may be used with other wood pulp processes, including various sulfite processes, alcohol-based processes, various MgO processes, and office waste de-inking processes. Any of these processes typically produces a pulp that has a lignin content of from 0-6% and is suitable for the powerful oxygen bleaching step.
- the method handles pulp with higher hexeneuronic acid content, i.e., some or even all of the pulp is from hardwood trees.
- the process is also suitable for pulp that is entirely softwood or combinations of hardwood or softwood.
- the pretreatment step may include application of an oxidizing agent such as ClO 2 applied at a kappa factor below 0.05 or some other oxidizing agent (such as ozone, per acidic acid, etc.) at an equivalent kappa factor.
- Acid may be added as part of the pretreatment step, with or without any oxidizing agent.
- the acid may comprise spent acid from a ClO 2 generation process or sulfuric acid or both.
- the pretreatment step may include a washing step in which a liquid acidic filtrate is separated from the pulp, downstream from the reaction tower.
- the acidic filtrate of this washing step is not processed by a chemical recovery system, thus avoiding scaling and/or corrosion in the chemical recovery system.
- a second aspect of the invention features a kraft method having steps (a) and (b) in which the bleaching stage b) includes a pre-treatment step which produces a clean well-washed pulp and a filtrate, low in transition metals, reduced hexeneuronic acid content, consistency between 9-15% and a kappa number of 10-30.
- the filtrate of this step is not processed in a chemical recovery system.
- the method includes a strong O 2 bleaching process having two separate O 2 reactors operated at high pressure.
- Pulp flow and system pressure are produced by at least one pump, a high-pressure pump producing a pressure of about 140-180 psi at the inlet to the first reactor.
- the pressure discharging from the second reactor is at least 50 psi.
- the first reactor may be supplied by a medium consistency pump standpipe reservoir, the top of which is usually at atmospheric pressure.
- the standpipe has a minimum operating level at least 20 feet above the pump suction.
- the standpipe is subjected to controlled gentle heating by mixing the pulp with steam having a pressure less than 5 psi at the point of mixing, so that the temperature of the pulp prior to entering the medium consistency pump is 170-205EF. There need be no additional heating downstream of the medium consistency pump and prior to the first reactor.
- the temperature of the pulp prior to entering the medium consistency pump is preferably 190-205 EF with no additional heating between the first and the second reactor.
- the temperature of the pulp prior to entering the medium consistency pump is 170-185EF and additional heating is used between the first and the second reactor.
- the high-pressure may also provided by a second high pressure pump operated in series with the first high pressure pump.
- the second high pressure pump may be positioned between the first pump and the first reactor, or the second pump may be positioned between the two reactors.
- High pressure oxygen is injected into stock at an oxygen injection point at or upstream of a high shear mixer which is positioned below the first reactor, so that piping between the oxygen injection point and the first reactor is free from bends in excess of 30E or other turbulence producing geometries.
- Oxygen injected at the oxygen injection point is between 25 and 100% of the total oxygen requirement for the two reactors.
- high pressure oxygen may be injected into stock at an oxygen injection point at or upstream of a high shear mixer which is positioned below the second reactor, piping between the oxygen injection point and the second reactor being free from bends in excess of 30E or other turbulence producing geometries, oxygen injected at the oxygen injection point being between 0 and 50% of the total oxygen requirement for the two reactors.
- high pressure oxygen injected at the point of highest stock pressure between any pump upstream of the first reactor and a control valve for the pump, and oxygen injected at that point is between 0-50% (in some cases, 0-20%) of the total oxygen requirement for the two reactors.
- the high pressure oxygen and the stock pressure are above 150 psi.
- the bleaching step may further include a peroxide stage after the second O 2 reactor, in which a fluidizing device is provided at the exit of the second reactor.
- the fluidizing device may be positioned between the outlet of the second reactor and the inlet of the hydrogen peroxide stage described below.
- the fluidizing device mixes the stock and hydrogen peroxide and, if necessary, metals control agents and/or a hydrogen peroxide stabilizer, the hydrogen peroxide charge being 1-8 pounds per ton of pulp, the pulp having a consistency of between 8 and 15%. This reaction continues for 20-60 minutes at a temperature between 170 and 212EF (preferably less than 20lF.
- the first and second reactors or between the second reactor and the peroxide stage there is no wash between the first and second reactors or between the second reactor and the peroxide stage.
- Stock may be washed downstream of the second reactor.
- the stock is washed downstream of the peroxide stage.
- filtrate from the wash is not processed by the chemical recovery system. This may be the only wash downstream of the second reactor or peroxide stage.
- a third aspect of the invention features further processing of an alkali/sulfur-treated pulp that has been previously delignified down to a kappa number of 4-12.
- This further treatment includes at least one ClO 2 stage followed by an alkaline hydrogen peroxide stage without intermediate washing. A wash is then performed, and the resulting pulp is 80-92 ISO brightness.
- This further processing may include a second ClO 2 stage and its subsequent wash. The second ClO 2 stage and its wash may be performed before or after the above-discussed combined ClO 2 /hydrogen peroxide process. This second ClO 2 stage can also be a combined ClO 2 /hydrogen peroxide process.
- the reaction time for hydrogen peroxide stage is 30-60 minutes at a temperature of 140-190EF at a final pH of 8.5-11 and a consistency of 3-6% and could be achieved at medium consistency (8-16%) or high consistency (17-35%).
- a metals control agent or a hydrogen peroxide stabilizer may be added during the hydrogen peroxide stage.
- a fourth aspect of the invention features powerful bleaching of low lignin pulp with O 2 , in which the filtrate is not processed by the chemical recovery treatment.
- the wood pulp used in this process B i.e., pulp having less than 6% lignin B may be obtained by any chemical treatment, including those which comprises a chemical recovery system, for example, a system of brown stock washing, evaporation, recovery boiler and recausticizing.
- the process for bleaching the low lignin pulp produce a product suitable for paper or tissue manufacture, and it includes: i) processing treated wood pulp having a kappa number of between 10 and 30, at low consistency between 2.0 and 6.0%, at 110-185EF for 15 to 60 minutes, pH between 2.0 and 4.0; and ii) powerful oxygen bleaching in which the filtrate is not processed by the chemical recovery system.
- Each aspect of the invention features pulp processes for making all types of paper products including paper, tissue, paper board, bleached pulp bales, wet laps, and slush to be de-inked. Other aspects of the invention will be apparent to those skilled in the art from the following description of the preferred embodiments and figures, and from the claims.
- FIG. 1 is a general flow diagram of the first stage of a kraft pulp bleaching process.
- Fig. 2 is a general flow diagram of the second stage of the kraft pulp bleaching process.
- the initial stage of the pulp bleaching process is shown in Fig. 1.
- wood is subjected to some mechanical treatment, and then to a NaOH/Na ⁇ chemical digestion.
- the result of these initial processes is a treated pulp brown stock 10 which includes metals, bound sodium, lignin, and cellulose in intimate association.
- the process also produces a by-product stream which includes spent chemicals and other by-products.
- a system for recovering and treating this byproduct stream is critical to the kraft process.
- the chemical recovery system includes brown stock washing, evaporation, recovery boiler and recausticizing.
- brown stock 10 is washed in washer 12 and the pulp is acidified with a mixture of spent acid 14 from a ClO 2 generator and/or sulfuric acid and recycled acidic filtrate 28 from the pre-treatment (Ad) stage wash.
- the pulp is low consistency (between 2.0 and 6.0%) with a kappa number of 10-30.
- ClO 2 is may be added in one or more stages 16.
- the mixture is reacted in Ad Tower 20 at 110- 185EF for 15 to 60 minutes, pH between 2.0 and 4.0.
- the product is washed in Ad washer 22 using DNP and O 2 filtrate 24 described below. Some fresh water may be used on the lowest shower.
- MgSO 4 is added to washer material and caustic (NaOH) is added to MC pump suction.
- the solids are conveyed by a screw conveyor 25 to a steam mixer 26 to a standpipe 30 which feeds the O 2 bleaching stage described below.
- the pre-treatment removes at least 10% of hexeneuronic acid in the treated pulp and some metals, including the majority of the manganese. It also removes some bound sodium and soluble organics.
- the resulting pre-treated pulp is clean, well washed, and suitable for oxygen bleaching to a lower a kappa number without excessive degradation of cellulose.
- the pre-treated pulp is then subjected to strong oxygen bleaching in at least two stages.
- This bleaching takes place under high pressure with efficient contact between oxygen and the pulp.
- this high-pressure two-stage bleaching can be accomplished with a single medium consistency oxygen pump.
- the top of standpipe 30 is at ambient pressure.
- Medium consistency pump 32 feeds the high-shear mixer 34 which is positioned directly below the first oxygen reactor 36, without turbulence producing geometries, such as bends. In that way, the pressure generated by pump 32 is effective to feed both O 2 reactors.
- Oxygen 38 is fed to the pulp upstream of the first reactor and at mixer 34. Oxygen can also be added at 99, between the MC pump and its level control valve for additional benefit — e.g., to add additional oxygen to handle additional kappa drop without exceeding the gas handling capability of the additional mixing points and reactors.
- Steam 40 is for start-up purposes only, if necessary.
- the pressure in reactor 36 is high as described above to maintain small bubbles and good reaction efficiency.
- the stock is then fed to the second reactor 42. Again, a high shear mixer 44 is used to introduce oxygen from line 38. The stock is heated by steam 40 and treated with caustic as indicated. The reference to H 2 O 2 is for start-up purposes only.
- From the second reactor 42 stock is fed to blow tank 46. Diluted hydrogen peroxide and metals control agents and/or peroxide stabilizers can be added to the fluidizing discharger at 51 on the top of the second reactor to use the blow tank as a hydrogen peroxide stage. From there the pulp flows to washer 48. Filtrate 50 is sewered or available for recycling options. The low chloride content of this filtrate enhances recycling/recovery options. Further whitening is accomplished by a ClO 2 (Dl) stage as follows.
- Pulp is heated in a steam mixer 52 and treated with ClO 2 and spent acid. The mixture is reacted in tower 54 and then treated with caustic and H 2 O 2 . Standard metals control agents (chelants, etc.) and/or hydrogen peroxide stabilizers (sodium silicate etc.) can also be added. This mixture is then sent to NP tower 56. There is no wash between tower 54 and tower 56. After tower 56 the pulp is washed in washer 58 and subjected to a second ClO 2 treatment in tower 60. The pH of the pulp is then treated with caustic and washed in washer 62. The resulting pulp is ready for paper/tissue/paper board manufacture. Other embodiments are within the following claims.
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- Life Sciences & Earth Sciences (AREA)
- Engineering & Computer Science (AREA)
- Wood Science & Technology (AREA)
- Paper (AREA)
Abstract
Description
Claims
Applications Claiming Priority (5)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
US13804399P | 1999-06-08 | 1999-06-08 | |
US138043P | 1999-06-08 | ||
US51014000A | 2000-02-22 | 2000-02-22 | |
US510140 | 2000-02-22 | ||
PCT/US2000/015263 WO2000075420A1 (en) | 1999-06-08 | 2000-06-02 | Bleaching pulp with high-pressure o¿2? |
Publications (2)
Publication Number | Publication Date |
---|---|
EP1244840A1 true EP1244840A1 (en) | 2002-10-02 |
EP1244840A4 EP1244840A4 (en) | 2003-04-16 |
Family
ID=26835817
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
EP00938089A Withdrawn EP1244840A4 (en) | 1999-06-08 | 2000-06-02 | Bleaching pulp with high-pressure o 2? |
Country Status (4)
Country | Link |
---|---|
EP (1) | EP1244840A4 (en) |
AU (1) | AU5317700A (en) |
CA (1) | CA2376528A1 (en) |
WO (1) | WO2000075420A1 (en) |
Families Citing this family (3)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US20050051288A1 (en) * | 2003-09-09 | 2005-03-10 | Caifang Yin | Extended retention and medium consistency pulp treatment |
SE528726C2 (en) * | 2004-12-30 | 2007-01-30 | Kvaerner Pulping Tech | Oxygen delignification of cellulose pulp into a high pressure part and a low pressure part |
FI122812B (en) | 2007-06-15 | 2012-07-13 | Andritz Oy | A method for treating fluid flows at a pulp mill |
Citations (11)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US3536577A (en) * | 1963-07-12 | 1970-10-27 | Hooker Chemical Corp | Bleaching of cellulosic materials with chlorine dioxide |
US3652385A (en) * | 1969-05-13 | 1972-03-28 | Mo Och Domsjoe Ab | Process for treating cellulosic materials from which metal ions have been removed with alkali and oxygen in the presence of complex magnesium salts |
US3725194A (en) * | 1967-06-20 | 1973-04-03 | South Africa Pulp And Paper In | Treatment of alkaline pulp with an acidic medium followed by oxygen bleaching and delignification |
US4507172A (en) * | 1982-09-16 | 1985-03-26 | St. Regis Paper Company | Kraft pulping process |
US5034094A (en) * | 1987-11-06 | 1991-07-23 | Kurple Kenneth R | Method of converting inorganic materials from kraft pulping liquor into pulping chemicals without passing them through a recovery furnace |
WO1991011554A1 (en) * | 1990-01-31 | 1991-08-08 | Eka Nobel Ab | Process for bleaching of ligno-cellulosic material |
WO1996012063A1 (en) * | 1994-10-13 | 1996-04-25 | Ahlstrom Machinery Oy | Method for removal of hexenuronic acid groups in cellulose pulp by heat treatment |
US5656130A (en) * | 1995-04-28 | 1997-08-12 | Union Camp Holding, Inc. | Ambient temperature pulp bleaching with peroxyacid salts |
EP0831170A2 (en) * | 1994-06-27 | 1998-03-25 | Champion International Corporation | Improved process for recycling bleach plant filtrate |
WO1998021400A1 (en) * | 1996-11-08 | 1998-05-22 | Sunds Defibrator Industries Ab | Prebleaching of paperpulp before a peroxide bleaching stage |
EP0899374A1 (en) * | 1997-09-01 | 1999-03-03 | Oji Paper Co., Ltd. | Method of producing a bleached pulp |
Family Cites Families (1)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
BE1005800A3 (en) * | 1992-05-22 | 1994-02-01 | Solvay Interox | Method for the delignification and bleaching of a chemical paper pulp |
-
2000
- 2000-06-02 AU AU53177/00A patent/AU5317700A/en not_active Abandoned
- 2000-06-02 CA CA002376528A patent/CA2376528A1/en not_active Abandoned
- 2000-06-02 EP EP00938089A patent/EP1244840A4/en not_active Withdrawn
- 2000-06-02 WO PCT/US2000/015263 patent/WO2000075420A1/en not_active Application Discontinuation
Patent Citations (11)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US3536577A (en) * | 1963-07-12 | 1970-10-27 | Hooker Chemical Corp | Bleaching of cellulosic materials with chlorine dioxide |
US3725194A (en) * | 1967-06-20 | 1973-04-03 | South Africa Pulp And Paper In | Treatment of alkaline pulp with an acidic medium followed by oxygen bleaching and delignification |
US3652385A (en) * | 1969-05-13 | 1972-03-28 | Mo Och Domsjoe Ab | Process for treating cellulosic materials from which metal ions have been removed with alkali and oxygen in the presence of complex magnesium salts |
US4507172A (en) * | 1982-09-16 | 1985-03-26 | St. Regis Paper Company | Kraft pulping process |
US5034094A (en) * | 1987-11-06 | 1991-07-23 | Kurple Kenneth R | Method of converting inorganic materials from kraft pulping liquor into pulping chemicals without passing them through a recovery furnace |
WO1991011554A1 (en) * | 1990-01-31 | 1991-08-08 | Eka Nobel Ab | Process for bleaching of ligno-cellulosic material |
EP0831170A2 (en) * | 1994-06-27 | 1998-03-25 | Champion International Corporation | Improved process for recycling bleach plant filtrate |
WO1996012063A1 (en) * | 1994-10-13 | 1996-04-25 | Ahlstrom Machinery Oy | Method for removal of hexenuronic acid groups in cellulose pulp by heat treatment |
US5656130A (en) * | 1995-04-28 | 1997-08-12 | Union Camp Holding, Inc. | Ambient temperature pulp bleaching with peroxyacid salts |
WO1998021400A1 (en) * | 1996-11-08 | 1998-05-22 | Sunds Defibrator Industries Ab | Prebleaching of paperpulp before a peroxide bleaching stage |
EP0899374A1 (en) * | 1997-09-01 | 1999-03-03 | Oji Paper Co., Ltd. | Method of producing a bleached pulp |
Non-Patent Citations (2)
Title |
---|
ROBITAILLE M A: "HYDROGEN PEROXIDE: A VERSATILE BLEACHING AGENT" PULP AND PAPER CANADA, ST LAURENT, CA, vol. 89, no. 12, 1988, pages 167-170, XP002930534 * |
See also references of WO0075420A1 * |
Also Published As
Publication number | Publication date |
---|---|
CA2376528A1 (en) | 2000-12-14 |
AU5317700A (en) | 2000-12-28 |
WO2000075420A1 (en) | 2000-12-14 |
EP1244840A4 (en) | 2003-04-16 |
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