CA2038651C - Method and apparatus for bleaching pulps - Google Patents
Method and apparatus for bleaching pulpsInfo
- Publication number
- CA2038651C CA2038651C CA 2038651 CA2038651A CA2038651C CA 2038651 C CA2038651 C CA 2038651C CA 2038651 CA2038651 CA 2038651 CA 2038651 A CA2038651 A CA 2038651A CA 2038651 C CA2038651 C CA 2038651C
- Authority
- CA
- Canada
- Prior art keywords
- materials
- fibrous
- bleaching
- feed hopper
- continuously
- 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.)
- Expired - Fee Related
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
- D21C9/1026—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
- D21C9/10—Bleaching ; Apparatus therefor
Landscapes
- Life Sciences & Earth Sciences (AREA)
- Engineering & Computer Science (AREA)
- Wood Science & Technology (AREA)
- Paper (AREA)
Abstract
This invention relates to a method and an apparatus for continuously bleaching fibrous lignocellulosic materials, for example wood pulps, in which the materials pre-impregnated with bleaching chemicals, form a continuous flow; the said materials being introduced by means of a feed hopper and a screwfeeder into a microwave cavity, heated and bleached by a supply of microwave energy and, after the completion of the heating, delivered from the said cavity into a retention chute where the bleaching action continues until its completion and, after the completion of bleaching, delivered from the bottom of said retention chute for further processing.
Description
: .
2~3865 1 METHOD AND APPARATUS FOR BLEACHING PULPS .:
.
BACKGROUND OF THE INVENTION
There is an increasing tendency toward the use of higher brigthness hign-yield pulps and mechanical pulps, particulary in the printing-writing paper are~. The production of such pulps requires the use of hydrogen peroxide bleaching formulations.
Because of the increasing costs associated with these chemicals, it is importa~t to achieve maximum chemical utilization in the bleaching process. One of the ~ays to improve this efficiency is to increase the beaching consistencies used from the-~dium consistency range (10-15%) to a high consistency range (> 20%), since it has lon;~-been recognized that bleaching efficiency increases as the consistency of the pulp inc,reases.
As the consistency of the pulp being bleached increases, the mechanical p~oblem of uniform application of the bleach liquor increases. Nonuniform application of the bleach liquor can cause marbling, or overbleached and underbleached spots :of the . ~ bleached pulp. There are several devices developed to overcome the mixing problem, such as the Frotapulper, Hobar Mixer, Micar Mixer, and Andritz HC Mixer which are known to the pulp and paper industry. Other approaches are also developed to-ln~prove the mixing of pulp with bleach liquor, for example, the dilution-extraction method by which the bleaching involves application of excess bleach liquor to the puf,~ and pressing out an excess liquor.
Although the problem of nonuniform mixing of the bleach liquor and the pulp at high consistency can be minimi7~d by the aforesaid approaches, there exists aproblem of heating very high consistency-pulp, e.g. at 30-45% range, because inEthese high consistencies the pulp fibers are aggregated into fiocs which are generally~-~ surrounded by a gas. The presence of gas in the pulp coupled with the poor the~nal 2~651 conduction properties of wood fibers makes heat transfer difficult and thus p~oduces nonuniform heating and decreased brightness and reduced production rate.
In a pulp bleaching process, the heating of pulp suspensions can be usually achieved either by electric heating or by indirect steam heating. However, -~ the consistency of pulp increases, the heating efficiency of these methods decreasesi These methods do not meet the demands of high consistency bleaching to guar~.ntee a satisfactory efficiency of bleaching. Primarily, this is due to the fact that the- heat transfer in a high-consistency pulp is greatly reduced.
The invention has for its object to eliminate the above-mentioned drawbacks in heating, improve the bleaching uniformity of the entire charge of pulp, and redpce the energy requirement in bleaching.
GENERAL DESCRIPTION OF THE INVENTION
According to this invention, it is possible to improve the heating and bleachingefficiency of high-consistency pulps, and reduce bleaching time, by using Illi~wave irradiation which can generate heat within the buLk of material and depends little on the thermal characteristics of the material. The presence of gas in the high-consistenc~ pulps should have no effect on microwave heating since the former is Ll~lsi)~enL to microwaves.
A constructional example of the subject of the invention is illustràted in simplified form in the drawing, which shows a vertical section through a hopper for feeding fibrous materials to be treated, a feed screw for conveying the fibrous m~-t~ri~l.c from the feed hopper into a microwave cavity where the fibrous m~t~ri:~1.c are irradiated by microwave energy, and a retention chute for receiving the heated fibrous m~t~ri~l.c delivered from the microwave chamber and for allowing the bleaching actions.within 2~3865 ~
the heated fibrous materials to complete. After a period of retention required for optimum bleaching the fibrous materials are discharged through the bottom of theretention chute for further processing such as washing and thickening.
SPECIFIC DESCRIPTION OF THE INVENTION
The illustrated arrangement 1 comprises a vertical cylindrical feed hopper 2, a feed screw 18 in a screw housing 16, a motor 20 which drives said feed scre~ 18. a microwave cavity 22, a magnetron 34 which provides microwave energy througn a wave guide 32, a vertical cylindrical retention chute 36 with a discharge slot 50.
In another aspect of the invention, a fibrous material pretreated with ble~chingagents, such as, in combination, of hydrogen peroxide or sodium hydrosulfite, ~odium hydroixde, sodium silicate, and chelating agents, etc., having a consistency rangm~ rrom about 10% up to about 70% on dry weight basis, can be fed via said cylindrical feed hopper 2 into said bleaching system 1. The bottom of said cylindrical feed hopper 2 has a rectangular slot 4 extending across the diameter of the bottom of said feed hopper 2, through which said fibrous material is fed to said feed screw 18. The bottom of said feed hopper 2 is connected to a screw housing 16.
The said cylindrical feed hopper 2 has a vertical stirrer 6 which has numerous horizontal bars 10 extending across the diameter of said feed hopper 2. Ihe saidhorizontal bars 10 are arranged in such a way that they are alternately spaced along the - shaft 12 of said stirrer 6 and are capable of causing a downward mouvement of said fibrous material to the bottom of said feed hopper 2. The lower end of said shaf~ 12 of said stirrer 6 has a scraping blade 14 extending across the diameter of the bottom.~f said feed hopper 2 and being capable of conveying said f1brous material through said retangular slot 4 and into said screw housing 16.
The said stirrer 6 is driven by a moter 8 being capable of driving said stirrer 6 at variable speeds.
After entering into said feed screw housing 16 via said rectangular slot 4, the said fibrous material is then fed by means of said feed screw 18 which is located inside Ssaid screw housing 16 and exlended across a microwave cavity 22. The said feed screw 18 is driven by a motor 20 located at one end of said screw housing 16.
The part 28 of said feed screw 18 extended outside of said microwave cavity 22 is made of metal of which the flange has a minimum clearance with said screw housing 16 in such a way that no leakage of microwaves would occur during the operation.10The said motor 20 is capable of driving said feed screw 18 at variable speeds.The other part 30 of said feed screw 18 located inside said microwave cavity 22 is made of material transparent to microwaves, such as Teflon or polyethylene.
The part 24 of said screw housing 16 located outside of said microwave cavity 22 and connected to the bottom of said feed hopper 2 is made of metal while the other 15part 26 located within said microwave cavity 22 is made of material transparent to microwaves, such as Teflon or polyethylene.
The said fibrous material fed by said feed screw 18 is exposed to microwave energy within said microwave cavity 22. The said microwave energy is supplied by a magnetron 34 via a wave guide 32. The microwave energy generated by said magnetron 2034 is capable of generating heat within said fibrous material and increasing the temperature of said fibrous material ranging from about 20C to about 50-100C, within a short time ranging from about 10 seconds to about 10 minutes.
The open end of said feed screw 18 is connected to a vertical cylindrical retention chute 36 into which said heated fibrous material falls by gravity. The said 25retention chute 36 is insulated and is capable of keeping said heated fibrous material at temperatures required for the bleaching reaction to complete, for example, 50 to ~0C.
~038~5 ~
The bottom of said retention chute 36 has a rectangular slot S0 extending acrossthe diameter of said bottom 48 of said relention chu~e 36. The said slot 50 has a movable cover 52 capable of regulating lhe discharge of said fibrous material.
The movement of the column of said fibrous material in said retention chute 36 is assisted by a vertical stirrer 38 which consists of a vertical shaft 44 and numerous horizontal bars 42 extending across the diameter of said retention chute 36. The said horizontal bars 42 are configurated along said shaft 44 in such a way that said horizontal bars 42 are capable of causing a downward movemenl of said fibrous material. Thelower end of said stirrer 38 has a scraping blade 46 which discharges said fibrous material through said discharge slot 50.
The said stirrer 38 is driven by a motor 40 being capable of driving said stirrer .-~- 38 at variable speeds.
.
BACKGROUND OF THE INVENTION
There is an increasing tendency toward the use of higher brigthness hign-yield pulps and mechanical pulps, particulary in the printing-writing paper are~. The production of such pulps requires the use of hydrogen peroxide bleaching formulations.
Because of the increasing costs associated with these chemicals, it is importa~t to achieve maximum chemical utilization in the bleaching process. One of the ~ays to improve this efficiency is to increase the beaching consistencies used from the-~dium consistency range (10-15%) to a high consistency range (> 20%), since it has lon;~-been recognized that bleaching efficiency increases as the consistency of the pulp inc,reases.
As the consistency of the pulp being bleached increases, the mechanical p~oblem of uniform application of the bleach liquor increases. Nonuniform application of the bleach liquor can cause marbling, or overbleached and underbleached spots :of the . ~ bleached pulp. There are several devices developed to overcome the mixing problem, such as the Frotapulper, Hobar Mixer, Micar Mixer, and Andritz HC Mixer which are known to the pulp and paper industry. Other approaches are also developed to-ln~prove the mixing of pulp with bleach liquor, for example, the dilution-extraction method by which the bleaching involves application of excess bleach liquor to the puf,~ and pressing out an excess liquor.
Although the problem of nonuniform mixing of the bleach liquor and the pulp at high consistency can be minimi7~d by the aforesaid approaches, there exists aproblem of heating very high consistency-pulp, e.g. at 30-45% range, because inEthese high consistencies the pulp fibers are aggregated into fiocs which are generally~-~ surrounded by a gas. The presence of gas in the pulp coupled with the poor the~nal 2~651 conduction properties of wood fibers makes heat transfer difficult and thus p~oduces nonuniform heating and decreased brightness and reduced production rate.
In a pulp bleaching process, the heating of pulp suspensions can be usually achieved either by electric heating or by indirect steam heating. However, -~ the consistency of pulp increases, the heating efficiency of these methods decreasesi These methods do not meet the demands of high consistency bleaching to guar~.ntee a satisfactory efficiency of bleaching. Primarily, this is due to the fact that the- heat transfer in a high-consistency pulp is greatly reduced.
The invention has for its object to eliminate the above-mentioned drawbacks in heating, improve the bleaching uniformity of the entire charge of pulp, and redpce the energy requirement in bleaching.
GENERAL DESCRIPTION OF THE INVENTION
According to this invention, it is possible to improve the heating and bleachingefficiency of high-consistency pulps, and reduce bleaching time, by using Illi~wave irradiation which can generate heat within the buLk of material and depends little on the thermal characteristics of the material. The presence of gas in the high-consistenc~ pulps should have no effect on microwave heating since the former is Ll~lsi)~enL to microwaves.
A constructional example of the subject of the invention is illustràted in simplified form in the drawing, which shows a vertical section through a hopper for feeding fibrous materials to be treated, a feed screw for conveying the fibrous m~-t~ri~l.c from the feed hopper into a microwave cavity where the fibrous m~t~ri:~1.c are irradiated by microwave energy, and a retention chute for receiving the heated fibrous m~t~ri~l.c delivered from the microwave chamber and for allowing the bleaching actions.within 2~3865 ~
the heated fibrous materials to complete. After a period of retention required for optimum bleaching the fibrous materials are discharged through the bottom of theretention chute for further processing such as washing and thickening.
SPECIFIC DESCRIPTION OF THE INVENTION
The illustrated arrangement 1 comprises a vertical cylindrical feed hopper 2, a feed screw 18 in a screw housing 16, a motor 20 which drives said feed scre~ 18. a microwave cavity 22, a magnetron 34 which provides microwave energy througn a wave guide 32, a vertical cylindrical retention chute 36 with a discharge slot 50.
In another aspect of the invention, a fibrous material pretreated with ble~chingagents, such as, in combination, of hydrogen peroxide or sodium hydrosulfite, ~odium hydroixde, sodium silicate, and chelating agents, etc., having a consistency rangm~ rrom about 10% up to about 70% on dry weight basis, can be fed via said cylindrical feed hopper 2 into said bleaching system 1. The bottom of said cylindrical feed hopper 2 has a rectangular slot 4 extending across the diameter of the bottom of said feed hopper 2, through which said fibrous material is fed to said feed screw 18. The bottom of said feed hopper 2 is connected to a screw housing 16.
The said cylindrical feed hopper 2 has a vertical stirrer 6 which has numerous horizontal bars 10 extending across the diameter of said feed hopper 2. Ihe saidhorizontal bars 10 are arranged in such a way that they are alternately spaced along the - shaft 12 of said stirrer 6 and are capable of causing a downward mouvement of said fibrous material to the bottom of said feed hopper 2. The lower end of said shaf~ 12 of said stirrer 6 has a scraping blade 14 extending across the diameter of the bottom.~f said feed hopper 2 and being capable of conveying said f1brous material through said retangular slot 4 and into said screw housing 16.
The said stirrer 6 is driven by a moter 8 being capable of driving said stirrer 6 at variable speeds.
After entering into said feed screw housing 16 via said rectangular slot 4, the said fibrous material is then fed by means of said feed screw 18 which is located inside Ssaid screw housing 16 and exlended across a microwave cavity 22. The said feed screw 18 is driven by a motor 20 located at one end of said screw housing 16.
The part 28 of said feed screw 18 extended outside of said microwave cavity 22 is made of metal of which the flange has a minimum clearance with said screw housing 16 in such a way that no leakage of microwaves would occur during the operation.10The said motor 20 is capable of driving said feed screw 18 at variable speeds.The other part 30 of said feed screw 18 located inside said microwave cavity 22 is made of material transparent to microwaves, such as Teflon or polyethylene.
The part 24 of said screw housing 16 located outside of said microwave cavity 22 and connected to the bottom of said feed hopper 2 is made of metal while the other 15part 26 located within said microwave cavity 22 is made of material transparent to microwaves, such as Teflon or polyethylene.
The said fibrous material fed by said feed screw 18 is exposed to microwave energy within said microwave cavity 22. The said microwave energy is supplied by a magnetron 34 via a wave guide 32. The microwave energy generated by said magnetron 2034 is capable of generating heat within said fibrous material and increasing the temperature of said fibrous material ranging from about 20C to about 50-100C, within a short time ranging from about 10 seconds to about 10 minutes.
The open end of said feed screw 18 is connected to a vertical cylindrical retention chute 36 into which said heated fibrous material falls by gravity. The said 25retention chute 36 is insulated and is capable of keeping said heated fibrous material at temperatures required for the bleaching reaction to complete, for example, 50 to ~0C.
~038~5 ~
The bottom of said retention chute 36 has a rectangular slot S0 extending acrossthe diameter of said bottom 48 of said relention chu~e 36. The said slot 50 has a movable cover 52 capable of regulating lhe discharge of said fibrous material.
The movement of the column of said fibrous material in said retention chute 36 is assisted by a vertical stirrer 38 which consists of a vertical shaft 44 and numerous horizontal bars 42 extending across the diameter of said retention chute 36. The said horizontal bars 42 are configurated along said shaft 44 in such a way that said horizontal bars 42 are capable of causing a downward movemenl of said fibrous material. Thelower end of said stirrer 38 has a scraping blade 46 which discharges said fibrous material through said discharge slot 50.
The said stirrer 38 is driven by a motor 40 being capable of driving said stirrer .-~- 38 at variable speeds.
Claims (6)
1. Apparatus for continuously bleaching fibrous lignocellulosic materials comprising in combination a vertically mounted cylindrical feed hopper; means in said feed hopper for continuously introducing fibrous lignocellulosic material impregnated with bleach liquor downward through said feed hopper; a feed screw for continuously conveying said treated fibrous lignocellulosic materials from said feed hopper into a heating section of said apparatus; a microwave cavity for continuouly and rapidly heating said impregnated lignocellulosic materials; a retention chute for retaining said heated lignocellulosic materials under bleaching conditions without further heating; means for continuously discharging bleached material from the bottom of said retention chute.
2. The apparatus combination of claim 1 in which said means in said feed hopper comprises a motorized stirrer with numerous horizontal bars and a scraping blade being capable of causing a downward movement of said impregnated fibrous materials through said feed hopper into said feed screw for continuously conveying said materials into said microwave cavity.
3. The apparatus combination of claim 1 in which said feed screw is located in a screw housing, extending across said microwave cavity. The part of said feed screw and said screw housing located within said microwave chamber are made of materials transparent to microwaves
4. The apparatus combination of claim 1 in which said microwave cavity is capable of raising the temperature of said impregnated fibrous materials up to about 100°C within from about 10 seconds to about 10 minutes.
5. The apparatus combination of claim 1 in which said retention chute comprises a motorized stirrer with numerous horizontal bars and a scraping blade being capable of causing a downward movement of said heated fibrous materials. The said retention chute is capable of keeping the temperature, about 50° to about 80°C, of said heated fibrous material suitable for bleaching ractions to continuously occur and capable of rataining said heated fibrous materials for an optimum period of time, about 10 to about 60 minutes, for the bleaching reactions to complete.
6. The apparatus combination of claim 1 in which said means for continuously discharging said bleached fibrous material from the bottom of said retention chute comprises a retangular slot equipped with a movable cover being capable of regulating the output of said bleached fibrous materials.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA 2038651 CA2038651C (en) | 1991-03-19 | 1991-03-19 | Method and apparatus for bleaching pulps |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA 2038651 CA2038651C (en) | 1991-03-19 | 1991-03-19 | Method and apparatus for bleaching pulps |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CA2038651A1 CA2038651A1 (en) | 1992-09-20 |
| CA2038651C true CA2038651C (en) | 1995-12-12 |
Family
ID=4147226
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA 2038651 Expired - Fee Related CA2038651C (en) | 1991-03-19 | 1991-03-19 | Method and apparatus for bleaching pulps |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA2038651C (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US11976416B2 (en) | 2019-02-07 | 2024-05-07 | Marinko Mikulic | Continuous process for production of cellulose pulp from grass-like feedstock |
Families Citing this family (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB2420542A (en) * | 2004-11-25 | 2006-05-31 | Kjell Ivar Kasin | Screw conveyor with microwave generator |
| CN101649572B (en) * | 2009-08-31 | 2011-03-16 | 华南理工大学 | Top unloader of pressure type upwash bleaching tower |
| DK3443159T3 (en) | 2016-04-15 | 2020-07-27 | Marinko MIKULIC | A CONTINUOUS PROCESS FOR THE MANUFACTURE OF CELLULOSE PULP |
-
1991
- 1991-03-19 CA CA 2038651 patent/CA2038651C/en not_active Expired - Fee Related
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US11976416B2 (en) | 2019-02-07 | 2024-05-07 | Marinko Mikulic | Continuous process for production of cellulose pulp from grass-like feedstock |
Also Published As
| Publication number | Publication date |
|---|---|
| CA2038651A1 (en) | 1992-09-20 |
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| US4363697A (en) | Method for medium consistency oxygen delignification of pulp | |
| FI67413C (en) | FOERFARANDE FOER BEHANDLING AV FINFOERDELAD FIBERHALTIG ELLER CELLULOSAHALTIG MASS SAMT ANORDNING FOER UTFOERANDE AV FOERFARANDET | |
| US4244778A (en) | Process for the chemical refining of cellulose pulp | |
| CA2265872C (en) | Method and apparatus for pulping with controlled heating to improve delignification and pulp strength | |
| CA2038651C (en) | Method and apparatus for bleaching pulps | |
| EP0112377B1 (en) | Ozone bleaching of cellulosic materials | |
| EP0515303B2 (en) | Method for ozone bleaching | |
| CA2450464C (en) | Four stage alkaline peroxide mechanical pulping | |
| NO179918C (en) | Process and apparatus for producing power mass | |
| CA1184709A (en) | Method and apparatus for oxygen delignification | |
| US4612088A (en) | Reactor to perform chemical reactions with a disintegrating disc | |
| FR2741638A1 (en) | CONTINUOUS PROCESS AND INSTALLATION FOR PREPARATION OF A CELLULOSE PASTE | |
| US20040200586A1 (en) | Four stage alkaline peroxide mechanical pulping | |
| DE69608910T2 (en) | DELIGNIFICATION OF A MEDIUM-CONSISTENCY PAPER-SELLED MATERIAL WITH OXYGEN | |
| JP2000515205A (en) | In particular, a method and apparatus for bleaching wood pulp containing waste paper | |
| US2963395A (en) | Process of bleaching lignocellulosic pulps | |
| WO2000050688A1 (en) | High pressure, high-speed primary and secondary refining | |
| RU2140475C1 (en) | Method and apparatus for continuous production of pulp | |
| CA1176408A (en) | Process for the oxygen delignification of pulp | |
| KR20220043942A (en) | Food Waste Treating Apparatus Having dry function and pellet forming function | |
| JPH0141441Y2 (en) | ||
| GB2265918A (en) | Method of and apparatus for producing cellulosic paper pulp | |
| CN214333340U (en) | Raw materials drying device for chemical production | |
| CN100567631C (en) | A kind of disc type heat dispersing method and device and application that is used for paper-making process | |
| CA1222156A (en) | Reactor to perform chemical reactions with dimensional reduction of solid materials |
Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| EEER | Examination request | ||
| MKLA | Lapsed |