CA1261182A - Method for treating stock for paper making - Google Patents
Method for treating stock for paper makingInfo
- Publication number
- CA1261182A CA1261182A CA000498982A CA498982A CA1261182A CA 1261182 A CA1261182 A CA 1261182A CA 000498982 A CA000498982 A CA 000498982A CA 498982 A CA498982 A CA 498982A CA 1261182 A CA1261182 A CA 1261182A
- Authority
- CA
- Canada
- Prior art keywords
- suspension
- percent
- consistency
- chest
- cellulosic material
- 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
Links
Classifications
-
- D—TEXTILES; PAPER
- D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
- D21D—TREATMENT OF THE MATERIALS BEFORE PASSING TO THE PAPER-MAKING MACHINE
- D21D5/00—Purification of the pulp suspension by mechanical means; Apparatus therefor
-
- D—TEXTILES; PAPER
- D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
- D21D—TREATMENT OF THE MATERIALS BEFORE PASSING TO THE PAPER-MAKING MACHINE
- D21D5/00—Purification of the pulp suspension by mechanical means; Apparatus therefor
- D21D5/02—Straining or screening the pulp
-
- D—TEXTILES; PAPER
- D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
- D21D—TREATMENT OF THE MATERIALS BEFORE PASSING TO THE PAPER-MAKING MACHINE
- D21D5/00—Purification of the pulp suspension by mechanical means; Apparatus therefor
- D21D5/28—Tanks for storing or agitating pulp
Landscapes
- Engineering & Computer Science (AREA)
- Mechanical Engineering (AREA)
- Paper (AREA)
Abstract
ABSTRACT
An improved method for treating cellulosic material recovered from a discrefiner in a mechanical pulp making process. Latency removal is conducted at a medium consistency of from about 8 to 15 percent in a medium consistency pump after which the suspension is removed at the same consistency to the storage tank. Screening and cleaning then take place at a low consistency. The method affords efficiencies in the nature of reduced capital costs and energy consumption.
An improved method for treating cellulosic material recovered from a discrefiner in a mechanical pulp making process. Latency removal is conducted at a medium consistency of from about 8 to 15 percent in a medium consistency pump after which the suspension is removed at the same consistency to the storage tank. Screening and cleaning then take place at a low consistency. The method affords efficiencies in the nature of reduced capital costs and energy consumption.
Description
The present invention relates to the manufacture of mechanical pulp and, in particular, to the treatment of refined cellulosic material prior to its introduction to a paper machine.
In the manufacture of mechanical pulp, wood chips are conventionally reduced to a cellulosic fibrous material by processing in one or more so called refiner apparatuses. In such apparatuses, a pair of opposed parallel discs having attrition elements on their adjacent faces are adapted for relative rotation with respect to each other and are enclosed in a housing. The discs may each be rotated in opposite directions, or one disc may be fixed while the other is rotated.
Wood chips or like mater;al to be refined are usually introduced between the plates at their centers and are refined by being advanced across the closely spaced attrition elements by centrifugal force. Free steam is generated by this refining process, and adjacent to the outer peripheral edge of the discs the refined material is discharged along with this steam to a fluid conveying means which removes the stream of steam and refined fibrous material through a port in the refiner.
Cellulosic material recovered in this way from the refiner is typically treated to remove a condition known as latency. This condition is caused by the twisting action on the fibers during refining. The twisting action introduces kinks and curves into the fibers which are then fro~en lnto the fibers as they are cooled. After latency removal, the pulp is also screened to remove over len~th reject fibers and cleaned to remove other oversized material.
Conventionally, the cellulosic material removed from the refiner is mixed with steam at a consistency of from abou~ 35 to 50 percent. This material is then diluted to a consistency of 4 percent or less for removal of latency in a tank known as a latency tanX by agitation of the stock at a temperature of from about 70C to 90~. Typically, this suspension will be further diluted to a consistency of about 1.5 percent prior to screening and then diluted to about 0.7 percent prior to cleaning in a cyclone cleaning apparatus. Screening and cleaning may be repeated at such consistencies one or more times prior to dewatering and introducing the stock to the paper machine.
In the present inventlon, water is added to the cellulosic material recovered from the refiner to form a suspension having a medium consistency of . i3 rt ~,~
from about 8 to 15 percent rather than to a low consistency as was heretofore the practice. At this medium consistency, latency is removed in a medium consistency pump, after which the suspension is also screened at medium consistency and then introduced to a storage chest. Upon removal from the storage chest the suspension is diluted to a low consistency and is then introduced to a cyclone separator for cleaning. Dewatering then takes place, and after storage first in a pulp chest and then a machine chest, the stock is then introduced to a paper machine.
The present invention is further described with reference to the accompanying drawing which is a schematic illustration of apparatus used in the practice of a preferred embodiment of the method of the present invention.
Referring to the drawing, wood chips are introduced to refiner 10 by conveyor 12. A mixture o~ steam and cellulosic material is recovered from the refiner and is conveyed in line 14 to head pipe 16. This mixture is 35 to 50 percent by weight cellulosic material. Water is introduced to the head pipe 16 in line 17 to form a suspension with the cellulosic material. The consistency of the suspension is from about 8 to 15 percent and preferably about 12 percent.
By means of a medium consistency pump 1i3, the suspension is removed from the head pipe 16 through line 20 to storage chest 22. A suitable medium consistency pump is described in ~.S. Patent No. 4,410,337 and is commercially available from Kamyr, Inc. located at Glens Falls, New York. It is found that latency characteristics are removed when the medium consistency suspension passes through a medium consistency pump as at pump 18. Preferably, the temperature of the suspension during such latency removal is from 50 to 90C.
The medium consistency of the suspension is maintained in the storage chest, but on removal it is diluted by means of water introduced in line 24 to a low consistency of about 3 percent. This diluted suspension is then removed in line 26 to feed tank 2i3 from where it is then removed in line 30 to screen 32. Before bein~ introduced into this screen, the suspension is preferably diluted to a consistency of about 1.5 percent by water introduced in line 34.
It would, however, be possible to screen the suspension at a consistency in the range of 0.5 to 3.5 percent.
The suspension passing through screen 32 is removed in line 36 to cyclone separator 3~3, after being diluted by water introduced in line 40 to a ~2~
consistency of Erom about 0.5 to 1.2 percent and, preferably, about 0.7 percent. The suspension passing throu~h the cleaner is removed in line 42 to - slusher 44 for dewatering.
The reject flow from screen 32 is removed in line 46 to dewatering press 48. The flow containing materials separated in cleaner 38 is removed in line 50 to line 46 and press 48 and to sewer 52 in line 54. Water is removed in line 56 from this press to tank 58. Dewatered reject cellulosic material is then removed in conveyor 59 to refiner 60 for further refining. The further refined cellulosic material is removed from the refiner 62 at a consistency of from 35 to 50 percent in line 62 to a second head pipe 64 where the suspension is diluted with water added in line 66 to a consistency of from about 8 to 15 percent and, preferably, about 12 percent. By means of medium consistency pump 68 the suspension is removed from the head pipe 64 in line 70 to feed tank 28.
Water is removed from slusher 44 in line 72 to tank 58. Water recirculated from downstream sources is also added to tank 58 in line 74, and water is removed from this tank in line ~6 and is recirculated to lines 17, 24, 34 and 40.
A suspension having a consistency of from 2 to 4 percent is removed from slusher 44 in line 78 to pulp chest 80. From pulp chest 80, the suspension is removed in line 82 to machine chest 84. Water is added in line 86 to dilute the suspension in the machine chest to a consistency of from 1 to 2 percent.
The suspension i5 then removed from the machine chest in line 88 to the paper machine 90. Water is added in line 92 to dilute the suspension to a consistency of from 0.5 to 1.5 percent and, preferably, from 0.5 to 1 percent.
Water is removed from the paper machine in line 94 from which water is recirculated to lines 86 and 92. Water is also diverted from line 94 in line 96 to white water chest 98 from where water is recirculated in line 100 to line 94.
It should be understood that the term "suspension" as used herein refers to a system in which particles of cellulosic material are distributed generally throughout a liquid medium. The term "consistency" as used herein refers to the relative amount by weight of cellulosic material in a suspension.
Consistency is expressed herein as the percenta~e of the wei~ht of the entire suspension which is represented by cellulosic material. The term "medium consistency-- as used herein refers to a suspension which is from about 8 to about 15 percent. The term '`low consistency'` as used herein refers to a suspension which is from about 0.5 to about 3.5 percent.
It will be appreciated that there has been described a method for treating stock for paper making which affords substantial efficiencies in the nature of redu~ed capital costs and energy consumption. ~mong the specific advantages of this method is that it avoids the need to procure a latency chest and to heat the large amount Ot water conventionally retained in that chest to effect latency removal. It will also be appreciated that the medium density storage feature of the present invention allows flexibility in operating the upstream pulp making and downstream paper making machinery at difEerent rates without the necessity of using a large low consistency storage chest as was heretofore conventional.
Although the invention has been described herein with a certain degree of particularity, it is to be understood that the present disclosure has been made only as an example and that the scope of the invention is defined by what is hereinafter claimed.
In the manufacture of mechanical pulp, wood chips are conventionally reduced to a cellulosic fibrous material by processing in one or more so called refiner apparatuses. In such apparatuses, a pair of opposed parallel discs having attrition elements on their adjacent faces are adapted for relative rotation with respect to each other and are enclosed in a housing. The discs may each be rotated in opposite directions, or one disc may be fixed while the other is rotated.
Wood chips or like mater;al to be refined are usually introduced between the plates at their centers and are refined by being advanced across the closely spaced attrition elements by centrifugal force. Free steam is generated by this refining process, and adjacent to the outer peripheral edge of the discs the refined material is discharged along with this steam to a fluid conveying means which removes the stream of steam and refined fibrous material through a port in the refiner.
Cellulosic material recovered in this way from the refiner is typically treated to remove a condition known as latency. This condition is caused by the twisting action on the fibers during refining. The twisting action introduces kinks and curves into the fibers which are then fro~en lnto the fibers as they are cooled. After latency removal, the pulp is also screened to remove over len~th reject fibers and cleaned to remove other oversized material.
Conventionally, the cellulosic material removed from the refiner is mixed with steam at a consistency of from abou~ 35 to 50 percent. This material is then diluted to a consistency of 4 percent or less for removal of latency in a tank known as a latency tanX by agitation of the stock at a temperature of from about 70C to 90~. Typically, this suspension will be further diluted to a consistency of about 1.5 percent prior to screening and then diluted to about 0.7 percent prior to cleaning in a cyclone cleaning apparatus. Screening and cleaning may be repeated at such consistencies one or more times prior to dewatering and introducing the stock to the paper machine.
In the present inventlon, water is added to the cellulosic material recovered from the refiner to form a suspension having a medium consistency of . i3 rt ~,~
from about 8 to 15 percent rather than to a low consistency as was heretofore the practice. At this medium consistency, latency is removed in a medium consistency pump, after which the suspension is also screened at medium consistency and then introduced to a storage chest. Upon removal from the storage chest the suspension is diluted to a low consistency and is then introduced to a cyclone separator for cleaning. Dewatering then takes place, and after storage first in a pulp chest and then a machine chest, the stock is then introduced to a paper machine.
The present invention is further described with reference to the accompanying drawing which is a schematic illustration of apparatus used in the practice of a preferred embodiment of the method of the present invention.
Referring to the drawing, wood chips are introduced to refiner 10 by conveyor 12. A mixture o~ steam and cellulosic material is recovered from the refiner and is conveyed in line 14 to head pipe 16. This mixture is 35 to 50 percent by weight cellulosic material. Water is introduced to the head pipe 16 in line 17 to form a suspension with the cellulosic material. The consistency of the suspension is from about 8 to 15 percent and preferably about 12 percent.
By means of a medium consistency pump 1i3, the suspension is removed from the head pipe 16 through line 20 to storage chest 22. A suitable medium consistency pump is described in ~.S. Patent No. 4,410,337 and is commercially available from Kamyr, Inc. located at Glens Falls, New York. It is found that latency characteristics are removed when the medium consistency suspension passes through a medium consistency pump as at pump 18. Preferably, the temperature of the suspension during such latency removal is from 50 to 90C.
The medium consistency of the suspension is maintained in the storage chest, but on removal it is diluted by means of water introduced in line 24 to a low consistency of about 3 percent. This diluted suspension is then removed in line 26 to feed tank 2i3 from where it is then removed in line 30 to screen 32. Before bein~ introduced into this screen, the suspension is preferably diluted to a consistency of about 1.5 percent by water introduced in line 34.
It would, however, be possible to screen the suspension at a consistency in the range of 0.5 to 3.5 percent.
The suspension passing through screen 32 is removed in line 36 to cyclone separator 3~3, after being diluted by water introduced in line 40 to a ~2~
consistency of Erom about 0.5 to 1.2 percent and, preferably, about 0.7 percent. The suspension passing throu~h the cleaner is removed in line 42 to - slusher 44 for dewatering.
The reject flow from screen 32 is removed in line 46 to dewatering press 48. The flow containing materials separated in cleaner 38 is removed in line 50 to line 46 and press 48 and to sewer 52 in line 54. Water is removed in line 56 from this press to tank 58. Dewatered reject cellulosic material is then removed in conveyor 59 to refiner 60 for further refining. The further refined cellulosic material is removed from the refiner 62 at a consistency of from 35 to 50 percent in line 62 to a second head pipe 64 where the suspension is diluted with water added in line 66 to a consistency of from about 8 to 15 percent and, preferably, about 12 percent. By means of medium consistency pump 68 the suspension is removed from the head pipe 64 in line 70 to feed tank 28.
Water is removed from slusher 44 in line 72 to tank 58. Water recirculated from downstream sources is also added to tank 58 in line 74, and water is removed from this tank in line ~6 and is recirculated to lines 17, 24, 34 and 40.
A suspension having a consistency of from 2 to 4 percent is removed from slusher 44 in line 78 to pulp chest 80. From pulp chest 80, the suspension is removed in line 82 to machine chest 84. Water is added in line 86 to dilute the suspension in the machine chest to a consistency of from 1 to 2 percent.
The suspension i5 then removed from the machine chest in line 88 to the paper machine 90. Water is added in line 92 to dilute the suspension to a consistency of from 0.5 to 1.5 percent and, preferably, from 0.5 to 1 percent.
Water is removed from the paper machine in line 94 from which water is recirculated to lines 86 and 92. Water is also diverted from line 94 in line 96 to white water chest 98 from where water is recirculated in line 100 to line 94.
It should be understood that the term "suspension" as used herein refers to a system in which particles of cellulosic material are distributed generally throughout a liquid medium. The term "consistency" as used herein refers to the relative amount by weight of cellulosic material in a suspension.
Consistency is expressed herein as the percenta~e of the wei~ht of the entire suspension which is represented by cellulosic material. The term "medium consistency-- as used herein refers to a suspension which is from about 8 to about 15 percent. The term '`low consistency'` as used herein refers to a suspension which is from about 0.5 to about 3.5 percent.
It will be appreciated that there has been described a method for treating stock for paper making which affords substantial efficiencies in the nature of redu~ed capital costs and energy consumption. ~mong the specific advantages of this method is that it avoids the need to procure a latency chest and to heat the large amount Ot water conventionally retained in that chest to effect latency removal. It will also be appreciated that the medium density storage feature of the present invention allows flexibility in operating the upstream pulp making and downstream paper making machinery at difEerent rates without the necessity of using a large low consistency storage chest as was heretofore conventional.
Although the invention has been described herein with a certain degree of particularity, it is to be understood that the present disclosure has been made only as an example and that the scope of the invention is defined by what is hereinafter claimed.
Claims (8)
IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A method for treating cellulosic material recovered from a refiner during the production of mechanical pulp, comprising the steps of:
(a) adding water to said cellulosic material to form a suspension having a medium consistency of from about 8 percent to about 15 percent and introducing said suspension into a medium consistency pump in which latency characteristics in the cellulosic material are at least partially removed;
(b) then by means of said medium consistency pump, removing the medium consistency suspension formed in step (a) to a storage chest;
(c) then removing the medium consistency suspension stored in step (b) to a storage chest and diluting said suspension to a low consistency of from about 0.5 percent to about 3.5 percent and then screening said diluted, low consistency suspension to remove reject cellulosic material; and (d) then adjusting the consistency suspension screened in step (c) to from about 0.5 percent to about 1.5 percent and introducing said suspension to a paper machine.
(a) adding water to said cellulosic material to form a suspension having a medium consistency of from about 8 percent to about 15 percent and introducing said suspension into a medium consistency pump in which latency characteristics in the cellulosic material are at least partially removed;
(b) then by means of said medium consistency pump, removing the medium consistency suspension formed in step (a) to a storage chest;
(c) then removing the medium consistency suspension stored in step (b) to a storage chest and diluting said suspension to a low consistency of from about 0.5 percent to about 3.5 percent and then screening said diluted, low consistency suspension to remove reject cellulosic material; and (d) then adjusting the consistency suspension screened in step (c) to from about 0.5 percent to about 1.5 percent and introducing said suspension to a paper machine.
2. The method defined in claim 1 wherein in step (c) the screened suspension is then diluted to a consistency of from about 0.5 percent to about 1.2 percent and is treated in a cyclone separator.
3. The method recited in claim 2 wherein after step (c) the suspension is removed from the cyclone separator and is dewatered to a consistency of from about 2 percent to about 4 percent and is then introduced to a pulp chest.
4. The method recited in claim 3 wherein prior to step (d) the suspension in the pulp chest is removed therefrom and is diluted to a consistency of from about 1 percent to about 2 percent and is then introduced to a machine chest.
5. The method recited in claim 4 wherein the suspension in the machine chest is removed therefrom and is diluted to a consistency of from about 0.5 percent to about 1.5 percent prior to being introduced to the paper machine.
6. The method recited in claim 1 wherein during step (c) a reject containing stream is recovered during screening and said stream is dewatered and introduced to a second refiner and then reintroduced to the medium consistency suspension formed in step (c) prior to screening.
7. The method recited in claim 6 wherein cellulosic material recovered from the second refiner undergoes latency removal prior to recycling.
8. The method recited in claim 1 wherein in step (a) the temperature of the suspension is from about 50°C to about 90°C when it is introduced to the medium consistency pump.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US71001285A | 1985-03-11 | 1985-03-11 | |
| US710,012 | 1985-03-11 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1261182A true CA1261182A (en) | 1989-09-26 |
Family
ID=24852248
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000498982A Expired CA1261182A (en) | 1985-03-11 | 1986-01-03 | Method for treating stock for paper making |
Country Status (2)
| Country | Link |
|---|---|
| CA (1) | CA1261182A (en) |
| SE (1) | SE8601062L (en) |
-
1986
- 1986-01-03 CA CA000498982A patent/CA1261182A/en not_active Expired
- 1986-03-07 SE SE8601062A patent/SE8601062L/en not_active Application Discontinuation
Also Published As
| Publication number | Publication date |
|---|---|
| SE8601062D0 (en) | 1986-03-07 |
| SE8601062L (en) | 1986-09-12 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |