CA1070536A - High temperature low consistency refining of thermo-mechanical pulp - Google Patents
High temperature low consistency refining of thermo-mechanical pulpInfo
- Publication number
- CA1070536A CA1070536A CA300,814A CA300814A CA1070536A CA 1070536 A CA1070536 A CA 1070536A CA 300814 A CA300814 A CA 300814A CA 1070536 A CA1070536 A CA 1070536A
- Authority
- CA
- Canada
- Prior art keywords
- refiner
- thermo
- refining
- inch
- intensity
- 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
- D21D1/00—Methods of beating or refining; Beaters of the Hollander type
- D21D1/20—Methods of refining
- D21D1/30—Disc mills
- D21D1/303—Double disc mills
-
- D—TEXTILES; PAPER
- D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
- D21D—TREATMENT OF THE MATERIALS BEFORE PASSING TO THE PAPER-MAKING MACHINE
- D21D1/00—Methods of beating or refining; Beaters of the Hollander type
- D21D1/20—Methods of refining
Landscapes
- Paper (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
A method of post-refining a thermo-mechanical pulp fiber suspension to reduce the high bulk characteristic of thermo-mechanical pulps and improve the paper quality made from such pulps. The pulp fiber suspension having a consistency of about 3 to 5% is refined at a temperature of 200 to 300°F under low intensity conditions. Optimum pulp development is thus obtained by using the lowest practical intensity at the highest practical operating tempera-ture.
-i-
A method of post-refining a thermo-mechanical pulp fiber suspension to reduce the high bulk characteristic of thermo-mechanical pulps and improve the paper quality made from such pulps. The pulp fiber suspension having a consistency of about 3 to 5% is refined at a temperature of 200 to 300°F under low intensity conditions. Optimum pulp development is thus obtained by using the lowest practical intensity at the highest practical operating tempera-ture.
-i-
Description
~070536 BA~K~GROUND OF THE INVEN'rlON
ield of thQ Invention ~ his invention is in the field of refining a thermo-mechan-ical p~llp immediately prior.to passing the same to the head box of a paper making maclline and involves re~ining the pulp at a high tempera-ture level and low intensity levels to reduce the bullc of the fibers and to reduce the amount of b.reakage of the fibers in the refiner.
DES~RlPr~ON OF T~E PRIOR ~RT
The thermo-mechanical pulping process has become wid~ly accepted in tlle paper industry for producing mechanical pulp from chips.
To a large extent, it has replaced the purely mechanical process in which the chips were ground by means of stone grinding wheels and cl~Qmical processes involving the use of sulfates or sulfites. Pulps produced by ~he thermo-mechanical pulping process exhil~it substantially higher strength properties than pulps produced by the stone groundwood prc)cess. While the chemical pulping methods produce a higher quality pulp,. they require extensive capital investment for high pressure treating vessels and the like.
One of the difficulties with thermo-mechanical pulp~, how-ever, is their higher bulk (lower d~nsity) in papers produced from such pulps. Tllis high bulk causes problems in printing and converting operations and may itsQlf be a pro~lem if'finished sheet tllickness, for a given basis weight, is crltical. Additionally, higher strength sl~eets can usually be obtained from a given pulp if the bulk is reduced, for example, by higher pressing pressures.
The processing of mechanicaI pulp suspensions by con-ventiona~ "post refining methods" in a refiner at a tow consistency of a~out 3 to 57c' has not proven completely satisfactory because of the .. .. _ _ ~070536 tendency to cut the fibers during refining. Although some reduction in bulk can be achieved in this way, the reduced fiber length caused by the broken fibers results in excessive freeness drop, and possible loss in sheet strength properties.
SUMMARY OF THE INVENTION
In accordance with the present invention, the fiber length reduction usually associated with post refining of mechanical pulps is reduced by increasing the refining temperature to the range of about 200 to 300F at which temperature the fibers are much more flexible and have less tendency to be cut in the refiner. In addition to the increased temperature, the refining is carried out under conditions of minimum practical intensity.
Specifically, the refiner is operated at an intensity of less than 40x10 applied horsepower per inch contacts per minute.
With conventional sized refiners, this means that the refiner operates at a peripheral speed in excess of 6000 feet per minute.
Additionally, a very fine bar pattern is used on the confronting stator and rotor plates so that high speed operation with this type of bar pattern on the plates results in maximum practical levels of inch-contacts per minute.
In a preferred form of the invention, the stator plates are composed of a synthetic resin such as a polysulfone resin, while the rotor plates are composed of steel. The widths of the alter-nating bars and grooves on both the rotor and stator surfaces should not exceed about 1/8 of an inch.
BRIEF DESCRIPTION OF T~E DRAWINGS
Other objects, features and advantages of the invention will be readily apparent from the following description of certain A
~07~)536 preferred embodiments thereof, taken in conjunction with the accompanying drawings, although variations and modifications may be effected without departing from the spirit and scope of the novel concepts of the disclosure, and in which:
Figure 1 is a partial block diagram illustrating some of the steps which may precede the post-refining operation with which the present invention is concerned;
Figure 2 is a fragmentary view with portions broken away to illustrate the interior of a refiner which can be used for the purposes of the invention; and Figure 3 is a greatly enlarged fragmentary cross-sectional view of the confronting rotor and stator plates which form the preferred embodiments of the invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Figure 1 of the drawings illustrates a flow diagram of a typical sequence which can include the post-refining step of the present invention. Specifically, the stock may be treated in one or more refiners lQ and then passed to one or more mixing chests 11 where suitable additives such as clay and the like may be added through a line 12. The thus treated stock is then passed to one or more machine chests 13 and ultimately to a post refiner 14, the details of which will be subsequently described. The stock entering the post refiner 14 is a suspension having a consistency of 3 to 5~. The thermo-mechanical pulp is characterized by the presence of softened lignin and by substantial freedom from chemical residues. In the post refiner stage 14, the stock is treated at a temperature of 200 to 300~F, and the refiner operates at an intensity of less than 40xlO 4 horsepower/inch contacts/
minute. Preferably, the intensity is less th~n 15xlO horse-power/inch contacts/minute.
A
107~53~
Conventional refi1-ers all act OIl tl~e fil)ers J~y means of at-trition. 1`1~re arc various types of refine-r config~Iratiolls, but most of tIlem make use of metal attrition members in tIle form of bars.
The intensIty of rcfining is defined as the net refining power divided by the number of b,lr crossings per unit time. Since the refining action of the fil~er takes place at the leading edge of the filling clement, the numher of inch contacts/millute can be delermilled from the following:
IncIl contacts/minute ~ Total length of bars in rotor x total length of b~rs in stator x refiner speed in rpm A tyI~icaI refiner which can be used for the purpos~s of the present invention is illustrated in Figure 2 of the drawings. It includes a ~ase 15 on whicII there is mounted a shaft 16 supported for rotation in a beariIlg 17. The shaft is driven from a coupling 18 con-nected to a suitable motor (not shown). I`he stocl; is introduced illto an inlet 19 and then flows into a refining cavity 20 whereupon the ~tock flow is~plit up by passing through a pair of perforated rotor clements 21 and 22 secured to a rotating head 23. Details of such rotor ~lements will be found described in U.S. Patent No. 3,438,586.
The rotor elements 21 and 22 are in confronting relation with stator plates 24 and 2S on opposed sides tllereof. The spacings between the rotor plates and the stator pl~tes is ~djusted by means of a worm gear 2~ which operates in conjunction with an adjllsting scrPw 27 W}1iCh in turn is connected to a gear motor 2~.
~ more clet~iIe~ view of the refiner plates is set forth in I~igure 3 of the drawil1gs. ~s illustrated in th~t fi~ure, Ih~
107~536 the rotor plate 22 is provided with a series of alternating bars 29 and grooves 30, the widths of the bars and grooves not exceeding 1/8 inch. Similarly, the stator 25 is provided with ribs 31 and grooves 32 in which the widths of the bars and the grooves do not exceed 1/8 inch. In the preferred form of the present invention, the rotor plate 22 is composed of stainless steel and the stator plate 25 is composed of a synthetic resin such as a polysulfone resin.
Fiber length reduction which is achieved in normal low consistency "post refining" of mechanical pulps can be attributed to the relatively high stiffness of the fiber. At normal refining temperatures of 110 to 140F, the brittle fibers are fractured when impacted by the impinging edges of the refiner. In accordance with the present invention, the refiner is operated at an increased temperature so that the lignin softening temperature is approached or exceeded. At these higher temperatures, the fibers are much more flexible and have a tendency to be cut in the refiner.
To further reduce fiber damage, the high temperature processing is carried out under conditions of minimum practical intensity in the refiner. To minimize the intensity, the refiner is operated at relatively high peripheral speeds, in excess of about 6,000 feet/minute. This high speed, coupled with the very fine pattern of bars in the stator and rotor results in maximum practical levels of inch-contacts/minute. Consequently, when relatively low power is applied to the refiner, the ~i'~
intensity will be at t~le lowest practical level.
Since the refiner operation is at relatively high speed, a considerable circulatillg load due to hydraulic losses will exist. This load is reduce(l sul)stantially by reducing the draft of the rotor plates, and this reduced draft becomes practical because of the -lower wear rate of the steel rotor whell operated against a synthetic resin stator. This reduction iJl load, tl~ere~ore, contributes to power savings.
~ s an i1lustration of the differences involved between the operation of the refiner according to the present invention and con-ventional practice, it might be noted that the normal operation of a 42 inch diameter xefiner makes use of bars alld grooves which are 3/16 inch in width, a rotational speed of about 514 rpm, and a net applied horsepower of 600. ln the refining operation of the present invention, the bar and groove widtll is reduced to 1/8 inch or less, the rotational speed of at least 600 rpm is used, and the net applied hor~epower is 300 or less.
It should l~e evident that v~rious modifications can be made to the described embodiments without departing from the- scope o~ the present invention.
.
. ~. . .
ield of thQ Invention ~ his invention is in the field of refining a thermo-mechan-ical p~llp immediately prior.to passing the same to the head box of a paper making maclline and involves re~ining the pulp at a high tempera-ture level and low intensity levels to reduce the bullc of the fibers and to reduce the amount of b.reakage of the fibers in the refiner.
DES~RlPr~ON OF T~E PRIOR ~RT
The thermo-mechanical pulping process has become wid~ly accepted in tlle paper industry for producing mechanical pulp from chips.
To a large extent, it has replaced the purely mechanical process in which the chips were ground by means of stone grinding wheels and cl~Qmical processes involving the use of sulfates or sulfites. Pulps produced by ~he thermo-mechanical pulping process exhil~it substantially higher strength properties than pulps produced by the stone groundwood prc)cess. While the chemical pulping methods produce a higher quality pulp,. they require extensive capital investment for high pressure treating vessels and the like.
One of the difficulties with thermo-mechanical pulp~, how-ever, is their higher bulk (lower d~nsity) in papers produced from such pulps. Tllis high bulk causes problems in printing and converting operations and may itsQlf be a pro~lem if'finished sheet tllickness, for a given basis weight, is crltical. Additionally, higher strength sl~eets can usually be obtained from a given pulp if the bulk is reduced, for example, by higher pressing pressures.
The processing of mechanicaI pulp suspensions by con-ventiona~ "post refining methods" in a refiner at a tow consistency of a~out 3 to 57c' has not proven completely satisfactory because of the .. .. _ _ ~070536 tendency to cut the fibers during refining. Although some reduction in bulk can be achieved in this way, the reduced fiber length caused by the broken fibers results in excessive freeness drop, and possible loss in sheet strength properties.
SUMMARY OF THE INVENTION
In accordance with the present invention, the fiber length reduction usually associated with post refining of mechanical pulps is reduced by increasing the refining temperature to the range of about 200 to 300F at which temperature the fibers are much more flexible and have less tendency to be cut in the refiner. In addition to the increased temperature, the refining is carried out under conditions of minimum practical intensity.
Specifically, the refiner is operated at an intensity of less than 40x10 applied horsepower per inch contacts per minute.
With conventional sized refiners, this means that the refiner operates at a peripheral speed in excess of 6000 feet per minute.
Additionally, a very fine bar pattern is used on the confronting stator and rotor plates so that high speed operation with this type of bar pattern on the plates results in maximum practical levels of inch-contacts per minute.
In a preferred form of the invention, the stator plates are composed of a synthetic resin such as a polysulfone resin, while the rotor plates are composed of steel. The widths of the alter-nating bars and grooves on both the rotor and stator surfaces should not exceed about 1/8 of an inch.
BRIEF DESCRIPTION OF T~E DRAWINGS
Other objects, features and advantages of the invention will be readily apparent from the following description of certain A
~07~)536 preferred embodiments thereof, taken in conjunction with the accompanying drawings, although variations and modifications may be effected without departing from the spirit and scope of the novel concepts of the disclosure, and in which:
Figure 1 is a partial block diagram illustrating some of the steps which may precede the post-refining operation with which the present invention is concerned;
Figure 2 is a fragmentary view with portions broken away to illustrate the interior of a refiner which can be used for the purposes of the invention; and Figure 3 is a greatly enlarged fragmentary cross-sectional view of the confronting rotor and stator plates which form the preferred embodiments of the invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Figure 1 of the drawings illustrates a flow diagram of a typical sequence which can include the post-refining step of the present invention. Specifically, the stock may be treated in one or more refiners lQ and then passed to one or more mixing chests 11 where suitable additives such as clay and the like may be added through a line 12. The thus treated stock is then passed to one or more machine chests 13 and ultimately to a post refiner 14, the details of which will be subsequently described. The stock entering the post refiner 14 is a suspension having a consistency of 3 to 5~. The thermo-mechanical pulp is characterized by the presence of softened lignin and by substantial freedom from chemical residues. In the post refiner stage 14, the stock is treated at a temperature of 200 to 300~F, and the refiner operates at an intensity of less than 40xlO 4 horsepower/inch contacts/
minute. Preferably, the intensity is less th~n 15xlO horse-power/inch contacts/minute.
A
107~53~
Conventional refi1-ers all act OIl tl~e fil)ers J~y means of at-trition. 1`1~re arc various types of refine-r config~Iratiolls, but most of tIlem make use of metal attrition members in tIle form of bars.
The intensIty of rcfining is defined as the net refining power divided by the number of b,lr crossings per unit time. Since the refining action of the fil~er takes place at the leading edge of the filling clement, the numher of inch contacts/millute can be delermilled from the following:
IncIl contacts/minute ~ Total length of bars in rotor x total length of b~rs in stator x refiner speed in rpm A tyI~icaI refiner which can be used for the purpos~s of the present invention is illustrated in Figure 2 of the drawings. It includes a ~ase 15 on whicII there is mounted a shaft 16 supported for rotation in a beariIlg 17. The shaft is driven from a coupling 18 con-nected to a suitable motor (not shown). I`he stocl; is introduced illto an inlet 19 and then flows into a refining cavity 20 whereupon the ~tock flow is~plit up by passing through a pair of perforated rotor clements 21 and 22 secured to a rotating head 23. Details of such rotor ~lements will be found described in U.S. Patent No. 3,438,586.
The rotor elements 21 and 22 are in confronting relation with stator plates 24 and 2S on opposed sides tllereof. The spacings between the rotor plates and the stator pl~tes is ~djusted by means of a worm gear 2~ which operates in conjunction with an adjllsting scrPw 27 W}1iCh in turn is connected to a gear motor 2~.
~ more clet~iIe~ view of the refiner plates is set forth in I~igure 3 of the drawil1gs. ~s illustrated in th~t fi~ure, Ih~
107~536 the rotor plate 22 is provided with a series of alternating bars 29 and grooves 30, the widths of the bars and grooves not exceeding 1/8 inch. Similarly, the stator 25 is provided with ribs 31 and grooves 32 in which the widths of the bars and the grooves do not exceed 1/8 inch. In the preferred form of the present invention, the rotor plate 22 is composed of stainless steel and the stator plate 25 is composed of a synthetic resin such as a polysulfone resin.
Fiber length reduction which is achieved in normal low consistency "post refining" of mechanical pulps can be attributed to the relatively high stiffness of the fiber. At normal refining temperatures of 110 to 140F, the brittle fibers are fractured when impacted by the impinging edges of the refiner. In accordance with the present invention, the refiner is operated at an increased temperature so that the lignin softening temperature is approached or exceeded. At these higher temperatures, the fibers are much more flexible and have a tendency to be cut in the refiner.
To further reduce fiber damage, the high temperature processing is carried out under conditions of minimum practical intensity in the refiner. To minimize the intensity, the refiner is operated at relatively high peripheral speeds, in excess of about 6,000 feet/minute. This high speed, coupled with the very fine pattern of bars in the stator and rotor results in maximum practical levels of inch-contacts/minute. Consequently, when relatively low power is applied to the refiner, the ~i'~
intensity will be at t~le lowest practical level.
Since the refiner operation is at relatively high speed, a considerable circulatillg load due to hydraulic losses will exist. This load is reduce(l sul)stantially by reducing the draft of the rotor plates, and this reduced draft becomes practical because of the -lower wear rate of the steel rotor whell operated against a synthetic resin stator. This reduction iJl load, tl~ere~ore, contributes to power savings.
~ s an i1lustration of the differences involved between the operation of the refiner according to the present invention and con-ventional practice, it might be noted that the normal operation of a 42 inch diameter xefiner makes use of bars alld grooves which are 3/16 inch in width, a rotational speed of about 514 rpm, and a net applied horsepower of 600. ln the refining operation of the present invention, the bar and groove widtll is reduced to 1/8 inch or less, the rotational speed of at least 600 rpm is used, and the net applied hor~epower is 300 or less.
It should l~e evident that v~rious modifications can be made to the described embodiments without departing from the- scope o~ the present invention.
.
. ~. . .
Claims (6)
OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. The method of refining a thermo-mechanical pulp fiber suspension in which the fibers are characterized by the presence of softened lignin and being substantially free from chemical residues which comprises refining such a suspension having a consistency of 3 to 5% at a temperature of 200 to 300°F in a refiner operating at an intensity of less than 40x10 4 horsepower/
inch contacts/minute.
inch contacts/minute.
2, The method of claim 1 in which said refiner is a disk-type refiner.
3. The method of claim 1 in which said refiner operates at an intensity of less than 15x10-4 horsepower/inch contacts/minute.
4. The method of claim 1 in which said refiner includes confronting rotor and stator surfaces each of which has a series alternating bars and grooves, the widths of said bars and grooves in each instance not exceeding 1/8 inch.
5. The method of claim 4 in which said rotor surfaces are composed of steel and said stator surfaces are composed of a synthetic resin.
6. The method of claim 1 in which said refiner operates at a peripheral speed in excess of 6,000 feet/minute.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US80451877A | 1977-06-08 | 1977-06-08 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1070536A true CA1070536A (en) | 1980-01-29 |
Family
ID=25189165
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA300,814A Expired CA1070536A (en) | 1977-06-08 | 1978-04-10 | High temperature low consistency refining of thermo-mechanical pulp |
Country Status (9)
| Country | Link |
|---|---|
| JP (1) | JPS546904A (en) |
| BR (1) | BR7802948A (en) |
| CA (1) | CA1070536A (en) |
| DE (1) | DE2825193C3 (en) |
| ES (1) | ES470123A1 (en) |
| FI (1) | FI63269C (en) |
| FR (1) | FR2393881A1 (en) |
| GB (1) | GB1591777A (en) |
| SE (1) | SE7805307L (en) |
Families Citing this family (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS60152699U (en) * | 1985-02-18 | 1985-10-11 | ベロイト コ−ポレ−ション | Post-stage refiner |
| SE463821B (en) * | 1986-02-11 | 1991-01-28 | Kamyr Ab | PROCEDURE TO REDUCE ENERGY CONSUMPTION BY REFINING A MIXTURE OR SUSPENSION OF FIBER MATERIAL |
Family Cites Families (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US2008892A (en) * | 1932-03-29 | 1935-07-23 | Defibrator Ab | Method of manufacture of pulp |
| US2791503A (en) * | 1952-05-08 | 1957-05-07 | Champion Paper & Fibre Co | Process for producing semichemical pulp |
| SE341322B (en) * | 1968-04-02 | 1971-12-20 | Defibrator Ab |
-
1978
- 1978-04-10 CA CA300,814A patent/CA1070536A/en not_active Expired
- 1978-05-05 GB GB17927/78A patent/GB1591777A/en not_active Expired
- 1978-05-10 BR BR7802948A patent/BR7802948A/en unknown
- 1978-05-10 SE SE7805307A patent/SE7805307L/en unknown
- 1978-05-23 ES ES470123A patent/ES470123A1/en not_active Expired
- 1978-05-26 FI FI781682A patent/FI63269C/en not_active IP Right Cessation
- 1978-05-31 FR FR787816202A patent/FR2393881A1/en active Granted
- 1978-06-08 JP JP6840578A patent/JPS546904A/en active Pending
- 1978-06-08 DE DE2825193A patent/DE2825193C3/en not_active Expired
Also Published As
| Publication number | Publication date |
|---|---|
| FI63269B (en) | 1983-01-31 |
| FR2393881B1 (en) | 1982-09-17 |
| FR2393881A1 (en) | 1979-01-05 |
| FI63269C (en) | 1983-05-10 |
| FI781682A (en) | 1978-12-09 |
| SE7805307L (en) | 1978-12-09 |
| DE2825193B2 (en) | 1980-06-04 |
| BR7802948A (en) | 1979-02-28 |
| GB1591777A (en) | 1981-06-24 |
| ES470123A1 (en) | 1979-10-01 |
| DE2825193C3 (en) | 1981-02-05 |
| DE2825193A1 (en) | 1978-12-21 |
| JPS546904A (en) | 1979-01-19 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |