CA1094761A - Cyclone separation in digester discharge - Google Patents
Cyclone separation in digester dischargeInfo
- Publication number
- CA1094761A CA1094761A CA264,775A CA264775A CA1094761A CA 1094761 A CA1094761 A CA 1094761A CA 264775 A CA264775 A CA 264775A CA 1094761 A CA1094761 A CA 1094761A
- Authority
- CA
- Canada
- Prior art keywords
- pulp
- knots
- shives
- pulp stock
- digester
- 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
- D21D5/18—Purification of the pulp suspension by mechanical means; Apparatus therefor with the aid of centrifugal force
- D21D5/24—Purification of the pulp suspension by mechanical means; Apparatus therefor with the aid of centrifugal force in cyclones
Abstract
ABSTRACT OF THE DISCLOSURE
A method and apparatus for the separation of knots and shives from pulp stock discharged from a continuous digester. Separation is performed by a cyclone separator.
The stored energy of the digester is utilized to obtain the necessary high density pulp velocity to achieve cyclone action. The separated components, knots, shives, and tramp material - and pulp fibers - are then treated separately by different devices depending upon final product desired, etc.
A method and apparatus for the separation of knots and shives from pulp stock discharged from a continuous digester. Separation is performed by a cyclone separator.
The stored energy of the digester is utilized to obtain the necessary high density pulp velocity to achieve cyclone action. The separated components, knots, shives, and tramp material - and pulp fibers - are then treated separately by different devices depending upon final product desired, etc.
Description
10!~47~;1 BACKGROUND AND SUMMARY OF THE INVENTION
The invention relates to a method and apparatus for the separation of knots, shives and/or tramp material from a continuous pulp digester discharge line. In continuous pulp processing systems, such as shown in U.S. Patent No. 3,427,218, it is conventional to subject the digested pulp, after dilution with water, to screening and refining operations for the purpose of removing unde~ired, coarse or non-digested material and/or tramp material. A conventional digester, though relatively efficient, does not normally reduce 100% of the wood chips or the like entering the digester so as to completely delignify the fibers. Consequently, the pulp discharged from a digester may contain up to 1% of undigested knots and possibly an additional 1% of small matchstick-like undigested particles known as "shivesn. Shives are wood chips or like particles that do not fully digest in the digester cooking stage because they were not fully impregnated in the liquor impregnation stage, either because they were too large to allow full internal liquor impregnation, they were of a different variety than was contemplated in digester design and liquor selection or all air was not steamed out of them prior to liquor impregnation. Tramp material is normally rocks or metal objects broken from tree chipping equipment that inadvertently are admitted to the aigestion system along with the cellulose chips.
In conventional screening operations to remove the knots, shives, etc. from the digested pulp, it is necessary to dilute the stock from its normal 10-20~ (approximately) by r 10~47fil weight consistency as discharged from the digester, to a consistency in the range of 1-4% (approximately). At these low consistencies, the stock is sufficiently diluted that it is possible to remove the knots and shives from the pulp stock by the use of various screening apparatus, after which the pulp must be again rethickened by means of deckers to consistencies in the range of 8-15% for storage and/or subsequent processing.
The screening operation is a wasteful one in that large amounts of water and electric power (for pumping the larger volumes of material) are consumed and much more machinery must be utilized to dilute, screen and thicken (in the vicinity of $2-3 million (U.S.) worth for a 500-1000 ton/day mill).
Dilution of the pulp material can be avoided through the use of one or more refiners (in series or parallel) at some convenient point in the digester discharge line (i.e., see our Canadian Patent No. 976,012, dated October 14, 1975, entitled "Method and Apparatus for Processing Pulp"). Refiners are devices with parallel plates which rotate relative to each other, both in opposite directions, or one being stationary and the other rotating, which plates may have protrusions or serrations formed on the faces thereof. ~he plates break the knots and shives to small fragments. Although this procedure does not result in the energy penalty associated with screening, since the broken up shives and knots have not been cooked, they cannot be bleached, and as such produce colored specks in paper produced from the pulp, and conse~uently a lower grade of paper.
Also, under some circumstances, it is possible that tramp material could harm the refiners, causing down-time thereof, or the tramp material could cause adverse effects on the final paper proauced.
~0~4761 According to the present invention, the problems inherent in each of the above conventional systems for removing knots and the like have been solved. According to the present invention, the energy already available in the pulp in the digester discharge line is utilized to achieve the separation of knots and the like from the digested pulp stock. The pulp stock in the discharge line is passed directly into a cyclone separator, wherein the heavier knots, shives and tramp material move by centrifugal force to the outside periphery of the cyclone to eventually migrate downwardly and out the bottom outlet of the cyclone, while the pulp fibers flow upwardly and out the cyclone central outlet pipe. Although the pulp stock is 10-20% in consistency, at high velocity (which is inherent in the digester discharge line) it becomes homogeneous, or more fluid. With fluid properties, it can be handled in conventional cyclone separators. Since cyclone separators require that the flowable materi~l be at very high velocity, their use usually is not practical for large volumes of high density material since the energy expended for accelerating the flowable ma~erial is enormous; however, according to the present invention, the flowable material is already at high velocity when it is discharged from the digester. Rather than letting (indeed effecting) this high-energy state material to dissipate, as is conventional in present digesting systems, the high-energy state is utilized to solve hitherto unsolved problems.
Once the knots and shives are separated from the pulp in the discharge line, they may be handled in one of several ways: Where the pulp is to be bleached, uncooked material may be passed through separators and washers ~o remove fibers and lOg4761 tramp material and then returned to the digester. Or, where the pulp is not to be bleached, uncooked material may be pa~sed back in line with the pulp after fragmentation tless energy is utilized than if all the pulp had to be passed through refiners).
It is the primary object of the present invention to provide for improved separation of knots, shives and the like from digested pulp stock, and to provide a more uniform grade of paper with less energy expenditure given a predetermined percentage of knots and shives in dige-~ter discharged pulp stock. This and other objects of the invention will become clear from an inspection of the detailed description of the inve~tion and from the appended claims.
BRIEF DESCRIPTION OF THE DRAWINGS
FIGURES la and lb are schematic showings of conventional prior art ways of dealing with knots and shives in digested pulp stock; and FIGURE 2 is a diagrammatic showing of exemplary apparatus according to the present invention.
DETAILED DESCRIPTION OF THE INVENTION
~onventional assemblies for digesting cellulose material and removing knots and shives therefrom are shown schematically in FIGURES la and lb. In the apparatus of FIGURE la, after chips have been treated in pre-impregnation vessel 12 and have been impregnated, cooked and washed in continuous digester 14, the resultant pulp stock passes through blow unit 16 to dilution station 18. At station 18, the pulp stock is thinned from about 10-20~ consistency to about 1-4%
consistency, the knots and shives are re~oved by screening apparatus 20 and deckers 22 or the like thicken the pulp back to about 8-15% consistency, whereupon it is passed to a further treatment station 24 for storage, bleaching or other operation steps. A great deal of water is consumed in diluting the pulp for screening and a great amount of energy is consumed in transporting the large volumes of material that ensue from the dilution process. Also, the dilution, screening and thickening equipment is relatively expensive.
When the conventional apparatus of FIGURE lb is utilized, from blow unit 16 the pulp stock is passed to a refiner 26. Extra refiners 26 can be utilized too, if desired, either arranged in series or in parallel with refiner 26. In refiner 26, the knots and shives are fragmented and pass with the rest of the pulp stock to further treatment station 24.
While relatively little energy is used in such an arrangement in comparison to the arrangement of FIGURE la, the final pulp stock has the uncooked knot and shive particles therein, and these particles will not bleach, but rather leave colored spots on the final paper produced. Also, all the pulp stock must pass through the refiners 26, not just the knots and shives, and tramp material in the pulp stock may shorten refiner life or have other adverse consequences.
Exemplary apparatus according to the present invention is shown in FIGURE 2, which apparatus does not have any of the drawbacks of the prior art apparatus. According to the present invention, chips are fed into chip bins 30 and are passed from there through chip meter 31 and low pressure feeder 32 into pre-steaming vessel 33. From vessel 33, they pass through chip chute 34 into high pressure feeder 35, and from there to pre-impregnation vessel 12. From vessel 12, the chips are fed to the top of continuous digester 14, which may be one such as shown in U.S. Patent No. 3,427,218. One or more flash tanks 36 are associated with the digester 14 and pre-steaming vessel 33.
Everything described so far is conventional.
After treatment (i.e., impregnation, cooking and washing) in digestex 14, the resultant pulp stock is passed through outlet 38 of digester 14. At this point, the pulp is in a high-energy state, a 10-20% (approximately) consistency material under a pressure as high as 200 PSIG. The pulp may pass through blow unit 16 and then is introduced tangentially into cyclone separator 40 of any suitable conventional type.
A blow unit 16 is only optional, there being no need to reduce the high-energy state of the pulp before introduction into cyclone 40, and the unit may be placed in line 42, if desired.
The material has fluid properties at this point and has high enough velocity so that cyclone separation thereof is practical.
~he pulp fibers are discharged through cyclone upper central outlet 42, while the knots, shives and tramp material are discharged through the lower outlet 44 since the heavi~r knots and shives move by centrifugal force to the outside periphery of the cyclone and eventually migrate downwardly.
After discharge through outlet 44 of cyclone separator 40, the knots, shives and the like can either be passed through line 45 to a conventional refiner 26 and then to blow tank 24 or through line 47 to a washer 51 to remove fibers and then directly back to the inlet to the chips bin 30. When tramp material is expected, separation means 43 for separating the 109`~76~
tramp material from the knots and shives should be utilized at outlet 44. Such means 43 may be of any conventional type, such as another cyclone separator, screening means or float and s~nk equipment. If the quality of material from outlet 44 is bad enough, all of it may be discarded.
When line 45 and refiner(s) 26 are utilized, the fragmented knots or shives pass through line 50 back to line 42 for transport to further treatment station 24. While line 50 would not normally be utilized when subsequent bleaching of the pulp stock was to be performed, the FIGURE 2 assembly, including line 50, is advantageous over the FIGURE lb arrangement when there is to be no subse~uent bleaching, since a lower volume of material passes through refiner(s) 26, and thus the refiner(s) may be smaller and less energy will be consumed thereby.
It will thus be seen that according to the method of the present invention, knots, shives and tramp material are separated from the pulp discharged from a continuous digester by passing the pulp through a cyclone separator, and the separated portions of the pulp are passed through different treatment stages.
While the invention has been herein shown and described in what is presently conceived to be the most practical and preferred embodiment, it will be apparent to those of ordinary skill in the art that many modifications may be made thereof within the scope of the invention, which scope is to be accorded the broadest interpretation of the appended claims so as to encompass all equivalent structures and methods.
The invention relates to a method and apparatus for the separation of knots, shives and/or tramp material from a continuous pulp digester discharge line. In continuous pulp processing systems, such as shown in U.S. Patent No. 3,427,218, it is conventional to subject the digested pulp, after dilution with water, to screening and refining operations for the purpose of removing unde~ired, coarse or non-digested material and/or tramp material. A conventional digester, though relatively efficient, does not normally reduce 100% of the wood chips or the like entering the digester so as to completely delignify the fibers. Consequently, the pulp discharged from a digester may contain up to 1% of undigested knots and possibly an additional 1% of small matchstick-like undigested particles known as "shivesn. Shives are wood chips or like particles that do not fully digest in the digester cooking stage because they were not fully impregnated in the liquor impregnation stage, either because they were too large to allow full internal liquor impregnation, they were of a different variety than was contemplated in digester design and liquor selection or all air was not steamed out of them prior to liquor impregnation. Tramp material is normally rocks or metal objects broken from tree chipping equipment that inadvertently are admitted to the aigestion system along with the cellulose chips.
In conventional screening operations to remove the knots, shives, etc. from the digested pulp, it is necessary to dilute the stock from its normal 10-20~ (approximately) by r 10~47fil weight consistency as discharged from the digester, to a consistency in the range of 1-4% (approximately). At these low consistencies, the stock is sufficiently diluted that it is possible to remove the knots and shives from the pulp stock by the use of various screening apparatus, after which the pulp must be again rethickened by means of deckers to consistencies in the range of 8-15% for storage and/or subsequent processing.
The screening operation is a wasteful one in that large amounts of water and electric power (for pumping the larger volumes of material) are consumed and much more machinery must be utilized to dilute, screen and thicken (in the vicinity of $2-3 million (U.S.) worth for a 500-1000 ton/day mill).
Dilution of the pulp material can be avoided through the use of one or more refiners (in series or parallel) at some convenient point in the digester discharge line (i.e., see our Canadian Patent No. 976,012, dated October 14, 1975, entitled "Method and Apparatus for Processing Pulp"). Refiners are devices with parallel plates which rotate relative to each other, both in opposite directions, or one being stationary and the other rotating, which plates may have protrusions or serrations formed on the faces thereof. ~he plates break the knots and shives to small fragments. Although this procedure does not result in the energy penalty associated with screening, since the broken up shives and knots have not been cooked, they cannot be bleached, and as such produce colored specks in paper produced from the pulp, and conse~uently a lower grade of paper.
Also, under some circumstances, it is possible that tramp material could harm the refiners, causing down-time thereof, or the tramp material could cause adverse effects on the final paper proauced.
~0~4761 According to the present invention, the problems inherent in each of the above conventional systems for removing knots and the like have been solved. According to the present invention, the energy already available in the pulp in the digester discharge line is utilized to achieve the separation of knots and the like from the digested pulp stock. The pulp stock in the discharge line is passed directly into a cyclone separator, wherein the heavier knots, shives and tramp material move by centrifugal force to the outside periphery of the cyclone to eventually migrate downwardly and out the bottom outlet of the cyclone, while the pulp fibers flow upwardly and out the cyclone central outlet pipe. Although the pulp stock is 10-20% in consistency, at high velocity (which is inherent in the digester discharge line) it becomes homogeneous, or more fluid. With fluid properties, it can be handled in conventional cyclone separators. Since cyclone separators require that the flowable materi~l be at very high velocity, their use usually is not practical for large volumes of high density material since the energy expended for accelerating the flowable ma~erial is enormous; however, according to the present invention, the flowable material is already at high velocity when it is discharged from the digester. Rather than letting (indeed effecting) this high-energy state material to dissipate, as is conventional in present digesting systems, the high-energy state is utilized to solve hitherto unsolved problems.
Once the knots and shives are separated from the pulp in the discharge line, they may be handled in one of several ways: Where the pulp is to be bleached, uncooked material may be passed through separators and washers ~o remove fibers and lOg4761 tramp material and then returned to the digester. Or, where the pulp is not to be bleached, uncooked material may be pa~sed back in line with the pulp after fragmentation tless energy is utilized than if all the pulp had to be passed through refiners).
It is the primary object of the present invention to provide for improved separation of knots, shives and the like from digested pulp stock, and to provide a more uniform grade of paper with less energy expenditure given a predetermined percentage of knots and shives in dige-~ter discharged pulp stock. This and other objects of the invention will become clear from an inspection of the detailed description of the inve~tion and from the appended claims.
BRIEF DESCRIPTION OF THE DRAWINGS
FIGURES la and lb are schematic showings of conventional prior art ways of dealing with knots and shives in digested pulp stock; and FIGURE 2 is a diagrammatic showing of exemplary apparatus according to the present invention.
DETAILED DESCRIPTION OF THE INVENTION
~onventional assemblies for digesting cellulose material and removing knots and shives therefrom are shown schematically in FIGURES la and lb. In the apparatus of FIGURE la, after chips have been treated in pre-impregnation vessel 12 and have been impregnated, cooked and washed in continuous digester 14, the resultant pulp stock passes through blow unit 16 to dilution station 18. At station 18, the pulp stock is thinned from about 10-20~ consistency to about 1-4%
consistency, the knots and shives are re~oved by screening apparatus 20 and deckers 22 or the like thicken the pulp back to about 8-15% consistency, whereupon it is passed to a further treatment station 24 for storage, bleaching or other operation steps. A great deal of water is consumed in diluting the pulp for screening and a great amount of energy is consumed in transporting the large volumes of material that ensue from the dilution process. Also, the dilution, screening and thickening equipment is relatively expensive.
When the conventional apparatus of FIGURE lb is utilized, from blow unit 16 the pulp stock is passed to a refiner 26. Extra refiners 26 can be utilized too, if desired, either arranged in series or in parallel with refiner 26. In refiner 26, the knots and shives are fragmented and pass with the rest of the pulp stock to further treatment station 24.
While relatively little energy is used in such an arrangement in comparison to the arrangement of FIGURE la, the final pulp stock has the uncooked knot and shive particles therein, and these particles will not bleach, but rather leave colored spots on the final paper produced. Also, all the pulp stock must pass through the refiners 26, not just the knots and shives, and tramp material in the pulp stock may shorten refiner life or have other adverse consequences.
Exemplary apparatus according to the present invention is shown in FIGURE 2, which apparatus does not have any of the drawbacks of the prior art apparatus. According to the present invention, chips are fed into chip bins 30 and are passed from there through chip meter 31 and low pressure feeder 32 into pre-steaming vessel 33. From vessel 33, they pass through chip chute 34 into high pressure feeder 35, and from there to pre-impregnation vessel 12. From vessel 12, the chips are fed to the top of continuous digester 14, which may be one such as shown in U.S. Patent No. 3,427,218. One or more flash tanks 36 are associated with the digester 14 and pre-steaming vessel 33.
Everything described so far is conventional.
After treatment (i.e., impregnation, cooking and washing) in digestex 14, the resultant pulp stock is passed through outlet 38 of digester 14. At this point, the pulp is in a high-energy state, a 10-20% (approximately) consistency material under a pressure as high as 200 PSIG. The pulp may pass through blow unit 16 and then is introduced tangentially into cyclone separator 40 of any suitable conventional type.
A blow unit 16 is only optional, there being no need to reduce the high-energy state of the pulp before introduction into cyclone 40, and the unit may be placed in line 42, if desired.
The material has fluid properties at this point and has high enough velocity so that cyclone separation thereof is practical.
~he pulp fibers are discharged through cyclone upper central outlet 42, while the knots, shives and tramp material are discharged through the lower outlet 44 since the heavi~r knots and shives move by centrifugal force to the outside periphery of the cyclone and eventually migrate downwardly.
After discharge through outlet 44 of cyclone separator 40, the knots, shives and the like can either be passed through line 45 to a conventional refiner 26 and then to blow tank 24 or through line 47 to a washer 51 to remove fibers and then directly back to the inlet to the chips bin 30. When tramp material is expected, separation means 43 for separating the 109`~76~
tramp material from the knots and shives should be utilized at outlet 44. Such means 43 may be of any conventional type, such as another cyclone separator, screening means or float and s~nk equipment. If the quality of material from outlet 44 is bad enough, all of it may be discarded.
When line 45 and refiner(s) 26 are utilized, the fragmented knots or shives pass through line 50 back to line 42 for transport to further treatment station 24. While line 50 would not normally be utilized when subsequent bleaching of the pulp stock was to be performed, the FIGURE 2 assembly, including line 50, is advantageous over the FIGURE lb arrangement when there is to be no subse~uent bleaching, since a lower volume of material passes through refiner(s) 26, and thus the refiner(s) may be smaller and less energy will be consumed thereby.
It will thus be seen that according to the method of the present invention, knots, shives and tramp material are separated from the pulp discharged from a continuous digester by passing the pulp through a cyclone separator, and the separated portions of the pulp are passed through different treatment stages.
While the invention has been herein shown and described in what is presently conceived to be the most practical and preferred embodiment, it will be apparent to those of ordinary skill in the art that many modifications may be made thereof within the scope of the invention, which scope is to be accorded the broadest interpretation of the appended claims so as to encompass all equivalent structures and methods.
Claims (4)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A method of producing homogeneous pulp stock comprising the steps of (a) digesting wood chips and the like in a continuous digester to produce high density pulp stock, having a consistency of approximately 10-20%, in a high-energy state;
(b) separating knots, shives and tramp material from the high density pulp stock discharged from the digester by passing the undiluted pulp stock through a cyclone separator;
and (c) feeding the pulp stock to a further treatment station.
(b) separating knots, shives and tramp material from the high density pulp stock discharged from the digester by passing the undiluted pulp stock through a cyclone separator;
and (c) feeding the pulp stock to a further treatment station.
2. A method as recited in Claim 1 comprising the further step of separating knots and shives separated from said pulp stock from tramp material separated from said pulp stock.
3. A method as recited in Claim 2 comprising the further step of fragmenting said knots and shives by passage thereof through one or more refiners.
4. A method as recited in Claim 3 comprising the further step of feeding fragmented knots and shives from said one or more refiners to said further treatment station to which said separated pulp stock is passed.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US62960475A | 1975-11-06 | 1975-11-06 | |
| US629,604 | 1975-11-06 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1094761A true CA1094761A (en) | 1981-02-03 |
Family
ID=24523698
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA264,775A Expired CA1094761A (en) | 1975-11-06 | 1976-11-01 | Cyclone separation in digester discharge |
Country Status (7)
| Country | Link |
|---|---|
| JP (1) | JPS5270101A (en) |
| BR (1) | BR7607423A (en) |
| CA (1) | CA1094761A (en) |
| DE (1) | DE2650735C2 (en) |
| FI (1) | FI763168A (en) |
| FR (1) | FR2330797A1 (en) |
| NO (1) | NO151123C (en) |
Families Citing this family (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| SE9400616L (en) * | 1994-02-23 | 1995-01-23 | Kvaerner Pulping Tech | Handling of twig during continuous cooking |
Family Cites Families (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US2803540A (en) * | 1956-03-06 | 1957-08-20 | Condi Engineering Corp | Wood chip digestion |
| GB1357249A (en) * | 1972-02-09 | 1974-06-19 | British Steam Spec | Non-return valves for fluids |
-
1976
- 1976-10-27 NO NO763671A patent/NO151123C/en unknown
- 1976-11-01 CA CA264,775A patent/CA1094761A/en not_active Expired
- 1976-11-04 FI FI763168A patent/FI763168A/fi not_active Application Discontinuation
- 1976-11-05 DE DE2650735A patent/DE2650735C2/en not_active Expired
- 1976-11-05 JP JP51132486A patent/JPS5270101A/en active Pending
- 1976-11-05 BR BR7607423A patent/BR7607423A/en unknown
- 1976-11-05 FR FR7633512A patent/FR2330797A1/en active Granted
Also Published As
| Publication number | Publication date |
|---|---|
| DE2650735C2 (en) | 1984-07-05 |
| DE2650735A1 (en) | 1977-05-12 |
| FR2330797B1 (en) | 1980-04-18 |
| FI763168A (en) | 1977-05-07 |
| NO151123C (en) | 1985-02-13 |
| FR2330797A1 (en) | 1977-06-03 |
| NO151123B (en) | 1984-11-05 |
| NO763671L (en) | 1977-05-09 |
| JPS5270101A (en) | 1977-06-10 |
| BR7607423A (en) | 1977-09-20 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |