CA1115575A - Continuous digester dimensioning - Google Patents
Continuous digester dimensioningInfo
- Publication number
- CA1115575A CA1115575A CA340,390A CA340390A CA1115575A CA 1115575 A CA1115575 A CA 1115575A CA 340390 A CA340390 A CA 340390A CA 1115575 A CA1115575 A CA 1115575A
- Authority
- CA
- Canada
- Prior art keywords
- zone
- digester
- sectional area
- digesting
- heating zone
- 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
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- Paper (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
CONTINUOUS DIGESTER DIMENSIONING
A continuous digester and the method of utilizing the same, to provide greater uniformity of treatment. Instead of small increases in diameter between the preliminary treatment, cooking, and washing zones, the inventive digester has large increases in cross-sectional area. For digester 14 feet or more in diameter, the cooking zone has a cross-sectional area 15-25% greater than that of the preliminary treatment zone, and the cross-sectional area of the primary washing zone is 10-20% greater than that of the cooking zone.
CONTINUOUS DIGESTER DIMENSIONING
A continuous digester and the method of utilizing the same, to provide greater uniformity of treatment. Instead of small increases in diameter between the preliminary treatment, cooking, and washing zones, the inventive digester has large increases in cross-sectional area. For digester 14 feet or more in diameter, the cooking zone has a cross-sectional area 15-25% greater than that of the preliminary treatment zone, and the cross-sectional area of the primary washing zone is 10-20% greater than that of the cooking zone.
Description
;5~5 BACKGROUND AND SUMMARY OF THE INVENTION
CONTINUOUS DIGESTER DIMENSIONING
The invention relates to a method and ~pparatus for the continuous digestion of cellulosic fiber material, wherein the digester is dimensioned in order to assure uniform flow of materials throughout.
Conventional continuous digesters, are ;~
generally efficient in effecting digestion of a wide variety of cellulosic fiber materials. However as digester size increases some difficulties have been encountered in conventional digesters in maintaining a uniform flow of materials throughout the digester.
One source of non-uniform flow results from the accumulation of fibrous materials on the walls of the digester. In order to prevent this accumulation and to aid in the continuous downflow of cellulosic particles throughout the digester, it is known to slightly widen the walls of the digester in a downward direction. However, it has been discovered that unless the walls of the digester are widened in a precisely defined manner, non-uniform flow may result from the complex interaction of heretofore unappreci~ted factors, especially in digesters over 14 feet in diameter.
Thus, it is an object of the invention to define the precise dimensions of a continuous digester, whereby uniform flow throughout is maintained, even for large di~es~ers.
It is a further object of the invention to provide a method for continuously digesting cellulosic fiber by passing it through zones of precisely defined dimensions, wherein a uniform flow ~, ,.
" .
- . ~ . .
. ~ "
55~5 of materials is maintained. This and other objects o~ the invention will become clear from an inspection of the detailed description of the invention, and from the appended claims.
BRIEF DESCRIPTION OF THE DRAWING
FIGURE 1 is a schematic view of a diyester dimensioned according to the present invention for ;~
providing uniform flow therethrough.
DETAILED DESCRIPTION OF THE INVENTION
An exemplary continuous digester according to the present invention is shown generally at 10 in FIGURE 1. The assembly 10 includes a conventional steaming vessel 11 or the like from which wood chips or like cellulosic fibrous material is fed through a ;
15 conventional high pressure feeder 12 into a conven-tional digester inlet or charging means 14. The charging means 14 feeds the cellulosic material entrained in digesting liquid into a series of zones A, B, C and D wherein this cellulosic material is 20 converted to pulp. Thus, the cellulosic material travels in a continuous downward fashion throughout the digester and is removed therefrom at line 20.
As the cellulosic material travels downward throughout the digester it is subjected to treatment 25 first in zones A and B. For the purposes of the specification and the claims which follow, zone A
will be termed a preliminary treatment (impregna-tion) zone. In this preliminary treatment zone A
the cellulosic material becomes impregnated with the 30 digesting liquor and may be adjusted to the proper digesting temperature~
~ 5S7~
zone B for the purposes of the specification and the claims which follow will be termed a heating zone in which the temperature of the cellulosic material is raised substantially to digesting temperature. Zone C is the digesting zone. In the digesting zone the cellulosic material is subjected to treatment with the digesting liquor at full digesting temperatures until delignification takes place.
After passing from the above chemical treatment zones the cellulosic material continues to move downward through the washing zone D. In the wash zone D the cellulosic material is cleansed of digesting liquor with a suitable rinse liquid. The 15 washing process in the wash zone generally takes place at elevated temperatures.
The diameters of the preliminary treatment zone A and the heating zone B; the digesting zone C;
and t~e zone D are represented in FIGURE l by E,F
and G, respectively. FIGURE 1 clearly shows that the lowermost portions of the digester have an increased diameter relative to the uppermost portions. This increase may be effected through the use of steps 22, 23 located in the vicinity (e.g.
25 just below~ the li~uid withdrawal screens 24, 25 respectively.
Various means for withdrawing liquid streams from the digester and recycling same are provided which means are conventional. The liquids 30 for the various zones may be introduced by conventional central plpes 30, and recirculation and heating of the liquids may be accomplished by conventional pumps 32, 33, 34 and 35, and conventional heaters 37, 38 and 39.
, : , . ~ . .
;S7~
It is important to the efficient operation of a continuous digester that uniform flow of materials be established. In other words with respect to the liquid flow, eddy currents, eruptions, turbulence or localized upward currents of liquid are to be minimized. Any of these factors may adversely affect the heating or chip column movement or cause channeling of liquor or chips within the digester.
As world demand for pulp has increased, a need has arisen for digester capable of producing larger quantities of pulp. Conventional continuous digesters have been developed which are capable of producing three to five hundred tons of pulp per day. In these digesters the diameters of the various zones are roughly equivalent. In scaling up these digesters to have a capacity of, for example, 1,000 tons per day one would expect that the dimensions of the larger digesters would be roughly equivalent to those of conventional smaller digesters. However, it has been discovered that in larger digesters a precise dimensional arrangement of the zones must be maintained. Thus, unexpec~
tedly, it appears that relatively small scale 25 digesters may not merely be scaled up to larger versions.
The factors which lead to the necessity of precisely dimensioning larger digesters are not fully appreciated. However, it appears that there is a conflict between the optimum diameter of the heating zone B and the diameter o~ the zone D, particularly in digesters having a production capacity over 500 tons per day, and/or over 14 feet in diameter~ and this conflict increases in 35 significance as the tonnage capacity keeps ~. -, , ;, - - ~ .: :
.
, .
~ 1LSS75 increasing. More particularly, it has been discovered that as the diameter o~ the heating zone increases it becomes increasingly difficult to maintain uniform flow therein. On the other hand, as the diameter of the washing zone decreases, the upflow of liquid increases such that the downward movement of cellulosic fibers is impeded or even stopped.
The problem of increasing the diameter in the heating zone appears to arise from the fact that, when the liquid must flow greater distances from the center of the zone to the periphery thereof where the liquid withdrawal means is located, a greater pressure drop is incurred. As a result, relatively small diameters are necessary for the heating zone. However, the washing zone demands an area directly proportional to the tonnage of the digester for a particular grade of pulp. As indicated previously, a large gallon per minute per square foot upflow will impede or even stop the downward movement of cellulosic fibers, which of course affects the production.
Accordingly, it has been discovered that a digester may be dimensioned such that the average cross-sectional area of the digesting zone C exceeds that of the heating zone B by 15-25~, and the average cross-sectional area of the primary washing zone D exceeds that of the digesting zone C by another 10-20%. By this dimensioning the cross-- 30 section of the washing zone D may be approximately 30% greater than that of the heating zone B. This dimensioning is especially appropriate for digesters having a capacity of over 500 tons of pulp per day, and/or having a diameter of 14 feet or more e.g., a 35 capacity of between 500 and 1,000 tons per day.
,, :, , ' : ; '': ' ' ' ~., ' , ' ~
- :, ~ ::
:
As illustrated in FIGURE 1, the various zones are not subdivided and are o~ uniform ~ross-sectional areas, Therefore, the cross-sectional ~;
areas of zones A, B; C, and D may be calculated using diameters E, F and G, respectively. In the drawing, the differences in diameters between the zones B,C and D are exaggerated for emphasis.
In one example of a digester according to the present invention, the inside diameter of the zone B is 17' 6"; of zone C, 19'; and of ~one D, 20'. In utilizing such a digester the uniformity of treatment is noticably greater than in conventional digesters wherein steps on the order of 6" are provided; in one example of a conventional digester, the zone B has an inside diameter of 15' 6"; zone C, 16'; and zone D, 16' 6".
It will be appreciated by those skilled in the art that the various zones illustrated in FIGURE
1 may be subdivided into additional zones. ~his subdivision may be accomplished by placing additional liquid withdrawal and recirculation means within the zone~
While the invention has been herein shown and described in what is presently conceived to be the most practical and preferred embodiment of the invention, many modifications may be made thereof within the scope of the invention, which scope is to be accorded ~he broadest interpretation of the , appended claims so as to encompass all equivalent ~ 30 structures and methods.
.. , ~.. . - . - :
: . , , ;
~, ~ ; . -, .
, `' . '
CONTINUOUS DIGESTER DIMENSIONING
The invention relates to a method and ~pparatus for the continuous digestion of cellulosic fiber material, wherein the digester is dimensioned in order to assure uniform flow of materials throughout.
Conventional continuous digesters, are ;~
generally efficient in effecting digestion of a wide variety of cellulosic fiber materials. However as digester size increases some difficulties have been encountered in conventional digesters in maintaining a uniform flow of materials throughout the digester.
One source of non-uniform flow results from the accumulation of fibrous materials on the walls of the digester. In order to prevent this accumulation and to aid in the continuous downflow of cellulosic particles throughout the digester, it is known to slightly widen the walls of the digester in a downward direction. However, it has been discovered that unless the walls of the digester are widened in a precisely defined manner, non-uniform flow may result from the complex interaction of heretofore unappreci~ted factors, especially in digesters over 14 feet in diameter.
Thus, it is an object of the invention to define the precise dimensions of a continuous digester, whereby uniform flow throughout is maintained, even for large di~es~ers.
It is a further object of the invention to provide a method for continuously digesting cellulosic fiber by passing it through zones of precisely defined dimensions, wherein a uniform flow ~, ,.
" .
- . ~ . .
. ~ "
55~5 of materials is maintained. This and other objects o~ the invention will become clear from an inspection of the detailed description of the invention, and from the appended claims.
BRIEF DESCRIPTION OF THE DRAWING
FIGURE 1 is a schematic view of a diyester dimensioned according to the present invention for ;~
providing uniform flow therethrough.
DETAILED DESCRIPTION OF THE INVENTION
An exemplary continuous digester according to the present invention is shown generally at 10 in FIGURE 1. The assembly 10 includes a conventional steaming vessel 11 or the like from which wood chips or like cellulosic fibrous material is fed through a ;
15 conventional high pressure feeder 12 into a conven-tional digester inlet or charging means 14. The charging means 14 feeds the cellulosic material entrained in digesting liquid into a series of zones A, B, C and D wherein this cellulosic material is 20 converted to pulp. Thus, the cellulosic material travels in a continuous downward fashion throughout the digester and is removed therefrom at line 20.
As the cellulosic material travels downward throughout the digester it is subjected to treatment 25 first in zones A and B. For the purposes of the specification and the claims which follow, zone A
will be termed a preliminary treatment (impregna-tion) zone. In this preliminary treatment zone A
the cellulosic material becomes impregnated with the 30 digesting liquor and may be adjusted to the proper digesting temperature~
~ 5S7~
zone B for the purposes of the specification and the claims which follow will be termed a heating zone in which the temperature of the cellulosic material is raised substantially to digesting temperature. Zone C is the digesting zone. In the digesting zone the cellulosic material is subjected to treatment with the digesting liquor at full digesting temperatures until delignification takes place.
After passing from the above chemical treatment zones the cellulosic material continues to move downward through the washing zone D. In the wash zone D the cellulosic material is cleansed of digesting liquor with a suitable rinse liquid. The 15 washing process in the wash zone generally takes place at elevated temperatures.
The diameters of the preliminary treatment zone A and the heating zone B; the digesting zone C;
and t~e zone D are represented in FIGURE l by E,F
and G, respectively. FIGURE 1 clearly shows that the lowermost portions of the digester have an increased diameter relative to the uppermost portions. This increase may be effected through the use of steps 22, 23 located in the vicinity (e.g.
25 just below~ the li~uid withdrawal screens 24, 25 respectively.
Various means for withdrawing liquid streams from the digester and recycling same are provided which means are conventional. The liquids 30 for the various zones may be introduced by conventional central plpes 30, and recirculation and heating of the liquids may be accomplished by conventional pumps 32, 33, 34 and 35, and conventional heaters 37, 38 and 39.
, : , . ~ . .
;S7~
It is important to the efficient operation of a continuous digester that uniform flow of materials be established. In other words with respect to the liquid flow, eddy currents, eruptions, turbulence or localized upward currents of liquid are to be minimized. Any of these factors may adversely affect the heating or chip column movement or cause channeling of liquor or chips within the digester.
As world demand for pulp has increased, a need has arisen for digester capable of producing larger quantities of pulp. Conventional continuous digesters have been developed which are capable of producing three to five hundred tons of pulp per day. In these digesters the diameters of the various zones are roughly equivalent. In scaling up these digesters to have a capacity of, for example, 1,000 tons per day one would expect that the dimensions of the larger digesters would be roughly equivalent to those of conventional smaller digesters. However, it has been discovered that in larger digesters a precise dimensional arrangement of the zones must be maintained. Thus, unexpec~
tedly, it appears that relatively small scale 25 digesters may not merely be scaled up to larger versions.
The factors which lead to the necessity of precisely dimensioning larger digesters are not fully appreciated. However, it appears that there is a conflict between the optimum diameter of the heating zone B and the diameter o~ the zone D, particularly in digesters having a production capacity over 500 tons per day, and/or over 14 feet in diameter~ and this conflict increases in 35 significance as the tonnage capacity keeps ~. -, , ;, - - ~ .: :
.
, .
~ 1LSS75 increasing. More particularly, it has been discovered that as the diameter o~ the heating zone increases it becomes increasingly difficult to maintain uniform flow therein. On the other hand, as the diameter of the washing zone decreases, the upflow of liquid increases such that the downward movement of cellulosic fibers is impeded or even stopped.
The problem of increasing the diameter in the heating zone appears to arise from the fact that, when the liquid must flow greater distances from the center of the zone to the periphery thereof where the liquid withdrawal means is located, a greater pressure drop is incurred. As a result, relatively small diameters are necessary for the heating zone. However, the washing zone demands an area directly proportional to the tonnage of the digester for a particular grade of pulp. As indicated previously, a large gallon per minute per square foot upflow will impede or even stop the downward movement of cellulosic fibers, which of course affects the production.
Accordingly, it has been discovered that a digester may be dimensioned such that the average cross-sectional area of the digesting zone C exceeds that of the heating zone B by 15-25~, and the average cross-sectional area of the primary washing zone D exceeds that of the digesting zone C by another 10-20%. By this dimensioning the cross-- 30 section of the washing zone D may be approximately 30% greater than that of the heating zone B. This dimensioning is especially appropriate for digesters having a capacity of over 500 tons of pulp per day, and/or having a diameter of 14 feet or more e.g., a 35 capacity of between 500 and 1,000 tons per day.
,, :, , ' : ; '': ' ' ' ~., ' , ' ~
- :, ~ ::
:
As illustrated in FIGURE 1, the various zones are not subdivided and are o~ uniform ~ross-sectional areas, Therefore, the cross-sectional ~;
areas of zones A, B; C, and D may be calculated using diameters E, F and G, respectively. In the drawing, the differences in diameters between the zones B,C and D are exaggerated for emphasis.
In one example of a digester according to the present invention, the inside diameter of the zone B is 17' 6"; of zone C, 19'; and of ~one D, 20'. In utilizing such a digester the uniformity of treatment is noticably greater than in conventional digesters wherein steps on the order of 6" are provided; in one example of a conventional digester, the zone B has an inside diameter of 15' 6"; zone C, 16'; and zone D, 16' 6".
It will be appreciated by those skilled in the art that the various zones illustrated in FIGURE
1 may be subdivided into additional zones. ~his subdivision may be accomplished by placing additional liquid withdrawal and recirculation means within the zone~
While the invention has been herein shown and described in what is presently conceived to be the most practical and preferred embodiment of the invention, many modifications may be made thereof within the scope of the invention, which scope is to be accorded ~he broadest interpretation of the , appended claims so as to encompass all equivalent ~ 30 structures and methods.
.. , ~.. . - . - :
: . , , ;
~, ~ ; . -, .
, `' . '
Claims (9)
1. An apparatus for the continuous digestion of cellulosic fibrous material, said apparatus comprising:
- a heating zone, - a digesting zone having an average cross-sectional area which is 15 to 25% greater than that of said heating zone, and - a washing zone having an average cross-sectional area which is 10 to 20% greater than that of said digesting zone.
- a heating zone, - a digesting zone having an average cross-sectional area which is 15 to 25% greater than that of said heating zone, and - a washing zone having an average cross-sectional area which is 10 to 20% greater than that of said digesting zone.
2. An apparatus according to Claim 1, wherein the cross-sectional area of said washing zone is approxi-mately 25%-40% greater than that of said heating zone.
3. An apparatus according to Claim 1, which has a capacity of over 500 tons of pulp per day.
4. An apparatus according to Claim 1, which has a capacity of between 500 and 1,000 tons of pulp per day.
5. An apparatus according to Claim 1, wherein the diameter of the heating zone is about 14 feet or more.
6. A method for treating cellulosic fibrous material utilizing a continuous digester, said method comprising the steps of continuously passing material into the digester heating zone; subsequently - passing the material into the digester digesting zone, which has an average cross-sectional area which is 15 to 25% greater than that of the heating zone; and subsequently - passing the material into the digester washing zone which has an average cross-sectional area whcih is 10 to 20% greater than that of the digesting zone.
7. A method according to Claim 6, wherein the cross-sectional area of the washing zone is approximately 30%-40% greater than that of the heating zone.
8. A method according to Claim 6, wherein said cellulosic fibrous material is passed through the digester at a rate sufficient to produce over 500 tons of pulp per day.
9. A method according to Claim 6, wherein said cellulosic fibrous material is passed through said digester at a rate sufficient to produce between 500 and 1,000 tons of pulp per day.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US2180479A | 1979-03-19 | 1979-03-19 | |
| US21804 | 1979-03-19 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1115575A true CA1115575A (en) | 1982-01-05 |
Family
ID=21806254
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA340,390A Expired CA1115575A (en) | 1979-03-19 | 1979-11-22 | Continuous digester dimensioning |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1115575A (en) |
-
1979
- 1979-11-22 CA CA340,390A patent/CA1115575A/en not_active Expired
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |