CA1116844A - Method and apparatus for uniformly drying a continuous web of cellulosic fibers - Google Patents
Method and apparatus for uniformly drying a continuous web of cellulosic fibersInfo
- Publication number
- CA1116844A CA1116844A CA000342507A CA342507A CA1116844A CA 1116844 A CA1116844 A CA 1116844A CA 000342507 A CA000342507 A CA 000342507A CA 342507 A CA342507 A CA 342507A CA 1116844 A CA1116844 A CA 1116844A
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- CA
- Canada
- Prior art keywords
- web
- moisture content
- dry
- moisture
- pathway
- 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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Classifications
-
- D—TEXTILES; PAPER
- D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
- D21F—PAPER-MAKING MACHINES; METHODS OF PRODUCING PAPER THEREON
- D21F7/00—Other details of machines for making continuous webs of paper
- D21F7/003—Indicating or regulating the moisture content of the layer
-
- D—TEXTILES; PAPER
- D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
- D21F—PAPER-MAKING MACHINES; METHODS OF PRODUCING PAPER THEREON
- D21F5/00—Dryer section of machines for making continuous webs of paper
- D21F5/02—Drying on cylinders
- D21F5/04—Drying on cylinders on two or more drying cylinders
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- Paper (AREA)
- Drying Of Solid Materials (AREA)
Abstract
A METHOD AND APPARATUS FOR
UNIFORMLY DRYING A CONTINUOUS WEB
OF CELLULOSIC FIBERS
Abstract of the Disclosure A method and apparatus used in the uniform drying of a continuous web, such as a sheet of paper or paperboard. A newly formed web of paper of wet cellulosic fibers and the necessary additives is initially directed through a press section where excessive water is squeezed from the web to reduce its moisture content to about 50-80 percent, by weight, for subsequent passage through a dryer section wherein the moisture content is further reduced to anywhere between 3 and 15 percent, depending on the quality of the paper being processed. The moisture content profile of the nearly dry web of paper is constantly monitored adjacent the discharge end of the dryer section for dry streaks which occasionally occur in the web. Moisture is added accord-ingly to the web when the web is relatively wet and has a moisture content of at least 25 percent to eliminate further dry streaks and provides a paper product which has a uniform moisture content.
UNIFORMLY DRYING A CONTINUOUS WEB
OF CELLULOSIC FIBERS
Abstract of the Disclosure A method and apparatus used in the uniform drying of a continuous web, such as a sheet of paper or paperboard. A newly formed web of paper of wet cellulosic fibers and the necessary additives is initially directed through a press section where excessive water is squeezed from the web to reduce its moisture content to about 50-80 percent, by weight, for subsequent passage through a dryer section wherein the moisture content is further reduced to anywhere between 3 and 15 percent, depending on the quality of the paper being processed. The moisture content profile of the nearly dry web of paper is constantly monitored adjacent the discharge end of the dryer section for dry streaks which occasionally occur in the web. Moisture is added accord-ingly to the web when the web is relatively wet and has a moisture content of at least 25 percent to eliminate further dry streaks and provides a paper product which has a uniform moisture content.
Description
11~
~ack~ nd of the Invention The invention is useful in the production of continuous webs of wet fibrous Materials, especially webs of cellulosic fibers used in the production of paper products, such as paper and paperboard. The drying of such webs i9 extremely important in the production of quality papers which should have as uniform moisture content as possible.
U.S. Patent 3,864,842 relates to a multicylinder dryer section of a paper machine, and discloses numerous defects which can occur as a result of the non-uniform drying of a web of paper.
This patent is typical of the many patents which are directed to the profiling of heat transversely of a traveling web by means of differently heated cylinders or streams of air to more uni-formly dry the web and eliminate wet or dry streaks in the web, i.e. streaks which extend in the machine direction or longitudi-nally of the web and wherein the moisture content is appreciably different from portions of the web adjacent the streaks.
U.S. Patent 3,948,721 relates the problems of dry streaking :~ in greater detail, and describes how atomized sprays of water are utilized at the discharge end of the dryer section to wet dry streaks which appear in the web, so that the final product will have a more uniform moisture content. It was found that this particular solution to the problem occasionally produced other undesirable side effects in the wetted areas of the paper; namely, unsightly water marks, wrinkles, and blackening of the paper during the calendering operation. The invention is directed to an improved method of adding water to the web to eliminate streaks in the web without experiencing any of the aforementioned side effects.
The term "dry end", as used herein and in the claims, means a point along the pathway or line which the web travels during processing, where the moisture content of the web is 20 percent "; ~
i84~
or less, by weight, whereas the term "wet end" means a point along the processing pathway or line where the moisture content of the web is at least 25 percent.
Briefly stated, the invention is in a method and apparatus used in the production of a continuous web composed of fibrous material, such as wood pulp used in the formation of a sheet of paper or paperboard. The method comprises the formation of wet fibrous material into a continuous web having a high moisture content which is reduced to about 50-70 percent, by weight, by passing the web through a press section, after which the web is guided through a dryer section, wherein the web is heated to reduce the moisture content even further to a desired level, e.g.
below 10 percent, as it moves longitudinally along a pathway or processing line through the dryer section. The web is constantly monitored at the dry end of the processing line for dry streaks.
In response to the sensing of a dry streak, a water spray that is upstream in the wet end of the processing line and longitu-dinally aligned with the dry streak sensed, is operated to accordingly wet the adjacent correlated area of the web to eliminate further dry streaks downstream in the dry end and con-sequently produce a web having a more nearly uniform moisture content.
An apparatus, designed to carry out the aforementioned process, comprises, for example, a series of heated cylinders which define the processing line, and associated felts for pressing the web against the heated cylinders. A sensor is located at the dry end of the processing line, usually adjacent the discharge end of the dryer section, whereas the sprays, responsive to the sensor, are positioned in the wet end of the processing line usually adjacent the charging end of the dryer section. T'ne sprays are positioned to spray water directly again~t areas of the web cor~elated to the dry streaks requiring ~0~4 additional mois~ure, or against sec~ions of a dryer felt which, in turn, contacts the corr~lated area of the web requiring wetting.
Another aspect of the invention is the provision of monitors in the dry end of the processing line to sense both dry and wet streaks. Similar correlated sprays and steam nozzles are lo-cated in the press section, just prior to the last press, to spray water or steam against appropriate sections of a felt that contact correlated areas of the web needing wetting or drying, prior to passage of the web through the last press of the press section. Water from the sprays cool the felt which, in turn, raises the viscosity of the water in the web which the felt contacts to subsequently reduce the amount of water removal in the press section, whereas steam from the nozzles has just the opposite effect, i.e. the steam heats the felt which lowers the viscosity of the water in the web which the felt contacts to improve the removal of water from the web in the press section.
Thus, both the wetness and dryness of the web can be alternately controlled by the application of water and steam in the wet end of the processing line.
Description of the Drawing The following description of the invention will be better understood by having reference to the annexed drawing wherein:
Fig. 1 is a schematic of a machine used in the production of paper, including the last press of a press section and a dryer section; and Fig. 2 is a perspective of a plurality of individual sprays which are disposed transversely across the traveling web to selectively add moisture to the web where needed.
Environment of the Invention With reference to Fig. 1, there is shown a conventional Fourdrinier, or other suitable papermaking machine 5, wherein fibrous material, such as wood pulp, is formed into a continuous sheet or web 6 of paper. The we~ 6 i.q successively guided through a press section 7 where excessive water is squeezed from the web to reduce the moisture content of the web 6 from, for example, ~0%-85a/o to 50%-70%, and a dryer section 8 where the moisture content of the web 6 is f~lrther reduced to 12~/o~15% or less, depending on the grade of paper being processed.
The press section 7 is comprised of a number of similar presses, e.g. press 10 which, in this instance, is the third ; and final press. The third press 10 comprises a pair of opposing cylinders 11,12 which form a nip 13 through which the web 6 travels for squeezing with a conventional press felt 14 that simultaneously passes through the nip 13 and around and between the vertically lowermost cylinder 12 and a plurality of staggered guide rollers 15-18 which take up the slack in the continuous felt 14.
The web 6, upon leaving the press section 7~ travels suc-cessively through the dryer section 8 which, in this instance, is a multicylinder dryer that consists of four individual drying sections 20-23 which are spaced along a pathway formed by a first - 20 series of staggered cylinders 24-28 in the first drying section 20 ~ a second series of staggered cylinders 29-40 in the second drying section 21~ a third series of staggered cylinders 41-52 in the third drying section 22 ~ and a fourth series of staggered cylinders 53-64 in the fourth and final drying section 23. The cylinders 24-64 are heated with steam to correspondingly heat the web 6 and reduce the moisture content thereof to the desired level as the web 6 exits the final drying section 23. A number of continuous dryer felts 65-71 are passed around and between the cylinders 24-64 and a series of strategically located guide rollers to press the web 6 against the heated cylinders 24-64 of the dryer section 8, so that there is a maximum transfer of heat to the web 6. The web 6 travels from the dryer section 8 ~.ff~4A
through a calender stack 72 onto a windup assembly 73. The following invention is also applicable to a dryer section which employs hot air nozzles for heating the traveling web 6.
The Invention Any suitable device 75, for sensing and measuring the moisture content of a web, is positioned at the dry end 76 of the processing line or pathway to monitor the moisture content of the traveling web 6 and sense the web 6 for dry streaks.
The sensing device 75, in this instance, is located adjacent the web 6 as it exits the final drying section 23, where the moîsture content of the web 6 may be 5%-7% for fine quality papers, or 10%-12% or higher for other grades of paper. The sensing device 75 may be alternately positioned adjacent the web 6 as it exits the third drying section 22. A good workable sensing device 75 is one manufactured by the Measurex Corporation, or the Industrial Nucleonics Corporation and comprises a cross machine profiling a sensor which moves laterally across the web 6 while checking the moisture content of adjacent portions of the web 6. The sensing device 75 records where the moisture content of the web 6 is appreciably lower than the desired moisture content of the remaining portions of the web 6, relative to its position transversely of the web 6.
As previously indicated, a spraying device 77 has been used to spray finely atomized water against appropriate areas of a sheet of paper at the dry end of the line as a means of elimi-nating dry streaks in the paper. The spraying device 77 has been tried, without complete success, in a number of alternate positions adjacent the web 6 as it enters and exits the final drying section 23 (note alternate location of sprays 77 in Fig. 1). It has been discovered to be far more desirable and advantageous to apply moisture to the web 6 when it is wet, not dry, i.e. when the moisture content of the web 6 is at least 25~/~ and preferably greater ~han 35% in the range of from 45a/o~ 65~/,., and, in some cases, when the web 6 is extremely wet, prior to passage through the last press 10 of the press section 7. Moisture added to a wet web is readily distributed by capillary action to all parts or interstices of the web during the course of the drying process, contrary to the resistance to distribution which moisture encounters when applied to the hard, dry surface of a dry web wherein the moisture content is less than 20%.
Accordingly, a spraying device 78 (Fig. 2), responsive to the sensing device 75, is positioned in the wet end of the processing line to wet areas of the web 6 which are correlated to the dry streaks sensed by the sensing device 75, i.e. areas of the web 6 which are in the wet end of the line upstream from and longitudinally aligned with, a dry streak sensed in the dry end of the line. The spraying device 78 is comprised of a number of individual sprays 79 which are spaced transversely across the web 6 and which are correlated and responsive to the sensing device 75 as it traverses the web 6.
The spraying device 78, as best seen in Fig. 1, can be located in a number of positions. For example, the spraying device 78 is best located for spraying water directly against the web 6 as it travels around the next to last cylinder 27 in the first drying section 20. Alternately, the spraying device 78 can be positioned for indirectly wetting the web 6 by spraying water against the dryer felts 66 or 67 adjacent the cylinders 34,29 or 35 in the second drying section 21, or by spraying water against the dryer felt 69 adjacent the first-to-encounter cylinder 41 in the third drying section 22.
In operation, the sensing device 75 constantly monitors the moisture content of the traveling web 6 at the dry end 76 of the line. Upon sensing a dry streak, the sensing device 75, ~ZL4 triggers, for example, a correlated visible or audible signal which locates the dry streak transversely of the web 6. The correlated individual spray 79 of the spraying device 78, located in any of the aforementioned locations, is manually actuated by an operator to correspondingly wet the area of the web 6 longitudinally upstream from the sensed dry streak to eliminate any further dry streaks in that parti.cular area of the web 6. Water i9 pumpecl through the individual sprays 79 from a source of supply 80 by any suitable pumping mechanism 81.
The disparity between monitoring the web 6 for dry streaks at the dry end of the line and applying the necessary moisture at the wet end of the line is inconsequential because of the high speeds of from 1200 to 3000 feet per minute (fpm) at which the web 6 travels along the processing line or pathway.
The web 6 can also be continuously monitored for abnormal wet streaks as well as for dry streaks and corresponding mechanisms actuated to, accordingly, decrease or increase the moisture content of the web 6 in a specific area to eliminate ~- any such streaks. For example, wet and dry streaks can be 20 regulated by the operation of a steam nozzle 82 or similar water spraying device 83 to influence the viscosity or amount of water in the felt 14 adjacent the last press 10 of the press section 7. The steam is received from any suitable source 84.
Instead of manually operating the individual sprays 79 of the spraying device 78 or the steam nozzle 82 in response to the sensing of a dry or wet streak. The sensing device 75 can be adapted to send an appropriately translated signal to - a computer 84 which, in turn, is programed to automatically control operation of the correct spray 79, or 83, or steam nozzle 82 to properly wet or dry the web 6 to eliminate ex-cessively dry or wet streaks occurring in the web 6 at the dry end of the line.
i~4 Thus, there has been described a simple method and apparatus for controllin~ the uniformity of the moisture content of a paper product by appropriately wetting or, if need be, drying the necessary area of the product in the wet end of the line to eliminate a correlated dry or wet streak occurring and sensed in the dry end of the line. The problems of water marks, wrinkling, and blackening of the paper occasioned with prior art devices is eliminated to produce a sheet of paper having a more nearly uniform moisture content.
~ack~ nd of the Invention The invention is useful in the production of continuous webs of wet fibrous Materials, especially webs of cellulosic fibers used in the production of paper products, such as paper and paperboard. The drying of such webs i9 extremely important in the production of quality papers which should have as uniform moisture content as possible.
U.S. Patent 3,864,842 relates to a multicylinder dryer section of a paper machine, and discloses numerous defects which can occur as a result of the non-uniform drying of a web of paper.
This patent is typical of the many patents which are directed to the profiling of heat transversely of a traveling web by means of differently heated cylinders or streams of air to more uni-formly dry the web and eliminate wet or dry streaks in the web, i.e. streaks which extend in the machine direction or longitudi-nally of the web and wherein the moisture content is appreciably different from portions of the web adjacent the streaks.
U.S. Patent 3,948,721 relates the problems of dry streaking :~ in greater detail, and describes how atomized sprays of water are utilized at the discharge end of the dryer section to wet dry streaks which appear in the web, so that the final product will have a more uniform moisture content. It was found that this particular solution to the problem occasionally produced other undesirable side effects in the wetted areas of the paper; namely, unsightly water marks, wrinkles, and blackening of the paper during the calendering operation. The invention is directed to an improved method of adding water to the web to eliminate streaks in the web without experiencing any of the aforementioned side effects.
The term "dry end", as used herein and in the claims, means a point along the pathway or line which the web travels during processing, where the moisture content of the web is 20 percent "; ~
i84~
or less, by weight, whereas the term "wet end" means a point along the processing pathway or line where the moisture content of the web is at least 25 percent.
Briefly stated, the invention is in a method and apparatus used in the production of a continuous web composed of fibrous material, such as wood pulp used in the formation of a sheet of paper or paperboard. The method comprises the formation of wet fibrous material into a continuous web having a high moisture content which is reduced to about 50-70 percent, by weight, by passing the web through a press section, after which the web is guided through a dryer section, wherein the web is heated to reduce the moisture content even further to a desired level, e.g.
below 10 percent, as it moves longitudinally along a pathway or processing line through the dryer section. The web is constantly monitored at the dry end of the processing line for dry streaks.
In response to the sensing of a dry streak, a water spray that is upstream in the wet end of the processing line and longitu-dinally aligned with the dry streak sensed, is operated to accordingly wet the adjacent correlated area of the web to eliminate further dry streaks downstream in the dry end and con-sequently produce a web having a more nearly uniform moisture content.
An apparatus, designed to carry out the aforementioned process, comprises, for example, a series of heated cylinders which define the processing line, and associated felts for pressing the web against the heated cylinders. A sensor is located at the dry end of the processing line, usually adjacent the discharge end of the dryer section, whereas the sprays, responsive to the sensor, are positioned in the wet end of the processing line usually adjacent the charging end of the dryer section. T'ne sprays are positioned to spray water directly again~t areas of the web cor~elated to the dry streaks requiring ~0~4 additional mois~ure, or against sec~ions of a dryer felt which, in turn, contacts the corr~lated area of the web requiring wetting.
Another aspect of the invention is the provision of monitors in the dry end of the processing line to sense both dry and wet streaks. Similar correlated sprays and steam nozzles are lo-cated in the press section, just prior to the last press, to spray water or steam against appropriate sections of a felt that contact correlated areas of the web needing wetting or drying, prior to passage of the web through the last press of the press section. Water from the sprays cool the felt which, in turn, raises the viscosity of the water in the web which the felt contacts to subsequently reduce the amount of water removal in the press section, whereas steam from the nozzles has just the opposite effect, i.e. the steam heats the felt which lowers the viscosity of the water in the web which the felt contacts to improve the removal of water from the web in the press section.
Thus, both the wetness and dryness of the web can be alternately controlled by the application of water and steam in the wet end of the processing line.
Description of the Drawing The following description of the invention will be better understood by having reference to the annexed drawing wherein:
Fig. 1 is a schematic of a machine used in the production of paper, including the last press of a press section and a dryer section; and Fig. 2 is a perspective of a plurality of individual sprays which are disposed transversely across the traveling web to selectively add moisture to the web where needed.
Environment of the Invention With reference to Fig. 1, there is shown a conventional Fourdrinier, or other suitable papermaking machine 5, wherein fibrous material, such as wood pulp, is formed into a continuous sheet or web 6 of paper. The we~ 6 i.q successively guided through a press section 7 where excessive water is squeezed from the web to reduce the moisture content of the web 6 from, for example, ~0%-85a/o to 50%-70%, and a dryer section 8 where the moisture content of the web 6 is f~lrther reduced to 12~/o~15% or less, depending on the grade of paper being processed.
The press section 7 is comprised of a number of similar presses, e.g. press 10 which, in this instance, is the third ; and final press. The third press 10 comprises a pair of opposing cylinders 11,12 which form a nip 13 through which the web 6 travels for squeezing with a conventional press felt 14 that simultaneously passes through the nip 13 and around and between the vertically lowermost cylinder 12 and a plurality of staggered guide rollers 15-18 which take up the slack in the continuous felt 14.
The web 6, upon leaving the press section 7~ travels suc-cessively through the dryer section 8 which, in this instance, is a multicylinder dryer that consists of four individual drying sections 20-23 which are spaced along a pathway formed by a first - 20 series of staggered cylinders 24-28 in the first drying section 20 ~ a second series of staggered cylinders 29-40 in the second drying section 21~ a third series of staggered cylinders 41-52 in the third drying section 22 ~ and a fourth series of staggered cylinders 53-64 in the fourth and final drying section 23. The cylinders 24-64 are heated with steam to correspondingly heat the web 6 and reduce the moisture content thereof to the desired level as the web 6 exits the final drying section 23. A number of continuous dryer felts 65-71 are passed around and between the cylinders 24-64 and a series of strategically located guide rollers to press the web 6 against the heated cylinders 24-64 of the dryer section 8, so that there is a maximum transfer of heat to the web 6. The web 6 travels from the dryer section 8 ~.ff~4A
through a calender stack 72 onto a windup assembly 73. The following invention is also applicable to a dryer section which employs hot air nozzles for heating the traveling web 6.
The Invention Any suitable device 75, for sensing and measuring the moisture content of a web, is positioned at the dry end 76 of the processing line or pathway to monitor the moisture content of the traveling web 6 and sense the web 6 for dry streaks.
The sensing device 75, in this instance, is located adjacent the web 6 as it exits the final drying section 23, where the moîsture content of the web 6 may be 5%-7% for fine quality papers, or 10%-12% or higher for other grades of paper. The sensing device 75 may be alternately positioned adjacent the web 6 as it exits the third drying section 22. A good workable sensing device 75 is one manufactured by the Measurex Corporation, or the Industrial Nucleonics Corporation and comprises a cross machine profiling a sensor which moves laterally across the web 6 while checking the moisture content of adjacent portions of the web 6. The sensing device 75 records where the moisture content of the web 6 is appreciably lower than the desired moisture content of the remaining portions of the web 6, relative to its position transversely of the web 6.
As previously indicated, a spraying device 77 has been used to spray finely atomized water against appropriate areas of a sheet of paper at the dry end of the line as a means of elimi-nating dry streaks in the paper. The spraying device 77 has been tried, without complete success, in a number of alternate positions adjacent the web 6 as it enters and exits the final drying section 23 (note alternate location of sprays 77 in Fig. 1). It has been discovered to be far more desirable and advantageous to apply moisture to the web 6 when it is wet, not dry, i.e. when the moisture content of the web 6 is at least 25~/~ and preferably greater ~han 35% in the range of from 45a/o~ 65~/,., and, in some cases, when the web 6 is extremely wet, prior to passage through the last press 10 of the press section 7. Moisture added to a wet web is readily distributed by capillary action to all parts or interstices of the web during the course of the drying process, contrary to the resistance to distribution which moisture encounters when applied to the hard, dry surface of a dry web wherein the moisture content is less than 20%.
Accordingly, a spraying device 78 (Fig. 2), responsive to the sensing device 75, is positioned in the wet end of the processing line to wet areas of the web 6 which are correlated to the dry streaks sensed by the sensing device 75, i.e. areas of the web 6 which are in the wet end of the line upstream from and longitudinally aligned with, a dry streak sensed in the dry end of the line. The spraying device 78 is comprised of a number of individual sprays 79 which are spaced transversely across the web 6 and which are correlated and responsive to the sensing device 75 as it traverses the web 6.
The spraying device 78, as best seen in Fig. 1, can be located in a number of positions. For example, the spraying device 78 is best located for spraying water directly against the web 6 as it travels around the next to last cylinder 27 in the first drying section 20. Alternately, the spraying device 78 can be positioned for indirectly wetting the web 6 by spraying water against the dryer felts 66 or 67 adjacent the cylinders 34,29 or 35 in the second drying section 21, or by spraying water against the dryer felt 69 adjacent the first-to-encounter cylinder 41 in the third drying section 22.
In operation, the sensing device 75 constantly monitors the moisture content of the traveling web 6 at the dry end 76 of the line. Upon sensing a dry streak, the sensing device 75, ~ZL4 triggers, for example, a correlated visible or audible signal which locates the dry streak transversely of the web 6. The correlated individual spray 79 of the spraying device 78, located in any of the aforementioned locations, is manually actuated by an operator to correspondingly wet the area of the web 6 longitudinally upstream from the sensed dry streak to eliminate any further dry streaks in that parti.cular area of the web 6. Water i9 pumpecl through the individual sprays 79 from a source of supply 80 by any suitable pumping mechanism 81.
The disparity between monitoring the web 6 for dry streaks at the dry end of the line and applying the necessary moisture at the wet end of the line is inconsequential because of the high speeds of from 1200 to 3000 feet per minute (fpm) at which the web 6 travels along the processing line or pathway.
The web 6 can also be continuously monitored for abnormal wet streaks as well as for dry streaks and corresponding mechanisms actuated to, accordingly, decrease or increase the moisture content of the web 6 in a specific area to eliminate ~- any such streaks. For example, wet and dry streaks can be 20 regulated by the operation of a steam nozzle 82 or similar water spraying device 83 to influence the viscosity or amount of water in the felt 14 adjacent the last press 10 of the press section 7. The steam is received from any suitable source 84.
Instead of manually operating the individual sprays 79 of the spraying device 78 or the steam nozzle 82 in response to the sensing of a dry or wet streak. The sensing device 75 can be adapted to send an appropriately translated signal to - a computer 84 which, in turn, is programed to automatically control operation of the correct spray 79, or 83, or steam nozzle 82 to properly wet or dry the web 6 to eliminate ex-cessively dry or wet streaks occurring in the web 6 at the dry end of the line.
i~4 Thus, there has been described a simple method and apparatus for controllin~ the uniformity of the moisture content of a paper product by appropriately wetting or, if need be, drying the necessary area of the product in the wet end of the line to eliminate a correlated dry or wet streak occurring and sensed in the dry end of the line. The problems of water marks, wrinkling, and blackening of the paper occasioned with prior art devices is eliminated to produce a sheet of paper having a more nearly uniform moisture content.
Claims (23)
1. A method of uniformly drying a continuous web of wet fibrous material as the web travels along a processing line, comprising:
(a) constantly monitoring the moisture content of the web to sense dry streaks therein below a certain desired moisture content, when the web is in a dry end of the line where the moisture content of the web is less than 20%, by weight, and (b) adding moisture to the web in areas thereof which are upstream from and longitudinally aligned with any dry streaks sensed in the dry end of the line, the moisture being added in accordance with the moisture content of any such dry streaks, when the web is in a wet end of the line where the moisture content of the web is greater than 25%.
(a) constantly monitoring the moisture content of the web to sense dry streaks therein below a certain desired moisture content, when the web is in a dry end of the line where the moisture content of the web is less than 20%, by weight, and (b) adding moisture to the web in areas thereof which are upstream from and longitudinally aligned with any dry streaks sensed in the dry end of the line, the moisture being added in accordance with the moisture content of any such dry streaks, when the web is in a wet end of the line where the moisture content of the web is greater than 25%.
2. The method of claim 1, wherein moisture is added when the web has a moisture content of at least 35%.
3. The method of claim 2, wherein moisture is added when the web has a moisture content in the range of from 45% to 65%.
4. The method of claim 1, wherein moisture is added via a dryer felt which contacts the web.
5. The method of claim 1, wherein the moisture content of the web is regulated via a dryer felt which is alternately wetted and cooled by water and heated by steam and which contacts the web, prior to squeezing of the web in the last-to-encounter press of a press section.
6. A method of producing a continuous web of cellulosic fiber, such as a sheet of paper or paperboard, comprising:
(a) forming wet cellulosic fibers into a continuous web having an initial moisture content, by weight, of at least 50%;
(b) moving the web along a pathway while intermittently squeezing the web to reduce the moisture content thereof;
(c) moving the web along the pathway while heating the web to still further reduce the moisture content thereof to a desired level below 10%-15%;
(d) monitoring the web transversely thereof to sense dry streaks therein at a point along the pathway where the web has a moisture content less than 20%, a dry streak having a moisture content which is less than a desired level whereat the moisture content is monitored;
(e) wetting an area of the web upstream from, and longi-tudinally aligned with, a dry streak sensed and at a point along the pathway where the area has a moisture content greater than 25%, the area correlated to the dry streak being wetted in accordance with the percent of moisture sensed, to eliminate further dry streaks transversely of the web.
(a) forming wet cellulosic fibers into a continuous web having an initial moisture content, by weight, of at least 50%;
(b) moving the web along a pathway while intermittently squeezing the web to reduce the moisture content thereof;
(c) moving the web along the pathway while heating the web to still further reduce the moisture content thereof to a desired level below 10%-15%;
(d) monitoring the web transversely thereof to sense dry streaks therein at a point along the pathway where the web has a moisture content less than 20%, a dry streak having a moisture content which is less than a desired level whereat the moisture content is monitored;
(e) wetting an area of the web upstream from, and longi-tudinally aligned with, a dry streak sensed and at a point along the pathway where the area has a moisture content greater than 25%, the area correlated to the dry streak being wetted in accordance with the percent of moisture sensed, to eliminate further dry streaks transversely of the web.
7. The method of claim 6, wherein the web is transversely monitored for dry streaks at a point along the pathway where the web has a moisture content less than 10%.
8. The method of claim 6, wherein an area correlated to a dry streak monitored downstream thereof, is wetted at a point along the pathway where the area has a moisture content of at least 35%.
9. The method of claim 8, wherein the web is wetted when the correlated area thereof has a moisture content in the range of from 45% to 65%.
10. The method of claim 6, wherein an area of the web is wetted via a dryer felt which is wetted accordingly and contacts the correlated area of the web.
11. The method of claim 6, which includes alternately con-tacting a dryer felt, used in the squeezing of the web, with steam and water to correspondingly heat and wet and cool an area of the web contacted thereby.
12. An apparatus used in the drying of a continuous wet web of fibrous material, comprising:
(a) means for heating and drying the web, the means defining a pathway along which the web travels through the apparatus;
(b) means at the dry end of the pathway for monitoring the moisture content profile of the web transversely thereof to sense dry streaks in the web wherein the moisture content is below a desired level;
(c) means at the wet end of the pathway and responsive to the monitoring means (b) for adding moisture to select areas of the web correlated to dry streaks sensed by the monitoring means.
(a) means for heating and drying the web, the means defining a pathway along which the web travels through the apparatus;
(b) means at the dry end of the pathway for monitoring the moisture content profile of the web transversely thereof to sense dry streaks in the web wherein the moisture content is below a desired level;
(c) means at the wet end of the pathway and responsive to the monitoring means (b) for adding moisture to select areas of the web correlated to dry streaks sensed by the monitoring means.
13. The apparatus of claim 12, wherein the heating and drying means includes:
(d) a plurality of heated cylinders around and between which the web travels and contacts in order to be dried; and (e) means for guiding a plurality of continuous dryer felts around certain of the cylinders to press the web against said certain cylinders.
(d) a plurality of heated cylinders around and between which the web travels and contacts in order to be dried; and (e) means for guiding a plurality of continuous dryer felts around certain of the cylinders to press the web against said certain cylinders.
14. The apparatus of claim 13, wherein the moisture content of the web is monitored in the dry end of the pathway at a point therealong where the moisture content is less than 10% to 15%.
15. The apparatus of claim 14, wherein the moisture adding means includes means for selectively applying moisture to a number of transversely spaced sections of a felt, prior to con-tact of the felt with the web.
16. The apparatus of claim 15 wherein the moisture adding means includes a plurality of individual sprays spaced trans-versely of the felt.
17. The apparatus of claim 13, which includes, (i) a press section wherein the web is squeezed to remove excess water therefrom, and (ii) means in the dry end for monitoring the wetness of the web to sense wet streaks having a moisture con-tent above a certain desired level, and wherein the moisture adding means includes, (I) a plurality of water sprays spaced transversely of a dryer felt used to contact the web as it passes through a press of the press section, and (II) a plurality of steam nozzles spaced transversely of the dryer felt for alternatively contacting the felt with steam, the individual sprays being operated to increase the moisture con-tent of the web in a particular area correlated to a dry streak in the dry end, and the steam nozzles being operated to effective-ly decrease the moisture content of the web in a particular area correlated to a wet streak in the dry end.
18. An apparatus used in the production of a continuous web of cellulosic fibers such as a sheet of paper or paperboard, comprising:
(a) means for forming wet cellulosic fibers into a con-tinuous web;
(b) a press section for squeezing excess liquid from the web as it travels along a pathway;
(c) a dryer section through which the web travels along the pathway subsequent to passage through the press section, the dryer section including means for heating the web to reduce the moisture content thereof to a desired level where the moisture content is less than 10% to 15%;
(d) means for monitoring the web to sense dry streaks at a point along the pathway where the web has a moisture content less than 20%, a dry streak having a moisture content below a desired level whereat the web is monitored; and (e) means for adding moisture to the web at an area up-stream from, and longitudinally aligned with, a sensed dry streak at a point along the pathway where the web has a moisture content greater than 25%, in accordance with the moisture content of the dry streak to eliminate further dry streaks in the web.
(a) means for forming wet cellulosic fibers into a con-tinuous web;
(b) a press section for squeezing excess liquid from the web as it travels along a pathway;
(c) a dryer section through which the web travels along the pathway subsequent to passage through the press section, the dryer section including means for heating the web to reduce the moisture content thereof to a desired level where the moisture content is less than 10% to 15%;
(d) means for monitoring the web to sense dry streaks at a point along the pathway where the web has a moisture content less than 20%, a dry streak having a moisture content below a desired level whereat the web is monitored; and (e) means for adding moisture to the web at an area up-stream from, and longitudinally aligned with, a sensed dry streak at a point along the pathway where the web has a moisture content greater than 25%, in accordance with the moisture content of the dry streak to eliminate further dry streaks in the web.
19. The apparatus of claim 18, wherein the moisture monitoring means are located at a point along the pathway where the moisture content of the web is less than 10%, and the moisture adding means are located at a point along the pathway where the moisture content of the web is greater than 35%.
20. The apparatus of claim 19, wherein the web heating means includes a number of cylinders staggered above and below a horizontal plane, and means for heating the cylinders.
21. The apparatus of claim 20, wherein the means for adding moisture to the web includes means for spraying liquid against a section of dryer felt which contacts and presses the web against a heated cylinder, a correlated area of web which is longitudinally upstream from a sensed dry streak.
22. The apparatus of claim 21, wherein the means for adding moisture to the web includes means for spraying liquid against a section of dryer felt which contacts the web prior to contact of the web with the press.
23. The apparatus of claim 22, which includes:
(f) means for monitoring the web to sense wet streaks having a moisture content above a desired level and at a point along the pathway where the moisture content of the web is less than 10% to 15%; and (g) means for directing steam against select sections of the dryer felt which contacts the web, prior to contact of the web with the press.
(f) means for monitoring the web to sense wet streaks having a moisture content above a desired level and at a point along the pathway where the moisture content of the web is less than 10% to 15%; and (g) means for directing steam against select sections of the dryer felt which contacts the web, prior to contact of the web with the press.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US97185478A | 1978-12-21 | 1978-12-21 | |
| US971,854 | 1978-12-21 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1116844A true CA1116844A (en) | 1982-01-26 |
Family
ID=25518874
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000342507A Expired CA1116844A (en) | 1978-12-21 | 1979-12-21 | Method and apparatus for uniformly drying a continuous web of cellulosic fibers |
Country Status (8)
| Country | Link |
|---|---|
| JP (1) | JPS5593897A (en) |
| AU (1) | AU5360779A (en) |
| BR (1) | BR7908310A (en) |
| CA (1) | CA1116844A (en) |
| FI (1) | FI793920A (en) |
| FR (1) | FR2444749A1 (en) |
| GB (1) | GB2039014A (en) |
| SE (1) | SE7910025L (en) |
Families Citing this family (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| PH25720A (en) * | 1982-09-30 | 1991-09-18 | Beloit Corp | Method, apparatus for controlling the moisture profile of a paper web in paper-making machine |
| FI91900C (en) * | 1990-12-17 | 1994-08-25 | Valmet Paper Machinery Inc | Process at the drying portion of a paper machine to reduce the curvature tendency and drying portion of the paper intended to carry out the procedure |
| DE29924829U1 (en) * | 1999-01-15 | 2005-12-08 | Voith Paper Patent Gmbh | Papermaking drying and calender stations has a controlled wetting action through water sprays according to moisture profile measurements to give the best possible lateral moisture profile with a calender directly after the drying section |
| DE19903581A1 (en) * | 1999-01-29 | 2000-08-03 | Voith Sulzer Papiertech Patent | Paper web drying and polishing stations moistens the web surface by pressure forces at the end of or after the drying station before it passes through the roller press gaps of the calender to set the web moisture content |
| FI109213B (en) | 2000-11-24 | 2002-06-14 | Metso Paper Inc | Method and apparatus for controlling the profile of the moisture content or coating amount of the paper web |
Family Cites Families (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3948721A (en) * | 1974-09-03 | 1976-04-06 | Winheim Karl H | Method and apparatus for wetting the web in paper making machines |
-
1979
- 1979-12-05 SE SE7910025A patent/SE7910025L/en not_active Application Discontinuation
- 1979-12-06 GB GB7942118A patent/GB2039014A/en not_active Withdrawn
- 1979-12-07 AU AU53607/79A patent/AU5360779A/en not_active Withdrawn
- 1979-12-14 FI FI793920A patent/FI793920A/en not_active Application Discontinuation
- 1979-12-14 FR FR7930677A patent/FR2444749A1/en active Granted
- 1979-12-19 BR BR7908310A patent/BR7908310A/en unknown
- 1979-12-20 JP JP16626379A patent/JPS5593897A/en active Pending
- 1979-12-21 CA CA000342507A patent/CA1116844A/en not_active Expired
Also Published As
| Publication number | Publication date |
|---|---|
| FI793920A (en) | 1980-06-22 |
| FR2444749A1 (en) | 1980-07-18 |
| SE7910025L (en) | 1980-06-22 |
| GB2039014A (en) | 1980-07-30 |
| BR7908310A (en) | 1980-07-22 |
| FR2444749B1 (en) | 1982-11-26 |
| AU5360779A (en) | 1980-08-07 |
| JPS5593897A (en) | 1980-07-16 |
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| MKEX | Expiry |