CA2025408A1 - Hood for a contact drying cylinder - Google Patents
Hood for a contact drying cylinderInfo
- Publication number
- CA2025408A1 CA2025408A1 CA002025408A CA2025408A CA2025408A1 CA 2025408 A1 CA2025408 A1 CA 2025408A1 CA 002025408 A CA002025408 A CA 002025408A CA 2025408 A CA2025408 A CA 2025408A CA 2025408 A1 CA2025408 A1 CA 2025408A1
- Authority
- CA
- Canada
- Prior art keywords
- hood
- drying
- partition wall
- cylinder
- drying gas
- 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.)
- Abandoned
Links
- 238000001035 drying Methods 0.000 title claims abstract description 75
- 238000005192 partition Methods 0.000 claims abstract description 50
- 238000010438 heat treatment Methods 0.000 claims abstract description 9
- 230000005855 radiation Effects 0.000 claims abstract description 4
- 238000009826 distribution Methods 0.000 claims description 3
- 230000001737 promoting effect Effects 0.000 claims description 2
- 238000001704 evaporation Methods 0.000 abstract description 10
- 230000008020 evaporation Effects 0.000 abstract description 10
- 238000007664 blowing Methods 0.000 abstract description 7
- 229910052729 chemical element Inorganic materials 0.000 abstract 1
- 239000007789 gas Substances 0.000 description 32
- 108091006146 Channels Proteins 0.000 description 18
- 239000000306 component Substances 0.000 description 3
- UGFAIRIUMAVXCW-UHFFFAOYSA-N Carbon monoxide Chemical compound [O+]#[C-] UGFAIRIUMAVXCW-UHFFFAOYSA-N 0.000 description 1
- 241001052209 Cylinder Species 0.000 description 1
- 206010013786 Dry skin Diseases 0.000 description 1
- 230000001609 comparable effect Effects 0.000 description 1
- 238000009833 condensation Methods 0.000 description 1
- 230000005494 condensation Effects 0.000 description 1
- 239000003546 flue gas Substances 0.000 description 1
- 229920000136 polysorbate Polymers 0.000 description 1
- 238000011084 recovery Methods 0.000 description 1
- 238000009827 uniform distribution Methods 0.000 description 1
Classifications
-
- 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
- D21F5/042—Drying on cylinders on two or more drying cylinders in combination with suction or blowing devices
- D21F5/044—Drying on cylinders on two or more drying cylinders in combination with suction or blowing devices using air hoods over the cylinders
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F26—DRYING
- F26B—DRYING SOLID MATERIALS OR OBJECTS BY REMOVING LIQUID THEREFROM
- F26B13/00—Machines and apparatus for drying fabrics, fibres, yarns, or other materials in long lengths, with progressive movement
- F26B13/10—Arrangements for feeding, heating or supporting materials; Controlling movement, tension or position of materials
- F26B13/14—Rollers, drums, cylinders; Arrangement of drives, supports, bearings, cleaning
Landscapes
- Engineering & Computer Science (AREA)
- Textile Engineering (AREA)
- Mechanical Engineering (AREA)
- General Engineering & Computer Science (AREA)
- Drying Of Solid Materials (AREA)
- Superstructure Of Vehicle (AREA)
- Current-Collector Devices For Electrically Propelled Vehicles (AREA)
- Scissors And Nippers (AREA)
Abstract
Abstract The invention relates to a hood (2) closed at both of its ends (15) and on its sides (14), intended for being fitted over the web-drying cylinder surface (1) segment of a contact drying cylinder, usually a so-called Yankee cylinder, in which hood the flow of the drying gas is promoted by means of a partition wall (4) which is substantially parallel to the cylinder sur-face (1), extends across the whole hood (2) and is at a dis-tance from the cylinder surface (1) and the hood mantle (3), in order to form two concentric flow channels having a longi-tudinal cross sectional shape of a circle arc and conjoining substantially at the ends of the hood. The outer flow channel has an inlet (11) for the drying gas, and in its vicinity there is an outlet (12) for the damp drying gas, separated from it by means of a transverse wall (10). According to the invention, when the partition wall (4) is located at such a distance from the cylinder surface that the velocity of the drying gas is high and when it is equipped with heating ele-ments (5) connected to an external source of energy, in order to transfer heat to the drying gas by convection and to the web (W) by radiation, as high a characteristic evaporation is accomplished as is by using high-capacity hoods based on nozzle-blowing.
Figure 1
Figure 1
Description
A hood for a contact drying cylinder The present invention relates to a hood, closed at both of its ends and on the sides and intended for being fitted over the web-drying cylinder surface segment of a contact drying cylin-der, e.g. a Yankee cylinder, and in particular to a hood which has a partition wall, substantially parallel to the cylinder surface and extending across the whole hood, at a distance from the cylinder and from the hood mantle, in order to form two concentric flow channels having a longitudinal cross-sectional shape of a circle arc and substantially conjoining at one end or b~th ends of the hood, there being in the outer flow channel an inlet for the drying gas and, preferably in the vicinity of this inlet, for example separated from it by a transverse wall, an outlet for the damp drying gas.
The diameter of a Yankee cylinder in a paper drying machine is 4-6 m, and it is needed either for producing gloss on paper or for drying sanitary papers, the drying of which must take place on one cylinder.
For many reasons, the characteristic evaporation of a Yankee cylinder is much higher than that of a conventional cylinder in a multiple-cylinder machine, the diameter of the latter cylinder being usually 1.5 - 1.8 m. Factors affecting this include:
~- a low contact resistance between the cylinder surface and the paper, which is due to the fact that the paper is pressed by the Yankee press intimately to the cylinder surface;
- for this same reason, drying ~elts which hamper the ~ `
transfer of both heat and stock are usually not used on the cylinders;
- owing to the long contact distance, the heating up-of the web on the cylinder represents a smaller proportion of the total drying time than it does on small cylinders;
~' ` .
The diameter of a Yankee cylinder in a paper drying machine is 4-6 m, and it is needed either for producing gloss on paper or for drying sanitary papers, the drying of which must take place on one cylinder.
For many reasons, the characteristic evaporation of a Yankee cylinder is much higher than that of a conventional cylinder in a multiple-cylinder machine, the diameter of the latter cylinder being usually 1.5 - 1.8 m. Factors affecting this include:
~- a low contact resistance between the cylinder surface and the paper, which is due to the fact that the paper is pressed by the Yankee press intimately to the cylinder surface;
- for this same reason, drying ~elts which hamper the ~ `
transfer of both heat and stock are usually not used on the cylinders;
- owing to the long contact distance, the heating up-of the web on the cylinder represents a smaller proportion of the total drying time than it does on small cylinders;
~' ` .
2~ $
- the internal heat transfer coefficient of the cylinders is high;
- in general the cylinders are dimensioned for a high steam pressure.
In order to control the flow of the drying air and also to promote drying, Yankee cylinders were initially equipped with a so-called low-pressure Yankee hood. An essential part of it was a partition wall which was installed at a suitable dis-tance from the web. In the clearance between it and the web, drying air flowed most preferably countercurrently in relation to the web. Thus a heat transfer coefficient which increased the characteristic evaporation was obtained on the air side, and the uniform distribution of air tended to improve the uni-formity of ~he intensity of drying in the lateral direction of the web. The dry-air blower and the air-heating ribbed-pipe radiator were preferably installed in connection with the heat recavery plant. At the heat recovery plant the initial heating ` of fresh drying air was carried out using outlet air withdrawn ;
from the hood by suction.
In the course of past decades, a high-capacity hood has usual-ly been constructed on a Yankee cylinder. The reason for this has been that the desired characteristic evaporation levels are so high that the capacity of a low-pressure hood has not been sufficient.
~, :
It is characteristic of a high-capacity hood that the improved charactéristic evaporation is accomplished by means of nozzle-blowing aimed at the web surface, which improves the heat transfer coefficient on the web surface. Thereupon the desired higher characteristic evaporation is produced at a lower web ; , .
temperature as compared with a low-pressure hood, and thus the flow of heat from inside the cylinder increases in proportion ~ to the difference`between the steam condensation temperature : ~ and the web temperature. Also, the flow of heat from the dry- -~
, 2~
ing air increases, although its relative proportion of the total heat flow is in general rather insignificant if the hood concerned is one in which the drying air is heated using a steam radiator.
The operating principle of a high-capacity hood involves a number of structural disadvantages, which are illustrated with the aid of a tangible example.
Let the length of the web contact surface be 12.5 m, the de-sired characteristic evaporation 0.0278 kg/m2s = 100 kg/m2h, which can be achieved at an approximate blown-air mass flow density of 0.8 kg/m2s relative to the web surface. In this case the heat transfer coefficient on the web surface is approx. 0.15 kW/m2C. Furthermore, let the moisture increase of the drying air be 0.2 kg H2O/kg of dry air (i.e. outlet air moisture content x ~ 0.21). With the help of these values it is possible to calculate that per one meter of the width of the web - evaporation is 0.347 kg/s drying air requirement is 1.74 kg/s requirement of nozzle-blown air is 10 kg/s.
Thus the circulation air flow (= the flow of nozzle-blown air) is almost six-fold as compared with the drying-air flow (= the flow of outlet air). In order that the circulation air blowers and the flow cross sections should not become unreasonably large, the custom is to divide the hood into several, two or three, sectors, which aré interconnected most preferably so;
that the drying air will flow from one sector to another coun-tercurrently in relation to t~e web.
For heating the circulation air, the structure must incor-porate - when the heating is by means of steam - ribbed-pipe radiators the thermal surface of which is in its order of mag-nitude approx. ten-fold as compared with the web surface, as ~ ~
:
2 J~
well as filters which will prevent the ribbed surfaces from becoming dusty. ~
Frequently the structure is such that, in order to accomplish uniform blowing, the hood needs to be divided in the lateral direction of the web into numerous pressure chambers and suc-tion chambers for the circulation air.
Overall, in order to implement the nozzle-blowing the struc-ture thus resorted to is complicated and expensive, as well as difficult to adjust, maintain, and repair.
: .
The above-mentioned disadvantage involved with nozzle-blowing, namely the increased size of blowers and circulation-air chan-nels, is often solved by placing only the nozzle boxes over the cylinder, whereas the blowers and radiators (or - when flue-gas heating of the circulation air is involved - the burners) are located separately alongside the drying machine.
~, , . : ' The object of the present invention is thus to provide for a contact drying cylinder a hood of the type mentioned in the preamble, i.e. a so-called low-pressure hood by means of which ; it is, nevertheless, possible to achieve the characteristic evaporation of the above-mentioned high-capacity hoad, i.e.
the object is to provide a hood for a contact drying cylinder, combining the advantages of the prior-art low-pressure hood and the high-capacity hood while avoiding their disadvantages.
.~.
The principal characteristics of the present invention are ` given in the accompanying claims.
, The characteristic evaporation of a low-pressure hood accord-`~` ing to the present invention can be raised to the same level ~; as that of a high-capacity hood by installing the partition wall at such a distance from the cylinder surface that the ~""
~ velocity of the drying gas will be high and by e~uipping the partition wall with heating elements connected to an external source of energy in order to transfer heat to the drying gas by convection and to the web by radiation.
In the contract drying cylinder hood according to the inven-tion the partition wall can be heated by means of resistor elements connected to an external source of energy, or the partition wall can be constructed as a heat exchanger which is placed so close to the cylinder surface that, by means of a high velocity of the air, heat transfer coefficients com-parable to those in nozzle-blowing can be achieved.
In a preferred embodiment of the invention, the partition wall can be converted to a heat exchanger by forming in it numerous conduits, for example pipes, extending substantially in the rotational direction of the cylinder, being connected to an external source of steam, and being at a distance from each other in the transverse direction of the partition wall, and possibly protrusions extending from these conduits to one or both sides of the partition wall, preferably at least as far as the inner flow channel, and promoting the transfer of heat, preferably being flanges which guide the drying gas and extend substantially in the rotational direction of the cylinder.
,.~
The conduits formed in the partition wall are preferably con-nected to a common tri~nsverse steam distribution conduit con-nected to an external source of steam, and their lower ends to a common transverse outlet conduit for condensate. The conden-., , i sate outlet conduits can be sealed to the hood ends, there being, in the partition wall edge parts adjoining the conden- ;
sate outlet conduits, openings through which the drying gas can ~low from the outer into the inner flow channel in order to provide locally promoted drying of the web.
The partition wall can also be divided into two partition wall parts successive as seen in the rotational direction of the ~ n, ~
..
cylinder, the parts having separate drying-gas inlets but ` preferably a common outlet for the damp drying gas. In this case the drying gas will flow cocurrently between one parti-tion wall part and the cylinder and countercurrently between the other partition wall and the cylinder in relation to the ,~ rotational direction of the cylinder. -,'' The invention is described below in greater detail, with ref-erence to the accompanying drawings, in which Figure 1 depicts a cross sectional end view of one preferred embodiment of the invention, installed on a contact drying cylinder, Figure 2 depicts a section along line I-I in Figure 1, Figure 3 depicts a cross sectional end view of one end of an alternative embodiment, and Figure 4 depicts a cross sectional end view of an alternative additional embodiment, in which the partition wall has been divided into two successive parts.
In Figure 1, the web-drying cylinder surface of a contact dry-ing cylinder, usually a Yankee cylinder, is generally indi-cated by reference numeral 1. The web W runs in the direction indicated by arrow B and is pressed against the cylinder sur-face 1 by rolls P. Over the cylinder surface 1 and the web W
which is against it there is fitted a hood according to the invention, which is generally indicated by reference numeral 2. The hood 2 is made up of a thermally insulated mantle 3, the sides of which are closed by gables 14 and both ends 15 of which are closed in such a manner that, when placed against the cylinder surface 1 and the web W on the cylinder, the hood forms together with the contact drying cylinder a substantial-ly gas-tight space. As can clearly be seen in Figure 1, the space delimited by the hood 2 and the cylinder surface 1 is divided into two concentric flow channels having the cross-sectional shape of a circle arc by a partition wall 4, which is at a small distance from the cylinder surface 1 and sub-~ ~,, ?"~
stantially parallel to it and extends between the gables 14 of ..
the hood 2 but terminates at a small distance from the hood 2 ends 15, so that drying gas can flow from one flow channel to another between the partition wall 4 front edge or respective-ly rear edge and the corresponding end 15 of the hood. Between the partition wall 4 and the thermally insulated mantle 3 of the hood 2 there is additionally a transverse wall 10, by means of which the outer flow channel is divided into two suc-cessive parts, the inlet 11 for drying gas being fitted at the beginning of the rear part and the outlet 12 for damp drying gas at the end of the leading part, so that drying gas will flow from the inlet 11 in the direction of arrow Al along the outer flow channel between the partition wall 4 and the hood 2 mantle 3 in the direction of arrow A2, turning in the direc-tion of arrow A3 through the clearance between the rear edge of the partition wall 4 and the end 15 of the hood 2 into the inner flow channel between the cylinder and the partition wall, where the drying gas will flow in the direction of arrow A4 countercurrently in relation to the travel direction of the web W on the cylinder surface 1, and finally the damp drying gas flow will turn again in the direction of arrow As through the clearance between the front edge of the partition wall 4 ~ -and the corresponding end 15 of the hood 2 into the leading ~: :
part of the outer flow channel, passing in the direction of arrow A6 into the outlet 12 for damp drying gas. In order to : ::
promote the yield of heat by the partition wall 4, in the leading part of the outer drying-gas flow channel and over the entire length of the inner drying-gas channel, there are fitted à plurality of flanges 7' and 7" extending substantial-ly in the rotational direction of the cylinder and fitted in the transverse direction at a distance from each other, the flanges at the same time guiding the flow of the gas.
As can be seen in Figure 1 and in greater detail in Figure 2, the partition wall 4 serves as a heat exchanger which yields heat by convection to the drying gas and additionally by radi-2 ~
8 . .
: .ation to the web W. The partition wall, which serves as a heat exchanger and is indicated generally by reference numeral 4 in Figure 2, is in a preferred embodiment of the invention made up of a plurality of curved pipes 5 fitted in parallel in the rotational direction of the cylinder surface, adjacently and at a small transverse distance from each other, the pipes be-ing interconnected in the transverse direction by partition wall components 6 and being additionally equipped with flanges 7' and 7" which are perpendicular to the partition wall com-ponents 6, extend to both sides of the partition wall 4, guide the drying-gas flow, promote the transfer of heat, and extend in the rotational direction of the cylindrical surface, the height of the flanges 7' being somewhat less than the distance between the pipes 5 and the thermally insulated mantle 3 of the hood and the height of the flanges 7" being somewhat less than the distance between the pipes 5 and the cylinder surface 1, including the thickness of the web W. The distance between the partition wall 4 and the cylinder surface 1 being rela-tively small, there form between the flanges 7" eddy pairs B
of eddies rotating in opposite directions, as seen in Figure 2. These eddy pairs notably improve the transfer of heat be-tween the partition wall 4 and the cylinder surface 1.
; ~, :~ By means of a hood 2 according to the present invention, equipped with a partition wall 4 which serves as a heat ex-changer, a very advantageous flow of drying gas is obtained and the same drying capacity is accomplished as in a high-capacity hood operating by nozzle-blowing, but with a lower I . , , , . ~
~ heat transfer coefficient. This is due to the fact that, owing `~ to the lack of circulation air, the drying air is dry when it flows in the direction of arrow A3 in Figure 1 into the inner : drying-gas channel delimited by the partition wall 4 and the cylinder surface 1, and therefore the temperature of the web W
is lower than in a high-capacity hood. This increases the : transfer of heat, not only from the drying gas to the web W
but also, above all, from the cylinder surface 1 to the web W. ;-.
' 3 ~ ~ ~ $
The partition wall 4 serving as a heat exchanger is heated by means of condensing steam introduced to it from an external source, and for this purpose the pipes 5 of the partition wall 4 are connected to a common steam-distribution pipe 8, as seen in Figure 1, and at both ends to a common condensate outlet pipe 9.
Figure 3 depicts an alternative embodiment, which differs from the embodiment depicted in Figure 1 in that both ends of the partition wall, with the condensate outlet pipes 9, are sealed to the ends 15 of the hood 2, the flow of drying gas from the outer flow channel to the inner one being arranged via a plu-rality of openings 13 at the ends of the partition wall com-ponents 6. This embodiment functions thus at the openings 13 in the manner of a nozzle dryer, whereby an area of enhanced drying is obtained at the ends of the hood 2, where drying gas flows at a high velocity towards the paper web W. Thus the drying intensity can be increased locally, and the arrangement has the further advantage that leaks into the surroundings are reduced.
Leaks to the surroundings or from the surroundings can further be reduced by using the alternative depicted in Figure 4, in which drying gas is fed to the central part of the hood through the inlets 11' and 11", and it flows around the outer edges of the partition wall 4' and 4", divided into two suc-cessive parts in the direction of arrows A3, and leaves the space between the partition wall parts 4' and respectively 4"
and the cylinder surface 1, i.e. the inner drying-gas channel, via an outlet 12 between the inlets 11' and 11". In this alternative the drying gas flows in one inner drying-gas chan-nel first cocurrently and thereafter in the subsequent outer drying-gas channel countercurrently in relation to the web W -on the cylinder surface 1.
. .
What is essential in the invention is that the partition wall, ;
`;
2~
' 10 . known of old from the low-pressure hoods for the cylinders, in :
particular Yankee cylinders, of contact drying machines, is constructed as a heat exchanger, which by convection through mediation of the drying gas (air), and additionally by radia-tion, yields heat to the web which is being dried by means of the hot surfaces of the cylinders (cylinder) of the contact drying machine. By dimensioning the structure of the hood so that the drying air has a high velocity, especially in the space between the drying surface and the heat exchanger, it is ! possible by using this structure to reach a similar drying intensity as is common with the high-pressure hoods, based on the nozzle-drying principle, which have now been used for a few decades.
,~
; ~:
:, `~` ~
;~
, ' : ` :
~: '
- the internal heat transfer coefficient of the cylinders is high;
- in general the cylinders are dimensioned for a high steam pressure.
In order to control the flow of the drying air and also to promote drying, Yankee cylinders were initially equipped with a so-called low-pressure Yankee hood. An essential part of it was a partition wall which was installed at a suitable dis-tance from the web. In the clearance between it and the web, drying air flowed most preferably countercurrently in relation to the web. Thus a heat transfer coefficient which increased the characteristic evaporation was obtained on the air side, and the uniform distribution of air tended to improve the uni-formity of ~he intensity of drying in the lateral direction of the web. The dry-air blower and the air-heating ribbed-pipe radiator were preferably installed in connection with the heat recavery plant. At the heat recovery plant the initial heating ` of fresh drying air was carried out using outlet air withdrawn ;
from the hood by suction.
In the course of past decades, a high-capacity hood has usual-ly been constructed on a Yankee cylinder. The reason for this has been that the desired characteristic evaporation levels are so high that the capacity of a low-pressure hood has not been sufficient.
~, :
It is characteristic of a high-capacity hood that the improved charactéristic evaporation is accomplished by means of nozzle-blowing aimed at the web surface, which improves the heat transfer coefficient on the web surface. Thereupon the desired higher characteristic evaporation is produced at a lower web ; , .
temperature as compared with a low-pressure hood, and thus the flow of heat from inside the cylinder increases in proportion ~ to the difference`between the steam condensation temperature : ~ and the web temperature. Also, the flow of heat from the dry- -~
, 2~
ing air increases, although its relative proportion of the total heat flow is in general rather insignificant if the hood concerned is one in which the drying air is heated using a steam radiator.
The operating principle of a high-capacity hood involves a number of structural disadvantages, which are illustrated with the aid of a tangible example.
Let the length of the web contact surface be 12.5 m, the de-sired characteristic evaporation 0.0278 kg/m2s = 100 kg/m2h, which can be achieved at an approximate blown-air mass flow density of 0.8 kg/m2s relative to the web surface. In this case the heat transfer coefficient on the web surface is approx. 0.15 kW/m2C. Furthermore, let the moisture increase of the drying air be 0.2 kg H2O/kg of dry air (i.e. outlet air moisture content x ~ 0.21). With the help of these values it is possible to calculate that per one meter of the width of the web - evaporation is 0.347 kg/s drying air requirement is 1.74 kg/s requirement of nozzle-blown air is 10 kg/s.
Thus the circulation air flow (= the flow of nozzle-blown air) is almost six-fold as compared with the drying-air flow (= the flow of outlet air). In order that the circulation air blowers and the flow cross sections should not become unreasonably large, the custom is to divide the hood into several, two or three, sectors, which aré interconnected most preferably so;
that the drying air will flow from one sector to another coun-tercurrently in relation to t~e web.
For heating the circulation air, the structure must incor-porate - when the heating is by means of steam - ribbed-pipe radiators the thermal surface of which is in its order of mag-nitude approx. ten-fold as compared with the web surface, as ~ ~
:
2 J~
well as filters which will prevent the ribbed surfaces from becoming dusty. ~
Frequently the structure is such that, in order to accomplish uniform blowing, the hood needs to be divided in the lateral direction of the web into numerous pressure chambers and suc-tion chambers for the circulation air.
Overall, in order to implement the nozzle-blowing the struc-ture thus resorted to is complicated and expensive, as well as difficult to adjust, maintain, and repair.
: .
The above-mentioned disadvantage involved with nozzle-blowing, namely the increased size of blowers and circulation-air chan-nels, is often solved by placing only the nozzle boxes over the cylinder, whereas the blowers and radiators (or - when flue-gas heating of the circulation air is involved - the burners) are located separately alongside the drying machine.
~, , . : ' The object of the present invention is thus to provide for a contact drying cylinder a hood of the type mentioned in the preamble, i.e. a so-called low-pressure hood by means of which ; it is, nevertheless, possible to achieve the characteristic evaporation of the above-mentioned high-capacity hoad, i.e.
the object is to provide a hood for a contact drying cylinder, combining the advantages of the prior-art low-pressure hood and the high-capacity hood while avoiding their disadvantages.
.~.
The principal characteristics of the present invention are ` given in the accompanying claims.
, The characteristic evaporation of a low-pressure hood accord-`~` ing to the present invention can be raised to the same level ~; as that of a high-capacity hood by installing the partition wall at such a distance from the cylinder surface that the ~""
~ velocity of the drying gas will be high and by e~uipping the partition wall with heating elements connected to an external source of energy in order to transfer heat to the drying gas by convection and to the web by radiation.
In the contract drying cylinder hood according to the inven-tion the partition wall can be heated by means of resistor elements connected to an external source of energy, or the partition wall can be constructed as a heat exchanger which is placed so close to the cylinder surface that, by means of a high velocity of the air, heat transfer coefficients com-parable to those in nozzle-blowing can be achieved.
In a preferred embodiment of the invention, the partition wall can be converted to a heat exchanger by forming in it numerous conduits, for example pipes, extending substantially in the rotational direction of the cylinder, being connected to an external source of steam, and being at a distance from each other in the transverse direction of the partition wall, and possibly protrusions extending from these conduits to one or both sides of the partition wall, preferably at least as far as the inner flow channel, and promoting the transfer of heat, preferably being flanges which guide the drying gas and extend substantially in the rotational direction of the cylinder.
,.~
The conduits formed in the partition wall are preferably con-nected to a common tri~nsverse steam distribution conduit con-nected to an external source of steam, and their lower ends to a common transverse outlet conduit for condensate. The conden-., , i sate outlet conduits can be sealed to the hood ends, there being, in the partition wall edge parts adjoining the conden- ;
sate outlet conduits, openings through which the drying gas can ~low from the outer into the inner flow channel in order to provide locally promoted drying of the web.
The partition wall can also be divided into two partition wall parts successive as seen in the rotational direction of the ~ n, ~
..
cylinder, the parts having separate drying-gas inlets but ` preferably a common outlet for the damp drying gas. In this case the drying gas will flow cocurrently between one parti-tion wall part and the cylinder and countercurrently between the other partition wall and the cylinder in relation to the ,~ rotational direction of the cylinder. -,'' The invention is described below in greater detail, with ref-erence to the accompanying drawings, in which Figure 1 depicts a cross sectional end view of one preferred embodiment of the invention, installed on a contact drying cylinder, Figure 2 depicts a section along line I-I in Figure 1, Figure 3 depicts a cross sectional end view of one end of an alternative embodiment, and Figure 4 depicts a cross sectional end view of an alternative additional embodiment, in which the partition wall has been divided into two successive parts.
In Figure 1, the web-drying cylinder surface of a contact dry-ing cylinder, usually a Yankee cylinder, is generally indi-cated by reference numeral 1. The web W runs in the direction indicated by arrow B and is pressed against the cylinder sur-face 1 by rolls P. Over the cylinder surface 1 and the web W
which is against it there is fitted a hood according to the invention, which is generally indicated by reference numeral 2. The hood 2 is made up of a thermally insulated mantle 3, the sides of which are closed by gables 14 and both ends 15 of which are closed in such a manner that, when placed against the cylinder surface 1 and the web W on the cylinder, the hood forms together with the contact drying cylinder a substantial-ly gas-tight space. As can clearly be seen in Figure 1, the space delimited by the hood 2 and the cylinder surface 1 is divided into two concentric flow channels having the cross-sectional shape of a circle arc by a partition wall 4, which is at a small distance from the cylinder surface 1 and sub-~ ~,, ?"~
stantially parallel to it and extends between the gables 14 of ..
the hood 2 but terminates at a small distance from the hood 2 ends 15, so that drying gas can flow from one flow channel to another between the partition wall 4 front edge or respective-ly rear edge and the corresponding end 15 of the hood. Between the partition wall 4 and the thermally insulated mantle 3 of the hood 2 there is additionally a transverse wall 10, by means of which the outer flow channel is divided into two suc-cessive parts, the inlet 11 for drying gas being fitted at the beginning of the rear part and the outlet 12 for damp drying gas at the end of the leading part, so that drying gas will flow from the inlet 11 in the direction of arrow Al along the outer flow channel between the partition wall 4 and the hood 2 mantle 3 in the direction of arrow A2, turning in the direc-tion of arrow A3 through the clearance between the rear edge of the partition wall 4 and the end 15 of the hood 2 into the inner flow channel between the cylinder and the partition wall, where the drying gas will flow in the direction of arrow A4 countercurrently in relation to the travel direction of the web W on the cylinder surface 1, and finally the damp drying gas flow will turn again in the direction of arrow As through the clearance between the front edge of the partition wall 4 ~ -and the corresponding end 15 of the hood 2 into the leading ~: :
part of the outer flow channel, passing in the direction of arrow A6 into the outlet 12 for damp drying gas. In order to : ::
promote the yield of heat by the partition wall 4, in the leading part of the outer drying-gas flow channel and over the entire length of the inner drying-gas channel, there are fitted à plurality of flanges 7' and 7" extending substantial-ly in the rotational direction of the cylinder and fitted in the transverse direction at a distance from each other, the flanges at the same time guiding the flow of the gas.
As can be seen in Figure 1 and in greater detail in Figure 2, the partition wall 4 serves as a heat exchanger which yields heat by convection to the drying gas and additionally by radi-2 ~
8 . .
: .ation to the web W. The partition wall, which serves as a heat exchanger and is indicated generally by reference numeral 4 in Figure 2, is in a preferred embodiment of the invention made up of a plurality of curved pipes 5 fitted in parallel in the rotational direction of the cylinder surface, adjacently and at a small transverse distance from each other, the pipes be-ing interconnected in the transverse direction by partition wall components 6 and being additionally equipped with flanges 7' and 7" which are perpendicular to the partition wall com-ponents 6, extend to both sides of the partition wall 4, guide the drying-gas flow, promote the transfer of heat, and extend in the rotational direction of the cylindrical surface, the height of the flanges 7' being somewhat less than the distance between the pipes 5 and the thermally insulated mantle 3 of the hood and the height of the flanges 7" being somewhat less than the distance between the pipes 5 and the cylinder surface 1, including the thickness of the web W. The distance between the partition wall 4 and the cylinder surface 1 being rela-tively small, there form between the flanges 7" eddy pairs B
of eddies rotating in opposite directions, as seen in Figure 2. These eddy pairs notably improve the transfer of heat be-tween the partition wall 4 and the cylinder surface 1.
; ~, :~ By means of a hood 2 according to the present invention, equipped with a partition wall 4 which serves as a heat ex-changer, a very advantageous flow of drying gas is obtained and the same drying capacity is accomplished as in a high-capacity hood operating by nozzle-blowing, but with a lower I . , , , . ~
~ heat transfer coefficient. This is due to the fact that, owing `~ to the lack of circulation air, the drying air is dry when it flows in the direction of arrow A3 in Figure 1 into the inner : drying-gas channel delimited by the partition wall 4 and the cylinder surface 1, and therefore the temperature of the web W
is lower than in a high-capacity hood. This increases the : transfer of heat, not only from the drying gas to the web W
but also, above all, from the cylinder surface 1 to the web W. ;-.
' 3 ~ ~ ~ $
The partition wall 4 serving as a heat exchanger is heated by means of condensing steam introduced to it from an external source, and for this purpose the pipes 5 of the partition wall 4 are connected to a common steam-distribution pipe 8, as seen in Figure 1, and at both ends to a common condensate outlet pipe 9.
Figure 3 depicts an alternative embodiment, which differs from the embodiment depicted in Figure 1 in that both ends of the partition wall, with the condensate outlet pipes 9, are sealed to the ends 15 of the hood 2, the flow of drying gas from the outer flow channel to the inner one being arranged via a plu-rality of openings 13 at the ends of the partition wall com-ponents 6. This embodiment functions thus at the openings 13 in the manner of a nozzle dryer, whereby an area of enhanced drying is obtained at the ends of the hood 2, where drying gas flows at a high velocity towards the paper web W. Thus the drying intensity can be increased locally, and the arrangement has the further advantage that leaks into the surroundings are reduced.
Leaks to the surroundings or from the surroundings can further be reduced by using the alternative depicted in Figure 4, in which drying gas is fed to the central part of the hood through the inlets 11' and 11", and it flows around the outer edges of the partition wall 4' and 4", divided into two suc-cessive parts in the direction of arrows A3, and leaves the space between the partition wall parts 4' and respectively 4"
and the cylinder surface 1, i.e. the inner drying-gas channel, via an outlet 12 between the inlets 11' and 11". In this alternative the drying gas flows in one inner drying-gas chan-nel first cocurrently and thereafter in the subsequent outer drying-gas channel countercurrently in relation to the web W -on the cylinder surface 1.
. .
What is essential in the invention is that the partition wall, ;
`;
2~
' 10 . known of old from the low-pressure hoods for the cylinders, in :
particular Yankee cylinders, of contact drying machines, is constructed as a heat exchanger, which by convection through mediation of the drying gas (air), and additionally by radia-tion, yields heat to the web which is being dried by means of the hot surfaces of the cylinders (cylinder) of the contact drying machine. By dimensioning the structure of the hood so that the drying air has a high velocity, especially in the space between the drying surface and the heat exchanger, it is ! possible by using this structure to reach a similar drying intensity as is common with the high-pressure hoods, based on the nozzle-drying principle, which have now been used for a few decades.
,~
; ~:
:, `~` ~
;~
, ' : ` :
~: '
Claims (5)
1. A hood (2), closed at both of its ends (15) and on the sides (14) and intended for being fitted over the web-drying cylinder surface (1) segment in a contact drying cylinder, the hood having a partition wall 4 substantially parallel to the cylinder surface (1) and extending across the whole hood (2) at a distance from the cylinder surface (1) and from the hood mantle (3), in order to form two concentric flow channels hav-ing the shape of a circle arc and conjoining substantially at least at one end of the hood, the outer flow channel having an inlet (11) for the drying gas and, preferably in the vicinity of the inlet, separated from it, for example, by a transverse wall (10), an outlet (12) for the damp drying air, charac-terized in that the partition wall (4) is equipped with heat-ing elements (5) connected to an external source of energy, for transferring heat to the drying gas by convection and to the web (W) by radiation.
2. A hood according to Claim 1, characterized in that the partition wall (4) has a plurality of conduits (5) at a dis-tance from each other in the transverse direction of the par-tition wall, the conduits extending substantially in the rota-tional direction of the cylinder surface (1) and being con-nected to an external source of steam, and possibly protru-sions extending from these conduits (5) to one or both sides of the partition wall (4), preferably at least as far as the inner flow channel, and promoting the transfer of heat, being preferably flanges (7', 7") which extend in the rotational di-rection of the cylinder surface (1) and at the same time guide the drying gas.
3. A hood according to Claim 2, characterized in that the conduits (5) are connected to a common transverse steam-distribution conduit (8) which is connected to an external source of steam, and their lower ends are connected to a com-mon transverse outlet conduit (9) for condensate.
4. A hood according to Claim 3, characterized in that the condensate outlet conduits (9) are attached to the ends (15) of the hood, and the partition wall (4) edge parts adjoining the condensate outlet conduits (9) have openings (13) which produce a locally enhanced drying-gas flow (A3) from the outer flow channel to the inner flow channel.
5. A hood according to any of the above claims, charac-terized in that it has two partition walls (4', 4"), succes-sive in the rotational direction of the cylinder surface (1), the partition walls having separate inlets (11', 11") for the drying gas and a common outlet (12) for the damp drying gas.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| FI894369A FI83679C (en) | 1989-09-15 | 1989-09-15 | HUVA FOER EN KONTAKTTORKCYLINDER. |
| FI894369 | 1989-09-15 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2025408A1 true CA2025408A1 (en) | 1991-03-16 |
Family
ID=8528997
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002025408A Abandoned CA2025408A1 (en) | 1989-09-15 | 1990-09-14 | Hood for a contact drying cylinder |
Country Status (6)
| Country | Link |
|---|---|
| AT (1) | ATA186090A (en) |
| CA (1) | CA2025408A1 (en) |
| DE (1) | DE4029098A1 (en) |
| FI (1) | FI83679C (en) |
| IT (1) | IT1247720B (en) |
| SE (1) | SE9002917L (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US6473997B1 (en) | 1998-09-04 | 2002-11-05 | Equitor Oy | Method and drying section for dewatering a fibrous web |
Families Citing this family (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| FI113790B (en) * | 1999-06-23 | 2004-06-15 | Metso Paper Inc | Method and apparatus for calendering |
| DE102008001410A1 (en) * | 2008-04-28 | 2009-10-29 | Voith Patent Gmbh | Machine for producing a one-sided smooth paper web |
-
1989
- 1989-09-15 FI FI894369A patent/FI83679C/en not_active IP Right Cessation
-
1990
- 1990-09-13 AT AT0186090A patent/ATA186090A/en not_active Application Discontinuation
- 1990-09-13 SE SE9002917A patent/SE9002917L/en not_active Application Discontinuation
- 1990-09-13 DE DE4029098A patent/DE4029098A1/en not_active Withdrawn
- 1990-09-14 CA CA002025408A patent/CA2025408A1/en not_active Abandoned
- 1990-09-14 IT IT04828190A patent/IT1247720B/en active IP Right Grant
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US6473997B1 (en) | 1998-09-04 | 2002-11-05 | Equitor Oy | Method and drying section for dewatering a fibrous web |
Also Published As
| Publication number | Publication date |
|---|---|
| IT1247720B (en) | 1994-12-30 |
| FI83679C (en) | 1991-08-12 |
| IT9048281A1 (en) | 1992-03-14 |
| IT9048281A0 (en) | 1990-09-14 |
| FI83679B (en) | 1991-04-30 |
| ATA186090A (en) | 1994-05-15 |
| SE9002917L (en) | 1991-03-16 |
| FI894369A0 (en) | 1989-09-15 |
| DE4029098A1 (en) | 1991-04-11 |
| SE9002917D0 (en) | 1990-09-13 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| FZDE | Discontinued |