EP0657580B1 - Dryer section of a paper machine - Google Patents

Abstract

A drying section of a paper making machine has a series of single tier drying groups, all with their respective felt belts arranged so that the drying cylinders are in contact with and dry one side of the web. The single tier groups are followed by one double tier drying group wherein the web passes such that the top side, then the bottom side, then the top side, then the bottom side, etc. of the web is in contact with successive drying cylinders arranged in two rows. Steam under pressure is supplied to all the drying cylinders. In the double tier group of drying cylinders, the steam pressure supplied to a first set of drying cylinders in sequence is higher than the steam pressure supplied to a second set of drying cylinders.

Description

The present invention relates to a dryer section a paper machine according to the preamble of the claim 1, and in particular the vapor pressure profile the drying cylinder of the dryer section.

In a paper machine, the paper web is made from a very wet pulp suspension formed, the first via a headbox into a wire section in which part of the water is removed. Then it is further dewatered in a press section, before being fed to a dryer section becomes. Such a dryer section of a paper machine typically includes a number of hollow metals Drying cylinders or dryers that are under Pressurized steam is supplied to the peripheral surfaces to heat the cylinder. That too drying paper is guided on a path that them with the peripheral surface of each drying cylinder sequentially in contact. That of the paper web heat supplied by the drying cylinders heats the paper web and in this way conveys it the evaporation of water from the paper web. Ultimately, a very high dry content of the Paper web can be reached. So the paper web owns for example when entering the dryer section a dry matter content of 45% and leaves the Drying section with a dry matter content of around 92% up to 98%. The amount of heat supplied to the paper web when passing each drying cylinder is one Function of the temperature of the peripheral surface of the corresponding Drying cylinder. The temperature is a function of the steam pressure in the drying cylinder. For example, there is a drying cylinder with higher steam pressure hotter than a drying cylinder with lower vapor pressure.

All drying cylinders in one dryer section are fed with steam, for example, from a common source of steam. The one in the pressure prevailing in different drying cylinders is set to different values so that different dry cylinder temperatures available are. The steam pressure can be controlled that the steam supply amount to the drying cylinders is adjustable by means of valves. If the paper web is progressively drier different cylinder temperatures to an optimally dried paper web.

The present invention is specific to one Arrangement of a dryer section applicable. A dryer section includes a number of drying cylinders, usually in several of each other separate dryer cylinder groups are operated. The drying groups are usually as single-row or two-tier dryer groups.

They are active in a two-tier dryer group heated drying cylinders grouped in two rows. The paper web passes through the two-row group, such that one side of the paper web initially with comes into contact with a drying cylinder in a row and then the other side of the paper web with a drying cylinder of the other series. This The process is then repeated until the end of the double row Drying group, so the paper web a meandering or zigzag Path describes where the paper web is the Drying cylinder rotates one after the other.

In contrast, in a single-tier dryer group only one side of the paper web, for example the underside, in contact with each drying cylinder brought to the group. Around the wrap angle around Raising each drying cylinder is a web guide roller or deflection roller provided, which is preferably designed as a suction roll and between adjacent drying cylinders in the drying group lies. The guide roller is placed so that the paper web takes up a significant portion of the circumference adjacent drying cylinder in the single row Wraps around the drying group.

For each single-tier dryer group there is one paper web supporting tape, namely a dry felt tape (hereinafter referred to as dry felt) provided. Likewise are dryer fabric belts usable, but only dry felt tapes is spoken. The dry felt supports and transports a surface of the paper web these within a single-tier dryer group from one drying cylinder to the next. On the other hand is in a typical two-tier dryer group the stretch of the paper web from a drying cylinder in a row to the drying cylinder the next row not through a dry felt supported. Such not supported by a dry felt Routes are called free trains.

Of course there are other drying cylinder arrangements known within a dry group.

In the early 80's, a hybrid design was developed known with at least one single row Drying group, according to which the partially dried Paper web through at least one double-row dryer group to be led. These designs include usually a small number of drying cylinders in the single-tier dryer group (s) to which a relatively larger number of drying cylinders in one or more two-tier dryer groups follows. The few drying cylinders in the single-tier dryer group instead of one Drying the paper web only for heating, to the actual in the two-tier dryer group to prepare for drying and to enable. As this hybrid arrangement in the was developed in the early 90s a large part of the drying cylinders in the single-tier dryer groups and a small part the drying cylinder in the two-row dryer groups. For this reason, most of the Drying takes place in the single-tier dryer groups, during the final drying in the double row Dry groups took place.

AT 3 84 254 B is a device for Use of excess steam in the steam condensate system of in individual groups with the same pressure level summarized drying facilities for paper and Coating machines emerge, the individual Groups in succession with steam each lower Pressure levels are heated. That of a group The condensate / steam mixture that has been removed becomes a separator for separation into the vapor phase and the liquid phase supplied, the steam with lower pressure supplied to the following group becomes.

DE-AS 11 94 692 describes a temperature control device for drying cylinders of a paper machine with their help from a central Make a shift in the temperature setpoints in a desired adjustable ratio is possible.

DE 94 14 963 U1 describes a dryer section to dry a running fibrous web, the single-tier dryer groups and double-tier dryer groups includes. The steam supply to the top and lower drying cylinders of a two-row Drying group is created using a single valve controlled. It is also proposed in a front Area of the two-tier dryer group Steam supply to the lower cylinders regardless of to control the steam supply to the upper cylinders.

From WO 93/22497 there is a two-row dryer group in which to influence the tendency to curl the steam supply to the top row the drying cylinder and the bottom row of the Drying cylinder set in this way by means of a control is that arranged between two adjacent Dryer a desired differential vapor pressure results.

In some paper machines, the dried paper web a further subsequent treatment subjected, for example, to a surface treatment in a coating press or online Coating machine. Efforts have been made and in the last section of the dryer section, especially in the two-tier dryer groups of the Hybrid arrangement, the temperature of the paper web at To control the end of the dryer section respectively regulate that an optimal paper web production is achieved. The present invention relates to a heat control system for a dryer section, which by control / regulation (in the following the Simplicity referred to simply as regulation) the supply of steam to at least some Drying cylinder is reached.

The object of the present invention is to produce a paper web with optimal quality, with the highest possible running efficiency (English: runability).

Another object of the present invention is in making the paper web with a certain reduced surface temperature as possible subsequent paper web post-treatment in the paper machine feed.

It is another object of the present invention the passage of the paper web through a hybrid dryer section, which are a number of drying cylinders in a row followed by one Number of drying cylinders in a double row Arrangement has to optimize.

Yet another object of the present invention is to make paper web in to optimize such a hybrid dryer section, by the vapor pressure in at least some of the drying cylinders compared to the other drying cylinders is reduced.

The present invention relates to a hybrid dryer section of at least one, preferably a few few, single-tier dryer groups, to which at least a two-tier dryer group End of the dryer section. In doing so, a not inconsiderable part of the warming and the Drying the paper web in the single row Dry groups (n) reached, the final Drying carried out in the two-tier dryer group becomes.

To achieve more effective paper web drying becomes a steam control device proposed that the feed to the drying cylinders Amount of steam and / or the steam pressure in the Drying cylinder controls / regulates such that a first group of drying cylinders of the double row Dry group has a higher vapor pressure than a subordinate second group of the double row Drying group. The temperatures are accordingly corresponding to the second group of drying cylinders the reduction in vapor pressure is reduced. The double row dryer group is preferred the last two-tier dryer group within the dryer section. Preferably a last one double-tier dryer section between the upstream lying group and the downstream Group of drying cylinders divided.

However, the present invention is not limited to that Use of a single double row Drying group limited. It is also possible that the two-row arrangement in two dryer groups is available. In every two-tier dryer group the top row of drying cylinders is an upper one endless dry felt assigned during the lower Row of drying cylinders one lower endless Dry felt is assigned. This dry felt arrangement is known. If the double row section the dryer section more than one dryer group , each group becomes an upper and assigned a lower dry felt.

The present invention relates to a final downstream group of drying cylinders a two-row section of a dryer section, being the drying cylinder with a lower Vapor pressure works upstream than the previous one lying group of drying cylinders of the double row dryer group. So that the Surface temperature of the downstream Reduce group of drying cylinders. To this Way, the temperature of the paper web is on Brought up level, which is a further aftercare enables very well.

Figur 1

eine schematische Darstellung einer Hybrid-Trockenpartie einer Papiermaschine, die einen einreihigen Trockenpartieabschnitt gefolgt von einem zweireihigen Trockenpariteabschnitt aufweist; und

Figur 2

eine schematische Darstellung des Dampfdruck-Verteilungssystems der Erfindung.

The invention will now be described in more detail using a preferred embodiment with reference to the figures. It shows:

Figure 1

a schematic representation of a hybrid dryer section of a paper machine which has a single-row dryer section followed by a double-row dryer section; and

Figure 2

is a schematic representation of the vapor pressure distribution system of the invention.

FIG. 1 shows a dryer section 10 of a paper machine, which is a wet paper web from a press section 11 is supplied. The paper web 30 goes through five consecutive single row Dryer groups 12, 13, 14, 15 and 16, which are the paper web 30 first heat and run then dry. The individual drying groups are in constructed essentially in the same way so that some of them in Figure 1 schematically as boxes are shown.

A more detailed description of a drying group should now take place on the basis of drying group 12. This includes a single row of drying cylinders 20, the individual drying cylinders with respective Alternate suction and deflection rollers 22. An endless one Drying felt 24 passes through drying group 12 zigzag over the suction roller 22, over the Drying cylinder 20, then again over a Suction roll 22 and a drying cylinder, etc. Am End of the drying group, which is behind in this example the last cylinder 20, the dry felt 24 deflected by means of the dry felt roller 23 and led back to the beginning of the drying group. Along the return path of the dry felt are additional dry felt rollers for guidance arranged.

The paper web 30 becomes when passing through the drying group on the one hand steered over the suction rolls 22, that the dry felt between paper web 30th and suction roller 22 is located. Then the Paper web 30 guided over the drying cylinder 20 that the paper web 30 between dry felt and drying cylinder lies and in direct contact reached with the drying cylinder 20. So press the dry felt 24 is the underside of the paper web secure against the drying cylinder that holds the paper web 30 heated so that the moisture from this evaporates when the paper web passes the drying cylinder 20 leaves.

The transfer of the paper web 30 from a drying group 12 to the next dryer group 13, in which the drying process described above continued is possible in many different ways, with the detailed description is dispensed with. In the dryer section shown is handed over between the single-tier dryer groups a paper web takeover by vacuum, the Paper web the last cylinder 20 in group 12 rotates, then on a dry felt 25 of the next Group 13 on the first suction roller 26 of this group 13 accumulates.

The single-tier dryer groups 12 to 12 shown 16 contain a total of 22 drying cylinders. At the end each dryer section is a two-tier dryer group 40 provided an upper row of Drying cylinders 42 and a lower row of drying cylinders 44 has. The paper web 30 passes the two-tier dryer section zigzag between the drying cylinders 44 of the lower row and the top row drying cylinders 42, wherein drying cylinders adjacent in the direction of transport in different rows. Here comes the Top of the paper web 30 in direct contact with the drying cylinders 44 of the lower row and the Bottom of the paper web in direct contact with the drying cylinders 42 of the upper row. This double-row dryer group are two dryer felts 46, 48 assigned, the dry felt 46 with the upper row of drying cylinders and the drying felt 48 interacts with the lower row of drying cylinders.

The upper dry felt 46 is over corresponding upper dry felt guide rolls 52 between adjacent ones Drying cylinders 42 out. The lower Drying felt 48 is passed over respective lower drying felt guide rolls 54 between adjacent drying cylinders 44 out. Both in the top and also in the lower drying cylinder row 42 or 44 the paper web will surface each drying cylinder by means of the respective dry felt web pressed.

Each of the drying cylinders in the drying groups can from a common with pressurized steam Steam generation point 60 are supplied. The respective pressure within the cylinder and hence the cylinder surface temperature is determined by the amount of steam supplied and the sequence the steam loading of the individual cylinders.

The example shown has a total of 30 drying cylinders of the same size. The first 22 that in Figure 2 with 1c to 22c are in five single-tier dryer groups 12 to 16 are arranged. The last eight cylinders, the 23c to 30c are part of a double row Drying group.

As shown in Figure 2, there is a common one Steam generation or supply point 60. The As shown in the example, steam becomes a cascade Arrangement fed. The drying cylinders are divided into four steam groups, however not with those defined by the dry felts Dry groups correspond. The first Steam group includes cylinders 1c to 5c second steam group the cylinders 6c to 12c, the third steam group 13c to 26c and the fourth Steam group the cylinders 27c to 30c. The one from the Steam generation point 60 supplied live steam is first the cylinders 13c to 26c in the third steam group supplied, the pressure value is highest here. This third steam group includes cylinders in the single-tier dryer groups 14, 15 and 16 and the first four cylinders 23 to 26 in the two-tier dryer group 40. The steam and the condensate will be from the third steam group the drying cylinder 13c to 26c to a common Condensate separator 63 passed. Then the steam becomes the second steam group the drying cylinder 6c to 12c passed. The cylinders 6c to 12c of the second steam group partly in the single-tier dryer group 13 partly in the single-tier dryer group 14. Falls The cylinders 6c to 12c may additionally be required Live steam via a feed line and a valve 68 can be supplied. To ensure, that the steam pressure in the second steam group the desired ratio to the vapor pressure in the third steam group, can be a vacuum source 71 connected to the drying cylinders 6c to 12c become.

Again, the steam and condensate are removed from the Drying cylinders 6c to 12c removed, the Condensate in a condensate separator 65 is separated. Finally, the steam of the first steam group with the drying cylinders 1c to 5c fed. However, this is done in reverse Order so that each of the drying cylinders 1c to 5c each in this order has increased vapor pressure, the corresponding Control by means of control valves, not shown he follows. Live steam can also be used in this case via a feed line and a valve 69, as required. To ensure, that the steam pressure in the first steam group a desired ratio to the vapor pressure in maintains the second and / or third steam group, can a vacuum source 73 with the drying cylinders 1c to 5c can be connected.

Form the last four drying cylinders 26c to 30c the fourth steam group and are separate from the Steam generation point 60 is supplied with steam. To the Steam temperature in these drying cylinders, for example to reduce about 70 ° C, the in vapor pressure contained in these drying cylinders a vacuum device 67 is reduced. To this The purpose is the outlets of the drying cylinders 27c up to 30c for steam and condensate with the condensate separator 65 connected via a line 66. The reduced pressure in the drying cylinders 26c to 30c leads to a decrease in Web temperature from the highest temperature on the drying cylinder 26.

The individual temperatures and individual vapor pressures then become dependent in the drying cylinders of the type of paper produced and the machine speed, as well as other factors, so that the exact specification of numerical values is not can be given for any situation. To be highlighted is, however, that the drying cylinders arranged at the end in the two-tier dryer group, the lie in the fourth steam group, their own something have different pressures and temperatures. Pressure and temperature are preferred lower in the cylinders of the fourth steam group than those of the third cylinder Steam group.

In a practical embodiment according to the invention is the vapor pressure difference of the drying cylinders 1c to 5c of the first steam group in the area from -0.483 bar to 1.38 bar (-7.0 to 20 psig); in the drying cylinders 6c to 12c of the second Steam group in a range of -0.103 bar to 3.79 bar (-1.5 to 55 psig); in the Drying cylinders 13c to 26c of the third steam group in a range from 0.207 bar to 5.17 bar (3-75 psig); and in the drying cylinders 27c to 30c of the fourth steam group in the range of -0.483 bar to 4.69 bar (-7 to 68 psig). The drying cylinders the fourth steam group, only the last four drying cylinders of the last two-row dryer group have a lower pressure than the drying cylinders in the third steam group and as the drying cylinders in the second steam group. The print areas previously mentioned partially overlap. In a special application however, these pressures can be selected that they don't overlap. In the aforementioned In the exemplary embodiment, there is a vapor pressure difference between the drying cylinders of the first and second steam groups of 0.345 bar up to 2.41 bar; between the drying cylinders of the second and third steam group from 0.31 bar to 1.38 bar; and between the third and fourth Steam group from 0 to 0.483 bar, but preferably a positive difference. The special ones Pressure levels and pressure differences are just mentioned as an example and not absolutely necessary. Rather, the basic idea of the invention lies in the pressure value differences, especially between the third and fourth steam group, and not in absolute pressure values.

The total number of drying cylinders and their Sizing in single-row and double-row Groups can vary with different applications, without the basic idea of the present Need to leave registration. The illustrated Dryer section 10 comprises five single-tier dryer groups 12 to 16 with a total of 22 drying cylinders 1c to 22c followed by one double-row dryer group 40 with eight cylinders 23c to 30c, the upstream four Cylinders 23c to 26c of the two-tier dryer group have a higher pressure and the downstream lying four cylinders 27c to 30c a lower one To have pressure. After the two-tier dryer group 40 runs the paper web in a known manner to subsequent after-treatment batches, for example a coating press, a coating section or a calender section.

It is also possible in an arrangement according to the invention not all of the above drying cylinders in the single-tier dryer group over a common one Steam generating station or under the same To supply steam pressure with steam, or the Vapor pressure inside the drying cylinder in the double row dryer group. Indeed own the last drying cylinders of the double-row dryer group in this hybrid arrangement usually a lower pressure value than that in the two-row dryer group in front of it Drying cylinder.

Incidentally, other combinations are the same as before mentioned features conceivable.

Claims (13)

1. Dryer section of a paper making machine comprising at least one single-row dryer group having a plurality of dryer cylinders, at least one two-row dryer group having a plurality of dryer cylinders and arranged after the single-row dryer group and a steam supply device which cooperates with the dryer cylinders, characterised by a steam control/regulating device which controls/regulates the quantity of steam supplied to the dryer cylinders and/or the steam pressure in the dryer cylinders such that a first group (23c to 26c) of the dryer cylinders of the two-row dryer group (40) has a higher vapour pressure than a following second group (27c to 30c) of the two-row dryer group.
2. Dryer section in accordance with claim 1, characterised by a first steam supply device (60) which supplies steam under pressure to a first number of dryer cylinders (1c to 22c) for the heating of these dryer cylinders, a second steam supply device which supplies steam with a first pressure value to the first group (23c to 26c) of the dryer cylinders of the two-row dryer group, with the first group having a plurality of sequential dryer cylinders, and by a third steam supply device which supplies steam to the second group (27c to 30c) of the dryer cylinders of the two-row dryer group, with the second group (27c to 30c) of the dryer cylinders having at least two adjacent dryer cylinders in the transport direction.
3. Dryer section in accordance with claim 2, characterized in that the second and the third steam supply devices are so set that the temperature of the first group (23c to 26c) of the dryer cylinders of the two-row dryer group is greater than the temperature of the second group (27c to 30c) of the dryer cylinders of the two-row group.
4. Dryer section in accordance with one of the preceding claims, characterized in that the first group (23c to 26c) of the two-row dryer group includes at least four dryer cylinders, and in that the second group of the two-row dryer group likewise includes at least four dryer cylinders which follow the first group - in the transport direction.
5. Dryer section in accordance with one of the preceding claims, characterized in that the two-row dryer group forms the end of the dryer section.
6. Dryer section in accordance with one of the preceding claims, characterized in that the second group of the dryer cylinders (27c to 30c) of the two-row dryer group are the last dryer cylinders of the dryer section.
7. Dryer section in accordance with one of the preceding claims, characterized in that the first steam supply device supplies steam at a greater pressure to the corresponding first number (1c to 22c) of dryer cylinders than the steam pressure delivered from the third steam supply device to the second group of dryer cylinders of the two-row dryer group.
8. Dryer section in accordance with claim 1, characterized in that the first number of dryer cylinders (1c to 22c) is greater than the second number (23c to 30c) of the dryer cylinders of the first and second groups of the two-row dryer group.
9. Dryer section in accordance with one of the preceding claims, characterized in that the first number (1c to 22c) of dryer cylinders is separated into a plurality of single row dryer groups and in that in each case an endless dryer felt belt and/or dryer screen belt is associated with each dryer group of the first number of dryer cylinders, with the respective dryer felt belt or dryer screen belt being alternatingly guided around a dryer cylinder and a paper web guide roll of the respective dryer cylinder.
10. Dryer section in accordance with one of the preceding claims, characterized in that each dryer felt belt and/or dryer screen belt of each dryer group of the first number is guided over the corresponding dryer cylinder such that the dryer felt belt or the dryer screen belt brings the first side of the paper web into contact with each of the dryer cylinders of the first number when the paper web and the dryer felt belt or dryer screen belt lying above the paper web wraps around the dryer cylinders.
11. Dryer section in accordance with one of the preceding claims, characterized in that the paper web guide device includes suction rolls, with the suction rolls being arranged between sequential neighbouring dryer cylinders of the row along the transport path so that the suction rolls cooperate with the paper web such that the paper web and the respective dryer felt belt or dryer screen belt wraps partly around each of the dryer cylinders of the first number.
12. Dryer section in accordance with one of the preceding claims, characterized in that a corresponding first endless dryer felt belt and/or dryer screen belt is guided in the second number (23c to 30c) of dryer cylinders about each of the dryer cylinders of the first row and is supported by means of the respective guide device in order to guide the paper web over the first row of dryer cylinders, with the first side of the paper web coming into contact with each dryer cylinder of the first row, and in that a second endless dryer felt belt or dryer screen belt is guided around each of the dryer cylinders of the second row and supported by the respective guide device in order to guide the paper web over the dryer cylinders of the second row, with the second side of the paper web coming into contact with the cylinders of the second row.
13. Dryer section in accordance with one of the preceding claims, characterized in that the first number of dryer cylinders and the guide device are so arranged that the one side of the paper web which comes into contact with the cylinders of the first row is the lower side of the paper web, and in that the second number of the dryer cylinders and the guide device are so arranged that the first side of the paper web is the upper side and the second side of the paper web is the lower side.

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