EP0657580A2 - 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 of a paper machine, and in particular to the vapor pressure profile of the dryer cylinders of the dryer section.

In a paper machine, the paper web is formed from a very wet fibrous suspension, which first reaches a wire section via a headbox, in which part of the water is removed. It is then further dewatered in a press section before being fed to a dryer section. Such a dryer section of a paper machine typically comprises a number of hollow metal drying cylinders or dryers, to which pressurized steam is supplied to heat the peripheral surfaces of the cylinders. The paper to be dried is guided on a path that sequentially brings it into contact with the peripheral surface of each drying cylinder. The heat supplied to the paper web by means of the drying cylinders heats the paper web and in this way promotes the evaporation of the water from the paper web. Ultimately, a very high dry matter content is said the paper web can be reached. For example, when entering the dryer section, the paper web has a dry content of 45% and leaves the dryer section with a dry content of approximately 92% to 98%. The amount of heat supplied to the paper web as it passes each drying cylinder is a function of the temperature of the peripheral surface of the corresponding drying cylinder. The temperature, on the other hand, is a function of the steam pressure in the drying cylinder. For example, a drying cylinder with a higher steam pressure is hotter than a drying cylinder with a lower steam pressure.

All drying cylinders in a dryer section are fed with steam, which comes, for example, from a common steam source. The pressure prevailing in the different drying cylinders is set to different values, so that different drying cylinder temperatures are present. The steam pressure can be controlled in that the amount of steam supplied to the drying cylinders can be adjusted by means of valves. If the paper web becomes increasingly dry, different cylinder temperatures lead to an optimally dried paper web.

The present invention is applicable to a special arrangement of a dryer section. A drying section comprises a number of drying cylinders, which are usually operated in several separate drying cylinder groups.

The dryer groups are usually designed as single-row or double-row dryer groups.

In a two-row dryer group, the actively heated drying cylinders are grouped in two rows. The paper web passes through the two-row group in such a way that one side of the paper web first comes into contact with a drying cylinder of one row and the other side of the paper web subsequently with a drying cylinder of the other row. This process is then repeated until the end of the two-row drying group, the paper web thus describing a meandering or zigzag path, with the paper web rotating around the drying cylinders one after the other.

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

For each single-tier dryer group there is a belt supporting the paper web, namely a dry felt belt (hereinafter referred to only as dry felt) intended. Likewise, dryer fabric belts can also be used, only dry felt belts being referred to below. The dry felt supports a surface of the paper web and transports it from one drying cylinder to the next within a single-row drying group. In contrast, in a typical two-row dryer group, the path of the paper web from one drying cylinder in one row to the drying cylinder in the next row is not supported by a drying felt. Such lines that are not supported by a dry felt are called free trains.

Of course, other drying cylinder arrangements within a drying group are also known.

In the early 1980s, a hybrid design with at least one single-row dryer group was known, according to which the partially dried paper web is passed through at least one double-row dryer group. These designs typically include a small number of drying cylinders in the single row dryer group (s) followed by a relatively larger number of drying cylinders in one or more double row dryer groups. The few drying cylinders in the single-row dryer group only lead to heating instead of drying the paper web in order to prepare and enable the actual drying taking place in the double-row dryer group. When this hybrid arrangement was further developed in the early 90s, a large part of the drying cylinders was placed in the single-row Dryer groups and a small part of the drying cylinders in the two-row dryer groups. For this reason, most of the drying took place in the single-tier dryer groups, while the last drying took place in the two-tier dryer groups.

In some paper machines, the dried paper web is subjected to a further subsequent post-treatment, for example a surface treatment in a coating press or an on-line coating machine. Efforts have been made to control or regulate the temperature of the paper web at the end of the dryer section in the last section of the dryer section, in particular in the double-row dryer groups of the hybrid arrangement, in such a way that optimum paper web production is achieved. The present invention relates to a heat control control for a dryer section, which is achieved by control / regulation (hereinafter referred to as control for reasons of simplicity) of supplying steam to at least some drying cylinders.

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

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

It is a further object of the present invention to optimize the passage of the paper web through a hybrid dryer section which has a number of drying cylinders in a single row arrangement followed by a number of drying cylinders in a double row arrangement.

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

The present invention relates to a hybrid dryer section of at least one, preferably a few, single-row dryer groups, which are followed by at least one double-row dryer group at the end of the dryer section. A not inconsiderable part of the heating and drying of the paper web is achieved in the single-row dryer group (s), the final drying being carried out in the double-row dryer group.

To achieve a more effective paper web drying, the first or upstream number of drying cylinders with a in a two-row dryer group, preferably in the last two-row dryer group of the dryer section operated high steam pressure, while the second or downstream number of drying cylinders are operated with a low steam pressure. Accordingly, the temperatures of the second number of drying cylinders are reduced in accordance with the decrease in the vapor pressure. A last two-row dryer group is preferably divided between the upstream and the downstream number of drying cylinders.

However, the present invention is not limited to the use of only a single two-tier dryer group. It is also possible for the two-row arrangement to be present in two drying groups. In each two-row dryer group, an upper endless drying felt is assigned to the upper row of drying cylinders, while a lower endless drying felt is assigned to the lower row of drying cylinders. This dry felt arrangement is known. If the double-row section of the dryer section has more than one dryer group, an upper and a lower dryer felt are assigned to each group.

The present invention relates to a last, downstream number of drying cylinders of a two-row section of a drying section, the drying cylinders operating with a lower vapor pressure than the previous upstream number of drying cylinders of the two-row section. This allows the surface temperature of the downstream number of drying cylinders to be reduced. In this way the temperature of the paper web is brought to a level that allows further post-treatment very well.

Figur 1

eine schematische Darstellung einer Hybrid-Trockenpartie einer Papiermaschine, die einen einreihigen Trockenpartieabschnitt gefolgt von einem zweireihigen Trockenpartieabschnitt 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, to which a wet paper web is fed from a press section 11. The paper web 30 passes through five successive single-row drying groups 12, 13, 14, 15 and 16, which first heat the paper web 30 during the passage and then dry it. The individual drying groups are constructed essentially in the same way, so that some of them are shown schematically in FIG. 1 as boxes.

A more detailed description of a drying group will now be given using the drying group 12. This comprises a single row of drying cylinders 20, the individual drying cylinders alternating with respective suction and deflection rollers 22. An endless one Drying felt 24 passes through the drying group 12 in a zigzag pattern over the suction roller 22, over the drying cylinder 20, then again over a suction roller 22 and a drying cylinder, etc. At the end of the drying group, which lies behind the last cylinder 20 in this example, the drying felt 24 is by means of the dry felt roller 23 deflected and led back to the beginning of the drying group. Further dry felt rolls are arranged along the return path of the dry felt for guidance.

The paper web 30 is guided on the one hand over the suction rollers 22 as it passes through the drying group such that the dry felt lies between the paper web 30 and the suction roller 22. The paper web 30 is then passed over the drying cylinder 20 such that the paper web 30 lies between the drying felt and drying cylinder and comes into direct contact with the drying cylinder 20. Thus, the drying felt 24 presses the underside of the paper web securely against the drying cylinder, which heats the paper web 30, so that the moisture evaporates therefrom when the paper web leaves the drying cylinder 20.

The transfer of the paper web 30 from one dryer group 12 to the next dryer group 13, in which the drying process described above is continued, is possible in many ways, the detailed description being dispensed with. In the dryer section shown, the transfer takes place between the single-tier dryer groups a paper web takeover by means of vacuum, the paper web running around the last cylinder 20 in group 12, then running onto a dry felt 25 of the next group 13 on the first suction roll 26 of this group 13.

The single-row dryer groups 12 to 16 shown contain a total of 22 drying cylinders. At the end of each dryer section, a two-row dryer group 40 is provided, which has an upper row of drying cylinders 42 and a lower row of drying cylinders 44. The paper web 30 passes through the two-row drying group in a zigzag shape between the drying cylinders 44 of the lower row and the drying cylinders 42 of the upper row, with adjacent drying cylinders lying in different rows in the transport direction. The top of the paper web 30 comes into direct contact with the drying cylinders 44 of the lower row and the underside of the paper web comes into direct contact with the drying cylinders 42 of the upper row. This two-row dryer group is assigned two dryer felts 46, 48, the dryer felt 46 interacting with the upper row of drying cylinders and the drying felt 48 with the bottom row of drying cylinders.

The upper drying felt 46 is guided between corresponding drying cylinders 42 via corresponding upper drying felt guide rollers 52. The lower drying felt 48 is guided between adjacent drying cylinders 44 via respective lower drying felt guide rollers 54. Both in the upper and in the lower row of drying cylinders 42 and 44 the paper web is pressed to the surface of each drying cylinder by means of the respective dry felt web.

Each of the drying cylinders in the drying groups can be supplied with pressurized steam from a common steam generation point 60. The respective pressure within the cylinder and therefore the cylinder surface temperature is determined by the amount of steam supplied and the order in which the steam is fed to the individual cylinders.

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

As shown in Figure 2, there is a common steam generation or supply point 60. The steam is, as shown in the example, fed to a cascade arrangement. The drying cylinders are divided into four steam groups, which however do not correspond to the drying groups defined by the drying felts. The first steam group comprises the cylinders 1c to 5c, the 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 live steam supplied by the steam generation point 60 is first fed to the cylinders 13c to 26c in the third steam group, the pressure value being the highest here. This third steam group comprises cylinders in the single-row dryer groups 14, 15 and 16 and the first four cylinders 23 to 26 in the double-row dryer group 40. The steam and the condensate become a common condensate separator 63 from the third steam group of the drying cylinders 13c to 26c headed. Then the steam is directed to the second steam group of the drying cylinders 6c to 12c. The cylinders 6c to 12c of the second steam group are located partly in the single-row dryer group 13 and partly in the single-row dryer group 14. If necessary, fresh steam can also be supplied to the cylinders 6c to 12c via a feed line and a valve 68. To ensure that the steam pressure in the second steam group maintains the desired ratio to the steam pressure in the third steam group, a vacuum source 71 can be connected to the drying cylinders 6c to 12c.

The steam and the condensate are again discharged from the drying cylinders 6c to 12c, the condensate being separated off in a condensate separating device 65. Finally, the steam is fed to the first steam group with the drying cylinders 1c to 5c. However, this takes place in the reverse order, so that each of the drying cylinders 1c to 5c has a slightly increased vapor pressure in this order, the corresponding regulation using control valves, not shown he follows. In this case too, live steam can be supplied via a supply line and a valve 69, as required. In order to ensure that the steam pressure in the first steam group maintains a desired ratio to the steam pressure in the second and / or third steam group, a vacuum source 73 can be connected to the drying cylinders 1c to 5c.

The last four drying cylinders 26c to 30c form the fourth steam group and are supplied with steam separately from the steam generation point 60. In order to reduce the steam temperature in these drying cylinders to, for example, approximately 70 ° C., the steam pressure contained in these drying cylinders is reduced by means of a vacuum device 67. For this purpose, the outlets of the drying cylinders 27c to 30c for steam and condensate are connected to the condensate separating device 65 via a line 66. The reduced pressure in the drying cylinders 26c to 30c leads to a reduction in the paper web temperature starting from the highest temperature on the drying cylinder 26.

The individual temperatures and individual vapor pressures in the drying cylinders are then selected depending on the type of paper produced and the machine speed, as well as other factors, so that the exact specification of numerical values cannot be given for every situation. It should be emphasized, however, that the drying cylinders arranged in the end in the two-row drying group, which are in the fourth steam group, have their own something have different pressures and temperatures. Preferably, the pressure and temperature in the cylinders of the fourth steam group are lower than those of the cylinders in the third steam group.

In a practical exemplary embodiment according to the invention, the vapor pressure difference of the drying cylinders 1c to 5c of the first steam group is in the range 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 from -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 fourth steam group drying cylinders 27c to 30c in the range of -0.483 bar to 4.69 bar (-7 to 68 psig). The drying cylinders of the fourth steam group, which only comprises the last four drying cylinders of the last two-row drying group, have a lower pressure than the drying cylinders in the third steam group and than the drying cylinders in the second steam group. The print areas mentioned above partially overlap. In a special application, however, these pressures can be chosen so that they do not overlap. In the aforementioned embodiment, there is a steam pressure difference between the drying cylinders of the first and the second steam group of 0.345 bar to 2.41 bar; between the drying cylinders of the second and third steam groups 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 pressure levels and pressure differences are only given as examples and are not absolutely necessary. The basic idea of the invention lies rather in the pressure value differences, in particular between the third and fourth steam groups, and not in the absolute pressure values.

The total number of drying cylinders and their size in the single-row and double-row groups can vary with different applications without having to leave the basic idea of the present application. The drying section 10 shown comprises five single-row dryer groups 12 to 16 with a total of 22 drying cylinders 1c to 22c, followed by a double-row dryer group 40 with eight cylinders 23c to 30c, the upstream four cylinders 23c to 26c of the double-row dryer group being at a higher pressure and the downstream four cylinders 27c to 30c have a lower pressure. After the double-row dryer group 40, the paper web runs in a known manner to subsequent post-treatment sections, for example a coating press, a coating section or a calender section.

It is also possible, in an arrangement according to the invention, not to supply all of the aforementioned drying cylinders in the single-row drying group with steam via a common steam generation point or under the same steam pressure, or the Adjust the steam pressure within the drying cylinders in the two-row drying group. However, the last drying cylinders of the two-row drying group in this hybrid arrangement usually have a lower pressure value than the drying cylinders in front of them in the two-row drying group.

Otherwise, other combinations of the aforementioned features are also conceivable.

Claims (12)

Dryer section of a paper machine, comprising:
a plurality of steam-loadable drying cylinders which are arranged along a transport path of a paper web (30) to be dried;
a device which cooperates with the drying cylinders (20; 42; 44) to guide the paper web (30) around the drying cylinders, the paper web (30) partially wrapping around each of the drying cylinders in the transport direction;
a first number of the drying cylinders (20) forming a single-row drying group and a second number of the drying cylinders (42; 44) forming a double-row drying group which is arranged on the downstream side of the single-row drying group and forms the end of the drying section and a first steam - Supply device (60) which leads pressurized steam to the first number of drying cylinders (20) for heating these drying cylinders; characterized by a second steam supply device which supplies steam with a first pressure value to a first group (23c to 26c) of the second number of drying cylinders (42, 44), the first group having a plurality of successive drying cylinders and a third steam supply device which supplies steam to a second group (27c to 30c) of the second number of drying cylinders, the second group (27c to 30c) following the first group (23c to 26c) of drying cylinders in the transport direction and wherein the second group of drying cylinders has at least two drying cylinders adjacent in the direction of transport, and wherein the third steam supply device controls the steam pressure in the second group (27c to 30c) of the second number (23c to 30c) of drying cylinders to a pressure which is less than the vapor pressure in the first group (23c to 26c) of the second number of cylinders. Dryer section according to claim 1, characterized in that the second and the third steam supply device are set so that the temperature of the first group (23c to 26c) of the second number (23c to 30c; 40) of drying cylinders is greater than the temperature of the second group (27c to 30c) of the second number (23c to 30c) of drying cylinders. Dryer section according to one of the preceding claims, characterized in that the first group (23c to 26c) of the second number of drying cylinders comprises at least four of the drying cylinders, and the second group of the second number likewise comprises at least four of the drying cylinders which, in the direction of transport follow the first group. Dryer section according to one of the preceding claims, characterized in that the second group (27c to 30c) of the second number of drying cylinders form the last drying cylinders in the drying section. Dryer section according to one of the preceding claims, characterized in that the first steam supply device supplies steam to the corresponding first number (1c to 22c) of drying cylinders with a greater pressure than that supplied by the third steam supply device to the second group of the second number of drying cylinders Vapor pressure. Dryer section according to claim 1, characterized in that the first number of drying cylinders (1c to 22c) is greater than the second number (23c to 30c) of drying cylinders. Dryer section according to one of the preceding claims, characterized in that the first number (1v to 22c) of drying cylinders is divided into several single-row drying groups, and that each drying group of the first number of drying cylinders is assigned an endless dry felt belt and / or dryer fabric belt, the each drying felt belt or dryer fabric belt is alternately guided around a drying cylinder and a paper web guide roller of the respective drying cylinder. Dryer section according to one of the preceding claims, characterized in that each dryer felt belt and / or dryer fabric belt of each dryer group of the first number is passed over the corresponding dryer cylinders, such that the dryer felt belt or dryer fabric belt contacts the first side of the paper web in contact with each of the dryer cylinders of the first number brings when the paper web and the drying felt belt or dryer fabric belt over the paper web loop around the drying cylinders. Dryer section according to one of the preceding claims, characterized in that the paper web guiding device comprises suction rolls, the suction rolls being arranged in succession along the transport path between successive adjacent drying cylinders, so that the suction rolls interact with the paper web in such a way that the paper web and the respective one Dry felt belt or dryer fabric belt partially wraps around each of the drying cylinders in the first number. Dryer section according to one of the preceding claims, characterized in that in the second number (23c to 30c) of drying cylinders, a corresponding first endless drying felt belt and / or dryer fabric belt is guided around each of the drying cylinders of the first row and is supported by the respective guiding device to the Guide the paper web over the first row of drying cylinders, with the first side of the paper web in Contact comes with each drying cylinder of the first row, and that a second endless drying felt belt or dryer fabric belt is guided around each of the drying cylinders of the second row and is supported by the respective guiding device in order to guide the paper web over the drying cylinders of the second row, the second side the paper web comes into contact with the cylinders in the second row. Dryer section according to one of the preceding claims, characterized in that the first number of drying cylinders and the guide device are arranged such that 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 drying cylinders and the guide device are arranged such that the first side of the paper web is the upper side and the second side of the paper web is the lower side. Dryer section of a paper machine with at least one single-row dryer group, which has several dryer cylinders,
at least one two-row drying group, which has a plurality of drying cylinders and is arranged downstream of the single-row drying group, and a steam supply device which interacts with the drying cylinders,
marked by
a steam control device that controls the amount of steam that can be supplied to the drying cylinders and / or the steam pressure in the drying cylinders, such that a first group (23c to 26c) of the drying cylinders of the two-row drying group (40) has a higher vapor pressure than a downstream second group (27c to 30c) of the two-row drying group.

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