FI84282C - FOERFARANDE FOER ATT FOERBAETTRA AV FUNKTIONEN AV ETT TORPARTI SAMT EN MAONGCYLINDERTORK FOER TILLAEMPNING AV FOERFARANDET. - Google Patents

Description

84282

Method for improving the performance of the drying section and a multi-cylinder dryer applying the method The method for improving the performance of the drying part 5 and the function of the multi-cylinder dryer

The invention relates to a method for improving the operation of a drying section, which method is applied in a multi-cylinder dryer with 10 successive wire groups each having a drying wire and one or two rows of cylinders, at least one row of cylinders being heated drying cylinders. .

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Recently, drying parts with a single wire outlet have become more common, in which the upper cylinders are steam-heated drying cylinders, against which the web comes into direct contact when pressed by the drying wire, and the lower cylinders are cylinders equipped with internal suction, e.g. "VAC-ROLL" (trademark) rollers through which a vacuum is applied through a perforated jacket to a groove around the cylinder liner from the inside of the pivot cylinder. Said vacuum effect is intended to effectively hold the web in the drying wire when the web is on the outer curve by the lower turning cylinders and to prevent transverse shrinkage of the web as the drying progresses.

Typically, a multi-cylinder dryer has 5-8 wire groups and the groups at the beginning of the drying section are normally shorter than the groups at the end-30.

It is the practice of the applicant and some other paper machine suppliers to dimension the wire tensions in the drying section so that the maximum wire tension is 2.5 kN / m. A wire tension of 1.7..2.0 35 kN / m is used as the practical driving range. This constant wire tension is used along the entire length of the drying section, and wire tension has not previously been realized to be used as an active process parameter in paper drying.

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The higher the wire tension, the higher the wire tension pressure p - T / R (where T is the wire tension per unit width and R is the cylinder radius) and the better the contact between the hot drying cylinder surface and the web and the lower the transverse impact. tistuma. The higher the vacuum of the suction cylinders, the greater the force applied to the paper web on its substrate and thus prevent it from shrinking.

Measurements have shown that at the beginning of the drying section, a rather small holding force of 10 is sufficient to prevent shrinkage.

The object of the present invention is to provide a new method for improving the operation of the drying section and promoting its efficiency without the actual additional equipment and additional investment.

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It is an object of the invention to provide a method and a drying section concept which can contribute to reducing and smoothing the transverse shrinkage of the web to be dried and to drying the web so as to achieve symmetrical drying and by this means an even lower tendency of the paper 20 to curl, e.g.

In order to achieve the above and later objects, the method of the invention is mainly characterized in that in the method the vacuum levels of the suction cylinders of successive different wire groups 25 are adjusted so that the vacuum of the suction cylinders is that the vacuum in the suction cylinders of the drying groups at the beginning of the drying section is considerably lower than the vacuum in the suction cylinders of the drying groups at the end of the drying section, the vacuum selection correspondingly the vacuum of the suction cylinders which for me, a lower holding pressure is sufficient to prevent transverse shrinkage.

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The drying section according to the invention, in turn, is mainly characterized in that the multi-cylinder dryer comprises control equipment from which control data is passed via a signal path to the pump , wherein a holding force is required to minimize the transverse shrinkage of the paper web, wherein lower vacuum pressures are applied to the suction cylinders at the initial end of the drying section where a lower holding force is sufficient to minimize shrinkage.

In the invention, the tensions of the wires of the different drying groups and the vacuum of the suction rolls 15 have been utilized as active process parameters, which can be used according to the invention to increase the efficiency of the drying section, reduce wreck removal problems and smooth and reduce transverse shrinkage of the web. How the wire tensions and the vacuum of the suction cylinders in each different drying section are tuned as a function of the dry matter content of the web also depends on the quality of the paper to be produced and the desired quality properties.

The drying parts currently supplied by the applicant already use such large diameters of drying cylinders and swivel cylinders as well as guide rollers and tension rollers that the method according to the invention can be implemented without significant additional costs and investments.

In the following, the invention will be described in detail with reference to some exemplary embodiments of the invention shown in the figures of the accompanying drawing, to the details of which the invention is in no way narrowly limited.

Figure 1 shows the transverse shrinkage of the paper as a percentage on the vertical axis and the horizontal axis on the dry matter content / drying section length of the paper web. The diagram shows the holding pressure of the suction cylinder 4,84282 on a straight line, the holding pressure of 2000 Pa on the broken line and the holding pressure of 4000 Pa on the dotted line.

Figure 2 shows a schematic side view of the drying section of the method according to the invention.

Figure 3 shows the development of the transverse shrinkage of the paper web in the drying section when the drying section is divided into two vacuum pressure zones of the suction cylinders.

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Figure 4 shows the development of the transverse shrinkage of the paper web in the drying section, respectively, in the case where the drying section is divided into three vacuum zones of the suction cylinders.

Fig. 1 is a diagram in which the vertical coordinate system has the transverse shrinkage of the paper web as a percentage of the initial width of the paper and the horizontal axis has the dry matter content of the paper web as a percentage / the length position of the drying section. The figure shows the transverse shrinkage as a function of the dry matter content in a straight line when the holding pressure of the suction cylinders 20 is 500 Pa, in broken lines when the holding pressure is 2000 Pa in the suction cylinders and most densely in broken lines when the holding pressure is 4000 Pa. In the dry matter content range of 0-60%, i.e. in the initial range of the drying section, there is a suction effect, the holding pressure of 500, 2000 or 4000 Pa was approximately the same.

Thus, in this range, a holding pressure of 500 Pa can be selected for the suction rollers 25 in the drying cylinder group. In the range of 60-70% of the dry matter content, a holding pressure of 2000 Pa is probably sufficient, and up to 70% of the dry matter content, it is preferable to use a holding pressure of 4000 Pa or even higher.

According to the invention, the drying part according to the invention takes into account the above-mentioned fact so that the drying part is functionally divided into at least two groups so that the holding pressure is applied only where it is necessary. Thus, a lower holding pressure is domesticated at the beginning of the drying section than at the end of the drying section. According to the invention, the above-mentioned holding pressure is changed by changing the tension of the wire and the vacuum level of the suction rolls. The wire tension and the vacuum of the suction rollers are higher at the end of the drying section than at the beginning of the drying section.

The control of the holding pressure according to the invention is reflected in lower investment costs. Because lower holding pressures and lower wire tension and lower suction are required at the beginning of the drying section, equipment costs and total energy costs are lower than in prior art solutions. Thus, in the drying section concept according to the invention it is realized to take the holding pressure as a design para 10 and according to the invention it is possible to form the drying section so that the diameters of the upstream rollers are chosen smaller than the downstream and likewise a lower vacuum is applied to the suction cylinders greater force is required to prevent transverse shrinkage of the paper web 15.

Figure 2 shows a typical multi-cylinder dryer with a single wire outlet, in which the method according to the invention is applied. The drying section comprises seven successive wire groups R1..R7, all of which apply single wire export. The various drying groups R 1 have steam-heated drying cylinders 20 and suction cylinders 21 with a perforated and grooved jacket 22 inside which a vacuum prevails.

According to Fig. 2, the paper web Win is introduced from the press section (not shown) to the drying wire 11 of the first group R1 for running after its guide roll, and the web W is attached to the drying wire 11 by means of a vacuum field of suction boxes. The dry matter content of the web W is usually in the range of -40% ... 45% as the web W enters the drying section and the first drying cylinder 20. When the web W leaves the last drying cylinder of the drying section, its dry matter content is -91% ... 98%. The total length of the drying section is marked L. The length L is usually in the range L - 60 m ... 100 m.

In Fig. 2, reference numeral 30 shows a control apparatus from which a signal path 31a, 31b leads to a pump apparatus 32a, 32b, from which pressures P1, P2, P3, P4 ... Pn are produced for each suction cylinder 21. Thus, a vacuum is applied inside the cylinders. When the rollers are perforated / grooved, the holding force is perforated in the paper web through the perforation / grooving. According to the invention, RltR21R3lR4 of each group is produced. . . for imusy-5 linters, a different vacuum compared to the groups so that the vacuum level rises along the drying section. In this way the holding force is increased towards the last groups of the drying section.

According to the invention, it is also possible to produce a different vacuum for each of the 10 cylinders within the groups, so that the highest vacuum is always produced within the group for the last cylinder in the group and thus the holding force is uniformly increased also within the groups. Thus, one of the parameters in the design of the drying group is also the vacuum applied to the suction cylinders and the force with which the web is pressed onto the surface of the wire and / or roll 15. Correspondingly, in each group, the wire tension is affected by using the wire tension parameter. The wire tension at the beginning of the drying group is selected to be lower than the wire tension at the end of the drying group.

Thus, the force exerted by the paper web against its drying substrate is effected by providing a desired amount of vacuum to the suction rolls of the groups and preferably also by providing a desired amount of wire compression by selecting the wire tension and cylinder size in a manner that performs the desired compression.

In a simpler form of the invention, the vacuum zones are selected so that there are only two vacuum zones along the entire length of the drying section.

In Fig. 2, the tensions 30 of the different drying fabrics 11,12,13,14,15,16 and 17 are denoted Tx, T2, T3, T4, T5, T6 and T7, respectively. According to the present invention, said tensions are preferably selected according to the following table.

35 7 84282 Τχ - 1.2 - 1.5 kN / m Τ5 - 2.5 - 4.0 kN / m Τ2 - 1.4 - 1.6 kN / m Τ6 - 4.0 - 6.0 kN / m Τ3 - 1.5 - 1.8 kN / m Τ7 - 3.0 - 5.0 kN / m Τ4 - 2.0 - 2.5 kN / m 5

It can be seen from the above table that the tension of the wire T is increased according to the invention as it moves from the beginning to the end of the drying section.

Figure 3 shows the transverse shrinkage of the paper web in the vertical coordinate system and the dry matter content of the paper web in the horizontal coordinate system, which also reflects the location on the drying section. Figure 3 shows the optimization of the drying operation so that the vacuum of the suction rolls and thus the holding force of the paper web is selected in an optimal way. The starting point 15 is the diagram shown in Fig. 1, on the basis of which it has been possible to select the optimal vacuum for the suction rollers. In the drying section concept of Fig. 3, a vacuum is selected for the suction rolls of the drying section so that the suction rollers at the beginning of the drying section have a vacuum of 500 Pa and the rolls at the end of the drying section have a vacuum of 4000 Pa. This vacuum is adapted to change 20 at a dry matter content of 60%. Figure 3 shows the transverse shrinkage of the web corresponding to the concept as a function of the drying station (dry matter content).

Figure 4 shows the optimization using three negative pressures, 500 Pa, 2000 Pa and 4000 Pa. In this case, up to a dry matter content of 60%, a vacuum of 500 Pam is used in the suction rolls at the beginning of the drying section, a vacuum of 2000 Pa is used from the 60% dry matter point and a vacuum of 4000 Pa is used in the suction rolls from a dry matter point of 70%. The combined diagram shown in Figure 4 is obtained. Thus, the insight according to the invention has a favorable effect on the transverse shrinkage of the paper web and further reduces the investment cost, since the required vacuum, fans and rollers can be selected at the beginning of the drying section on the basis of lower holding forces. Thus, lower vacuum is required and 35 is solved with lower energy costs. Correspondingly, when the holding force is affected by the wire tension. Lower holding forces e 84282 are required at the beginning of the drying section, whereby the wire tension may be lower at the beginning of the drying concept than at the end.

Claims (6)

A method for improving the function of a drying portion, which method is applied in a multi-cylinder dryer, having several wire groups 5 (R, ...) one after the other, each of which has a drying wire at least a row of drying cylinders (20) and Atminstone a row of suction cylinders (21), wherein the drying cylinders are heated drying cylinders (20) against the surface of which the web (W) coraras in immediate contact pressed by the tension pressure of the drying wire (11), and the suction cylinders (21). easter cams that the web is held at the surface of the wire by means of a vacuum produced within these dA the wire is passed along the suction cylinders (21) while the vacuum is directed to the paper web via the perforated and / or grooved ends of the suction cylinders, the web being attached to the web. the vacuum / cylinder surface having a suction effect, characterized in that in the process, the vacuum levels of the suction cylinders (21) in the various virus groups (R, R The steam cylinder dryer controlled in such a way that the vacuum of the suction cylinders is arranged to increase from the beginning of the drying portion towards the end of the drying portion, whereby actively suppressing such suppression in the suction cylinder (21) of the drying portion (21) of the drying portion ( Rj ...) at the beginning of the drying portion is considerably lower than the vacuum in the cylinders of the drying groups (Ra.Rn + iR ». · ·) At the end of the drying portion, whereby with the choice of vacuum on the suction cylinders (21) in the drying portion According to the invention, the transverse shrinkage of the paper web actively acts to reduce it by maintaining a higher holding force at those areas of the drying portion where an increase in holding force promotes a reduction of shrinkage and correspondingly reducing the vacuum of the suction cylinders (21). less holding power is sufficient to prevent a transverse shrinkage. 2. A method according to claim 1, characterized in that, in the process in each drying cylinder group (R, R,.. RJ of the drying portion, a vacuum for suction cylinders (21) is regulated in such a way that the vacuum increases from a group. to another dA moving towards the end of the drying section 3. A method according to claim 2, characterized in that in the process the vacuum of the suction cylinders (21) is regulated in one or more drying cylinder groups (R 1, R 2 ...) so that it increases towards the end of the drying portion. 4. A method according to any of the preceding claims, characterized in that a control system (30) is used in the process from which it leads a signal path (31) to a pumping plant, with which a vacuum is produced. (P2, P2, P} .PB) to each suction cylinder (21) such that the vacuum pressures achieved in the suction cylinders increase at a distance from the drying portion towards the end of the drying portion and / or are at most equal, however, so that the drying portion is at least two negative pressure regions on the suction cylinders, whereby at the first beginning end of the drying portion there is lower negative pressure in the suction cylinders (21) than in the second negative pressure region located at the end of the drying portion. 5. A method according to any of the preceding claims, characterized in that the method additionally affects the pouring force of the paper web to reduce the transverse shrinkage of the paper web by controlling the tension (T, ... TB) of the wire. (11), by regulating the wire tension so that within a stretch of the drying portion, it increases towards the end of the drying portion, whereby through the wire 25 the greatest pouring force is directed towards the paper web at the end of the drying portion, thus where one needs a pouring force to reduce the transverse direction. the shrinkage of the paper web. 6. Multi-cylinder dryer in a paper machine consisting mainly of single-wire cylinder groups (R 1, R 2 ...) in which there are such cylinder groups having meadow-heated cylinders (20) advantageously in the upper row and break cylinders, most preferably suction cylinders (21), advantageously in the lower row, through which the drying portion of the web (W) is guided, characterized in that the quantity cylinder dryer comprises a control system (30) from which via the signal path (31), control data is fed to the pump system, from which produces set values for the vacuum pressures (P, P2, P,...) on the suction cylinders (21) of the milling cylinder dryer pd, so that, at the beginning of the drying section, the suction cylinders (21) have lower vacuum than the suction cylinders (21). of the drying portion, whereby with a control of the underpressure, the hdll force is operated where it is most needed to minimize the transverse shrinkage of the paper web, whereby at the beginning of the drying portion therefore, a smaller holding force is sufficient to minimize the edge shrinkage, which regulates less vacuum for the suction cylinders (21). 10