FI83441C - FOERFARANDE FOER ATT FOERBAETTRA AV FUNKTIONEN AV ETT TORKPARTI SAMT EN MAONGCYLINDERTORK FOER TILLAEMPNING AV FOERFARANDET. - Google Patents

Description

83441

Method for improving the operation of the drying section and a multi-cylinder dryer applying the method The method for improving the function of the drying section 5 is similar to that of the rotary cylinder for the temperature of the 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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The invention further relates to a multi-cylinder dryer for a paper machine, consisting essentially of cylinder groups with single-wire outlets, consisting mainly of cylinder groups with steam-heated drying cylinders in the top row and inverted cylinders substantially in the bottom row, preferably a suction cylinder, open traction and ·

As is already known, in the drying section of a paper machine, either the so-called

25 single-wire exports or two-wire exports. Single-wire export, in which the drying wire also supports the web by tension between the rows of cylinders, is generally used at the beginning of the drying section. The single wire outlet can also be used along the entire length of the drying section.

Recently, single-wire outlet drying parts 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 with internal suction, e.g. "UNO-VAC" (trademark) cylinders 35 through a perforated jacket to apply a vacuum effect from the interior of the rotary cylinder to a groove surrounding the cylinder liner. The purpose of said vacuum effect is to effectively hold the web in the drying wire when the web is brought to the outer curve 2 by the downward turning cylinders 2 83441 ^ and to prevent transverse shrinkage of the web as the drying progresses.

It is also known to use the so-called. inverted wire groups, in which the reversing cylinders are groups of drying cylinders in the form of upper cylinders and hot drying cylinders, in particular for the purpose of achieving symmetrical drying of the web. In this regard, reference is made as an example to Beloit Corporation's FI patent applications Nos. 893748 and 893749 (corresponding PCT application publication WO88 / 06204). Em. the structure generally uses 10 inverted groups as every other single wire export group, which causes considerable difficulty in removing the wreck.

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-15.

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 20 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.

In some drying simulator studies performed by the applicant, it has been found that increasing the wire tension increases the evaporation efficiency of the drying cylinder to some extent. This is mainly based on the fact that 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 dry 30-cylinder surface and the web. . In particular, the air layer left between the cylinder surface and the web impairs evaporation, and this air layer can be reduced by increasing the wire tension.

In a drying simulator experiment performed by the applicant with a cylinder diameter of 0.45 m, it was found that the evaporation power at low stresses did not substantially increase as a function of stress. Instead, the 3 83441 ^ evaporation efficiency at a wire tension of 10 kN / m was about 25% higher than at a tension of 6 kN / m. It should be noted that due to the small diameter of the test cylinder, the above-mentioned stresses correspond to (1,8) m in the normal diameter of the drying cylinder (10 kN / m) -> 2,5 kN / m 5 and (6 kN / m) - > 1.5 kN / m.

In the article by Mike Rhyne: "Modern Dryer Fabric Design and Application", 1989, Practical Aspects of Pressing and Drying, the dependence between evaporation efficiency and drying wire on wire tensions of n.

10 0.5 ... - 1.8 kN / m. In this case, it has been observed that when the tension of the drying wire is increased approximately twofold at the end of the above-mentioned klreys region, the evaporation power increases by about 4-8%.

As is known, the drying section is used so that at the beginning of the drying section 15, where the web is wetter, a lower vapor pressure and a lower surface temperature are used in the drying cylinders, and the intention is to start the drying carefully. At the beginning of the drying section, the water in the web is mainly heated, while at the end of the drying section, the main evaporation of water takes place and its actual evaporation from the web.

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

It is a further object of the invention to provide a method and a drying section by means of which a sufficiently symmetrical drying is achieved so that no unsolved or unreasonable problems arise in the removal of the paper wreck.

It is a further object of the present invention to provide a method which contributes to reducing and smoothing the transverse shrinkage of the web to be dried and to drying the web so as to provide symmetrical drying and thereby an even lower tendency to curl the paper, e.g. for laser copying.

* 83441

In order to achieve the above and later objects, the method of the invention is mainly characterized in that in the method the tension of the drying wires of successive different wire groups is used as an when the concentration of the substance is higher than average, a wire tension of 10 to 10 times higher than at the beginning of the drying section is used.

The drying section according to the invention is in turn mainly characterized in that at the end of the drying section there is one, or at most two, inverted cylinder groups, the lower cylinders being heated drying cylinders and the upper cylinders being inverted cylinders, so that the opposite side of the web , that the diameters of the drying cylinders and the reversing cylinders, as well as the diameters of the guide rollers and the tension rollers, are chosen so that a higher wire tension than normal is available in the different groups and that a wire tension higher than other groups is available in the inverted group.

In the invention, the tensions of the wires of the different drying groups have been utilized as active process parameters, which can be used according to the invention to make drying more efficient, to reduce wreck removal problems and to smooth and reduce the transverse shrinkage of the web.

The drying parts currently supplied by the applicant have already used such large diameters of drying cylinders and reversing 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. How the wire tensions 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 characteristics, so it should be emphasized that the wire tensions and their ranges are only average and indicative.

II

5 83441 ^ separately tuned in the drying section and change this tuning when changing the quality.

As is known, the drying of the web must be started when it is relatively wet, with relative care. The present invention satisfies and in the invention increases the tension of the drying wire as the drying progresses and the web becomes more resistant to even high wire tension pressures without harmful side effects such as wire marking.

In the following, the invention will be described in detail with reference to some application examples 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 a schematic side view of a drying section applying the method of the invention.

Figure 2 shows a part of the drying section according to Figure 1 on a larger scale.

20

Fig. 3A shows, in a manner similar to Fig. 1, a schematic side view of a drying section applying the method of the invention.

Fig. 3B shows the distribution of the tensions 25 of the wires of the drying section of Fig. 3A along the entire length of the drying section.

Fig. 4 shows graphically in the dry matter coordinate system of the wire tension path the reference area within which the tensions of the different wires of the wire groups according to the invention are most preferably selected.

30

Figures 1 and 2 show 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 Rj_7 have 35 steam-heated drying cylinders 20 and reversing cylinders 21, 6 83441 ^ with a perforated and grooved jacket 22 inside which a vacuum prevails.

According to Fig. 1, a paper web Wln is introduced from a press section (not shown) 5 to a drying wire 11 of a first group R1 for running after its guide roll 18a, and a web W is attached to a drying wire 11 by means of a vacuum field 25 of suction boxes. The dry matter content of the web W is generally in the range of -40% to 45% as the web W enters the drying section and the first drying cylinder 20a. The web W leaving the dryer section 10 for the last drying cylinders 20b in the direction of the arrow Wout has a dry matter content of kaout - 91% ... 98%. The total length of the drying section is denoted by L. The length L is generally in the range L to 80 m ... 100 m. The height difference H between the cylinder rows 20.21 is generally in the range H to 1.3 to 1.7 m.

Figure 2 shows a more detailed structure of the multi-cylinder dryer according to Figure 1. According to Figure 2, the drying wire 14 of the fourth single wire group R4 differs from the web W following the surface of the cylinder 20 and moving to the drying wire 15 of the next group R5. , wherein the opposite side of the web W comes against the heated surfaces of the cylinders 20 'compared to the previous ones; towards the web of groups R 1, R 1 and the next group R 7. The transfer of the web W between the normal group Rs and the inverted group R6 takes place so that at the line S the web W leaves the wire 15 of the group R5 and follows the wire 16 of the inverted group R6 16 under the influence of the vacuum in the groove 22 on the outer surface of the cylinder 21 '.

The free sectors below the cylinders 20 of the normal (non-inverted) groups R have scrapers 23 which remove the impurity and a paper wreck 30 which thus passes to the pulper or scrap conveyor below. In the non-inverted groups Rj-Rj and R7, the removal of the wreck downwards by means of the pattern holes 23 is not problematic. Instead, in the inverted group. . R6 wreck removal is more problematic, and therefore the invention seeks to use only one or, exceptionally, at most two or three inverted groups.

In connection with the inlet nips N +, the drying cylinders 20 and 20 'have blow boxes 24 or similar static suction beams which prevent the induction of overpressure into the nip N + and the consequent detachment of the web W from the drying wire 11-17.

5

In Fig. 1, the tensions of the different drying fabrics 11,12,13,14,15,16 and 17 are denoted T ^ Tjj.Tj.T ^ Ts.Tg and T7, respectively. According to the present invention, said tensions are preferably selected according to the following table.

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Tj - 1.2 - 1.5 kN / m T5 - 2.5 - 4.0 kN / m T2 - 1.4 - 1.6 kN / m T6 - 4.0 - 6.0 kN / m T3 - 1.5 - 1.8 kN / m T7 - 3.0 - 5.0 kN / m T * - 2.0 - 2.5 kN / m 15

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. In addition, the inverted group R6 still uses a particularly increased tension T6 to 4.0 to 6.0 kN / m, even higher than the tension T7 of the last group. Mentioned wire tensions Tx-T7. . is provided by tension rollers 19, the tensioning forces F of which correspond to the above-mentioned wire tensions. Said tensions against the cylinder 20 and 20 'on the wires 11 ... 17 provide a tightening pressure p -T / R, where R - Di / 2.

25

According to the embodiment of the invention described above, the wire tension T is increased as the drying progresses. This procedure optimizes the drying optimally and so that even when the wire is raised, the tension T does not adversely mark the web to be dried, because the drier the web W, the higher the wire compression pressure p - T / R it can withstand without adverse side effects.

The increased wire tension also has the advantageous effect of making the web more firmly attached to the wire, thereby reducing and smoothing the harmful transverse itching of the web W, which has previously been a significant problem.

s 83441 The inverted group R6 is subjected to a particularly high tension in order to maximize the evaporation of the inverted group R6 and in this way the symmetry of the drying 5 of the different sides of the web W can be improved without causing insurmountable difficulties for track export and wreck removal.

The diameters D2f of the drying cylinders 22 normally used by the applicant, the diameters D2 of the turning cylinders 22 and the diameters D3 of the guide and tensioning rollers 18,19 10 already allow the use of the substantially raised wire tensions T already discussed above. Typically, the above-mentioned diameters D1, D2 and D3 are in the ranges D3 - 1.5 m ... 2.2 m, D2 - 1.0 m ... 1.8 m, D3 - 0.5 m ... 0, 9 m, the diameters of which ensure that the wire tensions T do not cause excessive deflections 20.21 in the blades and rollers 18 and 19 of the cylinder-15. One suitable combination of diameters D1 / D2 / D3 is e.g. 1.83 m / 1.5 m / 0.715 m.

Fig. 3A illustrates, in a manner similar to Fig. 1, another embodiment of the invention using first 20 normal (non-inverted) wire groups Rj.- Rj according to Fig. 1, then one inverted wire group R6 which is relatively long longer than average and substantially longer than four. the first group Rj .-. R * and the last normal group R7. According to Figure 3A, the inverted group R6 has six consecutive heated drying cylinders 20 'and six reversing cylinders 21', respectively.

Fig. 3B shows the distribution of the wire tension of the wire groups of the multi-cylinder dryer according to Fig. 3A in the longitudinal direction L of the drying section. The non-inverted first groups R1 ... RS use a standard vii-30 tension T: «T2» T3 «T * = T5 2.5 kN / m. In the inverted group R6, which is longer than normal, a particularly high wire tension T6 <6 kN / m is used. In the last untranslated group R7, the wire tension of normal groups T7 <2.5 kN / m is used again.

In the embodiment according to Figures 3A and 3B, it is preferred that the wire pitch Te of the inverted group R6 or the groups (there are at most two of these) be about 2 to 4 times as large as the wire distance T1 ... T7 of the normal groups. According to Figures 3A and 3B, a multi-cylinder configuration is obtained in which the evaporation of the inverted group R6 is particularly enhanced due to its length and in particular its particularly high wire tension T6, whereby there can be only one R6 of the inverted groups.

In preferred embodiments of the invention, the inverted group R6 or groups are placed at the end of the drying section, preferably so that when one inverted group R6 is used, this group is the second-last group followed by another normal group. The inverted group R6 is preferably dimensioned longer than the other groups on average and preferably uses 5-8 drying cylinders and a corresponding number of inverting cylinders.

15

Figure 4 shows, in cross-sectional area A, the tensions of the wire T as a function of the dry matter content ka of the web W. Tensions close to the lower limit of the range T2 (ka) are used in normal cylinder groups (Rj -.- Rj, R7) where the upper cylinders are heated cylinders. The tensions T at the upper limit T7 (ka) of the region A20 are used in the inverted wire group Re or groups, which are as small as possible, usually only one or exceptionally two, due to said wreck removal difficulties. Figure 4 is intended only as a general guide and the main principle for the selection of slope holes according to the invention. In some special cases, it may be necessary to deviate from area A shown.

The invention has been described above with reference only to the drying section provided with a single wire outlet. Exceptionally, the invention can also be applied to multi-cylinder dryers in which one or more two-wire outlet groups are used, in which case both the lower wire and the upper wire tension can be used according to the invention as an active process parameter. However, the invention at its most preferred is particularly applicable to multi-cylinder dryers which use, in all groups, or at least in almost all groups, a two-wire outlet 35 and generally only one inverted group Rg.

ίο 83 441 ^ The present invention provides an optimum efficiency of the evaporation of the drying section without harmful side effects.

According to the invention, it has been possible to create a new efficient process parameter from the wire tensions, which, when used wisely according to the invention, provides considerable advantages without any investment in equipment.

In some cases, the invention makes it possible to substantially shorten the drying section due to the more efficient drying and thereby reduce the investment cost of the paper machine link.

The following claims set forth within the scope of the inventive idea defined by the invention may vary and differ from those set forth above by way of example only.

15 20 25 30 35

II

Claims (9)

A method for improving the performance of a drying section, which method is applied in a multi-cylinder dryer having a plurality of 5 wire groups (^ ... ^) each having a drying wire (11 ... 17) and one or two rows of cylinders (20,22), of which the cylinders of at least the second row are heated drying cylinders (20), against the surface of which the web (W) comes into direct contact under the tensioning pressure of the drying wire (10 ... 17), characterized in that in the method 10 tension wires tension (Τχ ... T7) is used as an active process parameter to improve the drying process, for the above-mentioned purpose the drying wire tensions (T7 ... T7) of different wire groups (R7 ... R7) are selected to be W) when the dry matter content (ka) is higher than average, the higher is used on average a wire tension (T4 ... T7) than at the beginning of the drying section. Method according to Claim 1, characterized in that in the method the tension (Τχ ... T6) of the drying groups of the different groups is gradually increased as the dry matter portion (ka) of the web (W) increases from the beginning to the end of the drying section. Method according to Claim 1 or 2, characterized in that the wire tensions are selected at the beginning of the drying section in the range from 1.2 to 4 kN / m, gradually increasing the wire tension from the previous wire group (R „) to the next wire group (R ^ + χ), that in the last or last wire groups, the wire tension is selected in the range of 3.5 -5.0 kN / m and that in the inverted wire group (Rg) a particularly high wire tension of 30 to 6.0 kN / m is used. Method according to one of Claims 1 to 3, characterized in that in the method the web (W) is guided as a single-wire outlet and continuously supported by a drying wire (11 ... 17) or a cylinder surface, preferably a suction cylinder surface, so that the transverse web (W) shrinkage is substantially prevented and distributed substantially evenly over the entire width of the web (W). A multi-cylinder dryer for a paper machine, consisting essentially of cylinder groups R7) with 5 single-wire outlets, consisting mainly of cylinder groups with steam-heated drying cylinders (20) in the top row and reversing cylinders W, preferably suction cylinders (21) in the bottom row, substantially closed for export without long open strokes, characterized in that at the end of the drying section there is one, or at most two, inverted cylinder groups (R6), the lower cylinders being heated drying cylinders (20 ') and the upper cylinders being reversing cylinders (21'), that the opposite side of the web (W) faces the heated cylinder surface in the inverted group (R6) compared to the non-inverted groups, that the diameters (D1 (D2) of the drying cylinders (20,20 ') and the inverting cylinders (21,21') and the guide rollers ( 18) and the diameters (D3) of the tension rollers (19) are thus va that a higher than normal wire tension (Tx ... T7) is available in the different groups and that a higher stringency of vii-20 (T6) is available in the inverted group (R6) than in the other groups. A multi-cylinder dryer according to claim 5, characterized in that said inverted cylinder group (R6) is the second last group of the drying section and is followed by one or two normal groups (R7). Multi-cylinder dryer according to Claim 5 or 6, characterized in that the inverted group (Rg) has a plurality of drying cylinders (20 '), preferably about 5 to 8, so that the length of the inverted group (R6) is substantially greater than the average group length. Multi-cylinder dryer according to one of Claims 5 to 7, characterized in that the diameters (D7) of the heated drying cylinders are in the range Dx to 1.5 m to 2.2 m, that the diameters of the reversing cylinders (22) are in the range D2 to 1 .0 m ... 1.8 m, and that the diameters (D3) of the guide rollers (18) and the tension rollers (19) of the drying file 13 83441 ^ (11-17) are in the range D3 - 0.5 m ... 0 , 9 m. Multi-cylinder dryer according to one of Claims 5 to 8, characterized in that the web (W) to be dried is fed to the inverted cylinder group (R6) from a previous, non-inverted group (Rs) between two overlapping suction cylinders (21, 21 '). 16) by common running, that the web (W) is separated from the drying wire (15) of the previous group (Rs) and guided to the drying-10 wire (16) of the inverted group (R6) by means of a vacuum field (Figure 2). 15 20 25 30 35 i4 83441