FI70275C - TORKNINGSFOERFARANDE SAMT MAONGCYLIN- DERTORK FOER EN PAPPERSBANA. - Google Patents

Description

70275 1 Method for drying a paper web and a multi-cylinder dryer Torkningsförfarande samt mangsylindertork för en pappersbana 5

The invention relates to a method in a paper machine slot cylinder dryer, in which method the paper web to be dried is guided against the surfaces of the heated drying cylinders in direct contact, in which method the web is led in at least the first or first drying groups. as a single fabric outlet, in which the drying fabric, preferably a relatively open drying wire, passes from one row of drying cylinders or rolls to one knee so that even between said rows the web is supported by said drying fabric, and in which the webs of the second row and on the second row of cylinders or rollers, the drying wire is against the surface of the roll or cylinder and the web is at the same time outside the drying fabric.

The invention further relates to a multi-cylinder dryer for a paper machine, comprising one or more successive drying groups with two rows of cylinders and / or rolls and in which at least the first or first drying groups are provided with a so-called with a single fabric export such that the paper web to be dried is supported all the way through the drying group by said drying fabric so that said drying fabric presses the web to be dried in one row in direct contact against the surface of the drying cylinder and the drying fabric in a second row while the web is outside.

30

As is already known, the multi-cylinder dryers of a paper machine consist of two overlapping horizontal rows of drying cylinders, between which the paper web passes on its knees. Air-permeable drying fabrics are now used in connection with drying cylinders.

The drying section of the paper machine uses single and double wire outlets. By single-wire export is meant an export in which the web passes from one drying cylinder to another, supported by one and the same drying wire, also between cylinder rows. In a two-wire export using an upper and lower wire, the web has free unsupported gaps as it passes from one cylinder line to another. The present invention relates specifically to single wire.

The efficiency of contact drying is crucially dependent on the contact between the paper and the hot surface (cylinder surface). Improving this contact is the primary function of the drying wire. In the present invention, attention is paid to another important aspect in the operation of the wire, namely the temperature of the drying wire and its effect on the drying speed.

The drying fabrics are generally made open so that the space formed by the paper web, the drying fabric and the drying cylinder, the so-called pocket, air conditioning would be easier to arrange. Due to the openness of the drying fabrics, the general perception has been that water vapor travels without condensation through the wire into the environment on top of the cylinder.

For the prior art related to the present invention, reference is made as an example to U.S. Patent No. 3,503,139 to Beloit Corporation. This patent discloses the so-called a single fabric outlet in a drying cylinder comprising two horizontal rows of steam heated drying cylinders. This patent represents the common beliefs prevailing in the art. In proposing that those drying cylinders which are inside the monofilament export wire or felt loop, i.e. against which said felt or wire will be outside the web with these cylinders, use a higher temperature than the second row cylinders, i.e. the cylinders against which the web comes into direct contact.

The basic ideas underlying the present invention are contrary to the principles of the aforementioned U.S. patent.

There have been several drawbacks to the previously known single-cylinder multi-cylinder dryers, notably the differences in speed between the rows of cylinders-35 due to the different cylinder temperatures of the different rows and the different large thermal expansions, i.e. changes in diameter. There has also been a disadvantage in the cylinders in which the web 3 70275 to be dried is exposed, the tendency of the web to detach from the surface of the drying wire, a phenomenon which is further exacerbated by the overpressures induced in the inlet nip of the drying wire and the cylinder surfaces. Said detachment even causes breaks or at least web bagging and wrinkling. One disadvantage has also been the rapid wear of plastic drying fabrics in particular, which is due, at least in part, to being pressed in direct contact with the hot cylinder surface by the second cylinder row and varying tensions of the drying wire with rising and falling sections so that they can cause abrasive slippage. with a hot sy-10 linterl surface. The object of the present invention is to avoid said drawbacks with a new drying method and a drying section in which a single-wire export is applied, which in itself has several advantageous properties.

One of the starting points of the present invention has been the applicant's previous FI-pat.hak. No. 812089 (application date 2 July 1981, inventor Dr. Markku Lampinen). Em. FI-hak discloses a method for enhancing the operation of a paper machine or a similar dryer, in particular a multi-cylinder dryer, in which the dryer uses open drying wires which press 20 webs to be dried against the cylinder surface and / or support the web with inter-cylinder runs. Em. The invention disclosed in FI-hak is directed to multi-cylinder dryers using air-permeable drying lines having a permeability of more than 500 m / m / h when the pressure difference across the wire is 100 Pa. Em. FI-hak: its invention is based on studies according to which water vapor can be made to condense on a wire despite its openness when the temperature of the wire is sufficiently low. The mentioned phenomenon has also occurred to some extent on paper machines previously known from the above-mentioned FI-hak, but since the mentioned phenomenon was not previously known, it could not be utilized either. Em. The core of the invention was that the air conditioning in the drying section of the paper machine is intensified so that the drying wire, for example the single-fabric export wire, is set at the lowest possible temperature level.

Em. FI-hak 812089 also disclosed devices for carrying out said method, which devices were characterized in that the device comprises a wire pocket formed by the guide rollers of a refrigerated drying wire, which is vacuum-pressed by special devices so that the wire strands forming said pocket walls, a flow-through to cool the drying wire is provided. In addition, the above-mentioned FI-hak disclosed a device comprising housings or the like placed opposite each other on both sides of the drying wire run, of which the walls coming against the drying wire 5 are provided with perforations, slits or the like, which device includes fans or the like. through said housings a flow is obtained which passes through the eyes of the drying wire.

10 Em. However, the devices of FI-hak: its 812089 do not in practice succeed in cooling the wire, in particular the drying wire of the single-tissue export, sufficiently so that the intended beneficial effects can be obtained in practice at a sufficient level. These disadvantages are mainly due to the drying wire having time to heat up, which in turn is mainly due to the fact that the drying wire is in single wire outlet directly against the heated surface of the drying cylinder in another cylinder row, usually a lower cylinder row, where the paper web remains on the outer surface.

The object of the present invention is to avoid the above-mentioned drawbacks 20 and to provide a multi-cylinder dryer and drying method for a paper machine which can make better and more efficient use in practice of the advanced ideas presented in the above-mentioned FI patent application 812089.

It is a further object of the present invention to provide a multi-cylinder dryer for a paper machine in which the manufacturing costs of the structures can be substantially reduced.

It is a further object of the present invention to provide a drying section of a paper machine 30 which achieves lower energy consumption per production unit to be manufactured.

It is also an object of the present invention to provide a paper machine and its drying section with which a better runnability of the machine 35 can be realized, i.e. the purpose is to reduce web breaks and the downtime caused by them.

5 70275 1 It is an object of the present invention to provide a drying section which can be further considerably shortened, which in turn provides savings in reducing the space requirements of the paper machine room or the like.

5

It is an object of the invention to provide such a drying section in which the service life of the used drying wire can be extended.

In order to achieve the above and later objects, the method according to the invention is essentially characterized in that the drying fabric is cooled as it passes between cylinders with the web directly heated against the surface of the drying cylinder, and said cooling is performed by pressing the drying fabric immediately into contact with the cooling roll or against a cylinder surface 15 having a contact area large enough for said cooling.

The method according to the invention, on the other hand, is mainly characterized in that the cylinders or rolls in its row on which the web remains on the outside are, instead of heated drying cylinders, relatively large-diameter combined conductor and contact cooling rollers without actual heating devices.

The method and the drying section of the invention have been found to provide a temperature reduction of about 20-30 ° C on a single fabric drying wire, which in turn provides several different advantages, which will become more apparent from the following detailed description of the invention.

The invention will now be described in detail with reference to an embodiment of the invention shown in the figure of the accompanying drawing, to which the invention is not limited.

Figure 1 shows a schematic side view of a multi-cylinder dryer 35 according to the invention and a closed press section preceding it.

Figure 2 shows the development of the surface temperatures of the drying cylinders and the paper temperatures observed in the experiments performed in practice in the 1st drying group with the so-called drying group. lowered geometry.

Figure 3 shows, in a manner similar to Figure 2, the evolution of the surface temperatures of the drying cylinders and the temperatures of the wire and paper in the drying group 2, the operation of which has been modified to verify the effects of the invention.

The multi-cylinder dryer shown in Figure 1 is preceded by the so-called a closed portion of the press-10 into which the paper web W is introduced by the pick-up fabric 11. A first nip is formed between the upper press suction roll 13 (suction zone 13a) and the hollow surface roll 12. The first nip is double felt and its lower felt is a press felt 10. The web W follows the upper felt 11 over the suction sector 13a of the roll 13 to the second nip N 1. The suction sector 13a has a steam box 14 known per se. A second nip is formed between said press suction roll 13 and the smooth surface design 15. Against the smooth surface design 15 is a third nip N 1 formed in the center of the press fabric 16 guided by the press roll 17 and the guide rollers 18.

From the smooth surface of the stone roll 15, the web W is drawn using a release roll 19 so that the web W has the shortest possible free tension between the release roll 19 of the press roll 15. A drying wire 30 of the first drying group 20, which is, for example, a relatively open plastic wire with a permeability of the order of 25 500-1500 m3 / m 2 / h, is passed over the driven release roller 19.

After the release roll 19, the web W rests on the lower surface of the drying wire 30, on which it is guided to the first drying cylinder 21 or to the corresponding so-called for lead-in or baby cylinder. In the run between the release roll 19 and the first cylinder-30 blade 21, the retention of the web W on the outer surface of the wire 30 is ensured by vacuum-generating blow boxes 26, the construction and operation of which refer to the applicant's previous FI-pat.hak for details of export from the press section VJ to the drying section. No. 830422 (cf. U.S. Application No.).

In Fig. 1, the frame structures of the press section and the drying section shown schematically are indicated by the number 100 and the floor level 35 of the paper machine room by the number 110.

Figure 1 shows two successive drying groups 20 and 40 (wire groups), in which groups 20, 40 single wire export has been applied. In the case of the previously known single-wire outlet, the drying rows of the second row remain inside the wire loop and the cylinders of the second row remain inside the wire loop, so that for the cylinders outside the wire loop against the outside of the web.

After the drying group 40, two or three groups with two-wire outlets are generally followed in succession.

15

The upper cylinders 21,22,23,24 and 25 of the first group 20 are normal steam-heated drying cylinders. The first cylinder 21 has a coverage angle α1 to 90-180 ° of the drying wire 30 and the web W, and the subsequent cylinders 22-25 have a corresponding coverage angle, i.e. a sector in which the drying web W is pressed by the drying wire 30 directly against the cylinder surface. ^ ps 250 °. The aim is to make the sector α1 as large as possible in order to achieve the most efficient heat transfer from the surface of the cylinders 21-25, 41-44 to the web W to be dried.

According to the present invention, the cylinders of the second row of the multi-cylinder dryer which were steam heated according to the prior art, i.e. in the example of Figure 1 the lower row drying cylinders, have been replaced by contact cooling rollers 31,32,33,34 over which the wire 30 and web W pass so that the wire 30 to be cooled is directly against the surface of the cooling rollers 30-34 with the web W remaining outside. Rollers 31-34 also act as guide rollers. According to the present invention, said rollers 31-34 are not heated by steam or otherwise, but these rollers act specifically as contact members for cooling the wire 30. The rollers 31-34 may even be provided with cooling devices, for example those with which a cooling medium-35 is led inside the rollers 31-34 or air is blown against the free surface of the rollers 31-34.

8 70275

The coverage angle α1 of the wire 30 and the web W on the rollers 31-34 is substantially equal to the coverage angle α1 on the drying cylinders 21-24.

The rollers 31-34,51-54 are provided with an open surface, preferably a machine-5 with a helical groove surface of 35.55.

Air blowing devices 27 are arranged in the slots A of adjacent cylinders 21, 22, etc., the construction and operation of which are referred to as an example by the applicant's FI patent No. 65460 (cf. U.S. Pat. No. 328,793). With these devices 27, air is ejected from the inlet nipples N1 between the wire 30, outside which there is a web W, and the cylinders 31-34, in which an overpressure detaching the web W from the wire 30 tends to be generated. The devices 27 generate a nipple vacuum which also acts on the groove 35 in the surface of the rolls 31-34 in addition to what is already created by the groove alone and which ensures that the web W does not detach from the outer surface of the wire 30 due to centrifugal forces in said rolls 31-34. Due to the mentioned centrifugal forces, the rollers 31-34 must have a sufficiently large diameter ° 2 · 20 The actual drying cylinders 21-25 have scratches 28 in the free sectors below them between the rolls 31-34. To ensure adequate ventilation of the drying section, the rollers 31-34 have one so-called B. submersible devices 36.

As described above with respect to the first drying group 20, the same applies to the second drying group 40 having a drying wire 50 which provides a single fabric pass through the group 40 from the drying cylinder 25. The top row of the group 40 is formed by steam-heated drying cylinders 41, 42, 43, and 44, and the bottom row is the above-described grooved surface contact-30 cooling and guide rollers 51, 52, 53, and 54, which may be, as you say, even cooled. The last cylinder 44 of the group 40 is followed, for example, by a group of drying cylinders (not shown) in which the so-called double-tissue export and in which group there are both top-row and bottom-row cylinders heated by steam and the the group uses open web 35 pulls between cylinder rows. In the groups 20 and 40, the web W has already had such a high degree of dryness and strength that the essential hazards of breakage do not occur even with said open tensions of the web W.

9 70275

As one example of the dimensioning of groups 20 and 40, the following = 1830 mm = 1500 mm 5 ai = 248 ° a2 = 248 ° = 270 mm = 600 mm H = 1420 mm 10

In the figure, the planes 21-25, 41-44 of the cylinders of the top row are shown by the references Hj-H ^ and the planes 31-35.51-54 of the rollers 31-35.51-54 and the height difference of said planes are denoted by H.

In preferred embodiments of the invention, the above-mentioned blowing devices 26 and 27 patented by the applicant and the grooving 35.55 of the rollers 31-34.51-54 are used to ensure the export of the web W, to prevent the web W from coming loose and bagging. The runnability can be further improved by choosing the diameters of the rollers 31-34; 51-54 to be smaller than the diameters of the cylinders 20 21-25.41-44 and by compacting the structure of the drying section (dimensions A ^ and B ^ and H). At the same time, the length of the drying section and the entire length of the machine can be significantly reduced.

The runnability of the machine can be further improved by providing the drying section according to the invention with a bottom and / or top row drive of one or more rollers and / or cylinders, whereby the speed differences within the groups 20,40 are reduced. As is already known, both the upper and lower cylinders of the drying cylinder group are equipped with a common mechanical forced drive, whereby variations in the diameters of the cylinders cause detrimental differences in speed.

Since in the drying section according to the invention the rollers 31-34,51-54 do not heat the drying air, the conditioning of the drying section must be made more efficient, which can advantageously be done with the above-mentioned blowing devices 26,27 and 35 blow-down devices 36. In the application of the invention with a larger diameter.

10 70275

The drying section according to the invention is particularly suitable for use with a newsprint machine or other machines for making relatively light paper grades.

5 In order to prevent condensation and corrosion, the lower rollers 31-34,51-55 can be provided with various plastic coatings or equivalent, for example Teflon coatings. When using steel rolls, the surface temperatures of the rolls 31-34.51-54 are preferably in the range of 50-80 ° C and when using coated rolls, surface temperatures below 58 ° C can be used.

10

In the drying section and drying method according to the invention, the temperatures of the drying wire 30 or wires 30, 40, etc. are made substantially more odorous than before. In the experiments performed, a decrease in the temperature of the wires of 30.40 has been observed by about 20-30 ° C. This has resulted in quite substantial increases in drying power and substantially lower specific energy consumption in accordance with the basic principles described in more detail in the applicant's above-mentioned FI-hak 812089, which are confirmed on the basis of the following experimental example.

20 EXPERIMENTAL EXAMPLE

A series of experiments was performed to investigate the effect of the shutdown of the heating steam supply on the lower cylinders of the monorail outlet of a modern high-speed wide paper machine on machine production, driveability and energy economy.

Both in the normal running situation (TEST 1) and the single-cylinder outlet cylinders closed (TEST 2), the surface temperatures of the cylinders, the surface temperatures of the web, the surface temperatures of the 30 wire webs and the steam group per Production during the experiment was constant 2 (25.7 t / h of 80% thread and 48.8 g / m paper containing 20% pulp).

Figures 2 and 3 show the evolution of cylinder surface temperatures and wire and paper 35 temperatures in steam groups 1 and 2 under normal driving conditions (upper temperature values) and when the steam supply to the lower cylinders was closed (lower temperature values).

70275

In a normal driving situation, in the single-wire export area, the surface temperatures of the upper cylinders were 85-98 ° C and the surface temperatures of the lower cylinders 102-114 ° C. When the steam supply to the lower cylinders was shut off, their surface temperature dropped to 67-76 ° C. The difference was then 32-38 ° C. Due to the closure of the lower cylinders, the drying wire 5 was about 20 ° C colder in the 2nd steam group.

In the series of measurements, dry matter samples were taken from the drying section from the press, after groups 1, 2 and 3, and pope. Table 1 shows the specific evaporations calculated from dry matter measurements by vapor group.

10

Table 1. Specific vapor evaporations 15 Vapor group Specific- Specific- Note.

haihd. haihd.

kg / m2h kgH20 / m2h TEST 1. TEST 2.

20 1. hr A and Y ""] pur. k.a.p.

I 9.6 11.3 2nd hr A and YJ 43.4% (KOE 1.) 3. hr A and Y 23.3 42.8% 25 16.1 (KOE 2.) 4. hr A and Y 9.4 30 It can be seen from Table 1 that the specific evaporation obtained by calculating the dry matter samples has increased by about 17% for single-wire exports.

The total energy consumption of the machine was slightly lower with the lower cylinders closed than in the normal situation, as shown in the following table for 2 ha-35 power.

12 70275

Table 2. Steam and condensate flows Experiment 1. Experiment 2.

5 Steam for the machine kg / s 10.86 9.93

Condensate from machine kg / s 10.1 9.0 Flow steam for surface condenser 10 calculated kg / s 0.48 0.12 Steam for pocket kg / s for holding coils (calculated) 0.5 1.1 15 _

Total for machine 11.4 11.0 Differences in steam consumption are due to a decrease in the mass flow of flow and expansion steam (5 cyl. Closed).

20

When looking at the energy consumption index (amount of steam entering the machine / amount of evaporated water), it is observed that closing the lower cylinders slightly improves the energy economy of the machine. The ratio is 25 V * H 2 O: 1> 34 / 1’27 <Experiment 2.), i.e. an improvement of about 5%. Energy consumption can be further reduced if the single-wire export air conditioning is arranged in such a way that the efficiency of the air conditioning is improved and a rise in the temperature of the hood exhaust air is avoided.

30

The following are claims within the scope of which the various details of the invention may vary and differ from those set forth above.

35

Claims (14)

A method of drying a paper web in a multi-cylinder dryer of a paper machine, wherein the paper web to be dried is guided in contact with the surfaces of heated heating cylinders (21-25, 41-44), wherein the web is guided in at least the first or first drying groups (20.40). as a single fabric outlet, wherein the drying fabric, preferably a relatively open drying wire, passes from one row of drying cylinders or rollers to one knee so that even between said rows 10 the web (W) is supported by the surface of said drying fabric (30,50); (21-25,41-44) and / or rollers, the web (W) is directly against the heated surface of the drying cylinder (21-25,41-44) or the like and the second row of cylinders or rollers (31-34,51-54) has a drying wire is against the surface 15 of the roll or cylinder and at the same time outside the web (W) of the drying fabric (30.50), characterized in that in the method the drying fabric (30,50) is cooled as it passes between the cylinders with the web directly heated against the surface of the drying cylinder, and said cooling is performed by pressing the drying fabric immediately into contact with a cooling roll-20 or cylinder surface having a contact area sufficient for said cooling; not great. 1 Claims A method according to claim 1, characterized in that the temperature level of the drying fabric (30.50) by said cooling 25 is lowered by about 20-30 ° C compared to the temperature that the single-wire export fabric (30.50) would reach in a corresponding previously known multi-cylinder dryer with two rows of normally heated drying cylinders over which the corresponding drying wire would pass. Method according to Claim 1 or 2, characterized in that the contact cooling and guide rollers (31-34,51-54) which cool the drying fabric (30, 50) by direct contact are arranged to settle at a temperature level which they assume without substantial special heating. or cooling. A method according to claim 1 or 2, characterized in that said contact cooling rollers (31-34,51-54) between the steam-heated or respectively heated drying cylinders are cooled by introducing a cooling pressure medium such as gas and / or liquid, and / or by applying cooling jets of gas to the surface of said rollers (31-34,51-54). 5 Method according to one of Claims 1 to 4, characterized in that said contact cooling rollers (31-34.51-54) are open-surface, preferably grooved, rollers in the groove (35.55) of which a vacuum is arranged, and that said vacuum at least in part 10 prevents the web (W) from coming loose by said contact cooling rollers (31-34.51-54) from the outer surface of the drying fabric (30.50) due to centrifugal forces. Method according to one of Claims 1 to 5, characterized in that the web (W) is passed between the contact cooling rollers (31 to 34.51 to 54) between the drying cylinders (21 to 25.41 to 44) heated by steam or a similar medium. over a surface in a sector of size 2 to about 200-270 °, preferably about 250 °, said rollers (31-34.51-54) having diameters D2 = 800-1830 mm, preferably D2 = 1500 mm. 20 Method according to one of Claims 1 to 6, characterized in that in those drying groups (20, 40) in which the monofilament drying wire (30, 50) is cooled according to the method of the invention, the air conditioning of the drying group is intensified by means of blowing devices (27). , 50) and the inlet nipples (N) limited by said contact cooling rollers (31-34,51-54) and possibly the groove surface (35,55) of the contact drying rollers, and / or the so-called sub-blow devices (36) disposed between said contact cooling rollers (31-34,51-54). 30 A paper machine multi-cylinder dryer comprising one or more successive drying groups (20, 40) with two rows of cylinders and / or rolls, and in which at least the first or first (20, 40) drying groups are provided with a so-called with a single fabric export such that the web of paper (W) to be dried is supported all the way through the drying group (20, 40) by supporting said drying fabric (30.50) so that said drying fabric (30.50) presses the web (W) to be dried on the second row ) in contact with the surface of the drying cylinder (21-25,41-44) and in the second row the drying fabric, preferably an open-surface drying wire (30,50), is in direct contact with the surface of the cylinder or roll (31-34, 51-54) against the web (W) while being outside, characterized in that the cylinders or rolls of the row on which the web (W) is excluded are relatively large-diameter combined conductor and contact cooling rollers (31-34, 51-54) instead of heated drying cylinders. without actual heating devices. A multi-cylinder dryer according to claim 8, characterized in that said wire and contact cooling rollers (31-34,51-54) are rollers with an open groove surface (35,55). A multi-cylinder dryer according to claim 8 or 9, characterized in that the diameters of the actual steam-heated or correspondingly heated contact drying cylinders are in the range = 1500-2500 mm, preferably = 1830 mm, and in that the guide and contact cooling rollers are located as close as possible to their gaps (A). (31-34, 51-54) the diameters are slightly smaller, preferably about 20% smaller than the diameters (D 2) of the contact heating cylinders (21-25, 41-44) mentioned. A multi-cylinder dryer according to any one of claims 8 to 10, characterized in that the coverage angles of the web (W) and the drying wire (30, 50) on said contact heating cylinders and said contact cooling rollers (α1, α2) are about 200-270 °, preferably about 250 °. A multi-cylinder dryer according to any one of claims 8 to 11, characterized in that air blowing devices 30 (27) are arranged in the inlet nips (N) delimited by the drying wire (30,50) and the contact cooling roll, by means of which air is ejected from said nips (N 1) and possibly grooves in the groove surfaces (35.55) of the conductor and contact cooling rollers (31-34,51-54). A multi-cylinder dryer according to any one of claims 8 to 12, characterized in that said contact cooling rollers (31-34, 51-54) are provided with a metal or plastic coating, for example a Teflon coating. 16 702 75 13, 70275 Multi-cylinder dryer according to one of Claims 8 to 13, characterized in that one or more intermediate spaces (B) of adjacent contact cooling rolls are provided with a so-called blow molding machines (36). 5 10 15 20 25 30 35 17 70275