FI84379C - FOERFARANDE FOER VARMPRESSNING I EN PAPPERSBANA OCH TORKNINGSANORDNING FOER TILLAEMPNING AV FOERFARANDET. - Google Patents

Description

84379 1 Heat extrusion method for paper web and drying apparatus applying the method Förfarande för varmpressning i en pappersbana och torkningsanordning för tlllämpnlng av förfarandet 5

The invention relates to a method for pressing a paper web or the like and removing water from a web, which method utilizes a hot pressing step in which a wet paper web is pressed to a temperature above 100 ° C in direct contact with a heated cylinder surface or the like.

The invention further relates to a device for carrying out the method according to the invention, comprising a hot cylinder or a similar roll having a smooth heated jacket surface which can be heated to a temperature above 100 ° C before it immediately encounters the web to be pressed.

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It is an object of the present invention to provide improvements and modifications to the methods and apparatus disclosed in the applicant's earlier FI patent application 871870 (filed 28.A.1987).

The object of the present invention is to provide a method and an apparatus in which the hot pressing method disclosed in the above-mentioned FI application can be started in order to increase the efficiency of the method from an even higher dry matter content of the web.

It is a further object of the present invention to provide a method and apparatus in which the supply of energy to the web can be distributed other than to the heating cylinder or cylinders.

In the description of the invention, all the details of the method 35 and the device of the invention, which have already been presented in the applicant's above-mentioned FI application 871870, are repeated.

2 84379 ^ In order to achieve the above and later objects, the process of the invention is mainly characterized in that the process comprises the following steps in the order shown: (a) a preheating pressing step or steps using a relatively long pressing time and a relatively low pressing pressure, and wherein in the pre-stage, the surface layer on the surface heating side of the paper web is heated to a temperature above 100 ° C, this preheating pressing step or steps being arranged in such a way that water vapor is already blown through the web, thereby causing the water to be blown into the web fibers; b) after the above-mentioned preheating pressing step, a step 15 in which the pressing pressure on the paper web is lowered so that the evaporation of water in the paper web is intensified, and (c) after the previous step, a step in which the web is directed substantially immediately to an intense nip pressing step or the like, in which the paper web is pressed at a substantially higher, preferably an order of magnitude, peak pressure from the previous step. enhanced dewatering and (d) before and / or after the actual hot pressing steps (a), (b), (c) defined above, the web is passed through the heating step or steps and / or the heat pressing steps 30.

The device according to the invention is mainly characterized in that a press roll surrounded by a press conveyor belt guided by guide and tension rollers 35 and arranged to form a roll press nip with a heated surface of said hot cylinder nipper a long pressing zone with the surface substantially immediately before said roll nip 5 a water-receiving press fabric passed through said long nip and roll nip between the web to be pressed and said press conveyor through the press zones, and 10 before the hot press apparatus after the actual pre-heating / post-heating pressing arrangement.

According to the present invention, the preheating pressing step is arranged so that water vapor is blown through the web, thereby causing the water pressed between the web spaces of the web to be blown out into the press fabric.

In the device according to the invention, a plurality of paper web heating devices are preferably used before the hot pressing step according to the invention in order to maximize the dry matter content and the highest possible temperature of the paper web. Said hot pressing devices used before the actual hot pressing step are e.g. steam boxes, infrared heaters and / or high frequency heaters. Simultaneous use of all these preheaters is not always necessary.

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 which the invention is not limited.

Figure 1 shows a schematic cross-sectional view of a hot pressing device according to the invention.

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Fig. 1A shows the distribution of the compression pressure realized in the device according to Fig. 1.

4 84379 1 Figure 2 shows, in a manner similar to Figure 1, a variation of the invention comprising two roll nips and a long nip between them.

Fig. 2A shows the compression pressure distribution of the device of Fig. 2.

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Fig. 3 shows a modification of the embodiment of the invention according to Fig. 1, in which the contact sector of the heating cylinder and the web is extended both before and after the actual hot pressing steps.

Fig. 3A shows the compression pressure distribution of the device of Fig. 3.

Fig. 4 shows a modification of the device according to Fig. 2, in which the contact sector between the heating cylinder and the web is extended both before and after the actual hot pressing steps.

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Figure 5 shows a first embodiment of the placement of a hot / press device according to the invention in connection with the applicant's Sym Press section.

Figure 6 shows an embodiment of the invention in which two hot pressing devices according to the invention are used in succession in the press section.

The hot pressing device according to the invention comprises a relatively large diameter heated roll or cylinder 10 with a smooth outer surface 10 'and provided with a drive 10a. The surface of the cylinder or roll 10 is heated internally and / or externally by steam, flame heating, various radiations such as infrared radiation, high frequency heating or eddy current induction heating devices. Figures 1 and 2 schematically show an induction heating device 30, a flame heating device or an infrared heating device 11 which heats the surface 10 'of the cylinder 10 non-contact through the air gap liv, in a sector E, preferably greater than 90 °, e.g. about 180 °. The device also includes steam supply devices for conducting overpressure steam via a steam switch (not shown) at the end of the cylinder 10 inside the cylinder 10 via steam pipes, e.g. on the same principle as in the drying cylinders of the drying section known per se.

The surface T 'of the surface 10' of the cylinder 10 is arranged to have a temperature Tg> 100 ° C when the surface 10 'encounters a web W to be hot-pressed on the surface of the press felt 12, the dry matter content of which is marked KA 2. Depending on the placement of the hot pressing device according to the invention in the process, KA 2 varies between 5 KA = 15 ... 55%. in

The pressing shoe device 30 of the hot pressing device comprises a long nip pressing shoe 31 with a hydrostatic pressure chamber 32 opposite the impermeable conveyor belt 25. The pressing shoe device 30 comprises a frame beam 30a 10 extending over the entire width of the paper web W. A cylinder block 33 is arranged on the frame beam 30a, at the pressures 37 of which the pressure of the pressure medium or the pressures from the pressure source can be derived. The cylinder block 33 has a sealed piston 34 with a sliding surface acting in the long nip zone against the inner surface of the conveyor belt 25. A pressure lubricant is supplied from the pressure space to the hydrostatic pressure chamber 32 15 through boreholes.

If necessary, the lubrication of the inner surface of the conveyor belt 25 can be enhanced by spraying lubricant jets on the inlet side of the long nip zone. The lubricant is, for example, water or oil or an emulsion thereof. The shoe 31 of the long nip press-20 is hydrostatic, hydrodynamic, or a combination thereof.

With regard to the details of the construction of the long nip press, reference is made as an example to the applicant's earlier FI patents Nos. 65104, 70952 and 71369.

According to Fig. 1, the impermeable conveyor belt 25 is guided by the guide rollers 22 and 23 25 and the press roll 20, the tension roll 23A and the guide roll 23B. A splash water collecting trough 27 is arranged around the loop of the conveyor belt 25. The press roll 20 is provided with a smooth surface 20 'and a drive 20a and has a lubricant collecting trough 24 behind it, from which the lubricant is fed by a recycling device (not shown) for further use.

According to Figures 1 and 3, the heated cylinder 10 and the press roll 20 form a nip N between them, after which the web W separates from the press felt 12, which is led to be repaired. The web W then follows the smooth surface 10 'of the cylinder 10 35, from which it is separated by a guide roller 13 provided with a drive 13a and transferred to a support 6 of a drying fabric 15 guided by a guide roller 14, which takes the web W to a drying section.

The dry matter content of the web W after the hot pressing device is marked KA. In general, this dry matter content KA = 50 ... 70%.

The hot pressing device shown in Fig. 2 differs from that shown in Fig. 1 in that two roll nips are formed in connection with the heated cylinders 10 and between 3 ° there is a pressing shoe device 30 and its long nip pressing shoe 31. In other respects the structure is as shown in Fig. 1.

In Figures 1 and 2, the press felt 12 is separated from the web W and the belt 25 immediately after the nip Nj ^ q and further guided by the guide roll 19.

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Figures 3 and 3A show a modification of the device according to Figure 1 in which the web W entering the nip formed by the belt 25 and with it and supported by the felt 12 with the cylinder 10 is led before the long nip pressing step in the sector aQ 20 of the cylinder 10 to the preheating step 3 shown as a zone Aq, at which point the compression pressure p ^ = T / R prevails, where T is the tensioning tension of the belt 25 and R is is the radius of the cylinder 10. Respectively, the roll nip 20 and the central nip N of the cylinder 10 are followed by a post-compression step (pressure pQ) in the sector c1 of the cylinder 10, which step is denoted by Cq in Fig. 3A.

Figures 4 and 4A show a modification of the hot pressing apparatus according to Figure 2 in which the guide roll 22 of the strip 25 is positioned so that before the nip there is a preheating pressing step 30 in the sector aQ of the cylinder 10 with the above-mentioned prestressing pressure T of the strip 25. marked with pQ and the corresponding compression zone Antila. Correspondingly, after the latter nip, the sector eQ of the cylinder 10 has a post-compression step in which the above-mentioned pressure pQ caused by the tensioning of the strip 25 exists, which acts in the zone E 1 as shown in Fig. 4A.

7 84379 1 In the sectors a ^ and cq shown in Figs. 3 and 4 and the like

in zones A and C; a, e and A, E are obtained from the web W and the heating-o o ooJoo J

the contact time of the cylinder 10 is increased and the total time of the pressing steps is extended to obtain an even higher dry matter content KA of the web, out

A first embodiment of the method of the invention will now be described with reference to Figures 1 and 1A. The paper web W is pressed against the hot (T 1> 100 ° C) surface 10 'of the cylinder 10 by means of a belt 25 and a press-10 felt 12 by means of a relatively low-pressure (p 1) long nip press shoe 31 and causes the surface of the paper web W to heat over To a temperature of 100 ° C. Said surface temperature 10 'when it comes into contact with the web is in the range T = 105 ... 500 ° C. The corresponding temperature o when the web W separates from the surface 10 'is generally in the range 15 = 100 ... 300 ° C. The pressure level of the long nip press shoe 31 is e.g.

Pj = 0.1 ... 5 MPa, in which case, for example, water or a water-in-oil emulsion can be used as the lubricant to be fed by the devices 26. Higher pressure would require the use of lubricating oil, degreasing, and oil mist, resulting in the disadvantages discussed above.

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The long nip shoe 31 is hydrostatic, hydrodynamic or a combination thereof. After the long nip pressing step Aj, the pressure on the paper web W decreases to a level pQ determined by the tension of the belt 25 in the zone Bj, and the evaporation of water from the paper web W is enhanced by the pressure drop p ^ -> pQ 25. Pressure pQ = T / R, where T = the tension of the belt 25 and R * the radius of the cylinder 10. The zone Bj is followed by an intensive pressing step in the nip N, in which the paper web W is pressed with a high pressure between the cylinder 10 or the corresponding roll and the pressing roll 20. This step is shown in Fig. 1A by C 1 and the maximum compression pressure 30 is then preferably Pmax 7 MPa. In the pressing step Cj, water vapor is blown through the paper web W, causing it to blow out the water in the intermediate spaces of the fibers and thus an enhanced compression result and an even higher dry matter content KAQut.

35 As shown in Fig. 1A, since the compression pressure rises very sharply and rapidly from the intermediate pressure pmax to the maximum pressure Pmax, the colder water compressed from the paper web W on the surface side of the conveyor belt 25 comes into contact with 8 84379 water vapor, resulting in the collapse of the cavitation, ie the further intensification of dewatering.

5 The so-called conveyor belt 25 can also be used. an elastic belt, by means of which the zone of the roll nip and at the same time its pressing time can be extended and the pressing pulse can be increased. If necessary, a separate elastic band can also be used, which is passed between the conveyor belt 25 and the felt 12.

Since water cannot be pressed from the press felt 12 onto the hollow surfaces of the rollers, it is possible to make the hollow surface on the belt 25, to which the dashed line 25 'of the outer surface of the belt 25 refers.

The embodiment of the invention shown in Figures 2 and 2A differs from that shown in Figure I in that the device further comprises a press roll 21 located before the press shoe device 30, having a smooth jacket surface 21 'and provided with a drive 21a. The press roll 21 is placed inside the loop of the conveyor belt 25 and the roll 21 forms a nip with the hot cylinder 10. The web W is introduced directly into the nip under the support of the press felt 12 so that the web W comes immediately against the heated smooth surface 10 'of the blade 10 of the cylinder-20. Correspondingly, the press felt 12 is separated after the second nip N 1 q from the web W following the smooth surface 10 'of the cylinder 10, from which it is separated as a free tension W 1.

In the middle row (L) below the zone markings Ao-Cq and AE ^ 25, Figures 1A, 2A, 3A and 4A show examples of preferred lengths (mm) of said zones and corresponding residence times (mm) in the lower rows (t) when using a machine speed v = 20 rpm.

In Fig. 1A, step A1 can be called the preheating compression step, step Bj can be called the steam generation step due to the pressure drop, and step Cj can be called the actual (intensive) compression and blowing step.

In step A shown in Fig. 2A, where a peak compression pressure Pmaxj> is applied to the nipissM, it is a question of a first hot compression step.

35 Step B is the pressure lowering step, step C is the second preheating compression step and step D is the pressure lowering and vapor generation step, and step E is the actual (intensive) compression and blowing step.

9 84379 1 In Fig. 3A, in addition to the steps shown in Fig. 1A, the above-mentioned step A 1, which can be called a preheating compression step, is added because the compression pressure p 1 is quite low and is caused only by the belt tension tension T. Corresponding to Fig. 1A, Fig. 3A shows, after step Cj, a post-compression step Cq1 in which said external compression pressure p1 prevails.

In Fig. 4A, with respect to Fig. 2A, before step A, there is a preheating pressing step Aq with the above-mentioned low pressing pressure pQ, and after the nip pressing step E, respectively, a post-pressing step Eq with the above-mentioned low pressing pressure pQ.

Figures 5 and 6 show two preferred embodiments of the invention combined with the applicant's Sym-Press IIV compression part. The web W is formed on the forming wire 40, transferred to the felt 41 in the suction belt zone 41a of the pick-up roll. The web W is further transferred in the support of the felt 41 through a first nip formed between the press roll 43 and the suction roll 44. A lower compression felt N 1 passes through the nip Nj. In order to maximize the dry matter content and temperature of the paper web 20 before the KP or KP1 and KP2 hot presses, it is advantageous to use several paper web preheaters, Figures 1 and 2 showing a heater 49 against the suction sector 44a of the suction roll 44 against the press roll center roll 45 a heater 49a, a heater 49b acting against the suction sector 48a of the transfer roller 48, and a heater 49c upstream of the KP2 device. Em. the paper web heaters 49, 49a, 49b and 49c are, for example, steam boxes, infrared heaters or high-frequency heaters. Simultaneous use of all these different heating devices is not necessary. A second nip N 1 is formed between the suction roll 44 and the smooth-surfaced center 45. The web W adheres to the smooth surface 30 45 'of the center roll 45 and passes through it to the third nip N 1 formed between the center 45 and the hollow surface roll 46. A compression felt 47 passes through the third nip.

According to Figure 5, the web is transferred by a paper guide roll 52 to a suction transfer roll 35, in the suction zone 48a of which the web W is gripped by a press felt 12, in support of which the web W is guided by a single-stage hot pressing method and apparatus KP according to the invention.

84379 1 According to Fig. 6, two successive hot-pressing methods and devices KPj and KP ^ according to the invention are used, in which a web W is passed from a paper guide roll 52 to a first felt I2a and supported by a first hot-pressing step KP1 and further from a first hot-pressing cylinder 10A 12b and in its support via the second hot pressing cylinder 10B and the second hot pressing step KP 1 and further under the guidance of the guide roll 13b on the drying wire 15, on which the web W is gripped by the irrigating boxes 51 and guided by the drying wire over the drying section cylinders 50.

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When two successive hot pressing steps and devices KP ^ and KP ^ are used according to Fig. 6, a high dry matter content KA ^ ^ of the order of 65-70% is obtained. In addition, the advantage is obtained that by using two successive inverted devices arranged according to Fig. 2, the web W is pressed against the smooth surfaces 10 'of the hot cylinders 10A and 10B on both surfaces. Thus, the web W is made very symmetrical in structure and equal in both surfaces, which is an important feature especially on printing papers.

Thanks to the enhanced dewatering, the process according to the invention, which can be carried out in one or more stages, provides an even higher dry matter content KA of the press section, up to the order of 65-70%, especially when using several preheaters 49,49a, 49b and 49c and several stages (Fig. 6) implementation of the invention.

Within the scope of the invention, more than two hot pressing devices can be used in succession. These devices are not necessarily in immediate succession, but may be replaced by conventional steam-heated drying cylinders, over which the web to be dried is passed, instead of or in addition to the above-mentioned heating devices. In addition, it is important that with the hot pressing according to the invention, a high dry matter content of the web W can be achieved without compacting the web W too much, which is advantageous for several quality properties of the paper. A web W with a uniform surface and a very symmetrical structure is also obtainable, in particular with the two-step embodiment of the invention 35 shown in Fig. 6 above.

11 84379 1 The following are claims which, within the scope of the inventive idea defined by it, the various details of the invention may vary and differ from those set forth above by way of example only.

5 10 15 20 25 30 35

Claims (10)

84379 A method for pressing a paper web (W) or the like and removing water from a web (W), the method utilizing a hot-pressing step in which a wet paper web (W) is pressed above a cylinder surface (10 ') or a roll surface heated to a temperature of more than 100 ° C. in direct contact with, characterized in that the method comprises in combination the following steps: (a) a preheating step or steps using a relatively long pressing time and a relatively low pressing pressure and wherein the preheating step (10 ') heats the paper web (W) the surface layer is heated to a temperature above 100 ° C, this preheating step or steps being arranged in such a way that water vapor is already blown through the web (W), thereby causing water (W) pressed into the press fabric (12) to be blown into the press fabric (12). , (b) preheating the above after step (AjjC) the next 20 steps in which the compression pressure (pj -> p0) on the paper web (W) is calculated so that the evaporation of water in the paper web (W) is intensified, (c) after the previous step (b) the next hot pressing step in which the web (W) is directed substantially immediately to an intensive nip pressing step (C ^ .E) or the like, in which the paper web (W) is pressed at a peak pressure (praax, pm <2)> substantially higher than the previous step (b), preferably by an order of magnitude> ) presses more water into the press felt and further blows water vapor through the paper web (W), causing the pressurized water to be blown into the interstices of the fibers of the web (W) and thus the enhanced dewatering and (d) before and / or after the actual hot pressing steps (a) defined above; ), (c) the web is passed through the heating step or steps (49,49a, 49b, 49c) and / or the heat pressing steps (Αο, Οο, Εο ). 13 84379 Method according to Claim 1, characterized in that the preheating steps arranged before the actual hot pressing steps, in which the temperature level of the paper web is raised, are carried out by means of separate steam boxes, an infrared heater and / or a high-frequency heat suction. A method according to claim 2, characterized in that said preheating steps are performed by applying a heating effect to the web (W) in the suction sector (44a) of the press roll (44) of the press section, between the nips (N2, N3) of the press roll (45) sector and / or a suction sector (48a) of the transfer suction roll (48), over which the suction roll (48) is passed by a drying felt (12a) which takes the web (W) to the actual hot pressing step (Figures 5 and 6). Method according to one of Claims 1 to 3, characterized in that in the preheating pressing step (A *,) carried out before the actual hot pressing steps, the web (W) is pressed against the surface (10 ') of the heating cylinder (10) or roll under tensioning of the pressing belt loop (25). T) (Figures 3 and 4). Method according to one of Claims 1 to 4, characterized in that in the post-pressing step (C?, E0) carried out after the actual hot pressing steps, the web is pressed after the preceding nip pressing step (C ^ E) by the pressing pressure (T) 25 provided by the pressing belt (25). p0), after which the web (W) is detached from the press felt (12) and further passed. Apparatus for carrying out the method according to claim 1 or 2, comprising a hot cylinder (10) or a similar roll having a smooth heated jacket surface (10) which can be heated to a temperature above 100 ° C before it immediately encounters the web to be pressed (W ), characterized in that the device comprises in combination a press roll (20) around which a press conveyor belt (25) guided by guide and tension rollers (22, 23) is arranged and which press roll 14 84379 (20) is arranged to form a roll press nip (N; N2o) with said heated surface (10 ') of said hot cylinder (10), a press shoe-5 device (30) arranged before said roll press nip (N; N20), the nip press shoe (31) of which together with the surface (10') of said hot cylinder (10) a long compression zone substantially immediately before said roll compression nip (N; N 2 O) for water passed through said long nip and roll nip (N); a press fabric (12) to be passed between the web to be pressed (W) and said press conveyor belt (25) through press zones, and a preheating device (49, 49a, 49b, 49c) of one or more webs (W) 15 connected to the press section of the web before the hot press apparatus and / or a preheating / post-heating pressing arrangement (Αο, 0ο, Εο) placed before / after the actual hot spraying equipment. Apparatus according to claim 6, comprising two or more successive hot-pressing devices (KP1.KP2), characterized in that a web (W) is passed between said hot-pressing devices (KP1.KP2) by means of drying cylinders, an intermediate heating or heating device (49c). ) such as through a steam box, infrared heater and / or High frequency heater. 25 Device according to claim 6 or 7, characterized in that the preheating pressing arrangement has a pressing conveyor belt (25), preferably provided with a hollow surface (25 '), guided on the guide roller (22, 19) to sideways the surface (10') of said hot cylinder (10), 30 that before the press slide (31) or the press roll (21) the web (W) is pressed against the cylinder surface (10 ') by a tightening tension (T) of the press belt (25) in a certain sector (βο) of the hot cylinder (10) (Figs. 3 and 4). Device according to one of Claims 6 to 8, characterized in that, after the only or icy nip (N; N 2 O) 84 formed in connection with the hot cylinder (10), the compression conveyor belt (25) is arranged in the post-heating arrangement to guide the hot roll (19). cylinder (10) in a certain sector (c0, e0) such that in said sector (cQ; e0) the web (W) is pressed against the surface (10 ') of the hot cylinder (10) by means of the tensioning tension (T) of the press conveyor belt (25) (Figs. 3 and 4). 10. Pau. Device according to Claim 8 or 9, characterized in that the length of the preheating sector (aQ) and / or the post-heating sector (co, e0) 10 is in the range from 50 to 100 mm, preferably in the range from 60 to 80 mm. i6 84379