FI109210B - Method and apparatus for forming a cellulose web - Google Patents

Abstract

The invention relates to a method and an apparatus for pulp web formation. The method comprises feeding pulp, having a dry content of about 1,5 %, from a headbox (2) into a wedge-shaped converging space (5) defined by two wires (3, 4) or the like, said wires or the like being supported on chamber units (6, 7), including at a given time at least one water-receiving chamber (8), having its pressure adjustable in such a way that the pulp can be maintained at an overpressure in the space (5). The method comprises increasing the dry content of the pulp in the converging space (5) to a value which is at least about 10 % to about 12 %. According to the invention, the method comprises subjecting the pulp present between the wires (3, 4) or the like in the downstream section of the converging space, or in its substantially immediate vicinity, to a compression in perpendicular direction (z direction). In the method, the compression performed in the vicinity of the converging space (5) or its downstream section is used for increasing the dry content of the pulp to a value which is at least about 18 %, preferably to a value which is about 20 %.

Description

109210

METHOD AND DEVICE FOR CREATING A CELLULOSE FIBT

The present invention relates to a method for forming a cellulosic web according to the preamble of claim 1.

According to such a method, the pulp drying process and, more particularly, the pulping of the pulp can be carried out in an advantageous manner.

The invention also relates to a device according to the preamble of claim 8.

10

US 3823062 discloses a double wire web forming apparatus having a wedge-shaped twine formed by two wires into which pulp is fed to form a web. The wire formed mesh is shown to be provided with wire-supported dewatering boxes limited to the wire by a water-permeable pin-15. According to the publication, the stripping is controlled by measuring and strangling the amount of drained water flowing out of the dewatering boxes. This illustrates the process very schematically and has several disadvantages, especially if the corresponding process is applied to the pulp web. It has been found that with the present solution it is very difficult to control the formation of the web and its retention after the web, specifically on the thick web, as is typically the case with pulp. This solution also has its limitations in terms of dewatering efficiency, since it does not substantially exceed about 12% solids, since> * «: the pressure at the end of the python would increase enough to leave the pith:: uncontrolled, causing the wire parts to spread apart, so the web does not «· • ·; ] · '25 stay organized in a controlled fashion and the staging will fail.

Pulp drying apparatuses are known in the prior art comprising a forming wire forming section in which a pulp stock is introduced into the forming wire by means of a headbox. Water is removed from the pulp pulp with a wire portion, whereupon the dry matter content after the wire portion is typically about 20%. One problem with flat wire in connection with drying of pulp is one-way dewatering. At a certain stage there is a so-called.

: a layer formed from a web formed against a wet wire, which weakens the drainage of water from the web. This is known to be solved by equipping the wire section! : * * * • * 2 109210 ns. with reduced pressure dewatering equipment such as so-called. vacuum foil boxes or level action boxes that enhance dewatering by increasing the pressure difference that causes or promotes water separation. In such and similar forming parts, a vacuum system is a necessary element for operation.

However, in particular, the vacuum system constitutes a significant part of the equipment investment costs as well as the operating costs of the forming part of the pulp drying machine.

From Finnish Publication Publication 61218 is known a cellulose drying machine which forms a wet or wedge part, a register part comprising a plurality of 10 pairs of rolls, a front press part and a main press part which applies compression to the material to be dried. It is disclosed herein that the wet portion comprises suction boxes that absorb moisture through the wires. Also in such a solution, e.g. a vacuum system will bring the aforementioned disadvantages.

WO 97/42374 discloses a kind of pulp web, which again comprises many different subassemblies and is thus very complex in itself.

The object of the present invention is to eliminate the disadvantages of the prior art and to provide a completely novel solution for stripping and drying pulp, in which the disadvantages of the prior art are minimized.

I «·» · • 1 <: »·! In order to accomplish the objects of the invention, the method of the invention comprises t: forming a cellulosic web, wherein the pulp is fed into a wedge-like space formed by two wires or the like which are supported by chamber units having at least one water receiving chamber, in which method. . increasing the dry matter content of the pulp to at least * ·!. from about 10% to about 12%, characterized in that, in the process, the mass is independently controlled by its thickness (z-direction) compression force in a substantially immediate relationship with the tapered space I · t '· 30 (5) and / or its remainder.

* • «· • · · · · · i ♦» 3 109210

For the apparatus of the invention for forming a cellulosic web comprising a wedge-shaped tapered space formed by two wires or the like, into which is fed a first dry cellulose pulp from a headbox, and the wires or the like are supported in chamber units having at least one characterized in that in the remainder of the tapered space or in its substantially immediate connection there are sealing members for compressing the mass between the wires or the like in the thickness direction (z direction).

According to a preferred embodiment of the invention, the sealing member is a plane press.

The invention will now be described in more detail with reference to the accompanying drawings, in which: Figure 1 schematically shows an apparatus for forming a cellulose web according to the invention, Figure 2 schematically shows a modified way of implementing the device according to Figure 1; ·. Fig. 3 schematically shows a cellulose web of the invention comprising i. *. Fig. 4 is a front elevation view of the sealing member of Fig. 3, and Λ '! 25 * * Figure 5 illustrates an alternative embodiment of a sealing member.

v .: The apparatus 1 according to the invention schematically shown in Fig. 1 is a web W

»·» V: to form. The apparatus comprises a headbox 2 which, in accordance with the pulp drying process according to the invention, is fed into a pulp-like space 5 of about 1.5% dry dry:: ': material, formed by two ·· infinite wire loops such as upper wire 3 and lower wire 4. between. The space 5 is formed by arranging the wires 3, 4 to pass about the spaced apart rotating rollers 50 and 51 respectively at the beginning of the space 5 and thereafter to form a wedge-like space. Against the inner surface of the wires 3 and 4 (opposite to the mass flow), chamber 5 units 6 and 7, respectively, are provided, having a plurality of dewatering chambers 8, controlled by valves 22 and substantially full of water removed from the pulp. Dewatering chambers are provided with dewatering channels for directing the water removed from the dough to the treatment. The outlet ducts thus comprise valves 22 for controlling the flow by varying the amount of throttle. The figure shows the sake of clarity only the channels I to the underside of the chambers, but it is understood that; the upper side of the combs are connected to the respective channels, or, alternatively, left to the wellbeing of the chambers above and below, align themselves with the same, a common channel.

The pulp is fed at such a speed and pressure between the wires 3,4 as they pass 15 that there is excess pressure in said space 5. This overpressure causes the water of the pulp to drain through the wires into the dewatering chambers 8.

According to the invention, the pressure difference between space 5 and chambers 8 is continuously measured and this measurement value is used in process control. Dewatering • · · '; The chambers 8 are adjusted so that the velocity ratio is preferably about 0.9 to 1.1.

; 20 Speed ratio refers to the flow of liquid between chambers • »· * | in the direction of the web divided by the speed of the wire. The chambers 8 are otherwise substantially tight, but the surfaces facing the wires 3,4 are such that the water to be removed from the pulp may migrate into the chambers. The chambers 8 are preferably arranged in a plurality of * · · sequential positions such that the surface against the wires is, however, substantially continuous.

, Y. The discrete chamber units 6,7 begin substantially immediately after the pivoting rolls 50, 51 of the upper wire 3 and the lower wire 4 and continue over a distance to form a wedge tapered space 5 through which the upper and lower wire 3,4 pass. The chamber units 6.7 are preferably substantially symmetrical and solidly supported in a suitable Y position to provide a preferred wedge shape. In connection with the tapered space 5 formed by the chamber units 6,7 ': 30, there is a sealing member 9 in its remainder or in its immediate connection for adjusting a certain distance between the upper wire 3 and the lower wire 4 or the like. In Fig. 1, the sealing member is a planar press 9 10 10 10 10, the upper part 31, 34 of which is articulated with the lower part 30 being fixed. As the pulp is fed through space 5, water is discharged such that the pulp has a dry solids content of at least 12% prior to the flat press 9 and additional water is removed from the pulp by a flat press such that the solids content 5 is approximately 18%, preferably about 20%. Dry matter content can also be raised to about 18-20% in the already tapered space 5, and the leveling bar 9 is used substantially only to hold the mass protruding from the outlet of the space 5. The pulp coming out of the wedge-like space will exit high-pressure 5 and without the sealing members according to the invention, it would occur 10 uncontrollably spreading the wires 3,4 apart, causing the pulp web already formed to disintegrate. After the flat press 9, according to the invention, water is removed while the web W is supported between the two wires 3,4 by pressing the assembly between the two rolls 10,11. Thereafter, the upper wire 3 and the lower wire 4 are guided apart and the web W is guided further forward on the upper surface of the lower wire 4 according to the invention, the dry substance content of the web being approximately 28%. Thus, according to the invention, the web passes fully supported. If necessary, a so-called transfer suction box is arranged on the lower surface of the downstream stream to ensure the passage of the web with the downstream wire. The web W is further downstream. supported on the upper surface of the wire 4 through the press nip N comprising the upper one! 20, i.e. web W runs over the blanket and below the lower wire 4 in the nip N between the rolls 12,13. The nip is preferably formed by the * ns. a shoe press. In this treatment, the web W is dried so that its I · ·

I I

The dry matter content after N is approximately 40%. By the process of the invention described above, in a pulp drying machine, the web W is formed: V: 25 effectively and safely. This solution simplifies the forming of the web: ·: T: the forming part and the web W is fully supported until its dry ....: content is about 40%, whereby it is strong enough to withstand *: ··· without weaving first unsupported export to the next processing step.

In the process of the invention, the pulp web is also significantly packaged.

IMI

, ·. 30, so that, in accordance with the invention, the passage of the lower wire 4 to the extent it supports the web W is arranged to travel substantially straight.

6 109210 ί

The invention achieves considerable advantages which include: | - a much more efficient pulp stripping process than is known by the device, - a much smaller space than the known solutions for the pulp stripping component, which can save up to FIM millions in investment costs, increases overall machine efficiency.

The device 1 schematically depicted in Fig. 2 differs from the embodiment of Fig. 1 in that the flat clamp 9 is designed such that its upper and lower portions are adjustable. Further, Fig. 2 illustrates a control and control unit 21 which is connected to suitable measuring devices transmitting measurement data and which in turn transmits control commands to the appropriate different elements as illustrated by lines 15-20 in Example 15. According to the invention, this information includes some or all of the following: stern feed consistency, stern pressure, Ι chamber 5 pressure, chambers 8 pressure, wire speed, platen press force / pressure, water flow through valves 22. These or some advance. i. selected from these quantities are transmitted to a control / control unit, in which, in a desired manner, control commands are executed to control the drying process. The control may advantageously comprise the following controls: control of valves 22, load of the platen press, wire speed, control of the stern feed pump, »«: 'I': stern consistency control, etc. According to the invention, the platen 9 may comprise a force sensor and / or to measure the clamping force of the pressure gauge and adjust: Y: 25. A gauge is provided in connection with the chambers 8 for measuring the pressure from the chambers and, if desired, a pressure transmitter for measuring the pressure in the space 5 and / or for determining the pressure difference between the chamber 8 and the space 5, where:: **: chamber pressure adjusting the difference with state 5 e.g. valve 22 can be implemented. The dry matter content of the web W is also measured in a convenient 30 steps of the drying process, from which information can be used to make control commands, if necessary, by means of a control / control unit. Further, in accordance with the invention, the pressure can be adjusted as desired in space 5, as well as flat press 7109210 9 and press rollers 10,11 and 12,13 to adjust the dry matter content and water removal at various points. When the dewatering from the chamber 8 is fully controlled according to the invention, taking into account all relevant operating parameters of the dryer, based on the process data 5 itself, and not just the flow of water out of the chamber, the drying / dewatering process can be run as desired .

Figures 3 and 4 illustrate an embodiment of a flat press 9 having a fixed lower part 30 and an upper part 31 whose position relative to the lower part 30 can be adjusted. The upper portion 31 is pivoted at 32 to the remainder of the space 5. The pulp is introduced between the wires through a space 5 through slot 40. The part 31 is attached to the uprights 35 which are connected at their lower part by a connecting piece 37 which in turn is secured via bellows 36 to the fixed underside 15 of the flat press 9 according to the invention. is adjustable relative to each other and to the position of the chamber units.

... In addition, according to the invention, the loading of the flat compactor is carried out by means of • · · y. ' capable of receiving, to an appropriate degree, possible variations in the thickness of the web. Under normal conditions, the bench press is loaded with the desired force. : by means of adjustable adjusting pins 33 or the like with a specific force »· · •. ·. against these pins 33, which maintains a certain constant position. Thus, the position between the upper part 31 and: 'j': the lower part 30 can be mechanically limited by adjustable wool members. The loading may advantageously be carried out with bellows 36 using a compressible intermediate: V: 25, such as air, whereby, as the web thickness: temporarily increases, this is compensated by the compressibility of the medium.

; ··· When the fault is over, the distance is automatically restored. Thus: · ·: thus, any disturbances in the pulp, which cause thickness variations, are eliminated very simply by means of the spring • ,; 30 bytes. It is also possible to provide another type of distance control in which the position of the level press is adjusted by means of pressure and distance measurement.

8 109210

Above, the sealing member is shown as a flat clamp, but the invention can also be considered to be practiced using a nip press formed by two rolls, the nip of which is a substantially instantaneous outlet of the tapered space. in the vicinity. This can be accomplished, for example, as shown in Figure 5 by shaping the remainder of the chamber units 61 to extend close to the nip formed by the rolls 61.62.

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Claims (12)

A method of forming a cellulose web, in which method pulp having a dry content of about 1.5%, is measured from the inlet tray (2) to one of two wires (3,4) or correspondingly formed wedge-tapered space (5), which wires or the like are supported by chamber units (6,7), each of which has at least one water receiving chamber (8), which at least one water receiving chamber during the stationary state of the process is substantially filled with water separated from the pulp; there is provided a water drainage assembly and means (22) for controlling the water flow, in which the dry mass of the process is increased in the tapered space (5) to a value of at least about 10% - about 12%, characterized in that the process is applied in the tapered space (5) and / or in the substantially immediate connection to its end-end an independently adjustable pressing force in its thickness direction - (z-directed), as on mass For example, apply a pressure which is at least as great as the rescue pressure in the tapered space (5), with the aid of which the compressive force helps the dry content of the web to a value of at least about 18%. * ·; ·. ·, 20 2. The method according to claim 1, characterized in that, after applying a compressive force in the thickness direction (z-directional) to the cellulose web, it is conducted. ·. : the web further between two wires (3, 4) through a separate pressing zone (10, • I, 11), and then the Upper Wire (3) and the lower Wire (4) are led free from I ·. - each other and the web (W) is further measured on the upper side of the lower wire (4). - The method according to claim 2, characterized in that the web (W) is guided ', further supported on the upper side of the lower wire (4) by the press nip (N), which comprises an upper blanket (14). ), i.e. the web (W) runs with the top abutting against. The blanket and underside abut the lower wire (4) of the nip (N) between the wires (12, 13), in this treatment the wire (W) is dried so that its dry content after the nip is about 40%. 13 109210 The method according to claim 1, characterized in that said eating means has a water receiving chamber (8) having means for measuring the pressure in the chamber and control and control means (21) for using this pressure measurement 5 to control the process. The method according to claim 1, characterized in that the means (22) for regulating the flow of water are connected to a control / control unit (21), the control and control unit controlling the means for controlling the flow of water on the basis of data relating to the water flow. from the process. Apparatus for forming a cellulose web, said device (1) comprising one of two wires (3,4) or correspondingly formed wedge-shaped tapered space (5), to which space the cellulose mass having a first dry content is measured from the inlet carriage (2), and which wires or the like are supported in chamber units (6,7), which respectively have at least one water receiving chamber (8), which at least one water receiving chamber during the stationary state of the process is substantially filled with water separated from the pulp, and provided therein. vat- ·: ·. drainage units and means (22) for regulating the water flow, • · ·: ·. ·. Characterized in that the end end of the tapered space (5) or in its essential immediate connection has sealing means (9) for pressing the mass between the wires (3,4) or the equivalent in the thickness direction (z-direction), and that the sealing means (9) are provided with force devices with which the pressure is achieved with a pressure which is at least equal to the rescue pressure in the tapered space (5), to increase the dry content of the pulp to a heat: ·! those which are substantially greater than said first value. . 7. Device according to claim 6, characterized in that the sealing means. · ·. (9) are provided with power devices, comprising means (36) for torque. ·. Compensation of the web thickness variations in the machine direction. Device according to claim 7, characterized in that the means for instantaneous compensation of the thickness variations of the web in the machine direction in | Comprises an air bellows (36) with which the short-term movements of the sealing means (9) can be compensated. 9. Apparatus according to claim 6, characterized in that the sealing means (9) for pressing the mass between the wires (3,4) or correspondingly comprise measuring, control and control means (21) for controlling the pressing. 10. Device according to claim 9, characterized in that the sealing means 10 (9) for pressing the mass between the wires (3,4) or the like comprise measuring devices for measuring the compressive force and / or the pressure and measuring means for measuring the pressure in the space ( 5), and means for controlling the rescue pressure between the sealing means (9) to a pressure which is at least equal to the pressure in the space (5). Device according to claim 6, characterized in that the sealing means (9) is a plane press (30, 31), where the position between the upper part (31) and the lower part (30) can be mechanically limited by controllable means (33). »*» • · ·: 20 12. Apparatus according to claim 6, characterized in that the sealing means * I: consist of a nip press formed by two rollers (61,62). * t · * * * · * * I *! * 5 * ·) i