WO2008023098A1

WO2008023098A1 - Method and apparatus for the manufacture of a fibre web

Info

Publication number: WO2008023098A1
Application number: PCT/FI2007/050455
Authority: WO
Inventors: Matti Luukkanen
Original assignee: Metso Paper, Inc.
Priority date: 2006-08-25
Filing date: 2007-08-22
Publication date: 2008-02-28

Abstract

The invention relates to a method and an apparatus for manufacturing a fibre web out of a stock having a consistency of at least 2.5 % in a headbox (1). The pulp suspension is fed from the headbox (1) without a free slice jet into between two wires (4, 6), which form, while supported by sets of dewatering boxes (3, 5), a dewatering gap (2) which converges in a wedge-like manner and in which the pulp suspension is dewatered by means of pressure. Dewatering is controlled by changing the angle of convergence of the dewatering gap (2) converging in a wedge-like manner.

Description

METHOD AND APPARATUS FOR THE MANUFACTURE OF A FIBRE WEB

FIELD OF INVENTION

The invention relates to the method defined in the preamble of claim 1 and to the apparatus defined in the preamble of claim 11 for the manufacture of a fibre web. In this connection, by the "fibre web" is meant a paper, board or chemical pulp web.

BACKGROUND OF INVENTION

Production volumes and speeds of paper and board machine lines have increased rapidly in recent years, which has increased investment costs and operation costs.

In principle, the manufacture of paper and board is pumping water from one de- vice to another and removing water from pulp and web using various techniques. Different devices and methods have been studied and developed. However, devices allowing high-consistency stocks to be used in them have not been achieved for industrial applications.

Further, different wire sections and gap formers are previously known for use in the manufacture of paper. However, sufficient dewatering is not always achieved in the known gap formers.

US Patent 3,823,062 discloses a method of manufacturing paper, in which a pulp suspension is passed from a feed channel without a free stock jet into a dewatering gap, which converges in a wedge-like manner and which is defined by two form- ing fabrics supported by sets of dewatering boxes. The pressure of the pulp suspension causes water to be drained through the wires into the dewatering boxes. The dewatering boxes are filled with water and they are connected through discharge pipes to a wire pit. The discharge of water from individual dewatering boxes is controlled by means of valves arranged in the discharge pipes. When a multi-layer web is manufactured, the dewatering gap can be provided with a vane that keeps the pulp suspensions discharging from the feed channel separated from one another. The apparatus is not intended for high-consistency stocks. When a low-consistency stock is used, the dry solids content achieved is not very high. Also, the apparatus is not adaptable to the manufacture of a fibre web at different basis weights and at different production speeds.

FI Patent 109210 discloses a method and an apparatus for forming a pulp web, in which dewatering takes place in a space converging in a wedge-like manner, after which the pulp is compressed in the thickness direction with a pressure that is at least equal to the pressure prevailing in the converging space. Dewatering chambers defining the space converging in a wedge-like manner are fixedly mounted, but one or both halves of a plane press placed after them is/are articulated to be turnable. This arrangement makes it possible to affect the compression force of the plane press and, thereby, the dry solids content of the web coming out of the wire section, but not the initial dewatering in the space converging in a wedge-like manner. Because of the plane press, it is necessary to use an expensive special wire as the bottom wire because compression pressure wears out a normal wire in a very short time so that it need be replaced. This apparatus is not intended for high consistencies, either. Moreover, it cannot be used in a very broad range of basis weights and production speeds.

AIM OF INVENTION

An object of the invention is to_. solve the drawbacks associated with the prior art. In particular, an object of the invention is to disclose a new type of method and apparatus for dewatering a fibre web and for controlling dewatering in a wire section in a simple and easy manner. Moreover, the aim is to provide a method and an apparatus in which it is possible to use stocks having a higher consistency than conventional. An additional object of the invention is to provide an apparatus that allows a fibre web to be manufactured in a flexible manner at different basis weights and at different production speeds. A further object is to provide a former which is of lower investment cost than those of the prior art, and on which the forming of the web takes place at a considerably lower consumption of energy than on the arrangements in accordance with the state of the art.

SUMMARY OF INVENTION

The method and the apparatus according to the invention are characterized by what is stated in the claims.

In the method in accordance with the invention, a pulp suspension having a head- box consistency of at least 2.5 % is fed from the headbox without a free slice jet into between two wires, which form, while supported by sets of dewatering boxes, a dewatering gap which converges in a wedge-like manner and in which the pulp suspension is dewatered by means of pressure. It is characteristic of the arrangement that dewatering is controlled by changing the angle of convergence of the dewatering gap that converges in a wedge-like manner.

The apparatus for the manufacture of a fibre web in accordance with the invention comprises an approach system, a headbox supplied with a pulp suspension from the approach system at a consistency of at least 2.5 %, and a first wire and a second wire defining between themselves, while supported by sets of dewatering boxes, a dewatering gap that converges in a wedge-like manner. The sets of dewatering boxes are arranged to receive water draining through the wires due to the effect of pressure. The headbox is brought so close to the dewatering gap that the pulp suspension can be passed from the headbox to the dewatering gap without a free slice jet. It is characteristic of the arrangement that the angle of convergence of the dewatering gap converging in a wedge-like manner is adjustable.

A high-consistency headbox, which can be, for example, of the type described in US Patent 6,962,647, is used as the headbox.

Dewatering makes use of the pressure of the pulp suspension fed from the headbox to the dewatering gap and the drive powers of the wires, which are dependent on the convergence of the dewatering gap. In the dewatering gap, a pressure dif- ference is effective over both wires, which pressure difference causes water to move through the wire to the dewatering box situated behind it. The convergence of the dewatering gap causes the pressure to be maintained in the dewatering area. No suction is used for dewatering, so that the web will not be cooled and the temperature of the pulp suspension will be maintained in the wire section.

For different paper and board grades, the convergence of the gap can be dimensioned according to the need for dewatering. Advantageously, the angle of convergence of the gap is adjusted such that the first dewatering box of the dewatering box group located above the gap is provided with an articulated joint, with respect to which the group of dewatering boxes can be turned. The height position of the articulated joint is also adjustable, which makes it possible to run different basis weights. The first-mentioned adjustment changes the height of the outlet, i.e. the discharge opening, of the dewatering gap, while the latter adjustment changes the height of the inlet of the dewatering gap. The convergence and the profile of the gap are dimensioned according to the need for dewatering. The discharge opening is advantageously steplessly adjustable.

The size of the discharge opening of the dewatering gap and the changes of the gap angle are used for affecting the drive powers of the top and bottom wires and, thus, dewatering. Drive power is transmitted to dewatering by means of wires.

The smaller the discharge opening, the higher are the drive powers and the effi- ciency of dewatering in the converging gap. The dry solids content of the web then also increases.

Since the angle of convergence of the dewatering gap is adjustable, the dewater- ing in the dewatering gap is neither basis weight nor speed limited.

The dewatering in the converging gap can also be affected by controlling the flow of the headbox, which makes it possible to affect the pressure of the stock supplied from the headbox to the dewatering gap.

Water is removed from the web and collected by means of sets of dewatering boxes arranged in connection with the dewatering gap. The sets of dewatering boxes comprise several successive dewatering boxes, whose dewatering can be controlled individually or in groups. The dewatering boxes are substantially filled with water during operation, and they are connected through discharge pipes to a drainage water tank, to which the water removed from the web is passed. The discharge pipe must be substantially full during processing, and a so-called barometric leg phenomenon must be produced in it to achieve a good dewatering result.

Since dewatering takes place by means of pressure, and not by suction, separate vacuum pumps and additional heating are not needed for heating the web. Further, an advantage of the arrangement is that the temperature of the fibre web remains from the wire section to the press section almost the same as it is in the headbox. Furthermore, the dewatering in the wire section is neither basis weight nor speed limited.

In one embodiment of the invention, a multi-layer headbox is used for manufacturing a multi-layer fibre web. The multi-layer headbox can be, for example, a two-layer headbox for making a two-layer web or a three-layer headbox for mak- ing a three-layer web. In one embodiment of the invention, at least one vane is arranged in the dewater- ing gap to keep the stocks emerging from the multi-layer headbox separated from one another in the dewatering gap until a desired dry solids content is achieved in the fibre web. The layers of the fibre web are at first drained separately and then combined together at a dry solids content at which the layers adhere to one another very well. The purity of the layers will then remain excellent. Advantageously, the consistency of the stock layers is in a range of 6 - 12 % when they are combined together. This kind of arrangement allows the fines that improve bond strength to be retained in the stock layer surfaces on the side of the vane, and when these surfaces are joined together, good bond strength is achieved. The length of the vane can be selected according to the dry solids content at which it is desirable to join the layers together.

In conventional paper or board forming, the feed consistency of the pulp suspen- sion is in a range of 0.4 - 0.8 %. The method in accordance with the invention uses a high-consistency stock having a dry solids content of over 2.5 %, advantageously in a range of 3 - 5 %. Hence, the approach system of the headbox can be built without a wire pit, a centrifugal cleaner plant and a headbox feed pump. Because of the higher feed consistency, the water volumes handled at the wet end of the paper machine are reduced as much as 60 % from the conventional volumes, and the short circulation becomes simpler. In addition, since the consistency of the stock is high, the need for retention aids and other papermaking chemicals, such as starch, is significantly reduced or they can be even dispensed with entirely.

Advantageously, the approach system comprises a machine screen, from where accept is passed to the headbox and reject to a reject screen. Accept from the reject screen is returned to the inlet of the machine screen and reject is passed to a centrifugal reject cleaner plant, from where accept is returned to a mixing chest. A very low fibre loss is achieved by this kind of stock cleaning as compared with the arrangement in accordance with the state of the art. At the end of the forming section there can be a pre-press, i.e. a wire press, which compacts the web before it is transferred to the press section. Advantageously, this wire press is provided with a roll nip. The use of a stock that has a higher consistency than conventional and the efficient dewatering in the dewatering gap that converges in a wedge-like manner yield so high a dry solids content that it allows the use of a roll nip at the end of the wire section.

In one embodiment, the press section of the paper machine includes only one press nip, which is advantageously an extended nip press. This is possible because the dry solids content of the fibre web coming from the wire section is high. When desired, several presses can be used in the press section if the aim is to achieve very high dry solids contents.

In the arrangement in accordance with the invention, the dry solids content of the fibre web after the wire section is advantageously about 28 - 32 %. After the press section, the dry solids content of the fibre web can be about 47 - 52 %.

The method and the apparatus in accordance with the invention make it possible to reduce investment, energy and operation costs in the manufacture of paper or board or in the drying of chemical pulp. The apparatus is clearly simpler in structure, which reduces investment costs. Because of the smaller number of devices and the reduced pumping volumes of water, power demand is reduced. Operation costs are also lowered because of the smaller number of devices and the reduced need for spare parts. In addition, the apparatus in accordance with the invention is environmentally very friendly.

The arrangement of the invention is flexible such that it can be used in a wide basis weight and speed range. The arrangement in accordance with the invention is particularly efficient in rebuild concepts, in which the rebuild of the forming section considerably increases the capacity of the manufacturing line. In this connection, by "pulp" is meant any pulp known in itself and formed of fibres, for example, wood or plant fibres, such as chemical or mechanical pulp or recycled fibre pulp. By "fibre web" is meant in this connection any paper, board, chemical pulp or similar product formed of the above-mentioned pulp. The inven- tion is suitable for the manufacture of all above-mentioned fibre webs, but it is particularly advantageous to manufacture a chemical pulp web by a one-layer headbox and, correspondingly, a board web by a multi-layer headbox.

LIST OF FIGURES

In the following, the invention will be described by means of detailed exemplifying embodiments with reference to the appended figures.

Figure 1 shows an apparatus in accordance with the invention for the manufacture of a two-layer board.

Figure 2 shows a short circulation system of a fibre web machine.

Figure 3 is an enlarged view of a detail in Fig. 1.

DETAILED DESCRIPTION OF INVENTION

Fig. 1 shows a part of an apparatus in accordance with the invention, by which apparatus it is possible to manufacture a two-layer fibre web, such as two-layer board. The apparatus comprises a high-consistency headbox 1 , which is followed by a dewatering gap 2, which converges in a wedge-like manner and is defined by a top wire 4 supported by a set of dewatering boxes 3 located above and by a bottom wire 6 supported by a set of dewatering boxes 5 located underneath. The dewatering gap 2 is also closed on the sides. The headbox 1 is brought so close to guide rolls 7, 8 defining an inlet of the dewatering gap 2 that a pulp suspension can be fed from the headbox 1 to the dewatering gap 2 as a closed jet, i.e. without contact with ambient air. Because of this arrangement, the pressure of the pulp suspension is transferred from the headbox 1 to the dewatering gap 2 without any pressure losses caused by a free stock jet, and the pressure of the pulp suspension can be made use of in the dewatering in the dewatering gap 2.

The sets of dewatering boxes 3, 5 are placed obliquely with respect to each other such that they approach each other in the running direction of the web. Each set of dewatering boxes 3, 5 comprises several successive dewatering boxes 3a and 5a, which are substantially filled with water. Water draining into the dewatering boxes 3a, 5a through the wires 4, 6 is passed through discharge pipes 9, 10 to drainage water tanks 11, 12. The discharge pipes 9, 10 are arranged so that the water that is being removed flows below the surface of the drainage water tank 1 1, 12, with the result that the discharge pipes 9, 10 are filled with water at all times. The discharge pipes 9, 10 are provided with valves 13, 14, by means of which it is possible to control the dewatering of each individual dewatering box 3a, 5a. Alternatively, the dewatering boxes 3a, 5a can be grouped into sections, so that dewatering can be controlled in sections.

The dewatering in the dewatering gap 2 converging in a wedge-like manner can be affected by changing the convergence angle between the sets of dewatering boxes 3, 5. For this purpose, the upper set of dewatering boxes 3 is provided with an articulated joint 25, with respect to which the entire upper set of dewatering boxes 3 can be turned. In that connection, an end of the upper set of dewatering boxes 3 moves, in the manner indicated by the two-way arrow 26, upwards farther away from the lower set of dewatering boxes 5 or downwards closer to the lower set of dewatering boxes 5. The height of a discharge opening 51 of the dewatering gap 2 can also be affected by changing the inclination of the upper set of dewatering boxes 3. The upper set of dewatering boxes 3 can additionally be provided with means for changing the height position of the articulated joint 25 (not shown), thus also enabling the height of an inlet 52 of the dewatering gap 2 to be adjusted, which increases the flexibility of the apparatus and makes it possible to run different basis weights.

Water drains away from the dewatering gap 2 through the wires 4, 6 into the sets of dewatering boxes 3, 5 as a result of a pressure difference which is caused by the pressure of the pulp suspension discharging from the headbox 1 and which is effective over the wires 4, 6. The efficiency of dewatering can be affected not only by a change in the angle of convergence of the wedge-shaped dewatering gap 2 but also by a change in the pressure of the headbox 1.

When viewed from the side, the dewatering gap 2 converges gently with respect to the direction of running, maintaining pressure in spite of the water draining away. The convergence is dimensioned according to a given profile. The convergence ends at the steplessly adjustable discharge opening 51. The drive powers required for conveying the wires 4, 6 can be controlled by means of the convergence of the gap 2 and the size of the discharge opening 51.

The shape of the dewatering gap 2 is not limited to that shown in Fig. 1. The dewatering gap 2 can be convex, concave, straight, trumpet-shaped or of any other shape known in itself depending on the site of use and on desired dewatering.

The length of the sets of dewatering boxes 3, 5 can be selected according to the grade to be run. The arrangement of the invention makes it possible to shorten the length of the wire section.

The two-layer headbox 1 of Fig. 1 is used for manufacturing a two-layer board web out of a stock of higher consistency than conventional. Said headbox can be, for example, a high-consistency headbox described in US Patent 6,962,647. A first layer Ia of the headbox 1 is supplied with a first stock 15, of which the bot- torn layer of the board is made, and a second layer Ib of the headbox 1 is supplied with a second stock 16, of which the top layer of the board is made. The top layer of two-layer board is usually made of bleached pulp and the bottom layer is made of brown pulp. The top layer can be formed of a pulp made of bleached birch or eucalyptus. The bottom layer can be made of brown SRO pulp, BCTMP pulp, recycled fibres and/or a broke product or equivalent.

Inside the headbox 1, the pulp suspension layers are separated by a partition Ic, which continues in the form of a vane 17 that extends to the dewatering gap 2 and keeps the stock layers separate from each other until they have achieved a given dry solids content. In this way, the layer purity of the board can be caused to re- main good, and the partly drained bottom and top layers of the board can be caused to bond well to each other at the stage when the layers join. This follows from the fact that when the layers join, on that surface of both layers which lies against the vane 17 there is still left an abundance of fines needed for producing a good strength between the layers. By changing the length of the vane 17 and the efficiency of dewatering it is possible to affect the consistency at which the layers are joined together. Advantageously, the consistency of the stock layers is in a range of 6 - 12 % when they are joined together.

At the end of the dewatering gap 2 converging in a wedge-like manner, the top wire 4 is separated from the bottom wire 6 and the web W is passed on support of the bottom wire 6 to a press section. At the end of the wire section there is a wire press 18 as a pre-press, the function of which is to improve the strength of the web, increase its dry solids content about 2 - 4 %, and equalize the moisture content of the web before it is transferred at a pick-up point P from the bottom wire 6 to a fabric 19 of the press section.

Since the dry solids content of the web coming from the forming section is relatively high, advantageously about 30 %, one press nip 20 only is sufficient in the press section, said nip being advantageously an extended nip, i.e. a shoe nip. The extended nip 20 comprises a shoe roll 20a and a counter roll 20b, between which the web W is passed on support of two press fabrics 19, 21. The consistency of the pulp suspensions 15, 16 supplied to the headbox 1 is over 2.5 %, advantageously 3 - 5 %. The dry solids content of the web is about 28 - 32 % after the forming section and over 50 % after the press section. The use of high- consistency stock and the efficient dewatering in the wire section make it possible to use the wire press 18 provided with a roll nip, and make possible a press section that has only one press nip 20, which is advantageously an extended nip. The roll nip used as a pre-press in the wire section strains the forming wire less than the extended nip previously used as a wire press.

Fig. 2 shows an approach system and a short circulation of a fibre web machine making a one-layer web. It is understood that in a corresponding two-layer embodiment, separate short circulations would have to be arranged for the stocks of both layers in order that the stocks and waters of the different layers shall not be mixed with each other and the layer purity may be caused to remain good.

Stock 31 is supplied into a mixing chest 30 at a consistency of about 4 - 4.5 %. The consistency of wet broke 48 coming from a pulper (not shown) is about 5 %. In the mixing chest 30 the different stock components are mixed with one another and the stock mixture is diluted with circulation water 39 to a desired consistency. The stock is pumped from the mixing chest 30 along a line 34 to a machine chest 32, from there along a line 35 to a machine screen 33 and from there further along a line 36 to a headbox 1. A first feed pump 49 is placed in the stock line 34 between the mixing chest 30 and the machine chest 32, and a second feed pump 50 is placed in the stock line 35 between the machine chest 32 and the machine screen 33. A separate headbox feed pump is not needed in the stock line 36 between the machine screen 33 and the headbox 1, but the stock flows from the machine screen 33 to the headbox 1 by the pressure produced by the second feed pump 50. A flow which is of constant magnitude and whose consistency remains constant is circulated from the headbox 1 along a return line 37 back to the stock line 35, to the suction side of the pump 50. Consistency and flow measurements (not shown) are arranged between the headbox 1 and the machine chest 32.

The drainage waters of dewatering boxes 3, 5 defining a dewatering gap 2 are circulated through discharge pipes 9, 10 to drainage water tanks 11, 12, which can be connected together when manufacturing a one-layer web. Water is passed from the drainage water tanks 11, 12 to a circulation water tank 38, from where water is passed along the dilution water line 39 to stock consistency adjustments in the short circulation and for use, for example, in the startup and/or shutdown of the apparatus. Water is passed to the suction side of the stock feed pump 50. This line is pressure controlled. Excess water is passed from the circulation water tank 38 along a circulation water line 40 to a white water tower (not shown).

Reject from the machine screen 33 is passed along a reject line 41 to an interme- diate tank 42 and from there further to a reject screen 43, from where accept is passed along a line 44 back to the stock line 35 and reject is passed along a line 45 to a centrifugal reject cleaner plant 46. The stock passed to the centrifugal cleaner plant 46 is diluted to a consistency of about 0.7 %. Accept from the first stage of the centrifugal cleaner plant 46 is passed along a line 47 to the mixing chest 30.

The stock feed line 35, 36 of the short circulation lacks a wire pit, a centrifugal cleaner plant and a headbox feed pump. No wire pit is needed because the stock is fed to the headbox at the consistency to which it is diluted in the mixing chest 30. Advantageously, the consistency of the stock fed to the headbox is about 3 - 5 %. The lack of centrifugal cleaning makes it possible to use a high feed consistency because centrifugal cleaning generally requires a consistency of below 1 %. When the pressure losses caused by centrifugal cleaning are excluded, a separate headbox feed pump is not needed, but the stock can be fed to the headbox 1 by means of the pressure produced by the second feed pump 50. The material quantities pumped by the apparatus in accordance with the invention drop as much as 65 % from those of the prior art, depending on the consistency of the stock of the headbox.

Fig. 3 is an enlarged view of a dewatering gap 2, which converges in a wedge-like manner and is defined by a top wire 4 supported by a set of dewatering boxes 3 located above and by a bottom wire 6 supported by a set of dewatering boxes 5 located underneath. Both sets of dewatering boxes 3, 5 comprise several successive dewatering boxes 3a, 5a, the dewatering of each of which can be controlled separately or together. The arrows 3a, 5b designating dewatering illustrate how dewatering at the beginning of the dewatering gap 2 is more intense than at the end of the dewatering gap 2.

The upper set of dewatering boxes 3 is coupled by means of an articulated joint 25 to a paper machine frame such that the set of dewatering boxes 3 can be turned about the articulated joint 25 to change the angle of convergence of the dewatering gap 2. When the convergence angle between the sets of dewatering boxes 3 and 5 is changed, the height of a discharge opening 51 of the dewatering gap 2 changes at the same time. The convergence angle of the gap has been found to correlate clearly with dewatering efficiency: the sharper the dewatering angle, the more efficient dewatering.

In one embodiment of the invention the height position of the articulated joint 25 is adjustable, so that the height of an inlet 52 of the dewatering gap 2 can be changed. This makes it possible to run different basis weights.

It is also possible to provide both sets of dewatering boxes 3, 5 with an articulated joint, about which the set of dewatering boxes in question can be turned, and possibly with height adjustment of the articulated joint. In the embodiments of the figures the basis weight of the fibre web can be, for example, 1200 g/m² and the speed in the wire section 200 - 2000 m/min.

The embodiments of the invention are not limited to the examples described, but they can vary within the scope defined in the appended claims.

Claims

1. A method for manufacturing a fibre web out of a pulp suspension having a consistency of at least 2.5 % in a headbox (1), in which method the pulp suspension is fed from the headbox (1) without a free slice jet into between two wires (4, 6), which form, while supported by sets of dewatering boxes (3, 5), a dewatering gap (2) which converges in a wedge-like manner and in which the pulp suspension is dewatered by means of pressure, characterized by the step of controlling dewatering by changing the angle of convergence of the dewatering gap (2) converging in a wedge-like manner.

2. A method as claimed in claim 1, characterized by the step of adjusting the angle of convergence of the dewatering gap (2) by turning a set of dewatering boxes (3) with respect to an articulated joint (25), whereby the height of a dis- charge opening (51 ) of the dewatering gap (2) also changes.

3. A method as claimed in claim 2, characterized by the step of adjusting the height of an inlet (52) of the dewatering gap (2) by changing the height position of the articulated joint (25).

4. A method as claimed in any one of the preceding claims, characterized by the step of also controlling dewatering by changing the pressure of the headbox (1) by means of flow and/or pressure control.

5. A method as claimed in any one of the preceding claims, characterized by the step of controlling the dry solids content of the web (W) by controlling drive powers of the wires.

6. A method as claimed in any one of the preceding claims, characterized by the step of using a multi-layer headbox for making a multi-layer fibre web.

7. A method as claimed in claim 6, characterized by the step of arranging at least one vane (17) in the dewatering gap (2) converging in a wedge-like manner to keep stock layers coming from the multi-layer headbox separated from one another until a desired dry solids content is reached.

8. A method as claimed in claim 7, characterized by the step of joining the stock layers coming from the multi-layer headbox to one another at a dry solids content of 6 - 12 %.

9. A method as claimed in any one of the preceding claims, characterized in that the consistency of the pulp suspension in the headbox (1) is in a range of 3 - 5 %.

10. A method as claimed in any one of the preceding claims, characterized in that the sets of dewatering boxes (3, 5) comprise several successive dewatering boxes (3a, 5a) whose dewatering is controlled individually or in groups.

11. An apparatus for manufacturing a fibre web, which apparatus comprises an approach system (31-50), a headbox (1) supplied with a pulp suspension from the approach system at a consistency of at least 2.5 %, and a first wire (4) and a sec- ond wire (6) defining between themselves, while supported by sets of dewatering boxes (3, 5), a dewatering gap (2) that converges in a wedge-like manner, which sets of dewatering boxes (3, 5) are arranged to receive water draining through the wires (4, 6) due to the effect of pressure, in which apparatus the headbox (1) is brought so close to the dewatering gap (2) that the pulp suspension can be passed from the headbox (1) to the dewatering gap (2) without a free slice jet, characterized in that the angle of convergence of the dewatering gap (2) converging in a wedge-like manner is adjustable.

12. An apparatus as claimed in claim 1 1, characterized in that at least one of the sets of dewatering boxes (3) is provided with an articulated joint (25), with respect to which the set of dewatering boxes (3) is turnable.

13. An apparatus as claimed in claim 12, characterized in that the set of dewater- ing boxes (3, 5) is provided with means for moving the articulated joint (25) in the height direction.

14. An apparatus as claimed in claim 1 1, characterized in that the headbox (1) is a multi-layer headbox.

15. An apparatus as claimed in claim 14, characterized in that the dewatering gap (2) converging in a wedge-like manner is provided with at least one vane (17) to keep stocks (15, 16) coming from the multi-layer headbox (1) separated from one another until a desired dry solids content is reached.

16. An apparatus as claimed in any one of claims 11 to 15, characterized in that each set of dewatering boxes (3, 5) comprises several successive dewatering boxes (3a, 5a), which are each provided with regulation and/or control means to control dewatering in the dewatering gap (2).

17. An apparatus as claimed in any one of claims 11 to 16, characterized in that the approach system (31 -51 ) is arranged without a wire pit, a headbox feed pump and centrifugal cleaning of the stock supplied to the headbox.

18. An apparatus as claimed in claim 17, characterized in that the approach system (31-50) comprises a machine screen (33) whose reject is passed to a reject screen (43) whose reject is passed further to a centrifugal reject cleaning plant (46).

19. An apparatus as claimed in any one of claims 1 1 to 18, characterized in that it comprises a wire press (18) placed after the dewatering gap (2) converging in a wedge-like manner, after which there is a press section comprising only one press nip (20), which is an extended nip.

20. An apparatus as claimed in claim 19, characterized in that the wire press (18) comprises a roll nip.