EP2126202B1 - Method for dehydrating pulp, and dehydration machine for carrying out the method - Google Patents

Description

The invention relates to a method for dewatering pulp in a former, in which the pulp applied to a lower wire by a headbox is passed between the lower wire and an upper wire by means of a guide roller at least in sections forming a twin-wire zone.

Furthermore, the invention relates to a dewatering machine for pulp, comprising a former with a lower sieve and an upper sieve, which at least partially form a twin-wire zone and are guided with the lying between them, applied by a headbox on the lower wire pulp over a guide roller. The dewatering machine is particularly suitable for carrying out the method.

Such a dewatering machine is for example from the International Application WO 00/31336 A1 known. The relatively short twin-wire zone of this dewatering machine is preceded by a wedge-shaped converging space formed by the two screens into which a headbox introduces the pulp at a first dry content. The two sieves passing through the room are held on chamber units, each containing at least one white water receiving chamber.

The dewatering machine shown in Figure 2 of said document has the disadvantage that they only limited with a limited due to the respective limited drainage capacity of the chamber units Production speed, that is, Siebgeschwindigkeit can be operated. This is usually in a range of up to 200 m / min. Due to the reduced production speed of the dewatering machine also their production amount is also correspondingly low in a conventional machine width.

In addition, due to the limited drainage capacities of the chamber units, the dry contents of the pulp at the end of the former are not exceedingly good, so costly measures must be taken in the former downstream areas of the dewatering machine to ultimately dry the pulp to an acceptable level. And with lower pulp dry contents, of course, the wet strength of the pulp also decreases, making it more technologically difficult to handle.

The documents DE3414087 A1 . WO97 / 42374 and DE 3343941 A1 describe drainage devices for dewatering fibrous webs. The pulp suspension applied to a sieve by means of a headbox is partially dewatered in a first section through the sieve. In a second section, a twin-wire section with a second wire is provided in which the pulp suspension and the already partially formed pulp partial web are dewatered through the second wire.

It is therefore the object of the invention to develop a method and a dewatering machine of the aforementioned types such that the disadvantages of the prior art are overcome and that higher dry contents of the pulp can be achieved in an energy-efficient and cost-effective manner.

This object is achieved according to the invention in a method of the type mentioned above in that the pulp in a pre-dewatering zone upstream of the twin wire zone in the direction of the wire sieve of the lower wire the lower sieve is pre-dewatered and that the pulp is further dewatered in the double-wire zone having a further deflection roller by means of wire strains applied by the two sieves.

The object of the invention is completely solved in this way.

The process according to the invention makes it possible to achieve higher dry contents of the pulp due to improved, ie intensified dewatering of the pulp even at higher wire speeds. The intensification of the drainage takes place on the one hand by their division into different phases, on the other hand by the type of drainage. Thus, a drainage due to applied screen stresses, among other things, also much gentler than a drainage due to the introduction of pressure pulses, they are now mechanical or pneumatic. Thus, using the process of the invention, a greater amount of pulp can be produced with improved dry contents and improved properties.

In addition, when using the method according to the invention, it is possible to dispense with "energy-consuming" drainage elements as far as possible, preferably even completely. Thus, in comparison with the known methods for dewatering pulp in a former, the required drive power is reduced by about 25% and the vacuum requirement to be installed by about 40%.

In a first preferred embodiment it is provided that the lower sieve for further dewatering of the pulp, a lower wire tension of at least 20 kN / m, preferably at least 25 kN / m, in particular at least 30 kN / m yields, and that the upper sieve for further dewatering of the pulp an upper wire tension of at least 6 kN / m, preferably of at least 8 kN / m, in particular of at least 10 kN / m yields. These Siebspannungsbereiche improve the dry contents of the pulp substantially, and they can be realized both technologically and mechanical engineering without much effort.

In addition, a pulp having a basis weight of 600 to 1200 g / m ² and / or a consistency of 1.2 to 2.2%, also preferably at a screen speed of at least 200 m / min, preferably of at least 250 m / min, in particular of at least 300 m / min, drained. These screening speeds thus allow, in comparison with today's methods for Dewatering of pulp in a former, with up to 25% higher production volumes for a standard machine width, with at least the same good dry contents and lower drive capacities and reduced vacuum requirements. Consequently, the inventive method is characterized overall by a lower energy consumption.

With regard to a cost-effective and gentle initial dewatering, it is advantageous if the pulp is dehydrated in the region of the pre-dewatering zone with a vacuum of less than or equal to 0.1 bar, preferably less than or equal to 0.8 bar. In addition, the vacuum requirement to be installed is noticeably reduced.

The object of the invention is achieved in a dewatering machine of the type mentioned in that the Doppelsiebzone upstream in the wire running direction of the lower wire is formed from a portion of the lower sieve Vorentwässerungszone that the guide roller has a closed roll shell and provided on the outside with a catcher for thrown off white water is and that the guide roller in Sieblaufrichtung of the lower wire another, both screens leading guide roller having a closed roll shell and is provided on the underside with a catcher for thrown off white water downstream.

This results in the aforementioned advantages according to the invention over the known prior art. In addition, without expensive installations and without a spatial enlargement of the dewatering machine, a greater dewatering of the pulp can be achieved. And moreover, the two guide rollers can be made relatively cheap and any problems with wipers acting on them can be avoided.

In addition, the use of the inventive method of "energy-consuming" drainage elements largely, preferably even completely omitted. Thus, in comparison with the known dewatering machines, the required drive power is reduced by about 25% and the vacuum requirement to be installed by about 40%.

By such a design of the dewatering machine can be compared to the known embodiments dissipate extremely large amounts of white water from the pulp and thus achieve higher dry contents. Because of the closedness of the roll shells, no white water from the pulp can pass through the respective adjacent sieve in the direction of the roll shell in the respective looping area. In this area, the white water flows in the other direction due to the wire tension in the other direction, that is, to the outside and is thrown by the respective outer sieve by centrifugal force in the respective catcher. The dry contents of the pulp are thus markedly increased.

In order to ensure a sufficient dewatering length in order to achieve higher dry contents of the pulp, the two deflection rollers preferably each have a roll diameter in the range from 1,200 to 1,750 mm, preferably from 1,450 to 1,600 mm.

Furthermore, it is advantageous if the two wires preferably wrap around the first deflection roller with a first wrap angle in a range from 90 to 135 °, preferably from 110 to 125 °. This in turn increases the drainage length and thus the dry contents of the pulp with an extremely gentle dewatering.

In order for technologically favorable dewatering conditions to be present right from the beginning, the predewatering zone formed from a section of the lower screen may preferably be oriented horizontally or approximately horizontally. In addition, the dewatering behavior of the pulp can be relatively easily influenced and controlled in such an embodiment.

With regard to the achievement of the shortest possible dewatering machine and the avoidance of rewetting of the pulp, it is advantageous if the two wires preferably run in the lower half of the roll from the first guide roller. They run in a favorable manner - seen in the direction Sieblaufrichtung the lower sieve - in the first lower quadrant of the first guide roller and in the upper half of the roller on the second guide roller.

Again, it is advantageous if the two wires, the second guide roller preferably with a second wrap in a range of 125 to 180 °, preferably from 145 to 165 ° wrap around. This again increases the drainage length and thus the dry contents of the pulp with an extremely gentle dewatering.

Furthermore, the two screens preferably run in the lower half of the roller from the second guide roller. They run in a favorable manner - seen in Sieblaufrichtung of the lower sieve - in the first lower quadrant of the second guide roller preferably together. This again favors the achievement of the shortest possible dewatering machine and the avoidance of rewetting of the pulp.

In order for the required dewatering performance to be met as a result of applied wire tensions, the lower wire preferably has a lower wire tension of at least 20 kN / m, preferably of at least 25 kN / m, in particular of at least 30 kN / m, and the upper wire preferably has an upper wire tension of at least 6 kN / m, preferably at least 8 kN / m, in particular at least 10 kN / m.

Further features and advantages of the invention will become apparent from the following description of preferred embodiments with reference to the drawings.

The single figure shows a schematic side view of an embodiment of a dewatering machine 1 according to the invention for pulp 2, which comprises a former 3.

The former 3 has a lower sieve 4 and an upper sieve 5, which at least partially form a double-wire zone 6. In this case, the pulp 2 lying between them, applied by a merely indicated headbox 7 to the lower sieve 4, is guided over a deflecting roller 8.

The twin-wire zone 6 is preceded by a pre-dewatering zone 9 formed from a section of the lower wire 4 in the wire-running direction S (arrow) of the lower wire 4. This horizontally or approximately horizontally oriented pre-dewatering zone 9 has a length L.9 in the range of 5,000 to 8,000 mm and is provided on the underside, ie the lower sieve 4 and the pulp 2 lying thereon, with several known dewatering elements. These dewatering elements are provided with the reference numeral 10 and each generate a vacuum V.10 less than or equal to 0.1 bar, preferably less than or equal to 0.8 bar. The lower sieve 4 is guided before its entry into the pre-dewatering zone 9 around a breast roll 11, in the area of which the headbox 7 applies the pulp 2 to the same.

The guide roller 8 has a closed roller shell M.8 and is provided on the outside with a collecting device 12 for centrifuged white water (arrows). The collecting device 12 extends to an extent that all due to the action of centrifugal thrown off white water (arrows) is fully collected and can be reliably removed from the former 3, for example by means not shown, the expert but known white water gutter.

Further, the guide roller 8 has a roller diameter D.8 in the range of 1,200 to 1,750 mm, preferably from 1,450 to 1,600 mm, and is of the two wires 4, 5 with a first wrap angle A.8 in a range from 90 to 135 °, preferably from 110 to 125 °, looped. Thus, the two wires 4, 5 in the lower half of the roll, preferably in the first lower quadrant Q.8, from the first guide roller 8 from.

The deflection roller 8 is in Sieblaufrichtung S (arrow) of the lower sieve 4 another, both sieves 4, 5 leading guide roller 13, which in turn has a closed roll shell M.13 and bottom side with a collecting device 14 for thrown off white water (arrows), downstream. This collecting device 14 extends to an extent that all due to the action of centrifugal centrifugal force thrown off white water (arrows) is fully collected and can be reliably removed from the former 3, for example by means not shown, the expert but well known white water gutter.

The guide roller 13 has a roller diameter D.13 in the range of 1,200 to 1,750 mm, preferably from 1,450 to 1,600 mm. The two wires 4, 5 run in the upper half of the roll on the second guide roller 13 and wrap around it with a second wrap angle A.13 in a range of 125 to 180 °, preferably from 145 to 165 °. Subsequently, the two wires 4, 5 in the lower half of the roll, preferably in the first lower quadrant Q.13, preferably run together from the second deflection roll 13. Subsequently, the two sieves 4, 5 are guided over a separating sucker 15, in the area of which they are separated on the basis of the present geometry, and the twin-wire zone 6 is thus terminated. The pulp 2 is carried on the lower wire 4 after the separation of the two wires 4, 5 and transferred at a later time in a known manner in a press section of the dewatering machine 1, not shown.

The lower wire 4 has a lower wire tension T.4 (double arrow) of at least 20 kN / m, preferably of at least 25 kN / m, in particular of at least 30 kN / m, whereas the upper wire 5 has an upper wire tension T.5 (double arrow) of at least 6 kN / m, preferably of at least 8 kN / m, in particular of at least 10 kN / m.

The device 1 described in the single figure is particularly suitable for carrying out the method according to the invention for dewatering pulp 2 in a former 3, in which the pulp 2 applied from a headbox 7 to a lower wire 4 between the lower wire 4 and an upper sieve 5 is guided at least in sections forming a twin-wire zone 6 via a guide roller 8, wherein the pulp 2 is pre-dewatered by means of the lower sieve 4 in a pre-dewatering zone 9 upstream of the twin sieve zone 6 (arrow) of the lower sieve 4, and wherein Pulp 2 in which a further deflection roller 13 having double-wire zone 6 by means of the two screens 4, 5 applied screen stresses T.4 (double arrow), T.5 (double arrow) is further dewatered.

The pulp 2, which preferably has a basis weight F of 600 to 1200 g / m ² and / or a consistency K of 1.2 to 2.2%, can thus be at a screen speed v (arrow) of at least 200 m / min , preferably of at least 250 m / min, in particular of at least 300 m / min, dehydrate.

In summary, it should be noted that the invention improves both a method and a dewatering machine of the aforementioned types such that the disadvantages of the prior art are overcome and that higher dry contents of the pulp can be achieved efficiently and inexpensively.

LIST OF REFERENCE NUMBERS

1

dewatering machine

2

cellulose

3

molder

4

Lower sieve

5

Upper sieve

6

twin

7

headbox

8th

deflecting

9

pre-dewatering

10

dewatering element

11

breast roll

12

catcher

13

deflecting

14

catcher

15

suction separator

A.8

First wrap angle

A.13

Second wrap angle

D.8

Roll diameter

D.13

Roll diameter

F

grammage

K

consistency

L.9

length

M.8

roll shell

M.13

roll shell

Q.8

First lower quadrant

Q.13

First lower quadrant

S

Sieblaufrichtung (arrow)

T.4

Lower screen tension (double arrow)

T.5

Upper wire tension (double arrow)

V.10

vacuum

v

wire speed

Claims (13)

1. Method for dewatering pulp (2) in a former (3), in which the pulp (2), applied to a lower wire (4) by a headbox (7), is led between the lower wire (4) and an upper wire (5) over a deflection roll (8), forming a twin-wire zone (6), at least over some distance,
   the pulp (2) being pre-dewatered by means of the lower wire (4) in a pre-dewatering zone (9) arranged upstream of the twin-wire zone (6) in the wire running direction (S) of the lower wire (4), and
   the pulp (2) being dewatered further in the twin-wire zone (6) having a further deflection roll (13) by means of wire tensions (T.4, T.5) applied by the two wires (4, 5)
   characterized in that
   for the further dewatering of the pulp (2), the lower wire (4) produces a lower wire tension (T.4) of at least 20 kN/m, preferably of at least 25 kN/m, in particular of at least 30 kN/m,
   and in that, for the further dewatering of the pulp (2), the upper wire (5) produces an upper wire tension (T.5) of at least 6 kN/m, preferably of at least 8 kN/m, in particular of at least 10 kN/m.
2. Method according to Claim 1,
   characterized in that
   the pulp (2), having a weight per unit area (F) of 600 to 1200 g/m² and/or a consistency (K) of 1.2 to 2.2%, is dewatered at a wire speed (v) of at least 200 m/min, preferably of at least 250 m/min, in particular of at least 300 m/min.
3. Method according to one of the preceding claims,
   characterized in that
   in the area of the pre-dewatering zone (9), the pulp (2) is dewatered with a vacuum (V.10) of less than or equal to 0.1 bar, preferably less than or equal to 0.8 bar.
4. Dewatering machine (1) for pulp (2), comprising a former (3) having a lower wire (4) and an upper wire (5), which form a twin-wire zone (6), at least over some distance, and in this case are led over a deflection roll (8) with the pulp (2) located between them and applied to the lower wire (4) by a headbox (7),
   a pre-dewatering zone (9) formed from a section of the lower wire (4) being arranged upstream of the twin-wire zone (6) in the wire running direction (S) of the lower wire (4),
   the deflection roll (8) having a closed roll shell (M.8) and being provided on the outside with a collecting device (12) for white water that is thrown off, and
   a further deflection roll (13), which guides both wires (4, 5), has a closed roll shell (M.13) and is provided on the underside with a collecting device (14) for white water that is thrown off, being arranged downstream of the deflection roll (8) in the wire running direction (S) of the lower wire (4),
   characterized in that
   the lower wire (4) has a lower wire tension (T.4) of at least 20 kN/m, preferably of at least 25 kN/m, in particular of at least 30 kN/m, and
   in that the upper wire (5) has an upper wire tension (T.5) of at least 6 kN/m.
5. Dewatering machine (1) according to Claim 4, characterized in that
   the two deflection rolls (8, 13) each have a roll diameter (D.8, D.13) in the range from 1200 to 1750 mm, preferably from 1450 to 1600 mm.
6. Dewatering machine (1) according to Claim 4 or 5, characterized in that
   the two wires (4, 5) wrap around the first deflection roll (8) with a first wrap angle (A.8) in a range from 90 to 135°, preferably from 110 to 125°.
7. Dewatering machine (1) according to one of Claims 4 to 6,
   characterized in that
   the two wires (4, 5) run off the first deflection roll (8) in the lower roll half.
8. Dewatering machine (1) according to Claim 7, characterized in that
   the two wires (4, 5) - seen in the wire running direction (S) of the lower wire (4) - run off the first deflection roll (8) in the first lower quadrant (Q.8).
9. Dewatering machine (1) according to one of Claims 4 to 8,
   characterized in that
   the two wires (4, 5) run onto the second deflection roll (13) in the upper roll half.
10. Dewatering machine (1) according to one of Claims 4 to 9,
    characterized in that
    the two wires (4, 5) wrap around the second deflection roll (13) with a second wrap angle (A.13) in a range from 125 to 180°, preferably from 145 to 165°.
11. Dewatering machine (1) according to one of Claims 4 to 10,
    characterized in that
    the two wires (4, 5) run off the second deflection roll (13) in the lower roll half.
12. Dewatering machine (1) according to one of Claims 4 to 11,
    characterized in that
    the two wires (4, 5) - seen in the wire running direction (S) of the lower wire (4) - run off the second deflection roll (13), preferably together, in the first lower quadrant (Q.13).
13. Dewatering machine (1) according to one of Claims 4 to 12,
    characterized in that
    the upper wire (5) has an upper wire tension (T.5) of a least 8 kN/m, preferably of at least 10 kN/m, in particular of at least 12 kN/m.

Images