EP0971069B1 - Mixing and recirculation circuit - Google Patents

Abstract

The system for the mixing and recirculation of fiber pulp with returned extracted water from the fourdrinier section, at a machine for the production of paper or cardboard with a stock inlet using controlled dilution water, has a unit (17) to increase the pressure in the path between the mixing vessel (7) and the vessel (1) to hold extracted water from the fourdriniers. The mixing vessel (7) has one chamber (7.1) with a number of feeds (4-6), and a second chamber (7.2) with at least one take-off (15) to the extracted water vessel (1). An overflow (19) gives a flow connection between the two mixing vessel chambers (7.1,7.2). An impeller pump (17), between the mixing (7) and extracted water (1) vessels gives the increased pressure. A control valve (18) is in the connection between the two vessels (7,1). A control circuit (16.1,16.2) determines the fluid level in the mixing vessel (7). Two concentric feed pipes (19,20) give a feed of fresh matter and the return flow at the extracted water vessel (1). An additional concentric pipe (21) at the feed and backflow pipes (19,20) takes the inflow into the extracted water vessel (1) from the cleaning station overflow. A gap is between the pipes (19-21) in the flow direction, and their ends are positioned from the outwards towards the inwards, in sequence. The feed tube (21) for the backflow ends before the end of the feed pipe (19), A mixer, such as a propeller, is in the mixing vessel (7). An Independent claim is included for the operation of the system, where the extracted water is taken from the wet section of the machine to be passed to a container (1). The mixing vessel (7) takes the backflow from the recirculating pulp at the stock inlet, the usable suspension from at least one vertical sorting stage and the backflow from a pulp cleaning stage, to be mixed together. The backflow (4-6) is injected into the lower section of the extracted water vessel (1) through a pressure increase unit (17) such as a pump, to be mixed with the extracted water and fresh material (8). The mixture is delivered to the stock inlet through a cleaning stage and/or a vertical sorter. Preferred Features: The backflow (4-6) is fed into the first mixing chamber (7.1), to pass to the second chamber (7.2) through an overflow, and is passed to the extracted water vessel (1) by a pump (17). The backflow (4-6) is controlled by a level monitor at the mixing vessel (7). The backflow (4-6) and the fresh material (8) pass into the extracted water vessel (1) through two concentric pipes (19,20), and the overflow (22) from the cleaning stage is passed into the lower section of the extracted water vessel (1), using an assembly of three concentric pipes (19-21).

Description

The invention relates to a mixing and Recirculation cycle in the constant part of a Paper or board machine according to the preamble of Claim 1 and a method for mixing and Recirculation of stock suspensions, white water and Returns in a paper or board machine, especially in the constant part.

A similar cycle is from the patent US 4,477,313 known. According to this patent the white water caught in the paper machine in open white water tank introduced and in Mixing pumps with thick matter provide that again Headbox fed.

A similar device and method are from the published patent application DE 195 09 522 A1 known. Here is one about the machine width sectioned headbox through a variety of Suspensions feed lines from one Distributor fed with stock suspension. Part of the im Drainage area of the paper machine White water becomes sectional to the headbox returned and to the basis weight control after Dilution principle used.

In paper or board machines with known Embodiments of the constant part go through increasing machine speeds, as well at the same time increasing quality requirements for the Paper temporal fluctuations in mass per unit area and Fluctuations in the paper composition to the day are no longer acceptable.

It is therefore an object of the invention a mixing and Recirculation cycle in the constant part of a Paper or board machine and an improved one Process for mixing and recirculating Stock suspensions, white water and returns in one Paper or board machine, especially in constant Part to represent the the temporal fluctuations minimize the characteristics in the paper.

The object is achieved by the features of claim 1 and the features of the first method claim solved.

The inventor has recognized that it can solve this The task is to mix the different suspensions with mostly different Improve concentrations. This will be achieved that the returns, like good substances of the second Cleaner stage and the second vertical classifier stage and the headbox recirculation in one, from White water tank separate, mixed tank mixed and with a means to increase the pressure White water tank for further mixing with Fresh material, white water and if necessary Deculator overflow are fed. Preferably happens the pressure increase and the transfer of that Mixing container to the white water container with the help of a Pump.

According to a further development of the inventive concept it is proposed to mix the container with a first Chamber with several connected supply lines and a second chamber with at least one discharge line to be provided, the discharge line to White water tank leads and between the first and an overflow is provided in the second chamber.

In a further embodiment of the mixing and Recirculation cycle becomes a control loop Regulation of the liquid level in the mixing tank proposed. With this control loop the fill level of the mixing tank by a level transmitter determined. In the event of deviations from the nominal value, Example operated as a valve actuator, whereby the volume flow withdrawn from the mixing container so can be influenced that the level corresponds to the desired level. Instead of regulated valve can also be a pump be speed controlled.

A particularly advantageous embodiment of the mixing and Recirculation cycle provides that for Feeding of fresh material and return into the White water tank two concentric Feed pipes are provided. This is advantageous a particularly good mixing of the fresh substance with the entire return and the white water.

Furthermore, in the presence of a Deculators of the mixing and recirculation cycle too be designed so that for the feeding of Deculator overflow additionally another, concentric to the feed pipes for fresh material and return extending, feed pipe is provided. Preferably is the order of the pipes from the inside to the outside Fresh material supply, return, deculator overflow. This corresponds to the order of the accruing Volume flows. However, with limited Mix result also selected a different order become.

• es wird der Naßpartie Siebwasser entnommen und einem Siebwasserbehälter zugeführt,
• einem Mischbehälter wird der Rücklauf, bestehend aus mindesten der Rezirkulation des Stoffauflaufes, dem Gutstoff mindestens einer Vertikalsichterstufe und dem Gutstoff mindestens einer Cleanerstufe zugeführt und vermischt,
• von dem Mischbehälter wird der Rücklauf im unteren Bereich des Siebwasserbehälters mit Hilfe eines Mittels zur Druckerhöhung (z.B. eine Pumpe) eingedüst,
• zusammen mit dem Siebwasser und zugeführtem Frischstoff vermischt und
• über eine Trennvorrichtung, beispielsweise einer Cleanerstufe und/oder einen Deculator und/oder einem Vertikalsichter, zum Stoffauflauf gefördert.

According to the method according to the invention, the inventor proposes to mix and recirculate stock suspensions, white water and returns in a paper or board machine, in particular the constant part, consisting of at least one headbox, a white water tank, a vertical classifier stage, a cleaner stage and optionally a deculator the following process steps:

• white water is removed from the wet section and fed to a white water container,
• the return line, consisting of at least the recirculation of the headbox, the accept material of at least one vertical separator stage and the accept material at least one cleaner stage, is fed and mixed into a mixing container,
• the return pipe in the lower area of the white water tank is injected from the mixing tank with the aid of a pressure-increasing device (eg a pump),
• mixed together with the white water and added fresh material and
• conveyed to the headbox via a separating device, for example a cleaner stage and / or a deculator and / or a vertical classifier.

An advantageous embodiment of the method provides that the return is first in a first chamber of the Mixing container is mixed, then with an overflow is led into a second chamber of the mixing container and then conveyed to the white water tank.

Beneficial for good and even It is also mixed when the return and the Fresh material supply in the white water tank done concentrically in two tubes or if one Deculator is present in the lower section of the White water tank fed to the deculator overflow becomes.

Another advantageous embodiment of the method is that the deculator overflow, the rewind and the fresh substance in the white water tank done concentrically in three feed pipes. Through this Type of feed of deculator overflow, return and Fresh ingredient will be a very good and even one Mixing of the suspensions achieved. Since the Deculator overflow usually the largest volume flow represents, it is advantageous this outside, the to run concentric pipes. Corresponding the volume flow is followed by the entire return and finally the fresh material in the inner feed pipe.

Further refinements of the inventions are in the Subclaims and in the following Figure description shown.

Advantages of the invention also result from the following description of the preferred Embodiments with reference to the Drawings.

Figur 1:

Stand der Technik eines Mischkreislaufes mit Siebwasserbehälter in Altanlagen;

Figur 2:

Siebwasserbehälter einer Altanlage;

Figur 3:

Stand der Technik eines Mischkreislaufes mit Siebwasserbehälter und Standrohr;

Figur 4:

erfindungsgemäße Ausführung des Mischund Rezirkulationskreislaufes;

Figur 5:

weitere erfindungsgemäße Ausführung des Misch- und Rezirkulationskreislaufes mit Einspeisung des Deculatorüberlaufes.

The invention will be explained in more detail below with reference to the drawings. They represent:

Figure 1:

State of the art of a mixed circuit with white water tank in old plants;

Figure 2:

White water tank of an old plant;

Figure 3:

State of the art of a mixed circuit with white water tank and standpipe;

Figure 4:

Execution of the mixing and recirculation circuit according to the invention;

Figure 5:

Another embodiment of the mixing and recirculation circuit according to the invention with feeding of the deculator overflow.

To clarify the environment of the invention is an example of a mixing and mixing device currently customary in FIG Recirculation cycle in the constant part of Paper and board machines shown. However, it will noted that the invention is also different executed circuits works and by different designed circuits not the scope of the invention is left.

Figure 1 shows a schematically shown Wet section 24 with a dilution water controlled Headbox 23. The wet end becomes the white water withdrawn and via the white water inlet 3 to White water tank 1 supplied. Furthermore, flow into the White water tank 1 the headbox recirculation 4 from the headbox 23, the deculator overflow 22 from the Deculator 29, the good from the second Vertical classifier stage 26. The first and second cleaner stages 27, and 28 feed the deculator 29, which in turn the white water tank 1 and the first Vertical classifier level 25 feeds. From the White water tank 1 becomes a first part of the White water through a separator, here one Vertical classifier 30, led to the headbox 23. The Most of the white water mixes with the Fresh fabric. The circuit excess white water of the constant part can via the white water drain 31 escape from the circuit.

Figure 2 shows the known situation with a White water tank 1, in the one hand the White water inlet 3 is initiated and at the same time in the same large container the returns of the Headbox recirculation 4, the good substance of the second Vertical classifier level 5, the accepted substance of the second Cleaner level and possibly the deculator overflow 6 in the upper area of the white water tank 1 be initiated. In the lower part of the White water tank is fresh 8 via line 8 fed.

As discharge pipes from the white water tank the discharge lines are arranged from top to bottom 9 for the dilution water for the vertical classifiers and the cleaner system, then the white water inlet 10 to Headbox for the dilution water control and in lowest area of the stock suspension feed 11 to first cleaner stage or to the deculator.

With this type of execution, the problem arises from intense fluctuations in fabric density in the White water tank due to unstable currents the returns, for example the Headbox recirculation, the good substance of the Vertical sifter stage, or the second substance Cleaner stage. The interference of the returns in the usually large white water tank also leads to the disadvantage that when changing the paper type takes a very long time to become stable again Relationships in volume flow and consistency to adjust.

Another more modern but well known version of the Mixing and recirculation circuit in the constant part the paper machine is shown in FIG. Here a white water tank 1 is shown, in which on the The top of the white water supply 3 opens and the bottom Area a mixing tube 2 is introduced. In the Mixing tube 2 lead the headbox recirculation 4, the Acceptance of the second vertical classifier level 5 and Acceptable substance of the second cleaner level 6 and if necessary also the deculator overflow. Concentric in the mixing tube 2 is a supply line 8 for the supply of fresh material provided that also in the lower part of the White water tank is introduced. The Fresh material supply is exemplified here by a Control valve 14 and a flow meter device 13 in set the desired way. Because of the concentric Arrangement of the fresh material supply 8 in the mixing tube 2 is intends a good mixing of the fresh substance with the remaining suspension and the To reach white water. From the top of the White water tank 1 becomes the white water inlet 10 Headbox removed and in the lower area in the The proximity of the fresh material supply is via the Stock suspension to the first cleaner stage or to Deculator 11 the stock suspension with the help of a Pump 12 removed from the white water tank.

With this design of the material guide, the introduction of the returns is avoided directly into the white water tank with all the disadvantages resulting therefrom, but a major disadvantage of this embodiment is that the flow rate at the outlet of the mixing tube 2 is too low for thorough mixing, since the height difference Δh _{geo of} the fill levels is too low and therefore only slight flow velocity differences can be generated in the area of the mixing point.

FIG. 4 shows an embodiment according to the invention a mixed cycle. Accordingly, is a White water tank 1 and a mixing tank 7 provided that in via a line 15 in Connect. The mixing container 7 is with a first chamber 7.1 and a second chamber 7.2 executed. In the first chamber 7.1 Headbox recirculation 4, the good substance of Vertical classifier level 5 and the accepted material of the second Cleaner level 6 supplied. In this first chamber finds a good mix of the individual Material flows take place instead of and after mixing an overflow 32 into the second chamber 7.2. From this Chamber is the well mixed via line 15 Suspension (return) using a pump 17 and optionally a valve 18 sucks in and regulated via a feed pipe 19 to the white water tank 1 fed. The pumping process creates another one Improvement of the mixing of the entire return.

A second one is located concentrically in the feed pipe 19 smaller tube 20 in which the fresh material 8 is fed becomes. Because of the now adjustable speed the liquid through the pump 17 can be an injection the stock suspension with high pressure and high Speed made in the white water tank 1 become. This ensures good mixing of the White water with the supplied suspension and Fresh substance 8 reached. On the other hand, it is achieved that the white water inlet to the headbox 10 does not pass through the admixtures of the higher concentrated suspensions is affected, since this line in the upper area of the White water tank 1 is attached and thus only the white water of low concentration is removed.

The advantages are constant over time Concentration ratios in the Basis weight control used white water inlet 10 and thus better basis weight cross sections as well as a stable, good paper quality when changing grades.

Figure 5 shows another, improved Embodiment of the mixing and Recirculation circuit with an additional Infeed of the deculator circuit. The difference to execute the example from FIG. 3 consists in that in addition to the two concentric ones Feed pipes 19 and 20 for the returns and the Fresh a third, the others concentric enclosing feed pipe 21 is present, through the the deculator overflow is fed. Because usually the volume flow of the deculator overflow is greatest is also preferably the arrangement shown three feed pipes in order from the inside outside with fresh substance, collected returns and Deculator overflow selected.

In the two Figures 4 and 5 are two alternative Control circuits 16.1 and 16.2 for level control of the mixing container shown.

The control circuit 16.1 consists of a level transmitter LT for level control and a control valve 18 as Actuator for volume flow control. The pump 17 in this case works at constant speed.

The control loop 16.2 shown as an alternative consists of one level transmitter LT for level control and one speed-controlled pump 17 as an actuator for Flow control.

It goes without saying that others are well known Control mechanisms for level control respectively Volume flow control can be used without the Leave the scope of the invention.

For the sake of a better overview are in the figures 4 and 5 the actuators and control loops for Influencing the fresh material supply around supply pipe 20 not shown.

Through this type of execution on the one hand optimal mixing of the returns in the Mixing container 7 itself and another one Improvement of mixing through an additional Pump 17 reached. Furthermore, pump 17 high exit speeds at the end of the feed pipe 19 guaranteed for the returns, whereby in the further Optimal mixing of white water, Returns and fresh material in the outlet area of the White water tank 1 and - if available - des Deculator overflow occurs.

Another advantage is that this type the execution optimal for a modernization of existing old systems is suitable because a conversion of the White water I container is not required.

Another major advantage is that in the white water supply to one dilution-controlled headbox actually pure White water is used and therefore not a negative one Influencing the basis weight cross profile control too fear.

LIST OF REFERENCE NUMBERS

1

white water tank

2

mixing tube

3

Siebwasserzulauf

4

Stoffauflaufrezirkulation

5

Acceptance of the second Vertikalsichterstufe

6

Acceptable substance of the second cleaner level

7

mixing tank

7.1

first chamber

7.2

second chamber

8th

Fresh fuel supply

9

Dilution water for vertical classifiers and cleaner system

10

White water inlet to the headbox

11

Fabric suspension feed to the first Cleaner-stage

12

pump

13

flowmeter

14

control valve

15

Connection line between Mixing tank and white water tank

16.1

loop

16.2

alternative control loop

17

pump

18

control valve

19

Feed pipe for returns

20

Feed tube for fresh material

21

Feed pipe for deculator overflow

22

Deculatorüberlauf

23

headbox

24

wet end

25

first vertical classifier stage

26

second vertical classifier stage

27

first level of cleaner

28

second level of cleaner

29

Deculator

30

vertical screen

31

Siebwasserablauf

32

overflow

Claims (19)

1. A mixing and recirculation circuit in the constant section of a paper-making or board-making machine having the following properties:

   1.1 a headbox (23) with dilution control is provided,

   1.2 a white water tank (1) is provided, with

   1.3 the white water tank (1) having a feed pipe (3) for the white water and

   1.4 at least one feed pipe for pulp suspensions to be mixed into the white water, namely the returns (4, 5, 6) and

   1.5 a mixing tank (7) with a connection (15) to the white water tank (1) is provided, with furthermore

   1.6 at least one white water feed pipe (10) being provided between the white water tank (1) and the headbox,
   characterised in that

   1.7 a means for increasing pressure (17) is provided between the mixing tank (7) and the white water tank (1).
2. A mixing and recirculation circuit according to Claim 1, characterised in that the mixing tank (7) has a first chamber with a plurality of connected feed lines (4, 5, 6) and a second chamber with at least one discharge line (15) which leads to the white water tank (1), and an overflow (32) from the first chamber (7.1) to the second chamber (7.2) is provided.
3. A mixing and recirculation circuit according to one of Claims 1-2, characterised in that a feed pump (17) is provided between the mixing tank (7) and the white water tank (1) as means for increasing pressure.
4. A mixing and recirculation circuit according to one of Claims 1-3, characterised in that a control valve (18) is provided between the mixing tank (7) and the white water tank (1).
5. A mixing and recirculation circuit according to one of Claims 1-4, characterised in that a control circuit (16.1; 16.2) is provided for regulating the level of liquid in the mixing tank.
6. A mixing and recirculation circuit according to one of Claims 1-5, characterised in that two concentric feed pipes (19, 20) are provided for feeding fresh stock and returns into the white water tank (1).
7. A mixing and recirculation circuit according to Claim 6, characterised in that additionally a further feed tube (21), concentric to the feed tubes (19, 20) for fresh stock and returns, is provided in order to feed in deculator overflow.
8. A mixing and recirculation circuit according to one of Claims 6-7, characterised in that there is in each case a spacing in the direction of flow between the ends of the feed pipes (19, 20, 21).
9. A mixing and recirculation circuit according to one of Claims 8-9 [sic], characterised in that the feed pipes (19, 20, 21) in the direction of flow in their sequence end from the outside to the inside.
10. A mixing and recirculation circuit according to one of Claims 7-9, characterised in that the feed pipe (19) for the returns in the direction of flow ends before the feed pipe (20) for the fresh stock.
11. A mixing and recirculation circuit according to one of Claims 8-10, characterised in that the feed pipe (21) for the deculator overflow in the direction of flow ends before the feed pipe (19) for the returns.
12. A mixing and recirculation circuit according to one of Claims 1-11, characterised in that a mixing element, preferably a mixing propeller, is provided in the mixing tank (7).
13. A method for mixing and recirculating pulp suspensions, white water and returns in a paper-making or board-making machine, in particular the constant section, consisting of at least one headbox (23) with a wet section (24), a white water tank (1), a vertical screen stage (25, 26), a cleaner stage (27, 28) and optionally a deculator (29) comprising at least the following method steps:

    13.1 white water is taken from the wet section (24) and fed to a white water tank (1),

    13.2 the returns, consisting of at least the recirculated flow of the headbox (4), the accepted stock from at least one vertical screen stage (5) and the accepted stock from at least one cleaner stage (6) are fed to a mixing tank (7) and mixed,

    13.3 from the mixing tank (7) the returns (4, 5, 6) are sprayed via a means for increasing pressure (17) into the lower region of the white water tank (1),

    13.4 are mixed together with the white water and supplied fresh stock (8) and

    13.5 are supplied to the headbox via a separating means (30), for example a cleaner stage and/or a deculator and/or a vertical screen.
14. A method according to Claim 13, characterised in that the returns (4, 5, 6) are initially mixed in a first chamber (7.1) [of] the mixing tank (7), then are passed with an overflow into a second chamber (7.2) [of] the mixing tank (7) and then conveyed to the white water tank (1).
15. A method according to one of Claims 13-14, characterised in that the returns (4, 5, 6) are conveyed with the aid of a pump (17) from the mixing tank (7) to the white water tank (1).
16. A method according to one of Claims 13-15, characterised in that the returns (4, 5, 6) are regulated corresponding to the level of liquid in the mixing tank (7).
17. A method according to one of Claims 13-16, characterised in that the returns (4, 5, 6) and the supply of fresh stock (8) into the white water tank (1) takes place concentrically in two pipes (19, 20).
18. A method according to one of Claims 13-17, characterised in that the deculator overflow (22) is supplied in the lower region of the white water tank (1).
19. A method according to Claim 18, characterised in that the deculator overflow (22), the returns (4, 5, 6) and the fresh stock (8) are fed into the white water tank (1) concentrically in three pipes (19, 20, 21).

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