EP0898014B1 - Process and apparatus for controlling or regulating the basis weight of a paper- or board web - Google Patents

Description

The invention relates to a device and a Procedure for controlling or regulating the middle one Basis weight of a paper or cardboard web in Manufacturing process of a paper or board machine according to the preamble of claim 1 and the preamble of claim 10.

An essential quality factor of a paper or Cardboard web lies in the uniformity of the Basis weight of the web produced. in the Manufacturing process of such a web occur numerous confounding factors that affect uniformity of the basis weight across the machine width and also seen in the longitudinal direction, unfavorable can influence. These disruptive factors include for example temperature fluctuations, Pressure fluctuations and manufacturing tolerances or also Errors in the execution or setting of the Paper machine in the manufacturing process. Around negative disruptive factors as successful as possible turn off and produce evenly to get the paper web, devices and Process for controlling and regulating the Basis weight, in particular the basis weight cross section, used.

In the patent DE 35 35 849 it is described that Width of the outlet gap of a headbox to change certain points of the web width so that the throughput of the stock suspension accordingly changed locally. If the throughput of the Stock suspension with the same across the machine width Concentration changes locally, so this causes an influence on the amount of solids this point of the web in relation to the web width and thus a change in the basis weight on this Place or this lane.

In patent application DE 40 19 593 A1 there is one Device and a method for regulating the Basis weight cross-section of the web is described. According to this document, a deviation of the Basis weight cross-section of the paper web on one certain point of the web width, the concentration of the stock suspension stream changed at this point become. To achieve this, it is proposed that Headbox at least partially over the Machine width and with the help of regulated section flows with individual adjustable concentration. The individual adjustment of the concentration of the the respective section flow is carried out by a regulation the inflow conditions of two individual flows constant but different concentration. Due to the different content of the Section flows of solids result in a Change the basis weight on the corresponding Place the web width.

In the control procedure used here, this is Basis weight cross-section of the paper web at the end of the Paper machine measured and with a control loop Aperture on the headbox or the inflow conditions of individual flows of different concentrations for the respective sections regulated.

Such a control procedure with the measurement of the The basis weight cross-section is also, for example from the patent application DE 40 05 281 or from the DE 42 38 037 known. In the two above Fonts becomes the basis weight cross section of the Paper web measured at the end of the paper machine and the necessary adjustment via a process control system the actuators for influencing the section Basis weight causes.

From the published patent application DE 20 19 975 it is still known, with the help of two sensors a running path from a measured oblique profile and a longitudinal profile the actual Basis weight cross section and the actual Extract basis weight longitudinal profile and Control, or regulation of the Basis weight to use a web.

The control processes described above regulate in essentially the transverse profiles of the paper web. It is also known in the manufacturing process Paper web to use a control loop that the Basis weight of the finished paper web measures and based on the basis weight measured, this is usually the mean of the measured cross profile, the Regulates the amount of substance that is fed into the sieve cycle and thus the average basis weight of the generated paper web sets.

The problem with this prior art is that the known regulation of the basis weight relatively sluggish behavior with long reaction times having.

It is an object of the invention, the known Paper machine with a basis weight control and the corresponding procedure for this further develop that the response times of Regulation will be greatly shortened and therefore also Variations in the papermaking process are affected can be the one in their temporal course shorter wavelength than the running time of the paper web through the paper machine.

The object of the invention is characterized by the features of first device claim and the first Process claim resolved.

Accordingly, the known paper machine with a Regulation of the average basis weight of a paper or Cardboard web in the manufacturing process, some Headbox for machine-wide distribution of the Stock suspension on a sieve or between two sieves, at least one stock suspension feed to Headbox with at least one concentration and a first control loop with an actuator Setting the at least one concentration of at least one feed suspension, at least one means to determine the mean Basis weight of the finished web, at least one agent to change at least one concentration of at least one fed to the headbox Stock suspension and at least one agent for Adjustment of the at least one actuator Setting the at least one concentration of has at least one feed suspension, improved in that at least a second Control circuit for regulating the concentration of the Headbox fed stock suspension, added.

A further development of this Paper machine is that the second Control loop using at least one direct means or indirect determination of the mass per unit area of the emerging path has.

Another training is that the agent for the direct or indirect determination of the Basis weight of the resulting web in the wet area of the Paper machine is arranged. It can be this preferably by a measurement directly behind the Headbox nozzle, for example with the help of a radiometric sensor. There is also Possibility of the fabric suspension height on one Measuring fourdrinier sieve, this is preferably done behind the first roller and before the first Drainage unit, to be influenced by the Drainage unit arise to rule out. However, if there is also space or other circumstances is necessary, even after first drainage unit can be measured. Also at a twin wire can, for example with the help of a radiometric measurement, the basis weight of the emerging web can be determined in the wet area.

According to a further embodiment, the headbox can have two stock feeds with different stock concentrations C _L , C _H. These material feeds are designed such that at least one of the two material feeds splits into section streams at the headbox, which can be regulated individually. In this context, with regard to the possible designs of the headboxes, reference is made to the documents cited above relating to the headboxes which are controlled by the density.

According to another further inventive concept can one of the two material feeds via a further introduction regulated by the second control loop of a dilution or thickening fluid. As a dilution fluid, for example White water. There is also the thickening fluid Possibility of additional thick matter in one of the two Introduce stock feeds in a controlled manner. Other Dilution or thickening fluids, such as clear water, Clear filtrate or stock suspension with higher Concentration can also be used.

Another embodiment of the inventive concept may be that if the second Separate sensor in the wet area of the paper machine Fibers or ash content of the formed Paper web is measured or information via the paper consistency sensor is obtained, the appropriate individual Lack of fiber or ash fed and with it be balanced. It also does not go beyond the scope of the Leave invention, if for measuring the fibrous materials and the ash content of the resulting paper web two different sensors are used.

The problem outlined above also becomes the characteristics of the first claim. According to this Claim is the known method for regulating average mass per unit area of a paper or cardboard web, in which the basis weight of the web at the end of the Manufacturing process is determined, then the Deviation of the actual value from a given one Setpoint is calculated and from this the adjustment the concentration supplied to the headbox Stock suspension to correct the measured Deviation is carried out, improved in that that the basis weight of the resulting web directly or measured indirectly in the area in front of the dryer section and is fed to a second control loop.

Another embodiment of the invention accordingly, the second control loop regulates the Concentration of the headbox Stock suspension.

This method can be further developed that the concentration of the headbox fed stock suspension over the second Control loop is regulated in that the Stock suspension feed to the headbox one Thinning or thickening liquid more variable Amount is supplied.

Another embodiment of the method provides that the headbox has two suspension streams of different concentrations and the concentration control of the second control loop influence on at least one of the material feeds takes. This can happen, for example, that Actuators, such as throttle valves or speed controlled pumps, according to the measured Requirements are regulated.

Another design option of the The idea of the invention can be that the second Control loop with a density controlled Machine-wide headbox into the existing one Fabric density control intervenes. That means everyone Actuators existing over the machine width, the actually intended to control a cross section are influenced by the second control loop II and an even machine-wide adjustment this actuators is effected. this has for example the advantage that no additional Actuators are necessary and also a simple and easy extension of an existing one Paper machine with a density controlled Headbox by adding the second Control loop with a second sensor is enabled.

Further embodiments of the invention are in the Subclaims to claim 1 and in the following Figure descriptions shown.

It is understood that the above and features of the Invention not only in the specified Combination, but also in other combinations or can be used alone without the Leave the scope of the invention.

Figur 1:

Erfindungsgemäße Papiermaschine mit blendenverstellbarem Stoffauflauf,

Figur 2:

Papiermaschine mit sektional stoffdichtegeregeltem Stoffauflauf und zweitem Regelkreis II zur schnellen, maschinenbreiten Flächemasse-Regelung,

Figur 3:

Papiermaschine mit stoffdichtegeregeltem Stoffauflauf mit zusätzlicher, verstellbarer Blende, Querprofilregelung III und zweitem Regelkreis II zur schnellen Längsprofilregelung,

Figur 4:

Papiermaschine mit sektional stoffdichtegeregeltem Stoffauflauf und zweitem Regelkreis II zur schnellen, maschinenbreiten Flächenmasse-Regelung mit Beeinflussung der Dickstoffzufuhr,

Figur 5:

Papiermaschine mit blendenverstellbarem Stoffauflauf und zweitem Regelkreis II mit Beeinflussung einer drehzahlgeregelten Pumpe in der Dickstoffzuführung zur Stoffsuspensionszuführung,

Figur 6:

Papiermaschine mit stoffdichtegeregeltem Stoffauflauf mit zusätzlicher, verstellbarer Blende, Querprofilregelung III und einem zweitem Regelkreis II zur schnellen Längsprofilregelung mit einer maschinenbreit gleichmäßigen Beeinflussung der Stoffkonzentration über die Stellglieder der Querprofilregelung.

Further features and advantages of the invention result from the following description of preferred exemplary embodiments with reference to the drawing.

Figure 1:

Paper machine according to the invention with an adjustable headbox,

Figure 2:

Paper machine with sectionally controlled headbox and second control circuit II for fast, machine-wide area mass control,

Figure 3:

Paper machine with material density-controlled headbox with additional, adjustable aperture, cross profile control III and second control circuit II for fast longitudinal profile control,

Figure 4:

Paper machine with sectionally controlled headbox and second control circuit II for fast, machine-wide basis weight control with influencing of the thick matter supply,

Figure 5:

Paper machine with orifice-adjustable headbox and second control circuit II influencing a speed-controlled pump in the thick matter feed to the stock suspension feed,

Figure 6:

Paper machine with material density-controlled headbox with additional, adjustable orifice, cross profile control III and a second control circuit II for fast longitudinal profile control with a machine-wide uniform influence on the material concentration via the actuators of the cross profile control.

Figure 1 shows an embodiment of the invention a paper machine with a regulation of the middle Area mass of the manufactured web. The paper machine is schematic and only with those for the control loop according to the invention essential Machine parts shown. These are the Headbox 1 with the subsequent wet part 2. Am At the end of the machine there is a measuring frame 5 and a winding device 6 for the finished Paper web. The first control loop I for regulation the average basis weight of the paper web processes this signal according to the predetermined setpoint. About the control line 13 is a valve 14 or another actuator is actuated around the thick matter feed 15 to the stock suspension feed 16 to regulate and thus the concentration of the Headbox fed stock suspension in the desired way to influence. The Stock suspension feed 16 is in the closed White water circuit, takes the white water from the White water tank 10 and performs with thick matter enriched white water as a suspension of the Headbox 1 to. This one now described Control loop I corresponds to the state of the art. With this control loop I can only the middle Basis weight of the paper with respect to long-wave or low-frequency fluctuations regulated become. For the regulation of a basis weight cross section are usually additional Information of the measured cross profile to one further control loop, to influence the Basis weight cross section, passed on. This Control mechanism is not in this figure considered and described.

According to the invention, the one shown in FIG. Device a second control loop II. This Control circuit II receives its measured values from a sensor 18, via a measuring line 19. The sensor 18 is located itself in the wet part 2 of the paper machine, which has a revolving sieve 7, on which the headbox 1 puts on his stock suspension. The sensor 18 is in this example at the beginning of the drainage section arranged to be as short and quick as possible to receive responsive control loop II. The control loop II takes the measured information from sensor 18, the at least in some way with the Basis mass must be correlated on and calculated from this the fluctuations in the mass per unit area emerging paper web and the necessary Control interventions. In the present example in FIG. 1 sensor 18 represents a layer thickness meter, which gives its information about the layer thickness to the Control loop II passes on the measuring line 19. Assuming that the consistency of the Stock suspension constant across the machine width runs, a statement about the Fluctuations in the basis weight at the measured point or made about their fluctuations become. Control loop II receives information that a fluctuation in the layer thickness and thus the Basis mass occurs at the measuring location, so he can now necessary change in the concentration of Stock suspension that is fed into the headbox, calculate and this over the control line 23, which too an actuator - here a valve 24 - leads, influence by the amount of an additional Fluids that via line 25 of the Stock suspension line 16 is supplied, the Headbox 1 feeds, change. That way the control loop I a fast control loop II underlain. It is understood that this is only the short fluctuations, that is, fluctuations with small wavelength can be compensated. long-wave Fluctuations are still caused by the control loop I compensated.

An additional improvement in the accuracy of measurement Control loop II can be achieved in that Headbox 1 a further consistency sensor 21 is provided that the additional information on the consistency of the substance via the measuring line 22 to the Control loop II passes on. With the help of this additional information about the consistency of substances in Connection with, for example Layer height measurement of the resulting paper web the second sensor 18 is an even more accurate measurement of the basis weight at the measuring location is possible.

A major advantage of this system shown is that the admixture of the dilution or Thickening fluids via line 25 very close to Headbox 1 can be attached. Surrender in this way very short controlled systems it enable even very short-wave fluctuations in the System to compensate while the regulations over the control loop I run sluggishly.

This can further improve this system done that in control loop II an additional filter is provided so that through this control loop only the short-wave fluctuations of the corrected average basis weight of the paper web become. Likewise, alternatively or additively in Control loop I provided an additional filter that ensures that the control loop I only long-wave fluctuations in the medium Grammage of the paper web are corrected and thus a clear division of tasks between the Control loop I and control loop II takes place. Furthermore, an exchange of information between the control loop II and the control loop I take place, so that opposing control commands are avoided.

Another embodiment of the invention Paper machine with a regulation of the middle The mass per unit area of the web produced is shown in FIG. 2 shown. Figure 2 shows essentially the same schematic representation of the paper machine like FIG. 1, with the headbox 1, the wet part 2 and the web take-up 6. Again, before the Winding up the web a measuring frame 5 with a sensor 5.1 provided the information on the basis weight the paper web at the end of the manufacturing process passes the control loop I and an actuator 14 to Influencing the amount of thick matter fed via line 15 to stock suspension feeder 16 controls to the headbox.

In this embodiment, however, the Headbox 1 not only through the Stock suspension line 16, but it is an additional white water pipe 26 is provided the stock suspension of line 16 in the area of Headbox additionally diluted. Not in the figure the splitting of line 26 into one is shown Variety of machine-wide distributed individual lines in the area of the headbox. Regulated White water supply through the variety of Supply lines in the sections of the headbox 1 can a regulation of the basis weight cross section can be achieved. It goes without saying that for this basis weight cross profile control also Loop exists, however this will Control loop since it is not the average basis weight of the regulates the entire web, but only the profile regulates, not in this embodiment Considered.

According to the invention, a second control loop II is again provided his information on the adjacent mass from the wet part 2 of the Paper machine via the sensor 18 and the measuring line 19 receives. The measurement of the can be supported Basis weight by a consistency sensor 21, the is attached in the headbox 1 and its Information about the measuring line 22 to Process control system passes on. Is also a inductive flow meter 28 is provided which over the Measuring line 29, the control circuit II, the information of Flow through the stock suspension line 16 passes. In this way, fluctuations in the amount of stock suspension supplied via the pump 17 and the control line 31 regulated by the control circuit II be and possibly by the addition of the Diluent or thickener via the line 25, also from control loop II via the line 23 is controlled, balanced. additionally there is the possibility of controlling the two Pumps 17 and 27 the ratios of the headbox supplied stock suspension via line 16 and to influence the line 26 and thus also one To intervene in the consistency.

In Figure 3 is a paper machine with the Headbox 1 across the machine width is sectioned and material density controlled. A sensor 18 directly follows the headbox Measurement of the ejection from the headbox Suspension set. In this case it is a radiometric sensor for measuring the Mass. The wet part 2 follows the sensor Press section 3 and the dryer section 4 of the Paper machine. The closes in the machine direction Drying section 4 of the measuring frame 5, in this Example is equipped with two sensors 5.1 and 5.2, and finally the winder 6. The Sensors 5.1 and 5.2, of which at least the sensor 5.2 traversed across the machine width, give their Information on the basis weight and, if necessary also fiber orientation cross profile control loop and calculate the actual cross and longitudinal profile the paper web with subsequent control of the sectioned partial flows to the headbox. Out this measuring circuit is the information about the middle Areal mass of the paper web obtained and over the Line 13 passed to the control loop I. How already described above, the control loop I controls the Adding thick matter via line 15 to Main suspension stream to the headbox and thus the average basis weight of the manufactured Paper web.

In the manner according to the invention is also in this example the second control loop II provided its Information from the sensor 18 via the measuring line 19 receives and an additional feed of a Dilution fluids to the stock suspension main stream regulates. Here too, it will be advantageous enables the short-wave fluctuations of the average mass per unit area of the paper web produced, that cannot be influenced with the known control loop I. are to be adjusted and for an improved To worry about paper quality.

How the basis weight cross section control loop works 30, in the hatched part III is shown in the previously cited Patent specification DE 20 19 975 described in detail.

Figures 4 and 5 show embodiments of a Paper machine which is essentially the executions from Figures 2 and 1 correspond. The difference to Figures 2 and 1, however, in the Embodiments of Figures 4 and 5 control the substance concentration not by adding Dilution or thickening fluid in the feed made to the headbox, but the control loop I acts on an actuator, which is known in the existing dosing of the thick matter in the Main suspension stream of the headbox is fed, intervenes. This does hold the Disadvantage that the controlled system is somewhat longer and therefore the regulation is somewhat slower than in the Embodiments of Figures 1 to 3. However as a result, the technical effort is significantly lower and thus achieve a significant cost advantage. Such an execution can also be easily adapt existing paper machines.

Another embodiment variant according to the invention is shown in Figure 6. This corresponds to essential to the previously described execution of the Figure 3. However, here the control loop II is like this executed that his control information on the Control line 23 to the cross section control loop III act. This makes it a machine width Adjustment of the, for the regulation of the basis weight cross profile causes existing actuators and thus a machine-wide increase or decrease in Substance concentration reached.

With this embodiment is also a very to realize faster control loop, taking it from Advantage can be that no additional to those with a density-controlled headbox Actuators normally present are necessary are.

With the help of those described in the figures Embodiments and the other in writing described embodiments, it is compared to the State of the art possible, much better Results in the regulation of the middle Basis weight, in the manufacture of a paper or Cardboard web compared to the prior art, too to reach. In particular, is described by the Control mechanism it is now also possible to use shortwave Fluctuations in the average basis weight of the paper web to even out.

LIST OF REFERENCE NUMBERS

1

headbox

2

A wet section

3

press section

4

drying section

5

measuring frame

5.1, 5.2

sensor

6

rewinder

7

scree

10

white water tank

13

control line

14

Valve / actuator

15

Dick fuel supply

16

Stock suspension feed

17

pump

18

sensor

19

Measurement line

21

Stock consistency sensor

22

Measurement line

23

control line

24

Valve

25

management

26

additional white water pipe

27

pump

28

flowmeter

29

Measurement line

30

Basis weight cross-profile control loop

31

control line

32

Headbox cover with adjustment devices

33

control line

Claims (15)

1. Papermaking machine with control of the average mass per unit area of a paper or board web during the production process, having:

   1.1 at least one stock suspension line (16, 26) for feeding a stock suspension with a stock concentration to a flow box (1);

   1.2 a flow box (1) for the machine-wide distribution of the stock suspension to a wire (7) or between two wires; and

   1.3 at least one control unit (12) of a first control loop (I) having

   1.3.1 at least one means (5.1, 5.2) of determining the average mass per unit area of the paper or board web produced;

   1.3.2 at least one line (11) for transmitting the determined value of the average mass per unit area to the control unit (12);

   1.3.3 the control unit (12) being used to calculate a deviation of the actual value from a predefined desired value of the paper or board web produced and for the subsequent determination of an actuating value;

   1.3.4 at least one line (13) for leading the actuating value to an actuating element (14);

   1.3.5 the at least one actuating element (14) being used to regulate the stock concentration of the stock suspension fed to the flow box (1), in order in this way to correct the calculated deviation of the paper or board web produced;

   characterized in that

   1.4 in addition, at least one control unit (20) of a second control loop (II) is provided to regulate the stock concentration of the stock suspension fed to the flow box (1), having

   1.4.1 at least one means (18, 21, 28) of determining the average mass per unit area of the paper or board web being produced in the region upstream of the drying section (4);

   1.4.2 at least one line (19, 22, 29) for transmitting the determined value of the average mass per unit area to the control unit (20);

   1.4.3 the control unit (20) being used to calculate a deviation of the actual value from a predefined desired value of the paper or board web being produced and for the subsequent determination of an actuating value;

   1.4.4 at least one line (23, 31, 33) for leading the actuating value to an actuating element (17, 24, 27); and

   1.4.5 at least one actuating element (17, 24, 27) for regulating the stock concentration of the stock suspension fed to the flow box (1), in order in this way to correct the calculated deviation of the paper or board web being produced.
2. Papermaking machine according to Claim 1, characterized in that the second control loop (II) has at least one means (18, 21, 28) for the direct or indirect determination of the average mass per unit area of the paper or board web being produced.
3. Papermaking machine according to Claim 2, characterized in that the means (18) for the direct or indirect determination of the average mass per unit area of the paper or board web being produced is arranged in the wet section (2) of the papermaking machine.
4. Papermaking machine according to one of Claims 1 to 3, characterized in that the second control loop (II) has at least one actuating element (24) for regulating the amount of thick stock fed to the wire circulation.
5. Papermaking machine according to one of Claims 1 to 4, characterized in that the flow box (1) is fed from two stock suspension lines (16, 26) with different stock concentrations (C_L, C_H).
6. Papermaking machine according to Claim 5, characterized in that one of the stock suspension lines (16, 26) has a further introduction (25) of a dilution or thickening fluid, regulated by the second control loop (II).
7. Papermaking machine according to either of Claims 5 and 6, characterized in that at least one of the stock suspension lines (16, 26) to the flow box (1) divides upstream of the flow box (1) into a large number of branches, and in each branch there is a means of influencing the flow rate.
8. Papermaking machine according to either of Claims 6 and 7, characterized in that the introduction of the dilution or thickening fluid into the stock suspension line (16, 26) is carried out at a low stock concentration (C_L).
9. Papermaking machine according to one of Claims 6 to 8, characterized in that the introduction of the dilution or thickening fluid into the stock suspension line (16, 26) is carried out at a high stock concentration (C_H) .
10. Method of regulating the average mass per unit area of a paper or board web in the production process in a papermaking machine, having the following method steps:

    10.1 a stock suspension with a stock concentration is fed by means of at least one stock suspension line (16, 26) to a flow box (1);

    10.2 the stock suspension is distributed machine-wide onto a wire (7) or between two wires by means of the flow box (1);

    10.3 at the end of the production process, the average mass per unit area of the paper or board web produced is determined by means of at least one means (5.1, 5.2) and the value of the average mass per unit area is led to a control unit (12) of a first control loop (I);

    10.4 by means of the control unit (12), a deviation of the actual value from a predefined desired value of the paper or board web produced is calculated, and an actuating value is determined from this; and

    10.5 the stock concentration of the stock suspension fed to the flow box (1) is regulated in order to correct the calculated deviation of the paper or board web produced,
    characterized

    10.6 in that in addition the average mass per unit area of the paper or board web being produced is measured, directly or indirectly, in the region upstream of the drying section (4) by means of at least one means (18, 21, 28), and the value of the average mass per unit area is led to a control unit (20) of a second control loop (II);

    10.7 in that, by means of the control unit (20), the deviation of the actual value from a predefined desired value of the paper or board web being produced is calculated, and an actuating value is determined from this; and

    10.8 in that the stock concentration of the stock suspension fed to the flow box (1) is regulated by at least one actuating element (17, 24, 27), in order in this way to correct the calculated deviation of the paper or board web being produced.
11. Method according to Claim 10, characterized in that the stock concentration of the stock suspension fed to the flow box (1) is regulated via the second control loop (II) by a dilution or thickening fluid being fed in a variable quantity to the stock suspension line (16, 26) to the flow box (1).
12. Method according to Claim 10 or 11, characterized in that two stock suspensions of different stock concentration are fed to the flow box (1), and the stock concentration regulation of the second control loop (II) exerts an influence on the stock concentration of the stock suspension in at least one of the stock suspension lines (16, 26).
13. Method according to one of Claims 10 to 12, characterized in that a filter is connected upstream of the second control loop (II) in order to suppress low-frequency fluctuations.
14. Method according to one of Claims 10 to 13, characterized in that a filter is connected upstream of the first control loop (I) in order to suppress highfrequency fluctuations.
15. Method according to one of Claims 10 to 14, characterized in that between the first control loop (I) and the second control loop (II) an exchange of information takes place, which prevents opposing control of the respective actuating elements.

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