US20150292158A1

US20150292158A1 - Method for controlling the formation of a fiber web of a fiber or paper producing process

Info

Publication number: US20150292158A1
Application number: US14/432,242
Authority: US
Inventors: Oliver Kaufmann; Jens Haag
Original assignee: Voith Patent GmbH
Current assignee: Voith Patent GmbH
Priority date: 2012-09-28
Filing date: 2012-09-18
Publication date: 2015-10-15
Also published as: EP2900868A1; CN104704168B; CN104704168A; EP2900868B1; DE102012217729A1; WO2014048811A1

Abstract

A method for controlling the formation of a fiber web of a fiber or paper producing process includes a plurality of successive individual method steps in which controllable chemical and/or physical sequences or process steps are carried out in dependence on measured values. The materials required for the formation of the fiber web are treated, combined, and/or dewatered in the sequences or process steps. At least some of the measured values are detected inline and directly or indirectly used in order to control the formation. At least the manipulated variables, which influence the formation in a relevant manner, of the individual sequences or processes are formed dependent on definable secondary conditions during the entire process.

Description

The invention relates to a method for controlling the formation of a fiber web of a fiber or paper-producing process.
Fiber webs inter alia may also be a tissue or a cardboard web.
The process of fiber or paper production substantially is composed of a plurality of successive individual method steps in which controllable chemical and/or physical sequences or process steps, respectively, take place depending on measured values. In this fashion, the materials required for generating the fiber web are treated, combined, and/or dewatered in the individual process steps. The measured values may be detected inline and directly or indirectly used for controlling the formation. Besides, the measured values may however also be determined offline in a laboratory.
A particularly important measured variable in judging the quality of the fiber web is the formation, that is to say the distribution and composition of the fibers in the web. By employing powerful quality-measuring technology it is possible to obtain an exact online evaluation of the structure and the uniformity of the internal fiber distribution (paper formation) in the paper. With this, further quality parameters, such as printability, surface finish, strength, rigidity, optical quality, etc. may be improved.
The formation is influenced by various modifiable essential variables or manipulated variables, respectively, such as vacuum, wire tension, etc.. However, each re-adjustment of a manipulated variable not only influences the process said manipulated variable is intended to influence, but also downstream processes. Re-adjustments of a process thus cause consequential effects, such as, for example, increased wire wear, higher usage of chemicals, etc.. These effects thus always also affect the total costs.
A number of publications pertaining to controlling the formation are known from the prior art. In this fashion, a method for optimizing the formation by modifying the headbox feed consistency by way of the lip opening is known, for example. Further controls are disclosed in EP 1 454 012 A1 or WO 00/34575.
It is one of the objects of the invention to propose a formation control which improves the formation in the fiber web.
It is a further object of the invention to provide a method for controlling the formation, which enables the operation of the paper machine to be stabilized.
According to the invention a method for controlling the formation of a fiber web of the type mentioned at the outset is proposed, in which at least the manipulated variables of the individual sequences or processes, respectively, which influence the formation in a relevant manner in the entire process are generated depending on definable secondary conditions.
The formation is influenced by a plurality of successive individual method steps in which controllable chemical and/or physical sequences or process steps, respectively, take place depending on measured values, wherein at least some of the measured values are detected inline and directly or indirectly used for controlling the formation.
The materials required for generating the fiber web are treated, combined, and/or dewatered in successive individual method steps. In order for the entire process to be controlled, all measured values are processed in a data processing system, and manipulated values according to defined specifications are generated therefrom.
In turn, consequential effects which are undesirable arise when the control values are re-adjusted. In this fashion the formation may indeed be improved by re-adjusting a control value, but increased wire wear may arise as a consequential effect on account thereof, for example when the vacuum is set to be too high.
If, as proposed, the manipulated values of the individual sequences or processes, respectively, in the entire process are generated depending on definable secondary conditions, negative effects of this type may be prevented.
Secondary conditions in the sense of the invention are thus understood to be conditions which defines value ranges which must not be departed from or which permit a re-adjustment of the control values only within a defined range, respectively, such that the measured values at the measuring points which are assigned to the process do not overshoot and/or undershoot certain limits.
Furthermore, the manipulated variables may be generated depending on definable costing functions. One consequential effect may be the costs. In this fashion the formation or the entire process, respectively, may be additionally optimized with a view toward reducing costs, wherein at all times also the other secondary conditions and ultimately also the formation has to be within certain limits.
In this fashion, the costs of expenditure which arise as a result of the modification of the manipulated variables may also be evaluated by means of the costing function. Furthermore, the costing function however may also evaluate the consequential costs.
The secondary condition may be included in generating the limit values as an equality condition, for example formation=constant, or else as an inequality, for example increasing vacua in the wire station along the dewatering section, such as p1>p2>p3.
Furthermore, the secondary conditions may be generated depending on the initial materials or raw materials, respectively, and/or on the chemicals, auxiliaries, and energy supplied in the successive method steps, as well as on the materials and emissions to be disposed of.
In order to minimize the costs, an optimizing algorithm by means of which the costing functions may be optimized while adhering to the secondary conditions may be employed, in that, while considering the secondary conditions and the consequential effects, all decisive manipulated variables are only re-adjusted to the extent that the formation achieves a target value or a formation value, respectively.
In this fashion the optimizing algorithm, in order to adhere to the secondary formation conditions, may influence the manipulated variables influencing the individual sequences or processes, respectively, in the entire process such that the value of a potential deviation of the formation from the nominal value is minimized.
On the other hand, the optimizing algorithm may also be assigned a stored model which either by way of a-priori knowledge or by way of interpretation of the effects of previous re-adjustments reproduces the influence of the manipulated variables on the formation in a qualitative manner, on account of which the down times of the processes are advantageously conjointly considered.
However, both procedures may also be combined with each other, such that further optimization takes place.
The individual methods in the sense of the invention substantially take place in the stock preparation, the headbox feed, and the wet end of a fiber-web production machine; that is to say in those regions of a production machine for fiber webs where modifying or influencing the formation may take place.
In this fashion, at least one of the following manipulated variables may be used for controlling the formation in the stock preparation:

- type of retention agent
- dosing point of retention agent
- amount of retention agent
- grinding performance
- dispersion performance
- material composition
- amount of fixing agent.

In this fashion, at least one of the following manipulated variables may be used for controlling the formation in the headbox feed:

- suspension jet geometry
- lip opening
- aperture position
- lamella position
- inserts position
- speed differential between jet and wire.

Furthermore, at least one of the following manipulated variables may be used for controlling the formation in the wet end:

- dewatering strip geometry
- dewatering strip pressures
- vacuum
- wire tension.

However, the wire characteristics as well as the wire running time, in particular the change in the CFM value, have an influence on the stable running of the machines, as well as on the costs, and may be included in the secondary conditions as a function, for example.
In this fashion it is, however, also possible for the formation to be optimized in that the machine speed is modified, on account of which the risk of web rupturing is reduced, in particular in the case of raw materials which are difficult to process or else in the case of variable climatic conditions. Web rupturing has a great influence on the total costs.
It is one of the particular advantages of the invention that operational stability and the formation can be stabilized in such a manner that the costs of the entire process can be reduced to an optimal minimum.
Further features of the method according to the invention and further advantages of the invention are derived from the following description with reference to the drawing.

The invention will be explained in more detail in the following by means of diagrams, in which:

FIG. 1 shows a block diagram for illustrating the formation control,

FIG. 2 shows a line chart for illustrating the correlations between manipulated variables, secondary conditions, and costs relative to a constant formation.

FIG. 1 shows a block diagram for illustrating the formation control with the aid of which functioning of the system or of the control, respectively, of the formation may be described.
The system or the control 1, respectively, of the formation of a fiber web of a fiber or paper producing process depends on a multiplicity of successive individual method steps. In this fashion, various controllable chemical and/or physical sequences or process steps, respectively, take place in the individual methods steps, depending on measured values, in order to treat, combine, and/or to dewater the material required for the formation of the fiber web.
The individual method steps which are responsible for generating the formation have been compiled in FIG. 1 in block 3. The methods or processes may take place in the stock preparation, the wet end process, the headbox feed, and the former, wherein each process is capable of being influenced by at least one manipulated variable 2. Referring to the possible manipulated variables a1, a2, . . . , reference is made to those already mentioned, this not being a complete enumeration.
Besides the manipulated variables, the secondary conditions have an influence on the formation in that individual relevant manipulated variables are generated depending on definable secondary conditions.
The secondary conditions are defined in such a manner that a particularly stable operation of the paper machine is ensured. Certain measured values thus must not exceed certain limits which must be mandatorily adhered to in order for the formation to be optimized.
The control strategy may be implemented with the aid of an optimizing algorithm which minimizes the costing function and thereby adheres to the secondary conditions. These secondary conditions may be present as an equality condition (for example, formation=constant), as limit values (control limits, for example, 0.9<jet-wire ratio<1.1) or as an inequality (increasing vacua along dewatering, for example, p1>p2>p3).
The consequential effects 5 are derived from the individual re-adjustments of the manipulated variables of the processes. The consequential effects may be measured online or in the laboratory, and are directly or indirectly included in the secondary conditions. In other words, the limits of the secondary conditions are influenced by the consequential conditions. Consequential effects may include wear, energy consumption, consumption of chemicals, etc..
A line diagram for illustrating the correlations between manipulated variables, secondary conditions, and costs relative to a constant formation is illustrated in FIG. 2.
The essential variables (expenditure) which are re-adjustable by the control are evaluated as expenditure costs by way of a corresponding pricing function. The consequential costs which arise on account of the re-adjustable essential variables are likewise determined. The costing function thus calculates from the total cost from the expenditure and consequential costs of the setting of the manipulated variables which are relevant to the formation. This costing function is minimized by way of an optimizing algorithm, while adhering to the secondary conditions defined above, such that an (iterative) step-by-step modification of the setting takes place up to a cost-optimized operating point, wherein the formation remains as a variable within a permissible tolerance range.
In order to adhere to the secondary conditions of the formation, the optimizing algorithm does/can design re-adjusting such that the value of a potential deviation of the formation from the nominal value (range) is minimized (in an ideal case to 0). This may take place by way of a model which either by way of a-priori knowledge or by way of interpretation of the effects of the previous re-adjustments reproduces the influence of the manipulated variables on the formation in a quantitative manner.

LIST OF REFERENCE SIGNS

1 Block diagram
2 Manipulated variables
3 Method steps
4 Secondary conditions
4 a Limit values of secondary conditions for manipulated variable Y
4 b Limit values of secondary conditions for manipulated variable X
5 Consequential effects
6 Target value of formation
8 Range of validity
9 Cost expenditure

Claims

1-15. (canceled)

16. A method for controlling the formation of a fiber web in a production process (fiber or paper-production), the method comprising:

performing a plurality of successive individual method steps and thereby acquiring measured values;

carrying out controllable chemical and/or physical sequences or process steps, respectively, in which materials required for generating the fiber web are treated, combined, and/or dewatered in dependence on the measured values, and thereby detecting at least some of the measured values inline and directly or indirectly using the measured values for controlling the formation; and

generating at least manipulated variables of the individual sequences or processes, respectively, which influence the formation in a relevant manner in the entire process in dependence on definable secondary conditions.

17. The method according to claim 16, which comprises generating the manipulated variables depending on a definable costing function.

18. The method according to claim 17, wherein the costing function evaluates a cost of expenditures arising as a result of a modification of the manipulated variables.

19. The method according to claim 17, wherein the costing function evaluates consequential costs arising as a result of a modification of the manipulated variables.

20. The method according to claim 16, wherein one of the secondary conditions is an equality condition.

21. The method according to claim 16, wherein one of the secondary conditions is an inequality.

22. The method according to claim 16, which comprises generating the secondary conditions depending on the initial materials or raw materials, respectively, and/or on the chemicals, auxiliaries, and energy supplied in the successive method steps, as well as on the materials and emissions to be disposed of.

23. The method according to claim 17, which comprises minimizing the costs with the costing function by way of an optimizing algorithm while adhering to the secondary conditions.

24. The method according to claim 23, wherein the optimizing algorithm, in order to adhere to the secondary formation conditions, influences the manipulated variables influencing the individual sequences or processes, respectively, in the entire process so as to minimize a value of a potential deviation of the formation from a nominal value.

25. The method according to claim 23, which comprises assigning the optimizing algorithm a stored model which, either by way of a-priori knowledge or by way of interpretation of effects of previous re-adjustments, reproduces an influence of the manipulated variables on the formation in a qualitative manner.

26. The method according to claim 16, which comprises implementing the individual methods substantially in a stock preparation, a headbox feed, and at a wet end of a fiber-web production machine.

27. The method according to claim 26, which comprises using at least one of the following manipulated variables in the stock preparation for controlling the formation:

a type of retention agent;

a dosing point of retention agent;

an amount of retention agent;

a grinding performance;

a dispersion performance;

a material composition; and

an amount of fixing agent.

28. The method according to claim 26, which comprises using at least one of the following manipulated variables in the headbox feed for controlling the formation:

a suspension jet geometry;

a lip opening;

an aperture position;

a lamella position;

inserts position; and

a speed differential between jet and wire.

29. The method according to claim 26, which comprises using at least one of the following manipulated variables at the wet end for controlling the formation:

a dewatering strip geometry;

dewatering strip pressures;

a vacuum; and

a wire tension.

30. The method according to claim 16, wherein one of the manipulated variables is a machine speed.