EP1780333B1 - Method and machine for manufacturing a fibrous web - Google Patents

Abstract

Producing a paper web by distributing high- and low-consistency stock streams over common sections across the machine width, mixing the streams in each section in a variable ratio, feeding each mixed stream onto a wire through a headbox, and using the mixing ratio in each mixed stream as a control variable for controlling the transverse grammage profile of the web, comprises adjusting the pulp/filler ratio in the low-consistency stream before distributing it so that the filler content of the paper web can be adjusted independently of the grammage. An independent claim is also included for apparatus comprising devices for performing the above operations.

Description

The invention relates to a method for producing a fibrous web, in particular paper, board or tissue web, in which a stream of higher consistency and a stream of lesser consistency are divided to common sections across the machine width and the two streams of each section then each in a variable Ratio mixed with each other and the respective mixed stream is fed via a headbox as headbox jet of a wire section, the mixing ratio between these two streams of different consistency in the respective mixed stream as a control variable for controlling the basis weight of the fibrous web over the machine width. It further relates to a device according to the preamble of claim 17.

The EP-A-1 028 199 discloses a method according to the preamble of claim 1 and a device according to the preamble of claim 17.

In a dilution headbox, two streams of different consistency, e.g. are referred to as thick material or thin material, mixed in a variable across the machine width ratio. As a thinner white water is usually used. The mixture passes through the headbox jet into the wire section. The mixing ratio serves as a manipulated variable for the sectional control of the basis weight of the paper web over the machine width. It can thus, despite disturbances such. the across the width different shrinkage in the dryer section a cross-directionally constant basis weight can be adjusted.

With the composition of the thick and thin material can also vary with the mixing ratio, the ratio of filler to fibers in the suspension. In addition, an altered composition of the suspension jet leads to a Change in pulp retention and filler retention in the wire section. In general, therefore, the basis weight control also affects the filler content of the paper.

It would not only be desirable to have a constant basis weight over the machine width, but also to have a constant filler proportion over the machine width. However, since only one manipulated variable is available for these two controlled variables, the previous regulation can not generally do so.

The invention has for its object to provide a simple and inexpensive method and a correspondingly improved device of the type mentioned, in which the aforementioned disadvantages are reduced or even eliminated. It should be ensured in the simplest and most reliable manner, in particular, over the machine width at least substantially constant filler content of the fibrous web.

With regard to the method, this object is achieved in that the ratio between fiber content and filler content in the respective stream less consistency before its distribution is set or regulated so that the filler content in the fibrous web at least substantially independent of the basis weight is adjustable or regulated.

Due to the fact that the filler content in the fibrous web is essentially independent of the weight per unit area of the fibrous web, it is possible not only to set a surface weight constant over the width, but also a filler fraction of the fibrous web which is substantially uninfluenced by the basis weight control. With the appropriate adjustment or regulation of the ratio between pulp content and filler content in the stream of lesser consistency before its division is thus the influence of Basis weight control to the local filler content of the fibrous web reduced to a minimum.

To change the ratio between pulp content and filler content in the stream of lesser consistency, this can be supplied to this example, prior to the division into the various sections of fibers or filler or be removed from this.

If this changes the average filler content in the fibrous web over the width of the machine, it is advantageous if fibers or filler, in particular before the division, are added to or removed from the fabric flow of higher consistency in order to adjust or regulate the average filler fraction in the fibrous web , However, it is also possible that, for example, white water or fresh water or clarified filtrate is added to the stream of higher consistency prior to its division.

Preferably, the stream of lesser consistency is formed using white water and / or fresh water and / or clear filtrate.

According to a preferred practical embodiment of the method according to the invention, the ratio between pulp content and filler content in the stream of lesser consistency is continuously adjusted or regulated accordingly. In this connection, the feeding or removal of the fibers or the filler takes place continuously.

Advantageously, an online-regulation of the ratio between pulp content and filler content in the stream of lesser consistency can take place.

According to a practical embodiment of the method according to the invention, the transverse profile of the filler content is determined in the fibrous web and in the Adjustment or regulation of the ratio between pulp content and filler content in the stream of lesser consistency used with. It is useful if the cross profile of the fiber content in the fibrous web is determined continuously during operation.

The inventive method is particularly easy to apply when adjusting the ratio between fiber content and filler content in the stock suspension of lower consistency of the value of a manipulated variable for controlling the cross profile of the basis weight of the fibrous web, such as the respective valve position of the divided material flow of lower consistency, with each determined cross profile of the filler content in the fibrous web is compared to determine whether a local increase or decrease of the dilution water content leads to a locally higher or lower filler content in the fibrous web.

Here, preferably, the local filler content in the fibrous web is compared with the corresponding local dilution water content in the stock suspension, it makes sense if the shrinkage of the fibrous web is taken into account in this comparison.

In the event that a higher or lower dilution leads to a higher or lower filler content of the fibrous web, the material flow of lesser consistency before its division advantageously additional fibers added or removed filler or added in addition filler or fibers removed.

This means, for example, concretely, that with an increase in the dilution, which leads to a higher filler content of the fibrous web, additional fibers are added to the stock flow of lesser consistency before its division or filler is removed.

On the other hand, if a higher dilution leads, for example, to a lower filler content of the fibrous web, additional filler is added or fibers are taken from the stream of lesser consistency prior to its division.

A further embodiment of the method according to the invention provides that the adjustment or regulation of the ratio between pulp content and filler content in the stream of lesser consistency takes place taking into account the mass balance of the streams in the wire section.

It is particularly advantageous if the adjustment or regulation of the ratio between pulp content and filler content in the stream of lesser consistency taking into account the dependence of the pulp retention and the filler retention of the composition of the mixed stream or headbox jet occurs.

The filler retention and / or the fiber retention can be determined in a previous experiment. Usually only a few tests are sufficient.

With regard to the device, the object stated above is achieved according to the invention in that the ratio between pulp content and filler content in the stream of lesser consistency is adjustable or controllable prior to its division so that the filler fraction in the fibrous web can be adjusted or regulated at least substantially independently of the basis weight control is.

As a headbox, a dilution water headbox is preferably provided.

In a preferred practical embodiment of the device according to the invention, the ratio between pulp content and filler content in the Stream of lesser consistency continuously adjustable accordingly or regulated.

Advantageously, the device comprises means for continuously adding or removing fibers or filler for the corresponding adjustment or regulation of the ratio between pulp content and filler content in the stream of lesser consistency.

Preferably, means for continuously measuring the pulp fraction and / or filler fraction in the fibrous web and expediently also means for continuously determining the pulp retention and / or filler retention on the basis of the measured pulp fraction and / or filler fraction are provided.

In particular, an online regulation of the ratio between pulp content and filler content in the stream of lower consistency also brings advantages.

Preferably, means are also provided for determining a Füllstoffgehaltsquerprofils the fibrous web. In this case, the ratio between pulp content and filler content in the stream of lesser consistency is expediently adjustable or controllable as a function of the determined filler cross-content profile.

Fig. 1

eine schematische Teildarstellung einer Vorrichtung zur Herstellung einer Faserstoffbahn,

Fig. 2

ein Diagramm, das die Abhängigkeit der lokalen Faserretention vom lokalen Verdünnungswasseranteil zeigt,

Fig. 3

ein Diagramm, das die Abhängigkeit der lokalen Füllstoffretention vom lokalen Verdünnungswasseranteil zeigt,

Fig. 4

ein Diagramm, das die Abhängigkeit des Füllstoffanteils im Suspensionsstrahl vom lokalen Verdünnungswasseranteil zeigt,

Fig. 5

ein Diagramm, das die Abhängigkeit des Füllstoffanteils im Papier vom lokalen Verdünnungswasseranteil zeigt,

Fig. 6

ein Diagramm, das die Abhängigkeit des lokalen Flächengewichts vom lokalen Verdünnungswasseranteil zeigt,

Fig. 7

ein Diagramm, das die Abhängigkeit des Füllstoffanteils im Papier vom lokalen Verdünnungswasseranteil zeigt,

Fig. 8

ein Diagramm, das die Abhängigkeit des lokalen Flächengewichts vom lokalen Verdünnungswasseranteil zeigt, und

Fig. 9

ein Diagramm zur Massenbilanz von Stoffauflauf und Siebpartie,

Fig. 10

ein Diagramm bzgl. der Korrelation zwischen Füllstoffgehalt und dem Verdünnungswasserzusatz,

Fig. 11

ein weiteres Diagramm bzgl. der Korrelation zwischen Füllstoffgehalt und dem Verdünnungswasserzusatz.∫

The invention will be explained in more detail below with reference to exemplary embodiments with reference to the drawing; in this show:

Fig. 1

a schematic partial view of an apparatus for producing a fibrous web,

Fig. 2

a diagram showing the dependence of the local fiber retention on the local dilution water content,

Fig. 3

a diagram showing the dependence of the local filler retention on the local dilution water content,

Fig. 4

a diagram showing the dependence of the filler content in the suspension jet on the local dilution water content,

Fig. 5

a diagram showing the dependence of the filler content in the paper on the local dilution water content,

Fig. 6

a diagram showing the dependence of the local basis weight on the local dilution water content,

Fig. 7

a diagram showing the dependence of the filler content in the paper on the local dilution water content,

Fig. 8

a diagram showing the dependence of the local basis weight on the local dilution water content, and

Fig. 9

a diagram of the mass balance of headbox and wire section,

Fig. 10

a diagram with respect to the correlation between filler content and dilution water additive,

Fig. 11

another diagram concerning the correlation between filler content and dilution water additive.∫

Fig. 1 shows a schematic partial representation of an apparatus 10 for producing a fibrous web, for example a paper, board or tissue web. at the device 10 may thus be in particular a paper machine.

The apparatus 10 or paper machine comprises a wire section 12, a press section 14, a drying section 16, not shown here, and a take-up unit 18, in which the fibrous web 20 is finally rolled up by means of a pressure roller 22 to a winding 24.

A stream of higher consistency, i. higher solids content and a lower consistency pulp, i. lower solids content are divided into common sections across the machine width. Subsequently, the streams of each section are mixed in a variable ratio. The mixing flow thus obtained across the machine width, which can have a different mixing ratio between the flow of higher consistency and flow of lesser consistency across the machine width, is treated via a headbox 26, here for example a dilution water headbox, as headbox or suspension jet 28 fed to the wire section 12. The mixing ratio between the two streams of different consistency serves as a control variable for a regulation of the basis weight of the fibrous web 20 over the machine width.

The basis weight of the fibrous web 20 is usually measured in the region between the dryer section 16 and the take-up unit 18 by means of a corresponding measuring device 30. The basis weight is measured at various measuring points distributed over the machine width.

From this, the average basis weight of the fibrous web 20 is calculated.

The relevant mean value of the weight per unit area is fed to a consistency control device 32 in which it is compared with a desired value becomes. In this case, the desired value can be supplied by a control and / or evaluation unit, not shown. By means of the corresponding control, the actual value of the average basis weight is adapted to the desired value.

As based on the Fig. 1 can be seen, a material control valve 34 is controlled via the control device 32, which is arranged in a leading to a mixing point 36, high-viscosity containing line 41. As a result, the average basis weight is set. After the mixing point 36, the thick substance or material stream of higher consistency is fed to a transverse distribution device 49, by means of which the thick material is divided into several sections across the machine width.

According to the invention, the ratio between the pulp content and the filler content in the stream of lesser consistency is adjusted or regulated prior to its division such that the filler fraction in the fibrous web 20 can be adjusted or regulated at least substantially independently of the basis weight.

In the present embodiment according to the Fig. 1 a white water leading line 40 is provided, via which the coming of the mixing point 36 material flow dilution or white water can be supplied. The line 40 feeds via a transverse distribution device 43, in which the material flow of lesser consistency divided into different sections across the machine width, several juxtaposed across the machine width valves 42, each valve 42 is assigned in the machine width each section in the thick material is assigned ,

The valves 42 are connected via control / regulating lines 45 to the control device 32 of the basis weight, which outputs a control signal to each valve 42. The respective control signal is calculated taking into account the cross profile of the basis weight determined by the measuring device 30 to the valve 42 the corresponding section in the headbox 26, wherein the shrinkage of the fibrous web 20 is taken into account.

As a result, a mixed stream with variable ratio of stream of higher consistency and stream of lesser consistency can be generated in each section.

By adjusting the local amount of material flow with a lower consistency, so-called dilution water quantity, the local basis weight is set.

Via a measuring device 44, the filler or ash content and the fiber concentration of the guided in the line 40 white water are measured. The actual values are fed to a control device 46, which compares the respective actual values with nominal values supplied again by the control and / or evaluation unit and correspondingly activates a respective valve 48 in order to additionally add filler or fibers to the stream of lesser consistency before it is divided in the transverse distributor 43 ,

Furthermore, a measuring device 50 is provided, via which the transverse profile of the filler content of the fibrous web 20 is measured in the region between the dryer section 16 and the take-up unit 18.

The filler content measured by the measuring device 50 is output via a line 51 to the regulating device 46. In practice, the measuring devices 30 and 50 are usually designed as one unit.

Furthermore, according to a preferred embodiment of the invention, the position of the valves 42 is output via a line 52 to the control device 46. Alternatively, it is also conceivable that the control device 46 receives a corresponding signal directly from the control device 32.

The adjustment of the ratio between pulp content and filler content in the stock suspension of lesser consistency by the controller 46 is then taking into account the comparison between the determined cross profile of the filler in the fibrous web 20 and the manipulated variable for the control of the cross profile of the basis weight of the fibrous web 20, here in the form the position of the valves 42. By comparing it can be determined whether a local increase or decrease in the basis weight leads to a locally higher or lower filler content in the fibrous web 20.

wobei das Integral über die Maschinenbreite ausgeführt wird und x̂ (y) den Stellwert eines einem bestimmten Abschnitt zugeordneten Ventils 42 sowie Â(y) den Füllstoffanteil in der Faserstoffbahn 20 des betreffenden Abschnitts angibt, wobei die Schrumpfung der Faserstoffbahn mit berücksichtigt wird. Die Größen A und x geben die über die Maschinenbreite ermittelten Mittelwerte des Füllstoffanteil und des Stellwerts an.In the comparison, the average values of the manipulated variable and the filler fraction determined over the machine width can additionally be taken into account, resulting, for example, in the following correlation: $$\mathrm{K}\mathrm{=}\mathrm{\int }{\left(\hat{\mathrm{A}}\left(\mathrm{y}\right)\mathrm{-}\mathrm{A}\right)}^{\mathrm{*}}\left(\hat{\mathrm{x}}\left(\mathrm{y}\right)\mathrm{-}\mathrm{x}\right)\mathrm{d}\mathrm{y}$$

wherein the integral is carried out across the machine width and x (y) indicates the manipulated value of a valve 42 associated with a particular section, and  (y) indicates the proportion of filler in the fibrous web 20 of the section concerned, taking into account the shrinkage of the fibrous web. The sizes A and x indicate the mean values of the filler proportion and the manipulated value determined over the machine width.

In the FIGS. 10 and 11 Possible different correlations between the proportion of filler and the addition of stream of lesser consistency can be seen.

When in the FIG. 10 The correlation shown results in a correlation value K> 0, which means that a local increase of the material stream of lesser consistency -here in the two edge regions-leads to a local increase in the filler fraction in the fibrous web 20. By the control device 46, the ratio between filler and pulp content in the stream of lesser consistency prior to its division is set in this case such that at local addition of dilution water or stream less consistency of the filler content in the fibrous web 20 is not affected substantially.

In the case K> 0, i. that a higher dilution leads to a higher filler content of the fibrous web 20, fibers can be added to the material flow of lesser consistency or filler can be removed.

When in the FIG. 11 shown correlation results in a correlation value K <0, which means, for example, that a local increase of the material flow of lesser consistency -here in the two edge regions-leads to a local reduction of the filler content in the fibrous web 20. By the control device 46, the ratio between filler and pulp content in the stream of lesser consistency prior to its division is set in this case such that at local addition of dilution water or stream less consistency of the filler content in the fibrous web 20 is not affected substantially.

In the case K <0, i. that a higher dilution leads to a lower filler content of the fibrous web 20, the fabric flow of lesser consistency additional filler can be added or fibers are removed.

Alternatively, the adjustment of the ratio between pulp content and filler content in the lower consistency pulp stream may take into account the mass balance of the streams in the wire section, as well as the dependence of pulp retention and filler retention take place from the composition of the mixed stream or stream emergence jet.

By means of the respective control devices, the ratio between pulp content and filler content in the stream of lesser consistency can be continuously adjusted or regulated. For the corresponding adjustment or regulation of the ratio between pulp content and filler content in the stream of lesser consistency, as already mentioned, e.g. continuously added or removed fibers or filler.

To control the basis weight, the basis weight is preferably measured continuously. Correspondingly, the pulp retention can also be determined continuously by continuous measurement of the pulp content in the pulp web during operation.

The filler retention can be determined in a few previous experiments. However, this filler retention is preferably also determined continuously during operation by means of a continuous measurement of the filler content in the fibrous web 20, for example by means of the measuring device 50.

In particular, an online regulation of the ratio between pulp content and filler content in the stream of lesser consistency can take place.

If the ratio of fiber to filler content of the dilution water thus fulfills a specific condition, then the filler fraction in the fibrous web 20, here for example in the paper, can be set approximately independently of the basis weight control. The condition results from a mass balance of the streams in the wire section 12 and the knowledge of the dependence of the fiber retention and the filler retention on the composition of the suspension jet 28 at a given operating point.

According to the invention, the composition of the dilution water is adapted to the stated condition accordingly. If, as hitherto, white water is to be used as dilution water, it must be added or removed continuously, depending on the characteristics of the respective wire section 12, fibers or filler.

To determine the optimum composition, the retention at the operating point and its dependence on the composition of the suspension must be known. In the simplest case, the retentions can be determined once in one experiment. If they vary too much during operation, an online control can also be installed. For such on-line control, continuous measurement of the filler content in the web in the transverse direction is required. Any necessary adjustment of the composition of the dilution water results from a comparison of the Füllstoffquerprofils with the control profile of the headbox valves, in which comparison, the shrinkage of the web must be considered. If the locally higher dilution then leads to a higher filler content, fibers must be additionally added to the dilution water or filler must be removed.

The effect achieved with the method according to the invention and the device according to the invention results, for example, from a comparison of the following three cases:

1st case:

The ratio of filler to fibers in the dilution water is too high. A local dilution significantly increases the proportion of filler in the suspension jet. The filler retention Although falling off more strongly than the pulp retention, the filler content in the paper remains locally but still too high.

2nd case:

The ratio of filler to fibers in the dilution water is too low. At local dilution in the suspension jet, the filler content is insufficient to compensate for even lower filler retention. The paper leaves too few fillers locally.

3. Case:

The ratio of filler to fibers in the dilution water fits. At local dilution, the ratio of filler to fibers is initially higher in the suspension jet than on average over the machine width. However, due to the locally lower ratio of filler retention to pulp retention, the first of which falls more sharply than the second, the paper will again have the correct amount of filler.

As far as filler is mentioned here, this also includes a possible use of different types of fillers.

• Füllstoff bzw. Asche zu- oder abführen.
• Fasern zu- oder abführen.

With regard to the dewatering line, the following four possibilities arise with regard to the dosing and / or discharge points in question:

• Add or remove filler or ash.
• Add or remove fibers.

In this case, in particular, a selective measurement of the filler concentration in the white water strand is conceivable.

Corresponding constellations are possible for the thick matter jet.

Fig. 9 shows a diagram of the mass balance of headbox and wire section.

The following terms are used in this diagram and in the explanation below:

Symbols:

c

kg / m ³ consistency

m '

kg / (ms) mass flow

q

m ³ / (ms) volume flow

R

kg / kg retention

indices

A

ash

B

vat

F

fibers

J

beam

L

low consistency

H

high consistency

P

Entrance press

S

white water

placeholder

• i∈ {F A}
• j∈ {B, L, H, J, P, S}

streams 1. Flow rates

$$\mathrm{x}\mathrm{:}\mathrm{=}\frac{{\mathrm{q}}_{\mathrm{L}}}{{\mathrm{q}}_{\mathrm{J}}}$$

The jet is formed from a mixture of a low consistency and a high consistency content: $${\mathrm{q}}_{\mathrm{L}}\mathrm{+}{\mathrm{q}}_{\mathrm{H}}\mathrm{=}{\mathrm{q}}_{\mathrm{J}}$$

$$\mathrm{x}\mathrm{:}\mathrm{=}\frac{{\mathrm{q}}_{\mathrm{L}}}{{\mathrm{q}}_{\mathrm{J}}}$$

2. mass flows

The mass flows can be expressed as products of consistencies with the respective volume flow: $${\dot{\mathrm{m}}}_{\mathrm{i}\mathrm{.}\mathrm{j}}\mathrm{=}{\mathrm{c}}_{\mathrm{i}\mathrm{.}\mathrm{j}}{\mathrm{q}}_{\mathrm{j}}\mathrm{,}$$

The total mass flow (of the solids) consists of a fiber and an ash component: $${\stackrel{\mathrm{}}{\mathrm{m}}}_{\mathrm{F}\mathrm{.}\mathrm{j}}\mathrm{+}{\stackrel{\mathrm{}}{\mathrm{m}}}_{\mathrm{A}\mathrm{.}\mathrm{j}}\mathrm{=}{\stackrel{\mathrm{}}{\mathrm{m}}}_{\mathrm{j}}\mathrm{,}$$

Due to the mass conservation applies $${\stackrel{\mathrm{}}{\mathrm{m}}}_{\mathrm{i}\mathrm{.}\mathrm{L}}\mathrm{+}{\stackrel{\mathrm{}}{\mathrm{m}}}_{\mathrm{i}\mathrm{.}\mathrm{H}}\mathrm{=}{\stackrel{\mathrm{}}{\mathrm{m}}}_{\mathrm{i}\mathrm{.}\mathrm{j}}\mathrm{,}$$

retention

The retention is defined as the quotient of the mass flows after and before the wire section: $$\mathrm{R}\mathrm{:}\mathrm{=}\frac{{\stackrel{\mathrm{}}{\mathrm{m}}}_{\mathrm{P}}}{{\stackrel{\mathrm{}}{\mathrm{m}}}_{\mathrm{J}}}\mathrm{.}{\mathrm{R}}_{\mathrm{i}}\mathrm{=}\frac{{\stackrel{\mathrm{}}{\mathrm{m}}}_{\mathrm{i}\mathrm{.}\mathrm{P}}}{{\stackrel{\mathrm{}}{\mathrm{m}}}_{\mathrm{i}\mathrm{.}\mathrm{J}}}$$

Local variation of x

Through the valves of a dilution headbox, here, for example, a ModuleJet headbox, it is possible to vary the addition of dilution water locally (.): $$\hat{\mathrm{x}}\mathrm{:}\mathrm{=}\frac{{\hat{\mathrm{q}}}_{\mathrm{L}}}{{\hat{\mathrm{q}}}_{\mathrm{J}}}\mathrm{,}$$

This variation also influences the local retentions: $$\hat{\mathrm{R}}\mathrm{:}\mathrm{=}\frac{{\widehat{\stackrel{\mathrm{}}{\mathrm{m}}}}_{\mathrm{P}}}{{\widehat{\stackrel{\mathrm{}}{\mathrm{m}}}}_{\mathrm{J}}}\mathrm{.}{\hat{\mathrm{R}}}_{\mathrm{i}}\mathrm{=}\frac{{\widehat{\stackrel{\mathrm{}}{\mathrm{m}}}}_{\mathrm{i}\mathrm{.}\mathrm{P}}}{{\widehat{\stackrel{\mathrm{}}{\mathrm{m}}}}_{\mathrm{i}\mathrm{.}\mathrm{J}}}\mathrm{,}$$

Assuming that their change can be attributed primarily to a change in local bulk density, one can write: $${\hat{\mathrm{R}}}_{\mathrm{i}}\mathrm{=}{\mathrm{R}}_{\mathrm{i}}\mathrm{+}\frac{\mathrm{\partial }{\hat{\mathrm{R}}}_{\mathrm{i}}}{\mathrm{\partial }{\hat{\mathrm{c}}}_{\mathrm{J}}}{\mathrm{|}}_{{\hat{\mathrm{c}}}_{\mathrm{J}}\mathrm{=}{\mathrm{c}}_{\mathrm{J}}}\left({\hat{\mathrm{c}}}_{\mathrm{J}}\mathrm{-}{\mathrm{c}}_{\mathrm{J}}\right)\mathrm{+}\mathrm{...}$$

The ModuleJet headbox is designed so that a local variation of the white water content practically does not change the local total volume flow: $${\hat{\mathrm{q}}}_{\mathrm{L}}\mathrm{+}{\hat{\mathrm{q}}}_{\mathrm{H}}\mathrm{=}{\hat{\mathrm{q}}}_{\mathrm{J}}\mathrm{=}{\mathrm{q}}_{\mathrm{J}}\mathrm{,}$$

und nach der Siebpartie $${\widehat{\stackrel{}{\mathrm{m}}}}_{\mathrm{i}\mathrm{,}\mathrm{P}}\mathrm{=}{\hat{\mathrm{R}}}_{\mathrm{i}}{\widehat{\stackrel{}{\mathrm{m}}}}_{\mathrm{i}\mathrm{,}\mathrm{J}}\mathrm{=}{\hat{\mathrm{R}}}_{\mathrm{i}}\left[{\mathrm{c}}_{\mathrm{i}\mathrm{,}\mathrm{L}}\hat{\mathrm{x}}\mathrm{+}{\mathrm{c}}_{\mathrm{i}\mathrm{,}\mathrm{H}}\left(\mathrm{1}\mathrm{-}\hat{\mathrm{x}}\right)\right]{\mathrm{q}}_{\mathrm{J}}\mathrm{.}$$

Assuming that small local changes have no appreciable influence on the material densities c _{i, L} and c _{i, H} , then the local mass flows are in the beam $${\hat{\mathrm{m}}}_{\mathrm{i}\mathrm{.}\mathrm{J}}\mathrm{=}{\hat{\mathrm{c}}}_{\mathrm{i}\mathrm{.}\mathrm{J}}{\hat{\mathrm{m}}}_{\mathrm{i}\mathrm{.}\mathrm{J}}\mathrm{=}{\mathrm{c}}_{\mathrm{i}\mathrm{.}\mathrm{L}}{\hat{\mathrm{q}}}_{\mathrm{L}}\mathrm{+}{\mathrm{c}}_{\mathrm{i}\mathrm{.}\mathrm{H}}\left({\mathrm{q}}_{\mathrm{J}}\mathrm{-}{\hat{\mathrm{q}}}_{\mathrm{L}}\right)\mathrm{=}\left[{\mathrm{c}}_{\mathrm{i}\mathrm{.}\mathrm{L}}\hat{\mathrm{x}}\mathrm{+}{\mathrm{c}}_{\mathrm{i}\mathrm{.}\mathrm{H}}\left(\mathrm{1}\mathrm{-}\hat{\mathrm{x}}\right)\right]{\mathrm{q}}_{\mathrm{J}}$$

and after the wire section $${\widehat{\stackrel{}{\mathrm{m}}}}_{\mathrm{i}\mathrm{.}\mathrm{P}}\mathrm{=}{\hat{\mathrm{R}}}_{\mathrm{i}}{\widehat{\stackrel{}{\mathrm{m}}}}_{\mathrm{i}\mathrm{.}\mathrm{J}}\mathrm{=}{\hat{\mathrm{R}}}_{\mathrm{i}}\left[{\mathrm{c}}_{\mathrm{i}\mathrm{.}\mathrm{L}}\hat{\mathrm{x}}\mathrm{+}{\mathrm{c}}_{\mathrm{i}\mathrm{.}\mathrm{H}}\left(\mathrm{1}\mathrm{-}\hat{\mathrm{x}}\right)\right]{\mathrm{q}}_{\mathrm{J}}\mathrm{,}$$

oder mit der Näherung c_F,L ≈ 0 zu $${\widehat{\stackrel{}{m}}}_P\approx \left\{{\hat{R}}_F{c}_{F,H}\left(1-\hat{x}\right)+{\hat{R}}_A\left[c_{A,L}\hat{x}+c_{A,H}\left(1-\hat{x}\right)\right]\right\}{q}_J\mathrm{.}$$

This results in the local total mass flow after the wire section too $$\begin{array}{cc}\widehat{\begin{array}{c}\stackrel{}{\begin{array}{c}m\end{array}}\end{array}}& ={\displaystyle \underset{i}{\Sigma }}{\widehat{\stackrel{}{m}}}_{i.P}\hfill \\ & =\left\{{\hat{R}}_F[c_{F.L}\hat{x}+c_{F.H}\left(1-\hat{x}\right)]+{\hat{R}}_A\left[c_{A.L}\hat{x}+c_{A.H}\left(1-\hat{x}\right)\right]\right\}{q}_J\hfill \end{array}$$

or with the approximation c _{F, L} ≈ 0 $${\widehat{\stackrel{}{m}}}_P\approx \left\{{\hat{R}}_F{c}_{F.H}\left(1-\hat{x}\right)+{\hat{R}}_A\left[c_{A.L}\hat{x}+c_{A.H}\left(1-\hat{x}\right)\right]\right\}{q}_J\mathrm{,}$$

The local ash fraction is $$\begin{array}{ll}\hat{\mathrm{A}}& \mathrm{:}\mathrm{=}\frac{{\widehat{\stackrel{\mathrm{}}{\mathrm{m}}}}_{\mathrm{A}\mathrm{.}\mathrm{P}}}{{\widehat{\stackrel{\mathrm{}}{\mathrm{m}}}}_{\mathrm{P}}}\mathrm{+}\frac{{\hat{\mathrm{R}}}_{\mathrm{A}}\left[{\mathrm{c}}_{\mathrm{A}\mathrm{.}\mathrm{L}}\hat{\mathrm{x}}\mathrm{+}{\mathrm{c}}_{\mathrm{A}\mathrm{.}\mathrm{H}}\left(\mathrm{1}\mathrm{-}\hat{\mathrm{x}}\right)\right]}{{\hat{\mathrm{R}}}_{\mathrm{F}}\left[{\mathrm{c}}_{\mathrm{F}\mathrm{.}\mathrm{L}}\hat{\mathrm{x}}\mathrm{+}{\mathrm{c}}_{\mathrm{F}\mathrm{.}\mathrm{H}}\left(\mathrm{1}\mathrm{-}\hat{\mathrm{x}}\right)\right]\mathrm{+}{\hat{\mathrm{R}}}_{\mathrm{A}}\left[{\mathrm{c}}_{\mathrm{A}\mathrm{.}\mathrm{L}}\hat{\mathrm{x}}\mathrm{+}{\mathrm{c}}_{\mathrm{A}\mathrm{.}\mathrm{H}}\left(\mathrm{1}\mathrm{-}\hat{\mathrm{x}}\right)\right]}\\ & \mathrm{\approx }\frac{{\hat{\mathrm{R}}}_{\mathrm{A}}\left[{\mathrm{c}}_{\mathrm{A}\mathrm{.}\mathrm{L}}\hat{\mathrm{x}}\mathrm{+}{\mathrm{c}}_{\mathrm{A}\mathrm{.}\mathrm{H}}\left(\mathrm{1}\mathrm{-}\hat{\mathrm{x}}\right)\right]}{{\hat{\mathrm{R}}}_{\mathrm{F}}{\mathrm{c}}_{\mathrm{F}\mathrm{.}\mathrm{H}}\left(\mathrm{1}\mathrm{-}\hat{\mathrm{x}}\right)\mathrm{+}{\hat{\mathrm{R}}}_{\mathrm{A}}\left[{\mathrm{c}}_{\mathrm{A}\mathrm{.}\mathrm{L}}\hat{\mathrm{x}}\mathrm{+}{\mathrm{c}}_{\mathrm{A}\mathrm{.}\mathrm{H}}\left(\mathrm{1}\mathrm{-}\hat{\mathrm{x}}\right)\right]}\end{array}$$

sensibilities

ist, als auch der lokale Ascheanteil Â. Die beiden (normierten) Sensibilitäten gegenüber x̂, also (1/Â_P)(∂Â_P/∂x̂) und (1/ṁ_P)(∂ṁ_P/∂x̂), hängen vom mittleren globalen Verdünnungswasseranteil x ab.In the case of a local change in the addition of dilution water, both the local basis weight changes proportionally to ${\widehat{\stackrel{\mathrm{}}{\mathrm{m}}}}_{\mathrm{P}}$

is, as well as the local ash share. The two (normalized) sensitivities to x, ie (1 / Â _P ) (∂ _P / ∂x) and (1 / ṁ _P ) (∂ṁ _P / ∂x), depend on the mean global dilution water content x.

mit $$\mathrm{Z}\mathrm{=}\mathrm{-}{\stackrel{\mathrm{}}{\mathrm{m}}}_{\mathrm{F}\mathrm{,}\mathrm{P}}{\stackrel{\mathrm{}}{\mathrm{m}}}_{\mathrm{A}\mathrm{,}\mathrm{P}}\left(\frac{{\stackrel{\mathrm{}}{\mathrm{m}}}_{\mathrm{F}\mathrm{,}\mathrm{P}}}{{\mathrm{R}}_{\mathrm{F}}}\mathrm{+}\frac{{\stackrel{\mathrm{}}{\mathrm{m}}}_{\mathrm{A}\mathrm{,}\mathrm{P}}}{{\mathrm{R}}_{\mathrm{A}}}\mathrm{-}{\mathrm{c}}_{\mathrm{L}}{\mathrm{q}}_{\mathrm{J}}\right)\left(\frac{\mathrm{1}}{{\mathrm{R}}_{\mathrm{F}}}\frac{\mathrm{\partial }{\hat{\mathrm{R}}}_{\mathrm{F}}}{\mathrm{\partial }{\hat{\mathrm{c}}}_{\mathrm{J}}}{\mathrm{|}}_{{\stackrel{\mathrm{}}{\mathrm{c}}}_{\mathrm{J}}\mathrm{=}{\mathrm{c}}_{\mathrm{J}}}\mathrm{-}\frac{\mathrm{1}}{{\mathrm{R}}_{\mathrm{A}}}\frac{\mathrm{\partial }{\hat{\mathrm{R}}}_{\mathrm{A}}}{\mathrm{\partial }{\hat{\mathrm{c}}}_{\mathrm{J}}}{\mathrm{|}}_{{\stackrel{\mathrm{}}{\mathrm{c}}}_{\mathrm{J}}\mathrm{=}{\mathrm{c}}_{\mathrm{J}}}\right)\mathrm{+}\left({\mathrm{R}}_{\mathrm{A}}{\mathrm{c}}_{\mathrm{A}\mathrm{,}\mathrm{L}}{\stackrel{\mathrm{}}{\mathrm{m}}}_{\mathrm{F}\mathrm{,}\mathrm{P}}\mathrm{-}{\mathrm{R}}_{\mathrm{F}}{\mathrm{c}}_{\mathrm{F}\mathrm{,}\mathrm{L}}{\stackrel{\mathrm{}}{\mathrm{m}}}_{\mathrm{A}\mathrm{,}\mathrm{P}}\right){\mathrm{q}}_{\mathrm{J}}^{\mathrm{2}}$$

$$\mathrm{N}\mathrm{=}{\stackrel{\mathrm{}}{\mathrm{m}}}_{\mathrm{A}\mathrm{,}\mathrm{P}}\left\{\left(\frac{{\stackrel{\mathrm{}}{\mathrm{m}}}_{\mathrm{F}\mathrm{,}\mathrm{P}}}{{\mathrm{R}}_{\mathrm{F}}}\mathrm{+}\frac{{\stackrel{\mathrm{}}{\mathrm{m}}}_{\mathrm{A}\mathrm{,}\mathrm{P}}}{{\mathrm{R}}_{\mathrm{A}}}\mathrm{-}{\mathrm{c}}_{\mathrm{L}}{\mathrm{q}}_{\mathrm{J}}\right)\left(\frac{{\stackrel{\mathrm{}}{\mathrm{m}}}_{\mathrm{F}\mathrm{,}\mathrm{P}}}{{\mathrm{R}}_{\mathrm{F}}}\frac{\mathrm{\partial }{\hat{\mathrm{R}}}_{\mathrm{F}}}{\mathrm{\partial }{\hat{\mathrm{c}}}_{\mathrm{J}}}{\mathrm{|}}_{{\stackrel{\mathrm{}}{\mathrm{c}}}_{\mathrm{J}}\mathrm{=}{\mathrm{c}}_{\mathrm{J}}}\mathrm{-}\frac{{\stackrel{\mathrm{}}{\mathrm{m}}}_{\mathrm{A}\mathrm{,}\mathrm{P}}}{{\mathrm{R}}_{\mathrm{A}}}\frac{\mathrm{\partial }{\hat{\mathrm{R}}}_{\mathrm{A}}}{\mathrm{\partial }{\hat{\mathrm{c}}}_{\mathrm{J}}}{\mathrm{|}}_{{\stackrel{\mathrm{}}{\mathrm{c}}}_{\mathrm{J}}\mathrm{=}{\mathrm{c}}_{\mathrm{J}}}\right)\mathrm{+}\left[{\stackrel{\mathrm{}}{\mathrm{m}}}_{\mathrm{P}}\mathrm{-}\left({\mathrm{R}}_{\mathrm{F}}{\mathrm{c}}_{\mathrm{F}\mathrm{,}\mathrm{L}}\mathrm{+}{\mathrm{R}}_{\mathrm{A}}{\mathrm{c}}_{\mathrm{A}\mathrm{,}\mathrm{L}}\right){\mathrm{q}}_{\mathrm{J}}\right]{\mathrm{q}}_{\mathrm{J}}\right\}\mathrm{,}$$

so zeigt sich, dass dieser Quotient nicht von x abhängt. Unabhängig von der mittleren Verdünnungswasserzugabe wird damit bei einer Regelung des Flächengewichtsquerprofils mit Hilfe der ModulJet-Ventile das Aschequerprofil beeinflusst.The question arises as to whether the best possible sensitivity of the basis weight on the one hand and the lowest possible sensitivity of the ash content to x on the other hand can be achieved by the appropriate choice of a specific operating point x. Consider the quotient of the normalized sensibilities (to simplify the formula at the point x = x) $$\frac{\frac{\mathrm{1}}{{\hat{\mathrm{A}}}_{\mathrm{P}}}\frac{\mathrm{\partial }{\hat{\mathrm{A}}}_{\mathrm{P}}}{\mathrm{\partial }\hat{\mathrm{x}}}}{\frac{\mathrm{1}}{{\widehat{\stackrel{\mathrm{}}{\mathrm{m}}}}_{\mathrm{P}}}\frac{\mathrm{\partial }{\stackrel{\mathrm{}}{\mathrm{m}}}_{\mathrm{P}}}{\mathrm{\partial }\hat{\mathrm{x}}}}{\mathrm{|}}_{\hat{\mathrm{x}}\mathrm{=}\mathrm{x}}\mathrm{=}\frac{\mathrm{Z}}{\mathrm{N}}$$

With $$\mathrm{Z}\mathrm{=}\mathrm{-}{\stackrel{\mathrm{}}{\mathrm{m}}}_{\mathrm{F}\mathrm{.}\mathrm{P}}{\stackrel{\mathrm{}}{\mathrm{m}}}_{\mathrm{A}\mathrm{.}\mathrm{P}}\left(\frac{{\stackrel{\mathrm{}}{\mathrm{m}}}_{\mathrm{F}\mathrm{.}\mathrm{P}}}{{\mathrm{R}}_{\mathrm{F}}}\mathrm{+}\frac{{\stackrel{\mathrm{}}{\mathrm{m}}}_{\mathrm{A}\mathrm{.}\mathrm{P}}}{{\mathrm{R}}_{\mathrm{A}}}\mathrm{-}{\mathrm{c}}_{\mathrm{L}}{\mathrm{q}}_{\mathrm{J}}\right)\left(\frac{\mathrm{1}}{{\mathrm{R}}_{\mathrm{F}}}\frac{\mathrm{\partial }{\hat{\mathrm{R}}}_{\mathrm{F}}}{\mathrm{\partial }{\hat{\mathrm{c}}}_{\mathrm{J}}}{\mathrm{|}}_{{\stackrel{\mathrm{}}{\mathrm{c}}}_{\mathrm{J}}\mathrm{=}{\mathrm{c}}_{\mathrm{J}}}\mathrm{-}\frac{\mathrm{1}}{{\mathrm{R}}_{\mathrm{A}}}\frac{\mathrm{\partial }{\hat{\mathrm{R}}}_{\mathrm{A}}}{\mathrm{\partial }{\hat{\mathrm{c}}}_{\mathrm{J}}}{\mathrm{|}}_{{\stackrel{\mathrm{}}{\mathrm{c}}}_{\mathrm{J}}\mathrm{=}{\mathrm{c}}_{\mathrm{J}}}\right)\mathrm{+}\left({\mathrm{R}}_{\mathrm{A}}{\mathrm{c}}_{\mathrm{A}\mathrm{.}\mathrm{L}}{\stackrel{\mathrm{}}{\mathrm{m}}}_{\mathrm{F}\mathrm{.}\mathrm{P}}\mathrm{-}{\mathrm{R}}_{\mathrm{F}}{\mathrm{c}}_{\mathrm{F}\mathrm{.}\mathrm{L}}{\stackrel{\mathrm{}}{\mathrm{m}}}_{\mathrm{A}\mathrm{.}\mathrm{P}}\right){\mathrm{q}}_{\mathrm{J}}^{\mathrm{2}}$$

$$\mathrm{N}\mathrm{=}{\stackrel{\mathrm{}}{\mathrm{m}}}_{\mathrm{A}\mathrm{.}\mathrm{P}}\left\{\left(\frac{{\stackrel{\mathrm{}}{\mathrm{m}}}_{\mathrm{F}\mathrm{.}\mathrm{P}}}{{\mathrm{R}}_{\mathrm{F}}}\mathrm{+}\frac{{\stackrel{\mathrm{}}{\mathrm{m}}}_{\mathrm{A}\mathrm{.}\mathrm{P}}}{{\mathrm{R}}_{\mathrm{A}}}\mathrm{-}{\mathrm{c}}_{\mathrm{L}}{\mathrm{q}}_{\mathrm{J}}\right)\left(\frac{{\stackrel{\mathrm{}}{\mathrm{m}}}_{\mathrm{F}\mathrm{.}\mathrm{P}}}{{\mathrm{R}}_{\mathrm{F}}}\frac{\mathrm{\partial }{\hat{\mathrm{R}}}_{\mathrm{F}}}{\mathrm{\partial }{\hat{\mathrm{c}}}_{\mathrm{J}}}{\mathrm{|}}_{{\stackrel{\mathrm{}}{\mathrm{c}}}_{\mathrm{J}}\mathrm{=}{\mathrm{c}}_{\mathrm{J}}}\mathrm{-}\frac{{\stackrel{\mathrm{}}{\mathrm{m}}}_{\mathrm{A}\mathrm{.}\mathrm{P}}}{{\mathrm{R}}_{\mathrm{A}}}\frac{\mathrm{\partial }{\hat{\mathrm{R}}}_{\mathrm{A}}}{\mathrm{\partial }{\hat{\mathrm{c}}}_{\mathrm{J}}}{\mathrm{|}}_{{\stackrel{\mathrm{}}{\mathrm{c}}}_{\mathrm{J}}\mathrm{=}{\mathrm{c}}_{\mathrm{J}}}\right)\mathrm{+}\left[{\stackrel{\mathrm{}}{\mathrm{m}}}_{\mathrm{P}}\mathrm{-}\left({\mathrm{R}}_{\mathrm{F}}{\mathrm{c}}_{\mathrm{F}\mathrm{.}\mathrm{L}}\mathrm{+}{\mathrm{R}}_{\mathrm{A}}{\mathrm{c}}_{\mathrm{A}\mathrm{.}\mathrm{L}}\right){\mathrm{q}}_{\mathrm{J}}\right]{\mathrm{q}}_{\mathrm{J}}\right\}\mathrm{.}$$

it turns out that this quotient does not depend on x. Regardless of the average dilution water addition, the ash cross profile is thus influenced when controlling the basis weight cross-section with the help of the ModulJet valves.

However, the above formula also shows that with a suitable setting of other sizes, a reduction in the ratio of the two sensitivities can be achieved. If, for example, the retention and its dependencies on the material density are known, then it can be deduced from the equation

ṁ_P

= 54 kg/(m min)

A

= 0,3

q_J

= 7400 l/(m min)

x

= 0,15

c_A,L

= 4 g/l

R_F

= 0,65+0,016Δc_J/(g/l)

R_A

= 0,35+0,019Δc_J/(g/l)

etwa ergibt sich c_F,L = 3,5 g/l, c_F,H = 8,6 g/l und c_A,H = 6,7 g/l.Z = 0 and given c _{A, L determine} an appropriate c _{F, L.} With the values

ṁ _P

= 54 kg / (m min)

A

= 0.3

q _J

= 7400 l / (m min)

x

= 0.15

c _{A, L}

= 4 g / l

R _F

= 0.65 + 0.016Δc _J / (g / l)

R _A

= 0.35 + 0.019Δc _J / (g / l)

for example, c _{F, L} = 3.5 g / l, c _{F, H} = 8.6 g / l and c _{A, H} = 6.7 g / l.

Control of a dilution headbox generally affects both basis weight and filler content in the paper. With appropriate composition of the dilution water, the influence on the filler content according to the invention, however, can be minimized. Using a simplified model for the retention, this is shown below in an example:

machine data

The calculation is based on the following machine data: Dry content on the scooter T = 0.91 machine speed ν = 1080 m / min (Target) surface weight F = 55 g / m ² (Target) filler content paper A = 30% Volume flow jet q _J = 7400 l / (m / min) mean dilution water content x = 0.15 local retention fibers R _F = 0.65 + 0.016Δc _J (g / l) local retention fillers R _A = 0.35 + 0.019Δc _J / (g / l)

The two models for the local fiber retention R _F and the local filler retention R _A assume that the local retention for fibers and fillers can be approximately described as linear functions of the local material density. The fillers are more sensitive to the variations than the fibers.

Variation of the filler content of the dilution water

• - 2,2 g/l
• -- 3,7 g/l
• .. 5,2 g/l

In the first example, the pulp density of the dilution water is maintained at the constant value of c _{F, L} = 2.8 g / l. The filler content c _{A, L} is varied in three stages to 2.2, 3.7 and 5.2 g / l. The required fiber density of the thick material is obtained at c _{F, H} ≈ 8.76 g / l. Its filler content c _{A, H} is to be adjusted to 6.98, 6.71 and 6.45 g / l, respectively. The following diagrams show the different line types for the values of the filler content c _{A, L}

• - 2.2 g / l
• - 3.7 g / l
• .. 5.2 g / l

The diagram according to Fig. 2 shows the dependence of the local fiber retention R _F on the local dilution water content x. In the diagram according to Fig. 3 the dependence of the local filler retention R _A on the local dilution water content x is shown.

The diagrams according to the FIGS. 2 and 3 It can be seen that with a higher filler content of the dilution water, the proportion of dilution water influences the consistency and thus the retention a little less.

The diagram according to Fig. 4 shows the dependence of the filler fraction  _J on the local dilution water content x. From this diagram according to Fig. 4 shows that for the lowest value of the filler content of the dilution water, the quotients c _{A, L} / c _L and c _{A, H} / c _{H are} approximately equal. The relative proportion of filler in the suspension jet thus remains virtually unchanged during the variation of the local proportion of dilution water x. At higher c _{A, L} increases with the local dilution water content x and the filler fraction  _J.

The diagram according to Fig. 5 shows the dependence of the filler content _P in the paper on the local dilution water content x. At the lowest filler content of the dilution water, a higher dosing of the dilution water does not lead to a change in the proportion of filler in the jet (cf. Fig. 4 ), but to an excessive drop in filler retention (cf. FIGS. 2 and 3 ). As a result, the relative filler content in the paper decreases. Although at the highest filler content of the dilution water, the filler retention also falls, but this effect is overcompensated by the significantly higher filler content in the suspension jet. The mean value for c _{A, L} is close to the desired optimum, at which the filler fraction  _{P is} largely independent of the basis weight control and thus constant.

The diagram according to Fig. 6 shows the dependence of the local basis weight F on the local dilution water content x. It is important that at higher filler content of the dilution water, the influence of the dilution water content on the basis weight is somewhat lower, but the local basis weight F can be controlled by the local dilution water content x for all example values of c _{A, L.}

Variations in pulp density of the dilution water

• - 2,0 g/l
• -- 3,5 g/l
• .. 5,0 g/l.

With the same data as in the above example but with the three values of 2.0, 3.5 and 5.0 g / L for c _{F, L} and c _{A, L} = 4.0 g / L = const will be hereafter further bill carried out. The substance densities of the thick material are c _{F, H} ≈ 8.90, 8.64 and 8.37 g / l and c _{A, H} ≈ 6.66 g / l. The line types correspond to the following values of c _{F, L} :

• - 2.0 g / l
• - 3.5 g / l
• .. 5.0 g / l.

The diagram according to Fig. 7 shows the dependence of the filler content _P in the paper on the local dilution water content x. Even in the case of a variation c _{F, L} , it is again possible to adjust the dilution water such that the proportion of filler in the paper remains unaffected by the regulation. If you give too much fiber to the dilution water, then falls  _P x. With too few fibers, the effect is reversed.

The diagram according to Fig. 8 shows the dependence of the local basis weight F on the local dilution water content x. In any case, the basis weight can be influenced as desired.

LIST OF REFERENCE NUMBERS

10

contraption

12

Wire section

14

press section

16

drying section

18

rewinder

20

Fibrous web

22

pressure roller

26

Dilution headbox

28

Headbox, suspension jet

30

Measuring device for basis weight

32

Device for controlling the consistency

34

Valve

36

mixing point

38

management

40

management

42

a valve which extends across the machine width valve series

44

Device for measuring the filler content and the fiber concentration

46

Control device for controlling the filler and fiber concentration

48

Valve

50

Device for measuring the filler cross profile

Claims (25)

1. Method for producing a fibrous web (20), in particular a paper, board or tissue web, in which a stock stream of higher consistency and a stock stream of lower consistency are distributed to respectively common sections over the machine width and the stock streams of each section are then mixed with each other in a variable ratio in each case and the respective mixed stream is supplied to a wire section (12) via a headbox (26) as a headbox jet (28), the mixing ratio between the two stock streams of different consistency in the respective mixed stream being used as a manipulated variable for regulating the transverse profile of the grammage of the fibrous web (20),
   characterized in that
   the ratio between fibre content and filler content in the stock stream of lower consistency is adjusted or regulated before it is distributed, in such a way that the proportion of filler in the fibrous web (20) can be adjusted or regulated at least substantially independently of the grammage.
2. Method according to Claim 1, characterized in that the ratio between fibre content and filler content in the stock stream of lower consistency is continuously adjusted or regulated as appropriate.
3. Method according to Claim 1 or 2, characterized in that, for the appropriate adjustment or regulation of the ratio between fibre content and filler content, fibres or filler are added to or removed from the stock stream of lower consistency.
4. Method according to one of the preceding claims, characterized in that, in order to adjust or regulate the average proportion of filler in the fibrous web (20) over the machine width, fibres or filler are added to or removed from the stock stream of higher consistency.
5. Method according to one of the preceding claims, characterized in that the stock stream of lower consistency is formed by using white water.
6. Method according to one of the preceding claims, characterized in that online regulation of the ratio between fibre content and filler content in the stock stream of lower consistency is carried out.
7. Method according to one of the preceding claims, characterized in that the transverse profile of the proportion of filler in the fibrous web (20) is determined, and in that the transverse profile determined is used in the adjustment or regulation of the ratio between fibre content and filler content in the stock stream of lower consistency.
8. Method according to Claim 7, characterized in that the proportion of fibre in the fibrous web (20) is determined continuously during operation.
9. Method according to Claim 7 or 8, characterized in that, in order to adjust the ratio between fibre content and filler content in the stock suspension of lower consistency, the value of a manipulated variable for the regulation of the transverse profile of the grammage of the fibrous web (20) is compared with the transverse profile of the proportion of filler in the fibrous web (20) that is determined, in order to establish whether a local increase or reduction of the grammage leads to a locally higher or lower proportion of filler in the fibrous web (20).
10. Method according to Claim 9, characterized in that the manipulated variable comprises the position of the valve with which the stock stream of lower consistency is supplied in order to form the mixed stream.
11. Method according to one of Claims 9 to 10, characterized in that, during the comparison, the shrinkage of the fibrous web (20) is taken into account.
12. Method according to one of Claims 10 to 11, characterized in that, in the case in which a higher or lower dilution leads to a higher or lower proportion of filler in the fibrous web (20), fibres are additionally added to or filler is removed from the stock stream of lower consistency or filler is additionally added or fibres are removed.
13. Method according to one of the preceding claims, characterized in that the adjustment or regulation of the ratio between fibre content and filler content in the stock stream of lower consistency is carried out while taking into account the mass balance of the streams in the wire section (12).
14. Method according to one of the preceding claims, characterized in that the adjustment or regulation of the ratio between fibre content and filler content in the stock stream of lower consistency is carried out while taking into account the dependence of the fibre retention and the filler retention in the fibrous web on the composition of the mixed stream or headbox jet (28) at a predefined working point.
15. Method according to Claim 14, characterized in that the filler retention and/or the fibre retention is determined in a preceding trial.
16. Method according to Claim 14 or 15, characterized in that the filler retention is determined continuously during operation via a continuous measurement of the proportion of filler in the fibrous web (20).
17. Apparatus (10) for producing a fibrous web (20), in particular a paper, board or tissue web, having means (43, 49) for distributing a stock stream of higher consistency and a stock stream of lower consistency to respectively common sections over the machine width, and having means for mixing the two stock streams of different consistency of each section in a variable ratio, it being possible for the respective mixed stream to be supplied to a wire section (12) via a headbox (26) as a headbox jet (28), and having means (30, 32, 34) for regulating the grammage of the fibrous web (20) over the machine width by using the mixing ratio between the two stock streams as a manipulated variable, in particular for carrying out the method according to one of the preceding claims,
    characterized in that
    the ratio between fibre content and filler content in the respective stock stream of lower consistency can be adjusted or regulated before it is distributed, in such a way that the proportion of filler in the fibrous web (20) can be adjusted or regulated at least substantially independently of the grammage.
18. Apparatus according to Claim 17, characterized in that the headbox (26) provided is a dilution headbox.
19. Apparatus according to Claim 17 or 18, characterized in that the stock stream of lower consistency is formed by using an initial stock stream, means (46, 48) being provided in order to add or remove fibres or filler to or from the initial stock stream.
20. Apparatus according to Claim 19, characterized in that the initial stock stream provided is white water.
21. Apparatus according to one of Claims 17 to 20, characterized in that the ratio between fibre content and filler content in the stock stream of lower consistency can be adjusted or regulated continuously as appropriate.
22. Apparatus according to one of Claims 17 to 21, characterized in that online regulation of the ratio between fibre content and filler content in the stock stream of lower consistency is provided.
23. Apparatus according to one of Claims 17 to 22, characterized in that means (30) are provided for measuring the transverse profile of the proportion of fibre in the fibrous web (20) over the machine width.
24. Apparatus according to Claim 23, characterized in that the means (30) are suitable for measuring the proportion of fibre in the fibrous web (20) continuously.
25. Apparatus according to Claim 24, characterized in that the ratio between fibre content and filler content in the stock stream of lower consistency can be adjusted or regulated as a function of the transverse profile of the proportion of filler in the fibrous web (20) that is determined.

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