U.S. patent application number 12/364770 was filed with the patent office on 2009-08-13 for method for dewatering and a dewatering apparatus.
Invention is credited to Hartmut Abel, Armin Bauer, Jens Haag, Niels Hardt, Oliver Kaufmann, Rudolf Munch, Jorg Spindler.
Application Number | 20090199987 12/364770 |
Document ID | / |
Family ID | 40823209 |
Filed Date | 2009-08-13 |
United States Patent
Application |
20090199987 |
Kind Code |
A1 |
Spindler; Jorg ; et
al. |
August 13, 2009 |
METHOD FOR DEWATERING AND A DEWATERING APPARATUS
Abstract
This invention relates to a dewatering apparatus, in particular
a paper machine or a paperboard machine, for the adjustable, and
controllable dewatering of a fibrous material, which is conveyed as
a fibrous web that can be divided into at least two zones arranged
side by side in a cross direction (CD). The dewatering apparatus is
characterized in that the dewatering of the fibrous material is
adaptable to a dewatering curve defined in a machine direction on
the basis of measurements of the water weight of the fibrous
material taken by at least two water weight sensors, in particular
a one-dimensional or multi-dimensional sensor arrangement of water
weight sensors, which are assigned to a zone and arranged
preferably in pairs in mutually offset position in the CD
direction.
Inventors: |
Spindler; Jorg; (Schwabisch
Gmund, DE) ; Hardt; Niels; (Herbrechtingen, DE)
; Munch; Rudolf; (Konigsbronn, DE) ; Kaufmann;
Oliver; (Heidenheim, DE) ; Haag; Jens;
(Heidenheim, DE) ; Bauer; Armin; (Polten, AT)
; Abel; Hartmut; (Neu-Ulm, DE) |
Correspondence
Address: |
TAYLOR & AUST, P.C.
P.O. Box 560, 142. S Main Street
Avilla
IN
46710
US
|
Family ID: |
40823209 |
Appl. No.: |
12/364770 |
Filed: |
February 3, 2009 |
Current U.S.
Class: |
162/198 ;
162/258 |
Current CPC
Class: |
D21G 9/0027 20130101;
D21G 9/0036 20130101; D21F 7/003 20130101 |
Class at
Publication: |
162/198 ;
162/258 |
International
Class: |
D21F 11/00 20060101
D21F011/00; D21F 1/08 20060101 D21F001/08 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 11, 2008 |
DE |
10 2008 000 267.4 |
Claims
1. A dewatering apparatus for the adjustable controllable
dewatering of a fibrous material which is conveyed as a fibrous web
that is divided into at least two zones arranged side-by-side in a
cross direction (CD), the dewatering apparatus comprising: a
plurality of water weight sensors assigned to each of said at least
two zones including a first water weight sensor and a second water
weight sensor arranged in a mutually offset position in the CD
direction, said plurality of water weight sensors being arranged in
one of a one-dimensional and a multi-dimensional sensor
arrangement, said plurality of water weight sensors being
positioned and configured to carry out measurements of water weight
of the fibrous material, the dewatering apparatus being configured
to dewater the fibrous material dependent upon a dewatering curve
defined in a machine direction (MD) and upon said measurements of
water weight of the fibrous material.
2. The dewatering apparatus of claim 1, further comprising a
plurality of zonally adjustable dewatering elements in a wet
section of the dewatering apparatus, said dewatering elements being
at least one of a foil, a suction box, a pressing-on element in
combination with an opposing mesh and a headbox, the dewatering
apparatus being further configured to dewater the fibrous material
in a zonally adjustable manner dependent upon said measurements
taken by said water weight sensors.
3. The dewatering apparatus of claim 2, wherein said water weight
sensors and said dewatering elements are arranged in alternating
succession in the MD direction.
4. The dewatering apparatus of claim 3 further comprising at least
one forward-coupled control circuit configured to zonally adjust
the dewatering of the fibrous web.
5. The dewatering apparatus of claim 4, wherein said at least one
forward-coupled control circuit includes a microprocessor.
6. The dewatering apparatus of claim 3 further comprising at least
one backward-coupled control circuit configured to zonally adjust
the dewatering of the fibrous web.
7. The dewatering apparatus of claim 6, wherein said at least one
backward-coupled control circuit includes a microprocessor.
8. The dewatering apparatus of claim 2, wherein the dewatering
apparatus includes at least one section having at least one of a
steam blower box, a press, a headbox and a dilution water headbox,
said dewatering elements being arranged in said at least one
section.
9. The dewatering apparatus of claim 2, wherein the dewatering
apparatus is configured to influence a dewatering performance of
said dewatering elements by way of at least one of an adjustable
suction force, an adjustable layer thickness, an adjustable
consistency of the fibrous material emerging from said headbox and
an adjustable pressurization of the fibrous material by an opposing
element and said mesh.
10. The dewatering apparatus of claim 9, wherein said dewatering
performance of said dewatering elements in one of said at least two
zones is measured at a predetermined time by at least one of said
plurality of water weight sensors, a measurement point of said at
least one of said plurality of water weight sensors is freely
selectable in the MD direction.
11. The dewatering apparatus of claim 10, wherein at said
measurement point looking in the MD direction there is arranged at
least two of said plurality of water weight sensors in each of said
at least two zones arranged in a mutually offset position in the CD
direction.
12. The dewatering apparatus of claim 1, wherein at least one of
said plurality of water weight sensors is offset in the MD
direction and is assigned to one of said at least two zones, said
measurements of at least a part of said plurality of water weight
sensors being averaged.
13. The dewatering apparatus of claim 1, further comprising at
lease one microprocessor configured to adjustably control the
dewatering of the fibrous material.
14. The dewatering apparatus of claim 1, wherein the dewatering
apparatus is configured to provide an image of a dewatering
characteristic in at least one of the CD direction and the MD
direction by interpolation of the measurements of at least some of
said plurality of water weight sensors.
15. A method of adjustably controlling a dewatering of a fibrous
material in a dewatering apparatus in one of a paper machine and a
paperboard machine, the fibrous material being conveyed as a
fibrous web that is divided into at least two zones arranged
side-by-side in a cross machine direction (CD), the method
comprising the steps of: measuring a water weight of the fibrous
material by a plurality of water weight sensors which are assigned
to one of said at least two zones; and adapting the dewatering of
the fibrous material to a dewatering curve defined in a machine
direction (MD) dependent upon said measuring step.
16. The method of claim 15, wherein said plurality of water weight
sensors include at least one pair of water weight sensors arranged
in a mutually offset position in the CD direction.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] This invention relates to a dewatering apparatus, for a
paper machine or a paperboard machine, for the adjustable, in
particular controllable dewatering of a fibrous material which is
conveyed as a fibrous web.
[0003] 2. Description of the Related Art
[0004] Dewatering apparatuses and methods for adjusting the
dewatering of a fibrous material that is conveyed as a fibrous web,
in particular on a belt-shaped mesh, are used in particular in the
paper industry. On account of the continuous dewatering of the
fibrous material in the machine running direction, called MD
direction for short, a paper machine or a paperboard machine can be
regarded essentially as a dewatering apparatus for the fibrous
material. The machine running direction usually designates, as in
this publication, the direction in which the fibrous material is
moved during the paper production process on the paper machine or
paperboard machine.
[0005] At the headbox the consistency of the fibrous material in
the cross machine direction (CD), meaning in the direction at right
angles to the MD direction, as a rule the running direction of the
fibrous material, is first pre-adjusted usually by dilution water.
A headbox working with dilution water is referred to as a dilution
water headbox. Consequently there can arise, in particular in the
wet section of the paper machine or paperboard machine, deviations
of the dewatering in CD direction of the fibrous web from a
dewatering curve defined in the MD direction in particular for the
overall width of the fibrous web. Said deviations in dewatering
lead as a rule to deviations of the gsm substance in CD direction
of the furnace-dry paper. Such deviations have a negative impact on
the transverse formation profile in particular in the CD
direction--which is therefore referred to as the CD profile for
short--and are therefore unwelcome.
[0006] In spite of the consistency of the fibrous material being
adjusted by dilution water at the dilution water headbox, the
problem often arises in the MD direction, but in particular also in
the CD direction, of unsatisfactory formation profiles, in
particular unacceptable CD profiles, arising for example due to
uneven dewatering on the mesh.
[0007] After the fibrous material is applied onto the mesh, said
material continuously loses water due to gravitation or additional
vacuum extraction with the help of dewatering elements, with the
result that the water weight of the fibrous material on the mesh
decreases continuously in MD direction. The forming of the fibrous
material into paper, meaning the forming of a sheet, is thus
enabled. The dewatering of the fibrous material or the forming
paper continues also in the subsequent sections of the paper
machine or paperboard machine, for example in the pressing section
and drying section.
[0008] Known from WO 99/55959 A1 is an apparatus and a method for
sheet measurement and control on paper machines and paperboard
machines. The publication describes among other things the
measuring of CD profiles, in particular water weight profiles in
the CD direction of the paper machine or paperboard machine, with
the help of water weight sensors. A water weight sensor is
described which can be arranged underneath the mesh and used to
measure three properties of a material, in particular the fibrous
material on a paper machine or paperboard machine. Those properties
are the conductance or resistance, the dielectric constant and the
distance of the material from the water weight sensor, whereby one,
or more than one, of these properties dominates depending on the
material. The response time of such a water weight sensor lies at
approx. one millisecond.
[0009] Through the arrangement of the water weight sensors in the
CD direction the CD water weight profile is obtained
instantaneously, as the result of which the MD changes and CD
changes can be determined essentially in isolation. Cited in the
prior art as points of action for the control system are the raw
material supply rate at the beginning of the wet section,
controlling the steam quantity in the drying section or varying the
roller contact pressure in the pressing. Possibilities of actions
at numerous actuators, which are controllable independently of each
other in open-loop or closed-loop mode and extend in each control
range over the width of the fibrous material, are cited. For
example, the headbox and the steam generating system with numerous
steam actuators for controlling the quantity of heat applied onto
the individual zones across the sheet are cited. A similar
situation exists in the calender section where segmented calender
rolls have several actuators for controlling the roll contact
pressure which is applied onto the sheet between the rolls in
individual zones in the CD direction. By evaluating signals from
scanners the control system can adjust the actuators automatically
in the CD direction. Factors for uneven dewatering in the CD
direction, which ultimately are responsible for fluctuations in the
CD profile of the paper, are the irregular provision of fibrous
material at the headbox, the clogging of openings in the woven
plastic mesh, differences in the mechanical tension of the mesh,
and unbalanced vacuum extraction. The fact that the MD changes and
CD changes take place essentially in mutual isolation represents a
certain disadvantage.
[0010] Accordingly, paper properties are currently measured in the
wet section with only spot measurements or one-dimensional sensor
arrays in the MD direction or the CD direction. Other known
applications are traversing measurements or fixed, stationary
measurements in the drying section. A clear-cut assignment of MD
and CD variations is impossible with these known arrangements.
[0011] EP 1 624 298 A2 describes a microwave water weight sensor
and a method for measuring the water weight in a forming section of
a paper machine or paperboard machine using microwaves. The sensor
generates a microwave field which penetrates partly into the
material to be measured. The field is generated either with the
help of a microwave transmission device, which is embedded in a
ceramic film, or by way of a transmission antenna and a reception
antenna, which are coupled to the microwave field through the
material.
[0012] The dielectric constant of the material all around the
transmission device or in the space between the transmission
antenna and the reception antenna affects the wave propagation
speed. The measurement is based either on the propagation time or
on the phase or the phase displacement or the phase shift.
[0013] It is also possible to use a separating line resonator. The
resonator measures essentially the wave propagation speed in the
resonating structure. The operating frequency is selected such that
it lies significantly below the relaxation frequency of water
(approximately 22 GHz). The preferred frequency lies between 1 and
3 GHz, but other frequencies are also possible. The sensor can
measure the water weight in the forming section of the paper
machine or paperboard machine. In particular the sensor can be used
both upstream and downstream from the drying section. It can also
be used in double-belt forming sections.
[0014] The sensor signal is strong enough to take one-sided
measurements. In addition the sensor permits multi-sensor
configurations for measuring the water weight simultaneously at
various positions in the CD direction of the machine in order to
produce a non-sequentially scanned measurement profile. Several
sensors can be arranged such that they form a sensor arrangement or
a sensor field in the CD direction and/or in the MD direction.
Sensor fields arranged in the MD direction can be used
advantageously for determining dewatering profiles.
[0015] The sensor makes use of the fact that the dielectric
constant of the fibrous material in the forming section is affected
mainly by the water, which has a high relative dielectric constant
of around 80 at room temperature up to frequencies of several
GHz.
[0016] The publication also describes a method for monitoring a
layer of fibrous material on a production line, whereby the fibrous
material layer is penetrated by microwaves which have a frequency
lower than the relaxation frequency of water and whereby
measurements are taken of an effect which the fibrous material
layer has on the microwaves. Such a sensor can be used for the
present invention. The disclosure concerning the sensor is
incorporated in all points into the description of the present
invention.
[0017] EP 0 972 882 A1 describes a measurement system for measuring
certain properties of a material web, for example, in particular a
fibrous web on a paper and/or paperboard machine or a coating
machine, by at least one stationary cross profile measuring device
with at least one radiation source for irradiating the material web
in several defined different wavelength ranges and at least one
sensor for measuring the intensity of a radiation affected by the
material web, and by at least one electronic meter and/or analyzer,
whereby only one of the defined different wavelength ranges of the
radiation is recorded preferably by one respective sensor at a
certain time.
[0018] The paper industry has a need for methods which permit the
production of paper with a formation profile which is as uniform as
possible both in the MD direction and in the CD direction, meaning
a formation profile which corresponds to a flat desired profile
defined over the entire fibrous web, and for dewatering
apparatuses, in particular paper machines or paperboard machines,
which implement such methods.
SUMMARY OF THE INVENTION
[0019] This invention relates to a method for adjusting, in
particular controlling the dewatering of a fibrous material on a
dewatering apparatus, in particular a paper machine or a paperboard
machine, whereby the fibrous material is conveyed as a fibrous web
that can be divided into at least two zones arranged side by side
in the cross machine direction.
[0020] An exact measurement of the cross profile of certain
properties is possible. Measurement is possible also at relatively
inaccessible points and even in regions of closed conveyance in
which the material web in question is supported, for example, by a
roll, a belt, a mesh and/or a felt. It is possible to record, for
example, with a sensor, a radiation which is reflected from the
material belt or its covering. In addition or alternatively it is
also possible to record by way of a sensor a radiation which passes
through the material belt or its covering.
[0021] It is proficient to provide for at least two stationary
cross profile measurements set apart from each other in the MD
direction. In this case it is advantageous for at least two
stationary cross profile measuring devices, which are set apart
from each other in the MD direction, to be assigned respectively to
at least one unit such as the pressing section, the drying section
etc. of the paper and/or paperboard machine or coating machine.
[0022] With a view to short control times it is recommended in EP 0
972 882 A1 to arrange, respectively, at least one stationary cross
profile measuring device directly upstream and/or directly
downstream from at least one actuator or actuating element
affecting the respective cross profile.
[0023] The measuring system enables, respectively, at least one
stationary cross profile measuring device to be provided, at least
in the pressing section and/or drying section of a paper and/or
paperboard machine. Alternatively, or in addition, it is also
possible for at least one such stationary cross profile measuring
device to be provided in the mesh section and/or at the end of a
paper machine and/or a paperboard machine.
[0024] Filtering arrangement can be provided in order to filter out
certain interference variables and/or the influence of at least one
actuator or actuating element on the respective cross profile.
[0025] At least one stationary cross profile measurement can be
configured for the quantitative recording of the gsm substance,
moisture, thickness, specific constituents and/or other properties
of the material web.
[0026] In particular for measurement in regions of an open web draw
it is possible to provide for a respective stationary cross profile
measurement with at least one optical radiation source. The sensors
described in EP 0 972 882 A1 can also be used to advantage in the
present invention.
[0027] The inventive dewatering apparatus for the adaptable, in
particular controllable adjustment of the dewatering of a fibrous
material is based generically on a dewatering apparatus, for a
paper machine or a paperboard machine on which the fibrous material
is conveyed as a fibrous web that can be divided into at least two
zones arranged side-by-side in the CD direction.
[0028] According to the invention the dewatering of the fibrous
material is adjustable advantageously to a dewatering curve defined
in the MD direction on the basis of measurements of the water
weight of the fibrous material taken by at least two water weight
sensors which are assigned to a zone and arranged preferably in
pairs in mutually offset position in the CD direction. This
results, advantageously, in a saving of energy and an increase in
production. In addition there is an improvement in the formation of
the paper, which results in turn in an improved strength and
printability of the paper. Through the inventive dewatering
apparatus it is possible to keep the number of necessary sensors
advantageously low.
[0029] The dewatering of the fibrous material takes place "on the
basis of" measurements of the water weight taken by the water
weight sensors arranged in mutually offset position, as described
above, meaning that the sensor measurements are drawn on, albeit
not exclusively, for adapting the dewatering adjustments. Instead
of "on the basis of" you could also say "due to". The important
thing is that a causal relationship be constituted between the
measurement on the one hand and the adjustment on the other hand.
The causal relationship can be formed in very different ways, for
example, by a classic analog control system but also by a digital,
in particular very simple comparative control system or by fuzzy
logic systems or by artificial neural networks etc. Even networking
with a different system type, for example, a knowledge-based
system, in particular with a statistical process control system, is
a fundamentally conceivable and possible configuration of the
causal relationship.
[0030] The dewatering can take place "in accordance with" the
measurements of the water weight taken by the offset water weight
sensors. Instead of "in accordance with" you could also say "in
line with the level of". This should give expression to the fact
that the specific level of the measurements, meaning the
measurements according to their (calibrated) value, are channeled,
albeit not exclusively, into adapting the adjustment of the
dewatering. If the adaptation takes place in accordance with the
measurements, this signifies a value-related causal relationship
such as an in particular microprocessor-assisted calculation, for
example with filtering, smoothing, averaging, statistical
evaluation etc.
[0031] The dewatering apparatus has at least two machine elements
which are respectively zonally adjustable and are arranged in a
mutually offset manner to each other in the MD direction. The
elements can be, for example, foils, suction boxes, pressing-on
elements in connection with a second opposing mesh or a headbox.
Foils can be constructed more economically than foil strips. The
foil or foil strip is used for dewatering, for example by means of
turbulence. Dewatering elements can be arranged in particular in a
wet section of the dewatering apparatus. According to the present
invention the dewatering performance of the dewatering elements are
zonally adjustable on the basis of, in particular, in accordance
with, the measurements taken by the water weight sensors.
Adjustment to the optimum operating point of the dewatering
elements is thus achieved. In the case of suction boxes a vacuum
optimization of the suction boxes is now possible.
[0032] The water weight sensors and the dewatering elements are
arranged in alternating succession in the MD direction. Hence it is
possible to determine in near real-time the effect of the zonal
dewatering performance of a dewatering element.
[0033] According to the invention the dewatering is zonally
adjustable by means of at least one forward-coupled control circuit
or a "feedforward" system. If you consider a zonal dewatering
deviation detected by a sensor arrangement arranged between a first
and a second dewatering element, then the feedforward control
system can control the zonal dewatering performance of the second
dewatering element (in the MD direction) advantageously such that
the second dewatering element eliminates the deviation which had
previously occurred and was carried forward.
[0034] The dewatering is zonally adjustable by at least one
backward-coupled control circuit.
[0035] In the case of a feedback system, the zonal dewatering
performance of the first dewatering element (in the MD direction)
is adjusted advantageously such that consequently the deviation
does not occur at all or only to a reduced extent. The control
effort for an existing feedforward control system can be lowered,
advantageously, as the result.
[0036] The feedforward control system can be regarded as a cascaded
or additional control system which, compared to a simple feedback
control system, creates an improvement in the quality of the
fibrous material formation through a further reduction of
ACTUAL/DESIRED deviations. The stability of such a control cascade
must be taken into account or configured accordingly.
[0037] If forward and backward-coupled control circuits are
available simultaneously, which is considered a particularly
favorable version, then you can speak of a distributed control
system, in particular a control system acting in more than one
direction, namely a control system acting at least in forward and
backward direction in relation to the MD direction.
[0038] The dewatering elements are arranged, in at least one
section of the dewatering apparatus. They can be arranged favorably
in, or in a region of, a steam blow box or a press or a headbox, in
particular a dilution water headbox. In addition, the dewatering
performance can be influenced by an adjustable suction force and/or
an adjustable layer thickness and/or the preferably adjustable
consistency of the fibrous material emerging from the headbox
and/or a preferably adjustable pressurization of the fibrous
material by an opposing element and a second mesh. Through the
adaptation or control of dewatering elements, in particular of
different types of dewatering elements, in different sections of
the dewatering apparatus it is possible to achieve a particularly
exact control of the overall process near the predefined dewatering
curve in the MD direction.
[0039] The dewatering performance of a dewatering element in a zone
is measured at a certain time by at least one water weight sensor.
The measurement point of the water weight sensor in the MD
direction is in this case advantageously freely selectable. The
positioning of sensors both within one section and in different
sections can thus be selected or fixed advantageously in accordance
with the requirements of the overall process. In this way it is
possible to determine a measurement-based picture of the entire
fibrous web while still having to arrange only a manageable number
of measuring sensors.
[0040] At at least one measurement point, looking in the MD
direction, there are favorably at least two water weight sensors
per zone arranged in a mutually offset position in the CD
direction. Alternatively, there can also be a one-dimensional
sensor arrangement, which has more than two sensors and is
orientated in the CD direction, or there can also be a
multi-dimensional sensor field. In such a sensor arrangement, or
sensor field, it is possible for the sensors to be configured in an
integrally interconnected fashion. Through this rather more opulent
equipment arrangement it is possible to measure the dewatering more
informatively than with embodiments equipped with fewer
sensors.
[0041] The measurements of at least a part of the water weight
sensors, which are arranged in offset position in the MD direction
and are assigned to a zone, are averaged. The averaging produces a
slurred, or you could also say blurred, signal. The signal is
zonally averaged. You could also say that the signal is received
zonally slurred or blurred. Instead of averaging you can also speak
of filtering or smoothing. In conjunction with the offset
arrangement of the sensors it is possible to calculate,
advantageously, the water curve (ACTUAL) from the zonally averaged
or filtered or smoothed signal. As a further consequence the ACTUAL
curve can be adapted to the DESIRED curve of the dewatering
diagram.
[0042] Furthermore, a more exact image of the dewatering
characteristic in the CD direction and/or in the MD direction can
be determined through a suitable interpolation of measurement
values from the offset water weight sensors.
[0043] In addition the present invention relates to a method for
adjusting, in particular controlling the dewatering of a fibrous
material on a dewatering apparatus, in particular a paper machine
or a paperboard machine. The dewatering apparatus or the paper
machine or paperboard machine can be configured in accordance with
the present invention as described herein. The fibrous material is
conveyed as a fibrous web that can be divided into at least two
zones arranged side by side in the CD direction.
[0044] With the inventive method the dewatering of the fibrous
material is adaptable to a dewatering curve defined in the MD
direction on the basis of measurements of the water weight of the
fibrous material taken by at least two water weight sensors, in
particular sensor arrangements of water weight sensors, which are
assigned to a zone and arranged preferably in pairs in mutually
offset positions in the CD direction.
BRIEF DESCRIPTION OF THE DRAWINGS
[0045] Further advantageous properties and embodiments of the
invention will be described with reference to the drawings
explained below. In the drawings:
[0046] FIG. 1 shows a side view of a first embodiment of an
inventive dewatering apparatus of the present invention, namely the
wet section of a paper machine or paperboard machine, with
dewatering elements and water weight sensors arranged underneath
the long mesh;
[0047] FIG. 2 shows a plan view of the fibrous web, with a
dotted-line indication of the zones;
[0048] FIG. 3 shows a plan view of the wet section of the first
embodiment for clearer presentation of the mutual offsetting of the
water weight sensors in accordance with the present invention;
and
[0049] FIG. 4 shows a plan view of the wet section of a second
embodiment of an inventive paper machine or paperboard machine; the
mutual offsetting of the water weight sensors being configured
differently.
DETAILED DESCRIPTION OF THE INVENTION
[0050] Referring now to the figures there is described below a
first embodiment of an inventive dewatering apparatus 1, which in
this case is a paper machine or paperboard machine. The paper
machine or paperboard machine 1 implements the inventive
method.
[0051] The paper machine or paperboard machine 1 has a wet section
20 with a dewatering apparatus 21, in which a fibrous material 2 is
applied onto a long mesh 23 by a headbox 3. Headbox 3 is
constructed as a dilution water headbox. Dilution water headbox 3
has along CD direction 15 of a fibrous web 5 a plurality of fibrous
material outlet openings 4.
[0052] With the help of dewatering elements 16 there takes place a
first dewatering step for fibrous material 2 in fibrous web 5
conveyed on long mesh 23. Dewatering elements 16 are constructed
here as suction boxes 16. The embodiment shown includes two suction
boxes 16, whose dewatering performance is zonally adjustable. The
paper machine or paperboard machine 1 has further sections such as
a drying section, a pressing section and also a reel, which for the
sake of clarity are not shown. These sections can also contain
zonally adjustable dewatering elements 16, such as, for example,
segmented calender rolls (FIG. 1).
[0053] In MD direction 14 downstream from each dewatering element
16 and upstream from the first dewatering element 16 in MD
direction 14 there are arranged water weight sensors 12 for
measuring the dewatering of fibrous material 2 in the form of its
water weight. MD direction 14 is indicated in FIG. 1 by an arrow.
Water weight sensors 12 can be arranged directly in dewatering
elements 16, for example they could be integrally constructed with
elements 16.
[0054] Long mesh 23 is deflected and driven at the end receiving
the fibrous material by way a breast roll 22. Fibrous web 5 lies on
the upper side of long mesh 23 and is moved continuously by mesh 23
in MD direction 14 and hence away from dilution water headbox 3,
whereby the fibrous material is dewatered continuously by way of
dewatering elements 16. Here the dewatering takes place by
gravitation and in addition by way of vacuum extraction through
suction boxes 16.
[0055] Here fibrous web 5 includes two zones 6 and 7 (as shown in
FIG. 2). Zones 6 and 7 extend respectively over half of the total
transverse extension B of fibrous web 5. Fibrous web 5 could also
include more than two zones 6 and 7, for example it could include
as many zones as sections which can be adjusted in their dewatering
performance or zones which exist on a suction box 16. Zones 6 and 7
extend in both MD direction 14 and CD direction 15. Here zones 6
and 7 extend over the entire longitudinal extension L of fibrous
web 5. However they could also be constructed shorter. For example,
each of zones 6 and 7 could be divided at least once in MD
direction 14, thus creating at least four zones. Then there would
be respectively two zones arranged side by side in CD direction 15
and assigned to one suction box. There could also be more, in
particular substantially more than four zones which, adjacent to,
or apart from, each other, follow each other in pairs in both MD
direction 14 and CD direction 15.
[0056] The water weight sensors 12 are arranged in mutually offset
position. They are arranged in an offset position in both MD
direction 14 and CD direction 15. Here they are arranged on the
bottom side of fibrous web 5. They could also be arranged above
fibrous web 5. Water weight sensors 12 could also be available in
sections of the paper machine or paperboard machine 1 other than
wet section 20. They could also be available, for example in, or in
the region of, the press or the drying section etc.
[0057] Water weight sensors 12 are arranged preferably in pairs in
a mutually offset position fashion. Through the offset positioning
there results, in particular with more than two sensors 12 per
zone, a gapped arrangement of sensors 12. The arrangement of the
sensors 12 displays a periodicity. The periodicity can also be
described as a pattern. The periodic arrangement forms in both CD
direction 15 and MD direction 14 a significant gapped pattern. The
gapped line pattern in CD direction 15 and the gapped line pattern
in MD direction 14 are arranged such that sensors 12 are mutually
offset in pairs in both MD direction 14 and CD direction 15.
Through the specific offset arrangement there result gapped
one-dimensional sensor arrangements 61 or, as in this case, at
least one multi-dimensional sensor arrangement 17 of water weight
sensors 12 as shown in FIG. 3.
[0058] The dewatering of fibrous material 2 is monitored by
measurements of the water weight in fibrous material 2 using at
least two sensors 12 assigned to zone 6 and 7. On the basis of the
water weight measurements the dewatering can be adapted to a
defined dewatering curve 19 in MD direction 14. A dewatering curve
is usually plotted in the unit "grams of water per square meter"
(g/m2 H2O) over the entire length of fibrous web 5. This unit is
also used for dewatering curve 19 in FIG. 3, which presents fibrous
web 5 along its left side in MD direction 14. The term "on the
basis of" is used here to designate a causal relationship between
the measurement of the water weight on the one hand and the
adaptation of the ACTUAL dewatering state of fibrous material 2 to
the selectable or selected dewatering curve 19.
[0059] Dewatering apparatus 1 has at least two dewatering elements
which are respectively zonally adjustable and are arranged mutually
offset to each other in MD direction 14. Dewatering elements 16 are
constructed here as suction boxes. The dewatering performance of
dewatering elements 16 is zonally adjustable on the basis of the
measurements taken by water weight sensors 12.
[0060] Water weight sensors 12 and dewatering elements 16 are
arranged in alternating succession MD direction 14. Here there is
at least one water weight sensor 12 arranged upstream from the
first and downstream from the last dewatering element 16 looking in
MD direction 14. Arranged per measurement point 18 in the first
embodiment are, in concrete terms looking in MD direction 14, five
water weight sensors 12 with gaps in mutually offset position in CD
direction 15. Three one-dimensional sensor arrangements 13 are
available. Together the sensor arrangements form one
multi-dimensional sensor field 17.
[0061] The dewatering is zonally adjustable by at least one
backward-coupled control circuit 9. The control circuit 9 has
preferably at least one microprocessor 11.
[0062] The dewatering is, preferably in addition, zonally
adjustable by at least one forward-coupled control circuit 8, in
this case likewise with a microprocessor 11. There could be, albeit
less preferably, only at least one forward-coupled control circuit
8, meaning dewatering apparatus 1 could also be constructed without
a backward-coupled control circuit 9. For the sake of clarity the
forward and/or backward coupling loops 10, the control circuits 8
and 9 and the at least one microprocessor 11 are not shown in FIG.
3.
[0063] Inventive features not presented in FIG. 3 are shown in FIG.
4, which presents a second embodiment of the present invention.
[0064] Dewatering elements 16 are available in both embodiments
only in, or in the region of, wet section 20. However, dewatering
elements 16 could also be arranged, in particular respectively in
addition or solely, in at least one additional section of
dewatering apparatus 1, such as in a steam blower box or in a press
or in a headbox 3, in particular in a dilution water headbox 3.
[0065] The first embodiment has three one-dimensional sensor
arrangements 13 which are offset in pairs in CD direction 15 and
have five water weight sensors 12 each. Sensor arrangements 13 and
hence their sensors 12 are also set apart from each other in MD
direction 14. The result is therefore a very regular periodicity as
a pattern of sensors 12. A different pattern or different
periodicity of sensors 12 is implemented on the second embodiment,
which is presented in FIG. 4.
[0066] On the second embodiment the first sensor arrangement 13 in
MD direction 14 is equipped with two sensors 12 per zone 6 and 7.
Sensors 12 of first sensor arrangements 13 in MD direction 14 are
arranged, looking in MD direction 14, shifted rather to the left
edge of fibrous web 5. This illustrates a left-gapped sensor
arrangement 13.
[0067] The three sensors 12 per zone 6 and 7 of second sensor
phalanx 13, meaning the one arranged between two suction boxes 16,
are more narrowly gapped than the two sensors 12 of first sensor
arrangement 13. The three sensors per zone 6 and 7 of second sensor
phalanx 13 are arranged, in relation to CD direction 15, more
centrally in their respective zone than the two sensors 12 of a
zone in the first sensor arrangement 13. This illustrates a zonally
center- and narrow-gapped second sensor arrangement 13.
[0068] A third sensor arrangement 13 is arranged in MD direction 14
downstream from second suction box 16. The arrangement is
constructed, as far as the periodicity or pattern is concerned,
like first sensor arrangement 13, meaning similarly gapped with
regard to the sensor spacing. However, sensors 12 of third sensor
arrangement 13 are arranged, looking in MD direction 14, shifted
rather to the right edge of the fibrous web 5. This illustrates, in
analogy with first sensor arrangement 13, of a right-gapped third
sensor arrangement 13. Here sensors 12 of sensor arrangements 13
variously distributed in MD direction 14 form in turn a specific
pattern in which the total number of sensors 12 is reduced compared
to the first embodiment. This is owed in particular to the fact
that the first and the third sensor arrangement 13 is constructed
with rather wide gaps.
[0069] In both embodiments, the dewatering performance of
dewatering element 16 in zone 6 and 7 is measured at a certain time
by at least one water weight sensor 12. The measurement point 18
(see FIG. 4) of water weight sensor 12 in MD direction 14 is freely
selectable. Similarly in both embodiments, at least one measurement
point 18 looking in MD direction 14 there are at least two water
weight sensors 12 per zone 6 and 7 arranged in mutually offset
position in CD direction.
[0070] The measurements of at least a part of water weight sensors
12, which are arranged in an offset position in MD direction 14 and
are assigned to zone 6 and 7, are averaged. This describes a
blurring or slurring of the measurements. Similarly, the terms
filtering and smoothing also apply for this calculation process.
The averaging produces a slurred or blurred signal. In conjunction
with the offset-periodic arrangement of the sensors arranged as a
pattern it is possible to calculate the water curve (ACTUAL) from
the averaged or filtered or smoothed signal. As a further
consequence the ACTUAL curve can be adapted to the DESIRED curve of
dewatering diagram 19.
[0071] The adjustment, in particular control, of the dewatering
takes place with the involvement of at least one microprocessor 11.
The averaging is performed likewise preferably with the help of at
least one microprocessor. The result of such a calculation is
presented in the form of a water weight total cross profile 24 of
all the sensors 12 in FIG. 3 directly after the right-hand end of
fibrous web 5. A more exact image of the dewatering characteristic
in CD direction 15 and/or in MD direction 14 is determined in a
favorable manner through a suitable interpolation of measurement
values from offset water weight sensors 12.
[0072] As has now been made plausible, the dewatering apparatuses 1
of both embodiments implement the inventive method for adjusting,
in particular controlling, the dewatering of a fibrous material 2
which is conveyed as a fibrous web that can be divided into at
least two zones arranged side by side in CD direction 15.
Characteristic of the inventive method is the fact that the
dewatering of fibrous material 2 is adaptable to dewatering curve
19 defined in MD direction 14 on the basis of measurements of the
water weight of fibrous material 2 taken by at least two water
weight sensors 12 which are assigned to zone 6 and 7 and arranged
preferably in pairs in mutually offset position in both MD
direction 14 and CD direction 15.
[0073] Other embodiments of the inventive method or the inventive
dewatering apparatus are conceivable and possible. For example, the
patterns and/or the number of sensors could be configured
differently. For the two embodiments presented in detail, use is
made respectively of similar types of water weight sensors.
Depending on the section equipped with water weight sensors it can
make sense however to combine unlike water weight sensors. The
calculation of measured values from water weight sensors of
different types is also counterplated.
[0074] Through the specific gapped arrangement of the sensors in a
periodic pattern it is possible to adapt the total number of
sensors to the quality requirements on the one hand and to budget
requirements on the other hand. Furthermore, because the sensors
are gapped and periodically offset in all main directions they
result in blurring of the calculation and hence in an exact
adjustment, in particular control, of the dewatering that is not
disturbed by statistical interference.
[0075] While this invention has been described with respect to at
least one embodiment, the present invention can be further modified
within the spirit and scope of this disclosure. This application is
therefore intended to cover any variations, uses, or adaptations of
the invention using its general principles. Further, this
application is intended to cover such departures from the present
disclosure as come within known or customary practice in the art to
which this invention pertains and which fall within the limits of
the appended claims.
LIST OF REFERENCE NUMERALS
[0076] 1 Dewatering apparatus
[0077] 2 Fibrous material
[0078] 3 Headbox
[0079] 4 Fibrous material outlet openings
[0080] 5 Fibrous web
[0081] 6 Zone
[0082] 7 Zone
[0083] 8 Forward-coupled control circuit
[0084] 9 Backward-coupled control circuit
[0085] 10 Forward/backward coupling loop
[0086] 11 Microprocessor
[0087] 12 Water weight sensor
[0088] 13 One-dimensional sensor arrangement
[0089] 14 Machine running direction (MD direction)
[0090] 15 Cross machine direction (CD direction)
[0091] 16 Dewatering element
[0092] 17 Multi-dimensional sensor arrangement
[0093] 18 Measurement point
[0094] 19 Dewatering curve
[0095] 20 Wet section
[0096] 21 Dewatering apparatus
[0097] 22 Breast roll
[0098] 23 Long mesh
[0099] 24 Water weight total cross profile
[0100] L Longitudinal extension of the fibrous web
[0101] B Transverse extension of the fibrous web
* * * * *