Note: Descriptions are shown in the official language in which they were submitted.
CA 02569884 2006-12-08
METHOD AND MACHINE FOR PRODUCING A FIBROUS WEB
Cross Reference To Related Applications
[0001] This is a continuation of PCT application No. PCT/EP2005/005862,
entitled
"METHOD AND MACHINE FOR PRODUCING A FIBROUS WEB", filed June 1, 2005.
BACKGROUND OF THE INVENTION
1. Field of the Invention
[0002] The current invention relates to a method for the production of a
fibrous web in a
machine including a headbox, a wire section, a press section and a dryer
section wherein a first,
fiber-containing fibrous stock suspension is used in which the fibers are
loaded, at least partially,
in a precipitation process in a reactor with a precipitation product
representing a portion of the
ash contained in the fibrous web.
2. Description of the Related Art
[0003] A method for the production of a fibrous stock suspension which
contains a
precipitation product, namely calcium carbonate, is described in US 5,223,090,
wherein a fibrous
material with elongated fibers is used in which a cellulose wall surrounds a
hollow interior, and
wherein the fibers possess a moisture content sufficient to form a dewatered
slurry of a pulp.
The fibers have a moisture content which corresponds to 40 to 50% of the fiber
weight. The
water is present essentially in the interior of the fibers and inside of the
fiber walls. Calcium
oxide or alternatively calcium hydroxide is subsequently added to the pulp so
that at least a
portion of the added calcium oxide or calcium hydroxide is combined with the
water that is
contained in the pulp. The fibrous cellulose material is then brought into
contact with carbon
dioxide wherein it is subjected to a shear-mixing process at the same time, in
order to produce a
fibrous material having a substantial amount of calcium carbonate inside the
hollow interior and
within the fiber walls of the cellulose fibers.
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[0004] A method is known from JP-A-60-297 382 for adding calcium hydroxide
into a one-
percent suspension of a beaten or unbeaten pulp. Subsequently carbon dioxide
is added into the
fibrous stock suspension and calcium hydroxide mixture in order to convert the
calcium
hydroxide into calcium carbonate.
[0005] A method for loading of fibers with calcium carbonate ("Fiber Loading
Technology")
is known from DE 100 33 979 Al wherein a calcium oxide and/or calcium
hydroxide containing
medium is added to the fibrous stock suspension and wherein the herewith
treated fibrous stock
suspension is processed with additional pure carbon dioxide or a carbon
dioxide containing
medium in at least one reactor. During the course of the chemical reaction,
the essentially
complete conversion of the starting substances calcium oxide or calcium
hydroxide and carbon
dioxide into the reaction product calcium carbonate and water is ensured by
regulating the pH
value in the fibrous stock suspension accordingly.
[0006] DE 102 04 254 Al relates to a method for the processing of fibers
contained in a
fibrous stock suspension wherein the fibers which are loaded with the
precipitation product are
refined in order to produce precipitation product particles having optimum
dimensions in a range
of approximately 0.05 and approximately 5 . This produces crystalline
precipitation product
particles. The production of the crystalline precipitation product particles
occurs in an on-line
process, directly in the stock preparation line.
[0007] Papers containing fillers or ash are utilized in a multitude of
applications, for example
in the production of cigarette paper which has a base weight of between 16 to
26 g/m2. It is
frequently enhanced with a water mark and it should be very thin, capable of
glowing
combustion and tasteless. In addition it should possess good optical values
with regard to the
brightness. The glowing combustion capability is usually achieved by
impregnation in order to
leave behind a visually attractive white ash. Cigarette paper is usually
produced from linen or
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hemp fibers, cotton, sulfate pulp, paper machine broke as well as from other
sources of fiber.
The filler content in cigarette paper is between 5 and 40%, wherein 30% is
considered a standard
value.
[0008] The freeness value of cigarette paper varies between 100 and 25 CSF
(CSF = Canadian
Standard Freeness), or between 68 and 90 SR relative to the manufactured end
product.
[0009] The fibrous stock loaded with calcium carbonate can also be utilized in
the production
of packaging papers and cardboards. Here, a distinction can be made between
three main
categories: container board for packaging applications, container board for
applications in the
field of consumer packaging and specialty papers such as wall papers, book
spines, etc.
Packaging papers are usually produced as multi-ply products having base
weights higher than
150 g/m2. The freeness value varies from 600 to 50 CSF or 20 to 80 SR,
relative to the
manufactured end product.
[0010] Sack papers require a high porosity and a high mechanical strength in
order to meet the
high requirements which occur due to the rough handling during the filling
process and
throughout the duration of their use, as is the case for example with cement
bags. The paper
must be strong enough to absorb impacts and must therefore possess an
accordingly high energy
absorption rate. The sack paper must also be porous and sufficiently air
permeable in order to
ensure an effortless filling process. Sack papers are normally manufactured
from a long-fiber
kraft pulp as a product having a base weight of between 70 and 80 g/mz and
having a freeness
value of between 600 to 425 CSF or 20 to 30 SR. Moreover a medium freeness
value as
described above is strived for which is usually achieved through high
consistency refining while
low consistency refining is utilized for conventional paper grades, for
example graphic papers.
The result of high consistency refining is good adhesion of the fibers with
each other as well as
high porosity. The sack kraft paper is produced predominantly from bleached
and unbleached
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fibers, wherein a filler content of 5 to 15% may be present in the
manufactured sack paper.
[0011] Filter paper requires a high controlled porosity and pore distribution.
It must possess a
sufficiently high mechanical strength in order to counteract the flow of the
medium which is to
be filtered.
[0012] Filter paper is being produced, having a base weight of 12 to 1200
g/m2. In an air filter
for example said base weight is between 100 and 200 g/m2, in an oil or fuel
filter between 50 and
80 g/m2, in a food stuff filter as high as 1000 g/m2, in a coffee filter as
high as 100 g/mz, in a tea
bag between 12 and 20 g/m2 and in a vacuum cleaner bag between 100 and 150
g/m2. All filters
are produced from a plurality of fibers, such as chemical pulp fibers,
bleached and unbleached
fibers, kraft pulp, DIP (deinked) paper, recycled fibers, TMP ( thermo-
mechanical) paper, etc.,
wherein a freeness value of 600 to 350 CSF or 20 to 35 SR is strived for.
[0013] For the production process in modem paper machines for both the
manufacture of the
aforementioned types of paper as well as the manufacture of graphic papers
having a base weight
of 25 to 150 g/mz, it is necessary to maintain the ash content in the paper as
constant as possible
and to minimize process fluctuations. In current machinery for the production
of fiber webs the
ash content is kept constant by adding fresh ash in addition to the ash that
is carried along with
the fibers. The volume of fresh ash is controlled by way of measuring the ash
content in that
area of the paper in which the web is being wound to a roll.
[0014] The retention of the fiber web in the wire section is controlled in
that the amount of
retention agent is added according to the stock consistency measured in the
wire water and the
headbox. It has been demonstrated that a retention control results in an
improved constancy of
the fiber web characteristics, for example the stock consistency or the sheet
characteristics. It
also has an advantageous effect upon the runnability of the paper machine - or
in other words its
efficiency - and upon the paper quality.
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100151 What is needed in the art is to optimize the process of producing a
fiber web from a
loaded fibrous stock suspension.
SUMMARY OF THE INVENTION
[0016] The present invention provides a method wherein the ash content in the
fiber web
which is being produced from the fibrous stock suspension is measured during
the production of
said fiber web and wherein the addition of the precipitation product into the
fibrous stock
suspension entering the headbox is controlled, based on the measured ash
content in the fiber
web.
[0017] According to an embodiment of the present invention, the ash content in
a first fiber-
containing fibrous stock suspension which is being supplied to the machine is
controlled by
mixing, according to a measured value from the first fiber-containing fibrous
stock suspension,
the first fiber-containing fibrous stock suspension and a second fiber-
containing fibrous stock
suspension including a second plurality of fibers which at least essentially
does not include the
precipitation product, subsequently supplying to the headbox a mixture of the
first fiber-
containing fibrous stock suspension and the second fiber-containing fibrous
stock suspension.
[0018] It is also especially advantageous if the ash content in the fibrous
stock suspension
being supplied to the machine is controlled in the first fibrous stock
suspension through metering
of a first substance which is to be precipitated and a second substance which
causes the
precipitation reaction, thereby creating the precipitation product in the
first fibrous stock
suspension.
[0019] Calcium carbonate is an advantageous precipitation product which is
precipitated from
calcium hydroxide by way of carbon dioxide.
[0020] It is also advantageous if the ph-value of the first fibrous stock
suspension is controlled
during the precipitation in the reactor while producing the precipitation
product.
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[0021] Here it is advantageous if each pH value is compared with a
corresponding desired
value and the deviation is reduced or removed through at least one of the
following process
regulated conditions: dwell time of the fibrous stock reaction in the reactor,
infeed speed of the
fibrous stock suspension, pressure of the carbon dioxide, temperature of the
fibrous stock
suspension and/or the calcium hydroxide, pressure in the reactor, temperature
and/or pressure of
the carbon dioxide, concentration of the carbon dioxide in the liquid phase,
concentration of the
calcium hydroxide and the fibers, by way of a specific fiber surface.
[0022] A machine according to the present invention is characterized in that a
measuring
arrangement to measure the ash content is located in the machine, especially
in the wire section,
the press section, the dryer section or after the dryer section before a
calender, wherein said
measuring arrangement is connected via a signal line with a controller which
is located in a
device for the production of a fibrous stock suspension. The machine therefore
includes a
controller or regulator to adjust or control the ash content in the fiber web
which is being
produced from the fibrous stock suspension, which is located in the area of
the paper machine
after the headbox.
[00231 The present invention ensures constant processes for the production of
a fiber web,
leading to an increase in quality and efficiency. A metered addition of fresh
ash is no longer
necessary. Retention agents are being saved and the ash content which was
brought into the
fibrous stock suspension by way of the fiber loading process can be maximized
by regulating
said content through direct adjustment or control. This simplifies the overall
process and again
clearly reduces that component of ash which is not adhered to the fibers.
[0024] The regulating variable in the fiber loading process for controlling of
the ash content in
the paper is the metered addition of the calcium hydroxide component. Also, in
order to control
the degree of conversion of the Fiber Loading Reaction by way of regulating
the pH value and
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through the metered addition of the carbon dioxide the conversion of the milk
of lime into
calcium carbonate must also be verified. This, in combination with a retention
control leads to a
high stability of the processes, in other words a high stability in the fiber
loading process and the
paper manufacturing process. The ash content in the fibrous stock which is
loaded with calcium
carbonate amounts to between 0.05 and 60%, preferably between 1 and 40%.
BRIEF DESCRIPTION OF THE DRAWINGS
[0025] The above-mentioned and other features and advantages of this
invention, and the
manner of attaining them, will become more apparent and the invention will be
better understood
by reference to the following description of embodiments of the invention
taken in conjunction
with the accompanying drawings, wherein:
[0026] Fig. 1 is a schematic drawing illustrating a device for loading fibers
which are
contained in a fibrous stock suspension with a filler by way of a chemical
precipitation reaction,
with a pump disperger;
[0027] Fig. 2 is an illustration of the pump disperger according to Fig. 1, in
direction of the
arrows A;
[0028] Fig. 3 is an illustration of a machine for producing a fiber web, shown
in a simplified
illustration; and
[0029] Fig. 4 is a schematic of the control arrangement.
[0030] Corresponding reference characters indicate corresponding parts
throughout the several
views. The exemplifications set out herein illustrate one embodiment of the
invention, and such
exemplifications are not to be construed as limiting the scope of the
invention in any manner.
DETAILED DESCRIPTION OF THE INVENTION
[0031] Referring now to the drawings, and more particularly to Fig. 1, there
is shown a fiber
stock suspension being supplied in a device 10 (Fig. 1), to a pump disperger,
that is a pump
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fluffer 12, where it is treated by shear forces in order to break down the
fiber material into
individual fibers, exposing the fiber surfaces and increasing the contact
surfaces accordingly.
The pump disperger 12 is simultaneously utilized as a reactor for the chemical
precipitation
reaction. It can specifically be designed so that a reduction of the fibrous
suspension's flow
speed occurs in a reduction channel 14. In the present example it is designed
so that the fibrous
stock suspension is generally transported in radial direction toward the
outside, originating from
a central, radial inner area. A static mixer may be utilized in place of
and/or in conjunction with
the pump disperger 12.
[0032] The reaction channel 14 of the pump disperger 12 is restricted at least
partially by
structured surfaces which can be formed for example by bar or knife sets. The
reaction channel
14 is formed between two plates 16 which are located opposite each other and
which have
structured surfaces between which the fibrous stock suspension is transported
in radial direction
towards the outside.
[0033] A plug screw 18 is located prior to the pump disperger 12, in order to
compress the
fibrous suspension by forming a plug. The plug screwl8 is preceded by an
infeed screw 20
which is located in an at least essentially cylindrical channel or housing 22.
The channel 22 is
equipped with a connection 24 for admitting a mixture which consists for
example of at least the
fibrous stock suspension, water and calcium oxide and/or calcium hydroxide.
[0034] The plug screw 18 is located rotating in a cone-shaped channel 26 whose
cross section
tapers in the direction of the stock flow S, in order to compress the fibrous
suspension by way of
forming a plug in a channel 28 that links up with the plug screw 18,
immediately before the
pump disperger 12. This channel 28 which is located immediately before the
pump disperger 12
is equipped with a feed screw 30 and is equipped with a connection 32 for the
immediate supply
of carbon dioxide into the fibrous stock suspension which is no longer liquid,
but which is still
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moist. The screws 18, 20, 30 either share a common drive shaft 34, or they can
be driven
separately, at least partially. A swirl cross 36 which is located in the
center of the plug screw 18
serves to loosen the plug and the surfaces of the fiber material will be
accordingly enlarged. The
structured surfaces of the plates 16 that are located opposite each other
produce shear forces in
the fiber stock, causing enlargement of the contact surfaces of the carbon
dioxide which is
reacting with the calcium hydroxide that is attached on the fibers, thereby
ensuring a speedy and
efficient reaction.
[0035] The pump disperger 12 is equipped with an outlet 38 for the thickened
loaded fibrous
suspension which is located at least essentially tangential to the plates 16.
A carbon dioxide
supply line may also be provided as an option in this area for the purpose of
adjusting the desired
pH value.
[0036] In addition, the pump disperger 12 may be equipped with an inlet 40
that is located at
least essentially tangential to the plates 16 for the purpose of diluting the
loaded stock with water
and/or calcium hydroxide - especially stock from an upstream stock thickening
unit - to less than
6%, preferably 3% to 6%. Appropriate thinning will render the stock again
pumpable.
[0037] The fibrous suspension is produced, for example, by dissolving pulp or
waste paper
with additives in a pulper 42, or is supplied to the loading process as non-
dried fiber stock.
[0038] Subsequently calcium oxide or calcium hydroxide are added - the latter
in dry or liquid
form - in an area 44 and are mixed thoroughly into the fibrous stock
suspension. The fibrous
stock suspension is then thickened by way of dewatering in an area 46 to such
an extent as to
create a pulp that is still moist. This creates a fibrous stock suspension
which is no longer liquid,
but still moist.
[0039] The fibrous stock suspension is then routed from the area 46 into the
pump disperger 12
where the carbon dioxide is supplied.
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[0040] The device depicted in Figs. 1 and 2 for loading fibers which are
contained in a fibrous
stock suspension with a filler depict merely one possible arrangement from a
plurality of possible
devices. Additional devices with exemplary characteristics are known, for
example, from the
already mentioned German disclosure documents DE 100 33 979 Al and DE 102 04
254 Al,
wherein the German patent application "FL-high ash content" by the applicant
whose reference
is HPP11846 DE also describes a possible device.
[0041] Inside a machine 48 (Fig. 3) for the production of a fiber web 50,
which is located
adjacent to the area for the stock preparation illustrated in Figs. 1 and 2
and which includes a
headbox 52, a wire section 54, a press section 56, a dryer section 58, an
applicator unit 60 for the
application of adhesive, as well as calenders 62, 64 and a winder 66, a
measuring arrangement 68
is provided for on-line measuring of the ash content in the fiber web 50. Said
measuring
arrangement is located either in the wire section 54, in the press section 56
or in the dryer section
58 or following said dryer section, for example before the calender 64.
Installation of the
measuring arrangement 68 in the dryer section 58 is particularly advantageous.
The measuring
arrangement 68 is connected via a signal line 70 to a controller 72 (Fig. 4)
which is mounted
inside device 10 or following said device in order to regulate the composition
of the fibrous stock
suspension
[0042] The measuring arrangement measures- for example optically - the ash
content of the
fiber web 50 as a controlled variable and from this creates a signal value
that it supplied to the
controller 72. Said controller for its part produces signal values for the
addition of calcium oxide
or calcium hydroxide 74, for the associated stoichiometric carbon dioxide
addition 76, for the
addition of dilution water 78 and for the addition of additional chemicals 80,
for example a
retention agent in an area 82 which is located either inside the reactor for
the production of the
fibrous stock suspension containing loaded fibers, or located following the
reactor.
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[0043] The controller 72 also controls - if present - the addition of a
fibrous stock suspension
supplied from another apparatus via a line 84 through a valve 86 whose fibers
are not loaded
with calcium carbonate in order to reduce or increase the content of fibrous
stock suspension
containing loaded fibers which is supplied via a line 88 to the headbox 52.
[0044] 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.
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Component Identification
Device
12 Pump Fluffer
14 Reaction channel
16 Plates
18 Plug screw
Infeed screw
22 Channel or housing
24 Connection
26 Channel
28 Channel
Feeding screw
32 Connection
34 Drive shaft
36 Swirl cross
38 Outlet
Inlet
42 Pulper
44 Area
46 Area
48 Machine for the production of a fiber web
Fiber web
52 Headbox
54 Wire section
56 Press section
58 Dryer section
Applicator unit
62 Calender
64 Calender
66 Winder
68 Measuring arrangement
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70 Signal line
72 Controller
74 Addition of calcium oxide or calcium
hydroxide
76 Carbon dioxide addition
78 Addition of dilution water
80 Addition of additional chemicals
82 Area
84 Line
86 Valve
88 Line
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