Note: Descriptions are shown in the official language in which they were submitted.
P19299.501
CA 02312301 2000-06-20
The present application claims priority under 35 U.S.C. ~ 119 of German Patent
Application No. 199 28 488.1, filed on June 22, 1999, the disclosure of which
is expressly
incorporated by reference herein in its entirety.
1. Field of the Invention
The invention relates to a process for the metered dilution of fibrous
material suspension
in or in front of a material intake of a paper machine. The metered diluting
water is fed into the
fibrous material suspension at a plurality of metering points, and the
diluting water is derived from
the backwater accumulating at a pulp concentration.
2. piccussion of Background Information
In paper production, it is known for processes of the type generally discussed
above to be
used in order to exert a controlled influence on the operation of a material
intake. In particular,
with the metered addition of diluting water at a plurality of points in the
material intake, it is
possible to modify the consistency of the fibrous material suspension
contained therein and/or its
speed of flow. As these procedures are generally known, they do not require
description in greater
detail. The diluting water required by this process can contain fibers or
other solid matter only
to a very limited degree, since disturbances will otherwise occur in the
relatively sensitive
metering devices. Furthermore, the outcome, which is to bring about a local
dilution, is greatest
when the water is clearest.
While the use of fresh water for this purpose would be technically
advantageous, it is
impractical due to the level of fresh water consumption. Instead, it is
therefore customary to use
backwater which accumulates in the paper machine. The backwater is often
thoroughly purified
of fibers and other solids with separating processes suitable to this end,
e.g., microflotation or disk
filters. This kind of filtrate, which arises in large quantities, is also
highly suitable as diluting
water for the described application, but comes at the price of the additional
expense. The
unfiltered backwater can be used with the fibrous material and fine matter
contained in it, but in
order to ascertain that the diluting water does not then contain disruptive
parts, it must, as a rule,
be purified once more in a sorting machine ("police filter").
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The present invention provides a process with which diluting water can be made
available
for the above-noted purpose and in a particularly economical fashion.
In particular, the process includes treating the backwater in a filter device,
and drawing off
a cloudy filtrate that arises for use as diluting water.
The process according to the invention offers a very economical solution to
the problem
of preparing the required diluting water. It is known that backwater
accumulating at a pulp
concentration, e.g., in the wet section of the paper machine, contains a
certain portion of fibers,
fillers, and chemicals. In many modern paper factories, at least a large part
of the backwater
accumulating in the paper machine is clarified and returned as clear water at
various points in the
production circuit.
The clarification of backwater is advantageously performed with disk filters.
These
devices are known in a number of applications, e.g., DE 38 29 177 Al, in which
both primary (or
cloudy) filtrate and clear filtrate accumulates. As is known, with the
addition of a suitable
adjuvant, a filter cake forms in disk filters which is suitable for retaining
solids contained in the
backwater. Thus, a filter process is fundamentally different from a screening
process. In the
beginning portion of a disk filter, i.e., at the place where a filter cake has
not yet been able to form,
the portion of fibers and fine material in the filtrate is relatively high.
Therefore, this so-called
"cloudy filtrate" must be returned to the filtration process so as not to
lower the quality of the clear
filtrate. Moreover, if the cloudy filtrate is separately withdrawn and fed to
the material intake as
diluting water, the operation of the disk filter is substantially relieved,
without disadvantages
arising.
The present invention is directed to a process for metered dilution of fibrous
material
suspension in an apparatus including a material intake. The process includes
treating a portion
of backwater drained from the fibrous material suspension in a filter device,
drawing off a cloudy
filtrate arising in the filter device, forming diluting water from the cloudy
filtrate, and metering
the diluting water into the fibrous material suspension at a plurality of
metering points in the
material intake.
In accordance with a feature of the invention, the fibrous material suspension
may be
utilized in a paper machine.
According to another feature of the present invention, the filter device can
include a disk
filter with at least one filter disk divided into segments.
In accordance with another feature of the instant invention, the filter device
may include
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P19299.S01 CA 02312301 2000-o6-Zo
a filter press.
Further, the portion of the backwater to be treated in the filter device can
be composed of
backwater from the material intake. Further, the portion of the backwater to
be treated can include
second backwater of the apparatus. Still further, at least another portion of
the backwater can be
supplied to the fibrous material suspension.
In accordance with still another feature of the present invention, the cloudy
filtrate may
include a solid material content between about 100 ppm and S00 ppm. The at
least a portion of
the backwater to be treated in the filter device can have a solid material
content which is at least
about twice the solid material content of the cloudy filtrate.
According to an aspect of the invention, the at least a portion of the
backwater to be treated
in the filter device may have a solid material content of at least about 600
ppm.
Moreover, the at least a portion of the backwater may include a second
backwater which
is accumulated downstream, relative to a wire travel direction, of a first
backwater, which
comprises at least another portion of the backwater. Further, the process may
include supplying
the first backwater to a fibrous material supply. Also, the process can
include mixing the first
backwater with thick matter to form the fibrous material suspension, and
supplying the fibrous
material suspension to the material intake. The fibrous material suspension
fed to the material
intake may have a solids content of approximately 3.5% by wt. Still further,
the first backwater
may have a solids content of approximately 5000 ppm, and the second backwater
has a solids
content of approximately 2500 ppm.
According to a still further feature of the instant invention, the process can
include
supplying clear water to other portions of the apparatus. The clear water may
have a solids
content of approximately 50 ppm.
The cloudy filtrate can be formed at a beginning of a filtration process.
Further, the cloudy
filtrate may have a solids content of between approximately 100 and 500 ppm.
The filter device may form a filter cake, and, before the filter cake is
completely formed,
the cloudy filtrate can be produced. After the filter cake is completely
formed, the clear filtrate
can be produced.
The present invention is also directed to an apparatus for metered dilution of
a fibrous
material suspension. The apparatus includes a material intake, a plurality of
metering points
coupled to the material intake, a fibrous material suspension supply coupled
to the material intake,
and a filter device coupled to receive a portion of backwater drained from the
fibrous material
suspension. In this manner, a cloudy filtrate is produced. The apparatus also
includes a device
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CA 02312301 2000-06-20
to supply the cloudy filtrate to the plurality of metering points as diluting
water.
In accordance with a feature of the invention, the filter device can include a
disk filter with
at least one segmented filter disk.
According to another feature of the present invention, the filter device can
include a filter
press.
In accordance with still another feature of the instant invention, another
portion of the
backwater can include a first backwater, and the portion of the backwater can
include a second
backwater which is accumulated downstream, relative to a wire travel
direction, of the first
backwater. The apparatus may further include a device for supplying the first
backwater to the
fibrous material suspension. The device for supplying the first backwater can
include a mixing
device adapted to mix the first backwater with thick matter, whereby the
fibrous material
suspension is formed.
According to yet another feature of the invention, the apparatus can include a
device for
supplying a clear filtrate from the filter device to other portions of the
apparatus.
1 S Other exemplary embodiments and advantages of the present invention may be
ascertained
by reviewing the present disclosure and the accompanying drawing.
The present invention is further described in the detailed description which
follows, in
reference to a drawing by way of a non-limiting example of an exemplary
embodiment of the
present invention, and wherein:
The Figure schematically illustrates an exemplary embodiment of the process in
accordance with the instant invention.
The particulars shown herein are by way of example and for purposes of
illustrative
discussion of the embodiments of the present invention only and are presented
in the cause of
providing what is believed to be the most useful and readily understood
description of the
principles and conceptual aspects of the present invention. In this regard, no
attempt is made to
show structural details of the present invention in more detail than is
necessary for the
fundamental understanding of the present invention, the description taken with
the drawings
making apparent to those skilled in the art how the several forms of the
present invention may be
embodied in practice.
While the Figure illustrates a part of a paper machine 3 with a material
intake 1, it is noted
that the process of the instant invention is not limited to any specific type
of paper machine.
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However, paper machine 3 should include material intake 1 which is fed with a
fibrous material
suspension S that can be mixed in metered fashion with diluting water W via a
plurality of
metering points 2. After fibrous material suspension S has left material
intake 1, it is immediately
dewatered on the paper machine wire. In particular, a part of the water
contained therein passes
S through the paper machine wire as backwater, while the greatest portion of
the paper fibers
remains on the wire together with residual water and other materials, and is
transported away. In
the example shown here, two backwater qualities are separately handled,
specifically a first
backwater SW1 and a second backwater SW2. First backwater SW1 contains much
more solid
matter (e.g., fibers, fillers, etc.) than second backwater SW2.
The differences between the qualities of backwaters SW 1 (primary or cloudy
filtrate) and
SW2 (clear filtrate) have already been explained. The fibrous material
suspension S fed to the
material intake 1 is formed in a mixing pump 8 by mixing thick matter SO with
first backwater
SW1. A suspension formed in this way is generally known, and other similar
methods of are
conceivable. Second backwater SW2 can be introduced to a filter device 4.
1 S Filter device 4 can be, e.g., a disk filter, which may be particularly
suited for
implementation of the process. It is noted that the depiction of the exemplary
embodiment is
purely schematic and is intended to show only those functions that this disk
filter fulfills insofar
as they are important for the process according to the invention. Positioned
in a suspension
housing 6 is a rotor with at least one rotating filter disk 10. The filter
disk is divided into a
number of segments 5, which absorb the filtrate absorbed during filtering. The
filter area of
segments 5 mainly include a wire mesh, which becomes covered with fibrous
material and other
fine material by immersion in the suspension, i.e., second backwater SW2.
As already mentioned, at the beginning of the filtration process, while a
filter cake is either
not present or incomplete, an initial filtrate, i.e., cloudy filtrate TF, is
obtained, which differs from
clear filtrate KF that arises later in the filtration process, i.e., after the
formation of the filter cake,
in that it has a greater portion of solid particles and fibers. In order to
remove both filtrates
separately, i.e., cloudy filtrate TF and clear filtrate KF, a control head 7
is fixed in position in the
center of the rotor. The filter cake positioned in the region of segments 5 is
removed from this
region as a coarse fraction GF before segments 5 are again immersed in the
suspension being
filtered. The technical design of such disk filters is known and does not need
to be further
described. Whereas clear filtrate KF is normally used as clear water at
different points in the
paper factory, cloudy filtrate TF according to the invention can be supplied
to material intake 1
as diluting water W. A pump 9 can be employed to facilitate supplying cloudy
filtrate TF to
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material intake 1.
CA 02312301 2000-06-20
In an example of the process according to the exemplary embodiment, the
following solid
contents were measured:
15' backwater SW1: about 5000 ppm
2"d backwater SW2: about 2500 ppm
cloudy filtrate TF: about 300 ppm
clear filtrate KF: about SO ppm
fibrous material suspension S: about 3.5% by wt.
It is noted that the foregoing examples have been provided merely for the
purpose of
explanation and are in no way to be construed as limiting of the present
invention. While the
present invention has been described with reference to an exemplary
embodiment, it is understood
that the words which have been used herein are words of description and
illustration, rather than
words of limitation. Changes may be made, within the purview of the appended
claims, as
presently stated and as amended, without departing from the scope and spirit
of the present
invention in its aspects. Although the present invention has been described
herein with reference
to particular means, materials and embodiments, the present invention is not
intended to be limited
to the particulars disclosed herein; rather, the present invention extends to
all functionally
equivalent structures, methods and uses, such as are within the scope of the
appended claims.
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