U.S. patent application number 09/810672 was filed with the patent office on 2001-08-02 for process and flotation device for the removal of intereering materials from an aqueous fiber pulp suspension.
This patent application is currently assigned to VOITH SULZER PAPIERTECHNIK PATENT GmbH. Invention is credited to Britz, Herbert, Gommel, Axel, Holik, Herbert, Kemper, Martin, Kriebel, Almut, Mannes, Wolfgang, Reinholdt, Boris, Steinbild, Klaus.
Application Number | 20010010294 09/810672 |
Document ID | / |
Family ID | 7835879 |
Filed Date | 2001-08-02 |
United States Patent
Application |
20010010294 |
Kind Code |
A1 |
Britz, Herbert ; et
al. |
August 2, 2001 |
Process and flotation device for the removal of intereering
materials from an aqueous fiber pulp suspension
Abstract
The process is designed for the flotation of interfering
materials from an aqueous fibrous pulp suspension and is in
particular used in the processing of printed or used paper that is
otherwise contaminated. The separation of gas bubbles of the
suspension occurs in a flotation layer that has a maximum thickness
of approximately 100 mm. The process also achieves good flotation
results in fibrous pulp suspensions that have a fiber pulp content
significantly larger than 1 % by weight, for example around 2% by
weight. A flotation apparatus is provided for performing the
flotation process. The apparatus includes a flotation vessel, an
inlet, an outlet, and a skimmer device.
Inventors: |
Britz, Herbert; (Ravensburg
Weissenau, DE) ; Gommel, Axel; (Ravensburg, DE)
; Holik, Herbert; (Ravensburg, DE) ; Kemper,
Martin; (Ravensburg, DE) ; Kriebel, Almut;
(Weingarten, DE) ; Mannes, Wolfgang;
(Ravensburg-Bavendorf, DE) ; Reinholdt, Boris;
(Waldburg, DE) ; Steinbild, Klaus; (Ravensburg,
DE) |
Correspondence
Address: |
GREENBLUM & BERNSTEIN
1941 ROLAND CLARKE PLACE
RESTON
VA
20191
|
Assignee: |
VOITH SULZER PAPIERTECHNIK PATENT
GmbH
Heikenheim
DE
|
Family ID: |
7835879 |
Appl. No.: |
09/810672 |
Filed: |
March 19, 2001 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
09810672 |
Mar 19, 2001 |
|
|
|
08115672 |
Sep 2, 1993 |
|
|
|
Current U.S.
Class: |
209/165 ;
209/164 |
Current CPC
Class: |
B03D 1/1425 20130101;
D21B 1/327 20130101; B03D 1/1462 20130101; D21F 1/70 20130101; B03D
1/1493 20130101; B03D 1/02 20130101; B03D 1/16 20130101; Y02W 30/64
20150501; B03D 1/24 20130101; Y02W 30/646 20150501; B03D 1/1418
20130101 |
Class at
Publication: |
209/165 ;
209/164 |
International
Class: |
B03D 001/24 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 16, 1997 |
DE |
197304648 |
Claims
What is claimed:
1. A process for removal of interfering materials from an aqueous
fibrous pulp suspension, comprising: generating gas bubbles;
collecting the interfering materials by use of the gas bubbles; and
removing the interfering materials with a flotation foam, wherein
the fibrous pulp suspension and the gas bubbles are introduced into
a flotation layer having a maximum thickness of approximately 100
mm so as to separate the gas bubbles and the fibrous pulp
suspension, and wherein the gas bubbles are admixed with the
fibrous pulp suspension before the fibrous pulp suspension enters
the flotation layer.
2. A process in accordance with claim 1, wherein the flotation
layer has a maximum thickness of approximately 50 mm.
3. A process in accordance with claim 1, wherein the gas bubbles
are mainly air bubbles.
4. A process in accordance with claim 1, wherein the gas bubbles
are provided by a gas that is lighter than air.
5. A process in accordance with claim 1, wherein the fibrous pulp
suspension has a fiber pulp content of at least approximately 2% by
weight in the flotation layer.
6. A process in accordance with claim 1, including diluting the
fibrous pulp suspension after addition of the gas bubbles and
transformation into the flotation layer.
7. A process in accordance with claim 1, wherein the gas bubbles
are of different sizes and are added to the flotation layer,
whereby bubble size varies in a direction of flow of the
suspension.
8. A process in accordance with claim 1, including adding gas
bubbles of different sizes to the flotation layer, whereby the size
varies in a rising direction of the gas bubbles.
9. A process in accordance with claim 1, further comprising:
creating a local turbulence in a separation region of the flotation
layer, the separation region being between the suspension and the
flotation foam.
10. A process in accordance with claim 1, wherein the flotation
layer extends at least approximately 150 mm in a flow direction of
the flotation layer.
11. A process in accordance with claim 1, including subjecting the
fibrous pulp suspension to an initial processing in which the
fibrous pulp suspension is fed at a height that is greater than a
thickness of the flotation layer.
12. A process in accordance with claim 11, wherein the flotation
layer extends in the direction of flow to a length of between
approximately 1 mm and approximately 500 mm.
13. A process in accordance with claim 11, including creating
micro-turbulence in the fibrous pulp suspension before the initial
processing.
14. A process in accordance with claim 11, wherein the fibrous pulp
suspension is accelerated to at least twice an average flow
velocity during the entry into the flotation layer.
15. A process in accordance with claim 1, wherein a cleaned
suspension is diverted immediately down-stream of the flotation
layer.
16. A process in accordance with claim 1, wherein the separation
takes place in a gravity field that is greater than Earth's
gravity.
17. A process in accordance with claim 16, wherein the separation
is executed in a flotation cyclone.
18. A process in accordance with claim 17, wherein a portion of the
gas bubbles is added to the suspension before entry into the
flotation cyclone and remaining portion of the gas bubbles is added
afterward.
19. A process in accordance with claim 17, wherein the separation
is executed in a centrifuge.
20. A process for removal of interfering materials from an aqueous
fibrous pulp suspension, comprising: generating gas bubbles;
collecting the interfering materials by use of the gas bubbles; and
removing the interfering materials with a flotation foam; wherein
the fibrous pulp suspension and the gas bubbles are introduced into
a flotation layer so as to separate the gas bubbles and the fibrous
pulp suspension, and wherein vibrations are transmitted to the
flotation layer.
21. A process in accordance with claim 20, wherein the vibrations
are transmitted by shaking at least part of a flotation element
that is in contact with the flotation layer.
22. A process in accordance with claim 20, wherein the vibrations
are transmitted to the fibrous pulp suspension by an agitating
element.
23. A process in accordance with claim 20, wherein the vibrations
are transmitted to the fibrous pulp suspension by hydraulic
impulses.
24. A process in accordance with claim 20, wherein the vibrations
are transmitted to the fibrous pulp suspension by pneumatic
impulses.
25. A process in accordance with claim 24, including applying the
pneumatic impulses to a gas provided to supply the gas bubbles.
26. A flotation apparatus, comprising: a flotation vessel which
receives a fibrous pulp suspension to be cleaned; an inlet for
receiving the suspension; an outlet for discharging cleaned fibrous
pulp suspension; and a skimmer element for separation of flotation
foam from the suspension, wherein the skimmer element separates a
flotation chamber receiving the fibrous pulp suspension by setting
a filling height that does not exceed approximately 100 mm.
27. A flotation device in accordance with claim 26, wherein the
flotation chamber is substantially planar.
28. A flotation device in accordance with claim 26, wherein the
flotation chamber has a corrugated bottom wall, corrugations of the
wall extend perpendicular to a flow direction of the fibrous pulp
suspension.
29. A flotation device in accordance with claim 28, wherein gas
supply pipes are located on the corrugated bottom wall so as to add
gas bubbles to parts of flotation layers of the fibrous pulp
suspension, the gas bubbles being added to the flotation layers
having a predetermined depth.
30. A flotation device in accordance with claim 26, wherein the
flotation chamber is inclined towards the skimmer device for the
flotation foam.
31. A flotation device in accordance with claim 26, wherein a gas
supply box extends along the flotation chamber at least over a
portion of a flow path of the suspension.
32. A flotation device in accordance with claim 31, wherein a wall
having a number of openings is positioned between the gas supply
box and the flotation chamber.
33. A flotation device in accordance with claim 32, wherein the
wall is a perforated plate.
34. A flotation device in accordance with claim 32, wherein the
wall is a flexible fabric.
35. A flotation device in accordance with claim 31, wherein an air
supply is connected to the gas supply box to feed a pulsating flow
of gas to the fibrous pulp suspension.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] The present application is a continuation of U.S. patent
application Ser. No. 08/115,672 filed Jul. 15, 1998, which claims
the priority under 35 U.S.C. 119 of German Patent Application No.
197 30 464.8, filed on Jul. 16, 1997, the disclosures of which are
expressly incorporated by reference herein in their entireties.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The invention relates to a process and apparatus for the
removal of interfering materials from an aqueous fiber pulp
suspension.
[0004] 2. Discussion of Background Information
[0005] Processes of the aforementioned type are used in order to
remove at least a portion of the interfering pulp particles
suspended in a fibrous pulp suspension containing fiber pulp. It is
common knowledge that a foam or floating slurry, containing the
material to be removed, is created in a flotation process. A
typical case of application of such a process is the processing of
aqueous fibrous pulp suspensions that are produced from printed
used paper, whereby the ink is already dissolved from the fibers so
that it can be floated out. The flotation process described here
utilizes the differences between the fibrous pulp and the
undesirable solid particles such that the fibrous pulp, due to its
hydrophilic nature remains in the fibrous pulp suspension, while
the described solid particles exhibit hydrophobic behavior and
therefore end up with the air bubbles in the foam. Aside from the
ink particles there are also a large number of additional materials
that are hydrophobic and are able to be separated from the fibrous
pulp by flotation. Such materials are in particular adhesives, fine
synthetic material particles, and possibly also resins. When the
fibers are to be separated from contamination, i.e. not all solid
particles are to be sorted out, a selective flotation process is
performed. The term "flotation de-inking", also used, is generally
not only used for the removal process of ink particles, but also
used in a more general sense for the selective flotation of
contamination of fibrous pulp suspensions.
[0006] The state of the art in regards to flotation processes for
fibrous pulp suspensions is already at a very advanced state. There
are thus solutions which are quite suitable in removing a large
portion of the solid particles by flotation. However, the effect
weakens when the amount of fibers in the suspension is relatively
high, for example 2 %, instead of the conventional amount of around
or below 1 %. In such cases problems often occur since the
resistance for the gas bubbles is already high with a higher fiber
content, thereby making it difficult to separate the suspension.
Higher pulp densities, on the other hand, are desirable in order
achieve a higher throughput.
SUMMARY OF THE INVENTION
[0007] The aim of the invention is therefore to create a flotation
process in which good cleaning results can be achieved even when
the suspension for such processes has a relatively high fibrous
pulp content.
[0008] By the present invention, the difficulties, caused by the
high viscosity of the suspension, can be overcome. The gas bubbles,
loaded with interfering materials, have an increased resistance
while reaching from the suspension into the flotation foam by
following their tendency to rise. However, because of the fact that
the flotation process is executed with a relatively thin flotation
layer, the gas bubbles only have to travel a very short distance.
In embodiments of the process in accordance with the invention, the
gas bubbles' tendency to rise can be enhanced by applying a gravity
field which is greater than earth's gravity. Another possibility
makes provisions to accelerate the rise of the gas bubbles with the
aid of impulses or vibrations.
[0009] Thus, an aspect of the invention is to provide a process for
removing interfering materials from a fibrous pulp suspension by
generating air bubbles in the form of a gas, collecting the
interfering materials by using the gas bubbles, and removing the
interfering materials with a flotation foam. The fibrous pulp
suspension and the gas bubbles are introduced into a flotation
layer having a maximum thickness of approximately 100 mm so as to
separate the gas bubbles and the fibrous pulp suspension.
[0010] Another aspect of the process is to provide a flotation
layer with a thickness of approximately 50 mm.
[0011] A feature of the process is to provide the gas bubbles as
air bubbles, in the alternative, the bubbles may be provided by a
gas that is lighter than air.
[0012] Another feature of the process is to directly add the gas
bubbles to the flotation layer of the suspension and to admix the
bubbles prior to the time the fibrous pulp suspension enters the
flotation layer.
[0013] Another aspect is to transmit vibrations to the flotation
layer and to transmit the vibrations by shaking at least a part of
the flotation element that is in contact with the flotation layer.
Another feature is to transmit the vibrations by using an agitating
element, or hydraulic and/or pneumatic impulses.
[0014] Another concept of the process is to clean a fibrous pulp
suspension that has fiber pulp content of approximately 2% by
weight in the flotation layer and to dilute the pulp suspension
after the addition of the bubbles and transform the suspension in
the flotation layer and to add bubbles of different sizes to the
flotation layer so that the bubble size varies in the direction of
flow of the suspension. A feature is to also vary the size of the
bubbles in a rising direction of the bubbles.
[0015] Another feature is to create a local turbulence in a
separation region of the flotation layer, the separation region
being between the suspension and the flotation foam.
[0016] A further aspect of the process is to provide a flotation
procedure wherein the flotation layer extends approximately 150 mm
in a flow direction of the flotation layer.
[0017] A feature of the invention is to subject the suspension to
an initial processing in which the suspension is fed at a height
that is greater that a thickness of the flotation layer and to
provide a flotation layer that extends in its flow direction a
distance of between approximately 1 mm and approximately 500
mm.
[0018] A further feature is to create a micro-turbulence in the
suspension prior to the initial processing and to accelerate the
suspension to at least twice the average flow velocity during the
entry into the flotation layer.
[0019] Another characteristic of the invention is to divert the
cleaned suspension layer immediately downstream of the cleaning
process and to perform the separation in a gravity field that is
greater than earth's gravity while yet another aspect of the
invention is to perform the separation in a flotation cyclone.
[0020] Still a further aspect is to add some of the gas bubbles to
the suspension before entry into the flotation cyclone and add
additional bubbles afterwards and to perform the process in a
centrifuge.
[0021] A feature of the invention is to provide an apparatus in
which the flotation process is performed. The apparatus includes a
flotation vessel which receives the suspension to be cleaned, an
inlet for receiving the suspension and an outlet for discharging
the cleaned suspension. A skimmer element is provided for
separating flotation foam, created in the flotation process, from
the suspension. The skimmer separates a flotation chamber receiving
the suspension by setting a filling height that does not exceed
approximately 100 mm.
[0022] An aspect of the invention is to provide an apparatus for
carrying out the flotation process is also to provide a flotation
chamber that is substantially planar and to provide the chamber
with a corrugated bottom wall so that the corrugations extend
perpendicular to a flow direction of the fibrous pulp suspension
and to supply gas by way of pipes located in the bottom wall so ass
to add gas bubbles to parts of the flotation layers of the fibrous
pulp suspension, the gas bubbles being added to the flotation
layers having a predetermined depth.
[0023] Another aspect is to provide the apparatus with an incline
extending in the direction of the skimmer and to provide the gas
supply box so that it extends along the flotation chamber at least
over a portion of a flow path of the suspension.
[0024] The present invention is directed to a process for removal
of interfering materials from an aqueous fibrous pulp suspension
that includes generating gas bubbles, collecting the interfering
materials by use of the gas bubbles, and removing the interfering
materials with a flotation foam. The fibrous pulp suspension and
the gas bubbles are introduced into a flotation layer having a
maximum thickness of approximately 100 mm so as to separate the gas
bubbles and the fibrous pulp suspension, and the gas bubbles are
admixed with the fibrous pulp suspension before the fibrous pulp
suspension enters the flotation layer.
[0025] The present invention is directed to a process for removal
of interfering materials from an aqueous fibrous pulp suspension
that includes generating gas bubbles, collecting the interfering
materials by use of the gas bubbles, and removing the interfering
materials with a flotation foam. The fibrous pulp suspension and
the gas bubbles are introduced into a flotation layer so as to
separate the gas bubbles and the fibrous pulp suspension, and
vibrations are transmitted to the flotation layer.
[0026] Other features of the invention include providing a wall
with a large number of openings positioned between the gas supply
and the flotation chamber, provide the wall as a perforated plate
or a flexible fabric and to provide an apparatus in which an air
supply is connected to the gas supply so as to feed a pulsating
flow of gas to the suspension.
BRIEF DESCRIPTION OF THE DRAWINGS
[0027] The present invention is further described in the detailed
description which follows, with reference to the noted plurality of
drawings by way of non-limiting examples of preferred embodiments
of the present invention. In the drawings, like reference numerals
represent similar parts throughout the several views of the
drawings, and wherein:
[0028] FIG. 1 is a schematic representation of a flotation device
for carrying out the flotation process in accordance with the
invention;
[0029] FIG. 2 is a schematic perspective illustration of a
variation of the device of FIG. 1;
[0030] FIG. 3 is a side view of another variation of the device of
FIG. 1;
[0031] FIG. 4 is a side view of a further variation of the device
of FIG. 1;
[0032] FIG. 5 is a schematic side view of a centrifugal flotation
device of the invention;
[0033] FIG. 6 is a variation of the device of FIG. 5;
[0034] FIG. 7 is a schematic side view of a flotation cyclone of
the present invention;
[0035] FIG. 8 is a schematic side view of another aspect of the
present invention;
[0036] FIG. 9 is a schematic side view of another flotation device
of the present invention; and
[0037] FIG. 10 is a schematic side view of a further flotation
device of the present invention.
DETAILED DESCRIPTION OF THE INVENTION.
[0038] The particulars shown here 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 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.
[0039] The basic steps of the embodiment of the process in
accordance with the invention are shown in FIG. 1. The fibrous pulp
suspension S is fed into a flotation device. A flotation layer 3
with a thickness d of no more than 100 mm is created in a flotation
vessel 13. This thickness is specified by a dividing or separating
element 7, which is here provided as a height-adjustable foam weir
over which the flotation foam 2, for example, is drained into the
foam gutter 8. The relatively small thickness of the flotation
layer is critical for solving the problem of obtaining good
cleaning results. The dimension should be understood, such that the
stated thickness d can not be larger in the effective flotation
area - here referenced as flotation layer 3. However, this does not
mean that, for example, entirely different conditions can not exist
up-stream. Vessels, for example, in which the suspension is held
can exhibit a depth that goes far beyond this dimension. Such an
embodiment is explained later with the aid of FIG. 8. It is known
that a very large number of gas bubbles, in particular air bubbles,
are required for the flotation process, of which only a few are
illustrated here as gas bubbles 4. The gas bubble ascend through
the flotation and accumulate in the flotation foam 2 that floats on
top of the flotation layer 3 and are afterwards removed as reject R
with the aid of the foam gutter 8. The foam gutter 8 is here
arranged close to the down-stream end of the flotation layer 3.
However, the foam gutter 8 can also be positioned sideways so that
the flotation foam 2 runs off perpendicular to the flow.
[0040] The gas bubbles required for the flotation process can be
admixed in the suspension feed system or, as illustrated here, with
the aid of a gas feed box 5, located below the flotation layer 3.
Gas 4' is added to the gas feed box 5. The gas may be air or a gas
lighter than air, for example, helium or hydrogen. The gas bubbles
may be of the same size or different sizes. An optimal bubble size
depends upon which interfering material is to be separated by
flotation. Generally, the larger particles require larger air
bubbles. The bubble size can be changed by changing the air
velocity in the layer diffuser. It is advantageous to feed the
supplied gas 4' in pressure pulses so that vibrations are created
in the flotation layer 3. When a flexible and perforated wall, for
example an air-permeable fabric, is used between the gas supply box
5 and the flotation chamber 3', such a wall can also vibrate.
Another possibility for the creation of advantageous vibrations can
be, for example, providing for a shaking motion on one or more
walls of the flotation chamber 3'. The gas treatment of the
suspensions through the flotation process is known and can also be
varied. FIG. 2 thus shows a similar device as FIG. 1., for example.
However, in it a number of staggered diffusing devices 6, which
have the function of creating micro-turbulence and, at the same
time, of enabling a very simple gas feed mechanism 4' by injection,
are installed in the inlet region of the suspension S to the
flotation layer 3. In particular, when the flotation thickness is
relatively thin, the turbulence, in particular with pulp densities
around 2%, can loosen up the suspension and promote the ascending
effect of the air bubbles that are mixed with interfering
materials.
[0041] The flotation devices shown in FIG. 1 and 2 have a flotation
vessel 13 that is positioned essentially horizontally. However, it
is easily conceivable to provide a slight incline, in particular in
the direction of the foam gutter 8, in order to improve the foam
drainage. The flotation devices shown in FIG. 3 and 4 are, as an
example, arranged at an incline. However, these two figures show
additional special features. Because the wall of the flotation
vessel 13' is constructed in a corrugated fashion, the flow of the
fibrous pulp suspension S is directed in the flotation chamber 3 in
such a manner that the length of the rising or ascending path of
the gas bubbles 4 is different from one section of the chamber to
the next. It is particularly advantageous to provide for the
transport of the gas 4' with the aid of gas supply pipes 5", which
are each mounted at deep, vertically extended regions of the
corrugated wall. This arrangement provides for an increased time
for the interfering material to attach to the air bubbles, while
permitting a short target time for the separation of the gas
bubbles from the fibrous pulp suspension. The separation can
therefore unfold in a relatively short section, corresponding to
the thickness d. Another improvement can be derived from the
flotation device shown in FIG. 4, wherein the bottom wall is also
corrugated. Several foam gutters 8', arranged sequentially in the
direction of flow, are positioned along the separation line between
the fibrous pulp suspension S and the foam 2. The produced foam can
be removed relatively quickly, utilizing the above-described
advantage of a corrugated bottom wall. The advantages, resulting
from the repeated skimming of the flotation foam 2 by sequentially
arranged foam gutters, are of course also possible in the flotation
devices shown in FIG. 1 or 2.
[0042] Another efficient improvement can be achieved if the
flotation process is executed in a flotation device in which a
force field, critical for the rising or ascending tendency of the
gas bubbles, is strengthened with the aid of centrifugal forces.
Specific possibilities for the utilization of centrifugal forces in
the flotation process are shown in FIGS. 5 to 7. FIG. 5 illustrates
a flotation device with a tangential inlet for the fibrous pulp
suspension S, whereby the tangential inlet initiates a rotational
flow within the flotation vessel 13". The rotational flow can also
be assisted by a rotor 11 (eddy prop). The rotor 11 may strengthen
the rotational movement of the suspension which, without the rotor,
can only be achieved by tangential inflow. The rotor also
contributes to the mixing of the gas bubbles and the suspension and
it provides an energy supply to further the absorption of
interfering materials into the air bubbles. In addition, this rotor
can also be constructed and operated such that the mixing of the
fibrous pulp suspension S with the gas bubbles is promoted; the
attachment of the interfering particles to the air bubbles can be
improved as well. The rotation results in a swirling motion and an
accumulation of the flotation foam 2 on its surface. This also
results in a relatively short rising or ascending paths of the gas
bubbles through the suspension. The produced flotation foam 2
drains toward the exterior and can be removed as reject R. The
cleaned suspension S' in the shown example is here diverted,
radially or tangentially, at the bottom part of the flotation
vessel 11.
[0043] The flotation device shown in FIG. 6 also has a round, for
example cylindrical, flotation vessel 13'". In it, the fibrous pulp
suspension S is added in the bottom region and put into a
rotational flow, which again can be enhanced by a rotor 11. The
suspension extends into the flotation layer 3 above, which is
constructed in the form of a ring that is bound or adhered to the
outside by the flotation vessel 13'" and to the inside by a foam
trough 14. As a result of the rotational motion of the suspension,
the gas bubbles push towards the inside, are transported upwards,
and thus end up in the foam trough 14. The cleaned suspension flows
radially outward into an accepted-pulp ring chamber 15 and is
removed therefrom. The flotation foam 2, that has accumulated in
the foam trough 14 can, for example, be suctioned off as reject
using a foam pipe 16.
[0044] The use of cyclones for the flotation process is generally
known, but in the embodiment shown in FIG. 7 one can use the
advantage already mentioned since the flotation cyclone is
constructed such that the flotation layer 3 remains relatively
thin. The dividing or separating element 7', here constructed as a
ring weir on the foam skimmer that projects over the inner wall of
the flotation cyclone by a distance d1, serves this purpose. Thus,
not only a very short rising or ascending path of the gas bubbles
is made possible for the separation of the foam 2 and the
suspension S, but, due to frictional effects at the edges, results
in a further loosening of the suspension and thereby an improved
rising or ascending speed of the gas bubbles. In a flotation
cyclone, the gas supply can again be provided in different ways,
for example by admixing of gas 4' immediately before entry into the
flotation vessel (illustrated in dashes) or with the aid of a
porous exterior wall of a flotation vessel that is enclosed by a
gas supply box 5. Vibrations can also be produced in the various
ways already mentioned. The solution stated last should be
particularly advantageous with thin flotation layers 3--in
accordance with the invention--and a corresponding high pulp
density in the suspension. In the flotation cyclone shown here, the
suspension is added over one or more staggered diffusion devices 6,
producing a good mixing of the gas bubbles with the suspension and
an improved attachment of interfering material to the gas bubbles.
The turbulence that can be created in such staggered diffusion
devices also favor the separation of gas bubbles and the
suspension.
[0045] In the flotation device illustrated in FIG. 8, the flotation
layer 3 is produced at the outlet of a mixing vessel 9 in a
relatively short flow path. Due to the curvature of the outlet
piece 10, the flotation gravity field is increased by centrifugal
forces. The gravitational force is increased by the centrifugal
force by a multiple number of times, for example, up to
approximately 10 g and even 20 g or 30 g. A mixing zone is
preferably provided up-stream, i.e. in front of the flotation
section 3, wherein a good mixing of air and fibrous pulp suspension
and an intensive attachment of the interfering materials to the gas
bubbles is achieved at the same time with the aid of a mixing
device 11. The mixing device 11 can either be a mixer or a
stationary element. An initial separation of gas bubbles and
suspension can take place within the mixing vessel 9. The boundary
12 between the suspension S' and the flotation foam 2 is indicated
with a dashed, curved line in the figure. The dividing or
separating element 7" which is constructed as an adjustable
rotating weir.
[0046] FIG. 9 and 10 show flotation devices in which the processes
are varied further. The fibrous pulp suspension S in both examples
is first fed to an initial flotation process 1 and then reaches the
flotation layer 3, described previously. With the aid of this
combination, a maximum separation effect in a single flotation
device is achieved. A portion of the interfering materials migrate
into the flotation foam 2 in the region of the initial flotation
process 1, in particular that portion that can be floated out
particularly quickly. The other portion of interfering materials
that have to be floated out under particularly favorable conditions
is extracted afterwards from the flotation layer 3. Thus, it is
advantageous that the contamination concentration is already
lowered significantly due to the initial flotation process. In
particular with the use of an initial flotation process, it is
advantageous to feed the fibrous pulp suspension S into the
flotation vessel via a turbulence-producing device, such as a
staggered diffusion device 6. The reason for this is that the
micro-turbulence created thereby can significantly improve the
spontaneous flotation process.
[0047] In the majority of cases it is advantageous that the fibrous
pulp suspension S is accelerated in the transition from the initial
flotation process 1 to the flotation layer 3. The reason for this
is that the shear forces caused by the acceleration assist in
loosening of the fibrous pulp, which can be important with pulp
densities that lie significantly above 1 %. The acceleration can be
achieved by allowing the height h in the area of the initial
flotation process 1 to be significantly larger than the layer
thickness d of the flotation layer 3. The acceleration is a direct
result of application of Bernoulli's Law due to the reduction of
the cross-sectional area at the entrance to the flotation layer. In
the embodiment in accordance with FIG. 10, the gas bubbles also
only have a short rising or ascending height to the flotation foam
in the initial flotation process 1, and micro-turbulence,
introduced by the staggered diffusion devices, has an optimal
effect. The terminal wall 17 is almost vertical, which leads to an
abrupt acceleration with correspondingly high shear forces in the
suspension. Viewed as a whole, the micro-turbulence introduced
during the initial flotation 1 are utilized for the flotation
process, and in the subsequent acceleration process, additional
shear forces are produced that again serve the flotation
process.
[0048] It is noted that the foregoing disclosure has been provided
merely for the purpose of explanation and is in no way to be
construed as limiting of the present invention. While the present
invention has been described with reference to a preferred
embodiment, it is understood that the words that 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 invention in all of 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.
* * * * *