U.S. patent application number 09/991625 was filed with the patent office on 2002-09-12 for device for distributing cellulose pulp of low and medium consistency in order to form a uniform pulp web.
This patent application is currently assigned to Kvaerner Pulping AB. Invention is credited to Brottgardh, Goran, Clarstrom, Bo, Lamas, Axel.
Application Number | 20020124977 09/991625 |
Document ID | / |
Family ID | 20282763 |
Filed Date | 2002-09-12 |
United States Patent
Application |
20020124977 |
Kind Code |
A1 |
Brottgardh, Goran ; et
al. |
September 12, 2002 |
Device for distributing cellulose pulp of low and medium
consistency in order to form a uniform pulp web
Abstract
The distributor device is for cellulose pulp of low and medium
consistency and is used to form a uniform pulp web running from the
distributor device in an apparatus treating the cellulose pulp. The
distributor device has a cylindrical distributor housing arranged
horizontally and transverse to the pulp web, and an inlet for the
cellulose pulp at one end of the distributor housing and on the
pulp web side. Pulp is fed with feed screws from the inlet and
along the length of the distributor housing. The web is initially
formed via the outlets defined along a generatrix in the jacket
surface of the distributor housing. An optimum distribution of
low-concentration pulp is obtained with the holes arranged along
the generatrix in the jacket surface of the distributor housing.
The holes have a defined hole diameter (D) and are arranged at a
distance (X) from each other. The interaction with the feed screw
makes it possible to keep the holes free from clogging.
Inventors: |
Brottgardh, Goran;
(Karlstad, SE) ; Lamas, Axel; (Karlstad, SE)
; Clarstrom, Bo; (Kil, SE) |
Correspondence
Address: |
ROLF FASTH
189 CURTIS DRIVE
LONGVIEW
WA
98632-5374
US
|
Assignee: |
Kvaerner Pulping AB;
|
Family ID: |
20282763 |
Appl. No.: |
09/991625 |
Filed: |
November 6, 2001 |
Current U.S.
Class: |
162/56 ; 162/396;
162/60 |
Current CPC
Class: |
D21D 1/40 20130101; D21F
1/74 20130101; D21C 9/02 20130101 |
Class at
Publication: |
162/56 ; 162/60;
162/396 |
International
Class: |
D21B 001/34; D21C
009/02; D21F 003/02 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 26, 2001 |
SE |
0100259-1 |
Claims
1. Distributor device for cellulose pulp in the consistency range
of 2 to 12%, which distributor device is used to form a uniform
pulp web running from the distributor device in an apparatus
treating the cellulose pulp, preferably a wash press, and where the
distributor device comprises a cylindrical distributor housing with
its cylinder axis arranged horizontally and transverse to the web
of pulp, an inlet for the cellulose pulp in the distributor
housing, a rotating feed screw with its axis of rotation parallel
to the cylinder axis of the distributor housing and designed to
feed pulp from the inlet and along the entire length of the
distributor housing in the direction of its cylinder axis, and
outlets arranged substantially along a generatrix in the jacket
surface of the distributor housing, characterized in that the
outlets consist of holes arranged along the generatrix in the
jacket surface of the distributor housing, with a defined hole
diameter (d), and where the holes are arranged at a distance (x)
from each other.
2. Distributor device according to claim 1, characterized in that
the distance (x) exceeds the hole diameter (d).
3. Distributor device according to claim 1 or 2, characterized in
that the hole diameter lies in the range of 20 to 60 mm, preferably
with hole diameters of 40.+-.5 mm.
4. Distributor device according to claim 3, characterized in that
the hole diameter increases continuously as seen from the inlet of
the distributor housing.
5. Distributor device according to claim 3, characterized in that
the holes are distributed evenly across the entire width of the
pulp web formed from the distributor device.
6. Distributor device according to claims 2 to 5, characterized in
that the distance between the holes lies in the range of 40 to 90
mm, preferably at a distance of 75.+-.5 mm, and where the distance
is at least 150% of the hole diameter.
7. Distributor device according to claim 1 or 3, characterized in
that the holes are arranged in the lowest part of the jacket
surface of the distributor housing directed substantially straight
down from the distributor housing about a position corresponding to
6 o'clock, and within an area of rotation in the range of .+-.45
degrees.
8. Distributor device according to claim 1 or 3, characterized in
that the feed screw (4a, 4b) has a screw thread (15) whose crests,
during operation, sweep across the holes at a predefined distance
(Y) from the holes (7) in the inner jacket surface of the
distributor housing, which distance lies in the range of 5 to 20
mm, preferably 10.+-.2 mm.
9. Distributor device according to any of the preceding claims,
characterized in that the feed screw (4a, 4b) has a core (14) with
a diameter increasing continuously from the inlet (6a, 6b), and the
annular gap around the feed screw, in which the pulp is conveyed,
decreases continuously as seen from the inlet of the distributor
housing.
10. Distributor device according to claim 6 or 7, characterized in
that the feed screw (4a, 4b) has a decreasing thread pitch on its
screw blade (15).
Description
TECHNICAL FIELD
[0001] The invention relates to a distributor device according to
the preamble of Patent claim 1.
PRIOR ART
[0002] A number of distributor devices for low and medium
consistency pulp are known, these distributor devices being
intended to form a uniform pulp web.
[0003] Most distributor devices for cellulose pulp use very simple
solutions which do not guarantee an even distribution of the pulp
across the entire width of the web. Wash presses in most cases
simply use pulp troughs, of the types disclosed in U.S. Pat. No.
5,667,642, SE-A-9303382-7, SE-C-503010 and SE-C-501710 where the
trough runs across the entire width of the web which is to be
formed. Here, the drum on which the web is formed is allowed to
entrain the pulp, which is in most cases done in a non-uniform
manner and without positively acting distributor members in the
distributor device. If wash liquid is additionally added from a gap
which extends across the entire pulp web, this has the result that
the wash effect is uncontrolled. The non-uniform pulp web formed
then has non-uniform packing across its width, and as the water is
introduced into a gap the water tends to pass through the pulp bed
where it has the lowest degree of packing.
[0004] SE-A-9102370 discloses another device with a rotating
cross-slit rotor arranged in the inlet. Here, the cross-slit rotor
does not afford any positive distribution effects.
[0005] U.S. Pat. No. 4,085,003 discloses a variant with a uniform
throttle valve along the entire distributor device. This valve
cannot guarantee an even distribution across the width of the
entire web.
[0006] SE-C-448009 discloses a distributor device in which the pulp
is conveyed into an inlet at the end of a cylindrical distributor
housing. A feed screw with continuously increasing core diameter,
as seen from the inlet, then feeds the pulp out through a gap which
extends across the entire web which is to be formed. This solution
functions very well with an outlet gap which is arranged in the
upper half of the distributor housing, i.e. within positions of the
outlet gap between 8 o'clock and 4 o'clock on the distributor
housing. The feed screw, which has a continuously increasing core
diameter as seen from the inlet, contributes to the pulp
maintaining uniform pressure towards the outlet slit, after which
the pulp is tapped off from the outlet slit, at the same time as
the feed screw keeps the outlet free.
[0007] SE-C-500546 discloses another solution in which the pulp is
fed into the middle of a distribution box and is then forced to
flow across the upper edge of an upwardly convex crescent-shaped
distribution plate. The shape of the plate is intended to prevent
most pulp being distributed on the web at the inlet, where the
pressure is at its greatest. However, in practical application, it
has been found that the pulp tends to be poorly distributed at the
web edges. In addition, the same crescent shape does not give the
same effect at different consistencies, since lower consistencies
mean that the pulp flows more easily out to the edges of the
crescent and does not build up the same height at the inlet.
[0008] The abovementioned solutions are an indication of the large
number of proposals which have been considered and have been
applied in practice in distributor devices for cellulose pulp from
a low consistency of 2 to 5% and up to a medium consistency in the
range of about 12 to 14%. Most of these solutions have not taken
fully into consideration the importance of ensuring optimum uniform
distribution of the pulp across the whole width of the pulp web.
Only SE-C-448009 discloses a solution where a forced physical
distribution of the pulp is obtained. As soon as a lower degree of
packing of the pulp occurs in the pulp web, this has the effect
that the flow of wash liquid for treating the pulp web is
concentrated in these areas where there is a low degree of packing,
which results in non-uniform treatment and an uneven quality of the
treated pulp.
BRIEF DESCRIPTION OF THE INVENTION
[0009] The object of the invention is to obtain an optimum
uniformly formed pulp web when feeding cellulose pulp in the
consistency range of 2 to 14%. A bed which is packed uniformly
across the entire width of the pulp web means that subsequent
treatment, preferably washing/displacement wash, of the pulp web
takes place uniformly, so that an even quality of pulp is
obtained.
[0010] This object is achieved with the features which are set out
in the characterizing clause of Patent claim 1.
[0011] Another object is to obtain a distributor device with a high
level of operability, i.e. minimal operational faults, and which is
easy to start up with less need or no need for cleaning, dilution,
or emptying of the distributor device. The invention has its main
application in wash presses for cellulose pulp of the type which is
disclosed in SE-C-512753, where the distributor device is arranged
at the very top of a dewatering drum, and where the outlet forming
the pulp web from the distributor device is directed downwards from
the distributor device. The concept illustrated in SE-C-512753
initially utilizes gravitational forces for maximum dewatering
effect when the pulp is softest (lowest concentration), at the same
time as the available wash zone extends optimally across the
greatest possible extent of the drum, typically over 270
degrees.
[0012] The invention ensures that the pulp at a consistency of 2 to
12% does not flow out in an uncontrolled manner to the pulp web
around the pulp inlet from the distributor device, at which inlet
the pressure is at its highest. This effect is most marked in the
preferred embodiment where the outlet holes are arranged in the
lower part of the jacket surface of the distributor housing. The
interaction with the feed screw which, in a preferred embodiment,
has its thread crests sweeping closely across the outlet holes,
guarantees that the outlet holes are kept free without any risk of
becoming clogged.
[0013] Further characteristics, aspects and advantages of the
invention will become clear from the attached patent claims and
from the following detailed description of a number of
embodiments.
DESCRIPTION OF THE FIGURES
[0014] FIG. 1 shows a wash press in cross section, in which the
distributor device (2 of them) according to the invention is
used;
[0015] FIG. 2 shows the distributor device, viewed from above in
FIG. 1, with the distributor housing partially cut away to
illustrate the feed screw;
[0016] FIG. 3 shows the distributor housing, seen in a view
opposite to FIG. 2, with its outlet holes;
[0017] FIG. 4 shows an enlarged cross section A-A in FIG. 2 through
the distributor housing.
DETAILED DESCRIPTION OF THE INVENTION
[0018] FIG. 1 shows a wash press 1 in which cellulose pulp of low
consistency in the range of 2 to 12% is fed to the inlets 6a, 6b of
the wash press.
[0019] Wash Press Construction--General
[0020] The wash press is of a type which is disclosed in
SE-C-512753 in which the pulp is distributed via two inlets on
respective dewatering drums 2a, 2b. By means of an initial
distribution at the highest point of the drum, at 12 o'clock, an
optimum initial dewatering is obtained by using gravitational
forces, and at an initial stage when the cellulose pulp has its
lowest consistency.
[0021] The pulp web 21 is distributed on each drum 2a, 2b and runs
between drum and trough sweep over an angle range greater than 240
degrees, and at most 270 degrees, which gives the possibility of an
extremely long treatment zone over each drum.
[0022] The pulp webs 21 finally meet in a press nip 22 formed
between the drums where a last dewatering effect is obtained.
Normally a consistency of 30% or more can be obtained after the
press nip, and the washed and dewatered pulp is collected by a feed
screw 13.
[0023] This innovative construction principle of the wash press
permits excellent treatment of the pulp at a given drum size. The
concept permits a high wash capacity for the small available
surface in the pulp mill, for which reason it is well suited for
upgrading existing plants.
[0024] The wash press forms the pulp web 21 between the perforated
and dewatered outer surface of the drum 2a, 2b and the surrounding
trough sweep, of which a first section consists of pivotable trough
sweeps 10a, 10b and a final sweep section consists of a raisable
and lowerable trough base 11. The first sections can have weakly
converging trough sweeps with one or more wash liquid distributors
12 arranged transverse to the pulp web.
[0025] The Distributor Device According To The Invention
[0026] Each distributor housing 3a, 3b for each drum comprises a
feed screw 4a, 4b arranged in the cylindrical distributor housing
with its cylinder axis arranged horizontally and transverse to the
pulp web 21.
[0027] FIG. 2 shows one distributor housing seen from above in FIG.
1. The feed screw 4a, 4b is provided with a screw thread 15 with a
substantially constant pitch, and a screw core 14 with a
continuously increasing core diameter as seen from the inlet 6a,
6b, corresponding to that shown in SE-C-448009. The distributor
housing can, as is shown in SE-C-448009, have an inlet at one end
of the distributor housing, but in FIG. 2 the inlet is arranged at
the middle of the distributor housing, and the screw thread 15 of
the feed screw is mirror-inverted as seen from the centre of the
inlet for conveying the pulp out towards the end walls of the
distributor housing.
[0028] In this way it is possible to obtain a uniform pressing
force on the pulp remaining in the distributor housing, where the
remaining annular space for the pulp decreases continuously in the
feed direction of the screw. A compensation is thus obtained for
the pulp which is fed out nearest the pulp inlet 6a, 6b.
[0029] An alternative to a continuously increasing diameter of the
screw core 14 can be a continuously decreasing pitch of the screw
thread 15.
[0030] The screw is mounted 20 at each end and is driven by a motor
5, where the feed screw is arranged with its axis of rotation
parallel to the cylinder axis of the distributor housing and is
arranged to feed pulp from the inlet 6a, 6b and along the entire
length of the distributor housing in the direction of its cylinder
axis.
[0031] The figure also shows a shorter counter thread at the end of
the distributor housing, where a counter pumping effect is obtained
which is intended to counter the formation of plugs. This counter
thread can be completely or partially omitted depending on the
tendency of the pulp to form plugs and/or possible interaction with
cleaning nozzles which are activated for a short time during
stoppage or plugging tendencies. The counter thread can also be
placed in an area of the housing outside the width of the web
formed.
[0032] FIG. 3 shows how the outlets from the distributor housing
are arranged in the manner according to the invention. Instead of a
gap extending across the entire housing, as is shown in
SE-S-448009, the outlet consists of holes 7 arranged along the
generatrix of the distributor housing, in the jacket surface of
said distributor housing 3a, 3b, and with a defined hole diameter
D, and where the holes are arranged at a distance X from each
other.
[0033] The holes do not need to be so close when the pulp is
relatively easy-flowing under the conditions which prevail under
the action of the feed screw. The distance X between the holes
expediently exceeds the hole diameter.
[0034] Tests have shown that a good distribution function is
obtained with holes having a diameter of 40 mm, which holes are
separated by a distance of 75 mm. The hole size and the spacing can
vary, however, around these dimensions without unacceptably
affecting the distribution function. The hole diameter can
therefore vary within the range of 20 to 60 mm, and the distance
between the holes can vary within the range of 40 to 90 mm, while
the distance between the holes is at least 150% of the hole
diameter.
[0035] In certain applications with pulp in the lower range of
consistency, i.e. 2 to 5%, and/or in the case of a high initial
feed pressure of the pulp, the holes can also be given a
continuously increasing hole diameter as seen in the direction of
feed of the feed screw 4a, 4b and from the inlet of the distributor
housing. Such a design can give a certain throttle effect for the
pulp which flows out in the holes 7 arranged nearest to the inlet
6a, 6b. In combination with an increasing core diameter of the feed
screw (alternatively an increasing pitch of the thread), it is thus
possible to obtain a uniform outflow across the entire width of the
distributor housing.
[0036] As will be seen from FIG. 1, the outlets are arranged, for
maximum initial dewatering effect, at the top of the wash press,
with the outlets 7 arranged in the lower part of the distributor
housing, directed substantially straight downwards from the
distributor housing. The holes are intended to prevent pulp from
falling freely down towards the pulp web, and the holes form a
pressure drop which gives the pulp the possibility of being
distributed across the entire distributor housing before being fed
out from the housing. The holes are preferably arranged in the
lowest part of the jacket surface of the distributor housing
directed substantially straight down from the distributor housing
around a position corresponding to 6 o'clock, and within an area of
rotation in the range of .+-.45 degrees from this position.
[0037] FIG. 4 shows the interaction between the thread 15 of the
feed screw 4a, 4b and the outlet holes 7 in the inner jacket
surface of the distributor housing 3a, 3b. The thread 15 of the
feed screw 4a, 4b sweeps with its crests across the holes 7 at a
predefined distance Y from the holes 7 in the inner jacket surface
of the distributor housing. This interaction maintains continuous
exposure of the holes. This is very advantageous when restarting
after shutdown, as plug formations may have developed in and around
the holes 7.
[0038] The distance Y can be relatively large, up to 20 mm for
consistencies in the upper range of 7 to 12%, without this exposure
effect disappearing entirely. However, the distance Y can be
optimized as a function of the actual consistency, where the
optimum distance decreases as consistency increases.
[0039] The distance Y preferably lies in the range of 5 to 20 mm
and is more preferably 10.+-.2 mm.
[0040] The invention can be modified within the scope of the
attached patent claims. For example, the holes can be arranged
offset a slight distance either side of the generatrix of the
jacket surface.
[0041] The outlet holes 7 from the distributor device can also be
provided as tubular sleeve couplings nearest the distributor
housing, with transition to an elliptic cross section at the
outlets nearest the pulp web, and where the major axis of all
elliptic cross sections is parallel.
[0042] The outlet holes nearest the distributor housing can also be
slightly elliptic, the mean value of the minor axis and major axis
corresponding to the hole diameter specified in this application.
Each distributor device forming a pulp web can also contain two or
more distributor housings with two or more separate inlets for each
distributor housing.
* * * * *