Note: Descriptions are shown in the official language in which they were submitted.
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REVERSE CENTRIFUGAL CL~ANING
OF PAPER MAKING STOCK
Back~round of the ~nvention
Centrifugal cleaners have been employed for
many years in the paper industry for removing small
particles of higher specific gravity than paper
fibers from slurrles of paper making fiber, espe-
cially waste paper stocks.
In centrifugal cleaners used for that
purpose, in what is hereinafter referred to as
"conventional centrifugal cleaning technique," the
discharge outlet at the apex ~tip) of the
cylindrical-conical vessel is relatively small in
comparison with the inlet and accepts outlets, e.g.
1/8 inch in diameter as compared with 5/~ inch
diameters for the other two ports in a conventional
cleaner 3 inches in diameter. In such conventional
cleaning operations, therefore, the reject discharge
through the apex outlet is correspondingly small in
comparison with the accepts flow, e.g. 3% and 97%
respectively.
In comparatively recent years, there has
been an increasing use of centrifugal cleaners to
separate good paper fibers from contaminants of
closely similar or lower specific gravity such that
they cannot be readily separated by conventional
centrifugal cleaning technique.
In general, cleaners for such "reverse"
centrifugal cleaning have been made by modifying the
construction and/or operation of a conventional
cleaner to provide operating conAitions which cause
the good fiber to be discharged through the apex
outlet as the accepts flow while the lights are
discharged as reject through the base (top) outlet
which is the accepts outlet in conventional centri-
fugal cleaning. For an extended discussion of prior
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and up dated reverse centrifugal cleaning develop-
ments, reference is made to Seifert et al. U.S.
Patent No. 4,155,839 wherein the present inventor
was a joint patentee.
Summary of the Invention
A primary object of this invention is to
provide a centrifugal cleaner particularly adapted
for reverse centrifugal cleaning wherein both of the
discharge ports, for the two fractions into which
the cleaner separates the feed flow, are located
adjacent the apex end of the cleaner, so that there
is no reversal of flow within the cleaner as in past
practice for both conventional and reverse cleaning.
More specifically, in a reverse centrifugal
cleaner in accordance with the invention, the apex
outlet, which heretofore has been used as the outlet
for the "heavy" fraction, whether it be reject in
conventional cleaning or accepts in reverse cleaning,
becomes the outlet for the light fraction which
constitutes rejects in reverse centrifugal cleaning.
The cleaner of the invention is provided with a
second discharge outlet in its side wall, and
preferably at the downstream end of the conical
portion of the interior of the cleaner, which is
then the discharge outlet for the heavy fraction
constituting the accepts flow in reverse centrif~gal
cleaning.
Thus in the practice of the invention,
there is a through flow of the feed stock from the
base end to the apex end of the cleaner, with no
reverse flow through the central part of the cleaner
as in both conventional and reverse cleaning as
heretofore practiced. This feature is of particular
value in the application of the invention to cyclone
assemblies or "canister" cleaners wherein multiple
individual centrifugal cleaners are assembled in
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parallel relation within a common canister whose
interior is divided into feed, accepts and reject
chambers which connect respectively with the inlet
and discharge ports of all of the individual
cleaners.
Further on this feature of the invention,
when conventional cleaners are assembled in a
canister, for example as shown in Rastatter U.S.
Patent No. 3,940,331, the reverse flow within each
of the individual cleaners creates substantial
opposed forces ttensile loading) and stresses on the
individual cleaners by reason of the opposed flows
within each cleaner. With the cleaners of the
invention, however, wherein the flow within each
cleaner is all in one direction, there are no such
opposing forces, and the stresses and strains on the
cleaners are correspondingly reduced.
Brief Description of the Drawinqs
Fig. 1 is a view in axial section of a
reverse cleaning unit in accordance with the
invention;
Fig. 2 is a fragmentary view similar to
Fig. 1 and showing a modified inlet port arrangement;
and
Fig. 3 is a fragmentary view illustrating
the application of the invention to a canister-type
cyclone assembly.
Description of the Preferred Embodiments
A typical reverse centrifugal cleaner
indicated generally at 10 is shown in Fig. 1 as
housed in a casing 11 which has its interior divided
by partitions 12 and 13 into a supply or feed
chamber 15 at one end of the casing 11, a reject
chamber 16 at the other end of the casing, and an
accepts chamber 17 located intermediate the chambers
15 and 16, each of these chambers being provided
with its own port 20, 21 and 22, respectively.
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The cleaner 10 comprises a main tuhular
vessel 25 the interior of which is cylindrical over
a portion of its length and frusto-conical through-
out its remaining portion. A housing 26 is threaded
on the smaller end oE the vessel 25, and a tubular
tip piece 27 is secured within the housing 26 by a
retainer nut 28 as shown. The cylindrical bore 29
within the tip piece 27 forms a continuation of the
interior of housinq 25 which leads to the discharge
port 30.
The housing 26 has one or more radially or
tangentially arranged ports 31 therethrough which
provide a total flow area larger than that of the
port 30 leading into the interior of the reject
chamber 16. The lower end of the housing ~6 is
closed ~y a threaded cap 33 which extends through an
opening in the end wall 34 of the casing 11 and
clamps the casinq wall against the end of housing 26
to the casing wall. The base end of the vessel 25
is provided with a closure plug 35 which is threaded
into the end of the vessel 25 and also clamps the
partition 13 between itself and the vessel 25.
A helical groove 40 on the outer surface of
the plug 35 forms the inlet port to the interior of
the cleaner vessel 25, the spiral configuration of
this groove assuring that stock to be cleaned will
be deLivered from the interior of the feed chamber
15 to the interior of the vessel 25 with a substan-
tial circumferential flow component. The plug 35 is
otherwise solid, but it includes a cylindrical
extension 41 on its inner end which acts in part as
a vortex finder but more particularly as a stabilizer
for the air core which forms during operation of the
cleaner. The groove 40 may be duplicated around the
periphery of plug 35 to increase the effective inlet
port size as needed.
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In addition to the outlet port 30 at its
apex, the cleaner ]0 is provided with one or more
outlet ports 44 at the lower end of the frusto-
conical portion of vessel 25. The outlet ports 44
are preferably arranged tangentially of the vessel
25, in the same direction as the circulatory move-
ment of stock within the vessel, and these ports
lead into the chamber 15 within the casing 11.
Preferably, the tip piece 27 include~s a cylindrical
extension 45 which projects upstream therefrom into
the interior of the vessel 25 sufficiently far so
that it at least radially overlies the outlet port
or ports 44 and thus serves as a baffle preventing
direct flow therefrom to the interior of tip piece
27 and the outlet port 30~ and the upstream end of
the extension 45 thus effectively is the apex outlet
port of the vessel 25.
The inlet construction shown in Fig. 1 has
special advantages in that it assures the all stock
entering the cleaner will continue to flow with a
substantial component lengthwise of the cleaner,
rather than having some heavy particles tend to
orbit the inlet end of the cleaner and thereby wear
away its inner wall surface. The invention can be
practiced, however, with the alternative inlet
construction shown in Fig. 2, which is essentially
the same as in the above noted patent No. 4,155,839.
It includes a plug 35' which differs from plug 35
only in having no groove 40 in its outer surface.
3~ Instead, an inlet port 40' of rectangular shape
leads tangentially through the wall of vessel 25 as
shown in patent No. 4,155,839. The position of the
partition 12 with relation to the vessel 25' there-
fore has to be shifted so that the port 40' will be
open to the feed chamber 15, and the partition 13 is
therefore clamped between a shoulder 46 on the
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vessel 25l and a nut 47 threaded on the vessel 25'
in opposed relation with the shoulder 46.
In the use of a cleaner of the construction
described in connection with Figs. 1 and 2, the
slurry to be cleaned is delive{ed to the supply
chamber 15 at the appropriate pressure to cause it
to enter the inlet port 40 or 40' at the desired
flow rate and velocity as described in patent No.
4,155,83~, to develop within the vessel 25 centri-
fugal force conditions causing vortical separationof the slurry into an outer fraction containing the
large majority of the paper fibers, an inner
fraction oontaining the large majority of light
contaminant particles, and commonly also an
innermost air core.
The outer fraction will travel down the
frusto-conical portion of the interior of vessel 25
until it reaches the discharge port or ports 44, and
it will exit through those ports to the accepts
discharge chamber 17 and its outlet port 22. The
inner fraction will enter the upstream end of the
extension 45 and travel therethrough and through the
interior of the tip piece 27 and the outlet port 30
to the reject discharge chamber 16 and its port 21.
Separation of the heavy and light fractions
which form within the cleaner as they discharge
therefrom is readily controlled by regulating the
respective discharge flows from the chambers 16 and
17, by means such as valves 50 and 51 on the lines
30 52 and 53 leading from the ports 21 and 22. Deter-
mination of the proper flow splits from the two
discharge chambers will usually involve some
experimentation, depending upon the nature of the
feed stock, the feed flow rate and the feed pressure,
and satisfactory results have been obtained under
test conditions with this split varied from approxi-
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mately equal flows from both discharge chambers toapproximately 80~ from the accepts chamber 17 and
20~ from the reject chamber 16.
As a more specific example of the practice
of the invention, test runs were made with a cleaner
constructed as shown in Fig. 2 wherein the inlet
port 44' had a flow area of 0.625 sq. in., the
minimum flow area of the apex outlet port was 0.785
sq. in., and there were two outlet ports 40 each of
a flow area of approximately 0.25 sq. in. In a test
run wherein the feed flow rate was 50 gallons/minute
at 30 p.s.i.g., satisfactory results were obtained
with flows from the discharge chambers 16 and 17 of
approximately 26 and 24 gallons/minute. Better
results were obtained with a feed flow rate of 68
g.p.m. at a feed pressure of 40 p.s.i.g~, and with
the flows from the discharge chamber 16 and 17 at
the rate of 54.5 and 13.5 g.p.m. respectively.
The invention has also been tested with a
cleaner constructed as shown in Fig. 1 wherein the
inlet port flow area was 0.625 sq. inO, the minimum
flow area of the apex port was 0.306 sq. in., and
the accepts port 40 was rectangular, similarly to
the inlet port 40' in Fig. 2, with dimensions of 1.5
25 inches x 3/8 in. and a flow area of 0.47 sq. in.
~ighly satisfactory results were obtained with a
feed flow at 80 gallons/minute and a pressure of 45
p.s.i.g. with the flow from the chambers 16 and 17
at the rates of 8.5 and 71.9 gallons/minute.
As pointed out hereinabove, the invention
is especially applicable to cleaner assemblies of
the canister type, as illustrated in Fig. 3, wherein
the canister 60 has internal walls 61 and 62 dividing
its interior into a central chamber 63 and opposite
35 end chambers 64 and 65. Multiple cleaners 10 of the
construction described in connection with Fiq. 1 are
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shown as mounted within the canister 60, with the
interior walls 61 and 62 and end wall 66 providing
the same mounting and partitioning functions as the
partitions 12 and 13 and end wall 34 in Fig. 1.
The operation of a canister cleaner
assembly of the invention as shown in Fig. 3 is the
same as already described in connection with Fig.
1. The chamber 64 serves as the feed chamber and is
provided with an appropriately located port for
receiving the inlet flow of feed stock, and the
chambers 63 and 65 become the reject and accept
chambers as described in connection with the chambers
16 and 17 in Fig. 1, Since there is no reverse flow
within any of the cleaners 10, the individual
cleaner bodies are not subjected to tension strains
but need only support the compression loads imposed
by the pressures within the chambers 33-65, and
since the maximum pressure is in the feed chamber
64, no practical problem is involved. It should
also be noted that the canister cleaner of Fig. 3
can in effect can be made double-ended by doubling
the length of the canister, installinq a second set
of partition walls and cleaners opposite the set
shown in Fig. 3, and then using chamber 64 as the
feed chamber for both sets of cleaners.
While the process and forms of apparatus
herein described constitute preferred embodiments of
this invention, it is to be understood that the
invention is not limited to this precise process and
these forms of apparatus, and that changes may be
made therein without departing from the scope of the
invention.
