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Патент USA US3096285

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. July 2, 1963
e. H. TOMLINSON 1| ~
METHOD FOR SEPARATING DIRT FROM AQUEOUS
3,096,275
SUSPENSIONS 0F PULP FIBERS
3 Sheets-Sheet 1
Filed Sept. 26, 1961
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July 2, 1963
e. H. TOMLINSON n
‘METHOD FOR SEPARATING DIRT FROM AQUEOUS‘
SUSPENSIONS OF PULP FIBERS
Filed Sept. 26, 1961
3,096,275
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July 2, 1963
G. H. TOMLINSON n
METHOD FOR SEPARATING DIRT FROM AQUEOUS‘
3,096,275
SUSPENSIONS OF‘ PULP FIBERS .
5 Sheets-Sheet 3
Filed Sept. 26, 1961
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3,096,275
United States Patent 0 ' 1C6
1
3,13%,275
METHOD FOR SEPARATING DIRT FROM
AQUEOUS SUSPENSIONS 0F PULP FIBERS
George H. Tomlinson 1!, Long Sauit, Ontario, Canada
Filed Sept. 26, 1961, Ser. No. 140,702
3 Claims. (Cl. 209—2)
This invention relates to a new and el?cient method
for cleaning an ‘aqueous suspension of pulp or paper
making ?bres whereby objectionable foreign material, in
cluding so-called “dirt,” is removed by means of com
bined centrifugal force and shear action in a device which
Patented July 2, 1963
2
be unreasonably high at any point along the system, this
normally resulting in lower pulp yields and sometimes in
excessive degradation of the pulp.
The control of “bark dirt” has been an even more
serious problem. Whereas the shive is normally some
what longer than it is wide this enhancing its chance of
being rejected by the screen, bark dirt tends to be ran
dom in shape, approaching a sphere. Moreover, it is
less susceptible to bleaching out. Thus conventionally,
10 to obtain a ?ne paper free of bark dirt, it has been neces
sary to take extra precautions with the wood used.
This
has meant recycling of logs through the barking drums
to remove all traces of adhering bark. However, logs
contain ingrown bark around knots, etc., and many mills
application is a continuation-in-part of my earlier ?led
application, Serial No. 363,277, ?led June 22, 1953, now 15 have restorted to treatment with “rossers,” “Wood
peckers,” etc., to remove both wood and bark around
Patent No. 3,037,628 issued June 5, 1962, which was
the most seriously affected areas.
a continuation-in-part of my earlier ?led application,
The minimization of high speci?c gravity extraneous
Serial No. 205,655, ?led January 12, 1951, now aban
can be classed as a vortex type separator, and this
doned.
dirt has ‘been normally accomplished by taking precau
In the conversion of wood or other ?brous material 20 tions to avoid its entry to the system by providing for
thorough washing of the logs and ?ltration of process
water,
etc., by riffling in the pulp mill, and by the use
or “dirt” are encountered.
of
stationary
cylindrical centrifugal cleaning tubes in the
(1) Portions ‘of the wood which have not completely
paper mill, all three methods usually being used in com
broken down into individual ?bres as a result of the
chemical and/ or mechanical action. A particle of such 25 bination.
It is thus apparent that through direct and indirect
material may be relatively large such as an unde?bred
to pulp and paper three main classes of foreign matter
expense the cost involved in producing a clean sheet
of pulp or paper is extremely high. The individual con
ventional
means of cleaning are normally speci?c for
as a “shive.”
one
type
and/
or size of “dirt,” and even for that type
30
(2) Pieces of bark which do not disintegrate in cook
and/or size the et?ciency is often low, while for types
ing and remain as black or dark coloured specks in the
and sizes of “dirt” other than that for which the equip
?nial pulp.
ment was designed, the ef?ciency may be essentially zero.
(3) Foreign matter of non-?brous origin that enters
By the methods of the present invention shive, bark
the system with the wood or at any subsequent stage,
chip or knot, but when broken down to size such as
might be imbedded in a sheet of paper it is referred to
this including sand, pipe-scale, fly-ash, cinders, etc.
On account of the extremely divergent physical char
acter and size of the “dirt” particles that may be present
many varied methods of cleaning cellulosic pulp have
been devised and have been conventionally employed in
combination in order to obtain a ?nal product which is
reasonably uncontaminated with foreign materials that
35 “dirt” and high speci?c gravity dirt can all be removed si
multaneously from the ?bre, and, within certain wide lim
itations, this is accomplished regardless of the size of the
particles. Furthermore, by the choice of certain dimen
sions of the individual cleaning units, which will modify
the flow of the separated dirt within the unit, it has ‘been
found possible to extend the range in .the size of particles
removed in one direction or the other as may be desired.
would mar the appearance and serviceability of the ?nal
This combination of results, which has been obtained
sheet of pulp or paper.
in a vortex type separator, has never been described as
Prior to the present invention the most frequently used
method of cleaning cellulosic pulp was screening a dilute 45 having been accomplished by any previously ‘available
means or device.
aqueous suspension of the pulp. However, in order to
Prior to the present invention it had not been con
prevent plugging and matting it is necessary to use slots
sidered possible to e?fectively separate shives from pulp
or holes many times greater than the ?bre width. Inas
much as screens are not completely selective in their
action, multiple screening has been often used, but in
spite of this, some shive normally carries through. By
cooking the pulp using relatively drastic conditions the
quantity of initial shive is diminished, and in bleaching,
by means of centrifugal cleaners. Sampson and Group
in U.S. Patent 2,377,524, who developed the hydrocyclone,
a conical centrifugal unit somewhat similar to a gas cy
clone in general shape, for continuously removing dirt
from aqueous cellulosic pulp suspensions, stated that the
shive components of the dirt have a reaction to centrifu
further “chemical cleaning” of shive is obtained ‘due to
removal of li-gnin which binds the ?bres together. In 55 gal force which is so nearly the same as that of the
individual ?bers that they are ‘hardly separable by cen
addition to “chemical cleaning,” mechanical attrition re
trifugal action from the regular ?bres. In one of their
sults from the action in pumps through the pulp mill, as
most e?‘icient cleaning units, which ‘had a diameter of
well as in the beater, jordan or other re?ning equipment
3.08 inches and a capacity of 20 gallons per minute, they
in the paper mill whereby many of the individual shives
are torn apart. By a balance of multiple screening with 60 noted that 44.7% of the shives which were not disinte
grated due to mechanical action were rejected with
chemical and mechanical de?bring it has been possible to
23.5% of the good ?bres. Thus 76.5% acceptable pulp
control shive content in the ?nal fine paper to a rea
contained 55.3% of the shives. ‘From this it follows
sonably low level, with the chemical cleaning normally
that 100 parts accepted ?ber would contain
acting as the control point-that is, the amount of chemi 65
cal or temperature or time at the cooking or bleaching
stages being increased when the shive count appears to
100
3,096,275
of the non-disintegratable shive carried from the initial
pulp indicating that such equipment is obviously unsuit
A
of the centrifugal forces to the angular velocity gradient
at said maximum having a value of 16><1O—2 or greater,
able for producing a shive-free pulp.
According to the teachings of said U.S. patent a dirt
particle is subjected to centrifugal force which Carries
'sec.-1 ft.‘1 or greater.
it to the wall where it advances to the apex of the cone
invention reference will be had to the accompanying draw
and is rejected. However, opposing this effect is the in
and the angular velocity gradient having a value of 600
Proceeding now to a more detailed description of the
ings, in which:
ward radial ?ow so that material not readily separated
FIGURE 1 is a View, partly in vertical section and
by centrifugal force will be carried in to the center and
partly in side elevation, of one type of a vortex separator
out the top outlet With the accepted stock. Thus they 10 embodying my invention;
concluded that the only way to improve the e?‘iciency
FIGURES 2 and 3 are sectional views showing the ap
of the unit was to use a ‘unit of decreased diameter which
plications of conical ?ttings to vary the effective diameter
increases the angular velocity and therefore the centrifugal
of the dirt discharge aperture of the conical separating
force and to increase cone length which decreases the in
chamber forming part of the apparatus shown in FIG
ward radial ?ow. They concluded that a useful unit for 15 URE 1.
pulp cleaning would be in the size range of 2.0 to 4.2
FIGURES 4, 5, 6 and 7 show the variation with radius
inches diameter and would have a length of 5 to 15 times
within the unit of pressure, velocity, centrifugal force and
this diameter.
I have now found that excellent removal of shive, to a
angular velocity gradient respectively in three selected
units.
degree considered impossible in the prior art, is achieved 20 The separator shown in FIGURE 1 comprises a rela
in a hydrocyclone unit having a markedly greater diam
tively large diameter hollow truncated cone section 5 of
eter, and hence considerably lesser centrifugal force, than
a length considerably greater than its maximum diameter.
those obtained in said U.S. patent.
The upper or larger end of cone section 5 is joined to a
This surprising ?nding results ‘from the previously un
cylindrical head section 7 provided with a tangential stock
recognized fact that shive and other large light particles, 25 inlet 8, preferably of rectangular cross section, elongated
particularly of elongated shape, are drawn to the center
in the direction of the axis of the unit. A cleaned stock
of small diameter units as a result of the high velocity
outlet pipe 9 extends ‘below the level of the tangential
gradient or shear which prevails, the particles passing to
stock inlet 8 in axial ‘alignment with rejects discharge
zones of higher velocity gradient which are towards the
aperture 6, situated at the truncated apex of the cone, to
center of the unit, in spite of the high opposing centrifugal 30 provide a stock outlet of greater diameter than said
force.
rejects discharge aperture.
I have found, more generally, that when an aqueous
The cleaned stock may be delivered through outlet pipe
suspension of ?bres is introduced tangentially into a coni
9, pipe reducer 15 and elbow 16 to a throttling valve 17
cal chamber, such as a hydrocyclone, to produce a whirl
and thence, through suitable pipe ‘connections 19, to any
ing motion ‘about a central axis, the suspension as it whirls 35 suitable point of delivery such as to the next process stage.
inwardly and downwardly forms a conical vortex wherein
A pressure gauge 20 may be provided immediately ahead
two zones are clearly distinguishable; an outer zone char
acterized by angular velocities increasing inwardly along
of throttling valve 17.
The included cone angle of cone section 5 is an im
the radius and an inner zone wherein the angular velocity
portant factor and may be of the order of 10° to 18°.
of the liquid is substantially constant. The shear forces 40 When the area of stock inlet 8 is approximately 12.5
arising from the angular velocity gradient are instru
square inches and the inside diameter of cylindrical head
mental in separating the wood dirt or shive from the ?bres.
section 7 is 12 inches, the inside diameter of cone section
The shive thus freed from the ?bres are carried by the
5 at aperture 6 should be ‘approximately 2 inches. For
centrifugal forces, simultaneously developed, toward the
wall of the conical chamber whence it is carried to the
apex of the cone and eventually rejected. I have found
that effective separation of shive from the ?bre 'and sub
sequent ejection of shive through the cone apex will occur
certain purposes, a smaller diameter at aperture 6 may
be desirable. In this event, separately formed ?anged
conical ?ttings 12 ‘and 13 may be provided and selectively
secured to ?ange 14 of cone section 5, as shown in FIG
URES 2 and 3. The minimum internal diameter of the
only where the centrifugal force and angular velocity
cones of conical ?ttings 12 and 13 are 1.75 inches and
gradient generated in the vortex bear a ratio to one an 50 1.5 inches respectively so that an ‘appropriate rejection
other a‘bove a certain minimum value.
outlet size may be provided, while maintaining the angle
I have further found that the magnitude of the centrif
ugal force and the ‘angular velocity gradient thus gener
ated, and consequently the ratio of such forces to one an
of the cone down to the smaller diameter. In like man—
ner, ‘a rejects outlet diameter of 1.25 inches or any other
desired size may be obtained by the use of additional
?ttings similar to the ?ttings 12 and 13. The stock outlet
pipe 9 extends to the lower end of cylindrical head sec
tion 7. The internal cross section of outlet pipe 9 may
unique relationship between any particular combination
be approximately equal to the cross section of inlet 8,
of values for such variables and the ratio of centrifugal
this corresponding in the present instance to a diameter
force to angular velocity gradient, and hence the separa~ 60 of- approximately 4 inches. When stock is pumped
tion e?iciency of the chamber.
through this unit a liquid-free column 21 forms at the
Accordingly, the present invention provides a continu
axis ‘extending between apex outlet 6 and outlet pipe 9,
other, are determined by the geometrical variables of the
conical chamber, viz, diameter of chamber, cone angle,
inlet diameter, top outlet diameter and that there is a
ous method of separating, from an aqueous suspension
of cellulose ?bres, “dirt” particles of Widely varying sizes
including those having essentially the same speci?c gravity
as the cellulose ?bres, wherein the suspension is introduced
under pressure tangentially into the wider end of a
conical separation chamber thereby to produce a vortex
of conical form, ‘said vortex having an outer zone of
this column being surrounded by liquid stock suspension
22 which is in rapid rotation about this column.
When unri?ied and unscreened sulphite pulp‘ at a pres
sure of 45 pounds per square inch was supplied to the
unit it was found to have a capacity of 705 U.S. gallons
per minute. When connected with a 1.25 inch apex out
let, and operating without back pressure, it was found to
radially inwardly increasing angular velocities and an 70 repect 4.0 U.S. gallons per minute at a ‘consistency of
inner zone wherein the angular velocity is constant, the
centrifugal forces and the shear forces being at maximum
1.2%, this discharge being ‘in the form of a hollow cone
spray having an included angle of 100° and amounting to
in the outer zone of increasing angular velocities at a
0.57% of the inlet volume and containing 1.31% of the
point close to the radius of transition between the outer
total entry solids. This remarkable small flow through a
zone and the zone of constant angular velocity, the ratio 75 1.25 inch outlet results from the fact that the region sur
3,096,275
6
When a single large object, such as a woody knot, say
1/2 inch x 1/2 inch x 3%; inch enters the unit described
above it is not rejected but orbits against the cone wall
until it is worn by attrition to a size that will reject. By
rounding the central axis is completely void of liquid,
this resulting from the high centrifugal force within the
unit. The rejection ori?ce is normally set to a diameter
just larger ‘than that of the liquid-free column, thus mini
mizing the quantity of rejects which must be rehandled,
yet being of sufficient size to prevent pluggage. The ac
cepted stock, in the foregoing example, was found to be
using a transparent cone it was possible to measure the
velocity of the orbiting knot. The orbit established was
speci?c for its size and as the knot was worn away its
position advanced towards the apex of the cone. A rub
somewhat cleaner than that obtained with the use of
ber Number 2 laboratory stopper, which showed similar
the conventional rif?ing and ?ne screen system which was
10 behavior but without changing orbit due to attrition, was
running in parallel, using identical feed stock.
introduced with the feed to a 12 inch diameter unit having
It was found that when the 15° conical section was
a 12.5 square'inch inlet and a 4 inch diameter top out
replaced with one of 10° it was necessary to increase
let
and a 10° cone, this being operated at 45 pounds per
the apex ori?ce diameter to 1.5 inches in order to obtain
square inch inlet pressure and without pressure at the
a rejection discharge. With this modi?cation cleaning
efficiency was improved, and the capacity of the unit in 15 outlet. The throughput was 800 U.S. gallons per minute,
from which its calculated velocity, at point of entry, was
creased from 705 to 800 U.S. gallons per minute.
20.5
feet per second. Thet stopper was found to orbit
An installation of vortex cleaners of the above dimen
at the point where the cone was 1.8 inches in radius.
sions, using the 10° cone, was made in an alkaline process
The velocity of the orbiting stopper, as measured with
pulp mill located at Cornwall, Ontario, producing 150‘ to
a
strobortac,
was 4,300 r.p.rn. corresponding to a velocity
20
ZOO-tons pulp per day from mixed hardwood. In this
of 67.6 feet per second at the cone wall.
installation the stock from the brown stock washers was
When -a body of a ?uid rotates about the central axis
passed through a coarse screening system and then through
of a vessel the extreme cases of either a “free vortex” or
three vortex cleaners connected in parallel. The rejects
a “forced vortex” may develop depending on the condi
from the coarse screening system and the vortex cleaners
that initiate and maintain the whirl. In the “free
were combined, diluted, and passed through another 25 tions
vortex”
both the angular and tangential velocities increase
vortex cleaner with the accepted stock being recycled
as the axis of rotation is approached, according to the
through the system and the rejects sewered. The stock
relationship.
was then thickened, bleached and next passed through
a second bank of four cleaners in parallel, with the rejects
V1><R1=V2XR2
(1)
being diluted and pumped to a secondary cleaner, the 30
accepted stock being returned to the system and the
where V1 and V2 are the tangential velocities at radii R1
rejected stock being sewered. The total sewered rejects
and R2 respectively.
at the unbleached system amounted to 0.15% by weight
In the “forced vortex” the ‘angular velocity is constant,
of the accepted stock and consisted of shive, bark dirt
that
is, the ?uid rotates as though it were a solid wheel,
and miscellaneous gritty material together with a small 35 with the tangential velocity decreasing as the axis is ap
amount of ?ber. The total rejection at the bleached stage
proached. The corresponding relationship is
amounted to 0.067% of the accepted stock.
After the above installation was made it was found that
the previously used conventional system for handling the
unbleached screen rejects consisting of a rotary screen 40
and a ?at screen was no longer required. This was also
the case with the bleached stock ri?iers and ?ne screens
From the above equations, it was possible to calculate
the theoretical velocity at 1.8 inches radius for the two
types of flow assuming that the tangential velocity at
the outside of the cylindrical section (having a radius of
ment was removed from the plant. Hourly dirt count
6 inches) is the same as the entry velocity, namely 20.5
tests in this mill, taken over an eight month period fol 45 feet per second. Also since the orbiting stopper occupied
(primary and secondary systems) and all of this equip
lowing the installation, showed an average count of 1
square millimeter equivalent black area per 1000‘ square
inches of pulp sheet surface with only 2.9% of the counts
a wide radius band it was not certain as to the actual
radius at which the liquid velocity coincided with that
of the velocity of the stopper, but for the purpose of this
calculation it was taken at the cone wall. A comparison
installation none of the counts were as low as 1 and 98% 50 of the experimental value with those calculated for free
were above 4. Because of the high cleanliness with the
and forced vortices are shown in Table I.
new system it was found possible to use 14% less chem~
ical ‘at the digester than previously inasmuch as it was no
TABLE 1
being above 4. In the corresponding period prior to this
longer necessary to periodically raise the charge for “dirt
55
control.”
With conventional operation, it had been necessary to
use only wood from which the bark had been removed and
which had been carefully cleaned. It was found that with
Radius, inches
Angular
centrifugal
in feet
per second
velocity
in r.p.n1.
force in
number of
times
the vortex separators in operation, totally unbarked wood
could be successfully used and that essentially all of the 60
bark particles were removed. With unbarked wood, the
total rejection rate at the unbleached stages increased
from approximately 0.22% of the accepted stock to ap
proximately 1.66% of the accepted stock due to the
large number of bark particles.
Calculated
Velocity
gravity
(1) Experimentally found, 1.8--.(2) Calculated values:
(a) Free vortex ?ow:
6.0 (at entry) _ _ _ _
67. 6
4, 300,
946
_ ._
20. 5
392
1. 8 _______________ __
68.3
4, 350
26. 2
20. 5
392
26. 2
392
7.9
968
(b) Forccdvortex ?ow:
6.0 (at entry) ______ __
65
1.8 __________________ __
6. 15
It has been found that the type of rejection of the
vortex cleaners is dependent, in an inter-related way, on
a number of the dimensions of the unit which include
Comparison of the data of Table I shows that the remark
able acceleration of the ?uid can be explained by the
both the absolute and relative size of the inlet and outlet
connections, the diameter and the cone angle. It has 70 formation of a free vortex in the unit. In Table I the
centrifugal force values were calculated according to the
been possible to study the nature of the motion within
the unit and its effect on entrained solid material, all as
related to the dimensions involved so that it thus becomes
possible to predict the type of action which may be ob
75
tained with any proposed unit which may be built.
equation,
(3)
3,096,275
7
8
where
F=the centrifugal force in number of gravities
V=velocity in feet per second
The basic ?ow pattern Within the unit is as follows:
The stock, entering under pressure initiates a swirling
motion in the whole unit, the liquid simultaneously spiral
ling inwardly and downwardly at increasing velocity. An
R=radius in feet
g=acceleration due to gravity=32.2 feet per second2
At a radius of 1.8 inches the calculated value of cen
trifugal force is 968 with free vortex ?ow compared with
only 7.9 for forced vortex ?ow illustrating the magnitude
up?owing helical stream, having a maximum diameter
approximately equal to that of the accepted stock outlet
pipe, develops about an air column which forms at the
central axis, this up?owing stream being maintained by
a liquid ?ow transferring from the downward spiral flow.
of the separating forces that can be developed in this type 10 The apex outlet size, when set to a diameter just larger
than the air column, allows for the fractionation or clas
Due to the increasing velocity obtained with free vortex
si?cation to take place. This fractionation depends on the
?ow considerable shear forces develop as the ?uid spirals
fact that the material being removed follows a different
toward the axis. The shear forces arise as a consequence
pattern than the main liquid stream. Under normal op
of the angular velocity gradient S de?ned as:
15 erating conditions most of the ?bre follows the main liquid
of equipment.
dw
_21rdR
stream. Particles such as fly ash or bark, under the in
(4)
where “w” is the angular velocity in radians per second
and “R” is as ‘de?ned in Equation 3.
It is to be understood that the more common de?nition
of the angular velocity gradient is given by the formula
S
?uence of centrifugal force, work their way through the
pulp, which is in a non-?occulated state because of shear,
to the cone wall, where they are carried by the downward
component of flow to the apex outlet where they are
rejected. Heavy objects such as knots are also carried to
the cone wall and are carried down by the downward
liquid ?ow. However, as they approach the apex the high
centrifugal force developed tends to push them back to
where w is the angular velocity measured in radians per 25 zones of greater radius so that an equilibrium orbit is
established.
second and R is radius in feet. However, it can be readily
With shive, a di?’erent pattern occurs. Whereas the
appreciated that the formula used herein and the more
presence of a shear ?eld is essential to the primary sepa
common de?nition of angular velocity gradient differ
ration of the dirt from the ?bre, it can also give rise to
only ‘by the term 211-, a constant. Computed values of
angular velocity gradient as given herein may be readily
converted to computations of angular velocity gradient
under the formula
30 vre-entrainment towards the apex of the cone.
Shive nor
mally also has a somewhat greater length than thickness
or breadth and in a unit such as that described it tends
to be drawn into the up-?owing stream from regions of
high shear but because of its greater mass as compared
dw
35 with that of the individual ?bres its tendency to be thrown
S_ d R
out from the up?owing column towards the wall is very
much greater. The tangential momentum developed by
simply by multiplying the given values by 6.28.
the shive in the high centrifugal ?eld of the up-?owing
The desirability of shear can best be appreciated from
column is generally su?icient to carry it out towards the
a consideration of the results obtained when centrifugal
cone wall against the in-?owing stock and through regions
force only is applied. When a suspension of pulp ?bres
of high shear to regions of lesser shear at the wall whence
with randomly distributed dirt of the character normally
it carries down and is eventually rejected. This recycling
present is placed in a laboratory centrifuge tube and sub
jected to a high centrifugal ?eld, high speci?c gravity
of the shive within the unit results in an increased con
centration as compared with the feed to the unit in spite
tube, and while both the ?bre and wood dirt concentrate 45 of the fact that its mass is too small to allow the estab
lishment of an orbit of the type described for knots.
towards the end of the tube, the wood dirt remains ran
Thus a counterbalance is set up between the shear effect
domly distributed amongst the ?bre. That is, the migra—
material such as sand will settle at the lower end of the
tion of wood dirt through the ?bre is largely prevented
in the absence of shear. By contrast, in the apparatus of
drawing the concentrated shive into the centre column,
from the region ‘of the ‘apex of the cone, and the centrif
the present invention a high concentration of such wood 50 ugal action which throws it back to the wall. If the
dirt results from the shear at right angles to the centrifugal
‘shear force is relatively great, in relation to the centrif
?eld which is characteristic of “free-vortex” ?ow, and
ugal force, a high concentration of shive develops, and
which breaks up the ?bre ?ocks, allowing such material
some carries through in the accepted stock. By modi
to work through the ?bre.
?cation of the dimensions of the unit the relation be
The shear forces also play an important role in keep 55 tween the centrifugal and shear forces can be varied thus
ing the pulp ?bre from centrifuging out from the suspen
increasing or decreasing the e?iciency of separation of
sion. The ?bres contained in pulp stocks are of apprecia
such material which for certain units may be zero.
ble size, approximately 20 to 30‘ microns in diameter and
The movement of the shive into zones of high shear
1000 to 3000 microns in length, with their mass approxi
appears
to result from the “Magnus effect” as referred
mating that of a solid sphere of 65 microns diameter. It 60
to by D. L. Streeter in “Fluid Dynamics” p. 143
might be expected that due to the high centrifugal forces
(McGraw-Hill, ?rst edition 1948). By this elfect a rotat
developed in the equipment of the present invention they
ing cylinder will move at right angles to the direction
would centrifuge out, and in fact there is considerable
of ?uid ?ow as a result of the velocity gradient obtained
separation of ?bre as indicated by the increased consist
ency of the rejects discharge. Fortunately, however, it is 65 by this motion. The Flettner rotor ship, with ‘circular
rotating cylinders with axis vertical to the ship, operates
possible to control the apparatus so that the major portion
on this principle. The air ?owing past the cylinder on
of the ?bre is carried in the upward helical ?ow. It is
believed that this results from the ?exibility and shape of
the side rotating in the direction of the Wind moves at
the ?bres, with their high ratio of length to diameter.
a faster rate than that on the opposite side, which is
Thus their tendency to settle towards the wall is partially 70 turning against the wind, this resulting in a thrust into
counter-balanced by the tendency of the ends of the ?bres
the direction of high air velocity, i.e., at right angles to
to be caught in the more rapidly rotating inward spirals
the direction of the wind. In the case of pulp suspen
which carry them toward the centre of the unit. The
sions in the vortex cleaners the shive is rotated as a result
shear elfect is most marked and concentrated in regions
of the shear not only in its axial direction, but also end
of small diameter.
76 over end, etc. and in zones with very high shear rates
3,096,275
l9 '
in relation to shive size the thrust obtained can be
greater than that obtained by the centrifugal force.
With a 12 inch diameter unit with 2 inch diameter
inlet and top outlet connections and a 10° cone small
shive of 1A inch length and 1/16 inch thickness, and smaller
was rejected with very high efficiency. However, unlike
tion and liquid viscosity, all of which reduce the velocity
below that predicted by the free vortex equation. The
free vortex equation can be rewritten as:
where “11" is the velocity exponent which has a value of
1 for an ideal free vortex and —'l for a forced vortex.
The velocity exponents as obtained by ?tting the data to
with high ef?ciency, shive having a length of 1A1 to 1/2
Equation 6 for the three units are given in Table II, line
inch and a thickness of 1/s to 3716 inch, as it approached
I
the apex, was carried back into the up-?owing column 10 11.Similarly,
the peripheral velocity, as calculated from the
from which it recycled to the cone wall as described
pressure-radius
relationship was found to be somewhat
above with about 10% being accepted and the balance
lower than the entry velocity, the latter being calculated
being rejected. Still larger sizes of shive were all carried
from the size of the entry connection and the volumetric
in the accepted stock.
throughput
of the liquid. The relationship is given in
However, a unit of similar diameter, and cone angle, 15
the unit previously described which rejected large shive
and having the same 2 inch diameter inlet, but with a
the following equation:
V,=CVp
(7)
four inch diameter top outlet gave excellent rejection of
large shive with relatively little, if any, recycling of the
where V, and V1, are inlet and peripheral velocities respec
shive to the up-?owing column. When the velocity was
tively and C is the inlet velocity coef?cient. Values for
measured at 1.8 inches radius, using the method previ 20 the inlet velocity coefficient are given on line 5 of Table II.
ously described, it was found that the velocity was mate
'From the tangential velocity-radius relationship the cen
rially less than for the similar unit but having a 12.76
trifugal ‘force and angular velocity gradient can be cal
square inch inlet and that the free vortex showed a
transition to forced vortex in the general region in which
the measurement was being made. Unfortunately it was 25
di?icult to accurately establish the true transition radius
with this technique because of the relatively wide radius
band occupied by the orbiting rubber stopper.
culated using Equations 3 and 4 respectively. The rela
tionship between centrifugal force and radius and between
angular velocity gradient and radius are illustrated in
FIGURES 6 and 7 respectively.
The principal data of FIGURES 4 to 7 inclusive are
summarized in Table II. Comparing two units with the
It was found possible, by means of a different tech
same ratio of inlet to outlet, unit “A” having a 4 inch
nique, to establish the flow pattern with somewhat greater 30 diameter inlet and outlet and unit “B” having a 2 inch
accuracy. Prandtl and Tietjens, “Fundamentals of Hydro
diameter inlet and outlet it will be noted, that unit “B”
and Aeromechanics,” p. 214 (1st edition, McGraw-Hill,
(with the smaller inlet-outlet connections) has markedly
1934) show that the change in pressure as a function of
smaller throughput, much lower values of velocity, cen
radius for a free vortex surrounding a forced vortex is
given by the equation:
trifugal force and angular velocity gradient at the periph
ery.
V2
ET: = Pi
( 5)
However, as a consequence of the low peripheral
velocity, the value of the radius at which transition be
tween the free vortex and forced vortex zones occurs is
only half that of unit “A” i.e., 0.6 inch compared to 1.2
inches and since the tangential velocities at the transition
where
P is the pressure at any point in the vortex,
R is the corresponding radius,
V is the corresponding tangential velocity, and p is the
radius in this case are nearly the same the maximum value
of the centrifugal force in unit “B” is approximately twice
that of unit “A” and the maximum value of the angular
velocity gradient is ‘approximately four times as great.
Test cleaners were ?tted ‘with taps for pressure meas
Thus the ratio of centrifugal force to shear in unit “B”
urement placed down the full length of the cone and the 45 is approximately one-half that of unit “A,” i.e. 29X 104
values of pressure as obtained by means of a mercury
compared to 61 x 10-2.
column were plotted against the radius. Typical curves
As previously noted, unit B rejected bark particles and
as obtained with 40 pounds per square inch on the header
small shive with extremely high efficiency, gave interme
density.
are shown in FIGURE 4. Each of these curves is con
diate e?iciency on medium size shive 'which recycles be
vex at large radii, such curve shape being typical of the 50 tween the inner and outer stream, and zero ef?ciency for
pressure pro?le for free vortex motion; at smaller radii
large shive, which, being drawn into the upgoing stream
the curves show an in?ection point followed by a con
by the shear forces, cannot penetrate through the zones
of high shear and therefore carries with the accepted
sure pro?le for forced vortex motion. The three curves
stock from the top of the unit.
differ appreciably in shape and in the value of the radius 55
In contrast to this, unit A having lower centrifugal
at which the transition from free vortex to forced vortex
‘force but also having lower shear and higher ratio of cen
motion occurs, the value of the transition radius being
trifugal force to angular velocity gradient, rejects all
largest with the unit having the two inch diameter inlet
sizes of shive with good e?iciency though its efficiency
and four inch diameter outlet, and smallest with the unit
on very small sizes of dirt is somewhat less than that of
cave section, a concave shape being typical of the pres
having the two inch diameter inlet and two inch diameter 60 unit B.
outlet. At still smaller radii, in each unit, the pressure
The effect of increasing the top outlet diameter in re
decreases to zero and thereafter the central axis of the
lationship to the inlet diameter can be seen by comparing
unit is void of liquid.
unit C, with the 2 inch diameter inlet and 4 inch diameter
When the pressure-radius curves of FIGURE 4 are
outlet to, unit B. The peripheral velocity is increased,
analyzed in accordance with Equation 4 the velocity 65 which has the effect of moving the transition radius away
radius curves shown in FIGURE 5 are obtained.
In
each case, the velocity increases exponentially as the
radius decreases reaching a maximum value at the tran~
from the centre of the unit i.e., from 0.6 inch to 1.5 inches
and thereby reducing the centrifugal force to about one
third, and the angular velocity gradient to one-eighth the
sition radius and then decreases linearly as predicted by
value for unit B. The ratio of centrifugal force to angu
the forced vortex equation.
70 lar velocity gradient is also increased by a factor of 2.5.
It was found with this improved technique that the ve
These changes have the effect of allowing all sizes of shive
locity-radius function does not follow the free vortex
to be rejected with good ef?ciency and with a minimum
equation exactly, i.e.,
of recycle between the upward and downward streams.
The e?iciency on small dirt is reduced because of the
V1R1=VaR2
(1)
the departure being due to axial and radial motion, fric 75 lower maximum centrifugal force.
11
3,096,275
12
'- A number of units having other combinations of inlet
general, these 6 inch diameter units, which can be rela
tively light in construction, are particularly useful in re-'
moving “chop” and “birdsced” which are small, short
chunks of unde?bered wood occurring in chip ground
and outlet connection diameters, maximum cone diam
eters and cone angles were constructed and the pressure
radius relationship established when operating at 40
pounds per square inch pressure. The various relation
ships, as shown in Table II, were calculated for these
units. The important values obtained are summarized
wood as produced by re?ning chips, high yield semi
chemical pulps, etc.
Similarly it is also possible to construct units larger
than 12 inch diameter having essentially the character
in Table III, the three units already described being shown
again as Examples 3, 1 and 6.
istics of say the unit with 3 inch inlet and 4 inch outlet.
The data are arranged in groups of decreasing diam 10 However, when this is carried to its extreme, say units
eter, and, in each group the units are arranged in order
of 36 inches diameter, the unit does not develop suffi
of decreasing peripheral velocity. It can be seen that for
cient centrifugal force to allow efficient removal of shive
each group and in the range examined, increasing the top
and ?ne dirt. However, such units may be used for re
outlet diameter has the effect of increasing the peripheral
moving knots and other heavy dirt.
velocity. In each of these sub groups, decreasing the in 15
The effect of change in cone angle, other dimensions
let size also has the effect of increasing the peripheral
equal, can be seen in the case of the 6 inch diameter unit
velocity. High peripheral velocity results in a large tran
by comparison of data obtained with a 71/2" cone (Ex
sition radius, a low centrifugal force, a low velocity gra
ample 11) and a 15° cone (Example 12). With the
dient and a high ratio of centrifugal force to angular
smaller
cone angle the throughput is somewhat greater
velocity gradient, with the actual magnitude of each being 20 which has
the effect of producing a high entry velocity, a
dependent on the diameter of the unit. For instance the
larger transition radius, and therefore lower centrifugal
ratio of centrifugal force to angular velocity gradient is
force and shear. In these examples the ratio of centrifugal
greater for units of 12 inch diameter than for geometri~
force to shear is little different in the two units.
cally similar units of smaller diameter.
The 3 inch diameter unit described in Example 13 of
Dealing speci?cally with the 12 inch diameter unit the 25
Table ‘III having a ‘0.5 inch inlet, a 0.63 inch outlet and
highest ratio of centrifugal force to shear is obtained with
the unit having a 3 inch inlet and a 4 inch outlet, Exam
5° cone angle was the unit selected by Sampson and
ple 2, Table III. This unit will give complete elimination
of all sizes of shive from pulp suspensions of low ?bre
Group for actual use in cleaning pulp suspensions.
It
was found to have a very small transition radius, 0.07
concentration and has excellent e?iciency at ?bre concen 30 inch, high centrifugal force and extremely high velocity
trations of about 0.75% which is a normal concentration
gradient. The ratio of centrifugal force to velocity gra
prevailing in the manufacture of pulp and paper. It is
dient of 3.5 ><il0—2 is too low to allow removal of any
also effective on bark and other types of dirt and has a
shive more than 3/16 inch in length.
high capacity. The value of 725 for centrifugal force
By enlarging the outlet size to 1.06 inches (Example
and 925 sec.-1 ft.—1 for angular velocity gradient are ade 35
14) it was found possible to improve the rejection of
quate. This unit is preferred to the unit with a 2 inch inlet
shive so that it is possible to reject shive having a length
and 4 inch outlet (Example 1) which has excellent e?i—
ciency on all sizes of shive at low ?bre concentration but
because of the lower values of centrifugal force and angu~
of 1A to 1/2 inch and a thickness of 1A; to 9/16 inches
similar to that obtained with the unit having a 12 inch
lar velocity gradient tends to lose in efficiency rapidly as 40 diameter and ?tted with a 2 inch inlet and outlet con
the ?bre concentration is increased. It is also more ef
nections (Example '6). However this unit is effective
fective than the unit with the 4 inch inlet and 4 inch out
only at very low ?bre concentrations.
let (Example 3) because of the higher ratio of centrifugal
The ratio of centrifugal force to velocity gradient is
force to angular velocity gradient, i.e. 79 x10-2 compared
greater for geometrically similar units being approxi
to 61 ><*10-2.
The unit with the 3 inch inlet and 3 inch outlet (Ex 45 mately twice as great for units of twice the diameter
therefore giving ‘better shive removal for that unit. How
ever, with any unit size the ratio of centrifugal force to
ample 4) has a centrifugal force to angular velocity
gradient ratio of 49><10-2. Its high centrifugal force
and velocity gradient give it improved cleaning perform
velocity gradient can be increased by increasing the outlet
pipe
in relationship to the inlet pipe. However, when
larly adapted for use in the production of newsprint which 50
this is carried to extremes the centrifugal force and shear
ance on types of dirt other than large shive. ‘It is particu
otherwise contains considerable small shive and other dirt
but does not contain very large shive.
The unit with the 2 inch diameter inlet and 2.5 inch
outlet (Example 5) is a lower capacity unit and has a
values become low and the unit is ineffective for direct
removal except at extreme low ?bre concentrations.
When the pressure to a unit is increased the through
centrifugal force to velocity gradient ratio of 3<8><10—2. 55 put, tangential velocity, centrifugal force and velocity
gradient are all increased. However the location of the
transition radius is not altered and within the range of 10
to 60 pounds per square inch there is no major change in
This unit is useful on bleached pulps and ?ne papers
where extreme cleanliness in regard to ?ne particles is
required and where only small shive may be present in
the initial stock. This unit is preferred to the similar
the classi?cation of shive that is obtained, although the
unit but with a 2 inch diameter outlet (Example 6) which 60 cleaning efficiency is increased.
has a rather similar value for centrifugal force and a
Generally, I have found that a centrifugal force to
lower ratio of centrifugal force to velocity gradient.
velocity gradient of 16 ><10—2 or higher is necessary to
This last named unit, with 2 inch diameter inlet and
give adequate removal of shive from ?bre in commercial
outlet was initially used to remove conducting particles
pulps. Units working at a centrifugal force to velocity
from a paper machine furnish for the production of
65
ta‘bulating card stock with outstanding results compared
to any other cleaning device used previously for this
grade of paper.
The dimensions of the 9 inch diameter unit (Example
7) were so selected as to give a similar result to that ob
tained with the 12 inch diameter unit with the 2 inch
inlet and outlet connections referred to above (Example
6,). It is also possible to achieve approximately the same
results using a 6 inch diameter unit but using outlet diam
eters considerably larger than the inlet diameter.
In
gradient of 60><l0r2 and higher will reject dirt of all
type and have particularly high ef?ciency on large shive
of the type found in unscreened unbleached pulps. Units
working in the range of 25 to 60><'10—2 are suitable for
pulps which have already been subjected to some pre
cleaning and do not contain the largest shive sizes, being
particularly effective on bark specks, on shive having a
size of 1/4 inch length and 1/16 inch thickness and even up
to 1/2 inch length and 1A5 inch thickness which are difficult
to bleach.
3,096,275‘
13
TABLE II
Characteristics of 12 Inch Diameter Units Fitted With
10° Cones Operating at 40 Pounds per Square Inch
Pressure
velocity is substantially constant, the ?rst and second zones
meeting at a radial ‘distance from the central axis at which
the centrifugal force and angular velocity gradient are at
5 a maximum, the ratio of centrifugal force to angular
.
Unit’imot size'outlet diameter
“A”
“B”
“on
128 Sq_
inichelzls?
2 inches’
2inchcs
2 inches’
4i11ches
40
4O
40
£38
3288
.98
360
(7) Peripheral centrifugal force,
24 8
71
34 6
.
21 6
aVl
.
cien -____
16S _________________ __
ien
124
(10) Transition radius, inche
(11) velocity exponent
(12)
_
I
.
a
.
.
.
.
-
63
16
~
,
-
-
‘
.
of centrifugal force to velocity gradient has a value with
i
1n the range of 16><1()-2 Ito 79><1O—Z.
20
3. The method of separating from an aqueous pulp
.
,
'
suspension of cellulose ?bers dirt particles of widely v-ary
1.20
,57
0.60
_66
1.56
46
.
.
I ‘
‘
.
_
mg
sizes
characterized
by the use of an apparatus having
498
4M
445
a diameter at the larger end thereof between 6 in. and
770
1490
490
'
k
12 1n.,
a ,cone angle between
7.5 c ‘and 15 o , an inlet
diam
25 eter between -1 1n. and 4 1n., an axial accepted stock outlet
1240
5150
too
.
.
.
between 1 1n.
and 4 1n.,
and a reJected
stock outlet of
61
29
74
a1
orce a
(13 ) entrifu
mm menus,
gramme? _____ n
(14) Angular velocity gradient at
transition radius,
mi
___________________sec.“l
-
.
u3
, seer ___________ __
ratio at periphery x10
.‘
cellulose ?bers rand withdrawing at‘the end remote ‘from
.
.4
20
(9) Centrifugal mm to Shear
gra
‘
the apex end a stream of suspension which contains a
15 mayor proportion of the cellulose ?bers.
2&0
2. A method according to claim 1 wherein the ratio
.
.
(a) rezrrip‘iiiemti anguilar velocity
.
the apex end said dirt and a minor proportion of the
2392
(1)98
33.5
5) Inlet veloci y coe
.
at said radial distance being less than 29,000 sec.“1 ft?1
rlrtnrtougiliputt o?s/gais/mmn
(4) Peripheral geiocit?g, ft./§ec___
E6) Peripheralpressqre,Msecm
. 5G0 ....... .._
l
10 while operating at 40 p.s.i. feed pressure, and continuously
withdrawing from the central portion of the vortex at
(1) Pressure to unit’ Minn?“
V8 061 y,
.
velocity gradient at said radial distance being at a value
greater than 16x10“2 and an angular velocity gradient
no es
e
14
angular velocities and a second zone wherein the angular
(15) Riiftiiiiigiftyczigrciigiiilégrireanq
smallersize than said accepted stock outlet, whirling the
sition radius. X10‘2 ------ --
suspension in the separating chamber to produce a vortex
‘
0 of conical form, said vortex having a zone of high shear
1 Equivalent to a 4-inch diameter radius.
3
TABLE III
Behaviour of Vortex Cleaners 0]‘ Various Dimensions
OPERATING AT 40 POUNDS PER SQUARE INCH PRESSURE
Diameter, inches
Transition radius-inches
Cone
Ex,
Top
C one Inlet
12
12
l2
12
12
12
9
8
6
6
6
6
3
3
2
3
4
3
2
2
1. 66
1.5
1.0
1. 0
1.0
1.0
0. 5
0. 5
Velocity
angle, at 40 p.s.i., at inlet
deg.
outlet
4
4
4
3
2. 5
2.0
2.0
1. 5
1. 63
1. 36
1.0
1.0
.63
1. 06
Capacity
U.S. .gals/
ft./secs.
nun.
10
10
10
10
10
10
10
10
15
15
7. 5
15
5
5
380
540
790
420
266
230
165
112
83
73
70
56
21.2
28. 0
38. 9
24. 5
20.6
19.1
27. 2
23. 6
24. 6
20. 4
34
29. 9
28. 7
23
34. 6
45. 7
Periph-
Inlet
erial
velocity
it./secs
cient
velocity,
coe?i-
23. 6
21.0
19. 8
15.0
14.0
10. 7
15.0
11.3
21. 6
16.8
13. 6
12. 5
15. 5
33.0
. 61
. 86
. 98
. 79
. 51
. 46
. 61
.55
. 63
.56
.48
.54
.45
. 69
I claim:
'l. The method of separating from an aqueous pulp
suspension of cellulose ?bers dirt particles of Widely vary
ing sizes characterized by the use of an apparatus com
prising a separating chamber having at least a portion
thereof of conical form, a tangential inlet at the larger
end thereof, an axial accepted stock outlet at said larger
end and an axial dirt discharge outlet at the apex of the
chamber, the diameter at the larger end of said chamber
being from 3 in. up to less than 36 in., the cone angle
Velocity ex-
Transi
tion
ponent . radius
in inches
. 46
. 68
. 57
. 70
. 63
. 66
. 56
.66
. 53
. 60
. 54
. 63
.23
—~. 19
1. 5
1. 5
1.2
. 90
. 72
. 60
. 50
. 36
. 54
. 45
. 33
. 27
. 07
.35
Veloe- Centrifugal Velocity
ity,
force
gradient,
ft./sec. gravities see-1 ftrl
44. 5
54. 0
49. 8
56. 5
53. 6
49.0
51. 6
49. 8
53. 3
52. 5
44. 8
56.8
31.0
25.0
490
725
770
1, 340
1, 490
1, 490
1, 990
2, 560
1, 630
2, 280
2, 260
4, 680
5, 140
670
660
925
1, 240
2, 730
3, 900
5, 150
7, 410
14, 700
6, 420
9, 580
14, 500
29, 000
180, 000
3, 820
Ratio cen
trifugal
force to
velocity
gradient
74><10~a
79Xl0-I
61 X10-2
49x10-1
321x104
29x10"2
27x10-2
17Xl0'7
25Xl0'1
24><10~?
16x10-2
17x10"2
2. 9X10-2
17. 5X10-a
forces as measured by the ‘angular velocity gradients act
ing simultaneously with centrifugal force, an angular
velocity gradient created in said zone not greater than
29,006 sec.“1 ftfl while operating at 40 p.s.i. feed pres
sure, a ratio of centrifugal force to angular velocity gra
dient at the point substantially of maximum value of said
0
forces being greater than 16x10"2 whereby dirt particles
are concentrated in the outer centrifugal ?eld of the vortex
together with a minor proportion of the cellulose ?bers,
and continuously withdrawing from the rejected sto'c‘k
being between 5° and 18°, said inlet diameter being 5 outlet said dirt particles including shive and a minor pro
portion of ?ber and withdrawing from the accepted stock
greater than 0.5 in., and said axial accepted stock out-let
outlet a stream of suspension containing a major propor
being not less than 1 1n., the method comprising intro
tion of the cellulose ?ber.
References Cited in the ?le of this patent
of widely varying sizes including shive, whirling the sus
UNITED STATES PATENTS
pension in the separating chamber to produce a vortex of 70
2,878,934
Tomlinson ___________ ___ Mar. 24, 1959
conical forms having a ?rst zone of radially increasing
ducing an aqueous suspension of cellulose ?bers into the
tangential inlet, the suspension containing dirt particles
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