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Патент USA US3045835

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July 24, 1962
F. J‘ FONTEIN
PROCESS AND APPARATUS FOR SEPARAT
OF PARTICLES ACCORDING TO
3,045,823
A MIXTURE
ZE
Filed Sept. 2, 1958
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FIG.2
m
117
is.
3,045,823
’
Patented July 24, 1962
1
2
in which the same pressure is created on both sides of the
'
3,045,823
PROCESS AND APPARATUS FOR SEPARATHNG
A’ MIXTURE 0F PARTICLES ACCGRDING T0
SIZE
.
-
Freerk J..Fontein, Heerlen, Netherlands, assignor to
Stamicarbon N.V., Heerlen, Netherlands
Filed Sept. 2, 1958, Ser. No. 758,406
Claims priority, application Netherlands Sept. 4, 1957
'
8 Claims.
surface, the classi?cation is in some places ?ner than in
others, so that a certain non-uniformity of the classi?cation
over the surface is observed. Probably, this phenomenon
is to be ascribed to liquid currents from the space adjoining
the feed side of the surface to the space adjoining the other
side, and vice versa. A liquid current from the feed side
of the surface to the throughput side occurring at a certain
spot will cause a coarser classi?cation at this spot, whereas
a current in the reverse direction will cause a ?ner classi?
(Cl. 209-273)
This invention relates to particle separation and more
particularly to improvements in method and apparatus for
separating particles suspended in a liquid.
In my copending application, Serial No. 475,251, ?led
December 14, 1954, which matured into Patent No.
cation. The feed side is'to be understood in this descrip
tion as the surface of the classifying device on which the
suspension?ows.
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is
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>
"
r'
It is an object of the subject invention not only to
eliminate the above-mentioned disadvantages, but also to
provide a control at will, of the ?neness of the classi?ca
2,916,142, there is disclosed a process which comprises the
steps of: establishing at a feeding position a layer forma
tion.
tion flow of particles and a suspending liquid and support
ing one surface thereof; interrupting the support of the
Another object of the present invention is the provision
of a method of separating particles suspended in a liquid
one surface of said layer formation flow for a ?xed dis
tance measured in the direction of ?ow; blocking the ?ow
in which the ratio between the overpressures or under
pressures prevailing on both sides of the separating sur
of an incremental layer, having a thickness substantially
less than said ?xed distance of support interruption, from
the one surface of the unsupported layer formation flow
the ?neness'of separation can be regulated within certain
so that the particles in the blocked incremental layer "of .
a size less than twice the thickness of the incremental layer »
together with a substantial portion of the suspending liquid
in said incremental layer will be separated from the layer
-
face in at least one part thereof can be controlled so that
limits.
.
A further object of the present invention is the provision
'of an apparatus for separating particles suspended in a
liquid which is‘ provided with means fo'r'controlling the
ratio between the overpressures or underpressures on both
formation ?ow; supporting the one surface of the re
‘sides of the separating surface of the apparatus in at least
mainder of the layer formation flow a second ?xed dis 30 one part thereof so that the ?neness of separation can be
tance measured in the direction of ?ow; and successively
' regulated within certain limits.
repeating the steps of interrupting the support, blocking
the ?ow of an incremental layer, and supporting the re
mainder of said layer ‘formation ?ow, between said feed
ing position and a discharge position throughout a path
generally conforming to a surface generated by moving a
line parallel to itself so that a given point on the line moves
in a plane perpendicular to the moving line while maintain
ing a predetermined minimum velocity gradient in said
layer formation ?ow between said feeding position and
said discharge position.
According to the aforementioned speci?cation, the sus~
pension to be separated is fed tangentially to the concave
side of a curved screening deck, in a direction perpendicu
lar to the generatrices thereof. The screening deck con
sists of a curved plate having circular or slot-like apertures,
the greatest dimension of the latter being parallel to the
generatrices of the screening deck, or of bars substantially
rectangular or trapezium~shaped in section, which bars
Still another object of the present invention is the
provision of an apparatus of the type described having
improved means for controlling the pressures on opposite
sides of the screening surfaces.
These and other objects of the present invention will
become more apparent during .the course of the follow
ing detailed description‘ and appended claims.
7
The invention may best be understood with reference
40 to the accompanying drawings wherein illustrative em
bodiments ‘are shown.
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, In the drawings:
FIGURE 1 is -a diagram of an embodiment of an appa
ratus according to the invention;
FIGURE 2 is a diagram of another embodiment;
. FIGURE 3 is a diagram of still another embodiment,
with a curved screen deck.
'
a
.
Referring now more particularly to the drawings, there
is shown in FIGURE 1 a diagram of an apparatus‘ em
are disposed in a direction parallel to the generatrices of
bodying the principles of the present invention, which
the screening deck.
includes a screening deck 1, having a screening surface
I
a
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It is well known that by means of an apparatus equipped
with a screening deck as described above, which apparatus
is known by the name of sieve ‘bend, a separation can be
which faces downwardly. Surrounding the screening sur
face is a housing 2, the side walls of which are joined
to the sides of the screening deck. Adjoining the screen.
carried out in which substantially all of the solid particles 55 ing deck and housing 2 atone end is a feed chamber 3,
taken along through the openings by the greater part of the
and a discharge chamber 4 for the over?ow fraction is
liquid are not greater than half the width of the slot-like
disposed at the opposite end thereof. The chambers 3
apertures or than one quarter of the diameter of the circu
and 4- are preferably provided with shutoff valves 5 and
lar apertures, so that the danger of blockage is very small.
6, respectively. The housing 2. includes a substantially
_ The good operation of the sieve bend is to be ascribed 60 horizontal wall 7 which is disposed at a greater distance
to the phenomenon that, as a result of the high speed at
from the screening deck near the feed end thereof than
which the suspension travels on the screening deck, each
near the delivery end. On the throughput side of the
time the suspension crosses a slot-like aperture, a thin layer
screen deck 1 there is a plurality of chambers '8 having
of liquidis separated from it, which layer is considerably
walls,9-which are joined to the throughput side of the
thinner than the slot width and is in the main not thicker 65 screening deck, the arrangement heingsuch that all the
than 1A of the slot width; particles which are embedded for
suspension ?owing through the apertures in the screen
at least half of their ‘diameter in this layer are entrained by
deck is collected in these chambers. Each chamber is
it, with the consequence that the maximum diameter of a
provided ‘with a discharge pipe 10‘, through which the
particle removed through a slot is not greater than half - throughput can- be controlled, e.g., by means of ‘a valve 11.
the slot width.
70 By controlling the amount of throughput through each
It has. been found that when, a classi?cation is carried '. valve 11, the extremely small» pressure diiferences pre
out under pressure over a sieve bend in a closed housing
vailing at both faces of the screen may be controlled‘.
3,045,823
ll.
3
The suspension to be screened is supplied at A. The
pressure under the screen deck was kept the same, which
meant a heightening of the pressure difference, it was
oversize or over?ow fraction is discharged at B, the
undersize or throughput fractions are discharged at C.
found that the 50% particle size increased to 88/14, the
95% size of 142g. The experiments proved that by a
Example I
di?erentation the pressure difference between the feed side
and the throughput ‘side of the screen deck the particle
size of separation can be altered.
Referring now more particularly to FIGURE 2, there
is shown a modi?ed apparatus embodying the principles
mm., a screen length of 760 mm., a screen width of 200
mm. and a distance between wall 7 and screening deck 10 of the present invention which includes a screening deck
110, preferably constructed of bars perpendicular to the
varying from 15 to 71/2 mm. At the side of the
plane of the drawing or of a perforated plate, by prefer
chamber 8 there is maintained back pressure somewhat
ence one having slot-like openings normal to the plane of
greater than the aforesaid pressure at the feed side so as
the drawing. The screening deck 110 divides ‘a closed
to produce a thinner layer on the feed side with a smaller
housing, having an upper substantially horizontal wall 111,
particle size. The feed was 34.4 cu. m./h., the through
into two compartments 112 and 1713, the part 112 being
put 9.6 cu. rn./h.
A suspension of sand in water was supplied under an
overpressure of, for example, one atmosphere, to the
feed side of a ?at sieve bend having a slot width of 0.4
on th e upper feed side and the part 113 on the lower
The screening results are given in the table below, in
throughput side of the screening deck. Adjoining the
throughput side of the screening deck there are chambers
which the screening results measured in the eight suc
cessive chambers are stated separately.
Throughput in chambers
Sample
Over
new
Concentration in glliter__-.-
1
2
3
4
5
6
7
8
27
12
15
18
17
19
21
18
Grain size
508
Percent
>490
13. 3
350-420 ...... __
300-350 ...... ._
250-300...
7. 7
2. 8
1. 4
210-250 ____________________ __ 3. 6
105-210 ____________________ __ 51. 7
<105 ______________________ -_ 43. 3
0. 2
0.3
0. 7
0. 4
O. 6
0. 7
0. 3
27. 6
0.3
0. 6
9. 6
89. 9
12. 5
86. 8
1. 2
18. 9
79. 2
0.8
l4. 7
84. 1
1. 3
22. 7
75. 4
1. 5
27. 7
70. 1
0.8
22. 3
76. 6
8.1
37. 0
9. 6
By separately collecting the throughput fractions of ~
the chambers and taking in account the measured con
centrations of the said fraction, the average throughput
114 adjoining each other and extending from the feed end
to the delivery end, each chamber having a discharge
aperture 115, e.g., a slot, whose surface is at most equal
to the total of the surfaces of ‘the slots in the correspond
ing part of the screening ‘deck. The slots 115 all open
put multiplied with the total throughput provides the total
amount of solid particles in the throughput. The total 40 into the space 113. Preferably, the area of the discharge
apertures will be such that these apertures can discharge
amount ‘of solid particles in the over?ow is found by
the amount of suspension under normal conditions sepa
multiplying the concentration of the over?ow-fraction
rated off by the screen apertures, without a back pressure
with the capacity of the over?ow-fraction
being created in the chambers 114. Thus, the genera
of the screens can be determined. This average through
' tion of counter currents from the space 113 to the cham
By ‘making a graph, wherein the vertical axis indicates
the percentage and the horizontal axis the size of the
bers 114 is prevented. As shown in the drawing, the
particles a curve is formed, wherein from every grain size
the percentage present in the over?ow fraction can be.
determined, such graphs are well known in the art of
the screen deck 110 and its narrowest passage area near
screening.
The 95% particle measured 127;», the 50% particle
85/1,. At equal pressures at both faces of the screen, e.g.
when the screen is positioned in the open atmosphere, if
no back pressure had been exerted on the chambers 8, the
95% particle would have measured about 200a.
By
“50%” and “95%” particles is to be understood the
particle sizes of which 50% and 95%, respectively, get
into the over?ow fraction.
Example II
In an experimental installation having a screen length
of 75 mm. and a screen width of 2.35 mm, a slot width
of 0.2 mm., a bar width of 0.9 mm, a suspension of coal
in water was passed over the screen surface at a feed
pressure of 0.2 atm. gauge, while equal overpressures
were maintained at both sides of the screen deck.
The feed amounted to 35.48 cu. rn./h., the solids con
space 112 has its widest passage area near the feed end of
the delivery end, the area decreasing gradually. The
passage area of the space 113 increases correspondingly.
As a result, the formation of eddies in the spaces 112 and
1113 is largely avoided. The feed and the pressures in the
spaces 112 and 113 are controlled by any suitable means,
such as valves 116, 117, and 118.
The apparatus according to the invention prevents the
formation of a current from the delivery end of the space
112 through the screening deck and the space 113 to the
feed end thereof, and back through the screening deck to
the feed end of the space 112. -Moreover, the apparatus
60 provides the possibility of controlling the ?neness of the
screening through control ‘of the pressure di?erence be
tween the spaces 113 and 112.
It is not essential that the chambers 114 have the same
shape as shown in the drawing. Several variations are
' possible, without departing from the invention.
Referring now more particularly to FIGURE 3, there
is shown an apparatus similar to that shown in FIG
URE 2, except that the screening deck 1110 is cylindrically
centration in it being 69.4 g./l., so that the supply of solid
bent, as indicated at 110’ and the chambers are corre
substance amounted to 2.469 t./h.
The throughout fraction amounted to 0.16 cu. m./h.,
spondingly shaped as indicated at 112' and 113'. The
apparatus shown in FIGURE 3 also includes the remain
ing elements similar to those of the apparatus shown in
the solids concentration was 7.9 g./l., and the discharge
of solid substance was 0.001 t./h. The size of the 50%
particle was 76a, that of the 95 % particle 1331.0. When
the feed was increased to 37.17 cu. m./h., while the over
FIGURE 2 designated by the corresponding primed nu
meral.
Thus, the apparatus of FIGURE 3 includes a cy
75 lindrical wall 111', a plurality of chambers 114', slots
3,045,825
115' and Valves 116', 117' and 118', all related in the
bounding one. chamber is kept as constant as possible,
as pressure differences in the region over a chamber have
same manner described above in regard to FIGURE 2.
It can thus be seen that the ?neness of separation in one
or more parts of the separating surface in all the embodi
ments shown is controlled by means of a control of the
ratio between the loverpressures or underpressures prevail
ing on both sides of the separating surface in this part or
to be kept small. Also, care should be taken that the
or
flow pro?le on the feed side of the classifying device over
a chamber is su?iciently high as compared with the
length, so that the pressure difference between the initial
and ?nal parts of the pro?le over a chamber cannot be
come unduly high. However, eddy currents in this part
parts. In this way, the classi?cation over the entire sepa
rating surface can be controlled, while the ?neness can
of the housing should also be guarded against. Favor
be regulated within certain limits in one and the same ap 10 able dimensions are such at which the area of the slots
paratus.
It can also be seen that a rise in the pressure prevailing
on the throughput side causes a slight raising of the liquid
layer ?owing across the opening, so that the lowermost
layer which is separated off becomes thinner ‘and conse
quently smaller particles are entrained. When the pres
of a chamber is, at most, four times the mean passage
area over this chamber at the feed side of the screening
deck.
The invention can be applied not only to sieve bends
which are enclosed in a housing, and in which, as is
known, the suspension is fed tangentially onto the con
sure on the‘feed side is raised with respect to the pressure
cave side of the screening deck in a direction perpendicu
lar torthe generatrices of the screening deck and in which .
the slot-like apertures are parallel to the generatrices,
' ing the throughput fractions?owing through the above 20 while the radius of curvature of the screening deck may
mentioned part or parts in separate spaces adjoining each
be in?nite. It may also be applied to classifying devices
‘of these parts, and controlling the discharge of the above
whose section perpendicular to the direction of flow of
rnentioned fraction or fractions from this space or spaces.
the material has a curved shape and in which, if the
on the throughput side the ‘opposite will happen.
Preferably, the pressure ratio is controlled by collect
an;M
and.»
In general, the apparatus of the present invention util
device has slot-like openings, the slots are perpendicular
izes _a closed housing provided with feed apertures and 25 to the direction of ?ow‘ of the material. Care will have
controllable discharge apertures, which housing. is divided
to be taken that in a flow pro?le the height over the
into two compartments by a classifying device constituted
screening deck is about the same in all places.
by a plate provided with circular or slot-like apertures
With the apparatus according to the invention it is not
or by parallel bars of rectangular or trapezium-shaped
‘necessary that the feed side of the separating deck faces
section, separated by slot~like openings, said apparatus 30 upwards. For instance, if a ?at separating deck is used
further comprising means for supplying the material to
as shown in FIGURE 1, this may be so placed that the
be classi?ed, which means deliver the material in the
feed
{It thus
side faces
will be
down
seenand
that
thethe
throughput
objects ofside
thisfaces
invention
direction towards and parallel to the feed end of the
classifying device and onto this feed end in a sense
have been fully and effectively accomplished. It will
perpendicular to the slots, means for discharging the 35n-be realized, however, that the foregoing speci?c embodi
separated fractions, and means for creating an over
ment has been shown and described only for the purpose
_ pressure in the two parts of the housing, as described,
.of illustrating the principles of this invention and is sub
e.g., in the above said patent application. According to
ject to extensive change without departure from such
the invention there‘are means, at least extending over
principles. Therefore, this invention includes all modi
a part of the classifying device and bounding on the 40 ?cations encompassed within the spirit and scope of
throughput side thereof, for collecting and controlling the
the following claims.
amount of material ?owing through this part. These
I claim:
.
means for collecting and controlling may, according to
1. A process of separating a mixture of particles ac
the invention, consist of one or more collecting cham
cording to size which comprises the steps of: establish
hers, the side walls of which form the bounding planes
ing at a feeding position a layer formation flow of parti
of the above-mentioned parts, each of which chambers
cles and a suspending liquid and supporting one surface
is provided with at least one discharge aperture.
thereof; interrupting the support of the one surface of
To insure good operation of the apparatus according
said layer formation ?ow for a ?xed distance measured
to the invention, it is necessary that from every chamber
in the direction of ?ow; blocking the flow of an incremen
an amount of suspension can ?ow that is of the same 50 tallayer having a thickness substantially less than said
order of magnitude as the amount which would flow
?xed distance of support interruption from the one sur
through the apertures of the part of the classifying device
face of the unsupported layer formation ?ow so that the
lying over the chamber, if ‘the classifying device were in
particles in the blocked incremental layer of a size less
stalled in the open atmosphere while the suspension were
than twice the thickness of the incremental layer together
passed across the classifying device at the same rate.
with a substantial portion of the suspending liquid in
To this end,’the chambers and/ or their discharge aper
said incremental layer will be separated from the layer
tures must be given such a shape that through these dis
formation ?ow; supporting the one surface of the remain
charge apertures the above-mentioned amount of ma
der of the layer formation ?ow a second ?xed distance
terial can flow. This may be attained by seeing to it
measured in the direction of flow; successively repeating
that in the chambers a su?iciently high resistance is cre 60 the steps of interrupting the support, blocking the flow
ated when the suspension is ?owing through, or by giving
of an incremental layer, and supporting the remainder
the apertures in the chambers the required size.
of said layer formation flow between said feeding posi
In one embodiment of the invention the part of the
tion and a discharge position throughout a smooth path
housing adjoining the throughput side of the classifying
generally conforming to a surface generated by moving
device is divided by means of partitions into a number 65 a line parallel to itself so that a given point on the line
moves in a plane perpendicular to the moving line while
of chambers each of which is provided with one or more '
discharge apertures.
maintaining a predetermined minimum velocity gradient
In the above-described apparatus according to the
in said layer formation ?ow between said feeding posi—
invention the ?neness of separation in each chamber can
tion and said discharge position con?ning the incremental
be controlled through a suitable control of the discharge 70 layers and associated liquid separated from said layer for
apertures of these chambers. In another embodiment
mation ?ow at a plurality of positions throughout said
the chambers debouch in the part of the housing situated
path, maintaining pressures in the layer and in the sepa
on the throughput side of the classifying device.
rated incremental layers and associated liquid diifering
It is import-ant that the rate at which the suspension
from the atmospheric pressure and differing in the layer
supplied ?ows across a part of the classifying device 75 on the one side and the incremental layers and associated
3,045,823
7
8
liquid at the other side and controlling in at least one po
tion of ?ow of the- material to be screened not exceed
sition along said path said last differences by controlling at
ing the dimensions perpendicular to said direction, each
aperture being de?ned by at least one surface facing in
least one of the separated, emanating volumes of the said
a direction opposed to the local direction of flow of the
2. Apparatus for separating a mixture of particles ac C1 material and disposed in a plane transverse relative to the
screening surface, a housing surrounding said screening
cording to size comprising a screening deck having a
deck on the screening side thereof, means for feeding par
screening surface generally conforming to a smooth sur
ticles and a suspending liquid at a pressure different from
face generated by moving a line perpendicular to a ?at
the atmospheric pressure adjacent the feed end of said
plane along a line in said plane, a feed end at one end
of said surface and a discharge end at the other end of 10 screening deck and past the screening surface in confined
relation to said housing so that the surface de?ning said
said surface, so that material fed onto said surface
apertures facing in the direction of the feed end will
travels along the screening line in a general direction
engage incremental layers of a thickness substantially less
perpendicular to said moving line, said surface being
than the width of the associated screening and particles
provided with apertures the dimensions whereof measured
in the incremental layers of a size less than twice the
in the direction of flow of the material to be screened
thickness thereof and a substantial portion of the suspend
not exceeding the dimensions perpendicular to said di
ing liquid will pass through the apertures and the remain
rection, each aperture being defined by at least one sur
ing particles and liquid will pass on to the discharge end
face facing in a direction opposed to the local direction of
of the screening deck, adjustable means for discharging
flow of the material and disposed in a plane transverse
relative to the screening surface, a housing surrounding 20 from said housing the particles and liquid remaining on
the screening surface at the discharge end thereof, and
said screening deck on the screening side thereof and
means surrounding at least a portion of said screening
tapering toward the screening deck from the feed end to
deck on the side thereof opposite from said screening sur
the discharge end thereof to provide a continually reduced
face for collecting and controlling the amount and size
cross-sectional area, means for feeding particles and a
of particles and suspending liquid passing through the
suspending liquid at a pressure different from the at
associated screening apertures and including a plurality
mospheric pressure adjacent the feed end of said screen
of collecting chambers between the feed end and dis
ing deck and past the screening surface in con?ned rela
charge end of said screening deck, each of said chambers
tion to said housing so that the surface de?ning said
having a discharge opening.
apertures facing in the direction of the feed end will
5. Apparatus as de?ned in claim 4 including means for
engage incremental layers of a thickness substantially less 30
controlling the area of each discharge opening.
than the width of the associated screening and particles
6. Apparatus as de?ned in claim 4 wherein each dis
in the incremental layers of a size less than twice the
charge opening is so shaped that the amount of particles
thickness thereof and a substantial portion of the sus
and suspending liquid that can ?ow therethrough is of
pending liquid will pass through the apertures and the
the same order of magnitude as the amount which would
remaining particles and liquid will pass on to the dis
?ow through the associated screening apertures when
charge end of the screening deck, adjustable means for
operating at atmospheric pressure.
discharging from said housing the particles and liquid
7. Apparatus as de?ned in claim 4 wherein the area
remaining on the screening surface at the discharge end
of the screening apertures associated with each chamber
thereof, and means surrounding at least a portion of said
is at most equal to four times the mean area under the
screening deck on the side thereof opposite from ‘said
chamber at the feed side of the screening deck.
screening surface for collecting and controlling the
8. Apparatus as de?ned in claim 4 wherein said hous
amount and size of particles and suspending liquid pass
ing includes a portion surrounding the discharge open
ing through the associated screening apertures.
ings of said chambers, said housing portion having a pas
33. Apparatus as de?ned in claim 2 wherein said last
sage area which gradually increases from the feed end
mentioned means comprises a collecting chamber having
of said screening deck to the delivery end thereof, the
sides de?ning the boundary of said screening deck por
area at any position being such that it is at least equal
tion, said chamber having at least one discharge opening
to the joint areas of the chamber discharge openings lying
therein.
upstream from such position.
4. Apparatus for separating a mixture of particles ac
cording to size comprising a screening deck having a
References Cited in the ?le of this patent
screening surface generally conforming to a smooth sur
face generated by moving a line perpendicular to a ?at
UNITED STATES PATENTS
layer.
plane along a line in said plane, a feed end at one end
of said surface and a discharge end at the other end of
said surface, so that material fed onto said surface travels
along the screening line in a general direction perpendicu
lar to said moving line, said surface being provided with
apertures the dimensions whereof measured in the direc
1,135,304
Liggett et al ___________ __ Apr. 13, 1915
2,912,109
2,916,142
Mitchell _____________ __ Nov. 10, 1959
Fontein ______________ __ Dec. 8, 1959
FOREIGN PATENTS
722,195
Great Britain _________ __ Jan. 19, 1955
vv-
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