U.S. patent number 3,563,454 [Application Number 04/737,897] was granted by the patent office on 1971-02-16 for method of and apparatus for separating the various phases of a fluid mixture.
Invention is credited to Pierre H. L. Saget.
United States Patent |
3,563,454 |
Saget |
February 16, 1971 |
METHOD OF AND APPARATUS FOR SEPARATING THE VARIOUS PHASES OF A
FLUID MIXTURE
Abstract
A method of separating the various phases of a fluid mixture in
which the mixture is subjected to a centrifugal field and
simultaneously suddenly diverted along the whole of its flow path
which is substantially perpendicular to the centrifugal directions.
Also included is an apparatus for use in carrying out the
method.
Inventors: |
Saget; Pierre H. L. (Paris, 16,
FR) |
Family
ID: |
8633525 |
Appl.
No.: |
04/737,897 |
Filed: |
June 18, 1968 |
Foreign Application Priority Data
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|
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Jun 21, 1967 [FR] |
|
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PV111,337 |
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Current U.S.
Class: |
494/53; 34/58;
494/68; 494/900; 494/50; 494/69 |
Current CPC
Class: |
B04B
1/04 (20130101); Y10S 494/90 (20130101) |
Current International
Class: |
B04B
1/00 (20060101); B04B 1/04 (20060101); B04b
007/00 () |
Field of
Search: |
;233/44,40,27--39 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Price; William I.
Claims
I claim:
1. Centrifugal apparatus for effecting separation of a mixture
comprising a rotatable vessel, a plurality of axially spaced plates
mounted in said vessel for rotation about the same axis as said
vessel, means for admitting said mixture to said vessel whereby the
mixture is subjected to a centrifugal force, said axially spaced
plates having a plurality of spaced openings arranged such that the
spaced openings of adjacent plates are nonaligned, whereby mixture
flowing axially from one spaced opening of one plate is directed
toward a solid portion of another plate between the spaced openings
in the latter plate, said mixture flow being thereby diverted
laterally in that said diverted flow is in a general direction
substantially perpendicular to a plane defined by the longitudinal
axis of the vessel and by a radial line of said vessel.
2. An apparatus according to claim 1, characterized in that the
openings in the plates are elongated slots.
3. An apparatus according to claim 2, characterized in that the
slots are straight and radial.
4. An apparatus according to claim 2, characterized in that the
slots are arcuate relative to a radial line.
5. An apparatus according to claim 2, characterized in that the
slots lead to the peripheral edges of the plates.
6. An apparatus according to claim 2, characterized in that the
plates have edges along the slots which are bent back in an
upstream direction relative to the axial flow of the mixture to be
treated.
7. An apparatus according to claim 6, characterized in that the
plates are shaped between the slots in the form of two converging
wall sections to form swirl channels.
8. An apparatus according to claim 1, characterized in that the
plates comprise a plate assembly which is in the form of a
truncated cone.
9. An apparatus according to claim 1, characterized in that the
plates of the stack have same dimensions.
10. An apparatus according to claim 1, characterized in that the
external diameter of each plate is variable according to its
position in the stack.
11. An apparatus according to claim 1, characterized in that the
internal diameter of each plate is variable according to its
position in the stack.
12. An apparatus according to claim 1, characterized in that the
plates are cut away over a part of their length.
13. An apparatus according to claim 1, characterized in that the
spacing of the plates is uniform.
14. An apparatus according to claim 1, characterized in that the
spacing of the plates is variable as a function of their position
in the stack.
15. An apparatus according to claim 1, characterized in that the
plates are driven in synchronism with the rotatable container.
16. An apparatus according to claim 1, characterized in that the
plates are driven at a speed slightly different from that of the
rotatable container.
17. An apparatus according to claim 1, characterized by a
peripheral helicoidal conveyor to which the plates are coupled.
18. An apparatus according to claim 1, characterized in that the
container walls are continuous.
19. An apparatus according to claim 1, characterized by a drying
container constituting the rotatable container.
Description
This invention relates to a method and apparatus for treating a
mixture of materials so as to separate the various phases
thereof.
It is known to use centrifugal apparatus for phase separation and,
as will be seen from FIG. 1 which is a diagrammatic axial section,
these generally comprise a rotatable container 1 and a central hub
2 which widens towards the bottom of the container. The mixture to
be treated is introduced through the hub and driven in rapid
rotation by the container so as to produce within the mixture a
centrifugal field, the intensity of which is a function of the
nature of the mixture.
The heavy phase is driven under the action of the centrifugal field
towards the container 1, while the light phase moves towards the
hub 2, whence it is evacuated by overflowing through an opening
3.
In known centrifugal apparatus having containers of large diameter
three phenomena appear during their operation which reduce the
efficiency thereof. These are as follows:
The decantation distance, i.e. the distance d over which the heavy
particles must pass to reach the wall of the container 1, is
considerable and the separation time is therefore increased in
comparison to what it would be in a centrifugal apparatus of small
diameter;
The movement of the various annular layers of mixture relative to
each other and to the container is such that the speed of rotation
of the container is not attained by the layers and the centrifugal
field is therefore not as intense as it should be within the
mixture;
Various turbulences due to the impulsion in the feeding zone, to
thermal gradients and to the driving energy of the centrifugal
field itself are set up in the mixture and disturb the
decantation.
In order to remedy these disadvantages with a view to improving the
efficiency of these known centrifugal apparatuses, various means
have been employed.
In a first known method of operation, illustrated by the
diagrammatic axial section of FIG. 2, truncated cone-shaped parts
4, generally known as plates, are positioned in the container 1 and
rotatably driven in synchronism therewith. For this purpose the
plates 4 are located one above the other and separated by uniform
distances and are fixed to the lower widened end 5 of the hub 2.
The assembly constituted by this hub, the plates and the container
1 is rotatably driven and, as in the previous case, the mixture to
be treated is introduced through the hub and circulates in the
container and between the plates. The light phase is evacuated
through the opening 3, while the heavy phase moves toward the
internal wall of the container 1.
The plates 4 enable the decantation distance d to be reduced and
constitute a collection element for the heavy particles. They
eliminate cohesive turbulence by dividing the flow of mixture into
thin layers. They also improve the rotational propulsion of the
mixture by internal friction.
However, these plates have numerous disadvantages:
Because of their truncated cone shape they increase the vertical
size of the apparatus and complicate its shape. This results in an
increase in the cost of manufacture of such an apparatus and of the
ratio of the cost to the amount of mixture treated. Moreover, their
own net cost is high;
the angle of the plates is not always the same and it must in
effect be modified in numerous cases to take into account the
coefficient of friction of the deposited sediments. The
construction of the apparatus must thus be adapted to each
particular treatment;
the sediments which reach the periphery of the plates fall back
into the feeding zone of the latter and are partially brought back
into suspension;
the flow of mixture between the plates is subjected to a radial
centripetal component which reduces the efficiency of decantation.
This component increases when the mixture moves towards the center,
the annular flow section decreasing. The centrifugal field
diminishes when the treated mixture moves towards the center and
the separation effect is thus reduced. Under these conditions,
since, for the mixture circulating from the periphery towards the
center, the separation effect diminishes and since, by contrast,
the propulsion effect increases, only the peripheral zones of the
plates operate efficiently;
cleaning of the plates is almost unavoidable in numerous cases due
to imperfect sliding of the sediments towards the periphery. Such
cleaning is difficult, especially if the plates are very close
together to provide efficient separation;
when a mixture of two liquids is to be treated, regulation of the
surface of separation of the two liquids must be effected with
precision because this surface must be stabilized in a narrow zone
defined by holes formed in the plates. The less dense liquid,
located on the side of the surface of separation corresponding to
the holes, must be evacuated through these holes towards a central
opening, the denser liquid at the other side of the surface being
evacuated towards a peripheral opening.
A second known method of operation has also been put into effect to
obviate the disadvantages of centrifugal apparatuses such as that
known in FIG. 1. In this second method of operation which is
represented in FIGS. 3 and 4, which are an axial section and a
diametric section respectively, the centrifugal apparatus has
radial partitions 6 located within the rotatable container 1 and
driven in synchronism therewith. These partitions have the
advantage of ensuring good propulsion of the mixture at the speed
of rotation of the container, but they do not enable the
decantation distance to be reduced, and neither do they diminish
the cohesive turbulence.
Moreover, they frequently lead to preferential concentrations 7 of
sediments deposited against the lateral wall of the container, and
this is especially so for apparatuses of large diameter. These
concentrations are theoretically distributed in zones which are
regularly disposed at the periphery, but in practice this
distribution can occur other than aforesaid and lead to static and
dynamic imbalances. Finally, when the container holds a
considerable quantity of sediments the multiple radial partitions 6
are deeply buried in the sediment and their extraction can become
particularly difficult.
A main object of the present invention is to combine the advantages
of the two known methods of operation while removing their
disadvantages, particularly in order to obtain maximum efficiency
in centrifugal apparatuses.
According to the invention, a method of treating a mixture of
various phases in order to separate them is characterized in that
the mixture is subjected to a centrifugal field and the mixture
flow is suddenly diverted along the whole of its flow path, which
is substantially perpendicular to the centrifugal directions.
From another aspect, the invention includes an apparatus for
carrying out the aforesaid method and comprising, within a
rotatable container, a stack of plates concentrically surrounding
the axis of the container and rotatably driven, the plates being
spaced from each other and having angularly staggered orifices such
that the plates constitute deflectors whose general direction is
substantially axial.
In a preferred embodiment, the plate orifices are slots, preferably
straight and radial and leading to the peripheral edges of the
plates. The edges of the slots may be bent back towards the
upstream direction of the zigzag axial flow path of the mixture to
be treated. The plates may, moreover, be profiled between the slots
to form swirl channels.
In order that the invention may be more fully understood, various
embodiments in accordance therewith will now be described, by way
of example, with reference to FIGS. 5 to 13 of the accompanying
drawings, in which:
FIG. 5 is a partial perspective view showing the means
characteristic of the invention, i.e. the slotted plates;
FIG. 6 is a diagrammatic end view of FIG. 5 illustrating the method
of the invention;
FIG. 7 is a plan view of the stack of plates;
FIGS. 8 and 9 are views similar to FIG. 7 showing alternative
embodiments;
FIGS. 10 and 11 are views similar to FIG. 6 showing other
variants;
FIGS. 12 and 13 are diagrammatic axial partial sections showing
several embodiments of the apparatus in which said plates are
included.
FIGS. 14 and 15 are diagrammatic axial sections showing several
embodiments of the apparatus in which said plates are included.
Referring to the drawings, the apparatus of the invention comprises
a container 1 in which are mounted plates 8 concentrically
surrounding its axis. The plates are driven in rotation and spaced
one from the other so as to form free annular spaces through which
the mixture to be treated can circulate. These plates are
essentially characterized by the fact that they have orifices 9
which are angularly staggered from one plate to the next.
Thus, the free spaces between the plates and the staggered orifices
in the plates constitute zigzag passages whose general direction is
substantially parallel to the axis of rotation of the assembly.
This results in the flow of mixture in the axial directions 10
being diverted each time it passes through a plate (FIGS. 5 and 6).
Thus, there is produced a centrifugal effect f in the bends 11 and
12 of this flow 10 which tends to propel the heavy particles to the
outside of the bends, i.e. towards the plate opposite along the
trajectories 13.
The foregoing illustrates the operation of the method of the
invention, which consists in subjecting the mixture to a
centrifugal field F while suddenly diverting the flow 10 of the
mixture along the whole of its substantially axial path. In other
words, the effects of the centrifugal force F applied to the heavy
particles or droplets (which centrifugal force is due to the
rotation of the assembly of the container 1 and plates 8) are
combined with the effects of the centrifugal force f due to the
sudden changes in direction of the streams of treated fluid flowing
in general axial directions.
The heavy particles or droplets propelled by the less dense fluid
along the zigzag axial flow path 10 thus tend, at each sudden
change of direction, to continue their trajectory in a straight
line and hit the opposite plate 8, as in impact filters. The main
centrifugal field F acts on all the heavy particles or droplets and
causes them to move towards the periphery, and this is so for those
within the mixture, as well as for those which are thrown against
the plate 8. The main centrifugal effect F is orthogonal to the
aforesaid deflection effect on which it has no direct disturbing
influence and it is observed that it entirely retains its
separating effect.
Moreover, the deflection effect tends to amass to heavy particles
or droplets on the plates 8 along which the main centrifugal field
causes them to slide rapidly towards the periphery. Under these
conditions, amassing of the particles or droplets due to the
deflection effect increases the volume/outer surface ratio of the
particles or droplets and thus increases the speed of separation
thereof. It is important to note that collection of the heavy
particles or droplets occurs in a "dead zone" due to the effect of
the wall. This results in these particles or droplets being no
longer subjected to the propulsion effect of the circulating fluid,
and this increases the efficiency of the centrifugal field.
Moreover, the passage of the mixture through the orifices and
between the plates encourages rotation of the mixture at the
angular speed of the rotor, so that movement of the fluid layers
relative to each other and to the rotor is diminished, or even
eliminated. The apparatus thus possesses the advantages of radial
partition centrifugal apparatuses, but without their drawback of
periodicity in the distribution of the sediments. Again, the choice
of an angle of taper is no longer of prime importance, as in the
plate type centrifugal apparatuses. The field of application of the
method and apparatus of the invention is very wide and can include
the treatment of liquids loaded with solid particles, as well as
mixtures of liquids, or again gas loaded with solid particles or
droplets and also includes washing gases by collecting water on the
plates, etc...
In the embodiment shown as a preferred but nonlimitative example in
FIGS. 5 to 7, the plates 8 are flat annular discs in which the
orifices are constituted by slots 9. These discs are coaxially
stacked and conveniently separated one from the other, being fixed
together and to the rotatable assembly which includes the
container. However, during stacking and fixing of the discs, it is
necessary to take the precaution of staggering, by half the width
of a plate portion between two slots, the slots of discs in even
rows relative to the slots of the discs in odd rows, with the
object of creating through the system of these slots zigzag paths
having an axial direction.
The slots 9 can be straight (FIGS. 7 and 8) or curved (FIG. 9) and
they can extend radially (FIG. 7) or with a certain incidence so as
to take into account the sliding of the layers, even though this is
reduced to a minimum. The slots can lead to the peripheral edge of
the discs (FIG. 7), or to the central edge of the discs (FIG. 9),
or may not lead to either of these edges. Moreover, the slots,
instead of being elongated, can be formed in the discs as a series
of holes of any shape. The width of the slots is preferably
uniform, but it can also be variable from the center towards the
periphery to take into account flow variations in the fluid
streams.
A simple means for mounting the discs 8 in the container 1
consists, as shown in FIG. 13, in tying them together in the
vicinity of their central edges by means of rings 14 and fixing the
stack thus constituted, by means of tie bars for example, to the
lower widened portion 5 of the hollow central hub 2, radial arms 15
also being used to connect the upper disc 8 to the hub. There is
thus obtained a perfectly rigid assembly which is very easy to
construct.
The distance between the discs is generally constant, but it can
nevertheless be varied from one end of the container 1 to the other
as a function of the denseness obtained and the possible losses of
pressure which result therefrom.
It is indicated in the foregoing, considering the axial zigzag flow
of the mixture, that it forms "dead zones" 16 (FIG. 6) downstream
of the slots on the plates situated opposite, in which zones the
heavy particles or droplets collect due to the deflection effect
and avoid being propelled by the zigzag flow of the fluid streams.
In order to accentuate the aforesaid deflection effect and at the
same time produce the "dead zone," it is advantageous to provide
turned back edges 17 on the plates 8, as shown in FIGS. 10 and 11,
which edges extend along the whole length of the slots 9 and
projecting in the upstream direction of the zigzag fluid flow 10.
These edges 17 can be formed by pressing from the discs and their
edges can be sharp at the points where they meet the fluid
streams.
The deflection effect can be further improved by shaping the
unslotted portions 18 of the discs 8 between the slots 9 to form V
sections pointing in the upstream direction. (FIG. 11). This
particular shaping can moreover be dimensioned to give rise to
small localized swirls in the "dead zones" 16 tending to in crease
the effects of collection and evacuation of the heavy particles or
droplets.
The bent back edges 17 and the shaped portions 18 form gutters in
which the heavy particles or droplets collected under the
deflection effect are channeled and directed under the effect of
the centrifugal force towards the periphery. It is clear that the
annular discs 8, instead of being flat, can have a slight conicity,
which is much less accentuated than that of known plates. This
conicity of the discs 8 is intended to take advantage of the main
centrifugal force so that the latter tends to maintain the heavy
particles or droplets applied against the walls 18 of the discs,
whilst projecting them towards the periphery.
The discs 8 can have the same dimensions so as to form a
cylindrical stack (FIG. 13). In certain cases, however, the stack
can have a different shape in order to adapt the apparatus to
particular problems which may arise. Thus, the outer diameter of
the discs 8 can be variable so as to form, for example, a stack
comprising two truncated cones producing an expanded median zone
(FIG. 12). This particular embodiment is extremely advantageous in
the case of an apparatus in which the heavy phase is automatically
evacuated at the periphery, the container 1 of such apparatus
having evacuation nozzles, valves, openings etc. at 19. In a
similar manner the inner diameter of the discs can vary.
It is moreover possible, by variations in diameter or by cavities,
to form preferential zones 20 (FIG. 13) intended to ensure, for
example, the collection of light compact sediments, in which zone
known means are provided for their removal.
Moreover, since the slots 9 extend largely radially, there no
longer exists any difficulty in regulating the surface of
separation of two liquids, which surface can, in effect, be located
on any diameter, providing that it still passes through the
slots.
In the foregoing the discs 8 are fixed together and to the
container so that their angular speed is always strictly equal to
that of the latter. In certain cases, it can be advantageous to
drive the discs at a speed which is slightly different from that of
the container, so as to produce a rotational movement of the discs
relative to the container. For this purpose, the disc assembly is
mounted on a rotatable support distinct from the container and
driven at an appropriate speed. This embodiment is important when
the container includes a peripheral helicoidal conveyor to propel
the separated heavy products. In this case the conveyor is fixed to
the stack of discs.
Naturally, the discs 8 having staggered slots 9 of the invention
are applicable not only to centrifuges having plane walled
containers 1, but also to dryers having perforated containers to
facilitate the central flow of large quantities of liquid.
The invention is not limited to the embodiments shown and described
in detail, since various modifications can be made thereto without
departing from its scope.
* * * * *