EP0287462A2 - Method and apparatus for the centrifugal separation of a mixture of several phases - Google Patents

Abstract

The mixture is driven through a rotor under the combined effect of a drop in pressure between the upstream side and downstream side of this rotor, and the rotation of the latter. According to the invention, the rotor consists of a stack of joined discs (36), each of which is pierced with a set of helical passages (62). Each of these passages (62) is limited by solid walls (64, 66, 68, 70) and opens out on the upstream face (37) and downstream face (39) of the disc (36) in inlet apertures (63) and outlet apertures (65) respectively. An outlet aperture (63) on a given disc is situated exactly opposite an inlet aperture (65) of the following disc. Application to the separation of the constituents of a mixture. <IMAGE>

Description

The present invention relates to a separation method and device using centrifugal force to separate the immiscible constituents of a mixture of various phases, for example: gas in liquid, liquid in gas, liquid in liquid, solid dispersed in a gas or liquid, or any other combination of products that are not fully miscible with each other.

Centrifugal separation methods and devices are known at the present time in which the mixture to be treated is rotated through a rotor in order to create an intense centrifugal field inside the mixture.

The sectional view of Figure 1 attached illustrates such a centrifugal separation assembly.

This, bearing the general reference 10, first comprises a substantially cylindrical enclosure 12 and arranged vertically, the mixture to be treated arriving at the lower part of this enclosure via a pipe 14. The centrifuge device proper, bearing the reference 16, is located above the enclosure 12. It is rotated by a motor assembly 18 connected to the device 16 by a bearing system 20. A pipe 22 makes it possible to create a pressure drop through the device 16 thanks to a fan (not shown) and to extract the mixture which has passed through the centrifuge device 16. Optionally, part of the mixture extracted by the pipe 22 can be recycled by means of a pipe 24 opening into the pipe 14. The heavy dust or phases which have been separated by the device 16 fall into a space 26 at least partially surrounding the enclosure 12 and, from there, fall into a cyclone or other equivalent device 26 by the i ntermediate of a pipe 28. A pipe 30 to the part bottom of cyclone 26 allows dust or heavy phases to be removed, while part of the gas passing through cyclone 26 can be returned to line 14 (in the example illustrated here, the latter is arranged so as to connect the upper part of cyclone 26 to the lower part of enclosure 12). It can also be seen in FIG. 1 that the pipe 14 opens tangentially to the base of the enclosure 12, which already gives the mixture a helical movement which allows a first separation of certain constituents, these being evacuated by a pipe 32 provided at the lower part of the enclosure 12. Optionally, a filter 34 can be provided immediately below the device 16, that is to say upstream thereof if we consider the direction of flow of the mixture at through this device.

This may include, as described for example in document FR-A-2 468 410, a stack of discs 17 arranged so that a pressure drop between the upstream and downstream of the stack causes the passage of the mixture through this stack following helical veins. Optionally, a rotary inlet distributor 19 can be provided upstream of the stack of discs 17 and a rectifier 21 immediately downstream of this stack.

The stack described in document FR-A-2 468 410 is illustrated in Figures 2 and 3 attached. Figure 2 is a developed section of the stack of discs and Figure 3 a section along line III-III of Figure 2. The stack consists of a series of discs 36 each consisting of a thin plate located a certain distance from the adjacent upstream and downstream discs. Each disc 36 has a number of openings 38 angularly offset from each other and arranged in staggered rows from one disc to the next. Thus a solid part 40a of the disc 36a (Figure 2) is located immediately below an opening 38b of the disc 36b. It can be seen that, even if this stack does not rotate, the existence of a pressure drop between the upstream and downstream of this stack of discs causes the passage of the mixture following helical veins. This pressure drop can be obtained by any known means, for example a fan placed at the outlet of the rotor so as to create a vacuum downstream thereof or by a fan placed upstream so as to create an overpressure upstream. In the present description, the expressions "upstream" and "downstream" should be understood with respect to the direction of flow of the mixture to be treated through the rotor.

In the particular case of FIG. 2, it can be seen experimentally that the gaseous veins flow along helical trajectories. However, a mixing stream leaving an openwork of a row n disc does not cross the openwork placed immediately in front of the disc n + 1, but the next openwork.

If the distance between two consecutive discs is equal to the width of the openings, the slope of the veins relative to the discs is equal to 1/3.

The mixture is divided into a number of live veins 42 passing through the openings 38 of the discs 36. Between the live veins 42 are dead veins 44 in which the gas does not flow continuously, but where the the presence of vortices 46 is noted.

It can also be seen in FIG. 2 that flanges 48 have been provided perpendicular to the plane of the discs along the front edge of each perforation 38. The words "front" and "rear" must be understood with respect to the direction of flow mixing through the discs. These flanges act as blades which accelerate the entrainment of the mixture when the rotor is rotated. The height of the flanges 48 is equal to one third of the distance between two consecutive discs. This condition is necessary so that the live streams 42 can flow normally through the rotor. In fact, if the height of the rim were greater, it would enter the circulation zone, that is to say into a vein 42 and strongly disturb it, reducing the flow rate and greatly altering the purification characteristics. So that it remains good, the flows through the rotor must be substantially laminar. If, on the contrary, the flange was too short, the rotation of the rotor to the fluid would be poorly transmitted and the latter would then slide backwards relative to the rotor. There would also be a very significant disturbance in the quality of purification, the circulating veins being ill-defined and largely turbulent.

It can be seen that, when a pressure drop is created between the upstream and downstream of the rotor and, in addition, the latter is rotated, the mixture passes through the rotor with an angular speed greater than that of the latter. . It can also be seen that an intense centrifugal field is created inside the live streams 42, causing the evacuation of the heavy phase or phases towards the periphery of the rotor. A centrifugal field is also created inside the vortex veins 44, but it is less intense. As these veins are also the seat of many vortices, the evacuation and separation are not as good as in the live veins 42. In addition, transient deposits are observed on the discs, on the upstream and downstream faces of the solid parts 40 separating the openings 38, in the vicinity of the rim 48 and on the rear face of the latter.

However, these deposits are temporary and end up being evacuated under the effect of centrifugal force. But they can be more or less important and require stopping the device for dismantling the rotor for cleaning the discs.

To improve the separation efficiency, a solution has been proposed, illustrated in the section view of FIG. 4. This solution consists in using discs which are no longer perpendicular to the axis of rotation of the rotor, but of diverging conical shape. upstream: in other words, each disc makes an angle α with a plane perpendicular to the axis of rotation of the rotor.

The orientation of the veins is disturbed and they mix. The heavy phases present in the vortex veins are ejected more efficiently than in the case of Figure 3 and quickly meet a solid surface on which they agglomerate and are guided gradually to the periphery.

The present invention aims to further improve the separation by providing a method and a device for centrifugal separation of a mixture of several phases leading to a more efficient and more selective separation.

Its purpose is to generate in the mixture a very intense centrifugal field and much higher than that to which the rotor which is at the origin of the treatment is subjected. Thanks to this characteristic, the design and manufacture of the rotor are simplified and less costly than for a device of the prior art leading to a centrifugal field of the same intensity. Mass production techniques, such as foundry or the use of plastics, then become possible.

Another object of the invention is to improve the efficiency of separation of phases having very similar specific masses, as well as the evacuation of the separated product out of the treatment zone without risk of remixing.

It also aims to reduce to a minimum value the energy necessary for the acceleration of the mixtures to be treated thanks to an efficient device for recovering kinetic energy at the outlet of the rotor.

It optionally allows, when the carrier fluid is gaseous, to lower its temperature by expansion at the inlet of the rotor, which can be used to lead to condensation and the evacuation in liquid form of an initially gaseous phase.

More specifically, the subject of the invention is a process for centrifugal separation of a mixture of several phases comprising at least one heavy phase in which the mixture is passed through a rotor rotating at a given speed, the mixture being divided into a plurality of parallel veins flowing through the rotor along helical paths and being driven to an angular speed higher than that of the rotor. This has the effect of creating a centrifugal field inside the veins, which allows the ejection of the heavy phase.

According to the invention, the veins are limited by solid walls linked to the rotor, a centrifugal field being thus created on the surface of these solid walls, and the heavy phase ejected under the action of the centrifugal field prevailing in the veins is collected on trap elements associated with the solid walls; in addition, it is guided towards the periphery of the rotor by guiding devices associated with these walls, the heavy phase moving towards the periphery of the rotor under the effect of the centrifugal field created on the surface of these walls.

According to another characteristic of the process which is the subject of the invention, in order to drive the mixture in rotation, it is subjected on the one hand to the action of driving the rotor in rotation and, on the other hand, to a pressure drop between upstream and downstream of the rotor, the latter being arranged so that this pressure drop causes the mixture to pass through the rotor along helical paths.

According to another aspect of the invention, the helical flow of the mixture is transformed into axial flow downstream of the rotor.

According to another advantageous aspect of the invention, the kinetic energy of rotation of the mixture is recovered at the outlet of the rotor to drive the latter in rotation.

The invention also relates to a device for implementing this method. This device comprises, in a known manner:
- a rotor through which the mixture to be treated can pass,
means for creating a pressure drop through this rotor, the latter being arranged so that the mixture passes through it by following helical veins under the effect of this pressure drop, and
means for driving the rotor in rotation about an axis.

According to the invention, the rotor comprises:
- solid walls limiting said helical veins,
- trap elements, associated with these walls, for collecting said heavy phase, and
- guide elements associated with these walls, to guide said heavy phase towards the periphery of the rotor.

According to a particular embodiment, the rotor comprises a set of contiguous discs whose axis coincides with the axis of rotation of the rotor, each disc having an upstream face and a downstream face and comprising at least one channel for circulation of the mixture. disposed along a portion of a propeller and limited by solid walls, this channel opening onto the upstream face by an inlet openwork and on the downstream face by an outlet openwork. In this case, the outlet opening of a channel formed in a given disc is immediately opposite the entry opening of a channel formed in the next disc, said openings having the same shape.

Thus, there are created through the rotor continuous circulation channels of helical shape and limited by solid walls.

As for the expression "contiguous disks", it means that two consecutive disks of the stack are in contact with one another on at least part of their surface. As will be seen below, in a preferred embodiment, the discs are in peripheral contact thanks to studs formed on the upstream face of one and which rest on the downstream face of the other, these studs being separated by slots allowing the extraction of certain particles.

According to one embodiment, said channel being of helical shape with respect to the axis of the rotor and being limited by a lower wall, an upper wall and two side walls, the latter being concentric with the axis of the rotor, the lower wall and / or the upper wall includes (s) grooves, the edges of which are arranged radially relative to the disc.

According to another embodiment, still in the case where the channels are helical in shape and bounded by a wall lower, an upper wall and two side walls, the latter being concentric with the axis of the rotor, the lower wall and / or the upper wall has (s) at least one protruding element arranged in a portion of a helix relative to the rotor axis.

The upstream and downstream faces of each disc can be flat and perpendicular to the axis of the rotor. However, in another embodiment, the upstream and downstream faces of each disc can be designed so as to present a part in the form of a truncated cone of the same angle at the top and diverging upstream relative to the direction of flow of the mixture. through the rotor.

In another embodiment, each disc has the form of a hollow circular case comprising:
- an entry openwork on its upstream face,
- an outlet opening on its downstream face,
guiding means forcing the mixture to perform at least one complete revolution inside the disc between these two openings,
- a set of elements in the form of truncated cones, located inside the housing and diverging upstream, and
- a peripheral slot for the ejection of the heavy phase.

This device can also comprise, upstream of the rotor, a rotary distributor comprising a set of blades oriented from the center towards the periphery and whose concavity opens downstream, each blade having a trailing edge whose inclination corresponds to the slope of said helical veins relative to the rotor. According to a preferred embodiment, the trailing edges of the blades are integral with the first upstream disc of the rotor and coincide with the rear edges of the openings provided on the upstream face of this disc.

The device may also include, downstream of the rotor, a rectifier comprising a set of blades oriented from the center towards the periphery and whose concavity opens upstream, each blade having a leading edge whose inclination by ratio to the rotor corresponds to the slope of said veins helical. Advantageously in this case, the leading edges of the blades coincide with the front edges of the outlet openings of the last downstream disc of the rotor.

According to another aspect of the invention, the rotor is placed inside an enclosure having an internal surface which diverges upstream.

In a first embodiment, the internal surface of the enclosure is smooth and of generally conical shape diverging upstream.

According to another embodiment, usable when the rotor consists of a stack of discs, the internal surface of the enclosure has a set of circular parts, each of which faces the lateral edge of a disc of the rotor, the diameter said circular parts increasing from downstream to upstream. In this case, the distance between the edge of a disc and the internal face of the enclosure can be constant or increase regularly from downstream to upstream.

• - la figure 1 est une vue schématique en coupe verticale de l'ensemble d'un système de séparation centrifuge dans lequel peut être utilisé le dispositif de l'invention,
• - la figure 2 est une vue schématique en coupe développée du rotor décrit dans le document FR-A-2 468 410,
• - la figure 3 est une section suivant la ligne III-III de la figure 2,
• - la figure 4 est une vue semblable à la figure 3 dans le cas où les disques présentent une partie conique,
• - la figure 5 est une vue schématique en coupe et en perspective d'un dispositif de séparation centrifuge conforme à l'invention,
• - la figure 6 est une vue schématique en perspective d'un empilement de disques utilisés dans le dispositif de l'invention, les faces amont et aval des disques étant perpendiculaires à l'axe de rotation du rotor,
• - la figure 7 est une vue semblable à la figure 6 dans le cas où les faces amont et aval des disques présentent une partie conique,
• - la figure 8 est une vue schématique en perspective d'un disque tel que ceux illustrés à la figure 6 montrant comment on peut prévoir des rainurages sur les parois supérieures et inférieures des canaux hélicoïdaux ménagés dans les disques,
• - les figures 9a à 9d sont des vues en coupe développée montrant diverses formes possibles pour ces rainurages,
• - la figure 10 est une vue schématique en perspective semblable à la figure 8 montrant une autre forme possible pour les éléments proéminents prévus sur les parois supérieures et inférieures des canaux hélicoïdaux,
• - la figure 11 est une vue schématique en coupe et en perspective montrant une autre forme de réalisation possible d'un disque utilisé dans le dispositif objet de l'invention, et
• - la figure 12 est une vue schématique en coupe d'un empilement de disques semblables à celui qui est illustré à la figure 11, certains disques étant représentés coupés suivant un secteur seulement.

The invention will appear more clearly on reading the description which follows, given by way of purely illustrative and in no way limitative example, with reference to the appended drawings, in which:

• FIG. 1 is a schematic view in vertical section of the assembly of a centrifugal separation system in which the device of the invention can be used,
• FIG. 2 is a schematic view in developed section of the rotor described in document FR-A-2 468 410,
• FIG. 3 is a section along line III-III of FIG. 2,
• FIG. 4 is a view similar to FIG. 3 in the case where the discs have a conical part,
• FIG. 5 is a schematic sectional and perspective view of a centrifugal separation device according to the invention,
• - Figure 6 is a schematic perspective view of a stack of discs used in the device the invention, the upstream and downstream faces of the discs being perpendicular to the axis of rotation of the rotor,
• FIG. 7 is a view similar to FIG. 6 in the case where the upstream and downstream faces of the discs have a conical part,
• FIG. 8 is a schematic perspective view of a disc such as those illustrated in FIG. 6 showing how grooves can be provided on the upper and lower walls of the helical channels formed in the discs,
• FIGS. 9a to 9d are views in developed section showing various possible shapes for these grooves,
• FIG. 10 is a schematic perspective view similar to FIG. 8 showing another possible shape for the prominent elements provided on the upper and lower walls of the helical channels,
• FIG. 11 is a schematic sectional and perspective view showing another possible embodiment of a disc used in the device which is the subject of the invention, and
• - Figure 12 is a schematic sectional view of a stack of discs similar to that illustrated in Figure 11, some discs being shown cut along a sector only.

Referring to FIG. 5, it can be seen that the device which is the subject of the invention is located inside an enclosure 50. The rotor essentially consists of a stack 17 of discs 36 mounted on an axis 52. It can be rotated by a motor (not shown in Figure 5). In the particular case described here, the axis 52 is vertical, but it would not go beyond the scope of the invention to arrange this axis in another direction, horizontal or oblique. A fan 54 placed above the stack 17 makes it possible to create a pressure drop across the rotor. This fan may consist of a set of blades 56 mounted on the axis 52 and made integral with the latter, the gas or the mixture being evacuated by a tangential tube 58. The fan 54 is housed inside a volute 60 connected to the enclosure 50 by a converging connector 62. The tangential tube 58 makes it possible to evacuate the treated mixture free of heavy phases.

Of course, the fan can be of another type, for example an axial fan, and can be replaced by a compressor arranged upstream. The main thing is to have a device allowing a pressure drop to be created across the rotor, from upstream to downstream, considering the direction of flow of the mixture. In the case where the latter is a liquid, a suction or discharge pump can be used to create this pressure drop. In certain particular cases, the device intended to ensure the circulation of the mixture through the rotor can be outside the enclosure and driven by an independent motor.

We see, in the lower part of Figure 5, the enclosure 12 inside which circulates the mixture to be treated before arriving at the rotor; the space 26 between the enclosure 12 and the enclosure 50 is used for the evacuation of the heavy phases ejected under the effect of the centrifugal fields created inside the mixture and falling by gravity.

We also see the rotary distributor 19 provided at the bottom of the stack of discs, that is to say upstream of the rotor. This distributor consists of a set of vanes 23 arranged so as to deflect the mixture flowing under the effect of this pressure drop along helical paths. For this, each blade has a concavity oriented downstream if we consider the direction of flow of the mixture and each blade has a trailing edge (not visible in Figure 5) whose inclination relative to the rotor axis is equal to the slope of the helical veins of the mixture in the rotor. Preferably, this trailing edge coincides with the front edge of an inlet opening of the first upstream disc at the lower part of the stack 17: thus, the space between two successive vanes of the distributor 19 constitutes a continuous path with the helical channel, the inlet opening of which is located at this point on the disc. Thus, the distributor 19 transforms the axial speed of the mixing upstream of the rotor at helical speed through the rotor, reducing turbulence and corresponding energy losses. In addition, as a result of the deflection it creates, the distributor 19 also has a primary heavy phase separation function which it channels towards the periphery. The curvature of the concavity of the vanes 23 and the conformation of their leading edge are established as a function of the aero or hydrodynamic characteristics of the mixture and of the operating regime.

Likewise, at the outlet of the rotor, a rectifier 21 constituted by a turbine with a given action or degree of reaction can be provided. This rectifier consists of a set of blades 27 whose concavity is turned upstream, if one considers the direction of flow of the mixture through the rotor. Each blade 27 has a leading edge which coincides with the front edge of an outlet perforation on the downstream face of the last disc of the stack 17 and the inclination of this leading edge is equal to the slope of the veins helical following which the mixture circulates inside the rotor. Since the mixture circulates along a helical trajectory, its speed has a tangential component and an axial component. The design of the concavity of the blades 27 is designed so as to cancel the tangential component. There therefore remains only the axial component and the mixture leaves the rectifier 21 in a direction parallel to the axis 52.

Another interesting aspect of the rectifier 21 is that the mixture leaving the last disc at the upper part of the rotor has a certain speed, therefore at a certain kinetic energy. This kinetic energy pushes the rectifier 21 in the direction of rotation of the rotor and therefore contributes to driving it in rotation. This makes it possible to reduce the necessary power of the drive motor of the shaft 52. The vanes 27 of the rectifier 21 also have a finishing function and guide the separated fractions towards the periphery. In the example described here, the rotor 17, the distributor 19, the rectifier 21 and the fan 54 are mounted on the same shaft 52 and therefore rotate in synchronism. We would not, however, depart from the scope of the invention by using an assembly in which some of these elements are driven independently of the others. This device is also useful for ensuring suction by the fan 54 under satisfactory efficiency conditions. In the case, in fact, where the flow is not straightened, and according to a phenomenon well known to professionals, the component of rotation of the mixture very greatly alters the performance of the fan 54. The curvature of the concavity of the blades 27 and the conformation of their trailing edge are determined according to the aero or hydrodynamic characteristics of the mixture and the operating regime. In addition, the conformation of the blades 27 is such that they channel towards the periphery the residual traces of heavy phase.

It can also be seen in FIG. 5 that the enclosure 50 has an internal surface 51 which diverges downwards, that is to say upstream by considering the direction of flow of the mixture through the rotor. In the example described here, the surface 51 has a number of circular parts 53 whose height is equal to the thickness of each disc. There is thus a surface 53 facing the lateral edge of each disc.

In the particular case illustrated in FIG. 5, the diameter of the discs is constant and that of the parts 53 increases from downstream to upstream, which means that the thickness of the space 26 also increases from downstream to upstream by considering the direction of flow of the mixture through the rotor. However, it would not be departing from the scope of the invention to use discs of variable diameter so that the distance between the lateral edge of a disc and the parts 53 of the surface 51 is constant.

Neither would it depart from the scope of the invention by using discs whose diameter would increase from downstream to upstream, but slower than that of the parts 51, the diameter of the space 26 thus increasing, or by using a smooth surface 51 of conical shape diverging upstream.

The major advantage of this provision lies in the use of each instantaneous variation of the diameter of the rotor, combined with the corresponding variation of the internal diameter of the body, to generate a gas blowing or liquid pumping effect, driving the heavy phases collected towards the zone of larger diameter of the rotor and stator. These successive stages operate in series with each other. Peripheral or axial clearances are calculated as a function of the flow performance and concentration of heavy phases extracted to be ensured.

FIG. 6 illustrates a first embodiment of a disk usable in the device which is the subject of the invention. In this embodiment, a stack of discs 36 of constant thickness p is used. Each disc is pierced with a number of helical passages or channels 62. Each of these channels 62 opens onto the upstream or lower face 37 of the disc by an inlet cut-out and opens onto the upper face 39 of the disc 36 by a outlet aperture 65. The arrangement is such that the outlet aperture 65 located on the upper face of a given disc is located exactly opposite the inlet aperture 63 located on the underside of the following disc. One thus defines, through the stack of disks, practically continuous helical channels 69 limited by solid walls. So that the heavy phases routed to the periphery are effectively collected on the inner wall of the enclosure 5 and do not tend to resuspend inside the rotor due to various phenomena such as turbulence and twists, the transfer of the rotor towards the fixed wall 51 takes place through peripheral slots formed between the successive discs, as shown at 71 in FIG. 6. These slots are however locally interrupted by studs 73 whose purpose is to improve the rigidity of the rotor. They indeed support the successive discs on each other. Their internal profile is provided to avoid accumulations of separate heavy phase.

The fact that the discs are joined allows to obtain, subject to sufficient axial tightening, a very rigid monobloc rotor. This arrangement results in an effective separation between the interior of the rotor and the area between it and the wall of the fixed body, which limits the re-dispersion. In addition, it is possible to reach higher speeds of rotation, therefore more intense separating fields, than with the devices of the prior art, while avoiding the risks of deformation.

In the particular case illustrated in Figure 6, the openings 65 are distributed equianglely on a given disc and extend from the center to the periphery. They are separated by solid parts 67. If we consider the direction of rotation T of the discs, the outlet opening of a given channel is located downstream of the entry opening. In FIG. 6, the openings 65 are limited by radii of the disc 36 and therefore have a substantially trapezoidal shape, as do the parts 67. Each channel 62 is thus limited by a lower wall 64, an upper wall 66 and two walls lateral 68 and 70. The lower 64 and upper 66 faces are generally helical in shape with the same slope as that of the channels. As will be seen below, they can be provided with steps or steps intended to trap locally and temporarily the constituents of the mixture and to facilitate the agglomeration of the heavy phases. The first lateral face 68 limiting a channel 62, that is to say that which is closest to the axis of the rotor, is cylindrical and of axis coincident with that of the rotor. The other lateral face 70 is located in the vicinity of the periphery of the disc and it is inclined relative to the axis of the rotor. In other words, it is in the form of a portion of truncated cone diverging upstream if we consider the direction of flow of the mixture through the rotor.

The mixture is thus separated into a plurality of helical veins. Since the mixture is subjected on the one hand to the pressure drop through the rotor and, on the other hand, to the effect of driving the latter in rotation, it flows at through the discs with a tangential speed greater than that of the rotor. We note that, for a rotor rotating at speed ω, the absolute tangential speed of a particle located at a radial distance R is:
- ω * R if this particle is in a sequestration zone of the mixture,
- ω * R + V _t if this particle is in the circulating part of the vein, at the tangential speed V _t .

The tangential speed V _t varies approximately as k / R, k being a constant depending on the geometry of the rotor and proportional to the flow through the rotor. The centrifugal force at radius R is therefore written:

When R varies, this function has a minimum and, on either side of this minimum, the centrifugal field increases. This therefore results in a high centrifugal field in the vicinity of the axis of rotation, unlike what happens in conventional centrifuges. In addition, at all points on the curve F _c (R), the value of F _c is much higher than for a conventional centrifuge rotating at the same angular speed.

Similarly, when the flow rate of the mixture varies, the separation efficiency goes through a minimum for a value of k = ω * R². It always remains higher than that of a conventional centrifuge for all the values of the flow, for a dimensioning of the rotor and an identical rotation speed (k is directly proportional to the flow).

This phenomenon, as well as the results exposed hereafter which ensue from it, are unpredictable and unexpected in the classic frame of centrifugation. These are the facts based on the method and apparatus of the invention which ensure the veracity of the results obtained.

It is in fact verified that the heavy particles of the helical veins subjected to a very intense centrifugal foam precipitate towards the periphery by slowing down and agglomerating before reaching the annular zone of minimal centrifugal force, then, from this zone, accelerate again in larger masses towards the periphery.

However, during this centrifugal movement, the heavy particles (solid or liquid) migrate, for various reasons explained below, towards the dead zones or the low pressure zones in which they are captured and trapped. These dead or low pressure zones are obtained by means of steps or other prominent elements provided on the lower and upper faces of the channels 62, as will be described later.

These heavy particles are then taken up by a centrifugal force, certainly lower, but high enough to transport them inevitably to the periphery. During this routing, trap elements and conducting elements, defined below, oppose the return of the particles towards the delivery veins and participate in their routing towards the periphery where they precipitate on the internal wall 51 of the pregnant 50.

The angular offset of the discs and the thickness p of these, as well as the shape and dimensions of the openings are chosen to precisely determine the relative slope P of the helical veins (i.e. their slope relative to the discs when they spin). The parameters in question therefore make it possible to adjust the separating power and the flow rate of the device. In general, these parameters are constant for a given device, but it may be advantageous to vary them from upstream to downstream depending on the rate of operation of the device, and that of the treatment to be obtained.

In any case, the choice of these parameters allows, in relation to the regime of the apparatus and the composition of the mixture, to define the preferred helical path of the mixing veins through the openings of a disc. The mixture can continue its journey by crossing the homologous perforation of the next disc, that is to say the one which is offset downstream of the angle of offset of the discs. This offset angle is such that the outlet opening of the first disc is opposite the inlet opening of the second disc.

The preceding discussion shows that the aero or hydrodynamic flow of the mixture through the apparatus undergoes, between the upstream and the interior of the rotor, an increasing variation in speed. Consequently, there is quite naturally an expansion within the rotor, and consequently a drop in temperature which can be used to condense a vapor phase during the separation.

Figure 7 is a view similar to Figure 6 and illustrates a variant in which the upstream and downstream faces of the discs 36 are no longer perpendicular to the axis of rotation of the rotor, but are inclined upstream by an angle α with respect to a plane perpendicular to this axis. In other words, the upper face 39 and the lower face 37 are in the form of truncated cones diverging upstream relative to the direction of flow of the mixture through the rotor. It was found that the best results were obtained when the value of the angle α was close to 30 °. The arrangement of the openings and the helical channels in the discs of FIG. 7 is exactly the same as in the case of FIG. 6.

It would not go beyond the scope of the invention to give still other shapes to the upstream and downstream faces of the discs.

The latter may include curved generators and, if they are straight or curved, concurrent with or left with respect to the axis of rotation with any angle of index. In other words, the discs can be delimited by regulated surfaces, such as conics or any balanced surfaces of revolution, which does not can constitute a major difficulty of execution since the discs can be, because of the reduced stresses which they undergo, manufactured by molding and even out of plastic.

The perspective view of FIG. 8 shows how steps, projections or other prominent elements can be provided on the lower and / or upper faces of the channels 62. In FIG. 8, we only see the steps 72 on the lower face of the channels 62, but there are identical steps on the upper face, the latter being invisible in FIG. 8.

The developed section views of FIGS. 9a to 9d show other possible shapes for these prominent elements.

In the case of FIG. 9a, the upper and lower surfaces of the channel 62 have steps whose edges constitute radial edges, that is to say that these edges are perpendicular to the axis of rotation of the rotor. In the case of FIG. 9a, the steps 72 appear as the steps of a spiral staircase whose axis would be that of the rotor. The internal angles of the steps are therefore right angles.

The edges of the steps have two different functions depending on whether it is the upper wall or the lower wall limiting the channel 62. In the first case (steps 72a on the upper wall of the channel 62), the radial vertical surfaces of the bleachers create low-pressure areas which tend to trap impurities in the attached vortex they create. In the second case (steps 72b on the bottom wall of the channel 62), the radial vertical surfaces function as multiple impact separators. They temporarily stop heavy particles or droplets. The agglomeration effect which they bring accelerates the routing towards the periphery of the heavy phases and correlatively improves the overall efficiency of the device.

In the case of FIG. 9b, the internal angles of the steps are more acute than in the case of FIG. 9a in order to increase the retention effect of the heavy phases.

In the case of FIG. 9c, two different arrangements are combined. The steps 72b of the lower wall are identical to those of FIG. 9a. As for the steps of the upper wall of the channel 62, they have inclined parts 74 whose slope is slightly greater than the slope chosen for the helical veins of the mixture, the parts 74 being connected by parts 76 whose height is less than the width of the parts 74. A chamfer 75 is provided at the lower part of the lower face 64, but this is not compulsory. This arrangement causes alternating diverging and converging oblique zones, which creates a more pronounced undulation of the mixing vein and a higher probability of lateral exit of the heavy fractions which are then collected in the steps.

Finally, in the case of FIG. 9d, the steps 72 are replaced by grooves 78 of semi-circular section and arranged radially, that is to say that their axis is perpendicular to the axis of rotation of the rotor. The semi-circular radial channels thus created are at the origin of vortex zones which slow down and collect the heavy phases.

Other arrangements can also be used, for example forms of radial machining which do not penetrate into the circulating vein, but play a role of extraction of the heavy phases and a role of agglomeration, which increases the overall efficiency. of the device.

FIG. 10 illustrates a variant in which the prominent elements for collecting the heavy phases are arranged in a tangential and not radial direction. We see in this figure that the bottom wall of each channel 62 has two prominent elements 80 each arranged in a helix around the axis of the rotor. These elements consist of two faces connected by an upper edge. The two faces are parallel to the flow of the mixture relative to the rotor. The radial displacement of heavy phases under the action of the centrifugal field brings into contact with the internal face of the elements 80. This contact creates a gathering effect of the heavy phases which then slide on the surface and are resuspended but after having been more or less strongly agglomerated. The consequent increase in their particle size accelerates their radial movement towards the periphery of the rotor and correlatively increases the separation efficiency of the device.

Figures 11 and 12 illustrate another embodiment in which each disc 36 is in the form of a hollow circular housing. The disc 36 consists of a lower wall 82 having the shape of a flat disc, connected to an upper wall 84 by a ferrule 86. The upper wall 84 has a central part 87 having the shape of a flat disc of the same axis than the wall 82, but of smaller diameter. The part 87 is connected to a peripheral edge 88 by a part in the form of a truncated cone 90. The edge 88 is circular and of the same diameter as the bottom wall 82. It is separated from the latter by a peripheral slot 92, the width is less than the distance between the lower wall 82 and the central part 87 of the upper wall. A set of elements in the form of a frustoconical cone or frustoconical ferrules 94 is provided inside the housing thus defined. In the particular case described here, the frustoconical ferrules 94 have an upper edge which is welded to the central part 87 of the upper wall 84 while their lower edge is located at a certain distance from the lower wall 82.

FIGS. 11 and 12 also show an inlet opening 63 formed in the bottom wall 82 and an outlet opening 65 formed in the central part 87 of the upper part 84. The angular position of the openings 63 and 65 relative to the disc 36 is exactly the same. A deflector 96 has a lower edge welded to the lower wall 82 behind the perforation 63 and an upper edge welded to the upper wall 84 in front of the perforation 65. Thanks to this arrangement, the mixture which enters the disc by the openwork 63 is forced to do one complete turn, walking in the spaces between the frustoconical ferrules 94 before exiting through the outlet perforation 65. The deflector 96 must ensure a good seal to prevent direct leakage of the mixture from the inlet perforation to the perforation Release. Thanks to this arrangement, the radial displacement of the heavy phases under the action of the centrifugal field brings them into contact with the surface of these ferrules. This contact creates a gathering effect of the heavy phases, which then slide on the surface and are resuspended, but after having been more or less strongly agglomerated. The consequent increase in their particle size accelerates their radial movement towards the periphery of the rotor and correlatively increases the separation efficiency of the device. The frustoconical ferrules 94 also play a role of guiding surface and limiting turbulence, their surface being parallel to the direction of flow of the mixture inside the disc.

This arrangement leads, for the same rotor dimensions, the same number of discs and the same flow rate, to a tangential speed of the mixture relative to the rotor which, being inversely proportional to the slope of the veins, and maximum for the flow at a single vein, has one revolution per disc.

au rayon R, p étant l'épaisseur du disque.The average slope per disc is then equal to:

at radius R, p being the thickness of the disc.

The centrifugal field is also maximum for this configuration, since it is proportional to the square of the sum of the tangential drive speed and the tangential speed of the mixture relative to the rotor.

The invention is not limited to the embodiments and to the embodiments shown and described in detail in the above, since various modifications can be made thereto without departing from its scope.

The method and apparatus which are the subject of the invention are usable for separation in a mixture of any state phases.

More specifically, they are applicable to the elimination of oily mists such as those generated by machine tools, stamping presses, spray lubrication devices, to the elimination of water mists on washing machines. processes at the outlet of air washing devices, the elimination of heavy solvent mists on polymerization ovens, printing dryers, the washing with oil of various gases, the clarification of soluble oils on machine tool tubs, clarification of laundry baths on industrial washing machine tubs, clarification of gas washing water, clarification of polluted water in general, pre-clarification of liquids before centrifuges high efficiency or finishing filters, etc.

The method and the device of the invention apply particularly well in the nuclear field, in particular for the separation of solid or liquid dispersions and the separation of gas phases at the molecular level. They are also well suited for difficult special applications in certain industries, for example in continuous processes or for certain operations hitherto difficult to carry out, such as the sterilization of air by centrifugation or the elimination of very active toxic products.

Claims (21)

1. A method of centrifugal separation of a mixture of several phases comprising at least one heavy phase in which the mixture is passed through a rotor (17) rotating at a given speed, the mixture being divided into a plurality of parallel veins ( 69) flowing through the rotor (17) along helical paths and being driven at an angular speed greater than that of the rotor (17), a centrifugal field allowing the ejection of said heavy phase being thus created inside of said veins, characterized in that the latter are limited by solid walls (64, 66) linked to the rotor (17), a centrifugal field being thus created on the surface of these solid walls (64, 66), and in that the heavy phase ejected under the action of the centrifugal field prevailing in the veins is collected on trap elements (72) associated with said solid walls and guided towards the periphery of the rotor (17) by guide devices associated with these walls (64, 66), phase l urde moving towards the periphery of the rotor (17) under the effect of the centrifugal field created on the surface of these walls (64, 66). 2. Method according to claim 1, characterized in that, in order to drive the mixture in rotation, it is subjected on the one hand to the action of driving in rotation of the rotor (17) and, on the other hand, to a pressure drop between upstream and downstream of this rotor (17), the latter being arranged so that this pressure drop causes the mixture to pass through the rotor (17) along helical paths. 3. Method according to claim 1, characterized in that the helical flow of the mixture is transformed into axial flow downstream of the rotor (17). 4. Method according to claim 3, characterized in that the kinetic energy of rotation of the mixture is recovered to drive the rotor (17) in rotation. 5. Device for implementing the method according to claim 1, comprising:
- a rotor (17) through which the mixture can pass,
means (54) for creating a pressure drop across this rotor (17), the latter being arranged so that the mixture passes through it following helical veins under the effect of this pressure drop, and
- means for driving the rotor (17) in rotation about an axis,
characterized in that the rotor comprises:
- solid walls (64, 66) limiting said helical veins,
- trap elements (72) for collecting said heavy phase, and
- guide elements for guiding said heavy phase towards the periphery of the rotor. 6. Device according to claim 5, characterized in that the rotor comprises a set of contiguous discs (36) of generally circular shape whose axis is coincident with that of the rotor (17) and each having an upstream face (37) and a downstream face (39), each disc (36) comprising at least one channel (62) for circulation of the mixture limited by solid walls (64, 66) and opening onto the upstream face (37) by an inlet perforation ( 63) and on the downstream face (39) by an outlet perforation (65). 7. Device according to claim 6, characterized in that the outlet perforation (65) of a channel formed in a given disc is located immediately opposite the inlet perforation (63) of a channel formed in the following disc, said openings (63, 65) having the same shape. 8. Device according to claim 6, characterized in that, said channel (62) being of helical shape with respect to the axis of the rotor (17) and being limited by a lower wall (64), an upper wall (66) and two side walls (68, 70), the latter being concentric with the axis of the rotor, the lower wall (64) and / or the upper wall (66) comprises (s) protruding elements (72) having edges arranged radially with respect to the disc (36). 9. Device according to claim 6, characterized in that, said channel (62) being helical in shape and being bounded by a lower wall (64), an upper wall (66) and two side walls (68, 70), the lower wall (64) and / or the wall upper (66) has (s) at least one prominent element (80) disposed along a portion of a helix relative to the axis of the rotor (17). 10. Device according to claim 6, characterized in that the upstream (37) and downstream (39) faces of each disc (36) are plane and perpendicular to the axis of the rotor. 11. Device according to claim 6, characterized in that the upstream (37) and downstream (36) faces of each disc have a part in the form of a truncated cone of the same angle at the top and diverging upstream relative to the direction flow of the mixture through the rotor (17). 12. Device according to claim 6, characterized in that each disc has the shape of a hollow circular case comprising:
- an inlet opening (63) on its upstream face,
- an outlet opening (65) on its downstream face,
- guide means (96) forcing the mixture to perform at least one complete revolution inside the disc between these two openings (63, 65),
- a set of elements (94) in the form of truncated cones located inside the housing, and
- A peripheral slot (92) for the ejection of the heavy phase. 13. Device according to claim 5, characterized in that it comprises, upstream of the rotor (17), a rotary distributor (19) comprising a set of vanes (23) oriented from the center towards the periphery and whose concavity s' opens downstream, each blade (23) having a trailing edge whose inclination corresponds to the slope of said helical veins relative to the rotor (17). 14. Device according to claim 13, characterized in that the trailing edges of the blades (23) are integral with a disc coupled to the rotor and coincide with the rear edges of the openings of this disc. 15. Device according to claim 5, characterized in that it comprises, downstream of the rotor, a rectifier (21) comprising a set of vanes (27) oriented from the center towards the periphery and whose concavity opens towards the 'upstream, each blade having a leading edge whose inclination relative to the rotor (17) corresponds to the slope of said helical veins. 16. Device according to claim 15, characterized in that the leading edges of the blades (27) coincide with the front edges of the outlet openings of the last downstream disc of the rotor (17). 17. Device according to claim 4, characterized in that the rotor (17) is placed inside an enclosure (50) having an internal surface (51) diverging upstream. 18. Device according to claim 17, characterized in that the internal surface (51) of the enclosure (50) is smooth and of generally conical shape diverging upstream. 19. Device according to claim 17, characterized in that, the rotor (17) consisting of a stack of discs, the internal surface (51) of the enclosure (50) has a set of circular parts (53) of which each is facing the lateral edge of a rotor disc and whose diameter increases from downstream to upstream. 20. Device according to claim 19, characterized in that the distance between the lateral edge of a disc (36) and the internal face (51) of the enclosure (50) is constant. 21. Device according to claim 19, characterized in that the distance between the lateral edge of a disc (36) and the internal surface (51) of the enclosure (50) increases from downstream to upstream.

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