EP0104966B1 - Centrifuge with energy recuperation - Google Patents

Description

The invention relates to an energy recovery centrifuge, more particularly intended for the separation of immiscible liquids of different densities and in which solid particles are dispersed, the centrifuge comprising two rotary coaxial drums, a device for discharging solid materials. and an energy recovery device.

Industrial centrifuges intended for the separation of emulsions of liquids or suspensions of solids in liquids are machines intended to treat continuously large flows. In addition to their high price, the significant consumption of energy necessary for their functioning greatly hindered their development and their use was limited to the chemical and petroleum industries in which they are used for the separation of products having a certain commercial value.

When it comes to products of negligible value such as those contained in industrial effluents, one is generally satisfied with a separation by decantation carried out for more or less long times in tanks or basins. As pollution problems become more and more acute, the content of pollutants in discharges, for example sludge, emulsions or suspensions of oil or grease, is gradually lowered and compliance with these standards will require the use of high-speed centrifuges. and whose operating costs are not prohibitive.

This is how patent FR-A-1,455,032 describes a centrifuge with a plate separator. The plate separator is integral with a shaft which rotates axially in an external drum which is itself rotating. The liquid to be purified crosses the separator from the center to the periphery.

The plate separator includes a pre-clarification propeller and, at its periphery, a propeller which is integral with it and which transports the materials deposited on the external drum towards the downstream end of the centrifuge. The purified liquid and the deposited materials exit through openings provided on the external drum.

The centrifuge has a considerable length as a result of the preclarification propeller. The energy of the purified liquid is not recovered at its exit.

US-A-2,741,793 describes a centrifuge with a vertical axis specially adapted to low flow rates and liquids with little charge, such as those in engine oil circuits. The centrifuge only has a rotating drum and the extraction of separated materials is done by disassembly. The oil to be purified moves in a centripetal direction in the plate separator and the purified liquid exits through ejectors in the form of tangential jets which strike the wall of a fixed circular chamber. The outlet reaction turnstile allows energy from the purified liquid to be recovered, which relieves the pump of the oil circuit accordingly.

Such a centrifuge does not make it possible to process large flow rates of liquids whose concentration of impurities after purification must be 100 times lower than that of the starting liquid.

The present invention concentrates a device as referred to in the preamble of claim 1 (FR-A-1.455.032) and as set out in claim 1.

The centrifuge, according to the invention, obviates the drawbacks of known centrifuges and allows the treatment of high flow rates with minimized energy consumption, while having particularly reduced dimensions.

It comprises a rotor essentially constituted by a stack of centrifugation plates rotating at high speed between two coaxial cylindrical drums, means for continuously introducing and discharging the liquid, said liquid completely filling the internal space of the rotor, and means for selective extraction of separated impurities.

A first characteristic of the machine is that in the interval between the external cylindrical drum and the internal drum, driven in coaxial rotation independently and respectively provided with means for evacuating the separate phases, is stacked plates which rotates with the internal drum and which is supplied with liquid to be purified by an axial inlet and a centrifugal impeller.

Another characteristic of the invention is a device for recovering the energy of the liquid discharged.

This device comprises at the outlet of the purified liquid an outlet impeller which comprises vanes integral with the internal drum and forming a centripetal turbine, this turbine being followed by tangential ejectors integral with the external drum and constituting a reaction turnstile, arranged so that the absolute exit speed of the purified liquid is substantially zero.

In this way, the turbine and the turnstile restore the majority of the angular momentum communicated to the liquid in the form of a torque-motor, which makes it possible to reduce, to compensate for friction losses, the power required in continuous mode for the operation of the machine.

• La figure 1 représente en coupe longitudinale une centrifugeuse selon l'invention.
• La figure 2 est une vue à plus grande échelle d'une partie de la figure 1.
• La figure 3 est une vue partielle en coupe radiale selon III-III de la figure 2.
• La figure 4 est une vue partielle en coupe radiale selon IV-IV de la figure 2.
• La figure 5 est un schéma de la composition des vitesses du fluide sortant d'un éjecteur du dispositif de récupération de l'énergie.
• La figure 6 est une vue à plus grande échelle d'une partie de la figure 1 d'un autre exemple de réalisation.
• La centrifugeuse à axe horizontal, montrée sur les figures 1 à 4, comprend schématiquement un tambour intérieur A, un tambour extérieur B, un dispositif d'évacuation des matières solides C et un dispositif de récupération d'énergie D.
• Le liquide à épurer pénètre côté amont par le raccord 1, équipé d'un assemblage tournant d'étancheité 2, et prolongé par un manchon intérieur fixe 3, dans l'arbre creux 6 dont l'extrémité opposée se raccorde au tambour intérieur A.

The explanations and figures given below by way of example will make it possible to understand how the invention can be implemented.

• Figure 1 shows in longitudinal section a centrifuge according to the invention.
• FIG. 2 is an enlarged view of part of FIG. 1.
• FIG. 3 is a partial view in radial section along III-III of FIG. 2.
• FIG. 4 is a partial view in radial section on IV-IV of FIG. 2.
• FIG. 5 is a diagram of the composition of the speeds of the fluid leaving an ejector of the energy recovery device.
• Figure 6 is an enlarged view of a portion of Figure 1 of another embodiment.
• The centrifuge with horizontal axis, shown in FIGS. 1 to 4, schematically comprises an internal drum A, an external drum B, a device for discharging solid materials C and an energy recovery device D.
• The liquid to be purified enters the upstream side by the connector 1, equipped with a rotating sealing assembly 2, and extended by a fixed inner sleeve 3, in the hollow shaft 6 whose opposite end is connected to the inner drum A.

The shaft 4 is supported by a double ball bearing 5 between the flanges which is provided with a pulley 6 keyed onto the shaft and driven by a belt (not shown). The hollow shaft 4 is connected by a tight elastic coupling 7 to the tubular end 8 of the inner drum A. The corresponding end 9 of the outer drum B is supported by an outer ball bearing 10 and has a pulley 11 which allows its drive at a speed different from that of the inner drum. A sealed ball bearing 12 is disposed between the exterior and interior drums. The other end of the outer drum B is supported by a ball bearing 13. The corresponding end of the inner drum A is held by a sealed ball bearing 14 disposed between the drums.

The centrifugation bowl, forming the largest part of the external drum B, consists of a cylindrical hollow body extended on the upstream side by a cylindroconical flange secured to its end 9 supported by the bearing 10, and on the downstream side by a flared flange 15 carrying a circular flange 16. On this flange is fixed a head 17 whose cylindrical end 18 is supported by the bearing 13. The head 17 internally carries a movable conical bottom 19, which slides tightly on the one hand, on two stepped surfaces 20, 21 provided in the part of the head adjacent to the flange 16 and on the other hand, in a tubular sleeve 22 attached to the head 17 (see the enlarged view of FIG. 2).

The movable bottom 19 delimits on the one hand with the flared flange 15 a mud chamber 23 and on the other hand with the part of the inner head 17 within its internal reach 21, a pressure chamber 24 supplied via the channel 25 from a weir 26 which will be described later.

As shown in Figure 3, the flange 16 of the bowl, pressed against the periphery of the head 17, is not continuous but has bosses 27 regularly distributed all around the flange, separated by passages 28 and crossed by bolts mounting 29.

When the movable base 19 is in the position shown in FIGS. 1 and 2, the periphery is axially pressed against an internal radial surface of the flange 16 blocks any communication between the interior of the bowl and the exterior. When the bottom 19 is moved to the right of the drawing, the periphery uncovers the passages 28, which allow, by a simple centrifugal effect, the emptying of the mud chamber 23.

The internal drum A is connected by its tubular end 8 to the end of the hollow shaft 4 through which the effluent or the mixture to be treated is introduced, which reaches the annular space comprised between the external surface 30 of the inner drum A and the inner wall of the outer drum B by inclined channels 31 forming an input wheel. As shown in Figure 3, the outer surface 30 carries longitudinal ribs 32 forming keys by which is driven in rotation a stack of conical plates 33 (shown partially). These plates of frustoconical shape are spaced from each other by stamped or attached radial spacers 33a, their spacing being a function of the size of the particles to be separated and the expected flow. The small bases of the plates are directed downstream in the axial direction of circulation of the liquid to be treated. The stack of plates is maintained on the upstream side by a plate 34 and on the downstream side by a plate press 35.

At the periphery of the plates is fixed, by means of the plate 34, a scraper screw 36. This screw is constituted for example by a rectangular profile wound in a helix on a cage 37 formed by the assembly of peripheral rings 37a and longitudinal bars 37b. The outside diameter of the screw 36 is slightly smaller than the inside diameter of the bowl B so that it can scrape the solid particles accumulated on the wall and discharge them axially towards the mud chamber 23, the progression resulting from the difference in the speeds of rotation between the inner drum A and the outer drum B.

At the downstream end of the set of plates 33 is provided a radial centripetal impeller 38 in the form of a frustoconical envelope integral with the plate press 35 on the surface of which vanes 39 are fixed projecting into the space between the plate press 35 and the movable bottom 19 of the outer drum B.

The impeller 38 forms the first stage of the energy recovery device D, the second stage of which consists of a series of ejectors 40 forming a tourniquet fixed on the cylindrical surface 41 of the external drum B extending its head 17. The ejectors 40 formed of added blocks 42 receive the purified fluid by radial channels 43 (FIG. 4) making communicate with the interior of the bowl their ejection nozzles 44, the axis of which is directed substantially tangentially with respect to the cylindrical surface 41 of the head 17 of the outer drum B. The tangential jets coming from the ejectors 40 reach a crown of fixed vanes 45, disposed between two radial flanges 46 attached in the cylindrical volute 47 for the outlet of the purified liquid. This volute is fixed to the bearing B of the centrifuge support. The vanes 45 are advantageously adjustable in orientation to conserve the residual angular momentum and arranged according to a spiral to facilitate the evacuation of fluid.

The recovery of kinetic energy can be explained as follows:

où P est la masse volumique du fluide, ω la vitesse angulaire de rotation et R le rayon de giration au point considéré.The centrifuge is supplied in the axis, the rotation of the liquid creates an overpressure at all points

where P is the density of the fluid, ω the angular speed of rotation and R the radius of gyration at the point considered.

où W est la vitesse relative du fluide par rapport à la buse. Si l'orientation et la section des buses sont convenablement choisies, la vitesse W ainsi créée est égale en module à la vitesse périphérique de rotation. La vitesse absolute du fluide Va par rapport à un référentiel extérieur à la machine, est la somme géométrique de la vitesse relative IV et de la vitesse d'entraînement V =c.oR au point considéré:

Donc si W etV sont colinéaires, de sens opposés et de même module, Va est nulle et l'énergie cinétique résiduelle est entièrement récupérée. Pour des raisons pratiques, l'angle de sortie de l'éjecteur est choisi de sorte que la vitesse absolue soit faible, mais non nulle, pour faciliter l'évacuation (figure 5).The pressure is converted into speed in the nozzle 44 of an ejector according to the equation

where W is the relative speed of the fluid with respect to the nozzle. If the orientation and the section of the nozzles are suitably chosen, the speed W thus created is equal in module to the peripheral speed of rotation. The absolute speed of the fluid Va with respect to a reference frame external to the machine, is the geometric sum of the relative speed IV and the driving speed V = c.oR at the point considered:

So if W and V are collinear, of opposite directions and of the same modulus, Va is zero and the residual kinetic energy is fully recovered. For practical reasons, the exit angle of the ejector is chosen so that the absolute speed is low, but not zero, to facilitate evacuation (Figure 5).

The central part of the internal drum A has an axial cylindrical cavity 48 placed in communication with the outside of the drum by orifices 49. These orifices allow the passage of the lightest fluid which flows along the external wall 30 and comes gather on the periphery of the cavity 48 which constitutes a reservoir from which an extraction tube 50 permanently scoops the fluid, held by centrifugation against the wall, to evacuate it towards the outside of the centrifuge.

The solids evacuation device is composed as previously described of the scraper screw 36 and of the hydraulic evacuation device C, a part of which is constituted by the movable base 19.

The overflow 26 is formed of a cylindrical ring 51 fixed on the head 17 and carrying in inner projection two rings 52, 53, axially spaced and of unequal heights, the ring 52 having an inner diameter smaller than that of the ring 53 The ring 52 delimits with the external face 54 of the head 17 a first channel 55 and with the ring 53 a second channel 56. A water supply stock 57 passes through the central openings of the rings and opens into the first channel 55, the bottom of which communicates by a channel 58 with an annular chamber 59 situated at the periphery of the movable bottom 19 between the stepped surfaces 20, 21 of the head 17 of the external drum B. This chamber, provided with a leakage orifice calibrated 60 opening into a passage 28, receives continuously by the fixed butt 57, the channel 55 and the channel 58 a flow of water greater than that flowing through the leak 60. The excess water overflows from the first channel in filling the second channel 56. A radial perc channel é in the bottom of the chamber 56 communicates via the channel 25 with the pressure chamber 25 delimited by the movable bottom 19 and the internal face 61 of the head 17. Due to the rotation the centrifuged water exerts a pressure sufficient against the movable base 19 to maintain its periphery in axial abutment on the radial surface 62 of the flange 16, position in which it closes the passages 28 making the mud chamber communicate with the outside.

When it is desired to evacuate the sludge accumulated in the mud chamber 23, the water supply is interrupted by the butt 57. The leakage orifices 60 ensure the emptying of the water chamber 59 and orifices 63 judiciously placed allowing the pressure chamber 24 to be emptied. The internal pressure in the bowl B acting on the other face of the movable bottom 19, it moves to the right in the drawing, uncovering the passages 28. The bottom 19 closes when the weir 26 is powered again.

The operation of the centrifuge according to the invention is described below.

The fluid to be treated enters continuously into the centrifuge which it completely fills, through the axial hollow shaft 8 in which it begins to acquire a relatively low speed of rotation. A first speeding up is carried out during the passage of the fluid in the inclined channels 31 of the input wheel, connecting the hollow shaft to the annular space comprised between the drums in which the stacking of plates 33 rotates at high speed. , integral with the inner drum A. The fluid to be purified then crosses the set of plates (arrows in strong line) where the centrifugal separation takes place and which constitutes a second stage of speed setting: in known manner, the fluid to be purified is accelerated by viscosity in the spaces separating the plates 33 so that the solid particles are centrifuged against the wall of the external drum B, while the heavier fluid thus purified (arrows in dashed lines) flows axially in the space located at the periphery of the stack of plates and is brought back towards the axis by crossing the centripetal impeller 38, which recovers part of its rotational energy. The lightest fluid, under the effect of the centrifugal field, migrates (arrows in thin lines) towards the inner periphery of each plate and coalesces in the form of a film which flows towards the axis of the centrifuge. Arrived at the inner edge of the plate, the film is divided into large droplets which are captured very quickly on the surface 30 of the inner drum A and flow through the orifices 49 into the tank 48 where it is recovered by the scooping tube 50.

The heaviest fluid, thus freed, of solid particles and of the lighter fluid, reaches, after passing through the impeller 38, in the tubular end of the movable bottom 19 and in the radial channels 43, to the ejectors 42 attached to the head 17 of the drum B which ensure a very low absolute speed of exit of the fluid and thus recover its residual kinetic energy.

The fixed vanes 45 and the volute 47 exploit the balance of kinetic energy of the fluid to create the slight pressure necessary for its evacuation.

• Le débit est de 100 m³/h pour une concentration d'huile à l'entrée variant de 100 PPM à plus de 2000 PPM et en sortie inférieure ou égale à 20 PPM. Le pouvoir séparateur pour les gouttelettes en suspension d'un diamètre supérieur à 2 pm est total pour une différence de densité eau/huile de 0,15.
• La vitesse de rotation de l'ensemble: tambour intérieur, porte-assiettes et vis est de 5000 t/mn et celle du bol extérieur de ±200 t/mn par rapport au tambour extérieur.
• Le nombre d'assiettes est de 560 et l'espace interassiettes de l'ordre de 0,5 mm.
• La centrifugeuse a une longueur de 2,5 mètres pour un diamètre de l'ordre de 0,70 m.
• Le rendement de récupération est de l'ordre de 95% rapporté à la puissance cinétique transmise au fluide.
• La dispositif d'évacuation des matières solides, à fond mobile, précédemment décrit peut présenter des inconvénients lorsqu'il est utilisé avec des chambres à boue de volume modéré. En effet, les temps d'ouverture ne peuvent être suffisamment courts, et une grande quantité de liquide est évacué avec les matières solides à chaque ouverture, ce qui provoque un déséquilibre dans l'écoulement des phase liquides.
• La figure 6 montre un dispositif d'évacuation à clapets qui peut remplacer avantageusement le dispositif à fond mobile. Il présente également l'avantage d'une fabrication plus simple et de moindre coût.

According to an exemplary embodiment, a centrifuge, according to the invention, intended for the treatment of petroleum production waters and in particular for the separation of the oil / water emulsion and solid particles, has the following characteristics:

• The flow rate is 100 m ³ / h for an oil concentration at the inlet varying from 100 PPM to more than 2000 PPM and at output less than or equal to 20 PPM. The separating power for the droplets in suspension with a diameter greater than 2 μm is total for a difference in water / oil density of 0.15.
• The speed of rotation of the assembly: inner drum, plate holder and screw is 5000 rpm and that of the outer bowl of ± 200 rpm compared to the outer drum.
• The number of plates is 560 and the space between plates on the order of 0.5 mm.
• The centrifuge has a length of 2.5 meters for a diameter of the order of 0.70 m.
• The recovery efficiency is around 95% based on the kinetic power transmitted to the fluid.
• The mobile bottom evacuation device described above can have drawbacks when used with mud chambers of moderate volume. In fact, the opening times cannot be short enough, and a large quantity of liquid is evacuated with the solid materials at each opening, which causes an imbalance in the flow of the liquid phases.
• Figure 6 shows a valve discharge device which can advantageously replace the movable bottom device. It also has the advantage of simpler and lower cost manufacturing.

The elements of the device identical to those of the device described above bear the same references.

Said evacuation device consists as previously described of the scraper screw 36 and the hydraulic evacuation device. The mud chamber 23 is defined between the inner wall of the flared flange 15 and the conical fixed bottom 64 forming the inner wall of the head 17. The flange 16 of the bowl, pressed against the periphery of the head 17, carries evenly distributed all around the flange, radial orifices 65 which communicate by longitudinal passages 66 with radial grooves 67 formed in the face of the flange 16. The longitudinal passages 66 receive sockets 68, one of the ends of which forms the seat of valves 69 provided in the periphery of the head 17.

The channels 58, provided in the head 17, open on one side into the channel 55, receiving water from the supply stock 57, and on the other into the valve chambers 70. The movable parts of the valves 71 slide with play in bores 72 drilled parallel to the axis at the periphery of the head. Sealed passages 73, mounted on the free openings of the bores, carry a thread 74 receiving screw stops 75. These stops make it possible to adjust the opening between the movable bodies of the valves and their seats.

The operating mode of the valve sludge evacuation device is as follows: the water arriving through the supply stock 57 pours into the channel 55 of the weir 26 and is sent under the action of centrifugal force, by the channel 58 in the valve chamber 70. The water exerts a pressure against the rear face of the movable body of the valve and maintains it against the seat 68 by closing the communication between the mud chamber 23 and the groove 67 leading to the outside. Part of the water in the chamber 70 flows around the valve body 71 towards the outside as a result of the clearance provided between the bore and the mobile body. The excess water (relative to the continuous flow due to the play) arriving in the channel 55 escapes through the central opening of the ring 53 of the weir 26.

As in the previous example, when the water supply to the stock 57 is cut off, the pressure exerted by the sludge and the liquid against the movable body of the valve is no longer balanced by the pressure in the valve chamber 70 and there is a drain which is stopped by the restoration of the water supply by the butt 57.

The above explanation was given in relation to a valve. The different valves distributed around the head 17 operate simultaneously in the same way.

The continuous leakage of water that occurs as a result of the game is intended to avoid the deposition of solids which could cause the mobile body to block in its bore.

The solids discharge sections (5 to 10 mm ² ) are chosen according to the volume of the mud chamber and the flow velocities to obtain easily controllable opening times (10 to 30 s) without risk of disturbing the liquid flows.

The construction described above is relatively simpler than that with a movable bottom. In fact, the overflow 26 only has more than one channel 55, and is no longer in communication with the chamber 24. The moving parts (valves) are protected against the accumulation of solids by a continuous circulation of water.

The sludge accumulates in the chamber 23 and during the evacuation the compactness of the sludge can prevent part of this sludge located between two holes is not properly driven out. They then form small mounds which risk disturbing the balance of the centrifuge. To avoid this drawback, scraper vanes 76 which sweep the chamber 23 are provided at the end of the scraper screw 36 and of the vanes 39 in order to avoid asymmetrical accumulations of solids during the emptying phases.

Claims (11)

1. High-output industrial centrifuge with improved energy efficiency, for purifying a liquid containing denser solid particles in suspension and/or droplets of a less dense fluid in emulsion, of the type comprising a rotor essentially consisting of a stack of centrifuging dishes rotating at high speed between two coaxial drums, means for continuously introducing and discharging the liquid, and means for the selective extraction of the separated impurities, said centrifugre being provided, in the space between an outer cylindrical drum (B) and an inner drum (A), -which drums are independently driven in coaxial rotation and are respectively provided with means for the discharge of the separated phase-, with a stack of dishes (33) which rotates with the inner drum and which is fed with liquid to be purified through an axial inlet, characterized in that the purified liquid passes out of the said space through an outlet wheel composed of blades (39) fastened to the inner drum (A) and forming an centripetal turbine, and then through tangential ejectors (40) fastened to the outer drum (B) and forming a reaction turnstile arranged in such a manner that the absolute exit speed of the purified liquid will be substantially zero, so that the said turbine and bhe said turnstile restore in the form of a driving torque the major part of the kinetic moment imparted to the liquid, and that in consequence the driving power required under continuous operating conditions is limited to compensation for frictional losses.

2. Centrifuge according to claim 1, in which the ejectors of the reaction turnstile provide jets of purified liquid that impinge on fixed blades, characterized in that said blades (45) are mounted to be orientable and/or arranged in a spiral in a volute (47) of revolution.

3. Centrifuge according to claim 1 or 2, in which the means of extracting the solid particles comprise a scraper screw (36) which is situated on the periphery of the stack of dishes (3) and brings the particles that have accumulated on the wall of the outer drum (B), into a chamber (23) provided at the end of the outer drum, characterized in that said chamber is peripherally disposed and discharges to the outside by way of radial passages (28) normally closed by the periphery of an axially movable plate (19) situated at the end of the outer drum (B).

4. Centrifuge according to claim 3, characterized in that the movable plate (19) and the outer drum (B) bound an annular chamber (59) which leads to the outside through a calibrated outlet aperture (60) and into which a greater flow of water or other liquid is introduced under a pressure sufficient to hold the said plate in the closed position.

5. Centrifuge according to claim 4, characterized in that the annular chamber (59) communicates through a channel (58) with the bottom, of smaller radius, of an annular gutter (55) provided on the outer wall of the outer drum (B) and open towards its axis, into which gutter the water is poured through a fixed pipe (57) shaped like a crozier.

6. Centrifuge according to claim 5, characterized in that the movable plate (19) and the outer drum (B) bound a second annular chamber (24) inside the first chamber and leading into the interior of the drum through judiciously disposed channels (63), into which second chamber a fraction of the water or other liquid flowing from the gutter (55) into an adjacent gutter (56) is injected under pressure by way of a duct (25).

7. Centrifugre according to claim 6, characterized in that the peripheral chamber (23) leads to the outside via passages normally closed by valve devices (66, 69) disposed in the periphery at the end of the outer drum (B).

8. Centrifuge according to claim 7, characterized in that the valve devices (69) communicate via a channel (58) with an annular gutter (55) provided on the outer wall of the drum (B) and open towards its axis, into which gutter the water is poured through a fixed pipe (57) shaped like a crozier.

9. Centrifuge according to claim 8, characterized in that a play is provided between a moving valve body (71) and the bore (72) in which it slides, the said play permitting a continuous exit of water coming from the annular gutter (55).

10. Centrifuge according to claim 3, characterized in that the means of extracting the solid particles comprise in addition scraper blades (76) which sweep the peripheral chamber (23) disposed at the end of the outer drum.

11. Centrifuge according to any one of the foregoing claims, characterized in that the means for extracting less dense fluid comprise radial passages (49) passing through the wall of the outer drum (A) and a fixed axial extraction tube (50) shaped like a crozier, scooping up the said fluid which has accumulated in the said drum.

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