EP0104966A2 - Centrifuge with energy recuperation - Google Patents

Abstract

Centrifuge comprising two drums (1,2) with coaxial horizontal axes. The inner drum carries a set of plates (33) and on the periphery a scraper screw (36). A mud chamber (23) provided at one end of the external drum (2) which communicates by passages (28) which can be closed off by a discharge device with the outside. The centrifuge comprises a double energy recovery device comprising a centripetal impeller (38) and a crown (40) of ejectors secured to the inner drum and a fixed vane (42) opposite the ejectors. The ejectors (42) are directed so that the absolute speed of the fluid leaving the centrifuge is low. The discharge device comprises a weir (26) continuously supplied to maintain by pressure a movable bottom (19) in the closed position in front of the passages (28). Application to the treatment of effluents or waste water, especially in the petroleum industry.

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.

French patent 2,361,942 describes a centrifuge with coaxial drums and a horizontal axis used in the paper industry to separate solids from liquids. The charged liquid arrives in the space separating two cylindrical-conical drums. rotating at high speed, a fixed differential speed being produced between the outer drum and the inner drum. The inner drum is provided with a fin constituting an Archimedes screw which permanently removes the deposits of solid materials and evacuates them towards the conical end of the drums. The liquid is discharged at the cylindrical end.

The separation is not very thorough and the finest particles remain in suspension.

In order to increase the efficiency of a centrifuge, French Patent 2,326,981 proposes to equip a centrifuge bowl with vertical axis with a set of conical plates wedged on the central axis. The plates are separated from each other by a small space into which the charged liquid enters and where it separates from its solid particles. The liquid is evacuated towards the interior of the bowl while the particles collect in a biconical chamber, formed by the wall of the bowl, before being expelled radially outwards by operation of an evacuation device.

The industrial centrifuge with high flow rate and improved energy efficiency, which is the subject of the invention, is particularly suitable for purifying a liquid including in suspension denser solid particles and / or in emulsion droplets of a less dense fluid. .

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 placed the stacking of 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 a outlet wheel 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 speed of output of the purified liquid is substantially nothing.

In this way, the turbine and the turnstile restore most of the angular momentum communicated to the liquid in the form of engine torque, which makes it possible to reduce the compensation for friction loss compensation for 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.

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 part of Figure 1 of another embodiment.

The centrifuge with horizontal axis, shown in FIGS. 1 to 4, schematically comprises an interior drum A, an exterior drum B, a device for removing 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 _o 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 outer drum B, consists of a cylindrical hollow body extended on the upstream side by a cylindrical-conical 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 bearing 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 added in 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 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, its periphery 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, its periphery uncovers the passages 28, which allow, by a simple centrifugal effect, the emptying of the mud chamber 23.

The inner drum A is connected by its tubular end 8 to the end of the hollow shaft 4 by which the effluent or the mixture is introduced. treat, which reaches the annular space between the outer 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 rotated a stack of conical plates 33 (shown partially). These frustoconical plates 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 stacking 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 which is in the form of a frustoconical envelope integral with the plate press 35 to the surface of which are fixed vanes 3 ₉ 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 is constituted by. a series of ejectors 40 forming a tourniquet fixed on the cylindrical surface 41 of the exterior drum B extending its head 17. The ejectors 40 formed of attached blocks 42 receive the purified fluid by radial channels 43 (FIG. 4) communicating with the inside 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 external drum B. The tangential jets coming from the ejectors 40 reach a ring of fixed vanes 45, disposed between two radial flanges 46 added in the cylindrical volute 47 for leaving the purified liquid. This volute is fixed to the bearing B of the centrifuge support. The vanes 45 are advantageously adjustable in orientation to preserve the residual angular momentum and arranged in a spiral to facilitate the evacuation of fluid.

• L'alimentation de la centrifugeuse se faisant dans l'axe, la mise en rotation du liquide crée en tout point une surpression
  
  où p est la masse volumique du fluide, ω la vitesse angulaire de rotation et R le rayon de giration au point considéré_o

The recovery of kinetic energy can be explained as follows:

• 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 _o

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 absolue du fluide Va par rapport à un référentiel extérieur à la machine, est la somme géométrique de a vitesse relative W et de la vitesse d'entraînement V =ωR au point considéré : Va = W+V. Donc si W et V 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).Pressure is converted into speed in nozzle 44 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 Go relative to a reference frame external to the machine, is the geometric sum of a relative speed W and drive speed V = ωR at the point considered: Go = W + V . So if W and V are collinear, of opposite directions and of the same module, Go 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 by a cylindrical ring 51 fixed on the head 17 and bearing in internal 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 defines with the external face 54 of the head 17 a first channel 55 and with l 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 bottom mobile 19 between the stepped surfaces 20, 21 of the head 17 of the external drum B. This chamber, provided with a calibrated leak orifice 60 opening into a passage 28, receives continuously by the fixed stock 57, the channel 55 and the channel 58 a flow of water greater than that flowing through the leakage 60. The excess water overflows from the first channel by filling the second channel 56. A radial channel pierced in the bottom of the chamber 56 communicates by intermediate of channel 25 with pressure chamber 24 del imitated by the movable bottom 19 and the internal face 61 of the head 17. Due to the rotation the centrifuged water exerts sufficient pressure against the movable bottom 19 to maintain its periphery in axial abutment on the radial bearing 62 of the flange 16 , position in which it closes the passages 28 communicating the mud chamber 23 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 allow the pressure chamber 24 to be emptied. The internal pressure in the bowl B acting on the other face of the movable base 19, it moves to the right in the drawing, revealing the passages 28. The bottom 19 closes when the weir 26 is again supplied.

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 interior 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 setting in speed: 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 heaviest 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 interior edge of the plate, the film is divided into large droplets which are very quickly captured on the surface 30 of the interior drum A and flow through the orifices 49 in the reservoir 48 where it is recovered by the tube of shell 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 100m³/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 µm est total pour une différence de densité eau/huile de 0,15.

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 100m 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 inter-plate space is around 0.5 mm.

The centrifuge has a length of 2.5 meters for a diameter of about 0.70 m.

The recovery yield is of the order of 95%. related to the kinetic power transmitted to the fluid.

The device for evacuating solid materials, with a movable bottom, 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 170

The channels 58, provided in the head 17, open out from a side in the channel 55, receiving water from the supply stock 57, and on the other in the valve chambers 70. The movable parts of the valves 71 slide in with play / dea 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 _o The water exerts a pressure against the rear face of the movable body of the valve and keeps 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 re-establishment 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 _o 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 evacuation sections (5 to 10mm ² ) are chosen according to the volume of the mud chamber and the flow speeds to obtain easily controllable opening times (10 to 30s) without risk of disturbing the flows. liquid.

The construction described above is relatively simpler than with mobile bottom _o Indeed the weir _{February 6} no longer includes a channel 55, and is no longer in communication with the chamber 24. The movable parts (flaps) are protected against accumulation of solids, by a continuous circulation of water _o '

The sludge accumulates in the chamber 23 and during evacuation the compactness of the sludge can prevent a portion of this sludge located between two orifices from being properly removed. 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 (14)

1 ₀ Industrial centrifuge with high flow rate and improved energy efficiency, for the purification of a liquid including in suspension denser solid particles and / or in emulsion droplets of a less dense fluid, of the type comprising a rotor essentially formed of '' a stack of centrifuge plates rotating at high speed between two coaxial cylindrical drums, means for the continuous introduction and evacuation of the liquid and means for the selective extraction of separated impurities, characterized in that in the the interval between an external cylindrical drum (B) and an internal drum (A), driven in coaxial rotation independently and respectively provided with means for evacuating the separate phases, is arranged a stack of plates (33) rotating with the internal drum and supplied with liquid to be purified through an axial inlet followed by a centrifugal impeller, and in that the purified liquid leaves said space through a so-called impeller rtie consisting of vanes (39) integral with the inner drum (A) and forming a centripetal turbine, then through tangential ejectors (40) integral with the outer drum (B) and forming a reaction turnstile, arranged so that the speed absolute outlet of the purified liquid is substantially zero, so that said turbine and said turnstile restore in the form of engine torque most of the angular momentum communicated to the liquid, and that consequently, the motive power required in continuous regime is limited to compensation for friction losses. 2. Centrifuge according to claim 1, characterized in that the jets of purified liquid from the ejectors (40) strike fixed vanes (45) arranged and acting to facilitate its evacuation. 3. Centrifuge according to claim 2, characterized in that the fixed blades (45) are mounted orientable and / or arranged in a spiral in a volute (47) of revolution. 4. Centrifuge according to any one of claims 1 to 3, characterized in that the means for extracting solid particles comprise a scraper screw (36) which surrounds the stack of plates (3) integral with the inner drum (A ) and axially expels the particles accumulated on the cylindrical wall of the outer drum (B) rotating at slightly different speed to bring them into a peripheral chamber (23) formed at the end of said outer drum. 5. Centrifuge according to claim 4, characterized in that the peripheral chamber (23) opens to the outside by radial passages (28) normally closed by the periphery of an axially movable bottom (19) arranged at the end of the outer drum (B). 6. Centrifuge according to claim 5, characterized in that the movable bottom (19) and the external drum (B) delimit an annular chamber (59) opening to the outside by a calibrated orifice (60) of leakage and in which a higher flow of water or other liquid is introduced under sufficient pressure to maintain said bottom in the closed position. 7. Centrifuge according to claim 6, characterized in that the annular chamber (59) communicates by a channel (58) with the bottom of the lower radius of an annular channel (55), arranged on the outer wall of the outer drum (B) and open towards its axis, in which the water is poured out by a fixed stock (57). 8. Centrifuge according to claim 7, characterized in that the movable bottom (19) and the outer drum (B) delimit a second annular chamber (24) inside the first and opening into the inside of the drum through channels (63 ) judiciously arranged, into which is injected under pressure through a channel (25) a fraction of the water or other liquid pouring from the channel (55) into an adjacent channel (56). 9. Centrifuge according to claim 4, characterized in that the peripheral chamber (23) opens to the outside by passages normally closed by valve devices (66,69) arranged in the periphery at the end of the outer drum (B) . 10.Centrifuge according to claim 9, characterized in that the valve devices (69) communicate by a channel (58) with an annular channel (55), arranged on the external wall of the drum (B) and open towards its axis, in which the water is poured out by a fixed stock (57). 11. Centrifuge according to claim 10, characterized in that between a movable valve body (71) and the bore (72), in which it slides, is provided a clearance allowing a continuous leakage of water from the annular channel (55). 12. C. centrifuge according to any one of the preceding claims, characterized in that the means of less dense fluid extraction comprise radial passages (49) passing through the wall of the outer drum (A) and a fixed axial stock (50) scooping said fluid accumulated in said drum. 13. Centrifuge according to claim 4, characterized in that the scraper screw (36) carries at its end scraper paddles (76) which scan the peripheral chamber (23). 14 ₀ Centrifuge according to any one of the preceding claims, characterized in that it is used for the purification of effluents or waste water, in particular in the petroleum industry.

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