WO1986004270A1

WO1986004270A1 - Centrifugal separator

Info

Publication number: WO1986004270A1
Application number: PCT/NO1986/000006
Authority: WO
Inventors: Helge Kind
Original assignee: Knut Malmberg A/S
Priority date: 1985-01-22
Filing date: 1986-01-21
Publication date: 1986-07-31
Also published as: JPS62501485A; EP0208761A1; FI863821A; DK450586A; DK450586D0; FI863821A0; NO850266L

Abstract

A centrifugal separator for separating a discontinuous phase from a continuous phase comprises a number of conically shaped centrifugal chambers symmetrically arranged about a vertical axis, and each centrifugal chamber being connected with a common inlet (1) for liquid to be separated, a lamella pack (4), a compression zone (9) for discontinuous phase, and a conveyer means for separated discontinuous phase to an outlet (12) said discharge means (11) comprising at least two conveyer screws arranged each at one end of a common shaft, so that each screw serves to feed out from two opposite centrifugal chambers with which they are connected, and said centrifugal separator, furthermore, being provided with a lamella pack (4) comprising a number of double lamellae which are closed toward a distribution zone (3) and at one end are connected with an outlet (7) for the continuous phase, and the other end of which opens into compression zone (9) for the discontinuous phase.

Description

Centrifugal separator

The present invention relates to a centrifugal separator of the kind as stated in the preamble of claim 1, to which a fluid comprising a continuous and a discontinuous phase is passed via an inlet zone (1) to at least one centrifugal chamber (5) provided with coalescence lamellae (12), and outlets (14, 21) for the separated phase.

A general discussion of centrifugal processes and centrifug¬ al means is, inter alia, found in Kirk Othmer "Encyclopedia of Chemical Technology", second edition, volume 4, pages 710 - 758. Further mention of liquid-solid separation is to be found in "Current Liquid-Solid Separation Technology" ,

Filtration & Separation, July/August 1980, pages 326 - 335.

The present centrifugal separator is of the kind that is intended for continuous operation with fields of application comprising separation of particles from a suspension contain- ing particles the specific weight of which is higher than that of the liquid phase. The centrifugal separator can substitute sedimentation basins of most kinds, other forms of centrifugation in industry, it may be used in stead of cyclones in oil and petroleum industry to remove particles, for sludge treatment, as well as for separation of emulsions where the densities of various fractions permit centrifugal separation.

From US-PS No. 2 270 173 a centrifugal separator is known where a rotating liquid ring is formed to which conduits extend for introduction of the liquid mixture or for separation of two non-intermixable phases with different specific weight that are to be treated. The liquid conduits used to introduce the mixture to be treated is shown in the patent having a slightly conical shape opening into the rotating liquid ring. There is deposition on an interior periphery surface of a rotating drum, whereas excess liquid overflows across an inner circular edge and is ejected. The solids deposited on said interior surface of the rotating drum must be removed at intervals.

From SE-PS No. 218 947 a centrifugal means is known compris¬ ing a drum that is rotatable about a vertical axis and is in the upper region provided with a centrally mounted cylind- rical supply pipe and is below said supply pipe also provid¬ ed with a corresponding outlet pipe extending centrally about said axis. Said drum is partitioned into an upper and a lower half by the aid of an intermediate bottom having a smaller diameter than the interior diameter of said drum, so that liquid can flow between the upper and lower drum port¬ ions around the outer wall of said intermediate bottom. This means that all liquid must pass the outside edge of said intermediate bottom at a minimum distance from the axis of rotation and it ensures that all suspended particles are subjected to a minimum centrifugal force determined by the velocity of drum rotation and the radius of said interme¬ diate bottom. The drum is provided with outlet openings for separate particles said openings discharging into a conical- ly shaped pocket that may be closed by the aid of a plug or the like. The discharge opening for separated solids is controllable, as desired, dependent on the amount of solids to be separated, etc.

DE-AS No. 11 58 905 discloses a centrifugal means co pris- ing two centrifugal drums connected in series the interior of which is divided into two chambers by a partition wall forcing the liquid flowing through outwards into a certain distance from the axis of rotation. In the periphery of the centrifugal drums discharge openings are provided in a portion of the centrifugal drum showing a conical cross section. Said openings can be closed or adjusted by the aid of suitable control means. GB-PS No. 1 465 311 shows a centrifugal means comprising conically shaped separation chambers symmetrically arranged about a vertical axis. Each separator chamber is arranged in such a manner that the approximately cone-shaped separation chamber has its top point furthest off the vertical axis of the centrifugal means. When said means rotates and makes the separation chambers rotate the heavier particles present in the liquid inside each separation chamber will, thus, be urged outwards towards the top points of the cones due to centrifugal force.

In the top points of the cones an adjustable valve means is provided permitting adjustment of the discharge of solid particles that "wandered" towards the top point of the cone due to centrifugal force.

It is disclosed in the patent that said valves can be opened in a time-controlled manner or by the aid of a sensor means sensing the fact that a sufficient amount of solids has collected in the top-points of the respective conical chamb¬ ers. The shown centrifugal device can be utilized for classification of different components when a number of such units are connected in series about one and the same axis of rotation.

In US-PS No. 1 124 907 a centrifugal machine for separating solids from liquids is shown in cross section. The centri¬ fuge per se is shaped like a straight truncated cone that is rotated about its geometrical axis and to which rotational body the liquid to be purified is supplied centrally. Particles present in the liquid will be carried outwards to the outside periphery of the rotational body, where discharge conduits are provided for the liquid en- riched with the heavier particles. In stead of valves in the discharge pipes, as used in the above mentioned US patent the discharge pipes are inclined to the axis of rotation so that the liquid flowing out is forced to flow in a direction opposed by the centrifugal force. To permit adjustment of the discharge of liquid enriched as regards particles pre¬ sent said pipes are telescopic, permitting adjustment of the distance between the outlet openings and the axis of rotation by the aid of a suitable mechanism. By adjusting the center distance of said outlet openings from the axis of rotation the amount of liquid discharged through the outlet openings and consequently the concentration of material suspended in said liquid can, thus, be adjusted. The liquid depleted as regards solid particles is discharged from the centrifuge in a conventional manner.

In an embodiment of the centrifugal machine according to. said US-PS No. 1 124 907 the outlet pipes inclined to the axis of rotation are not provided with a telescopic arrange¬ ment, but with Archimedes' screws by the aid of which the enriched solids may be discharged against the effect of the centrifugal force. Said screws in the discharge pipes are driven by the aid of a suitable gear means.

Furthermore, it is well known to provide lamellae inside a separator, partly to control the liquid flow through a centrifugal separator, and partly to enhance coalescence or "bonding together" of the particles suspended in the liquid phase. The utilization of lamellae is, thus, e.g. known from SE-PS No. 227 106 and GB-PS No. 1 544 755.

The present centrifugal means is partly based on the centri¬ fugal structure disclosed in GB-PS No. 465 311 and partly on the structure disclosed in US-PS No. 1 124 907. It, thus, comprises a vertical axis about which a number of conically shaped separation chambers are arranged, the top-points of said conical chambers being furthest off the axis of rota¬ tion and the top-point of each chamber being provided with a discharge pipe that is bent towards said axis of rotation, but the discharge pipe is provided with a special feeding out screw for feeding out liquid enriched as regards suspended particles. This combination of separate separation chambers with separate discharge pipes with screw feeding-out provid¬ es the centrifugal means with good and easily adjustable separation properties rendering it especially suited for liquid - liquid separation. For feeding-out enriched solids feeding-out screws of variable discharge velocity are pre- ferably used.

Further new features of the invention, inter alia, comprise a special outlet opening for depleted liquid which is in direct contact with a special lamella pack used in the pre- sent centrifugal means.

Below "he liquid enriched as regards suspended substances and the liquid partly freed from such substances will be denoted the enriched. phase and the depleted phase, respect- ively.

Since the enriched phase is made to flow toward the axis of the centrifugal means, .it must be possible to adjust the velocity of flow by the aid of said feed-out screw, so that the particles in the enriched phase can be carried to the openings of the discharge pipes against the effect of the centrifugal force.

Liquid/solids separation tests, however, showed that due to variations of the composition of solids it is necessary to use a conveyer worm of the kind as disclosed in US-PS 1 124 907 in order to achieve stable conditions.

The centrifugal means will now be disclosed in more detail with reference to the attached drawings, where Figure 1 is a side elevation of a centrifugal means according to the in¬ vention, and Figure 2 is a plan view of the centrifugal means of Figure 1. Figure 3 is a side elevation of the feed¬ ing-out portion of the centrifugal means for the enriched phase, the screw drive being disclosed in more detail.

The centrifugal separator is constructed for supply according to the vortex principle to accelerate the non-purified liquid introduced into the centrifugal separator. The liquid is introduced into an inlet zone 1, from which it is fed to an acceleration zone 2 with increasing radius. It is then conducted to a distribution chamber 3 and into a lamella pack with double lamellae having rounded edges facing the distri¬ bution chamber to prevent fibres and the like from adhering. Said double lamellae have several functions, i.e. to serve as a separation member 5 , to transport separated phase to the outlet portion 8 of the lamellae, which with a widened outlet will result in an advantageous separation of the two phases. In the drawing the flow path of the phase flowing inwards and the phase flowing outwards are indicated by solid arrows, whereas the path of movement of the enriched phase is indicat¬ ed by dotted arrows. As indicated in the drawing, the liquid flowing down along separation zone 5 will deflect at the end of said zone and be conducted upwards through discharge port-

J ion 6 for the depleted phase.

This kind of lamellae may also be used in conventional cir¬ cular centrifugal means. The depleted phase is fed out of the centrifugal separator in an outlet zone 7. In a conventional manner sludge will collect against said lamellae and slide down along them to enter a sludge outlet zone 8. Due to the acceleration forces the sludge will be introduced into a compression zone 9 and be fed into a pressure conveyance zone 10. It will be fed towards a conveyer screw 11 convey¬ ing the sludge to a circular outlet chamber 12 for sludge which is provided with guide channels at the outlet for enriched phase. 13 indicates an outlet for flowing sludge for intermittent draw-off. As will appear from Figure 1 and especially Figure 2 the sludge will automatically flow off in case of shutdown. Draw-off may also be carried out when the centrifugal separa¬ tor is running.

In Figure 2 corresponding parts are designated by the same reference numbers as in Figure 1. From this figure it will, inter alia, appear or be understood that the depleted phase moving upwards in the direction of the arrow in the interior of a double lamella will move in a tangential direction and into outlet zone 7 connecting the respective lamella outlets. It will also appear from Figure 2 that the flowing sludge is fed out of chamber 2 in case of a shutdown of the centri¬ fugal separator, since the supplied liquid will sink to the bottom of chamber 2 in stead of lying like a water level along partition means dividing chambers 2 and 3.

^In Figure 3 a special embodiment of the feeding-out screw is shown. Two opposite screws 11 are connected with a common through shaft, which makes the screw arrangement self-balan¬ cing. Consequently, the bearing arrangement is relatively simple and heavy and expensive thrust bearings are not necessary, because the bearings substantially must absorb loads only in a radial direction. The screws are driven by the aid of a couple of cooperating bevel pinions 15 and 16, said bevel pinions being secured to a shaft 14 that is driven/braked by the aid of a separate electrical motor. When there is a difference of rotational speed between drive shaft 18 and the coaxial shaft 14, screw 11 will, thus, be rotated and convey the sludge in an axial direction to feed it to chamber 12.

According to Figure 1 the sludge in the pressure conveyance zone is conveyed towards the screw in its axial direction. There is, however, nothing preventing the zone where compress ion takes place to be constructed in such a manner that the enriched phase is conveyed directly down towards the active portion of the screw, which may be advantageous for feeding- out heavier particles that might otherwise be difficult to urge towards the screw in its axial direction.

The centrifugal separator works as follows. On the basis of knowledge of the suspension to be centrifugated or experi¬ ments the velocity of rotation of feeding out screw 11 is set, and the centrifugal separator is made to operate with the desired velocity of rotation. The suspension is fed to inlet zone 1, which provides a vortex before the suspension flows into acceleration zone 2 and from there into the respective distribution zones 3, and from there into lamella pack 4) where separation of solid particles starts in that said particles are, due to the centrifugal force, conveyed off the axis of the centrifugal separator and slide down along the- lamella plates to be fed off to compression zone 9 at. the outlet of the lamellae. The depleted phase will float., as indicated by an arrow, and will then flow out through out¬ let 7, whereas the enriched phase, as mentioned above, is conveyed towards the axis of the centrifugal separator by the aid of screws 11 and is fed out of the centrifugal sepa¬ rator via the circular outlet chambers 12.

It is possible to achieve relatively high concentrations of solids by the aid of the present centrifugal separator, due to the design of the centrifugal chambers, and industrial experiments carried out so far are described as very success- ful.

Claims

CLAIMS:

1. A centrifugal separator for separating a discontin¬ uous phase from a continuous phase, comprising a number of conically shaped centrifugal chambers symmetrically arranged about a vertical axis, and each centrifugal chamber being connected with a common inlet (1) for liquid to be separated, a lamella pack (4), a compression zone (9) for discontinuous phase, and a conveyance means for separated discontinuous phase to an outlet (12), c h a r a c t e r i z e d i n that the discharge means (11) comprises at least two conveyer screws arranged one at each end of a common shaft, so that each screw serves to feed out from two opposite centrifugal chambers with which said screws are connected.

2. A centrifugal separator as defined in claim 1, c h a r a c t e r i z e d i n that the velocity of rota¬ tion of the conveyer screw is variable.

3. A centrifugal separator as defined in claim 1, c h a r a c t e r i z e d i n that the lamellae of lamella pack (4) comprise a number of double lamellae which are closed toward a distribution zone (3) and at said end are connected with an outlet (7) for the continuous phase, and the other end of which opens into compression zone (9) for the discontinuous phase.