US 3410481 A
Description (OCR text may contain errors)
Nov. 12, 1968 B. DAHLBERG ET AL 3,410,481
CENTRIFUGE Filed Dec. 1, 1966 f/g. Z
United States Patent 3,410,481 CENTRIFUGE Bengt Ingmar Dahlberg and .larl Gregar Volle, Tullinge, Sweden, assignors to Alta-Laval AB, Tumba, Sweden, a corporation of fiweden Filed Dec. 1, 1966, Ser. No. 598,247 7 Claims. (Cl. 233-29) The present invention relates to a centrifuge for the separation of two liquids from each other while keeping a substantially constant interface between these liquids.
In the separation of water-containing mineral oil, for example, the specific gravity of the oil usually varies to such an extent that in order to keep the interface between oil and water at a fairly constant level in the separation chamber, it is necessary to have available a number of gravity disks of various sizes so that a disk of the selected proper size can be used as overflow for the separated water, the oil being discharged by suitable means such as a paring member. It is important that the level of the interface be kept within a limited zone to insure an optimal separation result. Since it is impossible to replace the gravity disk while the centrifuge is in operation, the variation of the specific gravity of the oil constitutes a complicating factor in operation.
The present invention reduces or eliminates the need of exchanging the gravity disk by providing a centrifuge having a liquid inlet and two liquid outlets, one of which is of the level maintaining type (overflow or paring member) and the other of which is of a type that may be throttled by means of a movable wall (a piston or diaphragm) which is subjected on opposite sides to the pressure, produced by the centrifugal force, of columns of different size of substantially the same liquid and which, on one of the sides, is preferably subjected also to an additional force. A variation of the specific gravity of the liquid discharged through the outlet Which can be throttle-d involves a variation of the liquid pressures acting upon the movable Wall, so that the latter is displaced to a new position corresponding to the balance between the forces acting upon the wall. The resulting modification of the throttling of this outlet causes a new adjustment of the size of the liquid columns or the magnitude of the liquid pressures acting upon the movable wall whereby the previously indicated level of the interface remains essentially unchanged.
According to a preferred embodiment, one of the liquid outlets is formed by an overflow, and the other liquid outlet, preferably the one which can be throttled, comprises a paring member, preferably a paring disk.
If desired, a channel may be provided which leads from the space on one side of the movable wall to a point which, in the radial direction, lies beyond the interface level in the separation chamber, and this space may have an inlet for liquid, the additional force being arranged to act upon the movable wall in a direction which is opposite to that of the action of said liquid. The supply of liquid to this space is preferably arranged so as to issue from the paring member.
If one of the liquids in the liquid mixture to be separated constitutes a small quantity in relation to the other liquid, the supply of the liquid mixture to the centrifuge may be effected entirely or partly to the abovementioned space.
According to a preferred embodiment, the additional force may be generated by a spring. However, it is also possible to replace the additional force by an arrangement according to which the movable wall is constituted by a cylindrical piston of which one of the sides 3 ,4 16,43 1 Patented Nov. 12, 1968 subjected to liquid pressure has a smaller radius than the other side.
The invention is described more in detail below, reference being made to the attached drawing in which FIG. 1 is a vertical sectional view of the right-hand half of a centrifuge, and FIG. 2 is a similar view through part of a modification of the same centrifuge.
In FIG. 1, reference numeral 1 designates a centrifuge rotor with a hood 2 and a lock-ring 3. Reference numeral 4 designates a supply pipe for the liquid mixture to be separated (assumed in the following to be a water-containing mineral oil). A disk set 7 is inserted between a distributor 5 and a top disk 6. An overflow 8 for separated water is arranged at the top of the hood. This overflow is normally constituted by a specially mounted gravity disk. A paring chamber 10 and a liquid feed chamber 11 are arranged in the neck 9 of the top disk. These chambers are separated by a horizontal wall 12. A stationary par-ing disk 13 constituting the outlet for separated oil is arranged in the paring chamber 10. A pipe 15 branches from a paring channel 14 in the paring disk and opens into the chamber 11. From the latter, a channel 16 extends into the separating chamber 17 and opens at its outer end 16a at a region located radially outward from the interface 18 between oil and water, it being this interface which is to be kept at a nearly constant level. A channel 19, which conveys separated clean oil to the paring chamber :10, is arranged in the neck 9 of the top disk 6.
The lower orifice 20 of the channel 19 is throttled by a cylindrical piston 21 movable in vertical direction. This piston, due to a small clearance in relation to the inside of the top disk neck 9, moves nearly Without friction. On its upper side, the piston 21 is urged downwards by an oil layer having a free level 22, and on its underside the piston is urged upward by an oil layer with a free level 23 and by the additional force of a spring 24 clamped between the piston 21 and the upper edge of the distributor 5. The spring 24 may, of course, be replaced by a spring pulling in the upward direction and inserted between the piston 21 and the wall 12.
In the separation of water-containing oil, the centrifuge operates as follows:
The oil is fed into the separating chamber 17 through inlet pipe 4, separated water travelling along the upper side of the hood 2 to reach the overflow 8 from which it is discharged. Separated clean oil reaches the inner edges of the disk set 7 and flows through the channel 19 to the paring chamber 10 to be discharged by the paring disk 13. A small portion of the oil flowing through the paring channel 14 is diverted by the pipe 15 to the chamber 11 and fills the channel 16 up to its opening 16a into the separating chamber 17. The oil flowing out from opening 16a travels inward toward the disk set 7. The pressure of the oil column contained in the channel 16 and the chamber 11 balances the pressure of the water column which extends from the orifice 16a of the channel 16 in the separating chamber to the overflow 8. The size of this water column is constant. The pressure of the oil column which extends between the levels 18 and 23 balances the pressure of the shorter Water column which extends between the level 18 and the overflow 8. The position of the level 23 is determined by the throttling of the orifice 20 of the channel 19.
The control of the interface 18 according to the invention may briefly be explained as follows:
If the specific gravity of the oil which is fed to the centrifuge increases, a shorter oil column is required to balance the corresponding water column; that is, the oil level 22 moves radially outward. Consequently, the pressure against the upper side of the piston 21 is reduced and therefore the spring 24 and the liquid pressure acting upon the underside of the piston displace the piston upward. In this way, the area of the orifice 20 increases so that the resistance to flow encountered by the oil on its way to the paring chamber 10 is reduced. As a result,
the oil level 23 also travels outward so that the oil column, between the levels 18 and 23 becomes shorter. This caiuses a displacement of the level 18 which is considerably less than would have been the case Without the present control means. That is, the displacement will amount to only one tenth, for example, of that in a centrifuge of the convention type.
In FIG. 2, the spring 24 has been eliminated by providing a piston 21a having opposite sides 21b and 21c of different areas which are subjected to the pressure of a liquid. By means of packings (not shown), piston 21a slides with a liquid-tight fit against the surfaces 9a and 9b of the inside of the top disk neck 9.
As may be seen in FIG. 2, the pressure exerted by a liquid layer on the underside of the piston 21a balances, without the assistance of any spring, the pressure exerted by a liquid layer on the upper side of the piston, the latter layer being thicker but located at a smaller radius. As may be easily understood, the result of this embodiment is similar to the result of the embodiment according to FIG. 1.
1. A centrifuge for separating two liquids from each other while maintaining a substantially constant interface between the liquids, the centrifuge comprising a centrifugal rotor having an inlet for a mixture of the two liquids and also having two outlets for the respective separated liquids, one of said outlets being of the level maintaining type and the second outlet being of the type adapted to be throttled, and a movable wall for throttling said second outlet and subjected on opposite sides in the rotor to the pressures, generated by centrifugal force, of liquid columns of diiferent size and of substantially the same liquid.
2. A centrifuge according to claim 1, comprising also means subjecting said movable wall to an additional force on One of its sides.
3. A centrifuge according to claim 1, in which said outlet of the level maintaining type is an overflow outlet, said second outlet including a paring member.
4. A centrifuge according to claim 1, in which the rotor forms spaces at opposite sides of said movable wall, the rotor having a channel leading from one of said spaces to a region in the rotor located radially outward from the level of said interface, said one space having an inlet for liquid, the centrifuge comprising also means subjecting said movable wall to an additional force in a direction opposite to that of liquid in said one space.
5. A centrifuge according to claim 4, in which said second outlet includes a paring member, the centrifuge comprising also means for supplying liquid from said paring member through said inlet to said one space.
6. A centrifuge according to claim 1, comprising also a spring subjecting said movable wall to an additional force on one of its sides.
7. A centrifuge according to claim 1, in which said movable wall is formed by a cylindrical piston, one side of said piston having a smaller radius than the opposite side.
References Cited UNITED STATES PATENTS 1,158,959 11/1915 Beach 233-27 2,622,796 12/1952 Steinacker et al. 233-19 X 2,862,659 12/1958 Nyrop 23320 WILLIAM I. PRICE, Primary Examiner.