US3752389A

US3752389A - Centrifugal separator with control means

Info

Publication number: US3752389A
Application number: US00204529A
Authority: US
Inventors: V Nilsson
Original assignee: Alfa Laval AB
Current assignee: Alfa Laval AB
Priority date: 1970-12-07
Filing date: 1971-12-03
Publication date: 1973-08-14
Anticipated expiration: 1990-08-14
Also published as: SE348121B; JPS5648216B1; SU577946A3; DE2160455A1; GB1359157A; DE2160455C2; IT941394B; FR2117350A5

Abstract

The rotor has a central outlet for a separated light liquid component, an intermittently opened peripheral outlet for separated sediment, and a third outlet for a separated heavy liquid component, there being a passage for conducting liquid from the third outlet to a reception place for heavy liquid component. Means are provided for controlling liquid flow to this reception place through said passage, and further means are provided for sensing when separated heavy liquid component is at a predetermined level in the rotor, said last means being operable upon such sensing to actuate the controlling means to effect liquid flow to the reception place through said passage.

Description

United States Patent [191 Nilsson 5 1 CENTRIFUGAL SEPARATOR wrru CONTROL MEANS [75] Inventor: Vllgot Raymond Nllsson, l-lagersten,

Sweden [73] Assignee: Alla-Laval AB, Tumba Sweden 22 Filed: Dec. 3, 1971 [211 App]. No.: 204,529

[30] Foreign Application Priority Data Dec. 7, 1970 Sweden 16515/70 [52] U.S. Cl. 233/20 R, 233/46 [51] Int. Cl 1304b 11/00 [58] Field of Search 233/16, 19 R, 19 A, 233/20 R, 20 A, 46, 47 R, 27, 28; 210/104, 105, 371, 372

[56] References Cited UNITED STATES PATENTS Aug. 14, 1973 Primary ExaminerGeorge 1-1. Krizmanich Attorney-Cyrus S. l-lapgood [57] ABSTRACT The rotor has a central outlet for a separated light liquid component, an intermittently opened peripheral outlet for separated sediment, and a third outlet for a separated heavy liquid component, there being a passage for conducting liquid from the third outlet to a reception place for heavy liquid component. Means are provided for controlling liquid flow to this reception place through said passage, and further means are provided for sensing when separated heavy liquid component is at a predetermined level in the rotor, said last means being operable upon such sensing to actuate the 3,445,061 5/1969 Nilson 233/20 R controlling means to effect liquid flow to the reception 3,261,546 7/1966 Gruver.., 233/20 R place through said passage. 3,052,401 9/1962 Thylefors 233/19 R 3,396,910 8/1968 Steinacker 233/20 R 12 Claims, 3 Drawing Figures 30 r- 32 4 I 22? I t D 26 .'T' N27 23 4 7 l y Mr- 29 v as 1 2 Sheets-Sheet 2 LII/l/l/I/Il/l/Il/I/f 1 CE NT-RIFUGAL SEPARATOR WITH CONTROL MEANS The present invention relates to centrifugal separators of the type in which the rotor has an inlet for a mixture, to be separated, a central outlet for one separated light liquid constituent of the mixture, an outlet at the periphery. for separated sediment, which is arranged to be opened intermittently, and a further outlet situated radially between these outlets and serving to discharge a separated heavy liquid constituent of the mixture, a passage being arranged to conduct liquid from the lastmentioned outlet to a reception place for heavy liquid constituent.

A centrifugal separator of this type has means whereby the interface formed between light and heavy liquid constituent of the separated mixture is maintained in the rotor at a certain level located radially inside the outlet for the heavy liquid constituent. This means, in its simplest embodiment, includes two fixed overflow outlets, differently located near the rotor axis, forthe two. liquid constituents of the mixture. One disadvantage of centrifugal separators of this kind is that when the separated mixture contains a. relatively small amount of heavy liquid constituent, the space in the rotor usable for an effective separation is reduced by the necessity of keeping the said interface radially inside the outlet for the heavy liquid constituent. This results in a less effective separation of the light liquid constituent, sincethe latter will have a shorter throughflow time in the rotor.

The separated light liquid constituent tends to leave the rotor through the outlet for heavy liquid constituent, a s a result of the sediment being intermittently discharged through the peripheral outlet of the rotor, whereby the said interface is displaced radially outward. To avoid, this tendency, it is common practice to supply only heavy liquid constituent to the rotor during a. short period of time either before the peripheral outlet isopened or immediately after this outlet has been opened and shut again. The necessity of such operations in connection with discharge of sediment is a drawback in centrifugal separators of this kind.

Anobject of thepresent invention is to eliminate the above-described disadvantages, and it resides in providing centrifugal separators of this kind with a first means arranged to either allow or prevent liquid flow to the said reception place for heavy liquid constituent throughthesaid passage, and with a second means arranged to indicate when separated heavy liquid constituent" is at a predetermined level within the rotor and then to influence said first means to allow liquid flow to the reception; place through the said passage.

Byan arrangement of this kind, it is no longer necessary to maintain an interface between light and heavy liquid constituent radially inside a certain level in the rotor. The interface can be allowed to move radially outside the rotor outlet for heavy liquid constituent, without having light liquid constituent lost therethrough.

in centrifugal separators of the kind involved here, the. peripheral outlet of the rotor often is arranged to be openedat equal intervals. l (*Control equipment is previously known for initiating operations at equal intervals for opening of the peripheral outlet of the rotor.) The period of time between two opening occasions is determined-in. this case by the estimated content .of sediment inthemixture to be separated. However, this content of sediment seldom is constant during the entire separating operation but can vary within very wide limits. It sometimes happens that so much sediment is separated in the rotor between two opening occasions that the so called disc stack within the rotor is clogged, which means taking the centrifugal separator out of operation and cleaning the rotor manually.

For this reason, it is desirable that the time intervals between the opening occasions be kept as short as possible. However, it is desirable not to have too short a time interval between the opening occasions, since this burdens the opening mechanism of the rotor to an undesired degree. Also, the separation is disturbed at each opening occasion.

In a centrifugal separator according to the invention, it is possible to avoid clogging of the disc stack despite a high content of sediment in the mixture to be separated, without having the above-mentioned disadvantages. The said sensing means is arranged to make a signal, necessary for opening of the peripheral outlet of the rotor, when heavy liquid constituent is sensed at the predetermined level in the rotor. The rotor peripheral outlet will not open immediately when a pre-set time interval has passed, if during this interval separated sediment has not forced the interface between light and heavy liquid constituents of the separated mixture inward to the said predetermined level in the rotor. Thus, if the relation between the amounts of light and heavy liquid constituents is substantially unchanged, the time interval between the opening occasions will automatically be longer at a low than at a high content of sediment in the separated mixture. Another advantage of this arrangement is that the peripheral outlet of the rotor is not opened until the interface between light and heavy liquid constituents is situated inside a certain level, whereby loss of light liquid constituent through the peripheral outlet can be avoided. To prevent separated sediment from being packed too hard in the rotor during the said time intervals (which thus would be long if the separated mixture contained a relatively small amount of sediment and heavy liquid constituent), it is possible to charge the rotor with a certain additional amount of heavy liquid constituent during the separation, either intermittently or continuously, so that the time intervals are shortened.

In the centrifugal separator according to the invention, the sensing means for indicating when separated heavy liquid constituent is at a predetermined level in the rotor may be either of a first kind for sensing a difference between light liquid constituent and heavy liquid constituent (for instance, a difference between their dielectric constants) or of a second kind for comparing the liquid pressures at a certain distance from the rotor axis, on one hand in the separating chamber of the rotor, and on the other hand in a connection extending inwardly to the rotor axis from a point radially outside the said predetermined level in the separating chamber of the rotor.

If sensing means of saidv first kind is used, it is assured that a liquid flow to the reception place for heavy liquid constituent will occur even in such cases when, after the rotor has been totally emptied through its periphery outlet, the incoming mixture consists of only heavy liquid constituent and sediment. in such cases, a desired indication can not be obtained by means of a pressure comparing means. If such cases can be excluded, however, a pressure comparing means may well be used, in

which case it suffices to form the central outlet of the rotor for light liquid constituent as an overflow outlet which serves as means for maintaining a constant liquid pressure in the rotor at this outlet, independently of the liquid flow therethrough, and to connect a pressure sensing instrument to the above-mentioned connection within the rotor. This pressure sensing instrument can be adjusted for direct indication of the pressure difference, on the basis of which a liquid flow to the reception place for heavy liquid constituent should occur.

If the sensing means is arranged to indicate a difference between two liquids, the centrifugal separator is preferably provided with a channel leading from the predetermined level in the rotor, and with means for creating a liquid flow through this channel from the predetermined level in the rotor, the sensing means being arranged to indicate a change of the liquid flowing through the channel. By an arrangement of this kind, the sensing means need not be rotating together with the rotor. The sensing means may, for instance, be arranged to indicate a change of the flowing liquid as to its viscosity, density, electrical conductivity, etc. Different optical measurement methods also may be used.

In a preferred embodiment of the invention, the said channel and the previously mentioned passage have at least partly a common extension. Further, the channel preferably opens into the supply conduit of the rotor for mixture to be separated, whereby a constant circulation of liquid can be obtained through a sensing instrument situated outside the rotor.

Within the scope of the invention, it is possible to allow liquid to flow at certain time intervals from said predetermined level in the rotor to the reception place for heavy liquid constituent, and to sense whether this liquid is light or heavy liquid constituent of the mixture supplied to the rotor. Then, if heavy liquid constituent is sensed, the device which controls said intermittent flow may be switched off and a continuous flow may be allowed, i.e., a flow which continues for as long as it is required.

The invention is further described below with reference to the accompanying drawings, wherein FIG. 1 is a vertical sectional view of a rotor of a centrifugal separator according to the invention,

FIG. 2 is a flow chart wherein the centrifugal separator is a part, and

FIG. 3 is a schematic view of a sensing means.

The centrifuge rotor of FIG. 1 comprises a lower part 1 and an upper part 2, these parts being held together by means of a locking ring 3. The rotor is supported by a drive shaft 4 having a central channel 5 for the supply of a mixture to be separated in the rotor. The mixture is directed by a distributor 7 provided with entraining members 6 (radial wings) into the rotor separating chamber 8, where a stack of conical discs 9 is arranged. Sediment separated from the mixture supplied to the rotor is collected at 10 in the separating chamber 8. For intermittent discharge of this sediment during operation of the centrifugal separator, the rotor has a number of outlet openings 11 situated at its periphery. A valve disc 12 forming the bottom of the separating chamber 8 is arranged to open and close these outlets. The valve disc 12 is operable in a known manner by means of a liquid supplied to the lower side of it through a supply member 13 surrounding the drive shaft 4. When liquid is supplied to an interspace 14 between the lower part 1 of the rotor and the valve disc 12, the valve disc 12 is kept in its upper position, where it is pressed against the upper part 2 of the rotor. Liquid flows out of the interspace 14 through throttled openings 15 in the rotor part I. When the supply of liquid to the interspace 14 is interrupted, this interspace is emptied of liquid through the openings 15, the valve disc then being pressed downward by the liquid pressure in the separating chamber 8, so that the openings 11 are uncovered. When the supply of liquid to the interspace 14 is resumed, the valve disc 12 again will be pressed upward, so that the openings 11 are closed.

Liquid constituent separated from the mixture supplied to the rotor leaves the separating chamber 8 through a centrally situated overflow outlet 16, and flows thence into a chamber 17. By means of a paring disc 18 arranged in this chamber, the separated liquid constituent is then pumped through an outlet conduit 19.

From the radially outer portion of the rotor separating chamber 8 (i.e., in the area of the outer edges of the plates 9), a channel 20 extends inward toward the rotor axis to a central chamber 21. Within the chamber 21 a paring disc 22 is arranged to pump liquid from the chamber out through a conduit 23, which thus constitutes a continuation of the channel 20. Liquid flowing through the channel 20 passes an overflow outlet 24 on its way into the chamber 21.

In FIG. 2, a centrifugal separator S comprises a rotor of the kind described above. A supply conduit for mixture to be separated in the rotor is designated 25. This conduit is connected to the channel 5 in the rotor drive shaft 4 (FIG. 1). Sediment separated from the mixture is led away through a conduit 26, while separated light liquid constituent is led away through the conduit 19, and separated heavy liquid constituent through the conduit 23.

From the conduit 23 leads another conduit 27 which is connected to the inlet conduit 25 for mixture to be separated. In the conduit 27 is a throttle 28 and beyond this, seen in the direction of liquid flow through the conduit, is a check valve 29 arranged to open only when a certain liquid pressure is attained in the conduit.

Means 30 are arranged to sense the dielectric constant of the liquid flowing through the conduit 23. The sensing means 30, in response to the sensed value of the dielectric constant of the liquid, operates through a connection 31 to actuate a valve 32 situated in the conduit 23 beyond the point from where the conduit 27 begins. Through a connection 33, the sensing means 30 also actuates the control equipment of the centrifugal separator for the opening and closing of the sediment outlets I1 situated at the periphery of the rotor. This control equipment, which in the drawing is designated 34, is arranged to initiate in a conventional manner at certain time intervals (the length of which has been determined with reference to the estimated content of sediment in the mixture to be separated) an operation for opening of the sediment outlet openings 11.

Connected to the inlet conduit 25 for mixture to be separated, and near the conduit 27, is a conduit 35 for adding an extra amount of heavy liquid constituent to the rotor. In the conduit 35 is a pump 36.

In FIG. 3 there is shown a part of the conduit 23 and means for sensing the dielectric constant of liquid flowing through the conduit 23. Such means comprises a sensing member 37 and an indicating instrument 39 connected thereto through a connection 38. The indicating instrument, connected on one hand to a source of current 40 and on the other hand through a connection 41 to the conduit 23, comprises an oscillator (not shown). Means of this kind are conventional and need no further description. The operation of the centrifugal separator described above is as follows:

Through the conduit 25 and the channel 5 in the rotor drive shaft 4, the rotor is charged with a mixture consisting of one light liquid constituent (for instance, oil), one heavy liquid constituent (for instance, water), and a sediment, the density of which is greater than that of the two liquid constituents. In the rotor, separated sediment will thus be collected at the periphery, and an interface between light and heavy liquid constituents will be formed between the opening of the channel 20, in the separating chamber 8, and the rotor periphery. Separated light liquid constituent will leave the rotor separating chamber, on one hand over the central overflow outlet 16, and on the other hand through the channel over the overflow outlet 24. While liquid entering chamber 17 through the overflow outlet 16 is pumped further through the conduit 19 by the paring disc 18 to a reception place for separated light liquid constituent, liquid entering the chamber 21 through the overflow outlet 24 is pumped out through conduit 23 by means of the paring disc 22 and through the conduit 27 back to the inlet conduit 25 for mixture to be separated. The valve 32 is closed in a starting position.

During the separation, more and more sediment and heavy liquid constituent are collected in the rotor separating chamber. The interface between light and heavy liquid constituents is thus moved radially inward, and gradually it reaches a level at the opening of the channel 20 in the separating chamber 8. In FIG. 1, this level is shown by a dotted line 42. Instead of separated light liquid constituent, separated heavy liquid constituent now begins to flow through the channel 20, the chamber 21, the paring disc 22 and the conduit 23. This is sensed by means of the sensing means which then actuates the valve 32 so as to open it. The separated heavy liquid constituent thus will not be returned to the inlet conduit 25 through the conduit 27 but will continue through the conduit 23 to a reception place for 2 heavy constituent. This reception place (which is not shown in the drawing) may be constituted by a receptacle but can also be an outlet. When the valve 32 is opened, the liquid pressure in the conduit 27 is lowcred, whereby the check valve 29 is automatically closed.

At the same time as the valve 32 is actuated by the sensing means 30, a signal is given by the latter to the 4 centrifugal separator control equipment 34, without which signal this equipment can not perform an operation for opening the rotor periphery outlet 11. Thus, if the interface in the rotor between light and heavy liquid constituents has not yet reached the opening of the channel 20, when a period of time for the opening of the periphery outlet 11 (predetermined for the control charged (continuously or intermittently) with a small additional amount of heavy liquid constituent by means of the pump 36 through conduit 32 and the inlet conduit 25. If the interface between light and heavy liquid constituents reaches the opening of the channel 20, however, before the adjusted period of time for the opening of the peripheral outlet 11 has passed, the separation is continued until the period of time has passed, the interface then remaining at the level 42 shown in FIG. 1. Due to the overflow outlet 24, the interface is prevented from moving back radially outward during the separation. This effect would also be achieved without an overflow outlet, if the valve 32 in the conduit 23 were a so-called constant pressure valve, i.e., a valve with automatically controllable transmitting capacity, so that the pressure in the conduit 23 is kept at a predetermined value independently of the magnitude of the flow therethrough.

It has been assumed above that the sensing means is of a kind that can sense a change of the liquid which flows through the conduit 23. However, the sensing means 30 can also be a pressure sensing means con nected to and arranged to sense the pressure in the channel 20. In the embodiment shown in the drawings, the pressure in the conduit 23 (due to the throttle 28 that limits the flow through the conduits 23 and 27) will become directly responsive to the pressure in the chan' nel 20. A certain pressure or pressure change in the conduit 23 then can be used as an indication that the interface between light and heavy liquid constituents in the rotor has moved radially inward to a certain level, which will thus result in a signal, on one hand to the valve 32 (that is, to open it for the separated heavy liquid constituent) and on the other hand to the control equipment 34, so that sediment can be discharged through the peripheral outlet 11.

If the liquid pressure in the channel 20 is chosen as an indication of the position of the interface in the rotor between light and heavy liquid constituents, a circulation as described above need not necessarily be provided. The conduit 27 can then be omitted. The pressure in the channel 20 may be sensed in many different ways, as by pumping in air at a suitable level below the liquid surface formed in the chamber 21, and measuring a change of the resistance to this supply of air. The overflow outlet 24 is not necessary.

The conduit 27 also can be omitted, if a sensing means is used that is arranged to directly sense the position of the said interface in the rotor. A sensing means of this kind can be fixed to and rotate with the rotor.

Further modifications can be made within the scope of the present invention. Thus, the sensing means 30 may comprise both means for sensing a difference between two liquids, and means for sensing a pressure change in the rotor, the valve 32 in the conduit 23 being arranged to open only when a predetermined pressure as well as heavy liquid constituent are sensed by the sensing means. It is also possible to have two or more connections with different capacities between the channel 20 in the rotor and the reception place for heavy liquid constituent, for instance, a first connection with a relatively small capacity arranged to open when heavy liquid constituent is sensed in the conduit 23, and a second connection with greater capacity ar' ranged to open only when the pressure in the conduit, after having occasionally dropped, has risen to a certain value. In an arrangement of this kind, the control equipment 34 can be arranged to open the rotor peripheral outlet upon information from the sensing means that heavy liquid constituent as well as a certain pressure is sensed in the conduit 23, even if a time interval (predetermined for the control equipment) between two opening occasions has not yet run out. The pressure necessary for such information to the control equipment should be higher than that required for the opening of the said connection with greater capacity to the reception place for heavy liquid constituent. This prevents heavy liquid constituent from leaving through the central outlet of the rotor for light liquid constituent, if some fault should arise in the valves in the connections to the reception place for heavy liquid constituent.

The valve 32, of course, can be replaced by a threeway valve at the point where the conduit 27 begins in the conduit 23, or by any suitable arrangement for preventing or admitting liquid flow through the conduit 23 to the reception place for heavy liquid constituent.

I claim:

1. A centrifugal separator comprising a rotor provided with an inlet for a mixture to be separated, the rotor forming a separating chamber having three outlets for discharging from the rotor, namely, a central outlet for a separated light liquid component of the mixture, an intermittently opened outlet at the rotor periphery for separated sediment, and a third outlet for a separated heavy liquid component of the mixture, said third outlet being located between the other two outlets, and means forming a passage for discharging liquid from said third outlet to a reception place for heavy liquid component, the separator being characterized by control means associated with said passage and operable to alternately prevent and allow liquid flow therethrough to said reception place, and means for sensing when separated heavy liquid component is at a predetermined level within the rotor and operable in response to such sensing to actuate said control means to allow liquid flow through said passage to the reception place.

2. The separator of claim 1, in which said control means are a valve in said passage.

3. The separator of claim 1, comprising also means under control of said sensing means for opening said rotor outlet for separated sediment.

4. The separator of claim 1, in which said central outlet is adapted to maintain the liquid pressure therein constant, said third outlet being formed by a channel extending toward the rotor axis from a point in the separating chamber located radially outside said predetermined ievel, said sensing means being a pressure sensing device communicating with said channel.

5. The separator of claim 1, in which said sensing means are operable to sense a difference between such light and heavy liquid components.

6. The separator of claim 1, in which said sensing means are operable to sense a difference between the dielectric constants of said light and heavy liquid components.

7. The separator of claim 1, in which said third outlet is formed by a channel extending from a point in the separating chamber located substantially at said predetermined level, the separator comprising also means for creating a liquid flow through the channel from said point, said sensing means being operable to sense a change in the liquid flowing through said channel.

8. The separator of claim 1, comprising also means for returning liquid from said third outlet to said rotor inlet.

9. The separator of claim 8, in which said returning means lead from said passage at a region thereof located between said third outlet and said control means.

10. The separator of claim 8, comprising also a device for blocking liquid flow through said returning means in response to liquid flow through said passage to said reception place.

11. The separator of claim 9, comprising also a valve located in said returning means and operable to permit liquid flow therethrough only while a predetermined minimal pressure prevails in said passage.

12. The separator of claim 9, comprising also a throttle in said returning means, said control means being a valve having a greater throughflow capacity than the throttle, said sensing means being a pressure sensing device communicating with said passage at a region thereof located between said third outlet and said returning means.

Claims

4. The separator of claim 1, in which said central outlet is adapted to maintain the liquid pressure therein constant, said third outlet being formed by a channel extending toward the rotor axis from a point in the separating chamber located radially outside said predetermined level, said sensing means being a pressure sensing device communicating with said channel.