US3750940A

US3750940A - Control means for self-discharging centrifuge

Info

Publication number: US3750940A
Application number: US00204625A
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: 1973-08-07
Anticipated expiration: 1990-08-07
Also published as: SE345603B; IT941789B; GB1315250A; FR2117188A5; JPS5648217B1; DE2160476A1; SU597323A3

Abstract

The centrifugal rotor has an inlet for the mixture to be separated, a central outlet for a separated liquid component of the mixture, and peripheral outlets for separated sediment of the mixture, means being provided for alternately opening and closing the peripheral outlets. The rotor is charged with a special liquid having a density intermediate those of the separated liquid component and the separated sediment, whereby an interface is formed in the rotor between the separated liquid component and the special liquid; and means are provided for sensing when this interface has moved radially inward to a predetermined level in the rotor.

Description

United States Patent 1191 1111 3,750,940 Nilsson Aug. 7, 1973 [54] CONTROL MEANS FOR 3,189,268 6/1965 Nilsson 233/20 R SELFJHSCHARGING CENTRIFUGE 3,396,910 8/1968 Steinacker 233/20 R 3,445,061 5/1969 NllSOl) 233/20 R [75] Inventor: Vilgot Raymond Nilsson, Hagersten,

Sweden FOREIGN PATENTS OR APPLICATIONS Assignee: Agfa Laval Tumba Sweden 1,203,177 8/1970 Great Britain 233/19 R [22] Filed: Dec. 3, 1971 Primary ExaminerGeorge 1-1. Krizmanich [21] AppL No: 204,625 Attorney-Cyrus S. Hapgood 57 ABSTRACT [-30] Foreign Application Priority Data I Dec 7 1970 SW den 5514/70 The centrifugal rotor has an inlet for the mixture to be e separated, a central outlet for a separated liquid component of the mixture, and peripheral outlets for separated sediment of the mixture, means being provided for alternately 0 enin and closing the eri heral out [58] Field of Search 233/12 14R 16 P g P P 20 46 4 lets. The rotor is charged with a special liquid having 1 a density intermediate those of the separated liquid component and the separated sediment, whereby an [56] References Cited interface is formed in the rotor between the separated UNITED STATES PATENTS liquid component and the special liquid; and means are 3,410,479 I 1/1968 NilSOn 233/20 R provided for sensing when this interface has moved ra- 3301476 1/1967 Hemfo" 233/20 R dially inward to a predetermined level in the rotor. 3,261,546 7/1966 Gruver 233/20 R 3,508,704 4/1970 Hemfort 233/20 R 8 Claims, 3 Drawing; Figures PAIENIED AUG 7 I975 SHEEI 2 OF 2 MIIIIL CONTROL MEANS FOR SELF-DISCHARGING CENTRIFUGE 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 a separated liquid component, and peripheral outlets for separated sediment.

One problem for which a better solution is still sought in centrifugal separators of this type, in spite of many proposed solutions, is how to perform a sufficiently accurate and reliable measurement of the amount of sediment separated in the rotor so that when a predetermined amount of sediment is measured, a signal created during operation of the centrifugal separator will cause opening of the outlets situated at the rotor periphery.

Disregarding the fact that the separated sediment is always situated in a space that is very difficult to get at during the operation of the centrifugal separator, one essential reason for this measurement problem is that most kinds of sediment lack definite measurable properties or physical magnitudes. Another important reason for the problem is the difficulty of obtaining a sharp delineation between separated sediment and the separated liquid component in the rotor. For these reasons, proposals made so far for measuring of the amount of sediment in the rotor, which generally have been based upon the difference between the consistency (density) of the sediment and that of the separated liquid component, have proved to be quite unsatisfactory in practice.

An object of the present invention is to provide a centrifugal separator of the type mentioned, wherein the above-described measurement problem is solved in a satisfactory manner.

This object is achieved by providing the centrifugal separator with means for charging the rotor with a special liquid having a density greater than that of the light liquid component but lower than that of the sediment, and means for sensing when an interface (formed in the rotor) between the separated light liquid component and the said special liquid has moved radially inward to a predetermined level in the rotor, the sensing means being arranged to actuate means for opening the outlets situated at the periphery of the rotor.

The invention thus resides in charging the rotor with a liquid having predetermined measurable properties or physical magnitudes, there being created in the rotor an interface between this special liquid and the separated light liquid component, so that the position of this interface can easily be determined. During the progress of the separation, separated sediment takes the place of the somewhat lighter liquid, so that the said interface is moved radially inward in the rotor. When the interface has reached a predetermined level in the rotor, this indicates (if a predetermined quantity of the spe cial liquid has been supplied to the rotor) that so much sediment has been separated that the peripheral outlets should be opened. The said quantity of liquid is preferably supplied to the rotor immediately after the peripheral outlets have been opened.

Instead of charging the rotor with a certain quantity of the special liquid, it may be suitable in certain cases to charge the rotor with a predetermined quantity of this liquid per unit of time. A supply of this kind (performed intermittently or continuously) serves to limit the time interval between the occasions when the pcripheral outlets are opened. This prevents separated sediment from being packed too hard in the rotor and thereby making it difficult or impossible to empty the rotor.

Since the sensing of sediment in the centrifugal separator, according to the invention, means sensing of the position of an interface between two liquids in the ro tor, conventional measuring methods may be used. In one embodiment of the invention, the rotor of the centrifugal separator is therefore provided with a channel extending from the radially outer part of the rotor toward the rotor axis, means being arranged to compare the liquid pressures at a certain distance from the rotor axis, on one hand in this channel, and on the other hand in the separating chamber of the rotor (see for instance British Patent Specification No. 1,236,718). If the central outlet of the rotor for separated liquid component is an overflow outlet, which serves the same function as a valve in this outlet (that is, arranged to maintain the pressure of the liquid flowing through the outlet constant, independently of the magnitude of the liquid flow) the said pressure comparing means may be constituted by a single pressure-sensing instrument connected tothe channel.

However, since a liquid having easily measurable properties or physical magnitudes can now;be utilized as a measuring object instead of the sediment itself, the invention opens the possibility of using those previously proposed measuring methods which could not be successfully used before. Instead of measuring the pressure, the measuring may be performed by means arranged to sense a difference between the liquid component separated in the rotor and the said supplied special liquid, for instance the difference between the dielectric constants of these two liquids. Several other physical magnitudes, such as viscosity, density, etc. may be the base for measurements. Optical and electrical measurement methods of different kinds can also be used.

An arrangement for sensing a difference between the separated liquid component and a special liquid supplied to the rotor may be placed in the rotor and thus be rotated with it. However, in a preferred embodiment the centrifugal separator has a channel beginning at the previously-mentioned predetermined level in the rotor, and means for creating a liquid flow through this channel from the predetermined level in the rotor. The arrangement for sensing a difference between the separated liquid component and the special liquid supplied to the rotor may then be arranged for a direct sensing of the liquid flowing through this channel.

It is not necessary that liquid flow constantly through this channel. There may also be an arrangement for creating an intermittent flow. According to a preferred embodiment of the invention, a continuous flow takes place through the channel, the end of the channel remote from the said predetermined level in the rotor being in communication with the conduit of the rotor for supplying the mixture to be separated. In this way, the requireemnt of special control equipment for this flow is avoided, and loss of separated liquid is also avoided.

As can be seen from the above, the present invention provides a solution to the previously described measurement problem, which solution gives the desired re- I liability and accuracy of the measurement values. The

invention also makes it possible, by so-called partial emptying of the rotor through the outlets situated at its periphery, to discharge all of the separated sediment without having any part of the separated liquid component (of the mixture supplied to the rotor) leaving the rotor the same way. The partial emptying of the rotor can be controlled so that all of the sediment and only a portion of the sepcial liquid supplied to the rotor (for sensing) leave the rotor through its periphery outlets. It is previously known per se to displace a liquid separated in the rotor by means of a somewhat heavier liquid, immediately before the rotors peripheral outlets are to be opened. In these cases, however, the opening in itself has been initiated by a special means for sensing how much sediment has been separated in the rotor. According to the invention, these two functions (i.e., on one hand the sensing operation and on the other hand the displacement) are combined so that separate equipments for these functions are not necessary.

The invention is further described in the following with reference to the accompanying drawings, in which FIG. 1 is a vertical sectional view of a rotor ofa 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 equipment in one embodiment.

The centrifuge rotor in FIG. 1 comprises a lower part 1 and an upper part 2, which parts are 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 wings 6, into the rotor separating chamber 8, wherein a set of conical discs 9 is arranged. Sediment separated from the mixture supplied to the rotor is collected at 10 in the rotor sediment chamber 8. For intermittent discharge of this sediment during the operation of the centrifugal separator, the rotor has a number of openings 11 situated at the periphery. A valve disc 12 forming the bottom of the separating chamber 8 is arranged to uncover and close these openings. 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 a space 14 between the lower part 1 of the rotor and the valve disc 12, the valve disc 12 is kept at its upper position, in which it is pressed against the upper part 2 of the rotor. Through throttled openings 15 in the rotor part 1, liquid flows out of the space 14. When the liquid supply to the space 14 is interrupted, this space is emptied of liquid through the openings 15, the valve disc being pressed downward by the liquid pressure in the separating chamber 8, so that the openings 11 are uncovered. When the liquid supply to the space 14 is resumed, the valve disc 12 is pressed upward again, so that the openings 11 are closed.

The liquid component which is 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 component is then pumped through an outlet conduit 19.

From the radially outer portion of the rotor separating chamber (i.e., in the region of the outer edges of the discs 9) a channel 20 extends inward toward the rotor axis to a central chamber 21. In the chamber 21 a paring disc 22 is arranged to pump liquid from this chamher out through a conduit 23, which thus constitutes a continuation of the channel 20.

In FIG. 2, a conduit 24 supplies a mixture to be separated in a centrifugal separator S. The conduit 24 is thus directly connected to the channel 5 in the drive shaft 4 (see FIG. 1). Sediment separated from the mixture is led away through the conduit 19. The conduit 23 beginning at the paring disc 22 in the chamber 21 (FIG. 1) is connected to the inlet conduit 24, as can be seen from FIG. 2, and contains a throttling device or restriction 26 for restricting the flow through it. To the inlet conduit 24 there is also connected a conduit 27, which is arranged for the supply of a special liquid to the rotor. A pump 28 for this supply is arranged in the conduit 27.

By means of conventional control equipment 29, all functions of the centrifugal separator S are controlled. Through a connection 30 illustrated by a dashed line, the control equipment 29 receives from a sensing means 31, connected to the conduit 23, a certain indication of the liquid flow in the conduit 23. This indication can be the liquid pressure in the conduit 23, the rate of the flow through the conduit 23, or whether a liquid of one kind or the other is flowing through the conduit 23. Means of sensing a difference between two different liquids is previously known in varying embodiments depending on which property or physical magnitude of the liquids is to be sensed and compared (FIG. 3). If the indication is the pressure of the liquid in the conduit 23, the conduit can be essentially closed beyond the pressure indicator (in other words, no flow of liquid through the conduit is necessary). Of course, the liquid pressure in the chamber 21 can be sensed in many other ways.

The operation of the above-described centrifugal separator is as follows:

Through the conduit 24 and the channel 5 the rotor is charged with a mixture consisting mainly of one liquid component and one solid component, here referred to as the sediment. Simultaneously a further or special liquid is supplied by means of the pump 28 to the rotor through the

conduits

27 and 24 and the channel 5, the density of this liquid being lower than that of the sediment separated in the rotor but greater than that of the liquid component separated in the rotor. In the rotor, the sediment will consequently be collected at the rotor periphery, and an interface will be formed between the separated liquid component and the said special liquid. While the separated liquid component continuously leaves the rotor separating chamber 8 through the overflow outlet 16, the said interface is slowly displaced radially inward in the rotor, partly depending on the fact that the amount of so-called special liquid in the rotor is increasing, and on the other hand depending on the fact that the amount of sediment separated in the rotor is increasing. The amount of special liquid supplied to the rotor per unit of time may be varied with regard to the expected content of sediment in the separated mixture and/or the tendency toward hard packing of sediment at the rotor periphery. Normally the supplied amount of so-called special liquid is considerably smaller than the amount of mixture to .be separated.

From the rotor separating chamber, a stream of liquid is pumped through the channel 20 and the chamber 21 and out through the conduit 23, from where it is led back into the rotor through the inlet conduit 24 and the channel 5. As long as the said interface is situated radially outside the opening of the channel 20 in the rotor, separated liquid component flows through the conduit 23, the pressrue therein being essentially constant; but when the interface has reached the said opening (see the dashed line 32 in FIG. 1), the pressure in the conduit 23 will drop rapidly, and the said special liquid will begin to flow through conduit 23. When the interface then continues to move toward the rotor axis, the pressure in the conduit 23 will rise further.

When the interface reaches the opening of the channel 20 in the rotor, this is sensed by the sensing means 31, regardless of whether such means are arranged to sense the liquid pressure in the conduit 23 or to sense a change of another kind in the liquid flowing through the conduit. Through the connection 30, the control equipment 29 of the centrifugal separator is informed of this sensing and then functions, in a previously described manner, so that the rotor peripheral outlets 11 are uncovered to discharge separated sediment.

It has been assumed above that so-called special liquid is continuously supplied to the rotor in a certain amount per unit of time. Depending upon the kind and the amount of sediment in the separated mixture, it is also possible (each time the rotor periphery outlets 11 have been opened) to supply to the rotor a certain amount of special liquid. (*This may be controlled in an obvious manner from the control equipment 29 through a connection 29a between this equipment and the said pump 28.) In this case, the time interval between the occasions when the rotor peripheral outlets ll are opened will be entirely dependent on the content of sediment in the mixture separated.

Of course, the so-called special liquid may be supplied to the rotor in other ways than described here. It is also possible to omit the pumping arrangement for the circulation of liquid through the conduit 23. The position of the interface fon'ned in the rotor between separated liquid component and said special liquid can be sensed in otherways, as by means of members placed within or at the outside of the rotor. If the liquid pressure in chamber 21 is chosen as the value indicating the position of the said interface, this pressure can be sensed by pumping in air at a suitable level below the liquid surface formed in the chamber 21, a change of resistance to thus supply of air being'measured.

In FIG. 3 there is schematically shown a previously known arrangement for sensing the dielectric constant of a liquid flowing through a conduit. This equipment comprises a sensing member 33 arranged in the eonduit, and an indicator 35 connected to a source of power 34 and including an oscillator. The indiator is connected on one hand to the sensing member-33 and on the other hand to the conduit 23, through which the liquid to be sensed is flowing. As this equipment is conventional, there is no need for any further description of it here.

I claim:

1. A centrifugal separator comprising a rotor having a separating chamber provided with an inlet for a mixture to be separated, said mixture including a liquid component and sediment, the separating chamber having a central outlet for said liquid component separated from the mixture, said chamber also having peripheral outlets for said sediment separated from said mixture, control means for alternately closing and opening said pripheral outlets during operation of the rotor, a source of special liquid having a density greater than that of said liquid component but smaller than that of said sediment, and means for charging the separating chamber with said special liquid, whereby an interface is formed in said chamber between said separated liquid component and said special liquid, the separator being characterized by means for sensing when said interface has moved radially inward to a predetermined level in the separating chamber.

2. A separator according to claim 1 comprising also means operatively connected to said sensing means, and responsive to said sensing, for actuating said control means to open said peripheral outlets.

3. A separator according to claim 1, in which said charging means are operable to feed said special liquid to the rotor at a predetermined rate.

4. A separator according to claim 1, in which said charging means areoperable to feed said special liquid continuously to the rotor.

5. A separator according to claim 1, in which said sensing means include a device for sensing a difference between said separatedv liquid component and said special liquid. i

6. A separator accordingto claim 5, in which said device is operable to sense a difference between the dielectric constants of said liquid component and said special liquid. i

7. A separator according to claim 1, in which the rotor includes a channel beginning at said predetermined level, the separator comprising also means for creating a liquid flow through said channel from said level, said sensing means being operable to sense a change in the liquid flowing through said channel.

8. A separator according to claim 7, comprising also a conduit for supplying said mixture to said rotor inlet, said channel having its outlet end in communication with said conduit.

Claims

4. A separator according to claim 1, in which said charging means are operable to feed said special liquid continuously to the rotor.

5. A separator according to claim 1, in which said sensing means include a device for sensing a difference between said separated liquid component and said special liquid.

6. A separator according to claim 5, in which said device is operable to sense a difference between the dielectric constants of said liquid component and said special Liquid.