US3606146A - Centrifugal separator - Google Patents

Abstract

A CONTINUOUS CENTRIFUGAL SEPARATOR COMPRISING A CASING, AND AN INTEGRATED ROTOR ROTATABLY SUPORTED THEREIN, SAID ROTOR BEING PROVIDED WITH SEPARATING CHAMBERS IN THE FORM OF HOLLOWS FORMED IN THE PORTIONS OF THE ROTOR REMOTE FROM THE CENTER THEREOF, AN OPENING FOR INTRODUCING A MIXTURE TO BE TREATED INTO SAID SEPARATING CHAMBERS, AN OPENING FOR DISCHARGING THE SEPARATED HEAVY FRACTION ANOTHER OPENING FOR DISCHARGING THE SEPARATED HEAVY FRACTION THAT IS PROVIDED AT A POINT RADIALLY FARTHER FROM THE ABOVE OPENINGS, AND FURTHER PROVIDED WITH PASSAGES FOR RESPECTIVELY COMMUNICATING SAID OPENINGS TO THE OUTSIDE.

Description

Sept. 20, 1971 osAMu FUJll ETAL CENTRIFUGAL SEPARATOR Filed Feb. 12, 1969 FIG. 1

3 Sheets-Sheet 1 INVENTORS Sept. 20,1911 OSAMU FUJII EI'AL 3,606,146

GENTRIFUGAL SEPARATOR Filed Feb. 12, 1969 3 Sheets-Sheet 5 United States Patent 3,606,146 CENTRIFUGAL SEPARATOR Osamu Fujii, Michio Ishigaya, and Hiroyuki Nakamoto, Hiroshima, Japan, assignors to Mitsubishi Jukogyo Kabushiki Kaisha, Tokyo, Japan Filed Feb. 12, 1969, Ser. No. 798,680 Claims priority, application Japan, Feb. 15, 1968, ifs/9,153; June 18, 1968, 43/ 42,049 Int. Cl. B04b 9/06 US. Cl. 233-24 2 Claims ABSTRACT OF THE DISCLOSURE A continuous centrifugal separator comprising a casing, and an integrated rotor rotatably supported therein, said rotor being provided with separating chambers in the form of hollows formed in the portions of the rotor remote from the center thereof, an opening for introducing a mixture to be treated into said separating chambers, an opening for discharging the separated light fraction, another opening for discharging the separated heavy fraction that is provided at a point radially farther from the above openings, and further provided with passages for respectively communicating said openings to the outside.

BACKGROUND OF THE INVENTION This invention relates to a centrifugal separator, and more specifically to a high-speed centrifugal separator capable of continuously separating substances of little difference in specific gravity, e.g., isotopes U235 and U238 of natural uranium, from each other.

Centrifugal separators of continuous-flow type most commonly in use can be broadly classified by design into three groups: (1) cone disc type, (2) hollow cylindrical type, and (3) screw (decanter) type. In the centrifuges of these types, the centrifugal force that governs separation increases proportionally to rw, where r is the radius and w is the angular velocity of the rotor. Actually, however, limitations due to rotational stress inherent to the structures have rendered it impossible to increase the peripheral velocities of rotors of conventional machines beyond certain values. Thus, the peripheral velocities of the rotors and the centrifugal effects thereby attained are limited to the values generally as tabled below. With such conventional centrifugal machines, extreme difiiculties are involved in separating mixtures of substances having little different in specific gravity into the individual components. For successful separation of such a mixture, the operation must be carried out in several stages, thus necessitating a highly complicated procedure, which is at a disadvantage.

In the conventional centrifugal separators, for work at higher speeds especially, the rotors are subjected to great frictional resistance because of air present in the space between the rotor and the casing of the centrifuge in which the rotor is accommodated. This leads to development of heat and power loss which are both undesirable. In order to avoid such possibilities the space inside the casing must be evacuated, and this calls for the provision of powerful vacuum pump.

For high-speed operations, those centrifugal machines are usually driven in two ways. In one method the power is supplied from an ordinary electric motor running at commercial frequency i.e., 50 or 60 c.p.s. via step up gears,

and in the other the machine is directly driven by a highfrequency motor connected to a high-frequency power source. Either method adds to the complicacy of the construction and invites additional troubles. In the latter case, particularly where a plurality of centrifugal separators coupled to the respective high-frequency motors are driven thereby with power from a common, singular source, all of the machines must be stopped, should any of them go out of order, because in order to restore a repaired machine, the frequency of the power source must be once lowered and then gradually increased to a level due to a characteristic of high frequency motors. This provides much inconvenience and the downtime inevitably results in a drop of the operation efliciency. Another disadvantage that has been associated with the use of the latter method is that the speed control of the individual centrifugal separators is never possible because only a given high-frequency current is supplied to their motors by a single power source.

SUMMARY OF THE INVENTION One of the characteristics of the present invention is the provision of a continuous centrifugal separator equipped with a rotor capable of rotating at a far higher peripheral velocity than those of the rotors of conventional centrifuges of the type described, and which hence has a far greater ability to separate mixtures.

Another characteristic of the present centrifugal separator the provision of a rotor of integrated construction which is adapted to attain a remarkably increased peripheral velocity.

Another characteristic of the present invention is the provision of a centrifugal separator driven by a steam turbine which is free from the disadvantages of the conventional electric drives.

According to the present invention, the steam turbine and the centrifugal rotor can be housed in a common casing and therefore a centrifugal separator of simplest design is provided.

A further characteristic of the present invention is that there is provided a centrifugal separator capable of achieving high-speed operations by dint of less frictional resistance than in conventional machines because the casing of the machine is evacuated without resorting to any vacuum pump as usual.

These characteristics of the present invention are realized by accommodating a centrifugal rotor and a steam turbine in a same casing as above described and by communicating the space between the rotor and casing to a condenser. By so doing it is made possible to use only two bearings for the rotor which otherwise requires at least four bearings. The centrifugal separator of the invention can achieve high-speed operations, say at more than 100,000 rpm.

The present invention will be more fully described hereunder with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWING FIGS. 1 and 2 show an example of the embodiment of the centrifugal separator according to the invention, FIG. 1 being a vertical sectional view of the lower half of a rotor and, FIGS. 2(a), (b) and (0) representing the sections of said rotor along the lines II, IIII and IIIIII, respectively, of FIG. 1;

FIGS. 3(a), (b) and (c) and FIGS. 4(a), (b) and (c) are sectional views of rotors of two other embodiments of the invention, corresponding to FIGS. 2(a) and (0), respectively;

FIG. 5 is a vertical sectional view of the lower half of still another form of device embodying the invention;

FIG. 6 is a side view of a part of the device shown in FIG. 5;

FIG. 7 is a cross sectional view taken along the line AA of FIG. and

FIG. 8 is a similar cross sectional view taken along the line B-B of FIG. 5.

The other halves of the views given in FIGS. 5 through 8 are omitted because they are substantially symmetrical with and same as the halves illustrated.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to FIGS. 1 and 2, a casing is generally indicated at 1, in which a integrated rotor 2 is rotatably supported by shaft 4 through bearings 3, 3, in such a manner that the rotor 2 can be rotated at a high speed by coupling the shaft 4 to a suitable driving means not shown. Casing 2 is provided with an inlet port 8 for a liquid or gaseous mixture to be handled centrifugally. Near both ends of the rotor, or of the major axis of the rotor 2 whose sectional contour is substantially elliptically shaped as shown in FIG. 2, there are formed separating chambers 9 in the form of axially extending hollows. Casing 2 is also provided with an outlet port 10 for the light fraction separated from the mixture and an outlet port 11 for the heavy fraction separated from the mixture. Passages 12 for the mixture are radially formed in the rotor 2 so that they are open at one end in the separating chambers 9 and at the other end in a center hole 12' formed in the shaft 4. These passages 12 communicate through the center hole 12' and another passage 12 formed in the casing 1 to the inlet port 8. Other passages 13 are formed radially in the rotor 2, with one end open in the separating chambers 9 and the other end open open in a center hole 13' formed in the shaft 4. These passages 13 communicate through the center hole 13 and another passage 13" formed in the casing 1 to the outlet port 10.

Passages 14 for the heavy fraction are formed radially of the rotor 2. One end of each passage 14 extends to a point near the bottom of each separating chamber 9 (i.e., the portion of the separating chamber remotest from the center of rotation of the rotor 2), and the extension is formed with an inlet port 15 for the heavy fraction. The other ends of the passages 14 communicate to the outlet port 11 through an annular passage 14' formed in the shaft 4 and a passage 14" formed in the casing 1. At the connection between the center hole 12 of the shaft 4 and the passage 12 of the casing 1, there is provided a shaft seal means 5 consisting of two L-shaped seal rings 6 fitted back to back in a recess 7, in order to maintain the connection in a gastight and liquidtight state. Shaft seal means 5' and 5 of the same construction are also provided, respectively, at the connections between the annular passage 14' and the passage 14" and between the center hole 13' and the passage 13". These shaft seal means 5, 5 and 5 may be of labyrinth type when the mixture to be handled is in a gaseous form. Between the shaft 4 and the casing 1 several labyrinth seal means 16 are fitted. An exit 17 for removing the leaking fluid from the shaft seal means 5 and 5" to the outside is formed in the casing 1. Also, between the casing 1 and the rotor 2 there is formed an air exhaust port 18 for drawing off the air and frictional heat that is developed during high-speed running of the rotor 2. This exhaust port 18 communicates with a vacuum pump not shown.

With the construction as above described, the rotor is driven at a high speed and a mixture to be treated is fed in through the inlet port 8. The mixture flows through the passage 12", center hole 12' and passages 12 into the separating chambers 9. In the chambers the mixture is centrifugally separated into the light and heavy fractions. The light fraction of low specific gravity that collects inwardly is extracted through the passages 13, center hole 13 and passage 13" and finally through the outlet port 10 to the outside, while the heavy fraction of high specific gravity that collects outwardly of the separating chambers (or to the bottom of each chamber) is taken out through the outlet ports 15, passages 14, annular passage 14 and passage 14" and finally through the outlet port 11.

The embodiment above described, for example with a rotor 2 having a maximum outside diameter of 20 cm. and separator chambers 9 having a diameter of 15 cm. each, when experimentally driven with a rotor speed of 53,000 r.p.m., showed a peripheral velocity of the separating chambers at 420 m./ sec. and gave a centrifugal effect of 236,000 g. Thus, with this embodiment, it has been ascertained that the rotor 2 can run at a remarkably high peripheral velocity and thereby achieve an amazingly great centrifugal effect. This leads us to a belief, with full justification, that the adoption of the present invention will make it possible to effect continuously and most efiiciently the centrifugal separation of substances in mixture of such inappreciable difference in specific gravity that their separation has hitherto been next to impossible, e.g., the isotopes U235 and U238 of natural uranium in the purification of nuclear fuel.

While the section of the integrated rotor 2 of the embodiment above described that is perpendicular to the axis is shown to be substantially elliptical in FIG. 2, it is also possible to modify the section to a substantially square contour as shown in FIG. 3 or to a circular one as shown in FIG. 4 with the provision of additional separating chambers 9 for an enhanced capacity of separating mixed solutions into the components. In FIGS. 3 and 4 the parts corresponding to those shown in FIG. 2. are indicated with like numerals.

The present inventor calculated the rotational stresses produced by the integrated rotors of the present invention with contours shown in FIGS. 2 and 4 and compared the results with that of the hollow rotors of conventional separators having similar contrours with the same dimensions and the same rotational speeds as those of the present invention, and has found that the rotational stresses generated by the integrated rotors of the separator according to the present invention as illustrated in FIGS. 2 and 4 are, respectively, one quarter and one half those of the conventional hollow rotors. Inasmuch as the rotational stress of the rotor of the type described generally increases proportionally to the square of the number of revolutions, the numbers of revolutions of the integrated rotors in the centrifuge of the invention as illustrated in FIGS. 2 and 4 can be increased, respectively, to 2 and 1.4 times those of the hollow rotors of the conventional centrifuges. It has also been found that the peripheral velocities of the rotors according to the invention can be increased to 2 and 1.4 times greater than those of the conventional rotors and the centrifugal effect can be enhanced to 4 and 2 times those of the latter. 'Ihus, according to the present invention, the peripheral velocity and centrifugal effect of a integrated rotor 2 are remarkably high and permit continuous centrifugal separation of substances in mixture that are otherwise difficult to separate because of negligible difference in specific gravity. Further, the invention makes it possible to achieve a separation capacity more than four times greater than the capacities of conventional centrifuges.

The sectional contour of the separating chambers 9 is not limited to circle but may be modified to various other shapes. For example, from the sectional views given in FIGS. 2(a) through (c), it is noted that if the width of each separating chamber 9 is decreased, the bend stress of the outer shell of the chamber 9 will decrease in proportion to the square of the width. On the other hand, the centrifugal separation coefiicieut rises with the increases of the distances between the center of rotation of the rotor 2 and the bottom of each separating chamber 9 and between the center of rotation and the ceiling (the portion nearest to the center of rotation) of each separating chamber 9. This leads to an increased separation ethciency. It is therefore advisable to shape the section of each separating chamber 9 as an ellipse elongated in the direction of radius of rotation of the rotor 2.

In the separator of the invention the energy (or centrifugal force) required to feed a mixture from the center of axis to the separating chambers is utilized for removal of the separated components, or the light and heavy fractions, from the separating chambers through the center of axis to the outlet port open in the casing. For this reason, the power to be consumed by the feeding of the mixture is limited to that by frictional loss of the mixture, and therefore the electricity consumption is quite meagre at an economic advantage.

Another embodiment of the invention illustrated in FIGS. to 8 will now be described.

Throughout these figures, a rotor, generally indicated at 101, consists of a turbine rotor assembly 101, centrifugal rotor assembly 101" and shaft 101". An impeller casing 102 encloses and rotatably supports the rotor 101 therein. Rotor shaft 101" is borne by bearings 103, 104. Turbine-rotor assembly 101' is provided with a turbine impeller wheel 105, which faces a group of nozzles 106 provided opposite thereto and connected with a steam chamber 107 for supply of steam. A steam inlet port 108 communicates to a boiler not shown. Between the rotor 101 and casing 102 is defined a space 109 which serves as an exhaust chamber for the turbine. An exhaust port 110 open in the casing 102 communicates with the space 109 inside the casing and a condenser 110'. Separating chambers 111 for the centrifugal separation of a mixture are formed within the centrifugal rotor assembly 111". More particularly, the chambers are provided, as shown in FIGS. 7 and 8, symmetrically near the both ends of the major axis of the rotor assembly 101" which is substantially oval-shaped in cross section and take the form of axially extending cylindrical hollows. An inlet port 112 for the supply of a mixture to be centrifugally separated is communicated at one end of the rotor shaft to a center hole provided in the shaft center of rotor 101" via a shaft seal means. Passages 114 for the mixture are pro vided radially of the rotor assembly 101", open at one end into the separating chambers 111 and open at the other end in the center hole 113. Similar passages 115 for the light fraction separated from the mixture are provided radially of the rotor assembly 101", open at one end into the separating chambers 111 and open at the other end into a center hole 116 formed in the shaft center of rotor 101 and which extends to the extremity of the shaft. These passages 115 communicate to an outlet port 117 for the light fraction formed in the casing which encloses the center hole 116 and the rotor shaft end. Similar passages 118 for the heavy fraction are formed radially of the rotor assembly 101" and extend at one end toward the bottoms of the separating chambers 111, or to points near the walls of the chambers remotest from the center of rotation of the rotor 101", the extensions being provided with inlet tubes 119 for the heavy fraction. The other ends of the passages 118 communicate to an outlet port 122 for the heavy fraction through an annular passage 120 formed along the rotor shaft center and concentrically with the center hole 116 outwardly thereof and through an opening 121 on the periphery of the shaft, via a shaft seal means. Around the portions of the shaft 101" of rotor 101 which extend through the casing 102 are provided labyrinth seals 123, 124 as shaft seal means, which are supplied with sealing steam from feed ports 125, 126 for added sealing effects. As shaft seal means already mentioned for the parts near the points for supply of the mixture to be centrifuged and for the discharge of the separated fractions, labyrinth seal means 127, 127 are disposed as shown, and exits 128, 128 for the removal of fluid leaking through the seal means to the outside are also provided as shown.

With the construction as above described, the device operates in the following way. As steam from a boiler not shown is introduced through the steam inlet 108 into the steam chamber 107, it is injected in the form of a highspeed jet through the group of nozzles 106 against the opposing turbine impeller wheel 105, thereby to produce sufficient rotational power for high-speed running of the turbine rotor assembly 101' and hence: the rotor assembly formed integrally therewith. Meanwhile, the mixture to be centrifuged is introduced from the feed port 112 into the center hole 113 of rotor 101, and thence through the passages 114 of the centrifugal rotor assembly 101" into the separating chambers 111. In these chambers the mixture is subjected to great centrifugal force and is separated by the difference of specific gravity into two portions, or light and heavy fractions. The light fraction is discharged through the passages 115 and center hole 116 and finally out of the outlet port 117 at the end of rotor shaft, while the heavy fraction is urged from the bottoms of separating chambers 111 into the tubes 119 and is continuously taken out of the outlet 122 by way of the passage 118, annular passage 120 and opening 121 on the shaft.

Steam discharged from the impeller wheel 105 immediately expands with a reduction of pressure in the space 109 inside the casing that serves as the exhaust chamber of a turbine and then is condensed in a separator not shown. Thus, with the present embodiment, it was experimentally found that the degree of vacuum attained in the space 109 of casing, as measured in the vicinity of the exhaust port 110, reached about 720 mm. Hg (at the cooling water temperature of 20" C. in the condenser) and, consequently, the frictional resistance to the gas of the rotor 101 running at a high speed was practically negligible.

In an experiment with a form of the embodiment above described, a centrifugal effect of275,000 g. was achieved with a rotor 101 having a maximum diameter of 210 cm. and a speed of 53,000 rpm. and with separating chambers 111 driven at a peripheral velocity of 470 m./sec.

It should be appreciated that the present invention is not restricted to the embodiments hereinabove described but numerous modifications are possible without departing from the scope and spirit of the invention. For example, turbines of any types may be employed provided that they are equipped with condensing equipment. Also, the working medium is not limited to steam and the, Ilse of any other suitable medium such as Dowtherm is not objectionable where necessary.

We claim:

1. A continuous centrifugal separator comprising a casing, and an integrated rotor rotatably supported therein, said rotor being provided with separating chambers in the form of hollows formed in the portions of the rotor remote from the center thereof, an opening for introducing a mixture to be treated into said separating chambers, an opening for discharging the separated light fraction, another opening for discharging the separated heavy fraction that is provided at a point radially farther from the above openings, and further provided with passages for respectively communicating said openings to the outside.

2. A turbine-driven centrifugal separator according to claim 1 wherein the rotor of the centrifugal separator is formed integrally with a steam turbine rotor, supported jointly by a single shaft, and accommodated in a common casing, and the space inside the casing is communicated to the condenser of the steam turbine.

References (Iited UNITED STATES PATENTS

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