US3774376A

US3774376A - Centrifugal gas separator

Info

Publication number: US3774376A
Application number: US00153510A
Authority: US
Inventors: Y Takashima; Y Endo; K Saitou
Original assignee: Tokyo Shibaura Electric Co Ltd
Current assignee: Toshiba Corp
Priority date: 1970-06-17
Filing date: 1971-06-16
Publication date: 1973-11-27
Anticipated expiration: 1990-11-27
Also published as: GB1349164A; FR2099753A5; NL161072C; DE2129786A1; DE2129786C3; DE2129786B2; JPS496411B1; NL7108253A; NL161072B

Abstract

A centrifugal gas separator is disclosed which employs a cylindrical centrifuge drum having a hollow shaft mounted on suitable bearings within a housing. Supply means are provided for feeding a mixed gas to be separated into the drum. The supply means has openings located radially near the inner periphery of the drum and axially at approximately the center of the drum. Each opening in the supply means communicates with the hollow shaft. Thus the mixed gas to be separated enters the centrifuge drum near the inner periphery thereof, and the gas is then able to attain a relatively high angular velocity, whereby the separating power of the centrifuge is elevated.

Description

United States Patent 11 1 Takashima et al. Nov. 27, 1973 [54] CENTRIFUGAL GAS SEPARATOR 2,936,110 5/1960 Cohen 55 17 x 2,872,105 21959 R h' 233 1 RX [75] Inventors Takashma 5/1966 N eivg zr d at al 55 1 x Yoshitami Endo, Kawasaki; Kenya Saitou, Yokohama, all of Japan Assignee: Tokyo Shibaura Electrical Company Ltd., Kawasaki-shi, Japan Filed: June 16, 1971 Appl. No.: 153,510

Foreign Application Priority Data June 17, 1970 Japan 45/52594 US. Cl 55/407, 55/17, 233/13, 233/47 Int. Cl. B0ld 45/12 Field of Search 55/17, 400, 407; 233/1 R, 11,13, 27, 28, 46, 47 R References Cited 7 UNITED STATES PATENTS 10 1971 Oyama eta] 2'33 13 I Primary ExaminerFrank W. Lutter Assistant Examiner-William Chuchlinski AttorneyNorman F. Oblon et al.

[57 ABSTRACT A centrifugal gas separator is disclosed which employs a cylindrical centrifuge drum having a hollow shaft mounted on suitable bearings within a housing. Supply means are provided for feeding a mixed gas to be separated into the drum. The supply means has openings located radially near the inner periphery of the drum and axially at approximately the center of the drum. Each opening in the supply means communicates with the hollow shaft. Thus the mixed gas to be separated enters the centrifuge drum near the inner periphery thereof, and the gas is then able to attain a relatively high angular velocity, whereby the separating power of the centrifuge is elevated.

8 Claims, 5 Drawing Figures Patented Nov. 27, 1973 ,5 Shes ts-Shaet 1 INVENTORS YOICHI TAKASHIMA YOSHITAMI ENDO KENYA SA/TOU PRIOR ART AT TO R NEYS RADIUS Patented Nov. 27, 1973,

2 SheetsShaet 2 FIG. 5

C ENTRIFUGAL GAS SEPARATOR BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to gas separators and more particularly to centrifugal gas separators for an isotopic separation.

2. Description of the Prior Art Gas centrifuges of the type having a countercurrent with circulation customarily included an elongated cylindrical drum vertically oriented and having a hollow centrally located shaft. A mixed gas to be processed is supplied to the drum at the' central portion thereof through the hollow shaft to fill the drum. The 'mixed gas in the drum is rotated at an extremely high angular speed, thereby subjecting it to a large centrifugal force. Hence, by pressure diffusion, the gas near the inner periphery of the drum becomes enriched with heavier molecules and the gas near the central portion of the drum becomes enriched with lighter molecules. In order to obtain a countercurrent, several alternative methods may be used. For example, a heater and a cooler may be provided for causing'a thermal convection, thus establishing a countercurrent. One end of the centrifuge drum may be kept at a slightly elevated temperature, and the other end at a somewhat lower temperature than that of the gas. At the warm end, the gas flows radially inward, while the gas flows radially outward at the cool end. In the inward flow, as the gas is directed to the center of the drum, the gas should be reduced in volume. However, since a reduction in the volume of the gas is impossible near the center portion of the drum, the excess volume of gas has to flow off in an axial direction. The volume of the gas will tend to increase as the gas moves outwardly, whereby the gas is withdrawn axially through the central portion of the drum. In the relatively smaller radius portion of the drum, the gas flows from the warm side to the cold side. Along the cylinder wall, the gas flows from the cold side to the warm side in a thin stream. Thus the gas of lighter molecular weight collects near the cold end while the heavier gas collects near the warm end.

It is well known that the maximum separating power of the gas centrifuge is proportional to the length l of the drum in the axial direction and to the fourth power of the peripheral velocity (5 of the gas, where r denotes the inner radius of the drum and (0,, denotes the angular velocity of the drum.

In reality, however, the separating power obtained is substantially smaller than the above described theoretical value for various reasons, such as failure to obtain a suitable countercurrent and flow pattern, for example. In addition, as there exists an outward gas flow in a radial direction due to the influx of mixed. gas to be processed through the hollow shaft at the center of the drum, the greater part of the gas has a smaller angular velocity than that of the drum.

In case there is no supply or exhaust of the gas into and from the drum, the viscosity of the gas causes the portion of the gas in contact with the cylindrical drum wall to have a velocity substantially equal to that of the drum wall. This part of gas imparts the same circular motion to an inner ring-like portion of the gas due to the viscosity thereof. Accordingly, the gas in the drum comes to have an angular velocity equal to that of the drum in the steady state. But, where there is a supply of gas at the central portion of the drum and a radially outward flow, most of the gas in the drum has a smaller angular velocity than that of the drum. This phenomena may be understood by a calculation taking the viscosity of the gas into consideration.

SUMMARY OF THE INVENTION Briefly stated, a centrifugal gas separator in accordance with the invention employs a drum which is rotatably supported within an enclosed housing and driven by a suitable means, and exhaust means for removing separated gases. There is provided means for supplying the mixed gas to be separated into the drum at one or more portions a distance from the axis of rotation of the drum.

BRIEF DESCRIPTION OF THE DRAWINGS The instant invention will' be better understood and its various objects and advantages will be more fully appreciated from the following description taken in conjunction with the accompanying drawings in which:

FIG. 1 is a sectional view of a first embodiment of the present invention;

FIG. 2 shows a cross sectional view of an upper portion of the drum of the first embodiment shown in FIG. Itaken along a line 22 of FIG. 1;

FIG. 3 is a plot of the angular velocity of a gas in a centrifuge drum with respect to radial distance where the ordinate is labeled with ratio of angular velocity of the gas to that of the centrifuge drum, and the abscissa is labeled with distance in the radial direction from an axis of the drum;

FIG. 4 shows a sectional view of a second embodiment of the instant invention; and,

FIG. 5 is a sectional view illustrating an alternative gas exhaust structure.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS ing devices 14 and 15 for rotatably supporting a hollow shaft 16 and a shaft 17 of the drum with a damping and sealing action. The supporting device may include a bearing, the outer race thereof being carried by a resilient member such as a rubber damper which is mounted on the housing 1 l, and a sealing member such as a face seal arrangement.

The drum 10 comprises a cylindrical wall 18, a top disc member or lid 19 having the hollow shaft 16 secured thereto for supplying a mixed gas to be processed into the drum l0, and a bottom disc member or lid 20 having the shaft 17 secured thereto. The top disc 19 is provided with a center hole 19a and a plurality of conduits 19b (shown in FIG. 2) extending radially outwardly from the hole 19a. Thus, the hole 19a communicates with the hollow portion of shaft 16 and with the radial conduits 19b. The top lid 19 may either be made of a single plate or may be formed of two parts, i.e., an upper and a lower disc. In latter case, the lower disc may be made as an integral part of an inner cylindrical member or cylinder 21. The inner cylinder 21 has an axial length about onehalf of that of the drum, and is mounted beneath the upper disc 19 so as to provide a ring-like clearance 22 between its outer wall and the wall 18 of the drum 10. At the top and bottom outer peripheral portions of the inner cylinder 21, there may be provided a plurality of projections 21a with a suitable spacing therebetween for fixedly securing the inner cylinder 21 to the wall 18 of the drum 10. The ring-like gap 22 communicates with the outer end portions of the conduits 19b of the disc member 19. Accordingly, a supply of the mixed gas is provided through the conduit which is formed of the hollow shaft 16, hole 19a, the radial conduits 19b and the gap 22, which opens at the lower end into the inner cylinder 21. When the mixed gas passes through the radial conduits and the gap successively, it is given rotational motion. The mixed gas comes to a circulating speed substantially equal to that of the drum wall 18 and is fed into the drum through a ring-like opening 22a between the lower edge of the inner cylinder 21 and the drum wall 18.

Through the upper lid 19, there are provided a plurality of small holes or openings 19c oriented parallel to hollow shaft 16, and disposed in a circle of about one half the radius of the drum, with a suitable spacing with respect to each other so as not to communicate with the radial conduits 19b of the disc 19. These holes 196 serve to exhaust the lighter portion of the separated gas. Through the lower disc member 20, there are also provided a plurality of small openings a similar to the openings 190 of the upper disc 19, which serve to exhaust the heavier portion of the'separated gas.

There are provided ring-

like baffle members

23 and 24 mounted on the housing 11 to form a relatively small gap therebetween. A chamber 25 defined by the drum 10, the

baffles

23 and 24, and housing 11, is filled with a gas such, for example, as helium supplied through an inlet 26 for preventing each of the separated gases in the upper chamber 27 and lower chamber 28 from flowing into the common area 25 to recombine. The separated gases in the upper and

lower chambers

27 and 28 are exhausted together with a small quantity of the helium gas flowing from the common area 25 through a pair of

outlets

29 and 30 to the next processes (not shown).

There are further provided a cooler 31 and a heater 32 for cooling and heating the upper and

lower discs

19 and 20, respectively, so that a thermal convection may be obtained to establish a countercurrent. The upper lid 19 may be cooler than the lower lid 20 by 10 to 20 C.

In operation, the centrifuge drum 10 is driven by a suitable drive such as an electric motor to rotate it at an extremely high speed. Then the mixed gas is put into the drum and subjected to centrifugal force so that the gas of lighter molecular weight tends to move radially inward and the gas of heavier molecular weight tends to move radially outward by pressure diffusion.

At the same time, along the upper lid 19 which is relatively cooler than the gas, the gas flows radially outward by thermal convection. On the other hand, along the lower lid 20, which is warmer than the gas, the gas flows radially inward by thermal convection. Then the portion of gas positioned away from the drum wall 18 flows upward, and the gasnear the drum wall flows downward along the drumf wall in a relatively thin stream.

Accordingly, as a whole, the lighter gas gathers near the top lid 19 and is exhausted through the openings 190 to fill an upper chamber 27. The small amount of the gas, which flows through the gap between the drum 18 and the baffle 23 from the chamber 25, and the lighter gas in the upper chamber 27 are taken out through the outlet 29, and then separated from each other by a suitable separator such, for example, as a cold trap device (not shown). Similarly, the heavier gas gathers near the bottom lid 20 and is exhausted through the openings 20a to fill the lower chamber 28. The heavier gas mixed with a small amount of the gas from the common chamber 25 is taken out through the outlet 30 and then further separated.

In accordance with the invention, the mixed gas to be separated is supplied from the ring-like opening 22a defined by the inner cylinder 21 and the drum wall 18, and the separated gases are withdrawn from the openings 19c and 20a provided on the upper and lower lids l9 and 20 respectively. In other words, the gas is supplied at larger radius positions of the drum and exhausted at smaller radius positions. Hence, there occurs an inward flow in the radial direction as a whole. Furthermore, the supplied mixed gas from the opening 22a has a peripheral velocity substantially equal to that of the drum wall 18.

As there exists a radially inward flow of the mixed gas having a peripheral velocity substantially equal to r w the angular velocity (u of the gas in the drum 18 comes to have a larger angular velocity than a) where r denotes the inner radius of the drum wall 18, and w denotes the angular velocity of the gas portion at radius r. This is shown in FIG. 3 in a quantative manner, wherein the ordinate represents w/m the abscissa represents r, and the

curves

1 and 2 respectively represent the prior art and the instant invention. This phenomena may be understood through calculations taking the viscosity of the gas into consideration.

Thus, according to the instant invention, the major portion of the gas in the drum has a larger velocity than that of the centrifuge drum, and the separating power of the system is consequently substantially increased because it is proportional to the fourth power of the angular velocity of the gas, as hereinbefore set forth.

Since the gas in the upper portion of the drum is enriched with the lighter gas and the gas in the lower portion with the heavier gas, there exists a concentration gradient along the axial direction of the drum with respect to the heavier and lighter gases. The supply of the mixed gas to be separated is preferably made at the portion in the drumhaving a mixture of lighter and heavier gases substantially equal to that of the mixed gas to be supplied. Accordingly, the length of the inner cylinder 21 in the axial direction is selected to be about a half of the inner axial length of the drum 18.

The radially inward flow is obtained by the displacement, in the radial direction, of the position where the gas is exhausted from the position where the gas is supplied. The openings provided on the upper and lower lids for exhausting the separated gases are preferably positioned at as small a radius as possible. However, the nearer they are positioned to the center, the smaller is the gas pressure, so that it is more difficult to exhaust the separated gases. Hence, the openings for exhausting the separated gases are arranged on circle of about one half the radius of the lids in this embodiment of the instant invention.

Referring now to FIG. 4 which shows another embodiment of the instant invention, the hollow shaft 16 is shown extending axially down through the upper lid 19into the central portion of the drum l8. Secured to the lower end of the hollow shaft 16 is a pipe member 41 extending radially in four directions so as to form four radial passages, each communicating with the hollow shaft 16 at one end and having an outlet 42 at the other end, opening near the inner periphery of the drum 18. The top lid 19 does not include the radial conduits 19b as shown in FIG. 1, but does include the central opening for the shaft 16 and the exhausting openings 190. j

The operation of this embodiment is substantially identical to that of FIG. 1, and will be understood from the description above.

In these embodiments, there are provided a plurality of openings on the upper and lower lids of the drum for taking out the separated gases. However, other devices can be used for this purpose.

One example of such a device, illustrated in FIG. 5, employs a stationary pipe 44, which passes through the hollow shaft 16 with a clearance therebetween, having a rectangular bend therein as it enters the drum 18 near the lid 19, and having an inlet opening 46 at one half the radius of the drum [8. In this case the shaft 17 is replaced with a hollow shaft 47 as the lower drum support shaft.A pipe 48, substantially identical to the pipe 44 is positioned inside the hollow shaft 47. Further, to prevent disturbance caused by the stationary pipes in the drum, a pair of baffle members of disc shape 49 having small penetrating holes 50 may be disposed near the stationary

exhausting pipes

44 and 48 so as tov form a chamber for the stationary pipes. In this embodiment, the gas in the chamber 25 and the

baffle members

23 and 24 for preventing recombination of the separated gases are not necessary, but the construction of the centrifuge is rather complicated so that difficulties in maintenance and inspection, and the like, may arise.

According to this invention, as it is possible to obtain radially inward flow in a centrifuge drum, and the gas in the drum is able to attain larger angular velocity than that of the drum, thereby to achieve an increased separating power.

Obviously, numerous additional modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described herein.

What is claimed as new and desired to be secured by letters patent of the united states is:

l. A centrifugal gas separator comprising:

drum means driven at a high rotational speed and adapted to receive a mixed gas to be separated;

a housing for enclosing said drum means;

means for rotatably supporting said drum within said one of said disc members which is secured to said hollow shaft; and, an inner cylindrical member mounted inside said cylindrical wall of said drum to form a passage between said cylindrical member and said cylindrical wall, said passage communicating with said conduit. 2. A centrifugal gas separator according to claim 1, wherein:

said supply means has at least one opening communicating with said hollow shaft, said opening being axially disposed at an intermediate portion of said drum near the inner periphery of said cylindrical wall. 3. A centrifugal gas separator according to claim 1, wherein said supply means comprises:

an axial passage extending from said hollow shaft along an axis of said drum and communicating therewith; and, at least one passage extending radially from a free end of said axial passage and communicating therewith and having an opening near the inner periphery of said cylindrical wall of said drum. 4. A centrifugal gas separator according to claim 3, wherein:

the length of said axial passage is approximately one half that of said drum. 5. A centrifugal gas separator according to claim 1, wherein said exhaust means comprises:

a plurality of perforations in each said disc member at an intermediate portion thereof; and, separating means for preventing a gas exhausted from said perforations one of said disc members from mixing with another gas exhausted from said perforations in said other of said disc members. 6. A centrifugal gas separator comprising: an enclosed housing; I a drum adapted to receive a mixed gas to be separated and-having a cylindrical wall with disc members positioned at either end thereof, said drum driven at a high rotational speed; apair of shafts mounted to said disc members along an axis of said drum; bearing means for rotatably supporting said shafts within said housing; exhaust means for exhausting separated gases; one of said shafts being hollow for passing said mixed gas to be separatedinto said drum, supply means for feeding-said mixed gas flowing through said hollow shaft into said drum, near the periphery of said cylindrical wall, wherein said supply means comprises at least one conduit provided in housing; means for feeding said mixed gas to be separated into said drum means at at least one position which is at an intermediate portion thereof and is a radial distance from the axis of said drum means; and, exhaust means for. exhausting separated gases, said exhaust means located nearer said axis than said feeding means, or creating a radially inward gas flow whereby said mixed gas attains a higher rotational speed than said drum means. 7. A centrifugal gas separator according to claim 6, wherein said supply means comprises:

duit.

8. A centrifugal gas separator according to claim 6, wherein:

the axial length of said inner cylindrical member is approximately one half that of said drum.

Claims

1. A centrifugal gas separator comprising: drum means driven at a high rotational speed and adapted to receive a mixed gas to be separated; a housing for enclosing said drum means; means for rotatably supporting said drum within said one of said disc members which is secured to said hollow shaft; and, an inner cylindrical member mounted inside said cylindrical wall of said drum to form a passage between said cylindrical member and said cylindrical wall, said passage communicating with said conduit.

2. A centrifugal gas separator according to claim 1, wherein: said supply means has at least one opening communicating with said hollow shaft, said opening being axially disposed at an intermediate portion of said drum near the inner periphery of said cylindrical wall.

3. A centrifugal gas separator according to claim 1, wherein said supply means comprises: an axial passage extending from said hollow shaft along an axis of said drum and communicating therewith; and, at least one passage extending radially from a free end of said axial passage and communicating therewith and having an opening near the inner periphery of said cylindrical wall of said drum.

4. A centrifugal gas separator according to claim 3, wherein: the length of said axial passage is approximately one half that of said drum.

5. A centrifugal gas separator according to claim 1, wherein said exhaust means comprises: a plurality of perforations in each said disc member at an intermediate portion thereof; and, separating means for preventing a gas exhausted from said perforations in one of said disc members from mixing with another gas exhausted from said perforations in said other of said disC members.

6. A centrifugal gas separator comprising: an enclosed housing; a drum adapted to receive a mixed gas to be separated and having a cylindrical wall with disc members positioned at either end thereof, said drum driven at a high rotational speed; a pair of shafts mounted to said disc members along an axis of said drum; bearing means for rotatably supporting said shafts within said housing; exhaust means for exhausting separated gases; one of said shafts being hollow for passing said mixed gas to be separated into said drum, supply means for feeding said mixed gas flowing through said hollow shaft into said drum, near the periphery of said cylindrical wall, wherein said supply means comprises at least one conduit provided in housing; means for feeding said mixed gas to be separated into said drum means at at least one position which is at an intermediate portion thereof and is a radial distance from the axis of said drum means; and, exhaust means for exhausting separated gases, said exhaust means located nearer said axis than said feeding means, or creating a radially inward gas flow whereby said mixed gas attains a higher rotational speed than said drum means.

7. A centrifugal gas separator according to claim 6, wherein said supply means comprises: at least one conduit provided in one of said disc members which is secured to said hollow shaft; and, an inner cylindrical member mounted inside said cylindrical wall of said drum to form a passage between said cylindrical member and said cylindrical wall, said passage communicating with said conduit.

8. A centrifugal gas separator according to claim 6, wherein: the axial length of said inner cylindrical member is approximately one half that of said drum.