US3007629A - Centrifuges - Google Patents

Description

Nov. 7, 1961 A. BOYLAND 3,007,629

CENTRIFUGES Filed Feb. 19. 1947 2 Sheets-Sheet 1 l7 DRIVING MOTOR AND VACUUM GLAND I5 20 I9 I 8 EVACUATING PUMP IN VEN TOR.

EVACUATING PUMP United States Patent 3,007,629 CENTRIFUGES Donald Arthur Boyland, Kenton, Middlesex, England ljlle d Feb. 19, 1947, Ser. No. 729,600 Claims priority, application Great Britain Feb. 27, 1946 Claims. (Cl. 233-21) This invention relates to centrifuges comprising rotors arranged for operation at high peripheral velocities and has for one object the provision of improved means of w thdrawing from the rotor the lighter fractions of centrifuged fluid.

In centrifuges operating at high speeds, for example for the separation of gases of high molecular weight, the pressure difference inside the rotor between the axial region and the peripheral region is substantial. Whereas in an evaporative centrifuge the pressure at the periphery may be of the order of 1000 mm. Hg, the pressure near the axis, where the concentration of the lighter constituent of the fluid is greatest, may be of the order of 0.001 millimetre of mercury or less. Difliculty then arises in the withdrawal of the fluid from the axis of the rotor at a rate adequate to maintain useful separation of the constituents.

A further object of the invention is to enable the exhaust apertures through which fluid is withdrawn from the rotor of a centrifuge to be made of generous area without undue mechanical weakening of the rotor structure.

Other objects of the invention will be apparent from the following description and from the appended claims. In accordance with the present invention there are provided in the rotor radial channels or sections communieating with the axial part of the main space within the rotor and with an external exhaustchamber so that the light fraction of the fluid is evacuated by a centrifugal pumping action within the centrifuge in conjunction with such normal external pumping as may be necessary.

The adoption of this form of construction, in which part of the pumping means for exhausting the centrifuge is made integral with the centrifuge rotor, enables the exhaust apertures in the centrifuge proper to be made of generousarea without undue mechanical weakening of the rotor structure. This eliminates difficulties which arise when attempts are made to exhaust gas at low pressure through small-area outlets from a centrifuge.

The invention will be described by Way of example with reference to the accompanying drawings in which FIG. 1 is a somewhat diagrammatic part-sectional View one the line I-I of FIG. 2 of a centrifuge according to the invention,

FIG. 2 is a view in cross-section to an enlarged scale of the rotor of the centrifuge of FIG. 1, and

FIG. 3 is a fragment of the view in FIG. 2 and illustrates a modification according to the invention.

Referring to FIGURES 1 and 2, a centrifuge comprises a fixed outer casing consisting of a cylindrical body and two end plates 11 and 12. Within the casing is rotatably mounted a rotor, of length substantially greater than its diameter, comprising a substantially cylindrical shell 13, having the contour shown in FIGURE 2 which forms the subject of British patent specification No. 6,125/46, having its ends closed by end plates 14 and 15. The rotor is suspended by a hollow spindle 16 which passes through suitable glands (not shown) to a driving motor 17 which may for example be of the turbine type. At the lower end of the rotor is a hood 18 having an upturned flange 19 overlapping a spigot 20' on the end plate and forming therewith a labyrinth packing to prevent excessive passage of gaseous fluid. Within the flange 19 is a boss 21 connected to the flange by spider arms 22. p The boss is apertured to receive a short spindle 23 projecting from the endplate 15 to provide a lower bearing for the rotor, the bearing being connected by the spider arms 22 to the hood 18.

The hood 18 is slidably mounted on a seating 24 carried by a partition 24 apertured at 25. The slidable mounting permits of small amounts of motion of the lower end of the rotor (for example when passing through a critical speed), and the friction between the surfaces of hood 18 and seating 24 provides desirable damping. An exhaust pipe 26 is fixed to the partition in communication with the space 27 within the hood 18 and extends through the end plate 12 to the outside and thence to a pump 28. The space within the casing 10, 11, 12 and without the rotors 13, 14, 15 is in connection through aperture 25 with a pipe 29 through which this space may be evacuated by means of a pump 30.

The rotor comprises radial webs 31 and sheet metal partitions 32 both extending over substantially the whole internal axial length of the rotor. The partitions 32 are anchored along their inner edges 33 to the hub portion 34 of the rotor at the roots of the webs 31 and'are fixed to the webs 31 at an intermediate radial distance along them as at 35. Apertures 36 connect the interior of the extraction chambers formed between the webs 31 and the partitions 32 with the space 27, these apertures being near the radially outer parts of the extraction chambers. The partitions are apertured at 37 near the radially inner parts of the extraction chambers to connect these chambers with the space within the rotor and without the extraction chambers.

In operation fluid to be centrifuged is introduced into the rotor through the hollow spindle 16 and passages 38.

I When the rotor is rotated at high speed, the lighter fraction collecting near the axis passes through the apertures 37 into the extraction chambers enclosed by partitions 32 and webs 31, is centrifuged outwards to emerge through apertures 36 into the space 27 within the hood 18 and from here is pumped out through the pipe 26 by the pump 28. A suitable vacuum is maintained in the space be tween the rotor and the casing by the pump 30 which also extracts any of the lighter fraction which reaches this space. 1

The fact that the only inlets 37 to the extraction chambers are near the axis of the rotor ensures that only the lighter fraction enters these chambers whilst the disposition of the outlets 36 from these chambers at a substantially greater radial distance from the axis than the inlets, provides a substantial increase in the pressure of the lighter fraction at the outlets compared with the inlets. The chambers, therefore, materially assist the extraction or removal of the lighter fraction from the interior of the rotor.

The provision of apertures 37 distributed along the axial length of the rotor has the advantage that fluid can pass into the extraction chambers 32 from the space within the rotor and without the extraction chambers in a radial direction without any appreciable axial component of movement. which tends to occur when there is any considerable axial component of flow of the fluid. A further advantage of the use of a number of apertures is that their total crosssectional area can be made relatively large in the region where the pressure is low. The cross-sectional area of the passages 36 can on the other hand be relatively small since they are situated where the pressure is relatively high, namely in the radially outer regions of the extraction chamber.

During the separation process, the fraction that is at any time being removed from the rotor, will be lighter This prevents re-mixing of constituentsing of the last fraction into the last container may be continued until the rotor has been substantially emptied of fluid. Alternatively, the centrifuging process may be interrupted at any time by allowing the rotor to come to rest, the residue within the rotor being then removed in any convenient manner.

During operation of the centrifuge a substantial pressure gradient obtains in a radial direction in the extraction chambers as in the main cavities of the rotor. Hence a usefully high pressure of exhaust gas is maintained and the pump 28 is therefore substantially assisted by the centrifugal pumping effect within the extraction chambers.

The gas which emerges from the rotor may be allowed to flow directly into the space between the rotor and the stationary casing instead of into the hood 18. It will, however, be appreciated that, with a very high speed rotor, it is desirable (as a practical matter) to run it in a space maintained at a comparatively low pressure in order to prevent excessive windage losses. Where the gas is allowed to discharge direct into the casing, it then becomes necessary to provide pumps which will maintain a sufficiently low pressure in the casing despite the eflluent gas from the rotor. Where the gas emerges in a separate end hood as shown in FIGURE 1, the capacity of the pump 30 used for exhausting the main casing can be somewhat reduced since the pump has to deal only with that part of the eflluent gas from the rotor which succeeds in leaking through the narrow clearance between 19 and 20.

In an evaporative centrifuge, fluid vapourising near the periphery and moving inwardly suffers a continuous fall-in circular speed. Hence its pressure on the forward web is greater than on the rear web. Accordingly, when the direction of rotation is that indicated by the arrow 39 in FIGURE 2, it is preferable to locate each partition 32 as shown adjacent to the forward web of each compartment of the rotor to take advantage of the higher pressure existing there.

The partitions 32 may be relatively rigid but they are preferably flexible so that during rotation of the rotor they are suspended as loops between their anchorages 33 and 35. If they are made relatively rigid, their shape may approximate to such suspended loops.

Another construction of the extraction chambers is shown in FIGURE 3. Here they are constituted by a flexible metal sheet 40, for example of a suitable aluminum alloy, extending substantially the full internal axial length of the rotor and formed as complete loops. The material of the loops may be quite thin. The two walls of the loops are apertured at 41. The inner end of the loop is anchored to the hub of the rotor by a solid key or wedge 42 and the outer end may be located by bosses such as 43 upon the end plates of which only the plate is shown. Apertures 36' are provided, as in FIGURES 1 and 2, to connect the extraction chambers enclosed by the loops with the space 27 of FIGURE 1.

Where gases at very low pressures are to be pumped away from the central region near the hub 34, the circumferential cross section of the loop in this central region should have an area of approximately the same value as the cross sectional area remaining in the segment external to the loop. Thus, referring to FIGURE 3, the circumferential length between points A and A along a circle passing through the centres of apertures 41 should be approximately equal to half the circumferential length along the same circle between points B and B.

The material forming the outside edge 44 of the loops should be stiff enough to withstand the slight bending forces necessary to keep the two walls of the loop at the correct distance apart.

I claim:

1. A centrifuge for centrifuging fluid comprising a casing which in operation is fixed, a hollow rotor mounted for rotation within said casing about an axis, an inlet passage in said rotor for the introduction of fluid to be centrifuged therein, an external exhaust chamber within said casing but exterior to said rotor for receiving a relatively light fraction of said fluid, at least one extraction chamber within said rotor extending over at least the greater part of the axial length of said rotor and apertured at at least a plurality of points distributed along its axial length relatively near said axis to receive said lighter fraction from the space within said rotor and without said extraction chamber, and a fluid passage for said lighter fraction connecting a region of said extraction chamber relatively remote from said axis with said exhaust chamber.

2. A centrifuge for centrifuging fluid comprising a casing which in operation is fixed, a hollow rotor mounted for rotation within said casing about an axis, an inlet passage in said rotor for the introduction of fluid to be centrifuged therein, an external exhaust chamber within said casing but exterior to said rotor for receiving a relatively light fraction of said fluid, a plurality of extraction chambers within said rotor and extending radially with respect to said axis extending over at least the greater part of the axial length of said rotor and having walls apertured at at least a plurality of points distributed along their axial length in a region relatively near to said axis to communicate with the space within said rotor and without said extraction chambers and apertured in a region relatively remote from said axis to communicate with said exhaust chamber.

3. A centrifuge for centrifuging fluid comprising a casing which in operation is fixed, a hollow rotor mounted for rotation within said casing about an axis, an inlet passage in said rotor for the introduction of fluid to be centrifuged therein, an external exhaust chamber within said casing but exterior to said rotor for receiving a relatively light fraction of said fluid, pump means for withdrawing said light fraction from said rotor to said exhaust chamber and centrifugal means within said rotor for assisting said withdrawal, said centrifugal means comprising at least one chamber extending radially with respect to said axis, extending over at least the greater part of the axial length of said rotor and having a wall apertured at at least a plurality of points distributed along its axial length and in a region relatively near said axis to communicate with the space within said rotor and Without said extraction chamber and apertured in a region relatively remote from said axis to communicate with said exhaust chamber.

4. A centrifuge for centrifuging fluid comprising a casing which in operation is fixed, a hollow rotor mounted for rotation within said casing about an axis and provided with an inlet passage for the introduction into said rotor of fluid to be centrifuged therein, said rotor comprising a substantially cylindrical shell, end plates forming closures at each end of said shell, a hub portion and a plurality of webs extending between said end plates and connecting said shell and said hub portion, and a partition associated with at least one of said Webs, extending between said end plates and forming with a part thereof and with parts of said end plates the wall of an extraction chamber, said wall being apertured at at least a plurality of points distributed along its axial length and relatively near to said axis to communicate with the space within said rotor and without said extraction chamber and apertured relatively remote from said axis for the withdrawal of fluid from said rotor.

5. A centrifuge for centrifuging fluid comprising a casing which in operation is fixed, a hollow rotor mounted for rotation within said casing about an axis and provided with an inlet passage for the introduction into said rotor of fluid to be centrifuged therein, said rotor comprising a substantially cylindrical shell, end plates forming closures at each end of said shell, a hub portion, a plurality of webs connecting said shell and said hub portion, and a partition associated with each of said webs, said partition extending between said end plates, having an inner edge connected to said hub portion, an outer edge connected to the associated web and a part intermediate said edges spaced from the associated web to form an extraction chamber, said partitions being apertured at at least a plurality of points distributed along its axial length and near to said inner edges thereof to provide communication between the space within each extraction chamber and the space outside such extraction chamber but within said rotor and at least one of said end plates being apertured to provide for each of said extraction chambers near to the radially outer part thereof a communicating passage between such extraction chamber and the space within said casing but without said rotor.

6. A centrifuge for centrifuging fluid comprising a casing which in operation is fixed, a hollow rotor mounted for rotation within said casing about an axis, an inlet passage in said rotor for the introduction of fluid to be centrifuged therein, pump means for extracting fluid from the space between said rotor and said casing, a plurality of extraction chambers Within said rotor and extending radially with respect to said axis, extending over at least the greater part of the axial length of said rotor and having walls apertured at at least a plurality of points distributed along its axial length and in a region relatively near to said axis to communicate with the interior of said rotor outside said chambers and apertured in a region relatively remote from said axis to communicate with said space.

7. A centrifuge for centrifuging fluid comprising a casing which in operation is fixed, a hollow rotor mounted for rotation within said casing about an axis, an inlet passage in said rotor for the introduction of fluid to be centrifuged therein, a hood fixed to said casing and forming with a part of said rotor an exhaust chamber, a plurality of extraction chambers within said rotor and extending radially with respect to said axis, extending over at least the greater part of the axial length of said rotor and having walls apertured at at least a plurality of points distributed along its axial length and in a region relatively near to said axis to communicate with the space within said rotor and without said extraction chamber and apertured in a region relatively remote from said axis to communicate with said exhaust chamber.

8. A centrifuge according to claim 2, wherein each of said extraction chambers within said rotor is constituted by a closed loop of flexible metal sheet having its inner end anchored to the rotor near the axis thereof.

9. A centrifuge for centrifuging fluid comprising a casing which in operation is fixed, a hollow rotor mounted for rotation within said casing about an axis, an inlet passage in said rotor for the introduction of fluid to be centrifuged therein, an external exhaust chamber within said casing but exterior to said rotor for receiving a relatively light fraction of said fluid, at least one extraction chamber within said rotor apertured relatively near said axis to receive said lighter fraction from the space within said rotor and without said extraction chamber, and a fluid passage for said lighter fraction connecting a region of said extraction chamber relatively remote from said axis with said exhaust chamber, said apertures relatively near said axis and having a cross-sectional area which is much greater than that of said fluid passage which is relatively remote from said axis.

References Cited in the file of this patent UNITED STATES PATENTS 576,357 Anderson Feb. 2, 1897 621,619 Salenius Mar. 21, 1899 625,067 Schroeter May 16, 1899 717,385 Gathmann Dec. 30, 1902 1,208,960 Hedderich Dec. 19, 1916 1,695,990- Altpeter Dec. 18, 1928 1,821,6Q7 Andersson et a1. Sept. 1, 1931 2,422,882 Bramley June 24, 1947 FOREIGN PATENTS 640,550 Germany Jan. 7, 1937

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