US2970750A - Centrifugal gas compression - Google Patents

Description

Feb. 7, 1961 J. 5. SWEARINGEN CENTRIFUGAL GAS COMPRESSION 6 Sheets-Sheet 1 Filed Feb. 6, 1956 IN VEN TOR.

Feb. 7, 1961 J. s. SWEARINGEN CENTRIFUGAL GAS COMPRESSION 6 Sheets-Sheet 2 Filed Feb. 6, 1956 INVENTOR.

(/0000/7 J. Jwear/nyefl .1. s. SWEARINGEN 2,970,750

6 Sheets-Sheet 3 w am V m t J R Q N mm & J A lR n L 1 a M M 1/ K i nn u I \M t I: I ll... a $9 7 6 I CENTRIFUGAL GAS COMPRESSION Feb. 7,1961

Filed Feb. 6, 1956 CENTRIFUGAL GAS COMPRESSION Filed Feb. 6, 1956 6 Sheets-Sheet 4 IIIIIIH! m4 m3 M2 (/UO/JOIT J. Jwear/n en INVENTOR.

7 Feb. 7, 1961 J. 5 SWEARINGEN 2,970,750

CENTRIFUGAL GAS COMPRESSION Filed Feb. 6, 1956 6 Sheets-Sheet 5 (/UO J0/7 J. 0" we err/aye 5/ IN VEN TOR.

United States Patent CENTRIFUGAL GAS COMPRESSION Judson S. Swearingen, San Antonio, Tex. (12401 W. Olympic Blvd., Los Angeles 64, Calif.)

Filed Feb. 6, 1956, Ser. No. 563,692

14 Claims. (Cl. 230-204) This invention relates broadly to the pumping of a corrosive gas within a centrifugal compressor. In one of its aspects, it relates to-an improved centrifugal gas compressor from which gas losses are low, and within which the pumped gas is protected from contamination by outside sources such as air. In another of its aspects, this invention relates to a novel method of sealing about the rotatable shaft of such a compressor.

The invention is particularly well suited for the pumping of corrosive, high molecular weight gasses containing entrained solids, in which the gases are to be compressed at an elevated temperature through a large compression ratio and wherein the gases sublime at a temperature not far below that at suction conditions. It is more especially adapted to the compression of titanium tetra-iodide vapor containing free iodine Where the suction pressure is low, such as ofthe order of one millimeter absolute.

In a process for producing high purity titanium metal, a titanium compound is treated with iodine to produce titanium tetra-iodide, available at a pressure of about 1 millimeter absolute. In the process, this titanium iodide vapor is compressed, condensed, and the pure titanium metal recovered from it. The object of the process is to produce pure titanium. It is necessary that the compressor not contaminate the titanium tetra-iodide with anything that will be recovered with the metal. This includes air because nitrogen or oxygen is injurious to the process. Further, since the gas is corrosive and expensive, it is necessary that the losses from the compressor be low. Furthermore, since the process must handle commercial quantities of titanium, it is necessary that the compressor have high capacity since the volume of the gas at these very low pressures is great.

Conventional reciprocal compressors would be out of the question for this and similar purposes because of the requirements of a very large capacity, low loss, and low contamination, and due to the considerable amounts of suspended matter in the gas. Centrifugal or axial compressors of conventional design fail to satisfactorily meet the requirements in several respects since, for examp'e, the whirling action of the rotating element of such compressors would centrifuge out the solid particles which would collect on the impellers to clog and unbalance them. Furthermore, it would be difiicult in conventional designs to provide a rotating seal to avoid contamination and excessive leakage, and the pulsating pressure exsting at the point of seal about the shaft in most centrifugal compressors would add to the difliculty of sealing. Also, the various mechanical arrangements of conventional centrifugal pumps adapt themselves to neither high temperature operation nor very low leakage specifications, and the maintenance requirements for conditions as would prevail under the circumstances contemplated by the present invention are such that conventional arrangements would make maintenance excessively costly. Operation at high temperature causes expansion and align- 2,970,750 Patented Feb. 7, 1961 2 ment problems which are likewise difiicult in most conventional machines. Axial compressors in particular do not perform well when used in scrim for high compression ratios, such as to 1 and greater. Further, the viscosity drag through them is too great for satisfactory performance under these conditions.

Accordingly, one object of my invention is to provide a centrifugal compressor which'will compress gas under the conditions herein described through a large compression ratio at reasonable efiiciency and without the solid particles entrained in the gas collecting in the impeller.

Another object is to provide a compressor of the type described which will operate at elevated temperature without complicating the alignment and vacuum tightness of the machine, and which will not excessively heat the gas during compression.

Still another object is to provide in a centrifugal compressor for gas of the type described, a shaft seal that neither permits serious contamination of the gas nor leakage of the gas out past the seal, and which is further capable of convenient maintenance and replacement.

Still another object of my invention is to provide a centrifugal compressor for gas as described which has a controlled pressure at the shaft seal point in the com pressor.

Still another object of my invention is to provide a centrifugal compressor for gas of the type described which is convenient to maintain, the essential parts of which can be replaced without disturbing the piping, and which is inexpensive to build.

Still another object of my invention is to provide a centrifugal compressor of the type described which has a shaft seal assembly sealably attached to the pump case at a point where the temperature is low such that a rubber gasket may be used.

Still another object of my invention is to provide a centrifugal compressor of the type described in which more than one stage may be attached to the same shaft.

Still another object of my invention is to provide a multi-stage centrifugal compressor of the type described in which the rotating impellers are so attached to the shaft that angular misalignment does not statically unbalance a particular impeller.

Still another object of my invention is to provide a centrifugal compressor of the type described in which small pockets which may disturb leak testing are vented.

A further object is to provide, during the pumping of a corrosive gas within a centrifugal compressor, a method of reducing the loss of such gas through a small radial clearance about the compressor shaft while at the same time avoiding contamination of the gas. It is a more particular object to practice such a method when the gas is titanium tetra-iodide vapor.

A still further object is to provide an improved mechanical seal for a rotatable shaft which is adapted to be maintained in operative position about the shaft during the maximum speed of rotation thereof.

Still a further object is to provide an improved leakproof joint between the inner walls of a vessel lined with corrosive resisting alloy.

Other objects, advantages and features of this invention will be apparent to one skilled in the art upon a consideration of the written specification, the attached claims and the annexed drawings.

In the drawings, wherein like reference characters are used through out to designate like parts:

Fig. 1 is a diagrammatic view of one form of a compressor constructed in accordance with this invention, with the housing thereof in section to illustrate schematically the flow path of the pumped gas;

a fioabn Fig.2 is a view similar to Fig. 1 of another form of the invention;

Fig. 3A is an enlarged partial sectional view of the rightmost end of the compressor of Fig. 1;

i Fig. 3B is a continuation of Fig. 3A and showing the leftmost end of the compressor of Fig. 1 which includes the shaft bearing;

Fig. 4 is an enlargement of a part of the sealing assembly of Fig. 3B;

Fig. 5 is a detailed view of a joint at one corner of the compressor housing shown in Fig. 1;

Fig. 6A is an enlarged partial sectional view of the leftmost end of the form of compressor shown in Fig. 2;

Fig. 6B is a continuation of Fig. 6A and showing the rightmost end of the shaft extension;

Fig. 7 is a cross-sectional view, taken substantially along broken line 7--7 of Fig. 6A and showing the diaphragm intermediate the two stages of the compressor of Fig. 2; and

Figs. 8 and 9 are perspective views, broken away in part, of the impeller wheels at the two stages of the compressors of this invention.

The form of the compressor shown diagrammatically in Fig. 1 comprises a housing It) made up of an inner case 11 supported by brackets 11a with-in an outer case 12 and having a suction inlet 13 thereto and a discharge outlet 14 therefrom. Within the inner case 11 is a twostage pump unit comprising first and second stage impeller wheels 16 and 17 affixed to a rotatable shaft 15 and --an interstage diaphragm 18 connected to the inner case and disposed between the impellers. An extension 1 on the end of the shaft extending through a removable back plate 20 of the housing is 'journaled in a bearing assembly 21 attached to the back plate, as indicated diagrammatically at 21a and as will be described hereinafter.

Referring now to each of the impeller wheels 16 and 17 shown in Figs. 8 and 9, and particularly to wheel 16, will be seen to include a rotatable hub 22 and impeller blades 23 attached at their inner ends to the hub and extending radia ly outwardly therefrom in spaced apart relation. Mounted substantially transversely of the hub and secured to one side edge of the impeller blades 23 {is a disc 24, the outer periphery of which is substantially coextensive with the outer ends of the impeller blades. A truncated cone-shaped shroud 25 is secured to the other side edge of the impeller blades to define passages between adiacent impeller bades, the inlet ends of said passages being substantially axial of the wheel and the outlets from the passages being disposed peripherally thereof. More particularly, the inner diameter of the shroud 25 is spaced concentrically of the hub so as to provide the axial inlets to the passages between leading edges of the adjacent blades, and the outer diameter of the shroud is substantially coextensive with the outer periphery of the disc 24 so as to define the aforesaid peripheral outlets from the passages between the outer ends of adjacent blades. As also shown in Figs. 8 and 9, the disc 24 is braced with respect to the hub 22 by means of a truncated cone-shaped member 26 secured thcrebetween.

Inasmuch as the various parts of the impeller wheel 17 correspond in most respects except size to those of the impeller wheel 16, most of the same reference characters are used throughout, and the description of these parts will not be repeated. One exception to the foregoing is that the hub 22a of the impeller wheel 17 projects outwardly therefrom, as also shown in Fig. 3A, for connection coaxially with the hub 22 of impeller wheel 16. Thus, the hub 22a is provided with a pair of bolt holes 27 for accommodating bolts 28 which connect the hubs 22 and 22a together and provide a driving con nection therebetween (see Fig. 3A). From the foregoing, it is obvious that the interconnected and coaxial.

4 hubs 22 and 2211 form the shaft "15 with which impeller wheels 16 and 17 are rotatable.

Referring to the diaphragm 18, it will be seen from Figs. 1 and 3A to be provided with radially extending vanes 29 which terminate short of the outer end of shell 11b. More particularly, the diaphragm 18 is sup ported from a shell 11]) which is secured within and to the inner case by perforated brackets so as to be fixed with respect to rotation of the shaft 15', and is provided at its inner diameter with a. labyrinth type seal 30 closely surrounding the shaft intermediate the first and second stage impeller wheels. Labyrinth type seals are also provided at 30a between shell 11]) and impeller wheel 16 and at 3% between diaphragm 18 and impeller wheel 17 so that the passages through the diaphragm between vanes 29 communicate at opposite ends with the outlet from the first-stage impeller wheel16 and the inlet to the second-stage impeller wheel 17. Further more, as also shown in Fig. 1, the shell 11b, is spaced within the inner case to provide an annular passage which permits the flow of fluid from the outlet of the second-stage impeller 17 to a collection space 31 adjacent the outlet 14 from the housing. Thus, the collection space 31 is formed intermediate the inner case and shell, independently of the diaphragm 18.

As distinguished from the form of Fig. l, in the form of the invention shown in Fig. 2, the housing 32 is formed without an inner case and has an inlet 33 thereto and an outlet 34 therefrom. Thus, in the form of Fig. 2, a collection space 35 is formed by a one-piece diaphragm 36 together with the back plate 37 of the housing 32, in a manner to be described hereinafter.

Referring now to the operation of the form of the compressor shown in Fig. 1, the gas to be pumped enters suction inlet 13 and passes into impeller wheel 16, where it is accelerated to a high velocity which may well be above the velocity of sound in the gas, and then discharged through the outlets from the wheel passages into a space 38 which is a vaneless diffuser. In this large annular space, a large part of the kinetic energy of the gas is converted to pressure energy.-- The gas isthen returned from the space 38 into the passages between the vanes 29 of the diaphragm 18 to the inlet or suction openings into the impeller Wheel 17. In the sec-' ond-stage impeller wheel, the gas is again accelerated to a high velocity and discharged to its vaneless diffuser 39 wherein kinetic energy is again converted to pressure energy. From the space 39, the gas passes through the annular passage between the inner case 11 and shell 11b and then to the collection space 31 and discharge 14.

The flow path of the pumped gas through the form of the compressor shown in Fig. 2 will be obvious from the foregoing and in view of the arrows shown in Fig. 2.

With reference again to Figs. 8 and 9, each of the novel impeller wheels 16 and 17 outwardly looks like a conventional mixed flow impeller in that the inlet portion thereof has radial vanes and the outer portion of the wheel looks like that of a conventional centrifugal pump. In a mixed flow impeller, the inlet vanes cut into the inlet gas creating a relative velocity between the gas and wheel of near the absolute velocity of the wheel, the gas being relatively stationary. The passages through the wheel are streamlined as well as possible to avoid shock, and they are usually gradually increased in cross section so as to smoothly reduce the velocity of the gas relative to the wheel (which means acceleration of the gas).

In the wheels 16 and 17 the relative rotational velocity of the gas is reduced to near zero in the inlet end 'of the wheel passages and the gas is caused to haveonly radial flow relative to the wheel at the inner diameter of the shroud. Beyond this point, the passages follow a path which is as nearas possibleto .being in. linewith the resultant of the centrifugal and the tangential acceleration forces acting on a component of the stream. It is desirable to follow this path because it places the walls of the passages parallel to the forces acting to deposit entrained solids on the wall. Ordinarily, the angle the blade forms with a radius for these conditions decreases with increasing radius and at the wheel tip is to It is influenced by the next preceding angle.

The large angles associated with smaller radii are avoided by the blade shape at its inlet end out to the inner shroud diameter, as described above. Then with a radial direction flow at this point where the radius is larger, the angle meeting the requirement that the blade wall be parallel to the sum of the acceleration forces is rather smalli.e., close to radial. It tends to increase and then decrease, but within such a small range that a small angle on out to the periphery of the wheel is acceptable.

It is less important that the prescribed angle be closely met toward the tip of the wheel because the angle is small and the centrifugal force great, thereby in most cases preventing accumulation of entrained solids. Thus if, for reasons of wheel strength or efiiciency or pressure characteristics, the angle near the tip must deviate some from the prescribed angle, performance can still be attained. Deposits are not formed in the inlet end of the passages because the gas is accelerated by impact with gas already in the wheel which occurs at the nearest possible points to the center of the stream where the summation of momentums involved is a minimum.

The back plate of the housing and the inner case 11 attached thereto by brackets 11a are separable from the remainder of the outer case 12 which carries inlet 13 and outlet 14, such that upon removal of back plate 20, the inner case, together with shell 11b, diaphragm 18 and impeller wheels 16 and 17, may be removed therefrom as a unit. The outer ends of the back plate are sealed with respect to the rest of the outer case by a gasket type joint 40a as shown in Fig. 5 and to be described hereinafter. Such a joint renders the prede termined axial position of the back plate, and thus the inner case 11, somewhat indefinite. To accommodate this situation, the inner case is provided with a part surrounding an opening 40 therethrough which is fiexible upon movement against the inner end of conduit 41 forming discharge 14 to provide a fluid tight seal therewith. That is, the inner case is of such size that as the bolts 42 (Fig. 5) are made up to secure the back plate 20 to the open end of the fixed part of the outer case, the portion thereof surrounding opening 40 will be flexed inwardly to sealably bear upon the end of conduit 41.

Due to the large overhanging load, the shaft of the compressor requires considerable rigidity. At the same time, the seals within the bearing assembly are advantageously of small diameter. To satisfy both of these conditions, the shaft extension 19 of the form of compressor shown in Fig. l is provided with an enlarged diameter portion 43 intermediate journal bearing 44 and ball bearing 45, which acts as a thrust bearing (see Fig. 3B). Alternatively, the shaft extension may be provided with a removable stiffener sleeve 46, as shown in Fig. 6B in connection with the compressor form of Fig. 2, such that the journal hearing may be removed without removal of the shaft. As shown in Fig. 6B, the end of the sleeve nearest the compressor housing may be provided with a shoulder 47 and the shaft extension 48 with a mating shoulder 49 so that they may be abutted by means of a clamp nut 50 near the journal hearing. The sleeve provides maximum stiffness by means of stepped sections 51 which closed fit the shaft extension, as shown in Fig. 6B, at each end and intermediate thereof.

Both of the journal and ball bearings are carried within a housing 52 of the bearing assembly 21 which defines a chamber 53 about the shaft extension intermediate the journal and ball bearings. Lubricating oil may be supplied through an inlet 54 to the housing and through a drilled hole 55 directly to the journal bearing 44. This lubricating oil supply is also directed through a drilled hole 56 to a nozzle 57 from which it is jetted onto the ball bearing 45. All of this lubricating oil is collected in the chamber 53 and delivered to the drain 58 for reuse. The oil which drains to the outside of ball bearing 45 is collected by cap 59 and returned by way of opening 6%) to the chamber 53.

A flange member 61 is fitted against the inner end of bearing housing 52 to define another chamber 62 about the shaft extension and inwardly or toward the compressor housing from the journal bearing 44. The lubricating oil which drains inwardly from the journal hearing 44 collects in this chamber 62 and returns to the chamber 53 through an opening 63 in the bearing housing 52. The lubricating oil within chamber 62 is prevented from running into the compressor housing by means of a mechanical shaft seal which is designated in its entirety by the reference character 64. More particularly, a carbon ring 65 is clamped in fixed position with respect to the rotating shaft assembly and against a shoulder on the fiange member 61 such that a rotating seal element of the mechanical shaft seal 64 rubs in sealing contact therewith.

More particularly, and with specific reference to Fig. 4, the rotating seal element 66 is received about the shaft extension 19 with a small clearance and is provided with a face 67 for sealing engagement with a mating face 68 on carbon ring 65. Pinned at 69 to the seal element 66 for relative axial movement with respect thereto is a second element 70 also received with slight clearance about the shaft and defining with the rotatable seal element 66 an annular recess for carrying a compressible seal ring '71 about the shaft extension. Disposed between the element '76 and a part 72 fixed with respect to the shaft extension are axially extending coil springs 73 for compressing the seal ring 71 and urging the face 67 of seal element 66 into sealing engagement with mating face 68 of carbon ring 65. The seal element 66 is thus centered by the compressible ring 71 which in combinatlon with the springs 73 has the characteristic of radial elasticity. There is a speed at which the centrifugal force on the rotatable seal element is greater than such elasticity so that above this speed the centering or alignment of the seal is disturbed. In accordance with the present invention, the seal ring and springs hear such relation that the radial spring characteristic of the seal ring is greater than the centrifugal force on the rotatable sealing element at the maximum speed at which it is contemplated the shaft extension will be rotated. This relationship may be determined by using a desired length of seal ring or other packing or springs of greater rate.

The lubricating oil within the chamber 62 is subject to considerable heating both because of turbulence within the chamber due to the high speed at which the shaft extension rotates as well as heat conducted from within the compressor housing. This heat is carried away by the oil stream discharged through opening 63. Nevertheless, the temperature may become excessive, and for this purpose an auxiliary stream of cool lubricating oil is delivered tothe chamber 62 through a passage 74a leading from drilled opening 55 in the bearing housing, which passage meters the oil from the inlet into the chamber 62.

Although the pumped gas at the clearance between the back plate 26 of the housing and the shaft may be at only a few millimeters pressure, it is, as contemplated by the present invention, at a high temperature and is highly corrosive. Thus, it must not be allowed to come in contact with the mechanical seal 64 or it would react with the lubricating oil at that point to damage the seal ring and also contaminate the gas. Furthermore, because of its high sublimation temperature, the gas would beat the seal and itself be condensed, in which case the seal would be damaged and the chambers in the bearing 54 directly same 7 assembly would the filled with condensed gas. To prevent such conditions from arising, and in accordance with the present invention, another seal in the form of restrictions about the shaft extension is carried by the bearing assembly intermediate the pumped gas within the compressor housing and the mechanical seal 64.

This latter seal means is designated in its entirety by the reference character 74 and, with reference to Fig. 4, will be seen to comprise a pair of carbon rings 75 and 76 which are urged apart and against the side walls of an annular chamber 78 by means of a spring 77 disposed therebetween. As shown in Fig. 3B, a suitable sealing gas may be conducted through an inlet 79 for passage ,into the chamber 78 and the space between the carbon .rings 75 and 76, for a purpose to be described hereinafter.

As can be best seen from Fig. 4, the carbon rings 75 and 76 are keyed against rotation by means of a pin 81) journaled at opposite ends in the side walls of the chamber 78 and received within radial slots in the carbon rings 75 and 76. Since the rings may expand due to the temperature to which they are exposed by the pumped gas, it may be necessary that they move radially. Therefore, the inner diameter of the rings are of such size as to permit a slight amount of free movement radially, whereby the rotating shaft pushes the rings to .a position where they barely touch the shaft and the friction between them and the side walls of the chamber 78 hold them in position. It will also be seen from Fig. 4 that the side walls of the chamber and the outer side of each of the rings are oppositeiy beveled so as to permit free radial movement of the ring relative to the walls. This construction has been found desirable ,due to the fact that deposits form on the side walls of the chamber which, without such construction, would offer resistance to the radial movement of the rings men tioned above. It will also be noted in this respect that the radial slots for accommodating pin 80 are of such ,depth as to permit such radial movement.

Referring now to Fig. 3B, it will be seen that the seal gas inlet 79 communicates with the chamber 73 by means of a passage 81 formed in part at its end closest the chamber 78 by an opening through a flange member .82 fitted between the flange member 62 and a flanged portion 83 on back plate 29, and further formed in part .at its end nearest the inlet 7h between the aforementioned flange member 82 and flanged portion 83 of the back plate 20. The chamber 78 is defined between a recessed portion of flange member 32 and a ring 84 secured to said flange member. Communicating with the seal ring 76 by means of a passage 86 defined between the inner portion of flange member 82 and an outer portion of flange member 61 is an outlet 85 for the seal gas, to which a vacuum pump may be applied. More particularly, the passage 86 communicates at its inner end with the space between the seal means 74 and the mechanical shaft seal 64.

As also shown in Fig. 3B, each of the bearing housing 52, flange member 61, flange member 82, and flanged portion 83 of the back plate 2%) are secured together by means of bolts 87 in such a manner as to confine an O-ring or other sealing element 88 between flange member 61 and flange portion 83 as well as an outer flange 89 of member 82. It is obvious from the foregoing that this sealing element 88 not only serves to define the fluid-tight passage 81, but also the fluid-tight passage 86. In connection with this same figure, it will still further be noted that the outer Wall 89 of flange member 61 is sloped downwardly from the space between seal means 64 and 74 and toward the seal gas outlet 85. Thus, any liquid particles in the seal gas will tend to adhere to the sloping wall in their travel toward the ,outlet, such an arrangement being desirable for a reason to be described hereinafter.

The seal gas which is pumped into the inlet 7% and ithrough the passage 81 will pass into the space between the carbon rings 75 and 76, from which it flows between the rings and the shaft extension in both axial directions along the shaft extension. For the purpose of preventing contamination with the pumped gas, the seal gas should thus be one which is inert to such pumped gas and not interfere with the desired metallurgical process, and in the process for which this invention is particularly well suited, the seal gas is Argon. In accordance with the present invention, that portion of the seal gas which flows axially past carbon ring 75 which is in most direct communication with the pumped gas and toward the compressor housing sweeps the pumped gas back and prevents practically all of it from flowing into contact with the mechanical shaft seal 64.

The velocity of flow of the seal gas past the ring 75 must be sufficiently rapid to overcome any back diffusion. Although such a rate may be determined experimentally, it has been found that a compressor of the type herein described having a shaft 2 and /1 inches in diameter operated satisfactorily while the compressor discharged against a pressure of about 130 millimeters absolute and rotated about 9200 rpm, The seal gas rate was 250 cc. per minute, half of which was withdrawn from the space between the mechanical shaft seal and the seal 74 and the other half of which was flowing into the pumped stream of gas.

This requirement for the minimum rate of flow is greater if the pressure at the seal ring 75 fluctuates, because obviously the pressure of the seal gas in the chamber 78 must always be above that of the pumped gas. Thus, when the pumped gas pressure decreases, the rate of flow of the seal gas past the carbon ring increases. Such a fluctuation in pressure would cause a surging of gas flow back and forth under the carbon rings which would act to increase the contamination of the pumped gas with lubricating oil vapor. Thus, it is of distinct advantage to have a controlled or relatively fixed pressure at a point just inwardly of the carbon ring '75, or at the point in the bearing assembly 21*. which is in most direct communication with the pumped gas. It is also advantageous for the gas pressure at this point to be low because the mass rate of flow of gas past the carbon ring 75 is lower at low pressure for an equal pressure drop.

in the form of compressor shown in Fig. 1, this purpose is accomplished by the provision of a passage 90 which connects the portion of the bearing assembly in most direct communication with the pumped gas with the suction or inlet portion of the compressor housing 1%). In this manner, the point of the seal assembly adjacent carbon ring 75 is in direct communication with the pumped gas pressure which is much more stable than the pressure thereof behind the impeller wheels. Aso, of course, the suction pressure is at a much lower pressure than in other portions of the compressor housing which, as previously mentioned, is of considerable advantage.

With reference to Figs. 3B, 5, and 1, it can be seen that the passage 90 is formed at its innermost end between flange member 82 and a ring 91 secured thereto, as shown, in closely spaced relation about the shaft extension 19. The ring 91 is in turn provided with a face 92 mating with a face 93 upon a large disc 94 which extends outwardly and coextensively with the inner case ii for securement to the bracket 11a, as shown in Fig. 5. This disc 94 is also secured at its inner end to the back plate 20, as shown in Fig. 3B. Openings 95 are provided through the bracket 11a to provide a continuation of the passage 99 which connects with that portion thereof defined between the inner case 11 and outer case 12, as

est shown in Fig. 1. that the openings 95 may be closed and other openings (not shown) provided through the disc 94 such that the seal ring 75 would be in direct communication with the pumped gas at discharge or outlet pressure. It will also be seen from Fig. 4 that a. lower inwardly turned end :96

It will be understood, of course.

on ring 91 is disposed opposite a labyrinth type seal 97 on an inner flange of hub 22a. In this manner, the turbulent pumped gas adjacent impeller wheel 17 is prevented from communication with the aforementioned point of the seal assembly in most direct communication with the pumped gas through the passage 90.

With reference now to the form of compressor shown in Figs. 2 and 6A, it can be seen that the seal assembly 98 in most direct communication with the pumped gas within the compressor housing is subject to the pressure of the gas adjacent impeller wheel 17 which, as previously mentioned, will cause fluctuation. For the purposes previously mentioned, the seal means 98 is of such construction as to compensate for the surging of gas therepast. Thus, with particular reference to Fig. 6A, the seal means comprises two metal sleeves 99 and 100 mounted in fixed spaced relation to one another and with a small clearance about the shaft or hub 101 for impeller wheel 17. Preferably, the metal sleeves are made of Hastelloy B and type 316 stainless steel, the former being a nickel alloy containing about 24 to 32% molybdenum, 3 to 7% iron, and 0.02 to 0.12 carbon.

Seal gas is introduced into an inlet 102 and through passage 103 into a space 104 intermediate the sleeve 100 and a mechanical seal 105 which may be similar to that described in connection with the form of compressor shown in Fig. l. The space 106 between the sleeves 99 and 100 is closed so as to form a chamber of sufficient size to compensate for the surges in pressure of the gas past the sleeves 99 and 100.

It has been found that during the sweeping of the pumped gas from the clearance between the rotatable shaft and the restrictions or seal means in most direct communication with the pumped gas, there is deposited within such restrictions a non-seizing film which not only protects the surfaces of the shaft and sealing members, but also reduces the clearance within the restriction so as to improve the sealing characteristics in accordance with the foregoing description. In fact, it is conventionally next to impossible to maintain a clearance between the restrictions and the shaft of less than 0.006 inch because of the danger of rubbing or seizure. Although no explanation is made herein for the reaction between the gas and some of the residual oil vapor in the seal gas which forms the film, it has actually been observed and its advantages accomplished.

Referring again specifically to Fig. 3B, the seal gas which does not flow axially past carbon ring 75 will flow past carbon ring 76 and into the space between the mechanical shaft seal 64 and the seal means 74. As previously mentioned, this space communicates by means of passage 86 with the seal gas outlet 85. It has been found that there will be a small leakage of lubricating oil past the mechanical shaft seal 64 and into this space, and the passage 86 is preferably formed at the lower end of the bearing assembly so that the oil will flow outwardly therefrom. Also, the previously mentioned slop ing Wall 89 is continuous with the inner portion of the passage 86 communicating with the space between seal means 64 and 74 so that the oil will adhere to the sloping wall 89 and the surfaces of passage 86 forming a continuation thereof. If it were not for an arrangement of this type, the oil particles would flow along the inside of sleeve 107 of flange member 82 which, as will be appreciated from the proximity of the flange member to the compressor housing, is quite hot. Although not serious, the high temperature from this sleeve 107 would tend to vaporize the lighter constituents of the lubricating oil and contaminate the seal gas in the passage 86.

From the foregoing, it will be appreciated that the small amount of lubricating oil which leaks past the mechanical shaft seal is disposed of through the seal gas outlet 85. As previously mentioned. this outlet may have attached to it a vacuum pump (not shown) for withdrawing gas which leaks past carbon ring 76. This carries with it any air dissolved in the lubricating oil leaking past the mechanical shaft seal and any oil vapor which may be formed in the space between such seal and the seal means 74. Alternatively, this space may be closed, although remct'al of the seal gas and oil vapor is preferred in that it might otherwise diffuse or flow past the carbon rings and contaminate the gas which enters the compressor housing.

With further reference to the details of the bearing assembly of the compressor shown in Fig. 3B, it has been previously mentioned that flange 89 of member 82 is clamped between flange member 61 and the flanged portion 83 of back plate 20. It will be further noted that a thin radial disc 108 connecting the sleeve 107 of member 82 with the main body thereof, acts as a spring so that a shoulder 109 of the flange member may abut tightly against a gasket110- adjacent a part of back plate 20 such that the gasket forms an annular seal at this point. Of course, the disc 108 is caused to act as a spring due to the making up of the entire bearing assembly with the flanged portion 83 of back plate 20 and the bolting of such members together by means of bolt 87.

The flanged portion 83 is integrally connected to the main portion of the back plate 20 by means of a thin sleeve 111 which is of considerable axial extent to provide most of the temperature gradient. Such an arrangement is of considerable advantage inasmuch as the main portion of back plate 20 is subject to substantial quantities of heat while, on the other hand, the flanged portion 83 is adequately cooled by conduction through the metal parts to which it is adjacent which, in turn, are cooled by the oil bath in chamber 62. By means of this arrangement, it is possible to use as the sealing element 88 a rubber O-ring.

The bearing assembly housing 52, and flange members 61 and 82 are connectable together to form, together with the various seal elements, an assembly which may be handled as a unit. That is, this assembly may be removed along with the shaft extension 19, in a manner to be described hereinafter, so that the shaft and assembly constitute a spindle and seal assembly which may be operated away from the compressor housing and thus assembled, tested and handled as an integral unit. In this respect, threads 113 on an inner surface of the flange member 82 adjacent part 89 provide a means of connection with flange member 61 when such members are separated from the compressor housing. Furthermore, cap screws v (not shown) through the flanged portion of the assembly housing 52 for accommodating the bolts 87 as well as a similar portion of the flange member 61 permit these two members to be held together during such handling and testing.

As previously mentioned, the member 94 which defines part of passage 90 is of considerable radial extent. It is necessary that the inwardly turned part 96 of disc 91 be aligned true with respect to the rotating shaft so that the labyrinth type seal 97 on the impeller wheel 17 will run close to it and thus provide an effective seal'against pressure fluctuations adjacent such wheel without seizing part 96. Of course, inasmuch as the part 94 is disposed within the compressor housing, it may have considerable thermal expansion which would seriously affect the radial position of inwardly extending part 96 if the part 94 and disc 91 were integral with one another. However, as shown in Fig. 3B, and as previously mentioned, the disc 91 has a surface 92 for engagement with a mating surface 93 on the inner end of part 94, and these surfaces are so arranged that considerable radial expansion of part 94 relative to the disc 91 may take place without affecting the position of inwardly extending part 96. Furthermore, these surfaces are so positioned with respect to one another that as the bearing azsembly to which the disc 91 is attached is made up with flanged portion 83 of the back plate 20, the surface 92 is caused to be spring-pressed against surface 93 such that a :seal is provided therebetween. This flexing between the mating surfaces compensates for the difficulty '-in matching of the two surfaces due to machining tolerances, unequal expansion, etc. Furthermore, such flexure is enhanced by the connection of the disc 91 to the flange member 82 by means of the screws shown at a point located radially inwardly from its surface 92. Ohviously, the disc 91 is removable and insertable with the rest of the bearing assembly.

As previously mentioned, the hubs 22 and 22a supporting the impeller wheels 16 and 17, respectively, are connected to the shaft extension 19 so that, upon removal of back plate 21 the impellers may be removed from within the inside of the form of compressor shown in Fig. 1 without disturbing the outer case or its support. On some occasions, it may be desirable to service the seal means or the hearings, or to change the shaft extension 19, without going to the trouble of moving the entire assembly from within the compressor housing. For this purpose, the shaft extension 19 is hollow to provide an axial passage 114 therethrough which will accommodate a bolt 115 for releasably securing the shaft extension to the hub 22a. Dowels 116 are provided between the shaft extension and hub 22a to provide a driving connection therebetween when they are threadedly connected at a point axially therebetween by means of the connecting bolt 115. The hollow end of the shaft opposite connecting bolt 115 may be closed by a plug 117 having means 118 for further connection with a driving member so as to impart rotary movement to the shaft extension and the hubs attached thereto. Thus, upon removal of bolts 87, plug 117 and bolt 115, the bearing assembly 21 may be removed from the compressor housing separately of the parts disposed within such housing. It will be understood from Figs. 3A and 313 that such removal of the shaft extension will leave the impeller wheels 16 and 17 attached to one another in position within the compressor housing and resting upon the labyrinth type seals provided therefor at 311a and 3%.

With reference particularly to Fig. 33, it will be seen that the plug 117 is attached to the end of shaft extension 19 by means of cap screws 119 in such a manner as to dispose an O-ring 120 adjacent a hollow inner portion of the shaft extension such that a seal is formed therebetween. Obviously, upon removal of plug 117, a socket wrench may be extended through the passage 114 of the shaft extension for removing the bolt 115.

As will be seen from Fig. 3B, the passage 114 within the hollow shaft extension 19 and the space 121 behind the end of connecting bolt 115 are communicable, respectively, with the annular space between the bolt and the opening 122 which receives it and the threaded 123 within hub 220. These small annular passages are in turn communicable with the pumped gas through the abutting faces 132 of the shaft extension and hub 22a such that, unless otherwise provided for, gas at atmospheric pressure and trapped within these spaces might leak into the housing and upset leak testing. According to the present invention, however, the annular clearance about the bolt within opening 122 is vented past abutting bolt head 124 and shaft shoulder 125 and into passage 114 by means of a vent passage 126. The passage 114 is then in turn vented at 127 with the space between seal means 64 and 74 communicating with the seal gas outlet 85 to which, as previously mentioned, a vacuum pump may be connected.

With reference to the form of compressor shown in Fig. 6A, it can be seen that the hubs 128 and 101 for impeller wheels 16 and 17, respectively, are connected to shaft extension 48 by a bolt 1311 received through openings in the hubs and threaded within a socket in the socket in the shaft extension. Unless otherwise provided for, the radial clearances about this bolt would be subject to corrosion due to the pumped gas adjacent inlet 33 to the compressor housing. However, a small passage 'wheels will not rotate square with the shaft.

.spectively.

130a (shown rotated in the drawings) is provided through the extension to connect space 104 and the aforementioned clearances such that the latter are swept by seal gas from inlet 102.

It will be noted from Figs. 3A and 313 that at the abutting faces 131 and 132 between the hubs 22 and 22a and hub 22a and shaft extension 19, respectively, there are provided cylindrical pilots 133 and 134. If the planes of the faces 131 and 132 are not accurately perpendidular to the axis of rotation of the shaft, the impeller To avoid the necessity of such close tolerances, each of the pilots of faces 131 and 132 are located axially adjacent the center of gravity of the impeller wheels 16 and 17, re-

In this manner, for example. an error in perpendicular angularity of faces 132 will not shift the cente of gravity of impeller wheel 17. Although such error may shift the center of gravity of wheel 16, this is only one of three and the shift would at least be greatly minimized. Also, the fact that location of faces 132 adjacent the center of gravity of wheel 17 will result in its disposal within the extremities of the wheel, rather than in back of it, and thus in and of itself move such faces closer to the center of gravity of wheel 16 to reduce the effect thereon of its perpendicular misalignment.

Referring to Figs. 5 and 6A, it can be seen that inside walls of the outer case of each form of compressor are lined at 135 with a corrosion resistant alloy. The thin cladding indicated at 135 is not thick enough to accommodate a machined gasket groove, however, so a deep groove 136 is cut in the plate of such a width as to extend from about the middle of the face of gasket 40a to the cladding on the back plate. This groove is filled with corrosion resistant weld metal 137, and a groove 138 is then machined therein to receive the inner half of the gasket, the other half of which is received in a matching groove of the back plate. In this manner, the corrosion resistant metal is continuous out to the middle of the gasket face. The inlay 137 of metal may have pin hole leaks in it so that if it extended all the way out under the gasket face, a leak might result which would be difficult to find and repair.

Referring now to the diaphragm 36 for the form of compressor shown diagrammatically in Fig. 2, it will be seen from Figs. 6A and 7 to include spaced apart spiral vanes 139 which extend radially outwardly from a hub 140 surrounding the shaft with a small clearance at 141. These vanes are secured at one edge between a large disc 142 sp ced at its outer end from the outer case and secured at its inner end to the hub 140. and at an opposite edge to annular disc 143 which defines with ring 14311 a part of collection chamber 35 and a slanting wall 144 which separates the stages by surrounding a labyrinth type seal 145 about impeller wheel 17 at its inner end. Secured between the disc 143 and wall 144 is an eccentricall'y arranged spiral ring 146, the inner side of which confines the flow of pumped gas from the diaphragm into the impeller wheel 17, as indicated by the arrows of Fig. 2. The outer side of this ring forms a part of collection space 35 which expands in volume from the outlet from wheel 17. The diaphragm is supported within the housing by bolts 147 secured to the back plate 37.

It will be noted that several of the features of the form of compressor shown in Fig. 2 correspond to similar features of the form of Fig. 1 so that a detailed description thereof is unnecessary.

From the foregoing it will be seen that this invention is one well adapted to attain all of the ends and objects hereinabove set forth, together with other advantages which are obvious and which are inherent to the apparatus and method.

It will be understood that certain features and subcombinations are of utility and may be employed without reference to other features and subcombinations.

13 This is contemplated by and is within the scope of the claims.

As many possible embodiments may be made of the invention withoutdeparting from the scope thereof, it is to be understood that all matter herein set forth or shown in the accompanying drawings is to be interpreted as illustrative and not in a limiting sense.

The invention having been described, what is claimed is:

- 1. In centrifugal compressor apparatus having a housing, a shaft rotatable within the housing, impeller wheels on the shaft within the housing, and a lubricated mechanical seal for the shaft mounted outside the housing and spaced apart therefrom; means for protecting the mechanical seal from fluid being compressed within the housing, said protecting means comprising three spaced apart annular restrictions arranged in series axially of the shaft, two of said annular restrictions being disposed exteriorly of the housing in the space between said mechanical seal and housing and the other of said annular restrictions being disposed within the housing intermediate the impeller wheels and said two exterior annular restrictions, a flow passage connecting the space between said inner annular restriction and the exterior annular restriction adjacent thereto with a point upstream from the impeller wheels, means for introducing a sealing fluid into the space between said two exterior restrictions, and means for withdrawing fluid from the space between said mechanical seal and the annular restriction adjacent thereto.

2. Centrifugal compressor apparatus according to claim 1 wherein said inner annular restriction comprises labyrinth type seal, and said outer annular restrictions comprise carbon rings.

3. Centrifugal compressor apparatus according to claim 2 wherein the means for withdrawing fluid comprises a passageway having a portion thereof extending substantially longitudinally of the shaft, the innermost wall of said portion being sloped in a direction to cause a small volume of liquid particles to adhere thereto in flowing toward the outer end of the passageway.

4. Centrifugal compressor apparatus according to claim 1 wherein said means for protecting the mechanical seal includes a body having an annular chamber therein surrounding the shaft, said exterior annular restrictions comprising carbon rings disposed within the chamber and closely fitting about the shaft, and spring means urging said rings apart and against opposite walls of the chamber, said walls and rings being oppositely beveled at their outer edges and permitting free radial movement of the rings relative to the walls.

5. Centrifugal compressor apparatus according to claim 1 wherein said means for protecting the mechanical seal includes a body for containing said exterior annular re strictions, a backplate on the housing, said body being sealably attached to the housing by means which includes a rubber sealing element disposed between the body and backplate, and said back plate being constructed so that under normal operating conditions of the compressor the portion thereof adjacent to which the sealing element is disposed is below the permissible temperature for such element.

6. Centrifugal compressor apparatus according to claim 5 wherein said body is flexible axially for tight abutment with another portion of the backplate.

7. Centrifugal compressor apparatus according to claim 6 wherein said inner annular restriction comprises .a labyrinth type seal having a part fixed with respect to rotation of the shaft and secured to said body in a manner to define said flow passage, a wall in the housing extending radially of the shaft and spaced from the backplate, said fixed labyrinth part having a face-which is axially flexible with a complementary face on the wall as the body is attached to the housing in a manner to permit relative radial movement therebetween, said part and wall forming a continuation of the flow passage.

8. Centrifugal compressor apparatus, comprising a housing, a shaft rotatable within and extending exteriorly of the housing, impeller wh els on the shaft, within the housing, a mechanical seal about the shaft exteriorly of 5 the housing, and means for protecting the mechanical seal from fluid being compressed in the housing, said protecting means including an annular restriction about the shaft between the impeller wheels and the mechanical seal, means for introducing a seal gas into a space between 10 the annular restriction and mechanical seal, and means comprising a flow passage connecting the space to the suction side of the compressor, to maintain the pumped gas passing through the annular restriction into the space at a relatively stable pressure.

15 9. Centrifugal compressor apparatus, comprising a housing, a shaft rotatable within and extending exteriorly of the housing, a mechanical seal about the shaft exteriorly of the housing, and means for protecting the mechanical seal from fluid in the housing, said protecting means including an annular restriction about the shaft between the interior of the housing and the mechanical seal, means for introducing a seal gas into a space between the annular restriction and mechanical seal, and means for maintaining the gas passing through the annular restriction into the space at a relatively stable pressure.

10. Apparatus of the character defined in claim 9, wherein said last-mentioned means comprises a surge chamber connecting with the space.

11. In a centrifugal compressor, having a housing, a shaft rotatable within the housing with a portion of the shaft extending outward from the housing, and a mechanical seal for the shaft mounted outside the housing and spaced apart therefrom; means for protecting the mechanical seal from fluid being pumped within the housing, said protecting means comprising two spaced apart annular restrictions arranged in series with the mechanical seal axially of the shaft, said annular restrictions being disposed between the mechanical seal and the housing and being spaced apart from said shaft to provide a relatively small annular space circumferentially of the shaft and extending longitudinally therealong, a surge chamber connecting with said relatively small annular space between said spaced apart annular restrictions, said surge chamber being relatively large with respect to said relatively small annular space, and means for introducing a sealant gas into said relatively small annular space between said mechanical seal and the annular restriction adjacent thereto.

12. In a centrifugal compressor, a housing in which 50 fluid may be compressed and having a backplate, a shaft rotatable within the housing and having a portion extending outwardly therefrom through the backplate, a bearing assembly about the shaft extension, a mechanical seal within the bearing assembly, and means for protecting the mechanical seal from fluid being compressed within the housing, said protecting means being disposed within the bearing assembly between the mechanical seal and housing, said shaft extension, bearing assembly, mechanical seal and means for protecting the mechanical seal being removable as a unit form the housing without removal of the backplate.

13. In a method of pumping a corrosive fluid within a centrifugal compressor, wherein a shaft rotatable within the compressor has a portion extending outwardly from the compressor and through a restriction in a bearing assembly which has a small radial clearance about the shaft in direct communication with the pumped fluid, the step of directing a seal gas, which is inert to the pumped fluid and has residual oil vapor therein, into the pumped fluid passing from the compressor through the clearance to sweep it from the clearance and form a non-seizing corrosive film within said clearance for reducing the clearance without causing seizure of the parts.

14. In a method of the character defined in claim 13,

References Cited in the file of this patent UNITED STATES PATENTS 574,353 Garlock Dec. 29, 1896 875,934 King Jan. 7, 1908 1,326,690 Rice Dec. 30, 1919 1,441,381 Slater Jan. 9, 1923 1,609,545 Hanf Dec. 7, 1926 16 Pochobradsky Sept. 13, 1927 Keyser Mar. 6, 1928 Ogden Apr. 3, 1934 Stroebel Apr. 30, 1940 Holliday Mar. 17, 1942 Van Rijswijk May 28, 1946 Concordia et a1 Oct. 11, 1949 Montgomery Feb. 12, 1952 Chambers May 6, 1952 Torrey Oct. 14, 1952 Oechslin Jan. 21. 195

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