US3102680A - Multistage centrifugal gas compressor - Google Patents

Description

Sept. 3, 1963 s. F. FQGLEMAN ETAL 3,102,680

MULTISTAGE CENTRIFUGAL GAS COMPRESSOR Filed June 27, 1961 INVEN TOR. 5AM E FbGLEA IAM, Gus A. FOGLEMAN JR.

HERBERT C. 5CHULZE ATTORNEY United States Patent 3,102,686 MULTISTAGE CENTRIFUGAL GAS QOMPRESSOR Sam F. Fogleman, 4941 Mount Frissell Drive, San Diego, Calif., and Gus A. Fogleman, Jr., 3365 llnverness St, Riverside, Calif.

Filed June 27, 1961, Ser. No. 119,990

2 Claims. (Cl. 230-130) This invention relates generally to centrifugal gas or vapor compressors and particularly to devices in which the gases re-enter the impeller in multiple stages from annular gas passages which are disposed axially around the impeller shaft centerline.

The main objective of this invention is to provide an improved means of interstage labyrinth sealing between the multistage rotating impeller and the stationary casing.

Another objective of this invention is to provide an improved impeller structural rigidity by means of spacer rings interposed between adjoining stages of the multistage impeller.

Re-entry type centrifugal compressors of the adjacent parallel flow type in the past have not been commonly marketed, because manufacturing costs were too high to obtain reasonable efiiciencies. To achieve reasonable efiiciencies interstage gas leakage must be minimized particularly at the outer periphery of the impeller. Since labyrinth seal leakage varies directly with the diameter of the seal it is important to minimize the diameter at the labyrinth seal interface.

The impeller of this type compressor in vicinity of the second and higher stages is conventionally supported in a cantilever manner from the main backplate of the first stage impeller. A rigid, reinforced impeller construction is desirable to allow the impeller stages to be bolted or riveted together so as to minimize axial wobble of the components as well as to minimize radial displacement of the components relative to shaft centerline. This rigid, reinforced construction of the cantilever supported impeller resists the distortion effects of centrifugal force and allows minimum vibration plus confinement of the impeller to a more concentric shape which allows the labyrinth seal radial clearances to be held to a minimum with reduced labyrinth seal leakage. Labyrinth seal leakage varies approximately as the second power of thisinterface radial clearance.

Freon refrigerants when compressed exhibit a much higher degree of compressibility than air or monatomic gases. The machine to be described herein will be used primarily for compressing Freon refrigerants and as such the axial impeller vane width at impeller tip is considerably reduced in relation to vane axial width near the inlet with gas passages that are gradually tapered to narrower axial widths as the gas flow progresses radially outward. These tapered gas passages for Freons are more pronounced than in air compressors and relatively large axial gaps are inherently required between adjacent stage enclosures. An objective of this invention is to utilize these axial gaps as locations for interstage labyrinth seals and for impeller reinforcing spacer rings.

The foregoing and other objects and advantages of this invention will be clear to those skilled in the art upon reading the following specification in connection with the attached drawings, in which:

FIGURE -1 is a perspective view of the compressor representing a preferred embodiment of the invention; and

FIGURE 2 is a vertical sectional view.

Referring to the drawings in which a preferred embodiment of the invention is disclosed, a conventional vertically positioned electric driving motor is referred to generally as M. Gas leakage along the motor drive shaft 10 is restricted by a labyrinth seal 12 that is secured to a bottom or base 14 that flares outwardly at 16 into a vertically disposed cylindrical compressor casing 18. The casing bottom or base 14 is apertured at 20 to receive the motor shaft 10. The casing 18 is gradually curved at 22 to merge into a flat section 24 projecting from the flared portion 16.

The compressor outer casing 18 has a cover 26 connected thereto by means of a plurality of bolts or attachment screws 27. A low pressure gas inlet pipe 28 projects through and is secured centrally to the cover 26. The connection of the cover 26 and inlet pipe 28 forms a gradually curved inner surface 29. The inlet pipe 2.8 depends downwardly to a point immediately adjacent a multistage centrifugal impeller, later to be described. The cover 26 also has secured and depending therethrough one or more high pressure gas outlet pipes 30.

A first stage impeller back plate 32 has a hub 34 keyed at 36 on the motor shaft .10. Secured to the back plate 32 are a multiple of first stage impeller vanes 38 projecting upwardly and diagonally outward therefrom. The multiple vanes 38 taper gradually toward the outer periphery of the backplate 32. A bell-shaped stage dividing member 40 is secured to and overlies the multiple impeller vanes 38. The inner upper edges of the central opening of the first division bell 40 have seal seating surfaces 42 that are either seated or in close proximity to coinciding surfaces 44- on a labyrinth seal ring 46 secured about the lower end of the lower pressure inlet pipe 28. The division bell 40 is gradually and concentrically curved at 48 into a gradual downward taper to ward the outer periphery of the first stage back plate 32 and upon the similarly tapered multiple vanes 38. A first stage outer seal seat ring 50 having sealing surfaces 52 is secured upon and adjacent the outer periphery of the first division bell 40. A second stage back plate 54 overlies the division bell 4G and is secured inwardly thereto at 56. The back plate 54 is supported on as well as attached at 58 to the first stage outer labyrinth seal ring 50.

The high pressure gases expelled from the constricted bladed peripheral openings 59 in the first stage multiple impeller are projected radially outward toward the inher surface of the outer casing 18. An annular first stage diffusion chamber 60 is provided to contain the high pressure gases by means of a disc-shaped outer partition 62 within and spaced from the outer casing 18. The partition 62 is connected for assembly purposes in one plural manner designated 64 to an inner and upper circular disc partition 66 that is supported at 6-7 by one or both of the high pressure outlet pipes 30. The partition 62 is formed with a flat lower surface 68 that is fixedly sustained immediately adjacent the rapidly rotating peripheral edge of the second stage back plate 54. The flat surface 68 is curved concentrically and. gradually at 70 to merge into vertical circular sides of the casing 62'. The vertical sides are curved gradually at 74 to merge with and be connected in the plural bolted rnanner 64 to an outer annular peripheral edge '78 of the inner circular partition 66. The partition 66 is curved gradually at 79. The completely open concentric diffuser chamber 60 is formed to circulate the high pressure gas or vapor from the first stage of the multiple re-entry compressor generally designated C.

An outer stationary labyrinth seal ring is secured to the under fiat lower surface 68 of the outer partition or disc 62. The seal ring 80 has sealing surfaces 82 coinciding in conventional manner with the adjacent surfaces 52 on the first stage impeller outer labyrinth seal ring 50. The labyrinth sealing means heretofore described restricts any interstage gas leaks. The annular first stage difiusion chamber 60 directs the highside vapors radially outward, upward and inward to the second stage inlet annular space between Walls of pipe 28. The gas flow is uninterrupted in a gradually curved manner until it re-enters a bell-shaped second stage impeller inlet 8 60f the second stage of the multistage compressor C.

The impeller outer labyrinth seal ring 50 is shown as as a separated part. An alternate type construction would be to have the configuration of the labyrinth seal ring 50 cast or formed as an integral part of either the first division bell 40, or as an integral part of the second stage back plate 54.

The second stage back plate 54 has a multiple of second stage impeller vanes 90 thereon which are radially disposed and taper outwardly in a manner similar to the first stage impeller vanes 38. The second stage vanes 90, however, are somewhat smaller than the vanes 38. A second stage division bell 92 overlies and is secured on the upper edges of the second stage impeller vanes 99. The bell 92 tapers outwardly and a series of inner edges 94 on an open centering ring 96 provide sealing surfaces with coinciding portions 98 on a second stage stationary labyrinth seal ring 100 on the lower peripheral edge of the previously described upper and inner annularly disposed partition or disc 66. The bell 92 is gradually curved at 102 to provide the gas re-entry bell shaped opening 86. The first and second stage bells, 40' and 92 respectively, are curved and tapered in parallel planes to form smooth compressor re-entry gas passages or diffusion chamber 103. The second stage impeller compresses the gases through impeller passages (which are slightly reduced in size and area. This second stage impeller size and area reduction is required to accommodate a gas which is compressed or more dense than that flowing in the first stage impeller. A third stage impeller back plate 104 is secured at its inner edge 1% to the bell 92 and at its outer end is attached upon a second stage outer labwinth sealing ring 108. A second concentric disc or partition 110 positioned inwardly of the first outer partition 62 has its upper inner edge 112 bolted in a plural manner at 114 to the outer peripheral edge .116 of a second upper and inner disc shaped partition 118. The disc 118 is secured to and supported at 120 by one of the high pressure outlets 30. The second partition 110 has a lower flat side 122 and an inner circular edge 124 assumes a stationary position immediately adjacent the rotating peripheral edge of the back plate 104. A stationary circular sealing ring 126 is attached to the under side of the flat surface 122 and the inner edges 128 thereof coincide in the usual manner with the seating surfaces on the second stage labyrinth outer seal ring 108. As stated before, the labyrinth sealing devices restrict interstage gas leakage.

The movement of the compressor vapors in the second stage of the compressor C is exactly the same as described for the first stage. The third stage impeller back plate 104 has also a series of multiple impeller blades 136 thereon which are somewhat smaller but formed in exactly the same manner as first and second stage vanes 38 and 90 respectively. A third stage division bell 13 8 smaller but of larger inside diameter and formed the same as the first and second stage bells, has an inner central rim 140 that also has sealing surfaces 142 thereon. The upper and inner second stage disclike partition 118 has a stationary labyrinth sealing ring 144 on its lower edge that engages the sealing surfaces 142. An annular open faced disc 146 of torous or doughnut shape is supported from one of the high pressure outlets 30. The disc .146 has a third stationary labyrinth seal 148 secured to its lower side for sealing surface engagement with a third stage outer labyrinth seal 150 secured adjacent the outer edge of the third stage bell 138. A diffusion conduit 152 connects the third stage higher pressure impeller blades 136 with an annular chamber 154 that has communication with one or more of the high' pressure outlets 31].

The impeller outer labyrinth seal ring 108 is shown as a separated part. An alternate type construction would be to have the configuration of the labyrinth seal ring 10 8 cast or formed as an integral part of either the second stage division bell 92, or as an integral part of the third stage backplate 104.

Although the drawings disclose a triple stage re-entry type compressor, it is contemplated that two or more stages may be used depending upon requirements of pressure and volume flowing. Fabrication of an eight stage compressor of the present type would merely result in reduction of impeller diameter and size of the compressor housing.

As far as the operation is concerned, the impeller output and return of gases thereto through the three stages has been described in detail. The parallel flow of gases of each stage within the impeller and casing have only the tin partitions or division members between the parallel flows such that the labyrinth seals described and as shown are located outside the main gas passages to minimize the main gas flow resistance.

The tapered gas passages enclosing the impeller vanes necessitate gaps between adjoining impeller stages near the outer periphery of the impeller. These gaps are blocked-oil by the labyrinth seal rings 50 and 108 and consequently the labyrinth seals between 50 and 82 and between 108 and 128 are located outside the main gas flows. The gap space required between impeller stages allows the labyrinth seal rings 50 and 108 to occupy some axial length. This inherent axial length of 50 and 108 is desirable for use as generous labyrinth sealing surfaces. The labyrinth seal rings 50 and 108 serve as structural reinforcement to prevent axial wobble of the division bells 40 and 92 and to the impeller back plates 54 and 104.

tWhile the embodiment of our invention shown herein is fully capable of performing the objects and advantages desired, it will be apparent to those skilled in the art that numerous modifications may be made without departing from the inventive concept disclosed herein. It is not intended that this invention be limited by the embodiments disclosed but only as necessary in accordance with the appended claims.

We claim: 1. In a multistage centrifugal compressor, comprising: an impeller having all parallel gas flow passages for each impeller stage, said passages separately enclosed by partitions, said partition of subsequent stages axially separated from' each other on the outer periphery of the impeller,

rotating spacer rings disposed annularly on a centerline common with the impeller centerline and disposed at a diameter less than impeller outside diameter and disposed axially between and abutting to two of said partitions of two subsequent impeller stages,

void spaces in the impeller between sub-sequent impeller stages, said void impeller spaces defined on the outer periphery by the outside diameter of the impeller, said void spaces defined on the inside diameter \by said spacer rings, said void spaces defined axially on the sides by two partitions of two subsequent impeller stages,

labyrinth seal seating surfaces on the outer periphery of said spacer rings, and casing partitions with annular labyrinth packing located within the afore mentioned impeller void spaces, said larbyrinth packing also located in proximity to and spaced therefrom, said labyrinth seal seating surfaces of said spacer rings, for the purpose of minimizing interstage gas leakage.

2. A device as claimed in claim 1 wherein a multistage impeller with gas passages having a large axial width near impeller gas inlet and a relatively smaller axial width near impeller gas outlet,

partitions enclosing gas passages, said passages to have a gradually downward taper toward the outer periphery, said partitions to define the differences in said axial widths of impeller inlet and impeller outlet, labyrinth packing located between tapered partitions of subsequent impeller stages, said packing occupying an axial width approximately equal to the difierence between the axial widths of said impeller gas inlet and said gas outlet, whereby the assembly of the impeller with tapered gas passages does not require any increase in overall impeller axial width to provide axial space for the labyrinth packing.

References Cited in the file of this patent UNITED STATES PATENTS Anderson Sept. 4, 1917 Frame July 8, 1919 FOREIGN PATENTS Switzerland Apr. 16, 1921 Great Bn'tain Jan. 22, 1931 Germany Dec. 17, 1921

Claims (1)

1. IN A MULTISTAGE CENTRIFUGAL COMPRESSOR, COMPRISING: AN IMPELLER HAVING ALL PARALLEL GAS FLOW PASSAGES FOR EACH IMPELLER STAGE, SAID PASSAGES SEPARATELY ENCLOSED BY PARTITIONS, SAID PARTITION OF SUBSEQUENT STAGES AXIALLY SEPARATED FROM EACH OTHER ON THE OUTER PERIPHERY OF THE IMPELLER, ROTATING SPACER RINGS DISPOSED ANNULARLY ON A CENTERLINE COMMON WITH THE IMPELLER CENTERLINE AND DISPOSED AT A DIAMETER LESS THAN IMPELLER OUTSIDE DIAMETER AND DISPOSED AXIALLY BETWEEN AND ABUTTING TO TWO OF SAID PARTITIONS OF TWO SUBSEQUENT IMPELLER STAGES, VOID SPACES IN THE IMPELLER BETWEEN SUBSEQUENT IMPELLER STAGES, SAID VOID IMPELLER SPACES DEFINED ON THE OUTER PERIPHERY BY THE OUTSIDE DIAMETER OF THE IMPELLER, SAID VOID SPACES DEFINED ON THE INSIDE DIAMETER BY SAID SPACER RINGS, SAID VOID SPACES DEFINED AXIALLY ON THE SIDES BY TWO PARTITIONS OF TWO SUBSEQUENT IMPELLER STAGES, LABYRINTH SEAL SEATING SURFACES ON THE OUTER PERIPHERY OF SAID SPACER RINGS, AND CASING PARTITIONS WITH ANNULAR LABYRINTH PACKING LOCATED WITHIN THE AFOREMENTIONED IMPELLER VOID SPACES, SAID LABYRINTH PACKING ALSO LOCATED IN PROXIMITY TO AND SPACED THEREFROM, SAID LABYRINTH SEAL SEATING SURFACES OF SAID SPACER RINGS, FOR THE PURPOSE OF MINIMIZING INTERSTAGE GAS LEAKAGE.

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