Regenerative centrifugal compressor

Abstract: A regenerative centrifugal compressor has an impeller disk (32) with axial impeller blades (72) on either side of the impeller disk rim (36), and a support housing (12, 14) for rotationally supporting the drive shaft (34) of the impeller disk (32). The housing also defines annular compression chambers (22) that respectively surround one or the other of the rows (46) of impeller blades (72). The annular compression chambers (22) that respectively surround one or the other of the rows (46) of impeller blades (72). The annular compression chambers (22) extend in the rotation direction of the impeller from an inlet (18) to an outlet (2⊘), with a stripper section (48) extending from the outlet to the inlet in the rotation direction. Stripper seal inserts (48) formed of a low-friction material softer than the impeller blades (72) are fastened into stripper receptacles (5⊘) on either side of the housing (12, 14) at the stripper section. A baffle (58) at the inlet (18) conducts inlet air around the impeller to a radially inward side thereof. Annular running seals (4⊘) are provided between the rim (36) of the impeller and the housing (12, 14). The impeller blades (72) are shaped for optimal efficiency and compression.

Description: This invention is directed to regenerative centrifugal pumps or blowers, and is more particularly concerned with improved regenerative devices having greater efficiency and power. Regenerative compressors are rotor-dynamic fluid handling machines that, with a single bladded impeller disk, achieve a compression ratio that is the equivalent of several centrifugal stages having the same blade tip speed. The impeller disk can have a set of blades or vanes projecting axially at one or both sides of the disk rim. A housing encases the impeller disk and defines annular compression chambers between an inlet port and an outlet or discharge port. A stripper seal is provided between the outlet port and the inlet port. This stripper seal achieves a close clearance over the blades so that only the gas present between the vanes passes from the outlet port back into the inlet port end of the compression chamber. Each annular compression chamber has a cross section that is more or less circular, and a solid core can be provided at the tip of the vanes or blades. The blades drive gasses in the chamber radially outward, and the gasses are guided by the core and the chamber walls back to the radially inward or intake edge of the impeller blades, which then again propel the gases outwards. The gasses follow a generally helical path encountering the impeller blades several times in the course of their journey through the compression chamber. Each passage through the vanes or blades compresses the gasses, and is the equivalent of a single stage of conventional centrifugal compression (see for example US-A-4 279 570 FR-A-2 305 619). However, these machines have had limited applicability because of limited efficiency and tendency to dissipate power. Generally, regenerative centrifugal compressors have an isothermic efficiency of fifty percent or less. A great deal of turbulence is created in the compression chamber because gas is ejected into gasses already in the chamber. In FR-A-2 305 619, it has been proposed in order to reduce the turbulence to put a diverter at the inlet of the compression chamber. Unfortunately, the diverter does not provide a limitation of the turbulence, due to the absence of any annular core extending within said compression chamber and adjacent the axial tips of the blades. Other apparatus such as described in WO 89/06318 have been proposed in order to improve the adiabatic efficiency. To that effect, a baffle plate is positionned between the compression chamber and the inlet. However, the inlet of this compressor extends axially, thus limitating said compressor to having blades only on one side of the rotor. In addition, this plate does not efficiently reduce or avoid the turbulence. Other types of compressors are known from US-A-2 306 951 and DE-A-1 817 430 wherin the inlet is axially oriented. Also, previous designs for stripper seals have been unable to avoid problems of leakage and noise, and require a relatively large clearance for the impeller blades. On the other hand, these compressors are often preferable to the more efficient reciprocal compressors, especially in applications that require high reliability and which must be relatively free of operation or maintenance problems. Pumps of this type have also been employed for pumping liquids. It is an object of this invention to provide a regenerative centrifugal pump or blower which has improved efficiency. It is another object to provide a regenerative centrifugal compressor with improved compression characteristics and reduced leakage characteristics. It is a further object of this invention to provide a regenerative centrifugal compressor with a more effective, serviceable stripper seal. According to an aspect of the present invention, the compressor has an impeller or rotor disk that is rotationally supported in a housing. There are two rows of axial impeller blades at the rim of the rotor disk, and the housing defines a pair of annular compression chambers, with the two rows of blades each travelling through a respective one of the compression chambers. The housing has an air or gas inlet port and an exhaust or outlet port, with the compression chambers extending from the inlet port to the outlet port in the rotation direction of the impeller disk. At the inlet port, inlet baffles guide the intake air (or other gas) around the blades and compression chamber to enter the chamber at the low pressure, i.e. radially inward, side of the impeller blades. The compression chambers are generally round in cross section, and each includes an annular core that extends within the compression chamber alongside the axial tips of the impeller blades to define a torsional pathway for the gasses discharged from the blades. Each core extends from the inlet port, where its end is integrally formed with the inlet baffle, to the outlet port. The core favorably is of generally D-shaped cross section. The stripper seal extends from the outlet port to the inlet port in the rotation direction of the impeller. The stripper seal has an open passage of substantially the same cross section as the impeller blade profile. Compressed gasses in the compression chamber are stripped from the impeller blades and blocked from flowing from the outlet around the blades to the inlet. In the preferred embodiment the stripper seal includes respective channel member inserts formed of Teflon (i.e. PTFE) or another low-friction synthetic resin that is softer than the material (e.g. aluminum) of the impeller blades. The inserts fit into respective receptacles at the stripper region of the housing, i.e. between the outlet and inlet ports. The stripper inserts are preferably in the form of an arcuate channel with a web portion that secures to the housing receptacles and inner and outer coaxial circumferential flanges disposed respectively at the intake and discharge edges of the impeller blades. The inner flange is of a greater circumferential extent than the outer flange, so that the spaces between successive impeller blades are closed off at their intake side before being closed off at their discharge side when the blades encounter the stripper seal. Also, the spaces open first at the outer or discharge side when the blades leave the stripper seal and enter the inlet region. This reduces the turbulence from compressed gasses that are carried in the spaces between blades from the outlet to the inlet regions. For improved fluid dynamics, the blades are configured as forward sloping, with an L-shaped profile having a round inner or intake edge, a generally straight lead-in portion, an arcuate bend, a generally straight exit portion, and a flat, narrow discharge outer edge. Successive blades define between them spaces that are each of generally constant width from the intake edges to the arcuate bends, and then open gradually from the arcuate bends to the discharge edges. The two rows of blades are preferably staggered, so that blades on one side of the impeller disk are aligned with the spaces between blades on the other side of the disk. Running seals, i.e. annular rings of Teflon or the like, can be disposed between the radially inward portion of the housing and a facing generally cylindrical surface of the rim of the impeller disk. These seals help contain compressed gasses in the compression chambers. The regenerative compressor of this invention, with its inventive improvements, is quieter and more reliable than previous designs, and achieves a greater pressure ratio at improved efficiency. If the stripper seals become damaged, they can be easily replaced. The above and many other objects, features, and advantages of this invention will become apparent to those skilled in the art from the ensuing description of a preferred embodiment, which should be read in conjunction with the accompanying Drawing. Figs. 1 and 2 are left and right side elevations of a regenerative centrifugal compressor according to one preferred embodiment of this invention. Fig. 3 is a sectional elevation taken at 3-3 of Fig. 2. Fig. 4 is a top plan view of the compressor of this embodiment, taken at 4 - 4 of Fig. 2. Fig. 5 is a partial sectional view taken at 5 - 5 of Fig. 4. Fig. 6 illustrates an alternative shaft seal arrangement for a portion of the embodiment illustrated in Fig. 3. Fig. 7 is a partial assembly view of the impeller and stripper seal of the preferred embodiment of this invention. Fig. 8 is a partial elevational view of the preferred embodiment. Fig. 9A to 9I are cross sectional views of one of the compression chambers, taken at 9A to 9I of Fig. 8, respectively. With reference to the Drawing, and initially to Figs. 1 and 2, a compressor assembly 1⊘ is shown to comprise a right housing half 12 and a left housing half 14. An impeller drive shaft 16 extends out a bearing support in the housing half 12. In this embodiment, the motor (not shown) is attached to the shaft 16 at the right housing half 12 as shown in Fig. 1. The direction of rotation of the impeller shaft 16 is as indicated by an arrow, which can be embossed or molded on the housing. An inner port 18 and an outer port 2⊘ are provided at an upper part of the compressor assembly 1⊘. A generally toroidal compression chamber 22 is formed in each half 12, 14 of the compressor housing, and each chamber 22 extends in the rotation direction from the inlet port 18 to the outlet port 2⊘. A stripper portion 24 then continues in the rotation direction the short distance from the outlet port to the inlet port. Stands or feet 26 are attached onto the compressor assembly and serve for mounting the same. As shown in large detail in Fig. 3, the inlet port 18 has a J-shaped cross section, and inlet air is carried from the mouth of the inlet port 18 around to an underside or radially inward portion of the compression chamber 22 at the inlet port. As also shown in Fig. 3, there is a shaft seal 28, which can be of labyrinth seal design, to seal the housing half 12 about the shaft 16. Bearings 3⊘ of known design can support the shaft 16 rotationally. Within the housing, and driven by the shaft 16, is an impeller disk 32 having a hub 34 that is mounted on the shaft, and a peripheral rim 36. The rim has a cylindrical surface 38 that faces radially inwards on either axial side of the disk 32. A low-friction ring-type running seal 4⊘ is provided on an inner cylindrical face 42 of each housing half 12, 14 that faces a respective cylindrical surface 38. The seals 4⊘ block the escape of high pressure gasses from the compression chamber 22 into a low-pressure enclosed area 44 between the hub 34 and the rim 36 of the impeller. If desired outer running seals can be provided between outer cylindrical surfaces of the rim 36 and facing surfaces of the housing halves 12, 14. As shown here generally and in more detail later, on each axial face of the impeller rim 36 there is a respective row 46 of rotor blades, which drive the air or other gasses centrifically outward into the compression chamber for centrifugal compression, as the gas travels from the inlet port to the outlet port. Stripper seals 48 are provided in the form of inserts of a low- friction material that is softer than the rotor blades. The stripper seals are attached into receptacles 5⊘ in the stripper area 24, with one such stripper seal 48 being attached into each one of the housing halves 12, 14. As also shown in Fig. 3, each of the chambers 22 has a generally annular core 52 at the center of the chamber adjacent the axial tips of the impeller blades. Here, the cores are of a generally D-shaped cross section. The cores have a straight or generally flat surface adjacent the blades and a generally round or torsional surface that, together with the inside of the chamber 22, defines a circular path of air discharged from the radially outward side of the blades back to the radially inwards side thereof. As shown in Figs. 4 and 5, the inlet and outlet ports 18, 2⊘ have flanges 54, 56, respectively, to which pneumatic tubing or piping can be connected. A baffle 58 is provided in the inlet port, the baffle 58 extending into each housing half 12, 14, to carry intake air out around the rows 46 of impeller blades to the radial underside of the chamber 22, i.e., to the intake side of the impeller blades. As shown in Fig. 6, a gas seal 6⊘ can be employed in lieu of a labyrinth type seal, if the compressor assembly 1⊘ is used for a gas other than air, for example, argon, natural gas, or the like, to prevent gas from escaping out along the drive shaft 16. Details of the impeller 32 and the stripper seal 48 can be explained with reference to Fig. 7. The stripper seal 48, only one of which is shown here, is in the form of an arcuate channel-shaped member having a flat web portion 62 with countersunk screw holes 64, through which machine screws 66 can fasten the stripper seal 48 into the receptacle 5⊘ that is provided for it. The stripper seal 48 has a radially outer flange 68 that is generally cylindrical and extends in the circumferential direction between the outlet port and the inlet port. A generally cylindrical inner flange 7⊘, which is co-axial with the outer flange 68, has a greater circumferential extent, both at the inlet side and at the outlet side. The stripper seal 48 is made of a softer material than the blades of the impeller, so that the fit between the impeller blades 46 and the stripper seal 48 can be as close as possible, without significant risk of damage to the blades. The stripper seal 48 can be molded or machined of Teflon (polytetrafluoroethylene) or another suitable synthetic resin with low friction characteristics. As also shown in Fig. 7, each impeller blade row 46 is formed of a succession of blades 72 and spaces 74 between the blades. Each of the blades 72 has a generally L-shaped profile, with a rounded intake edge 76 at its radially inward side, a straight portion leading to a generally arcuate bend 78 at its mid portion, and a generally straight exit portion leading to a flat, narrow discharge edge 8⊘ at its radially outward side. As also shown in Fig. 7, in the preferred mode the blades 72 are positioned alternately, i.e. staggered, so that the blades 72 on each side of the impeller rim 36 are at the locations of spaces 74 between blades on the other side of the rim 36. The successive blades then define between them the spaces 74 that are of generally constant width from the intake edges 76 to the bends 78, and then open gradually to the arcuate bends 78 to the discharge edges 8⊘. Fig. 8 shows details of the position of the stripper 48 and the chamber 22 at the inlet and outlet ports 18, 2⊘. Figs. 9A - 9I are sections of the chamber for one side only of the housing, taken along the planes indicated in Fig. 8. Figs. 9A and 9B show the general configuration of the baffle 58, which defines the J-shaped cross section for the air inlet so that it opens onto the intake edge 76 of the impeller blades 72. As shown in Figs. 9C and 9D, at the intake end of the chamber 22, the baffle 58 begins to assume a D-shaped section and this becomes the annular core 52, which is supported at one or more points by posts 82. At positions significantly away from the inlet and outlet ports 18 and 2⊘, the chamber has the cross section as generally shown in Fig. 9E. Figs. 9F, 9G, 9H, 9I show the cross section of the chamber 22 at the outlet port 2⊘, as the impeller nears the stripper area 24, where the impeller blades 72 pass through the stripper seal 48. Here, as shown in Figs. 9F, 9G, and 9H, the radially outward part of the chamber 22 begins to open outward while the radially inward part of the chamber 22 becomes sealed off and joins with the stripper area. As shown in Fig. 9G the longer lower or inner flange 7⊘ of the stripper seal 48 is encountered first. This serves to cut off the intake edges of the spaces 74 between the blades prior to closure of the discharge edges thereof. This feature permits a pressure between the blades to be reduced somewhat at the stripper seals to reduce noise and increase efficiency. As shown in Fig. 9I the stripper seal 48 occupies all the area that is not required for the impeller 32. The stripper seal thus blocks the flow of high pressure gas from the outlet port 2⊘ to the inlet port 18. While this invention has been described in detail with respect to a preferred embodiment, it should be understood that the invention is not limited to that precise embodiment. Rather, many modifications and variations would present themselves to those skilled in the art without departing from the scope and spirit of this invention, as defined in the appended claims. spirit of this invention, as defined in the appended claims.

Claims: A regenerative centrifugal compressor in which a rotor (32) has an axis (34), a rim (36), and a row (46) of impeller blades (72) that extend axially from one side of the rim, said blades having a radially inward intake edge (76) and a radially outward discharge edge (80); a housing (12, 14) for said rotor has a gas inlet (18) and a compressed gas outlet (20) angularly spaced apart, a generally annular compression chamber (22) formed in said housing having a radial extent to envelop said impeller blades (72) and extending circumferentially from said gas inlet (18) to said gas outlet (20) in the rotation direction of said rotor, the housing including an annular core (52) extending within said compression chamber (22) adjacent said axial tips of said impeller blades (72) to define a toroidal pathway for gas that is impelled by said blades, the core extending generally from said inlet (18) to said outlet (20) in the rotational direction of the rotor to guide gas impelled by said blades (72) from the radially inner intake edges (76) to the radially outer discharge edges (80) of said impeller blades ; and a stripper seal (48) extends from said outlet (20) to said inlet (18) in the rotation direction of the rotor, said stripper seal having an open passage of substantially the same cross section as said blades to strip compressed gas in said compression chamber and block compressed gas from flowing from the outlet (20) to the inlet (18) ; said gas inlet (18) and compressed gas outlet (20) being radially oriented, ; characterized in that : an inlet baffle (58) is formed in said housing at said inlet for guiding inlet gas around said impeller blades (72) and said compression chamber (22) to enter the compression chamber only at a radially inward side thereof. The regenerative compressor of claim 1, further characterized in that said inlet baffle (58) extends radially inward past the impeller blades (72) and said compression chamber (22). The regenerative compressor of claims 1 or 2 further characterized in that said inlet baffle (58) defines an inlet duct of generally J-shaped section. The regenerative compressor of claims 1 or 2 further characterized in that said inlet baffle (58) is integrally formed with said core (52) at an inlet end thereof. The regenerative compressor of claims 1 to 4 further characterized in that said stripper seal (48) is in the form of an arcuate channel having inner and outer coaxial circumferential flanges (70, 68) respectively adjacent the intake edges (76) and discharge edges (80) of the impeller blades (72), said inner circumferential flange (70) extending further into said inlet (18) than said outer circumferential flange so that spaces between the impeller blades open first at their discharge edges as said impeller blades enter the inlet from the stripper seal. The regenerative centrifugal compressor of any of the preceding claims, further characterized in that said stripper seal (48) is formed of a low-friction material softer than the material of said blades (72) and fitted into a receptacle (50) in the housing (12, 14) for the stripper seal. The regenerative compressor of claim 6 further characterized in that said stripper seal (48) is formed of a low-friction synthetic resin. The regenerative compressor of claim 7 further characterized in that said stripper seal is formed of PTFE. The regenerative centrifugal compressor of any of the preceding claims, and further characterized in that the housing (12, 14) has a circumferential surface facing an inner circumferential edge (38) of the rim (36) of said rotor (32) ; and a low friction seal ring (40) disposed on said housing circumferential surface to seal against said inner circumferential edge of said rotor rim (32). The regenerative compressor of claim 9 characterized in that said sealing ring (40) is a low friction synthetic resin. The regenerative compressor of claim 10 characterized in that said sealing ring (40) is PTFE. The regenerative compressor of any preceding claims, characterized in that said blades (72) have a generally L-shaped profile having in succession a rounded intake edge (76), a generally straight leading portion, an arcuate bend (78), a generally straight exit portion, and a flat narrow discharge edge (80). The regenerative compressor of claim 12, further characterized in that successive ones of said blades (72) define between them a space (74) that has a generally constant width from the intake edges to the arcuate bends (78), and then opens gradually from the arcuate bends to the discharge edges (80) of the blades. The regenerative compressor of any preceding claims, further characterized in that said annular core (52) has a generally D-shaped cross section with a generally flat side facing the axial tips of the respective impeller blades (72) and with a round outer guide surface to guide the gas impelled by said blades from the radially outer discharge edges (80) to the radially inner intake edges (76) thereof.

Inventors: DITTLER BARRY, VERNEAU ALAIN, DITTLER, BARRY, VERNEAU, ALAIN
Applicants: LAMSON CORP, LAMSON CORPORATION
Application year: 1991
Main classification: F04D23
IPC codes: F04D23, F04D29