Method Of Changing Capacity Of Fluid Reaction Device

Abstract

The capacity of a centrifugal compressor having an overhung rotor with a plurality of separate stage impellers is changed by machining the free curved edge of each impeller blade by an equal amount for each impeller along the entire curved edge length from the radially extending axial flow edge to the axially extending radial flow edge. Additional separate shrouds are provided that differ in diameter from the shrouds supplied with the impellers before machining by an amount equal to the diametric change occurring during machining. Further, separate annular diffusers are provided, with each diffuser having integral blades with free terminal edges lying in a common plane perpendicular to the axis of rotation and engaging the adjacent shroud, so that these radially extending diffuser blade edges may be machined by an amount equal to the axial component of machining on the corresponding impeller blades.

Description

BACKGROUND OF THE INVENTION

Fluid reaction and pumping machinery, for example turbines and compressors, are required for many different predictable loads so that one capacity machine cannot be efficiently manufactured for all situations. Thus, the usual practice is to produce several lines of machines to be matched fairly efficiently with the various expected capacities over a given range. However, this considerably increases the cost of each machine due to the number of different parts that must be manufactured and the inventories involved, as well as considerably reducing the flexibility of the machine after it has once been purchased and installed.

Although many attempts have been made to standardize certain parts of the machines so that only some of the parts need changing for a change of capacity, these attempts still involve considerable expense and relatively high inventories without satisfactorily maintaining efficiency for each capacity. In the Canadian Pat. No. 578,473, to Buchi, issued June 30, 1959, the capacity of a three-stage centrifugal compressor is changed by picking corresponding internal parts without changing the external physical features of the compressor. This patent still involves the manufacture and inventory of a plurality of compressor rotors, which in a multi-stage device are quite expensive, particularly with high speed operation wherein the rotor must be precisely balanced and exceptionally strong materials must be used due to the abrasive affects that increase rapidly with speed. Thus, one of the most expensive components needs to be replaced according to this patent. A similar interchange of rotors is taught by the British Pat. No. 785,419, issued Oct. 30, 1957.

While the machining of the radially extending axial flow edges of an open type impeller to change its capacity is taught by the British Pat. No. 613,892, issued Dec. 3, 1958, such machining will considerably reduce the efficiency of the total device, particularly with respect to blades that are peripherally twisted from their axially extending edges to their radially extending edges. Further, if the same diffusers are employed, their efficiency will be greatly reduced when the capacity is changed by machining only the rotor.

CROSS REFERENCE TO RELATED APPLICATIONS

The features of the invention of this application may be used in combination with the features of the inventions in applicant's following related applications of the same filing date and assignee as the present application, the disclosures of which are incorporated herein in their entirety by reference: "Compressor Barrel Assembly", Ser. No. 44,446; "Compressor Power Recovery", Ser. No. 44,463; "Interchangeable Compressor Drive", Ser. No. 44,403 now abandoned; "Compressor Base and Intercoolers", Ser. No. 44,034.

SUMMARY

It is an object of the present invention to overcome the disadvantages of the prior art as mentioned above, particularly with respect to a high speed multi-stage compressor wherein tolerances, efficiency, and rotor expense are exceptionally high and critical.

The foregoing is accomplished by machining the curved edge of each impeller blade by a desired amount for each impeller, from its radially extending axial flow edge to its axially extending radial flow edge. An additional shroud is provided that is oversize by an amount diametrically and axially equal to the machining of the blades so that it will efficiently cooperate with the machined blades. Correspondingly, the free edges of the diffuser blades that extend in a common radial plane and abut against the adjacent shroud are machined an amount corresponding to the axial component of the machining on the impeller blades, so that the diffusers will operate efficiently at the new capacity. The shrouds and diffusers are made as small as possible and separate so that the diffuser blades may be readily removed and machined and the shrouds may be readily removed and replaced with minimum expense and storage facilities. To this latter end, separate fluid chamber rings are provided around the diffusers and shrouds for conducting fluid in cooperation with a one-piece cast casing having fluid channels therein, so that all of the components may be releasably clamped as a removable barrel within the casing to facilitate change of capacity. In this manner, the capacity of the compressor may be easily changed with minimum expense and expenditure of time and effort, while maintaining high efficiency even with respect to high speed, multi-stage compressors.

BRIEF DESCRIPTION OF THE DRAWING

Further objects, features, and advantages of the present invention will become more clear from the following detailed description of the drawing, wherein:

FIG. 1 is an axial cross section through a preferred embodiment of a compressor according to the present invention set up for operation at its highest capacity, with the capacity changing machining being indicated by dotted lines and with ancillary portions of the compressor removed; and

FIG. 2 shows the lower capacity shrouds of the preferred embodiment that replaced the shrouds shown in FIG. 1 after machining.

DETAILED DESCRIPTION OF THE DRAWING

The compressor shown in FIG. 1 has a one-piece cast iron casing 1, which is annular and has a through cylindrical opening therein formed with fluid guide channels 2. A plurality of annular fluid guides 3, corresponding in number to the number of stages, are axially stacked within the casing 1 to form annular fluid chambers 4. Axially interposed between the fluid guides 3, are shrouds 5, 6, 7 and separate diffusers 8, 9, 10, which correspond to the three separate stages. All of the elements 2-10 are axially stacked and securely clamped by means of a bolt 11 threaded in a housing 12, which is rigidly secured relative to the casing 1 by any known means.

An overhung rotor 13 is rotatably mounted within a bearing 14 mounted within the housing 12 and provided with suitable seals between the stages formed by its impellers 15, 16, 17. The impeller 15, shroud 5 and diffuser 8 form a first stage of the compressor discharging into annular chamber 4, for interstage cooling at a location not shown. The thus cooled fluid from the first stage travels between the impeller 17, shroud 7 and diffuser 10 of the second stage for discharge into the adjacent annular chamber 4 to again be cooled by a second interstage cooler (not shown). Thereafter, the thus cooled fluid from the second stage passes between the impeller 16, shroud 6 and diffuser 9 of the third stage for discharge into the adjacent annular chamber 4 from where it is conducted to a point of usage.

While the principles of the present invention are specifically related advantageously to a high speed centrifugal compressor operating at approximately 54,000 r.p.m., with three-stage compression, the broader aspects of the invention may be employed with other fluid reaction type devices, for example low speed pumps or high speed turbines.

Preferably, the casing 1 is constructed of cast iron, fluid guides 3 are constructed of aluminum, the shrouds 5, 6, 7 are constructed of aluminum, the diffusers 8, 9, 10 are constructed of aluminum and the rotor 13, including its blades is integrally constructed of stainless steel. Thus, it is seen that the diffusers may be easily machined, the shrouds are relatively cheaply constructed and easily replaced, the shrouds and diffusers are of minimum size by utilizing the stacked construction of separate components, the shrouds, diffusers and rotor may be easily removed by the removable barrel stacked construction, and the rotor 13 is an item of considerable relative expense. The expense and criticality of the rotor flow from its construction from stainless steel to resist the extreme corrosive and abrasive affects of any fluid at the high speeds contemplated, its integral construction necessary to obtain an extremely rigid rotor that may be overhung, its extreme sensitivity to vibrations due to its cantilevered overhung mounting, and its extreme sensitivity to vibrations due to the high speeds of operation. Thus, the rotor construction is quite critical and expensive requiring accurate balancing and rigid construction made quite difficult by the general difficulty of working stainless steel. Thus, the replacement of this rotor would involve a considerable expense and stocking of separate rotors would be prohibitive in price. Further, the shape of the blades, conforming configuration between the blades and adjacent shrouds, and the diffuser through flow areas are all critical at the high speeds of operation contemplated and the high pressures encountered with a multi-stage compressor. Inaccuracies or mismatching of these items with the capacity would be disastrous with respect to efficiency of operation.

The capacity of the preferred embodiment of the compressor shown in FIGS. 1 and 2 is changed by the following procedure. The bolt 11 is removed and the stacked items of the barrel assembly are axially removed from the casing 1 to disassemble the fluid guides 3, shrouds 5, 6, 7, and diffusers 8, 9, 10 from the rotor 13 along with the miscellaneous components required for sealing the chambers. After disassembly, each blade is machined by an amount that is the same for each impeller, which amount will most likely vary from impeller to impeller. From the drawing it is seen that the impellers for each stage are of the same type, that is they have open centrifugal blades, so that the specific description of one impeller will suffice for all of the impeller blades. Therefore, with reference to impeller 15, each blade has a radially extending free edge 18 for axial fluid flow, a free axially extending edge 19 for radial fluid flow, a portion 20 extending between edges adjacent the impeller hub 21, and a free curved edge 22 extending from the radially extending edge 18 to the axially extending edge 19. The blades are twisted to correspondingly twist the curved edge 22 by circumferentially offsetting the edges 18 and 19 for each blade. During the machining of the impellers, the machining is conducted along the entire length of each curved edge 22 down to the dotted lines to reduce the radial extent of each blade an equal amount for any one impeller or a predetermined varying amount.

After the machining of all the impellers by the desired amount, the diffusers are correspondingly machined to reduce their capacity by substantially equal amounts. Each of the diffusers is of a similar type so that the specific description of one will suffice for all. The diffuser 8 includes an annular body portion 23 and a plurality of peripherally spaced diffuser blades 24 oriented in a known manner. Each of the blades 24 has an outer free edge 25, with all of the edges 25 being contained within a common radial plane and abutting against the adjacent shroud 5 in the assembled position. To change the capacity of the diffuser 8, all of the edges 25 are machined an equal amount along their entire length so that they will lie in a new common plane generally indicated by the dotted lines passing through the blades 24.

After the machining of the impellers on the rotor 13 and the machining of the blades on the diffusers 8, 9, 10, the compressor is reassembled, but this time with the shrouds 5', 6', 7' of FIG. 2 replacing the shrouds 5, 6, 7, respectively. For efficient cooperation with the newly machined impellers and diffusers, the shrouds of FIG. 2 are correspondingly larger than the shrouds 5, 6, 7. Thus, the annular surfaces 26', 27', 28' of the shrouds 5', 6', 7' are larger than the surfaces 26, 27, 28, respectively, of the shrouds 5, 6, 7. The amount of this enlargement occurs at least within the zone of the surfaces that are directly opposite the curved edges 22 of the impeller blades, with the enlargement being axially and radially correlated to the axial and radial dimension changes of the impeller blades caused by machining for adjacent areas. In addition, the over-all axial length of each shroud 5', 6', 7' is greater than the over-all axial length of each shroud 5, 6, 7, respectively, by an amount substantially corresponding to the axial change in dimension of the impeller blades caused by machining. Further, the axial dimension of each flange 29', 30', 31', of the shrouds 5', 6', 7' is larger than the axial dimension of the flanges 29, 30, 31 of the shrouds 5, 6, 7, respectively, by an amount substantially equal to the axial change in dimension of the blades 24 caused by machining the diffusers.

While a single preferred embodiment of the present invention has been specifically illustrated and described without illustrating any variations, modifications or other embodiments, there is no intention to be solely limited thereto, and further modifications, embodiments and variations are contemplated according to the broader aspects of the present invention. The teachings of the present invention may be employed in other and quite different fluid reactor device environments although they are specifically well suited to the critical requirements of the specifically set forth embodiment of a high speed compressor.

The compressor of the present invention is provided with two sets of shrouds, which are constructed of relatively cheap material, for example aluminum, and of a minimum dimension to reduce their over-all storage bulk and expense. For a change of capacity, the compressor is constructed for easy disassembly and uniform machining of the impeller blades along their curved intermediate free edges and uniform machining of the diffuser blades only along a common radial plane, which radial plane machining is the easiest to accomplish and least expensive. The machining of the diffusers is further facilitated by the minimum size of the diffusers, their separate construction and the use of an easily machinable material such as aluminum. With the proper sizing of the replacement shrouds, the clearances between impeller blades and the shrouds are maintained for maximum performance and efficiency, and the through flow cross section of the diffusers is changed expeditiously to correspond to the change in capacity of the impellers. The machining of the impeller blades along their curved free edges 22 will assure a maximum efficiency of the impeller blades both before and after machining by maintaining their design shapes, which is particularly seen if laminar flow through the impellers is assumed and the machining is conducted along one of the lines of flow so that the inner flow characteristics through the impellers are substantially unchanged by machining. This last analysis would also be true of flow through the diffusers. Further advantages or machining along the curved edges of the impeller blades are realized from the fact that this will have a minimum affect upon the rotor balance, which is critical for high speed operation; this is true because a very small total quantity of metal will be removed due to the thinness of the blades adjacent their edges 22. Machining of the diffuser blades will be particularly inexpensive and easy to accomplish due to the fact that it is conducted along a common plane for each diffuser.

Thus, the capacity of the compressor may be changed with a minimum amount of effort while maintaining the efficiency of the device even at high speeds. Further, the extremely expensive and critical rotor does not have to be replaced and there is no added expense of buying and storing a separate rotor, because it is only necessary to purchase a second replacement set of relatively small inexpensive shrouds which will take up little room in storage.

Claims

What is claimed is:

1. A method of changing the capacity of a fluid reaction device having a fluid reaction wheel provided with a plurality of blades peripherally arranged on a hub, with each blade having an axially extending radial flow edge, a radially extending axial flow edge, a root portion extending between said edges and a connecting outer free edge extending between the axial flow and radial flow edges, and a stationary shroud having an annular surface substantially corresponding to and closely adjacent the connecting edges of the blades, including the steps of: providing a second shroud having an annular surface corresponding in shape to the connecting edges of the blades and having diameters correspondingly less than the diameters of the connecting edges; and machining the entire connecting edge of each blade by an amount for operative reception within the second shroud to produce a reduced flow capacity upon relative rotation.

2. The method of claim 1 including providing an annular stationary diffuser separate from the shrouds and provided with integral diffuser blades having free radially extending edges, with all of the edges lying in a common radial plane; and machining the free radially extending edge of each diffuser blade by an amount that will produce a corresponding diffuser capacity change.

3. The method of claim 2, including providing structural means separate from the shrouds and diffuser to form an annular chamber in direct fluid communication with the space between diffuser blades and further providing a cylindrical casing separately receiving therein said diffuser, the shrouds and the means forming the chamber.

4. The method of claim 1 wherein each of said steps is repeated on other fluid reaction wheels mounted on a common rotor to constitute separate fluid reaction stages.

5. The method of claim 1 wherein each blade has its axial and radial edges peripherally offset to correspondingly twist its curved edge.

6. The method of claim 1 wherein the fluid reaction device is a multi-stage compressor having an overhung rotor.