Gas compression apparatus and method with noise attenuation

Background

This invention is directed to a gas compression apparatus and method in which the acoustic energy caused by a rotating impeller of the apparatus is attenuated.

Gas compression apparatus, such as centrifugal compressors, are widely used in different industries for a variety of applications involving the compression, or pressurization, of a gas. These types of compressors utilize an impeller that rotates in a casing at a relatively high rate of speed to compress the gas. However, a typical compressor of this type produces a relatively high noise level, caused at least in part, by the rotating impeller, which is an obvious nuisance and which can cause vibrations and structural failures. International patent application WO 02/052110 A1 discloses a double layer acoustic liner for attenuating noise and consisting of a plurality of uniform depth cells formed in a plate in a manner to form an array of resonators to attenuate the dominant frequency of an axial compressor in a casing. United Kingdom patent application GB 2 237 323 A discloses a fan silencer apparatus where a plurality of differently tuned attenuating chambers are disposed upstream or downstream of a fan. The attenuating chambers are employer as Helmholtz resonators through a hole in one wall of each chamber. The holes may be of different sizes to suppress different frequencies. The transverse dimensions of the chambers vary, but the chambers all employ constant depth. International patent application WO 02/052109 A1 discloses an acoustic attenuation liner for attenuating noise by means of a plurality of constant depth cells formed in a plate to provide an array of resonators to suppress sound in an axial compressor where an impeller rotates within a casing.

Brief Description of the Drawings

Fig. 1 is a cross-sectional view of a portion of a gas compression apparatus incorporating acoustic attenuation according to an embodiment of the present invention.

Fig. 2 is an enlarged cross-sectional view of a base plate of the apparatus of Fig. 1.

Fig. 3 is a view, similar to that of Fig. 2, but depicting an alternate embodiment of the base plate of Fig. 2.

Detailed Description

Fig. 1 depicts a portion of a high pressure, gas compression apparatus, such as a centrifugal compressor, including a casing 10 having an inlet 10a for receiving a fluid to be compressed, and an impeller cavity 10b for receiving an impeller 12 which is mounted for rotation in the cavity. It is understood that a power-driven shaft (not shown) rotates the impeller 12 at a high speed, sufficient to impart a velocity pressure to the gas drawn into the casing 10 via an inlet 10a. The casing 10 extends completely around the shaft and only the upper portion of the casing is depicted in Fig. 1.

The impeller 12 includes a plurality of impeller blades 12a (one of which is shown) arranged axi-symmetrically around the latter shaft and defining a plurality of passages 12b. Due to centrifugal action of the impeller blades 12a and the design of the casing 10, gas entering the impeller passages 12b from the inlet 10a is compressed to a relatively high pressure before it is discharged into a diffuser passage, or channel, 14 extending radially outwardly from the impeller cavity 10b and defined between two annular facing interior walls 10c and 10d in the casing 10. The channel 14 receives the high pressure gas from the impeller 12 before the gas is passed to a volute, or collector, 16 also formed in the casing 10 and in communication with the channel. The channel 14 functions to convert the velocity pressure of the gas into static pressure, and the volute 16 couples the compressed gas to an outlet (not shown) of the casing. It is understood that conventional labyrinth seals, thrust bearings, tilt pad bearings and other similar hardware can also be provided in the casing 10 which function in a conventional manner and therefore will not be shown or described.

An annular plate 20 is mounted in a recess, or groove, formed in the interior wall 10a, with only the upper portion of the plate being shown, as viewed in Fig. 1. As better shown in Fig. 2, a plurality of relatively large-diameter cells, or openings, three of which are shown in Fig. 2 and referred to by the reference numerals 34a, 34b and 34c, are formed through one surface of the plate 20.

Also, a plurality of series of relatively small-diameter cells, or openings, three of which are shown and referred to by the reference numerals 36a, 36b and 36c, are formed through the opposite surface of the plate. Each cell in the series 36a bottoms out, or terminates, at the bottom of the cell 34a so that the depth of the cell 34a combined with the depth of each cell of the series 36a extend for the entire thickness of the plate 20. The series 36b is associated with the cell 34b, and the series 36c is associated with the cell 34c in an identical manner. The number of cells in each series 36a, 36b, and 36c can vary according to the application and they can be randomly disposed relative to their corresponding cells 34a, 34b, and 34c, respectively, or, alternately, they can be formed in any pattern of uniform distribution.

The cells 34a, 34b, and 34c, and the cells of the series 36a, 36b, and 36c can be formed in any conventional manner such as by drilling counterbores through the corresponding opposite surfaces of the plate 20. As shown in Fig. 1, the cells 34a, 34b, and 36c are capped by the underlying wall of the aforementioned groove formed in the casing 10, and the open ends of the cells in the series 36a, 36b, and 36c communicate with the diffuser channel 14.

As better shown in Fig. 2, the depth, or thickness of the plate 20 is constant over its entire area and the respective depths of the cells 34a, 34b, and 34c, and the cells in the series 36a, 36b, and 36c and 36 vary in a radial direction relative to the plate 20. In particular, the depths of the cells 34a, 34b, and 34c decrease from the radially outer portion of the plate 20 (the upper portion as viewed in Fig. 2) to the radially inner portion of the plate. Thus, the depths of the cells of the series 36a, 36b, and 36c increases from the radially outer portion to the radially inner portion of the plate 20.

Although only three large-diameter cells 34a, 34b, and 34c and three series of small-diameter cells 36a, 36b, and 36c are shown and described herein, it is understood that additional cells are provided that extend around the entire surfaces of the annular plate 20.

In operation, a gas is introduced into the inlet 10a of the casing 10, and the impeller 12 is driven at a relatively high rotational speed to force the gas through the inlet 10a, the impeller cavity 10b, and the channel 14, as shown by the arrows in Fig. 1. Due to the centrifugal action of the impeller blades 12a, the gas is compressed to a relatively high pressure. The channel 14 functions to convert the velocity pressure of the gas into static pressure, and the compressed gas passes from the channel 14, through the volute 16, and to the outlet of the casing 10 for discharge.

Due to the fact that the cells in the series 36a, 36b, and 36c connect the cells 34a, 34b, and 34c to the diffuser channel 14, all of the cells work collectively as an array of acoustic resonators which are either quarter-wave resonators or Helmholtz resonators or in accordance with conventional resonator theory. This significantly attenuates the sound waves generated in the casing 10 caused by the fast rotation of the impeller 12, and by its interaction with diffuser vanes in the casing, and eliminates, or at least minimizes, the possibility that the noise will by-pass the plate 20 and pass through a different path.

Moreover, the dominant noise component commonly occurring at the passing frequency of the impeller blades 12a, or at other high frequencies, can be effectively lowered by tuning the cells 34a, 34b, and 34c, and the cells in the series 36a, 36b, and 36c so that the maximum sound attenuation occurs around the latter frequency. This can be achieved by varying the volume of the cells 34a, 34b, and 34c, and/or the cross-sectional area, the number, and the depth of the cells in the each series 36a, 36b, and 36c. Also; given the fact that the frequency of the dominant noise component varies with the speed of the impeller 12, the number of the cells in each series 36a, 36b, and 36c per each larger cell 34a, 34b, and 34c, respectively, can be varied spatially across the plate 20 so that noise is attenuated in a relatively broad frequency band. Consequently, noise can be efficiently and effectively attenuated, not just in constant speed devices, but also in variable speed devices.

In addition, the employment of the acoustic resonators, formed by the cells 34a, 34b, and 34c and the cells in the series 36a, 36b, and 36c, in the plate, as a unitary design, preserves or maintains a relatively strong structure which has little or no deformation when subject to mechanical and thermal loading. As a result, these acoustic resonators have no adverse effect on the aerodynamic performance of the gas compression apparatus.

An alternate version of the plate 20 is depicted in Fig. 3 and is referred to, in general, by the reference numeral 40. The plate 40 is mounted in the same manner and at the same location as the plate 20 and only the upper portion of the plate is shown in Fig. 3. The depth, or thickness, of the plate 40 decreases from the radially outer portion of the plate (the upper portion as viewed in Fig. 3) to the radially inner portion of the plate.

A plurality of relatively large-diameter cells, or openings, three of which are shown in Fig. 3 and referred to by the reference numerals 44a, 44b and 44c, are formed through one surface of the plate 40. Also, a plurality of series of relatively small-diameter cells, or openings, three of which are shown and referred to by the reference numerals 46a, 46b and 46c, are formed through the opposite surface of the plate.

Each cell in the series 46a bottoms out, or terminates, at the bottom of the cell 44a so that the depth of the cell 44a combined with the depth of each cell of the series 46a extend for the entire thickness of the corresponding portion of the plate 40. The series 46b is associated with the cell 44b and the series 46c is associated with the cell 44c in an identical manner. The number of cells in each series 46a, 46b, and 46c can vary according to the application, and the latter cells can be randomly disposed relative to their corresponding cells 44a, 44b, and 44c, respectively or, alternately, can be formed in any pattern of uniform distribution.

The cells 44a, 44b, and 44c, and the cells of the series 46a, 46b, and 46c can be formed in any conventional manner such as by drilling counterbores through the corresponding opposite surfaces of the plate 40. As in the case of the plate 40 of Fig. 2 the cells 44a, 44b, and 46c, when placed in the casing 10, are capped by the underlying wall of the aforementioned groove formed in the casing 10, and the open ends of the cells in the series 46a, 46b, and 46c communicate with the diffuser channel 14.

The respective depths of the cells 44a, 44b, and 44c, and the cells in the series 46a, 46b, and 46c increase with the thickness of the plate 40 from the radially outer portion of the plate (the upper portion as viewed in Fig. 3) to the radially inner portion of the plate.

Although only three large-diameter cells 44a, 44b, and 44c and three series of small-diameter cells 46a, 46b, and 46c are shown and described in connection with the embodiment of Fig. 3, it is understood that they extend around the entire surfaces of the annular plate 40.

Thus, the plate 40, when mounted in the casing 10 in the same manner as the plate 20 enjoys all the advantages discussed above in connection with the plate 20.

Variations and Equivalents

The specific technique of forming the cells 34a, 34b, 34c, 44a, 44b, and 44c and the cells in the series 36a, 36b, 36c, 46a, 46b, and 46c can vary from that discussed above. For example, a one-piece liner can be formed in which the cells are molded in their respective plates.

The relative dimensions, shapes, numbers and the pattern of the cells 34a, 34b, 34c, 44a, 44b, and 44c and the cells in the series 36a, 36b, 36c, 46a, 46b, and 46c can vary.

The above design is not limited to use with a centrifugal compressor, but is equally applicable to other gas compression apparatus in which aerodynamic effects are achieved with movable blades.

The plates 20 and 40 can extend for 360 degrees around the axis of the impeller as disclosed above; or it can be formed into segments each of which extends an angular distance less than 360 degrees.

The spatial references used above, such as "bottom," "inner," "outer," "side," "radially outward," "radially inward," etc., are for the purpose of illustration only and do not limit the specific orientation or location of the structure.

Since other modifications, changes, and substitutions are intended in the foregoing disclosure, it is appropriate that the appended claims be construed broadly and in a manner consistent with the scope of the invention.