Methods and mechanisms for surge avoidance in multi-stage centrifugal compressors

Abstract

A turbomachine includes a casing having an inlet end opposite an outlet end along a longitudinal axis of the casing; a shaft assembly provided within the casing, the shaft assembly extending from the inlet end to the outlet end; a plurality of rotating impellers extending radially outward from the shaft assembly; and a communication channel defined between two adjacent impellers to permit a backflow of fluid from a diffuser channel of a downstream impeller to a return channel of an adjacent upstream impeller.

Claims

1. A turbomachine, comprising: a casing having an inlet end opposite an outlet end along a longitudinal axis of the casing; a shaft assembly provided within the casing, the shaft assembly extending from the inlet end to the outlet end; a plurality of rotating impellers extending radially outward from the shaft assembly; and a communication channel defined between two adjacent impellers to permit a backflow of fluid from a diffuser channel of a downstream impeller to a return channel of an adjacent upstream impeller, wherein the communication channel is a borehole defined in the casing between the two adjacent impellers.

2. The turbomachine of claim 1, wherein the communication channel is defined in the casing between the two adjacent impellers.

3. The turbomachine of claim 1, wherein the two adjacent impellers are positioned directly next to each other on the shaft assembly without an additional impeller positioned therebetween.

4. The turbomachine of claim 1, wherein the turbomachine is a multi-stage centrifugal compressor.

5. The turbomachine of claim 1, wherein a control valve is positioned within the communication channel to control a volume of fluid that is directed through the communication channel.

6. The turbomachine of claim 5, wherein the control valve is a check valve.

7. The turbomachine of claim 5, wherein the control valve is configured to permit the fluid to flow upstream, while preventing the fluid from flowing downstream between the two adjacent impellers.

8. The turbomachine of claim 5, wherein the control valve is configured to permit the fluid to flow upstream between the two adjacent impellers only after a predetermined pressure is achieved with the fluid.

9. A turbomachine, comprising: a casing having an inlet end opposite an outlet end along a longitudinal axis of the casing; a shaft assembly provided within the casing, the shaft assembly extending from the inlet end to the outlet end; a plurality of rotating impellers extending radially outward from the shaft assembly; a communication channel defined between two adjacent impellers to permit a backflow of fluid from a diffuser channel of a downstream impeller to a return channel of an adjacent upstream impeller; and a disk member rotatably positioned on the shaft assembly between the two adjacent impellers.

10. The turbomachine of claim 9, wherein the disk member defines at least one opening that is configured to be rotated between a first position in which the at least one opening is in line with the communication channel and a second position in which the at least one opening is rotated away from the communication channel.

11. The turbomachine of claim 9, further comprising a control mechanism configured to rotate the disk member.

12. The turbomachine of claim 9, wherein the communication channel is defined in the casing between the two adjacent impellers.

13. The turbomachine of claim 9, wherein the two adjacent impellers are positioned directly next to each other on the shaft assembly without an additional impeller positioned therebetween.

14. The turbomachine of claim 9, wherein the communication channel is a borehole defined in the casing between the two adjacent impellers.

15. The turbomachine of claim 9, wherein the turbomachine is a multi-stage centrifugal compressor.

16. The turbomachine of claim 9, wherein the disk member defines a plurality of circumferentially spaced openings.

17. A method of reducing surge in a turbomachine, comprising: directing fluid through an inlet of the turbomachine; directing the fluid through at least one stage of the turbomachine; recycling a portion of the fluid upstream from a downstream impeller to an adjacent upstream impeller via a communication channel defined in the turbomachine between the two adjacent impellers, wherein the communication channel is a borehole defined in a casing between the two adjacent impellers; and directing the recycled fluid downstream in the turbomachine.

18. The method of claim 17, wherein a control valve is positioned within the communication channel.

19. The method of claim 17, wherein a disk member is provided between the adjacent impellers to control a flow of fluid through the communication channel.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a partial-cutaway perspective view of a multi-stage, centrifugal-flow turbomachine in accordance with a prior art example;

(2) FIG. 2 is a schematic cross-sectional view of one stage of the turbomachine shown in FIG. 1;

(3) FIG. 3 is a cross-sectional view of a turbomachine according to an example of the present disclosure;

(4) FIG. 4 is a cross-sectional view of a portion of a turbomachine according to another example of the present disclosure;

(5) FIG. 5 is another cross-sectional view of the turbomachine of FIG. 4;

(6) FIG. 6 is a cross-sectional perspective view of the turbomachine of FIG. 4;

(7) FIG. 7 is another cross-sectional perspective view of the turbomachine of FIG. 4; and

(8) FIG. 8 is a cross-sectional perspective view of the turbomachine of FIG. 4 according to another example of the present disclosure.

DETAILED DESCRIPTION OF THE INVENTION

(9) For purposes of the description hereinafter, the terms “end”, “upper”, “lower”, “right”, “left”, “vertical”, “horizontal”, “top”, “bottom”, “lateral”, “longitudinal”, and derivatives thereof shall relate to the invention as it is oriented in the drawing figures. However, it is to be understood that the invention may assume various alternative variations and step sequences, except where expressly specified to the contrary. It is also to be understood that the specific devices and processes illustrated in the attached drawings and described in the following specification are simply exemplary embodiments or aspects of the invention. Hence, specific dimensions and other physical characteristics related to the embodiments or aspects disclosed herein are not to be considered as limiting.

(10) With reference to FIG. 3, a multi-stage centrifugal compressor 200, such as the turbomachine shown in FIGS. 1 and 2, is illustrated. The compressor 200 may include a shaft 202 supported within a casing 204 by a pair of bearings. The compressor 200 may include a plurality of stages to progressively increase the fluid pressure of the working fluid through the compressor 200. Each stage is successively arranged along the longitudinal axis of the compressor 200, and all stages may or may not have similar components operating on the same principle.

(11) With continued reference to FIG. 3, each stage of the compressor 200 may include an impeller 205 that includes a plurality of rotating blades circumferentially arranged and attached to the impeller 205 which is in turn attached to the shaft 202. A plurality of impellers 205 may be spaced apart in multiple stages along the axial length of the shaft 202. The rotating blades may be fixedly coupled to the impeller 205 such that the rotating blades along with the impeller 205 rotate with the rotation of the shaft 202. The working fluid, such as a gas mixture, enters and exits the compressor 200 generally in the radial direction of the shaft 202. The rotation of the blades supplies the energy to the fluid. In a centrifugal compressor, the cross-sectional area between the rotating blades 60 within the impeller 205 decreases from an inlet end to a discharge end, such that the working fluid is compressed as it passes across the impeller 205.

(12) Working fluid, such as a gas mixture, moves from an inlet end (suction end) 206 to an outlet end (discharge end) 208 of the compressor 200. A diffuser channel 212 is provided at the outlet of the rotating blades of the impeller 205 for homogenizing the fluid flow coming off the rotating blades. The diffuser channel 212 optionally has a plurality of diffuser vanes extending within the casing 204. In a multi-stage compressor 200, a plurality of return channels 214 are provided at the outlet end of a fluid compression stage for channeling the working fluid to the rotating blades of the next successive stage. The last impeller 205 in a multi-stage turbomachine typically only has a diffuser channel 212, which may be provided with or without the diffuser vanes. The last diffuser channel 212 directs the flow of working fluid to a discharge casing (generally volute) having an exit flange for connecting to the discharge pipe.

(13) With continued reference to FIG. 3, internal recycling of the working fluid is performed by establishing connections or communication channels 216 between the diffuser channel 212 of a downstream impeller 205 and the return channel 214 of an upstream impeller 205. In a specific example, a communication channel 216 is established between a diffuser channel 212 of a given stage and the upstream return channel 214 at multiple, equally circumferentially spaced locations in the compressor 200. In one example, the communication channel 216 is established between two directly adjacent impellers 205 such that there is no additional impeller positioned between the two adjacent impellers 205. A portion of the working fluid is internally recycled from the diffuser channel 212 of the given stage back to the upstream return channel 214 via the communication channel 216. In one example of the present disclosure, the communication channel 216 may be an aperture or borehole defined in the casing 204 of the compressor 200 that permits the working fluid to pass through to reduce the surge in the compressor 200.

(14) The recycled fluid enters the impeller 205 downstream of the return channel 214 and thus increases the impeller through flow and moves impeller operating conditions away from the surge phenomenon. In another example, the communication channel 216 includes a control valve 218 housed within an aperture defined in the casing 204 of the compressor 200. The control valve 218 may be a check valve or any other valve that is configured to control the flow of working fluid therethrough. In one example, the check valve 218 may only permit the working flow to move from the diffuser channel 212 to the upstream return channel 214 but not from the upstream return channel 214 to the downstream diffuser channel 212. The control valve 218 may only permit the working fluid to pass therethrough after a predetermined pressure has been reached by the working fluid. While only a single communication channel 216 is shown in FIG. 3, it is to be understood that a plurality of communication channels 216 may be provided at the same or similar locations spaced circumferentially from one another about the same point between the diffuser channel 212 and the return channel 214. In one example, each of the plurality of communication channels 216 at the same point are circumferentially equally spaced from one another. The plurality of communication channels creates a generally uniform distribution of flow from the downstream diffuser channel 212 to the upstream return channel 214. The check valves may be operated using an active feedback or a passive feedback mechanism utilizing electrical, magnetic, mechanical, pneumatic, or hydraulic mechanisms.

(15) With continued reference to FIG. 3, in another example of the present disclosure, the compressor 200 may include an arrangement 215 for global recycling in the compressor 200 as well as the stage-by-stage recycling described above. The arrangement 215 may include a return channel 217 that directs working fluid that exits the outlet end 208 to the inlet end 206 of the compressor 200 to further assist in reducing surge in the compressor 200. A global recycling arrangement 215 delivers a metered amount of additional flow from the compressor outlet end 208 to the flow through the inlet end 206 (generally across pressure boundary) in order to move the compressor 200 toward operating conditions away from the surge. It is called global because the said fluid is delivered to the first stage and travels the entire compressor flow path regardless of which stage is in surge.

(16) The internal stage-wise recycling of the working fluid provides a much more controlled flow recycling to affect only those stages of the compressor 200 that may be on the verge of surge. The amount of working fluid flow needed for such an arrangement is much smaller than highly conservative global recycling arrangements. Furthermore, the working fluid flow does not leave the compressor casing 204 and, therefore, does not cross the pressure boundary. In comparison to global recycling arrangements, the currently disclosed internal stage-wise recycling arrangement has less pressure loss depending on the application and specific control design.

(17) With reference to FIG. 4, another example of the present disclosure is shown and described. In this example, instead of providing the control valve 218 in the communication channel 216, a slotted disk member 220 intersecting with the communication channel 216 is provided within the casing 204. The disk member 220 may be rotationally held on the shaft 202 that extends longitudinally through the casing 204 of the compressor 200 such that the disk member 220 may be rotated about the shaft 202. In one example, the disk member 220 may be held between diaphragms 221 provided in two adjacent stages of the compressor 200. Actuation of the disk member 220 may be achieved using a control mechanism 222 operated by a user of the compressor 200. It is also contemplated that the control mechanism 222 includes pre-programmed instructions for actuating the disk member 220 based on predetermined conditions of the compressor 200 or predetermined time intervals during operation of the compressor 200. According to an example, the control mechanism 222 may be a hydraulic, pneumatic, electric, magnetic, or mechanical actuator that is placed outside of the compressor casing 204.

(18) With reference to FIGS. 5-7, the slotted disk 220 may define a plurality of circumferentially spaced openings 224 that extend therethrough. In one example, the openings 224 are circular in shape, but it is also contemplated that the openings 224 can have other shapes as well, including square, triangular, oval, and any other suitable shape. As shown in FIG. 8, in another example of the present disclosure, the openings 224 are generally rectangular in shape. During operation of the recycling process, the openings 224 of the slotted disk 220 are configured to align with a respective communication channel 216 defined in the casing 204 of the compressor 200. The disk member 220 may be rotated tangentially to establish and prevent fluid communication through the communication channel 216 via the openings 224 of the disk member 220. During rotation of the disk member 220, the alignment of the openings 224 with the communication channel 216 varies, allowing varying volumes of working fluid flow to pass therethrough.

(19) In one position of the disk member 220, the communication channel 216 is completely blocked off by the disk member 220, thereby providing a complete stoppage of working fluid flow between the two stages of the compressor 200. A suitable sealing arrangement is also provided between the disk member 220 and the casing 204 of the compressor 200 to prevent unintentional leakage. In this position, the openings 224 of the disk member 220 are not aligned with the respective communication channel 216. In another position of the disk member 220, at least one opening 224 of the disk member 220 is aligned with the communication channel 216, thereby permitting a working fluid flow through the communication channel 216 to be directed from the downstream stage of the compressor 200 to the adjacent upstream stage of the compressor 200 to avoid surge in the compressor 200. This use of the disk member 220 provides an improved stage-to-stage surge control arrangement that utilizes stage return flow control valves to control the volume of working fluid that is directed from a downstream stage of the compressor 200 to an upstream stage of the compressor 200. The disk member 220 may be housed in the diaphragm 221 between adjacent stages of the compressor 200, such that the compressor 200 will include a corresponding number of disk members 220 and diaphragms 221. For example, a five-stage compressor would include four rotatable disk members 220. It is also contemplated that the number of openings 224 defined in the disk member 220 would correspond to the number of communication channels 216 defined in the casing 204 of the compressor 200 at the corresponding stage. By using the disk member 220, only a single moving component and one penetration to the exterior of the compressor casing 204 is required for the recycling process. This present stage-to-stage recycling arrangement provides a wider operating range for the compressor 200 and a faster response to changing operating conditions within the compressor 200.

(20) In another example of the present disclosure, a method of recycling working fluid within the compressor 200 to avoid surge in the compressor 200 is also provided. Using this method, the working fluid is recycled between adjacent impeller stages instead of from the outlet or discharge end 208 of the compressor 200 all the way back to the inlet end 206 of the compressor 200 (see FIG. 3). In one example, the working fluid may be directed into the inlet end 206 of the compressor 200. The working fluid is then directed through at least two stages of the compressor 200. At least a portion of the working fluid is recycled from the downstream impeller 205 to the upstream impeller 205 via a connection or communication channel 216 defined in the compressor 200 between the two adjacent impellers 205. The recycled working fluid may then be directed downstream again toward the downstream impeller 205.

(21) It is to be understood that the invention may assume various alternative variations and step sequences, except where expressly specified to the contrary. It is also to be understood that the specific devices and processes illustrated in the attached drawings and described in the specification are simply exemplary embodiments or aspects of the invention. Although the invention has been described in detail for the purpose of illustration based on what are currently considered to be the most practical and preferred embodiments or aspects, it is to be understood that such detail is solely for that purpose and that the invention is not limited to the disclosed embodiments or aspects, but, on the contrary, is intended to cover modifications and equivalent arrangements that are within the spirit and scope thereof. For example, it is to be understood that the present invention contemplates that to the extent possible, one or more features of any embodiment or aspect can be combined with one or more features of any other embodiment or aspect.