US20130019600A1

US20130019600A1 - Turbine exhaust arrangement

Info

Publication number: US20130019600A1
Application number: US13/185,145
Authority: US
Inventors: Sudhakar Neeli; Joshy John; Antanu Sadhu
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 2011-07-18
Filing date: 2011-07-18
Publication date: 2013-01-24
Also published as: FR2978201A1; DE102012106398A1; RU2012131213A

Abstract

An exhaust arrangement for a turbine is provided having an inner turbine casing, a condenser, an exhaust arrangement structure, and a bearing cone. The inner turbine casing includes a plurality of last stage buckets. A steam flow passes through the inner turbine casing and out of the plurality of last stage buckets. The condenser for receives the steam flow. The exhaust arrangement structure has a diffuser, a lower section and an upper section. The lower section has an exhaust section. The lower section receives the steam flow from the last stage buckets of the inner turbine casing through the diffuser and guides the steam flow out of the exhaust section in a direction generally towards the condenser. The upper section has a receiving section and a guiding section.

Description

BACKGROUND OF THE INVENTION

The subject matter disclosed herein relates to an exhaust arrangement for a turbine, and more specifically to an exhaust arrangement for a turbine having an exhaust arrangement structure for guiding steam flow into a condenser.
The steam exiting the last stage buckets of a steam turbine flows through a passage in a turbine casing and into a collector or exhaust hood. The steam then travels into a condenser. In one type of a steam turbine having a down flow type exhaust hood, the condenser is located below the exhaust hood and the steam is directed into the condenser in a generally downward direction. The exhaust hood typically includes an upper exhaust hood and a lower exhaust hood. A portion of the steam is directed into the lower exhaust hood and flows directly in the downward direction and into the condenser. The remaining steam in the upper exhaust hood is usually guided by a steam guide located in the upper exhaust hood and into the condenser. Specifically, the steam located in the upper exhaust hood is guided by the steam guide from a vertically upward direction into a vertically downward direction over an inner casing of the turbine. This arrangement tends to create a vortex flow behind the steam guide in the upper exhaust hood. The vortex flow reduces the effective flow area between the steam guide and an outer wall of the exhaust hood. The vortex flow also increases back pressure in the top portion of the exhaust hood, which in turn reduces the turbine's efficiency.
In an effort to increase turbine efficiency, the steam exiting the exhaust hood and entering the condenser should also have a generally smooth flow. However, achieving a relatively smooth flow into the condenser may be challenging because the steam flows in an axial direction out of the last stage buckets, but then changes direction and flows in a radial direction into the condenser. Several approaches exist to reduce or substantially eliminate the occurrence of vortex flow in the upper exhaust hood and provide a generally smooth flow of steam into the condenser. For example, in one approach an exhaust arrangement structure is placed within the exhaust hood. The exhaust arrangement structure includes a downstream channel that directs steam located in the upper exhaust hood into the condenser. However, this approach involves increasing the shaft length of the turbine, and also reduces the bearing cone foundation.
In another approach, multiple sets of vanes are placed in the exhaust hood. The vanes generally direct the steam exiting the last stage buckets from an axial direction into a radial direction. However, the vanes may not be effective at re-directing the flow of steam into the radial direction at some operating conditions. Therefore, it would be desirable to provide a cost effective and efficient exhaust flow arrangement that directs steam in the upper exhaust hood to the condenser.

BRIEF DESCRIPTION OF THE INVENTION

According to one aspect of the invention, an exhaust arrangement for a turbine is provided having an inner turbine casing, a condenser, an exhaust arrangement structure, and a bearing cone. The inner turbine casing includes a plurality of last stage buckets. A steam flow passes through the inner turbine casing and out of the plurality of last stage buckets. The condenser receives the steam flow. The exhaust arrangement structure has a diffuser, a lower section and an upper section. The lower section has an exhaust section. The lower section receives the steam flow from the last stage buckets of the inner turbine casing through the diffuser and guides the steam flow out of the exhaust section in a direction generally towards the condenser. The upper section has a receiving section and a guiding section. The receiving section receives the steam flow from the last stage buckets of the inner turbine casing through the diffuser. The guiding section is oriented in a direction generally radially outwardly from a center axis of the turbine and is in fluid communication with the receiving section. The exhaust section of the lower section is in fluid communication with the guiding section to direct the steam flow into the condenser. The bearing cone is positioned along the center axis of the turbine and partially defines the steam flow path in the lower section and the upper section.
These and other advantages and features will become more apparent from the following description taken in conjunction with the drawings.

BRIEF DESCRIPTION OF THE DRAWING

The subject matter, which is regarded as the invention, is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other features, and advantages of the invention are apparent from the following detailed description taken in conjunction with the accompanying drawings in which:

FIG. 1 is a cross-sectioned view of an exemplary steam turbine having an exhaust arrangement structure;

FIG. 2 is a cross-sectioned view of the exhaust arrangement structure shown in FIG. 1;

FIG. 3 is a perspective view of the exhaust arrangement structure shown in FIG. 1;

FIG. 4 is a bottom view of a portion of the exhaust arrangement structure shown in FIG. 1;

FIG. 5 is a perspective view of the exhaust arrangement structure shown in FIG. 1; and

FIG. 6 is an alternative embodiment of the exhaust arrangement structure shown in FIG. 5.

The detailed description explains embodiments of the invention, together with advantages and features, by way of example with reference to the drawings.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 is an illustration of an exemplary steam turbine 10 having a rotor 12, a plurality of turbine buckets 14, an inner turbine casing 16, a steam inlet 20, a condenser 22, and a guide plate that is an exhaust arrangement structure 30. In the embodiment as shown, the steam turbine 10 is a down flow type steam turbine where the condenser 22 is located below the exhaust arrangement structure, and steam is directed into the condenser 22 in a generally downward direction. In one exemplary embodiment, the steam turbine 10 could also be a double flow steam turbine, where opposing turbine buckets could be located on opposite axial sides of the turbine 10 to drive the rotor 12. The inner turbine casing 16 includes the plurality of turbine buckets 14 that provide a steam flow through the inner turbine casing 16. The steam flows out of the inner turbine casing 16 though a plurality of last stage buckets 32. The exhaust arrangement structure 30 is mounted to the inner turbine casing 16. Specifically, in the embodiment as shown, the exhaust arrangement structure 30 is attached to a downstream end 34 of the inner turbine casing 16. The condenser 22 is mounted in a location that is generally below the exhaust arrangement structure 30 for receiving steam flow.
A diffuser 40 is created between a bearing cone 44 and steam guides 46. The diffuser 40 is located between the downstream end 34 of the inner turbine casing 16 and is part of the exhaust arrangement structure 30. The diffuser 40 is employed to guide steam out of the inner turbine casing 16 and into the exhaust arrangement structure 30. The bearing cone 44 may include a generally frustoconical outer profile. The bearing cone 40 is placed in an axial direction that is generally parallel to a center axis A-A of the turbine 10, and is placed on the rotor 12 and located within the exhaust arrangement structure 30.
The exhaust arrangement structure 30 is employed to guide a steam flow 50 exiting the last stage buckets 32 of the inner turbine casing 16 and into the condenser 22. The exhaust arrangement structure 30 includes a lower section 54 and an upper section 56, a front wall 57 and an end wall 58. In the embodiment as shown, a portion of the front wall 57 creates the diffuser 40. The steam flow 50 exits the last stage buckets 32 flowing in a generally axial direction that may be substantially parallel with the center axis A-A of the turbine 10. The steam flow 50 is then re-directed by the lower section 54 and the upper section 56 of the exhaust arrangement structure 30 into a generally radial direction towards the condenser 22. Specifically, the lower section 54 of the exhaust arrangement structure 30 directs the steam flow 50 exiting the last stage buckets 32 in a generally radial direction with respect to the center axis A-A of the turbine 10, and towards the condenser 22. A lower portion 60 of the diffuser 40 and the steam guides 46 cooperate together to guide steam out of the last stage buckets 32 and into the lower section 54 of the exhaust arrangement structure 30. A lower outer surface 62 of the bearing cone 44 and the lower portion 60 of the diffuser 40 create a passageway 64 that defines a path for the steam flow 50. The steam flow 50 is guided though the passageway 64 and out of the exhaust arrangement structure 30 into the condenser 22. Specifically, an exhaust section 74 of the lower portion 54 guides the steam flow 50 in a generally radial direction into the condenser 22.
The upper section 56 of the exhaust arrangement structure 30 includes a receiving section 70 and a guiding section 72. The upper section 56 of the exhaust arrangement structure 30 is in fluid communication with the lower portion 54 of the exhaust arrangement structure 30. Specifically, the exhaust section 74 of the lower portion 54 receives the steam flow 50 from the upper section 56 and guides the steam flow 50 in a generally radial direction into the condenser 22. An upper portion 76 of the diffuser 40 and the steam guides 46 cooperate to guide the steam flow 50 exiting the last stage buckets 32 in an axial direction and into the receiving section 70 of the upper section 56 of the exhaust arrangement structure 30. An upper outer surface 78 of the bearing cone 44 and the upper portion 76 of the diffuser 40 create a passageway 80. As shown in FIG. 1, a portion of the steam flow 50 in the upper section 56 is guided though the passageway 80 and flows from a generally axial direction and into a generally vertical direction away from the condenser 22. That is, the steam flow 50 flowing through an uppermost portion 81 of the upper portion 56 of the exhaust structure 30 (shown in FIGS. 1-3) is oriented in a generally vertical direction away from the condenser 22.
Turning now to FIGS. 2-3, the exhaust arrangement structure 30 is illustrated. FIG. 2 is a side view of the exhaust arrangement structure 30. The exhaust arrangement structure 30 includes a front end 82 that attaches to the downstream end 34 of the inner turbine casing 16 (FIG. 1). The lower section 54 and the upper section 56 are each located between the front wall 57 and the end wall 58. FIG. 3 is a perspective view of the exhaust arrangement structure 30. Referring now to FIGS. 1-3, the guiding section 72 of the upper portion 56 is in fluid communication with and receives the steam flow 50 from the receiving section 70. The guiding section 72 is oriented to guide the steam flow 50 in a radial direction. Specifically, the steam flow 50 is guided in a direction that is oriented generally radially outwardly from the center axis A-A of the turbine 10. The exhaust section 74 of the lower section 54 is in fluid communication with and receives the steam flow 50 from the guiding section 72 of the upper section 56. The guiding section 74 directs the steam flow into the condenser 22 (shown in FIG. 1). FIGS. 2-3 also illustrate the steam flow 50 being guided out of the lower section 54 of the exhaust arrangement structure 30.
The vortex flow that occurs in conventional down flow exhaust hoods is reduced or substantially eliminated in the steam flow 50 located in the upper section 56 of the exhaust arrangement structure 30. Also, flow diffusion of the steam flow 50 in the upper section of the exhaust arrangement structure 30 is typically increased when compared to conventional down flow exhaust hoods. Increased flow diffusion usually results in a reduction of back pressure of the turbine, which results in greater turbine efficiency. Moreover, the exhaust arrangement structure 30 may be less expensive and complex when compared to some down flow hoods that are currently available. This is because the outer casing of the hood can be omitted, as the exhaust arrangement structure 30 acts as a guide to receive the steam flow from the last stage buckets 32 of the inner turbine casing 16. The exhaust arrangement structure 30 can be supported directly by a foundation of the turbine 10 (not shown), which results in enhanced machine reliability. Some approaches that are currently available may reduce vortex flow in a conventional exhaust hood, however some of these approaches involve increasing the shaft length of the turbine. Increasing the shaft length of the turbine will in turn increase the overall axial dimensions of the turbine. In contrast, the exhaust arrangement structure 30 does not substantially increase the length of the turbine 10.
Turning now to FIG. 4, a bottom view of a portion of the exhaust flow arrangement structure 30 is shown. The steam flow 50 enters the exhaust flow arrangement 30 at an inlet 94 located at the front end 82. A flow diffusion portion 90 of the exhaust arrangement structure 30 is indicated by a phantom line. The flow diffusion portion 90 of the exhaust arrangement structure 30 represents where flow diffusion of the steam flow 50 occurs. This is because a remaining portion 92 of the exhaust flow structure 30 is generally located within the inner turbine casing 16 (which is shown in FIG. 1), and therefore flow diffusion of the steam flow 50 can not typically occur. The flow diffusion portion 90 of the exhaust flow arrangement 30 has a height H that is measured between the end wall 58 of the exhaust arrangement structure 30 and an outer surface 97 of the exhaust arrangement structure 30. The height H can be adjusted depending on the particular system requirements of the turbine 10. Specifically, an increased height H of the portion 90 results in a greater Effective Area Ratio (EAR). The EAR is the ratio between the inlet 94 of the exhaust arrangement structure 30 and an outlet 96 (shown in FIG. 1) of the exhaust arrangement structure 30. A greater EAR results in greater pressure recovery of the steam flow 50 that flows through the exhaust flow arrangement 30.
FIGS. 5-6 illustrate a portion of the outer profile of the exhaust arrangement structure 30. Turning now to FIG. 5, in one embodiment, the flow diffusion portion 90 of the exhaust arrangement structure 30 includes an edge surface 98. Turning now to FIG. 6, in an alternative embodiment of an exhaust arrangement structure 130, a flow diffusion portion 190 may include a filleted edge 198 instead. The filleted edge 198 represents where the inner wall (not shown) of the exhaust arrangement structure 130 corresponds to the filleted edge 198. That is, an inner wall of the exhaust arrangement structure 130 includes a generally curved profile. The inner wall may also include other non-rectangular cross-sections as well, such as, for example, an elliptical profile. The curved profile may be used in an effort to enhance the flow characteristics of the exhaust arrangement structure 130.
While the invention has been described in detail in connection with only a limited number of embodiments, it should be readily understood that the invention is not limited to such disclosed embodiments. Rather, the invention can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the invention. Additionally, while various embodiments of the invention have been described, it is to be understood that aspects of the invention may include only some of the described embodiments. Accordingly, the invention is not to be seen as limited by the foregoing description, but is only limited by the scope of the appended claims.

Claims

1. An exhaust arrangement for a turbine, comprising:

an inner turbine casing including a plurality of last stage buckets, a steam flow passing through the inner turbine casing and out of the plurality of last stage buckets;

a condenser for receiving the steam flow;

an exhaust arrangement structure comprising:

a diffuser for guiding the steam flow out of the plurality of last stage buckets of the inner turbine casing;

a lower section having an exhaust section, the lower section receiving the steam flow from the plurality last stage buckets of the inner turbine casing through the diffuser and guiding the steam flow out of the exhaust section in a direction generally towards the condenser;

an upper section having a receiving section and a guiding section, the receiving section receiving the steam flow from the plurality of last stage buckets of the inner turbine casing through the diffuser and the guiding section oriented in a direction generally radially outwardly from a center axis of the turbine and in fluid communication with the receiving section, and the exhaust section of the lower section in fluid communication with the guiding section to direct the steam flow into the condenser; and

a bearing cone positioned along the center axis of the turbine and partially defining the steam flow path in the lower section and the upper section.

2. The exhaust arrangement of claim 1, wherein the exhaust arrangement structure is attached to a downstream end of the inner turbine casing.

3. The exhaust arrangement of claim 1, comprising a plurality of steam guides, wherein the diffuser and the steam guides cooperate together to guide the steam flow out of the plurality of last stage buckets of the inner turbine casing.

4. The exhaust flow arrangement of claim 1, wherein the bearing cone is positioned within the exhaust arrangement structure, and partially defines the lower section and the upper section.

5. The exhaust flow arrangement of claim 1, wherein the exhaust arrangement structure includes a flow diffusion portion, wherein flow diffusion of the steam flow occurs within the flow diffusion portion.

6. The exhaust flow arrangement of claim 5, wherein the flow diffusion portion includes a height that is measured between an end wall of the exhaust arrangement structure and an outer surface of the exhaust arrangement structure.

7. The exhaust flow arrangement of claim 6, wherein the height is adjustable depending on the system requirements of the turbine.

8. The exhaust flow arrangement of claim 7, wherein increasing the height results in a greater Effective Area Ratio (EAR), and wherein the EAR is the ratio between an inlet of the exhaust arrangement structure and an outlet of the exhaust arrangement structure.

9. The exhaust flow arrangement of claim 1, wherein a portion of an outer surface of the exhaust arrangement structure includes a filleted edge, and wherein an inner wall of the exhaust arrangement structure corresponds to the filleted edge.

10. The exhaust flow arrangement of claim 1, wherein the turbine is a double flow steam turbine.

11. A steam turbine, comprising:

an inner turbine casing having a downstream end and including a plurality of last stage buckets, a steam flow passing through the inner turbine casing and out of the plurality of last stage buckets;

a condenser for receiving the steam flow;

an exhaust arrangement structure attached to a downstream end of the inner turbine casing, the exhaust arrangement structure comprising:

a lower section having an exhaust section, the lower section receiving the steam flow from the plurality of last stage buckets of the inner turbine casing through the diffuser and guiding the steam flow out of the exhaust section;

a bearing cone positioned along the center axis of the and within the exhaust arrangement structure, the bearing cone partially defining the steam flow path in the lower section and the upper section.

12. The steam turbine of claim 11, comprising a plurality of steam guides, wherein the diffuser and the steam guides cooperate together to guide the steam flow out of the plurality of last stage buckets of the inner turbine casing.

13. The steam turbine of claim 11, wherein the exhaust arrangement structure includes a flow diffusion portion, wherein flow diffusion of the steam flow occurs within the flow diffusion portion.

14. The steam turbine of claim 13, wherein the flow diffusion portion includes a height that is measured between an end wall of the exhaust arrangement structure and an outer surface of the exhaust arrangement structure.

15. The steam turbine of claim 14, wherein the height is adjustable depending on the system requirements of the turbine.

16. The steam turbine of claim 15, wherein increasing the height results in a greater Effective Area Ratio (EAR), and wherein the EAR is the ratio between an inlet of the exhaust arrangement structure and an outlet of the exhaust arrangement structure.

17. The steam turbine of claim 11, wherein a portion of an outer surface of the exhaust arrangement structure includes a filleted edge, and wherein an inner wall of the exhaust arrangement structure corresponds to the filleted edge.

18. The steam turbine of claim 11, wherein the turbine is a double flow steam turbine.

19. A steam turbine, comprising:

a condenser for receiving the steam flow;

an exhaust arrangement structure comprising:

an upper section having a receiving section and a guiding section, the receiving section receiving the steam flow from the plurality of last stage buckets of the inner turbine casing through the diffuser and the guiding section oriented in a direction generally radially outwardly from a center axis of the turbine and in fluid communication with the receiving section, and the exhaust section of the lower section in fluid communication with the guiding section to direct the steam flow into the condenser;

a flow diffusion portion where flow diffusion of the steam flow occurs, the flow diffusion portion including a height that is measured between an end wall of the exhaust arrangement structure and an outer surface of the exhaust arrangement structure, the height being adjustable depending on the system requirements of the steam turbine; and

20. The steam turbine of claim 19, comprising a plurality of steam guides, wherein the diffuser and the steam guides cooperate together to guide the steam flow out of the plurality of last stage buckets of the inner turbine casing.