Patent Application
20130019600
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.
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.
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:
The detailed description explains embodiments of the invention, together with advantages and features, by way of example with reference to the drawings.
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
Turning now to
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
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.
