Patent Application
20120328409
The present application and the resultant patent relate generally to turbo-machinery such as steam turbines and the like and more particularly relates to systems and methods for cooling the early stages of high pressure and intermediate pressure sections of a steam turbine and a rotor extending therebetween while limiting leakage flows therein.
Steam turbines extract work from a flow of steam to generate power. A typical steam turbine may include a rotor associated with a number of wheels. The wheels may be spaced apart from each other along the length of the rotor and define a series of turbine stages. The turbine stages are designed to extract useful work from the steam traveling on a flow path from an entrance to an exit of the turbine in an efficient manner. As the steam travels along the flow path, the steam causes the wheels to drive the rotor. The steam gradually may expand and the temperature and pressure of the steam gradually may decrease. The steam then may be exhausted from the exit of the turbine for reuse or otherwise. Higher temperature steam turbines may generate increased output as the increased temperature of the steam increases the overall energy available for extraction.
Generally described, a typical steam turbine may include a high pressure section, an intermediate pressure section, and a low pressure section. The sections may be arranged in series with each section including any number of stages. Within the sections, work is extracted from the steam to drive the rotor. Between the sections, the steam may be reheated for performing work in the next section. The high pressure and the intermediate pressure sections may operate at relatively high temperatures so as to increase the overall steam turbine output.
Although most of the flow of steam performs work in the steam turbine by flowing through the stages as described above, a portion of the flow of steam may be lost due to leakage. The steam in the leakage flow does not rotate the rotor or perform useful work. Leakage steam thus represents a loss of rotor torque and overall steam turbine output and efficiency.
Sealing members may be used in the steam turbine to reduce the leakage flow. Overall rotor torque thus may be increased by reducing the amount of the leakage flow. An example of a sealing member is an end packing head. The end packing head may be positioned near end portions of a pressurized section of the steam turbine. For example, one end packing head may be disposed over a portion of the rotor at an upstream side of a first stage bucket. The end packing head may be configured to reduce an amount of steam flowing between the end packing head and the rotor in a direction away from the first stage bucket. A measurable amount of leakage steam, however, still may pass between the rotor and the end packing head.
There is therefore a desire for improved systems and methods for cooling the wheel spaces of high temperature sections and reducing leakage steam, particularly in the case of leakage steam that has not performed useful work. Such improved systems and methods should improve overall system efficiency and output.
The present application and the resultant patent thus provide a section cooling system for a steam turbine to limit a leakage flow therethrough. The section cooling system may include a first pressure flow extraction from a first section to a shaft packing location between the first section and a second section and a rotor aperture extending towards the first section. The first pressure flow extraction diverts the leakage flow from the first section into the rotor aperture so as to limit the leakage flow to the second section.
The present application and the resultant patent further provide a method of limiting a leakage flow between a high pressure section and an intermediate pressure section of a steam turbine. The method may include the steps of directing a high pressure steam extraction from the high pressure section to a shaft packing location, splitting the high pressure steam extraction into a high pressure flow directed towards the high pressure section and an intermediate pressure flow directed towards the intermediate pressure section, diverting the leakage flow towards the high pressure section with the high pressure flow, and cooling the intermediate pressure section with the intermediate pressure flow therethrough.
The present application and the resultant patent further provide for a section cooling system for a steam turbine to limit a leakage flow therethrough. The section cooling system may include a high pressure flow extraction from a high pressure section to a shaft packing location between the high pressure section and an intermediate pressure section and a rotor aperture extending through a rotor towards the high pressure section. The high pressure flow extraction diverts the leakage flow from the high section into the rotor aperture so as to limit the leakage flow into the intermediate pressure section.
These and other features and improvements of the present application and the resultant patent will become apparent to one of ordinary skill in the art upon review of the following detailed description when taken in conjunction with the several drawings and the appended claims.
Referring now to the drawings, in which like numerals refer to like elements throughout the several views,
In use, the flow of steam 40 enters the HP section 15 about the high pressure bowl 74. A portion of a flow of steam 40 escapes as the leakage flow 60 from the high pressure bowl 74 as well as from upstream and downstream sides of the first stage bucket 65 near the diaphragm 70 and extends along the rotor 30 towards the intermediate pressure section 20. This leakage flow 60 thus may be used to cool the wheel space 88 about the first stage bucket 80 of the IP section 20. This leakage flow 60 may be aided by a high pressure extraction 90 from the HP section 15. This high pressure extraction 90 may be from the sixth stage or other location of the HP section 15. The HP extraction 90 mixes with the leakage flow 60 and cools the leakage flow 60 coming from the high pressure section diaphragm 70 before entering into the first stage bucket 80 of the IP section 20. Other configurations and other components may be used herein.
As described above, the leakage flow 60 may have high enthalpy given that the leakage flow 60 has not performed any useful work with the turbine sections. The leakage flow 60 thus reduces overall steam turbine performance and efficiency. Further, the leakage flow 60 requires additional cooling from the high pressure extraction 90, resulting in a further performance toss, before being used to cool the early stage buckets 80 of the IP section 20.
The steam turbine 100 further includes an IP section 170. The IP section 170 also includes a number of intermediate pressure stages 180 with a first stage bucket and wheel 190 shown. Any number of intermediate pressure stages 180 may be used herein. The flow of steam 40 may enter the IP section 170 by an intermediate pressure bowl 200 about the bucket wheel 190 of the first intermediate pressure stage 180 through a first stage partition 195.
The steam turbine 100 also includes a shaft packing location 210 extending between the HP section 110 and the IP section 170. In this example, the shaft packing location N2 is shown. Other shaft packing locations 210 may be used herein. An end packing head 220 may be positioned about the rotor 140. The end packing head 220 includes a number of seal members 230 thereon. Any number and type of seal members 230 may be used herein. The length and configuration of the end packing head 220 may vary herein.
The steam turbine 100 also may include a section cooling system 240. The section cooling system 240 may include a high pressure extraction 250. The high pressure extraction 250 may be taken from about the second stage 122 or any other stage of the HP section 110 based upon temperature and pressure. The high pressure extraction 250 may split into a high pressure flow 260 and an intermediate pressure flow 270. The high pressure flow 260 may block the leakage flow 60 from reaching the IP section 170 coming from the HP section first stage 121. Rather, the leakage flow 60, as well as the high pressure flow 260, may be diverted downstream into the HP section 110 via a rotor aperture 280. The rotor aperture 280 may extend through the rotor 140 or otherwise to any stage 120 of the HP section 110. The rotor aperture 280 may be in communication with, for example, the fourth stage 124 or any other stage 120 of the HP section 110 based upon temperature and pressure. Further, a portion of the intermediate pressure flow 270 may be diverted by an intermediate pressure flow extraction 290. The intermediate pressure flow extraction 290 may be returned to the fifth stage 125 or any other stage 120 within the HP section 110. The remaining intermediate pressure flow 270 may be used to cool the IP stages 180 as described above. Other configurations and other components may be used herein. Dumping the flow through the rotor aperture 280 and the intermediate pressure extraction 290 will improve overall system efficiency and output. The intermediate pressure extraction 290 also may be directed to the intermediate pressure bowl 200 or any intermediate pressure stage 180 of the IP section 170.
The section cooling system 240 described herein thus uses cooler steam from the second stage 122 or any stage 120 of the HP section 110 based upon pressure and temperature as the high pressure extraction 250 into the shaft packing location N2. The use of the HP extraction 250 along with the rotor aperture 280 largely prevents or eliminates the leakage flow 60 from reaching the IP section 170. A resulting performance benefit thus is expected given that the leakage flow 60 is forced back into the HP section 110 so as to produce useful work instead of only being used for cooling. The amount of steam leaking towards the IP section 170 also may be reduced due to the temperature of the steam in the high pressure extraction 250 as opposed to the flow of steam 40 entering the intermediate pressure bowl 200. Increased efficiency thus may be provided herein without sacrificing the cooling efficiency and performance of the IP stages 180 using lower grade rotor materials in the high temperature sections. Lower cost rotor material also may help in bringing down the overall cost of the system. Moreover, higher steam temperatures may be used about the high pressure bowl 160 and the HP section 110 for further performance enhancements and improvements. A reduction in the overall span of the rotor 140 also may be possible. Overall costs likewise will be reduced.
It should be apparent that the foregoing relates only to certain embodiments of the present application and the resultant patent. Numerous changes and modifications may be made herein by one of ordinary skill in the art without departing front the general spirit and scope of the invention as defined by the following claims and the equivalents thereof.
