CLOSED LOOP AIR COOLING SYSTEM FOR COMBUSTION TURBINES

Abstract: Convective cooling of turbine hot parts using a closed loop system is disclosed. Preferably, the present invention is applied to cooling the hot parts of combustion turbine power plants, and the cooling provided permits an increase in the inlet temperature and the concomitant benefits of increased efficiency and output. In preferred embodiments, methods and apparatus are disclosed wherein air is removed from the combustion turbine compressor (22, 26) and delivered to passages internal to one or more of a combustor and turbine hot parts (100). The air cools the combustor and turbine hot parts via convection and heat is transferred through the surfaces of the combustor and turbine hot parts.

Description: CLOSED LOOP AIR COOLING SYSTEM FOR COMBUSTION TURBINES FTFT.Π ΩF THF TNVCTJTTΠN The present invention relates to turbomachinery, and more specifically, to the design of the cooling systems for combustion turbines. RArK-rtROTuMT) OF TWF. TWFNTTOTM The performance of a turbine can be enhanced by increasing the inlet temperature. However, as a result of the increased temperature, the turbine blades also operate at elevated temperatures, and these temperatures are often so high that they approach the material failure temperature for the turbine components. Schemes must therefore be devised to cool these "hot part" components, and in particular the fan blades, in order to ensure efficient and useful life cycles for these components. Typical "hoc parts" include the combustor basket, transitions, and turbine vane rotor and shaft components. It will be understood, however, that the cooling technique described herein is applicable to any component of a turbine that is at an elevated temperature. Prior art combustion turbines utilize cooling techniques that rely upon a film of cooler gases to prevent components such as the combustor from reaching critically high temperatures. A coolant, usually air, flows through passages within the components, and then is ejected througr. orifices in the surface of the component. A cool layer c. gases is created on the surface, thereby protecting the components from the heat generated in the main combustor c: by gases within the mam portion of the turbine. The techniques of cooling have grown more sophisticated as the inlet temperatures have increased and the sate of the art has advanced. For example, U.S. Patent 3 , 515,499--Beer et al discloses turbine blades that are created by being built up from individual "wafers" there by permitting the formation of internal fluid flow passageways and slots, thereby permitting airflow to more effectively cool the turbine blade. It is also well known to bleed coolant air from the compressor portion of a gas turbine and route this relatively cooler air to the hollow interior of the turbine blades. The heat transferred to this coolant is typically exhausted, thus creating an open loop system. The bled air effects not only the thermal balance of the equipment, but also impacts the performance by changing the characteristics of the flows within the turbine, altering the types of flow, film thicknesses and other important operating parameters This technique allows combustor inlet temperature, and thus turbine operating temperatures, to be increased beyond the allowable operating limits of the components, thereby increasing efficiency and output. It has been found, however, that the process of injecting the fluid into the main gas hot path is itself a detriment to combustion turbine output and efficiency in several ways. First, the election of coolant through the surface of the hot parts disrupts the flowfields around them and causes mixing losses, both of which the pressure losses through the system and decrease turbine expansion efficiency. Second, the main combustor hot gas path is cooled as the coolant is mixed into it, thereby decreasing turbine output and combustion turbine efficiency. It is also known to take advantage of the mechanical forces created by the rotation of the blade to effect heat transfer. If a liquid of appropriate specific gravity occupies a partially-filled cavity within a turbine blade, rotation of the blade will tend to force the fluid to the extreme tip of the cavity. However, this is the area of greatest heat, thus the liquid will vaporize and be displaced by any remaining liquid. The displaced gas will, by reason of the constant volume of the cavity, settle at the root section of the cavity, where it will give up heat and condense to a liquid, beginning the process all over again. This technique is explained, for example, in U.S. Patent No. 5, 201, 634--Hough discloses a turbine blade that has a core and internal passages filled with sodium. Centrifugal force and the temperature gradient between the core and the tips of the blades create a pressure gradient that causes the sodium to be vaporized and condensed. The heat required to effect vaporization is taken from the hot portion of the blade, and the heat given up upon condensation is absorbed at the internal core and transferred to cooler regions of the device. Similarly, U.S. Patent No. 4, 190, 398--Corsmeier et al . discloses individually cooling the blades of a turbine by the internal circulation of a fluid coolant. Heat from the fluid inside the turbine blades is transferred to engine lubrication oil, which is in turn cooled by transferring heat from the oil to the turbine fuel, thus at least a portion of the heat from the turbine blades is added back to the power cycle. U.S. Patent No. 3 , 738, 771--Delarbe et al . discloses hollow helical passageways that extend from the root to the tip of a turbine blade. The passageways are closed and partially filled with a fluid such as liquid sodium or potassium that is chosen so that the portion near the tip will be vaporized at the temperature encountered at the tip, while the area of the cavity near the root will remain liquified under most conditions. Finally, U.S. Patent No. 2, 782, 000--Ledinegg discloses a system wherein blades having fluid-filled internal cavities are arrayed as a subset around individualized heat exchanges such that one turbine row is essentially a self-contained unit that can be removed and maintained without interfering with the heat exchange capabilities of the rest of the turbine assembly. It is also known that the air cooling and internal closed loop liquid cooling techniques described above can be combined in one turbine blade as shown in U.S. Patent No. 4, 302, 153--Tubbs in which a turbine blade that is cooled by permitting cooling air to enter through an entry aperture and exit through orifices on the leading edge of the airfoil. Another cooling path is provided by that is filled with liquid sodium. The liquid path is from the interior of the root of the blade through internal passageways that begin at the trailing edge of the blade and end near the leading edge. The hot leading edge gives up heat to the liquid, vaporizing it. The hot vapor is routed through a return passage back to the cooler core, where it is condensed. However, all of the cooling systems to date suffer from one or more major drawbacks. In particular, as explained above, the existing air flow cooling systems disturb the flow fields within the turbine, while the closed loop liquid systems are complicated, expensive and less effective and reliable. Therefore, it would be desirable to provide an air flow-based cooling system that did not unduly disturb the flow of gas through a turbine structure, but still enables heat from the hot parts to be extracted. Additionally, it would be further desirable to transfer heat from critical components to another part of the turbine where heat is being added, rather than ejecting the heat from the hot parts as waste heat. If the heat reduces the amount of fuel required by the system, the overall efficiency of such an improved system would be raised. It is therefore an object of the present invention to provide an air flow cooling system for a turbine in which heat is transferred from the turbine hot parts to another section of the turbine. BTTMMAPV OF THF TNVFNTTON It has now been found, however, that the deficiencies of the prior art can be overcome by methods and apparatus for cooling combustion turbine power plants in which air is removed air from the combustion turbine compressor and delivered to air passages internal to one or more of a combustor and turbine hot parts. The air cools the combustor and turbine hot parts via convection and heat is transferred through the surfaces of the combustor and turbine hot parts. In certain embodiments, the step of removing air comprises removing air from the compressor discharge or the combustor shell . If the turbine hot parts are moving parts, a small leakage of cooling air is preferably permitted to enter a gas path within the combustion turbine for positive ventilation of the air passages. In the case of rotating blades and the rotor shaft, coolant is pumped through the rotor shaft and passing the coolant through the rotating turbine blades. In certain preferred embodiments, efficiency is further enhanced by returning heated air leaving the combustor and turbine hot parts to the combustor shell, or alternatively, by returning heated air leaving the combustor and turbine hot parts to the combustor. Coolant may also be returned to the rotor shaft and extracting the coolant prior to being injected into the combustor shell or the combustor itself. In other preferred embodiments, the coolant is discharged into the combustor shell through slots or holes in a first stage turbine disk assembly. In certain embodiments, air is removed from the compressor discharge or compressor shell and cooled with incoming combustion turbine fuel and/or water taken form the cooling system or bottoming cycle. The air may optionally be compressed slightly in an auxiliary cooling air compressor to provide enough excess air pressure to drive it through the cooling system prior to its introduction into the combustor shell or the combustor itself. The compression should be of an additional amount required to drive it through the closed loop turbine cooling system and may occur prior to its being extracted from the compressor discharge or the combustor shell. In certain embodiments, at least a portion of air exiting the auxiliary cooling air compressor is reheated by allowing heat exchange with at least some of the cooling air extracted from the compressor exit or combustor shell. RP TFF DKfiCR T PTTON OF TTTF nPAWTNfifl FIG. 1 is a partially schematic, partially diagrammatic view of a portion of a turbine and associated components that incorporates the present invention. DF.TA T T .Fn TIF.qrF T PTTON OF THF PRFFFFRFH FMROnTMF.NT.q Referring now to FIG 1, the general layout and operation of several embodiments of the present invention are illustrated. As set forth below, the illustration of FIG. 1 incorporates several alternative constructions and options, all of which are useful in various embodiments of the present invention. It is to be understood that certain of these features may be deleted or may be used in various sub-combinations to achieve the benefits of the present invention. Those of skill in the art will be familiar with the construction and operation of the equipment used in combustion turbine power plants. In order to more clearly illustrate the present invention, miscellaneous equipment is illustrated schematically or not shown, while important components of the turbine are shown diagrammatically in a cross-section broken away at the turbine centerline. As seen in FIG. 1, a typical system includes a combustion turbine combustor 10 that receives a flow of an or other gases from a combustion turbine compressor 20 at ar. inlet point 22. The combustor 10, and other hot parts including the combustor basket, transitions, and turbine vane rotor and shaft components, have internal passageways 100 that admit an airflow from the turbine compressor 20, and this relatively cooler air flow cools the components via convection through the hot part surfaces. For moving parts, or parts where a completely closed passage is not practical, a small leakage of cooling air is permitted to enter the gas path for positive ventilation of cooled cavities. As the combustor 10 or turbine hot parts are cooled by the air, the air is itself heated, and this heated air is returned to the combustor shell at an inlet point 32 or, in some embodiments, to the combustor 10 itself at another inlet point 34. Thus, the present invention provides a cooling system in which the heat absorbed by the coolant while passing through the hot parts is returned to the combustion turbine. In other words, at least a portion of he heat from the turbine blades is added back to the power cycle. Although FIG. 1 specifically illustrates cooling the combustor 10, it is known in the prior art to provide rotating turbine blades and a rotor shaft with closed loop passageways. However, as explained above, in the prior art, these passageways were always filled with a liquid and the energy lost and gained through vaporization and condensation effected the heat transfer. In the present invention, a coolant comprised of air or another gas is instead pumped through internal passageways in the rotor shaft and passed through internal passageways in the rotating turbine blades. The relatively cooler air absorbs heat and it is either then returned to the rotor shaft and extracted prior to being injected into the combustor shell or, in some embodiments, to the combustor itself, or the heated air is merely discharged into the combustor shell through slots or holes int he first stage turbine disk assembly. Thus, regardless of the portion of the turbine that is cooled using air in a closed loop system in accordance with the present invention, the loss mechanisms described above are substantially eliminated since the present invention eliminates the need to eject coolant from the combustor and/or turbine hot parts. As a result there are significant increases in both thermal efficiency and output for combustion turbine simple cycles, as well as combined cycle power plants. Referring again to FIG. 1, it can be seen that in some embodiments, air is removed from the compressor discharge or compressor shell and cooled with incoming combustion turbine fuel and/or water taken from the cooling system or bottoming cycle. The air is them compressed slightly in an auxiliary cooling air compressor to provide enough excess air pressure to drive it through the closed loop cooling system and then send the air through the closed lop cooling system prior to its introduction into the combustor shell or the combustor itself. Alternatively, the air may be compressed the additional amount required to drive it through the closed loop turbine cooling system prior to its being extracted from the compressor discharge or the combustor shell. In another embodiment, the some or all of the cooling air exiting the axillary cooling air compressor is reheated by allowing heat exchange with some or all of the cooling air extracted from the compressor exit or combustor shell. In yet another embodiment the cooling air is not cooled after it is extracted from the compressor exit or combustor shell. output. The present invention greatly increases combustion turbine thermal efficiency and output, thereby allowing for corresponding increases in thermal efficiency and output, for both simple and combined cycle power plants that utilize combustion turbines. Furthermore, since almost all of the air compressed in the compressor is delivered to the combustor, either directly or through the closed loop cooling system, the present invention also provides reduced power plant emissions since the greater degree of premixing available, due to the presence of the turbine cooling air, allows for lower flame temperatures, and therefore lower emissions of NO x . Although certain embodiments of the present invention have been set forth herein and described with particularity, these descriptions are meant to illustrate the nature of the present invention and are not limitative Upon review of the foregoing specification, various modifications, adaptations and improvements to the methods and apparatus disclosed will immediately present themselves to those of skill in the art. Such specification, various modifications, adaptations and improvements will not depart from the spirit of the present invention and thus, in order to apprehend the full scope of the present invention, reference should be made to the appended claims.

Claims: CLAIMS: 1. A method of cooling combustion turbine power plants comprising the steps of: removing air from the combustion turbine compressor delivering the air to passages internal to one or more of a combustor and turbine hot parts, wherein the air cools the combustor and turbine hot parts via convection and heat is transferred through the surfaces of the combustor and turbine hot parts. 2. The method of claim 1, wherein the step of removing air comprises removing air from the compressor discharge or the combustor shell. 3. The method of claim 1, wherein the turbine hot parts are moving parts, further comprising the additional step of permitting a small leakage of cooling air to enter a gas path within the combustion turbine for positive ventilation of the air passages. 4. The method of claim 1, wherein the turbine hot parts are rotating blades and the rotor shaft, the additional step of pumping coolant through the rotor shaft and passing the coolant through the rotating turbine blades. 5. The method of claim 1, further comprising the step of returning heated air leaving the combustor and turbine hot parts to the combustor shell. 6. The method of claim 1, further comprising the step of returning heated air leaving the combustor and turbine hot parts to the combustor. 7. The method of claim 1, further comprising the step of returning the coolant to the rotor shaft and extracting the coolant prior to being injected into the combustor shell or the combustor itself. 8. The method of claim 1, further comprising the step of discharging the coolant into the combustor shell through slots or holes in a first stage turbine disk assembly. 9. The method of claim 1, wherein air is removed from the compressor discharge or compressor shell and cooled with incoming combustion turbine fuel and/or water taken form the cooling system or bottoming cycle. 10. The method of claim 9, wherein the air is compressed slightly in an auxiliary cooling air compressor to provide enough excess air pressure to drive it through the cooling system prior to its introduction into the combustor shell or the combustor itself. 11. The method of claim 9, wherein the air is compressed the additional amount required to drive it through the closed loop turbine cooling system prior to its being extracted from the compressor discharge or the combustor shell. 12. The method of claim 1, wherein at least ι portion of air exiting the auxiliary cooling air compressc: is reheated by allowing heat exchange with at least some ci the cooling air extracted from the compressor exit cr combustor shell. 50 - 12 - 13. A combustion turbine comprising a combustion turbine combustor 10 that receives a flow of gas from a turbine compressor 20 at an inlet point 22, wherein the internal passageways 100 that admit at least a portion of the flow from the turbine compressor 20, whereby the relatively cooler flow cools the components via convection. 14. The combustion turbine of claim 13, further comprising one or more of a combustor basket, one or more transitions, a turbine vane rotor, one or more shaft components, each having internal passageways that receive a portion of said flow from the turbine compressor 20. 15. The combustion turbine of claim 13, wherein air heated by heat removed from the combustor or other parts of the turbine is returned to the combustor shell at an inlet point 32. 16. The combustion turbine of claim 13, wherein air heated by heat removed from the combustor or other parts of the turbine is returned to the combustor 10 itself at an inlet point 34. 17. The turbine of claim 13, wherein heat absorbed by the flow passing is returned to the combustion turbine, whereby at least a portion of he heat from the turbine blades is added back to the power cycle. 18. The turbine of claim 13, wherein the internal passageways comprise an orifice to permit a leakage of cooling air for positive ventilation. 19. The turbine of claim 13, further comprising rotating turbine blades and a rotor shaft with closed loop passageways filled with a coolant comprised of air or another gas, whereby the relatively cooler air absorbs heat and it is then returned to the rotor shaft and extracted prior to being injected into the combustor shell. 20. The turbine of claim 13, further comprising rotating turbine blades and a rotor shaft with closed loop passageways filled with a coolant comprised of air or another gas, whereby the relatively cooler air absorbs heat and it is then returned to the rotor shaft and extracted prior to being injected into the combustor itself. 21. The turbine of claim 13, further comprising rotating turbine blades and a rotor shaft with closed loop passageways filled with a coolant comprised of air or another gas, whereby the relatively cooler air absorbs heat and it is then returned to the rotor shaft and extracted prior to being discharged into the combustor shell through orifices in a first stage turbine disk assembly.

Inventors: BRIESCH MICHAEL S, HUBER DAVID J, BRIESCH, MICHAEL, S., HUBER, DAVID, J.
Applicants: WESTINGHOUSE ELECTRIC CORP, WESTINGHOUSE ELECTRIC CORPORATION
Application year: 1997
Main classification: F02C7
IPC codes: F02C7