Patent Application
20090285677
The invention generally relates to turbines and more specifically relates to systems and methods for cooling heated components in turbines.
In a turbine, such as a gas turbine, certain components, such as nozzles, turbines, buckets, or the shroud, are positioned in the hot gas path and subjected to hot gases that may be at a temperature higher than the melting point of one or more of the components. In certain current generation gas turbines the temperature of the hot gases may reach up to 1600° C. Therefore, in many circumstances, the components positioned in the hot gas path are cooled during operation of the turbine. In exemplary conventional systems, air bled out from a compressor of the gas turbine acts to cool the components. However, this air has already spent a lot of work or energy bypassing combustion chamber of the gas turbine. The air then enters the components like turbine buckets or nozzles to cool them, so they can survive in the hot gas path. Thereafter, the air is released back into the hot gas path. Since the air bypasses the combustion chamber it does not burn any fuel and does not gain additional momentum. Therefore, this air cannot do useful work in other turbine stages. As a result, the efficiency of the gas turbine decreases.
In other exemplary conventional systems, the heated components may be cooled by steam rather than air taken out of the compressor. The steam may be withdrawn from a steam turbine and piped into the heated turbine component positioned in the hot gas path. The steam generally has a higher heat transfer coefficient and thus absorbs more heat from the turbine component in the hot gas path. Accordingly, steam cooling may provide an improved solution over air cooling solutions. The steam may be taken from the gas path and reintroduced to the steam turbine. Some of the heat energy that the steam derives from the hot gas path may therefore be recovered in the steam turbine to develop additional useful work. Thus, in exemplary cases, the efficiency of steam cooled gas turbines may be greater than air cooled gas turbines.
However, conventional steam cooling systems may be quite complicated. For example, the steam is taken from stationary pipes and has to be routed into rotating buckets. The steam supply and recovery system has to be kept well sealed because the steam exists at a very high pressure and would otherwise create a leak in the steam system. Moreover, because the steam travels back to the steam turbine, the steam system also should be sealed to maintain purity.
Accordingly, there exists a need for systems and methods for cooling heated components in turbines.
Embodiments of the invention can address some or all of the needs described above. Embodiments of the invention are directed generally to systems and methods for cooling heated turbine components in a turbine engine.
According to one exemplary embodiment of the invention, a system for cooling heated components in a hot gas path of a turbine is provided. The exemplary system may include at least one liquid source which may include a coolant liquid. The system may also include at least one liquid nozzle in fluid communication with the liquid source or sources and operable to deliver the coolant liquid in an atomized form adjacent to at least one heated turbine component positioned in a hot gas path of the turbine. According to this exemplary embodiment, upon delivering the atomized coolant liquid adjacent to the heated turbine component or components, at least a portion of the coolant liquid substantially changes phase to a gas.
According to another exemplary embodiment of the invention, a method for cooling heated components in a hot gas path of a turbine is provided. This exemplary method may include providing at least one liquid source comprising a coolant liquid and in fluid communication with at least one liquid nozzle, wherein the liquid nozzle or nozzles are positioned adjacent to at least one heated turbine component positioned in a hot gas path of the turbine. The method may further include atomizing the coolant liquid from the liquid source or sources and delivering the atomized coolant liquid adjacent to the heated turbine component or components. According to this exemplary embodiment, upon delivering the atomized coolant liquid adjacent to the heated turbine component or components, at least a portion of the coolant liquid substantially changes phase to a gas.
According to yet another exemplary embodiment of the invention, a method for operating a turbine is provided. This exemplary method may include starting the turbine, increasing the turbine speed to operate at a predetermined load, and atomizing a coolant liquid. The method may further include delivering the atomized coolant liquid adjacent to at least one heated turbine component positioned in a hot gas path of the turbine subsequent to increasing the turbine speed to operate at the predetermined load, wherein upon delivering the atomized coolant liquid, at least a portion of the coolant liquid substantially changes phase to a gas. The method may further include reducing the turbine speed to operate below the predetermined load and purging excess liquid from the hot gas path subsequent to reducing the turbine speed below the predetermined load.
Other embodiments and aspects of the invention will become apparent from the following description taken in conjunction with the following drawings.
Having thus described embodiments of the invention in general terms, reference will now be made to the accompanying drawings, which are not drawn to scale, and wherein:
Exemplary embodiments of the invention now will be described more fully hereinafter with reference to the accompanying drawings, in which some, but not all embodiments are shown. Indeed, the invention may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will satisfy applicable legal requirements. Like numbers refer to like elements throughout.
Starting and increasing the speed of a turbine causes combustion in a combustion chamber of the turbine. During combustion, the temperature of the hot gases produced may be well above the melting point of various turbine components located in the hot gas path. Thus, to cool the heated turbine components in the hot gas path of the turbine, a coolant liquid may be atomized and delivered to or near the heated turbine components. Because of the greater energy absorbed by the coolant liquid, such as water for example, during its phase change from a liquid to a gas, supplying the atomized coolant liquid at or near the heated turbine components more efficiently cools the components than in only steam cooled or only air cooled turbines. Further, mixing the coolant liquid into air additionally acts as a cooling mechanism for the air before the air and gas mixture is delivered to the heated turbine components.
To cool the turbine bucket 102, air is delivered from a compressor 106 of the gas turbine. The air may first pass through an inner space 108 of the turbine nozzle 104. After exiting the turbine nozzle 104, the air passes through an inducer 110 that further releases the air adjacent to a root 112 of the turbine bucket 102. The root 112 is the most radially inward portion of the turbine bucket 102. The root 112 usually has an attachment feature (as illustrated in
In various exemplary embodiments, the liquid nozzle 118 may be located inside a turbine wheel or outside a turbine shroud. The location of the liquid nozzle 118 determines the location for releasing the coolant liquid at or near the heated turbine component 102. In various exemplary embodiments, the liquid nozzle 118 may be of an injector type, a venturi type, or the like.
If the coolant liquid delivered from the liquid nozzle 118 directly contacts a heated turbine component, such as the turbine bucket 102, the coolant liquid may cause a substantial decrease in temperature at a local zone where the coolant liquid contacts. This may cause a high temperature gradient within the material of the component, possibly causing a high stress gradient in the material of the heated component, such that cracking may develop at the point contacted by the coolant liquid. To avoid such damages to the heated turbine component, in one exemplary embodiment, the coolant liquid is released into the air in an atomized form and at least a portion of the coolant liquid changes phase from liquid to gas upon mixing with the air and being exposed to high temperatures. A phase change to gas avoids direct contact by the coolant liquid in liquid form at a point on the heated component.
In some situations, the coolant liquid exiting the liquid source 116 may be at a pressure lower than the pressure of the air exiting the compressor 106. In such a case, the coolant liquid may not be released into the air in atomized form and thus may not distribute uniformly through the air medium. Accordingly, the coolant liquid may be pressurized prior to releasing it into the air medium. Thus, in one exemplary embodiment, a pressurizing pump may be utilized to pressurize the coolant liquid so that the coolant liquid may exit to the air medium substantially atomized and be uniformly distributed through the air medium at or near the heated turbine component. For example, the coolant liquid may be pressurized to a pressure of approximately 2.8×106 N/m2 (400 psi) or greater.
Mixing the coolant liquid with the air prior to introducing air adjacent to the heated turbine component, such as the turbine bucket 102, also may benefit cooling the heated turbine component, as the latent heat of vaporization of the coolant liquid is very high compared to the specific heat of the coolant liquid and the gaseous form of the coolant liquid and the air. For example, if the coolant liquid is water, then the latent heat of vaporization of water, specific heat of water and specific heat of steam are approximately 2.26×102 J/kg, 4.184 J/kg-° C. and 2 J/kg-° C., respectively. Accordingly, in a steam cooled turbine, 2 Joules of heat may be absorbed on an increase of approximately 1° C. for each kilogram of steam, and in a water cooled turbine, 4.184 Joules of heat may be absorbed on an increase of approximately 1° C. for each kilogram of water. However, in a system, such as the system 100, where water is converted to steam, 2.26×102 Joules of heat may be absorbed by each kilogram of water upon conversion to steam. Furthermore, this happens at a constant temperature of approximately the boiling point of water. The water absorbs heat at 2.26×102 J/kg-° C. until substantially all of the water is converted into steam. This provides a large heat extraction capacity to the coolant liquid. Further, the mixing of the coolant liquid into the air and its subsequent conversion into gas acts as a cooling mechanism for the air before the air and gas mixture is delivered adjacent to the heated turbine component, such as the turbine bucket 102. In the exemplary embodiment cooling at least one turbine bucket 102, once the coolant liquid phase changes into the gaseous medium, the gas and air mixture may enter an inner space 120 of the turbine bucket 102 through the root 112.
In one exemplary embodiment, a pipe system 122 may optionally be provided to couple the liquid source 116 to the liquid nozzle 118 and to ensure proper delivery of the coolant liquid from the liquid source 116 and the liquid nozzle 118. Further, the pipe system 122 could be in an environment where the temperatures are so substantially high that the phase of the coolant liquid changes into the gaseous form. This causes the coolant liquid to lose some of the heat extraction capacity, which is better reserved for the heated turbine component 102. To avoid the phase change of the coolant liquid into the gas, the pipe system 122 may be thermally insulated from its surroundings. Additionally, the pipe system 122 may corrode due to the corrosion effect of the coolant liquid. Accordingly, in one exemplary embodiment, the pipe system 122 may be provided with the corrosion protective coating.
In some situations during operation of the system 100, the speed of the gas turbine is reduced such that the gas turbine is no longer operating at a predetermined load. The gas turbine may require purging the excess coolant liquid from the hot gas path that is not converted into the gaseous phase. Thus, in one exemplary embodiment, a purging unit 124 is optionally provided in the gas turbine. However, exemplary gas turbines may typically include a drainage system for draining the unburnt fuel from within the gas turbine. Accordingly, in one exemplary embodiment, the fuel drainage system may be extended as the purging unit 124 to purge any excess coolant liquid remaining in the path.
It is appreciated that the turbine bucket 202 is provided merely for illustrative purposes, and that other heated turbine components in a hot gas path 216 may be cooled in a manner similar as that described herein. In various different exemplary embodiments, the heated turbine component may be, but not limited to, a turbine nozzle, a turbine bucket, a turbine wheel, a turbine shroud, or a combination thereof.
The exemplary method begins at block 302. At block 302, at least one liquid source is provided to supply a coolant liquid to, adjacent to, or near one or more heated turbine components. In various different exemplary embodiments, the heated turbine component may be, but not limited to, a turbine nozzle, a turbine bucket, a turbine wheel, a turbine shroud, or a combination thereof. In one exemplary embodiment, the coolant liquid may be water, though other coolants may be supplied. The liquid source is in fluid communication with at least one liquid nozzle positioned adjacent to or near the heated turbine component or components. Accordingly, the one or more liquid nozzles are operable to supply the coolant liquid from the liquid source to or near the one or more heated turbine components. The liquid nozzle or nozzles may be an injector type, a venturi type, or the like.
In one example, a pipe system from the liquid source to the liquid nozzle may provide the fluid communication therebetween. In exemplary embodiments, the pipe system may be subjected to substantially high temperatures, such as during turbine operation, which may cause the coolant liquid to change phase at least partially within the pipe system. Thus, in one exemplary embodiment, the method may further include thermally insulating the pipe system to avoid heat transfer to the coolant liquid inside of the pipe system from its surroundings.
Block 304 follows block 302, in which the coolant liquid from the liquid source is substantially atomized. The liquid nozzle may be operable to substantially atomize the coolant liquid. Further, in other exemplary embodiments, the turbine may include a pressurizing pump for pressurizing the coolant liquid received from the liquid source and also for aiding in atomization of the coolant liquid.
Block 306 follows block 304, in which the liquid nozzle delivers the atomized coolant liquid to the air adjacent to or near the heated turbine component or components. Delivering the atomized coolant liquid substantially uniformly to air delivered from the compressor, allows the coolant liquid mixed with the air to substantially change phase to gas when exposed to the higher temperatures within the hot gas path.
In one exemplary embodiment, the method may include providing a purging unit to remove the coolant liquid from the hot gas path if the speed of the turbine is reduced below a predetermined load. In one example, the purging of the coolant liquid from the hot gas path may be performed prior to a next start-up of the turbine. In another example, the coolant liquid may be purged upon shut-down of the turbine.
The exemplary method begins at block 402. At block 402, the turbine is started. Block 404 follows block 402 in which the speed of the turbine is increased to operate the turbine at a predetermined load. Starting and increasing the speed of the gas turbine leads to combustion process in a combustion chamber of the gas turbine. In an exemplary embodiment, the temperature of the hot gases produced may be well above the melting point of various turbine components located in the hot gas path.
Block 406 follows block 404, in which a coolant liquid received from the liquid source is atomized, which may be employed to cool the one or more heated turbine components in the hot gas path of the turbine. In one exemplary method, a liquid nozzle in liquid communication with the liquid source substantially atomizes the coolant liquid. In exemplary embodiments, the coolant liquid may be water, though other coolants may be supplied.
Block 408 follows block 406, in which the atomized coolant liquid is delivered adjacent to or near the heated turbine component or components. In this exemplary method, since the coolant liquid is delivered in an atomized form and to air in the hot gas path, which has a temperature higher then a boiling point of the coolant liquid, at least a portion of the coolant liquid undergoes phase change and is converted into a gas phase. In exemplary embodiments, the heated turbine component or components may include a turbine bucket, a turbine nozzle, a turbine wheel, a turbine shroud, or the like.
Block 410 follows block 408, in which the speed of the turbine is reduced so that the turbine operates below the predetermined load, such as during slow-down or shut-down. It may be possible that while reducing the load or momentarily stopping the operation of the turbine, some of the coolant liquid may not undergo a phase change. Remaining liquid in the turbine may lead to corrosion of turbine components and may eventually lead to generation of cracks in the turbine components due to high stress factor. Accordingly, block 412 follows block 410, in which any excess of such coolant liquid is purged from the hot gas path. In one example, the purging of the coolant liquid from the hot gas path may be performed prior to a next start-up of the turbine. In another example, the coolant liquid may be purged upon shut-down of the turbine.
In various turbines, the turbine efficiency may be affected by the introduction of the air into the hot gas path as a result of the air undergoing substantial work during the compressor stage. Introduction of a coolant liquid into the air, such as that described above, increases the cooling efficiency and therefore aids in reducing the amount of air used for cooling the heated turbine component.
Many modifications and other embodiments of the exemplary descriptions set forth herein to which these descriptions pertain will come to mind having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. Thus, it will be appreciated the invention may be embodied in many forms and should not be limited to the exemplary embodiments described above. Therefore, it is to be understood that the invention is not to be limited to the specific embodiments disclosed and that the modification and other embodiments are intended to be included within the scope of the appended claims. Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.
