System and method for recirculating and recovering energy from compressor discharge bleed air

A system includes a gas turbine, an inlet bleed circuit, and a controller. The gas turbine includes a compressor and a turbine. The compressor is configured to produce pressurized air and bleed air. The turbine is configured to produce a first output. The inlet bleed circuit includes a turbo-expander configured to produce a second output from a non-zero first portion of the bleed air. The inlet bleed circuit is also configured to direct a part of the bleed air to an inlet of the compressor. The controller is configured to adjust the gas turbine and the inlet bleed circuit to control the second output of the turbo-expander.

BACKGROUND OF THE INVENTION

The subject matter disclosed herein relates to gas turbine systems having an improved method for recovering energy from compressed bleed air discharged from a compressor of a gas turbine.

In certain applications, gas turbine pressure ratios may reach a limit for a compressor of the gas turbine. For instance, in applications where low-BTU (British thermal units) fuels are used as fuel sources in a combustion chamber of the gas turbine, in locations characterized by lower ambient temperatures, or in applications with lower gas turbine loads, the pressure ratio of the compressor may become lower than the pressure ratio of a turbine of the gas turbine. Variations in the compressor pressure ratio may cause surge or stall conditions that affect the operation of the gas turbine.

BRIEF DESCRIPTION OF THE INVENTION

In one embodiment, a system includes a gas turbine with a compressor, a combustion chamber, a turbine, and an inlet bleed circuit. The compressor includes an inlet, an outlet, and a bleed outlet. The compressor is configured to produce pressurized air and bleed air. The combustion chamber is configured to combust the pressurized air to generate exhaust gases. The turbine is configured to produce a first output using the exhaust gases. The inlet bleed circuit is coupled between the bleed outlet and the inlet of the compressor. The inlet bleed circuit is configured to receive the bleed air from the bleed outlet. The inlet bleed circuit includes a first bleed path, a second bleed path, and a first valve assembly. The first bleed path includes a turbo-expander configured to receive and expand a non-zero first portion of the bleed air to produce a second output. The second bleed path is configured to receive and direct a second portion of the bleed air to the inlet of the compressor. The first valve assembly is configured to couple the first bleed path and the second bleed path.

In another embodiment, a system includes a gas turbine, an inlet bleed circuit, and a controller. The gas turbine includes a compressor and a turbine. The compressor is configured to produce pressurized air and bleed air. The turbine is configured to produce a first output. The inlet bleed circuit includes a turbo-expander configured to produce a second output from a non-zero first portion of the bleed air. The inlet bleed circuit is also configured to direct a part of the bleed air to an inlet of the compressor. The controller is configured to adjust the gas turbine and the inlet bleed circuit to control the second output of the turbo-expander.

In yet another embodiment, a method of operating a gas turbine system includes compressing air within a compressor of the gas turbine to produce pressurized air and bleed air. The method also includes producing a first output with a turbine of the gas turbine system. The first output drives the compressor. The method also includes directing the bleed air to an inlet bleed circuit coupled to an inlet of the compressor. The bleed air includes a non-zero first portion and a second portion. The method includes expanding the non-zero first portion within a turbo-expander to produce a second output. The method also includes recirculating a part of the bleed air to the inlet of the compressor, wherein the part of the bleed air includes a sub-portion of the non-zero first portion, the second portion, or a sub-portion of the non-zero first portion and the second portion. The method includes controlling the first output and the second output.

DETAILED DESCRIPTION OF THE INVENTION

A system and method for recirculating and recovering energy from compressor discharge bleed air as described herein includes an inlet bleed circuit coupled between a bleed outlet and an inlet of the compressor of a gas turbine system. Bleeding a portion of the compressed air from the compressor of the gas turbine may help protect the compressor from surge or stall conditions. However, bleeding compressed air discharged from the compressor may decrease net efficiency of the gas turbine system, since the energy expended to raise the pressure of the air within the compressor is not recovered. The amount of bleed air that is bled to protect the compressor may be a function of ambient conditions and gas turbine output. Increasing the temperature and decreasing the density of air at the compressor inlet may affect the gas turbine output and/or help protect the compressor. However, heating air at the compressor inlet uses energy. The compressor heats the air as it is pressurized, thus the energy of the bleed air may be used to heat the air at the compressor inlet. The energy of the bleed air may also be expanded in a turbomachine (e.g., turbo-expander) to recover some of the energy used to pressurize the bleed air to produce a second output. Recirculating the heated bleed air at the inlet may be an irreversible process, whereas expanding the bleed air in a turbo-expander and recirculating the expanded bleed air may be a reversible process that also cools the bleed air. The irreversible process of heating the air at the compressor inlet may readily protect the compressor from stall and/or surge conditions; however, it may reduce the output and heat rate more than the reversible process of expanding the bleed air to recover energy and recirculating the expanded bleed air portion. Controlling a split of the bleed air to be expanded and recirculated from the bleed air to be recirculated may increase the flexibility of the gas turbine system to protect the compressor for a wider range of operating conditions (e.g., fuel quality, ambient temperature, load, and so forth).

The bleed air may be directed along a first bleed path and/or a second bleed path. The first bleed path includes the turbo-expander and may be configured to direct a first bleed air portion of the bleed air to the inlet of the compressor. The first bleed air portion may be any non-zero portion of the bleed air. The first bleed path may also be configured to cool the first bleed air portion of the bleed air. The second bleed path may be configured to direct the remainder (e.g., a second bleed air portion) of the bleed air directly to the inlet of the compressor. A first valve assembly may couple the first and second bleed paths to the inlet of the compressor and be configured to adjust the inlet temperature of the compressor by controlling the split between the first and second bleed air portions of the bleed air that flows into the inlet of the compressor. The first valve assembly may also be configured to adjust the density and quantity of the recirculated air directed into the inlet. In an embodiment, a second valve assembly may be coupled to the bleed outlet, the first bleed path, and the second bleed path. The second valve assembly may be configured to adjust the bleed air as a percentage of the pressurized air directed to a combustor and/or to adjust a ratio between the first and second bleed air portions of the bleed air. Presently contemplated embodiments may include the first valve assembly alone, the second valve assembly alone, or both the first and second valve assemblies.

In certain embodiments, a controller may be configured to control the first valve assembly and/or the second valve assembly. In this way, the controller may be configured to control the inlet temperature, the density and quantity of the air at the inlet, the percentage of the bleed air, and the split between the first and second bleed air portions of the bleed air. The controller may also be configured to control a first output of the turbine and/or a second output of the turbo-expander. The controller may also be configured to control the first and/or second bleed air portions of the bleed air directed to the first bleed path based at least in part on an operating condition of the gas turbine (e.g., air quality, fuel quality, ambient temperature), a compression ratio of the compressor, a desired heat rate of the system, or a desired output of the system or combinations thereof. In some embodiments, the second output may be mechanically or electrically coupled with the first output to a common load.

Turning now to the drawings,FIG. 1illustrates a block diagram of an embodiment of a gas turbine system10having an inlet bleed circuit38. As depicted, one or more fuel nozzles12directs fuel14(e.g., a liquid fuel and/or gas fuel, such as natural gas) into a combustor16. The combustor16ignites and combusts the air-fuel mixture18, and then passes hot pressurized exhaust gas20into a turbine22. The exhaust gas20passes through turbine blades of a turbine rotor in the turbine22, thereby driving the turbine22and the coupled shaft24to rotate. The shaft24is coupled to several components (e.g., compressor26, load28, and so forth) throughout the gas turbine system10. Eventually, the exhaust gases20of the combustion process may exit the gas turbine system10via an exhaust outlet30.

In an embodiment of the gas turbine system10, compressor vanes or blades are included as components of the compressor26. Blades within the compressor26are coupled to the shaft24, and will rotate as the shaft24is driven by the turbine22. The compressor26may intake ambient air32to the gas turbine system10via an air intake34. Further, the shaft24may be coupled to and drive the load28. As will be appreciated, the load28may be any suitable device that may generate power via the rotational output of the gas turbine system10, such as a power generation plant or an external mechanical load. For example, the load28may include an electrical generator, a propeller of an airplane, and so forth. The air intake34draws the ambient air32into the gas turbine system10via a suitable mechanism, such as a cold air intake, for subsequent mixture of the ambient air32with the fuel14via the fuel nozzle(s)12. The air intake34may also draw recirculated air36from an inlet bleed circuit38. The compressor26is configured to receive the ambient air32and the recirculated air36, collectively as inlet air37, at an inlet40. The compressor26may compress the inlet air37into pressurized air42by rotating blades within the compressor26. A portion of the pressurized air42(e.g., bleed air44) may be bled from the compressor26into the inlet bleed circuit38. When the compressor26compresses the inlet air37, the compressor26adds energy to the inlet air37to increase the pressure, and incidentally increase the temperature. Thus, the pressurized air42and bleed air44are warmer and at higher pressures than the ambient air32. The pressurized air42may be fed from an outlet46into the one or more fuel nozzles12, which may mix the pressurized air42and the fuel14to produce an air-fuel mixture18suitable for combustion. Again, the turbine22is driven by the exhaust gases20, and the turbine22drives the compressor26and the load28.

The inlet bleed circuit38is coupled to the inlet40of the compressor26and a bleed outlet48of the compressor26. The bleed outlet48is configured to direct the bleed air44along the inlet bleed circuit38. As discussed in detail below, the inlet bleed circuit38may be configured to expand a portion of the bleed air44to produce an output, to direct all or part of the bleed air44to the inlet40to protect the compressor26, or combinations thereof. In some embodiments, directing all or part of the bled air44through a turbo-expander may also protect the compressor26. The inlet bleed circuit38includes a first bleed path50and a second bleed path52. Each bleed path50,52is configured to receive all or part of the bleed air44. Each bleed path50,52is in fluid connection with the bleed outlet48and the inlet40to enable the bleed air44to recirculate through the compressor26.

The first bleed path50is configured to receive a first bleed air portion54of the bleed air44and the second bleed path52is configured to receive a second bleed air portion56of the bleed air44. The bleed air44may be divided completely between the first bleed air portion54along the first bleed path50and the second bleed air portion56along the second bleed path52. The first bleed air portion54may include the entire flow of bleed air44or any non-zero portion of the bleed air44. For example, in some embodiments the first bleed air portion54may be approximately ⅛, ¼, ⅓, ⅜, ½, ⅝, ⅔, ¾, or ⅞ of the bleed air44. The second bleed air portion56is the balance of the bleed air44after subtracting out the first bleed air portion54.

The first bleed path50includes a turbo-expander58configured to expand the first bleed air portion54to extract energy. The turbo-expander58may, for instance, be a turbine configured to expand high-pressure gases (e.g., the first bleed air portion54) to produce work. However, the turbo-expander58may also be any suitable equipment capable of recovering the pressure energy of the first bleed air portion54. The turbo-expander58may be used to drive the load28and/or a supplementary load60(e.g., a supplementary electrical generator). In certain embodiments, the first bleed air portion54may be expanded within the turbo-expander58to drive a supplementary load60(e.g., generator, fan). In some embodiments, the turbo-expander58may be coupled to the shaft24as shown by the dashed lines. In other embodiments, the turbo-expander58and supplementary load60may be separate from the load28(i.e., not coupled to the shaft24). In this way, various embodiments of the turbo-expander58may be configured to drive only the supplementary load60, only the load28, or both the supplementary load60and the load28. By recovering the energy stored within the pressurized first bleed air portion54through the turbo-expander58, the efficiency of the entire gas turbine system10may remain relatively high. The turbo-expander58may expand the first bleed air portion54isentropically, resulting in an expanded portion62with a decreased pressure and temperature. In some embodiments, the expansion of the first bleed air portion54within the turbo-expander58is a substantially reversible process. The turbo-expander58may efficiently recover most of the energy used by the compressor26to pressurize the first bleed air portion54. In some embodiments, the expanded portion62may be further cooled along the first bleed path50. The first bleed path50may direct a sub-portion63(e.g., 0 to 100% of the expanded portion62) to the inlet40and the rest of the expanded portion62to a vent64. In some embodiments, the first bleed path50may direct the entire expanded portion62to the inlet40or to the vent64. The vent64may be along the first bleed path50or part of a valve assembly as discussed below.

The expanded portion62may have a temperature greater than or equal to the ambient air32, and be at a pressure greater than or equal to the ambient air32. The sub-portion63of the expanded portion62and the second bleed air portion56may be directed to the inlet40to mix with the ambient air32to heat the inlet air37to a desired temperature. Heating the inlet air37may decrease the mass flow of inlet air37into the compressor because of a decrease in corrected speed. Directing the first bleed air portion54of the bleed air44through the turbo-expander58enables the turbo-expander58to capture power that would otherwise be lost if the first bleed air portion54was directed to the inlet40along the second bleed path52. The turbo-expander58is configured to decrease the temperature of the first bleed air portion54and expand the first bleed air portion54. In some embodiments, directing the cooled expanded portion62to the inlet40(in lieu of increasing the temperature at the inlet40via directing the second bleed air portion56to the inlet40) may also protect the compressor26from a surge or stall condition by lowering the operating line. Extracting the bleed air44from the compressor26, without heating the inlet air37to the compressor26may reduce the mass flow into the turbine22and reduce the turbine inlet pressure. The operating line for a gas turbine is defined at the inlet to the turbine22and is governed by relationships that include mass flow into the turbine22and temperature of the mass flow. Directing the entire bleed air44through the second bleed path52to the inlet40inlet in an irreversible manner may heat the inlet air37and lower the corrected speeds of the compressor22. The corrected speed may be lowered to reduce the mass flow to the turbine22and thus lower the operating line as needed to provide adequate surge margin. Directing a non-zero portion (e.g., first bleed air portion54) of the bleed air44through the first bleed path50and turbo-expander58enables the operating line of the compressor26to be lowered to protect the compressor26from surge conditions. Directing the non-zero portion of the bleed air44through the first bleed path50also enables the mass flow to the turbine22to be reduced without increasing the temperature of the inlet air37as much as with only the second bleed path52. Thus, directing a non-zero portion of the bleed air44along the first bleed path50with the turbo-expander58enables a reduced effect of the bleed air44on the compressor corrected speed, as compared to a only directing the bleed air44along the second bleed path52(e.g., the inlet bleed heat system) to the inlet40. The first bleed path50with the turbo-expander58enables compressor surge protection without substantially affecting other operating parameters, such as the compressor discharge temperature, corrected speeds, exhaust energy, and so forth.

The inlet bleed circuit38includes at least one valve assembly66. The at least one valve assembly66is configured to couple the first bleed path50and the second bleed path52. In some embodiments, a first valve assembly68couples the first and second bleed paths50,52at a diverging point70. In other embodiments, a second valve assembly72couples the first and second bleed paths50,52at a converging point74. Some embodiments may have both the first valve assembly68and the second valve assembly72. Each valve assembly66may include one or more gate valves, butterfly valves, globe valves, ball valves, check valves, and so forth. A valve assembly66may include combinations of valves76. Each valve76may be configured to adjust flow through the inlet bleed circuit38. For example, a closed valve76may block substantially all flow through the valve76, whereas a partially open valve76may reduce a flow through the valve76. In some embodiments, the first valve assembly68may have a first valve78downstream of the diverging point70along the first bleed path50and a second valve80along the second bleed path52. The first valve78and second valve80may be configured to be adjusted concurrently to divide the bleed air44into the non-zero first bleed air portion54and the second bleed air portion56. For example, closing the second valve80completely directs the entire flow of bleed air44through the first bleed path50, thus the first bleed air portion54is the entire flow of bleed air44. In some embodiments, opening the first and second valves78,80may increase the bleed air44as a percentage of the pressurized air42. Partially opening the first and second valves78,80may divide the bleed air44into the first bleed air portion54and second bleed air portion56based at least in part on a relative ratio between the openness of the first and second valves78,80. Partially closing the first and second valves78,80may reduce the bleed air44as a percentage of the pressurized air42. In some embodiments, fully closing the first and second valves78,80may block the entire bleed air44into the first and second bleed paths50,52, thus eliminating the recirculated air36component of the inlet air37. In certain embodiments, the first valve assembly68may have a valve76upstream of the diverging point70that is configured to adjust the bleed air44as a percentage of the pressurized air42(i.e. mass flow of the bleed air44).

In some embodiments, the second valve assembly72at the converging point74couples the first and second bleed paths50,52with the inlet40. The second valve assembly72may also couple the first and second bleed paths50,52with the air intake34upstream of the inlet40. The second valve assembly72is configured to receive and join the second bleed air portion56and the entire expanded portion62or the second bleed air portion56and the sub-portion63of the expanded portion62into the recirculated air36directed to the inlet40. As discussed above with the first valve assembly68, the second valve assembly72may include one or more valves76of the same or different type. The second valve assembly72may be configured to adjust the total mass flow of the recirculated air36directed to the inlet40. For example, the second valve assembly72may adjust the total mass flow of the recirculated air36to be less than approximately 5%, 10%, 15%, or 25% of the mass flow of the inlet air37. The mass flow of the second bleed air portion56and expanded portion62may be greater than a desired recirculated airflow36. The second valve assembly72may be configured to vent the second bleed air portion56and expanded portion62to produce the desired recirculated airflow36. For example, the vent64may be a part of the second valve assembly72. In some embodiments, the second valve assembly72may be configured to separately adjust the mass flow of the expanded portion62and the mass flow of the second bleed air portion56to adjust the relative quantities of each in the recirculated air36. In this manner, the second valve assembly72may be configured to adjust the inlet temperature of the inlet air37. For example, in an embodiment where the bleed air44is evenly split between the first and second bleed air portions54,56, the second bleed air portion56component may be at approximately 417° C. (782° F.), the expanded portion62may be at approximately 89° C. (193° F.), and the ambient air32may be at approximately 15° C. (59° F.). The combined output of the turbine22and turbo-expander58may be approximately 248 MW. The corrected speed ratio of the compressor26may be approximately 97.6%. The second valve assembly72may be configured to shut off the second bleed air portion56and increase the expanded portion62so that the inlet temperature of the inlet air37is approximately 19° C. (66° F.). The combined output of the turbine22and turbo-expander58may be approximately 262 MW. The corrected speed ratio of the compressor26may be approximately 99.3%. Other embodiments of gas turbine systems10may have different configurations with different outputs and corrected speed ratios. Through adjustment of the total mass flow of the recirculated air36and the temperature of the inlet air37, the second valve assembly72may be configured to adjust the total output of the gas turbine system10.

The first valve assembly68and the second valve assembly72may be used together to affect the inlet air37directed to the inlet40and the bleed air44extracted through the bleed outlet48of the compressor26. For example, the first valve assembly68may direct substantially the entire flow of bleed air44through the first bleed path50to produce a second output with the turbo-expander58. Directing the entire flow of bleed air44through the turbo-expander58may increase the second output and increase the efficiency of the gas turbine system10through the recovery of energy. Directing the entire flow of bleed air44along the first bleed path50may recover more energy than directing the entire flow of bleed air44through the second bleed air path52. The flow rate of the expanded portion62may be greater than desired flow rate of recirculated air36, so the second valve assembly72may be adjusted to restrict the flow of the expanded portion62or vent the expanded portion62at the vent64or second valve assembly72. In some embodiments, the vent64may release some of the expanded portion62and direct the remaining sub-portion63to the converging point74and the inlet40.

As another example of affecting the flow of the inlet air37and the bleed air44, the first valve assembly68may be configured to adjust the flow of bleed air44as a percentage of the pressurized air42to protect the compressor26from surge or stall conditions, and the second valve assembly72may be configured to adjust the expanded portion62and the second bleed air portion56to produce the recirculated air36at a desired mass flow, temperature, or pressure, or combinations thereof. The first valve assembly68may be configured to divide the bleed air44into the non-zero first bleed air portion54and second bleed air portion56components. Some energy of the first bleed air portion54may be recovered by the turbo-expander58, lowering the energy of the expanded portion62. The expanded portion62may also be cooler than the first bleed air portion54. The second bleed air portion56may have more energy in the form of pressure and heat than the expanded portion62. Both the expanded portion62and the second bleed air portion56components of the recirculated air36may be used to warm the ambient air32to a desired inlet temperature. The expanded portion62and the second bleed air portion56may be combined in varying amounts at the second valve assembly72to produce a desired mass flow of the recirculated air36with a desired energy (e.g., temperature and/or pressure). In some embodiments, the recirculated air36is the entire second bleed air portion56while the entire first bleed air portion54is expanded through the turbo-expander58to produce the second output. In some embodiments, the recirculated air36is a combination of the second bleed air portion56with the expanded portion62or a sub-portion63. The second valve assembly72may be configured to adjust the expanded portion62and the second bleed air portion56components of the recirculated air36so that the inlet air37has a desired mass flow, temperature, or pressure, or combinations thereof. In this way, the first and second valve assemblies68,72may be configured to adjust the mass flow of the bleed air44to protect the compressor26, to direct the first bleed air portion54to recover energy of the bleed air44, and to use the heat of the expanded portion62and/or the second bleed air portion56to adjust the inlet temperature of the compressor26.

Presently contemplated embodiments include a controller82coupled to the inlet bleed circuit38. The controller82may be coupled to the at least one valve assembly66to control the one or more valves76through control lines84. The controller82may be configured to open and close the valves76to control the bleed air portion44through the inlet bleed circuit38. In certain embodiments, the controller82may include a memory86to store instructions and a processor88configured to process the instructions. The controller82may include an operator interface90configured to receive operator input. In some embodiments, the controller82may be configured to control the flow of bleed air44as a percentage of the compressed air42through adjusting the first or second valve assembly68,72. The controller82may be configured to divide the bleed air44into the non-zero first bleed air portion54and second bleed air portion56. By dividing the bleed air44, the controller82is configured to direct the first bleed air portion54to the first bleed path50and to direct the second bleed air portion56to the second bleed path. The controller82may also be configured to control the vent64and to direct the entire expanded portion62or the sub-portion63to the inlet40. In some embodiments, the controller82may control the second valve assembly72to combine the second bleed air portion56and expanded portion62or sub-portion63to form the recirculated air36component of the inlet air37. By controlling the bleed air44, the first bleed air portion54, the second bleed air portion56, and the inlet air37, the controller82may control the performance of the compressor26and the output of the turbine22.

The controller82may be configured to control the performance of the compressor26by adjusting the properties of the inlet air37. Controlling the bleed air44as a percentage of the pressurized air42affects the mass flow to the combustor16or the turbine22to protect the compressor26from stall or surge operating conditions (e.g., high pressure downstream of the compressor outlet46). By controlling the first bleed air portion54, the second bleed air portion56, and properties (e.g., temperature, mass flow) of the recirculated air36, the controller82may adjust the output of the turbine22and the efficiency of the gas turbine system10by affecting the inlet air37. For example, high temperature inlet air37may decrease the mass flow of pressurized air42exiting the compressor26and decrease the output of the turbine22. Low temperature inlet air37may increase the mass flow of the pressurized air42and increase the output of the turbine22. The controller82may also adjust the first bleed air portion54to adjust the output of the turbo-expander58and the efficiency of the gas turbine system10. For example, expanding the first bleed air portion54along the first bleed path50in a substantially reversible process recovers at least some of the energy of the bleed air44and increases the efficiency of the gas turbine system10. The turbo-expander58enables the inlet bleed circuit38to recover energy from the bleed air44while protecting the compressor26from surge or stall conditions. In some embodiments, the recovered energy may be combined with the energy extracted through the turbine22to drive the common load28. Alternatively, the recovered energy may drive the supplementary load60.

FIGS. 2 and 3illustrate relationships between properties of the gas turbine system10and the bleed air44of the embodiments discussed above.FIG. 2illustrates the heat rate and output of embodiments of the gas turbine system10in a first chart100.FIG. 3illustrates the temperature of the compressor discharge and the temperature of the compressor inlet of embodiments of the gas turbine system10in a second chart102. The X-axis104of each chart is the bleed air44as a percentage of the pressurized air42produced by the compressor26. The bleed air44as a percentage may range from approximately 0 to 15%, 1 to 10%, or approximately 3 to 6%, or any subrange therein. The charts100and102depict embodiments where the bleed air44is between 0 and 6% of the pressurized air42, although presently contemplated embodiments are not limited to bleed air portions less than 6%. In each chart, a first set106of curves illustrates the properties of the gas turbine system10where the entire flow of bleed air44is directed through the first bleed path50and the turbo-expander58in a substantially reversible process. A second set108of curves illustrates the properties of the gas turbine system10where the entire flow of bleed air44is directed through the second bleed path52(e.g., IBH system) in a substantially irreversible process. The first and second sets106,108of curves for each property have the same values where the bleed air44is 0% because no bleed air portion is available to the turbo-expander58or the IBH system to affect the properties of the system. In some embodiments, the differences between directing the bleed air44through the first bleed path50or the second bleed path52are greater when the percentage of bleed air44is greater.

The chart100ofFIG. 2illustrates a heat rate and output of embodiments of the gas turbine system10discussed above. The left Y-axis110is the heat rate (i.e., a measure of efficiency) of the gas turbine system10and the right Y-axis112is the combined output of the gas turbine system10from the turbine22and turbo-expander58. The first heat rate curve114and first combined output curve116of the first set of curves106illustrate embodiments where the entire flow of bleed air44is directed along the first bleed path50having the turbo-expander58to recover energy from the bleed air44. The second heat rate curve118and the second output curve120illustrate embodiments where the entire flow of bleed air44is directed along the second bleed path52, such as an inlet bleed heat system. The first heat rate curve114is less than the second heat rate curve118for the illustrated embodiments. The heat rate110is a measure of the efficiency of a system, and may be in units of British Thermal Units (BTUs) per kilowatt-hour (kWh). A low heat rate110indicates a high efficiency as less energy (BTU) through fuel is used to produce mechanical or electrical energy (kWh). In the illustrated embodiments, the first heat rate curve114may increase between approximately 9,100 and 9,300 BTU/kWh and the second heat rate curve118may increase between approximately 9,100 and 10,000 BTU/kWh for bleed air portions between 0 and 6%. Directing the entire flow of bleed air44through the IBH system (e.g., the second bleed path52) may increase the heat rate110and decrease the efficiency of the system because some of the energy in the bleed air44is lost through the substantially irreversible process. As discussed above, directing all or part of the bleed air44through the turbo-expander58(e.g., the first bleed path50) enables the system to recover some of the energy of the bleed air44through the substantially reversible process. The recovered energy may be used to drive a supplementary load60alone and/or to drive a common load28with the gas turbine. In this way, the recovered energy produces an output and increases the efficiency of the gas turbine system10. In some embodiments, the energy lost by directing the entire flow of bleed air44through the turbo-expander58is approximately 25%, 50%, or 75% less than the energy lost by directing the entire flow of bleed air44of the same mass flow through the IBH system.

The first combined output curve116is greater than the second output curve120for the illustrated embodiments, thus directing the entire flow of bleed air44through the turbo-expander58, resulting in greater combined output of the system than directing the entire flow of bleed air44through the IBH system. The combined output112may be in units of kWh or BTUs. In the illustrated embodiments, the first combined output curve116may decrease between approximately 255,000 and 250,000 BTUs and the second output curve120may increase between approximately 255,000 and 234,000 BTUs for bleed air portions increased from 0 and 6%. Directing the entire flow of bleed air44through an inlet bleed heat system may decrease the total output of the system because some of the energy used to compress the bleed air44is lost. Directing a non-zero portion of the bleed air44through the turbo-expander58may enable the recovery of some of the energy of the bleed air44so that the total combined output of the system may decrease less compared to directing the bleed air44through the inlet bleed heat system. For example, directing the entire flow of bleed air44through the turbo-expander58may decrease the energy output lost by up to approximately 25%, 50%, or 75% or more than the energy output lost by directing the entire flow of bleed air44through the inlet bleed heat system.

The second chart102ofFIG. 3illustrates the compressor inlet temperature122on the right Y-axis and the compressor discharge temperature124on the left Y-axis. As discussed above withFIG. 1, the compressor26is configured to receive inlet air37at an inlet temperature122at the compressor inlet40. The compressor inlet temperature122affects the density, temperature (e.g., compressor discharge temperature124), and mass flow of the pressurized air42at the outlet46and bleed air44at the bleed air outlet48(FIG. 1). In the illustrated embodiments, the first inlet curve126may increase between approximately 15° C. and 18° C. and the second inlet curve128may increase between approximately 15° C. and 41° C. for bleed air portions between 0 and 6%. The pressurized air42and bleed air44may be warmer than the ambient air32. Directing the entire flow of bleed air44along the substantially irreversible second bleed path52(e.g., IBH system) as indicated by the second inlet curve128may increase the compressor inlet temperature122. Directing the entire flow of bleed air44along the first bleed path50(e.g., the turbo-expander58) may cool the bleed air44so that the inlet temperature122does not warm as much as with the IBH system. In some embodiments, the first bleed path50may cool the bleed air44to approximately the temperature of the ambient environment so that the compressor inlet temperature shown by the first inlet curve126increases less than the second inlet curve128as the bleed air44percentage increases. Thus, increasing the bleed air44directed along the first bleed path50as shown by the first inlet curve126may affect the compressor inlet temperature122less than increasing the bleed air44directed along the second bleed path52, as shown by the second inlet curve128. Cooler inlet air temperatures122may result in greater mass flows through the compressor26and greater output of the turbine22. Warmer inlet air temperatures122may protect the compressor26in low load conditions. Cooler inlet air temperatures122may protect the compressor26at higher load conditions.

In some embodiments, the compressor discharge temperature124of the first discharge curve130may decrease or stay approximately the same as the amount of bleed air44directed along the first bleed path50increases. In the illustrated embodiments, the first discharge curve130may decrease between approximately 404° C. and 400° C. and the second discharge curve132may increase between approximately 404° C. and 433° C. for bleed air portions between 0 and 6%. The cooler inlet air temperature122may result in a dense air flow through the compressor26, and the first discharge curve130may decrease at least in part due to less energy applied by the compressor26per unit of mass of the dense air flow. Increasing the amount of bleed air44recirculated along the second bleed path52may decrease the density and mass flow through the compressor26. Less mass flow through the compressor26may increase the compressor discharge temperature124as shown by the second discharge curve132. Additionally, the inlet temperature122is higher and may thus increase the compressor discharge temperature124. A low compressor discharge temperature124may enable more fuel14to be combusted in the combustor16than a high compressor discharge temperature124. In some embodiments, a low compressor discharge temperature124may enable the pressurized air42to rise in temperature in the combustor16more than a high compressor discharge temperature124, which may result in a greater output from the turbine22.

Presently contemplated embodiments are not limited to directing the entire flow of bleed air44along either the first bleed path50as indicated by the first set of curves106or the second bleed path52as indicated by the second set of curves108. As discussed above, the controller82may be configured to adjust the first bleed air portion54directed along the first bleed path50and the second bleed air portion56directed along the second bleed path52to produce any desired division of the bleed air44into the non-zero first bleed air portion54and the second bleed air portion56. The controller82may be configured to adjust the split of the bleed air44by controlling one or more valve assemblies66. In this manner, the controller82may be configured to adjust the heat rate110, output112, compressor inlet temperature122, or compressor discharge temperature124, or combinations thereof. The controller82may be configured to divide the bleed air44into the first bleed air portion54and the second bleed air portion56to produce one or more desired properties of the system. For example, directing a 3% first bleed air portion54and a 3% second bleed air portion56along the first and second bleed paths50,52respectively may result in a heat rate between approximately 9,200 and 9,500 BTU/kWh (e.g., 9,350 BTU/kWh) and a system output between approximately 245,000 and 253,000 BTUs (e.g., 249,000 BTUs). Similarly, directing a 3% first bleed air portion54and a 3% second bleed air portion56along the first and second bleed paths50,52respectively may result in a compressor inlet temperature between approximately 16° C. and 28° C. (e.g., 22° C.) and a compressor discharge temperature between approximately 403° C. and 419° C. (e.g., 411° C.).

Presently contemplated embodiments discussed above include directing bleed air44of pressurized air42from a compressor26to protect the compressor26from surge and/or stall conditions and recovering energy from the bleed air44to drive a supplementary load60or contribute to driving a common load28. Technical effects of the invention include adding flexibility to a gas turbine system10by offering an inlet bleed circuit38with multiple bleed paths50,52to adjust the protection offered to the compressor26and output produced by the gas turbine system10. Directing the bleed air44directly to the compressor inlet (e.g., IBH system) may stabilize the operation of the compressor26and protect against surge and stall conditions at low loads while decreasing the output of the gas turbine system10. Directing the bleed air44through a turbo-expander58before directing the bleed air44to the inlet may stabilize the operation of the compressor26at higher loads without decreasing the output of the gas turbine system10as much as with the IBH system alone. In this way, the operational range of the gas turbine system10may be expanded to provide compressor protection at a range of load conditions with greater output at higher loads. Adjusting the quantity of the bleed air44as a percentage of the pressurized air42and adjusting how the bleed air44is recirculated to the compressor inlet enables control of the output of the gas turbine system10in a variety of operating and load conditions. The controller82may dynamically adjust the inlet bleed circuit38during operation to control the gas turbine system10as described above.