Patent Application
20090235634
The present invention relates to the operation of a turbomachine, and more particularly to a system for extending the turndown range by heating the inlet-air.
Turbomachines, such as gas turbines, aero-derivatives, or the like, commonly operate in a combined-cycle and/or cogeneration mode. In combined-cycle operation, a heat recovery steam generator, which generates steam, receives the exhaust-gas from the turbomachine; the steam then flows to a steam turbine that generates additional electricity. In a co-generation operation, a portion of the steam generated by the heat recovery steam generator is sent to a separate process requiring the steam.
Combined-cycle and cogeneration plants are rated to generate the maximum amount of energy (mechanical, electrical, etc) while operating at baseload. However, baseload operation, though desired by operators, is not always feasible. There may not be a demand in the energy market (electrical grid, or the like) for all of the energy generated at baseload. Here, the powerplant must either shutdown or operate at partload, where less than the maximum amount of energy is generated.
Turbomachines are typically required to maintain emissions compliance while generating power. A turbomachine operating at partload, may not maintain emissions compliance over the entire partload range, (from spinning reserve to near baseload). Turndown range may be considered the loading range where the turbomachine maintains emissions compliance. A broad turndown range allows operators to maintain emissions compliance, minimize fuel consumption, and avoid the thermal transients associated with shutting down the powerplant.
For the foregoing reasons, there is a need for a system for extending the turndown range. The system should reduce the fuel consumed by the turbomachine while operating at the partload range. The system should not require significant changes to the turbomachine.
In accordance with an embodiment of the present invention, a system for extending a turndown range of a turbomachine operating at partload, the system comprising: a turbomachine comprising a compressor, which receives an inlet-air; a combustion system; and a turbine section; wherein the turbomachine produces an exhaust-gas; a heat recovery steam generator (HRSG), wherein the HRSG receives a portion of the exhaust-gas and produces steam; and at least one air preheater comprising at least one heat exchanging section, wherein the at least one air preheater heats the inlet-air before the inlet-air flows to the compressor; wherein a portion of the at least one heat exchanging section receives a fluid at a temperature allowing for heating of the inlet-air; and wherein the fluid flows from a source external to the turbomachine; and wherein heating the inlet-air reduces an output of the turbomachine and extends the turndown range.
The following detailed description of preferred embodiments refers to the accompanying drawings, which illustrate specific embodiments of the invention. Other embodiments having different structures and operations do not depart from the scope of the present invention.
The present invention may be applied to a wide variety of turbomachines including, but not limiting of, gas turbines, aero-derivative combustion turbines, and the like. An embodiment of the present invention takes the form of an application and process that may heat the air entering a turbomachine (hereinafter “gas turbine”) to increase the turndown range.
An embodiment of the present invention has the technical effect of extending the turndown range by heating the air (hereinafter “inlet-air”) entering the compressor of the gas turbine. As described below, the inlet-air is heated by an energy source external to the gas turbine.
Referring now to the Figures, where the various numbers represent like elements throughout the several views,
During baseload operation, the combustion system 135 may ensure that the exhaust-gas 150 flowing out of the stack 115 meets the site emissions requirements. Depending on the turndown range of the gas turbine 105, certain partload operations may violate the site emissions requirements, which may require the shutdown of the gas turbine 105. An increase in the turndown range may avoid the need to shutdown the gas turbine 105. Also, an extended turndown range allows for operating the gas turbine 105 at lower loads, while maintaining emissions compliance and consuming less fuel 140.
The present invention extends the turndown range by heating the inlet-air 130. Generally, the output (electrical, mechanical, or the like) of a gas turbine 105 is governed by the amount of mass-flow entering the compressor 120. The mass-flow may be considered the product of the density and the volume-flow of the inlet-air 130 entering the compressor 120. The amount of volume-flow entering the compressor 120 may vary on the ambient temperature conditions and the angle of Variable Inlet Guide Vanes (IGVs), if present on the gas turbine 105. The IGV angle may determine the flow area at the inlet of the compressor 120. The IGV angle may be reduced to a minimum angle, limiting the amount of turndown. At the minimum IGV angle, a corresponding minimum volume-flow is drawn into the compressor 120.
In the present invention, the heating of the inlet-air 130 decreases the density, allowing less dense inlet-air 130 to enter the compressor 120. Here, at a given load point the volume-flow entering the compressor 120 may remain constant, however the mass-flow decreases due to the decrease in density of the inlet-air 130. As discussed, the output of the gas turbine 105 may be determined by the mass-flow entering the gas turbine 105; therefore less output is produced due to the heating of the inlet-air 130, compared to not heating of the inlet-air 130.
The heating of the inlet-air 130 also increases the temperature (hereinafter “compressor discharge temperature”) of the air 130 exiting the compressor 120. This heated inlet-air 130 then enters the combustion system 135. The heated air 130 aids in reaching the overall universal reference temperature (“firing temperature”) of the gas turbine 105. The heated inlet-air 130 allows the gas turbine 105 to consume less fuel 140 to obtain the firing temperature. Here, more fuel 140 would be consumed if unheated inlet-air 130 entered the compressor 120.
Overall, the present invention incorporates at least one air preheater 155, which may be installed upstream of the compressor 120. The air preheater 155 may be a heat exchanger, or the like. The air preheater 155 may be sized to adequately heat the inlet-air 130 to a temperature that increases the turndown range.
Generally, the temperature of the unheated inlet-air 130 may be determined by the ambient conditions or the outlet temperature of any air conditioning system (not illustrated) located upstream of the air preheater 155. An embodiment of the present invention may increase the temperature of the inlet-air 130 to any temperature allowed for by the air preheater 155. However, the increase in temperature of the inlet-air 130 may be limited by at least one of several factors, such as but not limiting of, the geometrical limitations of the air preheater 155; a temperature that may violate a thermal, operational, or mechanical limitation; or the like. For example, but not limiting of, the system 100 may increase the temperature of the inlet-air 130 from approximately 59 degrees Fahrenheit to approximately 120 degrees Fahrenheit. Here, the inlet-air 130 may have an inlet flowrate of 3,000,000 pounds/hour.
The system 100, illustrated in
This first embodiment of the present invention allows a user to determine where the exhaust-gas 150 is extracted from on the HRSG 110. The present invention may allow a user to optimize the location on the HRSG 110 where the exhaust-gas 150 is extracted and sent to the air preheater 155. A user may consider a variety of factors when determining the optimized location on the HRSG 110. These factors may include, for example, but not limiting of, the following. Temperature: the temperature of the fluid used to increase the temperature of the inlet-air 130 (exhaust-gas 150, water, steam, or the like), should be higher than the maximum desired temperature that the inlet-air 130 may be raised to by the air preheater 155. The maximum desired temperature might be used for sizing the air preheater 155. Flow: flow of the fluid should be sufficient to supply the air preheater 155, while maintaining sufficient flow for other demands from the HRSG 110, or the like. Fluid type: the use of water, if available, as the fluid for increasing the temperature of the inlet-air 130 may be optimum, possibly requiring less mass-flow and a relatively smaller sized air preheater 155. Energy Source: the fluid may derive from an energy source that may be utilized without negatively impacting the overall benefits of heating the inlet-air 130. The energy source may include, for example, but not limiting of, outlet from a condenser or fuel heater 175; packing flows, or the like; exhaust-gas 150: discharge from the stack 115; any other energy source external to the bottoming cycle.
For example, but not limiting of, an operator of the site may use a portion of the exhaust-gas 150 flowing towards the condenser (not illustrated). Here, this energy may be considered ‘low value’ because the energy needed to create steam may have been already extracted. However, another site, may extract the exhaust-gas 150 from another area of the HRSG 110. Here, for example, but not limiting of, an operator may decide that instead of restricting the flow of the exhaust-gas 150 entering a section of the HRSG 110, divert a portion of the exhaust-gas 150 to the air preheater 155.
In use, the system 100 operates while the gas turbine 105 is not at baseload. As the gas turbine 105 unloads, the present invention may divert a portion of the exhaust-gas 150 to the air preheater 155 via the preheater supply 160. The exhaust-gas 150 may flow through an inlet portion of the air preheater 155. As the inlet-air 130 flows through the air preheater 155, the heat from the exhaust-gas 150 is transferred to, and increases the temperature of, the inlet-air 130. After flowing through the air preheater 155, the exhaust-gas 150 may flow through the preheater discharge line 165 to the stack 115 and/or the HRSG 110.
The EES 170 may provide sufficient energy to heat the inlet-air 130 to the temperature that allows for extending the turndown range. As illustrated in
The EES 170 may include at least one of the following energy systems: a wind turbine, a boiler, an engine, an additional combustion turbine, an additional HRSG, a power plant, a solar energy source, geothermal energy source, fuel cell/chemical reaction, external process, and combinations thereof; none of which are illustrated in
For example, but not limiting of, a wind turbine may indirectly increase the temperature of the inlet fluid 130. Here, the energy generated by the wind turbine may heat water within a tank (not illustrated) integrated with the preheater supply line 160. The heated water may flow through the preheater supply line 160 to the air preheater 155. After flowing through the air preheater 155, the heated water may flow through the preheater discharge line 165, which may be integrated with the EES 170. Alternatively, for example, but not limiting of, a boiler may directly increase the temperature of the inlet fluid 130. Here, the preheater supply line 160 may be integrated with a portion of the boiler. The steam or hot water generated by the boiler may flow through the preheater supply line 160 and the air preheater 155. After flowing through the air preheater 155, the steam or hot water may flow through the preheater discharge line 165, which may be integrated with the EES 170.
As illustrated in
In this third embodiment, the preheater supply line 160 may be integrated with a fuel heater supply line 180. Here, a portion of the exhaust-gas 150 may flow into the fuel heater 175. Another portion of the exhaust-gas 150 may flow into the air preheater 155. After flowing through the fuel heater 175, the exhaust-gas 150 may flow through the fuel heater discharge line 185 to the air preheater 155. After flowing to the air preheater 155, the exhaust-gas 150 may then flow through the preheater discharge line 165 to the stack 115 and/or the HRSG 110, as previously described.
In this fourth embodiment of the present invention, an end of the preheater supply line 160 is connected to a portion of the stack 115, where the exhaust-gas 150 is extracted. The exhaust-gas 150 may flow through the preheater supply line 160, which may have an opposite end connected to a portion of the air preheater 155.
The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof.
Although specific embodiments have been illustrated and described herein, it should be appreciated that any arrangement, which is calculated to achieve the same purpose, may be substituted for the specific embodiments shown and that the invention has other applications in other environments. This application is intended to cover any adaptations or variations of the present invention. The following claims are in no way intended to limit the scope of the invention to the specific embodiments described herein.
