Abstract:
A system and method for supercharging a combined cycle system includes a forced draft fan providing a variable air flow. At least a first portion of the air flow is directed to a compressor and a second portion of the airflow is diverted to a heat recovery steam generator. A control system controls the airflows provided to the compressor and the heat recovery steam generator. The system allows a combined cycle system to be operated at a desired operating state, balancing cycle efficiency and component life, by controlling the flow of air from the forced draft fan to the compressor and the heat recovery steam generator.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is related to application Ser. No. 13/485,216, titled GAS TURBINE COMPRESSOR INLET PRESSURIZATION AND FLOW CONTROL SYSTEM, filed jointly in the names of John Anthony Conchieri, Robert Thomas Thatcher, and Andrew Mitchell Rodwell and application Ser. No. 13/485,273, titled GAS TURBINE COMPRESSOR INLET PRESSURIZATION HAVING A TORQUE CONVERTER SYSTEM, filed jointly in the names of Sanji Ekanayake and Alston I. Scipio, each assigned to General Electric Company, the assignee of the present invention. 
     
    
     TECHNICAL FIELD 
       [0002]    The subject matter disclosed herein relates to combined cycle power systems and more particularly to supercharged combined cycle systems with air flow bypass. 
       BACKGROUND 
       [0003]    Combined cycle power systems and cogeneration facilities utilize gas turbines to generate power. These gas turbines typically generate high temperature exhaust gases that are conveyed into a heat recovery steam generator (HRSG) that produces steam. The steam may be used to drive a steam turbine to generate more power and/or to provide steam for use in other processes. 
         [0004]    Operating power systems at maximum efficiency is a high priority for any generation facility. Factors including load conditions, equipment degradation, and ambient conditions may cause the generation unit to operate under less than optimal conditions. Supercharging (causing the inlet pressure to exceed the ambient pressure) turbine systems as a way to increase the capacity of gas-turbine is known. Supercharged turbine systems typically include a variable speed supercharging fan located at the gas turbine inlet that is driven by steam energy derived from converting exhaust waste heat into steam. The supercharging fan is used to increase the air mass flow rate into the gas turbine so that the gas turbine shaft horsepower can be augmented. 
         [0005]    Additional high priorities for operators of generation facilities are maintenance costs and availability. One component of maintenance costs is equipment life. There are many factors that influence equipment life, among them are the type of fuel used, the operating hours at base load, the operating hours at peak load, and water steam injection into the compressor airflow. These factors influence the life of hot gas path parts. Increased temperatures in the turbine may have an impact on the lifetime of the components positioned along the hot gas path and elsewhere. Typically, operations above base load will reduce the lifetime of the hot gas path components while operations below base load generally will extend component lifetime. Under some conditions an operator may be willing to sacrifice efficiency for extended life of hot gas path parts in order to lessen maintenance costs. However, conventional combined cycle systems do not provide an adequate level of control of hot gas path parts life. 
       BRIEF DESCRIPTION OF THE INVENTION 
       [0006]    In accordance with one exemplary non-limiting embodiment, the invention relates to a method for extending life of hot gas path parts of a turbine system. The method includes the steps of determining a desired load; determining a nominal firing temperature for the desired load; and determining a supercharged firing temperature for the desired load. The method further includes the steps of determining a first mass flow quantity of air to be provided to a compressor in the turbine system to achieve the supercharged firing temperature for the desired load; providing an air flow; and conveying the first mass flow quantity of air into the compressor. 
         [0007]    In another embodiment, the invention relates to a method for extending hot gas path parts life in a turbine system. The method includes the steps of determining a desired load; determining an efficiency trade off; and determining a desired maintenance factor. The method further includes the steps of determining an amount of supercharging required to achieve the desired maintenance factor for the desired load. The method includes determining a first mass flow quantity of air to be provided to a compressor to achieve the amount of supercharging; and determining a second mass flow quantity of air to be provided to a heat recovery steam generator. The method further includes the steps of providing an air flow; conveying the first mass flow quantity of air into the compressor; and conveying the second mass flow quantity of air to the heat recovery steam generator. 
         [0008]    In another embodiment, the invention relates to a method for ramping up a combined cycle system having a gas turbine and a heat recovery steam generator. The method includes the steps of determining a desired load; determining a present load; and determining whether the desired load is greater than the present load. The method further includes the steps of determining an incremental load increase; and determining a desired firing temperature for the present load plus the incremental load increase. The method further includes the steps of calculating a first supercharged mass flow to the gas turbine to achieve the desired firing temperature for the present load plus the incremental load increase; increasing the load to the present load plus the incremental load increase; and providing the first supercharged mass flow to the gas turbine. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    Other features and advantages of the present invention will be apparent from the following more detailed description of the preferred embodiment, taken in conjunction with the accompanying drawings which illustrate, by way of example, the principles of certain aspects of the invention. 
           [0010]      FIG. 1  is a schematic illustration of an embodiment of a supercharged combined cycle system with air bypass. 
           [0011]      FIG. 2  is a schematic illustration of another embodiment of a supercharged combined cycle system with air bypass. 
           [0012]      FIG. 3  is a flow chart of an embodiment of a method implemented by a supercharged combined cycle system with air bypass. 
           [0013]      FIG. 4  is a chart illustrating a result accomplished by a supercharged combined cycle system with air bypass. 
           [0014]      FIG. 5  is a flow chart of an embodiment of a method implemented by a supercharged combined cycle system with air bypass. 
           [0015]      FIG. 6  is a chart illustrating a result accomplished by a supercharged combined cycle system with air bypass. 
           [0016]      FIG. 7  is a chart illustrating a result accomplished by a supercharged combined cycle system with air bypass. 
           [0017]      FIG. 8  is a schematic illustration of another embodiment of a supercharged combined cycle system with air bypass. 
           [0018]      FIG. 9  is a schematic illustration of an embodiment of a control system used to control a supercharged combined cycle system with air bypass. 
           [0019]      FIG. 10  is a schematic illustration of an embodiment of a prime mover used to drive a forced draft fan. 
           [0020]      FIG. 11  is a schematic illustration of an embodiment of a prime mover used to drive a forced draft fan. 
           [0021]      FIG. 12  is a schematic illustration of an embodiment of a prime mover used to drive a forced draft fan. 
           [0022]      FIG. 13  is a schematic illustration of an embodiment of a prime mover used to drive a forced draft fan. 
           [0023]      FIG. 14  is a schematic illustration of an embodiment of a prime mover used to drive a forced draft fan. 
           [0024]      FIG. 15  is a schematic illustration of an embodiment of a prime mover used to drive a forced draft fan. 
           [0025]      FIG. 16  is a table summarizing the advantages and disadvantages of different prime movers. 
           [0026]      FIG. 17  is a chart showing the relationship between output and a change in T-fire for a gas turbine that is not supercharged (nominal) and a gas turbine that is supercharged by 10%. 
           [0027]      FIG. 18  is a chart illustrating the impact of supercharging on the maintenance factor. 
           [0028]      FIG. 19  is a chart illustrating the impact of supercharging on T-fire, heat rate and output at peak load. 
           [0029]      FIG. 20  is a chart illustrating the impact of supercharging on T-fire, heat rate and output at base load. 
           [0030]      FIG. 21  is a chart illustrating the impact of supercharging on T-fire, heat rate and output at 90% load. 
           [0031]      FIG. 22  is a chart illustrating the impact of supercharging on T-fire, heat rate and output at 80% load. 
           [0032]      FIG. 23  is a flow chart for a method for extending the life of hot gas path parts of a gas turbine system using supercharging. 
           [0033]      FIG. 24  is a flowchart of a method for reducing a maintenance factor in a turbine system. 
           [0034]      FIG. 25  is a flow chart of a method for operating a combined cycle system having a gas turbine and an HRSG. 
           [0035]      FIG. 26  is a flow chart for a method for ramping up a combined cycle system having a gas turbine and an HRSG. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0036]      FIG. 1  is a schematic illustration of a supercharged combined cycle system with air bypass (SCCAB system  11 ) in accordance with one embodiment of the present invention. The SCCAB system  11  includes a gas turbine subsystem  13  that in turn includes a compressor  15 , having a compressor inlet  16 , a combustor  17  and a turbine  19 . An exhaust duct  21  may be coupled to the turbine  19  and a heat recovery steam generator subsystem (HRSG  23 ). The HRSG  23  recovers heat from exhaust gases from the turbine  19  that are conveyed through HRSG inlet  24  to generate steam. The HRSG  23  may also include a secondary burner  25  to provide additional energy to the HRSG  23 . Some of the steam and exhaust from the HRSG  23  may be vented to stack  27  or used to drive a steam turbine  26  and provide additional power. Some of the steam from the HRSG  23  may be transported through process steam outlet header  28  to be used for other processes. The SCCAB system  11  may also include an inlet house and cooling system  29 . The inlet house and cooling system  29  is used to cool and filter the air entering the compressor inlet  16  to increase power and avoid damage to the compressor  15 . 
         [0037]    The SCCAB system  11  also includes a forced draft fan  30  used to create a positive pressure forcing air into the compressor  15 . Forced draft fan  30  may have a fixed or variable blade fan (not shown). Forced draft fan  30  may be driven by a prime mover  31 . The forced draft fan  30  provides a controllable air stream source though a duct assembly  32  and may be used to increase the mass flow rate of air into the compressor  15 . The quantity of air going into the compressor is controlled by the prime mover  31 . The compressor inlet  16  may be configured to accommodate slight positive pressure as compared to the slight negative pressure of a conventional design. 
         [0038]    The SCCAB system  11  may also include a bypass  33  (which may include external ducting) that diverts a portion of the air flow from forced draft fan  30  into the exhaust duct  21 . This increased air flow provides additional oxygen to the secondary burner  25  to avoid flame out or less than optimal combustion. Bypass  33  may be provided with a flow sensor  35  and a damper valve  37  to control the airflow through the bypass  33 . A control system  39  may be provided to receive data from flow sensor  35  and to control the damper valve  37  and the prime mover  31 . Control system  39  may be integrated into the larger control system used for operation control of SCCAB system  11 . The airflow from the bypass is conveyed to the exhaust duct  21  where the temperature of the combined air and exhaust entering the HRSG  23  may be modulated. 
         [0039]    Illustrated in  FIG. 2  is another embodiment of a SCCAB system  11  that includes a pair of gas turbine subsystem(s)  13 . In this embodiment, the exhaust of the pair of gas turbine subsystem(s)  13  is used to drive a steam turbine  26 . In this embodiment, an inlet house  41  is positioned upstream of the forced draft fan  30 , and a cooling system  43 , where the airflow from the fan may be cooled, is positioned downstream of the forced draft fan  30 . The bypass  33  is coupled to the cooling system  43 . One of ordinary skill in the art will recognize that although in this embodiment two gas turbine subsystem(s)  13  are described, any number of gas turbine subsystem(s)  13  in combination with any number of steam turbine(s)  27  may be used. 
         [0040]    In operation, the SCCAB system  11  provides increased air flow into the HRSG  23  resulting in a number of benefits. The SCCAB system  11  may provide an operator with the ability to optimize combined cycle plant flexibility, efficiency and lifecycle economics. For example, boosting the inlet pressure of the gas turbine subsystem  13  improves output and heat rate performance. The output performance of the SCCAB system  11  may be maintained flat (zero degradation) throughout the life cycle of SCCAB system  11  by increasing the level of supercharging (and parasitic load to drive the forced draft fan  30 ) over time commensurate with the degradation of SCCAB system  11 . Another benefit that may be derived from the SCCAB system  11  is the expansion of the power generation to steam production ratio envelope. This may be accomplished by modulating the exhaust gas temperature at HRSG inlet  24  with air from the forced draft fan  30 . Another benefit that may be derived from the SCCAB system  11  is an improved start up rate as a result of the reduction in the purge cycle (removal of built up gas). The SCCAB system  11  may also provide an improved load ramp rate resulting from the modulation of the exhaust temperature at the exhaust duct  21  with air from the forced draft fan  30  provided through the bypass  33 . The forced draft fan  30  of the SCCAB system  11  also provides an effective means to force-cool the gas turbine subsystem  13  and HRSG  23 , reducing maintenance outage time and improving system availability. The forced draft fan  30  provides comparable benefit for simple cycle and combined-cycle configurations for all gas turbine subsystem(s)  13  delivering in the range of 20% output improvement under hot ambient conditions with modest capital cost. 
         [0041]    The SCCAB system  11  may implement a method of maintaining the output of a combined cycle plant over time (method  50 ) as illustrated with reference to  FIG. 3 . In step  51 , the method  50  may determine the current state, and in step  53 , the method  50  may determine a desired state. The desired state may be to maintain a nominal output over time to compensate for performance losses. Performance losses typically arise as a result of wear of components in the gas turbine over time. These losses may be measured or calculated. In step  55 , the method  50  may determine the required increased air mass flow to maintain the desired output. Based on that determination, the method  50  may, in step  57  adjust the air mass flow into the compressor inlet  16 . In step  59 , the method  50  may adjust the combined air and exhaust mass flow into the HRSG inlet  24 . 
         [0042]      FIG. 4  illustrates the loss of output and heat rate over time (expressed in percentages) of a conventional combined cycle system and a SCCAB system  11 . Gas turbines suffer a loss in output over time, as a result of wear of components in the gas turbine. This loss is due in part to increased turbine and compressor clearances and changes in surface finish and airfoil contour. Typically maintenance or compressor cleaning cannot recover this loss, rather the solution is the replacement of affected parts at recommended inspection intervals. However, by increasing the level of supercharging using forced draft fan  30 , output performance may be maintained, although at a cost due to the parasitic load to drive the forced draft fan  30 . The top curve (unbroken double line) illustrates the typical output loss of a conventional combined cycle system. The second curve (broken double lines) illustrates the expected output loss with periodic inspections and routine maintenance. The lower curve (broken triple line) shows that the output loss of an SCCAB system  11  may be maintained at near 0%. Similarly, the heat rate degradation of a conventional combined cycle system (single solid curve) may be significantly improved with an SCCAB system  11 . 
         [0043]      FIG. 5  illustrates a method of controlling the steam output of a SCCAB system  11  (method  60 ). In step  61 , method  60  may initially determine the current state. In step  63 , the method  60  may also determine the desired output and steam flow. In step  65 , the method  60  may determine the required increased air flow to the compressor inlet  16  and the HRSG inlet  24 . In step  67 , method  60  may then adjust the air flow into the compressor inlet  16  and in step  69 , adjust the combined exhaust and air flow into the HRSG inlet  24 , to provide the desired steam output. 
         [0044]      FIG. 6  illustrates an expanded operating envelope available to maintain constant steam flow. The vertical axis measures output in MW and horizontal axes measures steam mass flow. The interior area (light vertical cross hatch) shows the envelope of a conventional combined cycle system. The envelope of an SCCAB system  11  is shown in diagonal cross hatching, and a larger area illustrates the performance of an SCCAB system  11  combined with secondary firing in the HRSG  23 . 
         [0045]      FIG. 7  is a chart that illustrates the improved operational performance of an SCCAB system  11  at a specific ambient temperature in comparison with conventional combined cycle systems at minimum and base loads. The horizontal axis measures output in MW and the vertical axis measures heat rate (the thermal energy (BTU&#39;s) from fuel required to produce one kWh of electricity). The chart illustrates the improved efficiency delivered by the SCCAB system  11 . 
         [0046]    Illustrated in  FIG. 8  is a schematic illustration of a combined cycle system  111  in accordance with another embodiment of the present invention. The combined cycle system  111  includes a gas turbine subsystem  113  that in turn includes a compressor  115 , having a compressor inlet  116 , a combustor  117  and a turbine  119 . An exhaust duct  121  may be coupled to the gas turbine subsystem  113  and a heat recovery steam generator subsystem (HRSG  123 ). The HRSG  123  recovers heat from exhaust gases from the gas turbine subsystem  113  that are conveyed through HRSG inlet  124  to generate steam. Some of the steam and exhaust from the HRSG  123  may be used to drive a steam turbine  126  and provide additional power, or vented to stack  127 . Some of the steam from the HRSG  123  may be transported through process steam outlet header  128  to be used for other processes. 
         [0047]    The combined cycle system  111  also includes a forced draft fan  130  used to create a positive pressure forcing air into the compressor  115 . Forced draft fan  130  may be a fixed or variable blade fan. Forced draft fan  130  may be driven by a prime mover  131 . The forced draft fan  130  provides a controllable air stream source though a duct assembly  132  and may be used to increase the mass flow rate of air into the gas turbine subsystem  113 . The quantity of air going into the gas turbine subsystem  113  is controlled by the prime mover  131 . 
         [0048]    The combined cycle system  111  may also include an inlet house  141  and cooling system  143 . The inlet house  141  and cooling system  143  cool and filter the air entering the gas turbine subsystem  113  to increase power and avoid damage to the compressor. In some embodiments the inlet house  141  and the cooling system  143  may be combined and disposed downstream from the forced draft fan  130 . 
         [0049]    The combined cycle system  111  may also include a bypass  133  (which may include external ducting) that diverts a portion of the air flow from forced draft fan  130  into the exhaust duct  121 . Bypass  133  may be provided with a flow sensor  139  and a bypass damper valve  137  to control the airflow through the bypass  133 . The airflow from the bypass is conveyed to the exhaust duct  121  where the temperature of the combined air and exhaust entering the HRSG  123  may be modulated. 
         [0050]    The combined cycle system  111  may also include a drive bypass  145  coupled to the prime mover  131 . The drive bypass  145  is provided with a drive damper valve  146  and a drive system sensor  147 . The prime mover  131  may also be provided with a secondary conduit  148  having a secondary damper valve  149  and a secondary sensor  150 . The prime mover is coupled to the forced draft fan  130  by a conduit  151 . In some embodiments, the exhaust of the prime mover  131  may be conveyed to the HRSG  23  through a drive exhaust conduit  155 . 
         [0051]    In operation, the prime mover  131  drives the forced draft fan  130  to provide an air flow at a predetermined mass flow rate. The air flow may be cooled by cooling system  143 . The airflow may be divided into a first mass flow quantity to be conveyed to the compressor inlet  116 , a second mass flow quantity to be conveyed to the exhaust duct  121 , and in some cases a third mass flow quantity to be conveyed to the prime mover  131 . Control of the first mass flow quantity, the second mass flow quantity, and the third mass flow quantity is effected through the controls of bypass damper valve  137 , drive damper valve  146 , and secondary damper valve  149 . By controlling the first mass flow quantity, the second mass flow quantity and the third mass flow quantity the operator is provided with more effective control of the operating envelope of the combined cycle system  111 . 
         [0052]      FIG. 9  illustrates the control system  161  used to control bypass damper valve  137 , drive damper valve  146  and secondary damper valve  149 . Control system  161  receives readings from flow sensor  139 , drive system sensor  147  and secondary sensor  150 . The control system  161  may be a conventional General Electric Speedtronic™ Mark VI Gas Turbine Control System. The SpeedTronic controller monitors various sensors and other instruments associated with a gas turbine. In addition to controlling certain turbine functions, such as fuel flow rate, the SpeedTronic controller generates data from its turbine sensors and presents that data for display to the turbine operator. The data may be displayed using software that generates data charts and other data presentations, such as the General Electric Cimplicity™ HMI software product. 
         [0053]    The Speedtronic™ Mark VI Gas Turbine Control System is a computer system that includes microprocessors that execute programs to control the operation of the gas turbine using sensor inputs and instructions from human operators. The control system includes logic units, such as sample and hold, summation and difference units, which may be implemented in software or by hardwire logic circuits. The commands generated by the control system processors cause actuators on the gas turbine to, for example, adjust the fuel control system that supplies fuel to the combustion chamber, set the inlet guide vanes to the compressor, and adjust other control settings on the gas turbine. 
         [0054]    Illustrated in  FIG. 10  is an embodiment where the prime mover  131  is a gas turbine  159 . Gas turbine  159  provides certain benefits over another type of prime mover  131 . These benefit include greater reliability, particularly in applications where sustained high power output is required and high efficiencies at high loads. The drawbacks to the use of a gas turbine  159  as a prime mover  131  include lower efficiency than reciprocating engines at part loads and higher costs. In operation the gas turbine  159  receives supercharged and cooled air through drive bypass  145  and its exhaust may be conveyed to the HRSG  123  though drive exhaust conduit  155  for best cycle efficiency and flexibility. This results in excellent full-load and part-load efficiency and operational flexibility. The forced draft fan  130  driven by gas turbine  159  eliminates output degradation over time by trading efficiency to make up for output degradation. The forced draft fan  130  driven by gas turbine  159  also provides the operator with the ability to expand the power generation to steam production ratio envelope. Furthermore, the forced draft fan  130  driven by gas turbine  159 , increases net power production and improves efficiency of gas turbine subsystem  113  and combined cycle system  111 . By expanding the operating envelope, the operator may reduce the negative capital &amp; operating cost impact of needing to add a unit at a multi-unit power block where there is a partial output shortfall. The use of a gas turbine  159  has the disadvantages of high capital and maintenance costs. Gas turbine  159  provides a subsystem of medium complexity with high cycle efficiency and very high peak output at fixed supercharger boost. 
         [0055]      FIG. 11  illustrates another embodiment where an aeroderivative gas turbine  171  is used as the prime mover  131 . An aeroderivative gas turbine  171  is a gas turbine derived from an aviation turbine. The decision to use aeroderivative gas turbine  171  is mainly based on economical and operational advantages. They are relatively light weight and offer high performance and efficiency. Aeroderivative gas turbine  171  permits efficient control of torque together with potential for integrated control. Common economic/operational advantages and benefits of the aeroderivative gas turbine  171  compared to conventional heavy frame gas turbine drivers are a 10 to 15 percent improvement in efficiency. An aeroderivative gas turbine  171  provides a smooth, controlled start. Aeroderivative gas turbine  171  has higher availability and operational reliability and its wide load range permits economically optimized power control. An aeroderivative gas turbine  171  also provides an advantage over conventional heavy frame gas turbine drivers due to its ability to be shut down, and ramped up rapidly and to handle load changes more efficiently. An aeroderivative gas turbine  171  provides high cycle efficiency and very high peak output at a fixed supercharger boost. The advantages of the aeroderivative gas turbine  171  for this application must be balanced against some disadvantages, including high capital costs and very high maintenance costs. 
         [0056]      FIG. 12  illustrates another embodiment where a steam turbine  173  is used as the prime mover  131 . A steam turbine is a device that extracts thermal energy from pressurized steam and uses it to do mechanical work on a rotating output shaft. The use of a steam turbine  173  provides the advantage of being able to use wide range of fuels to drive the steam turbine  173 . In comparison to the other prime movers, the steam turbine has an average capital cost, maintenance cost, cycle efficiency, and peak output at fixed supercharger boost. Steam turbine  173  also has a high subsystem complexity. However, steam turbine  173  has the disadvantage of requiring boiler and other equipment and a higher price-to-performance ratio. A steam turbine  173  has a slow load change behavior, which means once running the steam turbine  173  cannot be stopped quickly. A specific amount of time is needed to slow down its revolutions. A steam turbine  173  also has poor part load performance. 
         [0057]      FIG. 13  illustrates another embodiment where an induction motor  175  is used as the prime mover  131 . An induction motor  175  is a type of AC motor where power is supplied to the rotor by means of electromagnetic induction, rather than a commutator or slip rings as in other types of motors. Induction motor  175  has the advantage of being rugged, easy to operate, and having low capital and maintenance costs. Induction motor  175  also has the advantage of providing a subsystem of low complexity. Another advantage of an induction motor  175  is the ability to regulate the torque output and modulate the energy output of the induction motor  175 . Induction motor  175  has the disadvantage of low cycle efficiency and low peak output at fixed supercharger boost. 
         [0058]      FIG. 14  illustrates another embodiment where a reciprocating engine  177  is used as the prime mover  131 . The reciprocating engine  177 , also often known as a piston engine, is a heat engine such as a diesel engine that uses one or more reciprocating pistons to convert pressure into a rotating motion. Use of a reciprocating engine  177  to drive the forced draft fan  130  has the advantage of providing high efficiencies at part load operation and high cycle efficiencies. Peak output at fixed supercharger boost is very high with a reciprocating engine  177 . Additionally a reciprocating engine  177  has short start-up times to full loads. A reciprocating engine has average capital costs and maintenance cost. The complexity of the subsystem is average when compared to other prime movers. 
         [0059]    Illustrated in  FIG. 15  is another embodiment where a variable frequency drive (VFD  179 ) is used as the prime mover  131 . VFD  179  is a drive that controls the rotational speed of an electric motor by controlling the frequency of the electrical power supplied to the motor. VFD  179  provides a number of advantages, including low subsystem complexity and low maintenance costs as well as energy savings from operating at lower than nominal speeds. VFD  179  has average capital costs when compared with other prime movers and provides average cycle efficiency. Another advantage is that VFD  179  may be gradually ramped up to speed, lessening the stress on the equipment. A disadvantage is lower than average peak output at a fixed supercharger boost. 
         [0060]    The advantages and disadvantages of the different prime mover(s)  131  are summarized in the table in  FIG. 16 . 
         [0061]    Illustrated in  FIG. 17  is the relationship between output and a change in the firing temperature (“T-fire”) for a gas turbine that is not supercharged (nominal) and a gas turbine that is supercharged by 10%. From the chart it is apparent that for a given output, a lower T-fire can be obtained with supercharging. The difference is most pronounced at peak loads where under nominal operations the change in T-fire is positive (i.e. T-fire increases when compared to T-fire at base load.). But, under supercharged conditions the change in T-fire remains negative. 
         [0062]    Illustrated in  FIG. 18  is the impact of supercharging on the maintenance factor. Again, at peak loads the maintenance factor is significantly lower in the supercharged case compared to the maintenance factor for the nominal case. 
         [0063]      FIG. 19  illustrates the impact of supercharging on T-fire, heat rate and output at peak load. From the delta T-fire curve, it can be ascertained that significant negative change in T-fire may be obtained by supercharging without any impact on output.  FIGS. 20-22  illustrate the impact of supercharging on T-fire, heat rate and output at base load, 90% load, and 80% load respectively. The charts illustrate the impact of supercharging on delta T-fire, in effect demonstrating that supercharging can reduce T-fire at different loads without having a significant impact on the output. 
         [0064]    Illustrated in  FIG. 23  is a flowchart for a method  200  for extending the life of hot gas path parts of a gas turbine system using supercharging. 
         [0065]    In step  210 , the method  200  determines a desired load. 
         [0066]    In step  220 , the method  200  determines a nominal T-fire for the desired load. 
         [0067]    In step  230 , the method  200  determines the available reduction in T-fire with supercharging for the desired load. 
         [0068]    In step  240 , the method  200  determines a desired reduction in T-fire. 
         [0069]    In step  250 , method  200  calculates the supercharged mass flow required to achieve the reduction in T-fire. 
         [0070]    In step  260 , the method  200  increases the load to the desired load. 
         [0071]    In step  270 , the method  200  provides the supercharged mass flow required to achieve the reduction in T-fire. 
         [0072]    If the gas turbine system includes an HRSG, the method  200  may implement a step  280  to determine a nominal HRSG inlet temperature. 
         [0073]    In step  290 , the method  200  may determine the available HRSG inlet temperature reduction with supercharging. 
         [0074]    In step  300  the method  200  may determine the desired steam turbine inlet temperature reduction to achieve a desired HRSG inlet temperature. The method  200  proceeds to step  242  to determine the desired T-fire reduction. By reducing T-fire and the HRSG inlet temperature an operator can decrease the maintenance factor hot gas path components of the gas turbine and hot gas path components of the steam turbine coupled to the HRSG. 
         [0075]    Illustrated in  FIG. 24  is a flowchart of a method  400  for reducing a maintenance factor in a turbine system. 
         [0076]    In step  410 , the method  400  determines a desired load. 
         [0077]    In step  420 , the method  400  determines a nominal maintenance factor for the desired load. 
         [0078]    In step  430 , the method  400  determines the available maintenance factor decrease for the desired load with supercharging. 
         [0079]    In step  440 , the method  400  determines the desired maintenance factor. 
         [0080]    In step  450 , the method  400  calculates the supercharged mass flow required to achieve the desired maintenance factor. 
         [0081]    In step  460 , the method  400  ramps up the supercharge to the desired boost pressure and mass flow. 
         [0082]    In step  470 , the method  400  provides the supercharge mass flow to achieve the desired maintenance factor to the combustor exhaust. 
         [0083]    In step  480  the gas turbine system is adjusted to the desired load and maintenance factor. 
         [0084]    Illustrated in  FIG. 25  is a flow chart of a method  500  for operating a combined cycle system having a gas turbine and an HRSG. 
         [0085]    In step  510 , the method  500  determines a desired output. 
         [0086]    In step  520 , the method  500  determines the nominal T-fire for the desired output. 
         [0087]    In step  530 , the method  500  determines the nominal HRSG inlet temperature for the desired output. 
         [0088]    In step  540 , the method  500  determines the T-fire reduction available with supercharging. 
         [0089]    In step  550 , the method  500  determines the available steam turbine inlet temperature with supercharging. 
         [0090]    In step  560 , the method  500  determines the desired T-fire. 
         [0091]    In step  570 , the method  500  determines the desired HRSG inlet temperature. 
         [0092]    In step  580 , the method  500  calculates the supercharged mass flow required to achieve the reduction in T-fire. 
         [0093]    In step  590 , the method  500  calculates the supercharged mass flow (second supercharged mass flow provided at a predetermined temperature) that is required to achieve the desired HRSG inlet temperature. 
         [0094]    In step  600 , the method  500  increases the amount of supercharging to increase the boost pressure and mass flow to the required level. 
         [0095]    In step  610 , the method  500  provides the desired load, the desired gas turbine maintenance factor and the HRSG inlet temperature. 
         [0096]    Illustrated in  FIG. 26  is a flow chart for a method  700  for ramping up a combined cycle system having a gas turbine and an HRSG. 
         [0097]    In step  710 , the method  700  determines the desired load. 
         [0098]    In step  720 , the method  700  determines the present load. 
         [0099]    In step  730 , the method  700  determines whether the present load is equal to the desired load. If the present load is equal to desired load the method ends (step  740 ). If the present load is not equal to the desired load, then the method proceeds to step  750 . 
         [0100]    In step  750 , the method  700  determines an incremental change in load. 
         [0101]    In step  760 , the method  700  determines a desired T-fire. The desired T-fire may be determined by determining the nominal T-fire of the gas turbine the present load plus the incremental change in the load (step  770 ). 
         [0102]    In step  780 , the method  700  may determine the T-fire reduction available with supercharging. 
         [0103]    In step  790 , the method  700  may calculate the mass flow to be provided by the supercharger to the gas turbine in order to achieve the desired T-fire. 
         [0104]    In step  800 , the method  700  ramps up the load by the incremental load. 
         [0105]    If the system has an HRSG, then the method  700  may determine in step  810  a desired HRSG inlet temperature. 
         [0106]    In step  820 , the method  700  may calculate the mass flow to be provided by the supercharger to the HRSG to achieve the desired HRSG inlet temperature. 
         [0107]    In step  830 , the method  700  may provide the HRSG supercharge mass flow (secondary supercharged mass flow, controlled through bypass damper valve  137 ) to the HRSG. 
         [0108]    In step  840 , the method  700  may provide the supercharged mass flow to the gas turbine, and repeat step  720  to determine the present load and step  730  to determine if the present load is equal to the desired load. 
         [0109]    The foregoing detailed description has set forth various embodiments of the systems and/or methods via the use of block diagrams, flowcharts, and/or examples. Insofar as such block diagrams, flowcharts, and/or examples contain one or more functions and/or operations, it will be understood by those within the art that each function and/or operation within such block diagrams, flowcharts, or examples can be implemented, individually and/or collectively, by a wide range of hardware. It will further be understood that method steps may be presented in a particular order in flowcharts, and/or examples herein, but are not necessarily limited to being performed in the presented order. For example, steps may be performed simultaneously, or in a different order than presented herein, and such variations will be apparent to one of skill in the art in light of this disclosure. 
         [0110]    This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.