Abstract:
The present invention discloses a novel apparatus and methods for augmenting the power of a gas turbine engine, improving gas turbine engine operation, and reducing the response time necessary to meet changing demands of a power plant. Improvements in power augmentation and engine operation include systems and methods for preheating piping of a power augmentation system and directing flows of hot compressed air, steam or a combination thereof into the gas turbine engine.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation-in-part of copending U.S. patent application Ser. No. 14/534,347 filed Nov. 6, 2014, which is incorporated by reference herein in its entirety. 
     
    
     TECHNICAL FIELD 
       [0002]    The invention relates generally to gas turbine engine power systems incorporating a power augmentation system. More specifically, improvements relating to steam and air power augmentation are provided. 
       BACKGROUND OF THE INVENTION 
       [0003]    Currently, many gas turbine engines operating at power plants utilize steam injection systems as a low-cost form of power augmentation. Typically steam injection is considered a relatively constant process because the start-up time and shut-down time of the steam injection system is typically on the order of thirty to sixty minutes. 
         [0004]    Some steam injection systems of the prior art have a steam bleed near the injection point so that the steam can be used to heat the steam injection pipes. As steam injection is initiated through cold pipes, the hot steam condenses and forms water which is vented through the steam vent. Steam flow is gradually increased until the pipes are sufficiently heated, at which point water no longer forms. The steam vent then closes and the system is ready to inject steam into the gas turbine engine. This heating process for the steam pipes typically takes approximately thirty minutes. 
         [0005]    Other prior art steam injection systems heat the steam injection pipes by slowly adding steam to the steam injection pipe and any resulting water that forms is injected into the gas turbine. Since the flow rates are extremely low, as water is typically not desired to be injected through a steam injection system into the gas turbine, this process typically takes in excess of thirty minutes to complete. 
         [0006]    Steam is typically generated at a gas turbine site to either drive a steam turbine for producing additional power or is delivered to a supplemental process, such as an adjacent manufacturing facility, or in some cases both. When steam is generated for a supplemental process, the gas turbine power plant is referred to as a cogeneration plant, or cogen plant, because it is producing two products, electricity and steam. The recipient of the steam is called the steam host. Examples of a steam host can include a manufacturing or processing plant. Most cogen plants supply both electricity and steam to the steam host and sometimes the steam requirement and power requirement are not optimally balanced, so the cogen plant has to continuously optimize and balance the steam production and gas turbine output to try to meet the steam host&#39;s demand. This is a significant challenge, and as a result, there are periods when excess steam is produced as a result of the power requirement that cannot be avoided and in these cases, the cogen process loses efficiency. 
         [0007]    Steam injection power augmentation systems are not typically deployed to meet short term spot market demands because they can take too long to come online and be available. For example, if there is a spike in power demand that is not expected to last long, then the steam injection power augmentation system is not advantageous to use. Additionally, steam injection systems are not considered optimal for fast-acting regulation devices due to their slow start-up speed. 
         [0008]    A gas turbine incorporating a steam injection system in accordance with the prior art is depicted in  FIG. 1 . The gas turbine comprises a compressor  10  which compresses ambient air  20  to an elevated pressure and temperature and then discharges hot pressurized air into a compressor discharge case  14 , or CDC. The compressor discharge case  14  is sometimes referred to as a wrapper because it houses the combustion and transition section of the gas turbine. The hot pressurized air enters the combustion chamber  12  where fuel  24  is added. The mixture of fuel and air is ignited and forms combustion gases. The hot combustion gasses are directed to the turbine section  16  which produces about twice the power being consumed by the compressor and therefore, the net power is delivered to a generator  18  for the gas turbine. As the hot gasses  22  exit the turbine section  16 , the hot gasses  22  are directed into a heat recovery steam generator (HRSG)  605 , where pressurized water is turned into pressurized steam  603  which exits the HRSG  605  and is directed into a steam turbine, a steam process, or both ( 602 ). When power augmentation with steam injection is desired, the steam injection isolation valve  113  is opened, the steam injection valve  114  is partially opened and the steam vent valve  616  is opened to allow a small amount of steam to flow through the steam injection piping  601 . Water is typically formed as the steam system is warmed up and the water is drained as required through the vent valve  616 . When the steam pipes  601  are heated and condensation no longer forms, steam  615  flows out of the vent system, the steam vent valve  616  is closed and the steam injection valve  614  is opened to allow the desired amount of steam injection into the gas turbine. 
         [0009]    Typically the distance between the steam injection valve  114  and the steam injection isolation valve  113  can be several hundred feet. As a result, it takes about thirty minutes for the steam injection system to preheat to a desired operating temperature. Some steam injection systems do not have the steam vent valve  616  and therefore they can take even longer to preheat because of the sensitivity to injecting water into the gas turbine as the steam injection system is started up. 
       SUMMARY 
       [0010]    The current invention provides several embodiments for preheating a steam injection power augmentation system using compressed air to allow a rapid start of the steam injection system. 
         [0011]    One aspect of the present invention relates to methods and systems that allow gas turbine systems to bleed air from the steam injection site within the gas turbine towards the source of the steam in order to preheat the steam injection piping to reduce the chance of water formation during steam injection start-up. 
         [0012]    Another aspect of the present invention relates to methods and systems that allow gas turbine systems to bleed air from an external source of hot compressed air to the location of the steam injection near the gas turbine preheat the steam injection lines to eliminate the chance of water formation during steam injection initiation. 
         [0013]    One embodiment of the invention relates to adding an air bleed valve on a new or existing steam injection system near the site of the steam source to allow air to backflow from the gas turbine to the site near the source of the steam. 
         [0014]    Another embodiment of the invention relates to a system comprising a supplemental air injection system, such as a TurboPHASE system, providing hot compressed air to the gas turbine to preheat the steam injection piping. 
         [0015]    Another advantage of the preferred embodiment is a more efficient use of steam such that excess steam being produced can now be used to reduce plant steam output while at the same time increasing plant electrical power output. 
         [0016]    In another aspect of the present invention, a system and methods are provided for utilizing steam from a combined cycle power plant operation to provide additional mass flow to a gas turbine engine. Additional air is supplied to the gas turbine engine in order to provide power augmentation to the gas turbine engine. A power augmentation system is provided comprising a gas turbine engine, a heat recovery steam generator, steam injection piping connecting the gas turbine engine to the heat recovery steam generator, an air vent and air vent valve in communication with the steam injection piping, and an auxiliary air compression system comprising a fueled engine, an intercooled compressor, and a recuperator, where the recuperator heats air from the compressor with exhaust heat from the fueled engine. The steam injection valve, isolation valve, and air injection valve selectively permit a flow of steam from the heat recovery steam generator or air from the auxiliary air compression system, through the steam injection piping and into the gas turbine engine. A series of ways to operate the power augmentation system to improve gas turbine engine performance are also provided. 
         [0017]    Additional advantages and features of the present invention will be set forth in part in a description which follows, and in part will become apparent to those skilled in the art upon examination of the following, or may be learned from practice of the invention. The instant invention will now be described with particular reference to the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         [0018]    The present invention is described in detail below with reference to the attached drawing figures, wherein: 
           [0019]      FIG. 1  is a schematic drawing of a steam injection system on a gas turbine engine of the prior art. 
           [0020]      FIG. 2  is a schematic drawing of an embodiment of the present invention where an air bleed system is added to a new or existing steam injection system on a gas turbine engine. 
           [0021]      FIG. 3  is a flow diagram identifying a method of preheating a power augmentation system. 
           [0022]      FIG. 4  is a schematic drawing of an embodiment of the present invention where a supplementary source of compressed air is used to preheat the steam injection lines. 
           [0023]      FIG. 5  is a flow diagram identifying an alternate method for preheating a power augmentation system. 
           [0024]      FIG. 6  is a flow diagram depicting a method of providing power augmentation to a gas turbine engine utilizing steam injection and an auxiliary source of compressed air. 
           [0025]      FIG. 7  is a flow diagram depicting a method of improving the efficiency of a gas turbine engine utilizing air injection and steam injection. 
           [0026]      FIG. 8  is a flow diagram depicting a method of providing power augmentation to a gas turbine engine utilizing a combined air injection and steam injection process. 
           [0027]      FIG. 9  is a flow diagram depicting a method of improving the efficiency of a gas turbine engine utilizing steam injection. 
       
    
    
     DETAILED DESCRIPTION 
       [0028]    The present invention is disclosed in  FIGS. 2-9 . An aspect common to all embodiments of the present invention is an air vent valve  112  positioned near the source of the steam injection, typically very close to the steam injection valve  114 . Before steam injection is initiated, the air vent valve  112  is opened to allow air to flow through the steam injection piping, towards the steam source, and discharged into the atmosphere  156 . This allows the steam injection piping to be pre-heated to increase the speed that power augmentation with the steam injection system can be started. Various embodiments for heating the steam pipes are discussed herein. 
         [0029]    Typically, steam injection takes at least thirty minutes to initiate and achieve a desired steam injection level. With the steam system pre-heated, the steam injection system can be brought to full flow in less than three minutes. This same air bleed system can be used to purge the steam injection lines when the steam injection process is finished. Typically when the steam injection process is turned off, it is ramped down slowly, many times at a much slower pace than the start-up process. The steam flow is ramped down, because if the steam process is suddenly stopped, the steam injection piping will be full of steam and this steam will turn into water when the steam cools down. Utilizing an air purge system as disclosed herein allows the steam injection to be stopped rapidly, as the steam can be purged from the air steam lines with a process similar to the pre-heat cycle. 
         [0030]    An additional benefit of both the pre-heat and the post purge is that the reverse flow can purge out any foreign matter that might be obstructing the steam injection system. For example, on a General Electric Frame  7 FA gas turbine engine, the steam injection system has known operating issues such as plugging of the steam injection system. In this system, the steam is supplied to the gas turbine through a six inch pipe, which is a manifold to fourteen distinct combustors through a three inch pipe. Inside each combustor can there is an annulus that is approximately one inch wide by 0.75 inches tall that supplies ten steam pegs that have five holes approximately 0.030″ in diameter. If a foreign matter gets in the flow of steam, it will plug these small holes in the pegs. By purging air from these small holes, any foreign matter that might be caught in them can be flushed out to atmosphere or where ever the air vent is discharging the air. 
         [0031]    Referring now to  FIG. 2 , a system for preheating a power augmentation system of a power plant is provided. The system  250  comprises a gas turbine engine  1  comprising a compressor  10  coupled to a turbine  16  by a shaft  6 . The compressor  10  and turbine  16  are in fluid communication with one or more combustors  12 . The system  250  also comprises a heat recovery steam generator  605 , or HRSG. The HRSG  605  takes hot exhaust gases  22  from the turbine  16  and a water supply source (not shown) and generates a supply of steam  603 . 
         [0032]    The system  250  also comprises steam injection piping  601  connecting the gas turbine engine  1  to the HRSG  605 . More specifically, the steam injection piping  601  comprises a steam injection valve  114  and an isolation valve  113 . The system  250  also comprises an air vent  156  and air vent valve  112  that is in communication with the steam injection piping  601 . As will be discussed further below, the isolation valve  113  and air vent valve  112  selectively permit the flow of compressed air from the compressor  10 , and/or a compressor discharge plenum  14 , through the steam injection piping  601  and to the air vent  156 , thereby preheating the steam injection piping  601 . The steam injection piping also includes a steam vent valve  116  for venting steam to the atmosphere through a steam vent  115  when steam is flowing. 
         [0033]    It is important to note that the positions of the steam injection valve  114  and orientation of steam injection piping  601  is merely illustrative of an embodiment of the present invention. As such, it is envisioned that the steam injection valve  114  may be positioned closer to the HRSG  605 . For example, in one embodiment is is envisioned that the steam injection piping  601  between the steam injection valve  114  and gas turbine engine  1  could be a couple hundred feet in length. 
         [0034]    Steam  603  produced by the HRSG  605  can be used for multiple purposes. A portion of the steam  603  can be directed through steam injection piping  601 , as discussed herein, for injection in the gas turbine engine  1 . Alternatively, a portion of the steam  603  can be directed to an external process  602 , such as for use in an adjacent manufacturing plant. 
         [0035]    Referring now to  FIG. 3 , a method  300  of operating a gas turbine energy system is disclosed. In a step  302 , a gas turbine engine is operated where the gas turbine engine has a compressor coupled to a turbine, and the compressor and turbine are in fluid communication with one or more combustors. A steam injection system is also in communication with the gas turbine engine where the gas turbine engine produces a heated exhaust utilized by the steam injection system for producing steam. 
         [0036]    In a step  304 , a supply of steam is generated by the heated exhaust from the gas turbine engine. Then, in a step  306 , a portion of the air from the compressor, or compressor discharge plenum, is directed through at least a portion of the steam injection piping. As shown in  FIG. 2 , the steam injection piping utilizes an isolation valve adjacent the compressor and an air vent valve for permitting the flow of compressed air to pass from the compressor and through the steam injection piping. As a result of the flow of compressed air the temperature of the steam injection piping is increased and the piping is preheated. 
         [0037]    In a step  308 , a determination is made as to whether the steam injection piping temperature has reached an acceptable level. Generally speaking, for the Frame  7 FA gas turbine engine discussed above, the steam injection piping is desired to reach approximately 500 degrees Fahrenheit. If the temperature of the steam injection piping has not reached the desired temperature, then compressed air continues to pass through the steam injection piping in order to raise the temperature of the steam injection piping. As discussed above, an isolation valve and air vent valve are opened to permit the flow of compressed air from the gas turbine engine to preheat the steam injection piping. Furthermore, once the determination is made in step  308  that the piping has reached an acceptable temperature, the air vent valve closes and steam injection valve opens, directing steam from the HRSG through the piping. Once the steam injection piping has reached its desired operating temperature, then in a step  310 , the flow of air from the compressor to the piping is terminated and then in step  312 , at least a portion of the steam supply is directed through the piping and into the gas turbine engine. It is understood that the use of steam and compressed air could overlap such that both fluids could be passing through the piping. Furthermore, it is possible that steam and air could be vented from the piping simultaneously. 
         [0038]    Referring now to  FIG. 4 , an alternate system for preheating a power augmentation system is disclosed. The system disclosed in  FIG. 4  provides an alternate source of compressed air for preheating the steam injection piping. More specifically, the system  450  comprises a gas turbine engine  1  comprising a compressor  10  coupled to a turbine  16  by a shaft  6 . The compressor  10  and turbine  16  are in fluid communication with one or more combustors  12 . The system  450  also comprises a heat recovery steam generator  605 , or HRSG. The HRSG  605  takes hot exhaust gases  22  from the turbine  16  and a water supply source (not shown) and generates a supply of steam  603 . As will be discussed below, the HRSG  605  is in selective fluid communication with the gas turbine engine  1 . 
         [0039]    The system  450  also comprises steam injection piping  601  connecting the gas turbine engine  1  to the HRSG  605 . More specifically, the steam injection piping  601  comprises a steam injection valve  114 , a steam vent valve  116 , and an isolation valve  113 . The system  250  also comprises an air vent  156  and air vent valve  112  that are in communication with the steam injection piping  601 . As will be discussed further below, the isolation valve  113  and air vent valve  112  selectively permit the flow of compressed air to the steam injection piping  601 , thereby preheating the steam injection piping. The steam injection piping  601  also includes a steam vent valve  116  for venting steam to the atmosphere through a steam vent  115 . 
         [0040]    It is important to note that, as with the system  250  in  FIG. 2 , the positions of the steam injection valve  114  and orientation of steam injection piping  601  is merely illustrative of an embodiment of the present invention. As such, it is envisioned that the steam injection valve  114  may be positioned closer to the HRSG  605 . For example, in an embodiment of the present invention, steam injection piping  601  downstream of the steam injection valve  114  could be a couple hundred feet in length. 
         [0041]    Steam  603  produced by the HRSG  605  can be used for multiple purposes. A portion of the steam  603  can be directed through steam injection piping  601 , as discussed herein, for injection in the gas turbine engine  1 . Alternatively, a portion of the steam  603  can be directed to an external process  602 , such as for use in an adjacent manufacturing plant. 
         [0042]    The power augmentation system  450  also comprises an auxiliary air compression system  470  which provides a source of external heated compressed air. One such system is produced by PowerPHASE, LLC of Jupiter, Fla., the same assignee as the present invention. The auxiliary air compression system  470  is similar to that disclosed in co-pending patent applications including U.S. patent application Ser. Nos. 14/350,469, 14/351,245, 14/329,340, 14/329,433, 14/462,000, and 14/534,598. 
         [0043]    Such an auxiliary source of compressed air comprises a fueled engine  151  coupled to a multi-stage compressor  116 . The fueled engine  151  takes ambient air  150  and fuel  124  and through its operation provides mechanical output in the form of power to drive the shaft which is coupled to compressor  116  as well as exhaust heat  152 . The compressor  116  is a multi-stage intercooled compressor in which ambient air  115  is drawn into the compressor  116  and compressed to a higher pressure. After each stage of compression, the compressed air is cooled, thereby permitting further compression. After the air passes through the last stage of the intercooled compressor  116 , the compressed air  117  passes into a recuperator  155 . The recuperator  155  receives the compressed air  117  and exhaust heat  152  from the fueled engine  151 . The temperature of the compressed air  117  increases as it passes through the recuperator  155  which is heated with the exhaust heat  152  to produce hot compressed air  118 . The system  450  also comprises an air injection valve  111  located between the recuperator  155  and the steam injection piping  601 . That is, upon opening of the air injection valve  111  and valve  116 , heated compressed air from the auxiliary source of compressed air is directed into the steam injection piping  601 . The auxiliary source of compressed air can be used to preheat the steam piping  601 , inject air into the gas turbine  1 , and also inject steam and air into the gas turbine. 
         [0044]    Typically, the steam injection piping  601 , which in this case is also an air injection means, is designed such that the pressure of the hot compressed air  118 , or steam if it is being injected instead of air, is only about 5 to 10 psi higher than pressure in the gas turbine combustion discharge wrapper  14 . 
         [0045]    Referring now to  FIG. 5 , an alternate method  500  of operating a gas turbine energy system is provided. The method disclosed in  FIG. 5  corresponds to the system disclosed in  FIG. 4 . More specifically, in a step  502 , a gas turbine engine is operated where the gas turbine engine has a compressor coupled to a turbine, where the compressor and turbine are in fluid communication with one or more combustors. A steam injection system is also in communication with the gas turbine engine where the gas turbine engine produces a heated exhaust utilized by the steam injection system for producing steam. 
         [0046]    In a step  504 , a supply of steam is generated by heated exhaust from the gas turbine engine. Then, in a step  506 , heated compressed air from an auxiliary compressor and heated engine is generated. As shown in  FIG. 4 , the steam injection piping utilizes an isolation valve adjacent the compressor, an air injection valve, and an air vent valve for permitting the flow of compressed air to pass from the auxiliary source of compressed air and through the steam injection piping. As a result of the flow of compressed air the temperature of the steam injection piping is increased and the piping is preheated. 
         [0047]    In a step  508 , the heated compressed air from the auxiliary source of compressed air produced by the fueled engine and intercooled compressor is directed into the steam injection piping. Then, in a step  510 , a determination is made as to whether the steam injection piping temperature has reached an acceptable level. Generally speaking, for the Frame  7 FA gas turbine engine discussed above, the steam injection piping is desired to reach approximately 500 degrees Fahrenheit. If the temperature of the steam injection piping has not reached the desired temperature, then compressed air continues to pass through the steam injection piping in order to raise the temperature of the steam injection piping, as discussed with respect to step  508 . Once the steam injection piping has reached its desired operating temperature, then in a step  512 , the flow of air from the compressor to the piping is terminated. Once the steam injection piping is at its desired temperature, then in step  514 , at least a portion of the steam supply is directed through the piping and into the gas turbine engine. As discussed above, an air injection valve and air vent valve are opened to permit the flow of compressed air from the auxiliary source of compressed air to preheat the steam injection piping. Furthermore, once the determination is made in step  510  that the piping has reached an acceptable temperature, the air vent valve closes and steam injection valve opens, directing steam from the HRSG through the piping. It is understood that the use of steam and compressed air could overlap such that both fluids could be passing through the piping. Furthermore, it is possible that steam and air could be vented from the piping simultaneously. 
         [0048]    Typical steam injection systems utilize steam that is in a highly superheated phase because of the potential temperature drop and concern for water formation. Also, high pressure steam injection systems promote even distribution of the steam throughout the gas turbine and steam nozzles are employed at the point of injection to accomplish this. Therefore the steam that is used is in a very high energy state, typically accomplished by using higher pressure steam, typically 100 to 150 psi higher than the pressure in the gas turbine compress discharge wrapper  114 . With a combined air and steam injection system, the air  118  and steam  603  would be joined together and mix as they travel through the steam piping  601  and therefore, much lower quality steam can be used to accomplish the same level of power augmentation. Typically steam quality would be lowered by utilizing lower pressure steam source, and therefore, the steam would have been able to perform useful work in the steam turbine cycle before being extracted for injection, which improves the efficiency of the steam injection system. 
         [0049]    Referring now to  FIGS. 4 and 6-9 , a series of alternate embodiments of the present invention are disclosed. In one embodiment, a power augmentation system  450  for a gas turbine engine is provided including utilizing a steam flow to provide a source of additional mass flow to the gas turbine engine, such that power output from the gas turbine engine  1  can be maintained while consuming less fuel. Furthermore, the power augmentation system  450  can also provide additional power output by increasing the air flow through the gas turbine engine  1  via hot compressed air from an auxiliary air compression system  470 . 
         [0050]    The system  450  comprises a gas turbine engine  1  comprising a compressor  10  coupled to a turbine  16  by a shaft  6 . The compressor  10  and turbine  16  are in fluid communication with one or more combustors  12  through a compressor discharge case  14 . In fluid communication with the gas turbine engine  1  is a heat recovery steam generator (HRSG)  605  capable of producing steam for use in a power plant or external to the power plant. 
         [0051]    Steam injection piping  601  is connected to the gas turbine engine  1  and the HRSG  605 , where the steam injection piping  601  has a steam injection valve  114  and an isolation valve  113 . The exact locations of the steam injection valve  114  and isolation valve  113  can vary. However, in one embodiment, the steam injection valve  114  is positioned near the where steam from the HRSG  605  is split to go to an external process  602 , such as a steam turbine (not shown). 
         [0052]    The auxiliary air compression system  470  comprises a fueled engine  151  coupled to a multi-stage intercooled compressor  116 . Compressed air from the intercooled compressor  116  passes to a recuperator  155  where it is heated with exhaust heat from the fueled engine  151 . The resulting output from the recuperator  155  is hot compressed air  118 . 
         [0053]    The power augmentation system  450  also comprises an air vent and an air vent valve  112  for regulating the flow of air through an air vent and to the atmosphere  156 . Together, the air injection valve  111 , air vent valve  112 , and steam injection valve  114  are operable to selectively permit a flow of steam from the HRSG  605 , or hot compressed air  118  from the auxiliary air compression system  470  through the steam injection piping  601  and to the gas turbine engine  1 . 
         [0054]    As discussed above, the power augmentation system  450  comprises valving for selectively directing air from the compressor discharge case  14  to flow into the steam injection piping  601  to preheat the steam injection piping  601 . Heating the steam injection piping  601  prior to passing steam therethrough reduces the tendency for the steam flow to form condensation in the steam injection piping  601 . In order for the air from the compressor discharge case  14  to flow through the steam injection piping  601 , the isolation valve  113  is opened as well as the air vent valve  112 , while the air injection valve  111  and steam injection valve  114  remain closed. In this configuration, compressed air from the gas turbine engine  1  is bled through the isolation valve  113 , heats the steam injection piping  601  and vents to the atmosphere  156 . Thus, when the compressor discharge air flow is used to heat the steam injection piping  601 , it flow in a direction opposite of the flow of steam from the HRSG  605  or the air from the auxiliary air compression system  470 . 
         [0055]    As will be discussed in further detail below, the power augmentation system  450  provides a series of options to a gas turbine engine operator for injecting a steam flow, auxiliary source of compressed air, or a combination of the two into the gas turbine engine  1 . The exact injection point for the flow of steam or compressed air from the auxiliary air compression system  470  can vary. However, as one skilled in the art will understand, one such injection point is the compressor discharge case  14 , the area immediately upstream of the combustors  12  such that any work from the additional fluid provided to the gas turbine engine  1  is maximized by undergoing the combustion process. 
         [0056]    One such benefit of steam injection is the availability of what one skilled in the art of power plant operation knows as spinning reserve, or excess available generating capacity. Often times, there is a long start-up time (approximately 30 minutes) associated with bringing the steam injection process online to the point that it can be injected into a gas turbine engine. However, this timeframe can be drastically reduced if the steam injection piping is preheated. This allows for additional mass flow to be readily available to the gas turbine engine, providing a spinning reserve through the gas turbine engine  1 , should it be necessary in the event of an outage of another plant. 
         [0057]    Referring now to  FIG. 6 , a method  620  of providing power augmentation to a gas turbine engine is provided. In a step  622 , the piping of a power augmentation system is preheated with compressor discharge air taken from the gas turbine engine. Then, in a step  624 , once the piping is at the desired operating temperature, the flow of compressor discharge air is terminated. In a step  626 , steam flows from a HRSG, through the piping and to the gas turbine engine. While steam is flowing to the gas turbine engine, an auxiliary air compression system is started in a step  628 . Once the auxiliary air compression system is started and produces a flow of hot compressed air, then in a step  630 , the flow of steam is reduced while the flow of hot compressed air is directed to the gas turbine engine. Then, in a step  632 , the flow of steam to the gas turbine engine is terminated such that only hot compressed air is being added to the gas turbine engine, thereby providing power augmentation to the gas turbine engine. 
         [0058]    Referring to  FIG. 7 , a method  700  of improving the operating efficiency of a gas turbine engine is disclosed. The method  700  comprises a step  702  of starting an auxiliary air compression system to produce a flow of hot compressed air. Then, in a step  704 , the hot compressed air from the auxiliary air compression system flows through the piping and into the gas turbine engine. Then, in a step  706 , the flow of hot compressed air is reduced while a flow of steam is directed into the gas turbine engine. The flow of hot compressed air is then terminated in a step  708  such that only steam is injected into the gas turbine engine. Depending on operating conditions, the process outlined above can also include the step of preheating the piping with compressor discharge air prior to hot compressed air from the auxiliary air compression system passing through the piping. In the process outlined above, the auxiliary air compression system provides a source of increased power output via the hot compressed air prior to changing to steam injection, which provides additional mass flow to the gas turbine engine such that fuel consumption by the gas turbine engine is reduced. A reduction in the amount of fuel consumed to produce a specific power output results in cost savings to the engine operator. 
         [0059]    Turning now to  FIG. 8 , an alternate method of providing power augmentation to a gas turbine engine is disclosed. The method  800  comprises a step  802  of preheating the piping of the power augmentation system with compressor discharge air from the gas turbine engine. Once the piping is at a desired operating temperature the flow in the piping is replaced with steam from the HRSG in a step  804 . Then, in a step  806 , an auxiliary air compression system is started to produce a flow of hot compressed air. In a step  808 , the hot compressed air is directed to the gas turbine engine along with the flow of steam from the HRSG. 
         [0060]    Referring to  FIG. 9 , an alternate method of improving the efficiency of a gas turbine engine is provided. In a method  900 , the piping of the power augmentation system is preheated with compressor discharge air from the gas turbine engine in a step  902 . Then, in a step  904 , a supply of steam is produced in a HRSG. In a step  906 , a portion of the steam produced in the HRSG is directed through the piping of the power augmentation system, the piping being external to the gas turbine engine. Then, in a step  908 , the portion of the steam is directed into the gas turbine engine to provide an additional mass flow to the engine. 
         [0061]    While the invention has been described in what is known as presently the preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiment but, on the contrary, is intended to cover various modifications and equivalent arrangements within the scope of the following claims. The present invention has been described in relation to particular embodiments, which are intended in all respects to be illustrative rather than restrictive. 
         [0062]    From the foregoing, it will be seen that this invention is one well adapted to attain all the ends and objects set forth above, together with other advantages which are obvious and inherent to the system and method. It will be understood that certain features and sub-combinations are of utility and may be employed without reference to other features and sub-combinations. This is contemplated by and within the scope of the claims.