Abstract:
A method of operating a combustion turbine power generation system and derivatives thereof. The method provides at least one combustion turbine assembly including a compressor, an expansion turbine operatively associated with the compressor, a generator coupled with the expansion turbine; a combustor feeding the expansion turbine; flow path structure fluidly connecting an outlet of the compressor to an inlet of the combustor; a supplemental compressor structure; connection structure fluidly connecting an outlet of the supplemental compressor structure to a point upstream of the combustor, and valve structure associated with the connection structure to control flow through the connection structure. The valve structure is controlled selectively permit one of the following modes of operation: (a) a combustion turbine mode of operation wherein air compressed from the compressor moves through the flow path structure to the combustor feeding the expansion turbine such that the expansion turbine drives the generator, and (b) a power augmentation mode of operation wherein supplemental compressed air from the supplemental compressor structure is supplied through the connection structure and is directed to the combustor feeding the expansion turbine, in addition to compressed air passing through the flow path structure to the combustor feeding said expansion turbine, which increases mass flow of compressed air and gas to the expansion turbine.

Description:
[1]    1. This is a Continuation of U.S. patent application Ser. No. 09/363,186 filed Jul. 29, 1999, which is a Continuation-in-Part of U.S. patent application Ser. No. 09/110,672 filed on Jul. 7, 1998.  
     
    
     
         [2]    2. This invention relates to combustion turbine power plant and more particularly, to method of operating a combustion turbine power plant so as to restore a loss of power which may occur when the combustion turbine assembly is operating at high ambient temperature or with low air density and/or to generate power which exceeds a power production of a conventional combustion turbine assembly by use of supplementary air flow.  
         BACKGROUND OF THE INVENTION  
         [3]    3. A combustion turbine power plant is the power plant of choice for supplying peak power. For an overwhelming majority of electric power customers (in the U.S. and abroad) power consumption reaches its peak during the summertime, the time when the power production of combustion turbines is at its lowest, due to high ambient temperature. The simplified explanation of the reduced power production is that the high ambient temperature with associated lower inlet air density, reduces mass flow through a combustion turbine assembly with a respective reduction of the power produced. FIGS. 1 a ,  1   b , and  1   c  present simplified heat and mass balances of a conventional General Electric Frame 7 EA combustion turbine assembly  12  operating at three ambient temperatures: 59 F. (FIG. 1 a ), 0 F. (FIG. 1 b ) 90 F. (FIG. 1 c ). The combustion turbine  12  includes a compressor  14 , an expansion turbine  16 , a combustor  18  which feeds heated combustion product gas to the expansion turbine  16 . The expansion turbine  16  is coupled to drive the compressor  14  and an electric generator  20 , which is coupled to the electric grid  17 .   
           [4]    4.FIGS. 1 a - 1   c  demonstrate that the conventional General Electric combustion turbine assembly, rated at 84.5 MW at ISO conditions (59 F. with 60% relative humidity), will produce maximum power of approximately 102.5 MW when the ambient temperature is 0 F., and will drop power to approximately 76.4 MW at 90 F. The significant power loss by a combustion turbine assembly during high ambient temperature periods requires a utility to purchase additional peak capacities to meet summer peak demands. Power loses for a combined cycle power plant operating at high ambient temperatures are similar to those of combustion turbine assemblies.  
           [5]    5. There are conventional methods to partially restore the loss power of combustion turbines/combined cycle plants during high ambient temperature periods: evaporative cooling and various combustion turbine inlet air chillers (mechanical or absorption type). These methods result only in partial restoration of combustion turbine power while significantly increasing capital costs, which is not always justified for an operation limited to time periods with high ambient temperatures.  
           [6]    6. Accordingly, there is a need to develop a method which will allow a combustion turbine assembly to operate at maximum power, regardless of ambient temperature.  
           [7]    7. Similar power loss problems exist in the case of a combustion turbine assembly installed at high elevation. The problem in these applications is associated with lower air density and a corresponding loss of consumption turbine power. There are currently no methods to restore power loss associated with high elevation applications.  
           [8]    8. Accordingly, a need exists to develop a method which will allow a combustion turbine assembly to maintain maximum power even when operating at high elevations.  
         SUMMARY OF THE INVENTION  
         [9]    9. An object of the invention is to fulfill the needs referred to above. In accordance with the principles of the present invention, these objectives are obtained by a method of operating a combustion turbine power generation system and derivatives thereof. The method provides at least one combustion turbine assembly including a compressor, an expansion turbine operatively associated with the compressor, a generator coupled with the expansion turbine; a combustor feeding the expansion turbine; flow path structure fluidly connecting an outlet of the compressor to an inlet of the combustor; a supplemental compressor structure; connection structure fluidly connecting an outlet of the supplemental compressor structure to a point upstream of the combustor, and valve structure associated with the connection structure to control flow through the connection structure. The valve structure is controlled selectively permit one of the following modes of operation: (a) a combustion turbine mode of operation wherein air compressed from the compressor moves through the flow path structure to the combustor feeding the expansion turbine such that the expansion turbine drives the generator, and (b) a power augmentation mode of operation wherein supplemental compressed air from the supplemental compressor structure is supplied through the connection structure and is directed to the combustor feeding the expansion turbine, in addition to compressed air passing through the flow path structure to the combustor feeding said expansion turbine, which increases mass flow of compressed air and gas to the expansion turbine.  
           [10]    10. The above and other objects of the present invention will become apparent during the course of the following detailed description and appended claims.  
           [11]    11. The invention may be best understood with reference to the accompanying drawings wherein illustrative embodiments are shown, and like parts are given like reference numerals.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [12]    12.FIG. 1 a  is a schematic diagram of a conventional GE 7 EA combustion turbine operating at 59 F.:  
         [13]    13.FIG. 1 b  is a schematic diagram of a conventional GE 7 EA combustion turbine operating at 0 F.;  
         [14]    14.FIG. 1 c  is a schematic diagram of a conventional GE 7 EA combustion turbine operating at 90 F.;  
         [15]    15.FIG. 2. is an embodiment of a combustion turbine power generation system provided in accordance with the principles of the present invention;  
         [16]    16.FIG. 3 is another embodiment of a combustion turbine power generation system of the invention;  
         [17]    17.FIG. 4 is yet another embodiment of a combustion turbine power generation system of the invention having a bottom steam cycle;  
         [18]    18.FIG. 5 is a schematic diagram of operating parameters applicable to the embodiments illustrated in FIGS.  2  and  3  wherein a combustion turbine assembly operates in an air augmentation mode of operation at 90 F. ambient temperature;  
         [19]    19.FIG. 6 is another embodiment of a combustion turbine power generation system of the invention including humidification of the supplemental airflow;  
         [20]    20.FIG. 7 is a schematic diagram of operating parameters applicable to the embodiment illustrated in FIG. 6 wherein a combustion turbine assembly operates in an air augmentation mode of operation at 90 F. ambient temperature;  
         [21]    21.FIG. 8 is another embodiment of a combustion turbine power generation system of the invention which eliminates the compressed air storage but includes humidification of supplemental airflow; and  
         [22]    22.FIG. 9 is a schematic diagram of operating parameters applicable to the embodiment illustrated in FIG. 8 wherein a combustion turbine assembly operates in an air augmentation mode of operation at 90 F. ambient temperature.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [23]    23. With reference to FIG. 2, a combustion turbine power generating system provided in accordance with the principles of the present invention is shown, generally indicated at  10 .  It will be appreciated that the physics and mechanics of the inventive system  10  are identical for operation at high ambient temperature and at high elevations. Therefore, all explanations herein will describe the method and its effectiveness for the high ambient temperature application only. Further, it is to be understood that the invention applies equally to a combined cycle plant, where a combustion turbine is a main component.  
         [24]    24. Referring to FIG. 2, one embodiment of a combustion turbine power generation system  10  is schematically illustrated and includes a conventional combustion turbine assembly  12   which may be, for example, a GE 7 EA combustion turbine assembly. The combustion turbine assembly  12  includes a shaft assembly having a compressor  14 , an expansion turbine  16 , and a combustor  18  which feeds heated combustion product gas to the expansion turbine  16 . The expansion turbine  16  is coupled to drive the compressor  14  and is coupled with an electric generator  20 . The generator  20  is coupled to an electric grid  17 .  In a combustion turbine mode of operation, air is compressed in the compressor  14  and via a flow path structure  21 , the compressed air is sent to the combustor  18 , and thereafter heated combustion product gas is expanded in the expansion turbine  16  to produce power.  
         [25]    25. In accordance with the invention, the combustion turbine assembly  12  is provided so as to inject previously stored compressed air to an inlet of the combustor  18  feeding the expansion turbine  16 . If power is to be provided which exceeds power generated by the combustion turbine assembly  12 , a capacity of the generator may be upgraded, the function of which will be explained more fully below.  
         [26]    26. An additional compressed air compression storage and retrieval system (CACSRS) is provided and, in the embodiment illustrated in FIG. 2, includes a compressor train  32  to supply compressed air to a compressed air storage  28  via charging structure  34  in the form of piping. In the illustrated embodiment, the compressor train  32  includes first and second compressors  36  and  38 , respectively, driven by an electric motor  40 . An intercooler  42  may be provided between the first compressor  36  an the second compressor  38 . In addition, an aftercooler  44  may be provided between outlet of the second compressor  38   and an inlet to the compressed air storage  28 . A valve  46  is provided between the outlet of the second compressor  38  and an inlet to the aftercooler  44 . A valve  48  is provided between an outlet of the aftercooler and an inlet to the compressed air storage  28 . Valves  46  and  48  define a first valve system.  
         [27]    27. An outlet of the compressed air storage  28  is fluidly coupled to an inlet of the combustor  18  via connection structure  50 . In the illustrated embodiment, a recuperator  52  is provided between an outlet of the air storage  28  and an inlet to the combustor  18 . A valve  54  is provided between an outlet of the recuperator  52  and an inlet of the combustor  18  and a valve  55  is provided in the connection structure  50  between the outlet of the air storage  28   and the inlet to the recuperator  52 . Valves  54  and  55  define a second valve system. In addition, an optional valve  56  is provided downstream of a juncture between the charging structure  34  and the connection structure  50  leading to the air storage  28 . It can be appreciated that if the recuperator  52  is not provided, then valve  54  is not necessary. Similarly, if the aftercooler  44  is not provided, valve  46  is not necessary.  
         [28]    28. The electric motor  40  is coupled to the electric grid  17  such that during off-peak hours, the electric motor  40  may drive the compressor train  32  to charge the air storage  28 .  
         [29]    29. The compressed air storage may be a underground geological formation such as a salt dome, a salt deposition, an aquifier, or may be made from hard rock. Alternatively, the air storage  28  may be a man-made pressure vessel which can be provided above-ground.  
         [30]    30. The method of the present invention includes an integration of the combustion turbine assembly  12  and the additional compressed air charging storage and retrieval system to provide for three modes of operation:  
         [31]    31. (1) a compressed air storage system charging mode of operation, with a flow path going through the compressor train  32 ,  aftercooler  44 , charging structure  34  to the compressed air storage  28 ; wherein valves  46  and  48  in the charging structure  34   are open and valves  54  and  55  in connection structure  50  are closed; and the motor-driven compressor train  32 , using off-peak energy from the grid  17 ,  compresses the ambient air to the specified pressure in the air storage  28 .   
         [32]    32. (2) an air augmentation mode of operation, wherein the conventional combustion turbine assembly  12  operation is integrated with the compressed air flow from the air storage  28 ; air from the air storage  28  is preheated in the recuperator  52  and is injected upstream of the combustors  18 ; and wherein the compressed air from the air storage  28  goes through the connection structure  50 , through the recuperator  52  to a point upstream of the combustor  18 ; during this operation valves  46  and  48   in the charging structure  34  are closed and valves  54  and  55  in the connection structure  50  are open and control the additional flow from the air storage  28 ; this mode of operation results in power production significantly exceeding that of the combustion turbine assembly  12  because the power produced by the expansion turbine  16  results from the expansion of the total flow, which is a sum of the flow compressed by the compressor  14  and an additional flow from the compressed air storage  28 ; inlet guide vanes of compressor  14  may be closed to reduce power consumption by the compressor  14  to increase the electric power by the electric generator  20  to the electric grid  17 ; and  
         [33]    33. (3) a conventional combustion turbine mode of operation, where CACSRS is disconnected from the combustion turbine assembly  12 , and valves  46  and  48  in the charging structure  34  and valves  54  and  55  in the connection structure  50  are closed, permitting compressed air to move from the compressor  14  through the flow path structure  21  to the combustor  18  feeding the expansion turbine  16 .  
         [34]    34. Although only one combustion turbine assembly  12  is shown in the embodiments herein, it can be appreciated that numerous combustion turbine assemblies may be provided and coupled with a common air storage to provide the desired augmented air flow and thus, the desired power output.  
         [35]    35.FIG. 3 is a schematic illustration of a second embodiment of the invention and includes the combustion turbine assembly  12 . As above, there is a provision to inject previously stored compressed air upstream of combustor  18  and a provision to extract the compressed air downstream of the compressor  14  for a further intercooling in an intercooler  58  and compression in a boost compressor  60 . Also, the capacity of the electric generator  20  may be upgraded, if required.  
         [36]    36. The method also provides a CACSRS having an electric motor  40  driving the charging boost compressor  60  fed by the intercooler  58 . An aftercooler  44  is provided downstream of the boost compressor  60  and valves  46  and  48  are provided before and after the aftercooler, respectively, and are disposed in the charging structure  34 . Thus, a flow path is provided from an outlet of the compressor  14  through the intercooler  58 , disposed in integrating structure  62 , to an inlet of the boost compressor  60 , through the aftercooler  44  to the compressed air storage  28 . In addition, compressed air may flow from an outlet of the compressor  14  to an inlet of the combustor  18  via the flow path structure  21 . The compressed air storage fluidly communicates via connection structure  50  to a point upstream of combustor  18 . Valve  64  in the integrating structure  62 , together with valve  66  in the flow path structure  21 , valves  44  and  46  in the charging structure  34 , and valves  54  and  55  in the connection structure  50 , selectively control flow through the flow path structure  21 , the connection structure  50 , the charging structure  34  and the integrating structure  62 .  
         [37]    37. As in the first embodiment, the combustion turbine assembly  12  and the CACSRS are integrated to provide three modes of operation:  
         [38]    38. (1) a compressed air storage system charging mode of operation, wherein a flow path exists from the compressor  14 , through the integrating structure  62  containing the intercooler  58 , to the boost compressor  60 , through the charging structure  34   containing the aftercooler  44 , to the compressed air storage  28 ; a expansion turbine cooling flow of approximately 5-10% of the nominal flow is flowing from the compressed air storage  28  via the connection structure  50 , to the recuperator  52  and to the expansion turbine  16  via unfired combustor  18  and to the exhaust stack; valves  46  and  48  in the charging structure  34  are open, valves  54  and  55  in the connection structure  50  are partially open to provide the cooling flow via unfired combustor  18  to the expansion turbine  16 ; valve  64  in integrating structure  62  is open and valve  66  is closed; the combustion turbine electric generator  20 , fed by off-peak power from the grid  17 , drives the combustion turbine shaft and the boost compressor  60  is driven by the electric motor  40 , also fed by off-peak energy from the grid  17 ;   
         [39]    39. (2) an air augmentation mode of operation, wherein a conventional combustion turbine operation is integrated with the additional compressed air flow from the air storage  28 , which is preheated in the recuperator  52  and injected upstream of the combustor  18 ; thus, the compressed air from the air storage  28  goes through the connection structure  50 , through the recuperator  52  to a point upstream of the combustor  18 ; valves  46  and  48  in the charging structure  34  are closed, valves  55  and  54  in the connection structure  50  are open and control the additional flow from the air storage  28 ; valve  64  in the integrating structure  62  is closed and the valve  66  is open; this mode of operation results in power production significantly exceeding that of the combustion turbine assembly  12 , because the power produced by the expansion turbine  16  results from the expansion of the total flow, which is a sum of the flow compressed by the compressor  14  and an additional flow from the compressed air storage  28 ; inlet guide vanes of compressor  14  may be closed to reduce power consumption by the compressor  14  to increase the electric power by the electric generator  20  to the electric grid  17 ;   
         [40]    40. (3) a conventional combustion turbine mode of operation, wherein the CACSRS is disconnected from the combustion turbine assembly  12 , and valves  46  and  48  in the charging structure  34  and valves  55  and  54  in the connection structure  50  are closed and the valve  64  in the integrating structure  62  is closed while valve  66  in the flow path structure is open permitting compressed air to move from the compressor  14  through the flow path structure to the combustor  18  feeding the expansion turbine  16 .   
         [41]    41.FIG. 4 is a schematic illustration of a third embodiment of the invention and includes a combined cycle plant with a combustion turbine assembly  12  with a conventional bottoming steam cycle components: a heat recovery steam generator  68 , a steam turbine  70 , a generator  71  coupled with the turbine  70 , a condenser  72 , a deaerator  74  and pumps  76 .  The combustion turbine assembly requires a provision to inject previously stored compressed air upstream of combustor  18  and a provision to extract the compressed air downstream of the compressor  14  for a further intercooling and compression in the boost compressor  60 . Also, the capacity of the electric generator  20  may be upgraded if required.  
         [42]    42. The invented method also provides an additional CACSRS including an electric motor driven a boost compressor  60  fed by intercooler  58 , the aftercooler  44 , integrating structure  62  permitting communication between an outlet of the compressor  16  via the intercooler  58  to the boost compressor inlet and through the flow path structure  21  to the combustor  18  inlet. Charging structure  34  permits communication between an outlet of the boost compressor  60  and an inlet to the compressed air storage  28 . Connection structure  50  permits communication between the compressed air storage  28  and a point upstream of combustor  18 . Valves  46  and  48  are provided in the charging structure  34 , valve  55  is provided in the connection structure  50 , and valve  64  is provided in the integrating structure  62 , while valve  66  is provided in the flow path structure  21 , to selectively control flow through the charging structure  34 , the connection structure  50  and the integrating structure  62  and the flow path structure  21 .  
         [43]    43. The combustion turbine assembly  12  is integrated with a steam bottoming cycle, generally indicated at  78 , and the additional CACSRS to provide for three modes of operation:  
         [44]    44. (1) a compressed air storage charging mode of operation, wherein flow goes through the compressor  14 , through the integrating structure  62  having the intercooler  58 , to the boost compressor  60 , through the charging structure  34  having the aftercooler  44  to the compressed air storage  28 ; a turbine cooling flow, which is approximately 5-10% of the nominal flow is flowing from the compressed air storage  28  through the connection structure  50 , and via an unfired combustor  18 , to the expansion turbine  16  and then to the exhaust stack; valves  46  and  48  in the charging structure  34  are open, valve  55  in the connection structure  50  is partially open to provide the cooling flow via the unfired combustor  18  to the expansion turbine; and valve  64  in the integrating structure  62  is open and valve  66  is closed; the combustion turbine electric generator  20 , fed by off-peak power from the grid  17 , drives the combustion turbine shaft and the boost compressor  60  is driven by the electric motor  40 , also fed by off-peak energy from the grid  17 ;   
         [45]    45. (2) an air augmentation mode of operation, where a conventional combustion turbine operation is integrated with additional compressed air flow from the air storage  28 , which is injected upstream of the combustor  18 ; where compressed air from the air storage  28  goes through the connection structure  50  to a point upstream of the combustor  18 ; valves  46  and  48  in the charging structure  34  are closed, valve  55  in the connection structure  50  is open and controlling the additional flow from the air storage  28 ; valve  64  in the integrating structure  62  is closed and valve  66  is open; in addition, a conventional closed-loop steam/condensate flow path is provided where steam generated in the heat recovery steam generator  68  expands through the steam turbine  70  producing power to the grid  17 , and then goes through the condenser  72 , deaerator  74 ,  feedwater pumps  76  and back to the heat recovery steam generator  68 ; this mode of operation results in power production by the combustion turbine assembly  12   significantly exceeding that of the conventional combustion turbine assembly without the additional air flow, because the power produced by the expansion turbine  16  results from the expansion of the total flow, which is a sum of the flow compressed by the compressor  14  and an additional flow from the compressed air storage  28 ; also, an additional power is produced by the steam turbine of the bottoming cycle  78  due to additional steam flow by the heat recovery steam generator  68  recovering heat from the expansion turbine  16  exhaust; inlet guide vanes of compressor  14  may be closed to reduce power consumption by the compressor  14  to increase the electric power by the electric generator  20  to the electric grid  17 ; and  
         [46]    46. (3) a conventional combustion turbine mode of operation, wherein CACSRS is disconnected from the combustion turbine assembly  12 , and valves  46  and  48  in the charging structure  34 , valves  55  and  54  in the connection structure  50  are closed and the valve  66  in the flow path structure  21  is open permitting compressed air to move from the compressor  14  through the flow path structure to the combustor  18  feeding the expansion turbine  16 .   
         [47]    47. Practical applications of the inventive method are illustrated in FIG. 5, which is a schematic diagram with operating parameters applicable to the first and the second illustrative embodiments according to the present invention, where a GE Frame 7EA combustion turbine assembly  12  operates in an air augmentation mode and at 90 F. ambient temperature. FIG. 5 illustrates that during air augmentation at an elevated ambient temperature of 90 F., the additional compressed air flow of 168 lbs/sec is retrieved from the compressed air storage  28  and injected upstream of the combustor  18  to increase the combustion turbine power output to 129.2 MW from 76.4 MW for the conventional combustion turbine assembly operation at the same 90 F ambient temperature (see FIG. 1 c ). The amount of the retrieved air is limited by a number of design limitations. For a GE Frame 7 EA combustion turbine assembly, the limitation is the maximum expansion turbine power of 228 MW and is achieved when the combustion turbine assembly operates at 0  F. (see FIG. 1 b ).  
         [48]    48. Table 1a presents performance characteristics of the GE Frame 7 EA operating as a conventional combustion turbine assembly with air augmentation—applicable to the first and the second illustrative embodiments of the invention. Table 1a indicates that over the whole range of ambient temperatures higher than 0 F., air augmentation results in power increased by 52.8 MW for 90 F. ambient temperature and 32.8 MW for 59 F. Performance parameters for the air augmentation concept are heat rate characterizing the fuel consumption in BTU per kWh produced and an kWh consumption for the compressed air storage recharging. The cost of electricity (COE) produced is calculated as:  
         [49]    49. COE=(Heat rate, BTU/kWh)×(cost of fuel, $/BTU)+(the off-peak energy for the air storage recharging, kWh)×(cost of off-peak energy, $/kWh)/total kWh produced in the air augmentation mode of operation.   
                                                                             TABLE 1a                                                        0   59   70   90                        Frame 7EA CT-                               Gross Power, MW   102.5   84.4   82.4   76.4       Heat Rate (LHV   10,110   10.420   10.520   10,630       &amp; Natural Gas Fuel),       Btu/kWh       Augmentation               Gross Power Output,   102.5   118.0   122.2   129.2       MW       Incremental Gross   0.0   32.6   39.8   52.8       Power, MW       Heat Rate (LHV &amp; Nat.   10,110   9,610   9,510   9,140       Gas Fuel), btu/kWh       w/o recup.       Heat Rate with   N/A   8,680   8,340   8,010       recuperator       Time of Augmentation   N/A   9.8   8.5   6.0       Operation, Hours                        Compression Energy,   210       MH       Storage Type   Salt Dome       Volume, Million Cu. Ft.   5.385       Delta P in Cavern, psi   150                  
 
         [50]    50. Table 1b demonstrates performance characteristics of the third illustrative embodiment of the invention, i.e., the conventional combined cycle plant, based on GE Frame 7EA, and the plant operation in an air augmentation mode. The findings are similar to the first and second illustrative embodiments.   
                                                                             TABLE 1b                                                        0   59   70   90                        Frame 7EA CT-                               Gross Power, MW   155.6   134.1   130.7   123.4       Heat Rate (LHV   6,810   6,800   6,900   6,970       &amp; Natural Gas Fuel),       btu/kWh       Augmentation       based on Frame 7EA               Gross Power Output,   155.6   168.4   172.5   178.9       MW       Incremental Gross   0.0   34.3   41.9   55.6       Power, MW       Heat Rate (LHV &amp;   6,810   6,730   6,740   6,600       Natural Gas Fuel,       btu/kWh       Time of Augmentation   N/A   9.8   8.5   6.0       Operation, Hours                    Compression Energy, Mh   210       Storage Type   Salt Dome       Volume, Miliion Cu. Ft.   5.385       Delta P in Cavern, psi   150                  
 
         [51]    51. The cost of conversion of a combustion turbine system provided with air augmentation are as follows:  
         [52]    52. compressed air storage cost;  
         [53]    53. compressor train cost for the storage recharging;  
         [54]    54. costs of an interconnecting piping, valves and controls for the overall system integration  
         [55]    55. The compressed air storage shall be sized to store a sufficient mass of air to support air augmentation operations with maximum power output for a specified number of hours with elevated ambient temperatures. The stored compressed air pressure should be sufficient to inject the additional mass of air upstream of the combustor. For the embodiment shown in FIG. 5, and Tables 1a and 1b, when the air storage is sized to provide for continuous six (6) hours of operation at 90 F. with maximum power output of 129.2 MW, the properly sized compressed air storage in a salt dome requires 5.4 million cubic feet (with depth of approximately 1000 feet and the maximum minus minimum pressure difference of 150  p.s.i.) at cost of approximately $5 million. Engineering and cost estimates demonstrated that for the above conditions total costs for a providing the GE Frame 7EA combustion turbine assembly to include air augmentation are approximately $8.8 million with 52.8 MW additional power at 90 F ambient temperature (see Table la) or the specific cost of the modification is approximately $160/kW. This compares favorably with approximately $300/kW specific cost for a similar (50 MW) capacity combustion turbine assembly. A similar modification for a combined cycle plant (see Table 1b) will cost approximately $150/kW, which is even more attractive as compared with approximately $500/kW for a combined cycle power plant.  
         [56]    56. In accordance with another aspect of the invention, the embodiment of FIG. 2 has been modified and the modified system is shown in FIG. 6. Like numerals indicate like parts in FIGS.  2  and  6 . Thus, the embodiment of FIG. 6 includes a commercially available saturator  80  which defines a tower with internal packing to improve mixing of compressed air entering the saturator  80  via the connection structure  50 . A water heater  82  is coupled to the saturator  80  via inlet line  85  and exit line  87 . The water heater  82  is preferably a typical shell and tube design. A water pump  83  provides make-up water via piping  84  to the saturator  80  and a water pump  81  is provided in inlet line  85  to circulate water through the water heater  82 .   
         [57]    57. The compressed air from the air storage  28  is directed via the connection structure  50  to the saturator  80  where the compressed air is mixed with hot water heated in the water heater  82 . The compressed air is saturated and preheated in the saturator  80  and then is sent to the recuperator  52  for further heating before injection upstream of the combustor  18 . For the same maximum power and volumetric flow of turbine  16 , the required supplemental compressed airflow is established for given ambient temperature.  
         [58]    58. With the embodiment of FIG. 6, the humidification of the supplemental airflow significantly reduces the amount of the compressed air to be compressed by the compressor train  32  and stored in the compressed air storage  28 . FIG. 7 presents the heat and mass flow balance for the embodiment of FIG. 6 and shows that for 90 F. ambient air temperature and 60% humidity flow leaving the saturator  80 , the supplemental compressed airflow exiting the air storage 28 is 35 lbs/sec. For the same net power output this is a reduction, from 100 lbs/sec for the embodiment of FIG. 2 without humidification, of approximately 70%. (note—FIG. 5 shows the heat and mass flow balance for the embodiment of FIG. 2  wherein the gross power was 129.2 MW). Thus, the cost of the compressed air storage is reduced by approximately 70% and the cost of the compressor train  32  and the recuperator  52  can also be significantly reduced. Added costs for the saturator  80 , water heater  82  and pumps  81  and  83  are a small fraction of the costs savings associated with the storage volume reduction. FIG. 7 demonstrates the heat rate of 9012 Btu/kWh, which is similar to that of the embodiment of FIG. 5 (which does not provide humidification). Due to the fact that the supplemental airflow of the embodiment of FIG. 7 vs. the embodiment of FIG. 2 is reduced by 70%, in the embodiment of FIG. 7, the energy requirements for the storage recharging are also reduced by 70%. This reduces the cost of electricity (fuel and off-peak energy costs) for the system. Engineering and cost estimation efforts have established that the specific capital cost ($/incremental kW) for the system of FIG. 6 (approximately $170/kW) is reduced by approximately 40% as to compared to the system of FIG. 2.  
         [59]    59. Yet another embodiment of the invention is shown in FIG. 8. This embodiment is similar to that of FIG. 6 and like numbers indicate like parts. The embodiment of FIG. 8 differs from that of FIG. 6 in that in the embodiment of FIG. 8, the compressed air storage is eliminated and supplemental compressor structure in the form of the compressor train  32   is sized to provide full supplemental airflow (e.g., about 35 lbs/sec). It is noted that the compressor train of FIGS.  2  and  6  could be sized for airflow less than the full supplemental airflow and depends on the ratio of peak power production hours and off-peak hours available for charging the air storage.  
         [60]    60. The heat and mass balance of the of the system of FIG. 8 is shown in FIG. 9. For the incremental peak power generated, the supplemental airflow is continuously provided by the compressor train  32  with the compressor train discharge flow being saturated in the saturator  80  with the hot water produced in the hot water heater  82 . The saturated and preheated air is further heated in the recuperator  52  before being injected upstream of the combustor  18 .   
         [61]    61. The major advantage of the system of FIG. 8 is that it can operate continuously when power is being produced to provide incremental power. There is no limitation imposed by the compressed air storage sizing for particular peak hours. The air storage sizing could be limited by excessive capital costs or siting limitations. Also, the system of FIG. 8 is simple in operation and maintenance.  
         [62]    62. As shown in FIG. 9, the performance characteristics of the system of FIG. 8 are similar to those shown in FIG. 7. For example, both embodiments have the same operating costs associated with the fuel and off-peak energy. It is expected that, the system of FIG. 8 would have lower operating and maintenance costs due to the absence of the air storage. Engineering and costs estimate efforts have shown that the system of FIG. 8 has specific capital costs of approximately the same as those of the system of FIG. 6 (the cost increase for the larger flow compressor train is approximately equal the cost savings from the air storage elimination).  
         [63]    63. It has thus been seen that the objects of this invention have been fully and effectively accomplished. It will be realized, however, that the foregoing and preferred embodiments have been shown and described for the purposes of illustrating the structural and functional principles of the present invention, as well as illustrating the method of employing the preferred embodiments and are subject to change without departing from such principles. Therefore, this invention includes all modifications encompassed within the spirit of the following claims.