Abstract:
A method for operating a gas turbine engine including a compressor, combustor, and turbine is provided that includes channeling compressed airflow from the compressor to a heat exchanger having a working fluid circulating within, channeling the working fluid from the heat exchanger to a chiller, extracting energy from the working fluid to power the chiller, and directing airflow entering the gas turbine engine through the inlet chiller such that the temperature of the airflow is reduced prior to the airflow entering the compressor.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    This invention relates generally to gas turbine engines, and more specifically to methods and apparatus for operating gas turbine engines.  
           [0002]    Gas turbine engines generally include, in serial flow arrangement, a high-pressure compressor for compressing air flowing through the engine, a combustor in which fuel is mixed with the compressed air and ignited to form a high temperature gas stream, and a high pressure turbine. The high-pressure compressor, combustor and high-pressure turbine are sometimes collectively referred to as the core engine. Such gas turbine engines also may include a low-pressure compressor, or booster, for supplying compressed air to the high pressure compressor.  
           [0003]    Gas turbine engines are used in many applications, including in aircraft, power generation, and marine applications. The desired engine operating characteristics vary, of course, from application to application. More particularly, when the engine is operated in an environment in which the ambient temperature is reduced in comparison to other environments, the engine may be capable of operating with a higher shaft horse power (SHP) and an increased output, without increasing the core engine temperature to unacceptably high levels. However, if the ambient temperature is increased, the core engine temperature may rise to an unacceptably high level if a high SHP output is being delivered.  
           [0004]    To facilitate meeting operating demands, even when the engine ambient temperature is high, e.g., on hot days, at least some known gas turbine engines include inlet system evaporative coolers or refrigeration systems to facilitate reducing the inlet air temperature. Known refrigeration systems include inlet chilling. Other systems use water spray fogging or injection devices to inject water into either the booster or the compressor to facilitate reducing the operating temperature of the engine. However, within known gas turbine engines, heat energy removed from the working fluid or gas path air, while cooling the gas path air, is eventually lost to the atmosphere rather than used to further improve the efficiency of the turbine.  
         BRIEF DESCRIPTION OF THE INVENTION  
         [0005]    In one aspect, a method for operating a gas turbine engine including a compressor, combustor, and turbine is provided that includes channeling compressed airflow from the compressor to a heat exchanger having a working fluid circulating within to extract energy and thus reduce its temperature. The working fluid from the heat exchanger is channeled to a chiller, extracting energy from the working fluid to power the chiller, and directing airflow entering the gas turbine engine through the inlet chiller such that the temperature of the airflow is reduced prior to the airflow entering the compressor.  
           [0006]    In another aspect, a cooling system is provided for a gas turbine engine including a compressor and a turbine. The system includes a heat exchanger coupled downstream from the compressor, such that compressed discharge air from the compressor is routed through the heat exchanger. The heat exchanger has a working fluid circulating within. A chiller is coupled in flow communication to the heat exchanger and extracts energy from the working fluid to facilitate reducing the temperature of inlet air channeled to the compressor. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0007]    [0007]FIG. 1 is a block diagram of an exemplary gas turbine engine including a cooling system. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0008]    [0008]FIG. 1 is a block diagram of a gas turbine engine  10  which includes a system for cooling gas path air generally represented at  12 . With the exception of gas path air cooling system  12 , which will be described hereinafter, engine  10  is known in the art and includes, in serial flow relationship, a low pressure compressor or booster  14 , a high pressure compressor  16 , a combustor  18 , a high pressure turbine  20 , a low pressure, or intermediate, turbine  22 , and a power turbine or free turbine  24 . Low pressure compressor or booster  14  has an inlet  26  and an outlet  28 . High pressure compressor  16  includes an inlet  30  and an outlet  32 . Combustor  18  has an inlet  34  that is substantially coincident with high pressure compressor outlet  32 , and an outlet  36 . High pressure turbine  20  is coupled to high pressure compressor  16  with a first rotor shaft  40 , and low pressure turbine  22  is coupled to low pressure compressor  14  with a second rotor shaft  42 . Rotor shaft  42  is coaxially positioned within first rotor shaft  40  about a longitudinal centerline axis of engine  10 . Engine  10  may be used to drive a load (not shown) which may be located aft of engine  10  and is also drivingly coupled to a power turbine shaft  44 . Alternatively, the load may be disposed forward of engine  10  and coupled to a forward extension (not shown) of second rotor shaft  42 .  
         [0009]    In operation, outside air is drawn into inlet  26  of low pressure compressor  14 , and compressed air is supplied from low pressure compressor  14  to high pressure compressor  16 . High pressure compressor  16  further compresses the air and delivers the high pressure air to combustor  18  where it is mixed with fuel and the fuel ignited to generate high temperature combustion gases. The combustion gases are channeled from combustor  18  to drive turbines  20 ,  22 , and  24 .  
         [0010]    The power output of engine  10  is related to the temperatures of the gas flow at various locations along the gas flow path. More specifically, the temperature at high-pressure compressor outlet  32  and the temperature of combustor outlet  36  are closely monitored during the operation of engine  10 . Lowering the temperature of the gas flow entering the compressor generally results in increasing the power output of engine  10 .  
         [0011]    Cooling system  12  includes a heat exchanger  46  coupled in flow communication to low pressure compressor  14 , and a chiller  48  coupled in flow communication to heat exchanger  46 . Heat exchanger  46  has a working fluid flowing therethrough for storing energy extracted from the gas flow path. In one embodiment, the working fluid is at least one of, but is not limited to being steam or water. More specifically, heat exchanger  46  extracts heat energy from the gas flow path and uses the extracted energy to power chiller  48 . Specifically, the working fluid is routed to chiller  48  wherein energy is extracted from the working fluid to power chiller  48 . Chiller  48  facilitates cooling inlet air supplied to compressor inlet  26 . In one embodiment, the heat exchanger  46  is a heat recovery steam generator. In another embodiment, heat exchanger  46  is a water-to-air heat exchanger. In one embodiment, chiller  48  is an absorption chiller.  
         [0012]    Cooling system  12  also includes an intercooler  50  in flow communication with, and downstream from, heat exchanger  46 . Gas flow from heat exchanger  46  is channeled to intercooler  50  for additional cooling prior to being returned to high-pressure compressor  16 . In one embodiment, intercooler  50  is a heat exchanger.  
         [0013]    In operation, compressor discharge flow is channeled from low-pressure compressor  14  to heat exchanger  46 . Heat exchanger  46  extracts sufficient heat energy from the flow to power chiller  48 , while cooling the discharge flow in the process. The extracted energy is stored in the working fluid which is then channeled to chiller  48  and used to power chiller  48 . Chiller  48  reduces an operating temperature of inlet air entering low-pressure compressor  14 . Chiller  48  operates in a manner that is known in the art to provide cooling to reduce the operating temperature of the gas turbine inlet air.  
         [0014]    As an example, on a 110° F. day, cooling system  12 , with steam or hot water as a working fluid, can extract sufficient energy to chill the inlet air at low-pressure compressor inlet to at least 59° F., thus facilitating an improvement in both power output from turbine engine  10  and an increase in operating efficiency of engine  10 . In one embodiment, the low-pressure compressor discharge air is reduced at least 100° F. by using the process described herein.  
         [0015]    Heat exchanger  46  is in flow communication with intercooler  50  which receives cooled discharge air from heat exchanger  46 . The discharge air can be additionally cooled to a desired temperature using intercooler  50  before being returned to high-pressure compressor  16 . Such a reduction in the operating temperature of the gas flow facilitates reducing the power requirements for high-pressure compressor  16  and this leaves more energy available for power turbine  24 . In addition, the temperatures at high-pressure compressor outlet  32  is reduced so that the engine  10  operates with greater temperature margins relative to temperature design limits.  
         [0016]    The above-described cooling system provides a cost-effective and highly reliable method for gas flow cooling in a gas turbine engine. The cooling system uses heat energy removed from the gas path while cooling the gas path air to facilitate increasing the potential power output of the engine. Accordingly, a gas path cooling system is provided that facilitates reducing gas path temperatures thereby improving engine efficiency and reliability in a cost-effective manner.  
         [0017]    Exemplary embodiments of gas path cooling systems are described above in detail. The gas path cooling systems are not limited to the specific embodiments described herein, but rather, components of the system may be utilized independently and separately from other components described herein. Each gas path cooling component can also be used in combination with other gas path cooling components.  
         [0018]    While the invention has been described in terms of various specific embodiments, those skilled in the art will recognize that the invention can be practiced with modification within the spirit and scope of the claims.