Abstract:
The present invention discloses embodiments for a power augmentation system of a gas turbine engine resulting in performance improvements while also improving efficiency. The invention provides systems and methods for generating a heated air supply by way of mixing compressed air from an electrically-driven process with air drawn from the engine compressor discharge plenum.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority to U.S. Provisional Patent Application Ser. No. 62/293,894 filed on Feb. 11, 2016, which is hereby incorporated by reference in its entirety. 
     
    
     TECHNICAL FIELD 
       [0002]    This invention relates generally to electrical power systems, including generating capacity of a gas turbine engine, and more specifically to improving the efficiency and power output of the gas turbine engine by using an electrically driven air injection system. 
       BACKGROUND OF THE INVENTION 
       [0003]    Air compression systems are known as a way of providing power augmentation to gas turbine engines. One such process utilizes an auxiliary air compression process separate from the gas turbine engine. However, in certain locations it is not possible or desirable to use a separate engine to power and heat the auxiliary air compression process. 
         [0004]    Due to permitting restrictions in certain regions, it may be necessary to have an electric driven system for powering the air compression process. However, the electric driven system does not provide a way to heat the air prior to injection. Typically, air being injected into the gas turbine engine is required to be at least approximately 500 deg. F., such that when the air is injected into the gas turbine engine, the potential for thermal cracking and combustion instabilities is eliminated. 
         [0005]    For example, one such compressor used in an auxiliary air compression process is a multistage intercooled compressor, which typically has a compressed air exit temperature of about 220 deg. F. At this temperature, there is a need to develop an alternate method to heat the air being injected to at least 500 deg. F. In prior art configurations, such as in U.S. Pat. No. 6,305,158, Nakhamkin teaches using waste heat from the exhaust of the gas turbine engine to heat up the air from an electrical driven air injection system; however, this has two serious drawbacks. 
         [0006]    The first drawback of using the exhaust heat to raise the temperature of the compressed air is its effect on a combined cycle power plant, which are the most efficient types of plants generating the majority of energy on the grid. These plants offer the most attractive payback to potential customers having air injection systems because they operate more often than simple cycle gas turbine engines. In a combined cycle system, all of the waste heat is used in the steam bottoming cycle and, if some of the exhaust energy is to be used to heat the compressed air, then, the bottoming cycle loses power output and the overall efficiency of the system is negatively impacted. 
         [0007]    The second drawback of using the exhaust heat from the gas turbine engine to heat the compressed air is that installation of a recuperator is not practical inside an existing heat recovery steam generator (HRSG). Adding a recuperator to this system would add a significant level of complexity and a permanent increase in exhaust pressure drop, independent of the system actually running, and therefore causing a permanent efficiency penalty whether the system is running or not. 
         [0008]    Consequently, the only practical gas turbine engine from which to recover the exhaust energy is a simple cycle gas turbine engine. However, due to the low efficiency levels of a simple cycle gas turbine engine relative to combined cycle plants, simple cycle plants do not operate as frequently as combined cycle plants, making it difficult for customers to earn a reasonable return on their investment. 
       SUMMARY 
       [0009]    The current invention provides several embodiments for power augmentation of a gas turbine engine, resulting in performance improvements and improved efficiency. The current invention provides a method of heating compressed air generated by a compressor for injection into a gas turbine by mixing compressed air from the gas turbine&#39;s compressor discharge plenum with compressed air from the separate compressor. 
         [0010]    In an embodiment of the present invention, a method of operating a gas turbine energy system is provided. The method comprises operating a gas turbine engine having a compressor, a compressor discharge plenum, one or more combustors, and a turbine, all fluidly connected to each other, and operating an auxiliary air compression system comprising an intercooled compressor powered by an electric motor, where the intercooled compressor compresses ambient air to produce a primary air source at a first temperature. The method also directs a portion of air from the compressor discharge plenum through a blower pump so as to compress this air to a higher pressure and then mixes the primary air source and the air from the blower pump to produce a mixed compressed air at a temperature higher than the primary air source with the mixed compressed air being inject into the gas turbine engine. 
         [0011]    In an alternate embodiment of the present invention, a gas turbine energy system is provided comprising a gas turbine engine having a compressor, a compressor discharge plenum, one or more combustors, and a turbine, fluidly connected to each other. The system also comprises an auxiliary air compression system having an intercooled compressor powered by an electric motor, a blower pump powered by an electric motor, the blower pump in fluid communication with the compressor discharge plenum, and a conduit system coupling the blower pump and the auxiliary air compression system to the compressor discharge plenum. 
         [0012]    In yet another embodiment of the present invention, a method of operating a gas turbine energy system is provided. The method comprises operating a gas turbine system having a compressor, a compressor discharge plenum, one or more combustors, and a turbine, fluidly connected to each other and operating an intercooled compressor producing a primary air source at a temperature cooler than the compressor discharge plenum. The primary air source flows through a flow restriction device, creating a vacuum on an air supply of the compressor discharge plenum, causing the air supply to be drawn from the compressor discharge plenum. The intercooled primary air source and the air supply from the compressor discharge plenum are then mixed together, thereby producing a mixed compressed air at a temperature higher than the primary air source. The mixed compressed air is then returned to the gas turbine engine. 
         [0013]    In another embodiment of the present invention, a gas turbine energy system is provided comprising a gas turbine engine having a compressor, a compressor discharge plenum, one or more combustors, and a turbine, fluidly connected to each other and an intercooled compressor producing a primary air source at a temperature cooler than the compressor discharge plenum. The system also includes a flow restriction device positioned within a flow of the primary air source, creating a vacuum effect on an air supply in the compressor discharge plenum. A conduit for mixing the intercooled primary air source and the air supply vacuumed from the compressor discharge plenum is also provided with the conduit coupled to the compressor discharge plenum and an outlet region of the intercooled compressor. 
         [0014]    One aspect of the present invention relates to methods and systems where, for example, a multistage intercooled electrically driven compressor with pressurized air typically at a temperature of 220 deg. F. and pressure of 220 psi is mixed with air that is taken from the gas turbines compressor discharge plenum typically at 700-850 deg. F. and 215 psi. The air from the compressor discharge plenum is increased in pressure by a single stage blower to 220 psi, with the two streams then being joined together in approximately a 50/50 mass relationship, resulting in 500 to 550 deg. F air for injection into the gas turbine. 
         [0015]    Another aspect of the present invention relates to methods and systems where a multistage intercooled electrically driven compressor producing, for example, pressurized air typically at a temperature of 220 deg. F. and 220 psi is mixed with air that is withdrawn from the gas turbine compressor discharge plenum, by a vacuum effect, typically at 700-850 deg. F. and 215 psi. The air is then pumped up in pressure by a single stage booster pump to 220 psi, and the two streams are joined together in approximately a 50/50 mass relationship, resulting in 500 to 550 deg. F air for injection into the gas turbine. 
         [0016]    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 
         [0017]    The present invention is described in detail below with reference to the attached drawing figures, wherein: 
           [0018]      FIG. 1  depicts a schematic drawing of an electric driven air injection system including a blower pump used to pull air from the compressor discharge plenum of the gas turbine engine. 
           [0019]      FIG. 2  depicts a schematic drawing of an electric driven air injection system having a device is used to pull air from the gas turbine&#39;s compressor discharge plenum where the air is added to the relatively cool air coming from the electric driven air injection system. 
           [0020]      FIG. 3A  depicts a metering plate device through which air from the compressor discharge plenum flows in accordance with  FIG. 2 . 
           [0021]      FIG. 3B  depicts a venturi through which air from the compressor discharge plenum flows in accordance with  FIG. 2 . 
       
    
    
     DETAILED DESCRIPTION 
       [0022]    The present invention relates to gas turbine energy systems, and more specifically to ways of heating an auxiliary source of compressed air produced by an electric-driven compression system. 
         [0023]    Referring initially to  FIG. 1 , a gas turbine energy system is provided comprising a gas turbine engine  100  having a compressor  101 , a compressor discharge plenum  102 , one or more combustors  104 , and a turbine  103 , all in fluid communication. More specifically, ambient air is drawn into the engine compressor  101  and compressed to a higher pressure and temperature, typically about 750 deg. F. The compressed air flows out of the compressor  101  and into a compressor discharge plenum  102 . The air is then directed to one or more combustors  104 , where fuel is mixed with the air to form a combustible mixture and ignited to burn and generate hot combustion gases, which pass through, and rotate the turbine  103 . The turbine  103  is coupled to the compressor  101  by a shaft (not shown) such that rotational energy from the turbine powers the compressor. 
         [0024]    The present invention also comprises an auxiliary air compression system  110  having an intercooled compressor  113  powered by a motor  112 . More specifically, electrical energy  111  is used to drive the motor  112 , which provides power to the intercooled compressor  113 . Ambient air  118  is drawn in to the intercooled compressor  113  and compressed, albeit at a lower temperature due to the cooling between stages of the intercooled compressor  113 , resulting in a primary air source  115  of compressed air at approximately 220 deg. F. However, the ambient air  118  is compressed to a pressure higher than the pressure in the compressor discharge plenum  102 . 
         [0025]    A blower pump  123  is powered by a motor  122 , which consumes electrical energy  121  and extracts compressed air  128  from the compressor discharge case  102  prior to the air entering the combustors  104 . This compressed air  128  is typically about 750 deg. F. The blower pump  123  takes in the compressed air  128 , increases its pressure, and discharges it such that the primary air source  115  and the hot air  125  coming from the blower  123  join together in a conduit system  131  to create a mixed compressed air having a higher temperature than the primary air source  115 . Typically, air injected in this region should be about 500 deg. F. or higher in order to prevent the possibility of thermal cracking and combustion instability. That is, by utilizing a portion of the compressed air  128  from the compressor discharge plenum  102 , and further increasing its pressure, it can be mixed with cooler compressed air generated by the motor  112  and compressor  113  external to the gas turbine engine  100  at approximately 50/50 quantities of air from each source, and returned to the engine  100  at a suitable temperature and pressure level to provide power augmentation. This can be accomplished without having any adverse effects of using the gas turbine waste heat or negative effects on the bottoming cycle in combined cycle plants. 
         [0026]    Referring now to  FIG. 2 , an alternate embodiment of the present invention is disclosed. In this alternate embodiment, similar results to that of the system of  FIG. 1  are achieved, but with a different structure and process. The alternate embodiment utilizes the features of the gas turbine engine  100  and auxiliary air compression system  110  discussed above. However, this embodiment of the present invention utilizes a flow restriction device  300 , as shown in  FIGS. 3A and 3B , to create a local low pressure zone, or vacuum, which extracts hot compressed air  128 , typically about 750 deg. F., from the compressor discharge plenum  102  prior to the air going to the combustion system. The primary air source  115  generated by the intercooled compressor  113  and compressed air  128  drawn from the compressor discharge plenum  102  come together to create a mixed compressed air in a conduit  131  prior to being injected into the gas turbine engine  100 . Typically, the air being injected into the gas turbine engine  100  must be at least 500 deg. F., and the flow restriction device  300  serves to mix the air from the gas turbine engine  100  in approximately 50/50 relationship with the primary air source  115  from the intercooled compressor  113 . This is accomplished without having any adverse effects of using the gas turbine waste heat, which can have negative effects on the bottoming cycle in combined cycle plants. 
         [0027]    Referring now to  FIGS. 3A and 3B , more specific details of the flow restriction device  300  are depicted. The flow restriction device  300  creates a pressure drop, and as a result, a corresponding vacuum effect that pulls in compressed air  128  from the compressor discharge plenum  102 . Examples of acceptable flow restriction devices include an orifice plate  310 , as shown in  FIG. 3A  and a venturi  320 , as shown in  FIG. 3B . The vacuum device  300  can be a device positioned inside or adjacent to the gas turbine engine  100 , or alternatively, it can be a device positioned outside the gas turbine engine  100 , as depicted in  FIG. 2 , where all the primary air source  115  and the compressed air  128  are mixed outside the gas turbine engine  100  and then injected back into the engine. For example, on a General Electric Frame 7FA gas turbine engine, there is an inlet bleed heat (IBH) manifold that extracts air from four ports approximately evenly spaced around the gas turbine engine. The present invention can be incorporated into this engine by way of a second manifold that is added to the system and spaced axially aft of the existing IBH manifold and could then include four pipes coming from the IBH manifold, each one supplying the vacuum side of an orifice style or venturi style device,  310  or  320 , with the four mixed compressed air streams being individually injected back into the gas turbine engine compressor discharge case through a set of four different ports. Alternatively, the four mixed compressed air streams could be joined into one pipe and injected back into the gas turbine compressor discharge plenum at a single location. 
         [0028]    As one skilled in the art can appreciate, the temperatures and pressures mentioned above are typical values of “F-class” gas turbines. However, the same principles discussed herein will apply to other gas turbine engines. For example, if an air injection system as discussed herein is installed on a much higher pressure ratio gas turbine, such as an aero derivative engine, a similar configuration can be used to increase the injection air temperature of the primary air source that was already heated with another heat source, such as the exhaust of a reciprocating engine associated with the air injection system. For example, an LM6000 aero derivative engine produced by General Electric Company has a much higher pressure ratio with compressor discharge plenum temperatures approaching 1000 deg. F. An auxiliary air injection system, such as that produced by PowerPHASE LLC, the assignee of the present invention, generates hot compressed air with a fuel driven system at approximately 650 deg. F., and therefore, the compressor discharge case air of the aero derivative engine could be mixed with the air from the auxiliary air injection system to produce an air supply closer to the temperature of the air in the compressor discharge case. 
         [0029]    In an alternate embodiment of the present invention, the mixed compressed air in conduit  131  can be used for cooling one or more turbine components, instead of for power augmentation. As one skilled in the art understands, turbine components often operate above their material capability, but are actively and aggressively cooled in order to lower their effective operating temperatures. The mixed compressed air can be injected back into the gas turbine engine  100  and directed through pre-existing cooling channels or actively cooling turbine components such as turbine blades and vanes. 
         [0030]    Accordingly, the claims below are directed to both systems and methods capable heating injected air without the limitation of whether the primary air source is generated using a fueled engine with a recuperator or an electrically driven system, which inherently produces much cooler compressed air. 
         [0031]    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. 
         [0032]    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.