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 an electrical grid. Improvements in power augmentation and engine operation include systems and methods for providing rapid response given a change in electrical grid.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    None. 
       TECHNICAL FIELD 
       [0002]    The invention relates generally to electrical power systems, including generating capacity of a gas turbine, and more specifically to improving an increase or decrease in speed capability for a gas turbine generator. 
       BACKGROUND OF THE INVENTION 
       [0003]    Generators of gas turbine engines are used for up and down regulation and electrical capacity generation. However, these systems have characteristics where power increase or decrease can happen over several minutes. In order to maintain the stability of the electric grid, a major concern is the unexpected and sudden loss of electricity generation which will cause a frequency drop on the grid. Currently, the best source of fast acting regulation to support this drop condition is hydro power, or power generated from a water source, because hydro can act in seconds and can maintain the desired output. However, relying on hydro power is geographically limited and as the grid grows, a dis-proportionate low level of new hydro generation is being added due to environmental constraints. 
         [0004]    Gas turbine engines can also be used in support of this drop condition, but are not nearly as effective as hydro because they require a ramp rate to the desired load conditions which takes minutes, not seconds. Furthermore, in order to have this generating capacity available, the gas turbine engine must be online and at a power level below base load, which is a less efficient set point to operate a gas turbine. 
       SUMMARY 
       [0005]    The current invention provides several embodiments for storing and releasing compressed air to a gas turbine engine in a rapid manner to provide immediate support to a power plant in the event of a reduction in generating capacity on the grid. 
         [0006]    The invention disclosed herein pertains to the storage and use of hot compressed air and more specifically to systems and methods for providing hot compressed air that is ready to be dispatched by opening a valve and increasing the air mass flow to the gas turbine engine. This allows gas turbine engine to be operated at a higher, more efficient, load level and have the ability to add fast acting regulation in seconds. 
         [0007]    The present invention provides quick response to increasing output capacity on a gas turbine by delivering stored hot compressed air to the point of injection in the gas turbine engine, which allows power increase from the gas turbine engine in seconds. Another aspect of the present invention relates to methods of generating and operating systems for preheating the air injection piping between the stored hot air and the gas turbine engine by bleeding air from the gas turbine engine towards the storage tank or bleeding air from the storage tank towards the gas turbine engine. In another aspect of the present invention, the storage tank of compressed air is heated and maintained at an elevated temperature by an electrical resistor. 
         [0008]    In another aspect of the present invention, a continuous hot compressed air generation source, such as a TurboPHASE system produced by PowerPHASE LLC, is utilized with a source of stored hot compressed air, where the stored hot compressed air initially provides hot air to the gas turbine giving time for the TurboPHASE system to start and achieve operating speed, temperature and pressure. 
         [0009]    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 
         [0010]    The present invention is described in detail below with reference to the attached drawing figures, wherein: 
           [0011]      FIG. 1  is a schematic drawing of a stored compressed air injection system in accordance with an embodiment of the present invention. 
           [0012]      FIG. 2  is a flow diagram of a process for supplying additional compressed air to a gas turbine engine in accordance with an embodiment of the present invention. 
           [0013]      FIG. 3  is a schematic drawing of an embodiment of the present invention utilizing a stored compressed air injection system in conjunction with a supplementary source of compressed air in accordance with an embodiment of the present invention. 
           [0014]      FIG. 4  is a flow diagram of an alternate process for supplying additional compressed air to a gas turbine engine in accordance with an alternate embodiment of the present invention. 
           [0015]      FIG. 5  is a flow diagram of a process of responding to a change in an electric grid in accordance with an embodiment of the present invention. 
           [0016]      FIG. 6  is a flow diagram of an alternate process of responding to a change in an electric grid in accordance with an embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0017]    The present invention is disclosed in  FIGS. 1-6  and relates to methods and systems of generating and storing hot compressed air, keeping the stored compressed air heated, and then injecting the hot compressed air into the gas turbine engine in response to a change in an electric grid operation. Compressed air can be stored in a tank as well as be generated by an auxiliary system, such as the TurboPHASE system. 
         [0018]    Referring to  FIG. 1 , a system for providing a supply of compressed air to an energy system is provided. The system comprises a gas turbine engine  1  having a compressor  10  which compresses ambient air  20  to an elevated pressure and temperature and then discharges the air into a compressor discharge case (CDC)  14 . The CDC  14  is also commonly referred to as a wrapper because it houses the complete combustion and transition section of the gas turbine engine  1 . The hot pressurized air enters one or more combustion systems  12  where fuel  24  is added and the mixture is ignited to form hot combustion gasses. These hot combustion gases are directed into a turbine  16 , where the turbine  16  is coupled to the compressor  10  by a shaft  6 . The turbine  16  produces about two times the power that the compressor  10  is consuming, and therefore the net shaft power is delivered to a generator  18 . 
         [0019]    The present invention also comprises an air injection piping system  50  that is in fluid communication with the gas turbine engine  1 . For example, as shown in  FIG. 1 , the air injection piping system  50  is in selective fluid communication with the CDC  14  by way of an air injection valve  60 . 
         [0020]    As discussed above, the present invention provides a way of providing heated compressed air to the gas turbine engine  1  to increase output of the engine, thereby increasing output of the generator when there is a grid disruption. In an embodiment of the present invention, an additional supply of compressed air can be provided by a high pressure air storage system  70 . The high pressure air storage system  70  comprises a high pressure compressor  72 , a storage tank inlet valve  74 , a compressed air storage tank  75 , and a storage tank outlet valve  76 . In an embodiment of the present invention, the high pressure compressor  72  is a reciprocating compressor. The compressed air storage tank  75  can vary in volume depending on the amount of time which the high pressure air storage system  70  is to provide compressed air to the gas turbine engine  1 . The air being stored in the storage tank  75  is at an increased temperature, typically upwards of 500 deg. F. and is maintained at this elevated temperature by a heat source such as electric resistor heating element  73  and insulation applied to the storage tank  75 . As will be discussed in more detail below, the high pressure compressor  72  can compress ambient air or it can compress, to a high pressure ratio, air from the CDC  14 . Also, as one skilled in the art can appreciate, the pressure of the air in the storage tank  75  must be higher than the pressure of the compressor discharge region. 
         [0021]    Referring to  FIG. 2 , the operation  200  of the energy generating system of  FIG. 1  is depicted. More specifically, in a step  202 , a gas turbine engine is operated where the gas turbine engine has a compressor coupled to a turbine through a shaft, one or more combustion systems and a generator coupled to a shaft. In a step  204 , a flow of air is compressed in a high pressure compressor of an air storage system. Then, in a step  206 , the flow of air is directed from the high pressure compressor and into a compressed air storage tank. In a step  208 , the flow of air is stored in the compressed air storage tank until it is needed. As discussed above, the compressed air can be maintained at its elevated temperature by a heating element. Then, in a step  210 , a storage tank outlet valve and air injection valve adjacent the gas turbine engine are opened to permit the flow of compressed air to exit the compressed air storage tank and be injected into the gas turbine engine in a step  212 . The storage tank outlet valve and air injection valve are adjustable so as to allow for a constant flow of air from the storage tank even as the pressure in the storage tank decreases. 
         [0022]    As discussed above, the flow of air from the high pressure air storage system is injected into the gas turbine engine to increase power output from the engine to support grid fluctuations. As part of the air flow injection process, compressed air from the compressed air storage tank can bleed through the storage tank outlet valve and into the piping system  50  and out through a vent valve  52  and vent  54 , thereby preheating the air injection piping system  50 . Alternatively, the air injection piping system  50  can also be preheated by a flow of compressed air from the CDC  14  flowing through air inlet valve  60  and towards vent valve  58  and vent  56 . 
         [0023]    Referring now to  FIG. 3 , an alternate embodiment of the present invention is depicted. A system  300  is capable of providing a supply of hot compressed air to an energy generating system. The system comprises a gas turbine engine  1  having a compressor  10  which compresses ambient air  20  to an elevated pressure and temperature and then discharges the air into a compressor discharge case (CDC)  14 . The hot pressurized air enters one or more combustion systems  12  where fuel  24  is added and the mixture is ignited to form hot combustion gasses. These hot combustion gases are directed into a turbine  16 , where the turbine  16  is coupled to the compressor  10  by a shaft  6 . The turbine  16  produces about twice the power that the compressor  10  is consuming, and therefore the net power is used to drive the generator  18 . 
         [0024]    The system  300  also comprises an air injection piping system  50  that is in fluid communication with the gas turbine engine  1 . As shown in  FIG. 3 , the air injection piping system  50  is in selected fluid communication with the CDC  14  by way of an air injection valve  60 . 
         [0025]    The system  300  further comprises a high pressure air storage system  70  that is in selective fluid communication with the gas turbine engine  1  via the air injection piping system  50 . As discussed above, the high pressure air storage system  70  generally comprises a high pressure compressor  72 , a storage tank inlet valve  74 , a compressed air storage tank  75 , and a storage tank outlet valve  76 . In an embodiment of the present invention, the high pressure compressor  72  is a reciprocating compressor. The compressed air storage tank  75  can vary in volume depending on the amount of time which the high pressure air storage system  70  is to provide compressed air to the gas turbine engine  1 . The air being stored in the storage tank  75  is at an increased temperature and is maintained at this elevated temperature by a heat source such as electric resistor heating element  73  and insulation applied to the storage tank  75 . As will be discussed in more detail below, the high pressure compressor  72  can compress ambient air or it can compress, to a high pressure ratio, air from the CDC  14 . As one skilled in the art can appreciate, the valve must be sized such that when the tank is at full pressure, the valve is only partially opened and when the tank is almost empty, the valve will be opened up much more. The storage tank  75  is sized such that the power augmentation generated equals the power augmentation generated by the TurboPHASE system and can deliver this air flow while the TurboPHASE module is started. 
         [0026]    In this embodiment of the invention, the system  300  also comprises an auxiliary source of compressed air that is in selective fluid communication with the gas turbine engine  1  through the air injection piping system  50  and the air injection valve  60 . One such auxiliary source of compressed air is a TurboPHASE system produced by PowerPHASE LLC of Jupiter, Fla. The auxiliary source of compressed air comprises a fueled engine  151  that drives a multistage intercooled compressor  116 , where the compressor  116  takes in ambient air  115  and discharges warm compressed air  117 . The fueled engine  151  takes in ambient air  150  and fuel  124  and delivers the power to drive the compressor  116  and discharges hot exhaust  152 . The hot exhaust  152  passes through a recuperator  155  where it is used to heat the warm compressed air  117  from the compressor  116 , thereby resulting in hot compressed air  118  and cooler exhaust  153 . The hot compressed air then is directed through an auxiliary air injection valve  111  and into the air injection piping system  50 . When the auxiliary air injection valve  111  and air vent valve  52  are open, the hot compressed air  118  can flow from the auxiliary source of compressed air and through the air injection piping system  50  where it preheats the piping system  50  and vents the hot compressed air  118  through vent  54 . 
         [0027]    Referring now to  FIG. 4 , a method  400  of operating an energy generating system is disclosed. In a step  402 , a gas turbine engine is operated where the gas turbine engine has a compressor coupled to a turbine through a shaft, one or more combustion systems and a generator coupled to a shaft. In a step  404 , a flow of air is compressed in a high pressure compressor of an air storage system. Then, in a step  406 , the flow of air is directed from the high pressure compressor and into a compressed air storage tank. In a step  408 , the flow of air is stored in the compressed air storage tank until it is needed. As discussed above, the compressed air can be maintained at its elevated temperature by a heating element. Then, in a step  410 , the valves of the air injection piping system are opened to permit the flow of compressed air to exit the compressed air storage tank and be injected into the gas turbine engine in a step  412 . The storage tank outlet valve and air injection valve are opening as required and in a way so as to allow for a constant flow of air from the storage tank even as the pressure in the storage tank decreases. 
         [0028]    In a step  414  of an embodiment of the present invention, while the compressed air is injected from the air storage tank, the auxiliary source of compressed air is initiated. More specifically, the fueled engine is operated to drive the intercooled compressor. Then, in a step  416 , the compressed air from the compressor is heated in the recuperator, where the recuperator uses exhaust heat from the fueled engine to heat the compressed air. In a step  418 , the heated compressed air is directed into the gas turbine engine. 
         [0029]    While in the embodiment discussed above, the heated from air from the auxiliary source of compressed air, such as a TurboPHASE system, is injected into the gas turbine engine after the air from the compressed air storage tank, it is to be understood that in an alternate embodiment of the present invention, air can be injected into the gas turbine engine simultaneously from the compressed air storage tank and the auxiliary source of compressed air. By combining the storage and continuous generation of the air that is injected into the gas turbine, the process can be initiated in less than one second and then sustained indefinitely. 
         [0030]    As one skilled in the art understands, in order for the compressed air generated by the high pressure air storage system and the auxiliary source of compressed air to be injected into the gas turbine engine  1 , it is necessary for the compressed air generated by these systems to be greater than the pressure of the air in the gas turbine engine. Furthermore, in an embodiment of the present invention, the flow of compressed air being compressed by the high pressure compressor of the high pressure air storage system compresses the air passing therethrough to a pressure of at least 50% higher than compressed air in the gas turbine engine  1 . 
         [0031]    An auxiliary source of compressed air as disclosed above is capable of starting and coming up to desired operating conditions in under 2 minutes. The system can deliver approximately 12 lb/sec of 600 F, 220 psi air (air density=0.56 lb/ft 3 ) to the gas turbine engine continuously. Therefore, the high pressure air storage system also needs to be able to deliver 12 lb/sec of 600 F, 220 psi air for 2 minutes. When this level of air injection is applied to an F-Class gas turbine, 4.5 MW is produced from the gas turbine instantaneously. This equates to 1440 pounds of air to be discharged. Therefore, at a moderate storage pressure of 3600 psi, temperature of 600 F, with an air density of 9.15 lb/ft3, a storage volume of 168 ft 3  is required, or a single two foot diameter tank extending 27 feet in length. Therefore, a single storage tank can be integrated into the auxiliary source of compressed air, such as a TurboPHASE system, and deliver the stored air to the gas turbine engine and the power output from the gas turbine is increased virtually instantaneously while the auxiliary source of compressed air is brought on line and provides a continual source of compressed air. 
         [0032]    The power delivered from the present invention provides a fast-acting solution at an improved cost compared to other ways to add capacity to the electric grid. For example, a battery typically costs about $1000/kW. The present invention provides for the option of continuous capacity addition, and adds 4.5 MW to the engine performance, at an approximate cost of $67/kW. 
         [0033]    In an alternate embodiment of the present invention, methods of controlling a gas turbine engine in response to a rapid change in an electrical grid are disclosed in  FIGS. 5 and 6 . As discussed above, the rapid changes to the electrical grid can be a sudden increase or decrease in power supply, such as when the generating capacity suddenly and unexpectedly goes offline. 
         [0034]    Referring to  FIG. 5 , a method  500  of controlling a gas turbine engine comprises receiving a grid signal indicating a change in operation of the electrical grid in a step  502 . Then, in a step  504 , a signal is sent to a gas turbine controller of a parameter that is to be changed in order for the gas turbine engine, and the power it produces, to comply with the grid signal. In a step  506  the parameter to the combustion system is changed prior to the change in operation of the electrical grid occurring. As discussed above, the parameter of the combustion system being changed can be air flow, fuel flow, or gas turbine firing temperature. Such parameters alter the available power output, and thus electrical generating capacity, of the gas turbine engine. Then, in a step  508 , operation of the gas turbine engine is monitored to determine whether further changes to the parameter of the combustion system are necessary. 
         [0035]    Referring now to  FIG. 6 , an alternate method for controlling the gas turbine engine in response to a rapid change in an electrical grid is disclosed. The method  600  relates to controlling a gas turbine engine where an air supply is provided to the engine from an external source, such as a supplemental air injection system. In a step  602 , an air flow supply is injected from an air injection system and into the gas turbine engine and in a step  604 , a grid signal is received indicating a change in operation of the electrical grid is to occur. Then, in a step  606 , a signal is sent to a gas turbine controller of a parameter that is to be changed in order for the gas turbine engine, and the power it produces, to comply with the grid signal. In a step  608  the parameter to the combustion system is changed prior to the change in operation of the electrical grid occurring. As discussed above, the parameter of the combustion system being changed can be air flow, fuel flow, or gas turbine firing temperature. Such parameters alter the available power output, and thus electrical generating capacity, of the gas turbine engine. Then, in a step  610 , operation of the gas turbine engine is monitored to determine whether further changes to the parameter of the combustion system are necessary. 
         [0036]    Another characteristic of the disclosed invention is how it is controlled. Typically, the gas turbine control system reacts to changes, in other words, when the ambient temperature changes for example, the control system reacts to the physical measurements that are being measured real time, typically 10 times per second, and are constantly adjusting fuel flow, inlet guide vanes to operate the gas turbine according to a fixed schedule. One of the main considerations for these changes is the combustion stability, which is driven by fuel air ratio in the combustor and precisely where the fuel and air is being delivered. Most dry low NOx combustors have different circuits that are designed to promote flame stability as well as thorough mixing promoting low NOx. If a sudden addition of air is introduced, 2 second air injection testing has shown that the existing control system is adequate to adjust the fuel air mixture and not cause a lean blow out event, however, all combustion systems are different and there may be cases where the control system needs to be “warned” ahead of time in order to react to fast air injection. In this case, when a grid signal come in for a sudden regulation up, or sudden air injection, a signal can be sent to the gas turbine controller either at the same time or just ahead of time to slightly richen up or stabilize the combustor. Every combustion system is different and stabilizing the combustor could mean different things to different combustors. For example on a GE DLN1 combustion system, the percentage fuel going to the pilot circuit might be increased temporarily. Another example is on a DLN2.6 combustion system, increasing stability may be increasing PM1 fuel split temporally. 
         [0037]    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. 
         [0038]    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.