Abstract:
A combustion turbine which produces a reduced amount of NO x  is provided. The combustion turbine reduces the amount of NO x  produced by utilizing a secondary combustor. By using a secondary combustor the working gas of the combustion turbine does not need to be heated above 2500° F., the temperature at which a substantial amount of NO x  begins to form, until the working gas is entering the turbine assembly. The secondary combustor assembly heats the working gas by injecting a combustible gas, or compressed air if the primary combustor produces a fuel rich working gas, into the elevated temperature working gas. This gas combusts and heats the working gas adjacent to the beginning of the turbine assembly. Because the working gas is not raised above 2500° F. until it is about to enter the turbine assembly, the time during which NO x  is formed is reduced.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    This invention relates to combustion turbine power plants and, more specifically, to a secondary combustor which reduces the amount of NO x  produced by the combustion turbine power plant by heating the working gas to its highest temperature adjacent to the turbine assembly.  
           [0003]    2. Background Information  
           [0004]    A conventional combustible gas turbine includes a compressor assembly, a combustor assembly, a transition section, and a turbine assembly. The compressor assembly compresses the ambient air. The combustor assembly combines the compressed air with a fuel and ignites the mixture creating a working gas. The working gas travels through the transition section to the turbine assembly. Within the turbine assembly are a series of rows of stationary vanes and rotating blades. Each pair of rows of vanes and blades is called a stage. The rotating blades are coupled to a shaft. As the working gas expands through the turbine assembly, the working gas causes the blades, and therefore the shaft, to rotate.  
           [0005]    Conventional cycle combustible gas turbines produce an undesirable amount of Nitrogen Oxide, NO x . As described above, combustion turbines operate by passing a heated working gas through a turbine assembly having rows of rotating blades and stationary vanes. The temperature of the working gas may be 2800° F. (1537° C.) or more. Thus, in prior art combustion turbines having a single combustor assembly, the temperature of the working gas must be greater than or about 2800° F. (1537° C.) in the combustor assembly. NO x  is generally produced in high temperature (2650° F./1455° C. or greater) flame regions of the combustor assembly and the transition to the turbine assembly.  
           [0006]    The quantity of NO x  produced is a function of flame residence time and the time the working gas is at a high temperature, and the value of that temperature. Flame residence time is defined as the time that it takes the working gas to pass through the flame and so is a function of the size of the flame. The flame residence time for prior art combustors is approximately fifteen msec.  
           [0007]    In view of air quality emission limitations, it is desirable to reduce the amount of NO x  produced by a combustion turbine. Reduction in the amount of NO x  could be accomplished if the temperature in the combustor assembly could be reduced, while maintaining a sufficient temperature for the working gas as it enters the turbine assembly.  
           [0008]    Prior-art combustors reduce the amount of NO x  created by pre-mixing the fuel and air. This method is less than satisfactory as pre-mixing is not completely efficient, resulting a local high fuel/air ratio pockets burning at high temperatures and, because a diffusion pilot flame is often needed to stabilize the combustor flame. The pilot flame, while small, is a high temperature diffusion flame which produces NO x . Additionally, the working gas in the transition between the combustor and the turbine may exceed a temperature of about 2800° F. (1538° C.). When the working gas is at this temperature, NO x  also forms in the transition section.  
           [0009]    There is, therefore, a need for a device to heat the temperature of the working gas in the turbine assembly of a combustion turbine power plant so that the working gas may be at a lower temperature within the combustor assembly and the transition section.  
           [0010]    There is a further need for a working gas heating device having a low residence time flame.  
           [0011]    There is a further need for a working gas heating device which is compatible with existing combustion turbines.  
           [0012]    There is a further need for a working gas heating device which incorporates present technology used on combustion turbines.  
         SUMMARY OF THE INVENTION  
         [0013]    These needs and others are satisfied by the present invention which provides a secondary combustor assembly adjacent to or within the first row of stationary vanes within the turbine assembly, which heats the working gas to a final working temperature just before the working gas passes through the turbine assembly. The primary combustor, which is similar to prior art combustors but operating at a lower temperature, provides a working gas at &lt;2650° F. (1455° C.). Thus, the amount of NO x  produced in the combustor, as well as in the transition section, is reduced. The working gas at &lt;2650° F. (1455° C.) is delivered to the secondary combustor.  
           [0014]    Where the working gas is at &lt;2650° F. (1455° C.), and preferably &lt;2500° F. (1371° C.), the secondary combustor may be in one of three embodiments, or a combination thereof. First, the secondary combustor may be structured to inject fuel in first row of vanes or blades. Second, the secondary combustor may be structured as a fuel injection manifold just ahead of first vane. Third, using a rich primary combustor, the secondary combustor may be structured as an air injection manifold just ahead of first vane.  
           [0015]    The secondary combustor of the first embodiment supplies combustible gas through the stationary vanes and/or the rotating blades in a turbine assembly. Many turbine assemblies presently include internal cooling channels within the turbine assembly. Using these channels, the rotating blades and/or stationary vanes to allow a cooling gas or a steam to pass therethrough. The channels may have openings to allow the cooling gas or a cooling steam to join the working gas. The present invention provides a combustible gas, such as, but not limited to, natural gas, through the internal channels of the stationary vanes and/or rotating blades. As the combustible gas exits openings along the trailing edges of the stationary vanes and/or rotating blades, the combustible gas will spontaneously combust, or “auto-ignite,” upon being exposed to the heated working gas. The flame produced in the rotating blade and/or stationary vane portion of a turbine has a low residence time (typically 5 msec. or less), yet still provides enough energy to heat the working gas to a working temperature as the working gas enters the turbine assembly. Additionally, the openings along the trailing edge have a diameter of about 0.125 inch or less. The flames extending from these openings are micro-diffusion flames. That is, the flames do not have a surface area much greater than the surface area of the openings (0.012 in. 2 ).  
           [0016]    Alternatively, a manifold with small fuel injection holes may be installed just before the first turbine vane to add fuel to raise the working gas temperature to its final value. Again, a fuel is introduced into the working gas stream and will auto-ignite.  
           [0017]    With the working gas being heated in the rotating blade and/or stationary vane portion of the turbine assembly, the working gas may leave the combustor assembly at a much lower temperature, typically less than 2500° F. (1371° C.). Because substantial amounts of NO x  are created at a temperatures greater than about 2650° F. (1455° C.), the reduction in temperature greatly reduces the amount of NO x  produced by the combustion turbine power plant. No significant amount of NO x  is created in the rotating blade and/or stationary vane portion of the turbine due to the low residence time of the flame and the minimal amount of time the working gas is &gt;2650° F. (1538° C.).  
           [0018]    Another alternative embodiment uses a rich primary combustor to heat the working gas initially. The rich primary combustor limits the amount of air, and therefore oxygen, in the combustor. Thus, only a portion of the fuel combusts, raising the temperature of the working gas and unburned fuel to about 1600° F. (871° C.). To allow the unburned fuel to combust, compressed air is passed through channels and effusion openings at the downstream end of the transition section. When the compressed air mixes with the combustible gas, the unburned fuel will auto-ignite, raising the temperature of the working gas to a working temperature just as the working gas enters the turbine assembly. The primary rich combustor may be catalytic.  
           [0019]    The secondary combustor further provides advantage of having a primary combustion assembly which operates at a temperature approximately 800° F. (426° C.) lower than prior combustion turbines. A cost-savings can be realized by designing the combustor assembly and transition section to operate at the lower temperature. However, this device may also be used with current combustion turbine power plants which incorporate cooling passageways in the rotating blades and/or stationary vanes that are open to the working gas flow path.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0020]    [0020]FIG. 1 is a partial cross section of a combustion turbine showing the combustor assembly, the transition section, and the turbine assembly having a secondary combustor assembly among the turbine vanes.  
         [0021]    [0021]FIG. 2 is a cross sectional view of a vane incorporating fuel injection openings.  
         [0022]    [0022]FIG. 3 is a cross section of a combustion turbine showing the combustor assembly, the transition section, and the turbine assembly having a secondary combustor as a fuel manifold.  
         [0023]    [0023]FIG. 4 is a cross section of a combustion turbine showing the combustor assembly, the transition section, and the turbine assembly having a secondary combustor in the transition section. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0024]    As shown in FIG. 1, a combustion turbine power plant  1  includes a compressor assembly  10 , a combustible gas source  11 , a fuel delivery system  12 , a primary combustor assembly  14 , a transition section  16 , a secondary combustor assembly  20 ,  20 A (as shown in FIG. 3),  120  (as shown in FIG. 4) and a turbine assembly  30 . The secondary combustor assembly  20 ,  20 A, or  120  is located adjacent to the first row of vanes  34  (described below) in the turbine assembly  30 . The transition section  16  may have a plurality of effusion openings  17  (FIG. 4) located at its down stream end. Each opening is about 0.125 inches or less in diameter.  
         [0025]    In operation, the compressor assembly  10  inducts ambient air and compresses the air. The compressed air is channeled into the primary combustor assembly  14 . The primary combustor assembly  14  is coupled to the combustible gas source  11  through the fuel delivery system  12 . In the primary combustor assembly  14 , a combustible gas and the compressed air are mixed and ignited, thereby forming a working gas. The working gas in the primary combustor assembly  14  is at a temperature of less than about 2500° F. (1371° C.). The working gas is channeled from the primary combustor assembly  14  into the transition section  16 . The transition section  16  is coupled to both the primary combustor assembly  14  and the turbine assembly  30 .  
         [0026]    A turbine assembly  30  includes an elongated outer casing  32  defining a channel  31  which is the flow path for the working gas. A plurality of stationary vanes  33  are disposed in a first row  34  within the casing  32 . There may be additional rows  134 ,  234 ,  334  of stationary vanes  33 . A plurality of rotating blades  35  are disposed in at least one row  36 , extending circumferentially from a central shaft  38 . There may be additional rows  136 ,  236 ,  336  of rotating blades  35 . Shaft  38  extends axially within casing  32 . The rows of rotating blades  36 ,  136 ,  236 ,  336  are spaced to fit within the interstices between the rows of stationary vanes  34 ,  134 ,  234 ,  334 . As shown in FIG. 2, each of the vanes  33  or blades  35  have airfoil shaped bodies  39 .  
         [0027]    The secondary combustor assembly  20 ,  20 A, (FIG. 3),  120  (FIG. 4) is structured to heat the working gas to a temperature of about 2800° F. (1538° C.) at a location proximal to the down stream end of the transition section  16  and the first row of vanes  34  in the turbine assembly  30 . The secondary combustor  20 ,  20 A,  120  assembly heats the working gas by injecting a gas into the elevated temperature working gas. The gas injected by the secondary combustor  20 ,  20 A,  120  may be either a combustible gas or, if the primary combustor is fuel-rich, compressed air or oxygen.  
         [0028]    In one embodiment, shown in FIG. 1, the secondary combustor assembly  20  is a plurality of openings disposed among the vanes  33  and/or blades  35  which are coupled to the combustible gas source  11 . The combustible gas is injected into the flow stream. As the combustible gas is injected into the elevated temperature working gas, the combustible gas will auto-ignite. That is, the combustible gas will combust without the need for an igniter or pre-existing flame.  
         [0029]    In another embodiment, shown in FIG. 3, the secondary combustor assembly  20 A is a fuel manifold  60  with fuel injection openings  62  disposed just before the first turbine vane  34 . The fuel manifold  60  is coupled to the combustible gas source  11 . The combustible gas is injected through the fuel manifold  60  into the flow stream. As the combustible gas is injected into the elevated temperature working gas, the combustible gas will auto-ignite.  
         [0030]    In another embodiment, shown in FIG. 4, the secondary combustor assembly  120  cooperates with a fuel rich primary combustor assembly  114  (described below with respect to FIG. 4) which produces a fuel rich working gas. The fuel-rich primary combustor assembly  114  may be a catalytic combustor. In this embodiment, compressed air or oxygen is injected into the transition section  16 , via effusion openings  17 , adjacent to the turbine assembly  30 . As the compressed air/oxygen mixes with the fuel rich working gas, the mixture auto-ignites. The flame caused by auto-ignition has a low residence time.  
         [0031]    In one embodiment, shown in FIG. 1, the secondary combustor assembly  20  includes a secondary combustible gas pipe assembly  44  and internal channels  40  (FIG. 2) within the airfoil bodies  39  of the vanes  33  and/or blades  35 . The internal channels  40  are coupled to openings  42  (FIG. 2) along the trailing edge of the airfoil bodies  39 . The openings  42  are sized to create micro-diffusion flames and are about 0.125 inches or less in diameter. There are about twenty openings  42  spaced along the trailing edge of each body  39 . The internal channels  40  of the stationary vanes  33  and/or rotating blades  35  are coupled to the fuel delivery system  12  by pipe  44  or other such passageway. Combustible gas may pass through the secondary combustible gas pipe assembly  44  and into the internal channels  40 . By coupling the fuel delivery system  12  to the internal channels  40 , there is a continuous path between the combustible gas source  11  and the openings  42  in the vanes  33  and/or blades  35 . Thus, the combustible gas is provided to the first row of vanes  34  and/or blades  36  in the turbine assembly  30 . The first row of vanes  34  is adjacent to transition section  16  and is, effectively, the beginning of the turbine assembly  30 .  
         [0032]    The secondary combustible gas pipe assembly  44  may include at least one valve  46  for controlling the amount of combustible gas passing therethrough and a control system  50 . The control system  50  includes at least one sensor  52 , such as a temperature sensor, pressure sensor, or mass flow sensor, which gathers data relating to the condition of the working gas. The sensor  52  converts the data into an electrical output signal which is provided to a control unit  54 . The control unit  54  receives the output signal from said sensor and determines a parameter indicative of a characteristic, e.g. the temperature, of the working gas compared to a selected standard. The control unit  54  is also coupled to the valve  46  and will increase or decrease the flow of combustible gas through the valve  46  relative to the results of the comparison, to achieve a working gas temperature approximately equal to the selected standard.  
         [0033]    In operation, a portion of the combustible gas travels from the fuel delivery system  12  through the pipe  44  to the internal channels  40  of the stationary vanes  33  and/or rotating blades  35 . As the combustible gas travels through the internal channels  40  of the stationary vanes  33  and/or rotating blades  35 , the combustible gas absorbs heat thereby cooling the stationary vanes  33  and/or rotating blades  35 . When the combustible gas reaches one of the openings  42 , it passes into the working gas stream. When the combustible gas enters the working gas stream it will auto-ignite thereby heating the working gas. Preferably, the openings  42  are sized to create micro-diffusion flames having a low residence time, preferably less than  0 . 5  msec.  
         [0034]    In the primary combustor assembly  14 , the working gas is heated to about 2000° F. (1093° C.). The working gas maintains this temperature through transition section  16 . In the secondary combustor assembly  20 , combustible gas is injected into the working gas, preferably from the first row of vanes  34 . At a temperature at or about 2000° F. (1093° C.), the combustible gas will auto-ignite, producing a micro-diffusion flame. The micro-diffusion flame heats the working gas to a temperature of about 2800° F. (1538° C.) just as the working gas enters the majority of the turbine assembly  30 . The heating of the working gas by the secondary combustor assembly  20  may be controlled by the valve  46  working in conjunction with the control system  50 .  
         [0035]    An existing combustion turbine power plant can be adapted to have a secondary combustor assembly  20  by isolating the internal channels  40  in the first row of vanes  34  from the internal channels  40  within the other rows of vanes  134 ,  234 ,  334 . This may require replacing the first row of vanes  34  with new vanes  34  which have channels  40  which do not communicate with the channels  40  in other rows of vanes  134 ,  234 ,  334 . Thus, only the channels  40  in the first row of vanes  34  are coupled to the combustible gas pipe assembly  44 . The channels  40  in the subsequent rows of vanes  134 ,  234 ,  334  may still be coupled to a cooling gas or steam source (not shown) if desired.  
         [0036]    In an another embodiment, shown in FIG. 3, the components of the combustion turbine power plant  1  are substantially the same as described above, however, the secondary combustor  20 A injects the fuel through a fuel manifold  60  disposed just before the first turbine vane  34 . In this embodiment, the fuel delivery system  12  and pipe  44  are connected to the fuel manifold  60 . The fuel manifold  60  has a plurality of openings  62  in fluid communication with the transition section  16 . Again, the fuel is injected into the heated working gas just before the turbine assembly  30 . When the fuel auto-ignites, the working gas is heated to a working temperature of about 2800° F. (1538° C.) just as the working gas enters the majority of the turbine assembly  30 . In this embodiment, the channels  40  within the vanes  33  and blades  35  may be used to cool the turbine assembly  30  components. Alternatively, the first and second embodiments may be combined so that fuel is injected through both the vanes and blades  33 ,  35  and a fuel manifold  60 .  
         [0037]    In an another embodiment, shown in FIG. 4, the working gas is heated in a secondary combustor assembly  120  located in the transition section  16 . In this embodiment, the compressor assembly  10  includes a compressed air pipe assembly  15 . A portion of the compressed air from the compressor assembly  10  is passed through the compressed air pipe assembly  15  to effusion openings  17  at the downstream end of the transition section  16  adjacent to the turbine assembly  30 . By using a fuel rich primary combustor assembly  114 , which limits the amount of combustible gas burned by limiting the amount of compressed air, and therefore oxygen, available to combust the fuel, combustible gas is provided in the working gas. The working gas and the portion of unburned combustible gas are heated to a temperature of about 1600° F. When the unburned combustible gas combines with the compressed air, and oxygen, in the transition section  16 , the combustible gas will auto-ignite, heating the working gas to about 2800° F. just as it enters the turbine assembly  30 . The secondary combustor assembly  120  creates micro-diffusion flames having a low residence time, preferably less than 5 msec. The compressed air pipe assembly  15  includes a valve  146  and control system  150 , having a sensor  152  and control unit  154 , similar to the control system  50  described above.  
         [0038]    While specific embodiments of the invention have been described in detail, it will be appreciated by those skilled in the art that various modifications and alternatives to those details could be developed in light of the overall teachings of the disclosure. For example, the both fuel rich primary combustor assembly  114  and transition section secondary combustor assembly  120  as well as a vane and/or blade secondary combustor assembly  20  may be incorporated into a single system. In such a system, the working gas is heated three times; first by the fuel rich combustor assembly  114 , then by the transition section secondary combustor assembly  120 , then by the vane and/or blade secondary combustor assembly  20 . Only the vane and/or blade secondary combustor assembly  20  raises the working gas temperature to about 2800° F. Accordingly, the particular arrangements disclosed are meant to be illustrative only and not limiting as to the scope of invention which is to be given the full breadth of the claims appended and any and all equivalents thereof.