Abstract:
A method of operating a combustion turbine engine that includes separating a flow of compressed air into a first flow stream and a second flow stream. The method also includes preheating the first flow stream to produce a preheated flow stream and premixing the second flow stream with a flow of fuel to produce a premixture. The method further includes mixing the premixture with a portion of the preheated first flow stream to produce a combustible mixture and combusting the combustible mixture to produce a flow of hot products of combustion.

Description:
RELATED APPLICATION DATA  
       [0001]     This application is a divisional application of U.S. patent application Ser. No. 10/417,016 filed Apr. 16, 2003, the entire contents of which are herein incorporated by reference. 
     
    
     BACKGROUND  
       [0002]     The present invention relates to a system and apparatus for optimizing airflow to a combustor and particularly to a system and method for controlling airflow to the combustor. More particularly, the present invention relates to a system and method for controlling the quantity of airflow to the primary zone of the combustor.  
         [0003]     Present combustors are typically designed for a specific fuel to be combusted. Each fuel requires a specific fuel-to-air ratio (FAR) to be combusted efficiently without producing excessive undesirable emissions (e.g., NO x , CO, and unburned hydrocarbons). Thus, a combustor that operates well using natural gas may not be efficient or may produce undesirable emissions when operated using a different fuel such as butane. At present, fuel-staging is used to allow one combustor design to operate with multiple fuels. However, fuel-staging increases unwanted emissions when operating at part power.  
       SUMMARY  
       [0004]     The present invention provides a combustion turbine engine adapted for use with a source of fuel. The engine includes a compressor operable to produce a flow of compressed air, a recuperator, and a bypass duct extending around said recuperator. A flow divider selectively divides the flow of compressed air into a first flow of compressed air flowing through said recuperator and a second flow of compressed air flowing through said bypass duct around said recuperator. The first flow of compressed air is preheated within said recuperator. An adjustable valve operably interacts with at least one of said first and second flows of compressed air to selectively adjust the flow rate of the same. A premix chamber is adapted to receive a flow of fuel from the source of fuel. The premix chamber communicates with said bypass duct to receive said second flow of compressed air and to mix said flow of fuel and said second flow of compressed air into a premixture. The invention also includes a combustor having a primary zone in communication with both of said premix chamber and said recuperator such that said preheated first flow of compressed air from said recuperator and said premixture from said premix chamber are mixed within said primary zone to create a combustible mixture. The combustor combusts said combustible mixture to produce a flow of products of combustion. The invention further includes a power turbine driven by the flow of products of combustion from said combustor and a power generator generating power in response to operation of said power turbine, wherein the flow of products of combustion flows through said recuperator to preheat said first flow of compressed air.  
         [0005]     In another embodiment, the invention provides a combustion air delivery system comprising a compressor operable to provide a stream of compressed air and a bypass duct positioned to divide the stream of compressed air into a bypass flow stream and a primary flow stream. A recuperator is operable to preheat the primary flow to produce a flow of preheated compressed air. A premix chamber receives the bypass flow stream and mixes the bypass flow stream with a flow of fuel to produce a fuel-air flow. A can member at least partially defines a primary zone that receives the fuel-air flow and includes an aperture sized to admit a predetermined portion of the flow of preheated compressed air. The fuel-air flow and predetermined portion of the flow of preheated compressed air mix in the primary zone to produce a combustible flow. An igniter is operable to ignite the combustible flow.  
         [0006]     In yet another embodiment, the invention provides a method of operating a combustion turbine engine. The method includes separating a flow of compressed air into a first flow stream and a second flow stream and preheating the first flow stream to produce a preheated flow stream. The method also includes premixing the second flow stream with a flow of fuel to produce a premixture. The invention further includes mixing the premixture with a portion of the preheated first flow stream to produce a combustible mixture and combusting the combustible mixture to produce a flow of hot products of combustion.  
         [0007]     Additional features and advantages will become apparent to those skilled in the art upon consideration of the following detailed description of preferred embodiments exemplifying the best mode of carrying out the invention as presently perceived. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]     The detailed description particularly refers to the accompanying figures in which:  
         [0009]      FIG. 1  is a perspective view of a combustion turbine engine;  
         [0010]      FIG. 2  is a schematic illustration of a combustion system embodying the present invention and including a combustion section;  
         [0011]      FIG. 3  is a schematic illustration of another combustion system embodying the present invention;  
         [0012]      FIG. 4  is an enlarged view of an orifice plate;  
         [0013]      FIG. 5  is a cross-sectional view of the combustion section of  FIG. 2  and including a swirler head;  
         [0014]      FIG. 6  is a partially broken away perspective view of the swirler head of  FIG. 5 ;  
         [0015]      FIG. 7  is another perspective view of the swirler head of  FIG. 6 ; and  
         [0016]      FIG. 8  is a perspective view of the swirler head of  FIG. 6  with a skirt attached. 
     
    
     DETAILED DESCRIPTION  
       [0017]     With reference to  FIG. 1 , a combustion turbine engine  10  is illustrated as including a compressor  15 , a gasifier turbine  20 , a power turbine  25 , a recuperator  30 , a combustion section  35  including a combustor  37  ( FIGS. 2, 3 , and  5 ), and various air passages. In addition, the engine  10  generally includes a driven element such as a generator  40 . In a two-turbine engine  10  such as the one illustrated in  FIG. 1 , the gasifier turbine  20  is connected to the compressor  15  such that operation of the gasifier turbine  20  drives the compressor  15 . The power turbine  25  is connected to the generator  40  or another component to be driven (e.g., a pump) such that operation of the power turbine  25  drives the generator  40 . In a one-turbine engine  10 , the single turbine would be sized to drive both the compressor  15  and the generator  40 .  
         [0018]     During engine operation, atmospheric air is drawn into the compressor  15  and compressed to produce a flow of compressed air  45  (shown in  FIGS. 2 and 3 ). A portion of the flow of compressed air  45  flows through the recuperator  30  where it is preheated. The preheated compressed air  50  enters the combustion section  35  and combines with a flow of fuel  55  to produce a combustible fuel-air mixture  60  (shown in  FIGS. 2, 3 , and  5 ). The fuel-air mixture  60  is combusted to produce an expanding flow of combustion gas or products of combustion  65 . The flow of combustion gas  65  passes through the gasifier turbine  20  to power the gasifier turbine  20  and drive the compressor  15 . The flow of combustion gas  65  then flows through the power turbine  25  to drive the generator  40 . The flow of combustion gas  65  proceeds through the recuperator  30  and preheats the flow of compressed air  45   a  exiting the compressor  15  before being discharged to the atmosphere. In some constructions, the flow of combustion gas  65  leaving the recuperator  30  is used in another process before being discharged (e.g., heating water).  
         [0019]     Turning to  FIG. 2 , the engine air passages are illustrated in more detail. Before describing the passages, it should be noted that various terms such as “passage,” “duct,” “pipe,” and “flow path,” among others, are used herein to describe devices suited to conducting fluids from one point to another. These terms should be considered interchangeable and should not be read to limit the invention in any way. For example, and without limiting the foregoing, the term “pipe” should be interpreted broadly to include “duct,” “tube,” “plenum,” and “flow path” among other terms.  
         [0020]     The flow of compressed air  45  exits the compressor  15  and is divided into two distinct flow streams. The first flow stream  45   a  enters the recuperator  30  and is preheated as described above. The preheated compressed air  50  then flows to the combustion section  35 . The second flow stream  45   b , or bypass flow stream, enters a bypass duct  70  that directs the bypass flow stream  45   b  around the recuperator  30  and into the combustion section  35  without preheating the air.  
         [0021]     The second flow stream  45   b  is further divided into a plurality of flow paths  75 . Each of the plurality of flow paths  75  include a valve  80  that can control the flow through the individual flow path  75  and an orifice  85  that limits the amount of flow to a predetermined rate. In some constructions, the valve  80  itself acts as the orifice  85  by limiting the amount of flow even when fully opened. In other constructions, orifice plates  90  (shown in  FIG. 4 ) are positioned in each of the flow paths  75 . The use of the orifice plates  90  allows for precise control of the mass flow rate through each of the flow paths  75  under given operating conditions. In addition, the orifice plates  90  can be changed to increase or decrease the flow capacity of a particular flow path  75  if desired. It should be understood that even a pipe with no flow obstructions could be considered “orificed,” as the size or diameter of the pipe limits flow under any given operating condition. As such, the invention should not be limited to arrangements that require orifice plates  90  or other components that act as orifices  85 . Rather, the orifices  85  are used to increase the accuracy and predictability of engine performance.  
         [0022]     The use of multiple flow paths  75  allows for more refined control when compared to a single-path system, as one or more valves  80  can be partially or totally opened to allow the desired amount of air to bypass the recuperator  30 . In most constructions, each valve  80  is set to either an open position or a closed position to reduce the likelihood of air leakage at the valve  80 . Thus, the use of multiple valves  80  and multiple flow streams  75  allows for adequate control over the quantity of air being bypassed without the use of a complex control scheme or expensive valve.  
         [0023]     Turning now to  FIG. 3 , a second construction of the engine  10   a  is illustrated in which the second flow stream  45   b  is not divided into a plurality of flow paths  75 . Rather, the engine  10   a  includes a single flow path  45   b  having a controllable multi-position valve  95 . A controller  100  adjusts the valve  95  as needed based on one or more control parameters (e.g., turbine temperature, exhaust temperature, turbine inlet temperature, turbine exhaust composition, combustor pressure, fuel type, power level, operating temperature, ambient air temperature, etc.). In some constructions, the valve position is preset and is not adjusted during operation. For example, a particular engine that is capable of operating on several different fuels (e.g., natural gas, propane, butane, JP-8, etc.) operates most efficiently if the combustor  37  is specifically configured for the particular fuel being burned. A switch (not shown), operated by the user, repositions the controllable valve  95  to a fuel-specific position before operation of the engine  10   a.  Thus, the engine  10   a  operates efficiently with any of the fuels. In another construction, the valve  95  is controlled during engine operation by the controller  100 . One or more engine parameters are used to periodically or constantly adjust the position of the valve  95  to achieve the desired performance. As one of ordinary skill in the art will realize, many different control parameters and control systems could be used to control the valve position.  
         [0024]     A person of ordinary skill will also realize that the controller  100  and system as just described with regard to  FIG. 3  could be applied to the engine  10  of  FIG. 2  to achieve similar results. Thus, the use of controllable valves  95  should not be limited to constructions similar to that of  FIG. 3  alone. Furthermore, the valve  95  of  FIG. 3  could be manually controlled to achieve the desired results. In these constructions, the valve  95  is positioned in predetermined positions based on various factors (e.g., turbine temperature, exhaust temperature, turbine inlet temperature, turbine exhaust composition, combustor pressure, fuel type, power level, operating temperature, ambient air temperature, etc.).  
         [0025]      FIG. 5  shows a sectional view of a can-type combustor. As seen in  FIG. 5 , the combustor  37  is positioned within an outer wall  105 . In most constructions, the outer wall  105  is formed as part of the recuperator  30  as shown in  FIGS. 2 and 3 . This arrangement reduces the space occupied by the engine  10  and reduces the number of components such as pipes, flanges, and valves needed to assemble the engine  10 . Other constructions may employ a combustion section  35  spaced some distance from the recuperator  30  and use pipes or other ducts to direct the preheated compressed air  50  from the recuperator to the combustion section  35  and from the combustion section  35  to the turbine  20 .  
         [0026]     The combustor  37 , illustrated in  FIG. 5  includes a swirler head  110  attached to a can  115  and positioned substantially within the outer wall  105  defined by the recuperator  30 . The combustor  37  is generally divided into zones including a primary zone  120  and a secondary zone  125 , with many constructions also including a tertiary or dilution zone  130 . In general, combustion is initiated and maintained within the primary zone  120 . Additional air may be added in the secondary zone  125  to assure complete combustion and reduce the quantity of undesirable emissions. The tertiary or dilution zone  130 , if employed, receives a large quantity of air to cool the flow of combustion gas  65  to a desired combustor outlet temperature before the flow of combustion gas  65  enters the turbine  20 .  
         [0027]     The primary zone  120  is defined by a portion of the swirler head  110  and a portion of the combustor can  115 . The swirler head  110 , best illustrated in  FIGS. 6 and 7 , includes a body  135  that defines a premix chamber  140  (shown broken away in  FIG. 6  and in cross-section in  FIG. 5 ) and a plurality of flow guides  145 . The body  135  also includes a flange  150  that facilitates the attachment of the combustor  37  to the recuperator  30 . The flange  150  separates the swirler head  110  into an outer portion  155 , illustrated in  FIG. 6 , and an inner portion  160  illustrated in  FIG. 7 . The inner portion  160  is substantially within the primary zone  120  of the combustor  37 , while the outer portion  155  is not. As illustrated herein, the swirler head  110  is a separate component that attaches to the can  115 . However, other constructions employ a swirler head  110  that is formed as part of the can  115 . In still other constructions, the swirler head  110  is a separate component positioned away from the remainder of the combustion section  35 .  
         [0028]     The premix chamber  140  is an annular chamber within the body  135  of the swirler head  110 . As shown in  FIG. 6 , a bypass air inlet  170  and a fuel inlet  175  both attach to the outer surface of the cover plate  165  and/or the body  135  of the swirler head  110  to deliver bypass air and fuel to the combustor  37 .  
         [0029]     Also visible on the outer portion  155  of the swirler head  110  is a pilot fuel inlet  180  and an ignitor  185  that is received in a hole  187  in the head  110 . The pilot fuel inlet  180  provides a separate flow of fuel that may be used to maintain the flame stability within the combustor  37  at low power settings or to initiate combustion within the combustor  37  during an engine start. The igniter  185  is a spark-producing device that provides a spark to initiate combustion during engine start-up or at any other time when the flame is desired but not present. Alternatively, a heat-producing device such as a glow plug is used. As one of skill in the art will realize, many other devices are well suited to the task of initiating a flame and as such are contemplated by the present invention.  
         [0030]     Both the fuel inlet  175  and the pilot fuel inlet  180  receive a flow of fuel  55  from an external fuel source  190  ( FIGS. 2 and 3 ) such as a tank or gas line. In most constructions, a fuel pump/compressor and/or assorted valves are in fluid communication with the fuel source  190  and the swirler head  110  to control the rate of fuel flow. Thus, the engine  10  is able to deliver fuel at a desired rate to the combustor  37 .  
         [0031]     In one construction of a swirler head  110  shown in  FIG. 7 , the inner portion  160  includes the plurality of flow guides  145  that are partially encircled by a skirt  195  (shown in  FIGS. 5 and 8 ). The flow guides  145  are generally raised triangular blocks having two planar surfaces  200  and an arcuate outer surface  205 . The outer surfaces  205  and the skirt  195  cooperate to define a partial annular air chamber  210 . The planar surfaces  200  of each flow guide  145  are arranged such that they are substantially parallel to the planar surfaces  200  of the adjacent flow guides  145 . Using this arrangement, a plurality of flow paths  215 , or apertures, are defined between the annular air chamber  210  and a primary zone neck  220  ( FIG. 5 ). The skirt  195  guides compressed air exiting the recuperator  30  into the flow paths  215 . As one of ordinary skill will realize, many different arrangements are possible to direct compressed air into the primary zone  120 . As such, the present invention should not be limited to the aforementioned example.  
         [0032]     Within each flow path  215  are two fuel inlets. The first of the inlets  225  is located adjacent the flow path inlets and includes an injector  230  that directs the fuel flow in the flow direction of the compressed air. The first fuel inlet  225  is in fluid communication with, and receives a flow of fuel or fuel-air from the premix chamber  140 . The second fuel inlet  235  comprises a small bore located adjacent the individual flow path outlets. This inlet  235  is in fluid communication with the pilot fuel inlet  180 .  
         [0033]     The primary zone neck  220  is a substantially cylindrical region of the can  115  that defines a portion of the primary zone  120  of the combustor  37 . The flow paths  215  defined by the flow guides  145  direct the compressed air from the annular air chamber  210  into the primary zone neck  220 . The igniter  185  (shown in  FIG. 5 ) is positioned within the primary zone  120  to enable it to ignite the fuel-air mixture therewithin. Alternatively, the igniter  185  could be positioned elsewhere in the head  110  or neck  220 .  
         [0034]     The secondary zone  125  is positioned downstream of the primary zone  120  and includes additional apertures  240  that admit air. The apertures  240  direct compressed air along the inner wall of the can  115  in the secondary zone  125 . In other constructions, additional apertures may be used to admit air to further sustain combustion.  
         [0035]     The tertiary zone or dilution zone  130  is located downstream of the secondary zone  125  and includes large apertures  245  that admit the remaining compressed air into the combustor as the air exits the recuperator  30 . In other constructions, the flow of combustion gas  65  exits the can  115  and then mixes with the remaining compressed air before finally flowing to the turbine  20 . In either construction, the remaining compressed air mixes with the flow of combustion gas  65 .  
         [0036]     In operation, the compressed air exits the compressor  15  and divides into the two flow streams  45   a ,  45   b . The first flow stream  45   a  is directed to a plenum in the recuperator  30 , then through the recuperator  30  where the air is preheated until finally reaching the air space between the recuperator  30  and the combustor  37 . Meanwhile, the second flow stream (bypass air stream)  45   b  proceeds from the compressor  15  directly to the swirler head  110  without passing through the recuperator  30 .  
         [0037]     The bypass air enters the premix chamber  140  through the bypass air inlet  170 . For engines configured as shown in  FIG. 2 , a plurality of air inlets  170  may be used. However, in other constructions the bypass air is recombined into a single flow before being admitted into the premix chamber  140 . The premix chamber  140  for this construction would require only a single air inlet  170 , thereby simplifying the manufacture of the swirler head  110 . One of ordinary skill in the art will realize that the premix chamber  140  could be designed to have multiple air inlets  170  if desired, no matter the arrangement of the engine  10 .  
         [0038]     Within the premix chamber  140 , the bypass air and the fuel mix to produce a fuel-air mixture. The fuel inlet(s)  175  and air inlet(s)  170  are arranged such that the air and fuel mix thoroughly within the premix chamber  140 . The fuel/air ratio (FAR) of the mixture within the premix chamber  140  is typically too high (i.e., rich mixture) to sustain combustion. Thus, additional air must be added to the fuel-air mixture to initiate and sustain combustion. After mixing, the fuel-air mixture within the premix chamber  140  is injected into the primary zone  120  of the combustor  37  via the fuel inlets  225 .  
         [0039]     The flow paths  215  are sized to admit sufficient air into the primary zone  120  to sustain combustion at a desired or target equivalence ratio (ER). The ER is defined as the ratio of the actual FAR and the stoichiometric fuel-air ratio. The stoichiometric fuel-air ratio is the ideal ratio of a particular fuel and air for combustion. At the stoichiometric fuel-air ratio, all of the fuel and all of the oxygen are consumed during combustion.  
         [0040]     In one construction, the target ER value is 0.5. Thus, the fuel-air mixture in the primary zone  120  is lean (i.e., excess oxygen is available for combustion). The lean mixture reduces the undesirable engine emissions during operation.  
         [0041]     As an example, many combustion turbine engines  10  use natural gas as the primary fuel. Natural gas has a stoichiometric fuel-air ratio of 0.058 (i.e., for every kilogram of fuel, 17.25 kilograms of air are required). For a target equivalence ratio of 0.5 using natural gas, the actual FAR must be 0.029 (i.e., for every kilogram of fuel, 34.5 kilograms of air are supplied). A portion of the necessary air is supplied in the fuel-air mixture delivered from the premix chamber  140 . As such, the flow paths  215  in the swirler head  110  are sized to admit the remaining air. For example, at one operating condition, air may be supplied to the premix chamber  140  at a fuel-air ratio of 0.10 (i.e., for every kilogram of fuel, ten kilograms of air are supplied). Thus, the flow paths  215  must be sized to admit the remaining 24.5 kilograms of air needed to reach the targeted ER.  
         [0042]     During turndown (part load) operation, the mixture in the primary zone  120  tends to become more lean (excessive air). In some cases, the FAR can fall below the lean extinction FAR of the combustor  37 , thereby causing blowout, flame extinction, or other flame related problems. The present invention allows for the maintenance of the target ER during turndown operation by reducing the air flow into the premix chamber  140 . This has the desirable effect of reducing the total air in the primary zone  120  as the quantity of fuel is reduced.  
         [0043]     In addition to improved turndown operation, the present invention facilitates the efficient and clean operation of a single combustor  37  using multiple fuels. Continuing the example from above, if the combustor  37  were switched from natural gas to another fuel such as butane, its performance would suffer. Butane has a stoichiometric fuel-air ratio of 0.067 (i.e., for every kilogram of butane, 14.9 kilograms of air are required). Thus, to operate at an ER of 0.5, 29.8 kilograms of air must be admitted to the primary zone for each kilogram of fuel.  
         [0044]     The above-described combustor  37  includes flow paths  215  sized to admit 24.5 kilograms of compressed air for every kilogram of fuel. Thus, the ER would be 0.43 with the valves  80  and combustor  37  configured as above for natural gas (i.e., 10 kilograms of air being mixed with one kilogram of fuel in the premix chamber  140 ). This ER may be low enough to cause flame instability and other operational problems. To counteract this and return the combustor  37  to optimal performance, the flow rate of bypass air to the premix chamber  140  is reduced. To return the combustor  37  to an ER of 0.5, the actual FAR must be approximately 0.034. (i.e., for every kilogram of fuel, 29.8 kilograms of air are present). To achieve this, the valve or valves  80  are adjusted to allow the passage of 5.3 kilograms of air per kilogram of fuel, rather than the 10 kilograms passed when operating with natural gas as the fuel. The flow paths  215  remain fixed and admit the remainder of the required air (i.e., 24.5 kilograms per kilogram of fuel). As one skilled in the art will realize, the present system can be designed to operate efficiently with several different fuels rather than just the two described.  
         [0045]     It should be noted that the above description is for exemplary purposes only. The invention should in no way be limited to mass flow rates similar to those described, as larger or smaller fuel and air flow rates, as well as different ERs and FARs may be desirable and would be achievable with the invention as described herein.  
         [0046]     Although the invention has been described in detail with reference to certain preferred embodiments, variations and modifications exist within the scope and spirit of the invention as described and defined in the following claims.