Patent Publication Number: US-2006016195-A1

Title: Bypass and injection method and apparatus for gas turbines

Description:
The present invention relates to gas turbines, and more particularly, relates to a bypass air injection apparatus and method to increase the effectiveness of the combustor by quenching the combustion process.  
     BACKGROUND OF THE INVENTION  
      Gas turbine manufacturers are currently involved in research and engineering programs to produce new gas turbines that will operate at high efficiency without producing undesirable air polluting emissions. The primary air polluting emissions usually produced by gas turbines burning conventional hydrocarbon fuels are oxides of nitrogen, carbon monoxide and unburned hydrocarbons.  
      Catalytic reactors are generally used in gas turbines to control the amount of pollutants as a catalytic reactor burns a fuel and air mixture at lower temperatures, thus reduces pollutants released during combustion. As a catalytic reactor ages, the equivalence ratio (actual fuel/air ratio divided by the stochiometric fuel/air ratio for combustion) of the reactants traveling through the reactor needs to be increased in order to maximize the effectiveness of the reactor. Thus, there is a need to compensate for the degradation of the catalytic reactor.  
     BRIEF SUMMARY OF THE INVENTION  
      Accordingly, the present invention is directed to a bypass air injection apparatus and method to compensate for the degradation of a catalytic reactor and to increase combustor efficiency by extracting compressor discharge air prior to its entry into a combustion or reaction zone of the combustor, and re-injecting the extracted compressor discharge air into the combustor bypassing the catalytic reactor using a plurality of injection tubes located substantially in a common radial plane with an injection manifold. Compressor discharge air is received by the combustor in a first combustion chamber through a passageway, preferably an annulus defined between a combustor body with an inner liner and a casing enclosing the body. The first combustion chamber includes a pre-burner stage where fuel is mixed with compressor discharge air for combustion, thus raising the temperature of the hot gases sufficiently to sustain a reaction with the catalyst disposed downstream of the first combustion chamber. Hot gases flowing out of the first combustion chamber pass through a main fuel premixer (MFP) assembly for combustion in a main combustion chamber disposed downstream of the catalyst.  
      A predetermined amount of compressor discharge air, flowing through the annulus, and prior to reception in the first combustion chamber, is extracted into a manifold. The extraction manifold is disposed adjacent to an array of openings located in the casing enabling compressor discharge air to flow from the annulus into the extraction manifold. A bypass conduit connects the extraction manifold to an injection manifold. The injection manifold lies in communication with a plurality of injection tubes for injecting the extracted air into the combustor body bypassing the catalyst. As noted above, each injection tube and the injection manifold are disposed in a substantially common radial plane. Removable flange covers are provided on the injection manifold in substantial radial alignment with the respective injector tubes affording access to the tubes. The injection tubes are installed from the outside of the injection manifold at circumferentially spaced locations about the casing and the liner through flange covers. A bypass air (i.e., extracted air) path is therefore provided to bridge the backside cooling airflow annulus disposed between the combustor casing and the combustion liner.  
      In another embodiment, the combustor includes only one combustion chamber. Thus, the combustor is devoid of the catalyst and the MFP assembly. Here, main combustion occurs at the pre-burner stage where a greater amount of fuel is mixed with air in order for combustion to occur.  
      In one aspect, the present invention provides a combustor for a gas turbine having a combustor body, a casing enclosing the combustor body and defining an annular passageway therebetween for carrying compressor discharge air into the combustor body at one end thereof; a reaction zone within the combustor body for main combustion of fuel and air, a first annular manifold surrounding the casing and arranged to extract a predetermined amount of compressor discharge air from the annular passageway, a second annular manifold surrounding the casing and arranged to receive the extracted air, the second manifold located downstream of the first manifold in a combustion flow direction; a conduit for supplying the extracted air from the first manifold to the second manifold; and a plurality of injection tubes in communication with the second manifold for injecting the extracted air into the combustor body downstream of the reaction zone in the combustion flow direction to quench combustion, the injection tubes and the second manifold being disposed in a substantially common radial plane.  
      In another aspect, the present invention provides a combustor for a gas turbine including a combustor body with an inner liner, a casing enclosing the body and defining a passageway therebetween for carrying compressor discharge air, a catalytic reactor disposed in the body for controlling pollutants released during combustion; a first manifold for extracting a predetermined amount of compressor discharge air from the passageway, a second manifold for receiving the extracted air and supplying the extracted air to the body at a location bypassing the catalytic reactor, and a plurality of injection tubes in communication with the second manifold for injecting the extracted air into the body, the injection tubes and the second manifold being disposed in a substantially common radial plane.  
      In another aspect, the present invention provides a gas turbine having a compressor section for pressurizing air; a combustor for receiving the pressurized air; and a turbine section for receiving hot gases of combustion from the combustor, the combustor including a combustor body with an inner liner, a casing enclosing the body and defining a passageway therebetween for carrying compressor discharge air, a reaction zone within the combustor body for combustion of fuel and air, a first manifold surrounding the casing and arranged to exhaust a predetermined amount of compressor discharge air from the passageway, a second manifold surrounding the casing and arranged to receive the extracted air, the second manifold located downstream of the first manifold in a combustion flow direction; a conduit for supplying the extracted air from the first manifold to the second manifold; and a plurality of injection tubes in communication with the second manifold for injecting the extracted air into the combustor body downstream of the reaction zone in the combustion flow direction to quench combustion, the injection tubes and the second manifold are disposed in a substantially common radial plane.  
      In yet another aspect, the present invention provides a method for quenching combustion by extracting a predetermined amount of compressor discharge air, before the air flows into the reactor, from the passageway into the first manifold; supplying the extracted air from the first manifold to the second manifold via the conduit; injecting the extracted air received by the second manifold into the body at a location along the body bypassing the reactor using an array of injection tubes; and disposing the injection tubes and the second manifold in a substantially common plane.  
      In another aspect, the present invention provides a gas turbine having a compressor section for pressurizing air, a combustor for receiving the pressurized air, and a turbine section for receiving hot gases of combustion from the combustor, the combustor including a combustor body with an inner liner, a casing enclosing the body and defining a passageway therebetween for carrying compressor discharge air, a reaction zone within the combustor body for combustion of fuel and air, a first manifold surrounding the casing and arranged to exhaust a predetermined amount of compressor discharge air from the passageway, a second manifold surrounding the casing and arranged to receive the extracted air, the second manifold located downstream of the first manifold in a combustion flow direction; a conduit for supplying the extracted air from the first manifold to the second manifold; and a plurality of injection tubes in communication with the second manifold for injecting the extracted air downstream of the reaction zone in the combustion flow direction, wherein said injection tubes include a feedhole configuration adapted to channel air from the second manifold.  
      The present invention is better understood upon consideration of the detailed description below in conjunction with the accompanying drawings and claims. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a schematic cross-sectional illustration of a combustor forming a part of a gas turbine and constructed in accordance with the present invention;  
       FIG. 2  is a detailed illustration of the injection manifold and the bypass injection scheme of the present invention;  
       FIG. 3  illustrates another embodiment of the invention wherein a catalytic reactor is removed from the combustor;  
       FIG. 4  shows a section of the combustor casing, of  FIG. 1 , having an array of openings for extracting compressor discharge air;  
       FIG. 5  illustrates an exemplary injection tube design;  
       FIGS. 6A and 6B  illustrates an exemplary injection tube;  
       FIG. 7  illustrates an exemplary configuration of a plurality of injection tubes; and  
       FIG. 8  illustrates an exemplary flow conditioner.  
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
      As is well known, a gas turbine includes a compressor section, a combustion section and a turbine section. The compressor section is driven by the turbine section typically through a common shaft connection. The combustion section typically includes a circular array of circumferentially spaced combustors. A fuel/air mixture is burned in each combustor to produce the hot energetic gas, which flows through a transition piece to the turbine section. For purposes of the present description, only one combustor is discussed and illustrated, it being appreciated that all of the other combustors arranged about the turbine are substantially identical to one another.  
      Referring now to  FIG. 1 , there is shown a combustor generally indicated at  10  for a gas turbine including a fuel injector assembly  12  having a single nozzle or a plurality of fuel nozzles (not shown), a cylindrical combustor body  16 , and a casing  20  enclosing the body  16  thereby defining a passageway  18 , preferably an annulus  18  therebetween. An ignition device (not shown) is provided and preferably comprises an electrically energized spark plug. Discharge air received from a compressor  40  via an inlet duct  38  flows through the annulus  18  and enters the body  16  through a plurality of holes  22  provided on the pre-burner assembly  11 . Compressor discharge air enters body  16  under a pressure differential across the pre-burner assembly  11  to mix with fuel from the fuel injector assembly  12 . The mixture is burnt by the pre-burner assembly  11 . Combustion occurs in a first combustion chamber or first reaction zone  14  thus raising the temperature of the combustion gases to a sufficient level for the catalyst  27  to react. Combustion air from the first combustion chamber  14  flows through a main fuel premixer (MFP) assembly  24  and then through catalyst  27  into the main combustion chamber or main reaction zone  29  for combustion. Additional fuel is pumped into the MFP assembly to mix with hot gases, exiting the first combustion chamber  14 , and reacts through catalyst  27  thus producing a combustion reaction in the main combustion chamber  29 , whereby the hot gases of combustion pass through a transition piece  36  to drive the turbine  42 .  
      A predetermined amount of the compressor discharge air is extracted from the annulus  18  into a manifold  26  via an array of openings  25  ( FIG. 4 ) located in casing  20  and leading into an opening  28  which sealingly mates with one end of a bypass conduit  30 , while a second end of conduit  30  leads into an injection manifold  32 . A valve  31  regulates the amount of air supplied to manifold  32 . Additionally, a metering device such as an annubar flow-meter may be included to measure the quantity of air passing through conduit  30 , and a low pressure drop flow conditioner device such as VORTAB™ flow conditioner (see, e.g.,  FIG. 8 ) or perforated plate conditioner may be included that prepares the flow for more accurate flow measurements. Suitable metering devices include devices based on differential pressure or other suitable flow meters. A suitable metering device may further be advantageously coupled to a control system. Air received in manifold  32  is injected by a plurality of injection tubes  33  into body  16 , bypassing catalyst  27 . Each of the injection tubes  33  and manifold  32  are located substantially in a common radial plane. Further, each injection tube opens into body  16  through apertures  34  ( FIG. 2 ). Removable flange covers  23  are provided on the injection manifold in substantial radial alignment with the respective injector tubes  33  affording access to the tubes. The injection tubes are installed from the outside of the injection manifold at circumferentially spaced locations about the casing and the liner through flange covers. Members  35  and  39  ( FIG. 2 ) cooperate to secure each injection tube  33  to body  16  in a floating piston seal to provide a sealingly tight connection. Thus, injected air cools the reaction and quenches the combustion process.  
      Other exemplary bypass and injection systems are described in U.S. Pat. Nos. 6,449,956 and 6,568,188 both entitled “BYPASS AIR INJECTION METHOD AND APPARATUS FOR GAS TURBINES,” and both of which are incorporated by reference as if fully set forth herein.  
      Referring to  FIG. 3 , a second embodiment is illustrated wherein like elements as in the combustor of  FIG. 1  are indicated by like reference numerals preceded by the prefix “ 1 ”. Here, the combustor  110  comprises a combustion chamber or reaction zone  114  where main combustion occurs. Catalyst  27  and MFP assembly  24  are absent in this embodiment. Here, compressor discharge air from annulus  118  flows into manifold  126 , and from manifold  126  via conduit  130  flows into body  116  through injection tubes  133  bypassing the reaction zone  114 . Further, the amount of fuel supplied to mix with compressor discharge air is greater than the amount supplied in the presence of a catalyst. It will be appreciated that the location of the reaction zone  114  need not necessarily lie in close proximity to the fuel injector assembly  112 . Rather it may be located within body  116  between end member  143  and manifold  132 . Likewise, manifold  132  may be appropriately located along casing  120  to inject air into body  116  provided the reaction zone is bypassed in order to quench the combustion process. In other words, the manifold  132  and the injection of compressor discharge air into combustor body occurs downstream of the reaction zone  114  in a combustion flow direction, as apparent from  FIG. 3 .  
      Thus, the present invention has the advantages of maximizing the effectiveness of the catalytic reaction, thereby increasing the efficiency of the combustor. The present invention further provides a simple means of controlling the combustion process.  
      Another aspect of the present invention includes a combustion system having injection tubes adapted to extend into a plenum for receiving bypass air and re-inject the air downstream of the main combustion or reaction zone with reduced pressure drop resulting from flow losses at the injection tube feedholes. In one example, the feedhole sizes and/or shapes are adapted to reduce undesirable pressure drops near the injection tube feedholes. Further, an injection tube having one or more feedholes may be oriented with a greater feedhole area facing a flow of air in the plenum to channel or scoop the air with reduced pressure drops near the feedholes and reduce flow losses of the bypass system.  
       FIG. 5  illustrates an exemplary injection tube  500  including four circular feedholes  510 . The injection tube  500  and four circular feedholes  510  extend into a plenum where air is received through feedholes  510  and directed downstream of the reaction zone through injection tube  500 . In this example, each feedhole  510  is equally sized and spaced 90 degrees apart around the circumference of the injection tube. Testing and analysis revealed that there were significant losses in pressure near feedholes  510  of the injection tube  500  that may cause a decrease in flow capacity of the bypass system. Generally, increasing the diameter of injection tube  500  and/or the size of feedholes  510  has been found to reduce pressure drops near feedholes  510  thereby improving performance of the bypass system. Further, nonsymmetrical feedhole configurations that may be oriented with respect to an airflow direction have been found to reduce pressure drops near injection tube feedholes and also in the general flowpath.  
       FIGS. 6A and 6B  illustrate an exemplary injection tube  600  including a generally rectangular profile “scoop” feedhole design that may reduce pressure drops from the plenum, i.e., manifold  32  of  FIG. 1 , through the injection tube due to flow losses near the feedhole  610 . Additionally, the diameter of the injection tube  600  can be increased to further reduce pressure drops. In one example, the area of the opening of feedhole  610  relative to the outer surface area of injection tube  600  may be increased (as compared to injection tube  500 , for example), and may be configured in a bypass system to oppose or face the airflow in a plenum. The larger area feedhole  610  (compared to injection tube  500  and feedhole  510 ) and configuration facing the airflow allows the injection tube  600  to scoop or channel the air through feedhole  610  with reduced pressure loss near the feedhole  610 .  
      Generally, providing a large area opening in the injection tube allows little air passage out of the openings back into the plenum (e.g., manifold). Further, minimizing structures and tailoring geometries that reduce pressure by reducing or elimination eddies, vortices, and the like increases the bypass performance. Therefore, it is desirable to exclude sharp edges or curves in the openings that may create eddies and pressure fluctuations in the airflow.  
      Preferably, injection tube  600  includes a single feedhole  610  having a rectangular shaped opening with curved corners to reduce pressure fluctuations from eddies and the like; however, squared corners are possible. In other examples, feedhole  610  may include an elliptical shaped opening or other suitable shape, and injection tube  600  may include any number of feedholes  610  of various shapes and configurations. Additionally, trumpet shaped or NACA (National Advisory Committee for Aerodynamics) duct shape feedholes may also be used.  
      Generally, it is desired to configure one or more feedholes  610  to have a greater opening or receiving area facing the airflow to scoop or channel air from the airflow with reduced pressure loss near the opening. For example, in  FIG. 6B , injection tube  600  has an opening for intaking air from the left side, facing upstream of the airflow, and may thereby scoop air with reduced pressure loss and channel the air downstream of the main reaction zone, e.g., between the reaction zone and the turbine. In other examples, injection tube  600  could include an opening on the opposite side of feedhole  610  with a smaller opening area.  
       FIG. 7  illustrates a portion of an exemplary bypass system including a plurality of injection tubes  700  configured to scoop air from the plenum, e.g., manifold  732 , and inject the air through injection tubes  700  into combustor body  716 . Manifold  732  receives air from the conduit  730 , and feedholes  710  scoop air from the plenum and feed it to a point in the combustion systems downstream of the main reaction zone. The clocking or orientation of the feedholes  710 , shown here as rectangular scoops of the injection tubes  700 , may further reduce pressure drops near the feedholes  710 . The orientation of the feedholes  710  is relative to the air feed from conduit  730  into the spool shaped manifold  732  as shown generally by the arrows. In particular, feedholes  710  face upstream of the airflow through manifold  732 . However, alternative shapes and openings may be clocked differently.  
      In other examples, computational fluid dynamic analysis may be used to find a desirable orientation of the feedhole  710  relative to airflow based on the airflow characteristics within manifold  732 , the configuration of feedholes  710 , and the like. Test data has shown that the exemplary injection tubes  700  and design of scoop feedholes  710 , as well as increased injection tube  700  diameter, may greatly alleviate flow losses and increases flow capacity of the bypass system. It should be recognized by those of ordinary skill in the art that various feedhole configurations and injection tube configurations discussed herein may be used alone or in combination with various other devices and methods to reduce pressure drops and increase bypass system performance.  
      While the invention has been described in connection with what is presently considered to be the most practical and 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 included within the spirit and scope of the appended claims.