Patent Publication Number: US-11649965-B2

Title: Fuel nozzle for a gas turbine with radial swirler and axial swirler and gas turbine

Description:
TECHNICAL FIELD 
     Embodiments of the subject matter disclosed herein correspond to fuel nozzles for gas turbines with radial swirler and axial swirler and gas turbines using such nozzles. 
     BACKGROUND 
     Stability of the flame and low NOx emission are important features for fuel nozzles of a burner of a gas turbine. 
     This is particularly true in the field of “Oil &amp; Gas” (i.e. machines used in plants for exploration, production, storage, refinement and distribution of oil and/or gas). 
     For this purpose, swirlers are used in the fuel nozzles of gas turbines. 
     A double radial swirler is disclosed, for example, in US2010126176A1. 
     An axial swirler is disclosed, for example, in US2016010856A1. 
     A swirler wherein a radial flow of air and an axial flow of air are combined to form a single flow of air is disclosed, for example, in U.S. Pat. No. 4,754,600; there is a single recirculation zone that can be controlled. 
     BRIEF DESCRIPTION OF THE INVENTION 
     In order to achieve this goal, both a radial swirler and an axial swirler are integrated in a single fuel nozzle. 
     Recirculation in the combustion chamber, that is a stabilization mechanism, may depend on the load of the gas turbine, e.g. low load, intermediate load, high load. 
     Depending of the load of the gas turbine, recirculation in the combustion chamber may be provided only or mainly by the radial swirler, or only or mainly by the axial swirler, or by both swirlers. 
     Embodiments of the subject matter disclosed herein relate to fuel nozzles for gas turbines. 
     According to embodiments, a fuel nozzle comprises a radial swirler and an axial swirler; the radial swirler is arranged to swirl a first flow of a first oxidant-fuel mixture and the axial swirler is arranged to swirl a second flow of a second oxidant-fuel mixture. The first flow may be fed by a central conduit and the second flow may be fed by an annular conduit surrounding the central conduit. 
     Additional embodiments of the subject matter disclosed herein relate to gas turbines. 
     According to embodiments, a gas turbine comprises at least one fuel nozzle with a radial swirler and an axial swirler. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       The accompanying drawings, which are incorporated herein and constitute an integral part of the present specification, illustrate exemplary embodiments of the present invention and, together with the detailed description, explain these embodiments. In the drawings: 
         FIG.  1    shows a partial longitudinal cross-section view of a burner of a gas turbine wherein an embodiment of a fuel nozzle is located, 
         FIG.  2    shows a partial longitudinal cross-section view of the nozzle of  FIG.  1   , 
         FIG.  3    shows a front three-dimensional view of the nozzle of  FIG.  1   , 
         FIG.  4    shows a front three-dimensional view of the nozzle of  FIG.  1   , transversally cross-sectioned at the radial swirler, and 
         FIG.  5    shows two plots of Wg/Wa ratios of swirlers. 
     
    
    
     DETAILED DESCRIPTION 
     The following description of exemplary embodiments refers to the accompanying drawings. 
     The following description does not limit the invention. Instead, the scope of the invention is defined by the appended claims. 
     Reference throughout the specification to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with an embodiment is included in at least one embodiment of the subject matter disclosed. Thus, the appearance of the phrases “in one embodiment” or “in an embodiment” in various places throughout the specification is not necessarily referring to the same embodiment. Further, the particular features, structures or characteristics may be combined in any suitable manner in one or more embodiments. 
       FIG.  1    shows a partial longitudinal cross-section view of a burner  10  of a gas turbine  1  wherein an embodiment of a fuel nozzle  100  is located. 
     The burner  10  is annular-shaped, has a axis  11 , an internal (e.g. cylindrical) wall  12  and an external (e.g. cylindrical) wall  13 . A transversal wall  14  divides a feeding plenum  15  of the burner  10  from a combustion chamber  16  of the burner  10 ; the feeding plenum  15  is in fluid communication with a discharge chamber of a compressor of the gas turbine  1 . The burner  10  comprises a plurality of nozzles  100  arranged in a crown around the axis  11  of the burner  10 . The wall  14  has a plurality of (e.g. circular) holes wherein a corresponding plurality of (e.g. cylindrical) bodies of the nozzles  100  are fit. Furthermore, each nozzle  100  has a support arm  130 , in particular an L-shaped arm, for fixing the nozzle  100 , in particular for fixing it to the external wall  13 . 
     The nozzle  100  comprises a radial swirler, that is shown schematically in  FIG.  1    as element  111 , and an axial swirler, that is shown schematically in  FIG.  1    as element  121 B. As it will be described better with the help of  FIG.  2    and  FIG.  3    and  FIG.  4   , the axial swirler essentially consists of a set of vanes  121  and the radial swirler essentially consists of a set of channels  111 ; the vanes  121  develop substantially axially and the channels  111  develop substantially radially. It is to be noted that, in the embodiment of  FIG.  2    and  FIG.  3    and  FIG.  4   , each vane has a straight portion  121 A and a curved portion  121 B (downstream the straight portion  121 A); the curved portion  121 B provides radial swirl to a flowing gas (as explained in the following) and the straight portion  121 A houses a channel  111 , i.e. is hollow. 
     A body of the nozzle  100  develops in an axial direction, i.e. along an axis  101 , from an inlet side  103  of the nozzle to an outlet side  105  of the nozzle; the body may be, for example, cylindrical-shaped, cone-shaped, prism-shaped or pyramid-shaped. 
     The body of the nozzle  100  comprises a central conduit  110  developing in the axial direction  101  and an annular conduit  120  developing in the axial direction  101  around the central conduit  110 . The annular conduit  120  houses the vanes  121 . The channels  111  start on an outer surface of the body, pass through the straight portions  121 A of the vanes  121  and end in a chamber  112  being in a central region of the body; the chamber  112  is the start of the central conduit  110 . The channels  111  provide axial swirl to a flowing gas (as explained in the following). 
     Inside arm  130  there is at least a first pipe  131  for feeding a first fuel flow F 1  to the body of the nozzle  100 , in particular to its inlet side  103 , and a second pipe  132  for feeding a second fuel flow F 2  to the body of the nozzle  100 , in particular to its inlet side  103 ; there may be other pipes, in particular for other fuel flows. 
     A first flow A 1  of oxidant, in particular air, enters the central conduit  110  from the plenum  15  (in particular from the lateral side of the nozzle body through channels  111 ); a second flow A 2  of oxidant, in particular air, enters the annular conduit  120  from the plenum  15  (in particular from the inlet side  103  of the nozzle body). 
     The first fuel flow F 1  is injected axially into the central conduit  110  (this is not shown in  FIG.  1   , but only in  FIG.  2   ) and mixes with the first oxidant flow A 1 ; the second fuel flow F 2  is injected radially into the annular conduit  120  (this is not shown in  FIG.  1   , but only in  FIG.  2   ) and mixes with the second oxidant flow A 2 . 
     The channels  111  are tangential and are arranged to create radially swirling motion in the central conduit  110  around the axial direction  101 . The first fuel flow F 1  enters the chamber  112  tangentially and mixes with the first oxidant flow A 1  so a first flow A 1 +F 1  of a first oxidant-fuel mixture is created with radially swirling motion (in particular in the center of the nozzle body). The first oxidant flow A 1  and the first fuel flow F 1  are components of the first flow A 1 +F 1 . 
     The second oxidant flow A 2  enters the annular conduit  120  axially and mixes with the second oxidant flow A 2  so a second flow A 2 +F 2  of a second oxidant-fuel mixture is created with axially directed motion. The second oxidant flow A 2  and the second fuel flow F 2  are components of the second flow A 2 +F 2 . Feeding channels  122  are defined between airfoil portions of adjacent swirl vanes  121  and arranged to feed the second flow A 2 −F 2 . The second flow A 2 +F 2  flows in the channels  122  first between the straight portions  121 A of the vanes  121  and then between the curved portions  121 B so a flow with axially swirling motion is created (in particular close to the outlet side  105  of the nozzle body). 
     The central conduit  110  is arranged to feed the first flow A 1 +F 1  to the outlet side  105  of the nozzle body and the annular conduit  120  is arranged to feed the second flow A 2 +F 2  to the outlet side  105  of the nozzle body. 
     A first recirculation zone R 1  is associated to the radial swirler, and a second recirculation zone R 2  is associated to the axial swirler. In the embodiments of the figures, the second recirculation zone R 2  is at least partially downstream the first recirculation zone R 1 . 
     With reference to  FIG.  2   , the central conduit  110  starts with the chamber  112 , follows with a converging section  113  (converging with respect to the axial direction  101 ), and ends with a diverging section  115  (diverging with respect to the axial direction  101 ). In  FIG.  2   , the constricted section, after the section  113  and before section  115 , is extremely short. The converging section may correspond to an abrupt (as in  FIG.  2   ) or a gradual cross-section reduction. The diverging section corresponds typically to a gradual cross-section increase. 
     In the embodiment of  FIG.  2   , the end of the diverging section  115  of the central conduit  110  and the end of the annular conduit  120  are axially aligned at the outlet side  105  of the nozzle body. 
     In the embodiment of  FIG.  2   , the feeding channels  111  end in a region of the central conduit  110 , in particular in the chamber  112 , before the converging section  113  of the central conduit  110 . 
     As can be seen in  FIG.  2   , inside the nozzle body, there are annular pipes that feed the first input fuel flow F 1  to the central conduit  110  through a first plurality of little (lateral) holes, in particular to the chamber  112 , and the second input fuel flow F 2  to the annular conduit  120  through a second plurality of little (front) holes (see  FIG.  4   ). 
     The nozzle of  FIG.  2    and  FIG.  3    and  FIG.  4    comprises further a pilot injector  140  located in the center of the central conduit  110 , in particular partially in the chamber  112 . The pilot injector  140  receives a third fuel flow F 3  from a third pipe inside the support arm of the nozzle. The pilot injector  140  is cone-shaped at its end and an internal pipe feed the third fuel flow F 3  to its tip. A plurality of little holes at the tip (see  FIG.  4   ) eject the fuel into the central conduit  110 , in particular into the chamber  112 , in particular shortly upstream the converging section  113 . 
       FIG.  5    shows two plots: a first plot (continuous line labelled RAD) is a possible plot of a ratio between fuel gas mass flow rate Wg and oxidant gas (typically air) mass flow rate Wa in the radial swirler, and a second plot (dashed line labelled AX) is a possible plot of a ratio between fuel gas mass flow rate Wg and oxidant gas (typically air) mass flow rate Wa in the axial swirler. As it is known, the temperature of a flame is linked to the ratio between fuel gas mass flow rate and oxidant gas mass flow rate. 
     Both plots start from 0 at zero (or approximately zero) load of the gas turbine Lgt. 
     According to this embodiment, for example, both plots end approximately at the same point (the two points are not necessarily identical) at full (or approximately full) load of the gas turbine Lgt. In fact, it may be advantageous that the flame due to the radial swirler and the flame due to the axial swirler are approximately at the same temperature. 
     According to this embodiment, for example, the axial ratio is rather constant and approximately zero between 0% of load of the gas turbine and 30% of load of the gas turbine. 
     According to this embodiment, for example, the axial ratio is rather constant (to be precise, slowly decreasing) between 50% of load of the gas turbine and 100% of load of the gas turbine. 
     According to this embodiment, for example, the radial ratio gradually increases between 0% of load of the gas turbine and 30% of load of the gas turbine. 
     According to this embodiment, for example, the radial ratio gradually increases between 50% of load of the gas turbine and 100% of load of the gas turbine. 
     According to this embodiment, for example, the radial ratio drastically decreases between 30% of load of the gas turbine and 50% of load of the gas turbine. 
     According to this embodiment, for example, the axial ratio drastically increases between 30% of load of the gas turbine and 50% of load of the gas turbine. 
     The fuel gas mass flow rate in the radial swirler, in the axial swirler or in both swirlers may be controlled through a control system comprising for example a controlled valve or controlled movable diaphragm. 
     The oxidant gas mass flow rate in the radial swirler, in the axial swirler or in both swirlers may be controlled through a control system for example a controlled valve or controlled movable diaphragm. 
     This written description uses examples to disclose the invention, including the preferred embodiments, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.