Patent Publication Number: US-7707833-B1

Title: Combustor nozzle

Description:
CROSS REFERENCE TO RELATED APPLICATION 
   This application is a continuation of U.S. application Ser. No. 12/365,539, filed Feb. 4, 2009. 

   TECHNICAL FIELD 
   The present invention relates to combustors that may be used in combustion turbines. More specifically, the present invention relates to a nozzle system for injecting fuel into a combustor. 
   BACKGROUND 
   Gas turbines play a predominant role in a number of applications, namely in aircraft propulsion, marine, propulsion, power generation and driving processes, such as pumps and compressors. Typically, a gas turbine includes a compressor, a combustor and a turbine. In operation, air is fed into the system where it is compressed by a compressor and a portion of the air further mixed with fuel. The compressed air and fuel mixture are then burned to cause an expansion, which is responsible for driving the turbine. 
   In an effort to reduce emissions, combustors have been designed to premix fuel and air prior to ignition. Premixed fuel and air burn at a lower temperature than the stoichiometric combustion, which occurs during traditional diffusion combustion. As a result, premixed combustion results in lower NOx emissions. 
   A typical combustor includes a plurality of primary fuel nozzles that surround a central secondary nozzle. Traditional secondary nozzles may include passageways for diffusion fuel and premix fuel all within the same elongated tubular structure. This type of nozzle often includes a complex structure of passageways contained within a single tubular shell. The passageways for creating the diffusion flame extend through the length of the nozzle. Premix fuel is dispensed upstream of the diffusion tip in order to allow fuel to mix with compressed air flowing through the combustor prior to reaching the flame zone, which is located downstream of the nozzle. As a result, passageways for premix fuel are typically shorter than passageways for diffusion fuel. 
   Additionally, premix fuel may be mixed with air upstream of the diffusion tip and, more importantly, radially outward of the secondary nozzle structure. In this type of secondary nozzle, premix fuel is carried along only a portion of the nozzle length until it is passed radially outward from the nozzle body to a premix injector tip. At the injector tip, the premix fuel is dispensed into the air flow path. As the fuel and air continue to travel downstream along the remainder of the secondary nozzle length, they become mixed, allowing for more efficient combustion within the flame zone, downstream of the nozzle tip. 
   While compressed air is hot, fuel is typically cool in comparison. The temperature differentials flowing through the different passageways in the secondary nozzle may result in different levels of thermal expansion of the materials used to construct the nozzle. It is contemplated that it would be beneficial to simplify the secondary nozzles to reduce the high stresses on the nozzle structures resulting from their internal complexity, extreme operating conditions and thermal expansion differentials. 
   SUMMARY OF THE INVENTION 
   Provided is a secondary nozzle for inclusion within a combustor for a combustion turbine. The secondary nozzle comprises a flange and an elongated nozzle body extending from the flange. At least one premix fuel injector is spaced radially from the nozzle body and extends axially from the flange, generally parallel to the nozzle body. 
   The secondary nozzle comprises a fuel source, a flange and a first nozzle tube extending axially from the flange. At least one second nozzle tube is spaced radially outward from the first nozzle tube and has a proximal end fixed to the flange. The second nozzle tube is fluidly connected to the fuel source. The second nozzle tube has a distal end, axially spaced from the proximal end of the second nozzle and having at least one aperture therein. A passageway extends between the proximal end of the second nozzle tube and the distal end of the second nozzle tube, said passageway fluidly connects the fuel source and the at least one aperture. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a cross sectional view of an exemplary combustor for a combustion turbine having a plurality of primary nozzles and a secondary nozzle therein. 
       FIG. 2  is a perspective view of exemplary primary nozzles and a secondary nozzle. 
       FIG. 3  is a front elevational view of a plurality of primary nozzles and a secondary nozzle as shown in  FIGS. 1 and 2 . 
       FIG. 4  is a perspective view of a secondary nozzle as shown in  FIGS. 1-3 . 
       FIG. 5  is a partial perspective view of the secondary nozzle of  FIGS. 1-4 . 
       FIG. 6  is a cross sectional view of the secondary nozzle of  FIGS. 1-5 . 
       FIG. 7  is a schematic view of a portion of the secondary nozzle of  FIGS. 1-6 . 
       FIG. 8  is a schematic view of the primary operation of an exemplary combustor. 
       FIG. 9  is a schematic view of the lean-lean operation of an exemplary combustor. 
       FIG. 10  is a schematic view of the second-stage burning operation of an exemplary combustor. 
       FIG. 11  is a schematic view of the premix operation of an exemplary combustor. 
   

   DETAILED DESCRIPTION 
   Described herein is an exemplary combustor for use in a combustion turbine. The combustor of the type illustrated is one of a plurality of combustors, typically positioned after the compressor stage within the combustion turbine. 
   Referring now to the figures and initially to  FIG. 1 , the combustor is designated by the numeral  10  and as illustrated is a dual stage, dual mode combustor having a combustor flow sleeve  12 , a rear wall assembly  14  and a combustor wall  13 . Radially inward of the combustor wall  13  are provided a plurality of primary fuel nozzles  16  and a secondary fuel nozzle  18 . The nozzles  16 ,  18  serve to inject fuel into the combustor  10 . 
   Inlet air for combustion (as well as cooling) is pressurized by the turbine compressor (not shown) and then directed into the combustor  10  via the combustor flow sleeve  12  and a transition duct (not shown). Air flow into the combustor  10  is used for both combustion and to cool the combustor  10 . The air flows in the direction “A” between the combustor flow sleeve  12  and the combustor wall  13 . Generally, the airflow illustrated is referred to as reverse flow because the direction “A” is in an upstream direction to the normal flow of air through the turbine and the combustion chambers. 
   The combustor  10  includes a primary combustion chamber  42  and a secondary combustion chamber  44 , located downstream of the primary combustion chamber  42 . A venturi throat region  46  is located between the primary and secondary combustion chambers  42 ,  44 . As shown in  FIGS. 2 and 3 , the primary nozzles  16  are arranged in an annular ring around the secondary nozzle  18 . In  FIG. 1 , a centerbody  38  is defined by a liner  40  in the center of the combustor  10 . 
   Referring now to  FIGS. 1-3 , each of the primary nozzles  16  are mounted on a rear wall assembly  14 . The primary nozzles  16  protrude from the rear wall  14  and provide fuel to the primary combustion chamber  42 . Fuel is delivered to the primary nozzles  16  via a primary fuel source  20 . Spark or flame for combustion ignition in the primary combustion chamber  42  is typically provided by spark plugs or cross fire tubes (not shown). 
   Air swirlers may be provided in connection with the primary nozzles  16  to facilitate mixing of combustion air with fuel to provide an ignitable mixture of fuel and air. As mentioned above, combustion air is derived from the compressor and routed in the direction “A,” between the combustor flow sleeve  12  and the combustor wall  13 . Upon reaching the rear wall assembly  14 , the pressurized air flows radially inward between the combustor wall  13  and the rear wall  14  into the primary combustion chamber  42 . Additionally, the combustor wall  13  may be provided with slots or louvers (not shown) in both the primary and secondary combustion chambers  42 ,  44  for cooling purposes. The slots or louvers may also provide dilution air into the combustor  10  to moderate flame temperature within the primary or secondary combustion chambers  42 ,  44 . 
   Referring now to  FIGS. 1-4 , the secondary nozzle  18  extends from a flange  22  into the combustor  10  through the rear wall  14 . The secondary nozzle  18  extends to a point upstream of the venturi throat region  46  to introduce fuel into the secondary combustion chamber  44 . The flange  22  may be provided with means for mounting (not shown) the secondary nozzle  18  on the rear wall  14  of the combustor  10 . The mounting means may be a mechanical linkage, such as bolts, which serve to fix the flange  22  to the rear wall  14  and which facilitate the removal of the nozzle  18 , such as for repairs or replacement. Other means for attachment are also contemplated. 
   Fuel for the primary nozzles  16  is supplied by a primary fuel source  20  and is directed through the rear wall  14 . Secondary transfer and premix fuel sources  24 ,  25  are provided through the flange  22  to the secondary nozzle  18 . Although not shown here, the secondary nozzle  18  may also have a diffusion circuit or pilot circuit for injecting fuel into the combustor  10 . 
   The secondary nozzle  18  comprises a nozzle body  30  and at least one premix fuel injector  32 . The secondary nozzle  18  is located within the centerbody  38  and is surrounded by the liner  40 , as shown in  FIG. 1 . The premix fuel injectors  32  are arranged on the flange  22  in a generally annular configuration, around the nozzle body  30 , as best seen in  FIG. 3 . Each of the premix fuel injectors  32  has a generally oblong or elongated cross-sectional shape when viewed from the top. As best seen in  FIG. 3 , a first side or end  34  of the injectors  32  is disposed proximate the nozzle body  30 . A second side or end  36  of the injectors  32  is disposed radially outward of the first end  34 . 
   The premix fuel injectors  32  are shown aligned directly between the primary nozzles  16  and the nozzle body  30  to facilitate airflow through the centerbody  38  and around the nozzle body  30 . In such an arrangement, the second ends  36  of the premix fuel injectors  32  are disposed proximate the primary nozzles  16 . Air flow “A” into the combustor  10  travels radially inward from outside of the combustor wall  13 . A portion of this air travels downstream, into and through the primary combustion chamber  42 . Another portion of the air, by way of example 5 to 20% of the total air flow through the combustor, travels radially inward past the primary nozzles  16  and the primary combustion chamber  42  into the centerbody  38  before travelling downstream through the centerbody. The direction of this second portion of airflow along the flange  22  and rear wall  14  is denoted by the letter “B” in  FIG. 3 . While other configurations may be used, aligning the premix fuel injectors  32  radially inward of the primary nozzles  16 , between the primary nozzles  16  and the secondary nozzle  18 , allows for maximum airflow into the centerbody  38 . Likewise, while premix fuel injectors  32  shown have an elongated cross section, other shapes may also be used, such as round, rectangular, triangular, etc. 
   Referring now to  FIGS. 5-7  and with continued reference to  FIGS. 1-4 , the secondary nozzle  18  is shown including a nozzle body  30  and premix fuel injectors  32 . As described above, the secondary nozzle  18  is located in the centerbody  38  and surrounded by the liner  40  ( FIG. 1 ). The nozzle body  30  extends along the longitudinal axis of the centerbody  38 . The nozzle body  30  has a generally elongated cylindrical outer sleeve portion  52  which defines a cavity  31  therein. As shown, transfer fuel passages  64  are located within the outer portion of cavity  31 . The transfer fuel passages  64  extend distally from the flange  22  and are arranged at spaced locations in an annular configuration. Transferless variants are known and may also be utilized. 
   The transfer fuel passages  64  are fluidly connected to the transfer manifold  51 , which is fed by the transfer fuel source  24 . The transfer fuel passages  64  include a longitudinal tube  66  and at least one radial passageway  68 . The passageway  68  is directed radially outward from the tube  66  and is aligned with an aperture  71  in the wall of the nozzle body  30 . The passageway  68  jets the fuel through the opening  71  to the outside of the sleeve  52  to mix with the air flowing along the wall  52 . A second opening  70  is shown upstream of opening  71  and provides an inlet for air into the portion of the cavity  31  surrounding the central tube positioned within the nozzle body  30 . A portion of the air moving past the opening  70  is directed into the cavity  31  to cool the nozzle body  30 . The air in the cavity  31  is exhausted from the openings  58  on the end  54  of the nozzle. The central tube feeds fuel to the nozzle end  54  for supporting a flame in the secondary combustion chamber  44 . (See  FIG. 1  and  FIGS. 9-11 .) The openings  70  are separated from the fuel provided by passageway  68  and the additional fuel provided by injectors  32 . It is noted that additional openings may be provided to mix the flow of fuel outside the nozzle body  30  or to direct the flow of air into the nozzle cavity  31 . Also, the fuel passages  64  may be eliminated if desired. 
   The outer sleeve portion  52  of the nozzle body  30  extends from the flange  22  to a distal tip  54 . The tip  54  of the nozzle body  30  has at least one aperture  58  for allowing the passage of pressurized air from inside of the passageway  31  that surrounds the central tube portion. 
   As mentioned above, fuel is supplied to the secondary nozzle  18  through the transfer fuel source  24  and the premix fuel source  25 . As seen best in  FIG. 6 , the transfer fuel source  24  extends into the flange  22 , providing fuel to the transfer manifold  51 , which is fluidly connected to the transfer fuel passages  64 . The premix fuel source  25  extends into the flange  22  and is in fluid communication with premix manifold chamber  50 , which is fluidly connected to the premix fuel injectors  32 . 
   The premix fuel injectors  32  extend distally from the flange  22  having a length that is less than that of the nozzle body  30 . A distal end  60  of the premix fuel injectors  32  includes premix apertures  62  for dispensing fuel into the area of the centerbody  38  outside of the nozzle body  30 . The premix fuel is mixed with air flowing within the liner  40 . When the mixture reaches the secondary combustion chamber  44 , the mixture is optimized for efficient combustion in the secondary combustion chamber  44  (see  FIG. 1 ). 
   Unlike typical secondary nozzles, where diffusion and premix fuel is discharged through a single structure extending from a flange, use of a stand alone premix fuel injector  32  allows for a simplification of the nozzle body  30 . The injectors  32  shown allow for less internal passageways inside the nozzle body  30  than the typical nozzles. This simplification reduces the stress on the secondary nozzle  18  that may arise from heat differentials within the nozzle structures  18 ,  32  due to the variation in temperature of the fuel and the pressurized air. Additionally, the contemplated design is easier to maintain and allows for a degree of modularity not possible with traditional secondary nozzles. 
   In addition to the structures shown, the premix fuel injectors  32  may have a dispensing ring fluidly connected to one or more sets of the premix apertures  62 . Other dispenser tip structures may also be used with the premix fuel injectors  32  of the type particularly shown. 
   Referring now to  FIG. 8 , in a typical “primary” operation, flame  72  is first established in primary combustion chamber  42 , upstream of secondary combustion chamber  44 . The fuel for this initial flame, is provided solely through the primary nozzles  16 . In  FIG. 9 , a flame  72  is established in the secondary combustion chamber  44 , while flame  72  also remains in the primary combustion chamber  42 . To establish flame  72  in the secondary combustion chamber  44 , a portion of the fuel is injected, through the secondary nozzle  18 , while a majority of the fuel is sent through the primary nozzles  16 . By way of example, 30% of the total fuel discharge is injected through the secondary nozzle while 70% of the fuel is sent through the primary nozzles  16 . This flame pattern is indicative of a “lean-lean” type operation. 
   In  FIG. 10 , the entire fuel flow is directed through the nozzle body  30  of the secondary nozzle  18 , establishing a stable flame within the secondary combustion chamber  44 . The flame is extinguished in primary combustion chamber  42  by cutting off fuel flow to the primary nozzles  16 . During this “second-stage” burning operation, the fuel that was previously injected through the primary nozzles  16  is diverted to the secondary nozzle  18  through the transfer fuel passages  64 . The transfer and premix fuel is injected upstream of the flame  72 . The fuel and air flow through the secondary nozzle  18  is considered to be relatively “rich” at this stage because 100% of the fuel flows through the secondary nozzle  18  with only a portion of the air intended for combustion. 
   Referring now to  FIG. 11 , once a stable flame is established in the secondary combustion chamber  44  and the flame is extinguished in the primary combustion chamber  42 , fuel flow may be restored to the primary nozzles  16  and the fuel flow to the secondary nozzle  18  is reduced. Because the flame has been extinguished from the primary combustion chamber  42 , the primary nozzles  16  act as a premixer. During this “premix” operation mode, the flame is maintained in the secondary combustion chamber  44  as a result of the venturi throat region  46 . By way of example, 83% of the total fuel discharge may be sent through the primary nozzles  16 , while the remaining 17% of fuel is injected through the secondary nozzle  18 . Other relative percentages are also possible. 
   A variety of modifications to the embodiments described will be apparent to those skilled in the art from the disclosure provided herein. Thus, the invention may be embodied in other specific forms without departing from the spirit or essential attributes thereof and, accordingly, reference should be made to the appended claims, rather than to the foregoing specification, as indicating the scope of the invention.