Patent Publication Number: US-2018045414-A1

Title: Swirler, burner and combustor for a gas turbine engine

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is the US National Stage of International Application No. PCT/EP2016/055802 filed Mar. 17, 2016, and claims the benefit thereof. The International Application claims the benefit of European Application No. EP15162154 filed Apr. 1, 2015. All of the applications are incorporated by reference herein in their entirety. 
    
    
     FIELD OF INVENTION 
     The invention relates to a swirler for use in a combustor of a gas turbine engine, comprising a plurality of generally radially inwardly extending passages arranged circumferentially staggered in a circle, each passage having a radially outer inlet end, a radially inner outlet end, first and second generally radially inwardly extending lateral surfaces, and a base surface and top surface, in use of the swirler fuel and air travelling along the passages from their inlet ends to their outlet ends so as to create adjacent to the outlet ends a swirling fuel/air mixture, wherein at least one surface comprises at least one gas fuel injection hole. 
     Moreover, the invention relates to a burner for a gas turbine engine. 
     Furthermore, the invention relates to a combustor for a gas turbine engine. 
     BACKGROUND OF INVENTION 
     A gas turbine engine comprises an ambient air supply duct, a compressor, a combustor, an expander, i.e. a turbine, and an exhaust gas duct. 
     It is desired to reduce the polluting emissions, in particular nitrogen oxide (NO x ), carbon monoxide (CO), unburned hydro carbons (UHC), smoke and particle emissions, of gas turbine engines. 
     One way to reduce polluting emissions is to provide a burner in a combustor of a gas turbine engine with a swirler. The swirler is arranged in a passage through which compressed air is supplied to a combustion chamber of the combustor via the burner. The swirler is connected to a gas fuel supply device. The swirler gives the supplied air a tangential direction rotating the flow i.e. providing a swirling air flow to the combustion chamber. Simultaneously, gas fuel is introduced in the air through internal gas fuel passages arranged in the swirler. The swirling air/gas fuel mixture is supplied to the combustion chamber of the combustor. The swirling of the air/gas fuel mixture leads to a highly homogeneous air/gas fuel mixture in form of a lean gas fuel mixture. Such lean gas fuel mixtures burn at a lower combustion temperatures than rich gas fuel mixtures. Reduced combustion temperatures particularly lead to reduced nitrogen oxide emissions. 
     EP 1 867 925 A1 discloses a burner, in particular a gas turbine burner, comprises at least one swirler. The swirler having at least one air inlet opening, at least one air outlet opening positioned downstream to the air inlet opening and at least one swirler air passage) extending from the at least one air inlet opening to the at least one air outlet opening which is delimited by swirler air passage walls. The air passage walls comprising downstream wall sections adjoining the at least one air outlet opening; and a fuel injection system which comprises fuel injection openings arranged in at least one swirler air passage wall so as to inject fuel into the swirler air passage; in which at least the downstream section of one air passage wall is corrugated. 
     US2010/011770 A1 discloses a premixer for a gas turbine combustor includes an axial swirler including a plurality of turning vanes that impart swirl velocity to an axial airflow through the premixer and at least one fuel injection site enabling fuel to mix with the airflow in the premixer. The fuel injection site terminates in a cratered hole. The cratered hole increases mixing efficiency and increases flashback/flameholding resistance. 
     US2012/0111015A1 discloses a combustor having a radial swirler type burner wherein an air/fuel mixture is forced into a vortex by the swirler before being burned in the main combustor chamber. The radial swirler comprises an annular array of vanes that form air passages therebetween. The air passages are arranged generally radially inwardly to create a vortex. Fuel is mixed with the air in the passages. 
     SUMMARY OF INVENTION 
     It is an object of the invention to further reduce polluting emissions, in particular nitrogen oxide emissions, associated with the operation of gas turbine engines. 
     This object is solved by the independent claims. Advantageous embodiments are disclosed in the dependent claims which either by taken alone or in any combination with each other may relate to an aspect of the invention. 
     The swirler according to the invention for use in a combustor of a gas turbine engine comprises a plurality of generally radially inwardly extending passages arranged circumferentially staggered in a circle, each passage having a radially outer inlet end, a radially inner outlet end, first and second generally radially inwardly extending lateral surfaces, and a base surface and top surface, in use of the swirler fuel and air travelling along the passages from their inlet ends to their outlet ends so as to create adjacent to the outlet ends a swirling fuel/air mixture, wherein at least one surface of at least one passage comprises at least one gas fuel injection hole, wherein the surface, having the gas fuel injection hole, comprises at least one counterbore radially surrounding the gas fuel injection hole, and wherein the gas fuel injection hole is arranged at a base of the counterbore. 
     According to the invention the gas fuel injection hole is not arranged, as conventionally known, directly at the surface of the passage, but in the counterbore of the surface which defines a cavity in the surface. Through this, a low velocity region is created in the cavity, i.e. the counterbore, to reduce the momentum of a gas fuel jet exiting the gas fuel injection hole. Thereby, the incoming cross flow of air inside the cavity will mix with local recirculation in the cavity to enhance mixing of air and gas fuel. This enhanced or tailored mixing is attended by lower polluting emissions. Additionally, the enhanced or tailored mixing results in a reduction of the number of hot spots to further reduce pollution emissions. 
     Particularly, the cross flow velocity of compressed air streaming along the surface of the passage comprising the counterbore reduces the momentum of the gas fuel stream exiting the gas fuel injection hole by recirculation of air with low pressure inside the counterbore. Through this, the aerodynamics for mixing gas fuel and air are improved. 
     In contrast, known swirlers comprise passages with gas fuel injection holes directly arranged for example at a lateral surface which is defined by a lateral surface plane of a vane of the swirler without providing an inventive counterbore. This leads to less efficient and/or controlled mixing of gas fuel and air because the gas fuel streams coming from the gas fuel injection holes travel toward an expansion region of the combustion chamber of the combustor without being effectively influenced by mixing. 
     The inventive swirler can have one or more passages designed according to the invention. Especially, all passages of the swirler can be designed accordingly. The cross section of at least one passage can be rectangular, squared, circular, elliptical or the like. 
     The surface of the at least one swirler passage according to the invention can have two or more gas fuel injection holes. Each gas fuel injection hole communicates with at least one internal gas supply passage of the swirler. At least one surface can be flat-shaped, leaning, facet-shaped, curved-shaped or the like. 
     The counterbore can be optimized with respect to its mixing characteristics. For example the dimensions of the counterbore, such as its depth, diameter or the like, can be adapted to a specific use of the swirler in order to optimize the mixing characteristics of the swirler. 
     Advantageously, the counterbore is rectangular-shaped, oval-shaped, elliptical-shaped or circular-shaped. Other shapes of the counterbore are also possible to improve the mixing characteristics of the counterbore. 
     Advantageously, at least one surface comprises at least two gas fuel injection holes and at least one counterbore, the counterbore radially surrounding both gas fuel injection holes, wherein the gas fuel injection holes are arranged at a base of the counterbore. According to this, all gas fuel injection holes of a surface can be arranged in a common single counterbore of that surface. 
     Advantageously, wherein at least one surface comprises at least two gas fuel injection holes and at least two counterbores, wherein each gas fuel injection hole is radially surrounded by its own counterbore and is arranged at a base of this counterbore. According to this embodiment, more than one counterbore is arranged on one single surface of the swirler passage, each counterbore surrounding at least one gas fuel injection hole. 
     Advantageously, the surface, having the at least one gas fuel injection hole and the at least one counterbore, is a lateral surface. The lateral surface can be defined by a lateral surface of a vane of the swirler. 
     Advantageously, the surface, having the at least one gas fuel injection hole and the at least one counterbore, is the base surface. 
     The burner according to the invention for a gas turbine engine comprises at least one swirler according to any one of the preceding embodiments or any combination thereof. The above mentioned advantages connected with the swirler are correspondingly connected with the inventive burner. 
     The combustor according to the invention for a gas turbine engine comprises at least one burner according to the invention. The above mentioned advantages connected with the swirler are correspondingly connected with the inventive combustor. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above mentioned attributes and other features and advantages of this invention and the manner of attaining them will become more apparent and the invention itself will be better understood by reference to the following description of embodiments of the invention taken in conjunction with the accompanying drawings, wherein 
         FIG. 1  shows part of a turbine engine in a sectional view, 
         FIG. 2  shows a longitudinal section through a combustor of the turbine engine, 
         FIG. 3  shows a perspective view of an inventive swirler of the combustor, 
         FIG. 4  shows a perspective transparent drawing of a detail of an embodiment of the inventive swirler, 
         FIG. 5  shows a sectional view of the swirler shown in  FIG. 4 , 
         FIG. 6  shows a perspective transparent drawing of a detail of a further embodiment of the inventive swirler, 
         FIG. 7  shows a perspective transparent drawing of a detail of a further embodiment of the inventive swirler, and 
         FIG. 8  shows a perspective transparent drawing of a detail of a further embodiment of the inventive swirler. 
     
    
    
     DETAILED DESCRIPTION OF INVENTION 
       FIG. 1  is a schematic illustration of a general arrangement of a gas turbine engine  10  having an inlet  12 , a compressor  14 , a combustor system  16 , a turbine system  18 , an exhaust duct  20  and a twin-shaft arrangement  22 ,  24 . The gas turbine engine  10  is generally arranged about an axis  26  which for rotating components is their rotational axis. The arrangements  22 ,  24  may have the same or opposite directions of rotation. 
     The combustion system  16  comprises an annular array of combustor units, i.e. burner  36 , only one of which is shown. In one example, there are six burners  36  evenly spaced about the engine  10 . 
     The turbine system  18  includes a high-pressure turbine  28  drivingly connected to the compressor  14  by a first shaft  22  of the twin-shaft arrangement  22 ,  24 . The turbine system  18  also includes a low-pressure turbine  30  drivingly connected to a load (not shown) via a second shaft  24  of the twin-shaft arrangement. 
     The term axial is with respect to the axis  26 . The terms upstream and downstream are with respect to the general direction of gas flow through the engine  10  and as seen in  FIG. 1  is generally from left to right. 
     The compressor  14  comprises an axial series of stator vanes and rotor blades mounted in a conventional manner. The stator or compressor vanes may be fixed or have variable geometry to improve the airflow onto the downstream rotor or compressor blades. 
     Each turbine  28 ,  30  comprises an axial series of stator vanes and rotor blades mounted via rotor discs arranged and operating in a conventional manner. A rotor assembly comprises an annular array of rotor blades or blades and the rotor disc. 
     In operation air  32  is drawn into the engine  10  through the inlet  12  and into the compressor  14  where the successive stages of vanes and blades compress the air before delivering the compressed air into the combustion system  16 . In a combustion chamber of the combustion system  16  the mixture of compressed air and fuel is ignited. The resultant hot working gas flow is directed into, expands and drives the high-pressure turbine  28  which in turn drives the compressor  14  via the first shaft  22 . After passing through the high-pressure turbine  28 , the hot working gas flow is directed into the low-pressure turbine  30  which drives the load via the second shaft  24 . 
     The low-pressure turbine  30  can also be referred to as a power turbine and the second shaft  24  can also be referred to as a power shaft. The load is typically an electrical machine for generating electricity or a mechanical machine such as a pump or a process compressor. Other known loads may be driven via the low-pressure turbine  30 . The fuel may be in gaseous and/or liquid form. 
     The turbine engine  10  shown and described with reference to  FIG. 1  is just one example of a number of engines or turbomachinery in which this invention can be incorporated. Such engines can be gas turbines or steam turbine and include single, double and triple shaft engines applied in marine, industrial and aerospace sectors. 
       FIG. 2  shows a longitudinal section through a combustor  100  of the gas turbine engine. The combustor  100  comprises in flow direction series a burner  131  with swirler portion  102  and a burner-head portion  101  attached to the swirler portion  102 , a transition piece or combustion pre-chamber  103  and a main combustion chamber  104 . The main combustion chamber  104  has a diameter larger than the diameter of the pre-chamber  103 . The main combustion chamber  104  is connected to the pre-chamber  103  via a dome portion  110  comprising a dome plate  111  and which is divergent in the direction from the pre-chamber  103  to the main combustion chamber  104 . In general, the pre-chamber  103  may be implemented as a one part continuation of the burner  101  towards the combustion chamber  104 , as a one part continuation of the combustion chamber  104  towards the burner  101 , or as a separate part between the burner  101  and the combustion chamber  104 . The burner and the combustion chamber assembly generally symmetrical about a longitudinal axis S. 
     A fuel conduit  105  is provided for leading a gaseous or liquid fuel to the burner which is to be mixed with in-streaming air in the swirler  102 . The fuel/air mixture  107  is then led towards the primary combustion zone  109  where it is burnt to form hot, pressurised exhaust gases streaming in a direction  108  indicated by arrows to a turbine of the gas turbine engine. 
     An exemplary swirler  102  according to the present invention is shown in detail in  FIG. 3 . The swirler  102  comprises an annular array of swirler vanes  112  and in this example there are twelve swirler vanes  112  arranged on a swirler vane support  113  or plate. 
     Between neighbouring swirler vanes  112  air passages  114  are formed. The air passages  114  extend between an air inlet opening  116  and an air outlet opening  118 . The air passages  114  are defined by opposing side faces  120 ,  122  of the neighbouring swirler vanes  112 , by the surface  124  of the swirler vane plate  113 . The side faces  120 ,  122 , the surfaces of the swirler vane plate  113  and form the air passage walls defining the air passages  114 . A further plate or part of the combustor is situated on the opposite end surface of the swirler vanes to the support plate and therefore completes the definition of the air passages  114 . 
     The side faces  120 ,  122  are corrugated in their downstream sections so as to form mixing lobes  123  on the swirler vanes  112 . The corrugations of opposing side faces  120 ,  122  are complementary so as to lead to additional turbulence in the streaming fuel/air mixture and to a controlled fuel placement at the exit of the air passage. In other examples, the downstream or trailing edge of the swirler vanes  112  can be straight. 
     Fuel injection openings  126   a ,  126   b  are arranged in the side faces  120 . Further, fuel injection openings  128  are arranged in the swirler support  113 . The fuel injection openings  126   a ,  126   b ,  128  are pilot and main fuel injectors as known in the art. During operation of the burner, air flows into the air passages  114  through the air inlet openings  116 . Within the air passages  114  fuel is injected into the streaming air by use of fuel injection openings  126   a ,  126   b ,  128 . The fuel/air mixture then leaves the air passages  114  through the air outlet openings  118  and streams through a central opening  130  of the swirler vane array and into the pre-chamber  103 . From the pre-chamber  103  it streams into the combustion zone  109  of the main chamber  104  where it is burned. As shown in  FIG. 4 , there are arranged two first fuel injection openings in the side faces  120  of the swirler vanes  112  so to define bottom and top first fuel injection openings  126   a . Alternative locations of the fuel injection openings are shown as  126   b.    
       FIG. 4  shows a perspective transparent drawing of a detail of an embodiment of the inventive swirler  1  for use in a combustor of a gas turbine engine. 
     The swirler  102  comprises a plurality of generally radially inwardly extending passages  114  arranged circumferentially staggered in a circle, wherein only one passage  114  is shown in  FIG. 4 . The radially inwardly extending air passages  114  could also be said to be arranged tangential to a radius from the axis S of the swirler. The swirler is known as a radial swirler and its air passages  114  are arranged so that a component of their direction is in the radial direction. Each passage  114  having a radially outer inlet end  116  and a radially inner outlet end  118 , which are shown in  FIG. 3 . Each passage  114  is defined by surfaces  3 , wherein only one surface  3  is shown in  FIG. 4 . This surface  3  may be a lateral or side surface  120 ,  122 , a base surface  124  or a top surface. In use of the swirler  1  fuel and air travelling along the passages  114  from their inlet ends to their outlet ends so as to create adjacent to the outlet ends a swirling fuel/air mixture. 
     The surface  3  comprises two gas fuel injection holes  5  communicating with an internal gas fuel supply passage  4  of the swirler  102 . Additionally, the surface  3  comprises a rectangular-shaped, in particular box-shaped, counterbore  6  radially surrounding the gas fuel injection holes  5 . The gas fuel injection holes  5  are arranged at a base  38  of the counterbore  6 . Therefore, the common counterbore  6  radially surrounds both gas fuel injection holes  5 . The flow of gas fuel through the gas fuel supply passage  4  is indicated by the arrow  7 . 
       FIG. 5  shows a section view of the swirler  102  shown in  FIG. 3 . The air streaming along the surface  3  is indicated by the arrow  8 . The spirally-shaped lines  9  indicate how air circulates in said counterbore  6 , thereby reducing the momentum of a gas fuel jet exiting the gas fuel injection holes  5 . The incoming cross flow of air inside the counterbore  6  will mix with these local recirculation in the counterbore  6 , thereby enhancing the mixing of air and gas fuel. 
     The embodiment of the counterbore  6  shown in  FIGS. 4 and 5  is generally rectangular and has a depth D below the surface  3 , a width W normal to the direction of the air flow  8  and a length L generally in line with the direction of the air flow  8 . The gas fuel injection holes  5  have a diameter d. In this embodiment, advantageous relative parameters to the diameter d are length L at least 4d; width W at least 3d and depth D at least 2d. These minimum relative dimensions are known to provide the advantages mentioned below. 
       FIG. 6  shows a perspective transparent drawing of a detail of a further embodiment of the inventive swirler  102 . This embodiment differs from the embodiment shown in  FIG. 4  only in that the counterbore  6  is oval-shaped. 
     The embodiment of the counterbore  6  shown in  FIG. 6  is generally oval-shaped with its longer dimension a generally in line with the direction of the air flow  8 . The shorter dimension b is general normal to the direction of the air flow  8  and the longer dimension a. The counterbore  6  has a depth D below the surface  3 . The gas fuel injection holes  5  have a diameter d. In this embodiment, advantageous relative parameters to the diameter d are longer dimension a is at least 4d; shorter dimension W is at least 3d and depth D is at least 2d. These minimum relative dimensions are known to provide the advantages mentioned below. 
       FIG. 7  shows a perspective transparent drawing of a detail of a further embodiment of the inventive swirler  102 . This embodiment differs from the embodiment shown in  FIG. 4  only in that the counterbore  6  is circular-shaped. 
     The circular-shaped embodiment of the counterbore  6  shown in  FIG. 7  has a depth D below the surface  3  and a diameter L. The gas fuel injection holes  5  have a diameter d. In this embodiment, advantageous relative parameters to the diameter d are diameter L is at least 4d and the depth D is at least 2d. These minimum relative dimensions are known to provide the advantages mentioned below. 
       FIG. 8  shows a perspective transparent drawing of a detail of a further embodiment of the inventive swirler  102 . This embodiment differs from the embodiments shown in  FIG. 4  to  FIG. 7  in that the surface  3  comprises two gas fuel injection holes  5  and two counterbores  6 , wherein each gas fuel injection hole  5  is radially surrounded by its own counterbore  6  and is arranged at a base  38  of this counterbore  6 . 
     Each of the two counterbores  6  can be any one of the circular, rectangular or oval shaped counterbores  6  described above. However, in this embodiment, advantageous relative parameters to the diameter d are diameter L (or longer dimension L) is at least 2d and the depth D is at least 2d. In addition, the spacing X between the counterbores  6  is at least 2d. 
     In the described embodiments, the gas fuel injection holes  5  are arranged in a row with respect to the flow direction, indicated by the arrow  8 , of air streaming along the surface  3 . Alternatively, the gas fuel injection holes  5  may be arranged in a crosswise direction with respect to said flow direction. 
     The advantages of the embodiments of the counterbores and their location on the side surfaces of the swirler vanes  112  include reducing local hot spots, reduced NOx emissions by improved mixing of fuel and air and improved fuel placement. The mixing of fuel and air that flows across the side surface improves because of the local lowering of fuel momentum in the counterbore. Thus the local fuel-air ratio provided by the counterbores is closer to the local stoichiometric mixture fraction than other fuel injection means. 
     Although the invention has been explained and described in detail in connection with the preferred embodiments it is noted that the invention is not limited to the disclosed embodiments. A person skilled in the art can derive from these embodiments other variations without leaving the scope of protection of the invention.