Abstract:
The invention refers to burner arrangement for producing hot gases to be expanded in a gas turbine, including a burner inside a plenum, where the burner has means for fuel injection, means for air supply and means for generating an ignitable fuel/air mixture inside the burner, and a combustion chamber following downstream said burner having an outlet being fluidly connected to the gas turbine. The invention is characterized in that the means for air supply includes at least two separate flow passages, and that the one of the two flow passages is fed by a first supply pressure and the other flow passage is fed by a second supply pressure.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority to European Application 12175614.2 filed Jul. 10, 2012, the contents of which are incorporated herein in its entirety. 
       TECHNICAL FIELD 
       [0002]    The present invention relates to the field of stationary gas turbines, especially to a burner arrangement for producing hot gases to be expanded in a turbine, comprising a burner inside a plenum, said burner has means for fuel injection, means for air supply and means for generating an ignitable fuel/air mixture inside the burner, and a combustion chamber following downstream said burner having an outlet being fluidly connected to the gas turbine. 
       BACKGROUND 
       [0003]    In the development of gas turbines, both, an increased cycle performance and reduced pollutant emissions are key targets to minimize the environmental impact as well as maximize the economic benefit. In order to increase gas turbine efficiency, it is important that both the distribution of the air exiting the compressor and the distribution of the hot gases exiting the combustor are optimized, i.e. that the working fluid experiences the smallest possible pressure drop before it starts to expand in the turbine. 
         [0004]    The before goals may be achieved inter alia by arranging a cooling path for the combustor walls and the burner air path in parallel which is illustrated in  FIG. 2   a . Concerning  FIG. 2   a  a rough sketch of a burner arrangement is illustrated comprising a plenum  1  which is fluidly connected with a compressor stage of an stationary gas turbine (not shown), so that the volume of the plenum  1  is filled with compressed air  2  under a prevailing pressure p1. The plenum  1  encapsulates a burner arrangement comprising a burner section  3  which is surrounded by a burner hood  4  having means for fuel injections  5 , means for air supply  6  and means for generating a fuel/air mixture (not shown) which is ignited inside a combustion chamber  7  following downstream of the burner section  3 . Hot gases  8  which are produces inside said combustion chamber  7  exiting said burner arrangement directly into a turbine (not shown) for performing work by expanding. To avoid any thermal overloading of the burner arrangement especially of the combustor, the combustor wall provides a combustor liner containing an interspace  9  into which compressed air  2  form the plenum  1  respectively form the compressor enters the interspace  9  for cooling purpose. The interspace  9  represents a cooling air path to cool the combustor walls. The cooling air emits the cooling air path and enters the combustion chamber directly. Also a part of compressed air inside the plenum  1  enters the burner section  3  via the means for air supply in form of access openings  6  inside the burner hood  4  for mixing with fuel which is injected by the injection means  5  for generating an ignitable fuel/air mixture  11 . 
         [0005]    The drawback of such a system is however the fact that not all of the air which is fed by the compressor inside the plenum takes part into the combustion, therefore a higher flame temperature is achieved for the same hot gas temperature, with the consequence of higher NOx emissions. Alternatively, if the layout is targeting lower NOx, the hot gas temperature has to be reduced, thereby negatively impacting engine efficiency. 
         [0006]    An alternative System is often used, in which the cooling and burner air paths are connected in series, see  FIG. 2   b .  FIG. 2  contains same reference signs which label components already explained in  FIG. 2   a  so that for avoiding repetitions these components are not explained again. Here, the cooling path for the combustor which is the interspace  9  is fluidly connected with the burner section  3 , so that the cooling air enters the burner via means for air supply  6  to be mixed with fuel for generating the fuel/air mixture  11 . 
         [0007]    This has the advantage that the whole air massflow takes part into the combustion, therefore emissions are minimized, however the overall pressure loss may be higher in this case, and therefore efficiency is lower. With such a layout, the pressure loss of the cooling path can optionally be reduced by bypassing some of the air  11  directly from the plenum  1  to the burner hood  4 . The bypass air  11  is, however, still experiencing a pressure loss and thereby providing no additional benefit. 
       SUMMARY 
       [0008]    It is an object of the invention to provide burner arrangement for producing hot gases to be expanded in a gas turbine, comprising a burner inside a plenum, said burner has means for fuel injection, means for air supply and means for generating an ignitable fuel/air mixture inside the burner, and a combustion chamber following downstream said burner having an outlet being fluidly connected to the gas turbine, which enables operation at higher temperatures and at the same time achieving a reduction of NOx, CO emissions and lessening pressure drop problems. 
         [0009]    The object is achieved by the sum total of the features of claim  1 . The invention can be modified advantageously by the features disclosed in the sub claims as well in the following description especially referring to preferred embodiments. 
         [0010]    The inventive idea bases on the combination of the advantages of both known air distribution layouts as explained in  FIGS. 2   a  and  b  and avoid the respective drawbacks by making use of a burner arrangement according to the features of the preamble of claim  1  characterized by two separate flow paths for the combustion air, i.e. the means for air supply into the burner comprise at least two separate flow passages, in which one of the two flow passages is fed by a first supply pressure and the other flow passage is fed by a second supply pressure. 
         [0011]    In fact in an preferred embodiment of the burner arrangement the at least one of the two flow passages is fluidly connected to the plenum in which the first pressure prevails which is fluidly connected to a compressor and the other flow passage is fluidly connected to an interspace in which the second pressure prevails and which is bordered by a combustor liner having at least one fluidly access to the plenum. Both passages end in the burner section so that the whole amount of air fed through both passages is mixed with the fuel for forming the fuel/air mixture before being ignited within the combustion chamber. 
         [0012]    The way of feeding the air through each passage can be performed in two different ways, i.e. in series or parallel to the cooling air path which corresponds to the interspace within the combustion liner for cooling the combustion walls. In case of a series air flow a part of the compressed air inside the plenum enters via access openings the interspace of the combustion liner to cool the combustion wall first before entering the burner region via one of the flow passages for being mixed with the fuel. While passing the access openings for entering the interspace of the combustion liner the air for cooling the combustor experiences a pressure drop so that inside the combustion liner a flow pressure of p 2  prevails which is less than p 1 . In case of a parallel air flow another part of compressed air inside the plenum enters the burner via the other low passage directly without cooling the combustor walls significantly. So dividing the flow of combustion air entering the burner for producing the fuel/air mixture into at least two separate flow paths enables the possibility that one flow path is fed in parallel to the cooling air path and the other one in series to it simultaneously. 
         [0013]    Both flow passages are designed preferably such that one of the two flow passages is an outer flow passage which surrounds the other flow passage, which is a so called inner flow passage. In case of an axis symmetric burner the inner and outer flow passages are coaxial and each flow passage has a flow exit plane which is at the downstream end of each flow passage such that the exit plane of the inner flow passage is different, preferably upstream of the exit plane of the outer flow passage. 
         [0014]    Optionally, each flow passage may contain a flow swirler, which may differ between the inner and outer flow path, so that vorticity which is induced into the both flows can be adjusted separately for the purpose of an enhanced mixture process downstream with the injected fuel. 
         [0015]    The means for fuel injection can be designed and arranged in different style and at different locations. One preferred means for fuel injection concerns a fuel lance extending in or through the inner flow passage. Alternatively to or in combination with said fuel lance further means for fuel injection can be arranged like fuel ejecting nozzles which are allocated at the downstream edge of the channel wall encircling the inner flow passage, i.e. the at least one fuel nozzle is placed at the exit plane of the inner flow passage. Of course other techniques for fuel injection can be applied to the inventive burner arrangement smoothly. 
         [0016]    A further advantage feature to enhance the flow characteristic downstream of the inner passage is a lobed design of the exit rim of the channel wall encircling the inner flow passage. More details are given in combination with the following illustrated embodiments. 
     
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         [0017]    The invention shall subsequently be explained in more detail based on exemplary embodiments in conjunction with the drawings. In the drawings 
           [0018]      FIG. 1  shows an inventive burner arrangement with double air passage for combustor air, 
           [0019]      FIG. 2   a, b  show state of the art burner arrangement with a) parallel air cooling flow and b) with serial air cooling flow, 
           [0020]      FIG. 3  shows a sketch of the proposed double air passage concept, 
           [0021]      FIG. 4   a, b  show preferred embodiments a) with serial outer passage and parallel inner passage, b) with parallel outer passage and serial inner passage, 
           [0022]      FIG. 5  shows inventive burner with serial outer passage and parallel inner passage, based on a conical swirler, 
           [0023]      FIG. 6  shows inventive burner with serial outer passage and parallel inner passage, based on an axial swirlers, 
           [0024]      FIG. 7  shows a partial view of a longitudinal section of an inventive double flow passages with a lobed mixing edge, 
           [0025]      FIG. 8  shows a cutaway view of an inventive burner arrangement with double air passage of parallel outer passage and serial inner passage. 
       
    
    
     DETAILED DESCRIPTION 
       [0026]      FIG. 1  shows a schematically longitudinal section of a burner arrangement comprising a plenum  1  which is fluidly connected with a compressor stage of an stationary gas turbine (not shown), so that the volume of the plenum  1  is filled with compressed air  2  under a prevailing pressure p 1 . The plenum  1  encapsulates a burner arrangement comprising a burner section  3  which is surrounded by a burner hood  4  having means for fuel injections  5 , means for air supply  6 ,  6 ′ and means for generating a fuel/air mixture (not shown) which is ignited inside a combustion chamber  7  following downstream of the burner section  3 . Hot gases  8  which are produces inside said combustion chamber  7  exiting said burner arrangement directly into a turbine (not shown) for performing work by expanding. To avoid any thermal overloading of the burner arrangement especially of the combustor, the combustor wall provides a combustor liner containing an interspace  9  into which compressed air  2  from the plenum  1  respectively form the compressor enters via access openings  10  into the interspace  9  for cooling purpose. Due to drop of pressure caused by the access openings the pressure p 2  inside the interspace  9  is smaller than p 1 . The interspace  9  encloses a cooling air flow  13  to cool the combustor walls. After passing the interspace  9  in flow direction the cooling air flow  13  enters through openings  6 ′, which serves as means for air supply into an outer flow passage  14  which is closed at an upstream end (left hand side of the figure) and opens into the combustions chamber  7  at its downstream end. The outer flow passage, which is radially encircled by a preferably cylindrical shaped wall in which the openings  6 ′ are arranged, encloses an inner flow passage  15 . The inner flow passage  15  us fluidly connected with the plenum  1  and opens into the combustion chamber  7 . The outer and inner passages  14 ,  15  are arranged and designed coaxially and represent a double combustor air burner arrangement. The inner flow passage  15  enables a direct flow of compressed air from the plenum  1  into the burner section  3  under a pressure p 1 . The outer flow passage  14  enables entering the cooling air flow  13 , which cools the combustor wall first, into the burner section  3 . So both air flows ejecting from the inner and outer flow passage  14 ,  15  are mixed with fuel for generating the fuel/air mixture  11  which is ignited and burned in the combustion chamber  7  for producing hot gases  8  for powering the turbine stage downstream of the combustion chamber (not shown). 
         [0027]    The principle for such the double air passage burner is shown in  FIG. 3 . The outer flow passage, fed by a supply pressure p 2 , which is the pressure inside the interspace  9  of the combustor liner, surrounds the inner flow passage  15 , fed by a supply pressure p 1 , which is the pressure inside the plenum  1 . The mass flows m 1  and m 2  through the two flow passages are different preferably and can be adjusted suitably. 
         [0028]    Optionally, each flow path  14 ,  15  can be equipped with swirler  16 ,  17 , which may differ between the inner and outer flow path  14 ,  15  respectively. The inner flow path  15  contains a bluff body for fuel injection  5  which can be also a means for flow stabilization. The exit plane  18  of the inner flow passage  15  may differ from the exit plane  19  of the outer flow passage  14  and, in particular, may be located upstream of the exit plane  19  of the outer flow passage  14 . 
         [0029]    In case of an axis symmetric burner arrangement, where the two flow passages, i.e. outer and inner flow passage  14 ,  15 , are coaxially arranged, two basic layout options are proposed. 
         [0030]      FIG. 4   a  shows an embodiment in which the outer flow passage  14  is serially fed by the combustor cooling air  13  and the inner flow passage  15  is fed directly with compressed air from the plenum  1  parallel to it. Here it is assumed that the means for fuel injection  5  is also part of a flang to a gas turbine casing (not shown) which provides a fuel lance  5 ′ extending mostly through the whole inner flow passage  15 . At an upstream portion of a channel wall  20  which encircles the inner flow passage  15  an opening  21  is provided through which the compressed air from the plenum  1  enters the inner flow passage  15 . Inside the inner flow channel  15  a swirler  17  is arranged. 
         [0031]    The inner flow channel  15  is partially surrounded by the outer flow channel along its axis which itself is radially encircled by a channel wall  22 . Both channel walls  20 ,  22  are cylindrical in shape and arranged coaxial along one and the same burner axis. Along the outer flow channel swirler  16  are arranged also. As depicted in  FIG. 4   a  the flow pressure p 1  and the flow mass m 1  of the air flow entering the inner flow passage  15  which is directed parallel to the cooling air flow  13  are different to those p 2 , m 2  of the cooling air flow  13  when entering the outer flow passage  14 . 
         [0032]      FIG. 4   b  shows an embodiment in which the outer flow passage  14  is parallel fed by the compressed air from the plenum  1  and the inner flow passage  15  is fed serially fed by the combustor cooling air  13 . The burner hood  4  encloses the inner region of the burner and separates the volume of the plenum form the 
         [0033]      FIG. 5  shows a sectional view of a burner arrangement with double air passage, containing a serial outer flow passage  14  and a parallel inner flow passage  15 , based on a conical swirler  23 . Same as in all other illustrated embodiments the burner arrangement is enclosed by a plenum not shown. The inner flow passage  15  is fed with compressed air entering the upstream opening  24  under pressure p 1  and with a mass flow m 1 . Further a fuel lance  5 ′ extends into the inner flow passage  15  which injects fuel into the air flow swirled by the conical swirler  23 . Further the cooling air flow  13  enters the outer flow passage  14  after having cooled the combustor wall and getting swirled also by the conical swirler  23  while passing the outer flow passage  14 . So the air/fuel mixture which is produced along the inner flow passage  15  will be mixed after passing the exit plane  18  with the swirled additional air inside the outer flow passage  14 . The additional swirled air in the outer flow passage has a lower pressure p 2  and another mass flow m 2  so that mixture efficiency can be optimized within the outer flow passage  14  by adjusting p2 and m2 suitably for getting a completely and homogenously mixed fuel/air mixture before passing the exit plane  19  of the outer flow passage. 
         [0034]      FIG. 6  shows a sectional view of a burner arrangement with double air passage, containing a serial outer flow passage  14  and a parallel inner flow passage  15 , based on an axial swirler  23 . Same as in all other illustrated embodiments the burner arrangement is enclosed by a plenum  1 . The inner flow passage  15  is fed with compressed air entering the upstream opening  24  under pressure p 1  and with a mass flow m 1 . Further a fuel lance  5 ′ extends into the inner flow passage  15  for injecting fuel into both air flows each swirled by the conical swirler  23 . Fuel injection into both air flows takes place simultaneously at the exit plane  18  of the inner flow passage, at which both swirled air flows meet. 
         [0035]    In a preferred embodiment shown in  FIG. 7   a, b  the inner flow passage  15  is surrounded by a channel wall  20  which has an axial downstream edge  26  providing a lobed shape  27  (see  FIG. 7   a ) which can be seen from the cross section illustrated in  FIG. 7   b . Such lobed contour  27  is particularly suited for highly reactive fuels. 
         [0036]      FIG. 8  shows a burner arrangement according to the concept shown in  FIG. 4   b . The burner is encapsulated in a burner hood  4 . The cooling air flow  13  passing through the interspace  9  of the combustion liner enters the burner section inside the burner hood  4  after having cooled the combustor walls. The air flow then flows in series into the inner flow passage  15  through an entrance opening  28  at which several fuel injectors  5  are arranged. The serial air flow and the fuel are flowing in axial direction through the inner flow passage  15  and initially mixing only due to the fuel jet spreading. The axial fuel injection arrangement also allows to concentrate the fuel injection part of the burner on an extractable lance  5 ′ and to thus separate from the burner aerodynamics. 
         [0037]    In addition, the fuel injection location can be adjusted axially. The fuel injection in co-flow direction yields weaker oscillations of the fuel jets and thus leads to higher flame stability. 
         [0038]    The compressed air flow  2  is arranged in parallel and is fed directly from the plenum  1  at pressure p 2 . This compressed air flow  2  crosses the first cooled air flow  13  in separate flow channels arranged alternatively and then flows along the surface of the combustor front panel  29  in order to cool the front panel  29  convectively. Then the compressed air flow  2  flows around the burner diffuser part  30  and acquires angular momentum in circumferential direction of the burner. Finally the air flows through a number of elongated air slots  31  into the inner part of the burner, merging with the primary air stream and introducing swirl to the overall burner flow. The mixing of the secondary compressed air flow  2  with the first flow of air  13  and fuel occurs over a very short distance such that the overall mixture is sufficiently premixed before reaching the flame zone  32  which extends downstream of the burner and can reach as much upstream as the extend of the central bluff body  33 . In order to further enhance the mixing before the flame anchoring position  32 , the central body  33  could also be extended further downstream. An additional fuel injection in the outer fuel passage could provide additional fuel premixing and potential for lower emissions. 
         [0039]    The advantages of the inventive new burner concept can be summarized as follows:
       Potential for low emission operation at high hot gas temperature by avoiding air bypassing the burner like in case of the burner illustrated in  FIG. 2   a.      Reduced overall combustor pressure drop by optimizing the air split between the two inventive flow passages.   Potential for improved pulsation behavior by thermoacoustically decoupling the two flow passages.   Potential for having different flow characteristics. e.g. swirl, turbulence level, in the two flow passages to better cope with different operating conditions (e.g. bad) or other boundary conditions (e.g. fuel type, fuel composition).   The high pressure drop available for one of the two flow paths may be used as best suitable, e.g. for improving fuel mixing, for imparting higher swirl and achieve better flow stabilization, for achieving high velocity and avoid flashback for highly reactive fuels.   The interface region where the two flow streams merge can be designed to optimize different parameters, e.g. mixing between the two air streams and fuels, flame stabilization, flashback safety.   The mechanical parts creating and providing fuel to the two air passages may be separate from each other and, through modular design, allow easier change of configurations (e.g. for different fuels) as well as simpler design and improved manufacturing, assembly, inspection, and reconditioning.       
 
         [0047]    With respect to the proposed layouts described in  FIGS. 4   a  and  b , additional benefits of the first concept, see  FIG. 4   a , are:
       Reduced first and life cycle costs through simple design, because main parts may be formed by concentric tubes.   Further reduced pressure drop by allowing inflow in the two passages over a large cross section and with the minimum requirement of flow turns       
 
         [0050]    Additional benefits of the second concept, see  FIG. 4   b , are:
       Efficient use of compressor exit pressure to cool combustor front segment and burner front face, possibly by convective cooling       
 
         [0052]    Possible further embodiments of the inventive concept are:
       Application to can, annular, or silo combustors   Swirlers of different types (no swirl, axial, radial, conical swirlers, or combinations thereof for the different flow passages   Two coaxial flow passages or more, e.g. one serial to liner cooling, one serial to front segment cooling, one parallel to both)   Non-coaxial flow passages (e.g. splitting flow path from inner and outer liner cooling air)   Modular variants where one of the flow passages is fixed and the other one is optimized either for standard (NG, wet oil) or highly reactive fuels (H2-rich, dry oil), respectively, thereby allowing increased fuel flexibility with minimum hardware changes   Modular variants where the outer wall of the outer flow passage is connected to the front segment, while all fuel supply occur through the parts forming the central flow passage, thereby allowing air leakages between burner and front segment and increased design simplicity and robustness by having a smaller, retractable central body only   Variable air flow split between the different flow passages to be adjusted, e.g. by exchangeable sieves of different open area   Different fuel injection schemes combined with the different geometries/swirler types: cross-flow from inner/outer/intermediate walls, in-line injection from swirler or flow separating parts, from central/additional fuel lance(s)   Different and adjustable fuel flow split between the two passages       
 
         [0062]    In order to minimize thermoacoustic pulsation, it is known that a large time lag spread between the position of the flame and those of the originating points for the different flow disturbances and/or fuel injections is beneficial.
       The current burner concept is particularly suitable for this purpose, since swirl generators, fuel injection positions, and bulk flow velocities can be kept different for the different flow passages, thereby maximizing the time lag spread   Similarly, it could be convenient to place the tip of the central lance, the downstream edge of the separating wall between the two passages, and the burner exit edge at different axial positions       
 
         [0065]    In case of coaxial air passages, the downstream edge of the separating wall between the two passages can have a lobed shape arid optionally include the fuel injection holes. The advantages thereby are.
       Improved mixing with minimum pressure drop (possibility of keeping high bulk flow velocity and reduce flashback risk)   Minimum flow disturbances through absence of strong flow turns (reduce flashback risk)   Minimum flow disturbances through possibility of in-line injection from trailing edge (reduce flashback risk)       
 
         [0069]    This is, in particular, suitable for highly reactive fuels and could be realized within a burner concept as shown in  FIGS. 7   a  and  b.