Abstract:
The invention refers to a combustion chamber having a sleeve section which is at least partly enclosing a duct wall for guiding a cooling gas in a channel between the sleeve section and the duct wall along the outer surface of the duct wall. The sleeve section has one main inlet opening facing away from the duct wall wherein the cross sectional area of the main inlet opening is larger than 70% of the sum of the cross sections of all cooling openings to the sleeve section. The disclosure further refers to a gas turbine comprising such combustion chamber.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority to European application 14160407.4 filed Mar. 18, 2014, the contents of which are hereby incorporated in its entirety. 
       TECHNICAL FIELD 
       [0002]    The disclosure refers to a cooling arrangement for a combustion chamber, more particularly to an arrangement with a cooling sleeve guiding cooling gas along the walls of a combustion chamber. 
       BACKGROUND 
       [0003]    The thermodynamic efficiency of power generating cycles depends on the maximum temperature of its working fluid which, in the case for example of a gas turbine, is maximum temperature of the hot gas exiting the combustor. The maximum feasible temperature of the hot gas is limited by combustion emissions as well as by the operating temperature limit of the metal parts in contact with this hot gas, and on the ability to cool these parts below the their metal temperature limit. The cooling of the hot gas duct walls forming the hot gas flow paths of advanced heavy duty gas turbines is difficult and currently known cooling methods carry performance penalties, i.e. lead to a reduction in power and efficiency. 
         [0004]    Cooling of combustor walls exposed to the hot combustion gases is critical to assure life time of the gas turbine. Cooling sleeves for guiding cooling gas along the walls of combustion chambers have been suggested. For example a combination of sleeves to guide the cooling gas along the combustion chamber with impingement cooling has been disclosed in the EP13190131. For impingement cooling of a duct a sleeve is disposed a short distance away from the duct&#39;s outer surface. The impingement sleeve contains an array of holes through which compressed cooling gas discharges to generate an array of air jets which impinge on and cool the outer surface of the duct. After impingement the cooling gas flows in a cooling path delimited by the duct and the impingement sleeve towards one end of the duct. The impingement cooling has to be provided from all circumferential directions around the combustion chamber. The supply of sufficient cooling gas to feed the sleeve cooling can be difficult due to space constraints in the plenum surrounding a combustor arrangement in a gas turbine. These space constrains can lead to small cross sections in the supply channels for the sleeve cooling which in turn increase the pressure drop of the cooling arrangement. The increased pressure drop leads to corresponding high cooling gas supply pressure requirements which can be detrimental to the overall performance of the gas turbine. 
       SUMMARY 
       [0005]    The object of the present disclosure is to propose a combustion chamber which allows efficient cooling of a duct wall with a low pressure drop in the cooling gas flow. In this context a combustion chamber can comprise the section of a combustor in which the combustion takes place. It can also comprise the so called transition zone. This is a region downstream of the main combustion zone in which the cross sectional area of the combustor is progressively reduced in the downstream direction between the main combustion zone and the outlet guiding the hot gas flow towards the turbine inlet. 
         [0006]    The cooling gas can be air which has been compressed by a compressor of a gas turbine if the combustor is installed in an air breathing gas turbine. It can be any other gas or mixture of gases. For example it can be a mixture of air and flue gases for a gas turbine with flue gas recirculation into the compressor inlet. 
         [0007]    The disclosed combustion chamber comprises a sleeve section which is at least partly enclosing a duct wall also called combustion chamber wall for guiding a cooling gas in a channel between the sleeve section and the duct wall along the outer surface of the duct wall. The duct wall itself is guiding a hot gas flow in a hot gas flow path having an upstream end and a downstream end during operation. The sleeve section has one main inlet opening, which is facing away from the duct wall for supplying cooling gas into the cooling channel. The cross sectional area of the main inlet opening is larger than 70% of the sum of the cross sections of all cooling openings to the sleeve section. 
         [0008]    In a further embodiment the cross sectional area of the main inlet opening is even larger than 80% of the sum of the cross sections of all cooling openings to the sleeve section 
         [0009]    When installed in a gas turbine the singe main inlet opening of the combustion chamber can be orientated so that it faces a region in a compressor plenum in which the highest pressure prevails and which is sufficiently feed by cooling gas to feed the cooling channel between the sleeve and the duct wall. 
         [0010]    According to a specific embodiment the main inlet opening is the only cooling opening to the sleeve section. 
         [0011]    According to a further embodiment of the combustion chamber the main inlet opening is orientated to one side of the combustor. One side in this context means for example in case of a combustion chamber with a rectangular or trapezoidal cross section that the main inlet opening is only facing away from one side of the combustion chamber and the other three sides are closed. In case of a practically cylindrical or oval the one opening opens in a direction with an opening angle which can for example be less than 90° or less than 60° relative to a longitudinal axis of the combustion chamber. The main inlet opening can for example face towards the axis of a gas turbine when installed. 
         [0012]    According to another embodiment of the combustion chamber an orientation of the main inlet opening is normal to an axial extension of the combustor. 
         [0013]    To allow for a good distribution of the cooling gas in the cooling channel between the sleeve and the duct wall several advantageous geometrical forms of the main inlet opening are feasible. According to one embodiment the main inlet opening has a circular shape. 
         [0014]    The circular shape can be used to equally distribute cooling gas in all directions from the inlet opening. 
         [0015]    According to another embodiment of the combustion chamber the main inlet opening has a rectangular shape. 
         [0016]    The rectangular main inlet opening can be arranged with the larger extension perpendicular to the axial extension of the combustion chamber. 
         [0017]    According to yet another embodiment of the combustion chamber the main inlet opening has a triangular shape. 
         [0018]    The triangular shape can for example have a base which is orientated perpendicular to the axial extension of the combustion chamber and the two other sides extending under an angle in an upstream direction, i.e. a height of the triangular main inlet opening is parallel to the axial extension of the combustor. Cooling gas can be feed side wards and in upstream direction from these two sides orientated in upstream directions. 
         [0019]    According to still another embodiment the main inlet opening has a kidney like shape. 
         [0020]    The kidney shaped cooling opening can have a base line connecting two circular enlargements of the main inlet opening wherein the baseline is extending in a circumferential direction on the surface of the duct wall normal to the axial extension of the combustor. 
         [0021]    In other words a long side of the kidney like shape can extend perpendicular to the axial extension of the combustion chamber. The cross section of the kidney like shape increases towards the sides of the combustion chamber thus allowing a large flow of cooling gas to both sides of the combustion chamber, which can be advantageous to supply the cooling gas to the cooling channel section opposite of the main inlet opening. 
         [0022]    In a further embodiment of the combustion chamber the height of the cooling channel between the sleeve and the duct wall is decreasing in circumferential direction around a combustion chamber and/or axial direction of the combustion chamber from the main inlet opening. With increasing distance from the main inlet opening the effective flow area increases if the height of the flow channel is constant. To keep the flow velocity in the channel constant the height of the flow channel has to be reduced with increasing distance from the main inlet opening until the cooling gas is distributed around the combustor wall in circumferential direction relative to the axial extension of the combustion chamber. 
         [0023]    The height of the cooling channel can for example be a linear function of the distance from the geometrical center of the main inlet opening until a minimum height is reached. After reaching the minimum height the height can be kept constant. After a minimum height has been reached the channel height can also be increasing again to compensate for an increase in volume flow due to the heating of the cooling gas as it flows along the hot duct wall. The increase in channel height can be chosen such that the flow velocity is practically kept constant. 
         [0024]    In yet a further embodiment of the combustion chamber the main inlet opening comprises a bellmouth to recover dynamic pressure of inflowing cooling gas during operation. Typically the incoming cooling gas in a compressor plenum of a gas turbine has a high velocity. The kinetic energy of the inflowing gas can at least partly be recovered and used to increase the static pressure of the cooling gas by the bellmouth. 
         [0025]    In another embodiment of the combustion chamber heat transfer enhancers are applied on the duct wall. Alternatively or in combination heat transfer enhancers can be applied on the sleeve section. The heat transfer enhancers increase the heat transfer and cooling of the duct wall. A heat transfer enhancer on the duct wall facing the side of the cooling channel can typically increase the heat transfer better than a heat transfer enhancer on the sleeve. However, for manufacturing and cost reasons it can be advantageous to apply heat transfer enhancers on the sleeve. 
         [0026]    A heat transfer enhancers can for example be a turbulator. Among many possible shapes a turbulator can have 90° bend, a V-shape, or a W-shaped to enhance heat transfer. In combination or alternatively pin fields or surface roughness can be applied as heat transfer enhancers. 
         [0027]    In addition or in combination cooling gas can be supplied through secondary inlet openings to locally cool areas with high heat load or for which the convective cooling by the cooling gas in the cooling channel is not sufficient. 
         [0028]    In addition or in combination impingement cooling holes can be used to locally cool areas with high heat load or for which the convective cooling by the cooling gas in the cooling channel is not sufficient or not suitable. According to one embodiment less than 20% of the available cooling mass flow for the duct wall is used for impingement cooling and/or secondary cooling. 
         [0029]    In yet another embodiment of the combustion chamber a one rib for guiding the cooling gas is arranged in the channel between the sleeve and the duct wall. 
         [0030]    According to a further embodiment the rib at least partly extends in a circumferential direction around the combustor to guide cooling gas from the side of the main inlet opening to an opposite side of the combustor. 
         [0031]    Such a rib can for example extend circumferentially from the main inlet opening around the duct wall. 
         [0032]    The rib can also part a cooling gas flow into two flow directions. For example the cooling flow can be split into a first partial flow in axial direction and a second axial flow in circumferential direction around the duct wall. 
         [0033]    A rib can also be used to divert or bend a cooling gas flow. For example a flow can first be guided in circumferential direction around the combustor and then be redirected in a bend to a direction in counter flow to the main flow direction of hot gas in the combustion chamber. 
         [0034]    In another embodiment of the combustion chamber an aperture is introduced in a rib to allow a cross flow from a first section of the cooling channel on one side of a rib to a second section of the cooling channel on the other side of the rib. Such an aperture can be advantageous if the pressure in the first section of the cooling channel is higher than in the second section. Such a pressure difference can for example be due to different distances from the main inlet opening to the aperture with different pressure drops on both sides of the rib. Such a cross flow can increase the pressure in the second section. Further, the temperature of the cooling gas traveling the shorter distance might be lower, thus a cross flow can help to equalize the temperature distribution around the duct wall. 
         [0035]    Besides the combustion chamber a gas turbine comprising a compressor, a turbine and a combustor with a plurality of the above described combustion chambers is an object of the disclosure. 
         [0036]    Such a gas turbine comprises a plurality of combustion chambers with a sleeve section which is at least partly enclosing a duct wall for guiding a cooling gas in a channel between the sleeve section and the duct wall along the outer surface of the duct wall. The duct wall itself is guiding a hot gas flow in a hot gas flow path having an upstream end and a downstream end during operation. The sleeve section has one main inlet opening, which is facing away from the duct wall. The cross sectional area of the main inlet opening is larger than 70% or larger than 80% of the sum of the cross sections of all cooling openings to the sleeve section. 
         [0037]    According to a further embodiment the gas turbine comprises a plurality of combustion chambers which are circumferentially distributed around the axis of the gas turbine. The combustion chambers are arranged each with its main inlet opening facing towards the axis of the gas turbine. Further the gas turbine comprises a diffusor subsequent of the compressor with an outlet directed to the main inlet openings such that during operation of the gas turbine compressed gas leaving the diffusor impinges on the main inlet openings. 
         [0038]    Due to such an arrangement the kinetic energy of the compressed gas leaving the compressor can at least partly be recovered in the main inlet opening to increase the static pressure of the cooling gas in the combustion chamber&#39;s cooling channel. 
         [0039]    According to yet a further embodiment the gas turbine comprises a second diffusor for directing part of the compressor exit gas to the burners of the gas turbine. Thus the burners are optimally supplied with high pressure gas for combustion and good cooling of the combustor walls is assured. 
         [0040]    The gas turbine can have a conventional combustor with one combustion chamber. The gas turbine can also comprise a sequential combustor arrangement with at least two combustion chambers arranged downstream of each other. In a sequential combustor arrangement one or both combustion chambers can be configured with a combustion chamber having a sleeve section which is at least partly enclosing a duct wall for guiding a cooling gas in a channel between the sleeve section and the duct wall along the outer surface of the duct wall. The duct wall itself is guiding a hot gas flow in a hot gas flow path having an upstream end and a downstream end during operation. The sleeve section of the first, respectively the second combustion chamber has one main inlet opening, which is facing away from the duct wall. The cross sectional area of the main inlet opening is larger than 70% or larger than 80% of the sum of the cross sections of all cooling openings to the sleeve section of the respective combustion chamber. 
         [0041]    Different burner types can be used. For the first combustor so called EV burner as known for example from the EP 0 321 809 or AEV burners as known for example from the DE 195 47 913 can for example be used. Also a BEV burner comprising a swirl chamber as described in the European Patent application EP 12 189 388.7, which is incorporated by reference, can be used. In a can architecture a single or a multiple burner arrangement per can combustor can be used. Further, a flamesheet combustor as described in US  2004 / 0211186 , which is incorporated by reference, can be used as first combustor. 
     
    
     
       BRIEF DESCRIPTION 
         [0042]    The disclosure, its nature as well as its advantages, shall be described in more detail below with the aid of the accompanying schematic drawings. 
           [0043]    Referring to the drawings: 
           [0044]      FIG. 1  shows a gas turbine with a compressor, a combustion arrangement, and a turbine; 
           [0045]      FIG. 2   a  shows a cut through A-A of two combustion chambers of  FIG. 1 . 
           [0046]      FIG. 2   b  shows the static pressure distribution around the combustion chamber of  FIG. 2   a,    
           [0047]      FIG. 3  shows a gas turbine with a compressor, a combustion arrangement with a combustion chamber with a cooling sleeve comprising a main inlet opening, and a turbine; 
           [0048]      FIG. 4  shows a cut through B-B of a combustion chamber of  FIG. 3 ; 
           [0049]      FIG. 5  shows a gas turbine with a compressor, a combustion arrangement with a combustion chamber with a cooling sleeve comprising a main inlet opening, and a turbine; 
           [0050]      FIG. 6  shows a cut through C-C of a combustion chamber of  FIG. 5 , 
           [0051]      FIG. 7   a, b, c, d  shows a top view of cooling sleeve with different geometric shapes of the a main inlet opening; 
           [0052]      FIG. 8   a, b, c, d, e, f  shows a perspective view of combustion chamber with different rib arrangements for guiding the cooling gas flow in the cooling channel between the duct wall and cooling sleeve. 
       
    
    
     DETAILED DESCRIPTION 
       [0053]      FIG. 1  shows a gas turbine  1  with an impingement cooled combustor  4 . It comprises a compressor  3 , a combustor  4 , and a turbine  5 . 
         [0054]    Intake air  2  is compressed to compressed gas  8  by the compressor  3 . Fuel  28  is burned with the compressed gas  8  in the combustor  4  to generate a hot gas flow  9 . The hot gas  9  is expanded in the turbine  5  generating mechanical work. 
         [0055]    The combustor  4  is housed in a combustor casing  31 . The compressed gas  8  leaving the compressor  3  passes through a diffusor  19  for at least partly recovering the dynamic pressure of the gas leaving the compressor  3 . 
         [0056]    Typically, the gas turbine system includes a generator which is coupled to a shaft  2  of the gas turbine  1 . The gas turbine  1  further comprises a cooling system for the turbine  5 , which is not shown, as it is not the subject of this disclosure. 
         [0057]    Exhaust gas  7  leaves the turbine  5 . The remaining heat is typically used in a subsequent water steam cycle, which is also not shown here. 
         [0058]      FIG. 1  shows a combustor  4  with an impingement cooling arrangement for cooling the duct wall  10 . The combustor  4  comprises a burner  25  at the upstream end and a combustion chamber  26  extending from the burner to the downstream end. The combustion chamber  26  is delimited to the sides by the duct wall  10 . For the impingement cooling a sleeve  15  comprising apertures for impingement cooling of the duct wall  10  is arranged around the combustion chamber  26 . After the cooling gas  16  impinges on the duct wall  10  it flows in the cooling flow path formed by the duct wall  10  and the sleeve  15  towards the upstream end of the combustion chamber  26  in counter flow to the hot gas flow inside the combustion chamber  26 . After cooling the duct wall  10  the cooling gas  15  can flow into the combustion chamber  26  at the upstream end of the hot gas flow path to be further used as combustion gas. 
         [0059]      FIG. 2   a  shows the cut through section A-A of two neighboring combustion chambers  26  of  FIG. 1  as an example of a plurality of combustion chambers  26  arranged circumferentially distributed around the axis of the gas turbine. The duct walls  10  of the combustion chambers are enclosed by the sleeve section  15 . Each duct wall  10  defines the hot gas channel of on combustion chamber  26 . In this example the cross section of the combustion chamber  26  is basically rectangular and enclosed by a cooling channel, which is delimited by the sleeve section  15 . The channel has an inner channel side  12  facing in the direction of the axis of the gas turbine, a right channel side  11 , a left channel side  13 , and an outer channel side  14 . All channel sides  11 ,  12 ,  13 ,  14  are impingement cooled with cooling gas  16 . The cooling gas for cooling the left, right, and outer channel side  11 ,  13 ,  14  at least partly passes through a gap between the sleeves  15  of two neighboring combustion chambers  26 . Due to space restrictions this gap can be small leading to high cooling gas  16  flow velocities in the gap. Due to these high flow velocities the static pressure in the gap is reduced. Thus the cooling gas  16  entering the left and right channel side  11 ,  13  has a reduced pressure. Further, the flow through this gap causes a pressure drop such that the cooling gas  16  leaving the gap and feeding the outer channel side  14  has a reduced total pressure. 
         [0060]    The resulting static pressure distribution around the combustion chamber  26  of  FIG. 2   a  is shown in  FIG. 2   b  as a function of the angle y in clockwise direction around the duct wall  10 .  FIG. 2   b  indicates that the pressure in the inner channel side  12  is higher than on the outer channel side  14 . The cooling gas pressure on the left and right channel side is even lower than in the outer channel side  14 . Due to the different pressure levels in the different channel sides cooling differs considerably for the different sections of the duct wall. 
         [0061]      FIG. 3  is based on  FIG. 1  but has a modified sleeve section  15  to reduce differences in cooling gas pressure and resulting differences in cooling gas flow around different sections of the duct wall  10 . The sleeve section  15  has only one main inlet opening  17  for feeding the cooling channel surrounding the duct wall  10 . The cut of the gas turbine  1  shown in  FIG. 3  is not straight through but follows the contour of the duct wall  10  as indicated by the cut III-III in  FIG. 4 . Thus the streamlines of the cooling gas  16  flowing around the duct wall  10  can be shown in  FIG. 3 . For supplying the main inlet opening  17  with cooling gas  16  the compressor diffusor is divided into a first diffusor  19  which directs a large portion of the compressed gas  8  towards the burner  25 , and a second diffusor  24  with a deflector  20 , which directs the a portion of the compressed gas  8  towards the main inlet opening  17  for feeding the cooling channel surrounding the duct wall  10 . In this example the main inlet opening  17  comprises a bellmouth  18  in which the remaining kinetic energy of the compressed gas leaving the second diffusor can be further recovered to increase the static pressure of the cooling gas  16  in the cooling channel. 
         [0062]    The cross section B-B of the combustion chamber  26  in the region of the main inlet opening  17  is shown in  FIG. 4 . In this example the main inlet opening  17  is configured as a bellmouth  18  to recover dynamic pressure before the cooling gas  16  is guided in the channel between the duct wall  10  and the sleeve section  15  around the combustion chamber  26 . 
         [0063]      FIG. 5  shows another example of a gas turbine  1  according to the disclosure. The example of  FIG. 5  is based on  FIG. 3  but has only one compressor diffusor. For easy manufacturing the main inlet opening  17  is simply a hole in the wall of the sleeve section  15  without any aerodynamically contoured inlet. The gas turbine  1  further has only one compressor diffusor. Part of the compressed gas  8  is directed towards the main inlet opening  17  by a deflector  20 . 
         [0064]    The cut through the gas turbine  1  shown in  FIG. 5  is also not straight but follows the contour of the duct wall  10  as indicated by the cut V-V in  FIG. 6 . Thus the streamlines of the cooling gas  16  flowing around the duct wall  10  can be shown in  FIG. 5 . The main inlet opening  17  of this example is larger than in the example of  FIG. 3-4 . It practically spans from one side of the duct wall  10  to the other side of the duct wall  10  as can be seen in  FIG. 6  showing the cut through C-C of a combustion chamber  26  of  FIG. 5 , 
         [0065]    In a top view different examples of cooling sleeve sections  15  facing towards the axis of a gas turbine when installed with different geometric shapes of the a main inlet opening  17  are shown in  FIGS. 7   a, b, c , and  d.    
         [0066]      FIG. 7   a  shows an example with a main inlet opening  17  having a rectangular shape. The larger side of the rectangular main inlet opening is spanning around the sleeve section  15  in a direction perpendicular to the hot gas flow inside the combustion chamber when in operation. 
         [0067]      FIG. 7   b  shows an example with a main inlet opening  17  having a circular shape. 
         [0068]      FIG. 7   c  shows an example with a main inlet opening  17  having a kidney like shape. The kidney like shape has its largest extension in a direction perpendicular to the hot gas flow inside the combustion chamber when in operation. At both ends of this largest extension the cross section of the main inlet opening expands into a circular shape. These expansions facilitate the supply of cooling gas to the side of the combustion chamber. 
         [0069]      FIG. 7   d  shows an example with a main inlet opening  17  having the shape of an equilateral triangle. A height of the triangle is arranged parallel to the hot gas flow inside the combustion chamber when in operation. 
         [0070]      FIG. 8   a, b, c, d, e , and  f  show perspective views of examples for combustion chambers with different rib  21  arrangements for guiding the cooling gas  16  flow in the cooling channel between the duct wall and cooling sleeve. 
         [0071]      FIG. 8   a  shows a top-side view of the duct wall  10  with guiding ribs  21  and indicates the cooling gas  16  flow between the ribs. The cooling gas  16  enters from below the cooling duct through the main inlet opening (not shown) and is guided around the duct wall  10 . At the downstream end of the combustion chamber (for the hot gas during operation, left end in the  FIG. 8 ) the ribs  21  extend mainly in circumferential direction around the side walls of the duct before the ribs  21  turn in an axial direction (counter to the hot gas flow. These ribs  21  serve to guide cooling gas  16  from the main inlet opening around the side walls of the combustion chamber to the top and further counter flow towards the upstream end of the combustion chamber (right end of the combustion chamber in  FIG. 8 ). In addition a rib  21  is extending in flow direction in the upstream half of the side of duct wall  10 . 
         [0072]    The example of  FIG. 8   b  is based on  FIG. 8   a . In addition a cut out of the sleeve section  15  is shown. In this example additional secondary inlet openings  22  are shown in the sleeve section on the outer side. These secondary inlet openings  22  can be applied to locally improve the supply of cooling gas  16  to the cooling channel. The secondary inlet openings  22  can be configured as impingement cooling holes to locally impingement cool the duct wall  10 . 
         [0073]    The example of  FIG. 8   c  is based on  FIG. 8   b . Here the ribs  21  are y shaped with the single leg of the y directed upstream (relative to the hot gas flow in operation) 
         [0074]      FIG. 8   d  shows another example based on  FIG. 8   a . To improve heat transfer to the cooling gas  16  turbulators  27  are arranged on the duct wall  10  where needed to locally improve the cooling. In this example turbulators  27  are added in a top region and in an upstream region of the side walls. 
         [0075]      FIG. 8   e  shows another example based on  FIG. 8   a . In this example the ribs  21  on the side of the duct wall  10  do not extend all the way to the upstream end of the combustion chamber. The straight sections of the ribs  21  are not needed for guiding the cooling gas  16  flow in the upstream regions of this example. Manufacturing costs can be reduced by shorter ribs  21 . In addition a cross flow is possible in the regions without the ribs. 
         [0076]      FIG. 8   f  shows yet another example based on  FIG. 8   a . In this example the ribs  21  comprise apertures  23  which allow a cross flow. This cross flow can lead to a more homogeneous pressure distribution around the duct wall  10 .