Abstract:
The invention pertains to a coolable segment ( 1 ) for a turbo machinery ( 20 ), which turbo machinery ( 20 ) is operated with a hot fluid ( 29 ). The segment ( 1 ) comprises a cooling wall ( 2 ) extending in an axial direction ( 37 ) and in a circumerential direction ( 36 ) orthogonal to said axial direction ( 37 ); a hot fluid surface ( 3 ) to be exposed to the hot fluid ( 29 ). Between the wall ( 2 ) and the surface ( 3 ) a cooling structure ( 4 ) is arranged which is permeable to cooling fluid ( 5 ) and provides cooling surfaces ( 6 ) for cooling by heat transmission through radiation. The cooling structure ( 4 ) comprises either a netting, in particular a wire netting or a porous material. The invention further pertains to a combustion turbine ( 20 ) comprising a coolable segment ( 1 ).

Description:
BACKGROUND OF THE INVENTION  
         [0001]    Field of the Invention  
           [0002]    The invention relates to a coolable segment of a turbomachinery, in particular a shroud or guide blade plate (guide ring segment) of a combustion turbine. The invention also relates to a combustion turbine having a coolable segment.  
           [0003]    An important consideration in the design of a turbomachinery, in particular gas turbine engines or steam turbines, is to ensure that various components of the engine are maintained at safe operating temperatures. This is particularly true for elements of a gas turbine like combustor and turbine section, which are exposed to the highest operating temperatures in the engine, and which include turbine nozzles or vanes, turbine buckets or rotating blades and shrouds. A turbine nozzle directs hot gas within an annular gas path, to cause the adjacent following bucket row to rotate, producing power. A shroud defines a portion of the gas path radially outward of the rotating bucket row.  
           [0004]    In the turbine section of gas turbine engines, high thermal efficiency is dependent upon high turbine entry temperatures. These entry temperatures, in turn, are limited by the heat which the materials forming the turbine nozzles, buckets and shrouds can safely withstand. In cases in which the gas path temperatures are above the material limitations, the gas path surfaces of these components must be cooled to survive. Thus, in addition to improvements in the types of materials and coatings used to fabricate these components, continuous air cooling has been employed to permit the environmental operating temperature of the turbine to exceed the melting point of the materials forming the components without affecting their integrity.  
           [0005]    A number of fluid cooling techniques, in particular air cooling techniques, have been used in an attempt to effectively and uniformly cool the components of the turbine section, the combustor and other portions of gas turbine engines.  
           [0006]    In European Patent Application EP 1022437A1 to Tiemann at al. an element of a combustion turbine is disclosed which comprises a wall element having an internal coolable area. Between two of those wall elements a gap for allowing compensation of thermal expansion is sealed off by a seal element. The internal coolable area is supplied with cooling air which exits the wall element through a bore opening into the gap whereby the cooling air exiting the bore cools by impingement cooling the wall of the adjacent wall element. After exiting the gap the cooling air flows along an outer surface of the wall element thereby shielding the outer surface from a stream of hot gas flowing in the combustion turbine.  
           [0007]    In International publication WO 00/60219A1 to Tiemann et al a turbine-engine with an array of wall elements that can be cooled and method of cooling an array of wall element is described. This method includes the step of cooling a first element, in particular a rude portion of a turbine vane by impingement cooling and a further step which includes the using the same cooling fluid for cooling a second component downstream of the first component. For reducing a cooling fluid lost by leakage a cooling passage is formed between the first and the second component for which the cooling fluid flows after cooling the first component. The second component, which is preferably a shroud, is cooled by a cooling fluid in a convection-cooling manner.  
           [0008]    Published German patent application DE 19727407 A1 to Krebs refers to a heat shield plate for a combustor of a gas turbine. On the internal wall of the combustor the plates are mounted forming a cavity with the combustors wall. In the wall of the combustor cooling fluid channels directed perpendicular to the walls surface and having openings formed as nozzle into the cavity. These nozzles serve to improve the impingement cooling by a cooling fluid being directed to the plate. The plate itself has a number of diffusion cooling channels leading from the cavity to the outer surface of the plate and being inclined by an angle of about 30 degrees with respect to the outer surface of the plate.  
           [0009]    In WO 98/13645 A1 to Gross et al. a closed loop air cooled heat shield component is disclosed. This heat-shield component comprises a cooling-fluid return, a hot-gas wall to be cooled, an inlet duct for conducting a cooling fluid and an outlet duct for returning the cooling fluid. The inlet duct is directed towards the hot-gas wall and widens in a direction of the hot-gas wall.  
           [0010]    In WO 99/47874 A1 to Becker at al. a wall segment for a combustion chamber is described which is exposed to a hot combustion gas. The wall segment has a metal support structure and a heat protection element secured thereon. The metal support structure is provided, at least partially covered with a thin heat resistant separating layer. The separating layer is arranged between the metal support structure and the heat protection element. The heat protection element is in addition cooled by cooling gas.  
           [0011]    U.S. Pat. No. 5,823,741 to Predmore at al. describes a gas turbine plant, in which components of a nozzle structure are sealed through a seal joint including a sealing member for sealing segmented components of a gas turbine engine. The seal joint is spaced from the gas path to provide more effective cooling. The segments include radial extension flanges spacing the seal joint from the gas path. For the cooling of the segmented components cooling arrangements are shown to provide for open or closed circuit impingement or convection cooling plus film cooling.  
         SUMMARY OF THE INVENTION  
         [0012]    It is an object of the invention to provide a coolable segment for a turbomachinery to be exposed to a hot fluid with enhanced cooling features. It is a further object of the invention to provide a combustion turbine with an enhanced cooling of segments being exposed to a hot fluid which operates the combustion turbine.  
           [0013]    With the forgoing and other objects in view there is provided in accordance with the invention, a coolable segment for a turbomachinery, which turbomachinery is operated with a hot fluid. The segment comprises a cooling wall extending in an axial direction and in a circumferential direction orthogonal to said axial direction and a hot fluid surface to be exposed to said hot fluid. Between said cooling wall and said hot fluid surface a cooling structure permeable to cooling fluid and providing cooling surfaces for cooling by heat transmission through radiation is foreseen.  
           [0014]    The invention takes into consideration the perception that in a turbomachinery having segments being exposed to high temperatures, those segments having wall structures with a wall thickness being higher than the preferred thickness for cooling purposes as to assure the requirements on mechanical strength of the segments. This takes into account that by given internal/external heat transmission coefficient and temperature of the hot fluid the temperature of the material, in particular of the cooling wall increases with increasing thickness of the wall. This leads on the one side to the effect that either the segment has to withstand a higher temperature, which would lead to a reduction in mechanical strength or lifetime. On the other side it would be necessary to provide more cooling fluid for adjusting the material temperature under a given threshold. Using more cooling fluid, in particular cooling air, would lead to a reduced overall efficiency of the combustion turbine as the cooling air is normally separated from the air, which is fed to the combustor. Therefore using more cooling air should be avoided.  
           [0015]    The invention overcomes this problem by introducing a cooling structure, which allows an additional cooling process based on heat transmission by radiation to contribute to the overall cooling process including cooling by convection. In a segment having a hot fluid surface being exposed to a hot fluid and inner surfaces in a cooling structure at a lower temperature heat radiation is emitted from one surface to other surfaces arranged in the neighbourhood. As long as opposing surfaces have almost the same temperature no temperature change in the segment occurs by emitting and receiving heat radiation. Introducing a cooling structure in which neighbouring surfaces are kept on a lower temperature an additional heat transfer from the hot fluid surface being exposed to the hot fluid into the segment directed towards the cooling wall can be obtained. The amount of heat which can be transferred is proportional to the difference of temperatures to the power four (T Wall   4 −T surfaces   4 ). This implicates that the amount of heat which can be transferred through radiation not only depends on the temperature difference between neighbouring surfaces but also on the actual temperature of the surfaces itself. So the cooling process by heat radiation can significantly increase the overall cooling efficiency by adding to the other cooling processes like impingement cooling and/or convective cooling. The cooling structure provides “cold” cooling surfaces in the neighbourhood of the hot fluid surface to be exposed to the hot fluid for using the high potential of the cooling by heat radiation.  
           [0016]    In accordance with another feature the cooling structure comprises a netting, in particular a wire netting. The netting increases the internal heat transmission. The netting may fill a cavity or a chamber to which the cooling fluid is fed so that in addition to the cooling of the inner surface of the cooling wall a cooling by heat radiation throughout the whole cooling channel or chamber can be obtained. The cooling structure in form of the netting provides a number of additional cooling surfaces, namely the surfaces of the wires or fibres, which receive and emit heat radiation from or to other surfaces. So the cooling surfaces in the vicinity of the hot fluid surface receive heat by radiation and retransmit the heat to other colder cooling surfaces of the netting. So by successive heat transmission by radiation from wire to wire a flow of heat throughout the netting is directed away from the hot fluid surface to the cooling wall. This intensive cooling of the hit fluid surface by virtue of the cooling surfaces of the netting leads to an enlarged temperature difference between the hot fluid surface and the cooling wall. The cooling fluid further contributes to the cooling process by flowing though the permeable netting and absorbing heat when passing along the wires.  
           [0017]    In accordance with a further feature the cooling structure comprises a porous material. The porous material also provides many cooling surfaces capable to receive and transmit heat via radiation and so leading to a flow of heat from the hot fluid surface to the cooling wall. Due to the porosity cooling fluid can flow through the porous material and so also provides a convective cooling. The amount of porosity is adjusted to the cooling fluid used, in particular cooling air, the expected temperature of the hot fluid surface and the cooling wall temperature as well as on the flow velocity of the cooling fluid and the amount of cooling fluid which passes through the porous material per time and others relevant parameters.  
           [0018]    In accordance with an added feature the porous material of the cooling structure is manufactured by casting and leaving holes for forming the porosity in the casted material. Those holes forming the porosity can be obtained by using different methods, in particular by using distinct small kernels which after the casting of the cooling structure are removed, so that the casted cooling structure is permeable for cooling fluid. The porous cooling structure may be in mechanical contact either with the cooling wall and/or the hot fluid surface, which itself can be part of a hot fluid wall. This leads to a thermal connection between the cooling wall and the porous structure and/or the hot fluid surface and the cooling structure so that a direct thermal connection between the wall and hot fluid surface can be obtained which leads to an improved convective cooling. The cooling structure itself by being connected to the hot fluid surface functions as fins or rips which also improves the convective cooling.  
           [0019]    The permeability for cooling fluid of the netting and the porosity of the porous material may be adjusted in advance according to the expected temperature and other constraints within the turbomachinery. By choosing a cooling structure for a preferred operation condition of the turbomachinery it has to be considered that with decreasing mass density, e.g. increasing porosity, the cooling by heat radiation decreases too, as there are less cooling surfaces available for receiving and emitting heat radiation. On the other side with increasing mass density the pressure loss of the cooling fluid flowing through the cooling structure increases so that the amount of cooling fluid, in particular cooling air, flowing through the cooling structure is reduced. In this case a gain on improvement of cooling efficiency is reduced due to a greater demand for cooling fluid to flow through the cooling structure. Within these two extremes there is a range which allows an efficient extra cooling due to heat radiation depending on the temperature within the turbomachinery. On a theoretical basis the highest cooling efficiency due to heat radiation is achieved with a cooling structure having such a porosity/permeability that the heat emitted by the hotter surface is exactly absorbed by the colder surface. Preferably the heat emitting area (surfaces) per volume unit of the cooling structure is made as large as possible. This can be expressed in terms of the coefficient k t  of extinction for absorbing radiation divided by the product of heat transmitting area per volume (A v ) and heat transition coefficient (α) is as little as possible (k t /(αA v  is small).  
           [0020]    In accordance with an additional feature the hot fluid surface is formed by a hot fluid wall. Preferably between this hot fluid wall and the cooling wall a cavity, a channel or in general a space is formed which is at least partially filled with a cooling structure. Furthermore it is possible that, when using a porous material for the cooling structure the hot fluid surface itself may form a portion of the porous material being exposed to the hot fluid. The space formed between hot fluid wall and the cooling wall can be filled in different ways and to different degrees with a cooling structure. Furthermore two or more distinct cooling structures can be arranged, in particular with distinct permeability for cooling fluid or with distinct porosity. It is further possible that between the hot fluid wall and the cooling wall through channel sidewalls or chamber sidewalls a number of distinct chambers or channels can be formed which may be filled with different cooling structures or even some of the chambers or channels do not even need to have a cooling structure. So a variety of possibilities for adjusting the cooling capacity and efficiency of the coolable segment can be obtained.  
           [0021]    In accordance with yet another feature the hot fluid wall is covered with a protective layer, in particular a thermal barrier layer and/or a corrosion protective layer. Applying a protective layer on the hot fluid wall may reduce the necessity and the amount of cooling for the segment as well as increase the lifetime of the segment. A corrosion or erosion protective layer furthermore protects the hot fluid wall of being mechanically or chemically destroyed or of being altered in its material composition due to corrosion or other chemical effects. This also leads to an improved lifetime of the coolable segment. Applying protective layers to the components of a combustion turbine is well known for those persons skilled and active in the art. Thermal barrier layers may be preferably made of ceramic materials like zirconia partially stabilised with yttria, alumina, or the like. Corrosion and erosion protective layers may be made of materials widely known as MCrAlY layers, aluminides or others. The protective layer may also comprise two or three different layers. Also an adhesion or bonding layer may be provided for bonding a ceramic layer to the hot fluid wall.  
           [0022]    In accordance with yet a further feature, the cooling structure comprises a heat conducting material, in particular a metal or a heat conducting ceramic. A preferable heat conducting ceramic may be a silicon carbide (SiC). Silicon Carbide has good heat conductivity and also the ability to withstand high temperature conditions. As suitable metals all those metals can be used which withstand temperatures occurring in the turbomachinery. Preferably for providing a cooling structure comprising a netting such metals are used which are easy to manufacture as wires or fibres. For providing a cooling structure with a porous cast material preferably those metals are chosen which are easy to cast.  
           [0023]    In accordance with yet an added feature the cooling structure is connected to the cooling wall to allow heat transfer from the cooling structure into the cooling wall. The cooling structure, in particular a netting is welded or braised to the cooling wall. A cooling structure comprising a cast porous material is preferably casted together with the cooling wall in one manufacturing step. A netting braised to the cooling wall serves as an additional cooling fin or cooling rip and so not only contributes to a cooling by heat radiation but also to a convective cooling. Unlike a usual cooling fin the netting builds up a new boundary layer which shows a high heat transition. Furthermore compared to a usual cooling fin the heat transition may be obtained throughout the whole space between the hot fluid surface and the cooling wall.  
           [0024]    In accordance with yet an additional feature at least two cooling channels are formed between the cooling wall and the hot fluid surface, allowing cooling fluid to flow along the axial direction wherein at least one cooling channel comprises the cooling structure. The at least two cooling channels, which are axial or longitudinal cooling channels providing a flow of cooling fluid in the same direction as the hot fluid expanding in the turbomachinery can be obtained by introducing longitudinal sidewalls in the space between the hot fluid surface and the cooling wall. These axial channels are simple and inexpensive to manufacture. Using those cooling channels leads to an effective additional cooling by radiation in particular for temperatures, up to which the cooling fluid can absorb sufficient heat by convective cooling also at the end of the cooling channel.  
           [0025]    In accordance with a concomitant feature the cooling segment comprises at least two cooling chambers formed between the cooling wall and the hot fluid surface, allowing cooling fluid to flow from the cooling wall to the hot fluid surface, i.e. almost perpendicular to the cooling wall. The cooling chamber maybe formed as a cooling channel extending in the circumferential direction or having a more or less square cross-section. The cooling fluid in the cooling chamber is more or less directly directed from the cooling wall to the hot fluid surface and not along the axial direction which means that it flows from the cooling wall to the hot fluid surface. So the distance the cooling fluid travels from the cooling wall to the hot fluid surface is sufficient short so that the cooling fluid has a low temperature and can absorb heat whilst travelling to the hot fluid surface for all relevant temperatures achieved within a turbomachinery. These temperatures can be up to 1300° C. or even more. Having two or more cooling chambers it is possible to supply cooling fluid with a low temperature all over the segment to the cooling chambers. So a high cooling efficiency is obtained with a small amount of cooling fluid needed. Furthermore the problem of heating up the cooling fluid is avoided, which may occur when the cooling fluid travels a long distance in the axial direction. So in case of particular high temperatures a flow of the cooling fluid perpendicular to the cooling wall instead of axial direction can be more appropriate.  
           [0026]    Providing a cooling chamber with an almost square cross-section leads to a space between the cooling wall and the hot fluid surface, which is almost a cube formed by sidewalls in the circumferential direction and the axial direction. The temperature in the cooling structure increases from the cooling wall to the hot gas surface, wherein the increase is almost continuous. Furthermore the temperature of the cooling fluid travelling from the cooling wall to the hot fluid surface increases, in particular also continuously. So between the cooling structure and the cooling fluid in any location between the cooling wall and the hot gas surface a temperature difference exists which is almost constant. This leads to a high amount of convective cooling throughout the cooling structure. Having a number of cooling chambers for a perpendicular flow of the cooling fluid and/or cooling channels for axial flow of the cooling fluid the cooling efficiency can be adjusted to the operating conditions of the turbine machinery by choosing a cooling structure having a certain permeability for cooling fluid or porosity. Furthermore the amount of cooling fluid to flow per second through the channels or chambers can be locally adjusted to the local heat conditions of the channels or chambers and the hot fluid surface. By using cooling chambers with perpendicular flow of the cooling fluid parameters like porosity or amount of cooling fluid can be chosen within wide range without being restricted to the thermal conditions existing at the most endangered portion of the segment.  
           [0027]    In according with again another feature the coolable segment comprises a cooling fluid supply passage through the cooling wall for cooling fluid to enter the cooling structure. The cooling fluid supply passage maybe a bore in the cooling wall. According to the geometry of the space between the cooling wall and the hot fluid surface, in particular formed as an axial cooling channel, a circumferential cooling channels or cube like cooling chamber number and location of the fluid supply passages can be chosen.  
           [0028]    In accordance with again a further feature the cooling fluid supply passage acts as a throstle performing a higher pressure loss than within the cooling structure. As the pressure loss of the cooling fluid in the cooling structure increases with higher temperatures of the cooling fluid due to the absorption of heat from the cooling structure, this may lead to a situation that in the hotter portions of the cooling structure through which cooling fluid needs to flow for cooling purposes less cooling fluid flows than through those portions which are colder. This situation can be avoided by shifting the smallest fluid cross section at the entrance of the cooling structure so that the pressure loss which dominates the throughflow of the cooling fluid lies at a location with constant cooling temperature. So within the cooling structure a blocking of cooling passages can be avoided and an almost homogeneous distribution of cooling fluid throughout the cooling structure regardless of hotter or colder portions can be obtained. Furthermore a throstle in a fluid supply passage allows an adjustment of the amount of cooling fluid passing through the cooling structure to the pressure imposed by the hot fluid on the hot fluid surface. This is for example of interest in a combustion turbine wherein the coolable segment is a guide ring, as due to the relative short length of the guide ring relatively high differences in the amount of pressure imposed by the hot fluid exist over the guide ring.  
           [0029]    In accordance with again an added feature cooling fluid supply passages are distributed along the axial direction. In case of cooling channels allowing cooling fluid to flow in the axial direction fresh cooling fluid with a low temperature can be introduced in the cooling channel via the cooling fluid supply passages so that the cooling fluid has enough capacity to absorb heat either by convective heat transition or by heat radiation within all locations of the axial channel. In case of a number of circumferential cooling channels or cube like cooling chambers arranged along the axial direction to each of these cooling channels or cooling chambers cooling fluid can be supplied through at least one supply passage.  
           [0030]    In accordance with again an additional feature the hot fluid surface comprises at least one aperture along the axial direction for cooling fluid to exit the cooling structure. In the case of cooling channels extending along the axial direction the apertures or the at least one aperture is located in the area of a downstream end of the cooling channel. So cooling fluid may flow from an upstream end of the cooling channel towards the downstream end whilst cooling the coolable segment, in particular the hot fluid surface all along this way. In case of cooling chambers, in particular cooling channels extending in a circumferential direction or cube like cooling chambers, at least one aperture, preferably more than two apertures are located in the circumferential direction or the cross section of the cooling chamber. With a number of cooling chambers arranged in the axial direction also a number of apertures are assigned to different cooling chambers and distributed along the axial direction, which allows cooling fluid to exit all over the hot fluid surface. This leads to an improved film cooling of the hot fluid surface and gives the opportunity to arrange cooling chambers in different patterns between the hot fluid surface and the wall for achieving a high cooling efficiency.  
           [0031]    Those chambers in particular formed between side walls directed in the circumferential direction and side walls extending in the axial direction, give the opportunity to provide cooling fluid through a number of cooling fluid supply passages. A cooling fluid supply passage is in particular a supply bore in the cooling wall. Furthermore a number of cooling fluid exits may be arranged in the hot fluid surface for cooling fluid to exit the cooling structure. So a predefined perpendicular flow of cooling fluid leads to an improved cooling efficiency. Arranging chambers with circumferential and axial sidewalls also increases the surface area for heat transmission via radiation and so further improves the cooling efficiency.  
           [0032]    Instead of having a number of exits in the hot fluid surface, which may be made by a number of bores or holes in a hot fluid wall the hot fluid surface itself could be the surface of the porous material of the cooling structure or the surface of a netting exposed to the hot fluid. In this case the hot fluid surface is provided by the cooling structure itself. So the cooling fluid does not leave the cooling structure through a limited number of discrete exits, in particular bores but through a plurality of openings or spaces within the cooling structure itself which all have different size, different opening angles etc. This further reduces the formation of hot spots along the hot fluid surface and allows by performing the effusion cooling a very high cooling efficiency with very little consumption of cooling fluid. Due to the cooling structure with a permeability and porosity which can be chosen in a wide range it is also possible for each of the cooling chambers, which may form more a less a cube, to adjust the amount of cooling fluid to flow through the chamber with respect to the local pressure of the hot fluid acting on the hot fluid surface.  
           [0033]    It is also possible to arrange circumferentially extending side walls and axial extending side walls so that cooling chambers allowing a flow of cooling fluid perpendicular to the cooling wall arranged in the neighbourhood of cooling channels allowing cooling fluid to flow in the axial direction between the wall and the hot fluid surface. For those cooling chambers allowing axial flow of cooling fluid two or more cooling supply openings in the wall can be arranged in the axial direction for introducing new cooling fluid downstream the first supply opening so as to ensure that the temperature of the cooling fluid in the cooling chamber is always sufficient low. The locations, distribution and number of cooling chambers and cooling channels can be determined in advance by those skilled and active in the technical field according to the operating conditions of the turbine machinery and the cooling effect which has to be obtained  
           [0034]    In accordance with still another feature the coolable segment comprises a partition for guiding the flow of cooling fluid in one direction and back in the opposite direction for increasing the travel period of the cooling fluid before exiting the segment. Preferably the partition extends in the axial direction. The partition separates the space between the cooling wall and the hot fluid surface in two spaces one defined between the cooling wall and the partition and the other defined between the partition and the hot fluid surface. In this case the cooling fluid may travel in the first portion in the axial direction downstream and then in the second portion back upstream. It is also possible to have more than one partition dividing the space between cooling wall and hot fluid surface in more than two portions so that the cooling fluid is slowly heated up. This even leads to higher thermal separation between the colder cooling wall and the hotter hot fluid surface. This can be under certain conditions desirable.  
           [0035]    In accordance with still an added feature the cool able segment is an element of a combustion turbine, in particular a heat shield element for a combustion chamber, a shroud portion of a turbine vane or a guide ring segment for forming a wall portion opposing rotating turbine blades. Those parts of the combustion turbine are exposed to high temperatures for example to up to and over the 1300° C. and therefore the cooling structure as described above assures an efficient cooling of these components and temperature is well kept under critical temperatures of the materials used for these components.  
           [0036]    In accordance with still an additional feature the coolable segment is arranged in a combustion turbine, in particular a turbine for a jet engine or in a stationary gas turbine, which stationary gas turbine may serve for the generation of electrical power. The coolable segment may also be arranged in a combustion turbine used for submarines and earthbound vehicles, like cars or trucks.  
           [0037]    In accordance with another object of the invention it is provided a combustion turbine comprising a hot gas chamber having a hot gas flow region. The turbine further comprises a wall structure surrounding the hot gas flow region and having a coolable segment with a cooling wall extending in an axial direction and in a circumferential direction orthogonal to the axial direction. The coolable segment further has a hot fluid surface to be exposed to the hot gas, wherein between the cooling wall and the hot fluid surface a cooling structure providing cooling surfaces for cooling by heat transmission through radiation is arranged, which cooling structure is permeable to cooling fluid. For the cooling structure as well as for the cooling process for cooling the combustion turbine the same advantages hold as described above. Preferably the cooling segment further comprises at least one cooling fluid supply passage through the cooling wall for cooling fluid to enter the cooling structure, wherein the cooling fluid supply passages are arranged in the axial direction. Furthermore apertures or openings in the hot fluid surface for cooling fluid to exit the cooling structure along the axial direction are foreseen.  
           [0038]    Although the invention is illustrated and described herein as embodied in a coolable segment and in a combustion turbine, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of protection of the claims.  
           [0039]    The construction of the coolable segment and the combustion turbine of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in conjunction with the accompanying drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0040]    [0040]FIG. 1 is a fragmentary, diagrammatic, longitudinal, sectional view of a combustion turbine;  
         [0041]    [0041]FIG. 2 is an enlarged fragmentary, cross-sectional view of a guide ring along the main axis of a combustion turbine;  
         [0042]    [0042]FIG. 3 shows a fragmentary view of the guide ring according to FIG. 2 along line III-III;  
         [0043]    [0043]FIG. 4 is an enlarged fragmentary, cross-sectional view of a another example of a guide ring along a main axis of a combustion turbine;  
         [0044]    [0044]FIG. 5 is a fragmentary cross-sectional view along line V-V of the guide ring of FIG. 4;  
         [0045]    [0045]FIG. 6 is a fragmentary, cross-sectional view of a further example of a guide ring in a combustion turbine;  
         [0046]    [0046]FIG. 7 is a fragmentary perspective view of an additional example of a guide ring of a combustion turbine;  
         [0047]    [0047]FIG. 8 is an enlarged fragmentary, cross-sectional view of the guide ring according to FIG. 7;  
         [0048]    [0048]FIG. 9 is a plot diagram showing schematically the temperature profile within the guide ring according to FIG. 8. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0049]    In the drawing throughout the figures like reference numerals have the same meaning.  
         [0050]    Referring now to the figures of the drawings in detail and first, in particular, to FIG. 1 thereof, there is shown in a cross-sectional view a stationary combustion turbine  20  as a turbomachinery extending along a main axis  21 . The combustion turbine  20  comprises a compressor  22  for compressing air  33  which serves for the combustion process, a annular combustion chamber  23  having a number of burners  34  for a liquid or gaseous fuel and a turbine section  24 , which turbine section  24  drives the compressor  22  and a not shown generator for generating electrical power. The combustion turbine  20  further comprises a turbine rotor  31  on which in the turbine section  24  four rows of rotating blades  26  being spaced apart along the main axis  21 . The turbine section  24  further comprises an inner turbine housing  28  to which four rows of guide blades  25  (vanes) are attached in a circumferential direction. The first row of guide blades  25  is located upstream of the first row of rotating blades  26  and between the remaining rows of rotating blades  26  one row of guide blades  25  is arranged. A pair of adjacent rows of guide blades  25  and rotating blades  26  is called as turbine stage. Each of the guide blades  25  has a shroud  27 , which is attached to the inner turbine housing  28 . Opposite to each row of rotating blades  26  guide rings  32  are arranged in a circumferential direction and attached to the inner turbine housing  28 . The guide rings  32  and the shrouds  27  attached to the inner turbine housing  28  form a hot gas channel  30  of the turbine section  24 .  
         [0051]    During the operation of the combustion turbine  20  atmospheric air  33  is fed to the compressor  22  and compressed therein. A small portion of this compressed air  33  (&lt;5%) is branched of out of the compressor  22  and serves as cooling fluid, e.g. cooling air  5 . The remaining major portion of the compressed air  33  is fed to the combustion chamber  23 . In the combustion chamber  23  through the burner  34  a not shown fuel is burned with the compressed air  33  to a high-pressure hot fluid  29  (hot gas). This hot gas  29  flows through the hot gas channel  30  thereby passing through the rows of guide blades  25 , which serves as nozzles to direct the flow of hot gas  29  in a predefined way to the rotating blades  26  thereby forcing the rotating plates  26  to rotate. The hot gas  29  also flows along the shroud  27  and guide rings  32  arranged in the turbine section  24 . So each shroud  27  and each guide ring  32  are elements of the turbomachinery  20  which are exposed to a high thermal load, in particular are exposed to temperatures up to over 1200° C. As will be explained in more detail with respect to FIG. 2, a guide ring  32  is a coolable segment  1  which has a hot fluid surface  3  being exposed to the hot gas  29 . The guide ring  32  as coolable segment  1  is cooled by cooling fluid  5  which is air branched of from the flow of air  33  passing through the compressor  22 . The combustion chamber  23  and the turbine section  24  including the hot gas channel  30  each represent a hot-gas flow region. Each hot-gas flow region is surrounded by a respective wall structure, e.g. the inner turbine housing or the combustion chamber wall  39 .  
         [0052]    [0052]FIG. 2 shows an enlarged cross sectional view of a guide ring  32  as coolable segment  1  along the main axis  21  of the combustion turbine  20 . The guide ring  32  has a wall-structure  7  with hook like end portions  8  for attaching the guide ring  32  to the inner turbine housing  28 . It further comprises a cooling wall  2  which gives the guide ring  32  a mechanical stability and serves for conducting heat away from the hot gas channel  30 . The guide ring  32  further comprises a hot fluid surface  3  which is exposed to the hot gas  29 . The hot fluid surface  3  is the surface of a structure made of a hot fluid wall  9  which is covered by a protective layer  10 . The protective layer  10  itself may consist of two or more layers one of which being exposed to the hot gas  29  is a thermal barrier layer, in particular made of a ceramic material like zirconia partial stabilised with yttria. One of the other layers can be an anchoring or an adhesion layer which serves for binding the ceramic layer to the hot fluid wall  9  and which is preferably made of the suitable heat resistant metal. Between the hot fluid surface  3  and the cooling wall  2  a porous cooling structure  4  is arranged having cooling surfaces  6  for emitting and receiving heat radiation. These porous cooling structures  4  may be casted together with the wall structure  7  of the coolable segment  1 . Due to the porosity of the cooling structure  4  cooling fluid  5 , in particular air, can flow from a upstream end region  11  of the cooling structure  4  mainly in an axial direction  37  to a downstream end region  12  of the cooling structure  4 . In the upstream end region  111  of the wall structure  7 , in particular in the cooling wall  2  at least one fluid supply passage  16 , in particular a bore, allows cooling fluid  5  to enter the cooling structure  4 . At the down stream end region  12  at least one aperture  13  in the hot fluid wall  9 , i.e. in the hot fluid surface  3 , allows cooling fluid  5  to exit the cooling structure  4  and to flow into the hot gas channel  30  thereby mixing with the hot gas  29 . The aperture  13  is preferably inclined to the hot fluid wall  9  by a small angle to achieve a film cooling when the cooling fluid  5  exits the cooling structure  4 .  
         [0053]    The porous cooling structure  4  may be casted together with the wall structure  7  using the same heat conducting material, in particular a metal, for example heat resisting steel. It may also be manufactured in a different way and using a different material like a heat conducting ceramic like Silicon carbide. The cooling structure  4  is directly connected to the cooling wall  2  as well as to the hot fluid wall  9  so that by means of heat conduction the hot fluid surface  3  is cooled. Furthermore, due to the pores within the cooling structure  4  which form the cooling surfaces  6  between which heat can be transmitted from a hotter surface via heat radiation to a colder surface the transfer of heat is directed from the hot fluid surface  3  to the cooling wall  2 . So the porous cooling structure  4  provides two cooling processes for cooling the hot fluid surface  3  namely: connective cooling and cooling by heat transmission through radiation from a hotter surface to a colder surface within the porous cooling structure  4 . The porous cooling structure  4  itself may serve to improve the mechanical stability of the coolable segment  1 , e.g. each guide ring  32 , so that the hot fluid wall  9  may be much thinner than the cooling wall  2 .  
         [0054]    For improving the mechanical stability of the guide ring  32  axial side walls  14  extending in the direction of the main axis  21  are arranged between the hot fluid wall  9  and the cooling wall  2  (see FIG. 3). Those sidewalls  14  may extend over the whole length of the guide ring  32  in the direction of the main axis  21  thereby providing at least two cooling channels  15  through which cooling fluid  5  flows in the axial direction  37  from the upstream end region  11  to the downstream end region  12  in the cooling structure  4 .  
         [0055]    [0055]FIG. 4 shows an enlarged cross section of view of another embodiment of a coolable segment  1  in form of a guide ring  32 . The guide ring  32  according to FIG. 4 has many features quite similar to the guide ring  32  described above with respect to FIG. 2. It is therefore referred to this portion of the description for these features. The guide ring  32  shown in FIG. 4 differs from that guide ring  32  of FIG. 2 in particular with respect to the cooling structure  4  between the hot fluid wall  9  and the cooling wall  2 . A space  19  is formed in which the cooling fluid  5  flows from the up stream end region  11  to the down stream end region  12 . This space  19  is filled with a cooling structure  4  which is a wire netting consisting of metallic fibres. The space  19  is closed by access covers  17  at the upstream end region  11  as well as at the downstream end region  12 . The access covers  17  can be removed during maintenance of the combustion turbine  20  giving the possibility to replace the cooling structure  4 , in particular the wire netting by a new one during repair or maintenance of the combustion turbine  20 . The space  19  (see FIG. 5 which is a fragmentary cross section of view along line V-V of FIG. 4 of the guide ring  32 ) is divided by axial sidewalls  14  in a number of cooling channels  15  extending in the axial direction  37 . Each of these cooling channels  15  is filled with the cooling structure  4 , e.g. with the wire netting. The axial sidewalls  14  comprise cross-over holes  18  for allowing cooling fluid  5 , e.g. air, to flow from one cooling channel  15  to a neighbouring cooling channel  15 .  
         [0056]    As the hot fluid wall  9  do not need to distribute to mechanical stability of the guide ring  32  it is much thinner than the cooling wall  2 , whereby the cooling wall  2  gives the guide ring  32  a sufficient mechanical stability. The thin hot fluid wall  9  is mechanically supported by the axial sidewalls  14  so that it does not bend or deform more than a pre-determined amount. The axial sidewalls  14  furthermore act as cooling fins or cooling ribs which even increase the surface contributing to the cooling by transmitting heat radiation. They also ensure that in the unlikely event of a local failure of the hot fluid wall  9  the guide ring  32  is still cooled in the areas covered by the other cooling channels  15 .  
         [0057]    [0057]FIG. 6 shows a cross sectional view of a further embodiment of a guide ring  32  similar to those described and shown in FIG. 2 and FIG. 4. The guide ring  32  includes a partition  35  for guiding the flow of cooling fluid  5  in the axial direction  37  aligned to the main axis  21  of the turbine  20 . At the downstream end region  12  cooling fluid  5  is deflected and flows back along the axial direction  37  to the up stream end region  11 . There the cooling fluid  5  exits the space  19  and the cooling structure  4  through an aperture  13 . The partition  35  divides the space  19  in a subspace between the partition  35  and the cooling wall  2  and another subspace between the partition  35  and the hot fluid wall  9 . As discussed above the space  19  and so the subspace separated by the partition  35  may include cooling channels  15  which are separated by axial sidewalls  14 . By introducing the partition  35  the length of the flow path of the cooling fluid  5  in the cooling structure  4  can be increased so that the cooling fluid  5  is heated up slowly which leads to an even higher thermal separation between the hot fluid wall  9  and the cooling wall  2 .  
         [0058]    [0058]FIG. 7 shows a fragmentary and perspective view of a guide ring  32  extending along an axial direction  37 , which is almost parallel to the main axis  21  of the turbine  20 , and in a circumferential direction  36 . The guide ring  32  is with respect to many features similar to those described in FIGS. 2, 4 and  6  and with respect to those features in particular the wall structure  7 ,  8  of the cooling wall  2 , the hot fluid wall  9 , the protective layer  10  and the materials used for the permeable cooling structures  4  it is referred to the description of these figures. The space  19  between the hot fluid wall  9  and the cooling wall  2  of the guide ring  32  according to FIG. 7 is separated in a number of cooling chambers  38 . The cooling chamber  38  are formed by circumferential sidewalls  40  extending in the circumferential direction  36  and by axial sidewalls  14  extending in the axial direction  37 . In all of the cooling chambers  38  a cooling structure  4  is foreseen between the hot fluid wall  9  and the cooling wall  2 . For the sake clarity only in one cooling chamber  38  the cooling structure  4  is shown in FIG. 7. The cooling chambers  38  located near the up stream end region  11  have one cooling fluid supply passage  16  in the axial direction  37  and one or more cooling fluid supply passages  16  in the circumferential direction  36 . These cooling chamber  38  also have apertures  13  for cooling fluid  5  to exit the cooling chamber  38  arranged in a row along the circumferential direction  36 . So in these cooling chambers  38  located near the up stream end region  11  the cooling fluid  5  flows almost in the axial direction  37  before exiting the cooling chamber  38 . The cooling chambers  38  arranged in the centre of the guide ring  32  with respect to the axial direction  37  and those arranged near the down stream end region  12  have a number of rows of cooling fluid supply passages  16  both in the axial direction  37  and in the circumferential direction  36 . They also have apertures  13  in the hot fluid wall  9  distributed in the circumferential direction  36  as well as in the axial direction  37 . The arrangement of cooling fluid supply passages  16  as well as apertures  13  leads to a flow of cooling fluid  5  directed perpendicular to the cooling wall  2  and to the hot fluid wall  9 . So in these cooling chambers  38  the temperature of the cooling fluid  5  is as low as possible, because cooling fluid  5  is supplied over the whole surface area of the cooling wall  2  and cooling fluid  5  after being heated up exits the cooling structure  4  all over the hot fluid surface  3 . This leads to a high cooling efficiency by using a low amount cooling fluid  5 . Furthermore, the apertures  13  are positioned off the cooling fluid supply passages  16  so that also an impingement cooling of the hot fluid wall  9  can be obtained.  
         [0059]    [0059]FIG. 8 shows an enlarged view of a cooling chamber  38  of the guide ring  32  of FIG. 7. The apertures  13  are positioned with an offset with respect to the cooling fluid supply passages  16 . Cooling fluid  5  flows in a direction perpendicular to the cooling wall  2  through the porous cooling structure  4 . Due to the porosity of the cooling structure  4  a number of cooling surfaces  6  are formed from which heat is transferred by radiation to other cooling surfaces  6 .  
         [0060]    In FIG. 9 the temperature T over the width W of the coolable segment  1  e.g. the guide ring  32  is shown. The temperature of both the cooling fluid T C  and the temperature T S  of the cooling structure  4  are lowest at the cooling wall  2 . The temperature difference ΔT between the temperature T S  of the cooling structure  4  and the temperature T C  of the cooling fluid  5  is almost constant over the width W of the cooling structure  4 . This is due to the fact that the cooling fluid  5  as well as the cooling structure  4  have a temperature, which increases from the cooling wall  2  to the hot fluid surface  3 .  
         [0061]    List of Reference Numerals  
         [0062]    [0062] 1  coolable segment  
         [0063]    [0063] 2  wall  
         [0064]    [0064] 3  hot fluid surface  
         [0065]    [0065] 4  cooling structure  
         [0066]    [0066] 5  cooling fluid  
         [0067]    [0067] 6  cooling surfaces  
         [0068]    [0068] 7  wall structure  
         [0069]    [0069] 8  hook-like end-portion  
         [0070]    [0070] 9  hot fluid wall  
         [0071]    [0071] 10  protective layer  
         [0072]    [0072] 11  upstream end region  
         [0073]    [0073] 12  down stream end region  
         [0074]    [0074] 13  aperture  
         [0075]    [0075] 14  axial sidewall  
         [0076]    [0076] 15  cooling channel  
         [0077]    [0077] 16  supply passage  
         [0078]    [0078] 17  access cover  
         [0079]    [0079] 18  cross-over holes  
         [0080]    [0080] 19  space between cooling wall and hot gas wall  
         [0081]    [0081] 20  turbomachinery, combustion turbine  
         [0082]    [0082] 21  main axis of turbine  
         [0083]    [0083] 22  compressor  
         [0084]    [0084] 23  combustion chamber  
         [0085]    [0085] 24  turbine section  
         [0086]    [0086] 25  guide blades, vanes  
         [0087]    [0087] 26  rotating blades  
         [0088]    [0088] 27  shroud of vane  
         [0089]    [0089] 28  inner turbine housing  
         [0090]    [0090] 29  hot gas, hot fluid  
         [0091]    [0091] 30  hot gas channel of turbine section  
         [0092]    [0092] 31  turbine rotor  
         [0093]    [0093] 32  guide ring  
         [0094]    [0094] 33  air  
         [0095]    [0095] 34  burner  
         [0096]    [0096] 35  partition  
         [0097]    [0097] 36  circumferential direction  
         [0098]    [0098] 37  axial direction  
         [0099]    [0099] 38  cooling chamber  
         [0100]    [0100] 39  combustion chamber wall  
         [0101]    [0101] 40  circumferential sidewall  
         [0102]    W width of segment  
         [0103]    T temperature along width  
         [0104]    T C  temperature of cooling fluid  
         [0105]    T S  temperature of cooling structure