Abstract:
A gas turbine and a method for operating a gas turbine includes a combustion chamber, a turbine having rows of blades, an air compressor, a combustion-air line for feeding compressed air into the combustion chamber, a fuel supply unit, at least one fuel line, at least one cooling-air line. Some of the blades have an interior defining cavities whereby first cavities direct at least a portion of fuel to the combustion chamber through the first cavities at least in a section of the blades, thereby preheating the fuel before being introduced into the combustion chamber. The system defined by the first cavities and the section of the blades is closed relative to an interior of the gas turbine. Second cavities fluidically connect to the air compressor and receive at least a portion of the cooling air for cooling the blades.

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
       [0001]    This application is a continuation of copending International Application No. PCT/DE99/02985, filed Sep. 17, 1999, which designated the United States. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    Field of the Invention  
           [0003]    The invention related to a method of operating a gas turbine having a combustion chamber, a turbine including at least two rows of blades, and an air compressor. Compressed air and fuel are fed to the combustion chamber and cooling air is fed to the turbine. The invention also relates to a gas turbine working, in particular, according to the method.  
           [0004]    The invention relates, in particular, to a gas turbine that works in combination with a steam turbine such that exhaust gas flowing out of the gas turbine is utilized for providing high-pressure steam expanded in the steam turbine while performing mechanical work. Such combinations of gas turbines and steam turbines are realized, for example, in combined-cycle power plants; they permit the generation of electrical power with efficiencies of 50% and more.  
           [0005]    A gas turbine is generally a combination of a compressor for air, at least one combustion chamber for burning a fuel with the air compressed by the compressor, and a turbine in the actual sense, in which the hot flue gas produced in the combustion chamber is expanded to perform work. As a rule, the compressor and the turbine are mechanically coupled to one another. The air compressor is frequently a turbocompressor.  
           [0006]    During operation of a gas turbine, the blades of the turbine are normally cooled. Thus, a large number of documents disclose providing an open cooling system for forming film cooling with cooling air, the open cooling system directing the cooling air used for the cooling through the blades of the turbine. A portion of the compressed air is used as cooling air, which then discharges in the turbine from open blades and is admixed with the flue-gas flow. As a result of the outflow of the cooling air from guide and/or moving blades, the open air cooling of the blades leads to a reduction in the temperature of the flue gases inside the turbine and downstream of the turbine on the outflow side. Such a reduction in temperature reduces the efficiency of the gas turbine.  
           [0007]    In addition, the thermodynamic efficiency of a combination of a gas turbine and a steam turbine is not only determined by the efficiency of the gas or steam turbine, but, to a great extent, is also dependent on the thermodynamic coupling of the two machines. An essential determining factor is the temperature of the exhaust gas flowing out of the gas turbine.  
           [0008]    To achieve a high efficiency, the prior art includes heating the compressed air by indirect heat exchange with the exhaust gas from the turbine.  
           [0009]    To increase the exhaust-gas temperature, a concept for a guide blade of a gas turbine is described in German Published, Non-Prosecuted Patent Application DE 43 30 613 A1. The concept disclosed therein directs a small fraction of fuel directly to the turbine in an open cooling system with the cooling air. As a result, interheating of the exhaust gas is achieved without expensive measures in terms of equipment, which leads to an increase in the efficiency.  
           [0010]    Cooling concepts that direct cooling fluid in a closed system instead of in an open system likewise increase the efficiency.  
           [0011]    For example, German Published, Non-Prosecuted Patent Application DE 196 21 385 A1 discloses directing a first substance for cooling the guide blades in a closed cooling system in a guide blade and a moving blade. The first substance endothermically reacts with a second substance. The energy required for an endothermic reaction can preferably be effected by the absorption of heat from the hot flue-gas flow. The reaction product is then fed to the combustion chamber. The chemically bonded reaction energy and the heat absorbed by the substances are released in the combustion process. The release reduces the fuel consumption and, consequently, increases the efficiency of the gas turbine.  
         SUMMARY OF THE INVENTION  
         [0012]    It is accordingly an object of the invention to provide a fuel preheating in a gas turbine that overcomes the hereinafore-mentioned disadvantages of the heretofore-known devices and methods of this general type and that provides a fuel preheating method that achieves a good cooling of the turbine blades and an increased efficiency, and a gas turbine suitable, in particular, for carrying out the method, the turbine having a high efficiency.  
           [0013]    With the foregoing and other objects in view, there is provided, in accordance with the invention, a method of operating a gas turbine, including the steps of providing a gas turbine having a combustion chamber, a turbine having at least two rows of blades, at least some of the blades having an interior defining first cavities and second cavities, and an air compressor, feeding compressed air and fuel to the combustion chamber, feeding cooling air to the turbine, directing at least a portion of fuel at least in a section of the blades through the first cavities and simultaneously preheating the portion of fuel before the portion of fuel is introduced into the combustion chamber, and directing cooling air fed to the turbine in a further section of the blades through the second cavities and discharging the cooling air at least partly at the blades.  
           [0014]    The objectives of the invention are achieved with the method according to the invention by virtue of the fact that at least one portion of the fuel, before it is introduced into the combustion chamber, flows in a section of the blades through cavities formed in the interior space of the blades and in the process is preheated simultaneously. The thermal energy that is, thus, absorbed by the fuel advantageously no longer needs to be dissipated through a cooling fluid, for example, cooling air. The cooling air that is, thus, saved reduces the work of the air compressor, which otherwise would have to be performed by the turbine. In addition, preheated fuel passes into the combustion chamber. Consequently, the efficiency of the gas turbine is increased.  
           [0015]    In accordance with another mode of the invention, the cavities formed in the blades and in which the fuel flows form a closed system relative to the interior of the gas turbine. The system ensures that the fuel no longer comes into contact with other flow media, such as, for example, a cooling fluid or the flue gas (action fluid). In particular, due to the closed system, uncontrolled combustion outside the combustion chamber is ruled out.  
           [0016]    In accordance with a further mode of the invention, a very simple embodiment is characterized by the fact that the fuel successively flows through a plurality of rows, in particular, through all the rows, of blades and is then fed to the combustion chamber.  
           [0017]    In accordance with an added mode of the invention, the fuel is fed separately, i.e., in separate flows, through a plurality of rows of blades and is then respectively fed separately or as a uniform flow to the combustion chamber. Such a fuel feed advantageously permits load-dependent control of the gas turbine.  
           [0018]    In accordance with an additional mode of the invention, the cooling air fed to the turbine advantageously flows in a further section of the blades through other cavities formed in the interior space of the blades. The cooling air discharges at least partly at the blades in a preferred manner such that an air film forms on the outer surface of the blades.  
           [0019]    In accordance with yet another mode of the invention, small fractions of fuel, which burn in the turbine, are preferably admixed with the cooling air to increase the temperature of the exhaust gas flowing out of the turbine.  
           [0020]    With the objects of the invention in view, there is also provided gas turbine, including a combustion chamber, a turbine having at least two rows of blades, at least some of the blades having an interior defining first cavities and second cavities, an air compressor, a combustion-air line for feeding compressed air into the combustion chamber, the combustion-air line fluidically connected to the air compressor and the combustion chamber, a supply unit for supplying fuel, at least one fuel line for feeding fuel into the combustion chamber, the at least one fuel line fluidically connected to the combustion chamber and to the supply unit, at least one cooling-air line for feeding cooling air into the turbine, the at least one cooling-air line fluidically connected to the turbine and to the air compressor, the first cavities fluidically connected to the combustion chamber and to the supply unit for directing at least a portion of fuel to the combustion chamber from the supply unit through the first cavities at least in a section of the blades and, thereby, preheating the portion of fuel before being introduced into the combustion chamber, a system defined by the first cavities and the section of the blades being closed relative to an interior of the gas turbine, and the second cavities fluidically connected to the air compressor and receiving at least a portion of the cooling air through the second cavities for cooling the blades.  
           [0021]    The gas turbine includes a combustion chamber, a turbine having at least two rows of blades, an air compressor, a combustion-air line for feeding compressed air, at least one fuel line for feeding fuel into the combustion chamber, and at least one cooling-air line for feeding cooling air into the turbine. The objectives of the invention are achieved in the gas turbine of the invention where at least a portion of the fuel is directed to the combustion chamber from a supply unit through cavities formed in the interior space of the blades and which, at least in a section of the blades, form a closed system relative to the interior of the gas turbine.  
           [0022]    In accordance with yet a further feature of the invention, the fuel is preferably fed successively through a plurality of rows, in particular, through all the rows, of blades to the combustion chamber.  
           [0023]    In accordance with a concomitant feature of the invention, alternatively, the fuel is preferably fed separately through a plurality of rows of blades and then respectively separately or as a uniform flow to the combustion chamber, a factor which, in particular, has an advantageous effect on the controllability of the gas turbine.  
           [0024]    The advantages achieved with the invention include, in particular, the fact that, by feeding fuel through cavities that are formed in the interior space of the blades and that form a closed system relative to the interior of the gas turbine, the fuel absorbs thermal energy which otherwise would have to be dissipated by a cooling fluid. Where the fuel consumption is reduced by heating the fuel on one hand, cooling air for the turbine is saved on the other hand. And, the work of the air compressor that otherwise would have to be performed by the turbine is reduced. Consequently, the efficiency of the gas turbine is increased. In addition, efficiency losses in the turbine due to mixing of hot action fluid with cooling air are reduced due to the fact that cooling air discharges at the blades only to a reduced extent.  
           [0025]    Other features that are considered as characteristic for the invention are set forth in the appended claims.  
           [0026]    Although the invention is illustrated and described herein as embodied in a fuel preheating in a gas turbine, it is, nevertheless, not intended to be limited to the details shown because various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.  
           [0027]    The construction and method of operation 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 connection with the accompanying drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINQS  
       [0028]    [0028]FIG. 1 is a block circuit diagram of a gas turbine according to the invention; and  
         [0029]    [0029]FIG. 2 is a cross-sectional view of a blade for the gas turbine according to FIG. 1. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0030]    In all the figures of the drawing, sub-features and integral parts that correspond to one another bear the same reference symbol in each case.  
         [0031]    Referring now to the figures of the drawings in detail and first, particularly to FIG. 1 thereof, there is shown a gas turbine  31 . The gas turbine includes a turbine  33  with an air compressor  34  coupled through a turbine shaft  35  and a generator  36 . The turbine also includes a combustion chamber  32  connected upstream of the turbine  33 . The air compressor  34  has an intake line  37  on the suction side and at least one cooling-air line  43  on the pressure side. The intake line  37  opens into the turbine  33 . In addition, the air compressor  34  has a combustion-air line  38  on the pressure side. The combustion-air line  38  opens into the combustion chamber  32 .  
         [0032]    For the fuel fraction to be preheated, a fuel line  40  leads from a supply unit  39  to the turbine  33 . Furthermore, a fuel line  41  for the preheated fuel  6  is connected to the turbine  33 . In addition, the turbine  33  has an exhaust-gas line  44 . A flue-gas line  45  connects the combustion chamber  32  to the turbine  33 . Furthermore, the combustion chamber  32  is also connected directly to the supply unit  39  through a fuel line  42 .  
         [0033]    The turbine  33  includes at least two rows  46 ,  47  of blades  1 , in particular, a guide wheel  46  and an impeller  47 . Cavities  20 ,  22 ,  22   a ,  23 ,  23   a  are formed in the interior  21  of the blades  1 . The cavities  20 ,  22 ,  22   a ,  23 ,  23   a  formed in the interior of the blades  1  form, at least in a section of the blades, a closed system relative to the interior of the gas turbine  31 . In a further section of the blades  1 , other cavities  25 ,  25   a  formed in the interior of the blades  1  form an open system.  
         [0034]    [0034]FIG. 2 illustrates the constructional and functional features in cross section of a preferred use of a blade  1  of a gas turbine  31 . The blade  1  extends along a main axis  19 . The blade  1  may be curved or twisted along the main axis  19  so that the cross section of the blade  1 , shown in FIG. 2, may vary over the main axis  19 . At its non-illustrated end, the blade  1  has a blade root for fastening the blade  1 . The blade  1  has a wall structure  2  having an inflow region  8 , an outflow region  9 , a pressure side  10 , and a suction side  11 , which are, respectively, disposed opposite one another. In addition, the wall structure  2  has an outer wall  3 , which encloses an interior space  21 . Cavities  20 ,  22 ,  22   a ,  23 ,  23   a ,  25 ,  25   a  that are separate from one another, in particular, fuel feeds  22 ,  22   a , fuel discharges  23 ,  23   a , and cooling-air feeds  25 ,  25   a , are provided in the interior space  21  and are respectively directed essentially parallel to the main axis  19 . The feeds  22 ,  22   a ,  25 ,  25   a  and discharges  23 ,  23   a  extend from the non-illustrated blade root up to a non-illustrated second end, opposite the first end of the blade  1 , where they are closed. A hot gas  18  (action fluid) flows around the blade  1  so that an outer surface  14  of the outer wall  3  can be acted upon by the hot gas  18 . The hot gas  18  flows against the blade  1  at the inflow region  8  and flows along the blade  1  up to the outflow region  9 . The cooling-air feed  25  of the inflow region  8 , the fuel discharge  23 , the fuel feed  22 , the fuel discharge  23   a , the fuel feed  22   a , and the cooling-air feed  25   a  of the outflow region  9  are disposed one after the other in the interior space  21  in the direction of flow of the hot gas  18 . On the suction side  11  and the pressure side  10 , the wall structure  2  has a plurality of chambers  20  disposed one behind the other. Further non-illustrated chambers are provided on the suction side  11  and on the pressure side  10  in the direction of the main axis  19 . The chambers  20  are disposed between an inner wall  4  facing the interior space  21  and the outer wall  3 . Each chamber  20  has a respective inlet  15  for fuel  6 , which in each case is connected to an associated fuel feed  22 ,  22   a . The inlet  15  of a respective chamber  20  extends along an inlet axis  24  that is essentially perpendicular to the outer wall  3 . As a result, additional impingement cooling of the outer wall  3  can be achieved when the fuel  6  flows into the chamber  20 . Furthermore, each chamber  20  has an outlet  16 , which produces a fluidic connection between the chamber  20  and an associated fuel feed  23 ,  23   a . Respectively, the fuel  6  can flow through the chambers  20  in the direction of flow or against the direction of flow of the hot gas  18 . A plurality of heat-transfer elements  7  disposed one after the other are preferably disposed in each chamber  20  in the direction of flow  12  of the fuel  6 . Further heat-transfer elements  7  disposed in the chambers  20  along the axis  19  are not shown. The heat-transfer elements may be offset in the direction of flow  12  relative to the heat-transfer elements  7  that are shown. As a result, high heat transfer in the chambers  20  can be achieved.  
         [0035]    During operation of the gas turbine  31 , a first partial flow of fuel  6 , preferably fossil fuel, for example, natural gas or coal gas, is fed to the combustion chamber  23  through the fuel line  42 . In addition, a second partial flow of fuel  6  that has been preheated in the turbine  33  is fed to the combustion chamber  32  through the fuel line  41 . The fuel  6  is preferably preheated by allowing the fuel  6  fed through the fuel line  40  to the turbine  33  to flow through the cavities  20 ,  22 ,  22   a ,  23 ,  23   a , formed in the interior space  21  of the blades  1  as a closed system relative to the interior of the gas turbine  31 , and for the fuel  6  to absorb thermal energy in the process. The fuel  6  flows into the blade  1  at a non-illustrated first end and flows through the blade  1  up to the non-illustrated second end. In each case, a portion of the fuel  6  is drawn off into each chamber  20 , disposed axially one above the other such that the fuel portion absorbs heat through heat exchange with the outer wall  3  and the heat-transfer elements  7 . As a result, the fuel  6  is preheated and the outer wall  3  is cooled at the same time. After flowing through the chamber  20 , the fuel  6  enters a fuel discharge  23 ,  23   a . The fuel flow combined again in the fuel discharges  23 ,  23   a  passes out of the blade  1  again through the non-illustrated first end.  
         [0036]    The fuel  6  is either fed successively through a plurality of rows  46 ,  47 , in particular, through all the rows, of blades  1  of the turbine or separately, i.e., in separate flows, through a plurality of rows  46 ,  47  of blades  1  of the turbine and then, in each case, separately or as a uniform flow to the combustion chamber  32 .  
         [0037]    The splitting of the fuel  6  into partial flows advantageously permits better load-dependent controllability of the turbine  33 .  
         [0038]    In a preferred exemplary embodiment, fuel lines  40 ,  41 ,  42  and the cavities  20 ,  22 ,  22   a ,  23 ,  23   a  formed in the interior space  21  of the blades  1  as a closed system relative to the interior of the gas turbine  31  are configured to feed the fuel  6  to the combustion chamber  32  such that it is mainly preheated, and, at best, fully preheated.  
         [0039]    The fuel  6  thus preheated is burned in the combustion chamber  32  together with the fuel fed directly through the fuel line  42  if need be and with the compressed combustion air or with fresh air. The hot flue gas  18  (action fluid) produced during the combustion is directed through the flue-gas line  45  into the turbine  33 . The flue gas expands there and drives the turbine  33 . The turbine  33 , in turn, drives the air compressor  34  and the generator  36 . The flue gas  18  leaves the turbine  33  as exhaust gas through the exhaust-gas line  44  in the direction of a non-illustrated stack. Alternatively, the exhaust gas can also preferably be utilized for generating steam in a heat-recovery steam generator of a gas- and steam-turbine plant. European Patent EP 0 410 111 B1, for example, discloses such a gas- and steam-turbine plant.  
         [0040]    The flue gas  18  has a high temperature of more than 1100° C. when entering the turbine  33 . Therefore, parts of the turbine  33 , in particular, the blades  1 , must be additionally cooled. Most of the thermal energy to be dissipated is absorbed by the fuel  6  and dissipated in those sections of the blades  1  through which the fuel flows. In the remaining sections of the blades  1 , in particular, in the inflow region  8  and outflow region  9 , cooling air  6   a  flows through other cavities  25 ,  25   a  formed as an open system in the interior space  21  of the blades  1 . The cooling-air feed  25 , shown in FIG. 2, has a plurality of outlets  16  in the inflow region  8 , through which outlets  16  the cooling air  6   a  reaches the outer surface  14  of the blade  1 . The configuration ensures additional film cooling of the blades  1  by the cooling air  6   a . The cooling-air feed  25   a  of the outflow region  9  likewise has an outlet  16   a  for the outflow of cooling air  6   a . Heat-transfer elements  7  are disposed between the outer walls of the suction side  11  and the pressure side  10 .  
         [0041]    Alternatively or cumulatively, small fractions of fuel  6  that burn in the turbine  33  may be admixed with the cooling air  6   a  to increase the temperature of the exhaust gas flowing out of the turbine  33 .  
         [0042]    The blades  1  preferably used in the turbine  33  are characterized in that the outer wall  3  of the blades  1 , on the suction side  11  and the pressure side  10 , have a system that is closed relative to the interior of the gas turbine  31  and through which at least some of the fuel  6  flows before it is introduced into the combustion chamber  32 , cools the blades  1  and in the process is preheated at the same time without passing into the flow of a hot action fluid  18  flowing around the blades  1 . In addition, the inflow region  8  and outflow region  9  of the blades  1  may be cooled with an open system, in which case, cooling air is preferably used.  
         [0043]    The invention is characterized in that, by feeding fuel  6  through cavities  20 ,  22 ,  22   a ,  23 ,  23   a  that are formed in the interior space  21  of the blades  1  and that form a closed system relative to the interior of the gas turbine  31 , the fuel  6  absorbs thermal energy that otherwise would have to be dissipated by a cooling fluid. The fuel consumption is reduced by heating the fuel  6  on one hand, and cooling air  6   a  for the turbine  33  is saved on the other hand. Thus, the work of the air compressor  34  that otherwise would have to be performed by the turbine  33  is reduced. The efficiency of the gas turbine  31  is, consequently, increased. In addition, efficiency losses in the turbine  33  due to mixing of hot action fluid  18  with cooling air  6   a  are reduced due to the fact that cooling air  6   a  discharges at the blades  1  only to a reduced extent.