Abstract:
A combustion chamber for an industrial gas turbine has thermal protective elements which are installed along the inner circumference of its casing. The thermal protective elements are cooled by cooling air which is added to the fuel in the region in front of a front casing section after the cooling. A brush seal is installed between the front casing section and the thermal protective elements, where the brush seal is configured in segments. The combustion chamber can be sealed against leakages of cooling air in all operating states of the combustion chamber.

Description:
CROSS-REFERENCE TO RELATED PATENT APPLICATIONS 
   This application is based on and claims priority under 35 U.S.C. §119 to Swiss Application No. 00798/04, filed May 5, 2004 and is a continuation application under 35 U.S.C. §120 of International Application No. PCT/EP2005/051807, filed Apr. 22, 2005 designating the U.S., the entire contents of both of which are hereby incorporated by reference. 
   BACKGROUND 
   A combustion chamber is disclosed for a gas turbine with a thermal protective lining, as is a seal for the semi-static region between elements of the thermal protective lining. Combustion chambers of this type can be used in large gas turbines, such as stationary, industrial gas turbines. 
   The combustion chambers for gas turbines are typically lined with thermal protective elements which protect the combustion chamber casing from hot gas of the combustion chamber, and for this purpose, are fastened on supports in the combustion chamber casing, in the form of segments arranged in series along the circumference of the combustion chamber. The protective lining is cooled by cooling air which flows between the supports and the segments. The cooling air can be guided in the direction of the combustion chamber axis, and subsequently added to the fuel in the region of the combustion chamber inlet. Seals are installed at the combustion chamber inlet of the combustion chamber, between the thermal protective elements and the combustion chamber casing. They can prevent cooling air from reaching the combustion chamber between protective elements and casing and influencing the combustion process. 
   The thermal protective elements can be subjected to movements of varied magnitude and varied frequency. 
   Movements of lower frequency due to thermal expansions, which are also known as so-called “low cycle fatigue movements”, can occur in the axial direction and also in the radial direction. They can be especially significant in large, stationary industrial gas turbines, since there the thermal expansions, on account of the large dimensions of the component parts, are in a large ratio to the precision with which the gas turbine and combustion chamber are manufactured. The thermally conditioned relative movements mean a challenge in the seal between the thermal protective elements and also in the region around the protective elements. Movements of higher frequency of the thermal protective elements can result from vibrations which can occur during general combustion chamber operation. The operation can induce vibrations of varied frequencies in the protective elements, which due to the natural frequencies of the protective elements can lead to increased vibrations of protective elements and supports. They are also known as so-called “high cycle fatigue movements”, and are of smaller magnitude and of higher frequency in comparison to the thermally induced movements. They can especially reduce the reliable operating period of the protective elements. 
   The thermal protective elements, their supports, and also adjacent component parts are basically static. Since the interspaces between individual protective elements and also the spaces between the protective elements and adjacent component parts, however, are subjected to the aforementioned relatively large movements, the protective elements and the seals for the interspaces can be considered to be in a semi-static range. 
   There are various measures which are known for damping of vibrations in a combustion chamber. For example, the magnitudes of vibrations can be reduced by the amplitudes and frequencies of the vibrations being damped or interrupted. This, for example, can be realized by conscious control of the combustion process, or by acoustic damping elements in the combustion chamber which dissipate the energy of the oscillations. 
   EP 990 851 discloses a method for acoustic damping of vibrations inside combustion chambers by Helmholzt damping. There, a combination of Helmholtz resonators with a further damping medium, such as a plurality of plates with openings for a cooling flow, is disclosed. 
   U.S. Pat. No. 6,357,752 discloses the use of brush seals in the region between the end, in the flow direction, of a combustion chamber for a gas turbine and the first stator row of the gas turbine. It involves there a brush seal of double construction, wherein the pressure drops across the first seal and second seal in opposite directions. The disclosures of EP 990,851 and U.S. Pat. No. 6,357,752 are hereby incorporated by reference in their entireties. 
   SUMMARY 
   A combustion chamber is disclosed for a gas turbine, such as for large, stationary, industrial gas turbines. The combustion chamber, especially in the region of protective elements on the casing wall of the combustion chamber at the combustion chamber inlet, can be configured so that as far as possible no cooling air for cooling of the protective elements gets into the combustion chamber, which would interfere with the combustion process. This can be provided especially in the case of the basically static protective elements being in a semi-static range in that they are subjected to large thermal movements and also vibrations, and the sizes of the distances between the protective elements and the front casing being subjected to correspondingly large fluctuations. 
   An exemplary combustion chamber for a gas turbine comprises a combustion chamber casing and a front casing section. At the inner circumference of the wall of the combustion chamber casing, a plurality of thermal protective elements are installed in segmented fashion over the circumference of the combustion chamber, which protect the combustion chamber casing from the radiation of the combustion process. For cooling of the protective elements, a cooling air flow flows between the thermal protective elements and the combustion chamber casing wall and in the direction from the region of the combustion chamber outlet to the region of the combustion chamber inlet, wherein the cooling air finally reaches a cavity outside the front casing of the combustion chamber. A brush seal can be installed between the front casing section of the combustion chamber and the thermal protective elements, which extends beyond the circumference of the front casing section. 
   An exemplary combustion chamber has a brush seal which seals the cavity outside the front casing section, into which the cooling air flows, from the inner cavity of the combustion chamber. It can provide especially a uniform seal over the circumference of the combustion chamber, and a temporally uniform seal during the various operating states of the combustion chamber. It can prevent an uncontrolled penetration of cooling air into the combustion chamber and prevents influences on the combustion process which result from it. As a result, a temporally stable and also spatially uniform and reproducible combustion can be achieved by the combustion chamber. Thus, the brush seal provides a sealing effect even during large, thermally conditioned relative movements (“low cycle fatigue movement”) of the component parts, since they inherently provide a large, elastic flexibility. This seal is able to prevent a cooling air leakage even during thermal movements of the type in which a protective element bends in the opposite direction, so instead of into the usual curvature in accordance with the shape of the combustion chamber casing wall it bends inwards in the opposite direction. 
   The combustion chamber can be especially advantageous in large, industrial gas turbines, since there the thermal movements are large, especially in comparison to the precision to which the component parts of the gas turbine are arranged with respect to each other. 
   The brush seal can provide a reliable seal even with high frequency oscillations (“high cycle fatigue movement”) of the component parts which are in contact with the seal. 
   During high and low frequency oscillations of the thermal protective elements, the brush seal brings about a damping of the high and low frequency oscillations, in addition to its sealing function. On the one hand, this can be produced by friction damping by relative sliding movements of the combustion chamber casing and the protective elements. On the other hand, it can be produced by deformation or bending of the bristles on account of the pressure force which is exerted on the bristles during thermal movements. As a result, a type of spring action is produced. The damping of the oscillation can also be produced by a combination of friction damping and deformation of the bristles. 
   As a consequence, the oscillations are dissipated or even canceled out, a result of which the oscillation is reduced. This type of oscillation damping can be achieved for all oscillation frequencies which occur in all operating states of the combustion chamber. By the damping of the oscillations of the protective elements, on one hand the seal can be further improved, and on the other hand the period of operational use of the protective elements extended. 
   In a first exemplary embodiment, the brush seal is configured in segments which are arranged in series over the circumference of the combustion chamber, wherein each of the segments of the brush seal is in contact with at least two thermal protective elements in each case. 
   In a second exemplary embodiment, the brush seal is fastened in the front casing of the combustion chamber, and the bristles extend in the direction of the thermal protective elements. This can be advantageous when considering that the oscillations of the front casing are smaller than those of the protective elements. In corresponding situations, it is also realizable to fasten the brush seal to the protective elements. 
   In a further embodiment, the brush seal can be configured with the bristles being oriented at an angle to the radial direction to the longitudinal axis of the combustion chamber. In particular, the bristles can be oriented at an angle in the direction of the circumferential tangent. This also allows a sealing action in the varying radial gap between the combustion chamber front casing and thermal protective elements which encompass the front casing. The angle of orientation is arbitrary, however is preferably 45°±5°, or lesser or greater. 
   In an exemplary embodiment, brush seals are used which by pressing in are fastened in a frictional and positive locking manner in a slot with clamping effect. Such brush seals provide the advantage that they can be installed in a small space, and installed in component parts with a small arbitrary radius of curvature. 
   In a further variant, the surface with which the bristles of the brush seal are in contact is provided with a coating to protect against wear. This coating, for example of Cr 3 C 2 , provides an exceptionally smooth surface over which the bristles can slide without digging into the component part, as a result of which the wear of the bristles is much reduced. As a result, the coating brings about an increase in the friction damping and ensures a higher sealing action with longer service life of the bristles. 
   In a further embodiment, the bristles of the brush seal have a pretensioning in the axial direction, wherein in this case it means the direction of the combustion chamber casing. A pretensioning provides a good seal in the particular case of a small pressure drop across the seal. In an exemplary combustion chamber, the pressure drop is small in comparison with the pressure drop with other seals, such as with a brush seal on a turbine rotor. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  shows a section through a segment of an exemplary annular combustion chamber for a gas turbine, and an arrangement of the combustion chamber casing, the front casing section and the thermal protective elements; 
       FIG. 2  shows the detail II according to  FIG. 1 , and an exemplary seal between the front casing and thermal protective element against a leakage flow into the combustion chamber; 
       FIG. 3  shows the cross section which is indicated in  FIG. 1  by III-III, and an exemplary segment-like arrangement of the thermal protective elements and the brush seal; 
       FIG. 4  shows an exemplary brush seal according to detail IV with reference to  FIG. 3 , and its arrangement along the circumference of the annular combustion chamber; and 
       FIG. 5  shows an exemplary brush seal for pressing in with axial pretensioning, for use in the combustion chamber. 
   

   DETAILED DESCRIPTION 
   An exemplary combustion chamber  1  for a gas turbine in section along the longitudinal axis  2  of a burner  3  is shown in  FIG. 1 . The burner  3 , through which fuel flows in the indicated direction  4 , is schematically shown at the combustion chamber inlet. The combustion chamber  1  is enclosed by a circular-symmetrical combustion chamber casing  6  which extends in the longitudinal direction from the burner  3  as far as the combustion chamber outlet  5  to which is attached the first stator row of the gas turbine. The combustion chamber  1  has a front casing  7  with an opening in which the burner  3  is installed. The inner surface of the combustion chamber casing  6 ,  6 ′ is lined with thermal protective elements  8  which are fastened on the casing wall  6 ,  6 ′, for example by means of supports. In order to withstand the temperatures of the hot gas inside the combustion chamber, the thermal protective elements are cooled by a cooling air flow  10 . The cooling air, which, for example is extracted from the compressor for the gas turbine, is guided through openings  11  in the combustion chamber casing  6 ,  6 ′ into the interspace  12  between the combustion chamber casing wall  6 ,  6 ′ and the thermal protective elements  8 , and is guided in the axial direction in the opposite direction of flow of the fuel into a cavity  13  outside the front casing  7  of the combustion chamber. There, it is fed through openings  14  in the casing of the burner  3  to the fuel flow. 
   The front casing  7  of the combustion chamber  1  is fastened on the combustion chamber casing  6 ,  6 ′ by struts  15 . It has an opening  16  in which the burner  3  is installed. Areas of a possible leakage flow  17  of cooling air into the cavity  18  of the combustion chamber are located between adjacent struts  15 , and between the front casing  7  and the oppositely disposed thermal protective element  8 , in each case. 
   A seal  19  is installed in the region between the front casing  7  and protective elements  8 . It can be fastened in a slot  20  let in in the front casing  7 , and extends up to the surface of the thermal protective element  8 . The thermal protective elements  8  are fastened and fixed at a point, for example in the region of the first turbine stator row, from which the thermal movements emanate in the axial and radial direction. 
     FIG. 2  shows a detailed view of the region II in  FIG. 1  in which are shown a part of the front casing  7  and a part of the oppositely disposed thermal protective element  8  and the combustion chamber casing wall  6 . The cooling air flow  10 , which flows through the interspace  12  between protective element and casing wall, is shown in turn between the casing wall  6  and the protective element  8 . A slot  20 , which has an undercut, is located on the front casing  7  on the side facing the combustion chamber casing. A brush seal  19  is installed in the slot  20 . A brush seal can be used which was manufactured by a pressing in method by means of a clamp  21 . The bristles  22  extend in the indicated plane radially (with regard to the axis  2 ) towards the protective element. 
     FIG. 3  shows the upper half of the annular combustion chamber in a section through the front casing  7  according to III-III in  FIG. 1 . There are several openings  16  shown for the burners, which are located along the circumference of the annular combustion chamber. The struts  15  along the circumference of the front casing  7 , by which it is fastened on the combustion chamber casing  6 ,  6 ′, are indicated by broken lines. The thermal protective elements  8  are fastened on the inner wall of the combustion chamber casing  6 , both on the outer casing wall  6  and also on the inner casing wall  6 ′ of the ring. They extend over a segment of the whole circumference in each case. Seals, which prevent hot gas getting into the combustion chamber casing  6 , are attached between the individual protective elements  8 . A cavity  12 , through which flows the cooling air flow, is located between combustion chamber casing wall  6  and protective elements  8 . The seal  19  can extend from the front casing  7  to the protective elements  8 , wherein the bristles are orientated at an angle to the radial direction. The seal  19  is installed in segmented fashion. As a result, a single sealing segment  19 ′ is in contact with at least two adjacent thermal protective elements  8 . The transition from one brush seal element  19 ′ to the next brush seal element  19 ′, is almost seamless as a consequence, and can be located approximately at the height of the middle of a thermal protective element  8 . The transitions can basically be positioned at any point with regard to the protective elements, including at points between two adjacent protective elements. 
     FIG. 4  shows a further detail according to IV in  FIG. 3 . The detail shows the orientation of the bristles of the brush seal  19  with regard to the radial direction of the combustion chamber. The bristles are inclined from the radial in the direction of the circumferential tangent by an angle α in any range, for example, in a range of 40-50°. 
   An inclination of the bristles away from the radial and towards the circumferential tangent results in the interface being reliably sealed, and uniformly sealed over the circumference, even with large fluctuations of the distance between the front casing circumference  7  and the thermal protective element  8 . As a result of this, cooling air does not reach the interior of the combustion chamber during all operating states of the gas turbine and the burner. In any event, some cooling air gets into the combustion chamber, wherein, however, this occurs evenly over the circumference of the front casing, which still ensures a controlled operation of the combustion chamber. 
   In a further exemplary embodiment of the combustion chamber, the brush seal is designed specially for use in the case of small pressure drops. The brush seal in this case is designed especially with a pretensioning of the bristles in the direction opposite the leakage flow. The pretensioning is produced during the manufacture of the seal by placing the clamp  24  over the part of the bristles  25  which is wound around a round rod  26 , wherein the ends of the clamp  24  are inclined at a predetermined angle, and not parallel, to the run of the bristles  25 , as shown in  FIG. 5 . By the pressing into the slot  20  of the front casing section  7 , the bristles are again set straight, as shown in  FIG. 2 . As a result, the bristles maintain a pretensioning. The greater the desired pretensioning is, the larger the angle is selected to be. 
   It will be appreciated by those skilled in the art that the present invention can be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The presently disclosed embodiments are therefore considered in all respects to be illustrative and not restricted. The scope of the invention is indicated by the appended claims rather than the foregoing description and all changes that come within the meaning and range and equivalence thereof are intended to be embraced therein.