Abstract:
An exhaust gas liner for a gas turbine includes an annular inner shell and an annular outer shell, which are arranged concentrically around a machine axis of the gas turbine to define an annular exhaust gas channel in between. The inner shell and/or said outer shell are composed of a plurality of liner segments, which are attached to a support structure. To compensate thermal expansion and achieving resistance against dynamic loads, the liner segments are fixed to the support structure at certain fixation spots, which are distributed over the area of said liner segments, such that said liner segments are clamped to said support structure through a whole engine thermal cycle without hindering thermal expansion.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to European application 14173014.3 filed Jun. 18, 2014, the contents of which are hereby incorporated in its entirety. 
     TECHNICAL FIELD 
     The present invention relates to the technology of gas turbines. It refers to an exhaust gas liner for a gas turbine according to the preamble of claim  1 . 
     It further refers to a gas turbine with such an exhaust gas liner. 
     BACKGROUND 
     Document EP 2 565 400 A2 discloses a gas duct for a gas turbine, which gas duct is formed by a concentric inner casing and an outer casing which concentrically encompasses the inner casing at a distance, and through which the exhaust gases from the gas turbine discharge to the outside. The inner casing and the outer casing are interconnected by means of a multiplicity of radial support struts. The support struts, the outer casing and the inner casing are equipped in each case with a heat-resistant lining for protection against the hot exhaust gases. Easy accessibility and an extensive reduction of thermal stresses is achieved by the linings of the support struts of the outer casing and of the inner casing being divided in each case into a plurality of separate segments which are fastened on a support structure in such a way that an individual thermal expansion of the individual segments is possible. 
     However, for the fixation of the segments, carrier beams are used. These carrier beams and a specific “star” form of inner/outer flanges are exposed to high temperatures and stresses in steady state, and therefore certain criteria of Low Cycle Fatigue (LCF) and creep of the support structure are failed. 
     Furthermore, connection bolts are exposed to the main gas flow. A high temperature of the bolts and connected parts and temperature gradients in both transient and steady state could lead to creep of bolt material and consequently to the loss of bolt&#39;s pretension. 
     SUMMARY 
     It is an object of the present invention to provide a new exhaust gas liner design, which avoids the drawbacks of the known design, and which compensates thermal expansion and is resistant against dynamic loads. 
     It is a further object of the present invention to provide a gas turbine with such an exhaust gas liner. 
     These and other objects are obtained by an exhaust gas liner according to claim  1  and a gas turbine according to claim  15 . 
     The exhaust gas liner for a gas turbine according to the invention comprises an annular inner shell and an annular outer shell, which are arranged concentrically around a machine axis of said gas turbine to define an annular exhaust gas channel in between, whereby said inner shell and/or said outer shell are composed of a plurality of liner segments, which are attached to a support structure. 
     It is characterized in that said liner segments are fixed to said support structure at certain fixation spots, which are distributed over the area of said liner segments, such that said liner segments are clamped to said support structure through a whole engine thermal cycle without hindering thermal expansion. 
     According to an embodiment of the inventive exhaust gas liner all liner segments comprise a central fixation spot, where said liner segments are fixed on said support structure such that a movement of said liner segments in axial, radial and tangential direction is prevented. 
     Specifically, said liner segments are fixed at said central fixation spot by means of a fixation bolt, which is screwed through a holder at the backside of said liner segments into a fixation pin being fixed on said support structure. 
     More specifically, said fixation pin is fixed on said support structure by means of a fixation pipe, which is fixed at one end on said support structure and receives at the other end said fixation pin. 
     According to another embodiment of the invention all liner segments comprise an axially guiding fixation spot located on an axial centreline of said segments, where said liner segments are fixed on said support structure such that a movement of said liner segments in tangential direction is prevented. 
     Specifically, said liner segments are fixed at said axially guiding fixation spot by means of an axial guide pin, which is fixed to a holder at the backside of said liner segments and engages in a sliding fashion a fixation pin being fixed on said support structure. 
     More specifically, said fixation pin is fixed on said support structure by means of a fixation pipe, which is fixed at one end on said support structure and receives at the other end said fixation pin. 
     According to a further embodiment of the invention said exhaust gas liner can be separated into two parts at a parting line, and all of said liner segments except those split line segments of said inner shell abutting said parting line, comprise four side fixation spots located at four edges of said segments, where said liner segments are fixed on said support structure such that a movement of said liner segments in radial direction is prevented but a thermal expansion composed of axial and tangential components is allowed. 
     Specifically, said liner segments are fixed at said side fixation spots by means of a fixation bolt, which is screwed through a holder at the backside of said liner segments into a fixation pin being fixed on said support structure, whereby said holder comprises an elongated hole with location specific orientation and length. 
     More specifically, said fixation pin is fixed on said support structure by means of a fixation pipe, which is fixed at one end on said support structure and receives at the other end said fixation pin. 
     According to just another embodiment of the invention said inner shell and outer shell are connected by means of a plurality of radial struts, and each of said struts comprises a radial rib, which is covered by front and rear strut segments having a leading edge and trailing edge, which front and rear strut segments are each fixed on said radial rib at a plurality of fixation spots distributed along said leading and trailing edge. 
     Specifically, each of said front and rear strut segments has three fixation spots comprising a middle fixation spot, a hub side fixation spot and a tip side fixation spot. 
     More specifically, at the middle fixation spot of the front strut segment a fixation bolt is used to fix said front strut segment in radial, axial and tangential direction, while at the hub and tip side fixation spots a thermal expansion in radial direction is allowed. 
     More specifically, at the middle fixation spot of the rear strut segment an axial guiding pin is used to fix said rear strut segment thereby allowing a thermal expansion in axial direction only, while at the hub and tip side fixation spots a thermal expansion in radial and axial direction is allowed. 
     The gas turbine according to the invention comprises a compressor, at least one combustor and one turbine, and an exhaust gas liner, through which hot exhaust gas exits said gas turbine. 
     It is characterized in that the exhaust gas liner is an exhaust gas liner according to the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention is now to be explained more closely by means of different embodiments and with reference to the attached drawings. 
         FIG. 1  shows a partial section of a gas turbine of the type GT24/26, which may use the exhaust gas liner of the present invention; 
         FIG. 2  shows in a perspective view the various liner segments (with their fixation spots) of an exhaust gas liner according to an embodiment of the invention; 
         FIG. 3  shows the (in this example six) fixation spots of an inner liner segment of the exhaust gas liner according to  FIG. 2 ; 
         FIG. 4  shows the (in this example six) fixation spots of an outer liner segment of the exhaust gas liner according to  FIG. 2 ; 
         FIGS. 5 and 6  show the configuration of a central fixation means of the inner segment liner of  FIG. 3 , which fixes the segment in radial, axial and tangential (or circumferential) direction; 
         FIG. 7  shows the configuration of the four edge-located fixation means of the inner segment liner of  FIG. 3 , which fix the segment in radial direction, but allow thermal expansion in a combined axial and tangential direction; 
         FIGS. 8 and 9  show the configuration of an axially guiding fixation means of the inner segment liner of  FIG. 3 , which fixes the segment in tangential (or circumferential) direction, but allows thermal expansion in radial and axial direction; 
         FIG. 10  shows the upper half of the support structure used to support the liner segments of the exhaust gas liner according to  FIG. 2 ; 
         FIG. 11  shows a strut of the exhaust gas liner according to  FIG. 2  with its front and rear liner segments and their (in this case three) fixation spots; 
         FIG. 12  shows the configuration of the hub and tip fixation means of the rear liner segment of  FIG. 11 , which fixes the segment in circumferential direction, but allows thermal expansion in radial and axial direction; 
         FIG. 13  shows the configuration of the central fixation means of the front liner segment of  FIG. 11 , which fixes the segment in circumferential, radial and axial direction; and 
         FIG. 14  shows the configuration of the hub and tip fixation means of the front liner segment of  FIG. 11 , which fixes the segment in circumferential and axial direction, but allows thermal expansion in radial direction. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  shows a partial section of a gas turbine of the type GT24/26, which may use the exhaust gas liner of the present invention. Gas turbine  10  of  FIG. 1  is of the reheat type comprising sequential combustion. It has a rotor  11 , which is surrounded by a casing  12  and rotates around a machine axis A. A compressor  13  compresses air, which is used in a first combustor  14  to burn a fuel in order to generate hot gas. The hot gas from the first combustor  14 , which still contains oxygen, drives a high pressure (HP) turbine  15 , and is then used to burn a fuel in a second combustor  16 . The reheated hot gas of the second combustor  16  then drives a low pressure (LP) turbine  17  and finally exits gas turbine  10  through an exhaust gas liner  18 . 
     Exhaust gas liner  18  comprises ( FIG. 2 ) in a concentric configuration around the machine axis A an inner shell  21  and an outer shell  19 , which are connected by a plurality of radial struts  20  and are equally distributed over the circumference. 
     The present invention now deals with the principle of attaching the various gas liner annulus segments ( 22 ,  23  and  26 ,  27  and  28  in  FIG. 2 ) and flow straightening struts ( 24 ,  25  in  FIG. 2 ) to the casing and its support structure (see  FIG. 10 ). The design of the fixation means of the various segments shall compensate thermal expansion and be resistant against dynamic loads. 
     In general, the various segments of the inner and outer shell  19 ,  21  and the struts  20  are fixed to the support structure by controlled cold bolt pretension. According to the present invention the parts are clamped through the whole engine thermal cycle, but still are allowed to undergo unhindered thermal growth. 
     As shown in the embodiment of  FIG. 2 , there are ten struts  20 . One strut is positioned on the 6 o&#39;clock position. Each strut  20  has left and right outer liner segments  22 ,  23 , left and right inner liner segments  26 ,  27 , and front and rear strut segments  24 ,  25 . 
     Each liner segment (inner and outer) has all together six fixation spots/connections  29   a - c  and  30   a - c  (see  FIGS. 3 and 4 ) to support structure, with exception of split line segments  28  on the inner shell  21 , which are rather narrow and contain no space for a full fixation set, but use three fixation spots instead. 
     The liner segments  23 ,  27  with their six fixation spots/connections  29   a - c  and  30   a - c  are connected to the support structure ( 31  in  FIG. 10 ) with the following segments fixation principle and thermal expansion capability:
         1. A central fixation (fix point)  29   b  or  30   b  (see  FIGS. 5 and 6 ) prevents movement in all three directions (x: axial, R: radial and φ: tangential; see the respective symbols in  FIGS. 5 and 6 ).   2. Side fixations  29   a ,  30   a  (see  FIGS. 3, 4 and 7 ) prevent movement in radial direction, but allow thermal expansion of the segments  23 ,  27  composed of axial and tangential components (x and φ;  FIG. 7( c ) ). As temperature differences on a single segment (axial average vs. tangential average over time) are not so significant, the thermal movements in both directions are considered simultaneous and linearly dependant on average segment temperature. Freedom to move is achieved by elongated hole ( 54  in  FIG. 7( c ) ) on a segment holder  33   a , with location specific orientation and length. Bolt connection (fixation bolt  35   a ) with controlled pretension assures contact between the segment and fixation during the whole thermal cycle, producing the friction force opposing thermal growth/dilatation.   3. Axial guide key ( 30   c  in  FIGS. 3, 8 and 9 ) prevents movement in tangential direction (φ). The guide with axial guide pin  35   c  located on a centreline of the segment is needed to keep the segments in symmetric position during the thermal cycle, which is important for keeping control over variation of intersegment gap sizes during the cycle.       

     At the central fixation spot  29   b ,  30   b  ( 1 ) a holder  33   b  is welded on the backside of the segment  27  just below an opening  32   b  ( FIG. 5, 6 ). A support plate  34   b  reinforces the base of holder  33   b . A fixation bolt  35   b  is screwed through a bore in holder  33   b  and support plate  34   b  into a fixation pin  36   b . Fixation pin  36   b  is received by and welded to a fixation pipe  37   b , which is fixed on the support structure  31 . The height of the fixation pin  36   b  can be adjusted by sliding it relative to fixation pipe  37   b  before welding.  FIG. 6  shows the section along line A 1 -A 1  in  FIG. 5 . 
     At the side fixation spots  29   a ,  30   a  ( 2 ) a holder  33   a  is welded on the backside of the segment  27  just below an opening  32   a  ( FIG. 7 ). A support plate  34   a  reinforces the base of holder  33   a . A fixation bolt  35   a  is screwed through an elongated hole  54  bore in holder  33   a  and support plate  34   a  into a fixation pin  36   a . Fixation pin  36   a  is received by and welded to a fixation pipe  37   a , which is fixed on the support structure  31 . The height of the fixation pin  36   a  can be adjusted by sliding it relative to fixation pipe  37   a  before welding.  FIG. 7( b )  and  FIG. 7( c )  show the sections along line A 2 -A 2  and A 3 -A 3  in  FIG. 7( a ) . 
     At the axial guiding fixation spot  29   c ,  30   c  ( 3 ) a holder  33   c  is welded on the backside of the segment  27  just below an opening  32   c  ( FIGS. 8 and 9 ). A support plate  34   c  reinforces the base of holder  33   c . An axial guide pin  35   c  engages in a sliding fashion a fixation pin  36   c . Fixation pin  36   c  is received by and welded to a fixation pipe  37   c , which is fixed on the support structure  31 . The height of the fixation pin  36   c  can be adjusted by sliding it relative to fixation pipe  37   c  before welding.  FIG. 9  shows a section along line A 4 -A 4  in  FIG. 8 . 
     Struts  20  are covered by front (leading edge LE) and rear (trailing edge TE) strut segments  24 ,  25  which are finally (after assembly into support structure) welded in the middle of strut. Segments  24  and  25  each have three fixation spots  40 - 42  and  43 - 45  ( FIG. 11 ). Strut cover fixation spots are all lying in one plane. 
     The fixation principle with regard to thermal expansion is as follows:
         1. Fix point is placed on LE side (strut segment  24 ), in the middle of the gas channel, forcing the strut cover to equally expand in radial direction towards the hub and the tip. A fixation bolt  51  ( FIG. 13 ) is placed on LE (segment  24 ) middle of strut  20  (fixation spot  41 ) to prevent axial, radial and tangential movement (x, R and φ).  FIG. 13( b )  is a section along line A 5 -A 5  in  FIG. 13( a ) . The fixation bolt  51  is screwed through a bore in connection plate  50  of strut segment  24  into a fixation pin  52 , which is screwed into and welded to a rib  39  of the support structure  31  or  38 .   2. Fixations on LE hub and tip side (fixation spots  40  and  42 ) allow thermal expansion in radial direction (R, with friction caused by bolt pretension), but prevent movement in axial and tangential directions (x and φ). The configuration is shown in  FIG. 14 . Freedom to move is achieved by elongated hole  54 ′ on a segment, radial oriented ( FIG. 14( a ) ). A fixation bolt  48  is screwed through elongated hole  54 ′ in connection plate  47  of strut segment  24  into a fixation pin  52 , which is screwed into and welded to a rib  39  of the support structure  31  or  38 . In all cases, a washer  53  is used for the bolt.   3. Fixation pin on TE (segment  25 ) middle (fixation spot  44 ) match radial location of a fix point on LE side (segment  24 ) and allows thermal movement in axial direction only.   4. Fixation pins ( 46  in  FIG. 12 ) of TE (segment  25 ) hub and tip side (fixation spots  43  and  45 ) allow thermal expansion in radial and axial direction (R and x). Fixation pin  46  is screwed into a welded to rib  39 . It extends through a radial elongated hole  54 ′ in connection plate  47  of strut segment  25 .  FIG. 12( b )  is a section of  FIG. 12( a ) .