Patent Publication Number: US-8978382-B2

Title: Combustion device with a layered wall structure for a gas turbine

Description:
CROSS REFERENCE TO PRIOR APPLICATIONS 
     Priority is claimed to European Patent Convention Application No. EP 10 154 284.3, filed Feb. 22, 2010, the entire disclosure of which is incorporated by reference herein. 
     FIELD 
     The present invention relates to a combustion device for a gas turbine. In an embodiment, the present invention refers to lean premixed low emission combustion devices. The combustion device may be the first and/or the second combustion device of a sequential combustion gas turbine or a combustion device of a traditional gas turbine (i.e. a gas turbine not being a sequential combustion gas turbine). For sake of simplicity and clarity, in the following only reference to a reheat combustion device (i.e. the second combustion device of a sequential combustion gas turbine) is made. 
     BACKGROUND 
     During gas turbine operation, heavy thermo acoustic pulsations may be generated in the combustion chamber, due to an unfavourable coupling of acoustic and fluctuation of heat release rate (combustion). The risk of thermo acoustic pulsation generation is particularly high when the gas turbine is provided with lean premixed low emission combustion devices. 
     These pulsations act upon the hardware of the combustion device and the turbine to heavy mechanical vibrations that can result in the damage of individual parts of the combustion device or turbine; therefore pulsation must be suppressed. 
     In order to suppress oscillations, combustion devices are usually provided with damping devices; typically damping devices consist of quarter wave tubes, Helmholtz dampers or acoustic screens. 
     US2005/0229581 discloses a reheat combustion device with a mixing tube and a front plate. The front plate has an acoustic screen having holes; parallel to the acoustic screen and apart from it, an impingement plate also provided with holes, ensuing cooling of the device, is provided. 
     During operation, air (from a plenum containing the combustion device) passes through the impingement plate, impinges on the acoustic screen (cooling it) to then pass through the acoustic screen and enter the combustion chamber. Nevertheless this damping system has some drawbacks. In fact, cooling of the acoustic screen requires a large air mass flow, which must be diverted from the plenum into the damping volume in order to cool it. 
     This, in addition to reducing the damping efficiency, also increases the air mass flow, which does not take part in the combustion, such that the flame temperature increases and the NOx emissions are consequently high. 
     SUMMARY OF THE INVENTION 
     An aspect of the present invention is therefore to provide a combustion device by which the said problems of the known art are eliminated. 
     An embodiment of the invention provides a combustion device in which a reduced air mass flow (when compared to traditional combustion devices) is diverted from the plenum into the damping volume. 
     Another embodiment of the invention provides a combustion device that has a high damping efficiency and limited NOx emissions when compared to corresponding traditional devices. 
     Advantageously, the cooling device in the embodiments of the invention does not have any influence or only a limited influence on the damping performance in terms of frequency and efficiency. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Further characteristics and advantages of the invention will be more apparent from the description of a preferred but non-exclusive embodiment of the combustion device according to the invention, illustrated by way of non-limiting example in the accompanying drawings, in which: 
         FIG. 1  is a schematic view of a reheat combustion device; 
         FIG. 2  is a cross section of the front plate of the mixing tube; 
         FIG. 3  is a cross section through lines III-III of  FIG. 2 ; 
         FIG. 4  is a top view cross section through lines IV-IV of  FIG. 2  of plate portions for manufacturing a front plate; 
         FIG. 5  is a top view cross section through lines V-V of  FIG. 2  of plate portions for manufacturing a front plate; 
         FIG. 6  is a top view cross section through lines VI-VI of  FIG. 2  of plate portions for manufacturing a front plate; 
         FIG. 7  is a top view cross section through lines VII-VII of  FIG. 2  of plate portions for manufacturing a front plate; 
         FIG. 8  is a top view cross section through lines VIII-VIII of  FIG. 2  of plate portions for manufacturing a front plate; 
         FIGS. 9-12  are different embodiments of the plate defining conduits parallel to a wall delimiting the interior of the combustion device; and 
         FIG. 13  is a further embodiment of the plate defining conduits parallel to a wall delimiting the interior of the combustion device; the conduits have a coil shape. 
         FIG. 14  is a further embodiment of the cross section of the front plate of the mixing tube where the inner wall and the further intermediate layer are one piece. 
         FIG. 15  is a further embodiment of the cross section of the front plate of the mixing tube where the outer wall and the further intermediate layer are one piece. 
     
    
    
     DETAILED DESCRIPTION 
     With reference to the figures, these show a combustion device generally indicated by the reference number 1. 
     The combustion device  1  has a mixing tube  2  and a combustion chamber  3  connected to each other via a front plate  4 ; these elements are contained in a plenum  5  into which compressed air coming from a compressor (the compressor of the gas turbine) is fed. 
     Above a combustion device being the second combustion device of a sequential combustion gas turbine was described, it is anyhow clear that in different embodiments of the invention the combustion device may also be the first combustion device of a sequential combustion gas turbine or also the combustion device of a traditional gas turbine having one single combustion device or combustion device row. These combustion devices are well known in the art and are not described in detail in the following; for sake of simplicity and clarity reference only to the second combustion device of a sequential combustion gas turbine is hereinafter made. 
     The combustion device  1  comprises portions  6  provided with an inner and an outer wall  7 ,  8 . 
     These portions  6  may be located at the front plate  4  and partly at the combustion chamber wall (as shown in  FIG. 1 ) or, in other embodiments, at the mixing tube wall, at the front plate, at the combustion chamber wall or also a combination thereof (i.e. at the wall of the mixing tube  2  and/or combustion chamber  3  and/or front plate  4 ). 
     The inner wall  7  has first passages  9  connecting the zone between the inner and outer wall  7 ,  8  to the inside  10  of the combustion device  1 . 
     In addition second passages  12  are provided, having inlets  13  connected to the outer  14  of the combustion device  1  and passing through the outer wall  8  for cooling the inner wall  7 . 
     Between the inner and outer wall  7 ,  8  an intermediate layer  17  is provided defining a plurality of chambers  18 . 
     Each chamber  18  is connected to one or more than one first passage  9  and a plurality of second passages  12  and defines one or a plurality of Helmholtz dampers. 
     The second passages  12  open in third passages  22  connected to the chamber  18 ; in addition, the second passages  12  have facing outlets  23 . 
     The third passages  22  open at the same side of the chambers  18  as the first passages  9  and the second passages  12  have a portion extending parallel to the inner wall  7 . 
     For sake of clarity, in  FIG. 2  the first passage  9  and the third passage  22  are shown with a different diameter; it is anyhow clear that in different embodiments their diameter may also be the same or each between the first passage  9  and the third passage  22  may have the largest and/or the smallest diameter. 
     As shown, the second passages  12  have portions associated in couples with overlapping longitudinal axis  25 . 
     Preferably, between the facing outlets  23  of the associated second passages  12  an obstacle  26  in provided, for example defined by a wall interposed between the associated passages  12 . 
     In addition, advantageously each of the second passages  12  has a diffuser  27  at its outlet  23 . 
     The portion  6  has a layered structure made of at least the inner wall  7 , the intermediate layer  17  and outer wall  8  (and eventually also one or more further layers interposed between the first and second wall  7 ,  8 ); this layered structure is made of a plurality of plates (defining the inner and outer wall  7 ,  8 , the interposed layer  17  and the eventual further layers) connected one to the other and provided with apertures to define the first, the second and the third passages  9 ,  12 ,  22  and the chambers  18 . 
     In one embodiment the apertures defining the first, the second and the third passages  9 ,  12 ,  22  and the chambers  18  are through apertures; this embodiment is shown in  FIG. 2 . 
     In this embodiment between the first and the second wall  7 ,  8 , in addition to the intermediate layer  17 , also two further layers  29  (cooling passage layer),  30  (separation layer) are provided, such that the layered structure is made of five plates one connected to the other (for example brazed or via screws). 
     In a different embodiment the apertures defining the first, the second and the third passages  9 ,  12 ,  22  and the chambers  18  comprise one or more blind apertures. 
     In this respect the inner wall  7  and the layer  29  may be manufactured in one element, in this case the portions of the first passages  12  in the layer  29  are defined by blind apertures (for example blind millings); the portions of the third passages  22  are defined by a portion of the same millings or by a blind aperture connected thereto (for example a blind hole, example not shown). The portions of the first passages  9  in the wall  7  and layer  29  are defined by through apertures (for example through holes). 
     The layer  30  may be realised in one element with through apertures (such as through holes) defining the portion of the first, second and third passages  9 ,  12 ,  22  through it. 
     The outer wall  8  and the intermediate layer  17  may be realised in one element with through apertures (through holes) defining the portion of the second passages  12  through it and blind apertures (blind holes) defining the chambers  18 . 
     Naturally further different embodiments are possible, for example the inner wall  7  may be manufactured in one element, the two layers  29 ,  30  may also be manufactured in one element and the intermediate layers  17  and outer wall  8  in one element; alternatively the outer layers may be manufactured in one element, the layers  17  and  30  in one element and the inner wall  7  and layer  29  in one element. It is clear that also further embodiments are possible that are not described in detail for brevity and because they are clear for the skilled in the art on the basis of what explained. 
     For sake of clarity,  FIGS. 4-8  show a possible implementation of a layered structure made of five different elements; all the apertures in these elements are through apertures (holes or millings). 
       FIG. 4  shows the outer wall  8 ; in this figure the apertures defining the portion of the second passages  12  through this wall are shown; in addition the chamber  18  (defined in the intermediate layer  17 ) is shown in dotted line. 
       FIG. 5  shows the intermediate wall  17 ; in this figure the apertures defining the portion of the second passages  12  through this wall and the chamber  18  are shown. 
       FIG. 6  shows the layer  30 ; in this figure the apertures defining the portion of the second passages  12  and of the first passages  9  and, in addition, the third passage  22  through this wall are shown; in addition the chamber  18  (defined in the intermediate layer  17 ) is shown in dotted line. 
       FIG. 7  shows the layer  29 ; in this figure the apertures (millings) defining the portion of the second passages  12  and the aperture (typically a hole) defining the portion of the first passages  9  through this wall are shown; the third passage  22  (defined in the layer  30 ) and the chamber  18  (defined in the intermediate layer  17 ) are also shown in dotted line; in addition the portion of the third passages  22  in the layer  29  and the outlets  23  are indicated. Also the obstacle  26  is shown in this figure. 
       FIG. 8  shows the inner wall  7 ; in this figure the portion of the first passage  9  through this wall is shown; in addition the chamber  18  (defined in the intermediate layer  17 ) is also shown in dotted line. 
     In compliance with what already described,  FIGS. 9-11  show further possible embodiments for the layer  29 . Like reference numbers define in these figures identical or similar elements; the other walls and layer must be modified accordingly and are not shown in the attached figures. Also in these figures all apertures are through apertures. 
       FIG. 9  shows an embodiment with four apertures (millings) defining portions of the second passages  12 , also in this figure the aperture (hole) defining the portion of the first passages  9  through this wall is shown. Moreover, the third passage  22  (defined in the layer  30 ), the chamber  18  (defined in the intermediate layer  17 ), the outlets  23  defined when the layers  29  and  30  are connected one onto the other are shown. 
       FIG. 10  shows an embodiment with two apertures (being millings) having the diffuser  27 ,  FIG. 11  shows an embodiment without the obstacle  26  between the second passages  12  and  FIG. 12  shows an embodiment with three second passages  12  having facing outlets  23  associated to each third passage  22 . 
       FIG. 13  shows a further embodiment with two coil shaped apertures. 
     The operation of the combustion device in the embodiments of the invention is apparent from what described and illustrated and is substantially the following. 
     Air enters via the inlet  13  and passes through the second passages  12 , cooling the portion  6 ; afterwards air is discharged into the chamber  18 . In addition, hot gas oscillates in the first passage  9  damping acoustic pulsations. 
     When entering the chamber  18 , since each air flow coming from a passage  12  impinges on another air flow coming from a facing passage  12 , there is no intense air flow entering the chamber  18 , but air enters the chamber  18  spreading in all directions; this avoids the formation of an air recirculation zone inside the chamber  18  that may influence the gas oscillation through the first passage  9  affecting the damping effect. For the same reason, the obstacle  26  is preferably provided, such that before each air flow impinges on another air flow, it impinges on the obstacle  26  spreading towards the chamber  18  in all directions. 
     Likewise, the diffuser  27  causes the air flow that enters the chamber  18  to reduce its kinetic energy, in order to reduce the probability of formation of air recirculation zones within the chamber  18 . 
     Since cooling is very efficient a reduced amount of air may be provided via the second passages  12  into the chambers  18  in order to cool the chambers  18  and the layered structure; this allows high damping efficiency and reduced NOx emissions. 
     In addition, thanks to the improved cooling, an impact of the cooling on the damping performance is prevented or hindered. 
     Naturally the features described may be independently provided from one another. 
     In practice the materials used and the dimensions can be chosen at will according to requirements and to the state of the art. 
     REFERENCE NUMBERS 
     
         
           1  combustion device 
           2  mixing tube 
           3  combustion chamber 
           4  front plate 
           5  plenum 
           6  portion 
           7  inner wall 
           8  outer wall 
           9  first passages 
           10  interior of  1   
           12  second passages 
           13  inlet of  12   
           14  outer of  1   
           17  intermediate layer 
           18  chambers 
           22  third passages 
           23  outlets of  12   
           25  longitudinal axis of portion of  12   
           26  obstacle 
           27  diffuser 
           29  cooling passage layer 
           30  separation layer