Abstract:
A thermal acoustic insulation structure including: a metal internal sheet having an exposed surface configured to be exposed to a hot gas, an external sheet and an insulation sandwiched between the internal and external sheets; a bar secured to the metal internal sheet and extending through at least a portion of the insulation; a bracket connected to the external sheet or to a support plate extending from the external sheet, wherein the bracket includes an opening configured to receive an end of the bar; a fastener securing the end of the bar to the bracket, and an insulating washer separating the bracket from the bar and the fastener.

Description:
RELATED APPLICATION 
       [0001]    This application claims the benefit of the European patent application EP14305776.8 filed May 23, 2014, the entirety of which is incorporated by reference. 
       BACKGROUND OF THE INVENTION 
       [0002]    The invention relates to a thermal-acoustic protection sheet assembly for an exhaust duct of a rotary machine or boiler associated with the machine. 
         [0003]    Rotary machines, such as industrial gas turbines, and boilers discharge exhaust gases that require exhaust ducts. The exhaust gases typically leave the rotary machines at high velocities and high temperatures such as in excess of 600° C. (degrees Celsius). Exhaust ducts, such as diffusers, include passages that direct the exhaust gases from the rotary machines or boilers to heat recovery steam generators (HRSG) or other systems that receive the exhaust gases. 
         [0004]    Exhaust ducts tend to be relatively large structures that provide a gas passage for large volumes of exhaust gases. A typical exhaust duct may have a cross-sectional dimension of 100 to 900 square feet (9 to 100 square meters). The cross-sectional area of the exhaust duct may increase as the exhaust gas flows from the rotary machine to the HRSG. The exhaust duct may have a generally square, circular or conical cross section. The exhaust duct may be connected to the discharge end of the rotary machine or boiler by an expansion joint. 
         [0005]    The walls of an exhaust duct are typically formed by insulated sheet assemblies. These assemblies are arranged side-by-side and supported by a framework of ribs to form the wall of a passage for the exhaust gases. Each sheet assembly includes an internal stainless steel sheet, an external steel sheet and an intermediate layer (or layers) of insulation between the internal and external sheets. Insulation in the walls suppresses the transmission of heat and acoustic noise from the hot gases to the environment surrounding the exhaust duct. 
         [0006]    The insulation in the intermediate layer is typically formed of mineral fibers, glass fibers, bio-soluble fibers or rock wool. The insulation is arranged in layers or may be packed as a cushioning material between the interior and external sheets. The materials and thicknesses of the intermediate layer(s) of the exhaust duct is typically selected to attain a certain low heat transfer coefficient through the intermediate layer. The insulation is generally configured to prevent the material from disintegrating over time and facilitate the handling of the insulation during installation of the insulation into the sheet assemblies. 
         [0007]    The sheet assembly includes support plates also referred to as separators that extend through the intermediate layer to support the internal and external sheets and provide spacing for the intermediate layer. 
         [0008]    The support plates are typically perpendicular to the internal and external sheets. An edge of each support plate is fixed or welded to an internal surface of the external sheet. An opposite edge of each support plate is attached to a bolt that extends through the internal sheet. A nut and washer are fastened to the bolt to secure the internal sheet to the support plate. The assembly of nuts, washers and support plates form a framework that holds together the internal sheet, the intermediate layer and the external sheet. 
         [0009]    The bolts and support plates tend to conduct heat through the sheet assembly. Heat is conducted because the bolts and support plates form a metal path through the intermediate layer. The bolts are fasten to the hot internal sheet and may be directly exposed to the hot exhaust gases if they extend through the internal sheet. The bolts conduct heat to the support plates. If an edge of the support plate is in contact with the internal sheet, heat from the internal sheet may be conducted directly to the support plate. The metal material of the bolts and support plates conducts heat to a much greater extent than does the insulation of the intermediate layer. The metal paths of the bolts and support plates form thermal bridges through the insulation of the intermediate layer of the sheet assembly. 
       BRIEF DESCRIPTION OF THE INVENTION 
       [0010]    There is a long felt need for a thermal acoustic sheet assembly for a wall of an exhaust duct that effectively suppresses the transmission of heat and acoustic noise and lacks thermal bridges that conduct heat through the sheet assembly. A thermal acoustic insulating sheet assembly has been conceived and is disclosed here for a hot gas exhaust duct of a rotary machine, a boiler or other source of a large volume of hot gases. The conceived thermal acoustic insulating sheet assembly avoids the heat conductive paths formed by bolts and support plates of a conventional sheet assembly. 
         [0011]    The thermal acoustic insulating sheet assembly may comprise an internal sheet, an external sheet parallel to the internal sheet and a thermally insulating layer or layers between the sheets. The internal sheet may be formed of stainless steel or other metal, the external sheet may be steel or another metal and the insulation in the intermediate layer includes insulation formed of layers or cushioning material formed of, for example, of mineral fibers, glass fibers, bio-soluble fibers or rock wool. 
         [0012]    The thermal acoustic insulating sheet assembly also includes bars and thermally insulating support brackets for connecting the bars to the external sheet. The bars and support brackets replace the bolts and support plates of a conventional insulting sheet assembly. The support brackets may include insulated washers and non-conductive layers that thermally isolate the bar from the support bracket. 
         [0013]    A thermal acoustic insulation structure has been conceived and is disclosed here that includes including: a metal internal sheet having an exposed surface configured to be exposed to a hot gas, an external sheet and an insulation sandwiched between the internal and external sheets; a bar secured to the metal internal sheet and extending through at least a portion of the insulation; a bracket connected to the external sheet or to a support plate extending from the external sheet, wherein the bracket includes an opening configured to receive an end of the bar; a fastener securing the end of the bar to the bracket, and an insulating washer separating the bracket from the bar and the fastener. 
         [0014]    An exhaust gas duct has been conceived and is disclosed here that includes: a gas passage, and a wall of the gas passage, wherein the wall forms a closed perimeter of a cross section of the gas passage, and the wall includes: a metal internal sheet having an exposed surface configured to be exposed to a hot gas, an external sheet and an insulation layer sandwiched between the internal and external sheets; a bar secured to the metal internal sheet and extending through at least a portion of the insulation; a bracket fixed to the external sheet, wherein the bracket includes an opening configured to receive an end of the bar; a fastener securing the end of the bar to the bracket, and an insulating washer separating the bracket from the bar and the fastener. 
         [0015]    A method to assembly a thermal acoustic wall structure has been conceived and is disclosed here that includes: sandwiching an insulation layer between a metal internal sheet having an exposed surface configured to be exposed to a hot gas and an external sheet and an insulation sandwiched between the internal and external sheets; fastening a bar to the metal internal sheet and extending the bar through at least a portion of the insulation; fastening the bar to a bracket fixed to the external sheet or to a support plate extending from the external sheet, wherein the bracket includes an opening configured to receive an end of the bar; securing the end of the bar to the bracket, and installing an insulating washer to separate the bracket from the bar and the fastener. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]      FIG. 1  is a side view of a cross section of a conventional acoustic thermal sheet assembly; 
           [0017]      FIG. 2  is a side view of the conventional acoustic thermal sheet assembly; 
           [0018]      FIG. 3  is a side view of a bar fitted on a novel support element in an acoustic thermal sheet assembly; 
           [0019]      FIG. 4  is a side view of a second embodiment of a bar fitted on a novel support element arranged in a thermal acoustic sheet assembly; and 
           [0020]      FIG. 5  is a side view of bars fitted to the support element in a thermal acoustic sheet assembly, wherein the view is along a line parallel to the support element. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0021]      FIG. 1  illustrates a conventional thermal acoustic sheet assembly  10  for an exhaust duct of a rotary machine. The insulation structure  10  comprises an internal sheet  1  and an external sheet  2 . An insulation layer  3  is between the internal  1  and external sheet  2 . A bar  4  extends through the insulation layer. A first end  4   a  of each bar is welded to an internal surface (insulation side) of the external sheet  2  such that the bar is perpendicular to the external sheet. The opposite end  4   b  of the bar extends through a hole in the internal sheet  1 . The opposite end  4   b  is threaded and receives a nut  6  that with a washer  7  secures the internal sheet to the bar. Several bars, nuts and washers are arranged in the insulation structure and hold together the assembly of the internal sheet, insulation layer and external sheet. 
         [0022]      FIG. 2  illustrates the conventional thermal acoustic sheet assembly  10  with an internal sheet  1  and an external sheet  2 . An insulation layer  3  is between the sheets  1 ,  2 . Bars  4  extend partially through the insulation layer and are fitted to a support plate  5  between the sheets. The support plate  5  may be a flat plate extending through the insulation layer and oriental perpendicularly to the internal and external sheets. The support plate  5  is parallel to other support plates in the sheet assembly. The support plates are at regular intervals across the width of the insulation structure. The support plate has a straight edge  5   a  adjacent the internal sheet. The opposite edge of the support plate includes V-shaped cuts and feet  5   b  between the cuts. The feet  5   b  are welded to an internal surface (insulation side) of the external sheet  2 . 
         [0023]    One end  4   a  of each bar  4  is welded to one of the plates  5  above the V-shaped cuts in the plate. The opposite end  4   b  of each bar is aligned with and extends through a hole in the internal sheet  1 . Nuts  6  engage threads on the end  4   b.  Annular washers  7  are fitted on the end  4   b  on opposite sides of the internal sheet. The washers and nut secure the bar and the plate to the internal sheet. The nuts and washers engage the threaded end  4   b  of the each bar such that the internal sheet compresses the insulation layer  3 . 
         [0024]    The side of the internal sheet  1  opposite to the insulation layer is exposed to hot gases discharged from the rotary machine. Because the threaded ends  4   b  of the bars  4  extend through the internal sheet, the ends of the bars are exposed to the hot gases. Heat from the hot gases conducts through the internal sheet, the bars and into the metal support plates  5 . The conducted heat through the bars and support plates allows heat to flow past the insulation layer  3  and conduct heat into the external sheet. The conduction of heat through the support plate forms a thermal bridge through the insulation layer that reduces the effectiveness of the insulation layer in suppressing the transfer of heat from the hot exhaust gas to the external sheet and to the ambient air environment beyond the insulation structure  10 . 
         [0025]      FIG. 3  illustrates a first embodiment a thermal-acoustic sheet assembly  20  for ducting exhaust gas from a rotary machine to a HRSG or other system. The elements of the structure  20  that are similar to elements of the conventional insulation structure bear the same reference numbers. 
         [0026]    The thermal-acoustic sheet assembly  20  includes one or more internal sheets  1  each having a surface exposed to the hot gases discharged from the rotary machine and one or more external sheets  2  each having a side exposed to ambient air. An insulating layer(s)  3 , such as an insulating mattress, is sandwiched between the internal and external sheets  1  and  2 . The internal and external sheets may be substantially parallel to each other, such as within five degrees of parallel. The materials and structure of the insulation layer  3  may be conventional and are not show so that the details of the connecting bars may be illustrated. 
         [0027]    Bars  22  may be arranged in a regular pattern and at regular distances in the thermal acoustic sheet assembly  20 . The bars  22  provide structural support for the thermal acoustic structure, such as providing the separation between the internal and external sheets and a compression of the insulation layer. The bars may be metal rods and formed steel or stainless steel for example. The bars may be threaded along their entire length or threaded just at their ends.  FIG. 3  shows the end sections  22   a  and  22   b  of the bar but does not show the middle section of the bar as the middle section is not necessary for the description of the invention. The entire length (L) of the bar extends from one end  22   a  to the other end  22   b  of the rod. 
         [0028]    The bars may extend the thickness of the thermal acoustic structure  20  and extend entirely through the insulation layer  3 . The bars  22  may be oriented substantially perpendicular to the internal and external sheets, such as within ten degrees of perpendicular. 
         [0029]    The bars  22  are separated from the external sheet  2  by an insulated support element  24 . The insulated support element supports the end  22   a  of the bar  22 . The insulated support element  24  is fixed to the external sheet. The insulated support element  24  provides the junction between the bar  22  and the external sheet  2 . 
         [0030]    The bar  22  is not in direct contact with the external sheet  2 . The lack of direct contact and the insulation in the insulated support element  24  prevents thermal conduction heat transfer from the bar  22  to the external sheet  2 . Because there is only minimal thermal conduction at the junction between the junction between the bar and support element, the amount of heat transferred from the bars to the external sheet is substantially reduced, such as by 70 to 90 percent or more, as compared to the heat transfer if the bar was directly connected to the external sheet or a support plate. 
         [0031]    An insulated support element  24  is at the end  22   a  of each bar  22 . The insulated support element may include a U-shaped bracket  26  that extends the length of the thermal acoustic structure  20  along a direction parallel to the exhaust gas flow. The U-shaped bracket  26  may also be configured as a platform for a single bar  22 . The U-shape of the bracket  26  refers to a cross sectional shape of the bracket which appears as an upside down U. The cross section shape may have other shapes, such as an O, L or C shape. 
         [0032]    The U-shaped bracket  26  is fixed to the insulation side of the external sheet  2 . The U-shaped bracket  26  has legs  28  that are welded to the external sheet  2 , such as by a fillet weld  30 . The legs may or may not directly contact the surface of the external sheet. A slight separation between the legs and the external sheet assists in suppressing heat transfer. The fillet weld  30  may create the separation between the legs and external sheet. 
         [0033]    A bridge portion  32  of the U-shaped bracket  26  is spaced by the length of the legs  28  from the external sheet  2 . The bridge portion  32  may be welded to the legs  28  to form the U-shaped bracket  26 . The bracket may also be formed by bending a band of metal to form the legs with the bridge on either side of the legs. The bracket may also be formed from a metal piece having a U-shape cross section. The legs  28  may form a ninety degree angle with respect to the bridge. The angle between the legs and bridge may be greater or smaller than 90 degrees such that the legs splay outward of the bridge or are canted inward of the bridge. The angle between the leg and bridge may be between 45 to 135 degrees. 
         [0034]    The bridge portion includes a circular opening  34  sized to receive an insulated washer  36 . The washer  36  is annular and has a center aperture to receive the bar  22 . The washer is an annular disc positioned on one side of the bridge  32  and may include a rim covering the perimeter of the opening  34 . A second washer  38  covers an opposite side of the bridge. Both washers  36 ,  38  are centered on the opening  34  in the bridge. Alternatively, the washers  36 ,  38  is on an opposite side of the bridge. The washers  36 ,  38  separate the metal nut or nuts  40 ,  41  on the end  22   a  of the bar from the metal of the bridge  32 . 
         [0035]    The washers  36 ,  38  provide a thermal barrier to prevent heat conduction between the nuts and the bridge. An inner insulating cylindrical rim of the washer  36  prevents heat conduction between the bar  22  and the bridge. The washers  36 ,  38  are formed of a material having a low heat transfer coefficient material such as non-metal material. The washers may be formed of a ceramic, fiber glass reinforced composite or Polytetrafluoroethylene (PTFE). The washers may also be formed of a metal coated with an insulation layer. The washers provide a thermal barrier between the metal of the bar  22  and nuts  40  and the metal of the bracket  26 . The washers  36 ,  38  may also be embodied as a brushing that seats in the opening  34 . 
         [0036]    The nuts  40 ,  41  such as hex nuts, engage the threads of the end  22   a  of the bar  22 . The nuts fasten the bar  22  to the U-shaped bracket. The nuts  40 ,  41  are on opposite sides of the bridge portion  32  of the U-shaped bracket such that the bridge is clamped between the nuts. The torque applied to the nuts is sufficient to secure the nuts and bars to the U-shaped bracket without damaging the insulation of the washer  36 . The washer may be held under compression by the nuts. The upper nut  40  may be welded  42  to the bar  22  after a desired amount of torque is applied to the nut. The lower nut  41  may be secured against rotation on the bar by an annular plate or stub  44  that receives the nut and is welded  46  to one or both of the legs  28 . The weld  42  to the upper nut may be applied after the lower nut is secured against rotation. 
         [0037]    Exemplary dimensions of the insulated support element  24  include a diameter of the washers  36 ,  38  being 20 millimeters (20 mm) and in a range of 15 mm to 25 mm. A gap  48  between the lower end of the bar  22   a  or lower surface of the nut  40  is in a range of 3 mm to 15 mm. The gap  48  provides insulation due to the air gap between the lower surface of the nut or bar and the external sheet or support plate. The gap may also allow for expansion and contraction of the length of the bar  22  and prevent the bar from expanding into contact with the external sheet. 
         [0038]    The opposite end  22   b  of the bar is secured to the internal sheet  1 . The end  22   b  extends through an opening  50  in the internal sheet  1 . The opening  50  may have a diameter of 5 to 50 mm, and have sufficient clearance from the bar to permit variations in the thermal expansion and contraction of the sheet and bar. A washer  52  is welded to the bar and forms a flange that engages an insulation side surface of the internal sheet. The threads of the end  22   b  engage a nut  54  that secures the bolt  22  to the gas exposed surface of the internal sheet. 
         [0039]    There is no support plate shown in the embodiment shown in  FIG. 3 . A support plate may be included in another embodiment of the thermal acoustic sheet assembly. The support plate may be connected along one edge to the internal sheet and along an opposite edge to bars. The bars would connect the U-shaped bracket fixed to the external sheet. 
         [0040]      FIG. 4  is a side view of an alternative embodiment of a thermal acoustic sheet assembly  60  that includes an internal sheet(s)  1 , an external sheet(s)  2  and an insulation layer  3 . The same reference numbers have been used to identify the components of the thermal acoustic structure  60  that are similar to the components of the other thermal acoustic structure  20 . 
         [0041]    The thermal acoustic structure  60  includes a second nut  62  that engages the end  22   b  of the bar  22  and the internal sheet  1 . The second nut  62  is used in place of the washer welded to the bar shown in  FIG. 3 . A washer  52  may be between either or both of the nuts  54 ,  62  and the internal sheet. The two nuts  54 ,  62  secure the bar  22  to the internal sheet such that the sheet may not slide with respect to the bar. The two nuts also provide a means to adjust the distance between the internal and external sheets. This adjustment also is used to set a compression on the insulation layer. 
         [0042]    The U-shaped bracket  26  is seated on an insulation layer  64  on the external sheet  2 . The insulation layer may be formed of a material have a low heat transfer coefficient such as a ceramic, fiber glass reinforced composite or Polytetrafluoroethylene (PTFE). The insulation layer  64  may also be positioned in the gap between the end of the nut  41  and the external sheet  2 . The insulation layer may be relatively thin, e.g., 2 mm to 4 mm between the legs  28  and the external sheet, and be relatively thick, e.g., 3 mm to 5 mm, between the nut  41  and the external sheet. 
         [0043]    A signal nut  41  may secure the end  22   a  of the bar to the U-shaped bracket  26 . The single nut is below the bridge  32  and is held in place by the bridge, threaded end  22   a  and insulation layer  64 . The nut  41  is prevented from rotation by the plate or stub  44  welded to the U-shaped bracket. A washer  66  separates the nut  41  from the U-shaped bracket to prevent conduction of heat between the nut and the bracket. The washer has a low heat transfer coefficient and may be formed of materials such as a ceramic, fiber glass reinforced composite or Polytetrafluoroethylene (PTFE). The washer  66  may also include an annular rim that covers the inner perimeter of the opening  34  in the bridge and separates the bridge from the bar. 
         [0044]      FIG. 5  is a side view of the thermal acoustic structure  60  show from a view parallel to the length of the U-shaped bracket  26 . In this embodiment, the U-shaped bracket  26  extends the length of the thermal acoustic structure  60 . The bars  22  are arranged at regular intervals along the length of the U-shaped bracket  26 . The brackets  26  may be arranged parallel to each other across the width of the structure  60  and in a direction parallel to the exhaust gas flow. 
         [0045]    The insulation layer  3  is sandwiched between the internal and external sheets  1  and  2 . The insulation layer covers the external sheet  2  except where the U-shaped bracket covers the sheet. The insulation layer fits around the U-shaped bracket but need not be within the bracket. 
         [0046]    Unlike the embodiment shown in  FIG. 4 , the embodiment shown in  FIG. 5  does not have an insulation layer that extends the length of the U-shaped bracket and fits between the legs of the bracket and external sheet. In the embodiment shown in  FIG. 5 , an insulation pad  68  is between the nut  62  and the external sheet  2 . The insulation pad may be inserted through a slot  70  in one or both of the legs  28  of the U-shaped bracket. The slot is adjacent the end  22   b  of the bar. The insulation pad has a low heat transfer coefficient and may be formed of mineral fibers, glass fibers, bio-soluble fibers, PTFE or rock wool. 
         [0047]    The thermal acoustic structure  60  may be connected at one end to an expansion joint  80  which is connected to a gas discharge  82  of a rotary machine such as a stationary gas turbine. The thermal acoustic structure may be assembled with other similar structures to form an exhaust duct defining a gas passage  84  through which flows the exhaust gas from the rotary machine. The gas passage may have a cross section that is circular, oval, rectangular or other entirely curved, curvilinear or straight sided shape. 
         [0048]    While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiment, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.