Patent Publication Number: US-2023138080-A1

Title: Expansion joint and incineration ash treatment equipment

Description:
TECHNICAL FIELD 
     The present disclosure relates to expansion joints in piping systems through which powdery or granular materials are transferred and in particular to an expansion joint that is located at a point of connection of pipes in a region where a powdery or granular material is transferred by gravity and that absorbs displacement between the connected pipes. The present disclosure also relates to incineration ash treatment equipment including the expansion pipe. 
     BACKGROUND ART 
     Conventionally, there is known an expansion joint included in equipment for treatment of powdery or granular materials and used at a connection point where displacement between connected parts occurs, such as at a point of connection between a vibrator and a pipe. The present applicant has proposed such a kind of expansion joint in Patent Literature 1. 
     The expansion joint of Patent Literature 1 includes an outer tube, an inner tube located inside the outer tube, and an elastic closure (bellows) closing a gap between the upstream ends of the inner and outer tubes. The downstream end of the outer tube is connected to a downstream pipe, and the upstream end of the inner tube is connected to an upstream pipe. The upstream ends of the inner and outer tubes are located at substantially the same height. In the expansion joint of Patent Literature 1, the downstream end of the inner tube and the closure are far enough from each other to prevent contact between the closure and a hot transferred material getting in between the inner and outer tubes. 
     CITATION LIST 
     Patent Literature 
     PTL 1: Japanese Laid-Open Patent Application Publication No. 2018-173117 
     SUMMARY OF INVENTION 
     Technical Problem 
     Expansion joints are inserted between upstream and downstream pipes placed beforehand. Expansion joints are heavy, and may be located at great heights or in narrow places. With the use of the expansion joint of Patent Literature 1 in such a situation, the expansion joint mounting work including connecting the inner tube to the upstream pipe and attaching the closure could be cumbersome because the upstream end of the outer tube, the upstream end of the inner tube, and the downstream end of the upstream pipe are located at substantially the same height. 
     The present disclosure has been made in view of the above circumstances, and an object of the present disclosure is to propose an expansion joint in which the downstream end of an inner tube and a closure are far enough from each other and which can easily be mounted and removed. 
     Solution to Problem 
     An expansion joint according to one aspect of the present disclosure is an expansion joint that absorbs displacement occurring at a point of connection between upstream and downstream pipes through which a powdery and/or granular material is transferred by gravity, the expansion joint including: 
     an outer tube including opposite first and second ends and extending from the first end to the second end in an axial direction of the expansion joint, the outer tube further including a first flange and a second flange, the first flange being located at the first end, the second flange being located at the second end and connectable to the downstream pipe; 
     an inner tube including opposite third and fourth ends and extending from the third end to the fourth end in the axial direction, the inner tube being located inside the outer tube and further including a third flange and a middle flange, the third flange being located at the third end and connectable to the upstream pipe, the middle flange being located at a middle portion between the third and fourth ends; and 
     a closure including an outer peripheral portion connected to the first flange, an inner peripheral portion connected to the middle flange, and an elastic portion connecting the outer peripheral portion to the inner peripheral portion, wherein 
     the first end is spaced from the third end in the axial direction and located between the third and fourth ends in the axial direction. 
     Incineration ash treatment equipment according to one aspect of the present disclosure includes: a vibrator that treats incineration ash; a pipe that delivers the incineration ash to the vibrator; and the expansion joint as defined above, the expansion joint being located between an outlet of the pipe and an inlet of the vibrator. 
     In the expansion joint and incineration ash treatment equipment configured as described above, the middle flange, to which the closure is attached, is spaced from the fourth end (i.e., downstream end) of the inner tube in the axial direction. Thus, the fourth end of the inner tube and the closure can be spaced a distance corresponding to the distance between the fourth end and middle flange of the inner tube in the axial direction. This can reduce the likelihood that the transferred material entering the gap between the inner tube and the outer tube from the fourth end of the inner tube comes into contact with the closure  4 . 
     In the expansion joint and incineration ash treatment equipment configured as described above, the first flange located at the first end of the outer tube and the third flange located at the third end of the inner tube are spaced from each other in the axial direction. The space between the first flange and the third flange in the axial direction can be used as a workspace for connection (or disconnection) of the third flange and the upstream pipe. Thus, connection and disconnection of the expansion joint and the upstream pipe can easily be performed. 
     In the expansion joint and incineration ash treatment equipment configured as described above, the third end of the inner tube connected to the upstream pipe and the first end of the outer tube are spaced from each other in the axial direction. Thus, the dimension of the outer tube in the axial direction is smaller than the vertical dimension of a mounting region extending between the upstream pipe and the downstream pipe. As such, the outer tube with the inner tube inserted therein can easily be carried into the mounting region. After the inner tube and the outer tube are placed in the mounting region, the closure can be carried into the mounting region by utilizing a gap between the upstream pipe and the outer tube. Additionally, the space between the third flange and the middle flange in the axial direction can be used as a workspace for attachment (or detachment) of the closure. Thus, attachment and detachment of the closure are easy. 
     Advantageous Effects of Invention 
     The present disclosure can propose an expansion joint in which the downstream end of an inner tube and a closure are far enough from each other and which can easily be mounted and removed. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG.  1    shows a schematic configuration of incineration ash treatment equipment including an expansion joint according to an exemplary embodiment of the present disclosure. 
         FIG.  2    shows the expansion joint according to the exemplary embodiment of the present disclosure and is an end view of the expansion joint cut along a plane including the central axis of the expansion joint. 
         FIG.  3    shows an outer tube as viewed in the axial direction. 
         FIG.  4    shows an inner tube as viewed in the axial direction. 
         FIG.  5    shows a closure as viewed in the axial direction. 
         FIG.  6    is a view taken along the arrow VI-VI of  FIG.  2   . 
         FIG.  7    illustrates how to mount the expansion joint. 
         FIG.  8    illustrates how to mount the expansion joint. 
         FIG.  9    illustrates how to mount the expansion joint. 
         FIG.  10    illustrates how to mount the expansion joint. 
         FIG.  11    shows an expansion joint according to a first variant and is an end view of the expansion joint cut along a plane including the central axis of the expansion joint. 
         FIG.  12    shows an expansion joint according to a second variant and is an end view of the expansion joint cut along a plane including the central axis of the expansion joint. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Hereinafter, exemplary embodiments of the present disclosure will be described with reference to the drawings.  FIG.  1    shows a schematic configuration of incineration ash treatment equipment  7  including an expansion joint  10  according to an exemplary embodiment of the present disclosure. The incineration ash treatment equipment  7  is adapted to finely grind incineration ash generated, for example, in a coal-fired boiler or garbage incinerator. 
     The incineration ash treatment equipment  7  of  FIG.  1    includes a grinder  75  that finely grinds incineration ash  70 , a conveyor  74  that transfers the incineration ash  70  to the grinder  75 , and a hopper  76  that receives the incineration ash  70  ground by the grinder  75 . A vibrating mill can be used as the grinder  75 . In a typical vibrating mill, a grinding medium and a material to be ground collides with each other in a rapidly vibrating drum, and thus the material is finely ground. 
     The conveyor  74  and the grinder  75  are connected by a piping system through which the incineration ash  70  in the form of grains or aggregates is transferred. The piping system includes a vibrating pipe  78  coupled to the inlet of the grinder  75 , a fixed pipe  77  located upstream of the vibrating pipe  78 , and an expansion joint  10  connecting the fixed pipe  77  to the vibrating pipe  78 . The terms “upstream” and “downstream”, as used in the specification and the appended claims, respectively refer to upstream and downstream in the direction of flow of the material (incineration ash  70 ) transferred through the piping system. The fixed pipe  77  is an “upstream pipe” for the expansion joint  10 , and the vibrating pipe  78  is a “downstream pipe” for the expansion joint  10 . 
     The fixed pipe  77  is fixed relative to a structure including a device upstream of the grinder  75  (the device is, for example, the conveyor  74  or an unshown device used for another coal treatment process). The vibrating pipe  78  vibrates in conjunction with vibration of the drum of the grinder  75 . Thus, displacement occurs at a point of connection between the fixed pipe  77  and the vibrating pipe  78  due to the vibration of the vibrating pipe  78 . The expansion joint  10  absorbs the displacement occurring at the point of connection between the fixed pipe  77  and the vibrating pipe  78 . The expansion joint  10  according to the present disclosure is applicable also in the case where both the fixed pipe  77  and the vibrating pipe  78  are movable. 
     [Structure of Expansion Joint  10 ] 
     Hereinafter, the expansion joint  10  will be described in detail.  FIG.  2    shows the expansion joint  10  according to an exemplary embodiment of the present disclosure and is an end view of the expansion joint  10  cut along a plane including the central axis of the expansion joint  10 . The expansion joint  10  is generally shaped as a solid of revolution. The direction in which the axis of revolution extends is referred to as the “axial direction X” of the expansion joint  10 , and the axis of revolution is referred to as the “central axis” of the expansion joint  10 . The expansion joint  10  is mounted in a space between the fixed pipe  77  and the vibrating pipe  78  in the up-down direction. The space between the fixed pipe  77  and the vibrating pipe  78  in the up-down direction will be referred to as a “mounting region A” hereinafter. When the vibrating pipe  78  is at rest, a straight line drawn between the center of the opening of the fixed pipe  77  and the center of the opening of the vibrating pipe  78  is parallel to the axial direction X of the expansion joint  10 . 
     The expansion joint  10  of  FIG.  2    includes an outer tube  2 , an inner tube  3  located inside the outer tube  2 , and a closure  4  closing a gap between the outer tube  2  and the inner tube  3 . The inner circumference of the inner tube  3  defines a transfer path  11  along which the transferred material (e.g., the incineration ash  70 ) flows through the expansion joint  10 . 
       FIG.  3    shows the outer tube  2  as viewed in the axial direction X. As shown in  FIGS.  2  and  3   , the outer tube  2  is a metallic tubular body extending from its upstream end (first end) to its downstream end (second end) in the axial direction X. The outer tube  2  includes a first flange  21  located at the upstream end of the outer tube  2 , a second flange  22  located at the downstream end of the outer tube  2 , a barrel  23  connecting the first flange  21  to the second flange  22 , and a baffle plate  24  located on the inner circumference of the barrel  23 . Each of the first and second flanges  21  and  22  includes circumferentially arranged insertion holes. Bolts are inserted into the insertion holes. 
     The second flange  22  is connected to an inlet flange  78   a  located at the upstream end of the vibrating pipe  78 . Between the second flange  22  and the inlet flange  78   a  there is a lower gasket  37  that provides hermeticity. The outer tube  2  vibrates in conjunction with vibration of the vibrating pipe  78 . 
     The inner diameter D 21  of the first flange  21  is greater than the inner diameter D 22  of the second flange  22 . The barrel  23  is tapered downward to smoothly connect the first and second flanges  21  and  22  having different inner diameters. The outer tube  2  structured as described above can ensure a range over which the outer tube  2  is displaceable relative to the inner tube  3  in a direction perpendicular to the axial direction X and at the same time allow for quick movement or transfer of the material from the outer tube  2  to the vibrating pipe  78 . 
     The baffle plate  24  serves to prevent the transferred material accumulated in the transfer path  11  of the expansion joint  10  from entering the gap between the outer tube  2  and the inner tube  3 . The baffle plate  24  is shaped as an annular disc and located at approximately the center of the barrel  23  in the axial direction X. The inner diameter D 24   a  of the baffle plate  24  is greater than the inner diameter D 22  of the second flange  22 . The outer diameter D 24   b  of the baffle plate  24  is smaller than the inner diameter D 21  of the first flange  21 . The outer periphery of the baffle plate  24  is welded to the inner circumferential surface of the barrel  23 . 
       FIG.  4    shows the inner tube  3  as viewed in the axial direction X. As shown in  FIGS.  2  and  4   , the inner tube  3  is a metallic tubular body extending from its upstream end (third end) to its downstream end (fourth end) in the axial direction X. The inner tube  3  includes a third flange  31  located at the upstream end of the inner tube  3 , a barrel  32  extending downward from the third flange  31 , and a middle flange  33  located at a middle portion of the barrel  32  in the axial direction X. The middle flange  33  includes circumferentially arranged insertion holes. Bolts are inserted into the insertion holes. 
     The third flange  31  is connected to an outlet flange  77   a  located at the downstream end of the fixed pipe  77 . The outer diameter D 31  of the third flange  31  is smaller than the outer diameter of the outlet flange  77   a . The third flange  31  is placed between retainers  25  and the outlet flange  77   a , and the retainers  25 , outlet flange  77   a , and third flange  31  are fastened together by bolts inserted through the retainers  25  and the outlet flange  77   a . The retainers  25  (the number of which is, for example, four) are arranged along the outer periphery of the third flange  31 . Each of the retainers  25  is shaped as a segment of a ring, and the retainers  25  form the ring together. Each of the retainers  25  includes a cut at its upper inner periphery, and the third flange  31  is fitted in the cut. Thus, the third flange  31  of the inner tube  3  is restricted from moving relative to the outlet flange  77   a  of the fixed pipe  77  in the radial and up-down directions in the event that the point of connection between the fixed pipe  77  and the inner tube  3  is subjected to vibration. Each of the retainers  25  includes at least one insertion hole  25   a  for insertion of a bolt. Between the retainers  25  and the outlet flange  77   a  there is an upper gasket  36  that provides hermeticity. 
     The middle flange  33  protrudes radially outward from the outer circumferential surface of the barrel  32 . The outer diameter D 33  of the middle flange  33  is greater than the inner diameter D 24   a  of the baffle plate  24  and smaller than the outer diameter D 24   b  of the baffle plate  24 . To improve the handleability of the inner tube  3 , the outer diameter D 31  of the third flange  31  is desirably smaller than the outer diameter D 33  of the middle flange  33 . 
       FIG.  5    shows the closure  4  as viewed in the axial direction X. As shown in  FIGS.  2  and  5   , the closure  4  is shaped as an annular disc. The closure  4  includes an inner peripheral portion  41 , an outer peripheral portion  42 , and an elastic portion  43  located between the inner peripheral portion  41  and the outer peripheral portion  42 . Each of the inner and outer peripheral portions  41  and  42  includes circumferentially arranged insertion holes. Bolts are inserted into the insertion holes. 
     The inner diameter D 41  of the closure  4  is greater than the outer diameter D 32  of the barrel  32  of the inner tube  3  (i.e., the inner diameter of the middle flange  33 ) and smaller than the outer diameter D 33  of the middle flange  33 . The outer diameter D 42  of the closure  4  is greater than the inner diameter D 21  of the first flange  21  of the outer tube  2 . 
       FIG.  6    is a view taken along the arrow VI-VI of  FIG.  2   . As shown in  FIGS.  2  and  6   , the inner peripheral portion  41  of the closure  4  is connected to the middle flange  33  of the inner tube  3 . The inner peripheral portion  41  is placed between the middle flange  33  of the inner tube  3  and retainers  28 , and the retainers  28 , inner peripheral portion  41 , and middle flange  33  are fastened together by bolts inserted through the retainers  28 , inner peripheral portion  41 , and middle flange  33 . The retainers  28  (the number of which is, for example, four) are arranged in a ring along the inner peripheral portion  41 . Each of the retainers  28  is shaped as a segment of a ring, and the retainers  28  form the ring together. 
     The outer peripheral portion  42  of the closure  4  is connected to the first flange  21  of the outer tube  2 . The outer peripheral portion  42  is placed between the first flange  21  of the outer tube  2  and retainers  26 , and the retainers  26 , outer peripheral portion  42 , and first flange  21  are fastened together by bolts inserted through the retainers  26 , outer peripheral portion  42 , and first flange  21 . The retainers  26  (the number of which is, for example, four) are arranged in a ring along the outer peripheral portion  42 . Each of the retainers  26  is shaped as a segment of a ring, and the retainers  26  form the ring together. 
     The elastic portion  43  is expanded or contracted to absorb displacement of the outer peripheral portion  42  relative to the inner peripheral portion  41  in the axial direction X and the radial direction. The elastic portion  43  shown in  FIG.  2    is made of rubber, resin, or fabric and includes one or more corrugations arranged in the radial direction. The elastic portion  43  is not limited to being corrugated. For example, the elastic portion  43  of the closure  4  may be shaped as a flat sheet insofar as the elastic portion  43  is made of elastic rubber or resin. In the case where the material to be transferred is hot, a heat-resistant material is desirably used for the elastic portion  43 . 
     As shown in  FIG.  2   , for the expansion joint  10  configured as described above, the dimension of the outer tube  2  in the axial direction X is referred to as “outer tube height H 2 ”, the dimension of the inner tube  3  in the axial direction X is referred to as “inner tube height H 3 ”, the dimension of the inner tube  3  from its upstream end to the middle flange  33  in the axial direction X is referred to as “protrusion height H 3   a ”, the dimension of the closure  4  in the axial direction X is referred to as “closure height H 4 ”, and the dimension of the mounting region A in a direction parallel to the axial direction X is referred to as “mounting region height H 0 ”. 
     The outer tube height H 2  is smaller than the mounting region height H 0 . The sum of the outer tube height H 2  and the closure height H 4  is desirably smaller than the mounting region height H 0 . 
     The inner tube height H 3  is smaller than the mounting region height H 0 . The sum of the inner tube height H 3  and the closure height H 4  is desirably smaller than the mounting region height H 0 . The protrusion height H 3   a  is desirably greater than the closure height H 4 . 
     The sum of the outer tube height H 2 , the protrusion height H 3   a , the thickness of the upper gasket  36 , and the thickness of the lower gasket  37  is substantially equal to the mounting region height H 0 . 
     [How to Mount Expansion Joint  10 ] 
     The following describes how to mount the expansion joint  10 .  FIGS.  7  to  10    illustrate how to mount the expansion joint  10 . 
     First, as shown in  FIG.  7   , the outer tube  2  and the inner tube  3  are combined into an assembly  20 . To construct the assembly  20 , the inner tube  3  is inserted into the outer tube  2  from above. In the assembly  20 , the upper surface of the baffle plate  24  of the outer tube  2  is in contact with the lower surface of the middle flange  33  of the inner tube  3 . Thus, the inner tube  3  is stably supported by the outer tube  2  and restricted from moving downward relative to the outer tube  2 . 
     The assembly  20  is placed into the mounting region A, and the second flange  22  of the outer tube  2  is placed onto the inlet flange  78   a  of the vibrating pipe  78 . The dimension of the assembly  20  in the axial direction X is referred to as “assembly height H 20 ”. The assembly height H 20  is smaller than the mounting region height H 0  by approximately an extension amount H 24  corresponding to the length from the baffle plate  24  to the first flange  21  in the axial direction X. As the assembly height H 20  is smaller than the mounting region height H 0 , the assembly  20  can easily be brought into the mounting region A in a direction perpendicular to the axial direction X. 
     Next, as shown in  FIG.  8   , the closure  4  is placed into the mounting region A. The sum of the assembly height H 20  and the closure height H 4  is desirably smaller than the mounting region height H 0  so that the closure  4  can easily be brought into the mounting region A in a direction perpendicular to the axial direction X. As the closure  4  is elastically deformable, the size of the gap between the fixed pipe  77  and the assembly  20  may be slightly smaller than the closure height H 4 . 
     Subsequently, as shown in  FIG.  9   , the inner tube  3  is raised a distance equal to the extension amount H 24  relative to the outer tube  2  to bring the third flange  31  of the inner tube  3  into contact with the outlet flange  77   a  of the fixed pipe  77 . As a result, the location of the middle flange  33  of the inner tube  3  in the axial direction X becomes approximately the same as the location of the first flange  21  of the outer tube  2  in the axial direction X. 
     Afterwards, as shown in  FIG.  10   , the outlet flange  77   a  of the fixed pipe  77  and the third flange  31  are fastened by bolts. The inlet flange  78   a  of the vibrating pipe  78  and the second flange  22  are fastened by bolts, the inner peripheral portion  41  of the closure  4  and the middle flange  33  are fastened by bolts, and the outer peripheral portion  42  of the closure  4  and the first flange  21  of the outer tube  2  are fastened by bolts. The bolt fastening may be performed at any time during the mounting work. 
     The expansion joint  10  can be removed by a reverse procedure to the mounting of the expansion joint  10 . That is, the expansion joint  10  can be removed from the mounting region A by unfastening the bolts, lowering the inner tube  3  toward the outer tube  2 , removing the closure  4  from the mounting region A, and removing the assembly  20  from the mounting region A. 
     As described above, incineration ash treatment equipment  7  according to an exemplary embodiment includes a grinder  75  serving as a vibrator that treats incineration ash, a pipe (a fixed pipe  77  serving as an upstream pipe) that delivers the incineration ash to the grinder  75 , and an expansion joint  10  located between an outlet of the pipe and an inlet of the grinder  75  (or a vibrating pipe  78  serving as a downstream pipe). The expansion joint  10  absorbs displacement occurring at a point of connection between the upstream and downstream pipes  77  and  78  through which a powdery and/or granular material is transferred by gravity. The expansion joint  10  includes an outer tube  2 , an inner tube  3  located inside the outer tube  2 , and a closure  4  closing a gap between the outer tube  2  and the inner tube  3 . The outer tube  2  includes opposite first and second ends (upstream and downstream ends) and extends from the first end to the second end in an axial direction X of the expansion joint  10 . The outer tube  2  further includes a first flange  21  and a second flange  22 , the first flange  21  being located at the first end, the second flange  22  being located at the second end and connectable to the downstream pipe. The inner tube  3  includes opposite third and fourth ends (upstream and downstream ends) and extends from the third end to the fourth end in the axial direction X. The inner tube  3  further includes a third flange  31  and a middle flange  33 , the third flange  31  being located at the third end and connectable to the upstream pipe, the middle flange  33  being located at a middle portion between the third and fourth ends. The closure  4  includes an outer peripheral portion  42  connected to the first flange  21 , an inner peripheral portion  41  connected to the middle flange  33 , and an elastic portion  43  connecting the outer peripheral portion  42  to the inner peripheral portion  41 . 
     In the expansion joint  10  according to the above embodiment, the first flange  21  of the outer tube  2  secured to the downstream pipe  78  and the middle flange  33  of the inner tube  3  secured to the upstream pipe  77  are at the same location in the axial direction X. The statement that “the first flange  21  and the middle flange  33  are at the same location in the axial direction X” is intended to include not only the case where the location of the first flange  21  in the axial direction X and the location of the middle flange  33  in the axial direction X are exactly the same, but also the case where the distance between the locations of the first flange  21  and the middle flange  33  in the axial direction X is equal to or below a threshold. For example, the threshold is equal to, and desirably smaller than, the dimension of the closure  4  in the axial direction X (i.e., the closure height H 4 ). 
     The present disclosure is not limited to the expansion joint  10  in which the first flange  21  of the outer tube  2  secured to the downstream pipe  78  and the middle flange  33  of the inner tube  3  secured to the upstream pipe  77  are at the same location in the axial direction X. In the expansion joint  10 , the first end (upstream end) of the outer tube  2  may be spaced from the third end (upstream end) of the inner tube  3  in the axial direction X and located between the third end and the fourth end (downstream end) of the inner tube  3  in the axial direction X. 
     In the expansion joint  10  and incineration ash treatment equipment  7  configured as described above, the middle flange  33 , to which the closure  4  is attached, is spaced from the fourth end of the inner tube  3  in the axial direction X. Thus, the downstream end of the inner tube  3  and the closure  4  can be spaced a distance corresponding to the distance between the downstream end and middle flange  33  of the inner tube  3  in the axial direction X. This can reduce the likelihood that the transferred material entering the gap between the inner tube  3  and the outer tube  2  from the downstream end of the inner tube  3  comes into contact with the closure  4 . 
     In the expansion joint  10  and incineration ash treatment equipment  7  configured as described above, the first flange  21  located at the first end of the outer tube  2  and the third flange  31  located at the third end of the inner tube  3  and connected to the upstream pipe  77  are spaced from each other in the axial direction X. The space between the first flange  21  and the third flange  31  in the axial direction X can be used as a workspace for connection (or disconnection) of the third flange  31  and the upstream pipe  77 . Despite the first flange  21  being located radially outside the third flange  31 , the work of connecting the third flange  31  and the upstream pipe  77  is not disturbed by the first flange  21 . Thus, connection and disconnection of the expansion joint  10  and the upstream pipe  77  can easily be performed. 
     In the expansion joint  10  and incineration ash treatment equipment  7  configured as described above, the third end (upstream end) of the inner tube  3  connected to the upstream pipe  77  and the first end (upstream end) of the outer tube  2  connected to the downstream pipe  78  are spaced from each other in the axial direction X. Thus, the dimension of the outer tube  2  in the axial direction X (outer tube height H 2 ) is smaller than the vertical dimension of the mounting region A extending between the upstream pipe  77  and the downstream pipe  78  (mounting region height H 0 ). As such, the outer tube  2  with the inner tube  3  inserted therein (i.e., the assembly  20 ) can easily be carried into the mounting region A. After the assembly  20  constructed of the inner tube  3  and the outer tube  2  is placed in the mounting region A, the closure  4  can be carried into the mounting region A by utilizing a gap extending downward from the upstream pipe  77  and having a size corresponding to the extension amount H 24 . Additionally, the space between the third flange  31  connected to the upstream pipe  77  and the middle flange  33  can be used as a workspace for attachment (or detachment) of the closure  4 . Thus, attachment and detachment of the closure  4  are easy, and this is advantageous not only in mounting/removing work but also in maintenance work in which only the closure  4  is replaced by a new one. 
     In the expansion joint  10  and incineration ash treatment equipment  7  according to the above embodiment, the downstream end of the inner tube  3  and the closure  4  are far enough from each other to avoid contact between the transferred material and the closure  4 . The expansion joint  10  serves the same function as the conventional expansion joint disclosed in Patent Literature 1 and is easier to mount and remove than the conventional expansion joint. 
     In the expansion joint  10  according to the above embodiment, the outer diameter D 33  of the middle flange  33  is greater than the inner diameter D 22  of the second flange  22  and smaller than the inner diameter D 21  of the first flange  21 . 
     Thus, the inner tube  3  is stably supported by the outer tube  2  in the assembly  20  constructed by inserting the inner tube  3  into the outer tube  2 . 
     In the expansion joint  10  according to the above embodiment, the outer tube  2  includes a baffle plate  24  shaped as an annular disc that projects radially from an inner circumferential surface of the outer tube  2 . Although the baffle plate  24  according to the above embodiment is shaped as an annular disc that is circumferentially continuous, the baffle plate  24  may be shaped as an annular disc that is circumferentially discontinuous. 
     The baffle plate  24  serves to prevent the transferred material from reaching the closure  4  through the gap between the outer tube  2  and the inner tube  3 . This can reduce the likelihood of contact between the transferred material and the closure  4 . 
     In the above expansion joint  10 , the baffle plate  24  is located between the middle flange  33  and the second flange  22  in the axial direction X, and the outer diameter of the middle flange  33  is greater than the inner diameter of the baffle plate  24  and smaller than the outer diameter of the baffle plate  24 . 
     Thus, in the assembly  20  constructed by inserting the inner tube  3  into the outer tube  2 , the middle flange  33  is in contact with, and supported by, the baffle plate  24 . As such, the inner tube  3  is stably supported by the outer tube  2 . 
     The expansion joint  10  according to the above embodiment further includes first retainers  25  arranged circumferentially along an outer periphery of the third flange  31  to hold the third flange  31  between the upstream pipe  77  and the first retainers. Each of the first retainers  25  includes at least one insertion hole  25   a  for insertion of a bolt. 
     The insertion holes through which bolts are inserted to connect the third flange  31  to the outlet flange  77   a  of the upstream pipe  77  are included in the first retainers  25 , rather than the third flange  31 . This eliminates the need to adjust the rotational position of the inner tube  3  to align the outlet flange  77   a  and the third flange  31 . Additionally, each of the first retainer  25  is not shaped as a circular ring but a segment of a circular ring, and thus the first retainers  25  can be arranged around the third flange  31  without having to pass the inner tube  3  through the central opening of the circular ring formed by the first retainers  25 . As such, mounting and removal of the expansion joint  10  are simplified. 
     The expansion joint  10  according to the above embodiment further includes second retainers  28  arranged circumferentially along the inner peripheral portion  41  of the closure  4  to hold the inner peripheral portion  41  between the middle flange  33  and the second retainers  28 . The expansion joint  10  according to the above embodiment further includes third retainers  26  arranged circumferentially along the outer peripheral portion  42  of the closure  4  to hold the outer peripheral portion  42  between the first flange  21  and the third retainers  26 . 
     Each of the second retainers  28  and the third retainers  26  is not shaped as a circular ring but a segment of a circular ring. Thus, the second retainers  28  can be arranged along the inner peripheral portion  41  of the closure  4  without having to pass the outer tube  2 , inner tube  3 , and closure  4  through the central opening of the circular ring formed by the second retainers  28 . The third retainers  26  can be arranged along the outer peripheral portion  42  of the closure  4  without having to pass the outer tube  2 , inner tube  3 , and closure  4  through the central opening of the circular ring formed by the third retainers  26 . 
     Although the foregoing has described a preferred embodiment of the present disclosure, the scope of the present disclosure embraces modifications made to the details of the structure and/or function of the above embodiment without departing from the gist of the present disclosure. 
     For example, although the outer tube  2  of the expansion joint  10  according to the above embodiment includes the baffle plate  24 , the baffle plate  24  is not essential and may be omitted. 
       FIG.  11    shows an expansion joint  10 A according to a first variant and is an end view of the expansion joint  10 A cut along a plane including the central axis of the expansion joint  10 A. The expansion joint  10 A of  FIG.  11    includes an outer tube  2 A, which is devoid of the baffle plate  24 . In the assembly  20  constructed of the outer tube  2 A and the inner tube  3 , the middle flange  33  of the inner tube  3  is in contact with the inner circumferential surface of the barrel  23  of the outer tube  2 A. Thus, the inner tube  3  is supported by the outer tube  2 A and restricted from moving downward relative to the outer tube  2 A. Despite the absence of the baffle plate  24 , the likelihood of contact between the transferred material and the closure  4  can be reduced since the closure  4  is maximally far from a point where the transferred material enters the gap between the inner tube  3  and the outer tube  2 A. 
       FIG.  12    shows an expansion joint  10 B according to a second variant and is an end view of the expansion joint  10 B cut along a plane including the central axis of the expansion joint  10 B. The expansion joint  10 B of the  FIG.  12    includes an outer tube  2 A, which is devoid of the baffle plate  24 . The expansion joint  10 B includes an inner tube  3 A including a lower flange  34  located below the middle flange  33 . The lower flange  34  protrudes radially outward from the outer circumferential surface of the barrel  32 . The outer diameter of the lower flange  34  is smaller than the outer diameter D 33  of the middle flange  33 . In the assembly  20  constructed of the outer tube  2 A and the inner tube  3 A, the lower flange  34  of the inner tube  3  A is in contact with the inner circumferential surface of the barrel  23  of the outer tube  2 A. Thus, the inner tube  3 A is supported by the outer tube  2 A and restricted from moving downward relative to the outer tube  2 A. Despite the absence of the baffle plate  24 , the likelihood of contact between the transferred material and the closure  4  can be reduced since the lower flange  34  serves to prevent the transferred material from entering the gap between the inner tube  3 A and the outer tube  2 A. 
     INDUSTRIAL APPLICABILITY 
     The expansion joint according to the present disclosure is not limited to the embodiments described above, and can be widely used as an expansion unit included in a piping system through which a powdery or granular material is transferred, in particular as an expansion unit that is located at a point of connection of pipes in a region where the material is transferred by gravity and that absorbs displacement between the connected pipes. 
     REFERENCE SIGNS LIST 
     
         
         
           
               2 : outer tube 
               3 : inner tube 
               4 : closure 
               7 : incineration ash treatment equipment 
               10 : expansion joint 
               21 : first flange 
               22 : second flange 
               24 : baffle plate 
               25 ,  26 ,  28 : retainer 
               31 : third flange 
               33 : middle flange 
               41 : inner peripheral portion 
               42 : outer peripheral portion 
               43 : elastic portion 
               70 : incineration ash 
               77 : fixed pipe (upstream pipe) 
               78 : vibrating pipe (downstream pipe)