Patent Publication Number: US-2023151962-A1

Title: Plate-shaped heat insulator, combustion chamber, boiler and water heater

Description:
TECHNICAL FIELD 
     The present disclosure relates to a plate-shaped heat insulator, a combustion chamber, a boiler, and a water heater. 
     BACKGROUND ART 
     Boilers and water heaters have been used as devices for supplying steam and hot water using fuels such as oil. 
     In boilers and water heaters, a fuel is combusted in a combustion chamber, and the combustion heat is transferred to water through a water pipe in the combustion chamber for heat exchange, whereby steam and hot water are generated from water. 
     The combustion chamber is subjected to high temperatures and is thus usually protected with a refractory or a heat insulator to protect peripheral devices from heat damage and to reduce energy loss (for example, see Patent Literature 1 and Patent Literature 2). 
     Common refractories or heat insulators for use particularly in the combustion chamber subjected to high temperatures from a combustion gas include one obtained by pouring a fluid containing a heat-resistant material onto a surface of an object to be insulated and solidifying the fluid thereon. Such a material is also referred to as a castable material. 
     CITATION LIST 
     Patent Literature 
     
         
         Patent Literature  1 : JP  4946594  B 
         Patent Literature  2 : JP  4640705  B 
       
    
     SUMMARY OF INVENTION 
     Technical Problem 
     While the castable material can follow a surface of any shape to impart heat insulation, the castable material is formed integrally with a surface of an object to be insulated, so that the castable material is susceptible to damage such as breakage and cracking due to thermal shrinkage. 
     The present disclosure was made to solve the above issue. An object of the present disclosure is to provide a plate-shaped heat insulator less susceptible to damage caused by thermal shrinkage. 
     Solution to Problem 
     Specifically, the plate-shaped heat insulator of the present disclosure includes an aggregate of multiple heat insulating members containing inorganic fibers, wherein the plate-shaped heat insulator is intended to be disposed in a combustion chamber. 
     The plate-shaped heat insulator of the present disclosure includes an aggregate of multiple heat insulating members, so that stress due to thermal shrinkage is dispersed instead of being locally concentrated, as compared to an integrated heat insulator. Thus, damage caused by thermal shrinkage is less likely to occur. 
     Preferably, the plate-shaped heat insulator of the present disclosure is a stack of the multiple heat insulating members stacked in a thickness direction of the plate-shaped heat insulator. 
     In the case of a single thick plate-shaped heat insulator, stress due to thermal shrinkage is concentrated on a surface of the plate-shaped heat insulator, the surface being adjacent to a combustion chamber. This sometimes increases the risk of causing damage such as cracking in the surface of the plate-shaped heat insulator, the surface being adjacent to the combustion chamber. In contrast, the plate-shaped heat insulator of the present disclosure is a stack of multiple heat insulating members stacked in the thickness direction of the plate-shaped heat insulator and thus can reduce the risk described above. 
     In the plate-shaped heat insulator of the present disclosure, preferably, at least one of the multiple heat insulating members of the stack includes a recess in a surface facing another heat insulating member. 
     With such a configuration, an air layer can be formed between two heat insulating members stacked in the thickness direction. This can improve the heat insulation. 
     Preferably, the plate-shaped heat insulator of the present disclosure is a sheet including the multiple heat insulating members disposed in a plane direction of the plate-shaped heat insulator. 
     The plate-shaped heat insulator of the present disclosure is a sheet including the multiple heat insulating members disposed in the plane direction of the plate-shaped heat insulator and thus can reduce or prevent breakage or cracking associated with thermal shrinkage in the plane direction. 
     In the plate-shaped heat insulator of the present disclosure, preferably, two heat insulating members facing each other in the plane direction among the multiple heat insulating members of the sheet are configured such that cross sections thereof parallel to a direction in which the two heat insulating members face each other and parallel to the thickness direction of the plate-shaped heat insulator have shapes that fit each other. 
     When the two heat insulating members facing each other in the plane direction have cross sectional shapes that fit each other, heat transfer in the thickness direction between the heat insulating members of the sheet can be reduced or prevented. This can improve the heat insulation. 
     Preferably, the plate-shaped heat insulator of the present disclosure is a multilayer sheet including multiple sheets stacked in the thickness direction of the plate-shaped heat insulator, each sheet being the one defined above, and a position wherethe multiple heat insulating members faces each other in the plane direction varies among the multiple sheets. 
     With such a configuration, positions where heat transfer in the thickness direction is likely to occur in the sheets do not overlap each other. This improves the heat insulation as a whole. 
     In the plate-shaped heat insulator of the present disclosure, preferably, the two heat insulating members facing each other in the plane direction are in contact with each other without a gap. 
     When the two heat insulating members facing each other in the plane direction are in contact with each other without a gap, the heat insulation of the plate-shaped heat insulator can be improved. 
     In the plate-shaped heat insulator of the present disclosure, preferably, a gap is present between the two heat insulating members facing each other in the plane direction, and the gap is filled with an amorphous material containing an inorganic material. 
     When the gap between the two heat insulating members facing each other in the plane direction is filled with the amorphous material, a reduction in heat insulation due to the gap between heat insulating members can be reduced or prevented. 
     In the plate-shaped heat insulator of the present disclosure, preferably, the inorganic fibers include at least one selected from the group consisting of biosoluble fibers, alumina fibers, rock wool, and glass fibers. 
     When the inorganic fibers include any of these materials, the resulting plate-shaped heat insulator has excellent heat resistance. 
     In the plate-shaped heat insulator of the present disclosure, preferably, the inorganic fibers have an average fiber length of 0.05 to 3.0 mm. 
     The inorganic fibers having an average fiber length in the above range result in a stack of plate-shaped molded products with less uneven distribution of the inorganic fibers, thus stabilizing the bulk density and heat insulation properties. 
     In the plate-shaped heat insulator of the present disclosure, preferably, the heat insulating member has a bulk density of 0.2 to 0.6 g/cm 3 . 
     When the heat insulating member has a bulk density in the above range, an increase in weight of the combustion chamber can be reduced or prevented as compared to a refractory material or a heat insulator containing an amorphous material. 
     In the plate-shaped heat insulator of the present disclosure, preferably, the heat insulating member is a plate-shaped product of papermaking. 
     The plate-shaped product of papermaking is a plate-shaped molded product obtained by pouring slurry containing an inorganic fiber into a mold and dehydrating by suction (papermaking molding) and drying. Such a plate-shaped product of papermaking is characteristically less deformable with less uneven distribution of the inorganic fibers and is thus suitable as a heat insulating member to be disposed in a combustion chamber. 
     The combustion chamber of the present disclosure includes a metal container and the plate-shaped heat insulator of the present disclosure on an inner wall surface of the metal container. 
     Since the combustion chamber of the present disclosure includes the plate-shaped heat insulator of the present disclosure on the inner wall surface of the metal container, the plate-shaped heat insulator is less susceptible to breakage. 
     In the combustion chamber of the present disclosure, preferably, the plate-shaped heat insulator includes a recess in a surface adjacent to the metal container. 
     When the plate-shaped heat insulator includes a recess in the surface adjacent to the metal container, the recess can function as an air layer to improve the heat insulation. 
     In the combustion chamber of the present disclosure, preferably, the plate-shaped heat insulator includes a groove in a surface away from the metal container. 
     When the plate-shaped heat insulator includes a groove in the surface away from the metal container, such a configuration can reduce or prevent cracking in the plate-shaped heat insulator due to thermal shrinkage, specifically in the surface adjacent to the combustion chamber where the plate-shaped heat insulator is particularly susceptible to heating. 
     The width and depth of the groove in the surface away from the metal container may vary among parts of the groove. 
     Variation in the width and depth of the groove depending on parts can alleviate stress resulting from the difference in amount of applied heat among parts of the plate-shaped heat insulator, and cracking can be more effectively reduced or prevented. 
     In the combustion chamber of the present disclosure, preferably, the plate-shaped heat insulator is on a top surface or a bottom surface of the metal container, and a space between a side surface of the plate-shaped heat insulator and an inner surface of the metal container is filled with an amorphous material containing an inorganic material. 
     In some cases, it is difficult to completely adjust the dimension of the metal container and the dimension of the plate-shaped heat insulator such that no gap is present therebetween. Even in such cases, a reduction in heat insulation can be reduced or prevented when the space between the side surface of the plate-shaped heat insulator and the inner surface of the metal container is filled with the amorphous material. 
     The boiler of the present disclosure includes the combustion chamber of the present disclosure. 
     The boiler of the present disclosure, which includes the combustion chamber of the present disclosure, can reduce or prevent heat damage to peripheral devices. The boiler of the present disclosure can also reduce or prevent a reduction in energy efficiency associated with damage to the plate-shaped heat insulator. 
     The water heater of the present disclosure includes the combustion chamber of the present disclosure. 
     The water heater of the present disclosure, which includes the combustion chamber of the present disclosure, can reduce or prevent heat damage to peripheral devices. The water heater of the present disclosure can also reduce or prevent a reduction in energy efficiency associated with damage to the plate-shaped heat insulator. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG.  1    is a schematic perspective view of an example of a plate-shaped heat insulator according to a first embodiment of the present disclosure. 
         FIG.  2    is a cross-sectional view taken along line A-A in  FIG.  1   . 
         FIG.  3    is a schematic cross-sectional view of an example of a plate-shaped heat insulator according to a second embodiment of the present disclosure. 
         FIG.  4    is a schematic cross-sectional view of an example of a plate-shaped heat insulator according to a third embodiment of the present disclosure. 
         FIG.  5    is a schematic cross-sectional view of an example of a plate-shaped heat insulator according to a fourth embodiment of the present disclosure. 
         FIG.  6    is a schematic cross-sectional view of an example of a plate-shaped heat insulator according to a fifth embodiment of the present disclosure. 
         FIG.  7    is a schematic perspective view of an example of a plate-shaped heat insulator according to a sixth embodiment of the present disclosure. 
         FIG.  8    is a schematic perspective view of an example of a plate-shaped heat insulator according to a seventh embodiment of the present disclosure. 
         FIG.  9    is a schematic perspective view of an example of a plate-shaped heat insulator according to an eighth embodiment of the present disclosure. 
         FIG.  10    is a cross-sectional view taken along line B-B in  FIG.  9   . 
         FIG.  11    is a schematic cross-sectional view of an example of a plate-shaped heat insulator according to a ninth embodiment of the present disclosure. 
         FIG.  12    is a schematic cross-sectional view of an example of a plate-shaped heat insulator according to a tenth embodiment of the present disclosure. 
         FIG.  13    is a schematic cross-sectional view of an example of a combustion chamber according to an eleventh embodiment of the present disclosure. 
         FIG.  14    is a cross-sectional view taken along line C-C in  FIG.  14   . 
         FIG.  15    is a schematic cross-sectional view of an example of a combustion chamber according to a twelfth embodiment of the present disclosure. 
         FIG.  16    is a schematic cross-sectional view of an example of a combustion chamber according to a thirteenth embodiment of the present disclosure. 
         FIG.  17    is a schematic cross-sectional view of an example of a combustion chamber according to a fourteenth embodiment of the present disclosure. 
         FIG.  18    is a schematic cross-sectional view of an example of a boiler according to a fifteenth embodiment of the present disclosure. 
         FIG.  19    is a schematic cross-sectional view of an example of a water heater according to a sixteenth embodiment of the present disclosure. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     [Plate-Shaped Heat Insulator] 
     First, the plate-shaped heat insulator of the present disclosure is described. 
     The plate-shaped heat insulator of the present disclosure includes an aggregate of multiple heat insulating members containing inorganic fibers, wherein the plate-shaped heat insulator is intended to be disposed in a combustion chamber. 
     Herein, the term “plate-shaped” refers to a shape having two relatively large main surfaces facing each other and a side surface connecting the two main surfaces. The direction in which the two main surfaces extend is also referred to as the plane direction, and the direction in which the two main surfaces are connected is also referred to as the thickness direction. At least one of the two main surfaces facing each other may be curved. 
     First Embodiment 
       FIG.  1    is a schematic perspective view of an example of a plate-shaped heat insulator according to a first embodiment of the present disclosure.  FIG.  2    is a cross-sectional view taken along line A-A in  FIG.  1   . 
     A plate-shaped heat insulator  1  shown in  FIG.  1    includes an aggregate of multiple heat insulating members  11  and  12  each containing inorganic fibers. 
     As shown in  FIG.  1    and  FIG.  2   , the plate-shaped heat insulator  1  includes a sheet  100  including the multiple heat insulating members  11  and  12  disposed in the plane direction (xy-plane direction) of the plate-shaped heat insulator. 
     The plate-shaped heat insulator  1 , which includes the sheet  100  including the multiple heat insulating members  11  and  22  disposed in the plane direction (xy-plane direction) of the plate-shaped heat insulator  1 , can reduce or prevent breakage or cracking associated with thermal shrinkage in the plane direction. 
     The heat insulating member  11  has a plate shape including a first main surface  11   a  and a second main surface  11   b  having relatively large areas and facing each other, and side surfaces  11   c  and  11   d  connecting the first main surface  11   a  and the second main surface  11   b.    
     The heat insulating member  12  also has a plate shape including a first main surface  12   a  and a second main surface  12   b  having relatively large areas and facing each other, and side surfaces  12   c  and  12   d  connecting the first main surface  12   a  and the second main surface  12   b.    
     The plate-shaped heat insulator  1 , which includes the sheet  100  including the multiple heat insulating members  11  and  22  disposed in the plane direction (xy-plane direction) of the plate-shaped heat insulator  1 , can reduce or prevent breakage or cracking associated with thermal shrinkage in the plane direction. 
     The first main surface  11   a  of the heat insulating member  11  and the first main surface  12   a  of the heat insulating member  12  are also collectively referred to as the first main surface of the sheet  100  or the first main surface of the plate-shaped heat insulator  1 . The second main surface lib of the heat insulating member  11  and the second main surface  12   b  of the heat insulating member  12  are also collectively referred to as the second main surface of the sheet  100  or the second main surface of the plate-shaped heat insulator  1 . 
     The side surface lid of the heat insulating member  11  and the side surface  12   d  of the heat insulating member  12  are in contact with each other without a gap, but these surfaces may not necessarily be in contact with each other. 
     In  FIG.  1    and  FIG.  2   , the side surface lid of the heat insulating member  11  and the side surface  12   d  of the heat insulating member  12  in contact with each other without a gap are shown as the same surface. 
     When the two heat insulating members  11  and  12  facing each other in the plane direction (xy-plane direction) are in contact with each other without a gap, the heat insulation of the plate-shaped heat insulator  1  can be improved. 
     When the side surfaces of the heat insulating members are not in contact with each other, the gap between heat insulating members not in contact with each other may be filled with an amorphous material containing an inorganic material. 
     When the gap between the two heat insulating members facing each other in the plane direction is filled with the amorphous material, a reduction in heat insulation due to the gap between heat insulating members can be reduced or prevented. 
     The multiple heat insulating members may or may not be bonded to each other via an adhesive or the like. 
     The multiple heat insulating members may have the same shape or different shapes. When the multiple heat insulating members have the same shape, the production cost can be reduced. 
     The heat insulating member contains inorganic fibers. 
     Preferably, the inorganic fibers include at least one selected from the group consisting of biosoluble fibers, alumina fibers, rock wool, and glass fibers. 
     The biosoluble fibers can be alkaline earth silicate fibers. 
     When the inorganic fibers include any of these materials, the resulting plate-shaped heat insulator has excellent heat resistance. 
     The heat insulating member may be a molded product of a solidified amorphous material, a product of papermaking, or a needled product. The heat insulating member may be a plate-shaped molded product, a plate-shaped product of papermaking, or a plate-shaped needled product. 
     The molded product of a solidified amorphous material is a product obtained by solidifying, drying, and molding an amorphous material containing an inorganic material. The plate-shaped molded product is a product obtained by solidifying, drying, and molding the amorphous material into a plate shape. 
     The product of papermaking is a molded product obtained by a papermaking method including pouring slurry containing an inorganic fiber into a mold and dehydrating the slurry by suction (papermaking molding) and drying the resulting product. The plate-shaped product of papermaking is a plate-shaped product obtained by the papermaking method. 
     The needled product is a molded product obtained by needling an aggregate of inorganic fibers. The plate-shaped needled product is a plate-shaped product obtained by needling. 
     Of these, the heat insulating member is preferably a product of papermaking, more preferably a plate-shaped product of papermaking. 
     The plate-shaped product of papermaking is characteristically less deformable with less uneven distribution of the inorganic fibers and is thus suitable as a heat insulating member to be disposed in a combustion chamber. 
     The multiple heat insulating members can be aggregated by a method such as one in which the multiple heat insulating members are disposed with a gap or without a gap on a: surface of an object to be insulated; one in which the multiple heat insulating members are disposed with a gap on a surface of an object to be insulated, and then the gap is filed with an amorphous material containing an inorganic material; or one in which the multiple heat insulating members are bonded to each other with an adhesive or the like. 
     The average fiber diameter of the inorganic fibers is not limited, but it is preferably 2.0 to 15.0 μm when the heat insulating member is a product of papermaking. 
     When the heat insulating member is a product of papermaking, the inorganic fibers having an average fiber diameter in the above range result in a dense product of papermaking with less uneven distribution of the density. 
     The average fiber length of the inorganic fibers is not limited, but it is preferably 0.05 to 3.0 mm when the heat insulating members is a product of papermaking. 
     When the heat insulating member is a product of papermaking, the inorganic fibers having an average fiber length in the above range result in a plate-shaped multilayer molded product with less uneven distribution of the inorganic fibers, thus stabilizing the bulk density and heat insulation properties. 
     The bulk density of the heat insulating member is not limited, but it is preferably 0.2 to 0.6 g/cm 3  when the heat insulating member is a product of papermaking. 
     When the heat insulating member has a bulk density in the above range, an increase in weight of the combustion chamber can be reduced or prevented as compared to a refractory material or a heat insulator containing an amorphous material. 
     In the case of a molded product of an amorphous material containing inorganic fibers, the bulk density can be adjusted by adjusting the amount of water in the amorphous material before drying and solidifying. In the case of a product of papermaking, the bulk density can be adjusted by adjusting compression conditions during dehydration of the slurry and compression conditions during drying. In the case of a needled product, the bulk density can be adjusted by adjusting the needle density during needling and the number of times of needling. 
     The bulk density of a molded product obtained by drying and solidifying an amorphous material containing inorganic fibers is usually about 0.7 to 1.5 g/cm 3 . This does not satisfy the preferred bulk density of the heat insulating member described above. The needled product usually has a bulk density of about 0.07 to 0.18 g/cm 3 . Thus, the heat insulating member is preferably a product of papermaking or a needled product, more preferably a product of papermaking, to adjust the bulk density of the heat insulating member in a suitable range. 
     Each heat insulating member may include a hole penetrating the heat insulating member in the thickness direction. 
     Such a hole in the heat insulating member facilitates covering of inner wall surfaces of the combustion chamber including pipes such as a water pipe and a flue gas pipe with the heat insulating member. 
     The heat insulating member may contain one or more components in addition to the inorganic fibers. 
     Examples of the one or more components in addition to the inorganic fibers include inorganic particles, inorganic binders, organic binders, and coagulants. 
     Example of the inorganic particles include silica particles, alumina particles, titania particles, zirconia particles, and natural mineral particles. 
     Examples of the inorganic binder include silica sol, alumina sol, titania sol, zirconia sol, and fumed silica. 
     Examples of the organic binder include polyvinyl alcohol, starch, acrylic resin, and polyacrylamide. 
     Preferably, the weight percentage of inorganic fibers in each heat insulating member is 30 to 97 wt %. 
     Preferably, each heat insulating member has a volume of 700 to 150000 cm 3 . When each heat insulating member has a volume in the above range, damage caused by thermal shrinkage is particularly less likely to occur. 
     The plate-shaped heat insulator of the present disclosure may include a recess or a groove in the surface. 
     Herein, the recess and the groove are distinguished from each other by the ratio of the length in a width direction (hereinafter, width dimension) to the length in a depth direction (hereinafter, depth dimension) of the recess and the groove in a cross section perpendicular to the direction in which the recess and the groove extend. Specifically, one in which the ratio of the width dimension to the depth dimension is 5 or more is a recess, and one in which the above ratio is less than 5 is a groove. 
     The groove may partially vary in width and depth. 
     Variation in the width and depth of the groove depending on parts can alleviate stress resulting from the difference in amount of applied heat among parts of the plate-shaped heat insulator, and cracking can be more effectively reduced or prevented. 
     In the plate-shaped heat insulator of the present disclosure, preferably, two heat insulating members facing each other in the plane direction among the multiple heat insulating members of the sheet are configured such that cross sections thereof parallel to the direction in which the two heat insulating members face each other and parallel to the thickness direction of the plate-shaped heat insulator have shapes that fit each other. 
     When the two heat insulating members facing each other in the plane direction have cross sectional shapes that fit each other, heat transfer in the thickness direction between the heat insulating members of the sheet can be reduced or prevented. This can improve the heat insulation. 
     Herein, the expression “shapes that fit each other” refers to the shapes that allow the two heat insulating members facing each other to be combined together with hardly any gap therebetween when brought into contact with each other. However, when each heat insulating member has a side surface that connects at the shortest distance between one main surface and the other main surface of the heat insulating member, such a side surface does not fall in the above expression. For example, although no gap is present between the heat insulating member  11  and the heat insulating member  12  shown in  FIG.  2   , these heat insulating members do not have shapes that fit each other. 
     An example of a case where the two heat insulating members facing each other in the plane direction have cross-sectional shapes that fit each other is described below as second to fifth embodiments. 
     Second Embodiment 
       FIG.  3    is.a schematic cross-sectional view of an example of a plate-shaped heat insulator according to a second embodiment of the present disclosure. 
     A plate-shaped heat insulator la shown in  FIG.  3    includes a sheet  100   a  including multiple heat insulating members  13  and  14  disposed in a plane direction (xy-plane direction). 
     A side surface  13 d, which faces the heat insulating member  14 , of the heat insulating member  13  and a side surface  14 d, which faces the heat insulating member  13 , of the heat insulating member  14  each have a shape tilted relative to a thickness direction (z-direction) of the plate-shaped heat insulator. Thus, when seen in the cross section, the two heat insulating members  13  and  14  of the sheet  100   a  have cross-sectional shapes that fit each other. 
     When the heat insulating members  13  and  14  are configured such that their side surfaces facing each other are tilted when viewed in the cross section, heat transfer in the thickness direction between the heat insulating members of the sheet can be reduced or prevented. This can improve the heat insulation. 
     When the heat insulating members are configured such that their side surfaces facing each other are tilted, preferably, their side surfaces facing each other each form an angle of 30° to 80° with the first and the second main surfaces of the respective heat insulating members. 
     Third Embodiment 
       FIG.  4    is a schematic cross-sectional view of an example of a plate-shaped heat insulator according to a third embodiment of the present disclosure. 
     A plate-shaped heat insulator lb shown in  FIG.  4    includes a sheet  100   b  including multiple heat insulating members  15  and  16  disposed in a plane direction (xy-plane direction). 
     A side surface  15   d , which faces the heat insulating member  16 , of the heat insulating member  15  and a side surface  16   d , which faces the heat insulating member  15 , of the heat insulating member  16  each have a tilted shape that is changed by rounding the obtuse angle thereof. Thus, when seen in the cross section, the two heat insulating members  15  and  16  of the sheet  100   b  have cross-sectional shapes that fit each other. 
     The shape obtained by changing the tilted shape is not limited to the above-described shape. For example, the tilted shape may be changed by rounding the acute angle thereof, or the tilted shape may be changed by rounding both the obtuse and acute angles thereof. 
     Fourth Embodiment 
       FIG.  5    is a schematic cross-sectional view of an example of a plate-shaped heat insulator according to a fourth embodiment of the present disclosure. 
     A plate-shaped heat insulator  1   c  shown in  FIG.  5    includes a sheet  100   c  including multiple heat insulating members  17  and  18  disposed in a plane direction (xy-plane direction). 
     A side surface  17 d, which is facing the heat insulating member  18 , of the heat insulating member  17  and a side surface  18   d , which is facing the heat insulating member  17 , of the heat insulating member  18  each have an L-shape. Thus, when seen in the cross section, the two heat insulating members of the sheet  100   c  have cross-sectional shapes that fit each other. 
     Fifth Embodiment 
       FIG.  6    is a schematic cross-sectional view of an example of a plate-shaped heat insulator according to a fifth, embodiment of the present disclosure. 
     A plate-shaped heat insulator ld shown in  FIG.  6    includes a sheet  100   d  including multiple heat insulating members  19  and  20  disposed in a plane direction (xy-plane direction). 
     A side surface  19   d , which is facing the heat insulating member  20 , of the heat insulating member  19  and a side surface  20   d , which is facing the heat insulating member  19 , of the heat insulating member  20  each have a hook shape. Thus, when seen in the cross section, the two heat insulating members of the sheet  100   d  have cross-sectional shapes that fit each other. 
     In each of the first to fifth embodiments above, an example was described in which the plate-shaped heat insulator of the present disclosure includes a sheet including two heat insulating members disposed in the plane direction of the plate-shaped heat insulator. 
     In the plate-shaped heat insulator of the present disclosure, the sheet may include three or more heat insulating members. 
     Examples of a case where the sheet includes three heat insulating members are described below as a sixth embodiment and a seventh embodiment. 
     Sixth Embodiment 
       FIG.  7    is a schematic perspective view of an example of a plate-shaped heat insulator according to a sixth embodiment of the present disclosure. 
     As shown in  FIG.  7   , a plate-shaped heat insulator  2  includes ;a sheet  110  including multiple heat insulating members  21 ,  22 , and  23  disposed in a plane direction (xy-plane direction). 
     The heat insulating members  21 ,  22 , and  23  of the sheet  110  each have a fan shape in a planer view, which is obtained by dividing the circle into three equal parts with central angles of 120°. These parts have the same shape. 
     Seventh Embodiment 
       FIG.  8    is a schematic perspective view of an example of a plate-shaped heat insulator according to a seventh embodiment of the present disclosure. 
     As shown in  FIG.  8   , a plate-shaped heat insulator  3  includes a sheet  120  including multiple heat insulating members  24 ,  25 , and  26  disposed in a plane direction (xy-plane direction). 
     The heat insulating members  24 ,  25 , and  26  of the sheet  120  each have a shape obtained by using a straight line extending in the x-direction through the center of the circle as a reference and trisecting the straight line in the x-direction. 
     The heat insulating member  24  and the heat insulating members  26  have the same shape. The heat insulating member  25  has a shape different from that of the heat insulating members  24  and  26 . 
     In each of the first to seventh embodiments above, an example was described in which the plate-shaped heat insulator of the present disclosure includes a sheet including multiple heat insulating members disposed in the plane direction of the plate-shaped heat insulator. 
     The plate-shaped heat insulator of the present disclosure may include a stack of multiple heat insulating members stacked in the thickness direction of the plate-shaped heat insulator. 
     In the case of a single thick plate-shaped heat insulator, stress due to thermal shrinkage is concentrated on a surface of the plate-shaped heat insulator, the surface being adjacent to a combustion chamber. This sometimes increases the risk of causing damage such as cracking in the surface of the plate-shaped heat insulator, the surface being adjacent to the combustion chamber. In contrast, the plate-shaped heat insulator, which includes a stack of multiple heat insulating members stacked in the thickness direction of the plate-shaped heat insulator, can reduce the risk described above. 
     Examples of a case where the plate-shaped heat insulator includes a stack are described below as an eighth embodiment and a ninth embodiment. 
     Eighth Embodiment 
       FIG.  9    is a schematic perspective view of an example of a plate-shaped heat insulator according to an eighth embodiment of the present disclosure.  FIG.  10    is a cross-sectional view taken along line B-B in  FIG.  9   . 
     A plate-shaped heat insulator  4  shown in  FIG.  9    includes an aggregate of multiple heat insulating members  31  and  32  containing inorganic fibers. 
     As shown in  FIG.  9    and  FIG.  10   , the plate-shaped heat insulator  4  includes a stack  200  of the multiple heat insulating members  31  and  32  stacked in a thickness direction (z-direction) of the plate-shaped heat insulator. The heat insulating member  31  has a plate shape including a first main surface  31   a , a second main surface  31   b , and a side surface  31   c  connecting the first main surface  31   a  and the second main surface  31   b.    
     The heat insulating member  32  has a plate shape including a first main surface  32   a , a second main surface  32   b , and a side surface  32   c  connecting the first main surface  32   a  and the second main surface  32   b.    
     As shown in  FIG.  10   , the second main surface  31   b  of the heat insulating member  31  and the first main surface  32   a  of the heat insulating member  32  face each other. 
     Ninth Embodiment 
     In a plate-shaped heat insulator according to a ninth embodiment of the present disclosure, preferably, at least one of the multiple heat insulating members of the stack includes a recess in a surface facing another heat insulating member. 
     With such a configuration, an air layer can be formed between two heat insulating members stacked in the thickness direction. This can improve the heat insulation. 
       FIG.  11    is a schematic cross-sectional view of an example of a plate-shaped heat insulator according to a ninth embodiment of the present disclosure. 
     A plate-shaped heat insulator  5  shown in  FIG.  11    includes an aggregate of multiple heat insulating members  33  and  34  containing inorganic fibers. 
     As shown in  FIG.  11   , the plate-shaped heat insulator  5  includes a stack  210  of the multiple heat insulating members  33  and  34  stacked in a thickness direction (z-direction) of the plate-shaped heat insulator. A second main surface  33   b  of the heat insulating member  33  and a first main surface  34   a  of the heat insulating member  34  face each other. Further, the heat insulating member  34  includes a recess  50  in the first main surface  34   a.    
     As shown in  FIG.  11   , when one of the multiple heat insulating members includes a recess in a main surface (here, the first main surface  34   a  of the heat insulating member  34 ) facing the other heat insulating member, an air layer can be formed between the two heat insulating members stacked in the thickness direction. This can improve the heat insulation. 
     The plate-shaped heat insulator of the present disclosure may be one including multiple heat insulating members in the thickness direction of the plate-shaped heat insulator and including multiple heat insulating members also in the plane direction of the plate-shaped heat insulator. An example of such a case is described below as a tenth embodiment. 
     Tenth Embodiment 
     Preferably, a plate-shaped heat insulator according to a tenth embodiment of the present disclosure is a multilayer sheet including multiple sheets stacked in the thickness direction of the plate-shaped heat insulator. Further, preferably, a position where the multiple heat insulating members face each other in the plane direction varies among the multiple sheets. 
       FIG.  12    is a schematic cross-sectional view of an example of a plate-shaped heat insulator according to a tenth embodiment of the present disclosure. 
     A plate-shaped heat insulator  6  shown in  FIG.  12    includes a multilayer sheet  300  including multiple sheets  100   e  and  100   f  stacked in the thickness direction of the plate-shaped heat insulator. 
     The sheet  100   e  includes multiple heat insulating members  41  and  42  disposed in a plane direction (xy-plane direction) of the plate-shaped heat insulator. 
     The sheet  100   f  includes multiple heat insulating members  43  and  44  disposed in the plane direction (xy-plane direction) of the plate-shaped heat insulator. 
     In the plane direction, a position where the heat insulating member  41  and the heat insulating member  42  face each other is different from a position where the heat insulating member  43  and the heat insulating member  44  face each other. In other words, when seen in the cross section, the position where the heat insulating members  41  and  42  face each other (a position between a side surface  41   d  of the heat insulating member  41  and a side surface  42   d  of the heat insulating member  42 ) and the position where the heat insulating members  43  and  44  face each other (a position of a side surface  43   d  of the heat insulating member  43  and a side surface  44   d  of the heat insulating member  44 ) do not overlap each other in a thickness direction (z-direction) of the plate-shaped heat insulator  6 . 
     With such a configuration, positions where heat transfer in the thickness direction is likely to occur in the sheets do not overlap each other. This improves the heat insulation as a whole. 
     The plate-shaped heat insulator of the present disclosure has been described so far. 
     Hereinafter, a combustion chamber of the present disclosure including any of the plate-shaped heat insulators of the present disclosure is described. 
     [Combustion Chamber] 
     The combustion chamber of the present disclosure includes a metal container and the plate-shaped heat insulator of the present disclosure on an inner wall surface of the metal container. 
     Since the combustion chamber of the present disclosure includes the plate-shaped heat insulator of the present disclosure on the inner wall surface of the metal container, the plate-shaped heat insulator is less susceptible to breakage. 
     Eleventh Embodiment 
       FIG.  13    is a schematic cross-sectional view of an example of a combustion chamber according to an eleventh embodiment of the present disclosure.  FIG.  14    is a cross-sectional view taken along line C-C in  FIG.  14   . 
     As shown in  FIG.  13    and  FIG.  14   , a combustion chamber  510  includes a metal container  150  and two plate-shaped heat insulators  1  on inner wall surfaces of the metal container. Each plate-shaped heat insulator  1  is the plate-shaped heat insulator of the present disclosure. 
     An inner space of the metal container  150  is defined by a top surface  150   a , a bottom surface  150   b , and an inner surface  150   d  of the metal container  150 . The top surface  150   a , the bottom surface  150   b , and the inner surface  150   d  of the metal container  150  are inner wall surfaces of the metal container  150  when the metal container  150  is seen from inside. 
     One of the two plate-shaped heat insulators  1  is disposed to cover the top surface  150   a  of the metal container from the inside, and the other is disposed to cover the bottom surface  150   b  of the metal container from the inside. 
     One of the main surfaces of each plate-shaped heat insulator  1  is the first main surface adjacent to the metal container  150  (adjacent to the top surface  150   a  or the bottom surface  150   b  of the metal container  150 ), and the, other main surface is the second main surface away from the metal container  150  (away from the top surface  150   a  and the bottom surface  150   b  of the metal container  150 ). 
     The inner diameter dimensions of the top surface  150   a  and the, bottom surface  150   b  of the metal container match the outer dimension of the plate-shaped heat insulator  1 . In a plane direction (xy-plane direction) of the plate-shaped heat insulator  1 , no gap is present between the plate-shaped heat insulator  1  and the inner surface  150   d  of the metal container  150 . 
     In the combustion chamber of the present disclosure, a recess or a groove may be provided in a surface of the plate-shaped heat insulator, or a gap between the plate-shaped heat insulator and the metal container may be filled with an amorphous material containing an inorganic material. Examples of such cases are described below as twelfth to fourteenth embodiments. 
     Twelfth Embodiment 
     In the combustion chamber of the present disclosure, preferably, the plate-shaped heat insulator includes a recess in a surface adjacent to the metal container. 
     When the plate-shaped heat insulator includes a recess in the surface adjacent to the metal container, the recess can function as an air layer to improve the heat insulation. 
       FIG.  15    is a schematic cross-sectional view of an example of a combustion chamber according to a twelfth embodiment of the present disclosure. 
     As shown in  FIG.  15   , a combustion chamber  520  includes the metal container  150  and two plate-shaped heat insulators  7  on the top surface  150   a  and the bottom surface  150   b  of the metal container  150 . 
     Each plate-shaped heat insulator  7  includes the recess  50  in a surface adjacent to the metal container  150 . 
     When the plate-shaped heat insulator  7  includes the recess  50  in the surface adjacent to the metal container .  150 , the recess  50  can function as an air layer to improve the heat insulation of the plate-shaped heat insulator  7 . 
     Thirteenth Embodiment 
     In the combustion chamber of the present disclosure, preferably, the plate-shaped heat insulator includes a groove in a surface away from the metal container. 
     When the plate-shaped heat insulator includes a groove in the surface away from the metal container, such a configuration can reduce or prevent cracking in the plate-shaped heat insulator due to thermal shrinkage, specifically in the surface adjacent to the combustion chamber where the plate-shaped heat insulator is particularly susceptible to heating. 
       FIG.  16    is a schematic cross-sectional view of an example of a combustion chamber according to a thirteenth embodiment of the present disclosure. 
     As shown in  FIG.  16   , a combustion chamber  530  includes the metal container  150  and two plate-shaped heat insulators  8  on the top surface  150   a  and the bottom surface  150   b  of the metal container  150 . 
     Each plate-shaped heat insulator  8  includes a groove  60  in a surface away from the metal container  150 . 
     When the plate-shaped heat insulator  8  includes the groove  60  in the surface away from the metal container  150 , such a configuration can reduce or prevent cracking in the plate-shaped heat insulator  8  due to thermal shrinkage, specifically in the surface adjacent to the combustion chamber where the plate-shaped heat insulator  8  is particularly susceptible to heating. 
     Fourteenth Embodiment 
     In the combustion chamber of the present disclosure, preferably, the plate-shaped heat insulator is on atop surface or a bottom surface of the metal container, and a space between a side surface of the plate-shaped heat insulator and an inner surface of the metal container is filled with an amorphous material containing an inorganic material. 
     In some cases, it is difficult to completely adjust the dimension of the metal container and the dimension of the plate-shaped heat insulator such that no gap is present therebetween. Even in such cases, a reduction in heat insulation can be reduced or prevented when the space between the side surface of the plate-shaped heat insulator and the inner surface of the metal container is filled with the amorphous material. 
       FIG.  17    is a schematic cross-sectional view of an example of a combustion chamber according to a fourteenth embodiment of the present disclosure. 
     As shown in  FIG.  17   , a combustion chamber  540  includes the metal container  150  and two plate-shaped heat insulators  9  on the top surface  150   a  and the bottom surface  150   b  of the metal container  150 . 
     The plan view dimension (outer diameter dimension) of each plate-shaped heat insulator  9  is smaller than the inner diameter dimension of the inner surface  150   d  of the metal container  150 . Thus, a gap is present between a side surface  9   c  of the plate-shaped heat insulator  9  and the inner surface  150   d  of the metal container. The gap is filled with an amorphous material  80  containing an inorganic material. When the gap between the side surface  9   c  of the plate-shaped heat insulator  9  and the inner surface  150   d  of the metal container  150  is filled with the amorphous material  80 , a reduction in heat insulation can be reduced or prevented. 
     The combustion chamber of the present disclosure can be used in a device including a combustion chamber. Examples of the device including a combustion chamber include boilers and water heaters. 
     [Boiler] 
     The boiler of the present disclosure includes the combustion chamber of the present disclosure. 
     The boiler of the present disclosure, which includes the combustion chamber of the present disclosure, can reduce or prevent heat damage to peripheral devices. The boiler of the present disclosure can also reduce or prevent a reduction in energy efficiency associated with damage to the plate-shaped heat insulator. 
     An example of the boiler of the present disclosure is described below as a fifteenth embodiment. 
     Fifteenth Embodiment 
       FIG.  18    is a schematic cross-sectional view of an example of a boiler according to a fifteenth embodiment of the present disclosure. 
     A boiler  600  includes a combustion chamber  550  and water pipes  180  in the combustion chamber  550 . 
     The combustion chamber  550  is a combustion chamber of the present disclosure including a metal container  160  and the plate-shaped heat insulators  1  of the present disclosure on a top surface  160   a  and a bottom surface  160   b  of the metal container  160 . 
     Water is supplied into the water pipes  180  from a lower portion of the combustion chamber  550 . Water flowing through the water pipes  180  is heated into steam in the combustion chamber  550 , and the steam is exhausted from an upper portion of the combustion chamber  550 . 
     The exhausted steam after water separation of the liquid or overheating as needed is used for applications such as power generation, heating, washing, cooking, drying, disinfection, and sterilization. 
     [Water Heater] 
     The water heater of the present disclosure includes the combustion chamber of the present disclosure. 
     The water heater of the present disclosure, which includes the combustion chamber of the present disclosure, can reduce or prevent heat damage to peripheral devices. The water heater of the present disclosure can also reduce or prevent a reduction in energy efficiency associated with damage to the plate-shaped heat insulator. 
     An example of the water heater of the present disclosure is described below as a sixteenth embodiment. 
     Sixteenth Embodiment 
       FIG.  19    is a schematic cross-sectional view of an example of a water heater according to a sixteenth embodiment of the present disclosure. 
     A water heater  700  includes a combustion chamber  560  and a heat exchanger  190  in the combustion chamber  560 . 
     The combustion chamber  560  is a combustion chamber of the present disclosure including a metal container  170  and the plate-shaped heat insulators  1  of the present disclosure on a top surface  170   a  and a bottom surface  170   b  of the metal container  170 . 
     Water flows in the heat exchanger  190 . The water in the heat exchanger  190  is heated into hot water in the combustion chamber  560 , and the hot water is supplied to the outside of the water heater  700 . 
     The temperature of hot water to be supplied can be suitably adjusted by adjusting the amount of fuel to be combusted in the combustion chamber and the amount of water flowing through the heat exchanger per unit time. 
     REFERENCE SIGNS LIST 
       1 ,  1   a,    1   b,    1   c,    1   d,    2 ,  3 ,  4 ,  5 ,  6 ,  7 ,  8 ,  9  plate-shaped heat insulator
       9   c  side surface of plate-shaped heat insulator  11 ,  12 ,  13 ,  14 ,  15 ,  16 ,  17 ,  18 ,  19 ,  20 ,  21 ,  22 ,  23 ,  24 ,  25 ,  26 ,  31 ,  32 ,  33 ,  34 ,  41 ,  42 ,  43 ,  44  heat insulating member  11   a ,  12   a ,  13   a ,  14   a ,  15   a ,  16   a ,  17   a ,  18   a,    19   a,    20   a ,  31   a ,  32   a ,  33   a ,  34   a  first main surface of heat insulating member  11   b ,  12   b ,  13   b,    14   b,    15   b,    16   b,    17   b,    18   b,    19   b,    20   b ,  31   b ,  32   b ,  33   b,    34   b  second main surface of heat insulating member  11   c ,  12   c ,  24   c,    25   c,    26   c,    31   c ,  32   c ,  33   c,    34   c  side surface (outside) of heat insulating member     11   d ,  12   d ,  13   d,    14   d,    15   d ,  16   d ,  17   d,    18   d ,  19   d ,  20   d ,  41   d ,  42   d ,  43   d,    44   d  side surface (inside) of heat insulating member     50  recess     60  groove     80  amorphous material containing inorganic material     100 ,  100   a ,  100   b ,  100   c ,  100   d ,  100   e ,  100   f ,  110 ,  120  sheet     150 ,  160 ,  170  metal container     150   a ,  160   a ,  170   a  top surface of metal container     150   b ,  160   b ,  170   b  bottom surface of metal container     150   d  inner surface of metal container     180  water pipe     190  heat exchanger     200  stack     300  multilayer sheet     510 ,  520 ,  530 ,  540 ,  550 ,  560  combustion chamber     600  boiler     700  water heater