Patent Publication Number: US-2002005152-A1

Title: High temperature air heater and waste treatment equipment

Description:
TECHNICAL FIELD  
       [0001] The present invention relates to the heat recovery from gas of elevated temperature. More particularly, the invention relates to an apparatus for heating high-temperature air that is capable of recovering heat energy out of burnt exhaust gas of elevated temperature by heat exchange with air and hence of using the resultant heat energy to advantage, where exhaust gas occurs during incineration of wastes (in which are included combustibles of general wastes such as municipal wastes disposed of by households and offices and also of industrial wastes such as waste plastics, shredded car dusts, waste office equipment, waste electronic equipment, waste cosmetic containers and the like) in a incinerator for municipal wastes and in an incinerator for industrial wastes. The invention also relates to an apparatus for disposing of wastes which is provided with the above heating apparatus.  
       BACKGROUND ART  
       [0002] An incinerator for municipal wastes and an incinerator for industrial wastes have been equipped with an apparatus for heating high-temperature air in order to recover and utilize the heat energy of burnt gas of elevated temperature derived by incinerating those wastes. This heating apparatus of high-temperature air is so designed that heat is recovered by allowing air to flow through a heat transfer conduit formed of a metal, followed by heating of the air on heat exchange with the burnt gas of elevated temperature. The heat energy thus recovered is utilized as a heat source in decomposing wastes thermally, in generating electricity and in other systems.  
       [0003] In FIG. 49, there is shown one form of a conventional heating apparatus of high-temperature air. A burning melting portion  49  is located upwardly of a burning melting furnace  53 , and a heating apparatus  1  of high-temperature air is disposed downwardly of that apparatus. In the burning melting portion  49 , gas and air for use in combustion are supplied to a burner  56  so as to burn combustible components such as wastes at a high temperature of about 1300° C. so that a melted slug  53   f  and a burnt exhaust gas G are generated. Usually, the burnt exhaust gas G contains dust (refuse) and constitutes a highly corrosive gas including corrosive materials such as chlorine and hydrogen chloride which, however, depend on the kind of wastes. In such furnace, the burnt exhaust gas flows at a temperature of 1000-1100° C. and at a flow rate of about 2-3 m/sec. The heating apparatus  1  of high-temperature air is essentially constructed with a heat transfer conduit  9  arranged to recover the heat from the burnt exhaust gas G of high temperature stated above. For the heating apparatus  1  of high-temperature air to entrap heated air in a large quantity, the heat transfer conduit  9  is structured to be elongate and is usually disposed in a plurally paralleled posture.  
       [0004] It is required, therefore, that such heat transfer conduit located in the incineration furnace and exposed to a high temperature and to a highly corrosive gas atmosphere should be sufficiently durable, in respect of both the material and the structure, with respect to the corrosive gas of elevated temperature noted above. As means for imparting improved corrosion resistance to the heating apparatus of high-temperature air, it is thought that a stud pin could be welded to the heat transfer conduit formed of a metal, and an castable refractory material could be placed in surrounded relation to that pin and that refractory bricks basically of a rectangular parallelopiped shape could be arranged with their joints connected lengthwise and widthwise. These systems permit such a refractory material to act as a physical barrier against convection and mutual diffusion in a corrosive gas phase, and therefore, can somewhat prevent the heat transfer conduit from getting corroded.  
       PROBLEMS TO BE SOLVED BY THE INVENTION  
       [0005] However, each such system leads to cracked refractory material, eventually resulting in corroded and impaired fixing jig for the refractory material, or in damaged and detached refractory material itself, because of the difference in thermal expansion which arises from combination of different materials between the refractory material and the metallic heat transfer conduit. This causes a serious corrosion phenomenon in which the metallic heat transfer conduit becomes corrosively damaged, creating the problem that the heating apparatus of high-temperature air suffers from shortened service life and hence from reduced working efficiency with consequent decline in the efficiency of heat recovery upon heat exchange.  
       [0006] Moreover, the heat transfer conduit has the problem that it is rather elongate and hence liable to be thermally deformable and bendable. Another problem is that since a plurality of heat transfer conduits are disposed in parallel to each other, dust contained in an exhaust gas gets deposited between those conduits, thus inviting reduced efficiency of heat recovery based on heat exchange.  
       [0007] One object of the present invention is to attain prolonged service life in an apparatus for heating high-temperature air and also to make the apparatus highly efficiently workable, thereby gaining improved efficiency of heat recovery through heat exchange. For other objects, the invention provides an apparatus for heating high-temperature air which is less thermally deformable and less susceptible to dust deposition, and further an apparatus for disposing of wastes which is provided with such heating apparatus.  
       DISCLOSURE OF THE INVENTION  
       [0008] In order to achieve the foregoing objects, the present invention is constructed as will be described hereinbelow.  
       [0009] In the invention recited in claim  1 , there is provided an apparatus for heating high-temperature air characterized in that such appratus is located for use in an atmosphere containing a gas of elevated temperature and has a heat transfer conduit disposed to heat, by means of heat exchange with the gas of elevated temperature, air to be heated and caused to flow through the heat transfer conduit, and such heat transfer conduit comprises a heat transfer pipe arranged to flow the air to be heated therethrough, and a refractory protective pipe formed of a refractory material and held in coaxially covered relation to the heat transfer pipe with a gapping defined between the protective pipe and the heat transfer pipe.  
       [0010] According to this invention, the heat transfer pipe (usually formed of a metal) and the refractory protective pipe formed of a refractory material are less susceptible, by the provision of such gapping, to mutual propagation of those effects attributable to different thermal expansion of the different materials used for formation of both pipes. This makes it possible to reduce damaged and detached portion of the refractory material which tends to result from such varied thermal expansion.  
       [0011] In the invention recited in claim  2 , there is provided an apparatus for heating high-temperature air characterized in that such apparatus is located for use in an atmosphere containing a gas of elevated temperature and has a heat transfer conduit disposed to heat, by means of heat exchange with the gas of elevated temperature, air to be heated and flowing through the heat transfer conduit, and such heat transfer conduit comprises an inner heat transfer pipe formed of a metal and opened at a tip thereof, and an outer heat transfer pipe formed of a refractory material and held in coaxially covered relation to the inner metallic heat transfer pipe with a spacing defined between the outer and inner pipes, and after being caused to flow through the inner metallic heat transfer pipe, the air to be heated is heated with the gas of elevated temperature while the former air is being passed at from the open tip of the inner pipe through the spacing between the inner and outer pipes.  
       [0012] In this invention, damaged and detached portion of the refractory material due to the different thermal expansion stated above can likewise be reduced by the provision of such gap passage.  
       [0013] The invention recited in claim  3  is as set forth in claim  1  or  2  and is characterized in that the refractory protective pipe or the outer refractory heat transfer pipe is structured to have an angular face in cross section, and the heat transfer conduit is disposed in a plural number and fixed in face-to-face contact with the adjoining protective pipe or heat transfer pipe at its sectional angular face.  
       [0014] According to this invention, the refractory protective pipe or the outer refractory heat transfer pipe is formed to be angular in a tetrahedral shape or the like when seen cross-sectionally, and the heat transfer conduit is disposed in a plural number and fixed in face-to-face contact with the adjoining protective pipe or heat transfer pipe. Therefore, the heating apparatus of high-temperature air so constructed leads to improved structural rigidity, resulting in a marked decrease in the thermal decomposition discussed above. Furthermore, such face-to-face arrangement renders the apparatus flat throughout the surface thereof and hence less prone to dust deposition on the surface than an arrangement having a concave and convex surface so that the efficiency of heat transfer can be maintained on a high level and over an extended period of time.  
       [0015] The invention recited in claim  4  is as set forth in claim  1  or  3  and is characterized in that the heat transfer pipe of the heat transfer conduit comprises an inner heat transfer pipe formed of a metal, and an outer heat transfer pipe formed of a metal and held in covered relation to the inner metallic heat transfer pipe with a spacing defined between the two pipes, the air to be heated is heated with the gas of elevated temperature while the former air is being passed through the spacing disposed between the inner and outer pipes, and such refractory protective pipe is arranged to cover the outer metallic heat trandfer pipe and disposed coaxially of the latter pipe with a gapping defined between the protective and outer pipes.  
       [0016] The invention recited in claim  5  is as set forth in claim  1  or  3  and is characterized in that the heat transfer pipe of the heat transfer conduit comprises an outer heat transfer pipe formed of a metal, and an inner pipe arranged to communicate with one end of the outer pipe with a spacing defined between the outer and inner pipes, the inner pipe is formed into a thermally insulated structure with a lower thermal conductivity than the metal, and the air to be heated is heated with the gas of elevated temperature along an outer wall of the outer metallic heat transfer pipe while the former air is being passed through the spacing defined between the outer metallic heat transfer pipe and the inner thermal insulating pipe.  
       [0017] According to these inventions, the air to be heated is heated alone which is allowed to flow through the spacing defined between the outer metallic heat transfer pipe and the inner thermally insulating pipe, but the air being passed through the inner thermally insulating pipe is not heated together with the former air. Namely, the air present in the inner pipe is thermally isolated such that the temperature change of the air to be heated in the inner pipe is held to so small an extent as to be acceptable. Enhanced heat transfer efficiency as well as simplified temperature control is thus feasible.  
       [0018] More specifically, with use of the heat transfer conduit constructed such that the heat of the gas of elevated temperature is recovered by allowing air to be heated to flow through the spacing defined between the outer metallic heat transfer pipe and the inner heat transfer pipe, followed by discharging of the resultant heat through the inner heat transfer pipe at from the one end thereof made to communicate with the outer heat transfer pipe, or with use of the heat transfer conduit constructed such that the heat recovery is effected by flowing the air in a reverse direction, the heat of the gas of elevated temperature is recovered by the air being flowed in the spacing between such outer and inner pipes and along the metallic wall of the outer pipe. In this case, the recovered heat gets transmitted along the metallic wall of the inner heat transfer pipe up to the air flowing through such inner pipe. For that reason, conventional practice has the problem that the air present in the inner heat transfer pipe is markedly changeable in temperature, and the air to be heated when taken outside is variable in temperature, the efficiency of heat transfer being thus difficult to obtain as desired. In order to gain desired heat transfer efficiency, the air present in the outer heat transfer pipe located outwardly of the inner heat transfer pipe is required to be unnecessarily higher. This invites a small temperature difference between a gas of elevated temperature and an air in the outer heat transfer pipe with eventual need for a wide area of heat transfer, forcing conventional practice to employ an apparatus of a large scale. The present invention is so constructed that the heat of a gas of elevated temperature is transmitted solely to an air to be heated and caused to flow through the spacing between the outer metallic heat transfer pipe and the inner thermally insulating pipe. That is to say, such gas heat can be prevented from transmission up to an inner wall of the inner pipe. Hence, a desirable efficiency of heat transfer is obtainable.  
       [0019] The invention recited in claim  6  is as set forth in claim  5  and is characterized in that the inner pipe is formed of a thermally insulating material of low thermal conductivity other than a metal. The invention recited in claim  7  is characterized in that the inner pipe is brought into a thermally insulated structure in which the thermally insulating material is sandwiched with metallic tubes. The invention recited in claim  8  is characterized in that the inner pipe is brought into a thermally insulated structure in which such pipe is formed of a metal and in a double-piped vacuum-drawn arrangement. In the invention recited in claim  9 , the thermal insulating material is specified to be ceramics. A highly thermally insulating material such as for example ceramics is used, as claimed, as a material itself for formation of the inner pipe so that structural simplicity is attained.  
       [0020] The invention recited in claim  10  is as set forth in any one of claims  4 - 9  and is characterized in that the air to be heated is caused to flow in a direction reverse to that of the gas of elevated temperature through the spacing between the inner pipe and the outer pipe, both of which pipes are arranged to constitute the heat transfer conduit. This is conducive to improved efficiency of heat transfer.  
       [0021] The invention recited in claim  11  is as set forth in any one of claims  1 ,  3 - 9  and is characterized in that a plurality of support materials are fixedly placed outwardly of the heat transfer pipe to thereby support the refractory protective pipe.  
       [0022] These support materials allow the gapping between the heat transfer pipe and the refractory protective pipe to be substantially uniform throughout the length thereof. As a consequence of provision of the support materials, even if such conduit and pipe are elongate, they are free from fear of being in partial contact with each other. Additionally, the refractory protective pipe of great mass can be held in firmly supported relation to the heat transfer pipe with the result that the former pipe is less likely to become unstable.  
       [0023] The invention recited in claim  12  is as set forth in any one of claims  4 - 11  and is characterized in that the gapping is defined to communicate with a passageway for flow of the air to be heated with a through hole made in a wall of the outer metallic heat transfer pipe.  
       [0024] This construction imparts to the gapping a positive pressure with respect to the external atmosphere, thus decreasing a tendency for the gas of elevated temperature to intrude from the outside into the refractory protective pipe. The outer metallic heat transfer pipe can thus be reliably prevented from getting corrosively deteriorated.  
       [0025] The invention recited in claim  13  is as set forth in any one of claims  1 - 12  and is characterized in that a partitioned gapping is defined at a region where a tip of the heat transfer pipe is opposed to a tip of the refractory protective pipe or the refractory heat transfer pipe, and the air to be heated is introduced into such space partitioned at the pipe tips. The same beneficial effects as in the invention of claim  12  are obtainable also in the partitioned space.  
       [0026] The invention recited in claim  14  is as set forth in any one of claims  4 - 11  and is characterized in that means is disposed for introducing extraneous air into the gapping between the refractory protective pipe and the outer metallic heat transfer pipe.  
       [0027] In this invention, because the extraneous air is introduced into the gapping between the refractory protective pipe and the outer metallic heat transfer pipe, a corrosive gas can be completely avoided from becoming reversely diffused toward and intermixed with the air to be heated as would be encountered in purging the corrosive gas by leakage of the air to be heated out of an opening made in a wall of the heat transfer pipe. This reveals enhanced anticorrosion and improved reliability concerning the associated apparatus.  
       [0028] The invention recited in claim  15  is as set forth in claim  14  and is characterized in that a partitioned gapping is defined at a region where a tip of the outer metallic heat transfer pipe is opposed to a tip of the refractory protective pipe, and the extraneous air is introduced into such gapping partitioned at the pipe tips. The same beneficial effects as noted in the invention of claim  14  are attained also in the partitioned gapping.  
       [0029] The invention recited in claim  16  is as set forth in any one of claims  1 - 15  and is characterized in that the tip of the refractory protective pipe or the outer refractory heat transfer pipe is formed in a convex shape so as to be less resistant to gas flow of elevated temperature.  
       [0030] In this invention, such convex tip has a role to relax those thermal effects of concentrated thermal stress and the like arising from contact of the refractory protective pipe or the outer refractory heat transfer pipe with the gas flow of elevated temperature, eventually leading to reduced damage of wear and breakage as to the top end of either of such pipes.  
       [0031] The invention recited in claim  17  is as set forth in claim  16  and is characterized in that the convex shape is of a hemispherical shape. This hemispherical shape makes it possible to uniformly distribute those thermal effects having produced on the tip, contributing to further reduced damage to the tip.  
       [0032] Additionally, the convex shape may be a conical shape as in the invention recited in claim  18  and a polyhedral convex shape as in the invention recited in claim  19 . The conical shape stated here includes a shape in which the top end is chamfered, and the polyhedral convex shape stated here denotes a convexity shaped to have a polyhedron such as a polypyramid, a polygon or the like. In brief, the convex shape may be of a convexity shaped by a planar face and either one or both of curved faces as in the invention recited in claim  20 , and no particular restriction should be imposed on the convex shape. A convexly streamlined shape may also be included.  
       [0033] The invention recited in claim  21  is as set forth in any one of claims  16 - 20  and is characterized in that the refractory protective pipe or the outer refractory heat transfer pipe of the heat transfer conduit is shaped like a circular pillar when seen outwardly sectinonally, and either such pipe is formed to be smoothly extensive from its convex tip to its base portion. The invention recited in claim  22  is as set forth in any one of claims  16 - 20  and is characterized in that the refractory protective pipe or the outer refractory heat transfer pipe of the heat transfer conduit is shaped like a tetrahedral pillar when seen outwardly sectinonally, and either such pipe is formed to be smoothly extensive from its convex tip to its base portion. Here, the smoothly extensive structure is exemplified to be obtainable as by chamfering. This structure can decrease those stepped or angular portions tending to take place from the tip to the base, alleviating the problems of wear and damage of the above pipe which would result from contact with the gas of elevated temperature flowing at a high speed.  
       [0034] The invention recited in claim  23  is as set forth in any one of claims  1 - 15  and is characterized in that the tip of the refractory protective pipe or the outer refractory heat transfer pipe is formed as a refractory removable cap member.  
       [0035] Therefore, even when the cap member is centrally worn or damaged due to collision with the burnt exhaust gas of elevated temperature caused to flow at a high speed, such cap is easily replaced by a new one.  
       [0036] Now, in the case where the outer metallic heat transfer conduit is constructed with the refractory protective pipe located to flow the air to be heated therethrough, the protective pipe disposed to cover the heat transfer pipe with the gapping defined between the two pipes, and the cap member is screwed with the space provided at a region where the tip of the protective pipe is opposed to the tip of the heat transfer pipe, and in the case where the outer metallic heat transfer pipe is provided with a through hole for the air to be heated and caused to pass therethrough to be partly flowed into the gapping, such cap is spirally secured, i.e., fixedly screwed. The cap is therefore held by means of spiral line contact. This means that no particular stress concentration is existent even if the temperature change (thermal cycling) is present between room temperature and high temperature, and detachment and damage are less likely to take place. Since, moreover, the gapping can be so made in its inside as to have a positive pressure, the gas of elevated temperature is prevented against intrusion from the outside into the refractory protective pipe and the refractory cap member. Also with this point taken in view, part of the refractory material can be alleviated from being impaired, and prolonged cycle of replacement is rendered possible.  
       [0037] To form the cap member into a rotatably screwing type, it is required that, in the case where the heat transfer conduit is arranged in a plural number and on a parallel with each other with no gap left therebetween and with the refractory protective pipe or the outer refractory heat transfer pipe longitudinally positioned in parallel with the direction of gas flow, the outside diameter of the cap member be so decided that the caps of two adjacent heat transfer conduits are not impinged on each other during rotation thereof.  
       [0038] The invention recited in claim  24  is as set forth in claim  23  and is characterized in that the cap member is formed in a convex shape so as to be less resistant to flow of the gas of elevated temperature. By use of this convex cap, those impacts brought about by gas flow of elevated temperature are relaxed so that the cap itself is prevented from wear and damage, and the cycle of replacement is prolonged.  
       [0039] The invention recited in claim  25  is as set forth in claim  23  or  24  and is characterized in that the cap member is screwed to the tip of the heat transfer pipe with a gapping defined at an opposed tip portion, the screwing is effected with a partial gap, and the heat transfer pipe is provided atits tip with a through hole for the air to be heated and caused to pass therethrough to be partly flowed into the gapping. Because the gapping at the screwed portion can be so made in its inside as to have a positive pressure with respect to the external atmosphere, the gas of elevated temperature is prevented against intrusion from the outside into the refractory cap member and subsequent contact with the metallic heat transfer pipe at the screwed portion.  
       [0040] The invention recited in claim  26  is as set forth in any one of claims  23 - 25  and is characterized in that the refractory protective pipe or the outer refractory heat transfer pipe of the heat transfer conduit is shaped like a circular pillar when seen outwardly sectinonally, and the cap member and either such pipe are connected to each other in an externally smoothly extensive manner. The invention recited in claim  27  is as set forth in any one of claims  23 - 25  and is characterized in that the refractory protective pipe or the outer refractory heat transfer pipe of the heat transfer conduit is shaped like a tetrahedral pillar when seen outwardly sectionally, and the cap member and either such pipe are connected to each other in an externally smoothly extensive manner. Here, the externally smoothly extensive shape is obtainable by forming such cap and pipe to have the same outside diameter, or by chamfering such cap and pipe when they are different in outside diameter.  
       [0041] The invention recited in claim  28  is as set forth in any one of claims  1 - 27  and is characterized in that the apparatus for heating high-temperature air comprises a first air heater positioned upstream of a passage for flow of the gas of elevated temperature, wherein a second air heater positioned downward of such flow passage, the air to be heated is supplied to and heated in the second air heater, and the resultant air is then transported to and heated in the first air heater.  
       [0042] The invention recited in claim  29  is as set forth in claim  28  and is characterized in that the apparatus for heating high-temperature air comprises a first air heater positioned upstream of a passage for flow of the gas of elevated temperature, and a second air heater positioned downward of such flow passage, the air to be heated is supplied to and heated in the first and second air heaters, respectively, and the two sorts of air heated are combined together and then taken outside.  
       [0043] In the apparatus for heating high-temperature air constructed as set forth in claim  28  or  29 , the heat transfer conduit can be made short in length and light in weight. This makes the associated suspension support structure relatively light in weight and moreover permits simple operation when in dismantling the heat transfer conduit from the flow passage for the gas of elevated temperature during maintenance. Namely, the present invention enables the heat energy of the gas of elevated temperature to be recovered by the use of air, and the apparatus for heating high-temperature air for use of the heat energy to advantage can lead not only to shortened length per one heat transfer conduit and simplified support structure and maintenance operation, but also to simplified installation in terms of space and precision and reduced deformation arising from thermal strain. Thus, improved efficiency of heat transfer is attained.  
       [0044] In the apparatus for heating high-temperature air set forth in claim  28 , low-temperature air to be heated is supplied to and heated in the second air heater. The outer heat transfer pipe and the inner heat transfer pipe, both of which are arranged to constitute the second air heater, are made to communicate with each other at one end of each pipe, specifically at a lower end of each pipe. The low-temperature air to be heated is selectively heated by either one of a system in which such air is supplied through the inner pipe to and heated in the outer pipe, and a system in which such air is supplied through the outer pipe to and heated in the inner pipe. The former system may be preferred from the point of view of thermal efficiency.  
       [0045] After being heated at a given temperature in the second air heater as stated above, the air to be heated is heated by either one of a system in which such air is supplied through the first air heater-constituting outer heat transfer pipe to and heated in the inner tube, and a system in which such air is supplied through the inner pipe to and superheated in the outer tube. The latter system may desirably be employed.  
       [0046] On the other hand, in the apparatus for heating high-temperature air set forth in claim  29 , the low-temperature air to be heated is supplied to and heated in the first air heater and the second air heater, respectively. With use of the apparatus for heating high-temperature air thus constructed, the area for the flow passage of the air to be heated can be made greater than that of the gas of elevated temperature with eventual decline in pressure loss of the air to be heated. In such instance, the low-temperature air to be heated is heated by selecting either one of a system in which such air is supplied through the second air heater-constituting inner pipe to and heated in the outer heat transfer pipe, and a system in which such air is supplied through the outer heat transfer pipe to and heated in the inner pipe. When thermal efficiency is taken in view, the former system may be desired. The air to be heated and conveyed to the first air heater is heated, as in the second air heater, by selecting either one of a system in which such air is supplied through the inner pipe to and heated in the outer heat transfer pipe, and a system in which such air is supplied through the outer heat transfer pipe to and heated in the inner pipe. The latter system of the two selections is liable to suffer from increased temperature of the air at an inlet of the gas of elevated temperature, increased temperature of the pipe walls and increased temperature of the refractory material. In view of durability, therefore, the former system may be suitably selected.  
       [0047] The invention recited in claim  30  is as set forth in claim  29  and is characterized in that the air to be heated is partly supplied through either one of the first air heater-constituting heat transfer pipe or outer pipe and the inner pipe to and heated in either the inner pipe or the outer pipe, and the remaining portion of the the air to be heated is supplied through either one of the second air heater-constituting heat transfer pipe or outer pipe and the inner pipe to and heated in either the inner pipe or the outer pipe.  
       [0048] The invention recited in claim  31  is directed to the structure of a partition wall for use in an heat exchanger, which partition wall is disposed to separate an air passage from an exhaust gas passage, characterized in that the partition wall comprises a metallic wall placed in contact on one side with the air passage, and a refractory wall placed in contact on one side with the gas passage, a first gapping is defined between the other side of the metallic wall and the other side of the refractory wall and made to communicate with a through hole made in the metallic wall, thereby flowing burnt exhaust gas containing corrosive components and dust into the exhaust gas passage, and a plurality of support materials are securely attached to the other side of the metallic wall so as to support the refractory wall. The invention recited in claim  32  is as set forth in claim  31  and is characterized in that a second gapping is defined between the support materials and the refractory wall and made to communicate with the first gapping.  
       [0049] By the provision of these support materials, the gapping between the metallic wall and the refractory wall can be rendered substantially uniform throught the length thereof, and the refractory wall of great mass can also be held in firmly supported relation to the metallic wall. This gives least fear of the refractory wall becoming unstable. Further, since the air is flowed via the through hole into both the first gapping and the second gapping, the gas of elevated temperature can be prevented from intrusion into these spacings, and the metallic wall and the support materials can be reliably avoided from corrosion. Hence, the metallic wall and the like are noticeably prolonged in service life. In addition, the metallic wall is less corrosive even at high temperature so that it is possible to heat air at high temperature by heat exchange with a larger quantity of heat than is in conventional practice. Energy efficiency can thus be improved as to the finished apparatus on the whole.  
       [0050] In the invention recited in claim  33 , there is provided a process for producing a partition wall for use in a heat exchanger wherein the partition wall is disposed to separate an air passage from an exhaust gas passage, the partition wall comprising a metallic wall placed in contact on one side with the air passage, and a refractory wall placed in contact on one side with the gas passage, a first gapping is defined between the other side of the metallic wall and the other side of the refractory wall and made to communicate with a through hole made in the metallic wall, thereby flowing burnt exhaust gas containing corrosive components and dust into the exhaust gas passage, and a plurality of support materials are securely attached to the other side of the metallic wall so as to support the refractory wall, characterized in that such process comprises the steps of disposing an interlaminar material over the other side of the metallic wall by covering vinyl sheet or paper tape thereover, or by coating tar or paint thereover, coating or spraying over the interlaminar material a water-containing castable material in a predetermined thickness, heating the castable material to dry and calcinate the same to thereby form the refractory wall and to remove the interlaminar material therefrom, and subsequently defining the first gapping on the refractory wall where the interlaminar material has been removed.  
       [0051] The invention recited in claim  34  is as set forth in claim  33  and is directed to the process for producing the partition wall wherein a second gapping is defined between the support materials and the refractory wall and made to communicate with the first gapping, characterizied in that such process comprises the steps of disposing an interlaminar material over the support materials, prior to or after welding of the the support materials to the metallic wall, by winding insulating tape made of polyvinyl chloride thereover, by covering vinyl hose cut short thereover, by coating aqueous paint thereover, or by immersing the support materials in stock solution of the aqueous paint, coating or spraying over the interlaminar material a water-containing castable material in a predetermined thickness, heating the castable material to dry and calcinate the same to thereby form the refractory wall and to remove the interlaminar material therefrom, and subsequently defining the second spacing on the support materials where the interlaminar material has been removed.  
       [0052] By use of these processes, a heat exchanger can be produced as desired by the present invention.  
       [0053] In the invention recited in claim  35 , there is provided an apparatus for disposing of wastes which is provided with a thermal decomposition reactor in which wastes are thermally decomposed to generate a thermally decomposed gas and a thermally decomposed residue, a separator in which the thermally decomposed residue is separated into combustible components and incombustible components, a burning melting furnace in which the thermally decomposed gas and the combustible components are burnt at a temperature at which to melt ash to thereby discharge incombustible matter as melted slug, and an apparatus for heating high-temperature air in which the heat of gas of elevated temperature is recovered by heat exchange with air, characterized in that such apparatus for heating high-temperature air is as set forth in any one of claims  1 - 30 . This apparatus for disposing of wastes can be improved in its operating efficiency in line with improved operating efficiency of the apparatus for heating high-temperature air. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0054]FIG. 1 is a longitudinally sectional view showing important parts of one form of the apparatus for heating high-temperature air according to the present invention.  
     [0055]FIG. 2 is a horizontally sectional view showing important parts of one form of the apparatus for heating high-temperature air according to the invention.  
     [0056]FIG. 3 is a schematically longitudinally sectional view showing one form of the apparatus for heating high-temperature air according to the invention.  
     [0057]FIG. 4 is a longitudinally sectional view showing important parts of another form of the apparatus for heating high-temperature air according to the invention.  
     [0058]FIG. 5 is a longitudinally sectional view showing important parts of a further form of the apparatus for heating high-temperature air according to the invention.  
     [0059]FIG. 6 is a view showing the analysis results of air temperatures in a heat transfer pipe of a comparative example.  
     [0060]FIG. 7 is a view showing the analysis results of air temperatures in the heat transfer conduit of the invention.  
     [0061]FIG. 8 is a longitudinally sectional view showing important upper parts of still another form of the apparatus for heating high-temperature air according to the invention.  
     [0062]FIG. 9 is a longitudinally sectional view showing important top parts of still another form of the apparatus for heating high-temperature air according to the invention.  
     [0063]FIG. 10 is a perspective view showing another form of the heat transfer conduit of the apparatus for heating high-temperature air according to the invention.  
     [0064]FIG. 11 is a perspective view showing still another form of the heat transfer conduit of the apparatus for heating high-temperature air according to the invention.  
     [0065]FIG. 12 is a longitudinally sectional view showing top parts of still another form of the apparatus for heating high-temperature air according to the invention.  
     [0066]FIG. 13 is a longitudinally sectional view showing top parts of still another form of the apparatus for heating high-temperature air according to the invention.  
     [0067]FIG. 14 is a perspective view showing important parts of a heat transfer pipe of the heat transfer conduit according to the invention.  
     [0068]FIG. 15 is a perspective view showing still another form of the heat transfer conduit of the apparatus for heating high-temperature air according to the invention.  
     [0069]FIG. 16 is a side view showing important parts of still another form of the heat transfer conduit of the apparatus for heating high-temperature air according to the invention.  
     [0070]FIG. 17 is a side view showing important parts of still another form of the heat transfer conduit of the apparatus for heating high-temperature air according to the invention.  
     [0071]FIG. 18 is a perspective view showing important parts of still another form of the heat transfer conduit of the apparatus for heating high-temperature air according to the invention.  
     [0072]FIG. 19 is a perspective view showing one form of the apparatus for heating high-temperature air according to the invention.  
     [0073]FIG. 20 is a perspective view showing another form of the apparatus for heating high-temperature air according to the invention.  
     [0074]FIG. 21 is a longitudinally sectional view showing important top parts of a further form of the apparatus for heating high-temperature air according to the invention.  
     [0075]FIG. 22 is a perspective view showing still another form of the heat transfer conduit of the the apparatus for heating high-temperature air according to the invention.  
     [0076]FIG. 23 is a perspective view showing still another form of the heat transfer conduit of the the apparatus for heating high-temperature air according to the invention.  
     [0077]FIG. 24 is a perspective view showing important parts of still another from of the heat transfer conduit of the the apparatus for heating high-temperature air according to the invention.  
     [0078]FIG. 25 is a longitudinally sectional view showing important top parts of still another from of the apparatus for heating high-temperature air according to the invention.  
     [0079]FIG. 26 is a perspective view showing still another form of the heat transfer conduit of the the apparatus for heating high-temperature air according to the invention.  
     [0080]FIG. 27 is a perspective view showing still another form of the heat transfer conduit of the the apparatus for heating high-temperature air according to the invention.  
     [0081]FIG. 28 is a perspective view showing still another form of the heat transfer conduit of the the apparatus for heating high-temperature air according to the invention.  
     [0082]FIG. 29 is a longitudinally sectional view showing important top parts of still another from of the apparatus for heating high-temperature air according to the invention.  
     [0083]FIG. 30 is a perspective view showing still another form of the heat transfer conduit of the the apparatus for heating high-temperature air according to the invention.  
     [0084]FIG. 31 is a longitudinally sectional view showing important top parts of still another from of the apparatus for heating high-temperature air according to the invention.  
     [0085]FIG. 32 is a longitudinally sectional view showing important top parts of still another from of the apparatus for heating high-temperature air according to the invention.  
     [0086]FIG. 33 is a longitudinally sectional view showing important top parts of still another from of the apparatus for heating high-temperature air according to the invention.  
     [0087]FIG. 34 is a longitudinally sectional view showing important top parts of still another from of the apparatus for heating high-temperature air according to the invention.  
     [0088]FIG. 35 is a schematically longitudinally sectional view showing still another from of the apparatus for heating high-temperature air according to the invention.  
     [0089]FIG. 36 is a schematically longitudinally sectional view showing still another from of the apparatus for heating high-temperature air according to the invention.  
     [0090]FIG. 37 is a schematically longitudinally sectional view showing still another from of the apparatus for heating high-temperature air according to the invention.  
     [0091]FIG. 38 is a schematically longitudinally sectional view showing still another form of the apparatus for heating high-temperature air according to the invention.  
     [0092]FIG. 39 is a schematic view showing one form of the apparatus for disposing of wastes according to the invention.  
     [0093]FIG. 40 is a longitudinally sectional view showing important parts of still another form of the apparatus for heating high-temperature air according to the invention.  
     [0094]FIG. 41 is a longitudinally sectional view showing the heat exchanger of FIG. 40.  
     [0095]FIG. 42 is a horizontally sectional view taken along the line IVI-IVI of FIG. 41.  
     [0096]FIG. 43 is a sectional view, partly enlarged, of the heat exchanger of FIG. 40.  
     [0097]FIG. 44 is a horizontally sectional view taken along the line IVIV-IVIV of FIG. 43.  
     [0098]FIG. 45 is a front elevational view showing part of a surface of a metallic sheet.  
     [0099]FIG. 46 is a sectional view showing important parts as concerns experiments of the heat exchanger of FIG. 40.  
     [0100]FIG. 47 is a horizontally sectional view similar to FIG. 42.  
     [0101]FIG. 48 is a sectional view, as partly enlarged, of FIG. 47.  
     [0102]FIG. 49 is a schematically sectional view showing an apparatus for heating high-temperature air according to the prior art. 
    
    
     MODES OF CARRYING OUT THE INVENTION  
     [0103] Embodiment 1  
     [0104] With reference to the drawings, certain specific embodiments of the apparatus for heating high-temperature air according to the present invention are described hereinbelow.  
     [0105]FIG. 1 is a longitudinally sectional view, vertically cut, of one form of the apparatus for heating high-temperature air according to the invention, and FIG. 2 is a horizontally sectional view, laterally cut, of one form of the apparatus for heating high-temperature air according to the invention and also is a sectional view taken along the line II-II of FIG. 3 to be described later. FIG. 3 is a schematically side view showing the manner in which the apparatus for heating high-temperature air according to the invention is installed.  
     [0106] In the embodiment shown in the figures, an apparatus  1  for heating high-temperature air has a heat transfer conduit  5  constructed with an inner metallic heat transfer pipe  2  opened at its tip and an outer metallic heat transfer pipe  4  closed at its tip with a spacing  3  defined between the two pipes. A refractory protective pipe  6  closed at its tip and formed of a refractory material is disposed in coaxially covered relation to the heat transfer conduit  5  with a gapping  7  defined between such protective pipe and the outer pipe  4  of the conduit  5 .  
     [0107] As metals for use in constituting the heat transfer conduit  5 , SUS  310  and the like are preferable which are excellent in heat resistance and corrosion resistance. In addition, the section thicknesses of the inner pipe  2  and the outer pipe  4  of the heat transfer conduit  5  are desirably in the range of about 4-6 mm in consideration of strength, durability, weight and the like. Preferably, the inside diameter of the inner pipe  2  acting as a passage for air flow is in the range of 30-70 mm, and the width (½ of the difference between the inside diameter of the outer pipe and the inside diameter of the inner pipe) between the outer pipe  4  and the inner pipe  2  is preferably in the range of 10-30 mm. It can be said to be more desirable that a corrosion-resistant film is formed on an outer surface of the outer heat transfer  4 . Suitable materials for use in the corrosion-resistant film are sole oxides such as alumina, silica and the like, or complex oxides such as mulite, spinel and the like, and the film thickness is chosen as is needed in attaining corrosion resistance, thermal cycling and the like. Thus, the outer pipe  4  can be more reliably protected from corrosion.  
     [0108] As refractory materials used for the refractory protective pipe  6 , refractories are suitable which do not form low-melting compounds even upon reaction with components contained in waste-incinerated ash. For instance, a high-alumina refractory, a chromia refractory, a silicon carbide refractory and the like are preferred. The section thickness of the protective pipe  6  is preferably in the range of about 20-30 mm so as to obtain heat transfer efficiency and corrosion resistance. Moreover, the gapping  7  between the protective pipe  6  and the outer heat transfer pipe  4  is preferably in the range of about 1-2 mm (½ of the difference between the inside diameter of the protective pipe  6  and the outside diameter of the outer pipe  4 ). Too large a spacing is responsible for reduced efficiency of heat transfer and also for large-sized apparatus  1  for heating high-temperature air. Conversely, too small a spacing fails to sufficiently avoid damage which would result from the difference in thermal expansion.  
     [0109] Void filling of such a refractory can remarkably decrease the quantity of gas tending to diffusively transmit the protective pipe  6  and can also enhance the corrosion resistance of the refractory itself. This void filling may be effected by immersing the refractrory protective pipe  6  in a liquid such as alumina sol, alumina slurry or the like that clogs the voids of the refractory, followed by drying and subsequent calcination of the immersed pipe. By means of the void filling, for example, an average void diameter of 10 μm or so prior to treatment may be reduced to that of 5 μm or below.  
     [0110] The apparatus  1  for heating high-temperature air is so arranged that the heat transfer conduit  5  and the refractory protective pipe  6  are positioned to be axially vertical. The protective pipe  6  has inverted triangular holes  6   a ,  6   b  made on an inner surface of a sealing end area  6 A thereof, whereas the outer pipe  4  has pawl-shaped protrusions  4   a ,  4   b  formed on an outer surface of a sealing end area  4 A thereof, these protrusions being interengageable with the holes  6   a ,  6   b  of the protective pipe  6 . The protective pipe  6  is supported with respect to the heat transfer conduit  5  by interengagement of the holes  6   a ,  6   b  with the protrusions  4   a ,  4   b . In the embodiment seen in FIG. 1, the protective pipe  6  is supported by the heat transfer conduit  5  only with the holes  6   a ,  6   b  and the protrusions  4   a ,  4   b  interengaged with each other, and other support members for use in supporting the weight of such protective pipe are not disposed.  
     [0111] The apparatus  1  for heating high-temperature air in this embodiment is located vertically in a gas stream (arrowed by G) of elevated temperature and high corrosiveness in an incinerator. Air  8  to be heated descends through the inner heat transfer pipe  2  and then ascends (arrowed) from an open tip  2 A of the inner pipe  2  through the spacing  3  defined between the inner pipe  2  and the outer pipe  4 . During that time, the air to be heated is subjected to heating by the external gas flow G of elevated temperature and high corrosiveness.  
     [0112] At a base end (top end) of the heat transfer conduit  5 , there are located means for introducing the air  8  to be heated and means for discharging the heated air, neither of which is shown. The heat energy recovered is thus used to advantage.  
     [0113] In the apparatus  1  for heating high-temperature air, the heat transfer conduit  5  is covered on its outer side by the refractory protective pipe  6  so that such conduit is protected from corrosion on contact with the gas of elevated temperature and high corrosiveness and hence is made highly durable. Furthermore, even where the difference in thermal expansion takes place between the metal constituting the outer heat transfer pipe  4  and the refractory constituting the refractory protective pipe  6 , those dimensional changes related to thermal expansion are less likely to mutually propagate because of the gapping  7  provided between the outer pipe  4  and the protective pipe  6 . Hence, the protective pipe  6  is prevented from damage, delamination, detachment and the like. Additionally, the support structure is simple between the refractory protective pipe  6  and the outer heat transfer pipe  4 , and the jointing ratio is small as to the refractory in the refractory protective pipe  6 . This serves to prevent the outer heat transfer pipe  4  from impairing.  
     [0114] Moreover, as viewed in FIG. 2 and FIG. 3, a plurality of heat transfer conduits  9  constituted with the heat transfer pipe  5  and the refractory protective pipe  6  are formed in a sectionally square shape and secured in series and in face-to-face contact with the adjoining conduit  9  and the protective pipe  6 . That is to say, the heat transfer conduits  9  except for the two outermost ones are placed on left and right sides in face-to-face contact with the adjoining conduits  9 . Such conduits are mutually fixed by use of connecting means not shown so that they are highly rigid and wholly resistant to thermal decomposition. Each of the heat transfer conduits  9  is so arranged as to be coextensive and flat on its outer surface as shown in FIG. 2. This coextensive flat surface contributes to reduced deposition of dust.  
     [0115] Owing to the above face-to-face contact fixing in series according to the present invention, the apparatus  1  for heating high-temperature air is rendered highly rigid enough to be wholly resistant to thermal decomposition. Thus, such thermal decomposition is conspicuously decreased in a high-temperature atmosphere, especially in a passage for the flow of burnt exhaust gas immediately after combustible residues such as ash and the like are incinerated at a high temperature (1200° C. or higher) into molten slug.  
     [0116] Embodiment 2  
     [0117] Embodiment 2 of the present invention is described with reference to FIG. 4. The heat transfer conduit  9  of the heating apparatus of high-temperature air is arranged, as shown in FIG. 4, in an atmosphere containing a corrosive gas G of elevated temperature discharged as from an incinerator not shown. An air  8  to be heated and caused to flow through a metallic heat transfer pipe  5  is heated by heat exchange with the gas G of elevated temperature, the heat transfer pipe  5  being covered by a refractory protective pipe  6 . The heat transfer pipe  5  is constructed with an outer metallic heat transfer pipe  4  sealed at one end with a sealing material  10 , and an inner tube  2  inserted in and communicating with the outer pipe  4  through an open tip  2 A of the latter pipe. A gapping  7  is defined between the outer heat transfer pipe  4  and a refractory protective pipe  6 , and the air  8  is flowed counter to the flow of the gas G of elevated temperature in the inner pipe  2  and in a spacing  3  as an air passageway between the outer pipe  4  and the inner pipe  2 . In the present invention, the inner pipe  2  is brought into a thermally insulated structure with use of a material of a lower thermal conductivity than a metal. The inner pipe  2  is made to communicate at its base end, not shown, with an inlet of the air to be heated.  
     [0118] More specifically, the inner pipe  2  shown in the embodiment of FIG. 4 is constructed in double-piped form and also in a thermally insulated structure in which a thermal insulating material  11  is sandwiched and filled as shown between the two pipes, or in a thermally insulated structure in which vacuum is drawn in between the two pipes (not shown). Moreover, the inner pipe  2  may be brought into a thermal insulated structure in which the whole is formed of ceramics as seen in FIG. 5.  
     [0119] With use of the above thermal insulating structure, the air  8  to be heated and flowed through the spacing  3  is heated alone without the air  8  to be heated in the inner pipe  2  exposed to simultaneous heating. Thus, the temperature change of the air  8  to be heated in the inner pipe  2  is held to so small an extent as to be acceptable.  
     [0120] To allow the air  8  to be heated to flow counter to the flow of the gas G of elevated temperature in the spacing  3 , the air  8  to be heated may be flowed in two varying directions according to the flow direction of the the gas G of elevated temperature. That is, when the gas G of elevated temperature is flowed as shown by the arrow Gd, the air  8  to be heated is flowed and heated as arrowed by  8   d  as through an air supply tube  12  so connected to the spacing  3  as to introduce the air  8 , and the air  8  is caused to return at a top end of the inner tube  2  into the latter tube and thereafter taken outside. As another way of flow, where the gas G of elevated temperature is flowed in a direction reverse to the arrow Gd, the air to be heated is first flowed in the inner pipe  2  and returned at the top end into the spacing  3  of the outer heat transfer pipe  4  and in a direction reverse to the arrow  8   d . Thus, the heat of the gas of elevated temperature is recovered and then taken outside. In both ways of flow, the air alone flowing through the spacing  3  recovers the heat of such gas, while the air flowing through the inner pipe  2  stands thermally isolated.  
     [0121] The outer heat transfer pipe  4  is covered by the refractory protective pipe  6  with the gapping  7  interposed therebetween. When used at high temperature, a top end of the refractory protective pipe  6  is made movable downwardly of the heat transfer pipe  5  as by a bellows not shown in order to compensate for the different thermal expansion coefficients between the outer pipe  4  and the protective pipe  6 . With the heat transfer pipe  5  and the refractory protective pipe  6  caused to relatively move with use of the gapping  7  at room temperature and at high temperature, the heat transfer pipe  5  and the refractory protective pipe  6  are preveted from getting mutually impaired in respect of their respective thermal expansions even at high temperature. Desirably, extraneous air for example be introduced in the gapping  7  to thereby avoid a corrosive gas of elevated temperature from intrusion into a wall of the refractory protective pipe  6  and subsequent contact with the heat transfer pipe  5 . The refractory protective pipe  6  is secured at its tip to a tip protecting material  13  of a refractory nature that is disposed to cover a sealing material  10 , and gappings  7  are also defined between the refractory protective pipe  6  and the outer heat transfer pipe  4  on its outer surface and between the tip protecting material  13  and the sealing material  10 , these gappings being partitioned from the above stated gapping.  
     [0122] Also in this embodiment, the outer heat transfer pipe  4  is covered on its outer surface with the refractory protective pipe  6  with the result that the former pipe is protective against the gas of elevated temperature and high corrosiveness and hence excellent in durability. Furthermore, because of provision of the gapping  7  between the outer heat transfer pipe  4  and the refractory protective pipe  6 , the dimensional changes of both pipes resulting from thermal expansion do not mutually propagate even if the difference in thermal expansion occurs between the metal constituting the outer heat transfer pipe  4  and the refractory constituting the refractory protective pipe  6 . In consequence, the refractory protective pipe  6  is prevented from damage, delamination and detachment. Besides and preferably, the heat transfer pipe constututing metal is SUS  310  or the like which is highly resistant to heat and to corrosion. The section thicknesses of the inner pipe  3  and the outer heat transfer pipe  1  are set to be preferably in the range of about 4-6 mm, but they are decided in terms of strength, durability, weight and the like. The inside diameter of the inner pipe  2  for use as a passage of the air  8  to be heated is preferably in the range of 30-70 mm, and the width (½ of the difference between the inside diameter and the outside diameter of the inner pipe) of the spacing  3  between the outer heat transfer pipe  4  and the inner pipe  2  is preferably in the range of 10-30 mm.  
     [0123] Next, this embodiment is described with regard to its operation and with reference to FIG. 4. The heat transfer pipe  5  is arranged in a vertical posture in a gas stream (arrowed by Gd) of elevated temperature and high corrosiveness in an incinerator so that the air  8  to be heated is introduced into the spacing  3  of the outer heat transfer pipe  4  and descends in the spacing  3  and then ascends through the open tip  2 A of the inner pipe  2  in the latter pipe (arrowed by  8   d ). During that time, such air is heated with an external gas stream of elevated temperature through the refractory protective pipe  6  and the wall of the outer heat transfer pipe  4 . In this instance, the air  8  to be heated and caused to pass through the spacing  3  is heated alone with the gas G of elevated temperature, but the the air  8  to be heated and caused to pass through the inner pipe  2  thermally insulated is not exposed to heating. Namely, since the air contained in the inner pipe  2  is thermally isolated, the temperature change of the air  8  to be heated is held in the inner pipe  2  to small an extent as to be acceptable. Hence, high efficiency of heat transfer is attainable.  
     [0124] The analysis results as to the relationship between the length of the heat transfer pipe in the heat transfer pipe  5  of this embodiment and the temperature of the air are shown in FIG. 6 and FIG. 7. In these drawings, La refers to the inner pipe, Lb to the spacing and Lc to the gas of elevated temperature. FIG. 6 is directed to a comparative example and hence to the analysis results obtained for an inner metallic heat transfer pipe formed of a carbon steel in common use, but not of a thermally insulated structure. This case reveals that the temperature of an air to be heated reaches the highest at a tip of the heat transfer pipe and that after being flowed and returned in such pipe, the air causes a sharp decline in temperature at a base end (discharge outlet) of such pipe. As contrasted, where the inner pipe is of a thermally insulated structure as viewed in FIG. 7, the decrease in temperature of the air to be heated in the inner pipe is small between a tip end of the heat transfer pipe and a base end thereof as shown. When FIG. 6 and FIG. 7 are compared with each other, it is found that the inner pipe of a thermally insulated structure allows the temperature change of the air to be heated in such pipe to be held to so small an extent as to be acceptable.  
     [0125] Embodiment 3  
     [0126] Embodiment 3 of the present invention is described with reference to FIG. 8 and FIG. 9.  
     [0127] As shown in FIG. 8 and FIG. 9, an apparatus for heating high-temperature air is so constituted that a heat transfer conduit  9 , i.e., a metallic heat transfer pipe  5  covered with a refractory protective pipe  6 , is used in heating an air  8  to be heated and caused to flow in the heat transfer pipe  5  upon heat exchange with a gas G of elevated temperature. The heat transfer pipe  5  is constructed with an outer heat transfer pipe  4  and an inner pipe fixed thereto and opened at its tip end with a spacing  3  defined between both pipes for use as a flow passage of the air  8  to be heated. An upper port  14  is secured to an upper outer surface of the outer heat transfer pipe  4  with hermetic sealability retained.  
     [0128] Defined between the outer heat transfer pipe  4  and the refractory protective pipe  6  is a gapping  7  in which means  16  (air introducing pipe) is provided for introducing therein extraneous air so as to purge the corrosive gas G of elevated temperature. That is, an extraneous air  17  is introduced in the gapping between the outer heat transfer pipe  4  and the refractory protective pipe  6 , such extraneous air being completely isolated from the air  8  to be heated, so that even upon intrusion of the corrosive gas of elevated temperature through a wall of the refractory protective pipe  6  into the gapping  7 , this gas is prevented from getting reversely diffused toward the air  8  to be heated or intermixed therewith. This makes the heat transfer pipe and the like highly durable against corrosion at high temperature.  
     [0129] The upper port  14  of the heat transfer pipe is attached on a lower surface to an upper end surface of a bellows  18 , and the bellows  18  is secured on its lower end surface to an upper end surface of a refractory presser  19 . These attachments are effected as by welding so as to provide hermetic sealability. The refractory protective pipe  6  is secured at one end to a lower end surface of the refractory presser  19 . When in use at high temperature, an upper end of the refractory protective pipe  6  is moved downwardly of the heat transfer pipe  5  by the action of the bellows  18  due to the difference in thermal expansion between the outer heat transfer pipe  4  and the refracrtory protective pipe  6 . By the provision of the bellows  18 , the extraneous air  17  can be introduced at high temperature while the outer heat transfer pipe  4  and the refracrtory protective pipe  6  are being relatively moved at room temperature and at high temperature. The extraneous air  17  flows along the inner surfaces of the bellows  18  and the refractory presser  19  and also along an outer surface of a fixing fitment not shown for use in fixing the protective pipe  6 , eventually filling up the gapping  7 .  
     [0130] In this embodiment, the refractory protective pipe  6  is fixed at its tip end to a refractory top end  15  placed to cover a lower sealing portion  10  of the outer heat transfer pipe  4  by the use of a male screw  20  and a female screw  21 . That is, the male screw  20  is protruded downwardly in the lower sealing portion  10  of the outer heat transfer pipe  4 . The female screw  21  is interengaged with the male screw  20  in the refractory top end  15  and with the gapping  7  provided. By means of the male screw  20  and the female screw  21 , the refractory protective pipe  6  is spirally interengaged at a lower end with the refractory top end  15  with the gapping  7  defined therebetween. The gapping  7  in this top end is partitioned by the lower sealing portion  10  from the other gapping  7  stated above, and a through hole  23  is made in the lower sealing portion  10  so that the extraneous air  17  is introduced also into the gapping  7  in the top end.  
     [0131] In this embodiment, it is desired that the metallic material used to constitute the heat transfer pipe, the section thicknesess of the inner heat transfer pipe and the outer heat transfer pipe, the inside diameter of the inner heat transfer pipe, the spacing  3  between the outer and inner pipes and the like be set as in Embodiment 1 or 2.  
     [0132] Embodiment 4  
     [0133] Embodiment 4 of the present invention is described below with reference to the drawings.  
     [0134]FIG. 10 is a perspective view showing one form of the heat transfer conduit of the apparatus for heating high-temperature air according to the invention, and FIG. 11 is a perspective view showing another form of the heat transfer conduit. Heat transfer conduits  9  shown in these drawings have a refractory protective pipe  6  disposed over their respective surfaces and provide an elongate tetraheral shape as seen horizontally sectionally. These conduits are arranged in a flow passage of a burnt exhaust gas G of elevated temperature which is derived by burning combustible components such as wastes or the like at a temperature as high as about 1300° C. so that heat recovery is carried out from the burnt exhaust gas G of a high temperature of 1000-1100° C. allowed to flow at a speed of 2-3 m per second. For use in formation of the refractory protective pipe  6 , refractory materials are employed which are composed predominantly of alumina and also contain chromium oxide, zirconia and the like. The refractory protective pipe  6  of the heat transfer conduit  9  is formed at its tip end  24  into a convex hemispherical shape that is less resistant to the stream of gas. In this embodiment, such protective pipe is formed in such a manner that the diameter of such semispherical portion is substantially identical to the length of one side of such tetrahedral portion.  
     [0135] The tip end  24  in the convex shape acts to relax those thermal effects such as concentrated thermal stress arising from contact with a stream of gas of elevated temperature with consequent reduction of such tip end in respect of damage such as wear and breakage. In particular, since the convex portion of the tip end  24  is formed in the semispherical shape, those thermal effects applied to the tip end  24  are uniformly distributed throughout the latter end. This serves to further decrease damage to the tip end  24 .  
     [0136] In the heat transfer conduit  9  seen in FIG. 10, the semispherical tip end  24  and a base end of the sectionally tetraheral shape have stepped portions  25  formed at their conrners. Desirably, each such stepped portion  25  is formed as small as possible to preclude the concentrated thermal stress noted above. Illustrated in FIG. 11 is a heat transfer conduit  9  constructed in consideration of that point, and this conduit is devoid of those stepped portions. Namely, the heat transfer conduit  9  is made smoothly extensive from the tip end  24  to the base end with the heat transfer conduit  9  of FIG. 10 subjected to a chamfering  26  at its stepped portions on four corners.  
     [0137]FIG. 12 is a sectional view showing the tip end of the heat transfer conduit  9  viewed in FIG. 11 and taken along the line XII-XII. As seen in FIG. 12, the heat transfer conduit  9  is so constructed that an air  8  to be heated and allowed to flow through an outer heat transfer pipe  4  is heated on heat exchange with a gas G of elevated temperature by use of such outer heat transfer pipe formed of a metal and covered with a refractory protective pipe  6 . The refractory protective pipe  6  has an inverted triangular hole  24   a  made on an inner surface the tip end  24 , and the outer heat transfer pipe  4  has a pawl-like protrusion  4   a  formed on an outer surface of the top end. The refractory protective pipe  6  and the outer heat transfer pipe  4  are brought into integral relation to each other by interengagement of the hole  24   a  with the protrusion  4   a.    
     [0138] An heat transfer pipe  2  is inserted in the outer heat transfer pipe  4  sealed at one end with a sealing member  4 A such that the pipe  2  is made to communicate with the pipe  4  through an opened top end  2 A. A gapping  7  is defined between the outer heat transfer pipe  4  and the refractory protective pipe  6 , and the air  8  to be heated is flowed counter to the flow of the gas G of elevated temperature. A base end, not shown, of the inner heat transfer pipe  2  is made to communicate with a supply source of the air  8  to be heated.  
     [0139] Owing to provision of the gapping  7  between the outer heat transfer pipe  4  and the refractory protective pipe  6 , the dimensional changes of both pipes resulting from thermal expansion do not mutually propagate even when the difference in thermal expansion takes place between the metal used to form the outer pipe  4  and the refracory used to form the protective pipe  6 . Thus, the refractory protective pipe  6  is prevented from becoming impaired, delaminated or detached. Moreover, the outer heat transfer pipe  4  is provided with minute through holes  27  from which part of the air  8  to be heated and caused to flow in the pipe  4  is flowed into the gapping  7 . Since, therefore, the gapping  7  has a positive pressure with respect to an ambient atmosphere (passage of the gas G of elevated temperature), the gas of elevated temperature is less likely to permeate the refractory protective pipe  6  and to intrude thereinto. With the two beneficial effects produced by the action of the convex tip end  24  and by the freedom from permeation of the gas of elevated temperature, damage and the like to the tip end  24  of the refractory protective pipe  6  are further alleviated. At the same time, the gas of elevated temperature is free from permeation to the refractory protective pipe  6  and subsequent contact with the outer metallic heat transfer pipe  4 . Thus, the outer pipe  4  can be prevented with reliability against corrosive deterioration.  
     [0140] A heat transfer conduit  9  shown in FIG. 13 is constructed with an outer metallic heat transfer pipe  2  opened at its tip end and an outer refractory heat transfer pipe  29  placed to be coaxial relative to the pipe  2  and to cover the pipe  2  with a gap passage  28  provided between both pipes. After being passed through the outer metallic heat transfer pipe  2 , an air  8  to be heated is heated with the gas of elevated temperature while such air is being passed out of the open tip end  2 A of the inner tube  2  through the gap passage  29  between the inner pipe  2  and the outer pipe  29 . In an apparatus for heating high-temperature air of such structure, a top end  24  of the outer refractory heat transfer pipe  29  is also formed in the same convex shape as viewed in FIG. 12. FIG. 14 is a perspective view showing a pawl-like protrusion  2   a  of the inner heat transfer pipe  2  at its tip end.  
     [0141]FIG. 15 is a perspective view showing still another form of the heat transfer conduit according to the present invention. Although the heat transfer conduit  9  is shown in FIG. 10 as being in a tetrahedral shape when seen horizontally sectionally, a heat transfer conduit illustrated in this embodiment is formed to be sectionally circular. Namely, a refractory protective pipe  6  is an elongate member in a sectionally circular shape. In this embodiment, the diameter of a convex tip portion is set to be substantially identical to the diameter of a base portion, and therefore, no problems are created as related to the sepped portions discuused above. Other structural details are the same as in FIG. 10.  
     [0142] The convex shape of the heat transfer conduit  9  at its top end  24  may be conical as seen in FIG. 16, or may be polyconically convex as seen in FIG. 17. The conical shape of FIG. 16 is chamfered at its top end. The polyconically convex shape is not limited to a shape shown in FIG. 17 and formed with two conical planes, but may be a polycone such as a tetrahedral cone and the like and a polygon shown in FIG. 18 and formed convex on a polyplane. In short, the above convex shape of the top end  24  may be formed as a convex made up of either one or both of a plane and a curve and should not be construed as being restricted to any particular shape.  
     [0143]FIG. 19 and FIG. 20 each are perspective views showing important parts of the apparatus for heating high-temperature air according to the present invention. In FIG. 19, four heat transfer conduits  9  are arranged in intimate contact with each other as taking the heat transfer conduit  9  of FIG. 10 as a unit, and this conduit arrangement is disposed in three arrays and placed in a suspended posture in a gas atmosphere of elevated temperature. In FIG. 20, four heat transfer conduits  9  are arranged in intimate contact with each other as taking the heat transfer conduit  9  of FIG. 11 as a unit, and this conduit arrangement is disposed in three arrays and placed in a suspended posture in a gas atmosphere of elevated temperature. In each case, a plurality of tetrahedral pillar-shaped heat transfer conduits  9  are disposed in series with no gap left between and among these conduits. This is capable of reducing dust deposition on the refractory protective pipe  6  as compared to the arrangement of FIG. 15 in which cylindrical heat transfer conduits  9  are disposed in series.  
     [0144] In this embodiment, as described hereinabove, the top end of the refractory protective pipe of the heating apparatus of high-temperature air is in a convex shape that is less resistant to the gas flow of elevated temperature. Thus, those thermal effects such as concentrated thermal stress and the like are relaxed which are caused upon contact with the gas flow of elevated temperature, and the top end of the refractory protective pipe is alleviated against damage such as wear, breakage and the like.  
     [0145] Embodiment 5  
     [0146] Embodiment 5 ot the present invention is described below with reference to the drawings.  
     [0147]FIG. 21 is a sectional view showing important parts of one form of the heat transfer conduit of the apparatus for heating high-temperature air according to the invention, and FIG. 22 is a perspective view showing the appearance of the heat transfer conduit. A heat transfer conduits  9  shown in FIG. 22 has a refractory protective pipe  6  disposed over its surface and provides an elongate tetraheral shape as seen horizontally sectionally. This conduit is arranged in a flow passage of a burnt exhaust gas G of elevated temperature which is derived by burning combustible components such as wastes or the like at a temperature as high as about 1300° C. so that heat recovery is carried out from the burnt exhaust gas G of a high temperature of 1000-1100° C. allowed to flow at a speed of 2-3 m per second. For use in formation of the refractory protective pipe  6 , refractory materials are employed which are composed predominantly of alumina and also contain chromium oxide, zirconia and the like.  
     [0148] More specifically, as shown in FIG. 21, the heat transfer conduit  9  is so constructed that an air  8  to be heated and caused to flow through an outer heat transfer pipe  4  is heated upon heat exchange with a gas G of elevated temperature with use of such outer heat transfer pipe formed of a metal and covered with the refractory protective pipe  6 . An inner metallic heat transfer pipe  2  is inserted in the outer heat transfer pipe  4  sealed at one end with a sealing member  10  such that the inner tube  2  is made to communicate through its open top end  2 A with the outer pipe  4 . The air  8  to be heated is allowed to flow in the inner pipe  2  and through a spacing  3  between the outer pipe  4  and the inner pipe  2  and in a direction opposite to the flow of the gas G of elevated temperature. Further, a gapping  7  is defined between the outer heat transfer pipe  4  and the refractory protective pipe  6 . A base end, not shown, of the inner heat transfer pipe  2  is made to communicate with a supply source of the air  8  to be heated.  
     [0149] The refractory protective pipe  6  shown in FIG. 22 in this embodiment is provided at its top end with a refractory cap  30  which is substantially of the same shape as and of the same outside diameter as the protective pipe  6  and is freely detachable. The cap  30  is screwed, as shown in FIG. 21, to the sealing member  10  of the outer heat transfer pipe  4  opposed to the tip end with the gapping  7  partitioned from the other gapping. That is to say, the cap  30  is screwed into and fixed to a male screw  31  formed in the sealing member  10 . A female screw  32  is formed at a portion at which to be engaged with the male screw  31 . Designated at  33  in that figure is refractory mortar disposed to maintain hermetic sealability against an external atmosphere when the cap  30  is fixed.  
     [0150] In the above structure, the cap  30  can be removed and replaced by a new one even when such cap is subjected to partly concentrated wear and damage. Replacement is thus made with utmost ease. Additionally, the cap  30  is attached by screwing and hence supported by spiral line contact so that no particular stress concentration is present even if the temperature is variable between at room temperature and at high temperature, and delamination and damage are less likely to occur.  
     [0151] Furthermore, the gapping  7  is defined between the outer heat transfer pipe  4  and the refractory protective pipe  6  or the cap  30 . In this instance, even when the difference in thermal expansion takes place between the metal used to form the outer heat transfer pipe  4  and the refractory used to form the refractory protective pipe  6  or the cap  30 , the dimensional changes caused by the thermal expansions do not propagate toward each other. The refractory protective pipe  6  or the cap  30  can thus be avoided from getting damaged, delaminated or detached.  
     [0152] Moreover, in this embodiment as shown in FIG. 21, the outer heat transfer pipe  4  is provided with minute through holes  27  from which part of the air  8  to be heated and caused to flow in the pipe  4  is flowed into the gapping  7 . Since, therefore, the gapping  7  has a positive pressure with respect to an ambient atmosphere (passage of the gas G of elevated temperature), the gas of elevated temperature is less likely to permeate the refractory protective pipe  6  or the refractory cap  30  and to intrude thereinto. With the beneficial effect produced by the freedom from permeation of the gas of elevated temperature, damage and the like to the cap  30  are further alleviated. At the same time, the gas of elevated temperature is free from permeation to the refractory protective pipe  6  or the cap  30  and subsequent contact with the outer metallic heat transfer pipe  4 . The outer pipe  4  can thus be reliably prevented against corrosive deterioration.  
     [0153]FIG. 23 is a perspective view showing the appearance of still another form of the heat transfer conduit according to the present invention. Although the heat transfer conduit  9  is shown in FIG. 22 above as being in a tetrahedral shape when seen horizontally sectionally, a heat transfer conduit illustrated in this embodiment is formed to be sectionally circular. Namely, a refractory protective pipe  6  is an elongate member in a sectionally circular shape. Portions where the cap  30  and the refractory protective pipe  6  are connected to each other are formed to be smoothly coextensive when seen externally.  
     [0154]FIG. 24 is a perspective view showing the appearance of still another form of the heat transfer conduit according to the present invention. The outside diameter of a sectionally tetrahedral cap  30  is made smaller than that of a refractory protective pipe  6 . The reason for this is that in the case where a cap not of a sectionally circular, but of for example a sectionally tetrahedral shape, is formed into a rotary screwing type, the outside diameter of the cap is required to be set for the caps of adjoining heat transfer conduits  9  to be not impinged with each other during rotation when a plurality of heat transfer conduits  9  are arranged with no gap left therebetween as will be described later.  
     [0155]FIG. 25 is a sectional view showing important parts of still another of the heat transfer conduit according to the present invention. This figure is different from FIG. 21 in that a cap  30  is formed in a convex shape that is less resistant to the flow of gas, in a semispherical shape in this embodiment. The diameter of the semispherical cap is made substantially identical to the length of one side of the tetrahedral shape. Other structural details are the same as in FIG. 21. Further explanation is omitted with like parts designated by like reference numerals.  
     [0156] By provision of the convex cap  30 , those thermal effects such as concentrated thermal stress and the like caused by contact with a gas flow of elevated temperature are relaxed with consequent alleviation of wear, breakage and the like. In particular, the semispherical shape makes those thermal effects uniformly distributive throughout a top end of the cap  30 , contributing to further reduction in damage and the like with regard to the cap  30  itself.  
     [0157]FIG. 26 is a perspective view showing the appearance of the heat transfer conduit of FIG. 25, and FIG. 25 is a sectional view taken along the line XXV-XXV of FIG. 26. FIG. 27 is a perspective view showing the appearance of another form of the heat transfer conduit of FIG. 25, and FIG. 25 is a sectional view also taken along the line XXV-XXV of FIG. 27. In a heat transfer conduit  9  of FIG. 26, the top cap  30  and the sectionally tetrahedral shape at its base end have stepped portions formed on their corners. In order to avoid the thermal stress mentioned above, it is desired that the stepped portions  25  be made as small as possible. A heat transfer conduit  9  constructed in consideration of that respect is shown in FIG. 27, and this conduit is free of those stepped portions. That is, the heat transfer conduit  9  is formed smoothly extensive from the cap  30  to the base end with the heat transfer conduit  9  of FIG. 26 chamfered at  26  at its stepped portions on four corners.  
     [0158]FIG. 28 is a perspective view showing the appearance of still another form of the heat transfer conduit according to the present invention. Although the heat transfer conduit  9  is shown in FIG. 26 as being in a tetrahedral shape when seen horizontally sectionally, a heat transfer conduit illustrated in this embodiment is formed to be sectionally circular. Namely, a refractory protective pipe  6  is an elongate member in a sectionally circular shape. Portions where the semispherical cap  30  and the rfractory protective pipe  6  are connected to each other are of the same diameter and are smoothly coextensive. Hence, no problems concerning stepped portions are present.  
     [0159]FIG. 29 is a sectional view showing important parts of still another form of the heat transfer conduit according to the present invention. A cap  30  is screwed into a male screw  31  located in a sealing member  10  of a outer heat transfer pipe  4 , and spacings  34 ,  35  hermetically sealed are defined at the screwed portion. The spacing  35  noted here is a spacing partly defined in the above screwed portion. Minute through holes  36  are made at a portion where the male screw  31  is disposed, which holes allow an air  8  to be heated to partly flow into the spacings  34 ,  35 . This embodiment is so constructed that part of the air  8  to be heated is supplied through the spacings  34 ,  35  to a gapping  7  of the above top end. Other structural details are the same as in FIG. 25, and further explanation is omitted with like parts designated by like reference numerals.  
     [0160] Consequently, since the spacings  34 ,  35  of the cap-screwed portion can have a positive pressure with respect to the ambient atmosphere, an external gas G of elevated temperature is alleviated from becoming permeated to the refractory cap  30 . Also from this point, the cap itself can be prevented against damage and the like.  
     [0161]FIG. 30 is a perspective view showing important parts of the apparatus for heating high-temperature air according to the present invention. In this figure, four heat transfer conduits  9  are arranged in intimate contact with each other as taking the heat transfer conduit  9  of FIG. 27 as a unit, and this conduit arrangement is disposed in three arrays and placed in a suspended posture in a gas atmosphere of elevated temperature. A plurality of tetrahedral pillar-shaped heat transfer conduits  9  are longitudinally disposed in series with no gap left between and among these conduits and in parallel to the flow of gas. This leads to reduced dust deposition on the refractory protective pipe  6 .  
     [0162] In the foregoing embodiments, the convex shape of the cap  30  is described as being in a semispherical shape. The present invention is not limited to that shape. For instance, polyplanar convex shapes such as a cone, a pyramid, a polygon and the like are suitably useful. To attach the cap  30  to and detach from a refractory protective pipe  6 , various systems may be chosen in place of the above screwing system. In one such system, a stopper portion is formed in the cap and inserted connectedly in a hole made in the refractory protective pipe.  
     [0163]FIG. 31 shows another example in which a top sealing member  10  is attached as by welding to a top end of an outer heat transfer pipe  4 , and a female screw hole  37  is made in the sealing member  10 . A triangular hole  38  is recessed in a refractory cap  30 , and a support bolt  39  is embedded at its triangular head in the hole  38 . A stem portion of the support bolt  39  is twisted into the female screw hole  37 . In the sealing member  10  and the support bolt  39 , through holes  36 ,  40  are made in straightly joined relation to each other in order to partly introduce an air  8  to be heated so that an surface of the support bolt  39  is protected.  
     [0164] In an example shown in FIG. 32, a female screw hole  41  is made in a top surface portion of a heat transfer pipe  4 , and a stem portion of a support bolt  39  is screwed in the female screw hole  41 . A ring-like refractory material receptor  42  is placed over the support bolt  39 , and a refractory protective pipe  6  is supported by the refractory material recepter  42 . The support bolt  39  has a hole  43  made therein, which hole flows an air  8  to be heated out of the through hole  40 . Other structural details are the same as in FIG. 31. In FIG. 31 and FIG. 32, the refractory protective pipe  6  is extremely firmly held by the support bolt  39 .  
     [0165] In an example shown in FIG. 33, the cap of FIG. 31 is attached to an top end of the heat transfer conduit  9  constructed with the the inner metallic heat transfer pipe  2  and the outer refractory heat transfer pipe  29  as seen in FIG. 13. In an example shown in FIG. 34, the cap of FIG. 32 is attached to an top end of the heat transfer conduit  9  constructed with the the inner metallic heat transfer pipe  2  and the outer refractory heat transfer pipe  29  as seen in FIG. 13.  
     [0166] Embodiment 6  
     [0167] Embodiment 6 of the apparatus for heating high-temperature air according to the present invention is described below with reference to FIG. 35 to FIG. 38. In these figures, like reference numerals denote like parts.  
     [0168] An apparatus  1  for heating high-temperature air shown in FIG. 35 is constructed with a first air heater  45  located upstream of a flow passage  44  of gas of elevated temperature and a second air heater  46  located downstream of that flow passage. More specifically, the first air heater  45  and the second air heater  46  are provided, respectively, with a heat transfer conduit  9  shown for example in FIG. 25. Namely, such heaters are provided with heat transfer pipes  501 ,  502  constituted with outer heat transfer pipes  401 ,  402  covered with a refractory protective pipe  6  and inner heat transfer pipes  201 ,  202  arranged coaxially of the outer heat transfer pipes  401 ,  402 . The inner heat transfer pipe  201  used to constitute the first air heater  45  is connected to a line L 1  of an air to be heated, whereas the inner heat transfer pipe  202  used to constitute the second air heater  46  is connected to a line L 1 ′ of an air to be heated. Moreover, the outer heat transfer pipe  401  of the first air heater  45  and the outer heat transfer pipe  402  of the second air heater  46  are joined by a connoting pipe  47 .  
     [0169] In the apparatus  1  for heating high-temperature air thus constructed, an air  8   g ′ of low temperature supplied from the line L 1 ′ of an air to be heated to the second air heater is heated with a burnt exhaust gas G of elevated temperature while such air is being flowed through the inner heat transfer pipe  202  into the outer heat transfer pipe  402 , and the heated air  8   g ′ to be heated is heated through the connecting pipe  47  in the outer heat transfer pipe  402  of the first air heater  45  so that an air  8   g  of a higher temperature is provided which is utilized as other heat sources from the inner heat transfer pipe  202  and the line L 1  of an air to be heated.  
     [0170]FIG. 36 shows still another example. An air  8   g   1  of high temperature heated in the second air heater  46  is supplied through the connecting pipe  47  to the inner heat transfer pipe  201  and the outer heat transfer pipe  401  of the first air heater  45  and heated therein into an air  8   g  of a higher temperature which is utilized as other heat sources from the line L 1  of an air to be heated.  
     [0171] In each of the above examples, the apparatus  1  for heating high-temperature air is described in which the air  8   g ′ of low temperature to be heated is first supplied to inner heat transfer pipe  202  of the second air heater  46 . The air  8   g ′ may be supplied, where desired, to the outer heat transfer pipe  402  of the second air heater  46 .  
     [0172]FIG. 37 and FIG. 38 show still another examples of the apparatus  1  for heating high-temperature air. In an apparatus  1  for heating high-temperature air shown in FIG. 37, an air  8   g ′ of low temperature to be heated is partly supplied from a bifurcated pipe L′ 1   a  to the outer heat transfer pipe  401  of the first air heater  45  and heated therein, whereas the remainder of such air is supplied from a bifurcated pipe L′ 1   b  to the inner heat transfer pipe  202  of the second air heater  46  and heated therein. An air  8   g  of a higher temperature heated in the first air heater  45  and the second air heater  46  is supplied through the line L 1  of an air to be heated to other facilities.  
     [0173] In an apparatus  1  for heating high-temperature air shown in FIG. 38, an air  8   g ′ of low temperature to be heated is partly supplied from a bifurcated pipe L′ 1   a  to the inner heat transfer pipe  202  of the first air heater  45  and heated therein. An air  8   g  of a higher temperature thus heated is supplied through the line L 1  of an air to be heated to other facilities. Each of these example illustrates that an air  8   g ′ of low temperature to be heated is partly supplied from a bifurcated pipe L′ 1   a  to the outer heat transfer pipe  401  or the inner heat transfer pipe  202  of the first air heater  45  and heated therein, whereas the remainder of such air is supplied from a bifurcated pipe L′ 1   b  to the inner heat transfer pipe  202  of the second air heater  46  and heated therein. The remainder of an air  8   g ′ of low temperature to be supplied in the second air heater  46  may be supplied, where needed, to the outer heat transfer pipe  402 . Thus, the air  8   g ′ to be heated may be selectively supplied to the first air heater  45  and the second air heater  46 . In particular, in the case of supply to the first air heater, the air is supplied to the outer heat transfer pipe  201 . In such instance, an air  8   g ′ of a relatively low temperature to be heated is introduced in a lower end or high-temperature portion so that the temperatures of air, pipe walls and refractories are prevented from rise at that portion. The apparatus for heating high-temperature air can thus be rendered highly durable.  
     [0174] According to the apparatus for heating high-temperature air shown in this embodiment, a given air to be heated is obtained by use of the first air heater and the second air heater as stated hereinabove. In consequence, the length can be small with eventual weight saving of a support structure for use in suspending the heating apparatus. Also advantageously, it is markedly simple for the heating apparatus to be taken out upwardly of a flow passage for a gas of elevated temperature during maintenance. Additionally, the flow area for an air to be heated with respect to the flow area for a gas of elevated temperature is made sufficiently large so that the flow rate can be reduced in obtaining a given air to be heated, and this is effective for decreasing pressure loss.  
     [0175] Next, one embodiment of the apparatus for disposing of wastes is described which is provided with the apparatus for heating high-temperature air according to the present invention. FIG. 39 is a schematic view showing one form of the apparatus for disposing of wastes.  
     [0176] In the apparatus for disposing of wastes of this embodiment, a waste  50   a  such as city waste or the like is crushed for example by a biaxial shearing crusher to provide a grain of 150 mm or below which is charged as by a conveyor into a charge chamber  50 . the waste  50   a  placed in the charge chamber  50  is supplied through a screw feeder to a thermal decomposition reactor  52 . As the thermal decomposition reactor  52 , a horizontal rotary drum is used in this embodiment, and such drum is maintained in low oxygen atmosphere by means of a sealing mechanism not shown.  
     [0177] The waste  50   a  is thermally decomposed in the thermal decomposition reactor  52 , and a heat source is a heated air  8   g  (heat medium) supplied through a heated line L 1  of an air heated by the apparatus  1  for heating high-temperature air which is an heat exchanger located rearwardly of a burning melting furnace  53  to be described later.  
     [0178] By use of the heated air  8   g , the thermal decomposition reactor  52  is maintained at 300-600° C., usually at 450° C. or so.  
     [0179] Further, the waste  50   a  heated with the heated air  8   g  is thermally decomposed into a thermally decomposed gas G 1  and a thermally decoposed residue  54  composed chiefly of nonvolatile components which are transported to a dischager  55  where such gas is separated from such residue. The thermally decomposed gas G 1  separated in the discharger  55  is supplied through a thermally decomposed gas line L 2  to a burner  56  of the burning melting furnace  53 . The thermally decomposed residue  54  taken out of the discharger  55  is relatively high in temperature, say about 450° C., and hence is cooled to about 80° C. by a cooler  57 , followed by supply to a separator  58  which is made up of for example a magnetically selective type, an eddy current type, a centrifugal type or a wind selective type alone or in combination, all of which are in common use. In this separator, the residue is separated into a fine combustible component  58   d  (inclusive of ash) and a crude incombustible component  58   c , and the incombustible component  58   c  is recovered for reuse in a container  59 .  
     [0180] Moreover, the combustible component  58   d  is pulverized for example into 1 mm or below with use of a pulverizer  60 , supplied through a combustible component line L 3  to the burner  56  of the burning melting furnace  53  and burnt in a high temperature region of about 1300° C. together with the thermally decomposed gas G 1  supplied from the thermally decomposed gas line L 2  and an air  61   e  for use combustion supplied from a blower  61 . An ash generated at that time is converted by means of the burning heat to a melt slug  53   f  which deposits on an inner surface of the burning melting furnace  53  and further flows down along the inner surface and drops through a bottom outlet  62  into a water pool  63  in which such slug solidifies by cooling.  
     [0181] The burning melting furnace generally called a dissolution furnace permits the combustible component  58   d  such as carbon or the like to burn at a high temperature of about 1300° C. and to melt the incombustible component containing ash, generating the melt slug  53   f  and a burnt exhaust gas G 2  of elevated temperature. The melt slug  53   f  is dropped into the water pool  63  and then solidified. On the other hand, the burnt exhaust gas G 2  is heat recovered as a gas stream of 2-3 m per second in flow rate and of 1000-1100° C. by the apparatus  1  for heating high-temperature air located downstream of the furnace.  
     [0182] The apparatus  1  for heating high-temperature air in this embodiment is constructed with either one or a suitable combination of the high-temperature air heaters stated above. As seen in FIG. 25, one example is constituted of a pair of heat transfer pipes and a refractory protective pipe  6  provided at a top end with a detachable cap  30 . That is, as mentioned above, even when the cap  30  gets centrally worn or damaged upon contact with a gas flow of elevated temperature, the cap alone can be simply replaced by a new one.  
     [0183] The burnt exhaust gas G 2  having passed partly through the apparatus  1  for heating high-temperature air is heat recovered through a flue gas line L 5  in a waste heat boiler  64  and dust removed in a dust collector  65 . After removal of poisonous components in a exhaust gas cleaner  66 , such gas is discharged as a clean exhaust gas G 3  in the atmosphere by an induction blower  67  and from a chimney  68 . Steam obtained from the waste heat boiler  64  is utilized for electricity generation by means of an electricity generator  69  provided with a steam turbine. Part of the clean exhaust gas G 3  is supplied through a cold gas line L 6  to a cooler  57  with use of a fan  70 .  
     [0184] According to the apparatus for disposing of wastes illustrated in this embodiment, the apparatus for heating high-temperature air is made wholly highly durable so that improved working efficiency is attained as concerns the apparatus for disposing of wastes. Although the present invention has been described in great detail with regard to the embodiments shown in the drawings, the invention should not be considered restrictive to these embodiments. It is to be noted that various changes and modification s may be made without departing from the spirit of the invention.  
     [0185] Embodiment 7  
     [0186]FIG. 40 is a partial sectional view showing embodiment 7 of the present invention.  
     [0187] A passage wall for an exhaust gas G of high temperature arranged to partition a passage for an exhaust gas of high temperature from the external atmosphere is provided with a heat exchanger, and an apparatus  1  for heating an high-temperature air is located coaxially of the heat exchanger and in an exhaust passage surrounded by the heat exhanger. The high-temperature air heating apparatus  1  has a heat transfer conduit  9  constructed with an inner metallic heat transfer pipe  2 , an outer metallic heat transfer pipe  4  sealed at a top portion and disposed as a metallic wall for coaxially covering the inner heat transfer pipe  2  with a gapping  3  defined as an air passage between the inner and outer pipes, and a refractory protective pipe  6  sealed at a top portion and disposed to coaxially cover the heat transfer pipe.  
     [0188] The outer heat transfer pipe  4  communicating on an inner surface with the gapping  3  for use as the air passage is disposed to cooperate with the refractory protective pipe  6  communicating on an outer surface with an exhaust gas passage  44  in forming a partiotion wall  71  soa as to separate the air passage from the exhaust gas passage.  
     [0189] A first gapping  7  is defined between an outer surface of the outer heat transfer pipe  4  and an inner surface of the refractory protective pipe  6 , and the outer heat transfer pipe  4  has a plurality of through holes communicating with the first gapping  7 .  
     [0190] The refractory protective pipe  6  is provided with on an inner surface of a sealed end  6 A of the top portion with ant holes  6   a ,  6   b , while the outer heat transfer pipe  4  is provided on an outer surface of a sealed end  4 A of the top portion with ant-shaped protrusions  4   a ,  4   b  disposed to be interengageable with the ant holes  6   a ,  6   b , respectively. By interengagement of the ant holes  6   a ,  6   b  with the protrusions  4   a ,  4   b , the outer portion of the refractory protective pipe  6  is positioned with respect to the outer heat transfer pipe  4 .  
     [0191] A plurality of anchors  72  are attached by welding to the outer surface of the outer heat transfer pipe  4 , which anchors act to support the refractory pipe  6 , so that the first narrow gapping  7  defined between the outer heat transfer pipe  4  and the refractory pipe  6  is rendered substantially uniform over its entire length. Even with the first gapping  7  provided, the refractory pipe  6  of great mass is held in securely supported relation to the outer heat transfer pipe  4  by means of the anchors  72 . A second gapping  73  is further defined between the anchord  72  and the refractory pipe  6  and made to communicate with the first gapping  7 .  
     [0192] Next, the structure of a heat exchanger  100  is described with reference to FIG. 40, which heat exchanger is arranged on a wall of the exhaust gas passage surrounding the high-temperature air heating apparatus  1 . The heat exchanger  100  is attached to a furnace wall of a burning melting furnace at its exhaust gas outlet. In the heat exchanger  100 , a partition wall  101  is located to separate an exhaust gas of high temperature and low pressure (for example, a gas inlet temperature T=about 800 to 1500° C. and a gas inlet pressure P 1 =about −100 to 4900 Pa) containing corrosive components such as hydrogen chloride and the like and dusts from an air passage  102  defined to flow an air  105  of a lower temperature and a higher pressure than those of the burnt exhaust gas G (for example, of an air inlet temperature T 3 =about 300° C. and of an air inlet passage P 3 =about +1000 to 10000 Pa). In that way, the heat of the burnt exhaust gas G is transmitted to the air  105 .  
     [0193] A burnt exhaust gas G of a pressure P 2  cooled to a temperature T 2  (for example, to about 500 to about 1300° C.) by means of the heat exchanger is further subjected to heat recovery as by a waste heat boiler and then transported to an exhaust gas treating stage in which a suction blower has been installed. At this exhaust gas treating stage, the burnt exhaust gas G is treated to collect dusts, to remove poisonous materials and to avoid fumes, followed by escaping of the treated gas through a chimney in the atmosphere.  
     [0194] The heat exchanger  100  is further described in greater detail.  
     [0195]FIG. 41 is a longitudinal sectional view showing the above heat exchanger, and FIG. 42 is a horizontal sectional view taken along the line IVI-IVI of FIG. 41. As shown in FIG. 41, the exhaust gas passage  44  of a sectinally rectangular shape is widely provide at a central portion of the heat exchanger  100  of a sectionally rectangular shape on the whole, and the air passage  102  is partitioned by the partition wall  101  and located in a sectionally angular rectangular shape and around the exhaust gas passage  44 .  
     [0196] The partition wall  101  has a plurality of through holes  103  made at predetermined regions (see FIG. 40, or FIG. 43 and FIG. 44 to be described later). Additionally, this partition wall has a metallic plate  106  disposed on one side (i.e., on an outer peripheral surface  104 ) for use as a metallic wall of good thermal conductivity to be contacted with an air  105  and also a porous refractory ceramic layer  109  disposed for use as a refractory wall to be contacted on a surface with the burnt exhaust gas on the other side (i.e., on an inner peripheral surface  107 ) of the whole metallic plate  106  with a first gapping  108  (see FIG. 40, or FIG. 43 and FIG. 44 to be described to be later) defined between the metallic plate and the ceramic layer.  
     [0197] As the ceramic layer  109 , it is desired that a castable refractory material for example of silicon carbide (SiC) of high thermal conductivity and high heat resistance be coated or sprayed entirely of the inner peripheral surface  107  of the metallic plate  106  and in a thickness of about 10 to about 50 mm. An alumina-rich refractory and a chromia refractory material may also be used for the ceramic layer  109 .  
     [0198] The ceramic layer  109  has contained therein a multiplicity of air spaces (i.e., voids) which permit a gas to pass through such layer. Because the ceramic layer  109  is disposed over the inner peripheral surface  107  of the metallic plate  106 , a burnt exhaust gas G of high temperature containing corrosive components is not brought into direct contact with the metallic plate  106  so that such plate is prevented against a large degree of corrosion.  
     [0199] The air passage  102  is provided between the metallic plate  106  and an outer wall plate  106  outwardly disposed with a given gap left relative to the metallic plate  106 .  
     [0200] A lower end portion  111  of the air passage  102  is so made as to communicate with a lower air chamber  112  arranged to equalize the pressure of the air  105  having been supplied thereto and to flow such air uniformly fully in the air passage  102 . An upper end portion  113  of the air passage  102  is made to communicate with an upper air chamber  115  arranged to equalize the pressure of a heat exchange-derived high-temperature air  114  and to discharge such air uniformly fully from the air passage  102 .  
     [0201] Subsequently, the structure of the passage wall for the heat exchanger  100  is described with reference to FIG. 43 to FIG. 45. FIG. 43 is a sectional view, partly enlarged, of the heat exchanger  100 , and FIG. 44 is a horizontal sectional view taken along the line IVIV-IVIV of FIG. 43. FIG. 45 is a front elevational view showing part of a surface portion of the metallic plate of FIG. 43.  
     [0202] As shown in FIG. 43 to FIG. 45, the metallic plate  106  contacted with the passage  102  for the air  105  has a plurality of through holes  103  made at given regions, and the ceramic layer  109  disposed on one surface (a front side  116 ) in contact with the passage  44  for the burnt exhaust gas G is arranged on the inner peripheral surface  107  of the metallic plate  106 .  
     [0203] In use of the heat exchanger  100 , the first gapping  108  of a given size (preferably of 1 to 3 mm) is present between the full inner peripheral surface  107  of the metallic plate  106  and the other full surface (back side  117 ) of the ceramic layer  109 , and the gapping  108  is in communication with the through holes  103 . The metallic plate  106  provided therein with the through holes  103  is of a plate-like shape noted above, but may be of a plate or the like having a network structure so long as the latter plate is provided therein with openings like the through holes.  
     [0204] The anchors  118  in a plural number are secured in place to the inner peripheral surface  107  of the metallic plate  106 , which anchors serve as support members to support the ceramic layer  109  when in defining the first gapping  108 . The partition wall-constituting anchors  118  are formed of iron and in V-shaped rod-like arrangement, and are fixed at their bottom portions to the metallic plate  106  by means of welding and embedded at their body portions in the ceramic layer  109 . Thus, such anchors firmly hold the ceramic layer  109  in place.  
     [0205] In the case of use of the heat exchanger  100 , the second gapping  119  of a given size (preferably of 1 to 3 mm) is present between the whole surface of each of the anchors  118  and the ceramic layer  109  and is in communication with the first gapping  108 . The second gapping  119  may in some instances be omitted.  
     [0206] In order to define the first and second gappings  108 ,  119 , an interlaminar material is firstly disposed by winding vinyl resin such as vinyl sheet, vinyl tape or vinyl hose, or paper tape, or by coating tar or paint.  
     [0207] More specifically, prior to formation of the ceramic layer  109 , the inner peripheral surface  107  of the metallic plate  106  is wholly covered with polyvinyl chloride sheet, or is wholly coated with aqueous paint.  
     [0208] Meanwhile, before or after being welded to the metallic plate  106 , each of the anchors  118  is wound with insulating tape formed of polyvinyl chloride, covered with commercially available vinyl hose to be used for tap water and cut short, or coated with aqueous paint. Alternatively, the anchor  118  may be immersed in the stock liquid of the aqueous paint.  
     [0209] Subsequently, a water-containing silicon carbide castable material (or alumina-rich or chromia castable material) is coated or sprayed on a whole surface of the above vinyl sheet or the like (i.e., interlaminar material) disposed over the metallic plate  106 , followed by drying and calcination of the castable material upon heating up to for example about 500 to about 600° C., whereby the ceramic layer  109  is obtained.  
     [0210] During that heating, the vinyl sheet or the like mentioned above is melted and vaporrized at from about 150° C. or above to about 200° C. or above and thus is finally removed.  
     [0211] It is noted that the anchor  118  has a larger thermal expansion coefficient than the ceramic layer  109 . In such case, the gapping  119  may be defined in advance at room temperature (for example, at 20° C.) between the anchor  118  and the ceramic layer  109  so that even if the anchor  118  gets expanded more greatly than the ceramic layer  109  upon exposure of the heat exchanger  100  to a high temperature when in use, the gapping  119  can absorb the difference in thermal expansion coefficient.  
     [0212] Consequently, the finished structure is free of stresses which would be apt to arise from the difference in thermal expansion coefficient while in heating and cooling of that structure. The ceramic layer  109  can thus be prevented against cracking or breakage.  
     [0213] In addition to the above attention drawn to the difference in thermal expansion coefficient, it is desired that the second gapping  119  be previously set to have a larger size when being defined at room temperature such that this gapping provides a desired size during use of the heat exchanger.  
     [0214] In that case, even when the heat exchanger  100  is operated with heating at a high temperature, the difference in thermal expansion coefficient can be absorbed, and the second gapping  119  is rendered always present between the whole surface of the anchor  118  and the ceramic layer  109 . The second gapping  119  and the first gapping  108 , therefore, are always in communication with each other.  
     [0215] When the air  105  flowing through the air passage  102  is compared to the burnt exhaust gas G flowing through the exhaust gas passage  44 , both passages being separated by the partition passage  100 , the air  105  has a higher pressure than the burnt exhaust gas G.  
     [0216] Thus, the high-pressure air  105  flowing in the air passage  102  intrudes into the ceramic layer  109 , while utilizing the pressure difference as an impulsion, through both the through holes  103  and the first gapping  108 . In the case where the second gapping  119  located around the anchor  118  and then to intrude into the ceramic layer  109 .  
     [0217] The air  105  is then flowed through the cavities of the ceramic layer  109  toward the exhaust gas passage  44  as arrowed at  120 , and upon arrival at the surface  116  of the ceramic layer  109 , is flowed into the exhaust gas paasage  44  and mixed with the burnt exhaust gas G.  
     [0218] In this embodiment, the ceramic layer  109  of great mass disposed with respect to the metallic plate  106  and with the first gapping  108  provided between such layer and such plate is securely held in place by the anchors  118  in a plural number. The ceramic layer  109  is thus supported with great dirmness and sufficient stability so that the gapping  108  of a small size (for example, of 1 to 3 mm) can always be retained with uniformity.  
     [0219] Moreover, since an air stream is directed to the exhaust gas passage  44  in the whole ceramic layer  109 , the burnt echaust gas G is pushed back even when such gas tends to intrude into the ceramic layer  109  amd to flow toward the metallic plate  106  and the anchors  118 .  
     [0220] For that reason, the burnt exhaust gas G does not almost intrude into the ceramic layer  109 , nor does it contact the metallic plate  106  and the anchors  118 . Hence, the metallic plate  106  and the anchors  118  are protected from corrosion in the influence of those corrosive components contained in the burnt exhaust gas G. This imparts markedly prolonged service lif to each of the members  106 ,  118 .  
     [0221] For failure of the burnt exhaust gas G to enter the ceramic layer  109  in this embodiment, the surface  116  of such layer is made free of deposition of the dusts contained in the burnt exhaust gas G so that the surface  116  is maintained necessarily clean. Thus, no corrosion arising from dust deposition occurs in the metallic plate  106 , avoiding reduced efficiency of heat transfer. To be more specific, the service life of the heat exchanger  100  is greatly improved in this embodiment because the metallic plate  106  and the anchors  118  are prolonged in relation to service life.  
     [0222] Besides and owing to the provision of the first gapping  108 , those portions which are devoid of air flow in the ceramic layer  109  are not present between and among adjacent through holes  103 . Additionally, even in the case of irregular voids in the ceramic layer  109 , it does not occur that the burnt exhaust gas G reversely flows and eventually contacts the metallic plate  106 .  
     [0223] Therefore, it is made possible to set pitches e, f of each through hole  103  in terms of the diameter d (hole diameter) to be larger than in the heat exchanger od the prior art(Japanese Utility Model Laid-Open No. 6-40668), thereby decreasing the number of through holes  103  to be made. This results in saved boring of the through holes  103  and hence simplified production of the heat exchanger  100 .  
     [0224] In FIG. 46, there are shown the experimental results obtained with the heat exchanger of this embodiment. As seen in that figure, a plurality of through holes  202  are provided in a metallic plate  201 , and a gapping  204  of a given size (for example, h=2 to 3 mm) is defined between a refractory material wall  203  (for example, castable refractory material such as silicon carbide) and the metallic plate  201 , the gapping  204  being in communication with the through holes  202 .  
     [0225] Thus, when an air  206  is supplied in an air chamber  205  located backward of the metallic plate  201 , the air  205  having passed via the through holes  202  gets substantially uniformly pressurized in the gapping  204  serving as a pressure chamber, consequently flowing upwardly in the refractory material wall  203 . This has been confirmed by those bubbles of aqueous soap coated over one surface of the refractory material wall  203  and generated uniformly throughout the such wall surface.  
     [0226]FIG. 47 and FIG. 48 show still another form of the heat exchanger  100  according to the present invention. FIG. 47 is a horizontal sectional view similar to FIG. 42, and FIG. 48 is a sectional view in partial enlargement of FIG. 47. A heat exchanger  100  of this form is substantially identical in its longitudinal section to the structure of FIG. 41.  
     [0227] The above heat exchanger  100 , like the form seen in FIG. 42, is such wherein a partition wall  101  is provided to separate an exhaust gas passage  44  in which to flow burnt exhaust gases of high temperature and of low temperature containing corrosive components and dusts from an air passage  102  in which to flow airs  105  of lower temperature and of higher temperature than the burnt exhaust gases so that the heat of such gases is transmitted to the airs  105 .  
     [0228] The partition wall  101  has a plurality of through holes  103  made at given regions thereof, metallic pipes  106  each provided on one surface (inner surface  104 ) with a metallic wall for contact with the air  105 , a porous ceramic layer  109  located opposite to the other surface (outer surface  107 ) of the metallic pipe  106  and provided on one surface (front surface  116 ) with a refractory material wall for contact with a burnt exhaust gas G, and a plurality of anchors  118  disposed as support members to support the ceramic layer  109 .  
     [0229] When in use of the heat exchanger  100 , a first gapping  108  is defined between the whole outer surface  107  of the metallic pipe  106  and the other whole surface (back surface  117 ) of the ceramic layer  109 , the first gapping  108  being made to communicate with the through holes  103 .  
     [0230] As shown in FIG. 47, the heat exchanger  100  is formed to be generally rectangular in its entire section like that viewed in FIG. 47, and an exhaust gas passage  44  is thus provided widely centrally of the heat exchanger  100 .  
     [0231] The metallic pipes  106  in a plural number for use as metallic walls serve in their respective insides as air passages  102  and are arranged vertically of and around the exhaust gas passage  44  of the heat exchanger  100 . The metallic pipes  106  are secured respectively to a connecting plate  121 .  
     [0232] The metallic pipes  106  have through holes  103  bored at given portions and in a desired number. For instance, all o the metallic pipes  106  may be provided with a plurality of through holes  103 , but a metallic pipe  106  with through holes  103  and a metallic pipe  106  without through holes  103  can be alternately placed as shown in FIG. 48. This leads to reduced number of metallic pipes  106  requiring provision of the through holes  103 , resulting in saved boring of the through holes  103 .  
     [0233] The first gapping  108  is present between the ceramic layer  109  and the metallic pipes  106  and between the ceramic layer  109  and the connecting plate  121 , which gapping is in communication with the through holes  103 .  
     [0234] The ceramic layer  109  is of the same material as in the foregoing embodiment (FIG. 41). The ceramic layer  109  is held along the exhaust gas passage  44  by means of the anchors  118  in a plural number fixed as the support members at given locations of either one or both of each metallic pipe  106  and the connecting plate  121 . Each such anchors  118  is usually in an iron-made plate-like shape, but may be in a V-shaped rod-like shape.  
     [0235] In this embodiment, each anchor  118  is welded at its base portion to the outer surface  107  of the metallic pipe  106  and is embedded at its body portion in the ceramic layer  109 . Thus, the ceramic layer  109  is firmly held with respect to the metallic pipes  106 , and the first gapping  108  is always maintained at a given size (for example, of 1 to 3 mm). In use of the heat exchanger  100 , a second gapping  119  of a given size (For example of 1 to 3 mm) is also present between the whole surface of each anchor  118  and the ceramic layer  109 , this second gapping being in communication with the first gapping  108 .  
     [0236] The first and second gappings  108 ,  119  in this embodiment are formed in the same manner as the first and second gappings  108 ,  119  shown in the preceding embodiment of FIG. 41.  
     [0237] Since the second gapping  119  is provided with the heat exchanger  100  placed in heated condition, the difference in thermal expansion coefficient between the anchors  118  and the ceramic layer  109  can be absorbed as stated above even when this heat exchanger is exposed to a high temperature while being used. Further, a gap is always present between the whole surface of each anchor  118  and the ceramic layer  109  so that the second gapping  119  is in continuous communication with the first gapping  108 .  
     [0238] An air  105  in the air passage  102  passes via the through holes  103  and the first gapping  108  by utilizing the pressure difference as an impulsion, thus intruding into the ceramic layer  109 . Part of the air  105  flows from the first gapping  108  to the second gapping  119  running around the anchors  118  and then intrudes into the ceramic layer  109 . The air  105  continues to pass through the voids interspersed in the ceramic layer  109  in a direction arrowed at  122  and toward the exhaust gas passage  44  with eventual entry in the exhaust gas passage  44 .  
     [0239] As stated above, the ceramic layer  109  retains an air tending to flow toward the exhaust gas passage  44 . Hence, a burnt exhaust gas  122  is pushed back by such air flow as arrowed at  122  even if the gas is forced to intrude into the ceramic layer  109  and to flow toward the metallic pipes  106  and the connecting plate  121 .  
     [0240] Accordingly, the burnt exhaust gas does not almost intrude into the ceramic layer  109 , nor does it contact the metallic pipes  106 , the connecting plate  121  and the anchors  118 . This permits the metallic pipes  106 , the connecting plate  121  and the anchors  118  to be protected against corrosion resulting from those corrosive components contained in the burn exhaust gas, thereby prolonging the service lives of the members  106 ,  121 ,  118  to a great extent.  
     [0241] The same advantages as those obtained in connection with the embodiment of FIG. 41 can be made feasible because the first and second gappings  108 ,  119  are provided, and the ceramic layer  109  is firmly supported by the anchors  118 .  
     [0242] Heretofore, anchors  118  have got seriously corroded upon contact with a burnt exhaust gas having intruded into a ceramic layer  109 . These anchors have thus been covered with a castable material for purposes of anticorrosion.  
     [0243] In this embodiment, in contrast to the prior art practice, part of the air flows from the second gapping  119  through the ceramic layer  109  toward the exhaust gas passage  44 . The burnt exhaust gas can therefore be prevented from intrusion into the ceramic layer  109  and subsequent contact with the anchors  118 . This dispenses with the above castable material for use in gaining anticorrosion, making the resultant heat exchanger strructurally simple and easy to produce the same.  
     [0244] In the partition wall constructed above, a plurality of support members are fixed to the metallic walls to thereby hold the refractory material wall with respect to each such metallic wall. Thus, a minute gap can be always uniformly maintained between the metalli wall and the refractory material wall.  
     [0245] In addition, even in the case of the provision of such gapping between the metallic wall and the refractory material wall, such refractory wall of great mass can be firmly supported relative to the metallic wall. This makes it possible to locate the heat exchanger not only vertically but also laterally and slantly, imposing no restriction on positioning of the heat exchanger.  
     [0246] Furthermore, a multiplicity of anchors (support members) formed of iron and having a high thermal conductivity are secured to the metallic plate and the like so that, upon heating of the anchors by a burnt exhaust gas, the resulting heat is transmitted to the metallic plate and the like. The finished heat exchanger is thus improved in respect of the efficiency of heat transfer.  
     [0247] Each of the preceding embodiments is shown such that an combustion air in a burning melting furnace is burnt by means of a heat exchanger. This air is not particularly restrictive for burning by the heat exchanger, but an air for use in a thermal decomposition drum (not shown) and other airs may be acceptable.  
     [0248] Although the first and second gappings are used in each such embodiment, the first gapping alone may be accepted with the second gapping omitted.  
     [0249] The heat exchanger may also be formed to be circular, polygonal, ellipse or the like as seen entirely sectionally, in addition to a rectangular shape illustrated in each of the preceding embodiments. In the relevant figures, like or similar parts are designated by like referece numerals.