Heat exchanger and burner

Abstract

Provided is a heat exchanger that comprises a honeycomb structure 100 including an outer peripheral wall 10, a first intermediate wall 20, a second intermediate wall 30, a first partition wall 40, a second partition wall 50, and a third partition wall 60. The first intermediate wall 20 and the second intermediate wall 30 include a portion that is disposed at the inner side of the outer peripheral wall 10. The first partition wall 40 is disposed at the inner side of the first intermediate wall 20 so as to form a plurality of separate cells 70a which each serve as a flow path of a first fluid. The second partition wall 50 is disposed between the first intermediate wall 20 and the second intermediate wall 30 so as to form a plurality of separate cells 70b which each serve as a flow path of a second fluid. The third partition wall 60 is disposed between the second intermediate wall 30 and the outer peripheral wall 10 so as to form a plurality of separate cells 70c which each serve as a flow path of a third fluid. The flow paths (cells 70a) of the first fluid, the flow paths (cells 70b) of the second fluid, and the flow paths (cells 70c) of the third fluid are coaxially positioned.

Description

Heat exchangers and burners

[0001] The present invention relates to a heat exchanger and a burner.

[0002] Heat exchangers that use heat sources such as exhaust gas to preheat combustion air or steam are being introduced into various products. Devices equipped with such heat exchangers can reduce energy consumption by reusing waste heat energy.

[0003] For example, burners (known as "recuperator burners" or "radiant tube burners") are known and are used as heating sources for industrial furnaces and the like, recovering exhaust heat by exchanging heat between combustion air and exhaust gas (see Patent Documents 1 and 2). These burners have a heat exchanger located outside the flow path through which fuel gas flows, for recovering heat from the exhaust gas and preheating the combustion air. The heat exchanger used in the burner exchanges heat between gases. Because the heat transfer coefficient between gases is lower than that between liquids and gases, it is necessary to increase the surface area by providing fins or the like in the flow paths of each gas.

[0004] However, increasing the surface area by providing fins or the like in the flow paths of each gas results in an increase in the size of the heat exchanger. Furthermore, the fins provided in the flow paths of heat exchangers used in conventional burners are often made of heat-resistant metals such as stainless steel, but their heat resistance is not sufficient. In particular, to improve the energy efficiency of the burner, it is effective to increase the temperature of the exhaust gas flowing into the heat exchanger to raise the temperature of the combustion air. However, due to the heat resistance of the heat-resistant metal, the exhaust gas temperature must be limited to 1000°C or less. Therefore, conventional burners have only been applicable to industrial furnaces used in relatively low furnace temperatures of 1000°C or less.

[0005] On the other hand, a ceramic structure having a predetermined flow path structure has been proposed as a heat exchanger element effective for heat exchange between gases (Patent Document 3). However, although the heat exchanger element of Patent Document 3 has good heat resistance because it is mainly composed of ceramics, it does not have a structure suitable for use in a burner because it is mainly used in the exhaust systems of automobiles.

[0006] Japanese Patent Laid-Open No. 7-208708 Japanese Patent Laid-Open No. 2016-142443 Japanese Patent Laid-Open No. 2015-42934

[0007] The present invention has been made to solve the above-mentioned problems, and aims to provide a heat exchanger that has excellent heat resistance and heat exchange efficiency and can be used in a burner. Another aim of the present invention is to provide a burner that is highly energy efficient and can be used in industrial furnaces used in temperatures exceeding 1000°C.

[0008] As a result of extensive research into honeycomb structures containing ceramics as a main component, the present inventors have found that the above-mentioned problems can be solved by providing an outer peripheral wall, a first intermediate wall, a second intermediate wall, a first partition wall, a second partition wall, and a third partition wall so that three flow paths are positioned coaxially, and have thus completed the present invention. That is, the present invention is exemplified as follows.

[0009] <1> A heat exchanger comprising a honeycomb structure mainly composed of ceramics, the honeycomb structure having: an outer peripheral wall; first intermediate walls and second intermediate walls including portions disposed inside the outer peripheral wall; first partition walls disposed inside the first intermediate wall and defining a plurality of cells that become a first flow path; second partition walls disposed between the first intermediate wall and the second intermediate wall and defining a plurality of cells that become a second flow path; and third partition walls disposed between the second intermediate wall and the outer peripheral wall and defining a plurality of cells that become a third flow path, the honeycomb structure being configured so that the first flow path, the second flow path, and the third flow path are positioned coaxially.

[0010] <2> The heat exchanger according to <1>, wherein the first flow path is a flow path for a first fluid, the second flow path is a flow path for a second fluid, and the third flow path is a flow path for a third fluid, and heat exchange is possible between the second fluid and the third fluid.

[0011] <3> The heat exchanger according to <1>, wherein the first flow path and the second flow path are flow paths for a first fluid, and the third flow path is a flow path for a third fluid, and heat exchange is possible between the first fluid and the third fluid.

[0012] <4> The heat exchanger according to any one of <1> to <3>, wherein both end portions of the outer peripheral wall are located more inward than both end portions of the first intermediate wall and the second intermediate wall in the axial direction of the honeycomb structure.

[0013] <5> The heat exchanger according to any one of <1> to <4>, wherein, in a cross section perpendicular to a direction in which the cells extend, the second partition walls and the third partition walls have circumferential partition walls extending in a circumferential direction and radial partition walls extending in a radial direction.

[0014] <6> The heat exchanger according to any one of <1> to <5>, further comprising an outer tubular member fitted to at least a portion of the outer peripheral wall, the outer tubular member having an inlet and an outlet for a fluid.

[0015] <7> The heat exchanger according to any one of <1> to <6>, wherein the first intermediate wall is an inner circumferential wall, and the inside of the inner circumferential wall is a hollow region that does not have the first partition wall.

[0016] <8> The heat exchanger according to <7>, further comprising an inner cylindrical member fitted to at least a portion of the inner circumferential wall, the inner cylindrical member having an inlet and an outlet for a fluid.

[0017] <9> The heat exchanger according to <2>, wherein the flow direction of the first fluid and the second fluid is opposite to the flow direction of the third fluid.

[0018] <10> The heat exchanger according to <3>, wherein a flow direction of the first fluid circulating through the first flow path is opposite to a flow direction of the first fluid circulating through the second flow path.

[0019] <11> The heat exchanger according to <10>, wherein a flow direction of the first fluid flowing through the second flow path is opposite to a flow direction of the third fluid flowing through the third flow path.

[0020] <12> A heat exchanger described in <11>, further comprising a folding member on one end face of the honeycomb structure perpendicular to the direction in which the cells extend, for supplying the first fluid flowing through the second flow path to the first flow path.

[0021] <13> The heat exchanger according to any one of <1> to <12>, wherein the ceramic is silicon carbide.

[0022] <14> A burner that mixes and burns fuel gas and air, comprising the heat exchanger according to <2>, wherein the first fluid is the fuel gas, the second fluid is the air, and the third fluid is a combustion exhaust gas of the fuel gas and the air.

[0023] <15> A burner that mixes and burns fuel gas and air, comprising the heat exchanger according to <3>, wherein the first fluid is the air, the third fluid is a combustion exhaust gas of the fuel gas and the air, and the heat exchanger is used to preheat the air.

[0024] According to the present invention, a heat exchanger having excellent heat resistance and heat exchange efficiency and usable for a burner can be provided. Furthermore, according to the present invention, a burner having high energy efficiency can be provided that can be applied to industrial furnaces used in a temperature range exceeding 1000°C.

[0025] 5a , 5b, 5c, 5d, 5e, 5f, 5g, 5g, 5h, 5h, 5h, 5h, 5b, 5c, 5d, 5e, 5f, 5g ...f, 5g, 5h, 5b, 5c, 5d, 5f, 5f, 5g, 5h, 5b, 5c, 5d, 5f, 5f, 5f, 5f, 5f, 5f, 5f, 5f, 5f, 5f, 5f, 5f, 5f, 5f, 5f, 5f, 5f, 5f, 5f, 5f, 5f, 5f, 5f, 5f, 5f, 5f, 5 FIG. 10 is a cross-sectional view of another heat exchanger according to the third embodiment of the present invention, taken along a line parallel to the extending direction of the cells of the honeycomb structure.

[0026] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. The present invention is not limited to the following embodiments, and it should be understood that modifications and improvements made to the following embodiments based on the ordinary knowledge of those skilled in the art without departing from the spirit of the present invention are also within the scope of the present invention.

[0027] <Embodiment 1> (1) Heat Exchanger A heat exchanger according to embodiment 1 of the present invention includes a honeycomb structure mainly composed of ceramics. By using a honeycomb structure mainly composed of ceramics, heat resistance can be improved. Here, in this specification, "mainly composed of ceramics" means that the proportion of ceramics in all components is 50 mass% or more.

[0028] FIG. 1a is a cross-sectional view of a heat exchanger according to a first embodiment of the present invention, taken along the line a-a' in FIG. 1a (a cross-sectional view of the heat exchanger perpendicular to the cell extension direction of the honeycomb structure). As shown in FIGS. 1a and 1b, the heat exchanger according to the first embodiment of the present invention includes a honeycomb structure 100 having an outer peripheral wall 10, first intermediate walls 20, second intermediate walls 30, first partition walls 40, second partition walls 50, and third partition walls 60. The first intermediate walls 20 and the second intermediate walls 30 include portions disposed inside the outer peripheral wall 10. The first partition walls 40 are disposed inside the first intermediate walls 20 and define a plurality of cells 70a that form first flow paths. The second partition walls 50 are disposed between the first intermediate walls 20 and the second intermediate walls 30 and define a plurality of cells 70b that form second flow paths. The third partition wall 60 is disposed between the second intermediate wall 30 and the outer peripheral wall 10 and defines a plurality of cells 70c that form the third flow paths. The first flow path (cell 70a), the second flow path (cell 70b), and the third flow path (cell 70c) are coaxially positioned. In this heat exchanger, the first flow path is a flow path for the first fluid, the second flow path is a flow path for the second fluid, and the third flow path is a flow path for the third fluid. By providing a honeycomb structure 100 with such a structure, heat exchange between the second fluid and the third fluid can be achieved, and the heat exchange efficiency can be improved, making it suitable for use in a burner.

[0029] Since the first flow path, the second flow path, and the third flow path are positioned coaxially, the outer peripheral wall 10, the first intermediate wall 20, and the second intermediate wall 30 that form these flow paths are also positioned coaxially. Therefore, the first intermediate wall 20 and the second intermediate wall 30 extend in the circumferential direction like the outer peripheral wall 10 in a cross section perpendicular to the extension direction of the cells 70 a, 70 b, and 70 c.

[0030] Since the peripheral wall 10 is the outer surface of the honeycomb structure 100, it is preferable that the thickness of the peripheral wall 10 be greater than that of the partition walls (first partition walls 40, second partition walls 50, and third partition walls 60) constituting the honeycomb structure 100, from the viewpoint of improving resistance to external impact. Specifically, the thickness of the peripheral wall 10 is preferably 1.2 to 15 times, and more preferably 1.5 to 10 times, the thickness of the partition walls. By controlling the thickness of the peripheral wall 10 to such a value, it is possible to improve resistance to external impact, etc. The thickness of the peripheral wall 10 is not particularly limited, but is preferably 0.1 to 10 mm, and more preferably 0.5 to 3 mm.

[0031] In the axial direction X of the honeycomb structure 100, both end portions (end portions 11, 12) of the outer peripheral wall 10 are preferably located more inward than both end portions (end portions 21, 22 of the first intermediate wall 20 and end portions 31, 32 of the second intermediate wall 30) of the first intermediate wall 20 and the second intermediate wall 30. By locating both end portions of the outer peripheral wall 10 in such positions, it becomes easier to provide an inlet and an outlet for the third fluid flowing between the outer peripheral wall 10 and the second intermediate wall 30, avoiding the flows of the first fluid and the second fluid.

[0032] The distance L1 between each end of the outer peripheral wall 10 and each end of the first intermediate wall 20 and the second intermediate wall 30 may be adjusted appropriately depending on the overall size of the honeycomb structure 100, but is preferably 2 to 150 mm, more preferably 5 to 50 mm. By controlling the distance L1 in this manner, it becomes easier to stably ensure the above-mentioned effects.

[0033] 2, a constricted portion 80 may be formed by partially not providing the outer peripheral wall 10 and the third partition wall 60 in the axial direction X of the honeycomb structure 100. Even when the constricted portion 80 is formed, it becomes easier to provide an inlet and an outlet for the third fluid flowing between the outer peripheral wall 10 and the second intermediate wall 30 while avoiding the flows of the first fluid and the second fluid. Note that FIG. 2 is a cross-sectional view of the heat exchanger parallel to the extension direction of the cells 70a, 70b, and 70c of the honeycomb structure 100.

[0034] The position of the constricted portion 80 may be adjusted appropriately depending on the overall size of the honeycomb structure 100, but the distance L2 from the ends 11, 12 of the outer peripheral wall 10 to the constricted portion 80 is preferably 2 to 100 mm, more preferably 5 to 50 mm. The length L3 of the constricted portion 80 is preferably 3 to 100 mm, more preferably 5 to 50 mm.

[0035] The first intermediate wall 20 is a wall that exists between the first flow path and the second flow path. The second intermediate wall 30 is a wall that exists between the second flow path and the third flow path. Therefore, it is preferable that the first intermediate wall 20 has a thickness that prevents the fluids flowing through the first flow path and the second flow path from mixing, and the second intermediate wall 30 has a thickness that prevents the fluids flowing through the second flow path and the third flow path from mixing. Specifically, the thickness of the first intermediate wall 20 and the second intermediate wall 30 is preferably greater than the thickness of the partition walls (first partition wall 40, second partition wall 50, third partition wall 60) that constitute the honeycomb structure 100, more preferably 1.2 to 15 times, and even more preferably 1.5 to 10 times, the thickness of the partition walls. By controlling the thickness of the first intermediate wall 20 and the second intermediate wall 30 to such values, it is possible to increase the pressure resistance and suppress the mixing of the fluids. The thickness of the first intermediate wall 20 and the second intermediate wall 30 is not particularly limited, but is preferably 0.1 to 10 mm, and more preferably 1 to 5 mm.

[0036] The second partition wall 50 and the third partition wall 60 have circumferential partition walls 51, 61 extending in the circumferential direction and radial partition walls 52, 62 extending in the radial direction in a cross section perpendicular to the extension direction of the cells 70 a, 70 b, 70 c. By providing the circumferential partition walls 51, 61 and the radial partition walls 52, 62, thermal conductivity in the radial direction is improved, and therefore the heat exchange efficiency between the fluids flowing through the second flow path and the third flow path can be increased.

[0037] The thickness of the partition walls (first partition wall 40, second partition wall 50, and third partition wall 60) is not particularly limited, but is preferably 0.1 to 1 mm, more preferably 0.2 to 0.5 mm. By controlling the thickness of the partition walls within this range, it is possible to increase the mechanical strength and heat exchange efficiency while suppressing the pressure loss of each fluid.

[0038] In a cross section perpendicular to the direction in which the cells 70a, 70b, and 70c extend, the ratio of the cross-sectional area of ​​the second flow path to the cross-sectional area of ​​the third flow path is preferably 1:10 to 10:1, and more preferably 1:2 to 2:1. By controlling the cross-sectional areas of the flow paths within this range, it is possible to increase the efficiency of heat exchange between the fluids flowing through the second flow path and the third flow path.

[0039] The cell density of each flow path (i.e., the number of cells per unit cross-sectional area of ​​each flow path) is not particularly limited, and may be set appropriately depending on the thickness of each partition wall, etc., from the viewpoint of the structural strength of the honeycomb structure 100. The total number of cells in the honeycomb structure 100 is not particularly limited, but is preferably 16 to 10,000, and more preferably 50 to 2,000.

[0040] The cross section perpendicular to the axial direction X (the direction in which the cells 70a, 70b, and 70c extend) of the honeycomb structure 100 is not limited to a circular shape as shown in Fig. 1b, but may be an elliptical shape, an oval shape formed by combining circular arcs, a quadrangle, or any other polygonal or prismatic shape. When this cross section is circular, its diameter is not particularly limited, but is preferably 300 mm or less, more preferably 200 mm or less.

[0041] The shape of each cell (cells 70a, 70b, 70c) can be various shapes such as a circle, an ellipse, a triangle, a rectangle, a hexagon, or other polygons in a cross section perpendicular to the direction in which each cell extends. Furthermore, the shapes of the cells of each flow path may be the same or different.

[0042] The honeycomb structure 100 preferably has a thermal conductivity of 100 W / (m·K) or more, more preferably 120 to 300 W / (m·K), and even more preferably 150 to 300 W / (m·K). By setting the thermal conductivity within this range, the thermal conductivity is improved, and the heat exchange efficiency between the fluids flowing through the second flow path and the third flow path can be increased. Here, the thermal conductivity is measured by calculating the value at room temperature using the thermal diffusivity measured by the optical alternating current method, the specific heat measured by the DSC (Differential Scanning Calorimetry) method, and the density measured by the Archimedes method for a test piece cut out from the honeycomb structure 100.

[0043] The honeycomb structure 100 preferably has a high emissivity in the near to far infrared region. Specifically, the honeycomb structure 100 preferably has an emissivity of 30% or more, more preferably 50% or more, at wavelengths of 2 to 20 μm. By controlling the emissivity within this range, the effect of radiative heat transfer is improved, and the heat exchange efficiency between the fluids flowing through the second flow path and the third flow path can be increased. Here, the emissivity is measured at 25°C using an existing emissivity measuring device.

[0044] The ceramics used in the honeycomb structure 100 are preferably ceramics with excellent heat resistance, and SiC (silicon carbide) is particularly preferable when considering thermal conductivity and emissivity. Since porous SiC (silicon carbide) does not provide high thermal conductivity, it is preferable to impregnate it with silicon during the manufacturing process of the honeycomb structure 100 to form a dense structure (Si-impregnated SiC). A dense structure provides high thermal conductivity. For example, while porous SiC (silicon carbide) provides a thermal conductivity of approximately 20 W / (m·K), a dense structure can provide a thermal conductivity of approximately 150 W / (m·K).

[0045] Specific examples of ceramics that can be used in the honeycomb structure 100 include SiC and Si-impregnated SiC, as well as (Si + Al)-impregnated SiC, metal composite SiC, recrystallized SiC, and Si3N4. However, from the viewpoint of heat exchange efficiency, it is preferable to use Si-impregnated SiC or (Si + Al)-impregnated SiC to form a dense structure. Si-impregnated SiC has a structure in which the surfaces of SiC particles are surrounded by a solidified material of metal silicon melt and the SiC is integrally bonded via the metal silicon. This isolates the silicon carbide from an oxygen-containing atmosphere and prevents oxidation. Furthermore, while SiC has the characteristics of high thermal conductivity and easy heat dissipation, Si-impregnated SiC exhibits high thermal conductivity and heat resistance, is densely formed, and exhibits sufficient strength as a heat transfer member. In other words, the honeycomb structure 100 made of Si-SiC-based (Si-impregnated SiC, (Si+Al)-impregnated SiC) material exhibits excellent properties such as heat resistance, thermal shock resistance, oxidation resistance, and corrosion resistance against acids and alkalis, as well as high thermal conductivity.

[0046] The porosity of the intermediate walls (first intermediate walls 20, second intermediate walls 30) and partition walls (first partition walls 40, second partition walls 50, third partition walls 60) of the honeycomb structure 100 is not particularly limited, but is preferably 10% or less, more preferably 3% or less. By controlling the porosity within such a range, the thermal conductivity can be improved.

[0047] The types of the first, second, and third fluids flowing through the first, second, and third flow paths are not particularly limited, and various gases can be appropriately selected depending on the application. In particular, when a heat exchanger including the honeycomb structure 100 is used in a burner, the first fluid is fuel gas, the second fluid is air, and the third fluid is a combustion exhaust gas of the fuel gas and air. Since the second and third flow paths are formed by a plurality of cells 70b, 70c, the contact area can be increased. In addition, the thermal conductivity of each partition wall and intermediate wall forming the cells 70b, 70c is high, thereby improving heat exchange efficiency.

[0048] It is preferable that the flow direction of the first and second fluids is opposite to the flow direction of the third fluid within the honeycomb structure 100. By controlling the flow directions of the fluids in this way, it is possible to improve the heat exchange efficiency, particularly between the second and third fluids.

[0049] The honeycomb structure 100 can be manufactured according to a method known in the art. For example, the honeycomb structure 100 can be manufactured according to the method described below. First, a clay containing ceramic powder is extruded into a desired shape to produce a honeycomb formed body. At this time, by selecting an appropriate die and jig, the thickness of the outer wall 10, each intermediate wall (first intermediate wall 20 and second intermediate wall 30), and each partition wall (first partition wall 40, second partition wall 50, and third partition wall 60), the shape of each cell (70a, 70b, 70c), the cell density, etc. can be controlled. For example, when manufacturing a honeycomb formed body mainly composed of Si-impregnated SiC, a binder and water or an organic solvent are added to a predetermined amount of SiC powder, and the resulting mixture is kneaded to form a clay, which is then molded to obtain a honeycomb formed body of a desired shape.

[0050] Next, portions of the outer peripheral wall 10 and the third partition walls 60 are removed from the honeycomb formed body to form a desired shape. For example, when producing a honeycomb structure 100 having the structure shown in FIG. 1a, both end side regions of the outer peripheral wall 10 and the third partition walls 60 may be removed by grinding or the like. Furthermore, when producing a honeycomb structure 100 having the structure shown in FIG. 2, the regions of the outer peripheral wall 10 and the third partition walls 60 that become the constricted portions 80, and one end side region of the outer peripheral wall 10 and the third partition walls 60 may be removed by grinding or the like. Next, the honeycomb formed body processed as described above is dried, and then impregnated with metal Si and fired in a reduced pressure inert gas or in vacuum, thereby obtaining the honeycomb structure 100. Note that, in the above description, the processing for removing portions of the outer peripheral wall 10 and the third partition walls 60 is performed on the honeycomb formed body, but this processing may also be performed after firing the honeycomb formed body.

[0051] As shown in FIGS. 3 and 4 , the heat exchanger according to the first embodiment of the present invention can further include an outer tubular member 110 fitted to at least a portion of the outer peripheral wall 10. The outer tubular member 110 has an inlet 111 and an outlet 112 for a fluid (third fluid). This structure can protect the honeycomb structure 100. Furthermore, particularly when the heat exchanger is used in a burner, mixing of the second fluid and the third fluid can be suppressed, thereby stably improving the heat exchange efficiency between the second fluid and the third fluid. Note that FIG. 3 is a cross-sectional view of the heat exchanger parallel to the extension direction of the cells 70 a, 70 b, and 70 c of the honeycomb structure 100, and shows an example in which the outer tubular member 110 is provided on the outer peripheral wall 10 of the honeycomb structure 100 of FIG. 1 a. 4 is a cross-sectional view of the heat exchanger parallel to the direction in which the cells 70a, 70b, and 70c of the honeycomb structure 100 extend, showing an example in which an outer casing member 110 is provided on the outer peripheral wall 10 of the honeycomb structure of FIG.

[0052] The outer tube member 110 is preferably longer than the length of the outer peripheral wall 10 in the axial direction X. Controlling the length of the outer tube member 110 in this manner improves the degree of freedom in the placement of the inlet 111 and outlet 112 for the fluid (third fluid). For example, as shown in Fig. 3 , the outlet 112 for the third fluid can be placed at a position perpendicular to the flow direction of the third fluid.

[0053] The outer tubular member 110 preferably has heat resistance and corrosion resistance, and examples thereof include ceramic pipes, SUS pipes, copper pipes, and brass pipes. The outer tubular member 110 is preferably fitted to the honeycomb structure 100. In this specification, "fitting" refers to being fixed in a mutually fitted state. Therefore, the fitting between the honeycomb structure 100 and the outer tubular member 110 includes fixing methods such as clearance fit, interference fit, and shrink fit, as well as methods in which the honeycomb structure 100 and the outer tubular member 110 are fixed to each other by brazing, welding, diffusion bonding, and the like. When a ceramic pipe is used as the outer tubular member 110, it is preferable that the outer tubular member 110 and the honeycomb structure 100 are integrally formed. Furthermore, from the viewpoint of durability and reliability against thermal stress, it is preferable that the outer tubular member 110 and the honeycomb structure 100 are made of the same material or materials with similar thermal expansion coefficients.

[0054] An intermediate material made of a material having a lower Young's modulus than the outer tubular member 110 may be disposed between the honeycomb structure 100 and the outer tubular member 110. By providing the intermediate material at such a position, it is possible to improve the adhesion (sealing property) between the honeycomb structure 100 and the outer tubular member 110. Examples of the intermediate material include a heat insulating mat and a graphite sheet.

[0055] (2) Burner The burner according to the first embodiment of the present invention mixes and burns fuel gas and air, and includes the heat exchanger according to the first embodiment of the present invention, in which the first fluid is fuel gas, the second fluid is air, and the third fluid is a combustion exhaust gas of the fuel gas and air. The heat exchanger according to the first embodiment of the present invention has excellent heat resistance, and therefore can be used as a burner that can be applied to industrial furnaces used in temperature ranges where the furnace temperature exceeds 1000°C. Furthermore, the heat exchanger according to the first embodiment of the present invention has excellent heat exchange efficiency between the second fluid (air) and the third fluid (combustion exhaust gas), and therefore can be used as a burner with high energy efficiency.

[0056] <Embodiment 2> (1) Heat Exchanger FIG. 5a is a cross-sectional view of a heat exchanger according to Embodiment 2 of the present invention, parallel to the extension direction of the cells of the honeycomb structure. FIG. 5b is a cross-sectional view of the heat exchanger taken along line b-b' in FIG. 5a (a cross-sectional view of the heat exchanger perpendicular to the extension direction of the cells of the honeycomb structure). As shown in FIGS. 5a and 5b, the heat exchanger according to Embodiment 2 of the present invention differs from the heat exchanger according to Embodiment 1 of the present invention in that it includes a honeycomb structure 200 in which the first intermediate wall 20 is an inner peripheral wall 90 and the inside of the inner peripheral wall 90 is a hollow region 95 without a first partition wall 40. The rest of the structure is the same as that of the heat exchanger according to Embodiment 1 of the present invention, and therefore a description thereof will be omitted. Even with a honeycomb structure 200 having such a structure, heat exchange between fluids flowing through the second flow path and the third flow path is possible, and the heat exchange efficiency can be improved, making it suitable for use in a burner.

[0057] The material and thickness of the inner peripheral wall 90 in the honeycomb structure 200 are not particularly limited, and can be the same as those of the first intermediate wall 20 in the honeycomb structure 100. The honeycomb structure 200 can also be manufactured in a manner similar to that of the honeycomb structure 100. Specifically, when manufacturing a honeycomb formed body, a die and a jig having an appropriate shape may be selected and extrusion molding may be performed so that the inner peripheral wall 90 is formed.

[0058] As shown in FIG. 6 , the heat exchanger according to the second embodiment of the present invention can further include an outer tubular member 110 fitted to at least a portion of the outer peripheral wall 10, similar to the heat exchanger according to the first embodiment of the present invention. The heat exchanger according to the second embodiment of the present invention can further include an inner tubular member 120 fitted to at least a portion of the inner peripheral wall 90. The inner tubular member 120 has an inlet 121 and an outlet 122 for a fluid (first fluid). The provision of the inner tubular member 120 can facilitate the supply of the fluid (first fluid) into the honeycomb structure 200. Note that FIG. 6 is a cross-sectional view of the heat exchanger parallel to the extension direction of the cells 70 a, 70 b, and 70 c of the honeycomb structure 200, and illustrates an example in which the outer tubular member 110 is provided on the outer peripheral wall 10 and the inner tubular member 120 is provided on the inner peripheral wall 90 of the honeycomb structure 200 of FIG. 5 a.

[0059] The inner cylindrical member 120 is preferably longer than the length of the inner peripheral wall 90 in the axial direction X. Controlling the length of the inner cylindrical member 120 in this manner improves the degree of freedom in the placement of the inlet 121 and outlet 122 for the fluid (first fluid). Furthermore, the material of the inner cylindrical member 120 is not particularly limited, and can be the same material as the outer cylindrical member 110.

[0060] (2) Burner A burner according to a second embodiment of the present invention mixes and burns fuel gas and air, and includes the heat exchanger according to the second embodiment of the present invention, in which the first fluid is fuel gas, the second fluid is air, and the third fluid is a combustion exhaust gas of the fuel gas and air. The heat exchanger according to the second embodiment of the present invention has excellent heat resistance, and therefore can be used as a burner that can be applied to industrial furnaces used in temperature ranges where the furnace temperature exceeds 1000°C. Furthermore, the heat exchanger according to the second embodiment of the present invention has excellent heat exchange efficiency between the second fluid (air) and the third fluid (combustion exhaust gas), and therefore can be used as a burner with high energy efficiency.

[0061] <Embodiment 3> (1) Heat Exchanger The heat exchanger according to Embodiment 3 of the present invention is the same as the heat exchanger according to Embodiments 1 and 2 of the present invention, except that the type of fluid flowing through each flow path is different. Cross-sectional views of the heat exchanger according to Embodiment 3 of the present invention, parallel to the extension direction of the cells of the honeycomb structure, are shown in FIGS. 7a and 7b. Note that the components of the heat exchanger according to Embodiment 3 of the present invention are the same as those of the heat exchangers according to Embodiments 1 and 2 of the present invention, and therefore their description will be omitted. As shown in FIGS. 7a and 7b, in the heat exchanger according to Embodiment 3 of the present invention, the first flow path (cell 70a) and the second flow path (cell 70b) are flow paths for the first fluid, and the third flow path (cell 70c) is a flow path for the third fluid. The honeycomb structures 100 and 200 having such a structure enable heat exchange between the first fluid and the third fluid, thereby increasing the heat exchange efficiency, making them suitable for preheating a fluid (e.g., air) used in a burner.

[0062] It is preferable that the flow direction of the first fluid circulating through the first flow path is opposite to the flow direction of the first fluid circulating through the second flow path. With this configuration, the first fluid that has circulated through the second flow path can be circulated back into the first flow path. It is also preferable that the flow direction of the first fluid circulating through the second flow path is opposite to the flow direction of the third fluid circulating through the third flow path. With this configuration, it is possible to increase the heat exchange efficiency between the first fluid circulating through the second flow path and the third fluid circulating through the third flow path.

[0063] As shown in Figures 8a and 8b, the heat exchanger according to the third embodiment of the present invention can further include an outer tubular member 110 fitted to at least a portion of the outer peripheral wall 10 of the honeycomb structure 100, 200. The outer tubular member 110 can have an inlet 111 and an outlet 112 for a fluid (third fluid). This structure protects the honeycomb structure 100, 200 and prevents the first fluid and the third fluid from mixing. Furthermore, as shown in Figure 8b, it is preferable that the position of the inlet 111 of the outer tubular member 110 extends outward beyond the end 12 of the honeycomb structure 200. This structure makes it easier to supply the third fluid to the third flow path.

[0064] 8a and 8b, the heat exchanger according to the third embodiment of the present invention can further include a folding member 130 that supplies the first fluid flowing through the second flow path to the first flow path, on one end face perpendicular to the extension direction of each cell of the honeycomb structure 100, 200. Specifically, the folding member 130 can be provided on the outlet side of the second flow path through which the first fluid flows. By providing the folding member 130 at such a position, the first fluid flowing through the second flow path can be supplied to the first flow path.

[0065] The structure of the folding member 130 is not particularly limited as long as it has a structure that allows the first fluid flowing through the second flow path to be supplied to the first flow path. For example, the folding member 130 may have a U-shape as shown in Fig. 8a or a semicircular shape as shown in Fig. 8b in a cross section parallel to the direction in which the cells of the honeycomb structure extend.

[0066] The material of the folding member 130 is not particularly limited, and may be the same material as the outer cylindrical member 110 and the inner cylindrical member 120, but it is preferable to use a highly thermally conductive material such as Si-impregnated SiC (porous SiC with the pores impregnated with metallic Si). By selecting a highly thermally conductive material, heat exchange between the first fluid and the third fluid can be performed via the highly thermally conductive material, thereby improving the heat exchange efficiency.

[0067] The method for arranging the folded-back member 130 is not particularly limited, and any known method can be used. Known methods include fixing methods using a fit such as a clearance fit, an interference fit, or a shrink fit, as well as brazing, welding, diffusion bonding (including bonding by Si impregnation), and the like.

[0068] As shown in FIG. 8b, the heat exchanger according to the third embodiment of the present invention can further include an inner tubular member 120 fitted to at least a portion of the inner peripheral wall 90 of the honeycomb structure 200. The inner tubular member 120 has an inlet 121 and an outlet 122 for a fluid (first fluid). The outlet 122 of the inner tubular member 120 is preferably positioned outward from the end 31 of the honeycomb structure 200. This structure can prevent the first fluid from being supplied and the first fluid from being discharged from mixing. Furthermore, the inlet 121 of the inner tubular member 120 is preferably positioned closer to the end 31 than the axial center of the honeycomb structure 200. This structure can prevent the first fluid from exchanging heat between the vicinity of the inlet of the second flow path and the vicinity of the outlet of the first flow path.

[0069] (2) Burner A burner according to a third embodiment of the present invention burns a mixture of fuel gas and air, and includes the heat exchanger according to the third embodiment of the present invention, in which the first fluid is air and the third fluid is a combustion exhaust gas of the fuel gas and the air, and the heat exchanger is used to preheat the air. The heat exchanger according to the third embodiment of the present invention has excellent heat resistance, and therefore can be used as a burner that can be applied to industrial furnaces used in temperature ranges where the furnace temperature exceeds 1000°C. Furthermore, the heat exchanger according to the third embodiment of the present invention has excellent heat exchange efficiency between the first fluid (air) and the third fluid (combustion exhaust gas), and therefore can effectively preheat the first fluid (air), resulting in a burner with high energy efficiency.

[0070] DESCRIPTION OF SYMBOLS 10 Outer peripheral wall 11, 12 End portion 20 First intermediate wall 21, 22 End portion 30 Second intermediate wall 31, 32 End portion 40 First partition wall 50 Second partition wall 51 Circumferential partition wall 52 Radial partition wall 60 Third partition wall 61 Circumferential partition wall 62 Radial partition wall 70a, 70b, 70c Cell 80 Neck portion 90 Inner peripheral wall 95 Hollow region 100, 200 Honeycomb structure 110 Outer cylindrical member 111 Inlet 112 Outlet 120 Inner cylindrical member 121 Inlet 122 Outlet 130 Fold-back member

Claims

1. A heat exchanger having a honeycomb structure mainly composed of ceramics, the honeycomb structure comprising: an outer peripheral wall; a first intermediate wall and a second intermediate wall including portions disposed inside the outer peripheral wall; a first partition wall disposed inside the first intermediate wall and defining a plurality of cells which become a first flow path; a second partition wall disposed between the first intermediate wall and the second intermediate wall and defining a plurality of cells which become a second flow path; and a third partition wall disposed between the second intermediate wall and the outer peripheral wall and defining a plurality of cells which become a third flow path, the honeycomb structure comprising: a honeycomb structure mainly composed of ceramics, the first flow path, the second flow path, and the third flow path being configured to be positioned coaxially.

2. A heat exchanger as described in claim 1, wherein the first flow path is a flow path for a first fluid, the second flow path is a flow path for a second fluid, and the third flow path is a flow path for a third fluid, and heat exchange is possible between the second fluid and the third fluid.

3. A heat exchanger as described in claim 1, wherein the first flow path and the second flow path are flow paths for a first fluid, and the third flow path is a flow path for a third fluid, and heat exchange is possible between the first fluid and the third fluid.

4. A heat exchanger according to any one of claims 1 to 3, wherein, in the axial direction of the honeycomb structure, both ends of the outer peripheral wall are located more inward than both ends of the first intermediate wall and the second intermediate wall.

5. A heat exchanger as described in any one of claims 1 to 3, wherein in a cross section perpendicular to the direction in which the cells extend, the second partition wall and the third partition wall have a circumferential partition wall extending in a circumferential direction and a radial partition wall extending in a radial direction.

6. A heat exchanger according to any one of claims 1 to 3, further comprising an outer tubular member fitted onto at least a portion of said outer peripheral wall, said outer tubular member having an inlet and an outlet for fluid.

7. A heat exchanger according to any one of claims 1 to 3, wherein the first intermediate wall is an inner circumferential wall, and the inside of the inner circumferential wall is a hollow region not having the first partition wall.

8. A heat exchanger according to claim 7, further comprising an inner cylindrical member fitted onto at least a portion of said inner circumferential wall, said inner cylindrical member having an inlet and an outlet for fluid.

9. The heat exchanger according to claim 2, wherein the flow directions of the first fluid and the second fluid are opposite to the flow direction of the third fluid.

10. The heat exchanger according to claim 3, wherein a flow direction of the first fluid circulating through the first flow path is opposite to a flow direction of the first fluid circulating through the second flow path.

11. The heat exchanger according to claim 10, wherein a flow direction of the first fluid flowing through the second flow passage is opposite to a flow direction of the third fluid flowing through the third flow passage.

12. A heat exchanger as described in claim 11, further comprising a folding member on one end face of the honeycomb structure perpendicular to the direction in which the cells extend, for supplying the first fluid circulating through the second flow path to the first flow path.

13. A heat exchanger according to any one of claims 1 to 3, wherein the ceramic is silicon carbide.

14. A burner for mixing and burning fuel gas and air, comprising the heat exchanger according to claim 2, wherein the first fluid is the fuel gas, the second fluid is the air, and the third fluid is the combustion exhaust gas of the fuel gas and the air.

15. A burner which mixes and burns fuel gas and air, comprising the heat exchanger according to claim 3, wherein the first fluid is the air, the third fluid is a combustion exhaust gas of the fuel gas and the air, and the heat exchanger is used to preheat the air.

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