JP7633820B2 - Heat exchangers and reformers - Google Patents

Description

The present invention relates to a heat exchanger and a reformer.

Patent Document 1 discloses the following technology for improving fuel efficiency by reforming fuel for an internal combustion engine. That is, a part of exhaust gas from an exhaust passage of an internal combustion engine is recirculated to an intake passage as EGR (exhaust gas recirculation) gas, and a reforming fuel injection valve for injecting reforming fuel and a fuel reforming catalyst for reforming the reforming fuel are arranged in the middle of the EGR passage. Then, the reforming fuel injected by the reforming fuel injection valve and moisture (water vapor) in the EGR gas are reformed by the fuel reforming catalyst to generate hydrogen (H ₂ ) and carbon monoxide (CO), thereby reforming the reforming fuel to generate a highly combustible reformed gas, and the reformed gas is supplied to the intake passage of the internal combustion engine. In addition, the amount of injection of the reforming fuel is controlled so as to be within a control region set based on the temperature of the fuel reforming catalyst and the amount of the reformed gas, thereby suppressing deterioration of the fuel reforming catalyst and improving the reforming performance.

The above fuel reforming catalyst absorbs heat from the exhaust gas when water vapor and hydrocarbons react in the reformer. Therefore, the fuel reforming catalyst is configured to be able to exchange heat with the exhaust gas flowing through the exhaust pipe, supplying heat from the exhaust gas and promoting the reforming reaction.

Patent Document 1 does not disclose the specific materials or configuration of the fuel reforming catalyst, but in order to promote the reaction in the reformer, a temperature of 600°C or higher is required, and it is believed that the material that constitutes the fuel reforming catalyst must be able to withstand temperatures of 600°C or higher and have a heat exchange function.

On the other hand, Patent Document 2 discloses a heat exchanger having a monolithic ceramic structure in which a first layer and a second layer having flow paths are stacked in a direction intersecting each other and sintered.

JP 2015-166591 A Japanese Unexamined Patent Publication No. 7-151478

It is assumed that a heat exchanger such as that disclosed in Document 2 is used as a heat exchanger carrying a catalyst for a fuel reforming catalyst disclosed in Patent Document 1. In a heat exchanger having such a configuration, each layer is bonded via an adhesive layer, and a coating layer is formed on the outer circumferential surface. A heat exchanger is usually used while being held in a metal case via a retaining mat, but in the usage environment, the metal case expands due to heat, which reduces the holding force, so it is necessary to hold the heat exchanger in advance by applying high pressure via the retaining mat.
However, if there is a temperature difference between the fluids flowing through the first flow passage and the second flow passage, a local expansion difference occurs in the heat exchanger, which can easily cause cracks to occur in the adhesive layer and the coating layer.

The present invention has been made to solve the above problems, and aims to provide a heat exchanger in which a first honeycomb structure in which first flow passages are arranged in parallel in the longitudinal direction separated by a partition wall and a second honeycomb structure in which second flow passages are arranged in parallel in the longitudinal direction separated by a partition wall are combined so that the first flow passages and the second flow passages intersect with each other via an adhesive layer, and a coating layer is formed on the outer peripheral surface, in which the adhesive layer and the coating layer are not easily damaged even at high temperatures, and a reformer equipped with the heat exchanger.

In order to achieve the above object, the heat exchanger of the present invention is a columnar heat exchanger including a first honeycomb structure in which a number of cells serving as first fluid flow passages are arranged in parallel in the longitudinal direction with partition walls therebetween, and a second honeycomb structure in which a number of cells serving as second fluid flow passages are arranged in parallel in the longitudinal direction with partition walls therebetween, the first flow passages and the second flow passages being combined via an adhesive layer such that the first flow passages and the second flow passages are perpendicular to each other,
The heat exchanger has the first flow passage opening at both end surfaces and the second flow passage opening at an outer circumferential surface,
Except for the opening of the second honeycomb structure formed on the outer peripheral surface, other portions are covered with a coating layer,
The present invention is characterized in that when the thermal expansion coefficients of the first honeycomb structure and the second honeycomb structure are C1, the thermal expansion coefficient of the adhesive layer is C2, and the thermal expansion coefficient of the coating layer is C3, the thermal expansion coefficients are set to satisfy C1<C2≦C3.

According to the heat exchanger of the present invention, when the thermal expansion coefficients of the first honeycomb structure and the second honeycomb structure are C1, the thermal expansion coefficient of the adhesive layer is C2, and the thermal expansion coefficient of the coating layer is C3, the thermal expansion coefficients are set to satisfy C1<C2≦C3. Therefore, even if a temperature difference occurs between the second honeycomb structure and the first honeycomb structure and the heat exchanger expands partially, the adhesive layer and coating layer are more likely to expand, so that cracks are less likely to occur in the adhesive layer and coating layer.
In addition, when the heat exchanger is stored in a metal container such as a reformer via a retaining mat, the retaining force of the retaining mat changes little, so that the heat exchanger can be reliably prevented from falling off the metal container.

In the heat exchanger of the present invention, it is desirable that the thermal expansion coefficient C1 is 2.80 to 4.50×10 ⁻⁶ K ⁻¹ , and the thermal expansion coefficients C2 and C3 are 3.05 to 4.75×10 ⁻⁶ K ⁻¹ .
In the heat exchanger of the present invention, when the thermal expansion coefficient C1 of the first honeycomb structure and the second honeycomb structure, the thermal expansion coefficient C2 of the adhesive layer, and the thermal expansion coefficient C3 of the coating layer are the above-mentioned values, cracks are less likely to occur in the adhesive layer and the coating layer.

In the heat exchanger of the present invention, it is preferable that the difference between the thermal expansion coefficient C3 and the thermal expansion coefficient C1 be expressed by the following inequality (1).
C2-C1≧0.05×10 ^-6 ...(1)
In the heat exchanger of the present invention, when the difference between the thermal expansion coefficient C3 and the thermal expansion coefficient C1 is the value expressed by the above inequality (1), cracks are less likely to occur in the adhesive layer and the coating layer.

In the heat exchanger of the present invention, it is preferable that three of the first honeycomb structures and four of the second honeycomb structures are alternately arranged with adhesive layers interposed therebetween.
In the heat exchanger of the present invention, when three of the first honeycomb structures and four of the second honeycomb structures are arranged alternately with adhesive layers interposed therebetween, the contact area between the second honeycomb structures and the first honeycomb structures is large, enabling efficient heat exchange.

In the heat exchanger of the present invention, it is desirable that a catalyst is supported on the partition walls of the cells that constitute the first honeycomb structure.

In the heat exchanger of the present invention, when a catalyst is supported on the partition walls of the cells that make up the first honeycomb structure, a reforming reaction can take place inside the first honeycomb structure, and by receiving heat from the exhaust gas that has flowed into the second honeycomb structure, the catalyst can fully function as a reforming catalyst.

In the heat exchanger of the present invention, it is desirable that the first honeycomb structure and the second honeycomb structure are made of silicon carbide and silicon.

In the heat exchanger of the present invention, when the first honeycomb structure and the second honeycomb structure are made of silicon carbide and silicon, they have excellent thermal conductivity and heat resistance, and therefore have good heat exchange function, and are less likely to break even when a large temperature difference occurs.

In the heat exchanger of the present invention, it is desirable that the adhesive layer is made of silicon carbide and silicon.
In the heat exchanger of the present invention, when the adhesive layer is made of silicon carbide and silicon, the adhesive layer has excellent thermal conductivity, and the heat exchange performance between the first honeycomb structure and the second honeycomb structure can be further improved.

The reformer of the present invention is a reformer equipped with the heat exchanger having the above configuration,
The second honeycomb structure is configured to allow exhaust gas discharged from an internal combustion engine and flowing through a main exhaust pipe to pass therethrough, and the first honeycomb structure is configured such that a reforming catalyst is supported on the partition walls and exhaust gas that flows into an exhaust gas recirculation pipe branched off from the main exhaust pipe to pass therethrough.

When the reformer of the present invention is configured as described above, it is possible to effectively supply exhaust gas heat from the second honeycomb structure to the first honeycomb structure, and it is possible to effectively perform as a reformer that reforms fuel for an internal combustion engine to improve fuel efficiency. Furthermore, when the heat exchanger is made of silicon carbide and silicon, it is not easily corroded by the hydrogen contained in the reformed gas.

In the reformer of the present invention, it is preferable that the heat exchanger is housed, via a retaining mat, in a metal container connected to the main exhaust pipe and the exhaust gas recirculation pipe.
In the reformer of the present invention, when the heat exchanger is housed in a metal container via a retaining mat, cracks are unlikely to occur in the adhesive layer even if the heat exchanger becomes hot.

FIG. 1A is a perspective view illustrating a heat exchanger according to a first embodiment of the present invention. FIG. 1B is a cross-sectional view of the heat exchanger shown in FIG. 1A taken along line AA. FIG. 2A is a perspective view that shows a schematic diagram of a support mat used when the heat exchanger having the above-mentioned configuration is housed in a reformer. FIG. 2B is an explanatory diagram that shows a schematic diagram of a method for winding the support mat around a heat exchanger. FIG. 3A is a perspective view illustrating a heat exchanger according to a second embodiment of the present invention. FIG. 3B is a cross-sectional view of the heat exchanger shown in FIG. 3A taken along line BB. FIG. 4 is an explanatory diagram showing a schematic diagram of a fuel reforming gasoline engine system equipped with a reformer of the present invention.

Detailed Description of the Invention
The heat exchanger of the present invention will now be described.
The heat exchanger of the present invention is a columnar heat exchanger in which a first honeycomb structure in which a number of cells serving as first flow passages for a fluid are arranged in parallel in the longitudinal direction with partition walls therebetween, and a second honeycomb structure in which a number of cells serving as second flow passages for a fluid are arranged in parallel in the longitudinal direction with partition walls therebetween, are combined via an adhesive layer such that the first flow passages and the second flow passages are perpendicular to each other,
The heat exchanger has the first flow passage opening at both end faces and the second flow passage opening at the outer peripheral face, and except for the opening of the second honeycomb structure formed on the outer peripheral face, other parts are covered with a coating layer, and the thermal expansion coefficients are set so as to satisfy C1<C2≦C3, where C1 is the thermal expansion coefficient of the first honeycomb structure and the second honeycomb structure, C2 is the thermal expansion coefficient of the adhesive layer, and C3 is the thermal expansion coefficient of the coating layer.

FIG. 1A is a perspective view that illustrates a heat exchanger according to a first embodiment of the present invention, and FIG. 1B is a cross-sectional view of the heat exchanger illustrated in FIG. 1A taken along line AA.
As shown in Figures 1A and 1B, the heat exchanger 100 of the present invention is a columnar heat exchanger 100 which is configured by combining a first honeycomb structure 10 in which a number of cells 13 which become first flow passages for fluid are arranged in parallel in the longitudinal direction separated by partition walls 12, and a second honeycomb structure 20 in which a number of cells 23 which become second flow passages for fluid are arranged in parallel in the longitudinal direction separated by partition walls 22, such that the first flow passages (cells 13) and the second flow passages (cells 23) are perpendicular to each other.

In the heat exchanger 100 shown in Figures 1A and 1B, three first honeycomb structures 10 and four second honeycomb structures 20 are arranged alternately with adhesive layers 18 between them. In the heat exchanger 100 shown in Figures 1A and 1B, the first honeycomb structure 10 is constituted by one honeycomb segment 11, but the first honeycomb structure 10 may be constituted by two or more honeycomb segments 11 bonded together with adhesive layers 18. Therefore, in the present invention, the assembly of one or more honeycomb segments 11 sandwiched between the second honeycomb structures 20 is referred to as the first honeycomb structure 10. The honeycomb segment is a member having the same structure as the honeycomb structure.

The second honeycomb structure 20 is formed by bonding two honeycomb segments 21 with an adhesive layer, but may be formed by one honeycomb structure 20, or may be formed by bonding three or more honeycomb segments 21 with an adhesive layer 18. Therefore, in the present invention, the assembly of one or two or more honeycomb segments 21 sandwiched between the first honeycomb structures 10 is referred to as the second honeycomb structure 20. However, the second honeycomb structure 20 may be located on the outermost side, in which case the assembly of the outermost one or two honeycomb segments 21 is also the second honeycomb structure 20.

In Figures 1A and 1B, the extension direction of the cells 13 constituting the first honeycomb structure 10 is the vertical direction, and the extension direction of the cells 23 constituting the second honeycomb structure 20 is the horizontal direction, and the flow paths are perpendicular to each other, making it easy to circulate two types of fluids (gases) and allowing efficient heat exchange.

In the heat exchanger 100 shown in Figures 1A and 1B, cells 13 that become the first flow passages of the first honeycomb structure 10 open on both end faces, cells 23 that become the second flow passages of the second honeycomb structure 20 open on the outer peripheral face, the entire surface of the first honeycomb structure 10 that constitutes the outer peripheral face is covered with a coating layer 32, and the surface of the second honeycomb structure 20 that constitutes the outer peripheral face is covered with coating layers 31a and 31b except for a square-shaped opening 34 with chamfered corners 34a.

The corners 34a of the opening 34 may be chamfered with a straight C-shape, but as shown in FIG. 1A, it is preferable that the corners 34a are chamfered with an R-shape having a radius of curvature of 1 to 15 mm.
In order to increase the heat exchange efficiency, the percentage of the area of the opening 34 to the total area of the opening 34 and the coating layers 31a, 31b, 32 (opening/opening+coating) is preferably 72-93%, more preferably 75-85%. The thickness of the coating layers 31a, 31b, 32 is preferably 0.1-0.5 mm, more preferably 0.2-0.3 mm.

In the heat exchanger of the present invention, when the thermal expansion coefficients of the first honeycomb structure and the second honeycomb structure are C1, the thermal expansion coefficient of the adhesive layer is C2, and the thermal expansion coefficient of the coating layer is C3, the thermal expansion coefficients are set so as to satisfy C1<C2≦C3.
That is, the thermal expansion coefficient C2 of the adhesive layer is larger than the thermal expansion coefficient C1 of the first honeycomb structure and the second honeycomb structure. It is also preferable that the thermal expansion coefficient C2 of the adhesive layer and the thermal expansion coefficient C3 of the coating layer are the same, or that the thermal expansion coefficient C3 of the coating layer is larger than the thermal expansion coefficient C2 of the adhesive layer. In this specification, the term "heat exchanger of the present invention" refers to the heat exchanger according to the first embodiment described above, the heat exchanger according to the second embodiment described later, and other components constituting the heat exchangers according to all embodiments of the present invention, and the components related to the heat exchangers described above.

In the heat exchanger of the present invention, when the thermal expansion coefficients of the first honeycomb structure, the second honeycomb structure, the adhesive layer and the coating layer are set as described above, even if a temperature difference occurs between the second honeycomb structure and the first honeycomb structure and the heat exchanger expands partially, the adhesive layer and the coating layer are more likely to expand, so that cracks are less likely to occur in the adhesive layer and the coating layer.
Furthermore, when the heat exchanger is housed in a metal container such as a reformer via a retaining mat, even if the metal container thermally expands due to an increase in temperature, the adhesive layer and coating layer also expand in the same way as the metal container, so there is little change in the holding force of the retaining mat, and the heat exchanger can be reliably prevented from falling off the metal container.

In the heat exchanger of the present invention, the thermal expansion coefficient C1 of the first honeycomb structure and the second honeycomb structure, the thermal expansion coefficient C2 of the adhesive layer, and the thermal expansion coefficient C3 of the coating layer are set to satisfy C1<C2≦C3, and further, it is desirable that the thermal expansion coefficient C1 of the first honeycomb structure and the second honeycomb structure is 2.80 to 4.50× ^10−6K − ¹ , and the thermal expansion coefficient C2 of the adhesive layer and the thermal expansion coefficient C3 of the coating layer are 3.05 to 4.75× ^10−6K − ¹ .
In the heat exchanger of the present invention, when the thermal expansion coefficient C1 of the first honeycomb structure and the second honeycomb structure, the thermal expansion coefficient C2 of the adhesive layer, and the thermal expansion coefficient C3 of the coating layer are the above-mentioned values, cracks are less likely to occur in the adhesive layer and the coating layer.

In the heat exchanger of the present invention, it is preferable that the difference between the thermal expansion coefficient C3 and the thermal expansion coefficient C1 be expressed by the following inequality (1).
C2-C1≧0.05×10 ^-6 ...(1)
That is, it is desirable that the thermal expansion coefficient C2 of the adhesive layer and the thermal expansion coefficient C3 of the coating layer are larger than the thermal expansion coefficient C1 of the first honeycomb structure and the second honeycomb structure by 0.05×10 ⁻⁶ or more.
When the thermal expansion coefficients C1 of the first honeycomb structure and the second honeycomb structure, the thermal expansion coefficient C2 of the adhesive layer, and the thermal expansion coefficient C3 of the coating layer are set as described above, cracks are less likely to occur in the adhesive layer and the coating layer. The thermal expansion coefficient C3 of the coating layer may be larger than the thermal expansion coefficient C2 of the adhesive layer.

In order to set the thermal expansion coefficient C1 of the first honeycomb structure and the second honeycomb structure, the thermal expansion coefficient C2 of the adhesive layer, and the thermal expansion coefficient C3 of the coating layer as described above, it is necessary to change the compositions of the first honeycomb structure and the second honeycomb structure, the adhesive layer, and the coating layer.
In other words, when the above components are made of SiC and silicon, SiC has a higher thermal expansion coefficient, so by increasing the SiC content, the thermal expansion coefficient can be made higher.

In the heat exchanger of the present invention, the fluid to be subjected to heat exchange may be a liquid such as water, an organic solvent such as ethylene glycol, or a liquefied gas, or a gas, but a gas is preferable, and exhaust gas is more preferable.

The volume of the heat exchanger according to the first embodiment of the present invention is preferably 1.2 to 3.2 liters.
In the heat exchanger of the present invention, when the volume of the heat exchanger is 1.2 to 3.2 liters, the heat exchanger has an appropriate volume, making it easy to mount on a vehicle, etc., and capable of fully exerting its effect as a heat exchanger.

If the volume of the heat exchanger is less than 1.2 liters, the heat exchanger volume is too small and it becomes difficult to support a sufficient amount of catalyst, while if the volume of the heat exchanger exceeds 3.2 liters, the reformer capacity becomes too large, making it difficult to install in a vehicle.

In the heat exchanger of the present invention, the materials of the first honeycomb structure and the second honeycomb structure or the honeycomb segments which are their constituent members are not particularly limited, and examples thereof include oxide-based ceramics such as cordierite, alumina, silica, and mullite; carbide-based ceramics such as silicon carbide, zirconium carbide, titanium carbide, tantalum carbide, and tungsten carbide; nitride-based ceramics such as aluminum nitride, silicon nitride, boron nitride, and titanium nitride; and composite materials of these ceramics and metals. Among these, composite materials of silicon carbide are preferred, and composite materials of silicon and silicon carbide are particularly desirable.

Although the specific configuration of the composite material made of silicon and silicon carbide is not particularly limited, a composite material of silicon and silicon carbide in which silicon fills the gaps between silicon carbide particles and independent silicon carbide particles are bonded together by the silicon present around them is desirable.
A composite material made of silicon and silicon carbide in this manner can be produced by bringing a degreased honeycomb formed body into contact with molten silicon, as described below.
The porous sintered silicon carbide may have open pores filled with silicon.

When molten silicon is brought into contact with silicon carbide, the degreased bodies of multiple honeycomb molded bodies are brought into contact with the molten silicon while being in close contact with each other via an adhesive layer containing silicon carbide, and an adhesive layer consisting of silicon carbide and silicon is also formed, making it possible to create a heat exchanger in which multiple honeycomb structures (or honeycomb segments) are bonded together with an adhesive layer consisting of silicon carbide and silicon.

In the heat exchanger of the present invention, the adhesive layer that bonds the honeycomb structures (or honeycomb segments) together is not particularly limited, but is preferably a composite material in which silicon fills the gaps between silicon carbide particles, similar to the honeycomb structures (or honeycomb segments). As described below, such a composite material can be produced by applying an adhesive layer paste with a higher silicon carbide content than the raw material paste to the side walls to bond the honeycomb bodies together, drying the honeycomb bodies after bonding them together, and contacting them with molten silicon.

In the heat exchanger of the present invention, it is desirable that the thickness of the partition walls of the first honeycomb structure and the second honeycomb structure is uniform. Specifically, the thickness of the partition walls of the first honeycomb structure that supports the catalyst is desirably 0.08 to 0.30 mm, and more desirably 0.10 to 0.20 mm. Because the thickness of the partition walls of the first honeycomb structure is thin, the surface area is large, making it possible to support a larger amount of catalyst.

The thickness of the partition walls of the second honeycomb structure is preferably 0.10 to 0.40 mm, and more preferably 0.15 to 0.30 mm. Because the partition walls of the second honeycomb structure are thick, the heat capacity is large and a large amount of heat can be supplied to the first honeycomb structure.

When the thickness of the partition walls of the first honeycomb structure and the second honeycomb structure are set as described above, a larger amount of catalyst can be supported, improving the reforming efficiency, and a larger amount of heat can be supplied from the second honeycomb structure to the first honeycomb structure, thereby increasing the activity of the catalyst.

In the heat exchanger of the present invention, the shape of the cells constituting the honeycomb structure is preferably, for example, a quadrangular prism with rectangular end faces as a whole, but may also be a triangular prism or hexagonal prism.
The shapes of the cells may be different, but it is preferable that they are all the same. In other words, it is preferable that the size of the cells surrounded by the partition walls is the same in a cross section perpendicular to the longitudinal direction of the honeycomb structure. This is because it is easy to manufacture.

In the heat exchanger of the present invention, the cell density in a cross section perpendicular to the longitudinal direction of the cells of the first honeycomb structure is preferably 46 to 124 cells/cm ² (300 to 800 cells/inch ² ), and more preferably 62 to 93 cells/cm ² (400 to 600 cells/inch ² ). This is because the surface area becomes large and a large amount of catalyst can be supported.
The cell density in a cross section perpendicular to the longitudinal direction of the cells of the second honeycomb structure is preferably 16 to 78 cells/ ^cm2 (100 to 500 cells/ ^inch2 ), and more preferably 31 to 62 cells/ ^cm2 (200 to 400 cells/ ^inch2 ).The heat capacity becomes large, and a large amount of heat can be supplied to the first honeycomb structure.

In the heat exchanger of the present invention, it is preferable that a catalyst is supported on the cells constituting the first honeycomb structure, and it is more preferable that a fuel reforming catalyst is supported on the cells.
The catalyst is preferably Co, Ni, Rh, Pt, Pd, more preferably Rh. The catalyst supported on a support is preferably Rh/ _ZrO2 , Rh/ _CoO2 . The support may be other ceramics such as silica, alumina, etc.

[Method of manufacturing heat exchanger]
Next, a method for producing the heat exchanger of the present invention will be described.
When manufacturing the heat exchanger of the present invention, a heat exchanger including a first honeycomb structure and a second honeycomb structure is manufactured through the steps shown below. In the following, a case where silicon carbide and silicon are used as materials constituting the honeycomb structure will be described, but the materials constituting the honeycomb structure are not limited to the above materials.

The heat exchanger of the present invention includes a molding process for producing a honeycomb molded body having a plurality of cells arranged in parallel in the longitudinal direction separated by partitions by molding a raw material paste containing, for example, silicon carbide powder, an organic binder, etc.; a drying process for drying the honeycomb molded body formed by the molding process; and a honeycomb aggregate production process for producing an aggregate of honeycomb molded bodies (honeycomb aggregate) by bonding the honeycomb molded body that becomes the first honeycomb structure dried by the drying process and the honeycomb molded body that becomes the second honeycomb structure together via an adhesive layer paste that serves as an adhesive layer. The honeycomb aggregate is processed into a cylindrical shape in a columnar body fabrication process, a coating layer paste application process is performed in which a coating layer paste is applied to the outer periphery of the columnar body processed into a circumferential shape to form a coating layer paste layer, and a degreasing, impregnation, and adhesion process is performed in which the columnar body to which the coating layer paste has been applied is degreased, heated to a high temperature, and the degreased body is impregnated with molten silicon to produce a heat exchanger composed of a honeycomb structure made of a composite material of silicon carbide and silicon, an adhesive layer, and a coating layer.

(Molding process)
In the molding process, first, silicon carbide powder, an organic binder, and the like are mixed to prepare a raw material paste.
The raw material paste may further contain a pore-forming agent, a forming aid, a dispersion medium such as water, and the like.

The organic binder is not particularly limited, but examples include methyl cellulose, carboxymethyl cellulose, hydroxyethyl cellulose, polyethylene glycol, phenolic resin, epoxy resin, etc., and two or more types may be used in combination.

The pore-forming agent is not particularly limited, but examples include acrylic resin, coke, starch, etc. The pore-forming agent is a material used to introduce pores into the honeycomb structure (or honeycomb segment) when manufacturing the honeycomb structure (or honeycomb segment).

The molding aids are not particularly limited, but include ethylene glycol, dextrin, fatty acids, fatty acid soaps, polyalcohols, etc., and two or more of them may be used in combination.

The dispersion medium is not particularly limited, but examples include water, organic solvents such as benzene, and alcohols such as methanol, and two or more of these may be used in combination.

When preparing the raw material paste, it is desirable to mix and knead the ingredients. Mixing may be performed using a mixer, attritor, etc., or kneading may be performed using a kneader, etc.

In the molding step, the raw material paste is extrusion molded to obtain a honeycomb molded body in which a plurality of cells are arranged in parallel in the longitudinal direction with partition walls between them.
The shape of the honeycomb formed body is not particularly limited, but a prismatic shape is preferable, and a quadrangular prismatic shape is more preferable. In addition, since it is preferable that the honeycomb formed body to become the first honeycomb structure (or honeycomb segment) and the honeycomb formed body to become the second honeycomb structure (or honeycomb segment) have different partition wall thicknesses and cell densities, it is necessary to prepare honeycomb formed bodies having shapes that match these.

When the end face of the honeycomb formed body is rectangular, it is desirable that the length of the longer side is 20 to 50 mm. This is because when the end face of the honeycomb formed body is rectangular and the length of the longer side is 20 to 50 mm, the shape of the honeycomb structure (or honeycomb segment) produced is sufficiently small, so that even if a large temperature difference occurs across the entire heat exchanger, damage is unlikely to occur.

(Drying process)
Next, a drying step is carried out to dry the honeycomb formed body to obtain a dried honeycomb body.
In the drying step, the honeycomb molded body is dried using a dryer such as a microwave dryer, a hot air dryer, a dielectric dryer, a reduced pressure dryer, a vacuum dryer, or a freeze dryer to produce a dried honeycomb body.
By this step, a dried honeycomb body for the first honeycomb structure (or honeycomb segment) and a dried honeycomb body for the second honeycomb structure (or honeycomb segment) are produced.

(Honeycomb aggregate manufacturing process)
In this process, an adhesive layer paste, which has approximately the same composition as the raw material paste but has a higher SiC content than the raw material paste, is used to bond the dried honeycomb bodies via the adhesive layer paste to produce an aggregate of the dried honeycomb bodies (honeycomb aggregate).
In this case, by undergoing the degreasing, impregnation, and bonding processes, the two types of honeycomb dried bodies having different shapes as described above, i.e., a honeycomb dried body for a first honeycomb structure (or honeycomb segment) and a honeycomb dried body for a second honeycomb structure (or honeycomb segment), are combined and bonded together to form the heat exchanger of the present invention.

(Columnar body manufacturing process)
In this step, the honeycomb aggregate having a rectangular column shape is cut using a cutting tool such as a diamond cutter to process it into a cylindrical shape.

(Coating layer paste application process)
Next, a paste for a coating layer is applied to the area where the coating layer shown in FIGS. 1A and 1B or 3A and 3B is to be formed, and then dried and solidified to form a layer that will become the coating layer.
The coating layer paste may have substantially the same composition as the raw material paste, but may contain a higher proportion of SiC than the raw material paste.
After the degreasing, impregnation and adhesion steps described below, a coating layer paste application step may be carried out, and the coating layer paste may be dried and solidified to form the coating layer.

(Degreasing, impregnation, and adhesion processes)
In this step, a honeycomb aggregate that has been machined into a cylindrical shape and on which a layer that will become a coating layer is formed is subjected to a degreasing step, and then an impregnation and adhesion step is subsequently performed.
Therefore, in this process, silicon (metallic silicon) is placed on the bottom of a ceramic container with an open top, and a honeycomb aggregate is placed inside the container via a support made of porous ceramic. After a degreasing process, the impregnation and bonding process is carried out.

In the degreasing process, the honeycomb dried body assembly dried in the drying process is heated at a temperature of 400 to 1400°C to burn off the organic matter contained in the honeycomb dried body. The degreasing temperature is preferably 400 to 600°C. The atmosphere is preferably an oxygen-containing atmosphere.

This is followed by the impregnation and adhesion process. That is, the degreased body that has undergone the degreasing process is heated at a temperature of 1420 to 2000°C to produce a composite material of silicon carbide and silicon. The heating temperature is preferably 1420 to 1600°C. The atmosphere is preferably an inert gas atmosphere.
By heating at the above temperature, the molten silicon (silicon metal) penetrates by capillary action through the porous support into the gaps between the silicon carbide particles that make up the partitions of the degreased body, and the silicon is impregnated into the gaps.

In addition, the molten silicon also penetrates between the degreased body of the adhesive layer paste and the degreased body of the coating layer paste, forming a composite material with the silicon carbide contained in the degreased body, forming an adhesive layer that firmly bonds the honeycomb structures (or honeycomb segments) together and also forms a coating layer that covers the outer periphery.
In the above temperature range, the heat exchanger obtained is an unsintered honeycomb structure in which most of the silicon carbide, which is a component of the heat exchanger, is not sintered and silicon carbide particles and silicon exist independently. That is, the partition walls constituting the honeycomb structure (or honeycomb segment) are composed of a composite material of silicon and silicon carbide in which independent silicon carbide particles are bonded by silicon existing around them. This unsintered honeycomb structure has a high Young's modulus and is difficult to deform, and is useful as a heat exchanger.

Furthermore, by going through the above process, it is possible to produce a heat exchanger in which a first honeycomb structure in which a large number of cells that become the first flow passages for fluid are arranged in parallel in the longitudinal direction separated by partition walls, and a second honeycomb structure in which a large number of cells that become the second flow passages for fluid are arranged in parallel in the longitudinal direction separated by partition walls are combined so that the first flow passages and the second flow passages are perpendicular to each other.

In the method for manufacturing a heat exchanger of the present invention, a degreasing process is performed to degrease each of the dried honeycomb bodies, followed by a normal firing process to produce a honeycomb fired body made of a porous sintered silicon carbide body, after which a bonding process for bonding the honeycomb fired bodies together, a processing process for processing them into a circumferential shape, an impregnation/bonding process for impregnating them with silicon, a process for forming a coating layer, etc. may be performed.

(Catalyst supporting process)
In the present invention, by supporting a catalyst such as a fuel reforming catalyst on the heat exchanger of the present invention, it can be used as a fuel reforming catalyst.
As a method for supporting a catalyst such as a fuel reforming catalyst made of a precious metal such as rhodium on the above-mentioned heat exchanger, for example, a method in which a honeycomb structure is immersed in a solution containing precious metal particles or complexes, then pulled out and heated can be mentioned.

Figure 2A is a perspective view showing a retaining mat used when storing the heat exchanger of the above configuration in a reformer, and Figure 2B is an explanatory diagram showing a method of wrapping the retaining mat around the heat exchanger.

The retaining mat 50 has a convex portion 51a and a concave portion 51b at both ends of the mat 51, and mat openings 51c, 51d, 51e, 51f, 51g, and 51h are formed so that the cells 23, which are the fluid inlet and fluid outlet, are exposed when the mat 50 is wrapped around the heat exchanger 100. As shown in FIG. 2B, when the mat 50 is wrapped around the heat exchanger 100, the cells 23, which are the fluid inlet and fluid outlet, are exposed through the mat openings 51c, 51d, 51e, 51f, 51g, and 51h, and by pushing the retaining mat 50 into the metal container that constitutes the reformer and fixing it, the mat 50 is securely stored in the reformer with the cells 23, which are the fluid inlet and fluid outlet, exposed.

Figure 3A is a perspective view showing a schematic diagram of a heat exchanger according to a second embodiment of the present invention, and Figure 3B is a cross-sectional view of the heat exchanger shown in Figure 3A along line B-B.

As shown in Figures 3A and 3B, the heat exchanger 200 according to the second embodiment of the present invention is a columnar heat exchanger 200 configured by combining a first ceramic honeycomb structure 110 in which a number of cells 113 serving as first fluid flow paths are arranged in parallel in the longitudinal direction separated by partition walls 112, and a second ceramic honeycomb structure 120 in which a number of cells 123 serving as second fluid flow paths are arranged in parallel in the longitudinal direction separated by partition walls 122, such that the first flow paths (cells 113) and the second flow paths (cells 123) are perpendicular to each other.

In the heat exchanger 200 according to the second embodiment, a second honeycomb structure 120 is arranged on both sides of a first honeycomb structure 110 via an adhesive layer 118. As in the first embodiment, the first honeycomb structure 110 and the second honeycomb structure 120 may be composed of one honeycomb segment as shown in Figures 3A and 3B, or three or more honeycomb segments may be bonded together via an adhesive layer to form one first honeycomb structure 110 or the second honeycomb structure 120.

In Figures 3A and 3B, the extension direction of the cells 113 constituting the first honeycomb structure 110 is the vertical direction, and the extension direction of the cells 123 constituting the second honeycomb structure 120 is the horizontal direction, and the flow paths are perpendicular to each other, making it easy to circulate two types of fluids (gases) and allowing efficient heat exchange.

In the heat exchanger 200 shown in Figures 3A and 3B, cells 113 that become the first flow passages of the first honeycomb structure 110 open on both end faces, and cells 123 that become the second flow passages of the second honeycomb structure 120 open on the outer peripheral face, and the entire surface of the first honeycomb structure 110 that constitutes the outer peripheral face is covered with a coating layer 132, and the surface of the second honeycomb structure 120 that constitutes the outer peripheral face is covered with coating layers 131a and 131b except for a square-shaped opening 134 with chamfered corners 134a.

Therefore, even if a large thermal stress acts, the thermal stress does not concentrate at the corner 134a of the opening 134, and damage, etc., is unlikely to occur in the surrounding coating layers 131a, 131b, and 132.

The corners 134a of the opening 134 may be chamfered with a straight C-shape, but it is preferable that they are chamfered with an R-shape having a curvature radius of 1 to 15 mm.
In order to increase the heat exchange efficiency, the percentage of the area of the opening 134 to the total area of the opening 134 and the coating layers 131a, 131b, and 132 (opening/opening+coating) is preferably 72 to 93%, and more preferably 75 to 85%. The thickness of the coating layers 131a, 131b, and 132 is preferably 0.1 to 0.5 mm, and more preferably 0.2 to 0.3 mm.
The volume of the heat exchanger according to the second embodiment of the present invention is preferably 1.2 to 3.2 liters.

In the heat exchanger of the present invention, when the thermal expansion coefficients of the first honeycomb structure and the second honeycomb structure are C1, the thermal expansion coefficient of the adhesive layer is C2, and the thermal expansion coefficient of the coating layer is C3, the thermal expansion coefficients are set so as to satisfy C1<C2≦C3.
That is, the thermal expansion coefficient C2 of the adhesive layer is larger than the thermal expansion coefficient C1 of the first honeycomb structure and the second honeycomb structure. It is also preferable that the thermal expansion coefficient C2 of the adhesive layer and the thermal expansion coefficient C3 of the coating layer are the same, or that the thermal expansion coefficient C3 of the coating layer is larger than the thermal expansion coefficient C2 of the adhesive layer.

In the heat exchanger of the present invention, when the thermal expansion coefficients of the first honeycomb structure, the second honeycomb structure, the adhesive layer and the coating layer are set as described above, even if a temperature difference occurs between the second honeycomb structure and the first honeycomb structure and the heat exchanger expands partially, the adhesive layer and the coating layer are more likely to expand, so that cracks are less likely to occur in the adhesive layer and the coating layer.
Furthermore, when the heat exchanger is housed in a metal container such as a reformer via a retaining mat, even if the metal container thermally expands due to an increase in temperature, the adhesive layer and coating layer also expand in the same way as the metal container, so there is little change in the holding force of the retaining mat, and the heat exchanger can be reliably prevented from falling off the metal container.

In the heat exchanger of the present invention, the thermal expansion coefficient C1 of the first honeycomb structure and the second honeycomb structure, the thermal expansion coefficient C2 of the adhesive layer, and the thermal expansion coefficient C3 of the coating layer are set to satisfy C1<C2≦C3, and further, it is desirable that the thermal expansion coefficient C1 of the first honeycomb structure and the second honeycomb structure is 2.80 to 4.50× ^10−6K − ¹ , and the thermal expansion coefficient C2 of the adhesive layer and the thermal expansion coefficient C3 of the coating layer are 3.05 to 4.75× ^10−6K − ¹ .

In the heat exchanger of the present invention, it is preferable that the difference between the thermal expansion coefficient C3 and the thermal expansion coefficient C1 be expressed by the following inequality (1).
C2-C1≧0.05×10 ^-6 ...(1)
That is, it is desirable that the thermal expansion coefficient C2 of the adhesive layer and the thermal expansion coefficient C3 of the coating layer are larger than the thermal expansion coefficient C1 of the first honeycomb structure and the second honeycomb structure by 0.05×10 ⁻⁶ or more.

In the heat exchanger according to the first embodiment, three of the first honeycomb structures and four of the second honeycomb structures are arranged alternately, and in the heat exchanger according to the second embodiment, the second honeycomb structures are arranged on both sides of the first honeycomb structure. However, the heat exchanger of the present invention is not limited to these embodiments. As long as a first honeycomb structure in which a large number of cells serving as a first flow passage for a fluid are arranged in parallel in the longitudinal direction separated by a partition wall and a second honeycomb structure in which a large number of cells serving as a second flow passage for a fluid are arranged in parallel in the longitudinal direction separated by a partition wall are combined so that the first flow passage and the second flow passage are perpendicular to each other, the number of combinations is not limited, but it is preferable that the first honeycomb structures and the second honeycomb structures are arranged alternately.

The reformer of the present invention is a reformer including the above-mentioned heat exchanger,
The second honeycomb structure is configured to allow exhaust gas discharged from an internal combustion engine and flowing through a main exhaust pipe to pass therethrough, and the first honeycomb structure is configured such that a reforming catalyst is supported on the partition walls and exhaust gas that flows into an exhaust gas recirculation pipe branched off from the main exhaust pipe to pass therethrough.

FIG. 4 is an explanatory diagram showing a schematic diagram of a fuel reforming gasoline engine system equipped with a reformer of the present invention.
In this fuel reforming gasoline engine system 300, an exhaust pipe 42 through which exhaust gas discharged from a gasoline engine 41 passes is branched into a main exhaust pipe 43 and an exhaust gas recirculation pipe 44 (hereinafter referred to as an EGR pipe), and a reformer 60 containing a heat exchanger 100 functioning as a fuel reforming catalyst and a retaining mat 50 is disposed in the EGR pipe 44. As shown in FIG. 4, the main exhaust pipe 43 is also connected to the reformer 60, and gas flowing through the main exhaust pipe 43 is introduced into and discharged from the cells of the second honeycomb structure through mat openings 51c, 51d, 51e, 51f, 51g, and 51h of the retaining mat 50 and mat openings which are the fluid inlet and fluid outlet of the heat exchanger 100, while gas flowing through the EGR pipe 44 passes through the cells of the first honeycomb structure constituting the heat exchanger 100 and undergoes heat exchange. In addition, in the figure, 45 is an automatic valve that opens and closes as appropriate depending on the situation.

A reforming fuel injection device 46 is disposed at the entrance of the reformer 60 in the EGR pipe 44, and reforming fuel is injected from this reforming fuel injection device 46. Meanwhile, a port-type fuel injection device 48 is disposed in the intake pipe 49 of the gasoline engine 41, and engine fuel is injected at the time of intake.

In the reformer 60, the fuel injected from the reforming fuel injection device 46 reacts with the water vapor in the exhaust gas and the hydrocarbons that are the main components of gasoline fuel, activated by the fuel reforming catalyst supported on the heat exchanger 100, and is converted into hydrogen, carbon monoxide, and methane. The hydrogen-containing gas with this composition mixes with the intake air of the engine and also with the fuel injected from the port-type fuel injection device 48, forming an air-fuel mixture that enters the gasoline engine 41 and is burned inside the gasoline engine 41. The hydrogen mixed into the air-fuel mixture can increase the combustion speed and improve the combustion efficiency of the gasoline engine 41.

In the first honeycomb structure in the reformer 60, heat is absorbed by an endothermic reaction in the presence of the above-mentioned fuel reforming catalyst, but in the heat exchanger of the present invention, the heat of the exhaust gas can be effectively supplied from the second honeycomb structure to the first honeycomb structure, the temperature drop is suppressed, and the performance as a reforming catalyst that reforms the fuel of an internal combustion engine (gasoline engine) to improve fuel efficiency can be effectively exhibited. Furthermore, when the heat exchanger is made of silicon carbide and silicon, it is not easily corroded by the hydrogen contained in the reformed gas.
Furthermore, since the thermal expansion coefficients of the honeycomb structure, adhesive layer and coating layer constituting the heat exchanger are appropriately set, cracks are unlikely to occur in the adhesive layer and coating layer.

(Example)
EXAMPLES Hereinafter, examples will be given that more specifically disclose the embodiments of the present invention, however, the present invention is not limited to these examples.

Example 1
56.3% by weight of coarse silicon carbide powder having an average particle size of 22 μm and 24.1% by weight of fine silicon carbide powder having an average particle size of 0.5 μm were mixed, and 4.4% by weight of an organic binder (methyl cellulose), 0.8% by weight of a lubricant (UNILUB manufactured by NOF Corporation), 0.8% by weight of glycerin, 2.2% by weight of oleic acid, and 11.4% by weight of water were added to the resulting mixture and kneaded to obtain a raw material paste.

Then, using a mold for manufacturing the honeycomb segments that constitute the first honeycomb structure and a mold for manufacturing the honeycomb formed body that constitutes the second honeycomb structure, the raw material paste was extrusion molded to produce a honeycomb formed body.

The honeycomb molded body for the honeycomb segment constituting the first honeycomb structure produced by the above process had a rectangular end face shape of 14.6 mm x 105.4 mm, a length of 140 mm, a cell density of 47 cells/ ^cm2 (300 cells/ ^inch2 ), and a partition wall thickness of 0.25 mm, and the honeycomb molded body for the honeycomb segment constituting the second honeycomb structure had a rectangular end face shape of 14.6 mm x 70 mm, a length of 105 mm, a cell density of 47 cells/ ^cm2 (300 cells/ ^inch2 ), and a partition wall thickness of 0.25 mm.

Then, the raw honeycomb molded body was dried using a microwave dryer to produce a dried honeycomb molded body.

Next, 53.5% by weight of coarse silicon carbide powder having an average particle size of 22 μm was mixed with 22.9% by weight of fine silicon carbide powder having an average particle size of 0.5 μm, and 4.4% by weight of organic binder (methyl cellulose), 0.8% by weight of lubricant (UNILUBE manufactured by NOF Corp.), 0.8% by weight of glycerin, 2.2% by weight of oleic acid, and 15.4% by weight of water were added to the resulting mixture and kneaded to obtain a paste for the adhesive layer.

The obtained honeycomb dried bodies for the honeycomb segments constituting the first honeycomb structure and the honeycomb dried bodies for the honeycomb segments constituting the second honeycomb structure were used, and the adhesive layer paste was used as an adhesive to combine and dry the honeycomb dried bodies so that the assembly (honeycomb assembly) of the honeycomb dried bodies after the manufacturing process had the configuration of the heat exchanger 100 shown in Figures 1A and 1B. The adhesive layer paste was applied so that the thickness of each adhesive layer was 1 mm.

The resulting honeycomb dried body assembly was machined into a cylindrical shape with a diameter of 105 mm and a length of 140 mm so that both end faces of the first honeycomb structure would become the end faces of the first honeycomb structure. Furthermore, a coating layer paste was applied to the second honeycomb structure that constitutes the outer peripheral surface of the cylindrical honeycomb assembly so that a rectangular opening of 120 mm in length and 14.6 mm in width with a chamfered corner with a radius of curvature of 10 mm was formed, and the thickness of the coating layer was 0.3 mm on the other parts of the periphery. The coating layer paste used was the same as the adhesive layer paste described above. The opening length was measured along the curved surface of the periphery.

The honeycomb dried body assembly with the coating layer formed thereon was placed, via a support, in a ceramic container with metal silicon placed on the bottom, and then carried into a heating furnace. After a degreasing process in which the honeycomb dried body was degreased at 400°C in an air atmosphere, the atmosphere inside the heating furnace was replaced with argon gas, and the impregnation and adhesion process was carried out under heating conditions of 1450°C for 1 hour.

The obtained heat exchanger having the configuration shown in FIG. 1 had an outer diameter of 105 mm and a length of 140 mm, the honeycomb segments 11 constituting the first and second honeycomb structures had a cell density of 47 cells/ ^cm2 (300 cells/ ^inch2 ), and the partition wall thickness was 0.25 mm.
The first honeycomb structure was one honeycomb segment, and the second honeycomb structure was two honeycomb segments bonded together with an adhesive layer to form one first and second honeycomb structure, with three first honeycomb structures 10 and four second honeycomb structures 20 arranged alternately with adhesive layers 18 in between. In addition, the flow paths of the honeycomb segment 21 constituting the second honeycomb structure 20 and the flow paths of the honeycomb segment 11 constituting the first honeycomb structure 10 were arranged so as to be perpendicular to each other.

(Comparative Example 1)
A heat exchanger was manufactured in the same manner as in Example 1, except that the adhesive layer paste and the coating layer paste had the same compositions as the raw material paste.

(evaluation)
[Canning]
The manufactured heat exchangers of Example 1 and Comparative Example 1 were wrapped with a retaining mat as shown in Figures 2A and 2B and housed in a cylindrical metal case. It was confirmed that the retaining mat was not damaged and that there was no gas leakage from the outer periphery of the heat exchanger.

[Durability and heat exchange efficiency test]
A gas at 900°C was passed through the cells constituting the second honeycomb structure of the heat exchangers of Example 1 and Comparative Example 1, which were housed in a metal case having a similar structure to the reformer, at a flow rate of 50 g/sec, and a gas at 500°C was passed through the cells constituting the first honeycomb structure at a flow rate of 15 g/sec for one minute, and then it was observed whether or not cracks had occurred in the adhesive layer or coating layer of the heat exchanger.

As a result, it was found that no cracks occurred in the adhesive layer or coating layer of the heat exchanger of Example 1, and the heat exchanger functioned well. In addition, the gas flowing out of the first honeycomb structure was heated to 710°C, proving that the heat exchanger exhibited good heat exchange performance.

On the other hand, cracks occurred in the adhesive layer of the heat exchanger in Comparative Example 1, and it was found that cracks are likely to occur in the adhesive layer when the honeycomb structure and the adhesive layer have the same thermal expansion coefficient.

Reference Signs List 10, 110 First honeycomb structure 11, 21 Honeycomb segment 12, 22, 112, 122 Partition wall 13, 23, 113, 123 Cell 18, 118 Adhesive layer 20, 120 Second honeycomb structure 31a, 31b, 32, 131a, 131b, 132 Coat layer 34, 134 Opening 34a, 134a Corner 41 Gasoline engine 42 Exhaust pipe 43 Main exhaust pipe 44 Exhaust gas recirculation pipe (EGR pipe)
45 Automatic valve 46 Reforming fuel injection device 48 Port type fuel injection device 49 Intake pipe 50 Retaining mat 51 Mat 51a Convex portion 51b Concave portions 51c, 51d, 51e, 51f, 51g, 51h Mat opening 60 Reformer 100, 200 Heat exchanger 300 Gasoline engine system

Claims (9)

A columnar heat exchanger comprising a first honeycomb structure in which a number of cells serving as first fluid flow passages are arranged in parallel in the longitudinal direction with partition walls therebetween, and a second honeycomb structure in which a number of cells serving as second fluid flow passages are arranged in parallel in the longitudinal direction with partition walls therebetween, the first flow passages and the second flow passages being combined via an adhesive layer such that the first flow passages and the second flow passages are perpendicular to each other,
The heat exchanger has the first flow passage opening at both end surfaces and the second flow passage opening at an outer circumferential surface,
Except for the opening of the second honeycomb structure formed on the outer peripheral surface, other portions are covered with a coating layer,
A heat exchanger characterized in that, when the thermal expansion coefficients of the first honeycomb structure and the second honeycomb structure are C1, the thermal expansion coefficient of the adhesive layer is C2, and the thermal expansion coefficient of the coating layer is C3, C1 < C2 ≦ C3 is satisfied. (correction)
2. The heat exchanger according to claim 1, wherein the thermal expansion coefficient C1 is 2.80 to 4.50×10 ⁻⁶ K ⁻¹ , and the thermal expansion coefficients C2 and C3 are 3.05 to 4.75×10 ⁻⁶ K ^{−1 .} 3. The heat exchanger according to claim 1, wherein a difference between the thermal expansion coefficient C3 and the thermal expansion coefficient C1 is expressed by the following inequality (1).
C2-C1≧0.05×10 ^-6 ...(1) The heat exchanger according to any one of claims 1 to 3, wherein three of the first honeycomb structures and four of the second honeycomb structures are alternately arranged with adhesive layers interposed therebetween. A heat exchanger according to any one of claims 1 to 4, in which a catalyst is supported on the partition walls of the cells that constitute the first honeycomb structure. The heat exchanger according to any one of claims 1 to 5, wherein the first honeycomb structure and the second honeycomb structure are made of silicon carbide and silicon. The heat exchanger according to any one of claims 1 to 6, wherein the adhesive layer and the coating layer are made of silicon carbide and silicon. A reformer comprising the heat exchanger according to any one of claims 1 to 7,
A reformer characterized in that the second honeycomb structure is configured to allow exhaust gas emitted from an internal combustion engine and flowing through a main exhaust pipe to pass therethrough, and the first honeycomb structure has a reforming catalyst supported on its partition walls and is configured to allow exhaust gas that flows into an exhaust gas recirculation piping branched off from the main exhaust pipe to pass therethrough. The reformer according to claim 8, wherein the heat exchanger is housed via a retaining mat in a metal container connected to the main exhaust pipe and the exhaust gas recirculation pipe.

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