Heat exchangers and reformers

Abstract

To provide a heat exchanger in which a coat layer is hard to be broken, even if the heat exchanger is held with high pressure through a holding mat and the like, when the heat exchanger formed with the coat layer on an outer peripheral surface is used as a reforming catalyst.SOLUTION: In a columnar heat exchanger, a first honeycomb structure which becomes a first circulation path of a fluid in which a large number of cells is separated with partition walls and arranged in parallel in a longitudinal direction, and a second honeycombs structure which becomes a second circulation path of the fluid in which a large number of cells is separated from partition walls and arranged in parallel in a longitudinal direction are assembled so as to make the first circulation path and the second circulation path orthogonal to each other. In the heat exchanger, the first circulation path opens on both end surfaces, and the second circulation path opens on an outer peripheral surface. The entire surface of the first honeycomb structure configuring the outer peripheral surface is coated by a coat layer, and a surface of the second honeycomb structure configuring the outer peripheral surface is coated by the coat layer except for a square-shaped opening portion with chamfered corners.SELECTED DRAWING: Figure 1A

Description

[Technical field]

[0001] The present invention relates to a heat exchanger and a reformer. [Background technology]

[0002] 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 (H2) 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.

[0003] The above-mentioned 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 to promote the reforming reaction.

[0004] Patent Document 1 does not disclose the specific materials or configuration of the fuel reforming catalyst. However, in order to promote the reaction in the reformer, a temperature of 600°C or higher is required, and it is considered that the material constituting the fuel reforming catalyst must be able to withstand temperatures of 600°C or higher and have a heat exchange function.

[0005] 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 fired. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2015-166591 A [Patent Document 2] Japanese Patent Application Publication No. 7-151478 Summary of the Invention [Problem to be solved by the invention]

[0007] It is assumed that a heat exchanger such as that disclosed in Document 2 is used as a heat exchanger carrying a catalyst for the fuel reforming catalyst disclosed in Patent Document 1. In this case, the heat exchanger is housed in a metal container via a retaining mat. Since the exhaust gas introduced into the heat exchanger is under high pressure, the heat exchanger needs to be firmly held by the retaining mat, and the pressure from the retaining mat on the heat exchanger needs to be high. In order to firmly hold the heat exchanger with the support mat, a coating layer is formed on the outer periphery of the heat exchanger, but this coating layer is easily damaged by thermal stress. In addition, when damage such as cracks occurs in the coating layer, the cracks also propagate to the honeycomb structure, causing the fluids flowing through the flow passages to leak out and become mixed.

[0008] The present invention has been made to solve the above problems, and has an object to provide a heat exchanger having a coating layer formed on its outer peripheral surface, in which the coating layer is less likely to be damaged by thermal stress even when the heat exchanger is held at high pressure via a retaining mat or the like, when the heat exchanger is used as a reforming catalyst, and a reformer equipped with such a heat exchanger. [Means for solving the problem]

[0009] 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 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, the first flow passages and the second flow passages being combined with each other so that they 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, The entire surface of the first honeycomb structure constituting the outer peripheral surface is covered with a coating layer, The surface of the second honeycomb structure constituting the outer circumferential surface is characterized in that it is covered with a coating layer except for a rectangular opening having chamfered corners.

[0010] According to the heat exchanger of the present invention, the first flow passage and the second flow passage are combined so as to be perpendicular to each other, thereby improving heat exchange performance and enabling two types of fluids performing heat exchange to flow smoothly from different directions.

[0011] In addition, since the surface of the second honeycomb structure constituting the outer peripheral surface has square openings with chamfered corners, even if a large thermal stress acts on the surface, the thermal stress does not concentrate on the corners, and the surrounding coating layer is less likely to be damaged. In addition, since the coating layer is not damaged, the fluid flowing through the first flow passage and the fluid flowing through the second flow passage can be prevented from mixing with each other.

[0012] In the heat exchanger of the present invention, it is desirable that the corners of the rectangular opening are chamfered with a radius of curvature of 1 to 15 mm. In the heat exchanger of the present invention, if the corners of the rectangular opening are chamfered with a radius of curvature of 1 to 15 mm, thermal stress is less likely to concentrate on the corners, and damage to the coating layer is less likely to occur.

[0013] If the radius of curvature of the corners of the opening is less than 1 mm, the stress concentration at the corners cannot be alleviated, and the coating layer may be prone to damage. On the other hand, if the radius of curvature of the corners of the opening exceeds 15 mm, the opening area becomes small and the heat exchange capacity decreases.

[0014] In the heat exchanger of the present invention, it is desirable that on the surface of the second honeycomb structure constituting the outer peripheral surface, the percentage of the area of ​​the opening to the total area of ​​the opening and the coating layer (opening / opening+coating layer) is 72 to 93%. In the heat exchanger of the present invention, when the ratio of the area of ​​the opening to the total area of ​​the opening and the coating layer on the surface of the second honeycomb structure constituting the outer peripheral surface (opening / opening+coating layer) is 72 to 93%, the area of ​​the opening is relatively large, so that the heat exchange efficiency can be improved, and thermal stress is less likely to concentrate at the corners, making it less likely that breakage will occur.

[0015] If the ratio of the area of ​​the opening to the total area of ​​the opening and the coating layer (opening / opening+coating layer) is less than 72%, the area of ​​the opening will be too small, resulting in reduced heat exchange capacity. On the other hand, if the ratio of the area of ​​the opening to the total area of ​​the opening and the coating layer (opening / opening+coating layer) is more than 93%, the area of ​​the coating layer will be too small, resulting in the coating layer being more susceptible to damage.

[0016] In the heat exchanger of the present invention, the coating layer preferably has a thickness of 0.1 to 0.5 mm. In the heat exchanger of the present invention, when the thickness of the coating layer is 0.1 to 0.5 mm, the thickness of the coating layer is relatively thin, so that the thermal stress applied to the outermost surface of the coating layer can be reduced and breakage is unlikely to occur.

[0017] If the thickness of the coating layer is less than 0.1 mm, the coating layer is too thin and prone to damage, while if the thickness of the coating layer exceeds 0.5 mm, the coating layer is too thick, causing a temperature difference between the outermost surface of the coating layer and the part in contact with the honeycomb structure, again making the coating layer prone to damage.

[0018] 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 in the heat exchanger. 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, the contact area between the second honeycomb structures and the first honeycomb structures is large, and heat exchange can be performed efficiently.

[0019] In the heat exchanger of the present invention, it is preferable that a catalyst is supported on the partition walls of the cells constituting the first honeycomb structure.

[0020] In the heat exchanger of the present invention, when a catalyst is supported on the partition walls of the cells constituting the first honeycomb structure, a reforming reaction can be carried out inside the first honeycomb structure, and the catalyst can fully function as a reforming catalyst by receiving heat from the exhaust gas flowing into the second honeycomb structure.

[0021] 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.

[0022] 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 be damaged even when a large temperature difference occurs.

[0023] In the heat exchanger of the present invention, the first honeycomb structure and the second honeycomb structure are bonded to each other via an adhesive layer, and it is desirable that the adhesive layer be 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.

[0024] 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 emitted 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.

[0025] When the reformer of the present invention is configured as described above, the second honeycomb structure can effectively supply heat of the exhaust gas to the first honeycomb structure, and the reformer can effectively perform the performance of reforming the fuel of the 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 hydrogen contained in the reformed gas.

[0026] 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, the heat exchanger can be held firmly in place and can function as a reformer. [Brief description of the drawings]

[0027] [Figure 1A] FIG. 1A is a perspective view illustrating a heat exchanger according to a first embodiment of the present invention. [Figure 1B] FIG. 1B is a cross-sectional view of the heat exchanger shown in FIG. 1A taken along line AA. [Figure 2A] FIG. 2A is a perspective view that typically shows a support mat used when housing the heat exchanger having the above-described configuration in a reformer. [Figure 2B] FIG. 2B is an explanatory diagram that shows a schematic diagram of a method for winding the support mat around a heat exchanger. [Figure 3A] FIG. 3A is a perspective view illustrating a heat exchanger according to a second embodiment of the present invention. [Figure 3B] FIG. 3B is a cross-sectional view of the heat exchanger shown in FIG. 3A taken along line BB. [Figure 4] FIG. 4 is an explanatory diagram that shows a schematic diagram of a fuel reformed gasoline engine system equipped with a reformer of the present invention.

[0028] 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 including 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, the first flow passages and the second flow passages being combined with each other so that they are perpendicular to each other, The heat exchanger is characterized in that the first flow passage opens at both end faces and the second flow passage opens at the outer peripheral face, the entire surface of the first honeycomb structure constituting the outer peripheral face is covered with a coating layer, and the surface of the second honeycomb structure constituting the outer peripheral face is covered with a coating layer except for a rectangular opening having chamfered corners.

[0029] 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 the line AA. As shown in Figures 1A and 1B, the heat exchanger 100 of the present invention is a columnar heat exchanger 100 configured by combining a first honeycomb structure 10 in which a number of cells 13 serving as 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 serving as 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.

[0030] In the heat exchanger 100 shown in Figs. 1A and 1B, three first honeycomb structures 10 and four second honeycomb structures 20 are alternately arranged with adhesive layers 18 interposed therebetween. In the heat exchanger 100 shown in Figs. 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, an 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.

[0031] The second honeycomb structure 20 is constituted by two honeycomb segments 21 bonded with an adhesive layer 18, but may be constituted by one honeycomb structure 20, or may be constituted by three or more honeycomb segments 21 bonded with an adhesive layer 18. Therefore, in the present invention, the second honeycomb structure 20 refers to an assembly of one or two or more honeycomb segments 21 sandwiched between the first honeycomb structures 10. 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.

[0032] 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 of the cells are perpendicular to each other, making it easy to circulate two types of fluids (gases) and enabling efficient heat exchange.

[0033] 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 peripheral face, the entire surface of the first honeycomb structure 10 that constitutes the peripheral face is covered with a coating layer 32, and the surface of the second honeycomb structure 20 that constitutes the peripheral face is covered with coating layers 31a and 31b except for a rectangular opening 34 with chamfered corners 34a.

[0034] Therefore, even when a large thermal stress acts, the thermal stress does not concentrate on the corner 34a of the opening 34, and damage or the like is unlikely to occur in the surrounding coating layers 31a, 31b, 32. Furthermore, since the coating layers 31a, 31b, 32 are not damaged, it is possible to prevent the fluid flowing through the cell 13 serving as the first flow passage and the fluid flowing through the cell 23 serving as the second flow passage from mixing with each other.

[0035] The corners 34a of the opening 34 may be chamfered with a straight C-shape to prevent stress concentration, but as shown in Fig. 1A, it is preferable to chamfer them with a R-shape with a radius of curvature of 1 to 15 mm. The radius of curvature of the R-shape is more preferably 5 to 10 mm. In the case of the C-shape, the chamfering depth is preferably 3.5 to 7 mm. The chamfering depth refers to the distance from the vertex to the point where the straight line of the C-shape reaches the side, assuming that there is no chamfering. In order to increase the heat exchange efficiency, the opening 34 and the coating layers 31a and 31b are b The ratio of the area of ​​the openings 34 to the total area (openings / openings+coating layer) is preferably 72 to 93%, and more preferably 75 to 85%. The thickness of the coating layers 31a, 31b, and 32 is preferably 0.1 to 0.5 mm, and more preferably 0.2 to 0.3 mm.

[0036] 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. In this specification, when the term "heat exchanger of the present invention" is used, it is intended to describe characteristics, conditions, etc. common to the heat exchanger according to the first embodiment described above, the heat exchanger according to the second embodiment described below, and the like, components constituting the heat exchangers according to all embodiments of the present invention, and components related to the above heat exchangers.

[0037] The volume of the heat exchanger according to the first embodiment of the present invention is desirably 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.

[0038] If the volume of the heat exchanger is less than 1.2 liters, the volume of the heat exchanger is too small, making it difficult to support a sufficient amount of catalyst, whereas if the volume of the heat exchanger exceeds 3.2 liters, the capacity of the reformer becomes too large, making it difficult to install it in a vehicle.

[0039] In the heat exchanger of the present invention, the material of the first honeycomb structure and the second honeycomb structure or the honeycomb segments which are the constituent members thereof is not particularly limited, and examples thereof include oxide-based ceramics such as cordierite, alumina, silica, mullite, etc., carbide-based ceramics such as silicon carbide, zirconium carbide, titanium carbide, tantalum carbide, tungsten carbide, etc., nitride-based ceramics such as aluminum nitride, silicon nitride, boron nitride, titanium nitride, etc., and composite materials of these ceramics and metals, etc. Among these, a composite material of silicon carbide is preferable, and a composite material of silicon and silicon carbide is particularly desirable.

[0040] 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.

[0041] When the 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, thereby forming an adhesive layer consisting of silicon carbide and silicon, and a heat exchanger can be created in which multiple honeycomb structures (or honeycomb segments) are bonded together with an adhesive layer consisting of silicon carbide and silicon.

[0042] The adhesive layer for bonding 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 a raw material paste containing silicon carbide to the side walls in order to bond the honeycomb molded bodies together, drying the honeycomb molded bodies after bonding them together, and bringing them into contact with molten silicon.

[0043] In the heat exchanger of the present invention, the partition walls of the first honeycomb structure and the second honeycomb structure desirably have a uniform thickness. Specifically, the partition walls of the first honeycomb structure that supports the catalyst desirably have a thickness of 0.08 to 0.30 mm, and more desirably 0.10 to 0.20 mm. Since the partition walls of the first honeycomb structure are thin, the surface area is increased, making it possible to support a larger amount of catalyst.

[0044] 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. Since the partition walls of the second honeycomb structure are thick, the heat capacity is increased and a large amount of heat can be supplied to the first honeycomb structure.

[0045] 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.

[0046] 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.

[0047] 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 46 to 124 cells / cm. 2 (300~800 pieces / inch 2 ) is preferable, and 62 to 93 pieces / cm 2 (400~600 pieces / inch 2 ) is more preferable because it has a large surface area and can support a large amount of catalyst. The cell density in a cross section perpendicular to the longitudinal direction of the second honeycomb structure is 16 to 78 cells / cm. 2 (100~500 pieces / inch 2 ) is preferable, and 31 to 62 pieces / cm 2 (200~400 pieces / inch 2) is more preferable. The heat capacity becomes large, and a large amount of heat can be supplied to the first honeycomb structure.

[0048] 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, or Pd, more preferably Rh. The catalyst supported on a support is preferably Rh / ZrO2 or Rh / CoO2. The support may be other ceramics such as silica or alumina.

[0049] [Heat exchanger manufacturing method] 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 described 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.

[0050] The heat exchanger of the present invention includes, for example, a forming step of forming a honeycomb formed body having a plurality of cells arranged in parallel in the longitudinal direction with partition walls therebetween by forming a raw material paste containing silicon carbide powder, an organic binder, etc., a drying step of drying the honeycomb formed body formed by the forming step, and a honeycomb aggregate fabricating step of bonding the honeycomb formed body to be a first honeycomb structure and the honeycomb formed bodies to be a second honeycomb structure, both of which have been dried by the drying step, via an adhesive layer paste to form an adhesive layer, to fabricate an aggregate of honeycomb formed bodies (honeycomb aggregate). The heat exchanger can be manufactured by carrying out a process comprising the steps of: a columnar body fabrication process in which the honeycomb aggregate is processed into a cylindrical shape; a coating layer paste application process 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 bonding process in which the columnar body to which the coating layer paste has been applied is degreased, heated to a high temperature and impregnated with molten silicon to manufacture a heat exchanger consisting of a honeycomb structure made of a composite material of silicon carbide and silicon, an adhesive layer and a coating layer.

[0051] (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.

[0052] The organic binder is not particularly limited, but examples thereof include methyl cellulose, carboxymethyl cellulose, hydroxyethyl cellulose, polyethylene glycol, phenol resin, epoxy resin, and the like, and two or more of these may be used in combination.

[0053] The pore-forming agent is not particularly limited, and examples thereof include acrylic resin, coke, starch, etc. The pore-forming agent refers to a material used for introducing pores into the inside of a honeycomb structure (or a honeycomb segment) when manufacturing the honeycomb structure (or a honeycomb segment).

[0054] The molding aid is not particularly limited, but examples thereof include ethylene glycol, dextrin, fatty acid, fatty acid soap, polyalcohol, etc., and two or more of these may be used in combination.

[0055] The dispersion medium is not particularly limited, but examples thereof include water, organic solvents such as benzene, and alcohols such as methanol, and two or more of these may be used in combination.

[0056] When preparing the raw material paste, it is desirable to mix and knead the ingredients. The ingredients may be mixed using a mixer, an attritor, or the like, or kneaded using a kneader, or the like.

[0057] 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.

[0058] 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. 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 manufactured honeycomb structure (or honeycomb segment) is sufficiently small, so that even if a large temperature difference occurs throughout the heat exchanger, breakage or the like is unlikely to occur.

[0059] (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.

[0060] (Honeycomb assembly manufacturing process) In this step, an adhesive layer paste having substantially the same composition as the raw material paste is used, and the dried honeycomb bodies are bonded via the adhesive layer paste to produce an assembly of the dried honeycomb bodies (honeycomb assembly). In this case, the two types of dried honeycomb bodies having different shapes as described above, i.e., a dried honeycomb body for a first honeycomb structure (or honeycomb segment) and a dried honeycomb body for a second honeycomb structure (or honeycomb segment), are combined and bonded together through the degreasing, impregnation and bonding processes to form the heat exchanger of the present invention.

[0061] (Cylinder 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.

[0062] (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. 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 heated to solidify, thereby forming a coating layer.

[0063] (Degreasing, impregnation, and adhesion processes) In this process, the honeycomb aggregate, which has been processed into a cylindrical shape and on which a layer that will become a coating layer has been formed, is subjected to a degreasing process, and then to an impregnation and adhesion process. 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 the degreasing process, the impregnation and bonding process is carried out.

[0064] In the degreasing process, the aggregate of the dried honeycomb bodies dried in the drying process is heated at a temperature of 400 to 1400° C. to burn off the organic matter contained in the dried honeycomb bodies. The degreasing temperature is more preferably 400 to 600° C. The atmosphere is preferably an oxygen-containing atmosphere.

[0065] Subsequently, the impregnation and adhesion process is carried out. That is, the degreased body after 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 more 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.

[0066] 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, which acts as an adhesive layer that firmly bonds the honeycomb structures (or honeycomb segments) together and also forms a coating layer that covers the outer periphery. Within the above temperature range, the heat exchanger obtained is an unsintered honeycomb structure in which most of the silicon carbide, which is a constituent of the heat exchanger, is not sintered, and silicon carbide particles and silicon exist independently. That is, the partition walls that constitute 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, making it useful as a heat exchanger.

[0067] Furthermore, by undergoing the above-mentioned steps, it is possible to produce a heat exchanger in which a first honeycomb structure in which a number of cells that become 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 number of cells that become second flow passages for fluid are arranged in parallel in the longitudinal direction separated by partition walls, are combined such that the first flow passages and the second flow passages are perpendicular to each other.

[0068] 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, and then a normal firing process is performed to produce a honeycomb fired body made of a porous silicon carbide sintered body. Then, a bonding process is performed to bond the honeycomb fired bodies together, a processing process is performed to process the honeycomb fired bodies into a circumferential shape, an impregnation / bonding process is performed to impregnate the honeycomb fired bodies with silicon, a process is performed to form a coating layer, and other processes may be performed.

[0069] (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.

[0070] FIG. 2A is a perspective view showing a retaining mat used when housing the heat exchanger having the above-described configuration in a reformer, and FIG. 2B is an explanatory diagram showing a method of wrapping the retaining mat around the heat exchanger.

[0071] The retaining mat 50 has convex portions 51a and concave portions 51b at both ends of the mat 51, and has mat openings 51c, 51d, 51e, 51f, 51g, and 51h formed therein so that the cells 23, which are the fluid inlet and fluid outlet, are exposed when the retaining mat 50 is wrapped around the heat exchanger 100. As shown in FIG. 2B, when the retaining 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 a metal container that constitutes the reformer and fixing it, the retaining mat 50 is securely stored in the reformer with the cells 23, which are the fluid inlet and fluid outlet, exposed.

[0072] FIG. 3A is a perspective view illustrating a heat exchanger according to a second embodiment of the present invention, and FIG. 3B is a cross-sectional view of the heat exchanger illustrated in FIG. 3A taken along line BB.

[0073] As shown in Figures 3A and 3B, a heat exchanger 200 according to a second embodiment of the present invention is a cylindrical heat exchanger 200 configured by combining a first ceramic honeycomb structure 110 in which a number of cells 113 serving as first fluid flow passages 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 passages are arranged in parallel in the longitudinal direction separated by partition walls 122, such that the first flow passages (cells 113) and the second flow passages (cells 123) are perpendicular to each other.

[0074] In a heat exchanger 200 according to the second embodiment, a second honeycomb structure 120 is disposed 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 Fig. 3A and Fig. 3B, or three or more honeycomb segments may be bonded together via an adhesive layer to form one first honeycomb structure 110 or form the second honeycomb structure 120.

[0075] 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 of the cells 123 are perpendicular to each other, making it easy to circulate two types of fluids (gases) and enabling efficient heat exchange.

[0076] 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 circumferential face, and the entire surface of the first honeycomb structure 110 that constitutes the outer circumferential face is covered with a coating layer 132, and the surface of the second honeycomb structure 120 that constitutes the outer circumferential face is covered with coating layers 131a and 131b except for a rectangular opening 134 with chamfered corners 134a.

[0077] Therefore, even if a large thermal stress acts, the thermal stress does not concentrate on the corner 134a of the opening 134, and damage or the like is unlikely to occur in the surrounding coating layers 131a, 131b, 132. Furthermore, since the coating layers 131a, 131b, 132 are not damaged, it is possible to prevent the fluid flowing through the cell 113 serving as the first flow passage and the fluid flowing through the cell 123 serving as the second flow passage from mixing with each other.

[0078] Corner 134a of opening 134 may be chamfered with a straight C-shape to prevent stress concentration, but is preferably chamfered with a R-shape with a radius of curvature of 1 to 15 mm. The radius of curvature of the R-shape is more preferably 5 to 10 mm. In the case of C-shape, the chamfering depth is preferably 3.5 to 7 mm. In order to increase the heat exchange efficiency, the opening 134 and the coating layers 131a and 131b are b The ratio of the area of ​​the openings 134 to the total area (openings / openings+coating layer) 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 desirably 1.2 to 3.2 liters.

[0079] The materials of the honeycomb structure constituting the heat exchanger according to the second embodiment of the present invention, the type of catalyst supported, and other configurations of the heat exchanger are the same as those of the honeycomb structure according to the first embodiment, and the manufacturing method of the heat exchanger is also the same as that of the honeycomb structure according to the first embodiment, so the description thereof will be omitted.

[0080] In addition, in the heat exchanger of the first embodiment, three of the first honeycomb structures and four of the second honeycomb structures are arranged alternately, and in the heat exchanger of 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, and as long as a first honeycomb structure in which a number of cells serving as a first flow passage for fluid are arranged in parallel in the longitudinal direction separated by a partition wall and a second honeycomb structure in which a number of cells serving as a second flow passage for 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.

[0081] 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 emitted 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.

[0082] FIG. 4 is an explanatory diagram that shows a schematic diagram of a fuel reformed 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) in the middle of the exhaust pipe, and a reformer 60 containing a heat exchanger 100 and a retaining mat 50 functioning as a fuel reforming catalyst is disposed in the middle of the EGR pipe 44. As shown in FIG. 4, the main exhaust pipe 43 is also connected to the reformer 60, and the 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 the gas flowing through the EGR pipe 44 passes through the cells of the first honeycomb structure constituting the heat exchanger 100 and heat exchange is performed. In addition, in the figure, 45 is an automatic valve that opens and closes as appropriate depending on the situation.

[0083] 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 an intake pipe 49 of the gasoline engine 41, and fuel for the engine is injected at the time of intake.

[0084] 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 combusted inside the gasoline engine 41. The hydrogen mixed into the air-fuel mixture can increase the combustion speed, thereby improving the combustion efficiency of the gasoline engine 41.

[0085] 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 efficiently 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 efficiently 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. In addition, since the rectangular openings of the coating layer constituting the heat exchanger are chamfered, the coating layer is less likely to be damaged.

[0086] (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.

[0087] Example 1

[0088] 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 (UNILUBE manufactured by NOF Corp.), 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.

[0089] After that, the raw material paste was extrusion molded using a mold for manufacturing honeycomb segments that constitute the first honeycomb structure, and a mold for manufacturing a honeycomb molded body that constitutes the second honeycomb structure, to produce a honeycomb molded body.

[0090] The honeycomb formed 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 × 105.4 mm, a length of 140 mm, and a cell density of 47 cells / cm. 2 (300 pieces / inch 2), the thickness of the partition wall is 0.25 mm, and the honeycomb formed body for the honeycomb segment constituting the second honeycomb structure has an end face shape of a rectangle of 14.6 mm × 70 mm, a length of 105 mm, and a cell density of 47 cells / cm 2 (300 pieces / inch 2 ), and the thickness of the partition was 0.25 mm.

[0091] Next, the green honeycomb formed body was dried using a microwave dryer to prepare a dried honeycomb formed body.

[0092] The obtained dried honeycomb bodies for the honeycomb segments constituting the first honeycomb structure and the dried honeycomb bodies for the honeycomb segments constituting the second honeycomb structure were combined using the raw material paste as an adhesive so that the assembly of the dried honeycomb bodies after the manufacturing process (honeycomb assembly) had the configuration of the heat exchanger 100 shown in Fig. 1. The thickness of each adhesive layer was set to 1 mm.

[0093] The obtained honeycomb dried body aggregate was machined into a cylindrical shape with a diameter of 102 mm and a length of 140 mm so that both end faces of the honeycomb structure became the end faces of the first honeycomb structure. Furthermore, the second honeycomb structure constituting the outer peripheral surface of the cylindrical honeycomb aggregate was coated with a coating material on the other parts of the outer periphery so that a rectangular opening of 120 mm in length and 14.6 mm in width with a rounded corner chamfered with a curvature radius of 10 mm was formed. The coating material was the same as the adhesive described above. The opening length was measured along the curved surface of the outer periphery.

[0094] 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 an impregnation and adhesion process was carried out under heating conditions of 1450°C for 1 hour.

[0095] The obtained heat exchanger having the configuration shown in FIG. 1 had an outer diameter of 102 mm and a length of 140 mm, and the cell density of the honeycomb segments 11 constituting the first and second honeycomb structures was 47 cells / cm. 2 (300 pieces / inch 2 ), and the thickness of the partition is 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.

[0096] Comparative Example 1 A heat exchanger was manufactured in the same manner as in Example 1, except that the other parts of the outer periphery were coated with a coating material so as to form a rectangular opening of 120 mm in length and 14.6 mm in width with no chamfered corners.

[0097] (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.

[0098] [Durability and heat exchange efficiency test] A gas at 800°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 openings of the heat exchanger.

[0099] As a result, it was found that no cracks were generated in the opening of the heat exchanger according to Example 1, and that by making the shape of the opening a rectangle of length 120 mm x width 14.6 mm with the corners chamfered with a radius of curvature of 10 mm, no cracks were generated in the coating layer, and the heat exchanger functioned well. In addition, the gas flowing out of the first honeycomb structure was heated to 653°C, proving that the heat exchanger exhibited good heat exchange performance.

[0100] On the other hand, cracks occurred at the opening of the heat exchanger according to Comparative Example 1, and it was found that if the opening is a rectangle with no chamfering, stress is concentrated at the corners, making it easy for cracks to occur. [Explanation of symbols]

[0101] 10, 110 First honeycomb structure 11, 21 Honeycomb segment 12, 22, 112, 122 bulkhead 13, 23, 113, 123 cells 18, 118 Adhesive layer 20, 120 Second honeycomb structure 31a, 31b, 32, 131a, 131b, 132 Coating layers 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 Fuel injection device for reforming 48 Port fuel injection system 49 Suction piping 50 Retaining Mat 51 Matt 51a Convex part 51b Recess 51c, 51d, 51e, 51f, 51g, 51h Matte opening 60 Reformer 100, 200 heat exchanger 300 Gasoline Engine System

Claims

1. A columnar heat exchanger including 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, the first flow passages and the second flow passages being combined with each other so 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, The entire surface of the first honeycomb structure constituting the outer peripheral surface is covered with a coating layer, The surface of the second honeycomb structure constituting the outer peripheral surface is covered with a coating layer except for a rectangular opening having chamfered corners, A heat exchanger comprising: said first honeycomb structure and said second honeycomb structure bonded to each other via an adhesive layer.

2. 2. The heat exchanger according to claim 1, wherein corners of the rectangular opening are chamfered to have a radius of curvature of 1 to 15 mm.

3. A heat exchanger as described in claim 1 or 2, wherein on the surface of the second honeycomb structure constituting the outer surface and sandwiched between the first honeycomb structure, the percentage of the ratio of the area of ​​the opening to the sum of the area of ​​the opening and the coating layer (opening / opening + coating layer) is 72 to 93%.

4. The heat exchanger according to any one of claims 1 to 3, wherein the coating layer has a thickness of 0.1 to 0.5 mm.

5. The heat exchanger according to any one of claims 1 to 4, wherein three of the first honeycomb structures and four of the second honeycomb structures are alternately arranged in the heat exchanger.

6. 6. The heat exchanger according to claim 1, wherein a catalyst is supported on partition walls of cells constituting the first honeycomb structure.

7. 7. The heat exchanger according to claim 1, wherein the first honeycomb structure and the second honeycomb structure are made of silicon carbide and silicon.

8. A heat exchanger according to any one of claims 1 to 7, wherein the adhesive layer comprises silicon carbide and silicon.

9. A reformer comprising the heat exchanger according to any one of claims 1 to 8, 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.

10. 10. The reformer according to claim 9, 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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