JP7633819B2 - 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 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.

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

In the reforming method described in Patent Document 1, the pressure from the exhaust gas environment is high, so the heat exchanger needs to be maintained at a high canning pressure. When using the heat exchanger described in Reference 2 in the method described in Reference 1, a cylindrical heat exchanger is sometimes required instead of a prismatic shape due to the installation location, piping arrangement, and other factors. However, when the heat exchanger described in Reference 2 is deformed into a cylindrical shape and used in the method described in Reference 1, problems arise in that the heat exchanger is damaged by the high canning pressure, and when the canning pressure is set to a level that does not damage the heat exchanger, the position of the heat exchanger is shifted due to the exhaust gas pressure.

The present invention was made to solve the above problems, and aims to provide a heat exchanger that is less susceptible to damage and misalignment, and a reformer equipped with such a heat exchanger.

The heat exchanger of the present invention is a heat exchanger in which a first honeycomb structure in which a number of cells serving as a first flow passage for a fluid are arranged in parallel in the longitudinal direction separated by partition walls and a second honeycomb structure in which a number of cells serving as a second flow passage for a fluid are arranged in parallel in the longitudinal direction separated by partition walls are combined so that the first flow passage and the second flow passage intersect, and the heat exchanger has a substantially cylindrical shape in which the first flow passage opens at both end faces and the second flow passage opens at the outer peripheral surface, and of the outer peripheral surface of the heat exchanger, the first The entire surface of the honeycomb structure is covered with a coating layer, and the surface of the second honeycomb structure on the outer peripheral surface of the heat exchanger has an opening region where the second flow passage opens onto the outer peripheral surface of the heat exchanger, and plugging regions are provided on both end faces of the heat exchanger relative to the opening region, and the second flow passage is plugged with a plugging material, and the ratio of the area of the opening region to the total area of the opening region and the plugging region is 72 to 93%.

According to the heat exchanger of the present invention, the first flow passage and the second flow passage are combined so as to intersect, thereby improving heat exchange performance and allowing two types of fluids performing heat exchange to flow smoothly from different directions.
In this specification, the term "intersection" refers to a state in which the first flow passage and the second flow passage intersect on different planes (so-called three-dimensional intersection). In addition, the intersection of the first flow passage and the second flow passage can also be said to mean that the extension direction of the first flow passage and the extension direction of the second flow passage intersect.

Furthermore, in the heat exchanger of the present invention, the entire surface of the first honeycomb structure on the outer peripheral surface of the approximately cylindrical shape is covered with a coating layer, and a portion of the surface of the second honeycomb structure is a plugged region in which the second flow passage is plugged with a plugging material.
The portion covered with the coating layer has a higher mechanical strength than the portion not covered with the coating layer. Also, the sealing region has a higher mechanical strength than the opening region. Therefore, the portion covered with the coating layer and the sealing region can be used as the portion to which the canning pressure is applied.
By canning so that pressure is applied to the portion covered with the coating layer and the sealing region, the heat exchanger is less likely to be damaged even if the canning pressure is increased.

Furthermore, in the heat exchanger of the present invention, a portion of the second flow passage is sealed with a sealing material. Since no fluid flows through the sealed second flow passage, temperature changes due to fluid flow are slow, and the second flow passage functions as a mass (heat capacity) that stores heat. Furthermore, the sealing material present in the second flow passage itself functions as a mass (heat capacity) that stores heat. Therefore, even if the temperature of the exhaust gas flowing into the second honeycomb structure drops, a high temperature can be maintained, and the reforming ability at the inlet can be improved.

In the heat exchanger of the present invention, the ratio of the area of the opening area to the total area of the opening area and the plugging area is 72 to 93%. Therefore, there is a good balance between the ratio of the second flow passage (opening area) used for heat exchange with the first honeycomb structure under normal conditions and the ratio of the second flow passage (plugging area) that functions as a heat capacity when the exhaust gas temperature drops, and it is possible to improve the reforming at the inlet when the exhaust gas temperature drops while ensuring sufficient heat exchange efficiency under normal conditions.

In the heat exchanger of the present invention, it is desirable that the second flow passage is sealed with the sealing material to a depth of 1 to 30 mm from the outer peripheral surface of the heat exchanger.

When the second flow passage is sealed with the sealing material to a depth of 1 to 30 mm from the outer circumferential surface of the heat exchanger in the sealing region, the heat exchanger is less likely to be damaged even when the canning pressure is increased, and it can also fully function as a heat storage mass.

In the heat exchanger of the present invention, it is desirable that the second honeycomb structure is arranged on both sides of the first honeycomb structure.

In the heat exchanger of the present invention, when the second honeycomb structure is arranged on both sides of the first honeycomb structure, heat can be transmitted from the second honeycomb structures on both sides, and heat can be efficiently supplied to the first honeycomb structure.

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 both 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 both 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. Furthermore, they are less likely to corrode due to the hydrogen contained in the reformed gas.

In the heat exchanger of the present invention, it is desirable that the first honeycomb structure and the second honeycomb structure each be made up of a plurality of ceramic honeycomb segments bonded together via an adhesive layer.

In the heat exchanger of the present invention, if the first honeycomb structure and the second honeycomb structure each have a structure in which multiple ceramic honeycomb segments are bonded together via an adhesive layer, the size of each honeycomb segment can be reduced, and the adhesive layer acts as a buffer, making it less likely to break even if a large temperature difference occurs across the entire heat exchanger.

In the heat exchanger of the present invention, it is preferable 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, it has excellent thermal conductivity and can further improve the heat exchange performance between the first honeycomb structure and the second honeycomb structure.

In the heat exchanger of the present invention, it is desirable that the volume of the heat exchanger is 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 volume of the heat exchanger is too small, making it difficult to support a sufficient amount of catalyst, while if the volume of the heat exchanger exceeds 3.2 liters, the capacity of the heat exchanger becomes too large, making it difficult to install it in a vehicle.

In the heat exchanger of the present invention, the first honeycomb structure and the second honeycomb structure are arranged alternately, and it is desirable that the heat exchanger includes three layers of the first honeycomb structure and four layers of the second honeycomb structure.

In the heat exchanger of the present invention, the first honeycomb structures and the second honeycomb structures are arranged alternately, and when the heat exchanger includes three layers of the first honeycomb structures and four layers of the second honeycomb structures, the contact area between the second honeycomb structures and the first honeycomb structures is large, and efficient heat exchange can be performed.

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

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.

In the reformer of the present invention, it is desirable that the heat exchanger is housed via a retaining mat in a metal casing 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 via a retaining mat in a metal casing connected to the main exhaust pipe and exhaust gas recirculation piping, damage to the coating layer and sealing area is unlikely to occur even if the heat exchanger becomes hot.

FIG. 1 is a perspective view illustrating a heat exchanger according to a first embodiment of the present invention. FIG. 2 is a cross-sectional view of the heat exchanger shown in FIG. 1 taken along line II-II. FIG. 3 is a perspective view that diagrammatically shows one example of a honeycomb aggregate for manufacturing the heat exchanger shown in FIG. FIG. 4 is a perspective view that shows a schematic view of a support mat that is used when the heat exchanger shown in FIG. 1 is housed in a reformer. FIG. 5 is an explanatory view that illustrates a method for wrapping the support mat shown in FIG. 4 around the heat exchanger shown in FIG. FIG. 6 is a perspective view illustrating a heat exchanger according to a second embodiment of the present invention. FIG. 7 is a cross-sectional view of the heat exchanger shown in FIG. 6 taken along line VII-VII. FIG. 8 is an explanatory diagram showing a schematic diagram of a fuel reformed 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 heat exchanger obtained by combining a first honeycomb structure having a large number of cells arranged in parallel in the longitudinal direction across partition walls to become first flow passages for a fluid, and a second honeycomb structure having a large number of cells arranged in parallel in the longitudinal direction across partition walls to become second flow passages for a fluid, such that the first flow passages and the second flow passages intersect, the heat exchanger having a substantially cylindrical shape with the first flow passages opening at both end faces and the second flow passages opening at an outer peripheral surface, and the first and second flow passages of the outer peripheral surface of the heat exchanger are arranged in a substantially cylindrical shape with the first and second flow passages opening at both end faces and the second flow passages opening at an outer peripheral surface of the heat exchanger. the entire surface of the honeycomb structure is covered with a coating layer, and among the outer peripheral surface of the heat exchanger, the surface of the second honeycomb structure has an opening region where the second flow passage opens to the outer peripheral surface of the heat exchanger, and plugging regions which are provided on both end face sides of the heat exchanger with respect to the opening region and where the second flow passage is plugged with a plugging material, and the ratio of the area of the opening region to the total area of the opening region and the plugging region is 72 to 93%.

FIG. 1 is a perspective view showing a heat exchanger according to a first embodiment of the present invention, and FIG. 2 is a cross-sectional view taken along line II-II of the heat exchanger shown in FIG.
As shown in Figures 1 and 2, the heat exchanger 100 is a generally cylindrical heat exchanger formed by combining a first honeycomb structure 10 in which a number of first cells 13, which serve as first flow passages for fluid, are arranged in the longitudinal direction separated by a first partition wall 12, and a second honeycomb structure 20 in which a number of second cells 23, which serve as second flow passages for fluid, are arranged in the longitudinal direction separated by a second partition wall 22, such that the first flow passages (first cells 13) and the second flow passages (second cells 23) intersect.
In addition, when there is no particular distinction between the first honeycomb structure and the second honeycomb structure, they are also simply referred to as honeycomb structures. Similarly to the honeycomb structure, when there is no particular distinction between the first cells and the second cells, and the first partition walls and the second partition walls, they are also simply referred to as cells and partition walls.

In Figures 1 and 2, the extension direction of the first cells 13 constituting the first honeycomb structure 10 is the vertical direction (the direction indicated by the arrow z in Figures 1 and 2). The extension direction of the second cells 23 constituting the second honeycomb structure 20 is the horizontal direction (the direction indicated by the arrow y in Figure 1). In the first honeycomb structure 10 and the second honeycomb structure 20, the flow passages intersect with each other, making it easy to circulate two types of fluids (especially gases) and allowing efficient heat exchange.

The heat exchanger 100 shown in Figures 1 and 2 includes first honeycomb structures 10 and second honeycomb structures 20 arranged alternately with adhesive layers 19 interposed therebetween, and includes three layers of the first honeycomb structures 10 and four layers of the second honeycomb structures 20.
1 and 2, one first honeycomb segment 11 constitutes one layer of the first honeycomb structure 10, but two or more first honeycomb segments 11 may be bonded together via an adhesive layer to constitute one layer of the first honeycomb structure 10. Therefore, in the present invention, an assembly of one or more first honeycomb segments 11 sandwiched between second honeycomb structures 20 is counted as one layer of the first honeycomb structure 10. The first honeycomb segment is a member having the same structure as the first honeycomb structure.

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 understood to mean the heat exchanger according to the first embodiment described above, the heat exchanger according to the second embodiment described below, and the like, and to describe characteristics, conditions, etc. common to the components constituting the heat exchangers according to all embodiments of the present invention, and the components related to the above-mentioned heat exchangers.

In the heat exchanger 100 shown in FIGS. 1 and 2, one layer of the second honeycomb structure 20 is formed by bonding two second honeycomb segments 21 together via an adhesive layer 18 .
The second honeycomb structures 20 are counted in the same way as the first honeycomb structures 10, and an assembly of one or two or more second honeycomb segments 21 sandwiched between the first honeycomb structures 10 is referred to as one layer of the second honeycomb structure 20. However, the second honeycomb structure 20 may be located on the outermost side, in which case the assembly of one or two or more outermost second honeycomb segments 21 is also one layer of the second honeycomb structure 20.
When there is no particular distinction between the first honeycomb segment and the second honeycomb segment, they are also simply referred to as honeycomb segments.

The first honeycomb structure and the second honeycomb structure constituting the heat exchanger of the present invention may each be composed of one ceramic honeycomb segment, or may be composed of multiple ceramic honeycomb segments bonded together via an adhesive layer.

The number of honeycomb segments constituting the first honeycomb structure and the second honeycomb structure may be the same or different from each other.

In the heat exchanger of the present invention, it is preferable that the second honeycomb structure is disposed on both sides of the first honeycomb structure.
When the second honeycomb structure is arranged on both sides of the first honeycomb structure, heat can be transmitted from the second honeycomb structures on both sides, and heat can be efficiently supplied to the first honeycomb structure.

In a first embodiment of the heat exchanger of the present invention, the heat exchanger is composed of first honeycomb structures and second honeycomb structures arranged alternately, and desirably includes three layers of the first honeycomb structures and four layers of the second honeycomb structures.
When the heat exchanger includes three layers of the first honeycomb structure and four layers of the second honeycomb structure, in which the first honeycomb structure and the second honeycomb structure are alternately arranged, the contact area between the second honeycomb structure and the first honeycomb structure is large, and efficient heat exchange can be performed.

In the heat exchanger 100 having an approximately cylindrical shape shown in Figures 1 and 2, first cells 13 which serve as first flow passages of the first honeycomb structure 10 open on both end faces, and second cells 23 which serve as second flow passages of the second honeycomb structure 20 open on the outer circumferential face.
A part of the outer peripheral surface is covered with a coating layer 32. The coating layer 32 has a coating layer 32a that covers the entire surface of the first honeycomb structure 10 that constitutes the outer peripheral surface, and a coating layer 32b that covers a part of the surface of the second honeycomb structure 20 that constitutes the outer peripheral surface.
The portion covered with the coating layer 32 has a higher mechanical strength than the portion not covered with the coating layer, and therefore the portion covered with the coating layer 32 can be used as a portion to which the canning pressure is applied.

In addition, since the entire surface of the first honeycomb structure 10 that constitutes the outer peripheral surface is covered with the coating layer 32a, it is possible to prevent the fluid flowing through the first cells 13 that form the first flow passages from mixing with the fluid flowing through the second cells 23 that form the second flow passages.

The thickness of the coating layer is not particularly limited, but is preferably 0.1 to 0.5 mm.
If the thickness of the coating layer is less than 0.1 mm, the coating layer is too thin and may be damaged by the pressure during canning, whereas if the thickness of the coating layer is more than 0.5 mm, the coating layer is too thick and may be damaged by the temperature difference between the outermost surface of the coating layer and the part in contact with the honeycomb structure.

In the heat exchanger of the present invention, a portion of the second flow passage is sealed with a sealant.
Since no fluid flows through the plugged second flow passage, the temperature change due to the flow of the fluid becomes slow, and the plugging material present in the second flow passage itself functions as a mass (heat capacity) that stores heat. Therefore, even if the temperature of the exhaust gas flowing into the second honeycomb structure drops, a high temperature can be maintained, and the reforming ability at the inlet can be improved.

The surface of the second honeycomb structure 20 constituting the outer peripheral surface has an opening region A1 (region surrounded by a dashed line in FIG. 1) where the second cells 23 serving as the second flow passages are open to the outer peripheral surface, and plugging regions A2 and A3 (regions surrounded by dashed lines in FIG. 1) where the second cells 23 serving as the second flow passages are plugged with plugging materials 31 a and 31 b, respectively. The plugging regions A2 and A3 are disposed on both end face sides (both end face sides in the z direction) of the heat exchanger 100 with respect to the opening region A1.
The sealing regions A2 and A3 have a higher mechanical strength than the opening region A1, and therefore can be used as the regions to which the canning pressure is applied.

The ratio of the area of the open region A1 to the total area of the open region A1 and the sealing regions A2 and A3 is 72 to 93%, and preferably 72 to 83%.
When the above ratio is 72 to 93%, a good balance is achieved between the ratio of the second flow passages (open area) used for heat exchange with the first honeycomb structure under normal conditions and the ratio of the second flow passages (sealed area) that function as a heat capacity when the exhaust gas temperature drops, and the reforming ability at the inlet portion when the exhaust gas temperature drops can be improved while sufficiently ensuring heat exchange efficiency under normal conditions.
When the above ratio is 72 to 83%, the balance between the ratio of the second flow passages (open area) used for heat exchange with the first honeycomb structure under normal conditions and the ratio of the second flow passages (sealed area) functioning as a heat capacity when the exhaust gas temperature drops is particularly good, and the reforming ability at the inlet portion when the exhaust gas temperature drops can be further improved while further ensuring the heat exchange efficiency under normal conditions.

If the above ratio is less than 72%, the ratio of the second flow passages (open area) used for heat exchange with the first honeycomb structure under normal conditions is too small, resulting in a decrease in the heat exchange efficiency under normal conditions. On the other hand, if the above ratio exceeds 93%, the ratio of the second flow passages (sealed area) that function as a heat capacity when the exhaust gas temperature drops is too small, resulting in a decrease in the reforming ability at the inlet when the exhaust gas temperature drops. Furthermore, the area for holding the second honeycomb structure during canning is too small, which may damage the heat exchanger.

In the sealed region, the second flow passage is desirably sealed with a sealing material to a depth of 1 to 30 mm from the outer circumferential surface of the heat exchanger.
When the second flow passage is sealed with a sealant to a depth of 1 to 30 mm from the outer circumferential surface of the heat exchanger, the heat exchanger is less likely to be damaged even when the canning pressure is increased, and the heat exchanger can fully function as a heat storage mass.
If the second flow passages are sealed with a plugging material only to a depth of less than 1 mm from the outer peripheral surface of the heat exchanger, the plugging material may not function sufficiently as a heat capacity. On the other hand, if the second flow passages are sealed with a plugging material to a depth of more than 30 mm from the outer peripheral surface of the heat exchanger, cracks may occur in the honeycomb structure due to uneven drying during the formation of the plugged region.

In this specification, the second flow passage being plugged with a plugging material refers to a state in which the plugging material penetrates from the outer peripheral surface of the heat exchanger in the depth direction of the second flow passage. Therefore, when the plugging material does not penetrate into the second flow passage in the depth direction, for example, when only the surface of the second honeycomb structure constituting the outer peripheral surface of the heat exchanger is covered with the same material as the plugging material, this does not correspond to a state in which the second flow passage is plugged with a plugging material, and this portion is not included in the plugged region.
However, a coating layer may be further formed on the surface of the second honeycomb structure constituting the plugging region.

The plugged regions are provided on both end face sides of the heat exchanger with respect to the open region. Therefore, even if the second flow passages are plugged with plugging material in the surface of the second honeycomb structure constituting the outer peripheral surface of the heat exchanger in a region other than the both end face sides of the open region, such a region does not correspond to the plugged region. Therefore, for example, even if the second flow passages are plugged with plugging material in the region where the coating layer 32b of the heat exchanger 100 shown in FIG. 1 is formed, the region is not included in the plugged region.
In addition, in the heat exchanger 100 shown in FIG. 1, the region where the coating layer 32b is formed covers a portion of the surface of the second honeycomb structure constituting the outer peripheral surface, but is not located on either end face side of the heat exchanger relative to the opening region. Therefore, even if the coating layer penetrates in the depth direction of the second flow passage, this region is not included in the area of the plugged region.

The depth of the sealing material from the outer peripheral surface of the heat exchanger can be confirmed by observing a cut surface of the heat exchanger cut along the direction in which the second flow passage extends.

In the heat exchanger of the present invention, the material of the honeycomb structure or the honeycomb segments which are its constituent members is 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. Of these, composite materials of silicon carbide are preferable, and composite materials of silicon and silicon carbide are particularly preferable.

The specific configuration of the composite material made of silicon and silicon carbide is not particularly limited, but 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.

The material of the adhesive layer that bonds the honeycomb structures (or honeycomb segments) together is not particularly limited, but it is desirable to use a composite material in which silicon fills the gaps between the 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 to bond the honeycomb bodies together, drying the honeycomb bodies after bonding them together, and then contacting them with molten silicon.

The thickness of the adhesive layer that bonds the honeycomb structures (or honeycomb segments) together is not particularly limited, but it is desirable for it to be 0.5 to 2.0 mm.

The material of the coating layer is not particularly limited, but is desirably a composite material in which silicon fills the gaps between silicon carbide particles, similar to the honeycomb structure (or honeycomb segment) and adhesive layer.
As described below, such a composite material can be produced by applying a raw material paste containing silicon carbide to the portion of the outer surface of a cylindrical honeycomb dried body that will become the first honeycomb structure, drying it, and then contacting it with molten silicon.

The material of the plug is not particularly limited, but is desirably a composite material in which silicon fills the gaps between silicon carbide particles, similar to the honeycomb structure (or honeycomb segment), adhesive layer, and coating layer.
As described below, such a composite material can be produced by filling a raw material paste containing silicon carbide into the openings of the outer surface of a cylindrical honeycomb dried body, which will become the cells of the second honeycomb structure, drying the body, and then contacting the body 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 are uniform. Specifically, the thickness of the partition walls of the first honeycomb structure that support 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 (first 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 ). When the first cell density is in the above range, the surface area of the first honeycomb structure becomes large, and a large amount of catalyst can be supported.
Furthermore, the cell density (second cell density) in a cross section perpendicular to the longitudinal direction of the cells of the second honeycomb structure is desirably 16 to 78 cells/ ^cm2 (100 to 500 cells/ ^inch2 ), and more desirably 31 to 62 cells/ ^cm2 (200 to 400 cells/ ^inch2 ). When the second cell density is within the above range, the heat capacity of the second honeycomb structure 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 the first cells constituting the first honeycomb structure support a catalyst, and it is more preferable that the first cells support a fuel reforming catalyst.
The catalyst is preferably Co, Ni, Rh, Pt or Pd, and more preferably Rh.
The catalyst may be supported on a carrier and supported in the first cell constituting the first honeycomb structure. The catalyst supported on the carrier is preferably Rh/ _ZrO2 or Rh/ _CoO2 . The carrier may be other ceramics such as silica or alumina.

The volume of the heat exchanger according to the first embodiment of the present invention is preferably 1.2 to 3.2 liters.
If the volume of the heat exchanger is 1.2 to 3.2 liters, the heat exchanger has an appropriate volume, so that it can be easily mounted on a vehicle or the like and can fully exert its effect as a heat exchanger.
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, while if the volume of the heat exchanger exceeds 3.2 liters, the capacity of the heat exchanger becomes too large, making it difficult to install it in a vehicle.

[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; a honeycomb aggregate production process for bonding the honeycomb molded body to become the first honeycomb structure dried by the drying process and the honeycomb molded body to become the second honeycomb structure via an adhesive layer paste to produce an aggregate of honeycomb molded bodies (honeycomb aggregate); a columnar body production process for processing the honeycomb aggregate into an approximately cylindrical shape; The heat exchanger can be manufactured by carrying out a coating layer paste application process in which a coating layer paste is applied to part of the outer periphery of a columnar body that has been machined into a columnar shape to form a coating layer paste layer, a plugging paste filling process in which plugging paste is filled into some of the cells that open to the outer periphery of the columnar body, and a degreasing, impregnation, and adhesion process in which the columnar body that has been applied with the coating layer paste and filled with the plugging paste is degreased, heated to a high temperature, and impregnated with molten silicon to manufacture a honeycomb structure made of a composite material of silicon carbide and silicon, an adhesive layer, a coating layer, and a plugging material.

(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 the first honeycomb segment) and the honeycomb formed body to become the second honeycomb structure (or the second honeycomb segment) have different partition wall thicknesses and cell densities, it is necessary to prepare honeycomb formed bodies having shapes that match these.

If the end face of the honeycomb molded body is rectangular, it is desirable for the length of the longer side to be 20 to 120 mm.

(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 the first honeycomb segment) and a dried honeycomb body for the second honeycomb structure (or the second honeycomb segment) are produced.

(Honeycomb aggregate 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, 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 a first honeycomb segment) and a honeycomb dried body for a second honeycomb structure (or a second honeycomb segment), are combined and bonded together to form the heat exchanger of the present invention.

FIG. 3 is a perspective view that typically shows one example of a honeycomb aggregate for manufacturing the heat exchanger shown in FIG.
The honeycomb dried body assembly 90 shown in Fig. 3 is a prismatic honeycomb assembly 90 in which first honeycomb structures 10 and second honeycomb structures 20 are alternately stacked and bonded via adhesive layers 19. The honeycomb assembly 90 has three layers of first honeycomb structures 10 and four layers of second honeycomb structures 20. One layer of the first honeycomb structure 10 is made of one first honeycomb segment 11. One layer of the second honeycomb structure 20 is made of two second honeycomb segments 21 bonded via adhesive layers 18.

(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 form a cylindrical shape having second flow passages of a second honeycomb structure opening on the outer circumferential surface.

(Coating layer paste application process)
The paste for the coating layer is applied to the entire surface of the first honeycomb structure constituting the outer peripheral surface of the pillar-shaped body, 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 the coating layer.

(Sealing paste filling process)
The plugging region can be formed by filling a part of the cells that become the second flow passages that open to the surface of the second honeycomb structure that constitutes the outer peripheral surface of the columnar body with a plugging paste and drying and solidifying it. The part of the surface of the second honeycomb structure that constitutes the outer peripheral surface of the columnar body that is not filled with the plugging paste becomes the open region.
The paste for the plug material may have substantially the same composition as the raw material paste.
After the degreasing, impregnation and adhesion steps described below, a plugging paste filling step may be performed, and the plugging paste may be dried and heated to solidify, thereby forming a plugging region.

The order of carrying out the coating layer paste applying step and the plug material paste filling step is arbitrary, and the plug material paste filling step may be carried out first, and then the coating layer paste applying step may be carried out.
In addition, after applying the coating layer paste and filling the plug material paste, the coating layer paste and the plug material paste may be dried and solidified simultaneously, thereby performing the coating layer paste applying process and the plug material paste filling process simultaneously.

The plug paste is filled so that it penetrates into the second flow passage in the depth direction. In contrast, the coating layer paste is applied to the surface of the honeycomb structure exposed to the outer circumferential surface. Therefore, the coating layer paste does not penetrate into the second flow passage in the depth direction.

A coating layer paste may be applied to the surface of the applied sealing material paste. In this case, a coating layer is formed on the surface of the sealing area.

(Degreasing, impregnation, and adhesion processes)
In this process, the honeycomb aggregate is processed into a cylindrical shape, a layer that will become the coating layer is formed, and some of the cells are filled with plugging paste. After the degreasing process, the honeycomb aggregate is subsequently subjected to the impregnation and bonding 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 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.

The molten silicon also penetrates between the degreased body of the adhesive layer paste, the degreased body of the coating layer paste, and the degreased body of the plugging material paste, and forms a composite with the silicon carbide contained in the degreased bodies. The degreased body of the adhesive layer paste becomes an adhesive layer that firmly bonds the honeycomb structures (or honeycomb segments) together. The degreased body of the coating layer paste becomes a coating layer that covers the outer periphery. The degreased body of the plugging material paste becomes a plugging material that seals the openings of some of the cells that make up the second honeycomb structure.

When the temperature of the impregnation and bonding process is within the above temperature range, the resulting heat exchanger is an unsintered honeycomb structure in which most of the silicon carbide, which is a constituent of the heat exchanger, is not sintered and the silicon carbide particles and silicon exist independently. In other words, the partition walls that make up the honeycomb structure (or honeycomb segment) are made of a composite material of silicon and silicon carbide in which the independent silicon carbide particles are bonded by the silicon that exists around them. This unsintered honeycomb structure has a high Young's modulus and is difficult to deform, making it 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 the 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 the 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 intersect.

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 is performed to bond the honeycomb fired bodies together, a processing process to process them into a circumferential shape, an impregnation/bonding process to impregnate them with silicon, a process to form a coating layer, a process to form a sealing region, 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 4 is a perspective view showing a retaining mat used when storing the heat exchanger shown in Figure 1 in a reformer, and Figure 5 is an explanatory diagram showing a method of wrapping the retaining mat shown in Figure 4 around the heat exchanger shown in Figure 1.

The retaining mat 50 has convex portions 51a and concave portions 51b at both ends of the mat 51, and mat openings 51c, 51d, 51e, 51f, 51g, and 51h are formed so that the second 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. 5, when the support mat 50 is wrapped around the heat exchanger 100, the second cells 23, which are the fluid inlet and the fluid outlet, are exposed through the mat openings 51c, 51d, 51e, 51f, 51g, and 51h.
The heat exchanger 100 is pressed into and fixed in the metal container constituting the reformer via the retaining mat 50, so that the heat exchanger 100 is securely housed in the reformer with the second cell 23, which is the fluid inlet and fluid outlet, exposed.

Figure 6 is a perspective view showing a schematic diagram of a heat exchanger according to a second embodiment of the present invention, and Figure 7 is a cross-sectional view of the heat exchanger shown in Figure 6 taken along line VII-VII.

As shown in Figures 6 and 7, the heat exchanger 200 according to the second embodiment of the present invention is a columnar heat exchanger 200 in which a first ceramic honeycomb structure 110 in which a number of first cells 113 serving as first fluid flow paths are arranged in parallel in the longitudinal direction separated by a first partition wall 112, and a second ceramic honeycomb structure 120 in which a number of second cells 123 serving as second fluid flow paths are arranged in parallel in the longitudinal direction separated by a second partition wall 122 are combined so that the first flow paths (first cells 113) and the second flow paths (second cells 123) intersect.

In Figures 6 and 7, the extension direction of the first cells 113 constituting the first honeycomb structure 110 is the vertical direction (the direction indicated by the arrow z in Figures 6 and 7). The extension direction of the second cells 123 constituting the second honeycomb structure 120 is the horizontal direction (the direction indicated by the arrow y in Figure 6). Since the flow passages of the first honeycomb structure 110 and the second honeycomb structure 120 intersect with each other, it is easy to circulate two types of fluids (especially gases) and heat exchange can be performed efficiently.

In the heat exchanger 200 according to the second embodiment, the second honeycomb structure 120 is disposed on both sides of the first honeycomb structure 110 via an adhesive layer 119. Thus, the heat exchanger 200 has one layer of the first honeycomb structure 110 and two layers of the second honeycomb structures 120.
As in the first embodiment, each of the first honeycomb structure 110 and the second honeycomb structure 120 may be constructed by bonding two or more honeycomb segments together via an adhesive layer.

In the heat exchanger 200 shown in Figures 6 and 7, first cells 113 that serve as first flow passages of the first honeycomb structure 110 open on both end faces, and second cells 123 that serve as second flow passages of the second honeycomb structure 120 open on the outer circumferential face.
A part of the outer peripheral surface is covered with a coating layer 132. The coating layer 132 has a coating layer 132a that covers the entire surface of the first honeycomb structure 110 that constitutes the outer peripheral surface, and a coating layer 132b that covers a part of the surface of the second honeycomb structure 120 that constitutes the outer peripheral surface.
The portion covered with the coating layer 132 has a higher mechanical strength than the portion not covered with the coating layer, and therefore the portion covered with the coating layer 132 can be used as a portion to which the canning pressure is applied.

In addition, the entire surface of the first honeycomb structure 110 that constitutes the outer peripheral surface is covered with the coating layer 132, which prevents the fluid flowing through the first cells 113 that form the first flow passages from mixing with the fluid flowing through the second cells 123 that form the second flow passages.

The thickness of the coating layer is not particularly limited, but is preferably 0.1 to 0.5 mm.
If the thickness of the coating layer is less than 0.1 mm, the coating layer is too thin and may be damaged by the pressure during canning, whereas if the thickness of the coating layer is more than 0.5 mm, the coating layer is too thick and may be damaged by the temperature difference between the outermost surface of the coating layer and the part in contact with the honeycomb structure.

In the heat exchanger of the present invention, a portion of the second flow passage is sealed with a sealant.
Since no fluid flows through the plugged second flow passage, the temperature change due to the flow of the fluid becomes slow, and the plugging material present in the second flow passage itself functions as a mass (heat capacity) that stores heat. Therefore, even if the temperature of the exhaust gas flowing into the second honeycomb structure drops, a high temperature can be maintained, and the reforming ability at the inlet can be improved.

The surface of the second honeycomb structure 120 constituting the outer peripheral surface has an opening region A101 (region surrounded by a dashed line in FIG. 6 ) where the second cells 123 that become the second flow passages open to the outer peripheral surface, and plugged regions A102 and A103 (regions surrounded by dashed lines in FIG. 6 ) where the second cells 123 that become the second flow passages are plugged with plugging materials 131 a and 131 b, respectively.
The sealing regions A102 and A103 are respectively arranged on both end face sides (both end face sides in the z direction) of the heat exchanger 200 with respect to the opening region A101.
The sealing regions A102 and A103 have a higher mechanical strength than the opening region A101. Therefore, the sealing regions A102 and A103 can be used as the regions to which the canning pressure is applied.

The ratio of the area of the open region A101 to the total area of the open region A101 and the sealing regions A102 and A103 is 72 to 93%, and preferably 72 to 83%.
When the above ratio is 72 to 93%, a good balance is achieved between the ratio of the second flow passages (open area) used for heat exchange with the first honeycomb structure under normal conditions and the ratio of the second flow passages (sealed area) that function as a heat capacity when the exhaust gas temperature drops, and the reforming ability at the inlet portion when the exhaust gas temperature drops can be improved while sufficiently ensuring heat exchange efficiency under normal conditions.
When the above ratio is 72 to 83%, the balance between the ratio of the second flow passages (open area) used for heat exchange with the first honeycomb structure under normal conditions and the ratio of the second flow passages (sealed area) functioning as a heat capacity when the exhaust gas temperature drops is particularly good, and the reforming ability at the inlet portion when the exhaust gas temperature drops can be improved while sufficiently ensuring heat exchange efficiency under normal conditions.

The volume of the heat exchanger according to the second embodiment of the present invention is preferably 1.2 to 3.2 liters.
When the volume of the heat exchanger according to the second embodiment of the present invention is 1.2 to 3.2 liters, the heat exchanger has an appropriate volume, making it easy to install in a vehicle, etc., and capable of fully exerting its effect as a heat exchanger.
If the volume of the heat exchanger according to the second embodiment of the present invention is less than 1.2 liters, the volume of the heat exchanger will be too small, making it difficult to support a sufficient amount of catalyst, whereas if the volume of the heat exchanger according to the second embodiment of the present invention exceeds 3.2 liters, the capacity of the heat exchanger will be too large, making it difficult to install it in a vehicle.

The material 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 constituting the heat exchanger according to the first embodiment. In addition, the manufacturing method of the heat exchanger according to the second embodiment of the present invention is also the same as that of the heat exchanger according to the first embodiment of the present invention, so the description thereof will be omitted.

The heat exchanger according to the first embodiment has three layers of the first honeycomb structure and four layers of the second honeycomb structure, and the heat exchanger according to the second embodiment has one layer of the first honeycomb structure and two layers of the second honeycomb structure, but the heat exchanger of the present invention is not limited to these embodiments. Therefore, as long as a first honeycomb structure in which a large number of cells serving as a first flow passage of 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 of a fluid are arranged in parallel in the longitudinal direction separated by a partition wall are combined so that the direction in which the first flow passage extends and the direction in which the second flow passage extends cross each other, the number of combinations is not limited. However, it is preferable that the first honeycomb structure and the second honeycomb structure are arranged alternately.

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

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.

The reformer of the present invention is preferably housed via a retaining mat in a metal casing connected to the main exhaust pipe and exhaust gas recirculation pipe.

In the reformer of the present invention, when the heat exchanger is housed via a retaining mat in a metal casing connected to the main exhaust pipe and exhaust gas recirculation piping, damage to the coating layer and sealing area is unlikely to occur even if the heat exchanger becomes hot.

FIG. 8 is an explanatory diagram showing 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 80 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. 8, the main exhaust pipe 43 is also connected to the reformer 80, 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 heat exchange is performed. 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 inlet of the reformer 80 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 80, 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 80, heat is removed by an endothermic reaction in the presence of the fuel reforming catalyst described above, 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 demonstrated. 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.

(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 die for manufacturing the honeycomb segments that make up the first honeycomb structure and a die for manufacturing the honeycomb molded body that makes up the second honeycomb structure, the raw material paste was extrusion molded to produce a honeycomb molded body.

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 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. The honeycomb formed body for the honeycomb segment constituting the second honeycomb structure produced by the above process had a rectangular end face shape of 14.6 mm x 70 mm, a length of 105 mm, a cell density of 47 cells/ ^cm3 (300 cells/ ^inch3 ), 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.

The obtained honeycomb dried body for the honeycomb segment constituting the first honeycomb structure and the honeycomb dried body for the honeycomb segment constituting the second honeycomb structure were used, and the raw material paste was used as an adhesive to combine the honeycomb dried bodies so that the assembly (honeycomb assembly) of the honeycomb dried bodies after the manufacturing process had the configuration shown in Fig. 3. The thickness of each adhesive layer was set to 1 mm. The first honeycomb structure was composed of one first honeycomb segment, and the second honeycomb structure was composed of two second honeycomb segments.
The dimensions of the dried honeycomb body were such that the surface of the second honeycomb structure where the second flow passages were exposed was a substantially rectangular parallelepiped shape with a width of 108.2 mm, a length of 140 mm, and a depth of 105 mm.

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 dried body were the end faces of the first honeycomb structure. Furthermore, a coating layer paste was applied to the entire surface of the first honeycomb structure constituting the outer peripheral surface of the cylindrical honeycomb aggregate and a part of the surface of the second honeycomb structure, and then dried and solidified.
Next, the cells that would become the second flow passages, located in a region up to 5 mm inward from both end faces of the second honeycomb structure that constitutes the side surface of the columnar body, were filled to a predetermined depth with a plug paste, which was then dried and solidified.

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 surface, 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 in the heating furnace was replaced with argon gas, and an impregnation and bonding process was carried out under heating conditions of 1450°C for 1 hour, to obtain a heat exchanger with the configuration shown in Figure 1.

The obtained heat exchanger having the configuration shown in FIG. 1 had an outer diameter of 102 mm and a length of 140 mm, the cell density of the honeycomb segments constituting the first and second honeycomb structures was both 47 cells/ ^cm2 (300 cells/ ^inch2 ), and the partition wall thickness was both 0.25 mm.
The first honeycomb structure was composed of one first honeycomb segment, and the second honeycomb structure was composed of two second honeycomb segments bonded together via end faces with an adhesive layer. In addition, the flow paths (cells that become first flow paths) of the first honeycomb segment constituting the first honeycomb structure and the flow paths (cells that become second flow paths) of the second honeycomb segment constituting the second honeycomb structure were arranged to intersect with each other.
The ratio of the area of the open region to the total area of the open region and the sealed region was 90%. In the sealed region, the cells that would become the second flow passages were sealed with a sealing material to a depth of 5 mm from the outer circumferential surface of the heat exchanger.

(Example 2, Comparative Examples 1 and 2)
The heat exchangers of Example 2 and Comparative Examples 1 and 2 were manufactured in the same manner as Example 1, except that the ratio of the area of the opening area to the total area of the opening area and the sealing area was changed to the value shown in Table 1 by changing the position and number of the cells filled with the plugging paste.

(Comparative Example 3)
The heat exchanger of Comparative Example 3 was manufactured in the same manner as in Example 1, except that instead of filling the cells with the plugging material paste, a coating layer paste was applied to the area corresponding to the sealing area to form a coating layer.

(Comparative Example 4)
A heat exchanger according to Comparative Example 4 was manufactured in the same manner as in Example 1, except that the plugging paste was not filled into the cells and the portions that were to become the sealing regions were left as open regions.

(evaluation)
[Canning ability]
The heat exchangers manufactured according to Examples 1 and 2 and Comparative Examples 1 to 4 were wrapped with a retaining mat as shown in Figures 4 and 5, and housed in a cylindrical metal case, and the heat exchangers were evaluated for damage according to the following criteria. The results are shown in Table 1.
However, the thickness and basis weight of the retaining mats were all the same, and the size of the openings in the retaining mats was adjusted to the size of the opening area in Examples 1-2 and Comparative Examples 1-2, and was the same as Example 1 in Comparative Examples 3-4.
[Evaluation of Canning Properties]
◯: No damage such as cracks occurred in the heat exchanger after canning.
×: Damage such as cracks occurred in the heat exchanger after canning.

[Heat exchange test and retention stability measurement]
A gas at 800°C was passed through the cells constituting the second honeycomb structure 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 10 minutes. After 10 minutes, the temperature of the gas flowing out of the first honeycomb structure was measured and evaluated according to the following criteria. The results are shown in Table 1.
Also, it was confirmed whether the retaining mat and/or the heat exchanger were displaced before and after this operation. The results are shown in Table 1.
[Evaluation of heat exchange efficiency]
◯: The temperature of the gas flowing out from the first honeycomb structure is 600° C. or more.
×: The temperature of the gas flowing out from the first honeycomb structure is less than 600°C.
[Evaluation of retention stability]
◯: No misalignment of the retaining mat and the heat exchanger is observed.
×: Misalignment of the retaining mat and/or heat exchanger is observed.

[Temperature drop test]
After measuring the heat exchange efficiency, the temperature of the gas supplied to the cells constituting the second honeycomb structure was changed to 700° C., and the temperature of the gas flowing out from the first honeycomb structure was measured 10 minutes after the change. The results are shown in Table 1.

As shown in Table 1, in the heat exchangers of Examples 1 and 2, even when the temperature of the gas flowing into the cells constituting the second honeycomb structure decreased, the temperature of the gas flowing out of the first honeycomb structure was able to be maintained at 600°C or higher.
The heat exchanger according to Comparative Example 1 was damaged during canning. This is believed to be because the region (plugging region) where the second honeycomb structure contacts the support mat is narrower than in Examples 1 and 2, and excessive pressure was applied to the plugging region, leading to the damage. It was found that when the basis weight of the support mat was adjusted so that the heat exchanger according to Comparative Example 1 would not be damaged during canning, the heat exchanger was displaced in the heat exchange test, and the support stability was insufficient.
In the heat exchanger according to Comparative Example 2, the temperature of the gas flowing out from the first honeycomb structure during normal heat exchange was less than 600° C. This is believed to be due to the fact that the ratio of the plugged region was too high, which reduced the heat exchange efficiency during normal heat exchange.
In the heat exchangers according to Comparative Examples 3 and 4, the gas temperature in the temperature drop test was less than 600° C. This is believed to be due to the absence of a sealing material that functions as a mass (heat capacity) for storing heat.

10, 110 First honeycomb structure 11, 111 First honeycomb segment 12, 112 First partition wall 13, 113 First cell (first flow passage)
18, 19, 119 Adhesive layer 20, 120 Second honeycomb structure 21, 121 Second honeycomb segment 22, 122 Second partition wall 23, 123 Second cell (second flow passage)
31a, 31b, 131a, 131b Sealing material 32, 32a, 32b, 132, 132a, 132b Coating layer 41 Gasoline engine 42 Exhaust pipe 43 Main exhaust pipe 44 Exhaust gas recirculation pipe (EGR pipe)
Reference Signs List 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 Opening 80 Reformer 90 Honeycomb dried body assembly 100, 200 Heat exchanger 300 Gasoline engine system A1, A101 Opening area A2, A102, A3, A103 Sealing area

Claims (10)

A heat exchanger comprising 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 together such that the first flow passages and the second flow passages intersect,
the heat exchanger has a generally cylindrical shape with the first flow passage opening at both end surfaces and the second flow passage opening at an outer circumferential surface thereof,
The entire surface of the first honeycomb structure of the outer peripheral surface of the heat exchanger is covered with a coating layer,
Among the outer peripheral surface of the heat exchanger, a surface of the second honeycomb structure has an opening region where the second flow passage opens to the outer peripheral surface of the heat exchanger, and plugging regions provided on both end face sides of the heat exchanger with respect to the opening region, and the second flow passage is plugged with a plugging material,
A heat exchanger characterized in that a ratio of an area of the opening region to a total area of the opening region and the sealing region is 72 to 93%. The heat exchanger according to claim 1, wherein the second flow passage is sealed with the sealing material to a depth of 1 to 30 mm from the outer peripheral surface of the heat exchanger. The heat exchanger according to claim 1 or 2, wherein the second honeycomb structure is disposed on both sides of the first honeycomb structure. A heat exchanger according to any one of claims 1 to 3, 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 4, wherein the first honeycomb structure and the second honeycomb structure are both made of silicon carbide and silicon. The heat exchanger according to any one of claims 1 to 5, wherein the first honeycomb structure and the second honeycomb structure are each made of a plurality of ceramic honeycomb segments bonded together via an adhesive layer. The heat exchanger of claim 6, wherein the adhesive layer is made of silicon carbide and silicon. The heat exchanger according to any one of claims 1 to 7, wherein the first honeycomb structure and the second honeycomb structure are alternately arranged, and the heat exchanger includes three layers of the first honeycomb structure and four layers of the second honeycomb structure. 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. The reformer according to claim 9 , wherein the heat exchanger is housed, via a retaining mat, in a metal casing connected to the main exhaust pipe and the exhaust gas recirculation pipe.

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