JP2863330B2 - Resistance adjustment type heater - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heater comprising a honeycomb structure and having a resistance adjusting function. They can be suitably used as consumer heaters such as a hot air heater, and industrial heaters such as a pre-heater for purifying exhaust gas of automobiles.

[0002]

Becomes Recently, nitrogen oxides in the exhaust gas discharged from an internal combustion engine such as an automobile (NO _X), carbon monoxide (CO), a catalyst for purifying hydrocarbons (HC),
As catalyst supports and the like, metal honeycomb structures have been attracting attention in addition to conventionally known porous ceramic honeycomb structures.

On the other hand, with the tightening of exhaust gas regulations, development of heaters and the like for reducing emissions at the time of cold start is also desired. As such a honeycomb structure, for example, those described in JP-B-58-23138 and JP-A-63-67609 have been proposed.

Japanese Patent Publication No. 58-23138 discloses a foil-type metal honeycomb structure. In this honeycomb structure, a flat plate is mechanically deformed to form a waveform, which is rolled up together with the flat plate to form a metal substrate. Then, the surface of the metal substrate is oxidized to form an aluminum oxide film, a high-surface-area oxide such as alumina is supported on the film, and a noble metal or the like is impregnated with the film to form a catalyst for purifying automobile exhaust gas. is there.

Further, Japanese Utility Model Application Laid-Open No. 63-67609 discloses the use of an electrically conductive metal monolith catalyst obtained by coating a metal carrier with alumina as a preheater.

[0006]

However, in the foil type metal honeycomb structure described in Japanese Patent Publication No. 58-23138, adhesion to the catalyst layer is poor due to poor porosity of the metal substrate on which the film is formed. However, there is a disadvantage that the catalyst is easily peeled off due to a difference in thermal expansion between the ceramic catalyst and the metal substrate. Also, during the operation cycle, the telescope phenomenon that the metal-metal junction is peeled off and deforms into a convex part in the gas flow direction is likely to occur, which may be a serious hindrance in operation, and furthermore, the production of foil type metal honeycomb. Thus, there is a problem that the rolling yield of the foil is low and the production cost is high. 63
The pre-heater disclosed in Japanese Patent Publication No.
As in JP-A-138, there is a disadvantage that the catalyst is easily peeled off due to the difference in thermal expansion between alumina and the metal carrier, and at the same time, the metal-metal junction of the metal base is peeled off during operation, and an insulating part is formed. There is a problem that current unevenness occurs and uneven heat generation occurs.

Further, the preheater disclosed in Japanese Utility Model Application Laid-Open No. 63-67609 simply energizes from the inner periphery to the outer periphery of a foil type metal honeycomb structure to generate heat, and its resistance is not adjusted ( That is, material, dimensions,
The desired resistance is not adjusted only by the rib thickness), and the temperature rise characteristics are not sufficient. In addition, since the electrode is provided on the inner periphery, the center does not act as a catalyst. In addition, there is a problem of causing a pressure loss. Further, there is a disadvantage that the electrode is easily detached by the gas flow.

In view of this, the present applicant has previously proposed a heater having at least two electrodes for supplying electricity to the honeycomb structure and having a resistance adjusting mechanism between the electrodes (Japanese Patent Application No. 2-96866). The present invention provides a further improvement of this heater.

[0009]

That is, according to the present invention, a honeycomb structure having a large number of through holes is provided with at least two electrodes for energization, and a partition wall of the honeycomb structure is provided between the electrodes. A resistance adjusting heater, wherein a slit is formed at a predetermined angle to adjust the resistance between the electrodes to heat the gas fluid in the through hole in the honeycomb structure.

Further, according to the present invention, there is provided a resistance-adjustable heater having a heater function and an exhaust gas purifying function in which a catalyst is supported on the honeycomb structure. Further, in the above description, it is preferable to use a material obtained by forming a powder material into a honeycomb shape and sintering the same as the honeycomb structure.

[0011]

According to the present invention, electrodes are provided on a honeycomb structure having a large number of through holes, and slits are formed between the electrodes at a predetermined angle with respect to the partition walls of the honeycomb structure to adjust the resistance between the electrodes. It is a resistance-adjustment type heater. That is, the heat generation can be controlled by adjusting the resistance, and the temperature can be locally or entirely raised according to various uses.

The above-mentioned honeycomb structure is preferably manufactured by forming a powdery material into a honeycomb shape and sintering it. In this case, it is preferable to use a so-called powder metallurgy and an extrusion molding method, and there is an advantage that the process can be simplified and the cost can be reduced. In addition, it is preferable that the heater be a honeycomb structure (integral body) using a powder raw material, since a telescopic phenomenon does not occur and uniform heat generation can be achieved.

Japanese Patent Application No. Hei 2-9686, which is the prior application of the present applicant.
In No. 6, the example suggests that each cell of the honeycomb structure is substantially square, and that a slit as a resistance adjusting mechanism is provided in the same direction as the cell partition,
In that case, when a current flows between the electrodes, no current flows through all the ribs (partitions) between the electrodes (the portion does not generate heat),
It has been found that the heat generation as a whole may be insufficient.

In the present invention, the above problem is solved by forming a slit so as to have a predetermined angle with respect to the partition wall of the honeycomb structure instead of the same direction. When the slit is formed in this manner, a current flows through all the ribs (partitions) between the electrodes, so that the heat generation area increases as compared with the above case, and as a result, the heat exchange surface area increases.

This will be described with reference to the drawings. When the slits 11 are formed so as to have a predetermined angle with respect to the direction of the partition walls 10 of the honeycomb structure, the square cell structure 12 between the slits 11 is formed as shown in FIG. It is in a state having a predetermined angle with respect to the current flow direction. On the other hand, Japanese Patent Application Hei 2-
In the case of the heater of No. 96866, as shown in FIG. 2, the square cell structure 12 between the slits 11 has half of the partition walls 10a formed in the same direction as the current flow direction. Therefore, in the case of the cell structure of FIG. 1, a current flows through many ribs (partitions) 10 as compared with the cell structure of FIG. 2, and the resistance increases and the heat generation area increases.

The resistance-adjustment type heater according to the present invention is characterized in that the surfaces of the partition walls and pores of the metallic honeycomb structure are made of Al ₂ O.
₃ , it is preferable to coat with a heat-resistant metal oxide such as Cr ₂ O ₃ because heat resistance, oxidation resistance and corrosion resistance are improved.

The constituent material of the honeycomb structure, which is the base of the present invention, is not limited as long as it is made of a material which generates heat when energized, and may be metallic or ceramic, but metallic has high mechanical strength. Therefore, it is preferable. In the case of metal, for example, stainless steel, Fe-Cr-Al, Fe-
Cr, Fe-Al, Fe-Ni, W-Co, Ni-Cr
And the like. Among the above, Fe-Cr-Al, Fe-Cr, and Fe-Al are preferable because they are excellent in heat resistance, oxidation resistance, and corrosion resistance, and are inexpensive. Further, in the case of metal, a foil type may be used.

The honeycomb structure of the present invention may be porous or non-porous. However, when a catalyst is supported, the porous honeycomb structure has strong adhesion to the catalyst layer. This is preferable because the catalyst is hardly peeled off due to the difference in thermal expansion. Further, even in the case of a non-porous honeycomb structure, in the present invention, since a resistance adjusting mechanism such as a slit is provided, thermal stress is reduced, and cracks and the like hardly occur.

Next, an example of a method for manufacturing a metallic honeycomb structure among the honeycomb structures of the present invention will be described. First, for example, Fe powder, Al powder, C
A metal powder raw material is prepared from r powder or an alloy powder thereof. Next, after mixing the thus prepared metal powder raw material, an organic binder such as methyl cellulose and polyvinyl alcohol, and water, the mixture is extruded into a desired honeycomb shape.

When mixing the metal powder raw material with the organic binder and water, an antioxidant such as oleic acid is mixed with the metal powder before adding water, or a metal powder which has been subjected to a treatment which is not oxidized in advance is used. Is preferred. Next, the extruded honeycomb formed body is fired at 1000 to 1400 ° C. in a non-oxidizing atmosphere. Here, when calcination is performed in a non-oxidizing atmosphere containing hydrogen, the organic binder can be decomposed and removed using Fe or the like as a catalyst, and a favorable sintered body can be obtained, which is preferable.

If the firing temperature is lower than 1000 ° C., the compact does not sinter, and if the firing temperature exceeds 1400 ° C., the obtained sintered body is undesirably deformed. Preferably, the surfaces of the partition walls and pores of the obtained sintered body are then covered with a heat-resistant metal oxide. As a method of coating with the heat-resistant metal oxide, the following method is preferred.

The metal honeycomb structure is placed in an oxidizing atmosphere at 70
Heat treatment at 0-1100 ° C. Al and the like are plated (for example, vapor phase plating) on the surfaces of the partition walls and pores of the sintered body, and heat-treated at 700 to 1100 ° C. in an oxidizing atmosphere. Immersion in molten metal such as Al, 700-1100 ° C in oxidizing atmosphere
Heat treatment. Alumina sol or the like is used to cover the surfaces of the partition walls and pores of the sintered body, and then,
Heat treatment at ℃.

The heat treatment temperature is preferably 900 to 1100 ° C. from the viewpoint of heat resistance and oxidation resistance. Next, in the obtained honeycomb structure, slits are provided between the electrodes described below in various modes. In the above case,
Although the formation of the slit in the honeycomb structure was performed after firing,
It can be performed after drying or after molding.

The metallic honeycomb structure obtained as described above is usually provided with electrodes by means of brazing, welding, or the like on the partition wall or inside thereof at the outer periphery thereof.
The resistance-adjusting heater of the present invention is manufactured. This metallic honeycomb structure has an overall resistance value of 0.001.
It is preferable to form it so as to be in the range of Ω to 0.5Ω.

It is preferable that a catalyst be further supported on the surface of the metallic honeycomb structure, since a temperature rise due to a purification reaction of exhaust gas (eg, heat of oxidation reaction) can be expected.

The catalyst supported on the surface of the metallic honeycomb structure is obtained by supporting a catalytically active substance on a carrier having a large surface area. Here, as the carrier having a large surface area, for example, Al ₂ O ₃ type, TiO ₂ type, SiO ₂
-Al ₂ O ₃ type and perovskite type are typical examples. Examples of the catalytically active substance include noble metals such as Pt, Pd, and Rh, Cu, Ni, Cr, and C.
and base metals such as o. Of the above,
10-100 g of Pt, Pd and Rh in γ-Al ₂ O ₃ system
/ Ft ³ is preferred.

Although the honeycomb shape of the honeycomb structure of the present invention is not particularly limited, specifically, for example, 6 to 1500 cells / In ² (0.9 to 233 cells / c)
m ² ) is preferably formed to have a cell density in the range. Further, the thickness of the partition walls is preferably in the range of 50 to 2000 μm.

As described above, the honeycomb structure may be porous or non-porous, and the porosity is not limited. However, the strength characteristic is preferably in the range of 0 to 50%, preferably less than 25%. It is desirable from the viewpoint of oxidation resistance and corrosion resistance.
When a catalyst is supported, the catalyst preferably has a porosity of 5% or more from the viewpoint of adhesion to the catalyst layer.

In the present invention, the honeycomb structure is
Refers to an integrated structure having a large number of through-holes separated by partition walls, and its outer shape can be rectangular, elliptical, etc. in addition to a columnar shape. For example, the cross-sectional shape (cell shape) of a through-hole is circular, Various arbitrary shapes such as a square shape and a corrugated shape can be used.

[0030]

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to these Examples.

(Example 1) Preparation of sample A: Fe-20C
Fe powder and F so that the composition becomes r-5Al (% by weight).
An e-Cr powder and an Fe-Al powder are blended, and an organic binder (methylcellulose), an antioxidant (oleic acid) and water are added thereto to prepare a kneaded material, which is extruded and dried. Rib thickness 8 mil, cell density 300
110 mmφ outer diameter with square cells of pieces / square inch,
A dried honeycomb body having a thickness of 30 mm is prepared, and then the number of cells between the slits 11 is set to six and ribs (partition walls) are formed.
A molded body having a honeycomb structure in which 11 slits 11 provided in the same direction as the partition walls 10a of half of the 10 were obtained.

Next, this honeycomb formed body was fired in an H ₂ atmosphere to obtain a honeycomb structure 13 having an outer diameter of 92 mmφ and a thickness of 25 mm. Next, this honeycomb structure 13
Is coated with γ-Al ₂ O ₃ and then the noble metal Pt
Pd respectively ^{30g / ft 3, 6g / ft} 3 carrying the, 6
By firing at 00 ° C., a honeycomb structure 13 supporting the catalyst was obtained. Thereafter, two electrodes 14 were set on the outer wall to obtain a heater catalyst A.

Production of sample B: A molded article having the same honeycomb structure obtained by the same extrusion molding and drying method using the same material as in the production of sample A described above is provided with the same slit interval, With slit length and number of slits,
As shown in FIG. 4, a honeycomb structure 13 provided with a slit 11 so that the slit direction is 45 ° with respect to the cell partition wall 10 was obtained.

Further, a heater catalyst B having the same shape and the same heat-generating cross-sectional area as that of the heater catalyst A and having a different slit angle with respect to the cell partition was obtained from the honeycomb structure 13 through the same steps as the sample A. .

Prior to the evaluation, the electric resistances of the heater catalysts A and B were measured. As a result, they were the same as 0.04Ω, respectively, and the effective catalyst volume was the same as 133 cm ³ .

[Evaluation] The performance evaluation of the heater catalyst is shown in FIG.
This was performed using the apparatus shown in FIG. That is, the exhaust gas from the gasoline engine 20 is cooled to 120 ° C. by the cooler 21 and then introduced into the heater catalyst 22. At the same time as the evaluation start time, the temperature of the thermocouple 24 in the heater catalyst 22 is supplied to the heater catalyst 22 by the 24 V battery 23. The heater 25 was energized for 60 seconds while performing on / off control by the controller 25 so that the temperature became 350 ° C. The time of 60 seconds HC, CO, an average purification rate of the NO _X was measured with the exhaust gas measuring instrument 26. Table 1 shows heater catalysts A and B.
Shows the average purification rate.

[0037]

[Table 1]

[0038]

As described above, according to the present invention,
It is possible to provide a resistance-adjustable heater that has excellent durability, has excellent temperature rising characteristics and uniform heat generation characteristics, and can control heat generation.

[Brief description of the drawings]

FIG. 1 is an explanatory view showing a square cell structure between slits in the present invention.

FIG. 2 is an explanatory view showing a cell structure in which a partition wall 10a is formed in the same direction as a current flow direction.

FIG. 3 is a perspective view showing a heater catalyst A.

FIG. 4 is a perspective view showing a heater catalyst B.

FIG. 5 is an explanatory view showing an apparatus for evaluating the performance of a heater catalyst.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Partition wall 11 Slit 12 Cell structure 13 Honeycomb structure 14 Electrode

Claims (3)

(57) [Claims] A honeycomb structure having a large number of through holes is provided with at least two electrodes for energization, and a slit is formed between the electrodes at a predetermined angle with respect to a partition wall of the honeycomb structure to form a gap between the electrodes. A resistance of the honeycomb structure, and heating of the gas fluid in the through holes in the honeycomb structure. 2. A resistance-adjustable heater having a heater function and an exhaust gas purifying function in which a catalyst is supported on the honeycomb structure according to claim 1. 3. The resistance-adjustable heater according to claim 1, wherein the honeycomb structure is obtained by forming a powdery raw material into a honeycomb shape and sintering it.