JP2703727B2 - Si-impregnated SiC-based honeycomb structure and honeycomb-shaped regenerator using the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a Si-impregnated SiC honeycomb structure used at a high temperature of 1000 ° C. or higher and in a corrosive atmosphere, and a honeycomb heat storage body using the same.

[0002]

2. Description of the Related Art Conventionally, in a combustion heating furnace used for general industries such as a steel furnace, an aluminum melting furnace, and a glass melting furnace, waste heat of a combustion gas is used to preheat combustion air to increase thermal efficiency. As a heat storage element used for this purpose, one using ceramic spheres as described in JP-A-58-26036 or one using a honeycomb-shaped structure as described in JP-A-4-251190 Etc. were known.

In the above-described conventional heat storage element, first, a high-temperature combustion exhaust gas is brought into contact with a spherical or honeycomb-shaped heat storage element to store the heat of the combustion exhaust gas in the heat storage element. By heating the gas to be heated by contacting the heat storage body, the waste heat of the combustion exhaust gas is efficiently used.

[0004]

However, among the above-mentioned heat accumulators, when ceramic spheres are used, the ventilation resistance of the ceramic spheres is increased and the contact area between the ceramic spheres and the ventilation gas is small. There was a problem that heat exchange could not be performed in a specific manner, and the heat storage body had to be made large in size.

On the other hand, when the heat storage body has a honeycomb structure,
Since the geometric specific surface area is larger than the volume, effective heat exchange can be performed with a compact size. However, in an actual industrial furnace, natural gas, light oil, heavy oil, and the like are used as fuel, and corrosive gases such as SOx and NOx are generated. In the case of an aluminum melting furnace, alkali metals and fluorine are contained in exhaust gas. And the like are contained at a high concentration. Therefore, in a cordierite-type automotive exhaust gas purifying catalyst carrier as described in JP-A-4-251190,
There was a problem in terms of corrosion resistance.

Further, in order to improve the corrosion resistance, it has
No. 23950 proposes to use alumina as a heat storage body. However, if a honeycomb structure of alumina is used, alumina has a high coefficient of thermal expansion.
There is a problem in that when a cooling cycle with a large temperature difference is applied, it is broken by a thermal shock.

Further, as a heat-resistant material having excellent corrosion resistance, a sintered body of SiC, in particular, Si-impregnated SiC has been known, but has a problem in terms of oxidation resistance. A technique for improving the problem of oxidation resistance is disclosed in Japanese Patent Application Laid-Open No. 5-270917.
It is disclosed in JP-A-6-92735. However, the objects of these prior arts are simple shapes such as a furnace core tube for firing a semiconductor, a roller for a roller hearth kiln, a tube for a heat exchanger, and a shelf for firing a ceramic product. Therefore, when these Si-impregnated SiC sintered bodies are used for a honeycomb structure that is most suitable for forming a honeycomb-shaped heat storage body, oxidation resistance can be obtained, but in some cases, Si
Burrs due to bleeding were generated in the fired honeycomb structure, and there was a problem that the honeycomb structure was not used as a honeycomb structure in terms of pressure loss and the like.

An object of the present invention is to solve the above-mentioned problems,
An object of the present invention is to provide a Si-impregnated SiC-based honeycomb structure suitable for forming a heat storage body used under a high-temperature corrosive atmosphere of 1000 ° C. or more, and a honeycomb-shaped heat storage body using the same.

[0009]

The Si-impregnated SiC of the present invention
Porous honeycomb structure is made of Si-impregnated Si having a porosity of 3% or less.
C, wherein the wall thickness is 0.5 mm or more.

[0010] The honeycomb-shaped regenerator of the present invention is formed by stacking a plurality of Si-impregnated SiC-based honeycomb structures having the above-described configuration so that the flow paths composed of through holes are aligned in one direction. The exhaust gas and the gas to be heated are alternately passed to recover waste heat in the exhaust gas.

[0011]

In the above-described structure, Si having excellent corrosion resistance is used.
By forming a honeycomb structure in which C is a main component and impregnated with metal Si, the SiC-impregnated SiC-based honeycomb structure is a dense body, can have improved oxidation resistance, and can have aluminum, copper, and the like. Since it has the same thermal conductivity as that of the honeycomb structure, the temperature distribution in the honeycomb structure is hard to stick, and the thermal shock resistance can be improved. Therefore, this Si
If the honeycomb-shaped regenerator is formed from the impregnated SiC-based honeycomb structure, heat exchange can be performed with high efficiency without breaking even when used for a high-temperature corrosive gas.

The reason why the porosity of the Si-impregnated SiC honeycomb structure is limited to 3% or less is that if the porosity exceeds 3%, the improvement in oxidation resistance due to densification becomes insufficient. When considering the characteristics of the honeycomb structure, for example, the ventilation resistance, it is preferable that the porosity be 0.1 to 1%, as is clear from the examples described later. Further, the reason why the wall thickness of the honeycomb structure is 0.5 mm or more is that the wall thickness is 0.5 mm
If it is less than this, a large amount of burrs are deposited in the honeycomb structure cells, and the ventilation resistance is deteriorated. Further, the opening ratio of the honeycomb structure is not particularly limited, but is preferably 60% or more when it is configured as a honeycomb-shaped heat storage body.

[0013]

FIG. 1 is a view for explaining an example of a Si-impregnated SiC-based honeycomb structure of the present invention and a honeycomb-shaped regenerator using the same. In the example shown in FIG. 1, the honeycomb-shaped heat storage body 1 is configured by stacking a plurality of Si-impregnated SiC-based honeycomb structures 2 such that the flow paths formed of the through holes 3 are aligned in one direction. What is important in the present invention is
Each honeycomb structure 2 is made of Si-impregnated SiC having a porosity of 3% or less, preferably 0.1 to 1%.
The point is that the thickness of the wall 4 constituting the through hole 3 is 0.5 mm or more, and preferably the opening ratio is 60% or more.

The Si-impregnated SiC-based honeycomb structure 2 having the above-described structure can be manufactured, for example, by the following manufacturing method. First, SiC powder,
A carbon powder, an organic binder, and water or an organic solvent are prepared, and the raw materials for forming are kneaded to obtain extrudable clay, and then extruded into a honeycomb shape. After sufficiently drying the obtained honeycomb structure, the dried honeycomb structure is placed in a reduced-pressure inert gas atmosphere or vacuum under a metal silicon atmosphere, and the honeycomb structure is impregnated with metal silicon. It is fired to obtain a Si-impregnated SiC honeycomb structure. In addition, as the inert gas atmosphere, S
Considering the reactivity with iC, the nitrogen gas atmosphere is inappropriate, and other atmospheres such as argon gas and helium gas are preferable.

In the above-described manufacturing method, Si is impregnated in SiC which has been formed into a honeycomb structure in advance, so that the constituent components are substantially determined by the green density of the honeycomb structure formed in advance. In order to obtain the Si-impregnated SiC-based honeycomb structure 2 having a porosity of 3% or less in the present invention, the kneaded material is extruded to a green density of about 2.1 g / cc. Preferably, the components are 65-85% by weight SiC and 15-35% by weight Si.

In the above-mentioned manufacturing method, it is conceivable to impregnate metal Si excessively in order to reduce the porosity and achieve densification. However, it is possible to impregnate metal Si uniformly in a complicated shape such as a honeycomb structure. It is difficult to do so, and there is a possibility that excessive metal Si partially exudes and fills the cells of the honeycomb structure. In the case of a tube or a shelf with a simple shape, the metal Si that has exuded can be easily removed with a sandblaster or the like, but in a honeycomb structure with a complicated shape, the metal Si that has extruded into the cell can be removed. Have difficulty.
Burrs remaining inside the honeycomb structure increase ventilation resistance, which is an important characteristic when used as a honeycomb-shaped heat storage body. Therefore, it is desirable to control the amount of metal Si impregnation so that the porosity is 0.1% or more.

Further, as the wall thickness of the honeycomb structure becomes thinner, the exudation due to the impregnation of the metal Si becomes easier, and a lot of burrs precipitate in the cells of the honeycomb structure. Therefore, the wall thickness is made 0.5 mm or more. It is desirable. The manufacturing method of the present invention is not limited to the above-described manufacturing method, and it goes without saying that other manufacturing methods can be used as long as a Si-impregnated SiC-based honeycomb structure having predetermined characteristics can be manufactured.

FIG. 2 is a view showing an example in which a heat exchanger using the honeycomb regenerator of the present invention is installed in a combustion chamber of a combustion heating furnace. In the example shown in FIG.
Reference numerals 1 and 12-2 denote a honeycomb-shaped regenerator having the structure shown in FIG.
3-1 and 13-2 are honeycomb-shaped regenerators 12-1 and 12-
The heat exchangers 14-1 and 14-2 are fuel inlets provided in the heat exchangers 13-1 and 13-2.
In the example shown in FIG. 2, two heat exchangers 13-1, 13
The reason for providing -2 is that when one is storing heat by flowing high-temperature exhaust gas, the other is configured to simultaneously heat the low-temperature gas to be heated, thereby efficiently performing heat exchange. .

In the example shown in FIG. 2, first, as shown by the arrow in the figure, air as the gas to be heated is supplied to the heat exchanger 13-1 previously stored in the honeycomb-shaped heat storage body 12-1, and at the same time, fuel is supplied. Fuel is injected from the port 14-1, and high-temperature exhaust gas in the combustion chamber 11 is passed through the heat exchanger 13-2. In this state, the air is preheated and supplied to the combustion chamber together with the fuel, and the honeycomb-shaped regenerator 12-2 of the heat exchanger 13-2 is stored.

Next, the gas flow is switched so that the gas flows in the direction opposite to the arrow in FIG.
Air as the gas to be heated is caused to flow through 2 and fuel is injected from the fuel inlet 14-2, and high-temperature exhaust gas in the combustion chamber 11 is passed through the heat exchanger 13-1. By repeating the above steps continuously, heat exchange can be performed.

Hereinafter, an actual example will be described. Example 1 The characteristics of Si-impregnated SiC-based honeycomb structures manufactured in various metallic Si atmospheres were evaluated. First, as a forming raw material, a SiC coarse powder having an average particle diameter of 100 μm, a fine powder having an average particle diameter of 10 μm, and a carbon powder having an average particle diameter of 30 μm are mixed, and formed into a honeycomb formed body using an organic binder and water or an organic solvent. The resulting clay was extruded into a honeycomb shape having a green density of 2.1 g / cc. The obtained honeycomb structure was fired under the following firing conditions. That is, the metal Si atmosphere was adjusted so as to change the composition ratio of Si / SiC (the metal Si was melted during firing, and the molded body was placed under the liquid phase of the metal Si). In this metal Si atmosphere and in a reduced pressure inert gas atmosphere or in a vacuum, firing was performed at 1350 to 2500 ° C. 1 to 10 Si-impregnated SiC-based honeycomb structures were obtained.

The porosity, oxidation resistance, electric furnace spalling, and appearance after firing of the honeycomb were examined for the obtained Si-impregnated SiC honeycomb structure. The porosity was measured by a mercury intrusion method. Oxidation resistance is 75mm x 75mm x
A 50 mm Si-impregnated SiC honeycomb structure was
The mixture was kept in a mixed gas of H ₂ O and O ₂ at 10 ° C. for 10 hours to be oxidized, and a change in weight of the honeycomb structure was observed. In the electric furnace spalling, after a 75 mm × 75 mm × 50 mm Si-impregnated SiC honeycomb structure was kept in an electric furnace in an air atmosphere for 1 hour, it was taken out into the air and rapidly cooled to observe a breaking temperature. The appearance after baking of the honeycomb was indicated by ○ when there was no burrs due to exudation, Δ when there was some burrs, and × when there were many. Table 1 shows the results.

[0023]

[Table 1]

From the results shown in Table 1, the composition after firing (Si / SiC) was obtained by firing in various metallic Si atmospheres.
It can be seen that the porosity of the honeycomb structure changes correspondingly. That is, the porosity increases as the Si value decreases. In addition, as the porosity increases, the oxidation resistance of SiC increases quadratically with the increase in porosity. When the oxidation proceeds (when the rate of weight increase increases), a chemical change of SiC into SiO ₂ due to oxidation occurs, resulting in resistance to oxidation. It also has an adverse effect on corrosiveness. Test No. Comparing Example 8 with other examples shows that the porosity needs to be 3% or less.

On the other hand, the S (Si / SiC)
When the i value increases and the porosity becomes extremely small, extra metal Si from the honeycomb structure seeps onto the wall surface of the honeycomb structure. As a result, a large number of burrs are generated due to exudation of metal Si inside the cells of the honeycomb structure, and the ventilation resistance, which is an important characteristic of the honeycomb-shaped heat storage element of the main application of the honeycomb structure, is increased, and the pressure loss increases. This is not preferable as a honeycomb-shaped heat storage body. That is, the test No. If the porosity is less than 0.1% as shown in 1 and 2, burrs are generated in the honeycomb structure, and the oxidization resistance is good but the airflow resistance is adversely affected. It is understood that the above is preferable.

The test No. 9 and 10 show the results of evaluation of each characteristic when the cell thickness (wall thickness) of the honeycomb structure was changed. From these, if the wall thickness is less than 0.5 mm, the wall thickness is too small, metal Si is easily exuded, and burrs are frequently generated. As described above, the problem of airflow resistance occurs. Is found to be 0.5 mm or more.

Example 2 A honeycomb-shaped regenerator composed of a Si-impregnated SiC honeycomb structure of the present invention was evaluated. Si-impregnated Si of the present invention
As shown in FIG. 1, a plurality of C-type honeycomb structures are stacked so that a flow path composed of through holes is aligned in one direction.
A honeycomb-shaped regenerator having a size of 5 mm × 75 mm × 50 mm and a wall thickness of 1 mm was prepared, and as a comparative example, a honeycomb-shaped regenerator having the same shape was prepared from other materials conventionally used as a regenerator. And, the porosity, thermal expansion coefficient, corrosion resistance, oxidation resistance,
Electric furnace spalling was measured. The coefficient of thermal expansion is 40 ~
It was determined as an average over 800 ° C. In addition, each measurement other than the thermal expansion coefficient was performed in the same manner as in Example 1, and
Good corrosion resistance and oxidation resistance were indicated by ○, medium ones by Δ, and poor ones by X. Table 2 shows the results.

[0028]

[Table 2]

Usually, as important characteristics of the honeycomb-shaped heat storage body, when used as a honeycomb-shaped heat storage body, the exhaust gas often contains corrosive gas, and it is preferable that the honeycomb-shaped heat storage body has excellent corrosion resistance. In addition, since high-temperature exhaust gas and low-temperature air alternately flow in the honeycomb-shaped heat storage body, it is desired that the thermal shock resistance, that is, the breaking temperature of the electric furnace spalling be high.

From the above, when examining the results in Table 2, first, the honeycomb-shaped regenerator made of cordierite is:
Although the breaking temperature of the electric furnace spalling is remarkably superior to other materials, it can be seen that the corrosion resistance is poor. Also, it can be seen that the honeycomb-shaped regenerator made of alumina has excellent corrosion resistance, but has a remarkably low breakdown temperature in electric furnace spalling. Furthermore, it can be seen that the honeycomb-shaped regenerator made of SiC has poor oxidation resistance, and the oxidation progresses during long-term use, and the corrosion resistance may be deteriorated. On the other hand, the honeycomb-shaped regenerator made of the Si-impregnated SiC-based honeycomb structure according to the present invention has oxidation resistance several times better than SiC due to low porosity, is excellent in corrosion resistance, and has high thermal conductivity. From the fact that it is good, it is understood that the breaking temperature of the electric furnace spalling is high.

[0031]

As is apparent from the above description, since the honeycomb structure impregnated with metal Si is mainly composed of SiC having excellent corrosion resistance, the Si impregnated S
The iC-based honeycomb structure is a dense body, can improve oxidation resistance, and has the same thermal conductivity as aluminum and copper. Can also be improved. Therefore, if a honeycomb-shaped regenerator is formed from the Si-impregnated SiC-based honeycomb structure, heat exchange can be performed with high efficiency without breaking even when used for a high-temperature corrosive gas.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of an example of a honeycomb-shaped regenerator including a Si-impregnated SiC-based honeycomb structure of the present invention.

FIG. 2 is a diagram showing an example in which a heat exchanger using the honeycomb-shaped regenerator of the present invention is installed in a combustion chamber of a combustion heating furnace.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Honeycomb-shaped heat storage body 2 Si-impregnated SiC-based honeycomb structure 3 Through hole 4 Wall 11 Combustion chamber 12-1, 12-
2 Honeycomb regenerator 13-1, 13-2 Heat exchanger 14-1, 14-2
Fuel inlet

Claims (3)

(57) [Claims] 1. A Si-impregnated SiC honeycomb structure comprising a Si-impregnated SiC material having a porosity of 3% or less and a wall thickness of 0.5 mm or more. 2. The SiC-impregnated SiC honeycomb structure according to claim 1, wherein the porosity is 0.1 to 1.0%. 3. The Si-impregnated S according to claim 1 or 2,
The iC-based honeycomb structure is stacked so that the flow path composed of the through holes is aligned in one direction, and the exhaust gas and the gas to be heated are alternately passed through the through holes to collect waste heat in the exhaust gas. A honeycomb-shaped regenerator characterized by comprising.