JPH1130491A - Honeycomb heat storage structure - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a honeycomb heat storage structure in which it is protected against even high temperature waste gas and is effectually heat exchanged, and effectually demonstrate a cost merit including the running cost. SOLUTION: A honeycomb heat storage structure 1 is adapted such that it is constructed by superimposing a plurality of honeycomb structures 2, and it recovers waste heat in waste gas by alternately passing the waste gas and gas to be heated to a flow passage composed of a through-hole 3. In the structure, voids of the honeycomb structure 2 on a high temperature side that at least makes contact with high temperature waste gas are lower than that of the honeycomb structure 2 on a low temperature side other than the former voids, and the high and low temperature side honeycomb structures 2 are constructed with a same raw material.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a stack of a plurality of honeycomb structures, and the exhaust gas and the gas to be heated are alternately passed through a flow path composed of through holes to recover waste heat in the exhaust gas. The present invention relates to a honeycomb-shaped heat storage element, and more particularly to a honeycomb-shaped heat storage element that can be suitably used for high-temperature exhaust gas.

[0002]

2. Description of the Related Art Conventionally, in a general industrial combustion heating furnace used for melting and heating of steel, aluminum, glass, etc., in order to improve energy efficiency, waste heat in exhaust gas is recovered and air for combustion is recovered. Is preliminarily heated. Conventionally, ceramic balls, saddles, pellets and the like have been used as described in JP-A-58-26036, for example, when exhaust gas or combustion air passes through the heat storage. Since the pressure loss is high and the heat exchange area per volume is small, it is necessary to increase the volume of the heat storage body.

In order to improve this, in recent years, it has been proposed to use a honeycomb structure as a heat storage body.
This is performed as described in Japanese Patent No. 1190.
Since the pressure loss in passing the exhaust gas and the like is low in the honeycomb structure and the heat exchange area per volume is large, the honeycomb structure can perform very efficient heat exchange. However, these honeycomb structures also have the following problems. That is, since the honeycomb structure is composed of very thin cell walls, there are problems in strength, heat durability, and the like, as compared with conventionally used ceramic balls and the like. For this reason, the honeycomb structure may be damaged by a shock or contact with an abnormally high-temperature gas or the like, and may not function as a heat storage body. In the worst case, there is a problem that the system stops.

[0004]

In order to solve the above-mentioned problems, the present applicant has filed a Japanese Patent Application No. 7-342634.
Proposed a heat storage body using a honeycomb structure made of aluminum titanate. It is known that aluminum titanate is a material having excellent heat resistance. However, over long periods of use, aluminum titanate tends to decompose and is a very expensive material. Therefore, even if the thermal efficiency is improved by using the honeycomb structure made of aluminum titanate, the use of these honeycomb structures made of aluminum titanate has a problem that the cost merit over the conventional ceramic balls or the like can be expected to be equal or only slightly. . Therefore, it has been necessary to develop a heat storage body that can effectively exhibit cost advantages including running costs.

An object of the present invention is to solve the above-mentioned problems,
An object of the present invention is to provide a honeycomb-shaped heat storage element that can efficiently perform heat exchange without breaking even high-temperature exhaust gas and that can effectively exhibit cost advantages including running costs.

[0006]

According to the present invention, there is provided a honeycomb regenerator in which a plurality of honeycomb structures are stacked, and the exhaust gas and the gas to be heated are alternately passed through a flow path composed of through holes. In the honeycomb-shaped regenerator for recovering waste heat therein, at least the porosity of the honeycomb structure on the high-temperature side in contact with the high-temperature exhaust gas is lower than the porosity of the honeycomb structure on the other low-temperature side, and The honeycomb structure and the honeycomb structure on the low temperature side are made of the same material.

Before describing the embodiments of the present invention, the technical operation of the above configuration will be described below. The problem when using the honeycomb structure as a heat storage is
As described above, it is destroyed due to strength and heat resistance, and is expensive. It is a matter of course for those skilled in the art to use materials capable of withstanding the actual use temperature in order to improve heat resistance. For example, when conventionally known alumina is used, although the heat resistance temperature of alumina can sufficiently withstand actual use, it is known to those skilled in the art that alumina has a high thermal expansion and is very weak against thermal shock. Widely known to.

When honeycomb structures are combined to form a honeycomb-shaped regenerator, if the honeycomb structures are deformed or the like, a gap is generated between the outer peripheral walls of the upper and lower honeycomb structures stacked at that portion, The flow velocity of exhaust gas and combustion air passing through the honeycomb structure increases,
Since these gases pass through the honeycomb-shaped regenerator without heat exchange, they cause a thermal shock to the honeycomb-shaped regenerator. In the present invention, in order to clear the problem of strength, at least the high-temperature side honeycomb structure in contact with the high-temperature exhaust gas has a porosity lower than that of the other low-temperature side honeycomb structures, and is the same as the high-strength honeycomb structure. A honeycomb structure having a composition is used.

In general, in order to lower the porosity, it is easiest to shrink the honeycomb structure by increasing the firing temperature. However, since the shrinkage is large, the honeycomb structure is deformed. It often happens. When the honeycomb structure deformed in this way is used for all the heat storage bodies,
As described above, a gap is generated and high-temperature exhaust gas or combustion air passes through without heat exchange. Therefore, a thermal shock is generated in the honeycomb structure, and cracks and cracks are generated in the honeycomb structure.

Therefore, in the present invention, a honeycomb structure having a low sintering temperature, a high porosity, and excellent dimensional accuracy is used for a portion of the honeycomb structure having a low requirement for heat resistance on the low temperature side. By doing so, even when the honeycomb-shaped heat accumulators are formed by stacking, no gap is formed between the outer peripheral walls of the upper and lower honeycomb structures, not only solving the problem of cracks but also reducing the manufacturing cost of the honeycomb structures. It can be cheap.

In order to carry out the constitution of the present invention, it is preferable to use a single metal oxide such as alumina and zirconia. That is, the porosity of the single metal oxide can be easily changed depending on the firing temperature. On the other hand, when a composite metal compound or the like is used, decomposition, generation of foreign substances, and the like occur depending on the sintering temperature, so that it is difficult to change the porosity only by the sintering temperature. Here, in selecting the material, if the material has a high melting point with respect to the temperature of the exhaust gas to be used and is not easily softened, the problem such as cracks can be solved by using the above technology, and any conventionally known material can be used. Materials can also be used.

Further, in the present invention, as a more preferable example, the opening ratio of the honeycomb structure on the high temperature side is made larger than the opening ratio of the honeycomb structure on the low temperature side. Thereby, when recovering waste heat from the high-temperature exhaust gas, the temperature absorption rate becomes slow, and the durability characteristics of the honeycomb structure used at a high temperature can be further improved.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a diagram showing a configuration of an example of a honeycomb heat storage body of the present invention. In the example shown in FIG.
The honeycomb-shaped regenerator 1 has a rectangular parallelepiped honeycomb structure 2.
Are stacked (here, stacked in two stages) so that the flow paths constituted by the through holes 3 are aligned in one direction. In FIG. 1, the upper part in the figure is the honeycomb structure 2 on the high temperature side in contact with the exhaust gas, and the lower part in the figure is the other honeycomb structure 2 on the low temperature side. A feature of the present invention is that, in the honeycomb-shaped regenerator 1 having the above-described configuration, the porosity of the honeycomb structure 2 on the high-temperature side is lower than the porosity of the honeycomb structure 2 on the low-temperature side, and the honeycomb structure on the high-temperature side. The point is that the body 2 and the honeycomb structure 2 on the low temperature side are formed of the same material.

In order to obtain the honeycomb structure 2 having a changed porosity, the porosity is changed by changing the firing temperature from the viewpoint of keeping the contraction rate small and preventing the deformation of the honeycomb structure 2 as described above. Is preferred. As the material of the honeycomb structure 2 on the high-temperature side and the honeycomb structure 2 on the low-temperature side, any material conventionally known as a material for a heat storage material such as alumina and zirconia can be used. It is preferable to use a single metal oxide such as alumina, zirconia, or the like because the porosity can be easily changed by changing the firing temperature. In contrast, when a composite metal compound or the like is used, decomposition and decomposition may occur depending on the firing temperature.
Since the generation of foreign substances and the like occurs, it is difficult to change the porosity only by the sintering temperature, and as a result, the production cost is increased.

FIG. 2 is a diagram showing the configuration of another example of the honeycomb heat storage body of the present invention. In the example shown in FIG. 2, the honeycomb-shaped heat storage body 11 is composed of the honeycomb structure 2 on the high-temperature side and the honeycomb structure 2 on the low-temperature side having the configuration shown in FIG. 1. On the surface of the body in contact with the gas to be heated, a layer made of a honeycomb structure 12 made of cordierite, mullite or the like is provided. In the example shown in FIG. 2, the same effect as the example shown in FIG. 1 can be obtained, and in addition to the use of cordierite, mullite, etc., compared to the example shown in FIG. The body 11 can be made. Also,
Honeycomb structure 1 made of cordierite, mullite, etc.
2 is a preferable example because it is provided only in a low-temperature place, and is less likely to be affected by a thermal shock due to contact with high-temperature exhaust gas.

In the examples shown in FIGS. 1 and 2, the cell opening ratio between the honeycomb structure 2 on the high temperature side and the honeycomb structure 2 on the low temperature side is not particularly mentioned. When the opening ratio of the honeycomb structure 2 on the lower side is made larger than the opening ratio of the honeycomb structure 2 on the lower side, the temperature absorption rate becomes slower when recovering waste heat from the high-temperature exhaust gas, and the honeycomb structure used at a high temperature This is preferable because the durability characteristics of the body can be further improved.

FIG. 3 is a view 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. In the example shown in FIG. 3, 21 is a combustion chamber, 22-
Reference numerals 1 and 22-2 denote honeycomb-shaped heat storage bodies having the structure shown in FIG. 1 or FIG. 2, and 23-1 and 23-2 denote honeycomb-shaped heat storage bodies 22-.
1, heat exchangers composed of 22-2, 24-1, 24
-2 is a fuel inlet provided in the heat exchangers 23-1 and 23-2. In the example shown in FIG. 3, two heat exchangers 23-
1, 23-2 is provided so that when one is storing heat by flowing high-temperature exhaust gas, the other can simultaneously heat the low-temperature gas to be heated, and heat exchange is efficiently performed. That's why.

In the example shown in FIG. 3, combustion air enters from below one side of the honeycomb regenerator 22-1. After passing through the honeycomb-shaped regenerator 22-1, the fuel inlet 24
-1 and is ignited in the combustion chamber 21. The burned exhaust gas enters from the upper part of the other honeycomb-shaped heat storage body 22-2, and the waste heat is discharged from the honeycomb-shaped heat storage body 2-2.
Exhaust gas that has been stored at 2-2 and has become low temperature is discharged to the outside. Next, the entry direction of the combustion air is switched, and the combustion air enters from the lower part of the honeycomb-shaped heat storage body 22-2 on the side where the waste heat has been recovered earlier. At this time, heat exchange is performed,
The combustion air is preheated and mixed with the fuel supplied from the fuel inlet 24-2 at the upper part of the honeycomb-shaped regenerator 22-2,
It is ignited in the combustion chamber 21. The exhaust gas is discharged through the other honeycomb-shaped regenerator 22-1. At this time, waste heat is recovered by the honeycomb-shaped regenerator 22-1 as described above.

[0019]

An actual example will be described below. Honeycomb structures A to D made of alumina having the shapes and characteristics shown in Table 1 below are prepared, and the high temperature side heat storage material A and the low temperature side heat storage material B are mixed with the above alumina honeycomb as shown in Table 2 below. Honeycomb regenerators (test Nos. 1 to 16) having the shape shown in FIG. 1 were prepared by selecting from structures A to D. Next, each of the obtained honeycomb-shaped regenerators was incorporated into an experimental apparatus, and an aging test was performed in which the honeycomb-shaped regenerator was maintained at a predetermined temperature for 1000 hours. After the aging test, the appearance and dimensional shrinkage of each heat storage body were examined. Further, the firing energy ratio and the heat exchange area ratio of each honeycomb-shaped regenerator were determined. Table 2 shows the results.

In the results shown in Table 2, the appearance of the heat storage bodies A and B is ◎ in the case where no defect is present, ○ in the case where the defect is slightly present but does not hinder the actual use, and Δ in the case where the crack is generated. And an example in which cracks occurred is indicated by x. Thermal storage A
And the dimensional shrinkage of B were determined from the dimensions of each heat storage body before and after firing. The firing energy ratio of each honeycomb-shaped regenerator is determined based on the energy required for firing the alumina honeycomb structure D, which requires the least energy for firing, in an electric furnace. And the ratio to the energy required for firing. Further, the heat exchange area ratio of each honeycomb-shaped regenerator was determined from the area of the portion of the through hole contacting the gas determined from the geometric specific surface area.

[0021]

[Table 1]

[0022]

[Table 2]

As is clear from the results of Tables 1 and 2, the honeycomb-shaped regenerator of the present invention example (Test Nos. 2, 4,
In 10 and 12), there was no problem of cracking or cracking in the honeycomb structure on both the high temperature side (heat storage body A) and the low temperature side (heat storage body B). On the other hand, the honeycomb-shaped heat storage material of the comparative example using the same honeycomb structure having low porosity (alumina honeycomb structures A and D) on both the high temperature side and the low temperature side (Test N)
o. In 1 and 11), cracks and cracks occurred in the honeycomb structure. This is because when the honeycomb structures used on the low temperature side are combined, deformation is large, gaps are formed between the honeycomb structures, and the low-temperature firing air enters the upper part without heat exchange and cracks due to thermal shock. Is considered to have occurred. Some cracks also occurred in the honeycomb structure used on the low-temperature side, but the high-temperature exhaust gas passed through the gap and entered the low-temperature portion without heat exchange, causing thermal shock. It is considered that a crack was caused by the occurrence.

Further, a honeycomb-shaped heat storage body of a comparative example using a honeycomb structure having a high porosity on the high temperature side (test No. 2).
5-8 and 13-16), the shrinkage due to the high-temperature exhaust gas was large, which caused cracking. in this case,
Regardless of whether a honeycomb structure with a high porosity is used on the lower low-temperature side or a honeycomb structure with a low porosity is used, the gap is opened because the honeycomb structure on the upper high-temperature side shrinks. It is probable that high-temperature exhaust gas or low-temperature combustion air entered through the gap and cracks were generated in the same manner as above. Further, the shrinkage of the lower-side low-temperature-side honeycomb structure also increased, which resulted in promoting the generation of the cracks.

On the other hand, in the honeycomb heat storage body of the present invention in which a honeycomb structure having a low porosity is used on the upper high temperature side and a honeycomb structure having a high porosity is used on the lower low temperature side, the upper and lower honeycomb structures are used. Both bodies showed little shrinkage and no cracks or cracks occurred. Further, among the present invention examples, the honeycomb-shaped regenerator (test No. 4) of the present invention example using a high-temperature-side honeycomb structure having a large opening ratio was used.
Further, the durability was improved.

The present invention is not limited to the above-described embodiment, but can be variously modified and changed. For example,
In the embodiment described above, only one high-temperature-side honeycomb structure in contact with high-temperature exhaust gas is provided, but it is needless to say that the present invention is not limited to one layer. For example, when the height of one layer is low, a honeycomb structure on the high temperature side may be formed from a honeycomb structure having two or more layers and a low porosity.

[0027]

As is apparent from the above description, according to the present invention, the porosity of the honeycomb structure on the high-temperature side is made lower than the porosity of the honeycomb structure on the low-temperature side, and both are made of the same material. Therefore, it is possible to obtain a honeycomb-shaped regenerator capable of efficiently exchanging heat without breaking even high-temperature exhaust gas. In addition, it is not necessary to use an expensive material such as aluminum titanate, and in that case, the porosity can be controlled by changing the firing temperature, so that the honeycomb-shaped heat storage body can be obtained at low cost.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of an example of a honeycomb heat storage body of the present invention.

FIG. 2 is a diagram showing a configuration of another example of the honeycomb heat storage body of the present invention.

FIG. 3 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]

1, 11, 22-1, 22-2 honeycomb-shaped regenerator,
2, 12, honeycomb structure, 3 through-hole, 23-1,
23-2 heat exchanger, 24-1, 24-2 fuel inlet

Claims (5)

[Claims] 1. A plurality of honeycomb structures are stacked,
The porosity of the honeycomb structure on the high-temperature side at least in contact with the high-temperature exhaust gas in the honeycomb-shaped regenerator for recovering waste heat in the exhaust gas by alternately passing the exhaust gas and the gas to be heated through the flow path composed of the through-holes However, the porosity of the other honeycomb structure on the low temperature side is lower than that of the other honeycomb structure, and the honeycomb structure on the high temperature side and the honeycomb structure on the low temperature side are made of the same material. 2. The honeycomb regenerator according to claim 1, wherein a layer made of a honeycomb structure made of cordierite or mullite is provided on a surface of the honeycomb structure on the low temperature side in contact with the gas to be heated. 3. An opening ratio of the high-temperature-side honeycomb structure is as follows:
The honeycomb-shaped heat storage body according to claim 1 or 2, wherein the opening ratio of the other honeycomb structure on the low temperature side is larger than that of the honeycomb structure. 4. The porosity of the honeycomb structure on the high temperature side;
The honeycomb heat storage body according to claim 2 or 3, wherein the porosity of the other honeycomb structure on the low temperature side is controlled by changing the firing temperature of the honeycomb structure made of the same raw material before firing. 5. The honeycomb heat storage body according to claim 1, wherein a main component of the honeycomb structure is a single metal oxide.