JP3260580B2 - Thermal storage for thermal storage burners - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a regenerator for a regenerative burner, and more particularly, to a regenerator for a regenerative burner which is suitable for a combustion device such as a regenerative burner and which is composed of an aggregate of honeycomb structures. It is related.

[0002]

2. Description of the Related Art As is well known, a regenerative burner is provided with a regenerator along with the burner for the purpose of heat recovery or heat storage. As well-known materials, Japanese Patent Laid-Open No.
There is a honeycomb-shaped regenerator disclosed in Japanese Patent Application Publication No. 0-205. FIG.
1 shows an example of a heating furnace using a conventional regenerative burner. In the figure, 3 is a heating furnace, 4a and 4b are burners, 5a and 5b are heat storage bodies, 6a and 6b are fuel cutoff valves, 7
Is a four-way valve for switching between supply of combustion air and suction of combustion exhaust gas, and 8 is a combustion exhaust gas outlet. 9 is heating furnace 3
The object to be heated.

In the heating furnace 3, it is assumed that the burner 4a is in a combustion state. For example, the temperature of the combustion air supplied to the heat storage element 5a is 30 ° C.
The preheated air at 250 ° C. is supplied to the burner 4a.
The preheated air burns together with the combustion gas and is supplied into the heating furnace 3. A part of the combustion exhaust gas passes through the burner 4b,
At a temperature of 350 ° C., the heat is absorbed by the heat storage element 5b to heat the heat storage element 5b and is exhausted as combustion exhaust gas at 200 ° C. Further, the remaining combustion gas is exhausted from the exhaust port 8 to the outside of the furnace.
Switching between the burner 4a and the burner 4b is performed by the fuel cutoff valve 6
a, 6b and the switching of the combustion air and combustion exhaust gas switching four-way valve 7 are performed.

The heating furnace 3 incorporates an exhaust heat recovery system in which heat storage and heat radiation are repeatedly performed in a short period of time, and heat storage bodies 5a and 5b are provided to improve heat recovery efficiency.

The heat storage bodies 5a and 5b preferably have a structure in which the heat exchange area per unit volume is large, the gas passage area is large, and the pressure loss during passage of the fluid is small.
For example, a honeycomb structure is suitable. For this reason, a honeycomb-shaped heat storage element is used as the heat storage element of the regenerative burner. Further, as a material of the honeycomb-shaped regenerator, for example, ceramics that do not melt at a high temperature is used because a high-temperature combustion gas of 1300 ° C. or more passes therethrough.
Such a ceramic honeycomb is manufactured by sintering an extruded material. Therefore, in the heat storage body made of ceramic honeycomb, the cross-sectional shape of the honeycomb is constant in the flow path direction.

[0006]

Heretofore, there has been a problem that cracks occur when ceramics are used for the honeycomb-shaped regenerator. The cause was presumed to be as follows. That is, in the use state of the honeycomb-shaped heat storage body,
The temperature is high on the burner side, the temperature is low on the anti-burner side,
The temperature gradient of the honeycomb-shaped regenerator becomes steep. The honeycomb-shaped regenerator tends to thermally expand and deform in accordance with this temperature gradient.However, since the honeycomb-shaped regenerator is a mechanically strong structure, free deformation is hindered. It was presumed that internal heat was generated in the thermal storage medium and cracked.

[0007] Assuming that the above-mentioned phenomenon causes cracks in the honeycomb regenerator of the heating furnace, a part of the flow path expands, the flow rate of the combustion exhaust gas increases, and the combustion on the discharge side of the regenerator starts. There has been a problem that the exhaust gas temperature rises, the heat loss of the exhaust gas increases, and the thermal efficiency deteriorates. The management of such a defect has been performed by observing a change in the temperature of the combustion gas of the regenerator for the regenerative burner, determining cracks in the regenerator, and exchanging the regenerator in a short period of time. As a result, there has been a problem that the production opportunity loss during the facility suspension period due to the heat storage material exchange and the heat storage material replacement cost increase. Furthermore, as a method of reducing the value of the heat storage body internal stress that was estimated to be the cause of cracks,
There is a method in which a honeycomb-shaped heat storage body is cut and divided into small pieces and then assembled into an original shape for use. But with this method,
Not only does it take time to install and replace the heat storage body,
There is a possibility that the flow path between the adjacent heat storage bodies may be shifted due to thermal expansion or the like during use of the heat storage body, and the flow path may be partially or entirely narrow, and the flow resistance of the heat storage body increases. there were.

[0008] As described above, a method of reducing the internal stress value of the heat storage body, which is the cause of the cracks in the honeycomb heat storage body, and dispersing the cracks to eliminate the cracks, cutting the honeycomb heat storage body into small pieces, It was conceived to reassemble and use it in its original shape. However, there has been no idea that the internal temperature distribution of the honeycomb-shaped heat storage body is positively changed to suppress the generation of the internal stress of the heat storage body.

SUMMARY OF THE INVENTION The present invention has been made in consideration of the above-described problems, and has as its object to provide a heat storage element for a heat storage type burner having a temperature distribution that does not cause cracking due to an internal temperature distribution of the heat storage element. Is what you do.

[0010]

In order to solve the above-mentioned problems, a regenerator for a regenerative burner according to a first aspect of the present invention comprises a multiplicity of thin tubes through which combustion air and fuel exhaust gas alternately flow while changing their flow directions. Is formed of at least two or more honeycomb structures, and the honeycomb structures are stacked in a direction in which the combustion air is fed, and the thin tubes of the honeycomb structure forming the heat storage bodies in a stacked manner are formed. A heat storage element for a regenerative burner, characterized in that the cross-sectional area of the thin tube of the anti-combustion side honeycomb structure is smaller than that of the thin tube of the combustion side honeycomb structure. Further, the second invention is the first invention.
In the invention, there is provided a heat storage element for a heat storage type burner, wherein a spacer is provided between the honeycomb structures to provide a gap. In a third aspect of the present invention, in the first and second aspects, the material of the combustion-side honeycomb structure of the heat storage body having a stacked structure of the honeycomb structure is ceramics, and the material of the anti-combustion-side honeycomb structure is metal. A heat storage element for a heat storage type burner, comprising:

[0011]

The honeycomb regenerator used in the regenerative burner is regarded as an aggregate of thin tubes. The relationship between the heat transfer between the thin tube formed in a honeycomb shape and the gas passing therethrough is determined by the Nusselt number Nu in a general thin tube (the definition is shown by the formula (1)). The values have been found to be consistent with the measured values. The relational expression of the Nusselt number Nu is shown below. Nu = D · h / k (1) where D: hydraulic diameter of the thin tube (m) h: heat transfer coefficient between the honeycomb and the gas (W / m ^2.
K) k: Thermal conductivity of gas (W / m · K)

FIG. 4 shows an example of the time average value of the measured temperature distribution inside the heat storage element during the operation of the heat storage type burner. The vertical axis indicates the temperature, and the horizontal axis indicates the position A of the honeycomb heat storage element. , B, C, and D are shown. The honeycomb-shaped regenerator used in this experiment had a square cross section (2.5 m long).
m, 2.5 mm in width), and is formed by stacking three honeycomb-shaped regenerators in the gas flow direction (flow path direction). Note that the solid line in the figure is the calculated value of the temperature according to the equation (1), and the dot-shaped symbols are the measured temperature values at the positions A, B, C, and D of the heat storage body shown in the figure. Position A is on the high temperature side and D is on the low temperature side.

In a heat storage element using three honeycomb-shaped heat storage elements having the same flow channel cross-sectional area of a thin tube, as is apparent from FIG.
It can be seen that the temperature gradient inside becomes large at the position A on the high-temperature side of the regenerator. In this experiment, it was found that the heat storage body cracked on the high temperature side, but did not crack on the low temperature side. Therefore, in order to investigate the cause of the cracks, various temperature distributions were given to the heat storage bodies having different materials and shapes, and the presence or absence of cracks was investigated. As a result, the crack of the heat storage body is determined by the ratio of the thermal strain generated in the heat storage body to the strength of the heat storage body, hereinafter referred to as a cracking index S. It became clear that the occurrence can be determined by the crack index S. That is, it has been found that if the crack index S is smaller than a predetermined value, no crack occurs.

S = (G · b · W · E · L) / T (2) G: Temperature gradient of gas entering and exiting the heat storage unit (K / m) b: Coefficient of linear expansion of the heat storage unit (1 / K) W: typical dimension of heat storage unit (m) = projected area in gas passage direction / perimeter of heat storage unit gas passage direction E: Young's modulus of heat storage unit (N / m ² ) L: length of heat storage unit in gas flow direction (m) T : Thermal storage material tensile strength (N / m ² ) That is, when a thermal storage material is selected, the tensile strength T, Young's modulus E, and linear expansion coefficient b of the thermal storage material are determined. Shape (W · L) to prevent heat storage body from cracking and to facilitate handling
In order to increase the temperature, it is conceivable to reduce the temperature gradient G of the gas entering and exiting the regenerator.

On the other hand, as is apparent from the equation (1), when the hydraulic diameter D of the thin tube is increased, the heat transfer coefficient decreases,
This indicates that heat transfer between the gas and the ceramic honeycomb is suppressed. Therefore, in such a case, the temperature change of the gas during the passage of the heat accumulator becomes small, and at the same time, the temperature gradient in the longitudinal direction of the narrow tube of the ceramic honeycomb becomes small, so that it becomes difficult to crack. However, if the thin tube is made thicker over the entire length of the thin tube, sufficient heat exchange cannot be performed unless the heat storage material is made longer, causing a problem that the heat storage material becomes larger. Therefore, a heat storage body composed of an aggregate in which a plurality of honeycomb structures divided in the flow direction (flow channel direction) are stacked is formed, and the crack coefficient S of each honeycomb structure is smaller than a predetermined value. The cross-sectional area of the thin tube that becomes the temperature gradient may be determined by calculating for each honeycomb structure. Considering these, in the case of the honeycomb-shaped regenerator, the cross-sectional area of the narrow tube of each honeycomb structure should be selected so as to increase on the high temperature side (combustion side) and gradually decrease on the low temperature side (anti-combustion side). It will be good.

The above objects have been achieved by means for solving the problems which have been made from such a viewpoint. According to claim 1, the heat storage body provided with a large number of thin tubes through which the combustion air passes is formed of at least two or more honeycomb structures, and the honeycomb structure is formed in a direction in which the combustion air is sent. The heat storage is performed by reducing the cross-sectional area of the thin tubes of the honeycomb structure that are stacked and forming the heat storage body by laminating the cross-sectional area of the thin tubes of the anti-combustion honeycomb structure with respect to the cross-sectional area of the thin tubes of the combustion honeycomb structure. The effect is to enhance the effect and to reduce the temperature gradient of the regenerator for the regenerative burner to prevent cracking.

According to the second aspect, a spacer through which gas can pass is provided between adjacent honeycomb structures,
A regenerator for a regenerative burner characterized by having a gap between adjacent honeycomb structures, which prevents a flow path from being discontinuous between the honeycomb structures and increasing flow resistance, There is no deterioration in combustion efficiency.

According to a third aspect of the present invention, in the heat storage element for a regenerative burner having a laminated structure of honeycomb structures, the material of the honeycomb structure on the combustion side is ceramics, and the material of the honeycomb structure on the non-combustion side is ceramics. By using metal, the thermal efficiency of the heating furnace can be increased, and the occurrence of cracks in the heat storage body can be prevented. Further, the heat storage rate can be increased by using a metal having a high specific heat for the honeycomb structure.

[0019]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a partially cutaway perspective view showing one embodiment of a heat storage body for a heat storage type burner according to the present invention. This regenerator for a regenerative burner is a regenerator used for a heating furnace as shown in FIG. 3 and is provided in each burner of the heating furnace 3. In FIG. 1, reference numeral 1 denotes a honeycomb-shaped heat storage body having a shape in which three honeycomb structures made of ceramics are stacked in a flow direction of combustion air, and the honeycomb-shaped heat storage body 1 includes first to third honeycomb structures 1a, 1b and 1c. A large number of small tubes 3a, 3b, 3c through which combustion air and combustion exhaust gas pass are formed in the honeycomb structures 1a, 1b, 1c, respectively.

Describing each honeycomb structure, the first honeycomb structure 1a is provided on the burner side (combustion side). The first honeycomb structure 1a includes a large number of thin tubes 3a.
Are formed, and the cross-sectional shape of the channel is square.
The pitch P1 of a is 4 mm. In the second honeycomb structure 1b, a large number of thin tubes 3b are formed, the cross-sectional shape of the flow channel is square, and the pitch P2 is 3 mm. Third
Is provided on the anti-combustion side. A large number of thin tubes 3c are formed in the third honeycomb structure 1c, the cross-sectional shape of the channels is square, and the pitch P3 is 2 m.
m. Narrow tubes 3a, 3 provided in each honeycomb structure
The flow channel cross-sectional areas b and 3c are formed to be the widest since the honeycomb structure 1a is located closest to the combustion side, and are gradually narrowed as the distance from the combustion side increases. The external dimensions of these honeycomb structures 1a, 1b, 1c are the same.

Reference numeral 2 denotes a spacer. The spacer 2 is a first
Honeycomb structure 1a and second honeycomb structure 1b, and second honeycomb structure 1b and third honeycomb structure 1c
Between them. The distance separating the adjacent honeycomb structures by the spacer 2 is set to be equal to or more than the hydraulic diameter of the thin tubes of the honeycomb structure, so that the thin tubes 3a, 3b, 3
It does not increase the flow resistance of the fluid passing through c.
Further, the honeycomb structures 1a, 1b, 1
The external dimensions of the honeycomb-shaped regenerator in which c are collected are the same as those of the conventional regenerator.

Next, the temperature distribution of the honeycomb regenerator when the honeycomb regenerator of the above embodiment is used in a heating furnace as shown in FIG. 3 will be described. Honeycomb regenerator 1
The internal temperature distribution of the honeycomb-shaped regenerator was measured by setting the temperature conditions of the combustion air inlet and outlet sides to the same as those in FIG. FIG.
The vertical axis indicates the temperature, and the horizontal axis indicates the temperature measurement position of the honeycomb-shaped regenerator. A, B, C, and D in FIG. 5 indicate the temperature measurement positions of the honeycomb-shaped regenerator indicated by dots, where the measurement position A is on the combustion side and the measurement position D is on the anti-combustion side.

As a result of measuring the temperature distribution, the temperature distribution shown in FIG. 5 was obtained. In the temperature distribution of FIG. 5, it can be seen that the temperatures at points B and C of the honeycomb-shaped heat storage body 1 are higher than those in the temperature distribution of FIG. That is, it is shown that the honeycomb-shaped heat storage body 1 of FIG. 1 has a higher heat storage effect than the conventional heat storage body. Also, the flow resistance of the honeycomb-shaped heat storage body 1 was equivalent to the conventional one. In addition, cracks occurred on the high-temperature side in the conventional heat storage body, but the temperature gradient in the flow path direction of the honeycomb structure on the high-temperature side was slower than in the past. It turned out that it can withstand long-term use.

Next, another embodiment of the regenerative burner regenerator according to the present invention will be described with reference to a partially cutaway perspective view of FIG. In FIG. 1, reference numeral 1 denotes a honeycomb heat storage body 1 formed of an aggregate having a honeycomb structure. The material of a honeycomb structure 1 d is made of ceramic, and the material of a honeycomb structure 1 e is metal. 3d and 3e are thin tubes through which combustion air and combustion exhaust gas pass. The honeycomb structure 1d is on the burner side (combustion side) of the heating furnace, and the honeycomb structure 1e
Is the combustion air inflow side or the combustion exhaust gas outflow side (anti-combustion side). Further, the flow channel cross-sectional area of the thin tube 3d of the honeycomb structure 1d is larger than the flow channel cross-sectional area of the thin tube 3e of the honeycomb structure 1e. The material of the honeycomb structure 1d is ceramic on the high temperature side (combustion side) and low temperature side (anti-combustion side).
Is a metal. 2 is a spacer. The gap formed by the spacer 2 may be set in the same manner as in the embodiment of FIG. The external dimensions of the honeycomb structures 1d and 1e are the same. The heat storage effect is enhanced by using a metal having a higher specific heat on the low temperature side.

As in the above embodiment, the regenerative burner regenerator according to the present invention is a honeycomb regenerator composed of an aggregate of honeycomb structures. Is wider than the cross-sectional area of the flow channel of the honeycomb structure. In other words, by reducing the heat exchange of the honeycomb structure on the high-temperature side and increasing the heat exchange on the low-temperature side, the heat storage effect and the heat recovery efficiency are maintained, and the occurrence of cracks in the honeycomb-shaped heat storage body is eliminated. It was done. Needless to say, the cross-sectional shape of the flow passage of the thin tube of the honeycomb-shaped heat storage body is rectangular in the embodiment, but it is apparent that the shape is not limited to this embodiment and may be rectangular, triangular, hexagonal, or the like. .

[0026]

As described above, according to the present invention, it is possible to prevent the heat storage body from cracking and to operate the regenerative burner stably for a long time without lowering the heat exchange efficiency. is there. Therefore, unlike the related art, there is an advantage that the heat storage body is not broken, the heat storage body flow path is partially expanded, the temperature of the combustion gas at the side of the heat storage body increases, the heat loss of the exhaust gas increases, and the heat efficiency does not deteriorate. . Also, in the conventional heat storage,
While monitoring the rise of the outlet combustion gas temperature, etc., it was determined that the heat storage material was cracked, and the heat storage material was replaced, or the heat storage material was replaced regularly every few months. Although there were drawbacks such as loss of production opportunities during the suspension period and heat storage unit replacement costs, according to the present invention, it is possible to reduce the frequency of replacement of the heat storage units. There is the advantage that it can be extended and the management cost can be reduced.

Therefore, according to the present invention, there is no production loss during the equipment downtime, and the cost of exchanging the heat storage material is reduced to about 1/3 of the conventional cost. In addition, the reason for the inspection and replacement of the heat storage element is not cracking of the heat storage element, but inspection of deterioration of the heat storage element due to the chemical reaction of the combustion gas or the heat storage element in the gas, and dust blocking the heat storage element and increasing the pressure loss. In this case, there is an advantage that the number of work steps can be reduced only when cleaning is performed.

[Brief description of the drawings]

FIG. 1 is a partially cutaway perspective view showing one embodiment of a heat storage body for a heat storage type burner of the present invention.

FIG. 2 is a partially cutaway perspective view showing another embodiment of the heat storage body for a heat storage type burner of the present invention.

FIG. 3 is a diagram showing an outline of a regenerative burner.

FIG. 4 is a diagram showing a temperature distribution of a conventional heat storage body.

FIG. 5 is a diagram showing a temperature distribution of a heat storage body for a heat storage type burner of the present invention.

[Description of sign]

 DESCRIPTION OF SYMBOLS 1 Honeycomb heat storage body 1a-1e Honeycomb structure 2 Spacer 3a-3e Thin tube

Continued on the front page. (72) Isao Mori, 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Nippon Kokan Co., Ltd. (72) Ryoichi Tanaka 2-53, Shirate, Tsurumi-ku, Yokohama, Kanagawa, Japan Nihon Furnace Industries (72) Inventor: Mamoru Matsuo 2-53-1, Shirite, Tsurumi-ku, Yokohama-shi, Kanagawa Prefecture In-house company of Japan Furnace Industries Co., Ltd. (58) Field surveyed (Int. Cl. ⁷ , DB name) F28D 17 / 02 F28D 20/00 F28D 19/04

Claims (3)

(57) [Claims] 1. A regenerator for a regenerative burner, wherein at least two or more honeycomb structures are provided with a plurality of thin tubes through which combustion air and exhaust gas for fuel alternately flow while changing the flow direction. And, the honeycomb structure is stacked in a direction in which the combustion air is sent,
The heat storage type wherein the cross-sectional area of the thin tube of the honeycomb structure in which the heat storage body is formed in a lamination is made smaller in cross-sectional area of the thin tube of the anti-combustion side honeycomb structure with respect to the cross-sectional area of the thin tube of the combustion side honeycomb structure. Thermal storage for burner. 2. The heat storage element for a regenerative burner according to claim 1, wherein a spacer is arranged between said honeycomb structures to provide a gap. 3. The heat storage body having a laminated structure of the honeycomb structures, wherein a material of the combustion-side honeycomb structure is ceramics, and a material of the non-combustion-side honeycomb structure is metal. Or the regenerator for a regenerative burner according to 2.