JP2001324289A - High temperature heat exchanger - Google Patents

Abstract

PROBLEM TO BE SOLVED: To protect an outer tube against damage due to high temperature in a heat exchanger which can recover heat from high temperature combustion gas generated from a furnace for combusting refuse at a high temperature. SOLUTION: In a double tube heat exchanger having an outer tube 10 and an inner tube 14, protrusions and recesses 12, e.g. ridge-like protrusions or columnar protrusions, are formed on the inner face at the top 11 of hemispherical closed end of the outer tube in order to increase the contact area between a heat exchanging fluid pressure fed from the inner tube 14 and the inner face at the closed end of the outer tube thus cooling a required part of the outer tube 10 simultaneously with heat exchange.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-temperature heat exchanger for recovering heat from high-temperature combustion gas generated from a furnace for burning waste such as municipal waste.

[0002]

2. Description of the Related Art Conventionally, municipal refuse and industrial waste have been incinerated in an incinerator. However, in recent years, harmful substances such as dioxin have been detected from incinerated ash and flue gas after combustion, which has become a problem. It has been found that this dioxin will not be generated if it is burned at 1200 ° C. or higher, and furnaces for increasing the burning temperature have been developed and used.

By the way, such a high-temperature combustion gas is
Since discharging directly into the atmosphere leads to a great loss of energy, attempts have been made to recover it. For example, in Japanese Patent Application Laid-Open No. 11-213375, a single-ended bottomed cylindrical heat exchange tube for heat exchange is inserted into a combustion gas exhaust duct of a combustion furnace, and heat is recovered from the combustion gas to produce combustion air. It is described that it is used for preheating and power generation, and as a material for heat transfer tubes for such heat exchange,
1200 ° C. by using a silicon carbide sintered body
It also describes that it can be used in a temperature environment of 1300 ° C.

[0004] In a high-temperature heat exchanger, when heat is recovered from combustion exhaust gas by heat exchange, it is necessary to perform heat exchange at as high a temperature as possible in order to improve heat exchange efficiency. Further, by arranging a plurality of heat exchangers in parallel in the exhaust duct and recovering heat from each of the heat exchangers, it is possible to improve the heat recovery rate. By the way, when many heat exchangers are arranged in parallel in the exhaust duct, the tip of the heat exchanger is exposed to a higher temperature than the straight body, so that this portion is damaged. That is, as shown in FIG. 5 which is a schematic view of a combustion furnace provided with such a combustion heat recovery device, when a plurality of bottomed cylindrical heat exchangers are arranged in parallel in an exhaust duct, Since the straight body portion has a large airflow resistance, a large amount of high-temperature exhaust gas passes through the gap between the exhaust duct wall surface and the heat exchanger, and the end portion of the heat exchanger is particularly exposed to high temperatures. At such a high temperature, even when a silicon carbide heat exchanger having corrosion resistance is used, the process of oxidation and formation of a glass layer on the silicon carbide surface due to the corrosive atmosphere and further elution are repeated. At the tip of the heat exchanger, which is severe, the thickness of the heat exchanger is reduced due to deterioration, and eventually, a hole may be formed in the outer tube of the heat exchanger. As described above, in order to exchange heat at 1000 ° C. or more in a combustion furnace taking measures against recent dioxins and the like, it is necessary to prevent such a heat exchanger from being thinned or perforated to improve its useful life. Is important.

[0005]

SUMMARY OF THE INVENTION The present invention has been made in order to solve the above-mentioned problems in recovering heat from an exhaust duct of a high-temperature combustion furnace. An object of the present invention is to provide a heat exchanger that can efficiently recover heat.

[0006]

Means for Solving the Problems In order to solve the above-mentioned problems of the conventional heat exchanger, the present inventors have made intensive studies particularly on a structure for effectively cooling a portion exposed to a high temperature. It is. That is, the present invention is a single-ended heat exchanger for recovering heat from high-temperature combustion gas discharged from an exhaust duct of a high-temperature combustion furnace, one end of which is closed to form a hemispherical closed end, An outer tube formed of a cylindrical body having the other end opened and forming a flange for attachment to the exhaust duct; and an outer end inserted coaxially and with a gap in the outer tube, and an open end connected to the outer tube. An inner end for adjoining the closed end of the tube, the other open end being positioned adjacent to a flange of the outer tube, for supplying a heat exchange fluid into the outer tube. A heat exchanger for high temperature, comprising: a single-end type high-temperature heat exchanger having a tube and a concave portion provided on at least a hemispherical closed end on the inner surface of the outer tube.

Further, the present invention is the high-temperature heat exchanger, wherein the uneven portion provided on the inner surface of the hemispherical closed end is a ridge, a groove or a column.

[0008]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a cross-sectional view showing a state where the high-temperature heat exchanger of the present invention is attached to an exhaust duct wall surface.
In the drawing, reference numeral 10 denotes an outer tube of a cylindrical body of the single-end type heat exchanger, one end of which is closed by a hemispherical closed end 11. The other end is open, and a flange 13 is provided at the end of the cylindrical body. The heat exchanger is fixed to the combustion furnace exhaust duct wall 17 by the flange 13, and the outer pipe 10 recovers the fluid used as the heat exchange medium at the flange portion. It is connected to the high temperature fluid outlet path 15. FIG. 2 shows the outer tube 10 of the high-temperature heat exchanger of FIG.
1 shows a perspective view of a cross section obtained by cutting a half.

A heat exchanger inner pipe 14 is inserted into the outer pipe 10 from the flange side end of the heat exchanger outer pipe 10 and is fixed coaxially with a gap provided therebetween. . The inner tube 14 is a cylindrical body that is open at both ends, and one of the open ends of the inner tube 14 is disposed close to the inner surface of the hemispherical closed end of the outer tube. The other open end of 14 is fixed to the wall of the heat exchange fluid inflow passage 16 near the flange side end of the outer tube 10, and is used to feed the heat exchange fluid into the inner tube 14. Although not shown, it is connected to a heat exchange fluid feeding pump.

The heat exchange fluid press-fitted from the heat exchange fluid inflow passage 16 using the pump passes through the inside of the inner tube 14 and is closed at the hemispherical closed end 11 of the outer tube 10. After colliding with the inner surface of the outer pipe 10, the heat is exchanged through the gap formed by the outer pipe 10 and the inner pipe 14, and the air is exhausted from the heat exchange fluid outlet path 15. Although not shown, the waste heat is supplied to a generator or the like so that the waste heat can be effectively used.

The present invention provides the heat exchanger for high temperature described above,
By making at least the hemispherical closed end on the inner surface of the heat exchanger outer tube 10 an uneven surface, by locally lowering the temperature of the closed side end of the outer tube 10 in which erosion is remarkable. The erosion reaction is suppressed.

As described above, in the present invention, the outer tube 1 is used.
At the hemispherical closed end of 0, it is important to increase the contact area between the outer tube wall and the heat exchange fluid, and the flow of the heat exchange fluid is disturbed near the outer tube closed end. When the fluid stays or stagnates, the heat transfer coefficient of the fluid rapidly decreases, and it becomes impossible to effectively remove heat from the outer tube. Therefore,
In order to effectively conduct heat exchange at the closed end of the outer tube without opposing the flow of the heat exchange fluid, the uneven portion at the top of the closed end went from the center to the periphery along the flow line of the heat exchange fluid. It is important to arrange in the direction. In addition, the uneven portion provided on the inner surface of the hemispherical closed end of the outer tube is a protrusion formed at the center of the top, a ridge-shaped protrusion protruding from the inner surface, or a groove depressed from the inner surface. Preferably, these ridges or grooves extend radially from the center of the closed end to the periphery.

FIGS. 1 and 2 show an example in which a ridge-like projection is formed on the inner surface of the hemispherical closed end of the outer tube 10 as an uneven portion. A ridge-like projection 12 extends radially from the top 11 of the hemispherical closed portion of the outer tube 10. Further, the ridge-shaped projection may have a rectangular, trapezoidal, or triangular cross section. FIG. 4 shows an example of a groove formed as an uneven portion on the inner surface of the top of the hemispherical closed end of the outer tube 10.
2 extend.

In the present invention, the width of the ridge-shaped protrusion or groove is preferably in the range of 0.25 to 10 mm. If the width of the ridge-shaped protrusions or grooves is less than this range, the effect is lost because almost no flow into the grooves occurs, and if the width is more than this range, there is a problem that the heat transfer area is not improved. Yes, neither is appropriate.

FIG. 3 shows an example of a projection formed on a hemispherical closed portion as an uneven portion, and a columnar projection 32 is arranged at the center of the top of the hemispherical closed portion. In the present invention, the columnar projection can be formed in a columnar shape, a conical shape, a prismatic shape, or a pyramid shape. As described above, any shape may be used as long as it does not hinder the flow of the heat exchange fluid and increases the area of the inner surface of the top of the hemispherical closed end of the outer tube.

In the present invention, it is also effective that the above-mentioned uneven portion extends from the hemispherical closed end to the straight portion on the inner surface of the outer tube.

The material of the outer tube that can be used in the present invention is that the outer tube is exposed to a high-temperature atmosphere.
It is desirable to make it from a silicon carbide sintered body with high high-temperature strength. Similarly, the material of the inner tube may be a silicon carbide sintered body, or may be a heat-resistant metal. The use of a ceramic material has a higher high-temperature strength, but is more difficult to be processed into a desired shape, and tends to increase the cost. Further, in the present invention, it is desirable that the material of the ridge-shaped protrusion member is made of a heat-resistant metal or normal pressure sintered silicon carbide. From the viewpoint of reducing thermal stress caused by thermal shock and temperature difference,
It is desirable that the ridge-shaped protrusion and the outer tube main body are made of the same material or a material having a small difference in thermal expansion coefficient is selected.

Next, a structure for attaching the high-temperature heat exchanger of the present invention to a combustion furnace will be described with reference to FIG. FIG.
FIG. 4 is a block diagram schematically showing a high-temperature heat exchanger of the present invention attached to an incinerator exhaust duct. In the figure, 55 is an incinerator main body, and the incinerator main body has a gas supply port 56 for supporting combustion such as air. As described above, the combustibles are burned at a high temperature exceeding 1000 ° C. in the combustion furnace so that no harmful substances are generated by the combustion, and the high-temperature combustion gas is discharged out of the combustion furnace through the exhaust duct 57. However, a hole is formed in the intermediate portion wall surface 58 of the exhaust duct, and the heat exchanger 50 of the present invention is inserted therein. The heat exchanger for high temperature according to the present invention is desirably inserted from the hole formed in the wall surface of the exhaust duct toward the other side. This facilitates installation and fixing of the heat exchanger.
Further, a pump for feeding a heat exchange fluid (not shown) is connected to the high temperature heat exchanger, and a fluid is supplied from a heat exchange fluid introduction passage 53 of the high temperature heat exchanger. The water is supplied to the heat exchanger 50 and passes through the outer pipe 51 via the inner pipe 52. Then, the heat exchange fluid heated by the combustion gas passing through the exhaust duct 57 on the surface of the outer pipe 51 of the high temperature heat exchanger is taken out from the recovered high temperature fluid outlet 54 and used.

As the heat exchange fluid that can be used in the present invention, a gas or liquid that is stable at a temperature of about 1300 ° C. can be employed, but air and nitrogen gas are particularly preferable from the viewpoint of cost.

[0020]

An embodiment of the present invention will be described below with reference to rain 3 and FIG. 3 and 4 show the outer tube of the present invention in which the distal end portion is divided into four parts in parallel with the axis. The dimensions of the outer tube created in the embodiment of the present invention are all φ.
It is 90 mm (inner diameter φ76 mm) × L1590 mm.

Example 1 First, an outer tube having a columnar projection shown in FIG. 3 was formed on the inner surface of the closed end of the outer tube having the above dimensions. The size of the columnar projection is 12.
0 mm, the diameter of the base is 6.3 mm, and the heat transfer area of the inner surface of the hemispherical portion of the outer tube having no unevenness is defined as a reference.
The heat transfer area was designed to increase by about 5.4%. Using this outer tube, a heat exchanger for high temperature shown in FIG. 1 was manufactured, inserted into a heating furnace, and an air heat medium at 500 ° C. was introduced at a flow rate of 70 m ³ / h from the fluid inflow passage 16 for heat exchange. At this time, the temperature of the furnace was adjusted so as to flow out at 750 ° C. from the recovered high-temperature fluid outlet passage 15, and the temperature of the hemispherical closed end of the outer tube became 912 ° C. A temperature drop of about 5 ° C. was detected as compared with the case where no sample was present. At the same time, when heat transfer analysis was performed by computer simulation, a temperature decrease of 4 ° C. was obtained as a solution, which was in good agreement with the experimental results.

(Example 2) Next, as Example 2, on the inner surface of the hemispherical closed end of the outer tube having the above dimensions, as shown in FIG. Radially, 24 ridge-shaped projections were formed at regular intervals. A heat transfer analysis was performed using this outer tube under the same conditions as in Example 1 above, assuming that there was no significant change in the heat transfer coefficient at the inner surface portion. .

[0023]

According to the present invention, since the temperature at the closed end of the single-end type heat exchanger is remarkably reduced as compared with the conventionally known heat exchanger, it can be contained in the waste combustion gas. The reaction between the highly heat-resistant substance such as alkali and halogen and the ceramic material constituting the outer tube of the heat exchanger is suppressed, so that the wear of the outer tube of the heat exchanger is suppressed and the service life thereof is remarkably improved. .

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating a state where a single-end heat exchanger of the present invention is attached to an exhaust duct.

FIG. 2 is a perspective view in which an outer tube of the single-ended heat exchanger of the present invention is cut in half.

FIG. 3 is a cross-sectional view showing a main part of an outer pipe, which is another example of the single-ended heat exchanger of the present invention, divided into four parts.

FIG. 4 is a cross-sectional view showing a main part of an outer pipe that is divided into four parts, which is still another example of the single-ended heat exchanger of the present invention.

FIG. 5 is a schematic block diagram of an incinerator using a single-ended heat exchanger.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 ... Heat exchanger outer pipe 11 ... Heat exchanger outer pipe closed end top part 12 ... Ridge projection 13 ... Flange 14 ... Heat exchanger inner pipe 15, 53 ... Heat exchange fluid introduction path 16, 54 ... Recovered high temperature fluid Outlet passages 17, 58 ... Exhaust duct wall surface 32 ... Columnar projection 42 ... Groove 50 ... High temperature heat exchanger 51 ... High temperature heat exchanger outer tube 52 ... High temperature heat exchanger inner tube 55 ... Combustion furnace 56 ... Air supply Mouth 57 ... Exhaust duct

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (reference) F23G 5/48 ZAB F23G 5/48 ZAB

Claims (3)

[Claims] 1. A single-ended high-temperature heat exchanger for recovering heat from high-temperature combustion gas discharged from an exhaust duct of a high-temperature combustion furnace, wherein one end is closed to form a hemispherical closed end. An outer tube formed of a cylindrical body having the other end opened and forming a flange for attachment to the exhaust duct;
The open end is inserted coaxially and with a gap in the outer tube, and one open end is located near the closed end of the outer tube, and the other open end is located near the flange of the outer tube. A single-type high-temperature heat exchanger provided with an inner tube for feeding a heat exchange fluid into the outer tube, wherein at least a hemispherical closed end is formed on the inner surface of the outer tube. A heat exchanger for high temperature characterized by having a part. 2. The high-temperature heat exchanger according to claim 1, wherein the concave and convex portions provided on the inner surface of the hemispherical closed end are ridge-shaped projections. 3. The high-temperature heat exchanger according to claim 1, wherein the uneven portion provided on the inner surface of the hemispherical closed end is a groove.