JPH0520642B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a ferrule inserted into a heated gas inflow end of a heat exchanger tube such as a smoke tube of a fire tube boiler.

For example, in a fire tube boiler, as shown in FIG. 1, high-temperature combustion gas combusted in a furnace tube 1 passes through a smoke chamber 2, changes direction, and enters a smoke tube 3, as shown by the arrow. The smoke pipe 3 is immersed in canned water 4, and heat transfer from the combustion gas to the canned water 4 is mainly performed through the smoke pipe 3.

By the way, the combustion gas inflow end 5 of the smoke pipe 3 protrudes several mm from the tube plate 6 toward the smoke chamber 2 due to manufacturing reasons. The flow velocity of combustion gas in smoke pipe 3 is 30~
The velocity is approximately 60 m/s, so the Reynolds number is approximately 15,000 to 30,000, and the gas flow is turbulent. In such a state, the heat transfer coefficient from the combustion gas to the smoke pipe 3 increases by 2 to 2.5 times at the inlet end 5 of the smoke pipe 3 compared to the smoke pipe portion sufficiently downstream. The inflow end 5 also receives radiant heat from the wall surface 7 of the smoke chamber 2. Furthermore, since the inflow end 5 protrudes, the cooling effect of the canned water 4, which is a cooling source, is also small.
For these reasons, the inlet end 5 will be overheated.

According to actual measurements, when the saturation temperature of the canned water 4 is 170 to 180℃, the temperature of the smoke pipe 3 is generally 5 to 10 degrees higher than the saturation temperature.
℃ higher, whereas the temperature at the inlet end 5 is
It has been confirmed that temperatures reach as high as 300℃.

On the other hand, these fire tube boilers are repeatedly fired and extinguished every day or at any time depending on changes in steam demand. Each time, the inlet end, which is locally overheated and cooled, undergoes repeated thermal expansion and contraction, creating thermal stress, and during long-term use, loosening and cracks occur at the joint between the smoke pipe 3 and the tube plate 6. and pressurized canned water 4
will leak out.

These problems are noticeable in furnace tube boilers, but they also apply to heat transfer tubes in heat exchangers into which high-temperature heating gas generally flows, and even in cases where there are no protruding parts, there are differences in severity.
The same is true.

Furthermore, the heated gas inlet end of such a heat exchanger tube protrudes from the tube sheet 6, or even if it does not protrude, it constitutes an inlet corner with respect to the tube sheet 6, so that the flow once contracts within the heat exchanger tube and then enters the tube again. This is undesirable as it causes pressure loss and creates flow path resistance.

On the other hand, the combustion gas comes into contact with the inner surfaces of the furnace cylinder 1 and the smoke tube 3, but if the saturation temperature of the canned water 4 is 170 to 180°C, as mentioned above, the temperature of most of the inner surfaces is lower than the saturation temperature. Since the temperature is about 5 to 10 degrees Celsius higher, carbon content in the combustion gas resulting from incomplete combustion is discharged outside the system as soot, which is undesirable as a cause of air pollution.

The present invention has been made to solve these difficulties of the prior art, and its purpose is to prevent and suppress overheating of the heated gas inlet end of the heat exchanger tube, and
It is an object of the present invention to provide a technology that burns unburned substances such as carbon in combustion gas and reduces the amount of dust emitted outside the system.

That is, the present invention provides a ceramic ferrule inserted into the heated gas inflow end of the heat transfer tube through which high-temperature heated gas flows, the tubular portion having an outer diameter not larger than the inner diameter of the inflow end. and,
The ferrule comprises a flange portion having an outer diameter larger than the outer diameter of the inflow end, and a hollow portion of the tubular portion and/or the flange portion is provided with an air-permeable solid.

Hereinafter, the present invention will be explained in detail with reference to the drawings.

As shown in FIGS. 2 and 3, the ferrule 10 according to the embodiment of the present invention is composed of a tubular portion 11, a flange portion 13, and a honeycomb body 16 that is an air-permeable solid. Flange part 13
The honeycomb body 16 is integrally formed of ceramic such as cordierite having a low coefficient of thermal expansion, and the honeycomb body 16 is made of ceramic such as aluminum titanate having a lower coefficient of thermal expansion.

As can be seen from FIG. 4, the tubular portion 11 is a portion inserted into the smoke tube 3, which is a heat transfer tube. The outer diameter of the tubular part 11 is therefore equal to or smaller than the inner diameter of the smoke tube 3. Tubular part 11
The wall thickness is made as thin as possible within a range that is not subject to manufacturing technology or strength constraints to ensure a sufficiently large cross-sectional area of the heating gas flow path. Further, the length of the tubular portion 11 is generally 1.5 to 3 times the outer diameter of the tubular portion 11. Further, the inner circumferential surface 17 of the tubular portion 11 is tapered gently so as to increase in diameter from the end on the flange portion 13 side toward the other end, thereby reducing flow path resistance.
Moreover, such a taper is particularly advantageous when mass-producing ferrules. That is, the tubular part 11 and the flange part 1 of this ferrule
3 and 3 are integrally manufactured using a mold consisting of an outer frame and a core, it has the advantage that the core mold can be easily removed after molding.

These advantages are noticeable when the inner circumferential surface 17 is tapered, but similar advantages are also obtained when the outer circumferential surface of the tubular portion 11 is tapered.

The outer shape of the flange portion 13 is a hexagonal column shape that is vertically and horizontally symmetrical, and is larger than the outer diameter of the tubular portion 11. The internal shape of the flange portion 13 forms a cylindrical hollow portion with an inner diameter larger than the inner diameter of the tubular portion 11 on the combustion gas inlet side, which is then reduced in diameter by the tapered portion, and then passes through the rounded portion 15 to form a hollow cylindrical portion with an inner diameter larger than the inner diameter of the tubular portion 11. Smoothly connected to the inner circumferential surface.
Similarly, the flange portion 13 and the tubular portion 11 are smoothly connected to each other via the rounded portion 14 in terms of their outer shapes.

In the ferrule of the present invention, the tubular portion 11 and the flange portion 13 may be connected without having a rounded portion in both the inner and outer shapes, but may be connected with a rounded portion as shown in FIG. It is desirable to be present. As a result, compared to the case where there is no rounded portion, the degree of concentration of stress due to heating and cooling on this portion is reduced, making it difficult for the ferrule to be damaged, and furthermore, the flow path resistance is reduced.

According to various study results, the radius of curvature of the radiused portion 15 is 0.2 to 0.6 times the inner diameter of the tubular portion 11, and the radius of curvature of the radiused portion 14 is 0.2 to 0.6 times the radius of curvature of the radiused portion 15.
It has been found that when the ratio is 0.4 to 1.2 times, the effects of preventing stress concentration due to local superheating and supercooling of the ferrule as described above and preventing pressure loss due to flow path resistance are excellent.

A honeycomb body 16 is provided in the cylindrical hollow part on the combustion gas inlet side of the flange part 13 and is bonded between the outer periphery and the inner periphery of the flange part 13 by interposing an inorganic heat-resistant adhesive or the like. It is being used. Here, the honeycomb body 16 is an inorganic molded body integrally formed into a thin partition wall so as to have a large number of small lattice-like passages such as square, hexagonal, triangular, circular, etc. is placed parallel to the In addition, in FIGS. 2 to 6, FIG. 9, and FIG. 12, the honeycomb body 16 is illustrated without considering the thickness of its partition walls.

As shown in FIG. 4, the ferrule 10 of the present invention is attached to the heated gas inflow end of the smoke tube 3, which is a heat transfer tube. That is, the tubular part 11 is inserted into the smoke pipe 3, and the flange part 13 is positioned on the side of the tube plate 6. If there is a clearance between the smoke pipe 3 and the tubular part 11, between the tube plate 6 and the flange part 13, and between adjacent flange parts 13, a heat-resistant adhesive 9 such as fire-resistant mortar is filled as necessary. be done. In this case, the outer peripheral surface of the tubular portion 11 and/or
Alternatively, appropriate grooves, protrusions, recesses, protrusions, etc. may be provided on the surface of the flange portion 13 on the tube plate 6 side to improve adhesion and prevent slippage during installation. Note that the use of such heat-resistant adhesive 9 is not essential.

Generally, smoke pipe groups are arranged in a staggered manner, so
When the ferrules shown in FIG. 3 are attached to the inlet end of each smoke pipe, they are arranged in a honeycomb shape as shown in FIG. It will be covered.
By doing so, the inlet end of the smoke pipe is prevented from overheating due to convective heat transfer from the combustion gas flow and radiant heat transfer from the wall surface 7 of the smoke chamber, and pressure loss at the inlet end is also reduced. Become. Furthermore, the fifth
In the figure, illustration of the clearance between the flange parts is omitted.

The hexagonal outer shape of the flange portion is appropriately selected, such as a regular hexagon or a hexagon slightly elongated in the vertical direction, based on the dimensions of the staggered arrangement of the smoke pipe group. Further, when the smoke pipe group is arranged in an orthogonal arrangement such as a checkerboard pattern, it is preferable that the outer shape of the flange portion is a square. Although the outer shape of the flange portion 13 may be circular or the like, by forming the flange portion into a polygonal shape, particularly a hexagonal or square shape, it is possible to substantially The entire surface of the ferrule can be filled with only the flange portion, and mutual movement and rotation are restrained to prevent peeling and falling off.Also, since it is only necessary to prepare a type of ferrule with substantially the same shape, mass production is possible. It will also be suitable for Furthermore, by employing such a ferrule, even if a part of the ferrule is damaged, it is not necessary to replace the entire ferrule group, and only the ferrule concerned can be replaced.

A ferrule 10 according to another embodiment of the present invention shown in FIG. 6 includes a tubular portion 11 whose inner peripheral surface is not tapered, a flat flange portion 13, and a hollow portion of the tubular portion 11. A honeycomb body 16 is bonded to and provided on.

A plurality of plate-shaped fins 20 are arranged parallel to the axis of the tubular portion 11 of the ferrule according to still another embodiment of the present invention shown in FIG. 7, and as shown in FIG. The plurality of plate-shaped fins 20 are arranged centripetally from the inner periphery, and form an air-permeable solid body.

In the tubular portion 11 of the ferrule, which is another embodiment of the present invention shown in FIG. 8, a number of rod-shaped pins 21 are disposed centripetally from the inner periphery of the tubular portion 11, as shown in FIG. A large number of rod-shaped pins 21 form a breathable fixing.

In a tubular portion 11 of a ferrule according to still another embodiment of the present invention shown in FIG. 9, a honeycomb body 16 is disposed so as to fit into an annular groove provided on the inner periphery of the tubular portion 11. Such an arrangement method can be achieved, for example, by fitting the honeycomb body 16 into the tubular part 11 that is divided into two parts parallel to the axis, and then joining the divided surfaces, thereby preventing the honeycomb body 16 from shifting during use. few.

Therefore, the ferrule of the present invention has a tubular portion and/or
Alternatively, a honeycomb body 16 or an air-permeable solid body composed of a plurality of fins 20, pins 21, etc. is provided in the hollow part of the flange part. When high-temperature combustion gas passes through the ferrule, the heat transfer rate from the combustion gas to the breathable solid is tens to hundreds of kcal/m ² /hr/
℃, and the surface temperature of the breathable solid is approximately equal to the combustion gas temperature. In the case of a furnace and smoke tube boiler, the temperature of the combustion gas flowing into the combustion gas inlet end 5 is 900~
Since the temperature is 1200°C, the carbon contained in the combustion gas is brought into contact with the surface of the high-temperature air-permeable solid and re-burned, and the amount of soot and dust discharged outside the system is greatly reduced. This effect is remarkable for heavy oil combustion gas containing a large amount of carbon.

When the breathable solid is provided in the hollow part of the flange portion 13, the cross-sectional area of the combustion gas passage can be increased, which is advantageous in terms of reducing pressure loss. If flow path resistance is relatively not a problem, the tubular portion 11
An air permeable solid may be provided in the hollow part of. The honeycomb body 16 is preferable as the shape of the breathable solid because it can provide a large contact surface area, but the fins 20 described above are preferable.
or a pin 21, and other suitable shapes can also be adopted.

The ferrule of the present invention is made of ceramics. It is preferable that the tubular portion 11 and the flange portion 13 are formed integrally from the same material, and specific examples of the material include cordierite, zirconia, aluminum titanate, mullite, silicon nitride, silicon carbide, alumina, etc. Among them, cordierite, mullite, etc. are preferable because they have high thermal shock resistance and high heat insulation properties. On the other hand, the breathable solid material such as the honeycomb body 16 may be made of the same material as the tubular portion 11, etc., but it is often preferable that it be made of ceramics with higher thermal shock resistance, and the materials exemplified above can be used. Among these, aluminum titanate and cordierite are particularly desirable.

Since the ferrule of the present invention is constructed and functions as described above, it is extremely advantageous in preventing overheating of the heated gas inlet end of the heat transfer tube and preventing air pollution.

[Brief explanation of the drawing]

Fig. 1 is a cross-sectional view of the main parts of a fire tube boiler, Fig. 2 is a cross-sectional view of a ferrule according to an embodiment of the present invention, and Fig.
The figure is a view taken along the line A-A in Figure 2, Figure 4 is an enlarged sectional view of the main part of the furnace and smoke tube boiler equipped with the ferrule shown in Figure 2, and Figure 5 is a view taken along the line B-B in Figure 4. The perspective view, FIG. 6, is a sectional view of a ferrule according to another embodiment of the present invention. 7, 8, and 9 are sectional views of a portion corresponding to section C in FIG. 6 of another embodiment of the present invention, and FIGS. 10, 11, and 12 are sectional views, respectively. It is a DD line arrow view in FIG. 7, FIG. 8, FIG. 10...Ferrule, 11...Tubular part, 13...
...Flange portion, 16...Honeycomb body, 20...Fin, 21...Pin.

Claims (1)

[Claims] 1. A ceramic ferrule inserted into the heated gas inflow end of the heat transfer tube through which high-temperature heated gas flows, the tubular portion having an outer diameter not larger than the inner diameter of the inflow end; 1. A ferrule comprising: a flange portion having an outer diameter larger than an outer diameter of an end thereof; and a hollow portion of the tubular portion and/or the flange portion is provided with an air-permeable solid.