JP2003185364A - Double-pipe heat exchanger - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a double pipe heat exchanger capable of being properly used as a heat exchanger for corrosive fluid. <P>SOLUTION: In this double-pipe heat exchanger wherein a double pipe for heat exchanging is connected by a curved pipe having a curving angle of 90° or more, a replaceable short pipe part is mounted just at a downstream side of the curved pipe. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a double-tube heat exchanger, and more particularly to a double-tube heat exchanger suitable for heat exchange of corrosive fluids. is there.

[0002]

2. Description of the Related Art A conventional double-tube heat exchanger is shown in FIG.
As shown in FIG. 2, it is widely known that two double tubes 1 for heat exchange are connected by a curved tube 2 having a single tube structure. The double pipe heat exchanger supplies a fluid for heat exchange from an inlet 5 of the double pipe to an inner pipe of the double pipe, and a cooling medium or a heating medium is heat exchanged from an inlet 7 of the outer pipe. It is characterized in that heat is exchanged between the high temperature fluid and the low temperature fluid inside the double pipe portion by supplying the fluid so as to flow countercurrently with the fluid. The double pipe heat exchanger can be easily manufactured by simply welding the inner and outer pipes, and the heat transfer area can be easily adjusted by increasing or decreasing the number of double pipes to be connected. It is used as a heat exchanger.
For example, JP 2001-252678 A, JP 20
No. 01-293487, or Japanese Patent Laid-Open No. 2001-29
It is also used as a heat exchanger for heating the wastewater of a wastewater treatment plant using the catalytic wet oxidation treatment system disclosed in Japanese Patent No. 3488. The catalytic wet oxidation treatment system uses a molecular oxygen-containing gas (for example, air) at high temperature and high pressure in the presence of a solid catalyst to remove organic and / or inorganic substances from carbon dioxide gas, water, nitrogen, and harmless substances. It is a system that processes into inorganic ions.

[0003]

According to the knowledge of the present inventors, when a conventional double-tube heat exchanger is used as a heat exchanger of a corrosive wastewater treatment plant, Corrosion may occur on the inner wall of the inner pipe. In particular,
001-252678, JP 2001-2934A.
In the wet oxidation method as disclosed in Japanese Unexamined Patent Publication No. 87 or JP 2001-293488A, since the molecular oxygen-containing gas is added to the wastewater, the wastewater is heated by the heat exchanger, so that the heat exchanger is used. Corrosion may occur on the inner pipe of the. This corrosion is prominently seen on the inner wall surface of the inner pipe of the double pipe immediately downstream of the curved pipe of the heat exchanger.For example, depending on the operation period of the wastewater treatment, from the connecting portion of the double pipe and the curved pipe, The length of the corroded portion may range from about 50 cm to about 1 m. If the inner wall of the double pipe is corroded in this way, the entire double pipe or the entire inner pipe must be replaced due to its structure, resulting in a high repair cost and a large amount of repair work. Therefore, there is a problem that the operation of wastewater treatment must be stopped for a certain period of time.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a double-tube heat exchanger which can be suitably used as a heat exchanger for corrosive fluids.

[0005]

The present invention, which has been able to solve the above-mentioned problems, means that the double tubes for heat exchange are connected by a bending tube having a bending angle of more than 90 °. In the heat exchanger, a replaceable short tube portion is provided immediately downstream of the bending tube, and the double tube heat exchanger is characterized. If a replaceable short tube is provided on the downstream side of the curved tube, corrosion will occur mainly in the short tube section.If corrosion occurs, replace the short tube section. Because it is good. The curved tube and the short tube portion are preferably integrated or separate. Further, it is preferable that the bending angle is approximately 180 °, and the bending tube and / or the short tube portion is a double tube or a single tube. INDUSTRIAL APPLICABILITY The heat exchanger of the present invention is suitably used as a heat exchanger for corrosive fluids, and more particularly as a heat exchanger for corrosive fluids that is a mixture of a molecular oxygen-containing gas and a liquid (for example, waste water). be able to. A mixture of a molecular oxygen-containing gas and a liquid (for example, waste water), particularly the above-mentioned mixture in which the pH of the liquid (for example, waste water) is 7 to 14 becomes a corrosive fluid having extremely high corrosiveness. Therefore, even if corrosion occurs inside the heat exchanger due to such a corrosive fluid, it is possible to easily repair or replace the corroded portion by making the portion that causes significant corrosion a replaceable short tube portion. .

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION The double pipe heat exchanger of the present invention is a double pipe heat exchanger in which double pipes for heat exchange are connected by a curved pipe having a bending angle of more than 90 ° (degrees). The heat exchanger is characterized in that a replaceable short tube portion is provided immediately downstream of the bending tube.

The double tube for heat exchange is composed of an outer tube 3 and an inner tube 4, and is designed so that fluids of different temperatures flow through the outer tube 3 and the inner tube 4, respectively. There is no particular limitation, and in general, the end portion of the outer pipe 3 may be fixed to the inner pipe 4 by welding, or the outer pipe 3 and the inner pipe 4 may be loosely fixed via a flange or the like. The structure of the double tube is not particularly limited, and examples thereof include a smooth tube type, a vertical fin tube type, and a direct fin tube type. When the two fluids that exchange heat have similar properties, it is preferable that the double tube has a smooth structure. In the smooth type, the outer tube 3 and the inner tube 4 are concentrically arranged, and a special member for adjusting fluidity and heat exchange rate of fluid is provided inside the outer tube 3 and the inner tube 4. There is no type. Further, when one fluid is a gas or a high-viscosity liquid and the film heat transfer coefficient thereof is extremely smaller than the film heat transfer coefficient of the other fluid, the structure of the double pipe is a vertical fin tube type, It is preferably a horizontal fin tube type. The inner tube diameter and the outer tube diameter of the double tube and the length of the double tube for heat exchange are not particularly limited, and the flow rate of the fluid or medium to be heat-exchanged, the viscosity, the heat exchanger. It may be designed as appropriate according to the size of the plant in which is used.

The number of double tubes for heat exchange can be increased or decreased according to the intended heat transfer area. The arrangement of the double pipes is not particularly limited, but for example, two double pipes are connected in parallel in a horizontal direction by a curved pipe to form one set (horizontal arrangement), 2
With the set (total of four double tubes) as one stage, as the heat transfer area is increased, the number can be increased to two stages and three stages in the vertical (vertical) direction. Such a multi-stage horizontal arrangement of double tubes is a preferable arrangement also in terms of efficiently installing the double tubes and downsizing the heat exchanger.

In the present invention, the double tube for heat exchange is 90
Connected by a bending tube having a bending angle exceeding 0 °, a replaceable short tube portion is provided immediately downstream of the bending tube. Here, the bending angle means, as shown in FIG. 2, the center line 9 of the pipe at one end of the bending pipe and the center line 1 of the pipe at the other end.
An angle θ formed by 0 and 0. For example, the curved tube 2 of FIG.
The bending angle θ is 135 °, and the bending tube 2 in FIG.
This is the case where the bending angle θ is 45 °. Then, like the semi-circular curved tube 2 shown in FIG. 4, the tube center line 9 at one end is
And the center line 10 of the tube at the other end are parallel, the bending angle θ is 180 °. In theory, the bending angle θ is 180
Although it may be considered that the angle exceeds θ, the bending angle θ is 1 with the other end symmetrically arranged with respect to the center line 9 of the tube at one end.
It may be handled as a curved tube within 80 °.

In the present invention, the bending angle of the bending tube to which the double tube for heat exchange is connected is set to be more than 90 ° because the corrosion inside the heat exchanger is directly downstream of the bending tube. This is because it is conspicuous that the flow of the corrosive fluid is partly caused by some load in the curved portion, for example, change from laminar flow to turbulent flow.

In the present invention, a replaceable short pipe portion is further provided on the downstream side of the bending pipe (hereinafter, the bending pipe and the short pipe portion for connecting the double pipe will be collectively referred to as "connecting pipe"). It may be said). If a replaceable short pipe part is provided on the downstream side of the curved pipe, corrosion will occur at the short pipe part provided on the downstream side of the bending part, so the short pipe part was significantly corroded. This is because, in such a case, the short pipe section may be replaced. In the present invention, the upstream side means the side where the heat-exchanged fluid flows into the bending tube with the bending tube as the center, and the downstream side means the fluid that exchanges heat from the bending tube flows. Shall mean the side. The shape of the short tube portion is
There is no particular limitation as long as it does not give a large load to the flow of the fluid to be heat-exchanged, but a straight tube or a substantially straight tube is preferable.

In the present invention, the bending tube and the short tube portion may be integrated or separate. The integral of the curved pipe and the short pipe portion means that the curved pipe and the short pipe portion form a single connecting pipe. When corrosion occurs in a single connecting pipe including the curved pipe portion and the short pipe portion, the single connecting pipe may be replaced.
In addition, the fact that the bending tube and the short tube section are separate bodies means that the bending tube and the short tube section are made of different members. That is, the short pipe portion is a short pipe different from the curved pipe, and when significant corrosion occurs in the short pipe portion immediately downstream of the curved pipe, the short pipe portion may be replaced.
It is preferable that the curved tube and the short tube section are separate bodies from the viewpoint of convenience and economy that only the short tube section that easily corrodes can be replaced. The shape of the short tube portion is not particularly limited, but is preferably a straight tube or a substantially straight tube. This is because the load of the flow of the corrosive fluid does not become large if it is a straight tube or a substantially straight tube. The connection form between the curved pipe and the short pipe part or the connection form between the double pipe and the connection pipe is not particularly limited, and for example, a general flange form for pipes or the like, or a sanitary fixed with a clamp. You can list the format.

Further, in the present invention, it is preferable that the bending angle of the bending tube is approximately 180 °. The bending angle is approximately 180
By setting the angle to °, the double tubes for heat exchange can be arranged substantially in parallel, and the heat exchanger can be downsized. Note that about 180 ° is not always exactly 18
It does not have to be 0 °, which means that an allowable range of deviation is included. The deviation of the permissible range is not particularly limited, but is preferably −30 ° to 30 °, preferably −15 ° to 15 °. further,
In the present invention, a replaceable short tube portion is provided also on the upstream side of the bending tube having a bending angle of about 180 °, and the two short tube portions and the bending tube form a substantially U-shaped connecting pipe. Is also preferable. In the conventional heat exchanger, as shown in FIG. 1, since the double pipes are symmetrically arranged with the connecting portion as the center, if the connecting pipe is a substantially U-shaped connecting pipe, which has a symmetrical shape, it is as it is. This is because it can be applied to conventional heat exchangers.

In the present invention, the structures of the curved pipe and the short pipe portion are not particularly limited, but are preferably double pipes or single pipes, and can be appropriately selected according to the following purposes. If both the curved pipe and the short pipe portion are double pipes, the heat transfer area as a heat exchanger can be increased. Further, if both the bending pipe and the short pipe portion are single pipes, the production of the connecting pipe is facilitated and the cost of the connecting pipe is reduced, so that both the bending pipe and the short pipe portion are single pipes. Doing is also a preferred embodiment. Further, either one of the curved pipe or the short pipe portion may be a single pipe or a double pipe, but a fluid to be heat-exchanged and a flow passage such as a cooling medium or a heating medium are designed. It gets complicated.

The length of the short tube portion is at least 20 cm.
Is preferred. This is because if it is less than 20 cm, the corrosion will proceed to the inside of the double pipe depending on the operation period. The upper limit of the length of the short tube portion is not limited, but preferably 400 cm or less and 300 cm or less. This is because if it exceeds 400 cm, the heat transfer area decreases with respect to the capacity of the heat exchanger.

Hereinafter, an embodiment of the heat exchanger of the present invention is shown in FIGS. In FIG. 5, the double pipes 1 for heat exchange are arranged in parallel, and the connecting pipe 16 has the short pipe portion 1 on the upstream side.
2 and the short tube portion 13 on the downstream side, and the curved tube 2. The short pipe portions 12 and 13 and the bending pipe 2 are separate bodies, and are detachably connected by a flange 15. Since the short pipe portions 12 and 13 are straight pipes and the bending pipe 2 has a bending angle of about 180 °, the connecting pipe 16 is generally U-shaped as a whole. Since the short pipe portions 12 and 13 and the curved pipe 2 are detachably connected by a flange 15, when the short pipe portion 13 on the downstream side of the curved pipe 2 is corroded, the short pipe portion 13 is removed. Can be replaced, and repair is easy. FIG. 6 shows a case where the short pipe portions 12 and 13 and the bending pipe 2 form an integral connecting pipe 16. If corrosion occurs inside the connecting pipe 16, the connecting pipe 16 may be replaced. FIG. 7 is a modification of the bending tube 2. The connecting pipe 16 may have a substantially U shape, and the bending pipe 2 may have a semicircular shape. When the bending tube 2 has a semicircular shape, its radius is not particularly limited, and may be appropriately set in consideration of the arrangement of the double tubes and the tube diameters of the double tube and the bending tube. The radius is, for example, about 2 cm to
It is about 2 m, preferably 30 cm to 1.5 m. FIG. 8 shows a case where the bending pipe 2 and the short pipe portions 12 and 13 form an integral connecting pipe, and the connecting pipe 16 has a double pipe structure. The outer diameter and the inner diameter of the double pipe of the connecting pipe 16 are
By matching with the double tube of the heat exchanger body,
Outer pipe and inner pipe of connecting pipe and outer pipe of double pipe of main body 3
And the flow path of the inner pipe 4 can be communicated. Although FIG. 8 shows only a double tube structure in which the bending tube 2 and the short tube portions 12 and 13 are integrated, the bending tube 2 and the short tube portions 12 and 13 may be separate bodies. Is as described above.

In FIG. 9, the short pipe portion 13 is provided only on the immediate downstream side of the bending pipe 2, the connecting pipe 16 is formed into a substantially J shape, and the position of the double pipe is moved accordingly. A morphological example is shown. The double tubes for heat exchange can be arranged in parallel while keeping the same length as the double tubes in the configurations of FIGS. 5 to 8, and heat can be exchanged without reducing the heat transfer area. it can. Further, in the case where significant corrosion occurs immediately downstream of the bending tube, it is possible to deal with it by replacing the portion. In addition, in the embodiment example of FIGS. 5 to 9, for example, a fluid to be heat-exchanged is supplied from the inlet 5 of the double pipe,
The heating or cooling medium may be supplied from the inlet 7 of the outer tube so as to have a counter flow, and heat exchange may be performed inside the double tube.

Next, an example of usage of the heat exchanger of the present invention will be described. The heat exchanger of the present invention can be suitably used as a heat exchanger for corrosive fluids. This is because, as compared with the conventional heat exchanger, repair and replacement when corrosion occurs immediately downstream of the bending tube is easier. Examples of the corrosive fluid include a fluid containing a corrosive substance and a case where the fluid component itself is a corrosive substance, and is not limited as long as it is likely to cause corrosion of the heat exchanger material. Examples of the corrosive substances include halogens such as halogens and halides, sulfurs such as sulfur, sulfuric acid, sulfurous acid, and sulfides, organic acids such as formic acid, oxalic acid, and citric acid, sodium hydroxide, and hydroxide. Examples thereof include alkalis such as potassium and sodium sulfide. The corrosive substance is
Two or more kinds may be contained in the corrosive fluid.

Examples of the corrosive fluid include corrosive liquids, corrosive gases (gases), and mixtures of corrosive liquids and gases. As the corrosive liquid or the corrosive gas, for example, chemical plants, electronic parts manufacturing equipment, food processing equipment, metal processing equipment, metal plating equipment, printing plate making equipment, photographic equipment such as wastewater and exhaust gas from various industrial plants, Furthermore, waste water and exhaust gas from thermal power generation and nuclear power generation facilities can be mentioned. This is because the wastewater and exhaust gas discharged untreated from various plants contain the corrosive substances as described above, and many of them have corrosive properties.

Therefore, the heat exchanger of the present invention can be suitably used as a heat exchanger of the wastewater treatment plant of the above wastewater, for example, Japanese Patent Laid-Open Nos. 2001-252678 and 2001-293487, Or Japanese Patent Laid-Open No. 2
It can be suitably used as a heat exchanger of a wastewater treatment plant using a wet oxidation treatment system as disclosed in Japanese Patent Publication No. 001-293488. In the wastewater treatment plant in the wet oxidation method, a mixture of wastewater as a corrosive liquid and a molecular oxygen-containing gas (for example, air), generally, an alkaline substance such as sodium hydroxide is added to the wastewater, pH
= 7-14, usually handled as a highly alkaline mixture of pH = 10-13, so not only corrosive drainage but also molecular oxygen-containing gas promotes corrosion of the heat exchanger inner tube, and further, Since the mixture is heated in the heat exchanger, the inner tubes of the heat exchanger are exposed to a very severe corrosive environment. Further, in the case of a corrosive fluid that is a mixture of such a corrosive liquid (for example, waste water) and a molecular oxygen-containing gas, the flow of the corrosive fluid is loaded at the curved portion, and the flow state is It is considered that the corrosion of the inner pipe immediately downstream of the curved pipe has become more prominent due to the change.

As the corrosive waste water, for example, EO
Wastewater from G manufacturing facilities, alcohol manufacturing facilities such as methanol, ethanol and higher alcohols, especially aliphatic carboxylic acids and their esters such as acrylic acid, acrylic acid ester, methacrylic acid, methacrylic acid ester, or terephthalic acid, terephthalic acid ester Examples of the organic acid-containing wastewater discharged from the process for producing an aromatic carboxylic acid or an aromatic carboxylic acid ester such as Further, it may be wastewater having a pH of 7 to 14, wastewater containing a thiosulfate ion or sulfide ion, a sulfur compound such as dimethylsulfoxide, and domestic wastewater such as sewage or night soil. Further, wastewater containing toxic substances such as organic halogen compounds such as dioxins and freons, diethylhexyl phthalate and nonylphenol, and environmental hormone compounds can be mentioned. In particular, the present invention is pH = 7-14.
The present invention is preferably applied to highly basic waste water, or waste water in which an alkaline substance is added to the waste water and pH is adjusted to 7-14. Examples of such waste water include amine, imine, ammonia, and hydrazine. Wastewater containing nitrogen compounds, wastewater from power plants, wastewater from ethylene production facilities, etc. can be mentioned.

Hereinafter, an example of usage of the heat exchanger of the present invention applied to a wastewater treatment plant for oxidizing and / or decomposing wastewater will be described with reference to the drawings. FIG. 10 shows a schematic diagram of the wastewater treatment process. The drainage which is a corrosive fluid is supplied to the heat exchanger 20 through the drainage line 18 by the drainage supply pump 19. At that time, an oxygen-containing gas, for example, air compressed by the compressor 21 is supplied to the wastewater from the gas supply line 22, and the wastewater and the oxygen-containing gas are mixed and supplied to the heat exchanger 20. In the heat exchanger 20, the wastewater is preheated by using the residual heat of the wastewater (treated water) treated in the reactor 26. Then, the waste water is heated in the heat exchanger 23 using steam as a heating medium. The temperature at which the wastewater is heated should be appropriately set according to the type of wastewater and the type of reaction applied in the reactor 26, but is preferably 0 ° C.
Or higher, more preferably 20 ° C. or higher, preferably 370
It is preferable that the heating is performed at a temperature of not higher than 0.degree. C., more preferably not higher than 250.degree. Further, the supply speed of the waste water to the heat exchanger should be appropriately set, but in the case of a liquid, the linear speed is preferably 0.0
5 to 10 m / s, more preferably 0.1 to 5 m / s. In the case of gas, 0.1-3
It is set to 0 m / s, preferably 1 to 20 m / s.

The heated waste water is supplied to the lower part of the reactor 26 and subjected to oxidation and / or decomposition treatment. A solid catalyst layer for oxidizing and / or decomposing the waste water is provided inside the reactor 26, and the waste water is oxidized and / or decomposed when passing through the solid catalyst layer. The wastewater (treated water) treated by the reactor 26 was returned from the treated water line 27 to the heat exchanger in order to heat the wastewater by utilizing the residual heat of the treated water itself or to cool the treated water itself. It is taken out later.

[0024]

Since the heat exchanger of the present invention is provided with a removable short tube portion immediately downstream of the curved tube where corrosion is likely to occur, when significant corrosion occurs in the short tube portion, Only the relevant part can be replaced or repaired. That is,
According to the present invention, when corrosion occurs, replacement and repair of parts of the heat exchanger can be performed easily and at low cost. In addition, since it is not necessary to replace the heat exchanger itself or a part thereof and to stop the operation of the plant for a long period of time, which has been conventionally performed, as a result, the wastewater treatment efficiency is improved.

[Brief description of drawings]

FIG. 1 is a conventional double-tube heat exchanger.

FIG. 2 is an explanatory view of a bending tube having a bending angle of 135 °.

FIG. 3 is an explanatory view of a bending tube having a bending angle of 45 °.

FIG. 4 is an example of a semi-circular curved tube with a bend angle of 180 °.

FIG. 5 is a cross-sectional view of an example embodiment of a heat exchanger of the present invention.

FIG. 6 is a cross-sectional view of an example embodiment of a heat exchanger of the present invention.

FIG. 7 is a cross-sectional view of an example embodiment of a heat exchanger of the present invention.

FIG. 8 is a cross-sectional view of an example embodiment of a heat exchanger of the present invention.

FIG. 9 is a cross-sectional view of an example embodiment of a heat exchanger of the present invention.

FIG. 10 is a schematic diagram of a wastewater treatment process in a wastewater treatment plant.

[Explanation of symbols]

1: Double pipe, 2: Curved pipe, 3: Outer pipe, 4: Inner pipe, 5: Double pipe inlet, 6: Double pipe outlet, 7: Outer pipe inlet, 9:
Center line at one end of the bending tube, 10: Center line at the other end of the bending tube, θ: Bending angle, 12: Short tube portion on the upstream side, 1
3: Short pipe part on the downstream side, 15: Flange, 16: Connection pipe,
17: connecting path of outer pipe, 18: drainage line, 19: drainage supply pump, 20: heat exchanger, 21: compressor,
22: Gas supply line, 23: Heat exchanger, 24: Steam line, 25: Steam drain line, 26: Reactor, 27: Treated water line

Claims (6)

[Claims] 1. A double pipe heat exchanger in which a double pipe for heat exchange is connected by a bending pipe having a bending angle of more than 90 °, and a replaceable short pipe is provided immediately downstream of the bending pipe. A double-tube heat exchanger characterized by having a tube section. 2. The double pipe heat exchanger according to claim 1, wherein the bending pipe and the short pipe portion are integrated or separate bodies. 3. The double pipe heat exchanger according to claim 1, wherein the bending angle is about 180 °, and the bending pipe and / or the short pipe portion is a double pipe or a single pipe. . 4. The double-tube heat exchanger according to claim 1, wherein the heat exchanger is for exchanging heat with a corrosive fluid. 5. The double-tube heat exchanger according to claim 4, wherein the corrosive fluid is a mixture of a molecular oxygen-containing gas and a liquid. 6. The double-tube heat exchanger according to claim 5, wherein the liquid has a pH of 7-14.