JP2002364997A - Heat exchange system for combustion gas - Google Patents

Abstract

PROBLEM TO BE SOLVED: To exchange heat efficiently between a combustion gas flowing through heat transfer tubes such as heat pipes and the like by natural convection and a liquid contacting the outer peripheries of the heat transfer tubes and uniformly over the whole contact surfaces thereof. SOLUTION: In a heat exchange system for exchanging heat between a combustion gas flowing through heat transfer tubes by natural convection and a liquid contacting the outer peripheries of the heat transfer tubes, each heat transfer tube comprises a heat insulating cylindrical sleeve fitted to the inner surface thereof and a heat insulating spiral mixer provided therein to adjust the temperature thereof. In addition, the heat transfer tubes respectively comprises flue ducts at least partially made of a heat insulating member provided at the outlets thereof to suppress the reduction of chimney effect due to the temperature drop of the combustion gas and adjust the residence time of the combustion gas in the heat transfer tubes. These sleeves, the spiral mixers and the heat insulating members can be partially or entirely made of a ceramic material.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a combustion gas heat exchange system, and more particularly, to a heat exchanger having a tubular heat transfer surface such as a heat pipe, which gently heats a liquid to be heated and efficiently heats the liquid. Regarding the exchange system.

[0002]

2. Description of the Related Art Conventionally, an aim is to increase the heat exchange efficiency of a heat exchanger.
The static mixer element is a cylindrical tube.
Used inside a heat transfer tube. FIG.
Is a typical heat exchanger of the related art, and the inside of the heat transfer tube 13
180 ° right-handed blade 11 and 180 ° left-handed blade 12
Static mixer consisting of spiral elements
Of double-pipe heat exchangers arranged at right angles to each other
It is a schematic sectional drawing of a longitudinal direction. Static mixer
The passing fluid is subject to the following four mixing actions by the element:
And mixed. First, two fluids in the first element
And flows along the shape of the element.
Is further divided into two, and the total is divided into four
You. Thus, each time the fluid passes through the element,
Numerically divided and mixed. Next, turn the element right
Fluid is arranged alternately with left-handed
The flow reverses each time it passes through the port. Third, the fluid is d
From the center to the wall, along the twisted surface of the
Moves more continuously to the center. This enhances the mixing effect
Not only the heat exchange performance between the pipe wall and the fluid
Give effect. Finally, the flow is continuously split, inverted,
Is mixed and radial mixing occurs, thus reducing the mixing effect.
Better, no velocity distribution in the axial direction, close to piston flow
The ideal flow is obtained. In this way, the inside of the heat transfer tube
The passing fluid is passed through a static mixer element.
Heat exchange while being divided, mixed and stirred
Is performed.

[0003] Such a static mixer element can be formed by twisting a metal plate such as stainless steel around a central axis in the longitudinal direction. The right-handed spiral element and the left-handed spiral element are welded by, for example, brazing. In FIG. 3, reference numeral 14 denotes a jacket tube (outer tube).
Is provided outside the heat transfer tube 13 so as to surround the heat transfer tube in the longitudinal direction. Heat exchange is performed by passing a heat medium flow, for example, a refrigerant, through the gap between the heat transfer tube 13 and the jacket tube 14 to cool the fluid flowing in the heat transfer tube.

[0004]

However, such a fluid heat exchanger is used exclusively for heat exchange of a liquid or viscous fluid, and the fluid to be exchanged flows through the heat transfer tube. For this purpose, it is necessary to force the fluid to flow using a pump or the like.

Therefore, the present invention is to uniformly and efficiently perform heat exchange between a combustion gas flowing in a heat transfer tube such as a heat pipe by natural convection and a liquid in contact with the outside of the heat transfer tube over the entire contact surface. As an issue.

[0006]

Means for Solving the Problems In order to solve the above-mentioned problems, the present inventors have made intensive studies and as a result, transmitted a cylindrical sleeve and a helical mixer using a heat insulating material such as ceramics. By arranging the heat transfer tube inside the heat transfer tube, it has been found that the heat transfer from the combustion gas flowing by natural convection in the heat transfer tube to the heat transfer tube can be uniformed to adjust the temperature of the heat transfer tube. Further, by providing a flue at the outlet of the heat transfer tube, it was possible to adjust the residence time of the combustion gas, and it was found that the heat exchange rate of the combustion gas was remarkably improved, thereby completing the present invention.

That is, the present invention relates to a heat exchange system between a combustion gas flowing inside a heat transfer tube by natural convection and a liquid coming into contact with the outside of the heat transfer tube. A heat exchange system for combustion gas, characterized in that the temperature of the heat transfer tube is adjusted by providing a sleeve and a helical mixer having heat insulation provided inside the heat transfer tube. .

In a preferred embodiment, in the heat exchange system for combustion gas, a decrease in the chimney effect due to a decrease in the temperature of the combustion gas is suppressed by providing a flue at least partly made of a heat insulating material at the outlet of the heat transfer tube. The residence time of the combustion gas in the heat transfer tube is adjusted.

[0009] In still another preferred embodiment, the spiral mixer comprises one or more torsion blades.

[0010] In one embodiment of the present invention, the helical mixer is formed by connecting two or more torsional blades, and the shape and / or shape of the torsional blades constituting the mixer are combined.
Alternatively, the material is a combination of two or more different materials.

[0011] These sleeves, mixers and / or heat insulating materials can be manufactured partially or entirely using ceramics.

[0012]

An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic diagram for explaining a combustion gas heat exchange system of the present embodiment. In FIG. 1, a cylindrical sleeve 23 is mounted so as to be substantially in close contact with the inner wall of the heat transfer tube 21, a spiral mixer 22 is disposed inside the heat transfer tube 21, and a flue 27 are provided. Heat exchange is performed by passing the liquid through the gap between the heat transfer tube 21 and the jacket tube 30. The liquid may be water, oil, or any other liquid that is usually used after heating.

The combustion gas flowing into the heat transfer tube 21 is prevented from being overheated in the vicinity of the entrance of the heat transfer tube 21 by the heat insulating effect of the cylindrical sleeve 23 which is attached almost in close contact with the inner wall of the heat transfer tube 21. If there is a gap, the combustion gas flows in and the heat insulation effect is impaired, which is not preferable. Further, the combustion gas flows toward the flue 27 while swirling along the spiral mixer 22 disposed inside the heat transfer tube 21, so that the combustion gas is easily mixed in the radial direction, and the heat exchange rate is improved. . The pressure drop created by the mixer 22 increases the residence time of the combustion gases, but the insulation time and / or the length of the flue 27 can be adjusted to optimize the residence time of the combustion gases.

The heat transfer tube 21 and the sleeve 2 used here
3 and the mixer 22 may be of any size, and the outer diameter of the sleeve 23 and the diameter of the blades of the mixer are adjusted according to the inner diameter of the heat transfer tube 21. The thickness of the sleeve 23 can be varied depending on the temperature of the combustion gas or energy consumption to adjust the heat insulation.
The sleeve 23 and the mixer 22 may be arranged on either the inlet side or the outlet side of the combustion gas. Further, a gap may be provided between the inner wall of the heat transfer tube 21 and the mixer 22. A plurality of heat transfer tubes 21 may be provided in series or in parallel so as to satisfy a heat transfer area according to the target performance. Further, they can be arranged horizontally, vertically or diagonally according to the purpose.

The helical mixer 22 of the present embodiment has 1 or 2
It consists of the above-mentioned torsion blades, which may cross each other at right angles, or may form a continuous spiral. In addition, the sleeve 23 and the spiral mixer 22 of the present embodiment,
Although it can be manufactured using various materials such as metals and ceramics, it is preferable that a part or all of the material is made of ceramics, and it is more preferable that the material is refractory ceramics.

The ceramics may be any ceramics as long as they are fire-resistant ceramics, but are preferably impact-resistant ceramics which are porous, have heat insulation properties, and are resistant to sudden temperature changes. Examples of such ceramics include diatomaceous earth, cordierite, β-
Examples include spudumene, alumina, mullite, and silicon carbide.

The shape of the blades of the mixer 22 may be any shape. The deeper the grooves of the blades, the smaller the space occupancy in the heat transfer tube 21.
1 can be increased. By adjusting these space occupancies, the most appropriate mixer 22 for the heat transfer tube 21 to be used is appropriately selected. Further, by manufacturing using ceramics of various materials, torsional blades having various properties can be manufactured from those having a small specific heat and a small thermal inertia to those having a high heat storage property.

The torsion blades constituting the mixer 22 may be manufactured as an integral type, or those manufactured for each unit may be connected and used. Preferably, the central axis in the longitudinal direction of the heat transfer tube 21 is a torsion axis, and the blade extending in the radial direction substantially contacts the inner wall surface of the heat transfer tube 21. The blade is twisted right or left about the torsion axis to form a torsion blade.

More preferably, the blade is a torsion blade obtained by twisting blades extending in two opposite directions about the torsion axis, or a blade extending in three or more directions at an appropriate angle about the torsion axis. Twisted blades.
It is preferable that the blades have the same thickness in the radial direction of the heat transfer tube 21 from the torsion shaft, or that the thickness of the torsion shaft portion is thicker and gradually reduced in the radial direction of the heat transfer tube 21.

As described above, by using the units of the torsion blades having different shapes and / or materials in combination, it is possible to adjust the amount of liquid to be subjected to heat exchange, the temperature, etc.
A combustion gas heat exchange system can be freely constructed.

The number of rotations of the torsion is preferably one or more,
More preferably, the torsion on the combustion gas inlet side is reduced and the torsion on the combustion gas outlet side is increased. When the torsion blades are manufactured and connected for each unit, they may all be connected with the same twist, but it is preferable to connect a weakly twisted one to the combustion gas inlet side and a strongly torsioned one to the outlet side.

FIG. 2 shows another embodiment of the present invention. FIG. 2 shows a heat transfer tube 21 provided in parallel in an oil tank 29, a combustion chamber 26 for sending out a combustion gas from a combustion device such as a gas burner to an entrance side of the heat transfer tube 21, and a heat transfer tube 21 at an outlet side of the heat transfer tube 21. In a gas fryer having a flue 27 for discharging combustion gas, the combustion gas does not directly hit the inner wall of the heat transfer tube on the side of the combustion gas inlet, thereby preventing partial overheating of the heat transfer tube. Cylindrical sleeve 23
A helical mixer 22 disposed inside the heat transfer tube 21 for increasing the heat exchange efficiency by increasing the mixing time and residence time of the combustion gas flowing through the heat transfer tube; An inlet guide 24 for introduction into the inside 21, a heat insulating material 25 arranged between the combustion chamber 26 and the oil tank wall on the inlet side of the combustion gas, and a height provided at the upper part of the flue 27, the height of which is adjusted. And a conditioning flue 28 for optimizing the flow time of the combustion gases.

[0023]

DESCRIPTION OF THE PREFERRED EMBODIMENTS As an embodiment of the present invention, an apparatus schematically shown in FIG. 2 is manufactured as a prototype, and the results of a combustion test when oil is heated using the apparatus will be described. However, the present invention is not limited to this.

In a stainless steel tank (390 mm x 325 mm x 265 mm) having the shape shown as the oil tank 29 in FIG.
Heat transfer tube (outside diameter 89.1 mm, thickness 1.2 mm, length 3)
25 mm). A thermocouple for measuring the oil temperature on the inlet side and the outlet side of the combustion gas was attached to the upper part of each heat transfer tube in the tank. 22 liters of soybean oil in this oil tank
In addition, the upper part of the heat transfer tube was immersed about 65 mm below the oil surface. Four or six tubes on the combustion gas inlet side of each heat transfer tube
A book burner was installed. The energy consumption was calculated by measuring the gas flow rate. The temperature of the oil was measured at about the center of the oil tank, 15 mm above the heat transfer tube and 15 mm above the heat transfer tube using a thermocouple. The exhaust gas temperature was measured at the outlet of the combustion gas with a thermocouple.

A ceramic torsion blade made of diatomaceous earth (trade name: Isolite) having an axial length of about 260 mm (length: 65 mm, centered on the torsion axis) is provided at a substantially central portion in the three heat transfer tubes. With wings extending in two opposite directions, approximately 9
Twenty torsion blades twisted clockwise by 0 ° were connected by four metal bolts). The left heat transfer tube has a deep groove and small space occupancy, the central heat transfer tube has a shallow groove and large space occupancy, and the right heat transfer tube has a deep groove and near the combustion gas inlet. The thing which reduced the air resistance by cutting the splash was arranged. In each case, the length of the blade in the radial direction was 84 mm at the maximum and was slightly smaller than the inner diameter of the heat transfer tube.
Also, a cylindrical sleeve made of 6 mm thick and 65 mm long isolite so as to be in close contact with the combustion gas inlet side heat transfer tube, and the oil tank wall around the combustion gas inlet side and the combustion chamber Was fitted with a thermal insulator made of Isolite. In addition, a flue stack of three refractory blocks is provided on the combustion gas outlet side, and a ceramic board with a height of 45 m
A 0 mm controlled flue was constructed. In addition, a refractory block was cut off to form a combustion chamber also serving as an entrance guide so that the heat insulating effect was enhanced and the combustion gas flowed smoothly into the heat transfer tube.

Using this apparatus, the gas was burned so that the oil temperature would be 180 ° C. according to the experimental conditions shown in Table 1, and the exhaust temperature and the return time (the oil temperature was from 170 ° C. to 180 ° C.)
The time required to return to the above condition) was measured for the maximum temperature of the heat transfer tube (the maximum value of the upper temperature of the heat transfer tube) and the temperature difference between the front and rear of the heat transfer tube (the temperature difference near the combustion gas inlet and the outlet near the heat transfer tube).

[0027]

[Table 1]

Comparing Experiment Nos. 1 and 2 in Table 1, the temperature difference before and after the heat transfer tube was reduced to about 1/2 to 1/10 and the recovery time was reduced to about 1/2 by installing the sleeve and the mixer. became. That is, by using the sleeve and the mixer in combination, the temperature distribution of the heat transfer tubes was made uniform, and the heat exchange efficiency was almost doubled. Experiment Nos. 2 to 5 show measurement results at different energy consumptions by changing the number and strength of gas burners. From these results, the left heat transfer tube, that is, the combination of the left sleeve and the mixer, had a tendency that the temperature difference before and after the heat transfer tube varied slightly when the gas burner was changed, but the central heat transfer tube, that is, the center sleeve And the combination of mixers was relatively stable. Also, when calculating the applied calories until the temperature returns to 10 ° C, 8,200 kcal / h is 405 kcal for each burner.
9,430 kcal / h is 380 kcal and 10,950 kcal / h is 338 k
In cal, 14,200 kcal / h returned to 10 ° C at 331 kcal, and the stronger the gas burner, the more efficient the return.

In Experiment Nos. 6 and 7, when the effect of the length of the flue was examined, the return time was not changed, but the temperature difference before and after the heat transfer tube was reduced. Further, in Experiment Nos. 8 and 9, the effect of the mixer was examined, and it was found that the presence / absence of the mixer had a great effect on shortening the recovery time.

Experiment Nos. 9 and 10 examined the effect of the sleeve. The sleeve reduced the temperature difference between the front and rear of the heat transfer tube and reduced the maximum temperature of the heat transfer tube by 40 ° C. without increasing the recovery time. You can see that. This is achieved by making the sleeve according to the characteristics of the mixer.
This shows the possibility that the temperature difference before and after the heat transfer tube can be reduced sufficiently without lengthening the recovery time.

Next, when the temperature of the torsion blades installed in the three heat transfer tubes was made the same, the temperature of the central heat transfer tube tended to be higher than the temperature of the left and right heat transfer tubes. . In addition, when the flame from the gas burner was observed, it tended to gather at the center. Therefore, a test was conducted in which the thickness of the sleeve was changed and the opening cross-sectional area of the combustion gas inlet portion of the heat transfer tube was changed. The experimental conditions were that the combustion gas energy was
9,430 kcal / h, twisting blades are about 130mm long (65m long
m, two torsion blades twisted clockwise approximately 180 degrees clockwise, with blades extending in two opposite directions about the torsion axis, connected by metal bolts) to the rear end of the torsion blades and the heat transfer tube Was installed in such a manner that the end of the combustion gas coincided with the end of the combustion gas.
Others are the same as the experimental conditions in Table 1. Table 2 shows the results.
It was shown to.

[0032]

[Table 2]

Experiment Nos. 11 to 13 in Table 2 show that the temperature of the heat transfer tube can be freely adjusted by adjusting the thickness of the sleeve and adjusting the opening cross-sectional area of the combustion gas entering the heat transfer tube with respect to the temperature unevenness of the burner. It can be seen that the temperature can be adjusted, and finally, the temperature difference between the heat transfer tubes almost disappears.

[0034]

According to the combustion gas heat exchange system of the present invention, it is possible to optimize the residence time of the combustion gas by natural convection,
By making the temperature distribution in the heat transfer tube uniform or the like, overheating is suppressed, deterioration of the liquid to be heated is reduced, and an efficient heat exchange system is provided. The present system can be used for various liquid heating systems, and provides a heating device that is friendly to the liquid to be heated and that is extremely excellent in energy efficiency.

[Brief description of the drawings]

FIG. 1 is a schematic view showing an embodiment of a combustion gas heat exchange system of the present invention.

FIG. 2 is a schematic view showing another embodiment of the combustion gas heat exchange system of the present invention.

FIG. 3 is a schematic view showing one embodiment of a conventional combustion gas heat exchange system.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 Right twisting blade 12 Left twisting blade 13, 21 Heat transfer tube 14, 30 Jacket tube 22 Mixer 23 Sleeve 24 Entrance guide 25 Insulation material between combustion chamber oil tanks 26 Combustion chamber 27 Flue 28 Control flue 29 Oil tank

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI theme coat ゛ (Reference) F28F 1/00 F28F 1/00 C 21/04 21/04 (72) Inventor Shinichi Miyazaki Hagiyama, Toyokawa City, Aichi Prefecture 2-15 Machi F-term (reference) 3K070 BA03 BA15 3L103 AA39 BB03 CC08 CC27 DD08 DD38 DD98

Claims (5)

[Claims] 1. A heat exchange system between a combustion gas flowing inside a heat transfer tube by natural convection and a liquid in contact with the outside of the heat transfer tube, comprising: a heat-insulating cylindrical sleeve mounted on an inner wall of the heat transfer tube; A heat exchange system for combustion gas, comprising: a spiral mixer having a heat insulating property disposed inside the heat transfer tube to adjust the temperature of the heat transfer tube. 2. The heat exchange system for a combustion gas according to claim 1, wherein a flue at least partially made of a heat insulating material is provided at an outlet of the heat transfer tube, so that a residence time of the combustion gas in the heat transfer tube. A combustion gas heat exchange system, characterized in that: 3. The combustion gas heat exchange system according to claim 1, wherein said spiral mixer comprises one or more torsion blades. 4. The spiral mixer in which two or more torsion blades are connected, wherein the shape and / or material of the torsion blades constituting the mixer are two or more different combinations. The combustion gas heat exchange system according to claim 1, wherein: 5. The heat gas exchange system according to claim 1, wherein the sleeve, the mixer, and / or the heat insulating material are partially or entirely made of ceramics.