JPH01296088A - Bayonet type heat exchanger made of ceramic - Google Patents

Abstract

PURPOSE:To prevent the breakage of an outer tube made of ceramics due to heat shock, by a method wherein a distance between the closed end face of the outer tube and the outlet of an inner tube is limited within a specified range or a guide cap for converting the flow of fluid is provided at the outlet of the inner tube. CONSTITUTION:When a distance L between the closed surface of an outer tube and the end of an inner tube is specified as shown by a formula L>=3d with respect to the inner diameter (d) of an inner tube, turbulent flow zone is grown and a flow speed at a converting part of the flow of fluid as well as a flow speed in the outlet of the inner tube become sufficiently small and a temperature difference between the inner surface of the outer tube made of ceramics and the outer surface of the same is not generated whereby the breakage of the outer tube due to heat shock will never be generated. When the value of the distance L becomes 30d or more, dead water zone of the flow of gas is grown and thereby deteriorating the performance of the title heat exchanger. Accordingly, the distance is preferably within the range of 3d<=L<=30d. On the other hand, a metallic guide cap 13 is provided at the outlet of the inner tube whereby the breakage of the outer tube made of ceramics due to heat shock may be prevented.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention provides a ceramic bilayer net heat exchanger suitable as an air preheater for recovering thermal energy from high-temperature gases, particularly gases that are corrosive at high temperatures. It is related to.

[Conventional technology]

Conventional air preheaters made of steel pipes are used as air preheaters to recover thermal energy from high-temperature, corrosive gases such as urban incineration exhaust gas, but they have problems with heat resistance and corrosion resistance, making them difficult to use. This is difficult, so conventionally it has been common practice to cool the high-temperature gas to a temperature range where corrosion is less likely and then recover the heat. However, although it is possible to prolong life to some extent by adopting such measures, it is far from perfect.

In recent years, various heat exchangers having ceramic heat exchanger tubes have been actively developed as heat exchangers for recovering heat from high-temperature gas.

A bail net heat exchanger has been proposed as a type of ceramic heat exchanger (Utility Model Publication No. 61-141571).
(Japanese Patent Application Laid-Open No. 61-285597).

Because the bail net heat exchanger has a structure that allows completely free movement based on the difference in thermal expansion between the inner and outer tubes, the temperature difference between the fluid outside the outer tube and the fluid on the tube side is extremely large. This is a type of heat exchanger used in some cases. In other words, it is the best heat exchanger for recovering thermal energy from high-temperature combustion exhaust gas and preheating room-temperature gas.

Although ceramics have superior heat resistance, corrosion resistance, and wear resistance compared to metals, they have the disadvantage of being brittle and susceptible to thermal shock. In particular, when low-temperature fluid is introduced from one end of the inner tube and guided from the other end to the junction between the inner and outer tubes, and when the outer tube is attached, the outer tube near the outlet of the inner tube is Although there is a problem of damage due to thermal shock, the above-mentioned publication does not describe any means for solving this problem.

In addition, although the efficiency of the bail net heat exchanger is high because the ratio of the outer diameter of the inner tube to the outer diameter of the outer tube is relatively small, in this case, there is a problem that the ceramics may be damaged due to contact between the inner tube and the outer tube. be. In particular, when using a combination of multiple bail net heat exchangers, or when the bail net heat exchanger is installed at a certain angle to the vertical, the inner tube and outer tube come into contact with each other. It is especially important to solve the above problems when there is a risk of this happening.

As described above, conventional ceramic bi-net heat exchangers have insufficient measures against thermal shock, which is an essential drawback of ceramics. At the same time, since no consideration was given to mutual contact between the inner tube and outer tube, strict dimensional accuracy was required to avoid mutual contact, making it expensive, difficult to upsize, and requiring the use of ceramics during assembly. This method has the disadvantage that it is difficult to install the inner tube and the outer tube at a certain angle with respect to the vertical.

The lack of such countermeasures has delayed the commercialization of ceramic bilayer net heat exchangers.

[Problem that the invention seeks to solve]

As mentioned above, the ceramic bi-net type heat exchanger has the following problems: - When low-temperature fluid is introduced from one end of the inner tube, there is a risk that the outer tube may be damaged due to thermal shock at the outlet of the inner tube.

・It is difficult to increase the size.

- It is difficult to install the inner pipe and outer pipe at a certain angle.

A friend who has similar problems.

The present invention solves the above problems.
It provides a net type heat exchanger.

[Rounding method to solve problems]

The present inventors have made it in view of the above-mentioned conventional problems, and the present invention provides a ceramic pipe-filled heat exchanger in which a low-temperature fluid is introduced from one end of the inner tube. Even if the temperature difference between the side fluid and the low-temperature side fluid, which is the fluid to be heated, is extremely large, the distance between the closed surface area of the outer tube and the outlet of the inner tube is defined within a certain range, or Alternatively, a ceramic pionet heat exchanger with a metal guide cap at the outlet of the inner tube to reverse the flow, and a structure in which the outer ceramic tube is not damaged by thermal shock, is also available. By providing an expansion joint in the part that is not inserted into the tube, and by providing a spacer in the inner tube, no unreasonable force is applied to the ceramic outer tube, and the distance between the inner tube and the outer tube is reduced. This is a piellonet type heat exchanger made of ceramics that can maintain a constant temperature, easily scale up, and allow the inner and outer tubes to be installed at a certain angle to the vertical.

In particular, as will be explained later, when an expansion joint or a spacer is provided, the flow direction in the heat exchanger is not limited. The fluid may be directed to the tube opening side and flowed out from the side supported by the tube plate of the inner tube, since the fluid flows through the inner tube of the outer tube.
This is because KFB flows, so when it flows along the inside of the outer tube, a boundary film is created and the outer tube is not subject to thermal shock and there is no risk of damage. In this case, the distance between the closed end of the outer tube and the open end of the inner tube may be determined by taking into account the gas flow resistance.
There is no need for the relationship 3d≦L.

Next, the present invention will be explained in detail based on the drawings.

FIG. 1 shows a vertical cross-sectional view of a piezo net type heat exchanger manufactured by Nanau Mix. In FIG. 1, reference numeral 1 indicates a ceramic outer tube, and 2 indicates a metal inner tube. The outer tube 1 is held by a retaining ring 3 fixed by a fixing bolt 4.
It is fixed to the tube plate 9 via the cushion ring 6.

On the other hand, the inner tube 2 is fixed to the tube plate 10 as shown in FIG. High-temperature noble gas flows 1m outside the outer tube and is at a low temperature.
Im gas flows in from the inner tube inlet in the direction of the arrow, and while exchanging heat with the gas on the outside of the inner tube, it reaches the eight inner tube outlet (open end), where the flow is reversed and it further exchanges heat with the high temperature side gas. It flows out through the space between the inner and outer tubes. When the low-temperature gas passes through the inner tube, the amount of heat exchanged by the low-temperature gas is small, and the temperature at the entrance to the inner tube and the temperature at the outlet (open south) of the inner tube are almost the same.
If the temperature difference between the high-temperature side gas and the low-temperature side gas is as large as 700C or more, and the distance between the closed outer surface of the outer tube and the outlet of the inner tube is small, a high temperature difference will occur between the inside and outside of the closed surface of the outer tube. Thermal shock resistance temperature difference 5 represented by 8iC, alumina, etc.
Ordinary ceramics with a temperature of 50C or less generate large thermal stress and eventually break.

Moreover, even if the thermal shock resistance temperature difference represented by ;-dayerite and silicon nitride is 550 C or more, a similar situation will occur if the temperature difference between the high-temperature noble gas and the low-temperature side gas becomes even larger.

Through experiments, the inventors discovered a structure in which the ceramic outer tube does not suffer damage due to thermal shock even under such conditions.

In other words, the outer tube made of 7-units should not be damaged by thermal shock.
In order to achieve this, it is important not to allow the low-temperature side gas, which has a temperature difference from the high-temperature side gas, to directly collide with the closed surface of the outer tube. Alternatively, if the distance between the closed surface of the outer tube and the open end of the inner tube is L, and the inner diameter of the inner tube is t-d, it is necessary that L≧3d, and if x- is less than 5d. Similar to the potential core region in a free jet, the central flow velocity of the gas reaches the closed surface of the outer tube. Upon collision, a film is not formed on the surface and a large temperature difference occurs in the ceramic outer tube, which eventually causes the closed end of the outer tube to break due to thermal shock.

On the other hand, when ≧3 dK, a turbulent flow region develops and the flow velocity at the reversal section becomes sufficiently small compared to the flow velocity at the inner tube outlet.
As the membrane develops, the temperature difference between the inner and outer surfaces of the ceramic outer tube becomes dominated by heat conduction within the ceramic. Therefore, no significant temperature difference occurs, and no damage due to thermal shock occurs.

From the above results, there is an appropriate range for the dimensions of the ceramic piellonet heat exchanger, and the range is 3d≦L≦30d.

Furthermore, when the value of L exceeds 301, the gas flow becomes
A dead water region develops, the effective area of the heat exchanger decreases, and the performance as a piellonet heat exchanger deteriorates, so a range of 54≦L30 (1 is desirable).

By adopting this structure, if the local pressure loss coefficient at the outlet of the inner tube is small, the length of the inner tube can be made smaller, so the efficiency as a heat exchanger will not decrease and the pressure loss will be small. A ceramic Bayonets) E heat exchanger can be obtained.

The inventors also proposed a round guide cap 13 for reversing the flow made of metal at the outlet of the inner tube, as shown in FIG.
It has been found that damage to the Seven Fix outer tube due to thermal shock can be prevented by creating a structure in which low-temperature gas does not directly collide with the closed surface of the outer tube 1 at high speed. FIG. 5 shows the section WJ at A-A'llK in FIG. In this case, the gap between the guide cap 15 and the closed round surface of the outer tube 1 may be a distance such that they do not come into contact with each other.

The material of the guide cap is not limited to metal, and any material may be used as long as it does not reduce the function of inverting the low temperature side gas. Furthermore, the structure of the guide cap may be either cylindrical or prismatic, with one end closed and the other open, and the point is that the surface against which the fluid ejected from the inner tube collides is completely closed. There may also be holes cut into the side.

9. As shown in FIG.
If the outer tube 1 and the inner tube 2 are completely fixed, unless the assembly precision is very high, the outer tube 1 and the inner tube 2 will come into contact during assembly, and an unreasonable force will be applied to the ceramic outer tube 1. may lead to damage, but expansion joints 15 as shown in FIG.
By providing K in the part of the inner tube 2 where the outer tube 11/c is not inserted, even if the outer tube 1 and the inner tube come into contact, no unreasonable force is applied to the outer tube, which facilitates manufacturing. A friend who found out.

By adopting such a structure, IP# can be used for large O heat exchangers in which there are multiple combinations of outer tube 1 and inner tube 2, and for IP This means that the heat exchanger II can be easily manufactured even when installed in a

Furthermore, by installing spacers 16 and 17 on the inner tube as shown in FIG. 4, it is possible to maintain the distance between the outer tube 1 and the inner tube 2 almost constant.

In this case, by attaching the spacer 16t at a position where it contacts the presser ring 5, and also making the inner diameter of the presser ring 5 slightly smaller than the inner diameter of the outer tube 1, the spacer 16 intentionally comes into contact with the presser ring 5. By doing so, even if the centers of the outer tube 1 and the inner tube 2 are misaligned, the inner tube 2 is pushed by the holding ring 5 via the spacer 16, and the expansion joint 15 be corrected. Most of the pressing force is absorbed by the expansion joint 15, and the force acting on the spacer 17 in contact with the ceramic outer tube 1 can be made very small.

However, the closer the position of the spacer 17 is to the opening of the inner tube, the smaller the deviation in parallelism (angle #) between the central axes of the inner tube and the outer tube, but the position of the spacer 17 is particularly limited to the vicinity of the open end. It's not something you can do.

In this way, even if the outer tube 1 and the inner tube 2 are misaligned, the structure is such that almost no force is applied to the ceramic outer tube 1, and as a result, the outer tube 1 and the inner tube It is now possible to easily create a large-scale heat exchanger with a plurality of combinations of 2, and it has also become possible to install the inner tube and outer tube at a certain angle R with respect to the vertical direction.

Incidentally, FIGS. 5 and 6 show examples of how to attach the spacer.

〔Example〕

FIG. 7K shows an embodiment in which heat is recovered from combustion exhaust gas of a municipal waste incinerator.

Municipal waste incineration exhaust gas is used as the high temperature side gas, and room temperature air is used as the low temperature side gas.

The low-temperature gas flows in from the low-temperature side gas inlet nozzle 18 at one end of the inner tube 2, and after leaving the outlet of the inner tube 2 at the other end, the flow is reversed, causing a high temperature to flow between the inner tube and the outer tube. It flows in the opposite direction while exchanging heat with the side gas, and the low temperature side gas outlet nozzle 1
9. It gets heated and flows out. On the other hand, the high temperature side gas flows outside the outer tube 1.

The outer tube 1 is made of ceramics made of p-sic and has an inner diameter of 80 W, and the inner tube 2 is made of a stainless steel pipe with an inner diameter (1) of 42.6 mm.

Furthermore, since the inner tube 2 is provided with an expansion joint 15, a spacer 16, and a spacer 17, it can be easily attached even when it is used horizontally as shown in FIG. Further, the spacer 16 is installed at a position where it contacts the presser ring 5, and the spacer 17 is installed near the inner tube outlet. The inner diameter of the retainer ring 5 is 78 mm, which is smaller than the outer tube 1 made of ceramics. By doing so, the structure is such that no unreasonable force is applied to the ceramic outer tube 1.

In this example, when the distance L between the closed surface of the ceramic outer tube 1 and the outlet of the inner tube 2 is 5Gsow (this corresponds to I, a-el, 2tlK), K is the distance between the ceramic outer tube 1 and the outlet of the inner tube 2. At the closed nine end of the outer tube 1,
Damage due to thermal shock occurred.

The operating conditions at this time were that the low temperature side gas inlet temperature was 30C, and the low temperature side gas outlet 19 temperature was 250C.

The gas temperature on the high temperature side was 820C, and under these conditions the outlet temperature of the inner tube 2 was about 40G and %L was small, so damage occurred due to thermal shock.

On the other hand, when L111250■, that is, L5.9d, was operated under the same conditions, the performance as a heat exchanger was the same, no thermal shock damage occurred, and continuous operation for more than 500 hours was possible.

Another embodiment is shown in FIGS. 8 and 9.
9 and 9 show a large-capacity ceramic pionet type heat exchanger equipped with a plurality of heat exchange tubes consisting of an inner tube and an outer tube, when installed horizontally, and an expansion joint 15.
, by providing the spacer 16 and the spacer 171,
It becomes possible to assemble easily. In addition, Fig. 9 is the 8th
It is a sectional view taken along the line BB' in the figure.

〔Effect of the invention〕

In the ceramic I (ionet type heat exchanger) according to the present invention, even if the temperature difference between the low-temperature side gas temperature and the high-temperature side gas temperature is extremely large, the ceramic outer tube may fracture due to thermal shock. In addition, by installing expansion joints and spacers in the inner tube, even in large heat exchangers that require many combinations of ceramic outer tubes and inner tubes, it is possible to prevent the outer tube and inner tube from being perpendicular to each other. Even when installed at a certain angle, no unreasonable force is applied to the ceramic outer tube, making it easy to manufacture and assemble.

[Brief explanation of the drawing]

1, 2, and 4 are longitudinal sectional views of the piezo net type heat exchanger of the present invention, FIG. 5 is a sectional view taken along line OA-A' in FIG. 2, and FIGS. 5 and 6. Figure 7 shows an example of spacer installation, Figure 7 is a detailed explanation of the present invention, and Figures 8 and 9 show an example of a combination of multiple bi-blind net heat exchangers. 9 is a sectional view taken along the line OB-B' in FIG. 8. 1°-outer tube, 2°-inner tube, 3...presser ring, 4...
・IJ fixed bolt, 5...Stain ring washer, 6...
- Cushion ring, 7... Packing, B... Positioning pipe, 9.10... Tube plate, 11... Castable, 12... Castable anchor, 13... Guide cap, 14... - Naport, 15... Expansion joint, 14.17... Spacer, 18... Low temperature side gas inlet nozzle, 19... Low temperature side gas outlet nozzle, d...
Inner tube inner diameter, L...distance between the closed surface of the outer tube and the outlet of the inner tube, θ...displacement angle between the outer tube and the inner tube Fig. 1 Fig. 2 I+5 Fig. 31g1 Fig. 4 Fig. 5 6TIJ Figure 8

Claims (1)

[Claims] 1. A ceramic outer tube with one end supported by a tube sheet and the other end closed, and an inner tube with one end supported by another tube sheet and inserted into the outer tube with the other end open. A bayonet type system in which low-temperature fluid flows in from one end of the inner tube on the tube plate side, guides it between the inner tube and outer tube from the other open end, and flows out from the side of the outer tube supported by the tube plate. A bayonet heat exchanger made of ceramics, characterized in that a distance L between the closed end of the outer tube and the open end of the inner tube is within a range expressed by the following formula. 3d≦L, where d indicates the inner diameter of the inner tube. 2. Claim 1, wherein the distance L between the closed end of the outer tube and the open end of the inner tube is within a range expressed by the following formula:
Ceramic bayonet heat exchanger as described in section. 3d≦L≦30d where d indicates the inner diameter of the inner tube. 3. It is composed of a ceramic outer tube whose one end is supported by a tube sheet and whose other end is closed, and an inner tube whose one end is supported by another tube sheet and which is inserted into the outer tube and whose other end is open. In the bayonet type heat exchanger, the low-temperature fluid is introduced from one end on the tube plate side of the tube, guided from the other open end to between the inner tube and the outer tube, and flows out from the side of the outer tube supported by the tube plate. A bayonet heat exchanger made of ceramics, characterized in that a guide cap for reversing low temperature fluid is provided at the open end of the inner tube on the closed end side of the outer tube. 4. A bayonet consisting of a ceramic outer tube with one end supported by a tube sheet and the other end closed, and an inner tube with one end supported by another tube sheet, inserted into the outer tube, and the other end open. A bayonet type heat exchanger made of ceramics, characterized in that an expansion joint is provided in a portion of the inner tube that is not inserted into the outer tube. 5. The ceramic bayonet heat exchanger according to claim 3, wherein a spacer is provided at the insertion portion of the inner tube into the outer tube and on the outside near the open end.