JPS60205108A - Protector structure of heat transfer tube - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

Detailed Description of the Invention [Field of Application of the Invention] The present invention relates to a heat exchanger tube protector structure, and particularly to a heat exchanger tube protector structure suitable for preventing wear and high temperature corrosion of heat exchanger tubes caused by exhaust steam and combustion ash from a soot blower. The present invention relates to a heat tube protector structure.

[Background of the invention]

Heavy oil, coal In boilers that use a mixture of heavy oil and coal as fuel, impurities in the fuel, such as S, ■, and Na, produce ash when burned, and this ash is particularly concentrated in superheating tubes and reheater transfers. It adheres and accumulates thickly on the outer surface of heat pipes. This accumulated ash (also called fly ash) significantly reduces the heat transfer characteristics of the heat transfer tube and causes wear and tear on the heat transfer tube.
It is well known that ash erosion phenomenon, which causes thinning, occurs. In particular, ash erosion becomes a problem in primary superheaters and energy savers where the fuel gas concentrates and flows unevenly near the boiler wall, resulting in a high gas flow rate.

By periodically removing the ash adhering to the heat exchanger tubes in this way, thick adhesion of ash is suppressed.

Conventionally, one method for removing this ash is to connect the secondary superheater outlet coil 3 on the ivy 2 side to the secondary superheater outlet housed in the boiler 1, as shown in Figure 1 (2). Between the superheater intermediate coil 4 or the secondary superheater intermediate coil 4
Soot blowers 68 to 6d are installed between the coil and the secondary superheater inlet coil 5, respectively, to blow out high-pressure steam. In this method, the ash adhering to the surfaces of the heat transfer coils 3, 4.5 can be effectively removed by the high pressure steam from the soot blowers 6a to 6d.

However, since the steam ejected from the soot propellers 6a to 6d contains ash in the fuel gas, the ejected steam directly hits the jacket surface of the heat transfer tube. For example, secondary superheater outlet coil 3
The heat exchanger tube 7 in the lower stage of the grain or the heat exchanger tube in the lowest stage of the secondary superheater intermediate coil 4? In this case, wear occurs due to the ejected steam containing ash, and in severe cases, the annual amount of wall loss can reach more than one day.

Therefore, it is necessary to take measures to prevent wear on the heat exchanger tubes 7.8 that are directly hit by the ejected steam.

As a method for preventing wear of the heat exchanger tubes due to such blown steam containing ash, there is a method to prevent heat exchanger tubes 7 and 8 that are directly hit by the blown steam.
There is a method of thermally spraying oxide-based ceramics such as pure chromium or alumina, which have excellent wear resistance, on the surface of the heat exchanger tube. However, with this conventional method, the temperature of the outer surface of the heat exchanger tube is
If the temperature exceeds 00° C., the difference in thermal expansion between the ffi phase heat exchanger tube and the sprayed layer becomes large, so there is a risk that the sprayed fM may easily peel off due to temperature changes associated with starting and stopping the boiler. Therefore, when applying this method to a superheater or reheater heat exchanger tube, it is necessary to improve the thermal spraying method and solve problems such as post-heat treatment. Furthermore, this method has the disadvantage that it is necessary to blast the base material to improve adhesion, making it unsuitable for on-site work.

Another method for preventing wear of heat exchanger tubes is to make the outer layer of the heat exchanger tube a metal material with excellent wear resistance, such as 25% trichromium-20tinite (JISSUS 310S, etc.), and make the inner layer of the heat exchanger tube a normal heat exchanger tube material. Alternatively, if necessary, it may have a double-tube structure made of a material with excellent high-temperature strength. This heat exchanger tube having a double tube structure is very expensive, and since it is used in large quantities, there is a problem in that the material cost for the entire boiler becomes extremely high.

Compared to the above-mentioned method, a method that is relatively inexpensive and reliably prevents wear caused by ejected steam or ash erosion is a method of installing a protector made of a material with excellent wear resistance on the outside of the heat transfer tube.

FIG. 2 is an explanatory perspective view showing an example of a conventional structure in which a protector is installed on a heat exchanger tube. That is, in this heat exchanger tube protector structure, the protector 10 is installed so as to be loose on the outer surface of the heat exchanger tube 9, which is directly hit by the I-purchased steam. In this example, the protector 10 is a semi-cylindrical holding jig 11.
The protector 10 is held at both ends by welds 12, and one end of the protector 10 is fixed by welds 13 so as not to move. This holding jig 11 holds the protector 10 &
The protector 10 is configured to be slidable on the surface of the heat exchanger tube by thermal expansion of the protector 10.

As a material for the conventional protector 10, SOS 31.0 and the like, which are excellent in wear resistance and high temperature oxidation resistance, are widely used.

However, the conventional heat exchanger tube protector structure has the following problems.

The first problem is that, as shown in Fig. 3, a gap is created between the heat exchanger tube 9 and the poufector 10 due to the difference in thermal expansion due to temperature changes, so fuel ash 14 infiltrates and accumulates (the two heat exchanger tubes significantly reduces the heat absorption of

The accumulated fuel ash 14 may be caught by the protector 10 and cannot be removed by the ejected steam.

Since the heat exchanger tube 9 is cooled by the steam flowing inside the tube,
The outer surface temperature of the heat exchanger tube 9 is kept below the melting point of the ash deposited in the gap. Therefore, there is no risk that the heat exchanger tubes 9 will be exposed to high temperature corrosion. On the other hand, the protector 1 facing the heat exchanger tube 9
As shown in FIG. 3, the inner surface of the protector 10 is exposed to high-temperature fuel gas, reaching a high temperature of 800° C., melting the fuel ash 14 deposited in the gaps, and causing significant corrosion of the protector 10. If the corrosion progresses significantly in this manner, the protector 10 will be eroded and will no longer function as a protector. Incidentally, since the ash is removed from the outer surface of the protector 10 by the jetted steam, there is no problem of high-temperature corrosion.

The second problem is that during boiler operation, the temperatures of the heat exchanger tubes 9 and the protector 10 become extremely high, and stress is exerted on the welded part 13 between the heat exchanger tubes 9 and the protector 10 due to the difference in thermal expansion, resulting in thermal fatigue. υ cracks occur. Therefore, there is a possibility that the protector 10 may fall off from the heat exchanger tube 9.

In order to solve the above problems, the protector 10 is formed from a material that has both wear resistance against ejected steam containing ash and corrosion resistance against fuel ash, especially ash erosion resistance, and it is also welded. It is necessary to avoid structure.

Ceramics such as alumina and silicon carbide can be considered as materials that meet such requirements.

However, although ceramics are excellent at high temperature corrosion in one direction, they are weak at 8 m, making them unsuitable as protector materials.

[Purpose of the invention]

The purpose of the present invention is to prevent ash erosion and thinning of heat exchanger tubes during high-temperature corrosion caused by combustion ash and abrasion of heat exchanger tubes due to steam ejected from the soot blower, which has a negative effect on boiler heat exchanger tubes. An object of the present invention is to provide a suitable heat exchanger tube protector structure.

[Summary of the invention]

The gist of the present invention is to provide a heat exchanger tube protector structure in which a protector is provided on the outer surface of a boiler heat exchanger tube.
For cylindrical chromium-based stainless steel such as US3708, 1. A sprayed layer of high chromium alloy or ceramics such as zirconium oxide is provided on the inner or outer surface facing the heat transfer tube of the protector made of aluminum, aluminum alloy, copper, or copper alloy. This is a heat exchanger tube protector structure characterized by:

The rice protector according to the present invention has a structure in which it is slidably attached to the heat exchanger tube via a holding jig.

Embodiments of the present invention will be described below based on the drawings.

FIG. 4 is a perspective view showing a state in which the protector is attached to the heat transfer U in the heat transfer chamber protector structure according to the present invention;
The figure is a longitudinal sectional view of the heat exchanger tube protector structure. 15 is a heat transfer tube a housed in the boiler, and a protector 19 is attached to the outer surface of the heat transfer tube 15 via holding jigs 16 to 18.
5.・The door can be attached freely. Holding jig 1
6 and 17 are fixed to the transmission line ρ so as to lock both ends of the protector 19. In this embodiment, the holding jig 16,
17, a lag method is adopted. Further, the center portion of the protector 19 is held by a holding jig 18, that is, a semicircular portion. The holding jig 18 consisting of a semi-conforming ring has both ends attached to the welded portions 13 on both sides of the protector 19.
connected by. The inner surface of the protector 19, which is held facing the heat transfer tube in this way, is thermally sprayed by a professional engineer with excellent high-temperature corrosion resistance. 420 is coated.

In addition, the material of the protector 19 is
jf/= 1t of 5US310S etc. which has suffered from wear and tear on both sides
Preferably, chromium 7 stainless steel or aluminum or copper alloys are used. The sprayed layer coated on the inner surface of the protector 19 may be made of a high chromium negative alloy such as 50 chromium or 50 chromium, which has poor corrosion resistance, or a ceramic such as zirconium oxide. Since the sprayed layer 20 is provided on the inner surface of the protector 19 facing the heat exchanger tubes 15, even if it is peeled off from the protector 19 due to temperature changes during startup and shutdown of the boiler, there will be a gap between the heat exchanger tubes 15 and the protector 19. It will not fall off. Therefore, since the sprayed layer 2° further protects the inner surface of the protector 19, an excellent anti-corrosion effect can be expected over a long period of time against the combustion ash 14 that has entered the gap between the protector 19 and the heat transfer tube 15. Note that the thickness of the sprayed layer 2o is preferably about 1 m in consideration of peeling resistance.

The protector 19 is attached to the heat transfer tube 15 by loosely fitting it between both lugs 16 and 17 as shown in the figure, so both ends of the protector 19 are not constrained and can be freely adjusted as the temperature changes. Thermal expansion occurs, and the expansion stress is absorbed by the protector 19 itself. The problem of the protector falling off, which was a problem with the conventional welding method, does not occur at all.Furthermore, it is possible to prevent the protector 19 from moving.In order to do this effectively, the edges of the protector 19 and the lug 16 must be It is necessary to set the interval between lugs 16 and 17 to an appropriate size.For example, in the case of a protector made of 5US310S and about 1 m in length, the interval between lug 16 and 17 and the end of protector 19 should be 2 to 3 times. On the other hand, the lugs 16, 17 and the heat exchanger tubes 15 are joined by welding, but this welding 13 may be done over the entire circumference of the lugs 16, 17, or by welding in several parts. However, since the lugs 16 and 17 are fixed to the heat exchanger tube 15 by welding, the metal warmth inside the lugs is almost the same as that of the heat exchanger tube 15. Therefore, the lugs may be damaged by the combustion ash that has entered the gap. Since corrosion is slight, the material of the lug should be the same as that of the protector.

FIGS. 6 and 7 are a perspective view and a longitudinal sectional view showing an embodiment in which a protector is held on a heat exchanger tube via a semi-cylindrical holding member. This heat exchanger tube protector structure holds the protector 19 by welding both open ends of large-diameter semi-cylindrical holding members 213 to 21c, which are concentric with the heat exchanger tube and have a large diameter, to the side lines of the protector. Stopper 222, 22
b are fixed apart from each other. In this case, the inner surface of the protector is provided with a thermally sprayed layer of a material with excellent corrosion resistance, as in the above example, but the protector 1 on the heat exchanger tube 15 is
9 is attached using semi-cylindrical holding members 21a to 21b, and movement of the protector 19 is prevented by stoppers 22a and 22b welded to the heat transfer tube 15. In this embodiment, the retainers 218 to 21C are welded to both ends and the center of the protector 19, but the number of retainers may be attached only to both ends depending on the length of the protector and the degree of vibration of the heat exchanger tube. , only the central part may be used.

FIG. 8 is a longitudinal sectional view showing another embodiment of the present invention,
A sprayed layer 20 is provided on the inner surface of the protector 19, and further,
A ceramic plate 23 with excellent heat resistance and corrosion resistance is attached to the top surface with high temperature adhesive, and a protector 19 and a heat exchanger tube 1 are attached.
5 shows a heat exchanger tube protector structure in which no gap is formed between the heat exchanger tubes. This heat exchanger tube protector structure is extremely effective when used in environments where extremely corrosive combustion ash is formed, and even a small amount of ash intrusion can cause significant corrosion. .

As the material for the ceramic grating 23, it is preferable to use silicon carbide, boron nitride, etc., which have good thermal conductivity, in order to lower the metal temperature on the inner surface of the protector and reduce the corrosion rate.

FIG. 9 is also a longitudinal sectional view showing another embodiment of the invention, in which the inner surfaces of the lugs 16, 17 shown in FIG.
is press-fitted to prevent the protector 19 from vibrating. This structure is extremely effective when used in environments where the flow rate of ejected steam is high and the protector vibrates violently. Note that the wedge 24 may be made of the same material as the protector 19 because it is not affected by the intruding ash.

Using the same concept, the holding jig 16 shown in Fig. 5 and 'dJJ7
It is also preferable to insert a wedge between the holding jig and the heat exchanger tube and fix the holding jig and the wedge by welding.

FIG. 10 is a perspective view showing another embodiment of the present invention, and the method for slidably attaching the protector 19 to the heat transfer tube 15 is the same as that shown in FIG. The present invention is characterized in that a thermal spray layer 20 made of metal or ceramics having excellent corrosion resistance is provided on the outer surface.

In such a heat exchanger tube protector structure, it is effective to improve the ash erosion resistance when the protector 19 is made of aluminum, an aluminum alloy, copper, or a copper alloy with good thermal conductivity.

The reason why the protector is made of aluminum or copper is that these materials have thermal conductivity more than 10 times that of austenitic stainless steel, which is the usual protector material. This is because the thermal conductivity of the protector does not decrease in any way by attaching the protector. Another advantage is that these materials are also highly ductile.
The gap that occurs between the heat exchanger tube and the protector can be removed after installation.
・It is possible to reduce the amount as much as possible by shaping it with a marker or the like, that is, the adhesion can be increased. On the other hand, in terms of wear resistance, these materials are worse than carbon steel and low-alloy steel, which are normal conductor pipe materials, so their outer surface is coated with high-chromium metal or high-chromium metal with excellent wear resistance. A sprayed layer made of ceramic material such as aluminum oxide or zirconium oxide is provided. In this case, since aluminum and copper materials are soft, surface treatment is easy and an extremely good anchor pattern can be obtained, so the adhesion of the irradiation layer is better than when ordinary steel is used as θ neo. It also has the characteristic of being extremely high.

FIG. 11 is a sectional view taken along the line A-A in FIG. 10, and is an example in which a thermal spray layer 20 is provided on the entire outer surface of the protector 19 on the fuel gas side. In such a heat exchanger tube protector structure, it is appropriate to form a thermal spray layer on a portion of the outer surface depending on the characteristics of ash erosion, as shown in FIG.

FIG. 13 shows an example in which a heat exchanger tube protector structure according to the present invention is attached to a heat exchanger tube that has already experienced buildup erosion and thinning.

According to this embodiment, since the protector 19 is highly ductile, after the protector 19 is attached to the heat exchanger tube 15,
By shaping the protector 19 with a hammer or the like according to the outer shape of the portion 25 eroded by ash erosion, the gap between the heat transfer tube 15 and the protector 19 can be minimized.

Therefore, it is particularly effective when repairing heat exchanger tubes on-site.

The operating temperature limit of this protector is approximately 500℃ for aluminum-based and approximately 800℃ for copper-based.
Compared to austenitic stainless steel, it can only be used in a low temperature range, but since the gas temperature in the primary superheater and economizer, where ash erosion is usually a problem, is 600℃ or less, it is fully usable and heat resistant. There is no particular problem in this respect.

〔Effect of the invention〕

As is clear from the above description, according to the present invention, it is possible to prevent high-temperature corrosion, especially ash erosion, on the inner surface of the protector due to the intrusion of combustion ash, and there is no problem of the protector falling off during use, and the soot blower can be removed from the soot blower. It is possible to stably prevent wear of the heat transfer tubes due to the ejected steam over a long period of time, and its industrial value is extremely large.

[Brief explanation of the drawing]

Fig. 1 is a structural diagram of a boiler superheater, Fig. 2 is a perspective view showing an example of attaching a protector to a conventional heat transfer tube, and Fig. 3 is a cross-sectional view showing the state of corrosion in an actual machine. Fig. 4 is a perspective view showing an embodiment of the mounting of the protector according to the present invention;
The figure is a vertical sectional view showing an embodiment of the mounting of the protector according to the present invention, and FIG. 6 is a perspective view showing another embodiment according to the present invention.
FIG. 7 is a longitudinal sectional view showing another embodiment of the present invention;
The figures are also longitudinal cross-sectional views showing other embodiments of the present invention, FIG. 9 is a longitudinal cross-sectional view showing other embodiments of the present invention, and FIGS.
The figure is an explanatory diagram showing an example in which a thermal spray layer is formed on the outer surface of the protector according to the present invention. 13... Welded part, 15... Heat exchanger tube, 16-18...
- Holding jig, 19... protector, 20... thermal spray layer. Agent Tatsuyuki Unuma Figure 1 Figure 2 Figure 3 Figure 4 Figure 6 Figure 7 Figure 8 Figure 5 Figure 9 5 Figure 10 Figure 11 Figure 12 Figure 13

Claims (6)

[Claims] (1) A heat exchanger tube protector structure in which a protector is provided on the outer surface of a boiler heat exchanger tube, characterized in that a sprayed layer of a high chromium alloy, zirconium oxide, or other ceramic is formed on the inner surface of the protector facing the heat exchanger tube. Heat exchanger tube protector structure. (2) Claim 1, characterized in that the heat exchanger tube is made of 5US310S or other high chromium stainless steel.
Heat exchanger tube protector structure described in section. (3) Claim 1, characterized in that the heat exchanger tube is made of aluminum, aluminum alloy, copper, or copper alloy.
Heat exchanger tube protector structure described in section. (4) A heat exchanger tube protector structure according to claim 1, characterized in that the protector has a ceramic plate adhered to the inner surface facing the heat exchanger tube. (5) % Permissible The heat exchanger tube protector structure according to claim 2, wherein the retaining jig for the protector is a lug fixed to the heat exchanger tube at both ends of the protector. (6) The outer surface of the protector facing the heat exchanger tube is provided with a thermal sprayed layer made of metal or ceramics having excellent heat resistance and L x o -ion resistance. The heat exchanger tube protector structure described in Section 3.