JPH0558133B2 - - Google Patents

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to a high-temperature corrosion monitoring device, and is particularly suitable for detecting corrosive low-melting compounds produced by the adhesion of combustion ash on the surfaces of components such as boiler heat exchanger tubes. The present invention relates to a high-temperature corrosion monitoring device suitable for.

[Background of the invention]

In boilers that use heavy oil, coal, or a mixture of these as fuel, the metal temperature on the surface of the heat exchanger tube is
It is well known that in regions where the temperature exceeds 500°C, a phenomenon in which heat exchanger tubes are eroded by combustion ash adhering to the surface of the heat exchanger tubes, that is, high-temperature corrosion occurs. This corrosion phenomenon is affected by the composition of the adhering ash, metal temperature, gas temperature, etc., but in severe cases, the amount of annual wall loss may exceed 1 mm.
This has become an important problem in boiler maintenance management.

FIG. 6 shows a schematic cross-sectional view of a heat exchanger tube that has undergone thinning due to high-temperature corrosion, and as is clear from the figure, the position where the thinning has occurred coincides with the position where combustion ash has adhered. In addition, adhering ash is usually divided into an inner layer 19 that is highly corrosive and an outer layer 18 that is less corrosive, and thinning occurs in the lower part of the inner layer 19, and from this inner layer 19, the melting point is lower than the metal temperature on the outer surface of the heat exchanger tube. material,
For example, large amounts of vanadylvanadate (Na ₂ O-V ₂ O ₅ type compound) are detected in oil-fired boilers, and alkali iron sulfate complexes [(Na, K) ₃ Fe(SO ₄ ) ₃ ] are detected in coal-fired boilers. There is. From this, it is clear that the thinning of heat exchanger tubes due to high temperature corrosion is closely related to the low melting point compounds in the ash adhering to the heat exchanger tube surfaces.

The formation of low-melting point compounds in adhering ash depends on the properties of the fuel used, and in boilers that use heavy oil or S with high sulfur (S) and vanadium (V) contents, and coal with high alkaline content, low melting point compounds are generated in the attached ash. A large amount of melting point compounds may be generated, and thinning of heat exchanger tubes due to high-temperature corrosion must be strictly controlled. The usual management method is to measure the wall thickness or outer diameter of heat transfer tubes in areas where high-temperature corrosion is likely to occur, such as the outlet coil of the secondary superheater, during periodic inspections, and replace the heat transfer tubes or wash them with water to prevent corrosion. A method of removing ash, etc. is adopted. However, in order to measure wall thickness or outer diameter, it takes a lot of time to remove adhering ash and secure footholds for this work.

[Purpose of the invention]

The object of the present invention is to eliminate the drawbacks of the prior art described above, and to provide a high-temperature solution that can easily measure and monitor high-temperature corrosion caused by corrosive low-melting compounds produced by adhesion of combustion ash, without requiring work to remove adhering ash. It consists in resisting corrosion monitoring equipment.

[Summary of the invention]

The present invention focuses on endothermic or exothermic reactions accompanying the melting or solidification of low-melting compounds produced by the adhesion of combustion ash, and is stable at the temperature of the part to which combustion ash is attached and in a high-temperature atmosphere when starting or stopping the equipment. It is possible to detect low-melting point compounds in combustion ash based on the temperature difference between the temperature and the standard sample body.

[Embodiments of the invention]

Embodiments of the present invention will be described using the drawings. 1st
The figure shows the structure and principle of an embodiment of the high-temperature corrosion monitoring device according to the present invention.

In Figure 1, heat exchanger tube 1 is used as a standard sample.
A ceramic sprayed layer 2 of alumina, zirconia, etc. is coated on the surface of the ceramic sprayed layer 2.
A thermocouple 3 for differential heat measurement having a contact point is installed on the surface of the heat exchanger tube 1 inside and in the vicinity thereof. Further, a temperature measuring thermocouple 4 for measuring the temperature of the ceramic sprayed layer is installed in the ceramic sprayed layer 2. These thermocouples are led out of the furnace through a side wall tube 5, the differential heat measurement thermoelectric body 3 is connected to a recorder 7 through an amplifier 6, and the temperature measurement thermocouple 4 is directly connected to the recorder 7. .

FIG. 2 is a schematic diagram showing a method of attaching a high-temperature corrosion monitoring device to an actual heat transfer tube. Since the thermocouple is exposed to high temperature combustion gas, it is protected by a protection tube 8. These thermocouples with protection tubes are installed on the anti-gas side (the heat exchanger tube side opposite to the heat exchanger tube side facing the direction of flow of combustion gas) in order to avoid the influence of combustion gas as much as possible, and are further protected by support bands 9. It is fixed to the heat exchanger tube 1. On the other hand, the contact point 10 of each thermocouple is located on the combustion gas side (the heat exchanger tube side facing the flow of combustion gas) to which highly corrosive ash adheres.

When a high-temperature corrosion monitoring device as shown in Fig. 2 is attached to the heat exchanger tubes of a boiler, the thermal sprayed layer 2 and heat exchanger tube 1, which are standard samples, will By measuring the temperature difference between the combustion ash adhering to the surface with a thermocouple 3 for measuring differential heat, and by measuring the temperature of the ceramic sprayed layer 2 with a thermocouple 4 for temperature measurement, the molten salt in the combustion ash ( Low melting point compounds) can be detected.

In other words, if there is a low melting point compound in the combustion ash that has a melting point lower than the metal temperature during boiler operation, an endothermic reaction will occur as the low melting point compound melts during the temperature increase process when the boiler is started, and the boiler operation will stop. During the temperature cooling process, an endothermic or exothermic reaction occurs as the low melting point compound melts and solidifies.

On the other hand, the ceramic sprayed layer 2 is stable at a high temperature comparable to the metal temperature during boiler operation, and no change in state occurs. Therefore, a temperature difference occurs between the surface of the heat exchanger tube to which combustion ash is attached and the ceramic sprayed layer 2 during the temperature increasing process when the boiler is started and the temperature decreasing process when the boiler is stopped. This temperature difference is detected as an electromotive force by a thermocouple 3 for measuring differential heat, magnified by an amplifier 6, and recorded on a recorder 7 (for example, a pen recorder).At the same time, the electromotive force by the thermocouple 4 for temperature measurement is also detected by the recorder 7 to be recorded.

FIG. 4 is an example of a record when an actual boiler is started and stopped. In FIG. 4, the line indicated by A is the temperature record of the ceramic sprayed layer 2 by the temperature measuring thermocouple 4, and since there is no change in the state of the ceramic sprayed layer 2, the temperature is almost close to the metal temperature. Fourth
In the figure, the line indicated by B (broken line) and the line indicated by C (solid line) are examples of recording by the thermocouple 3 for differential thermal measurement. In the line indicated by B (broken line), there is no change in potential difference during the temperature rising process when the boiler is started and the temperature falling process when the boiler is stopped, so no phenomena due to endothermic or exothermic reactions of low melting point compounds are observed. Therefore, in this case, it is determined that there are no low melting point compounds in the combustion ash. In the line C (solid line), there are changes in the potential difference in both the temperature rising process when the boiler is started and the temperature falling process when the boiler is stopped, so a phenomenon due to an endothermic reaction of a low melting point compound is observed. In this case, it is determined that a low melting point compound is present in the combustion ash. Therefore, if there is a potential difference peak due to an endothermic reaction at the melting point of the corrosive low-melting compound during at least one of the temperature raising process when starting the boiler and the temperature decreasing process when the boiler is stopped, the The generation will be detected. Furthermore, the melting point of the low melting point compound (molten salt) can be estimated from the intersection of the vertical axis direction line and the line A at the peak of the potential difference of the line C (solid line).

FIG. 3 shows an embodiment in which a high-temperature corrosion monitoring device as shown in FIG. 2 is attached to a heat transfer tube hanging type boiler. In the heat transfer tube connecting the secondary superheater intermediate header 11 and the secondary superheater outlet header 12,
It is the secondary superheater outlet coil 13 that is most likely to undergo high temperature corrosion, and in FIG. The secondary superheater outlet header 12 is located within the wall tube 16 and is installed in a tube adjacent to the secondary superheater outlet header 12. If the thermoelectromotive force measuring section 14 is installed too close to the ceiling wall tube 16, the amount of combustion ash attached will be small, and the gas temperature will be high in the center of the coil. 1
The optimal position is about 1 m below 6. Furthermore, since the corrosive environment is different for each group of heat transfer tubes, in order to accurately grasp the degree of damage caused by high temperature corrosion to the entire heat transfer tube group, it is desirable to install at least one thermoelectromotive force measurement unit 14 in each group of heat transfer tubes. .

Thermocouple protection tubes are not designed to be cooled, so they reach high temperatures during boiler operation, and there is a strong possibility that combustion ash will adhere to them and cause severe high-temperature corrosion. Therefore, they should be made of ceramics that are stable at high temperatures, such as alumina. It's good to do that. On the other hand, the thermocouple is preferably made of platinum or Pt-PtRh because of the temperature of the atmosphere in which the thermocouple is used (maximum, 1000°C).

The ceramic sprayed layer used as a standard sample is alumina or zirconia, which is stable up to high temperatures, so there is no problem, but the ceramic sprayed layer may peel off at the interface with the base material during use.
It was necessary to use a Ni-based metal sprayed layer as a binder layer between the ceramic sprayed layer and the matrix. In addition, the thickness of the sprayed layer should be determined in consideration of peeling resistance.
0.5 to 1 mm is appropriate.

FIG. 5 shows another embodiment of the invention. In this embodiment, the electromotive force detection section is not attached to the heat transfer tube but is of a probe type.

The tube body 17 of the probe is made of ceramics such as alumina, and a small hole is provided in a part of the tube body 17, and a contact point is provided at a point exposed to the outside through the small hole. A thermocouple 3 for differential heat measurement located inside the body is installed. This thermocouple 3 for differential heat measurement is adapted to measure the temperature difference between the combustion ash adhering to the vicinity of the contact point exposed to the outside through the small hole and the tube body 17 serving as a standard sample. The thermocouple 3 for differential measurement is connected to a recorder 7 via an amplifier 6.
Furthermore, a temperature measuring thermocouple 4 having contacts is installed inside the tube body 17, and this thermocouple 4 is connected to a recorder 7.

In the case of such a probe-type electromotive force detection section as well, it is desirable that the installation position thereof be suspended approximately 1 mm below the ceiling wall pipe 16 for the reasons mentioned above.

In this embodiment as well, the presence or absence of a molten salt, the melting point of the molten salt, etc. can be determined from records such as those shown in FIG. Further, in this embodiment, since the tube body 17 is not designed to be cooled, the temperature of the outer surface of the tube body 17 rises to the gas temperature. Therefore, since the temperature of the tube body 17, which serves as a standard sample, rises above the metal temperature of the heat exchanger tube, the fluctuation of the potential difference by the thermocouple 3 for differential thermal measurement occurs in the region above the gas temperature, which is higher than the metal temperature of the heat exchanger tube. Occur. Therefore, in addition to low melting point compounds, compounds having a melting point higher than the metal temperature of the heat exchanger tube are also detected. Furthermore, in this embodiment, the probe-type electromotive force detection unit is carried out of the furnace during normal operation and only needs to be inserted into the furnace when the boiler is started or stopped, thereby extending the life of the high-temperature corrosion monitoring device. be able to.

In the above-described embodiment, a high-temperature corrosion monitoring device was installed on the outlet coil of the secondary superheater of a boiler where high-temperature corrosion caused by combustion ash is a problem, but in addition to the exit coil of the secondary superheater, Needless to say, high-temperature corrosion monitoring devices can be installed in other equipment parts of the boiler where high-temperature corrosion caused by corrosion is a problem. Furthermore, the present invention can be applied to any equipment other than boilers where high-temperature corrosion caused by combustion ash is a problem.

〔Effect of the invention〕

As described above, according to the present invention, by accurately measuring and monitoring the presence, melting point, etc. of low-melting point compounds in combustion ash attached to equipment members such as boiler heat exchanger tube groups, equipment members caused by high-temperature corrosion can be prevented. The extent of damage can be grasped. Therefore, based on the data obtained by the apparatus of the present invention, it is possible to easily determine the range of wall thickness measurements of heat exchanger tubes, etc. during periodic inspections, whether or not it is necessary to remove adhesion by washing with water, etc., thereby shortening the inspection period. Maintenance management becomes easier.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view showing the configuration of an embodiment of a high temperature corrosion monitoring device according to the present invention, FIG. 2 is a schematic diagram showing a method of attaching the embodiment to a heat exchanger tube according to the present invention,
The figure is a side view showing the installation position of the embodiment according to the present invention, FIG. 4 is a diagram showing measurement results at startup and stop according to the embodiment according to the present invention, and FIG. 5 is another embodiment according to the present invention. FIG. 6 is a schematic diagram showing a cross section of a heat exchanger tube in which high-temperature corrosion occurred. 1... Heat exchanger tube, 2... Ceramics sprayed layer, 3
... thermocouple for differential heat measurement, 4 ... thermocouple for temperature measurement, 5 ... wall surveyor, 6 ... amplifier, 7 ... recorder, 8 ... protection tube, 9 ... support band, 10 ... …
Contact, 11... Secondary superheater intermediate header, 12...
Secondary superheater outlet header, 13... Secondary superheater outlet coil, 14... Thermoelectromotive force measuring section, 15... Front row heat exchanger tube, 16... Ceiling wall tube, 17... Pipe body, 1
8...Ashes attached to the outer layer, 19...Ashes attached to the inner layer.

Claims (1)

[Scope of Claims] 1. On or near the surface of equipment components where high-temperature corrosion caused by low-melting-point compounds in combustion ash is a problem, between a part to which combustion ash adheres and a standard sample part to which combustion ash does not adhere. a first thermocouple having a contact point for measuring a temperature difference; a second thermocouple having a contact point for measuring the temperature of the standard sample portion;
The generation of low melting point compounds in the combustion ash on the surface of the equipment member and/or the melting point thereof can be determined from the peak of the potential difference by the first thermocouple and the potential by the second thermocouple during the heating process and/or cooling process of the equipment. 1. A cooling corrosion monitoring device, comprising: a means for detecting temperature-cooling corrosion. 2. The standard sample part is made of a ceramic layer provided on the surface of an equipment member where high-temperature corrosion caused by low-melting compounds in combustion ash is a problem, and the contact point of the first thermocouple is between the surface of the equipment member and the 2. The high-temperature corrosion monitoring device according to claim 1, wherein the high-temperature corrosion monitoring device is installed in a ceramic layer, and a contact point of the second thermocouple is installed in the ceramic layer. 3. The standard sample section is made of a ceramic tube, and includes a first thermocouple having a contact point exposed to the outside through a hole formed in the tube body and a contact point arranged inside the tube body; 2. The high-temperature corrosion monitoring device according to claim 1, wherein the high-temperature corrosion monitoring device is of a probe type and includes a second thermocouple having a contact installed inside. 4. The high-temperature corrosion monitoring device according to claim 1, wherein the equipment member is a heat exchanger tube of a boiler. 5. The high-temperature corrosion monitoring device according to claim 1, wherein the ceramic layer is a ceramic sprayed layer.