Protective structure for thermocouple of power station boiler and preparation method of protective structure

Abstract

The invention provides a protection structure for a thermocouple of a power station boiler and a preparation method of the protection structure, the protection structure comprises a thermocouple sleeve and a protection coating, the thermocouple sleeve is coated with the protection coating, and the protection coating comprises ceramic filler layers and mica sheet layers which are alternately stacked. On one hand, strong corrosion resistance of the ceramic packing layer and the mica sheet layer is utilized, on the other hand, weak binding force between the ceramic packing layer and the mica sheet layer is utilized, when coking blocks are formed on the ceramic packing layer, especially when the coking blocks are large, the coking blocks fall off along with the mica sheet layer, and the remaining coating continues to be protected until all the coatings lose efficacy. And the service life is prolonged while the coking phenomenon is avoided.

Description

Technical Field

[0001] The present application belongs to the technical field of high-temperature protective coatings, and in particular, relates to a protective structure for a thermocouple of a power station boiler and a preparation method thereof. Background Art

[0002] During operation, power station boiler thermocouples are prone to high-temperature corrosion, contamination and slagging, flow rate wear and other problems, resulting in poor reliability and stability of thermocouple temperature measurement, and the service life is significantly lower than the design life.

[0003] In order to solve the problem of high-temperature corrosion of thermocouples, the currently published thermocouple protection sleeves generally use tungsten-cobalt alloys, stainless steel, aluminum oxide and other materials to improve the protection performance of thermocouples. For example: In the patent "High-temperature and corrosion-resistant thermocouple protection sleeve and its production method" (CN202211217356.1), for the coal-powder furnace environment, a multi-alloy element configuration and corresponding smelting, casting, and heat treatment processes are used to obtain a wear-resistant and high-temperature resistant thermocouple protection sleeve. However, its corrosion resistance is poor, and there is coking and slagging, which leads to a short life in a high-temperature corrosive environment and poor temperature measurement stability. Summary of the invention

[0004] The technical problem solved by the present application is: how to provide a high temperature corrosion resistant and anti-coking protective structure for power station boiler thermocouples and a preparation method thereof.

[0005] The present application provides a protective structure for a thermocouple of a power station boiler, the protective structure comprising a thermocouple sleeve and a protective coating, the protective coating is coated on the thermocouple sleeve, and the protective coating comprises alternately stacked ceramic filler layers and mica sheet layers.

[0006] Optionally, the innermost layer and the outermost layer of the protective coating are both ceramic filler layers.

[0007] Optionally, the protective coating includes at least three ceramic filler layers and at least two mica flake layers.

[0008] The present application also provides a method for preparing a protective structure for a thermocouple of a power station boiler, the preparation method comprising:

[0009] Surface treatment of thermocouple sleeves;

[0010] Ceramic filler layers and mica sheet layers are alternately made on the outside of the thermocouple sleeve to form a protective coating.

[0011] Optionally, the method for surface treatment of the thermocouple sleeve comprises:

[0012] The thermocouple sleeve is sandblasted to remove surface oxide layer and dirt.

[0013] Optionally, the method of alternately manufacturing ceramic filler layers and mica sheet layers on the outer side of the thermocouple sleeve includes:

[0014] The outer side of the thermocouple sleeve is covered with a refractory fiber cloth soaked with ceramic filler, and then mica flake powder is adhered to the outer side of the refractory fiber cloth, and dried and solidified to form a ceramic filler layer and a mica flake layer;

[0015] Repeat the above process at least once to form a protective coating.

[0016] Optionally, the preparation method further comprises:

[0017] A ceramic filler layer is made on the outermost mica sheet layer.

[0018] Optionally, the preparation method further comprises preparing a ceramic filler, comprising:

[0019] Selecting at least one of aluminum oxide, boron nitride, silicon carbide and chromium trioxide to prepare aggregate;

[0020] Selecting magnesium oxide and at least one of aluminum dihydrogen phosphate and water glass to prepare a binder;

[0021] The aggregate and the binder are mixed, deionized water is added and stirred to obtain a ceramic filler.

[0022] The present application also discloses a power station boiler thermocouple, which includes the above-mentioned protective structure for the power station boiler thermocouple, or the power station boiler thermocouple includes the protective structure prepared by the above-mentioned method for preparing the protective structure for the power station boiler thermocouple.

[0023] The present application provides a protective structure for a thermocouple of a power station boiler, which has the following technical effects:

[0024] 1. The protective structure for thermocouples in power station boilers prepared in this application solves the problem that ordinary thermocouple ceramic coatings are prone to produce a large amount of coking after use. In the protective structure for thermocouples in power station boilers in this application, the bonding force between the mica layer and the adjacent ceramic filler coating is not strong. When the coking block is large, the coking block of the outermost ceramic filler layer will fall off together with the mica layer. After peeling off, the second outermost ceramic filler layer will continue to play a protective role. Repeat the above cycle, peel off layer by layer, until all coatings fail. Its effective protective life is at least 3 times that of ordinary coatings.

[0025] 2. The preparation method of the protective structure of the thermocouple for the power station boiler in the present application has a simple preparation process, low construction requirements, strong operability, and can significantly reduce the manpower and economic costs of the subsequent use and maintenance of the thermocouple. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 A schematic diagram of a protective structure for a thermocouple of a power plant boiler according to one or more embodiments;

[0027] Figure 2 The figure is a cross-sectional schematic diagram of a protection structure for a thermocouple of a power plant boiler according to one or more embodiments.

[0028] The corresponding relationship between the reference numerals and the component names is as follows:

[0029] Thermocouple sleeve - 10, protective coating - 20, ceramic filler layer - 21, mica sheet layer - 22, junction box - 100, temperature measuring end - 200. DETAILED DESCRIPTION

[0030] In order to make the purpose, technical solution and advantages of the present application more clearly understood, the present application is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0031] Before describing the various embodiments of the present application in detail, the technical concept of the present application is first briefly described: the thermocouple protection sleeves currently used in power station boilers have problems such as poor corrosion resistance and coking and slagging. For this reason, the present application provides a protective structure for power station boiler thermocouples and a preparation method thereof. A protective coating is coated on the outside of the thermocouple sleeve. The protective coating includes alternating stacked ceramic filler layers and mica sheets. On the one hand, the strong corrosion resistance of the ceramic filler layers and the mica sheets is utilized. On the other hand, the weak bonding force between the ceramic filler layers and the mica sheets is utilized. When coking blocks are formed in the ceramic filler layers, especially when the coking blocks are large, they will fall off with the mica sheets, and the remaining coatings will continue to provide protection until all coatings fail, thereby avoiding coking and extending the service life. The specific principles of the protective structure for power station boiler thermocouples of the present application are described below in conjunction with more embodiments.

[0032] Specifically, Figure 1 and Figure 2 As shown, the protective structure for a thermocouple of a power plant boiler in the first embodiment includes a thermocouple sleeve 10 and a protective coating 20 . The protective coating 20 is coated on the thermocouple sleeve 10 . The protective coating 20 includes ceramic filler layers 21 and mica sheets 22 that are alternately stacked.

[0033] In one or more embodiments, the innermost layer and the outermost layer of the protective coating 20 are both ceramic filler layers 21. Exemplarily, the protective coating 20 includes at least three layers of ceramic filler layers 21 and at least two layers of mica sheets 22. When the outermost ceramic filler layer 21 produces a large block of coking, it drives the outermost ceramic filler layer 21 and the adjacent mica sheets 22 to fall off together, and the remaining coating continues to protect and fall off layer by layer. When the innermost ceramic filler layer 21 remains, it can continue to protect the thermocouple sleeve 10 for a period of time, so as to avoid the thermocouple sleeve 10 being immediately exposed to the environment and damaged when all the mica sheets 22 fall off, and provide a buffer time for replacing the thermocouple.

[0034] Exemplarily, the power plant boiler thermocouple includes the above-mentioned protective structure, the junction box 100 and the temperature measuring end 200, the junction box 100 and the temperature measuring end 200 are respectively located at the two ends of the thermocouple sleeve 10, and the junction box 100 and the temperature measuring end 200 are directly connected through a connection penetrated inside the thermocouple sleeve 10, so that the electrical signal generated by the temperature measuring end 200 during the measurement process can be transmitted to the junction box 100, and the thermocouple sleeve 10 can prevent the wiring from being damaged.

[0035] In one or more embodiments, a method for preparing a protective structure for a power station boiler thermocouple comprises the following steps:

[0036] Step S10, performing surface treatment on the thermocouple sleeve 10;

[0037] Step S20 , alternately forming ceramic filler layers 21 and mica sheet layers 22 on the outer side of the thermocouple sleeve 10 to form a protective coating 20 .

[0038] Exemplarily, the method for surface treatment of the thermocouple sleeve 10 includes sandblasting the thermocouple sleeve to remove the surface oxide layer and dirt, reveal the metallic luster, and achieve a surface roughness of 10-35 μm to obtain the surface treated thermocouple sleeve 10. It should be noted that the protective coating 20 should be made as soon as possible after the surface treatment, and the longest interval should not exceed 4 hours.

[0039] In one or more embodiments, the method of alternately making ceramic filler layers and mica sheet layers on the outside of the thermocouple sleeve includes: using a refractory fiber cloth impregnated with ceramic fillers to cover the outside of the thermocouple sleeve 10, and then adhering mica sheet powder to the outside of the refractory fiber cloth, drying and curing to form a ceramic filler layer 21 and a mica sheet layer 22; repeating the above process at least once to form a protective coating 20. Then, a ceramic filler layer 21 is made on the outermost mica sheet layer 22. The thickness of the mica sheet is 100μm to 300μm, the thickness of the protective coating 20 is 600-1200μm, the porosity is 1%-3%, the bonding strength is 15-45Mpa, and the high temperature corrosion resistance performance index is 0.126-0.327mg / mm 2 Among them, the heating rate is ≤5℃ / h, the insulation temperature is between 90℃ and 120℃, and the insulation time is ≥2h.

[0040] In one or more embodiments, before performing the above steps, a ceramic filler is prepared, which specifically includes the following steps:

[0041] At least one of aluminum oxide, boron nitride, silicon carbide and chromium trioxide is selected to prepare aggregate, and the average particle size of the aggregate is between 5 μm and 50 μm;

[0042] Selecting magnesium oxide and at least one of aluminum dihydrogen phosphate and water glass to prepare a binder;

[0043] The aggregate and the binder are mixed, deionized water is added and stirred to obtain a ceramic filler.

[0044] In one example, 5kg of chromium trioxide, 7kg of boron nitride and 28kg of aluminum oxide are mixed evenly to obtain aggregate; 45kg of aluminum dihydrogen phosphate with a mass concentration of 85% and 5kg of magnesium oxide are mixed evenly to obtain a binder; the above aggregate and binder are added with 10kg of deionized water and stirred evenly to obtain a ceramic filler. Next, the refractory fiber cloth fully impregnated with the ceramic filler is evenly and tightly wrapped around the surface-treated thermocouple sleeve 10. Before the slurry is dried, a layer of mica flake powder is applied, dried and cured to obtain a single-layer structure of a ceramic filler layer 21 and a mica flake layer 22. Exemplarily, the thickness of the mica flake powder is 300μm, and the parameters for drying and curing are: a heating rate of 5℃ / h, a holding temperature of 90℃, and a holding time of 2h. Repeat this step twice, and make the outermost ceramic filler layer 21 to form the final protective coating 20.

[0045] After obtaining the protective structure of the above example, the thickness of the protective coating is 1000 μm and the porosity is 1% measured by metallographic microscope; the bonding strength of the protective coating is 30 MPa according to GB / T8642-2002; and the protective coating is 2 mg / cm 2The high temperature corrosion resistance of the composite ceramic coating was tested by high temperature corrosion of KCl and Na2SO4 mixed salt for 60 hours, and the mass change was 0.327 mg / mm 2 .

[0046] In another example, 5kg of chromium trioxide, 12kg of silicon carbide and 28kg of aluminum oxide are mixed evenly to obtain aggregate; 40kg of aluminum dihydrogen phosphate with a mass concentration of 85% and 10kg of magnesium oxide are mixed evenly to obtain a binder; the above aggregate and binder are added with 5kg of deionized water and stirred evenly to obtain a ceramic filler. Next, the refractory fiber cloth fully impregnated with the ceramic filler is evenly and tightly wrapped around the surface-treated thermocouple sleeve 10. Before the slurry is dried, a layer of mica flake powder is applied, dried and cured to obtain a single-layer structure of a ceramic filler layer 21 and a mica flake layer 22. Exemplarily, the thickness of the mica flake powder is 200μm, and the parameter conditions for drying and curing are: heating rate 5℃ / h, insulation temperature 90℃, and insulation time 2h. Repeat this step three times, and make the outermost ceramic filler layer 21 to form the final protective coating 20.

[0047] After obtaining the protective structure of the above example, the thickness of the protective coating is 800 μm and the porosity is 1% measured by metallographic microscope; the bonding strength of the protective coating is 40 MPa according to GB / T8642-2002; and the bonding strength of the protective coating is 2 mg / cm2 at 650 °C. 2 The high temperature corrosion resistance of the protective coating was tested by high temperature corrosion of KCl and Na2SO4 mixed salt for 60 hours, and the mass change was 0.126 mg / mm 2 .

[0048] In another example, 5kg of chrome green, 7kg of boron nitride and 23kg of alumina are mixed evenly to obtain aggregate; 48kg of water glass with a modulus of 3.2 and 7kg of magnesium oxide are mixed evenly to obtain a binder; the above aggregate and binder are added with 10kg of deionized water and stirred evenly to obtain a ceramic filler. Next, the refractory fiber cloth fully impregnated with the ceramic filler is evenly and tightly wrapped around the surface-treated thermocouple sleeve 10. Before the slurry is dried, a layer of mica flake powder is applied, dried and cured to obtain a single-layer structure of a ceramic filler layer 21 and a mica flake layer 22. Exemplarily, the thickness of the mica flake powder is 100μm, and the parameters for drying and curing are: a heating rate of 5°C / h, a holding temperature of 90°C, and a holding time of 2h. Repeat this step three times, and make the outermost ceramic filler layer 21 to form the final protective coating 20.

[0049] After obtaining the protective structure of the above example, the thickness of the protective coating was measured by metallographic microscope to be 600 μm and the porosity was 1%. The bonding strength of the protective coating was tested according to GB / T8642-2002 to be 35 MPa. The test results of 2 mg / cm 2 The high temperature corrosion resistance of the protective coating was tested by high temperature corrosion of KCl and Na2SO4 mixed salt for 60 hours, and the mass change was 0.234 mg / mm 2 .

[0050] The specific implementation methods of the present application are described in detail above. Although some embodiments have been shown and described, those skilled in the art should understand that these embodiments can be modified and improved without departing from the principles and spirit of the present application whose scope is defined by the claims and their equivalents. These modifications and improvements should also be within the scope of protection of the present application.

Claims

1. A protective structure for a thermocouple of a power station boiler, characterized in that: The protective structure comprises a thermocouple sleeve and a protective coating, wherein the protective coating is coated on the thermocouple sleeve and comprises ceramic filler layers and mica sheet layers which are alternately stacked.

2. The protective structure for thermocouples of power station boilers according to claim 1, characterized in that: The innermost layer and the outermost layer of the protective coating are both ceramic filler layers.

3. The protective structure for a thermocouple of a power station boiler according to claim 2, characterized in that: The protective coating comprises at least three ceramic filler layers and at least two mica sheet layers.

4. A method for preparing a protective structure for a thermocouple of a power station boiler, characterized in that: The preparation method comprises: Surface treatment of thermocouple sleeves; Ceramic filler layers and mica sheet layers are alternately made on the outside of the thermocouple sleeve to form a protective coating.

5. The method for preparing a protective structure for a thermocouple of a power station boiler according to claim 4, characterized in that: The method for surface treatment of a thermocouple sleeve comprises: The thermocouple sleeve is sandblasted to remove surface oxide layer and dirt.

6. The method for preparing a protective structure for a thermocouple of a power station boiler according to claim 4, characterized in that: The method of alternately manufacturing ceramic filler layers and mica sheet layers on the outer side of the thermocouple sleeve comprises: The outer side of the thermocouple sleeve is covered with a refractory fiber cloth soaked with ceramic filler, and then mica flake powder is adhered to the outer side of the refractory fiber cloth, and dried and solidified to form a ceramic filler layer and a mica flake layer; Repeat the above process at least once to form a protective coating.

7. The method for preparing a protective structure for a thermocouple of a power station boiler according to claim 6, characterized in that: The preparation method further comprises: A ceramic filler layer is made on the outermost mica sheet layer.

8. The protective structure for thermocouples of power station boilers according to claim 4, characterized in that: The preparation method also includes making a ceramic filler, including: Selecting at least one of aluminum oxide, boron nitride, silicon carbide and chromium trioxide to prepare aggregate; Selecting magnesium oxide and at least one of aluminum dihydrogen phosphate and water glass to prepare a binder; The aggregate and the binder are mixed, deionized water is added and stirred to obtain a ceramic filler.

9. A power station boiler thermocouple, characterized in that: The power station boiler thermocouple includes the protective structure for the power station boiler thermocouple described in any one of claims 1 to 3, or the power station boiler thermocouple includes the protective structure prepared by the preparation method of the protective structure for the power station boiler thermocouple described in any one of claims 4 to 8.

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