An anti-coking nano-ceramic coating and its construction method

Abstract

The present invention provides an anti-coking nano-ceramic coating. This anti-coking nano-ceramic coating is a composite powder component, which includes a nano-ceramic matrix and calcium molybdate. The addition amount of calcium molybdate in the coating should be controlled at 7.3 - 10 wt%, and the uniformly mixed anti-coking nano-ceramic coating powder needs to be sprayed by a thermal spraying process to form a coating. The coating formed on the inner wall parts such as boiler equipment and flue ducts after the construction of the nano-ceramic coating of this application has a certain anti-coking effect, can effectively improve the coking phenomenon caused by long-term contact with high-temperature flue gas, and thus extend the service life of the coating.

Description

Technical Field

[0001] The present invention belongs to the technical field of protective coatings, and particularly relates to an anti-coking nano-ceramic coating and a construction method thereof. Background Art

[0002] Nano-ceramic coatings are a new type of functional coating material that combines the advantages of nanotechnology and ceramic materials. By using nano-scale particles as fillers or active ingredients, the coatings are endowed with a series of excellent properties.

[0003] Ceramic powders such as alumina and zirconia can be used to make protective coatings with high temperature resistance and corrosion resistance. Due to differences in construction processes and coating components, the finally formed coatings will have different performance manifestations.

[0004] When nano-ceramic coatings are applied in boiler equipment, supporting water-cooling equipment, flue gas duct equipment, dust removal equipment, etc., since the boiler equipment, supporting water-cooling equipment, flue gas duct equipment, dust removal equipment, etc. will be in long-term contact with high-temperature flue gas, coking will occur on the coating surface. Coking will bring a series of adverse effects, such as a decrease in thermal efficiency, an increase in energy consumption, and an increased risk of equipment damage due to local overheating.

[0005] The more common methods are mechanical cleaning, chemical cleaning, etc. However, once the coking tendency is large, frequent cleaning is required, which will undoubtedly affect normal production and operation management. Therefore, how to reduce the coking tendency on the coating surface in this application scenario is an important research direction. Summary of the Invention

[0006] In view of the above technical problems, the present application proposes an anti-coking nano-ceramic coating and a construction method thereof. The specific technical solutions are as follows:

[0007] On the one hand, the present application provides an anti-coking nano-ceramic coating, which is a composite powder component, including a nano-ceramic matrix and calcium molybdate. The addition amount of calcium molybdate in the coating should be controlled at 7.3 - 10 wt% to ensure that the nano-ceramic coating has sufficient bonding strength and at the same time improve the anti-coking ability of the formed coating. When the addition amount of calcium molybdate is too low, the anti-coking ability is not obvious. When the addition amount of calcium molybdate is too high, it will affect the hardness of the coating formed by the nano-ceramic coating, and thus affect the wear resistance.

[0008] The nano-ceramic matrix is one or more of silicon dioxide, alumina, zirconia, titanium oxide, and magnesium oxide, and all are in the form of nano-scale powders, and the particle size can be selected from 20 - 100 nm; the nano-ceramic matrix is, for example, alumina, for example, alumina and silicon dioxide, for example, alumina, zirconia and silicon dioxide, for example, alumina and zirconia.

[0009] In the optional range of 7.3 to 10 wt%, the optimal addition amount of calcium molybdate is 8.6 wt%.

[0010] In a more preferred embodiment, the nano-ceramic matrix should include silica, and the addition amount of silica should not exceed 20 wt%. Considering the actual operation, the addition amount of silica should not exceed 17.2 wt%.

[0011] When silica is included in the nano-ceramic matrix, the performance of the obtained coating can be further optimized by adding a certain amount of carbon powder. In particular, the ratio of the addition amount of carbon powder to calcium molybdate and silica is (1 to 2):2.51:2.

[0012] On the other hand, the present application also discloses a method for constructing a coating from the above anti-coking nano-ceramic coating. This method requires using a thermal spraying process to spray the uniformly mixed anti-coking nano-ceramic coating powder to form a coating.

[0013] The beneficial effects of the present invention are as follows: The coating formed on the inner wall parts of boiler equipment, flue ducts, etc. after the construction of the nano-ceramic coating of the present application has a certain anti-coking effect, can effectively improve the coking phenomenon caused by long-term contact with high-temperature flue gas, and thus extend the service life of the coating. Detailed Embodiments

[0014] In the following description, certain specific details are set forth in order to provide a thorough understanding of various embodiments. However, those skilled in the art should understand that the present invention can be practiced without these details. In other instances, well-known structures have not been shown or described in detail to avoid unnecessarily obscuring the description of the embodiments. Unless the context otherwise requires, throughout the specification and the appended claims, the word "comprising" shall be interpreted in an open, inclusive sense, i.e., as "including but not limited to".

[0015] Unless otherwise specified, the reagents, raw materials, etc. in the following examples and comparative examples of the present application are all commercially available. Example 1

[0016] This example provides 10 kg of anti-coking nano-ceramic coating, which includes 57.7 wt% of alumina, 35 wt% of zirconia, and 7.3 wt% of calcium molybdate. Example 2

[0017] This example provides 10 kg of anti-coking nano-ceramic coating, which includes 56.9 wt% of alumina, 35 wt% of zirconia, and 8.1 wt% of calcium molybdate. Example 3

[0018] This embodiment provides 10 kg of anti-coking nano-ceramic coating. The nano-ceramic coating includes 56.4 wt% of alumina, 35 wt% of zirconia, and 8.6 wt% of calcium molybdate. Example 4

[0019] This embodiment provides 10 kg of anti-coking nano-ceramic coating. The nano-ceramic coating includes 56 wt% of alumina, 35 wt% of zirconia, and 9 wt% of calcium molybdate. Example 5

[0020] This embodiment provides 10 kg of anti-coking nano-ceramic coating. The nano-ceramic coating includes 55.5 wt% of alumina, 35 wt% of zirconia, and 9.5 wt% of calcium molybdate. Example 6

[0021] This embodiment provides 10 kg of anti-coking nano-ceramic coating. The nano-ceramic coating includes 55 wt% of alumina, 35 wt% of zirconia, and 10 wt% of calcium molybdate.

[0022] Comparative Example 1

[0023] This embodiment provides 10 kg of anti-coking nano-ceramic coating. The nano-ceramic coating includes 59 wt% of alumina, 35 wt% of zirconia, and 6 wt% of calcium molybdate.

[0024] Comparative Example 2

[0025] This embodiment provides 10 kg of anti-coking nano-ceramic coating. The nano-ceramic coating includes 54 wt% of alumina, 35 wt% of zirconia, and 11 wt% of calcium molybdate.

[0026] Sample Preparation

[0027] In Comparative Example 1, Examples 1 to 6, and Comparative Example 2, the content of zirconia remains unchanged, and the content of calcium molybdate increases.

[0028] The nano-ceramic coating mixed powders of Examples 1 to 6 and Comparative Examples 1 and 2 above were made into coatings by thermal spraying. The method is as follows:

[0029] (1) Surface pretreatment:

[0030] Clean the surface of the substrate to remove oil and oxides;

[0031] Perform sandblasting to increase surface roughness and improve coating adhesion;

[0032] Before spraying, the substrate is usually preheated to 100°C to 300°C to reduce thermal stress and improve coating adhesion;

[0033] (2) Spraying process:

[0034] The dry nano-ceramic coating mixed powder is fed into the plasma spray gun through a powder feeder, and the powder feeding rate is usually 20 to 100 g / min;

[0035] The powder is melted or semi-melted at high temperature and sprayed onto the substrate surface at high speed to form a dense coating. The spraying particle speed is about 200 to 400 m / s; Main gas (such as argon) flow rate: 30 to 60 L / min; Auxiliary gas (such as hydrogen) flow rate: 5 to 15 L / min.

[0036] (3) Cooling and post-treatment:

[0037] After spraying, the coating is cooled naturally.

[0038] Performance detection

[0039] The hardness and anti-coking performance of the coating are detected. Among them, the hardness detection adopts the standard of GB / T 16534-2009; The method for anti-coking performance is: Place the substrate with the coating prepared in cinder with an alkali metal content of 44.29% at 800 °C for 72 hours and then take it out, and observe whether there is coking on the surface of the sample.

[0040] The performance test results are shown in Table 1:

[0041]

[0042] In Table 1, for the anti-coking performance, " / " indicates that no coking phenomenon occurs, and "%" indicates that coking occurs on the surface of the sample coating, and the proportion of the coking area to the total area of the sample coating.

[0043] Combined with the results in Table 1 above, it can be seen that as the addition amount of calcium molybdate increases, the hardness value of the coating gradually decreases, and the anti-coking performance gradually improves. On the one hand, according to the recommendation of the standard T / CEC 685-2022 "Technical Specification for High-temperature Nano-ceramic Identification Coating on Boiler Heating Surface", the hardness of the coating should be greater than 800 HV, so the addition amount of calcium molybdate cannot exceed 10 wt%. On the other hand, to avoid coking during the actual use of the coating, the addition amount of calcium molybdate should also be restricted not to be lower than 7.3 wt%, otherwise the coking phenomenon of the coating will be more obvious. At the same time, it is observed that when the addition amount of calcium molybdate reaches 8.6 wt%, coking does not occur stably. Therefore, 8.6 wt% is the optimal addition value of calcium molybdate. Example 7

[0044] This example provides 10 kg of anti-coking nano-ceramic coating, and the nano-ceramic coating includes 74.2 wt% of alumina, 17.2 wt% of silica and 8.6 wt% of calcium molybdate. Example 8

[0045] This embodiment provides 10 kg of anti-coking nano-ceramic coating. The nano-ceramic coating includes 78.17 wt% of alumina, 13.23 wt% of silica, and 8.6 wt% of calcium molybdate. Example 9

[0046] This embodiment provides 10 kg of anti-coking nano-ceramic coating. The nano-ceramic coating includes 80.65 wt% of alumina, 10.75 wt% of silica, and 8.6 wt% of calcium molybdate.

[0047] Comparative Example 3

[0048] This embodiment provides 10 kg of anti-coking nano-ceramic coating. The nano-ceramic coating includes 66.4 wt% of alumina, 25 wt% of silica, and 8.6 wt% of calcium molybdate.

[0049] Comparative Example 4

[0050] This embodiment provides 10 kg of anti-coking nano-ceramic coating. The nano-ceramic coating includes 56.4 wt% of alumina, 35 wt% of silica, and 8.6 wt% of calcium molybdate.

[0051] Sample Preparation

[0052] In Comparative Example 4, Comparative Example 3, and Examples 7 - 9, the content of calcium molybdate remains unchanged, and the content of silica decreases.

[0053] The mixed powders of the nano-ceramic coatings of Examples 7 - 9 and Comparative Examples 3 and 4 are made into coatings by thermal spraying. The method is the same as that of Example 1 above.

[0054] Performance Detection

[0055] Detect the hardness, anti-coking performance, and thermal shock resistance of the coatings. Among them, the hardness is detected according to the standard of GB / T 16534 - 2009; the anti-coking performance is detected by the following method: Place the substrate with the coating prepared in cinder with an alkali metal content of 44.29% at 800 °C for 120 hours and then take it out, and observe whether there is coking on the surface of the sample; the thermal shock resistance is detected by the following method: Heat the substrate with the coating prepared to 1000 °C, quench it with cold water, and after 40 cycles, observe the cracking and peeling of the coating.

[0056] The performance test results are shown in Table 2:

[0057]

[0058] In Table 2, for the anti-coking performance, " / " indicates no coking phenomenon, "%" indicates coking on the surface of the sample coating, and the percentage of the coking area in the total area of the sample coating. "No" indicates that there are no cracks or peeling on the sample coating, and "Yes" indicates that there are cracks or peeling on the sample coating.

[0059] Combined with the results in Table 2 above, it can be seen that after replacing zirconia with silica, the greater the addition amount of silica, the greater the impact on the hardness of the coating. And the addition amount of silica should not exceed 25%, or rather, the addition amount of silica should be at least lower than 25%, or even lower, to ensure the basic hardness requirements of the coating. On the other hand, the thermal shock resistance was additionally tested. Since the excessive addition of silica has a thermal expansion mismatch with the ceramic matrix material, it intensifies the thermal stress and reduces the thermal shock resistance. Therefore, the addition amount of silica should be controlled within a relatively low range. Secondly, during the anti-coking performance test, the heat preservation time was extended, and it was also found that better anti-coking performance can be obtained when the addition amount of silica is lower. The preferred choice is that the addition amount of silica is 10.75wt%, and at this time, the mass ratio of silica to calcium molybdate is 1:0.8. Example 10

[0060] This example provides 10 kg of anti-coking nano-ceramic coating. The nano-ceramic coating includes 78.5wt% of alumina, 10.75wt% of silica, 8.6wt% of calcium molybdate, and 2.15wt% of carbon powder. Example 11

[0061] This example provides 10 kg of anti-coking nano-ceramic coating. The nano-ceramic coating includes 76.36wt% of alumina, 10.75wt% of silica, 8.6wt% of calcium molybdate, and 4.29wt% of carbon powder. Example 12

[0062] This example provides 10 kg of anti-coking nano-ceramic coating. The nano-ceramic coating includes 74.21wt% of alumina, 10.75wt% of silica, 8.6wt% of calcium molybdate, and 6.44wt% of carbon powder. Example 13

[0063] This example provides 10 kg of anti-coking nano-ceramic coating. The nano-ceramic coating includes 72.07wt% of alumina, 10.75wt% of silica, 8.6wt% of calcium molybdate, and 8.58wt% of carbon powder. Example 14

[0064] This example provides 10 kg of anti-coking nano-ceramic coating. The nano-ceramic coating includes 71.73wt% of alumina, 13.23wt% of silica, 8.6wt% of calcium molybdate, and 6.44wt% of carbon powder.

[0065] Comparative Example 5

[0066] This example provides 10 kg of anti-coking nano-ceramic coating. The nano-ceramic coating includes 69.93 wt% of alumina, 10.75 wt% of silica, 8.6 wt% of calcium molybdate, and 10.72 t% of carbon powder.

[0067] Comparative Example 6

[0068] This example provides 10 kg of anti-coking nano-ceramic coating. The nano-ceramic coating includes 84.04 wt% of alumina, 7.36 wt% of silica, and 8.6 wt% of calcium molybdate.

[0069] Sample Preparation

[0070] In Examples 10 - 13 and Comparative Example 5, the contents of silica and calcium molybdate remain unchanged, and the content of carbon powder increases; in Example 14 and Example 12, the contents of calcium molybdate and carbon powder are the same, and the silica content in Example 14 is greater than that in Example 12; Comparative Example 6 does not contain carbon powder, and the silica content is lower than that in Example 12.

[0071] The mixed powder of the nano-ceramic coatings of Examples 10 - 13 and Comparative Examples 5 and 6 was made into a coating by thermal spraying, and the method was the same as that in Example 1 above.

[0072] Performance Detection

[0073] The hardness, anti-coking performance, thermal shock resistance, and high-temperature resistance of the coating were detected. Among them, the hardness was detected according to the standard of GB / T16534 - 2009; the anti-coking performance was detected by the following method: the substrate with the coating was placed in cinder with an alkali metal content of 44.29% and kept at 800 °C for 120 hours, and then taken out to observe whether there was coking on the surface of the sample; the thermal shock resistance was detected by the following method: the substrate with the coating was heated to 1000 °C and then quenched with cold water, and after 40 cycles, the cracking and peeling of the coating were observed; the high-temperature resistance was detected by the following method: the substrate with the coating was kept at 1400 °C for 10 h in an air atmosphere, and the cracking and peeling of the coating were observed.

[0074] The performance test results are shown in Table 3:

[0075]

[0076] In Table 3, for the anti-coking performance, " / " indicates no coking phenomenon, and "%" indicates coking on the surface of the sample coating, and the proportion of the coking area to the total area of the sample coating; for the thermal shock resistance, "no" indicates that there is no cracking or peeling of the sample coating, and "yes" indicates that there is cracking or peeling of the sample coating; for the high temperature resistance, "no" indicates that there is no cracking or peeling of the sample coating.

[0077] Combined with the results in Table 3 above, it can be seen that after adding a certain amount of carbon powder, the hardness of the coating will be affected, and as the carbon powder addition increases, the hardness of the coating shows a trend of first increasing and then decreasing. When the carbon powder addition is 4.29 - 8.58 wt%, the hardness of the coating can be improved. At the same time, adding carbon powder can improve the anti-coking performance of the coating. Since the addition amounts of calcium molybdate and silicon dioxide remain unchanged, the mass ratio of calcium molybdate, silicon dioxide, and carbon powder, that is, 2.51:2:(1 - 2), should be considered more. And the preferred ratio of the three is 2.51:2:1.5.

[0078] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it.

Claims

1. An anti-coking nano-ceramic coating, characterized in that: The coating is a mixed powder including a nano-ceramic matrix and calcium molybdate, wherein the addition amount of the calcium molybdate is 7.3-10wt%, and the nano-ceramic matrix is ​​one or more of silicon dioxide, aluminum oxide, zirconium oxide, titanium oxide, and magnesium oxide, and all of them are nano-grade powders.

2. The anti-coking nano-ceramic coating according to claim 1, characterized in that: The added amount of calcium molybdate is 8.6wt%.

3. The anti-coking nano-ceramic coating according to claim 1, characterized in that: The nano-ceramic matrix includes silicon dioxide, and the added amount of the silicon dioxide does not exceed 17.2wt%.

4. The anti-coking nano-ceramic coating according to claim 3, characterized in that: The added amount of the silicon dioxide does not exceed 10.75wt%.

5. The anti-coking nano-ceramic coating according to claim 3, characterized in that: Also includes toner.

6. The anti-coking nano-ceramic coating according to claim 5, characterized in that: The mass ratio of the calcium molybdate, silicon dioxide and carbon powder is 2.51:2:(1~2).

7. The anti-coking nano-ceramic coating according to claim 6, characterized in that: The mass ratio of the calcium molybdate, silicon dioxide and carbon powder is 2.51:2:1.

5.

8. The construction method of the anti-coking nano-ceramic coating is characterized in that: The method comprises: uniformly mixing the anti-coking nano-ceramic coating powder according to any one of claims 1 to 7 and then forming a coating by a thermal spraying process.

9. The construction method of the anti-coking nano-ceramic coating according to claim 8, characterized in that: Before thermal spraying, the substrate to be sprayed is subjected to surface pretreatment, and the surface pretreatment includes cleaning and / or sandblasting.

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