Corrosion-resistant coating for heat exchanger tube in high-temperature chloride molten salt environment and preparation method of corrosion-resistant coating

Abstract

The invention provides a corrosion-resistant coating for a heat exchanger tube in a high-temperature chloride molten salt environment and a preparation method thereof, and the preparation method comprises the following steps: mixing, stirring and drying aluminum powder, aluminum chloride powder, yttrium chloride powder and cerium chloride powder to obtain a mixture 1; mixing the mixture 1 with chloride mixed salt to obtain a mixture 2; and in the inert gas environment, the mixture 2 is heated to be in a liquid state, the liquid mixture 2 wraps the surface of the heat exchanger, an anti-corrosion coating is generated on the surface of the heat exchanger tube under the heat preservation condition, and the anti-corrosion coating comprises, by mass, 10%-20% of aluminum, 1%-4% of chromium, 0.5%-2% of nickel, 0.02%-0.1% of a cerium-yttrium mixture and the balance iron. The corrosion-resistant coating on the surface of the heat exchanger tube is prepared during molten salt flowing, so that the corrosion resistance of the heat exchanger tube is improved by more than 10 times, and the problem of strong corrosion of an alloy material under high-temperature molten chlorate in next-generation solar thermal power generation is solved.

Description

Technical Field

[0001] This invention belongs to the field of molten salt energy storage technology, specifically to a corrosion-resistant coating for heat exchanger tubes in a high-temperature chloride molten salt environment and its preparation method. Background Technology

[0002] Molten salt thermal energy storage technology using chloride mixed salts can increase the maximum operating temperature of existing commercial molten salts from 550°C to over 800°C, thereby significantly improving the thermoelectric conversion efficiency of power cycle systems. Using advanced supercritical carbon dioxide Brayton power cycle systems, this could theoretically increase efficiency from the current approximately 40% to over 55%, while also significantly reducing thermal energy storage costs, lowering the levelized cost of electricity (LCOE) of solar thermal power plants to below 5 cents per kilowatt-hour. In addition to CSP (Combined Solar Power Systems), this advanced molten salt high-temperature thermal energy storage technology can also be used in Carnot batteries, increasing the energy storage efficiency of Carnot batteries based on commercial nitrate molten salt thermal energy storage technology (up to 70%) to over 90%, while also significantly reducing energy storage costs. This will help realize the large-scale commercial application of Carnot batteries in future energy systems.

[0003] Chlorides are diverse and generally inexpensive, and can be formulated into mixed salts with different melting points as required. They also possess a relatively large latent heat of phase change. However, the disadvantages of chlorides as molten salts include the difficulty in determining their upper operating temperature limit, and the fact that most are highly corrosive. To ensure a 30-year service life for commercial concentrated solar power (CSP) plants, the corrosion rate of molten salt mixtures containing sodium chloride, potassium chloride, and magnesium chloride on CSP system storage tanks must be less than 20 micrometers per year. However, tests show that molten chlorides can corrode bare stainless steel alloys at rates as high as 4500 micrometers per year.

[0004] Currently, there are two main methods for modifying alloy materials in the field of solar thermal power generation: alloy surface pretreatment and alloy surface coating. Studies have shown that pre-oxidation of the alloy surface can form a protective Al2O3 layer, which can effectively inhibit the dissolution of chromium and iron and the extensive penetration of corrosive impurities. The formed Al2O3 can significantly improve the strength and creep resistance of the alloy and effectively reduce the corrosion rate. For example, using alloy surface pre-oxidation to slow down corrosion, the surface passivation of the alloy forming alumina after pre-oxidation is measured. The dense and uniform Al2O3 formed during pre-oxidation can protect the alloy from molten chloride corrosion. However, the Al2O3 layer formed in a pure Ar atmosphere is usually too thin, so 20% O2 needs to be added for pretreatment. The protective behavior of the Al2O3 layer is attributed to the formation of a stable α-phase. α-Al2O3 usually forms at temperatures above 1150℃. Metastable γ-Al₂O₃ and θ-Al₂O₃ layers formed at lower temperatures contain lattice defects and offer little protection compared to α-Al₂O₃. They are readily consumed in chloride molten salts, and when the vapor pressure of chlorides is sufficiently high, their combination with oxygen-containing compounds creates a harsh atmosphere, typically detrimental to common chromium-formed alloys. Studies have shown that coating alloy samples with an aluminide paste and then exposing them to molten chlorides at 700°C, where the performance of the aluminide coating is determined by the intrinsic concentration of secondary phases precipitated in the FeAl, (Fe, Ni), or other intermetallic compound aluminide matrix, presents a more suitable method for Fe-rich high-temperature alloys. Since Cr has a higher solubility in iron aluminides than in nickel aluminides, Fe-rich aluminide coatings are more resistant to molten chlorides than Ni-rich coatings. The Cr-rich phase selectively dissolves during exposure, making this method more suitable for Fe-rich high-temperature alloys. Summary of the Invention

[0005] To address the problems existing in the prior art, this invention provides a corrosion-resistant coating for heat exchanger tubes in a high-temperature chloride molten salt environment and a preparation method thereof. The corrosion-resistant coating is prepared on the surface of the heat exchanger tubes during the molten salt flow process, thereby improving the corrosion resistance of the alloy. The corrosion resistance of the heat exchanger tubes is increased by more than 10 times, solving the problem of severe corrosion of alloy materials under high-temperature molten chloride salt in next-generation solar thermal power generation technology.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a corrosion-resistant coating for heat exchanger tubes in a high-temperature chloride molten salt environment, wherein the coating comprises, by mass fraction: 10%~20% aluminum, 1%~4% chromium, 0.5%~2% nickel, 0.02%~0.1% cerium-yttrium mixture, and the remainder being iron.

[0007] Furthermore, the heat exchanger tubes are made of any type of 18-8 series stainless steel.

[0008] The present invention also provides a method for preparing the above-mentioned corrosion-resistant coating for heat exchanger tubes in a high-temperature chloride molten salt environment, the specific steps of which are as follows: Aluminum powder, aluminum chloride powder, yttrium chloride powder, and cerium chloride powder are mixed, stirred, and dried to obtain mixture 1; Mixture 1 is mixed with a chloride mixed salt to obtain mixture 2; In an inert gas environment, mixture 2 is heated to a liquid state, and the liquid mixture 2 coats the surface of the heat exchanger. Under heat preservation conditions, a corrosion-resistant coating is formed on the surface of the heat exchanger tubes.

[0009] Furthermore, by mass fraction, mixture 1 comprises: 90% to 97% aluminum powder, 1% to 4% aluminum chloride powder, 1% to 3% yttrium chloride powder and 1% to 3% cerium chloride powder.

[0010] Furthermore, the drying temperature is 100℃~120℃, and the drying time is 20h~25h.

[0011] Furthermore, the amount of mixture 1 added to the chloride mixed salt is 1% to 3% by mass fraction.

[0012] Furthermore, the chloride molten salt includes at least two of potassium chloride, sodium chloride, magnesium chloride, and zinc chloride, and the addition ratio is arbitrary.

[0013] Furthermore, in an inert gas environment, mixture 2 is heated to 700℃~750℃ to obtain liquid mixture 2. Liquid mixture 2 coats the surface of the heat exchanger, and the heat preservation time is less than 10 hours, thereby generating a corrosion-resistant coating on the surface of the heat exchanger tubes.

[0014] Furthermore, the heat exchanger tubes are made of any one of the 18-8 series stainless steels.

[0015] The present invention also provides a corrosion-resistant heat exchanger tube for use in a high-temperature chloride molten salt environment, wherein the surface of the corrosion-resistant heat exchanger tube has a corrosion-resistant coating, which is prepared by the above-described preparation method.

[0016] Compared with the prior art, the present invention has at least the following beneficial effects: This invention provides a corrosion-resistant coating for heat exchanger tubes in high-temperature chloride molten salt environments. It exhibits excellent corrosion resistance under the harsh corrosive conditions of high-temperature chloride molten salt, effectively solving the industry pain point of severe corrosion of alloy materials by high-temperature molten chloride in next-generation solar thermal power generation technology, and improving the corrosion resistance of heat exchanger tubes by more than 10 times. 10%~20% aluminum in the coating is the core corrosion-resistant element, forming a dense aluminum-rich layer on the alloy surface, preventing the intrusion of corrosive ions in the molten salt and the diffusion and escape of active metal elements from the matrix. 1%~4% chromium and 0.5%~2% nickel work synergistically, relying on the passivation properties of chromium and the high-temperature stability of nickel to further enhance the coating's resistance to chloride corrosion. Simultaneously, they form a multi-element alloy phase with aluminum, improving the bonding strength between the coating and the 18-8 stainless steel substrate, preventing peeling and cracking of the coating during molten salt flow. The 0.02%–0.1% cerium-yttrium mixture in the coating serves as a rare earth modifier, refining the coating's microstructure, increasing density, blocking chloride molten salt penetration, and reducing the risk of intergranular corrosion. It also forms stable intermetallic compounds with aluminum and iron to enhance the coating's high-temperature stability, while promoting uniform aluminum diffusion, inhibiting the loss of active elements from the matrix, and improving the alloy's corrosion resistance. This coating composition design balances corrosion resistance, adhesion, and high-temperature stability, with each element working synergistically. Furthermore, it is suitable for the actual operating conditions of solar thermal power generation systems, providing an efficient material solution for corrosion control of heat exchanger tubes in high-temperature chloride molten salt environments.

[0017] The in-situ preparation method of the corrosion-resistant coating of this invention relies on the molten salt flow process to generate a coating on the surface of heat exchanger tubes. It is a green and efficient preparation process adapted to high-temperature chloride molten salt environments. Compared with traditional surface modification methods, it has significant advantages such as low implementation requirements, simple operation, low energy consumption, environmental friendliness, and no complicated process steps. At the same time, it can reduce the corrosiveness of chloride molten salt while preparing the coating, achieving the dual effects of molten salt modification and coating preparation. The method prepares a mixture 1 by mixing aluminum powder, aluminum chloride powder, yttrium chloride powder, and cerium chloride powder, and then compounding it with a chloride mixed salt to obtain a mixture 2. After heating to a liquid state in an inert gas environment, the mixture is coated on the surface of the heat exchanger. After heat preservation, in-situ aluminizing film formation is completed. The entire process is completed in-situ within the molten salt system, without the need for additional coating, spraying, or other equipment. The process is compatible with existing molten salt storage tanks and other devices in solar thermal power generation systems, and is easy to promote and apply industrially. During the preparation process, aluminum powder serves as the core aluminizing source, reacting with impurities in the chloride molten salt to effectively reduce the corrosion rate of the molten salt. The generated gaseous aluminum chloride spontaneously flows within the molten salt, forming an interface layer on the heat exchanger alloy surface and undergoing adsorption and decomposition reactions to generate active [Al] which diffuses into the substrate, achieving in-situ aluminizing and forming a dense aluminum-rich layer. Cerium and yttrium elements diffuse with the gaseous aluminum chloride, synergistically promoting the enrichment and diffusion of active [Al]; they participate in the interface reaction and disperse uniformly, refining the coating structure and increasing density; they inhibit excessive aluminum oxidation, promote metallurgical bonding between the coating and the substrate, and enhance coating adhesion. Furthermore, the inert gas environment effectively prevents the oxidation of raw materials and coatings at high temperatures, ensuring the purity and performance stability of the coating. The liquid mixture 2 coats the heat exchanger surface, allowing the coating to conform to the surface morphology of the heat exchanger tubes without dead corners, making it suitable for the preparation of heat exchanger tubes with complex structures. This preparation method achieves precise control and efficient utilization of elements in terms of process design. The introduction of cerium and yttrium elements further enhances the performance of the coating. At the same time, the process itself is both economical and practical, providing a feasible path for the industrial preparation of corrosion-resistant coatings for heat exchanger tubes in high-temperature chloride molten salt environments.

[0018] This invention further limits the parameters of the corrosion-resistant coating preparation method, achieving precise control of the preparation process and ensuring the performance stability and batch consistency of the corrosion-resistant coating. Each parameter is optimized around the coating composition design and the efficient functioning of cerium and yttrium, adapting to the requirements of in-situ aluminizing processes using high-temperature chloride molten salts. In mixture 1, 90%–97% aluminum powder provides a sufficient primary source for aluminizing, 1%–4% aluminum chloride powder assists in improving aluminum diffusion efficiency, and 1%–3% yttrium chloride powder and 1%–3% cerium chloride powder ensure that cerium and yttrium fully play their role in refining the microstructure and increasing density, while avoiding coating performance degradation caused by excessive rare earth elements. Drying parameters of 100℃–120℃ and 20h–25h effectively remove moisture from the raw materials, preventing bubbles from forming in the molten salt during high-temperature heating and affecting the coating film quality, while also preventing reactions between moisture and chloride salts, ensuring the effectiveness of the raw materials. The addition of 1% to 3% of the chloride mixed salt balances the diffusion efficiency and the stability of the molten salt system. This provides sufficient active elements for in-situ aluminizing without causing abnormal molten salt viscosity due to excessive addition, ensuring the effective flow and coating of the molten salt. The chloride molten salt uses at least two compounds, such as potassium chloride and sodium chloride, suitable for a heating temperature of 700℃ to 750℃, forming a stable liquid molten salt system that provides a good medium for element diffusion. The heating temperature of 700℃ to 750℃ is the optimal range for the diffusion of aluminum and cerium yttrium, ensuring effective diffusion of active [Al] and cerium yttrium ions while avoiding coarsening of the matrix grains due to excessive temperature. The heat preservation process provides sufficient time for coating formation and uniform element distribution. The heat exchanger tubes are made of 18-8 series stainless steel, matching the iron-based composition of the coating, improving the bonding strength between the coating and the substrate. The synergistic effect of various parameters makes the preparation process more operable and ensures that the coating performance meets the standards.

[0019] The corrosion-resistant heat exchanger tube for high-temperature chloride molten salt environments of this invention achieves a significant improvement in corrosion resistance by preparing the aforementioned corrosion-resistant coating on its surface using a corresponding in-situ preparation method. This effectively solves the severe corrosion problem of alloy heat exchanger tubes in next-generation solar thermal power generation technology under high-temperature molten chloride salt conditions, increasing the corrosion resistance of the heat exchanger tube by more than 10 times and providing core equipment protection for the long-term stable operation of solar thermal power generation systems. The core advantage of this corrosion-resistant heat exchanger tube lies in the metallurgical bonding between its surface corrosion-resistant coating and the substrate. This effectively blocks the intrusion of corrosive ions in the chloride molten salt and inhibits the diffusion and escape of active elements such as Fe, Cr, and Ni from the substrate into the molten salt, fundamentally solving the corrosion failure problem of the heat exchanger tube. Furthermore, the coating of this heat exchanger tube is prepared in-situ during the molten salt flow process, integrating the coating preparation with the actual operating conditions of the solar thermal power generation system. No additional offline treatment of the heat exchanger tube is required, significantly reducing equipment processing and maintenance costs. Moreover, the preparation process is low-energy-consuming and environmentally friendly, meeting the development requirements of industrial energy conservation and environmental protection. Compared to traditional unmodified heat exchanger tubes and those using other surface modification methods, the corrosion-resistant heat exchanger tubes of this invention have a longer service life in high-temperature chloride molten salt environments, effectively reducing the frequency of equipment replacement and maintenance, and lowering the operating costs of solar thermal power generation systems. Simultaneously, the reaction between aluminum powder and molten salt impurities during coating preparation further reduces the corrosiveness of chloride molten salt, achieving dual optimization of the heat exchanger tubes and the molten salt system. This corrosion-resistant heat exchanger tube fills the technological gap for high-efficiency corrosion-resistant heat exchanger tubes in high-temperature chloride molten salt environments. Its preparation process is adapted to the needs of industrial production, and the coating performance closely matches the actual operating conditions of solar thermal power generation. It not only provides crucial equipment support for the upgrading and development of solar thermal power generation technology but also offers a referable technical solution for the protection of alloy equipment in other high-temperature molten salt corrosion environments. It possesses significant technological innovation, industrial practicality, and economic and social benefits, and has broad prospects for widespread application. Attached Figure Description

[0020] Figure 1 The cross-sectional morphology of the 316L heat exchanger alloy after in-situ preparation of a corrosion-resistant coating.

[0021] Figure 2 The molten salt corrosion morphology of a 316L heat exchanger after in-situ preparation of a corrosion-resistant coating.

[0022] Figure 3 This is a performance comparison between the embodiments and comparative examples of the present invention. Detailed Implementation

[0023] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0024] This invention provides a corrosion-resistant coating for heat exchanger tubes in a high-temperature chloride molten salt environment. The coating consists of the following components by mass fraction: 10%~20% aluminum, 1%~4% chromium, 0.5%~2% nickel, 0.02%~0.1% cerium-yttrium mixture, and the remainder being iron.

[0025] The aforementioned corrosion-resistant coating is prepared on the surface of heat exchanger tubes made of 18-8 series stainless steel. The heat exchanger tubes with this coating exhibit a more than 10-fold increase in resistance to high-temperature molten salt corrosion. This invention does not alter the physicochemical properties of chloride molten salts, but significantly improves corrosion resistance.

[0026] The specific method for in-situ preparation of the corrosion-resistant coating for heat exchanger tubes in a high-temperature chloride molten salt environment is as follows: Step 1: Mix aluminum powder (90%~97%), aluminum chloride powder (1%~4%), yttrium chloride powder (1%~3%), and cerium chloride powder (1%~3%) in a certain proportion, stir mechanically until uniform, and pre-dry in a drying oven to obtain mixture 1. Step 2: Add mixture 1 to the chloride mixed salt at a mass fraction of 1% to 3%, and stir thoroughly to obtain mixture 2. Step 3: Fill the molten salt storage tank with mixture 2, purge the air from the tank with inert gas, and heat it to 700℃~750℃ at a heating rate not exceeding 20℃ / min to obtain liquid mixture 2. Driven by the molten salt pump, the liquid mixture 2 is used to coat the cleaned heat exchanger surface and kept at that temperature for no less than 10 hours to obtain a heat exchanger tube with a corrosion-resistant coating.

[0027] Preferably, in step one, the drying temperature is 100℃~120℃ and the drying time is 20h~25h.

[0028] Preferably, in step two, the chloride molten salt includes at least two of potassium chloride, sodium chloride, magnesium chloride, and zinc chloride, and the addition ratio is arbitrary.

[0029] Preferably, in step two, the heat exchanger tubes are made of any one of the 18-8 series stainless steel.

[0030] Example 1 Taking a high-temperature molten salt heat exchanger made of 316L stainless steel as an example, the composition and preparation steps of a corrosion-resistant coating for heat exchanger tubes in a high-temperature chloride molten salt environment according to the present invention are as follows: First, 90% aluminum powder, 4% aluminum chloride powder, 3% yttrium chloride powder and 3% cerium chloride powder were mixed in proportion and mechanically stirred until uniform. The mixture was then pre-dried in a drying oven to obtain mixture 1. The drying temperature was 120℃ and the drying time was 24h.

[0031] Next, add mixture 1 to the chloride mixed salt at a mass fraction of 1.5%, and stir thoroughly to obtain mixture 2; the chloride mixed salt contains 30% potassium chloride, 30% sodium chloride, and the remainder is magnesium chloride.

[0032] Then, the molten salt tank is filled with mixture 2, the air in the tank is purged with inert gas, and heated to 700°C at a heating rate not exceeding 20°C / min to obtain liquid mixture 2. Under the drive of the molten salt pump, the liquid mixture 2 is used to coat the cleaned heat exchanger surface and kept at the temperature for 10 hours to obtain heat exchanger tubes with corrosion-resistant coating.

[0033] The corrosion-resistant coating prepared by the above method, by mass fraction, comprises 11.2% aluminum, 3.6% chromium, 1.7% nickel, 0.09% a mixture of cerium and yttrium, with the remainder being iron. The corrosion-resistant coating is metallurgically bonded to the base material; its microstructure is shown in [details omitted]. Figure 1 .

[0034] Using the aforementioned chloride mixed salt as the corrosive medium, the corrosion performance of the in-situ aluminized 316L heat exchanger prepared in this embodiment was tested. The test results show that the corrosion depth of the 316L stainless steel after corrosion at 700℃ for 200 hours in the molten salt of this embodiment is 33.9 μm. The morphological characteristics of the corrosion products are shown in [details omitted]. Figure 2 .

[0035] Example 2 Taking a high-temperature molten salt heat exchanger made of 316L stainless steel as an example, the composition and preparation steps of a corrosion-resistant coating for heat exchanger tubes in a high-temperature chloride molten salt environment according to the present invention are as follows: First, aluminum powder with a mass fraction of 97%, aluminum chloride powder with a mass fraction of 1%, yttrium chloride powder with a mass fraction of 1%, and cerium chloride powder with a mass fraction of 1% are mixed in a certain proportion, mechanically stirred until uniformly mixed, and then pre-dried in a drying oven to obtain mixture 1; the drying temperature is 120℃ and the drying time is 24h.

[0036] Next, add mixture 1 to the chloride mixed salt at a mass fraction of 3%, and stir thoroughly to obtain mixture 2; the chloride mixed salt contains 30% potassium chloride, 30% sodium chloride, and the remainder is magnesium chloride.

[0037] Then, the molten salt tank is filled with mixture 2, the air in the tank is purged with inert gas, and heated to 700°C at a heating rate not exceeding 20°C / min to obtain liquid mixture 2. Under the drive of the molten salt pump, the liquid mixture 2 is used to coat the cleaned heat exchanger surface and kept at the temperature for 15 hours to obtain heat exchanger tubes with corrosion-resistant coating.

[0038] The corrosion-resistant coating prepared by the above method comprises, by mass fraction, 18.9% aluminum, 2.9% chromium, 2.0% nickel, 0.02% cerium-yttrium mixture, and the remainder iron.

[0039] Using the aforementioned chloride mixed salt as the corrosive medium, the corrosion performance of the in-situ aluminized 316L heat exchanger prepared in this embodiment was tested. The test results show that the corrosion depth of 316L stainless steel after corrosion at 700℃ for 200 hours in the molten salt of this embodiment is 11.2 μm.

[0040] Example 3 Taking a high-temperature molten salt heat exchanger made of 316L stainless steel as an example, the composition and preparation steps of a corrosion-resistant coating for heat exchanger tubes in a high-temperature chloride molten salt environment according to the present invention are as follows: First, 95% aluminum powder, 1% aluminum chloride powder, 2% yttrium chloride powder and 2% cerium chloride powder were mixed in proportion and mechanically stirred until uniform. The mixture was then pre-dried in a drying oven to obtain mixture 1. The drying temperature was 120℃ and the drying time was 24h.

[0041] Next, add mixture 1 to the chloride mixed salt at a mass fraction of 2%, and stir thoroughly to obtain mixture 2; the chloride mixed salt contains 30% potassium chloride, 30% sodium chloride, and the remainder is magnesium chloride.

[0042] Then, the molten salt tank is filled with mixture 2, the air in the tank is purged with inert gas, and heated to 700°C at a heating rate not exceeding 20°C / min to obtain liquid mixture 2. Under the drive of the molten salt pump, the liquid mixture 2 is used to coat the cleaned heat exchanger surface and kept at the temperature for 15 hours to obtain heat exchanger tubes with corrosion-resistant coating.

[0043] The corrosion-resistant coating prepared by the above method comprises, by mass fraction, 10.1% aluminum, 3.1% chromium, 1.9% nickel, 0.03% cerium-yttrium mixture, and the remainder iron.

[0044] Using the aforementioned chloride mixed salt as the corrosive medium, the corrosion performance of the in-situ aluminized 316L heat exchanger prepared in this embodiment was tested. The test results show that the corrosion depth of 316L stainless steel after corrosion at 700℃ for 200 hours in the molten salt of this embodiment is 14.5 μm.

[0045] Example 4 Taking a high-temperature molten salt heat exchanger made of 316L stainless steel as an example, the composition and preparation steps of a corrosion-resistant coating for heat exchanger tubes in a high-temperature chloride molten salt environment according to the present invention are as follows: First, aluminum powder (94% by mass), aluminum chloride powder (2% by mass), yttrium chloride powder (2% by mass), and cerium chloride powder (2% by mass) are mixed in proportion, mechanically stirred until uniform, and then pre-dried in a drying oven to obtain mixture 1; the drying temperature is 120℃ and the drying time is 24h.

[0046] Next, add mixture 1 to the chloride mixed salt at a mass fraction of 2%, and stir thoroughly to obtain mixture 2; the chloride mixed salt contains 30% potassium chloride, 30% sodium chloride, and the remainder is magnesium chloride.

[0047] Then, the molten salt tank is filled with mixture 2, the air in the tank is purged with inert gas, and heated to 700°C at a heating rate not exceeding 20°C / min to obtain liquid mixture 2. Under the drive of the molten salt pump, the liquid mixture 2 is used to coat the cleaned heat exchanger surface and kept at the temperature for 20 hours to obtain heat exchanger tubes with corrosion-resistant coating.

[0048] The corrosion-resistant coating prepared by the above method comprises, by mass fraction, 10.5% aluminum, 3.1% chromium, 1.8% nickel, 0.03% cerium-yttrium mixture, and the remainder iron.

[0049] Using the aforementioned chloride mixed salt as the corrosive medium, the corrosion performance of the in-situ aluminized 316L heat exchanger prepared in this embodiment was tested. The test results show that the corrosion depth of 316L stainless steel after corrosion at 700℃ for 200 hours in the molten salt of this embodiment is 15.6 μm.

[0050] Example 5 The chloride mixed salt contains 30% potassium chloride by mass, with the remainder being magnesium chloride. The rest is consistent with Example 2.

[0051] Using the aforementioned chloride mixed salt as the corrosive medium, the corrosion performance of the in-situ aluminized 316L heat exchanger prepared in this embodiment was tested. The test results show that the corrosion depth of 316L stainless steel after corrosion at 700℃ for 200 hours in the molten salt of this embodiment is 15.3 μm.

[0052] Example 6 The chloride mixed salt contains 50% sodium chloride by mass, with the remainder being zinc chloride. The rest is consistent with Example 2.

[0053] Using the aforementioned chloride mixed salt as the corrosive medium, the corrosion performance of the in-situ aluminized 316L heat exchanger prepared in this embodiment was tested. The test results show that the corrosion depth of 316L stainless steel after corrosion at 700℃ for 200 hours in the molten salt of this embodiment is 15.6 μm.

[0054] Example 7 The chloride mixed salt contains 70% sodium chloride by mass, with the remainder being magnesium chloride. The rest is consistent with Example 2.

[0055] Using the aforementioned chloride mixed salt as the corrosive medium, the corrosion performance of the in-situ aluminized 316L heat exchanger prepared in this embodiment was tested. The test results show that the corrosion depth of 316L stainless steel after corrosion at 700℃ for 200 hours in the molten salt of this embodiment is 15.1 μm.

[0056] Example 8 The heat exchanger is made of 304L stainless steel. Everything else is the same as in Example 2.

[0057] Using the aforementioned chloride mixed salt as the corrosive medium, the corrosion performance of the in-situ aluminized 304L heat exchanger prepared in this embodiment was tested. The test results show that the corrosion depth of 304L stainless steel after corrosion at 700℃ for 200 hours in the molten salt of this embodiment is 29.3 μm.

[0058] Example 9 The heat exchanger is made of 347. Everything else is the same as in Example 2.

[0059] Using the aforementioned chloride mixed salt as the corrosive medium, the corrosion performance of the in-situ aluminized 347L stainless steel heat exchanger prepared in this embodiment was tested. The test results show that the corrosion depth of 347L stainless steel after corrosion at 700℃ for 200 hours in the molten salt of this embodiment is 32.6 μm.

[0060] Comparative Example 1 Mixture 1 was not added; otherwise, it was the same as in Example 2.

[0061] In this embodiment, the corrosion depth of 316L stainless steel after corrosion at 700℃ for 200 hours in molten salt was 81.5μm.

[0062] Comparative Example 2 Mixture 1 does not contain yttrium chloride or cerium chloride, and the rest is the same as in Example 2.

[0063] In this embodiment, the corrosion depth of 316L stainless steel after corrosion at 700℃ for 200 hours in molten salt was 56.3 μm.

[0064] like Figure 3 As shown, comparing the corrosion depth of Comparative Example 1 with that of Examples 1-4, it can be seen that the corrosion resistance of the 316L stainless steel heat exchanger with the corrosion-resistant coating of the present invention is significantly improved, and the service temperature is higher, thus having broad practical value.

[0065] In summary, this invention provides a corrosion-resistant coating for heat exchanger tubes in a high-temperature chloride molten salt environment and its preparation method. The preparation steps are as follows: aluminum powder, aluminum chloride powder, yttrium chloride powder, and cerium chloride powder are mixed, stirred, and dried to obtain mixture 1; mixture 1 is mixed with a chloride mixed salt to obtain mixture 2; under an inert gas environment, mixture 2 is heated to a liquid state, and the liquid mixture 2 coats the surface of the heat exchanger. Under heat preservation conditions, a corrosion-resistant coating is generated on the surface of the heat exchanger tubes. By mass fraction, the composition of the corrosion-resistant coating is: 10%~20% aluminum, 1%~4% chromium, 0.5%~2% nickel, 0.02%~0.1% cerium-yttrium mixture, and the remainder is iron. This invention prepares a corrosion-resistant coating on the surface of heat exchanger tubes in molten salt flow, which improves the corrosion resistance of heat exchanger tubes by more than 10 times, solving the problem of strong corrosion of alloy materials in next-generation solar thermal power generation under high-temperature molten chloride salt conditions.

[0066] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A corrosion-resistant coating for heat exchanger tubes in a high-temperature chloride molten salt environment, characterized in that, The coating consists of the following components by mass fraction: 10%–20% aluminum, 1%–4% chromium, 0.5%–2% nickel, 0.02%–0.1% cerium-yttrium mixture, and the remainder iron.

2. The corrosion-resistant coating for heat exchanger tubes in a high-temperature chloride molten salt environment according to claim 1, characterized in that, The heat exchanger tubes are made of any type of 18-8 series stainless steel.

3. The method for preparing a corrosion-resistant coating for heat exchanger tubes in a high-temperature chloride molten salt environment as described in claim 1 or 2, characterized in that, The specific steps are as follows: Aluminum powder, aluminum chloride powder, yttrium chloride powder, and cerium chloride powder are mixed, stirred, and dried to obtain mixture 1; Mixture 1 is mixed with a chloride mixed salt to obtain mixture 2; In an inert gas environment, mixture 2 is heated to a liquid state. Under heat preservation conditions, the liquid mixture 2 coats the surface of the heat exchanger, forming a corrosion-resistant coating on the surface of the heat exchanger tubes.

4. The method for preparing a corrosion-resistant coating for heat exchanger tubes in a high-temperature chloride molten salt environment according to claim 3, characterized in that, By mass fraction, mixture 1 comprises: 90% to 97% aluminum powder, 1% to 4% aluminum chloride powder, 1% to 3% yttrium chloride powder and 1% to 3% cerium chloride powder.

5. The method for preparing a corrosion-resistant coating for heat exchanger tubes in a high-temperature chloride molten salt environment according to claim 3, characterized in that, The drying temperature is 100℃~120℃, and the drying time is 20h~25h.

6. The method for preparing a corrosion-resistant coating for heat exchanger tubes in a high-temperature chloride molten salt environment according to claim 3, characterized in that, The amount of mixture 1 added to the chloride mixed salt is 1% to 3% by mass fraction.

7. The method for preparing a corrosion-resistant coating for heat exchanger tubes in a high-temperature chloride molten salt environment according to claim 3, characterized in that, The chloride molten salt includes at least two of potassium chloride, sodium chloride, magnesium chloride, and zinc chloride, and the addition ratio is arbitrary.

8. The method for preparing a corrosion-resistant coating for heat exchanger tubes in a high-temperature chloride molten salt environment according to claim 3, characterized in that, In an inert gas environment, mixture 2 is heated to 700℃~750℃ to obtain liquid mixture 2. Liquid mixture 2 coats the surface of the heat exchanger and is kept at that temperature for less than 10 hours, thus forming a corrosion-resistant coating on the surface of the heat exchanger tubes.

9. The method for preparing a corrosion-resistant coating for heat exchanger tubes in a high-temperature chloride molten salt environment according to claim 8, characterized in that, Mixture 2 is filled into a molten salt storage tank, the air in the tank is purged with inert gas, and heated to 700℃~750℃ at a heating rate not exceeding 20℃ / min to obtain liquid mixture 2. Under the drive of the molten salt pump, the liquid mixture 2 is used to coat the cleaned heat exchanger surface and kept at the temperature for not less than 10 hours to obtain a heat exchanger tube with a corrosion-resistant coating.

10. A corrosion-resistant heat exchanger tube for use in a high-temperature chloride molten salt environment, characterized in that, The surface of the corrosion-resistant heat exchanger tube has a corrosion-resistant coating, which is prepared by the method described in any one of claims 3 to 9.

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