Anti-corrosion method for internal coating of urea hydrolyzer

Abstract

The invention relates to the technical field of power plant chemistry, and discloses an anti-corrosion method for an internal coating of a urea hydrolyzer, which comprises the following steps: performing sand blasting, polishing and cleaning on the inner surface of the urea hydrolyzer; preparing a bottom layer coating turbid liquid, and coating the inner surface of the cleaned urea hydrolyzer; preparing middle-layer coating turbid liquid, and coating the bottom-layer coating with the middle-layer coating turbid liquid; preparing a surface coating turbid liquid, and coating the middle-layer coating with the surface coating turbid liquid; and carrying out high-temperature sintering on the inner surface of the urea hydrolyzer subjected to the coating process. The invention aims at providing a systematic solution for NH3 gas permeation, gas-liquid two-phase scouring and temperature alternating working conditions, and the metal-coating binding force is improved through the silane coupling agent modified bottom coating; a multi-stage barrier is constructed through the nanofiller and the glass flakes, so that corrosion media are prevented from permeating; the organic silicon modified polyurethane middle layer and the PTFE surface coating layer cooperate to resist high-temperature degradation; according to the process, internal stress of the coating is eliminated through temperature zone curing and high-temperature sintering, and a compact structure is formed.

Description

Technical Field

[0001] The present invention relates to the technical field of surface protection of industrial equipment, and relates to a method for preventing corrosion of the inner coating of a urea hydrolyzer. Background Art

[0002] The urea hydrolyzer is the core device of the selective catalytic reduction (SCR) denitration system, and generates ammonia through the following reaction: (NH2)2CO + H2O → 2NH3 + CO2 During operation, the inner wall of the equipment is in long-term contact with reactants and is in a high-temperature and high-humidity environment. The temperature fluctuation range is 120 - 200 °C, and the water vapor partial pressure is as high as 0.5 - 1.0 MPa; the urea solution concentration is often between 10 - 25%, which is corrosive; and the intermediate products ammonium carbamate (NH2COONH4), gaseous NH3 and trace acidic impurities (such as formic acid, acetic acid) also belong to corrosive media; the urea tank is constantly scoured by the gas-liquid two-phase flow, and the high-speed flowing gas-liquid mixture (flow rate 5 - 15 m / s) aggravates the surface wear.

[0003] Existing single coating materials often show limitations. Epoxy resin coatings, although they have excellent low-temperature corrosion resistance (<100 °C), are prone to cross-linking structure degradation at high temperatures (>150 °C), resulting in coating embrittlement and peeling; and they have insufficient resistance to NH3 gas penetration (penetration coefficient > 5×10 -10 cm 2 / s); enamel coatings, although they have good high-temperature resistance (≤250 °C), are brittle, and are prone to microcracks when the substrate deforms, and the difference in thermal expansion coefficients between the enamel and the carbon steel substrate (the enamel is about 1.0×10 -6 / °C, which is significantly different from that of carbon steel at about 11.0×10 -6 / °C) leads to interfacial stress concentration, and peeling occurs after 1 - 2 years of service; polytetrafluoroethylene (PTFE) spraying, although it has excellent chemical corrosion resistance, has weak adhesion to the metal substrate and relies on a porous transition layer (such as a molybdenum bottom layer), and the construction process is complex and costly.

[0004] Traditional construction processes also have some deficiencies. The roughness of the substrate pretreatment is too low (Ra < 6.3 μm), resulting in insufficient mechanical bite force of the coating; single-layer thick coating is prone to form internal pores in the coating (porosity > 8%), becoming a penetration channel for corrosive media; the curing process does not consider the thermal expansion matching of multi-layer coatings, resulting in interlayer stress concentration (such as the thermal expansion difference between epoxy resin and PTFE reaches 15×10 -6 / °C) at 180 °C. Summary of the Invention

[0005] To solve the existing problems, the present invention provides a method for preventing corrosion of the internal coating of a urea hydrolyzer, aiming to propose a systematic solution for NH3 gas penetration, gas-liquid two-phase scouring, and temperature alternating conditions. The metal-coating bonding force is enhanced by modifying the bottom coating with a silane coupling agent; a multi-level barrier is constructed by nano-fillers and glass flakes to block the penetration of corrosive media; the organic silicon-modified polyurethane intermediate layer and the PTFE surface coating cooperate to resist high-temperature degradation; in terms of process, curing in temperature zones and high-temperature sintering are carried out to eliminate the internal stress of the coating and form a dense structure.

[0006] To achieve the above object, the present invention provides the following technical solutions.

[0007] The present invention discloses a method for preventing corrosion of the internal coating of a urea hydrolyzer, including the following steps: sandblasting and polishing the inner surface of the urea hydrolyzer and cleaning it; preparing a bottom coating suspension and coating the cleaned inner surface of the urea hydrolyzer; preparing a middle coating suspension and coating it on the bottom coating; preparing a surface coating suspension and coating it on the middle coating; performing high-temperature sintering on the inner surface of the urea hydrolyzer after the coating process is completed.

[0008] As a further improvement of the present invention, the sandblasting and polishing use quartz sand with a particle size of 0.8 - 1.2 mm.

[0009] As a further improvement of the present invention, the cleaning includes the following steps: immediately blowing with high-pressure dry air after sandblasting and polishing, and then wiping with anhydrous ethanol.

[0010] As a further improvement of the present invention, the preparation of the bottom coating suspension includes the following steps: modifying epoxy resin with γ-aminopropyltriethoxysilane, and then adding nano-aluminum oxide and graphene to prepare a dispersion liquid together.

[0011] As a further improvement of the present invention, the preparation of the middle coating suspension includes the following steps: modifying polyurethane with organic silicon, and then adding glass flakes and silicon carbide micropowder to prepare a dispersion liquid together.

[0012] As a further improvement of the present invention, the aspect ratio of the glass flakes is 50 - 100.

[0013] As a further improvement of the present invention, the average particle size of the silicon carbide micropowder is 8 μm.

[0014] As a further improvement of the present invention, the preparation of the surface coating suspension includes the following steps: adding an appropriate amount of nano-titanium dioxide and 15 - 20% by weight of molybdenum disulfide (MoS2) to the polytetrafluoroethylene (PTFE) aqueous dispersion to prepare a dispersion liquid together.

[0015] As a further improvement of the present invention, the surface coating is applied by electrostatic spraying.

[0016] As a further improvement of the present invention, the high-temperature sintering is to heat to 380 °C and then perform furnace cooling after heat preservation.

[0017] The present invention has the following beneficial effects: The present invention provides a method for preventing corrosion of the inner coating of a urea hydrolyzer. By means of layered coating (bottom layer, middle layer, surface layer) and high-temperature sintering, a multi-layer protection structure is formed, significantly improving the adhesion, corrosion resistance and mechanical strength of the coating, and extending the service life of the urea hydrolyzer.

[0018] Optionally, the quartz sand has a high hardness (Mohs 7), which can effectively remove the oxide layer and impurities on the inner surface, improving the adhesion of the subsequent coating; using quartz non-steel sand can also avoid the electrochemical corrosion caused by the residue of iron ions; the particle size is moderate, avoiding excessive wear of the substrate, and at the same time ensuring that the surface roughness is suitable for coating bonding.

[0019] Preferably, high-pressure dry air quickly removes the residual sand grains and dust, preventing particle contamination of the coating interface during coating; anhydrous ethanol dissolves organic pollutants (such as oil stains and polar impurities), ensuring surface cleanliness and avoiding affecting the curing and performance of the coating.

[0020] Preferably, γ-aminopropyltriethoxysilane can enhance the chemical bonding between the epoxy resin and the metal substrate, improving heat resistance and corrosion resistance; the silane molecule generates Si-OH groups through hydrolysis, forming Si-O-Me covalent bonds with the hydroxyl groups on the metal surface, and at the same time the amino group reacts with the epoxy group of the epoxy resin to achieve the chemical bonding of "metal-silane-resin"; nano-aluminum oxide can improve the hardness and wear resistance of the coating, while filling the micropores of the coating, reducing the porosity and inhibiting the penetration of urea solution, and also improving the hardness of the coating; the two-dimensional sheet structure of graphene forms a "zigzag path", which can form a dense shielding layer to block the diffusion of corrosion media (such as NH3, H2O), and improve conductivity to reduce electrochemical corrosion.

[0021] Preferably, the organosilicon-modified polyurethane combines the elasticity of polyurethane and the high-temperature resistance of organosilicon, adapting to the temperature fluctuations of the urea hydrolyzer; the layered structure of the glass flake hinders the penetration of corrosion media, and the optimized aspect ratio can reduce the interlayer voids; the silicon carbide micropowder has extremely high hardness, which can resist the wear of urea crystallization and extend the coating life.

[0022] Preferably, the aspect ratio of the glass flake is 50-100, which can make the flakes arrange parallel in the thickness direction of the coating, forming a multi-layer reflection barrier, extending the penetration path of the corrosion medium, and significantly reducing the penetration rate of the corrosion medium.

[0023] Preferably, the particle size of the silicon carbide is 8 μm, forming a dense outer layer structure with extremely high hardness, close to diamond, which can resist the mechanical impact on the coating when urea crystals precipitate, reducing the risk of surface scratches.

[0024] Preferably, PTFE provides an extremely low coefficient of friction and chemical inertness, resists corrosion by urea solution and crystalline adhesion; nano-TiO2 enhances the mechanical strength and ultraviolet stability of the coating. If the equipment is exposed to a light environment, nano-TiO2 decomposes trace acidic substances through photocatalytic effect to inhibit the initiation of pitting corrosion; MoS2 (15-20%) acts as a solid lubricant to reduce the coefficient of friction of the coating, prevent erosion damage caused by urea particles scouring and wear caused by jamming.

[0025] Preferably, the electrostatic field enables the coating to be evenly adsorbed on the complex inner wall, reduces sagging and uneven thickness, and ensures the denseness of the coating.

[0026] Preferably, high-temperature sintering promotes the cross-linking and curing of the coating components, eliminates residual solvents and stresses, forms an amorphous dense layer, and improves the overall temperature resistance (adapts to the temperature of urea hydrolysis reaction); slow cooling avoids sudden cooling and cracking, and ensures the thermal expansion matching between the coating and the substrate. Description of the Drawings

[0027] The drawings described herein are for illustrative purposes only and do not limit the scope of the disclosure of the present invention in any way. Additionally, the shapes and proportional dimensions of the components in the drawings are only schematic and are used to assist in understanding the present invention, rather than specifically defining the shapes and proportional dimensions of the components of the present invention. In the drawings: Figure 1 is a schematic diagram of a method for preventing corrosion of the inner coating of a urea hydrolyzer in an embodiment of the present invention; Figure 2 is a schematic diagram of the inner coating formed after adopting a method for preventing corrosion of the inner coating of a urea hydrolyzer in an embodiment of the present invention; wherein, 1. Inner wall of the urea hydrolyzer; 2. Substrate sandblasting layer; 3. Bottom coating; 4. Middle coating; 5. Top coating. Detailed Embodiments

[0028] In order to enable those skilled in the art to better understand the technical solutions in the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the scope of protection of the present invention.

[0029] It should be noted that when an element is referred to as being "disposed on" another element, it can be directly on the other element or there can also be an intermediate element. When an element is considered to be "connected to" another element, it can be directly connected to the other element or there may be an intermediate element at the same time. The terms "vertical", "horizontal", "left", "right" and similar expressions used herein are only for illustrative purposes and do not represent the only embodiments.

[0030] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which this invention belongs. The terms used herein in the description of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention. The term "and / or" used herein includes any and all combinations of one or more of the related listed items.

[0031] Embodiment A method for preventing corrosion of the internal coating of a urea hydrolyzer, comprising the following steps: Sandblast and polish the inner surface of the urea hydrolyzer and clean it; Prepare a bottom layer coating suspension and coat the cleaned inner surface of the urea hydrolyzer; Prepare a middle layer coating suspension and coat it on the bottom layer coating; Prepare a top layer coating suspension and coat it on the middle layer coating; Perform high-temperature sintering on the inner surface of the urea hydrolyzer that has completed the coating process.

[0032] In this embodiment, a certain urea hydrolyzer, a carbon steel container with a diameter of φ3000mm, is used as a specific implementation display.

[0033] The cleaning includes the following steps: Immediately after sandblasting and polishing, blow with high-pressure dry air and then wipe with anhydrous ethanol.

[0034] The sandblasting and polishing uses quartz sand with a particle size of 0.8 - 1.2mm to ensure uniform roughness of the polished surface, and the roughness Ra is maintained in the range of 6.3 - 12.5μm, which can significantly improve the adhesion of the coating. The quartz sand has high hardness (Mohs 7), can effectively remove the oxide layer and impurities on the inner surface, and improve the adhesion of the subsequent coating; using quartz non-steel sand can also avoid electrochemical corrosion caused by iron ion residues; the particle size is appropriate, avoiding excessive wear of the substrate and ensuring that the surface roughness is suitable for coating adhesion.

[0035] Specifically, the sandblasting equipment used is a suction type sandblaster and a screw air compressor, and the exhaust volume of the air compressor is 10m 3 / min. The sand used for sandblasting is quartz sand with a particle size of 1.0 mm, the sandblasting angle is about 75°, the distance is 20 cm, and the pressure is 0.5 MPa. The surface roughness Ra of the carbon steel container is 8.2 μm, and the salt pollution level < 5 μg / cm 2 (adopting the ISO 8502-6 standard). Specifically, the purity of anhydrous ethanol is higher than 99%, which can remove surface oil stains and polar impurities, ensuring that the surface energy of the substrate > 45 mN / m. High-pressure dry air quickly removes residual sand grains and dust, preventing particle contamination of the coating interface during coating; anhydrous ethanol dissolves organic pollutants (such as oil stains and polar impurities), ensuring surface cleanliness and avoiding affecting coating curing and performance.

[0036] The preparation of the bottom coating suspension includes the following steps: modifying epoxy resin with γ-aminopropyltriethoxysilane, and then adding nano-aluminum oxide and graphene to prepare a dispersion. γ-aminopropyltriethoxysilane can enhance the chemical bonding between epoxy resin and metal substrate, improving heat resistance and corrosion resistance; the silane molecule generates Si-OH groups through hydrolysis, forming Si-O-Me covalent bonds with the hydroxyl groups on the metal surface, and at the same time the amino group reacts with the epoxy group of the epoxy resin to achieve the chemical bonding of "metal-silane-resin"; nano-aluminum oxide can improve the hardness and wear resistance of the coating, while filling the micropores of the coating, reducing the porosity, inhibiting the penetration of urea solution, and also enhancing the coating hardness; the two-dimensional sheet structure of graphene forms a "zigzag path", which can form a dense shielding layer to block the diffusion of corrosive media (such as NH3, H2O), and enhance conductivity to reduce electrochemical corrosion.

[0037] Specifically, epoxy resin E-51 is modified with γ-aminopropyltriethoxysilane KH-550, with a grafting rate of 15%, and the weight after modification is 100 g; the average particle size of nano-aluminum oxide α-Al2O 3， is 50 nm, and the weight taken is 25 g; the polyamide curing agent is type 650, and the weight taken is 1 g; the graphene aqueous dispersion has a solid content of 5%, a sheet diameter of 5-10 μm, and the weight taken is 10 g. The above components are added to the dispersion and dispersed with ultrasonic waves at a frequency of 40 kHz for half an hour. The two-dimensional sheet structure in the graphene dispersion forms a "zigzag path", significantly reducing the NH3 permeability coefficient, which is significantly lower than that of pure epoxy resin.

[0038] The inner surface of the cleaned urea hydrolyzer is coated using air-assisted spraying. Specifically, the spray gun pressure is selected as 0.3 MPa, and it is evenly applied to ensure that the wet film thickness is about 80 μm. After air spraying, it is dried in an oven, with the selected parameters being 90°C and a wind speed of 2 m / s, and the drying duration is 45 min, finally forming a dry film thickness of about 60 μm.

[0039] The preparation of the intermediate layer coating suspension includes the following steps: modifying polyurethane with silicone, and then adding glass flakes and silicon carbide micropowder to prepare a dispersion together. The silicone-modified polyurethane combines the elasticity of polyurethane and the high-temperature resistance of silicone, adapting to the temperature fluctuations of the urea hydrolyzer; the layered structure of the glass flakes hinders the penetration of corrosive media, and the optimized aspect ratio can reduce the interlayer voids; the silicon carbide micropowder has extremely high hardness, which can resist the wear of urea crystallization and extend the coating life.

[0040] The aspect ratio of the glass flakes is 50 - 100. The aspect ratio of 50 - 100 of the glass flakes can make the flakes arrange parallelly along the thickness direction in the coating, forming multiple reflection barriers, extending the penetration path of the corrosive medium, and significantly reducing the penetration rate of the corrosive medium.

[0041] Preferably, the glass flakes are pre-dispersed in acetone and dispersed by ultrasonic waves for 15 minutes; the aspect ratio of the glass flakes is 80, the thickness is 5 μm, and the weight is 35 g; silicon carbide micropowder (α-SiC), with a hardness of 2800 HV and a particle size of 8 μm, and the weight is 12 g; polyether defoamer (BYK-066N), with a weight of 2 g; silicone-modified polyurethane, with a Si content of 10%, and the weight of the silicone-modified polyurethane is 100 g. The above components are added to the dispersion and mixed. The silicone-modified polyurethane (Si-PU) combines the flexibility of polyurethane and the high-temperature resistance of silicone, and the mass loss during long-term service at 150°C is significantly reduced, which is better than that of pure polyurethane. The silicon carbide micropowder can improve the wear resistance of the coating, and the wear rate is greatly reduced under gas-liquid scouring. The particle size of the silicon carbide is 8 μm, forming a dense outer layer structure with extremely high hardness, close to diamond, which can resist the mechanical impact on the coating when urea crystals precipitate and reduce the risk of surface scratches.

[0042] For the coating on the bottom layer, high-pressure airless spraying is used. The electrostatic field makes the coating evenly adsorb on the complex inner wall, reducing sagging and uneven thickness, and ensuring the density of the coating. Specifically, the spraying pressure is selected at 20 MPa, and uniform application ensures that the wet film thickness is 300 μm. After spraying, the intermediate layer coating needs to be cured. The wet film is left standing at room temperature (25°C, humidity 60%) for 1 hour; then the intermediate layer coating is heated to 130°C at a rate of 5°C / min and cured for 2 hours. After drying, a dry film is formed with a thickness of about 180 μm.

[0043] The preparation of the surface coating suspension comprises the following steps: adding an appropriate amount of nano titanium dioxide and 15-20% by weight of molybdenum disulfide (MoS2) to a polytetrafluoroethylene (PTFE) aqueous dispersion to prepare a dispersion. PTFE provides an extremely low friction coefficient and chemical inertness, and is resistant to urea solution corrosion and crystal adhesion; nano TiO2 enhances the mechanical strength and ultraviolet stability of the coating. If the equipment is exposed to a light environment, nano TiO2 decomposes trace acidic substances through a photocatalytic effect to inhibit the initiation of pitting corrosion; MoS2 (15-20%) acts as a solid lubricant to reduce the friction coefficient of the coating and prevent urea particle scouring damage and wear caused by stagnation.

[0044] Specifically, the solid content of the PTFE aqueous dispersion is 60%, the average particle size is 0.2 μm, and the weight is 100 g; the molybdenum disulfide powder has a particle size of 2 μm and a weight of 18 g; the nano-TiO2 is anatase type with a particle size of 20 nm and a weight of 6 g.

[0045] The topcoat is applied by electrostatic spraying. Specifically, the spray gun voltage is 60 kV, the atomization air pressure is 0.2 MPa, and the wet film thickness is 150 μm.

[0046] The high temperature sintering is to heat to 350°-400°, keep warm and then cool with the furnace. High temperature sintering promotes cross-linking and curing of coating components, eliminates residual solvents and stress, forms an amorphous dense layer, and improves overall temperature resistance (adapts to the reaction temperature of urea hydrolysis); slow cooling avoids sudden cooling and cracking, and ensures that the thermal expansion of the coating matches that of the substrate.

[0047] Specifically, the temperature was raised to 380°C at 10°C / min, kept at that temperature for 1.5 hours, and cooled to room temperature with the furnace. The dry film thickness was 90μm. At 350-400°C, the PTFE particles melted and cross-linked (melting point 327°C) to form an amorphous dense layer. According to estimates, the porosity is less than 0.5%, which can block the corrosive medium molecules below 100nm (NH3 molecule diameter 0.3nm).

[0048] The inner coating prepared by the above method, such as Figure 2 As shown, from inside to outside, there are substrate sandblasting layer 2, bottom layer coating 3, middle layer coating 4, and top layer 5. The surface of the inner wall 1 of the urea hydrolyzer forms a dense structure for corrosion protection of the urea hydrolyzer. Through layered coating (bottom layer, middle layer, top layer) and high-temperature sintering, a multi-layer protective structure is formed, which significantly improves the adhesion, corrosion resistance and mechanical strength of the coating and prolongs the service life of the urea hydrolyzer.

[0049] In this embodiment, the same material as the carbon steel container of the urea hydrolyzer was selected to prepare the test slices for the following tests. The above specific methods and parameters were adopted for the test slices, and the performance results are shown as follows: 1. Adhesion test (ASTM D3359 cross-cut method) Testing tool: scribing knife with a pitch of 1 mm and a load of 10 N; Results: All in Example 1 were Grade 0 (coating peeling area < 5%), while the traditional epoxy coating was Grade 2 (peeling area 15 - 35%).

[0050] 2. High-temperature aging test (GB / T 1865 - 2009) Test conditions: oven at 200 °C for 2000 h; Results: The coating of the present invention showed no discoloration or cracks; the traditional epoxy coating turned yellow after 200 h and became powdery on the surface after 500 h.

[0051] 3. Corrosion resistance test in urea solution (ASTM G31 - 72 immersion method) Test conditions: 50% urea aqueous solution, temperature 150 °C, pressure 0.8 MPa; Duration: 3000 h; Results: The weight loss rate of the coating of the present invention was 0.008 g / m 2 ·h, and the corrosion rate was 0.009 mm / a; the weight loss rate of the enamel coating was 0.08 g / m 2 ·h, and the corrosion rate was 0.09 mm / a.

[0052] 4. Gas-liquid erosion wear test Test medium: urea solution containing 5% solid particles (quartz sand, particle size 50 μm), flow rate 12 m / s, temperature 180 °C; Duration: 500 h; Results: The wear depth of the coating of the present invention was 50 μm, and the wear depth of the traditional epoxy coating was 200 μm, resulting in coating failure.

[0053] The examples of the present invention were horizontally compared with the traditional epoxy coating and the enamel coating, and had the following characteristics:

[0054] Example 2 The difference between this example and Example 1 is that: the aspect ratio of the glass flakes is 50. The glass flakes are prone to curling or agglomeration, resulting in voids or stress concentration inside the mixture.

[0055] Example 3 The difference between this example and Example 1 is that: the aspect ratio of the glass flakes is 100. The contact area between the glass flakes (low aspect ratio) and the substrate decreases, and the interfacial adhesion force decreases.

[0056] The above embodiments are merely one of the implementation manners capable of implementing the technical solution of the present invention. The scope of protection required by the present invention is not only limited by this embodiment, but also includes any changes, substitutions and other implementation manners that are easily conceivable by those skilled in the art within the technical scope disclosed by the present invention. Although the embodiments of the present invention have been shown and described, those of ordinary skill in the art can understand that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principle and spirit of the present invention. The scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for preventing corrosion of the internal coating of a urea hydrolyzer, characterized in that, It includes the following steps: Sandblast, grind and clean the inner surface of the urea hydrolyzer; Prepare the bottom layer coating suspension and coat the cleaned inner surface of the urea hydrolyzer; Prepare the middle layer coating suspension and coat it on the bottom layer coating; Prepare the top layer coating suspension and coat it on the middle layer coating; Perform high-temperature sintering on the inner surface of the urea hydrolyzer that has completed the coating process.

2. The anti-corrosion method for the internal coating of a urea hydrolyzer according to claim 1, wherein, The sandblasting uses quartz sand with a particle size of 0.8 - 1.2 mm.

3. The method for preventing corrosion of the internal coating of a urea hydrolyzer according to claim 1, wherein, The cleaning includes the following steps: Immediately blow with high-pressure dry air after sandblasting and grinding, and then wipe with anhydrous ethanol.

4. A method for preventing corrosion of the internal coating of a urea hydrolyzer according to claim 1, characterized in that, The preparation of the bottom layer coating suspension includes the following steps: Modify epoxy resin with γ-aminopropyltriethoxysilane, and then add nano-aluminum oxide and graphene to jointly prepare a dispersion.

5. A method for preventing corrosion of the internal coating of a urea hydrolyzer according to claim 1, characterized in that, The preparation of the middle layer coating suspension includes the following steps: Modify polyurethane with silicone, and then add glass flakes and silicon carbide micropowder to jointly prepare a dispersion.

6. The anti-corrosion method for the internal coating of a urea hydrolyzer according to claim 5, characterized in that, The aspect ratio of the glass flakes is 50 - 100.

7. A method for preventing corrosion of the internal coating of a urea hydrolyzer according to claim 5, characterized in that, The average particle size of the silicon carbide micropowder is 8 μm.

8. A method for preventing corrosion of the internal coating of a urea hydrolyzer according to claim 1, characterized in that, The preparation of the top layer coating suspension includes the following steps: Add an appropriate amount of nano-titanium dioxide and 15 - 20% by weight of molybdenum disulfide (MoS2) to the polytetrafluoroethylene (PTFE) aqueous dispersion to jointly prepare a dispersion.

9. The anti-corrosion method for the internal coating of a urea hydrolyzer according to claim 1, characterized in that, The top layer coating is applied by electrostatic spraying.

10. A method for preventing corrosion of the internal coating of a urea hydrolyzer according to claim 1, characterized in that, The high-temperature sintering is to heat to 380 °C, keep warm and then cool with the furnace.

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