A method for preventing scale formation on the tubes of an evaporator

Abstract

This application discloses a method for preventing scaling in evaporator tubes, relating to the field of evaporator anti-scaling technology. The method involves first adding precisely measured amounts of barium nitrate to the reaction solution after limestone digestion to obtain an evaporation feed with a significantly reduced sulfate concentration. Simultaneously, a modified coating is applied to the inner wall of the evaporator tubes. The evaporation feed is then concentrated through the evaporator tubes. By addressing both nucleation and adhesion conditions, scaling in the evaporator tubes is inhibited. The method provided in this application eliminates the need for shutdown and alkaline cleaning, and balances scale prevention, production continuity, and energy saving. It can be adapted to existing production line modifications and is easily industrially promoted.

Description

Technical Field

[0001] This application relates to the field of evaporator anti-scaling technology, and in particular to a method for preventing scale buildup in evaporator tubes. Background Technology

[0002] Evaporators are core equipment in chemical, food, pharmaceutical, seawater desalination, wastewater treatment, and environmental protection industries for solution concentration and solvent recovery. Shell-and-tube evaporators are widely used due to their compact structure, large heat transfer area, and high processing capacity. In these evaporators, the feed liquid typically flows through the tubes and exchanges heat with the heating medium, while the solvent vaporizes, gradually increasing the solute concentration. However, during the evaporation and concentration process, as water continuously evaporates, scale-forming components in the solution (such as calcium carbonate, calcium sulfate, silicates, phosphates, and other inorganic salts) easily reach supersaturation, subsequently precipitating, accumulating, and growing on the inner wall of the tubes, forming a hard, dense, or viscous scale layer.

[0003] Scaling in the tubes and shells severely restricts the long-term, high-efficiency operation of evaporation units. Scale buildup significantly increases thermal resistance, leading to a substantial decrease in the overall heat transfer coefficient and a significant increase in evaporation energy consumption. Scale formation also reduces the effective flow cross-sectional area of ​​the tubes and shells, increasing fluid resistance and, in severe cases, clogging pipes and forcing unplanned shutdowns. Restoring the heat transfer performance of the tubes and shells often requires frequent chemical or mechanical cleaning, which not only consumes large amounts of cleaning agents and manpower, generating difficult-to-treat cleaning waste, but also causes production interruptions, shortens equipment lifespan, and poses dual safety and environmental risks.

[0004] Therefore, there is a need to develop a method that overcomes the above-mentioned defects, can operate stably online, and is cost-effective in preventing scaling in evaporator tubes. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this application provides a method for preventing scaling in evaporator tubes. By first adding precisely measured amounts of barium nitrate to the reaction solution after limestone digestion, an evaporation feed with a significantly reduced sulfate concentration is obtained. Simultaneously, a modified coating is applied to the inner wall of the evaporator tubes. The evaporation feed is then concentrated through the evaporator tubes. This method addresses both nucleation and adhesion conditions, thus inhibiting scaling in the evaporator tubes. The method provided in this application eliminates the need for shutdown and alkaline cleaning, and balances scale prevention, production continuity, and energy saving. It can be adapted to existing production line modifications and is easily industrially scalable.

[0006] To achieve the above objectives, this application adopts the following technical solution: This application provides a method for preventing scale buildup in evaporator tubes, comprising the following steps: The sulfate content of the reaction solution after the raw limestone is digested is detected to obtain the initial concentration of sulfate in the reaction solution; Barium nitrate solution was added to the reaction solution, and the reaction conditions were controlled to obtain a mixture. The mixture is fed into a filter press for solid-liquid separation to obtain an evaporation feed. The evaporation feed is then evaporated and concentrated through an evaporator tube with a modified coating on its inner wall. The modified coating comprises a base resin, modified functional filler, hydrogen-containing silicone oil, and additives; the base resin comprises any one of phenyl vinyl silicone resin, vinyl MQ silicone resin, and methyl vinyl MQ silicone resin; the modified functional filler is obtained by modifying a mixture of nano-silica, nano-zirconium dioxide, and nano-titanium dioxide.

[0007] This application proposes a method to prevent scaling in evaporator tubes by addressing both nucleation and adhesion conditions.

[0008] Regarding nucleation conditions, the core scaling factor in the reaction solution after limestone digestion is sulfate, which can combine with a large number of calcium ions in the system. During evaporation, calcium sulfate will precipitate supersaturated on the surface of the high-temperature heat exchange tubes, forming difficult-to-remove calcium sulfate scale. This application utilizes the fact that barium ions and sulfate can form barium sulfate precipitate, and its solubility product is much lower than that of calcium sulfate. Therefore, sulfate can be removed deeply by preferentially forming barium sulfate, significantly reducing the formation of calcium sulfate from a thermodynamic source, thereby preventing the formation of scale.

[0009] Regarding adhesion conditions, this application significantly reduces the formation of calcium sulfate by coating the inner wall of the evaporator tubes with a modified coating, thereby reducing the adhesion of the remaining small amount of scale. This dual action achieves long-term scale prevention, which is far superior to single scale prevention methods. In the modified coating, the base resin is silicone resin, with a Si-O-Si main chain molecular structure, high bond energy, and excellent temperature resistance, chemical corrosion resistance, and low surface energy, making it suitable for the harsh operating conditions of evaporators under high temperature and acid / alkali corrosion. Further mixing of hydrogen-containing silicone oil and silicone resin forms a dense three-dimensional cross-linked network, further improving the density, water resistance, and low surface energy of the modified coating. Fluorosilane-modified nano-inorganic fillers, on the one hand, can improve compatibility with the resin matrix through coupling agent grafting, preventing agglomeration; on the other hand, the introduced fluorine groups can further reduce the surface energy of the resulting modified coating. Simultaneously, the nano-inorganic fillers can construct a micro-nano rough structure, producing a lotus leaf-like superhydrophobic effect, thereby significantly reducing the adhesion of precipitated scale to the inner wall of the tube. Even if a small amount of scale still precipitates, it is easily washed off by the slurry during the evaporation and concentration process. These two aspects work together to achieve a significant anti-scaling effect.

[0010] In one feasible implementation, the molar ratio of barium ions in the barium nitrate solution to sulfate ions in the reaction solution is (1.05-1.2):1.

[0011] Based on the dissolution equilibrium of barium sulfate precipitation, this application adds a slightly excess of barium ions to further promote the precipitation reaction and significantly reduce the residual concentration of sulfate in the solution. At the same time, the molar ratio of barium ions in the barium nitrate solution to sulfate ions in the reaction solution is controlled at (1.05-1.2):1, which ensures the removal rate of sulfate ions while avoiding problems such as increased reagent costs and barium ion residual pollution.

[0012] In one feasible implementation, the reaction conditions include: a temperature of 40-60°C, a stirring rate of 200-400 rpm, and a stirring time of 20-40 min.

[0013] This application, through optimized reaction conditions, can reduce reaction energy consumption, improve production efficiency, and adapt to the pace of continuous industrial production.

[0014] In one feasible implementation, the mass ratio of the matrix resin, modified functional filler, hydrogen-containing silicone oil and additives in the modified coating is (30-55):(8-22):(30-45):(1-3).

[0015] This application optimizes the proportions of each component in the modified coating to achieve the best possible effect for each component. Specifically, the matrix resin, as the main film-forming component, is neither too low (resulting in a failure to form a continuous film) nor too high (causing a decline in the coating's wear resistance and antifouling properties). The modified functional filler, as the functional reinforcing phase, is neither too low (preventing the construction of micro / nano structures) nor too high (causing filler agglomeration and coating defects). Simultaneously, the hydrogen-containing silicone oil, as a crosslinking component and a low surface energy component, is neither too low (leading to incomplete crosslinking and insufficient hydrophobicity) nor too high (causing increased coating brittleness and decreased adhesion). Finally, the additives, as components improving application and curing performance, are neither too low (ineffective) nor too high (resulting in residue precipitation that affects coating performance).

[0016] In one feasible implementation, the viscosity of the hydrogen-containing silicone oil is 26 mm. 2 / s (25℃), with a hydrogen content of 1.6%. Other viscosities and hydrogen contents of hydrogen-containing silicone oils can also be used, but the performance of the resulting modified coating will be relatively poor.

[0017] In one feasible implementation, the additives include a Karstedt catalyst, a leveling agent, a defoamer, and a dispersant; wherein the mass ratio of the Karstedt catalyst, the leveling agent, the defoamer, and the dispersant is (5-10):(20-30):(10-20):(50-60).

[0018] In one feasible implementation, the leveling agent includes any one of BYK-307, BYK-310, BYK-322, and BYK-333; the defoamer includes any one of BYK-065, BYK-066N, BYK-067A, and BYK-077; and the dispersant includes any one of BYK-P104, BYK-P104S, BYK-110, and BYK-180.

[0019] In one feasible implementation, the method for preparing the modified functional filler includes: Mix the fluorinated silane coupling agent, anhydrous ethanol and deionized water in a certain proportion, adjust the pH of the system to 4-6, and stir at 200-400 rpm for 10-20 min at room temperature to obtain the coupling agent hydrolysate. Nano-silica, nano-zirconium dioxide, and nano-titanium dioxide are added to a high-speed mixer in a certain proportion and stirred at 900-1200 rpm for 20-30 minutes to obtain a mixed powder, while maintaining stirring. The coupling agent hydrolysate is added to the mixed powder while it is being stirred in the form of a spray. After the addition is complete, stirring is continued for 5-10 minutes. Then the material is discharged, the air is vented, and the mixture is sealed and stored for 16-24 hours to obtain the modified functional filler.

[0020] The fluorinated silane coupling agent hydrolyzes under weakly acidic conditions to generate silanol groups, which can undergo dehydration condensation with the hydroxyl groups on the surface of inorganic nano-oxides, covalently grafting low surface energy fluorinated groups onto the powder surface to achieve hydrophobic modification and improve the compatibility between the powder and the silicone resin matrix. High-speed premixing ensures uniform dispersion of the three types of nano-powders, allowing the hydrolysate of the coupling agent added by spraying to fully contact the surface of the mixed powder, achieving a uniform modification effect. Sealing and curing for 16-24 hours after discharge further ensures that the fluorinated silane coupling agent fully reacts and grafts with the powder, ensuring the modification effect.

[0021] In one feasible implementation, the mass ratio of the fluorosilane coupling agent, anhydrous ethanol, and deionized water in the coupling agent hydrolysate is (20-30):(50-65):(10-20); the mass ratio of nano-silica, nano-zirconium dioxide, and nano-titanium dioxide in the mixed powder is (60-80):(10-25):(5-20); and the amount of the coupling agent hydrolysate added is 2%-5% of the mass of the mixed powder.

[0022] The proportions of each component in the coupling agent hydrolysate ensure complete hydrolysis of the fluorinated silane coupling agent, resulting in a hydrolysate with good stability. Among the inorganic nanoparticles, nano-silica is the main component, ensuring the overall dispersibility of the filler and the adhesion of the resulting coating. The addition of nano-zirconia enhances the hardness, wear resistance, and temperature resistance of the resulting coating. The addition of nano-titanium dioxide improves the self-cleaning properties of the resulting coating. Furthermore, the amount of coupling agent hydrolysate added effectively matches the specific surface area of ​​the mixed powders, achieving uniform surface modification and avoiding incomplete modification and powder agglomeration.

[0023] In one feasible implementation, the average particle size of the nano-silica, nano-zirconium dioxide, and nano-titanium dioxide is 10-50 nm.

[0024] In one feasible implementation, the fluorinated silane coupling agent comprises any one of trifluoropropyltrimethoxysilane, trifluoropropylmethyldimethoxysilane, trifluoropropyltriethoxysilane, and nonafluorohexyltrimethoxysilane.

[0025] The fluorinated silane coupling agents used in this application all contain hydrolyzable alkoxy groups, which can be efficiently grafted onto the surface of the mixed powder. At the same time, the introduced fluorinated alkyl groups have extremely low surface energy, good compatibility with the matrix resin, and excellent hydrophobic, oleophobic, and chemical corrosion resistant properties. Ultimately, they can significantly reduce the surface energy of the modified coating, improve the hydrophobic and anti-scaling effect, and at the same time improve the coating density, interfacial adhesion, and resistance to media corrosion.

[0026] In one feasible implementation, the method for preparing the modified coating includes: Mix the matrix resin with hydrogen-containing silicone oil and stir at 300-500 rpm for 20-30 minutes at room temperature to obtain the resin base liquid; Then, add the modified functional filler to the resin base liquid and stir at 600-800 rpm for 30-60 minutes to obtain the mixed slurry. Add the additives to the mixed slurry, continue stirring for 10-20 minutes, and then pass it through a 200-mesh sieve to obtain the modified coating slurry; After sandblasting the inner wall of the evaporator tubes, blow them with compressed air for 5-10 minutes, then rinse them with anhydrous ethanol for 10-20 minutes, and then dry them at 60-80℃ to obtain the pretreated evaporator tubes. Subsequently, the modified coating slurry was applied to the inner wall of the pretreated evaporator tubes by spraying. After the modified coating slurry is applied, the evaporator tubes are first left to stand at room temperature for 15-30 minutes, then kept at 80-100℃ for 30-60 minutes, then heated to 180-220℃ and kept at 1-2 hours, and finally cooled naturally to room temperature to obtain the modified coating on the inner wall of the evaporator tubes.

[0027] In the preparation of the mixed slurry, stepwise mixing ensures uniform dispersion of the modified functional filler in the resin base liquid. Subsequent sieving removes large particles, preventing defects such as particle protrusions and pinholes from appearing on the surface of the final modified coating. Pretreatment of the inner wall of the evaporator tubes further ensures the adhesion of the modified coating. In the subsequent staged curing process, the coating is first allowed to stand at room temperature, then kept at an appropriately elevated temperature to slowly evaporate the solvent and prevent cratering. Then, it is kept at a higher temperature to achieve full cross-linking and curing of the components in the modified coating. Finally, natural cooling prevents excessive temperature differences that could cause cracking due to internal stress. Ultimately, this significantly improves both the adhesion and anti-scaling effects of the modified coating.

[0028] In one feasible implementation, after sandblasting, the surface cleanliness level of the inner wall of the evaporator tubes is Sa2 or Sa2.5.

[0029] This can significantly improve the adhesion between the modified coating and the inner wall of the evaporator tubes, preventing the coating from peeling off under high temperature and slurry scouring conditions, while ensuring that the coating completely covers the inner wall of the evaporator tubes, without any exposed points causing local scaling and corrosion.

[0030] In one feasible implementation, the thickness of the modified coating is 80-200 μm.

[0031] If the thickness of the modified coating is less than 80μm, it may not be able to completely cover the inner wall of the evaporator tubes, and thin spots and pinholes may easily appear, resulting in insufficient corrosion resistance and wear resistance of the modified coating. If the thickness of the modified coating is greater than 200μm, it may cause cracking and peeling due to excessive internal stress. At the same time, an excessively thick coating will increase thermal resistance, reduce the heat exchange efficiency of the evaporator, and increase material costs.

[0032] Beneficial technical effects: This application proposes a method to prevent scaling in evaporator tubes by addressing both nucleation and adhesion conditions.

[0033] Regarding nucleation conditions, the core scaling factor in the reaction solution after limestone digestion is sulfate, which can combine with a large number of calcium ions in the system. During evaporation, calcium sulfate will precipitate supersaturated on the surface of the high-temperature heat exchange tubes, forming difficult-to-remove calcium sulfate scale. This application utilizes the fact that barium ions and sulfate can form barium sulfate precipitate, and its solubility product is much lower than that of calcium sulfate. Therefore, sulfate can be removed deeply by preferentially forming barium sulfate, significantly reducing the formation of calcium sulfate from a thermodynamic source, thereby preventing the formation of scale.

[0034] Regarding adhesion conditions, this application significantly reduces the formation of calcium sulfate by coating the inner wall of the evaporator tubes with a modified coating, thereby reducing the adhesion of the remaining small amount of scale. This dual action achieves long-term scale prevention, which is far superior to single scale prevention methods. In the modified coating, the base resin is silicone resin, with a Si-O-Si main chain molecular structure, high bond energy, and excellent temperature resistance, chemical corrosion resistance, and low surface energy, making it suitable for the harsh operating conditions of evaporators under high temperature and acid / alkali corrosion. Further mixing of hydrogen-containing silicone oil and silicone resin forms a dense three-dimensional cross-linked network, further improving the density, water resistance, and low surface energy of the modified coating. Fluorosilane-modified nano-inorganic fillers, on the one hand, can improve compatibility with the resin matrix through coupling agent grafting, preventing agglomeration; on the other hand, the introduced fluorine groups can further reduce the surface energy of the resulting modified coating. Simultaneously, the nano-inorganic fillers can construct a micro-nano rough structure, producing a lotus leaf-like superhydrophobic effect, thereby significantly reducing the adhesion of precipitated scale to the inner wall of the tube. Even if a small amount of scale still precipitates, it is easily washed off by the slurry during the evaporation and concentration process. These two aspects work together to achieve a significant anti-scaling effect. Attached Figure Description

[0035] Figure 1 This is a photograph of the inner wall of the evaporator tubes coated with the modified coating prepared in Example 3. Detailed Implementation

[0036] To facilitate understanding of the content described in this application, the technical solutions described herein are further explained below with reference to specific embodiments; however, this application is not limited thereto. All equivalent transformations or simple substitutions made based on the substantive content of this application should fall within the protection scope of this application.

[0037] The singular forms “for,” “or,” “a,” “any,” and “the” used in this application are intended to include the plural forms unless the context clearly indicates otherwise.

[0038] The following describes in detail, with reference to different embodiments, a method for preventing scaling in evaporator tubes provided in this application.

[0039] Example 1 A method for preventing scale buildup in evaporator tubes includes the following steps: Preparation of modified functional fillers: 1. Mix trifluoropropyltrimethoxysilane, anhydrous ethanol and deionized water in a certain proportion, adjust the pH of the system to 4, and stir at 200 rpm for 10 min at room temperature to obtain the coupling agent hydrolysate. The mass ratio of trifluoropropyltrimethoxysilane, anhydrous ethanol, and deionized water is 20:65:15. 2. Add nano-silica, nano-zirconia and nano-titanium dioxide into a high-speed mixer in proportion, stir and mix at 900 rpm for 20 minutes to obtain a mixed powder, and keep stirring. The mass ratio of nano-silica, nano-zirconium dioxide, and nano-titanium dioxide is 60:25:15; the average particle size of nano-silica, nano-zirconium dioxide, and nano-titanium dioxide is 10 nm. 3. Add the coupling agent hydrolysate to the mixed powder while it is being stirred in the form of a spray. After the addition is complete, continue stirring for 5 minutes, then discharge the material, vent the air, seal and store for 16 hours to obtain the modified functional filler. The amount of coupling agent hydrolysate added is 2% of the mass of the mixed powder; Preparation of modified coatings: 4. Mix phenyl vinyl silicone resin with hydrogen-containing silicone oil and stir at 300 rpm for 20 minutes at room temperature to obtain a resin base liquid; 5. Then add the modified functional filler to the resin base liquid and stir at 600 rpm for 30 minutes to obtain the mixed slurry; 6. Add the additives to the mixed slurry, continue stirring for 10 minutes, and then pass it through a 200-mesh sieve to obtain the modified coating slurry; The mass ratio of phenyl vinyl silicone resin, modified functional filler, hydrogen-containing silicone oil and additives is 30:22:45:3; the additives are composed of Karstedt catalyst, BYK-307, BYK-065 and BYK-P104, and the mass ratio of Karstedt catalyst, BYK-307, BYK-065 and BYK-P104 is 5:30:15:50. 7. After sandblasting the inner wall of the evaporator tubes to achieve a surface cleanliness level of Sa2.5, blow with compressed air for 5 minutes, rinse with anhydrous ethanol for 10 minutes, and then dry at 60°C to obtain the pretreated evaporator tubes. 8. Subsequently, the modified coating slurry is applied to the inner wall of the pretreated evaporator tubes by spraying. 9. After the modified coating slurry is applied, the evaporator tubes are first left to stand at room temperature for 15 minutes, then kept at 80°C for 30 minutes, then heated to 180°C and kept at 1 hour, and finally cooled naturally to room temperature to obtain the evaporator tubes with the modified coating on the inner wall. The thickness of the modified coating is 80 μm. Methods to prevent scaling: 10. The sulfate content of the reaction solution after the raw limestone is digested is detected to obtain the initial concentration of sulfate in the reaction solution; 11. Add barium nitrate solution to the reaction solution and react at a temperature of 60℃, a stirring speed of 200 rpm, and a stirring time of 20 min to obtain a mixed solution; The molar ratio of barium ions in the barium nitrate solution to sulfate ions in the reaction solution is 1.05:1. 12. The mixture is fed into a filter press for solid-liquid separation to obtain an evaporation feed. The evaporation feed is then evaporated and concentrated through an evaporator tube with a modified coating on its inner wall.

[0040] Example 2 A method for preventing scale buildup in evaporator tubes includes the following steps: Preparation of modified functional fillers: 1. Mix nonafluorohexyltrimethoxysilane, anhydrous ethanol and deionized water in a certain proportion, adjust the pH of the system to 6, and stir at 400 rpm for 20 min at room temperature to obtain the coupling agent hydrolysate. The mass ratio of nonafluorohexyltrimethoxysilane, anhydrous ethanol and deionized water is 30:50:20. 2. Add nano-silica, nano-zirconia and nano-titanium dioxide into a high-speed mixer in proportion, stir and mix at 1200 rpm for 30 minutes to obtain a mixed powder, and keep stirring. The mass ratio of nano-silica, nano-zirconium dioxide, and nano-titanium dioxide is 80:10:10; the average particle size of nano-silica, nano-zirconium dioxide, and nano-titanium dioxide is 50 nm. 3. Add the coupling agent hydrolysate to the mixed powder while it is being stirred in the form of a spray. After the addition is complete, continue stirring for 10 minutes, then discharge the material, vent the air, seal and store for 24 hours to obtain the modified functional filler. The amount of coupling agent hydrolysate added is 5% of the mass of the mixed powder; Preparation of modified coatings: 4. Mix methyl vinyl MQ silicone resin with hydrogen-containing silicone oil and stir at 500 rpm for 30 minutes at room temperature to obtain a resin base liquid; 5. Then add the modified functional filler to the resin base liquid and stir at 800 rpm for 60 minutes to obtain the mixed slurry; 6. Add the additives to the mixed slurry, continue stirring for 20 minutes, and then pass it through a 200-mesh sieve to obtain the modified coating slurry; The mass ratio of methyl vinyl MQ silicone resin, modified functional filler, hydrogen-containing silicone oil and additives is 55:8:36:1; the additives are composed of Karstedt catalyst, BYK-310, BYK-066N and BYK-P104S, and the mass ratio of Karstedt catalyst, BYK-310, BYK-066N and BYK-P104S is 10:20:10:60. 7. After sandblasting the inner wall of the evaporator tubes to achieve a surface cleanliness level of Sa2, blow it with compressed air for 10 minutes, then rinse it with anhydrous ethanol for 20 minutes, and finally dry it at 80°C to obtain the pretreated evaporator tubes. 8. Subsequently, the modified coating slurry is applied to the inner wall of the pretreated evaporator tubes by spraying. 9. After the modified coating slurry is applied, the evaporator tubes are first left to stand at room temperature for 30 minutes, then kept at 100℃ for 60 minutes, then heated to 220℃ and kept at 2 hours, and finally cooled naturally to room temperature to obtain the evaporator tubes with the modified coating on the inner wall. The thickness of the modified coating is 200μm. Methods to prevent scaling: 10. The sulfate content of the reaction solution after the raw limestone is digested is detected to obtain the initial concentration of sulfate in the reaction solution; 11. Add barium nitrate solution to the reaction solution and react at a temperature of 40℃, a stirring speed of 400 rpm, and a stirring time of 40 min to obtain a mixed solution; The molar ratio of barium ions in the barium nitrate solution to sulfate ions in the reaction solution is 1.2:1. 12. The mixture is fed into a filter press for solid-liquid separation to obtain an evaporation feed. The evaporation feed is then evaporated and concentrated through an evaporator tube with a modified coating on its inner wall.

[0041] Example 3 A method for preventing scale buildup in evaporator tubes includes the following steps: 1. Mix trifluoropropylmethyldimethoxysilane, anhydrous ethanol and deionized water in a certain proportion, adjust the pH of the system to 4.5, and stir at 250 rpm for 12 min at room temperature to obtain the coupling agent hydrolysate. The mass ratio of trifluoropropylmethyldimethoxysilane, anhydrous ethanol and deionized water is 25:65:10. 2. Add nano-silica, nano-zirconium dioxide and nano-titanium dioxide into a high-speed mixer in proportion, stir and mix at 950 rpm for 22 minutes to obtain a mixed powder, and keep stirring. The mass ratio of nano-silica, nano-zirconium dioxide, and nano-titanium dioxide is 75:20:5; the average particle size of nano-silica, nano-zirconium dioxide, and nano-titanium dioxide is 20 nm. 3. Add the coupling agent hydrolysate to the mixed powder while it is being stirred in the form of a spray. After the addition is complete, continue stirring for 6 minutes, then discharge the material, vent the air, seal and store for 18 hours to obtain the modified functional filler. The amount of coupling agent hydrolysate added is 2.5% of the mass of the mixed powder; Preparation of modified coatings: 4. Mix vinyl MQ silicone resin with hydrogen-containing silicone oil and stir at 350 rpm for 22 minutes at room temperature to obtain a resin base liquid; 5. Then add the modified functional filler to the resin base liquid and stir at 650 rpm for 35 minutes to obtain the mixed slurry; 6. Add the additives to the mixed slurry, continue stirring for 12 minutes, and then pass it through a 200-mesh sieve to obtain the modified coating slurry; The mass ratio of vinyl MQ silicone resin, modified functional filler, hydrogen-containing silicone oil and additives is 47:20:30:3; the additives consist of Karstedt catalyst, BYK-322, BYK-077 and BYK-180, and the mass ratio of Karstedt catalyst, BYK-322, BYK-077 and BYK-180 is 6:28:16:50. 7. After sandblasting the inner wall of the evaporator tubes to achieve a surface cleanliness level of Sa2.5, blow with compressed air for 6 minutes, rinse with anhydrous ethanol for 12 minutes, and then dry at 65°C to obtain the pretreated evaporator tubes. 8. Subsequently, the modified coating slurry is applied to the inner wall of the pretreated evaporator tubes by spraying. 9. After the modified coating slurry is applied, the evaporator tubes are first allowed to stand at room temperature for 18 minutes, then kept at 85°C for 35 minutes, then heated to 190°C and kept at that temperature for 1.2 hours. Finally, they are allowed to cool naturally to room temperature, resulting in evaporator tubes with the modified coating on the inner wall. The thickness of the modified coating is 100 μm. The actual product is shown in the image. Figure 1 As shown; Methods to prevent scaling: 10. The sulfate content of the reaction solution after the raw limestone is digested is detected to obtain the initial concentration of sulfate in the reaction solution; 11. Add barium nitrate solution to the reaction solution and react at a temperature of 50℃, a stirring speed of 250 rpm, and a stirring time of 25 min to obtain a mixed solution. The molar ratio of barium ions in the barium nitrate solution to sulfate ions in the reaction solution is 1.08:1. 12. The mixture is fed into a filter press for solid-liquid separation to obtain an evaporation feed. The evaporation feed is then evaporated and concentrated through an evaporator tube with a modified coating on its inner wall.

[0042] Example 4 A method for preventing scale buildup in evaporator tubes includes the following steps: Preparation of modified functional fillers: 1. Mix trifluoropropyltriethoxysilane, anhydrous ethanol and deionized water in a certain proportion, adjust the pH of the system to 5.5, and stir at 350 rpm for 18 min at room temperature to obtain the coupling agent hydrolysate. The mass ratio of trifluoropropyltriethoxysilane, anhydrous ethanol and deionized water is 28:52:20. 2. Add nano-silica, nano-zirconia and nano-titanium dioxide into a high-speed mixer in proportion, stir and mix at 1100 rpm for 28 minutes to obtain mixed powder, and keep stirring. The mass ratio of nano-silica, nano-zirconium dioxide, and nano-titanium dioxide is 65:15:20; the average particle size of nano-silica, nano-zirconium dioxide, and nano-titanium dioxide is 40 nm. 3. Add the coupling agent hydrolysate to the mixed powder while it is being stirred in the form of a spray. After the addition is complete, continue stirring for 8 minutes, then discharge the material, vent the air, seal and store for 22 hours to obtain the modified functional filler. The amount of coupling agent hydrolysate added is 4.5% of the mass of the mixed powder; Preparation of modified coatings: 4. Mix phenyl vinyl silicone resin with hydrogen-containing silicone oil and stir at 450 rpm for 28 minutes at room temperature to obtain a resin base liquid; 5. Then add the modified functional filler to the resin base liquid and stir at 750 rpm for 55 minutes to obtain the mixed slurry; 6. Add the additives to the mixed slurry, continue stirring for 18 minutes, and then pass it through a 200-mesh sieve to obtain the modified coating slurry; The mass ratio of phenyl vinyl silicone resin, modified functional filler, hydrogen-containing silicone oil and additives is 40:15:43:2; the additives are composed of Karstedt catalyst, BYK-333, BYK-067A and BYK-110, and the mass ratio of Karstedt catalyst, BYK-333, BYK-067A and BYK-110 is 8:22:20:50. 7. After sandblasting the inner wall of the evaporator tubes to achieve a surface cleanliness level of Sa2, blow with compressed air for 8 minutes, rinse with anhydrous ethanol for 18 minutes, and then dry at 75°C to obtain the pretreated evaporator tubes. 8. Subsequently, the modified coating slurry is applied to the inner wall of the pretreated evaporator tubes by spraying. 9. After the modified coating slurry is applied, the evaporator tubes are first left to stand at room temperature for 25 minutes, then kept at 95°C for 55 minutes, then heated to 210°C and kept at 210°C for 1.8 hours, and finally cooled naturally to room temperature to obtain the evaporator tubes with the modified coating on the inner wall. The thickness of the modified coating is 150 μm. Methods to prevent scaling: 10. The sulfate content of the reaction solution after the raw limestone is digested is detected to obtain the initial concentration of sulfate in the reaction solution; 11. Add barium nitrate solution to the reaction solution and react at a temperature of 55℃, a stirring speed of 350 rpm, and a stirring time of 35 min to obtain a mixed solution; The molar ratio of barium ions in the barium nitrate solution to sulfate ions in the reaction solution is 1.15:1. 12. The mixture is fed into a filter press for solid-liquid separation to obtain an evaporation feed. The evaporation feed is then evaporated and concentrated through an evaporator tube with a modified coating on its inner wall.

[0043] Example 5 A method for preventing scale buildup in evaporator tubes includes the following steps: Preparation of modified functional fillers: 1. Mix trifluoropropyltrimethoxysilane, anhydrous ethanol and deionized water in a certain proportion, adjust the pH of the system to 5, and stir at 300 rpm for 15 min at room temperature to obtain the coupling agent hydrolysate. The mass ratio of trifluoropropyltrimethoxysilane, anhydrous ethanol and deionized water is 25:60:15. 2. Add nano-silica, nano-zirconium dioxide and nano-titanium dioxide into a high-speed mixer in proportion, stir and mix at 1000 rpm for 25 minutes to obtain a mixed powder, and keep stirring. The mass ratio of nano-silica, nano-zirconium dioxide, and nano-titanium dioxide is 70:18:12; the average particle size of nano-silica, nano-zirconium dioxide, and nano-titanium dioxide is 30 nm. 3. Add the coupling agent hydrolysate to the mixed powder while it is being stirred in the form of a spray. After the addition is complete, continue stirring for 7 minutes, then discharge the material, vent the air, seal and store for 20 hours to obtain the modified functional filler. The amount of coupling agent hydrolysate added is 3% of the mass of the mixed powder; Preparation of modified coatings: 4. Mix vinyl MQ silicone resin with hydrogen-containing silicone oil and stir at 400 rpm for 25 minutes at room temperature to obtain a resin base liquid; 5. Then add the modified functional filler to the resin base liquid and stir at 700 rpm for 45 minutes to obtain the mixed slurry; 6. Add the additives to the mixed slurry, continue stirring for 15 minutes, and then pass it through a 200-mesh sieve to obtain the modified coating slurry; The mass ratio of vinyl MQ silicone resin, modified functional filler, hydrogen-containing silicone oil and additives is 42:18:38:2; the additives are composed of Karstedt catalyst, BYK-310, BYK-067A and BYK-P104, and the mass ratio of Karstedt catalyst, BYK-310, BYK-067A and BYK-P104 is 7:25:13:55. 7. After sandblasting the inner wall of the evaporator tubes to achieve a surface cleanliness level of Sa2.5, blow with compressed air for 7 minutes, rinse with anhydrous ethanol for 15 minutes, and then dry at 70°C to obtain the pretreated evaporator tubes. 8. Subsequently, the modified coating slurry is applied to the inner wall of the pretreated evaporator tubes by spraying. 9. After the modified coating slurry is applied, the evaporator tubes are first left to stand at room temperature for 20 minutes, then kept at 90°C for 45 minutes, then heated to 200°C and kept at 200°C for 1.5 hours, and finally cooled to room temperature naturally to obtain the evaporator tubes with the modified coating on the inner wall. The thickness of the modified coating is 120 μm. Methods to prevent scaling: 10. The sulfate content of the reaction solution after the raw limestone is digested is detected to obtain the initial concentration of sulfate in the reaction solution; 11. Add barium nitrate solution to the reaction solution and react at a temperature of 45℃, a stirring speed of 300 rpm, and a stirring time of 30 min to obtain a mixed solution; The molar ratio of barium ions in the barium nitrate solution to sulfate ions in the reaction solution is 1.1:1. 12. The mixture is fed into a filter press for solid-liquid separation to obtain an evaporation feed. The evaporation feed is then evaporated and concentrated through an evaporator tube with a modified coating on its inner wall.

[0044] Example 6 A method for preventing scale buildup in evaporator tubes includes the following steps: Preparation of modified functional fillers: 1. Mix nonafluorohexyltrimethoxysilane, anhydrous ethanol and deionized water in a certain proportion, adjust the pH of the system to 5.2, and stir at 320 rpm for 16 min at room temperature to obtain the coupling agent hydrolysate. The mass ratio of nonafluorohexyltrimethoxysilane, anhydrous ethanol and deionized water is 22:63:15. 2. Add nano-silica, nano-zirconia and nano-titanium dioxide into a high-speed mixer in proportion, stir and mix at 1050 rpm for 26 minutes to obtain mixed powder, and keep stirring. The mass ratio of nano-silica, nano-zirconium dioxide, and nano-titanium dioxide is 72:16:12; the average particle size of nano-silica, nano-zirconium dioxide, and nano-titanium dioxide is 25 nm. 3. Add the coupling agent hydrolysate to the mixed powder while it is being stirred in the form of a spray. After the addition is complete, continue stirring for 9 minutes, then discharge the material, vent the air, seal and store for 21 hours to obtain the modified functional filler. The amount of coupling agent hydrolysate added is 4% of the mass of the mixed powder; Preparation of modified coatings: 4. Mix methyl vinyl MQ silicone resin with hydrogen-containing silicone oil and stir at 380 rpm for 26 minutes at room temperature to obtain a resin base liquid; 5. Then add the modified functional filler to the resin base liquid and stir at 720 rpm for 48 minutes to obtain the mixed slurry; 6. Add the additives to the mixed slurry, continue stirring for 16 minutes, and then pass it through a 200-mesh sieve to obtain the modified coating slurry; The mass ratio of methyl vinyl MQ silicone resin, modified functional filler, hydrogen-containing silicone oil and additives is 38:14:45:3; the additives are composed of Karstedt catalyst, BYK-322, BYK-065 and BYK-110, and the mass ratio of Karstedt catalyst, BYK-322, BYK-065 and BYK-110 is 6:26:14:54. 7. After sandblasting the inner wall of the evaporator tubes to achieve a surface cleanliness level of Sa2, blow with compressed air for 9 minutes, rinse with anhydrous ethanol for 16 minutes, and then dry at 72°C to obtain the pretreated evaporator tubes. 8. Subsequently, the modified coating slurry is applied to the inner wall of the pretreated evaporator tubes by spraying. 9. After the modified coating slurry is applied, the evaporator tubes are first left to stand at room temperature for 22 minutes, then kept at 92°C for 48 minutes, then heated to 205°C and kept at 205°C for 1.6 hours, and finally cooled naturally to room temperature to obtain the evaporator tubes with the modified coating on the inner wall. The thickness of the modified coating is 180 μm. Methods to prevent scaling: 10. The sulfate content of the reaction solution after the raw limestone is digested is detected to obtain the initial concentration of sulfate in the reaction solution; 11. Add barium nitrate solution to the reaction solution and react at a temperature of 48℃, a stirring speed of 320 rpm, and a stirring time of 32 min to obtain a mixed solution; The molar ratio of barium ions in the barium nitrate solution to sulfate ions in the reaction solution is 1.12:1. 12. The mixture is fed into a filter press for solid-liquid separation to obtain an evaporation feed. The evaporation feed is then evaporated and concentrated through an evaporator tube with a modified coating on its inner wall.

[0045] Comparative Example 1 This comparative example provides a method for preventing scaling in evaporator tubes. The difference between this comparative example and Example 3 is that no barium nitrate is added. Other process parameters and operating steps are exactly the same as in Example 3.

[0046] Comparative Example 2 This comparative example provides a method for preventing scaling in evaporator tubes. The difference between this comparative example and Example 3 is that no modified coating is applied to the inner wall of the evaporator tubes. Other process parameters and operating steps are exactly the same as in Example 3.

[0047] Comparative Example 3 This comparative example provides a method for preventing scaling in evaporator tubes. The difference between this comparative example and Example 3 is that neither barium nitrate is added nor a modified coating is applied to the inner wall of the evaporator tubes. Other process parameters and operating steps are exactly the same as in Example 3.

[0048] Performance testing: Referring to GB / T 9286-2021, the adhesion level of the modified coatings applied to the inner wall of the evaporator tubes provided in Examples 1-6 and Comparative Examples 1-3 was tested by cross-cut test to reflect the magnitude of their adhesion.

[0049] Referring to GB / T30693-2014, a contact angle meter is used to test the water contact angle of the modified coating applied to the inner wall of the evaporator tubes to reflect its water resistance.

[0050] The evaporator tubes provided in Examples 1-6 and Comparative Examples 1-3 were used for 720 hours of continuous evaporation and concentration. The amount of scale (g / m²) on the inner wall of the evaporator tubes was then measured after the operation. 2 This demonstrates its anti-scaling effect.

[0051] The test results are shown in Table 1.

[0052] Table 1. Anti-scaling test results of evaporator tubes in the methods provided in Examples 1-6 and Comparative Examples 1-3.

[0053] As shown in Table 1, the cutting nozzles coated with highly adhesive catalytic coating materials prepared in Examples 1-6 generally outperformed those in Comparative Examples 1-3.

[0054] The main reason is that the preparation method of the cutting nozzle coated with high adhesion catalytic coating material obtained in Examples 1-6 proposes a method to prevent scale formation in evaporator tubes by addressing both nucleation conditions and adhesion conditions.

[0055] Regarding nucleation conditions, the core scaling factor in the reaction solution after limestone digestion is sulfate, which can combine with a large number of calcium ions in the system. During evaporation, calcium sulfate will precipitate supersaturated on the surface of the high-temperature heat exchange tubes, forming difficult-to-remove calcium sulfate scale. This application utilizes the fact that barium ions and sulfate can form barium sulfate precipitate, and its solubility product is much lower than that of calcium sulfate. Therefore, sulfate can be removed deeply by preferentially forming barium sulfate, significantly reducing the formation of calcium sulfate from a thermodynamic source, thereby preventing the formation of scale.

[0056] Regarding adhesion conditions, this application significantly reduces the formation of calcium sulfate by coating the inner wall of the evaporator tubes with a modified coating, thereby reducing the adhesion of the remaining small amount of scale. This dual action achieves long-term scale prevention, which is far superior to single scale prevention methods. In the modified coating, the base resin is silicone resin, with a Si-O-Si main chain molecular structure, high bond energy, and excellent temperature resistance, chemical corrosion resistance, and low surface energy, making it suitable for the harsh operating conditions of evaporators under high temperature and acid / alkali corrosion. Further mixing of hydrogen-containing silicone oil and silicone resin forms a dense three-dimensional cross-linked network, further improving the density, water resistance, and low surface energy of the modified coating. Fluorosilane-modified nano-inorganic fillers, on the one hand, can improve compatibility with the resin matrix through coupling agent grafting, preventing agglomeration; on the other hand, the introduced fluorine groups can further reduce the surface energy of the resulting modified coating. Simultaneously, the nano-inorganic fillers can construct a micro-nano rough structure, producing a lotus leaf-like superhydrophobic effect, thereby significantly reducing the adhesion of precipitated scale to the inner wall of the tube. Even if a small amount of scale still precipitates, it is easily washed off by the slurry during the evaporation and concentration process. These two aspects work together to achieve a significant anti-scaling effect.

[0057] In contrast, in Comparative Example 1, no barium nitrate was added, so a large amount of sulfate ions and calcium ions combined in the system. However, due to the presence of the modified coating, the increase in scale was not too significant.

[0058] In Comparative Example 2, no modified coating was applied to the inner wall of the evaporator tubes, so it was impossible to achieve long-term scale prevention through the dual action, and it was also impossible to significantly reduce the adhesion between the precipitated scale and the inner wall of the tubes. As a result, the water contact angle was significantly reduced and the amount of scale increased significantly.

[0059] In Comparative Example 3, neither barium nitrate was added nor a modified coating was applied to the inner wall of the evaporator tubes, resulting in the smallest water contact angle and the largest amount of scaling.

[0060] The above results demonstrate and describe the basic principles and main features of this application, as well as its advantages.

[0061] Those skilled in the art should understand that this application is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of this application. Various changes and modifications can be made to this application without departing from the spirit and scope thereof, and all such changes and modifications fall within the scope of this application as claimed. The scope of protection of this application is defined by the equivalents of the appended claims.

Claims

1. A method for preventing scaling in evaporator tubes, characterized in that, Includes the following steps: The sulfate content of the reaction solution after the raw limestone is digested is detected to obtain the initial concentration of sulfate in the reaction solution; Barium nitrate solution was added to the reaction solution, and the reaction conditions were controlled to obtain a mixture. The mixture is fed into a filter press for solid-liquid separation to obtain an evaporation feed. The evaporation feed is then evaporated and concentrated through an evaporator tube with a modified coating on its inner wall. The modified coating comprises a base resin, modified functional filler, hydrogen-containing silicone oil, and additives; the base resin comprises any one of phenyl vinyl silicone resin, vinyl MQ silicone resin, and methyl vinyl MQ silicone resin; the modified functional filler is obtained by modifying a mixture of nano-silica, nano-zirconium dioxide, and nano-titanium dioxide.

2. The method for preventing scaling in evaporator tubes according to claim 1, characterized in that, The molar ratio of barium ions in the barium nitrate solution to sulfate ions in the reaction solution is (1.05-1.2):

1.

3. The method for preventing scaling in evaporator tubes according to claim 1, characterized in that, The reaction conditions include: a temperature of 40-60℃, a stirring rate of 200-400 rpm, and a stirring time of 20-40 min.

4. The method for preventing scaling in evaporator tubes according to claim 1, characterized in that, In the modified coating, the mass ratio of the base resin, modified functional filler, hydrogen-containing silicone oil and additives is (30-55):(8-22):(30-45):(1-3).

5. The method for preventing scaling in evaporator tubes according to claim 1, characterized in that, The preparation method of the modified functional filler includes: Mix the fluorinated silane coupling agent, anhydrous ethanol and deionized water in a certain proportion, adjust the pH of the system to 4-6, and stir at 200-400 rpm for 10-20 min at room temperature to obtain the coupling agent hydrolysate. Nano-silica, nano-zirconium dioxide, and nano-titanium dioxide are added to a high-speed mixer in a certain proportion and stirred at 900-1200 rpm for 20-30 minutes to obtain a mixed powder, while maintaining stirring. The coupling agent hydrolysate is added to the mixed powder while it is being stirred in the form of a spray. After the addition is complete, stirring is continued for 5-10 minutes. Then the material is discharged, the air is vented, and the mixture is sealed and stored for 16-24 hours to obtain the modified functional filler.

6. The method for preventing scaling in evaporator tubes according to claim 5, characterized in that, In the coupling agent hydrolysate, the mass ratio of fluorinated silane coupling agent, anhydrous ethanol, and deionized water is (20-30):(50-65):(10-20); in the mixed powder, the mass ratio of nano-silica, nano-zirconium dioxide, and nano-titanium dioxide is (60-80):(10-25):(5-20); the amount of coupling agent hydrolysate added is 2%-5% of the mass of the mixed powder.

7. The method for preventing scaling in evaporator tubes according to claim 6, characterized in that, The fluorinated silane coupling agent includes any one of trifluoropropyltrimethoxysilane, trifluoropropylmethyldimethoxysilane, trifluoropropyltriethoxysilane, and nonafluorohexyltrimethoxysilane.

8. The method for preventing scaling in evaporator tubes according to claim 1, characterized in that, The method for preparing the modified coating includes: Mix the matrix resin with hydrogen-containing silicone oil and stir at 300-500 rpm for 20-30 minutes at room temperature to obtain the resin base liquid; Then, add the modified functional filler to the resin base liquid and stir at 600-800 rpm for 30-60 minutes to obtain the mixed slurry. Add the additives to the mixed slurry, continue stirring for 10-20 minutes, and then pass it through a 200-mesh sieve to obtain the modified coating slurry; After sandblasting the inner wall of the evaporator tubes, blow them with compressed air for 5-10 minutes, then rinse them with anhydrous ethanol for 10-20 minutes, and then dry them at 60-80℃ to obtain the pretreated evaporator tubes. Subsequently, the modified coating slurry was applied to the inner wall of the pretreated evaporator tubes by spraying. After the modified coating slurry is applied, the evaporator tubes are first left to stand at room temperature for 15-30 minutes, then kept at 80-100℃ for 30-60 minutes, then heated to 180-220℃ and kept at 1-2 hours, and finally cooled naturally to room temperature to obtain the modified coating on the inner wall of the evaporator tubes.

9. A method for preventing scaling in evaporator tubes according to claim 8, characterized in that, After sandblasting, the surface cleanliness level of the inner wall of the evaporator tubes is Sa2 or Sa2.

5.

10. A method for preventing scaling in evaporator tubes according to claim 1, characterized in that, The thickness of the modified coating is 80-200 μm.

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