Environment-friendly scale inhibitor for boiler and preparation method thereof

Abstract

The application discloses an environment-friendly scale inhibitor for a boiler and a preparation method thereof. According to weight parts, the scale inhibitor comprises the following raw materials: 25-35 parts of a branched corrosion and scale inhibitor, 30-40 parts of polyvinyl alcohol, 17-24 parts of sodium alginate, 3-7 parts of glutaraldehyde, 5-10 parts of calcium chloride and 1000-2100 parts of water. The scale inhibitor has good corrosion and scale inhibition effects, and can effectively prolong the service life of the boiler.

Description

Technical Field

[0001] This invention belongs to the field of water treatment, specifically relating to an environmentally friendly scale inhibitor for boilers and its preparation method. Background Technology

[0002] Boilers, as enclosed devices that consume fuel and output heat energy, play an indispensable role in industrial production and residential life. In actual operation, to reduce corrosion, boilers generally maintain an alkaline operating environment. This makes it easy for dissolved calcium and magnesium ions in natural water to form scale on the boiler's heat transfer surfaces. The deposition of scale on these surfaces reduces heat transfer efficiency, significantly increasing boiler energy consumption; it also raises the temperature of the metal walls, leading to creep, deformation, and bulging of load-bearing components. Adding scale inhibitors to the water is an efficient and practical method to solve the boiler scaling problem.

[0003] Scale inhibitors disperse sparingly soluble inorganic salts in water, preventing or interfering with the formation of precipitates and scale on metal surfaces. With further research, scale inhibitors have evolved from simple inorganic substances to high-molecular polymers, and their functions have expanded from single scale inhibition properties to multifunctional agents combining scale prevention, corrosion prevention, and sterilization. Currently, with the implementation of various national environmental protection regulations, scale inhibitors are rapidly developing towards environmentally friendly, multifunctional, and highly efficient products.

[0004] Patent CN116874095B discloses a phosphorus-free mixture for boiler shutdown protection and daily operation chemical treatment. This phosphorus-free mixture has excellent corrosion inhibition, scale inhibition, and dispersing capabilities, improving the corrosion resistance of shutdown protection. It can also solve the problems of complex switching between daily operation and shutdown protection of low-pressure boilers and high water consumption. However, the mixture is added intermittently, which, although it can slow down the scaling and corrosion rate to a certain extent, has problems such as uneven or insufficient addition, high mixture consumption, and unstable effect. Patent CN114890557B discloses a slow-release solid scale inhibitor and its application, which can precisely control the release of the effective components of the scale inhibitor. The long-term slow-release effect can reach 200 days, effectively solving the problems of excessively rapid release and poor scale inhibition effect of traditional scale inhibitors. However, the preparation of this scale inhibitor mixture requires hydroxyethylidene diphosphonic acid, which is not very environmentally friendly. Summary of the Invention

[0005] This invention provides an environmentally friendly scale inhibitor for boilers and its preparation method. The scale inhibitor has good corrosion inhibition and scale inhibition effects, which can effectively improve the service life of boilers. Furthermore, by subjecting the scale inhibitor to slow-release treatment, it can exert its scale inhibition effect for a long time. Moreover, the slow-release treatment can also refine the viscous oily branched corrosion and scale inhibitor, further inhibiting the formation of scale crystal nuclei.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] The present invention provides a corrosion-inhibiting and deoxygenating furnace shutdown protection agent, which, by weight, comprises the following raw materials: 25-35 parts of branched corrosion and scale inhibitor, 30-40 parts of polyvinyl alcohol, 17-24 parts of sodium alginate, 3-7 parts of glutaraldehyde, 5-10 parts of calcium chloride, and 1000-2100 parts of water.

[0008] In some embodiments, the preparation steps of the branched corrosion and scale inhibitor are as follows:

[0009] S1. Mix 2-quinoline carboxylic acid, hydroxyethyl acrylate and dichloromethane evenly, then add 1,3-dicyclohexylcarbodiimide and 4-dimethylaminopyridine, stir for 2-3 hours and then separate the oily liquid to obtain reaction solution A;

[0010] S2. Mix diethylenetriamine and methanol evenly, add the reaction solution A from step S1 dropwise, stir at 30-35℃ for 20-25 hours, and then evaporate by rotary evaporation to obtain the branched corrosion and scale inhibitor.

[0011] In some embodiments, the mass ratio of 2-quinoline carboxylic acid, hydroxyethyl acrylate, and 1,3-dicyclohexylcarbodiimide in step S1 is 1:(0.67-0.70):(1.0-1.4).

[0012] In some embodiments, the mass ratio of diethylenetriamine in step S2 to hydroxyethyl acrylate in step S1 is (1.18-1.74):1.

[0013] In some embodiments, the addition of reaction solution A from step S1 in step S2 is carried out under the protection of an ice-water bath and nitrogen, and the addition time is controlled at 90-120 min.

[0014] In recent years, to reduce environmental pollution, researchers have been committed to replacing traditional phosphorus-containing scale inhibitors with new green and environmentally friendly scale inhibitors. To further improve the scale inhibition effect of environmentally friendly scale inhibitors on boiler water, the applicant has developed a branched corrosion and scale inhibitor. First, 2-quinoline carboxylic acid is esterified with hydroxyethyl acrylate to form a corrosion inhibition chain. Since the highest occupied orbital and lowest empty orbital of 2-quinoline carboxylic acid are mainly concentrated on the quinoline ring and oxygen atom, it has multiple adsorption sites and can interact with the d orbitals of boiler iron, thereby enabling 2-quinoline carboxylic acid to be adsorbed on the boiler surface. Then, a branched corrosion and scale inhibitor is prepared by Michael addition with diethylenetriamine. Branched scale inhibitors can utilize their spatial structure and large molecular volume to induce irregular growth of crystals such as CaCO3, slow down crystal growth, disrupt crystal formation, and change the crystal form of calcium scale crystals. However, an increase in branched structure does not necessarily promote scale inhibition, as the introduced functional groups may create steric barriers. In the branched corrosion and scale inhibitor of this invention, 2-quinoline carboxylic acid, after being adsorbed on the boiler surface, can also pull the molecular chains, making the molecular chains less prone to entanglement, reducing steric barriers, and achieving a good scale inhibition effect.

[0015] The non-entangled molecular chains in scale inhibitors readily adsorb onto the crystal surface. This encapsulates the formed fine crystals, preventing further microcrystal growth; simultaneously, it forms a double electron layer with the same charge, causing free metal ions to repel each other and achieving good dispersion. Furthermore, the oxygen atoms in the molecular chains have a high negative charge density, which can react with the Ca atoms in the scale crystals. 2+ They interact with each other, thereby significantly enhancing the adsorption behavior on the crystal surface and causing crystal distortion.

[0016] Because the environmentally friendly scale inhibitor of this invention needs to withstand high temperature and high pressure in the boiler, and the boiler water is mostly alkaline, the ester group is easily hydrolyzed under these conditions. Regarding the branched corrosion and scale inhibitor of this invention, if the ester bond breaks, both the separated corrosion-inhibiting chain and the scale-inhibiting chain will have reduced effectiveness, as analyzed below:

[0017] The branched scale inhibitor chains after severing from 2-quinoline carboxylic acid may cause side reactions such as internal cyclization and bridging of branched molecules during boiler water heating, reducing the capture of scale. At higher temperatures, some of the corrosion inhibitor chains adsorbed on the boiler surface will detach, exposing the metal surface directly and resulting in a certain degree of reduction in corrosion inhibition rate.

[0018] Therefore, this invention, through specific selection of raw materials and preparation processes, achieves two advantages: firstly, the ester groups in the branched corrosion and scale inhibitor have a high electron cloud density, i.e., increased bond strength, effectively reducing the ester group breakage rate; secondly, the quinoline ring with adsorption properties improves the heat resistance of the scale inhibitor, and can also reduce the effect of the environment on individual adsorption sites through the synergistic effect between active adsorption sites connected by the main chain, preventing them from detaching from the metal surface.

[0019] In some embodiments, the degree of alcoholysis of the polyvinyl alcohol is 87-89%.

[0020] Another aspect of the present invention provides a method for preparing an environmentally friendly scale inhibitor for boilers, comprising the following steps:

[0021] (1) Prepare polyvinyl alcohol solution, sodium alginate solution and calcium chloride solution respectively with water and polyvinyl alcohol, sodium alginate and calcium chloride respectively;

[0022] (2) Stir the polyvinyl alcohol solution and sodium alginate solution for 20-40 minutes, add the branched corrosion and scale inhibitor, homogenize, and obtain a dispersion.

[0023] (3) While stirring, add calcium chloride solution to the dispersion in step (2), stir for 30-40 minutes and remove 50-75 wt% water, then add glutaraldehyde, adjust pH to 2-3, let stand for 40-50 minutes, wash and dry to obtain the environmentally friendly scale inhibitor.

[0024] In some embodiments, the concentration of the polyvinyl alcohol solution in step (1) is 10-14 wt%.

[0025] In some embodiments, the concentration of sodium alginate solution in step (1) is 1-3 wt%.

[0026] In some embodiments, the concentration of the calcium chloride solution in step (1) is 22-28 wt%.

[0027] In some embodiments, the stirring rate in step (2) is 1500-1800 rpm.

[0028] To address the problem of excessively rapid release of scale inhibitors in traditional intermittent feeding systems, this invention employs polyvinyl alcohol, sodium alginate, and calcium chloride to coat and slow-release the scale inhibitor, enabling it to exert a long-lasting scale-inhibiting effect in circulating water. Furthermore, this slow-release treatment refines the viscous, oily branched corrosion and scale inhibitor, allowing for uniform distribution in boiler water. By specifically selecting the degree of alcoholysis of polyvinyl alcohol and the concentration of the reaction solution, this invention creates a near-spherical structure of the refined branched corrosion and scale inhibitor molecules, resulting in a nanoscale internal surface area. This allows the inhibitor to firmly adsorb onto the active growth sites of calcium scale crystals, further inhibiting crystal nucleation.

[0029] Compared with the prior art, the present invention has the following beneficial effects:

[0030] 1. This invention provides a new type of green and environmentally friendly scale inhibitor to replace the traditional phosphorus-containing scale inhibitor. This scale inhibitor has good corrosion inhibition and scale inhibition effects, which can effectively improve the service life of boilers.

[0031] 2. The 2-quinoline carboxylic acid in the scale inhibitor of this invention can not only be adsorbed on the boiler surface to play a corrosion inhibition role, but also reduce the steric barrier in the branched structure by pulling the molecular chain, making the molecular chain less prone to entanglement and achieving a good scale inhibition effect.

[0032] 3. By specifically selecting raw materials and preparation processes, this invention enables the ester groups in the scale inhibitor to have a high electron cloud density, effectively reducing the ester group breakage rate in alkaline boiler water environments and reducing side reactions such as internal cyclization and bridging of the branched scale inhibitor chains after chain breakage with 2-quinoline carboxylic acid during heating. Furthermore, the synergistic effect between the active adsorption sites connected by the main chain weakens the environmental effect on individual adsorption sites and prevents the corrosion inhibitor chains from detaching from the metal surface at high temperatures.

[0033] 4. This invention performs a slow-release treatment on the synthesized branched corrosion and scale inhibitor, enabling it to exert a long-term scale inhibition effect in circulating water. Furthermore, this slow-release treatment can refine the viscous, oily branched corrosion and scale inhibitor, allowing it to be evenly distributed in boiler water. The spherical structure of the refined branched corrosion and scale inhibitor molecules forms a nanoscale internal surface area, which can be firmly adsorbed onto the active growth sites of calcium scale crystals, further inhibiting the formation of crystal nuclei. Detailed Implementation

[0034] The present invention will be described below with reference to specific embodiments. It should be noted that the following embodiments are examples of the present invention and are used only to illustrate the invention, not to limit it. Other combinations and various modifications within the scope of the present invention can be made without departing from its spirit or scope.

[0035] To facilitate implementation of this invention by those skilled in the art, some raw materials and manufacturers of the embodiments and comparative examples are described below:

[0036] Polyvinyl alcohol was purchased from Shanxi Sanweishengtai New Material Technology Co., Ltd., with a degree of alcoholysis of 88%, grade 17-88, and 80 mesh.

[0037] Preparation Example 1

[0038] The preparation steps of branched corrosion and scale inhibitor-A are as follows:

[0039] S1. Mix 100g of 2-quinoline carboxylic acid, 68.5g of hydroxyethyl acrylate and 1200g of dichloromethane evenly, then add 120g of 1,3-dicyclohexylcarbodiimide and 3.5g of 4-dimethylaminopyridine, stir for 2.5h and then separate the oily liquid to obtain reaction solution A;

[0040] S2. Under the protection of ice water bath and nitrogen, 100g of diethylenetriamine and 210g of methanol are mixed evenly, and 1360g of reaction solution A from step S1 is added dropwise over 110min. The mixture is stirred at 33℃ for 22h and rotary evaporated until the quality is stable to obtain the branched corrosion and scale inhibitor-A.

[0041] Preparation Example 2

[0042] The preparation steps of branched corrosion and scale inhibitor-B are as follows:

[0043] The difference between this preparation example and preparation example 1 is that 118g of 2-quinoline carboxylic acid was used in step S1.

[0044] Preparation Example 3

[0045] The preparation steps of branched corrosion and scale inhibitor-C are as follows:

[0046] The difference between this preparation example and preparation example 1 is that 84g of 2-quinoline carboxylic acid was used in step S1.

[0047] Preparation Example 4

[0048] The preparation steps of branched corrosion and scale inhibitor-D are as follows:

[0049] The difference between this preparation example and preparation example 1 is that 120g of diethylenetriamine was used in step S2.

[0050] Preparation Example 5

[0051] The preparation steps of branched corrosion and scale inhibitor-E are as follows:

[0052] The difference between this preparation example and preparation example 1 is that 80g of diethylenetriamine was used in step S2.

[0053] Preparation Example 6

[0054] The preparation steps of the branched scale inhibitor are as follows:

[0055] S1. Mix 68.5g of hydroxyethyl acrylate and 1200g of dichloromethane evenly to obtain reaction solution A;

[0056] S2. Under the protection of ice water bath and nitrogen, 100g of diethylenetriamine and 210g of methanol are mixed evenly, and the reaction solution A from step S1 is added dropwise over 110 minutes. The mixture is stirred at 33°C for 22 hours and then rotary evaporated to obtain the branched scale inhibitor.

[0057] Example 1

[0058] An environmentally friendly scale inhibitor for boilers, comprising the following raw materials by weight: 30 parts branched corrosion and scale inhibitor-A, 35 parts polyvinyl alcohol, 21 parts sodium alginate, 5 parts glutaraldehyde, 7 parts calcium chloride, and 1307 parts water.

[0059] This embodiment describes a method for preparing an environmentally friendly scale inhibitor for boilers, comprising the following steps:

[0060] (1) Prepare polyvinyl alcohol solution, sodium alginate solution and calcium chloride solution with water respectively, with concentrations of 12wt%, 2wt% and 25wt%;

[0061] (2) Stir the polyvinyl alcohol solution and sodium alginate solution at 1650 rpm for 30 min, add branched corrosion and scale inhibitor-A, stir, and obtain a dispersion.

[0062] (3) While stirring, add calcium chloride solution to the dispersion in step (2), stir for 35 min, remove 60 wt% water by vacuum distillation, then add glutaraldehyde, adjust pH to 2.2 with 1M hydrochloric acid, let stand for 45 min, wash and dry to obtain the environmentally friendly scale inhibitor.

[0063] Example 2

[0064] An environmentally friendly scale inhibitor for boilers, comprising the following raw materials by weight: 27 parts branched corrosion and scale inhibitor-A, 32 parts polyvinyl alcohol, 18 parts sodium alginate, 3 parts glutaraldehyde, 5 parts calcium chloride, and 2088 parts water.

[0065] This embodiment describes a method for preparing an environmentally friendly scale inhibitor for boilers, comprising the following steps:

[0066] (1) Prepare polyvinyl alcohol solution, sodium alginate solution and calcium chloride solution with water respectively, with concentrations of 10wt%, 1wt% and 22wt%;

[0067] (2) Stir the polyvinyl alcohol solution and sodium alginate solution at 1600 rpm for 40 min, add branched corrosion and scale inhibitor-A, stir, and obtain a dispersion.

[0068] (3) While stirring, add calcium chloride solution to the dispersion in step (2), stir for 35 min, remove 50 wt% water by vacuum distillation, then add glutaraldehyde, adjust pH to 2.0 with 1M hydrochloric acid, let stand for 40 min, wash and dry to obtain the environmentally friendly scale inhibitor.

[0069] Example 3

[0070] An environmentally friendly scale inhibitor for boilers, comprising the following raw materials by weight: 35 parts branched corrosion and scale inhibitor-A, 40 parts polyvinyl alcohol, 24 parts sodium alginate, 7 parts glutaraldehyde, 10 parts calcium chloride and 1048 parts water.

[0071] This embodiment describes a method for preparing an environmentally friendly scale inhibitor for boilers, comprising the following steps:

[0072] (1) Prepare polyvinyl alcohol solution, sodium alginate solution and calcium chloride solution with water respectively, with concentrations of 14wt%, 3wt% and 28wt%;

[0073] (2) Stir the polyvinyl alcohol solution and sodium alginate solution at 1800 rpm for 20 min, add branched corrosion and scale inhibitor-A, stir, and obtain a dispersion.

[0074] (3) While stirring, add calcium chloride solution to the dispersion in step (2). After stirring for 40 minutes, remove 75 wt% water by vacuum distillation. Then add glutaraldehyde, adjust the pH to 2.8 with 1M hydrochloric acid, let stand for 50 minutes, wash and dry to obtain the environmentally friendly scale inhibitor.

[0075] Example 4

[0076] This embodiment provides an environmentally friendly scale inhibitor for boilers and its preparation method. The specific implementation method is the same as that in Embodiment 1, except that the branched corrosion and scale inhibitor-A in the raw materials is replaced by an equal part of branched corrosion and scale inhibitor-B.

[0077] Example 5

[0078] This embodiment provides an environmentally friendly scale inhibitor for boilers and its preparation method. The specific implementation method is the same as that in Embodiment 1, except that the branched corrosion and scale inhibitor-A in the raw materials is replaced by an equal part of branched corrosion and scale inhibitor-C.

[0079] Example 6

[0080] This embodiment provides an environmentally friendly scale inhibitor for boilers and its preparation method. The specific implementation method is the same as that in Embodiment 1, except that the branched corrosion and scale inhibitor-A in the raw materials is replaced by an equal part of branched corrosion and scale inhibitor-D.

[0081] Example 7

[0082] This embodiment provides an environmentally friendly scale inhibitor for boilers and its preparation method. The specific implementation method is the same as that in Embodiment 1, except that the branched corrosion and scale inhibitor-A in the raw materials is replaced by an equal part of branched corrosion and scale inhibitor-E.

[0083] Comparative Example 1

[0084] This comparative example provides an environmentally friendly scale inhibitor for boilers and its preparation method. The specific implementation method is the same as in Example 1, except that the branched corrosion and scale inhibitor-A in the raw materials is replaced by an equal part of branched scale inhibitor.

[0085] Performance testing:

[0086] The scale inhibitors of each embodiment and comparative example, as well as the simple branched corrosion and scale inhibitor-A, were diluted with water to prepare a 20 wt% test solution, and the following tests were performed:

[0087] 1. Corrosion Inhibition Effect Test

[0088] Immerse 20 carbon steel in the above test solution and let it stand at room temperature for 3 hours. Remove the 20 carbon steel, wash the surface with deionized water, and dry it at room temperature. Then, perform a drop test with acidic copper sulfate solution. Drop 1 drop of acidic copper sulfate solution onto the surface of the 20 carbon steel and record the time when the surface of the test piece first turns red. The longer the time, the better the protective effect. Take the average value of 6 points for each sample. The acidic copper sulfate solution consists of 20 mL of 10% NaCl solution, 40 mL of 0.4 mol / L CuSO4 solution, and 15 mL of 0.1 mol / L HCl solution.

[0089] 2. Scale inhibition performance test

[0090] The scale inhibition rate was tested according to GB / T16632-2019 standard, and the calculation formula is as follows:

[0091]

[0092] In the formula:

[0093] ρ4 represents the mass concentration of calcium ions after the addition of scale inhibitor to the test solution, in mg / mL.

[0094] ρ3 represents the calcium ion concentration after the test of the solution without scale inhibitor, in mg / mL.

[0095] ρ represents the mass concentration of calcium ions in the prepared water, in mg / mL.

[0096] 3. Static sustained-release performance test

[0097] Take 500 mL of the test solution and place it in a flat-bottomed flask. Conduct a static release test at a constant temperature of 70°C. Take out 100 mL of the solution every 5 days and add 100 mL of distilled water. Test the scale inhibition performance of the taken-out test solution according to the standard described in Performance Test 2. Record the number of days when the scale inhibition rate of the taken-out solution differs from that of the initial test solution by more than 7%.

[0098] The test results are detailed in Table 1.

[0099] Table 1 Performance Test Results

[0100] Corrosion inhibition effect (color change / s) Scale inhibition effect / % Static sustained release / day Example 1 167.4 99.9 70 Example 2 162.1 99.8 70 Example 3 159.8 99.8 70 Example 4 129.8 98.2 65 Example 5 121.6 97.5 65 Example 6 143.4 93.1 45 Example 7 144.5 93.6 50 Comparative Example 1 24.5 94.8 55 Branched corrosion and scale inhibitor - A 147.2 92.4 10

[0101] As shown in Table 1, the environmentally friendly scale inhibitors of Examples 1-3 exhibit excellent corrosion resistance and scale inhibition properties, and their scale inhibition time can be maintained for up to 70 days. Compared with the branched corrosion and scale inhibitor-A without slow-release treatment, its scale inhibition performance is superior. This may be because the slow-release treatment refines the viscous, oily branched corrosion and scale inhibitor, allowing it to distribute evenly in boiler water. The spherical structure of the refined branched corrosion and scale inhibitor molecules forms a nanoscale internal surface area, which can be firmly adsorbed onto the active growth sites of calcium scale crystals, further inhibiting the formation of scale crystal nuclei and prolonging the onset time. As shown in Examples 1, 4-5, and Comparative Example 1, the 2-quinoline carboxylic acid chain in the scale inhibitor effectively plays a corrosion inhibition role. It can also reduce the steric barrier in the branched structure by pulling the molecular chain, making the molecular chain less prone to entanglement and achieving a good scale inhibition effect. As shown in Examples 1 and 6-7, changes in the raw materials of the branched corrosion and scale inhibitor will reduce corrosion resistance and scale inhibition properties.

[0102] The embodiments and comparative examples described above do not limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. An environmentally friendly scale inhibitor for boilers, characterized in that, By weight, it contains the following raw materials: 25-35 parts branched corrosion and scale inhibitor, 30-40 parts polyvinyl alcohol, 17-24 parts sodium alginate, 3-7 parts glutaraldehyde, 5-10 parts calcium chloride and 1000-2100 parts water. The preparation steps of the branched corrosion and scale inhibitor are as follows: S1. Mix 2-quinoline carboxylic acid, hydroxyethyl acrylate and dichloromethane evenly, then add 1,3-dicyclohexylcarbodiimide and 4-dimethylaminopyridine, stir for 2-3 hours and then separate the oily liquid to obtain reaction solution A; S2. Mix diethylenetriamine and methanol evenly, add the reaction solution A from step S1 dropwise, stir at 30-35℃ for 20-25 hours, and then evaporate by rotary evaporation to obtain the branched corrosion and scale inhibitor. In step S1, the mass ratio of 2-quinoline carboxylic acid, hydroxyethyl acrylate, and 1,3-dicyclohexylcarbodiimide is 1:(0.67-0.70):(1.0-1.4). The mass ratio of diethylenetriamine to hydroxyethyl acrylate in step S1 in step S2 is (1.18-1.74):

1.

2. The environmentally friendly scale inhibitor for boilers according to claim 1, characterized in that, In step S2, the reaction solution A from step S1 is added dropwise under the protection of an ice-water bath and nitrogen, and the dropwise addition time is controlled at 90-120 min.

3. The environmentally friendly scale inhibitor for boilers according to claim 1, characterized in that, The degree of alcoholysis of the polyvinyl alcohol is 87-89%.

4. A method for preparing an environmentally friendly scale inhibitor for boilers according to any one of claims 1-3, characterized in that, Includes the following steps: (1) Prepare polyvinyl alcohol solution, sodium alginate solution and calcium chloride solution respectively with water and polyvinyl alcohol, sodium alginate and calcium chloride respectively; (2) Stir the polyvinyl alcohol solution and sodium alginate solution for 20-40 minutes, add the branched corrosion and scale inhibitor, stir, and obtain a dispersion. (3) While stirring, add calcium chloride solution to the dispersion in step (2), stir for 30-40 minutes and remove 50-75 wt% water, then add glutaraldehyde, adjust pH to 2-3, let stand for 40-50 minutes, wash and dry to obtain the environmentally friendly scale inhibitor.

5. The preparation method of the environmentally friendly scale inhibitor for boilers according to claim 4, characterized in that, The concentration of the polyvinyl alcohol solution in step (1) is 10-14 wt%.

6. The preparation method of the environmentally friendly scale inhibitor for boilers according to claim 4, characterized in that, The concentration of sodium alginate solution in step (1) is 1-3 wt%.

7. The preparation method of the environmentally friendly scale inhibitor for boilers according to claim 4, characterized in that, The stirring speed in step (2) is 1500-1800 rpm.

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