A method for inhibiting scale and corrosion in a circulating water system for a galvanized sheet cooling tower

Abstract

The application provides a scale and corrosion inhibition method for a galvanized plate cooling tower circulating water system, and relates to the technical field of industrial circulating water systems. The method uses a composite scale inhibitor and a composite corrosion inhibitor. The composite scale inhibitor contains hydrolyzed polymaleic anhydride (HPMA), a pH value regulator and benzotriazole (BTA). The composite corrosion inhibitor contains zinc salt, AMPS terpolymer, HPMA, acrylic acid-acrylate copolymer (T-225) and a tracer. The AMPS terpolymer is acrylic acid-acrylate-sulfonate copolymer. During use, the composite scale inhibitor is used to increase the scale dispersion function of the system, and the pH value of the system is adjusted, so that the pH value of the circulating water is stably controlled between 8.0 and 8.4. The amount of the composite scale inhibitor is adjusted in real time through online pH value. In this way, the corrosion prevention requirement can be ensured, and the galvanizing layer can be effectively stabilized and prevented from being damaged.

Description

Technical Field

[0001] This invention relates to the field of industrial circulating water system technology, and in particular to a method for scale inhibition and corrosion inhibition in circulating water systems for galvanized steel cooling towers. Background Technology

[0002] A cooling tower is a device that uses water as a circulating coolant to absorb heat from a system and release it into the atmosphere, thereby lowering the water temperature. The manufacturing process of a cooling tower requires a shell made of galvanized steel sheet, where the zinc acts as an anode to protect the system. However, zinc is a reactive metal, making the galvanized layer highly susceptible to corrosion and damage, resulting in the galvanized sheet turning black and affecting the cooling tower's lifespan.

[0003] To improve cooling tower efficiency, existing systems with high heat loads, especially data centers, often use evaporative cooling or open-type cooling towers with galvanized coatings. While this tower design improves heat reduction and enhances corrosion resistance in the early stages of use, the galvanized coating itself is highly susceptible to corrosion. During operation, the circulating water, after concentration, experiences a significant increase in alkalinity, hardness, and salinity, with the pH typically stabilizing between 8.8 and 9.3. This alkalinity and pH level accelerates the degradation of the galvanized coating.

[0004] The aforementioned damage manifests as the complete disappearance of the galvanized layer within a single cooling season, leaving the galvanized sheet surface whitish-black and losing its anodic protection function. Corrosion of the tower plates increases the iron ion content in the system, accelerating further corrosion. Currently, some organizations replenish the zinc coating by repainting with zinc-rich paint after the cooling season. However, this method suffers from the inability to replenish the galvanized film in a timely manner and directly causes irreversible corrosion of the plates and the system. Therefore, alternative methods for corrosion protection of galvanized cooling tower plates are needed. Summary of the Invention

[0005] To address the technical problem of easy corrosion of galvanized steel sheets in existing technologies, this invention provides a method for scale and corrosion inhibition in the circulating water system of galvanized steel sheet cooling towers. The method employs separate addition of a composite corrosion inhibitor and a composite scale inhibitor, allowing for flexible control and maintaining the circulating water within the stable range of the galvanized steel sheet, thereby reducing zinc corrosion and consumption.

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

[0007] A method for scale inhibition and corrosion inhibition in a circulating water system for a galvanized steel cooling tower, characterized in that the method uses a composite scale inhibitor and a composite corrosion inhibitor.

[0008] The composite scale inhibitor contains hydrolyzed polymaleic anhydride (HPMA), a pH adjuster, and benzotriazole (BTA).

[0009] The composite corrosion inhibitor contains zinc salt, AMPS terpolymer, HPMA, acrylic acid-acrylate copolymer (T-225), and tracer, wherein the AMPS terpolymer is an acrylic acid-acrylate-sulfonate copolymer.

[0010] This invention incorporates HPMA into both the composite scale inhibitor and the composite corrosion inhibitor, primarily as a dispersant. Its addition to circulating water enhances the scale inhibition effect. Furthermore, HPMA increases the solubility of BTA and zinc salts, preventing reagent precipitation due to temperature changes or prolonged circulation.

[0011] Preferably, in the composite scale inhibitor, the mass percentage of HPMA is 25-35%, the mass percentage of pH adjuster is 5-15%, the mass percentage of BTA is 1-3%, and the balance is water.

[0012] Preferably, in the composite scale inhibitor, the mass percentage of HPMA is 30%, the mass percentage of pH adjuster is 10%, the mass percentage of BTA is 1.2%, and the remainder is water.

[0013] Preferably, in the composite corrosion inhibitor, the mass percentage of zinc salt is 5-10%, the mass percentage of AMPS terpolymer is 20-30%, the mass percentage of HPMA is 10-20%, the mass percentage of T-225 is 15-25%, the mass percentage of tracer is 0.5-3‰, and the balance is water.

[0014] Preferably, in the composite corrosion inhibitor, the mass percentage of zinc salt is 7%, the mass percentage of AMPS terpolymer is 25%, the mass percentage of HPMA is 15%, the mass percentage of T-225 is 20%, the mass percentage of tracer is 1‰, and the balance is water.

[0015] Since the circulating water is alkaline, this invention only adds acid to adjust the pH value. Preferably, the pH adjuster is an organic acid and / or an inorganic acid, wherein the organic acid is selected from at least one of acetic acid, sulfamic acid, and citric acid; and the inorganic acid is selected from at least one of hydrochloric acid, sulfuric acid, and nitric acid. The pH adjuster preferably uses both organic and inorganic acids simultaneously, wherein the inorganic acid can rapidly degrade the alkalinity in the water, while the organic acid can effectively remove alkali for a longer period. Both the organic and inorganic acids are used as aqueous solutions with a mass concentration of 1-10%.

[0016] Preferably, the zinc salt is selected from at least one of zinc sulfate heptahydrate and anhydrous zinc chloride.

[0017] Preferably, the tracer is tetrasodium pyrene tetrasulfonate.

[0018] This invention also provides a method for preparing the composite scale inhibitor, comprising the following steps: first, add approximately 60% bottom water, then add an organic acid; after the organic acid dissolves, add an inorganic acid; mix thoroughly, then add BTA; after all the BTA dissolves, add HPMA; stir for approximately 30 minutes, and then package for later use. When preparing the composite scale inhibitor, adding all the water first as a solvent, then adding the inorganic acid first to increase the dissolution rate, then adding the organic acid later to increase the dissolution of BTA, and finally adding HPMA to the system ensures the overall scale inhibition and dispersion effect of the agent.

[0019] This invention also provides a method for preparing the composite sustained-release agent, comprising the following steps: first, adding approximately 33% water, then adding HPMA and mixing thoroughly, followed by adding zinc salt. After complete dissolution, adding AMPS terpolymer and stirring thoroughly, then adding T-225 and stirring for 30 minutes, and finally packaging for later use. When preparing the composite sustained-release agent, adding all the water first as a solvent, and then adding HPMA, can improve the solubility of the zinc salt; AMPS terpolymer has poor solubility and needs to be added before the zinc salt, with T-225 added after the zinc salt is completely dissolved.

[0020] The method for scale inhibition and corrosion prevention in the circulating water system of a galvanized steel cooling tower includes the following steps:

[0021] (1) Using a composite corrosion inhibitor as the main agent, add it to the circulating water of the cooling tower and use a fluorescent tracer as the detection substance to detect whether the dosage of the agent in the circulating water reaches the control amount.

[0022] (2) Test the pH value of the circulating water in real time, and adjust the amount of composite scale inhibitor added according to the pH value data to keep the pH value of the circulating water at 8.0-8.4.

[0023] Preferably, in step (1), the concentration of the composite corrosion inhibitor added to the circulating water, i.e., the controlled amount, is 40-60 ppm.

[0024] Preferably, in step (2), 8.0-8.4 is the pH range in which metallic zinc is stably present. The amount of composite scale inhibitor can be increased when the pH exceeds 8.3 and decreased when it is below 8.0.

[0025] The present invention has the following beneficial effects:

[0026] This invention provides a method for scale and corrosion inhibition in the circulating water system of a galvanized steel cooling tower, employing a composite corrosion inhibitor and a composite scale inhibitor. The composite corrosion inhibitor is the main agent, capable of controlling scale inhibition in the system and providing corrosion protection for the galvanized steel. This configuration effectively ensures the requirements for scale and corrosion inhibitors are met, while allowing for flexible adjustment of the total pH value of the circulating water and the scale dispersion effect by controlling the dosage of the scale inhibitor, thus maintaining the pH value of the circulating water within a certain range. This avoids the drawbacks of using a single agent that only controls corrosion or solely controls pH for scale inhibition.

[0027] During use, a composite scale inhibitor is used to enhance the system's scale inhibition and dispersion function. Simultaneously, the system pH is adjusted to stably control the circulating water pH between 8.0 and 8.4. The dosage of the composite scale inhibitor is adjusted in real-time based on the online pH reading. This ensures corrosion protection while effectively preventing damage to the galvanized layer. Detailed Implementation

[0028] To make the technical problems, technical solutions and advantages of the present invention clearer, a detailed description will be given below in conjunction with specific embodiments.

[0029] Example

[0030] (1) Using a composite corrosion inhibitor as the main agent, add it to the circulating water of the cooling tower. Use a fluorescent tracer as the detection substance to detect whether the dosage of the agent in the circulating water reaches the control amount of 40-60 ppm. If the control amount is reached, stop adding the composite corrosion inhibitor; if the control amount is not reached, continue adding the composite corrosion inhibitor.

[0031] (2) Test the pH value of the circulating water in real time, and adjust the amount of scale inhibitor added according to the pH value data. When the pH value exceeds 8.3, increase the amount of scale inhibitor and when it is below 8.0, reduce the amount of scale inhibitor to keep the pH value of the circulating water between 8.0 and 8.4.

[0032] The composite scale inhibitor contains 30% HPMA by mass, the pH adjuster contains 10% acid by mass, including 7% acetic acid and 3% sulfuric acid by mass, the BTA by mass is 1.2%, and the remainder is water.

[0033] In the composite corrosion inhibitor, the zinc salt is zinc sulfate heptahydrate with a mass percentage of 7%, the AMPS terpolymer has a mass percentage of 25%, HPMA has a mass percentage of 15%, T-225 has a mass percentage of 20%, the tracer is tetrasodium pyrene sulfonate with a mass percentage of 1‰, and the balance is water.

[0034] During the above process, the dosage of the composite corrosion inhibitor in the circulating water should be controlled at 40-60 ppm. The dosage of the composite scale inhibitor varies depending on the water quality. The actual dosage should be based on the on-site water quality, and the pH value of the circulating water should be controlled between 8.0 and 8.3.

[0035] The circulating water was tested using a rotating plate tester for 72 hours according to the on-site control indicators. The galvanized steel sheet of the cooling tower showed no weight loss (0% weight loss, the surface of the galvanized sheet remained glossy, and there were no whitening or blackening phenomena; no corrosion was observed after on-site use). After another cooling season (early May to mid-September each year), the appearance of the galvanized sheet remained unchanged.

[0036] Comparative Example 1

[0037] In the composite scale inhibitor, sulfuric acid is used as the pH adjuster, and the mass percentage of the pH adjuster is 10%. The rest is the same as in the example.

[0038] Using the same method as in the previous example, the galvanized sheet showed no significant weight loss after 72 hours of testing. However, using sulfuric acid alone can lead to rapid pH adjustment of the circulating water, but it can also cause localized whitening of the galvanized sheet.

[0039] Comparative Example 2

[0040] HPMA was not added to the composite corrosion inhibitor; otherwise, it was the same as in the example.

[0041] Using the same method as in the previous example, the galvanized sheet showed no significant weight loss after 72 hours of testing. However, when the temperature was below 5°C, the zinc salt in the composite corrosion inhibitor easily precipitated, leading to a decrease in the stability of the reagent.

[0042] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for scale inhibition and corrosion inhibition in a circulating water system for a galvanized steel cooling tower, characterized in that, The method uses a composite scale inhibitor and a composite corrosion inhibitor. The composite scale inhibitor contains hydrolyzed polymaleic anhydride, a pH adjuster, and benzotriazole. The composite corrosion inhibitor contains zinc salt, AMPS terpolymer, hydrolyzed polymaleic anhydride, acrylic acid-acrylate copolymer and tracer, wherein the AMPS terpolymer is an acrylic acid-acrylate-sulfonate copolymer. The pH adjuster is an organic acid and / or an inorganic acid, wherein the organic acid is selected from at least one of acetic acid, aminosulfonic acid, and citric acid; and the inorganic acid is selected from at least one of hydrochloric acid, sulfuric acid, and nitric acid. The method for scale inhibition and corrosion inhibition in the circulating water system of a galvanized steel cooling tower includes the following steps: (1) Using a composite corrosion inhibitor as the main agent, add it to the circulating water of the cooling tower and use a fluorescent tracer as the detection substance to detect whether the dosage of the agent in the circulating water reaches the control amount. (2) Test the pH value of the circulating water in real time, and adjust the amount of composite scale inhibitor added according to the pH value data to keep the pH value of the circulating water at 8.0-8.

4.

2. The method for scale inhibition and corrosion inhibition in a circulating water system for a galvanized steel cooling tower according to claim 1, characterized in that, The composite scale inhibitor contains 25-35% hydrolyzed polymaleic anhydride, 5-15% pH adjuster, 1-3% benzotriazole, and the remainder is water.

3. The method for scale inhibition and corrosion inhibition in a circulating water system for a galvanized steel cooling tower according to claim 2, characterized in that, The composite scale inhibitor contains 30% hydrolyzed polymaleic anhydride, 10% pH adjuster, 1.2% benzotriazole, and the remainder is water.

4. The method for scale inhibition and corrosion inhibition in a circulating water system for a galvanized steel cooling tower according to claim 1, characterized in that, The pH adjuster uses both organic and inorganic acids, and both organic and inorganic acids are aqueous solutions with a mass concentration of 1-10%.

5. The method for scale inhibition and corrosion inhibition in a circulating water system for a galvanized steel cooling tower according to claim 1, characterized in that, The composite corrosion inhibitor comprises 5-10% zinc salt, 20-30% AMPS terpolymer, 10-20% hydrolyzed polymaleic anhydride, 15-25% acrylic acid-acrylate copolymer, 0.5-3‰ tracer, and the remainder is water.

6. The method for scale inhibition and corrosion inhibition in a circulating water system for a galvanized steel cooling tower according to claim 1, characterized in that, The composite corrosion inhibitor comprises 7% zinc salt, 25% AMPS terpolymer, 15% hydrolyzed polymaleic anhydride, 20% acrylic acid-acrylate copolymer, 1‰ tracer, and the remainder is water.

7. A method for scale inhibition and corrosion inhibition in a circulating water system for a galvanized steel cooling tower according to claim 6, characterized in that, The zinc salt is selected from at least one of zinc sulfate heptahydrate and anhydrous zinc chloride, and the tracer is tetrasodium pyrene sulfonate.

8. The method for scale inhibition and corrosion inhibition in a galvanized steel cooling tower circulating water system according to claim 1, characterized in that, In step (1), the concentration of the composite corrosion inhibitor added to the circulating water is 40-60 ppm; And / or, in step (2), the amount of composite scale inhibitor is increased when the pH value exceeds 8.3 and decreased when it is below 8.0.