Composition for reducing corrosion of softened water in circulating water system and method for reducing corrosion of softened water

Abstract

The invention relates to a composition for reducing the corrosivity of softened water in a circulating water system and a method for reducing the corrosivity of the softened water. The composition contains an alkaline substance, hydrogen peroxide, inorganic zinc salt and an organic phosphine compound, the weight ratio of the alkaline substance to the hydrogen peroxide to the inorganic zinc salt to the organic phosphine compound in the composition is 1: (5-20): (0.05-0.8): (0.1-1.6). The composition disclosed by the invention can still effectively reduce the corrosion rate of carbon steel when deoxygenization treatment is not carried out on softened water, the operation process is simple, and the operation cost is relatively low.

Description

Technical Field

[0001] This application relates to the field of water treatment, and more specifically, to a composition and method for reducing the corrosivity of softened water in a circulating water system. Background Technology

[0002] Softened water is often used as makeup water in closed-loop water systems and can also be used in boiler systems. Softened water removes hardness and other metal ions, significantly reducing its scaling potential. Protective deposits cannot form on metal surfaces, and anions remain in the softened water. Therefore, softened water is more corrosive than raw water and demineralized water. Softened water only removes hardness, not dissolved oxygen and anions. Studies have shown that dissolved oxygen gains electrons at the metal cathode and undergoes a reduction reaction (1 / 2O₂ + H₂O + 2e⁻ → 2OH⁻). - This accelerates the oxidation reaction of the metal at the anode (Fe - 2e → Fe), thus accelerating the release of electrons. 2+ Dissolved oxygen in softened water accelerates metal corrosion. Therefore, dissolved oxygen in softened water has a significant impact on the corrosion of closed systems, and the main methods to deal with oxygen corrosion are deoxygenation or the addition of corrosion inhibitors.

[0003] Currently, commonly used deoxygenation methods include physical and chemical methods. Physical methods mainly employ thermal deoxygenation, vacuum deoxygenation, and desorption deoxygenation. However, these methods suffer from incomplete deoxygenation and therefore often need to be combined with chemical deoxygenation methods to remove residual oxygen. Chemical deoxygenation methods include chemical reagent deoxygenation and resin deoxygenation. Commonly used deoxygenating agents include sodium sulfite, hydrazine, acetone oxime, and isoascorbic acid. Although chemical deoxygenating agents provide relatively thorough deoxygenation, their toxicity limits their effectiveness.

[0004] In addition to deoxygenation, the corrosion rate of the system can also be reduced by adding oxygen-resistant corrosion inhibitors.

[0005] For example, CN113912197A proposes a corrosion inhibitor for a softened water closed system, comprising the following components by weight percentage: 3-8 parts of hydroxypropyl acrylate copolymer, 5-10 parts of hydroxyethylidene diphosphate, 3-5 parts of copper corrosion inhibitor, 1-5 parts of sodium tungstate, 2-8 parts of ammonium molybdate, and 9-15 parts of deionized water.

[0006] CN110158093A discloses a corrosion inhibitor for a closed-loop cooling system for softened water, comprising the following components by weight percentage: 1%-3% molybdate, 3%-9% copper corrosion inhibitor, 10%-15% corrosion inhibitor synergist, 7.5%-8.5% pH adjuster, 2.5%-3.5% complexing agent, and the balance being deionized water.

[0007] The corrosion inhibitors disclosed in the prior art contain molybdates, tungstates, etc., which are expensive and have limited applications. Furthermore, the corrosion inhibitors in the prior art are generally only suitable for corrosion inhibition in low-temperature closed systems below 80°C, and their effectiveness is poor in high-temperature closed systems above 80°C. Summary of the Invention

[0008] The purpose of this disclosure is to provide a composition and a method for reducing the corrosivity of softened water in a circulating water system. The composition can effectively reduce the corrosion rate of carbon steel even when the softened water is not deoxygenated, and the operation process is simple and the operating cost is low.

[0009] To achieve the above objectives, the first aspect of this disclosure provides a composition for reducing the corrosivity of softened water in a circulating water system, the composition containing an alkaline substance, hydrogen peroxide, an inorganic zinc salt, and an organophosphorus compound;

[0010] The weight ratio of the alkaline substance, the hydrogen peroxide, the inorganic zinc salt, and the organophosphorus compound in the composition is 1:(5-20):(0.05-0.8):(0.1-1.6).

[0011] Optionally, the weight ratio of the alkaline substance, the hydrogen peroxide, the inorganic zinc salt, and the organophosphorus compound in the composition is 1:(6-15):(0.1-0.4):(0.2-1.0).

[0012] Optionally, the alkaline substance is selected from one or more of inorganic bases, organic bases, and strong base-weak acid salts; preferably, the inorganic base is selected from one or more of sodium hydroxide, potassium hydroxide, and ammonia water; the organic base is selected from one or more of ethanolamine, ethylenediamine, and triethylamine; the strong base-weak acid salt is selected from sodium carbonate and / or sodium bicarbonate; more preferably, the alkaline substance is sodium bicarbonate.

[0013] The inorganic zinc salt is selected from one or more of zinc sulfate, zinc chloride, and zinc nitrate;

[0014] The organophosphine compound is selected from one or more of 2-hydroxyphosphonoacetic acid, hydroxyethylidene diphosphonic acid, and 2-phospho-1,2,4-tricarboxylate butane.

[0015] The second aspect of this disclosure provides a method for reducing the corrosivity of softened water in a circulating water system, the method comprising: sequentially adding an alkaline substance and hydrogen peroxide to the softened water, followed by adding an inorganic zinc salt and an organophosphorus compound.

[0016] Optionally, the amount of alkaline substance used relative to 1L of softened water is 10-30mg, preferably 15-25mg;

[0017] The amount of hydrogen peroxide used is 100-400 mg, preferably 150-350 mg, and more preferably 200-300 mg;

[0018] The amount of the inorganic zinc salt used is 1-5 mg, preferably 2-4 mg;

[0019] The amount of the organophosphorus compound used is 2-10 mg, preferably 4-8 mg / L.

[0020] Optionally, the alkaline substance is selected from one or more of inorganic bases, organic bases, and strong base-weak acid salts; preferably, the inorganic base is selected from one or more of sodium hydroxide, potassium hydroxide, and ammonia water; the organic base is selected from one or more of ethanolamine, ethylenediamine, and triethylamine; the strong base-weak acid salt is selected from sodium carbonate and / or sodium bicarbonate; more preferably, the alkaline substance is sodium bicarbonate.

[0021] The inorganic zinc salt is selected from one or more of zinc sulfate, zinc chloride, and zinc nitrate;

[0022] The organophosphine compound is selected from one or more of 2-hydroxyphosphonoacetic acid, hydroxyethylidene diphosphonic acid, and 2-phospho-1,2,4-tricarboxylate butane.

[0023] Optionally, the step of adding an alkaline substance and hydrogen peroxide sequentially to softened water, followed by adding an inorganic zinc salt and an organophosphorus compound, comprises: in a closed system at 25-200°C, adding an alkaline substance and hydrogen peroxide sequentially to softened water, followed by adding an inorganic zinc salt and an organophosphorus compound.

[0024] Optionally, in a closed system at 120-200°C, alkaline substances and hydrogen peroxide are added sequentially to softened water, followed by inorganic zinc salts and organophosphorus compounds.

[0025] Optionally, the pH value of the softened water after adding the alkaline substance and hydrogen peroxide is above 8, preferably 9-11.

[0026] Optionally, the dissolved oxygen concentration of the softened water is 2-10 mg / L, the calcium hardness is 0-10 mg / L, and the total hardness is 0-10 mg / L.

[0027] The method disclosed herein has the following advantages through the above technical solution:

[0028] (1) When the composition disclosed herein is used in a circulating water system, it is not necessary to remove dissolved oxygen from the softened water in advance, that is, no deoxygenation pretreatment or deoxygenating agent is required, which is simple and easy to implement.

[0029] (2) The compositions disclosed herein are particularly suitable for reducing the corrosiveness of softened water in high-temperature closed systems.

[0030] Other features and advantages of this disclosure will be described in detail in the following detailed description section. Attached Figure Description

[0031] The accompanying drawings are provided to further illustrate the present disclosure and form part of the specification. They are used together with the following detailed description to explain the present disclosure, but do not constitute a limitation thereof. In the drawings:

[0032] Figure 1 This is the XPS spectrum of the test piece after the experiment in Embodiment 1 of this disclosure.

[0033] Figure 2 This is the XPS spectrum of a brand new 20# carbon steel standard corrosion test piece. Detailed Implementation

[0034] The following provides a detailed description of specific embodiments of this disclosure. It should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit this disclosure.

[0035] The first aspect of this disclosure provides a composition for reducing the corrosivity of softened water in a circulating water system, the composition containing an alkaline substance, hydrogen peroxide, an inorganic zinc salt, and an organophosphorus compound; the weight ratio of the alkaline substance, hydrogen peroxide, inorganic zinc salt, and organophosphorus compound in the composition is 1:(5-20):(0.05-0.8):(0.1-1.6).

[0036] The composition disclosed herein can effectively reduce the corrosivity of softened water in circulating water systems without the need to remove dissolved oxygen from the softened water beforehand, and is easy to use.

[0037] In a preferred embodiment of this disclosure, the weight ratio of the alkaline substance, the hydrogen peroxide, the inorganic zinc salt, and the organophosphorus compound in the composition is 1:(6-15):(0.1-0.4):(0.2-1.0). The composition having this composition has a superior effect in reducing the corrosiveness of softened water in circulating water systems.

[0038] According to this disclosure, the alkaline substance is selected from one or more of inorganic bases, organic bases, and strong base-weak acid salts; preferably, the inorganic base is selected from one or more of sodium hydroxide, potassium hydroxide, and ammonia water; the organic base is selected from one or more of ethanolamine, ethylenediamine, and triethylamine; the strong base-weak acid salt is selected from sodium carbonate and / or sodium bicarbonate; more preferably, the alkaline substance is sodium bicarbonate.

[0039] According to this disclosure, the inorganic zinc salt may be selected from one or more of zinc sulfate, zinc chloride, and zinc nitrate; the organophosphorus compound may be selected from one or more of 2-hydroxyphosphonoacetic acid (HPAA), hydroxyethylidene diphosphonic acid (HEDP), and 2-phospho-1,2,4-tricarboxylate butane (PBTCA).

[0040] The second aspect of this disclosure provides a method for reducing the corrosivity of softened water in a circulating water system, the method comprising: sequentially adding an alkaline substance and hydrogen peroxide to the softened water, followed by adding an inorganic zinc salt and an organophosphorus compound.

[0041] The inventors of this disclosure unexpectedly discovered that by sequentially adding alkaline substances and hydrogen peroxide to softened water, followed by the addition of inorganic zinc salts and organophosphorus compounds, an oxide film and a zinc phosphorus deposition film can be formed on the surface of materials such as carbon steel in the circulating water system. This effectively reduces the corrosiveness of softened water to the circulating water system. Moreover, this method does not require the prior removal of dissolved oxygen from the softened water, and is simple, easy to implement, and inexpensive.

[0042] This disclosure does not restrict the order in which the inorganic zinc salt and organophosphorus compound are added, as long as they are added after the alkaline substance and hydrogen peroxide. In one embodiment, after adding the alkaline substance and hydrogen peroxide to the softened water in sequence, the inorganic zinc salt is added first, followed by the organophosphorus compound; in another embodiment, after adding the alkaline substance and hydrogen peroxide to the softened water in sequence, the organophosphorus compound is added first, followed by the inorganic zinc salt; in yet another embodiment, after adding the alkaline substance and hydrogen peroxide to the softened water in sequence, the inorganic zinc salt and organophosphorus compound are mixed and added together.

[0043] According to this disclosure, the amount of alkaline substance can vary within a wide range. In one specific embodiment, the amount of alkaline substance relative to 1L of softened water is 5-50mg, preferably 10-40mg, and more preferably 20-30mg. The appropriate amount of alkaline substance within the above range makes the method of this disclosure more effective in reducing the corrosiveness of softened water.

[0044] According to this disclosure, the amount of hydrogen peroxide used can vary within a wide range. In one specific embodiment, the amount of hydrogen peroxide used relative to 1L of softened water is 100-400mg, preferably 150-350mg, and more preferably 200-300mg. The appropriate amount of hydrogen peroxide within the above range makes the method of this disclosure more effective in reducing the corrosiveness of softened water.

[0045] According to this disclosure, the amounts of the inorganic zinc salt and organophosphorus compound can vary within a wide range. In one embodiment, the amount of inorganic zinc salt can be 1-5 mg, preferably 2-4 mg; the amount of organophosphorus compound is 2-10 mg, preferably 4-8 mg / L. The appropriate amount of hydrogen peroxide within the above range makes the method of this disclosure more effective in reducing the corrosiveness of softened water.

[0046] According to this disclosure, the alkaline substance is selected from one or more of inorganic bases, organic bases, and strong base-weak acid salts; preferably, the inorganic base is selected from one or more of sodium hydroxide, potassium hydroxide, and ammonia water; the organic base is selected from one or more of ethanolamine, ethylenediamine, and triethylamine; the strong base-weak acid salt is selected from sodium carbonate and / or sodium bicarbonate; more preferably, the alkaline substance is sodium bicarbonate.

[0047] According to this disclosure, the inorganic zinc salt may be selected from one or more of zinc sulfate, zinc chloride, and zinc nitrate; the organophosphorus compound may be selected from one or more of 2-hydroxyphosphonoacetic acid, hydroxyethylidene diphosphonic acid, and 2-phospho-1,2,4-tricarboxylate butane.

[0048] In one specific embodiment of this disclosure, the step of sequentially adding an alkaline substance and hydrogen peroxide to softened water, followed by the addition of inorganic zinc salt and organophosphorus compound, comprises: adding an alkaline substance and hydrogen peroxide sequentially to softened water in a closed system at 25-200°C, followed by the addition of inorganic zinc salt and organophosphorus compound. Preferably, this is done in a closed system at 120-200°C. The method of this disclosure is more conducive to the formation of oxide films and zinc phosphorus deposits when used in high-temperature, closed circulating water systems under the above conditions, and can more effectively reduce the corrosiveness of softened water.

[0049] In one specific embodiment of this disclosure, the pH value of the softened water after adding the alkaline substance and hydrogen peroxide is 8 or higher, preferably 9-11.

[0050] According to this disclosure, the method is particularly suitable for softened water with a dissolved oxygen concentration of 2-10 mg / L, a calcium hardness of 0-10 mg / L, and a total hardness of 0-10 mg / L. The method of this disclosure has a good effect on reducing the corrosiveness of softened water to circulating water systems.

[0051] The present disclosure will be further illustrated by the following examples, but the present disclosure is not limited thereto.

[0052] The softened water used in all examples and comparative examples was softened water of the same quality from a petrochemical company, with an initial dissolved oxygen concentration of 8 mg / L, a calcium hardness of 2 mg / L, and a total hardness of 2.5 mg / L. During the experiment, nitrogen purging was used only to obtain softened water with different dissolved oxygen concentrations.

[0053] The following examples and comparative examples used 20# carbon steel standard corrosion test pieces as the corrosion material, and the corrosion rate of carbon steel was calculated by continuous operation for 15 days. According to the requirements of Q / SH 0628.2-2014 "Technical Requirements for Water Management Part 2: Circulating Water" standard, the circulating water treatment effect of chemical enterprises should meet the following requirement: carbon steel corrosion rate ≤ 0.075 mm / a.

[0054] Example 1

[0055] Before the experiment, the dissolved oxygen concentration of the softened water was purged with nitrogen to 4 mg / L. Sodium bicarbonate (15 mg / L) was added to the softened water and stirred thoroughly. Then, hydrogen peroxide (200 mg / L) was added, bringing the pH of the softened water to 9.46. Next, zinc chloride (2 mg / L) and HEDP (4 mg / L) were added. The experiment was conducted at 120℃. The results are shown in Table 1, and the same applies below.

[0056] Meanwhile, XPS analysis was performed on the test specimens after the experiment in this embodiment and on brand new 20# carbon steel standard corrosion test specimens. The XPS spectra are shown below. Figure 1 and Figure 2 Elemental analysis results showed that the iron content on the surface of the treated specimen decreased while the oxygen content increased. This indicates that an oxide film was formed on the surface of the specimen treated by the method of this disclosure, which protected the carbon steel specimen. The zinc content on the surface of the specimen treated with zinc salts and organophosphorus compounds was higher than that of the new specimen, and the phosphorus content was 2.87%, while phosphorus was not detected on the surface of the new specimen. This indicates that the method of this disclosure also forms a phosphorus-zinc deposition film on the surface of the specimen to protect the carbon steel specimen, thereby effectively reducing the corrosiveness of softened water.

[0057] Example 2

[0058] Without treating the dissolved oxygen in the softened water, the dissolved oxygen concentration was 8 mg / L. Sodium bicarbonate 25 mg / L was added to the softened water and stirred evenly. Then hydrogen peroxide 300 mg / L was added. At this time, the pH value of the softened water was 9.61. Then zinc sulfate 4 mg / L and HPAA 8 mg / L were added. The test temperature was 160℃.

[0059] Example 3

[0060] Before the experiment, the dissolved oxygen concentration of the softened water was purged with nitrogen to 6 mg / L. Sodium bicarbonate 20 mg / L was added to the softened water and stirred evenly. Then hydrogen peroxide 250 mg / L was added. At this time, the pH value of the softened water was 9.53. Then zinc nitrate 6 mg / L and PBTCA 6 mg / L were added. The test temperature was 200℃.

[0061] Example 4

[0062] Before the experiment, the dissolved oxygen concentration of the softened water was purged with nitrogen to 2 mg / L. 10 mg / L of sodium bicarbonate was added to the softened water and stirred evenly. Then, 150 mg / L of hydrogen peroxide was added. At this time, the pH value of the softened water was 9.32. Then, 4 mg / L of zinc chloride and 8 mg / L of HPAA were added. The test temperature was 40℃.

[0063] Example 5

[0064] Before the experiment, the dissolved oxygen concentration of the softened water was purged with nitrogen to 4 mg / L. 10 mg / L of sodium bicarbonate was added to the softened water and stirred evenly. Then, 140 mg / L of hydrogen peroxide was added. At this time, the pH value of the softened water was 10.14. Then, 4 mg / L of zinc sulfate and 8 mg / L of HPAA were added. The test temperature was 120℃.

[0065] Example 6

[0066] Before the experiment, the dissolved oxygen concentration of the softened water was purged with nitrogen to 4 mg / L. Sodium bicarbonate 20 mg / L was added to the softened water and stirred evenly. Then hydrogen peroxide 250 mg / L was added. At this time, the pH value of the softened water was 9.57. Then zinc chloride 1 mg / L and HEDP 2 mg / L were added. The test temperature was 120℃.

[0067] Example 7

[0068] Before the experiment, the dissolved oxygen concentration of the softened water was purged with nitrogen to 4 mg / L. Sodium bicarbonate 20 mg / L was added to the softened water and stirred evenly. Then hydrogen peroxide 250 mg / L was added. At this time, the pH value of the softened water was 9.55. Then zinc sulfate 4 mg / L and HPAA 8 mg / L were added. The test temperature was 120℃.

[0069] Example 8

[0070] The experiment was conducted using the same method as in Example 1, except that the amount of sodium bicarbonate used was 10 mg / L, the amount of hydrogen peroxide used was 100 mg / L, the pH value of the softened water after adding sodium hydroxide and hydrogen peroxide was 9.38, and then 1 mg / L of zinc chloride and 2 mg / L of HEDP were added.

[0071] Example 9

[0072] The experiment was conducted using the same method as in Example 1, except that the test temperature was 100°C.

[0073] Example 10

[0074] Before the experiment, the dissolved oxygen concentration of the softened water was purged with nitrogen to 4 mg / L. 10 mg / L of sodium bicarbonate was added to the softened water and stirred evenly. Then 50 mg / L of hydrogen peroxide was added. At this time, the pH value of the softened water was 9.40. Then 4 mg / L of zinc sulfate and 8 mg / L of HPAA were added. The test temperature was 120℃.

[0075] Example 11

[0076] Before the experiment, the dissolved oxygen concentration of the softened water was purged with nitrogen to 6 mg / L. 5 mg / L of sodium bicarbonate was added to the softened water and stirred evenly. Then, 100 mg / L of hydrogen peroxide was added. At this point, the pH value of the softened water was 9.28. Then, 4 mg / L of zinc sulfate and 8 mg / L of HPAA were added. The experimental temperature was 120℃.

[0077] Example 12

[0078] Before the experiment, the dissolved oxygen concentration of the softened water was purged with nitrogen to 2 mg / L. 15 mg / L of sodium bicarbonate was added to the softened water and stirred evenly. Then 200 mg / L of hydrogen peroxide was added. At this time, the pH value of the softened water was 9.50. Then 0.5 mg / L of zinc chloride and 4 mg / L of HEDP were added. The experiment was started at 120℃.

[0079] Example 13

[0080] Before the experiment, the dissolved oxygen concentration of the softened water was purged with nitrogen to 2 mg / L. 15 mg / L of sodium bicarbonate was added to the softened water and stirred evenly. Then, 200 mg / L of hydrogen peroxide was added. At this time, the pH value of the softened water was 9.52. Then, 2 mg / L of zinc chloride and 1 mg / L of HEDP were added. The experiment was started at 120℃.

[0081] Comparative Example 1

[0082] Before the experiment, the dissolved oxygen concentration of the softened water was purged with nitrogen to 4 mg / L. 200 mg / L of hydrogen peroxide was added to the softened water and stirred evenly. Then, 20 mg / L of sodium bicarbonate was added. At this time, the pH value of the softened water was 9.55. Then, 4 mg / L of zinc sulfate and 8 mg / L of HEDP were added. The test temperature was 160℃.

[0083] Comparative Example 2

[0084] Before the experiment, the dissolved oxygen concentration of the softened water was purged with nitrogen to 4 mg / L. Hydrogen peroxide and sodium bicarbonate were prepared into a solution and added to the softened water. The concentrations of hydrogen peroxide and sodium hydroxide in the softened water were 200 mg / L and 20 mg / L, respectively. At this time, the pH value of the softened water was 9.49. Then, zinc sulfate 4 mg / L and PBTCA 8 mg / L were added. The experimental temperature was 120℃.

[0085] Comparative Example 3

[0086] According to the weight percentage, 4 parts of deionized water and 8 parts of ammonium molybdate are added to the reactor and stirred evenly. Then, 8 parts of hydroxyethylidene diphosphate are added, the temperature is raised to 50°C, and stirring is continued for 30 minutes. The mixture is then cooled to room temperature to obtain polymer A. 4 parts of deionized water and 4 parts of sodium tungstate are added to the reactor and stirred evenly. The temperature is raised to 45°C, 5 parts of copper corrosion inhibitor are added, and stirring is continued for 30 minutes until completely dissolved. Then, 8 parts of hydroxypropyl acrylate copolymer are added and stirring is continued for 30 minutes. The mixture is then cooled to room temperature and stirred for 60 minutes to obtain polymer B. B is added to A, and 4 parts of deionized water are added and stirred thoroughly for 60 minutes until a homogeneous liquid is obtained, which is the corrosion inhibitor for the softened water closed system.

[0087] Before the test, the dissolved oxygen concentration in the softened water was purged with nitrogen to 2 mg / L. The corrosion inhibitor was then added to the softened water at a concentration of 50 mg / L. The test was conducted at a temperature of 120°C.

[0088] Table 1

[0089]

[0090]

[0091] As can be seen from the above, the compositions and methods disclosed herein can effectively reduce the corrosiveness of softened water, and are particularly suitable for reducing the corrosiveness of softened water in high-temperature sealing systems.

[0092] The preferred embodiments of this disclosure have been described in detail above. However, this disclosure is not limited to the specific details of the above embodiments. Within the scope of the technical concept of this disclosure, various simple modifications can be made to the technical solutions of this disclosure, and these simple modifications all fall within the protection scope of this disclosure.

[0093] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, this disclosure will not describe the various possible combinations separately.

[0094] Furthermore, various different embodiments of this disclosure can be combined in any way, as long as they do not violate the spirit of this disclosure, they should also be regarded as the content disclosed in this disclosure.

Claims

1. A composition for reducing the corrosivity of softened water in a circulating water system, said composition comprising an alkaline substance, hydrogen peroxide, an inorganic zinc salt, and an organophosphorus compound; The weight ratio of the alkaline substance, the hydrogen peroxide, the inorganic zinc salt, and the organophosphorus compound in the composition is 1:(5-20):(0.05-0.8):(0.1-1.6).

2. The composition according to claim 1, wherein, The weight ratio of the alkaline substance, the hydrogen peroxide, the inorganic zinc salt, and the organophosphorus compound in the composition is 1:(6-15):(0.1-0.4):(0.2-1.0).

3. The composition according to claim 1, wherein, The alkaline substance is selected from one or more of inorganic bases, organic bases, and strong base-weak acid salts; preferably, the inorganic base is selected from one or more of sodium hydroxide, potassium hydroxide, and ammonia water; the organic base is selected from one or more of ethanolamine, ethylenediamine, and triethylamine; the strong base-weak acid salt is selected from sodium carbonate and / or sodium bicarbonate; more preferably, the alkaline substance is sodium bicarbonate. The inorganic zinc salt is selected from one or more of zinc sulfate, zinc chloride, and zinc nitrate; The organophosphine compound is selected from one or more of 2-hydroxyphosphonoacetic acid, hydroxyethylidene diphosphonic acid, and 2-phospho-1,2,4-tricarboxylate butane.

4. A method for reducing the corrosivity of softened water in a circulating water system, the method comprising: After adding alkaline substances and hydrogen peroxide to the softened water, inorganic zinc salts and organophosphorus compounds are added.

5. The method according to claim 4, wherein, The amount of alkaline substance used relative to 1L of softened water is 10-30mg, preferably 15-25mg; The amount of hydrogen peroxide used is 100-400 mg, preferably 150-350 mg, and more preferably 200-300 mg; The amount of the inorganic zinc salt used is 1-5 mg, preferably 2-4 mg; The amount of the organophosphorus compound used is 2-10 mg, preferably 4-8 mg / L.

6. The method according to claim 4, wherein, The alkaline substance is selected from one or more of inorganic bases, organic bases, and strong base-weak acid salts; preferably, the inorganic base is selected from one or more of sodium hydroxide, potassium hydroxide, and ammonia water; the organic base is selected from one or more of ethanolamine, ethylenediamine, and triethylamine; the strong base-weak acid salt is selected from sodium carbonate and / or sodium bicarbonate; more preferably, the alkaline substance is sodium bicarbonate. The inorganic zinc salt is selected from one or more of zinc sulfate, zinc chloride, and zinc nitrate; The organophosphine compound is selected from one or more of 2-hydroxyphosphonoacetic acid, hydroxyethylidene diphosphonic acid, and 2-phospho-1,2,4-tricarboxylate butane.

7. The method according to claim 4, wherein, The process of sequentially adding an alkaline substance and hydrogen peroxide to softened water, followed by the addition of inorganic zinc salt and organophosphorus compound, comprises: in a closed system at 25-200°C, sequentially adding an alkaline substance and hydrogen peroxide to softened water, followed by the addition of inorganic zinc salt and organophosphorus compound.

8. The method according to claim 7, wherein, In a closed system at 120-200℃, alkaline substances and hydrogen peroxide are added to softened water in sequence, followed by inorganic zinc salts and organophosphorus compounds.

9. The method according to claim 4, wherein, The softened water after adding the alkaline substance and hydrogen peroxide has a pH value of 8 or higher, preferably 9-11.

10. The method according to claim 4, wherein, The softened water has a dissolved oxygen concentration of 2-10 mg / L, a calcium hardness of 0-10 mg / L, and a total hardness of 0-10 mg / L.

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