JP5499823B2 - Cooling water treatment method - Google Patents

Description

  The present invention relates to a cooling water treatment method for forming an anticorrosion film on the surface of a cooling water metal member.

  Ferrous metals generally used as materials for members such as heat exchanger tubes and pipes of a circulating cooling water system are subject to significant corrosion when in contact with water. For this reason, a corrosion prevention method has been performed in which various corrosion inhibitors are added to the cooling water to form a thin anticorrosion film on the surface of the iron-based metal member.

  This corrosion prevention method has a basic treatment process performed at the start of operation of the circulating cooling water system and a normal treatment process performed during normal operation after performing the basic treatment.

  In general, at the start of operation of the circulating cooling water system, the anticorrosion film is not formed on the surface of the metal member, and corrosion is very likely to occur. In the basic treatment process, an anticorrosion film is formed on the surface of the iron-based metal member with a relatively high concentration of corrosion inhibitor.

  In the normal treatment process, the anticorrosion film is maintained with a low concentration corrosion inhibitor on the iron-based metal member on which the anticorrosion film is formed in the basic treatment process.

  Conventionally, as an initial basic treatment step of the circulating cooling water system, an inorganic phosphate and a zinc compound are added to the cooling water, and the cooling water is circulated for a certain period of time, so that an anticorrosive film is formed on the surface of the iron-based metal member. Methods of forming are known.

  The thus formed anticorrosion film has a two-layer structure of a dense underlayer mainly composed of iron phosphate and iron oxide and a dense surface layer mainly composed of zinc phosphate. And this dense two-layered anticorrosion film exhibits the functions of anode anticorrosion and cathodic anticorrosion, and it is possible to prevent the corrosion of the iron-based metal member (Japanese Patent Laid-Open No. 2003-105573).

In paragraph 0037 of JP-A-2003-105573, the basic treatment step is a sodium hexametaphosphate pH 7 having a calcium hardness of 120 mg CaCO ₃ / L, a zinc ion concentration of 0.13 mmol / L, and a phosphorus atom concentration of 1.58 mmol / L. It is described to be performed under the condition of 0.0. In the paragraph 0045 of the same publication, the basic treatment step is performed under the conditions of a calcium hardness of 240 mg CaCO ₃ / L, a zinc ion concentration of 0.13 mmol / L, and a phosphorus atom concentration of 3.16 mmol / L sodium hexametaphosphate pH 7.0. Described below is what to do.

  The initial anticorrosive film forming treatment using phosphorus and zinc is also described in paragraph 0004 of JP-A-2005-290419.

JP 2003-105573 A JP 2005-290419 A

  An object of this invention is to provide the processing method of the cooling water type | system | group which can form the anti-corrosion film with a high anti-corrosion effect by a basic treatment process.

The cooling water system treatment method of the present invention (Claim 1) is a basic treatment step of forming an initial anticorrosion film on the surface of a metal member of the cooling water system by adding a phosphate and a zinc compound to the aqueous system when the cooling water system is started. In the treatment method of the cooling water system in which the basic treatment step is performed, in the basic treatment step, the total phosphoric acid concentration is 70 to 120 mg PO ₄ / L, the zinc concentration is 10 to 30 mg Zn / L, the calcium hardness is 25 to 75 mg CaCO ₃ / L, pH 6.0 or more and 7.0. The basic treatment process is performed for 5 to 36 hours under the condition of less than the above, and then the basic treatment is further performed at pH 7.0 to 7.5.

  A cooling water treatment method according to claim 2 is characterized in that, in claim 1, the first basic treatment step is performed for 5 to 24 hours.

A cooling water treatment method according to a _third aspect is characterized in that, in the first or second aspect, the calcium hardness is set to 40 to 60 mg CaCO ₃ / L in the first basic treatment step.

  An anticorrosion film having a high anticorrosion effect is formed by the method of the present invention. The details of this mechanism are not necessarily clear, but are presumed to be as follows.

In the first basic treatment step of the cooling water treatment method of the present invention, iron is eluted from the iron-based metal member by an anodic reaction, and this iron ion reacts with phosphate ion in water to produce iron phosphate. the reaction by OH ^- is produced, this OH ^- zinc hydroxide is produced by the reaction with zinc ions. Under the conditions of the first basic treatment step of the method of the present invention, these iron phosphate and zinc hydroxide are efficiently produced, and a dense anticorrosive film incorporating them is formed. After this basic treatment step, when the basic treatment is further carried out at a pH of 7.0 to 7.5, calcium ions and phosphate ions in water react to produce calcium phosphate, which is further coated on the anticorrosion coating. As a result, the anticorrosion film becomes stronger overall.

It is a graph which shows an experimental result. It is a schematic diagram explaining a test method. It is a graph which shows an experimental result. It is a systematic diagram of the real machine used by the Example and the comparative example.

  Hereinafter, the present invention will be described in more detail.

In the present invention, in the basic treatment step, the component concentration in water is the total phosphoric acid concentration of 70 to 120 mg PO ₄ / L, the zinc concentration of 10 to 30 mg Zn / L, the calcium hardness of 25 to 75 mg CaCO ₃ / L, pH 6.0 or more and less than 7.0. Then, an initial anticorrosive film is formed on the surface of the metal member by performing the basic treatment in the first half of the period, which is maintained for 5 to 36 hours under these conditions, and then further performing the basic treatment at a pH of 7.0 to 7.5.

  As the metal member, an iron-based metal member, particularly a carbon steel member is suitable. As the cooling water system, an open circulation type cooling water system is suitable.

As the water quality of the aqueous system to which the method of the present invention is applied, the calcium hardness contained in the water is preferably 25 to 75 mg-CaCO ₃ / L, particularly 40 to 60 mg-CaCO ₃ / L. When the calcium hardness is less than 25 mg-CaCO ₃ / L, it is not possible to sufficiently form an anticorrosion film composed of phosphorus and calcium produced by the action of phosphate and calcium, and when it exceeds 75 mg-CaCO ₃ / L, phosphorus and calcium There is concern about the deposition and adhesion of scale. When the water quality of the water system to be treated is out of the above range, the water quality may be adjusted by adding or removing calcium hardness components such as calcium nitrate and calcium chloride.

For such aqueous, the phosphorus-based corrosion components such as phosphoric acid and / or salt thereof, the total concentration of phosphoric acid aqueous after addition _70~120mg-PO 4 / L, especially _80~110mg-PO 4 / Add to L. If the phosphoric acid concentration after addition of the anticorrosive agent is less than 70 mg-PO ₄ / L, a sufficient anticorrosion film cannot be formed, and if it exceeds 120 mg-PO ₄ / L, the concentration becomes high and there is a concern about the influence on the environment. Is done. In addition, it is preferable to add phosphoric acid or the like to maintain the minimum required phosphoric acid concentration when the basic anticorrosive film formation step is below the minimum necessary phosphoric acid concentration due to consumption of anticorrosive components, etc. .

  Examples of phosphorus-based anticorrosive ingredients include phosphoric acid and / or a salt thereof such as sodium phosphate, potassium phosphate, disodium hydrogen phosphate, dipotassium hydrogen phosphate, sodium dihydrogen phosphate, potassium dihydrogen phosphate, Use polymerized phosphoric acid such as pyrophosphate, tripolyphosphate, hexametaphosphate, alkali metal pyrophosphate such as potassium pyrophosphate and sodium pyrophosphate, dihydrogen pyrophosphate such as disodium dihydrogen pyrophosphate, etc. These may be used alone or in combination of two or more.

  As zinc, zinc chloride, zinc sulfate and the like are suitable, and the amount added is 10 to 30 mg Zn / L, preferably 15 to 25 mg Zn / L. In the present invention, such a phosphoric acid-based and zinc-based anticorrosive agent is added to the aqueous system, and the initial pH is adjusted to 6.0 or more and less than 7.0, preferably 6.0 to 6.5. If the initial pH is 7 or more, there is little elution of iron from the iron-based metal member. Therefore, iron phosphate as a corrosion protection film component cannot be sufficiently formed on the surface of the iron-based metal member. As a result, the corrosion of the metal to be treated and other metal materials existing in the system are concerned about the progress of temporary corrosion. The method for adjusting the initial pH is not particularly limited, but a method of adjusting by adding an acid such as hydrochloric acid or sulfuric acid is preferable.

In the present invention, the addition of anticorrosive preferable M alkalinity of the water was adjusted initial pH below 6 or 7 is less than 10mg-CaCO ₃ / L or more 20mg-CaCO ₃ / L.

  The basic treatment process is usually carried out at room temperature, but the anticorrosive agent, for example, when a high-temperature part is generated depending on the condition of the treatment target (for example, when the initial anticorrosion film forming treatment is carried out while operating the heat exchanger). In order to prevent adverse effects due to excessive precipitation and adhesion of calcium phosphate scale composed of components and aqueous calcium to the metal member surface, a polymer electrolyte having an effect of preventing precipitation and / or adhesion of calcium phosphate scale is added as necessary. . The polymer electrolyte is not particularly limited as long as it has an effect of preventing scale precipitation and / or adhesion. However, a monomer comprising (meth) acrylic acid or a salt thereof and a monomer containing a sulfonic acid group Acrylic acid-based polymers obtained by copolymerization with the above are used. As such a polymer electrolyte, a copolymer of (meth) acrylic acid or a salt thereof and 3-hydroxy-2-allyloxypropanesulfonic acid, (meth) acrylic acid or a salt thereof, isoprenesulfonic acid and / or hydroxy Examples thereof include a copolymer with ethyl methacrylate. These polymer electrolytes are usually added in a range of about 50 to 300 mg / L, particularly about 10 to 100 mg / L as a solid content, depending on the situation of the water system to be treated.

  The basic treatment step for forming the initial anticorrosion film is performed for 5 to 36 hours, preferably 5 to 24 hours.

  In the present invention, after this early basic treatment is completed, the pH is adjusted to 7.0 to 7.5, and further basic treatment (late basic treatment) is performed. As a result, a calcium phosphate-based film is formed on the anti-corrosion film that has been formed so far, thereby further strengthening the anti-corrosion film.

In order to increase the pH to 7.0 to 7.5, an alkali is added. As this alkali, it is preferable to use sodium carbonate or sodium bicarbonate in order to prevent the pH from rising rapidly. Adjustment of pH7.0~7.5 is achieved by a 20mgCaCO ₃ / L or more 40mgCaCO ₃ / below L and M alkalinity.

  The total time of the basic treatment process including the first basic treatment process and the latter basic treatment process is preferably about 70 to 150 hours, particularly about 70 to 100 hours.

  After this basic treatment is completed, the concentration of the aqueous system is gradually increased, and the normal operation is started.

  In this invention, you may add a slime inhibitor, a scale inhibitor, and another anticorrosive agent to a water system in a basic treatment process and a subsequent process.

  Hereinafter, the present invention will be described more specifically with reference to test examples, examples and comparative examples.

[Test Example 1]
The effect of the treatment time in the basic treatment process was tested.

A 1 L beaker is filled with RO water (reverse osmosis treated water, calcium hardness 0 mg CaCO ₃ / L), calcium hardness 50 mg CaCO ₃ / L (added drug: Ca (NO ₃ ) ₂ ), M alkalinity 50 mg CaCO ₃ / L (added drug: NaHCO ₃ ), and after adding the additive so that the total phosphoric acid concentration is 100 mg PO ₄ / L (added agent: sodium hexametaphosphate) and the zinc concentration is 20 mg Zn / L (added agent: zinc chloride), the pH is adjusted to 6.0 with sulfuric acid. did.

  An iron sensor (material: SS400, 10φ × 30 mm iron rod) and a SUS sensor (10φ × 30 mm stainless steel rod) were immersed in a thermostatic bath at 30 ° C. as shown in FIG.

  After basic treatment for 1, 2, 3, 4, 5, 24, 48 or 72 hours, sodium carbonate solution was added to adjust the pH to 7.0 to 7.1. Thereafter, the basic treatment was completed by stirring with a stirrer for another 3 days.

  In order to test the corrosion resistance of the iron sensor (iron bar) subjected to this basic treatment, the water in the beaker was switched to Nogicho water, and stirring was further performed for 3 days. On the third day, the corrosion rate of the iron sensor was measured with a corrosion meter (K-600, manufactured by Toho Giken).

  The test results are shown in FIG. As shown in FIG. 3, the corrosion rate is remarkably reduced by setting the time for maintaining the pH at 6.0 in the basic treatment step in the previous period to be 5 to 36 hours, particularly 5 to 24 hours.

[Test Example 2]
The test was conducted in the same manner as in the case of pH 6.0 maintenance time = 5 hr in Test Example 1 except that the calcium hardness in the beaker water was 0, 25, 40, 60, 75 or 100 mg CaCO ₃ / L. The measurement results of the corrosion rate are shown in FIG.

As shown in FIG. 1, when the calcium hardness was 25 to 75 mg CaCO ₃ / L, particularly 40 to 60 mg CaCO ₃ / L, it was recognized that the corrosion rate was reduced.

[Example 1]
The test was conducted in an open circulation type cooling water system having a circulating water amount of 15000 m ³ / hr shown in FIG. The water quality of the cooling water has a calcium hardness of 50 mg CaCO ₃ / L and an M alkalinity of 50 mg CaCO ₃ / L.

To this actual cooling water system, sodium hexametaphosphate and zinc sulfate were added to give a total phosphoric acid concentration of 100 mg PO ₄ / L and a zinc concentration of 20 mg Zn / L, and the pH was adjusted to 6.5 with sulfuric acid. Thereafter, the circulation pump was started, and the pH was adjusted with sulfuric acid so that the pH was less than 6.5 to 7.0 for 5 hours. Thereafter, the pH adjustment with sulfuric acid was stopped, and it was confirmed that the pH was naturally 7.1 after 20 hours. A carbon steel tube (STB340) was installed as a monitor heat exchanger beside the cooling tower. Then, water vapor was circulated in the tube, and evaluation was performed by shell-side water passage for circulating circulating cooling water outside the tube (shell side). The shell side water flow was set at a flow rate of 0.1 m / s, and heat exchange of ΔT 5 ° C. (cooling water inlet temperature 30 ° C. → cooling water outlet temperature 35 ° C.) was performed by steam heating. The basic treatment was carried out in this state for 3 days.

Retention treatment for about 1 month (conditions: (water quality) pH 8.5 to 9.0, calcium hardness 150 to 250 mg CaCO ₃ / L, M alkalinity 150 to 250 mg CaCO ₃ / L (addition agent) hydroxyethylidene diphosphonic acid, zinc chloride , Acrylic acid / allyloxyhydroxypropane sulfonic acid (AA / HAPS) copolymer added to total phosphoric acid 3-7 mg PO ₄ / L, zinc concentration 1-3 mg Zn / L, 5-15 mg solid / L, respectively) After that, the carbon steel tube was removed from the monitor heat exchanger unit and the pitting depth was measured. As a result, the maximum pitting depth was 0.4 mm.

[Comparative Example 1]
In Example 1, the pH was first adjusted to 6.5, but the pH was not adjusted thereafter. As a result, pH became 7.1 when 10 minutes passed after the circulation pump was started. The pH after 3 days was 7.5. Otherwise, the test was performed under the same conditions as in Example 1, and the corrosion rate was measured. As a result, the maximum pitting depth was 0.6 mm, which was 1.5 times that of Example 1.

  Thus, the maximum pitting corrosion depth of Example 1 is about 67% of Comparative Example 1, and the anticorrosion effect is improved. As a result, according to the present invention, it was confirmed that the life of the heat exchanger can be extended.

Claims (3)

In the cooling water system treatment method of performing a basic treatment step of forming an initial anticorrosive film on the surface of a metal member of the cooling water system by adding a phosphate and a zinc compound to the water system at the time of starting the cooling water system,
In the basic processing step,
Total phosphate concentration 70~120mgPO ₄ / L,
Zinc concentration 10-30 mg Zn / L,
Calcium hardness 25-75 mg CaCO ₃ / L,
Cooling is characterized in that after the basic treatment step is performed for 5 to 36 hours under the condition of pH 6.0 or more and less than 7.0, the basic treatment is further performed at pH 7.0 to 7.5. Water treatment method.   2. The cooling water treatment method according to claim 1, wherein the first basic treatment step is performed for 5 to 24 hours. The cooling water treatment method according to claim 1 or 2, wherein the calcium hardness is set to 40 to 60 mg CaCO ₃ / L in the basic treatment step in the previous period.

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