JP2000254689A - Method for preventing sticking of silica based scale - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent sticking of silica based scale from occurring in a cooling water system by maintaining a sulfuric acid ion concentration in circulation water in the cooling water system of a heat exchanger of a building air conditioner, a plant, a petroleum chemical combined plant, etc. SOLUTION: It is found that the sulfuric acid ions react to silicic acid ions in the water so as to inhibit polymerization of the silicic acid by maintaining the sulfuric acid ion concentration not less than a specified concentration with respect to the water containing a scale component. Thus, by maintaining the sulfuric acid concentration in circulation water in the cooling water system at >=300 mg/liter, the sticking of the silica based scale in the cooling water system is effectively prevented. Other scale preventives, a corrosion preventive, and a slime control agent are used together as necessary. As the scale preventives used together, a copolymer of vinyl monomer copolymerizable with polyacrylic acid, acrylic acid, polymaleic acid, or a copolymer of vinyl monomer copolymerizable with maleic acid, maleic anhydride, etc. are listed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a water treatment method for efficiently preventing silica-based scale in a cooling water system of a heat exchanger of a building air conditioner, a general factory, a petrochemical complex or the like.

[0002]

2. Description of the Related Art Usually, scale disturbances due to calcium salts, magnesium salts, silica and the like often occur on heat transfer surfaces and pipes in contact with water, such as cooling water systems and boiler water systems. In particular, from the standpoint of saving resources and energy, when performing high concentration operation with less discharge of cooling water (blow) to the outside of the system, the dissolved salts are concentrated and the heat transfer surface is easily corroded, There is an increasing risk of scaling as sparingly soluble salts. The scale generated in this way causes serious troubles in the operation of the boiler and the heat exchanger, such as a decrease in thermal efficiency, blockage of pipes, and a failure of the water quality measuring device sensor. In particular, silica has low solubility and is scaled at a concentration of about 100 to 150 mg / liter or more. Conventionally, various scale inhibitors have been used in accordance with the type of scale. For example,
Calcium carbonate, calcium sulfate, calcium sulfite,
Calcium phosphate, magnesium hydroxide, zinc phosphate,
In general, carboxyl groups such as maleic acid, acrylic acid, and itaconic acid are effective for preventing scale such as zinc hydroxide and basic zinc carbonate, and if necessary, vinyl sulfonic acid, allyl sulfonic acid, and 2-acrylamide. Vinyl monomers having a sulfonic acid group such as 2-methylpropanesulfonic acid, copolymers obtained by combining nonionic vinyl monomers such as acrylamide, and inorganic polyphosphoric acids such as sodium hexametaphosphate and sodium tripolyphosphate; hydroxyethylidene diphosphonic acid; Phosphonic acids such as nobutantricarboxylic acid have been used.
Further, for example, in order to prevent silica-based scale such as silica, calcium silicate and magnesium silicate, an acrylamide-based scale inhibitor (Japanese Patent Application Laid-Open No. 61-107998).
JP-A No. 7-25), a cationic scale inhibitor (JP-A-7-25)
No. 6266) and a method using polyethylene glycol (JP-A-2-31894) have been proposed, and various polymers are properly used depending on the scale type. However, when performing a high concentration operation in an open circulation type cooling water system, generation of silica scale cannot be prevented. In general, water used in a cooling water system is industrial water, tap water, groundwater, and the like, and thus various ionic species are present in the water. Therefore, especially when performing a high concentration operation, a scale inhibitor which can effectively cope with all scale types is required, but such a scale inhibitor is not known. In particular, there is no known scale inhibitor effective for preventing silica-based scale from adhering during high concentration operation. For example, the acrylamide-based scale inhibitor has a scale preventing effect when the silica concentration is low, but the scale preventing effect disappears when the silica concentration is high. In addition, a scale inhibitor composed of a known cationic polymer (Japanese Patent Application Laid-Open No. Hei 7-256266) is a quaternary ammonium salt and has a very strong cationic property. It forms a gel-like reactant and easily causes troubles such as blockage of passages in the piping.In addition, since it is cationic, it adsorbs to the metallic material of the piping and is used as a scale inhibitor that is consumed in the system. There are drawbacks such as significant consumption. Also,
The method using polyethylene glycol has an effect of suppressing the adhesion of scale when the silica concentration is low, but has a disadvantage that it is easily affected by coexisting ions and the effect of preventing scale fluctuates and is not stable.

[0003]

SUMMARY OF THE INVENTION The present invention relates to a building air conditioner,
An object of the present invention is to provide a scale prevention technique which is extremely effective for preventing adhesion of scale generated in a cooling water system of a heat exchanger of a general factory, a petrochemical complex, or the like, particularly for a silica-based scale.

[0004]

Means for Solving the Problems As a result of intensive studies, the present inventor has found that sulfate ions act on silicate ions in water by maintaining sulfate ions at a certain concentration or more in water containing scale components, The present inventors have found an action mechanism for suppressing the polymerization of silicic acid, have conceived that the addition of high-concentration sulfate ions to circulating water can prevent the generation of silica-based scale, and have completed the present invention. That is, the present invention
The method comprises a method for preventing the silica-based scale from adhering to the cooling water system, wherein the sulfate ion concentration in the circulating water of the cooling water system is maintained at 300 mg / liter or more.

[0005]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Apparatuses to which the method of the present invention is applied include, for example, heat exchangers for building air conditioners, general factories, petrochemical complexes, etc., and a cooling water system heat exchanger that circulates the apparatus. This is to prevent scales adhering to devices such as water pits, cooling towers, and piping. The present invention is intended to prevent the generation of silica-based scales such as polymerized silica, calcium silicate, and magnesium silicate. In addition, by using the present technology in combination with a conventional scale inhibitor, the present invention can be applied to other scale types generally causing problems in a cooling water system. Other scale species include, for example, calcium carbonate, calcium sulfate, calcium sulfite, calcium phosphate, zinc phosphate, zinc hydroxide, basic zinc carbonate, and the like.
The sulfate ion used in the present invention is not particularly limited as a sulfate ion source, but is preferably a sulfate ion source in order to avoid corrosion problems in the heat exchanger body and piping. For example, sodium sulfate, calcium sulfate, sodium hydrogen sulfate, ammonium sulfate, potassium sulfate, magnesium sulfate, and the like can be used as a sulfate ion source. Particularly, sodium sulfate and magnesium sulfate are preferable in terms of stability, solubility, and safety. It is. Sulfate ions, which are usually present in industrial water at a concentration of about 20 mg / liter, can be used as they are in the specified sulfate ion concentration of the present invention without being removed. In the method of the present invention, the scale inhibitor may maintain a required amount of sulfate ion in the circulating water. Therefore, as with the conventional scale inhibitor, the place of addition of the circulating water path is not particularly limited and is preferably selected for operational convenience. Position. The sulfate used in the method of the present invention can be added as it is as a powder, or may be added in the form of an aqueous solution dissolved in water. When used in combination with other chemicals such as other scale inhibitors, anticorrosives, slime control agents, etc., they can be added to the combined chemicals and added to the circulating water.

In the method of the present invention, the required amount of sulfate ion is effective if it is at least 300 mg / liter with respect to the circulating water of the cooling water system.
/ Liter, particularly preferably 500 mg / liter or more. On the other hand, the upper limit of the addition amount is not particularly limited. However, judging from the efficiency of the scale prevention effect corresponding to the addition amount, 10%
00 mg / liter can be the upper limit. In the method of the present invention, if necessary, it can be used in combination with other scale inhibitors, anticorrosives and slime control agents. As the scale inhibitor used in combination with the method of the present invention, a known scale inhibitor can be used without particular limitation. For example, polyacrylic acid, a copolymer with a vinyl monomer copolymerizable with acrylic acid, polymaleic acid, a copolymer with a vinyl monomer copolymerizable with maleic acid or maleic anhydride, polyitaconic acid, copolymer with itaconic acid Organic polymers such as copolymers with a polymerizable vinyl monomer, and phosphorus-based compounds such as nitrilotrimethylenephosphonic acid, hydroxyethylidenephosphonic acid, phosphonobutanetricarboxylic acid, and sodium hexametaphosphate can be suitably used in combination. As the anticorrosive used in combination with the method of the present invention, a known anticorrosive can be used without particular limitation. For example, heavy metal salts such as chromates and zinc salts, the above-mentioned phosphorus compounds, anionic organic polymers and the like can be used in combination. Further, as the slime control agent used in combination with the present invention, a known slime control agent can be used without particular limitation. For example, conventional slime control agents such as hydrazine and organic halogen compounds can be used in combination. In the method of the present invention, the sulfate ion of the present invention does not inhibit the action of the other drugs, and acts independently, when used in combination with the above other drugs as appropriate according to the slime species of the circulating water. Since the effect is achieved, it is possible to comprehensively prevent the clogging of the pipe due to foreign matter such as scale by being used in combination with other chemicals.

[0007]

The present invention will be described below in more detail with reference to examples and comparative examples. Examples and comparative examples were performed according to the following operating procedures. Calcium hardness = 210 mg / liter (Ca
CO ₃ conversion), M alkali = 210 mg / liter (Ca
CO ₃ conversion), magnesium hardness 120 mg / l (CaCO ₃ conversion), SiO ₂ = 350 mg / l, pH
= 8.9 was prepared and heated to 30 ° C in a thermostatic water bath while stirring with a magnetic stirrer. When the temperature became constant, each drug was added in a predetermined amount, sampled at regular intervals, filtered through a 0.1 μm filter, and then measured for SiO ₂ concentration. Table 1 shows the results of tests in which the drugs indicated by the following abbreviations were added at the indicated concentrations in Examples and Comparative Examples. Abbreviations of drugs used in Examples and Comparative Examples are as follows. A: sodium sulfate (special grade reagent) B: magnesium sulfate (special grade reagent) P-1: polymaleic acid (molecular weight 5000) P-2: polyacrylic acid (molecular weight 3000)

[0008]

[Table 1]

Note 1) Addition amount of drugs A and B is concentration as SO ₄ ion. Addition amount of drugs P-1 and P-2 is concentration as pure polymer weight. Example 1
In Nos. 6 to 6, the SiO ₂ concentration was kept high even after 24 hours, which means that SiO ₂ scale was easily generated.
Even under the condition of 0 mg / liter, the amount of precipitated silica was very small, indicating that there was a remarkable scale suppressing effect. On the other hand, in Comparative Example 1 of the blank test, the SiO ₂ concentration started to decrease after about 4 hours, and 200 mg after 24 hours.
/ Liter or less. This indicates that the conditions of this example are conditions under which silica scale is very easily generated. Under the conditions of Comparative Example 1, in the tests of Comparative Examples 4 to 7 in which a conventionally known silica scale inhibitor was added, the SiO ₂ concentration was reduced to 200 mg / L or less after 24 hours. As a result, the results showed no silica scale suppressing effect at all.

[0010]

The present invention achieves a particularly remarkable effect of preventing the generation of silica-based scale in a high concentration operation by maintaining the sulfate ion in the circulating water at a certain high concentration or higher. In the method of the present invention, other known scale inhibitors can be used in combination, and the scale inhibitor of the method of the present invention has an advantage of not inhibiting the effect of other scale inhibitors, and is present in circulating water. By using a known scale inhibitor in combination with other scale species to be used, scale generation can be prevented comprehensively.

Claims (2)

[Claims] (1) The concentration of sulfate ions in the circulating water of the cooling water system is 3
A method for preventing adhesion of silica-based scale in a cooling water system, which is maintained at not less than 00 mg / liter. 2. The method according to claim 1, wherein another scale inhibitor is used in combination.