JP5128839B2 - Water treatment method for open circulation type cooling water system and water treatment agent for open circulation type cooling water system - Google Patents

Description

  The present invention relates to a water treatment method in an open circulation type cooling water system and a water treatment agent for an open circulation type cooling water system.

  As a circulating cooling water system for cooling circulating cooling water with a cooling tower, an open circulating cooling water system is widely used. In this open circulation type cooling water system, air is forced into the cooling tower and brought into contact with the circulating cooling water to evaporate a part of the circulating cooling water, and the temperature of the water is reduced by the heat of vaporization taken at that time. The principle is to lower.

  In the open circulation type cooling water system, the circulating cooling water is gradually concentrated by evaporation and scattering of the circulating cooling water. For this reason, the concentration of salts (for example, bicarbonate ions and calcium ions derived from makeup water) in the circulating cooling water gradually increases, and scales due to precipitation of calcium carbonate and the like are likely to occur. Further, when the concentration of corrosive ions such as chloride ions and sulfate ions is increased, pitting corrosion is likely to occur. Furthermore, if the residence time of the circulating cooling water is increased, contamination due to microorganisms and suspended particles is likely to occur.

In order to solve the above problems, a part of the concentrated circulating cooling water is blown, replenished with new water, and operated so as to maintain the concentration of 2 to 6 times. Yes.
In addition, corrosion inhibitors using heavy metals such as zinc salts, chromates and molybdates, and various phosphorus compounds such as high-concentration inorganic phosphates have also been used to inhibit corrosion of ferrous metals. It was.

  However, since corrosion inhibitors using these heavy metals cause environmental problems, many corrosion inhibitors not using heavy metals have been proposed in recent years.

For example, the use of an organic phosphonic acid compound or an organic phosphinic acid compound having a low phosphorus content in the molecule has been proposed, and a corrosion prevention method and a scale inhibition method with organic phosphonic acid such as 1-hydroxyethylidene-1,1-diphosphonic acid ( For example, see Patent Document 1), 2-phosphonobutane-1,2,4-tricarboxylic acid, 1-phosphonopropane-2, 3-dicarboxylic acid, corrosion inhibitors and scale formation inhibitors by phosphonocarboxylic acids such as phosphonosuccinic acid. (For example, see Patent Document 2), a method for inhibiting metal corrosion with 2-hydroxyphosphonoacetic acid and a method for preventing scale deposition (for example, see Patent Document 3), and co-use of maleic acid and amylene as an environmentally friendly treatment agent that does not contain phosphorus. Metal corrosion inhibitors using polymers (see, for example, Patent Document 4), maleic anhydride and acrylic acid, Scale precipitation inhibiting method and metal corrosion inhibiting method (see, for example, Patent Document 5) using a terpolymer comprising acrylic acid, alkyl acrylate, etc. and styrene, styrene sulfonic acid, etc., maleic anhydride 99- A scale (canestone) precipitation suppression method using a water-soluble maleic acid copolymer of 80% by weight and a monoethylenically unsaturated monomer 1-20% by weight (see, for example, Patent Document 6), maleic anhydride Method for inhibiting corrosion of metal surfaces of boilers and evaporators to which a copolymer hydrolyzate of acid and monoethylenically unsaturated monomer is added and a method for inhibiting precipitation molding (see, for example, Patent Document 7), maleic anhydride and carbon the number (see e.g., Patent Document 8) scale inhibition method in boilers and evaporators by 5-12 olefin copolymer, calcium hardness 10-300 mg-CaCO ₃ In an open circulating cooling water system that is / L, an alkali metal hydroxide is added to the circulating cooling water in an amount of 20 to 300 mg / L, and a ritner index (40 ° C.) of the circulating cooling water is set to 4.0 to 6.0. Examples include a method for inhibiting corrosion of an open circulating cooling water system to be maintained (see, for example, Patent Document 9).

  Further, although it is a technology in a technical field different from the technical field of the present invention, the metal of water supply pipes that do not have a cooling tower such as water pipes, water supply / hot water supply pipes for buildings, various water pipes, drain pipes, etc. In order to suppress corrosion of steel, a corrosion prevention method using calcium hydroxide and carbon dioxide in combination is known (Non-Patent Document 1).

Japanese Patent Publication No. 48-39348 Japanese Patent Publication No. 53-15707 Japanese Patent Publication No. 3-2953 Japanese Patent Publication No. 61-19714 Japanese Patent Laid-Open No. 2-115384 JP 63-182318 A Japanese Patent Publication No.54-29998 Japanese Patent Publication No. 5-81320 Japanese Patent Laying-Open No. 2005-200721 Proceedings of the 51st Materials and Environmental Discussion Meeting, 201-202, 2004

  It is an object of the present invention to provide an open circulation type cooling water system water treatment method and an open circulation type cooling water treatment agent capable of suppressing metal corrosion and scale adhesion without using heavy metals. Let it be an issue.

  In order to solve the above problems, the inventor has focused on calcium hydroxide, which has not been used as a water treatment agent for an open circulation cooling water system. Calcium hydroxide is used to suppress metal corrosion in water supply pipes that are closed systems that do not have cooling towers, such as water pipes, water supply and hot water supply pipes for buildings, various water pipes, and drain pipes. Used in combination with carbon dioxide. (Refer nonpatent literature 1). However, this method cannot be directly applied to a water treatment method of an open circulation cooling water system. This is because, in an open circulating cooling water system, as described above, the circulating cooling water is gradually concentrated by evaporation and scattering of the circulating cooling water (usually, the circulating cooling water is operated so as to maintain a concentration of 2 to 6 times. The concentration of bicarbonate ions and calcium ions gradually increases. If calcium hydroxide is further added there, the increase in calcium ions and pH increase may cause scale failure due to precipitation of calcium carbonate and magnesium silicate, and also promotes corrosion of copper and copper alloys. The For this reason, the method of adding calcium hydroxide or calcium oxide to an open circulation cooling water system has not been performed so far.

  Of course, it is conceivable to use carbon dioxide together with calcium hydroxide to lower the pH and prevent scale failure, but an extremely large amount of carbon dioxide is required in an open circulation cooling water system. In addition, a carbon dioxide supply device is required, and necessary equipment and management costs are also required, leading to an increase in water treatment costs.

  Therefore, the inventor considered using the contact between cooling water and air, which is a feature of the open circulation cooling water system. That is, since carbon dioxide is contained in the air, it was considered to lower the pH of the cooling water with the carbon dioxide in the air. Furthermore, in order to prevent the precipitation of calcium carbonate scale, it was found that metal corrosion can be suppressed and scale adhesion can be suppressed by using a threshold inhibitor that suppresses crystal growth of calcium carbonate, and the present invention was completed. It came to do.

  That is, the water treatment method of the open circulation type cooling water system according to the present invention is the water treatment method of the open circulation type cooling water system in which the circulating cooling water and the outside air are brought into contact with each other in a cooling tower to cool the circulating cooling water. Calcium hydroxide and / or calcium oxide and a threshold inhibitor that suppresses crystal growth of calcium carbonate are added to water.

  In the present invention, calcium hydroxide and / or calcium oxide and a threshold inhibitor that suppresses crystal growth of calcium carbonate are added to the circulating cooling water in the open circulation type circulating water system. These drugs have the following roles.

  That is, by adding calcium hydroxide and / or calcium oxide, the calcium ion concentration and pH in the circulating cooling water are increased, and a calcium carbonate film that plays a role of anticorrosion is easily formed on the piping of the open circulating cooling water system, Metal corrosion is prevented. In addition, calcium hydroxide and / or calcium oxide dissolves in water to produce calcium ions and hydroxide ions, and the hydroxide ions in the circulating cooling water react with carbon dioxide in the atmosphere in the cooling tower to generate heavy ions. Carbonate ions and carbonate ions are generated. By the pH buffering action of the carbonate thus produced, the pH of the circulating cooling water is automatically adjusted to an appropriate range without adding an acidic substance such as carbon dioxide.

  Moreover, the addition of a threshold inhibitor that suppresses the crystal growth of calcium carbonate can prevent troubles due to scale such as clogging of piping due to excessive precipitation of calcium carbonate scale.

That is, in the present invention, the addition of calcium hydroxide and / or calcium oxide promotes the formation of a calcium carbonate film that plays a role of anticorrosion, and the addition of a threshold inhibitor prevents precipitation of calcium carbonate as a scale.
Therefore, according to the water treatment method of the circulating cooling water of the present invention, metal corrosion can be suppressed and scale adhesion can be suppressed without using heavy metals.

  In the water treatment method for circulating cooling water according to the present invention, it is preferable to control the circulating coolant at 40 ° C. so that the Ritzner index is 3.5 to 6. When the Ritzner index is less than 3.5, no further increase in the corrosion inhibition effect can be expected, and the scale deposition tendency increases, which may cause scale failure. On the other hand, if the Ritzner index exceeds 6, a sufficient corrosion inhibiting effect cannot be obtained. By controlling the Ritzner index to be 3.5 to 6, metal corrosion can be suppressed and scale adhesion can be suppressed.

ここで、
ｐＫ_２：Ｈ_２ＣＯ_３の第２解離定数
ｐＫs：ＣａＣＯ_３の溶解度積
ｐＣａ＝−ｌｏｇ［循環冷却水のＣａ硬度］（ｍｇ−ＣａＣＯ_３／ｌ）
ｐＡ＝−ｌｏｇ［循環冷却水のＭアルカリ度］（ｍｇ−ＣａＣＯ_３／ｌ）
μ：イオン強度であり、次式で算出される。
μ＝［循環冷却水の電気伝導率］（μＳ／ｃｍ）×０.００００１７５ The Ritzner index (RI) is an index indicating the precipitation tendency of calcium carbonate, and is a numerical value defined by the following formula.
RI = 2 × pHs−pH
(Here, pH is the pH of the circulating cooling water, and pHs is the pH at which calcium carbonate is saturated under the condition of the target circulating cooling water represented by the formula (1).)

here,
pK ₂ : Second dissociation constant of H ₂ CO ₃ pK s: Solubility product of CaCO ₃ pCa = −log [Ca hardness of circulating cooling water] (mg-CaCO ₃ / l)
pA = −log [M alkalinity of circulating cooling water] (mg-CaCO ₃ / l)
μ: Ionic strength, calculated by the following formula.
μ = [Electric conductivity of circulating cooling water] (μS / cm) × 0.00000175

  In order to control the Ritzner index (RI) to be 3.5-6, in addition to adjusting the addition of calcium hydroxide and / or calcium oxide, the amount of makeup water to the circulating cooling water and the amount of blowdown water Can be controlled by adjusting. Addition of calcium hydroxide and / or calcium oxide increases the Ca hardness and M alkalinity of the circulating cooling water, and as a result, the Ritzner index (RI) decreases. Further, when the amount of blowdown water is increased and the amount of water is replenished with makeup water, the M alkalinity and the concentration of calcium ions are lowered, and the Ritzner index (RI) is increased.

The calcium hardness in the circulating cooling water is preferably 100 to 300 mg-CaCO ₃ / L. According to the inventor's test results, if the calcium hardness in the cooling water is within this range, the Ritzner index (RI) can be controlled to be 3.5-6.

  It is also preferable to add an alkali metal hydroxide in the range of 20 to 300 mg / L to the circulating cooling water. Alkali metal hydroxides have a higher pH-increasing action than calcium hydroxide and calcium oxide, so that the Ritzner index (RI) can be changed more greatly. However, when an alkali metal hydroxide is added, not only calcium hydroxide and / or calcium oxide but also the addition amount of alkali metal hydroxide is taken into consideration so that the Ritzner index is 3.5-6. To control.

  Threshold inhibitors include organic phosphonic acids and salts thereof, phosphinopolycarboxylic acids and salts thereof, phosphonocarboxylic acids and salts thereof, maleic polymers and salts thereof, and monoethylenically unsaturated monomers having sulfonic acid groups. One or more selected from the group consisting of a copolymer of a monomer and (meth) acrylic acid and a salt thereof are preferable.

The water treatment agent for open circulation type cooling water according to the present invention is characterized by containing calcium hydroxide and / or calcium oxide and a threshold inhibitor that suppresses crystal growth of calcium carbonate as active ingredients.
As described above, when such an open circulation type cooling water treatment agent is used, heavy metals are not used, metal corrosion can be suppressed, and scale adhesion can be suppressed.

  The amount of the threshold inhibitor added to the circulating cooling water is preferably in the range of 0.5 to 200 mg / L. If the addition amount of the threshold inhibitor is within this range, a sufficient scale prevention effect can be obtained.

  The present invention can be applied to an open circulation cooling water system that is used by incorporating industrial water, tap water, well water, etc. from rivers, lake water, ground water, rain water, and the like. As such an open circulation type cooling water system, for example, open circulation cooling in various manufacturing industries such as petroleum refining industry, petrochemical industry, paper pulp manufacturing industry, textile industry, paint industry, synthetic rubber latex industry, power plant, air conditioning system, etc. An aqueous system is mentioned.

  Since calcium oxide becomes calcium hydroxide when dissolved in water, either calcium hydroxide or calcium oxide may be used, or a mixture of these may be used. Calcium hydroxide or calcium oxide may be added to the open circulation cooling water system as a solid, or may be added as an aqueous solution or slurry.

  Any threshold inhibitor may be used as long as it has an effect of suppressing the crystal growth of calcium carbonate. Organic phosphonic acid and its salt, phosphinopolycarboxylic acid and its salt, phosphonocarboxylic acid and its One or more selected from the group consisting of a salt, a maleic acid polymer and a salt thereof, a copolymer of a monoethylenically unsaturated monomer having a sulfonic acid group and (meth) acrylic acid, and a salt thereof; It is preferable to do.

  The organic phosphonic acid is an organic compound having one or more phosphono groups in the molecule, specifically, 1-hydroxyethylidene-1, 1-diphosphonic acid, aminotrimethylenephosphonic acid, ethylenediaminetetramethylenephosphonic acid, Examples include diethylenetriaminepentamethylenephosphonic acid and hexamethylenediaminetetramethylenephosphonic acid. Among these, 1-hydroxyethylidene-1, 1-diphosphonic acid can be particularly preferably used.

  The phosphonocarboxylic acid is an organic compound having one or more phosphono groups and one or more carboxyl groups in the molecule. Specifically, 2-phosphonobutane-1,2,4-tricarboxylic acid, hydroxy Examples thereof include phosphonoacetic acid, phosphonopolymaleic acid, and phosphonic succinic acid. Among these, 2-phosphonobutane-1,2,4-tricarboxylic acid and phosphonopolymaleic acid are particularly suitable.

  The phosphonopolymaleic acid can be produced by heating phosphorous acid and maleic acid in a neutral to alkaline aqueous solvent in the presence of a free radical initiator (see JP-A-4-334392). ), And commercially available from Rhodia under the trade name BRICORRR288.

The phosphinopolycarboxylic acid is a compound having one or more phosphino groups and two or more carboxyl groups in the molecule. Specifically, it is a bisphenol obtained by reacting acrylic acid and hypophosphorous acid. -Reaction of poly (2-carboxyethyl) phosphinic acid, bis-poly (1,2-dicarboxyethyl) phosphinic acid obtained by reacting maleic acid and hypophosphorous acid, maleic acid, acrylic acid and hypophosphorous acid And poly (2-carboxyethyl) (1,2-dicarboxyethyl) phosphinic acid, a reaction product of acrylic acid, 2-acrylamido-2-methylpropanesulfonic acid and hypophosphorous acid, and the like. Among these, poly (2-carboxyethyl) (1,2-dicarboxyethyl) phosphinic acid can be particularly preferably used.
The preparation of phosphinopolycarboxylic acid is usually carried out by heating hypophosphorous acid and unsaturated carboxylic acid in the presence of a free radical initiator in an aqueous solvent. For example, Japanese Patent Publication No. Sho 54-29316, This is disclosed in Japanese Patent Publication No. 5-57992 and Japanese Patent Publication No. 6-47113. Further, phosphinopolycarboxylic acids are commercially available from BWA under trade names such as BELCLENE 500, BELPERSE 164, BELCLENE 400, and the like.

The maleic acid polymer is a copolymer of a homomaleic acid polymer and an unsaturated monomer copolymerizable with maleic acid. Examples of such unsaturated monomers include monoethylenically unsaturated sulfonic acid 2-acrylamido-2-methylpropanesulfonic acid, 3-allyloxy-2-hydroxy-1-propanesulfonic acid, conjugated diene sulfonated product, styrene Sulfonic acid, sulfoalkyl (meth) acrylate ester, sulfoalkyl (meth) allyl ether, sulfopheno (meth) allyl ether, (meth) allylsulfonic acid, etc .; (meth) acrylic acid alkyl ester (meth) acrylic acid ester, ( (Meth) acrylic acid hydroxyl alkyl ester; (meth) acrylamide (meth) acrylamide, N-alkyl substituted (meth) acrylamide; olefins having 2 to 8 carbon atoms such as ethylene, propylene, isopropylene, butylene, isobutylene, hexene, 2- D Tilhexene, pentene, isopentene, octene, isooctene and the like; vinyl methyl ether of vinyl alkyl ether, vinyl ethyl ether; maleic acid alkyl ester, and the like, and one or more of them are used.
The maleic acid polymer is a copolymer obtained from 30 to 99% by weight of maleic acid and 1 to 70% by weight of the unsaturated monomer, and among them, a homomaleic acid polymer is preferable. Further, the weight average molecular weight of the maleic acid polymer is preferably 300 to 20000, and more preferably 400 to 1000.

The method for producing a maleic acid polymer can be produced by heating maleic anhydride or maleic acid in an organic solvent or an aqueous solvent in the presence of a free radical initiator. For example, it is disclosed in Japanese Patent No. 2964154, Japanese Patent Publication No. 7-49450, Japanese Patent Laid-Open No. 6-298874, and the like.
The copolymer of (meth) acrylic acid and a monoethylenically unsaturated monomer having a sulfonic acid group is a sulfonic acid group copolymerizable with (meth) acrylic acid and (meth) acrylic acid. It is a copolymer with a monoethylenically unsaturated monomer. Monoethylenically unsaturated monomers having copolymerizable sulfonic acid groups include 2-acrylamido-2-methylpropanesulfonic acid, 3-allyloxy-2-hydroxy-1-propanesulfonic acid, conjugated diene sulfonated products, Examples thereof include styrene sulfonic acid, sulfoalkyl (meth) acrylate ester, sulfoalkyl (meth) allyl ether, sulfopheno (meth) allyl ether, (meth) allyl sulfonic acid and the like. Moreover, the multicomponent copolymer containing a monoethylenically unsaturated monomer monomer other than this may be sufficient. Examples of such monoethylenically unsaturated monomer monomers include (meth) acrylic acid ester (meth) acrylic acid alkyl esters, (meth) acrylic acid hydroxyl alkyl esters; (meth) acrylamide (meth) Acrylamide, N-alkyl substituted (meth) acrylamide; ethylene, propylene, isopropylene, butylene, isobutylene, hexene, 2-ethylhexene, pentene, isopentene, octene, isooctene, etc. of olefins having 2 to 8 carbon atoms; vinyl alkyl ether Examples thereof include vinyl methyl ether, vinyl ethyl ether; maleic acid alkyl ester, and one or more of them are used.
The copolymer of (meth) acrylic acid and a monoethylenically unsaturated monomer having a sulfonic acid group is preferably monoethylenically unsaturated having 30 to 99% by weight of (meth) acrylic acid and a sulfonic acid group. It is a copolymer obtained from 1 to 70% by weight of monomer, and a more preferable monomer ratio is 80:20 to 40:60. Moreover, the weight average molecular weight of this copolymer is preferably 1,000 to 100,000, more preferably 4,000 to 20,000.
A copolymer of (meth) acrylic acid and a monoethylenically unsaturated monomer having a sulfonic acid group is preferably a copolymer of (meth) acrylic acid and 2-acrylamido-2-methylpropanesulfonic acid. 1 type selected from a copolymer, a copolymer of (meth) acrylic acid and 3-allyloxy-2-hydroxy-1-propanesulfonic acid, a copolymer of (meth) acrylic acid and a conjugated diene sulfonated product, or 2 or more types.

The threshold inhibitor is a copolymer of at least one selected from organic phosphonic acid, phosphinopolycarboxylic acid, phosphonocarboxylic acid and maleic acid polymer, and acrylic acid and monoethylenically unsaturated sulfonic acid. The composition containing these is preferable. The ratio of acrylic acid and monoethylenically unsaturated sulfonic acid in the composition in this case is usually 10:90 to 90:10, preferably 20:80 to 80:20.
More preferably, the threshold inhibitor is at least one selected from organic phosphonic acids, phosphinopolycarboxylic acids, phosphonocarboxylic acids and maleic polymers, acrylic acid and 2-acrylamido-2-methylpropane. A composition comprising a copolymer of sulfonic acid (AMPS) and one or more selected from a copolymer of acrylic acid and 3-allyloxy-2-hydroxy-1-propanesulfonic acid (AHPS). The ratio of the composition in this case is usually 10:90 to 90:10, preferably 30:70 to 70:30.

The threshold inhibitor may be in the form of an acid that has not been neutralized, or in the form of a salt that has been neutralized with an alkali metal hydroxide or the like. When a threshold inhibitor is added in the form of an unneutralized acid, calcium hydroxide and / or calcium oxide will be partially neutralized, but usually calcium hydroxide and / or calcium oxide rather than a threshold inhibitor. Therefore, the threshold inhibitor does not completely neutralize calcium hydroxide and / or calcium oxide.
The amount of the threshold inhibitor added to the circulating cooling water is preferably 0.5 to 200 mg / L. If the addition amount of the threshold inhibitor is within this range, a sufficient scale prevention effect can be obtained.

  Calcium hydroxide and / or calcium oxide and the threshold inhibitor may be added separately to the open circulation cooling water system, or may be added after mixing them.

  About the addition amount of calcium hydroxide and / or calcium oxide and a threshold inhibitor, the amount is appropriately adjusted depending on the water quality of the target water system, the type and concentration of corrosion inhibition, the degree of scale inhibition, and the like. Usually, 20 to 300 mg / L is an appropriate range as the total amount in terms of calcium hydroxide in calcium hydroxide and / or calcium oxide with respect to the aqueous system. If the added amount is less than 20 mg / L as the total amount in terms of calcium hydroxide, a sufficient anticorrosive effect cannot be expected. On the other hand, if the amount added as the total amount in terms of calcium hydroxide exceeds 300 mg / L, no further increase in corrosion inhibition effect can be expected, and calcium hydroxide does not dissolve and remains undissolved, which is not preferable. . On the other hand, since calcium hydroxide has a limited solubility in water, it is advantageous in that there is no adverse effect of scale failure due to excessive addition as in water quality regulators with high solubility such as calcium chloride and sodium carbonate.

  The addition amount of the threshold inhibitor is preferably 0.5 to 200 mg / L, more preferably 1 to 50 mg / L. If the added amount of the threshold inhibitor is less than 0.5 mg / L, sufficient scale inhibitory effect and corrosion inhibitory effect cannot be expected. If the added amount exceeds 200 mg / L, further scale inhibitory effect and corrosion inhibitory effect will increase. It is not preferable because it cannot be expected and the scale is increased.

The method of adding calcium hydroxide and / or calcium oxide and a threshold inhibitor is not particularly limited, and it may be usually added using an injection device such as a chemical injection pump. You may add using a blower.
In addition, regarding the addition place of the threshold inhibitor, it may be added to any place of the open circulation type cooling water system, but the calcium hydroxide and / or calcium oxide component is not directly added to the circulation cooling water, It is preferable to add to make-up water. This is because make-up water has a lower pH and calcium hardness than circulating cooling water, so that calcium hydroxide and / or calcium oxide is easily dissolved.

  About the effect | action and effect in the case of performing the water treatment method of this invention, it is as follows. That is, calcium hydroxide and / or calcium oxide added to the circulating cooling water is dissolved to generate calcium ions and hydroxide ions. Then, hydroxide ions come into contact with the atmosphere in the cooling tower and react with carbon dioxide in the atmosphere to become bicarbonate ions. And the pH of circulating cooling water is stably maintained in the region of 8.5 to 9.5 by the buffering action of this bicarbonate. The calcium ions and bicarbonate ions generated in this way react with the hydroxide ions generated by the cathode reaction (oxygen reduction reaction) on the metal surface, and reach the cathode part on the metal surface from a single molecule to several molecular levels. A thin and dense calcium carbonate protective film is formed to suppress corrosion. Furthermore, scale action of calcium carbonate, calcium hydroxide, etc. can be effectively prevented by the action of the threshold inhibitor, and the corrosion inhibition effect is exhibited not only on iron-based metals but also on copper and copper alloys. The threshold inhibitor does not inhibit the formation of calcium carbonate at a single molecule to several molecules level, but inhibits the nucleation and crystal growth of calcium carbonate corresponding to the critical radius exceeding several molecules level. Generation | occurence | production of the scale of a calcium carbonate can be suppressed, without inhibiting formation.

  In addition, when the copper alloy is used in the location which contacts the cooling water of an open circulation type cooling water system, it is preferable to add the aromatic azole compound which is corrosion inhibition of a copper alloy. Examples of the aromatic azole compound include tolyltriazole, benzotriazole, halo-substituted benzotriazole, halo-substituted tolyltriazole, mercaptobenzothiazole and the like.

  It is also preferable to add a slime control agent in order to suppress microorganism-related obstacles in the open circulation cooling water system. In the water treatment method of the present invention, since the pH of the cooling water is increased, it is most preferable to add a bromine-based disinfectant having an excellent sterilizing effect even at a high pH. The bromine-based disinfectant is not particularly limited as long as it produces hypobromite in water. For example, hypobromite, bromochlorodimethylhydantoin, dibromodimethylhydantoin, bromine chloride, hypochlorous acid And a reaction product of bromide and the like.

Examples in which the present invention is embodied will be described below in comparison with comparative examples.
<Adjustment of open circulation cooling water treatment agent>
In the examples, a slurry in which calcium hydroxide and a threshold inhibitor were mixed was used as an open circulation cooling water treatment agent. As the threshold inhibitor, the following various organic phosphonic acids and various copolymers were used alone or in combination.

(Organic phosphonic acid used as a threshold inhibitor)
HEDP: 1-hydroxyethylidene-1, 1-diphosphonic acid sodium salt PBTC: 2-phosphonobutane-1,2,4-tricarboxylic acid sodium salt
(Copolymer used as threshold inhibitor)
AA-AMPS: Acrylic acid and 2-acrylamido-2-methylpropanesulfonic acid
Sodium salt of a copolymer of [polymerization ratio (weight) 60:40, weight average
Molecular weight 10,000]
AA-AHPS: acrylic acid and 3-allyloxy-2-hydroxy-1-propanesulfur
Sodium salt of copolymer of phonic acid [polymerization ratio (weight) 50:50, heavy
Weight average molecular weight 5,000]
PMA: Polymaleic acid sodium salt “BELCLENE200LA” (trade name, BW
A company), [active content 50%]
AMP: sodium salt of acrylic acid-maleic acid-hypophosphorous acid copolymer (molar ratio 2: 1: 1)

(Examples 1-6 and Comparative Examples 1-9)
Table 1 shows the compositions of the water treatment agents for open circulation type cooling water of Examples 1 to 6 and the compositions of water treatment agents of Comparative Examples 1 to 9. In addition, PAA (polyacrylic acid sodium salt [weight average molecular weight 2,200]) added with calcium hydroxide in Comparative Example 8 is a dispersant and not a threshold inhibitor that suppresses crystal growth of calcium carbonate. .

<Evaluation method>
The evaluation of the water treatment method was performed in accordance with the on-site test method of JIS G0593-2002 “Test Method for Evaluation of Corrosion and Scale Prevention of Water Treatment Agent”.
Moreover, evaluation was performed using the open circulation type cooling water system shown in FIG. In this open circulation type cooling water system, an induced draft counterflow contact type cooling tower 1 having a cooling capacity of 1.8 cooling tons, a water tank 2 and a heat exchanger 3 are connected by a pipe 4. Cooling water can be circulated in the pipe 4 by a circulation pump 5 installed on the way. The water capacity of the entire system including the water tank 2 and the pipe 4 is 62L. Connected to the water tank 2 are a water treatment agent injection device 6 for supplying a water treatment agent, a makeup water pipe 7 for supplying makeup water, a drain pipe 8 for draining water, and a blowdown pump 8a. ing. In addition, a water temperature control device 9 is also installed in the water tank 2.

  An electrical conductivity measurement cell 10, a flow rate adjustment valve 11, and a flow meter 12 are provided in the pipe 4 a that connects the circulation pump 5 and the heat exchanger 3. The pipe 4b connecting the heat exchanger 3 and the cooling tower 1 is provided with a test piece holder 13 for holding a test heat transfer tube for performing a corrosion test.

  Further, in this open circulation type cooling water system, an electrical conductivity control device 14 is provided for controlling the injection amount of the water treatment agent injection device 6 and the drainage amount of the blow-down pump 8a in accordance with a signal from the electrical conductivity measurement cell 10. ing.

<Corrosion test 1>
A corrosion test was conducted using the above open circulation cooling water system. That is, Yokkaichi city water was sprinkled in the water tank 2, and sodium hexametaphosphate 75 mg / L and zinc chloride 40 mg / L were added as an initial treatment. After circulating at room temperature for 48 hours, the whole amount was discharged. The water quality of Yokkaichi city water is pH: 7, electrical conductivity: 12.6 mS / m, Ca hardness: 37 mg-CaCO ₃ / L, Mg hardness 8 mg-CaCO ₃ / L, M alkalinity: 39 mg-CaCO ₃ / L ,
Chloride ion: 7 mg / L, sulfate ion: 11 mg / L, silica: 10 mg / L.

Thereafter, Yokkaichi city water was newly spread on the water tank, and a test heat transfer tube made of a carbon steel pipe STKM11A (JIS G3445) having an outer diameter of 12.7 mm and a length of 510 mm was attached to the test piece holder 13. 200 mg / L was added to start circulation and heat load was started. The water temperature of the water tank 2 was controlled by the water temperature control device 9 so as to be 35 ° C. The cooling water is circulated by the circulation pump 5 while controlling the flow rate adjusting valve 11 so that the flow rate is 210 L / h corresponding to the linear flow rate of 0.3 m / s of the test heat transfer tube evaluation unit, and the heat flow of the heat exchanger 3 The bundle was 70 kW / m ² . The temperature difference between the circulating cooling water at the inlet and outlet of the cooling tower was 15 ° C. The amount of evaporated water was 4.4 L / h, the amount of makeup water was 5.5 L / h, the amount of blowdown water was 1.1 L / h, and the concentration was 5 times. The electric conductivity of the circulating cooling water is continuously measured by the electric conductivity measuring cell 10 and the electric conductivity corresponding to 3.5 times the concentration is obtained from the electric conductivity input signal using the electric conductivity controller 14. The blowdown pump 8a was controlled so that

  Two days after the start of the heat load, when the concentration reached 3.5 times, blowdown was started to maintain the concentration at 3.5 times. Simultaneously with the start of blowdown, 200 mg / L of water treatment agent was added to the blowdown amount by the water treatment agent injection device 6. The test period was 30 days.

Table 2 shows the average quality of the circulating cooling water during the corrosion test 1. In Examples 1 to 6 to which calcium hydroxide was added, M alkalinity and Ca hardness were remarkably increased as compared with Comparative Examples 2 to 7 to which calcium hydroxide was not added. In Examples 1 to 6, the pH of the test water when not passing through the cooling tower 1 was 10.3. By circulating water through the cooling tower 1, the pH of the test water was absorbed by absorbing carbon dioxide in the atmosphere. Dropped to 9.0. In addition, the Ritsner index was 4.8 in Examples 1 to 6 and was almost stable. On the other hand, in the comparative examples 2 to 7, the Ritzner index was 6.0, and in the comparative example 9, it was 6.2.

After completion of the corrosion test, the test heat transfer tube was removed, and the average corrosion rate, maximum corrosion depth, and average deposition rate were measured. As a result, as shown in Table 3, Examples 1 to 6 all exhibited a sufficient corrosion inhibiting effect and a scale inhibiting effect. On the other hand, Comparative Example 1 in which only the calcium hydroxide alone and the threshold inhibitor was not added, and Comparative Examples 2 to 7 in which calcium hydroxide was not added and only the threshold inhibitor was added, showed sufficient corrosion inhibiting effects. In addition, the scale suppression effect was not sufficient.

<Corrosion test 2>
In corrosion test 2, an aluminum brass tube C6871 (JIS H3300) having an outer diameter of 12.7 mm and a length of 510 mm is used as a test heat transfer tube, and is a corrosion inhibitor for copper alloys for all water treatment agents. Tolyltriazole was added at 1 mg / L. The other conditions are the same as those in the corrosion test 1 and will not be described.

As a result, as shown in Table 4, Examples 1 to 6 all exhibited a sufficient corrosion inhibiting effect and a scale inhibiting effect. In contrast, Comparative Example 1 in which only the calcium hydroxide alone was not added with the threshold inhibitor and Comparative Example 2 in which the calcium hydroxide and the flocculant PAA were mixed and the threshold inhibitor was not added were sufficient. The corrosion inhibitory effect was not exhibited, and the scale inhibitory effect was not sufficient.

＜腐食試験３＞
上記実施例７〜１０の開放循環式冷却水用水処理剤を用いて、腐食試験を行った。すなわち、実施例１〜６の場合と同様、水槽２に四日市市水を張り、初期処理としてヘキサメタリン酸ソーダ
７５ｍｇ／Ｌと塩化亜鉛４０ｍｇ／Ｌとを添加して、常温で４８時間循環後、全量を排出した。 (Examples 7 to 10)
In Examples 7-10, the water treatment agent for open circulation type cooling water of the composition shown in Table 5 was used.

<Corrosion test 3>
A corrosion test was conducted using the open-circulation cooling water treatment agents of Examples 7-10. That is, as in the case of Examples 1 to 6, Yokkaichi city water was added to the water tank 2, and sodium hexametaphosphate 75 mg / L and zinc chloride 40 mg / L were added as an initial treatment, and the whole amount was circulated at room temperature for 48 hours. Was discharged.

  After that, a new Yokkaichi city water was put on the water tank and a test heat transfer tube made of a carbon steel pipe STKM11A (JIS G3445) having an outer diameter of 12.7 mm and a length of 510 mm was attached to the specimen holder 13 and then circulation was started. Then, heat load was started. Two days after the start of the heat load, when the concentration reached 3.5 times, blowdown was started to maintain the concentration at 3.5 times. Simultaneously with the start of blowdown, 300 mg / L of water treatment agent was added to the blowdown amount by the water treatment agent injection device 6. The test period was 30 days.

Table 6 shows the average water quality of the circulating cooling water during the corrosion test 3. As a result, the Ritzner index was in the range of 4.1 to 5.3.

After completion of the corrosion test, the test heat transfer tube was removed, and the average corrosion rate, maximum corrosion depth, and average deposition rate were measured. As a result, as shown in Table 7, all of Examples 7 to 10 showed a sufficient corrosion inhibiting effect and a scale inhibiting effect.

  The present invention can be suitably used as a water treatment method in an open circulation type cooling water system and a water treatment agent for an open circulation type cooling water system.

It is a systematic diagram of the open circulation type cooling water system used for the Example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Cooling tower, 2 ... Water tank, 3 ... Heat exchanger, 4 ... Piping, 5 ... Circulation pump,
DESCRIPTION OF SYMBOLS 6 ... Water treatment agent injection | pouring apparatus, 7 ... Supply water pipe, 8 ... Drain pipe, 8a ... Blow-down pump 9 ... Water temperature control apparatus, 10 ... Electric conductivity measuring cell, 11 ... Flow control valve 12 ... Flow meter, 13 ... Test Single holder, 14 ... Electric conductivity controller

Claims (5)

In the water treatment method of the open circulation type cooling water system in which the circulating cooling water and outside air are brought into contact with each other in the cooling tower to cool the circulating cooling water,
Add calcium hydroxide and / or calcium oxide to the circulating cooling water, and a threshold inhibitor that suppresses crystal growth of calcium carbonate,
Ritsuna index in 40 ° C circulating coolant without dispersing calcium carbonate particles in the thus cooled water to be controlled to be 3.5 to 6, dense metal surface constituting the opening circulating cooling water system A water treatment method for circulating cooling water, characterized by forming a protective coating of calcium carbonate to suppress corrosion . Water treatment method of the open circulation type cooling water system according to claim 1, characterized in that the calcium hardness of the circulating cooling water and 100~300mg-CaCO ₃ / L.   The water treatment method for an open circulation type cooling water system according to claim 1 or 2, wherein an alkali metal hydroxide is further added in a range of 20 to 300 mg / L to the circulating cooling water.   Threshold inhibitors include organic phosphonic acids and their salts, phosphinopolycarboxylic acids and their salts, phosphonocarboxylic acids and their salts, maleic polymers and their salts, monoethylenically unsaturated monomers having sulfonic acid groups The open-circulation type cooling according to any one of claims 1 to 3, wherein the cooling is one or more selected from the group consisting of a copolymer of a polymer and (meth) acrylic acid and a salt thereof. Water-based water treatment method. A water treatment agent for use in the open-circulation cooling water system water treatment method according to any one of claims 1 to 4,
A water treatment agent for open circulation type cooling water containing calcium hydroxide and / or calcium oxide and a threshold inhibitor that suppresses crystal growth of calcium carbonate as active ingredients.

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