JP5531430B2 - Scale inhibitor and scale control method - Google Patents

Description

  The present invention relates to an aqueous scale inhibitor and a method for suppressing scale.

  With recent energy savings and cost savings, various water systems such as boiler water systems, cooling water systems, and exhaust gas dust collection water systems are desired to save water consumption. Therefore, the amount of water blown out of the system is reduced and concentrated. There are many water systems to operate.

  In such an aqueous system, scale components such as calcium and magnesium also become high in concentration, precipitate as scaled, causing a decrease in thermal efficiency, clogging, and the like. In particular, in boiler water systems, scale components such as calcium and magnesium brought into the boiler can scale on the heat transfer surface with high heat load and adhere to the heat transfer surface, causing heat transfer obstruction and causing overheating of the steel material. It causes expansion, curvature, rupture and reduced thermal efficiency.

  In a water system such as a boiler water system that is operated for concentration, as a method of suppressing such scale troubles, raw water such as city water or groundwater is treated using a water softener or a reverse osmosis membrane separator, and calcium, magnesium, etc. It is known to supply water to an aqueous system after setting the hardness component of the water to a very low concentration.

  However, even when water with low hardness is supplied to the boiler using a water softener or reverse osmosis membrane separation device, scale may be generated when the concentration operation is performed as described above. In such a case, it is necessary to suppress the adhesion of the scale component brought into the aqueous system into the system by using a scale inhibitor, and to discharge it outside the system by blowing.

  Conventionally, as scale inhibitors, those using phosphates such as trisodium phosphate, dipotassium phosphate and sodium hexametaphosphate, and those using low molecular weight sodium polyacrylate and polymethacrylate ( Patent documents 1 to 3) are widely adopted.

  However, the above-described scale suppression method has the following problems.

  First, when phosphate is used as a scale inhibitor, boiler water containing phosphorus is discharged in large quantities as waste water. Here, in the closed water areas of Tokyo Bay, Ise Bay, and Seto Inland Sea, nitrogen and phosphorus, which are eutrophication-causing substances, were added as emission control targets due to the fifth water quality control established in 2001. Regulations on phosphorus emissions are becoming stricter.

  For this reason, phosphorus contained in wastewater needs to be discharged after being treated below the discharge standard in wastewater treatment, which may cause a load on the wastewater treatment facility or increase the wastewater treatment facility. . Therefore, there is a strong demand for a technique that can suppress scale while using a scale inhibitor that does not contain phosphorus. This requirement is not limited to the boiler water system, and the same applies to the cooling water system.

  In recent years, due to the increasing social demand for safety, there has been a growing demand for the development of scale inhibitors composed of ingredients that meet the standards for food additives. On the other hand, sodium polyacrylate generally used as a scale inhibitor has a molecular weight as low as several thousand to several tens of thousands and a degree of polymerization of 1000 or less, and therefore does not satisfy the standards for food additives. Therefore, it is also conceivable to use carboxymethylcellulose or a salt thereof as such a component (Patent Document 4).

JP-A 63-166980 Japanese Unexamined Patent Publication No. 63-166981 Japanese Unexamined Patent Publication No. 63-166982 JP 2007-144369 A

  However, the scale inhibitor shown in Patent Document 4 has an essential requirement that the degree of substitution of the carboxymethyl group of carboxymethyl cellulose is high, but carboxymethyl cellulose having a high degree of substitution of carboxymethyl group has many special uses, Since the circulation amount is small, it is expensive. In addition, since there are few types, it is difficult to obtain physical properties suitable for formulation and products with high standards (high viscosity, difficulty in commercialization, only industrial grade, not food additives, etc.). For this reason, the scale inhibitor which has a favorable scale inhibitory effect regardless of the substitution degree of the carboxymethyl group of carboxymethylcellulose is desired.

  The present invention has been made in view of the above circumstances, and a scale inhibitor and a scale inhibition method capable of exhibiting a good scale inhibitory effect while using carboxymethylcellulose or a salt thereof having a wide degree of substitution of carboxymethyl groups. The purpose is to provide.

  In the water system in which the total concentration of calcium and magnesium in the water supply is X mg / L as a calcium carbonate equivalent, the concentration factor is Y, and the product of X and Y is 30 or less, The inventors have found that a good scale inhibitory effect can be obtained regardless of the degree of substitution of the carboxymethyl group of the carboxymethylcellulose or a salt thereof contained in the scale inhibitor, and have completed the present invention. Specifically, the present invention provides the following.

(1) When the total concentration of calcium and magnesium in the feed water is X mg / L as calcium carbonate equivalent, and the concentration factor is Y times, the water system is operated so that the product of X and Y is 30 or less. A scale inhibitor comprising carboxymethyl cellulose or a salt thereof, which is substantially free of phosphates and has a carboxymethyl group substitution degree of 0.6 to 0.9 .

(2) Calcium in water at a site where scales are desired to be suppressed with a scale inhibitor containing carboxymethyl cellulose or a salt thereof substantially free of phosphates and having a carboxymethyl group substitution degree of 0.6 to 0.9. And a method for suppressing scale added to an aqueous system in which the total concentration of magnesium is 30 mg / L or less in terms of calcium carbonate.

  (3) The water system is operated so that the product of X and Y is 30 or less when the total concentration of calcium and magnesium in the feed water is X mg / L as calcium carbonate equivalent and the concentration factor is Y times. The scale suppression method according to (2).

(4) addition of the scale inhibitor, as the concentration carboxymethylcellulose converted value at the portion to be suppressed scale in an aqueous system, 20-fold concentration (mg / L) of the product of the values of X and Y and so as (3) The scale suppression method according to (3).

  Here, in the specification and claims of the present application, “scale suppression” means to suppress the generation of scale due to precipitation of substances mainly composed of calcium salts and / or magnesium salts in an aqueous system, and It means that the growth of the scale due to the precipitation of calcium salts and / or magnesium salts on the scale existing in is suppressed.

  According to the present invention, since the total concentration of calcium and magnesium in water at a site where scales are to be suppressed is added to an aqueous system having a calcium carbonate equivalent of 30 mg / L or less, carboxymethylcellulose or a salt thereof used as a scale suppression component Regardless of the degree of substitution of the carboxymethyl group, the scale can be satisfactorily suppressed.

  Hereinafter, although one embodiment of the present invention is described, the present invention is not limited to this.

[Scale inhibitor]
The scale inhibitor according to the present invention is an aqueous system in which the total concentration of calcium and magnesium in the feed water is X mg / L as a calcium carbonate equivalent, the concentration factor is Y, and the product of X and Y is 30 or less. Is added to suppress the scale well.

  The product (X × Y) of the calcium carbonate equivalent value X (mg / L) of the total concentration of calcium and magnesium in the water supply and the value of the aqueous concentration rate Y (times) is preferably 30 or less, and 15 or less. It is more preferable that it is 10 or less. When the value of X × Y exceeds 30, when the degree of substitution of the carboxymethyl cellulose or the salt thereof used as the scale inhibiting component is low, a sufficient scale inhibiting effect may not be obtained.

  The values of X and Y are not particularly limited as long as the product of X and Y is 30 or less. In general, the calcium carbonate equivalent value X of the total concentration of calcium and magnesium in the feed water is 1 mg / L in consideration of the feed water quality of the low pressure soft water feed boiler (P4 special circulation boiler, P5 water pipe boiler, etc.) of JISB8223: 2006. It is preferable that: The aqueous concentration ratio Y is preferably 30 times or less, and more preferably 15 times or less. If the concentration rate is too high, there is a possibility that the concentration of the components in the system may be shaded, and there may be a place where the product of X and Y substantially exceeds 30.

  In the aqueous system using the scale inhibitor of the present invention, the calcium carbonate equivalent X (mg / L) and the concentration factor Y (times) are constant during the operation of the aqueous system as long as the product of X and Y is 30 or less. Or may vary. However, it is preferable that the X and Y values are operated under constant conditions in that a stable scale suppression effect can be obtained. Note that there may be a condition in which the product of X and Y temporarily exceeds 30 as long as the time does not adversely affect the scale suppression.

  Specific examples of the water system in which the scale inhibitor of the present invention is used include a boiler water system, a cooling water system, a dust collection water system, and the like, and a boiler water system is particularly preferable.

  When the water system in which the scale inhibitor is used is a boiler water system, the boiler is not particularly limited, and may be an arbitrary boiler such as a special circulation boiler, a water pipe boiler, a round boiler, or an exhaust heat recovery boiler. In addition, when the pressure of the boiler is excessively high, the scale inhibitor is thermally decomposed and the scale suppressing effect is likely to be lowered, and therefore, it is usually preferably 4.0 MPa or less.

  In the present invention, water of low hardness is supplied to the water system to be subjected to scale suppression. The low-hardness water supply type is not particularly limited, and may be pure water supply, soft water supply, reverse osmosis membrane treated water supply, or the like.

  The form of the scale inhibitor according to the present invention is not particularly limited, and may be liquid (solution or slurry), paste, or solid. The liquid preparation may be prepared, for example, by a method of dissolving or dispersing the components of the scale inhibitor in water, a water-soluble organic solvent such as methanol or ethanol, or an aqueous solution of the water-soluble organic solvent. The pasty preparation may be prepared by, for example, a method of adding a known thickener after preparing a liquid preparation, or a method of dispersing or dissolving the components of the scale inhibitor in a liquid having a water-soluble viscosity. . The solid preparation may be prepared according to a known method using excipients such as prepared lactose, fructose, sucrose, glucose, powdered sugar, dextrin, mannitol, erythritol, xylitol, maltitol, sorbitol, and the like.

(Carboxymethylcellulose or a salt thereof)
The scale inhibitor of the present invention contains carboxymethyl cellulose or a salt thereof.

  The content of carboxymethylcellulose or a salt thereof in the scale inhibitor of the present invention is not particularly limited as long as the object of the present invention is not impaired, and may be appropriately adjusted in consideration of the water quality of the aqueous system.

  In the scale inhibitor of the present invention, the concentration of carboxymethyl cellulose or a salt thereof at a site where scales in the aqueous system are to be suppressed is preferably 1 to 20 times the product of X and Y, in terms of carboxymethyl cellulose (mg / L), more preferably in an amount such that the concentration is 2 to 10 times the product of X and Y (mg / L).

  Carboxymethylcellulose or a salt thereof employed as a scale inhibitor in the present invention introduces a carboxymethyl group by reacting cellulose with heating in the presence of an amount of monochloroacetic acid or the like that provides an appropriate degree of substitution. Obtained.

  In the present specification, the degree of substitution of the carboxymethyl group is defined as follows.

  One unit of anhydroglucose has three OH groups. Of these three OH groups, the number of carboxymethyl groups substituted is defined as the degree of substitution of carboxymethyl groups. Accordingly, the degree of substitution theoretically takes a numerical value of 0 to 3.

  In an aqueous system that satisfies the above-described conditions, carboxymethyl cellulose or a salt thereof exhibits excellent scale inhibiting ability regardless of the degree of substitution of the carboxymethyl group. For this reason, the substitution degree in this invention can be suitably selected from wide arbitrary values. However, carboxymethyl cellulose having a substitution degree of 0.6 to 1.6 or a salt thereof is generally commercially available and is preferable in terms of easy availability. Further, sodium carboxymethylcellulose having a carboxymethyl group substitution degree of 0.6 to 0.9 is more preferable because safety is established as an additive for boilers of the US Food and Drug Administration (FDA).

  The salt of carboxymethyl cellulose is preferably a sodium salt, potassium salt, ammonium salt or the like, and particularly a sodium salt is preferable because safety is established as a food additive.

(Other ingredients)
The scale inhibitor of the present invention can exhibit a high scale inhibitory effect without using phosphates. For this reason, it is preferable that the scale inhibitor of the present invention does not substantially contain phosphates such as trisodium phosphate, dipotassium phosphate, and sodium hexametaphosphate, which are subject to wastewater regulation. “Substantially not containing” includes not only containing it at all, but also containing a small amount inevitably mixed in, or containing an amount within an allowable limit for detour purposes.

  Furthermore, the scale inhibitor of the present invention may contain a pH adjuster, an anticorrosive, an oxygen scavenger and the like as long as the object of the present invention is not impaired.

  Examples of the pH adjuster suitably used for the scale inhibitor of the present invention include sodium hydroxide, potassium hydroxide, aqueous ammonia, alkanolamines such as monoethanolamine and tripropanolamine, methylamine, isopropylamine and the like. Examples include alkylamine and morpholine.

  Examples of the anticorrosive agent suitably used for the scale inhibitor of the present invention include compounds such as oxycarboxylic acid and salts thereof, succinic acid, thiazoles, triazoles, amines, and hydroxamic acid.

  Examples of oxygen scavengers suitably used for the scale inhibitor of the present invention include sulfurous acid, ascorbic acid, erythorbic acid, tannic acid, or salts thereof, azodicarbonamide, 1-aminopiperazine, 1-aminopyrrolidine, 1-amino. Examples include -4-methylpiperazine and carbazic acid esters.

[Scale suppression method]
The aqueous scale suppression method according to the present invention includes a step of adding carboxymethyl cellulose or a salt thereof to an aqueous system in which the total concentration of calcium and magnesium in water at a site where scales are to be suppressed is 30 mg / L or less as a calcium carbonate equivalent value. Have.

  In such an aqueous system, it is preferable that the calcium carbonate equivalent value of the total concentration of calcium and magnesium in the water at the site where the scale is to be suppressed is always 30 mg / L or less during the operation of the aqueous system. However, even in an aqueous system in which the calcium carbonate conversion value of the total concentration of calcium and magnesium exceeds 30 mg / L during stable operation, there is a period of 30 mg / L or less (for example, immediately after the start of the aqueous concentration operation). The method of the present invention can be performed at least during that period.

  The scale suppression method of the present invention is an aqueous system in which the total concentration of calcium and magnesium in the feed water is X mg / L as a calcium carbonate conversion value, the concentration factor is Y, and the product of X and Y is 30 or less. Applying this method is preferable in that a stable scale inhibitory effect is obtained, and there is no need to change the scale inhibitor according to the water quality and the operating conditions of the aqueous system.

  When using a pH adjuster, anticorrosive, oxygen scavenger, etc. in addition to carboxymethylcellulose or a salt thereof, one prepared in advance as the aforementioned scale inhibitor may be added to the aqueous system. Each of the ingredients mentioned may be added individually. The method of adding what was previously prepared as a scale inhibitor is preferable in that the components to be added to the aqueous system can be separately stored and distributed, or the complexity of mixing operations at the site of use can be eliminated.

  The addition location of carboxymethylcellulose or its salt and other components in the aqueous system is not particularly limited as long as the components added by circulation of water in the aqueous system have a substantially uniform concentration, and any location in the aqueous system. Often, it is usually at or upstream of where the scale should be suppressed.

  The concentration of carboxymethyl cellulose or a salt thereof at a site where the scale in the aqueous system is to be suppressed is 1 to 20 times the product of X and Y as a carboxymethyl cellulose equivalent (mg / L). More preferably, it is added to the aqueous system in such an amount that the concentration (mg / L) is 2 to 10 times the value of the product of X and Y. If the amount added is too small, the effect of suppressing the scale is not clear, and if it is too large, it is disadvantageous in terms of cost effectiveness. The concentration of carboxymethylcellulose or its salt at the site where scale is to be suppressed is calculated based on the amount of water held at the site where scale is to be suppressed and the supply and discharge of carboxymethylcellulose or its salt to the site where scale is to be suppressed. it can.

  The addition method of carboxymethylcellulose or a salt thereof is not particularly limited, and a predetermined amount may be added before the start of the aqueous system operation. As the aqueous system operation starts, water supply or scale to the aqueous system is continuously or intermittently performed. You may add to the site | part which wants to suppress. When carboxymethyl cellulose or a salt thereof is added to the water supply to the aqueous system, the addition amount may be determined in consideration of the concentration ratio in the aqueous operation. When the concentration of carboxymethyl cellulose or a salt thereof at a site where the scale is desired to be suppressed is higher than a desired concentration, a portion of the water enriched with carboxymethyl cellulose or a salt thereof is discharged out of the aqueous system and carboxymethyl cellulose or a salt thereof. What is necessary is just to adjust the density.

  In addition, since the detail of the component added to an aqueous system is the same as that of what was described by the scale inhibitor, it abbreviate | omits.

  According to the method of the present invention, scale can be suppressed in various water systems such as a boiler water system, a cooling water system, and a dust collecting water system by containing carboxymethyl cellulose or a salt thereof in the water system.

  Hereinafter, the present invention will be further described with reference to specific examples, but the present invention is not limited thereto.

[Examples 1-2, Reference Examples 3-4 , Comparative Examples 1-4]
A small once-through boiler was operated under the conditions shown in Table 1 to generate steam.

As a scale inhibitor, sodium carboxymethylcellulose, polyacrylic acid, acrylic acid / 2-acrylamido-2-methylpropanesulfonic acid copolymer, or acrylic acid / 2-hydroxy-3-allyloxy-1-propanesulfonic acid listed in Table 2 using the copolymer.

  Addition of a scale inhibitor at a concentration of 5 mg / L to water supply consisting of soft water substantially free of calcium and magnesium obtained by softening city water with an ion exchange resin increases the concentration sufficiently. The operation was continued until the concentration of the scale inhibitor in the can reached a steady state. After the operation is in a steady state, the scale inhibitor is continuously supplied from the feed water at a concentration of 5 mg / L, and the scale inhibitor corresponding to the supply amount from the feed water is purged outside the boiler water system. The boiler was operated so that the concentration of the scale inhibitor was stabilized at a concentration of about 50 mg / L.

  After boiler operation was in a steady state, the addition of scale components to the feed water was started. The addition concentration of the scale component was 1 mg / L as a calcium carbonate equivalent (0.67 mg / L as calcium carbonate equivalent, and 0.33 mg / L as magnesium carbonate equivalent). Of the scale components, the calcium component was added as an aqueous calcium chloride solution, and the magnesium component was added as an aqueous magnesium sulfate solution.

  After 180 hours from the start of the addition of the scale component, the operation of the boiler was stopped, the adhered scale component was dissolved with a chelating agent (EDTA), and the amount of the adhered scale was measured from the concentration of the scale component in the solution. . The calcium and magnesium concentrations in the lysate were analyzed by flame atomic absorption after diluting the lysate. Moreover, the addition amount of the scale component was calculated from the amounts of the added calcium chloride aqueous solution and magnesium sulfate aqueous solution. Table 2 shows the amount of scale adhesion, the amount of scale component added, and the scale inhibition rate calculated from the amount of scale component added and the amount of scale adhesion in each Example and Comparative Example.

In Table 2, scale inhibitors A to G represent the following.
A: Carboxymethyl cellulose sodium with a substitution degree of carboxymethyl group 0.65 B: Carboxymethyl cellulose sodium with a substitution degree 0.88 of carboxymethyl group C: Carboxymethyl cellulose sodium with a substitution degree 1.29 of carboxymethyl group D: Carboxymethyl group Sodium carboxymethylcellulose having a substitution degree of 1.50: E: polyacrylic acid F: acrylic acid / 2-acrylamido-2-methylpropanesulfonic acid copolymer G: acrylic acid / 2-hydroxy-3-allyloxy-1-propanesulfonic acid copolymer Polymer copolymer

In Examples 1 and 2 and Reference Examples 3 and 4, both the calcium-based scale and the magnesium-based scale were significantly higher than Comparative Examples 1 to 4. Thereby, it was confirmed that scale can be suppressed satisfactorily while using sodium carboxymethylcellulose as a scale inhibitor.

In particular, in Examples 1 and 2 and Reference Examples 3 and 4, the suppression rate of the magnesium-based scale was significantly higher than those in Comparative Examples 2-4. Thereby, it was also confirmed that magnesium-based scale can be particularly favorably suppressed by using sodium carboxymethylcellulose.

Moreover, there was no big difference in the suppression rate of any of calcium-based scale and magnesium-based scale between Examples 1 and 2 and Reference Examples 3 and 4. As a result, in a low hardness aqueous system such that the total concentration of calcium and magnesium in water at a site where scale suppression is desired is 30 mg / L or less in terms of calcium carbonate, carboxymethylcellulose sodium is used regardless of the degree of substitution of carboxymethyl groups. Thus, it was confirmed that excellent scale suppression ability can be exhibited.

Example 5
The amount of scale component added to the water supply is 2.5 mg / L as calcium carbonate equivalent (calcium is 1.68 mg / L as calcium carbonate equivalent, and magnesium is 0.82 mg / L as calcium carbonate equivalent), And the test was conducted using the scale inhibitors listed in Table 3 in the same manner as in Example 1 except that the test time was 72 hours from the start of the addition of the scale component to the water supply. Table 3 shows the amount of scale adhesion, the amount of scale component added, and the scale inhibition rate calculated from the amount of scale component addition and the amount of scale adhesion in Example 5.

[Comparative Example 5]
The amount of scale component added to the water supply is 5.0 mg / L as a calcium carbonate equivalent (3.35 mg / L as calcium carbonate equivalent, 1.65 mg / L as magnesium carbonate equivalent), The test was conducted using the scale inhibitors listed in Table 3 in the same manner as in Example 1 except that the test time was 36 hours from the start of the addition of the scale component to the water supply. Table 3 shows the amount of scale adhesion, the amount of scale component added, and the scale inhibition rate calculated from the amount of scale component addition and the amount of scale adhesion in Comparative Example 5.

Implementation in which the product of the calcium carbonate conversion value of the total concentration of calcium and magnesium in the feed water and the concentration rate of the boiler is 30 or less by comparing the scale suppression rate of the feed water of Example 2 and Example 5 and Comparative Example 5 In the conditions of Example 2 and Example 5, the scale is satisfactorily suppressed using sodium carboxymethylcellulose having a substitution degree of 0.89. However, in the condition of Comparative Example 1 in which the product value exceeds 30, the calcium-based scale is suppressed. It was confirmed that the rate dropped significantly.

Claims (4)

When the total concentration of calcium and magnesium in the water supply is X mg / L as calcium carbonate equivalent, and the concentration factor is Y times, it is used for an aqueous system operated so that the product of X and Y is 30 or less, The scale inhibitor which does not contain phosphates substantially, and contains the carboxymethylcellulose whose substitution degree of a carboxymethyl group is 0.6-0.9, or its salt. A scale inhibitor containing carboxymethyl cellulose or a salt thereof substantially free of phosphates and having a carboxymethyl group substitution degree of 0.6 to 0.9 The scale suppression method added to the aqueous system whose total density | concentration is 30 mg / L or less as a calcium carbonate conversion value.   The water system is operated so that the product of X and Y is 30 or less when the total concentration of calcium and magnesium in the feed water is X mg / L as calcium carbonate equivalent and the concentration factor is Y times. Item 3. The scale suppression method according to Item 2. Claims the addition of the scale inhibitor, as the concentration carboxymethylcellulose converted value at the portion to be suppressed scale in aqueous, performed so that 1 to 20 times the concentration of the value of the product of X and Y (mg / L) Item 4. The scale suppression method according to Item 3.