JP2007144369A - Scale inhibiting agent and method for water system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a scale inhibiting agent which has high scale inhibiting effect in a water system, especially a boiler water system, without using phosphates, and has high safety, and a method for employing the agent. <P>SOLUTION: The scale inhibiting agent contains carboxymethylcellulose with a substitution degree of a carboxymethyl group of ≥1.0, or its salt, and a scale inhibiting method employs the agent. By specifying the substitution degree, the carboxymethylcellulose or its salt exhibits an excellent scale inhibiting effect. As sodium carboxymethylcellulose is approved as a food additive, it can respond to a request for higher safety. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an aqueous scale inhibitor and a method for suppressing scale. In particular, the present invention relates to a scale inhibitor and a scale suppression method that are suitable for boilers and have excellent safety.

With recent energy saving and cost saving, cooling water system, boiler water system, exhaust gas dust collection water system, etc.
In various aqueous systems, it is desired to save the amount of water used. Therefore, there are many aqueous systems that operate with high concentration by reducing the amount of water blown out of the system.

In such an aqueous system, scale components such as calcium and magnesium in the water also have a high concentration, and are scaled and deposited, causing a decrease in thermal efficiency and blockage. Especially in the boiler water system, scale components such as calcium, magnesium and iron 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 inhibition,
It causes expansion, bending, rupture and deterioration of thermal efficiency due to overheating of steel materials.

In order to suppress such scale troubles, it is necessary to perform treatment using a scale inhibitor to suppress the adhesion of the scale components brought into the water system into the system and to discharge it outside the system by blowing.

Therefore, conventionally, for example, a method of adding a phosphate such as trisodium phosphate, dipotassium phosphate or sodium hexametaphosphate or a polymer such as sodium polyacrylate or sodium polymethacrylate as a scale inhibitor has been widely adopted. Yes.

On the other hand, sodium carboxymethyl cellulose has been described as an additive for boilers of the US Food and Drug Administration (FDA) for those having a carboxymethyl group substitution degree of up to 0.9, and has been put into practical use as a scale inhibitor. Such sodium carboxymethylcellulose alone usually does not have a sufficient scale inhibitory effect. For example, JP-B-6-75714 discloses a scale inhibitor used in combination with an organic acid such as gluconic acid or glucoheptonic acid.
Japanese Examined Patent Publication No. 6-75714

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

First, when phosphate is used, boiler water containing phosphorus is discharged in large quantities as waste water.

  Nitrogen and phosphorus, the causative substances of eutrophication, have been added as emission control targets due to the fifth total water quality regulation established in 2001 in closed water areas of Tokyo Bay, Ise Bay and Seto Inland Sea, Regulations on phosphorus emissions are becoming stricter.

For this reason, when phosphate is used, it is necessary to discharge the phosphorus contained in the wastewater after processing it below the discharge standard in the wastewater treatment. In some cases, it is necessary to enhance the scale with a scale inhibitor that does not contain phosphorus or a method that suppresses scale with a drug that does not contain phosphorus. This is not limited to the boiler water system, and the same tendency exists in the cooling water system.

On the other hand, sodium polyacrylate used as a scale inhibitor is approved as a food additive for those having a high degree of polymerization, but those generally used as scale inhibitors have molecular weights of several thousand to several tens of thousands. Since the degree of polymerization is 1000 or less, it does not meet the standards for food additives and is not approved as a food additive.

In recent years, water treatment chemicals composed of food additive materials have been increasingly demanded due to increasing social demand for safety, but as a scale inhibitor, so far, phosphate-based chemicals However, application is greatly limited due to the above problems, and non-phosphorous and highly safe drugs are required.

This invention solves the said subject, and aims at provision of the scale inhibitor which is high in the scale inhibitory effect in a water system, especially a boiler water system, and is also safe, and its usage method, without using a phosphate.

The present invention is the following aqueous scale inhibitor and scale suppression method.
(1) A scale inhibitor containing carboxymethyl cellulose or a salt thereof having a carboxymethyl group substitution degree of 1.0 or more. (2) The aqueous scale inhibitor as described above, wherein the degree of substitution of the carboxymethyl group is 1.1 to 1.6. (3) The aqueous scale inhibitor as described above, which does not contain phosphates as a scale inhibitor. (4) A water-based scale suppression method in which a predetermined amount of a scale inhibitor containing carboxymethyl cellulose having a carboxymethyl group substitution degree of 1.0 or more or a salt thereof is added to the target aqueous system. (5) The degree of substitution of the carboxymethyl group is 1.1 to 1.
6. The water-based scale suppression method according to the above, which is 6. (6) The aqueous scale suppression method according to the above, which does not contain phosphates as a scale inhibitor.

As described above, the scale inhibitor employed in the present invention is an anionic water-soluble polymer mainly composed of cellulose. Therefore, even when carboxymethyl cellulose or a salt thereof is used as a scale inhibitor, it is derived from the scale inhibitor. Phosphorus is not discharged into the wastewater. Further, unlike conventional polymers such as sodium polyacrylate, sodium carboxymethylcellulose is described as a food additive and is safer than before.

  In the present invention, an aqueous system means an aqueous system with scale deposition, such as a cooling water system, a boiler water system, and a dust collection water system.

Carboxymethylcellulose or a salt thereof employed as a scale inhibitor in the present invention is a compound obtained by introducing a carboxymethyl group in an amount that provides an appropriate degree of substitution into cellulose and reacting under heating.

  In the present invention, 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. Therefore, theoretically, a numerical value of 0 to 3 is taken.

  Of these, as described in the background section above, sodium carboxymethylcellulose having a carboxymethyl group substitution degree of up to 0.9 is described as an additive for boilers of the U.S. Food and Drug Administration (FDA). Since it is less effective in use, it is used in combination with phosphates. The present invention was obtained as a result of studying a scale inhibitor effective with carboxymethylcellulose or a salt alone by paying attention to this degree of substitution, and such a study has never been made.

In the present invention, the scale inhibitor includes carboxymethyl cellulose or a salt thereof having a higher degree of substitution of carboxymethyl groups than products described in FDA. That is, it includes carboxymethyl cellulose or a salt thereof having a carboxymethyl group substitution degree of 1.0 or more, preferably 1.1 to 1.6.

In the present invention, a predetermined amount of a scale inhibitor containing carboxymethyl cellulose or a salt thereof having a carboxymethyl group substitution degree of 1.0 or more, preferably 1.1 to 1.6 as described above is added to the target aqueous system. And it is the scale suppression method which suppresses the scale of the said water system.

Examples of the salts include sodium salts, potassium salts, ammonium salts and the like, and sodium salts are particularly preferable because they are described as food additives.

In order to obtain carboxymethyl cellulose having a substitution degree of such a carboxymethyl group or a salt thereof, an amount that gives a predetermined substitution degree may be reacted.

When the degree of substitution of the carboxymethyl group is less than 1.0, the effect of inhibiting the scale by carboxymethylcellulose or its salt alone is deteriorated and it cannot be put into practical use. On the other hand, commercially available carboxymethyl cellulose has a substitution degree in the range of 0.6 to 1.6, and 1
. If the degree of substitution exceeds 6, the circulation amount is small and the cost is high, which is economically disadvantageous.

The scale inhibitor of the present invention exhibits a high scale inhibitory effect without containing phosphate. The scale suppression method of the present invention using the scale inhibitor provides a scale suppression method having a high scale suppression effect without using phosphates.

In using the scale inhibitor of the present invention, carboxymethylcellulose or a salt thereof used in the present invention is used by dissolving in water, but is not limited thereto, and if necessary, a pH adjuster or an anticorrosive, You may mix and use with 1 or more types of well-known chemical | medical agents chosen from an oxygen scavenger.

Examples of such known pH adjusters include sodium hydroxide, potassium hydroxide, aqueous ammonia, alkanolamines such as monoethanolamine and tripropanolamine,
Examples thereof include alkylamines such as methylamine and isopropylamine, and morpholine.

Known anticorrosive agents include compounds such as oxycarboxylic acid and salts thereof, succinic acid, thiazoles, triazoles, amines, and hydroxamic acid.

Similarly, as the oxygen scavenger, sulfurous acid, ascorbic acid, erythorbic acid, tannic acid, or salts thereof, azodicarbonamide, 1-aminopiperazine, 1-aminopyrrolidine, 1-amino-4-methylpiperazine, carbazates, etc. Can be mentioned.

When a boiler water system is selected as the target water system of the present invention, the target boiler is not particularly limited, and can be applied to any boiler such as a special circulation boiler, a water pipe boiler, a round boiler, and a waste heat recovery boiler.

  Even when viewed from the type of water supply, there is no particular limitation such as pure water supply, soft water supply, reverse osmosis membrane treated water supply, and the like.

As the pressure of the applied boiler, the higher the pressure is, the more the scale inhibitor is thermally decomposed and the effect is lowered. Therefore, the use at a pressure of 4.0 MPa or less is usually preferable.

The amount of the scale inhibitor of the present invention added to the target aqueous system is 0.5 gm / l or more, preferably 5 to 500 mg / l as carboxymethylcellulose or a salt thereof.
If the amount is less than 0.5 mg / l, the scale-inhibiting effect is not clear. On the other hand, even if the amount exceeds 500 mg / l, the effect approaches the upper limit, which is disadvantageous in terms of economy.

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

  A small once-through boiler was operated under the conditions shown in Table 1 to generate steam.

Here, polyacrylic acid soda, sodium dihydrogen phosphate (comparative example), and carboxymethyl cellulose sodium salts (examples) having various degrees of substitution of carboxymethyl groups shown in Table 2 were used as scale inhibitors.

As a scale inhibitor, 10 mg / l of polyacrylic acid soda (weight average molecular weight of about 4,000) and disodium hydrogen phosphate as phosphoric acid are used as scale inhibitors for soft water obtained by softening city water with ion-exchange resin. 3.8 mg / l and 10 mg / l of various carboxymethylcellulose sodium salts were added, and the operation was continued until the concentration became 10 times and the concentration of the scale inhibitor in the can reached a steady state. Thereafter, the addition of 10 mg / l calcium carbonate (6.7 mg / l calcium as calcium carbonate and 3.3 mg / l magnesium as calcium carbonate) was started as a scale component in the water supply. In addition, calcium chloride and magnesium sulfate were used. In addition, the same operation was performed when no scale inhibitor was added.

After 18 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. . Moreover, the addition amount of the scale component was calculated from the amounts of added calcium chloride and magnesium sulfate, and the scale adhesion inhibition rate was calculated from the addition amount of the scale component and the adhesion amount of the scale. The results are shown in Table 2.

From Table 2, when no scale inhibitor was added (blank test), the scale adhesion inhibition rate was 37.6%, but in the case of the sodium salts of various carboxymethyl celluloses of the present invention, the degree of substitution of the carboxymethyl group. In the sodium salt of carboxymethyl cellulose having a ≧ 1.0, the scale adhesion inhibition rate exceeds 80%, and it can be seen that it has the same scale inhibition effect as polyacrylic acid soda and phosphate used conventionally. .

The aqueous scale inhibitor and the suppression method provided by the present invention are applied to an aqueous system to which scale may adhere. In particular, in the case of a boiler water system, the present invention can be applied to any boiler such as a round boiler, a water tube boiler, a once-through boiler, and a special boiler. In addition, the drug used is registered as a food additive and is safer.

Claims (6)

A water-based scale inhibitor comprising carboxymethyl cellulose having a carboxymethyl group substitution degree of 1.0 or more or a salt thereof. The aqueous scale inhibitor according to claim 1, wherein the degree of substitution of the carboxymethyl group is 1.1 to 1.6. The aqueous scale inhibitor according to claim 1 or 2, wherein the scale inhibitor does not contain phosphates. An aqueous scale suppression method comprising adding a predetermined amount of a scale inhibitor containing carboxymethyl cellulose or a salt thereof having a carboxymethyl group substitution degree of 1.0 or more to a target aqueous system. The water-based scale suppression method according to claim 4, wherein the degree of substitution of the carboxymethyl group is 1.1 to 1.6. The aqueous scale suppression method according to claim 4 or 5, wherein the scale inhibitor does not contain phosphates.