JP5903953B2 - Iron scale inhibitor and method for preventing steam generator - Google Patents

Description

  The present invention relates to an iron scale inhibitor for preventing generation of iron scale in a water-side can of a steam generator such as a boiler, and an iron scale prevention method using the iron scale inhibitor.

  In boiler water, iron brought from the feed water becomes iron oxide or iron hydroxide, which adheres and accumulates on the inner surface of the boiler tube and causes corrosion, heat transfer failure, and the like. Patent Document 1 discloses that polyacrylamide having a molecular weight of 200 to 100,000 or a partial hydrolyzate thereof and an acrylate polymer having a molecular weight of 300 to 100,000 are used to prevent the iron oxide from adhering to the inner surface of the boiler tube. An iron dispersant for boiler water is disclosed.

  As boiler scale inhibitors, phosphates such as trisodium phosphate, dipotassium phosphate, sodium hexametaphosphate, sodium polyacrylate, and sodium polymethacrylate are widely used. There is a concern about conversion.

  Sodium carboxymethylcellulose 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. In many cases, such sodium carboxymethylcellulose alone is not sufficient in the scale inhibiting effect. Therefore, Patent Document 2 discloses a scale inhibitor that uses carboxymethyl cellulose and an organic acid such as gluconic acid or glucoheptonic acid in combination. Patent Document 3 describes a scale inhibitor containing carboxymethyl cellulose or a salt thereof having a carboxymethyl group substitution degree of 1.0 or more.

  In Patent Document 4, when the total concentration of calcium and magnesium in the water supply is X mg / L as a calcium carbonate conversion value and the concentration factor is Y times, the product of X and Y is operated to be 30 or less. And a scale inhibitor containing carboxymethylcellulose or a salt thereof.

JP-A-62-144741 Japanese Examined Patent Publication No. 6-75714 JP 2007-144369 A JP 2010-221198 A

  An object of the present invention is to improve the iron scale dispersing action of an iron scale inhibitor containing a water-soluble polymer compound having a carboxyl group such as carboxymethyl cellulose. Moreover, an object of this invention is to provide the iron scale prevention method using this iron scale inhibitor.

  In the iron scale inhibitor of the present invention, a water-soluble polymer having a carboxyl group, a water-soluble calcium salt, and a stabilizer composed of at least one of gluconic acid, gluconate, glucoheptonic acid and glucoheptonic acid are dissolved. It consists of an aqueous solution.

  The iron scale prevention method of this invention adds this iron scale prevention agent in the water side can of a steam generator, or its water supply.

  As described in Patent Document 2, when carboxymethyl cellulose (CMC) is added to boiler feed water, the amount of iron scale deposited decreases due to the dispersion action, and the amount of iron scale attached to the inner surface of the boiler pipe decreases. And the amount of iron scale discharged | emitted out of a boiler with a blow increases.

  As a result of repeated research by the present inventors, when not only water-soluble polymers having a carboxyl group such as CMC but also calcium salts are added to boiler feed water, iron compounds brought from the feed water are probably due to the action of calcium ions. It has been found that tempering (for example, improved crystallinity) further reduces the adhesion of iron scale to the inner surface of boiler tubes.

  Calcium ions are a hardness component of boiler water, and it is predicted that adding calcium salt to boiler water will increase the amount of scale generated, so the effect of preventing iron scale adhesion by adding calcium salt is not predicted at all. By the way.

  If this calcium salt and CMC are made into one aqueous solution (so-called single agent), the addition work to the boiler water system becomes simple. However, simply coexisting calcium salt with CMC or the like causes calcium ions and CMC or the like to bind and gel, making it unsuitable to be added to the boiler water system as an iron scale inhibitor. Boiler chemicals are generally alkaline, and calcium is precipitated and precipitated as calcium hydroxide and calcium carbonate.

  As a result of further research by the inventor, when a water-soluble polymer having a carboxyl group such as CMC, a water-soluble calcium salt, and gluconic acid and / or glucoheptonic acid or a salt thereof coexist, calcium ions and carboxyl groups It has been found that the gelation reaction with a water-soluble polymer having water and precipitation of calcium under alkaline conditions are prevented, and the water-soluble polymer and calcium salt remain stably dissolved. The present invention is based on such knowledge.

  In the iron scale inhibitor of the present invention, a water-soluble polymer having a carboxyl group and a calcium salt are stably dissolved by the action of a stabilizer in an alkaline solution, and when added to a boiler water system or the like, Iron scale that is difficult to adhere and deposit is generated by the action of the functional polymer, and calcium ions act on this to make the iron scale less adherent and depositable. The iron scale adheres to and deposits on the inner surface of the boiler tube. Is further suppressed.

  The iron scale inhibitor of the present invention is an agent composed of an aqueous solution in which the water-soluble polymer and the calcium salt are stably dissolved, so that it can be easily added to an aqueous system. In addition, material management such as purchase and stockpiling of iron scale inhibitors becomes easy.

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

  The iron scale inhibitor of the present invention comprises an aqueous solution in which a water-soluble polymer having a carboxyl group, a water-soluble calcium salt, and a stabilizer such as gluconic acid are dissolved.

<Water-soluble polymer having carboxyl group>
As the water-soluble polymer having a carboxyl group, in addition to carboxymethylcellulose (CMC), polyacrylic acid and / or a salt thereof, polymaleic acid and / or a salt thereof, polyitaconic acid and / or a salt thereof, polymethacrylic acid and / or a component thereof Examples thereof include a salt and a copolymer or a terpolymer obtained by copolymerizing at least two types of monomer components constituting these homopolymers.

  In addition, at least one monomer component (acrylic acid (AA), maleic acid (MA), etc.) constituting the homopolymer, sodium 3-allyloxy-2-hydroxypropanesulfonate (HAPS) or 2-acrylamide-2 -Copolymers with sodium methylpropanesulfonate (AMPS) (AA-HAPS, AA-AMPS, etc.) and bis (poly-2-carboxyethyl) phosphinic acid and / or its salts are also mentioned.

  In addition, the carboxyl group of carboxymethylcellulose may be —COOH or —COONa. That is, the carboxymethyl cellulose may be sodium carboxymethyl cellulose. The degree of substitution of the carboxymethyl group of carboxymethyl cellulose is not particularly limited.

  The weight average molecular weight of the water-soluble polymer having a carboxyl group is preferably about 1,000 (1,000) to 100,000, particularly about 2000 to 70,000.

<Water-soluble calcium salt>
As the water-soluble calcium salt, those having high solubility such as calcium chloride, calcium nitrate, calcium lactate and the like are suitable.

<Stabilizer>
As the stabilizer, gluconic acid, gluconate, glucoheptonic acid, glucoheptonic acid salt is used, and gluconic acid or gluconate is particularly preferable. As the salt, sodium salt, potassium salt and the like are suitable.

<Combination ratio>
The iron scale inhibitor of the present invention comprises an aqueous solution of a water-soluble polymer, a calcium salt and a stabilizer. The concentration of the aqueous solution constituting the iron scale inhibitor is not particularly limited as long as each dissolved component does not precipitate and the viscosity is easy to handle.

  The water-soluble polymer in the iron scale inhibitor may be about 0.1 to 100 g / L, particularly about 0.5 to 70 g / L in consideration of the viscosity of the iron scale inhibitor.

The ratio of the water-soluble polymer to the calcium salt is such that the ratio P / C of the content (weight) P of the water-soluble polymer to the content (weight) C of calcium salt in terms of CaCO ₃ is 0.5 to 10. It is preferable that it is the range which becomes about ~ 5.

The content (weight) of the stabilizer is preferably 9 to 130 times, particularly 20 to 120 times, especially 30 to 100 times the content (weight) of the CaCO ₃ equivalent calcium salt.

<PH of iron scale inhibitor>
In order to prevent corrosion of the piping and suppress slime, the pH of the iron scale inhibitor is preferably 9 or more and less than 15, particularly 10 or less and less than 15, particularly about 12 to 14.5. The pH of the iron scale inhibitor is preferably adjusted to the above range with sodium hydroxide or potassium hydroxide.

<Other ingredients>
The iron scale inhibitor of the present invention includes amine-based anticorrosive agents such as neutralizing amines and film-forming amines, succinic acid, sodium succinate, citric acid, citrate, tartaric acid, tartrate, malic acid, malate, etc. Corrosion inhibitors, chelating agents such as EDTA, oxygen scavengers such as hydrazine and tannin, phosphates and the like.

<Amount of iron scale inhibitor added to water>
The iron scale inhibitor of the present invention is added to the water retained in steam generation equipment such as a boiler or its water supply. When an iron scale inhibitor is added to the water supply, the amount of calcium salt added is 0.3 to 10 times, especially 0.5 to 7 times, especially 1 to 5 times, as CaCO ₃ equivalent weight, relative to the amount of iron (weight) in the water supply. It is preferable to add so that it becomes.

  In this way, by adding the iron scale inhibitor of the present invention to the aqueous system, the iron scale dispersing action of the water-soluble polymer and the iron scale adhesion / deposition reducing action by the calcium salt are superimposed, so that the iron scale Adhesion / deposition on the inner surface of the boiler tube is suppressed.

  Although this iron scale inhibitor contains a calcium salt, precipitation of a gel-like substance is prevented by the action of gluconic acid or glucoheptonic acid or a salt thereof. Calcium ions generated from the calcium salt added to the aqueous system are dispersed by the polymer, or combined with the iron scale and discharged out of the system together with the blow water, so that the calcium concentration in the boiler water does not increase excessively. .

  Hereinafter, examples and comparative examples will be described.

  The following agents were used in the following examples and comparative examples.

Water-soluble polymer: Carboxymethylcellulose (hereinafter referred to as CMC; manufactured by Daicel)
Polyacrylic acid (hereinafter referred to as PAA; manufactured by Nippon Shokubai Co., Ltd.)
Weight average molecular weight 4000)
Acrylic acid and 2-acrylamido-2-methylpropanesulfonic acid
Copolymer with sodium (hereinafter referred to as AA-AMPS. BWA)
Made. Weight average molecular weight 10,000)

  As stabilizers, sodium gluconate, gluconic acid, sodium glucoheptonate, and glucoheptonic acid were used in the examples, and citric acid, succinic acid, or tartaric acid was used in the comparative examples.

  Further, potassium hydroxide having a concentration of 48% by weight was used as the alkali.

[Comparative Examples 1-6]
When the chemical | medical agent was melt | dissolved in the pure water of 40 degreeC in the ratio of Table 1, a white deposit produced | generated immediately after melt | dissolution, there was no stability, and it was recognized that it is unsuitable as an iron scale inhibitor.

[Examples 1-7]
The drug was dissolved in 40 ° C. pure water at the blending ratio shown in Table 2, and then allowed to cool, followed by observation at room temperature for XX days. That is, it was recognized that the addition of gluconic acid, glucoheptonic acid or a salt thereof prevents white turbidity and precipitation of gelled substances.

  Then, each iron scale inhibitor was added to the feed water of the test boiler as follows, and the scale prevention effect was tested.

  That is, ferric chloride was added to the softened treated water (silica: 25 mg / L, M alkalinity: 30 mg / L) of Nogi-cho, Tochigi Prefecture so that the Fe concentration of the feed water would be 3 mg / L. A water supply was prepared. To this water supply, the iron scale inhibitors of Examples 1 to 8 were added so that the addition amount of the water-soluble polymer was 6.0 mg / L as the water-soluble polymer solid content. Using a stainless steel test boiler tester with a capacity of 5 L, the operation was performed for 48 hours under the conditions of a pressure of 0.7 MPa, an evaporation amount of 8 L / h, and a concentration factor of 10 times (10% blow).

After completion of the test, the heat transfer tube (made of stainless steel, three surface areas of 200 cm ² ) was taken out, the surface of the heat transfer tube was washed with an aqueous HCl solution to which an anticorrosive agent was added, the iron concentration in the washing solution was measured, and the amount of scale adhered was determined. . The results are shown in Table 2.

[Comparative Example 7]
For comparison, the same test was conducted for the case where no iron scale inhibitor was added to the boiler feed water, and the amount of scale adhered was 110 mg.

[Comparative Example 8]
In Comparative Example 7, when the same test was conducted except that only CMC was added to the boiler water as a solid content of 6.0 mg / L in the same manner as in the Example, the scale adhesion amount was 70 mg.

[Comparative Example 9]
A test was conducted in the same manner as in Comparative Example 8 except that sodium gluconate was added in the same amount as in Example 2 together with CMC. As a result, the scale adhesion amount was 60 mg.

  As is clear from Examples 1 to 8 and Comparative Examples 7 to 9, not only CMC but also calcium salt is added to boiler feed water, and a stabilizer is added to the iron scale inhibitor together with calcium salt. It was confirmed that the amount of scale adhered was significantly reduced as compared with the case where only CMC was added. Moreover, it was confirmed that the iron scale inhibitor is stable and white precipitation and precipitation of gel-like substances are also prevented.

Claims (11)

A water-soluble polymer having a carboxyl group;
Water-soluble calcium salt,
An iron scale inhibitor comprising an aqueous solution in which a stabilizer comprising at least one of gluconic acid, gluconate, glucoheptonic acid and glucoheptonic acid is dissolved. The water-soluble polymer having a carboxyl group according to claim 1,
Carboxymethylcellulose;
(Meth) acrylic acid, (meth) acrylate, maleic acid, maleate, itaconic acid, a polymer obtained by polymerizing or copolymerizing at least one monomer of itaconic acid salt; and at least one of the monomers Copolymer with sodium 3-allyloxy-2-hydroxypropanesulfonate or sodium 2-acrylamido-2-methylpropanesulfonate;
An iron scale inhibitor characterized by comprising at least one of the following.   The iron scale inhibitor according to claim 1, wherein the water-soluble polymer having a carboxyl group is carboxymethylcellulose.   The iron scale inhibitor according to claim 2 or 3, wherein the water-soluble polymer has a weight average molecular weight of 1,000 or more and 100,000 or less.   The iron scale inhibitor according to any one of claims 1 to 4, wherein the water-soluble calcium salt is at least one of calcium chloride, calcium nitrate, and calcium lactate. 6. The iron scale inhibitor according to claim 5, wherein the content (weight) of the water-soluble polymer is 0.5 to 10 times the content (weight) of the calcium salt in terms of CaCO ₃ .   The iron scale inhibitor according to any one of claims 1 to 6, wherein the stabilizer is gluconic acid and / or gluconate. 8. The iron scale inhibitor according to claim 7, wherein the content (weight) of the stabilizer is 9 to 130 times the content (weight) of the calcium salt in terms of CaCO ₃ .   The iron scale inhibitor according to any one of claims 1 to 8, wherein the iron scale inhibitor has a pH of 9 or more and less than 15 by containing an alkali hydroxide.   A method for preventing iron scale in a steam generator, wherein the iron scale inhibitor according to any one of claims 1 to 9 is added to a water-side can of the steam generator or to its water supply. Steam generation according to claim 10, wherein the iron scale inhibitor is added so that the CaCO ₃ equivalent addition amount (weight) of the calcium salt is 0.3 to 10 times the amount of iron brought in from the water supply. To prevent the iron scale in the vessel.