KR20030043705A - Water treatment agent - Google Patents

Abstract

PURPOSE: To provide a chemical for inhibiting corrosion and scale formation occurring under the influence of water. CONSTITUTION: The water treating agent is a chemical for inhibiting corrosion and scale formation occurring under the influence of water and contains silica, a pH modifier, and an anti-scaling agent.

Description

Water treatment agent

The present invention relates to a water treatment agent for inhibiting the generation of corrosion and scale generated on the heat transfer surface of a boiler system, for example, a boiler water pipe or an economizer water pipe due to the influence of water.

Conventionally, there are three main causes of corrosion of the boiler system: water supply or irrigation water is high in ① dissolved oxygen concentration, ② out of the proper range of pH (11.0 to 11.8), and ③ high concentration of harmful ions such as chloride ions and sulfate ions. There is a point.

First, the method of removing dissolved oxygen is performed using a deaerator or a deoxidizer. As a degassing apparatus, a vacuum degassing apparatus, a heating degassing apparatus, a membrane type degassing apparatus, etc. are mentioned. By degassing using a degasser, the oxygen which is a corrosion factor of a boiler system can be removed reliably. Moreover, hydrazine, a sulfite, etc. are mentioned as a deoxidizer. However, hydrazine has the drawback that the reaction rate is slow, and sulfite increases the corrosive factor.

Subsequently, a method of adjusting the pH to an appropriate range is performed using a pH adjuster. In the case of boiler water supply having a M alkalinity above a certain concentration, a component (mainly hydrogen carbonate) showing M alkalinity is contained in a boiler drum. Pyrolysis can generate the carbonate, hydroxide ions and the like to increase the pH of the irrigation water. In addition, carbonate ions, hydroxide ions and the like, which are nonvolatile components, are also concentrated in the boiler tube to increase the pH. Therefore, when the M alkali component contained in boiler feed water is more than a predetermined concentration, pH can be made into a suitable range, without using a pH adjuster. However, when the M alkalinity is low, the addition of a pH adjuster is necessary.

In addition, the method of making noxious ion below a fixed concentration is performed by blowing water. By controlling the blow, the concentration of harmful ions due to the concentration of the irrigation water is prevented.

Moreover, as a method of preventing corrosion of a boiler system, the method of injecting a film-forming corrosion inhibitor into a feed water is mentioned. The film formation of the corrosion inhibitor prevents the water pipe from directly contacting the irrigation water, and thus exhibits a corrosion protection effect regardless of dissolved oxygen, pH, and harmful ions. However, molybdates, tannins, lignins, sugars, organic acid salts, phosphates, etc., which are used as a film-forming corrosion inhibitor, have higher concentrations necessary for exerting corrosion protection, and also remove dissolved oxygen, adjust pH, The wastewater treatment takes more time and effort than the method of lowering the concentration of harmful ions.

The main factor causing scale generation in the boiler system is the scaling by the hardness component and silica contained in feed water or irrigation water, which is likely to generate scale on the heat transfer surface in contact with water vapor or water. Such generation of scale may cause deterioration of the performance of the apparatus or failure, or the life of the apparatus may be shortened, and various methods for suppressing generation of such scale have been studied.

In order to effectively suppress the generation of scale on the heat transfer surface due to the influence of water, there is a method of removing the hardness component in water. As a method of removing the hardness component from water, a mechanical removal method of softening treatment by a softening device to remove the hardness component is performed. When the softening device causes leakage of the hardness component, it is difficult to suppress the generation of scale.

In view of such a problem, an object of the present invention is to provide a water treatment agent which does not generate a problem of drainage treatment and suppresses generation of scale and corrosion caused by the influence of moisture.

This invention is made | formed in order to solve the said subject, and contains a silica, a pH adjuster, and a scale inhibitor as a chemical agent for suppressing the corrosion and the generation | occurrence | production of the scale which arise by the influence of moisture. In addition, examples of the pH adjuster include hydroxides of alkali metals. Examples of scale inhibitors include ethylenediaminetetraacetic acid and salts thereof.

This water treatment agent normally contains 0.12 mass% or more of silica, 0.2 mass% or more of pH adjuster, and 0.03 mass% or more of scale inhibitor, respectively.

The water treatment agent of the present invention is for suppressing the generation of corrosion and scale caused by the influence of moisture, and contains a silicone, a pH adjuster and a scale inhibitor.

Silica used in the present invention is a component for forming a film for suppressing corrosion due to moisture on the surface of the heat transfer surface. Specifically, due to the influence of dissolved oxygen and chloride ions, which are corrosion promoting factors contained in water, silica acts on the component eluted from the heat transfer surface, and a corrosion-resistant film (so-called corrosion) on the contact surface side of the heat transfer surface in contact with moisture. Protective film). In particular, dissolved oxygen or chloride ions express a local anode on the heat transfer surface, which may cause corrosion. Since silica contained in water exists as an anion or a negatively charged micelle, It is easy to be adsorbed by the same anion, and it is easy to form a corrosion protection film selectively in the corresponding part.

In addition, silica means that it contains not only silicic acid but the salt of silicic acid (that is, silicate). Silicates include orthosilicates (n SiO ₂ · (n + 1) M (I) ₂ O), polysilicates (nSiO ₂ · (n) M (I) ₂ O, nSiO ₂ · (n-1) M (I ) ₂ O and nSiO ₂ · (n-2) M (I) ₂ O) or these hydrates. In the formula of the salt, M (I) represents a metal element such as an alkali metal or an alkaline earth metal. When the metal element is M (II), the number of molecules of M (I) is half. In the chemical formula of polysilicate, n is larger than 2. Hereinafter, when referring to silica, it may mean a concept including the above salt. Here, two or more types of silica may be used together.

In the water treatment agent of this invention, it is preferable that the ratio of silica is normally set to 0.12 mass% or more of the total mass, and it is more preferable to set it to 0.6 mass% or more. When this content is less than 0.12 mass%, it may become difficult to form the predetermined | prescribed film for corrosion prevention on a heat transfer surface.

In addition, as a silica in the corrosion inhibitor of this invention, the thing of powder form may be used and the thing of aqueous solution form may be used.

The pH adjuster used in the present invention is a component that raises the pH of water in order to adjust the heat transfer surface to a pH region which is difficult to corrode. The kind of pH adjuster which can be used here is not specifically limited, There exist various things, such as an alkali metal hydroxide and an alkali earth metal hydroxide. Two or more types of these may be used together. Among these, it is especially preferable to use the hydroxide of an alkali metal in this invention. Since an alkali metal hydroxide is a chemical | medical agent which does not contain hardness components, such as calcium and magnesium, it is applicable because it does not promote production | generation of this scale.

In the water treatment agent of this invention, it is preferable that the ratio of a pH adjuster is normally set to 0.2 mass% or more of total mass, and it is more preferable to set it to 1.0 mass% or more. When the content is less than 0.2% by mass, there is a possibility that the pH raising function will not be sufficient.

The scale inhibitors used in the present invention include a hardness component that causes the scale to be generated on the contact surface side of the heat transfer surface in contact with water, for example, a function for chelating calcium ions or magnesium ions in water. There are several chelating agents, and polymers for exerting the function of suppressing the growth of scale crystal nuclei. The types of chelating agents that can be used here are not particularly limited, but there are various types of citric acid, ethylenediaminetetraacetic acid, and salts thereof. In addition, there are no particular limitations on the polymer pharmaceuticals available here, and there are various types such as polyacrylic acid and polymaleic acid. And they may use more than two kinds of things properly. Of these, it is particularly preferable to use ethylenediaminetetraacetic acid salts of alkali metals in the present invention. Ethylenediaminetetraacetic acid salts of alkali metals do not contain any hardness components such as calcium or magnesium, so they can be applied as ones that do not promote scale production.

In the water treatment agent of the present invention, the ratio of the scale inhibitor is usually set to at least 0.03% by mass of the total mass, and more preferably at least 0.15% by mass. If the content is less than 0.03% by mass, there is a possibility that it is difficult to promote the chelation of the hard components contained in the moisture or to inhibit the growth of the scale crystal nuclei.

Here, the water treatment agent of the present invention may contain various additives as necessary, in addition to the above-mentioned essential components. As the additive, for example, metal ion sequestrants such as nitrilo-triacetic acid (NTA) and salts thereof can be used.

The water treatment agent of the present invention is used to suppress the corrosion of heat transfer surfaces and the generation of scale due to moisture. More specifically, for example, in a device that generates steam, such as a boiler, it is used to suppress corrosion and scale properties due to heat transfer tubes (such as heat transfer surfaces) that generate steam and other moisture in the heat transfer surfaces. ．

When the water treatment agent of the present invention is used to suppress corrosion and generation of scale of the heat transfer tube for steam generation of the boiler, the water treatment agent of the present invention is injected into a water supply furnace that supplies water to the boiler. The water treatment agent injected into the feedwater is mixed in the feedwater and flows into the boiler together with the feedwater. As a result, the pH adjuster in the water treatment agent increases the pH of the water, the silica in the water treatment agent forms a film on the side of the contact surface with the water in the heat transfer tube, and the scale inhibitor in the water treatment agent is the chelating agent of the hardness component in the water. Promote anger, or inhibit the growth of scaled nuclei. As a result, the heat transfer tubes and other heat transfer surfaces of the boiler are effectively suppressed from corrosion and production of scale due to moisture.

In this case, the injection rate of the water treatment agent of the present invention for the above water supply channel is generally set so that the total concentration of silica, pH regulator, and scale inhibitor in water is not less than 1.75 mg / l, and is not less than 8.75 mg / l. It is preferable to set as much as possible. In addition, the water treatment agent may be injected continuously and intermittently injected into the water supply, provided that the total concentration of silica, pH regulator, and scale inhibitor is the same as above.

The water treatment agent of the present invention usually exhibits a basic pH of 9 to 12.5 when diluted in water in a similar dilution to the same concentration as above. In addition, this water treatment agent may be used in combination with a water treatment agent such as sodium sulfite or tannin.

(Example)

Examples 9-1

The mixture was stirred with a drop of distilled water in a mixture of sodium silicate, sodium hydroxide and ethylenediaminetetraacetic acid disodium. As a result, it was possible to obtain a water treatment agent for its purpose. Here, the ratio of each component contained in this water treatment agent is the same as the bar shown in Table 1.

Example 4

The mixture was mixed with silicic acid, potassium hydroxide and polyacrylic acid while dropping distilled water. This has enabled us to obtain a water treatment agent for this purpose. Here, the ratio of each component contained in this water treatment agent is the same as the bar shown in Table 1.

Examples # 5 and # 6

The mixture of potassium silicate, sodium hydroxide and ethylenediaminetetraacetic acid was stirred while dropping distilled water. This has enabled us to obtain a water treatment agent for this purpose. Here, the ratio of each component contained in this water treatment agent is the same as the bar shown in Table 1.

Example 7

The mixture was stirred with sodium silicate, sodium hydroxide and ethylenediaminetetraacetic acid tetrasodium tetrahydride while dropping distilled water. This has enabled us to obtain a water treatment agent for this purpose. Here, the ratio of each component contained in this water treatment agent is the same as the bar shown in Table 1.

Example

The mixture was mixed with silicic acid, potassium hydroxide and ethylenediaminetetraacetic acid disodium distilled with distilled water. As a result, it was possible to obtain a water treatment product for its purpose. Here, the ratio of each component contained in this water treatment agent is the same as the bar shown in Table 1.

Example

The mixture was stirred with dropping distilled water into a mixture of silicic acid, sodium hydroxide and polyacrylic acid. As a result, it was possible to obtain a water treatment agent for the purpose. Here, the ratio of each component contained in this water treatment agent is the same as the bar shown in Table 1.

Example 90

The mixture of potassium silicate, potassium hydroxide and ethylenediaminetetraacetic acid was stirred while dropping distilled water. This has enabled us to obtain a water treatment agent for this purpose. Here, the ratio of each component contained in this water treatment agent is the same as the bar shown in Table 1.

Example 11

The mixture was mixed with sodium silicate, potassium hydroxide, and ethylenediaminetetraacetic acid-4 sodium, dropping distilled water. This has enabled us to obtain a water treatment agent for this purpose. Here, the ratio of each component contained in this water treatment agent is the same as the bar shown in Table 1.

Example 21

The mixture was mixed with silicic acid, sodium hydroxide, and ethylenediaminetetraacetic acid sodium diacetate, with distilled water. This has enabled us to obtain a water treatment agent for this purpose. Here, the ratio of each component contained in this water treatment agent is the same as the bar shown in Table 1.

Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Silicic acid 20.00 Sodium silicate 9.66 1.26 5.46 Potassium Silicate 1.00 0.50 Sodium hydroxide 4.00 1.40 4.00 20.00 5.00 Potassium hydroxide 2.00 EDTA-2Na 0.30 3.00 0.15 EDTA-4Na EDTA 5.00 20.00 Polyacrylic acid 0.20 Distilled water 86.04 94.34 90.39 77.80 74.00 74.50

Example 7 Example 8 Example 9 Example 10 Example 11 Example 12 Silicic acid 2.00 0.60 1.00 Sodium silicate 13.00 26.00 Potassium silicate 26.00 Sodium hydroxide 1.00 20.00 5.00 Potassium hydroxide 20.00 1.50 1.00 EDTA-2Na 1.00 20.00 EDTA-4Na 15.00 3.00 EDTA 0.50 Polyacrylic acid 20.00 Distilled water 71.00 77.00 59.40 72.00 70.00 74.00

(Evaluation １)

Corrosion inhibitory properties were measured for the case of injecting the water treatment agent obtained in Examples 1-3 and the case of not injecting the drug. In this case, a permeation boiler of 1.35 kg / h evaporation was supplied with 500 mg / l of soft water added to the water treatment agent. The maximum value of the depth of the pit (the erosion in the form of a hole facing toward the opposite side of the thickness direction occurring on the contact surface side of the heat transfer tube in contact with water) was investigated. The results are shown in Table 2. In this case, the water used for the water supply was prepared by artificially preparing soft water in Osaka City. The water quality is as follows.

pH ： 7.5

Electrical Conductivity: 25mS / m

M alkalinity: 20mg-CaCO ₃ / ℓ

Water sample Maximum value of planting depth (µm) Do not inject drugs 230 Example 1 8 Example 2 125 Example 3 32

(Evaluation ２)

The increase in calcium solubility was measured in the case of injecting the water treatment agent obtained in Examples 1 to 3 and in the case of not injecting the chemical. In this case, the boiler was fed with a steam evaporation rate of 2.8 kg / hour and a soft water containing 500 mg / l of water treatment agent and continuously generating steam with a pressure of 0.5 MPa, and the boiler was operated at a blow rate of 10%. The increase in calcium solubility after 48 hours was examined. The results are shown in Table 3 below. In this case, the number of soft water used in the water supply was artificially prepared from the softened water in Osaka City. The water quality is as follows.

pH ： 7.5

Electrical Conductivity: 25mS / m

M alkalinity: 20mg-CaCO ₃ / ℓ

Feed Sample Relative increase in calcium solubility (mg / ℓ) Do not inject drugs 0.00 Example 1 4.00 Example 2 37.00 Example 3 2.40

From Table 2, it can be seen that when the water treatment agents of Examples 1 to 3 were injected, the corrosion inhibitory performance was superior to the result obtained when no drugs were injected. From Table 3, it was found that the water treatment agents of Examples 1 to 3 increased the solubility of calcium in comparison with the case where no chemical was injected. In addition, the same effects can be obtained in Examples 4 to 12 as well.

As described above, according to the present invention, the generation of corrosion and scale generated by the influence of moisture can be suppressed.

Claims (4)

A water treatment agent that contains silica, pH regulators, and scale inhibitors to suppress corrosion and scale production caused by the effects of moisture. The water treatment agent according to claim 1, wherein the pH regulator is a hydroxide of an alkali metal. The water treatment agent according to claim 1 or 2, wherein the scale inhibitors are ethylenediaminetetraacetic acid and salts thereof. The water treatment agent according to any one of claims 1 to 3, wherein the silica is 0.12 mass% or more, the pH regulator is 0.2 mass% or more, and the scale inhibitor is 0.03 mass% or more, respectively.