KR100992095B1 - Water treatment agent for boiler water - Google Patents

Abstract

The present invention relates to a water treatment agent for a boiler for suppressing the generation of corrosion and scale generated in the heat transfer surface in contact with the boiler water.

The water treatment agent for a boiler of the present invention is a medicament for inhibiting corrosion and scale generation on the heat transfer surface of a boiler. Contains species

Water treatment agent for boiler, alkali metal salt of silicic acid or silicic acid, hydroxide of alkali metal, ethylenediamine tetraacetic acid

Description

Water treatment agent for boiler water

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a water treatment agent for boilers for suppressing generation of corrosion and scale generated on heat transfer surfaces such as water pipes of boilers and water pipes of economizers in contact with boiler water.

Conventionally, the main causes of corrosion of the boiler's heat transfer surface are water supply or boiler water ① high dissolved oxygen concentration, ② out of the proper range of pH (11.0 ~ 11.8), ③ high concentration of harmful ions such as chloride ion or sulfate ion. There are a few points.

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 a proper range is performed using a pH adjuster. When boiler feed water having a M alkalinity of a predetermined concentration or higher, a component (mainly hydrogen carbonate) showing M alkalinity is a boiler tube. It thermally decomposes and produces | generates carbonate ion, hydroxide ion, etc., and it has the effect | action which raises pH of 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 heat-transfer surface, the method of injecting a film-forming corrosion inhibitor into a feed water is mentioned. The film formation of this corrosion inhibitor prevents the water pipe from directly contacting the boiler water, thus exhibiting 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 that causes scale generation on the boiler heat transfer surface is scaling by the hardness component and silica contained in feed water or boiler 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 performance degradation or failure of the apparatus, or may shorten the life of the apparatus, and various methods for suppressing generation of such scale have been studied.

In order to effectively suppress the formation of scale on the heat transfer surface of the boiler, 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 for a boiler which suppresses the generation of corrosion and scale generated on the heat transfer surface of the boiler in contact with the boiler water without causing a problem of drainage treatment.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and as a corrosion inhibitor component in a water treatment agent for a boiler for suppressing the generation of corrosion and scale generated on the heat transfer surface of a boiler in contact with boiler water, (A) silicic acid or alkali thereof It contains one type of metal salt and the hydroxide of (B) alkali metal, and contains one type of (C) ethylenediamine tetraacetic acid or its alkali metal salt as a scale inhibitory component.

This boiler water treatment agent usually contains 0.12 mass% or more of silicic acid or 1 type of its alkali metal salts, 0.2 mass% or more of hydroxide of an alkali metal, and 0.03 mass% or more of 1 type of ethylenediamine tetraacetic acid or its alkali metal salts, respectively. Doing.

The water treatment agent for a boiler of the present invention is for suppressing the generation of corrosion and scale generated by the heat transfer of the boiler in contact with the boiler water, and as a corrosion inhibiting component, one of (A) silicic acid or its alkali metal salt and (B) alkali metal Hydroxide is contained and (C) ethylenediamine tetraacetic acid or one of its alkali metal salts is contained as a scale suppression component.

Component (A) used in the present invention, i.e., silicic acid or one of its alkali metal salts, is a component for forming a film for suppressing corrosion due to boiler water on the surface of the thermoelectric surface. Specifically, silicic acid or silicate acts on the components eluted from the heat-transfer surface due to the influence of dissolved oxygen or chloride ions, which are corrosion promoting factors contained in the boiler water, and a corrosion-resistant film on the contact surface side of the heat-transfer surface with the boiler water. A so-called anticorrosion film is formed. In particular, dissolved oxygen or chloride ions express local anodes on the heat transfer surface, which may cause corrosion. The silicic acid or silicate contained in the boiler water exists as an anion or negatively charged micelle. Since it is easy to adsorb | suck to such anions, it is easy to form a corrosion prevention film selectively in the said part.

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 an alkali metal. In the chemical formula of polysilicate, n is larger than 2. Hereinafter, when referred to as a silicate may mean a concept including the salt as described above. Here, two or more types of silicic acid or a silicate may be used together.

 In the water treatment agent of this invention, it is preferable that the ratio of 1 type in silicic acid or its alkali metal salt is normally set to 0.12 mass% or more of whole 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.

Moreover, the powder form may be used as the silicic acid or its alkali salt of the present invention, or an aqueous solution form may be used.

Component (B) used in the present invention, i.e., hydroxide of alkali metal, is a component that raises the pH of the boiler water in order to adjust the heat transfer surface to a pH range which is difficult to corrode. Two or more types of alkali metal hydroxides may be used in combination.

In the water treatment agent of this invention, it is preferable that the ratio of the hydroxide of an alkali metal 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.

One of the components (C) used in the present invention, ie, ethylenediamine tetraacetic acid and its alkali metal salts, is a hardness component which causes the generation of scales generated on the contact surface side of the heat transfer surface, for example, calcium contained in boiler water. It is a component for releasing the function to chelate ions or magnesium ions.

In the water treatment agent of the present invention, the proportion of ethylenediamine tetraacetic acid or one of its alkali metal salts is generally 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 essential ingredients (A) to (C). As the additive, for example, metals such as nitrilotriacetate (NTA) and salt salts thereof may be used. Ion blockers can be lifted.

The water treatment agent of the present invention is used to suppress the generation of corrosion and scale on heat transfer surfaces of boilers in contact with boiler water. More specifically, it is used to suppress corrosion and scale properties due to the number of boilers on the heat transfer pipe (an example of the heat transfer surface) that generates steam such as boiler water pipes and other 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 boiler generation, 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 alkali metal in the water treatment agent increases the pH of the boiler water, and one type of silicic acid in the water treatment agent or one of its alkali metal salts forms a film on the side of the boiler water of the heat transfer tube, and also the ethylene in the water treatment agent. One of diamine tetraacetic acid or an alkali metal salt thereof promotes chelation of the hardness component in boiler water. As a result, the heat transfer pipe and other heat transfer surfaces of the boiler are effectively suppressed from corrosion and scale generation due to the number of boilers.

In this case, the injection amount of the water treatment agent of the present invention for the above water supply channel is generally set so that the total concentration of the essential components (A) to (C) is not less than 1.75 mg / l in the water supply, and is 8.75 mg / l. It is preferable to set it so that the error is corrected. In addition, the water treatment agent may be continuously injected into the water supply passage, or may be injected intermittently if the total concentration of the essential components (A) to (C) 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, similar to the above concentration. 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 of silicic acid, sodium hydroxide, and ethylenediaminetetraacetic acid sodium diacetate was stirred with distilled water. As a result, a target water treatment agent was obtained. Here, the ratio of each component contained in this water treatment agent is as showing 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, and the boiler was operated at a blow rate of 10% while continuously generating steam with a pressure of 0.3 MPa. 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. Here, the boiler was fed to a perfusion boiler with evaporation rate of 2.8 kg / hr, with 500 mg / l of water added to the water treatment agent, and continuously generating steam at a pressure of 0.5 MPa and operating the boiler 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 properties were superior to the results when no drugs were injected. Table 3 shows that the calcium solubility of the water treatment agents of Examples 1 to 3 is increased compared with the case where no drug is injected. Moreover, the same effect was acquired also about Examples 4-12.

As described above, according to the present invention, it is possible to suppress the generation of corrosion and scale generated by the influence of moisture.

Claims (4)

In the water treatment agent for the boiler to suppress the formation of corrosion and scale formed on the boiler heat transfer surface in contact with the boiler water, As a corrosion inhibiting component, (A) silicic acid or its alkali metal salt, and (B) alkali metal hydroxide are contained, (C) Boiler water treatment agent containing 1 type in (C) ethylenediamine tetraacetic acid or its alkali metal salt as a scale suppression component. The boiler according to claim 1, which contains at least 0.12% by mass of silicic acid or an alkali metal salt thereof, at least 0.2% by mass of hydroxide of alkali metal, and at least 0.03% by mass of ethylenediamine tetraacetic acid or alkali metal salt thereof. Water treatment ． delete delete