JP6859901B2 - Sulfurous acid-based water treatment agent and water treatment method - Google Patents

Description

The present invention relates to a sulfite-based water treatment agent containing a sulfite, which is used as an anticorrosive agent for boilers.

Conventionally, a technique of adding an oxygen scavenger as a water treatment agent to boiler water supply has been known in order to suppress corrosion occurring on a heat transfer surface such as a boiler water pipe that comes into contact with boiler water. Corrosion of the heat transfer surface of the boiler is mainly caused by dissolved oxygen in the water. Therefore, by adding an oxygen scavenger to the boiler water supply, the amount of dissolved oxygen in the water can be reduced and corrosion can be suppressed. As such an oxygen scavenger, for example, sulfites and the like are used.

Has a deoxidizing effect sulphite excellent, itself generates the Sulfate ion (SO 4 ^_2-) are corrosive factors by being oxidized, there is a problem that the corrosion factor in the heat transfer surface of the boiler .. Therefore, a technique is known in which silicic acid, silicate, or the like is added to a water treatment agent in addition to sulfites to form a film on the heat transfer surface on the contact surface side with boiler water to suppress corrosion ( For example, see Patent Document 1 below).

On the other hand, a method of removing dissolved oxygen contained in boiler feed water using a degassing device without using a deoxidizing agent such as sulfites has been carried out, and water containing silica, a scale inhibitor, etc. A technique for preventing corrosion and scale of the heat transfer surface by a treatment agent is known (see, for example, Patent Document 2 described later).

Japanese Unexamined Patent Publication No. 63-166982 Japanese Unexamined Patent Publication No. 2003-159597

By the way, the amount of silicic acid, silicate, etc. added to the water treatment agent preferably needs to be adjusted according to the amount of silica (generally referred to as silicic acid, silicate, etc.) contained in the raw water. is there. The content of silica contained in the raw water varies depending on the water intake source, etc., but if the amount of silica in the boiler feed water becomes excessive, scale will occur on the heat transfer surface of the boiler, resulting in a decrease in the thermal efficiency of the boiler and failure. This is because it may cause a problem.

To solve the above problem, after performing the primary treatment with a sulfite-based water treatment agent that does not contain silicic acid or silicate, the water treatment agent that contains silicic acid or silicate is used as the amount of silica in the raw water. It is preferable to carry out a two-step water treatment method in which a secondary treatment of addition is carried out accordingly.
Therefore, there has been a demand for the development of a sulfite-based water treatment agent that can be formed without containing silicic acid, silicate, etc. and has high storage stability.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a sulfite-based water treatment agent which can be constructed without containing silicic acid, silicate or the like and has high storage stability.

The present invention is a sulfite-based water treatment agent added to boiler water supply, which contains sulfite, sorbic acid or a salt thereof, and an alkali metal hydroxide, and the concentration of sulfite is 10 to 25. It is mass%, and the concentration of sorbic acid or a salt thereof is 0.5 to 1.5 mass%, and the ratio of potassium ion concentration ([K ⁺ ]) to sodium ion concentration ([Na ⁺ ]) ([ K ⁺ ] / [Na ⁺ ]) relates to a sulfite-based water treatment agent which is 1/5 to 7/2.

Moreover, the sulfite is preferably sodium sulfite.

Moreover, it is preferable to contain potassium sorbate as the sorbic acid or a salt thereof.

The alkali metal hydroxide is preferably potassium hydroxide.

Further, the present invention comprises a step of adding 0.001 to 0.1 parts by volume of a sulfite-based water treatment agent to 100 parts by volume of boiler water supply, and a silicic acid or silicic acid or silicic acid or The present invention relates to a water treatment method including a silicic acid-based water treatment agent chemical injection step of adding a silicic acid-based water treatment agent containing a silicate.

According to the present invention, it is possible to provide a sulfite-based water treatment agent which can be formed without containing silicic acid, silicate or the like and has high storage stability.

Hereinafter, embodiments of the present invention will be described. The present invention is not limited to the following embodiments.
The sulfite-based water treatment agent according to the present embodiment is used to suppress corrosion that occurs on the heat transfer surface of the boiler that comes into contact with the boiler water.

The sulfite-based water treatment agent according to the present embodiment contains a sulfite, sorbic acid or a salt thereof, and an alkali metal hydroxide. Further, water, particularly pure water, is preferably used as the solvent.

Sulfites are salts of sulfites that have a sulfite group in the molecule. Sulfites are ionized in aqueous solution to produce sulfite ions. Sulfate ion reacts with dissolved oxygen according to the following formula to become sulfate ion. That is, it has a deoxidizing effect that reduces the amount of dissolved oxygen.

2SO ₃ ^2- + O ₂ → 2SO ₄ ^2-

A water treatment agent containing sulfites is added to the boiler water supply and reacts with dissolved oxygen in the boiler feed water as described above, and also reacts with oxygen in the air during storage of the water treatment agent to produce sulfate ions. There is a possibility that Sulfate ion is a corrosive factor that not only has no deoxidizing effect but also causes corrosion on the heat transfer surface of the boiler. Therefore, it is necessary to prevent such oxidation of sulfite ions during storage of a water treatment agent containing a sulfite.

Examples of the sulfite used in the present embodiment include sodium sulfite (Na ₂ SO ₃ ), _{sodium dissulfite (Na 2} S ₂ O ₅ ), sodium hydrogen sulfite (NaHSO ₄ ), and ammonium sulfite ((NH _{4 ) 2} ). SO ₃ ), ammonium hydrogen sulfite ((NH ₄ ) HSO ₃ ), potassium sulfite (K ₂ SO ₃ ), potassium hydrogen sulfite (KHSO ₃ ) and the like can be mentioned, but it is preferable to use sodium sulfite. Since sodium sulfite is a highly safe compound that is also used as a food additive, the use of sodium sulfite as a water treatment agent ensures safety during handling.

The concentration of sulfite in the water treatment agent is 10 to 25% by mass, preferably 15 to 25% by mass. The required amount of sulfite varies depending on the amount of water treatment agent added to the boiler water supply, the dissolved oxygen concentration in the boiler water supply, etc., but 0.001 to 0.1 parts by volume with respect to 100 parts by volume of untreated boiler water supply. When the water treatment agent is added, generally, if the concentration of sulfites in the water treatment agent is less than 10% by mass, a sufficient deoxidizing effect cannot be obtained. Further, when the concentration of sulfites in the water treatment agent exceeds 25% by mass, crystallization of sulfites during storage of the water treatment agent is likely to occur. In addition, since a large amount of sulfate ion, which is a corrosive factor, is generated, preferable corrosion resistance of the boiler water pipe cannot be obtained.

Sorbic acid is _{an unsaturated fatty acid represented by the composition formula of C 6} H ₈ O ₂ , and sorbic acid salt is a salt of sorbic acid and an alkali metal or the like. Sorbic acid or a salt thereof has a function as a stabilizer for sulfite ion. That is, the addition of sorbic acid or a salt thereof to a water treatment agent containing a sulfite is expected to have an effect of preventing oxidative deterioration of sulfite ions during storage of the water treatment agent.

Examples of the sorbate salt used in the present embodiment include sodium sorbate, potassium sorbate, calcium sorbate and the like, and among them, potassium sorbate is preferably used.
Potassium sorbate does not contain a hardness component and is a highly safe compound that is also used as a food additive. Therefore, potassium sorbate is used as a water treatment agent from the viewpoint of scale control and safety during handling. It is preferable to use it.

Further, the water treatment agent according to the present embodiment can be composed without containing silicic acid, silicate or the like. Here, by using potassium sorbate instead of the commonly used potassium silicate, potassium sorbate becomes a source of potassium ions. As described above, in the water treatment agent according to the present embodiment, it is preferable to use sodium sulfite as the sulfite. Therefore, by using potassium sorbate as the water treatment agent, potassium sorbate is replaced with potassium silicate. It serves as a source of ions, and it becomes easy to balance the ions of potassium ion and sodium ion, which will be described later. As a result, the crystallization of sulfites can be suppressed, so that a water treatment agent having excellent storage stability can be obtained.

The concentration of sorbic acid or a salt thereof in a water treatment agent is 0.5 to 1.5% by mass. If the concentration of sorbic acid or a salt thereof in the water treatment agent is less than 0.5% by mass, preferable storage stability of the water treatment agent cannot be obtained. Further, when the concentration of sorbic acid or a salt thereof in the water treatment agent exceeds 1.5% by mass, sorbic acid may be precipitated during the storage of the water treatment agent, and preferable storage stability of the water treatment agent can be obtained. I can't.

The alkali metal hydroxide has a function as a pH adjuster that raises the pH of the boiler feed water so that the heat transfer surface of the boiler water pipe is less likely to be corroded. That is, the pH of the boiler feed water is adjusted to the alkaline side by the pH adjuster, so that corrosion of the boiler water pipe is suppressed. Examples of alkali metal hydroxides used as such pH adjusters include sodium hydroxide and potassium hydroxide, which are strong bases and therefore have a high effect of raising pH, or from the viewpoint of preventing scale generation. It is preferably used.
As described above, in the water treatment agent according to the present embodiment, it is preferable to use sodium sulfite as the sulfite. Therefore, by using potassium hydroxide as the water treatment agent, potassium hydroxide becomes a source of potassium ions and will be described later. It becomes easy to balance the potassium ion and sodium ion of potassium ion and sodium ion. As a result, the crystallization of sulfites can be suppressed, so that a water treatment agent having excellent storage stability can be obtained.

In the sulfite-based water treatment agent according to the present embodiment, the ratio ([K ⁺ ] / [Na ⁺ ]) ^{of the potassium ion concentration ([K +} ]) to the sodium ion concentration ([Na ^{+]) is 1/5.} It is ~ 7/2, preferably 1/5 to 2/1.
Although the principle is not always clear, the present inventors, when a pH adjuster is blended with a sulfite, a sulfite is used when a potassium salt such as potassium hydroxide is used as compared with a case where a sodium salt is used. It was confirmed that the crystallization of potassium hydroxide can be suppressed and good storage stability can be obtained. That is, when the ratio of the potassium ion concentration to the sodium ion concentration is within the above range, it is possible to suppress the precipitation and crystallization of sulfites.

The sulfite-based water treatment agent according to the present embodiment may contain components other than the above-mentioned components as long as the above-mentioned effects are not impaired. For example, catalysts used to improve the deoxidizing capacity of sulfites, other oxygen scavengers such as vitamin C and its salts, tannins, other scale dispersants such as citric acid and polyacrylic acid salts, aminomethyl. Neutralizing amines such as propanol and cyclohexylamine may be contained.

Subsequently, a water treatment method using the water treatment agent according to the present embodiment will be described.
The water treatment method according to the present embodiment is a chemical injection step of adding 0.001 to 0.1 parts by volume of the water treatment agent according to the present embodiment to 100 parts by volume of boiler water supply (hereinafter, "first chemical injection step". ”), And a silicic acid-based water treatment agent chemical injection step (hereinafter referred to as“ second chemical injection step ”) in which a silicic acid-based water treatment agent containing silicic acid or silicate is added to the boiler water supply. To be equipped.

In the first chemical injection step, the injection amount of the water treatment agent in the boiler feed water is adjusted within the above range, and the chemical is injected into the water supply channel that supplies water to the boiler. By setting the injection amount of the water treatment agent in the boiler feed water within the above range, the sulfite ion in the boiler feed water can be set to a preferable concentration. Further, it is preferable to adjust the injection amount of the water treatment agent within the above range according to the dissolved oxygen concentration in the boiler feed water. Since the dissolved oxygen concentration in the boiler feed water is greatly contributed by the water temperature, the injection amount may be adjusted according to the water temperature of the boiler feed water.

In the second chemical injection step, a silicic acid-based water treatment agent containing silicic acid or silicate is added into the water supply channel that supplies water to the boiler.

Silicic acid is a compound containing silicon, oxygen, and hydrogen, and silicate is a salt of silicic acid and an alkali metal. These compounds are composed of silicon dioxide (SiO ₂ ) and are collectively called "silica".
Silica is adsorbed on the contact surface side of the heat transfer surface with the boiler water to form a film, and by covering the heat transfer surface of the boiler water pipe with this film, as a film forming component that imparts preferable corrosion resistance to the boiler water pipe. Function. That is, since the film formed by silica covers the heat transfer surface of the boiler water pipe, the influence of dissolved oxygen contained in the boiler water and corrosive factors such as sulfate ion and chloride ion is suppressed, so that the boiler is suppressed. The preferable anticorrosive property of the water pipe can be obtained. In particular, dissolved oxygen and chloride ions develop local anodes on the heat transfer surface, which can lead to corrosion, but silica, which exists as anions and negatively charged micelles in boiler water, is such an anode. It is easy to be adsorbed on the surface, and it is easy to selectively form an anticorrosive film on the portion. Therefore, as compared with other film-forming anticorrosive agents, silica can impart preferable anticorrosive properties to the boiler water pipe with a relatively small amount of addition.

The injection amount of the silicic acid-based water treatment agent in the second chemical injection step is preferably adjusted according to the injection amount of the water treatment agent according to the present embodiment in the first chemical injection step. That is, the amount of sulfate ion, which is a main corrosive factor contained in the boiler feed water, increases in proportion to the injection amount of the sulfite-based water treatment agent according to the present embodiment, which is chemically injected in the first chemical injection step. .. The required amount of silica, which is a film-forming agent, also changes depending on the amount of the corrosive factor.
Here, silica is contained not only in the silicic acid-based water treatment agent but also in the raw water, but the content thereof varies depending on the water intake source and the like. Therefore, it is more preferable to subtract the amount of silica contained in the raw water or the boiler feed water from the required amount of silica to determine the injection amount of the silicic acid-based water treatment agent in the second chemical injection step. In addition, the amount of chloride ions, which are other corrosive factors contained in the boiler feed water, fluctuations in raw water quality, and drain recovery (steam generated in the boiler is heat exchanged and condensed on the load side (heat exchanger, etc.)). It is possible to correct the injection amount of the silicic acid-based water treatment agent in the second chemical injection step according to the corrosive factor and the change in the concentration of silica due to water (drain water) being recovered for reuse). More preferred.

By controlling the injection amount in this way, it is possible to obtain preferable anticorrosion property by the water treatment agent and to suppress unnecessary chemical injection, so that the cost can be reduced. In addition, it is possible to prevent an increase in corrosive factors due to unnecessary chemical injection and scaling of silica, and stable water management can be performed.

In the present embodiment, the method of chemical injection in the second chemical injection step is not particularly limited, and the injection may be continuous or intermittent with respect to the boiler water supply. Similarly, in the first drug injection step, the method of drug injection is not particularly limited as long as the injection amount is within the above range. In addition, a tank is provided to store the medicated boiler water supply for a certain period of time before it is supplied into the boiler system, and the injection amount so that the injection amount of the water treatment agent for the boiler water supply in the tank is within the above range. May be adjusted.

Further, in the present embodiment, which of the first drug injection step and the second drug injection step may be provided first, or the drug injection may be performed at the same time. That is, the first drug injection step may be provided first, the injection amount in the second drug injection step may be calculated from the actual injection amount in the first drug injection step, and the drug may be injected in the second drug injection step. The injection amount in each of the first chemical injection step and the second chemical injection step is calculated in advance from the dissolved oxygen concentration, temperature, silica amount, etc. of the water supply, and the second chemical injection step is provided first, or the first chemical is added. The drug may be injected at the same time in the injection step and the second drug injection step.

Next, the present invention will be described in more detail based on examples, but the present invention is not limited thereto.
<Examples 1 to 7 and Comparative Examples 1 to 6>
The contents of sodium sulfite (manufactured by Wako Pure Chemical Industries, special grade reagent), potassium sorbate (manufactured by Wako Pure Chemical Industries, Ltd.), potassium hydroxide (manufactured by Wako Pure Chemical Industries, special grade reagent) and distilled water as a solvent are shown in Table 1 (Table 1). Unit: mass%), and the ratio of potassium ion concentration to sodium ion concentration ([K ⁺ ] / [Na ⁺ ]) in the water treatment agent is the value shown in Table 1 by mixing. Water treatment agents of Examples and Comparative Examples were prepared.

[Storage stability]
The water treatment agents of Examples and Comparative Examples were stored at −5 ° C. and 5 ° C. for 270 days. The appearance of the water treatment agent after storage was visually observed to confirm the presence or absence of changes. If there is no change, it is set as "A". If crystals or precipitates are settled at -5 ° C, it is set as "B". If there is no change, crystals or precipitates are settled at -5 ° C and 5 ° C. Was evaluated as "C", and the evaluation B or higher was judged to be acceptable, and C was judged to be unacceptable. The results are shown in Table 1.

[Deoxidizing effect]
The water treatment agents of Examples and Comparative Examples were added at 400 mg / L to distilled water at 50 ° C. adjusted to pH 11, and the dissolved oxygen concentration 30 minutes after the addition was measured with a dissolved oxygen concentration meter. The amount of reduced dissolved oxygen before the addition of the water treatment agent is evaluated as "A" when it is less than 1.0 ppm, "B" when it is 1.0 to 2.0 ppm, and "C" when it exceeds 2.0 ppm. Passed and C were judged to be rejected. The results are shown in Table 1.

From the comparison between Example 2 and Comparative Example 1, it was confirmed that the water treatment agent having a sulfite content of less than 10% by mass did not obtain a preferable deoxidizing effect. Further, from the comparison between Example 3 and Comparative Example 2, it was confirmed that when the amount of sulfites exceeds 25% by mass, the storage stability of the water treatment agent deteriorates.
From these results, it was confirmed that by setting the concentration of sulfite in the water treatment agent to 10 to 25% by mass, both a preferable deoxidizing effect and storage stability of the water treatment agent can be achieved.

From the comparison between Example 4 and Comparative Example 3, it was confirmed that the water treatment agent having no sorbic acid or a salt thereof did not obtain preferable storage stability. Further, from the comparison between Example 5 and Comparative Example 4, it was confirmed that when the amount of sorbic acid or a salt thereof exceeds 1.5% by mass, the storage stability of the water treatment agent deteriorates.
From these results, it was confirmed that preferable storage stability of the water treatment agent can be obtained by setting the concentration of sorbic acid or a salt thereof in the water treatment agent to 0.5 to 1.5% by mass.

From the comparison between Example 6 and Comparative Example 5, the ratio of the potassium ion concentration ([K ⁺ ]) to the sodium ion concentration ([Na ⁺ ]) in ^{the water treatment agent ([K +} ] / [Na ⁺ ]] ) Is less than 1/5, it was confirmed that favorable storage stability cannot be obtained. Further, from the comparison between Example 7 and Comparative Example 6, the ratio of the potassium ion concentration ([K ⁺ ]) to the sodium ion concentration ([Na ⁺ ]) in ^{the water treatment agent ([K +} ] / [Na]). ^{It was confirmed that a water treatment agent having a +} ]) content of more than 7/2 also did not obtain favorable storage stability.
From these results, the ratio ([K ⁺ ] / [Na ⁺ ]) of the potassium ion concentration ([K ⁺ ]) to the sodium ion concentration ([Na ⁺ ]) in the water treatment agent is 1/5 to 7 /. When it was 2, it was confirmed that preferable storage stability of the water treatment agent could be obtained.

Claims (5)

Sulfurous acid-based water treatment agent added to boiler water supply
Containing sulfites, sorbic acid or salts thereof, and alkali metal hydroxides,
The concentration of sulfite is 10 to 25% by mass,
The concentration of sorbic acid or a salt thereof is 0.5 to 1.5% by mass.
A sulfite-based water treatment agent having a ratio ([K ⁺ ] / [Na ⁺ ]) of a potassium ion concentration ([K ⁺ ]) to a sodium ion concentration ([Na ^{+]) of 1/5 to 7/2.} The sulfite-based water treatment agent according to claim 1, wherein the sulfite is sodium sulfite. The sulfite-based water treatment agent according to claim 1 or 2, which contains potassium sorbate as the sorbic acid or a salt thereof. The sulfite-based water treatment agent according to any one of claims 1 to 3, wherein the alkali metal hydroxide is potassium hydroxide. A step of adding 0.001 to 0.1 parts by volume of the sulfite-based water treatment agent according to any one of claims 1 to 4 to 100 parts by volume of boiler water supply, and a step of injecting a sulfurous acid-based water treatment agent.
A water treatment method comprising a silicic acid-based water treatment agent chemical injection step of adding a silicic acid-based water treatment agent containing silicic acid or a silicate to the boiler water supply.