JPH03277790A - Method for preventing corrosion of boiler - Google Patents

Abstract

PURPOSE:To effectively prevent the corrosion of a boiler operated or stopped by incorporating a compd. forming tin ion in water, an org. compd. such as erythorbic acid and an aliphatic hydroxycarboxylic acid in the boiler water respectively in a specified concn. CONSTITUTION:From 10 to 200mg Sn/l of a compd. (a) generating tin ion or tin complex ion in water, 5-300mg/l of <=1 kind of org. compd. or its salt (b) among erythorbic acid, ascorbic acid, sorbic acid, gallic acid and catechol and 30-100mg/l of an aliphatic hydroxycarboxylic acid or its salt (c) are incorporated in the boiler water. Stannous chloride is preferably used as the compd. (a). Gluconic acid or its salt and/or citric acid or its salt are preferably used as the salt (c). The corrosion of the boiler operated or stopped is prevented, and the boiler is again operated as such after stoppage.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a boiler corrosion prevention method, and particularly to a boiler corrosion prevention method that is effective not only when the boiler is in operation but also when the boiler is stopped.

[Prior art]

As a method for preventing corrosion of boilers, a method of adding a combination of molybdenum compounds, aliphatic oxycarboxylic acids, inorganic heavy metal compounds, etc. to boiler water (Japanese Patent Publication No. 62-2715
7) and a method of controlling the divalent tin concentration and pH of the boiler water system within an appropriate range (Japanese Patent Application Laid-open No. 73093/1983). However, these conventional methods have the disadvantage that they have poor corrosion protection effect when the boiler is stopped and are difficult to apply to actual boiler water systems. In other words, boilers are generally operated and stopped repeatedly depending on the usage status of the generated steam, but depending on the number of boilers installed and the operating method, the cycle of operation and stopping can often extend from several days to several weeks. . However, although the above corrosion prevention method is effective when the boiler is in operation (i.e., in a high temperature state),
Corrosion resistance weakens when the water temperature drops when the product is stopped, so
Even if steam is not needed to prevent corrosion inside the boiler, the boiler may be maintained at a high temperature, or even if the boiler is shut down, other corrosion protection measures (for example, so-called oxygen scavengers such as hydrazine or sulfite) may be used when the boiler is shut down. (e.g., adding a high concentration to the boiler water system), and when restarting operations, it is necessary to replace the boiler water with one containing anticorrosive agent for use during operation, which complicates operation work. There was a problem in that not only was the running cost increased, but the running cost also increased.

[Problem to be solved by the invention]

Therefore, the present invention can exert its anticorrosion effect not only while the boiler is in operation, but also when the boiler is stopped without any additional measures, and even if the boiler is restarted without any problems. The present invention aims to provide a boiler corrosion prevention method.

[Means for Solving the Problems] As a result of intensive research to achieve the above object, the present inventors added a certain specific compound to the boiler water system that produces tin ions or tin complex ions in water. It has been found that by adding a combination of organic compounds, the surface of the steel material inside the boiler can be well protected against corrosion regardless of whether the boiler is in operation or stopped.

That is, the present invention contains 10 to 2 of the compound (a) that produces tin ions or tin complex ions in boiler water.
00■Sn/j! , erythorbic acid, ascorbic acid, sorbic acid, gallic acid, and catechol.
) of 5 to 300 ■/l, and compound (c) consisting of an aliphatic oxycarboxylic acid or its salt at 30 to 1000 ■/l.
This is a method for preventing corrosion of a boiler, characterized in that the boiler corrosion prevention method is characterized by causing the presence of

Examples of the compound (a) used in the present invention include inorganic salts of tin such as stannous chloride and stannous sulfate, organic salts of tin such as tin acetate, sodium stannate, potassium stannite, etc. Examples include compounds that generate tin ions or tin complex ions in water, such as stannic acid compounds and stannous acid compounds.

In addition, the compound (c) used in the present invention includes:
Examples include aliphatic oxycarboxylic acids such as glycolic acid, tartaric acid, lactic acid, citric acid, and malic acid, and alkali metal salts thereof.

Although the anticorrosion mechanism in the present invention is not clear, the compound (a
) does not exist, or even if it does exist, the concentration is low, no anticorrosion effect can be obtained both during operation and when stopped. Furthermore, if the compound (c) is not present or is present but at a low concentration, the anticorrosion performance may not be exhibited regardless of the operation stoppage, depending on the concentration of the compound (a) and the pH of the boiler water system. Further, if compound ('b) is not present or is present but at a low concentration, there is a tendency for the anticorrosion performance to deteriorate overall, and the deterioration in the anticorrosion performance is particularly noticeable when the boiler is stopped. As mentioned above, if even one of the three components is absent, or even if it is present, the concentration is low, the above problems cannot be solved. Further, even if each component is present in a concentration exceeding the above range, no improvement in anticorrosion effect can be expected, and running costs only increase, which is impractical.

Furthermore, in the present invention, other anticorrosive agents, scale inhibitors, condensate treatment agents, etc. can be used in combination as long as the effects of the present invention are not impaired. Such agents include hydrazine, sulfites, phosphates, phosphonic acid compounds, volatile amines,
Examples include water-soluble organic polymer compounds such as polyacrylic acid.

[Example 1] An electric heater (heat transfer area: 0.335M) is immersed in water and holds 2.5 I of water! autoclave equipment,
The autoclave was operated at a steam pressure of 8 kgf/cd and a steam generation rate of 2.5 kg/h while supplying water and chemicals at the rates shown in Table 1 to obtain 10 times concentrated water (boiler water) in the autoclave. Next, install the heater into a boiler steel tube (STB4).
2), and continued to operate for 4 hours at a blow rate of 10%, a steam pressure of 8 kgf/CIA, and a steam generation of 12.5 kg/h while continuously replenishing water containing chemicals at the ratio shown in Table 1. Thereafter, the operation was stopped, and the water temperature was maintained at 60° C. with the lid open until the next day. On the next day, the same operation was repeated again, and after 4 days of operation in this manner, the number of pittings that occurred in the heater was counted. The results are shown in Table 1.

The quality of the water supply used in the experiment is as follows.

Womb 1 (K! pH 7.4 Electrical conductivity (μ5101): 780 Chloride ion CI (■mue): 200 Total hardness (*CaC0
z/l): less than 1 M - full brittleness
C ■ CaC0z/ 1 ): 4 4 silica (
■5iOz/1'): 23 total iron (+qr
Fe/jri ・Less than 0.05 (■Sn/7ri (■/l') (■/7ri ES: 0 #:30 GA: 0 GL: 450 〃:150 〃:150 '':150 ES : 300 〃: 120 〃: 450 : Control method ES: Sodium erythorbate GA: Sodium gallate GL Sodium nigerconate [Example 2] Carpenter boiler water adjusted to the following water quality and Add the chemicals in the proportions shown in Table 2, raise the water temperature to 60℃ in a constant temperature bath, and then
A mild steel plate of size M was hung and attached so as to be immersed in boiler water. It was left in a sealed state for 30 days while maintaining the water temperature at 60° C. in a constant temperature bath. After the test was completed, the test piece was taken out, the weight loss was measured, and the degree of corrosion (a+dd) was calculated. The results are shown in Table 2.

Chokatachisui water l pH・11.8 Electrical conductivity (μs/cm): 5430 Total hardness (W CaC0z/I!): Less than 1 P-Al straightness (■CaC0:+/J):
1 1 0 0 chloride ion (■C1/l):
600 sulfate ion (■S04/l): 100 silica (■5iOz/jri: 250 total iron (
■Fe/l) Less than 0.05 ES: 120 〃:60 〃:30 〃:15 〃:3 〃:30 〃:300 SB:30 〃:3 〃300 GA: 30 〃:120 AS: 30 C＾ :30 〃:60 〃:30 〃:450 ”:450 〃:450 〃:450 〃:450 CT: 450 *: Target method ES: Sodium erythorbate SB: Potassium sorbate GA: Sodium gallate AS: Sodium ascorbate CA: Catechol GL Sodium nigerconate CT: Potassium citrate [Effects of the invention] According to the boiler corrosion prevention method of the present invention, the boiler operation can be stopped without replacing the boiler water containing the anticorrosion agent used during boiler operation. The boiler is also effectively protected from corrosion, and there is no need to replace the boiler water when restarting the boiler.Therefore, it is extremely easy to start and stop the boiler, and the amount of water treatment chemicals used can be reduced, making it economical.

Claims (3)

[Claims] (1) Add 10 to 200 mg of the compound (a) that produces tin ions or tin complex ions in boiler water.
/l, erythorbic acid, ascorbic acid, sorbic acid,
5 to 300 m of compound (b) consisting of one or more organic compounds selected from gallic acid and catechol or a salt thereof
g/l, and a compound (c) consisting of an aliphatic oxycarboxylic acid or a salt thereof in an amount of 30 to 1000 mg/l. (2) The boiler corrosion prevention method according to claim 1, wherein the compound (a) is stannous chloride. (3) The boiler corrosion protection method according to claim 1, wherein the compound (c) is gluconic acid or a salt thereof, and/or citric acid or a salt thereof.