JP6314560B2 - Water treatment method for steam generating equipment - Google Patents

Description

  The present invention relates to a water treatment method in a facility for generating steam, such as a boiler and a steam generator, and more specifically, in a steam generation facility that operates by supplying water containing copper, copper on the inner surface that comes into contact with water. The present invention relates to a water treatment method that suppresses heat transfer inhibition and poor water circulation due to adhesion of scales containing water.

  In equipment that generates steam by heating feed water such as a boiler and a steam generator, copper-based materials are used for various heat exchangers such as an air handling unit and an absorption refrigerator in the steam line. Therefore, when the condensed water in which steam is condensed in these heat exchangers is recovered as condensate and reused as part of the water supply, copper is contained in the water supply.

When operating steam generating equipment with water containing copper, copper scales in the can, causing heat transfer obstruction on the heat transfer surface and poor water circulation, reducing heat transfer efficiency, and heat transfer surface due to overheating. Causes blasting due to cracking, swelling, partial overconcentration due to poor circulation and air blowing.
In particular, if the makeup water is demineralized water such as ion-exchanged water, or when the makeup water recovery rate is high and the electrical conductivity of the feedwater is low even when the demineralization treatment is not performed, the boiler blow rate is reduced. In the case of setting and increasing the concentration factor of the can water, even if the copper concentration in the feed water is very small, copper is concentrated in the system, so it becomes easier to scale in the can, Often manifests as trouble.

  With respect to this problem, in Japanese Patent No. 5066972 (Patent Document 1), any one or more of succinic acid or a salt thereof, sorbic acid or a salt thereof so that the redox potential of blow water is 0 mV or more in ORP. A treatment method in which an anticorrosive agent containing is added is shown.

Japanese Patent No. 5066972

However, in the method of Patent Document 1, it cannot be said that the effect of suppressing copper scaling is sufficient, and there is a problem in that the progress of copper scale adhesion over time may not be negligible.
Such a problem has been found in some facilities when soft water is used as make-up water, and it has been found that many cases are observed when demineralized water such as ion exchange water is used as make-up water.

  Therefore, an object of the present invention is to provide a water treatment method that stably suppresses the scaling of copper in any facility in a steam generation facility that operates using feed water containing copper.

As a result of intensive studies to solve the above problems, the present inventors have added a reducing agent that cools the blow water of the steam generating facility to room temperature and sets the oxidation-reduction potential measured with an ORP meter to less than 0 mV. It was found that copper scaling can be stably suppressed by adding an alkaline agent so that the pH of the water system of the steam generating facility is not less than a predetermined value. Moreover, it discovered that the higher copper scale inhibitory effect was acquired by using a specific polymer together.
The present invention has been achieved based on such findings, and the gist thereof is as follows.

[1] In a water treatment method for suppressing adhesion of copper scale in a steam generation facility to which water containing copper is supplied , makeup water in the steam generation facility is demineralized water having an electric conductivity of 1 mS / m or less, and the steam Without adding a reducing agent that cools the blown water of the generating facility to room temperature and makes the oxidation-reduction potential measured by an ORP meter less than 0 mV, and the pH of the water system of the steam generating facility is 11. A water treatment method for a steam generating facility, wherein an alkali agent is added to the water system of the steam generating facility so as to be 6 or more.

[2] The water treatment method for a steam generation facility according to [1], wherein a water-soluble polycarboxylic acid and / or a salt thereof is added to the water system of the steam generation facility.

[3] In [2], the water-soluble polycarboxylic acid and / or salt thereof is polyacrylic acid, polyacrylic acid salt, polymethacrylic acid, and polymethacrylic acid salt having a molecular weight of 1,000 to 50,000. A water treatment method for steam generating equipment, wherein the water treatment method is at least one selected from the group consisting of:

  ADVANTAGE OF THE INVENTION According to this invention, in steam generation facilities, such as a boiler and a steam generator which operate by supplying the water containing copper, scaling of copper can be suppressed stably. For this reason, it suppresses adhesion of copper scale to the inner surface where water comes in contact with water such as boiler cans of steam generation equipment, and it will be stable and efficient for a long time without causing scale failures such as heat transfer inhibition and poor water circulation. Driving can be continued.

  Embodiments of the water treatment method for steam generating equipment according to the present invention will be described in detail below.

The water treatment method for steam generating equipment according to the present invention uses an ORP meter to cool the blow water of the steam generating equipment to room temperature in order to suppress adhesion of copper scale in the steam generating equipment to which water containing copper is supplied. Without adding a reducing agent for reducing the measured oxidation-reduction potential to less than 0 mV (hereinafter sometimes referred to as “ORP reducing reducing agent”), the pH of the water system of the steam generating facility is 11.3 or more. Thus, an alkali agent is added to the water system of the steam generating facility.
In addition, in this invention, normal temperature refers to the temperature within the range of 20-30 degreeC.

  Here, the ORP reducing reducing agent is such that when it is added to the water system of the steam generating facility, the redox potential measured by the ORP meter after cooling the blow water of the steam generating facility to room temperature is less than 0 mV. Various reducing agents such as hydrazine, sodium sulfite, erythorbic acid and salts thereof, ascorbic acid and salts thereof, tannic acid and salts thereof, gallic acid and sugars, gluconic acid and salts thereof, Although anticorrosive agents, such as glucoheptonic acid and its salt, are mentioned, it is not limited to these at all.

  In the present invention, the above-described ORP reducing reducing agent is not added at all, and the pH of the water system of the steam generating facility (hereinafter sometimes referred to as “boiler water”) is 11.3 or more, preferably Is added with an alkaline agent so as to be 11.6 or more.

  The alkali agent to be added may be any sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate or the like as long as the boiler water rises to the above pH, but carbonates such as sodium carbonate and potassium carbonate are It is preferable to use sodium hydroxide or potassium hydroxide because carbon dioxide gas is generated by pyrolysis inside the steam generator and the pH of steam condensed water may be lowered to increase the elution of copper.

  In JIS B 8223 “Boiler Feed Water and Boiler Water Quality”, the water quality of the boiler water is low in the case of using a soft water feed low pressure boiler with a pH of 11.0 to 11.8 and ion exchange water as make-up water. In the boiler, the pH is set to 10.5 to 11.5, but in the present invention, an alkaline agent is added so that the pH of the boiler water is 11.3 or more, preferably 11.6 or more. The upper limit of the pH is 12.5 or less, desirably 12.2 or less, more preferably 12.0 or less. If this upper limit is exceeded, there is concern about the carryover of boiler water and the occurrence of alkaline corrosion.

  In the present invention, copper is prevented from being scaled by adjusting to a predetermined pH by adding an alkaline agent without adding the ORP reducing reducing agent as described above, but the ORP reducing reducing agent is added in this way. By not doing, normally, the redox potential measured by the ORP meter after cooling the blow water of the steam generating equipment to be treated in the present invention to room temperature is about 5 to 80 mV.

  In this invention, while adjusting pH of boiler water as mentioned above, addition of water-soluble polycarboxylic acid and / or salt can suppress copper scaling further more significantly. Here, as the water-soluble polycarboxylic acid and / or its salt, polyacrylic acid and its salt, copolymer of acrylic acid and 2-acrylamido-2-methylpropanesulfonic acid and its salt, acrylic acid and 2 -Hydroxy-3-allyloxy-1-propanesulfonic acid copolymer and salts thereof, polymethacrylic acid and salts thereof, polymaleic acid and salts thereof, and the like. Examples of the polycarboxylate include sodium salt, potassium salt, ammonium salt and the like.

As the water-soluble polycarboxylic acid and / or salt, polyacrylic acid having a molecular weight of 1,000 to 50,000 and a salt thereof, or polymethacrylic acid having a molecular weight of 1,000 to 50,000 and a salt thereof are particularly suitable. Of these, polymethacrylic acid having a molecular weight of 1,000 to 50,000 and a salt thereof are optimal.
These water-soluble polycarboxylic acids and / or salts may be used alone or in combination of two or more.

  The addition amount of the water-soluble polycarboxylic acid and / or salt is 1.0 weight times or more, preferably 3.0 weight times or more with respect to the copper concentration in the feed water, in order to effectively obtain the addition effect. Is preferred. As the upper limit, there is no problem as long as the concentration in the can water is 500 mg / L or less. If the concentration of the water-soluble polycarboxylic acid and / or salt in the can water exceeds 500 mg / L, the occurrence of carryover is a concern.

  Such a water treatment method for steam generating equipment according to the present invention can be applied to any steam generating equipment such as special circulation boilers, water pipe boilers, round boilers, exhaust heat recovery boilers and the like into which copper (ions) is brought. However, it is effectively applied to a steam generation facility using demineralized water having an electric conductivity of 1 mS / m or less, for example, 0.01 to 1 mS / m as makeup water. Here, examples of the desalted water include ion-exchanged water, reverse osmosis membrane treated water, and electrodesalted treated water, but the production method is not particularly limited. When demineralized water is used as make-up water, the bicarbonate concentration decreases, so the M alkalinity in the feed water decreases, and the concentration of caustic alkali generated by thermal decomposition in the can water decreases. Therefore, it is particularly necessary to adjust the pH by adding an alkali agent according to the present invention.

  The operating pressure of the steam generating equipment to which the present invention is applied is usually 3 MPa or less, particularly 2.5 MPa or less, for example 0.4 to 2.5 MPa, from the viewpoint of preventing alkaline corrosion by keeping the pH of boiler water high. It is.

  In the present invention, as long as it is a chemical other than the ORP reducing agent, a general water treatment agent (corrosion inhibitor, scale inhibitor) in addition to the above alkaline agent, water-soluble polycarboxylic acid and / or salt. Etc.) may be used in combination.

  Corrosion inhibitors include water supply pipes, economizers that exchange heat between exhaust gas and water, and steam generators that do not raise the ORP of the cans, such as succinic acid and its salts, citric acid and its salts, Examples include sorbic acid and its salt, silicic acid and its salt, and the like. Examples of the steam condensate corrosion inhibitor include 2-amino-2-methyl-1-propanol, morpholine, monoisopropanolamine, monoethanolamine, diethanolamine, methoxypropylamine, monoglycolamine, diglycolamine, cyclohexylamine and the like. And long-chain aliphatic amines such as octadecylamine and the like. These drugs may be used alone or in combination of two or more. Since these steam condensate corrosion inhibitors reduce copper elution, they are effective in suppressing copper scale in the can.

  Examples of the scale inhibitor include various phosphoric acids and salts thereof such as trisodium phosphate and tribasic potassium phosphate, polyphosphoric acid and salts thereof such as tripolyphosphoric acid and salts thereof, hexametaphosphoric acid and phosphonic acid and salts thereof, and the like. Examples include phosphonic acids and salts thereof such as -hydroxyethylidene-1,1-diphosphonic acid and salts thereof, and 2-phosphonobutane-1,2,4-tricarboxylic acid and salts thereof. These may be used alone or in combination of two or more.

  Hereinafter, the present invention will be described more specifically with reference to examples.

[Comparative Example 1]
Copper chloride (II) is added to pure water (electric conductivity 0.06 mS / m) at 40 ° C. so as to be 5 mg-Cu / L, and the pH of the blow water is 11.0 to 11.1. A sodium hydroxide aqueous solution was added to the test boiler, which was supplied to a test boiler and operated for 120 hours under the following operating conditions.

<Test boiler operating conditions>
Water supply amount: 10L / hr
In-can pressure: 1.0 MPa
Blow rate: 10%
After this operation test, the amount of copper adhering to the heat transfer surface was measured. Also, during this test period, the copper concentration in the blow water was measured to determine the copper discharge from the blow water as the average copper concentration of the blow water, and the copper from the blow water relative to the amount of copper added from the feed water. The emission rate was calculated. During the test period, the pH and redox potential of blow water were measured.
The measurement method and test conditions for each item are as shown below.
The test results are shown in Table 1.

<Copper adhesion amount on heat transfer surface>
After the test, the test tube (surface area: 972 cm ² ), which is the heat transfer section of the test boiler, was washed twice with 1 wt% ammonia water heated to 50 ° C., and the copper ion concentration in the wash water was measured by atomic absorption spectrometry. . The amount of copper adhering to the test tube surface was determined from the copper ion concentration and the total amount of washing water.

<Copper emissions and rate>
During the test period, the blow water was sampled six times, the ammonia water was added to the blow water and heated to dissolve the copper in the blow water, and the copper concentration was measured by atomic absorption analysis. The average value of the copper concentration of water was calculated. In addition, by multiplying the average copper concentration of blow water and the amount of blow water, the amount of copper discharged by blow water is obtained, the amount of copper added to the feed water and brought into the test boiler, and the amount of copper discharged by blow water The copper discharge rate was calculated from the following formula.
Copper emission rate (%) = (Copper discharge by blow water / Amount of copper added to the feed water and brought into the test boiler) x 100

<Blow water pH and redox potential>
During the test period, the blow water was heat-exchanged and cooled to room temperature (25 ° C.), and the pH and oxidation-reduction potential were determined by measuring with a pH meter and an ORP meter (both manufactured by Toa DKK), respectively.

[Comparative Examples 2 to 6]
Hydrazine added to feed water at 8 mg / L (Comparative Example 2), potassium tannic acid potassium hydroxide added at 15 mg / L (Comparative Example 3), trisodium citrate added at 20 mg / L (Comparative Example 4), molecular weight Except for the addition of 15 mg / L of 4,000 sodium polyacrylate (Comparative Example 5), 20 mg / L of trisodium citrate and 15 mg / L of polysodium polyacrylate having a molecular weight of 4,000 (Comparative Example 6) In the same manner as in Comparative Example 1, the test was performed. The results are shown in Table 1.

[Comparative Example 7]
The test was conducted in the same manner as in Comparative Example 1 except that 15 mg / L of tannic acid was added to the feed water, and sodium hydroxide was added so that the pH of the blow water was 11.6. The results are shown in Table 1.

[Example 1]
The test was performed in the same manner as in Comparative Example 1 except that sodium hydroxide was added so that the pH of the feed water was 11.3. The results are shown in Table 1.

[Examples 2-3]
Sodium hydroxide was added so that the pH of the blow water was 11.3, 15 mg / L of polyacrylic acid soda having a molecular weight of 4,000 was added to the feed water (Example 2), and polymethacryl having a molecular weight of 30,000. The test was conducted in the same manner as in Comparative Example 1 except that 15 mg / L of sodium acid was added (Example 3). The results are shown in Table 1.

[Examples 4 to 6]
Sodium hydroxide was added so that the pH of the blow water was 11.6, 15 mg / L of sodium polyacrylate having a molecular weight of 52,000 was added to the feed water (Example 4), and a polyacryl having a molecular weight of 4,000. The test was conducted in the same manner as in Comparative Example 1 except that 15 mg / L of sodium acid was added (Example 5) and 15 mg / L of polysodium methacrylate having a molecular weight of 30,000 was added (Example 6). The results are shown in Table 1.

[Example 7]
Comparative Example 1 except that sodium hydroxide was added so that the pH of the blow water was 12.0, and 15 mg / L of poly (sodium methacrylate) having a molecular weight of 30,000 was added to the feed water (Example 7). The test was conducted. The results are shown in Table 1.

In addition, in the following Table 1, an additive chemical | medical agent was described with the following symbol.
TA · KOH: Potassium hydroxide salt of tannic acid Na citrate ₃ : Trisodium citrate PANa (4000): Sodium polyacrylate with a molecular weight of 4,000 PMNa (30000): Polysodium methacrylate with a molecular weight of 30,000 PANa 52000): Sodium polyacrylate having a molecular weight of 52,000

The following can be seen from the results in Table 1.
In Comparative Examples 1 to 6 in which the pH of the blow water is 11.0 to 11.1, the copper adhesion amount on the heat transfer surface is large. Among these, in Comparative Examples 2 and 3 to which hydrazine having a deoxygenation function and potassium hydroxide salt of tannic acid were added, corrosion of the steel material can be reduced, but the redox potential of blow water is less than 0 mV, and the heat transfer surface is reduced. The amount of copper adhesion is particularly large.
In Comparative Example 7 in which the pH of the blow water was 11.6 and tannic acid was added, the amount of copper adhering to the heat transfer surface was less than that in Comparative Examples 1 to 6 due to the increase in pH. The potential is as low as less than 0 mV, and the amount of copper adhering to the heat transfer surface is large.
In contrast, in Examples 1 to 7 in which the pH of the blow water was 11.3 to 12.0 and no ORP reducing reducing agent was added, the redox potential was about 30 to 70 mV, and the blow water was oxidized. The reduction potential is as high as 0 mV or more, and not only can the corrosion of the steel material be reduced, but also the amount of copper adhering to the heat transfer surface is much smaller than in Comparative Examples 1-7. In particular, in Examples 2, 3, and 5 to which a (meth) acrylic acid polymer having a suitable molecular weight was added, particularly in Examples 3, 6, and 7 to which a methacrylic acid polymer having a suitable molecular weight was added, to the heat transfer surface It was possible to significantly reduce the amount of copper deposited.

Claims (3)

In a water treatment method for suppressing adhesion of copper scale in a steam generation facility to which water containing copper is supplied, the makeup water of the steam generation facility is demineralized water having an electric conductivity of 1 mS / m or less, and the steam generation facility Without adding a reducing agent that cools the blow water to room temperature and makes the redox potential measured with an ORP meter less than 0 mV, and the pH of the water system of the steam generating facility is 11. A water treatment method for a steam generating facility, wherein an alkali agent is added to the water system of the steam generating facility so as to be 6 or more.   The water treatment method for a steam generation facility according to claim 1, wherein a water-soluble polycarboxylic acid and / or a salt thereof is added to the water system of the steam generation facility.   3. The water-soluble polycarboxylic acid and / or salt thereof according to claim 2, selected from polyacrylic acid, polyacrylic acid salt, polymethacrylic acid, and polymethacrylic acid salt having a molecular weight of 1,000 to 50,000. A water treatment method for a steam generating facility, wherein the water treatment method is one or more.