JP2006274427A - Water treating agent and water treatment method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a water treating agent capable of preventing full surface corrosion and local corrosion of a heat transfer surface of a boiler tube and obtaining excellent heat transfer characteristics and a water treatment method using the water treating agent. <P>SOLUTION: The water treating agent is constituted by using water as a principal component and compounding a film forming agent forming a film on the heat transfer surface of the boiler tube, a deoxidant, an anti-scaling agent and a pH modifier with the water. The corrosion prevention and scale inhibition of the heat transfer surface of the boiler tube are performed with good balance by injecting the water treating agent into boiler feedwater. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a water treatment agent and a water treatment method, and in particular, a water treatment agent capable of preventing overall corrosion and local corrosion of a heat transfer surface of a boiler water pipe and obtaining excellent heat transfer characteristics, and the water treatment agent. The present invention relates to a water treatment method using

  A boiler is a device that generates steam by being widely used as an energy supply facility for heating and power generation. The inner surface of the water pipe that generates steam in the boiler (the heat transfer surface of the boiler water pipe) is in a high-temperature and high-pressure environment, and this heat transfer surface contains calcium contained in the water supplied to the boiler (boiler feed water). These components adhere as a scale (scaling) or corrode by boiler feed water. When the scale adheres to the heat transfer surface, heat transfer is hindered by the scale, and heat transfer characteristics such as boiler efficiency are deteriorated. Further, when the heat transfer surface is corroded, the boiler water pipe is damaged by this corrosion, and the boiler operation may be stopped depending on the damage of the boiler water pipe.

  Therefore, conventionally, in order to prevent (suppress) scaling and corrosion on the heat transfer surface of the boiler water pipe, agents such as a scale inhibitor and a pH adjuster have been added to the boiler feed water as a water treatment agent. However, conventional water treatment agents are used individually to prevent scaling and corrosion of the heat transfer surface of the boiler water pipe, and at the same time balance scaling prevention and corrosion prevention of the heat transfer surface of the boiler water pipe. It was difficult to do. That is, when a water treatment agent is added to boiler feed water for the purpose of preventing scaling of the heat transfer surface, it is not sufficient to prevent corrosion of the heat transfer surface of the water pipe even if the heat transfer surface can be prevented from scaling. . On the other hand, when a water treatment agent is added to boiler feed water for the purpose of preventing corrosion of the heat transfer surface, it is not sufficient to prevent scaling of the heat transfer surface even though corrosion of the heat transfer surface can be prevented.

For this reason, silica and a pH adjuster are used as a water treatment agent capable of simultaneously performing scaling prevention and corrosion prevention of the heat transfer surface in a well-balanced manner in order to suppress corrosion of the heat transfer surface and scale formation caused by the influence of moisture. A water treatment agent comprising a scale inhibitor is proposed (for example, see Patent Document 1).
Japanese Patent Laying-Open No. 2003-159597 (2nd page)

  In order to prevent corrosion of the heat transfer surface of the boiler water pipe, the water treatment agent described in Patent Document 1 uses a silica component and a pH adjuster to form a silica layer and an iron hydroxide layer (for preventing corrosion on the heat transfer surface). For example, iron oxyhydroxide) is formed. However, if the thickness of the silica layer and the iron hydroxide layer formed on the heat transfer surface is insufficient, the anticorrosive action is not exhibited, and thus the heat transfer surface may be corroded. When the heat transfer surface is covered with the corrosion product, the heat conductivity of the corrosion product is small, so that there is a problem that the heat transfer characteristic of the boiler is deteriorated. Further, when the silica layer and the iron hydroxide layer cannot cover the entire heat transfer surface substantially uniformly, local corrosion (pitting corrosion) may occur on the heat transfer surface. If the heat transfer surface is locally corroded, a hole penetrating the boiler water pipe may be formed, and there is a problem that water leaks from the hole into the boiler furnace.

  An object of the present invention is to provide a water treatment agent capable of preventing overall corrosion and local corrosion of a heat transfer surface of a boiler water pipe and obtaining excellent heat transfer characteristics, and a water treatment method using the water treatment agent. It is in.

  The present invention has been made to solve the above problems, and the invention of claim 1 is based on water, and a film forming agent that forms a film on the heat transfer surface of a boiler water pipe, an oxygen scavenger, A scale inhibitor and a pH adjuster are blended in the water. With this configuration, a film capable of suppressing corrosion is formed on the heat transfer surface of the boiler water pipe by the film forming agent, dissolved oxygen in the boiler feed water is removed by the oxygen scavenger, and scaling of the heat transfer surface of the boiler water pipe is scaled down. The pH of the boiler feed water is adjusted by the agent.

  The invention of claim 2 is characterized in that the film forming agent of claim 1 is composed of at least one or more of silica, sodium silicate, potassium silicate, orthosilicate, and polysilicate. It is said. With this configuration, a film capable of suppressing corrosion on the heat transfer surface of the boiler water pipe is formed from at least one or more of silica, sodium silicate, potassium silicate, orthosilicate, and polysilicate.

  In the invention of claim 3, the oxygen absorber according to claim 1 or 2 is vitamin C and a salt thereof, tannin, a sugar-type oxygen absorber, erythorbic acid and a salt thereof, or a sulfite. It is characterized by comprising more than seeds. Here, the reason why vitamin C and its salt are used as an oxygen scavenger is that oxygen dissolved in boiler feed water can be removed by a strong reducing power and there is no toxicity like hydrazine. Boiler feed water from which dissolved oxygen has been removed has less corrosive action on the heat transfer surface of the boiler water pipe. With this configuration, dissolved oxygen in boiler feedwater is removed by an oxygen scavenger consisting of at least one or more of vitamin C and its salts, tannins, sugar-type oxygen absorbers, erythorbic acid and its salts, and sulfites. Is done.

  The invention according to claim 4 is the scale inhibitor according to claim 1, 2 or 3, wherein the scale inhibitor is at least one of citric acid, ethylenediaminetetraacetic acid and its salt, polyacrylic acid and its salt, polymaleic acid and its salt Or it consists of 2 or more types. Here, the scale inhibitor is used because it is possible to prevent the scale from adhering to the heat transfer surface of the boiler water pipe (scaling). That is, when citric acid, ethylenediaminetetraacetic acid and salts thereof are used as the scale inhibitor, calcium ions and magnesium ions contained in the boiler feed water are chelated by the scale inhibitor, It becomes impossible to adhere as a scale to the heat transfer surface. In addition, when polyacrylic acid, polymaleic acid, or the like is used as the scale inhibitor, the growth of scale crystal nuclei formed by calcium ions or magnesium ions is hindered, and the scale is reduced against the heat transfer surface of the boiler water tube. Can not adhere as. With this configuration, the scale of the heat transfer surface of the boiler water pipe is scale inhibitor composed of at least one or more of citric acid, ethylenediaminetetraacetic acid and its salt, polyacrylic acid and its salt, polymaleic acid and its salt Is prevented.

  Further, the invention according to claim 5 is the pH regulator according to claim 1, 2, 3 or 4, wherein at least one or two of alkali metal hydroxides such as sodium hydroxide and potassium hydroxide are used. It is characterized by the above. Here, this pH adjuster is used to adjust the pH of the boiler feed water to the alkali side in order to prevent corrosion of the heat transfer surface of the boiler water pipe. With this configuration, the pH of boiler feed water is adjusted by a pH adjuster composed of at least one or two or more of alkali metal hydroxides such as sodium hydroxide and potassium hydroxide.

  Further, the invention of claim 6 is a process of adjusting the water treatment agent according to claim 1, 2, 3, 4 or 5 to a predetermined concentration, and the concentration of silica dissolved in the water supply tank and the amount of dissolved oxygen. It comprises a step of detecting and a step of controlling the amount of the water treatment agent supplied to the water supply tank. With this configuration, when fluctuation occurs in the silica concentration or dissolved oxygen amount in the boiler feed water, a film forming agent that forms a film on the heat transfer surface of the boiler water pipe, an oxygen scavenger, a scale inhibitor, and a pH adjuster As for the water treatment agent adjusted to a predetermined concentration, the amount supplied to the water supply tank can be controlled in accordance with the fluctuation.

According to the first aspect of the present invention, it is possible to prevent the overall corrosion and local corrosion of the heat transfer surface of the boiler water pipe and to obtain excellent heat transfer characteristics.
According to the second aspect of the present invention, since the coating capable of suppressing corrosion is formed on the heat transfer surface of the boiler water tube by silica or the like as a film forming agent, the entire surface corrosion and local corrosion of the heat transfer surface of the boiler water tube are prevented. While preventing further, the outstanding heat-transfer characteristic can be acquired.

According to the invention described in claim 3, since dissolved oxygen in the boiler feed water is removed by a non-toxic oxygen scavenger such as vitamin C, further corrosion and local corrosion of the heat transfer surface of the boiler water pipe are further prevented. In addition, excellent heat transfer characteristics can be obtained.
According to the invention described in claim 4, since the scaling of the heat transfer surface of the boiler water pipe is prevented by ethylenediaminetetraacetic acid and its salt which are scale inhibitors, the overall corrosion and local corrosion of the heat transfer surface of the boiler water pipe In addition, it is possible to obtain more excellent heat transfer characteristics.

Furthermore, according to the invention described in claim 5, since the pH of the boiler feed water is adjusted by a pH adjusting agent such as sodium hydroxide, it prevents overall corrosion and local corrosion of the heat transfer surface of the boiler water pipe, Excellent heat transfer characteristics can be obtained.
Further, according to the invention described in claim 6, even when the silica concentration or the dissolved oxygen amount in the boiler feed water varies, the water treatment agent is adjusted to a predetermined concentration, and this concentration-adjusted water treatment agent is obtained. By controlling the amount of water supplied to the water supply tank in response to the fluctuation, it is possible to prevent overall corrosion and local corrosion on the heat transfer surface of the boiler water pipe and to obtain excellent heat transfer characteristics.

BEST MODE FOR CARRYING OUT THE INVENTION

  The present invention comprises water as a main component, and a film forming agent that forms a film on the heat transfer surface of the boiler water pipe, an oxygen scavenger, a scale inhibitor, and a pH adjuster are blended in the water. It is realized by.

  As the film forming agent for the water treatment agent, at least one or more known materials such as silica (anhydrous silicic acid), sodium silicate, potassium silicate, orthosilicate, polysilicate and the like are used. This film forming agent is adsorbed on the heat transfer surface of the boiler water tube to form a film, and the heat transfer surface of the boiler water tube is covered with this film. The film formed by this film forming agent acts as a barrier layer (shielding layer) by covering the heat transfer surface of the boiler water pipe and acts as a protective film against corrosion. Therefore, the transfer of the boiler water pipe covered with this protective film is performed. Corrosion is suppressed on the hot surface.

  The oxygen scavenger used together with the film forming agent includes at least one or more known ones such as vitamin C and salts thereof, tannin, saccharide type oxygen scavenger, erythorbic acid and salts thereof, and sulfites. Used. This oxygen scavenger has no toxicity like hydrazine and can remove oxygen dissolved in boiler feed water. Oxygen dissolved in the boiler feed water acts to corrode the heat transfer surface of the boiler water pipe as an oxidizing agent. For this reason, when oxygen dissolved in the boiler feed water is removed by the oxygen scavenger, the oxidant concentration in the boiler feed water becomes low, so that the overall corrosion on the heat transfer surface of the boiler water pipe is prevented. In addition, if oxygen dissolved in the boiler feed water is removed, the oxygen concentration non-uniformity is reduced on the heat transfer surface of the boiler water pipe, so that it is difficult to form an oxygen concentration cell, and in the heat transfer surface of the boiler water pipe. Local corrosion is also prevented. Here, it will be described in detail that local corrosion of the heat transfer surface of the boiler water pipe is prevented by the water treatment agent according to the embodiment of the present invention.

  In general, when a film capable of suppressing corrosion is formed on the heat transfer surface of the boiler water pipe, the material (for example, carbon steel) used for the heat transfer surface of the boiler water pipe is less likely to be corroded by the boiler feed water. The coating film formed on the heat transfer surface of the boiler water pipe is, for example, a silica component adsorbed on the surface of carbon steel or iron oxyhydroxide formed on the surface of carbon steel. However, the surface of the heat transfer surface of the boiler water pipe may have a portion (film defect portion) where the film formation is insufficient due to a factor that inhibits the film formation. Those that inhibit this film formation include the presence of chlorine ions that inhibit film formation in boiler feed water, surface non-uniformity due to surface segregation such as sulfur (sulfides) contained in carbon steel, There are various factors such as non-uniformity in the concentration of the film-forming agent due to the non-uniform flow rate of boiler feedwater flowing through. If there is a factor that hinders the formation of this film, the surface of the heat transfer surface of the boiler water pipe has a film part (sound film part) formed of silica or iron hydroxide, and this film is not sufficiently formed. There is a portion (film defect portion), a local battery is formed by a healthy film portion and a film defect portion, and local corrosion may occur.

  By the way, in general, local corrosion such as crevice corrosion and pitting corrosion (corresponding to corrosion caused by localized concentration of the metal surface is not uniform) is general corrosion (referred to as corrosion occurring almost uniformly on the metal surface). It is known to occur easily in an environment where it is difficult to occur. Since the general corrosion occurs almost uniformly on the metal surface, the metal surface is not locally corroded, whereas the local corrosion is totally suppressed by the passive film and protective film. It tends to occur at the film defect part when a sound film is formed and the overall corrosion is suppressed. This is because the film defect part is more easily corroded than the sound film part, and the film defect part is locally concentrated and corroded.

  That is, this film defect part forms a local battery with a healthy film part, and this film defect part is the anode electrode of the local battery (battery negative electrode, oxidation reaction takes place, metal is dissolved, ie, corrosion This is because the healthy film portion becomes the cathode electrode of the local battery (the positive electrode of the battery, a reduction reaction occurs, and the metal is not dissolved, that is, is not corroded). In this local battery, an oxygen concentration battery is formed, and the battery reaction proceeds. It is known that the oxygen concentration cell generally has a higher corrosion rate as the ratio of the oxygen amount (concentration) between the healthy film portion forming the cathode and the film defect portion forming the anode is larger (the cell electromotive force is larger). . In other words, this means that if the ratio of the oxygen amount (concentration) between the healthy film portion and the film defect portion can be reduced, local corrosion due to the film defect portion can be prevented (suppressed). ing.

  The water treatment agent of the present invention is the oxygen dissolved in the boiler feed water by the oxygen scavenger even if the film on the heat transfer surface of the boiler water pipe formed by the film forming agent forms a film defect part for some reason. Since it is difficult to form an oxygen concentration cell by reducing the amount (concentration), local corrosion is prevented. That is, when the oxygen amount (concentration) dissolved in the boiler feed water decreases, the absolute amount of oxygen (concentration) in the healthy film portion decreases, so the oxygen amount (concentration) in the healthy film portion and the film defect portion ) Ratio is small, the electromotive force of the oxygen concentration cell is small, and local corrosion can be prevented.

  In addition to the oxygen scavenger, the water treating agent of the present invention contains a scale inhibitor. As the scale inhibitor, at least one or more known substances such as citric acid, ethylenediaminetetraacetic acid and salts thereof, polyacrylic acid, and polymaleic acid are used. When citric acid, ethylenediaminetetraacetic acid and its salt (EDTA-Na) are used as the scale inhibitor, calcium ions and magnesium ions contained in the boiler feed water are chelated by the scale inhibitor, and the boiler Scale is less likely to adhere to the heat transfer surface of the water pipe. In addition, when polyacrylic acid and its salts, polymaleic acid and its salts, etc. are used as the scale inhibitor, the growth of the scale crystal nuclei formed by calcium ions and magnesium ions is hindered, and the propagation of the boiler water tube is prevented. Scale is less likely to adhere to the hot surface. Thus, when scale becomes difficult to adhere to the heat transfer surface of the boiler water pipe, the boiler can be operated while maintaining excellent heat transfer characteristics.

  Furthermore, a pH adjuster is blended in this water treatment agent. As the pH adjusting agent, at least one or more known substances such as alkali metal hydroxides such as sodium hydroxide and potassium hydroxide are used. This pH adjuster adjusts the pH of boiler feed water to the alkali side in order to prevent corrosion of the heat transfer surface of the boiler water pipe.

  By the way, although the film-forming agent, oxygen scavenger, scale inhibitor, and pH adjuster in the present invention can be supplied in the form of being dissolved in water as individual agents, the introduction of a water treatment agent (medical injection) Therefore, it is desirable to make a one-part preparation.

Hereinafter, one example of the water treatment agent according to the embodiment of the present invention will be described in detail based on Table 1 with reference to Example 1 to Example 3.

(1) Example 1
The water treatment agent of Example 1 shown in Table 1 is a mixture of a predetermined amount of a film forming agent, an oxygen scavenger, a scale inhibitor, and a pH adjuster in pure water per 100 g of the total amount of the water treatment agent. is there. That is, the water treatment agent of Example 1 is 1.26 g of sodium silicate (Wako Pure Chemicals, special grade reagent) as a film forming agent, and vitamin C (L-ascorbic acid) (Wako Pure Chemicals, special grade reagent) as an oxygen scavenger. ) 2.5 g, 0.4 g of EDTA-2Na (Wako Pure Chemical, special grade reagent) in the scale inhibitor, and 4.0 g of sodium hydroxide (Wako Pure Chemical, special grade reagent) in the pH adjuster. 500 mg per liter was put into softened water. Here, the water softened as the boiler feed water, that is, the artificially adjusted soft water of Osaka City is used, pH is 7.5, electric conductivity is 25 mS / m, M alkalinity is 20 mg. / Little-CaCO ₃ , having a water quality of 1 mg / Little-CaCO ₃ . As the water softened water used in Examples and Comparative Examples of this water treatment agent, water prepared by artificially adjusting the softened water of Osaka City is used, and description of the water softened is omitted below. To do.

(2) Example 2
In the same manner as the water treatment agent of Example 1, the water treatment agent of Example 2 contains a predetermined amount of a film forming agent, an oxygen scavenger, a scale inhibitor, and a pH adjuster per 100 g of the total amount of the water treatment agent. It is a blend. That is, the water treatment agent of Example 2 was 5.46 g of sodium silicate (Wako Pure Chemicals, special grade reagent) as a film forming agent, and vitamin C (L-ascorbic acid) (Wako Pure Chemicals, special grade reagent) as an oxygen scavenger. ) 5.0 g, 0.4 g of EDTA-2Na (Wako Pure Chemicals, special grade reagent) in the scale inhibitor, and 4.0 g of sodium hydroxide (Wako Pure Chemicals, special grade reagent) in the pH adjuster. 500 mg per liter was put into softened water.

(3) Example 3
In the same manner as the water treatment agent of Example 1, the water treatment agent of Example 3 contains a predetermined amount of a film forming agent, an oxygen scavenger, a scale inhibitor, and a pH adjuster per 100 g of the total amount of the water treatment agent. It is a blend. That is, the water treatment agent of Example 3 was 9.66 g of sodium silicate as a film forming agent, 7.5 g of vitamin C (L-ascorbic acid) (Wako Pure Chemicals, special grade reagent) as an oxygen scavenger, and scale suppression. EDTA-2Na (Wako Pure Chemicals, special grade reagent) 0.4g in the agent and sodium hydroxide (Wako Pure Chemicals, special grade reagent) 4.0g in the pH adjuster, which is mixed with softened water 500 mg was introduced per liter.

<Comparative example>
(1) Comparative Example 1
The water treatment agent of Comparative Example 1 is obtained by blending a predetermined amount of a film forming agent, a scale inhibitor, and a pH adjuster with pure water per 100 g of the total amount of the water treatment agent. That is, the water treatment agent of Comparative Example 1 has 0.04 g of sodium silicate (Wako Pure Chemical, special grade reagent) as a film forming agent and 0.4 g of EDTA-2Na (Wako Pure Chemical, special grade reagent) as a scale inhibitor. In addition, 4.0 g of sodium hydroxide (Wako Pure Chemicals, special grade reagent) was added to the pH adjuster, and 500 mg per liter was added to softened water.

(2) Comparative Example 2
Similar to the water treatment agent of Comparative Example 1, the water treatment agent of Comparative Example 2 is obtained by blending a predetermined amount of a film forming agent, a scale inhibitor, and a pH adjuster into pure water per 100 g of the total amount of the water treatment agent. . That is, the water treatment agent of Comparative Example 2 has 21.5 g of sodium silicate (Wako Pure Chemical, special grade reagent) as a film forming agent and 0.4 g of EDTA-2Na (Wako Pure Chemical, special grade reagent) as a scale inhibitor. In addition, 4.0 g of sodium hydroxide (Wako Pure Chemicals, special grade reagent) was added to the pH adjuster, and 500 mg per liter was added to softened water.

<Evaluation>
(1) Experimental conditions Using the boiler feed water to which a predetermined amount of the water treatment agent shown in Examples 1 to 3 and Comparative Examples 1 and 2 is added, the scale adhesion characteristics and corrosion on the heat transfer surface of the boiler water pipe are evaluated. It was. The scale adhesion characteristics and the corrosion were evaluated by adding soft water obtained by adding a predetermined amount of the water treatment agent shown in Examples 1 to 3 and Comparative Examples 1 and 2 to an experimental once-through boiler having an evaporation amount of 1.35 kg / hour. This was carried out using an experimental once-through boiler that was supplied for boiler feed water and was operated such that the blow rate of the boiler feed water was 10% while continuously generating steam having a pressure of 0.3 MPa. This experimental once-through boiler was operated continuously for 48 hours because the scale adhesion characteristics and corrosion evaluation on the heat transfer surface of the boiler water pipe were as close as possible to those of the actual machine. The scale adhesion characteristics on the heat transfer surface of the boiler water pipe are measured 24 hours after the start of operation of the boiler by collecting boiler water (referred to water heated by the water in the boiler water pipe) and measuring the Ca concentration in the boiler water. In addition to evaluating the solubility of Ca, an evaluation boiler water pipe was extracted from the experimental once-through boiler after 48 hours of operation, and the heat transfer surface of the boiler water pipe was observed and evaluated. Further, the corrosion on the heat transfer surface of the boiler water tube was evaluated by observing the heat transfer surface of the boiler water tube for evaluation.

(2) Evaluation of scale adhesion characteristics Scale adhesion characteristics on the heat transfer surface of the boiler water pipe are evaluated by the following procedure.
First, the boiler water is sampled 24 hours after the start of operation of the boiler, and the Ca concentration of the sampled boiler water is measured by an ICP emission analyzer, and the solubility of the Ca is evaluated from the measured Ca concentration. Scale adhesion characteristics on the heat transfer surface of the water pipe are evaluated. Here, the evaluation of the scale adhesion property by the evaluation of the Ca solubility is made by paying attention to the decrease in the Ca concentration of the boiler water, that is, the Ca solubility, when Ca is deposited as a scale on the heat transfer surface of the boiler water pipe. is there. Specifically, in the case where an experimental once-through boiler is operated with a boiler feed water containing a Ca concentration of 1.0 mg / liter-CaCO ₃ under a condition where the boiler blow rate is 10%, the heat transfer surface of the boiler water pipe has Ca. If it is not deposited as a scale, the Ca concentration is detected as a concentration maintaining about 10 mg / liter without reducing the Ca solubility of the boiler water. On the other hand, if Ca deposits as a scale on the surface of the heat transfer surface of the boiler water pipe, the Ca solubility of the boiler water is decreased, and the Ca concentration is detected as a concentration lower than 10 mg / liter.

  Next, after 48 hours from the start of boiler operation, the operation of the experimental once-through boiler is stopped, the boiler water pipe is extracted from the stopped boiler, and whether or not Ca adheres to the heat transfer surface of the boiler water pipe as a scale. Is observed with the naked eye and a magnifying glass to evaluate the scale adhesion characteristics. In addition, the scale adhesion property can be evaluated from the thickness of the scale by measuring the thickness of the scale adhered to the heat transfer surface of the boiler water pipe using a film thickness meter.

  Thus, in Table 1, about the boiler feed water to which a predetermined amount of the water treatment agent shown in Examples 1 to 3 and Comparative Examples 1 and 2 was added, as the Ca concentration after 24 hours from the start of operation of the boiler. The Ca solubility of boiler water is shown.

  According to the results shown in Table 1, the boiler feed water to which the predetermined amounts of the water treatment agents of Examples 1 to 3 and Comparative Example 1 were added had a Ca solubility of 10 mg / liter or more. On the other hand, the boiler feed water to which a predetermined amount of the water treatment agent of Comparative Example 2 was added had a Ca solubility of 10 mg / liter or less. In the water treatment agent of Comparative Example 2, the reason why the Ca solubility was small was that the concentration of sodium silicate in the boiler feed water was large, so that the silica component in the sodium silicate and the hardness (Ca) were combined and transferred to the boiler water pipe. It is because it adhered to the hot surface thickly.

(3) Evaluation of corrosion Evaluation of corrosion on the heat transfer surface of the boiler water pipe was performed according to the following procedure. First, the operation of the boiler is stopped after 48 hours, the boiler water pipe is extracted from the stopped boiler, and the scale is removed from the surface of the water pipe by water washing or pickling. Next, the surface of the boiler water pipe from which the scale has been removed is visually observed with the naked eye or a magnifying glass to examine whether there is any general corrosion. Finally, for local corrosion, the surface of the boiler water tube from which scale has been removed is examined by visual observation with the naked eye or a loupe to see if pitting corrosion (also called pitting) has occurred. Is measured with an optical displacement meter to determine the maximum depth of pitting corrosion.

  Table 1 shows boiler supply water to which a predetermined amount of the water treatment agent shown in Examples 1 to 3 and Comparative Examples 1 and 2 is added, whether or not there is general corrosion on the heat transfer surface of the boiler water pipe, whether or not there is local corrosion, Each maximum eclipse depth is shown.

  According to the results shown in Table 1, in the boiler feed water to which a predetermined amount of the water treatment agents of Examples 1 to 3 and Comparative Example 2 are added, overall corrosion and local corrosion of the heat transfer surface of the boiler water pipe are prevented. It was. On the other hand, in the boiler feed water to which a predetermined amount of the water treatment agent of Comparative Example 1 was added, overall corrosion was prevented, but local corrosion of the heat transfer surface of the boiler water pipe was not prevented.

  From the above, according to the water treatment agents according to Examples 1 to 3, a film capable of suppressing corrosion is formed on the heat transfer surface of the boiler water pipe by the film forming agent, and the dissolved oxygen in the boiler feed water is oxygen scavenger. In addition, scaling of the heat transfer surface of the boiler water pipe is prevented by the scale inhibitor, and the pH of the boiler feed water is adjusted to prevent overall corrosion and local corrosion of the heat transfer surface of the boiler water pipe. Heat transfer characteristics can be obtained.

Next, an embodiment of a water treatment method using the water treatment agent of the present invention in a steam boiler device will be described with reference to FIG. FIG. 1 shows a schematic configuration of a steam boiler apparatus.
In FIG. 1, the steam boiler device 1 includes a water supply unit 2, a steam boiler 3, a water treatment agent supply unit 4, and a control unit 5.

  The water supply unit 2 includes various pretreatment devices that supply boiler water to the steam boiler 3, and includes a water softener 21, a deaeration device 22, and a water supply tank 23. The water softener 21 is a device that softens (softens) supply water such as tap water or industrial water supplied from the outside through the supply water supply path W1. The reason why the makeup water is softened (softened) is to remove calcium ions and magnesium ions contained in the makeup water. Here, the reason why calcium ions and magnesium ions are removed is to prevent them from adhering as a scale to the heat transfer surface of the boiler water pipe and deteriorating heat transfer characteristics. The makeup water (soft water) softened by the water softener 21 is deaerated by the deaerator 22.

  The deaeration device 22 is a device that mainly removes dissolved oxygen in soft water in advance because dissolved oxygen is present in the soft water, so that the heat transfer surface of the boiler water pipe is easily corroded by the oxygen. As the deaerator 22, a gas separation membrane, a device that continuously removes oxygen by heating, a batch-type device that uses reduced pressure or ultrasonic waves, or the like is used. Among these, an apparatus using a gas separation membrane, which is a membrane that allows gas to pass and does not allow liquid to pass, is preferable because it is easy to operate, can be stably operated continuously, and is inexpensive. That is, in an apparatus using a gas separation membrane, softened water (soft water) is allowed to flow inside the gas separation membrane, and when the outside of the membrane is evacuated, the gas contained in the soft water is passed between the membranes. It can be exhausted to the outside of the membrane and the soft water can be degassed.

  The soft water from which dissolved oxygen has been removed by the degassing device 22 is stored in the water supply tank 23. Boiler feed water to be supplied to the steam boiler 3 is stored in the feed water tank 23, and a detection unit 24 that measures and detects the silica concentration and dissolved oxygen amount in the boiler feed water is provided. In this water supply tank 23, soft water deaerated by the deaerator 22 and condensate obtained by heat exchange of steam generated by the steam boiler 3 in a load device (not shown) are a condensate recovery path (not shown). Supplied via In addition, a water treatment agent stored in a water treatment agent tank 41, which will be described later, is supplied to the water supply tank 23 through a water treatment agent supply path W2 by a chemical supply pump P1 in order to perform chemical treatment of boiler supply water. This water treatment agent is the water treatment agent described in the embodiment of the present invention, a film forming agent that is mainly composed of water and forms a film on the heat transfer surface of the boiler water pipe, an oxygen scavenger, A scale inhibitor and a pH adjuster are blended. Therefore, when this water treatment agent is supplied to the boiler feed water, corrosion of the heat transfer surface of the boiler water pipe and adhesion of scale can be prevented. This boiler feed water is supplied from the feed water tank 23 to the steam boiler 3 via the feed water path W3 by the feed water pump P2.

  Here, the silica concentration detected by the detection unit 24 is a concentration as silica (silicon dioxide), which is measured and detected according to the molybdenum yellow absorptiometry described in JIS K 0101. The amount of dissolved oxygen is measured and detected according to the industrial water test method described in JIS K 0101.

In the steam boiler 3 supplied with this boiler feed water, steam is generated, and this steam is supplied to various load devices (not shown) via the steam line S1.
The steam boiler 3 generates steam by heating boiler feed water, and is in a high temperature and high pressure environment. In particular, a boiler water pipe (not shown) receives radiant heat directly from a heating source on the outer surface side of the pipe, and high-temperature / high-pressure boiler feed water or steam flows on the inner surface side (heat transfer surface of the boiler water pipe). In the environment. If the quality of the boiler feed water is poor, the heat transfer surface of the boiler water pipe may be corroded or scales attached, so that the steam boiler 3 may not be able to operate stably for a long period of time. is there. Therefore, the water quality management of boiler feed water is an important item, and a boiler feed water treatment method as shown in this embodiment is required.

  In the water treatment method of this embodiment, when fluctuations occur in the silica concentration or dissolved oxygen amount dissolved in the boiler feed water stored in the feed water tank 23, the water treatment agent tank is adjusted in advance to a predetermined concentration. In this method, the water treatment agent stored in 41 is supplied to the water supply tank 23 in response to the fluctuation. In this case, the supply amount of the water treatment agent supplied to the water supply tank 23 is controlled in accordance with fluctuations in the silica concentration and the dissolved oxygen amount. The supply amount of the water treatment agent is controlled by controlling the discharge amount of the chemical supply pump P1 of the water treatment agent supply unit 4 by the control unit 5 described later.

The water treatment agent supply unit 4 includes a water treatment agent tank 41 that stores the water treatment agent described above, and a chemical supply pump P <b> 1 that supplies the water treatment agent tank 41 to the water supply tank 23. The water treatment agent tank 41 stores a water treatment agent adjusted in advance to a predetermined concentration.
The fluctuation of the silica concentration and dissolved oxygen amount in the boiler feed water is detected by the detection unit 24 provided in the feed water tank 23, and the detected silica concentration and dissolved oxygen amount are detected. Based on this, the control unit 5 determines.

As shown in FIG. 1, the control unit 5 is electrically connected to each device constituting the water supply device unit 2 and the water treatment agent supply unit 4. Specifically, the control unit 5 is electrically connected to the detection unit 24 and the chemical supply pump P1 provided in the boiler water supply tank 23.
The control unit 5 is configured as a logic circuit centered on a microcomputer, and includes a CPU 51 of a central processing unit, a RAM 52 that temporarily stores data, a ROM 53 that stores processing programs, and an input / output that inputs and outputs various signals. A port 54 is provided. As described above, the control unit 5 inputs information related to the silica concentration and the dissolved oxygen amount from the detection unit 24, and based on this, outputs a control signal for the discharge amount of the drug supply pump P1, and outputs the control signal of the drug supply pump P1. Control the discharge rate.

  Here, the discharge amount of the chemical supply pump P1 is controlled when the supply amount of the water treatment agent supplied to the water supply tank 23 increases, the scale easily adheres to the heat transfer surface of the boiler water pipe, and the heat transfer characteristics This is to prevent this from happening. On the other hand, when the supply amount of the water treatment agent supplied to the water supply tank 23 decreases, the thickness of the silica layer or the iron hydroxide layer formed on the heat transfer surface of the boiler water pipe becomes thin, and the heat transfer surface of the boiler water pipe This is to prevent this from being totally corroded. Also, if the thickness distribution of the silica layer or iron hydroxide layer formed on the heat transfer surface of the boiler water pipe becomes uneven, the heat transfer surface of the boiler water pipe is likely to be locally corroded. is there.

  Thus, according to the water treatment method of the present embodiment, when fluctuation occurs in the silica concentration or dissolved oxygen amount in the boiler feed water, a film forming agent that forms a film on the heat transfer surface of the boiler water pipe, By controlling the amount supplied from the water treatment agent tank to the water supply tank for the water treatment agent adjusted to a predetermined concentration by blending the agent, the scale inhibitor, and the pH adjusting agent. In addition to preventing general corrosion and local corrosion on the heat transfer surface of the boiler water pipe, excellent heat transfer characteristics can be obtained.

It is a schematic block diagram of the steam boiler apparatus which concerns on Example 2 of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Steam boiler apparatus 2 Water supply apparatus part 3 Steam boiler 4 Water treatment agent supply part 5 Control part

Claims (6)

Water as the main component,
A film-forming agent that forms a film on the heat transfer surface of the boiler water pipe;
An oxygen scavenger;
A scale inhibitor;
a pH adjuster;
Is formulated in the water. The said film formation agent consists of at least 1 sort (s) or 2 or more types of silica, sodium silicate, potassium silicate, orthosilicate, and polysilicate, The water treatment agent of Claim 1 characterized by the above-mentioned. The said oxygen scavenger consists of at least 1 sort (s) or 2 or more types among vitamin C and its salt, tannin, saccharide type oxygen scavenger, erythorbic acid and its salt, and sulfite. Water treatment agent as described in 4. The scale inhibitor comprises at least one or more of citric acid, ethylenediaminetetraacetic acid and salts thereof, polyacrylic acid and salts thereof, polymaleic acid and salts thereof, and the like. Or the water treatment agent according to 3. The said pH adjuster consists of at least 1 sort (s) or 2 or more types of alkali metal hydroxides, such as sodium hydroxide and potassium hydroxide, The 1, 2, 3, or 4 characterized by the above-mentioned. Water treatment agent. Adjusting the water treatment agent according to claim 1, 2, 3, 4 or 5 to a predetermined concentration;
Detecting the concentration of silica dissolved in the water tank and the amount of dissolved oxygen;
And a step of controlling the amount of the water treatment agent supplied to the water supply tank.

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