WO2024084874A1 - Method for operating boiler - Google Patents

Method for operating boiler Download PDF

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WO2024084874A1
WO2024084874A1 PCT/JP2023/033824 JP2023033824W WO2024084874A1 WO 2024084874 A1 WO2024084874 A1 WO 2024084874A1 JP 2023033824 W JP2023033824 W JP 2023033824W WO 2024084874 A1 WO2024084874 A1 WO 2024084874A1
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water
boiler
compound
polyacrylic acid
acid compound
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PCT/JP2023/033824
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French (fr)
Japanese (ja)
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隆 二宮
亜衣 徳見
剛志 中野
陽介 菊池
伸司 松友
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三浦工業株式会社
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Publication of WO2024084874A1 publication Critical patent/WO2024084874A1/en

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  • the present invention relates to a method for operating a boiler, and in particular to a method for operating a boiler that generates steam by heating boiler water.
  • a typical boiler system for supplying steam to load equipment such as a heat exchanger generates steam by heating the water supplied to the boiler as boiler water, and supplies this steam to the load equipment through a steam path.
  • load equipment such as a heat exchanger
  • the heat transfer surfaces of the water tubes that generate the steam can become corroded or scale can form due to the influence of various dissolved components in the feed water. Scale that forms on the heat transfer surfaces impedes heat transfer, reducing the operating efficiency of the boiler. Furthermore, corrosion of the heat transfer surfaces can damage the water tubes as it progresses, hindering the stable and continuous operation of the boiler.
  • a combination of a silicic acid compound such as silica or silicate and a scale inhibitor is known as a water treatment agent to be added to the feed water.
  • the silicic acid compound forms a film on the heat transfer surface, which suppresses corrosion.
  • the scale inhibitor is a chelating agent such as ethylenediaminetetraacetic acid or a water-soluble polymer such as a polyacrylic acid compound.
  • the chelating agent suppresses the formation of scale by chelating calcium ions and magnesium ions in the boiler water, whereas the water-soluble polymer disperses scale substances derived from calcium ions and magnesium ions in the boiler water and suppresses the growth of scale crystal nuclei, thereby suppressing the formation of scale.
  • the corrosion that occurs on the heat transfer surface of a boiler is known to be either general corrosion, which progresses uniformly over the entire heat transfer surface, or pitting corrosion, which progresses locally in the thickness direction of the heat transfer surface in the form of holes.
  • General corrosion occurs when microscopic anode and cathode pairs occur over the entire heat transfer surface, and progresses due to a short-circuit cell between them, whereas pitting corrosion occurs when macroscopic anodes and cathodes occur locally on the heat transfer surface, and progresses due to a short-circuit cell between them.
  • Patent Documents 1 and 2 the silicate-based compounds used in these documents are effective in suppressing pitting corrosion, but cannot be expected to suppress general corrosion.
  • the present invention aims to suppress the formation of scale in boilers and to suppress both general corrosion and pitting corrosion in boilers by using a combination of a silicate-based compound and a polyacrylic acid-based compound.
  • the present invention relates to a method for operating a boiler that generates steam by heating boiler water.
  • This operating method controls the pH of the boiler water to an alkaline region, and also causes a polyacrylic acid-based compound with a mass average molecular weight of 2,000 to 40,000 to coexist in the boiler water in an environment in which a silicate-based compound is present.
  • the silicate-based compounds are derived from natural components contained in the water supplied to the boiler.
  • a chemical agent containing a silicate-based compound and the above-mentioned polyacrylic acid-based compound is added to the water supply to the boiler.
  • the pH of the boiler water is maintained in the alkaline region by adjusting the amount of the above-mentioned chemical agent supplied to the feed water and adjusting the concentration ratio of the boiler water, and the concentration of the silicic acid-based compound and the polyacrylic acid-based compound in the boiler water are controlled to the target concentrations of 100 to 600 mg/L in terms of silicon dioxide and 1 to 500 mg/L in terms of salt, respectively.
  • softened water is used as the feed water, and the concentration of the silicic acid-based compound and the concentration of the polyacrylic acid-based compound in the boiler water are controlled to the target concentrations when the ratio of the acid consumption (pH 4.8) to the electrical conductivity of the feed water (acid consumption (pH 4.8)/electrical conductivity) indicates a tendency for corrosion to occur in the boiler.
  • the present invention relates to a water treatment agent for boilers, which contains a silicate compound and a polyacrylic acid compound having a mass average molecular weight of 2,000 to 40,000.
  • the boiler water treatment agent of the present invention has a ratio (Y/X) of the content of the polyacrylic acid compound in salt equivalent (Y mass%) to the content of the silicic acid compound in silicon dioxide equivalent (X mass%), for example, set to 0.001 to 500.
  • the preferred boiler water treatment agent of the present invention has a total content of ethylenediaminetetraacetate and its alkali metal salt of less than 1 mass%.
  • the boiler operating method of the present invention maintains the pH of the boiler water in the alkaline region and also allows a polyacrylic acid-based compound with a mass average molecular weight in a specific range to coexist in an environment in which a silicate-based compound is present, thereby suppressing the formation of scale in the boiler and suppressing both general corrosion and pitting corrosion in the boiler.
  • the boiler water treatment agent of the present invention contains a silicic acid compound and a polyacrylic acid compound having a mass average molecular weight within a specific range, and by using it in the boiler operation method of the present invention, it is possible to suppress the formation of scale in the boiler and to suppress both general corrosion and pitting corrosion in the boiler.
  • 1 is a schematic diagram of one embodiment of a boiler apparatus in which an operating method according to the present invention can be implemented; 1 is a graph showing the relationship between the mass average molecular weight of sodium polyacrylate and the maximum pitting depth for Experimental Examples 2 to 17 and 19 to 33 based on the results shown in Table 1. 1 is a graph showing the relationship between the mass average molecular weight of sodium polyacrylate and the corrosion rate for Experimental Examples 2 to 17 and 19 to 33 based on the results shown in Table 1.
  • the boiler system 1 is for supplying steam to a load device 2, which is a steam-using facility such as a heat exchanger, a steam boiler, a reboiler, or an autoclave, and mainly comprises a water supply device 10, a boiler 20, a condensate pipe 30, and a chemical supply device 40.
  • a load device 2 which is a steam-using facility such as a heat exchanger, a steam boiler, a reboiler, or an autoclave, and mainly comprises a water supply device 10, a boiler 20, a condensate pipe 30, and a chemical supply device 40.
  • the water supply device 10 is for supplying feedwater to be used as boiler water in the boiler 20, and mainly comprises a water supply tank 11 for storing the feedwater, and a supply path 12 for supplying makeup water to be used as feedwater to the water supply tank 11.
  • the water supply tank 11 has a water supply path 13 that extends from its bottom to the boiler 20.
  • the water supply path 13 is connected to the boiler 20, and has a water supply pump 14 for sending the feedwater stored in the water supply tank 11 to the boiler 20.
  • the supply path 12 has a water injection line 15.
  • the water injection line 15 is for supplying make-up water to the water supply tank 11 from a raw water tank (not shown) that stores raw water supplied from a water source such as tap water, industrial water, or groundwater, and has a water softener 16 and a deoxygenator 17, in this order, toward the water supply tank 11.
  • the water softener 16 treats the make-up water from the raw water tank with sodium cation exchange resin, converting the hardness components in the make-up water, such as calcium ions and magnesium ions, into soft water by replacing them with sodium ions.
  • the deoxygenation device 17 is used to remove dissolved oxygen from the make-up water treated in the water softener 16, and various types are used, such as a type that uses a separation membrane to remove dissolved oxygen, a type that removes dissolved oxygen by placing the treated water in a reduced pressure environment, or a type that removes dissolved oxygen by heating the treated water.
  • the boiler 20 has many upright water tubes (not shown) inside, and stores the feedwater from the water supply line 13 as boiler water at the bottom. This boiler water is heated through the heat transfer surfaces of the water tubes to generate steam.
  • the water tubes are made of metals that do not naturally passivate in neutral aqueous solutions, such as carbon steel, cast iron, copper, or copper alloys.
  • the boiler 20 also has a blow path 21 for discharging the boiler water, and this blow path 21 has a control valve 22 for adjusting the amount of boiler water discharged. Furthermore, a steam supply pipe 23 that connects to the load device 2 extends from the top of the boiler 20.
  • the condensate pipe 30 extends from the load device 2 to the water supply tank 11 and has a steam trap 31.
  • the steam trap 31 is for separating steam and condensed water.
  • the chemical supply device 40 is for supplying a water treatment agent to the feedwater supplied from the water supply tank 11 to the boiler 20, and has a chemical tank 41 for storing the water treatment agent, a supply path 42 extending from the chemical tank 41 to the water supply path 13, and a supply pump 43 provided in the supply path 42.
  • the supply pump 43 sends the water treatment agent stored in the chemical tank 41 through the supply path 42 to the water supply path 13, and is capable of controlling the amount of water treatment agent supplied.
  • the water treatment agent stored in the chemical tank 41 of the chemical supply device 40 contains a silicic acid compound and a polyacrylic acid compound, and is preferably an aqueous solution containing a silicic acid compound and a polyacrylic acid compound.
  • the water used in this aqueous solution is usually purified water such as distilled water or ion-exchanged water.
  • the silicic acid-based compound contained in the water treatment agent is silicic acid or a silicate, and is a component for forming a film on the surface of the water tubes in the boiler 20 and suppressing corrosion of the water tubes.
  • the silicic acid is a silicon compound represented by the chemical formula [SiO x (OH) 4-2X ] n , and is usually silicic acid anhydride (SiO 2 ), orthosilicic acid (H 4 SiO 4 ), metasilicic acid (H 2 SiO 3 ), or metadisilicic acid (H 2 Si 2 O 5 ).
  • the silicate is, for example, an orthosilicate represented by the chemical formula nSiO 2 ⁇ (n+1)M 2 O or a hydrate thereof, or a polysilicate represented by the chemical formula nSiO 2 ⁇ nM 2 O, nSiO 2 ⁇ (n-1)M 2 O, or nSiO 2 ⁇ (n-2)M 2 O or a hydrate thereof.
  • n is an integer greater than 2
  • M represents a metal element such as an alkali metal such as sodium or potassium, or an alkaline earth metal such as calcium or magnesium. When the metal element is divalent, the number of molecules of M is halved.
  • the water treatment agent may contain two or more types of silicic acid compounds.
  • the polyacrylic acid compound contained in the water treatment agent is a component that inhibits the formation of scale in the boiler 20 and inhibits both general corrosion and local corrosion of the water tubes and the like in the boiler 20 by interacting with the silicic acid compound.
  • a water-soluble polymer compound containing a carboxyl group derived from at least one of acrylic acid and methacrylic acid or a salt thereof is usually used.
  • polyacrylic acid, polymethacrylic acid, copolymers or terpolymers using at least one of acrylic acid and methacrylic acid as a monomer, or salts thereof can be used.
  • the salt for example, an alkali metal salt such as a sodium salt or a potassium salt is used.
  • the polyacrylic acid compound is preferably polyacrylic acid and its salt.
  • the polyacrylic acid compound is selectively used if it has a mass average molecular weight in a specific range that can exert an anticorrosive effect by interacting with the silicic acid compound, specifically, if it has a mass average molecular weight of 2,000 to 40,000, preferably 3,000 to 20,000, more preferably 4,000 to 10,000.
  • the water treatment agent may contain two or more types of polyacrylic acid compounds.
  • the water treatment agent may contain other components such as a pH adjuster and an oxygen scavenger.
  • the pH adjuster suppresses corrosion within the boiler 20 by adjusting the pH of the boiler water to an alkaline region, and for example, an alkali metal hydroxide such as sodium hydroxide or potassium hydroxide is used. Two or more types of pH adjusters may be used in combination.
  • the oxygen scavenger suppresses corrosion within the boiler 20 by removing dissolved oxygen in the boiler water, and for example, ascorbic acid or a salt thereof, tannin, a sugar-type oxygen scavenger, erythorbic acid or a salt thereof, or a sulfite is used. Two or more types of oxygen scavengers may be used in combination.
  • General water treatment agents for boiler water often contain ethylenediaminetetraacetic acid (EDTA) or its alkali metal salts as a scale inhibitor, but these may promote corrosion inside the boiler 20. Therefore, the water treatment agent used in this embodiment is preferably one that is substantially free of EDTA and its alkali metal salts, for example one in which the total content of these is controlled to less than 1 mass%.
  • EDTA ethylenediaminetetraacetic acid
  • alkali metal salts as a scale inhibitor
  • the content of the silicic acid compound and the polyacrylic acid compound is preferably set so that the ratio (Y/X) of the content of the silicic acid compound in silicon dioxide equivalent (X mass%) to the content of the polyacrylic acid compound in salt equivalent (Y mass%) is 0.001 to 500, and more preferably 0.1 to 50, since it is easy to control the concentration of the silicic acid compound and the polyacrylic acid compound in the boiler water to the target concentrations described below.
  • the content of the polyacrylic acid compound in salt equivalent is the content converted by regarding the polyacrylic acid compound as a salt in which all carboxyl groups in the molecule form sodium salts.
  • make-up water is supplied from a raw water tank (not shown) through the water injection passage 15 to the feed water tank 11, and this make-up water is stored in the feed water tank 11 as boiler feed water.
  • the make-up water from the raw water tank is first treated in the water softener 16, where hardness components are removed to turn it into softened water.
  • the make-up water that has been softened in the water softener 16 is then deoxygenated in the deoxygenator 17. This removes dissolved oxygen from the make-up water, which promotes corrosion of water pipes, etc. in the steam boiler 20.
  • deoxygenated softened water is stored in the water supply tank 11 as supply water.
  • the feedwater stored in the feedwater tank 11 is supplied to the boiler 20 through the feedwater path 13.
  • the feedwater supplied to the boiler 20 is stored as boiler water, and this boiler water rises inside the water pipe while being heated through the water pipe, and becomes steam.
  • the steam generated in the water pipe is then supplied to the load device 2 through the steam supply pipe 23. As steam is generated in this way, the boiler water becomes concentrated.
  • the steam supplied to the load device 2 passes through the load device 2 and flows into the condensate pipe 30, where it loses latent heat and part of it turns into condensate, which is then separated from the steam in the steam trap 31 to become high-temperature condensate.
  • the condensate thus produced is collected in the feedwater tank 11 via the condensate pipe 30 and reused as feedwater. At this time, the feedwater stored in the feedwater tank 11 is heated by the high-temperature condensate, reducing the heating burden on the boiler 20.
  • the boiler apparatus 1 adjusts the control valve 22 to control the amount of boiler water discharged from the blow path 21, and controls the feed water pump 14 to adjust the amount of feed water supplied from the feed water tank 11 to the boiler 20, thereby controlling the concentration ratio of the boiler water, thereby adjusting the acid consumption of the boiler water (pH 4.8) and maintaining the pH of the boiler water in the alkaline region where corrosion is unlikely to occur, preferably at a pH of 11 to 12.5.
  • the acid consumption is the amount of hydrogen ions (amount of acid) required to neutralize alkalis such as hydrogen carbonate, carbonate, and hydroxide dissolved in the feed water to a specified pH (here, 4.8), converted into the amount of calcium carbonate equivalent to the hydrogen ions (acid), and expressed in mg per liter of feed water, and can be measured according to the method specified in JIS K 0101.
  • the chemical supply device 40 appropriately supplies water treatment agents to the feedwater flowing through the feedwater path 13 to the boiler 20.
  • the polyacrylic acid-based compounds suppress the growth of scale crystal nuclei in the water tubes, etc., thereby suppressing the generation of scale, and the silicic acid-based compounds form an anticorrosive film on the surfaces of the water tubes, etc., and the interaction between the silicic acid-based compounds and the polyacrylic acid-based compounds suppresses corrosion, particularly both general corrosion and localized corrosion.
  • the amount of the water treatment agent supplied from the chemical supply device 40 to the feed water by controlling the supply pump 43 and to adjust the concentration rate by the above-mentioned method to maintain the pH in the alkaline region, particularly 11 to 12.5, and to control the concentration of the silicic acid compound and the concentration of the polyacrylic acid compound having a specific mass average molecular weight to a predetermined target concentration.
  • the concentration of the silicic acid compound is controlled to 100 to 600 mg/L, particularly 200 to 500 mg/L, as a silicon dioxide (SiO 2 ) equivalent concentration
  • the concentration of the polyacrylic acid compound having a specific mass average molecular weight is preferably controlled to 1 to 500 mg/L, particularly 10 to 200 mg/L, as a salt equivalent concentration
  • the salt equivalent concentration is a concentration calculated by regarding the polyacrylic acid compound as a salt in which all carboxyl groups in the molecule form a sodium salt.
  • the addition of a water treatment agent to the feedwater is preferably carried out when the quality of the feedwater supplied from the feedwater tank 11 to the boiler 20 tends to easily cause corrosion in the water tubes of the boiler 20.
  • This tendency can be evaluated, for example, according to the water quality determination method described in Patent No. 4033667. Specifically, the acid consumption (pH 4.8) and electrical conductivity of the feedwater supplied from the feedwater tank 11 to the boiler 20 through the feedwater path 13 are continuously measured, and an index shown in the following formula (1) is obtained. If this index is 2.5 or more, the feedwater can be determined to have a water quality that is unlikely to corrode the water tubes.
  • the feedwater can be determined to have a water quality that is likely to corrode the water tubes, in particular, to cause pitting corrosion, which is localized corrosion, in the water tubes. Therefore, when the boiler unit 1 is in operation, if the index is less than 2.5, it is preferable to supply a water treatment agent to the feedwater from the chemical supply device 40 and control the concentration of silicic acid-based compounds in the boiler water and the concentration of polyacrylic acid-based compounds with a specific mass average content range to the above-mentioned target concentrations.
  • the acid consumption (pH 4.8) is as described above.
  • the electrical conductivity is equivalent to the reciprocal of the electrical resistivity ( ⁇ m) of the water supply at 25°C and is expressed in units of mS/m (millisiemens per meter), and like the acid consumption (pH 4.8), can be measured according to the method specified in JIS K 0101.
  • a water treatment agent containing silicic acid compounds is used, but if the water supplied to the boiler 20 contains a large amount of silicic acid compounds derived from the raw water and it is easy to increase the silicon dioxide concentration in the boiler water by increasing the concentration rate of the boiler water, a water treatment agent with a reduced content of silicic acid compounds or one that does not contain silicic acid compounds can also be used.
  • the boiler apparatus 1 was operated to examine the progress of corrosion on the heat transfer surface of the water pipes of the boiler 20 (made of STPG (carbon steel pipes for pressure piping) listed in JIS G 3454).
  • test water simulating tap water in the suburbs of Osaka City which is considered to have a highly corrosive water quality due to its relatively high concentrations of both chloride ions and sulfate ions, was supplied from the water injection channel 15 to the water supply tank 11 and stored there, and was supplied from this water supply tank 11 to the boiler 20 through the water supply path 13.
  • the water quality of the test water is as follows.
  • a chemical supply device 40 was placed in the water supply path 13, and the water treatment chemicals described below were added to the water supply as appropriate.
  • the operating conditions of the boiler 20 were set so that the operating pressure and concentration ratio were 0.3 MPa and 10 times, respectively.
  • the dissolved oxygen concentration of the feedwater supplied from the feedwater tank 11 to the boiler 20 was adjusted to 4.0 mg/L by treating the test water in the deoxygenation device 17. Furthermore, the water treatment agent was appropriately added to the water supplied to the boiler 20 from the chemical supply device 40, and the boiler water was discharged by controlling the control valve 22 to control the concentration ratio of the boiler water in the boiler 20 to 10 times, and the water quality of the boiler water was controlled as shown in Table 1.
  • the water treatment chemicals added in each experimental example were appropriately adjusted in concentration to sodium hydroxide, sodium silicate, and sodium polyacrylate so that the water quality of the boiler water was as shown in Table 1.
  • the sodium hydroxide concentration in the water treatment chemical was adjusted to be increased.
  • the silicon dioxide concentrations in Experimental Examples 1 to 17 are the results of test water having a silicon dioxide concentration of 7 mg SiO 2 /L being concentrated 10 times in the boiler.
  • mdd represents the mass loss (mg) of the water tube substrate per day per unit surface area (1 dm2 ) of the surface in contact with water, and the larger the mdd, the higher the corrosion rate and the more general corrosion progresses.
  • the evaluation results are shown in Table 1.
  • the evaluation results shown in Table 1 are relative values when the results of maximum pitting depth ( ⁇ m) and corrosion rate (mdd) in Experimental Example 1 are set as 100% values.
  • ⁇ m maximum pitting depth
  • mdd corrosion rate
  • Table 1 The results of Table 1 are shown in graphs in Figures 2 and 3.
  • Figure 2 shows that for Experimental Examples 19 to 33, in which the silicon dioxide concentration in the boiler water was increased by adding sodium silicate, a correlation was observed between the mass average molecular weight of sodium polyacrylate and the maximum pitting depth. Specifically, the maximum pitting depth tends to decrease as the mass average molecular weight of sodium polyacrylate increases.
  • Figure 3 shows that for Experimental Examples 19 to 33, in which the silicon dioxide concentration in the boiler water was increased by adding sodium silicate, a correlation was observed between the mass average molecular weight of sodium polyacrylate and the corrosion rate. Specifically, the corrosion rate tends to decrease as the mass average molecular weight of sodium polyacrylate decreases.
  • the maximum pitting depth and corrosion rate can be controlled by selecting the mass average molecular weight of the sodium polyacrylate that is coexistent in light of the above-mentioned correlation, which may enable precise corrosion management of water tubes.

Abstract

Water is softened in a water-softening device 16, is deoxidized in a deoxidization device 17, is retained in a water supply tank 11, and is supplied to a boiler 20 from the water supply tank 11 through a water supply path 13. The boiler 20 retains water supplied from the water supply path 13 as boiler water, and heats the boiler water by passing the same through a water pipe to generate steam. During this process, a water treatment agent containing a pH-adjusting agent, sodium silicate, and a sodium polyacrylate having a mass-average molecular weight of 2,000-40,000 is added from a drug supply device 40 to the water that is supplied from the water supply path 13 to the boiler 20. As a result, the pH of the boiler water is controlled in an alkaline range, and the sodium silicate and the polyacrylic acid compound having a mass-average molecular weight in the above-described range coexist in the boiler water.

Description

ボイラの運転方法How to operate a boiler
　本発明は、ボイラの運転方法、特に、ボイラ水を加熱することで蒸気を生成するボイラの運転方法に関する。本願は、２０２２年１０月２０日に日本に出願された特願２０２２－１６８１２９号に基づき優先権を主張し、その内容をここに援用する。 The present invention relates to a method for operating a boiler, and in particular to a method for operating a boiler that generates steam by heating boiler water. This application claims priority based on Japanese Patent Application No. 2022-168129, filed in Japan on October 20, 2022, the contents of which are incorporated herein by reference.
　熱交換器等の負荷装置へ蒸気を供給するための一般的なボイラ装置は、ボイラへの給水をボイラ水として加熱することで蒸気を生成し、この蒸気を蒸気経路を通じて負荷装置へ供給する。ボイラは、内部が高温高圧の環境にあることから、蒸気を生成する水管の伝熱面において、給水中の各種溶存成分の影響によりスケールが付着したり、腐食が生じたりする。伝熱面に付着したスケールは、熱伝導を妨げることからボイラの運転効率を損なう原因となる。また、伝熱面の腐食は、進行すると水管を破損することから、ボイラの安定的・継続的な運転の阻害原因となる。 A typical boiler system for supplying steam to load equipment such as a heat exchanger generates steam by heating the water supplied to the boiler as boiler water, and supplies this steam to the load equipment through a steam path. Because the inside of a boiler is a high-temperature, high-pressure environment, the heat transfer surfaces of the water tubes that generate the steam can become corroded or scale can form due to the influence of various dissolved components in the feed water. Scale that forms on the heat transfer surfaces impedes heat transfer, reducing the operating efficiency of the boiler. Furthermore, corrosion of the heat transfer surfaces can damage the water tubes as it progresses, hindering the stable and continuous operation of the boiler.
　そこで、ボイラ装置の運転では、通常、ボイラへの給水からスケールの原因となるカルシウムイオンやマグネシウムイオンを除去するとともに腐食の原因となる溶存酸素を除去し、併せて給水に対して水処理剤を添加することでボイラにおけるスケール生成および腐食の進行を抑制している。 When operating a boiler system, calcium ions and magnesium ions that cause scale are usually removed from the water supplied to the boiler, as well as dissolved oxygen that causes corrosion. Water treatment agents are also added to the water supply to suppress the formation of scale and the progression of corrosion in the boiler.
　給水へ添加する水処理剤として、特許文献１、２に記載のように、シリカやケイ酸塩のようなケイ酸系化合物とスケール抑制剤とを併用したものが知られている。ケイ酸系化合物は、伝熱面に皮膜を形成し、その皮膜によって腐食を抑えるものである。スケール抑制剤は、エチレンジアミン四酢酸等のキレート剤やポリアクリル酸系化合物等の水溶性ポリマーであり、キレート剤はボイラ水においてカルシウムイオンおよびマグネシウムイオンをキレート化することでスケールの生成を抑えるものであるのに対し、水溶性ポリマーはボイラ水においてカルシウムイオンおよびマグネシウムイオン由来のスケール物質を分散させ、スケールの結晶核の成長を抑えることでスケールの生成を抑えるものである。 As described in Patent Documents 1 and 2, a combination of a silicic acid compound such as silica or silicate and a scale inhibitor is known as a water treatment agent to be added to the feed water. The silicic acid compound forms a film on the heat transfer surface, which suppresses corrosion. The scale inhibitor is a chelating agent such as ethylenediaminetetraacetic acid or a water-soluble polymer such as a polyacrylic acid compound. The chelating agent suppresses the formation of scale by chelating calcium ions and magnesium ions in the boiler water, whereas the water-soluble polymer disperses scale substances derived from calcium ions and magnesium ions in the boiler water and suppresses the growth of scale crystal nuclei, thereby suppressing the formation of scale.
　ところで、ボイラの伝熱面に生じる腐食は、伝熱面の全体に均一に進行する全面腐食と、伝熱面の厚さ方向へ局部的に孔状に進行する孔食とが知られている。全面腐食は、伝熱面の全体に微視的なアノードとカソードとの対が発生し、その短絡電池により進行するものであるのに対し、孔食は、伝熱面の局所に巨視的なアノードとカソードとが発生し、その短絡電池により進行するものである。特許文献１、２によると、それらにおいて用いられるケイ酸系化合物は、孔食の抑制に効果が認められるが、全面腐食の抑制効果を期待できるものではない。 The corrosion that occurs on the heat transfer surface of a boiler is known to be either general corrosion, which progresses uniformly over the entire heat transfer surface, or pitting corrosion, which progresses locally in the thickness direction of the heat transfer surface in the form of holes. General corrosion occurs when microscopic anode and cathode pairs occur over the entire heat transfer surface, and progresses due to a short-circuit cell between them, whereas pitting corrosion occurs when macroscopic anodes and cathodes occur locally on the heat transfer surface, and progresses due to a short-circuit cell between them. According to Patent Documents 1 and 2, the silicate-based compounds used in these documents are effective in suppressing pitting corrosion, but cannot be expected to suppress general corrosion.
特開２００２－１８４８７号公報JP 2002-18487 A 特開２００３－１６０８８９号公報JP 2003-160889 A
　本発明は、ケイ酸系化合物とポリアクリル酸系化合物とを併用することで、ボイラでのスケールの生成を抑えるとともに、ボイラでの全面腐食および孔食の両方の腐食を抑えようとするものである。 The present invention aims to suppress the formation of scale in boilers and to suppress both general corrosion and pitting corrosion in boilers by using a combination of a silicate-based compound and a polyacrylic acid-based compound.
　本発明は、ボイラ水を加熱することで蒸気を生成するボイラの運転方法に関するものである。この運転方法は、ボイラ水のｐＨをアルカリ性領域に制御するとともに、ボイラ水において、ケイ酸系化合物の存在環境下において質量平均分子量が２，０００～４０，０００のポリアクリル酸系化合物を併存させる。 The present invention relates to a method for operating a boiler that generates steam by heating boiler water. This operating method controls the pH of the boiler water to an alkaline region, and also causes a polyacrylic acid-based compound with a mass average molecular weight of 2,000 to 40,000 to coexist in the boiler water in an environment in which a silicate-based compound is present.
　本発明の運転方法の一形態において、ケイ酸系化合物は、ボイラへの給水に含まれる天然成分に由来のものである。 In one embodiment of the operating method of the present invention, the silicate-based compounds are derived from natural components contained in the water supplied to the boiler.
　本発明の運転方法の他の形態では、ボイラへの給水にケイ酸系化合物および上記ポリアクリル酸系化合物を含む薬剤を添加する。 In another embodiment of the operating method of the present invention, a chemical agent containing a silicate-based compound and the above-mentioned polyacrylic acid-based compound is added to the water supply to the boiler.
　この形態に係る運転方法では、例えば、給水への上記薬剤の供給量を調整するとともにボイラ水の濃縮倍率を調整することで、ボイラ水のｐＨをアルカリ性領域に維持するとともに、ボイラ水におけるケイ酸系化合物濃度および上記ポリアクリル酸系化合物濃度をそれぞれ二酸化ケイ素換算濃度で１００～６００ｍｇ／Ｌおよび塩換算濃度で１～５００ｍｇ／Ｌの目標濃度に制御する。好ましくは、給水として軟化水を用い、給水について電気伝導率に対する酸消費量（ｐＨ４．８）の比（酸消費量（ｐＨ４．８）／電気伝導率）がボイラの腐食発生傾向を示すときにボイラ水のケイ酸系化合物濃度およびポリアクリル酸系化合物濃度をそれぞれ上記目標濃度に制御する。 In the operating method according to this embodiment, for example, the pH of the boiler water is maintained in the alkaline region by adjusting the amount of the above-mentioned chemical agent supplied to the feed water and adjusting the concentration ratio of the boiler water, and the concentration of the silicic acid-based compound and the polyacrylic acid-based compound in the boiler water are controlled to the target concentrations of 100 to 600 mg/L in terms of silicon dioxide and 1 to 500 mg/L in terms of salt, respectively. Preferably, softened water is used as the feed water, and the concentration of the silicic acid-based compound and the concentration of the polyacrylic acid-based compound in the boiler water are controlled to the target concentrations when the ratio of the acid consumption (pH 4.8) to the electrical conductivity of the feed water (acid consumption (pH 4.8)/electrical conductivity) indicates a tendency for corrosion to occur in the boiler.
　他の観点に係る本発明は、ボイラ用の水処理剤に関するものであり、この水処理剤は、ケイ酸系化合物と、質量平均分子量が２，０００～４０，０００のポリアクリル酸系化合物とを含む。 In another aspect, the present invention relates to a water treatment agent for boilers, which contains a silicate compound and a polyacrylic acid compound having a mass average molecular weight of 2,000 to 40,000.
　本発明のボイラ用水処理剤は、例えば、二酸化ケイ素換算でのケイ酸系化合物の含有量（Ｘ質量％）に対する塩換算でのポリアクリル酸系化合物の含有量（Ｙ質量％）の量比（Ｙ／Ｘ）が０．００１～５００に設定されている。 The boiler water treatment agent of the present invention has a ratio (Y/X) of the content of the polyacrylic acid compound in salt equivalent (Y mass%) to the content of the silicic acid compound in silicon dioxide equivalent (X mass%), for example, set to 0.001 to 500.
　本発明のボイラ用水処理剤として好ましいものは、エチレンジアミン四酢酸塩およびそのアルカリ金属塩の合計含有量が１質量％未満である。 The preferred boiler water treatment agent of the present invention has a total content of ethylenediaminetetraacetate and its alkali metal salt of less than 1 mass%.
　本発明に係るボイラの運転方法は、ボイラ水のｐＨをアルカリ性領域に維持するとともに、ケイ酸系化合物の存在環境下において質量平均分子量が特定範囲のポリアクリル酸系化合物を併存させていることから、ボイラでのスケールの生成を抑えるとともに、ボイラでの全面腐食および孔食の両方の腐食を抑えることができる。 The boiler operating method of the present invention maintains the pH of the boiler water in the alkaline region and also allows a polyacrylic acid-based compound with a mass average molecular weight in a specific range to coexist in an environment in which a silicate-based compound is present, thereby suppressing the formation of scale in the boiler and suppressing both general corrosion and pitting corrosion in the boiler.
　本発明のボイラ用水処理剤は、ケイ酸系化合物と、質量平均分子量が特定範囲のポリアクリル酸系化合物とを含むものであることから、本発明に係るボイラの運転方法において用いることで、ボイラでのスケールの生成を抑えるとともに、ボイラでの全面腐食および孔食の両方の腐食を抑えることができる。 The boiler water treatment agent of the present invention contains a silicic acid compound and a polyacrylic acid compound having a mass average molecular weight within a specific range, and by using it in the boiler operation method of the present invention, it is possible to suppress the formation of scale in the boiler and to suppress both general corrosion and pitting corrosion in the boiler.
本発明に係る運転方法を実施可能なボイラ装置の一形態の概略図。1 is a schematic diagram of one embodiment of a boiler apparatus in which an operating method according to the present invention can be implemented; 表１に示す結果に基づき、実験例２～１７および１９～３３についてポリアクリル酸ナトリウムの質量平均分子量と最大孔食深さとの関係を表したグラフ。1 is a graph showing the relationship between the mass average molecular weight of sodium polyacrylate and the maximum pitting depth for Experimental Examples 2 to 17 and 19 to 33 based on the results shown in Table 1. 表１に示す結果に基づき、実験例２～１７および１９～３３についてポリアクリル酸ナトリウムの質量平均分子量と腐食速度との関係を表したグラフ。1 is a graph showing the relationship between the mass average molecular weight of sodium polyacrylate and the corrosion rate for Experimental Examples 2 to 17 and 19 to 33 based on the results shown in Table 1.
　図１を参照して、本発明に係るボイラの運転方法を実施可能なボイラ装置の一形態を説明する。図１において、ボイラ装置１は、熱交換器、蒸気釜、リボイラ若しくはオートクレーブ等の蒸気使用設備である負荷装置２に対して蒸気を供給するためのものであり、給水装置１０、ボイラ２０、復水配管３０および薬剤供給装置４０を主に備えている。 With reference to Figure 1, one embodiment of a boiler system capable of implementing the boiler operation method according to the present invention will be described. In Figure 1, the boiler system 1 is for supplying steam to a load device 2, which is a steam-using facility such as a heat exchanger, a steam boiler, a reboiler, or an autoclave, and mainly comprises a water supply device 10, a boiler 20, a condensate pipe 30, and a chemical supply device 40.
　給水装置１０は、ボイラ２０においてボイラ水として用いられる給水を供給するためのものであり、給水を貯留するための給水タンク１１と、給水として用いられる補給水を給水タンク１１へ供給するための補給経路１２とを主に備えている。給水タンク１１は、その底部からボイラ２０へ延びる給水経路１３を有している。給水経路１３は、ボイラ２０に連絡しており、給水タンク１１内に貯留された給水をボイラ２０へ送り出すための給水ポンプ１４を有している。 The water supply device 10 is for supplying feedwater to be used as boiler water in the boiler 20, and mainly comprises a water supply tank 11 for storing the feedwater, and a supply path 12 for supplying makeup water to be used as feedwater to the water supply tank 11. The water supply tank 11 has a water supply path 13 that extends from its bottom to the boiler 20. The water supply path 13 is connected to the boiler 20, and has a water supply pump 14 for sending the feedwater stored in the water supply tank 11 to the boiler 20.
　補給経路１２は、注水路１５を有している。注水路１５は、水道水、工業用水若しくは地下水等の水源から供給される原水が貯留されている原水タンク（図示せず）から給水タンク１１へ補給水を供給するためのものであり、給水タンク１１へ向けて軟水化装置１６および脱酸素装置１７をこの順に有している。 The supply path 12 has a water injection line 15. The water injection line 15 is for supplying make-up water to the water supply tank 11 from a raw water tank (not shown) that stores raw water supplied from a water source such as tap water, industrial water, or groundwater, and has a water softener 16 and a deoxygenator 17, in this order, toward the water supply tank 11.
　軟水化装置１６は、原水タンクからの補給水をナトリウム型陽イオン交換樹脂により処理し、補給水に含まれる硬度成分であるカルシウムイオンおよびマグネシウムイオンをナトリウムイオンに置換して軟化水に変換するためのものである。 The water softener 16 treats the make-up water from the raw water tank with sodium cation exchange resin, converting the hardness components in the make-up water, such as calcium ions and magnesium ions, into soft water by replacing them with sodium ions.
　脱酸素装置１７は、軟水化装置１６において処理された補給水中の溶存酸素を除去するためのものであり、分離膜を用いて溶存酸素を除去する形式のもの、処理水を減圧環境下において溶存酸素を除去する形式のもの、若しくは、処理水を加熱して溶存酸素を除去する形式のものなどの各種の形式のものが用いられる。 The deoxygenation device 17 is used to remove dissolved oxygen from the make-up water treated in the water softener 16, and various types are used, such as a type that uses a separation membrane to remove dissolved oxygen, a type that removes dissolved oxygen by placing the treated water in a reduced pressure environment, or a type that removes dissolved oxygen by heating the treated water.
　ボイラ２０は、起立した多数の水管（図示省略）を内部に有しており、給水経路１３からの給水を底部にボイラ水として貯留し、このボイラ水を水管の伝熱面を通じて加熱することで蒸気を生成する。水管は、炭素鋼、鋳鉄、銅または銅合金等の中性水溶液中において自然には不動態化しない金属を用いて形成されている。また、ボイラ２０は、ボイラ水を廃棄するためのブロー経路２１を有しており、このブロー経路２１はボイラ水の廃棄量を調節するための制御弁２２を有している。さらに、ボイラ２０の上部は、負荷装置２に連絡する蒸気供給配管２３が延びている。 The boiler 20 has many upright water tubes (not shown) inside, and stores the feedwater from the water supply line 13 as boiler water at the bottom. This boiler water is heated through the heat transfer surfaces of the water tubes to generate steam. The water tubes are made of metals that do not naturally passivate in neutral aqueous solutions, such as carbon steel, cast iron, copper, or copper alloys. The boiler 20 also has a blow path 21 for discharging the boiler water, and this blow path 21 has a control valve 22 for adjusting the amount of boiler water discharged. Furthermore, a steam supply pipe 23 that connects to the load device 2 extends from the top of the boiler 20.
　復水配管３０は、負荷装置２から給水タンク１１へ延びており、スチームトラップ３１を有している。スチームトラップ３１は、蒸気と凝縮水とを分離するためのものである。 The condensate pipe 30 extends from the load device 2 to the water supply tank 11 and has a steam trap 31. The steam trap 31 is for separating steam and condensed water.
　薬剤供給装置４０は、給水タンク１１からボイラ２０へ供給される給水中へ水処理剤を供給するためのものであり、水処理剤を貯留するための薬剤タンク４１、薬剤タンク４１から給水経路１３へ延びる供給路４２および供給路４２に設けられた供給ポンプ４３を有している。供給ポンプ４３は、薬剤タンク４１に貯留された水処理剤を供給路４２を通じて給水経路１３へ送り出すものであり、水処理剤の供給量を制御可能である。 The chemical supply device 40 is for supplying a water treatment agent to the feedwater supplied from the water supply tank 11 to the boiler 20, and has a chemical tank 41 for storing the water treatment agent, a supply path 42 extending from the chemical tank 41 to the water supply path 13, and a supply pump 43 provided in the supply path 42. The supply pump 43 sends the water treatment agent stored in the chemical tank 41 through the supply path 42 to the water supply path 13, and is capable of controlling the amount of water treatment agent supplied.
　薬剤供給装置４０の薬剤タンク４１に貯留される水処理剤は、ケイ酸系化合物とポリアクリル酸系化合物とを含むもの、好ましくはケイ酸系化合物とポリアクリル酸系化合物とを含む水溶液である。この水溶液において用いられる水は、通常、蒸留水やイオン交換水などの精製水である。 The water treatment agent stored in the chemical tank 41 of the chemical supply device 40 contains a silicic acid compound and a polyacrylic acid compound, and is preferably an aqueous solution containing a silicic acid compound and a polyacrylic acid compound. The water used in this aqueous solution is usually purified water such as distilled water or ion-exchanged water.
　水処理剤に含まれるケイ酸系化合物は、ケイ酸またはケイ酸塩であり、ボイラ２０内の水管等の表面に皮膜を形成し、水管等の腐食を抑制するための成分である。ケイ酸は、［ＳｉＯＸ（ＯＨ）４－２Ｘ］ｎの化学式で表されるケイ素化合物であり、通常は無水ケイ酸（ＳｉＯ２）、オルトケイ酸（Ｈ４ＳｉＯ４）、メタケイ酸（Ｈ２ＳｉＯ３）またはメタ二ケイ酸（Ｈ２Ｓｉ２Ｏ５）である。また、ケイ酸塩は、例えば、ｎＳｉＯ２・（ｎ＋１）Ｍ２Ｏの化学式で表されるオルトケイ酸塩若しくはその水和物、または、ｎＳｉＯ２・ｎＭ２Ｏ、ｎＳｉＯ２・（ｎ－１）Ｍ２Ｏ若しくはｎＳｉＯ２・（ｎ－２）Ｍ２Ｏの化学式で表されるポリケイ酸塩若しくはその水和物などである。ケイ酸塩の化学式において、ｎは２よりも大きい整数であり、Ｍはナトリウムやカリウム等のアルカリ金属やカルシウムやマグネシウム等のアルカリ土類金属などの金属元素を示している。金属元素が二価の場合は、Ｍの分子数が半分になる。水処理剤は、２種類以上のケイ酸系化合物を含むものであってもよい。 The silicic acid-based compound contained in the water treatment agent is silicic acid or a silicate, and is a component for forming a film on the surface of the water tubes in the boiler 20 and suppressing corrosion of the water tubes. The silicic acid is a silicon compound represented by the chemical formula [SiO x (OH) 4-2X ] n , and is usually silicic acid anhydride (SiO 2 ), orthosilicic acid (H 4 SiO 4 ), metasilicic acid (H 2 SiO 3 ), or metadisilicic acid (H 2 Si 2 O 5 ). The silicate is, for example, an orthosilicate represented by the chemical formula nSiO 2 ·(n+1)M 2 O or a hydrate thereof, or a polysilicate represented by the chemical formula nSiO 2 ·nM 2 O, nSiO 2 ·(n-1)M 2 O, or nSiO 2 ·(n-2)M 2 O or a hydrate thereof. In the chemical formula of silicate, n is an integer greater than 2, and M represents a metal element such as an alkali metal such as sodium or potassium, or an alkaline earth metal such as calcium or magnesium. When the metal element is divalent, the number of molecules of M is halved. The water treatment agent may contain two or more types of silicic acid compounds.
　水処理剤に含まれるポリアクリル酸系化合物は、ボイラ２０内においてスケールの生成を抑制するとともに、ケイ酸系化合物との相互作用によりボイラ２０内の水管等の全面腐食と局部腐食の両方を抑制するための成分である。ポリアクリル酸系化合物としては、通常、アクリル酸およびメタクリル酸のうちの少なくとも一つに由来のカルボキシル基またはその塩を含む水溶性高分子化合物が用いられる。例えば、ポリアクリル酸、ポリメタクリル酸、アクリル酸およびメタクリル酸のうちの少なくとも一つを単量体として用いたコポリマー若しくはターポリマーまたはこれらの塩を用いることができる。塩としては、例えば、ナトリウム塩やカリウム塩等のアルカリ金属塩が用いられる。ポリアクリル酸系化合物として好ましいものは、ポリアクリル酸およびその塩である。ポリアクリル酸系化合物は、ケイ酸系化合物との相互作用により防食効果を発揮し得る特定範囲の質量平均分子量のもの、具体的には質量平均分子量が２，０００～４０，０００のもの、好ましくは３，０００～２０，０００のもの、より好ましくは４，０００～１０，０００のものが選択的に用いられる。水処理剤は、２種類以上のポリアクリル酸系化合物を含むものであってもよい。 The polyacrylic acid compound contained in the water treatment agent is a component that inhibits the formation of scale in the boiler 20 and inhibits both general corrosion and local corrosion of the water tubes and the like in the boiler 20 by interacting with the silicic acid compound. As the polyacrylic acid compound, a water-soluble polymer compound containing a carboxyl group derived from at least one of acrylic acid and methacrylic acid or a salt thereof is usually used. For example, polyacrylic acid, polymethacrylic acid, copolymers or terpolymers using at least one of acrylic acid and methacrylic acid as a monomer, or salts thereof, can be used. As the salt, for example, an alkali metal salt such as a sodium salt or a potassium salt is used. The polyacrylic acid compound is preferably polyacrylic acid and its salt. The polyacrylic acid compound is selectively used if it has a mass average molecular weight in a specific range that can exert an anticorrosive effect by interacting with the silicic acid compound, specifically, if it has a mass average molecular weight of 2,000 to 40,000, preferably 3,000 to 20,000, more preferably 4,000 to 10,000. The water treatment agent may contain two or more types of polyacrylic acid compounds.
　水処理剤は、ケイ酸系化合物およびポリアクリル酸系化合物の他に、ｐＨ調整剤や脱酸素剤等の他の成分を含んでいてもよい。ｐＨ調整剤は、ボイラ水のｐＨをアルカリ性領域に調整することでボイラ２０内での腐食を抑えるものであり、例えば、水酸化ナトリウムや水酸化カリウム等のアルカリ金属水酸化物が用いられる。ｐＨ調整剤は、２種以上のものが併用されてもよい。脱酸素剤は、ボイラ水中の溶存酸素を除去することでボイラ２０内の腐食を抑えるものであり、例えば、アスコルビン酸若しくはその塩、タンニン、糖類型脱酸素剤、エリソルビン酸若しくはその塩または亜硫酸塩などが用いられる。脱酸素剤は、２種以上のものが併用されてもよい。 In addition to the silicic acid-based compound and the polyacrylic acid-based compound, the water treatment agent may contain other components such as a pH adjuster and an oxygen scavenger. The pH adjuster suppresses corrosion within the boiler 20 by adjusting the pH of the boiler water to an alkaline region, and for example, an alkali metal hydroxide such as sodium hydroxide or potassium hydroxide is used. Two or more types of pH adjusters may be used in combination. The oxygen scavenger suppresses corrosion within the boiler 20 by removing dissolved oxygen in the boiler water, and for example, ascorbic acid or a salt thereof, tannin, a sugar-type oxygen scavenger, erythorbic acid or a salt thereof, or a sulfite is used. Two or more types of oxygen scavengers may be used in combination.
　なお、ボイラ水用の一般的な水処理剤は、スケール抑制剤としてエチレンジアミン四酢酸（ＥＤＴＡ）またはそのアルカリ金属塩を含むことが多いが、これらはボイラ２０内の腐食を助長する可能性がある。そこで、この実施の形態において用いられる水処理剤は、ＥＤＴＡおよびそのアルカリ金属塩を実質的に含有しないもの、例えば、これらの合計含有量を１質量％未満に制御したものが好ましい。 General water treatment agents for boiler water often contain ethylenediaminetetraacetic acid (EDTA) or its alkali metal salts as a scale inhibitor, but these may promote corrosion inside the boiler 20. Therefore, the water treatment agent used in this embodiment is preferably one that is substantially free of EDTA and its alkali metal salts, for example one in which the total content of these is controlled to less than 1 mass%.
　水処理剤において、ケイ酸系化合物とポリアクリル酸系化合物との含有量は、ボイラ水においてケイ酸系化合物濃度およびポリアクリル酸系化合物濃度を後記する目標濃度に制御しやすいことから、二酸化ケイ素換算でのケイ酸系化合物の含有量（Ｘ質量％）と塩換算でのポリアクリル酸系化合物の含有量（Ｙ質量％）との量比（Ｙ／Ｘ）が０．００１～５００になるよう設定するのが好ましく、０．１～５０になるよう設定するのがより好ましい。ここで、塩換算でのポリアクリル酸系化合物の含有量は、ポリアクリル酸系化合物をその分子中の全カルボキシル基がナトリウム塩を形成している塩とみなして換算した含有量である。 In the water treatment agent, the content of the silicic acid compound and the polyacrylic acid compound is preferably set so that the ratio (Y/X) of the content of the silicic acid compound in silicon dioxide equivalent (X mass%) to the content of the polyacrylic acid compound in salt equivalent (Y mass%) is 0.001 to 500, and more preferably 0.1 to 50, since it is easy to control the concentration of the silicic acid compound and the polyacrylic acid compound in the boiler water to the target concentrations described below. Here, the content of the polyacrylic acid compound in salt equivalent is the content converted by regarding the polyacrylic acid compound as a salt in which all carboxyl groups in the molecule form sodium salts.
　次に、上述のボイラ装置１の運転方法を説明する。
　蒸気ボイラ装置１の運転では、先ず、原水タンク（図示省略）から注水路１５を通じて給水タンク１１へ補給水を供給し、この補給水をボイラ給水として給水タンク１１に貯留する。 Next, a method of operating the above-mentioned boiler system 1 will be described.
In operation of the steam boiler apparatus 1, first, make-up water is supplied from a raw water tank (not shown) through the water injection passage 15 to the feed water tank 11, and this make-up water is stored in the feed water tank 11 as boiler feed water.
　この際、原水タンクからの補給水は、先ず、軟水化装置１６において処理され、硬度成分が除去されることで軟化水になる。軟水化装置１６において軟化水となった補給水は、次に、脱酸素装置１７において脱酸素処理される。これにより、補給水は、蒸気ボイラ２０において水管等の腐食を促進する溶存酸素が除去される。以上の結果、給水タンク１１には脱酸素処理された軟化水が給水として貯留されることになる。 In this case, the make-up water from the raw water tank is first treated in the water softener 16, where hardness components are removed to turn it into softened water. The make-up water that has been softened in the water softener 16 is then deoxygenated in the deoxygenator 17. This removes dissolved oxygen from the make-up water, which promotes corrosion of water pipes, etc. in the steam boiler 20. As a result of the above, deoxygenated softened water is stored in the water supply tank 11 as supply water.
　給水タンク１１に補給水が貯留された状態で給水ポンプ１４を作動させると、給水タンク１１に貯留された給水は、給水経路１３を通じてボイラ２０へ供給される。ボイラ２０へ供給された給水はボイラ水として貯留され、このボイラ水は水管を通じて加熱されながら水管内を上昇し、蒸気になる。そして、水管において生成した蒸気は、蒸気供給配管２３を通じて負荷装置２へ供給される。このような蒸気の生成に従い、ボイラ水の濃縮が進行する。 When the feedwater pump 14 is operated with makeup water stored in the feedwater tank 11, the feedwater stored in the feedwater tank 11 is supplied to the boiler 20 through the feedwater path 13. The feedwater supplied to the boiler 20 is stored as boiler water, and this boiler water rises inside the water pipe while being heated through the water pipe, and becomes steam. The steam generated in the water pipe is then supplied to the load device 2 through the steam supply pipe 23. As steam is generated in this way, the boiler water becomes concentrated.
　負荷装置２へ供給された蒸気は、負荷装置２を通過して復水配管３０へ流れ、そこで潜熱を失って一部が凝縮水に変わり、スチームトラップ３１において蒸気と凝縮水とが分離されて高温の復水になる。このようにして生成した復水は、復水配管３０を通じて給水タンク１１に回収され、給水として再利用される。この際、給水タンク１１に貯留された給水は、高温の復水により加熱されるので、ボイラ２０での加熱負担が軽減される。 The steam supplied to the load device 2 passes through the load device 2 and flows into the condensate pipe 30, where it loses latent heat and part of it turns into condensate, which is then separated from the steam in the steam trap 31 to become high-temperature condensate. The condensate thus produced is collected in the feedwater tank 11 via the condensate pipe 30 and reused as feedwater. At this time, the feedwater stored in the feedwater tank 11 is heated by the high-temperature condensate, reducing the heating burden on the boiler 20.
　ボイラ装置１は、上述のような運転中において、制御弁２２を調節してブロー経路２１からのボイラ水の廃棄量を制御するとともに給水ポンプ１４の制御により給水タンク１１からボイラ２０への給水の供給量を調節することでボイラ水の濃縮倍率を制御し、これによってボイラ水の酸消費量（ｐＨ４．８）を調整することでボイラ水のｐＨを腐食が生じにくいアルカリ性領域、好ましくはｐＨを１１～１２．５に維持する。 During operation as described above, the boiler apparatus 1 adjusts the control valve 22 to control the amount of boiler water discharged from the blow path 21, and controls the feed water pump 14 to adjust the amount of feed water supplied from the feed water tank 11 to the boiler 20, thereby controlling the concentration ratio of the boiler water, thereby adjusting the acid consumption of the boiler water (pH 4.8) and maintaining the pH of the boiler water in the alkaline region where corrosion is unlikely to occur, preferably at a pH of 11 to 12.5.
　なお、酸消費量（ｐＨ４．８）は、給水に溶けている炭酸水素塩、炭酸塩、水酸化物などのアルカリを所定のｐＨ（ここでは、４．８）に中和するのに要する水素イオンの量（酸の量）を、水素イオン（酸）に相当する炭酸カルシウムの量に換算して、給水１リットルについてのｍｇ数で表したものであり、ＪＩＳ Ｋ ０１０１に規定された方法に従って測定することができる。 The acid consumption (pH 4.8) is the amount of hydrogen ions (amount of acid) required to neutralize alkalis such as hydrogen carbonate, carbonate, and hydroxide dissolved in the feed water to a specified pH (here, 4.8), converted into the amount of calcium carbonate equivalent to the hydrogen ions (acid), and expressed in mg per liter of feed water, and can be measured according to the method specified in JIS K 0101.
　また、ボイラ装置１の運転中は、給水経路１３内をボイラ２０へ流れる給水に対し、適宜、薬剤供給装置４０から水処理剤を供給する。これにより、ボイラ水にはケイ酸系化合物とともに質量平均分子量が特定範囲のポリアクリル酸系化合物が併存した状態になる。この結果、ボイラ２０は、水管等において、ポリアクリル酸系化合物がスケールの結晶核の成長を抑えることでスケールの生成が抑えられるとともに、ケイ酸系化合物が水管等の表面に防食皮膜を形成することで、また、ケイ酸系化合物とポリアクリル酸系化合物との相互作用により腐食、特に、全面腐食と局部腐食の両方が抑えられる。 In addition, while the boiler apparatus 1 is in operation, the chemical supply device 40 appropriately supplies water treatment agents to the feedwater flowing through the feedwater path 13 to the boiler 20. This results in the boiler water containing both silicic acid-based compounds and polyacrylic acid-based compounds with a specific range of mass average molecular weight. As a result, in the boiler 20, the polyacrylic acid-based compounds suppress the growth of scale crystal nuclei in the water tubes, etc., thereby suppressing the generation of scale, and the silicic acid-based compounds form an anticorrosive film on the surfaces of the water tubes, etc., and the interaction between the silicic acid-based compounds and the polyacrylic acid-based compounds suppresses corrosion, particularly both general corrosion and localized corrosion.
　ここで、ボイラ水は、スケールの抑制効果並びに全面腐食および局部腐食の両方の防食効果を高める観点から、薬剤供給装置４０から給水への水処理剤の供給量を供給ポンプ４３の制御により調整するとともに既述の方法により濃縮倍率を調整することで、ｐＨをアルカリ性領域、特に、１１～１２．５に維持するとともに、ケイ酸系化合物濃度および質量平均分量が特定範囲のポリアクリル酸系化合物濃度を所定の目標濃度に制御するのが好ましい。具体的には、ケイ酸系化合物濃度は二酸化ケイ素（ＳｉＯ２）換算濃度として１００～６００ｍｇ／Ｌ、特に、２００～５００ｍｇ／Ｌに制御し、また、質量平均分子量が特定範囲のポリアクリル酸系化合物濃度は塩換算濃度として１～５００ｍｇ／Ｌ、特に、１０～２００ｍｇ／Ｌに制御するのが好ましい。ここで、塩換算濃度は、ポリアクリル酸系化合物をその分子中の全カルボキシル基がナトリウム塩を形成している塩とみなして換算した濃度である。 Here, in terms of enhancing the scale suppression effect and the corrosion prevention effect for both general corrosion and local corrosion, it is preferable to adjust the amount of the water treatment agent supplied from the chemical supply device 40 to the feed water by controlling the supply pump 43 and to adjust the concentration rate by the above-mentioned method to maintain the pH in the alkaline region, particularly 11 to 12.5, and to control the concentration of the silicic acid compound and the concentration of the polyacrylic acid compound having a specific mass average molecular weight to a predetermined target concentration. Specifically, the concentration of the silicic acid compound is controlled to 100 to 600 mg/L, particularly 200 to 500 mg/L, as a silicon dioxide (SiO 2 ) equivalent concentration, and the concentration of the polyacrylic acid compound having a specific mass average molecular weight is preferably controlled to 1 to 500 mg/L, particularly 10 to 200 mg/L, as a salt equivalent concentration. Here, the salt equivalent concentration is a concentration calculated by regarding the polyacrylic acid compound as a salt in which all carboxyl groups in the molecule form a sodium salt.
　給水に対する水処理剤の添加は、給水タンク１１からボイラ２０に供給する給水の水質がボイラ２０の水管等に腐食を発生させやすい傾向にあるときに実行するのが好ましい。この傾向は、例えば、特許第４０３３６６７号に記載の水質判定方法に従って評価することができる。具体的には、給水タンク１１から給水経路１３を通じてボイラ２０に対して供給する給水の酸消費量（ｐＨ４．８）と電気伝導率とを継続的に測定し、下記の式（１）で示される指数を求める。この指数が２．５以上の場合、給水は水管を腐食させにくい水質のものと判定することができる。一方、当該指数が２．５未満の場合、給水は水管を腐食させやすい傾向の水質のもの、特に、水管に局部腐食である孔食を発生させやすいものと判定することができる。そこで、ボイラ装置１の運転中は、当該指数が２．５未満の場合において、給水に対して薬剤供給装置４０から水処理剤を供給し、ボイラ水におけるケイ酸系化合物濃度および質量平均分量が特定範囲のポリアクリル酸系化合物濃度を上述の目標濃度に制御するのが好ましい。 The addition of a water treatment agent to the feedwater is preferably carried out when the quality of the feedwater supplied from the feedwater tank 11 to the boiler 20 tends to easily cause corrosion in the water tubes of the boiler 20. This tendency can be evaluated, for example, according to the water quality determination method described in Patent No. 4033667. Specifically, the acid consumption (pH 4.8) and electrical conductivity of the feedwater supplied from the feedwater tank 11 to the boiler 20 through the feedwater path 13 are continuously measured, and an index shown in the following formula (1) is obtained. If this index is 2.5 or more, the feedwater can be determined to have a water quality that is unlikely to corrode the water tubes. On the other hand, if the index is less than 2.5, the feedwater can be determined to have a water quality that is likely to corrode the water tubes, in particular, to cause pitting corrosion, which is localized corrosion, in the water tubes. Therefore, when the boiler unit 1 is in operation, if the index is less than 2.5, it is preferable to supply a water treatment agent to the feedwater from the chemical supply device 40 and control the concentration of silicic acid-based compounds in the boiler water and the concentration of polyacrylic acid-based compounds with a specific mass average content range to the above-mentioned target concentrations.
Figure JPOXMLDOC01-appb-M000001
Figure JPOXMLDOC01-appb-M000001
　ここで、酸消費量（ｐＨ４．８）は、既述のとおりである。また、電気伝導率は、２５℃の給水がもつ電気抵抗率（Ω・ｍ）の逆数に相当するものであってｍＳ／ｍ（ミリジーメンス毎メートル）の単位で表したものであり、酸消費量（ｐＨ４．８）と同じく、ＪＩＳ Ｋ ０１０１に規定された方法に従って測定することができる。 Here, the acid consumption (pH 4.8) is as described above. Also, the electrical conductivity is equivalent to the reciprocal of the electrical resistivity (Ω·m) of the water supply at 25°C and is expressed in units of mS/m (millisiemens per meter), and like the acid consumption (pH 4.8), can be measured according to the method specified in JIS K 0101.
　上述の実施の形態では、水処理剤としてケイ酸系化合物を含むものを用いているが、ボイラ２０への給水が原水に由来のケイ酸系化合物を多く含み、ボイラ水の濃縮倍率を高めることでボイラ水において二酸化ケイ素濃度を高めやすい場合、水処理剤としてケイ酸系化合物の含有量を抑えたものや、ケイ酸系化合物を含まないものを用いることもできる。 In the above-described embodiment, a water treatment agent containing silicic acid compounds is used, but if the water supplied to the boiler 20 contains a large amount of silicic acid compounds derived from the raw water and it is easy to increase the silicon dioxide concentration in the boiler water by increasing the concentration rate of the boiler water, a water treatment agent with a reduced content of silicic acid compounds or one that does not contain silicic acid compounds can also be used.
［実験例］
　上述の実施の形態に係るボイラ装置１を運転し、ボイラ２０の水管（ＪＩＳ Ｇ ３４５４に掲載されたＳＴＰＧ（圧力配管用炭素鋼鋼管）製）の伝熱面における腐食の進行を調べた。ここでは、塩化物イオンおよび硫酸イオンの両者が比較的高濃度であることから腐食性の強い水質と考えられる大阪市近郊の上水を模した試験水を注水路１５から給水タンク１１へ供給して貯留し、この給水タンク１１から給水経路１３を通じてボイラ２０へ給水した。試験水の水質は以下のとおりである。 [Experimental Example]
The boiler apparatus 1 according to the above-mentioned embodiment was operated to examine the progress of corrosion on the heat transfer surface of the water pipes of the boiler 20 (made of STPG (carbon steel pipes for pressure piping) listed in JIS G 3454). Here, test water simulating tap water in the suburbs of Osaka City, which is considered to have a highly corrosive water quality due to its relatively high concentrations of both chloride ions and sulfate ions, was supplied from the water injection channel 15 to the water supply tank 11 and stored there, and was supplied from this water supply tank 11 to the boiler 20 through the water supply path 13. The water quality of the test water is as follows.
（試験水水質）
ｐＨ：７．５
電気伝導率：２５ｍＳ／ｍ
酸消費量（ｐＨ４．８）：２０ｍｇＣａＣＯ３／Ｌ
二酸化ケイ素濃度：７ｍｇＳｉＯ２／Ｌ (Test water quality)
pH: 7.5
Electrical conductivity: 25 mS/m
Acid consumption (pH 4.8): 20 mg CaCO 3 /L
Silicon dioxide concentration: 7 mg SiO 2 /L
　この実験例では、給水経路１３に対して薬剤供給装置４０を配置し、後記の水処理剤を給水に対して適宜添加した。ボイラ２０の運転条件は、運転圧力および濃縮倍率がそれぞれ０．３ＭＰａおよび１０倍になるよう設定した。 In this experimental example, a chemical supply device 40 was placed in the water supply path 13, and the water treatment chemicals described below were added to the water supply as appropriate. The operating conditions of the boiler 20 were set so that the operating pressure and concentration ratio were 0.3 MPa and 10 times, respectively.
　ボイラ装置１の運転において、給水タンク１１からボイラ２０へ供給する給水の溶存酸素濃度は、試験水を脱酸素装置１７において処理することにより、４．０ｍｇ／Ｌとなるように調整した。さらに、ボイラ２０への給水に対して薬剤供給装置４０から水処理剤を適宜添加するとともに制御弁２２の制御によりボイラ水の廃棄量を調節することでボイラ２０におけるボイラ水の濃縮倍率を１０倍に制御し、ボイラ水の水質を表１に示すように制御した。各実験例において添加した水処理薬剤は、ボイラ水の水質が表１に示すようになるよう水酸化ナトリウム、ケイ酸ナトリウムおよびポリアクリル酸ナトリウムの濃度を適宜調整したものである。例えば、酸消費量（ｐＨ４．８）の分解に伴うｐＨ上昇のみでボイラ水のｐＨが十分に上昇しない場合には、水処理薬剤中の水酸化ナトリウム濃度を高めるよう調整した。なお、表１において、実験例１～１７の二酸化ケイ素濃度は、二酸化ケイ素濃度が７ｍｇＳｉＯ２／Ｌである試験水がボイラ内で１０倍濃縮したことによるものである。 In the operation of the boiler apparatus 1, the dissolved oxygen concentration of the feedwater supplied from the feedwater tank 11 to the boiler 20 was adjusted to 4.0 mg/L by treating the test water in the deoxygenation device 17. Furthermore, the water treatment agent was appropriately added to the water supplied to the boiler 20 from the chemical supply device 40, and the boiler water was discharged by controlling the control valve 22 to control the concentration ratio of the boiler water in the boiler 20 to 10 times, and the water quality of the boiler water was controlled as shown in Table 1. The water treatment chemicals added in each experimental example were appropriately adjusted in concentration to sodium hydroxide, sodium silicate, and sodium polyacrylate so that the water quality of the boiler water was as shown in Table 1. For example, when the pH of the boiler water did not rise sufficiently only due to the pH rise associated with the decomposition of the acid consumption (pH 4.8), the sodium hydroxide concentration in the water treatment chemical was adjusted to be increased. In Table 1, the silicon dioxide concentrations in Experimental Examples 1 to 17 are the results of test water having a silicon dioxide concentration of 7 mg SiO 2 /L being concentrated 10 times in the boiler.
　運転開始から４８時間後にボイラ２０の運転を停止し、このボイラ２０から評価用の水管を抜き取ってその表面における腐食の進行を局部腐食および全面腐食の両方について評価した。この評価において、局部腐食は伝熱面に生じた各孔食の深さを調べ、その最大深さを求めた。最大深さが大きいほど孔食が進行していることを意味する。また、全面腐食は、ｍｄｄ（ｍｇ／ｄｍ２／ｄａｙ）で表される腐食速度を求めた。なお、ｍｄｄとは、水との接触面の単位表面積（１ｄｍ２）における１日当りの水管素地の質量減少量（ｍｇ）を表現したものであり、ｍｄｄが大きいほど腐食速度が高く、全面腐食が進行していることを意味する。 The operation of the boiler 20 was stopped 48 hours after the start of operation, and the evaluation water tube was removed from the boiler 20 to evaluate the progress of corrosion on its surface for both localized corrosion and general corrosion. In this evaluation, the depth of each pitting corrosion that occurred on the heat transfer surface was examined to determine its maximum depth for localized corrosion. The larger the maximum depth, the more the pitting corrosion progressed. For general corrosion, the corrosion rate expressed as mdd (mg/ dm2 /day) was obtained. Note that mdd represents the mass loss (mg) of the water tube substrate per day per unit surface area (1 dm2 ) of the surface in contact with water, and the larger the mdd, the higher the corrosion rate and the more general corrosion progresses.
　評価結果を表１に示す。表１に示した評価結果は、実験例１における最大孔食深さ（μｍ）および腐食速度（ｍｄｄ）の結果を１００％値とした場合の相対値である。大阪市近郊水の上水を模した試験水を用いてボイラ２０を運転いた場合において相対値が５０％未満に抑制されている場合、出願人の経験則に照らすと、実用上、十分に腐食が抑制されているものと評価可能である。 The evaluation results are shown in Table 1. The evaluation results shown in Table 1 are relative values when the results of maximum pitting depth (μm) and corrosion rate (mdd) in Experimental Example 1 are set as 100% values. When boiler 20 is operated using test water simulating the drinking water in and around Osaka City, if the relative value is suppressed to less than 50%, then based on the applicant's experience, it can be evaluated that corrosion is sufficiently suppressed for practical purposes.
Figure JPOXMLDOC01-appb-T000002
Figure JPOXMLDOC01-appb-T000002
　表１の結果をグラフ化したものを図２、３に示す。図２によると、ケイ酸ナトリウムの添加によりボイラ水における二酸化ケイ素濃度を高めた実験例１９～３３については、ポリアクリル酸ナトリウムの質量平均分子量と最大孔食深さとに相関関係が認められる。具体的には、ポリアクリル酸ナトリウムの質量平均分子量が大きくなるに従って最大孔食深さが小さくなる傾向が認められる。また、図３によると、ケイ酸ナトリウムの添加によりボイラ水における二酸化ケイ素濃度を高めた実験例１９～３３については、ポリアクリル酸ナトリウムの質量平均分子量と腐食速度とにも相関関係が認められる。具体的には、ポリアクリル酸ナトリウムの質量平均分子量が小さくなるに従って腐食速度が遅くなる傾向が認められる。図２、３の結果に照らすと、ボイラ水において、ケイ酸ナトリウムの添加により二酸化ケイ素濃度を高めるとともに質量平均分子量が概ね２，０００～４０，０００の範囲にあるポリアクリル酸ナトリウムを併存させた場合において、孔食および全面腐食の両方の進行を抑えやすいことがわかる。 　The results of Table 1 are shown in graphs in Figures 2 and 3. Figure 2 shows that for Experimental Examples 19 to 33, in which the silicon dioxide concentration in the boiler water was increased by adding sodium silicate, a correlation was observed between the mass average molecular weight of sodium polyacrylate and the maximum pitting depth. Specifically, the maximum pitting depth tends to decrease as the mass average molecular weight of sodium polyacrylate increases. Also, Figure 3 shows that for Experimental Examples 19 to 33, in which the silicon dioxide concentration in the boiler water was increased by adding sodium silicate, a correlation was observed between the mass average molecular weight of sodium polyacrylate and the corrosion rate. Specifically, the corrosion rate tends to decrease as the mass average molecular weight of sodium polyacrylate decreases. In light of the results of Figures 2 and 3, it can be seen that in boiler water, when the silicon dioxide concentration is increased by adding sodium silicate and sodium polyacrylate with a mass average molecular weight in the range of approximately 2,000 to 40,000 is coexistent, the progression of both pitting corrosion and general corrosion is easily suppressed.
　また、図２、３によると、ボイラ水における二酸化ケイ素濃度を高めた場合、上述の相関関係に照らして併存させるポリアクリル酸ナトリウムの質量平均分子量を選択することで最大孔食深さおよび腐食速度を制御可能であることから、水管に対する細やかな腐食管理を実現できる可能性がある。 Furthermore, according to Figures 2 and 3, when the silicon dioxide concentration in the boiler water is increased, the maximum pitting depth and corrosion rate can be controlled by selecting the mass average molecular weight of the sodium polyacrylate that is coexistent in light of the above-mentioned correlation, which may enable precise corrosion management of water tubes.

Claims (8)

  1. 　ボイラ水を加熱することで蒸気を生成するボイラの運転方法であって、
    　前記ボイラ水のｐＨをアルカリ性領域に制御するとともに、前記ボイラ水において、ケイ酸系化合物の存在環境下において質量平均分子量が２，０００～４０，０００のポリアクリル酸系化合物を併存させる、
    ボイラの運転方法。     A method for operating a boiler that generates steam by heating boiler water, comprising the steps of:
    The pH of the boiler water is controlled to be in an alkaline region, and a polyacrylic acid-based compound having a mass average molecular weight of 2,000 to 40,000 is allowed to coexist in the boiler water in an environment in which a silicic acid-based compound is present.
    How to operate a boiler.
  2. 　前記ケイ酸系化合物は、前記ボイラへの給水に含まれる天然成分に由来のものである、
    請求項１に記載のボイラの運転方法。     The silicate-based compound is derived from a natural component contained in the water supplied to the boiler.
    A method for operating the boiler according to claim 1.
  3. 　前記ボイラへの給水にケイ酸系化合物および前記ポリアクリル酸系化合物を含む薬剤を添加する、請求項１に記載のボイラの運転方法。 The method for operating a boiler according to claim 1, further comprising adding a chemical agent containing a silicate compound and the polyacrylic acid compound to the water supplied to the boiler.
  4. 　前記給水への前記薬剤の供給量を調整するとともに前記ボイラ水の濃縮倍率を調整することで、前記ボイラ水のｐＨをアルカリ性領域に維持するとともに、前記ボイラ水におけるケイ酸系化合物濃度およびポリアクリル酸系化合物濃度をそれぞれ二酸化ケイ素換算濃度で１００～６００ｍｇ／Ｌおよび塩換算濃度で１～５００ｍｇ／Ｌの目標濃度に制御する、請求項３に記載のボイラの運転方法。 The method of operating a boiler according to claim 3, in which the pH of the boiler water is maintained in the alkaline region by adjusting the amount of the chemical agent supplied to the feed water and the concentration ratio of the boiler water, and the concentration of the silicic acid compound and the polyacrylic acid compound in the boiler water are controlled to target concentrations of 100 to 600 mg/L in terms of silicon dioxide and 1 to 500 mg/L in terms of salt, respectively.
  5. 　前記給水として軟化水を用い、前記給水について電気伝導率に対する酸消費量（ｐＨ４．８）の比（酸消費量（ｐＨ４．８）／電気伝導率）が前記ボイラの腐食発生傾向を示すときに前記ボイラ水の前記ケイ酸系化合物濃度および前記ポリアクリル酸系化合物濃度をそれぞれ前記目標濃度に制御する、請求項４に記載のボイラの運転方法。 The method for operating a boiler according to claim 4, wherein softened water is used as the feed water, and the concentration of the silicate compound and the concentration of the polyacrylic acid compound in the boiler water are controlled to the target concentrations when the ratio of the acid consumption (pH 4.8) to the electrical conductivity of the feed water (acid consumption (pH 4.8)/electrical conductivity) indicates a tendency for corrosion to occur in the boiler.
  6. 　ケイ酸系化合物と、
    　質量平均分子量が２，０００～４０，０００のポリアクリル酸系化合物と、
    を含むボイラ用水処理剤。     A silicic acid compound,
    A polyacrylic acid compound having a mass average molecular weight of 2,000 to 40,000;
    A boiler water treatment agent comprising:
  7. 　二酸化ケイ素換算での前記ケイ酸系化合物の含有量（Ｘ質量％）に対する塩換算での前記ポリアクリル酸系化合物の含有量（Ｙ質量％）の量比（Ｙ／Ｘ）が０．００１～５００に設定されている、請求項６に記載のボイラ用水処理剤。 The boiler water treatment agent according to claim 6, wherein the ratio (Y/X) of the content (X mass%) of the silicic acid compound calculated as silicon dioxide to the content (Y mass%) of the polyacrylic acid compound calculated as salt is set to 0.001 to 500.
  8. 　エチレンジアミン四酢酸およびそのアルカリ金属塩の合計含有量が１質量％未満である、請求項６または７に記載のボイラ用水処理剤。 The boiler water treatment agent according to claim 6 or 7, in which the total content of ethylenediaminetetraacetic acid and its alkali metal salts is less than 1 mass%.
PCT/JP2023/033824 2022-10-20 2023-09-19 Method for operating boiler WO2024084874A1 (en)

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Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2003160889A (en) * 2001-11-28 2003-06-06 Miura Co Ltd Water treatment agent
JP2003166085A (en) * 2001-11-29 2003-06-13 Miura Co Ltd Method for inhibiting corrosion of non-passivated metal body and boiler
JP2013194280A (en) * 2012-03-19 2013-09-30 Kurita Water Ind Ltd Water treatment method for boiler equipped with economizer
JP2018176064A (en) * 2017-04-12 2018-11-15 栗田工業株式会社 Scale prevention agent and scale prevention method
JP2021143792A (en) * 2020-03-12 2021-09-24 栗田工業株式会社 Method of suppressing corrosion fatigue of evaporation pipe in boiler

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2003160889A (en) * 2001-11-28 2003-06-06 Miura Co Ltd Water treatment agent
JP2003166085A (en) * 2001-11-29 2003-06-13 Miura Co Ltd Method for inhibiting corrosion of non-passivated metal body and boiler
JP2013194280A (en) * 2012-03-19 2013-09-30 Kurita Water Ind Ltd Water treatment method for boiler equipped with economizer
JP2018176064A (en) * 2017-04-12 2018-11-15 栗田工業株式会社 Scale prevention agent and scale prevention method
JP2021143792A (en) * 2020-03-12 2021-09-24 栗田工業株式会社 Method of suppressing corrosion fatigue of evaporation pipe in boiler

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