Boiler operation methods

Abstract

This method suppresses the contamination of steam generated from boiler water containing polyacrylic acid compounds with aldehydes. [Solution] Water is supplied to the boiler 20 through the water supply path 13. The boiler 20 stores the water from the water supply path 13 as boiler water and generates steam by heating this boiler water. At this time, a water treatment agent containing a polyacrylic acid compound such as sodium polyacrylate, which functions as a scale inhibitor, is added from the chemical supply device 40 to the water supply from the water supply path 13 to the boiler 20, and the boiler 20 controls the copper concentration of the boiler water to 3 mg / L or less in the presence of the polyacrylic acid compound derived from the water treatment agent. It is particularly preferable to use a polyacrylic acid compound with a residual monomer content of 1.0 mass% or less and to control its presence in the boiler water to 10 to 300 mg / L.

Description

Technical Field

[0001] The present invention relates to a method for operating a boiler, particularly a method for operating a boiler that generates steam by heating boiler water.

Background Art

[0002] A general boiler device for supplying steam to a load device such as a heat exchanger generates steam by heating feed water to the boiler as boiler water, and supplies this steam to the load device through a steam path. Since the inside of the boiler is in a high-temperature and high-pressure environment, scale adheres and corrosion occurs on the heat transfer surface of the water pipes that generate steam due to the influence of various dissolved components in the feed water. The scale adhering to the heat transfer surface hinders heat conduction and thus causes a loss of the boiler's operating efficiency. In addition, the corrosion of the heat transfer surface, if it progresses, will damage the water pipes, which becomes a cause for inhibiting the stable and continuous operation of the boiler.

[0003] Therefore, in the operation of a boiler device, usually, hardness components such as calcium ions and magnesium ions that cause scale are removed from the feed water to the boiler, and a chemical agent for scale inhibition and corrosion inhibition is added to the feed water to suppress the generation of scale and the progress of corrosion in the boiler. As an example of the chemical agent added to the feed water, Patent Document 1 discloses an aqueous composite boiler cleaning agent containing sulfite and sodium polyacrylate at the same time. Sulfite is a deoxidizer and can remove dissolved oxygen in the feed water that causes corrosion. On the other hand, sodium polyacrylate functions as a chelating agent that blocks calcium ions and magnesium ions in the boiler water and can suppress the growth of scale crystal nuclei by dispersing fine particles in the boiler water. By these actions, scale generation can be suppressed.

[0004] Polyacrylic acid compounds, such as sodium polyacrylate, have long been known as chemicals added to boiler feedwater as scale inhibitors, as mentioned above. However, in this section, their application as part of corrosion inhibitors is also being considered. For example, Patent Document 2 describes a water treatment agent that can suppress corrosion of boiler water tubes, containing polyacrylic acid compounds along with alkali metal hydroxides and hydrolyzable tannins. Patent Document 3 describes how using silicate compounds and polyacrylic acid compounds in combination can suppress scale formation and inhibit both overall corrosion and pitting corrosion in boilers. Thus, since polyacrylic acid compounds can be expected to suppress both boiler corrosion and scale formation, their use as water treatment agents added to boiler feedwater is expected to expand further. However, because they are polymers of acrylic acid compounds, they may decompose in high-temperature, high-pressure boiler water, potentially generating harmful substances such as formaldehyde and acetaldehyde. These generated aldehydes are volatile and can mix into the steam generated in the boiler, impairing steam quality. In other words, vapors containing aldehydes are restricted from use in food processing and pharmaceutical factories where high levels of safety and hygiene are required. When used for humidification, they not only cause odors in the humidified air but also raise concerns about adverse effects on human health and environmental pollution. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 63-166981 [Patent Document 2] Japanese Patent Publication No. 2019-65357 [Patent Document 3] Japanese Patent Publication No. 2024-60704 [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] This invention aims to suppress the contamination of steam generated from boiler water containing polyacrylic acid compounds with aldehydes. [Means for solving the problem]

[0007] This invention relates to a boiler operation method for generating steam by heating boiler water. In this operation method, the copper concentration of the boiler water is controlled to 3 mg / L or less in the presence of a polyacrylic acid compound.

[0008] In one embodiment of the operating method according to the present invention, a polyacrylic acid-based compound having a residual monomer content of 1.0% by mass or less is added to the feedwater of the boiler to control the amount of the polyacrylic acid-based compound present in the boiler water to 10 to 300 mg / L.

[0009] The operating method according to the present invention is generally preferred to be as follows. • The levels of lead and arsenic in boiler water will be regulated to be 3 mg / L or less. • Regulations will be implemented to ensure that the levels of reducing sugars, aldonates, tannins, and lignins in boiler water are all below the detection limit. • Further control the concentration of silicate compounds in the boiler water to 50-800 mgSiO2 / L.

[0010] The boilers to which the operating method according to the present invention is applied are typically those with a normal operating pressure of 3 MPa or less, such as multi-tube special circulating boilers.

[0011] The present invention, relating to another aspect, concerns a boiler water treatment agent, which comprises a polyacrylic acid-based compound having a residual monomer content of 1.0% by mass or less.

[0012] The following are preferred boiler water treatment agents of the present invention. • Polyacrylic acid compounds have lead and arsenic content of 2 μg / g or less and 3 μg / g or less, respectively. • The levels of reducing sugars, aldonates, tannins, and lignins are all below the detection limit. • Further contains silicate compounds. [Effects of the Invention]

[0013] The boiler operation method according to the present invention controls the copper concentration of the boiler water, and therefore, even when polyacrylic acid compounds are present in the boiler water, the inclusion of aldehydes in the generated steam can be suppressed.

[0014] The boiler water treatment agent according to the present invention contains a polyacrylic acid-based compound with regulated residual monomer content, thereby suppressing the contamination of steam generated in the boiler with aldehydes. [Brief explanation of the drawing]

[0015] [Figure 1] A schematic diagram of one embodiment of a boiler apparatus capable of implementing the operating method according to the present invention. [Modes for carrying out the invention]

[0016] Referring to Figure 1, one embodiment of a boiler apparatus capable of implementing the boiler operation method according to the present invention will be described. In Figure 1, the boiler apparatus 1 is for supplying steam to a load device 2, which is steam-using equipment such as a heat exchanger, steam boiler, reboiler, or autoclave, and mainly comprises a feedwater device 10, a boiler 20, condensate piping 30, and a chemical supply device 40.

[0017] The feedwater system 10 is for supplying feedwater to be used as boiler water in the boiler 20, and mainly comprises a feedwater tank 11 for storing feedwater and a supply route 12 for supplying makeup water to be used as feedwater to the feedwater tank 11. The feedwater tank 11 has a feedwater route 13 extending from its bottom to the boiler 20. The feedwater route 13 is connected to the boiler 20 and has a feedwater pump 14 for sending the feedwater stored in the feedwater tank 11 to the boiler 20.

[0018] The replenishment path 12 has a water injection path 15. The water injection path 15 is for supplying replenishment water from a raw water tank (not shown) in which raw water supplied from a water source such as tap water, industrial water, or groundwater is stored to the water supply tank 11, and has a water softening device 16 and a deoxygenation device 17 in this order toward the water supply tank 11.

[0019] The water softening device 16 is for treating the replenishment water from the raw water tank with a sodium-type cation exchange resin, replacing calcium ions and magnesium ions, which are hardness components contained in the replenishment water, with sodium ions, and converting it into softened water.

[0020] The deoxygenation device 17 is for removing dissolved oxygen in the replenishment water treated in the water softening device 16, and various types such as a type that removes dissolved oxygen using a separation membrane, a type that removes dissolved oxygen in a decompressed environment of the treated water, or a type that removes dissolved oxygen by heating the treated water are used.

[0021] In this embodiment, the materials forming the replenishment path 12 and the water supply path 13 of the water supply device are, for example, carbon steel, cast iron, stainless steel, copper, or copper alloy, etc., but lead-based materials may be used assuming old facilities.

[0022] The boiler 20 is usually an industrial boiler with a normal operating pressure of 3 Mpa or less. Applicable industrial boilers are, for example, round boilers, single-tube special circulation boilers, and multi-tube special circulation boilers. Usually, an internal structure such as a water pipe is formed using a metal that does not passivate naturally in a neutral aqueous solution such as carbon steel or cast iron. However, the operation method of this embodiment is particularly suitable for application to a multi-tube special circulation boiler. When the boiler 20 is a multi-tube special circulation boiler, this boiler 20 has a large number of upright water pipes (not shown) inside, stores the water supplied from the water supply path 13 as boiler water at the bottom, and generates steam by heating this boiler water through the heat transfer surface of the water pipes.

[0023] The boiler 20 has a blowdown path 21 for discharging boiler water, and this blowdown path 21 has a control valve 22 for adjusting the discharge rate of boiler water. Furthermore, a steam supply pipe 23 extends from the top of the boiler 20 to connect to the load device 2. The steam supply pipe 23 may also connect to the load device 2 via a steam header (not shown).

[0024] The condensate piping 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 from condensate. In this embodiment, the materials forming the load device 2 and the condensate piping 30 are, for example, stainless steel or steel.

[0025] The chemical supply device 40 is for supplying a water treatment agent to the feedwater supplied from the water tank 11 to the boiler 20, and includes a chemical tank 41 for storing the water treatment agent, a supply channel 42 extending from the chemical tank 41 to the water supply path 13, and a supply pump 43 provided in the supply channel 42. The supply pump 43 sends the water treatment agent stored in the chemical tank 41 to the water supply path 13 through the supply channel 42, and the amount of water treatment agent supplied can be controlled.

[0026] The water treatment agent stored in the chemical tank 41 of the chemical supply device 40 contains a polyacrylic acid compound. The polyacrylic acid compound contained in the water treatment agent is basically used to suppress scale formation in the boiler 20. As the polyacrylic acid compound, a water-soluble polymer compound containing a carboxyl group or a salt thereof derived from at least one of acrylic acid and methacrylic acid is usually used. For example, polyacrylic acid, polymethacrylic acid, copolymers or terpolymers using at least one of acrylic acid and methacrylic acid as monomers, or salts thereof can be used. As the salt, for example, alkali metal salts such as sodium salts and potassium salts can be used. Preferred polyacrylic acid compounds are polyacrylic acid or salts thereof, in particular sodium polyacrylate. The polyacrylic acid-based compound used as a scale inhibitor is not particularly limited in terms of mass-average molecular weight, etc., as long as it is used as such. However, a specific range of mass-average molecular weight that can exert a corrosion inhibitory effect through interaction with other compounds is preferred. For example, a mass-average molecular weight of 2,000 to 40,000 is preferred, 3,000 to 20,000 is more preferred, and 4,000 to 10,000 is particularly preferred. The polyacrylic acid-based compound contained in the water treatment agent may be two or more types.

[0027] The polyacrylic acid-based compound contained in the water treatment agent is particularly preferably one with a residual monomer content of 1.0% by mass or less. When the residual monomer of the polyacrylic acid-based compound contained in the water treatment agent is limited in this way, the steam generated from the boiler 20 in the operating method of this embodiment is more effectively suppressed in terms of aldehyde contamination. Here, the residual monomer is the unpolymerized monomer that remains during the manufacturing process of the polyacrylic acid-based compound.

[0028] Furthermore, the polyacrylic acid-based compounds contained in the water treatment agent are preferably those with lead and arsenic content of 2 μg / g or less and 3 μg / g or less, respectively. Both lead and arsenic act as catalysts that promote oxidation reactions in high-temperature, high-pressure boiler water, and readily decompose polyacrylic acid-based compounds, promoting the generation of aldehydes. Therefore, using polyacrylic acid-based compounds with their respective content regulated as described above makes it easier to suppress the mixing of aldehydes into the steam generated from the boiler 20.

[0029] Furthermore, the polyacrylic acid-based compounds contained in the water treatment agent contain sulfate ions (SO4), which promote corrosion of boiler 20. 2- Preferably, it is 0.48% by mass or less.

[0030] The above-mentioned content of residual monomers, lead, arsenic, and sulfate ions in polyacrylic acid compounds can be measured and confirmed based on the "Sodium Polyacrylate" section of the "10th Edition Food Additives Compendium 2024 D Component Standards and Preservation Standards" published by the Ministry of Health, Labour and Welfare and the Consumer Affairs Agency.

[0031] The water treatment agent may contain, in addition to polyacrylic acid compounds, pH adjusters, oxygen absorbers, and silicate compounds. The pH adjuster suppresses corrosion inside the boiler 20 by adjusting the pH of the boiler water to the alkaline range; for example, alkali metal hydroxides such as sodium hydroxide and potassium hydroxide are used. Two or more pH adjusters may be used in combination. The oxygen absorber suppresses corrosion inside the boiler 20 by further removing dissolved oxygen remaining in the feedwater; for example, ascorbic acid or its salts, erythorbic acid or its salts, or sulfites are used. Two or more oxygen absorbers may be used in combination.

[0032] While reducing sugars, aldonates, tannins, and lignins are also known as oxygen absorbers, these oxygen absorbers are known to undergo thermal decomposition in the boiler 20 to produce aldehydes (for example, Japanese Patent Publication No. 2002-220687 and Japanese Patent No. 5707723). Therefore, using these oxygen absorbers in the water treatment agent makes it easier for aldehydes to be mixed into the steam generated from the boiler 20. Accordingly, the water treatment agent used in the operating method of this embodiment is preferably one that is substantially free of reducing sugars, aldonates, tannins, and lignins, and in particular, one in which the content of each of these is below the detection limit (lower limit of quantification).

[0033] Here, tannins are generally classified into two groups: hydrolyzable tannins and condensed tannins, and both are assumed. Hydrolyzable tannins refer to the pyrogallol tannin group, which are broken down into alcohols and acids by acids, alkalis, or enzymes (tannase), such as gallnut tannin, chestnut tannin, tara tannin, oak tannin, sumac tannin, vallonia tannin, and miraborum tannin. On the other hand, condensed tannins are extracted from plants, such as quebracho tannin, mimosa tannin, radiata pine tannin, gambia tannin, and mangrove tannin. Furthermore, lignins include, for example, alcohol lignin, dioxan lignin, phenol lignin, hydrotropic lignin, mercapt lignin, thioglycolate lignin, lignin sulfonic acid, alkali lignin, thioalkali lignin, acid lignin, copper oxide-ammonia lignin, and periodate lignin, as well as their salts.

[0034] The content of reducing sugars in water treatment agents can be measured as the total sugar content measurable by the phenol-sulfuric acid method, with a detection limit of 10 mg / L. The content of aldonates can be measured as the sodium gluconate content by high-performance liquid chromatography-mass spectrometry (LC-MS), with a detection limit of 10 mg / L in this case. The content of tannins can be measured by the catechin analysis method using a spectrophotometer described in "Food Analysis Methods" edited by the Editorial Committee of Food Analysis Methods, Japan Society for Food Science and Technology, with a detection limit of 0.5 mg / L as ethyl gallate. The content of lignins can be measured as sodium lignosulfonate by high-performance liquid chromatography-mass spectrometry (LC-MS), with a detection limit of 10 mg / L in this case.

[0035] Silicate compounds can form a film inside the boiler 20, particularly on the surface of water tubes, and this film can suppress corrosion. However, interaction with polyacrylic acid compounds, especially with the aforementioned polyacrylic acid compounds with a mass-average molecular weight, can make it easier to suppress both general corrosion and pitting corrosion inside the boiler 20 (see Patent Document 3 referenced in the background art). Silicate compounds are silicic acid or silicates. Silicic acid is [SiO₂ X (OH) 4-2X ] n These are silicon compounds represented by the chemical formula nSiO2·(n+1)M2O, and are usually anhydrous silicic acid (SiO2), orthosilicic acid (H4SiO4), metasilicic acid (H2SiO3), or metadisiliic acid (H2Si2O5). Silicates, for example, are orthosilicates represented by the chemical formula nSiO2·(n+1)M2O or their hydrates, or polysilicates represented by the chemical formulas nSiO2·nM2O, nSiO2·(n-1)M2O, or nSiO2·(n-2)M2O or their hydrates. In the chemical formula of a silicate, n is an integer greater than 2, and M represents a metallic element such as an alkali metal such as sodium or potassium, or an alkaline earth metal such as calcium or magnesium. If the metallic element is divalent, the number of molecules of M is halved. Two or more types of silicic acid compounds may be used in combination.

[0036] Water treatment agents are typically aqueous solutions containing polyacrylic acid compounds and, if necessary, other components, as they allow for easy dispersion of the required components into the water supply. The water used in preparing these aqueous solutions is usually purified water, such as distilled water or deionized water.

[0037] Next, the operating method of the boiler device 1 described above will be explained. In the operation of the steam boiler system 1, first, makeup water is supplied from the raw water tank (not shown) to the feedwater tank 11 through the water injection channel 15, and this makeup water is stored in the feedwater tank 11 as boiler feedwater.

[0038] In this process, the makeup water from the raw water tank is first treated in the water softener 16, where hardness components that cause scale are removed, resulting in softened water. The makeup water, softened in the water softener 16, is then deoxygenated in the deoxygenation unit 17. This removes dissolved oxygen from the makeup water, which promotes corrosion of water pipes and other components in the steam boiler 20. As a result, deoxygenated softened water is stored in the feedwater tank 11 as feedwater.

[0039] When the feedwater pump 14 is operated with feedwater tank 11 containing makeup water, the feedwater stored in feedwater tank 11 is supplied to boiler 20 through the feedwater path 13. The feedwater supplied to boiler 20 is stored as boiler water, which is heated as it rises through the water tubes and turns into steam. The steam generated in the water tubes is then supplied to load device 2 through steam supply piping 23. As steam is generated in this way, the boiler water becomes concentrated.

[0040] The steam supplied to the load device 2 loses its latent heat and flows into the condensate pipe 30, with some of it turning into condensate. In the steam trap 31, the steam and condensate are separated to form high-temperature condensate. The condensate thus produced is collected in the feedwater tank 11 through 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, thus reducing the heating burden on the boiler 20.

[0041] During operation of boiler unit 1, a water treatment agent is supplied from the chemical supply device 40 to the feedwater flowing to boiler 20 through the feedwater path 13 as needed. This ensures that polyacrylic acid compounds are present in the boiler water, suppressing scale formation in water tubes and other parts of boiler 20. The concentration (amount) of polyacrylic acid compounds in the boiler water can be adjusted by controlling the concentration of polyacrylic acid compounds in the water treatment agent, the supply amount of the water treatment agent, and the concentration ratio. Generally, it is preferable to control the concentration to 10-300 mg / L from the viewpoint of effectively suppressing scale. The concentration of polyacrylic acid compounds here is the salt equivalent concentration. The salt equivalent concentration is the concentration calculated by considering the polyacrylic acid compound as a salt in which all carboxyl groups in its molecule form a sodium salt.

[0042] The concentration ratio of the boiler water can be controlled by adjusting the control valve 22 to control the discharge amount of boiler water from the blowdown path 21, and by controlling the feedwater pump 14 to adjust the amount of feedwater supplied from the feedwater tank 11 to the boiler 20.

[0043] During operation of boiler system 1 in this configuration, the copper concentration of the boiler water is monitored and regulated to be below a certain value. Here, copper concentration refers to the total amount of copper present in various forms, including ionic, oxide, hydroxide, phosphate, and complexes with organic matter, and means the copper concentration specified in B.10 of Annex B of Japanese Industrial Standard JIS B8223:2021. By regulating the copper concentration, the generation of aldehydes derived from polyacrylic acid compounds is suppressed, and the contamination of steam supplied to load device 2 with aldehydes is reduced. In particular, controlling the copper concentration of the boiler water to 3 mg / L or less significantly suppresses the generation of aldehydes, making it easier to suppress the formaldehyde concentration in the condensate obtained by steam condensation to 0.08 mg / L or less, which is the tap water standard specified in the "Water Testing Methods (2020 Edition)" compiled by the Japan Water Works Association. This is particularly noticeable when the concentration of polyacrylic acid compounds in boiler water is controlled to 10-300 mg / L as described above, and when the residual monomer content of the polyacrylic acid compounds used in the water treatment agent is 1.0% by mass or less.

[0044] The copper contained in boiler water may originate from the raw water, or, depending on the quality of the raw water (such as the presence of free carbon dioxide), may be due to leaching from the piping materials forming the feedwater system 10. Ionic copper originating from the raw water and ionic copper leached from the piping upstream of the water softener 16 can be removed by the water softener 16. However, boiler water contains copper leached downstream of the water softener 16, ionic copper remaining in the feedwater without being removed by the water softener 16, and other forms of copper, and the copper concentration increases as concentration progresses. Therefore, the copper concentration in boiler water is usually controlled to be below the above-mentioned regulatory value by adjusting the concentration ratio of the boiler water. The copper concentration in boiler water can be measured and confirmed by diethyldithiocarbamic acid spectrophotometric method, cuprizon spectrophotometric method, zincon spectrophotometric method, flame atomic absorption spectrometry, electrothermal atomic absorption spectrometry, ICP emission spectrometry, or ICP mass spectrometry, as specified in the Japanese Industrial Standard JIS B8224:2022, which specifies test methods for boiler water. However, it is particularly preferable to measure and confirm the concentration using the highly accurate ICP emission spectrometry or ICP mass spectrometry.

[0045] Furthermore, in this configuration, it is preferable to regulate the amount of lead and arsenic present in the boiler water to 3 mg / L or less during the operation of the boiler unit 1. By regulating the amount of lead and arsenic present in the boiler water, which promote the oxidation reaction of polyacrylic acid compounds, it becomes easier to suppress the mixing of aldehydes into the steam generated from the boiler 20.

[0046] The lead and arsenic present in boiler water are mainly due to the quality of the raw water, impurities in water treatment agents, and especially as contaminants in polyacrylic acid compounds. In the case of lead, it is also possible that it may leach from materials such as lead and bronze alloys used in the feedwater system 10. However, the concentration increases as the boiler water is concentrated. Therefore, it is generally preferable to control the amount of lead and arsenic in the boiler water to below the above-mentioned regulatory limits by adjusting the amount of water treatment agent added and the concentration ratio of the boiler water. The amount (concentration) of lead and arsenic in boiler water can usually be measured and confirmed by atomic absorption spectroscopy, ICP emission spectroscopy, or ICP mass spectrometry, but it is particularly preferable to measure and confirm it by high-precision ICP emission spectroscopy or ICP mass spectrometry.

[0047] When boiler water containing polyacrylic acid compounds is treated with a water treatment agent, if the amounts of reducing sugars, aldonates, tannins, and lignins—all sources of aldehydes—are below the detection limit in the added water treatment agent, then, since these substances cannot be present in the raw water unless intentionally added, the amounts of these substances are effectively regulated to be below the detection limit. In this case, the source of aldehydes in the boiler water becomes essentially only polyacrylic acid compounds, making it easier to suppress the contamination of steam from boiler 20 with aldehydes.

[0048] When the water treatment agent contains a silicate compound, it is preferable to further control the concentration of the silicate compound in the boiler water to 50-800 mgSiO2 / L. If this concentration is less than 50 mgSiO2 / L, the corrosion suppression effect of the silicate compound in the boiler 20 will be less apparent, and if it exceeds 800 mgSiO2 / L, scale formation by the silicate compound in the boiler 20 will progress more easily. The concentration of the silicate compound in the boiler water can be adjusted, as with the concentration of the polyacrylic acid compound, by adjusting the concentration of the silicate compound in the water treatment agent, the supply amount of the water treatment agent, and the control of the boiler water discharge rate to control the concentration ratio.

[0049] During operation as described above, the boiler unit 1 maintains the pH of the boiler water in an alkaline range less prone to corrosion, preferably at pH 11 to 12.5, by adjusting the concentration ratio to control the acid consumption (pH 4.8) of the boiler water and by adding a water treatment agent containing a pH adjusting agent. By suppressing corrosion of the boiler 20 through pH adjustment of the boiler water, it is possible to suppress the generation of aldehydes by eluting metals such as iron acting on polyacrylic acid compounds, thereby more effectively suppressing the mixing of aldehydes into the steam. The acid consumption (pH 4.8) is calculated by converting the amount of hydrogen ions (amount of acid) required to neutralize the alkalis such as bicarbonates, carbonates, and hydroxides dissolved in the feedwater to a predetermined pH (here, 4.8), into the amount of calcium carbonate equivalent to the hydrogen ions (acid), and expressing it in mg per liter of feedwater. This can be measured according to the method specified in JIS K 0101.

[0050] In the above-described embodiment, the steam generated in the boiler 20 contains carbon dioxide produced by the thermal decomposition of bicarbonates and carbonates, etc., which are related to the acid consumption (pH 4.8) in the boiler water. Therefore, when condensation occurs in the load device 2 and condensate piping 30, it easily acidifies the condensate, and acidic condensate promotes corrosion on the inner surfaces of the load device 2 and condensate piping 30. The boiler device 1 according to the above-described embodiment is equipped with a load device 2 and condensate piping 30 made of stainless steel or steel. However, if the load device 2 and condensate piping 30 are made of copper or copper alloy, copper is easily leached into the condensate due to corrosion of the load device 2 and condensate piping 30. As a result, the copper concentration in the feedwater stored in the feedwater tank 11 increases as condensate is recovered, which causes an increase in the copper concentration of the boiler water.

[0051] Therefore, when the load device 2 and condensate piping 30 are made of copper or copper alloy, it is preferable to take measures to suppress corrosion of the load device 2 and condensate piping 30 in order to prevent copper from dissolving into the condensate. Measures to suppress corrosion of the load device 2 and condensate piping 30 include adding a condensate treatment agent to the feedwater supplied to the boiler 20 to suppress corrosion of the load device 2 and condensate piping 30, improving the deoxygenation treatment of the feedwater to suppress the mixing of oxygen into the steam, or constructing the load device 2 and condensate piping 30 in a way that prevents condensate from accumulating inside by avoiding the provision of upright sections. These measures can also be used in combination.

[0052] The condensate treatment agents used here are, for example, volatile amines, film-forming amines, or film-neutralizing amines. Although ammonia is sometimes used as a condensate treatment agent, it is preferable to avoid using it here because it is prone to corroding copper-based materials. The condensate treatment agent may be added to the feedwater from the chemical supply device 40 as part of the water treatment agent, or it may be added to the feedwater separately from the water treatment agent. In the latter case, multiple chemical supply devices 40 are installed in the feedwater path 13, and the water treatment agent and the condensate treatment agent are added to the feedwater individually from the chemical supply devices 40. Alternatively, the condensate treatment agent may be added directly to the steam system, such as the steam supply piping 23 or steam header. Advanced methods for deoxygenating feedwater include installing multiple deoxygenation devices 17 with the same or different dissolved oxygen removal methods in series in the supply route 12 of the feedwater device 10 to repeatedly deoxygenate the feedwater; adding a deoxygenating agent to the feedwater before or after the deoxygenation device 17 in the supply route 12, in addition to the deoxygenating agent contained in the water treatment agent supplied to the feedwater from the chemical supply device 40; installing a deoxygenating device similar to the deoxygenation device 17 in the feedwater route 13; and combinations of these methods.

[0053] [Example of experiment] In the following experimental examples 1 and 2, the boiler apparatus 1 according to the above embodiment was operated, and the formaldehyde concentration in the steam generated in the boiler 20 was investigated. The boiler apparatus 1 used here had a steam extraction pipe branched off from the steam supply pipe 23, and this branch pipe was used to collect a portion of the steam generated in the boiler 20 as a sample. For the measurement of the aldehyde concentration, simulated feedwater was prepared by adding sodium polyacrylate and copper(II) chloride dihydrate (reagent grade from Fujifilm Wako Pure Chemical Industries, Ltd.) to distilled water, and the formaldehyde concentration in the condensate obtained by taking a portion of the steam generated from the boiler water using this simulated feedwater through the branch pipe and cooling it with a heat exchanger was analyzed. The operating conditions of the boiler 20 were set so that the operating pressure and concentration ratio were 0.8 MPa and 10 times, respectively, and sodium hydroxide (reagent grade from Fujifilm Wako Pure Chemical Industries, Ltd.) was separately added to the simulated feedwater so that the pH of the boiler water was 11.5. Furthermore, the formaldehyde concentration in the condensed water was analyzed according to the "Aldehyde Analysis Method" announced in the "Water Supply Testing Methods (2020 Edition)" compiled by the Japan Water Works Association.

[0054] Experimental Example 1: Simulated feedwater was prepared by adjusting the amounts of sodium polyacrylate and copper(II) chloride dihydrate added to boiler water in boiler 20 during operation so that the concentration of sodium polyacrylate in the boiler water was 10 mg / L, and the copper concentration was within the range of 0 to 5 mg / L shown in Table 1. Boiler 20 was operated using this simulated feedwater, and the formaldehyde concentration in the condensate was analyzed. The sodium polyacrylate used here was sodium polyacrylate (trademark "Acuzol 445NG" of Dow Chemical Japan Ltd.) confirmed to have a residual monomer content of 0, and sodium polyacrylate in which the residual monomer content was adjusted by adding sodium acrylate (acrylic acid (Wako Special Grade from Fujifilm Wako Pure Chemical Corporation) neutralized with sodium hydroxide (reagent grade from Fujifilm Wako Pure Chemical Corporation)) as a residual monomer. The results are shown in Table 1.

[0055] Experimental Example 2: Simulated feedwater was prepared by adjusting the amounts of sodium polyacrylate and copper(II) chloride dihydrate added to the boiler water of boiler 20 during operation so that the concentration of sodium polyacrylate in the boiler water was 300 mg / L, and the copper concentration was within the range of 0 to 5 mg / L shown in Table 1. The sodium polyacrylate used here had its residual monomer content adjusted in the same way as that used in Experimental Example 1. Boiler 20 was operated using this simulated feedwater, and the results of the analysis of the formaldehyde concentration in the condensate are shown in Table 2.

[0056] [Table 1]

[0057] [Table 2]

[0058] The evaluation results in Tables 1 and 2 are as follows: ◎: Formaldehyde concentration in condensed water is 0.04 mg / L or less ○: Formaldehyde concentration in condensed water exceeds 0.04 mg / L and is 0.06 mg / L or less. △: Formaldehyde concentration in condensed water exceeds 0.06 mg / L but is 0.08 mg / L or less. ×: Formaldehyde concentration in condensed water exceeds 0.08 mg / L

[0059] According to Tables 1 and 2, steam generated from boiler water with a copper concentration exceeding 3 mg / L in the presence of sodium polyacrylate has a high formaldehyde concentration. In particular, when the sodium polyacrylate concentration in the boiler water is 300 mg / L, the formaldehyde concentration in the condensate exceeds the tap water standard of 0.08 mg / L specified in the aforementioned "Water Supply Testing Methods (2020 Edition)". On the other hand, when the copper concentration in the boiler water is controlled to 3 mg / L or less, the formaldehyde concentration in the condensate is significantly reduced regardless of the sodium polyacrylate concentration in the boiler water. In particular, when the residual monomer content of the sodium polyacrylate used in the preparation of the simulated feedwater is 1.0% by mass or less, the formaldehyde concentration in the condensate is suppressed to less than half of the tap water standard.

[0060] This disclosure helps to suppress the contamination of steam with aldehydes in the steam generated in boilers, thereby contributing to the safe supply of steam and potentially contributing to the achievement of United Nations-led Sustainable Development Goal (SDG) 3, "Ensure healthy lives and promote well-being," or Goal 11, "Make cities and human settlements inclusive, safe, and resilient." [Explanation of Symbols]

[0061] 1. Boiler equipment 10 Water supply device 20 Boilers 30 Condensate piping 40. Drug supply device

Claims

1. A method of operating a boiler that generates steam by heating boiler water, The copper concentration of the boiler water is controlled to 3 mg / L or less in the presence of a polyacrylic acid compound. How to operate a boiler.

2. A method for operating a boiler according to claim 1, wherein the amount of polyacrylic acid-based compound present in the boiler water is controlled to be 10 to 300 mg / L by adding a polyacrylic acid-based compound having a residual monomer content of 1.0% by mass or less to the feedwater for the boiler.

3. The boiler operation method according to claim 1, wherein the amount of lead and arsenic present in the boiler water is regulated to be 3 mg / L or less.

4. The boiler operation method according to claim 1, wherein the amounts of reducing sugars, aldonates, tannins, and lignins in the boiler water are all regulated to be below the detection limit.

5. The silicate compound concentration in the boiler water is 50 to 800 mg SiO ２ The boiler operation method according to claim 2, further controlling the voltage to become / L.

6. The boiler operation method according to any one of claims 1 to 5, wherein the boiler has a normal operating pressure of 3 MPa or less.

7. The boiler operation method according to claim 6, wherein the boiler is a multi-tube special circulating boiler.

8. A boiler water treatment agent containing a polyacrylic acid-based compound with a residual monomer content of 1.0% by mass or less.

9. The boiler water treatment agent according to claim 8, wherein the polyacrylic acid compound has a lead content of 2 μg / g or less and a lead content of 3 μg / g or less, respectively.

10. The boiler water treatment agent according to claim 9, wherein the content of reducing sugars, aldonates, tannins, and lignins is all below the detection limit.

11. A boiler water treatment agent according to any one of claims 8 to 10, further comprising a silicate compound.

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