JP7655501B2 - Method for manufacturing corrosion inhibitor for boiler, boiler and method for inhibiting corrosion in boiler - Google Patents

Description

Article 30, paragraph 2 of the Patent Act applies. ・Proceedings of the 41st National Urban Cleaning Research and Case Presentation Conference (pages 80-82) National Urban Cleaning Conference, Public Interest Incorporated Association. Published on December 15, 2019. ・The 41st National Urban Cleaning Research and Case Presentation Conference, held on January 23, 2020.

The present invention relates to a method for efficiently producing a boiler corrosion inhibitor for inhibiting corrosion of boilers, particularly superheater tubes, by recycling combustion ash, such as molten fly ash and combustion fly ash, which have traditionally been treated as industrial waste and contain heavy metals such as Pb, Zn, and Cu, using the recycled ash as the main raw material, and to a boiler and a method for inhibiting corrosion of the boiler.

Direct landfill disposal of fly ash (incineration fly ash, molten fly ash) discharged from waste treatment facilities is prohibited, and it is disposed of as ordinary general waste in landfills after intermediate treatment such as melting and solidifying, cement solidification, chemical treatment, and discharge treatment using acids or other solvents. In addition, a method of recovering resources by extracting heavy metals from incineration fly ash and molten fly ash through reduction at the mine is used. Specific processing methods include melting treatment, wet methods, and chlorination volatilization methods. Zinc, lead, copper, etc. are recovered by these processing methods. The recovered metals are purified at smelters and reused as metallic materials. The recovered slag is reused as a cement raw material and a raw material for ironmaking. The solids other than the recovered slag are reused as raw materials for non-ferrous smelting.

Landfill disposal has low disposal costs, but serious problems include the difficulty of securing final disposal sites. For this reason, there is a need to increase the resource recovery rate of combustion fly ash and molten fly ash and reduce the amount disposed of at final disposal sites. The landfill method has high recyclability, but high disposal costs.

As a method for solving the above problem, Patent Document 1 describes a method in which the incineration ash generated by incinerating combustible waste is washed with water, then treated with hydrochloric acid, and then treated with alkali under heating, and then washed with water to remove the alkali, and then dried to recycle the waste incineration ash as a material with ion exchange and adsorption capabilities.

In the boiler superheater tubes (SH tubes) of waste treatment facilities that use biomass fuel, general waste from households _, waste tires, waste plastics, etc., incineration fly ash that has been washed with water, and molten fly ash as boiler fuel, corrosion caused by low-melting-point molten salts such as KCl, NaCl, _ZnCl2 , _PbCl2 , _K2SO4 , _{Na2SO4 , etc.} is a problem. In addition, while it is desired to increase the steam temperature in order to increase the power generation efficiency of the boiler, the corrosion problem caused by molten salts becomes even more serious as the temperature increases.

Patent Document 2 describes that the use of a compound containing at least one element selected from the group consisting of Ca, Si, Al, Mg, and Fe as its main component can suppress the progression of corrosion of boiler superheater tubes (SH tubes).

Japanese Patent Application Publication No. 11-207294 Patent No. 6046886

Patent Document 1 describes that a material with increased ion exchange capacity and adsorption capacity can be obtained by performing a water washing treatment, or performing a water washing treatment followed by a hydrochloric acid treatment. If a water washing treatment is performed as a pretreatment before the alkaline hydrothermal treatment, it is possible to remove NaCl, KCl, _PbCl2 , _CaCl2 , which are corrosion factors of boiler superheater tubes, and Ca(OH) ₂ , which is an inhibitor of corrosion inhibitors. In addition, if a strong acid pickling treatment is performed, it is possible to remove ZnO, CuO, PbSiO3 _{, etc.} , which are corrosion factors of boiler superheater tubes.
However, if the pickling treatment is too strong, the components Si and Al necessary for synthesizing the corrosion inhibitor will flow out, making it impossible to synthesize a corrosion inhibitor having a corrosion inhibitory effect, and therefore it is difficult to apply Patent Document 1 as it is.
Furthermore, if Ca is not sufficiently removed by the water washing treatment and the hydrochloric acid treatment, the proportion of calcium carbonate produced during the alkaline hydrothermal treatment increases, and the corrosion inhibition effect decreases. Patent Document 1 does not disclose a lower limit of the Ca content of the raw material used in the alkaline hydrothermal treatment.
Furthermore, when a corrosion inhibitor is synthesized using incineration fly ash with a low content of Si and Al, it is necessary to remove heavy metals Pb, Zn, and Cu, Ca, Na, K, and Cl while suppressing the elution of Si and Al by water washing and pickling. If the concentration of Si and Al is insufficient, the corrosion inhibitor is not produced or a corrosion inhibitor with a low corrosion inhibition effect is produced. However, Patent Document 1 does not disclose the lower limit of the content of Si and Al in the incineration fly ash used in the alkaline hydrothermal treatment.

The boiler superheater tubes in waste treatment facilities that use biomass fuels, general household waste, waste tires, waste plastics, etc., water-washed incineration fly ash, and molten fly ash as boiler fuel are in a severe corrosive environment that contains large amounts of heavy metals and Cl, which are corrosion factors, compared to the boiler superheater tubes of normal waste incinerators and waste treatment facilities that handle only general household waste. Therefore, simply adding a compound containing at least one of the elements Ca, Si, Al, Mg, and Fe as a main component as the corrosion inhibitor described in Patent Document 2 has little effect in inhibiting the corrosion of the boiler superheater tubes.

From the above, it is desired to produce a corrosion inhibitor that can efficiently remove corrosion factors such as Na, K, Cl, Pb, Zn, and Cu that corrode boilers (especially boiler superheater tubes (SH tubes)) and impurities (NaCl, CaCl 2, etc.) that do not contribute to the synthesis of the corrosion inhibitor while suppressing the elution of Si and Al, which are components of C-S-H (calcium silicate hydrate) and C-A-S-H (calcium _{aluminosilicate} hydrate), from refuse fusion fly ash and incineration fly ash that are treated as industrial waste and contain a lot of heavy metals but have a low content of Si and Al, and that does not require the addition of Si and Al in a post-acid pickling process. It is also desired to produce a corrosion inhibitor that has a corrosion inhibitor effect even in boiler superheater tubes that contain a lot of heavy metals and corrosion factors such as NaCl, KCl, and CaCl ₂ in fly ash and are in a severe corrosive environment. Furthermore, it is desired to recycle the removed heavy metals as a raw material for non-ferrous smelting.

The present invention has been made in consideration of the above circumstances, and aims to provide a method for producing a corrosion inhibitor for a boiler, which can efficiently remove corrosion factors that corrode the boiler and impurities that do not contribute to the synthesis of the corrosion inhibitor, and which can reduce the amounts of Si source and Al source added in the synthesis of the corrosion inhibitor, and a method for inhibiting corrosion of a boiler and a boiler. Another aim is to recycle the removed heavy metals as raw materials for non-ferrous refining.

In order to solve the above problems, the present invention proposes the following means.
(1) The method for producing a corrosion inhibitor for a boiler of the present invention includes an acquisition step of acquiring combustion ash containing Ca, Al, and Si, which is generated in a first waste treatment facility to which a first corrosion inhibitor for a boiler is added; a washing step of washing the combustion ash acquired in the acquisition step with water and pickling; and a production step of performing an alkaline hydrothermal treatment on the combustion ash washed with water and pickling in the washing step to obtain a second corrosion inhibitor for a boiler , characterized in that when the content of Ca contained in the combustion ash to be subjected to the alkaline hydrothermal treatment exceeds 16% by mass, the content of Ca is adjusted to be 16% by mass or less, and when the total content of Si and Al contained in the combustion ash to be subjected to the alkaline hydrothermal treatment is less than 11% by mass, a Si source or an Al source is added in performing the alkaline hydrothermal treatment so that the total content of Si and Al is 11% by mass or more .

According to this invention, it is possible to efficiently remove corrosion factors that corrode the boiler and impurities that do not contribute to the synthesis of the corrosion inhibitor, and to reduce the amount of Si source and Al source added in the synthesis of the corrosion inhibitor. It is also possible to obtain a corrosion inhibitor whose Ca content, Al content, and Si content are in the range suitable for the synthesis of the corrosion inhibitor.

(2) In the method for producing a corrosion inhibitor for a boiler, it is preferable that the average particle size (d ₅₀ ) of the corrosion inhibitor for a boiler obtained in the production step is 10 μm or more and 25 μm or less.

When the average particle size (d ₅₀ ) is 10 μm or more and 25 μm or less, the particle size is large enough to exhibit a corrosion inhibiting effect.

(3) In the method for producing a boiler corrosion inhibitor, it is preferable that the boiler corrosion inhibitor obtained in the production process contains 40% by mass or more of amorphous matter.

The corrosion inhibitor exhibits good corrosion inhibition effect due to the amorphous content of 40% by mass.

(4) In the method for producing the boiler corrosion inhibitor, it is preferable that the boiler corrosion inhibitor obtained in the production process contains, in addition to the amorphous phase, at least one or more selected from the group consisting of calcium phosphate, calcium carbonate, aluminate phase, hercynite, zeolite, gehlenite, magnesioferrite, magnesium zinc iron ion oxide, calcium titanate, zinc oxide, and akermanite.

By including these components in addition to the amorphous phase, impurities can be efficiently removed, and a corrosion inhibitor can be obtained whose Ca content, Al content, and Si content are in the range suitable for the synthesis of the corrosion inhibitor.

(5) In the manufacturing method of the boiler corrosion inhibitor, it is preferable that the second boiler corrosion inhibitor obtained in the manufacturing process is obtained by subjecting combustion ash that has been water-washed or acid-washed in the cleaning process to alkaline hydrothermal treatment.

(6) In the manufacturing method of the boiler corrosion inhibitor, it is preferable that an alkaline aqueous solution is used in the manufacturing process, and the second boiler corrosion inhibitor is obtained by washing away the alkaline aqueous solution.

By using an alkaline aqueous solution to produce a precipitate and then rinsing it with water, excess material adhering to the corrosion inhibitor surface can be removed, preventing the pores from becoming clogged, and a corrosion inhibitor for boilers with high corrosion inhibition effects can be obtained.

(7) In the above-mentioned method for producing a corrosion inhibitor for a boiler, it is preferable that the second corrosion inhibitor for a boiler obtained in the above-mentioned production step has a BET specific surface area of 90 m ² /g or more.

If the corrosion inhibitor has a BET specific surface area of 90 m ² /g or more, the surface has large irregularities and can adsorb corrosive substances onto the surface, thereby preventing the corrosive substances from reaching the superheating organs of the boiler.

(8) In the method for producing the boiler corrosion inhibitor, it is preferable that in the cleaning process, the combustion ash obtained in the obtaining process is subjected to an acid washing process.

Pickling treatment allows heavy metals to be dissolved from combustion ash that contains heavy metals, making it possible to remove them.

(9) In the above-mentioned method for producing a corrosion inhibitor for a boiler, it is preferable that the second corrosion inhibitor for a boiler obtained in the above-mentioned production step has a BET specific surface area of 60 m ² /g or more.

If the corrosion inhibitor has a BET specific surface area of 60 ^m2 /g or more, the surface has large irregularities and can adsorb corrosive substances to the surface, thereby preventing the corrosive substances from reaching the inner surface of the boiler (especially the superheating organ).

(10) In the method for manufacturing a corrosion inhibitor for boilers, it is preferable that the first waste treatment facility is a melting furnace, the combustion ash is molten fly ash containing heavy metals, and the cleaning process involves subjecting the combustion ash obtained in the obtaining process to an acid washing process.

Pickling treatment allows heavy metals to be dissolved from molten fly ash containing heavy metals, making it possible to remove them.

(11) In the method for producing the boiler corrosion inhibitor, it is preferable that the Zn contained in the combustion ash that has been pickled in the cleaning process is dissolved by the pickling process.

It is estimated that the Zn content is higher in combustion ash generated at a waste treatment facility where a corrosion inhibitor for boilers is added than in combustion ash generated at a waste treatment facility where a corrosion inhibitor for boilers is not added, due to the amount of the corrosion inhibitor added. Therefore, by dissolving Zn from the latter combustion ash, it is possible to efficiently recover Zn from the combustion ash.

(12) In the method for producing a corrosion inhibitor for boilers, it is preferable that the combustion ash that has been pickled in the cleaning process is in a slurry state, and that the pH of the combustion ash is 2.5 or more and 5.5 or less.

If the pH is less than 2.5, the elution rate of Si and Al, which are components of the corrosion inhibitor, increases. In addition, the viscosity of the slurry increases, making it difficult to separate the slurry into a liquid portion and combustion ash after pickling treatment in the subsequent process. If the pH is 2.5 or higher, the elution rate of Si and Al is suppressed. Note that the higher the slurry pH, the lower the elution rate of Pb, Zn, and Cu, which are corrosion factors of boiler superheater tubes, but the corrosion inhibition effect is still sufficient.

(13) In the method for producing a corrosion inhibitor for boilers, it is preferable that the first waste treatment facility is a stoker furnace, the combustion ash is incineration fly ash, and in the washing process, the combustion ash obtained in the obtaining process is washed with water.

The corrosion inhibitor of the present invention is preferably applied to a stoker furnace as a waste treatment facility. By using incineration fly ash as the combustion ash, water-soluble compounds including Pb, Ca, Na, and K contained in the incineration fly ash can be dissolved in water and separated. By removing these compounds, a corrosion inhibitor for boilers that has a corrosion inhibitory effect on boilers can be produced with little effort.

(14) In the method for producing a corrosion inhibitor for boilers, it is preferable that the cleaning treatment process is performed once.

In the cleaning process performed in this embodiment, water-soluble compounds containing at least one selected from the group consisting of Pb, Ca, Na, and K can be removed by dissolving them in a single cleaning process. Also, only one pickling process is required. In the prior art, for example, more than 10 pickling processes are required to dissolve an acid-soluble compound, but since only one pickling process is required, the pickling process can be simplified.

(15) In the manufacturing method of the boiler corrosion inhibitor, the first boiler corrosion inhibitor is preferably a boiler corrosion inhibitor obtained by subjecting combustion ash generated in the first waste treatment facility or combustion ash generated in a second waste treatment facility different from the first waste treatment facility to a water washing process or an acid washing process.

It is possible to provide a corrosion inhibitor that has been rid of the metal elements removed by water washing or pickling.

(16) In the method for producing the boiler corrosion inhibitor, in the acquisition process, it is preferable that the boiler corrosion inhibitor obtained in the production process is used as the first boiler corrosion inhibitor, and the acquisition process, the cleaning process, and the production process are repeated.

The corrosion inhibitor can be reused by repeatedly processing the combustion ash recovered from the boiler.

(17) In the method for producing a corrosion inhibitor for a boiler, it is preferable that the calcium carbonate content in the second corrosion inhibitor for a boiler obtained in the production process is 13 mass% or less.

By keeping the calcium carbonate content at 13% by mass or less, the deterioration of the corrosion inhibition effect can be suppressed.

( 18 ) The method for inhibiting corrosion of a boiler according to the present invention is a method for inhibiting corrosion of a superheating device provided in an exhaust gas passage through which combustion exhaust gas of a boiler passes, and is characterized in that a corrosion inhibitor for a boiler manufactured by the manufacturing method described in any one of (1) to (17) is supplied into the exhaust gas passage.

By supplying any of the corrosion inhibitors described above into the exhaust gas passage, corrosion of the superheating device installed in the exhaust gas passage through which the combustion exhaust gas of the boiler passes can be suppressed.

The present invention provides a method for producing a corrosion inhibitor that can efficiently remove corrosion factors that corrode boilers and impurities that do not contribute to the synthesis of the corrosion inhibitor, and can reduce the amounts of Si source and Al source added in the synthesis of the corrosion inhibitor.

1 is a flowchart showing a method for producing a corrosion inhibitor according to an embodiment of the present invention. FIG. 11 is a diagram showing the elution rate of an acid-soluble component (Pb) eluted into a filtrate obtained by solid-liquid separation of a fourth slurry in Example 1. FIG. 11 is a diagram showing the elution rate of an acid-soluble component (Zn) eluted into a filtrate obtained by solid-liquid separation of a fourth slurry in Example 1. FIG. 11 is a diagram showing the elution rate of an acid-soluble component (Cu) eluted into a filtrate obtained by solid-liquid separation of a fourth slurry in Example 1. FIG. 11 is a diagram showing the elution rate of an acid-soluble component (Si) eluted into a filtrate obtained by solid-liquid separation of a fourth slurry in Example 1. FIG. 11 is a diagram showing the elution rate of an acid-soluble component (Ca) eluted into a filtrate obtained by solid-liquid separation of a fourth slurry in Example 1. FIG. 11 is a diagram showing the elution rate of an acid-soluble component (Al) eluted into a filtrate obtained by solid-liquid separation of a fourth slurry in Example 1. FIG. 11 is a diagram showing the elution rate of an acid-soluble component eluted in a filtrate obtained by solid-liquid separation of a fourth slurry in Example 4. FIG. 1 is a diagram showing the weight loss rate of a boiler superheater tube at 550° C. in an example and a comparative example. FIG. 11 is a diagram showing the weight loss rate of a boiler superheater tube at 500° C. in an example. FIG. 2 is a diagram showing the results of EDS analysis of a cross section of a simulated superheater tube subjected to a corrosion test in Example 1. FIG. 1 is a diagram showing the results of color mapping of Si in a cross section of a simulated superheater tube subjected to a corrosion test in Example 1, which was investigated by EDS analysis. FIG. 2 is a diagram showing the results of color mapping of Al obtained by investigating the cross section of a simulated superheater tube subjected to a corrosion test by EDS analysis in Example 1. FIG. 1 is a diagram showing the results of investigating a cross section of a simulated superheater tube subjected to a corrosion test by EDS analysis and color mapping Na in Example 1. FIG. 1 is a diagram showing the results of investigating a cross section of a simulated superheater tube subjected to a corrosion test by EDS analysis and color mapping K in Example 1. FIG. 1 is a diagram showing the results of color mapping of Ca in a cross section of a simulated superheater tube subjected to a corrosion test in Example 1, which was investigated by EDS analysis. FIG. 1 is a diagram showing the results of color mapping of Cl obtained by investigating the cross section of a simulated superheater tube subjected to a corrosion test by EDS analysis in Example 1. FIG. 13 is a diagram showing the results of EDS analysis of a cross section of a simulated superheater tube subjected to a corrosion test in Example 5. FIG. 13 is a diagram showing the results of color mapping of Cl obtained by investigating the cross section of a simulated superheater tube subjected to a corrosion test by EDS analysis in Example 5. FIG. 13 is a diagram showing the results of color mapping of Si in a cross section of a simulated superheater tube subjected to a corrosion test in Example 5, which was investigated by EDS analysis. FIG. 13 is a diagram showing the results of color mapping of Ca in a cross section of a simulated superheater tube subjected to a corrosion test, which was investigated by EDS analysis, in Example 5. FIG. 13 is a diagram showing the results of investigating a cross section of a simulated superheater tube subjected to a corrosion test by EDS analysis and color mapping Pb in Example 5. FIG. 13 is a diagram showing the results of investigating the cross section of a simulated superheater tube subjected to a corrosion test by EDS analysis and color mapping K in Example 5. FIG. 13 is a diagram showing the results of an analysis of the components of corrosion products inside the corrosion product layer when a simulated superheater tube was coated with simulated molten fly ash and a mixture of the simulated molten fly ash and a corrosion inhibitor (Example 1) and the like, and a corrosion test was carried out at 550° C. for 100 hours. FIG. 13 is a diagram showing the results of an analysis of the components of corrosion products near the interface between the base material (simulated superheater tube) and the corrosion product when a simulated molten fly ash and a mixture of the simulated molten fly ash and a corrosion inhibitor (Example 1) were applied to a simulated superheater tube and a corrosion test was performed at 550° C. for 100 hours. FIG. 1 is a configuration diagram showing an example of a stoker furnace to which the corrosion inhibitor according to the present invention can be applied.

[Method of producing corrosion inhibitor]
Hereinafter, an embodiment of the method for producing a corrosion inhibitor according to the present invention will be described with reference to Fig. 1. Fig. 1 is a flow chart showing the method for producing a corrosion inhibitor according to the embodiment of the present invention.

The method for producing a corrosion inhibitor according to the present embodiment is a method for producing a second corrosion inhibitor for a boiler from at least one of molten fly ash and incineration fly ash generated in a first waste treatment facility to which a first corrosion inhibitor for a boiler described later is added. In the following description, ash containing at least one of molten fly ash and incineration fly ash may be referred to as combustion ash.
As shown in Fig. 1, the method for producing a corrosion inhibitor according to the present embodiment includes a first step (S1) of stirring and mixing a first slurry containing water and combustion ash, which is at least one of molten fly ash and incineration fly ash generated in a first waste treatment facility to which a first corrosion inhibitor for boilers is added, to dissolve water-soluble compounds, which contain at least one selected from the group consisting of Pb, Ca, Na and K, contained in at least one of the molten fly ash and incineration fly ash, to prepare a second slurry. This first step can be called a water washing treatment.

The corrosion inhibitor produced by the manufacturing method of the present embodiment described below from combustion ash generated in a waste treatment facility where no corrosion inhibitor for boilers is added can be used as the first corrosion inhibitor for boilers. Also, the corrosion inhibitor for boilers produced by the manufacturing method of the present embodiment described below from combustion ash generated in a waste treatment facility where a corrosion inhibitor for boilers produced by the manufacturing method of the present embodiment described below can be used as the first corrosion inhibitor for boilers. Also, the corrosion inhibitor produced by the manufacturing method of the present embodiment described below from combustion ash generated in a waste treatment facility operated using a corrosion inhibitor for boilers such as natural zeolite can be used as the first corrosion inhibitor for boilers.

The method for producing a corrosion inhibitor according to this embodiment includes a second step (S2) of separating the second slurry into a liquid portion and combustion ash, which is at least one of molten fly ash and incineration fly ash after water washing.

The method for producing a corrosion inhibitor according to the present embodiment includes a third step (S3) of adding hydrochloric acid or nitric acid to a third slurry containing combustion ash, which is at least one of the molten fly ash and the incineration fly ash after the water washing treatment, and water, while stirring and mixing the third slurry, thereby dissolving an acid-soluble compound containing at least one selected from the group consisting of Ca, Pb, and Cu contained in at least one of the molten fly ash and the incineration fly ash after the water washing treatment, to prepare a fourth slurry. This third step can be called an acid washing treatment. In addition, one or both of the water washing treatment and the acid washing treatment can be called a cleaning treatment step.
The method for producing a corrosion inhibitor according to this embodiment includes a fourth step (S4) of separating the fourth slurry into a liquid fraction and combustion ash, which is at least one of molten fly ash after pickling treatment and incineration fly ash.
The method for producing a corrosion inhibitor according to this embodiment includes a fifth step (S5) of synthesizing a corrosion inhibitor by performing an alkaline hydrothermal treatment in which a fifth slurry containing combustion ash, which is at least one of molten fly ash after pickling treatment and incineration fly ash, and an alkaline aqueous solution is heated, stirred, and mixed to synthesize a corrosion inhibitor.
The method for producing a corrosion inhibitor according to this embodiment includes a sixth step (S6) of separating the fifth slurry from the fifth step (S5) into a liquid portion (e.g., a filtrate) and a corrosion inhibitor to obtain the corrosion inhibitor.

The corrosion inhibitor obtained in this embodiment contains, for example, 40% or more by mass of amorphous material containing at least one of C-S-H (calcium silicate hydrate) and C-A-S-H (calcium aluminosilicate hydrate), or not containing these, or a combination of both of these amorphous materials as the main component, and contains at least one or more types selected from the group consisting of calcium phosphate, calcium carbonate, aluminate phase, hercynite, zeolite, gehlenite, magnesioferrite, magnesium zinc iron ion oxide, calcium titanate, zinc oxide, and akermanite.

(First step (S1))
The first step (S1) is a step of stirring and mixing a first slurry containing combustion ash, which is at least one of molten fly ash and incineration fly ash, and water, to elute water-soluble compounds contained in at least one of the molten fly ash and incineration fly ash, which contain at least one selected from the group consisting of Pb, Ca, Na, and K. That is, the first step (S1) is a step of eluting water-soluble compounds contained in the molten fly ash, incineration fly ash, or a mixture of the molten fly ash and incineration fly ash, which contain at least one selected from the group consisting of Pb, Ca, Na, and K.

In the first step (S1), combustion ash, which is at least one of molten fly ash and incineration fly ash, is added to water to prepare a first slurry.
The molten fly ash is soot generated when waste is melted in a gasification melting furnace or an ash melting furnace, and contains elements such as lead (Pb), calcium (Ca), sodium (Na), potassium (K), copper (Cu), and zinc (Zn). In detail, the molten fly ash contains water-soluble compounds containing at least one selected from the group consisting of Pb, Ca, Na, and K, and acid-soluble compounds. Examples of the water-soluble compounds include sodium chloride (NaCl), potassium chloride (KCl), calcium chloride (CaCl ₂ ), calcium hydroxide (Ca(OH) ₂ ), and lead (II) chloride (PbCl ₂ ). Examples of the acid-soluble compounds include copper (II) oxide (CuO), zinc oxide (ZnO), and lead metasilicate (PbSiO ₃ ). Melted fly ash has a Ca content of 15% by mass or more and 25% by mass or less, a Si content of 2.5% by mass or more and 6.0% by mass or less, an Al content of 0.5% by mass or more and 4% by mass or less, and a Pb content of 0.3% by mass. The Zn content is in the range of 1.0 to 6.0 mass%, the Cu content is in the range of 0.0 to 0.5 mass%, and the Cl content is in the range of 10 to 25 mass%.
In the method for producing a corrosion inhibitor according to the present embodiment, it is particularly preferable to use, as the molten fly ash, fly ash generated from a waste treatment facility where waste is treated by high-temperature melting.

Incineration fly ash is soot generated when waste is burned in a stoker furnace, a fluidized bed furnace, a rotary kiln furnace, etc., and contains elements such as lead (Pb), calcium (Ca), sodium (Na), potassium (K), copper (Cu), and zinc (Zn). In detail, incineration fly ash contains water-soluble compounds containing at least one selected from the group consisting of Pb, Ca, Na, and K, and acid-soluble compounds. Examples of water-soluble compounds include sodium chloride (NaCl), potassium chloride (KCl), calcium chloride (CaCl ₂ ), calcium hydroxide (Ca(OH) ₂ ), and lead (II) chloride (PbCl ₂ ). Examples of acid-soluble compounds include copper (II) oxide (CuO), zinc oxide (ZnO), and lead metasilicate (PbSiO ₃ ). The incineration fly ash has a Ca content of 15% by mass or more and 25% by mass or less, a Si content of 2.5% by mass or more and 6.0% by mass or less, an Al content of 0.5% by mass or more and 4% by mass or less, a Pb content of 0.3% by mass or more and 3% by mass or less, a Zn content of 1.0% by mass or more and 6.0% by mass or less, a Cu content of 0.0% by mass or more and 0.5% by mass or less, and a Cl content of 10% by mass or more and 25% by mass or less.
In the method for producing a corrosion inhibitor according to the present embodiment, it is particularly preferable to use incineration fly ash generated from a waste treatment facility where waste is completely combusted at high temperatures.
In addition, in the mixture of molten fly ash and incineration fly ash, the Ca content is in the range of 15% by mass or more and 25% by mass or less, the Si content is in the range of 2.5% by mass or more and 6.0% by mass or less, the Al content is in the range of 0.5% by mass or more and 4% by mass or less, the Pb content is in the range of 0.3% by mass or more and 3% by mass or less, the Zn content is in the range of 1.0% by mass or more and 6.0% by mass or less, the Cu content is in the range of 0.0% by mass or more and 0.5% by mass or less, and the Cl content is in the range of 10% by mass or more and 25% by mass or less.

In the first slurry, the ratio of combustion ash (molten fly ash and/or incineration fly ash) to water (molten fly ash/water) is preferably 1/20 or more and 1/5 or less, more preferably 1/10 or more and 1/5 or less, by mass ratio.

Examples of water that can be used include tap water and industrial water.

The first slurry is then stirred and mixed.
The method for stirring and mixing the first slurry is not particularly limited, but examples include a method of stirring using stirring blades such as inclined battle blades or turbine blades, a method of placing at least two baffle plates facing each other in a reaction vessel and stirring using stirring blades, etc.

The rotation speed of the stirring blades or the like when stirring the first slurry is not particularly limited as long as the molten fly ash and the incineration fly ash do not remain at the bottom of the reaction vessel. For example, the rotation speed is preferably 200 rpm or more and 400 rpm or less, and more preferably 250 rpm or more and 350 rpm or less.
If the rotation speed of the impeller or the like when stirring the first slurry is 400 rpm or more, the molten fly ash and the incineration fly ash will not remain at the bottom of the reaction vessel, but since the power required for stirring increases with increasing rotation speed, it is preferable to keep the rotation speed as low as possible. On the other hand, if the rotation speed of the impeller or the like when stirring the first slurry is 200 rpm or less, the molten fly ash and the incineration fly ash will remain at the bottom of the reaction vessel, and the elution of water-soluble compounds will decrease.

The temperature at which the first slurry is stirred and mixed is preferably 5°C or higher and 50°C or lower, and more preferably 10°C or higher and 35°C or lower.

The time for stirring and mixing the first slurry is preferably from 10 minutes to 60 minutes, more preferably 30 minutes or less, more preferably 20 minutes or less, and most preferably 10 minutes or less.
Even if the time for stirring and mixing the first slurry is 60 minutes or more, the dissolution rate of the water-soluble compound does not change significantly (converges). On the other hand, if the time for stirring and mixing the first slurry is 10 minutes or less, the dissolution rate of the water-soluble compound does not converge.

The first slurry is stirred and mixed once.

In this manner, in the first step (S1), a first slurry containing combustion ash, which is at least one of molten fly ash and incineration fly ash, and water is stirred and mixed to prepare a second slurry by dissolving water-soluble compounds, which are contained in at least one of the molten fly ash and incineration fly ash and contain at least one selected from the group consisting of Pb, Ca, Na, and K. The obtained second slurry contains water, combustion ash, which is at least one of the molten fly ash and incineration fly ash, dispersed in water, and water-soluble compounds, such as sodium chloride (NaCl), potassium chloride (KCl), calcium chloride (CaCl ₂ ), calcium hydroxide (Ca(OH) ₂ ), and lead (II) chloride (PbCl ₂ ), dissolved in water.

In the first step (S1), methods for confirming that the water-soluble compounds have been separated from the molten fly ash include, for example, ICP emission spectrometry, ion chromatography, and analytical methods using a detector tube.

(Second step (S2))
The second step (S2) is a step of separating the second slurry obtained in the first step (S1) into a liquid portion (e.g., filtrate) and combustion ash, which is at least one of molten fly ash and incineration fly ash after the water washing treatment.
The combustion ash, which is at least one of the molten fly ash and the incineration fly ash after the water washing treatment, refers to at least one of the molten fly ash and the incineration fly ash that has been subjected to a treatment in the first step (S1) of stirring and mixing the first slurry to elute water-soluble compounds containing at least one selected from the group consisting of Pb, Ca, Na and K contained in the combustion ash, which is at least one of the molten fly ash and the incineration fly ash.

The method for separating the liquid from the combustion ash, which is at least one of the molten fly ash and the incineration fly ash after the water washing treatment, is not particularly limited, but examples include solid-liquid separation using a cake filtering device (roller press, filter press, screw press, etc.), centrifugation, multiple disk rotary dehydration, and multiple vibration filters.

In addition, the combustion ash, which is at least one of the molten fly ash and the incineration fly ash after the liquid portion and the water washing treatment, may be separated by solid-liquid separation using a cake filtering device (roller press, filter press, screw press, etc.), centrifugal separation, multiple disk rotary dehydration, multiple vibration filter, etc., and then water may be dropped onto the combustion ash, which is at least one of the molten fly ash and the incineration fly ash, to wash away water-soluble compounds remaining on the surface of at least one of the molten fly ash and the incineration fly ash, such as sodium chloride (NaCl), potassium chloride ( _KCl ), calcium chloride (CaCl 2 ), calcium hydroxide (Ca(OH) ₂ ), and lead (II) chloride (PbCl ₂ ).

(Third step (S3))
The third step (S3) is a step of adding hydrochloric acid or nitric acid to a third slurry containing combustion ash, which is at least one of the molten fly ash and the incineration fly ash after the water-washing treatment, and water, while stirring and mixing the third slurry, thereby dissolving an acid-soluble compound, which contains at least one selected from the group consisting of Pb, Zn, and Cu, contained in the combustion ash, which is at least one of the molten fly ash and the incineration fly ash after the water-washing treatment.

In the third step (S3), first, combustion ash, which is at least one of the molten fly ash and the incineration fly ash after the water washing process, is added to water to prepare a third slurry.

Next, hydrochloric acid (HCl) or nitric acid (HNO ₃ ) is added to the third slurry while stirring and mixing the third slurry. At this time, the pH of the third slurry is preferably 2.5 to 5.5, more preferably 2.5 to 4.5, and even more preferably 2.5 to 4.0. That is, hydrochloric acid (HCl) or nitric acid (HNO ₃ ) is added to the third slurry so that the pH of the third slurry is within the above range. The pH of the third slurry is measured using a pH measuring device such as a pH meter.
If the pH of the third slurry is less than 2.5, the elution rate of heavy metals such as Pb, Zn, and Cu, which are corrosion factors of the boiler superheater tube, and the elution rate of Ca, which is an inhibitor when synthesizing the corrosion inhibitor, will be large, but the elution rate of Si and Al, which are components of the corrosion inhibitor, will also be large, which is not preferable. In addition, since the viscosity of the third slurry will be large, it will be difficult to separate the fourth slurry into at least one of the liquid portion and the molten fly ash and the incineration fly ash after the pickling treatment in the fourth step (S4). On the other hand, if the pH of the third slurry is 2.5 or more, and particularly if the pH of the third slurry is 3.5 to 5.5, the elution rate of Si and Al can be suppressed, which is preferable. It has been confirmed that the higher the pH of the third slurry, the lower the elution rate of Pb, Zn, and Cu, which are corrosion factors of the boiler superheater tube, but the corrosion inhibition effect can be obtained.

Examples of water that can be used include tap water and industrial water.

Examples of hydrochloric acid (HCl) and nitric acid (HNO ₃ ) that can be used include hydrochloric acid, concentrated hydrochloric acid, nitric acid, and concentrated nitric acid. The concentrations of hydrochloric acid and concentrated hydrochloric acid are about 0.5 N (mol/L) to 12.0 N (mol/L), and the concentrations of nitric acid and concentrated nitric acid are about 0.1 N (mol/L) to 10 N (mol/L), but any concentration may be used.

In the third slurry, the ratio of at least one of the molten fly ash and the incineration fly ash to the liquid content (total of water and hydrochloric acid or nitric acid) (molten fly ash/liquid content) is preferably 1/20 or more and 1/5 or less, more preferably 1/10 or more and 1/5 or less, by mass ratio.

A third slurry containing hydrochloric acid or nitric acid is then stirred and mixed.
The method of stirring and mixing the third slurry containing hydrochloric acid or nitric acid is not particularly limited, but examples include stirring with stirring blades such as inclined battle blades and turbine blades, and stirring with stirring blades by arranging at least two baffle plates facing each other in a reaction vessel.

The rotation speed of the stirring blades or the like when stirring the third slurry containing hydrochloric acid or nitric acid is not particularly limited, but is preferably, for example, 200 rpm or more and 400 rpm or less, and more preferably 250 rpm or more and 350 rpm or less.
If the rotation speed of the impeller or the like when stirring the third slurry containing hydrochloric acid or nitric acid is 400 rpm or more, the molten fly ash or the like will not remain at the bottom of the reaction vessel, but since the power required for stirring increases with increasing rotation speed, it is preferable that the rotation speed is as small as possible. On the other hand, if the rotation speed of the impeller or the like when stirring the third slurry containing hydrochloric acid or nitric acid is 200 rpm or less, the compounds that remain at the bottom of the reaction vessel will be reduced in elution.

The temperature at which the third slurry containing hydrochloric acid or nitric acid is stirred and mixed is preferably 20°C or higher and 80°C or lower, and more preferably 20°C or higher and 50°C or lower.

The time for stirring and mixing the third slurry containing hydrochloric acid or nitric acid is preferably 10 minutes or more and 60 minutes or less after the pH of the third slurry reaches the predetermined pH.
Even if the time for stirring and mixing the third slurry containing hydrochloric acid or nitric acid is 60 minutes or more, the dissolution of the acid-soluble compounds is almost completed. On the other hand, if the time for stirring and mixing the third slurry containing hydrochloric acid or nitric acid is 10 minutes or less, the reaction between the acid-soluble compounds and the acid may not proceed sufficiently.

The third slurry containing hydrochloric acid or nitric acid is stirred and mixed once.

In this way, in the third step (S3), the third slurry containing the combustion ash, which is at least one of the molten fly ash and the incineration fly ash after the water washing treatment, water, and an acid (hydrochloric acid or nitric acid) is stirred and mixed to dissolve the acid-soluble compound containing at least one selected from the group consisting of Pb, Zn, and Cu contained in the at least one of the molten fly ash and the incineration fly ash after the water washing treatment, to prepare a fourth slurry. The obtained fourth slurry contains water containing hydrochloric acid or nitric acid, the combustion ash, which is at least one of the molten fly ash and the incineration fly ash, dispersed in the water, and acid-soluble compounds such as copper (II) oxide (CuO), zinc oxide (ZnO), and lead metasilicate (PbSiO ₃ ) dissolved in the water containing hydrochloric acid or nitric acid.

In the third step (S3), as a method for confirming that the acid-soluble compounds have been separated from the combustion ash, which is at least one of the molten fly ash and the incineration fly ash after the water washing treatment, for example, a method is used in which the concentrations of Pb, Zn, Cu, Ca, Si, and Al dissolved in the liquid obtained in the fourth step are analyzed using ICP atomic emission spectrometry, a detector tube, etc. Alternatively, a method is used in which the concentrations of Pb, Zn, Cu, Ca, Si, and Al contained in the combustion ash, which is at least one of the molten fly ash and the incineration fly ash after the acid washing treatment obtained in the fourth step, are measured using X-ray fluorescence analysis, energy dispersive analysis (EDS), or ICP atomic emission spectrometry after wet dissolution.

(Fourth step (S4))
The fourth step (S4) is a step of separating the fourth slurry obtained in the third step (S3) into a liquid portion (e.g., filtrate) and combustion ash, which is at least one of the molten fly ash and the incineration fly ash after the pickling treatment.
The combustion ash, which is at least one of the molten fly ash and the incineration fly ash after the pickling treatment, is at least one of the molten fly ash and the incineration fly ash, which is subjected to a treatment in the third step (S3) in which a third slurry containing hydrochloric acid or nitric acid is added is stirred and mixed to elute an acid-soluble compound containing at least one selected from the group consisting of Pb, Zn and Cu contained in the combustion ash, which is at least one of the molten fly ash and the incineration fly ash after the water-washing treatment.

The method for separating the liquid from the combustion ash, which is at least one of the molten fly ash and the incineration fly ash after the water washing treatment, is not particularly limited, but examples include solid-liquid separation using a cake filtering device (roller press, filter press, screw press), centrifugation, multiple disk rotary dehydration, and multiple vibration filters.

In addition, the liquid and the combustion ash, which is at least one of the molten fly ash and the incineration fly ash after the acid washing treatment, may be subjected to solid-liquid separation using a cake filtering device (roller press, filter press, screw press), centrifugation, multiple disk rotary dehydration, multiple vibration filter, or the like, and then water may be dropped onto at least one of the molten fly ash and the incineration fly ash to wash away the acid remaining on the surface of the combustion ash, which is at least one of the molten fly ash and the incineration fly ash.
At least one of the molten fly ash and the incineration fly ash obtained after the pickling treatment as described above may be used as a corrosion inhibitor.

(Fifth step (S5))
The fifth step (S5) is a step of synthesizing a corrosion inhibitor by heating and stirring a fifth slurry containing combustion ash, which is at least one of the molten fly ash and the incineration fly ash after the pickling treatment, and an alkaline aqueous solution.

In the fifth step (S5), first, combustion ash, which is at least one of the molten fly ash after the pickling treatment and the incineration fly ash, is added to the alkaline aqueous solution to prepare a fifth slurry.

Examples of the alkaline aqueous solution include an aqueous solution of sodium hydroxide (NaOH), an aqueous solution of calcium hydroxide (Ca(OH) ₂ , an aqueous solution of potassium hydroxide ( _KOH ), an aqueous solution of sodium carbonate (NaCO2), and an aqueous solution of sodium hydrogen carbonate ( _NaHCO3 ). In addition, by using the alkaline effluent discharged in the second step, calcium ions in the effluent can be effectively utilized.
The concentration of the alkaline aqueous solution is preferably 1N or more and 4N or less.
If the concentration of the alkaline aqueous solution is too low, the elution of reactive components from the combustion ash, which is at least one of the molten fly ash and the incineration fly ash, is delayed, making it difficult to produce the corrosion inhibitor. Conversely, if the concentration is too high, the gel network structure becomes too strong, which excessively restricts the movement of each ion within the gel, making it difficult for the reaction to produce the corrosion inhibitor to occur.

In the fifth slurry, the ratio of combustion ash, which is at least one of molten fly ash and incineration fly ash after pickling treatment, to the alkaline aqueous solution (combustion ash/alkaline aqueous solution) is preferably 1/2 or more and 1/5 or less in mass ratio.

Next, the fifth slurry is heated and stirred and mixed to perform an alkaline hydrothermal treatment, thereby synthesizing a corrosion inhibitor containing 40 mass% or more of amorphous matter as a main component, which is an amorphous matter containing at least one of C-S-H (calcium silicate hydrate) and C-A-S-H (calcium aluminosilicate hydrate), or not containing these, or a combination of both of these amorphous matter, and further containing at least one or more kinds selected from the group consisting of calcium phosphate, calcium carbonate, aluminate phase, hercynite, zeolite, gehlenite, magnesioferrite, magnesium zinc iron ion oxide, calcium titanate, zinc oxide, and akermanite.
The method for stirring and mixing the fifth slurry is not particularly limited, but examples include stirring using stirring blades such as inclined battle blades and turbine blades, and stirring using stirring blades in which at least two baffle plates are placed opposite each other in a reaction vessel.

The rotation speed of the stirring blades or the like when stirring the fifth slurry is not particularly limited, but is preferably, for example, 200 rpm or more and 400 rpm or less, and more preferably 250 rpm or more and 350 rpm or less.
If the rotation speed of the impeller or the like when stirring the fifth slurry is 200 rpm or more, the molten fly ash will not remain at the bottom of the reaction vessel, but since the power required for stirring increases with increasing rotation speed, it is preferable that the rotation speed is as small as possible. On the other hand, if the rotation speed of the impeller or the like when stirring the fifth slurry is 200 rpm or less, the molten fly ash will remain at the bottom of the reaction vessel, which will reduce the contact rate between the combustion ash, which is at least one of the molten fly ash and the incineration fly ash contained in the fifth slurry, and the alkaline aqueous solution, thereby inhibiting the production of the corrosion inhibitor.

The fifth slurry is preferably stirred and mixed for at least 1 hour, and more preferably for at least 3 hours.

The fifth slurry is stirred and mixed once.

In the fifth step (S5), a Si source and an Al source are added to the fifth slurry so that the Ca content in the final corrosion inhibitor is 16 mass% or less, the ratio of Si to Al (Si/Al) is 1.2 or more by mass, and the total content of Si and Al is 11 mass% or more. This makes it possible to form a corrosion inhibitor while suppressing the inhibition of calcium carbonate formation by Ca and the reduction in the corrosion inhibition effect.

In the fifth step (S5), if the ratio of Si to Al (Si/Al) in the combustion ash, which is at least one of the molten fly ash and the incineration fly ash after pickling treatment recovered in the fourth step (S4), is less than 1.2 by mass and the total content of Si and Al is less than 11 mass%, a Si source and an Al source are added to the fifth slurry.

In the fifth step (S5), the Ca content, Al content, and Si content in the combustion ash, which is at least one of the molten fly ash and the incineration fly ash after the pickling treatment recovered in the fourth step (S4), can be confirmed using, for example, an X-ray fluorescence analyzer, an energy dispersive X-ray analyzer, an ICP emission spectrometer, or the like.

Examples of the Si source include silica sand, silicate glass, Si-containing fly ash, molten slag, steel slag, etc., but also include sodium metasilicate and sodium orthosilicate.
As the Al source, for example, sodium aluminate is generally used, but examples thereof include aluminum hydroxide, aluminum chloride, fly ash containing Al, molten slag, and steel slag.

(Sixth step (S6))
The sixth step (S6) is a step of separating the fifth slurry from the fifth step (S5) into a liquid fraction (e.g., a filtrate) and a corrosion inhibitor.

Methods for separating the liquid from the corrosion inhibitor are not particularly limited, but include, for example, solid-liquid separation using a cake filtering device (roller press, filter press, screw press, etc.), centrifugation, multiple disk rotary dehydration, and multiple vibration filters.

The recovered corrosion inhibitor may be subjected to solid-liquid separation using a cake filtering device (roller press, filter press, screw press, etc.), centrifugation, multiple disk rotary dehydration, multiple vibration filter, etc., and then water may be dripped onto the corrosion inhibitor to wash away the alkaline aqueous solution remaining on the surface of the corrosion inhibitor molten fly ash.

Through the first step (S1) to the sixth step (S6) as described above, the second corrosion inhibitor for a boiler is obtained.
The obtained second boiler corrosion inhibitor contains 40 mass% or more of amorphous material containing at least one of C-S-H (calcium silicate hydrate) and C-A-S-H (calcium aluminosilicate hydrate), or not containing these, or amorphous material as a main component combining both of these amorphous materials, and further contains at least one or more types selected from the group consisting of calcium phosphate, calcium carbonate, aluminate phase, hercynite, zeolite, gehlenite, magnesioferrite, magnesium zinc iron ion oxide, calcium titanate, zinc oxide, and akermanite.
Furthermore, this corrosion inhibitor has, for example, an average particle size (d ₅₀ median diameter) of 10 μm or more and 25 μm or less, and a large BET specific surface area of 30 to 140 m ² /g.
Therefore, when supplied to an exhaust gas passage of a boiler, for example, it adsorbs corrosive gases such as HCl and _SO2 in the exhaust gas passage, and when the corrosion inhibitor that has adsorbed corrosive gases and the corrosion inhibitor that has not adsorbed corrosive gases adhere to the surface of the corrosion layer formed on the metal interface or outer surface of the superheater tube, it captures _Cl2 and low-melting-point molten salts including _PbCl2 , _ZnCl2 , _CuCl2 , NaCl, and KCl generated by corrosion, thereby exerting a corrosion-inhibiting effect.
Although the average particle size (d ₅₀ median diameter) of the corrosion inhibitor is relatively large, being 10 μm or more and 25 μm or less, the BET specific surface area is large, being 30 to 140 m ² /g. Therefore, the above-mentioned corrosion inhibitor has excellent adsorption ability of corrosive substances, and has the effect of suppressing the corrosive substances from reaching the overheating organ. For the above reasons, it is desirable that the BET specific surface area is large, for example, preferably 60 m ² /g or more, and more preferably 90 m ² /g or more.

In addition, the main component amorphous in this embodiment may contain amorphous materials that do not contain C-S-H bonds or C-A-S-H bonds, such as C-S-H (calcium silicate hydrate) and C-A-S-H (calcium aluminosilicate hydrate), in addition to amorphous materials that contain one or two of C-S-H bonds and C-A-S-H bonds. The amorphous materials may contain at least one element contained in the combustion ash as an amorphous component.
In any case, the corrosion inhibitor of the present embodiment preferably contains 40 mass % or more of amorphous matter. The presence of both of these amorphous matters can be grasped by quantitative analysis using powder X-ray diffraction (XRD).

According to the hydrothermal treatment carried out in the fifth step in the manufacturing method of this embodiment, amorphous matter precipitates on the surfaces of the combustion ash particles, increasing the particle size. Furthermore, since the precipitated amorphous matter is in the form of small crystals, the specific surface area of the particles increases, and as a result, a corrosion inhibitor capable of adsorbing corrosive gases can be obtained.
In addition, during the alkaline hydrothermal treatment, a substance mainly composed of amorphous matter containing C-S-H and C-A-S-H is generated on the surface of the combustion ash particles, so that the average particle size of the corrosion inhibitor produced by the production method of this embodiment increases.
In the process of alkaline hydrothermal treatment, the amorphous particles generated on the surface of the combustion ash particles are small (several μm, for example, smaller than zeolite), which results in a large specific surface area of the corrosion inhibitor, allowing it to efficiently absorb corrosive gases.
According to the manufacturing method of this embodiment, it is presumed that components of the combustion ash dissolve during the alkaline hydrothermal treatment, and amorphous matter precipitates on the surface of the silica or alumina.

The corrosion inhibitor has a Si to Al ratio (Si/Al) of 1.2 or more by mass, and a total Si and Al content of 11% by mass or more. The corrosion inhibitor has an average particle size of 10 μm or more and 25 μm or less. The average particle size of the corrosion inhibitor is measured by a laser diffraction particle size distribution measuring device, a capillary flow porosimeter, a mercury intrusion porosimeter, or the like.

(Seventh step (S7))
The method for producing a corrosion inhibitor according to the present embodiment may also include a seventh step (S7) of adding an alkaline aqueous solution to the liquid fraction (filtrate) separated in the fourth step (S4).
This liquid is an aqueous solution containing compounds soluble in acid, such as copper (II) oxide (CuO), zinc oxide (ZnO), and lead metasilicate (PbSiO ₃ ).

Examples of the alkaline aqueous solution include an aqueous solution of sodium hydroxide (NaOH), an aqueous solution of calcium hydroxide (Ca(OH) ₂ ), etc. In addition, by using the alkaline effluent discharged in the second step, calcium ions in the effluent can be effectively utilized.
The concentration of the alkaline aqueous solution is not particularly limited.

In the seventh step (S7), an alkaline aqueous solution is added to the liquid fraction separated in the fourth step (S4) to adjust the pH of the liquid fraction to preferably 9.0 to 10.5, more preferably 9.5 to 10.0. The pH of the liquid fraction is measured using a pH measuring device such as a pH meter.
If the pH of the liquid fraction is 9.0 or higher, the Pb, Zn, and Cu contained in the liquid fraction separated in the fourth step (S4) react with the alkaline aqueous solution to form a precipitate. On the other hand, if the pH of the liquid fraction is 9.0 or lower or 10.5 or higher, a precipitate will form, but the heavy metal content in the precipitate will decrease.

By adding an alkaline aqueous solution to the liquid fraction separated in the fourth step (S4) in this way, at least one hydroxide selected from the group consisting of Pb, Zn, and Cu can be precipitated and the precipitate can be recovered. In addition, the waste liquid after the precipitate recovery can be effectively used as the water to be added in the first step.

As described above, according to the second corrosion inhibitor manufacturing method of the present embodiment, it is possible to efficiently remove corrosion factors that corrode the boiler and impurities (Pb, Ca, Na, K, Zn, Cu) that do not contribute to the synthesis of the corrosion inhibitor, and it is possible to obtain a corrosion inhibitor that allows the amounts of Si source and Al source to be reduced in the synthesis of the corrosion inhibitor.
Furthermore, in the manufacturing method for the second corrosion inhibitor according to the present embodiment, by adding a Si source and an Al source to the fifth slurry in the fifth step so that the ratio of Si to Al (Si/Al) in the corrosion inhibitor is 1.2 or more in mass ratio and the total content of Si and Al is 11 mass% or more, it is possible to obtain a second corrosion inhibitor having a Ca content, an Al content, and a Si content in a suitable range.

The second corrosion inhibitor obtained by the manufacturing method of the second corrosion inhibitor according to this embodiment can be supplied into an exhaust gas passage through which exhaust gas passes, thereby suppressing corrosion of the boiler of a waste treatment facility, particularly the boiler superheater tube.

The second corrosion inhibitor according to the present embodiment adsorbs corrosive gases such as HCl and _SO2 in the exhaust gas, particularly HCl gas, and further captures Cl2 and low-melting-point molten salts including _PbCl2 , _ZnCl2 , _CuCl2 , NaCl, and KCl generated by corrosion after the corrosion inhibitors with and without corrosive gases are attached to _the superheater tube, thereby suppressing the dissolution of oxide scale by the molten salts.
Furthermore, by suppressing the chlorination reaction that accelerates the corrosion of the superheater tube, corrosion products mainly composed of oxides that have a corrosion-inhibiting effect can be formed, thereby suppressing the corrosion of the superheater tube.

As an example, a boiler to which the second corrosion inhibitor according to this embodiment is applied is equipped with a combustion furnace 2 for burning fuel, an exhaust gas passage 3 through which the combustion exhaust gas generated in the combustion furnace 2 passes, a superheater 5 having a superheating organ 4 arranged in the exhaust gas passage 3, corrosion inhibitor supply devices 6, 7, and 8, and a control device (not shown), as shown in the boiler 1 in FIG. 26. The boiler 1 can generate high-temperature, high-pressure superheated steam by superheating the steam passing through the superheating organ 4 using the heat of the combustion exhaust gas generated by the combustion of the fuel. The high-temperature, high-pressure superheated steam generated in the boiler 1 is used to rotate the turbine of a generator (not shown).

The boiler 1 is provided with corrosion inhibitor supply devices 6, 7, and 8 for suppressing corrosion of the superheating organ 4. The corrosion inhibitor supply device 6 is provided at a position where the second corrosion inhibitor is supplied into the exhaust gas passage 3 (particularly preferably into the second flue 21 upstream of the superheating organ 4). The corrosion inhibitor supply device 7 is provided at a position where the corrosion inhibitor can be supplied to the flue on the front side of the superheating organ 4. The corrosion inhibitor supply device 8 is provided at a position where the corrosion inhibitor can be supplied to the main combustion chamber 14 described later. The corrosion inhibitor supply devices 6, 7, and 8 may be various devices for supplying corrosion inhibitors. If the second corrosion inhibitor is in particulate form, it is a particle supply device, and if the corrosion inhibitor is in slurry form, it is a slurry supply device.

The boiler 1 shown in FIG. 26 is an example of a waste heat recovery boiler, and is equipped with a combustion furnace 2 for incinerating waste, which is equipped with a hopper 12 for supplying waste. The hopper 12 is connected to the main combustion chamber 14 via a chute 13. The waste supplied from the hopper 12 is sent to the main combustion chamber 14 through the chute 13. The main combustion chamber 14 is provided with a drying stoker 15, a combustion stoker 16, and a post-combustion stoker 17. Primary air is sent into the main combustion chamber 14 from below each of the stokers 15, 16, and 17, and secondary air is sent into the main combustion chamber 14 from the ceiling 14a of the main combustion chamber 14.

The garbage thrown into the main combustion chamber 14 is first sent to the drying stoker 15, where it is dried and ignited by the primary air and the radiant heat of the main combustion chamber 14. The ignited garbage is sent to the combustion stoker 16. The ignited garbage also generates combustible gases due to pyrolysis. This combustible gas is sent by the primary air to the gas layer at the top of the main combustion chamber 14, where it flame-burns with the secondary air. The heat radiation from this flame combustion further raises the temperature of the garbage. Some of the ignited garbage is burned in the combustion stoker 16, and the remaining unburned garbage is sent to the post-combustion stoker 17. The unburned garbage is burned in the post-combustion stoker 17, and the incineration ash remaining after combustion is discharged to the outside through the chute 18.

The main combustion chamber 14 is connected to the radiation chamber 20, and the combustion exhaust gas generated by the combustion of the waste is sent to the radiation chamber 20. After being burned again in the radiation chamber 20, this combustion exhaust gas is led from the top of the radiation chamber 20 (first flue) through the second flue 21 to the third flue 22, and then is treated to be harmless in an exhaust gas treatment facility (not shown) before being released into the atmosphere. The radiation chamber 20, the second flue 21, and the third flue 22 form the exhaust gas passage 8 through which the exhaust gas from the incinerator 2 passes.

In the boiler 1, the substances volatilized during combustion and some of the incineration ash are carried along with the flow of the combustion exhaust gas to the radiation chamber 20, the second flue 21, and the third flue 22, where they adhere to and accumulate on the superheating organ 4. Conventionally, such highly corrosive combustion ash has been a factor in corroding the high-temperature superheating organ 4.

When the second corrosion inhibitor is supplied to the flue, the corrosion inhibitor adheres to the inner surface of the flue and the surface of the superheating organ 4 together with the combustion ash containing corrosive particles floating in the flue, and adsorbs the corrosive particles in the combustion ash. This allows the corrosion inhibitor to suppress corrosion of the superheating organ 4 and the inner surface of the flue.
26 is operated for a required period while supplying the second corrosion inhibitor, and the combustion ash obtained from the boiler 1 is treated according to the above-described method for producing further corrosion inhibitor. In this manner, the recovered combustion ash can be repeatedly treated and reused.

The present invention will be explained in more detail below with reference to examples and comparative examples, but the present invention is not limited to the following examples.

[Example 1]
A first slurry containing 2 kg of molten fly ash generated from a first waste treatment facility that treats waste by high-temperature melting and 10 kg of tap water was stirred and mixed for 10 minutes using four inclined paddle blades to dissolve water-soluble compounds contained in the molten fly ash, including Pb, Ca, Na, K, and Cl, to prepare a second slurry.
The first waste treatment facility has a melting furnace for pyrolyzing and gasifying fuel, a combustion chamber for completely burning the pyrolysis gas generated in the melting furnace, an exhaust gas passage through which the combustion exhaust gas generated in the combustion chamber passes, and a superheater tube disposed in the exhaust gas passage, and is a waste treatment facility in which the first corrosion inhibitor obtained by the same method as that for producing the second corrosion inhibitor obtained in Example 3 described later is applied to the exhaust gas passage. In this example, the corrosion inhibitor is applied to the exhaust gas passage of the first waste treatment facility, and the first waste treatment facility is operated for one month, and the above-mentioned molten fly ash obtained from the first waste treatment facility is used as combustion ash.
Table 1 shows an example of the components contained in the untreated molten fly ash generated from the first waste treatment facility and their contents (mass%). Each component was measured by X-ray fluorescence analysis, and heavy metals Pb, Zn, and Cu were measured by ICP atomic emission spectrometry after wet decomposition. As shown in Table 1, the molten fly ash contains heavy metals Pb, Zn, and Cu, which are corrosion factors of boiler superheater tubes, Cl, and Ca, which is an inhibitor in the synthesis of corrosion inhibitors. It also contains Si and Al, which can be components of corrosion inhibitors, but it can be seen that the Si and Al contents are very low compared to the waste incineration ash, coal combustion ash, etc. used in Patent Document 1. In this embodiment, the target is molten fly ash and incineration fly ash having a Ca content of 15% by mass to 25% by mass, a Si content of 2.5% by mass to 6.0% by mass, an Al content of 0.5% by mass to 4% by mass, a Pb content of 0.3% by mass to 3% by mass, a Zn content of 1.0% by mass to 6.0% by mass, a Cu content of 0.01% by mass to 0.5% by mass, and a Cl content of 10% by mass to 25% by mass.

Next, the second slurry was subjected to solid-liquid separation to separate it into a filtrate and molten fly ash after water washing treatment. The elution rates of water-soluble components eluted into the filtrate obtained by solid-liquid separation of the second slurry are shown in Table 2. The elution amount of each component contained in the filtrate was measured by ICP atomic emission spectrometry. The elution rates were calculated using the following formula (1).
Dissolution rate of water-soluble components (mass%)=each component contained in filtrate (g)/each component contained in untreated molten fly ash (g)×100 (1)

From Table 2, it was confirmed that water-soluble compounds including Pb, Zn, Ca, Na, K, and Cl can be removed by washing the molten fly ash with water.

Next, a third slurry containing 2 kg of the recovered molten fly ash after the water washing treatment (including water that could not be separated by solid-liquid separation) and 5.0 kg of water was prepared by stirring and mixing the third slurry using four inclined paddle blades while maintaining the pH of the third slurry at 1.0, 2.0, 2.5, 3.0, 3.5, 4.0, 4.5, and 5.5, respectively, and adding 2 mol/L of hydrochloric acid.
If the stirring and mixing of the third slurry is continued even after the addition of hydrochloric acid is stopped, the alkali content contained in the molten fly ash is gradually dissolved, and the pH of the third slurry increases. Then, the pH of the third slurry becomes greater than 1.0, greater than 2.0, greater than 2.5, greater than 3.0, greater than 3.5, greater than 4.0, greater than 4.5, and greater than 5.5, respectively. Therefore, the third slurry is stirred and mixed while adding hydrochloric acid again, and 2 mol/L hydrochloric acid is supplied until the pH of the third slurry becomes constant. When the pH of the third slurry becomes constant, the addition of hydrochloric acid is stopped, and the slurry is stirred for 10 minutes.

Next, the fourth slurry was subjected to solid-liquid separation to separate it into a filtrate and molten fly ash after pickling treatment (pre-hydrothermal treatment intermediate).
The elution rates of the acid-soluble components eluted in the filtrate obtained by solid-liquid separation of the fourth slurry are shown in Figures 2 to 7. The elution amount of each component contained in the filtrate was measured by ICP atomic emission spectrometry. The elution rates were calculated using the following formula (2).
Dissolution rate of acid-soluble components (mass%)=(g) of each component contained in filtrate/(g) of each component contained in untreated molten fly ash×100 (2)

From the results of Figures 2 to 7, it was confirmed that by subjecting the molten fly ash after the water-washing treatment to an acid-washing treatment, it is possible to remove heavy metals such as Pb, Zn, and Cu, and acid-soluble compounds including Ca, which could not be removed by the water-washing treatment.
2 to 7, it can be seen that when the pH of the fourth slurry is less than pH=2.5, the elution rates of Si and Al, which are components of the corrosion inhibitor, increase sharply. When the pH of the fourth slurry is pH=2.5 or more, the elution rates of Si and Al decrease. In particular, when the pH of the slurry is pH=3.5 or more, and further, when the pH is between pH=4.0 and pH=5.5, the elution rates of Si and Al decrease sharply.

The molten fly ash after acid treatment (intermediate before hydrothermal treatment) was dried at 105°C for 24 hours, and the results of the component analysis of the sample are shown in Table 3 as Example 8. The components were measured using an energy dispersive X-ray analyzer (EDS).

Next, 30 g of sodium orthosilicate was added to 270 g (dry weight) of the acid-treated molten fly ash recovered by solid-liquid separation of the fourth slurry having a pH of pH = 4.0, and 2 mol/L of sodium hydroxide aqueous solution was added so that the ratio of the acid-treated molten fly ash (including sodium orthosilicate) to the sodium hydroxide aqueous solution (the mass ratio of the molten fly ash in a dry state) was 1/4, and these were stirred and mixed to prepare a fifth slurry.
Next, the fifth slurry was stirred and mixed at 120° C. for 3 hours to synthesize a second corrosion inhibitor.
Next, the fifth slurry was subjected to solid-liquid separation to separate it into a filtrate and a corrosion inhibitor.
Next, tap water was added to the recovered corrosion inhibitor so that the ratio of the corrosion inhibitor to tap water (corrosion inhibitor (dry)/water) was 1/5 by mass, and the corrosion inhibitor was washed with water while the aqueous dispersion containing the corrosion inhibitor was subjected to solid-liquid separation.
The resulting second corrosion inhibitor was dried at 105° C. for 24 hours.

[Example 2]
To each of 240 g (dry weight) of the molten fly ash after the acid treatment recovered by solid-liquid separation of the fourth slurry pH = 4.0 in Example 1, 60 g of sodium orthosilicate was added, and 2 mol/L of aqueous sodium hydroxide solution was added so that the ratio of the molten fly ash after the acid treatment (including sodium orthosilicate) to the aqueous sodium hydroxide solution (molten fly ash (dry) + sodium orthosilicate (dry) / aqueous sodium hydroxide solution) was 1/4 in terms of mass ratio, and these were stirred and mixed to prepare a fifth slurry.
Next, the fifth slurry was stirred and mixed at 80° C. for 15 hours to synthesize a corrosion inhibitor.
Next, the fifth slurry was subjected to solid-liquid separation to separate it into a filtrate and a corrosion inhibitor.
Next, tap water was added to the recovered corrosion inhibitor so that the ratio of the corrosion inhibitor to tap water (corrosion inhibitor (dry)/water) was 1/5 by mass, and the second corrosion inhibitor was washed with water while the aqueous dispersion containing the corrosion inhibitor was subjected to solid-liquid separation.

[Example 3]
To 270 g (dry weight) of the molten fly ash after the acid treatment recovered by solid-liquid separation of the fourth slurry pH of Example 1 having a pH of 2.5, 30 g of sodium orthosilicate was added, and 2 mol/L of aqueous sodium hydroxide solution was added so that the ratio of the molten fly ash after the acid treatment (including sodium orthosilicate) to the aqueous sodium hydroxide solution ((molten fly ash (dry) + sodium orthosilicate (dry)) / aqueous sodium hydroxide solution) was 1/4 in terms of mass ratio, and these were stirred and mixed to prepare a fifth slurry.
Next, the fifth slurry was stirred and mixed at 120° C. for 3 hours to synthesize a corrosion inhibitor.
Next, the fifth slurry was subjected to solid-liquid separation to separate it into a filtrate and a corrosion inhibitor.
Next, tap water was added to the recovered corrosion inhibitor so that the ratio of the corrosion inhibitor to tap water (corrosion inhibitor (dry)/water) was 1/5 by mass, and the second corrosion inhibitor was washed with water while the aqueous dispersion containing the corrosion inhibitor was subjected to solid-liquid separation.

[Example 4]
A first slurry containing 2 kg of the same molten fly ash as that used in Example 1 and 10 kg of tap water was stirred and mixed for 10 minutes using four inclined paddle blades to dissolve water-soluble compounds contained in the molten fly ash, including Pb, Ca, Na, K, and Cl, to prepare a second slurry.

Next, the second slurry was subjected to solid-liquid separation to separate the filtrate and the molten fly ash after water washing.

Next, a third slurry containing 2 kg of the recovered molten fly ash after the water washing treatment (including water that could not be separated by solid-liquid separation) and 5.0 kg of water was stirred and mixed using four inclined paddle blades while maintaining the pH of the third slurry at 2.5, and 1 mol/L of nitric acid was added to prepare a fourth slurry.
If the stirring and mixing of the third slurry is continued even after the addition of nitric acid is stopped, the alkali contained in the molten fly ash is gradually dissolved, and the pH of the third slurry increases. Then, since the pH of the third slurry exceeds 2.5, the third slurry is stirred and mixed while adding nitric acid again, and 1 mol/L of nitric acid is supplied until the pH of the third slurry becomes constant. When the pH of the third slurry becomes constant, the addition of nitric acid is stopped, and the slurry is stirred for 10 minutes.

Next, the fourth slurry was subjected to solid-liquid separation to separate it into a filtrate and molten fly ash after pickling treatment (pre-hydrothermal treatment intermediate).
The elution rates of the acid-soluble components eluted in the filtrate obtained by solid-liquid separation of the fourth slurry are shown in Fig. 8. The elution amounts of each component contained in the filtrate were measured by ICP atomic emission spectrometry.

The results in Figure 8 confirm that even when the molten fly ash after the water washing process is pickled with nitric acid, it is possible to remove the heavy metals Pb, Zn, and Cu, as well as acid-soluble compounds including Ca, to the same extent as when it is pickled with hydrochloric acid.

Next, 60 g of sodium orthosilicate was added to 240 g (dry weight) of the molten fly ash after the acid treatment recovered by solid-liquid separation of the fourth slurry, and 2 mol/L of aqueous sodium hydroxide solution was added so that the ratio of the molten fly ash after the acid treatment (including sodium orthosilicate) to the aqueous sodium hydroxide solution ((molten fly ash (dry) + sodium orthosilicate (dry))) / aqueous sodium hydroxide solution) was 1/4 in terms of mass ratio, and these were stirred and mixed to prepare a fifth slurry.
Next, the fifth slurry was stirred and mixed at 80° C. for 15 hours to synthesize a corrosion inhibitor.
Next, the fifth slurry was subjected to solid-liquid separation to separate it into a filtrate and a corrosion inhibitor.
Next, tap water was added to the recovered corrosion inhibitor so that the ratio of the corrosion inhibitor to tap water (corrosion inhibitor (dry)/water) was 1/5 by mass, and the corrosion inhibitor was washed with water while the aqueous dispersion containing the corrosion inhibitor was subjected to solid-liquid separation.
The resulting second corrosion inhibitor was dried at 105° C. for 24 hours.

[Example 5]
In Example 1, 173 g of sodium metasilicate and 7 g of sodium aluminate were added to 120 g (dry weight) of the molten fly ash after the acid treatment recovered by solid-liquid separation of the fourth slurry, and a 2 mol/L aqueous sodium hydroxide solution was added so that the ratio of the molten fly ash after the acid treatment (including sodium metasilicate and sodium aluminate) to the aqueous sodium hydroxide solution (molten fly ash (dry) + sodium metasilicate (dry) + sodium aluminate (dry)) / aqueous sodium hydroxide solution) was 1/4 in terms of mass ratio, and these were stirred and mixed to prepare a fifth slurry.
Next, the fifth slurry was stirred and mixed at 120° C. for 3 hours to synthesize a corrosion inhibitor.
Next, the fifth slurry was subjected to solid-liquid separation to separate it into a filtrate and a corrosion inhibitor.
Next, tap water was added to the recovered corrosion inhibitor so that the ratio of the corrosion inhibitor to tap water (corrosion inhibitor (dry)/water) was 1/5 by mass, and the corrosion inhibitor was washed with water while the aqueous dispersion containing the corrosion inhibitor was subjected to solid-liquid separation.
The resulting second corrosion inhibitor was dried at 105° C. for 24 hours.

[Example 6]
In the third step, the amount of hydrochloric acid added was adjusted to obtain the acid-treated molten fly ash shown in Table 3. A 2 mol/L aqueous sodium hydroxide solution was added to 300 g of this molten fly ash so that the ratio of the molten fly ash after the water-washing treatment to the aqueous sodium hydroxide solution (molten fly ash (dry)/aqueous sodium hydroxide solution) was 1/4 in mass ratio when the molten fly ash was in a dry state, and these were stirred and mixed to prepare a slurry. Next, this slurry was stirred and mixed at 120° C. for 3 hours to synthesize a corrosion inhibitor.
Next, the slurry was subjected to solid-liquid separation to separate it into a filtrate and a corrosion inhibitor.
Water was added to the recovered corrosion inhibitor so that the ratio of the corrosion inhibitor to water (corrosion inhibitor/water) was 1/5 by mass, and the corrosion inhibitor was washed with water while filtering the aqueous dispersion containing the corrosion inhibitor.
The resulting second corrosion inhibitor was dried at 105° C. for 24 hours.

[Example 7]
A first slurry containing 2 kg of molten fly ash different from that in Example 1 and 10 kg of tap water was stirred and mixed for 10 minutes using four inclined paddle blades to dissolve water-soluble compounds contained in the molten fly ash, including Pb, Ca, Na, K, and Cl, to prepare a second slurry.

Next, the second slurry was subjected to solid-liquid separation to separate the filtrate and the molten fly ash after water washing.

Next, a third slurry containing 2 kg of the recovered molten fly ash after the water washing treatment (including water that could not be separated by solid-liquid separation) and 5.0 kg of water was prepared by stirring and mixing the third slurry using four inclined paddle blades while maintaining the pH of the third slurry at 4.0, and adding 2 mol/L of hydrochloric acid to the third slurry.
If the stirring and mixing of the third slurry is continued even after the addition of hydrochloric acid is stopped, the alkali contained in the molten fly ash is gradually dissolved, and the pH of the third slurry increases. Then, since the pH of the third slurry exceeds 4.0, the third slurry is stirred and mixed while adding hydrochloric acid again, and 2 mol/L of hydrochloric acid is supplied until the pH of the third slurry becomes constant. When the pH of the third slurry becomes constant, the addition of hydrochloric acid is stopped, and the slurry is stirred for 10 minutes.

Next, the fourth slurry was subjected to solid-liquid separation to separate it into a filtrate and molten fly ash after pickling treatment (intermediate before hydrothermal treatment).

Next, 60 g of sodium orthosilicate was added to 240 g (dry weight) of the molten fly ash after the acid treatment recovered by solid-liquid separation of the fourth slurry, and 2 mol/L of aqueous sodium hydroxide solution was added so that the ratio of the molten fly ash after the acid treatment (including sodium orthosilicate) to the aqueous sodium hydroxide solution (molten fly ash (dry) + sodium orthosilicate (dry)) / aqueous sodium hydroxide solution) was 1/4 in terms of mass ratio, and these were stirred and mixed to prepare a fifth slurry.
Next, the fifth slurry was stirred and mixed at 120° C. for 3 hours to synthesize a corrosion inhibitor.
Next, the fifth slurry was subjected to solid-liquid separation to separate it into a filtrate and a corrosion inhibitor.
Next, tap water was added to the recovered corrosion inhibitor so that the ratio of the corrosion inhibitor to tap water (corrosion inhibitor (dry)/water) was 1/5 by mass, and the corrosion inhibitor was washed with water while the aqueous dispersion containing the corrosion inhibitor was subjected to solid-liquid separation.
The resulting second corrosion inhibitor was dried at 105° C. for 24 hours.

[Comparative Example 1]
1.2 kg of a 2 mol/L aqueous solution of sodium hydroxide was added to 300 g of the same molten fly ash as that used in Example 1, and the mixture was stirred and mixed to prepare a slurry.
Next, the slurry was stirred and mixed for 3 hours at 120° C. to synthesize the corrosion inhibitor. Next, the slurry was filtered to separate the filtrate and the corrosion inhibitor.
Water was added to the recovered corrosion inhibitor so that the ratio of the corrosion inhibitor to water (corrosion inhibitor/water) was 1/5 by mass, and the corrosion inhibitor was washed with water while filtering the aqueous dispersion containing the corrosion inhibitor.
The resulting corrosion inhibitor was dried at 105° C. for 24 hours.

[Comparative Example 2]
10 kg of water was added to 2 kg of the same molten fly ash as that used in Example 1, and the mixture was stirred and mixed for 10 minutes to prepare a slurry.
Next, the slurry was subjected to solid-liquid separation to separate it into a filtrate and molten fly ash that had been washed with water.
Next, 1.2 kg of a 2 mol/L aqueous solution of sodium hydroxide was added to 300 g of the recovered molten fly ash after the water washing treatment, and the mixture was stirred and mixed to prepare a slurry.
Next, the slurry was stirred and mixed for 3 hours at 120° C. to synthesize a corrosion inhibitor. Next, the slurry was subjected to solid-liquid separation to separate into a filtrate and a corrosion inhibitor.
Water was added to the recovered corrosion inhibitor so that the ratio of the corrosion inhibitor to water (corrosion inhibitor/water) was 1/5 by mass, and the corrosion inhibitor was washed with water while filtering the aqueous dispersion containing the corrosion inhibitor.
The resulting corrosion inhibitor was dried at 105° C. for 24 hours.

[Comparative Example 3]
To 300 g (dry weight) of the acid-treated molten fly ash recovered by solid-liquid separation of the fourth slurry pH of Example 1 having a pH of 4.0, 2 mol/L of aqueous sodium hydroxide solution was added so that the mass ratio of the acid-treated molten fly ash to the aqueous sodium hydroxide solution (dry weight)/aqueous sodium hydroxide solution) was 1/4, and the mixture was stirred and mixed to prepare a fifth slurry.
Next, the fifth slurry was stirred and mixed at 120° C. for 3 hours to synthesize a corrosion inhibitor.
Next, the fifth slurry was subjected to solid-liquid separation to separate it into a filtrate and a corrosion inhibitor.
Next, tap water was added to the recovered corrosion inhibitor so that the ratio of the corrosion inhibitor to tap water (corrosion inhibitor (dry)/water) was 1/5 by mass, and the corrosion inhibitor was washed with water while the aqueous dispersion containing the corrosion inhibitor was subjected to solid-liquid separation.

[Comparative Example 4]
A first slurry containing 2 kg of the same molten fly ash as that used in Example 1 and 10 kg of tap water was stirred and mixed for 10 minutes using four inclined paddle blades to dissolve water-soluble compounds contained in the molten fly ash, including Pb, Ca, Na, K, and Cl, to prepare a second slurry.

Next, the second slurry was subjected to solid-liquid separation to separate the filtrate and the molten fly ash after water washing.

Next, a third slurry containing 2 kg of the recovered molten fly ash after the water washing treatment (including water that could not be separated by solid-liquid separation) and 5.0 kg of water was prepared by stirring and mixing the third slurry using four inclined paddle blades while maintaining the pH of the third slurry at 1.0 and adding 1 mol/L of nitric acid to the slurry.
If the stirring and mixing of the third slurry is continued even after the addition of nitric acid is stopped, the alkali contained in the molten fly ash is gradually dissolved, and the pH of the third slurry increases. Then, since the pH of the third slurry exceeds 1.0, the third slurry is stirred and mixed while adding nitric acid again, and 1 mol/L of nitric acid is supplied until the pH of the third slurry becomes constant. When the pH of the third slurry becomes constant, the addition of nitric acid is stopped, and the slurry is stirred for 10 minutes.

Next, the fourth slurry was subjected to solid-liquid separation to separate it into a filtrate and molten fly ash after pickling treatment (intermediate before hydrothermal treatment).

Next, 60 g of sodium orthosilicate was added to 240 g (dry weight) of the molten fly ash after the acid treatment recovered by solid-liquid separation of the fourth slurry, and 2 mol/L of aqueous sodium hydroxide solution was added so that the ratio of the molten fly ash after the acid treatment (including sodium orthosilicate) to the aqueous sodium hydroxide solution ((molten fly ash (dry) + sodium orthosilicate (dry))) / aqueous sodium hydroxide solution) was 1/4 in terms of mass ratio, and these were stirred and mixed to prepare a fifth slurry.
Next, the fifth slurry was stirred and mixed at 120° C. for 3 hours to synthesize a corrosion inhibitor.
Next, the fifth slurry was subjected to solid-liquid separation to separate it into a filtrate and a corrosion inhibitor.
Next, tap water was added to the recovered corrosion inhibitor so that the ratio of the corrosion inhibitor to tap water (corrosion inhibitor (dry)/water) was 1/5 by mass, and the corrosion inhibitor was washed with water while the aqueous dispersion containing the corrosion inhibitor was subjected to solid-liquid separation.
The resulting corrosion inhibitor was dried at 105° C. for 24 hours.

[Comparative Example 5]
In the third step of Example 1, the amount of hydrochloric acid added was adjusted to obtain molten fly ash having a Ca content of 18 wt % or more after the acid treatment. A 2 mol/L aqueous sodium hydroxide solution was added to 300 g (dry weight) of the molten fly ash after the acid treatment so that the mass ratio of the molten fly ash after the acid washing treatment to the aqueous sodium hydroxide solution was 1/4, and these were stirred and mixed to prepare a fifth slurry.
Next, the fifth slurry was stirred and mixed for 3 hours at 120° C. to synthesize a corrosion inhibitor. Next, tap water was added to the recovered corrosion inhibitor so that the ratio of the corrosion inhibitor to the tap water (corrosion inhibitor (dry)/water) was 1/5 by mass, and the corrosion inhibitor was washed with water while the aqueous dispersion containing the corrosion inhibitor was subjected to solid-liquid separation.

[evaluation]
(1) Identification of crystals of corrosion inhibitors For the corrosion inhibitors obtained in Examples 1, 2, 3, 4, 5, 6, 7, 8, and Comparative Examples 1, 2, 3, 4, and 5, the crystals were identified and the crystal grain size was measured by powder X-ray diffraction (XRD). The crystal grain size was measured using the median diameter ( _d50 median diameter: particle size at which the cumulative frequency is 50%) obtained from the particle size distribution obtained using a laser diffraction particle size distribution measuring device. The results are shown in Table 4 below.
Further, for Examples 1 to 8 and Comparative Example 5, a more detailed analysis was performed to identify the proportion (mass %) of the components contained in each Example. The results are shown in Table 5 below. The detailed components of each Example were analyzed by analyzing the results of X-ray diffraction measurement using the Rietveld method. Corundum (α-Al ₂ O ₃ ) was used as the internal standard substance. Note that in Example 8 in Table 5, the components other than the amorphous phase contained 9.1 mass % calcium sulfate.

From the results in Table 4, peaks of calcium carbonate and calcium hydroxide were observed in Comparative Example 1, which was not subjected to water washing and pickling, Comparative Example 1, which was not treated by water washing only, and Comparative Example 2, which was treated by water washing only. In Comparative Example 2, which was treated by water washing only, the Ca contained in the molten fly ash could not be sufficiently removed by water washing alone, and the Ca content after the addition of the Si source and Al source was high at 29%, so only peaks of calcium carbonate, calcium hydroxide, and anhydrous gypsum were observed. On the other hand, in Examples 1, 2, 3, 4, 5, 6, and 7, which were treated by water washing and pickling to reduce the Ca content after the addition of the Si source and Al source to 6 mass% or more and 16 mass% or less, and the Si + Al content after the addition of the Si source and Al source to 11 mass% or more and 17 mass% or less, peaks of C-S-H, C-A-S-H, calcium phosphate, aluminate phase, magnesioferrite, calcium titanate, zinc oxide, and compounds of magnesium and zinc were observed.

As shown in Table 5, a more detailed analysis of Examples 1 to 8 revealed that the following phases were present: zeolite, C-S-H, amorphous containing C-A-S-H, calcium phosphate (Ca(PO ₄ ) ₆ (OH) ₂ ), calcite or calcium carbonate (CaCO ₃ ), aluminate phase (or calcium aluminate trioxide or compound consisting of Ca, Al, and O: Ca ₉ (Al ₂ O ₆ ) ₃ C ₃ A), hercynite (or compound of Fe, Al, and O: FeAl ₂ O ₄ ), gehlenite (or compound of Ca, Al, Si, and O: FeAl ₂ O ₄ ), magnesium zinc iron ion oxide (compound of Mg, Zn, Fe, and O), magnesioferrite (MgF ₂ O ₄ ), calcium titanate (CaTiO ₃ ), zinc oxide (ZnO), and akermanite (or a compound of Ca, Mg, Si, and O) were found to be contained in the proportions (mass %) shown in Table 5.

(2) Corrosion test The test method is to prepare a test specimen by applying a mixture of simulated molten fly ash and a corrosion inhibitor to the surface of a simulated superheater tube made of SUS310, place the test specimen in a test room with a predetermined test temperature atmosphere, and supply a test gas (combustion exhaust gas) of a predetermined composition at a predetermined flow rate for a predetermined time into the test room. The test time is 100 hours (a mixture of simulated molten fly ash and a corrosion inhibitor is applied every 25 hours), and the test temperatures are 550°C and 500°C. The combustion exhaust gas conditions are HCl: 500 ppm, _SO2 : 50 ppm, _O2 : 5.0 vol%, _H2O : 20 vol%, and _N2 : 72 vol%.
The simulated molten fly ash and comparative materials A (natural zeolite), B (quartz sand), C (calcium hydroxide), D (C-S-H synthesized using a reagent), and corrosion inhibitors E (Example 1), F (Example 2), G (Example 3), H (Example 4), I (Example 5), J (Example 6), K (Comparative Example 1), L (Comparative Example 2), M (Comparative Example 3), and N (Comparative Example 4) were mixed under the following mixing conditions with respect to the surface area of the simulated superheater tube: the simulated molten fly ash was 20 mg/cm ² , and the comparative materials and corrosion inhibitors (Examples 1 to 6, Comparative Examples 1 to 4) were each 6.6 mg/cm ² . After the simulated exhaust gas was allowed to flow for 100 hours, the weight loss rate (%) of the boiler superheater tube was calculated using the following formula (3). The results of the corrosion test at 550° C. (the material of the simulated superheated organ was SUS310S) are shown in FIG. 9, and the results of the corrosion test at 500° C. (the material of the simulated superheated organ was SUS310S) are shown in FIG.
The "without corrosion inhibitor" condition shown in Figures 9 and 10 indicates a condition in which no corrosion inhibitor was mixed with the molten fly ash. The weight loss rate of the simulated superheater tube in the "without corrosion inhibitor" condition is set to 100%. The smaller the weight loss rate, the smaller the corrosion weight loss of the boiler superheater tube, indicating a higher corrosion inhibition effect.
Weight loss ratio (%)=(corrosion weight loss of boiler superheater tube treated with corrosion inhibitor (mg/cm ² )/(corrosion weight loss of boiler superheater tube containing only simulated molten fly ash (mg/cm ² )×100 (3)

9 and 10, it can be confirmed that the use of the corrosion inhibitors of Examples 1, 2, 3, 4, 5, 6, 7, and 8 (pickled fly ash) has a higher corrosion inhibition effect on the simulated superheater tube than the use of natural zeolite, silica sand, and calcium hydroxide. It can also be confirmed that the corrosion inhibition effect is observed in Example 3, which does not contain zeolite, and C-S-H synthesized using a reagent.
In addition, in Patent Document 2, the particle size of the corrosion-inhibiting particles is limited to 0.1 μm or more and less than 10 μm. However, from the test results shown in Figures 9 and 10 and the particle sizes shown in Table 4, it can be confirmed that even if the particle size of the corrosion inhibitor used in the present invention is 10 μm or more and 25 μm or less, it has a corrosion-inhibiting effect on the simulated superheater tube.
Furthermore, it is found that even if Zn remains in the corrosion inhibitor, it does not affect the corrosion inhibitory effect.
The reason why the corrosion inhibitor according to the present invention exhibits a corrosion inhibitory effect even when the particle size is large will be explained together with the measurement results of the specific surface area explained in the test examples below.
In Comparative Example 3, the total content of Si and Al in the starting material used in step 5 is 11 mass% or more (13.3 mass%), but the Ca content is 16 mass% or more (16.7 mass%), so the production of CaCO ₃ increases. It can be seen that CaCO ₃ and Ca(OH) ₂ contained in the molten fly ash recovered after step 5 have low corrosion inhibition effects.
In Comparative Example 4, the Ca content in the starting material used in step 5 is 16 mass% or less (9.6 mass%), but the total content of Si and Al is less than 11 mass% (8.7 mass%), which means that there is a shortage of Si and Al required for the formation of C-S-H or C-A-S-H, and the production rate of CaCO ₃ increases, which shows that the corrosion inhibition effect is low. It is clear that the CaCO ₃ and CaSO ₄ contained in the molten fly ash recovered after step 5 have a low corrosion inhibition effect.

Furthermore, the calcite content (mass%) and the weight loss rate (%) in the high-temperature corrosion test at 550°C described above were measured for the above-mentioned comparative agent A (natural zeolite), Example 1, Example 3, and Comparative Example 5. The results are as follows:
The weight loss rate of natural zeolite was 55.5%, that of Example 1 (calcium carbonate content: 5 mass%) was 42.3%, that of Example 3 (calcium carbonate content: 10.5 mass%) was 41%, and that of Comparative Example 5 (calcium carbonate content: 13.6 mass%) was 58.4%.
From the above comparison, it is considered that the calcium carbonate content is preferably 13 mass % or less.

Next, in order to investigate the adsorption capacity of the corrosion inhibitor, the cross section of the simulated superheater tube subjected to the corrosion test was investigated by EDS analysis. Figures 11 to 17 show color mapping of K, Na, Cl, Si, Al, and Ca in the cross section of the simulated superheater tube of Example 1. Figures 18 to 23 show color mapping of Cl, Si, Ca, Pb, and K in the cross section of the simulated superheater tube of Example 5.
The color mapping of each component shows the concentration distribution. The top color of the bar showing the shade displayed on the right side of each figure indicates high concentration, and the bottom color (black) indicates low concentration, but since the scales for each component are different, the component ratios cannot be compared between components. Note that Si and Ca are constituent elements of the corrosion inhibitor, and are not contained in the simulated molten fly ash. K is a component that is not contained in the corrosion inhibitor but is contained in the simulated molten fly ash. Cl is a component that is not contained in the corrosion inhibitor but is contained in the simulated molten fly ash and in the combustion exhaust gas. Pb is a component that is contained in the simulated molten fly ash.

11 to 17, it can be seen that Cl, which is not contained in the corrosion inhibitor, is distributed in the same region as Si and Al. It can also be seen that K is distributed in the same region as Si and Al in the corrosion inhibitor that does not contain K. Na is a constituent element of the corrosion inhibitor and molten fly ash, but since the distribution of K has been confirmed in fly ash-based zeolite that does not contain K, it is believed that ash components are also included. From this, it can be seen that the corrosion inhibitor adsorbs corrosive components NaCl and KCl, combustion exhaust gas component Cl, and Cl-based gases generated by corrosion.
18 to 23, it was also found that the corrosion inhibitor also adsorbed _PbCl2 , which is a corrosive component.

Next, in order to confirm the effect of the corrosion inhibitor, qualitative analysis and state analysis were performed by XPS on the corrosion products formed on the surface of the test piece of the simulated superheater subjected to the corrosion test. The analyzed surfaces were the vicinity of the outermost layer of the corrosion products, inside the corrosion product layer, and the vicinity of the base material interface. The analyzed surfaces were surfaced by cutting the corrosion product layer obliquely in the depth direction using a SAICAS device. The analysis using the XPS device first performed a qualitative analysis, and then performed a state analysis on the detected elements.
FIG. 24 shows the results of an analysis of the components of corrosion products inside the corrosion product layer when the simulated molten fly ash and the mixture of the simulated molten fly ash and the corrosion inhibitor (Example 1) were applied to a simulated superheater tube (Alloy 625) and a corrosion test was carried out at 550° C. for 100 hours.
Fig. 25 shows the results of analysis of the components of the corrosion products near the interface with the base material (simulated superheater tube) and the corrosion products when the simulated molten fly ash and the mixture of the simulated molten fly ash and the corrosion inhibitor (Example 1) were applied to a simulated superheater tube (Alloy 625) and a corrosion test was carried out at 550°C for 100 hours. Table 6 shows the results of the state analysis of Cr and Ni.

24 and 25, the Cl ratio tends to be higher on the base metal interface side than in the corrosive material layer. This is particularly noticeable in the simulated superheater tube with only simulated molten fly ash, where the Cl ratio on the base metal interface side is about 30%, which is three times that in the corrosion product layer. When the corrosion inhibitor of Example 1 is used, the Cl ratio is about 4% on the base metal interface side and about 1% in the corrosion product layer, which shows that the Cl ratio is very small. It can be seen that the O ratio tends to be higher in the corrosion product layer and the outermost surface than on the base metal interface side in the test piece with only simulated molten fly ash. On the other hand, when the corrosion inhibitor of Example 1 is used, the O ratio is about 50% both on the base metal interface side and in the corrosion product layer.
From Table 6, in the case of the simulated superheater tube containing only the simulated molten fly ash, it can be seen that the Cr on the base metal interface side is mainly oxide, and the Cr in the outermost layer and the corrosion product layer is mainly chloride (CrO ₂ Cl ₂ ), although the oxide peak intensity was also detected. It can be seen that the Ni on the base metal interface side is mainly chloride (NiCl ₂ ), although the oxide peak intensity was also detected, and the corrosion product layer and the outermost layer are mainly oxides and hydroxides. On the other hand, when the corrosion inhibitor of Example 1 was used, a weak chloride (CrO ₂ Cl ₂ ) peak was confirmed for Cr on the outermost surface and in the corrosion product layer, but the outermost surface, the corrosion product layer, and the base metal interface were all mainly Cr oxides. It can be seen that Ni is mainly oxide at the base metal interface.

11 to 17, 18 and 19, 18 to 25, and Table 6 show that the use of a corrosion inhibitor improves the corrosive environment at the interface between the base material and the corrosion product to a state in which corrosion products mainly made of oxides are formed by adsorbing NaCl, KCl, etc., which are corrosion factors, and corrosive gas components such _as HCl and Cl2, thereby suppressing the chlorination reaction of Cr oxides and Ni oxides, thereby exerting a corrosion inhibition effect on the simulated superheater tube. The adsorption of gas components and ash components described above is due to the adsorption ability of the corrosion inhibitor.

An experiment was carried out to recover heavy metals eluted in the acid washing treatment by using the filtrate obtained by solid-liquid separation of the fourth slurry in Example 1. The filtrate used in the test was the third slurry having a pH of 4.0.
The filtrate obtained by solid-liquid separation of the fourth slurry was taken in an amount of 300 mL each, and while stirring with a stirrer, 5 mol/L NaOH was added thereto until the pH of the filtrate stabilized at pH = 9.5 and pH = 10.0.

Next, the filtrate was subjected to solid-liquid separation to separate the precipitate and the filtrate.
The components of the resulting precipitate were determined by X-ray fluorescence spectroscopy, and the results are shown in Table 7 below.
The contents of Pb, Zn, and Cu remaining in the filtrate were analyzed by ICP emission spectrometry. The results are shown in Table 8 below.

Table 7 shows that the heavy metals that dissolved in the filtrate were successfully recovered. Table 8 also shows that the filtrate after the sediment was recovered contained almost no heavy metals.

Table 9 shows the test conditions for Examples 1 to 7 and Comparative Examples 1 to 4, including the water washing treatment in the first step, the pickling treatment in the third step, and the alkaline hydrothermal treatment in the fifth step.

Table 10 shows the percentages (wt%) of Si, Al and Ca in the intermediate before hydrothermal treatment.

The results of the BET specific surface area of the corrosion inhibitors of Examples 1 to 7 obtained in the previous test results are shown in Table 11 below. The BET method is a gas adsorption method in which gas molecules such as nitrogen (N ₂ ), argon (Ar), krypton (Kr), and carbon oxide (CO) are adsorbed on solid particles, and the specific surface area of the solid particles is measured from the amount of adsorbed gas molecules. In this test, nitrogen (N ₂ ) was used, and the monomolecular adsorption amount (Vm) was calculated by the BET equation (Brunauer, Emmet and Teller's equation) from the relationship between pressure (P) and adsorption amount (V). Vm means the mass of gas molecules adsorbed on the surface of the solid particles. Next, the specific surface area of the solid particles was calculated using the adsorption cross-sectional area (Am) of the gas molecules, etc.
In addition to the corrosion inhibitors of Examples 1 to 7, the fly ash after pickling was used as the corrosion inhibitor of Example 8 to determine the BET specific surface area, and the BET specific surface area of Comparative Example 1 was also determined. Furthermore, the BET specific surface areas of natural zeolite A from Shimane Prefecture, natural zeolite B from Fukushima Prefecture, and natural zeolite C from Fukushima Prefecture were measured as comparative objects. The relationship between the BET specific surface areas based on these measurement results and the median diameters shown in Table 4 above is shown in Table 11 below for comparison.

Referring to the median diameter in Table 11, the median diameters of Examples 1 to 8 are in the range of 10 μm or more and 25 μm or less, whereas the fly ash of Comparative Example 1 has a median diameter of less than 10 μm, and the median diameter of natural zeolite is distributed in a wide range of 3 to 36 μm.
As explained above, in the technology described in Patent Document 2, the particle diameter of the corrosion-inhibiting particles is specified to be 0.1 μm or more and less than 10 μm. However, the fact that Examples 1 to 8 have a median diameter in the range of 10 μm or more and 25 μm or less and exhibit excellent corrosion-inhibiting effects despite their large particle diameters shows that the corrosion inhibitor according to the present invention is a corrosion inhibitor that is completely different from the corrosion inhibitor described in Patent Document 2. The present inventor believes that the following explanation is relevant to the reason why the corrosion inhibitor according to the present invention exhibits excellent corrosion-inhibiting effects despite its large particle diameter.

As shown in Table 11, the corrosion inhibitors of Examples 1 to 7 have BET specific surface areas of 32 to 136 m ² /g, which are extremely large compared to the BET specific surface areas of natural zeolite and Comparative Example 1. It is described that the particle size of the corrosion inhibitor described in Patent Document 2 is small because, if the particle size of the corrosion inhibitor is large, corrosive substances pass through gaps between the corrosion inhibitors with large particle size and reach the overheating organ, and for this reason, the technology described in Patent Document 2 specifies the particle size as 0.1 μm or more and less than 10 μm.
In contrast, the corrosion inhibitors of Examples 1 to 8 have large particle sizes but large specific surface areas, and therefore can efficiently adsorb corrosion-causing substances onto their surfaces. As a result, they can prevent corrosion-causing substances from reaching overheated organs, and are therefore thought to have excellent corrosion inhibition effects.
In addition, it is believed that the corrosion inhibitors of Examples 1 to 8 are composed of corrosion inhibitor particles with large surface irregularities formed by mutual adhesion of multiple components, and that the large surface irregularities give rise to excellent adsorption performance for corrosive substances.

Table 12 shows the results of calculating the molten fly ash reduction rate and the molten fly ash recovery rate (%) from the weight of the molten fly ash before the pickling treatment and the weight of the molten fly ash after the pickling treatment and drying at 105° C. for 24 hours, in the cases of carrying out the pickling treatment at pH 2.5, pH 4.0, and pH 5.0 in the production of the corrosion inhibitor of Example 1.
Table 12 also shows the amount of Zn recovered calculated from the Zn content (%)/ratio in the Zn-containing material.
In comparison with these, Table 12 shows the molten fly ash recovery rate in the conventional technology described in "Non-Patent Document Murayama et al.: Evaluation of Coal Ash and Incineration Ash as Zeolite Raw Materials, Resources and Materials, 117 (2001) No. 6" and the molten fly ash recovery rate in the case where the pH is not controlled.

The Zn-containing material described in Table 12 refers to a precipitate that is collected when an alkaline aqueous solution is added to the liquid fraction (filtrate after pickling) collected in the fourth step while stirring, the pH of the liquid fraction is adjusted to 9.0 to 10.5, and the pH-adjusted solution is separated into a liquid fraction and a precipitate. This precipitate is a raw material for crude zinc oxide. The Zn-containing material refers to a precipitate that is formed by dissolving metals such as Zn in the filtrate after pickling.
The value of crude zinc oxide as a raw material is greater when the Zn content in the Zn-containing material is higher.
As shown in Table 12, the Zn recovery rate is higher when the pH is 2.5, but the value as a crude zinc oxide raw material is higher when the pH is 4.0 or 5.0.
As shown in Table 12, when the pH is 4.0 and 5.0, it is found that about 500 g of post-acid-washing corrosion inhibitor can be obtained from 1000 g of molten fly ash.

"HCl gas adsorption rate measurement test"
In order to measure the HCl gas adsorption rate, 15 g of each of the corrosion inhibitors of Examples 1, 3, 5, and 7 and the natural zeolite shown in Table 11 were filled in a ceramic container in a tubular furnace, and a simulated exhaust gas containing HCl: 500 ppm, SO ₂ : 50 ppm, O ₂ : 5.0 vol.%, H ₂ O: 20 vol.%, and N ₂ : 72 vol.% was passed through at a predetermined flow rate. The temperature conditions were assumed to be the gas temperature range in which the corrosion inhibitor is supplied in an actual machine, and the test was carried out at 450°C and 650°C. The gas flow time was 1 hour after the set temperature was reached, and the HCl gas adsorption rate was calculated from the ratio of the hydrogen chloride inlet concentration to the outlet concentration after passing through the corrosion inhibitor. The results are shown in Table 13 below.

From the test results shown in Table 13, it was confirmed that when the corrosion inhibitors of Examples 1, 3, 5, and 7 were used, the HCl gas adsorption performance was higher than when natural zeolites A, B, and C were used. It was also confirmed that Example 3, which does not contain zeolite, had a higher HCl gas adsorption performance than natural zeolites A, B, and C.

1...boiler, 2...combustion chamber, 3...exhaust gas passage, 4...superheater, 6, 7, 8...corrosion inhibitor supply device, 20...radiation chamber, 21...second flue, 22...third flue.

Claims (18)

An acquisition step of acquiring combustion ash generated in a first waste treatment facility to which the first boiler corrosion inhibitor has been introduced , the combustion ash containing Ca, Al, and Si ;
A washing process for washing and pickling the combustion ash obtained in the obtaining process;
and a manufacturing step of subjecting the combustion ash that has been subjected to the water washing treatment and the acid washing treatment in the washing treatment step to an alkali hydrothermal treatment to obtain a second boiler corrosion inhibitor ,
a method for producing a corrosion inhibitor for a boiler, comprising the steps of: adjusting the Ca content to 16 mass% or less when the Ca content contained in the combustion ash to be subjected to the alkaline hydrothermal treatment exceeds 16 mass%; and adding a Si source or an Al source when performing the alkaline hydrothermal treatment, so that the total content of Si and Al contained in the combustion ash to be subjected to the alkaline hydrothermal treatment is 11 mass% or more when the total content of Si and Al contained in the combustion ash to be subjected to the alkaline hydrothermal treatment is less than 11 mass%. 2. The method for producing a corrosion inhibitor for a boiler according to claim 1, characterized in that the average particle size (d ₅₀ ) of the corrosion inhibitor for a boiler obtained in the production process is 10 μm or more and 25 μm or less. The method for producing a corrosion inhibitor for boilers according to claim 1 or 2, characterized in that the second corrosion inhibitor for boilers obtained in the production process contains 40 mass% or more of amorphous matter. In addition to the amorphous phase, the second corrosion inhibitor for boilers obtained in the production process is further
4. The method for producing a boiler corrosion inhibitor according to claim 1, wherein the corrosion inhibitor contains at least one or more selected from the group consisting of calcium phosphate, calcium carbonate, aluminate phase, hercynite, zeolite, gehlenite, magnesioferrite, magnesium zinc iron ion oxide, calcium titanate, zinc oxide, and akermanite. 5. The method for producing a corrosion inhibitor for a boiler according to claim 1, wherein the second corrosion inhibitor for a boiler obtained in the production process is obtained by subjecting combustion ash that has been subjected to water washing and acid washing in the cleaning process to an alkaline hydrothermal treatment. The method for producing a boiler corrosion inhibitor according to claim 5, characterized in that an alkaline aqueous solution is used in the production process, and the second boiler corrosion inhibitor is obtained by washing away the alkaline aqueous solution. The method for producing a corrosion inhibitor for a boiler according to claim 6, wherein the second corrosion inhibitor for a boiler obtained in the production step has a BET specific surface area of 90 m ² /g or more. The method for producing a corrosion inhibitor for boilers according to any one of claims 1 to 4, characterized in that in the cleaning process, the combustion ash obtained in the obtaining process is subjected to an acid washing process. The method for producing a corrosion inhibitor for a boiler according to claim 8, wherein the second corrosion inhibitor for a boiler obtained in the production step has a BET specific surface area of 60 m ² /g or more. The first waste treatment facility is a melting furnace;
The combustion ash is molten fly ash containing heavy metals,
5. The method for producing a corrosion inhibitor for a boiler according to claim 1, wherein the cleaning step comprises pickling the combustion ash obtained in the obtaining step. The method for producing a corrosion inhibitor for boilers according to claim 4, characterized in that in the cleaning process, the combustion ash is subjected to an acid washing process to dissolve the Zn contained in the combustion ash. The method for producing a corrosion inhibitor for boilers described in claim 11, characterized in that the combustion ash that has been pickled in the cleaning process is in the form of a slurry, and the pH of the combustion ash is 2.5 or more and 5.5 or less. The first waste treatment facility is a stoker furnace;
The combustion ash is incineration fly ash,
5. The method for producing a corrosion inhibitor for a boiler according to claim 1, wherein the combustion ash obtained in the obtaining step is washed with water in the washing step. The method for producing a boiler corrosion inhibitor according to any one of claims 1 to 13, characterized in that the cleaning process is performed once. The method for producing a corrosion inhibitor for a boiler according to any one of claims 1 to 14, characterized in that the first corrosion inhibitor for a boiler is a corrosion inhibitor for a boiler obtained by subjecting combustion ash generated in the first waste treatment facility or combustion ash generated in a second waste treatment facility different from the first waste treatment facility to a water washing process or an acid washing process. In the obtaining step, the corrosion inhibitor for a boiler obtained in the production step is used as the first corrosion inhibitor for a boiler,
16. The method for producing a corrosion inhibitor for a boiler according to claim 1, wherein the obtaining step, the cleaning treatment step, and the producing step are repeated. The method for producing a corrosion inhibitor for boilers according to any one of claims 1 to 16, characterized in that the calcium carbonate content in the second corrosion inhibitor for boilers obtained in the production process is 13 mass% or less. A method for suppressing corrosion of a superheating device provided in an exhaust gas passage through which combustion exhaust gas of a boiler passes, comprising:
A second boiler corrosion inhibitor manufactured by the manufacturing method according to any one of claims 1 to 17 is supplied into the exhaust gas passage.
Methods for inhibiting boiler corrosion.

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