Method for cleaning biomass combustion ash

Abstract

An object of the present invention is to provide a method for washing biomass combustion ash that can efficiently reduce the alkaline components in the combustion ash. [Solution] A method for washing biomass combustion ash, comprising a water washing step (A) in which biomass combustion ash containing alkali-containing minerals is washed with water containing carbon dioxide.

Description

[Technical Field]

[0001] The present invention relates to a method for washing biomass combustion ash. [Background technology]

[0002] Combustion ash (bottom ash, fly ash, mixed ash, etc., hereinafter simply referred to as "combustion ash") generated when general waste, wood chips, etc. are burned has recently been effectively utilized as a cement raw material.

[0003] However, when combustion ash is used as a cement raw material, if the combustion ash contains a large amount of chlorine, sulfur (sulfuric acid), or alkaline components, this may have an adverse effect on cement burning or cement quality. Therefore, when combustion ash is used as a cement raw material, it is common to remove various harmful components such as chlorine contained in the combustion ash beforehand by washing with water or the like.

[0004] For example, Patent Document 1 proposes a technology that enables efficient removal or reduction of chlorine in incineration ash so that a larger amount of incineration ash can be used as a cement raw material. Specifically, the document discloses a method for efficiently removing or reducing chlorine in incineration ash by adding an acid when washing the incineration ash with water to control the pH of the washing solution to 6 to 10.

[0005] However, Patent Document 1 does not consider reducing the alkaline component. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 11-319769 Summary of the Invention [Problem to be solved by the invention]

[0007] The present invention has been made in view of the above-mentioned circumstances, and an object of the present invention is to provide a method for washing biomass combustion ash that can efficiently reduce the alkaline components in the combustion ash. [Means for solving the problem]

[0008] As a result of extensive research, the present inventors have found that some combustion ash contains poorly water-soluble alkali-containing minerals, and that in the case of such combustion ash, the alkali-containing minerals cannot be decomposed by conventional water-washing treatment alone, and alkali components remain in the combustion ash after the water-washing treatment. Based on the above findings, the inventors have conducted further research and have found that, when combustion ash containing alkali-containing minerals is subjected to a water-washing treatment with water containing carbon dioxide, the poorly water-soluble alkali-containing minerals can be decomposed and the alkali components in the combustion ash can be efficiently reduced, thereby completing the present invention.

[0009] That is, the gist and configuration of the present invention are as follows. [1] A method for producing a cement raw material, comprising a water-washing step (A) of washing combustion ash containing alkali-containing minerals with water containing carbon dioxide. [2] The method for producing a cement raw material according to [1] above, wherein the combustion ash is biomass combustion ash. [3] The water-washing treatment step (A) A combustion ash dispersion preparation step (AI-1) of mixing the combustion ash with water to obtain a combustion ash dispersion; A carbon dioxide supply / agitation step (AI-2) of supplying a gas containing carbon dioxide to the combustion ash dispersion and stirring the mixture; The method for producing a cement raw material according to [1] or [2] above, comprising: [4] The method for producing a cement raw material according to [3] above, wherein the gas contains 5% by volume or more of carbon dioxide. [5] An analysis step (B) of performing a composition analysis on at least one of the solid content and the liquid content of the combustion ash dispersion liquid that has been subjected to the water washing step (A) at least once; a water-washing continuation / termination determination step (C) for determining whether to continue or terminate the water-washing step (A) based on the analysis results obtained in the analysis step (B) and in relation to the target washing composition value of the solid content or liquid content; The method for producing a cement raw material according to any one of the above [1] to [4], further comprising: [Effects of the Invention]

[0010] According to the present invention, it is possible to provide a method for washing biomass combustion ash, which can efficiently reduce the alkaline components in the combustion ash. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a graph showing the X-ray diffraction peaks of combustion ash (combustion ash before water washing treatment, and combustion ash after water washing treatment obtained in Example 1 and Comparative Example 1). DETAILED DESCRIPTION OF THE INVENTION

[0012] An embodiment of the method for producing a cement raw material according to the present invention will be described in detail below.

[0013] The method for producing a cement raw material of the present invention is characterized by having a water-washing step (A) in which combustion ash containing alkali-containing minerals is washed with water containing carbon dioxide. According to the method for producing a cement raw material of the present invention, even if the combustion ash used contains alkali-containing minerals, washing with water containing carbon dioxide can decompose the alkali-containing minerals contained in the combustion ash and elute the alkali components into the washing liquid (water), thereby efficiently reducing the alkali components in the combustion ash.

[0014] <Alkali-containing minerals> In this specification, the term "alkali-containing mineral" refers to a mineral that is primarily derived from soil and contains alkali metals. In particular, if the alkali metal is dissolved in the alkali-containing mineral, it is difficult to reduce the alkali content of combustion ash containing the mineral by simply washing it with water.

[0015] Examples of such alkali-containing minerals include alkali feldspars (orthoclase and microcline), plagioclase (albite and anorthite), and feldspars.

[0016] Figure 1 shows the results of X-ray diffraction analysis that identified the alkali-containing minerals contained in the combustion ash. The X-ray diffraction peaks of the combustion ash shown in Figure 1 are a graph of the X-ray diffraction peaks of the combustion ash before the water washing treatment and the combustion ash after the water washing treatment obtained in Example 1 and Comparative Example 1. The measurement method will be explained in detail in the Examples section.

[0017] As shown in the X-ray diffraction peaks of the combustion ash before water washing in Figure 1, the diffraction peaks of minerals containing Na as an alkaline component, particularly plagioclase, such as labradrite and albite, are confirmed at 2θ ≒ 28°. In other words, it can be said that the combustion ash before water washing contains the above-mentioned alkali-containing minerals.

[0018] <Combustion ash> The combustion ash used in the present invention is not particularly limited as long as it contains an alkali-containing mineral, but examples thereof include combustion ash (incineration ash) obtained by incinerating general waste and biomass combustion ash emitted from biomass power plants that use wood chips or the like as their main fuel.

[0019] The alkali-containing minerals are generally known to be contained in soil. Therefore, when using biomass combustion ash, which is more likely to be contaminated with soil during the manufacturing process than incineration ash, the problem of reducing the alkali components becomes more pronounced. Therefore, the present invention is particularly suitable for use when biomass combustion ash is used as the combustion ash.

[0020] Furthermore, the combustion ash may contain various components other than alkali-containing minerals, such as chlorine, sulfur (sulfuric acid), alkaline earth elements, etc. Of these, chlorine and sulfur (sulfuric acid) can also be sufficiently removed by the water washing treatment of the present invention.

[0021] <Water washing process (A)> The water-washing step (A) is a step of washing combustion ash containing alkali-containing minerals with water containing carbon dioxide. In the production method of the present invention, by carrying out the water washing step (A), the alkali-containing minerals contained in the combustion ash can be decomposed, and the alkali components can be eluted into the washing liquid (water), thereby efficiently reducing the alkali components in the combustion ash.

[0022] The reason why washing combustion ash with water containing carbon dioxide can decompose and dissolve alkali-containing minerals contained in combustion ash is not entirely clear, but the inventors speculate as follows.

[0023] For example, in the case of Albite (NaAlSi3O8), the following reaction, known as weathering, is presumed to occur as a decomposition reaction with water containing carbon dioxide. 2NaAlSi3O8+2H2CO3+9H2O →2Na + +2HCO3 - +Al2Si2O5(OH)4+4H4SiO4 That is, when the combustion ash contains alkali-containing minerals such as albite, the washing treatment with water containing carbon dioxide is expected to cause the above-mentioned reaction, resulting in the decomposition of the alkali-containing minerals such as albite.

[0024] This coincides with the results of the X-ray diffraction peaks of the combustion ash (Example 1) after washing treatment with water containing carbon dioxide, as shown in Figure 1. That is, as shown in Figure 1, it was confirmed that the diffraction peaks of labradrite and albite (2θ ≒ 28°) observed in the combustion ash before washing treatment were smaller in the combustion ash (Example 1) after washing treatment with water containing carbon dioxide. This is presumably due to the decomposition of alkali-containing minerals by the above-mentioned reaction.

[0025] The water washing step (A) is not particularly limited as long as it is a method that can wash the combustion ash with water containing carbon dioxide, and can be carried out, for example, by the following methods I to III. Among them, method I is more preferred.

[0026] (Method I) Method I is a method carried out by a water washing process (AI) including a combustion ash dispersion preparation process (AI-1) in which combustion ash and water are mixed to obtain a combustion ash dispersion, and a carbon dioxide supply and stirring process (AI-2) in which a gas containing carbon dioxide is supplied to the combustion ash dispersion and stirred.

[0027] The mixing ratio of combustion ash to water is preferably 1:2 to 1:15 by mass (combustion ash:water), more preferably 1:2 to 1:10, and even more preferably 1:4 to 1:10. By adjusting the ratio within the above range, the stirring step and wastewater treatment step described below become efficient and effective treatments. If the amount of combustion ash is too small relative to the water, the amount of liquid discharged as wastewater in the solid-liquid separation step will be excessive, which tends to place a burden on the wastewater treatment step, and if the amount is too large, the viscosity of the combustion ash dispersion will increase, making stirring difficult.

[0028] The carbon dioxide-containing gas is preferably a gas containing 5% by volume or more of carbon dioxide, more preferably a gas containing 10% by volume or more, even more preferably a gas containing 15% by volume or more, and even more preferably a gas containing 18% by volume or more. By setting the concentration within the above range, carbon dioxide can be efficiently dissolved in water. If the carbon dioxide concentration is too low, the amount of carbon dioxide that dissolves in water will be small, and it will tend to be difficult to react with combustion ash. The upper limit of the carbon dioxide concentration is not particularly limited and may be, for example, 100% by volume. As the carbon dioxide concentration increases, the amount of carbon dioxide that dissolves in water tends to increase, but the amount of carbon dioxide that does not dissolve in water and is emitted also increases, which tends to have a greater impact on the environment. Examples of the gas containing carbon dioxide include a mixed gas of nitrogen, oxygen, and carbon dioxide. From the viewpoint of industrial economy, it is also preferable to use exhaust gas or the like.

[0029] The gas is preferably supplied into the combustion ash dispersion solution from the bottom of the stirring vessel in the form of fine bubbles. The aeration rate is not particularly limited and may be adjusted appropriately depending on the carbon dioxide concentration, stirring conditions, etc., and is preferably supplied at, for example, 50 to 1000 ml / min. By setting the aeration rate within the above range, carbon dioxide can be efficiently dissolved in water. The gas may be supplied continuously or discontinuously during this process. By supplying the gas continuously, the reaction with the combustion ash proceeds more efficiently.

[0030] The stirring method is preferably stirring using a stirring blade. The shape and size of the stirring blade are not particularly limited, and stirring blades such as those used in conventional combustion ash washing can be used as appropriate.

[0031] The stirring conditions are not particularly limited, but are preferably controlled as follows, for example. The treatment temperature is preferably 10 to 50°C, more preferably 15 to 40°C, and even more preferably 15 to 25°C. By setting the temperature within the above range, efficient treatment becomes possible. If the treatment temperature is too low, the reaction rate between carbon dioxide in water and combustion ash tends to decrease, and if it is too high, the amount of carbon dioxide that dissolves in water tends to decrease. The stirring time is preferably 2 to 48 hours, more preferably 5 to 36 hours, and even more preferably 5 to 24 hours. By setting the stirring time within the above range, effective treatment is possible. If the stirring time is too short, the reaction between the alkali-containing minerals contained in the combustion ash and the carbon dioxide in the water tends to be insufficient, while if the stirring time is too long, it is not economical and the amount of carbon dioxide used increases, which increases the amount of exhaust and tends to have a greater impact on the environment.

[0032] The stirring vessel is not particularly limited and can be appropriately adjusted depending on the scale of implementation, etc., and any known stirring vessel can be used.

[0033] (Method II) Method II is a method carried out by a water washing treatment step (A-II) including a carbon dioxide supply and stirring step (A-II-1) in which gas containing carbon dioxide is supplied to water and stirred, and a combustion ash dispersion stirring step (A-II-2) in which combustion ash is added to the water to which carbon dioxide has been supplied and further stirred.

[0034] The conditions can be the same as those in Method I except for the following conditions. In the carbon dioxide supply / stirring step (A-II-1), the time for stirring the water is preferably 0.5 to 5 hours, more preferably 1 to 3 hours. By setting the time within the above range, a sufficient amount of carbon dioxide will be dissolved in the water.

[0035] In the combustion ash dispersion stirring step (A-II-2), the stirring time for the combustion ash dispersion is preferably 2 to 36 hours, more preferably 5 to 24 hours. By setting the stirring time within the above range, the carbon dioxide in the water and the combustion ash can be reacted efficiently.

[0036] In the present method, in the combustion ash dispersion stirring step (A-II-2), the combustion ash dispersion may be stirred while further supplying a gas containing carbon dioxide to the combustion ash dispersion. In this case, the carbon dioxide and the combustion ash can be reacted efficiently.

[0037] (Method III) Method III is a method carried out by a water washing treatment step (A-III) including a carbon dioxide-containing water preparation step (A-III-1) for obtaining water containing carbon dioxide, and a combustion ash dispersion stirring step (A-III-2) for mixing and stirring combustion ash and the carbon dioxide-containing water.

[0038] The conditions can be the same as those in Method I or II, except for the following conditions. The method for obtaining water containing carbon dioxide is not particularly limited, but examples thereof include a method of supplying a gas containing carbon dioxide to water and stirring it, as in Method II above, a method of filling water with carbon dioxide using high-pressure carbon dioxide, and a method of obtaining commercially available water containing carbon dioxide.

[0039] The method of mixing the combustion ash and the carbon dioxide-containing water is not particularly limited, and the combustion ash may be added to the carbon dioxide-containing water and stirred, or the carbon dioxide-containing water may be supplied to the combustion ash and stirred. In particular, when the carbon dioxide-containing water is supplied to the combustion ash, a predetermined amount of the carbon dioxide-containing water may be supplied to the combustion ash all at once, or may be supplied continuously in small amounts. In particular, the case of continuously supplying the carbon dioxide-containing water in small amounts while stirring is preferred because the carbon dioxide concentration in the combustion ash dispersion can be continuously maintained high.

[0040] In the present method, in the combustion ash dispersion stirring step (A-III-2), the combustion ash dispersion may be stirred while further supplying a gas containing carbon dioxide to the combustion ash dispersion. In this case, the carbon dioxide and the combustion ash can be reacted efficiently.

[0041] The production method of the present invention preferably further includes an analysis step (B) and a water washing continuation / termination decision step (C) after at least one water washing step (A). By undergoing such an analysis step, the alkali components in the combustion ash can be reliably reduced to the target value.

[0042] <Analysis process (B)> This is a step of conducting a composition analysis on at least one of the solid content and the liquid content of the combustion ash dispersion that has been subjected to the water washing step (A) at least once. The analysis can be carried out by a known analytical method, for example, the following method.

[0043] (solids) When the analysis target is a solid content, the content of impairing components such as alkaline components in the solid content can be measured, for example, by a fluorescent X-ray analyzer. (liquid content) When the object of analysis is a liquid fraction, the content of impairing components such as alkaline components in the liquid fraction can be measured, for example, by an ion chromatograph or a high-frequency inductively coupled plasma atomic emission spectrometer. It is more preferable to use solids as the subject of analysis, from the viewpoint of being able to directly grasp the content of impurity components such as alkaline components in the cement raw materials.

[0044] <Process C: Determining whether to continue or stop washing> This is a step of determining whether to continue or terminate the water washing step (A) based on the analysis results obtained in the analysis step (B) and in relation to the target washing composition value of the solid or liquid content. The continuation or termination of the water washing step (A) is determined by checking whether the content of harmful components in the solids reaches a predetermined target composition for washing when the solids are the target, or whether the content of harmful components in the liquid reaches the difference (removal target amount) between the content of harmful components in the combustion ash before washing and a predetermined target composition for washing when the liquid is the target. As for the target composition values ​​for cleaning, in the case of solids, for example, when the content (mass) of each harmful component contained in the combustion ash before cleaning is taken as 100, the target composition values ​​for cleaning can be set to 90 or less in terms of oxide (Na2O), the target composition values ​​for K in terms of oxide (KO) of 80 or less, the target composition values ​​for S in terms of oxide (SO3) of 38 or less, and the target composition values ​​for Cl in terms of atom (Cl) of 8 or less.

[0045] The production method of the present invention preferably further comprises a solid-liquid separation step (D) after the water-washing step (A), which allows the cement raw material to be recovered as a solid content. <Solid-liquid separation process (D)> This is a process in which the solid and liquid components are separated from the combustion ash dispersion after the water washing process (A) and the solid components are recovered as a cement raw material.

[0046] (filtration process) The solid and liquid components can be separated by filtration, which can be carried out by a known method, such as suction filtration, filter press, or centrifugation. If necessary, as a finishing treatment for the filtration, the solids may be washed with clean water such as ion-exchanged water, industrial water, tap water, groundwater, etc. The amount of clean water may be adjusted as appropriate, but it is preferable to use an amount about 10 times the amount of the solids, for example.

[0047] The separated solid content may be used as a cement raw material as it is, but may be further subjected to a drying treatment or the like as required.

[0048] (Drying process) The drying treatment can be carried out by a known method, but it is preferable to carry out a drying treatment using, for example, kiln exhaust gas in order to utilize the exhaust heat.

[0049] The production method of the present invention preferably further comprises a wastewater treatment step (E) after the solid-liquid separation step (D), which makes it easier to reuse or discard the liquid separated in the solid-liquid separation step (D).

[0050] <Wastewater treatment process (E)> This is a step in which the liquid fraction separated in the solid-liquid separation step (D) is recovered and at least one of recycled use and discharged to the outside of the system.

[0051] (Recycling use) Recycling refers to reusing the recovered liquid as water to be used in other steps of the production method of the present invention. Here, the water to be used in other steps includes the water used in the water washing step (A) and the water used in the finishing treatment of filtration in the solid-liquid separation step (D). The recovered liquid can be used as is as water to be used in other steps of the production method of the present invention, but preferably the recovered liquid is subjected to water treatment and then used as water to be used in other steps of the production method of the present invention.

[0052] The water treatment of the recovered liquid can be carried out by a known method, for example, a coagulation sedimentation method.

[0053] (external discharge) Discharge to the outside of the system means that the recovered liquid is discharged without being reused in other steps of the production method of the present invention. The recovered liquid may be discharged directly from the system, or may be subjected to water treatment as necessary before being discharged from the system. The water discharged from the system may be discarded as waste liquid or may be reused in a method other than the production method of the present invention.

[0054] Incidentally, recycling and discharge from the system may be combined as necessary. In this case, part of the recovered liquid may be recycled and the remaining part may be discharged from the system.

[0055] <Cement raw materials> According to the method for producing a cement raw material of the present invention, it is possible to sufficiently reduce not only water-soluble alkali components but also alkali components derived from poorly water-soluble alkali-containing minerals, which have been difficult to reduce by conventional water-washing treatments, and therefore the resulting combustion ash can be suitably used as a cement raw material. Conventional combustion ash after water washing does not sufficiently reduce the alkaline components, so in order to avoid the adverse effects of the alkaline components contained in the combustion ash on cement, it was necessary to adjust the amount used to a low level when using it as a cement raw material. In contrast, the combustion ash used as a cement raw material in the present invention has a sufficiently reduced alkaline component content, so that the amount used as a cement raw material can be set to be larger than conventional amounts.

[0056] Although the embodiments of the present invention have been described above, the present invention is not limited to the above embodiments, but includes all aspects encompassed by the concept of the present invention and the scope of the claims, and can be modified in various ways within the scope of the present invention. [Example]

[0057] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples.

[0058] Example 1 A semi-sealed container (a small separable flask (volume 100 mL, made of borosilicate glass) with a cover and a vessel part connected with a clamp, unnecessary tubes blocked with a silicone stopper, and the space in the container was assembled so that it was filled with the gas described below) was charged with 5 g of combustion ash (biomass combustion ash) and 50 g of water, and the combustion ash and water were mixed with a stirring blade inserted from the center tube of the cover of the container to obtain a combustion ash dispersion. Next, a gas with a carbon dioxide concentration of 20% (carbon dioxide 20% by volume, oxygen 5% by volume, nitrogen 75% by volume) was supplied to the combustion ash dispersion from a nozzle inserted from the side tube of the cover of the container, and the combustion ash dispersion was stirred at 20 ° C. for 20 hours while bubbling through the combustion ash dispersion from the bottom of the flask at an aeration rate of 50 ml / min.

[0059] The combustion ash dispersion liquid after 20 hours of stirring was subjected to suction filtration to separate it into solid content and liquid content. The suction filtration was carried out using a suction bell and a funnel (manufactured by Kiriyama Seisakusho Co., Ltd.) with a filter paper (quantitative filter paper No. 5B, manufactured by Advantec). Further, ion-exchanged water (50 mL) was poured onto the solid content on the filter paper for washing with water. Thereafter, the solid content separated by filtration was dried at 105 °C for 20 hours using a constant temperature dryer (manufactured by Tokyo Rika Kikai Co., Ltd.) to obtain a cement raw material.

[0060] (Example 2) Example 2 obtained a cement raw material in the same manner as Example 1, except that the carbon dioxide-containing gas during bubbling into the combustion ash dispersion liquid was changed from a gas with a carbon dioxide concentration of 20% to a gas with 5% carbon dioxide (5% by volume of carbon dioxide, 5% by volume of oxygen, and 90% by volume of nitrogen).

[0061] (Example 3) Example 3 obtained a cement raw material in the same manner as Example 1, except that the carbon dioxide-containing gas during bubbling into the combustion ash dispersion liquid was changed from a gas with a carbon dioxide concentration of 20% to a gas with 10% carbon dioxide (10% by volume of carbon dioxide, 5% by volume of oxygen, and 85% by volume of nitrogen).

[0062] (Comparative Example 1) Comparative Example 1 obtained a cement raw material in the same manner as Example 1, except that no carbon dioxide-containing gas was supplied to the combustion ash dispersion liquid.

[0063] (Evaluation) The following evaluations were performed on the combustion ash before the water washing treatment and the cement raw materials (the combustion ash after the water washing treatment) prepared in the examples and comparative examples. The results are shown in FIG. 1 and Table 1.

[0064] <X-ray Diffraction Measurement> X-ray diffraction measurements were performed using a powder X-ray diffractometer (X'Pert Pro, PANalytical). The measurement conditions were CuKα X-ray source, 45 kV tube voltage, 40 mA tube current, 0.0167° step width, and 4.456° / min scan rate. The measurement samples were finely ground in advance using a grinder (Mortar Grinder RM200, Verder Scientific). The obtained X-ray diffraction profiles were used to identify each combustion ash using the crystal structure analysis software (X'Part High Score Plus version 2.1b, manufactured by PANalytical) installed in the powder X-ray diffractometer. Each mineral contained in the identified combustion ash was characterized based on the position and intensity of the diffraction lines. The results are shown in Figure 1.

[0065] <Component analysis> Component analysis was performed by energy dispersive X-ray fluorescence spectroscopy (ED-XRF). An energy dispersive X-ray fluorescence analyzer (Epsilon3, manufactured by PANalytical) was used. Measurements were performed using the Omnian program on this analyzer. The measurement samples were previously finely ground using a grinder. The results are shown in Table 1. In Table 1, Na, K, and S are shown as values ​​converted to their oxides based on the atomic weight of each analyzed element.

[0066] [Table 1]

[0067] As shown in Table 1, when the combustion ash before the water washing treatment contains alkali-containing minerals, it was confirmed that the water washing treatment alone reduces the chlorine and sulfur contents in the combustion ash, but hardly reduces the alkali components (Comparative Example 1).

[0068] In contrast, it was confirmed that washing the combustion ash with water containing carbon dioxide can reduce the alkali components even when the combustion ash before treatment contains alkali-containing minerals (Examples 1, 2, and 3). In particular, it was confirmed that the alkali components can be reduced more efficiently when the concentration of the supplied carbon dioxide gas is 10% by volume or more (Examples 1 and 3).

[0069] Furthermore, as shown in Figure 1, the diffraction peaks of labradrite and albite (2θ ≒ 28°) became smaller when the combustion ash was washed with water containing carbon dioxide. This confirmed that the alkali-containing minerals described above were decomposed and the alkali components in the combustion ash were reduced.

Claims

1. The method includes a water washing step (A) of washing biomass combustion ash containing alkali-containing minerals discharged from a biomass power plant with water containing carbon dioxide, The water washing step (A) A combustion ash dispersion preparation step (AI-1) of mixing the combustion ash with water to obtain a combustion ash dispersion; A carbon dioxide supply / stirring step (AI-2) for supplying a gas containing carbon dioxide to the combustion ash dispersion and stirring the mixture; Including, A method for cleaning biomass combustion ash, wherein the gas contains 5% by volume or more of carbon dioxide.

2. an analysis step (B) of performing a composition analysis on at least one of the solid content and the liquid content of the combustion ash dispersion that has been subjected to the water washing step (A) at least once; a water-washing continuation / termination determination step (C) for determining whether to continue or terminate the water-washing step (A) based on the analysis results obtained in the analysis step (B) and in accordance with the relationship between the solid content and the liquid content and a target cleaning composition value; 10. The method of claim 1 further comprising:

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