JP7600830B2 - Method for producing cement raw material and method for removing alkali metals from biomass combustion ash - Google Patents

Description

The present invention relates to a method for removing alkali metal components from biomass combustion ash generated by burning biomass, and a method for producing a cement raw material by removing alkali metal components from biomass combustion ash.

Wood biomass has been attracting attention as a renewable resource. Using wood biomass as fuel for power generation can reduce carbon dioxide emissions compared to using fossil fuels. The combustion ash (bottom ash, fly ash, etc.) generated by burning wood biomass contains alkaline earth metal components (mainly components containing Mg and Ca), and in recent years has been effectively used as a cement raw material, etc.

However, combustion ash derived from woody biomass (hereinafter referred to as "biomass combustion ash") contains a large amount of alkali metal components (components containing Na, K, etc.). When biomass combustion ash is used as a cement raw material, the alkali metals may have a negative effect on cement firing and cement quality. For this reason, when using biomass combustion ash, it is necessary to remove the alkali metals beforehand.

Various methods for removing alkali metals from biomass combustion ash have been investigated. Patent Document 1 discloses a method for removing alkali metals, which comprises mixing an alkali metal-containing material with a chlorine-containing material in a predetermined molar ratio and heating the mixture at 650°C to 1000°C to form an alkali metal chloride, forming a slurry of the heat-treated material and dissolving the alkali metal chloride into the liquid phase, and performing solid-liquid separation after dissolution to obtain a cake from which the alkali metal components have been removed. Patent Document 2 discloses a method for decomposing and removing poorly soluble alkali-containing minerals such as alkali feldspar and plagioclase by treating biomass combustion ash with water containing carbon dioxide.

JP 2020-157230 A JP 2020-158321 A

However, the method disclosed in Patent Document 1 did not sufficiently remove alkali metals. Therefore, if the resulting cake were to be used as a cement raw material, there was concern that the remaining alkali metals would affect the production and quality of cement.

The method disclosed in Patent Document 2 is effective in removing sparingly soluble alkali-containing minerals, but does not take into consideration the removal of alkali metals present in other forms. For this reason, even when biomass combustion ash is treated using the method disclosed in Patent Document 2, there is a problem in that alkali metals remain.

The present invention has been made in consideration of the above problems, and provides a method for efficiently removing alkali metals from biomass combustion ash. The present invention also provides a method for producing a cement raw material from biomass combustion ash by efficiently removing alkali metals from biomass combustion ash.

The inventors' investigations revealed that the amount of chlorine that contributed to the generation of alkali metal chlorides (i.e., the removal of alkali metals) estimated from the results of the examples in Patent Document 1 was low compared to the amount of chlorine-containing material added. By mixing biomass fuel ash with a chlorine-containing material and heating it, the alkaline earth metals (mainly Mg and Ca) react with the chlorine, and alkaline earth metal chlorides are also generated at the same time. However, the method in Patent Document 1 does not take into account the generation of the alkaline earth metal chlorides at all, and it was thought that as a result, the removal of alkali metals was insufficient.

As a result of investigations, the present inventors have found that the above problems can be solved by the following [1] to [10].
[1] A method for producing a cement raw material, comprising the steps of: mixing biomass combustion ash containing alkali metals and alkaline earth metals with a chlorine-containing substance to produce a mixture; heating the mixture to produce alkali metal chlorides and alkaline earth metal chlorides; mixing the heated mixture with water to produce a suspension and dissolving the alkali metal chlorides and the alkaline earth metal chlorides into the suspension; and subjecting the suspension to solid-liquid separation and recovering a cake as a cement raw material, wherein the chlorine-containing substance is added to the biomass combustion ash so that a molar equivalent ratio B/A is within a range of 0.5 to 1.5, where A is the sum of the molar equivalents of the alkali metals and the molar equivalents of the alkaline earth metals contained in the biomass combustion ash and B is the molar equivalent of chlorine in the chlorine-containing substance.
[2] The method for producing a cement raw material according to [1], wherein the biomass combustion ash and the chlorine-containing substance are mixed in a gas containing carbon dioxide.
[3] The method for producing a cement raw material according to [1] or [2], wherein the gas containing the carbon dioxide is supplied to the suspension and stirred.
[4] The method for producing a cement raw material according to any one of [1] to [3], wherein the mixture is heated at 200° C. or more and less than 650° C.
[5] The method for producing a cement raw material according to any one of [1] to [3], wherein the mixture is heated at 200° C. or more and 600° C. or less.

[6] A method for removing alkali metals from biomass combustion ash, comprising the steps of: mixing biomass combustion ash containing alkali metals and alkaline earth metals with a chlorine-containing substance to produce a mixture; heating the mixture to produce alkali metal chlorides and alkaline earth metal chlorides; mixing the heated mixture with water to produce a suspension and dissolving the alkali metal chlorides and the alkaline earth metal chlorides into the suspension; and subjecting the suspension to solid-liquid separation, wherein the chlorine-containing substance is added to the biomass combustion ash so that a molar equivalent ratio B/A is within a range of 0.5 to 1.5, where A is the sum of the molar equivalents of the alkali metals and the molar equivalents of the alkaline earth metals contained in the biomass combustion ash and B is the molar equivalent of chlorine in the chlorine-containing substance.
[7] The method for removing an alkali metal according to [6], wherein the biomass combustion ash and the chlorine-containing substance are mixed in a gas containing carbon dioxide.
[8] The method for removing an alkali metal according to [6] or [7], wherein the gas containing carbon dioxide is supplied to the suspension and stirred.
[9] The method for removing an alkali metal according to any one of [6] to [8], wherein the mixture is heated at 200° C. or higher and lower than 650° C.
[10] The method for removing an alkali metal according to any one of [6] to [8], wherein the mixture is heated at 200° C. or more and 600° C. or less.

According to the present invention, alkali metals can be efficiently removed from biomass combustion ash. The treated product (biomass combustion ash) obtained by the present invention has a sufficiently reduced concentration of alkali metals, so that when it is used as a cement raw material, the impact on the quality of cement, etc. can be suppressed.

The method for producing a cement raw material and the method for removing alkali metals from biomass combustion ash of the present invention are described in detail below.

[Method of manufacturing cement raw materials]
The method for producing a cement raw material of the present invention includes the steps of mixing biomass combustion ash containing an alkali metal and an alkaline earth metal with a chlorine-containing substance to produce a mixture, heating the mixture to produce an alkali metal chloride and an alkaline earth metal chloride, mixing the heated mixture with water to produce a suspension and dissolving the alkali metal chloride and the alkaline earth metal chloride into the water, and subjecting the suspension to solid-liquid separation and recovering a cake as a cement raw material, wherein the chlorine-containing substance is added to the biomass combustion ash so that the molar equivalent ratio B/A is within a range of 0.5 to 1.5, where A is the sum of the molar equivalents of the alkali metal and the molar equivalents of the alkaline earth metal contained in the biomass combustion ash and B is the molar equivalent of chlorine in the chlorine-containing substance.

[Method for removing alkali metals from biomass fuel ash]
The method for removing alkali metals from biomass combustion ash of the present invention includes the steps of mixing biomass combustion ash containing alkali metals and alkaline earth metals with a chlorine-containing substance to produce a mixture, heating the mixture to produce alkali metal chlorides and alkaline earth metal chlorides, mixing the heated mixture with water to produce a suspension and dissolving the alkali metal chlorides and the alkaline earth metal chlorides into the water, and subjecting the suspension to solid-liquid separation, in which the chlorine-containing substance is added to the biomass combustion ash so that the molar equivalent ratio B/A is within the range of 0.5 to 1.5, where A is the sum of the molar equivalents of the alkali metal and the molar equivalents of the alkaline earth metal contained in the biomass combustion ash, and B is the molar equivalent of chlorine in the chlorine-containing substance.

<Biomass combustion ash>
The biomass fuel ash to be treated in the present invention is bottom ash, fly ash, mixed ash, etc. obtained by incinerating woody biomass. Biomass combustion ash is discharged from power plants that use woody biomass as fuel. Examples of woody biomass include felled trees, forest residues, wood chips, construction waste, and lumber scraps.

Biomass combustion ash contains alkali metals and alkaline earth metals. The biomass combustion ash of the present invention contains mainly Na and K as alkali metals. In the present invention, "alkaline earth metals" refers to Mg, Ca, Sr, and Ba. Of these, the biomass combustion ash of the present invention contains mainly Mg and Ca as alkaline earth metals. The content of alkali metals and alkaline earth metals in the biomass combustion ash can be measured by X-ray fluorescence analysis.

Alkali metals and alkaline earth metals are contained in biomass combustion ash in the form of oxides, carbonates, sulfates, silicates, etc. Alkali metal silicates are contained as minerals such as alkali feldspars such as orthoclase and microcline, plagioclase such as albite, and feldsparoids. These minerals are poorly soluble in water. "Poorly soluble in water" means that the solubility in water is less than 1% by mass. In this specification, alkali metal-containing minerals that are contained in biomass combustion ash and are poorly soluble in water are referred to as "poorly water-soluble minerals."

The water-insoluble minerals in biomass combustion ash can be identified by X-ray diffraction analysis. The content of water-insoluble minerals in biomass combustion ash can be obtained by Rietveld analysis of the diffraction pattern obtained by X-ray diffraction analysis.

<Chlorine-containing substances>
The chlorine content in the chlorine-containing material used in the present invention is preferably 0.2% by mass or more, more preferably 0.5% by mass or more. From the viewpoint of efficient removal of alkali metals, the chlorine content in the chlorine-containing material is more preferably 4% by mass or more. The chlorine content in the chlorine-containing material can be measured by X-ray fluorescence analysis or microcoulometric oxidation method. The chlorine-containing material used in the present invention preferably has a low alkali metal content. Specifically, the alkali metal content in the chlorine-containing material is preferably 1.0% by mass or less, more preferably 0.5% by mass or less. In addition, the alkali metal content in the chlorine-containing material is preferably less than the chlorine content.

Examples of chlorine-containing substances include metal chlorides such as ferrous chloride, chlorine-containing ammonium salts such as ammonium chloride, chlorine-containing resins such as polyvinyl chloride, polyvinylidene chloride, chloroprene-based synthetic rubber, chloromethylated polystyrene, and chlorinated polyolefin, and chlorine-containing dust discharged from factory facilities. The chlorine-containing resin may be waste.
Examples of chlorine-containing dust include automobile shredder dust (ASR), paper sludge ash (PS ash), electrostatic precipitator ash (EP ash), secondary blast furnace ash, and waste solid fuel (RPF) combustion ash. By using chlorine-containing dust as a chlorine-containing material, waste can be effectively utilized and the environmental load can be reduced. Furthermore, chlorine-containing dust has the advantage that chlorine is mainly condensed on the dust surface, and therefore easily reacts with alkali metals and alkaline earth metals in biomass combustion ash. Among chlorine-containing dusts, it is particularly preferable to use automobile shredder dust, which has a high chlorine content.
The use of industrial raw materials such as metal chlorides and chlorine-containing ammonium salts as chlorine-containing substances is advantageous in that it reduces impurities mixed into the cement raw materials and suppresses the impact on cement quality.

Hereinafter, each step of the method for producing a cement raw material and the method for removing alkali metals will be described.
<Preparation process>
The components of the biomass fuel ash to be treated are analyzed in advance to measure the respective contents of alkali metals and alkaline earth metals. The respective contents of alkali metals and alkaline earth metals may be measured before the treatment described below. Alternatively, the respective contents may be measured for each lot received from the discharge facility.

The presence or absence of water-insoluble minerals and the mineral content of the biomass combustion ash to be treated may be measured in advance. Similarly, the content of each mineral may be measured before the treatment described below, or the value measured for each lot received from the discharge facility may be used.

The biomass combustion ash to be treated may be crushed in advance. By reducing the particle size of the biomass combustion ash, the contact area and contact probability with the chlorine-containing material can be increased in the mixing process described later. In addition, the chloride can be easily dissolved into water in the elution process described later. As a result, the effect of removing alkali metals from the biomass combustion ash can be improved. From the viewpoint of increasing the removal rate of alkali metals, the biomass combustion ash to be treated preferably has a particle size of 3 mm or less, more preferably 1 mm or less, and even more preferably 0.5 mm or less. In addition, from the viewpoint of suppressing dust generation and scattering, the biomass combustion ash to be treated preferably has a particle size of 0.1 mm or more. The biomass combustion ash can be crushed by a known crushing method such as a hammer crusher or a roll crusher. The particle size of the biomass combustion ash to be treated can be adjusted by using a sieve with a specified mesh size as specified in JIS Z 8801-1:2019 "Test sieves - Part 1: Metal mesh sieves" to collect the combustion ash that falls below the sieve and use it as the target for treatment.

The chlorine-containing material may be pre-adjusted in particle size in order to increase the contact area and contact probability with the biomass combustion ash and to increase the removal rate of alkali metals. The chlorine-containing material preferably has a particle size of 2 mm or less, more preferably 1 mm or less, and even more preferably 0.1 mm or less. From the viewpoint of handling, the particle size of the chlorine-containing material is preferably 0.01 mm or more. From the viewpoint of the removal efficiency of alkali metals, it is particularly preferable that the particle size of the chlorine-containing material is smaller than the particle size of the biomass combustion ash. As a method for adjusting the particle size of the chlorine-containing material, a combination of pulverization by a known method such as a hammer mill, a ball mill, or a jet mill and classification can be used. As a classification method, a sieve specified in JIS Z 8801-1:2019 "Test sieves - Part 1: Metal mesh sieves" can be used, and the chlorine-containing material below a sieve with a predetermined mesh size can be collected and used for processing.

<Mixing step>
In this step, biomass combustion ash and a chlorine-containing material are mixed to produce a mixture. In the present invention, when the total of the molar equivalents of the alkali metal and the molar equivalents of the alkaline earth metal contained in the biomass combustion ash is A and the molar equivalent of chlorine in the chlorine-containing material is B, the chlorine-containing material is added to the biomass combustion ash and mixed so that the molar equivalent ratio B/A is in the range of 0.5 to 1.5. If the molar equivalent ratio B/A is less than 0.5, the amount of chlorine contributing to the chlorination of the alkali metal is reduced, which is not preferable because the removal of the alkali metal is insufficient. If the molar equivalent ratio B/A exceeds 1.5, the amount of chlorine is relatively large, and the amount of chlorine remaining in the cake is high. The molar equivalent ratio B/A is preferably 0.60 or more, more preferably 0.70 or more, and preferably 1.4 or less, and more preferably 1.3 or less.

The means for mixing the biomass combustion ash and the chlorine-containing material is not particularly limited, and can be performed using a ball mill, a rod mill, or the like. In this process, the biomass combustion ash and the chlorine-containing material may be mixed and pulverized at the same time. In this case, the biomass combustion ash and the chlorine-containing material are preferably pulverized to a particle size of 2 mm or less, more preferably 1 mm or less. From the viewpoint of preventing scattering, etc., it is preferable that the biomass combustion ash and the chlorine-containing material are mixed and pulverized so that the particle size is 0.01 mm or more. The mixing time is not particularly limited, and can be set appropriately within a range that can be generally adopted when using the above-mentioned mixing means.

When the content of poorly water-soluble minerals in the biomass combustion ash is high (e.g., 5% by mass or more), it is preferable to mix the biomass combustion ash with the chlorine-containing material in a gas containing carbon dioxide. By mixing in a gas atmosphere containing carbon dioxide, the poorly water-soluble minerals in the biomass combustion ash can be reacted with the carbon dioxide and decomposed, and the decomposed products can be eluted into the suspension in the elution process described below. As a result, the removal rate of alkali metals can be further increased.

In this process, the term "gas containing carbon dioxide" refers to a gas having a higher carbon dioxide concentration than the atmosphere. Specifically, it is a gas containing 5% or more by volume of carbon dioxide. Taking into consideration the decomposition of poorly water-soluble minerals, the carbon dioxide concentration in the gas is more preferably 10% or more by volume, and even more preferably 15% or more by volume. There is no particular upper limit to the carbon dioxide concentration in the gas. The carbon dioxide concentration in the gas used can be set taking into consideration the content of poorly water-soluble minerals and the mixing time. There is no particular limit to the type of gas mixed with carbon dioxide in the production of the gas, but it is preferably air, oxygen, or nitrogen.

<Heating process>
In this process, a mixture of biomass combustion ash and a chlorine-containing material is heated. This process causes the alkali metals and alkaline earth metals in the biomass combustion ash to react with the chlorine in the chlorine-containing material to produce alkali metal chlorides (e.g., NaCl, KCl) and alkaline earth metal chlorides (e.g., CaCl ₂ , MgCl ₂ ). Alkali metal chlorides are more likely to be produced than alkaline earth metal chlorides. In the present invention, the molar equivalent ratio B/A is set to a range of 0.5 to 1.5, so that even biomass combustion ash containing alkaline earth metals has a sufficient amount of chlorine to react with alkali metals.
In the present invention, the biomass combustion ash may be further mixed with a chlorine-containing substance while being heated.

From the viewpoint of efficient production of alkali metal chlorides and alkaline earth metal chlorides, the heating temperature is preferably 200°C or higher. If the heating temperature is too high, the chlorine component may volatilize from the mixture during heating, causing the reactants to become lumpy. If the reactants become lumpy, it may be difficult for chlorides and the like to dissolve into the suspension in the dissolution step described below, and there is a risk that the amount of alkali metal components and chlorine components remaining in the cake may increase. From the viewpoint of suppressing the reactants from becoming lumpy, the heating temperature is preferably less than 650°C. From the viewpoint of energy saving and reducing the environmental load in the heating step (such as reducing carbon dioxide emissions), a lower heating temperature is preferable, and specifically, it is advantageous to set the heating temperature to 600°C or lower.

Heating means may be any known means, such as a rotary kiln, a fluidized bed furnace, or a tunnel furnace. The heating time may be set appropriately, taking into consideration the heating temperature, the progress of the chloride production reaction, the processing efficiency, etc.

<Elution step>
In this step, the mixture after heating (heat-treated product) is mixed with water to produce a suspension. In this step, the alkali metal chlorides and alkaline earth metal chlorides in the heat-treated product are dissolved into the suspension. Since alkali metal chlorides (e.g., NaCl, KCl) have high solubility in water, the alkali metal components can be effectively removed from the heat-treated product, which is a solid content.
In the dissolution step, it is preferable to stir the suspension. The conditions of the dissolution step are not particularly limited, but are preferably set in consideration of dissolution efficiency, energy saving, processing costs, etc. Specifically, it is preferable to set the suspension temperature in the range of 10°C to 50°C, and the dissolution time in the range of 1 hour to 80 hours. The amount of water added in this step is not particularly limited. However, in consideration of the ease of stirring the suspension and the amount of waste liquid generated in the solid-liquid separation step described later, it is preferable that the volume ratio of the heat-treated product to water (heat-treated product/water) is in the range of 1/3 to 1/10.

When the content of poorly water-soluble minerals in the biomass combustion ash is high (e.g., 5% by mass or more), it is preferable to supply a gas containing carbon dioxide to the suspension and stir it in the leaching process. By supplying a gas containing carbon dioxide to the suspension, part of the carbon dioxide dissolves in the suspension. The presence of carbon dioxide in the suspension causes the poorly water-soluble minerals in the heat-treated product to decompose and be leached into the suspension. As a result, the efficiency of removing alkali metals can be further increased.

In this process, the "gas containing carbon dioxide" refers to a gas having a higher carbon dioxide concentration than the atmosphere, specifically, a gas containing 5% or more by volume of carbon dioxide. There is no particular limit to the upper limit of the carbon dioxide concentration in the gas. The higher the carbon dioxide concentration in the gas, the more carbon dioxide dissolves in the suspension, and the more efficient the decomposition of the poorly water-soluble minerals can be. The carbon dioxide concentration in the gas is more preferably 10% by volume or more, and even more preferably 15% by volume or more. There is no particular limit to the upper limit of the carbon dioxide concentration in the gas. The carbon dioxide concentration in the gas used can be set taking into consideration the content of the poorly water-soluble minerals and the mixing time. There is no particular limit to the type of gas mixed with carbon dioxide in the production of the gas, but it is preferably air, oxygen, or nitrogen.

<Separation process, recovery process>
In this process, the suspension after the elution process is subjected to solid-liquid separation. The cake (solid phase) obtained by the separation is the treated biomass combustion ash. The cake is recovered as a cement raw material.
The separation means is not particularly limited, and a filter press, a screw press, a belt press, etc. can be used. The cake obtained by separation may be dried as necessary.

[Cement raw materials]
The cake obtained by the above separation and recovery has a reduced alkali metal content compared to the biomass combustion ash before treatment. The chlorine content in the cake is also low. Specifically, the amount of alkali in the cake (total alkali amount R ₂ O calculated in accordance with JIS R 5210: 2019 "Portland cement") is preferably 3.20 mass% or less, more preferably 2.70 mass% or less. The Na ₂ O and K ₂ O contents in the cake are measured by fluorescent X-ray analysis. The chlorine content in the cake measured by fluorescent X-ray analysis is preferably 0.10 mass% or less, more preferably 0.01 mass% or less. The total alkali amount and chlorine content are amounts that are considered to be ok in terms of cement quality when biomass combustion ash is used as a cement raw material.

The present invention will be described in more detail below with reference to examples, although the present invention is not limited to the following examples in any way.
As the biomass combustion ash, combustion ash of wood chip fuel recovered from a biomass power plant was used. The chemical composition of the biomass combustion ash used is shown in Table 1. The chemical composition of the biomass combustion ash was measured in accordance with JIS R 5204:2019 "Fluorescent X-ray analysis method for cement". In Table 1, "R ₂ O" represents the total alkali content specified in JIS R 5210:2019 "Portland cement".
The volume-based 50% particle size (D ₅₀ ) of the biomass combustion ash used was 0.27 mm. A laser diffraction particle size distribution analyzer (SALD-3100, manufactured by Shimadzu Corporation) was used to measure the particle size. Ethanol was used as the dispersion medium, and ultrasonic dispersion was performed for 10 minutes before measurement.

Ammonium chloride (special grade, manufactured by Kanto Chemical Co., Ltd.) was used as the chlorine-containing substance. The 50% particle size ( _D50 ) of the chlorine-containing substance based on volume was 0.08 mm. The particle size of the chlorine compound was measured in the same manner as the particle size measurement of the biomass combustion ash.

[Test 1]
Biomass combustion ash and ammonium chloride were weighed to have a molar equivalent ratio B/A shown in Table 2. In this example, the molar equivalent A is the sum of the molar equivalents of Na, K, Mg, and Ca in the biomass combustion ash, and was calculated from the chemical composition in Table 1. The molar equivalent B is the molar equivalent of Cl in ammonium chloride. The weighed biomass combustion ash and ammonium chloride were mixed in air for 30 minutes using a container rotation and rocking type powder mixer (Aichi Electric Co., Ltd., rocking mixer) to prepare each sample shown in Table 2.
In Table 2, the molar equivalent ratio B/A of "0.00" in Samples 1-1, 2-1, 3-1, 4-1, and 5-1 means that only biomass combustion ash is contained. Samples 1-1, 2-1, 3-1, 4-1, and 5-1 were prepared by putting only biomass combustion ash into a container rotary shaking type powder mixer and stirring for 30 minutes.

Using an electric furnace, each sample was heated for 30 minutes in an air atmosphere at the temperature (furnace temperature) shown in Table 2. In Table 2, Samples 1-1 to 1-5 were stored in an electric furnace (air atmosphere) set at 20° C. for 30 minutes and were not heated.
The treated material was removed from the electric furnace, and visually judged whether it was lumped or not. "Lump" refers to treated material with a diameter of 5 mm or more. The treated material was spread in a 625 mm x 410 mm stainless steel container to a thickness of about 1 cm, and the number of lumps was measured while checking the size of the lumps with a vernier caliper. In Table 2, "Yes" means that 10 or more lumped treated materials meeting the above diameter were confirmed. "No" means that no lumped treated materials were confirmed, or that there were less than 10 lumped treated materials. The judgment results are shown in Table 2.

The treated material was poured into 5 times the amount of water (20° C.) (treated material/water=1/5 (volume ratio)) and stirred for 24 hours to produce a suspension. Note that no gas was introduced into each suspension during stirring.
Thereafter, each suspension was suction filtered to separate it into a cake and a filtrate. The obtained cake was washed with a small amount of water. As the chemical composition of the cake after washing, the contents of Na ₂ O, K ₂ O, MgO, CaO and Cl were measured by fluorescent X-ray analysis. R ₂ O was calculated from the obtained contents of Na ₂ O and K ₂ O. The results of the component analysis are shown in Table 2.

In samples 2-1 to 2-5, the Na ₂ O and K ₂ O contents were reduced by mixing with ammonium chloride (chlorine-containing material) and then heating at 200° C., compared to sample 2-1 (B/A=0.00) which was not mixed, resulting in a lower R ₂ O. On the other hand, sample 2-5 (B/A=2.00) had a higher amount of chlorine remaining in the cake compared to samples 2-2 to 2-4 (B/A=0.50 to 1.50). From these results, samples 2-2 to 2-4 were able to effectively remove alkali metals from biomass combustion ash and also reduce the chlorine concentration remaining in the biomass combustion ash after treatment.
The same tendency as above was observed in Samples 3-1 to 3-5 (heating temperature 500° C.) and Samples 4-1 to 4-5 (heating temperature 600° C.).
In samples 5-2 to 5-5 (heating temperature 700°C), there was a tendency for R ₂ O to decrease when mixed with ammonium chloride (chlorine-containing substance) and heated. However, R ₂ O was higher than in samples heated at lower temperatures. Also, in samples 5-2 to 5-5, clumping of the treated products due to heating was confirmed. Therefore, even in samples 5-2 to 5-4, in which the molar equivalent ratio B/A was in the range of 0.5 to 1.5, the amount of chlorine remaining in the cake was higher than in samples heated at lower temperatures.

When treated at a temperature of 20° C. (when heating was not performed), Sample 1-1, which was not mixed with ammonium chloride (chlorine-containing substance), and Samples 1-2 to 1-5, which were mixed with ammonium chloride, had almost the same Na ₂ O and K ₂ O contents in the cake. All of Samples 1-1 to 1-5 had R ₂ O exceeding 3.20 mass%.

[Test 2]
Biomass combustion ash and ammonium chloride were weighed out so that the molar equivalent ratio B/A was 0.50.
Samples 6-1 to 6-3 and Samples 8-1 to 8-2 were prepared by the following process. Weighed amounts of biomass combustion ash and ammonium chloride were placed in a stainless steel tray and placed in a carbonation acceleration test device (MIT-639 model, manufactured by Marui Co., Ltd.). Gas (mixture of air and carbon dioxide) with the carbon dioxide (CO ₂ ) concentration shown in Table 3 was introduced into the device. An operator stirred the contents of the stainless steel tray every 10 minutes, and the contents were exposed to the gas for a total of 60 minutes.
Samples 7-1 to 7-3 were prepared by mixing weighed amounts of biomass combustion ash and ammonium chloride in air for 30 minutes using a container rotation and rocking type powder mixer (Aichi Electric Co., Ltd., Rocking Mixer). In Table 3, the "carbon dioxide (CO ₂ ) concentration" when the mixing process was carried out in air is indicated as "0 volume %."

Each sample was heated in an electric furnace at 200° C. (furnace temperature) in air for 30 minutes.
Each heat-treated product removed from the electric furnace was placed in five times the amount of water (20°C) (treated product/water = 5 (volume ratio)). Samples 7-1 to 7-3 and Samples 8-1 to 8-2 were stirred for 24 hours while bubbling with gas (mixture of air and carbon dioxide) having the carbon dioxide concentration shown in Table 3 to form a suspension. Samples 6-1 to 6-3 were stirred for 24 hours without bubbling to form a suspension.

Thereafter, each suspension was suction filtered to separate it into a cake and a filtrate. The obtained cake was washed with a small amount of water. As the chemical composition of the cake after washing, the contents of Na ₂ O, K ₂ O, MgO, CaO and Cl were measured by fluorescent X-ray analysis. R ₂ O was calculated from the obtained contents of Na ₂ O and K ₂ O. The results of the component analysis are shown in Table 3. For comparison, the results of the component analysis of sample 2-2 are also shown in Table 3.
Further, the diffraction pattern of each cake was measured using an X-ray diffractometer (X'Part Powder, manufactured by PANalytical Corporation).

In the samples 6-1 to 6-3 in which a gas containing carbon dioxide was introduced in the mixing step, the R ₂ O was reduced compared to the sample 2-2 in which the mixture was mixed in the air. In addition, in the samples 7-1 to 7-3 in which a gas containing carbon dioxide was introduced in the elution step, the R ₂ O was reduced compared to the sample 2-2. It was confirmed that the X-ray diffraction peak (2θ=27.9°) intensity of albite in all of the samples 6-1 to 6-3 and 7-1 to 7-3 was lower than that of the sample 2-2. This result indicates that the content of albite in the samples 6-1 to 6-3 and 7-1 to 7-3 is lower than that of the sample 2-2. From this, it can be said that the efficiency of removing alkali metals from biomass combustion ash was improved because albite, a poorly water-soluble mineral, was decomposed by performing the treatment while introducing a gas containing carbon dioxide in the mixing step or the elution step.
As shown in samples 8-1 and 8-2, by performing the treatment while introducing a gas containing carbon dioxide in both the mixing step and the elution step, R ₂ O was further reduced compared to samples 6-1 to 6-3 and samples 7-1 to 7-3. From this result, it can be said that the efficiency of removing alkali metals from biomass combustion ash was further improved by performing the treatment while introducing a gas containing carbon dioxide in both the mixing step and the elution step.

Claims (10)

mixing biomass combustion ash containing alkali metals and alkaline earth metals with a chlorine-containing material to produce a mixture;
heating the mixture to produce alkali metal chlorides and alkaline earth metal chlorides;
mixing the heated mixture with water to form a suspension, and dissolving the alkali metal chloride and the alkaline earth metal chloride into the suspension;
and subjecting the suspension to solid-liquid separation and recovering a cake as a cement raw material.
a molar equivalent ratio B/A of 0.5 or more and 1.5 or less, wherein A is the sum of the molar equivalents of the alkali metal and the molar equivalents of the alkaline earth metal contained in the biomass combustion ash and B is the molar equivalent of chlorine in the chlorine-containing substance. The method for producing a cement raw material according to claim 1, wherein the biomass combustion ash and the chlorine-containing material are mixed in a gas containing carbon dioxide. 2. The method for producing a cement raw material according to claim 1 , wherein a gas containing carbon dioxide is supplied to the suspension and stirred. The method for producing a cement raw material according to any one of claims 1 to 3, wherein the mixture is heated at 200°C or higher and lower than 650°C. The method for producing a cement raw material according to any one of claims 1 to 3, wherein the mixture is heated at 200°C or more and 600°C or less. mixing biomass combustion ash containing alkali metals and alkaline earth metals with a chlorine-containing material to produce a mixture;
heating the mixture to produce alkali metal chlorides and alkaline earth metal chlorides;
mixing the heated mixture with water to form a suspension, and dissolving the alkali metal chloride and the alkaline earth metal chloride into the suspension;
and subjecting the suspension to solid-liquid separation,
a molar equivalent ratio B/A of 0.5 or more and 1.5 or less, the molar equivalent ratio being ... The method for removing alkali metals according to claim 6, wherein the biomass combustion ash and the chlorine-containing material are mixed in a gas containing carbon dioxide. 7. The method for removing an alkali metal according to claim 6 , wherein a gas containing carbon dioxide is supplied to the suspension and stirred. The method for removing alkali metals according to any one of claims 6 to 8, wherein the mixture is heated at 200°C or higher but lower than 650°C. The method for removing alkali metals according to any one of claims 6 to 8, wherein the mixture is heated at 200°C or higher and 600°C or lower.