Method for producing cement raw material and method for removing alkali metals from biomass combustion ash

Abstract

To provide a method for efficiently removing alkali metals from biomass combustion ash and producing cement raw materials.SOLUTION: A method for producing cement raw materials includes the steps of: mixing a biomass combustion ash containing alkali metals and alkaline earth metals with a chlorine content to form a mixture; heating the mixture to generate alkali metal chloride and alkaline earth metal chloride; mixing the heated mixture with water to generate a suspension and eluting the alkali metal chloride and the alkaline earth metal chloride into the suspension; and solid / liquid-separating the suspension to recover a cake as cement raw materials. When the sum of the molar equivalent of the alkali metals and the molar equivalent of the alkaline earth metals contained in the biomass combustion ash is A and the molar equivalent of chlorine in the chlorine content is B, the chlorine content is added to the biomass combustion ash so that a molar equivalent ratio B / A is within a range of 0.5 or more and 1.5 or less.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a method for removing alkali metal components from biomass combustion ash generated by the combustion of biomass, and a method for producing a cement raw material by removing alkali metal components from biomass combustion ash. [Background technology]

[0002] Woody biomass has been attracting attention as a renewable resource. By using woody biomass as fuel for power generation, carbon dioxide emissions can be reduced compared to using fossil fuels. Combustion ash (bottom ash, fly ash, etc.) generated by burning woody biomass contains alkaline earth metal components (mainly components containing Mg and Ca), so in recent years it has been effectively used as a cement raw material, etc.

[0003] However, combustion ash derived from woody biomass (hereinafter referred to as "biomass combustion ash") contains a large amount of alkali metal components (components including 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.

[0004] Various methods for removing alkali metals from biomass combustion ash have been studied. Patent Document 1 discloses a method for removing alkali metals, which comprises mixing an alkali metal-containing material and 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 eluting the alkali metal chloride into a liquid phase, and performing solid-liquid separation after elution 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. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2020-157230 A [Patent Document 2] JP 2020-158321 A Summary of the Invention [Problem to be solved by the invention]

[0006] However, the method disclosed in Patent Document 1 does not sufficiently remove alkali metals. Therefore, when the resulting cake is used as a cement raw material, there is a concern that the remaining alkali metals may affect the production and quality of cement.

[0007] 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. Therefore, even when biomass combustion ash is treated using the method disclosed in Patent Document 2, there is a problem in that alkali metals remain.

[0008] The present invention has been made in view 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. [Means for solving the problem]

[0009] The inventors have studied and found that the amount of chlorine that contributed to the generation of alkali metal chlorides (i.e., removal of alkali metals) estimated from the results of the examples in Patent Document 1 is low compared to the amount of chlorine-containing material added. By mixing and heating biomass fuel ash and chlorine-containing material, alkaline earth metals (mainly Mg and Ca) react with chlorine, and alkaline earth metal chlorides are also generated at the same time. However, since the method in Patent Document 1 does not take into account the generation of the alkaline earth metal chlorides at all, it was thought that the removal of alkali metals was insufficient as a result.

[0010] 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 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 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], further comprising supplying the gas containing carbon dioxide to the suspension and stirring the suspension. [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 higher and lower 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.

[0011] [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 the molar equivalent ratio B / A is in the 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 alkali metals described in [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 higher and 600° C. or lower. Effect of the Invention

[0012] According to the present invention, it is possible to efficiently remove alkali metals from biomass combustion ash. The treated product (biomass combustion ash) obtained according to the present invention has a sufficiently reduced concentration of alkali metals, so that when the treated product is used as a cement raw material, the impact on the quality of cement can be suppressed. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] The method for producing a cement raw material and the method for removing alkali metals from biomass combustion ash of the present invention will be described in detail below.

[0014] [Manufacturing methods of cement raw materials] The method for producing a cement raw material 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 to recover a cake as a cement raw material, in which 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 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.

[0015] [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 this method, 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 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.

[0016] <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.

[0017] Biomass combustion ash contains alkali metals and alkaline earth metals. The biomass combustion ash of the present invention mainly contains Na and K as alkali metals. In the present invention, "alkaline earth metal" refers to Mg, Ca, Sr, and Ba. Of these, the biomass combustion ash of the present invention mainly contains 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 fluorescent X-ray analysis.

[0018] 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 feldspar. These minerals are poorly soluble in water. "Poorly soluble in water" means that the solubility in water is less than 1 mass%. In this specification, an alkali metal-containing mineral that is contained in biomass combustion ash and is poorly soluble in water is referred to as a "poorly water-soluble mineral."

[0019] 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 refinement of the diffraction pattern obtained by X-ray diffraction analysis.

[0020] <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.

[0021] 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-derived 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.

[0022] Each step of the method for producing a cement raw material and the method for removing alkali metals will be described below. <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.

[0023] In addition, the presence or absence of poorly water-soluble minerals and the content of minerals may be measured in advance for the biomass combustion ash to be treated. The content of each mineral may be similarly measured before the treatment described below, or the value measured for each lot received from the discharge facility may be used.

[0024] 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, chlorides 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 predetermined mesh size specified in JIS Z 8801-1:2019 "Test sieves - Part 1: Metal mesh sieves" to collect the combustion ash under the sieve and use it as the treatment target.

[0025] 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 under a sieve with a predetermined mesh size can be collected and used for processing.

[0026] <Mixing process> In this step, biomass combustion ash and a chlorine-containing material are mixed to produce a mixture. In the present invention, the chlorine-containing material is added to and mixed with 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 total molar equivalent of the alkali metal and the molar equivalent of the alkaline earth metal contained in the biomass combustion ash, and B is the molar equivalent of chlorine in the chlorine-containing material. 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 undesirable 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 more preferably 1.4 or less, and more preferably 1.3 or less.

[0027] The mixing means of 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 step, 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, it is preferable that the biomass combustion ash and the chlorine-containing material are mixed and pulverized to a particle size of 0.01 mm or more. The mixing time is not particularly limited, and can be appropriately set within a range that can be generally adopted when using the above-mentioned mixing means.

[0028] When the content of poorly water-soluble minerals in the biomass combustion ash is high (for example, 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 are reacted with carbon dioxide and decomposed, and the decomposed products can be eluted into the suspension in the elution step described below. As a result, the removal rate of alkali metals can be further increased.

[0029] In this process, the "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. In consideration of 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 in consideration of 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.

[0030] <Heating process> In this process, a mixture of biomass combustion ash and a chlorine-containing material is heated. In this process, the alkali metals and alkaline earth metals in the biomass combustion ash 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., CaCl2, MgCl2). Alkali metal chlorides are more easily 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.

[0031] 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 reaction product to become lumpy. If the reaction product becomes lumpy, chlorides and the like are less likely to be eluted into the suspension in the elution step described below, and there is a risk that the amount of residual alkali metal components and chlorine components remaining in the cake will increase. From the viewpoint of suppressing the reaction product 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), the heating temperature is preferably lower, and specifically, it is advantageous to set the heating temperature to 600°C or lower.

[0032] As the heating means, known means such as a rotary kiln, a fluidized bed furnace, a tunnel furnace, etc. can be used. The heating time can be appropriately set in consideration of the heating temperature, the progress of the chloride production reaction, the treatment efficiency, etc.

[0033] <Elution process> 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 elution step, it is preferable to stir the suspension. The conditions for the elution step are not particularly limited, but are preferably set in consideration of elution efficiency, energy saving, processing costs, and the like. Specifically, it is preferable to set the suspension temperature in the range of 10°C to 50°C and the elution 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 below, 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.

[0034] When the content of poorly water-soluble minerals in the biomass combustion ash is high (for example, 5% by mass or more), it is preferable to supply a gas containing carbon dioxide to the suspension and stir it in the elution step. By supplying a gas containing carbon dioxide to the suspension, a 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 eluted into the suspension. As a result, the efficiency of removing alkali metals can be further increased.

[0035] The "gas containing carbon dioxide" in this process is 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 mineral 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 in consideration of the content of the poorly water-soluble mineral 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.

[0036] <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 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.

[0037] [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 R2O 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 Na2O and K2O 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 acceptable in terms of cement quality when biomass combustion ash is used as a cement raw material. EXAMPLES

[0038] 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. The biomass combustion ash used was the combustion ash of wood chip fuel recovered from a biomass power plant. 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 "X-ray fluorescence analysis method for cement." In Table 1, "R2O" represents the total alkali content as specified in JIS R 5210:2019 "Portland cement." The 50% particle size (D) of the biomass combustion ash used was 50 ) 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.

[0039] [Table 1]

[0040] Ammonium chloride (special grade, manufactured by Kanto Chemical Co., Ltd.) was used as the chlorine-containing substance. 50 ) was 0.08 mm. The particle size of the chlorine compounds was measured in the same manner as for the particle size measurement of the biomass combustion ash.

[0041] [Test 1] Biomass combustion ash and ammonium chloride were weighed out to obtain the 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 rotation and shaking type powder mixer and mixing for 30 minutes.

[0042] Using an electric furnace, each sample was heated in an air atmosphere for 30 minutes at the temperature (furnace temperature) shown in Table 2. In addition, 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 had formed agglomerates or not. "Agglomerates" refers to treated material with a diameter of 5 mm or more. The treated material was spread to a thickness of about 1 cm in a 625 mm x 410 mm stainless steel container, and the number of agglomerates was counted while checking the size of the agglomerates with a vernier caliper. In Table 2, "Yes" means that 10 or more agglomerated treated materials meeting the above diameter were confirmed. "No" means that no agglomerated treated materials were confirmed, or that there were less than 10 agglomerated treated materials. The judgment results are shown in Table 2.

[0043] 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 form a suspension. Note that no gas was introduced into each suspension during stirring. Thereafter, each suspension was suction filtered to separate the cake and the filtrate. The obtained cake was washed with a small amount of water. The contents of Na2O, K2O, MgO, CaO and Cl were measured as the chemical composition of the washed cake by X-ray fluorescence analysis. R2O was calculated from the obtained contents of Na2O and K2O. The results of the component analysis are shown in Table 2.

[0044] [Table 2]

[0045] In samples 2-1 to 2-5, the Na2O and K2O 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 R2O. 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 lower 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 the R2O to decrease when mixed with ammonium chloride (chlorine-containing material) and heated. However, the R2O was higher than in samples heated at lower temperatures. Also, in samples 5-2 to 5-5, clumping of the treated material was confirmed by heating. Therefore, even in samples 5-2 to 5-4, which have a molar equivalent ratio B / A 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.

[0046] When treated at 20°C (without heating), the Na2O and K2O contents in the cakes of Sample 1-1, which was not mixed with ammonium chloride (chlorine-containing material), were almost the same as those of Samples 1-2 to 1-5, which were mixed with ammonium chloride. All of Samples 1-1 to 1-5 had an R2O content exceeding 3.20% by mass.

[0047] [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 (CO2) 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 (CO2) concentration" when the mixing process was carried out in air is indicated as "0 volume %."

[0048] 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.

[0049] 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. The contents of Na2O, K2O, MgO, CaO and Cl were measured as the chemical composition of the washed cake by fluorescent X-ray analysis. R2O was calculated from the obtained contents of Na2O and K2O. 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. In addition, the diffraction pattern of each cake was measured using an X-ray diffractometer (X'Part Powder, manufactured by PANalytical Corporation).

[0050] [Table 3]

[0051] Samples 6-1 to 6-3, which were mixed in the mixing process with a gas containing carbon dioxide, had a lower R2O than Sample 2-2, which was mixed in the air. Samples 7-1 to 7-3, which were mixed in the elution process with a gas containing carbon dioxide, had a lower R2O than Sample 2-2. It was confirmed that the X-ray diffraction peak (2θ=27.9°) intensity of albite for Samples 6-1 to 6-3 and 7-1 to 7-3 was lower than that for Sample 2-2. This result indicates that Samples 6-1 to 6-3 and 7-1 to 7-3 have a lower albite content than Sample 2-2. From this, it can be said that the introduction of a gas containing carbon dioxide during the mixing process or elution process decomposed albite, which is a poorly water-soluble mineral, and thus improved the removal efficiency of alkali metals from biomass combustion ash. As shown in Samples 8-1 to 8-2, by performing treatment while introducing a gas containing carbon dioxide in both the mixing step and the elution step, RO 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 by performing treatment while introducing a gas containing carbon dioxide in both the mixing step and the elution step, the removal efficiency of alkali metals from biomass combustion ash was further improved.

Claims

1. 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.

2. The method for producing a cement raw material according to claim 1, wherein the biomass combustion ash and the chlorine-containing substance are mixed in a gas containing carbon dioxide.

3. A method for producing a cement raw material as described in claim 1, wherein a gas containing carbon dioxide is supplied to the suspension and stirred.

4. 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.

5. 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.

6. 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 ...

7. 7. The method for removing an alkali metal according to claim 6, wherein the biomass combustion ash and the chlorine-containing substance are mixed in a gas containing carbon dioxide.

8. The method for removing alkali metals described in claim 6, wherein a gas containing carbon dioxide is supplied to the suspension and stirred.

9. The method for removing an alkali metal according to any one of claims 6 to 8, wherein the mixture is heated at a temperature of 200°C or higher and lower than 650°C.

10. The method for removing an alkali metal according to any one of claims 6 to 8, wherein the mixture is heated at 200°C or higher and 600°C or lower.

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