Alkali metal removal method

Abstract

To provide an alkali metal removal method that efficiently removes alkali metal from fly ash of woody biomass to effectively utilize the alkali metal as raw material for cement.SOLUTION: The present invention provides an alkali metal removal method that removes alkali metal from fly ash of burnt woody biomass, including the steps of (a) blending the fly ash with calcium source and chlorine source, temporarily or sequentially and (b) heating a mixture whose hydraulic modulus has been adjusted from the fly ash in the step (a) to give a heated product.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a method for removing alkali metals, and particularly to a method for removing alkali metals for effectively utilizing the combustion ash of lignocellulosic biomass as a cement raw material or the like.

Background Art

[0002] Regarding lignocellulosic biomass such as tree trunks, branches, wood chips, sawdust, bark, wood pellets, PKS (palm kernel shell), and construction waste, in parallel with the technological development of using them as fuels for power generation boilers and the like, the development of effective utilization technologies for the combustion ash generated by the combustion of lignocellulosic biomass (hereinafter sometimes referred to as "lignocellulosic biomass ash") has also been promoted.

[0003] Lignocellulosic biomass ash is characterized by a high content of alkali metals, particularly potassium, compared with, for example, coal ash and waste incineration ash. Therefore, for example, when applying the cement raw material technology that enables the effective utilization of a large amount of coal ash and waste incineration ash to lignocellulosic biomass ash, it is necessary to remove alkali metals from the lignocellulosic biomass ash because cement avoids alkali metal components. Furthermore, if alkali metals can be removed from the fly ash of lignocellulosic biomass ash, it will be possible to develop applications such as using the fly ash of lignocellulosic biomass ash as a concrete admixture or a cement admixture, as is the case with coal ash (fly ash).

[0004] As a technology for removing alkali metal components from lignocellulosic biomass ash, for example, Patent Document 1 below discloses a combustion apparatus and a combustion ash treatment method in which lignocellulosic biomass ash (fly ash) collected by a bag filter is classified at a predetermined classification point to separate and recover fine powder combustion ash with a high potassium concentration.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] However, since the fly ash of woody biomass ash contains alkali metals in ash of all particle sizes, simply removing the alkali metals present in the fine powder combustion ash is insufficient for use as a cement raw material or the like.

[0007] In view of the above problems, an object of the present invention is to provide a method for efficiently removing alkali metals from fly ash of woody biomass ash (hereinafter, sometimes referred to as "biomass ash") and effectively using it as a cement raw material or the like.

Means for Solving the Problems

[0008] As a result of intensive research, the present inventors have found that there are two types of alkali metals contained in biomass ash: water-soluble ones and those hardly soluble in water (hereinafter simply referred to as "hardly soluble"), and that this hardly soluble alkali metal can be changed into a water-soluble salt (alkali metal chloride) by heating with a chlorine source (so-called "chloridizing roasting").

[0009] Furthermore, as a result of repeated intensive research, the present inventors have found that by heating the biomass ash together with a chlorine source in a state where a calcium source is mixed, rather than simply heating the biomass ash together with a chlorine source, the removal rate of alkali metals can be further increased.

[0010] That is, the present invention is a method for removing alkali metals from fly ash of combustion ash of woody biomass, a step (a) of mixing a calcium source and a chlorine source with the fly ash at once or sequentially, and a step (b) of heating the mixture in a state where the hydraulicity is adjusted from the fly ash by the step (a) to obtain a heat-treated product.

[0011] The inventors of the present invention have considered the reasons why the removal rate of alkali metals can be further increased by mixing a calcium source with fly ash as follows.

[0012] In the process of heating a mixture of a chlorine source and biomass ash, melting and sintering of the biomass ash may occur depending on the heating temperature. Also, the water-soluble alkali metal chlorides (such as KCl, etc.) generated in this process will also be in a molten state.

[0013] After the heating process is completed, as the temperature decreases, the molten biomass ash solidifies into a solid. At this time, the molten alkali metal chloride aggregates and crystallizes inside the molten biomass ash due to differences in surface tension, etc. As a result, the biomass ash after cooling will be in a state of partially containing water-soluble alkali metal chloride. It is difficult to effectively remove the alkali metal chloride encapsulated in the biomass ash even by performing a water washing treatment.

[0014] In contrast, according to the above method, in the stage prior to the heating step (b), a chlorine source and a calcium source are mixed with the biomass ash (fly ash). As a result, in the heating step (b), Ca contained in the calcium source reacts with Si, etc. contained in the biomass ash to form a Ca-containing mineral. Examples of such Ca-containing minerals include CaSiO 3 (Wollastonite), CaAl 2 Si 2 O 8 (Anorthite), or Ca 2 Al 2 SiO 7 (Gehlenite), etc. These Ca-containing minerals have a higher melting point than the biomass ash.

[0015] Therefore, at least a part of the biomass ash is changed into a Ca-containing mineral by the heating step (b), so that the amount of the biomass ash to be melted and sintered is reduced. As a result, the amount of the molten alkali metal salt taken into the inside of the biomass ash can be reduced. For this reason, for example, by performing a water washing treatment to dissolve it in water, a residue with a reduced alkali metal content can be obtained. Also, the alkali metal salt may be removed (separated) from the heat-treated product by a method other than the water washing treatment. Since the residue from which the alkali metal salt has been removed has a significantly lower alkali metal content compared to the biomass ash (fly ash) before treatment, it can be effectively used as a cement raw material to replace coal ash.

[0016] Note that by heating in a state where a calcium source and a chlorine source are mixed, a part of Cl contained in the chlorine source reacts with Ca contained in the calcium source to be fixed as calcium chloride (CaCl 2 ). The volatilization rate of CaCl 2 is lower than that of Cl 2 or HCl. As a result, an effect of suppressing the amount of Cl contained in the introduced chlorine source that volatilizes without contributing to the reaction with the alkali metal contained in the biomass ash can also be obtained.

[0017] The alkali metal removal method may also include a step (c) of washing the heat-treated product obtained in the step (b) with water.

[0018] As described above, since the heat-treated product obtained in the step (b) contains a water-soluble alkali metal substance, it is eluted into the liquid phase by the water washing step (c). Therefore, for example, after passing through a solid-liquid separation step and removing the liquid containing the alkali metal, the residue (cake) obtained has a reduced alkali metal content compared to the biomass ash before treatment.

[0019] The step (a) may include a step of introducing the calcium source in an amount adjusted so that the hydraulicity of the mixture is 0.3 to 0.6.

[0020] In this specification, the hydraulicity may be defined by the following formula based on the composition ratios of CaO, SiO 2 , Al 2 O 3 , Fe 2 O 3 contained in the mixture. Hydraulicity (HM) = (CaO [%]) / {SiO 2 [%] + Al 2 O 3 [%] + Fe 2 O 3 [%]} Note that as the composition ratio of the mixture, the value obtained by the fluorescent X-ray analysis method (XRF) can be adopted.

[0021] By introducing a calcium source so that the hydraulicity is 0.3 or more, the removal rate of the alkali metal contained in the biomass ash can be sufficiently increased. On the other hand, when the calcium source is introduced to such an extent that the hydraulicity exceeds 0.6, the amount of biomass ash that can be heated at one time in the heating step (b) decreases. This is because there is a limit to the amount of powder that can be introduced into the combustion furnace for performing the heating step (b) at one time. That is, in the same time, the amount of biomass ash capable of removing the alkali metal decreases, so the processing speed decreases. From such a viewpoint, in the step (a), it is preferable to introduce a calcium source so that the hydraulicity of the mixture is 0.3 to 0.6.

[0022] The calcium source used in the step (a) may include one or more belonging to the group consisting of industrial raw materials and waste containing at least one of CaCO 3 and CaO.

[0023] Examples of such industrial raw materials include limestone, quicklime, and slaked lime. Examples of the waste include paper sludge, paper sludge incineration ash, and sewage sludge incineration ash.

[0024] The step (b) may be a step of heating at a temperature of 800°C to 1300°C.

[0025] When the heating step (b) is carried out at a temperature below 800 °C, it may be difficult to change the alkali metal into an alkali metal salt due to the low temperature. Also, when the heating temperature exceeds 1300 °C, the chlorine contained in the chlorine-containing substance is likely to volatilize, and the contact amount with the alkali metal decreases, which may reduce the reactivity.

[0026] The chlorine source used in the step (a) may include waste plastics and combustible waste mixed with inorganic compound chlorine.

[0027] According to the above method, waste with a high chlorine content and poor recyclability can be effectively utilized for removing alkali metals contained in biomass ash.

[0028] The chlorine source used in the step (a) may have a size of 80 mm or less.

[0029] By performing the heating step (b) in a state where the chlorine source of the above size is mixed with the biomass ash, the insoluble alkali metal contained in the biomass ash can be changed into a water-soluble salt at a high rate. When the size of the chlorine source is larger than 80 mm, sufficient volatilization of chlorine from the chlorine source may not occur during the execution of the heating step (b), and chlorination roasting of the biomass ash may be difficult to occur. Note that the size of this chlorine source is the size of the sieve opening, and a size of 80 mm or less means passing through a sieve with a 80 mm opening.

[0030] The step (a) may include a step of introducing the chlorine source in an amount adjusted so that the ratio (M2 / M1) of the molar amount (M2) of all chlorine in the chlorine source to the molar amount (M1) of all alkali metal components in the fly ash is within the range of 1 to 4.

[0031] According to the above method, most of the insoluble alkali metals contained in the biomass ash can be efficiently changed into water-soluble salts. When the value of M2 / M1 exceeds 4, chlorine that does not contribute to chlorination roasting remains, which may waste some chlorine sources. Also, when the value of M2 / M1 is less than 1, the heat-treated product obtained after the completion of the heating step (b) may still contain a certain amount of insoluble alkali metals.

[0032] The alkali metal removal method further includes a step (d) of classifying the fly ash into fine powder and coarse powder. The step (a) may be a step of mixing the calcium source and the chlorine source with respect to the coarse powder after the fly ash is classified by the step (d).

[0033] By performing the step (d), the biomass ash can be separated into fine powder containing a large amount of water-soluble alkali metals and coarse powder containing a large amount of insoluble alkali metals. Therefore, after mixing a calcium source and a chlorine source with respect to this coarse powder and then performing the heating step (b), alkali metals can be removed effectively and efficiently.

[0034] The step (d) may be a step of classifying with a classification point of 5 μm to 90 μm.

[0035] According to the above method, even for biomass ashes from different emission sources, fine powder corresponding to 20% to 50% by mass of the total amount can be ensured for most biomass ashes. In other words, the coarse powder to be subjected to the heat treatment according to the step (b) corresponds to 50% to 80% by mass of the total amount of the biomass ash. That is, since it is not necessary to heat the entire biomass ash, alkali metals can be removed with high heating efficiency.

[0036] The step (c) may be a step of washing the fine powder after the fly ash is classified by the step (d) in addition to the heat-treated product obtained in the step (b).

[0037] According to the above method, both the water-soluble alkali metal contained in a large amount on the fine powder side and the water-soluble alkali metal salt contained on the coarse powder side after the step (b) can be dissolved in water and removed by the water washing treatment according to the step (c).

[0038] The alkali metal removal method further includes a step (e) of pulverizing the coarse powder obtained by the step (d) to obtain a coarsely pulverized product. The step (a) may be a step of mixing the calcium source and the chlorine source with respect to the coarsely pulverized product obtained by the step (e).

[0039] It is assumed that the coarsely pulverized product after classification contains the water-insoluble alkali metal evenly throughout. By performing the pulverization step (e) on the coarsely pulverized product obtained by the classification step (d) for biomass ash as in the above method, the exposed area of the alkali metal increases. Therefore, by performing the heating step (b) after mixing the chlorine source and the calcium source with respect to the coarsely pulverized product (coarsely pulverized material) pulverized in this way, the reactivity with the chlorine contained in the chlorine source is improved, and it can be changed to alkali metal chloride with higher efficiency.

[0040] The step (e) is preferably a step of pulverizing so that the Blaine specific surface area of the coarsely pulverized product is 7,000 cm 2 / g or less. This Blaine specific surface area is more preferably 1,000 cm 2 / g to 7,000 cm 2 / g.

[0041] The step (b) may be a step of heating in an air atmosphere or may be a step of heating in an atmosphere with an oxygen concentration of 10% or less.

[0042] By performing the heating step (b) under a low oxygen concentration, the volatilization of the chlorine contained in the chlorine source is suppressed from proceeding too much, and the alkali metal contained in the biomass ash is more easily changed to a water-soluble alkali metal chloride.

Advantages of the Invention

[0043] According to the present invention, an alkali metal can be efficiently removed from biomass ash. As a result, for example, the biomass ash can be utilized as a cement raw material or the like.

Brief Description of the Drawings

[0044]

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Embodiments for Carrying Out the Invention

[0045] The biomass ash to which the present invention is applied contains alkali metals (Na, K) as chlorides, carbonates, sulfates, or silicate glass, etc., and contains about 3 mass% to 50 mass% in terms of R 2 O conversion (R 2 O = Na 2 O + 0.658 × K 2 O). Among these alkali metals, chlorides, carbonates, and sulfates are water-soluble, and silicate glass is hardly soluble.

[0046] According to the alkali metal removal method of the present invention, the concentration of alkali metals contained in the biomass ash can be reduced to 2.0 mass% or less, more typically 1.5 mass% or less in terms of the above R 2 O conversion, so that the biomass ash can be effectively utilized as a cement raw material or the like. The concentration of alkali metals in the biomass ash can be measured by a well-known method. For example, the FP method using a fluorescent X-ray device or wet analysis (acid decomposition - ICP emission spectrometry) is preferably exemplified.

[0047] Hereinafter, the present invention will be described more specifically with reference to the drawings. However, the present invention is not limited to the embodiments described together with these drawings.

[0048] [First Embodiment] The first embodiment of the alkali metal removal method according to the present invention will be described.

[0049] FIG. 1 is a flowchart schematically showing the procedure of the alkali metal removal method of the present embodiment. Further, FIG. 2 is a block diagram schematically showing an example of an apparatus (hereinafter referred to as "alkali metal removal apparatus") for carrying out the alkali metal removal method shown in FIG. 1. In FIG. 2, the flows of solids such as biomass ash and liquids such as water are shown by solid lines with arrows, and the gas flow is shown by a broken line with an arrow. The same applies to each of the figures described later.

[0050] As shown in FIG. 1, the alkali metal removal method of the present embodiment includes a mixing step S1, a heating step S2, and a water washing step S3.

[0051] Further, the alkali metal removal apparatus 1 shown in FIG. 2 includes a mixing device 5, a heating device 7, and a water washing device 9.

[0052] Hereinafter, the processing contents in each step shown in FIG. 1 will be described in detail with appropriate reference to FIG. 2.

[0053] (Mixing step S1) The mixing step S1 is a step of mixing a supplied biomass ash BA1 with a calcium source CA and a chlorine source CL. In the alkali metal removal apparatus 1 shown in FIG. 2, the mixing step S1 is executed by the mixing device 5.

[0054] For example, as shown in FIG. 2, the biomass ash BA1 is supplied from a storage tank 2 in which the biomass ash BA1 is stored toward the mixing device 5. The storage tank 2 may be provided with a supply device capable of adjusting the supply amount of the biomass ash BA1 to the mixing device 5.

[0055] The calcium source CA is not particularly limited as long as it contains calcium, but CaCO 3It is preferable that at least one of them and CaO is contained. Also, as the calcium source CA, industrial raw materials such as limestone, quicklime, and slaked lime, or wastes such as paper sludge, paper sludge incineration ash, sewage sludge incineration ash, waste concrete fine powder, and fresh concrete sludge can be preferably used in consideration of availability and environmental concerns. For example, the alkali metal removal device 1 may be provided with a storage tank for the calcium source CA (not shown), and the calcium source CA stored in this storage tank may be quantitatively supplied to the mixing device 5. More preferably, a discharge amount adjusting device such as a discharge amount adjusting valve is attached to the storage tank of the calcium source, and the supply amount of the calcium source CA may be adjusted by appropriately controlling this discharge amount adjusting device.

[0056] The calcium source CA preferably contains 10% by mass or more of calcium, more preferably 30% by mass or more, and particularly preferably 50% by mass or more. The concentration of calcium in the calcium source CA here can be measured by a well-known method. For example, the FP method using a fluorescent X-ray device or wet analysis (acid decomposition - ICP emission spectrometry) can be used.

[0057] The calcium source CA is introduced for the purpose of adjusting the hydraulicity of the biomass ash BA1. The hydraulicity is an index also referred to as HM. In this specification, it may be defined by the following formula based on the composition ratio of CaO, SiO 2 , Al 2 O 3 , Fe 2 O 3 contained in the object (biomass ash BA1, mixture BC). Here, the composition ratio of the object can be the value obtained by X-ray fluorescence analysis (XRF). Hydraulicity (HM) = (CaO [%]) / {SiO 2 [%] + Al 2 O 3 [%] + Fe 2 O 3 [%]}

[0058] In the mixing step S1, the input amount of the calcium source CA is adjusted so that the hydraulic ratio of the mixture of the biomass ash BA1 and the calcium source CA is preferably 0.3 or more. In this mixing step S1, in addition to the calcium source CA, a chlorine source CL is mixed with the biomass ash BA1, but it may be assumed that the hydraulic ratio of the mixture does not substantially vary due to the mixing of the chlorine source CL. That is, in this mixing step S1, the input amount of the calcium source CA is adjusted so that the hydraulic ratio of the mixture BC of the biomass ash BA1, the calcium source CA, and the chlorine source CL is preferably 0.3 or more. The hydraulic ratio of this mixture BC is more preferably 0.3 to 0.6.

[0059] The calcium source CA is mixed for the purpose of reacting with silicon components such as SiO 2 and K 2 O·4SiO 2 (potassium glass) contained in the biomass ash BA1 to form calcium-containing minerals when the subsequent heating step S2 is performed in a state of being mixed with the biomass ash BA1. From this viewpoint, the calcium source CA preferably has a size of 5 mm or less, more preferably 3 mm or less, and particularly preferably 1 mm or less in order to form a good mixed state with the biomass ash BA1. The size of the calcium source CA refers to the opening of the smallest sieve through which the calcium source CA passes.

[0060] From the above viewpoints, a classification device for removing coarse materials from the received calcium source CA or a pulverizing classification device for making the coarse materials into a predetermined particle size may be attached to the upstream side of the storage tank for storing the calcium source CA. These classification devices and pulverizing classification devices may be appropriately used according to the state of the received calcium source CA.

[0061] The chlorine source CL is not particularly limited as long as it contains chlorine, but waste plastics containing at least one organic chlorine in monomers such as waste polyvinyl chloride, and CaCl 2 , MgCl 2 , PbCl 2Inflammable waste contaminated with inorganic chlorine compounds such as the above can be suitably utilized. For example, the alkali metal removal device 1 may be provided with a storage tank for a chlorine source (not shown), and the chlorine source CL stored in this storage tank may be quantitatively supplied to the mixing device 5. More preferably, a discharge amount adjusting device such as a discharge amount adjusting valve is attached to the storage tank of the chlorine source CL, and the supply amount of the chlorine source CL may be adjusted by appropriately controlling this discharge amount adjusting device.

[0062] The chlorine source CL preferably contains 0.8 mass% or more of chlorine, more preferably 1.2 mass% or more of chlorine, and particularly preferably 2 mass% or more of chlorine. The concentration of chlorine in the chlorine source CL here can be measured by a well-known method. For example, the FP method using a fluorescent X-ray device or wet analysis (Eschka decomposition-ion chromatography method) can be used.

[0063] The chlorine source CL is mixed in a state of being mixed with the biomass ash BA1 so that the subsequent heating step S2 is performed, for the purpose of efficiently causing the chlorination volatilization of the alkali metal contained in the biomass ash BA1. From such a viewpoint, the chlorine source CL is preferably 80 mm or less in size, more preferably 40 mm or less in size, and particularly preferably 10 mm or less in size, in order to form a good mixing state with the biomass ash BA1 and to easily cause the volatilization of chlorine from the chlorine source CL. The size of the chlorine source CL refers to the opening of the smallest sieve through which the chlorine source CL passes.

[0064] From the above viewpoints, a classification device for removing coarse materials from the received chlorine source CL or a pulverization classification device for making the coarse materials into a predetermined particle size may be attached to the upstream side of the storage tank for storing the chlorine source CL. These classification devices and pulverization classification devices may be appropriately used according to the state of the received chlorine source CL.

[0065] The ratio of the biomass ash BA1 to the chlorine source CL is preferably set such that the value of the ratio (M2 / M1) of the molar amount (M22) of the total chlorine in the chlorine source CL to the molar amount (M1) of all the alkali metal components in the biomass ash BA1 is 1 to 4. Note that the value of the ratio (M2 / M1) is more preferably 2 to 4, and particularly preferably 2 to 3.

[0066] When the value of the ratio (M2 / M1) is less than 1, since the amount of chlorine contained in the mixture BC heated in the heating device 7 is small, a large amount of the alkali metal components in the biomass ash BA1 that cannot react with chlorine may remain. Conversely, when the value of the ratio (M2 / M1) exceeds 4, the amount of chlorine that volatilizes and dissipates increases, which may accelerate the corrosion of the equipment.

[0067] Note that in FIG. 2, it is assumed that the biomass ash BA1, the calcium source CA, and the chlorine source CL are mixed in the mixing device 5. However, the implementation mode of this mixing step S1 is not limited to the configuration shown in FIG. 2.

[0068] For example, as shown in FIG. 3, after the biomass ash BA1 and the calcium source CA are once mixed in the mixing device 5a, this mixture and the chlorine source CL may be further mixed in the mixing device 5.

[0069] As another example, as shown in FIG. 4, after the biomass ash BA1 and the calcium source CA are once mixed in the mixing device 5, this mixture and the chlorine source CL may be mixed in the heating device 7. In this case, the heating device 7 also serves as a part of the mixing device.

[0070] As yet another example, as shown in FIG. 5, the biomass ash BA1, the calcium source CA, and the chlorine source CL may be mixed in the heating device 7. In this case, the heating device 7 also serves as the mixing device.

[0071] This mixing step S1 corresponds to step (a).

[0072] Hereinafter, the description will continue with reference to the alkali metal removal device 1 shown in FIG. 2, but the same description is applicable when using the alkali metal removal device 1 in FIGS. 3 to 5.

[0073] (Heating step S2) The heating step S2 is a step of heating the mixture BC of the biomass ash BA1, the calcium source CA, and the chlorine source CL obtained by the mixing step S1. By this heating step S2, the insoluble alkali metal salts contained in the biomass ash BA1 are efficiently changed into water-soluble alkali metal salts (alkali metal chlorides). In the alkali metal removal device 1 shown in FIG. 2, the heating step S2 is executed by the heating device 7.

[0074] As described above, the heating device 7 heats the biomass ash BA1, the calcium source CA, and the chlorine source CL together. Thereby, the alkali metal in the biomass ash BA1 reacts with the chlorine volatilized from the chlorine source CL to form a water-soluble alkali metal salt.

[0075] From the viewpoint of efficiently causing chlorination roasting by the alkali metal in the biomass ash BA1 and the chlorine in the chlorine source CL while making it difficult to melt the biomass ash BA1, the heating temperature in the heating step S2 is preferably 800°C to 1300°C, more preferably 1000°C to 1200°C.

[0076] When the heating temperature is less than 800°C, the reaction of chlorination roasting becomes insufficient, and in some cases, water-soluble alkali metal salts may not be formed or the production efficiency may be low.

[0077] Incidentally, when a mixture of only the biomass ash BA1 and the chlorine source CL is heated at a high temperature of 1000°C or higher without mixing the calcium source CA, the biomass ash BA1 may be enlarged in diameter due to partial melting or sintering, and in this case, water-soluble alkali metal salts may be encapsulated. In this case, even if the water washing process S3 is performed later, the alkali metal salts remain without being dissolved in water. However, in the present embodiment, in addition to the biomass ash BA1 and the chlorine source CL, the calcium source CA is mixed and heated by the heating device 7. Therefore, when heated at a high temperature exceeding 1000°C, a part of the biomass ash BA1 generates minerals derived from Ca contained in the calcium source CA. Since this mineral has a higher melting point than the biomass ash BA1, the phenomenon of encapsulating the melted alkali metal salts hardly occurs. As a result, the ratio of removing the alkali metal salts is increased by the subsequent water washing process S3.

[0078] Note that depending on the existence form of the alkali metal contained in the biomass ash BA1, more preferable temperature conditions are different. Specifically, the biomass ash BA1 may contain an alkali metal in the form of feldspar, and when the abundance in this form is large, the effect of chlorination roasting may not be sufficiently obtained under temperature conditions of about 800°C. Therefore, it is more preferable to set the temperature to 1000°C to 1300°C. However, depending on the content of microcline contained in the biomass ash BA1, even at about 800°C, the alkali metal contained in the biomass ash BA1 can be efficiently changed to an alkali metal salt. Therefore, the heating temperature may be appropriately adjusted within the range of 800°C to 1300°C.

[0079] The heating time performed in the heating step S2 may be appropriately set within the range of 5 minutes to 2 hours according to the heating temperature. From the viewpoint of sufficiently reacting the alkali metal in the biomass ash BA1 and the chlorine in the chlorine source CL, this heating time needs to be short when the heating temperature is high and long when the heating temperature is low. Specifically, when the heating temperature is 800°C, it is preferably 30 minutes to 2 hours, when the heating temperature is 1000°C, it is preferably 10 minutes to 90 minutes, and when the heating temperature is 1200°C, it is preferably 5 minutes to 60 minutes.

[0080] The atmosphere inside the heating device 7 is not particularly limited and may be an oxidizing atmosphere or a reducing atmosphere. In the example shown in FIG. 2, the combustion air G1 is sent into the heating device 7 from the intake fan 33.

[0081] In the heating device 7, in order to efficiently cause the production reaction of the water-soluble alkali metal salt, it is desirable that the biomass ash BA1 and the chlorine source CL be heated in a sufficiently mixed state. From this viewpoint, the heating device 7 can be configured as an internal combustion rotary kiln. If it is a rotary kiln in which the firing furnace rotates, it is possible to perform the heat treatment while physically and continuously mixing and stirring the biomass ash BA1, the calcium source CA, and the chlorine source CL, which are the objects to be heat-treated.

[0082] Furthermore, from the above viewpoints, it can be said that an embodiment in which the mixture BC in a state where the biomass ash BA1, the calcium source CA, and the chlorine source CL are mixed is introduced into the heating device 7, like the alkali metal removal device 1 shown in FIGS. 2 to 3, is more preferable. However, as shown in FIGS. 4 to 5, even in an embodiment in which the chlorine source CL is mixed with the biomass ash BA1 in the heating device 7, by performing the heat treatment after sufficient mixing (or while mixing), the production reaction of the water-soluble alkali metal salt can be efficiently caused.

[0083] When the heating atmosphere in the heating device 7 (typically a rotary kiln) is the atmosphere G1, the atmosphere G1 as combustion air is supplied to the heating device 7 from the intake fan 33. In the rotary kiln, the atmosphere G1 used as the combustion air for the internal combustion burner 31 by the intake fan 33 flows through the inside of the kiln in a direction countercurrent to the flow of the coarse powder BA3 and the chlorine source CL, and then is discharged outside the kiln as the combustion exhaust gas G2.

[0084] When the heating atmosphere is a gas with a low oxygen concentration (e.g., nitrogen), instead of the atmosphere G1 in FIG. 2, a gas with a low oxygen concentration flows into the heating device 7. As the gas source of this gas with a low oxygen concentration, an air separation device that separates oxygen from air may be used, or a gas discharge path from which exhaust gas from another combustion furnace is discharged may be used. Further, as shown in FIG. 2, while allowing air to flow into the heating device 7 through the intake fan 33, the oxygen concentration in the atmosphere inside the heating device 7 may be reduced by adjusting the intake air volume and the fuel combustion amount.

[0085] The heating device 7 is not particularly limited as long as it can heat a mixture of biomass ash BA1 and chlorine source CL at a high temperature, typically in the temperature range of 800°C to 1300°C. Heating furnaces such as a fixed furnace, a stoker furnace, a rotary kiln, a fluidized bed furnace, a vertical furnace, and a multi-stage furnace can be used. Among them, from the viewpoint of being able to perform physical agitation, the above-mentioned rotary kiln is preferable.

[0086] Since both the alkali metal and chlorine are components that are likely to volatilize during the heat treatment, the combustion exhaust gas G2 may contain the alkali metal and chlorine. For this reason, precipitation of the chloride may occur at a location in the flue of the exhaust system of the heating device 7 where the temperature is below the freezing point of the chloride of the alkali metal. Such chloride can also be recovered and used for fertilizers and the like.

[0087] From the heating device 7, a heat-treated product P1 is discharged, which is a mixture of biomass ash BA1 in a state where the insoluble alkali metal has changed to a water-soluble salt, a Ca-containing mineral, a calcium source CA, and the incineration residue of the chlorine source CL. The discharged heat-treated product P1 is sent to the water washing device 9.

[0088] This heating step S2 corresponds to step (b).

[0089] (Water washing step S3) The water washing step S3 is a step of washing the heat-treated product P1 obtained in the heating step S2. By this water washing step S3, the water-soluble alkali metal salt contained in the heat-treated product P1 is dissolved and removed. In the alkali metal removing apparatus 1 shown in FIG. 2, this water washing step S3 is executed by a water washing apparatus 9.

[0090] As the solvent used in this water washing step S3, water is preferable.

[0091] In the water washing apparatus 9, after mixing the heat-treated product P1 supplied from the heating apparatus 7 and the water W1 to generate a slurry Lr1, the stirring of the slurry Lr1 is continued to dissolve the water-soluble alkali metal salt in the heat-treated product P1 in water.

[0092] As an example, the water washing apparatus 9 shown in FIG. 2 is provided with a supply hopper 11 for the heat-treated product P1 and a supply device 13 for the water W1. Further, the water washing apparatus 9 is provided with a slurry stirring device 35 for mixing the heat-treated product P1 and the water W1 and stirring the slurry Lr1 generated by the mixing. The slurry stirring device 35 is preferably a general paddle type or screw type, and in the example shown in FIG. 2, it is provided with stirring blades.

[0093] A pulverizing device for pulverizing large-diameter objects in the received heat-treated product P1 to an appropriate size may be attached upstream of the supply hopper 11. This pulverizing device may be appropriately used according to the state of the heat-treated product P1 supplied from the heating step S2.

[0094] The solubility of the water-soluble alkali metal salt in water is very high, and the solubility does not change significantly even when the water temperature is changed. For this reason, as the solvent used in the water washing step S3, normal-temperature water may be used in an amount of 3 times or more, preferably 4 times or more, more preferably 5 times or more the mass of the heat-treated product P1 (hereinafter sometimes referred to as the "water-washed product").

[0095] In the water washing step S3, the stirring time of the slurry Lr1 composed of the water-washed product and water is preferably 10 minutes or more, more preferably 15 minutes or more, and particularly preferably 20 minutes or more. Usually, since the water-soluble alkali metal salt is very soluble in water, no special conditions are required for stirring the slurry Lr1.

[0096] By such a water washing step S3, the alkali metal contained in the biomass ash BA1 is dissolved in water. The slurry Lr1 in a state where the alkali metal is dissolved in water is separated by a solid-liquid separation device 17 installed in the subsequent stage into a solid (cake C1) with a significantly reduced water content and usable as a cement raw material or the like and drainage W3.

[0097] When transporting the slurry Lr1 to the solid-liquid separation device 17, a general-purpose slurry liquid transport device (not shown) such as a slurry volute pump, a piston pump, a mono pump, or a hose pump may be used.

[0098] As the solid-liquid separation device 17, a general-purpose filtration device such as a filter press, a pressure leaf filter, a screw press, a belt press, or a belt filter may be used. In the embodiment shown in FIG. 2, a case where the solid-liquid separation device 17 is composed of a filter press is illustrated.

[0099] A supply device 15 for washing water W2 is attached to the solid-liquid separation device 17 to separate the transported slurry Lr1 into a cake C1 (solid phase) of the water-washed product and drainage W3 (liquid phase) containing an alkali metal. At this time, the cake C1 is separated while being washed with the washing water W2. As the washing water W2, water at normal temperature may be used in an amount of 3 times or more, preferably 4 times or more, and more preferably 5 times or more the mass of the water-washed product.

[0100] The cake C1 separated by the solid-liquid separation device 17 can be effectively used as a cement raw material or the like because the concentration of the alkali metal component is reduced to 2.0 mass% or less, more typically 1.5 mass% or less, and even more typically 1.0 mass% or less. The concentration of the alkali metal referred to here means the analytical value by a well-known method, for example, the analytical value by the FP method using a fluorescent X-ray device or the analytical value by wet analysis (acid decomposition-ICP emission spectrometry).

[0101] This water washing step S3 corresponds to step (c).

[0102] [Second Embodiment] The second embodiment of the alkali metal removal method according to the present invention will be described centering on the points different from the first embodiment.

[0103] FIG. 6 is a flowchart schematically showing the procedure of the alkali metal removal method of the present embodiment. Further, FIG. 7 is a block diagram schematically showing an example of an alkali metal removal device 1 for carrying out the alkali metal removal method shown in FIG. 6.

[0104] As shown in FIG. 6, the alkali metal removal method of the present embodiment is different in that it has a classification step S4 performed before the mixing step S1 as compared with the first embodiment.

[0105] (Classification Step S4) The classification step S4 is a step of separating the supplied biomass ash BA1 into fine powder BA2 and coarse powder BA3 at a predetermined classification point and recovering them separately. In the alkali metal removal device 1 shown in FIG. 7, the classification step S4 is executed by the classification device 3. Hereinafter, the biomass ash BA1 before the classification step S4 is sometimes referred to as "raw powder BA1".

[0106] Here, the fine powder BA2 of biomass ash (hereinafter simply referred to as "fine powder BA2") refers to biomass ash with a particle size finer than a defined classification point, and the coarse powder BA3 of biomass ash (hereinafter simply referred to as "coarse powder BA3") refers to biomass ash with a particle size coarser than the classification point. The classification point determined in the classification step S4 is preferably 5 μm to 90 μm, more preferably 10 μm to 75 μm, and particularly preferably 20 μm to 63 μm or less.

[0107] In this specification, the particle size of biomass ash (raw powder BA1, fine powder BA2, coarse powder BA3) refers to the measured value by the laser diffraction particle size distribution measurement method using ethyl alcohol as a solvent, unless otherwise specified. The particle size of generally available biomass ash varies depending on the type of biomass as fuel, the type of boiler for burning biomass, and the operation method, but the D 50 value by the laser diffraction particle size distribution measurement method is 15 μm to 200 μm, and the maximum value of the particle size (D 100 ) is 150 μm to 1000 μm. The D 50 value means the particle size at 50% cumulative in the volume-based particle size distribution.

[0108] The classification device 3 is not particularly limited as long as it can classify the raw powder BA1 of biomass ash at a classification point on the order of μm as described above. For example, sieves, inertial classification devices, centrifugal classification devices, gravity classification devices, etc. can be preferably used. From the viewpoint of classification accuracy, the use of a cyclone type air separator, a sieving device, etc. is preferred. In the embodiment shown in FIG. 7, the case where the classification device 3 is composed of a cyclone type air separator is illustrated.

[0109] Note that this classification step S4 may be performed dry or wet. When performed wet, it may be regarded as having undergone the water washing step S3 of the fine powder BA2 described later.

[0110] The classification device 3 may be provided with a storage tank for the raw powder BA1 of biomass ash. Further, a supply device for quantitatively supplying the raw powder BA1 from such a storage tank to the classification device 3 may be provided. These storage tanks and supply devices may be appropriately used according to the state of the received raw powder BA1 of biomass ash.

[0111] In the incinerator of the fluidized bed type, sand mainly composed of quartz as a fluidizing medium and limestone for desulfurization are charged. Therefore, the fly ash (raw powder BA1 of biomass ash) from such an incinerator contains relatively coarse molten and solidified or aggregated glass and sand-derived substances, and relatively fine volatile alkali metal salts and the aforementioned limestone-derived substances. That is, among the alkali metals (Na, K) contained in the raw powder BA1, chlorides, carbonates, and sulfates showing water solubility are present in large amounts on the side of the fine powder BA2, and silicate glass showing low solubility is present in large amounts on the side of the coarse powder BA3.

[0112] That is, by this classification step S4, the raw powder BA1 of biomass ash can be separated into a fine powder BA2 containing a relatively large amount of water-soluble alkali metal salts and a coarse powder BA3 containing a relatively large amount of poorly soluble alkali metal salts.

[0113] This classification step S4 corresponds to step (d).

[0114] (Mixing step S1) The coarse powder BA3 obtained by the classification step S4 is mixed with the calcium source CA and the chlorine source CL. In the example shown in FIG. 7, the mode in which the coarse powder BA3 supplied from the discharge port 3b of the classification device 3 is mixed with the calcium source CA and the chlorine source CL in the mixing device 5 is shown.

[0115] In the mixing step S1 of the present embodiment, the input amount of the calcium source CA is adjusted so that the hydraulic ratio of the mixture of the coarse powder BA3 and the calcium source CA is preferably 0.3 or more, more preferably 0.3 to 0.6. Since the implementation mode of the mixing step S1 overlaps with that of the first embodiment, the description is omitted.

[0116] When the classification step S4 is performed wet, a calcium source CA and a chlorine source CL may be added to and mixed with the slurry-like coarse powder BA3 obtained after classification.

[0117] Also in this embodiment, the implementation mode of the mixing step S1 can be carried out in the same manner as in FIGS. 3 to 5. The same applies to the third embodiment described later.

[0118] Note that by performing the classification step S4 as in this embodiment, a relatively large amount of calcium content (CaCO 3 , CaO, or CaSO 4 etc.) in the raw powder BA1 of biomass ash will be contained on the fine powder BA2 side. This is considered to be derived from the limestone for desulfurization introduced into the fluidized bed incinerator as described above. The limestone for desulfurization may be introduced in a finely pulverized state from the viewpoint of enhancing the reaction. As a result, substances containing calcium are assumed to have relatively fine particle sizes. In other words, the coarse powder BA3 obtained after classification has a lower Ca content than the raw powder BA1. Therefore, when the heating step S2 is performed on the coarse powder BA3 without adding the calcium source CA, it can be said that the phenomenon of melting and sintering is more likely to occur than in the raw powder BA1.

[0119] On the other hand, as in this embodiment, after the calcium source CA is mixed with the coarse powder BA3 obtained after classification so that the hydraulic ratio is 0.3 or more, the heating step S2 is executed, thereby suppressing the above-mentioned melting and sintering phenomenon. As a result, it becomes difficult for the alkali metal salt to be encapsulated in the coarse powder BA3.

[0120] (Heating step S2) Since the mixture BC as the object to be heated contains the coarse powder BA3 instead of the raw powder BA1 of biomass ash, except for this point, it is common to the first embodiment, so the description is omitted. Here, since the heating step S2 is performed only on the fine powder BA2, more raw powder BA1 of biomass ash can be processed, the energy used for heating, the calcium source CA, and the chlorine source CL can be reduced, and the environmental load is reduced.

[0121] (Water washing step S3) In the present embodiment, the water washing step S3 is a step of washing the fine powder BA2 separated and recovered in the classification step S4 and the heat-treated product P1 obtained in the heating step S2. By this water washing step S3, the water-soluble alkali metal salts contained in the fine powder BA2 and the heat-treated product P1 are dissolved and removed.

[0122] Compared with the first embodiment, in the water washing device 9 of the present embodiment shown in FIG. 7, in addition to the heat-treated product P1 supplied from the heating device 7, the fine powder BA2 separated and recovered by the classification device 3 and supplied from the discharge port 3a is washed, which is different, and the others are common.

[0123] As described above, since the fine powder BA2 contains a relatively large amount of water-soluble alkali metal, the alkali metal can be dissolved and removed by this water washing step S3. Also, although the coarse powder BA3 contains a relatively large amount of hardly soluble alkali metal, a part of the hardly soluble alkali metal has been changed to a water-soluble alkali metal salt by passing through the previous heating step S2, so the alkali metal contained in this alkali metal salt can be dissolved and removed.

[0124] According to the method of the present embodiment, the heating step S2 is performed only on the coarse powder BA3 containing a relatively large amount of hardly soluble alkali metal, and the alkali metal is removed from the fine powder BA2 by the water washing step S3. That is, since it is also possible to perform the water washing step S3 for the fine powder BA2 while performing the heating step S2 for the coarse powder BA3 in the heating device 7, the throughput of removing the alkali metal from the raw powder BA1 of biomass ash can be increased within the same time.

[0125] Normally, among all the alkali metal components contained in the raw powder BA1 of biomass ash, the alkali metal components in the form of water-soluble salts are 25% - 45% in terms of molar conversion in the whole 100%, and the alkali metal components in the form of hardly soluble salts are 55% - 75% in the whole 100%.

[0126] In addition, among all the alkali metal components contained in the raw biomass ash BA1, the alkali metal components contained in the biomass ash with a particle size of 30 μm or less, that is, the fine powder BA2, are 40% to 60% in the whole 100% in terms of molar conversion, and among them, 70% to 90% are water-soluble alkali metal components.

[0127] Therefore, after classifying the raw biomass ash BA1 into the fine powder BA2 and the coarse powder BA3 in the classification step S4, by washing the fine powder BA2 in the water washing step S3, 30% to 50% of all the alkali metal components contained in the raw biomass ash BA1 can be removed.

[0128] In addition, when the classification point of the raw biomass ash BA1 in the classification step S4 is 53 μm, by washing the fine powder BA2 with a particle size of 53 μm or less classified in the classification step S4 in the water washing step S3, 20% to 35% of all the alkali metal components contained in the raw powder BA1 can be removed.

[0129] Furthermore, with regard to the alkali metal components in the form of hardly soluble salts, which are contained in a large amount in the coarse powder BA3, they are subjected to chlorination roasting by being heated together with the chlorine source CL and changed into water-soluble salts. As a result, by washing in the water washing step S3, most of them are removed.

[0130] [Third Embodiment] The third embodiment of the alkali metal removal method according to the present invention will be described centering on the differences from the first embodiment and the second embodiment.

[0131] FIG. 8 is a flowchart schematically showing the procedure of the alkali metal removal method of this embodiment. FIG. 9 is a block diagram schematically showing an example of the alkali metal removal apparatus 1 for carrying out the alkali metal removal method shown in FIG. 8.

[0132] As shown in FIG. 8, the alkali metal removal method of this embodiment is different in that it has a pulverization step S5 performed after the classification step S4 as compared with the second embodiment.

[0133] (Crushing process S5) The crushing process S5 is carried out to make the particle size of the coarse powder BA3 classified in the classification process S4 finer. The coarsely pulverized powder BA3 with a finer particle size (hereinafter referred to as "coarse powder crushed product BA3a") is mixed with the calcium source CA and the chlorine source CL in the mixing process S1. In the alkali metal removal device 1 shown in FIG. 9, the crushing process S5 is executed by the crushing device 4. Note that, by crushing the coarse powder BA3 together with the calcium source CA and the chlorine source CL, the crushing process S5 and the mixing process S1 may be carried out simultaneously.

[0134] It is assumed that the coarse powder BA3 contains sparingly soluble alkali metal salts evenly throughout. By executing this crushing process S5 before the heating process S2, the exposed area of the alkali metal increases, so the reactivity with chlorine contained in the chlorine source CL in the heating process S2 is improved, and it can be changed to alkali metal salts with higher efficiency. Further, in the heating process S2, since the reactivity between the silicon content contained in the coarse powder BA3 and the calcium contained in the calcium source CA is improved, it becomes easier to form Ca-containing minerals, and melting and sintering of the coarse powder BA3 can be suppressed.

[0135] The Blaine specific surface area of the coarse powder crushed product BA3a after being crushed by the crushing process S5 is preferably 7,000 cm 2 / g or less, more preferably 1,000 cm 2 / g to 7,000 cm 2 / g, and particularly preferably 4,000 cm 2 / g to 7,000 cm 2 / g. The finer the coarse powder crushed product BA3a is made, the more the reactivity between the alkali metal contained in the coarse powder crushed product BA3a and the chlorine contained in the chlorine source CL is improved. On the other hand, the melting phenomenon of the coarse powder crushed product BA3a also tends to occur. When the coarse powder crushed product BA3a is made so fine that the Blaine specific surface area exceeds 7,000 cm 2 / g, melting occurs significantly during the heating process S2, and alkali metal salts are likely to be encapsulated.

[0136] The lower limit of the particle size of the coarsely pulverized material BA3a after being pulverized by the pulverization step S5 is a value such that the Blaine specific surface area is 7,000 cm 2 / g or less, for example, 0.5 μm or more. If the particle size of the coarsely pulverized material BA3a is pulverized to such an extent that it is less than 0.5 μm, it will be easily melted and sintered in the subsequent heating step S2.

[0137] Specifically, as the pulverizer 4, a tube mill, a vertical roller mill, a jaw crusher, a gyratory crusher, a cone crusher, an impact crusher, a roll crusher, an air fall mill, etc. can be preferably used. When a plurality of these devices are combined to form the pulverizer 4, by installing a classifier between each pulverizer to construct a closed-circuit pulverization system, a coarsely pulverized material BA3a with uniform particle size can be efficiently obtained. The classifier in this case is not particularly limited as long as it can classify the coarsely pulverized material BA3a at a predetermined classification point, and sieves (in-plane motion sieves, vibrating sieves), gravity classifiers, inertial force classifiers, centrifugal classifiers such as cyclones, centrifugal classifiers with rotating blades such as cyclone air separators, etc. can be preferably used. Among them, centrifugal classifiers with rotating blades such as cyclone air separators are preferred due to the simplicity of the equipment and the ease of operation and adjustment. As the pulverizer 4, a pulverizer incorporating a classifier or a sieve mesh can also be used.

[0138] This pulverization step S5 corresponds to step (e).

Example

[0139] Hereinafter, specific test examples are shown to explain the present invention in more detail, but the present invention is not limited to the aspects of these test examples.

[0140] (Verification 1: Verification about the classification step S4) As the raw powder BA1 of biomass ash, fly ash collected by an exhaust gas dust collector (bag filter) of a biomass power plant (circulating fluidized bed boiler) using PKS as the main fuel was used, and the effect of classifying this fly ash was verified.

[0141] The raw powder BA1 of biomass ash was classified into a fine powder BA2 and a coarse powder BA3 with a classification point of 53 μm. Then, the chemical compositions of the biomass ash BA1 before classification, the fine powder BA2 and the coarse powder BA3 after classification were examined. The results are shown in Table 1. In Table 1, for alkali metals, the values obtained by analysis using ICP emission spectrometry of an acid-digested sample were adopted, and for other chemical components, the values obtained by analysis using a fluorescence X-ray apparatus (manufactured by Rigaku Corporation, ZSX Primus II) (FP method: fundamental parameter method) were adopted.

[0142] "R 2 O" in Table 1 means, as described above, the value calculated as "R 2 O = Na 2 O + 0.658 × K 2 O" for the total amount of alkali metal components in the present composition.

[0143] Incidentally, when the particle size distribution of the raw powder BA1 of biomass ash before classification was measured based on the laser diffraction / scattering method, the D 10 value was 8.3 μm, the D 50 value was 44.3 μm, and the D 90 value was 274.7 μm.

[0144]

Table 1

[0145] Also, Table 2 shows the mass distribution ratio by classification of the raw powder BA1 of biomass ash, and the distribution ratios of K and Cl. Table 3 shows the concentration analysis results of K and Cl contained in each of the raw powder BA1, the coarse powder BA3, and the fine powder BA2.

[0146]

Table 2

[0147]

Table 3

[0148] Table 4 shows the XRD analysis results for the raw powder BA1 of biomass ash, the fine powder BA2, and the coarse powder BA3 obtained in the classification step S4. In Table 4, the results of the XRD analysis are indicated as follows: those for which the presence was confirmed are marked with "○", those for which the presence was confirmed in trace amounts are marked with "△", and those for which no presence was confirmed are marked with "×".

[0149]

Table 4

[0150] Based on the results in Table 1, the hydraulicity (HM) of the raw powder BA1 and the coarse powder BA3 of biomass ash was calculated. The results are shown in Table 5.

[0151]

Table 5

[0152] From the results of Tables 4 and 5, it can be seen that when the raw powder BA1 of biomass ash is classified, CaO, CaSO 4 , and CaCO 3 containing calcium, etc. are relatively more contained on the side of the fine powder BA2. As a result, the hydraulicity of the coarse powder BA3 is lower than that of the raw powder BA1.

[0153] (Verification 2: Verification regarding the water washing step S3) The effects of water washing were verified for the raw powder BA1 of biomass ash, and the coarse powder BA3 and the fine powder BA2 obtained in the above Verification 1, respectively.

[0154] The conditions of the water washing step are as follows. For each sample (raw powder BA1, coarse powder BA3, and fine powder BA2), it was stirred with four times the amount of water at room temperature for 30 minutes. After the obtained slurry Lr1 was suction filtered, it was washed and filtered with the same amount of water as when the slurry Lr1 was prepared to prepare a cake C1. For the obtained cake C1, the content of the alkali metal component was determined by analysis using ICP emission spectrometry for acid-digested samples. The results are shown in Table 6.

[0155]

Table 6

[0156] In Table 6 and the tables described later, the "K removal rate" adopted was the value calculated by the following formula (1). K removal rate = [d1 - {(1 - d2) - d3} × d4] / d1 …(1) However, each symbol in formula (1) has the following value respectively. d1: Content rate (concentration) of K (potassium) contained in the sample before treatment (raw powder BA1, coarse powder BA3, fine powder BA2) d2: Weight loss rate of the sample by the heating step S2 d3: Weight loss rate of the sample by the water washing step S3 d4: Content rate (concentration) of K contained in the cake C1 obtained after solid-liquid separation

[0157] However, in this verification 2, since the heating step is not performed, d2 = 0 in formula (1).

[0158] According to the results in Table 6, it can be seen that for the fine powder BA2 obtained after classification, K (potassium) can be efficiently removed by water washing. On the other hand, for the raw powder BA1 and the coarse powder BA3, it can be seen that simply performing the water washing step S3 alone cannot efficiently remove K. From this, it can be confirmed that the raw powder BA1 and the coarse powder BA3 contain a large amount of alkali metals containing hardly soluble K.

[0159] (Verification 3: Verification for raw powder BA1) After mixing the calcium source CA and the chlorine source CL with the raw powder BA1, a heating step was performed.

[0160] The mixing of the chlorine source CL was carried out by mixing a chlorine-containing substance (CaCl 2 reagent powder) having a molar number of a predetermined multiple with respect to the content (mol) of K (potassium) as an alkali metal component in the raw powder BA1.

[0161] The mixing of the calcium source CA was carried out by mixing calcium carbonate (CaCO 3 ) so that the hydraulicity of the mixture reached a predetermined value.

[0162] In addition, when mixing the calcium source CA and the chlorine source CL with respect to the raw powder BA1, it was carried out by bag mixing. Also, when heating the above mixture, 100 g of the mixture was put into an alumina crucible and heated for 60 minutes in a tabletop high-speed temperature-rising electric furnace (manufactured by Motoyama).

[0163] After performing the heating step S2 on the above mixture under different temperature conditions, a water washing step S3 was carried out on the heat-treated product P1 in the same manner as in Verification 2, and the content of the alkali metal component in the obtained cake C1 was determined. The results are shown in Table 7 and Figure 10. The calculation method of the K removal rate conforms to the above formula (1).

[0164]

Table 7

[0165] As shown in Table 7 and Figure 10, when the heating temperature was low, even if the hydraulicity HM was increased, the removal rate of K contained in the raw powder BA1 of the biomass ash did not change. On the other hand, when the heating temperature was 1000 °C, the K removal rate increased significantly.

[0166] From this, it can be seen that in the heating step S2, especially when heating the raw powder BA1 and the chlorine source CL at 800 °C or higher, by mixing the calcium source CA in advance to increase the hydraulicity, the alkali metals contained in the raw powder BA1 can be efficiently removed. By performing the heating step S2 in a state where the hydraulicity is increased, the melting and sintering of the raw powder BA1 are suppressed, and the water-soluble alkali metal salts are less likely to be incorporated into the particles of the raw powder BA1.

[0167] (Verification 4: Verification for the coarse powder BA3) For the crude powder BA3 obtained in Verification 1, a calcium source CA and a chlorine source CL were mixed and heat treatment was performed.

[0168] The step of mixing the chlorine source CL and the calcium source CA with the crude powder BA3, and the step of heating this mixture were carried out in the same manner as in Verification 3.

[0169] After performing the heating step S2 on the above mixture under different temperature conditions, a water washing step S3 was performed on the heat-treated product P1 in the same manner as in Verification 2, and the content of the alkali metal component in the obtained cake C1 was determined. The results are shown in Table 8 and Figure 11. The calculation method of the K removal rate conforms to the above formula (1).

[0170]

Table 8

[0171] As shown in Table 8 and Figure 11, when heating the crude powder BA3 of biomass ash, the K removal rate was increased by increasing the hydraulicity HM at any heating temperature between 800°C and 1200°C. This is considered to be due to the fact that the crude powder BA3 obtained by classifying the raw powder BA1 of biomass ash has a significantly lower hydraulicity HM compared to the raw powder BA1 (see Table 5 above). That is, when the hydraulicity is as low as 0.08 as in Samples #B1, #B4, #B7, and #B10, even when heating is performed together with the chlorine source CL, it can be seen that the amount of the obtained alkali metal salt that cannot be removed by the water washing step S3 is relatively large.

[0172] In particular, when comparing Sample #B1 and #B10 with a hydraulicity HM of 0.08, the K removal rate of Sample #B10 with a higher heating temperature is lower. This result suggests that due to heating at a high temperature in a situation where the hydraulicity HM is low, a part of the coarse powder BA3 melted and sintered, and the alkali metal salt was incorporated inside the coarse powder BA3. On the other hand, when comparing Samples #B2, #B5, #B8, and #B11 with a hydraulicity HM of 0.32, it can be seen that the K removal rate decreases as the heating temperature increases. Similar results are shown when comparing Samples #B3, #B6, #B9, and #B12 with a hydraulicity HM of 0.59.

[0173] From this, it can be seen that especially when the object to be treated is the coarse powder BA3, by mixing the calcium source CA to increase the hydraulicity HM and heating in a high-temperature environment together with the chlorine source CL, the contained alkali metal can be significantly removed.

[0174] (Verification 5: Verification for the Coarse Powder Ground Material BA3a) After further performing the grinding process S5 on the coarse powder BA3 obtained in Verification 1 and grinding it, the calcium source CA and the chlorine source CL were mixed, and heat treatment was performed. When grinding the coarse powder BA3, it was carried out using a fine grinder (manufactured by Hatzok Japan Co., Ltd.) using a tungsten vessel.

[0175] In addition, for the coarse powder ground material BA3a obtained after grinding, the process of mixing the chlorine source CL and the calcium source CA, and the process of heating this mixture were carried out in the same manner as in Verification 3.

[0176] By performing the pulverization step S5 with different pulverization times, coarse powder pulverized products BA3a with different Blaine surface areas were obtained. Then, a chlorine source CL and a calcium source CA were mixed with each of the coarse powder pulverized products BA3a, and the heating step S2 was performed. For the obtained heat-treated product P1, a water washing step S3 was performed in the same manner as in Verification 2, and the content of the alkali metal component in the obtained cake C1 was determined. The results are shown in Table 9 and FIG. 12. Note that the calculation method of the K removal rate conforms to the above formula (1). In Table 9, the results when using the coarse powder BA3 without performing the pulverization step S5 are shown for comparison.

[0177]

Table 9

[0178] From the results of Table 9 and FIG. 12, it can be seen that the K removal rate is increased by pulverizing the coarse powder BA3. By heating together with the chlorine source CL after pulverizing the coarse powder BA3, the exposed area of the alkali metal contained in the coarse powder BA3 is enlarged, the reactivity with Cl contained in the chlorine source CL is improved, and it is considered that the production amount of the water-soluble alkali metal salt is increased.

[0179] On the other hand, it was confirmed that when pulverizing finely to the extent that the Blaine specific surface area is 10,200 cm 2 / g, the K removal rate conversely decreases.

[0180] In view of the results of Table 9 and FIG. 12, as the Blaine specific surface area of the coarse powder pulverized product BA3a is made finer to 1,040 cm 2 / g, 2,630 cm 2 / g, 4,130 cm 2 / g, 6,580 cm 2 / g, it is considered that the reactivity between Cl and the alkali metal is improved.

[0181] On the other hand, when the Blaine specific surface area of the coarse powder pulverized product BA3a is changed from 6,580 cm 2 / g to 10,200 cm 2When it increases to / g, that is, when the coarse powder BA3 is made finer, the tendency for the coarsely pulverized product BA3a to melt and sinter during heating becomes more prominent than the degree of improvement in the reactivity between Cl and the alkali metal, and it is considered that the proportion of the water-soluble alkali metal salt encapsulated in the coarsely pulverized product BA3a has increased. In other words, when pulverizing the coarse powder BA3, the Blaine specific surface area of the coarsely pulverized product BA3a obtained after pulverization should preferably be below the upper limit threshold between 6,580 cm 2 / g and 10,200 cm 2 / g. In view of the results in Table 9 and Figure 12, this upper limit threshold can be set at 7,000 cm 2 / g.

Explanation of Symbols

[0182] 1: Alkali metal removal device 2: Storage tank 3: Classification device 3a: Discharge port 3b: Discharge port 4: Pulverizing device 5: Mixing device 5a: Mixing device 7: Heating device 9: Water washing device 11: Supply hopper 13: Supply device 15: Supply device 17: Solid-liquid separation device 31: Internal combustion burner 33: Intake fan 35: Slurry stirring device BA1: Biomass ash (raw powder) BA2: Fine powder BA3: Coarse powder BA3a: Coarsely pulverized product BC: Mixture C1: Cake CA: Calcium source CL: Chlorine source G1: Air G2: Combustion exhaust gas Lr1: Slurry P1: Heat-treated product W1: Water W2: Wash water W3: Drainage

Claims

1. A method for removing alkali metals from fly ash of combustion ash of woody biomass, comprising: Step (a) of mixing a calcium source and a chlorine source with the fly ash, either simultaneously or sequentially; Step (b) of heating the mixture in a state where the hydraulicity is adjusted from the fly ash by step (a) to obtain a heat-treated product; The alkali metal removal method, wherein step (a) includes a step of introducing an amount of the calcium source adjusted so that the hydraulicity of the mixture becomes 0.3 to 0.

6.

2. The alkali metal removal method according to claim 1, further comprising step (c) of washing the heat-treated product obtained in step (b) with water.

3. The calcium source used in the step (a) contains at least one selected from the group consisting of industrial raw materials and wastes containing at least one of CaCO 3 and CaO, and the method for removing an alkali metal according to claim 1 or 2.

4. The alkali metal removal method according to any one of claims 1 to 3, wherein step (b) is a step of heating at a temperature of 800°C to 1300°C.

5. The alkali metal removal method according to any one of claims 1 to 4, wherein the chlorine source used in step (a) has a size of 80 mm or less.

6. The alkali metal removal method according to any one of claims 1 to 5, wherein step (a) includes a step of introducing an amount of the chlorine source adjusted so that the ratio (M2 / M1) of the molar amount (M2) of all chlorine in the chlorine source to the molar amount (M1) of all alkali metal components in the fly ash is within the range of 1 to 4.

7. Further comprising step (d) of classifying the fly ash into fine powder and coarse powder, The alkali metal removal method according to any one of claims 1 to 6, wherein step (a) is a step of mixing the calcium source and the chlorine source with the coarse powder after the fly ash is classified by step (d).

8. Comprising step (c) of washing the heat-treated product obtained in step (b) with water, The alkali metal removal method according to claim 7, wherein step (c) is a step of washing the fine powder after the fly ash is classified by step (d) in addition to the heat-treated product obtained in step (b) with water.

9. Further comprising step (e) of pulverizing the coarse powder obtained by step (d) to obtain a coarse powder pulverized product, The alkali metal removal method according to claim 7 or 8, wherein step (a) is a step of mixing the calcium source and the chlorine source with the coarse powder pulverized product obtained by step (e).

10. The step (e) is a step of pulverizing so that the Blaine specific surface area of the coarse pulverized material is 7,000 cm 2 / g or less, and the method for removing an alkali metal according to claim 9, characterized in that.

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