JP7689891B2 - Alkaline metal removal method - Google Patents

Description

The present invention relates to a method for removing alkali metals, and in particular to a method for removing alkali metals from combustion ash of wood biomass in order to effectively use the ash as a raw material for cement, etc.

As for wood biomass, such as tree trunks and branches, cutting chips, sawdust, bark, wood pellets, PKS (palm kernel shells), and construction waste, in parallel with the development of technology to use it as fuel for power generation boilers, etc., development is also underway for the effective use of combustion ash (hereinafter sometimes referred to as "wood biomass ash") generated by the combustion of wood biomass.

Compared to coal ash and waste incineration ash, for example, wood biomass ash is characterized by its high content of alkali metals, especially potassium. For this reason, for example, when applying cement raw material technology that enables the effective use of the large amounts of coal ash and waste incineration ash generated to wood biomass ash, it is necessary to remove the alkali metals from the wood biomass ash so that the cement will avoid the alkali metal components. Furthermore, if the alkali metals can be removed from wood biomass ash fly ash, it will be possible to develop applications for wood biomass ash fly ash as a concrete admixture or cement mixture, just like coal ash (fly ash).

As a technique for removing alkali metal components from woody biomass ash, for example, Patent Document 1 below discloses a combustion device and a combustion ash processing method in which woody biomass ash (fly ash) collected by a bag filter is classified at a predetermined classification point to separate and recover fine combustion ash with a high potassium concentration.

JP 2017-122550 A

However, since alkali metals are present in all particle sizes of wood biomass fly ash, simply removing the alkali metals present in the fine combustion ash is insufficient for use as a cement raw material, etc.

In view of the above problems, the present invention aims to provide a method for efficiently removing alkali metals from fly ash of wood biomass ash (hereinafter sometimes referred to as "biomass ash") and effectively utilizing the resulting ash as a cement raw material, etc.

As a result of extensive research, the inventors have discovered that there are two types of alkali metals contained in biomass ash: water-soluble and poorly soluble in water (hereinafter simply referred to as "poorly soluble"). They have also discovered that the poorly soluble alkali metals can be converted into water-soluble salts (alkali metal chlorides) by heating them together with a chlorine source (so-called "chlorination roasting").

Furthermore, after extensive research, the inventors discovered that the removal rate of alkali metals can be further increased by heating biomass ash together with a chlorine source in a state where a calcium source is mixed in, rather than simply heating the biomass ash together with a chlorine source.

That is, the present invention is a method for removing alkali metals from fly ash of combustion ash of woody biomass, comprising the steps of:
(a) mixing the fly ash with a calcium source and a chlorine source, either simultaneously or sequentially;
and a step (b) of heating the mixture of the fly ash whose hydraulic ratio has been adjusted by the step (a) to obtain a heat-treated product.

The inventors consider the following reason why the rate of alkali metal removal is further increased by mixing a calcium source with fly ash.

In the process of heating the mixture of the chlorine source and biomass ash, the biomass ash may melt or sinter depending on the heating temperature. In addition, water-soluble alkali metal chlorides (e.g., KCl) produced in this process also become molten.

After the heating process is completed, the molten biomass ash solidifies as the temperature decreases. At this time, the molten alkali metal chlorides aggregate and crystallize inside the molten biomass ash due to differences in surface tension, etc. As a result, the biomass ash after cooling contains some water-soluble alkali metal chlorides. It is difficult to effectively remove the alkali metal chlorides contained in the biomass ash even by washing with water.

In contrast, according to the above method, a chlorine source and a calcium source are mixed with biomass ash (fly ash) prior to the heating step (b). As a result, in the heating step (b), Ca contained in the calcium source reacts with Si and the like contained in the biomass ash to form a Ca-containing mineral. Examples of such Ca-containing minerals include _CaSiO3 ( _wollastonite ), _CaAl2Si2O8 ( _anorthite ), _{and Ca2Al2SiO7} (gehlenite). These Ca-containing minerals have _a higher melting point than biomass ash.

Therefore, by converting at least a portion of the biomass ash into Ca-containing minerals by the heating step (b), the amount of biomass ash that is melted and sintered is reduced. As a result, the amount of molten alkali metal salts that are taken up inside the biomass ash can be reduced. For this reason, for example, by performing a water washing process to dissolve the biomass ash in water, a residue with a reduced alkali metal content can be obtained. In addition, the alkali metal salts may be removed (separated) from the heat-treated product by a method other than the water washing process. The residue from which the alkali metal salts have been removed has a significantly reduced alkali metal content compared to the biomass ash (fly ash) before treatment, and can therefore be effectively used as a cement raw material to replace coal ash.

In addition, by heating the calcium source and the chlorine source in a mixed state, a part of Cl contained in the chlorine source reacts with Ca contained in the calcium source and can be fixed as calcium chloride ( _CaCl2 ). The volatilization rate of _CaCl2 is slower than that of _Cl2 and HCl. As a result, the effect of suppressing the amount of Cl contained in the charged chlorine source that volatilizes without contributing to the reaction with the alkali metal contained in the biomass ash can be obtained.

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

As described above, the heat-treated product obtained in step (b) contains water-soluble alkali metal substances, and is therefore dissolved into the liquid phase by the water washing step (c). Therefore, for example, after a solid-liquid separation step, the residue (cake) obtained after the alkali metal-containing liquid is removed has a reduced alkali metal content compared to the biomass ash before treatment.

The step (a) may include a step of adding the calcium source in an amount adjusted so that the hydraulic hardness of the mixture is 0.3 to 0.6.

In this specification, the hydraulic ratio may be defined by the following formula based on the composition ratio of CaO, SiO ₂ , Al ₂ O ₃ , and Fe ₂ O ₃ contained in the mixture.
Hydraulic ratio (HM) = (CaO [%]) / {SiO ₂ [%] + Al ₂ O ₃ [%] + Fe ₂ O ₃ [%]}
The composition ratio of the mixture may be determined by X-ray fluorescence analysis (XRF).

By adding a calcium source so that the hydraulic ratio is 0.3 or more, the removal rate of alkali metals contained in biomass ash can be sufficiently increased. On the other hand, if the calcium source is added so that the hydraulic ratio 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 added at one time to the combustion furnace in which the heating step (b) is performed. In other words, the amount of biomass ash from which alkali metals can be removed in the same amount of time decreases, and the treatment speed decreases. From this perspective, it is preferable to add a calcium source in step (a) so that the hydraulic ratio of the mixture is 0.3 to 0.6.

The calcium source used in step (a) may include one or more of the group consisting of industrial raw materials and waste materials containing at least one of _CaCO3 and CaO.

Such industrial raw materials include, for example, limestone, quicklime, and hydrated lime. In addition, examples of waste materials include paper sludge, paper sludge incineration ash, and sewage sludge incineration ash.

Step (b) may be a heating step at a temperature of 800°C to 1300°C.

If the heating step (b) is carried out at a temperature below 800°C, the low temperature may make it difficult to convert the alkali metal into an alkali metal salt. Also, if the heating temperature exceeds 1,300°C, the chlorine contained in the chlorine-containing material may volatilize more easily, reducing the amount of contact with the alkali metal and decreasing reactivity.

The chlorine source used in step (a) may include waste plastics and combustible waste mixed with inorganic chlorine.

The above method makes it possible to effectively utilize waste materials that have a high chlorine content and therefore are poorly suited for recycling, in order to remove alkali metals contained in biomass ash.

The chlorine source used in step (a) may be 80 mm or less in size.

By carrying out the heating step (b) while mixing the chlorine source of the above size with the biomass ash, it is possible to convert a high proportion of the poorly soluble alkali metals contained in the biomass ash into water-soluble salts. If the size of the chlorine source is larger than 80 mm, chlorine may not be sufficiently volatilized from the chlorine source during the heating step (b), making it difficult to chlorinate the biomass ash. The size of the chlorine source refers to the size of the sieve openings, and a size of 80 mm or less refers to one that passes through a sieve with an opening of 80 mm.

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

According to the above method, most of the sparingly soluble alkali metals contained in the biomass ash can be efficiently converted into water-soluble salts. If the value of M2/M1 exceeds 4, chlorine that does not contribute to the chlorination roasting remains, and there is a risk that some of the chlorine source will be wasted. In addition, if the value of M2/M1 is below 1, there is a risk that the heat-treated product obtained after the completion of the heating step (b) still contains a certain amount of sparingly soluble alkali metals.

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 the coarse powder obtained after the fly ash is classified in the step (d).

By carrying out 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 sparingly soluble alkali metals. Therefore, by mixing the coarse powder with a calcium source and a chlorine source and then carrying out the heating step (b), the alkali metals can be effectively and efficiently removed.

The step (d) may be a step of classifying the particles with a classification point of 5 μm to 90 μm.

According to the above method, even if the biomass ash comes from different sources, fine powder equivalent to 20% to 50% by mass of the total amount can be obtained for most biomass ash. In other words, the coarse powder to be subjected to the heat treatment in step (b) corresponds to 50% to 80% by mass of the total amount of biomass ash. In other words, since there is no need to heat the entire biomass ash, alkali metals can be removed with high heating efficiency.

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

According to the above method, both the water-soluble alkali metals contained in large amounts in the fine powder and the water-soluble alkali metal salts contained in the coarse powder that has been through step (b) can be dissolved in water and removed by the water washing treatment in step (c).

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

It is assumed that the coarse powder after classification contains poorly soluble alkali metals evenly throughout. As in the above method, by performing the crushing step (e) on the coarse powder obtained by the classification step (d) of the biomass ash, the exposed area of the alkali metals increases. Therefore, by mixing the crushed coarse powder (crushed coarse powder) with a chlorine source and a calcium source and then performing the heating step (b), the reactivity with the chlorine contained in the chlorine source is improved, and it can be converted to alkali metal chloride more efficiently.

The step (e) is preferably a step of pulverizing the coarse powder so that the Blaine specific surface area of the pulverized coarse powder is 7,000 cm ² /g or less, and more preferably 1,000 cm ² /g to 7,000 cm ² /g.

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

By carrying out the heating step (b) under a low oxygen concentration, excessive volatilization of the chlorine contained in the chlorine source is suppressed, and the alkali metals contained in the biomass ash are more easily converted into water-soluble alkali metal chlorides.

According to the present invention, alkali metals can be efficiently removed from biomass ash. This allows the biomass ash to be used as a cement raw material, for example.

1 is a flow chart illustrating a schematic procedure of a first embodiment of a method for treating an alkali metal-containing material. FIG. 2 is a block diagram showing a schematic example of an apparatus for carrying out the method shown in FIG. 1. FIG. 2 is a block diagram showing a schematic diagram of another example of an apparatus for carrying out the method shown in FIG. 1 . FIG. 2 is a block diagram showing a schematic diagram of another example of an apparatus for carrying out the method shown in FIG. 1 . FIG. 2 is a block diagram showing a schematic diagram of another example of an apparatus for carrying out the method shown in FIG. 1 . 1 is a flowchart illustrating a procedure of a second embodiment of a method for treating an alkali metal-containing material. FIG. 7 is a block diagram showing a schematic example of an apparatus for carrying out the method shown in FIG. 6. 10 is a flowchart illustrating a procedure of a third embodiment of a method for treating an alkali metal-containing material. FIG. 9 is a block diagram illustrating an example of an apparatus for implementing the method shown in FIG. 8 . This is a graph comparing the K (potassium) removal rate for each condition when biomass ash raw powder BA1 is heated together with a chlorine source CL at different heating temperatures and hydraulic moduli HM. This is a graph comparing the K removal rate for each condition when coarse powder BA3 is heated together with a chlorine source CL while changing the heating temperature and hydraulic hardness HM. 1 is a graph showing the K removal rate when the coarse powder pulverized product BA3a is heated together with a chlorine source CL with varying degrees of pulverization, compared for each Blaine specific surface area of the coarse powder pulverized product BA3a.

Biomass ash to which the present invention is applied contains alkali metals (Na, K) in the form of chlorides, carbonates, sulfates, silicate glass, or the like, and contains about 3% to 50% by mass calculated as _R2O ( _R2O = _Na2O + 0.658 x _K2O ). Of these alkali metals, the chlorides, carbonates, and sulfates are water-soluble, while silicate glass is sparingly soluble.

According to the alkali metal removal method of the present invention, the concentration of alkali metals contained in biomass ash can be reduced to 2.0 mass % or less, more typically 1.5 mass % or less, calculated as _R2O , making it possible to effectively utilize the biomass ash as a cement raw material, etc. The concentration of alkali metals in biomass ash can be measured by a well-known method, and preferred examples of such methods include the FP method using an X-ray fluorescence device or wet analysis (acid decomposition-ICP atomic emission spectrometry).

The present invention will now be described in more detail with reference to the drawings. However, the present invention is not limited to the embodiments described with these drawings.

[First embodiment]
A first embodiment of the method for removing an alkali metal according to the present invention will be described.

Figure 1 is a flow chart that shows a schematic diagram of the procedure of the alkali metal removal method of this embodiment. Also, Figure 2 is a block diagram that shows a schematic diagram of an example of an apparatus (hereinafter referred to as "alkali metal removal apparatus") that performs the alkali metal removal method shown in Figure 1. In Figure 2, the flow of solids such as biomass ash and liquids such as water are shown by solid lines with arrows, and the flow of gas is shown by dashed lines with arrows. This is the same in each figure described later.

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

The alkali metal removal device 1 shown in FIG. 2 also includes a mixing device 5, a heating device 7, and a water washing device 9.

The processing steps in each step shown in Figure 1 will be described in detail below, with reference to Figure 2 as appropriate.

(Mixing step S1)
The mixing step S1 is a step of mixing the supplied biomass ash BA1 with a calcium source CA and a chlorine source CL. In the alkali metal removal apparatus 1 shown in FIG.

For example, as shown in FIG. 2, biomass ash BA1 is supplied from a storage tank 2 in which the biomass ash BA1 is stored to a mixer 5. The storage tank 2 may be equipped with a supply device that can adjust the amount of biomass ash BA1 supplied to the mixer 5.

The calcium source CA is not particularly limited as long as it contains calcium, but it is preferable that it contains at least one of _CaCO3 and CaO. In addition, from the viewpoints of ease of availability and environmental consideration, industrial raw materials such as limestone, quicklime, and slaked lime, and waste materials such as paper sludge, paper sludge incineration ash, sewage sludge incineration ash, waste concrete fine powder, and ready-mixed concrete sludge can be suitably used as the calcium source CA. 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 supplied quantitatively to the mixer 5. More preferably, the calcium source storage tank may be provided with a discharge amount adjustment device such as a discharge amount adjustment valve, and the supply amount of the calcium source CA may be adjusted by appropriately controlling this discharge amount adjustment device.

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 calcium concentration in the calcium source CA can be measured by a known method, for example, the FP method using an X-ray fluorescence device or wet analysis (acid decomposition-ICP emission spectrometry).

The calcium source CA is added for the purpose of adjusting the hydraulic ratio of the biomass ash BA1. The hydraulic ratio is an index also called HM, and in this specification, may be defined by the following formula based on the composition ratios of CaO, _SiO2 , _Al2O3 , and _Fe2O3 contained in the target material (biomass ash BA1, mixture BC ₎ . Here, the composition ratios of the target material _may be values obtained by X-ray fluorescence analysis (XRF).
Hydraulic ratio (HM) = (CaO [%]) / {SiO ₂ [%] + Al ₂ O ₃ [%] + Fe ₂ O ₃ [%]}

In the mixing step S1, the amount of calcium source CA added is adjusted so that the hydraulic ratio of the mixture of biomass ash BA1 and calcium source CA is preferably 0.3 or more. In this mixing step S1, in addition to calcium source CA, chlorine source CL is mixed with biomass ash BA1, but it is acceptable to assume that the hydraulic ratio of the mixture does not substantially change due to the mixing of chlorine source CL. In other words, in this mixing step S1, the amount of calcium source CA added is adjusted so that the hydraulic ratio of the mixture BC of biomass ash BA1, calcium source CA, and chlorine source CL is preferably 0.3 or more. It is more preferable that the hydraulic ratio of this mixture BC is 0.3 to 0.6.

The calcium source CA is mixed with the biomass ash BA1 in a mixed state in the subsequent heating step S2, whereby the calcium source CA reacts with _silicon components such as _SiO2 and _K2O.4SiO2 (potassium glass) contained in the biomass ash BA1 to produce calcium-containing minerals. From this viewpoint, in order to form a good mixed state with the biomass ash BA1, the calcium source CA is preferably 5 mm or less in size, more preferably 3 mm or less in size, and particularly preferably 1 mm or less in size. The size of the calcium source CA refers to the smallest sieve opening through which the calcium source CA can pass.

From the above viewpoint, a classification device for removing coarse particles from the received calcium source CA and a crushing and classification device for reducing the coarse particles to a predetermined particle size may be installed upstream of the storage tank for storing the calcium source CA. These classification devices and crushing and classification devices may be used appropriately depending on the condition of the received calcium source CA.

The chlorine source CL is not particularly limited as long as it contains chlorine, but it is possible to suitably use waste plastics containing at least one organic chlorine in monomers such as waste polyvinyl chloride, or combustible waste mixed with inorganic chlorine compounds such as CaCl ₂ , MgCl ₂ , and PbCl ₂ . 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 supplied quantitatively to the mixer 5. More preferably, the storage tank for the chlorine source CL may be provided with an emission control device such as an emission control valve, and the supply amount of the chlorine source CL may be adjusted by appropriately controlling this emission control device.

The chlorine source CL preferably contains 0.8% by mass or more of chlorine, more preferably 1.2% by mass or more, and particularly preferably 2% by mass or more. The concentration of chlorine in the chlorine source CL can be measured by a known method, for example, the FP method using an X-ray fluorescence device or wet analysis (Eschka decomposition-ion chromatography method).

The chlorine source CL is mixed with the biomass ash BA1 in the subsequent heating step S2 in a mixed state, for the purpose of efficiently chlorinating and volatilizing the alkali metals contained in the biomass ash BA1. From this perspective, 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, so as to form a good mixed state with the biomass ash BA1 and to facilitate the volatilization of chlorine from the chlorine source CL. The size of the chlorine source CL refers to the smallest sieve opening through which the chlorine source CL can pass.

From the above viewpoint, a classification device for removing coarse objects from the received chlorine source CL and a crushing and classification device for reducing the coarse objects to a predetermined particle size may be installed upstream of the storage tank for storing the chlorine source CL. These classification devices and crushing and classification devices may be used appropriately depending on the condition of the received chlorine source CL.

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

If the ratio (M2/M1) is below 1, the amount of chlorine contained in the mixture BC heated in the heating device 7 is small, and therefore many of the alkali metal components in the biomass ash BA1 cannot react with chlorine and may remain. Conversely, if the ratio (M2/M1) is above 4, the amount of chlorine that volatilizes and dissipates may increase, accelerating the progression of corrosion of the equipment.

Note that in FIG. 2, it is assumed that biomass ash BA1, calcium source CA, and chlorine source CL are mixed in the mixing device 5, but the embodiment of this mixing process S1 is not limited to the configuration shown in FIG. 2.

For example, as shown in FIG. 3, biomass ash BA1 and calcium source CA may be mixed in mixer 5a, and then this mixture may be further mixed with chlorine source CL in mixer 5.

As another example, as shown in FIG. 4, biomass ash BA1 and calcium source CA may be mixed in a mixer 5, and then this mixture may be mixed with a chlorine source CL in a heater 7. In this case, the heater 7 may also function as a part of the mixer.

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

This mixing step S1 corresponds to step (a).

The following explanation will be continued with reference to the alkali metal removal device 1 shown in Figure 2, but the same explanation can be applied when using the alkali metal removal device 1 shown in Figures 3 to 5.

(Heating process 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 in the mixing step S1. This heating step S2 efficiently converts poorly soluble alkali metal salts contained in the biomass ash BA1 into water-soluble alkali metal salts (alkali metal chlorides). In the alkali metal removal apparatus 1 shown in FIG. 2, the heating step S2 is performed by a heating device 7.

As described above, the heating device 7 heats the biomass ash BA1, the calcium source CA, and the chlorine source CL together. This causes the alkali metal in the biomass ash BA1 to react with the chlorine volatilized from the chlorine source CL to produce a water-soluble alkali metal salt.

The heating temperature in the heating step S2 is preferably 800°C to 1300°C, and more preferably 1000°C to 1200°C, 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 for the biomass ash BA1 to melt.

If the heating temperature is less than 800°C, the chlorination roasting reaction will be insufficient, and in some cases water-soluble alkali metal salts may not be produced or may be produced at a low efficiency.

However, when a mixture of biomass ash BA1 and chlorine source CL is simply heated at a high temperature of 1000°C or higher without mixing calcium source CA, biomass ash BA1 may be partially melted or sintered to increase in diameter, which may result in inclusion of water-soluble alkali metal salts. In this case, even if a water washing process is performed in the subsequent water washing step S3, the alkali metal salts will remain without being dissolved in water. However, in this embodiment, the mixture is heated in the heating device 7 in a state where calcium source CA is mixed in addition to biomass ash BA1 and chlorine source CL. Therefore, when heated at a high temperature exceeding 1000°C, a part of biomass ash BA1 produces minerals derived from Ca contained in calcium source CA. Since this mineral has a higher melting point than biomass ash BA1, the phenomenon of encapsulating molten alkali metal salts is unlikely to occur. As a result, the rate of alkali metal salts removed by the subsequent water washing step S3 is increased.

The more preferable temperature conditions vary depending on the form of the alkali metal contained in the biomass ash BA1. Specifically, the alkali metal may be contained in the form of feldspar in the biomass ash BA1. If the amount of alkali metal present in this form is large, the effect of chlorination roasting may not be sufficient at temperatures of around 800°C, so a temperature of 1000°C to 1300°C is more preferable. However, depending on the amount of potassium feldspar contained in the biomass ash BA1, the alkali metal contained in the biomass ash BA1 can be efficiently converted to an alkali metal salt even at around 800°C, so the heating temperature may be adjusted appropriately within the range of 800°C to 1300°C.

The heating time in the heating step S2 may be set appropriately within a range of 5 minutes to 2 hours depending on the heating temperature. From the viewpoint of sufficiently reacting the alkali metal in the biomass ash BA1 with 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, it is preferable to set the heating time to 30 minutes to 2 hours when the heating temperature is 800°C, 10 minutes to 90 minutes when the heating temperature is 1000°C, and 5 minutes to 60 minutes when the heating temperature is 1200°C.

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, air G1 for combustion is sent into the heating device 7 from the intake fan 33.

In the heating device 7, it is desirable to heat the biomass ash BA1 and the chlorine source CL in a fully mixed state in order to efficiently generate the reaction that produces the water-soluble alkali metal salt. From this perspective, the heating device 7 can be configured as an internal combustion rotary kiln. If the firing furnace is a rotary kiln that rotates, it is possible to perform the heat treatment while physically and continuously mixing and stirring the materials to be heated, that is, the biomass ash BA1, the calcium source CA, and the chlorine source CL.

Furthermore, from the above viewpoint, it can be said that an embodiment in which a mixture BC in which biomass ash BA1, calcium source CA, and chlorine source CL are mixed is introduced into the heating device 7, as in the alkali metal removal device 1 shown in Figures 2 and 3. However, even in an embodiment in which the chlorine source CL is mixed with the biomass ash BA1 in the heating device 7, as in Figures 4 and 5, the reaction to produce water-soluble alkali metal salts can be efficiently caused by performing the heat treatment after (or while) the mixture is thoroughly mixed.

When the heating atmosphere in the heating device 7 (typically a rotary kiln) is the atmosphere G1, the atmosphere G1 is supplied to the heating device 7 as combustion air 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 inside the kiln in a countercurrent direction to the flow of the coarse powder BA3 and the chlorine source CL, and is then discharged outside the kiln as combustion exhaust gas G2.

When the heating atmosphere is a gas with a low oxygen concentration (e.g., nitrogen), the gas with a low oxygen concentration is flowed into the heating device 7 instead of the atmosphere G1 in FIG. 2. The source of this gas with a low oxygen concentration may be an air separation device that separates oxygen from air, or a gas exhaust path through which exhaust gas from another combustion furnace is discharged. Furthermore, as shown in FIG. 2, the oxygen concentration of the atmosphere in the heating device 7 may be reduced by adjusting the amount of intake air and the amount of fuel burned while air is flowed into the heating device 7 through the intake fan 33.

The heating device 7 is not particularly limited as long as it can heat the mixture of biomass ash BA1 and chlorine source CL at high temperatures, typically in the temperature range of 800°C to 1300°C, and a heating furnace such as a fixed furnace, stoker furnace, rotary kiln, fluidized bed furnace, vertical furnace, or multi-tier furnace can be used. Among these, the above-mentioned rotary kiln is preferable from the viewpoint of physical stirring.

In addition, since alkali metals and chlorine are both components that tend to volatilize during heat treatment, the combustion exhaust gas G2 may contain alkali metals and chlorine. For this reason, in the flue of the exhaust system of the heating device 7, at points where the temperature is below the freezing point of the alkali metal chloride, precipitation of the chloride may occur. Such chlorides can be recovered and used as fertilizer, etc.

The heating device 7 discharges a heat-treated material P1, which is a mixture of biomass ash BA1 in which poorly soluble alkali metals have been converted into water-soluble salts, or incineration residues of Ca-containing minerals, a calcium source CA, and a chlorine source CL. The discharged heat-treated material P1 is sent to a water washing device 9.

This heating step S2 corresponds to step (b).

(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 with water. This water-washing step S3 dissolves and removes water-soluble alkali metal salts contained in the heat-treated product P1. In the alkali metal removal apparatus 1 shown in FIG. 2, this water-washing step S3 is performed by a water-washing device 9.

The solvent used in this water washing step S3 is preferably water.

In the water washing device 9, the heat-treated material P1 supplied from the heating device 7 is mixed with water W1 to produce slurry Lr1, and then the slurry Lr1 is continuously stirred to dissolve the water-soluble alkali metal salts in the heat-treated material P1 in the water.

As an example, the water washing device 9 shown in FIG. 2 is provided with a supply hopper 11 for the heat-treated material P1 and a supply device 13 for water W1. The water washing device 9 is also provided with a slurry agitator 35 for mixing the heat-treated material P1 and the water W1 and agitating the slurry Lr1 produced by the mixing. The slurry agitator 35 is preferably of a general paddle type or screw type, and is equipped with an agitator blade in the example shown in FIG. 2.

A crushing device may be provided upstream of the supply hopper 11 to crush large-diameter objects in the received heat-treated material P1 to an appropriate size. This crushing device may be used appropriately depending on the condition of the heat-treated material P1 supplied from the heating process S2.

The solubility of water-soluble alkali metal salts in water is very high, and the solubility does not change significantly even if the water temperature is changed. For this reason, room temperature water may be used as the solvent in the water washing step S3 in an amount of at least three times, preferably at least four times, and more preferably at least five times the mass of the heat-treated product P1 (hereinafter sometimes referred to as the "water-washed product").

In the water washing step S3, the stirring time of the slurry Lr1 consisting of the washed material and water is preferably 10 minutes or more, more preferably 15 minutes or more, and particularly preferably 20 minutes or more. Usually, water-soluble alkali metal salts are highly soluble in water, so no special conditions are required for stirring the slurry Lr1.

This water washing step S3 dissolves the alkali metals contained in the biomass ash BA1 in water. The slurry Lr1 in which the alkali metals are dissolved in water has its moisture content effectively reduced by the solid-liquid separator 17 installed downstream, and is separated into a solid material (cake C1) that can be used as a cement raw material, etc., and wastewater W3.

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 centrifugal pump, piston pump, mono pump, or hose pump may be used.

As the solid-liquid separator 17, a general-purpose filter such as a filter press, a pressurized leaf filter, a screw press, a belt press, or a belt filter may be used. In the embodiment shown in FIG. 2, the solid-liquid separator 17 is illustrated as being composed of a filter press.

The solid-liquid separator 17 is equipped with a supply device 15 for washing water W2, which separates the transported slurry Lr1 into a cake C1 (solid phase) of the washed product and wastewater W3 (liquid phase) containing alkali metals. At this time, the cake C1 is separated while being washed with the washing water W2. As the washing water W2, room temperature water may be used in an amount of at least three times, preferably at least four times, and more preferably at least five times the mass of the washed product.

The cake C1 separated by the solid-liquid separator 17 has an alkali metal component concentration reduced to 2.0% by mass or less, more typically 1.5% by mass or less, and even more typically 1.0% by mass or less, and can be effectively used as a cement raw material, etc. The alkali metal concentration here refers to an analytical value obtained by a known method, for example, the FP method using an X-ray fluorescence device, or a wet analysis (acid decomposition-ICP atomic emission spectrometry).

This water washing step S3 corresponds to step (c).

[Second embodiment]
A second embodiment of the method for removing an alkali metal according to the present invention will be described, focusing on the differences from the first embodiment.

Figure 6 is a flow chart that shows the steps of the alkali metal removal method of this embodiment. Also, Figure 7 is a block diagram that shows an example of an alkali metal removal device 1 that implements the alkali metal removal method shown in Figure 6.

As shown in FIG. 6, the alkali metal removal method of this embodiment differs from the first embodiment in that it includes a classification process S4 that is performed prior to the mixing process S1.

(Classification process 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 each separately. In the alkali metal removal apparatus 1 shown in Fig. 7, the classification step S4 is performed by a classifier 3. In the following, the biomass ash BA1 before the classification step S4 is performed may be referred to as "raw powder BA1".

Here, fine biomass ash powder BA2 (hereinafter simply abbreviated as "fine powder BA2") refers to biomass ash with a finer particle size than the determined classification point, and coarse biomass ash powder BA3 (hereinafter simply abbreviated as "coarse powder BA3") refers to biomass ash with a coarser particle size than the aforementioned classification point. The classification point determined in 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.

In this specification, the particle size of biomass ash (raw powder BA1, fine powder BA2, coarse powder BA3) refers to the measurement value by laser diffraction particle size distribution measurement method using ethyl alcohol as a solvent, unless otherwise specified. The particle size of commonly available biomass ash varies depending on the type of biomass fuel and the type and operation method of the boiler that burns the biomass, but the _D50 value by laser diffraction particle size distribution measurement method is 15 μm to 200 μm, and the maximum particle size ( _D100 ) is 150 μm to 1000 μm. The _D50 value means the particle size at 50% cumulative in the volume-based particle size distribution.

The classifier 3 is not particularly limited as long as it is a device that can classify the biomass ash raw powder BA1 at the classification points on the order of μm as described above. For example, a sieve, an inertial classifier, a centrifugal classifier, a gravity classifier, etc. can be suitably used, and from the viewpoint of classification accuracy, it is preferable to use a cyclone-type air separator or a sieving device. In the embodiment shown in Figure 7, the classifier 3 is illustrated as being composed of a cyclone-type air separator.

This classification step S4 may be performed either dry or wet. If it is performed wet, it may be considered that the water washing step S3 of the fine powder BA2 described below has been performed.

The classification device 3 may be provided with a storage tank for the biomass ash raw powder BA1. In addition, a supply device may be provided for quantitatively supplying the raw powder BA1 from the storage tank to the classification device 3. These storage tanks and supply devices may be used appropriately depending on the state of the received biomass ash raw powder BA1.

Fluidized bed incinerators are fed with sand, mainly composed of quartz, as a fluidizing medium, and limestone for desulfurization. The fly ash from such incinerators (raw biomass ash powder BA1) contains relatively coarse molten solidified or agglomerated glass and sand-derived materials, as well as relatively fine volatilized alkali metal salts and the aforementioned limestone-derived materials. In other words, of the alkali metals (Na, K) contained in the raw powder BA1, the chlorides, carbonates, and sulfates that are water-soluble are present in large amounts on the fine powder BA2 side, while the silicate glass that is sparingly soluble is present in large amounts on the coarse powder BA3 side.

In other words, this classification process S4 separates the raw biomass ash powder BA1 into fine powder BA2, which contains a relatively large amount of water-soluble alkali metal salts, and coarse powder BA3, which contains a relatively large amount of sparingly soluble alkali metal salts.

This classification process S4 corresponds to process (d).

(Mixing step S1)
The coarse powder BA3 obtained in the classification step S4 is mixed with the calcium source CA and the chlorine source CL. In the example shown in Fig. 7, the coarse powder BA3 supplied from the outlet 3b of the classifier 3 is mixed with the calcium source CA and the chlorine source CL in the mixer 5.

In the mixing step S1 of this embodiment, the amount of calcium source CA added is adjusted so that the hydraulic ratio of the mixture of coarse powder BA3 and calcium source CA is preferably 0.3 or more, more preferably 0.3 to 0.6. The implementation of mixing step S1 overlaps with the first embodiment, so a description thereof will be omitted.

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

In this embodiment, the mixing step S1 can be carried out in the same manner as in Figures 3 to 5. This also applies to the third embodiment described below.

In addition, by performing the classification step S4 as in this embodiment, a relatively large amount of calcium (CaCO ₃ , CaO, CaSO ₄ , etc.) contained in the raw powder BA1 of biomass ash is contained in the fine powder BA2. This is considered to be due to the limestone for desulfurization that is fed into the fluidized bed incinerator as described above. The limestone for desulfurization is sometimes fed in a finely pulverized state in order to enhance the reaction, and as a result, it is assumed that the calcium-containing substance has a relatively fine particle size. 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 feeding 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.

In contrast, in the present embodiment, the calcium source CA is mixed with the coarse powder BA3 obtained after classification so that the hydraulic coefficient is 0.3 or more, and then the heating step S2 is performed, thereby suppressing the melting and sintering phenomenon described above. As a result, the alkali metal salt is less likely to be encapsulated in the coarse powder BA3.

(Heating process S2)
The second embodiment is the same as the first embodiment except that the mixture BC as the object to be heated contains the coarse powder BA3 instead of the raw powder BA1 of biomass ash, and therefore the description thereof will be omitted. Here, the heating step S2 is performed only on the fine powder BA2, so that a larger amount of raw powder BA1 of biomass ash can be treated, and the energy required for heating and the amounts of the calcium source CA and chlorine source CL used can be reduced, resulting in a smaller environmental load.

(Water washing step S3)
In this 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 with water. This water-washing step S3 dissolves and removes water-soluble alkali metal salts contained in the fine powder BA2 and the heat-treated product P1.

Compared to the first embodiment, the water washing device 9 of this embodiment shown in FIG. 7 differs in that in addition to the heat-treated material P1 supplied from the heating device 7, fine powder BA2 separated and recovered by the classifier 3 and supplied from the discharge port 3a is washed with water, but the rest is the same.

As mentioned above, the fine powder BA2 contains a relatively large amount of water-soluble alkali metals, and the alkali metals can be dissolved and removed by this water washing step S3. In addition, the coarse powder BA3 contains a relatively large amount of sparingly soluble alkali metals, but by going through the previous heating step S2, some of the sparingly soluble alkali metals have been converted into water-soluble alkali metal salts, and the alkali metals contained in these alkali metal salts can be dissolved and removed.

According to the method of this embodiment, the heating step S2 is performed only on the coarse powder BA3, which contains a relatively large amount of sparingly soluble alkali metals, and the alkali metals are removed from the fine powder BA2 by the water washing step S3. In other words, while the heating step S2 is being performed on the coarse powder BA3 in the heating device 7, it is also possible to perform the water washing step S3 on the fine powder BA2, so that the amount of alkali metals removed from the biomass ash raw powder BA1 can be increased within the same time period.

Of the total alkali metal components contained in biomass ash raw powder BA1, alkali metal components in the form of water-soluble salts typically account for 25% to 45% of the total (100%), and alkali metal components in the form of sparingly soluble salts account for 55% to 75% of the total (100%), on a molar basis.

Of the total alkali metal components contained in the raw biomass ash powder BA1, the total alkali metal components contained in the biomass ash with a particle size of 30 μm or less, i.e., the fine powder BA2, is 40% to 60% of the total 100% in molar terms, of which 70% to 90% are water-soluble alkali metal components.

Therefore, after classifying the biomass ash raw powder BA1 into fine powder BA2 and coarse powder BA3 in the classification step S4, the fine powder BA2 is washed with water in the water washing step S3, thereby removing 30% to 50% of the total alkali metal components contained in the biomass ash raw powder BA1.

If the classification point of the raw powder BA1 of biomass ash in the classification step S4 is set to 53 μm, then the fine powder BA2 with a particle size of 53 μm or less classified in the classification step S4 is washed with water in the water washing step S3, thereby removing 20% to 35% of the total alkali metal components contained in the raw powder BA1.

Furthermore, the alkali metal components contained in the coarse powder BA3 in the form of sparingly soluble salts are chlorinated and roasted by heating together with the chlorine source CL, and are converted into water-soluble salts. As a result, most of them are removed by washing with water in the water washing step S3.

[Third embodiment]
A third embodiment of the method for removing an alkali metal according to the present invention will be described, focusing on differences from the first and second embodiments.

Figure 8 is a flow chart that shows the steps of the alkali metal removal method of this embodiment. Also, Figure 9 is a block diagram that shows an example of an alkali metal removal device 1 that implements the alkali metal removal method shown in Figure 8.

As shown in FIG. 8, the alkali metal removal method of this embodiment differs from the second embodiment in that it includes a crushing process S5 that is performed after the classification process S4.

(Crushing step S5)
The pulverization step S5 is performed to refine the particle size of the coarse powder BA3 classified in the classification step S4. The refined coarse powder BA3 (hereinafter referred to as "pulverized coarse powder BA3a") is mixed with the calcium source CA and the chlorine source CL in the mixing step S1. In the alkali metal removal device 1 shown in Fig. 9, the pulverization step S5 is performed by the pulverization device 4. The pulverization step S5 and the mixing step S1 may be performed simultaneously by pulverizing the coarse powder BA3 together with the calcium source CA and the chlorine source CL.

It is assumed that the coarse powder BA3 contains sparingly soluble alkali metal salts evenly throughout. By carrying out this crushing step S5 before the heating step S2, the exposed area of the alkali metal increases, improving the reactivity with the chlorine contained in the chlorine source CL in the heating step S2, and enabling more efficient conversion to alkali metal salts. Furthermore, in the heating step S2, the reactivity between the silicon contained in the coarse powder BA3 and the calcium contained in the calcium source CA improves, making it easier to become a Ca-containing mineral, and suppressing melting and sintering of the coarse powder BA3.

The Blaine specific surface area of the coarsely ground product BA3a after pulverization in the pulverization step 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 coarsely ground product BA3a, the higher the reactivity between the alkali metal contained in the coarsely ground product BA3a and the chlorine contained in the chlorine source CL, but on the other hand, the coarsely ground product BA3a is more likely to melt. If the coarsely ground product BA3a is finely ground to such an extent that the Blaine specific surface area exceeds 7,000 cm ² /g, melting occurs significantly during the heating step S2, and the alkali metal salt is more likely to be encapsulated.

The lower limit of the particle size of the coarsely pulverized product BA3a after pulverization in the pulverization step S5 may be a value that provides a Blaine specific surface area of 7,000 ^cm2 /g or less, for example, 0.5 μm or more. If the coarsely pulverized product BA3a is pulverized to a particle size of less than 0.5 μm, it will be easily melted and sintered in the subsequent heating step S2.

Specifically, the crushing device 4 can be suitably used with a tube mill, a vertical roller mill, a jaw crusher, a gyratory crusher, a cone crusher, an impact crusher, a roll crusher, an aerofoil mill, or the like. When a plurality of these devices are combined to form the crushing device 4, a classifier is provided between each crusher to construct a closed circuit crushing system, thereby efficiently obtaining a coarsely crushed product BA3a with a uniform particle size. In this case, the classifier is not particularly limited as long as it can classify the coarsely crushed product BA3a at a predetermined classification point, and a sieve (in-plane motion sieve, vibrating sieve), a gravity classifier, an inertia force classifier, a centrifugal classifier such as a cyclone, a centrifugal classifier with a rotating blade such as a cyclone air separator, or the like can be suitably used. Among them, a centrifugal classifier with a rotating blade such as a cyclone air separator is preferred because of the simplicity of the equipment and the ease of operation and adjustment. A grinding machine with a built-in classifier or sieve can also be used as the grinding device 4.

This grinding step S5 corresponds to step (e).

Specific test examples are presented below to explain the present invention in more detail, but the present invention is not limited to the aspects of these test examples.

(Verification 1: Verification of classification process S4)
As the biomass ash raw powder BA1, fly ash collected in an exhaust gas dust collector (bag filter) of a biomass power generation plant (circulating fluidized bed boiler) that uses PKS as the main fuel was used, and the effect of classifying this fly ash was verified.

The raw biomass ash powder BA1 was classified into fine powder BA2 and coarse powder BA3 with a classification point of 53 μm. The chemical composition of the biomass ash BA1 before classification, and the fine powder BA2 and coarse powder BA3 after classification was investigated. The results are shown in Table 1. Note that in Table 1, the values used for alkali metals were obtained by analysis of an acid-digested sample using ICP atomic emission spectrometry, and the values used for other chemical components were obtained by analysis using an X-ray fluorescence analyzer (Rigaku Corporation, ZSX Primus II) (FP method: fundamental parameter method).

"R ₂ O" in Table 1 indicates the total amount of alkali metal components in the composition, calculated from "R ₂ O = Na ₂ O + 0.658 x K ₂ O", as described above.

In addition, when the particle size distribution of the biomass ash raw powder BA1 before classification was measured based on the laser diffraction/scattering method, the _D10 value was 8.3 μm, the _D50 value was 44.3 μm, and the _D90 value was 274.7 μm.

Table 2 shows the mass distribution ratios by classification of biomass ash raw powder BA1, and the distribution ratios of K and Cl. Table 3 shows the results of the analysis of the concentrations of K and Cl contained in raw powder BA1, coarse powder BA3, and fine powder BA2.

Table 4 shows the results of XRD analysis for the raw biomass ash powder BA1, the fine powder BA2 obtained in the classification process S4, and the coarse powder BA3. In Table 4, the presence of a substance confirmed by XRD analysis is indicated as "○", the presence of a trace amount is indicated as "△", and the absence of a substance at all is indicated as "×".

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

From the results of Tables 4 and 5, it can be seen that when biomass ash raw powder BA1 is classified, calcium-containing substances such as CaO, _CaSO4 , and _CaCO3 are found in relatively large amounts on the fine powder BA2 side, and as a result, the hydraulic hardness rate of coarse powder BA3 is lower than that of raw powder BA1.

(Verification 2: Verification of the water washing step S3)
The effect of washing the biomass ash raw powder BA1, and the coarse powder BA3 and fine powder BA2 obtained in Verification 1 above was verified.

The conditions for the water washing step are as follows.
Each sample (raw powder BA1, coarse powder BA3, and fine powder BA2) was stirred with 4 times the amount of water at room temperature for 30 minutes, and the resulting slurry Lr1 was suction filtered, washed with the same amount of water as used for making the slurry Lr1, and filtered to produce cake C1. The content of alkali metal components in the resulting cake C1 was determined by analyzing the acid-decomposed sample using ICP atomic emission spectrometry. The results are shown in Table 6.

In Table 6 and tables described later, the "K removal rate" is calculated using the following formula (1).
K removal rate=[d1-{(1-d2)-d3}×d4]/d1...(1)
Here, each symbol in the formula (1) has the following value.
d1: Content (concentration) of K (potassium) in the samples before processing (raw powder BA1, coarse powder BA3, fine powder BA2)
d2: weight loss rate of the sample due to the heating step S2; d3: weight loss rate of the sample due to the water washing step S3; d4: content (concentration) of K contained in the cake C1 obtained after solid-liquid separation.

However, in this verification 2, since the heating process was not performed, d2 = 0 in equation (1).

The results in Table 6 show that for the fine powder BA2 obtained after classification, K (potassium) can be efficiently removed by washing with water. On the other hand, for the raw powder BA1 and coarse powder BA3, K cannot be efficiently removed by simply performing the water washing step S3. This confirms that raw powder BA1 and coarse powder BA3 contain large amounts of alkali metals, including the sparingly soluble K.

(Verification 3: Verification of raw powder BA1)
The raw powder BA1 was mixed with the calcium source CA and the chlorine source CL, and then a heating step was carried out.

The chlorine source CL was mixed by mixing a chlorine-containing substance ( _CaCl2 reagent powder) having a molar content of a predetermined multiple relative to the content (mol) of K (potassium) as an alkali metal component in the raw powder BA1.

The calcium source CA was mixed by mixing calcium carbonate (CaCO ₃ ) in an amount adjusted so that the hydraulic hardness of the mixture would be a predetermined value.

The calcium source CA and the chlorine source CL were mixed with the raw powder BA1 by bag mixing. The mixture was heated by placing 100 g of the mixture in an alumina crucible and heating it for 60 minutes in a tabletop high-speed heating electric furnace (manufactured by Motoyama Co., Ltd.).

The mixture was subjected to a heating step S2 under different temperature conditions, and then the heat-treated product P1 was subjected to a water washing step S3 in the same manner as in Verification 2, and the content of alkali metal components in the resulting cake C1 was determined. The results are shown in Table 7 and Figure 10. The method for calculating the K removal rate is based on the above formula (1).

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

From this, it can be seen that in the heating step S2, particularly when the raw powder BA1 and the chlorine source CL are heated to 800°C or higher, the alkali metals contained in the raw powder BA1 can be efficiently removed by increasing the hydraulic ratio by mixing the calcium source CA in advance. By performing the heating step S2 with the hydraulic ratio increased, melting and sintering of the raw powder BA1 is suppressed, and water-soluble alkali metal salts are less likely to be incorporated into the particles of the raw powder BA1.

(Verification 4: Verification of coarse powder BA3)
The coarse powder BA3 obtained in verification 1 was mixed with a calcium source CA and a chlorine source CL and subjected to a heat treatment.

The process of mixing the coarse powder BA3 with 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.

The mixture was subjected to a heating step S2 under different temperature conditions, and then the heat-treated product P1 was subjected to a water washing step S3 in the same manner as in Verification 2, and the content of alkali metal components in the resulting cake C1 was determined. The results are shown in Table 8 and Figure 11. The method for calculating the K removal rate is based on the above formula (1).

As shown in Table 8 and Figure 11, when biomass ash coarse powder BA3 was heated, the K removal rate was increased by increasing the hydraulic modulus HM regardless of the heating temperature between 800°C and 1200°C. This is thought to be due to the fact that the hydraulic modulus HM of the coarse powder BA3 obtained by classifying biomass ash raw powder BA1 is significantly lower than that of the raw powder BA1 (see Table 5 above). In other words, when the hydraulic modulus is as low as 0.08, such as in samples #B1, #B4, #B7, and #B10, even if heating is performed together with the chlorine source CL, a relatively large amount of the obtained alkali metal salt cannot be removed by the water washing step S3.

In particular, comparing samples #B1 and #B10, which have a hydraulic modulus HM of 0.08, the K removal rate is lower in sample #B10, which was heated at a higher temperature. This result suggests that heating at a high temperature with a low hydraulic modulus HM caused part of the coarse powder BA3 to melt and sinter, resulting in the alkali metal salt being incorporated inside the coarse powder BA3. On the other hand, comparing samples #B2, #B5, #B8, and #B11, which have a hydraulic modulus 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, which have a hydraulic modulus HM of 0.59.

This shows that, particularly when the material to be treated is coarse powder BA3, the contained alkali metals can be largely removed by mixing a calcium source CA to increase the hydraulic modulus HM and then heating it together with a chlorine source CL in a high-temperature environment.

(Verification 5: Verification of coarse powder BA3a)
The coarse powder BA3 obtained in the verification 1 was further pulverized in the pulverization step S5, and then mixed with the calcium source CA and the chlorine source CL and subjected to a heat treatment. The coarse powder BA3 was pulverized using a fine pulverizer (manufactured by Harzok Japan Co., Ltd.) using a tungsten vessel.

The process of mixing the chlorine source CL and the calcium source CA with the coarsely ground powder BA3a obtained after grinding, and the process of heating this mixture were carried out in the same manner as in Verification 3.

By performing the grinding step S5 for different grinding times, coarse ground powder BA3a with different Blaine surface areas was obtained, and then the chlorine source CL and calcium source CA were mixed with each of the coarse ground powders BA3a and the heating step S2 was performed. The obtained heat-treated product P1 was subjected to the water washing step S3 in the same manner as in Verification 2, and the content of alkali metal components in the obtained cake C1 was determined. The results are shown in Table 9 and Figure 12. The calculation method for the K removal rate is based on the above formula (1). For comparison, Table 9 also shows the results when using coarse powder BA3 that was not subjected to the grinding step S5.

The results in Table 9 and Figure 12 show that the K removal rate can be increased by crushing the coarse powder BA3. It is believed that by crushing the coarse powder BA3 and then heating it together with the chlorine source CL, the exposed area of the alkali metal contained in the coarse powder BA3 is increased, improving the reactivity with the Cl contained in the chlorine source CL and increasing the amount of water-soluble alkali metal salt produced.

On the other hand, it was confirmed that when the material was pulverized finely to such an extent that the Blaine specific surface area was 10,200 cm ² /g, the K removal rate was reduced.

Considering the results in Table 9 and Figure 12, it is considered that the reactivity of Cl with alkali metals was improved by finely refining the Blaine specific surface area of the coarse powder pulverized material BA3a to 1,040 ^cm2 /g, 2,630 ^cm2 /g, 4,130 ^cm2 /g, and 6,580 ^cm2 /g.

On the other hand, when the Blaine specific surface area of the coarse powder BA3a is increased from 6,580 cm ² /g to 10,200 cm ² /g, that is, when the coarse powder BA3 is further refined, the tendency of the coarse powder BA3a to melt and sinter when heated becomes more pronounced than the degree of improvement in the reactivity between Cl and alkali metals, and the proportion of water-soluble alkali metal salts contained in the coarse powder BA3a increases. In other words, when grinding the coarse powder BA3, it is preferable that the Blaine specific surface area of the coarse powder BA3a obtained after grinding is equal to or less than the upper threshold between 6,580 cm ² /g and 10,200 cm ² /g. In view of the results of Table 9 and FIG. 12, this upper threshold can be set to 7,000 cm ² /g.

Reference Signs List 1: Alkali metal removal device 2: Storage tank 3: Classifier 3a: Discharge outlet 3b: Discharge outlet 4: Crusher 5: Mixer 5a: Mixer 7: Heater 9: Water washing device 11: Supply hopper 13: Supply device 15: Supply device 17: Solid-liquid separator 31: Internal combustion burner 33: Intake fan 35: Slurry agitator BA1: Biomass ash (raw powder)
BA2: Fine powder BA3: Coarse powder BA3a: Coarse powder pulverized material BC: Mixture C1: Cake CA: Calcium source CL: Chlorine source G1: Air G2: Combustion exhaust gas Lr1: Slurry P1: Heat treatment material W1: Water W2: Washing water W3: Wastewater

Claims (10)

A method for removing alkali metals from fly ash of woody biomass combustion ash, comprising the steps of:
(a) mixing the fly ash with a calcium source and a chlorine source, either simultaneously or sequentially;
and a step (b) of heating the mixture of the fly ash having the hydraulic ratio adjusted by the step (a) to obtain a heat-treated product,
The method for removing an alkali metal, wherein the step (a) includes a step of adding the calcium source in an amount adjusted so that the hydraulic hardness of the mixture is 0.3 to 0.6. The method for removing alkali metals according to claim 1, further comprising a step (c) of washing the heat-treated product obtained in the step (b) with water. 3. The method for removing an alkali metal according to claim ₁ or 2, characterized in that the calcium source used in the step (a) includes one or more types belonging to the group consisting of industrial raw materials and waste materials containing at least one of CaCO3 and CaO. The method for removing alkali metals according to any one of claims 1 to 3, characterized in that step (b) is a step of heating at a temperature of 800°C to 1300°C. The method for removing alkali metals according to any one of claims 1 to 4, characterized in that the chlorine source used in step (a) has a size of 80 mm or less. The alkali metal removal method according to any one of claims 1 to 5, characterized in that step (a) includes a step of introducing an amount of the chlorine source adjusted so that the ratio (M2/M1) of the molar amount of total chlorine in the chlorine source (M2) to the molar amount (M1) of the total alkali metal components in the fly ash is within the range of 1 to 4. The method further comprises a step (d) of classifying the fly ash into fine powder and coarse powder,
The method for removing an alkali metal according to any one of claims 1 to 6, wherein the step (a) is a step of mixing the calcium source and the chlorine source with the coarse powder obtained after the fly ash is classified in the step (d). The method includes a step (c) of washing the heat-treated product obtained in the step (b) with water,
8. The method for removing an alkali metal according to claim 7, wherein the step (c) is a step of washing with water the fine powder obtained after the fly ash is classified in the step (d) in addition to the heat-treated product obtained in the step (b). The method further includes a step (e) of pulverizing the coarse powder obtained by the step (d) to obtain a coarse powder pulverized product,
9. The method for removing an alkali metal according to claim 7 or 8, wherein the step (a) is a step of mixing the calcium source and the chlorine source with the coarsely pulverized product obtained in the step (e). 10. The method for removing an alkali metal according to claim 9, wherein the step (e) is a step of pulverizing the coarse powder so that the Blaine specific surface area of the pulverized product is 7,000 cm ² /g or less.

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