Method for producing modified woody biomass ash

Abstract

To provide a method for simply and efficiently reducing an alkali metal from a predetermined woody biomass ash.SOLUTION: In a method for producing modified woody biomass ash, which includes heat-treating in water at 60-100°C woody biomass ash having a pH level of 12.5 or more when the woody biomass ash is made into slurry, where a total amount of alkali (R2O) of the woody biomass ash is preferably 4.0 wt.% or more.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a method for producing modified wood biomass ash having reduced alkali metal content. [Background technology]

[0002] Conventionally, coal ash generated in coal-fired power plants has been used as a cement raw material.

[0003] Meanwhile, in recent years, as part of the movement toward carbon neutrality, biomass power generation, which burns biomass fuels including wood chips and palm kernel shells (PKS), has become more common, and there are also plans to use the incineration ash generated by the combustion of this biomass as a raw material for cement.

[0004] However, while the content of this biomass fuel varies depending on the type and place of production, it generally contains a lot of alkali metals, especially potassium, compared to coal. Since alkali metals such as potassium are a cause of alkali-aggregate reactions, the content in cement is strictly regulated by product standards, making it difficult to use biomass incineration ash (biomass ash) as it is.

[0005] Under these circumstances, methods for reducing alkali metals from biomass ash have been proposed. For example, a method for removing alkali metals from fly ash of woody biomass has been proposed, which includes a step (a) of classifying the fly ash into fine powder and coarse powder, a step (b) of pulverizing the surface portion of the coarse powder obtained in step (a) to obtain a pulverized product, a step (c) of classifying the pulverized product obtained in step (b) into pulverized fine powder and pulverized coarse powder, a step (d) of heating the pulverized fine powder obtained in step (c) together with a chlorine source to obtain a heat-treated product, and a step (e) of washing the fine powder obtained in step (a) and the heat-treated product obtained in step (d) with water (see Patent Document 1).

[0006] In addition, a method for producing low-potassium wood biomass ash has been proposed, which includes a first step of heating wood biomass ash to 500 to 850°C and contacting the wood biomass ash with a gas containing hydrogen chloride, and a second step of washing the wood biomass ash after contact with water to remove soluble matter (see Patent Document 2).

[0007] Furthermore, a method for washing biomass combustion ash has been proposed, which includes a water washing step in which biomass combustion ash containing alkali-containing minerals is washed with water containing carbon dioxide (see Patent Document 3).

[0008] However, these methods require complicated operations, and there is a need for a method that can reduce alkali metals more simply and efficiently. If it becomes possible to reduce alkali metals from biomass ash more simply and efficiently, it will be possible to easily expand the use of biomass ash to cement raw materials, etc., in the same way as coal ash. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] Patent Publication No. 2021-146236 [Patent Document 2] JP 2021-104482 A [Patent Document 3] JP 2020-158321 A Summary of the Invention [Problem to be solved by the invention]

[0010] An object of the present invention is to provide a method for simply and efficiently reducing alkali metals from a given wood biomass ash. [Means for solving the problem]

[0011] As a result of intensive research to solve the above-mentioned problems, the inventors discovered that alkali metals in biomass ash that has a pH level of a certain level or higher can be effectively reduced by simply heating it in water, thereby completing the present invention.

[0012] That is, the present invention is as follows. [1] A method for producing modified wood biomass ash, characterized by heat-treating wood biomass ash having a pH of 12.5 or higher in water at 60 to 100°C. [2] The method for producing modified wood biomass ash according to [1] above, characterized in that the total alkali content (R2O) of the wood biomass ash calculated by the following formula is 4.0 mass% or more. Total amount of alkali (R2O) = amount of Na2O + 0.658 x amount of K2O [3] The method for producing modified wood biomass ash described in [1] above, wherein the mass ratio of the amount of alkali metals to the amount of calcium in the wood biomass ash ((Na2O+K2O) / CaO) is 0.3 or more. [4] The method for producing modified wood biomass ash described in [2] above, wherein the mass ratio of the amount of alkali metals to the amount of calcium in the wood biomass ash ((Na2O+K2O) / CaO) is 0.3 or more.

[0013] [5] A method for producing cement, comprising using modified wood biomass ash produced by any one of the methods described in [1] to [4] above as part of a raw material to produce cement. [6] A method for modifying biomass ash, comprising heat-treating wood biomass ash having a pH of 12.5 or higher in water at 60 to 100°C. Effect of the Invention

[0014] According to the method of the present invention, alkali metals can be simply and efficiently reduced from a given wood biomass ash. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] [Method for producing modified wood biomass ash and method for modifying wood biomass ash] The method for producing modified wood biomass ash and the method for modifying wood biomass ash of the present invention are characterized in that wood biomass ash having a pH of 12.5 or more is heat-treated in water at 60 to 100°C.

[0016] Alkali metals such as sodium and potassium in woody biomass ash are believed to be mainly present in amorphous glass (aluminosilicate structure), and usually cannot be reduced by washing with water or hot water. However, as described above, the alkali metals in woody biomass ash with a pH of 12.5 or more can be reduced by simply heating it in water at 60 to 100°C. The reduction rate is, for example, 40% or more, and preferably 50% or more.

[0017] The mechanism by which the effects of the present invention are produced is believed to be as follows. Free lime (CaO) is present in wood biomass ash, and it is assumed that this free lime exists as calcium hydroxide in the wood biomass ash slurry. The pH of this saturated calcium hydroxide aqueous solution is generally about 12.4. Therefore, it is believed that in the wood biomass ash slurry of the present invention having a pH of 12.5 or more, sodium hydroxide, potassium hydroxide, etc. are present in addition to calcium hydroxide generated from free lime. Therefore, it is believed that by performing heat treatment in the presence of these calcium hydroxide, sodium hydroxide, potassium hydroxide, etc., the aluminosilicate structure, which is the main component of wood biomass ash, is destroyed, alkali metals are eluted into water, and the alkali metals are removed from the wood biomass ash.

[0018] Furthermore, the method of the present invention can achieve sufficient effects even with normal heat treatment at about 60 to 100° C., so it consumes less energy, is low cost, and also leads to reduced CO 2 emissions.

[0019] Specific examples of wood biomass ash to be treated in the method of the present invention (hereinafter referred to as wood biomass ash of the present invention) include those obtained by burning wood resources such as waste wood, palm kernel shells (PKS), white pellets, black pellets, palm kernel fiber pellets (EFB), etc. Wood biomass ash may contain other incineration ashes, etc., to the extent that the effects of the present invention are not impaired.

[0020] As described above, the wood biomass ash of the present invention has a pH of 12.5 or more, preferably 13.0 or more. This pH refers to the pH when water is added to the wood biomass ash of the present invention to form a slurry, and more specifically, for example, refers to the pH of a slurry prepared by adding three times the amount of water by mass to the wood biomass ash.

[0021] Furthermore, the wood biomass ash of the present invention preferably has a total alkali content (RO) of 4.0 mass% or more, more preferably 4.5 mass% or more, and even more preferably 5.0 mass% or more. Wood biomass ash that exhibits a high total alkali content can remove a larger amount of alkali metals by heating it in water.

[0022] Total alkali content (R2O) is a conversion value that indicates the total alkali content specified in the JIS standard for cement, and is calculated using the following formula. Total amount of alkali (R2O) = amount of Na2O + 0.658 x amount of K2O

[0023] The wood biomass ash of the present invention preferably has a mass ratio of the amount of alkali metals to the amount of calcium ((Na2O+K2O) / CaO) of 0.3 or more, more preferably 0.35 or more, and even more preferably 0.38 or more.

[0024] In wood biomass ash, the greater the amount of alkali metal relative to the amount of calcium, the greater the reduction in alkali metals. This is thought to be because, although various aluminosilicate compounds with different amounts of calcium and alkali exist in the amorphous matter of wood biomass ash, aluminosilicates that contain a large amount of alkali metal relative to calcium are particularly likely to dissolve in water.

[0025] The total alkali content (R2O) in wood biomass ash and the mass ratio of the alkali metal content to the calcium content of wood biomass ash ((Na2O+K2O) / CaO) can be determined by a method based on JIS R5204 "Fluorescent X-ray analysis method for cement."

[0026] The heating temperature in the underwater heat treatment of the method of the present invention is 60 to 100°C, more preferably 70 to 100°C, even more preferably 80 to 100°C, and particularly preferably 100°C. When the treatment is performed at 100°C, heating may be performed while replenishing water to compensate for the amount of evaporated water, but from the viewpoint of efficient energy utilization, it is preferable to adopt a reflux system in which a heat exchanger is connected to the reaction tank and evaporated water is returned to the reaction tank. Note that heating may be performed under pressure to a temperature above 100°C to about 200°C.

[0027] The heating time is preferably from 1 to 24 hours, more preferably from 2 to 12 hours, and even more preferably from 3 to 8 hours.

[0028] The heating method is not particularly limited as long as it can heat to a desired temperature. For example, heating methods using electricity, heating oil, steam, etc. are included, and a direct heating method using steam is preferred.

[0029] The heat treatment is preferably carried out with stirring. Any stirring method can be used as long as it can uniformly mix the slurry to be treated, and a general stirrer can be used.

[0030] The manufacturing method of modified wood biomass ash and the method of modifying wood biomass ash of the present invention specifically include, for example, a mixing step of mixing wood biomass ash with water, a heating step of heat-treating the mixture, and a filtering and washing step of filtering and washing the treated ash. Since the heating step, which is an important step of the present invention, has been described above, the mixing step and the filtering and washing steps will be described below.

[0031] (Mixing process) The mixture mass ratio of wood biomass ash to water (wood biomass ash:water) is preferably in the range of 1:1.0-10.0, more preferably in the range of 1:1.0-5.0, and even more preferably in the range of 1:2.0-5.0. By being in this range, the wood biomass ash is sufficiently mixed with water, and the amount of water is not too much, so that wasteful use of heat energy can be suppressed. In this case, an alkaline earth component such as calcium hydroxide or calcium oxide may be added.

[0032] (filtration and washing process) The filtration and washing process is a process in which the woody biomass ash that has been subjected to the underwater heat treatment in the heating process is filtered and washed. Any method can be adopted for the filtration, and examples include methods using a filter press, a belt filter, a drum filter, etc. The filtration temperature can be any temperature because the dissolved sodium and potassium compounds (NaCl, KCl, NaOH, KOH) have high solubility and the solubility does not change significantly even if the water temperature is changed. The liquid used for washing can be industrial water, tap water, distilled water, ion-exchanged water, etc., and is preferably used in an amount three times or more, more preferably five times or more, by mass ratio relative to the woody biomass ash. The temperature of the washing water can also be any temperature for the above reasons.

[0033] [Cement manufacturing method] The modified wood biomass ash produced by the method of the present invention can be used as a part of a cement material. That is, the method of producing cement of the present invention is a method of producing cement using the modified wood biomass ash produced by the above-mentioned production method of the present invention as a part of a raw material. Specifically, for example, there can be mentioned a method of producing cement using cement clinker produced by using the modified wood biomass ash, and a method of producing cement using the modified wood biomass ash as an admixture with cement clinker or the like. EXAMPLES

[0034] [Example 1] 100 g of woody biomass ash (incinerated ash 1-3) and 300 g of ion-exchanged water were weighed into a 500 mL three-neck flask. The composition of the raw woody biomass ash used was analyzed according to JIS R 5204 "Fluorescent X-ray analysis method for cement". The analysis results are shown in Table 1.

[0035] [Table 1]

[0036] An Arlinn-type cooling tube through which cooling water adjusted to 25°C was passed using a circulating cooling water device, a thermometer (0-100°C mercury thermometer), and a PTFE stirring blade connected to a stirrer (three-one motor) were connected to a three-neck flask, and then the mixture was stirred at 200 rpm. The three-neck flask was heated using a mantle heater, and after reaching a predetermined temperature (reaction temperature), the mixture was maintained for a predetermined time (reaction time). After that, the mantle heater was removed from the flask to stop heating, and after confirming that the temperature had dropped to 40°C or less, the stirring by the stirrer was stopped, and the slurry in the flask was suction filtered (filter paper Advantec 5B) to filter out the solids. The filtered solids were washed with 500 mL of ion-exchanged water to obtain modified wood biomass ash.

[0037] The reaction conditions (reaction temperature, reaction time) and the analysis results of the modified wood biomass ash (conducted according to JIS R 5204 "Fluorescent X-ray analysis method for cement") are shown in Table 2.

[0038] [Table 2]

[0039] As shown in Table 2, the methods of Examples 1 to 5 of the present invention were able to effectively reduce the potassium content (KO), sodium content (NaO), and total alkali content (RO). In particular, the amount of alkali reduction was large in the ash of Example 2 in which the alkali (total amount of sodium + potassium) was high relative to calcium (ash with a high alkali / Ca ratio). The method of the present invention can reduce the alkali / Ca ratio to about 0.2, so it is particularly effective for wood biomass ash with an alkali / Ca ratio of 0.3 or more. Furthermore, in terms of the amount of substance, the amount of alkali reduction was greater than the amount of chlorine and sulfur.

[0040] In contrast, in Comparative Example 1, where no heat treatment was performed, little reduction in alkali was observed, and the reduction rate of RO was low at 27.2%. In Comparative Example 2, where wood biomass ash with an inherently low pH was used, the effect of the method of the present invention was limited. [Industrial Applicability]

[0041] The modified wood biomass ash produced by the method of the present invention can be used as a cement material, etc., and therefore the present invention is industrially useful.

Claims

1. A method for producing modified wood biomass ash, comprising heat-treating wood biomass ash having a pH of 12.5 or higher in water at 60 to 100°C.

2. The total alkali content of the wood biomass ash calculated by the following formula (R ２ 2. The method for producing modified wood biomass ash according to claim 1, characterized in that the content of .O) is 4.0 mass% or more. Total alkali amount (R ２ O) = Na ２ O amount + 0.658×K ２ O amount

3. The wood biomass ash has a mass ratio of alkali metal to calcium ((Na ２ O+K ２ 2. The method for producing modified wood biomass ash according to claim 1, wherein the ratio of CaO) / CaO) is 0.3 or more.

4. The wood biomass ash has a mass ratio of alkali metal to calcium ((Na ２ O+K ２ 3. The method for producing modified wood biomass ash according to claim 2, wherein the ratio of CaO) / CaO) is 0.3 or more.

5. A method for producing cement, comprising the steps of: producing cement by using modified wood biomass ash produced by the method according to any one of claims 1 to 4 as part of a raw material.

6. A method for modifying biomass ash, comprising heat-treating wood biomass ash having a pH of 12.5 or more in water at 60 to 100°C.

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