Production method for modified woody biomass ash

Abstract

A method for easily and efficiently reducing the amount of alkali metals in prescribed woody biomass ash, wherein woody biomass ash having a pH level of 12.5 or higher is subjected to a heat treatment at 60-100°C in water at normal pressure.

Description

Method for producing modified wood biomass ash

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

[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 trend toward carbon neutrality, biomass power generation, which involves burning biomass fuels such as wood chips and palm kernel shells (PKS), has become increasingly popular, and the use of incineration ash generated by the combustion of this biomass as a cement raw material is also being considered.

[0004] However, although the content of alkali metals in biomass fuels varies depending on the type and place of production, they generally contain a higher amount of alkali metals, especially potassium, than coal. Since alkali metals such as potassium cause alkali-aggregate reactions, the content of alkali metals in cement production is strictly regulated by product standards, making it difficult to use biomass incineration ash (biomass ash) as 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 ash has been proposed, which includes the steps of: (a) classifying the fly ash into fine powder and coarse powder; (b) pulverizing the surface of the coarse powder obtained in step (a) to obtain a pulverized product; (c) classifying the pulverized product obtained in step (b) into pulverized fine powder and pulverized coarse powder; (d) heating the pulverized fine powder obtained in step (c) together with a chlorine source to obtain a heat-treated product; and (e) 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 bringing the wood biomass ash into contact with a gas containing hydrogen chloride, and a second step of washing the wood biomass ash after contact with water to remove soluble components (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 a simpler and more efficient method for reducing alkali metals is desired. If it were possible to more simply and efficiently reduce alkali metals from biomass ash, it would be possible to easily expand its applications to cement raw materials, etc., similar to coal ash.

[0009] Japanese Patent Application Laid-Open No. 2021-146236 Japanese Patent Application Laid-Open No. 2021-104482 Japanese Patent Application Laid-Open No. 2020-158321

[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.

[0011] As a result of extensive research to solve the above problems, the inventors discovered that the alkali metal content of biomass ash exhibiting a pH above a certain level can be effectively reduced simply by 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 more in water at 60 to 100°C. [2] The total alkali content (R ２ The method for producing modified wood biomass ash according to [1] above, characterized in that the total alkali content (R ２ O) = Na ２ O amount + 0.658×K ２ [3] The wood biomass ash has a mass ratio of alkali metal to calcium ((Na ２ O+K ２ [4] The method for producing modified wood biomass ash according to the above [1], wherein the mass ratio of the alkali metal amount to the calcium amount ((NaO) / CaO) is 0.3 or more. ２ O+K ２The method for producing modified wood biomass ash according to [2] above, wherein the ratio of CaO) / CaO) is 0.3 or more.

[0013] [5] A method for producing cement using modified wood biomass ash produced by the method according to any one of [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 higher in water at 60 to 100°C.

[0014] According to the method of the present invention, alkali metals can be easily and efficiently reduced from a given wood biomass ash.

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

[0016] Alkali metals such as sodium and potassium in woody biomass ash are thought to exist mainly in amorphous glass (aluminosilicate structure), and typically cannot be reduced by washing with water or hot water. However, woody biomass ash with a pH of 12.5 or higher can have its alkali metal content reduced simply by heating it in water at 60 to 100°C, as described above. 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 achieved 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, whose pH is 12.5 or higher, sodium hydroxide, potassium hydroxide, and the like are present in addition to the calcium hydroxide produced from free lime. Therefore, it is believed that by performing a heat treatment in the presence of these calcium hydroxide, sodium hydroxide, potassium hydroxide, and the like, the aluminosilicate structure, which is the main component of wood biomass ash, is destroyed, and alkali metals are eluted into the water, thereby removing the alkali metals from the wood biomass ash.

[0018] Furthermore, the method of the present invention can achieve sufficient results even with ordinary heat treatment at about 60 to 100°C, so it consumes less energy, is low cost, and does not require CO ２ This will also lead to a reduction in CO2 emissions.

[0019] Specific examples of woody biomass ash to be treated in the method of the present invention (hereinafter referred to as woody 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. Woody biomass ash may contain other incineration ashes, etc., as long as the effects of the present invention are not impaired.

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

[0021] In addition, the wood biomass ash of the present invention has a total alkali content (R ２O) is preferably 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 have a larger amount of alkali metals removed by heating it in water.

[0022] Total alkali content (R ２ The total alkali content (R 0 ) is a conversion value that indicates the total alkali content specified in the JIS standard for cement, and is calculated using the following formula: ２ O) = Na ２ O amount + 0.658×K ２ O amount

[0023] The wood biomass ash of the present invention has a mass ratio of alkali metal to calcium ((Na ２ O+K ２ Preferably, the ratio (CaO) / CaO) is 0.3 or more, more preferably 0.35 or more, and even more preferably 0.38 or more.

[0024] In woody 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 calcium and alkali contents exist in the amorphous matter of woody biomass ash, aluminosilicates that contain a large amount of alkali metal relative to calcium are particularly likely to dissolve in water.

[0025] Total alkali content in wood biomass ash (R ２ O), and the mass ratio of the alkali metal content to the calcium content of wood biomass ash ((Na ２ O+K ２ The ratio of CaO to CaO can be determined by a method in accordance with 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 treatment is performed at 100°C, heating may be performed while replenishing water to compensate for the evaporation, but from the viewpoint of efficient energy utilization, it is preferable to employ a reflux system in which a heat exchanger is connected to the reaction vessel and the evaporated water is returned to the reaction vessel. Note that heating may be performed under pressure, to above 100°C to about 200°C.

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

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

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

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

[0031] (Mixing Step) The mixing mass ratio of woody biomass ash to water (woody biomass ash:water) is preferably in the range of 1:1.0 to 10.0, more preferably in the range of 1:1.0 to 5.0, and even more preferably in the range of 1:2.0 to 5.0. By keeping it in this range, the woody biomass ash is sufficiently mixed with water, and the amount of water is not too large, which prevents unnecessary use of thermal energy. At this time, 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 heat-treated in water in the heating process is filtered and washed. Any filtration method can be used, including methods using a filter press, belt filter, 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 do not change significantly even when 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, and more preferably five times or more, by mass relative to the woody biomass ash. For the above reasons, the temperature of the washing water can also be any temperature.

[0033] [Method for Producing Cement] The modified woody biomass ash produced by the method of the present invention can be used as part of a cement material. That is, the method for producing cement of the present invention is a method for producing cement using the modified woody biomass ash produced by the above-mentioned production method of the present invention as part of a raw material. Specific examples include a method for producing cement using cement clinker produced using the modified woody biomass ash, and a method for producing cement using the modified woody biomass ash as an admixture with cement clinker, etc.

[0034] Example 1: 100 g of woody biomass ash (incinerated ash 1 to 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 "X-ray fluorescence analysis method for cement." The analysis results are shown in Table 1.

[0035]

[0036] An Arlinn-type cooling tube, through which cooling water adjusted to 25°C using a circulating cooling water system, 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 the mixture was stirred at 200 rpm. The three-neck flask was heated using a mantle heater, and after reaching the specified temperature (reaction temperature), it was maintained for the specified time (reaction time). The mantle heater was then removed from the flask, heating was terminated, and after confirming that the temperature had dropped below 40°C, stirring by the stirrer was stopped. The slurry in the flask was suction filtered (Advantec 5B filter paper) to filter out the solids. The filtered solids were washed with 500 mL of ion-exchanged water to obtain modified wood biomass ash.

[0037] Table 2 shows 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").

[0038]

[0039] As shown in Table 2, in the methods of Examples 1 to 5 of the present invention, the potassium content (K ２ O), sodium content (Na ２ O), and the total alkali content (R ２ The alkali content was effectively reduced. In particular, the alkali content was greater in the ash of Example 2, which had a higher alkali content (total amount of sodium and potassium) 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, making it 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 alkali content was reduced more than the chlorine content and sulfur content.

[0040] In contrast, in Comparative Example 1, in which no heat treatment was performed, the alkali content was not significantly reduced, and R ２ The reduction rate of O was also low at 27.2%. In addition, in Comparative Example 2, which used wood biomass ash that originally had a low pH, the effect of applying the method of the present invention was limited.

[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 with reduced alkali metals, characterized by heat-treating wood biomass ash with a pH of 12.5 or higher in water at normal pressure and 60 to 100°C.

2. The total alkali content of the wood biomass ash calculated using the following formula (R ２ The method for producing modified wood biomass ash with reduced alkali metals according to claim 1, characterized in that the total alkali content (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 with reduced alkali metals according to claim 1, characterized in that 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 with reduced alkali metals according to claim 2, characterized in that the ratio of CaO) / CaO) is 0.3 or more.

5. A method for producing cement, comprising the steps of: producing cement 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 normal pressure and 60 to 100°C to reduce the alkali metal content of the wood biomass ash.

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