JP2002273374A - Method and device for treating alkaline fly ash - Google Patents

Abstract

PROBLEM TO BE SOLVED: To keep the moisture content of an alkaline fly ash within a specified range and thereby carbonate the fly ash very efficiently. SOLUTION: A spedified amount of the alkaline fly ash is introduced into a reaction device 4 and, after injecting water and stirring the fly ash and water, an exhaust gas is introduced into the reaction device 4 so as to achieve the carbonation of the fly ash. Next, the properties of the gas introduced into the reaction device 4 and the gas discharged from the reaction device 4 are measured respectively using measuring units 3 and 6, and the moisture content of the alkaline fly ash is calculated based on the measurement results. When the calculated value of the moisture content falls below a set range, a specified amount of water is supplied into the reaction device 4. After carbonating the fly ash, a heavy metal fixing agent is added into the reaction device 4, and later, water is injected into the device 4 to granulate the fly ash. Finally, the fly ash is discharged to the outside of the device 4.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for treating alkali fly ash containing heavy metals, and more particularly to a method and an apparatus suitable for preventing heavy metals and scale components from being eluted from alkali fly ash.

[0002]

2. Description of the Related Art When household garbage and industrial waste are incinerated in an incinerator, waste gas is generated. The waste gas contains dust containing heavy metals such as lead volatilized in the incinerator and strongly acidic gas such as hydrogen chloride (HCl) and sulfur oxide (SOx). And then released into the atmosphere. Fly ash is a dust component discharged after the treatment of the waste gas, and its composition varies depending on the treatment applied to the waste gas, and can be roughly classified into the following two types for each treatment method.

[0003] One treatment method is to use HCl or SO in waste gas.
This is a method in which a strongly acidic gas such as x is neutralized by adding an alkali powder such as slaked lime, and then dust is captured by a dust collector. Dust (fly ash) discharged by this method contains unreacted (excess) alkali powder such as slaked lime in addition to dust volatilized in the incinerator and a neutralization reaction product.
Shows strong alkalinity and is called alkaline fly ash.

Another method is a method of removing dust in waste gas by a dust collector and then neutralizing (absorbing) and removing acidic gas with an aqueous alkali solution such as caustic soda. Ash is almost neutral and is called neutral fly ash.

[0005] These fly ash are effectively used for landfill, ground construction, or the like, or are disposed of. In this case, since both the alkali fly ash and the neutral fly ash contain heavy metals, it is necessary to perform a treatment for preventing the contained heavy metals from being eluted in the effective use or disposal of the fly ash.

In particular, alkali fly ash contains a large amount of alkali such as unreacted slaked lime, so that the pH of the discharged liquid is high and lead and the like are easily eluted. In addition, elution of scale-forming components such as calcium may cause scale disturbance in fly ash treatment sewage facilities and water collection facilities in landfills. For this reason, for alkali fly ash, it is particularly important to perform a treatment for preventing elution of heavy metals and scale-forming components.

As one of the chemical treatment methods of the alkali fly ash, there is a phosphoric acid (salt) treatment method in which a specific amount of water-soluble phosphoric acid or a salt thereof is added to the fly ash to prevent elution of lead and cadmium. is there. As one type of this phosphoric acid treatment method, the required amount of water-soluble phosphoric acid or a salt thereof is reduced to reduce the cost of fly ash treatment, to prevent the elution of scale-forming components, and to further expose to acid rain. Japanese Patent Application Laid-Open No. 8-155417 discloses a method for treating alkali fly ash, which can reliably suppress the elution of heavy metals even when it is performed.

In the method of treating alkali fly ash disclosed in the same publication, alkalis in fly ash are neutralized with carbon dioxide before adding phosphoric acid or a salt thereof. After adding water to the ash and kneading, blow in carbon dioxide gas,
Next, a phosphoric acid-based heavy metal fixing agent is added and kneaded.

If unreacted slaked lime in alkali fly ash is reacted with carbon dioxide gas before the addition of phosphoric acid (salt) as described above, slaked lime becomes hardly soluble calcium carbonate. Elution is reduced. In addition, when phosphoric acid or a salt thereof is added and heavy metals such as lead and cadmium are immobilized as poorly soluble salts such as lead phosphate and cadmium phosphate, unreacted slaked lime is reduced, so unreacted lime is reduced. The amount of phosphoric acid or phosphate consumed by slaked lime is reduced, and the amount of phosphoric acid or phosphate required for immobilizing heavy metals can be reduced. Furthermore, since the treated fly ash has an enhanced pH buffering ability by coexisting calcium carbonate, it is possible to reduce a decrease in pH of the eluate due to acidic water, and to suppress elution of heavy metals and the like.

In this method, the amount of water added to the alkali fly ash and kneaded is 5 to 50% by weight, especially about 10 to 30% by weight, based on the subsequent neutralization efficiency. is there.

[0011] The amount of carbon dioxide blown is such that the pH of the water due to the eluate from the fly ash into the water after neutralization with carbon dioxide is 1%.
It is adjusted so as to be 0 to 12.5, preferably 11.0 to 12.0. Usually, the amount of carbon dioxide gas is about 5 to 60 liters per 100 g of alkali fly ash.

Phosphoric acid or a salt thereof is used as a phosphoric acid-based heavy metal fixing agent added after neutralization with carbon dioxide gas. Among these, phosphoric acid includes orthophosphoric acid, hypophosphorous acid, and the like.
Metaphosphorous acid, pyrophosphorous acid, orthophosphorous acid, hypophosphorous acid,
Examples include metaphosphoric acid, pyrophosphoric acid, triphosphoric acid, and condensed phosphoric acid. Examples of the phosphate include salts of these phosphoric acids, primary phosphates, and secondary phosphates. Particularly preferred are orthophosphoric acid (H ₃ PO ₄ ), dihydrogen-sodium phosphate (NaH ₂ PO ₄ ), and disodium hydrogen phosphate (N
a ₂ HPO ₄ ), condensed phosphoric acid and the like. The addition amount of these phosphoric acids and / or phosphates is about 1 to 30% by weight based on fly ash.

Another excellent method for treating heavy metal-containing ash with a phosphoric acid-based heavy metal fixing agent is disclosed in JP-A-11-1883.
No. 31 describes a method in which a phosphoric acid-based heavy metal fixing agent is added to a heavy metal-containing ash, kneaded, and then uniformly contacted with carbon dioxide gas or a gas containing carbon dioxide gas. Also in this method, carbon dioxide gas neutralizes and reacts with an alkali component (mainly Ca (OH) ₂ ) in the heavy metal-containing ash to lower the alkalinity of the ash, and makes the heavy metal in the heavy metal-containing ash hardly soluble. By using the carbonate, the elution effect of the heavy metal by the phosphate-based heavy metal fixing agent is enhanced.

In the method disclosed in JP-A-11-188331, the amount of kneading water added to the heavy metal-containing ash is about 10 to 60% by weight, especially about 20 to 40% by weight, based on the fly ash.

The phosphoric acid heavy metal fixing agent includes:
Phosphoric acid or a salt thereof is used. Among them, phosphoric acid includes orthophosphoric acid and hypophosphorous acid, metaphosphorous acid, pyrophosphorous acid, orthophosphorous acid, hypophosphoric acid, metaphosphoric acid, pyrophosphoric acid,
Triphosphoric acid and condensed phosphoric acid are used.
Salts of these phosphoric acids, first phosphates, second phosphate is used, preferably, orthophosphoric acid _(H 3 _PO 4), dihydrogen phosphate - sodium _(NaH 2 _PO 4), phosphoric acid - disodium hydrogen _(Na 2 _HPO 4), such as condensed phosphoric acid is used.

The amount of the phosphoric acid and / or phosphate added is 1 to 30% by weight, especially 4 to 1% by weight based on the heavy metal-containing ash.
It is about 0% by weight.

The phosphoric acid and / or phosphate is preferably added to the heavy metal-containing ash as an aqueous solution having a concentration of 20 to 80% by weight and kneaded.

[0018]

The above-mentioned JP-A-8-155
No. 417 and No. 11-188331 do not control the water content of the alkali fly ash during the treatment process.

In general, in the carbonation reaction between carbon dioxide gas and alkali fly ash, the higher the moisture content of the fly ash is within a certain range, the higher the reaction efficiency becomes. However, when the moisture content exceeds a certain range, the fly ash is granulated. Since the carbon dioxide does not penetrate into the inside of the grains, the reaction efficiency is reduced. Therefore, during the carbonation reaction, it is preferable that the water content of the fly ash be high enough that the fly ash does not granulate. On the other hand, when the fly ash is transported or landfilled after the treatment, the water content of the fly ash is preferably high enough to granulate the fly ash. However, Japanese Patent Application Laid-Open No. Hei 8-1
In Nos. 55417 and 11-188331, since the water content of the fly ash is not controlled, the water content in the fly ash decreases with the progress of the carbonation reaction, and the reaction efficiency decreases. Also,
Since the fly ash is transported or landfilled without being granulated, it is difficult to handle the fly ash and a large amount of the fly ash is scattered.

An object of the present invention is to solve the above-mentioned conventional problems and to provide a method and an apparatus for treating alkaline fly ash, which can control the water content of the alkaline fly ash.

[0021]

According to a first aspect of the present invention, there is provided a method for treating alkali fly ash, comprising supplying water to a heavy metal-containing alkali fly ash and contacting the fly ash with carbon dioxide.
And a method of treating an alkali fly ash having a step of adding and mixing a heavy metal fixing agent to the alkali fly ash, wherein in the step of bringing the alkali fly ash and carbon dioxide gas into contact, the water content of the alkali fly ash falls within a predetermined range. Thus, the supply amount of water to the alkaline fly ash is controlled.

In the method for treating alkali fly ash, the alkali fly ash is supplied with water so that the water content of the alkali fly ash is within a range suitable for carbonation in the carbonation step of the alkali fly ash. The efficiency of the reaction can be increased.

In the method for treating alkali fly ash according to the present invention (claim 2), the alkaline fly ash is introduced into the stirring tank in a batch manner so that the water content of the alkali fly ash falls within the predetermined range. While adding water to the alkali fly ash and stirring,
Thereafter, a carbon dioxide gas-containing gas is introduced into the stirring tank to carbonize the alkali fly ash, and the alkali fly ash is discharged in a batch system. From the end to the end, the supply amount of water is controlled so that the water content of the alkali fly ash falls within the predetermined range.

In the method for treating alkaline fly ash, the alkaline fly ash is stirred in advance while adding water to the alkaline fly ash, and then the carbon dioxide-containing gas is introduced into the stirred vessel. Less scattering. In addition, since it is a batch type, and supplies water and introduces a carbon dioxide gas-containing gas while stirring the alkali fly ash in the carbonation step, the water content of the alkali fly ash is within a predetermined range over the entire area of the stirring tank. And carbonation can be performed efficiently. It is also possible to terminate carbonation early.

In the method for treating alkali fly ash of the present invention (claim 3), in claim 1, the alkali fly ash is introduced into the stirring tank in a batch system so that the water content of the alkali fly ash falls within the predetermined range. While adding water to the alkali fly ash and stirring,
Thereafter, a carbon dioxide-containing gas and water are introduced into the stirring tank to carbonize the alkali fly ash, and the alkali fly ash is discharged in a batch system. The amount of water introduced into the stirring tank is controlled so that the water content of the alkali fly ash falls within the predetermined range from the start to the end of the process.

In the method for treating alkaline fly ash, water is supplied to the alkaline fly ash by using water.
It is possible to quickly and finely adjust the amount of water, and it is easy to control the amount of water supply.

According to the present invention (claim 4), in the method for treating alkali fly ash according to claim 2, the carbon dioxide gas-containing gas contains water vapor, and the amount of water vapor in the carbon dioxide gas-containing gas is controlled. It controls the supply of water to the alkaline fly ash.

In the method for treating alkali fly ash, since the supply of moisture to the alkali fly ash is performed by the steam in the carbon dioxide gas-containing gas, the moisture can be supplied to a wide range in the stirring tank. It is possible to make the water content uniform throughout the fly ash.

The method for treating alkali fly ash according to the present invention (claim 5) is the method according to any one of claims 2 to 4, wherein the amount of water vapor in the carbon dioxide-containing gas and the amount of gas discharged from the stirring tank are determined. The water content in the alkali fly ash in the stirring tank is calculated based on the difference from the amount of water vapor in the stirrer, and the amount of water supply to the alkali fly ash is controlled such that the calculated value falls within a set range. .

In such a method for treating alkali fly ash, for example, the flow rate, humidity and temperature of the carbon dioxide-containing gas before and after introduction into the alkali fly ash are measured, and the alkali fly ash is measured based on the measurement results. The amount of change in water vapor in the carbon dioxide-containing gas before and after introduction into the ash is calculated. The water content in the alkali fly ash is calculated from the change in the water vapor, and the amount of water supplied to the alkali fly ash is controlled so that the calculated value falls within a set range.

In the method for treating alkaline fly ash, it is not necessary to collect the alkaline fly ash at regular time intervals and measure the water content in the fly ash, and it is not necessary to change the amount of water vapor in the gas containing carbon dioxide gas. , The water content of the fly ash can be calculated almost in real time, and the water supply amount can be controlled accurately.

In the method for treating alkali fly ash of the present invention (claim 6), a carbonation step of supplying and mixing a carbon dioxide-containing gas and water to a heavy metal-containing alkali fly ash, and adding a heavy metal fixing agent. In the treatment method having a fixing agent adding step of mixing and mixing, after the carbonation step is completed, water is added to the alkali fly ash and stirred to granulate the alkali fly ash, and then discharged from the stirring tank. Things.

In the method for treating alkaline fly ash, the fly ash is discharged after being granulated, so that the treated fly ash can be easily handled, and the fly ash can be transported during fly ash or landfilled. Can be reduced.

According to a seventh aspect of the present invention, there is provided an apparatus for treating alkali ash, comprising: a stirring tank for receiving and stirring heavy metal-containing alkali fly ash; a means for supplying a carbon dioxide gas-containing gas into the stirring tank; A water supply means for supplying water into the tank, a means for supplying a heavy metal fixing agent into the stirring tank, and the carbon dioxide-containing gas so that the water content of the alkali fly ash in the stirring tank is within a predetermined range. Control means for controlling the amount of water vapor therein and / or the amount of water supplied by the water supply means.

In the apparatus for treating alkali fly ash, the efficiency of the carbonation reaction is improved by setting the water content of the alkali fly ash in the alkali fly ash carbonation step within a range suitable for carbonation. Can be increased.

[0036] In the apparatus for treating alkali fly ash according to the present invention (claim 8), the means for measuring the amount of water vapor in the carbon dioxide gas-containing gas and the amount of water vapor in the gas discharged from the stirring tank may be used. Measuring means, comprising means for calculating the water content of the alkaline fly ash in the stirring tank based on the measured values of these measuring means, the control means, the calculated water content is set range and The control is performed so that

In such an apparatus for treating alkaline fly ash, it is not necessary to sample the alkaline fly ash at regular time intervals and measure the water content in the fly ash, and it is not necessary to change the amount of water vapor in the carbon dioxide-containing gas. From this, the water content of fly ash can be calculated almost in real time, and the water supply can be controlled accurately.

The apparatus for treating alkali fly ash according to the present invention (claim 9) is characterized in that, after the carbonation treatment of the alkali fly ash, the alkali fly ash has a water content exceeding the predetermined range. It is characterized by comprising a granulation control means for supplying water to the stirring tank to granulate alkali fly ash.

In such an alkaline fly ash treatment apparatus, the fly ash is discharged after being granulated, so that the treated fly ash can be easily handled, and the amount of fly ash during transportation and landfill disposal Can be reduced.

[0040]

Embodiments of the present invention will be described below in detail.

FIG. 1 is a system diagram of an alkali fly ash treatment apparatus suitable for carrying out the alkali fly ash treatment method of the present invention.

The carbon dioxide-containing gas (combustion exhaust gas in this embodiment) is supplied to the measuring unit 3 through the pipe 1. At this time, when it is necessary to lower the temperature of the carbon dioxide-containing gas, such as when ventilating exhaust gas,
The heat exchanger 2 is installed in front of the measurement unit 3, and the gas is cooled by the heat exchanger 2.

The measuring unit 3 includes a thermometer, a flow meter, and a hygrometer, and measures the temperature, flow rate, and humidity of the carbon dioxide-containing gas. These measuring instruments are generally commercially available. After the gas properties are measured by the measuring unit 3, the carbon dioxide-containing gas is fed to the reaction device (stirring tank) 4 and brought into contact with high alkali fly ash. The exhaust gas from the reaction device 4 is sent to the measurement unit 6 through the pipe 5, and the temperature, the flow rate, and the humidity are measured.

The method for treating alkali fly ash using the apparatus for treating alkali fly ash thus constructed will be described below.

After introducing a predetermined amount of alkali fly ash into the reactor 4 provided with a stirring means inside, a small amount of water is added to sufficiently mix the alkali fly ash and water. Here, the amount of water to be added is 5 to 50 with respect to the fly ash from the viewpoint of the efficiency of the carbonation reaction and the suppression of the fly ash scattering due to the aeration of the carbon dioxide-containing gas.
% By weight, particularly preferably 10 to 30% by weight.

Next, a combustion exhaust gas as a carbon dioxide-containing gas is introduced into the reactor 4, and carbonation is performed while stirring the alkaline fly ash. Since the carbonation of the alkali fly ash is promoted when the temperature of the exhaust gas introduced into the reactor 4 is lower, the exhaust gas is reduced to 80 ° C. or less, particularly 60 ° C. by the heat exchanger 2.
It is preferred that the temperature be lowered as described below and then introduced into the reactor 4.

In the carbonation step, the water in the fly ash evaporates due to the exothermic reaction between the carbon dioxide gas in the exhaust gas and the alkali component in the fly ash, and as a result, the water content of the fly ash decreases.
This causes a reduction in the reaction efficiency of carbonation and an increase in the amount of fly ash scattered by the exhaust gas. In order to prevent these, control is performed so that the moisture content of the alkaline fly ash becomes constant as described below.

That is, the measurement units 3 and 6 measure the flow rate, temperature and humidity of the exhaust gas upstream and downstream of the reactor 4. From these measurement results, the amount of water vapor contained in the exhaust gas upstream and downstream of the reactor 4 is calculated, and the difference is regarded as the amount of water released from the alkaline fly ash. The water content of the alkali fly ash is calculated from the amount of water released from the alkali fly ash and the weight of the alkali fly ash, and when this falls below a set range, a predetermined amount of water is supplied to the reactor 4.

In this embodiment, the water is supplied by adding water. However, the water may be supplied by controlling the amount of water vapor in the exhaust gas. In this case, since the exhaust gas has a saturated steam pressure after being cooled by the heat exchanger 2, the amount of water is controlled by changing the heat exchange amount of the heat exchanger 2 to adjust the temperature of the exhaust gas. . For example, if the amount of water vapor in the exhaust gas is too large, the temperature is further lowered by a heat exchanger to condense and remove the water.

The progress of carbonation is also monitored by monitoring means. That is, the measurement data of the CO ₂ concentration and the flow rate measured in the measurement units 3 and 6 are collected, and the amount of carbon dioxide gas consumed by the fly ash is calculated.
It is monitored whether or not the calculated value of the consumption of the carbon dioxide gas has reached the consumption required for the carbonation treatment of the alkaline fly ash, and the carbonation is continued until the consumption reaches the required consumption.

After the carbonation of the alkali fly ash is completed, the supply of exhaust gas to the reactor 4 is stopped, a heavy metal fixing agent is introduced into the reactor 4, and the fly ash is stirred and mixed. Thereafter, water is supplied into the reactor 4 to granulate fly ash, and the fly ash is discharged out of the reactor 4.

In this embodiment, the heavy metal fixing agent is introduced after the carbonation step is completed, but the heavy metal fixing agent is introduced before, simultaneously with, or after the carbonation step or the granulation step. There may be.

Examples of the heavy metal fixing agent include phosphate heavy metal fixing agents, chelating heavy metal fixing agents, clay mineral heavy metal fixing agents such as activated clay, polymer heavy metal fixing agents such as starch, and the like. A cement-based heavy metal fixing agent, an acidic solution-based heavy metal fixing agent such as sulfuric acid, and the like are used. The addition amount of the heavy metal fixing agent is preferably 1 to 30% by weight based on the fly ash.

In this embodiment, exhaust gas is used as a carbon dioxide gas supply source, but other carbon dioxide gas, for example, commercially available carbon dioxide gas may be used.

According to the method for treating alkali fly ash,
Since the water content in the alkali fly ash is controlled within the set range in the carbonation step, the reaction efficiency is high and the reaction time can be shortened. Further, the amount of flying ash can be reduced. The moisture content of the alkali fly ash can be measured by measuring unit 3,
Since the calculation is performed almost in real time based on the detection data of No. 6, the supply of water can be appropriately performed, and the water content can be accurately controlled. After carbonation, it is possible to reduce the amount of scattering at the time of transportation, landfilling, etc., from the point of transportation, landfilling and other disposal after granulation.

Next, an example of processing fly ash using this method of processing alkaline ash will be described.

In this processing example, municipal solid fly ash was used as the alkaline fly ash containing heavy metals. Table 1 shows the components of the fly ash.

[0058]

[Table 1]

Preliminary Experiment 12.0 kg of alkaline fly ash having a measured water content of less than 1% was charged into the reactor 4. Here, the measured water content refers to the ratio of the amount of water desorbed when the alkali fly ash is heated at 105 ° C. for 24 hours to the amount of the alkali fly ash before heating. Next, 3.0 kg of demineralized water (25% by weight based on the alkali fly ash) was poured into the reactor 4 and stirred for 3 minutes to uniformly mix the alkali fly ash and water.

While continuing stirring, CO ₂ was introduced into the reactor 4.
Carbon dioxide gas having a concentration of 10% was aerated at 300 L / min for 60 minutes. The flow rates and humidity of the carbon dioxide gas upstream and downstream of the reactor 4 were measured by the measurement units 3 and 6. These measurement data were collected at regular intervals, and changes in the water content in fly ash were calculated according to the following formula. F × W _θ / 18 = (G ₀ × Z ₀ × θ / 22.4-G × Z
× θ / 22.4) + F × W 0/18 where each symbol denotes the following. F: Fly ash amount (g) W _θ : Calculated value of water content of fly ash after θ hours (%) W ₀ : Calculated value of initial fly ash water content (%) (Fly ash of amount of water injected before ventilation) proportion to _{W 0} for) _{G 0:.} inlet gas flow rate (L / min) G: outlet gas flow rate (L / min) _{Z 0:} inlet gas steam mole fraction Z: exit gas steam mole fraction theta: elapsed Time (min) The left side of the above equation is the amount of water (molar amount) in the fly ash after θ hours. (G ₀ × Z ₀ × θ / 22.4-G on the right side
× Z × θ / 22.4) is the amount of water (molar amount) derived from water vapor in the carbon dioxide gas, and F × W _0/18 is the amount of water (molar amount) initially injected. FIG. 2 shows the measurement result of the humidity of the carbon dioxide gas, and FIG. 3 shows the calculation result of the water content.

The water content was calculated by the above calculation, and alkali fly ash was sampled at intervals of 10 minutes, and the water content in the fly ash was measured. FIG. 3 shows the measurement results.

From FIG. 2, it was confirmed that the ventilation of the reactor 4 increased the humidity of the carbon dioxide gas. From FIG. 3, it can be seen that the moisture content of the alkali fly ash decreases due to the aeration of the carbon dioxide gas, and that the calculated value of the moisture content and the decrease behavior of the actually measured value correspond to each other. It can be understood that the calculation can be performed in almost real time by the calculation using the equation. Note that, despite the addition of 25% by weight of water before the aeration of carbon dioxide gas, the actually measured initial water content was 19.1.
%, Which is considered to be due to a chemical reaction between the alkali component in the fly ash and water.

Example 1 The processing procedure is as follows. The P-alkalinity in the alkali fly ash was measured according to the following procedure. First, fly ash 1
After adding 1000 mL of demineralized water and stirring for 5 minutes, a predetermined amount of the mixed solution was collected, and 2-3 drops of a phenolphthalein solution were added as an indicator. Next, titration was performed using 0.02N-sulfuric acid until colorless, and the alkalinity in fly ash was determined from the titration amount. The alkalinity was calculated as CaCO ₃ conversion. Table 2 shows the alkalinity in fly ash.

Further, a dissolution test was conducted according to the Environment Agency Notification No. 13 test. Table 2 shows the measurement results.

[0065]

[Table 2]

Next, the reactor 4 was prepared in the same manner as in the preliminary experiment.
3.0 kg of demineralized water was injected into 12.0 kg of alkali fly ash and stirred, and then carbon dioxide gas having a CO ₂ concentration of 10% was aerated at a flow rate of 300 L / min. During the passage of the carbon dioxide gas, the flow rate, humidity and CO ₂ concentration of the carbon dioxide gas upstream and downstream of the reactor 4 were measured by the measurement units 3 and 6. The change in the water content in the fly ash was calculated from the measurement results of the flow rate and the humidity in accordance with the above formula, and the calculated value of the water content was 24% by weight.
At the time of the following, 1% by weight of water was injected each time. The CO ₂ utilization was calculated from the measured value of the CO ₂ concentration according to the following equation. CO ₂ utilization rate = (1−C / C ₀ ) / (1−C) Here, each symbol indicates the following. C ₀ : Inlet gas CO ₂ concentration (%) C: Outlet gas CO ₂ concentration (%) When the CO ₂ utilization rate becomes 0.1 or less, the carbonation of alkali fly ash and carbon dioxide gas is completed. No, the ventilation of carbon dioxide was stopped. Table 2 shows the time from the start to the end of carbon dioxide gas ventilation as the carbonation time.

After the completion of the carbon dioxide gas ventilation, a part of the fly ash was sampled, and the P-alkalinity in the fly ash was measured. Thereafter, 3% by weight of water and 8% by weight of a 80% by weight orthophosphoric acid solution were injected with respect to the fly ash in the reactor 4, and the mixture was stirred for 3 minutes. Then, the fly ash was collected. A dissolution test was performed according to the method described in Example 1. Table 2 shows the test results.

Comparative Example 1 Processing example 1 except that no water was injected during the carbon dioxide gas ventilation and no water was injected after the carbon dioxide gas ventilation was completed (only 80% by weight of the normal phosphoric acid solution was added at 8% by weight). Was performed in the same manner as described above. The results are shown in FIG.

The following was found from FIG. 4 and Table 2. The calculated value of the water content of the fly ash decreases with the carbonation time in Comparative Example 1, whereas in Example 1, 1% by weight of water was injected when the calculated value of the water content became 24% or less. By doing so, the water content could be maintained in the range of approximately 24 to 25%. Water was injected five times in total. In the case of Comparative Example 1, the carbonation time was 55.9 minutes, whereas in the case of Example 1, the carbonation time was 47.4 minutes. 15% reduction compared to This is presumed to be because carbonation was efficiently performed by maintaining the water content of the fly ash within the set range. In Example 1, by adding water after carbonation,
Fly ash could be granulated. The amount of heavy metal eluted from the fly ash could be suppressed by combining the carbonation of the alkali component in the fly ash by the aeration of carbon dioxide gas and the treatment with the heavy metal fixing agent.

[0070]

As described above, according to the method and apparatus for treating alkali fly ash of the present invention, the water content of the alkali fly ash can be kept within a range suitable for carbonation, and as a result, the carbonation time can be reduced. It is possible to Since the water content of the alkali fly ash is calculated almost in real time by measuring the properties of carbon dioxide before and after contact with the alkali fly ash, the water content can be accurately controlled. After carbonation, water is added and granulated before discharging, which makes handling easier and reduces the amount of fly ash scattered during transportation and landfill disposal.

[Brief description of the drawings]

FIG. 1 is a system diagram of an alkaline fly ash treatment apparatus according to an embodiment.

FIG. 2 is a diagram showing a change in humidity of alkaline fly ash in a carbonation step in a preliminary experiment.

FIG. 3 is a diagram showing a calculated value and a measured value of the moisture content of alkali fly ash in a carbonation step in a preliminary experiment.

FIG. 4 is a graph showing calculated values of the water content of alkali fly ash in the carbonation step in Example 1 and Comparative Example 1.

[Explanation of symbols]

 2 Heat exchanger 3, 6 Measurement unit 4 Reactor (stirring tank)

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Shogo Anzai 3-4-7 Nishishinjuku, Shinjuku-ku, Tokyo Kurita Industries Co., Ltd. (72) Inventor Mitsuru Takada 3-1 Honohara, Toyokawa, Aichi Prefecture Shinto (72) Inventor Hirofumi Asai 3-1 Honohara, Toyokawa, Aichi Prefecture Shintoh Industrial Co., Ltd. F-term (reference) 4D004 AA37 AB03 BA02 CA14 CA15 CA35 CB02 CB26 CC01 CC03 CC06 DA01 DA02 DA09 DA11

Claims (9)

[Claims] 1. A method for treating alkali fly ash, comprising: supplying water to alkali fly ash containing a heavy metal and bringing it into contact with carbon dioxide; and adding and mixing a heavy metal fixing agent to the alkali fly ash. Controlling the amount of water supplied to the alkali fly ash so that the water content of the alkali fly ash is within a predetermined range in the step of contacting the alkali fly ash with carbon dioxide gas. . 2. The alkaline fly ash according to claim 1, wherein the alkaline fly ash is introduced into the stirring tank in a batch system, and the mixture is stirred while adding water to the alkaline fly ash so that the water content of the alkaline fly ash falls within the predetermined range. A method of treating alkali fly ash, wherein a carbon dioxide gas-containing gas is introduced into the stirring tank to carbonize the alkali fly ash, and discharge the alkali fly ash in a batch manner. A method for treating alkali fly ash, comprising controlling a water supply amount such that the water content of the alkali fly ash is within the above-mentioned predetermined range until the end. 3. The method according to claim 1, wherein the alkali fly ash is introduced into the stirring tank in a batch system, and the mixture is stirred while adding water to the alkali fly ash so that the water content of the alkali fly ash falls within the predetermined range. A method of treating alkali fly ash by introducing a carbon dioxide-containing gas and water into the stirring tank to carbonize the alkali fly ash and discharge the alkali fly ash in a batch system. A method for treating alkali fly ash, comprising: controlling a supply amount of water introduced into the stirring tank so that the water content of the alkali fly ash falls within the predetermined range from the start to the end. 4. The method according to claim 2, wherein the carbon dioxide gas-containing gas contains water vapor, and the amount of water supplied to the alkali fly ash is controlled by controlling the amount of water vapor in the carbon dioxide gas-containing gas. Characteristic method of treating alkaline fly ash. 5. The stirring tank according to claim 2, wherein the amount of water vapor in the carbon dioxide gas-containing gas and the amount of water vapor in the gas discharged from the stirring tank are different. A method for treating alkali fly ash, comprising calculating a moisture content in the alkali fly ash and controlling a water supply amount to the alkali fly ash so that the calculated value falls within a set range. 6. A processing method comprising a carbonation step of supplying and mixing a carbon dioxide-containing gas and water to an alkali fly ash containing a heavy metal, and a fixing agent adding step of adding and mixing a heavy metal fixing agent. After the carbonation step, the alkaline fly ash is granulated by adding water to the alkaline fly ash and stirring, and then discharged from the stirring tank. 7. A stirring tank for receiving and stirring heavy metal-containing alkali fly ash, a means for supplying a carbon dioxide gas-containing gas into the stirring tank, a water supply means for supplying water to the stirring tank, and the stirring Means for supplying a heavy metal fixing agent into the tank; water supply in the carbon dioxide-containing gas and / or water supply by the water supply means such that the water content of the alkali fly ash in the stirring tank is within a predetermined range. An apparatus for treating alkaline fly ash, comprising: control means for controlling the amount. 8. A method according to claim 7, wherein said means for measuring the amount of water vapor in said carbon dioxide gas-containing gas, said means for measuring the amount of water vapor in said gas discharged from said stirring tank, and a measurement value of said measuring means. Means for calculating the water content of the alkaline fly ash in the stirring tank, wherein the control means performs control such that the calculated water content falls within a set range. Alkali fly ash processing equipment. 9. The alkali fly ash according to claim 8 or 9, wherein after the alkali fly ash is carbonated, water is supplied to the stirring tank so that the water content of the alkali fly ash exceeds the predetermined range. An alkaline fly ash processing apparatus, comprising: