JP6975757B2 - Neutral recycled soil production system and neutral recycled soil production method using carbon dioxide fixation technology - Google Patents

Description

The present invention modifies construction sludge that exhibits strong alkalinity, and efficiently immobilizes carbon dioxide gas as calcium carbonate in the modified soil to produce neutral reclaimed soil. Recycled soil production by carbon dioxide immobilization technology. Regarding the system and the method for producing neutral recycled soil.

Conventionally, in construction sludge generated at construction sites, solidifying materials such as cement and lime are often added and mixed to improve workability and perform so-called reformed solidification treatment to develop and increase strength. It has been. It has been pointed out that the reformed and solidified soil, which is the modified and solidified construction sludge, usually exhibits a strong alkalinity having a pH of about 9 to 12, and therefore has a limited use.

In order to deal with this problem, the inventors have already applied for a prior patent (see Patent Document 1) and obtained a patent relating to "recycled soil manufacturing system and manufacturing method" (see Patent Document 2).

Japanese Unexamined Patent Publication No. 2018-103071 Japanese Patent No. 6559644

Here, in Patent Document 2 (hereinafter referred to as "prior application patent"), a water-absorbent material and a cement-based solidifying material are added to reduce the pH to less than 12, and the recycled soil is made from solidified soil as a raw material. The method of manufacturing is shown. That is, the modifying material is limited to the water-absorbent material and the cement-based solidifying material, and the constraint conditions such as the exclusion of construction sludge having a pH of 12 or more are given.

Further, in the prior patent, it was necessary to provide a certain curing period before contacting the reformed solidified soil with carbon dioxide gas to promote the hydration reaction. This is because if the curing period is too short, the hydration reaction of the cement-based solidifying material becomes insufficient, and the surplus water generated by neutralization with carbon dioxide softens the soil, resulting in a situation where the soil cannot be finished as recycled soil. ..

Furthermore, in the prior patent, the rapid contact method using a rotary mixer, the flow-down contact method in which construction sludge is poured into the pit and carbon dioxide gas flows down from above, and the space is filled with carbon dioxide gas before construction. A neutralization treatment method such as a pool contact method in which sludge is charged is shown. Even with these neutralization treatment methods, it is possible to neutralize the construction sludge to produce recycled soil, but it is difficult to efficiently produce recycled soil depending on the water content of the construction sludge immediately before the neutralization treatment. It happened to be.

For example, when a rotary mixer is used, it is difficult to seal the inside of the mixer, and a part of carbon dioxide gas leaks to the outside of the mixer, so that a large amount of carbon dioxide gas is required. In addition, the excess water generated by the neutralization reaction with carbon dioxide may soften the construction sludge and may be further kneaded by stirring with a mixer. In the flow contact method, gas does not enter deeply unless the construction sludge pretreated to the ideal state is laid loosely. Therefore, the laying layer thickness is limited. In the pool contact method, the amount of construction sludge that can be neutralized is limited with respect to the space because carbon dioxide gas is dissipated to the outside of the system due to the wind pressure when the construction sludge is introduced.

An object of the present invention is a neutral recycled soil production system based on carbon dioxide immobilization technology, which reliably neutralizes alkaline construction sludge and efficiently produces high-quality neutral recycled soil that does not re-mud. It is to provide a method for producing neutral recycled soil.

That is, the present invention includes the following matters.
The neutral recycled soil production system by the carbon dioxide fixation technology of the present invention is
A modified solidification treatment area where alkaline modified solidifying material is added to construction sludge and mixed to generate modified solidifying treated soil.
A loosening granulation means for producing finely divided granulated soil by loosening the modified solidified soil at the stage of becoming semi-solid.
Drying / neutralization that promotes the drying and neutralization of the loosened granulated soil using hot compressed air and carbon dioxide gas, which are heated compressed air, and further fixes the carbon dioxide gas as calcium carbonate to the loosened granulated soil. With a carbon dioxide fixed area and <br />
The drying / neutralizing / carbon dioxide fixing area
The pit to put the loosened granulated soil and
It characterized Rukoto a inlet pipe for supplying hot compressed air and carbon dioxide to the granulation soil loosened from said bottom of said pits.
As a result, it is possible to efficiently produce high-quality neutral recycled soil that reliably neutralizes alkaline construction sludge and does not re-mud.
In addition, an efficient neutralization reaction can be realized by loosening the inside of the pit and sealing it with granulated soil to create a space under pressure and sending hot air and carbon dioxide gas.

In addition, the neutral recycled soil production system using the carbon dioxide fixation technology of the present invention is
The modified solidified soil is characterized in that it exhibits a strong alkalinity having a pH of 12 or more.
That is, according to the neutral recycled soil production system according to the embodiment, even a strongly alkaline modified solidified soil having a pH of 12 or more can be reliably neutralized.

In addition, the neutral recycled soil production system using the carbon dioxide fixation technology of the present invention is
First, heat-compressed air is supplied to the loosened granulated soil, and then hot compressed air and carbon dioxide gas are supplied to the loosened granulated soil.
This makes it possible to efficiently and reliably loosen carbon dioxide gas and fix it to the granulated soil.

In addition, the neutral recycled soil production system using the carbon dioxide fixation technology of the present invention is
Heat-compressed air and carbon dioxide gas are simultaneously supplied to the loosened granulated soil.
In this way, even if heat-compressed air and carbon dioxide gas are supplied at the same time from the beginning, the carbon dioxide gas can be loosened and fixed to the granulated soil.

In addition, the neutral recycled soil production system using the carbon dioxide fixation technology of the present invention is
It is characterized by being provided with a blower that recovers air containing excess carbon dioxide gas that has reached the ground surface in the pit and supplies it to the loosened granulated soil as heat compressed air again from the bottom surface of the pit.
In this way, by recovering and recycling the carbon dioxide gas that has reached the soil surface layer in the pit, it is possible to prevent the carbon dioxide gas from flowing out to the outside (outside the system). Moreover, since there is no leakage to the outside, carbon dioxide gas can be fixed to the soil more efficiently and reliably.

The method for producing neutral recycled soil by the carbon dioxide fixation technique of the present invention is
A reformed solidification process that produces modified solidified soil by adding an alkaline modified solidifying material to construction sludge and mixing it.
A loosening granulation step of producing finely divided granulated soil by loosening the modified solidified soil at the stage of becoming semi-solid.
Drying / neutralization that promotes the drying and neutralization of the loosened granulated soil using hot compressed air and carbon dioxide gas, which are heated compressed air, and further fixes the carbon dioxide gas as calcium carbonate to the loosened granulated soil. Carbon dioxide fixing process
Including
In the drying / neutralizing / carbon dioxide fixing process
It is characterized in that the loosened granulated soil is put into a pit and heat compressed air and carbon dioxide gas are supplied to the loosened granulated soil from the bottom of the pit .
As a result, it is possible to efficiently produce high-quality neutral recycled soil that reliably neutralizes alkaline construction sludge and does not re-mud.
In this way, an efficient neutralization reaction can be realized by loosening the inside of the pit and sealing it with granulated soil to create a space under pressure and sending hot air and carbon dioxide gas.

Further, the method for producing neutral recycled soil by the carbon dioxide fixation technique of the present invention can be used.
The modified solidified soil is characterized in that it exhibits a strong alkalinity having a pH of 12 or more.
That is, according to the neutral recycled soil production system according to the embodiment, even a strongly alkaline modified solidified soil having a pH of 12 or more can be reliably neutralized.

Further, the method for producing neutral recycled soil by the carbon dioxide fixation technique of the present invention can be used.
First, heat-compressed air is supplied to the loosened granulated soil, and then hot compressed air and carbon dioxide gas are supplied to the loosened granulated soil.
This makes it possible to efficiently and reliably loosen carbon dioxide gas and fix it to the granulated soil.

Further, the method for producing neutral recycled soil by the carbon dioxide fixation technique of the present invention can be used.
Heat-compressed air and carbon dioxide gas are simultaneously supplied to the loosened granulated soil.
In this way, even if heat-compressed air and carbon dioxide gas are supplied at the same time from the beginning, the carbon dioxide gas can be loosened and fixed to the granulated soil.

Further, the method for producing neutral recycled soil by the carbon dioxide fixation technique of the present invention can be used.
It is characterized in that the air containing excess carbon dioxide gas that has reached the ground surface is recovered in the pit and is again supplied as heat-compressed air from the bottom surface of the pit to the loosened granulated soil.
In this way, by recovering and recycling the carbon dioxide gas that has reached the soil surface layer in the pit, it is possible to prevent the carbon dioxide gas from flowing out to the outside (outside the system). Moreover, since there is no leakage to the outside, carbon dioxide gas can be fixed to the soil more efficiently and reliably.

According to the invention according to the present invention, neutral reclaimed soil by carbon dioxide immobilization technology that reliably neutralizes alkaline construction sludge and efficiently produces high-quality neutral reclaimed soil that does not re-mud. A manufacturing system and a method for producing neutral recycled soil can be provided.

It is a schematic diagram which shows the pit where the loose granulation soil which concerns on embodiment is put into.

Hereinafter, a neutral recycled soil production system and a production method based on the carbon dioxide immobilization technique according to the embodiment of the present invention will be described with reference to the drawings. First, the construction sludge discharged at the construction site is transported to the intermediate treatment facility. Here, the construction sludge transported to the intermediate treatment facility is an industrial waste exhibiting strong alkalinity. The cone index (qc) of this construction sludge is less than ^{200 kN / m 2.}

(Step S1: Modification and solidification (primary treatment) step)
Here, the alkaline construction sludge brought into the intermediate treatment facility will eventually solidify if left as it is. However, due to the space limitation of the intermediate treatment facility, it cannot be left as it is (cured) for a long period of time. Therefore, it is common to add a solidifying material exhibiting a strong alkali to reform it so that it can be handled promptly. In this case, there are cases where the pH becomes 12 or more due to the additional addition of the solidifying material.

In the present invention, the conventional technique is applied as it is to reform and solidify construction sludge. That is, in the reformed solidification treatment area of the intermediate treatment facility, an alkaline improving material is added to the construction sludge to reform and solidify. Examples of the alkaline improving material include cement-based solidifying materials, lime, PS (paper sludge) ash-based water-absorbing modifiers, and other materials exhibiting alkali.

The amount of the alkaline improving material added is not particularly limited, and the pH value of the construction sludge (hereinafter referred to as modified solidified soil) after the addition of the alkaline improving material is not limited. From the viewpoint of fixing a large amount of carbon dioxide gas, the modified solidification-treated soil is rather suitable so as to exhibit a strong alkali having a pH of 12 or more.
In such a reformed solidification (primary treatment) step, by adding a strong alkaline solidifying material to the construction sludge, the soft construction sludge is surely reformed and solidified, and a semi-solid reformed solidified treated soil is produced. ..

(Step S2: Loosening granulation (secondary treatment) step)
The semi-solid form of the modified solidified soil in the form of a mass is undergoing a hydration reaction, and if left as it is, it will solidify in the form of a mass. Therefore, the modified solidified soil that has become semi-solid is loosened and crushed using a granulation technique (see, for example, Japanese Patent Application Laid-Open No. 2015-127050) to be granulated.

Here, the suitability of loosening granulation is determined by the cone index test method (JIS A 1228). Normally, if the cone index of the reformed solidified soil is 100 kN / m ² or more, loosening granulation is possible, but finer-grained construction sludge (hereinafter referred to as loosening granulated soil) is produced by loosening granulation. to is preferably cone index modifying solidification soil is less than 400 kN / m ² or more 1800kN / m ^2. The machine (unraveling granulation means) used for the unraveling granulation treatment may be a backhoe, but a soil improving machine (plant) having a crushing function is preferable.

In the loosening granulation (secondary treatment) step, the modified solidification-treated soil, which is a semi-solid soil mass, is crushed to become fine-grained loose-granulation soil. For this reason, in the loosened granulated soil, the surface area of the particles is increased, and the soil is easily contacted with air and carbon dioxide gas, and the modified solidified soil is adjusted to a particle size that is easy to use as recycled soil.
In addition, the loosened granulated soil is in a state where it is easy to dry due to the increased surface area. At the same time, it reacts with carbon dioxide in the air to easily reduce the pH.

(Step S3: Drying / neutralization / carbon dioxide fixation (tertiary treatment) process)
Next, the loosened granulated soil, which is the refined solidified soil, is put into a pit arranged in a drying / neutralizing / carbon dioxide fixing area. FIG. 1 is a schematic view showing a pit into which the loosened granulated soil according to the embodiment is put. As shown in FIG. 1A, the pit 2 is a rectangular space formed on the ground. At the bottom of the pit 2, for example, a single grain crushed stone or the like is laid to form a base layer 6, and an inflow pipe 4 formed of a heat-resistant pipe or the like is embedded in the base layer 6 in advance. A high-pressure blower 8 is connected to the above-ground end of the inflow pipe 4.

In this state, the blower 8 is driven to supply hot air of compressed air at 100 ° C. or lower (hereinafter referred to as heat-compressed air) to the inflow pipe 4. In this way, supplying gas from the bottom of the pit 2 and allowing it to pass through the soil is called press-fitting contact. Here, by supplying hot air into the pit 2, the surface temperature of the base layer 6 rises to 60 ° C to 80 ° C. The surface temperature of the base layer 6 that rises due to hot air is preferably 100 ° C. or lower. Further, the diameter of the inflow pipe 4 may be reduced in the middle of the hot air. In this case, since frictional heat is generated in the portion where the diameter is narrowed, it is possible to raise the temperature efficiently.

Next, while supplying hot air to the inflow pipe 4, first, a small amount of loosened granulated soil, which is a refined solidified soil, is added. In this case, as shown in FIG. 1 (b), the water on the surface of the loosened granulated soil evaporates by hot air, and a dry earth and sand layer 12 is formed. Since the sediment layer 12 has a low water content, it is not compacted even when compacted, and voids in the sediment layer 12 remain. Hot air passes through this void and is ventilated.

Next, the loosened granulated soil is sequentially added from the top of the earth and sand layer 12. The added loosened granulated soil is warmed from the bottom of the pit 2, and the excess water in the loosened granulated soil becomes steam and evaporates. Alternatively, it accumulates in the base layer 6 formed at the bottom of the pit 2. The water collected in the base layer 6 is separately pumped up by a pump-up device (not shown) and discharged to the outside of the pit 2. Then, as the water content in the loosened granulated soil decreases (the water content of the loosened granulated soil decreases), the soil shrinks by drying and the air permeability is improved. That is, as shown in FIG. 1 (c), the thrown loose granulated soil forms the aeration layer 14.

At the stage when the loading of the loosened granulated soil is completed, the earth and sand layer 12 and the ventilation layer 14 in the pit 2 are finished in a state where appropriate voids are formed and the air permeability is good. In addition, since the water on the soil surface evaporates due to the hot air, the water content of the loosened granulated soil decreases, resulting in a smooth state with low viscosity. Furthermore, the temperature of the soil is rising due to the hot air.

While maintaining this state, as shown in FIG. 1 (d), carbon dioxide gas is press-fitted together with hot air. Then, due to the wind pressure of the hot air, carbon dioxide gas spreads to every corner of the soil. Further, in this state, the upper part of the pit 2 is covered with a cover material 16 such as a sheet. As a result, the air containing carbon dioxide gas that has reached the ground surface is suppressed from flowing out to the outside of the pit 2. The air containing carbon dioxide gas in the upper part of the pit 2 is collected by the blower 8 on the intake side and exhausted from the bottom surface again through the inflow pipe 4, so that the dissipation to the outside of the system can be minimized.

As a result, heat-compressed air spreads from the bottom of the pit 2 to every corner upward, the moisture contained in the loosened granulated soil evaporates and drying progresses, the volume of the soil shrinks, and the air permeability improves. do. Furthermore, carbon dioxide gas neutralizes the alkaline components in the soil and is fixed as calcium carbonate in the loosened granulated soil. The air containing excess carbon dioxide that has reached the ground surface is recovered by the blower 8 on the intake side, and is press-fitted into the soil as heat-compressed air from the bottom again to minimize the leakage of carbon dioxide to the outside of the system. Can be suppressed to.

According to the invention of this embodiment, neutral regeneration by carbon dioxide immobilization technology that reliably neutralizes alkaline construction sludge and efficiently produces high-quality neutral recycled soil that does not re-mud. A soil production system and a method for producing neutral recycled soil can be provided.

^{That is, a neutral reclaimed soil having a cone index of 800 kN / m 2} or more and a pH of 8.6 or less is produced by modifying construction sludge having a strong alkalinity of pH 12 or more, similar soil, and waste, which was difficult in the past. be able to. Since this neutral reclaimed soil has undergone a drying process with hot air, it is finished as high-quality reclaimed soil that does not re-mud.

Further, in the above-described embodiment, the inside of the pit 2 is sealed with the soil itself to create a space under pressure, the soil temperature is raised by using heat, and the water content of the reformed solidified soil is lowered. Carbon dioxide gas is in direct contact with every corner of the loosened granulated soil. In this way, an efficient neutralization reaction is realized by sending hot air and carbon dioxide gas using the voids in the soil.

Further, in the invention according to the present embodiment, in the neutralization method, the principle of directly spraying carbon dioxide gas onto the reformed solidified treated soil to bring it into contact is the same as that of the prior patent (Patent No. 6559644), but the temperature is high. The point that carbon dioxide gas is mixed with the heated hot compressed air and pressed into contact from the bottom of the soil is a big difference from the prior patent. Therefore, the neutralization efficiency is significantly improved as compared with the prior patent.

Further, by recovering and recycling the carbon dioxide gas that has reached the soil surface layer in the pit 2, it is possible to prevent the carbon dioxide gas from flowing out to the outside (outside the system). Moreover, since there is no leakage to the outside, carbon dioxide gas can be fixed to the soil more efficiently and reliably. This point is also a big difference from the prior patent from the viewpoint of neutralization efficiency.
Further, according to the invention of the present embodiment, the effects listed below can be obtained.

(1) Contribution to the recycling of waste Construction sludge with a pH of 12 or higher and other similar soil / waste can be reliably neutralized, and the neutral recycled soil is a high-quality recycled material. Can be used as. Of course, it is not limited to raw materials having a pH of 12 or more, and can be applied to construction sludge having an alkaline pH of less than 12 and other similar soils and wastes.

(2) Contribution to global warming countermeasures Global warming is various due to the rise in temperature and seawater temperature on a global scale, the shrinking of glaciers, and the rise in sea level, as seen in recent abnormal weather. It is a very urgent issue that causes various environmental problems. Problems have already become apparent, such as having an adverse effect on the natural ecosystem and the activities of human society. The biggest theme of these measures against global warming is the reduction of carbon dioxide emissions. Japan has set a reduction target of 80% in 2050 and has set out "carbon recycling" to reuse _{CO 2 as a carbon resource.}

The principle of neutralization in the present invention is that carbon dioxide gas is reacted with calcium hydroxide contained in the soil and fixed to calcium carbonate. This is in line with the principle of carbon recycling promoted by the Ministry of Economy, Trade and Industry, and greatly contributes to the reduction of carbon dioxide emissions, which is one of the measures against global warming.
[Neutralization reaction formula of alkaline lime with carbon dioxide]
Ca (OH) ₂ + CO ₂ = CaCO ₃ + H ₂ O (Equation a)

(3) Highly versatile conventional technology, when carbon dioxide gas is sprayed on strongly alkaline construction sludge, excess water (H ₂ O) is generated by the neutralization reaction as shown in the above (formula a), and in that state. When stirred, the reformed solidified soil was kneaded back and sometimes softened (re-sludged) again. This softening phenomenon is particularly remarkable in sludge with a high water content. On the other hand, in the present invention, the excess water generated in the neutralization reaction can be quickly evaporated by the heat-compressed air from the bottom of the pit. Further, since the neutralization treatment does not involve a stirring step, remudification due to stirring does not occur.

Furthermore, since the reformed solidified soil is sequentially poured into the pit while improving the air permeability with hot air, it is not necessary to make it loosely packed, and it is possible to neutralize even if the soil layer thickness is increased. .. As shown in Examples described later, recycled soil with a soil ^{layer thickness of 3 m (pits of about 150 m 3) can be produced at the actual machine level.} If the pressure of the heat-compressed air is increased to a higher pressure, the soil layer thickness can be further increased. As described above, there are almost no small constraints, so it is extremely versatile.

(4) Inexpensive The materials used in the present invention are only strong alkali improving materials (cement, lime, etc.), carbon dioxide gas, and heat-compressed air. Cement and lime are very inexpensive as improving materials. In addition, if carbon dioxide can also use by-products emitted from power plants and chemical plants, it will lead to cost reduction. Furthermore, when heat-compressed air is press-fitted into contact with a blower, frictional heat is generated by reducing the diameter of the pipe in the middle, and the temperature of the air can be easily raised, so no extra heat source is required (slightly). You only have to pay for electricity). If a recycled soil manufacturing facility is installed next to a power plant or chemical plant, the waste heat and residual heat can be used. In this way, recycled soil can be produced inexpensively without using special machinery, chemicals, or fuel.

(5) It is possible to produce a large amount of recycled soil. Alkaline improving material is added to and solidified in construction sludge, loosened and placed in a pit, and then contacted with carbon dioxide gas together with hot compressed air. If the yard can be secured, a large amount of recycled soil can be produced.

(6) Recycled soil is neutral and of high quality The produced reclaimed soil has a neutral range of pH = 5.8 to 8.6, and the cone index should ensure a strength of ^{800 kN / m 2 or more.} Can be done. Furthermore, it is possible to finish high-quality recycled soil that does not easily re-mud.
In the tertiary treatment step of the above-described embodiment, the heat-compressed air is first supplied to the inflow pipe 4 (see FIG. 1A), and after the ventilation layer is formed, the heat-compressed air and carbon dioxide gas flow in at the same time. Although the case of supplying to the tube 4 (see FIG. 1 (d)) is illustrated, hot compressed air and carbon dioxide gas may be supplied at the same time from the beginning.

Further, in the above-described embodiment, a carbon dioxide gas densitometer may be installed on the ground surface portion in the pit 2. As a result, it is possible to stop the press-fitting contact of hot air when the concentration reaches a certain level and continue to flow only carbon dioxide gas little by little. By adjusting the supply amounts of carbon dioxide gas and heat-compressed air according to the situation, the supply amount of carbon dioxide gas can be minimized, and neutralization can be achieved efficiently and at low cost.

In addition, raising the soil temperature is preferable as a contact reaction of carbon dioxide gas, but when the soil temperature rises to 100 ° C or higher, the adsorbed water and water of crystallization in the reformed soil disappear, and the soil deteriorates. It may not be a high quality recycled soil. Therefore, it is desirable that the temperature of the hot air is suppressed to 100 ° C. or lower, preferably 80 ° C. or lower. Of course, the purpose can be achieved by sending compressed air at room temperature, but it takes longer to neutralize.

Furthermore, the neutralization reaction between carbon dioxide and soil is more effective when it is contacted at a low concentration for a long time (several hours) rather than at a high concentration for a short time (several minutes). It has been confirmed by experiments that the fixation of carbon dioxide is also efficient. From that point of view, it can be said that it is a reasonable method to mix hot compressed air (hot air) and carbon dioxide gas to reduce the concentration of carbon dioxide gas and bring it into contact with the soil. The regenerated soil, which has been gradually neutralized over time, is not agitated in the middle, so that remudification due to re-kneading does not occur.

Next, an example of an experiment conducted using the recycled soil production method according to the embodiment will be described.
[Example 1]
^{30 kg / m 3 of} fresh lime was added and mixed with construction sludge A (pH = 11.6, qc = 63 kN / m ² , water content 33%), and the pH of the sample cured for 2 hours was 12.3. An indoor column test was carried out using this modified solidification-treated soil as a sample.
The column used was an acrylic pipe having an inner diameter of 150 mm and a length of 600 mm. The bottom of the acrylic pipe is sealed and fixed with a bottom plate, and the structure is such that carbon dioxide gas and hot air can be supplied from the bottom. In addition, a filter cloth was laid on the upper part of the bottom slab, and 500 mm of the modified solidified soil was put on the filter cloth. The volume of soil is approximately 9 L (liter). In this container, an injection test with carbon dioxide gas under the following two conditions was carried out.
Condition 1 With or without loosening: Case where the soil sample is packed in a container with the size of a soil mass (fist size) Yes: Case where the soil sample is loosened, sprinkled on a 19 mm fluid, and only the portion that has passed through the fluid is put into the container.
Condition 2 Presence or absence of compressed air by hot air None: Case where only carbon dioxide gas is injected Existence: Case where hot air at about 60 ° C is blown together with carbon dioxide gas

The injection amount of carbon dioxide gas was 1 L / min, the supply amount of hot air was 60 L / min, and the contact time of carbon dioxide gas and hot air with the soil was 6 hours (360 minutes). The amount of carbon dioxide supplied is 1 L / min x 360 min = 360 L, and the volume of soil is 9 L, so the ratio is 40 times. The test results are shown in Table 1. For the pH, samples were taken from three locations, the upper part, the center, and the lower part of the specimen, and the average value of the pH values at the three locations was used. In addition, after the test was completed, the specimen was disassembled, and a cone index test was carried out with a uniformly mixed sample to measure qc.

Case 1 is a case without loosening and without hot air. Even if carbon dioxide gas is brought into contact with the soil mass, the carbon dioxide gas does not penetrate to the core of the soil mass, and the pH is slightly lowered. In addition, since carbon dioxide gas reacts on the surface of the soil mass to generate water, there is no strong expression. In case 2, qc satisfies the target value of 800 kN / m ² or more due to hot air, but the pH does not fall below the target value of 8.6 because there is no loosening. In case 3, the pH satisfied the target value of 8.6 or less due to the loosening effect, but the intensity of qc was lower than the target value because there was no hot air. On the other hand, in Case 4, both pH and qc satisfied the target values.

From the above results, it can be seen that the loosening granulation step and the drying step with hot air are important for producing high-quality neutral recycled soil.
Results of column test (φ150 × 500mm)

[Example 2]
^{50 kg / m 3} of blast furnace cement B was added to and mixed with construction sludge B (pH = 11.4, qc = 118 kN / m ² , moisture content 29%), and the pH of the sample cured for 24 hours was 12.1. rice field. All of this modified solidified soil was loosened and subjected to a 19 mm flue, and an indoor column test was carried out using only the amount that passed through the flue (that is, the refined modified solidified soil).

The column used was an acrylic pipe having an inner diameter of 150 mm and a length of 2,000 mm. The bottom surface of the acrylic pipe was sealed and fixed with a bottom plate as in Example 1, and the structure was such that carbon dioxide gas and hot air could be supplied from the bottom surface. In addition, a filter cloth was laid on the upper part of the bottom slab, and 1,800 mm of finely divided reformed solidified soil was put on the filter cloth. The volume of the introduced soil is approximately 32 L. In this container, an injection test with carbon dioxide gas under the following three conditions was carried out.
Condition 1 How to make a specimen (how to pack soil)
Loose packing: A case where the soil sample is packed as loosely as possible Packing: A case where the soil sample is compacted every 30 cm layer thickness and packed tightly Condition 2 Presence or absence of compressed air by hot air: Only carbon dioxide gas is injected Yes: Case where hot air of about 60 ° C is blown together with carbon dioxide Condition 3 Presence or absence of circulating air Blow: Case where only gas is supplied from the bottom Yes: Carbonated gas that reaches the soil surface with an upper lid on the top of the column Exhaust air including
Instead, carbon dioxide gas is sent in from the bottom of the column again through the intake port.
Circular use case

The injection amount of carbon dioxide gas was 5 L / min, the supply amount of hot air was 60 L / min, and the contact time of carbon dioxide gas and hot air with the soil was 4 hours (240 minutes). The amount of carbon dioxide supplied is 5 L / min x 240 min = 1,200 L, and the volume of soil is 32 L, so the ratio is 37.5 times. The test results are shown in Table 2. The pH and qc are measured in the same manner as in Example 1. In the test of this example, a carbon dioxide densitometer was installed near the upper part of the column, and an alarm sound was set when the concentration of carbon dioxide reached 3,000 ppm or more. This is to confirm the leakage status of carbon dioxide gas from the column to the outside.
Results of long column test (φ150 × 1,800 mm)

Cases 5 to 8 are cases in which circulation ventilation is not applied. Of these, Case 5 and Case 6 are tested in a loosely packed state without compaction. In both of these two cases, the pH of the soil after the test achieved 8.6 or less. However, in Case 5, since hot air was not sent, moisture was generated by neutralization with carbon dioxide gas, and as a result, qc did not satisfy ^{800 kN / m 2 due to the effect.} On the other hand, in case 6, qc also exceeded ^{800 kN / m 2.}

On the other hand, Cases 7 to 9 are tests in a tightly packed specimen. Case 7 did not meet the target in both pH and qc. Further, in Case 8, it was expected that the air permeability would be improved by hot air, but the pH was slightly higher than the target value. It is considered that this is because the soil contracted due to the hot air, and as a result, a gap was created between the soil and the side surface of the column, and the air containing carbon dioxide gas was concentrated and flowed from there. To support this, in Cases 5 to 8, the alarm of the carbon dioxide densitometer kept sounding from the middle of the test. However, in Case 9, by adopting the circulation ventilation method, carbon dioxide gas leakage to the outside of the system did not occur, and the pH and the value became 8.6 or less.

From the above test results, even if the reformed solidified soil that has been loosened and granulated is in a densely packed state, by adopting a hot air and circulation ventilation system, carbon dioxide gas is surely fixed to the soil and neutralized. , Confirmed that high quality recycled soil can be produced.

[Example 3]
^{40 kg / m 3} of PS ash-based water-absorbing modifier was added to and mixed with the construction sludge-treated product C (pH = 11.4, qc = 419 kN / m ² , water content 30%), and the sample was cured for 24 hours. The pH was 11.5. All of this modified solidified soil sample was loosened and subjected to a 20 mm flue, and a prototype test was carried out in the field using only the portion that passed through the flue (hereinafter referred to as modified solidified soil C).

For the pit, a steel box (notch tank) having a width of 4.5 m, a depth of 1.5 m, and a height of 1.5 m was used. The structure of the pit is similar to that shown in FIG. The reformed solidified soil C was poured into this steel pit with a pay loader until it was full. The volume of the introduced soil is approximately 10,000 L = 10 m ³ . In this pit, a carbon dioxide injection test was carried out under the following two conditions.
Condition 1 Presence or absence of compressed air due to hot air None: Case where only carbon dioxide gas is injected Blower: Case where air at about 20 ° C is blown together with carbon dioxide gas Hot air: Case where hot air at about 60 ° C is blown together with carbon dioxide gas Condition 2 Circulating blast Presence / absence: Case where only gas is supplied from the bottom Yes: A sheet is placed on the top of the pit, and the air containing carbon dioxide gas that has reached the ground surface is removed as much as possible.
Instead of exhausting to the part, send it from the bottom of the pit again through the intake port and incorporate it, and charcoal
Case of recycling acid gas

The injection amount of carbon dioxide gas was 100 L / min, the supply amount of hot air was 4,100 L / min, and the contact time between carbon dioxide gas and hot air with the soil was 10 hours (600 minutes). The amount of carbon dioxide supplied is 100 L / min x 600 min = 60,000 L, and the volume of soil is 10,000 L, so the ratio is 6 times. The test results are shown in Table 3. For the pH, samples were taken from three locations in the upper, center, and lower parts in the depth direction of the specimen, and from three locations in the front, center, and back in a planar manner, and the pH values of a total of nine locations were set. The average value was used. The measurement of qc is the same as in Examples 1 and 2. Further, in the test shown in this example, a carbon dioxide densitometer was installed near the pit in the same manner as in Example 2, and the alarm sound was set when the gas concentration reached 3,000 ppm or more.
Results of steel pit test (W4.5m x L1.5m x H1.5mm)

Case 10 is a case in which ventilation and circulation ventilation are not applied. In the case where there was no ventilation, carbon dioxide gas did not reach the top of the pit, and the pH tended to be low only at the bottom. On the other hand, in the case 11 in which the air was blown, the pH value was below 8.5 on average, but the intensity did not reach the target value due to the generation of excess water. On the other hand, in case 12 and case 13 to which hot air was applied, qc exceeded the target value in both cases. Furthermore, in the case where the circulation air was blown, the alarm sound of the gas densitometer did not sound, and the decrease in pH was the largest. However, QC showed a larger value in Case 12. It is probable that this was due to the fact that part of the steam evaporated by the hot air circulated and was not released to the outside.

From the above test results, it was confirmed that the decrease in pH was improved by applying hot air rather than normal temperature air. It was also confirmed that the pH can be lowered more efficiently by reliably fixing the carbon dioxide gas to the soil without dissipating it to the outside by applying circulating air.

[Example 4]
The same modified solidified soil C used in Example 3 was used. ^{In addition, 30 kg / m 3 of} quicklime was added and mixed with the construction sludge-treated product D (pH = 11.3, qc = 483 kN / m ² , water content 31%), and the pH of the sample cured for 24 hours was 12.2. Met. This reformed solidified soil was loosened and granulated, and then subjected to a 20 mm flue, and only the portion that passed through the flue (hereinafter referred to as reformed solidified soil D) was subjected to the test. That is, in this example, a full-scale level verification test was carried out using two types of samples, the modified solidified soil C and the modified solidified soil D.

The pit was made of concrete with a width of 7.0 m, a depth of 7.0 m, and a height of 3.5 m. The structure of the pit is similar to that shown in FIG. Soil was poured into this pit to a thickness of 3.0 m with a pay loader. The volume of soil is approximately 150 m ³ . In this pit, a carbon dioxide injection test was conducted under the following two conditions.
Condition 1 Presence or absence of compressed air due to hot air None: Case where only carbon dioxide gas is injected Yes: Case where hot air at about 80 ° C is blown with a high-pressure blower together with carbon dioxide gas Condition 2 Blower and carbon dioxide gas injection procedure-: Carbon dioxide gas from the bottom Simultaneous: Case where hot air and carbon dioxide are injected at the same time Sequential: Case where hot air is blown first, and then hot air and carbon dioxide are injected at the same time.
The case I went to

Injection amount of carbon dioxide gas was set to 180 m ³ / time, the supply amount of hot air was 1440m ³ / time.
In the case of using the reformed solidified soil C, the contact time between the carbon dioxide gas and the hot air was set to 5 hours. The amount of carbon dioxide supplied is 180 m ³ / hour x 5 hours = 900 m ³ , and the volume of soil is 150 m ³ , so the ratio is 6 times.

On the other hand, in the case of the modified solidified soil D having a stronger alkalinity, the contact time between the carbon dioxide gas and the hot air was set to 24 hours. The amount of carbon dioxide supplied is 180 m ³ / hour x 24 hours = 4320 m ³ , and the volume of soil is 150 m ³ , so the ratio is about 29 times.

The test results are shown in Table 4. The measurement of pH and cone index is the same as in Example 3.
Results of concrete pit test (W7.0m x L7.0m x H3.0m)

Cases 14 and 15 are cases of soil with a relatively low pH. In the case 14 where there was no ventilation, the carbon dioxide gas did not reach the upper part of the pit, and the decrease in pH was extremely bad. On the other hand, in the case 15 to which hot air was applied, the pH value was lower than 8.5 and the qc was higher than ^{800 kN / m 2.}

In cases 16 to 18, samples having a pH higher than 12 before contact with carbon dioxide gas are used. In the case 16 where hot air is not sent, the pH value has not dropped to the target value. In addition, even in the case where hot air was added at the same time, the pH value slightly exceeded the target value. Then, in the case 18 in which hot air was injected in advance, the pH reached the neutral range and the qc also greatly exceeded the target value. This is because the soil is dried by injecting only hot air into the soil in advance, and then the carbon dioxide gas and hot air are used together to neutralize the soil, which makes the fixing of carbon dioxide gas more efficient and the excess water. It means that the soil is finished in good quality because the strength does not decrease due to the above.
From the above examples, it was confirmed that it is possible to reliably lower the pH and produce high-quality neutral recycled soil even with strong alkaline construction sludge by prioritizing hot air.

2 Pit 4 Inflow pipe 6 Base layer 8 Blower 12 Sediment layer 14 Ventilation layer 16 Cover material

Claims (10)

A modified solidification treatment area where alkaline modified solidifying material is added to construction sludge and mixed to generate modified solidifying treated soil.
A loosening granulation means for producing finely divided granulated soil by loosening the modified solidified soil at the stage of becoming semi-solid.
Drying / neutralization that promotes the drying and neutralization of the loosened granulated soil using hot compressed air and carbon dioxide gas, which are heated compressed air, and further fixes the carbon dioxide gas as calcium carbonate to the loosened granulated soil. With a carbon dioxide fixed area and <br />
The drying / neutralizing / carbon dioxide fixing area
The pit to put the loosened granulated soil and
The disentangling and wherein Rukoto a inlet pipe for supplying hot compressed air and carbon dioxide to the granulation earth, neutral reproduction soil preparation system according immobilization techniques of carbon dioxide from the bottom of the pit. The neutral recycled soil production system according to the carbon dioxide immobilization technique according to claim 1, wherein the modified solidified soil exhibits a strong alkalinity having a pH of 12 or more. Neutral recycled soil by the carbon dioxide immobilization technique according to claim 1 or 2, first supplying hot compressed air to the loosened granulated soil, and then supplying hot compressed air and carbon dioxide gas to the loosened granulated soil. Manufacturing system. The neutral recycled soil production system according to the carbon dioxide immobilization technique according to claim 1 or 2 , wherein hot compressed air and carbon dioxide gas are simultaneously supplied to the loosened granulated soil. Claims 1 to 4 include a blower that recovers air containing excess carbon dioxide gas that has reached the ground surface in the pit and supplies the air to the loosened granulated soil as heat-compressed air again from the bottom surface of the pit. Neutral recycled soil production system by the carbon dioxide immobilization technology described in any one of the above. A reformed solidification process that produces modified solidified soil by adding an alkaline modified solidifying material to construction sludge and mixing it.
A loosening granulation step of producing finely divided granulated soil by loosening the modified solidified soil at the stage of becoming semi-solid.
Drying / neutralization that promotes the drying and neutralization of the loosened granulated soil using hot compressed air and carbon dioxide gas, which are heated compressed air, and further fixes the carbon dioxide gas as calcium carbonate to the loosened granulated soil. Carbon dioxide fixing process
Including
In the drying / neutralizing / carbon dioxide fixing process
A method for producing neutral recycled soil by carbon dioxide immobilization technology , which comprises throwing the loosened granulated soil into a pit and supplying heat compressed air and carbon dioxide gas from the bottom of the pit to the loosened granulated soil. .. The method for producing neutral recycled soil by the carbon dioxide immobilization technique according to claim 6 , wherein the modified solidified soil exhibits a strong alkalinity having a pH of 12 or more. Neutral recycled soil by the carbon dioxide immobilization technique according to claim 6 or 7 , wherein first, heat-compressed air is supplied to the loosened granulated soil, and then hot compressed air and carbon dioxide gas are supplied to the loosened granulated soil. Production method. The method for producing neutral recycled soil by the carbon dioxide immobilization technique according to claim 6 or 7 , wherein hot compressed air and carbon dioxide gas are simultaneously supplied to the loosened granulated soil. Any of claims 6 to 9 , wherein the air containing excess carbon dioxide gas that has reached the ground surface is recovered in the pit and is again supplied as heat-compressed air from the bottom surface of the pit to the loosened granulated soil. A method for producing neutral recycled soil by the carbon dioxide immobilization technique described in item 1.

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