We claim;
1. A separation method for separating carbon particles and oxide particles from a mixture
which is derived from fly ash and in which the carbon particles and the oxide particles exist in
a mixed form, the method comprising:
a mixing step of mixing the mixture, water, and hydrophobic liquid having a larger specific
gravity than the water to generate a liquid mixture; and
a specific gravity separation step of separating the carbon particles and the oxide particles by
leaving the liquid mixture to stand still and separating the liquid mixture into a hydrophobic
liquid phase including the carbon particles and a water phase including the oxide particles.
2. The separation method as claimed in Claim1, further comprising:
a first collection step of collecting the oxide particles by separating the water from the water
phase separated in the specific gravity separation step.
3. The separation method as claimed in Claim 1or 2, further comprising:
a second collection step of collecting a carbon-containing powder by separating the
hydrophobic liquid from the hydrophobic liquid phase separated in the specific gravity
separation step,
wherein the carbon-containing powder contains the carbon particles and the oxide particles,
a content ratio of a carbon component in the carbon-containing powder is 50 mass% or more
and 95 mass% or less,
the oxide particles are particles consisting of a compound including any one or both of a SiO2
component or an Al2O3 component, a total content ratio of the SiO2 component and the Al2O3
component in the oxide particles is 75 mass% or more,
the carbon particles are porous particles in which a plurality of pores are formed, and
at least some of the oxide particles exist in the pores of the carbon particles.
4. The separation method as claimed in Claim 3,
wherein an N/C ratio that is a mass ratio of a nitrogen component to the carbon component
included in the carbon-containing powder is 0.02 or less.
5. The separation method as claimed in any one of Claims 1 to 4,
wherein a combination of the mixing step and the specific gravity separation step is repeated
through a plurality of stages by a countercurrent flow-type multistage continuous process 6. The separation method as claimed in any one of Claims 1 to 5, further comprising:
a crushing step of crushing the carbon particles included in a liquid mixture of any one or both
of a hydrophobic liquid or water and the mixture by carrying out a crushing treatment on the
liquid mixture before the specific gravity separation step or in the specific gravity separation
step.
7. The separation method as claimed in Claim 6,
wherein, in the crushing step, the carbon particles included in the liquid mixture are crushed
by the crushing treatment using beads.
8. The separation method as claimed in any one of Claims 1 to 7,
wherein the fly ash is generated by combusting coal,
the carbon particles are particles of residual unburnt carbon after the combustion, and
the oxide particles are granular particles obtained by melting an ash of the coal during the
combustion.
9. The separation method as claimed in any one of Claims 1 to 8,
wherein the specific gravity separation step includes
a crude separation step of separating the hydrophobic liquid phase including the carbon
particles and the water phase including the oxide particles by leaving the mixed solution to
stand still and
a water washing step of separating a hydrophobic liquid phase including the carbon particles
and a water phase including the oxide particles by adding water to and mixing with the
hydrophobic liquid phase separated in the crude separation step and leaving the mixed solution
of the hydrophobic liquid phase and water to stand still.

[Technical Field of the Invention]
[0001]
The present invention relates to a carbon-containing powder. [Related Art]
[0002]
A majority of fly ash generated during the generation of electric power in coal-fired power plants and the like is recycled as a raw material for concrete, a raw material for a building material, a raw material for cement, and the like. Fly ash includes an ash made of a metallic oxide such as AI2O3 or SiCh and unburnt carbon which is a carbon component remaining after combustion. Therefore, it is preferable to separate the unburnt carbon included in fly ash and decrease the concentration of the unburnt carbon in order to use the fly ash as a building material raw material, a raw material for concrete (admixture), or the like.
[0003]
As a method for separating unburnt carbon in fly ash, for example, an electrostatic separation method or a flotation method is known. The electrostatic separation method is a method in which fly ash is injected into parallel plate electrodes in a dried state, thereby attracting electrically charged unburnt carbon to a positive electrode side and separating the unburnt carbon. In addition, the flotation method is a method in which unburnt carbon is caused to adhere to micro air generated using a foaming agent in a slurry of fly ash through a trapping agent such as kerosene, thereby

floating and separating unburnt carbon particles.
[0004]
For example, Patent Document 1 discloses a method for removing unburnt carbon in fly ash by flotation. In the flotation method of Patent Document 1, first, a slurry produced by adding water to fly ash is stirred, thereby generating an activation energy on the surfaces of unburnt carbon particles and making the unburnt carbon particles lipophilic (hydrophobic). Next, a trapping agent such as kerosene or light oil and a foaming agent are added to the slurry including the lipophilic unburnt carbon, thereby causing the trapping agent to adhere to the unburnt carbon, causing the unburnt carbon to adhere to generated bubbles, and floating the unburnt carbon. Such a flotation method separates unburnt carbon from fly ash which is a mixture of the unburnt carbon (specific gravity: 1.3 to 1.5) which is hydrophobic particles and a metallic oxide (specific gravity: 2.4 to 2.6) which is hydrophilic particles. [Prior Art Document] [Patent Document]
[0005]
[Patent Document 1] Japanese Unexamined Patent Application, First Publication No. 2007-167825 [Disclosure of the Invention] [Problems to be Solved by the Invention]
[0006]
When fly ash is recycled, it is desirable to effectively use not only a metallic oxide such as AI2O3 or SiCh but also unburnt carbon.
[0007]

However, in the flotation method in which unburnt carbon included in fly ash is caused to adhere to bubbles and float as described in Patent Document 1, there is a problem in that the separation rate is slow and the separation efficiency is poor. Therefore, a number of fine particles of the metallic oxide remain in the separated unburnt carbon, and it is difficult to separate and collect only the unburnt carbon with a high carbon content ratio. Furthermore, in a dried state, the fine particles of the metallic oxide such as AI2O3 or SiCh are likely to agglomerate with other particles due to an attracting force such as a Van Der Waals force or an electrostatic force and thus also adhere to the unburnt carbon particles. Therefore, it is more difficult to appropriately separate unburnt carbon particles and the fine particles of a metallic oxide included in fly ash.
[0008]
For the above-described reasons, in the separation methods of the related art, it is difficult to separate unburnt carbon included in fly ash with a high carbon content ratio. Therefore, in the related art, it is not possible to clarify the characteristics of unburnt carbon separated and collected from fly ash in its pure form, which hinders the effective use of unburnt carbon. Therefore, in the related art, there has been a desire for separating a carbon-containing powder such as unburnt carbon having a high carbon content ratio from coal ashes such as fly ash, clarifying the characteristics thereof, and effectively using the carbon-containing powder.
[0009]
The present invention has been made in consideration of the above-described problem, and an object of the present invention is to provide a new and improved carbon-containing powder, a separation method, and a use of the carbon-containing

powder.
[Means for Solving the Problem]
[0010]
In order to solve the above-described problem, according to a certain viewpoint of the present invention,
a carbon-containing powder is provided comprising carbon particles; and oxide particles,
in which a content ratio of a carbon component in the carbon-containing powder is 50 mass% or more and 95 mass% or less,
the oxide particles are particles consisting of a compound including any one or both of a SiCh component or an AI2O3 component, a total content ratio of the SiCh component and the AI2O3 component in the oxide particles is 75 mass% or more,
the carbon particles are porous particles in which a plurality of pores are formed, and
at least some of the oxide particles exist in the pores of the carbon particles.
[0011]
The content ratio of the carbon component in the carbon-containing powder may be 70 mass% or more and 95 mass% or less.
[0012]
An N/C ratio that is a mass ratio of a nitrogen component to the carbon component included in the carbon-containing powder may be more than 0 and 0.02 or less.
[0013]
A particle diameter of the oxide particles may be 1 to 20 |im in terms of a

volume-based 50% particle diameter.
[0014]
An average value of degrees of circularity of the oxide particles may be more than 0.9 and 1 or less.
[0015]
A content ratio of the SiCh component in the oxide particles may be 50 mass% or more and 80 mass% or less, and
a content ratio of the AI2O3 component in the oxide particles may be 10 mass% or more and 30 mass% or less.
[0016]
A specific surface area of the carbon-containing powder may be 50 to 300 m2/g.
[0017]
In addition, in order to solve the above-described problem, according to another viewpoint of the present invention,
a separation method is provided for separating carbon particles and oxide particles from a mixture which is derived from fly ash and in which the carbon particles and the oxide particles exist in a mixed form, the method comprising:
a mixing step of mixing the mixture, water, and hydrophobic liquid having a larger specific gravity than the water to generate a liquid mixture; and
a specific gravity separation step of separating the carbon particles and the oxide particles by leaving the liquid mixture to stand still and separating the liquid mixture into a hydrophobic liquid phase including the carbon particles and a water phase including the oxide particles.

[0018]
The separation method may further include a first collection step of collecting the oxide particles by separating the water from the water phase separated in the specific gravity separation step.
[0019]
The separation method may further include a second collection step of collecting a carbon-containing powder by separating the hydrophobic liquid from the hydrophobic liquid phase separated in the specific gravity separation step,
in which the carbon-containing powder contains the carbon particles and the oxide particles,
in which a content ratio of a carbon component in the carbon-containing powder is 50 mass% or more and 95 mass% or less,
the oxide particles are particles consisting of a compound including any one or both of a SiCh component or an AI2O3 component, a total content ratio of the SiCh component and the AI2O3 component in the oxide particles is 75 mass% or more,
the carbon particles are porous particles in which a plurality of pores are formed, and
at least some of the oxide particles exist in the pores of the carbon particles.
[0020]
An N/C ratio that is a mass ratio of a nitrogen component to the carbon component included in the carbon-containing powder and may be 0.02 or less.
[0021]
A combination of the mixing step and the specific gravity separation step may be repeated through a plurality of stages by a countercurrent flow-type multistage

continuous process.
[0022]
The separation method may further include
a crushing step of crushing the carbon particles included in a liquid mixture of any one or both of a hydrophobic liquid or water and the mixture by carrying out a crushing treatment on the liquid mixture before the specific gravity separation step or in the specific gravity separation step.
[0023]
In the crushing step, the carbon particles included in the liquid mixture may be crushed by the crushing treatment using beads.
[0024]
The fly ash may be generated by combusting coal,
the carbon particles may be particles of residual unburnt carbon after the combustion, and
the oxide particles may be granular particles obtained by melting an ash of the coal during the combustion.
[0025]
The specific gravity separation step may include
a crude separation step of separating the hydrophobic liquid phase including the carbon particles and the water phase including the oxide particles by leaving the mixed solution to stand still and
a water washing step of separating a hydrophobic liquid phase including the carbon particles and a water phase including the oxide particles by adding water to and mixing with the hydrophobic liquid phase separated in the crude separation step and

leaving the mixed solution of the hydrophobic liquid phase and water to stand still.
[0026]
In addition, in order to solve the above-described problem, according to another viewpoint of the present invention,
a use of a carbon-containing powder is provided in which the carbon-containing powder is used as an alternative to coal used in a sintering machine, a combustion furnace, or a converter or utilized as an SO2 adsorbent or a denitration material.
[0027]
The carbon-containing powder may be used after the carbon-containing powder and additional powder are mixed together and a bulk specific gravity of the carbon-containing powder is increased. [Effects of the Invention]
[0028]
As described above, according to the present invention, it is possible to provide a new and improved carbon-containing powder, a separation method, and a use of the carbon-containing powder. [Brief Description of the Drawings]
[0029]
FIG. 1A is a front view schematically showing fly ash before a wet-type separation treatment according to a first embodiment of the present invention.
FIG. IB is a cross-sectional view schematically showing the fly ash before the wet-type separation treatment according to the same embodiment.
FIG. 2A is a front view schematically showing a carbon-containing powder

after the wet-type separation treatment according to the same embodiment.
FIG. 2B is a cross-sectional view schematically showing the carbon-containing powder after the wet-type separation treatment according to the same embodiment.
FIG. 3 A is a front view schematically showing a carbon-containing powder after a crushing treatment and a wet-type separation treatment according to a second embodiment of the present invention.
FIG. 3B is a cross-sectional view schematically showing the carbon-containing powder after the crushing treatment and the wet-type separation treatment according to the same embodiment.
FIG. 4 is a step diagram showing an outline of a manufacturing method of a carbon-containing powder according to the first embodiment of the present invention.
FIG. 5 is a step diagram showing a separation and collection method in the manufacturing method of a carbon-containing powder according to the same embodiment.
FIG. 6 is a pattern diagram showing a separation and collection device according to the same embodiment.
FIG. 7 is a step diagram showing a separation and collection method in a manufacturing method of a carbon-containing powder according to the second embodiment of the present invention.
FIG. 8 is a step diagram showing a modification example of the separation and collection method according to the same embodiment.
FIG. 9 is a step diagram showing another modification example of the separation and collection method according to the same embodiment.

FIG. 10 is a step diagram showing still another modification example of the separation and collection method according to the same embodiment.
FIG. 11 is a step diagram showing a separation and collection method by a countercurrent-flow type multistage continuous process according to a third embodiment of the present invention.
FIG. 12 is a graph showing a relationship between a bead diameter and a carbon content ratio of a carbon-containing powder according to Example 5-1 of the present invention.
FIG. 13 is a graph showing a change in the carbon content ratio in a solid matter of a water phase or a solvent phase through individual stages of a countercurrent flow-type four-stage continuous process according to Example 11 of the present invention. [Embodiments of the Invention]
[0030]
Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the present specification and the drawings, configurational elements having substantially the same functional configuration will be given the same reference sign and will not be repeatedly described.
[0031]
[1. Background and outline of present invention]
First, the background of the present invention and the outline of a carbon-containing powder according to an embodiment of the present invention and a manufacturing method thereof will be described.

[0032]
As described above, fly ash is one of coal ashes generated by the combustion of coal, and fly ash is generated by, for example, the combustion of fuel coal in a boiler or the like in a power plant. As fuel coal in power plants, bituminous coal or subbituminous coal is mainly used.
[0033]
Fly ash includes unburnt carbon (carbon component) that is a carbon component remaining after combustion together with a metal oxide (ash) made from a compound including an AI2O3 component, a SiCh component, or the like. The carbon content ratio (the content ratio of the carbon component) in fly ash is 1.5% to 15 mass%, and the content ratio of the metal oxide such as a SiCh component or an AI2O3 component is 75% to 98 mass%.
[0034]
In a combustion process of coal in a power plant or the like, the oxide such as a Si02 component or an AI2O3 component in the fuel coal temporarily melts, and thus, in fly ash after combustion, the oxide exists as substantially spherical shape particles having a small number of protrusions and recesses on the surface. The substantially spherical shape mentioned herein is not limited to a truly spherical shape, but may be a shape that has a small number of protrusions and recesses on the surface and is approximately similar to a sphere, and includes shapes such as an ellipsoidal shape and a polygonal sphere shape. The particle diameter of the oxide particle is approximately 200 jam or less in diameter, but 5% to 10 mass% of the oxide particles having a diameter of less than 1 jam are also included in many cases. Almost all of such oxide particles are, unlike porous particles like unburnt carbon particles described

below, substantially spherical solid particles, and no pores are formed in the surface layer of the oxide particle. As described above, fly ash includes a number of substantially spherical solid oxide particles, and thus the specific surface area of fly ash becomes as small as 0.5 to 10 m2/g. The particle diameter in fly ash is approximately 1 to 200 jam.
[0035]
On the other hand, In the case of manufacturing coke from bituminous coal or subbituminous coal, the bituminous coal or subbituminous coal is treated dry distillation in a coke furnace or the like. It is known that, in this dry distillation, the specific surface area of a dry distillation substance increases due to voids generated when a volatile component disappears by heating (Non-Patent Document 1).
Non-Patent Document 1: Takeshi Yukimoto and three more, "Discrimination between Coal and Cokes", report of the Central Customs Laboratory of the Ministry of Finance, Vol. 49, pp. 69 to 76, March 19, 2011).
[0036]
However, in a boiler of a power plant, coal is in a combusted state which is different from a dry distillation state as in the above-described coke furnace, and thus, in the related art, it is not clear whether or not activation is in progress on the surfaces of unburnt carbon particles in fly ash. Furthermore, in a dried state, due to an attracting force such as a Van Der Waals force or an electrostatic force, fine oxide particles are more likely to agglomerate with other particles as the particle diameter thereof decreases, and the content ratio of unburnt carbon particles in fly ash is small. Therefore, a number of the oxide particles adhere to the surfaces of the unburnt carbon particles. Therefore, it has not been possible to clarify the characteristics of unburnt

carbon particles remaining in a boiler after combustion in their pure form.
[0037]
Furthermore, even in a case where pores exist in the surface layers of unburnt carbon particles due to activation, fine oxide particles enter the pores and adhere thereto by an attracting force such as a Van der Waals force or an electrostatic force. Therefore, it is difficult to remove oxide particles from the pores in the unburnt carbon particles, and thus it has been more difficult to explain the characteristics of unburnt carbon particles in their pure form.
[0038]
In the above-described status, the present inventors found a method in which unburnt carbon particles in fly ash are preferably separated from oxide particles using a special wet-type separation method and a carbon-containing powder in which the unburnt carbon particles are condensed is manufactured, investigated and analyzed the characteristics of the carbon-containing powder manufactured using the above-described method, and found a variety of new characteristics.
[0039]
Specifically, first, it was found that the nitrogen content ratio in fly ash (coal ash) combusted in a boiler or the like in a power plant was low and the N/C ratio of the fly ash was 0.02 or less. In addition, it was found that fly ash contains unburnt carbon particles (carbon component) and oxide particles (ash) made from a compound including a SiCh component, an AI2O3 component, and the like; however, as shown in FIG. 1A and FIG. IB (hereinafter, collectively referred to as FIG. 1), unburnt carbon particles P2 are porous particles, and a number of pores P20 are formed in the surface layers of the unburnt carbon particles P2. Furthermore, it was found that there may

be a case where oxide particles PI are substantially spherical solid particles and adhere to the surfaces of the unburnt carbon particles P2, but there may be a case where the oxide particles PI enter the plurality of pores P20 formed in the surface layers of the unburnt carbon particles P2 and exist in the pores.
[0040]
Therefore, in order to separate the unburnt carbon particles P2 from fly ash in which the unburnt carbon particles P2 and the oxide particles PI exist in a mixed form and condense the unburnt carbon particles as shown in FIG. 1, in a manufacturing method of the carbon-containing powder according to the present embodiment, a special wet-type separation method as described below is used.
[0041]
First, a liquid mixture obtained by mixing and stirring water, a hydrophobic liquid (for example, a hydrophobic organic solvent), and fly ash is left to stand still, thereby separating a hydrophobic liquid phase including the unburnt carbon particles P2 and a water phase including the oxide particles PI (specific gravity separation step). Next, the hydrophobic liquid is separated from the hydrophobic liquid phase, thereby collecting a cake including the unburnt carbon particles P2 (solid-liquid separation step). After that, the cake is heated to volatilize the hydrophobic liquid, thereby collecting a carbon-containing powder in which the unburnt carbon particles P2 are condensed (collection step).
[0042]
It is possible to separate the unburnt carbon particles P2 from fly ash, condense the unburnt carbon particles, and obtain a carbon-containing powder having a high carbon content ratio (carbon content ratio: 50 mass% or more) using such a

manufacturing method. In this separation method, as shown in FIG. 2A and FIG. 2B (hereinafter, collectively referred to as FIG. 2), the fine oxide particles PI in the pores P20 in the unburnt carbon particles P2 are rarely removed, but almost all of the oxide particles PI adhering to the surfaces of the unburnt carbon particles P2 can be separated and removed.
[0043]
Furthermore, in a preceding step or a subsequent step of the specific gravity separation step, a crushing treatment is preferably carried out on the liquid mixture of fly ash and any one or both of the water and hydrophobic liquid (crushing step). As a crushing method, for example, a crushing treatment using ultrasonic waves, a crushing treatment using a high-speed shear mixer, a crushing treatment using a ball mill or a bead mill, and the like are exemplified. The hydrophobic liquid used in the crushing step may be identical to or different from the hydrophobic liquid L2 used in the specific gravity separation step.
[0044]
As shown in FIG. 3 A and FIG. 3B (hereinafter, collectively referred to as FIG. 3), such a crushing treatment crushes the unburnt carbon particles P2 in fly ash, divides the unburnt carbon particles into a plurality of pieces on fracture surfaces P21, and miniaturizes the unburnt carbon particles. Therefore, the substantially spherical oxide particles PI in the pores P20 in the vicinities of the fracture surfaces P21 are discharged from the pores P20. Therefore, not only the oxide particles PI adhering to the surfaces of the unburnt carbon particles P2 but also the oxide particles PI in the pores P20 are separated and removed from the unburnt carbon particles P2, and thus the unburnt carbon particles P2 and the oxide particles PI can be more preferably

separated from each other. Therefore, it becomes possible to obtain a carbon-containing powder having a higher carbon content ratio (carbon content ratio: 70 mass% or more) by carrying out the crushing treatment on fly ash.
[0045]
[2. Configuration of carbon-containing powder]
Next, the configuration of the carbon-containing powder mainly including unburnt carbon particles separated and collected from fly ash according to the present embodiment will be described in detail.
[0046]
[2.1. Characteristics of carbon-containing powder]
As a result of investigating and analyzing the components, physical property values, and the like of the carbon-containing powder (carbon content ratio: 50 mass% or more) collected from fly ash using the above-described manufacturing method, it was clarified that the carbon-containing powder has the following characteristics. Hereinafter, the characteristics of the carbon-containing powder according to the present embodiment will be described with reference to Table 1 in comparison with carbon-containing substances in the related art.
[0047]
[Table 1]
Table 1 Characteristics of carbon-containing powder

Particle characteristic Specific
surface
area
[m2/g] Composition of oxide particle Shape of
oxide
particle

Si02
[ mass%] A1203 [ mass%]
CA
[ mass%]
Anthracite coal Non-porous Less than 1 50 to 80 10 to 30 Irregular shape 80 or more

Bituminous coal and subbituminous coal Non-porous Less than 1 50 to 80 10 to 30 Irregular shape 80 or more
Active coke powder Porous 50 to 300 50 to 80 10 to 30 Irregular shape 80 to 90
Carbon-containing powder according to present embodiment Porous 50 to 300 50 to 80 10 to 30 Substantially
spherical
shape
(50% particle
diameter: 1
to 20 urn) 50 to 95 70 to 95
[0048]
(1) N/C ratio
The N/C ratio is the mass proportion between the amount of a nitrogen component (nitrogen content ratio) and the amount of a carbon component (carbon content ratio) in a certain material and is obtained by dividing the nitrogen content ratio by the carbon content ratio. The carbon-containing powder according to the present embodiment has a low nitrogen content ratio and a high carbon content ratio, and thus the N/C ratio of the carbon-containing powder is more than 0 and 0.02 or less and, for example, in a range of 0.0065 to 0.0196. While not shown in Table 1, the N/C ratios of anthracite coal, bituminous coal, and subbituminous coal are, for example, 0.008 to 0.03, and many of them have an N/C ratio of more than 0.02. The N/C ratio of the carbon-containing powder according to the present embodiment is in a low region in the range of the N/C ratio of anthracite coal, bituminous coal, and subbituminous coal. The N/C ratio of unburnt carbon included in original fly ash to be subjected to the wet-type separation step according to the present embodiment is 0.02 or less, and the nitrogen content ratio is low. Therefore, the N/C ratio of a carbon-containing powder mainly including separated and collected unburnt carbon also reaches 0.02 or less. As described below, it is thought that the N/C ratio decreases as the combustion temperature in a boiler in a power plant increases.

[0049]
(2) Carbon content ratio
The carbon content ratio CA of the carbon-containing powder collected from fly ash by wet-type separation according to the manufacturing method according to the present embodiment is 50 mass% or more and 95 mass% or less. Particularly, the carbon content ratio CA of the carbon-containing powder collected by the manufacturing method including the above-described crushing step is 70 mass% or more and 95 mass% or less.
[0050]
Therefore, in the carbon-containing powder manufactured by the manufacturing method according to the present embodiment, the carbon content ratio CA is 50 mass% or more and more preferably 70 mass% or more, and the N/C ratio is also as small as 0.02 or less. Therefore, the carbon-containing powder according to the present embodiment can be used as coal having a low nitrogen content ratio (low-nitrogen coal) and can be effectively used as an alternative to low-nitrogen coal of the related art which is used in coal treatment facilities such as sintering machines, power plants, converters, and the like. Particularly, in order to effectively use the carbon-containing powder as an alternative to low-nitrogen coal used in sintering machines, the N/C ratio is more preferably 0.015 or less. Therefore, it is extremely important and beneficial in an industrial sense that carbon-containing powder having a carbon content ratio approximately as high as that of low-nitrogen coal and a low N/C ratio can be collected from fly ash and recycled using the manufacturing method according to the present embodiment.
[0051]

(3) Specific surface area
As shown in FIG. 2 and FIG. 3, the unburnt carbon particles P2 included in the carbon-containing powder according to the present embodiment are porous particles having a number of pores P20 formed in the surface layers of the unburnt carbon particles P2. Therefore, the specific surface area of the carbon-containing powder according to the present embodiment is 50 to 300 m2/g, which is similar to that of active coke powder, and becomes approximately several ten times to hundred times larger than the specific surface area (0.5 to 10 m2/g) of fly ash before a separation treatment.
[0052]
(4) SO2 adsorption capacity and denitration capacity
As described above, the specific surface area of the carbon-containing powder according to the present embodiment is as extremely large as 50 to 300 m2/g. Therefore, the carbon-containing powder according to the present embodiment has an SO2 adsorption capacity and a denitration capacity and can be effectively used as an SO2 adsorbing material and a denitration material.
[0053]
(5) Component of oxide particle
The oxide particle PI is a particle made of a compound including at least any one or both of a SiCh component or an AI2O3 component. In fly ash, Si and Al are mainly included as a compound such as mullite (AI6S12O13), quartz (SiCh), or amorphous (nAkOs/mSiCh). Here, n and m are integers. These compounds correspond to the SiCh component or the AI2O3 component. In fly ash, the oxide particles PI made of such a compound are included. Therefore, in the carbon-

containing powder separated from the fly ash as well, some of the oxide particles PI made of the compound are left and included.
[0054]
The carbon-containing powder according to the present embodiment is powder mainly including unburnt carbon (carbon component), but also contains the oxide particles PI which cannot be separated by a specific gravity separation treatment described below. The content ratio of the oxide particles PI in the carbon-containing powder is less than 50 mass% and preferably less than 30 mass%. The total content ratio of the SiCh component and the AI2O3 component in the oxide particles PI is 75 mass% or more and 98 mass% or less. As described above, the oxide particles PI are made of a compound mainly including a SiCh component and an AI2O3 component, but may also include an oxide of an element other than the above-described elements. The content ratio of the Si02 component in the oxide particles PI is 50 mass% or more and 80 mass% or less, and the content ratio of the AI2O3 component in the oxide particles PI is 10 mass% or more and 30 mass% or less. As these content ratios, "average content ratios" are preferably used. The average content ratios are obtained by measuring the content ratios of the SiCh component and the AI2O3 component using a plurality of samples of the oxide particles PI and computing the averages of a plurality of the measurement values.
[0055]
(6) Particle diameter, degree of circularity, and existence form of oxide particle
In the carbon-containing powder according to the present embodiment, not only the unburnt carbon particles P2 but also the oxide particles PI exist in a mixed

form. These oxide particles PI are particles made of the ash of coal that has been melted by combustion heat and then cooled in a granular shape in the case of combusting the coal in a boiler or the like as described above, and almost all thereof are substantially spherical solid particles. Regarding the particle diameter of the oxide particle PI, the volume-based 50% particle diameter (median diameter D50) is 1 to 20 jam. The average value of the degrees of circularity of the oxide particles PI is more than 0.9 and 1 or less. Here, the degree of circularity of a particle refers to the ratio of the boundary length of a circle having the same area as the projection image of the particle to the boundary length of the projection image of the particle.
[0056]
At least some of such oxide particles PI enter a number of the pores P20 formed in the surface layers of the unburnt carbon particles P2 and exist therein. In a carbon-containing powder from which the oxide particles PI are separated from the surfaces by a specific gravity separation treatment, the content ratio of the oxide particles PI remaining in the pores P20 and the oxide particles PI included somewhere other than the pores P20 is more than 5 mass% and less than 50 mass%. As described above, the carbon-containing powder according to the present embodiment has a characteristic configuration in which a granular oxide having a 50% particle diameter of 1 to 20 jam and an average value of the degree of circularity of more than 0.9 and 1 or less (substantially spherical oxide particles PI) exists in the pores P20 in the porous unburnt carbon particles P2 in a mixed form. The carbon-containing powder having such a characteristic configuration is not known in the related art and can be said to be new and useful low-nitrogen coal powder.
[0057]

[2.2. Measurement method]
Next, measurement methods of the above-described characteristics of the carbon-containing powder according to the present embodiment will be described. [0058]
(1) Measurement method of specific surface area
The specific surface area (unit: m2/g) of a carbon-containing powder mainly including porous unburnt carbon particles can be measured using a fluid specific surface area measurement instrument (for example, FlowSorb II2300 manufactured by Shimadzu Corporation) and a gas adsorption method. In the gas adsorption method, a gas mixture of helium and nitrogen (volume ratio of 7:3) is used, and the monomolecular adsorption amount and specific surface area of the gas can be computed using a BET equation.
[0059]
(2) Measurement method of SO2 adsorption capacity
The carbon-containing powder (specimen, 5 to 50 ml) is fed into a reaction tank, the reaction tank temperature is set to 100°C, and a specimen gas is aerated for three hours. The composition of the specimen gas can be set to 2% by volume of SO2, 10% by volume of H2O, and 6% by volume of O2 with a remainder of nitrogen. After the aeration of the specimen gas, the carbon-containing powder is heated to 400°C under a nitrogen flow, SO2 generated is trapped, and the amount thereof is determined, whereby the SO2 adsorption capacity (unit: mg-SCh/g-carbon-containing powder) of the carbon-containing powder can be measured.
[0060]
(3) Measurement method of denitration capacity

The carbon-containing powder (specimen, 5 to 50 ml) is fed into a reaction tank for analysis, and a specimen gas is aerated for 10 hours in the reaction tank at a reaction tank temperature of 150°C and SV500h4. The composition of the specimen gas can be set to 200 ppm of NO, 200 ppm of NH3, 6% by volume of O2, and 10% by volume of H2O with a remainder of nitrogen. After the aeration of the specimen gas, the concentration of NO and the concentration of O2 in gas discharged from the reaction tank are measured, and a decrease rate of the concentration of NO in a steady state is computed, whereby the denitration rate (% by volume) by the carbon-containing powder can be obtained.
[0061]
(4) Measurement method of carbon content ratio and nitrogen content ratio
The carbon content ratio and the nitrogen content ratio of the carbon-
containing powder according to the present embodiment were measured according to
JISM8819.
[0062]
(5) Measurement method of sulfur content ratio
The sulfur content ratio of the carbon-containing powder according to the present embodiment was measured according to JIS M8813. [0063]
(6) Measurement method of particle diameter of oxide particle in carbon-
containing powder
The carbon-containing powder according to the present embodiment is fed into a crucible and heated at 600°C for two hours in the presence of air, thereby combusting the carbon component. Therefore, the granular oxide (substantially

spherical oxide particles PI) that is intervening particles in the carbon-containing powder can be obtained as a residue. Generally, at 600°C, a component mainly containing carbon is combusted, but the granular oxide does not melt, and thus it is possible to collect the granular oxide without changing the form thereof. Next, the particle size distribution of the granular oxide is measured using a laser diffraction-type particle size distribution measurement instrument, whereby the volume-based 50% particle diameter (median diameter D50) can be obtained. [0064]
(7) Measurement method of degree of circularity of oxide particle in carbon-
containing powder
The degree of circularity of the oxide particle PI collected in (6) can be obtained by analyzing the shape of the captured oxide particle using a particle image analyzer. For example, a suspension obtained by adding a dispersant aqueous solution to a specimen of the oxide particles and carrying out a dispersion treatment using ultrasonic waves is prepared. The oxide particles in the suspension can be captured as a still image by a sheath flow method using a flow-type particle image analyzer. The average value of the degrees of circularity may be the average of the degrees of circularity of a predetermined number or more of oxide particles measured in the specimen. The number of the oxide particles used for the computation of the average value may be, for example, 10,000 or more.
[0065]
(8) Measurement method of content ratios of SiCh component and AI2O3
component in oxide particle
The content ratio [mass%] of the SiCh component in the substantially

spherical oxide particles PI collected in (6) and the content ratio [mass%] of the AI2O3 component in the substantially spherical oxide particles can be measured by a fluorescent X-ray analysis method.
[0066]
The content ratio of SiCh can be quantitatively analyzed using a fluorescent X-ray analyzer (XRF) employing a glass bead method. Specifically, a plurality of measurement samples with a variety of content ratios are prepared from a measurement sample with a known content ratio of SiCh, and the Si-derived fluorescent X-ray intensities of the prepared measurement samples are measured using the fluorescent X-ray analyzer. A calibration curve showing a relationship between the content ratios and the fluorescent X-ray intensities of SiCh is produced in advance using the obtained Si-derived fluorescent X-ray intensities and the content ratios of SiCh. After that, for a specimen having an unknown content ratio of SiCh of interest, the Si-derived fluorescent X-ray intensity is measured using an X-ray fluorescence instrument, and the content ratio of SiCh can be specified using the obtained fluorescent X-ray intensity and the calibration curve. Therefore, the content ratio of the SiCh component in the oxide particles PI can be obtained.
[0067]
In addition, the content ratio of AI2O3 can be quantitatively analyzed using the fluorescent X-ray analyzer (XRF) employing the glass bead method. Specifically, a plurality of measurement samples with a variety of content ratios are prepared from a measurement sample with a known content ratio of AI2O3, and the Al-derived fluorescent X-ray intensities of the prepared measurement samples are measured using the fluorescent X-ray analyzer. A calibration curve showing a relationship between

the content ratios and the fluorescent X-ray intensities of AI2O3 is produced in advance using the obtained Al-derived fluorescent X-ray intensities and the content ratios of AI2O3. After that, for a specimen having an unknown content ratio of AI2O3 of interest, the fluorescent X-ray intensity of AI2O3 is measured using the fluorescent X-ray analyzer, and the content ratio of AI2O3 can be specified using the obtained fluorescent X-ray intensity and the calibration curve. Therefore, the content ratio CM of the AI2O3 component in the oxide particles PI can be obtained.
[0068]
The total content ratio CT [ mass%] of the SiC>2 component and the AI2O3 component in the oxide particles PI in the carbon-containing powder can be measured from the content ratio Csi[ mass%] of the Si02 component in the oxide particles PI and the content ratio CAI[ mass%] of the AI2O3 component in the oxide particles PI obtained as described above using Expression (1).
CT = Csi + CAi - (1)
[0069]
In the case of measuring the content ratios in (4), (5), and (8), the average value of a plurality of content ratios measured using a plurality of specimens may be computed, or the content ratio may be measured using only one specimen. From the viewpoint of measurement accuracy, the content ratio is preferably obtained using a plurality of specimens. This is also true for the particle diameter in (6) and the degree of circularity in (7).
[0070]
[2.3. Principle of decrease in N/C ratio of carbon-containing powder]
Next, the reason for the nitrogen content ratio and N/C ratio of the carbon-

containing powder according to the present embodiment being low will be described with reference to FIG. 4. FIG. 4 is a step diagram showing the outline of a manufacturing method of a carbon-containing powder PO according to the present embodiment.
[0071]
As shown in FIG. 4, in the manufacturing method of the present embodiment, fuel coal FC such as bituminous coal or subbituminous coal is combusted in, for example, a boiler 4 or the like in a heat power plant, and, as a result of this combustion, fly ash FA as coal ash is generated (combustion step). This fly ash FA is introduced to a separation and collection device 5 (the detail will be described below), separated into the oxide particles PI (ash) made up of a SiCh component and an AI2O3 component and the unburnt carbon particles P2 (carbon component) using a special wet-type separation method according to the present embodiment, and collected (separation and collection step). Therefore, the carbon-containing powder PO according to the present embodiment is manufactured through the combustion step in the boiler 4 and the separation and collection step in the separation and collection device 5. Here, the reason for the nitrogen content ratio of the carbon-containing powder PO according to the present embodiment being low is considered to arise from the combustion step of coal in the boiler 4.
[0072]
Generally, in a dry distillation step of coal in a coke furnace, a variety of dry distilled gases are generated. According to Non-Patent Document 2, while depending on the kind of coal, the generation of HCN and NH3 among nitrogen-based gases (HCN, NH3, and N2) in dry distilled gas begins at approximately 300°C and ends at

approximately 800°C. In contrast, it is known that N2 begins to be generated at approximately 600°C and is continuously generated at a high temperature of 800°C or higher at which the generation of the other nitrogen-based gases almost ends. In addition, generally, in dry distilled gas, carbon-based gases (CO, CH4, and HCN) are generated to a small extent. Therefore, it can be predicted that, during the dry distillation of coal, the N/C ratio of the coal decreases as the dry distillation temperature in the coke furnace increases.
Non-Patent Document 2: Yasuhiro Tobu and two more, "Distribution Behavior of Nitrogen in Coal Dry Distillation Step by Gas Real-time Measurement and XPS measurement", Material and Process, Vol. 25, No. 2, Page. ROMBUNNO. 36, September 1, 2012
[0073]
In the combustion step of the manufacturing method according to the present embodiment, the combustion temperature in the boiler 4 in a power plant is approximately 1,300°C to 1,500°C, the retention time of coal powder in the boiler 4 is approximately several seconds, which is extremely short compared with the retention time of coal powder in the coke furnace, and the coal powder in the boiler 4 is in a combusted state rather than in a dry distilled state. There is a concentration distribution of oxygen in the boiler 4, the concentration of oxygen is particularly low in the vicinity of the surface of the coal powder, and some of the coal powder is considered to be in a state similar to the dry distilled state. Therefore, it is thought that, similar to the above-described dry distillation step of coal, even in the combustion step in the boiler 4, only the surface layer portion of coal powder having a particle diameter of approximately several millimeters is dry distilled under a high temperature

condition under which the combustion temperature is 800°C or higher, a nitrogen compound included in the surface layer portion is decomposed and gasified, and thus the nitrogen component of the coal powder decreases. Therefore, it is thought that the nitrogen content ratio of the unburnt carbon particles P2 in the fly ash FA after the combustion step decreases, and the N/C ratio of the collected carbon-containing powder PO also decreases. In addition, it is thought that, as the combustion temperature in the boiler 4 increases, the N/C ratio of the carbon-containing powder PO decreases.
[0074]
[2.4. Characteristics of intervening particle in carbon-containing powder]
Next, the characteristics of the substantially spherical oxide particles PI included as intervening particles in the carbon-containing powder according to the present embodiment will be described in more detail with reference to FIG. 1 to FIG. 3.
[0075]
As shown in FIG. 1, in the fly ash FA before a wet-type separation treatment, a larger number of the substantially spherical oxide particles PI are included than the unburnt carbon particles P2, the oxide particles PI enter the pores P20 in the unburnt carbon particles P2, and the oxide particles PI cover the surfaces of the unburnt carbon particles P2. Therefore, in the related art, the characteristics of the unburnt carbon particles P2 in their pure form are not clear.
[0076]
Therefore, in a manufacturing method according to a first embodiment of the present invention described below, the unburnt carbon particles P2 and the oxide particles PI are separated from each other by a wet-type separation treatment which

does not accompany any crushing treatment and in which water and a hydrophobic liquid are used (refer to FIG. 5). Therefore, as shown in FIG. 2, the oxide particles PI adhering to the surfaces of the unburnt carbon particles P2 are removed, but it is difficult to remove the oxide particles PI that have entered the pores P20 in the unburnt carbon particles P2. The reason therefor is considered to be because, in the wet-type separation treatment, any one or both of water and the hydrophobic liquid are incapable of entering the inside of the pores P20 in the unburnt carbon particles P2, and thus it is difficult to discharge the oxide particles PI from the pores P20.
[0077]
Here, the case of using a carbon-containing powder including such unburnt carbon particles P2 as an SO2 adsorbent will be considered. The pores P20 in the unburnt carbon particles P2 that are blocked by the oxide particles PI are counted in the specific surface area of the carbon-containing powder. However, the oxide particles PI are held in the pores P20 in the unburnt carbon particles P2, and thus almost all exhaust gas (normal pressure) containing SO2 or the like is not capable of approaching deep portions of the pores P20. Therefore, it is not possible to effectively use the pores P20 in the unburnt carbon particles P2 as SO2 adsorption surfaces, and there is room for improvement in performance of the SO2 adsorbent.
[0078]
Therefore, in a manufacturing method according to a second embodiment of the present invention described below, a wet-type separation treatment accompanying a crushing treatment of the unburnt carbon particles P2 (refer to FIG. 7 to FIG. 10) is carried out. As shown in FIG. 3, such a crushing treatment easily crushes brittle porous unburnt carbon particles P2, and a plurality of the pores P20 is connected to

each other along the fracture surfaces P21, and thus the unburnt carbon particles P2 are easily miniaturized. Once the unburnt carbon particles P2 are crushed, the substantially spherical oxide particles PI in the pores P20 are capable of easily coming into contact with any one or both of water and the hydrophobic liquid, and a number of the oxide particles PI are discharged from the pores P20 and can be separated from the unburnt carbon particles P2. Therefore, a carbon-containing powder mainly including the unburnt carbon particles P2 from which the oxide particles PI are separated can be obtained. In this carbon-containing powder, the carbon content ratio increases, and the surface area of the carbon component which serves as an SO2 adsorption surface also increases. Therefore, the SCh-containing gas treatment capability of the carbon-containing powder is enhanced, and performance as an SO2 adsorbent improves.
[0079]
[3. Manufacturing method of carbon-containing powder]
Next, a manufacturing method of a carbon-containing powder according to the present embodiment will be described in detail.
[0080]
[3.1. Outline of manufacturing method of carbon-containing powder]
First, the outline of the manufacturing method of a carbon-containing powder according to the present embodiment will be described with reference to FIG. 4.
[0081]
As shown in FIG. 4, the manufacturing method of a carbon-containing powder according to the present embodiment includes a combustion step (SO) and a separation and collection step (SI). In the combustion step (SO), fuel coal FC is combusted using the boiler 4 in a heat power plant or the like, thereby generating fly ash FA as

coal ash. Next, in the separation and collection step (SI), the oxide particles PI and the unburnt carbon particles P2 are separated from the fly ash FA and each collected using the separation and collection device 5.
[0082]
[3.2. Specific gravity separation method]
Subsequently, a method for separating the fly ash FA into the oxide particles PI and the unburnt carbon particles P2 in the separation and collection step (SI) according to the present embodiment will be described in more detail.
[0083]
In the separation and collection step according to the present embodiment, a mixture which is derived from the fly ash FA and in which the oxide particles PI and the unburnt carbon particles P2 exist in a mixed form is separated in a wet-type manner into the carbon-containing powder PO mainly including the unburnt carbon particles P2 and the oxide particles PI.
[0084]
In this separation method, water is used as an extraction agent of the oxide particles PI which are hydrophilic particles, and, for example, a hydrophobic liquid having a larger specific gravity than water is used as an extraction agent of the unburnt carbon particles P2 which are hydrophobic particles. In addition, the water and the hydrophobic liquid are mixed into and stirred with the fly ash (solid content) FA which is a mixture of treatment subjects, thereby generating a liquid mixture in which the mixture is dispersed (first slurry) (mixing step). Next, the liquid mixture is left to stand still in a separation device (for example, a settler such as a settling tank or a still standing tank), whereby the liquid mixture is separated into two phases of a water

phase on the upper side and a hydrophobic liquid phase on the lower side using the specific gravity difference between the water and the hydrophobic liquid, the oxide particles PI (hydrophilic particles) are moved to the water phase, and the unburnt carbon particles P2 (hydrophobic particles) are moved to the hydrophobic liquid phase (specific gravity separation step). Furthermore, the oxide particles PI are separated and collected from the separated water phase (second slurry) (first collection step), and the unburnt carbon particles P2 are separated and collected from the hydrophobic liquid phase (third slurry) separated in the separation step (second collection step). With these steps, the oxide particles PI and the unburnt carbon particles P2 can be rapidly and efficiently separated from each other, and it is possible to respectively collect and reuse the oxide particles PI and the unburnt carbon particles P2 each having a high content ratio.
[0085]
Here, the hydrophobic liquid refers to a liquid having hydrophobicity, that is, a liquid having a low affinity to water (in other words, a liquid that does not easily dissolve in water or does not easily mix with water). The hydrophobic liquid may be a liquid having a solubility at 20°C in water of 0 g/L or more and 5.0 g/L or less. Hydrophobicity mentioned in the present specification is a property including lipophilicity. The hydrophobic liquid may be a hydrophobic organic solvent (hereinafter, referred to as the "hydrophobic solvent") or a variety of oils such as silicone oil. As the hydrophobic solvent, it is possible to use, for example, a fluorine-based, bromine-based, or chlorine-based organic solvent or the like. Such a hydrophobic liquid has a low affinity to water, and thus, in a case where the liquid mixture obtained by mixing and stirring the hydrophobic liquid and water is left to

stand still, the liquid mixture is separated into two phases of a water phase mainly including water and a hydrophobic liquid phase (for example, a hydrophobic solvent phase) mainly including the hydrophobic liquid (for example, the hydrophobic solvent).
[0086]
Table 2 shows examples of the hydrophobic liquid used in the separation method according to the present embodiment. All of the hydrophobic liquids exemplified in Table 2 have a specific gravity of more than 1, a solubility in water of 5.0 g/L or less, and hydrophobicity.

[0087]
[Table 2]
Table 2 Specific examples of hydrophobic liquid

General name Compound name Trade name
(Company
name) Boiling point
[°C] Specific gravity Solubilty in water
[g/L]
Fluorine-based organic solvent HFE-7200 (1-Ethoxy-
1,1,2,2,3,3,4,4,4-nonafluorobutane) - 76 1.43 Less than 0.02
Fluorine-based organic solvent HFE-347pc-f
((2,2,2-
Trifluoroethyl)(l,l,2,
2-
Tetrafluoroethyl)ethe
r) - 56 1.47 0.7
Bromine-based organic solvent 1-Bromopropane - 71 1.35 2.5
Chlorine-based organic solvent Trichloroethylene - 87 1.46 1.28
Chlorine-based organic solvent Tetrachloroethylene - 121 1.62 0.15
Silicone oil - SH 550 FLUID (manufactured by DuPont Toray Specialty Materials K.K.) 300 or higher 1.07 Almost 0
Silicone oil - FS 1265 300CS (manufactured by DuPont Toray Specialty Materials K.K.) 300 or higher 1.25 Almost 0

[0088]
In addition, the specific gravity of the hydrophobic liquid is preferably more than 1.05. In such a case, the liquid mixture can be rapidly separated into the water phase and the hydrophobic liquid phase within a short period of time, for example, approximately 1 to 30 seconds after the still standing of the liquid mixture using the specific gravity difference between the water and the hydrophobic liquid.
[0089]
The hydrophilic particles are particles having an affinity to water and have a property of more easily mixing with water than the hydrophobic liquid. The oxide particles PI included in the fly ash FA are hydrophilic particles. On the other hand, the hydrophobic particles are particles having an affinity to the hydrophobic liquid and have a property of more easily mixing with the hydrophobic liquid than water. The unburnt carbon particles P2 included in the fly ash FA are hydrophobic particles. Therefore, in the liquid mixture of water and the hydrophobic liquid, the hydrophilic particles (oxide particles PI) move to the water phase from the hydrophobic liquid phase and disperse and exist mainly in the water phase. On the other hand, the hydrophobic particles (unburnt carbon particles P2) move to the hydrophobic phase from the water liquid phase and disperse and exist mainly in the hydrophobic liquid phase.
[0090]
In addition, the specific gravity of the oxide particle PI which is a hydrophilic particle is, for example, 2.4 to 2.6. The specific gravity of the unburnt carbon particle P2 which is a hydrophobic particle is, for example, 1.3 to 1.5. Even in a case where the specific gravity of the hydrophobic particle is smaller than the specific gravity of

the hydrophilic particle, according to the separation method according to the present embodiment, it is possible to rapidly and efficiently separate both particles in a wet-type manner by lifting the hydrophilic particles to the water phase that is the upper phase and sinking the hydrophobic particles to the hydrophobic liquid phase that is the lower phase. Even in a case where the specific gravity of the oxide particle PI is smaller than the specific gravity of the unburnt carbon particle P2, it is possible to separate the oxide particles PI and the unburnt carbon particles P2 by the wet-type separation in which water and the hydrophobic liquid are used as described above. In the present specification, the specific gravity of a particle refers to the specific gravity (true specific gravity) of the particle itself, not to the bulk specific gravity of the particle.
[0091]
[3.3. Separation and collection method of carbon-containing powder]
Next, the separation and collection method in the manufacturing method of a carbon-containing powder according to the present embodiment will be described in detail with reference to FIG. 5. In the following description, an example of using the hydrophobic solvent as the hydrophobic liquid will be described.
[0092]
As shown in FIG. 5, the separation and collection step (SI) includes a specific gravity separation step (S2) and a collection step (S4). The specific gravity separation step (S2) includes a crude separation step (S21) and a water washing step (S22), and the collection step (S4) includes a solid-liquid separation step (S41) and a drying step (S42).
[0093]

In the crude separation step (S21) of the specific gravity separation step (S2), the fly ash FA, water LI, and a hydrophobic solvent L2 are mixed together. The liquid mixture is left to stand still, thereby being separated due to the specific gravities into a hydrophobic solvent phase ph2 mainly including the unburnt carbon particles P2 (in other words, carbon particles) as a solid content and a water phase phi mainly including the oxide particles PI. With this crude separation step (S21), the unburnt carbon particles P2 and the oxide particles PI in the fly ash FA can be crudely separated from each other. Therefore, it is possible to increase the content ratio of the unburnt carbon particles P2 (in other words, the carbon content ratio) in the solid content in the hydrophobic solvent phase ph2.
[0094]
Next, in the water washing step (S22), the water LI is added to and mixed with the hydrophobic solvent phase ph2 separated in the crude separation step (S21). The liquid mixture is left to stand still, thereby being separated due to the specific gravities into the hydrophobic solvent phase ph2 in which the unburnt carbon particles P2 are condensed as a solid content and the water phase phi mainly including residual oxide particles PI. With this water washing step (S22), it is possible to wash the hydrophobic solvent phase ph2 including the unburnt carbon particles P2 with the water LI and separate and remove the oxide particles PI remaining in the crude separation step (S21) from the unburnt carbon particles P2. Therefore, it is possible to condense the unburnt carbon particles P2 included in the hydrophobic solvent phase ph2 and further increase the content ratio of the unburnt carbon particles P2 (carbon content ratio) in the solid content in the hydrophobic solvent phase ph2.
[0095]

The water washing step (S22) may be carried out only once, but the content ratio of the unburnt carbon particles P2 in the solid content in the hydrophobic solvent phase ph2 (in other words, carbon content ratio) can be further increased by carrying out the water washing step a plurality of times (for examples, twice to four times). In the specific gravity separation step (S2), the water washing step (S22) is not essential, and only the crude separation step (S21) may be carried out. Even in this case, the unburnt carbon particles P2 and the oxide particles PI can be separated from each other to a certain extent, and it is possible to obtain the hydrophobic solvent phase ph2 having a high content ratio of the unburnt carbon particles P2.
[0096]
Next, in the solid-liquid separation step (S41) of the collection step (S4), with a solid-liquid separation treatment such as filtration or centrifugal separation, the hydrophobic solvent phase ph2 separated in the specific gravity separation step (S2) is separated into the hydrophobic solvent L2 that is a liquid content and the particles (mainly the unburnt carbon particles P2 and the residual oxide particles PI) that are a solid content, and the hydrophobic solvent L2 is removed from the particles that are a solid content. Therefore, a cake C2 mainly including the particles that are a solid content such as the unburnt carbon particles P2 is collected.
[0097]
After that, in the drying step (S42), the cake C2 is heated, thereby volatilizing the hydrophobic solvent L2 remaining in the cake C2. Therefore, the carbon-containing powder P0 mainly including the unburnt carbon particles P2 (carbon content ratio: 50 mass% or more) is collected.