WO2020189109A1 - フライアッシュの改質方法 - Google Patents
フライアッシュの改質方法 Download PDFInfo
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- WO2020189109A1 WO2020189109A1 PCT/JP2020/005521 JP2020005521W WO2020189109A1 WO 2020189109 A1 WO2020189109 A1 WO 2020189109A1 JP 2020005521 W JP2020005521 W JP 2020005521W WO 2020189109 A1 WO2020189109 A1 WO 2020189109A1
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B09—DISPOSAL OF SOLID WASTE; RECLAMATION OF CONTAMINATED SOIL
- B09B—DISPOSAL OF SOLID WASTE
- B09B3/00—Destroying solid waste or transforming solid waste into something useful or harmless
- B09B3/40—Destroying solid waste or transforming solid waste into something useful or harmless involving thermal treatment, e.g. evaporation
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B07—SEPARATING SOLIDS FROM SOLIDS; SORTING
- B07B—SEPARATING SOLIDS FROM SOLIDS BY SIEVING, SCREENING, SIFTING OR BY USING GAS CURRENTS; SEPARATING BY OTHER DRY METHODS APPLICABLE TO BULK MATERIAL, e.g. LOOSE ARTICLES FIT TO BE HANDLED LIKE BULK MATERIAL
- B07B9/00—Combinations of apparatus for screening or sifting or for separating solids from solids using gas currents; General arrangement of plant, e.g. flow sheets
- B07B9/02—Combinations of similar or different apparatus for separating solids from solids using gas currents
-
- C—CHEMISTRY; METALLURGY
- C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
- C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
- C04B7/00—Hydraulic cements
- C04B7/24—Cements from oil shales, residues or waste other than slag
- C04B7/26—Cements from oil shales, residues or waste other than slag from raw materials containing flue dust, i.e. fly ash
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B07—SEPARATING SOLIDS FROM SOLIDS; SORTING
- B07B—SEPARATING SOLIDS FROM SOLIDS BY SIEVING, SCREENING, SIFTING OR BY USING GAS CURRENTS; SEPARATING BY OTHER DRY METHODS APPLICABLE TO BULK MATERIAL, e.g. LOOSE ARTICLES FIT TO BE HANDLED LIKE BULK MATERIAL
- B07B7/00—Selective separation of solid materials carried by, or dispersed in, gas currents
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B07—SEPARATING SOLIDS FROM SOLIDS; SORTING
- B07B—SEPARATING SOLIDS FROM SOLIDS BY SIEVING, SCREENING, SIFTING OR BY USING GAS CURRENTS; SEPARATING BY OTHER DRY METHODS APPLICABLE TO BULK MATERIAL, e.g. LOOSE ARTICLES FIT TO BE HANDLED LIKE BULK MATERIAL
- B07B9/00—Combinations of apparatus for screening or sifting or for separating solids from solids using gas currents; General arrangement of plant, e.g. flow sheets
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B09—DISPOSAL OF SOLID WASTE; RECLAMATION OF CONTAMINATED SOIL
- B09B—DISPOSAL OF SOLID WASTE
- B09B3/00—Destroying solid waste or transforming solid waste into something useful or harmless
- B09B3/20—Agglomeration, binding or encapsulation of solid waste
- B09B3/25—Agglomeration, binding or encapsulation of solid waste using mineral binders or matrix
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B09—DISPOSAL OF SOLID WASTE; RECLAMATION OF CONTAMINATED SOIL
- B09B—DISPOSAL OF SOLID WASTE
- B09B5/00—Operations not covered by a single other subclass or by a single other group in this subclass
-
- C—CHEMISTRY; METALLURGY
- C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
- C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
- C04B18/00—Use of agglomerated or waste materials or refuse as fillers for mortars, concrete or artificial stone; Treatment of agglomerated or waste materials or refuse, specially adapted to enhance their filling properties in mortars, concrete or artificial stone
- C04B18/04—Waste materials; Refuse
- C04B18/06—Combustion residues, e.g. purification products of smoke, fumes or exhaust gases
- C04B18/08—Flue dust, i.e. fly ash
-
- C—CHEMISTRY; METALLURGY
- C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
- C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
- C04B20/00—Use of materials as fillers for mortars, concrete or artificial stone according to more than one of groups C04B14/00 - C04B18/00 and characterised by shape or grain distribution; Treatment of materials according to more than one of the groups C04B14/00 - C04B18/00 specially adapted to enhance their filling properties in mortars, concrete or artificial stone; Expanding or defibrillating materials
- C04B20/02—Treatment
- C04B20/04—Heat treatment
-
- C—CHEMISTRY; METALLURGY
- C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
- C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
- C04B7/00—Hydraulic cements
- C04B7/36—Manufacture of hydraulic cements in general
- C04B7/43—Heat treatment, e.g. precalcining, burning, melting; Cooling
- C04B7/438—Evacuating at least part of the heat treated material before the final burning or melting step, the evacuated material being used as a cement as such
-
- C—CHEMISTRY; METALLURGY
- C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
- C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
- C04B7/00—Hydraulic cements
- C04B7/36—Manufacture of hydraulic cements in general
- C04B7/43—Heat treatment, e.g. precalcining, burning, melting; Cooling
- C04B7/44—Burning; Melting
- C04B7/45—Burning; Melting in fluidised beds, e.g. spouted beds
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B09—DISPOSAL OF SOLID WASTE; RECLAMATION OF CONTAMINATED SOIL
- B09B—DISPOSAL OF SOLID WASTE
- B09B2101/00—Type of solid waste
- B09B2101/30—Incineration ashes
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02W—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO WASTEWATER TREATMENT OR WASTE MANAGEMENT
- Y02W30/00—Technologies for solid waste management
- Y02W30/20—Waste processing or separation
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02W—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO WASTEWATER TREATMENT OR WASTE MANAGEMENT
- Y02W30/00—Technologies for solid waste management
- Y02W30/50—Reuse, recycling or recovery technologies
- Y02W30/91—Use of waste materials as fillers for mortars or concrete
Definitions
- the present invention relates to a method for modifying fly ash to reduce the unburned carbon content of fly ash.
- fly ash When fly ash is used as a cement mixture or concrete mixture (hereinafter collectively referred to as a mixture), it is generally preferable that the fly ash contains a small amount of unburned carbon.
- the unburned carbon content of fly ash generated from coal-fired power plants varies, and the maximum content is about 15% by mass, and the current situation is that only a part of the fly ash is suitable as a mixed material. ..
- Patent Document 1 a method using a rotary kiln
- Patent Document 2 a method using a cyclone
- Patent Document 3 a method using fluidized bed heating
- fly ash In fluidized bed heating, fly ash is heated by supplying fly ash to a medium fluidized bed (hereinafter, simply referred to as a fluidized bed) formed of a heated fluidized medium (for example, alumina having a large particle size). Reduce unburned carbon content.
- a medium fluidized bed hereinafter, simply referred to as a fluidized bed
- a heated fluidized medium for example, alumina having a large particle size
- the method of reducing the unburned carbon content of the fly ash by heating the fluidized bed can increase the efficiency of removing the unburned carbon and also increase the processing efficiency of the fly ash.
- the residence time of fly ash in the fluidized bed can be lengthened, but the filling amount of the fluidized medium is also limited and is necessary. If the filling amount is increased more than this, the fluidized medium overflows to the outside of the fluidized bed and is mixed with the processed fly ash powder, or the fluidized medium is not normally fluidized in the fluidized bed. The problem arises.
- an object of the present invention is to provide a method for modifying fly ash, which can efficiently reduce unburned carbon contained in fly ash.
- the present inventors have found that unburned carbon contained in fly ash exists as particles of various sizes, and among them, those having a small diameter burn in a relatively short time, and those having a large diameter burn for a long time. We succeeded in efficiently reducing the amount of unburned carbon contained in fly ash.
- a heating device in which heating is performed by passing through a heated medium fluidized bed (media-fluidized bed) is used.
- c The entire amount of the fly ash raw powder charged into the heating device is heated by the medium fluidized bed and taken out from an outlet provided in the upper part of the heating device, forming the medium fluidized bed.
- the flow rate of the high temperature gas flow is set so that the medium particles are not discharged from the outlet.
- d The heated fly ash powder discharged from the outlet of the heating device is introduced into an air classifier and separated into fine powder and coarse powder.
- e The fine powder recovered by the air classifier is recovered as modified fly ash, and is recovered.
- f The crude powder recovered by the air classifier measures the unburned carbon content, and if the measured value is larger than a preset threshold value, it is reintroduced into the heating device and reheated. If the measured value is smaller than the threshold value, collect it as modified fly ash.
- a method for modifying fly ash is provided.
- the fly ash raw powder used for the treatment for reducing the amount of unburned carbon refers to general fly ash generated in equipment for burning coal such as a coal-fired power plant. In addition to coal, it also includes fly ash generated by co-firing fuels other than coal and combustible waste.
- Such fly ash generally contains silica (SiO 2 ) and alumina (Al 2 O 3 ) as main components (these inorganic components account for 70 to 80% of the total), and ferric oxide (Fe) as other components. 2 O 3 ), calcium oxide (CaO), magnesium oxide (MgO) and the like are contained.
- Such fly ash contains unburned carbon, which is considered to be unburned carbon content, and the content is large, about 15% by mass. If the amount of unburned carbon (hereinafter, may be referred to as LOI) is large, a problem occurs when fly ash is used as a mixed material. For example, when mixed with mortar or concrete, there is a high possibility that unburned carbon will emerge on these surfaces and black parts will be generated. In addition, there may be a problem that chemicals such as chemical admixtures adsorb to unburned carbon.
- LOI unburned carbon
- such an amount of unburned carbon is applied by heating using a fluidized bed heating device having a fluidized bed as a medium, and the obtained modified fly ash, that is, a fly having a reduced amount of unburned carbon. Efficiently collect ash.
- Various methods are known as methods for measuring the amount of unburned carbon. For example, a method of detecting CO 2 / CO gas generated by combustion by infrared rays, a method of measuring ignition loss, and the ignition loss are measured.
- a method of estimating the amount of unburned carbon from the above; a method of calculating based on the amount of methylene blue adsorbed; a density specific gravity test; a method of estimating the amount of unburned carbon by irradiating microwaves is known. , Any method can be adopted.
- Such an amount of unburned carbon may be hereinafter referred to as LOI (Loss on Ignition).
- FIG. 1 shows an example of the method of the present invention using a fluidized bed heating device.
- the fluidized bed heating device shown by 1 as a whole has an upright tubular shape, and is a medium separated from the combustion chamber 3 by a combustion chamber 3 and a dispersion plate 5 from the bottom to the top.
- a fluidized bed 7 (hereinafter referred to as a fluidized bed) and an empty head 9 are formed.
- the combustion chamber 3 is a region where a fuel such as a hydrocarbon is burned by a burner 11 to generate a high temperature gas.
- a gas generally air
- a gas containing the theoretical amount of oxygen required to completely burn the fuel and the amount of oxygen to burn the unburned carbon contained in the fly ash raw powder is supplied to the combustion chamber 3 together with the fuel, and is burned by the burner 11.
- the ascending flow of the high-temperature gas forms a fluidized layer 7 heated to a predetermined temperature, and further heats and fluidly conveys the fly ash raw powder supplied to the heating apparatus 1.
- This high temperature gas is hereinafter referred to as fluidized gas.
- the fluidized gas is a combustion gas (carbon dioxide or the like) generated by combustion of the fuel.
- Nitrogen is contained in addition to excess oxygen gas (excess oxygen gas) that was not consumed in combustion.
- the flow of the fluidized gas is indicated by a white arrow
- the flow of the fly ash powder supplied to the heating device 1 is indicated by a black arrow.
- the fluidized gas can be generated by a method other than the above-mentioned method.
- the temperature of the gas flowing by a method other than combustion can be raised, or an electric heater or flame can be generated from the outer peripheral portion of the heating device. It is also possible to adopt a method of heating using (external heating type).
- the fluidized bed 7 is formed of the medium particles 13 that are heated and flowing, and the fly ash raw powder is supplied from the raw material supply port 15 formed in the lower part of the fluidized bed 7. That is, the fluidized bed 7 is formed by heating and suspending the solid medium particles held on the dispersion plate 5 by the fluidized gas. Further, the fly ash raw powder is fluidly transported by the fluidized gas, but since the raw material supply port 15 is formed in the lower part of the fluidized bed 7, the fly ash raw powder introduced from the raw material supply port 15 flows. It is sufficiently heated by the chemical gas and the fluidized bed 7. Further, an empty tower portion 9 in which the medium particles 13 are not suspended is formed on the upper part of the fluidized bed 7. That is, the medium particles 13 forming the fluidized bed 7 are set so as not to be discharged to the outside of the heating device 1 by the fluidized gas.
- the medium particles 13 have a chemical composition similar to that of fly ash so as not to cause deterioration of the characteristics of fly ash even when mixed with fly ash, for example, SiO 2 , Al 2 O 3 , Fe. oxide particles or the like 2 O 3, CaO, etc. particles containing these oxides as the main component is suitably used.
- the particle size of the medium particles 13 needs to be larger than that of the fly ash raw powder introduced from the raw material supply port 15. This is because if the particle size is smaller than the particle size of the fly ash raw powder, the medium particles 13 are also discharged to the outside of the apparatus along with the flow of the fluidized gas. That is, the empty head 7 is not formed.
- the maximum diameter of the fly ash raw powder is about 300 ⁇ m or less, and the preferable particle diameter of the medium particle 13 is about 0.5 to 5 mm.
- the fly ash raw powder introduced into the fluidized bed 7 is heated in contact with the medium particles 13 forming the fluidized bed 7 and the fluidized gas, but the heating temperature is unburned carbon. Is the temperature at which the gas burns, generally 600 ° C. to 1100 ° C., preferably 750 ° C. to 1000 ° C. If the heating temperature is low, it becomes difficult to sufficiently burn and remove the unburned carbon, and if the heating temperature is higher than necessary, the fly ash may melt. Therefore, the temperature of the fluidized gas is adjusted to a high temperature so that the fly ash raw powder is heated to such a heating temperature.
- the heating temperature of the fly ash raw powder can be measured by inserting a thermocouple into the fluidized bed 7 (or the empty head 9).
- the fly ash raw powder is heated by the high-temperature fluidized gas (and the fluidized bed 7) supplied as described above, and the amount of unburned carbon (LOI) in the fly ash raw powder is reduced.
- the heated fly ash is discharged together with the fluidized gas from the outlet 17 formed at the top of the heating device 1. That is, the flow rate and the flow velocity of the fluidized gas are set so that substantially the entire amount of the fly ash raw powder introduced into the heating device 1 is taken out from the outlet 17. In short, the amount of fly ash raw powder charged into the heating device 1 and the amount of fly ash after heating taken out from the outlet 17 are maintained in an equilibrium state.
- the heated fly ash taken out from the outlet 17 has a smaller mass than the fly ash raw powder, at least by the amount of burned carbon.
- the heating device 1 In order to take out the entire amount of fly ash, it may be appropriately set according to the form of the heating device 1 to be used, but in general, fluidization supplied into the heating device 1 (combustion chamber 3).
- the amount of gas may be set so that the superficial velocity is 0.5 m / sec or more.
- the superficial velocity is a value obtained by dividing the amount of fluidized gas (m 3 / sec) by the cross-sectional area (m 2 ) at the maximum inner diameter of the medium fluidized bed heating device.
- the amount of fluidized gas is calculated using the above-mentioned value at the heating temperature.
- the superficial velocity of the fluidized gas is usually preferably at most about 3 m / sec.
- the fly ash powder (fly ash after heating) discharged from the outlet 17 of the heating device 1 is introduced into the air classifier 21 by the fluidized gas and is divided into fine powder and coarse powder. ..
- the unburned carbon particles react with oxygen and burn and disappear, or the unburned carbon particles that have not been completely burned are taken out together with the ash content and the heated fly ash powder. It is discharged.
- the unburned carbon particles relatively large particles may not be sufficiently burned under the above-mentioned heating conditions, and are discharged from the heating device 1 without burning.
- the fly ash taken out from the heating device 1 is introduced into the air classifier 21 and separated into fine powder and coarse powder.
- the fine powder separated by the air classifier 21 is supplied to the dust collector 23 together with the fluidized gas, where the fluidized gas is discarded and the fine powder is recovered as reformed fly ash.
- the coarse powder may contain a large amount of unburned carbon particles having a large particle size that is insufficiently burned, it is separated from the above fine powder.
- the separated coarse powder is supplied to the temporary storage silo 25, and the amount of unburned carbon (LOI) is measured by the LOI measuring device 27 attached to the silo 25, and the LOI is below a preset threshold value. If (LOI ⁇ threshold), collect as modified fly ash.
- the LOI exceeds a preset threshold value (LOI> threshold value)
- the LOI is returned to the heating device 1 (fluidized bed 7) and heated again to reduce the LOI.
- the coarse powder can be returned to the heating device 1 and heat-treated again.
- the above threshold value may be appropriately set according to the LOI required for fly ash used as a mixed material of cement or concrete. For example, it is preferably set in the range of 0.5 to 4% by mass, particularly 0.5 to 3% by mass.
- the coarse powder recovered as the modified fly ash from the temporary storage silo 25 is, of course, mixed with the modified fly ash (fine powder) recovered from the dust collector 23 described above and recovered. You can also do it.
- the classification point in the air classification in the range of 50 to 150 ⁇ m, particularly 100 to 150 ⁇ m.
- the air classifier 21 is not particularly limited, and for example, an air classifier using a centrifugal force field, a classifier using a gravitational field, a classifier using an inertial force field, and the like can be used.
- the dust collector 23 used for collecting the fine powder classified by the air classifier 21 is not particularly limited, and various types such as an electric dust collector, a gravity type dust collector, and a centrifugal force type dust collector may be used. Can be done.
- the LOI measurement by the LOI measuring device 27 attached to the temporary storage silo 25 may be performed by any known method as described above.
- a fly ash raw powder having a LOI of 10.0% by mass was prepared.
- the average particle size was 44 ⁇ m and the maximum particle size was about 300 ⁇ m.
- Fly ash raw powder is supplied to the heating device 1 shown in FIG. 1, and fluidized gas (air) is supplied at a superficial velocity of 0.64 m / sec and a heating temperature of 850 ° C to perform heat treatment, and an air classifier is used. It was classified into coarse powder and fine powder at 21. When the classification point was set to about 50 ⁇ m, the ratios of the recovered fine powder and the coarse powder were 63% by mass and 37% by mass, respectively, with respect to the fly ash raw powder, and the total amount of the fine powder and the coarse powder was 100% by mass. It was.
- the LOI of the fine powder was 1.1% by mass and the LOI of the coarse powder was 5.0% by mass.
- the LOI of the fine powder is sufficiently low, and it can be used as it is as a modified flasher.
- the LOI of the crude powder is high, which is a level that needs to be reheated in many applications.
- the LOI was measured by the ignition loss test method described in JIS A 6201.
- the superficial velocity of the fluidized gas is variously changed to heat the fly ash raw powder, and the superficial velocity and the discharge rate of the fly ash discharged from the heating device 1 (relative to the supplied fly ash raw powder). Percentage) was measured. The result is shown in FIG. As can be understood from the results of FIG. 2, by setting the superficial velocity to 0.5 m / sec or more, especially 0.6 m / sec or more, almost all of the fly ash raw powder is discharged to the outside of the device without staying. can do.
- Heating device 3 Combustion chamber 5: Dispersion plate 7: Fluidized bed 9: Empty head 11: Burner 13: Medium particles 15: Raw material supply port 17: Outlet 21: Air classifier 23: Dust collector 25: Temporary storage silo 27: LOI measuring instrument
Abstract
Description
a:前記フライアッシュ原粉を加熱する手段として、加熱された媒体流動層(media-fluidized bed)を通すことにより加熱が行われる加熱装置を使用し、
b:前記加熱装置内に高温ガス流を通すことにより、加熱された前記媒体流動層の形成と該媒体流動層内に投入された前記フライアッシュ原粉の流動搬送とを行い、
c:前記加熱装置に投入された前記フライアッシュ原粉の全量が、前記媒体流動層で加熱され且つ該加熱装置上部に設けられた取出口から取り出されるが、前記媒体流動層を形成している媒体粒子は該取出口から排出されないように、前記高温ガス流の流量を設定し、
d:前記加熱装置の取出口から排出された加熱後のフライアッシュ粉を、空気分級機に導入して微粉と粗粉とに分離し、
e:前記空気分級機により回収された微粉を改質フライアッシュとして回収し、
f:前記空気分級機により回収された粗粉は、未燃カーボン含有量を測定し、該測定値が予め設定した閾値よりも大きい場合には、前記加熱装置に再度導入して再加熱を行い、該測定値が閾値よりも小さい場合には、改質フライアッシュとして回収すること、
を特徴とするフライアッシュの改質方法が提供される。
(1)未燃カーボン含有量の測定値が予め設定した閾値よりも小さい粗粉を、前記空気分級により回収された微粉と混合して回収すること、
(2)未燃カーボン含有量の前記閾値が0.5~4質量%の範囲内に設定されていること、
(3)前記空気分級機の分級点は、50~150μmの範囲に設定されること、
(4)前記フライアッシュ原粉は、前記媒体流動層で600~1100℃の温度に加熱されること、
が好適である。
なお、未燃カーボン量の測定方法としては、種々の方法が知られており、例えば、燃焼させて発生したCO2・COガスを赤外線検出する方法、強熱減量を測定し、該強熱減量から未燃カーボン量を推定する方法;メチレンブルー吸着量に基づいて算出する方法;密かさ比重試験;マイクロ波を照射して未燃カーボン量を推定する方法等が知られており、本発明においては、何れの方法も採用することができる。
このような未燃カーボン量は、以下、LOI(Loss on Ignition)と呼ぶことがある。
図1において、全体として1で示す流動層加熱装置は、直立した筒状形態を有しており、下から上方に向かって、燃焼室3、分散板5によって燃焼室3と仕切られている媒体流動層7(以下、流動層と呼ぶ)及び空頭部9が形成されている。
例えば、この実施態様においては、燃料を完全に燃焼させるに必要な理論酸素量の1.05~5.0倍の酸素を供給することが好ましい。1.05倍未満だと、燃料の燃焼にほとんどすべての酸素が消費されてしまい、その後の未燃カーボンの燃焼に必要な酸素を残すことができない。
さらに、上記の流動層7の上部には、媒体粒子13が浮遊していない空塔部9が形成されている。即ち、流動層7を形成している媒体粒子13は、流動化ガスによって加熱装置1外に排出されないように設定されている。
なお、フライアッシュ原粉の加熱温度は、流動層7(或いは空頭部9)に熱電対を挿入して測定することができる。
なお質量で比較すると、取出口17から取り出される加熱後のフライアッシュは、少なくとも燃焼したカーボン量分は、フライアッシュ原粉よりも質量が小さくなっている。
なお、流動化ガスの空塔速度が過度に大きくなると、空頭部9が形成されず、媒体粒子13がフライアッシュと共に取出口17から排出されてしまう。このような不都合を回避するため、流動化ガスの空塔速度は、通常、大きくとも3m/秒程度とすることが好ましい。
本発明者らの研究によれば、未燃カーボン粒子の内、比較的大きな粒子については、前述した加熱条件では燃焼が十分に進行しないおそれがあり、この加熱装置1から燃焼することなく排出される可能性がある。一方で小さな未燃カーボン粒子は、上記加熱条件下でほとんどが燃焼してしまう。
このため、本発明では、加熱装置1から取り出されたフライアッシュを空気分級機21に導入し、微粉と粗粉とに分離する。
一方、粗粉には、燃焼不十分な大粒径の未燃カーボン粒子が多く含まれている恐れがあるため、上記の微粉と分離する。分離された粗粉は、一時貯蔵サイロ25に供給され、このサイロ25に取り付けられているLOI測定器27により、未燃カーボン量(LOI)が測定され、LOIがあらかじめ設定された閾値以下である場合には(LOI≦閾値)、改質フライアッシュとして回収する。また、LOIがあらかじめ設定された閾値を超えている場合には(LOI>閾値)、加熱装置1(流動層7)に戻し、再び加熱してLOIの低減を図るものとする。勿論、この場合、LOIが閾値と同じであったとき(LOI=閾値)、その粗粉を加熱装置1に戻して再度熱処理することもできる。
LOIが10.0質量%のフライアッシュ原粉を用意した。平均粒径は44μm、最大粒径は約300μmであった。
図1に示されている加熱装置1にフライアッシュ原粉を供給し、空塔速度0.64m/秒、加熱温度850℃で流動化ガス(空気)を供給して熱処理を行い、空気分級機21で粗粉と微粉に分級した。分級点をおよそ50μmに設定したところ、回収された微粉と粗粉の割合は、フライアッシュ原粉に対してそれぞれ63質量%、37質量%であり、微粉と粗粉の合計量は100質量%となっていた。
なおLOIは、JIS A 6201に記載の強熱減量試験法にて測定した。
図2の結果から理解されるように、空塔速度を0.5m/秒以上、特に0.6m/秒以上とすることで、フライアッシュ原粉のほぼ全量を滞留させずに装置外に排出することができる。
3:燃焼室
5:分散板
7:流動層
9:空頭部
11:バーナー
13:媒体粒子
15:原料供給口
17:取出口
21:空気分級機
23:集塵機
25:一時貯蔵サイロ
27:LOI測定器
Claims (5)
- 未燃カーボンを含むフライアッシュ原粉を加熱して未燃カーボン含量を低減させるフライアッシュの改質方法において、
a:前記フライアッシュ原粉を加熱する手段として、加熱された媒体流動層を通すことにより加熱が行われる加熱装置を使用し、
b:前記加熱装置内に高温ガス流を通すことにより、加熱された前記媒体流動層の形成と該媒体流動層内に投入された前記フライアッシュ原粉の流動搬送とを行い、
c:前記加熱装置に投入された前記フライアッシュ原粉の全量が、前記媒体流動層で加熱され且つ該加熱装置上部に設けられた取出口から取り出されるが、前記媒体流動層を形成している媒体粒子は該取出口から排出されないように、前記高温ガス流の流量を設定し、
d:前記加熱装置の取出口から排出された加熱後のフライアッシュ粉を、空気分級機に導入して微粉と粗粉とに分離し、
e:前記空気分級機により回収された微粉を改質フライアッシュとして回収し、
f:前記空気分級機により回収された粗粉は、未燃カーボン含有量を測定し、該測定値が予め設定した閾値よりも大きい場合には、前記加熱装置に再度導入して再加熱を行い、該測定値が閾値よりも小さい場合には、改質フライアッシュとして回収すること、
を特徴とするフライアッシュの改質方法。 - 未燃カーボン含有量の測定値が予め設定した閾値よりも小さい粗粉を、前記空気分級により回収された微粉と混合して回収する請求項1に記載のフライアッシュの改質方法。
- 未燃カーボン含有量の前記閾値が0.5~4質量%の範囲内に設定されている請求項1に記載のフライアッシュの改質方法。
- 前記空気分級機の分級点は、50~150μmの範囲に設定される請求項1に記載のフライアッシュの改質方法。
- 前記フライアッシュ原粉は、前記媒体流動層で600~1100℃の温度に加熱される請求項1に記載の改質方法。
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