JP2009132564A - Method of manufacturing artificial aggregate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide aggregate in which the elution of 6-valent chromium is made small even when a raw material containing chromium is used. <P>SOLUTION: The artificial aggregate is manufactured by firing an inorganic material. In the firing step at a temperature of ≥650°C, the oxygen concentration in the vicinity of the boundary between a solid to be fired and a firing atmospheric gas is controlled to ≤10%. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a method for manufacturing an artificial aggregate. In particular, the present invention relates to a method for producing an artificial aggregate produced by firing a raw material containing chromium.

  Currently, the development and use of highly water-absorbing aggregates is ongoing. That is, when water-absorbing aggregate is used for the roadbed, it absorbs and holds water such as rainwater. Therefore, even if there is no supply of water, when energy such as sunlight is supplied, the retained water is vaporized and the ambient temperature is lowered by the heat of vaporization. Therefore, it is expected that a superabsorbent aggregate is used for the roadbed as a countermeasure against heat island which is currently a problem in urban areas.

  Now, a highly water-absorbing aggregate (artificial aggregate) is manufactured by firing and sintering raw materials in a firing furnace. Generally, natural resources such as shale are used as raw materials. However, in recent years, it has been proposed to use waste incineration ash such as coal ash from the viewpoint of effective use of waste. That is, by adding water to the above waste incineration ash (usually, these incineration ash is in powder form) and granulating it, and firing it in a firing kiln such as a rotary kiln, etc., a high water absorption aggregate. (Artificial aggregate) is obtained.

  By the way, the industrial waste incineration ash often contains chromium (trivalent or hexavalent chromium. Usually, there are many trivalent chromium). When this type of incinerated ash is used as a raw material for artificial aggregates, particularly when fired at a high temperature of 1000 ° C. or higher in an air atmosphere, trivalent chromium is oxidized to hexavalent chromium. And when melted and sintered at a temperature higher than the melting point, hexavalent chromium may be fixed in the aggregate, but it is not fixed, that is, when immersed in water, it moves to the aqueous phase (elution) There is also hexavalent chromium. In general, the amount of hexavalent chromium to be eluted tends to increase as the particle size of the inclusions decreases.

  By the way, the target value of hexavalent chromium is determined by environmental standards. That is, the water quality standard is 0.05 mg / L or less, and the soil environment standard is 0.05 mg / L or less. Therefore, as described above, when an aggregate that is not completely melted (an aggregate having non-fixed hexavalent chromium) is used for a roadbed or banking, the environmental standard value may not be protected.

  As a method for reducing hexavalent chromium, a method in which a reducing agent is simultaneously added and baked has been proposed. For example, for the purpose of providing a cement capable of reducing hexavalent chromium contained in the cement clinker without deteriorating the quality of the cement clinker, the rotary kiln outlet side of the fired product is positioned higher than the highest temperature in the rotary kiln. A combustible substance is added to the material to be baked, for example, a range from a position about four times deeper inside the kiln inner diameter D from the material to be fired outlet side of the rotary kiln to the material to be baked rotary kiln, Alternatively, a combustible material having a combustion speed slower than that of the main fuel or a combustible material similar to that of the main fuel and coarser particles than the main fuel is added to the material to be fired at the inlet of the clinker cooler. A technique has been proposed (Japanese Patent Laid-Open No. 11-100284).

  In addition, it was introduced into a clinker cooler for the purpose of providing a cement clinker (or a hydraulic material using the clinker) that is free of solid combustibles during cooling and has a reduced content of harmful hexavalent chromium. A technique for supplying a solid combustible material having a particle diameter of more than 5 mm and not more than 100 mm to a region where the temperature of the cement clinker becomes 850 ° C. to 1000 ° C. has been proposed (Japanese Patent Laid-Open No. 2002-211961).

In addition, for the purpose of providing a cement clinker free from the elution of harmful hexavalent chromium, hexavalent chromium (Cr ⁶⁺ ) present in the granulated raw material particles or clinker particles in the cement clinker firing step. In the method of manufacturing a cement clinker that supplies combustible materials so that it can be reduced, the conditions for reducing hexavalent chromium (Cr ⁶⁺ ) are as follows: the particle size is 1 mm to 4 mm in the kiln from the clinker cooler side, and the pulverized coal A technique for supplying a combustible material having a particle size larger than the particle size has been proposed (Japanese Patent Laid-Open No. 2003-73154).
Japanese Patent Application Laid-Open No. 11-1000024 JP 2002-211961 A JP 2003-73154 A

  Now, although the technique proposed above is a technique related to cement production, it seems to be applicable to the production of artificial aggregates because it is a technique for reducing hexavalent chromium.

Therefore, the proposed technique was applied to the production of artificial aggregate.
However, my thoughts were completely out of sight. That is, the elution of hexavalent chromium exceeded the standard value.

  Therefore, the problem to be solved by the present invention is to provide an aggregate with a small elution amount of hexavalent chromium even when chromium is contained in the raw material.

  The inventor has earnestly pursued the cause of the problem (a large amount of hexavalent chromium is eluted) that occurred when the proposed cement manufacturing technique was applied to the aggregate manufacturing technique.

As a result, it has been found that this is due to the following.
That is, since cement is fired in a wet process and in a molten state, there is little space between clinker, and a sufficient reduction effect is obtained even with the above technique. On the other hand, the aggregate firing is a dry method, and there is a gap between the aggregates. Therefore, the contact area with air (gas) is large. Therefore, it was considered that the chromium contained in the aggregate was more likely to be oxidized in the case of manufacturing the aggregate than in the case of cement production, and that hexavalent chromium could easily be produced with the proposed technique.

  Therefore, it came to a revelation that the problem could be solved by firing in an atmosphere that is far less oxidized than the proposed technique. When the aggregate was produced by firing the powder in a firing atmosphere with less oxygen, it was found that this was an aggregate with a small amount of hexavalent chromium elution as expected.

  The present invention has been achieved based on the above findings.

That is, the above problem is
A method for producing an artificial aggregate by firing inorganic material,
In the firing step at a temperature of 650 ° C. or higher, the oxygen concentration in the vicinity of the interface between the solid to be fired and the firing atmosphere gas is controlled to 10% or less, which is solved by the method for manufacturing an artificial aggregate. The

  In particular, the method for producing an artificial aggregate, preferably solved by a method for producing an artificial aggregate, characterized in that the oxygen concentration in the gas atmosphere inside the layer to be fired is controlled to 3% or less. .

  Also, the method for producing an artificial aggregate, preferably solved by the method for producing an artificial aggregate, characterized in that a gas having an oxygen concentration of 3% or less is supplied into a firing container for firing an inorganic material. Is done.

  In addition, the above-described method for producing an artificial aggregate is preferably solved by a method for producing an artificial aggregate, characterized in that the firing is performed in the presence of a combustible substance in a firing container for firing an inorganic material. . As the combustible substance, preferably, coal, coke, activated carbon, charcoal, plastic, waste solid fuel, or the like is used.

  The artificial aggregate is preferably produced by a chromium content of preferably 100 to 2000 mg / kg, or a hexavalent chromium elution amount of 0.05 mg / L when fired at 1000 ° C. in an air atmosphere. In this method, an artificial aggregate is manufactured by firing an inorganic material containing a waste containing chromium in an amount exceeding.

  Aggregates with a small amount of hexavalent chromium are obtained from industrial waste containing chromium (inorganic raw materials: aggregate raw materials). That is, even if an aggregate obtained using chromium-containing waste as a raw material is used as a roadbed material, the amount of hexavalent chromium eluted is small, which is useful as a recycling technology.

  The present invention is a method for producing an artificial aggregate. In particular, it is a method for producing an artificial aggregate by firing an inorganic material. For example, it is a method for producing an artificial aggregate by firing one or more kinds selected from a group of wastes such as paper sludge incineration ash, fly ash, and construction generated soil. In particular, it is a method for producing an artificial aggregate by firing a granular material. Furthermore, it is a method for producing an artificial aggregate by firing an inorganic material containing a waste having a chromium content of 100 to 2000 mg / kg. Alternatively, artificial aggregates are manufactured by firing inorganic materials containing waste containing chromium in an amount of hexavalent chromium exceeding 0.05 mg / L when calcined at 1000 ° C. in an air atmosphere. It is a method to do. The firing temperature is preferably 800 to 1250 ° C. This is because when the firing temperature is too low, the strength of the obtained aggregate is poor, and conversely, when it is too high, the resulting aggregate has a low porosity and it is difficult to obtain an aggregate with high water absorption. is there. A more preferable firing temperature is 1000 to 1200 ° C. That is, it has the baking process baked at the temperature of 800-1250 degreeC (especially 1000 degreeC or more and 1200 degrees C or less). In the baking step at a temperature of 650 ° C. or higher, the vicinity of the interface between the solid as the object to be fired and the firing atmosphere gas (for example, the region within 30 cm from the solid surface of the material to be fired (solid phase-gas). In the firing step at a temperature of 450 ° C. or more, more preferably, the oxygen concentration in the region in the category within 30 cm on the gas phase side from the phase interface) is controlled to be 10% (especially 8%) or less. The oxygen concentration in the vicinity of the interface between the solid to be fired and the firing atmosphere gas is controlled to be 10% (especially 8%) or less, and of course, the oxygen concentration is controlled as described above even at 450 ° C. or less. For example, the oxygen concentration should be controlled as described above over a long range from the start of the firing reaction (starting temperature) to after firing (temperature in the cooling zone after firing). In particular, the oxygen concentration in the gas atmosphere inside the layer to be fired (between the powder (particles) to be fired) is controlled to be 3% or less. If the oxygen concentration in the vicinity of the interface with the atmospheric gas is controlled so as to be 10% or less, the oxygen concentration in the gas atmosphere is roughly 3% inside the layer to be fired (between the powder to be fired (particles)). However, in order to carry out more reliably, the oxygen concentration in the gas atmosphere inside the layer to be fired (between the powder to be fired (particles)) is controlled to be 3% or less. For example, a method of supplying a gas having an oxygen concentration of 3% or less into a firing container for firing the object to be fired, or a method of firing in the presence of a combustible substance in the firing container is conceivable. Of course, this The amount of coexistence is an amount that allows the oxygen concentration to satisfy the above requirements.As the combustible material, for example, coal, coke, activated carbon, charcoal (above carbide fuel), plastic, solid waste fuel, etc. are used. Desirably, solid combustible substances are used because they are easy to handle and can suppress rapid combustion reactions.

This will be described in more detail below.
First, an aggregate material is prepared. As raw materials, incinerated ash or treated soil containing chromium is used. Specifically, incinerated ash or treated soil with a chromium content of 100 mg / kg or more is used. According to the present invention, even if the chromium content in the raw material is 100 mg / kg or more, an aggregate having a hexavalent chromium elution amount of 0.05 mg / L or less after production can be obtained. If the chromium content of the raw material exceeds 2000 mg / kg, for example, a large amount of flammable substance is required, the temperature rise due to combustion of the flammable substance becomes excessive, and the firing operation becomes unstable. Therefore, the chromium content in the raw material is preferably 2000 mg / kg or less.

  The incineration ash used includes pulverized coal combustion ash, fluidized bed combustion coal ash, coke ash, waste incineration ash, sewage sludge incineration ash, paper sludge incineration ash, waste plastic incineration ash, and the like. The incinerated ash preferably has an average particle size of 44 μm or less. The reason is that if it is larger than this, granulation becomes difficult.

  Among the incineration ash, the papermaking sludge incineration ash has inorganic components such as Ca and Al as main components. And since papermaking sludge incineration ash is porous, papermaking sludge incineration ash is a preferable thing among incineration ash. In addition, ash from organic raw materials such as firewood, charcoal, waste wood, and food waste residue has a high water absorption characteristic because its internal structure is porous. Accordingly, since the aggregate sintered using these porous incineration ash as a raw material becomes a highly water-absorbing aggregate, the porous incineration ash is preferable as the aggregate raw material of the present invention.

  In addition to the incineration ash, construction generated soil can be used. For example, construction residual soil, contaminated soil, dredged soil and the like can be used. The construction generated soil preferably contains 80% or more of silty soil. This is because granulation was difficult when there was a lot of sand.

  In addition, the above-mentioned various incineration ash and construction generated soil are pulverized as necessary to obtain powder raw materials.

  And an aggregate raw material (for example, powder or particle | grains) is mixed with water, and the granulated material of several mm-dozens of mm is created. In this granulation, granulation may be performed using a granulation aid such as an inorganic substance such as bentonite or an organic substance such as lignin. For granulation, for example, a granulator such as a compression molding machine (roll press or the like), a rolling granulator (pan pelletizer or the like), an agitation granulator (Eirich mixer or the like) is used.

  After granulation, firing is performed at a temperature of 800 ° C. or higher (particularly 1000 ° C. or higher). For firing, a tunnel kiln, a roller house kiln, a fluidized bed, or a rotary kiln can be used. However, it is preferable to use a rotary kiln or a tunnel kiln for firing the aggregate from the viewpoint of ease of manufacture.

  The oxygen concentration during firing is controlled as described above. That is, the oxygen concentration of the burned product (the oxygen concentration between the powders (particles) to be fired) is 3% or less. This is because the elution amount of hexavalent chromium from the obtained aggregate exceeded 0.05 mg / L when firing was performed in an atmosphere where the oxygen concentration exceeded 3%. In the case of 3% or less, the elution amount of hexavalent chromium from the obtained aggregate was less than 0.05 mg / L, which satisfied the standard.

  As a method for achieving the condition where the oxygen concentration is 3% or less, there are a method of consuming oxygen using a combustible substance which is oxidized (combusted) at a high temperature and a method of passing a low oxygen gas. Any method may be used.

  In the case of using a method of consuming oxygen using a combustible material that is oxidized (combusted) at a high temperature as a method for achieving a condition where the oxygen concentration is 3% or less, examples of combustible materials include coal, coke, Carbide fuels such as activated carbon and charcoal are used. Alternatively, plastic or waste solid fuel can be used. In addition, only one kind selected from the above may be used, or two or more kinds may be used. In short, it is sufficient if oxygen is consumed by combustion. The combustible substance was preferably 80% by mass or more in the form of granules having a particle size of 0.3 to 10 mm. This is because if the particle size is too small, less than 0.3 mm, the combustible substance burns before reaching the vicinity of the burning point, and it is difficult to satisfy the condition that the oxygen concentration is 3% or less. Because it was. On the other hand, if it is too large exceeding 10 mm, it is difficult to input, and since the surface area is small, the combustion efficiency is poor and it is difficult to satisfy the condition of an oxygen concentration of 3% or less.

When a low oxygen gas is used, one or two or more gases such as halogen gas, nitrogen gas, and CO ₂ gas are used as the low oxygen gas. Note that any gas having a low oxygen concentration may be used. For example, exhaust gas after kiln combustion, saturated steam, and the like can be used.

Hereinafter, the present invention will be described with reference to specific examples.
[Example 1]
The materials shown in Table 1 below were used as raw materials for the artificial aggregate.
Table-1
Average particle size Cr content Papermaking sludge incineration ash 25.5μm 250mg / kg
Fly ash 11.3 μm 135 mg / kg
Construction generated soil Silt 212mg / kg

  An appropriate amount of water was added to the incinerated ash or construction generated soil shown in Table 1 above, and 2 g was put into a jig that could be molded on a cylinder with a diameter of 15 mm and molded by pressurizing at 100 N.

  Then, the molded product is placed in an electric furnace, and a mixed gas of nitrogen and air at a predetermined rate is passed through the electric furnace at a flow rate of 5 ml / min for a predetermined time, and then at a temperature of 1100 ° C. for 2 minutes. Heated and fired.

And since the elution amount of the hexavalent chromium of the aggregate obtained by baking was investigated, the result is shown in Table-2.
Table-2
Raw material oxygen concentration Cr ⁶⁺ elution amount Oxygen concentration in the vicinity of interface Oxygen concentration in inner layer of fired product (mg / L)
Papermaking sludge 16% 16% 0.24
Papermaking sludge 5% 5% 0.07
Papermaking sludge 3% 3% 0.05
Papermaking sludge 1% 1% 0.02 or less Papermaking sludge 0.5% 0.5% 0.02 or less Fly ash 5% 5% 0.08
Fly ash 3% 3% 0.05
Fly ash 1% 1% 0.02 or less Construction generated soil 5% 5% 0.09
Construction soil 3% 3% 0.04
Construction generated soil 1% 1% 0.02 or less * Oxygen concentration is determined from the oxygen concentration in the supply gas because the electric furnace is of a sealed structure.
* Cr ⁶⁺ elution amount was determined according to Environment Agency Notification No.46.

According to this, it can be seen that if the oxygen concentration in the inner layer of the article to be fired is controlled to 3% or less and firing is performed, an aggregate having a Cr ⁶⁺ elution amount equal to or less than a reference value is obtained.

  Further, paper sludge incineration ash and fly ash aggregates were porous. Therefore, the aggregate is rich in water retention.

[Example 2]
The incinerated ash or construction generated soil shown in Table 1 above was granulated to a diameter of 5 to 15 mm with a pan pelletizer. Then, using an internal heat rotary kiln and blowing coke, firing was performed at 1100 ° C. to obtain an aggregate.

The amount of hexavalent chromium eluted from the aggregate thus obtained was examined, and the results are shown in Table 3.
Table-3
Raw material Coke blowing amount Oxygen concentration Cr ⁶⁺ Elution amount
(Kg / h) Near the interface Inner layer to be fired (mg / L)
Papermaking sludge 0 16% 5% 0.10
Papermaking sludge 100 14% 5% 0.06
Papermaking sludge 150 9% 3% 0.05
Papermaking sludge 200 6% 1% 0.02 or less Fly ash 0 16% 6% 0.09
Fly ash 100 14% 5% 0.06
Fly ash 150 9% 3% 0.02 or less Fly ash 200 6% 2% 0.02 or less Construction generated soil 0 16% 4% 0.15
Construction soil 100 14% 4% 0.07
Construction soil 150 9% 2% 0.03
Construction generated soil 200 6% 2% 0.02 or less * As for the oxygen concentration, a predetermined part of gas was sucked by a stainless steel tube installed in the predetermined part, and the oxygen concentration was measured by an Olgart analyzer.

According to this, when the oxygen concentration in the vicinity of the interface is controlled to 10% or less, the oxygen concentration of the gas atmosphere in the inner layer is controlled to 3% or less, and when firing is performed in such an atmosphere, It can be seen that an aggregate having a Cr ⁶⁺ elution amount equal to or less than a reference value is obtained.

[Example 3]
The incinerated ash or construction generated soil shown in Table 1 above was granulated to an average diameter of 10 mm with a pan pelletizer. And the external heat rotary kiln which can interrupt | block an internal atmosphere from the outside was used, and the carbon dioxide-air mixing (mixing ratio is a predetermined ratio) gas was ventilated inside, and it baked at 1100 degreeC, and obtained the aggregate.

Since the elution amount of hexavalent chromium in the aggregate thus obtained was examined, the results are shown in Table-4.
Table-4
Raw material oxygen concentration Cr ⁶⁺ elution amount Oxygen concentration in the vicinity of interface Oxygen concentration in inner layer of fired product (mg / L)
Papermaking sludge 20% 20% 0.10
Papermaking sludge 5% 5% 0.07
Papermaking sludge 3% 3% 0.05
Papermaking sludge 1% 1% 0.02 or less Fly ash 5% 5% 0.08
Fly ash 3% 3% 0.05
Fly ash 1% 1% 0.02 or less Construction soil 5% 5% 0.08
Construction soil 3% 3% 0.04
Construction generated soil 1% 1% 0.02 or less * The oxygen concentration is determined from the mixing ratio in the mixed carbon dioxide-air mixture.

According to this, it can be seen that if the oxygen concentration in the inner layer of the article to be fired is controlled to 3% or less and firing is performed, an aggregate having a Cr ⁶⁺ elution amount equal to or less than a reference value is obtained.

Patent Applicant Taiheiyo Material Co., Ltd.
Representative Katsumi Udaka

Claims (6)

A method for producing an artificial aggregate by firing inorganic material,
In the firing step at a temperature of 650 ° C. or higher, the oxygen concentration in the vicinity of the interface between the solid to be fired and the firing atmosphere gas is controlled to 10% or less. 2. The method for producing an artificial bone material according to claim 1, wherein the oxygen concentration in the gas atmosphere inside the layer to be fired is controlled to 3% or less. 3. The method for producing an artificial bone material according to claim 1, wherein a gas having an oxygen concentration of 3% or less is supplied into a firing container for firing the inorganic material. The method for producing an artificial bone material according to any one of claims 1 to 3, wherein a combustible substance is allowed to coexist in a firing container for firing the inorganic material. The method for producing an artificial aggregate according to claim 4, wherein the combustible substance is one or more selected from the group consisting of coal, coke, activated carbon, charcoal, plastic, and solid waste fuel. An inorganic material containing waste containing chromium having a chromium content of 100 to 2000 mg / kg or containing chromium in an amount of hexavalent chromium exceeding 0.05 mg / L when calcined at 1000 ° C. in an air atmosphere The method for producing an artificial aggregate according to any one of claims 1 to 5, wherein the method is a method for producing an artificial aggregate by firing.