JP6548094B2 - Method of detoxifying fly ash - Google Patents

Description

  The present invention relates to a method for detoxifying fly ash containing dioxin.

The fly ash contained in the incineration waste gas generated when incinerating waste in the waste disposal facility may contain harmful substances such as dioxin. In recent years, fly ash has been used as a cement raw material for the purpose of reducing waste, but when using fly ash, harmful substances such as dioxins in fly ash are removed and rendered harmless There is a need.
As a method of removing dioxins from fly ash, it is practiced to heat the fly ash at a temperature higher than the decomposition temperature of dioxins. However, in general, the temperature at which dioxins are decomposed is a high temperature of 350 ° C. or higher, and if the fly ash is heated at such a high temperature, the fly ash solidifies and adheres to the inside of the heating device etc., which may damage the device. is there.
Therefore, in such a detoxifying treatment of fly ash, a heat treatment is carried out after mixing the component for preventing solidification with fly ash.

For example, patent document 1 describes that heat treatment is performed with a heating drum after mixing slaked lime with fly ash.
Patent Document 2 describes that heat treatment is performed after adding calcium hydroxide to fly ash.

According to the methods described in Patent Documents 1 and 2, it is possible to reduce sticking of fly ash by mixing slaked lime and calcium hydroxide with fly ash and then heating.
However, since slaked lime and calcium hydroxide have the property of solidifying when they absorb water, they have poor fluidity under normal storage conditions, making it difficult to mix them with fly ash. Therefore, there has been a problem that it is necessary to use after performing drying processing such as drying with drying air in advance, and it takes time and effort. Alternatively, it is necessary to set a larger amount of calcium hydroxide or calcium hydroxide to fly ash in order to prevent solidification, in anticipation of being difficult to mix uniformly with fly ash because of poor fluidity. .
When slaked lime and calcium hydroxide are mixed with the fly ash more than necessary, calcium remains in the fly ash after the heat treatment. After heat treatment, the fly ash is usually washed with a washing solution etc. However, if the fly ash containing a large amount of calcium is washed, a large amount of calcium dissolves in the washing solution, and calcium precipitates in the washing apparatus or piping There was a problem that it became easy.

Patent No. 4530336 Patent No. 4661577

  Therefore, in view of the problems of the prior art as described above, the present invention can easily reduce the solidification of fly ash and can reduce the amount of calcium remaining in fly ash after heat treatment. It is an issue to provide a detoxification treatment method.

The detoxifying method of fly ash according to the present invention mixes fly ash containing dioxin with dust contained in exhaust gas which contains calcium in an amount of 10% by mass to less than 40% by mass and which is discharged from a cement production facility. The method includes a mixing step of obtaining a mixture, a heat treatment step of heating the mixture above the decomposition temperature of dioxin, and a washing step of washing the heated mixture, and in the mixing step, dust in the mixture is added to the mixture. The fly ash and the dust are mixed such that the content of the resulting calcium is 1.1% by mass or more and 4.4 % by mass or less.

In the mixing step, the fly ash and the dust may be mixed such that the content of calcium in the mixture is 15 % by mass to 35 % by mass.

In the detoxifying treatment method of fly ash of the present invention, a mixture of fly ash containing dioxin and dust contained in exhaust gas containing 10% by mass or more and less than 40% by mass of calcium and discharged from a cement manufacturing facility is mixed. By including the mixing step of obtaining and the heat treatment step of heating the mixture above the decomposition temperature of dioxin, solidification of fly ash at the time of heat treatment can be suppressed. Moreover, the residual calcium of the fly ash after heat processing can be reduced by mixing the said dust with fly ash. Therefore, in the subsequent washing step, calcium eluted in the washing solution can be reduced, and precipitation of calcium on an apparatus or the like can be suppressed.
In addition, since the dust discharged from the cement manufacturing facility is used, the fluidity is relatively good without special treatment, and it is possible to easily mix uniformly with fly ash.

  The dust may be dust contained in an exhaust gas discharged from a cement kiln.

  The dust contained in the exhaust gas discharged from the cement kiln, in particular, is a fine dust and is easily obtained in a more dry state. Therefore, the fluidity is better, and it is easy to mix uniformly with fly ash.

  In the mixing step, the fly ash and the dust may be mixed such that the mixture contains 5% by mass to 40% by mass of dust.

  By mixing the fly ash and the dust so that the mixture contains 5% by mass to 40% by mass of dust, the sticking of the fly ash after the heat treatment can be sufficiently reduced, and after the treatment Can control residual calcium in fly ash.

  As described above, according to the method of detoxifying fly ash according to the present invention, solidification of fly ash can be easily reduced, and the amount of calcium remaining in fly ash after heat treatment can be reduced.

The graph which shows the difference in the hardness by the heating temperature of fly ash. The graph which shows the hardness of the fly ash which mixed calcium hydroxide. The graph which shows the hardness of fly ash which mixed demineralization bypass dust. The graph which shows the hardness of the fly ash which mixed electric dust collector dust. The diagram showing the test method.

Hereinafter, embodiments according to the present invention will be described.
The detoxifying treatment method of fly ash according to the present embodiment mixes fly ash containing dioxin with dust contained in exhaust gas which contains calcium in an amount of 10% by mass to less than 40% by mass and is discharged from a cement production facility. And a heat treatment step of heating the mixture above the decomposition temperature of dioxin, and a washing step of washing the heated mixture.

(Flying ash)
Incineration ash is generally divided into incineration main ash (bottom ash) recovered from the bottom of the incinerator and the like and fly ash floating in the incineration exhaust gas (fly ash). The fly ash is a solid particulate matter suspended in the incineration exhaust gas such as soot and ash, and is collected in collected ash, a boiler, a gas cooling chamber, a reburning chamber and the like.
The fly ash to be treated by the method of the present embodiment is dust generated by adding a neutralizing agent to the flue gas generated in a refuse treatment facility that treats municipal waste, industrial waste and the like. The fly ash can be reused for various purposes in order to reduce waste, and in particular, it is preferable to use it as a cement raw material.
Since fly ash may contain dioxin derived from waste which is a raw material, dioxin needs to be removed when it is used as a cement raw material.

(dust)
In the present embodiment, the dust mixed in the fly ash is a dust that contains calcium in an amount of 10% by mass to less than 40% by mass and is included in the exhaust gas of cement production equipment.
Examples of the dust include the exhaust gas of cement production equipment, such as dust contained in the exhaust gas discharged from a cement kiln.
The exhaust gas discharged from the cement kiln is, for example, an exhaust from a rising duct, a demineralized bypass dust, etc., which is disposed at a position between the cement kiln's butt and a heat exchange device including a calciner. The gas includes a gas exhausted from a heat exchanger including the preheater.
The exhaust gas exhausted from each of the above locations is separated into a solid component in the gas and a gas component by means such as a cyclone, a bag filter, an electrostatic precipitator or the like that separates the solid and the gas, and the solid component is obtained as dust. .
For example, the gas discharged from the desalination bypass is separated from the solid component and the gas component by a bag filter or other separation means, and the solid component is recovered as the desalination bypass dust.
In the gas obtained from the heat exchanger, a solid component and a gas component are separated by an electrostatic precipitator, and the solid component is recovered as an electrostatic dust (hereinafter also referred to as an EP dust). Further, fine powder finer than the EP dust is recovered by a bag filter provided between the electrostatic precipitator and a chimney for discharging a gas component.
In the present embodiment, as the dust, these desalted bypass dust, electric dust collector dust, fine powder and the like can be used.

The dust contained in the exhaust gas from the cement kiln contains a calcium compound such as calcium oxide, and the calcium content in the dust is about 10% by mass or more and less than 40% by mass as Ca.
When the dust is the desalted bypass dust, generally, the calcium content in the dust is about 10% by mass or more and less than 40% by mass as Ca, and when it is the EP dust, Generally, the calcium content in the dust is approximately 20% by mass or more and less than 40% by mass as Ca.

  In the present specification, the calcium content in the dust refers to an amount measured by ion chromatography, ICP emission spectroscopy, atomic absorption spectrometry, etc. Specifically, the method described in the examples described later Is the quantity measured by

The dust used in the present embodiment is dust contained in the exhaust gas of cement production equipment, and is usually separated from the high temperature exhaust gas, and thus is separated from the gas in a dried state. Therefore, it has high fluidity, even without being subjected to drying treatment and the like.
In particular, since the desalted bypass dust and the EP dust are easily obtained in a dried state and are fine particles, they are dusts having higher fluidity. Therefore, it is suitable as the dust of the present embodiment.

<< Mixing process >>
In the detoxifying treatment method of the fly ash of the present embodiment, first, the fly ash containing the dioxin and the dust contained in the exhaust gas of cement production equipment containing 10 mass% or more and less than 40 mass% of calcium are mixed A mixing step is performed to obtain a mixture.

As the fly ash, fly ash transported from a waste disposal facility or the like may be stored in a storage tank or the like, and a predetermined amount may be introduced from the storage tank to the mixing apparatus.
Examples of the mixing device include Henschel mixer (made by Nippon Coke Kogyo Co., Ltd.) which is a batch type mixer, Nauta mixer (made by Hosokawa Micron Corporation), batch and continuous mixer Pro shear mixer (made by Taiyo Kiko Co., Ltd.), etc. Known mixing devices can be mentioned.
On the other hand, it is preferable from the viewpoint of maintaining the flowability to introduce dust into the mixing apparatus immediately after separation from the exhaust gas, or after separation and stored in a closed space.
Furthermore, the dust may be introduced into the mixing device by pressure-feeding using air or the like. By introducing the dust by such pumping, the flowability of the dust can be further improved.
The mixing device may be disposed, for example, in a cement production facility, and dust generated in the cement production facility in which the mixing device is disposed may be used. In such a case, there is an advantage that the cost of transferring the dust can be reduced.

The amount of dust in the mixture is, for example, 5% by mass or more and 40% by mass or less, preferably about 10% by mass or more and 30% by mass or less.
When the mixing amount of the dust is 5 mass% or more and 40 mass% or less, sticking of fly ash after heat treatment can be sufficiently reduced, and residual calcium in fly ash after treatment can be suppressed. it can.
In addition, since the dust has good fluidity, it can be easily mixed uniformly. Therefore, solidification of the fly ash can be reliably reduced without increasing the amount of dust to the fly ash more than necessary.
In the present embodiment, the calcium content in the mixture of fly ash and dust is, for example, 15.0% to 35.0% by mass, preferably about 22.5% to 26% by mass, as the amount of Ca. Is preferred.

  In the present embodiment, as a condition for mixing fly ash and dust, for example, in the case of using a batch type mixing apparatus (Pro shear mixer or the like), the number of rotations is 50 to 500 rpm at a temperature of 5 ° C to 40 ° C. It is preferable to mix for 60 minutes.

  In this embodiment, since the dust is mixed with the fly ash, the flowability of the dust is good, and therefore, a mixture in which the dust and the fly ash are uniformly mixed can be obtained.

<< heat treatment process >>
Next, a heat treatment step of heating the mixture above the decomposition temperature of dioxin is carried out.
The mixture is transferred to a heating device for heat treatment.
Examples of the heating device include known heating devices such as JFE High Clean DX (manufactured by JFE Engineering Co., Ltd.), rotary kiln (manufactured by J Tech Co., Ltd.), and microwave dioxin detoxifying apparatus (manufactured by Japan Spindle Manufacturing Co.) .

The heating temperature of the fly ash in the heat treatment step may be at least the temperature at which dioxins are decomposed.
In general, dioxins are known to be decomposed at high temperatures of 800 ° C. or more in an oxygen-containing atmosphere and at high temperatures of 350 ° C. to 380 ° C. or more in an oxygen-deficient atmosphere.
Therefore, also in the heat treatment process of this embodiment, it is preferable to heat above the said temperature. Specifically, the heating temperature is preferably about 400 ° C. to 500 ° C. in an oxygen deficient atmosphere.
The oxygen-deficient atmosphere means an atmosphere having an oxygen concentration of about 1% by volume or less.

On the other hand, it is known that fly ash starts to solidify when heated at 300 ° C. or higher, and rapidly proceeds to solidify when it exceeds 400 ° C.
This is considered to be due to the following reasons.
That is, when the fly ash is heated, Ca (OH) ₂ in the fly ash reacts with CaCl ₂ in the fly ash to generate CaClOH. For example, when heated to a high temperature of 300 ° C. or higher, CaClOH forms a compact and high-strength sintered body. This sintered body is considered to be the cause of the solidification of fly ash.

On the other hand, when calcium components such as calcium hydroxide are mixed into the fly ash and then heated, a reaction of producing CaCO ₃ occurs by the action of calcium in the heat treatment step. That is, it is considered that the solidification can be reduced by inhibiting the reaction between Ca (OH) ₂ and CaCl ₂ by adding the calcium component and suppressing the formation of CaClOH which is the causative component of the solidification. .
However, when a large amount of calcium hydroxide or the like is added to the fly ash, a large amount of calcium remains in the fly ash, and when the fly ash is washed in the washing step described later, a large amount of calcium dissolves in the washing solution. Become.

In the present embodiment, the dust mixed with fly ash is dust contained in the exhaust gas of cement production equipment containing 10% by mass or more and less than 40% by mass, so the amount of calcium smaller than calcium hydroxide or slaked lime However, the same or more solidification control effect can be obtained.
The detailed reason why the dust contained in the exhaust gas of the cement production facility causes such a high solidification inhibiting effect is unknown, but probably other components contained in the dust contained in the exhaust gas of the cement production facility However, it can be inferred that there is an action to suppress the formation of CaClOH more in cooperation with calcium.

The treatment conditions of the heat treatment step in the treatment method of this embodiment are, for example, a temperature of 300 ° C. to 600 ° C., preferably 400 ° C. to 500 ° C., for 10 minutes to 180 minutes, preferably 30 minutes to 60 minutes. It is about less than a minute.
By being processing conditions of the said range, while being able to fully decompose | disassemble the dioxin in fly ash, solidification can be suppressed effectively.

Cleaning process
After the heat treatment step, a washing step of washing the heated mixture is performed.
In the cleaning step of the present embodiment, the mixture of fly ash and dust after the heat treatment is introduced, for example, into the washing tank together with the cleaning solution, and chlorine and the like in the fly ash can be removed by stirring.
Examples of the washing water include water such as fresh water, treated water, and distilled water, as well as washing liquids in which various components are mixed with the water.
Examples of the cleaning solution include aqueous solutions of acids such as hydrochloric acid, sulfuric acid and nitric acid.
Since the fly ash contains an alkali component, the slurry becomes strongly alkaline when washed with washing water, and if the fly ash contains a metal, the metal is eluted in the washing solution. It will be easier. In order to reduce the elution of such metals, the pH of the slurry of the mixture after the heat treatment and the washing solution is adjusted to about 3 so that it is weakly alkaline with a pH of about 8 to 10, preferably about 7.0. It is particularly preferred to use the prepared acidic solution as a washing solution.

  In the washing step, for example, the slurry obtained by mixing the mixture in the washing liquid at 5 ° C. or more and 40 ° C. or less in the washing tank is washed while being stirred at a predetermined strength for 1 minute to 300 minutes or less. Be

After carrying out the cleaning step, in the method for harmlessization treatment of fly ash according to the present embodiment, a solid-liquid separation step may be performed in which the slurry is solid-liquid separated.
As means for solid-liquid separation, known filtration devices such as a filter press, a belt press, a centrifuge, a decanter and the like can be used.
The processed fly ash separated as a solid component in the solid-liquid separation step can be used by being introduced into a cement kiln or the like as a cement raw material.
Since the fly ash treated by the treatment method of the present embodiment has dioxins sufficiently decomposed, it can be suppressed that dioxins are mixed in cement even when used as a cement raw material.
On the other hand, the washing solution of the liquid component separated in the solid-liquid separation step can reduce the elution amount of calcium as compared with the case where calcium hydroxide or slaked lime is added for preventing solidification of fly ash. Therefore, it is possible to suppress the precipitation of the calcium component in the cleaning and sweeping device, the discharge pipe of the cleaning liquid, and the like.

The detoxification treatment method of fly ash of the present embodiment may be carried out in a cement production facility where cement is produced from the cement raw material, when the fly ash after treatment is used as a cement raw material.
In this case, the fly ash after treatment can be used as a raw material in the same cement production facility, and there is an advantage that the transfer cost of fly ash after treatment can be reduced.
Moreover, the detoxification treatment method of the fly ash of this embodiment may be implemented in the same cement manufacturing equipment as the cement manufacturing equipment which a dust generate | occur | produces. In this case, the respective dust generated in the same cement production facility can be used, which has the advantage of reducing the cost of transferring the dust.
Furthermore, the detoxifying method of fly ash of the present embodiment is carried out in one cement production facility, and the fly ash is treated using dust generated from within the cement production facility, and the fly ash after the treatment is performed. May be used as a cement material in the cement production facility.

  The fly ash detoxification method according to this embodiment is as described above, but the embodiment disclosed this time should be considered as illustrative in all points and not restrictive. . The scope of the present invention is shown not by the above description but by the claims, and is intended to include all modifications within the meaning and scope equivalent to the claims.

  Hereinafter, examples of the present invention will be described.

(dust)
In this embodiment, the gas discharged from the desalination bypass provided at the end of the kiln of the cement production facility is cooled, and the dust separated by the cyclone (desalinated bypass dust) and the electrostatic precipitator dust (EP dust) Prepared.
The respective dusts were separated by a cyclone or an electrostatic precipitator and then stored in a storage tank in a sealed state.
The components of the dust used in this example are shown in Table 1 for the components of the desalted bypass dust and in Table 2 for the components of the EP dust.
The components of the dust are acid-dissolved or alkali-melted as pretreatment, and an ICP emission spectrometer (ICP: manufactured by Spectro), a flame atomic absorption spectrometer (atomic absorption analyzer: manufactured by Hitachi High-Technologies), etc. Can be measured.
In the present example, the apparatus used the ICP emission spectrometer.

(Calcium hydroxide)
The following were prepared as calcium hydroxide to be mixed with the above-described dust in the fly ash of the comparative example.
Calcium hydroxide: 95% or more purity, Kanto Chemical Co., Ltd., first grade reagent

<< Calculation of calcium amount >>
The amounts of calcium of the desalted bypass dust, EP dust and calcium hydroxide were calculated from Tables 1 and 2 using the following formula (1).
As a result, the calcium content of the desalted bypass dust was 22 mass%, the calcium content of the EP dust was 39 mass%, and the calcium content of calcium hydroxide was 51 mass% (the purity of calcium hydroxide was 95 Calculated as%).

Ca content = CaO component (%) × atomic weight of Ca (40.1) / molecular weight of CaO (56.1) (1)

(Flying ash)
We prepared fly ash discharged from municipal waste incinerators.
The components of the fly ash used in this example are as shown in Table 3.
The amounts of the components were measured in the same manner as the respective dusts.
Furthermore, the ignition loss was heated in an electric furnace at 950 ° C. in accordance with JIS R 5202, and the reduced mass was measured.

«Change in hardness due to heating of fly ash»
The hardness of the fly ash was measured after heating the fly ash in an electric furnace (device name: small box furnace, manufactured by Koyo Thermo System Co., Ltd.) for 1 hour. The heating temperature is 350 ° C., 400 ° C., 450 ° C., 500 ° C.
For hardness, a soil hardness tester (device name: Nakayama soil hardness tester, manufactured by Fujiwara Seisakusho) was used. The results are shown in FIG.
From the results shown in FIG. 1, it can be seen that although the hardness increases as the temperature increases, the hardness increases rapidly especially when the temperature exceeds 450 ° C.
The high hardness indicates that the solidification of the fly ash is progressing.

<< Change in hardness by mixing amount of dust / calcium hydroxide >>
Next, the hardness at the time of heating the mixture at the time of changing the mixing amount of demineralization bypass dust, EP dust, or calcium hydroxide to the said fly ash was measured.
As an example, a mixed sample is prepared by mixing desalted bypass dust or EP dust from 0% by mass to 40% by mass in increments of 5% by mass with respect to the total amount of the mixture with fly ash (Example 1, 2) After heating using the said electric furnace at 500 degreeC and 1 hour, respectively, hardness was measured using the said soil hardness meter.
As a comparative example, a mixed sample was prepared by mixing calcium hydroxide instead of the desalted bypass dust of the example or the EP dust, and the hardness after heating was similarly measured.
The amount of calcium added is converted from the amount of calcium contained in the mixed sample, and the influence of the amount of calcium added on hardness is shown in FIGS.
Further, a reference line of hardness reduction expected when calcium hydroxide is added to dust is shown in a straight line in FIGS. 2 to 4 with the hardness of calcium hydroxide alone being zero.
Further, Table 4 shows values obtained by converting the amount of added calcium when mixing 5% by mass, 10% by mass, and 20% by mass of each dust or calcium hydroxide into fly ash.

  As is clear from FIGS. 2 to 4 and Table 4, in Examples 1 and 2, even if the amount of added Ca is smaller than that of the comparative example in which calcium hydroxide is mixed with fly ash, the hardness can be suppressed to the same hardness.

<< Measurement of liquidity 1 >>
The bulk specific gravity was measured and compared about the fluidity of the desalted dust used in Example 1, the EP dust, and the calcium hydroxide used in the comparative example.
The method of measuring the flowability is as follows. First, using a funnel with a diameter of 85 mm, an outer diameter of 8.3 mm and a leg length of 81 mm, dropping dust or calcium hydroxide into a cylindrical container with a height of 100 mm to a volume of 50 ml. Measure the weight when packed in the natural state, and determine the bulk specific gravity at light compression. Next, gently tap the container on the ground 20 times to fill it with dust or calcium hydroxide, then drop more dust or calcium hydroxide from the funnel, pile it up, and gently tap the container on the ground 20 times, Fill with dust or calcium hydroxide, flatten with a spatula to make the top of the container uniform, and keep the height constant. Thereafter, bulk specific gravity is measured when filled and determined as bulk specific gravity at heavy compression.
A value obtained by subtracting the bulk specific gravity at light compression from the bulk specific gravity at heavy compression is obtained as a bulk specific gravity difference.
The smaller the bulk specific gravity difference, the less likely it is to clog and the powder is high in fluidity.
The results are shown in Table 5.

  From the results shown in Table 5, it is clear that the desalted bypass dust and the EP dust are more fluid than calcium hydroxide.

<< Measurement of liquidity 2 >>
With respect to the flowability of the desalted bypass dust used in the examples, the EP dust, and the calcium hydroxide used in the comparative examples, the angle of repose was measured and compared.
When 30 g of dust and calcium hydroxide are prepared, each is dropped from a height of 100 mm onto a plastic plate using a funnel (diameter 85 mm, foot outer diameter 8.3 mm, foot length 81 mm) to form a layer in a mountain shape The angle (the angle shown in FIG. 5) that the slope of the slope makes with the horizontal plane is measured.

  The results were demineralized dust 22 °, EP dust 35 °, calcium hydroxide 50 °. That is, it is apparent that each dust is more fluid than calcium hydroxide.

Claims (4)

A mixing step of mixing a fly ash containing dioxin and dust contained in an exhaust gas discharged from a cement production facility containing 10% by mass or more and less than 40% by mass of calcium to obtain a mixture;
A heat treatment step of heating the mixture above the decomposition temperature of dioxin;
And washing the heated mixture.
In the mixing step, the fly ash and the dust are mixed such that the content of calcium caused by the dust in the mixture is 1.1% by mass or more and 4.4 % by mass or less. Processing method. Wherein in the mixing step, detoxification of fly ash according to claim 1, wherein the content of calcium in the mixture with the fly ash so that 35 wt% or less than 15 wt% and the dust are mixed Method. The method according to claim 1 or 2 , wherein the dust is dust contained in an exhaust gas discharged from a cement kiln. The said mixing process WHEREIN: The said fly ash and dust are mixed so that 5 mass% or more and 40 mass% or less of dust may be contained in the said mixture, Detoxification of the fly ash as described in any one of Claim 1 thru | or 3 Processing method.