JP2004267806A - Method for detoxifying incineration ash or the like at high temperature - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a treatment method for detoxifying incineration ash or the like capable of heating fly ash at 400°C or above without fixing the same to decompose dioxins and capable of evaporating heavy metals in fly ash as chlorides to remove them. <P>SOLUTION: Mullite (2Al<SB>2</SB>O<SB>3</SB>-SiO<SB>2</SB>) is mixed with fly ash containing a harmful organochlorine compound and the resulting mixture is heated at 400°C or above, preferably 600°C or above, ideally 700°C or above to detoxify the fly ash. When the mixture of the fly ash and mullite is heated, the fly ash is held to a powdery state even at 400°C or above without being fixed. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for detoxifying incinerated fly ash or the like containing harmful organic chlorine compounds such as dioxins and harmful heavy metals.
In particular, the present invention relates to a detoxification method which is effective for preventing fly ash from solidifying and fixing when fly ash containing alkali fly ash neutralized by slaked lime or the like is heated at a high temperature.
[0002]
[Prior art]
In general waste incinerators and industrial waste incinerators, various methods have been proposed and adopted, such as introduction of various chemicals and secondary combustion of generated gas, in order to suppress the generation of dioxins.
However, since a large amount of dioxins is contained in the above incinerated fly ash, it is important to establish a method for detoxifying the incinerated fly ash in order to comply with the total amount regulation in the future.
[0003]
The incinerated fly ash includes fly ash that has been neutralized by spraying slaked lime or the like into cooling waste gas called alkali fly ash.
Dioxins do not decompose sufficiently unless heated to 400 ° C. or higher, ideally 700 ° C. or higher.
However, when the alkali fly ash is heated to a high temperature of 400 ° C. or higher, there is a problem that it becomes difficult to handle because it solidifies and adheres to the inner wall of the processing apparatus.
In particular, when continuous treatment is to be carried out in a rotary kiln or the like, it is a fatal problem that fly ash adheres in the kiln.
[0004]
Therefore, conventionally, as disclosed in, for example, Japanese Patent Publication No. 6-38863, a method has been proposed in which a specific agent capable of decomposing dioxins is decomposed even at a low temperature and dechlorination is performed in a reducing atmosphere.
However, in such a processing method, the processing steps become complicated and this is one of the causes of high cost.
[0005]
[Patent Document 1]
Japanese Patent Publication No. 6-38863 Patent Publication
[Problems to be solved by the invention]
The present invention has been made in view of the above-mentioned technical problems of the prior art, and is capable of heating to 400 ° C. or more to decompose dioxins without adhering fly ash, and capable of vaporizing and removing contained heavy metals as chlorides. The purpose is to provide a method for detoxifying ash etc.
[0007]
[Means for Solving the Problems]
The gist of the present invention is to mix mullite (2Al ₂ O ₃ .SiO ₂ ) with fly ash containing a harmful organic chlorine compound, and to 400 ° C. or higher, preferably 600 ° C. or higher, ideally 700 ° C. or higher. By heating, the fly ash is detoxified.
As described above, when mullite is mixed with the fly ash and heated, the powder of the fly ash is maintained without being adhered to each other even when the temperature of the ash reaches 400 ° C. or higher, or adhered around the heating device.
[0008]
Here, the organic chlorine compounds include dioxins.
The dioxins are defined as polychlorinated dibenzo-para-dioxin (PCDD), polychlorinated dibenzofuran (PCDF) and coplanar polychlorinated biphenyl (coplanar PCB) in the Law Concerning Special Measures against Dioxins.
Examples of organic chlorine compounds other than dioxins include dichloromethane, carbon tetrachloride, 1.2-dichloroethane, 1.1-dichloroethylene, cis-1.2-dichloroethylene, 1.1.1-trichloroethane, 1.1. 2-trichloroethylene, tetrachloroethylene, 1.3-dichloropropene and the like can be mentioned.
[0009]
Mullite is classified as a nesosilicate mineral and is a polymorph of oralite, sillimanite, and kyanite.
The chemical composition _is shown in 2Al ₂ O 3 · SiO _2, consists tetrahedral structure of SiO _2, it is known to have a structural defect in which the oxygen atoms are missing.
Mullite is hardly produced in nature, but is universally present as a component of ceramics and refractories.
It was also revealed that coal ash discharged from thermal power plants, etc. contained mullite along with quartz.
Therefore, if the fly ash is mixed with the fly ash and heated, not only can the fly ash be rendered harmless at a lower cost, but also a way to effectively utilize the fly ash is opened.
[0010]
Fly ash referred to in the present invention refers to slaked lime collected by advanced dust collectors and the like discharged from general waste incinerators and industrial waste incinerators specified by the "Law on the Treatment and Cleaning of Waste". This refers to fly ash containing an alkali neutralizer, and fly ash adhering to treatment equipment such as flue and chimney from an incinerator to a chimney.
[0011]
It has been reported that when a substance containing a mixture of an organic chlorine compound and heavy metals is heated to 400 ° C. or higher, preferably 700 ° C. or higher, most of the heavy metals can be chlorinated and vaporized and recovered. I have.
Therefore, in the present invention, if the fly ash can be heated to a high temperature without fixing the fly ash, the treatment of heavy metals can be facilitated.
[0012]
BEST MODE FOR CARRYING OUT THE INVENTION
Prior to the description of the fly ash detoxification method, first, fly ash discharged from the incinerator was subjected to component analysis by XRD (powder X-ray diffractometer), and the result of XRD of the fly ash before the heat treatment in FIG. Shown in the analysis chart.
As a result, it was found that the fly ash contained CaClOH.
This is presumed to be caused by the reaction of slaked lime with HCl in the gas due to slaked lime spray.
[0013]
Next, using an experimental apparatus as shown in FIG. 1, fly ash is used alone or a mixture of mullite, coal ash, and NaOH is mixed to prepare a heated sample. After heating, XRD component analysis and TG / DTA ( An analytical investigation by thermogravimetry-differential thermal analysis) was conducted.
As shown in FIG. 1, a sample (sample) was placed on a quartz filter in a quartz glass tube, placed on a sample bed holder, heated to 700 ° C. in an electric furnace, and then heated for 60 minutes.
At this time, air passed through a packed bed of activated carbon and silica gel was sent from above the quartz glass tube to elute components volatilized from the sample into ultrapure water in the air collection bottle.
[0014]
FIG. 3 shows an XRD analysis chart after heat treatment of only fly ash as a sample (a) at 700 ° C. FIG. 4 shows a sample (b) in which fly ash was mixed with 16.9% by mass of NaOH at 700 ° C. FIG. 5 shows an XRD analysis chart after heat treatment, and FIG. 5 shows an XRD analysis chart as a sample (c) after mixing fly ash with 50% by mass mullite and heat-treating it to 700 ° C.
As shown in FIG. 3, even if only fly ash is heated, CaClOH contained before heating remains stable even at a high temperature, but as shown in FIGS. 4 and 5, NaOH or mullite is mixed. Heating revealed that CaClOH was almost completely decomposed.
Note that CaO is presumed to have been generated by pyrolysis of Ca (OH) ₂ contained in the fly ash.
In the sample (a) obtained by heating only fly ash, the powder fly ash was fixed and solidified to form a soul-like mass, but the sample (b) mixed with NaOH and the sample (c) The mixture of mullite did not stick.
[0015]
FIG. 6 shows a TA / DTA analysis chart of sample (a) (fly ash only) after heat treatment, and FIG. 7 shows a TA / DTA analysis chart of sample (b) and FIG. 8 respectively.
As shown in FIG. 6, an endothermic peak indicating melting appears at around 370 ° C. and 500 ° C. when the temperature rises, and an exothermic peak showing solidification near 670 ° C. when the temperature falls.
On the other hand, the endothermic peak and the exothermic peak are small in the mixture of NaOH shown in FIG. 7, and the endothermic peak (melting) and the exothermic peak (coagulation) are recognized in the mixture of mullite as shown in FIG. I couldn't.
Therefore, when compared with the results of XRD, it can be said that CaClOH was not decomposed in the mixture of mullite, and no melting and solidification peaks were observed.
That is, it was clarified that when only fly ash was heated, it was fixed due to CaClOH, but that to which mullite was added was not fixed because CaClOH was decomposed and CaClOH was lost.
[0016]
Next, in order to investigate the influence of mullite on the adhesion of fly ash, a heating test was performed while changing the mixing ratio of mullite.
A sample was prepared by mixing mullite at a ratio of 0.025, 0.1, 0.15, 0.2, 0.25, 0.5, 1.0 with respect to the mass of fly ash 1 at 700 ° C x As a result of a heating test for 60 minutes, it was found that no solidification or solidification occurred at a rate of 0.25 or more.
Further, as a result of repeated mixing test of fly ash with mullite in a ball shape, fly ash does not adhere, and it is presumed that mullite has a catalytic action to decompose CaClOH.
[0017]
The dioxin concentration comparison between the graph 1 shown in FIG. 9 and the graph 2 shown in FIG. 10 was made by mixing fly ash alone or NaOH, mullite, coal ash [fly ash (coal)]. It is a comparative study of the concentration of dioxins in each fly ash when heat treatment was performed.
The dioxin concentration measurement is based on a method for measuring dioxins and coplanar PCB in JIS K0311 exhaust gas.
Here, FIG. 9 shows the measured concentrations of dioxins in Graph 1, and Graph 2 in FIG. 10 shows the toxic equivalents.
The toxic equivalent is obtained by multiplying the measured concentration of each isomer by the toxic equivalent coefficient (TEF).
The TEF used was WHO-TEF (1998).
As a result, when fly ash is heated to 400 ° C. or more, the concentration of dioxins decreases, and when it is 700 ° C. or more, dioxins further decrease. When mullite or coal ash (containing mullite) is mixed, toxicity and the like are reduced. The drop in volume is lower.
Thus, it was revealed that when mullite (coal ash) was mixed and heated, dioxins were decomposed without fixing fly ash, and the fly ash could be rendered harmless.
[0018]
In addition, the measurement result of the concentration of each isomer is shown in FIGS. 11 to 16 for reference.
FIG. 17 shows the results of a component analysis of coal ash by an energy dispersive X-ray fluorescence spectrometer (EDX), and other investigations revealed that coal ash contained mullite.
[0019]
【The invention's effect】
When mullite is mixed with fly ash containing a harmful organic chlorine compound, sticking and solidification by heating can be prevented, so that continuous detoxification treatment with a rotor kiln or the like becomes possible.
Further, by setting the temperature to be high, many heavy metals contained in the fly ash can be chlorinated.
If coal ash is used as a source of mullite, not only can it be obtained at low cost, but also coal ash can be reused.
[Brief description of the drawings]
FIG. 1 shows an experimental apparatus used in the present invention.
FIG. 2 shows an XRD analysis chart of fly ash before heat treatment.
FIG. 3 shows an XRD analysis chart obtained by heating only fly ash to 700 ° C.
FIG. 4 shows an XRD analysis chart obtained by heat-treating fly ash + NaOH to 700 ° C.
FIG. 5 shows an XRD analysis chart obtained by heat-treating fly ash + mullite to 700 ° C.
FIG. 6 shows a TG / DTA analysis chart after heat treatment of only fly ash.
FIG. 7 shows a TG / DTA analysis chart after heat treatment of fly ash + NaOH.
FIG. 8 shows a TG / DTA analysis chart after heat treatment of fly ash + mullite.
FIG. 9 shows a comparison of dioxin concentrations (measured concentrations).
FIG. 10 shows a comparison of dioxin concentrations (toxic equivalents).
FIG. 11 shows the results of measuring the concentration of dioxins before heat treatment of fly ash.
FIG. 12 shows the results of measuring the concentration of dioxins after heat treatment of fly ash at 400 ° C.
FIG. 13 shows the results of measuring the concentration of dioxins after heat treatment of fly ash at 700 ° C.
FIG. 14 shows the results of measuring the concentration of dioxins after heat treatment of fly ash + mullite at 700 ° C.
FIG. 15 shows the results of measuring the concentration of dioxins after heat treatment of fly ash + NaOH at 700 ° C.
FIG. 16 shows the results of measuring the concentration of dioxins after heat treatment of fly ash and coal ash at 700 ° C.
FIG. 17 shows the results of component analysis of coal ash by EDX.

Claims (3)

The fly ash containing harmful organic chlorine compounds, mullite _{(2Al 2 O 3 · SiO 2} ) were mixed by heating to above 400 ° C., innocuous, such as incineration fly ash, which comprises detoxified Treatment method. The method for detoxifying incinerated fly ash and the like according to claim 1, wherein the organic chlorine compound is a dioxin. 2. The method for detoxifying fly ash or the like according to claim 1, wherein the mullite is obtained from coal ash.

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