JP3867125B2 - Detoxification method for incineration fly ash, etc. (high temperature) - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a detoxification method for incinerated fly ash and the like contained in harmful organic chlorine compounds such as dioxins and harmful heavy metals.
In particular, the present invention relates to a detoxifying treatment method that is effective in preventing the fly ash from solidifying and adhering when heated fly ash containing alkali fly ash neutralized by slaked lime or the like is heated.
[0002]
[Prior art]
In general waste incinerators and industrial waste incinerators, in order to suppress the generation of dioxins, various methods such as introduction of various chemicals and secondary combustion of generated gas have been proposed and adopted.
However, since a large amount of dioxins is contained in the incineration fly ash, it is important to establish a detoxification method for the incineration fly ash in order to meet future total amount regulations.
[0003]
Incinerated fly ash includes fly ash that has been neutralized by spraying slaked lime or the like into a cooling waste gas called alkali fly ash.
Dioxins do not decompose sufficiently unless the temperature is 400 ° C. or higher, ideally 700 ° C. or higher.
However, when such 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 processing is performed using 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, etc., a method of introducing a specific drug that decomposes dioxins even at low temperatures and a method of dechlorination in a reducing atmosphere have been proposed.
However, in such a processing method, the processing process becomes complicated, which is one of the causes of high cost.
[0005]
[Patent Document 1]
Japanese Patent Publication No. 6-38863 Patent Publication [0006]
[Problems to be solved by the invention]
In view of the technical problems of the above prior art, the present invention is an incinerator that can be heated to 600 ° C. or higher without decomposing fly ash, decompose dioxins, and vaporize and remove heavy metals contained as chlorides. The purpose is to provide a method for detoxifying ash and the like.
[0007]
[Means for Solving the Problems]
The gist of the present invention is that mullite having a mass of 0.25 or more is mixed with fly ash mass 1 containing a harmful organochlorine compound and heated to 600 ° C. or higher, ideally 700 ° C. or higher. It is to detoxify fly ash.
As described above, when mullite is mixed with the fly ash and heated, the fly ash powder does not adhere to each other and does not adhere to the periphery of the heating device even when the temperature reaches 600 ° C. or higher, and the powdery state is maintained.
[0008]
Here, the organic chlorine compound includes dioxins.
Dioxins are defined as polychlorinated dibenzo-para-dioxin (PCDD), polychlorinated dibenzofuran (PCDF) and coplanar polychlorinated biphenyl (coplanar PCB) in the Special Measures Countermeasures 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. Examples include 2-trichloroethylene, tetrachloroethylene, 1.3-dichloropropene.
[0009]
Mullite is classified as a nesosilicate mineral and is a polymorphic form of beryl, wollastonite 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 rarely 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 together with quartz.
Therefore, if coal ash is mixed with the fly ash and heated, not only can the fly ash be detoxified at a lower cost, but a path for effective use of the coal ash will be opened.
[0010]
Fly ash as used in the present invention refers to slaked lime, etc. collected by advanced dust collectors discharged from general waste incinerators and industrial waste incinerators specified in the “Waste Treatment and Cleaning Law”. It refers to fly ash containing an alkali neutralizer and fly ash adhering to the processing equipment such as the flue from the incinerator to the chimney, and the chimney.
[0011]
It has been reported so far that when a substance containing a mixture of organochlorine compounds and heavy metals is heated to a high temperature of 400 ° C or higher, preferably 700 ° C or higher, most of the heavy metals are chlorinated and can be vaporized and recovered. Yes.
Accordingly, in the present invention, if the fly ash can be heated to a high temperature without fixing, the treatment of heavy metals becomes easy.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
Before explaining the fly ash detoxification method, first, the components of the fly ash discharged from the incinerator were analyzed by XRD (powder X-ray diffractometer). Shown in the analysis chart.
As a result, it was found that CaClOH was contained in the fly ash.
This is presumed that HCl in the gas and slaked lime reacted and formed by spraying slaked lime.
[0013]
Next, using an experimental apparatus as shown in FIG. 1, fly ash alone or mullite, coal ash, and NaOH are mixed to prepare a heated sample. After heating, XRD component analysis and TG / DTA ( (A thermogravimetric-differential thermal analysis).
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 heated for 60 minutes.
At this time, air that passed through the packed bed of activated carbon and silica gel was sent from above the quartz glass tube, and the components that volatilized from the sample were eluted into the ultrapure water in the air collection bottle.
[0014]
FIG. 3 shows an XRD analysis chart after heat treatment of only fly ash at 700 ° C. as sample (a), and FIG. 4 shows a sample (b) mixed with 16.9% by weight of NaOH at 700 ° C. Fig. 5 shows an XRD analysis chart after the heat treatment, and Fig. 5 shows an XRD analysis chart after mixing the fly ash with 50% by mass of mullite and heat-treating it at 700 ° C as a sample (c).
As shown in FIG. 3, even when only fly ash is heated, CaClOH contained before heating remains stable even at high temperatures, but as shown in FIGS. 4 and 5, NaOH and mullite are mixed. It was revealed that CaClOH was almost completely decomposed when heated.
In addition, it is estimated that CaO was produced by thermal decomposition of Ca (OH) ₂ contained in fly ash.
In addition, in the sample (a) which was heated only in the fly ash, the powdered fly ash was fixed and solidified to form a soul-like lump, 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 after heat treatment of sample (a) (only fly ash), FIG. 7 shows a sample (b), and FIG. 8 shows a TA / DTA analysis chart of sample (c).
As shown in FIG. 6, an endothermic peak indicating melting is observed at about 370 ° C. and about 500 ° C. when the temperature is increased, and an exothermic peak indicating solidification is observed at about 670 ° C. when the temperature is decreased.
In contrast, the mixture of NaOH shown in FIG. 7 has a small endothermic peak and exothermic peak, and the mixture of mullite as shown in FIG. 8 has an endothermic peak (melting) and an exothermic peak (solidification). I couldn't.
Therefore, it can be said that, compared with the XRD results, CaClOH is not decomposed in the mixture of mullite and melting and solidification peaks are not recognized.
That is, when only fly ash is heated, it is fixed due to CaClOH, but it is clear that the one added with mullite does not adhere because CaClOH is decomposed and CaClOH disappears.
[0016]
Next, in order to investigate the influence of mullite on the fixation of fly ash, a heating test was performed by changing the mixing ratio of mullite.
Samples were prepared by mixing mullite at a ratio of 0.025, 0.1, 0.15, 0.2, 0.25, 0.5, and 1.0 with respect to fly ash mass of 1, and 700 ° C × As a result of a heating test for 60 minutes, it became clear that it was not fixed or solidified at a rate of 0.25 or more.
Further, as a result of repeated mullite mixing tests with fly ash in the form of balls, it is estimated that mullite has a catalytic action for decomposing CaClOH because the fly ash does not stick.
[0017]
Comparison of concentration of dioxins in graph 1 shown in FIG. 9 and graph 2 shown in FIG. 10 shows that fly ash is used alone or mixed with NaOH, mulite, and coal ash (coal). This is a comparative investigation of dioxin concentrations for each fly ash when heat-treated.
The dioxin concentration measurement is based on the measurement method of dioxins and coplanar PCB in JIS K0311 exhaust gas.
Here, FIG. 9 shows the measured concentration of graph 1 dioxins, and graph 2 of FIG. 10 shows the toxic equivalent amount.
Toxicity equivalent is the actual concentration of each isomer multiplied by the toxicity equivalent factor (TEF).
In addition, WHO-TEF (1998) was used for TEF.
As a result, when fly ash is heated to 400 ° C or higher, the concentration of dioxins decreases, and at 700 ° C or higher, dioxins decrease further. When mullite or coal ash (containing mullite) is mixed, toxicity, etc. The decrease in quantity is lower.
As a result, when mullite (coal ash) was mixed and heated, dioxins were decomposed without fixing the fly ash, and it became clear that the fly ash can be rendered harmless.
[0018]
For reference, the concentration measurement results of each isomer are shown in FIGS.
FIG. 17 shows the result of component analysis of coal ash using an energy dispersive X-ray fluorescence spectrometer (EDX), and other studies revealed that mullite is contained in coal ash.
[0019]
【The invention's effect】
When mullite is mixed with fly ash containing harmful organic chlorine compounds, fixing and solidification by heating can be prevented, so that a continuous detoxification treatment with a rotor kiln or the like becomes possible.
Moreover, many heavy metals contained in fly ash can be chlorinated by raising the temperature.
If coal ash is used as a source of mullite, not only can it be obtained at a low cost, but the 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 in which only fly ash is heat-treated at 700 ° C.
FIG. 4 shows an XRD analysis chart in which fly ash + NaOH is heat-treated at 700 ° C.
FIG. 5 shows an XRD analysis chart in which fly ash + mullite is heat-treated at 700 ° C.
FIG. 6 shows a TG / DTA analysis chart after heat treatment of fly ash only.
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 dioxin concentration comparison (measured concentration).
FIG. 10 shows a comparison of dioxin concentrations (toxic equivalent amounts).
FIG. 11 shows the dioxin concentration measurement results before heat treatment of fly ash.
FIG. 12 shows dioxin concentration measurement results after heat treatment of fly ash at 400 ° C.
FIG. 13 shows the measurement results of dioxin concentrations after fly ash 700 ° C. heat treatment.
FIG. 14 shows dioxin concentration measurement results after 700 ° C. heat treatment of fly ash + mullite.
FIG. 15 shows dioxin concentration measurement results after 700 ° C. heat treatment of fly ash + NaOH.
FIG. 16 shows dioxin concentration measurement results after 700 ° C. heat treatment of fly ash + coal ash.
FIG. 17 shows the result of component analysis of coal ash by EDX.

Claims (3)

Harmless incineration fly ash, etc., characterized by mixing mullite with a mass of 0.25 or more to fly ash mass 1 containing harmful organochlorine compounds and heating to 600 ° C or higher to make it harmless Processing method. The method for detoxifying incineration fly ash or the like according to claim 1, wherein the organic chlorine compound is dioxins. The method for detoxifying incineration fly ash and the like according to claim 1, wherein the mullite is obtained from coal ash.

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