JP2004322010A - Decomposition method of dioxins by microwave plasma - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To make a harmful chemical substance harmless without burning the same by efficiently and completely decomposing the substance which is still adhering to solid materials at a site by affecting the decomposition onto the aromatic ring skeleton structure of the harmful chemical substance and which is carried out by using a low energy (a low output and a short time). <P>SOLUTION: The subject method for decomposing the harmful chemical substance contained in the solid material is carried out based on a microwave plasma by using a microwave having a frequency of 1-several GHz and an output of 50-1000 W to irradiate a low-temperature non-equilibrium plasma, particularly an atmosphere consisting of nitrogen gas or an inert gas. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

【００２７】
更に、ＳＥＭ−ＥＤＳ（ＪＥＯＬ ＪＳＭ−６６００）により飛灰の外観や元素含有比を調べた。得られた結果を図４に示す。これらによれば、飛灰の外観や性状には本発明のプラズマ分解処理による有意な変化は認められなかった。又、処理後の飛灰の重量には数％程度の減少が認められたが、これは飛灰中の水分やナトリウムのような低沸点金属が揮発したためと思われる。
【００２８】
【実施例２】
実飛灰への適用
以上の結果を基に、本発明を一般廃棄物焼却施設から排出された飛灰に適用した。
実施例１と同様の装置を使用して、実飛灰１ｇに対して、反応ガスとして窒素ガス（流速：７０ｓｃｃｍ）を用い、圧力１５Ｔｏｒｒに固定し、プラズマを変化させて（マイクロ波出力：１００Ｗ，２５０Ｗ）その分解を追跡した。
所定時間の分解処理後に、飛灰の一部（０．１０ｇ）を採取し、実施例１と同様に測定することによって、ダイオキシン類を定量した。得られた結果を以下の表２に示す。この結果から、実飛灰の処理においては、１００Ｗ、３０分間のプラズマ照射処理では約９８％のダイオキシン類に骨格が分解され、２５０Ｗでは５分間のプラズマ照射処理によってほぼ完全に（９９．９％以上）分解され、更に３０分間処理した場合には、ダイオキシン類は全く検出されず、実飛灰の無害化が達成されることが確認された。
【００２９】
【表２】

【００３０】
【発明の効果】
本発明のマイクロ波プラズマ処理により、飛灰等の固体物質中の有害化学物質、特にダイオキシン類を、低エネルギー（低出力及び短時間）で、その場で効率よく完全に分解することによって、有害化学物質を燃焼させないで無害化することに成功した。更に、処理中のガス温度が比較的低温ですむ為に、処理中の物質の不必要な燃焼、揮発及び溶融、又は処理施設の損傷等が回避されるという効果も達成される。
【図面の簡単な説明】
【図１】本発明装置の基本的な構成の一例を示す。
図中の符号の説明：
１：マイクロ波発振器、
２：マイクロ波導波管、
３：プラズマ反応菅（プラズマ発生菅）、
４：雰囲気（原料ガス）導入菅、
５：スタブチューナー、
６：アイソレーター、
７：パワーモーター、
８：ポンプ、
９：活性炭吸着装置、
１０：液体窒素コールドトラップ装置、
１１：真空ゲージ、
１２：プランジャー、
１３：飛灰、
１４：プラズマ。
【図２】プラズマ分解処理による、３種類のダイオキシン類の基本骨格の分解の様子を示すグラフである。縦軸は各物質の濃度（ｍｇ／ｇ）を示し、横軸は処理時間（分）を示す。
【図３】マイクロ波出力が１００Ｗでプラズマ照射開始３０分後に測定した発光スペクトル（実測スペクトル）を計算値スペクトルと比較によりプラズマ温度を推定した結果を示すグラフである。縦軸は発光強度を示し、横軸は波長（ｎｍ）を示す。
【図４】ＳＥＭ−ＥＤＳにより得られた飛灰の外観や元素含有比の結果を示す。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for decomposing harmful chemical substances in a solid substance, which comprises treating with a non-equilibrium plasma, and a microwave plasma decomposition apparatus used for the method.
[0002]
[Prior art]
Dioxin is known as a very toxic substance, and environmental pollution due to it is very problematic. The Environment Agency added dioxin to designated substances under the Air Pollution Control Law in December 1997, and the regulations on dust and soot in incinerators have been moved forward. In May 1998, WHO strengthened its risk assessment by considering dioxin as an endocrine disrupter, and decided that the daily intake of 10 picograms per kilogram of body weight was 4 picograms.
[0003]
Dioxin contamination was reported in various environments such as air, soil, and seafood, with dioxin being found in diesel exhaust in a survey by the Environment Agency in July 1998. In addition, dioxin is produced as a by-product during the production of trichlorophenol, and in recent years, solid substances such as combustion gas generated by incineration of municipal waste and fly ash collected by dust collectors (fly ash). It became clear that it was included.
[0004]
In particular, it is said that fly ash contains nearly 90% of dioxins generated by incineration of municipal waste and the like. Therefore, an effective and efficient method for detoxifying such harmful substances has been demanded.
[0005]
The main technologies that have been developed so far for detoxifying dioxins and the like in fly ash include (1) heat dechlorination, (2) high-temperature melting and solidification, and (3) microwaves. An irradiation method can be used.
[0006]
The method (1) performs dechlorination from a benzene ring at a high temperature of 1000 ° C. or more, and has the advantages of a simple system and easy introduction into existing facilities, but the benzene ring skeleton itself is decomposed. Therefore, there is a problem that the resynthesis of dioxins is resynthesized in the cooling step after the reaction.
[0007]
On the other hand, the method (2) also decomposes the benzene ring, but this method requires a large amount of energy of a high-temperature treatment at 1500 ° C. or more in a large-scale facility, and therefore has a large environmental load. Since a large amount of cost is required, it is difficult to provide dioxin and the like in all the fly ash that are currently generated. Further, there is a problem that the treatment facility is deteriorated by the corrosive high-temperature atmosphere.
[0008]
Further, the method (3) is, for example, as disclosed in Japanese Patent Application Laid-Open No. 2001-254929 (Patent Document 1). In this method, the benzene ring skeleton can be decomposed in a relatively low-temperature atmosphere, but in principle, when the specific molecules to be decomposed such as dioxin in the irradiated microwave energy absorb the resonance energy of rotation and vibration. Only those whose molecules are broken down. Therefore, as is usually the case, when an inorganic substance or the like other than dioxin or the like coexists in fly ash, there is a problem that the decomposition efficiency is reduced. In addition, in this method, since the treatment is performed in an oxidizing atmosphere, spontaneous combustion of the carbon compound is induced, and as a result, there is a problem that microwave irradiation efficiency is reduced due to unintended high-temperature overheating.
[0009]
Japanese Patent Application Laid-Open No. 2001-190926 (Patent Document 2) discloses a fluid treatment method in which a chemical fluid is subjected to pulse discharge at a frequency of about 1 to 500 KHz and the chemical substance itself is turned into plasma to react the chemical substance. It is disclosed, and dioxin is mentioned as an example of the target substance. However, specific examples are described for the production of ethylene and reformed gas from methane and carbon dioxide, the production of acetylene and hydrogen from methane, and the methane contained in diesel engine incomplete combustion gas. This is only an example relating to the processing of.
[0010]
[Patent Document 1]
Japanese Patent Application Laid-Open No. 2001-254929 [Patent Document 2]
Japanese Patent Application Laid-Open No. 2001-190926
[Problems to be solved by the invention]
As described above, a method for effectively treating harmful chemical substances in solid substances such as fly ash, particularly dioxin, has not yet been obtained. Thus, the present inventor has proposed that by decomposing such a harmful chemical substance efficiently and completely to its aromatic ring skeleton in situ with low energy (low output and short time) while remaining adsorbed on a solid. With the aim of developing a method of detoxifying harmful chemical substances without burning them, the present inventors have made intensive studies on a method using low-temperature non-equilibrium plasma as an exciting medium, particularly microwave plasma, and completed the present invention.
[0012]
[Means for Solving the Problems]
That is, the present invention relates to a method for decomposing harmful chemical substances in a solid substance, comprising treating with a non-equilibrium plasma.
Generally, plasma refers to a state in which almost the same number of positive and negative charged particles that move freely coexist and remains almost neutral electrically. A plasma in which the electron temperature indicated by the electrons is extremely high (about tens of thousands K). Such non-equilibrium plasma can be obtained by any method known to those skilled in the art, such as microwave irradiation of gas, other high-frequency irradiation, and direct current application.
[0013]
In a preferred embodiment of the present invention, microwave plasma is used as the non-equilibrium plasma. This microwave plasma is obtained by irradiating an atmosphere composed of an inert gas such as nitrogen gas or argon with a microwave by a method known to those skilled in the art, but the frequency and output of the microwave are not particularly limited. Absent. Normally, the frequency is 1 to several GHz, for example, 2.45 GHz, and the output is 50 to 1000 W. However, as shown in the examples, the microwave output is 100 to 100 W from the viewpoint of the decomposition effect and the energy efficiency. 250W is more preferred. The processing time by the non-equilibrium plasma is usually 1 to 60 minutes, more preferably 5 to 30 minutes, depending on the frequency and output of the microwave.
[0014]
Furthermore, as a pressure condition for generating a non-equilibrium plasma such as a microwave plasma, it is possible to use a normal pressure, but in that case, it becomes difficult to start the plasma, and the output and current become unstable. In addition, fly ash and the like may be scattered when the plasma is started. Therefore, it is preferable to generate non-equilibrium plasma under reduced pressure, for example, under reduced pressure of 1 to 6 KPa. Further, the flow rate of the gas introduced into the plasma generating section is not particularly limited, but 1 to 1000 sccm is appropriate.
[0015]
In the method of the present invention, the atmosphere temperature during the treatment can be suppressed to 800 ° C. or less, for example, in the range of 700 to 800 ° C., and as a result, unnecessary combustion, volatilization and melting of the substance during the treatment, or the treatment is performed. Facility damage is avoided. The temperature of the plasma gas during the decomposition treatment can be measured by any method known to those skilled in the art, for example, by emission spectrum analysis.
[0016]
Representative examples of the solid substance in the method of the present invention include, but are not limited to, incinerated fly ash such as municipal solid waste, and, for example, various industrial wastes and industrial by-products including harmful chemical substances. Is also included. Other typical solid substances according to the present invention include substances for removing harmful chemical substances such as dioxins, which are adsorbed as a result of removal of harmful chemical substances such as activated carbon.
[0017]
Furthermore, in a preferred embodiment of the present invention, the harmful chemicals in the solid substance include an organic chlorine compound, particularly, a dioxin. “Dioxin” is a general term for (poly) chlorodibenzo-p-dioxin in which a hydrogen atom of dibenzo-p-dioxin is substituted with chlorine, and is known as the most toxic dioxin as a typical compound, There is 3,7,8-tetrachlorodibenzo-p-dioxin (2,3,7,8-TCDD). Other organic chlorine compounds include, for example, (poly) chlorodibenzofuran (PCDF) in which a hydrogen atom of dibenzofuran is substituted by chlorine, polychlorobiphenyl (PCB), and the like. Incidentally, these organic chlorine compounds may be collectively referred to as "dioxins". Since the toxicity equivalent coefficient (TEF) indicating the toxicity of each dioxin compound when the toxicity of 2,3,7,8-TCDD is set to 1, the quantity of dioxins is Based on this, it is represented by a numerical value converted into 2,3,7,8-TCDD, and this is called a toxic equivalent (TEQ).
[0018]
The present invention also relates to a harmful substance decomposition treatment apparatus capable of performing the decomposition method of the present invention described above. As an example of such a decomposition apparatus, a microwave plasma decomposition processing apparatus having a microwave oscillator, a microwave waveguide, a reaction tube (plasma generation tube), and an atmosphere introduction tube can be given.
[0019]
BEST MODE FOR CARRYING OUT THE INVENTION
FIG. 1 shows an example of a basic configuration of the apparatus of the present invention. This is a microwave plasma decomposition apparatus having a microwave oscillator (1), a microwave waveguide (2), a plasma reaction tube (plasma generation tube: 3), an atmosphere (source gas) introduction tube (4), and the like.
Nitrogen gas is introduced from the upper part of a transparent quartz reaction tube having an inner diameter of 48 mm and installed perpendicular to the microwave waveguide, and discharged from the lower part. The pressure inside the building is maintained at a reduced pressure of 15 Torr by a rotary pump. A microwave of 2.45 GHz is guided from a microwave oscillator through a waveguide, and plasma is generated by exciting nitrogen gas in the tube. The input power is calculated from the difference between the incident wave and the reflected wave measured by the power monitor after adjusting the reflected wave to be the minimum.
A durable fly ash sample is placed in a quartz sample container supported by a support rod in the reaction tube. The sample container is covered with a lid to prevent scattering of the sample, but by making a cut in several places on the upper side of the container, a gap is provided between the container and the lid so that the atmosphere inside and outside the container becomes uniform. I do. In addition, the container is rotated at a predetermined rotation speed (for example, 16 rotations per minute) in order to eliminate non-uniformity of contact between the sample and the plasma.
In addition, an adsorber is provided downstream of the plasma reaction tube in order to remove dioxins that may remain in the exhaust gas. As the adsorbent, a dioxin remover and any commercially available preparation, for example, activated carbon pellets can be used.
[0020]
【Example】
Hereinafter, the present invention will be described in more detail with reference to Examples, but the technical scope of the present invention is not limited to these Examples. Unless otherwise specified, the following examples were performed using the above-described apparatus shown in FIG.
[0021]
Embodiment 1
Decomposition of model fly ash In order to examine the effect of the plasma treatment of the method of the present invention on the skeleton of dioxins in fly ash, model ash was prepared as a treatment target as follows. That is, coal fly ash generated in a thermal power plant was used as fly ash. In coal combustion, the amount of dioxins generated is much smaller than in general waste combustion because the chlorine content of the fuel is relatively low. Therefore, only the plasma decomposition of the dioxins added can be tracked. This coal fly ash (1 g) was impregnated with 3 mg of dioxins (dibenzodioxin, dibenzofuran, and biphenyl) in an amount of 2 mg to obtain model ash.
[0022]
With respect to 0.20 g of the model fly ash prepared in this manner, nitrogen gas (flow rate: 70 sccm) was used as a reaction gas, the pressure was fixed at 15 Torr, and the plasma was changed (microwave output: 50 W, 100 W, 250 W). ) The degradation was tracked.
After the decomposition treatment for a predetermined time, a part (0.10 g) of the model fly ash was collected and extracted with an appropriate organic solvent (toluene, diethyl ether, or the like), and the final amount of the extract was adjusted to 10.0 ml.
[0023]
Using an ultraviolet absorption spectrophotometer (JASCO V-550), an ultraviolet absorption spectrum (290 nm for dibenzodioxin and dibenzofuran, and 288 nm for bipheny) specific to three types of dioxins is measured and measured. The remaining amount of each compound was tracked based on the value. The results obtained are shown in FIG. Regarding any of the compounds, in the case of 100 W and 250 W, it is almost completely decomposed by the plasma irradiation treatment for 5 to 10 minutes, and even in the case of 50 W, 90% or more is decomposed by the plasma irradiation treatment for 30 minutes. found.
[0024]
FIG. 3 shows an emission spectrum (actually measured spectrum) measured 30 minutes after the start of plasma irradiation at a microwave output of 100 W, which was compared with a calculated value spectrum to estimate the plasma temperature. The emission spectrum was measured with a multi-channel spectrophotometer (manufactured by JASCO Corporation). The plasma gas temperature during the decomposition treatment measured by the emission spectrum analysis method was about 1700 ° C.
[0025]
Further, the extract was concentrated to a liquid volume of 1 ml, and dioxins were analyzed by GC / MS (SHIMAZU QP-5000) under the conditions shown in Table 1 below. As a result, these compounds are almost completely decomposed by the plasma irradiation treatment of the present invention for 15 to 30 minutes similarly to the analysis results in the ultraviolet absorption spectrum, and further, based on the aromatic compounds and the like expected as decomposition products. No new peak was observed.
Further, the washing solution and the cold trap on the inner wall of the reaction tube were analyzed in the same manner, but no peaks derived from dioxins were detected from them.
From the above, it is considered that the skeleton of the dioxins in the fly ash was completely decomposed, and it was confirmed that in the plasma decomposition treatment of the present invention, the regeneration of the dioxin skeleton in the latter stage of the processing apparatus can be suppressed.
[0026]
[Table 1]

[0027]
Furthermore, the appearance of fly ash and the element content ratio were examined by SEM-EDS (JEOL JSM-6600). FIG. 4 shows the obtained results. According to these, no significant change was observed in the appearance and properties of the fly ash due to the plasma decomposition treatment of the present invention. Further, the weight of the fly ash after the treatment was reduced by about several percent, which is considered to be due to the volatilization of low boiling point metals such as water and sodium in the fly ash.
[0028]
Embodiment 2
Application to actual fly ash Based on the above results, the present invention was applied to fly ash discharged from a general waste incineration facility.
Using the same apparatus as in Example 1, nitrogen gas (flow rate: 70 sccm) was used as a reaction gas for 1 g of actual fly ash, the pressure was fixed at 15 Torr, and the plasma was changed (microwave output: 100 W). , 250 W).
After the decomposition treatment for a predetermined time, a part (0.10 g) of fly ash was collected and measured in the same manner as in Example 1 to quantify dioxins. The results obtained are shown in Table 2 below. From these results, in the treatment of actual fly ash, the skeleton is decomposed into about 98% of dioxins by plasma irradiation at 100 W for 30 minutes, and almost completely (99.9%) by plasma irradiation at 250 W for 5 minutes. Above) When decomposed and further treated for 30 minutes, no dioxins were detected at all, and it was confirmed that detoxification of actual fly ash was achieved.
[0029]
[Table 2]

[0030]
【The invention's effect】
The microwave plasma treatment of the present invention efficiently and completely decomposes harmful chemical substances, especially dioxins, in solid substances such as fly ash with low energy (low output and short time), thereby reducing harmful substances. Successfully detoxified chemical substances without burning them. Further, since the gas temperature during the processing is relatively low, an effect that unnecessary burning, volatilization and melting of the material during the processing, damage to the processing facility, and the like are avoided.
[Brief description of the drawings]
FIG. 1 shows an example of a basic configuration of a device of the present invention.
Explanation of symbols in the figure:
1: microwave oscillator,
2: microwave waveguide,
3: Plasma reaction tube (plasma generating tube)
4: Atmosphere (source gas) introduction tube
5: Stub tuner,
6: isolator,
7: Power motor,
8: Pump,
9: activated carbon adsorption device,
10: liquid nitrogen cold trap device,
11: vacuum gauge,
12: plunger,
13: Fly ash,
14: Plasma.
FIG. 2 is a graph showing how a basic skeleton of three types of dioxins is decomposed by a plasma decomposition process. The vertical axis indicates the concentration (mg / g) of each substance, and the horizontal axis indicates the processing time (minute).
FIG. 3 is a graph showing a result of estimating a plasma temperature by comparing an emission spectrum (actually measured spectrum) measured 30 minutes after the start of plasma irradiation with a microwave output of 100 W with a calculated value spectrum. The vertical axis indicates the emission intensity, and the horizontal axis indicates the wavelength (nm).
FIG. 4 shows the results of the appearance and element content of fly ash obtained by SEM-EDS.

Claims (16)

A method for decomposing harmful chemicals in a solid material, comprising treating with a non-equilibrium plasma. The decomposition method according to claim 1, wherein microwave plasma is used as the non-equilibrium plasma. 2. The microwave plasma is obtained by irradiating an atmosphere made of nitrogen gas or an inert gas with a microwave having a frequency of 1 to several GHz and an output of 50 to 1000 W. Or the decomposition method according to 2. The decomposition method according to claim 3, wherein the frequency of the microwave is 2.45 GHz. The decomposition method according to claim 3, wherein an output of the microwave is 100 to 250W. The decomposition method according to any one of claims 1 to 5, wherein the treatment time is 1 to 60 minutes. The decomposition method according to claim 6, wherein the processing time is 5 to 30 minutes. The decomposition method according to any one of claims 1 to 7, wherein the treatment is performed under a reduced pressure of 1 to 6 KPa. The decomposition method according to any one of claims 1 to 8, wherein a gas having a flow rate of 1 to 1000 sccm is introduced into the plasma generation unit. The decomposition method according to any one of claims 1 to 9, wherein the atmosphere temperature during the treatment is 800 ° C or lower. The decomposition method according to any one of claims 1 to 10, wherein the solid substance is fly ash. The decomposition method according to any one of claims 1 to 10, wherein the solid substance is a removal substance on which a harmful chemical substance is adsorbed. The decomposition method according to any one of claims 1 to 12, wherein the harmful chemical substance in the solid substance includes an organic chlorine compound. The decomposition method according to claim 13, wherein the organic chlorine compound contains dioxin. An apparatus for decomposing harmful chemicals, capable of performing the decomposition method according to any one of claims 1 to 14. A microwave plasma decomposition processing apparatus having a microwave oscillator, a microwave waveguide, a plasma reaction tube (plasma generation tube), and an atmosphere introduction tube.

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