JP2006218405A - Method and apparatus for treating waste liquid containing hardly decomposable hazardous substance and nitrogen compound - Google Patents
Method and apparatus for treating waste liquid containing hardly decomposable hazardous substance and nitrogen compound Download PDFInfo
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Abstract
Description
本発明は、PCB(ポリ塩素化ビフェニル)やダイオキシンに代表される難分解性有害物質と窒素化合物の両方を含む廃液の処理方法および装置に関し、とくに、窒素化合物からの硝酸生成を抑制しつつ、難分解性有害物質を効率よく分解処理できるようにした、難分解性有害物質および窒素化合物を含む廃液の処理方法および装置に関する。 The present invention relates to a treatment method and apparatus for waste liquid containing both a hardly decomposable hazardous substance represented by PCB (polychlorinated biphenyl) and dioxin and a nitrogen compound, and in particular, while suppressing nitric acid production from the nitrogen compound, The present invention relates to a method and an apparatus for treating a waste liquid containing a hardly decomposable hazardous substance and a nitrogen compound, which can efficiently decompose the hardly decomposable harmful substance.
近年、高温高圧水、とくに超臨界水の存在下での水熱酸化反応を利用して、環境汚染物質等を分解、無害化する試みが注目されている。とくに、超臨界水の高い反応性を利用した超臨界水酸化により、従来技術では分解することが難しかった有害な難分解性の有機物、例えば、PCB、ダイオキシン、有機塩素系有機物等を分解して、二酸化炭素、水、無機塩などの無害な生成物に転化する試みが注目されている。この超臨界水とは、超臨界状態にある水、すなわち、水の臨界点を越えた状態にある水を言い、詳しくは、374.1℃以上の温度で、かつ22.04MPa以上の圧力下にある状態の水を言う。超臨界水は、有機物を溶解する溶解能が高く、有機化合物に多い非極性物質をも完全に溶解することができる一方、逆に、金属、塩等の無機物に対する溶解能は著しく低い。また、超臨界水は、空気や酸素、窒素などの気体と任意の割合で混合して単一相を構成することができる。 In recent years, attention has been paid to attempts to decompose and detoxify environmental pollutants using a hydrothermal oxidation reaction in the presence of high-temperature and high-pressure water, particularly supercritical water. In particular, supercritical water oxidation utilizing the high reactivity of supercritical water decomposes harmful and hardly decomposable organic substances, such as PCB, dioxin, and organic chlorinated organic substances, which were difficult to be decomposed by the prior art. Attempts to convert to harmless products such as carbon dioxide, water and inorganic salts are drawing attention. The supercritical water means water in a supercritical state, that is, water in a state exceeding the critical point of water. Specifically, it is at a temperature of 374.1 ° C. or higher and under a pressure of 22.04 MPa or higher. Says water in a state. Supercritical water has a high ability to dissolve organic substances, and can completely dissolve non-polar substances that are abundant in organic compounds. Conversely, the ability to dissolve inorganic substances such as metals and salts is extremely low. Supercritical water can be mixed with a gas such as air, oxygen, or nitrogen at an arbitrary ratio to form a single phase.
このような有機物の超臨界水酸化において、酸化剤を空気や酸素として窒素化合物を処理する場合において、反応温度が高いと硝酸が生成し、装置腐食が懸念される。そのため、反応温度を580〜620℃として硝酸の生成を抑制する手段が特許文献1に開示されている。 In such supercritical water oxidation of organic matter, when a nitrogen compound is treated using air or oxygen as an oxidant, nitric acid is generated at a high reaction temperature, and there is a concern about apparatus corrosion. Therefore, Patent Document 1 discloses means for suppressing the production of nitric acid by setting the reaction temperature to 580 to 620 ° C.
一方、PCBやダイオキシンに代表される難分解性有害物質を超臨界水酸化処理するに当たっては、超臨界水酸化の利点である反応速度の速さを生かしつつ、確実な処理を行うため、反応温度630℃程度で処理されている事例がある(非特許文献1)。
しかし、難分解性有害物質が混入した窒素化合物を含有する廃液を超臨界水酸化処理するに当たって、難分解性有害物質を確実に処理するために反応温度を630℃程度にすると、窒素化合物由来の硝酸が生成し、装置腐食を引き起こす恐れがある。この場合、耐食性を持たせるような構造、材料を採用することで、装置腐食を抑制できる場合もあるが、そうすると、設備費が嵩むという問題を招く。さらに、設備費が嵩むことを許容した場合でも、生成した硝酸を処理しなければならないという問題は残る。一方、硝酸生成を抑制するために反応温度を低くすると、未分解の難分解性有害物質が残存してしまうという問題が生じる。 However, when supercritical water oxidation treatment is performed on a waste liquid containing nitrogen compounds mixed with hardly decomposable harmful substances, if the reaction temperature is set to about 630 ° C. in order to reliably treat the hardly decomposable harmful substances, the nitrogen compound-derived Nitric acid may be generated, causing equipment corrosion. In this case, the corrosion of the apparatus may be suppressed by adopting a structure and material that give corrosion resistance, but this causes a problem that the equipment cost increases. Further, even when the equipment cost is allowed to increase, the problem that the generated nitric acid must be processed remains. On the other hand, if the reaction temperature is lowered in order to suppress nitric acid production, there arises a problem that undecomposed and hardly decomposable harmful substances remain.
そこで本発明の課題は、難分解性有害物質と窒素化合物の両方を含む廃液を処理するに際し、窒素化合物由来の硝酸の生成を抑制しつつ、難分解性有害物質を効率よく分解処理できるようにした廃液の処理方法および装置を提供することにある。 Accordingly, an object of the present invention is to efficiently decompose a hardly decomposable harmful substance while suppressing the production of nitric acid derived from the nitrogen compound when treating a waste liquid containing both the hardly decomposable harmful substance and the nitrogen compound. It is an object of the present invention to provide a method and apparatus for treating the waste liquid.
上記課題を解決するために、本発明完成に至る経過で、まず、高温での超臨界水酸化反応において硝酸生成を抑制する方法がないかを検討した。これまでの超臨界水酸化における空気酸化の結果では、高濃度、すなわち高発熱量の廃液を処理しているため、測定部の温度は600℃前後であるが、反応中心部の温度は発熱反応によって測定温度よりも高温であることが予想された。そこで、反応中心部温度の影響を検討するため、最終的な制御温度は630℃で一定として、処理対象廃液の発熱量を変更して実験を行なったところ、表1のような結果が得られた。 In order to solve the above problems, in the course of completing the present invention, first, it was examined whether there is a method for suppressing nitric acid production in a supercritical water oxidation reaction at a high temperature. As a result of air oxidation in supercritical water oxidation so far, waste liquid with high concentration, that is, high calorific value, is treated, so the temperature of the measuring part is around 600 ° C, but the temperature of the reaction center is exothermic reaction. It was expected that the temperature was higher than the measured temperature. Therefore, in order to examine the influence of the reaction center temperature, the final control temperature was constant at 630 ° C., and the experiment was performed by changing the heat generation amount of the waste liquid to be treated. The results shown in Table 1 were obtained. It was.
表1において、反応中心部想定到達温度とは、400℃から超臨界水酸化反応が開始し、全量が酸化した時の発熱量により到達する流体温度である。表1からは、発熱量と反応中心部想定到達温度の関係も分かる。このように、廃液の発熱量が異なることにより、硝酸転換率が大きく変わることが確認された。その結果、反応中心部の到達温度が高温であることが硝酸生成に影響しているものと考えられた。 In Table 1, the reaction center assumed temperature is the fluid temperature reached by the amount of heat generated when the supercritical water oxidation reaction starts at 400 ° C. and the entire amount is oxidized. Table 1 also shows the relationship between the amount of heat generated and the expected reaction center temperature. As described above, it was confirmed that the nitric acid conversion rate greatly changed due to the different calorific value of the waste liquid. As a result, it was considered that the temperature reached at the reaction center was high, affecting the nitric acid production.
ここで、上記の各実験において最終的な到達温度は630℃となっており、硝酸が生成していた実験番号1−2の反応中心部想定到達温度より高いにも関わらず、実験番号1−1では実質的に硝酸が生成していない。この原因として、以下のように考えられた。
(1)一般的なTOC(全有機体炭素)成分は、比較的速やかに反応が起こるため、反応中心部想定到達温度にてほぼ消失するが、窒素化合物については当該温度が低いと残存するものがある。
(2)高温での窒素化合物の単独反応ではなく、窒素化合物とTOC成分との複合反応により硝酸が生成する。
そこで、共存するTOC成分が硝酸生成に影響があるか否かを確認するために、TOC/TN(全窒素)モル比を変更して実験を行なったところ、表2のような結果が得られた。
Here, in each of the experiments described above, the final reached temperature was 630 ° C., and although it was higher than the expected reaction center portion reached temperature in Experiment No. 1-2 where nitric acid was generated, Experiment No. 1- In 1, no nitric acid was substantially generated. This was considered as follows.
(1) The general TOC (total organic carbon) component disappears at the reaction center expected temperature because the reaction occurs relatively quickly, but the nitrogen compound remains when the temperature is low. There is.
(2) Nitric acid is generated not by a single reaction of the nitrogen compound at a high temperature but by a combined reaction of the nitrogen compound and the TOC component.
Therefore, in order to confirm whether or not the coexisting TOC component has an influence on the nitric acid production, an experiment was conducted by changing the TOC / TN (total nitrogen) molar ratio, and the results shown in Table 2 were obtained. It was.
表2に示すように、前述の硝酸が生成したような反応中心部想定到達温度以上であるにも関わらず、TOC/TNモル比(C/Nモル比)が低い実験番号2−1から2−3では実質的に硝酸が生成しておらず、硝酸生成にはTOC成分の存在が関与していることが確認できた。 As shown in Table 2, the experiment numbers 2-1 to 2 having a low TOC / TN molar ratio (C / N molar ratio) despite the above-described reaction center temperature reaching the temperature at which the nitric acid was generated as described above. In -3, nitric acid was not substantially produced, and it was confirmed that the presence of the TOC component was involved in the nitric acid production.
以上の結果より、超臨界水酸化反応における窒素化合物からの硝酸生成は、以下の要件が重なっている時に起こるという結論が導き出された。
(1)窒素化合物存在下で、有機体炭素が多量に存在する。
(2)温度が高温である。
つまり、温度が高温であっても、有機体炭素が微量しか存在しなければ、硝酸は生成しない。一方、有機体炭素と窒素化合物を比べると、一般的には有機体炭素の方が中間温度域(難分解性有害物質分解必要温度に至らない温度条件)で酸化されやすい。したがって、一旦中間温度での水熱酸化反応により有機体炭素を低減した状態で、残存する難分解性有害物質を高温にて超臨界水酸化することにより、難分解性有害物質を完全分解できるとともに硝酸生成を抑制することが可能となることを突き止め、本発明を完成するに至った。
From the above results, it was concluded that nitric acid generation from nitrogen compounds in the supercritical water oxidation reaction occurs when the following requirements overlap.
(1) A large amount of organic carbon exists in the presence of a nitrogen compound.
(2) The temperature is high.
That is, even if the temperature is high, nitric acid is not generated if only a small amount of organic carbon is present. On the other hand, when organic carbon and nitrogen compounds are compared, in general, organic carbon is more likely to be oxidized in an intermediate temperature range (temperature condition that does not reach the temperature required to decompose hardly decomposable harmful substances). Therefore, once the organic carbon is reduced by the hydrothermal oxidation reaction at an intermediate temperature, the remaining hardly decomposed harmful substance can be completely decomposed by supercritical water oxidation at high temperature. Ascertaining that it is possible to suppress the production of nitric acid, the present invention has been completed.
すなわち、本発明に係る難分解性有害物質および窒素化合物を含有する廃液の処理方法は、難分解性有害物質分解必要温度には至らない中間温度で所定時間水熱酸化反応を行わせた後に、難分解性有害物質分解必要温度で超臨界水酸化反応を行わせることを特徴とする方法からなる。 That is, according to the present invention, a method for treating a waste liquid containing a hardly decomposable harmful substance and a nitrogen compound is used after performing a hydrothermal oxidation reaction for a predetermined time at an intermediate temperature that does not reach the temperature required for decomposing a hardly decomposable harmful substance. It comprises a method characterized in that a supercritical water oxidation reaction is carried out at a temperature required to decompose a hardly decomposable harmful substance.
この廃液の処理方法においては、反応による発熱と装置からの放熱のバランスをとることにより、前記中間温度に所定時間保つことが可能である。この中間温度としては、350℃〜550℃の範囲にあることが好ましい。 In this waste liquid treatment method, the intermediate temperature can be maintained for a predetermined time by balancing the heat generated by the reaction and the heat released from the apparatus. The intermediate temperature is preferably in the range of 350 ° C to 550 ° C.
また、上記所定時間は、上記中間温度で廃液中の有機体炭素の大部分を酸化するに十分な時間であることが好ましい。この所定時間としては、3秒以上であることが好ましい。すなわち、反応を伴わないで水および空気のみを加熱している場合には、350℃から550℃まで加熱するには効率的に行なっても5秒程度かかる。しかし、同一の加熱方法でも、廃液および空気を加熱している場合は、廃液中の有機物が急激に反応開始する温度(急激反応開始温度、例えば400℃)があり、この時の反応熱によって温度がより短時間で上昇する。発熱量が高い場合には、装置からの放熱に比べて反応による発熱が大きくなり、急激反応開始温度からわずか2秒程度でも550℃以上まで温度が急上昇する。したがって、廃液供給時に、急激反応開始温度より低い温度領域内で温度保持することで、急激反応を行なわせず、徐々に有機物の反応を進行させる必要がある。このような反応の時には、反応による発熱と装置からの放熱のバランスがとりやすく、温度の急上昇を抑制することができるとともに、TOC成分の低減を図ることができる。この温度域や必要保持時間は廃液の反応性や濃度によって異なるが、温度域は概ね350℃から550℃の間にあり、当該温度域でのTOC成分の低減には、概ね3秒以上を必要とする。もっとも、廃液の反応性が高い場合には温度域は低くなり、廃液の濃度が高い場合には、必要保持時間が長くなる。 The predetermined time is preferably a time sufficient for oxidizing most of the organic carbon in the waste liquid at the intermediate temperature. The predetermined time is preferably 3 seconds or longer. That is, when only water and air are heated without a reaction, heating from 350 ° C. to 550 ° C. takes about 5 seconds even if it is performed efficiently. However, even in the same heating method, when the waste liquid and air are heated, there is a temperature at which the organic matter in the waste liquid starts to react rapidly (rapid reaction start temperature, for example, 400 ° C.). Rises in a shorter time. When the calorific value is high, the heat generated by the reaction is larger than the heat released from the apparatus, and the temperature rapidly rises to 550 ° C. or more even in about 2 seconds from the rapid reaction start temperature. Therefore, when the waste liquid is supplied, it is necessary to keep the temperature within a temperature range lower than the rapid reaction start temperature, so that the reaction of organic matter is gradually advanced without performing the rapid reaction. At the time of such a reaction, it is easy to balance the heat generated by the reaction and the heat released from the apparatus, so that a rapid rise in temperature can be suppressed and the TOC component can be reduced. Although this temperature range and required retention time vary depending on the reactivity and concentration of the waste liquid, the temperature range is generally between 350 ° C and 550 ° C, and it takes approximately 3 seconds or more to reduce the TOC component in that temperature range. And However, when the reactivity of the waste liquid is high, the temperature range is low, and when the concentration of the waste liquid is high, the necessary holding time is long.
上記難分解性有害物質分解必要温度としては、600℃以上であることが好ましい。 The temperature required for decomposition of the hardly decomposable harmful substance is preferably 600 ° C. or higher.
本発明に係る難分解性有害物質および窒素化合物を含有する廃液の処理装置は、難分解性有害物質分解必要温度には至らない中間温度で所定時間水熱酸化反応を行わせる手段と、該水熱酸化反応後に、難分解性有害物質分解必要温度で超臨界水酸化反応を行わせる手段とを有することを特徴とするものからなる。 The apparatus for treating a waste liquid containing a hardly decomposable hazardous substance and a nitrogen compound according to the present invention comprises a means for performing a hydrothermal oxidation reaction for a predetermined time at an intermediate temperature that does not reach the required decomposition temperature of the hardly decomposable harmful substance, And a means for performing a supercritical water oxidation reaction at a temperature required for decomposition of a hardly decomposable hazardous substance after the thermal oxidation reaction.
この廃液の処理装置においては、後述の実施態様に示すように、廃液の流れ方向に、それぞれ独立して温度調節できる第1予熱器、中間反応器、第2予熱器、高温反応器の順に設けられている構成とすることができる。また、第1予熱器および中間反応器をまとめて中間温度用ベッセル反応器として構成することもできる。さらに、装置起動時には、この第2予熱器、中間温度用ベッセル反応器、高温反応器の順に廃液が流通されるようにして、付帯設備の削減を図ることができる。 In this waste liquid treatment apparatus, as shown in an embodiment described later, a first preheater, an intermediate reactor, a second preheater, and a high temperature reactor, each of which can be independently adjusted in temperature in the flow direction of the waste liquid, are provided in this order. It can be set as the structure currently provided. In addition, the first preheater and the intermediate reactor can be collectively configured as a Bessel reactor for intermediate temperature. Further, when the apparatus is started up, the waste liquid can be circulated in the order of the second preheater, the intermediate temperature vessel reactor, and the high temperature reactor, thereby reducing the incidental facilities.
本発明に係る難分解性有害物質および窒素化合物を含有する廃液の処理方法および装置によれば、中間温度で所定時間、水熱酸化反応を行わせた後に、高温で超臨界水酸化反応を行わせるようにしたので、難分解性有害物質を完全に分解できるとともに、硝酸生成を抑制することで、装置の腐食を抑制することができ、設備費の低減を図ることができる。また、有機体炭素濃度が高い場合にも、設備費、運転費を下げることが可能となる。 According to the method and apparatus for treating a waste liquid containing a hardly decomposable hazardous substance and a nitrogen compound according to the present invention, after a hydrothermal oxidation reaction is performed at an intermediate temperature for a predetermined time, a supercritical water oxidation reaction is performed at a high temperature. Thus, the hardly decomposable harmful substance can be completely decomposed, and the production of nitric acid can be suppressed, whereby the corrosion of the apparatus can be suppressed and the equipment cost can be reduced. In addition, even when the organic carbon concentration is high, the facility cost and the operating cost can be reduced.
以下に、本発明について、望ましい実施の形態とともに、詳細に説明する。
前述したように、従来の水熱反応装置では、反応器が一つの温度で制御されており、窒素化合物及び難分解性有害物質を含む廃液を処理する場合には、どちらか一方に適した温度とするしかなく、硝酸生成または難分解性有害物質の残存が起こっていた。例えば従来の水熱反応装置は、図5に示すように、酸化剤(例えば、空気)とともに供給されてきた被処理液(廃液)を反応温度まで昇温する予熱器101、反応温度にて所定時間保持するための反応器102で構成されている。図示しないが、当該装置には廃液や酸化剤の供給装置、処理済流体の冷却器や減圧弁等が付帯する。本装置構成では、反応温度の制御は1点のみであり、反応温度を高くすると硝酸が生成し、反応温度を低くすると難分解性有害物質が残存するという問題があった。
Hereinafter, the present invention will be described in detail together with preferred embodiments.
As described above, in a conventional hydrothermal reactor, the reactor is controlled at a single temperature, and when processing waste liquid containing nitrogen compounds and persistent decomposable substances, a temperature suitable for either one is used. However, nitric acid formation or persistent decomposable harmful substances had occurred. For example, as shown in FIG. 5, a conventional hydrothermal reaction apparatus has a preheater 101 that raises the liquid to be treated (waste liquid) supplied together with an oxidant (for example, air) to a reaction temperature, and a predetermined temperature at the reaction temperature. It consists of a reactor 102 for holding time. Although not shown, the apparatus is provided with a waste liquid and oxidant supply device, a cooler for a treated fluid, a pressure reducing valve, and the like. In this apparatus configuration, there is only one point of control of the reaction temperature, and there is a problem that nitric acid is generated when the reaction temperature is raised, and hardly decomposable harmful substances remain when the reaction temperature is lowered.
しかし、反応温度を下げると硝酸生成が抑制できるということに加えて、温度が高くとも有機体炭素の共存がなければ硝酸生成が抑制できるという新たな知見を発見した。その結果、一旦中間温度での水熱酸化反応により有機体炭素を低減した状態で、残存する難分解性有害物質を高温にて超臨界水酸化することにより、難分解性有害物質を完全分解するとともに硝酸生成を抑制可能であることが見出された。 However, in addition to being able to suppress nitric acid generation when the reaction temperature is lowered, we have discovered new findings that nitric acid generation can be suppressed if organic carbon does not coexist even at high temperatures. As a result, once the organic carbon is reduced by a hydrothermal oxidation reaction at an intermediate temperature, the remaining hardly decomposable hazardous substance is supercritically hydroxylated at a high temperature to completely decompose the hardly decomposable harmful substance. At the same time, it was found that nitric acid production can be suppressed.
そこで、本発明においては、硝酸生成を抑制するために、中間温度で所定時間、水熱酸化反応を行わせた後に、高温で超臨界水酸化反応を行わせる方法を採用した。従来法と本発明の方法の比較を行なうと、反応器各部位での温度分布(温度の推移)とTOC残存率は概ね図1(本発明方法)および図2(従来方法)のようになっているものと推定される。つまり、従来法では硝酸生成速度が大きくなる温度域(2点鎖線より上方)に到達した時点において、TOC残存率が高い(図2)が、本発明の方法では当該温度域において、TOC残存率が低い(図1)。したがって、本発明の方法によれば、高温状態での有機体炭素と窒素化合物の共存がなくなり、硝酸生成を抑制できる。なお、図1、図2において、装置内累積時間とは、被処理液としての廃液が装置内に供給された後の、装置内に存在していた時間の累積値を示している。 Therefore, in the present invention, in order to suppress the production of nitric acid, a method is adopted in which a hydrothermal oxidation reaction is performed at an intermediate temperature for a predetermined time and then a supercritical water oxidation reaction is performed at a high temperature. When the conventional method and the method of the present invention are compared, the temperature distribution (temperature transition) and the TOC residual ratio at each part of the reactor are as shown in FIG. 1 (method of the present invention) and FIG. 2 (conventional method). It is estimated that That is, in the conventional method, the TOC residual rate is high when reaching the temperature range (above the two-dot chain line) where the nitric acid production rate increases (FIG. 2), but in the method of the present invention, the TOC residual rate in the temperature range. Is low (FIG. 1). Therefore, according to the method of the present invention, there is no coexistence of organic carbon and a nitrogen compound at a high temperature, and nitric acid production can be suppressed. 1 and 2, the accumulated time in the apparatus indicates an accumulated value of the time that has existed in the apparatus after the waste liquid as the liquid to be treated is supplied into the apparatus.
窒素化合物を含有する廃液を超臨界水酸化処理した場合の結果の例を従来法と比較して表3に示す。中間での反応温度保持の有無以外、廃液性状や最終反応温度および最終反応温度での反応時間は同一である。この例に係る従来方法では、難分解性有害物質の完全分解を目的に630℃で処理しており、硝酸が生成した結果、処理水pHが低下し、装置腐食の懸念があった。しかし、本発明の方法では、最終的な超界水酸化温度は同一であるが、硝酸生成は抑制され、若干のpH低下はあるものの、装置腐食に関しては許容範囲内であった。 Table 3 shows an example of the results when supercritical water oxidation treatment is performed on a waste liquid containing a nitrogen compound in comparison with the conventional method. Except for the presence or absence of intermediate reaction temperature, the waste liquid properties, the final reaction temperature, and the reaction time at the final reaction temperature are the same. In the conventional method according to this example, the treatment is performed at 630 ° C. for the purpose of complete decomposition of the hardly decomposable harmful substance. As a result of the formation of nitric acid, the pH of the treated water is lowered, and there is a concern about the corrosion of the apparatus. However, in the method of the present invention, although the final supercritical water oxidation temperature is the same, nitric acid production is suppressed and there is a slight pH drop, but the apparatus corrosion is within an acceptable range.
上記実施例では、中間保持反応温度を385℃(設定温度であり、反応熱によりこの設定温度以上に上昇することもある)、中間保持反応時間を5秒としたが、中間温度でより反応が起こり易い有機体炭素を含有しており、かつ中間保持反応温度が高い場合や、有機体炭素の濃度が高い場合には、反応熱による温度上昇が装置からの放熱量以上となることもある。このような場合、中間保持反応温度を一定範囲内の温度に保持することが困難となり、温度上昇により硝酸が生成することがあるため、保持反応温度を低くする必要がある。中間保持反応温度はこのように廃液中の物質により異なるが、概ね350℃から550℃程度の範囲に入る。 In the above examples, the intermediate holding reaction temperature was 385 ° C. (set temperature, which may be raised to the set temperature or higher by reaction heat), and the intermediate holding reaction time was 5 seconds. When organic carbon that tends to occur is present and the intermediate holding reaction temperature is high, or when the concentration of organic carbon is high, the temperature rise due to reaction heat may exceed the amount of heat released from the apparatus. In such a case, it is difficult to maintain the intermediate holding reaction temperature at a temperature within a certain range, and nitric acid may be generated due to the temperature rise, so the holding reaction temperature needs to be lowered. The intermediate holding reaction temperature thus varies depending on the substance in the waste liquid, but generally falls within the range of about 350 ° C to 550 ° C.
また、廃液中のTOC濃度が高い場合には、中間保持反応温度にて有機体炭素濃度を十分に低くするために、中間保持反応時間を長くすることが必要となる。保持反応時間はこのように液中のTOC濃度に依存するが、一般的には前述の如く3秒以上確保することが好ましい。 When the TOC concentration in the waste liquid is high, it is necessary to lengthen the intermediate holding reaction time in order to sufficiently reduce the organic carbon concentration at the intermediate holding reaction temperature. Although the holding reaction time depends on the TOC concentration in the liquid as described above, it is generally preferable to secure 3 seconds or more as described above.
また、装置についてみるに、従来の水熱反応装置は、例えば図5に示すように、酸化剤(例えば、空気)とともに供給されてきた被処理液(廃液)を反応温度まで昇温する予熱器101、反応温度にて所定時間保持するための反応器102で構成されている。TICAは温度センサあるいは温度コントローラを示している。図示しないが、当該装置には廃液や酸化剤の供給装置、処理済流体の冷却器や減圧弁等が付帯する。本装置構成では、反応温度の制御は1点のみであり、反応温度を高くすると硝酸が生成し、反応温度を低くすると難分解性有害物質が残存するという問題があった。 As for the apparatus, a conventional hydrothermal reaction apparatus is, as shown in FIG. 5, for example, a preheater that raises the liquid to be treated (waste liquid) supplied together with an oxidizing agent (for example, air) to the reaction temperature. 101. It is comprised with the reactor 102 for hold | maintaining for predetermined time at reaction temperature. TICA indicates a temperature sensor or a temperature controller. Although not shown, the apparatus is provided with a waste liquid and oxidant supply device, a cooler for a treated fluid, a pressure reducing valve, and the like. In this apparatus configuration, there is only one point of control of the reaction temperature, and there is a problem that nitric acid is generated when the reaction temperature is raised, and hardly decomposable harmful substances remain when the reaction temperature is lowered.
これに対して、本発明の一実施態様に係る処理装置では、例えば図3に示すように、第1予熱器1、中間反応器2、第2予熱器3、高温反応器4で構成される。第1予熱器1で中間反応器2における反応温度まで昇温し、中間反応器2で大部分の有機体炭素を酸化する。次いで、第2予熱器3で高温反応器4における反応温度まで昇温し、高温反応器4で難分解性有害物質を分解することで、硝酸の生成も難分解性有害物質の残存も抑制することが可能となる。つまり、第1予熱器1と中間反応器2とで、とくに中間反応器2により、本発明における、難分解性有害物質分解必要温度には至らない中間温度で所定時間水熱酸化反応を行わせる手段が構成され、第2予熱器3と高温反応器4とで、とくに高温反応器4により、本発明における、前記水熱酸化反応後に、難分解性有害物質分解必要温度で超臨界水酸化反応を行わせる手段が構成される。図3では各予熱器1、3および各反応器2、4から構成されているが、中間反応温度の範囲内に、所定時間、温度を保持できるのであれば、これに限定されるものではなく、予熱器、反応器を1つずつとし、外部加熱量や被処理液供給量を調整することで、予熱器において所定時間当該温度を保持できるよう温度を制御させてもよい。また、図3では各予熱器1、3および各反応器2、4はチューブ型として示されているが、これに限定されるものではなく、予熱器や反応器にベッセル反応器を使用することもできる。また、各反応器において、反応温度が保持できるのであれば、保温だけを施し、ヒーターはなくてもよい。あるいは、図5に示す従来の装置において、予熱器部分に1個以上の温度センサーあるいは温度コントローラを設置して、中間反応温度上昇時に積極的に放熱、除熱、冷却を行うことで、中間反応温度を保持してもよい。また、予熱器内での反応開始に伴う温度上昇を抑え、予熱器内で中間温度域を保持するために、当該部分に、積極的に放熱、除熱、冷却を行う機構を設置してもよい。 On the other hand, the processing apparatus according to an embodiment of the present invention includes a first preheater 1, an intermediate reactor 2, a second preheater 3, and a high temperature reactor 4, for example, as shown in FIG. . The first preheater 1 raises the temperature to the reaction temperature in the intermediate reactor 2, and most of the organic carbon is oxidized in the intermediate reactor 2. Next, the temperature is raised to the reaction temperature in the high temperature reactor 4 by the second preheater 3, and the high temperature reactor 4 decomposes the hardly decomposable harmful substance, thereby suppressing the generation of nitric acid and the remaining of the hardly decomposable harmful substance. It becomes possible. That is, in the first preheater 1 and the intermediate reactor 2, in particular, the intermediate reactor 2 causes the hydrothermal oxidation reaction to be performed for a predetermined time at an intermediate temperature that does not reach the required decomposition temperature of the hardly decomposable hazardous substance in the present invention. Means, and the second preheater 3 and the high temperature reactor 4, particularly the high temperature reactor 4, after the hydrothermal oxidation reaction in the present invention, the supercritical hydroxylation reaction at the temperature required for decomposition of the hardly decomposable hazardous substance. The means to perform is comprised. In FIG. 3, each of the preheaters 1 and 3 and each of the reactors 2 and 4 is configured, but is not limited to this as long as the temperature can be maintained for a predetermined time within the range of the intermediate reaction temperature. The temperature may be controlled so that the preheater can hold the temperature for a predetermined time by using one preheater and one reactor and adjusting the amount of external heating and the amount of liquid to be processed. Moreover, in FIG. 3, although each preheater 1, 3 and each reactor 2, 4 are shown as a tube type, it is not limited to this, Use a Bessel reactor for a preheater or a reactor. You can also. Further, in each reactor, as long as the reaction temperature can be maintained, only the heat retention is performed, and the heater may not be provided. Alternatively, in the conventional apparatus shown in FIG. 5, one or more temperature sensors or temperature controllers are installed in the preheater portion, and when the intermediate reaction temperature rises, heat is dissipated, heat is removed, and cooling is performed. The temperature may be maintained. In addition, in order to suppress the temperature rise associated with the start of the reaction in the preheater and maintain the intermediate temperature range in the preheater, a mechanism that actively dissipates heat, removes heat, and cools may be installed in that part. Good.
有機物濃度が高く、廃液の持つ酸化反応熱が極端に高いような廃液を処理する場合に、中間温度で大部分の有機体炭素を分解させるために図3に示す装置を採用すると、第1予熱器1が大きくなる。このような場合、本発明の別の実施態様に係る装置として、例えば図4に示す装置が適している。図4に示した装置は、図3における第1予熱器および中間反応器をなくし、これらをまとめて中間温度用ベッセル反応器11とし、その後段に第2予熱器12、高温反応器13を順に接続したものである。ここでのベッセル反応器11は、廃液の持つ酸化反応熱を利用して反応温度を保持するベッセル反応器(例えば、特開平10-314768号公報に示されているようなもの)であり、運転中には超臨界水を供給せず、加熱も行わないことが好ましい。このタイプの反応器では、装置起動時に反応器内を超臨界状態とした後は、廃液のもつ酸化反応のエネルギーを利用することにより、廃液を常温で供給しても、反応器内を中間温度(大部分の有機体炭素が酸化する温度)に保持することができる。具体的な温度保持方法としては、例えば、中間温度用ベッセル反応器の温度を検出して、廃液の供給量を調節する方法がある。本法では、温度が高い場合には廃液の流量を減らし、温度が低い場合には廃液の流量を増やすことで反応器内に入る総発熱量を調整し、発熱量と放熱量のバランスを取ることで温度保持が可能となる。したがって、運転中は中間温度用ベッセル反応器11の加熱も不要となるため、設備費、運転費とも低減が図れるという利点がある。 If the apparatus shown in FIG. 3 is used to decompose most organic carbon at an intermediate temperature when treating a waste liquid having a high organic matter concentration and an extremely high oxidation reaction heat, the first preheating is performed. The vessel 1 becomes larger. In such a case, for example, the apparatus shown in FIG. 4 is suitable as an apparatus according to another embodiment of the present invention. The apparatus shown in FIG. 4 eliminates the first preheater and the intermediate reactor in FIG. 3 and combines them into an intermediate temperature vessel reactor 11, followed by a second preheater 12 and a high temperature reactor 13 in that order. Connected. The vessel reactor 11 here is a vessel reactor (for example, as shown in Japanese Patent Laid-Open No. 10-314768) that maintains the reaction temperature by utilizing the oxidation reaction heat of the waste liquid. It is preferable that supercritical water is not supplied and heating is not performed. In this type of reactor, after the inside of the reactor is brought into a supercritical state at the time of starting up the apparatus, even if the waste liquid is supplied at room temperature by using the energy of the oxidation reaction of the waste liquid, the reactor is kept at an intermediate temperature. (Temperature at which most organic carbon is oxidized). As a specific temperature maintaining method, for example, there is a method of detecting the temperature of the intermediate temperature vessel reactor and adjusting the amount of waste liquid supplied. In this method, when the temperature is high, the flow rate of the waste liquid is reduced, and when the temperature is low, the total heat value entering the reactor is adjusted by increasing the flow rate of the waste liquid to balance the heat value and the heat dissipation value. This makes it possible to maintain the temperature. Therefore, since heating of the intermediate temperature vessel reactor 11 is not required during operation, there is an advantage that both the equipment cost and the operation cost can be reduced.
なお、図4に示す装置において、中間温度用ベッセル反応器11に、起動時の加熱や保温のためのヒーターを設け、より温度制御性を向上させることもできるが、起動時の加熱用に第2予熱器12を使用し、起動時のみ第2予熱器12→中間温度用ベッセル反応器11→高温反応器13の順に流通させることにより、中間温度用ベッセル反応器11に必要な起動用ヒーターも不要となるため、設備費も低減できる。 In the apparatus shown in FIG. 4, the intermediate temperature vessel reactor 11 can be provided with a heater for heating and keeping warm at the time of starting, and the temperature controllability can be further improved. 2 The preheater 12 is used, and the starter heater necessary for the intermediate temperature vessel reactor 11 can be obtained by flowing the second preheater 12 → the intermediate temperature vessel reactor 11 → the high temperature reactor 13 in this order only at the time of activation. Since it becomes unnecessary, the equipment cost can be reduced.
本発明は、難分解性有害物質および窒素化合物を含む廃液の処理が要求されるものであれば、あらゆる分野における処理に適用できる。 The present invention can be applied to treatment in all fields as long as treatment of waste liquid containing a hardly decomposable harmful substance and a nitrogen compound is required.
1 第1予熱器
2 中間反応器
3、12 第2予熱器
4、13 高温反応器
11 中間温度用ベッセル反応器
DESCRIPTION OF SYMBOLS 1 1st preheater 2 Intermediate reactor 3, 12 2nd preheater 4, 13 High temperature reactor 11 Bessel reactor for intermediate temperature
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