JP4674040B2

JP4674040B2 - Sludge treatment method under conditions of high temperature and high pressure

Info

Publication number: JP4674040B2
Application number: JP2003112603A
Authority: JP
Inventors: 耕太郎池田
Original assignee: Metawater Co Ltd
Current assignee: Metawater Co Ltd
Priority date: 2003-04-17
Filing date: 2003-04-17
Publication date: 2011-04-20
Anticipated expiration: 2023-04-17
Also published as: JP2004313965A

Description

【０００１】
【発明の属する技術分野】
本発明は、脱水汚泥などの窒素成分と炭素成分の一方または双方を含む含水汚泥を、高温高圧下条件において処理して無害物質に転換する方法に関するものである。
【０００２】
【従来の技術】
【特許文献１】
特開２００２−１９２１９４号公報
【０００３】
高温高圧条件下において汚泥その他の廃棄物を分解処理する方法として、従来から超臨界水条件下で酸化反応を進行させる超臨界水酸化法と、亜臨界水条件下で酸化反応を進行させる湿式酸化法（特許文献１）とが知られている。
【０００４】
このうち超臨界水酸化法は窒素成分から生成されるアンモニアを分解できる利点があるが、そのためには２５ＭＰａ，６５０℃以上の厳しい条件が必要となる。このため、それに耐える設備の製作やそのメンテナンスに多くのコストがかかることとなり、安全性の面での不安もあるため、汚泥処理法としては実用化されていない。またこの方法は超臨界水を反応場とするため、汚泥の含水率を９０％以上としておくことが必要不可欠であり、脱水汚泥のような低含水率の汚泥の処理には不適当である。
【０００５】
一方、湿式酸化法は超臨界水酸化法よりも圧力・温度ともに低い亜臨界水条件下で反応を進行させるため、設備の製作やそのメンテナンスのコストが安価となるうえ、脱水汚泥のような低含水率の汚泥の処理にも適する。しかし湿式酸化法では、汚泥に含まれる窒素成分は液相条件下で加水分解されて難分解性のアンモニアが生成されるため、その処理が困難でなる。また汚泥に含まれる炭素成分は液相条件下で加水分解されて酢酸等の有機酸を生成するが、この有機酸も難分解性であってその処理が困難である。またアンモニアと有機酸との反応により別の難分解性成分が生成される。
【０００６】
このように、湿式酸化法は難分解性のアンモニア、有機酸などが生成されやすい欠点があり、触媒を用いることによってこれらの難分解性成分を除去することも考えられるが、コスト面での負担が大きくなる。さらに湿式酸化法には処理に長時間を要するという問題もあるため、やはり汚泥処理法としては実用化されていない。
【０００７】
【発明が解決しようとする課題】
本発明は上記した従来の問題点を解決し、亜臨界水条件下で、難分解性成分を生成させることなく、低水分の汚泥を窒素、二酸化炭素、水などの無害物質に分解処理することができる高温高圧下条件における汚泥処理方法を提供するためになされたものである。
【０００８】
【課題を解決するための手段】
上記の課題を解決するためになされた請求項１の発明は、汚泥を亜臨界条件にある予熱器と反応器とを用いて連続的に処理する方法であって、該予熱器は、内部温度が水分蒸発温度以下の液相条件下にあり、該予熱器の出口部では、内部温度が水分蒸発温度に維持され、該反応器は、内部温度が水分蒸発温度以上の気相条件下にあり、低含水率の汚泥を先ず、該予熱器に導入し、１０分以内で該予熱器出口に向けて通過させながら、汚泥温度を常温から水分蒸発温度まで昇温して加水分解することにより、該汚泥中の窒素成分の一部をアンモニアに転換し、次いで該反応器に移送して未反応の窒素成分を酸化反応により窒素酸化物に転換し、これらのアンモニアと窒素酸化物とを気相条件下で反応させて窒素を生成させることを特徴とするものである。
【０００９】
また請求項２の発明は、汚泥を亜臨界条件にある予熱器と反応器とを用いて連続的に処理する方法であって、該予熱器は、内部温度が水分蒸発温度以下の液相条件下にあり、該予熱器の出口部では、内部温度が水分蒸発温度に維持され、該反応器は、内部温度が水分蒸発温度以上の気相条件下にあり、低含水率の汚泥を先ず、該予熱器に導入し、１０分以内で該予熱器出口に向けて通過させながら、汚泥温度を常温から水分蒸発温度まで昇温して加水分解することにより、該汚泥中の炭素成分を低分子化し、次いで該反応器に移送して酸化させ二酸化炭素を生成させることを特徴とするものである。
【００１０】
請求項１の発明によれば、亜臨界水条件下で低水分の汚泥中の窒素成分を難分解性のアンモニアの発生を抑制しつつ窒素に転換することができる。また請求項２の発明によれば、亜臨界水条件下で低水分の汚泥中の炭素成分を難分解性の有機酸の発生を抑制しつつ二酸化炭素に転換することができる。また、アンモニアと有機物の反応から発生する難分解成分の生成も抑制できる。
【００１１】
【発明の実施の形態】
以下に本発明の好ましい実施形態を示す。
図１は請求項１の発明のフローを示すブロック図であり、１は高温高圧の亜臨界水条件下にある予熱器、２，３はその後段に配置された同じく亜臨界水条件下にある反応器である。予熱器１の温度は予熱器出口内部温度を水分蒸発温度に付近に維持し、汚泥中の水分を蒸発させ、反応器２、３の温度は水分蒸発温度以上に維持し、酸化剤を反応させる。
【００１２】
この実施形態では予熱器１は温度３１０℃、圧力１０ＭＰａに設定されており、反応器２は温度３００〜３５０℃、圧力１０ＭＰａ、反応器３は温度３５０〜４５０℃、圧力１０ＭＰａに設定されている。なおこれは一例を示すものであって、反応器の温度は２００〜５００℃、好ましくは３００〜４５０℃、圧力は５〜２０ＭＰａ，好ましくは７〜１２ＭＰａとすることができる。また水分蒸発温度決まってくるため圧力によって決まってくるために予熱器内部温度は圧力に依存する。また反応器２，３は一体化することもできる。
【００１３】
本発明では、水分が７０〜９０％の脱水汚泥が高圧ポンプ４によって加圧され予熱器１に供給される。また酸素も予熱器１に供給される。予熱器１は圧力容器である筒状の本体の外周にヒータ５を備え、また内部に送り羽根６を備えたもので、汚泥はこの液相条件下にある予熱器１の内部を通過する間に加水分解され、汚泥中に含まれる窒素成分はアンモニアに転換される。
【００１４】
前記したようにこのアンモニアは難分解性であるから、その発生量を抑制するために液相条件下における加水分解時間は短くすることが好ましく、このためにこの実施形態では予熱器１の内部に送り羽根６を設け、汚泥を速やかに送るようにして昇温時間を１時間以下に短縮している。
【００１５】
予熱器１を通過した汚泥は、次いで気相条件下にある反応器２に移送される。なお、反応器２，３も予熱器１と同様に筒状の本体の外周にヒータを備え、また内部に送り羽根を設けた構造としておくことが好ましい。この反応器２を通過する間に汚泥中の未反応の窒素成分は酸化反応により窒素酸化物ＮＯ_Ｘに転換される。そして予熱器１で生成されたアンモニアと、反応器２で生成された窒素酸化物ＮＯ_Ｘとを、反応器３において更に高温の気相条件下で反応させ、窒素Ｎ_２を生成させる。この結果、汚泥中の窒素成分の大部分は無害な窒素ガスに転換される。このプロセスを図２に示す。なお、反応器３の出口には固液分離装置７と気液分離装置８とが接続されており、反応生成物を残渣、排液、ガスに分離する。
【００１６】
後記する実施例のデータに示すように、予熱器１の昇温時間を短縮することにより、汚泥中の窒素成分の分解率を大幅に向上させることが可能となる。これは液相条件下での保持時間が長くなるほど窒素成分が難分解性のアンモニアに移行し、その後の気相条件下における窒素酸化物の生成量が減少するためである。
【００１７】
また汚泥中には窒素成分のほかに炭素成分が含まれている。請求項２の発明はこの炭素成分に着目してなされたものである。汚泥の処理プロセス自体は請求項１の実施形態と同様であり、低含水率の汚泥を先ず液相条件下にある予熱器１で熱分解して炭素成分を低分子化する。この場合にも内部に送り羽根６を設けた予熱器１を用い、昇温時間を短縮することにより、難分解性の酢酸等の有機酸の発生量を抑制する。
【００１８】
次いで熱分解物を気相条件下にある反応器２，３に移送して酸化させ、図３のように二酸化炭素を生成させる。請求項２の発明によれば、汚泥中の炭素成分も難分解性の有機酸を発生させることなく、無害な二酸化炭素に転換することができる。このプロセスを図３に示す。
以下に本発明の実施例を示す。
【００１９】
【実施例】
（実施例１）昇温時間の影響
含水率が９０％の下水脱水汚泥を、図１に示した装置を用いて処理した。予熱器の昇温時間を１３分、１１分、７.５分の３通りに変化させて、汚泥中の窒素成分及び炭素成分の分解率を測定した。その結果を表１に示す。この表１のデータから明らかなように、予熱器の昇温時間を短縮することにより、窒素成分、炭素成分ともに分解率を向上させることができた。
【００２０】
【表１】

【００２１】
(実施例２) 保持温度の影響
含水率が８４％の下水脱水汚泥を、図１に示した装置を用いて処理した。常温から水分蒸発温度である２９０℃よりも高い３００℃まで１０分以内に昇温したうえ、反応器において１時間保持したところ、窒素成分の７７.６％が窒素ガスに転換された。これに対して予熱器内で水分蒸発温度である２９０℃よりも低い２８０℃に１時間保持したうえ、反応器において３２０℃で１０分間保持した場合には、大部分の窒素成分がアンモニアに移行するため、窒素ガスへの転換率は１３.８％に過ぎなかった。
【００２２】
【発明の効果】
以上に説明したように、本発明の高温高圧下条件における汚泥処理方法によれば、安全性やランニングコストの面で超臨界水酸化法よりも優れた亜臨界水条件下の湿式酸化法によって、アンモニアや有機酸などの難分解性成分を生成させることなく、低水分の汚泥を窒素、二酸化炭素、水などの無害物質に分解処理することができる。また本発明によれば、超臨界水を反応場とする必要がないため、低水分の汚泥を処理することができる。このため本発明によれば、公害発生のおそれのある焼却炉等を全く用いることなく、下水汚泥などを分解処理することができる。
【図面の簡単な説明】
【図１】本発明の実施形態を示すブロック図である。
【図２】窒素成分の分解プロセスを示す説明図である。
【図３】炭素成分の分解プロセスを示す説明図である。
【符号の説明】
１予熱器、２反応器、３反応器、４高圧ポンプ、５ヒータ、６送り羽根、７固液分離装置、８気液分離装置[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for treating a hydrous sludge containing one or both of a nitrogen component and a carbon component, such as dehydrated sludge, under conditions of high temperature and high pressure to convert it into a harmless substance.
[0002]
[Prior art]
[Patent Document 1]
Japanese Patent Laid-Open No. 2002-192194
As a method for decomposing sludge and other wastes under high temperature and high pressure conditions, the conventional supercritical water oxidation method that allows the oxidation reaction to proceed under supercritical water conditions and the wet oxidation method that allows the oxidation reaction to proceed under subcritical water conditions. The law (Patent Document 1) is known.
[0004]
Among them, the supercritical water oxidation method has an advantage that ammonia generated from the nitrogen component can be decomposed, but for that purpose, severe conditions of 25 MPa and 650 ° C. or more are required. For this reason, the production and maintenance of the equipment that can withstand such a process are costly, and there are concerns about safety, so that it has not been put to practical use as a sludge treatment method. In addition, since this method uses supercritical water as a reaction field, it is indispensable to keep the moisture content of the sludge at 90% or more, and is not suitable for the treatment of sludge with a low moisture content such as dewatered sludge.
[0005]
On the other hand, the wet oxidation method allows the reaction to proceed under subcritical water conditions, which are lower in pressure and temperature than the supercritical water oxidation method. Suitable for treatment of sludge with moisture content. However, in the wet oxidation method, the nitrogen component contained in the sludge is hydrolyzed under liquid phase conditions to produce hardly decomposable ammonia, and thus the treatment becomes difficult. The carbon component contained in the sludge is hydrolyzed under liquid phase conditions to produce an organic acid such as acetic acid, but this organic acid is also hardly decomposable and difficult to treat. Moreover, another hardly decomposable component is produced | generated by reaction of ammonia and an organic acid.
[0006]
As described above, the wet oxidation method has a defect that it is easy to generate difficult-to-decompose ammonia, organic acid, etc., and it is conceivable to remove these hardly-decomposable components by using a catalyst. Becomes larger. Furthermore, since the wet oxidation method has a problem that it takes a long time to process, it has not been put to practical use as a sludge treatment method.
[0007]
[Problems to be solved by the invention]
The present invention solves the above-mentioned conventional problems, and decomposes low-moisture sludge into harmless substances such as nitrogen, carbon dioxide, and water under subcritical water conditions without generating hardly decomposable components. The present invention was made to provide a sludge treatment method under conditions of high temperature and high pressure.
[0008]
[Means for Solving the Problems]
The invention of claim 1 made to solve the above problems is a method of continuously treating sludge using a preheater and a reactor under subcritical conditions, wherein the preheater has an internal temperature. Is in a liquid phase condition below the water evaporation temperature, the internal temperature is maintained at the water evaporation temperature at the outlet of the preheater, and the reactor is in a gas phase condition above the water evaporation temperature. First, by introducing sludge having a low water content into the preheater and passing it toward the preheater outlet within 10 minutes, the sludge temperature is raised from room temperature to the water evaporation temperature and hydrolyzed, Part of the nitrogen component in the sludge is converted to ammonia, then transferred to the reactor, and the unreacted nitrogen component is converted to nitrogen oxides by an oxidation reaction. These ammonia and nitrogen oxides are converted into a gas phase. It is characterized by reacting under conditions to produce nitrogen It is.
[0009]
The invention of claim 2 is a method for continuously treating sludge using a preheater and a reactor under subcritical conditions, wherein the preheater has a liquid phase condition in which the internal temperature is equal to or lower than the water evaporation temperature. The internal temperature is maintained at the water evaporation temperature at the outlet of the preheater, and the reactor is in a gas phase condition where the internal temperature is equal to or higher than the water evaporation temperature. The carbon component in the sludge is reduced to a low molecular weight by introducing the preheater and hydrolyzing it by raising the sludge temperature from room temperature to the water evaporation temperature while passing it toward the preheater outlet within 10 minutes. And then transferred to the reactor and oxidized to produce carbon dioxide.
[0010]
According to the invention of claim 1, the nitrogen component in the low moisture sludge can be converted into nitrogen while suppressing the generation of hardly decomposable ammonia under subcritical water conditions. According to the invention of claim 2, the carbon component in the low moisture sludge can be converted to carbon dioxide while suppressing the generation of the hardly decomposable organic acid under the subcritical water condition. Moreover, the production | generation of the hardly decomposed component which generate | occur | produces from reaction of ammonia and organic substance can also be suppressed.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
Preferred embodiments of the present invention are shown below.
FIG. 1 is a block diagram showing the flow of the invention of claim 1, wherein 1 is a preheater under high-temperature and high-pressure subcritical water conditions, and 2 and 3 are also under subcritical water conditions arranged in the subsequent stage. Reactor. The temperature of the preheater 1 is maintained at the preheater outlet internal temperature close to the water evaporation temperature, the water in the sludge is evaporated, the temperatures of the reactors 2 and 3 are maintained at the water evaporation temperature or higher, and the oxidant is reacted. .
[0012]
In this embodiment, the preheater 1 is set to a temperature of 310 ° C. and a pressure of 10 MPa, the reactor 2 is set to a temperature of 300 to 350 ° C. and a pressure of 10 MPa, and the reactor 3 is set to a temperature of 350 to 450 ° C. and a pressure of 10 MPa. . In addition, this shows an example, The temperature of a reactor can be 200-500 degreeC, Preferably it is 300-450 degreeC, A pressure can be 5-20 MPa, Preferably it can be 7-12 MPa. In addition, since the water evaporation temperature is determined, the temperature inside the preheater depends on the pressure. The reactors 2 and 3 can also be integrated.
[0013]
In the present invention, dehydrated sludge having a moisture content of 70 to 90% is pressurized by the high-pressure pump 4 and supplied to the preheater 1. Oxygen is also supplied to the preheater 1. The preheater 1 is provided with a heater 5 on the outer periphery of a cylindrical main body, which is a pressure vessel, and a feed blade 6 inside, and sludge passes through the interior of the preheater 1 under this liquid phase condition. The nitrogen component contained in the sludge is converted to ammonia.
[0014]
As described above, since this ammonia is hardly decomposable, it is preferable to shorten the hydrolysis time under liquid phase conditions in order to suppress the generation amount. For this reason, in this embodiment, the ammonia is contained in the preheater 1. The feed blade 6 is provided, and the temperature rise time is shortened to 1 hour or less so as to feed the sludge quickly.
[0015]
The sludge that has passed through the preheater 1 is then transferred to the reactor 2 under gas phase conditions. As with the preheater 1, the reactors 2 and 3 are preferably provided with a heater on the outer periphery of a cylindrical main body and provided with a feed blade inside. Nitrogen unreacted components in the sludge during passage through the reactor 2 is converted to nitrogen oxides NO _X by an oxidation reaction. Then, the ammonia generated in the preheater 1 and the nitrogen oxide NO _X generated in the reactor 2 are reacted in the reactor 3 under a higher temperature gas phase condition to generate nitrogen N ₂ . As a result, most of the nitrogen component in the sludge is converted into harmless nitrogen gas. This process is illustrated in FIG. A solid-liquid separation device 7 and a gas-liquid separation device 8 are connected to the outlet of the reactor 3 to separate the reaction product into residue, drainage, and gas.
[0016]
As shown in the data of the examples described later, it is possible to greatly improve the decomposition rate of the nitrogen component in the sludge by shortening the temperature raising time of the preheater 1. This is because the nitrogen component shifts to less decomposable ammonia as the holding time under liquid phase conditions becomes longer, and the amount of nitrogen oxide produced under the subsequent gas phase conditions decreases.
[0017]
Sludge contains carbon components in addition to nitrogen components. The invention of claim 2 is made paying attention to this carbon component. The sludge treatment process itself is the same as that of the first embodiment, and the sludge having a low water content is first pyrolyzed in the preheater 1 under liquid phase conditions to lower the molecular weight of the carbon component. Also in this case, by using the preheater 1 in which the feed blade 6 is provided, and shortening the temperature raising time, the generation amount of organic acid such as hardly decomposable acetic acid is suppressed.
[0018]
Next, the pyrolyzate is transferred to the reactors 2 and 3 under gas phase conditions and oxidized to generate carbon dioxide as shown in FIG. According to the invention of claim 2, the carbon component in the sludge can be converted to harmless carbon dioxide without generating a hardly decomposable organic acid. This process is illustrated in FIG.
Examples of the present invention are shown below.
[0019]
【Example】
(Example 1) Influence of temperature rise time Sewage dewatered sludge having a water content of 90% was treated using the apparatus shown in FIG. The decomposition rate of the nitrogen component and the carbon component in the sludge was measured by changing the temperature raising time of the preheater in three ways of 13 minutes, 11 minutes, and 7.5 minutes. The results are shown in Table 1. As is apparent from the data in Table 1, the decomposition rate of both the nitrogen component and the carbon component could be improved by shortening the heating time of the preheater.
[0020]
[Table 1]

[0021]
(Example 2) Influence of holding temperature Sewage dewatered sludge having a moisture content of 84% was treated using the apparatus shown in FIG. When the temperature was raised from room temperature to 300 ° C., which is higher than the water evaporation temperature of 290 ° C., within 10 minutes and held in the reactor for 1 hour, 77.6% of the nitrogen component was converted to nitrogen gas. On the other hand, when the preheater is held at 280 ° C., which is lower than the water evaporation temperature of 290 ° C. for 1 hour, and kept at 320 ° C. for 10 minutes in the reactor, most of the nitrogen components are transferred to ammonia. Therefore, the conversion rate to nitrogen gas was only 13.8%.
[0022]
【The invention's effect】
As described above, according to the sludge treatment method under the high temperature and high pressure conditions of the present invention, the wet oxidation method under subcritical water conditions superior to the supercritical water oxidation method in terms of safety and running cost, Low moisture sludge can be decomposed into harmless substances such as nitrogen, carbon dioxide, and water without generating hardly decomposable components such as ammonia and organic acids. Further, according to the present invention, since it is not necessary to use supercritical water as a reaction field, low moisture sludge can be treated. Therefore, according to the present invention, sewage sludge and the like can be decomposed without using an incinerator or the like that may cause pollution.
[Brief description of the drawings]
FIG. 1 is a block diagram showing an embodiment of the present invention.
FIG. 2 is an explanatory view showing a decomposition process of a nitrogen component.
FIG. 3 is an explanatory view showing a decomposition process of a carbon component.
[Explanation of symbols]
1 Preheater, 2 Reactor, 3 Reactor, 4 High-pressure pump, 5 Heater, 6 Feed blade, 7 Solid-liquid separator, 8 Gas-liquid separator

Claims

A method of continuously treating sludge using a preheater and a reactor under subcritical conditions, wherein the preheater is in a liquid phase condition in which an internal temperature is equal to or lower than a water evaporation temperature, and the preheater At the outlet, the internal temperature is maintained at the water evaporation temperature, the reactor is in a gas phase condition where the internal temperature is equal to or higher than the water evaporation temperature, and sludge having a low water content is first introduced into the preheater. By passing the slurry toward the preheater outlet within minutes, the sludge temperature is raised from room temperature to the water evaporation temperature to hydrolyze, thereby converting a part of the nitrogen component in the sludge to ammonia, and then High temperature and high pressure characterized by converting unreacted nitrogen components into nitrogen oxides by oxidation reaction and transferring these ammonia and nitrogen oxides under gas phase conditions to generate nitrogen Sludge treatment method under the following conditions.

A method of continuously treating sludge using a preheater and a reactor under subcritical conditions, wherein the preheater is in a liquid phase condition in which an internal temperature is equal to or lower than a water evaporation temperature, and the preheater At the outlet, the internal temperature is maintained at the water evaporation temperature, the reactor is in a gas phase condition where the internal temperature is equal to or higher than the water evaporation temperature, and sludge having a low water content is first introduced into the preheater. By allowing the sludge temperature to rise from room temperature to the water evaporation temperature and hydrolyzing while passing it toward the preheater outlet within minutes,
A method for treating sludge under high-temperature and high-pressure conditions, characterized in that the carbon component in the sludge is reduced in molecular weight, then transferred to the reactor and oxidized to produce carbon dioxide.