JP2015067859A - Organic matter decomposition system using ozone and method for preventing crevice corrosion of anticorrosive metallic material - Google Patents
Organic matter decomposition system using ozone and method for preventing crevice corrosion of anticorrosive metallic material Download PDFInfo
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- 230000007797 corrosion Effects 0.000 title claims abstract description 140
- 238000005260 corrosion Methods 0.000 title claims abstract description 140
- CBENFWSGALASAD-UHFFFAOYSA-N Ozone Chemical compound [O-][O+]=O CBENFWSGALASAD-UHFFFAOYSA-N 0.000 title claims abstract description 82
- 238000000034 method Methods 0.000 title claims abstract description 23
- 239000007769 metal material Substances 0.000 title claims abstract description 21
- 239000005416 organic matter Substances 0.000 title claims description 22
- 238000000354 decomposition reaction Methods 0.000 title claims description 18
- VEXZGXHMUGYJMC-UHFFFAOYSA-M Chloride anion Chemical compound [Cl-] VEXZGXHMUGYJMC-UHFFFAOYSA-M 0.000 claims abstract description 80
- 229910002651 NO3 Inorganic materials 0.000 claims abstract description 34
- 239000007864 aqueous solution Substances 0.000 claims abstract description 34
- -1 nitrate ions Chemical class 0.000 claims abstract description 34
- 229910001220 stainless steel Inorganic materials 0.000 claims abstract description 24
- 239000010935 stainless steel Substances 0.000 claims abstract description 20
- 239000000243 solution Substances 0.000 claims abstract description 11
- NHNBFGGVMKEFGY-UHFFFAOYSA-N Nitrate Chemical compound [O-][N+]([O-])=O NHNBFGGVMKEFGY-UHFFFAOYSA-N 0.000 claims description 32
- 239000007788 liquid Substances 0.000 claims description 16
- 239000000126 substance Substances 0.000 claims description 16
- 238000005536 corrosion prevention Methods 0.000 claims description 3
- 238000002347 injection Methods 0.000 claims 7
- 239000007924 injection Substances 0.000 claims 7
- 239000007800 oxidant agent Substances 0.000 abstract description 5
- 229910001410 inorganic ion Inorganic materials 0.000 abstract description 3
- 230000003628 erosive effect Effects 0.000 description 39
- QAOWNCQODCNURD-UHFFFAOYSA-L Sulfate Chemical compound [O-]S([O-])(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-L 0.000 description 26
- 229910000831 Steel Inorganic materials 0.000 description 19
- 239000010959 steel Substances 0.000 description 19
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- 238000006243 chemical reaction Methods 0.000 description 10
- 230000000052 comparative effect Effects 0.000 description 9
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- 150000001450 anions Chemical class 0.000 description 8
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 8
- GRYLNZFGIOXLOG-UHFFFAOYSA-N Nitric acid Chemical compound O[N+]([O-])=O GRYLNZFGIOXLOG-UHFFFAOYSA-N 0.000 description 7
- 229910017604 nitric acid Inorganic materials 0.000 description 7
- BVKZGUZCCUSVTD-UHFFFAOYSA-M Bicarbonate Chemical compound OC([O-])=O BVKZGUZCCUSVTD-UHFFFAOYSA-M 0.000 description 6
- 239000002184 metal Substances 0.000 description 6
- 229910052751 metal Inorganic materials 0.000 description 6
- 150000002500 ions Chemical class 0.000 description 4
- 230000010287 polarization Effects 0.000 description 4
- 239000002699 waste material Substances 0.000 description 4
- 239000002351 wastewater Substances 0.000 description 4
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 3
- 238000011161 development Methods 0.000 description 3
- 229910052760 oxygen Inorganic materials 0.000 description 3
- 239000001301 oxygen Substances 0.000 description 3
- 239000010802 sludge Substances 0.000 description 3
- CURLTUGMZLYLDI-UHFFFAOYSA-N Carbon dioxide Chemical group O=C=O CURLTUGMZLYLDI-UHFFFAOYSA-N 0.000 description 2
- QAOWNCQODCNURD-UHFFFAOYSA-N Sulfuric acid Chemical compound OS(O)(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-N 0.000 description 2
- 238000004737 colorimetric analysis Methods 0.000 description 2
- 230000007423 decrease Effects 0.000 description 2
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- 238000004332 deodorization Methods 0.000 description 2
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- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 1
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- 229910052799 carbon Inorganic materials 0.000 description 1
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- 230000015556 catabolic process Effects 0.000 description 1
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- 230000000694 effects Effects 0.000 description 1
- 238000002848 electrochemical method Methods 0.000 description 1
- 230000005283 ground state Effects 0.000 description 1
- 239000003112 inhibitor Substances 0.000 description 1
- 230000002452 interceptive effect Effects 0.000 description 1
- 238000011835 investigation Methods 0.000 description 1
- 150000002739 metals Chemical class 0.000 description 1
- 239000000203 mixture Substances 0.000 description 1
- 239000011368 organic material Substances 0.000 description 1
- 238000005949 ozonolysis reaction Methods 0.000 description 1
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- 238000000926 separation method Methods 0.000 description 1
- 159000000000 sodium salts Chemical class 0.000 description 1
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Abstract
Description
本発明は、オゾンを用いて有機物を分解する水環境において使用する耐食金属材料のすきま腐食に関して、そのすきま腐食を抑制する方法および抑制する処理設備に関するものである。 The present invention relates to a crevice corrosion suppressing method and a treatment facility for crevice corrosion of a corrosion-resistant metal material used in an aqueous environment where organic substances are decomposed using ozone.
産業活動により公共用水域に排出される排水の水質は水質汚濁防止法等により厳しく制限されている。排水中の有機物に関しては主にＢＯＤ（生物化学的酸素要求量）やＣＯＤ（化学的酸素要求量）、場合によってはＴＯＣ（全有機炭素）が排水中に含まれる有機物の濃度指標として用いられる。排水中の有機物を除去する従来からの方法には、活性汚泥、凝集分離、生分解、高温熱分解など、多くの手段が存在する。なかでもオゾンの酸化力を用いた分解方式は、以下のような長所から、オゾンを用いた有機物の分解システムの他に、脱臭、漂白、殺菌、化学合成などのプロセス向けにも広範囲に開発および商品化されている。
（１）有機物が分解して生成する物質は二酸化炭素のため、処理後の廃棄物が少ない。
（２）運転温度は常温付近の比較的低温のシステムであり、安全性、信頼性が高い。
（３）オゾンの原料に空気を用いることができるため、経済的である。
（４）余剰のオゾンは容易に分解除去できる。
The quality of wastewater discharged into public water bodies due to industrial activities is strictly limited by the Water Pollution Control Law. Regarding organic matter in wastewater, BOD (biochemical oxygen demand), COD (chemical oxygen demand), and in some cases TOC (total organic carbon) are used as a concentration index of organic matter contained in wastewater. Conventional methods for removing organic substances in wastewater include many means such as activated sludge, coagulation separation, biodegradation, and high-temperature pyrolysis. In particular, the decomposition method using the oxidizing power of ozone has been developed and developed extensively for processes such as deodorization, bleaching, sterilization, and chemical synthesis, as well as the organic matter decomposition system using ozone. It has been commercialized.
(1) Since the substance produced by the decomposition of organic matter is carbon dioxide, there is little waste after treatment.
(2) The operating temperature is a relatively low temperature system near normal temperature and has high safety and reliability.
(3) Since air can be used as a raw material for ozone, it is economical.
(4) Excess ozone can be easily decomposed and removed.
一般的にはＳＵＳ３０４やＳＵＳ３１６Ｌ鋼等のステンレス鋼が経済性と耐食性を兼ね備えた汎用材料であることから、さまざまな分野で使用されている。オゾンが共存する場合においても同様である。しかし、被処理水に塩化物イオンが含まれる場合に孔食やすきま腐食が発生することがある。場合によっては粒界腐食、さらに応力が加わると応力腐食割れに進行し、重大な機器損傷をもたらすこともある。特に、溶接部およびその熱影響部ならびにフランジやスラッジの溜まり部など、すきまが形成される部位の耐食性が低く、すきま腐食の対策が重要となる。 In general, stainless steel such as SUS304 and SUS316L steel is a general-purpose material having both economical efficiency and corrosion resistance, and is therefore used in various fields. The same applies when ozone coexists. However, when the water to be treated contains chloride ions, pitting corrosion and crevice corrosion may occur. In some cases, intergranular corrosion, and when stress is applied, progresses to stress corrosion cracking, which may cause serious equipment damage. In particular, the corrosion resistance of the welded portion and its heat-affected zone and the portion where the gap is formed, such as the flange and sludge pool, is low, and countermeasures against crevice corrosion are important.
ステンレス鋼のすきま腐食の抑制方法として、特許文献１には水系中の塩化物イオンのモル濃度以上のモル濃度で塩化物イオン以外のアニオンを（特に硫酸イオン）を水系に共存させる方法が提案されている。 As a method for suppressing crevice corrosion of stainless steel, Patent Document 1 proposes a method in which an anion other than chloride ions (especially sulfate ions) coexists in an aqueous system at a molar concentration equal to or higher than the molar concentration of chloride ions in the aqueous system. ing.
オゾンを用いた有機物分解システムでは、特にオゾン等の強酸化剤が塩化物イオンと共存する環境においてステンレス鋼等の耐食金属材料のすきま腐食の課題が顕著となる。このような有機物分解システムに使用される耐食金属材料のすきま腐食を防止する方法として、オゾン分解前に腐食を促進する化学物質（たとえば 塩化物イオン）を除去することが解決方法の一つではある。しかしながら、脱イオン器、濾過機、化学成分調整機などの追加設備が必要であること、追加設備からの廃棄物が増えることにより、全体的な廃棄物を減少させるというオゾンを使用するためのメリットと逆行することになる。この他の防食方法としては腐食抑制剤を添加する方法、電気防食、犠牲陽極防食も腐食対策の方法の一つとして挙げられるが、いずれも新たな廃棄物を生むとともに、仕組みが複雑で限定的など必ずしも満足な結果が得られないことが多い。そのため、経済的であって簡便な耐食性を維持できるシステムが望まれている。 In the organic matter decomposition system using ozone, the problem of crevice corrosion of corrosion-resistant metal materials such as stainless steel becomes remarkable particularly in an environment where a strong oxidizing agent such as ozone coexists with chloride ions. As a method of preventing crevice corrosion of corrosion resistant metal materials used in such organic matter decomposition systems, one of the solutions is to remove chemical substances (such as chloride ions) that promote corrosion before ozonolysis. . However, the benefits of using ozone that reduce the overall waste by requiring additional equipment such as deionizers, filters, chemical composition regulators, and increasing waste from the additional equipment. And go backwards. Other anticorrosion methods include the addition of corrosion inhibitors, cathodic protection, and sacrificial anode protection, which can be cited as one of the countermeasures against corrosion, all of which produce new waste and have a complicated and limited mechanism. In many cases, satisfactory results are not always obtained. Therefore, an economical and simple system that can maintain corrosion resistance is desired.
一方、特許文献１には、塩化物イオンの濃度が低濃度域の水系中において、特定の無機イオン（硫酸イオン）を水系中の塩化物イオン濃度に対して特定の濃度以上存在させることによって、ステンレス鋼のすきま腐食を抑制できることが示されている。しかしながら、オゾン等の強酸化剤が塩化物イオンと共存する環境では、特許文献１の方法ではステンレス鋼の局部腐食、特にすきま腐食の発生・進展を十分抑制することはできなかった。なお、特許文献１ではオゾンと塩化物イオンと共存する環境中での腐食については議論されていない。 On the other hand, Patent Document 1 discloses that in a water system in which the concentration of chloride ions is low, a specific inorganic ion (sulfate ion) is present at a specific concentration or higher than the chloride ion concentration in the water system. It has been shown that crevice corrosion of stainless steel can be suppressed. However, in an environment where a strong oxidizer such as ozone coexists with chloride ions, the method of Patent Document 1 cannot sufficiently suppress the occurrence and development of local corrosion of stainless steel, particularly crevice corrosion. Patent Document 1 does not discuss corrosion in an environment in which ozone and chloride ions coexist.
本発明は、オゾン等の強酸化剤が塩化物イオンと共存する環境において使用するステンレス鋼等の耐食金属材料に生じる局部腐食、特にすきま腐食の発生および進展を抑制できるすきま腐食防止方法、並びに、有機物分解システムを提供することを目的とする。 The present invention is a crevice corrosion prevention method capable of suppressing the occurrence and development of local corrosion, particularly crevice corrosion, which occurs in a corrosion-resistant metal material such as stainless steel used in an environment where a strong oxidizing agent such as ozone coexists with chloride ions, and The object is to provide an organic matter decomposition system.
本発明者らが鋭意研究を行った結果、オゾンと塩化物イオンが共存する環境においては硝酸イオンを水系中の塩化物イオン濃度に対して特定の濃度以上に存在させることにより、ステンレス鋼等の耐食金属材料のすきま腐食を抑制できることを見出し、本発明に至った。 As a result of intensive studies by the present inventors, in an environment where ozone and chloride ions coexist, nitrate ions are made to exist above a specific concentration with respect to the chloride ion concentration in the aqueous system, so that stainless steel, etc. The present inventors have found that crevice corrosion of a corrosion-resistant metal material can be suppressed, and have reached the present invention.
本発明により、オゾン等の強酸化剤が塩化物イオンと共存する環境において使用するステンレス鋼等の耐食金属材料に生じる局部腐食、特にすきま腐食の発生および進展を防止できる、すきま腐食防止方法、並びに、有機物分解システムを提供することができる。 According to the present invention, a crevice corrosion prevention method capable of preventing the occurrence and development of local corrosion, particularly crevice corrosion, which occurs in a corrosion-resistant metal material such as stainless steel used in an environment where a strong oxidizing agent such as ozone coexists with chloride ions, and An organic matter decomposition system can be provided.
前述したように、オゾンと塩化物イオンが共存する環境においては特定の無機イオン特に硝酸イオンを水系中の塩化物イオン濃度に対して特定の濃度以上に存在させることにより、ステンレス鋼等の耐食金属材料のすきま腐食を抑制できる。そのための最低の硝酸イオン濃度が塩化物イオンのモル濃度に対してモル濃度比で０．２以上のモル濃度である。 As described above, in the environment where ozone and chloride ions coexist, corrosion resistance metals such as stainless steel can be obtained by allowing specific inorganic ions, especially nitrate ions, to exist above a specific concentration relative to the chloride ion concentration in the aqueous system. Can suppress crevice corrosion of materials. For this purpose, the minimum nitrate ion concentration is a molar concentration of 0.2 or more in molar ratio with respect to the molar concentration of chloride ions.
従来技術では、アニオン、特に硫酸イオンを添加することによりすきま腐食を防止する方法が提案されている。アニオンを添加することによりすきま腐食が防止できる要因は以下の通りである。すきま内はプラスに帯電しており、電荷を中和するためにマイナス電荷がすきま内に泳動する。すきま腐食を起こす原因物質である塩化物イオンはマイナス電荷をもっており、塩化物イオンがすきま内に移動することよりすきま腐食が引き起こされる。これに対して、塩化物イオン以外のマイナスチャージを持ったイオン（アニオン）を共存させることで、相対的にすきま内に移動する塩化物イオン量が減少し、すきま腐食が抑制されるためである。本発明者らが検討した結果、硫酸イオンより硝酸イオンの方がすきま腐食を抑制する効果が非常に高かった。この理由は明確にはできていないが、硝酸イオンの方が硫酸イオンより不動態化皮膜を作りやすいためと考えられる。 The prior art has proposed a method for preventing crevice corrosion by adding anions, particularly sulfate ions. Factors that can prevent crevice corrosion by adding anions are as follows. The gap is positively charged, and a negative charge migrates into the gap to neutralize the charge. Chloride ions that cause crevice corrosion have a negative charge, and crevice corrosion is caused by movement of chloride ions into the crevice. On the other hand, the coexistence of negatively charged ions (anions) other than chloride ions reduces the amount of chloride ions that move relative to the gap and suppresses crevice corrosion. . As a result of investigations by the present inventors, nitrate ions were much more effective in suppressing crevice corrosion than sulfate ions. The reason for this is not clear, but it is thought that nitrate ions are easier to make a passivating film than sulfate ions.
添加する硝酸イオンの対になるカチオンに特に制限はないが、一般的にはナトリウム塩を使用することができる。すきま腐食を防止するために必要な硝酸イオン量（濃度）は、そこの場所におけるオゾン濃度によって変化する。注入する硝酸イオン量は、その場におけるオゾン濃度を測定し、その環境において必要な硝酸イオン量を注入することにより、すきま腐食を防止することができる。
（実施例１）
すきま腐食の評価方法には、その環境においてすきま腐食が発生するかしないかを電気化学的な手法で評価することができる。その詳細は、ＪＩＳ Ｇ ０５９２：２００２に記載されている。この方法に従ってすきま再不動態化電位を測定した。図１は、塩化物イオン濃度１００ｐｐｍ、硝酸イオン濃度０ｐｐｍ、硫酸イオン濃度５１．７ｐｐｍ、５０℃の条件で測定したＳＵＳ３１６Ｌ材のすきま再不動態化電位を求めるための往復分極曲線である。再不動態化電位は０．４４Ｖ（ｖｓ．ＳＨＥ）である。図２は、塩化物イオン濃度１００ｐｐｍ、硝酸イオン濃度１７６ｐｐｍ、硫酸イオン濃度５１．７ｐｐｍ、５０℃の条件で測定したＳＵＳ３１６Ｌ材のすきま再不動態化電位を求めるための往復分極曲線である。すきま再不動態化電位は１．１０Ｖ（ｖｓ．ＳＨＥ）である。硝酸イオンを添加することにより、すきま再不動態化電位は０．６６Ｖほど貴側にシフトしている。すきま再不動態化電位が高ければ、その分だけ電位が貴側にある環境においてもすきま腐食を起こしにくいため、硝酸イオンを添加することによりすきま腐食が起こりにくくなっていることが分かる。
There are no particular restrictions on the cations that form a pair of nitrate ions to be added, but generally sodium salts can be used. The amount (concentration) of nitrate ions required to prevent crevice corrosion varies depending on the ozone concentration at the location. The amount of nitrate ions to be injected can prevent crevice corrosion by measuring the ozone concentration at the site and injecting the amount of nitrate ions required in the environment.
Example 1
As an evaluation method of crevice corrosion, it can be evaluated by an electrochemical method whether crevice corrosion occurs or not in the environment. The details are described in JIS G 0592: 2002. The clearance repassivation potential was measured according to this method. FIG. 1 is a reciprocal polarization curve for determining the clearance repassivation potential of a SUS316L material measured under the conditions of a chloride ion concentration of 100 ppm, a nitrate ion concentration of 0 ppm, a sulfate ion concentration of 51.7 ppm, and 50 ° C. The repassivation potential is 0.44 V (vs. SHE). FIG. 2 is a reciprocal polarization curve for determining the clearance repassivation potential of the SUS316L material measured under the conditions of a chloride ion concentration of 100 ppm, a nitrate ion concentration of 176 ppm, a sulfate ion concentration of 51.7 ppm, and 50 ° C. The clearance repassivation potential is 1.10 V (vs. SHE). By adding nitrate ions, the gap repassivation potential is shifted to the noble side by about 0.66V. If the crevice repassivation potential is high, crevice corrosion is less likely to occur even in an environment where the potential is on the noble side, so it can be seen that crevice corrosion is less likely to occur by adding nitrate ions.
図３にオゾンを注入した時の各種ステンレス鋼の腐食電位（定常電位）を示す。本評価では、塩化物イオン濃度１００ｐｐｍ、硝酸イオン濃度５０ｐｐｍ、硫酸イオン濃度１５ｐｐｍ、５０℃の条件で、オゾン濃度を０ｐｐｍ、０．１ｐｐｍ、１ｐｐｍ、１０ｐｐｍに変化させた場合の各種ステンレス鋼の腐食電位（定常電位）を測定した。ステンレス鋼は、ＳＵＳ３０４材、ＳＵＳ３１６Ｌ材、ＳＵＳ３１７Ｌ材、及び、ＳＵＳ３２９Ｊ４Ｌ材である。図３に示すように、いずれのステンレス鋼においてもオゾン濃度が増加するにつれて、腐食電位が貴側にシフトしていくことが分かる。したがって、オゾンを含まない塩化物水溶液よりもオゾンと塩化物イオンが共存する塩化物水溶液の方がすきま腐食が発生しやすく、オゾン濃度が増えるほどすきま腐食が発生しやすくなることが分かる。 FIG. 3 shows the corrosion potential (steady potential) of various stainless steels when ozone is injected. In this evaluation, the corrosion potential of various stainless steels when the ozone concentration was changed to 0 ppm, 0.1 ppm, 1 ppm, and 10 ppm under the conditions of chloride ion concentration of 100 ppm, nitrate ion concentration of 50 ppm, sulfate ion concentration of 15 ppm, and 50 ° C. (Steady potential) was measured. Stainless steel is SUS304 material, SUS316L material, SUS317L material, and SUS329J4L material. As can be seen from FIG. 3, the corrosion potential shifts to the noble side as the ozone concentration increases in any stainless steel. Therefore, it can be understood that crevice corrosion is more likely to occur in a chloride aqueous solution in which ozone and chloride ions coexist than in a chloride aqueous solution that does not contain ozone, and crevice corrosion is more likely to occur as the ozone concentration increases.
次に、すきま再不動態化電位と硝酸濃度の依存性について評価した結果を説明する。図４に硝酸イオンを添加した場合のＳＵＳ３０４のすきま再不動態化電位の硝酸濃度依存性を示す。図４では、塩化物イオンと硫酸イオンの濃度を一定とし、硝酸イオン濃度を変化させた場合のすきま再不動態化電位を白抜きで示している。ここで、塩化物イオン濃度は１００ｐｐｍ、硫酸イオン濃度は５１．７ｐｐｍである。また、図３に示したオゾン濃度が０．１ｐｐｍ，１．０ｐｐｍおよび１０ｐｐｍの場合のＳＵＳ３０４ステンレス鋼の腐食電位も併せて示している。白抜きで示したように、硝酸濃度を上昇させることによりすきま再不動態化電位は貴側にシフトしている。従って、ある濃度のオゾンが存在している場合、そのオゾン濃度での腐食電位より高い電位のすきま再不動態化電位を示す濃度の硝酸イオンを添加することによりすきま腐食を防止することができる。たとえばオゾン濃度が０．１ｐｐｍのときの腐食電位は約５００ｍＶ、これより高いすきま再不動態化電位になるようにするには硝酸イオンを注入し硝酸濃度と塩化物イオン濃度の比を約０．２以上にすれば良いことが分かる。一方、硝酸濃度と塩化物イオン濃度の比が０．２より低い場合には、オゾンと塩化物イオンが共存する環境下ではすきま腐食を十分に抑制できないことが分かる。換言すると、この結果から硫酸イオンのみではすきま腐食を十分に抑制できないことが分かる。 Next, the results of evaluating the dependence between the clearance repassivation potential and the nitric acid concentration will be described. FIG. 4 shows the nitric acid concentration dependence of the clearance repassivation potential of SUS304 when nitrate ions are added. In FIG. 4, the gap repassivation potential when the concentration of chloride ion and sulfate ion is constant and the concentration of nitrate ion is changed is shown in white. Here, the chloride ion concentration is 100 ppm, and the sulfate ion concentration is 51.7 ppm. 3 also shows the corrosion potential of SUS304 stainless steel when the ozone concentration shown in FIG. 3 is 0.1 ppm, 1.0 ppm, and 10 ppm. As shown in white, the clearance repassivation potential is shifted to the noble side by increasing the nitric acid concentration. Therefore, when a certain concentration of ozone is present, crevice corrosion can be prevented by adding nitrate ions having a concentration indicating a crevice repassivation potential at a potential higher than the corrosion potential at that ozone concentration. For example, when the ozone concentration is 0.1 ppm, the corrosion potential is about 500 mV, and in order to obtain a higher clearance repassivation potential, nitrate ions are injected and the ratio of the nitric acid concentration to the chloride ion concentration is about 0.2. It can be seen that the above is sufficient. On the other hand, when the ratio between the nitric acid concentration and the chloride ion concentration is lower than 0.2, it is understood that crevice corrosion cannot be sufficiently suppressed in an environment where ozone and chloride ions coexist. In other words, it can be seen from this result that crevice corrosion cannot be sufficiently suppressed only by sulfate ions.
図４に塩化物イオン濃度が１００ｐｐｍ、硝酸イオン濃度と塩化物イオン濃度との比が０．２８の条件において硫酸濃度を５１．７ｐｐｍから１５ｐｐｍに低下させた場合を黒塗りの点で示した。図４に示したように、硝酸イオン濃度と塩化物イオン濃度との比が同じ条件下で硫酸イオン濃度を低下させてもすきま再不動態化電位はほとんど変化していない。このことから、硫酸イオンはすきま再不動態化電位にほとんど寄与していないことが分かる。 In FIG. 4, the case where the sulfuric acid concentration was reduced from 51.7 ppm to 15 ppm under the condition that the chloride ion concentration was 100 ppm and the ratio of the nitrate ion concentration to the chloride ion concentration was 0.28 is indicated by black points. As shown in FIG. 4, the gap repassivation potential hardly changes even when the sulfate ion concentration is decreased under the same ratio of nitrate ion concentration to chloride ion concentration. This indicates that sulfate ions hardly contribute to the clearance repassivation potential.
以上の結果から、オゾンと塩化物イオンが共存する環境下おいては、硝酸イオンを水系中の塩化物イオン濃度に対して特定の濃度以上に存在させることにより、ステンレス鋼等の耐食金属材料のすきま腐食を抑制できる。
（実施例２）
塩化物イオン濃度８０ｐｐｍ、硝酸イオン濃度６０ｐｐｍ、及び、オゾン１ｐｐｍが共存した水溶液中にＳＵＳ３０４鋼を１０００ｈ浸漬させた場合のすきま最大浸食深さを測定した。結果を表１に示す。この時の［ＮＯ3 -］／［Ｃｌ-］モル濃度比は、０．８２であり、図６に示すすきま腐食抑制の条件を満たしている。すきま最大浸食深さは７μｍであり、すきま腐食は進行していないといえる。
（実施例３）
塩化物イオン濃度１５０ｐｐｍ、硝酸イオン濃度１００ｐｐｍ、及び、オゾン１ｐｐｍが共存した水溶液中にＳＵＳ３０４鋼を１０００ｈ浸漬させた場合のすきま最大浸食深さを測定した。結果を表１に示す。この時の［ＮＯ3 -］／［Ｃｌ-］モル濃度比は、０．７２９であり、図６に示すすきま腐食抑制の条件を満たしている。すきま最大浸食深さは８μｍであり、すきま腐食は進行していないといえる。
（実施例４）
塩化物イオン濃度１８０ｐｐｍ、硝酸イオン濃度２００ｐｐｍ、及び、オゾン１０ｐｐｍが共存した水溶液中にＳＵＳ３０４鋼を１０００ｈ浸漬させた場合のすきま最大浸食深さを測定した。結果を表１に示す。この時の［ＮＯ3 -］／［Ｃｌ-］モル濃度比は、１．１５であり、図６に示すすきま腐食抑制の条件を満たしている。すきま最大浸食深さは２μｍであり、すきま腐食は進行していないといえる。
（比較例１）
塩化物イオン濃度１５０ｐｐｍ、重炭酸イオン、及び、オゾン１ｐｐｍが共存した水溶液中にＳＵＳ３０４鋼を１０００ｈ浸漬させた場合のすきま最大浸食深さを測定した。結果を表１に示す。重炭酸イオンの濃度は、図６に示したすきま腐食抑制の領域のアニオン／塩化物イオンモル濃度比を満たすようにアニオン量を制御している。すきま最大浸食深さは１２０μｍであり、すきま腐食は進行しているといえる。すなわち、図６に示すすきま腐食抑制の条件を満たす同じモル濃度でも、硝酸イオンはすきま腐食を抑制するが重炭酸イオンはすきま腐食を抑制しないといえる。
（比較例２）
塩化物イオン濃度１５０ｐｐｍ、硫酸イオン、及び、オゾン１ｐｐｍが共存した水溶液中にＳＵＳ３０４鋼を１０００ｈ浸漬させた場合のすきま最大浸食深さを測定した。結果を表１に示す。硫酸イオンの濃度は、図６に示したすきま腐食抑制の領域のアニオン／塩化物イオンモル濃度比を満たすようにアニオン量を制御している。すきま最大浸食深さは２３５μｍであり、すきま腐食は進行しているといえる。すなわち、図６に示すすきま腐食抑制の条件を満たす同じモル濃度でも、硝酸イオンはすきま腐食を抑制するが硫酸イオンはすきま腐食を抑制しないといえる。
（比較例３）
塩化物イオン濃度１００ｐｐｍ、硝酸イオン濃度１０ｐｐｍ、及び、オゾン１ｐｐｍが共存した水溶液中にＳＵＳ３０４鋼を１０００ｈ浸漬させた場合のすきま最大浸食深さを測定した。結果を表１に示す。この時の［ＮＯ3 -］／［Ｃｌ-］モル濃度比は、０．１０９であり、図６に示すすきま非腐食抑制の条件となっている。すきま最大浸食深さは８５μｍであり、すきま腐食は進行しているといえる。
From the above results, in an environment where ozone and chloride ions coexist, the presence of nitrate ions above a specific concentration relative to the chloride ion concentration in the aqueous system, the corrosion resistant metal material such as stainless steel Can suppress crevice corrosion.
(Example 2)
The maximum clearance erosion depth was measured when SUS304 steel was immersed for 1000 hours in an aqueous solution in which a chloride ion concentration of 80 ppm, a nitrate ion concentration of 60 ppm, and ozone of 1 ppm coexisted. The results are shown in Table 1. The [NO 3 − ] / [Cl − ] molar concentration ratio at this time is 0.82, which satisfies the conditions for suppressing crevice corrosion shown in FIG. The crevice maximum erosion depth is 7 μm, and it can be said that crevice corrosion has not progressed.
(Example 3)
The maximum clearance erosion depth was measured when SUS304 steel was immersed for 1000 hours in an aqueous solution in which a chloride ion concentration of 150 ppm, a nitrate ion concentration of 100 ppm, and ozone of 1 ppm coexisted. The results are shown in Table 1. The [NO 3 − ] / [Cl − ] molar concentration ratio at this time is 0.729, which satisfies the conditions for suppressing crevice corrosion shown in FIG. The crevice maximum erosion depth is 8 μm, and it can be said that crevice corrosion has not progressed.
Example 4
The maximum clearance erosion depth was measured when SUS304 steel was immersed for 1000 h in an aqueous solution in which a chloride ion concentration of 180 ppm, a nitrate ion concentration of 200 ppm, and ozone of 10 ppm coexisted. The results are shown in Table 1. The [NO 3 − ] / [Cl − ] molar concentration ratio at this time is 1.15, which satisfies the conditions for suppressing crevice corrosion shown in FIG. The crevice maximum erosion depth is 2 μm, and it can be said that crevice corrosion has not progressed.
(Comparative Example 1)
The maximum clearance erosion depth was measured when SUS304 steel was immersed for 1000 h in an aqueous solution in which a chloride ion concentration of 150 ppm, bicarbonate ion, and ozone of 1 ppm coexisted. The results are shown in Table 1. The concentration of bicarbonate ions is controlled so as to satisfy the anion / chloride ion molar concentration ratio in the crevice corrosion inhibition region shown in FIG. The crevice maximum erosion depth is 120 μm, and it can be said that crevice corrosion is progressing. That is, even at the same molar concentration that satisfies the conditions for crevice corrosion inhibition shown in FIG. 6, it can be said that nitrate ions inhibit crevice corrosion but bicarbonate ions do not inhibit crevice corrosion.
(Comparative Example 2)
The maximum clearance erosion depth was measured when SUS304 steel was immersed for 1000 hours in an aqueous solution in which a chloride ion concentration of 150 ppm, sulfate ions, and ozone of 1 ppm coexisted. The results are shown in Table 1. The concentration of sulfate ions is controlled so as to satisfy the anion / chloride ion molar concentration ratio in the crevice corrosion inhibition region shown in FIG. The crevice maximum erosion depth is 235 μm, and it can be said that crevice corrosion is in progress. That is, it can be said that even at the same molar concentration satisfying the condition of crevice corrosion inhibition shown in FIG. 6, nitrate ions inhibit crevice corrosion but sulfate ions do not inhibit crevice corrosion.
(Comparative Example 3)
The maximum clearance erosion depth was measured when SUS304 steel was immersed for 1000 hours in an aqueous solution in which a chloride ion concentration of 100 ppm, a nitrate ion concentration of 10 ppm, and ozone of 1 ppm coexisted. The results are shown in Table 1. The [NO 3 − ] / [Cl − ] molar concentration ratio at this time is 0.109, which is a condition for suppressing the non-corrosion of the clearance shown in FIG. The crevice maximum erosion depth is 85 μm, and it can be said that crevice corrosion is progressing.
塩化物イオン濃度８０ｐｐｍ、硝酸イオン濃度６０ｐｐｍ、及び、オゾン１ｐｐｍが共存した水溶液中にＳＵＳ３１６Ｌ鋼を１０００ｈ浸漬させた場合のすきま最大浸食深さを測定した。結果を表２に示す。この時の［ＮＯ3 -］／［Ｃｌ-］モル濃度比は、０．８２であり、図６に示すすきま腐食抑制の条件を満たしている。すきま最大浸食深さは２μｍであり、すきま腐食は進行していないといえる。すきま最大浸食深さは、ＳＵＳ３０４の場合よりは小さい。
（実施例６）
塩化物イオン濃度１５０ｐｐｍ、硝酸イオン濃度１００ｐｐｍ、及び、オゾン１ｐｐｍが共存した水溶液中にＳＵＳ３１６Ｌ鋼を１０００ｈ浸漬させた場合のすきま最大浸食深さを測定した。結果を表２に示す。この時の［ＮＯ3 -］／［Ｃｌ-］モル濃度比は、０．７２９であり、図６に示すすきま腐食抑制の条件を満たしている。すきま最大浸食深さは６μｍであり、すきま腐食は進行していないといえる。すきま最大浸食深さは、ＳＵＳ３０４の場合よりは小さい
（実施例７）
塩化物イオン濃度１８０ｐｐｍ、硝酸イオン濃度２００ｐｐｍ、及び、オゾン１０ｐｐｍが共存した水溶液中にＳＵＳ３１６Ｌ鋼を１０００ｈ浸漬させた場合のすきま最大浸食深さを測定した。結果を表２に示す。この時の［ＮＯ3 -］／［Ｃｌ-］モル濃度比は、１．１５であり、図６に示すすきま腐食抑制の条件を満たしている。すきま最大浸食深さは０μｍであり、すきま腐食は進行していないといえる。すきま最大浸食深さは、ＳＵＳ３０４の場合よりは小さい。
（比較例４）
塩化物イオン濃度１５０ｐｐｍ、重炭酸イオン、及び、オゾン１ｐｐｍが共存した水溶液中にＳＵＳ３１６Ｌ鋼を１０００ｈ浸漬させた場合のすきま最大浸食深さを測定した。結果を表２に示す。重炭酸イオンの濃度は、図６に示したすきま腐食抑制の領域のアニオン／塩化物イオンモル濃度比を満たすようにアニオン量を制御している。すきま最大浸食深さは８０μｍであり、すきま腐食は進行しているといえる。すなわち、図６に示すすきま腐食抑制の条件を満たす同じモル濃度でも、硝酸イオンはすきま腐食を抑制するが重炭酸イオンはすきま腐食を抑制しないといえる。
（比較例５）
塩化物イオン濃度１５０ｐｐｍ、硫酸イオン、及び、オゾン１ｐｐｍが共存した水溶液中にＳＵＳ３１６Ｌ鋼を１０００ｈ浸漬させた場合のすきま最大浸食深さを測定した。結果を表２に示す。硫酸イオンの濃度は、図６に示したすきま腐食抑制の領域のアニオン／塩化物イオンモル濃度比を満たすようにアニオン量を制御している。すきま最大浸食深さは１６５μｍであり、すきま腐食は進行しているといえる。すなわち、図６に示すすきま腐食抑制の条件を満たす同じモル濃度でも、硝酸イオンはすきま腐食を抑制するが硫酸イオンはすきま腐食を抑制しないといえる。
（比較例６）
塩化物イオン濃度１００ｐｐｍ、硝酸イオン濃度１０ｐｐｍ、及び、オゾン１ｐｐｍが共存した水溶液中にＳＵＳ３１６Ｌ鋼を１０００ｈ浸漬させた場合のすきま最大浸食深さを測定した。結果を表２に示す。この時の［ＮＯ3 -］／［Ｃｌ-］モル濃度比は、０．１０９であり、図６に示すすきま非腐食抑制の条件となっている。すきま最大浸食深さは６８μｍであり、すきま腐食は進行しているといえる。
The maximum clearance erosion depth was measured when SUS316L steel was immersed for 1000 hours in an aqueous solution in which a chloride ion concentration of 80 ppm, a nitrate ion concentration of 60 ppm, and ozone of 1 ppm coexisted. The results are shown in Table 2. The [NO 3 − ] / [Cl − ] molar concentration ratio at this time is 0.82, which satisfies the conditions for suppressing crevice corrosion shown in FIG. The crevice maximum erosion depth is 2 μm, and it can be said that crevice corrosion has not progressed. The maximum clearance erosion depth is smaller than that of SUS304.
(Example 6)
The maximum clearance erosion depth was measured when SUS316L steel was immersed for 1000 h in an aqueous solution in which a chloride ion concentration of 150 ppm, a nitrate ion concentration of 100 ppm, and ozone of 1 ppm coexisted. The results are shown in Table 2. The [NO 3 − ] / [Cl − ] molar concentration ratio at this time is 0.729, which satisfies the conditions for suppressing crevice corrosion shown in FIG. The crevice maximum erosion depth is 6 μm, and it can be said that crevice corrosion has not progressed. The maximum clearance erosion depth is smaller than that of SUS304 (Example 7).
The maximum clearance erosion depth was measured when SUS316L steel was immersed for 1000 hours in an aqueous solution in which a chloride ion concentration of 180 ppm, a nitrate ion concentration of 200 ppm, and ozone of 10 ppm coexisted. The results are shown in Table 2. The [NO 3 − ] / [Cl − ] molar concentration ratio at this time is 1.15, which satisfies the conditions for suppressing crevice corrosion shown in FIG. The crevice maximum erosion depth is 0 μm, and it can be said that crevice corrosion has not progressed. The maximum clearance erosion depth is smaller than that of SUS304.
(Comparative Example 4)
The maximum clearance erosion depth was measured when SUS316L steel was immersed for 1000 h in an aqueous solution in which a chloride ion concentration of 150 ppm, bicarbonate ion, and ozone of 1 ppm coexisted. The results are shown in Table 2. The concentration of bicarbonate ions is controlled so as to satisfy the anion / chloride ion molar concentration ratio in the crevice corrosion inhibition region shown in FIG. The crevice maximum erosion depth is 80 μm, and it can be said that crevice corrosion is in progress. That is, even at the same molar concentration that satisfies the conditions for crevice corrosion inhibition shown in FIG. 6, it can be said that nitrate ions inhibit crevice corrosion but bicarbonate ions do not inhibit crevice corrosion.
(Comparative Example 5)
The maximum clearance erosion depth was measured when SUS316L steel was immersed for 1000 h in an aqueous solution in which a chloride ion concentration of 150 ppm, sulfate ions, and ozone of 1 ppm coexisted. The results are shown in Table 2. The concentration of sulfate ions is controlled so as to satisfy the anion / chloride ion molar concentration ratio in the crevice corrosion inhibition region shown in FIG. The crevice maximum erosion depth is 165 μm, and it can be said that crevice corrosion is in progress. That is, it can be said that even at the same molar concentration satisfying the condition of crevice corrosion inhibition shown in FIG. 6, nitrate ions inhibit crevice corrosion but sulfate ions do not inhibit crevice corrosion.
(Comparative Example 6)
The maximum clearance erosion depth was measured when SUS316L steel was immersed for 1000 h in an aqueous solution in which a chloride ion concentration of 100 ppm, a nitrate ion concentration of 10 ppm, and ozone of 1 ppm coexisted. The results are shown in Table 2. The [NO 3 − ] / [Cl − ] molar concentration ratio at this time is 0.109, which is a condition for suppressing the non-corrosion of the clearance shown in FIG. The crevice maximum erosion depth is 68 μm, and it can be said that crevice corrosion is in progress.
塩化物イオン濃度１００ｐｐｍ、硝酸イオン濃度５０ｐｐｍ、硫酸イオン濃度１５ｐｐｍ、及び、オゾン１ｐｐｍが共存した水溶液中にＳＵＳ３０４鋼を１０００ｈ浸漬させた場合のすきま最大浸食深さを測定した。結果を表３に示す。すきま最大浸食深さは２μｍであり、すきま腐食は生じていないといえる。この時の水溶液の電気伝導度は３２ｍＳ／ｃｍであった。また、［ＮＯ3 -］／［Ｃｌ-］モル濃度比は、０．６５であり、図６に示すすきま腐食抑制の条件を満たしている。
（実施例９）
塩化物イオン濃度２００ｐｐｍ、硝酸イオン濃度５０ｐｐｍ、硫酸イオン濃度０ｐｐｍ、及び、オゾン０．１ｐｐｍが共存した水溶液中にＳＵＳ３０４鋼を１０００ｈ浸漬させた場合のすきま最大浸食深さを測定した。結果を表３に示す。すきま最大浸食深さは５μｍであり、すきま腐食は生じていないといえる。この時の水溶液の電気伝導度は２５ｍＳ／ｃｍであった。また、［ＮＯ3 -］／［Ｃｌ-］モル濃度比は、０．２７３であり、図６に示すすきま腐食抑制の条件を満たしている。
（実施例１０）
塩化物イオン濃度１００ｐｐｍ、硝酸イオン濃度８８ｐｐｍ、硫酸イオン濃度０ｐｐｍ、及び、オゾン１ｐｐｍが共存した水溶液中にＳＵＳ３０４鋼を１０００ｈ浸漬させた場合のすきま最大浸食深さを測定した。結果を表３に示す。すきま最大浸食深さは１μｍであり、すきま腐食は生じていないといえる。この時の水溶液の電気伝導度は３０ｍＳ／ｃｍであった。また、［［ＮＯ3 -］／［Ｃｌ-］モル濃度比は、１．１０であり、図６に示すすきま腐食抑制の条件を満たしている。
（実施例１１）
塩化物イオン濃度１００ｐｐｍ、硝酸イオン濃度６０ｐｐｍ、硫酸イオン濃度６０ｐｐｍ、及び、オゾン１ｐｐｍが共存した水溶液中にＳＵＳ３０４鋼を１０００ｈ浸漬させた場合のすきま最大浸食深さを測定した。結果を表３に示す。すきま最大浸食深さは２μｍであり、すきま腐食は生じていないといえる。この時の水溶液の電気伝導度は４０ｍＳ／ｃｍであった。また、［ＮＯ3 -］／［Ｃｌ-］モル濃度比は、１．１０であり、図６に示すすきま腐食抑制の条件を満たしている。
（比較例７）
塩化物イオン濃度１００ｐｐｍ、硝酸イオン濃度１０ｐｐｍ、硫酸イオン濃度１５ｐｐｍ、及び、オゾン０．１ｐｐｍが共存した水溶液中にＳＵＳ３０４鋼を１０００ｈ浸漬させた場合のすきま最大浸食深さを測定した。結果を表３に示す。すきま最大浸食深さは１２０μｍであり、すきま腐食が進行しているのが分かる。この時の水溶液の電気伝導度は１５ｍＳ／ｃｍであった。また、［ＮＯ3 -］／［Ｃｌ-］モル濃度比は、０．１１であり、図６に示すすきま腐食非抑制の条件となっている。
（比較例８）
塩化物イオン濃度１００ｐｐｍ、硝酸イオン濃度０ｐｐｍ、硫酸イオン濃度６０ｐｐｍ、及び、オゾン０．１ｐｐｍが共存した水溶液中にＳＵＳ３０４鋼を１０００ｈ浸漬させた場合のすきま最大浸食深さを測定した。結果を表３に示す。すきま最大浸食深さは２２０μｍであり、すきま腐食が進行しているのが分かる。この時の水溶液の電気伝導度は２３ｍＳ／ｃｍであった。また、［ＮＯ3 -］／［Ｃｌ-］モル濃度比は０であり、図６に示すすきま腐食非抑制の条件となっている
The maximum erosion depth was measured when SUS304 steel was immersed for 1000 hours in an aqueous solution in which a chloride ion concentration of 100 ppm, a nitrate ion concentration of 50 ppm, a sulfate ion concentration of 15 ppm, and ozone of 1 ppm coexisted. The results are shown in Table 3. The crevice maximum erosion depth is 2 μm, and it can be said that crevice corrosion has not occurred. The electrical conductivity of the aqueous solution at this time was 32 mS / cm. The [NO 3 − ] / [Cl − ] molar concentration ratio is 0.65, which satisfies the conditions for inhibiting crevice corrosion shown in FIG.
Example 9
The maximum erosion depth was measured when SUS304 steel was immersed for 1000 hours in an aqueous solution in which a chloride ion concentration of 200 ppm, a nitrate ion concentration of 50 ppm, a sulfate ion concentration of 0 ppm, and ozone of 0.1 ppm coexisted. The results are shown in Table 3. The crevice maximum erosion depth is 5 μm, and it can be said that crevice corrosion has not occurred. The electrical conductivity of the aqueous solution at this time was 25 mS / cm. The [NO 3 − ] / [Cl − ] molar concentration ratio is 0.273, which satisfies the conditions for suppressing crevice corrosion shown in FIG.
(Example 10)
The maximum clearance erosion depth was measured when SUS304 steel was immersed in an aqueous solution in which a chloride ion concentration of 100 ppm, a nitrate ion concentration of 88 ppm, a sulfate ion concentration of 0 ppm, and ozone of 1 ppm coexisted for 1000 hours. The results are shown in Table 3. The crevice maximum erosion depth is 1 μm, and it can be said that crevice corrosion has not occurred. The electrical conductivity of the aqueous solution at this time was 30 mS / cm. The [[NO 3 − ] / [Cl − ] molar concentration ratio is 1.10, which satisfies the conditions for inhibiting crevice corrosion shown in FIG.
(Example 11)
The maximum clearance erosion depth was measured when SUS304 steel was immersed for 1000 hours in an aqueous solution in which a chloride ion concentration of 100 ppm, a nitrate ion concentration of 60 ppm, a sulfate ion concentration of 60 ppm, and ozone of 1 ppm coexisted. The results are shown in Table 3. The crevice maximum erosion depth is 2 μm, and it can be said that crevice corrosion has not occurred. The electrical conductivity of the aqueous solution at this time was 40 mS / cm. The [NO 3 − ] / [Cl − ] molar concentration ratio is 1.10, which satisfies the conditions for crevice corrosion inhibition shown in FIG.
(Comparative Example 7)
The maximum erosion depth was measured when SUS304 steel was immersed for 1000 hours in an aqueous solution in which a chloride ion concentration of 100 ppm, a nitrate ion concentration of 10 ppm, a sulfate ion concentration of 15 ppm, and ozone of 0.1 ppm coexisted. The results are shown in Table 3. The maximum erosion depth of the crevice is 120 μm, and it can be seen that crevice corrosion is in progress. The electrical conductivity of the aqueous solution at this time was 15 mS / cm. The [NO 3 − ] / [Cl − ] molar concentration ratio is 0.11, which is a condition for preventing crevice corrosion as shown in FIG.
(Comparative Example 8)
The maximum clearance erosion depth was measured when SUS304 steel was immersed for 1000 hours in an aqueous solution in which a chloride ion concentration of 100 ppm, a nitrate ion concentration of 0 ppm, a sulfate ion concentration of 60 ppm, and ozone of 0.1 ppm coexisted. The results are shown in Table 3. The crevice maximum erosion depth is 220 μm, and it can be seen that crevice corrosion is in progress. The electrical conductivity of the aqueous solution at this time was 23 mS / cm. Further, the [NO 3 − ] / [Cl − ] molar concentration ratio is 0, which is a condition for preventing crevice corrosion as shown in FIG.
実施例８−１１及び比較例７，８の結果から、硫酸イオン濃度がおおよそ３０ｐｐｍ以下である場合、少なくとも溶液の電気伝導度が２５ｍＳ/ｃｍ以上になるように硝酸イオン濃度（［ＮＯ3 -］／［Ｃｌ-］モル濃度比）を制御すれば、すきま腐食を防止することができる。ＳＵＳ３１６Ｌ等の他のステンレス鋼に関しても同様のことが言える。
（実施例１２）
図５は、本発明を適用したオゾンによる有機物分解システムの一例を示したものである。オゾン発生装置１０２は、コロナ放電などの放電式オゾン発生器で、放電時に酸素が一部オゾンへと化学変化する。所定の濃度になったオゾン含有気体は金属製の反応層１０５に送られる。有機物含有被分解物（タンク）１０４には有機物を含む被処理水が蓄えられており、反応槽１０５内でのオゾンによる分解反応の進行程度や液量に応じて適宜処理水が反応槽１０５に送液される。反応層１０５では注入されたオゾン含有気体によって有機物が分解される。また反応槽１０５には濃度、電位、電導度検出部（システム）が備えられており、その情報（信号）が液量制御部に送られ、その情報を元に薬液タンクから硝酸イオンを含む液が反応層に注入される。注入する硝酸量はたとえばオゾン濃度に基づく情報で制御する場合、濃度、電位、電導度検出部においてオゾン濃度、塩化物イオン濃度および硝酸イオン濃度を検出する。図６は、図３に示したＳＵＳ３０４またはＳＵＳ３１６Ｌ(両者に明確な差は見られない)基づいて作成したオゾン濃度とすきま腐食を防止するために必要な［ＮＯ3 -］／［Ｃｌ-］モル比との関係を示したものである。この図に基づいて、測定されたオゾン濃度と塩化物濃度の測定値から、すきま腐食を抑制するために必要な硝酸イオン濃度を求めることができる。この値と測定された硝酸イオン濃度とを比較して、足りない場合は薬液タンクから硝酸イオンを含む液が反応層に注入される。
From the results of Examples 8-11 and Comparative Examples 7 and 8, when the sulfate ion concentration is approximately 30 ppm or less, the nitrate ion concentration ([NO 3 − ]) is set so that at least the electric conductivity of the solution is 25 mS / cm or more. / [Cl − ] molar concentration ratio) can be controlled to prevent crevice corrosion. The same can be said for other stainless steels such as SUS316L.
(Example 12)
FIG. 5 shows an example of an organic matter decomposition system using ozone to which the present invention is applied. The ozone generator 102 is a discharge type ozone generator such as corona discharge, and oxygen partially changes into ozone during discharge. The ozone-containing gas having a predetermined concentration is sent to the metal reaction layer 105. Water to be treated containing organic matter is stored in the organic matter-containing material to be decomposed (tank) 104, and the treated water is appropriately supplied to the reaction tank 105 according to the degree of progress of the decomposition reaction by ozone in the reaction tank 105 and the amount of liquid. The liquid is sent. In the reaction layer 105, organic substances are decomposed by the injected ozone-containing gas. In addition, the reaction tank 105 is provided with a concentration, potential, and conductivity detection unit (system), and the information (signal) is sent to the liquid volume control unit. Is injected into the reaction layer. When the amount of nitric acid to be injected is controlled by information based on, for example, ozone concentration, the concentration, potential, and conductivity detectors detect the ozone concentration, chloride ion concentration, and nitrate ion concentration. FIG. 6 shows the ozone concentration and the [NO 3 − ] / [Cl − ] mole necessary for preventing crevice corrosion prepared based on SUS304 or SUS316L shown in FIG. 3 (there is no clear difference between them). It shows the relationship with the ratio. Based on this figure, the nitrate ion concentration required to suppress crevice corrosion can be obtained from the measured values of the ozone concentration and the chloride concentration. When this value is compared with the measured nitrate ion concentration, if it is insufficient, a liquid containing nitrate ions is injected from the chemical tank into the reaction layer.
電気伝導度を使用して、制御する場合も同様である。すなわち注入する硝酸量はたとえばオゾン濃度に基づく情報で制御する場合、濃度、電位、電導度検出部において電気伝導度を検出する。電気伝導度が２５ｍＳ／ｃｍに達していない場合は、その濃度に達するまで薬液タンクから硝酸イオンを含む液を反応層に注入することによりすきま腐食を防止することができる。 The same applies to the case of controlling using electric conductivity. That is, when the amount of nitric acid to be injected is controlled by information based on the ozone concentration, for example, the electrical conductivity is detected by the concentration, potential, and electrical conductivity detector. When the electrical conductivity does not reach 25 mS / cm, crevice corrosion can be prevented by injecting a liquid containing nitrate ions from the chemical tank into the reaction layer until the concentration is reached.
硝酸イオン濃度を測定するためには、隔膜式のイオン選択電極によるセンサーを適用できる。ただし、被処理水のイオン強度の影響や妨害イオンの存在が正確な値に至らないときがあるので、その場合は、測定された値の誤差範囲を把握し、データベースに反映するか、あるいは他の手段を用いる。塩化物イオン濃度も硝酸イオン同様に隔膜式のイオン選択電極を用いることができる。オゾン濃度は紫外線吸収法や比色法等が適用できるが、被処理水に溶解している溶存オゾン濃度を簡便に測定できる比色法を用いるのが好ましい。 In order to measure the nitrate ion concentration, a sensor using a diaphragm type ion selective electrode can be applied. However, the influence of the ionic strength of the water to be treated and the presence of interfering ions may not reach an accurate value. In that case, grasp the error range of the measured value and reflect it in the database, or other Is used. As for the chloride ion concentration, a diaphragm type ion selective electrode can be used as in the case of nitrate ion. As the ozone concentration, an ultraviolet absorption method, a colorimetric method, or the like can be applied, but it is preferable to use a colorimetric method that can easily measure the dissolved ozone concentration dissolved in the water to be treated.
すきま腐食が生じないかどうかを判定するには、ステンレス鋼の電位が図７に示すある任意のオゾン濃度における再不動態化電位より低くなっていることで確認することができる。濃度、電位、電導度検出部においてステンレス鋼の電位を検出することができる。電位は、参照電極を使用して対象とする構成材料であるステンレス鋼からなる金属電極との間の電位をボルテージフォロア型作動アンプを使用して測定する。これによりシステムの接地状態によらず正しい電位を測定することができる。参照電極を保護したい金属の近傍に設置することが可能である場合は、金属電極を設けずに直接保護したい金属と参照電極との間の電位差を測定し、これを腐食電位とすることも可能である。このようにして測定された腐食電位が、別途測定されたオゾン濃度と図７に示す関係から求めたすきま再不動態化電位と比較して、その値がすきま再不動態化電位より低ければすきま腐食が生じないと判定することができる。判定によりすきま腐食が抑制されていないとされた場合、前述したように硝酸イオンを添加することにより、すきま再不動態化電位を上げることの他に、オゾン濃度を下げることが挙げられる。反応層中のオゾン濃度が低下すれば図３に示すように腐食電位が低下するために、すきま再不動態化より腐食電位が低くなり、すきま腐食を抑制できるようになる。しかし、オゾン濃度が低下することにより有機物の分解速度は低下することになる。 To determine whether crevice corrosion does not occur, it can be confirmed that the potential of stainless steel is lower than the repassivation potential at an arbitrary ozone concentration shown in FIG. The potential of the stainless steel can be detected in the concentration, potential, and conductivity detector. The potential is measured using a voltage follower type operational amplifier with respect to a metal electrode made of stainless steel, which is a target constituent material, using a reference electrode. As a result, the correct potential can be measured regardless of the ground state of the system. If it is possible to install the reference electrode in the vicinity of the metal to be protected, the potential difference between the metal to be protected and the reference electrode can be directly measured without providing the metal electrode, and this can be used as the corrosion potential. It is. When the corrosion potential measured in this way is compared with the separately measured ozone concentration and the gap repassivation potential obtained from the relationship shown in FIG. 7, if the value is lower than the gap repassivation potential, crevice corrosion will occur. It can be determined that it does not occur. When it is determined that the crevice corrosion is not suppressed by the determination, it is possible to lower the ozone concentration in addition to increasing the gap repassivation potential by adding nitrate ions as described above. If the ozone concentration in the reaction layer decreases, the corrosion potential decreases as shown in FIG. 3, so that the corrosion potential becomes lower than the clearance repassivation, and the crevice corrosion can be suppressed. However, the degradation rate of the organic matter is lowered by decreasing the ozone concentration.
以上で説明した実施例によれば、塩化物イオンが含まれる被処理液中にオゾンを添加した時の強酸化環境によって引き起こされるすきま腐食を防止できる。また、システムを構成する金属材料にとって厳しい腐食環境下においても耐食性を維持することができる。これにより、汎用金属材料の使用が可能となり、信頼性が高く長寿命な有機物分解システムを提供することができる。 According to the embodiment described above, crevice corrosion caused by a strong oxidizing environment when ozone is added to a liquid to be treated containing chloride ions can be prevented. Further, the corrosion resistance can be maintained even in a severe corrosive environment for the metal materials constituting the system. Thereby, it is possible to use a general-purpose metal material, and it is possible to provide a highly reliable and long-life organic material decomposition system.
本発明は、オゾンを用いた漂泊、汚泥処理、殺菌、防汚、脱臭、医薬品合成等のプロセスにも適用することができる。 The present invention can also be applied to processes such as drifting using ozone, sludge treatment, sterilization, antifouling, deodorization, and pharmaceutical synthesis.
１０１ 薬液調整タンク
１０２ オゾン発生装置
１０３ 液量制御部
１０４ 有機物含有被分解物
１０５ 反応層
１０６ 濃度、電位、電導度検出
DESCRIPTION OF SYMBOLS 101 Chemical liquid adjustment tank 102 Ozone generator 103 Liquid volume control part 104 Organic substance containing to-be-decomposed thing 105 Reaction layer 106 Concentration, electric potential, and electrical conductivity detection
Claims (10)
前記有機物を含む被処理液中に硝酸イオンを注入する薬液注入システムを備え、
前記薬液注入システムは、被処理液中の塩化物イオン及び硝酸イオンの濃度、又は、被処理液の電気伝導度の情報に基づいて、被処理液中に注入する硝酸イオンの量を制御することを特徴とする有機物分解システム。 In organic matter decomposition system that decomposes organic matter using ozone,
A chemical solution injection system for injecting nitrate ions into the liquid to be treated containing the organic matter,
The chemical solution injection system controls the amount of nitrate ions injected into the liquid to be processed based on the concentration of chloride ions and nitrate ions in the liquid to be processed, or information on the electrical conductivity of the liquid to be processed. Organic matter decomposition system characterized by.
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| JP2020169364A (en) * | 2019-04-04 | 2020-10-15 | 日立Ｇｅニュークリア・エナジー株式会社 | Liquid treatment system and adsorption system |
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| JP2017218656A (en) * | 2016-06-10 | 2017-12-14 | 東京電力ホールディングス株式会社 | Local corrosion inhibition method of stainless steel and storage method of metal container |
| JP2020169364A (en) * | 2019-04-04 | 2020-10-15 | 日立Ｇｅニュークリア・エナジー株式会社 | Liquid treatment system and adsorption system |
| JP7312593B2 (en) | 2019-04-04 | 2023-07-21 | 日立Ｇｅニュークリア・エナジー株式会社 | Liquid handling system and adsorption system |
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