JP3546712B2 - Operating method of membrane deaerator - Google Patents
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【０００１】
【発明の属する技術分野】
本発明は膜脱気装置の運転方法に係り、特に、被処理水中のアルミニウム、鉄等の金属由来のスケールによる膜面の汚染を防止して膜脱気装置を長期に亘り安定に運転する方法に関するものである。
【０００２】
【従来の技術】
水の脱炭酸手段としては、脱気塔や脱炭酸塔が知られているが、最近では、装置の小型化が可能で安価な膜脱気装置がこれらに代る脱炭酸手段として用いられるようになってきている。
【０００３】
膜脱気装置は、テフロン系膜等の疎水性の高分子膜で内部を原水側と透過側とに仕切り、透過側を真空ポンプで減圧することにより、原水側に流入させた被処理水中の溶存ガスを膜透過させて除去するものである。
【０００４】
従来、このような膜脱気装置で脱炭酸処理を行う場合、被処理水中の炭酸成分を高度に除去するために、被処理水に酸を添加して被処理水をｐＨ酸性とし、被処理水中に炭酸水素イオン（ＨＣＯ３ −）として溶存している炭酸成分を炭酸ガス（ＣＯ２）に変え、その後膜脱気装置で脱気処理する方法が採用されている。
【０００５】
なお、このようにして膜脱気装置で脱炭酸を行った場合、炭酸成分の除去により脱炭酸処理後の水は、脱炭酸処理前の水よりもｐＨが上昇することが知られている。例えば“ＵＬＴＲＡ ＰＵＲＥ ＷＡＴＥＲ Ｖｏｌ．２ Ｎｏ．２（２０頁２４〜１５行）”には、このｐＨの上昇の程度は被処理水の炭酸ガス濃度によっても異なるが、一般にｐＨで１．５程度上昇する旨の記載がある。
【０００６】
【発明が解決しようとする課題】
このような膜脱気装置に、アルミニウム等の金属イオンを含有する水を通水して脱炭酸処理した場合、膜面に水酸化アルミニウム等の金属イオン由来のスケールが生成し、経時により膜性能が低下するという問題があった。
【０００７】
本発明は膜脱気装置に被処理水を通水して脱気処理するに当り、被処理水中の金属イオンに由来するスケールの生成を効果的に防止して、膜脱気装置を長期に亘り安定に運転することを可能とする膜脱気装置の運転方法を提供することを目的とする。
【０００８】
【課題を解決するための手段】
本発明の膜脱気装置の運転方法は、アルミニウム濃度が１０ｐｐｂ以上、又は鉄濃度が５０ｐｐｂ以上で、かつ炭酸成分を５ｍｇ／Ｌ（ＨＣＯ ３ − 換算）以上含む被処理水を、膜脱気装置に通水して処理するに当り、該膜脱気装置の出口水のｐＨが５．５以下となるように該被処理水のｐＨを調整することにより該膜脱気装置の膜面への金属由来のスケールの発生を防止することを特徴とする。
【０００９】
本発明者は、膜脱気装置の脱気膜面のスケールの発生要因とその防止策について検討を重ねた結果、次のような知見を得た。
【００１０】
即ち、被処理水中のＨＣＯ３ −をＣＯ２の形態とするために、被処理水に塩酸（ＨＣｌ）等の酸を添加して、例えばｐＨ５．５の酸性条件とした水を膜脱気装置に通水して脱炭酸を行った場合、前述の如く、脱炭酸によりｐＨが上昇し、系内の水のｐＨは６．５程度あるいはそれ以上となる。
【００１１】
この水酸化アルミニウムの溶解度は、ｐＨ５．５〜７．５の範囲ではｐＨの上昇と共に低下し、ｐＨ５．５では８８ｐｐｂ（ａｓ Ａｌ）であるのに対し、ｐＨ６．０での水酸化アルミニウムの溶解度は３ｐｐｂ（ａｓ Ａｌ）と格段に低下する。このため、被処理水中に３０ｐｐｂ程度のアルミニウムイオンが存在する場合、ｐＨ５．５の膜脱気装置入口水では水酸化アルミニウムの析出は起こらないが、膜脱気装置における脱炭酸処理後のｐＨが上昇した水では、水酸化アルミニウムの析出が起こる。そして、この析出した水酸化アルミニウムが膜面を覆い、膜性能を低下させる。このようなｐＨ上昇によるスケール析出は、アルミニウムに限らず鉄イオンに由来して起こる場合もある。
【００１２】
そこで、膜脱気装置の入口水のｐＨと出口水のｐＨとの関係について調べたところ、入口水のｐＨが６以下であっても、４．８を超える場合には、出口水のｐＨは１〜２程度上昇してｐＨが５．５を超えるようになり、スケールが生成するが、入口水のｐＨが４．８以下の場合には出口水のｐＨ値は殆ど上昇せずｐＨ５．５以下に維持されること、そして、出口水のｐＨが５．５以下であれば、水酸化アルミニウム等のスケールの生成は防止されることが判明した。
【００１３】
膜脱気装置の入口水のｐＨが４．８を超えると出口水のｐＨが上昇するのに対して、入口水のｐＨが４．８以下では出口水のｐＨが殆ど上昇しない理由は、ｐＨ４．８を超える水では水中の脱炭酸によりｐＨが上昇するが、ｐＨ４．８以下の水では、ｐＨ調整のために添加した塩酸等の酸やＨ形カチオン交換搭でのカチオン交換処理により生じたＨ＋のような酸成分が脱炭酸によるｐＨ上昇を阻止するためと考えられる。
【００１４】
このようなことから、膜脱気装置の入口水のｐＨを酸性に、好ましくはｐＨ４．８以下の酸性として膜脱気装置の出口水のｐＨが５．５以下となるようにすることにより、アルミニウム等の金属イオンに由来するスケール生成を防止して安定な運転を継続することが可能となる。
【００１５】
【発明の実施の形態】
以下に本発明の実施の形態を詳細に説明する。
【００１６】
図１（ａ）〜（ｃ）は本発明の実施の形態を示す系統図である。
【００１７】
本発明においては、膜脱気装置による脱気処理に当り、膜脱気装置出口水のｐＨが５．５以下となるように、被処理水に酸を添加するなどしてｐＨ調整する。出口水のｐＨが５．５を超えると、前述の如く、スケール析出が起こる。出口水のｐＨを５．５以下とすることにより、スケールの析出を防止することができる。
【００１８】
なお、本発明方法は、膜脱気装置出口水のｐＨが５．５以下となるように酸を注入するなどして被処理水のｐＨを調整する方法に限定されるものではなく、膜脱気装置入口水のｐＨを監視して好ましくは入口水のｐＨが４．８以下となるように酸を注入するなどしてｐＨ調整をしても良い。後者の場合でも、膜脱気装置出口水のｐＨを５．５以下として、スケール析出を防止することができる。
【００１９】
図１（ａ）の方法は、膜脱気装置出口水のｐＨに基いて酸の注入制御を行う方法であり、水道水等の被処理水を膜脱気装置１に通水するに当り、酸貯槽２から薬注ポンプＰによりＨＣｌ水溶液等の酸を添加し、ラインミキサー（スタティックミキサー）３で混合した後、膜脱気装置１に供給するが、その際、膜脱気装置１の出口水のｐＨをｐＨ計４で検出し、このｐＨ計４の検出値がｐＨ５．５以下の所定ｐＨとなるように比例制御にて薬注ポンプＰの作動を制御する。
【００２０】
図１（ｂ）の方法は、膜脱気装置入口水のｐＨに基いて酸の注入制御を行う方法であり、水道水等の被処理水を膜脱気装置１に通水するに当り、酸貯槽２から薬注ポンプＰによりＨＣｌ水溶液等の酸を添加し、ラインミキサー（スタティックミキサー）３で混合した後、膜脱気装置１に供給するが、その際、膜脱気装置１の入口水のｐＨをｐＨ計４で検出し、このｐＨ計４の検出値が好ましくはｐＨ４．８以下の所定ｐＨとなるように比例制御にて薬注ポンプＰの作動を制御する。この方法においても、膜脱気装置１の出口水のｐＨが５．５以下となるように被処理水のｐＨ調整がなされ、スケール析出を防止して安定な運転を継続することができる。
【００２１】
また、本発明における被処理水のｐＨ調整は酸の添加による他、Ｈ形カチオン交換処理によるものであっても良い。図１（ｃ）の方法は、被処理水をＨ形カチオン交換搭５に通水して所定のｐＨに調整した後、膜脱気装置１に通水する方法であり、膜脱気装置１の出口水のｐＨが５．５以下となるようにＨ形カチオン交換搭５で被処理水のカチオン交換処理が行われる。ここで、Ｈ形カチオン交換搭５のイオン交換樹脂としては、栗田工業（株）製「ＥＸ−ＣＧ」、バイエル社製「Ｌｅｗａｔｉｔ ＣＮＰ８０」等の酸性イオン交換樹脂を用いることができる。なお、この場合においてもｐＨ計４は膜脱気装置１の入口側に設け、膜脱気装置１の入口水のｐＨに基いて制御を行っても良い。
【００２２】
なお、本発明において、膜脱気装置出口水のｐＨは５．５以下であれば良く、ｐＨの下限値については特に制限はないが、系内の腐食、酸添加による薬剤コストやＨ形カチオン交換樹脂による処理コストを考慮した場合、入口水のｐＨ３〜４．８の範囲、出口水のｐＨ３〜５．５の範囲とするのが実用的である。
【００２３】
膜脱気装置に使用する膜としては、例えばポリプロピレンのように、疎水性で所定ｐＨ値の酸性水中での使用にも耐える素材のものであれば良く、中空糸型、スパイラル型等を用いることができ、特に制限はない。被処理水流路の配管、その他の機器材質については、酸注入点又はＨ形カチオン交換搭より下流側についてはステンレス鋼等の耐食性材料を用いる必要がある。
【００２４】
なお、図１に示す方法は本発明の一例であって、本発明はその要旨を超えない限り何ら図示のものに限定されるものではない。例えば、酸の添加は、配管に直接注入する他、別途、混合槽を設けて行うこともできる。
【００２５】
このような本発明の方法は、被処理水の脱気処理により炭酸成分が除去されて、膜脱気装置の入口水ｐＨ５．５程度、出口水ｐＨ６．５程度或いはそれ以上の通常の運転条件ではスケール析出の問題がある水の処理、即ち、次の(1) 及び (2)の条件を満たすような被処理水の処理に有効に適用される。
【００２６】
(1) アルミニウム濃度が１０ｐｐｂ以上でｐＨ上昇により水酸化アルミニウムスケー
ル析出の問題がある水。又は、鉄濃度が５０ｐｐｂ以上でｐＨ上昇により水酸化第
二鉄スケール析出の問題がある水。
(2) 炭酸成分を５ｍｇ／Ｌ（ＨＣＯ３ −換算）以上含み、炭酸ガス除去率７５％以上で
運転した場合、膜脱気装置入口水ｐＨ５．０程度の通常の運転条件ではｐＨが１．
５〜２．０程度上昇するような水。
【００２７】
【実施例】
以下に実施例及び比較例を挙げて本発明をより具体的に説明する。
【００２８】
実施例１
図１（ｂ）に示す方法で、厚木市水（Ａｌ濃度約３０ｐｐｂ、炭酸ガス濃度３０ｍｇ／Ｌ（ＨＣＯ３ −として）、溶存酵素（ＤＯ）濃度８ｍｇ／Ｌ）にＨＣｌを注入してｐＨ４．６に調整した水を膜脱気装置１に通水して脱気処理した。膜脱気装置１の出口水のｐＨは４．６〜４．７にすることができ、出口水のｐＨの上昇は殆ど認められなかった。また、通水初期の炭酸ガス除去率は８０％でＤＯ除去率は９５％であった。
【００２９】
この膜脱気装置１の運転を２ヶ月継続したところ、ＤＯ除去率は９４％で膜性能の低下は殆ど認められなかった。また、２ヶ月の通水後、脱気膜を解体して膜面のＳＥＭ分析を行い、膜面の水酸化アルミニウムスケールの有無を調べたところ、スケールの付着は認められなかった。
【００３０】
実施例２
実施例１と同じ原水を用いて、図１（ｃ）に示す如く、カチオン交換処理によりｐＨ調整した後、膜脱気装置１に通水した。Ｈ形カチオン交換搭５には栗田工業（株）製「ＥＸ−ＣＧ」酸性イオン交換樹脂を充填し、ＳＶ＝１５ｈｒ−１で通水した。このカチオン交換処理水のｐＨは３．２であった。このカチオン交換処理水を実施例１と同様の条件で膜脱気装置１に通水した。
【００３１】
その結果、膜脱気装置１の出口水のｐＨは３．２〜３．３でありｐＨの上昇は殆ど認められず、また初期のＤＯ除去率は９５％であった。
【００３２】
この膜脱気装置１を２ヶ月運転したところ、ＤＯ除去率は９４％で膜性能の低下は認められなかった。また、２ヶ月の通水後、脱気膜を解体して膜面のＳＥＭ分析を行ったところ、膜面の水酸化アルミニウムスケール付着は認められなかった。
【００３３】
比較例１
実施例１において、膜脱気装置の入口水のｐＨを５．０としたこと以外は全く同様にして処理を行ったところ、膜脱気装置出口水のｐＨは６．５に上昇した。また、通水初期のＤＯ除去率は実施例１と同等であったが、２ヶ月後のＤＯ除去率は６８％と大きく低下した。そして、２ヶ月通水後、実施例１と同様にして膜面を調べたところ、水酸化アルミニウムスケールが付着しており、これが膜面性能低下の原因となっていることが確認された。
【００３４】
【発明の効果】
以上詳述した通り、本発明の膜脱気装置の運転方法によれば、膜脱気装置に被処理水を通水して脱気処理するに当り、被処理水中の金属イオンに由来するスケールの生成を効果的に防止して、膜脱気装置を長期に亘り安定に運転することができる。
【図面の簡単な説明】
【図１】本発明の実施の形態を示す系統図である。
【符号の説明】
１ 膜脱気装置
２ 酸貯槽
３ ラインミキサー
４ ｐＨ計
５ Ｈ形カチオン交換搭[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for operating a membrane deaerator, and more particularly to a method for stably operating a membrane deaerator for a long period of time by preventing contamination of the membrane surface by scales derived from metals such as aluminum and iron in the water to be treated. It is about.
[0002]
[Prior art]
As dewatering means for water, degassing towers and decarbonating towers are known, but recently, an inexpensive membrane degassing apparatus that can be downsized and used as an alternative decarbonizing means has been used. It is becoming.
[0003]
The membrane deaerator is divided into a raw water side and a permeate side by a hydrophobic polymer membrane such as a Teflon-based membrane, and the permeate side is depressurized by a vacuum pump, so that the inside of the treated water flowing into the raw water side is reduced. The dissolved gas is removed through the membrane.
[0004]
Conventionally, when performing decarboxylation treatment with such a membrane deaerator, in order to remove carbonic acid components in the water to be treated to a high degree, an acid is added to the water to be treated to make the water to be treated with a pH acid, A method has been adopted in which the carbonic acid component dissolved in water as hydrogen carbonate ions (HCO 3 − ) is changed to carbon dioxide gas (CO 2 ), and then deaeration is performed by a membrane deaerator.
[0005]
It is known that when decarboxylation is performed by the membrane deaerator in this manner, the water after the decarboxylation treatment has a higher pH than the water before the decarboxylation treatment due to the removal of the carbonate component. For example, in "ULTRA PURE WATER Vol.2 No.2 (p.20, lines 24 to 15)", the degree of the increase in pH varies depending on the concentration of carbon dioxide in the water to be treated, but generally, the increase in pH is about 1.5. There is a statement to do.
[0006]
[Problems to be solved by the invention]
When water containing metal ions such as aluminum is passed through such a membrane deaerator and decarbonation treatment is performed, scales derived from metal ions such as aluminum hydroxide are generated on the membrane surface, and the membrane performance over time. However, there was a problem that was reduced.
[0007]
In the present invention, when dewatering is performed by passing water to be treated through a membrane deaerator, generation of scales derived from metal ions in the water to be treated is effectively prevented, and the membrane deaerator can be used for a long time. It is an object of the present invention to provide a method of operating a membrane deaerator that enables stable operation over a long period of time.
[0008]
[Means for Solving the Problems]
Method of operating a membrane degassing apparatus of the present invention, the aluminum concentration over 10 ppb, or iron concentration is more than 50 ppb, and a carbon component 5 mg / L - the water to be treated containing (HCO 3 basis) or more, membrane degasifier to hit the handle by passing water, membrane pH of outlet water degassing apparatus to the membrane surface of the membrane degasifier by adjusting the pH of該被treated water so that 5.5 or less It is characterized in that generation of scale derived from metal is prevented.
[0009]
The inventor of the present invention has repeatedly studied factors for generating scale on the degassing membrane surface of the membrane degassing device and measures for preventing the scale, and has obtained the following knowledge.
[0010]
That is, in order to convert HCO 3 — in the water to be treated into CO 2 , an acid such as hydrochloric acid (HCl) is added to the water to be treated, and the water is subjected to an acidic condition of pH 5.5, for example. When decarboxylation is performed by passing water through the system, as described above, the pH rises due to decarboxylation, and the pH of water in the system becomes about 6.5 or higher.
[0011]
The solubility of aluminum hydroxide decreases with increasing pH in the range of pH 5.5 to 7.5, and is 88 ppb (as Al) at pH 5.5, whereas the solubility of aluminum hydroxide at pH 6.0 is Is significantly reduced to 3 ppb (as Al). For this reason, when aluminum ions of about 30 ppb are present in the water to be treated, precipitation of aluminum hydroxide does not occur in the inlet water of the membrane deaerator at pH 5.5, but the pH after the decarbonation treatment in the membrane deaerator becomes lower. In the raised water, precipitation of aluminum hydroxide occurs. Then, the deposited aluminum hydroxide covers the film surface and lowers the film performance. Such scale precipitation due to an increase in pH may occur not only from aluminum but also from iron ions.
[0012]
Therefore, when the relationship between the pH of the inlet water of the membrane deaerator and the pH of the outlet water was examined, if the pH of the inlet water was 6 or less and the pH of the outlet water exceeded 4.8, the pH of the outlet water became The pH rises by about 1 to 2 so that the pH exceeds 5.5, and a scale is formed. However, when the pH of the inlet water is 4.8 or less, the pH value of the outlet water hardly increases and the pH of the water is 5.5. It has been found that if the temperature is maintained below, and if the pH of the outlet water is 5.5 or less, the formation of scale such as aluminum hydroxide is prevented.
[0013]
The reason why the pH of the outlet water rises when the pH of the inlet water of the membrane deaerator exceeds 4.8, whereas the pH of the outlet water hardly increases when the pH of the inlet water is 4.8 or less is that the pH 4 In the case of water exceeding 0.8, the pH increases due to decarboxylation in water, but in the case of water having a pH of 4.8 or lower, it is caused by an acid such as hydrochloric acid added for pH adjustment or by cation exchange treatment with an H-type cation exchange tower. It is considered that an acid component such as H + prevents a rise in pH due to decarboxylation.
[0014]
For this reason, by making the pH of the inlet water of the membrane deaerator acidic, preferably the acidity of pH 4.8 or less, and adjusting the pH of the outlet water of the membrane deaerator to 5.5 or less, It is possible to prevent the formation of scale derived from metal ions such as aluminum and to continue stable operation.
[0015]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail.
[0016]
1A to 1C are system diagrams showing an embodiment of the present invention.
[0017]
In the present invention, in the deaeration treatment by the membrane deaerator, the pH is adjusted by adding an acid to the water to be treated so that the pH of the outlet water of the membrane deaerator becomes 5.5 or less. When the pH of the outlet water exceeds 5.5, scale precipitation occurs as described above. By setting the pH of the outlet water to 5.5 or less, precipitation of scale can be prevented.
[0018]
The method of the present invention is not limited to the method of adjusting the pH of the water to be treated by, for example, injecting an acid so that the pH of the outlet water of the membrane deaerator becomes 5.5 or less. The pH may be adjusted by monitoring the pH of the gas inlet water and preferably by injecting an acid so that the pH of the inlet water is 4.8 or less. Even in the latter case, scale deposition can be prevented by adjusting the pH of the outlet water of the membrane deaerator to 5.5 or less.
[0019]
The method of FIG. 1A is a method of controlling the injection of an acid based on the pH of the outlet water of the membrane deaerator, and when the water to be treated such as tap water is passed through the membrane deaerator 1, An acid such as an aqueous HCl solution is added from the acid storage tank 2 by the chemical injection pump P, mixed with a line mixer (static mixer) 3, and then supplied to the membrane deaerator 1. At that time, the outlet of the membrane deaerator 1 The pH of the water is detected by the pH meter 4, and the operation of the chemical injection pump P is controlled by proportional control so that the detected value of the pH meter 4 becomes a predetermined pH of 5.5 or less.
[0020]
The method of FIG. 1B is a method of controlling the injection of an acid based on the pH of the water at the inlet of the membrane deaerator, and when the water to be treated such as tap water is passed through the membrane deaerator 1, An acid such as an aqueous HCl solution is added from the acid storage tank 2 by the chemical injection pump P, mixed with a line mixer (static mixer) 3 and then supplied to the membrane deaerator 1. The pH of the water is detected by the pH meter 4, and the operation of the chemical injection pump P is controlled by proportional control so that the detected value of the pH meter 4 is preferably a predetermined pH of 4.8 or less. In this method as well, the pH of the water to be treated is adjusted so that the pH of the outlet water of the membrane deaerator 1 becomes 5.5 or less, and scale deposition can be prevented and stable operation can be continued.
[0021]
Further, the pH of the water to be treated in the present invention may be adjusted not only by adding an acid but also by an H-type cation exchange treatment. The method shown in FIG. 1 (c) is a method in which the water to be treated is passed through an H-type cation exchange tower 5, adjusted to a predetermined pH, and then passed through a membrane deaerator 1. The cation exchange treatment of the water to be treated is performed in the H-type cation exchange tower 5 so that the pH of the outlet water of the above becomes 5.5 or less. Here, as the ion-exchange resin of the H-type cation exchange tower 5, an acidic ion-exchange resin such as "EX-CG" manufactured by Kurita Kogyo KK or "Lewatit CNP80" manufactured by Bayer AG can be used. Also in this case, the pH meter 4 may be provided on the inlet side of the membrane deaerator 1 and control may be performed based on the pH of the inlet water of the membrane deaerator 1.
[0022]
In the present invention, the pH of the water at the outlet of the membrane deaerator may be 5.5 or less, and the lower limit of the pH is not particularly limited. In consideration of the processing cost by the exchange resin, it is practical to set the pH of the inlet water to a range of 3 to 4.8 and the outlet water to a range of 3 to 5.5.
[0023]
The membrane used for the membrane deaerator may be any material that is hydrophobic and can withstand use in acidic water having a predetermined pH value, such as polypropylene, and may be a hollow fiber type, a spiral type, or the like. And there are no particular restrictions. It is necessary to use a corrosion-resistant material, such as stainless steel, for the piping of the water passage to be treated and other equipment materials downstream of the acid injection point or the H-type cation exchange tower.
[0024]
Note that the method shown in FIG. 1 is an example of the present invention, and the present invention is not limited to those shown in the drawings unless it exceeds the gist. For example, the addition of the acid can be performed by directly adding the acid to the pipe or separately providing a mixing tank.
[0025]
In the method of the present invention, the carbon dioxide component is removed by the degassing treatment of the water to be treated, and the pH of the inlet water of the membrane degassing apparatus is about 5.5, the pH of the outlet water is about 6.5, or more. in treatment of water it has a problem of scale deposition, i.e., Ru is effectively applied to treated water that meets the conditions of the following (1) and (2) process.
[0026]
(1) Water having a problem of aluminum hydroxide scale precipitation due to an increase in pH at an aluminum concentration of 10 ppb or more. Or, water having an iron concentration of 50 ppb or more and having a problem of ferric hydroxide scale precipitation due to a rise in pH.
(2) a carbonate component 5 mg / L - include (HCO 3 basis) or more, when the plant is operated with carbon dioxide gas removal rate of 75% or more, the pH is in the normal operating conditions of the membrane degasifier about inlet water pH 5.0 1.
Water that rises about 5 to 2.0.
[0027]
【Example】
Hereinafter, the present invention will be described more specifically with reference to Examples and Comparative Examples.
[0028]
Example 1
In the method shown in FIG. 1 (b), Atsugi City Water (Al concentration of about 30 ppb, carbon dioxide concentration 30mg / L (HCO 3 - as), dissolved enzyme (DO) concentration 8 mg / L) was injected HCl to pH 4. The water adjusted to 6 was passed through the membrane deaerator 1 to be deaerated. The pH of the outlet water of the membrane deaerator 1 could be 4.6 to 4.7, and almost no increase in the pH of the outlet water was observed. The removal rate of carbon dioxide in the initial stage of passing water was 80%, and the removal rate of DO was 95%.
[0029]
When the operation of the membrane deaerator 1 was continued for two months, the DO removal rate was 94%, and almost no decrease in membrane performance was observed. After passing water for 2 months, the degassed membrane was disassembled and the membrane surface was subjected to SEM analysis to examine the presence or absence of aluminum hydroxide scale on the membrane surface. As a result, no scale adhesion was observed.
[0030]
Example 2
Using the same raw water as in Example 1, the pH was adjusted by a cation exchange treatment as shown in FIG. The H-type cation exchange tower 5 was filled with "EX-CG" acidic ion exchange resin manufactured by Kurita Kogyo Co., Ltd., and water was passed at SV = 15 hr -1 . The pH of the cation exchange treated water was 3.2. This cation exchange treated water was passed through the membrane deaerator 1 under the same conditions as in Example 1.
[0031]
As a result, the pH of the outlet water of the membrane deaerator 1 was 3.2 to 3.3, almost no increase in pH was observed, and the initial DO removal rate was 95%.
[0032]
When the membrane deaerator 1 was operated for two months, the DO removal rate was 94%, and no decrease in membrane performance was observed. After two months of water flow, the degassed membrane was disassembled and subjected to SEM analysis on the membrane surface. As a result, no aluminum hydroxide scale adhered to the membrane surface.
[0033]
Comparative Example 1
In Example 1, when the treatment was carried out in exactly the same manner except that the pH of the inlet water of the membrane deaerator was set to 5.0, the pH of the outlet water of the membrane deaerator increased to 6.5. In addition, the DO removal rate at the beginning of water passage was the same as that in Example 1, but the DO removal rate after two months was significantly reduced to 68%. After passing the water for two months, the membrane surface was examined in the same manner as in Example 1. As a result, it was confirmed that aluminum hydroxide scale had adhered and this was the cause of the deterioration of the membrane surface performance.
[0034]
【The invention's effect】
As described above in detail, according to the operation method of the membrane deaerator of the present invention, when the water to be treated is passed through the membrane deaerator to perform the deaeration, the scale derived from metal ions in the water to be treated is used. Can be effectively prevented, and the membrane deaerator can be operated stably for a long period of time.
[Brief description of the drawings]
FIG. 1 is a system diagram showing an embodiment of the present invention.
[Explanation of symbols]
1 Membrane deaerator 2 Acid storage tank 3 Line mixer 4 pH meter 5 H-type cation exchange tower
Claims (2)
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP22185098A JP3546712B2 (en) | 1998-08-05 | 1998-08-05 | Operating method of membrane deaerator |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP22185098A JP3546712B2 (en) | 1998-08-05 | 1998-08-05 | Operating method of membrane deaerator |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| JP2000051844A JP2000051844A (en) | 2000-02-22 |
| JP3546712B2 true JP3546712B2 (en) | 2004-07-28 |
Family
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| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP22185098A Expired - Fee Related JP3546712B2 (en) | 1998-08-05 | 1998-08-05 | Operating method of membrane deaerator |
Country Status (1)
| Country | Link |
|---|---|
| JP (1) | JP3546712B2 (en) |
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1998
- 1998-08-05 JP JP22185098A patent/JP3546712B2/en not_active Expired - Fee Related
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| Publication number | Publication date |
|---|---|
| JP2000051844A (en) | 2000-02-22 |
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