JP4403622B2

JP4403622B2 - Electrodemineralization treatment method and electrodesalination treatment apparatus

Info

Publication number: JP4403622B2
Application number: JP2000011990A
Authority: JP
Inventors: 伸佐藤
Original assignee: Kurita Water Industries Ltd
Current assignee: Kurita Water Industries Ltd
Priority date: 2000-01-20
Filing date: 2000-01-20
Publication date: 2010-01-27
Anticipated expiration: 2020-01-20
Also published as: JP2001198578A

Description

【０００１】
【発明の属する技術分野】
本発明は電気脱塩装置による電気脱塩処理方法及び電気脱塩処理装置に係り、特に、電気脱塩装置におけるシリカ除去率を高めて著しく高水質の処理水を得る電気脱塩処理方法及び電気脱塩処理装置に関する。
【０００２】
【従来の技術】
近年、半導体製造工場、液晶製造工場、製薬工業、食品工業等の各種の産業ないし研究施設等において使用される純水や超純水の製造手段として、電極を備える電極室（陽極室と陰極室）の間に複数のアニオン交換膜及びカチオン交換膜を交互に配列して濃縮室と脱塩室とを交互に形成した電気脱塩装置が用いられるようになってきている。
【０００３】
電気脱塩装置は効率的な脱塩処理が可能であり、イオン交換樹脂のような再生を必要とせず、完全な連続採水が可能で、極めて高純度の水が得られるという優れた効果を奏する。なお、電気脱塩装置には、脱塩室にアニオン交換樹脂とカチオン交換樹脂とが混合して充填されているものと、脱塩室にイオン交換樹脂が充填されていないものとがあるが、処理水の水質向上の点では、脱塩室にイオン交換樹脂が充填されたものの方が効果的である。
【０００４】
電気脱塩装置では、脱塩室に流入した原水中のイオンが親和力、濃度及び移動度に基いて電位をかけた電極の方向（被処理水の流れに対して直角方向）に移動し、更に、脱塩室と濃縮室とを仕切るカチオン交換膜又はアニオン交換膜を横切って移動し、すべての室において電荷の中和が保たれるようになる。そして、イオン交換膜の半浸透特性及び電位により、原水中のイオンは脱塩室では減少し、隣りの濃縮室では濃縮されることになる。このため、脱塩室から脱塩水が回収される。
【０００５】
「イオン交換セミナー’９８」第２５頁〜第２９頁には、この電気脱塩装置の前段に逆浸透（ＲＯ）膜分離装置を設けたフローが示されており、その運転条件の一例として、電気脱塩装置の給水のＣＯ_２濃度１．３ｐｐｍでシリカ処理率９６．７％（処理水シリカ濃度８ｐｐｂ）であることが記載されている。
【０００６】
なお、このＣＯ_２濃度１．３ｐｐｍとは炭素換算濃度で３５５ｐｐｂであり、無機炭素（ＩＣ）濃度はこれを大幅に上回る量となる。即ち、ＩＣ濃度とは溶存ＣＯ_２（上記ＣＯ_２濃度）と重炭酸イオン（ＨＣＯ_３ ⁻）及び炭酸イオン（ＣＯ_３ ⁻）との合計を炭素換算した濃度であり、当然、溶存ＣＯ_２由来の炭素換算濃度よりも多い。
【０００７】
【発明が解決しようとする課題】
上記ＲＯ膜分離装置及び電気脱塩装置の組み合わせで達成されるシリカ除去率は９６．７％であるが、処理水のシリカ濃度は８ｐｐｂであり、電子産業等で使用される超純水に要求されるシリカ濃度（例えば０．１ｐｐｂ以下）を満足し得ない。このため、電気脱塩装置の後段には非再生型イオン交換装置を配置して、電気脱塩装置の処理水を更に処理する必要があるが、この場合において、電気脱塩装置の処理水のシリカ濃度が高いため非再生型イオン交換装置の交換頻度が高くなり、実用化に不利である。即ち、非再生型イオン交換装置の適用には、少なくともその交換頻度が３〜６ヶ月あるいはそれ以上であることが望まれるが、そのためには、電気脱塩装置の処理水のシリカ濃度は１ｐｐｂ以下である必要がある。
【０００８】
本発明は上記従来の問題点を解決し、電気脱塩装置におけるシリカ除去率を高めて著しく高水質の処理水を得ることができる電気脱塩処理方法及び電気脱塩処理装置を提供することを目的とする。
【０００９】
【課題を解決するための手段】
本発明の電気脱塩処理方法は、原水を電気脱塩装置で処理する方法において、該原水を無機炭素濃度低減手段で処理して、該電気脱塩装置の給水の無機炭素濃度を５０ｐｐｂ以下とする電気脱塩処理方法であって、該無機炭素濃度低減手段として、脱気装置と逆浸透膜分離装置とを用い、該逆浸透膜分離装置の透過水の一部を該逆浸透膜分離装置の入口側へ循環して処理する方法であって、該電気脱塩装置の給水の無機炭素濃度を測定し、この測定結果に基いて、該透過水の循環水量を制御することを特徴とする。
【００１０】
本発明の電気脱塩処理装置は、原水が導入される無機炭素濃度低減手段と該無機炭素濃度低減手段の処理水が導入される電気脱塩装置とを備え、該無機炭素濃度低減手段が、脱気装置と逆浸透膜分離装置とを備える電気脱塩処理装置であって、該逆浸透膜分離装置の透過水の一部を該逆浸透膜分離装置の入口側へ循環する循環手段と、該電気脱塩装置の給水の無機炭素濃度を測定する無機炭素濃度測定手段とを備え、該無機炭素濃度測定手段の測定結果に基いて、前記透過水の循環水量が制御され、該無機炭素濃度低減手段の処理水の無機炭素濃度が５０ｐｐｂ以下であることを特徴とする。
【００１１】
電気脱塩装置においては、電気脱塩装置の脱塩室に印加された直流電流により、水がＨ^＋とＯＨ⁻とに解離してシリカ（ＳｉＯ_２）が下記（１）の反応によりイオン状となることでシリカが除去されるものと考えられる。
【００１２】
ＳｉＯ_２＋ＯＨ⁻→ＨＳｉＯ_３ ⁻ …（１）
一方、水中の炭酸（ＣＯ_２）も同様の作用で下記（２）式によりイオン状となって除去される。
【００１３】
ＣＯ_２＋ＯＨ⁻→ＨＣＯ_３ ⁻ …（２）
上記（１），（２）式の反応には、いずれも水の解離で生成するＯＨ⁻が用いられるが、上記（２）式の反応は上記（１）式の反応に優先して起こるため、水中に炭酸が存在するとシリカの除去を十分に行えなくなる。
【００１４】
本発明では、電気脱塩装置の給水のＩＣ濃度を５０ｐｐｂ以下という著しく低い濃度にすることで、上記（２）式の反応を抑え、シリカ除去率を高める。
【００１５】
本発明において、無機炭素濃度低減手段としては、脱気装置とＲＯ膜分離装置とを併用するのが好ましい。即ち、ＲＯ膜分離装置ではイオン状の炭酸成分しか除去できず、一方、脱気装置ではＣＯ_２形態の炭酸成分しか除去できないため、これらを併用して両炭酸成分を効率的に除去することが好ましい。
【００１６】
また、水中の炭酸成分はそのｐＨ条件により形態が異なり、ｐＨが低い程溶存ＣＯ_２が多くなり、ｐＨが高い程イオン状の炭酸成分が多くなるため、脱気装置の前段にはｐＨ低下手段を設け、ＲＯ膜分離装置の前段にはｐＨ上昇手段を設けることが、各装置での炭酸成分除去効率の向上の面で好ましい。
【００１７】
この脱気装置としては、炭酸以外に酸素をも除去して後段の装置のバクテリア等の発生を防止し得る点、小型で省スペース化に有利である点などから脱気膜装置を用いるのが好ましい。
【００１８】
また、本発明においては、電気脱塩装置の給水のＩＣ濃度を測定し、この測定結果に基いてＲＯ膜分離装置の透過水の一部をＲＯ膜分離装置の入口側に循環して処理するのが、ＲＯ膜分離装置の給水のＩＣ濃度を確実に低減する上で好ましい。
【００１９】
【発明の実施の形態】
以下に図面を参照して本発明の実施の形態を詳細に説明する。
【００２０】
図１，３は本発明の電気脱塩処理方法及び電気脱塩処理装置の実施の形態を示す系統図である。
【００２１】
図１の実施の形態では、原水（一般的には水道水を活性炭処理した水）を脱気装置１で脱気処理してＣＯ_２形態の炭酸成分を除去し、その後、ＲＯ膜分離装置２で処理してイオン状の炭酸成分を除去し、電気脱塩装置３の給水のＩＣ濃度を５０ｐｐｂ以下に低減させて電気脱塩装置３で処理する。
【００２２】
脱気装置１における脱気処理に当たっては、前述の如く、炭酸成分を溶存ＣＯ_２の形態にすべく、ｐＨを６．０以下、特に４．０〜４．５程度に調整することが好ましい。このｐＨ調整のためには、ＨＣｌ，Ｈ_２ＳＯ_４等の酸を添加する他、後段の電気脱塩装置３の陽極液を添加しても良い。
【００２３】
脱気装置としては、脱気膜装置、真空脱気塔、窒素脱気塔、脱炭酸塔等を用いることができるが、中でも、脱気膜装置、真空脱気塔、窒素脱気塔は水中の酸素をも除去することができ、電気脱塩装置を含む後段の装置のバクテリア等の発生を防止し得ることから好ましい。とりわけ、その中でも、脱気膜装置は、他の装置に比べて小型で高さが低く、システム全体の省スペース化に有効である。
【００２４】
特に、本発明では、電気脱塩装置の給水のＩＣ濃度を５０ｐｐｂ以下とするために脱気装置としてＩＣ除去率の高いものを用いる必要があるが、このＩＣ除去率の点からも脱気膜装置を用いるのが好ましい。
【００２５】
このような脱気膜装置の脱気膜の形式としては、コンパクトなモジュールで大きな膜面積を得ることができる中空糸膜が最も好ましい。中空糸膜を使用する場合には内部還流型、外部還流型のどちらも使用することができるが、内部還流型中空糸モジュールにおいては、中空糸の内径が１９０μｍ以下、特に中空糸の内径が６０μｍ〜１９０μｍであることが好ましい。この内径が６０μｍ未満になると、中空糸内部を流れる水の圧力損失が極めて大きくなり、多量の水を処理することが困難となる。
【００２６】
また、使用される中空糸膜は、液体として水を透過せず脱気対象となる気体を十分良く透過させ、総括透過速度Ｑが膜自身の気体透過速度律速とならない膜であれば良いが、例えば、酸素透過速度が１×１０^−５ｃｍ^３／ｃｍ^２・ｓｅｃ・ｃｍＨｇ以上、水蒸気の酸素透過速度が４００ｃｍ^３（ＳＴＰ）／ｃｍ^２・ｓｅｃ・ｃｍＨｇ以下の膜が好ましい。なお、膜自身の気体の透過速度の測定はＡＳＴＭ−Ｄ１４３４に準拠して容易に行われる。また、膜の水蒸気透過速度の測定は、膜の一方の側に水を満たし、反対側を減圧し、透過してきた水をコールドトラップに捕捉し、その量を測定することにより、容易に求めることができる。このとき、膜の両側の水蒸気の圧力差は、水のその測定温度での飽和水蒸気から減圧側の真空度を減じた値とする。
【００２７】
膜の材質としては、疎水性の高い材質が好ましく、例えばポリオレフィン、ポリエチレン、ポリプロピレン、ポリフッ化ビニリデン、シリコーン、フッ素樹脂、ポリメチルペンテン等が挙げられる。親水性の膜は水の遮断性及び水蒸気の遮断性の点で好ましくない。
【００２８】
膜の構造は多孔膜、均質膜、複合膜、その他いずれでも良く特に制限するものではないが、不均質膜、特にポリメチルペンテンを主成分とする不均質膜が、ＣＯ_２、酸素等の気体透過速度が大きく、かつ水蒸気のバリヤー性が高く最も好ましい。
【００２９】
このような高効率の脱気膜を用いる場合、脱気膜装置に流入する水のｐＨは４〜６程度が好ましい。ｐＨが低すぎると加えられる酸が多く残留するようになるし、ｐＨが高すぎるとＩＣの除去効率が低下する。
【００３０】
また、このような高効率の脱気膜装置を用いる場合、透過されるガス側を真空ポンプで５０Ｔｏｒｒ以下とすることが好ましい。さらに、スイープガスとして、窒素ガス等を供給して透過ガス側のＣＯ_２等の分圧を低くし、水側から移動を妨げないようにすることがより好ましい。
【００３１】
脱気装置１の処理水は、次いでＲＯ膜分離装置２でイオン状の炭酸成分を除去する。このＲＯ膜分離装置２における処理に当っては、水中の炭酸成分をイオン状にすべく、ｐＨを７．５以上、特に８．５〜９．０程度に調整することが好ましい。このｐＨ調整のためには、ＮａＯＨ等のアルカリを添加する他、後段の電気脱塩装置３の陰極液を添加しても良い。
【００３２】
脱気装置１及びＲＯ膜分離装置２で十分に炭酸成分が除去され、ＩＣ濃度５０ｐｐｂ以下に低減された水は、電気脱塩装置３の給水として電気脱塩装置３に導入され、脱塩水を処理水として回収する。
【００３３】
なお、図１では、原水を脱気装置１で処理した後、ＲＯ膜分離装置２で処理するが、この処理手順を逆にして、ＲＯ膜分離装置２で処理した後脱気装置１で処理しても良い。ただし、添加する酸及びアルカリがＲＯ膜で除去され易い点からは、脱気装置１で処理した後、ＲＯ膜分離装置２で処理するのが好ましい。
【００３４】
本発明において、電気脱塩装置の給水のＩＣ濃度が５０ｐｐｂを超えると十分なシリカ除去率を得ることができない。このＩＣ濃度は特に１０〜５０ｐｐｂ程度であることがシリカ除去率及び処理効率の面で好ましい。
【００３５】
このような本発明の電気脱塩処理方法及び電気脱塩処理装置によれば、電気脱塩装置におけるシリカ除去率を９９．５〜９９．９％程度に高めて、シリカ濃度０．２〜１．０ｐｐｂ程度の高水質処理水を得ることができる。
【００３６】
なお、本発明においては、電気脱塩装置３の給水のＩＣ濃度を測定し、この測定値が確実に５０ｐｐｂ以下となるように処理条件を制御することが好ましい。
【００３７】
このＩＣ濃度の測定手段としては、シーバース社の全有機炭素分析装置８１０型等を用いることが好ましい。本装置は全炭素（ＴＣ）と全無機炭素（ＩＣ）を測定し、その差より、全有機炭素（ＴＯＣ）を測定するものであるが、前述のように同時にＩＣも測定できる。しかも、本目的の５０ｐｐｂ以下という低い濃度でも十分定量性があり、連続測定することもできるので、本発明のＩＣ濃度測定手段としても効果的に使用することができ、異常時の際には、メンテナンス等が容易となるので効果的である。
【００３８】
本発明においては、特に、ＲＯ膜分離装置２の透過水の一部をＲＯ膜分離装置２の入口側に循環して再処理するようにし、このようなＩＣ濃度測定手段で電気脱塩装置３の給水のＩＣ濃度を測定し、この測定結果に基いてこの循環水量を制御することにより、電気脱塩装置３の給水のＩＣ濃度を確実に５０ｐｐｂ以下に低減する。
【００３９】
この場合の具体的フロー例を図３に示す。この実施の形態では、図１の装置において電気脱塩装置３の入口にＩＣ分析計４を設置し、その前に設置した自動三方弁５により電気脱塩装置３の流入水量を一定としている。ここで、ＩＣ値が５０ｐｐｂ以上のときは、インバータ７の制御によりＲＯ膜分離装置２の高圧ポンプ６の通水圧を高くすることにより、三方弁５からの循環量が多くなり、原水を希釈することでＩＣ負荷を小さくできるため、徐々に電気脱塩装置３の流入水のＩＣが低くなる。このような微調整はコンピュータ８によるＰＩＤ制御等で行うことができ、これにより安定した運転を行うことが可能とされ、ある程度の原水の水質変動等に対応できるので経済的でもある。
【００４０】
【実施例】
以下に実施例、比較例及び実験例を挙げて本発明をより具体的に説明する。
【００４１】
実施例１
図１に示す装置で水道水を活性炭処理して得られる水を原水として処理した。
【００４２】
用いた装置の仕様は次の通りである。
〔脱気装置〕
ヘキスト社製脱気膜「リキセルＸ−４０」（４インチ×４本直列）
〔ＲＯ膜分離装置〕
日東電工社製ＲＯ膜「ＥＳ−２０」（８インチ×２本）
〔電気脱塩装置〕
栗田工業（株）社製「ピュアエース」
原水はＨ_２ＳＯ_４を添加してｐＨ４．５とした後２．７５ｍ^３／ｈｒの流量で脱気装置で脱気処理し、次いで、ＮａＯＨを添加してｐＨ８．０とした後２．７５ｍ^３／ｈｒの流量でＲＯ膜分離装置に通水してＲＯ膜分離処理した。このＲＯ膜分離装置の水回収率は８０％とし濃縮水０．５５ｍ^３／ｈｒは系外へ排出し、透過水２．２ｍ^３／ｈｒは電気脱塩装置に通水した。この電気脱塩装置では、０．２ｍ^３／ｈｒの濃縮水及び電極水を系外へ排出し、脱塩水（処理水）２．０ｍ^３／ｈｒを得た。
【００４３】
この処理において、電気脱塩装置の給水のＩＣ濃度及びシリカ濃度と処理水（脱塩水）のシリカ濃度を調べ、結果を表１に示した。
【００４４】
比較例１
実施例１において脱気装置による脱気処理を行わなかったこと以外は同様にして処理を行い、電気脱塩装置の給水のＩＣ濃度及びシリカ濃度と処理水（脱塩水）のシリカ濃度を調べ、結果を表１に示した。
【００４５】
【表１】

【００４６】
実験例１
実施例１において、脱気装置及びＲＯ膜分離装置の処理条件を種々変更し、電気脱塩装置の給水のＩＣ濃度を変えて処理を行い、得られた処理水のシリカ濃度からシリカの除去率を求め、シリカ除去率と電気脱塩装置の給水のＩＣ濃度との関係を図２に示した。
【００４７】
図２より、電気脱塩装置の給水のＩＣ濃度が５０ｐｐｂ以下であると、シリカ除去率が格段に向上することがわかる。
【００４８】
実験例２
図３の装置において、実施例１と同様の条件で通水した。ただし、原水に炭酸ガスを吹き込み、電気脱塩装置の給水のＩＣ濃度を１００ｐｐｂとした。
【００４９】
この時の電気脱塩装置入口シリカ濃度２５０ｐｐｂに対し、処理水シリカ濃度は３ｐｐｂ（除去率９８．８％）であった。
【００５０】
そこで、図３に示す装置により、自動三方弁にて循環量を少しづつ上げて、電気脱塩装置の給水のＩＣ濃度を４０ｐｐｂとなるように調整した。この時の循環量は１．８ｍ^３／ｈｒであり、インバータにより高圧ポンプ圧力を調整することで、ＲＯ透過水量を調整し、電気脱塩装置の流量は実施例１と同様にした。
【００５１】
この結果、電気脱塩装置入口シリカ濃度１８０ｐｐｂに対し、処理水シリカ濃度は０．６ｐｐｂ（除去率９９．７％）となった。
【００５２】
このようなＩＣ濃度の制御により、シリカ除去率９９％以上の運転が可能であった。
【００５３】
【発明の効果】
以上詳述した通り、本発明の電気脱塩処理方法及び電気脱塩処理装置によれば、電気脱塩装置におけるシリカ除去率を高めて著しく高水質の処理水を得ることができる。
【図面の簡単な説明】
【図１】本発明の電気脱塩処理方法及び電気脱塩処理装置の実施の形態を示す系統図である。
【図２】シリカ除去率と電気脱塩装置の給水ＩＣ濃度との関係を示すグラフである。
【図３】本発明の電気脱塩処理方法及び電気脱塩処理装置の他の実施の形態を示す系統図である。
【符号の説明】
１脱気装置
２ＲＯ膜分離装置
３電気脱塩装置[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an electrical desalination treatment method and an electrical desalination treatment apparatus using an electrical desalination apparatus, and more particularly to an electrical desalination treatment method and an electrical desalination treatment apparatus in which the silica removal rate in the electrical desalination apparatus is enhanced to obtain treated water of extremely high quality. The present invention relates to a desalting apparatus.
[0002]
[Prior art]
In recent years, as a means for producing pure water or ultrapure water used in various industries or research facilities such as semiconductor manufacturing plants, liquid crystal manufacturing plants, pharmaceutical industry, food industry, etc., electrode chambers equipped with electrodes (anode chamber and cathode chamber) ), An electric desalination apparatus in which a plurality of anion exchange membranes and cation exchange membranes are alternately arranged to alternately form concentration chambers and desalting chambers has been used.
[0003]
The electric desalination equipment is capable of efficient desalination treatment, does not require regeneration like an ion exchange resin, is capable of complete continuous water collection, and has the excellent effect of obtaining extremely high purity water. Play. In addition, in the electric desalination apparatus, there are a desalting chamber in which an anion exchange resin and a cation exchange resin are mixed and filled, and a desalting chamber in which an ion exchange resin is not filled, In terms of improving the quality of treated water, it is more effective to have a desalting chamber filled with an ion exchange resin.
[0004]
In the electric desalination apparatus, ions in the raw water flowing into the desalination chamber move in the direction of the electrode to which potential is applied based on the affinity, concentration and mobility (perpendicular to the flow of water to be treated). In other words, it moves across the cation exchange membrane or the anion exchange membrane that separates the desalting chamber and the concentration chamber, and the neutralization of the charge is maintained in all the chambers. Then, due to the semi-permeation characteristics and potential of the ion exchange membrane, ions in the raw water are reduced in the desalting chamber and concentrated in the adjacent concentration chamber. For this reason, desalted water is recovered from the desalting chamber.
[0005]
“Ion Exchange Seminar '98”, pages 25 to 29, shows a flow in which a reverse osmosis (RO) membrane separation device is provided in the previous stage of this electric desalination device. It is described that the silica treatment rate is 96.7% (treated water silica concentration is 8 ppb) at a CO ₂ concentration of 1.3 ppm in the feed water of the electric desalting apparatus.
[0006]
The CO ₂ concentration of 1.3 ppm is 355 ppb in terms of carbon, and the inorganic carbon (IC) concentration is much higher than this. That is, the IC concentration is a concentration obtained by converting the total of dissolved CO ₂ (the above-mentioned CO ₂ concentration), bicarbonate ion (HCO ₃ ⁻ ), and carbonate ion (CO ₃ ⁻ ) into carbon, and naturally it is derived from dissolved CO ₂ . More than the carbon equivalent concentration.
[0007]
[Problems to be solved by the invention]
The silica removal rate achieved by the combination of the RO membrane separation device and the electric desalting device is 96.7%, but the silica concentration of the treated water is 8 ppb, which is required for ultrapure water used in the electronics industry. The silica concentration (for example, 0.1 ppb or less) cannot be satisfied. For this reason, it is necessary to dispose a non-regenerative ion exchange device at the subsequent stage of the electrical desalting apparatus to further treat the treated water of the electrical desalting apparatus. Since the silica concentration is high, the replacement frequency of the non-regenerative ion exchange device is increased, which is disadvantageous for practical use. That is, for the application of the non-regenerative ion exchange apparatus, it is desired that the exchange frequency is at least 3 to 6 months or more. For this purpose, the silica concentration of the treated water in the electrodeionization apparatus is 1 ppb or less. Need to be.
[0008]
The present invention solves the above-mentioned conventional problems, and provides an electrical desalination treatment method and an electrical desalination treatment apparatus capable of increasing the silica removal rate in the electrical desalination apparatus and obtaining treated water of extremely high quality. Objective.
[0009]
[Means for Solving the Problems]
The electric desalination treatment method of the present invention is a method of treating raw water with an electric desalination apparatus, wherein the raw water is treated with an inorganic carbon concentration reducing means, and the inorganic carbon concentration of the feed water of the electric desalination apparatus is 50 ppb or less. And a reverse osmosis membrane separation device using the deaeration device and the reverse osmosis membrane separation device as the inorganic carbon concentration reducing means, and the reverse osmosis membrane separation device In which the inorganic carbon concentration of the feed water of the electric desalination apparatus is measured, and the amount of circulated water is controlled based on the measurement result. .
[0010]
The electric demineralization treatment apparatus of the present invention comprises an inorganic carbon concentration reducing means into which raw water is introduced and an electric desalination apparatus into which treated water of the inorganic carbon concentration reducing means is introduced , the inorganic carbon concentration reducing means comprising: a deaerator and reverse osmosis membrane separation apparatus and electrodeionization apparatus which Ru and a circulating means for circulating a portion of the permeate of the reverse osmosis membrane separation device to the inlet side of the reverse osmosis membrane separation device And an inorganic carbon concentration measuring means for measuring the inorganic carbon concentration of the feed water of the electric desalination apparatus, and based on the measurement result of the inorganic carbon concentration measuring means, the circulating water volume of the permeated water is controlled, and the inorganic carbon The inorganic carbon concentration of the treated water of the concentration reducing means is 50 ppb or less.
[0011]
In the electric desalting apparatus, water is dissociated into H ⁺ and OH ⁻ by a direct current applied to the desalting chamber of the electric desalting apparatus, and silica (SiO ₂ ) is ionized by the reaction (1) below. As a result, it is considered that silica is removed.
[0012]
SiO ₂ + OH ⁻ → HSiO ₃ ⁻ (1)
On the other hand, carbonic acid (CO ₂ ) in water is also removed in an ionic form by the following equation (2) by the same action.
[0013]
CO ₂ + OH ⁻ → HCO ₃ ⁻ (2)
In the reactions of the above formulas (1) and (2), OH ⁻ generated by the dissociation of water is used, but the reaction of the above formula (2) occurs in preference to the reaction of the above formula (1). If carbonic acid is present in the water, the silica cannot be removed sufficiently.
[0014]
In the present invention, by reducing the IC concentration of the feed water of the electric desalting apparatus to a remarkably low concentration of 50 ppb or less, the reaction of the above formula (2) is suppressed and the silica removal rate is increased.
[0015]
In the present invention, as the inorganic carbon concentration reducing means, it is preferable to use a deaeration device and an RO membrane separation device in combination. That can only remove ions like carbonate component in RO membrane separator, whereas, can not only remove carbonate component of CO ₂ form a degasser, be removed by a combination of these two carbon component efficient preferable.
[0016]
In addition, the form of the carbonic acid component in water varies depending on the pH condition. The lower the pH, the more dissolved CO ₂ , and the higher the pH, the more ionic carbonic acid component. It is preferable to provide pH raising means in the previous stage of the RO membrane separation device from the viewpoint of improving the carbonic acid component removal efficiency in each device.
[0017]
As this deaeration device, it is possible to use a deaeration membrane device because it can remove oxygen in addition to carbon dioxide to prevent the generation of bacteria in the subsequent device, and is advantageous for space saving because of its small size. preferable.
[0018]
In the present invention, the IC concentration of the feed water of the electrodeionization device is measured, and a part of the permeate of the RO membrane separation device is circulated to the inlet side of the RO membrane separation device based on the measurement result. This is preferable in order to surely reduce the IC concentration of the feed water of the RO membrane separation apparatus.
[0019]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
[0020]
1 and 3 are system diagrams showing an embodiment of an electric desalting treatment method and an electric desalting treatment apparatus according to the present invention.
[0021]
In the embodiment shown in FIG. 1, raw water (generally, water obtained by subjecting tap water to activated carbon) is deaerated by the deaerator 1 to remove carbon dioxide in the form of CO ₂ , and then the RO membrane separator 2. The ionic carbonic acid component is removed by the treatment, and the IC concentration of the water supplied to the electric desalting apparatus 3 is reduced to 50 ppb or less and the electric desalting apparatus 3 performs the processing.
[0022]
In the degassing process in the degassing apparatus 1, it is preferable to adjust the pH to 6.0 or less, particularly about 4.0 to 4.5 in order to make the carbonic acid component in the form of dissolved CO ₂ as described above. In order to adjust the pH, an acid such as HCl or H ₂ SO ₄ may be added, or an anolyte for the subsequent electric desalting apparatus 3 may be added.
[0023]
As the degassing device, a degassing membrane device, a vacuum degassing tower, a nitrogen degassing tower, a decarbonation tower, etc. can be used. Among them, the degassing membrane device, vacuum degassing tower, nitrogen degassing tower are underwater. This is preferable because it can also remove oxygen and can prevent the generation of bacteria and the like in the subsequent apparatus including the electrodesalination apparatus. In particular, the deaeration membrane device is smaller and lower in height than other devices, and is effective in saving the space of the entire system.
[0024]
In particular, in the present invention, it is necessary to use a deaeration device having a high IC removal rate in order to set the IC concentration of the feed water of the electric desalination device to 50 ppb or less. An apparatus is preferably used.
[0025]
As a degassing membrane type of such a degassing membrane device, a hollow fiber membrane that can obtain a large membrane area with a compact module is most preferable. When a hollow fiber membrane is used, either an internal reflux type or an external reflux type can be used. However, in the internal reflux type hollow fiber module, the inner diameter of the hollow fiber is 190 μm or less, particularly the inner diameter of the hollow fiber is 60 μm. It is preferable that it is -190 micrometers. When this inner diameter is less than 60 μm, the pressure loss of the water flowing inside the hollow fiber becomes extremely large, and it becomes difficult to treat a large amount of water.
[0026]
Further, the hollow fiber membrane used may be a membrane that does not pass water as a liquid and permeates the gas to be deaerated sufficiently well, and the overall permeation rate Q is not limited by the gas permeation rate of the membrane itself, For example, a film having an oxygen transmission rate of 1 × 10 ⁻⁵ cm ³ / cm ² · sec · cmHg or more and a water vapor oxygen transmission rate of 400 cm ³ (STP) / cm ² · sec · cmHg or less is preferable. In addition, the measurement of the gas permeation speed of the film itself is easily performed according to ASTM-D1434. Also, the water vapor transmission rate of the membrane can be easily determined by filling one side of the membrane with water, depressurizing the other side, capturing the permeated water in a cold trap, and measuring the amount. Can do. At this time, the pressure difference between the water vapors on both sides of the membrane is a value obtained by subtracting the degree of vacuum on the decompression side from saturated water vapor at the measured temperature of water.
[0027]
The material of the membrane is preferably a highly hydrophobic material, and examples thereof include polyolefin, polyethylene, polypropylene, polyvinylidene fluoride, silicone, fluororesin, and polymethylpentene. Hydrophilic membranes are not preferred in terms of water barrier properties and water vapor barrier properties.
[0028]
The structure of the membrane may be a porous membrane, a homogeneous membrane, a composite membrane, or the like, and is not particularly limited. A heterogeneous membrane, particularly a heterogeneous membrane containing polymethylpentene as a main component, is a gas such as CO ₂ or oxygen. Most preferred is a high permeation rate and a high barrier property of water vapor.
[0029]
When such a highly efficient degassing membrane is used, the pH of water flowing into the degassing membrane device is preferably about 4-6. If the pH is too low, a large amount of acid is added, and if the pH is too high, the IC removal efficiency decreases.
[0030]
Moreover, when using such a highly efficient deaeration membrane apparatus, it is preferable that the permeate | transmitted gas side shall be 50 Torr or less with a vacuum pump. Further, it is more preferable to supply nitrogen gas or the like as a sweep gas to lower the partial pressure of CO ₂ or the like on the permeate gas side so as not to prevent movement from the water side.
[0031]
The treated water of the deaeration device 1 is then removed of ionic carbonate components by the RO membrane separation device 2. In the treatment in the RO membrane separation apparatus 2, it is preferable to adjust the pH to 7.5 or more, particularly about 8.5 to 9.0 in order to make the carbonic acid component in water ionic. In order to adjust the pH, in addition to adding an alkali such as NaOH, the catholyte of the subsequent electrical desalting apparatus 3 may be added.
[0032]
The water in which the carbonic acid component is sufficiently removed by the deaeration device 1 and the RO membrane separation device 2 and the IC concentration is reduced to 50 ppb or less is introduced into the electric demineralization device 3 as the feed water of the electric demineralization device 3, Collect as treated water.
[0033]
In FIG. 1, the raw water is treated with the deaeration device 1 and then treated with the RO membrane separation device 2. However, the processing procedure is reversed and the treatment is performed with the RO membrane separation device 2 and then the treatment with the deaeration device 1. You may do it. However, from the viewpoint that the acid and alkali to be added are easily removed by the RO membrane, it is preferable to perform the treatment by the RO membrane separation device 2 after the treatment by the deaeration device 1.
[0034]
In the present invention, a sufficient silica removal rate cannot be obtained if the IC concentration of the feed water of the electrodeionization apparatus exceeds 50 ppb. The IC concentration is particularly preferably about 10 to 50 ppb in terms of silica removal rate and processing efficiency.
[0035]
According to such an electrical desalination treatment method and an electrical desalination treatment apparatus of the present invention, the silica removal rate in the electrical desalination apparatus is increased to about 99.5 to 99.9%, and the silica concentration is 0.2 to 1. High water quality treated water of about 0.0 ppb can be obtained.
[0036]
In the present invention, it is preferable to measure the IC concentration of the feed water of the electric desalting apparatus 3 and control the processing conditions so that the measured value is surely 50 ppb or less.
[0037]
As a means for measuring the IC concentration, it is preferable to use a total organic carbon analyzer 810 type manufactured by Seaverse. This device measures total carbon (TC) and total inorganic carbon (IC), and measures total organic carbon (TOC) from the difference, but it can also measure IC simultaneously as described above. Moreover, even at a concentration as low as 50 ppb or less for this purpose, it is sufficiently quantifiable and can be continuously measured, so it can be used effectively as an IC concentration measuring means of the present invention. This is effective because maintenance and the like are facilitated.
[0038]
In the present invention, in particular, a part of the permeated water of the RO membrane separation device 2 is circulated to the inlet side of the RO membrane separation device 2 to be reprocessed. IC concentration of the feed water was measured, and by on the basis of the measurement result to control the circulation water, surely reduced below 50ppb an IC concentration of water in the electrodeionization apparatus 3.
[0039]
A specific flow example in this case is shown in FIG. In this embodiment, an IC analyzer 4 is installed at the inlet of the electrical desalting apparatus 3 in the apparatus of FIG. 1, and the inflow water amount of the electrical desalting apparatus 3 is made constant by the automatic three-way valve 5 installed in front of it. Here, when the IC value is 50 ppb or more, the amount of circulation from the three-way valve 5 is increased by increasing the water flow pressure of the high-pressure pump 6 of the RO membrane separation device 2 under the control of the inverter 7 to dilute the raw water. Since the IC load can be reduced by this, the IC of the inflow water of the electric desalting apparatus 3 gradually decreases. Such fine adjustment can be performed by PID control or the like by the computer 8, which makes it possible to perform a stable operation and is economical because it can cope with a certain amount of raw water fluctuation.
[0040]
【Example】
Hereinafter, the present invention will be described more specifically with reference to examples, comparative examples, and experimental examples.
[0041]
Example 1
Water obtained by treating activated water with tap water using the apparatus shown in FIG. 1 was treated as raw water.
[0042]
The specifications of the equipment used are as follows.
[Deaerator]
Hoechst degassing membrane "Lixel X-40" (4 inches x 4 in series)
[RO membrane separator]
Nitto Denko RO membrane "ES-20" (8 inches x 2)
[Electric desalination equipment]
"Pure Ace" manufactured by Kurita Kogyo Co., Ltd.
The raw water was degassed with a degasser at a flow rate of 2.75 m ³ / hr after adding H ₂ SO ₄ to pH 4.5, and then adjusted to pH 8.0 by adding NaOH to 2.75 m. Water was passed through the RO membrane separator at a flow rate of ³ / hr to perform RO membrane separation treatment. The RO membrane separation device had a water recovery rate of 80%, 0.55 m ³ / hr of concentrated water was discharged out of the system, and 2.2 m ³ / hr of permeate was passed through an electric desalting device. In this electric desalting apparatus, 0.2 m ³ / hr of concentrated water and electrode water were discharged out of the system to obtain desalted water (treated water) of 2.0 m ³ / hr.
[0043]
In this treatment, the IC concentration and the silica concentration of the feed water of the electric desalting apparatus and the silica concentration of the treated water (desalted water) were examined, and the results are shown in Table 1.
[0044]
Comparative Example 1
In Example 1, the treatment was performed in the same manner except that the deaeration process was not performed by the deaerator, and the IC concentration and the silica concentration of the water supply of the electric demineralizer and the silica concentration of the treated water (demineralized water) were examined. The results are shown in Table 1.
[0045]
[Table 1]

[0046]
Experimental example 1
In Example 1, the treatment conditions of the deaeration device and the RO membrane separation device were changed variously, and the treatment was performed by changing the IC concentration of the feed water of the electrodeionization device, and the silica removal rate from the silica concentration of the obtained treated water FIG. 2 shows the relationship between the silica removal rate and the IC concentration of the feed water of the electrodeionizer.
[0047]
From FIG. 2, it is understood that the silica removal rate is remarkably improved when the IC concentration of the feed water of the electric desalting apparatus is 50 ppb or less.
[0048]
Experimental example 2
In the apparatus of FIG. 3, water was passed under the same conditions as in Example 1. However, carbon dioxide gas was blown into the raw water, and the IC concentration of the feed water of the electric desalting apparatus was set to 100 ppb.
[0049]
At this time, the silica concentration of the treated water was 3 ppb (removal rate 98.8%) with respect to the silica concentration of 250 ppb at the inlet of the electrodeionization device.
[0050]
Therefore, with the apparatus shown in FIG. 3, the circulating amount was gradually increased by an automatic three-way valve, and the IC concentration of the water supply of the electric desalting apparatus was adjusted to 40 ppb. The circulation amount at this time was 1.8 m ³ / hr, and the RO permeated water amount was adjusted by adjusting the high-pressure pump pressure with an inverter, and the flow rate of the electric desalting apparatus was the same as in Example 1.
[0051]
As a result, the silica concentration in the treated water was 0.6 ppb (removal rate 99.7%) with respect to the silica concentration 180 ppb at the inlet of the electrodeionization device.
[0052]
By controlling the IC concentration as described above, an operation with a silica removal rate of 99% or more was possible.
[0053]
【The invention's effect】
As described in detail above, according to the method for electro-desalting treatment and the apparatus for electro-desalting treatment of the present invention, it is possible to increase the silica removal rate in the electro-desalination apparatus and obtain treated water with extremely high quality.
[Brief description of the drawings]
FIG. 1 is a system diagram showing an embodiment of an electrical desalting treatment method and an electrical desalting treatment apparatus of the present invention.
FIG. 2 is a graph showing the relationship between the silica removal rate and the concentration of water supply IC in the electrodeionization apparatus.
FIG. 3 is a system diagram showing another embodiment of the electrical desalting treatment method and the electrical desalting treatment apparatus of the present invention.
[Explanation of symbols]
1 Deaerator 2 RO membrane separator 3 Electric demineralizer

Claims

In a method of treating raw water with an electric desalination apparatus,
An electrical desalination treatment method in which the raw water is treated with an inorganic carbon concentration reducing means, and the inorganic carbon concentration of feed water of the electrical desalination apparatus is 50 ppb or less ,
A method in which a deaeration device and a reverse osmosis membrane separation device are used as the inorganic carbon concentration reducing means, and a part of the permeated water of the reverse osmosis membrane separation device is circulated to the inlet side of the reverse osmosis membrane separation device. An electrical desalination treatment method characterized by measuring the inorganic carbon concentration of the feed water of the electrical desalting apparatus and controlling the amount of circulating water of the permeate based on the measurement result .

2. The inorganic carbon concentration reducing means according to claim 1, wherein the inorganic carbon concentration reducing means is one or both of a pH lowering means provided on the inlet side of the degassing device and a pH increasing means provided on the inlet side of the reverse osmosis membrane separation device. An electrical desalination treatment method comprising:

3. The electric demineralization method according to claim 1, wherein the deaeration device is a deaeration membrane device.

An inorganic carbon concentration reducing means to which raw water is introduced; and an electric demineralizer to which treated water of the inorganic carbon concentration reducing means is introduced, wherein the inorganic carbon concentration reducing means includes a deaeration device and a reverse osmosis membrane separation device. an electrical deionization apparatus in which Ru and a circulating means for circulating a portion of the permeate of the reverse osmosis membrane separation device to the inlet side of the reverse osmosis membrane separation device, water supply inorganic electrical desalter An inorganic carbon concentration measuring means for measuring the carbon concentration, and based on the measurement result of the inorganic carbon concentration measuring means, the circulating water amount of the permeated water is controlled, and the inorganic carbon concentration of the treated water of the inorganic carbon concentration reducing means Is an electric desalination treatment apparatus, characterized in that it is 50 ppb or less.

5. The inorganic carbon concentration reducing means according to claim 4, wherein the inorganic carbon concentration reducing means is one or both of a pH lowering means provided on the inlet side of the degassing device and a pH increasing means provided on the inlet side of the reverse osmosis membrane separation device. An electrical desalination treatment apparatus comprising:

6. The electric demineralization apparatus according to claim 4, wherein the deaeration device is a deaeration membrane device.