JP3895037B2

JP3895037B2 - Low pressure oxygen enrichment method

Info

Publication number: JP3895037B2
Application number: JP09973098A
Authority: JP
Inventors: 常雄三好; 義則松長
Original assignee: 昭和エンジニアリング株式会社
Priority date: 1998-04-10
Filing date: 1998-04-10
Publication date: 2007-03-22
Anticipated expiration: 2018-04-10
Also published as: JPH11292506A

Description

【０００１】
【発明の属する技術分野】
本発明は、ＰＳＡ法によって空気など窒素及び酸素を含む原料ガスから窒素を選択的に吸着分離して濃縮酸素を製造する低圧酸素濃縮法に関する。
【０００２】
【従来の技術】
ゼオライト等の分子ふるいを吸着剤として用い、空気など窒素及び酸素を含む原料ガスから吸着／脱着を繰り返しながら窒素を選択的に吸着分離して濃縮酸素を製造する方法としてプレッシャスイング吸着法（以下「ＰＳＡ法」と記す）が工業的に重要であり、深冷分離法と共に電炉製鋼、パルプ漂白、発酵、化学、水処理等、酸素を大量に使用する産業において広く用いられている。ＰＳＡ法によって酸素を濃縮する従来の技術としては一般に、吸着剤を含む吸着塔の数を３本とし、吸着、減圧、脱着、パージ等のステップを組み合わせて酸素回収率を高めるように工夫されたものが主流であった。
【０００３】
最近になって吸着剤の性能向上に伴って吸着塔の数を２本とするＰＳＡ法が採用されつつある。この２塔式ＰＳＡ法においては、一般に、圧力の回収及び酸素回収率の向上を図るため両塔問で均圧操作を行う必要があり、その効果を高めるために、吸着塔内の圧力は、３塔式ＰＳＡの場合は大気圧〜０．１kg/cm²G 程度であるのに対して、２塔式ＰＳＡでは０．５kg/cm²G 前後と高めの圧力を設定するのが通常である。このための空気供給手段としては定容型の空気圧縮機、特に圧力と到達速度とを考慮してルーツブロワーが一般的に使用されている。
【０００４】
例えば特公平６−１７０号公報では、吸着塔の最高圧が０．５８kg/cm²G とされ、この最高圧に達するに要する時間が２９秒とされていることから、使用されているブロワーはルーツタイプであることがわかる。その他、特開平８−２３９２０４号公報、特開平９−２３９２２６号公報等に記載された２塔式ＰＳＡにおいても吸着塔の昇圧にブロワーが用いられているが、いずれも使用条件からルーツタイプであることがわかる。
【０００５】
【発明が解決しようとする課題】
これら従来技術においては、何れも前記のように０．５kg/cm²G 前後の比較的高い塔内圧力を要するのでルーツブロワーが用いられ、その運転に要する電カが多大であるために濃縮酸素の製造コストが嵩み、他の酸素濃縮法例えば深冷分離法と比較するとき大きな問題となっている。またルーツブロワーは閉鎖系の圧力を直線的に上昇する特性があるため、塔内最高圧の制御やアンロード時の負荷軽減に特別な制御装置や煩雑な操作が必要であり、しかも騒音や振動が大きいのでその対策にも多大な経費を要すること、ギアボックス等付帯する機械の冷却や圧縮された空気の冷却と水滴除去が必要である等、設備コストや運転コストの面でも問題が多い。
【０００６】
前記のように、ＰＳＡ法を他の酸素濃縮法、例えば深冷分離法より有利にしようとすると、特に電力消費量と設備・運転費の低減が重要な課題であり現状ではまだ改良すべき点が多い。本発明の課題は、これらＰＳＡ法における従来技術の持つ欠点を改良することにある。従って本発明の目的は、ＰＳＡ法において電力消費量と設備・運転費が従来法より低減された酸素濃縮法を提供することにある。
【０００７】
【課題を解決するための手段】
前記の課題を解決するために本発明は、窒素を選択的に吸／脱着するゼオライト系分子ふるいを充填した２本の吸着塔Ａ，Ｂと、回収した濃縮酸素を蓄積しかつ使用のために抜き出す均圧器を用い、吸着塔Ａの供給口から酸素と窒素とを含む原料ガスを供給して窒素を吸着しその流出口から濃縮酸素を回収しこの間に吸着塔Ｂを再生する一連の運転操作を、前記吸着塔Ａ，Ｂを順次交替して繰り返すことにより濃縮酸素を製造する酸素濃縮法であって、前記吸着塔への原料ガスの圧入を、最高吐出圧０．３kg／cm²Ｇ以下の低圧ターボブロワーを用い、（１）原料ガスの供給を開始する吸着塔Ａの流出口と再生を開始する吸着塔Ｂの流出口とを均圧配管で連結して両塔間の圧力が実質的に等しくなるまで均圧化すると同時に吸着塔Ｂの供給口を減圧ポンプと連結して吸着塔Ｂの排気を開始し、この間前記低圧ターボブロワーは締切運転を行う均圧化ステップと、（２）前記均圧化ステップを終了し減圧状態とされた吸着塔Ａを、供給口からの自然吸気によりほぼ大気圧となるまで昇圧すると共に、吸着塔Ｂは供給口から引き続き減圧ポンプによって排気し、この間前記低圧ターボブロワーは引き続き締切運転を行う自然吸気ステップと、（３）自然吸気を終了した前記吸着塔Ａの供給口に、前記低圧ターボブロワーから原料ガスを圧入し、吸着塔Ａの流出口から濃縮酸素の回収を開始して前記均圧器に蓄積すると共に、吸着塔Ａの圧力を前記低圧ターボブロワーの可能な最高圧まで昇圧してこの圧力を維持し、この間吸着塔Ｂはその供給口から引き続き減圧ポンプによって排気して大気圧より低い最低圧に至らしめる酸素回収ステップと、（４）吸着塔Ａは引き続き前記低圧ターボブロワーから原料ガスを圧入して前記の最高圧を維持しつつその流出口から濃縮酸素を回収し、前記均圧器に濃縮酸素を送り続けると共に、この間、吸着塔Ｂはその供給口から引き続き減圧ポンプによって排気しつつ吸着塔Ａから濃縮酸素を導入して減圧状態を維持する範囲内で昇圧することと併せて吸着塔Ｂ内を向流にパージする切替準備ステップと、前記の吸着塔Ａと吸着塔Ｂとを交替して前記と同様に操作する（５）均圧化ステップと、（６）自然吸気ステップと、（７）酸素回収ステップと、（８）切替準備ステップとからなる一連の運転操作を繰り返して濃縮酸素を製造し、前記均圧器に濃縮酸素を蓄積すると共に、前記均圧器から抜き出して使用する低圧酸素濃縮法を提供する。
【０００８】
前記の低圧酸素濃縮法において、前記（２）の自然吸気ステップと前記（３）の酸素回収ステップとの間に、自然吸気を終了した前記吸着塔Ａの供給口に前記低圧ターボブロワーから原料ガスを圧入し、かつ吸着塔Ａの流出口を閉じて前記低圧ターボブロワーの可能な最高圧まで吸着塔Ａの圧力を昇圧し、この間吸着塔Ｂは供給口から引き続き減圧ポンプによって排気する（２＋）昇圧ステップと、前記（６）自然吸気ステップと前記（７）酸素回収ステップとの間に、前記（２＋）昇圧ステップの吸着塔Ａと吸着塔Ｂとを交替して行う（６＋）昇圧ステップとを挿入してもよい。
【０００９】
【発明の実施の形態】
次に本発明の好ましい実施の形態を図面を用いて説明する。
図１は本発明の方法を実施するための酸素濃縮装置の一例を示している。図１において、この装置は概略、２本の並列された吸着塔Ａ，Ｂ、これらの吸着塔に酸素と窒素とを含む原料ガスを圧入するための低圧ターボブロワー８、吸着塔の再生のための減圧ポンプ９、及び均圧器Ｃからなっている。
【００１０】
吸着塔Ａ，Ｂは同形であって、それぞれ供給口５Ａ，５Ｂと流出口７Ａ，７Ｂとを有し、この間に窒素を選択的に吸／脱着するゼオライト系分子ふるいからなる吸着剤１１Ａ，１１Ｂが充填されている。
低圧ターボブロワー８は、最高吐出圧が０．３kg/cm²G の低圧ターボブロワーである。均圧器Ｃは、回収した濃縮酸素を蓄積しかつ使用のために抜き出す空容器である。
【００１１】
吸着塔Ａの供給口５Ａと吸着塔Ｂの供給口５Ｂとは、それぞれ弁１Ａ，１Ｂを介して低圧ターボブロワー８に接続され、この低圧ターボブロワー８は原料ガスの吐出端に締切弁１４を有している。また低圧ターボブロワー８にはバイパス管１０が並設され、このバイパス管１０にはポジショナー付きの弁６が取付けられている。また、供給口５Ａ，５Ｂは、それぞれ弁４Ａ，４Ｂを介して減圧ポンプ（真空ポンプ）９に接続されている。
【００１２】
一方、それぞれ吸着塔Ａ，Ｂの流出口７Ａ，７Ｂは、並列配置されたポジショナー付きの均圧弁３及びパージ弁３Ｐを介して接続されると共に、それぞれが独立に弁２Ａ，２Ｂを介してかつ管１２を経由して均圧器Ｃに接続されている。均圧器Ｃからは、抜出管１３を通って濃縮酸素が抜出せるようになっている。
【００１３】
次に本発明の請求項１に従う低圧酸素濃縮法を、図２及び図３を参照して説明する。図２はこの方法における各ステップを示すものであり、説明に不要な要素は省略してある。図３は、前記各ステップにおける吸着塔Ａ，Ｂのそれぞれの圧力モードを示している。本発明の方法は、以下に説明するステップ１〜８を１サイクルとして継続運転される。このサイクルを、吸着塔Ａが再生を終了して吸着を開始し、吸着塔Ｂが吸着を終了して再生を開始する状態から説明する。
【００１４】
前提として、ステップ１〜８のサイクル期間中、低圧ターボブロワー８及び減圧ポンプ９は運転を継続する。
ステップ１（均圧化）：再生（窒素の脱着）を終了した吸着塔Ａと吸着を終了した吸着塔Ｂとは、均圧弁３を開くことで均圧化される。前ステップでは吸着塔Ａは再生処理により減圧状態（大気圧以下）とされ、吸着塔Ｂは加圧状態（大気圧以上）とされているので、このとき均圧弁３を通るガス流は吸着塔Ｂから吸着塔Ａへの方向となる。この間、前記低圧ターボブロワー８は締切弁１４を閉じて締切運転とされ、一方、減圧ポンプ９は吸着塔Ｂの排気を開始する。
【００１５】
ステップ２（自然吸気）：前記均圧化ステップを終了したとき、吸着塔Ａはなお減圧状態にある。そこで、均圧弁３を閉じ弁６を開くと吸着塔Ａ内は自然吸気によりほぼ大気圧まで昇圧する。この間、前記低圧ターボブロワー８は締切運転を続け、また減圧ポンプ９も吸着塔Ｂの排気を続ける。
【００１６】
ステップ３（酸素回収）：弁６を閉じ低圧ターボブロワー８の締切弁１４を開いて低圧ターボブロワー８から自然吸気を終了した吸着塔Ａに原料ガスを圧入して大気圧以上に昇圧し、同時に流出口７Ａから濃縮酸素の回収を開始し均圧器Ｃに蓄積する。このとき原料ガスの流入量と濃縮酸素の流出量とを調節しておけば、吸着塔Ａ内の圧力は、前記低圧ターボブロワー８の可能な最高圧（０．１kg/cm²G 〜０．３kg/cm²G ）まで急速に昇圧し、この圧力に維持される。この間も吸着塔Ｂは引き続き減圧ポンプ９によって排気され、大気圧より低い最低圧に達する。
【００１７】
ステップ４（切替準備）：吸着塔Ａは引き続き低圧ターボブロワー８から原料ガスを圧入して前記の最高圧を維持しつつ、流出口７Ａから濃縮酸素を回収し、均圧器Ｃに濃縮酸素を送り続ける。この間に吸着塔Ｂは、その供給口５Ｂから引き続き減圧ポンプ９による排気を続けながら、一方で、弁３Ｐを開いて吸着塔Ａから濃縮酸素を導入して減圧状態を維持する範囲内で昇圧する。これによって吸着塔Ｂ内は向流にパージされ、パージ終了時にも減圧状態が維持される。
【００１８】
次に吸着塔Ａと吸着塔Ｂとを切り替えて、前記と同様に
ステップ５（均圧化）、
ステップ６（自然吸気）、
ステップ７（酸素回収）、及び
ステップ８（切替準備）
の各ステップを順次行って１サイクルとし、このサイクルを繰り返して均圧器Ｃに濃縮酸素を蓄積すると共に抜出し管１３から抜出して使用する。
前記サイクルにおける各ステップの所要時間及び各弁の開閉プログラムを表１に示す。
【００１９】
【表１】

【００２０】
本発明の低圧酸素濃縮法は、原料ガスを吸着塔に圧入するブロワーとして最高吐出圧が０．３kg/cm²G 以下の低圧ターボブロワーを用いることを特徴としている。低圧ターボブロワーを用いる利点は、▲１▼吸着塔における最高圧までの到達時間を短縮し、しかも煩雑な圧力制御操作なしに最高圧が持続できること、▲２▼最高圧における電カ消費量が軽減できること、及び▲３▼締切運転の操作が簡単でしかも電力消費量が低減できることである。
【００２１】
前記▲１▼の利点を説明するために、低圧ターボブロワーを前記の低圧酸素濃縮法に用いたときの（３）酸素回収ステップと（４）切替準備ステップにおける吸着塔圧力の変化と吸着塔に圧入する空気量の変化との関係を図４に示す。また、低圧ターボブロワーの代わりに従来から用いられているルーツブロワーを用いたときの同一ステップにおける吸着塔圧力と空気量との関係を図５に示す。
これらを比較すれば明らかなように、ルーツブロワー（図５）は塔内圧力に係わらず常に一定量の空気を直線的に圧入するので、塔内圧を許容限度内に留めるために特別な制御操作が必要であるのに対して、低圧ターボブロワーは、塔内圧が低い時に圧入空気量が極めて多く、また塔内が一定圧に達した後ではそれ以上増圧しないので、加圧上限の制御操作が不要になるという特性を有している。この
特性によって、前記の▲１▼吸着塔における最高圧までの到達時間を短縮し、しかも煩雑な圧力制御操作なしに最高圧が持続できるという低圧ターボブロワーの利点が実現される。
【００２２】
次に、前記▲２▼の利点について説明すると、吸着塔における窒素の吸着量は平均吸着圧と吸着時間との積に比例するので、塔内圧力が直線的に上昇するルーツブロワー等に比べ、前記のように初期段階から比較的高い塔内圧を確保できる低圧ターボブロワーのほうが、一定量の窒素を吸着するに要する最高圧が低くて済むことになり、この結果、前記の▲２▼最高圧における電カ消費量が軽減できるという低圧ターボブロワーの利点が実現される。
【００２３】
次に、前記▲３▼の利点について説明する。前記（１）均圧化ステップ及び（２）自然吸気ステップにおけるブロワーのアンロード時における挙動を比較すると、従来用いられているルーツブロワー等においては、吐出側を閉め切ると内圧が急上昇しポンプが破損するため、吐出空気をアフタークーラーて冷却した後に入口側に循環したり、吐出配管に枝管を設けてバイパス放出を行うなど複雑な処理が必要でこのために経費がかかり、またアンロード中の電カ消費も無視できない。これに対して低圧ターボブロワーは、単に吸入側又は吐出側の何れかを締切るだけで、前記の特性によって一定圧以上には上昇せず、また最高圧力下にも電カ消費は極めて少ない。これにより前記の▲３▼締切運転の操作が簡単でしかも電力消費量が低減できるという低圧ターボブロワーの利点が実現される。
【００２４】
本発明の低圧酸素濃縮法においては、均圧化ステップの後に、自然吸気ステップによって減圧状態の吸着塔に自然吸気により原料ガスが導入される。この自然吸気ステップは低圧ターボブロワーの特性を考慮した上で付加されたステップである。すなわち、減圧状態の吸着塔に低圧ターボブロワーを用いて原料ガスを導入しようとすると、大量の空気が流れて電カを消費するので、自然吸気が可能な減圧状態の間はブロワーを締切運転として電力消費量を節減している。
【００２５】
本発明の請求項２の低圧酸素濃縮法においては、前記の（２）自然吸気ステップと（３）酸素回収ステップとの間、及び（６）自然吸気ステップと（７）酸素回収ステップとの間に、それぞれ図６に示すように、吸着塔の供給口に前記ターボブロワーから原料ガスを圧入し、かつ流出口７Ａ又は７Ｂを閉じて濃縮酸素を流出せずに前記低圧ターボブロワーの可能な最高圧まで吸着塔の圧力を昇圧する昇圧ステップ（２＋）及び（６＋）が挿入される。この昇圧ステップの挿入によって、次の酸素回収ステップでは初期から最高圧の濃縮酸素を回収することができ、製造工程をいっそう安定化することができる。
【００２６】
本発明において吸着塔に充填される吸着剤は、窒素を選択的に吸／脱着し得るものであれば特に制限はないが、一般にはゼオライト系の分子ふるいが好適である。特に本発明方法に適した吸着剤の例としては、直径２〜３mmの粒状又は直径１．４〜１．７mmの円筒状に成形され、カチオンの６０〜７０％がＣａイオンで置換されたＡ型またはＸ型のゼオライト系分子ふるいを挙げることができる。これらは、吸／脱着速度及び通過ガスの空間速度の観点から特に好ましい吸着剤である。
【００２７】
【実施例】
装置図１に示すＰＳＡ装置を用いた。図１において、吸着塔Ａ及び吸着塔Ｂは何れも、直径６００mm、高さ２５００mmの円筒形であり、塔の下部には脱水剤として活性アルミナ粒子が３００mmの厚さに充填され、その上層に、窒素ガス分離用吸着剤として、直径２mm〜３mmの粒状に成形され、カチオンの７０％をＣａイオンによって置換されたＸ型のゼオライト系分子ふるいが充填されている。均圧器Ｃは吸着塔と同じ容積をもつ空塔である。また原料ガス圧入ポンプ８は最高吐出圧０．３kg／cm²Gの低圧ターボブロワーであり、減圧ポンプ９は湿式２段式ルーツブロワーである。前記の低圧ターボブロワー８及び減圧ポンプ９はそれぞれ回転数可変であって、回転数を変えることで、低圧ターボブロワー８の場合は最高吐出圧と吸気速度を、また減圧ポンプ９の場合は吸気、排気速度が制御できるようになっている。なお、図示しないが吸着塔及び配管は恒温槽中に配置されており、実施例では恒温槽は３２℃に保たれている。
【００２８】
（実施例１）この実施例は前記請求項１に基づく低圧酸素濃縮法である。原料ガスとして空気を用い、図２及び表１に示すステップ及び弁操作により濃縮酸素の製造を行った。各ステップにおける吸着塔Ａ及び吸着塔Ｂの操作時間（秒）と圧力変化を図３に示す。運転期間中、吸着塔内の最高圧力（最高吸着圧）は０．２３kg／cm²Gであり、最低圧力（最低脱着圧）は−０．６８kg／cm²Gであった。運転時間は１サイクル１００秒とした。
【００２９】
この実施例における運転の結果は、９３％の酸素濃度で１８．６Nm³/h の製品酸素が得られ、この時の酸素回収率は５４％であった。また、１００％酸素濃度に換算した製品酸素１Nm³ あたりの電力消費量は、低圧ターボブロワー８が０．０５kwh であり、減圧ポンプ９が０．３０kwh であり、合計で０．３５kwh であった。
【００３０】
（比較例）
図１と同様の装置構成において、ただし圧入用のポンプとして低圧ターボブロワー８の代わりに従来から用いられている１段式ルーツブロワーを用いた。
原料ガスとして空気を用い、図７及び下記表２に示すステップ及び弁操作により濃縮酸素の製造を行った。図７において１段式ルーツブロワーは符号１５で示した。運転に際して、１段式ルーツブロワー１５のアンロード時には、ポンプの破壊を防ぐために吐出弁１４及び弁６を開いた状態で、吸入した空気を大気放出とした。また、ステップ２及び６は自然吸気によらず１段式ルーツブロワー１５からの原料ガスの供給及び均圧器Ｃからの濃縮酸素の供給によって吸着塔内をほぼ大気圧まで昇圧した。
【００３１】
【表２】

【００３２】
各ステップにおける吸着塔Ａ及び吸着塔Ｂの圧力変化を図８に示す。運転期間中、吸着塔の最高圧力（最高吸着圧）は０．４５kg/cm²G であり、最低圧力（最低脱着圧）は一０．６８kg/cm²G であった。運転周期は１サイクル１２０秒とした。
【００３３】
この比較例における運転の結果は、９３％の酸素濃度で１９．３Nm³/h の製品酸素が得られ、この時の酸素回収率は５０％であった。また、１００％酸素濃度に換算した製品酸素１Nm³ あたりの電力消費量は、１段式ルーツブロワー１５が０．１２kwh 、減圧ポンプ９が０．２８kwh であり、合計が０．４０kwh であった。
この比較例においては、吸着圧が実施例に比べて高いため、最低圧力が実施例と同じ一０．６８kg/cm²G であっても、減圧ポンプが吸着塔と連結して排気を行う期間の平均圧力が実施例より高くなり、このため減圧ポンプ９の動力消費は実施例より小さくなったものの、１段式ルーツブロワー１５の電カ消費量がその差を上回つて大きくなり、全体として不利になった。
【００３４】
【発明の効果】
本発明の低圧酸素濃縮法は、２塔式ＰＳＡ法において原料ガスの吸着塔への圧入を、最高吐出圧０．３kg/cm²G 以下の低圧ターボブロワーを用いて行うものであるので、吸着塔における最大吸着圧の制御やブロワーのアンロード時の運転操作が簡易化され、電力消費も軽減され、設備・運転コストが従来のルーツブロワー等を用いるＰＳＡ法に比べ、大幅に改善される。
【図面の簡単な説明】
【図１】本発明を実施する装置の一例を示す概略図
【図２】本発明の一実施例の各ステップを示すフロー図
【図３】前記実施例における操作時間と運転圧力との関係を示すグラフ
【図４】本発明の運転状態を示すグラフ
【図５】比較例の運転状態を示すグラフ
【図６】本発明の他の実施例におけるステップを示すフロー図
【図７】比較例の各ステップを示すフロー図
【図８】前記比較例における操作時間と運転圧力との関係を示すグラフ
【符号の説明】
Ａ…吸着塔
Ｂ…吸着塔
Ｃ…均圧器
１Ａ，１Ｂ，２Ａ，２Ｂ，４Ａ，４Ｂ，６…弁
３…均圧弁
３Ｐ…パージ弁
１４…締切弁
５Ａ，５Ｂ…供給口
７Ａ，７Ｂ…流出口
８…低圧ターボブロワー
９…減圧ポンプ
１０…バイパス管
１１Ａ，１１Ｂ…吸着剤
１２…管
１３…抜出端[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a low-pressure oxygen concentration method for producing concentrated oxygen by selectively adsorbing and separating nitrogen from a source gas containing nitrogen and oxygen such as air by a PSA method.
[0002]
[Prior art]
The pressure swing adsorption method (hereinafter "" is a method for producing concentrated oxygen by selectively adsorbing and separating nitrogen while repeating adsorption / desorption from a source gas containing nitrogen and oxygen such as air, using a molecular sieve such as zeolite as the adsorbent. The “PSA method” is industrially important, and is widely used in industries that use oxygen in large quantities, such as electric furnace steelmaking, pulp bleaching, fermentation, chemistry, and water treatment, together with the cryogenic separation method. As a conventional technique for concentrating oxygen by the PSA method, in general, the number of adsorption towers containing an adsorbent is three, and it has been devised to increase the oxygen recovery rate by combining steps such as adsorption, decompression, desorption, and purge. Things were mainstream.
[0003]
Recently, as the performance of the adsorbent is improved, the PSA method with two adsorption towers is being adopted. In this two-column PSA method, it is generally necessary to perform a pressure equalization operation in both towers in order to improve pressure recovery and oxygen recovery rate. In order to enhance the effect, the pressure in the adsorption tower is: for 3-tower PSA whereas atmospheric pressure ~0.1kg / cm ² of about G, is usual to set a double column PSA in 0.5 kg / cm ² G before and after the higher pressure . As an air supply means for this purpose, a constant volume type air compressor, in particular, a roots blower is generally used in consideration of pressure and arrival speed.
[0004]
For example, in Japanese Examined Patent Publication No. 6-170, the maximum pressure of the adsorption tower is 0.58 kg / cm ² G, and the time required to reach this maximum pressure is 29 seconds. It turns out that it is a roots type. In addition, in the two-column PSA described in JP-A-8-239204, JP-A-9-239226, etc., a blower is used for boosting the adsorption tower. I understand that.
[0005]
[Problems to be solved by the invention]
In these prior arts, as mentioned above, since a relatively high pressure in the tower of about 0.5 kg / cm ² G is required, a roots blower is used. The production cost is increased, which is a big problem when compared with other oxygen concentration methods such as a cryogenic separation method. Roots blowers have the characteristic of increasing the pressure of the closed system linearly, so special control devices and complicated operations are required to control the maximum pressure in the tower and to reduce the load during unloading, as well as noise and vibration. Therefore, there are many problems in terms of equipment cost and operation cost, such as requiring a large amount of cost for countermeasures, cooling of accompanying machines, cooling of compressed air, and removal of water droplets.
[0006]
As mentioned above, when trying to make the PSA method more advantageous than other oxygen concentration methods, such as the cryogenic separation method, reduction of power consumption and equipment / operating costs is an important issue, and there are still points to be improved at present. There are many. The object of the present invention is to improve the disadvantages of the prior art in these PSA methods. Accordingly, an object of the present invention is to provide an oxygen enrichment method in which power consumption and facility / operating costs are reduced in the PSA method as compared with the conventional method.
[0007]
[Means for Solving the Problems]
In order to solve the above-mentioned problems, the present invention provides two adsorption towers A and B filled with a zeolitic molecular sieve that selectively adsorbs / desorbs nitrogen, and accumulates the collected concentrated oxygen for use. A series of operation operations in which a source gas containing oxygen and nitrogen is supplied from the supply port of the adsorption tower A, adsorbed nitrogen, concentrated oxygen is recovered from the outlet, and the adsorption tower B is regenerated during this time, using a pressure equalizer that is extracted. Is an oxygen concentration method for producing concentrated oxygen by repeating the adsorption towers A and B in turn, and the injection of the raw material gas into the adsorption tower is performed at a maximum discharge pressure of 0.3 kg / cm ² G or less. (1) The outlet of the adsorption tower A for starting the supply of the raw material gas and the outlet of the adsorption tower B for starting the regeneration are connected by a pressure equalizing pipe so that the pressure between both towers is substantially reduced. Pressure equalization until the two become equal, and at the same time, the supply port of the adsorption tower B The vacuum pump is connected to a decompression pump to start exhausting the adsorption tower B. During this time, the low-pressure turbo blower performs a pressure equalization step for performing a shut-off operation, and (2) the adsorption tower A that has been decompressed after completing the pressure equalization step. Natural suction from the supply port until the pressure becomes almost atmospheric pressure, and the adsorption tower B is continuously exhausted from the supply port by a decompression pump, during which the low-pressure turbo blower continues to perform a shut-off operation, 3) A raw material gas is injected from the low-pressure turbo blower into the supply port of the adsorption tower A that has finished the natural intake, and the recovery of concentrated oxygen is started from the outlet of the adsorption tower A and is accumulated in the pressure equalizer. The pressure in the adsorption tower A is increased to the highest possible pressure of the low-pressure turbo blower and this pressure is maintained. During this time, the adsorption tower B is continuously evacuated from its supply port by a decompression pump. And oxygen recovery steps allowed to reach minimum pressure lower than pressure, (4) the adsorption tower A is concentrated oxygen is recovered from the outlet while maintaining the maximum pressure of the continues pressing the raw material gas from the low pressure turbo blower, with continued feeding the concentrated oxygen to the equalizing voltage divider, while this boosts within maintaining a reduced pressure state by introducing concentrated oxygen from the adsorption tower a while exhausting by adsorption column B continues reducing pump from the supply port In addition to this, a switching preparation step for purging the inside of the adsorption tower B counter-currently, the above-mentioned adsorption tower A and the adsorption tower B are replaced and operated in the same manner as described above (5) a pressure equalizing step, (6 ) A concentrated oxygen is produced by repeating a series of operation operations including a natural intake step, (7) an oxygen recovery step, and (8) a switching preparation step, and the concentrated pressure is accumulated in the pressure equalizer, and the pressure equalizer From To provide a low-pressure oxygen concentration method to be used out come.
[0008]
Material wherein Te low oxygen concentration method odor, between the oxygen recovery step of the said natural intake step (2) (3), from the low-pressure turbo blower to the supply port of the adsorption tower A finishing the naturally aspirated Gas is injected and the outlet of the adsorption tower A is closed to increase the pressure of the adsorption tower A to the highest possible pressure of the low-pressure turbo blower. During this time, the adsorption tower B continues to be exhausted from the supply port by a decompression pump (2+ And (6) natural pressure step and (7) oxygen recovery step. (6+) pressure increase step is performed by alternately changing the adsorption tower A and the adsorption tower B in the (2+) pressure increase step. And may be inserted.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
Next, preferred embodiments of the present invention will be described with reference to the drawings.
FIG. 1 shows an example of an oxygen concentrator for carrying out the method of the present invention. In FIG. 1, this apparatus is schematically shown as two parallel adsorption towers A and B, a low-pressure turbo blower 8 for injecting a raw material gas containing oxygen and nitrogen into these adsorption towers, and regeneration of the adsorption towers. Pressure reducing pump 9 and pressure equalizing unit C.
[0010]
Adsorption towers A and B have the same shape and have supply ports 5A and 5B and

outlets

7A and 7B, respectively, and

adsorbents

11A and 11B made of zeolitic molecular sieves that selectively adsorb / desorb nitrogen. Is filled.
The low pressure turbo blower 8 is a low pressure turbo blower having a maximum discharge pressure of 0.3 kg / cm ² G. The pressure equalizer C is an empty container for accumulating the collected concentrated oxygen and withdrawing it for use.
[0011]
The supply port 5A of the adsorption tower A and the supply port 5B of the adsorption tower B are connected to the low-pressure turbo blower 8 via valves 1A and 1B, respectively. The low-pressure turbo blower 8 has a shutoff valve 14 at the discharge end of the raw material gas. Have. The low-pressure turbo blower 8 is provided with a bypass pipe 10, and a valve 6 with a positioner is attached to the bypass pipe 10. The supply ports 5A and 5B are connected to a decompression pump (vacuum pump) 9 through

valves

4A and 4B, respectively.
[0012]
On the other hand, the

outlets

7A and 7B of the adsorption towers A and B are connected via a pressure equalizing valve 3 with a positioner and a purge valve 3P arranged in parallel, respectively, and independently through the valves 2A and 2B and The pressure equalizing device C is connected via the pipe 12. From the pressure equalizer C, concentrated oxygen can be extracted through the extraction pipe 13.
[0013]
Next, the low-pressure oxygen concentration method according to claim 1 of the present invention will be described with reference to FIGS. FIG. 2 shows each step in this method, and elements unnecessary for explanation are omitted. FIG. 3 shows the pressure modes of the adsorption towers A and B in each step. The method of the present invention is continuously operated with steps 1 to 8 described below as one cycle. This cycle will be described from the state in which the adsorption tower A finishes the regeneration and starts the adsorption, and the adsorption tower B finishes the adsorption and starts the regeneration.
[0014]
As a premise, the low-pressure turbo blower 8 and the decompression pump 9 continue to operate during the cycle period of steps 1-8.
Step 1 (pressure equalization): The adsorption tower A that has finished regeneration (desorption of nitrogen) and the adsorption tower B that has finished adsorption are equalized by opening the pressure equalization valve 3. In the previous step, the adsorption tower A is brought into a depressurized state (atmospheric pressure or less) by the regeneration process, and the adsorption tower B is brought into a pressurized state (above atmospheric pressure). The direction is from B to the adsorption tower A. During this time, the low-pressure turbo blower 8 is closed by closing the shut-off valve 14, while the decompression pump 9 starts exhausting the adsorption tower B.
[0015]
Step 2 (natural intake): When the pressure equalization step is completed, the adsorption tower A is still in a reduced pressure state. Therefore, when the pressure equalizing valve 3 is closed and the valve 6 is opened, the inside of the adsorption tower A is increased to almost atmospheric pressure by natural intake. During this time, the low-pressure turbo blower 8 continues the cutoff operation, and the decompression pump 9 also continues to exhaust the adsorption tower B.
[0016]
Step 3 (Oxygen recovery): The valve 6 is closed, the shut-off valve 14 of the low-pressure turbo blower 8 is opened, the raw material gas is injected from the low-pressure turbo blower 8 into the adsorption tower A where natural intake is completed, and the pressure is increased to atmospheric pressure or higher. Concentrated oxygen is recovered from the outlet 7A and accumulated in the pressure equalizer C. At this time, if the inflow amount of the raw material gas and the outflow amount of the concentrated oxygen are adjusted, the pressure in the adsorption tower A is the highest possible pressure (0.1 kg / cm ² G to 0. The pressure is rapidly increased to 3 kg / cm ² G) and maintained at this pressure. During this time, the adsorption tower B is continuously exhausted by the decompression pump 9 and reaches a minimum pressure lower than the atmospheric pressure.
[0017]
Step 4 (preparation for switching): The adsorption tower A continues to inject the raw material gas from the low-pressure turbo blower 8 to maintain the above-mentioned maximum pressure, collect concentrated oxygen from the outlet 7A, and send the concentrated oxygen to the pressure equalizer C. to continue. During this time, the adsorption tower B continues to be exhausted by the decompression pump 9 from the supply port 5B, while increasing the pressure within a range in which the valve 3P is opened and concentrated oxygen is introduced from the adsorption tower A to maintain the decompressed state. . As a result, the inside of the adsorption tower B is purged countercurrently, and the reduced pressure state is maintained even when the purge is completed.
[0018]
Next, switching between the adsorption tower A and the adsorption tower B, step 5 (pressure equalization) in the same manner as described above,
Step 6 (natural intake),
Step 7 (oxygen recovery) and step 8 (switching preparation)
These steps are sequentially performed to form one cycle, and this cycle is repeated to accumulate concentrated oxygen in the pressure equalizing unit C and to extract and use it from the extraction pipe 13.
Table 1 shows the time required for each step in the cycle and the opening / closing program for each valve.
[0019]
[Table 1]

[0020]
The low-pressure oxygen concentration method of the present invention is characterized in that a low-pressure turbo blower having a maximum discharge pressure of 0.3 kg / cm ² G or less is used as a blower for press-fitting a raw material gas into an adsorption tower. The advantages of using a low-pressure turbo blower are as follows: (1) The time to reach the maximum pressure in the adsorption tower can be shortened and the maximum pressure can be maintained without complicated pressure control operation. (2) Electricity consumption at the maximum pressure is reduced. And (3) the operation of the closing operation is simple and the power consumption can be reduced.
[0021]
In order to explain the advantages of (1) above, when the low-pressure turbo blower is used in the low-pressure oxygen concentration method, the change in the adsorption tower pressure in the (3) oxygen recovery step and (4) switching preparation step and the adsorption tower FIG. 4 shows the relationship with the change in the amount of air to be injected. Further, FIG. 5 shows the relationship between the adsorption tower pressure and the air amount in the same step when a conventional roots blower is used instead of the low pressure turbo blower.
As is clear from the comparison, the Roots blower (Fig. 5) always injects a certain amount of air linearly regardless of the pressure in the tower, so that a special control operation is performed to keep the pressure in the tower within the allowable limit. On the other hand, the low-pressure turbo blower has a very large amount of injected air when the internal pressure of the tower is low, and does not increase any more after the inside of the tower reaches a certain pressure. Is unnecessary. This characteristic realizes the advantage of the low-pressure turbo blower that shortens the time required to reach the maximum pressure in the (1) adsorption tower and can maintain the maximum pressure without complicated pressure control operation.
[0022]
Next, the advantage of the above (2) will be explained. Since the adsorption amount of nitrogen in the adsorption tower is proportional to the product of the average adsorption pressure and the adsorption time, compared with a roots blower or the like in which the pressure in the tower rises linearly, As described above, the low pressure turbo blower that can ensure a relatively high internal pressure from the initial stage requires a lower maximum pressure required to adsorb a certain amount of nitrogen. As a result, the above-mentioned (2) maximum pressure is achieved. The advantage of the low-pressure turbo blower that can reduce the electric power consumption is realized.
[0023]
Next, the advantage (3) will be described. Comparing the behavior of the blower during unloading in the (1) pressure equalization step and (2) natural intake step, in the conventional roots blower, etc., when the discharge side is closed, the internal pressure suddenly rises and the pump Because it is damaged, it requires complicated processing such as cooling the discharge air after cooling with an aftercooler and circulating it to the inlet side, or providing a branch pipe in the discharge pipe to perform bypass discharge, which is expensive and unloading. The power consumption is not negligible. On the other hand, the low-pressure turbo blower simply shuts off either the suction side or the discharge side, and does not increase above a certain pressure due to the above-mentioned characteristics, and the power consumption is extremely low even under the maximum pressure. As a result, the advantage of the low-pressure turbo blower that the operation of the above-mentioned (3) deadline operation is simple and the power consumption can be reduced is realized.
[0024]
In the low-pressure oxygen concentration method of the present invention, after the pressure equalization step, the raw gas is introduced into the adsorption tower in a reduced pressure state by the natural intake step by natural intake. This natural intake step is a step added in consideration of the characteristics of the low-pressure turbo blower. In other words, if a raw gas is introduced into the adsorption tower in a reduced pressure state using a low-pressure turbo blower, a large amount of air flows and consumes electric power. Power consumption is reduced.
[0025]
In the low pressure oxygen enrichment method according to claim 2 of the present invention, between (2) the natural intake step and (3) the oxygen recovery step, and (6) between the natural intake step and (7) the oxygen recovery step. Further, as shown in FIG. 6, respectively, the raw gas is press-fitted into the supply port of the adsorption tower from the turbo blower, and the

outlet

7A or 7B is closed so that the concentrated oxygen does not flow out. Steps (2+) and (6+) for increasing the pressure of the adsorption tower to a high pressure are inserted. By inserting this pressure-increasing step, the maximum oxygen concentration can be recovered from the initial stage in the next oxygen recovery step, and the manufacturing process can be further stabilized.
[0026]
In the present invention, the adsorbent packed in the adsorption tower is not particularly limited as long as it can selectively adsorb / desorb nitrogen, but a zeolite-based molecular sieve is generally preferable. As an example of an adsorbent particularly suitable for the method of the present invention, A-shaped particles having a diameter of 2 to 3 mm or a cylinder having a diameter of 1.4 to 1.7 mm, in which 60 to 70% of cations are substituted with Ca ions, are used. And zeolitic molecular sieves of type X or type X. These are particularly preferred adsorbents from the viewpoint of the adsorption / desorption rate and the space velocity of the passing gas.
[0027]
【Example】
Apparatus The PSA apparatus shown in FIG. 1 was used. In FIG. 1, both the adsorption tower A and the adsorption tower B have a cylindrical shape with a diameter of 600 mm and a height of 2500 mm. The lower part of the tower is filled with activated alumina particles as a dehydrating agent to a thickness of 300 mm. As an adsorbent for nitrogen gas separation, an X-type zeolite molecular sieve, which is formed into a granular shape having a diameter of 2 mm to 3 mm and in which 70% of the cations are replaced by Ca ions, is packed. The pressure equalizer C is an empty tower having the same volume as the adsorption tower. The raw material gas injection pump 8 is a low-pressure turbo blower having a maximum discharge pressure of 0.3 kg / cm ² G, and the decompression pump 9 is a wet two-stage roots blower. The low-pressure turbo blower 8 and the decompression pump 9 are variable in rotation speed, and by changing the rotation speed, in the case of the low-pressure turbo blower 8, the maximum discharge pressure and the intake speed, and in the case of the decompression pump 9, the intake air, The exhaust speed can be controlled. Although not shown, the adsorption tower and the piping are arranged in a thermostat, and in the embodiment, the thermostat is kept at 32 ° C.
[0028]
(Embodiment 1) This embodiment is a low-pressure oxygen concentration method based on the first aspect . Air was used as the source gas, and concentrated oxygen was produced by the steps and valve operations shown in FIG. 2 and Table 1. FIG. 3 shows the operation time (seconds) and pressure change of the adsorption tower A and adsorption tower B in each step. During the operation period, the maximum pressure (maximum adsorption pressure) in the adsorption tower was 0.23 kg / cm ² G, and the minimum pressure (minimum desorption pressure) was −0.68 kg / cm ² G. The operation time was 100 seconds per cycle.
[0029]
As a result of operation in this example, product oxygen of 18.6 Nm ³ / h was obtained at an oxygen concentration of 93%, and the oxygen recovery rate at this time was 54%. The power consumption per 1 Nm ^{3 of} product oxygen converted to 100% oxygen concentration was 0.05 kwh for the low-pressure turbo blower 8 and 0.30 kwh for the decompression pump 9, for a total of 0.35 kwh.
[0030]
(Comparative example)
In the apparatus configuration similar to that shown in FIG. 1, a single-stage roots blower conventionally used is used instead of the low-pressure turbo blower 8 as a pump for press-fitting.
Air was used as the source gas, and concentrated oxygen was produced by the steps and valve operations shown in FIG. 7 and Table 2 below. In FIG. 7, the single-stage roots blower is denoted by reference numeral 15. During operation, when the one-stage roots blower 15 was unloaded, the sucked air was released into the atmosphere with the discharge valve 14 and the valve 6 opened to prevent the pump from being destroyed. In Steps 2 and 6, the inside of the adsorption tower was increased to almost atmospheric pressure by supplying the raw material gas from the one-stage roots blower 15 and supplying the concentrated oxygen from the pressure equalizing unit C, regardless of natural intake.
[0031]
[Table 2]

[0032]
FIG. 8 shows changes in pressure in the adsorption tower A and the adsorption tower B in each step. During the operation period, the maximum pressure (maximum adsorption pressure) of the adsorption tower was 0.45 kg / cm ² G, and the minimum pressure (minimum desorption pressure) was 10.68 kg / cm ² G. The operation cycle was 120 seconds per cycle.
[0033]
As a result of operation in this comparative example, product oxygen of 19.3 Nm ³ / h was obtained at an oxygen concentration of 93%, and the oxygen recovery rate at this time was 50%. The power consumption per 1 Nm ^{3 of} product oxygen converted to 100% oxygen concentration was 0.12 kwh for the single-stage roots blower 15 and 0.28 kwh for the vacuum pump 9, and the total was 0.40 kwh.
In this comparative example, since the adsorption pressure is higher than that of the example, even when the minimum pressure is 10.68 kg / cm ² G which is the same as that of the example, the period during which the vacuum pump is exhausted by being connected to the adsorption tower. Therefore, although the power consumption of the pressure reducing pump 9 is smaller than that of the embodiment, the power consumption of the single-stage roots blower 15 becomes larger than the difference, and as a whole It became disadvantageous.
[0034]
【The invention's effect】
The low-pressure oxygen enrichment method of the present invention uses a low-pressure turbo blower with a maximum discharge pressure of 0.3 kg / cm ² G or less in the two-column PSA method to press the raw material gas into the adsorption tower. Control of maximum adsorption pressure in the tower and operation during unloading of the blower are simplified, power consumption is reduced, and facilities and operating costs are greatly improved as compared with the PSA method using a conventional roots blower or the like.
[Brief description of the drawings]
FIG. 1 is a schematic diagram showing an example of an apparatus for carrying out the present invention. FIG. 2 is a flow chart showing steps in an embodiment of the present invention. FIG. 3 shows the relationship between operation time and operating pressure in the embodiment. FIG. 4 is a graph showing the operating state of the present invention. FIG. 5 is a graph showing the operating state of the comparative example. FIG. 6 is a flowchart showing steps in another embodiment of the present invention. FIG. 8 is a flowchart showing each step. FIG. 8 is a graph showing the relationship between operating time and operating pressure in the comparative example.
A ... Adsorption tower B ... Adsorption tower C ...

Pressure equalizer

1A, 1B, 2A, 2B, 4A, 4B, 6 ... Valve 3 ... Pressure equalization valve 3P ... Purge valve 14 ... Cutoff valve 5A, 5B ...

Supply ports

7A, 7B ... Flow Outlet 8 ... Low-pressure turbo blower 9 ... Decompression pump 10 ...

Bypass pipes

11A, 11B ... Adsorbent 12 ... Pipe 13 ... Extraction end

Claims

Two adsorption towers A and B filled with zeolitic molecular sieves that selectively adsorb / desorb nitrogen, and a pressure equalizer that accumulates the recovered concentrated oxygen and draws it out for use. A series of operation operations for supplying a raw material gas containing oxygen and nitrogen, adsorbing nitrogen, recovering concentrated oxygen from the outlet, and regenerating the adsorption tower B in the meantime, are sequentially replaced with the adsorption towers A and B. An oxygen concentration method for producing concentrated oxygen by repeating,
For the press-fitting of the raw material gas into the adsorption tower, a low-pressure turbo blower with a maximum discharge pressure of 0.3 kg / cm ² G or less is used.
(1) The outlet of the adsorption tower A for starting the supply of the raw material gas and the outlet of the adsorption tower B for starting the regeneration are connected by a pressure equalizing pipe, and the pressure is equalized until the pressure between both towers becomes substantially equal. At the same time, the supply port of the adsorption tower B is connected to a decompression pump to start the exhaust of the adsorption tower B. During this time, the low-pressure turbo blower performs a pressure equalizing step, and (2) the pressure equalizing step. The adsorbing tower A, which has been completed and is in a depressurized state, is increased in pressure by the natural intake from the supply port until it becomes almost atmospheric pressure, and the adsorption tower B is continuously exhausted from the supply port by the decompression pump. Natural intake step for performing deadline operation; (3) Feed gas from the low-pressure turbo blower is injected into the supply port of the adsorption tower A after the completion of natural intake, and recovery of concentrated oxygen is started from the outlet of the adsorption tower A And said With accumulate divider, than the atmospheric pressure is evacuated by subsequently vacuum pump pressure of the adsorption tower A to maintain this pressure was increased to the maximum pressure possible in the low-pressure turbo blower, from this period the adsorption tower B is the supply port low and lowest oxygen recovery steps allowed to reach low pressure, (4) the adsorption column a is the concentrated oxygen is recovered from the outlet while continuing maintaining the maximum pressure of said press-fitting the material gas from the low pressure turbo blower, the average Concentrated oxygen continues to be sent to the pressure device , and during this time, the adsorption tower B continues to be evacuated from the supply port by a decompression pump, while the concentrated oxygen is introduced from the adsorption tower A and the pressure is increased within a range in which the decompressed state is maintained. A switching preparation step for purging the inside of the adsorption tower B counter-currently;
(5) Pressure equalization step, (6) Natural intake step, (7) Oxygen recovery step, (8) Preparation for switching A low-pressure oxygen concentration method characterized in that a series of operation operations including steps is repeated to produce concentrated oxygen, and the concentrated oxygen is accumulated in the pressure equalizer and is extracted from the pressure equalizer and used .

2. The low-pressure oxygen enrichment method according to claim 1 , wherein the low-pressure turbocharger is connected to the supply port of the adsorption tower A that has finished natural intake between the natural intake step of (2) and the oxygen recovery step of (3). The raw material gas is injected from the blower and the outlet of the adsorption tower A is closed to increase the pressure of the adsorption tower A to the highest possible pressure of the low-pressure turbo blower. During this time, the adsorption tower B continues to be exhausted from the supply port by a decompression pump. The (2+) pressurization step, the (6) natural intake step, and the (7) oxygen recovery step are performed by alternating the adsorption tower A and the adsorption tower B in the (2+) pressure increase step (6+ ) A low pressure oxygen enrichment method characterized by inserting a pressurizing step .