JP4230094B2 - Nitrogen production method and apparatus - Google Patents

Nitrogen production method and apparatus Download PDF

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JP4230094B2
JP4230094B2 JP2000158949A JP2000158949A JP4230094B2 JP 4230094 B2 JP4230094 B2 JP 4230094B2 JP 2000158949 A JP2000158949 A JP 2000158949A JP 2000158949 A JP2000158949 A JP 2000158949A JP 4230094 B2 JP4230094 B2 JP 4230094B2
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enriched
nitrogen
oxygen
gas
air
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JP2001336876A5 (en
JP2001336876A (en
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伸一郎 山本
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Taiyo Nippon Sanso Corp
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Description

【０００１】
【発明の属する技術分野】
本発明は、窒素製造方法及び装置に関し、詳しくは、空気を原料とし、液化精留分離（深冷分離）法により窒素を分離して採取するに際して、動力の増加を抑え、高い収率で効率よく窒素を製造することができる窒素製造方法及び装置に関する。
【０００２】
【従来の技術】
工業的に窒素を製造する方法として、空気を原料としてこれを液化し、その成分の沸点差を利用して精留分離する、いわゆる空気液化分離方法が多く採用されている。比較的純度の高い窒素を製造する目的で、この空気液化分離方法を用いた単一の精留塔を使用した装置が実用化されているが、窒素の製造コストを低減する工夫が常に工業的に要求されている。
【０００３】
この要求に対し、窒素の製造コストを低減するための様々なプロセスが提案されている。この中で、廃ガスの一部を精留塔下部の圧力まで昇圧してから再び精留塔へ導入することにより、窒素収率を改善する方法が知られている。この方法は、原料空気を分離し、製品として窒素を採取した残りの、本来廃ガスとして排出されるガス中には、まだ５０％以上の窒素が含まれていることに着目し、廃ガスの一部を排出せずに精留塔へ戻し、再び原料として使用することで、窒素収率の高いプロセスを実現するものである。
【０００４】
この方法の採用例として、特開平３−１３７４８４号公報には、図８に系統図で示すプロセスが記載されている。この方法では、空気圧縮機１で昇圧された原料空気は、アフタークーラー２，管３を経て吸着器４で水分及び炭酸ガスが吸着除去された後、管５を通って主熱交換器６に入り、ここで戻りガスと熱交換して冷却され、管７を経て精留塔８の下部に導入される。導入された原料空気は、該精留塔８において、塔上部の高純度の製品窒素ガスと、塔下部の酸素富化された液化空気（酸素富化液化空気）とに精留分離される。
【０００５】
製品窒素ガスＧＮは、精留塔８から管９に抜出され、管１０を通り、過冷器１１で酸素富化液化空気と、前記主熱交換器６で原料空気と、それぞれ熱交換して常温となった後、管１２を通って送出される。
【０００６】
一方、塔底部から管１３に抜出された酸素富化液化空気は、前記過冷器１１で過冷却された後、弁１４にて凝縮器１５で必要な圧力まで減圧された後、凝縮器１５に導入され、ここで精留塔８から管９、管１６を経て導入される窒素ガスと熱交換し、窒素ガスを液化することにより気化して酸素富化空気となる。液化窒素は管１７を通って精留塔８の上部に戻され、酸素富化空気は、管１８を通って前記過冷器１１で酸素富化液化空気と熱交換した後、管１９を通って主熱交換器６に導入される。この酸素富化空気の内、膨張タービン２０にて寒冷を発生させるのに必要な量が、主熱交換器中部から管２１に抜き出される。管２１に抜き出された酸素富化空気は、膨張タービン２０に導入されて膨張し、必要寒冷を発生して管２２に導出する。余剰の酸素富化空気は、管１９から分岐して弁２３で減圧された後、前記管２２からの酸素富化空気と管２４に合流し、主熱交換器６にて原料空気と熱交換して常温とされ、一部が前記吸着器４の再生ガスとして使用され、残りは廃ガスＷＧとして排出される。
【０００７】
また、酸素富化空気の一部は、主熱交換器６で常温となり、管２６から循環圧縮機２７に導入されて精留塔下部の圧力まで圧縮され、アフタークーラー２８、管２９を通り、主熱交換器６で再度冷却された後、管３０を通って精留塔８に循環する。
【０００８】
このように、循環圧縮機２７を設けて廃ガス（酸素富化空気）の一部を循環させることにより、窒素ガスの収率を上げることができるが、次のような欠点がある。すなわち、酸素富化空気中の酸素濃度が高くなるため、循環圧縮機として酸素仕様とする必要があり、酸素仕様の圧縮機は、保安上要求される仕様を満足するために、同程度の空気循環圧縮機と比較して高価なものとなる。また、酸素富化空気の酸素濃度が高くなると、凝縮器１５にて酸素富化液化空気を気化させるために必要な圧力が低くなる。このことは、製品窒素採取率が上昇するほど、循環圧縮機の吸入圧力が低くなり、動力が増加することを意味している。
【０００９】
また、特開平９−３０３９５８号公報には、図９の系統図に示すように、前述の循環圧縮機２７を設置するのに代えて空気圧縮機を２段構成とし、第１空気圧縮機１ａで一次昇圧した原料空気に、前記同様にして主熱交換器６から管２６に導出された酸素富化空気を合流させ、合流後の原料混合ガスを第２空気圧縮機１ｂで所定の圧力まで昇圧した後、吸着器４、主熱交換器６を通して管７から精留塔８の下部に導入するプロセスが開示されている。なお、以下の説明において、図８の装置と同一の構成要素には、それぞれ同一の符号を付して詳細な説明は省略する。
【００１０】
このプロセスでは、原料空気と酸素富化空気とが混合した原料混合ガスは、主熱交換器６を経て精留塔８に導入され、高純度の製品窒素ガスと酸素富化液化空気とに精留分離される。製品窒素ガスは、前記同様の経路を経て管１２から送出される。また、酸素富化液化空気は、凝縮器１５で気化して酸素富化空気となり、一部が主熱交換器６の中間部から膨張タービン２０に導入されて寒冷を発生させ、余剰の酸素富化空気と合流して管２５から排出される他、必要量の酸素富化空気は、主熱交換器６で常温となった後、管２６を通って第１空気圧縮機１ａの出口の空気と合流し、第２空気圧縮機１ｂを経て循環する。
【００１１】
このプロセスでは、空気圧縮機を循環圧縮機としても利用しているため、装置構成がシンプルとなるが、通常の空気圧縮機を利用して酸素富化空気を圧縮するため、合流後の原料混合ガス中の酸素濃度を安全性確保のために概略２５％以下にする必要があり、酸素富化空気の酸素濃度に制限が生じる。このため、製品窒素収率を大幅に上げることができないという欠点がある。
【００１２】
また、特許第２８７５２０６号公報には、図１０の系統図に示すプロセスを採用することによって循環ガス中の酸素濃度を下げることが記載されている。本プロセスにおいて、空気圧縮機１にて昇圧された原料空気は、吸着器４にて水分と炭酸ガスが吸着除去された後、循環する酸素富化空気と混合してから主熱交換器６を通って精留塔８に導入され、製品窒素と酸素富化液化空気とに分離する。酸素富化液化空気は、管１３から弁１４を通って減圧されて成分調整塔３１に導入され、塔上部に酸素富化空気が分離する。ここで分離した酸素富化空気は、管３２に抜出された後、その一部が管３３に分岐して主熱交換器６で常温となり、管３４を経て循環圧縮機３５にて昇圧され、アフタークーラー３６を通って管３７から前記管５の原料空気に合流し、原料混合ガスとなって主熱交換器６を通り、精留塔８に導入される第１の循環系を形成する。製品窒素ガスは、精留塔８から液体で管３８に抜出され、第二熱交換器３９で気化した後、主熱交換器６で原料混合ガスとの熱交換により常温となって管１２から送出される。
【００１３】
前記成分調整塔３１では、塔下部に設けた凝縮器１５で、精留塔８からの窒素ガスを液化することにより、酸素富化液化空気が気化して酸素富化空気となり、成分調整塔３１の上昇ガスとなる。成分調整塔３１下部の酸素富化空気は、管１８、管１９を通り、主熱交換器６の中部から抜き出されて膨張タービン２０に導入され、寒冷を発生して管２２に導出される。余剰の酸素富化空気は、管１９から弁２３方向に分岐し、該弁２３で減圧後に、管２２からの酸素富化空気と合流し、管２４、主熱交換器６、管２５を通って排出される。また、成分調整塔３１から前記管３２に抜出された酸素富化空気の一部は、管４０に分岐して膨張タービン２０で駆動される圧縮機４１で圧縮され、前記第二熱交換器３９で液化された後、弁４２で減圧してから成分調整塔３１の頂部に再導入されて第２の循環系を形成する。
【００１４】
このプロセスでは、製品回収率が高くなっても、循環ガスの酸素濃度を低く抑えることが可能となる。しかしながら、製品窒素ガスの回収率が上がると、凝縮器１５で蒸発する酸素富化液化空気の酸素濃度が上昇し、酸素富化液化空気を蒸発させるために必要な圧力を低くしなければならなくなる。このことは、成分調整塔３１の運転圧力が低下することを意味する。したがって、循環圧縮機３５の吸入圧力が、製品回収率の増加に伴って低くなり、圧縮動力が増加することとなる。
【００１５】
【発明が解決しようとする課題】
したがって、従来のプロセスでは、循環ガスである酸素富化空気中の酸素濃度を高くすると循環圧縮機を酸素圧縮機仕様としなければならない。さらに、酸素富化空気中の酸素濃度が高くなると、凝縮器で酸素富化液化空気を気化するために必要な圧力が下がる。また、通常の空気圧縮機を利用するためには、循環する酸素富化空気が合流した原料混合ガス中の酸素濃度を概略２５％以下にしなければならず、循環量に制限が生じてしまう。
【００１６】
そこで本発明は、プロセス全体の動力費の低減を図りながら高収率で製品窒素を製造することができる窒素製造方法及び装置を提供することを目的としている。
【００１７】
【課題を解決するための手段】
上記目的を達成するため、本発明の窒素製造方法は、原料空気を液化精留分離して製品窒素を採取する方法であって、原料空気を主精留部に導入して窒素ガスと酸素富化液化空気と窒素富化液化空気とに精留分離する工程と、該窒素富化液化空気を二次精留部に下降液として導入する工程と、前記酸素富化液化空気を前記窒素ガスの一部との熱交換により気化させて酸素富化空気とすると同時に該窒素ガスを液化して液化窒素とする工程と、該酸素富化空気を前記二次精留部に上昇ガスとして導入する工程と、該二次精留部に下降液として導入した前記窒素富化液化空気と上昇ガスとして導入した前記酸素富化空気とを窒素富化ガスと酸素富化液とに精留分離する工程と、該酸素富化液を前記窒素ガスの一部との熱交換により気化させて酸素富化ガスとすると同時に該窒素ガスを液化して液化窒素とする工程と、前記酸素富化液化空気及び酸素富化液との熱交換によって液化した液化窒素を前記主精留部に下降液として導入する工程と、前記窒素富化ガスを圧縮して主精留部に導入する工程と、前記二次精留部の酸素富化ガスを廃ガスとして導出する工程と、前記窒素ガスの残部を製品として導出する工程とを有していることを特徴としている。
【００１９】
さらに、本発明方法は、前記窒素富化ガスの酸素濃度が１０〜４０体積％であることを特徴としている。
【００２０】
また、本発明の窒素製造装置は、原料空気を液化精留分離して製品窒素を採取する装置であって、原料空気を窒素ガスと酸素富化液化空気と窒素富化液化空気とに精留分離する主精留塔と、前記窒素ガスの一部を液化する凝縮器と、前記酸素富化液化空気と窒素富化液化空気とを窒素富化ガスと酸素富化液とに精留分離する第二精留塔とを備えるとともに、前記窒素富化ガスを圧縮機で圧縮して前記主精留塔に再導入する循環経路と、前記窒素富化液化空気を前記主精留塔の中段部から抜出して前記第二精留塔の上部に導入する経路と、前記酸素富化液化空気を前記主精留塔の下部から抜出して前記凝縮器に導入する経路と、該凝縮器で気化した酸素富化空気を第二精留塔の下部に導入する経路と、前記酸素富化液を前記第二精留塔から抜出して前記凝縮器に導入する経路と、該凝縮器で気化した酸素富化ガスを廃ガスとして導出する経路と、前記窒素ガスを主精留塔から製品窒素として採取する経路とを備えていることを特徴としている。
【００２２】
【発明の実施の形態】
図１は、窒素製造装置の第１参考例を示す系統図である。なお、以下の各形態例においては、従来法との比較を容易にするため、前述の従来例装置の構成要素と同一又は類似の構成要素に同一符号を付して説明する。
【００２３】
第１参考例に示す窒素製造装置は、主要な構成機器として、原料空気を昇圧する空気圧縮機１、原料空気中の水分、炭酸ガス等の不純物を吸着除去する吸着器４、戻りガスによって原料混合ガスを冷却する主熱交換器６、原料混合ガスを精留分離する主精留部となる主精留塔８、酸素富化液化空気を蒸発気化させるとともに窒素ガスを液化させる凝縮器１５、寒冷を発生させる膨張タービン２０、循環ガスを昇圧して循環させる循環圧縮機３５を備えるとともに、循環する酸素富化空気の酸素濃度を低下させることを目的とした第二精留塔５１を備えている。
【００２４】
空気圧縮機１で所定圧力に昇圧した原料空気は、アフタークーラー２，管３を通って吸着器４に導入され、水分、炭酸ガスが除去される。吸着器４から管５に流出した原料空気は、循環圧縮機３５から管３７を経て循環する酸素富化空気と合流し、原料混合ガスとなって主熱交換器６に流入する。主熱交換器６で製品窒素ガス等の戻りガスと間接熱交換することによって所定温度に冷却された原料混合ガスは、管７を通って主精留塔８の下部に導入される。
【００２５】
主精留塔８における原料混合ガスの精留操作により、塔上部に窒素ガスが分離し、塔下部には、空気組成より酸素分に富む酸素富化液化空気が分離する。主精留塔８から管９に抜出された窒素ガスの一部が、管１０、過冷器１１、主熱交換器６を通り、管１２から製品窒素ガスＧＮとして採取される。また、残部の窒素ガスは、管９から管１６に分岐して凝縮器１５に導入され、酸素富化液化空気と間接熱交換を行い、凝縮液化して液化窒素となり、管１７を通って主精留塔８の上部に戻されて還流液（下降液）となる。
【００２６】
一方、主精留塔８の底部から管１３に抜出された酸素富化液化空気は、過冷器１１を通って過冷状態となった後、管５２と管５３とに分岐する。管５２を通る流れは、凝縮器１５で気化する圧力に弁１４で減圧された後、凝縮器１５に流入し、前記窒素ガスとの間接熱交換で全量が気化して酸素富化空気となる。この酸素富化空気は、管５４を通って第二精留塔５１の下部に導入され、第二精留塔５１の上昇ガスとなる。また、管５３を通る酸素富化液化空気は、弁５５で減圧した後、第二精留塔５１の上部に下降液として導入される。
【００２７】
第二精留塔５１では、前記酸素富化空気と酸素富化液化空気とで精留が行われ、上部に酸素富化空気よりも酸素分が低減して窒素分が富化されたガス（窒素富化ガス）が分離し、下部に酸素富化液化空気よりも酸素分が増加した液（酸素富化液）が分離する。
【００２８】
第二精留塔頂部から循環ガスの経路である管５６に抜出された窒素富化ガスは、過冷器１１を通り、主熱交換器６を通って常温となった後、管３４から循環圧縮機３５に導入され、所定圧力に昇圧される。昇圧後の循環ガス（窒素富化ガス）は、アフタークーラー３６、管３７を通って前記管５を流れる原料空気に合流し、原料混合ガスとなって主熱交換器６から主精留塔８へと循環する。
【００２９】
また、第二精留塔底部から管５７に抜出された酸素富化液は、弁５８でさらに減圧してから前記凝縮器１５に導入され、気化して酸素富化ガスとなる。この酸素富化ガスは、管５９から過冷器１１を通って管１９に流れ、その一部が主熱交換器６に導入されて主熱交換器中部から管２１に抜出される。管２１の酸素富化ガスは、膨張タービン２０で膨張して寒冷を発生して管２２に流出する。酸素富化ガスの残部は、管１９から分岐して弁２３で減圧した後、前記管２２からの酸素富化ガスと合流し、管２４を通って主熱交換器６に導入され、前記原料混合ガスと熱交換して常温となり、一部が前記吸着器４の再生ガスとして使用され、残りは管２５から廃ガスＷＧとして排出される。
【００３０】
このように、主精留塔８から抜出した酸素富化液化空気を分岐し、一方を凝縮器１５で気化させて第二精留塔５１の上昇ガスとし、他方を液状のまま第二精留塔５１の下降液として二次精留を行うことにより、酸素富化液化空気を、酸素分が空気と同等あるいはそれ以下に減少した窒素富化ガスと酸素分が増加した酸素富化液とに分離することができる。
【００３１】
したがって、第二精留塔５１で分離した窒素富化ガスを循環ガスとして使用することにより、該ガスを昇圧する循環圧縮機３５を酸素仕様とする必要がなくなり、安全性の向上と設備コストの削減とが図れる。さらに、循環するガス中の酸素濃度が下がることにより、主精留塔８の塔底から抜出す酸素富化液化空気の酸素濃度も、従来の廃ガス循環方式に比べて低くなるので、凝縮器１５で気化させるために弁１４で減圧した後の圧力を高くすることができる。これにより、凝縮器１５から第二精留塔５１に導入する酸素富化空気の圧力、すなわち第二精留塔５１の運転圧力を高くすることができるので、循環ガスとして使用する酸素富化液の圧力を高くすることができる。この結果、循環圧縮機３５の吸入圧力が高くなるので、循環圧縮機３５の動力を削減することができる。
【００３２】
また、凝縮器１５を主精留塔８及び第二精留塔５１から独立した状態で設けることにより、第二精留塔５１に不都合が生じた場合でも、従来の方法での運転が可能となる。すなわち、主精留塔８の下部から導出されて過冷器１１を経た酸素富化液化空気を、管５３に分岐させることなく全量を管５２に導入し、弁１４で減圧して凝縮器１５で全量気化又は部分気化し、第二精留塔５１に導入してそのまま全量を管５７に導出し、弁５８、凝縮器１５を通して排ガス経路である管１９に導くことにより、従来のプロセス、例えば図８に示したプロセスと同じ運転を行うことができる。
【００３３】
さらに、主精留塔８と第二精留塔５１とが一体のときは、主精留塔８の下降液の生成と、第二精留塔５１の上昇ガスの生成とが完全な比例関係にあり、これを変更することはできなかったが、主精留塔８と第二精留塔５１とを分離して独立した形態にすることにより、管５２と管５３とへの分岐量の調節で第二精留塔５１の上昇ガス量を調整することができるので、循環ガスの量も自由に調節することができる。
【００３４】
図２は、本発明の第１形態例を示す系統図である。本形態例では、主精留塔８の塔中部から管６１に主精留塔下降液の一部を抜出し、この液を第二精留塔５１の下降液として用いている。
【００３５】
まず、主精留塔８に導入された原料空気と循環ガスとからなる原料混合ガスは、塔上部の窒素ガスと、塔下部の酸素富化液化空気と、塔中部の窒素富化液化空気との３種に精留分離する。
【００３６】
空気組成より酸素分に富む酸素富化液化空気は、主精留塔８の塔底から管１３に抜出され、管５２から過冷器１１を経て弁１４で減圧された後、凝縮器１５で窒素ガスとの熱交換により完全に気化して酸素富化空気となり、管５４を通って第二精留塔５１の下部に上昇ガスとして導入される。
【００３７】
一方、この第二精留塔５１の下降液には、精留塔８の中部に分離した略空気組成乃至空気よりも窒素分に富んだ窒素富化液化空気が用いられている。すなわち、窒素富化液化空気を、塔中部から管６１に抜出して過冷器１１で冷却し、弁５５で減圧してから第二精留塔５１の上部に導入している。
【００３８】
したがって、第二精留塔５１では、酸素富化空気と窒素富化液化空気との間で精留が行われ、上部に窒素富化ガスが、下部に酸素富化液がそれぞれ分離する。このとき、窒素富化液化空気の組成は、第１形態例で下降液として使用した酸素富化液化空気に比べて窒素分が多いので、第二精留塔５１から抜出されて循環ガスとなる窒素富化ガスの組成も窒素分が多くなる。すなわち、第二精留塔５１の頂部から抜出す窒素富化ガスの組成、窒素含有率は、精留塔８の中部から抜出す窒素富化液化空気の窒素含有率を適当に設定することによって任意に調節することが可能となる。
【００３９】
図３は本発明の第２形態例を示す系統図であって、循環する窒素富化ガスの昇圧を、膨張タービン２０によって駆動される圧縮機４１で行うようにしたものである。第１，第２形態例と同様にして第二精留塔５１の頂部から管５６に抜出され、過冷器１１を経た窒素富化ガスは、主熱交換器６に流入することなく前記圧縮機４１に吸入され、低温状態で所定圧力に昇圧された後、管６２を通り、圧縮熱で昇温した温度に対応する位置で主熱交換器６に導入され、管５から主熱交換器６に流入した原料空気と合流して循環流を形成する。
【００４０】
図４は第２参考例を示す系統図であって、空気圧縮機を２段構成とし、主熱交換器６から管３４に導出した循環ガス（窒素富化ガス）を循環圧縮機で昇圧するのに代えて、第１空気圧縮機１ａで一次昇圧した原料空気に合流させて第２空気圧縮機１ｂで所定圧力に昇圧するようにしたものである。
【００４１】
図５は第３参考例を示す系統図であって、前記各形態例に設置されている過冷器１１を省略した例を示している。一般に、過冷器１１を設けて凝縮器１５に導入する酸素富化液化空気を過冷却状態にすることによって空気液化分離装置の性能向上を図ることができるが、このように過冷器を省略しても運転上は全く問題がな。
【００４２】
図６は第４参考例を示す系統図であって、主精留塔８の上部から抜出した窒素ガスを液化させる凝縮器として、前記各形態例で用いたドライ式凝縮器に代えて、液浸式凝縮器７１，７２を使用した例を示すものである。
【００４３】
一方の凝縮器７１の凝縮側には、主精留塔８の上部から管９に抜出されて管１６ａに分岐した窒素ガスが導入されており、蒸発側には、主精留塔８の底部から管１３に抜出され、管５２を通って弁１４で減圧した酸素富化液化空気が導入されている。この酸素富化液化空気は、該凝縮器７１で気化後に管５４を通って第二精留塔５１の下部に導入される。
【００４４】
また、他方の凝縮器７２の凝縮側には、前記管９から管１６ｂに分岐した窒素ガスが導入されており、蒸発側には、第二精留塔５１の底部から管５７に抜出され、弁５８で減圧した酸素富化液が導入されている。この酸素富化液は、該凝縮器７２で気化後に管５９を経て膨張タービン２０に向かう流れとなる。
【００４５】
両凝縮器７１，７２で液化した液化窒素は、管１７に合流して主精留塔８の上部に戻される。なお、各凝縮器７１，７２の底部には、液の一部を放出する保安弁７１ａ、７２ａがそれぞれ設けられている。また、ドライ式凝縮器も、このように酸素富化液化空気用と酸素富化液とに分けて設置することができる。
【００４６】
図７は第５参考例を示す系統図であって、第二精留塔５１に代えて、気液接触が可能な気液分離器７３を設置した例を示している。すなわち、凝縮器１５で気化した酸素富化空気を管５４から気液分離器７３の下部に導入するとともに、管５３からの酸素富化液化空気を気液分離器７３の上部に導入することにより、両者を気液分離器７３内で気液接触させるようにしている。この場合も、液とガスとの気液平衡の関係から、管５６に抜出す循環ガスの窒素濃度を高めて酸素濃度を低くすることができる。
【００５６】
【発明の効果】
以上説明したように、本発明によれば、循環ガス中の窒素濃度を高める（酸素濃度を低くする）ことができるので、循環ガス量を増加させて窒素収率を高めることができるとともに、窒素ガスとの熱交換を高い圧力で行えるので循環ガスを昇圧する循環圧縮機の動力を従来よりも削減することができる。また、循環圧縮機として通常の空気圧縮機を使用することが可能となるので、安全性の向上とコストの低減とを実現することができる。これにより、プロセス全体の動力費の低減を図りながら高収率で製品窒素を製造することができる。
【図面の簡単な説明】
【図１】 第１参考例を示す窒素製造装置の系統図である。
【図２】 本発明の第１形態例を示す系統図である。
【図３】 本発明の第２形態例を示す系統図である。
【図４】 第２参考例を示す系統図である。
【図５】 第３参考例を示す系統図である。
【図６】 第４参考例を示す系統図である。
【図７】 第５参考例を示す系統図である。
【図８】 従来の窒素製造プロセスの一例を示す系統図である。
【図９】 同じく他のプロセス例を示す系統図である。
【図１０】 さらに他のプロセス例を示す系統図である。
【符号の説明】
１…空気圧縮機、１ａ…第１空気圧縮機、１ｂ…第２空気圧縮機、４…吸着器、６…主熱交換器、８…主精留塔、１１…過冷器、１５…凝縮器、２０…膨張タービン、３５…循環圧縮機、４１…圧縮機、５１…第二精留塔、７１，７２…液浸式凝縮器、７３…気液分離器[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method and apparatus for producing nitrogen, and more particularly, when air is used as a raw material and nitrogen is separated and collected by a liquefied rectification separation (deep cold separation) method, an increase in power is suppressed, and a high yield is achieved. The present invention relates to a nitrogen production method and apparatus capable of producing nitrogen well.
[0002]
[Prior art]
As a method for industrially producing nitrogen, a so-called air liquefaction separation method in which air is used as a raw material and is liquefied and rectified and separated using a difference in boiling points of its components is widely used. For the purpose of producing relatively high-purity nitrogen, a device using a single rectification column using this air liquefaction separation method has been put into practical use, but a device for reducing the production cost of nitrogen is always industrial. Is required.
[0003]
In response to this demand, various processes have been proposed to reduce the production cost of nitrogen. Among these, a method is known in which a part of the waste gas is increased to a pressure below the rectification column and then introduced into the rectification column again to improve the nitrogen yield. This method focuses on the fact that 50% or more of nitrogen is still contained in the remaining gas from which the raw material air is separated and nitrogen is collected as a product and is originally discharged as waste gas. By returning a part to the rectification column without discharging it and using it again as a raw material, a process with a high nitrogen yield is realized.
[0004]
As an application example of this method, Japanese Patent Laid-Open No. 3-137484 discloses a process shown in a system diagram in FIG. In this method, the raw material air pressurized by the air compressor 1 is adsorbed and removed by the adsorber 4 through the aftercooler 2 and the pipe 3 and then adsorbed and removed by the adsorber 4 and then passed through the pipe 5 to the main heat exchanger 6. It enters here, is cooled by exchanging heat with the return gas, and is introduced into the lower part of the rectification column 8 via the pipe 7. The introduced raw material air is rectified and separated in the rectification column 8 into high-purity product nitrogen gas at the top of the column and oxygen-enriched liquefied air (oxygen-enriched liquefied air) at the bottom of the column.
[0005]
The product nitrogen gas GN is withdrawn from the rectification column 8 to the pipe 9, passes through the pipe 10, and exchanges heat with the oxygen-enriched liquefied air in the subcooler 11 and the raw air in the main heat exchanger 6. Then, after the temperature reaches normal temperature, it is sent out through the pipe 12.
[0006]
On the other hand, the oxygen-enriched liquefied air withdrawn from the bottom of the column to the pipe 13 is supercooled by the supercooler 11 and then depressurized to a required pressure by the condenser 15 by the valve 14. 15, where heat exchange is performed with the nitrogen gas introduced from the rectification column 8 through the pipe 9 and the pipe 16, and the nitrogen gas is liquefied to be vaporized to become oxygen-enriched air. The liquefied nitrogen is returned to the upper part of the rectification column 8 through the pipe 17, and the oxygen-enriched air is heat-exchanged with the oxygen-enriched liquefied air in the supercooler 11 through the pipe 18 and then passed through the pipe 19. Are introduced into the main heat exchanger 6. Of this oxygen-enriched air, an amount necessary to generate cold in the expansion turbine 20 is extracted from the central portion of the main heat exchanger to the pipe 21. The oxygen-enriched air extracted into the pipe 21 is introduced into the expansion turbine 20 to expand, generates necessary cold, and is led out to the pipe 22. Excess oxygen-enriched air branches from the pipe 19 and is decompressed by the valve 23, and then joins the oxygen-enriched air from the pipe 22 and the pipe 24, and exchanges heat with the raw air in the main heat exchanger 6. Then, the temperature is set to normal temperature, a part is used as the regeneration gas of the adsorber 4, and the rest is discharged as waste gas WG.
[0007]
Further, a part of the oxygen-enriched air becomes room temperature in the main heat exchanger 6, is introduced into the circulation compressor 27 from the pipe 26 and is compressed to the pressure below the rectification tower, passes through the after cooler 28 and the pipe 29, After being cooled again by the main heat exchanger 6, it is circulated to the rectification column 8 through the pipe 30.
[0008]
Thus, by providing the circulating compressor 27 and circulating a part of the waste gas (oxygen-enriched air), the yield of nitrogen gas can be increased, but there are the following drawbacks. That is, since the oxygen concentration in the oxygen-enriched air becomes high, it is necessary to use an oxygen specification as a circulating compressor, and an oxygen specification compressor has the same level of air as that required for safety. It becomes expensive compared with the circulation compressor. Further, when the oxygen concentration of the oxygen-enriched air is increased, the pressure required for vaporizing the oxygen-enriched liquefied air in the condenser 15 is decreased. This means that the higher the product nitrogen collection rate, the lower the suction pressure of the circulating compressor and the greater the power.
[0009]
Further, in Japanese Patent Laid-Open No. 9-303958, as shown in the system diagram of FIG. 9, instead of installing the above-described circulating compressor 27, the air compressor has a two-stage configuration, and the first air compressor 1a Then, the oxygen-enriched air led out from the main heat exchanger 6 to the pipe 26 is joined to the raw material air whose pressure has been primarily increased in the same manner as described above, and the mixed raw material gas is brought to a predetermined pressure by the second air compressor 1b. A process is disclosed in which the pressure is increased and then introduced into the lower part of the rectification column 8 from the pipe 7 through the adsorber 4 and the main heat exchanger 6. In the following description, the same components as those in the apparatus of FIG. 8 are denoted by the same reference numerals, and detailed description thereof is omitted.
[0010]
In this process, a raw material mixed gas in which raw material air and oxygen-enriched air are mixed is introduced into a rectifying column 8 via a main heat exchanger 6, and purified into high-purity product nitrogen gas and oxygen-enriched liquefied air. Is separated. Product nitrogen gas is delivered from the tube 12 through the same path as described above. Further, the oxygen-enriched liquefied air is vaporized by the condenser 15 to become oxygen-enriched air, and part of the oxygen-enriched liquefied air is introduced into the expansion turbine 20 from the middle part of the main heat exchanger 6 to generate cold, and excess oxygen-enriched air is produced. The required amount of oxygen-enriched air joins with the liquefied air and is discharged from the pipe 25. After the temperature reaches normal temperature in the main heat exchanger 6, the air passes through the pipe 26 and exits from the first air compressor 1a. And circulates through the second air compressor 1b.
[0011]
In this process, since the air compressor is also used as a circulating compressor, the system configuration is simple. However, since the oxygen-enriched air is compressed using a normal air compressor, the mixed raw materials are mixed. The oxygen concentration in the gas needs to be approximately 25% or less in order to ensure safety, and the oxygen concentration of the oxygen-enriched air is limited. For this reason, there exists a fault that a product nitrogen yield cannot be raised significantly.
[0012]
Japanese Patent No. 2875206 describes that the oxygen concentration in the circulating gas is lowered by adopting the process shown in the system diagram of FIG. In this process, the raw material air pressurized by the air compressor 1 is mixed with the circulating oxygen-enriched air after moisture and carbon dioxide gas are adsorbed and removed by the adsorber 4 and then passed through the main heat exchanger 6. It is introduced into the rectification column 8 and separated into product nitrogen and oxygen-enriched liquefied air. The oxygen-enriched liquefied air is depressurized from the pipe 13 through the valve 14 and introduced into the component adjustment tower 31, and the oxygen-enriched air is separated at the upper part of the tower. The oxygen-enriched air separated here is extracted into the pipe 32, and then a part of the oxygen-enriched air is branched into the pipe 33 to reach the normal temperature in the main heat exchanger 6, and is pressurized by the circulating compressor 35 via the pipe 34. Then, after passing through the after cooler 36, the pipe 37 merges with the raw material air of the pipe 5, forms a raw material mixed gas, passes through the main heat exchanger 6, and forms the first circulation system introduced into the rectification column 8. . The product nitrogen gas is extracted from the rectifying column 8 as a liquid into the pipe 38, vaporized in the second heat exchanger 39, and then brought to room temperature by heat exchange with the raw material mixed gas in the main heat exchanger 6. Is sent from.
[0013]
In the component adjustment tower 31, the nitrogen gas from the rectification tower 8 is liquefied by the condenser 15 provided in the lower part of the tower, whereby the oxygen-enriched liquefied air is vaporized to become oxygen-enriched air. Ascending gas. The oxygen-enriched air in the lower part of the component adjustment tower 31 passes through the pipes 18 and 19 and is extracted from the middle part of the main heat exchanger 6 and introduced into the expansion turbine 20, generates cold, and is led out to the pipe 22. . Excess oxygen-enriched air branches from the pipe 19 in the direction of the valve 23, is decompressed by the valve 23, merges with oxygen-enriched air from the pipe 22, and passes through the pipe 24, the main heat exchanger 6, and the pipe 25. Discharged. Further, a part of the oxygen-enriched air extracted from the component adjustment tower 31 to the pipe 32 is compressed by the compressor 41 that is branched to the pipe 40 and driven by the expansion turbine 20, and the second heat exchanger. After being liquefied at 39, the pressure is reduced by the valve 42 and then reintroduced to the top of the component adjustment tower 31 to form a second circulation system.
[0014]
In this process, the oxygen concentration of the circulating gas can be kept low even when the product recovery rate is high. However, when the recovery rate of product nitrogen gas increases, the oxygen concentration of the oxygen-enriched liquefied air that evaporates in the condenser 15 increases, and the pressure required to evaporate the oxygen-enriched liquefied air must be reduced. . This means that the operating pressure of the component adjustment tower 31 decreases. Therefore, the suction pressure of the circulating compressor 35 becomes lower as the product recovery rate increases, and the compression power increases.
[0015]
[Problems to be solved by the invention]
Therefore, in the conventional process, if the oxygen concentration in the oxygen-enriched air, which is the circulating gas, is increased, the circulating compressor must be made to be an oxygen compressor specification. Furthermore, as the oxygen concentration in the oxygen-enriched air increases, the pressure required to vaporize the oxygen-enriched liquefied air in the condenser decreases. Moreover, in order to use a normal air compressor, the oxygen concentration in the raw material mixed gas into which the circulating oxygen-enriched air has joined must be made approximately 25% or less, and the circulation amount is limited.
[0016]
Accordingly, an object of the present invention is to provide a nitrogen production method and apparatus capable of producing product nitrogen at a high yield while reducing the power cost of the entire process.
[0017]
[Means for Solving the Problems]
To achieve the above object, the nitrogen production method of the present invention is a method for collecting the product nitrogen liquefying rectification separation of raw material air, nitrogen gas and oxygen by introducing feed air into ShuseiTome portion a step of enriching liquefied air and nitrogen-enriched liquefied air and the rectification separation, a step of introducing a descending liquid the nitrogen-enriched liquefied air to the secondary rectification portion, the oxygen-enriched liquefied air in front Symbol nitrogen A process of vaporizing by heat exchange with part of the gas to form oxygen-enriched air and simultaneously liquefying the nitrogen gas to form liquefied nitrogen; and introducing the oxygen-enriched air into the secondary rectification section as a rising gas And rectifying and separating the nitrogen- enriched liquefied air introduced as a descending liquid and the oxygen-enriched air introduced as an ascending gas into a nitrogen-enriched gas and an oxygen-enriched liquid. And oxygen vaporizing the oxygen-enriched liquid by heat exchange with part of the nitrogen gas. At the same time as liquefied gas, the nitrogen gas is liquefied to form liquefied nitrogen, and liquefied nitrogen liquefied by heat exchange with the oxygen-enriched liquefied air and oxygen-enriched liquid is introduced as a descending liquid into the main rectifying section. A step of compressing the nitrogen-enriched gas and introducing it into the main rectifying unit, a step of deriving the oxygen-enriched gas of the secondary rectifying unit as a waste gas, and the remainder of the nitrogen gas as a product It has the process derived | led-out as follows.
[0019]
Furthermore, the method of the present invention is characterized in that the nitrogen-enriched gas has an oxygen concentration of 10 to 40% by volume.
[0020]
Furthermore, nitrogen production equipment of the present invention is an apparatus for collecting product nitrogen feed air liquefaction rectification separation to, rectification of feed air into nitrogen gas and oxygen-enriched liquefied air and nitrogen-enriched liquefied air Rectification separation of main rectifying column for distillation separation, condenser for liquefying a part of the nitrogen gas, and oxygen-enriched liquefied air and nitrogen-enriched liquefied air into nitrogen-enriched gas and oxygen-enriched liquid A circulation path for compressing the nitrogen-enriched gas with a compressor and reintroducing the nitrogen-enriched gas into the main rectifying tower, and a middle stage of the nitrogen- enriched liquefied air in the main rectifying tower A path to be extracted from the section and introduced to the upper part of the second rectifying column, a path to be used to extract the oxygen-enriched liquefied air from the lower part of the main rectifying column and to be introduced into the condenser, and the condenser was vaporized. A path for introducing oxygen-enriched air into the lower part of the second rectification column, and the oxygen-enriched liquid extracted from the second rectification column A path for introducing the nitrogen-enriched gas vaporized in the condenser as waste gas, and a path for collecting the nitrogen gas from the main rectification column as product nitrogen. It is characterized by.
[0022]
DETAILED DESCRIPTION OF THE INVENTION
Figure 1 is a system diagram showing a first reference example of the nitrogen production system. In the following embodiments, the same reference numerals are given to the same or similar components as those of the above-described conventional device in order to facilitate comparison with the conventional method.
[0023]
The nitrogen production apparatus shown in the first reference example includes, as main constituent devices, an air compressor 1 that pressurizes the raw material air, an adsorber 4 that adsorbs and removes impurities such as moisture and carbon dioxide in the raw material air, and a return gas for the raw material. A main heat exchanger 6 for cooling the mixed gas, a main rectifying column 8 as a main rectifying section for rectifying and separating the raw material mixed gas, a condenser 15 for evaporating oxygen-enriched liquefied air and liquefying nitrogen gas, An expansion turbine 20 that generates cold, a circulation compressor 35 that boosts and circulates the circulating gas, and a second rectifying column 51 that aims to reduce the oxygen concentration of the circulating oxygen-enriched air are provided. Yes.
[0024]
The raw material air pressurized to a predetermined pressure by the air compressor 1 is introduced into the adsorber 4 through the after cooler 2 and the pipe 3, and moisture and carbon dioxide gas are removed. The raw material air that has flowed out of the adsorber 4 into the pipe 5 joins the oxygen-enriched air that circulates from the circulating compressor 35 through the pipe 37 and flows into the main heat exchanger 6 as a raw material mixed gas. The raw material mixed gas cooled to a predetermined temperature by indirect heat exchange with the return gas such as product nitrogen gas in the main heat exchanger 6 is introduced into the lower portion of the main rectifying column 8 through the pipe 7.
[0025]
By the rectification operation of the raw material mixed gas in the main rectification column 8, nitrogen gas is separated at the upper part of the tower, and oxygen-enriched liquefied air richer in oxygen than the air composition is separated at the lower part of the tower. A part of the nitrogen gas extracted from the main rectification column 8 to the tube 9 passes through the tube 10, the subcooler 11, and the main heat exchanger 6 and is collected from the tube 12 as product nitrogen gas GN. The remaining nitrogen gas branches from the tube 9 to the tube 16 and is introduced into the condenser 15, performs indirect heat exchange with the oxygen-enriched liquefied air, condenses and liquefies into liquefied nitrogen, and passes through the tube 17. It is returned to the upper part of the rectifying column 8 and becomes a reflux liquid (falling liquid).
[0026]
On the other hand, the oxygen-enriched liquefied air extracted from the bottom of the main rectification column 8 to the pipe 13 is supercooled through the supercooler 11 and then branches into a pipe 52 and a pipe 53. The flow through the pipe 52 is depressurized by the valve 14 to the pressure vaporized by the condenser 15 and then flows into the condenser 15, and the entire amount is vaporized by indirect heat exchange with the nitrogen gas to become oxygen-enriched air. . This oxygen-enriched air is introduced into the lower part of the second rectifying column 51 through the pipe 54 and becomes the rising gas of the second rectifying column 51. The oxygen-enriched liquefied air passing through the pipe 53 is introduced as a descending liquid into the upper part of the second rectifying column 51 after being decompressed by the valve 55.
[0027]
In the second rectification column 51, rectification is performed with the oxygen-enriched air and the oxygen-enriched liquefied air, and the upper part of the gas (the oxygen content is reduced and the nitrogen content is enriched compared to the oxygen-enriched air) Nitrogen-enriched gas) is separated, and a liquid (oxygen-enriched liquid) having an oxygen content increased from that of oxygen-enriched liquefied air is separated in the lower part.
[0028]
The nitrogen-enriched gas extracted from the top of the second rectification column to the pipe 56, which is the circulation gas path, passes through the subcooler 11, passes through the main heat exchanger 6, and reaches the room temperature. The refrigerant is introduced into the circulation compressor 35 and is increased to a predetermined pressure. The pressure-recirculated gas (nitrogen-enriched gas) merges with the raw air flowing through the pipe 5 through the aftercooler 36 and the pipe 37 and becomes a raw material mixed gas from the main heat exchanger 6 to the main rectifying column 8. Circulate to
[0029]
Further, the oxygen-enriched liquid extracted from the bottom of the second rectification column to the tube 57 is further decompressed by the valve 58 and then introduced into the condenser 15 to be vaporized to become an oxygen-enriched gas. This oxygen-enriched gas flows from the pipe 59 through the supercooler 11 to the pipe 19, a part of which is introduced into the main heat exchanger 6 and extracted from the main heat exchanger to the pipe 21. The oxygen-enriched gas in the pipe 21 expands in the expansion turbine 20 to generate cold and flows out to the pipe 22. The remainder of the oxygen-enriched gas branches from the pipe 19 and is depressurized by the valve 23, and then merges with the oxygen-enriched gas from the pipe 22 and is introduced into the main heat exchanger 6 through the pipe 24. Heat exchange with the mixed gas results in normal temperature, a part is used as the regeneration gas of the adsorber 4, and the rest is discharged from the pipe 25 as waste gas WG.
[0030]
In this way, the oxygen-enriched liquefied air extracted from the main rectifying column 8 is branched, one is vaporized by the condenser 15 and used as the rising gas of the second rectifying column 51, and the other is in the liquid state as the second rectifying. By performing secondary rectification as the descending liquid of the column 51, the oxygen-enriched liquefied air is changed into a nitrogen-enriched gas having an oxygen content equal to or less than that of air and an oxygen-enriched liquid having an increased oxygen content. Can be separated.
[0031]
Therefore, by using the nitrogen-enriched gas separated in the second rectifying column 51 as a circulating gas, it is not necessary to make the circulating compressor 35 for boosting the gas have an oxygen specification, thereby improving safety and reducing the equipment cost. Reduction can be achieved. Furthermore, since the oxygen concentration in the circulating gas is lowered, the oxygen concentration of the oxygen-enriched liquefied air drawn from the bottom of the main rectifying column 8 is also lower than that in the conventional waste gas circulation system. The pressure after depressurizing with the valve 14 to evaporate at 15 can be increased. As a result, the pressure of the oxygen-enriched air introduced from the condenser 15 into the second rectifying column 51, that is, the operating pressure of the second rectifying column 51 can be increased, so that the oxygen-enriched liquid used as the circulating gas The pressure can be increased. As a result, the suction pressure of the circulating compressor 35 increases, so that the power of the circulating compressor 35 can be reduced.
[0032]
In addition, by providing the condenser 15 in a state independent of the main rectifying column 8 and the second rectifying column 51, it is possible to operate in the conventional method even when a problem occurs in the second rectifying column 51. Become. That is, the oxygen-enriched liquefied air led out from the lower part of the main rectification column 8 and passed through the supercooler 11 is introduced into the pipe 52 without branching it to the pipe 53, decompressed by the valve 14, and condensed into the condenser 15. The whole amount is vaporized or partially vaporized, introduced into the second rectification column 51 and led out as it is to the pipe 57, and led to the pipe 19 which is the exhaust gas path through the valve 58 and the condenser 15, thereby allowing the conventional process, for example, The same operation as the process shown in FIG. 8 can be performed.
[0033]
Further, when the main rectifying column 8 and the second rectifying column 51 are integrated, the generation of the descending liquid in the main rectifying column 8 and the generation of the rising gas in the second rectifying column 51 are completely proportional. However, it was not possible to change this, but by separating the main rectifying column 8 and the second rectifying column 51 into independent forms, the amount of branching into the pipe 52 and the pipe 53 can be reduced. Since the amount of ascending gas in the second rectifying column 51 can be adjusted by adjustment, the amount of circulating gas can also be freely adjusted.
[0034]
FIG. 2 is a system diagram showing a first embodiment of the present invention. In this embodiment, a part of the main rectifying tower descending liquid is extracted from the middle part of the main rectifying tower 8 to the pipe 61, and this liquid is used as the descending liquid of the second rectifying tower 51.
[0035]
First, the raw material mixed gas composed of the raw air introduced into the main fractionator 8 and the circulating gas is composed of nitrogen gas at the upper part of the tower, oxygen-enriched liquefied air at the lower part of the tower, and nitrogen-enriched liquefied air at the middle part of the tower. Rectified and separated into three types.
[0036]
Oxygen-enriched liquefied air richer in oxygen than the air composition is extracted from the bottom of the main rectifying column 8 to the pipe 13, decompressed from the pipe 52 via the supercooler 11, and then the condenser 15. Thus, it is completely vaporized by heat exchange with nitrogen gas to become oxygen-enriched air, which is introduced into the lower part of the second rectifying column 51 through the pipe 54 as an ascending gas.
[0037]
On the other hand, as the descending liquid of the second rectifying column 51, nitrogen-enriched liquefied air rich in nitrogen content than air or the substantially air composition separated in the middle of the rectifying column 8 is used. That is, the nitrogen-enriched liquefied air is extracted from the middle of the tower to the pipe 61, cooled by the supercooler 11, decompressed by the valve 55, and then introduced into the upper part of the second rectifying tower 51.
[0038]
Therefore, in the second rectification column 51, rectification is performed between the oxygen-enriched air and the nitrogen-enriched liquefied air, and the nitrogen-enriched gas is separated at the upper part and the oxygen-enriched liquid is separated at the lower part. At this time, the composition of the nitrogen-enriched liquefied air has a higher nitrogen content than the oxygen-enriched liquefied air used as the descending liquid in the first embodiment. The composition of the nitrogen-enriched gas also increases the nitrogen content. That is, the composition and nitrogen content of the nitrogen-enriched gas extracted from the top of the second rectifying column 51 are set by appropriately setting the nitrogen content of the nitrogen-enriched liquefied air extracted from the middle of the rectifying column 8. It can be arbitrarily adjusted.
[0039]
FIG. 3 is a system diagram showing a second embodiment of the present invention, in which the pressure of circulating nitrogen-enriched gas is increased by a compressor 41 driven by the expansion turbine 20. Similarly to the first and second embodiments, the nitrogen-enriched gas extracted from the top of the second rectification column 51 to the pipe 56 and passed through the subcooler 11 does not flow into the main heat exchanger 6. After being sucked into the compressor 41 and raised to a predetermined pressure in a low temperature state, it passes through the pipe 62 and is introduced into the main heat exchanger 6 at a position corresponding to the temperature raised by the compression heat. The raw material air flowing into the vessel 6 is merged to form a circulating flow.
[0040]
FIG. 4 is a system diagram showing a second reference example , in which the air compressor has a two-stage configuration, and the circulating gas (nitrogen-enriched gas) led out from the main heat exchanger 6 to the pipe 34 is boosted by the circulating compressor. Instead of this, it is made to merge with the raw material air pressure-primed primarily by the 1st air compressor 1a, and it is pressure | voltage-risen to predetermined pressure with the 2nd air compressor 1b.
[0041]
FIG. 5 is a system diagram showing a third reference example, and shows an example in which the supercooler 11 installed in each embodiment is omitted. In general, it is possible to improve the performance of the air liquefaction separation apparatus by providing the supercooler 11 and bringing the oxygen-enriched liquefied air introduced into the condenser 15 into a supercooled state, but thus the supercooler is omitted. But there is no problem in driving.
[0042]
FIG. 6 is a system diagram showing a fourth reference example . As a condenser for liquefying nitrogen gas extracted from the upper part of the main rectifying column 8, instead of the dry type condenser used in each of the above-described embodiments, An example using immersion condensers 71 and 72 is shown.
[0043]
On the condensing side of one condenser 71, nitrogen gas extracted from the upper part of the main rectifying column 8 to the pipe 9 and branched to the pipe 16 a is introduced, and on the evaporation side, the main rectifying column 8 Oxygen-enriched liquefied air that has been extracted from the bottom into the tube 13 and reduced in pressure by the valve 14 through the tube 52 is introduced. The oxygen-enriched liquefied air is introduced into the lower part of the second rectification column 51 through the pipe 54 after being vaporized by the condenser 71.
[0044]
Further, nitrogen gas branched from the tube 9 to the tube 16b is introduced to the condensing side of the other condenser 72, and extracted from the bottom of the second rectifying column 51 to the tube 57 on the evaporation side. The oxygen-enriched liquid decompressed by the valve 58 is introduced. The oxygen-enriched liquid becomes a flow toward the expansion turbine 20 through the pipe 59 after being vaporized by the condenser 72.
[0045]
The liquefied nitrogen liquefied by both condensers 71 and 72 joins the pipe 17 and is returned to the upper part of the main rectifying column 8. Note that safety valves 71a and 72a for discharging a part of the liquid are provided at the bottoms of the condensers 71 and 72, respectively. In addition, the dry condenser can also be installed separately for the oxygen-enriched liquefied air and the oxygen-enriched liquid.
[0046]
FIG. 7 is a system diagram showing a fifth reference example, and shows an example in which a gas-liquid separator 73 capable of gas-liquid contact is installed in place of the second rectifying column 51. That is, by introducing the oxygen-enriched air vaporized by the condenser 15 into the lower part of the gas-liquid separator 73 from the pipe 54 and introducing the oxygen-enriched liquefied air from the pipe 53 into the upper part of the gas-liquid separator 73. Both are brought into gas-liquid contact in the gas-liquid separator 73. Also in this case, the nitrogen concentration of the circulating gas extracted to the pipe 56 can be increased and the oxygen concentration can be decreased due to the vapor-liquid equilibrium relationship between the liquid and the gas.
[0056]
【The invention's effect】
As described above, according to the present invention, the nitrogen concentration in the circulating gas can be increased (the oxygen concentration can be decreased), so that the nitrogen yield can be increased by increasing the amount of the circulating gas, Since the heat exchange with the gas can be performed at a high pressure, the power of the circulating compressor for boosting the circulating gas can be reduced as compared with the conventional case. Moreover, since it becomes possible to use a normal air compressor as a circulation compressor, improvement in safety and reduction in cost can be realized. As a result, product nitrogen can be produced in a high yield while reducing the power cost of the entire process.
[Brief description of the drawings]
FIG. 1 is a system diagram of a nitrogen production apparatus showing a first reference example .
FIG. 2 is a system diagram showing a first embodiment of the present invention.
FIG. 3 is a system diagram showing a second embodiment of the present invention.
FIG. 4 is a system diagram showing a second reference example .
FIG. 5 is a system diagram showing a third reference example .
FIG. 6 is a system diagram showing a fourth reference example .
FIG. 7 is a system diagram showing a fifth reference example .
FIG. 8 is a system diagram showing an example of a conventional nitrogen production process.
FIG. 9 is a system diagram showing another example of the process.
FIG. 10 is a system diagram showing still another process example.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Air compressor, 1a ... 1st air compressor, 1b ... 2nd air compressor, 4 ... Adsorber, 6 ... Main heat exchanger, 8 ... Main fractionator, 11 ... Subcooler, 15 ... Condensation 20 ... expansion turbine, 35 ... circulating compressor, 41 ... compressor, 51 ... second rectification tower, 71, 72 ... immersion condenser, 73 ... gas-liquid separator

Claims (3)

原料空気を液化精留分離して製品窒素を採取する方法であって、原料空気を主精留部に導入して窒素ガスと酸素富化液化空気と窒素富化液化空気とに精留分離する工程と、該窒素富化液化空気を二次精留部に下降液として導入する工程と、前記酸素富化液化空気を前記窒素ガスの一部との熱交換により気化させて酸素富化空気とすると同時に該窒素ガスを液化して液化窒素とする工程と、該酸素富化空気を前記二次精留部に上昇ガスとして導入する工程と、該二次精留部に下降液として導入した前記窒素富化液化空気と上昇ガスとして導入した前記酸素富化空気とを窒素富化ガスと酸素富化液とに精留分離する工程と、該酸素富化液を前記窒素ガスの一部との熱交換により気化させて酸素富化ガスとすると同時に該窒素ガスを液化して液化窒素とする工程と、前記酸素富化液化空気及び酸素富化液との熱交換によって液化した液化窒素を前記主精留部に下降液として導入する工程と、前記窒素富化ガスを圧縮して主精留部に導入する工程と、前記二次精留部の酸素富化ガスを廃ガスとして導出する工程と、前記窒素ガスの残部を製品として導出する工程とを有していることを特徴とする窒素製造方法。This is a method of collecting product nitrogen by liquefying rectification separation of raw material air, and introducing rectification separation into nitrogen gas, oxygen-enriched liquefied air and nitrogen-enriched liquefied air by introducing the raw material air into the main rectification section step and a step of introducing the nitrogen-enriched liquefied air as the descending liquid in the secondary rectifying section, wherein the oxygen-enriched liquefied air is vaporized by heat exchange with part of the previous SL nitrogen gas and oxygen-enriched air At the same time, the step of liquefying the nitrogen gas to form liquefied nitrogen, the step of introducing the oxygen-enriched air into the secondary rectification section as an ascending gas, and the step of introducing a descending liquid into the secondary rectification section Rectifying and separating the nitrogen- enriched liquefied air and the oxygen-enriched air introduced as the rising gas into a nitrogen-enriched gas and an oxygen-enriched liquid; and the oxygen-enriched liquid as a part of the nitrogen gas; Is vaporized by heat exchange to produce an oxygen-enriched gas, and at the same time, the nitrogen gas is liquefied and liquefied nitrogen is obtained. A step of introducing liquefied nitrogen liquefied by heat exchange with the oxygen-enriched liquefied air and the oxygen-enriched solution into the main rectifying section as a descending liquid, and compressing the nitrogen-enriched gas to produce a main A step of introducing into the rectification unit, a step of deriving the oxygen-enriched gas of the secondary rectification unit as a waste gas, and a step of deriving the remainder of the nitrogen gas as a product. Nitrogen production method. 前記窒素富化ガスの酸素濃度が１０〜４０体積％であることを特徴とする請求項１記載の窒素製造方法。Nitrogen process according to claim 1 Symbol placement, wherein the oxygen concentration of the nitrogen-enriched gas is 10 to 40 vol%. 原料空気を液化精留分離して製品窒素を採取する装置であって、原料空気を窒素ガスと酸素富化液化空気と窒素富化液化空気とに精留分離する主精留塔と、前記窒素ガスの一部を液化する凝縮器と、前記酸素富化液化空気と窒素富化液化空気とを窒素富化ガスと酸素富化液とに精留分離する第二精留塔とを備えるとともに、前記窒素富化ガスを圧縮機で圧縮して前記主精留塔に再導入する循環経路と、前記窒素富化液化空気を前記主精留塔の中段部から抜出して前記第二精留塔の上部に導入する経路と、前記酸素富化液化空気を前記主精留塔の下部から抜出して前記凝縮器に導入する経路と、該凝縮器で気化した酸素富化空気を第二精留塔の下部に導入する経路と、前記酸素富化液を前記第二精留塔から抜出して前記凝縮器に導入する経路と、該凝縮器で気化した酸素富化ガスを廃ガスとして導出する経路と、前記窒素ガスを主精留塔から製品窒素として採取する経路とを備えていることを特徴とする窒素製造装置。A device for collecting product nitrogen by liquefying and rectifying raw material air, the main rectifying column for rectifying and separating raw material air into nitrogen gas, oxygen-enriched liquefied air and nitrogen-enriched liquefied air, and the nitrogen A condenser for liquefying a part of the gas, and a second rectifying column for rectifying and separating the oxygen-enriched liquefied air and the nitrogen-enriched liquefied air into a nitrogen-enriched gas and an oxygen-enriched liquid, A circulation path for compressing the nitrogen-enriched gas with a compressor and re-introducing it into the main rectification column, and extracting the nitrogen- enriched liquefied air from the middle stage of the main rectification column, A path for introducing the oxygen-enriched liquefied air from the lower part of the main rectifying column and introducing it into the condenser; and an oxygen-enriched air vaporized by the condenser in the second rectifying column. A path for introducing the oxygen-enriched liquid into the lower part, and a path for extracting the oxygen-enriched liquid from the second rectification column and introducing it into the condenser; Nitrogen producing apparatus characterized in that it comprises a path for deriving the oxygen-enriched gas is vaporized in the condenser as waste gas and path for collecting the nitrogen gas as a product nitrogen from Shusei column.
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