JP4050415B2

JP4050415B2 - Gas separation method

Info

Publication number: JP4050415B2
Application number: JP04289299A
Authority: JP
Inventors: 雅人川井
Original assignee: Taiyo Nippon Sanso Corp
Current assignee: Taiyo Nippon Sanso Corp
Priority date: 1999-02-22
Filing date: 1999-02-22
Publication date: 2008-02-20
Anticipated expiration: 2019-02-22
Also published as: JP2000237522A

Description

【０００１】
【発明の属する技術分野】
本発明は、ガス分離方法に関し、詳しくは、圧力変動吸着式ガス分離法により、ガス混合物中の易吸着ガスを吸着剤に選択的に吸着させて難吸着ガスを分離する方法に関するものであって、特に、空気から酸素を分離製造する方法に適したガス分離方法に関するものである。
【０００２】
【従来の技術及び発明が解決しようとする課題】
圧力変動吸着式ガス分離方法（以後ＰＳＡ法という）において、空気中の酸素と窒素とを分離して酸素を製造する方法は、ゼオライトを吸着剤としてすでに広く行われている。ゼオライトのような吸着剤を使用する場合、ゼオライトの易吸着物質である窒素に対する高い選択的吸着性によって空気から難吸着物質である酸素の分離ができる。しかし、ゼオライトは、空気中の約２１％の酸素と約０．９％のアルゴンとに対して略同一の吸着性能を有しているため、酸素とアルゴンとを分離することができない。したがって、ゼオライトで分離した酸素にはアルゴンが含まれるため、ＰＳＡ法による酸素の最高濃度は、概ね９５％とならざるを得ない。
【０００３】
概ね９５％の酸素の用途としては電気炉を用いた製鋼等があるが、酸素濃度が９９．５％程度以上でなければならない用途として、切断スピードの速さ及び切断面の滑らかさが必要な金属の切断や、病院等で用いられる医療用酸素等がある。なお、医療用酸素は、薬事法で９９．５％以上の酸素濃度が必要と指定されている。
【０００４】
しかしながら、現実には、大部分の酸素の用途は、９０％前後の酸素濃度が有れば十分であり、ＰＳＡ法で生産された酸素ガスは、この要求濃度を満足しているので現在工業的に広く使用されている。このため、濃度９０％前後の酸素を必要とする諸ユーザーに向けて酸素をより効率よく供給できるように、ＰＳＡ法による酸素の製造方法や装置に様々な改良が行われている。
【０００５】
改良の一つに、設備構成の簡略化により設備費を低減しようという試みがある。例えば、特開昭４９−３６５７９号公報には、単床式のＰＳＡ法を用いた酸素発生方法及び装置が開示されている。この発明では、吸着塔を一つとする（１塔式）だけでなく、原料空気を圧縮する圧縮機を再生工程では真空ポンプとしても使い、再生効率を向上させることが提案されている。
【０００６】
また、特開昭６０−１１０３１８号公報には、１塔式ＰＳＡのプロセスにおいて、発生したガスを貯留する製品タンクを設けることが示されている。また、該製品タンクを利用して、原料空気加圧と製品加圧とを同時に進行させる再加圧方法が示されている。
【０００７】
しかし、１塔式では、一般に複数塔式で性能向上の手段として用いられている均圧操作を実施することができないため、空気からの酸素回収率は、複数の吸着塔を用いた複数塔式と比較して低くなり、結果的に酸素発生量に対する電力消費量が多いという問題がある。
【０００８】
この改善策として、１塔式で均圧操作を実施するために、複数塔式と同じような均圧操作を行うための均圧ガスを収容する容器（均圧槽）を別に設けるということが容易に考えられる。この場合、均圧槽への均圧ガスの回収は、吸着工程終了時に、製品濃度が決められた製品品位より低下し始める前に、製品ガスとしてのガスの導出を打ち切って導出先を均圧槽へと切換え、吸着塔に残るＭＴＺ（物質移動帯）に相当する部分のガスを均圧槽に回収することにより行う。均圧槽に回収されたガスは、吸着塔が再生工程を行っているときに、再生用パージガスとして使ったり、再生工程を終了した時点で再加圧用ガスとして使ったりするという方法が考えられている。
【０００９】
例えば、特開平７−９６１２８号公報には、均圧槽に回収したガスを再加圧に用いる例が開示されている。また、特開昭４９−６４５６９号公報には、吸着塔から均圧槽へのガス回収を２段階で行い、最初に回収したガスは再加圧用、２段階目で回収したガスはパージ再生用に使用する例が開示されている。さらに、特開平９−１５００２８号公報には、均圧槽へのガスの回収は一回で行うが、回収ガスをパージ再生とその後の再加圧とに使う例が開示されている。
【００１０】
なお、１塔式で用いたプロセスは、複数の吸着塔を用いたプロセスにも容易に応用することができるので、特開平８−３０９１３９号公報には１塔式、２塔式について、前記特開平９−１５００２８号公報と同様な均圧回収ガスの使用例が開示されている。
【００１１】
このように、これらの従来技術では、１塔式、多塔式、それぞれの製品ガスの収率向上のために、各工程の組合わせや、均圧ガス等の有効利用の方法を模索しているが、未だ十分なものとはいえなかった。
【００１２】
すなわち、空気のようなガス混合物から酸素のような難吸着ガスを分離して製品とするＰＳＡ法では、均圧操作が通常実施されているが、これを１塔式プロセスに適用する場合及び多塔式プロセスに適用する場合における上述のような従来例においては、均圧の実施方法や、前記均圧方法の実施により得られる均圧ガスを効率よく再生に利用する方法が確立されていないという問題がある。また、酸素回収率を向上させ、動力消費量を低減させるという課題も解決されているとはいえない。
【００１３】
そこで本発明は、１塔式ＰＳＡ法における均圧操作を効果的に行うことができ、酸素回収率の向上や動力消費量の低減を図れ、複数塔式のＰＳＡ法にも適用が可能なガス分離方法を提供することを目的としている。
【００１４】
【課題を解決するための手段】
上記目的を達成するため、本発明のガス分離方法は、吸着剤を充填した１つの吸着塔と、製品ガス貯槽と、均圧槽とを使用し、前記吸着塔を、相対的に高い圧力の吸着工程と、相対的に低い圧力の再生工程とに切換えることにより、前記吸着剤に対する難吸着ガスと易吸着ガスとを含有するガス混合物から前記難吸着ガスを分離する圧力変動吸着式のガス分離方法において、前記吸着工程では、出口端を閉じた前記吸着塔の入口端から前記ガス混合物を塔内へ供給する加圧操作と、該加圧操作を継続しつつ、前記製品ガス貯槽からの難吸着ガスを吸着塔の出口端から塔内へ供給する製品・原料同時加圧操作と、ガス混合物を入口端から塔内へ供給しつつ、難吸着ガスを吸着塔の出口端から製品ガス貯槽に取出す製品製出操作とを行い、前記再生工程では、前記製品製出操作を終了した吸着塔内に残留する難吸着ガス分を吸着塔の出口端から前記均圧槽に回収する均圧操作と、該均圧操作を終了した吸着塔内のガスを脱着して吸着塔の入口端から系外へ放出する排気操作と、前記均圧操作で均圧槽に回収したガスを均圧槽から吸着塔の出口端を経て塔内に供給しつつ、前記排気操作を継続するパージ再生操作とを行うことを特徴とし、さらに、前記再生工程におけるパージ再生操作において前記均圧槽から吸着塔に供給する回収ガスの供給量を、前記排気操作において該吸着塔から放出する脱着ガスの放出量より多くすることを特徴としている。
【００１５】
また、本発明のガス混合物の分離方法は、吸着剤を充填した少なくとも２つの吸着塔と、製品ガス貯槽とを使用し、前記複数の吸着塔を、相対的に高い圧力の吸着工程と、相対的に低い圧力の再生工程とに順次切換えることにより、前記吸着剤に対する難吸着ガスと易吸着ガスとを含有するガス混合物から前記難吸着ガスを分離する圧力変動吸着式のガス分離方法において、前記吸着工程では、出口端を閉じた吸着塔の入口端から前記ガス混合物を該塔内へ供給する加圧操作と、該加圧操作を継続しつつ、前記製品ガス貯槽からの難吸着ガスを該吸着塔の出口端から該塔内へ供給する製品・原料同時加圧操作と、ガス混合物を入口端から該塔内へ供給しつつ、難吸着ガスを該吸着塔の出口端から製品ガス貯槽に取出す製品製出操作とを行い、前記再生工程では、前記製品製出操作を終了した吸着塔内に残留する難吸着ガス分を該吸着塔の出口端から該吸着塔とは別の吸着塔に回収する均圧操作と、該均圧操作を終了した該吸着塔内のガスを脱着して該吸着塔の入口端から系外へ放出する排気操作と、前記均圧操作で難吸着ガス分を回収した前記別の吸着塔内に残留する難吸着ガス分を均圧ガスとして該吸着塔の出口端から該塔内へ回収しつつ、前記排気操作を継続するパージ再生操作とを行うことを特徴とし、また、前記再生工程におけるパージ再生操作において該吸着塔に供給する均圧ガスの供給量を、前記排気操作において該吸着塔から放出する脱着ガスの放出量より多くすることを特徴としている。
【００１６】
また、前記吸着工程を、前記各操作に代えて、入口端を閉じた吸着塔の出口端から前記製品ガス貯槽からの難吸着ガスを該塔内へ導入する製品加圧操作と、該製品加圧操作を継続しつつ、前記ガス混合物を該吸着塔の入口端から該塔内へ供給する製品・原料同時加圧操作と、ガス混合物を入口端から該塔内へ供給しつつ、難吸着ガスを該吸着塔の出口端から製品ガス貯槽に取出す製品製出操作とで行うこともできる。
【００１７】
本発明方法は、前記ガス混合物が空気であり、前記難吸着ガスが酸素である場合に特に有効であり、この場合、前記吸着工程における加圧操作において、該吸着塔内が負圧のときは、大気中の空気を該吸着塔の入口端から該塔内へ直接吸引させることで行い、該吸着塔内が大気圧付近又はそれ以上の圧力ときは、空気を圧縮機により圧縮して該吸着塔の入口端から該塔内へ供給することにより、圧縮機の動力費を低減できる。
【００２０】
【発明の実施の形態】
図１は、本発明のガス分離方法を説明するためのガス分離装置の一形態例を示す系統図である。このガス分離装置は、１つの吸着塔Ａと、これに接続される製品ガス貯槽１１及び均圧槽１２と、真空ポンプとしても機能する圧縮機１３と、これらを接続する経路及び各経路に設けられた弁と、弁の開閉等を制御するための制御手段１４とにより形成されている。
【００２１】
吸着塔Ａの入口端（図１において下端）には、塔内に連通する吸着塔入口経路２１が設けられており、この吸着塔入口経路２１に、圧縮機１３の吐出側に高圧入口弁３１Ｖを介して接続する高圧経路３１と、圧縮機１３の吸入側に低圧入口弁３２Ｖを介して接続する低圧経路３２とがそれぞれ設けられている。また、高圧経路３１の高圧入口弁３１Ｖと圧縮機１３との間には、排気弁３３Ｖを有する排気経路３３が、低圧経路３２の低圧入口弁３２Ｖと圧縮機１３との間には、空気導入弁３４Ｖを有する原料空気導入経路３４が、それぞれ接続されている。
【００２２】
また、吸着塔Ａの出口端（図１において上端）には、塔内に連通する吸着塔出口経路２２が設けられており、この吸着塔出口経路２２と前記製品ガス貯槽１１との間には、製品取出弁３５Ｖを有する製品取出経路３５と、製品戻弁３６Ｖ及び流量調節弁３６Ｆを有する製品戻経路３６との２つの経路が設けられ、吸着塔出口経路２２と前記均圧槽１２との間には、均圧弁３７Ｖを有する均圧経路３７が設けられている。さらに、製品ガス貯槽１１には、製品送出弁３８Ｖを有する製品送出経路３８が設けられている。
【００２３】
前記各弁の中で、高圧入口弁３１Ｖ，低圧入口弁３２Ｖ及び均圧弁３７Ｖには、流量調節機能を有する弁が用いられており、これらの弁の開閉及び流量調節（開度調節）は、前記制御部１４によって行われる。なお、これらの弁も、製品戻弁３６Ｖ及び流量調節弁３６Ｆと同様に、通常の開閉弁と流量調節弁とを組合わせて形成してもよく、製品戻弁３６Ｖに流量調節機構を付加してもよい。
【００２４】
前記吸着塔Ａ内には、ガス混合物の分離に適した吸着剤が充填されている。例えば、空気を原料とし、酸素を製品として製造する場合には、ガス分離のための主たる吸着剤としてゼオライトが充填される。このゼオライトとしては、いわゆるＡ型ゼオライト（商品名モレキュラーシーブス５Ａ）、Ｘ型ゼオライト（商品名モレキュラーシーブ１３Ｘ）、モルデナイト、及びＸ型ゼオライトに各種金属イオンを導入した剤、例えばＣａ−Ｘ型ゼオライト、Ｌｉ−Ｘ型ゼオライト等が好適である。
【００２５】
また、ガス混合物が空気である場合には、空気が水蒸気を含むため、吸着塔Ａの入口端側には、活性アルミナ、シリカゲルあるいは水分吸着に適したゼオライトが充填される。なお、水蒸気を原料供給ラインの途中に設けた冷凍式除湿器等を用いてあらかじめ除去した場合には、水蒸気除去用のこれら吸着剤を充填する必要はない。これは勿論、吸着剤による水蒸気除去と他の除去手段との併用を否定するものではない。
【００２６】
次に、図２に示すプロセス説明図を参照しながら、本形態例装置により空気から酸素を分離するプロセスを説明する。
【００２７】
まず、吸着工程の最初の段階では、図２（ａ）に示すように、吸着塔出口側の全ての弁３５Ｖ，３６Ｖ，３７Ｖを閉じた状態で、吸着塔入口経路２１から塔内に原料空気を導入する加圧操作を行う。このとき、吸着塔Ａ内が負圧の場合には、吸着塔入口側の各弁３１Ｖ，３２Ｖ，３３Ｖ，３４Ｖを開くことにより、圧縮機１３に負荷を与えることなく、塔内への原料空気の導入を行うことができる。また、吸着塔Ａ内が大気圧付近又はそれ以上の圧力の場合は、低圧入口弁３２Ｖ及び排気弁３３Ｖを閉じた状態で原料空気導入弁３４Ｖと高圧入口弁３１Ｖとを開き、原料空気導入弁３４Ｖから吸入した原料空気を圧縮機１３で所定圧力に圧縮して高圧入口弁３１Ｖから塔内へ導入する。このように、加圧操作に入る時点で吸着塔Ａ内が負圧の場合には、加圧操作の初期段階において原料空気を圧力差で塔内に直接吸入させることにより、この間の圧縮機１３の動力費の節減が図れる。
【００２８】
上記加圧操作により吸着塔Ａ内が所定の圧力に達したら、図２（ｂ）に示すように、圧縮機１３により圧縮された原料空気の塔内への導入を継続しつつ、製品戻経路３６の製品戻弁３６Ｖを開き、製品ガス貯槽１１内の製品ガスの一部を流量調節弁３６Ｆで流量調節しながら製品戻経路３６を通して出口端から塔内に導入する製品・原料同時加圧操作を行う。この製品・原料同時加圧操作により、吸着塔Ａ内は、入口端から導入される原料空気と、出口端から導入される製品ガスとによって加圧される。
【００２９】
そして、上記製品・原料同時加圧操作で吸着塔Ａ内の圧力が製品ガス貯槽１１の圧力を超えたとき、製品戻弁３６Ｖを閉じて製品取出弁３５Ｖを開き、製品・原料同時加圧操作から製品製出操作に移る。この製品製出操作では、入口端から導入される原料空気により塔内のガスが出口端から押出される。これにより、難吸着ガスである製品酸素ガスが吸着塔Ａから導出され、吸着塔出口経路２２から製品取出弁３５Ｖ，製品取出経路３５を通って製品ガス貯槽１１に取出される。製品ガス貯槽１１内の製品ガス（酸素ガス）は、製品送出弁３８Ｖを経て製品送出経路３８から所定量が送出される。
【００３０】
この製品製出操作で吸着塔Ａに原料空気の導入を継続することにより、吸着塔Ａ内では、易吸着ガス（窒素）で飽和された吸着剤層が次第にガスの流れにおける下流側（本形態例では吸着塔の上方）に進み、ある程度の位置に達すると吸着塔Ａから導出される製品ガスの純度が低下する。そこで、製品ガス純度が許容される範囲を外れる直前で製品取出弁３５Ｖを閉じ、製品ガスの取出しを終了する。同時に、吸着塔入口側の高圧入口弁３１Ｖを閉じるとともに排気弁３３Ｖを開き、原料空気導入弁３４Ｖから圧縮機１３を通るガスを排気弁３３Ｖから大気に放出する。これにより、圧縮機１３の負荷を無くすことができ、動力費を低減できる。
【００３１】
これらの各操作により一連の吸着工程が終了し、続いて、吸着塔Ａ内の吸着剤に吸着している易吸着ガスを脱着させる再生工程に入る。この再生工程は、塔内の圧力を連続的に下降させることによって吸着剤から易吸着ガスを脱着する工程である。
【００３２】
上記吸着工程終了時における吸着塔Ａには、吸着塔出口部分にいわゆる物質移動帯（ＭＴＺ）があり、そこに製品品位よりは低いが大気濃度より濃縮された難吸着ガスである酸素が存在するので、図２（ｄ）に示すように、均圧弁３７Ｖを開いて吸着塔ＡのＭＴＺ部のガスを均圧経路３７から均圧槽１２に回収する均圧操作を行う。
【００３３】
この均圧操作は、吸着塔Ａと均圧槽１２の圧力が所定の圧力、通常は略同じ圧力になるまで行われて均圧弁３７Ｖが閉じられる。次に、吸着塔入口側の低圧入口弁３２Ｖが開き、原料空気導入弁３４Ｖが閉じて、図２（ｅ）に示す排気操作が行われる（排気弁３３Ｖは開状態継続）。このとき、圧縮機１３は真空ポンプとして機能し、吸着塔Ａ内のガス（易吸着ガスからなる脱着ガス）は、吸着塔入口経路２１から低圧経路３２を経て圧縮機１３に吸引され、排気経路３３から大気に放出される。
【００３４】
なお、この排気操作の初期において、吸着塔Ａ内の圧力が大気圧より高い間は、原料空気導入弁３４Ｖを開いたままにしておくことにより、また、高圧入口弁３１Ｖを開くことにより、吸着塔Ａ内のガスを、低圧経路３２から原料空気導入経路３４を通して、また、高圧経路３１から排気経路３３を通して放出することができ、これによって圧縮機１３の真空ポンプとしての負荷を軽減することができる。
【００３５】
このように、本形態例では、圧縮機１３を真空ポンプとしても利用し、原料空気の圧縮と塔内の真空排気とに用いているが、圧縮機と真空ポンプとを別々に用意し、原料空気供給系統と真空排気系統とを別に設けることも可能である。
【００３６】
再生工程の最後は、図２（ｆ）に示すように、均圧弁３７Ｖを開いて均圧槽１２に回収したガスを均圧経路３７を通して吸着塔出口端から塔内に導入するパージ再生操作である。このとき、上記排気操作の圧縮機１３による塔内の真空排気はそのまま継続されている。
【００３７】
このパージ再生操作で吸着塔Ａ内に導入されるガスは、前記均圧操作で吸着塔ＡのＭＴＺ部分に残るかなり濃縮された製品ガス成分を含むガスであるから、このようなガスでパージ再生を行うことは、吸着塔Ａの圧力低下により脱着して吸着剤周囲に存在する易吸着ガスを排気側に押しやるだけでなく、吸着剤周囲における易吸着ガスの分圧を低下させて吸着剤からの易吸着ガスの脱着を促進させる効果がある。しかも、従来は、製品ガスを使用して行うパージ再生を、製品にはならないが、製品濃度に近い酸素濃度のガスで行うため、パージ再生に使用する分量に見合った製品ガス採取量の増加が見込まれる。
【００３８】
上記パージ再生操作は、均圧槽１２から吸着塔Ａへのガス供給速度及び圧縮機１３の能力に応じて、吸着塔Ａ内の圧力を連続的に上昇させながら実施することもできるし、吸着塔Ａ内の圧力を連続的に降下させながら実施することもできる。また、これは、高圧入口弁３１Ｖ，低圧入口弁３２Ｖ及び均圧弁３７Ｖにおける流量調節機能を利用し、これらの開閉作動及び流量を関連付けて、それぞれの流量を制御することにより容易に実施することができる。このとき、吸着塔Ａの圧力を上げながら行えば圧縮機１３による排気の動力が削減でき、圧力を下げながら行えば再生をより完全に行えることになり、吸着剤量に対する製品発生量を多くすることが可能となる。
【００３９】
このようにしてパージ再生操作を終えた吸着塔Ａは、吸着工程の最初の加圧操作に戻り、上述の吸着工程及び再生工程の各操作を順次繰返すことにより、いわゆるＰＳＡ法によって空気から酸素を分離する。
【００４０】
なお、吸着塔Ａからの製品ガスの取出しは、吸着工程における製品製出操作の期間だけになるが、製品ガス貯槽１１からの製品ガスの送出は、製品ガス貯槽１１内に貯蔵された製品ガスを製品送出弁３８Ｖで流量を制限しながら送出することによって連続的に行うことができる。
【００４１】
このような構成の１塔式ガス分離装置における操作条件は、原料となる混合ガスや製品となるガスの種類や量等に応じて適宜に設定することができるが、例えば、空気から製品酸素を分離する場合は、一般的な操作条件として、原料空気の圧力は２０〜２００ｋＰａ、好ましくは３０〜５０ｋＰａとし、サイクルタイムは３０〜９０秒、好ましくは５０〜７０秒とし、再生圧力は−８０〜−３０ｋＰａ、好ましくは−５０〜−４０ｋＰａとすればよい。
【００４２】
また、本形態例装置の別のプロセスとして、吸着工程を下記のようにして行うこともできる。すなわち、吸着工程における前記原料空気による加圧操作に代えて、製品ガス貯槽１１内の製品ガスの一部を使用して塔内を加圧する製品加圧操作を行うこともできる。この製品加圧操作では、吸着塔入口側の高圧入口弁３１Ｖ及び低圧入口弁３２Ｖを閉じた状態として製品戻弁３６Ｖを開くことにより、流量調節弁３６Ｆで流量調節した製品ガスを製品戻経路３６から吸着塔出口経路２２を通して吸着塔Ａ内に導入する。
【００４３】
上記製品加圧操作によって吸着塔Ａ内が所定の圧力に達したら、製品加圧を継続しつつ、高圧入口弁３１Ｖ及び原料空気導入弁３４Ｖを開き、圧縮機１３で圧縮した原料空気を吸着塔入口端から塔内に導入して製品・原料同時加圧工程を行い、さらに、吸着塔Ａ内が製品取出圧力に達した時点で製品戻弁３６Ｖを閉じるとともに製品取出弁３５Ｖを開くことにより、製品・原料同時加圧操作から製品製出操作に移行し、吸着塔Ａから導出される製品ガスが製品取出経路３５を通って製品ガス貯槽１１に取出される。
【００４４】
このように、吸着工程の最初の操作を、原料空気による前記加圧操作に代えて上記製品加圧操作で行うことにより、最初から空気で加圧する方法に比べて、製品製出操作の初期の製品濃度を速やかに高めることができる。
【００４５】
次に、図３に示す系統図及び図４に示すプロセス説明図に基づいて複数の吸着塔を用いたプロセスの一形態例を説明する。まず、複数の吸着塔を用いる場合は、１塔式における均圧操作で使用するための回収ガスを貯蔵する均圧槽が不要となる。また、複数の吸着塔を用いる場合には、原料空気を供給するための圧縮機と、吸着塔内を排気するための真空ポンプとは、それぞれ別々に用意される。
【００４６】
すなわち、図３に示すように、２塔式の場合は、２つの吸着塔Ａ，Ｂ及び製品ガス貯槽５１と、原料空気を供給するための圧縮機５２と、吸着塔内を排気するための真空ポンプ５３と、これらを接続する経路及び各経路に設けられた弁と、弁の開閉等を制御するための制御手段５４とで形成される。
【００４７】
ここで、本形態例プロセスを、図４に示すプロセス説明図を参照しながら説明する。なお、図３において、共通する機器には５０番台の符号を付すとともに、吸着塔Ａに付属する経路や弁には６０番台、吸着塔Ｂに付属する経路や弁には７０番台の符号をそれぞれ一桁目を共通にして付してあり、以下の説明では、吸着塔Ａが吸着工程を開始してから再生工程を終えるまでで説明するが、吸着塔Ｂの吸着工程から再生工程は、６０番台の符号を７０番台の符号に読替えればよい。また、ガス混合物は前記同様に空気、難吸着ガス（製品）は酸素であり、最初の段階は、吸着塔Ａが吸着工程に入った段階としている。さらに、開動作の説明のない弁は原則として閉状態である。
【００４８】
吸着工程は、図４（ａ）に示すように、吸着塔Ａ内に原料空気を導入する加圧操作から行われる。この加圧操作は、入口弁６０Ｖを開いて行われるが、初期の段階で吸着塔Ａ内が負圧のときは、空気導入弁５５Ｖを開いて原料空気導入経路５５から入口経路６０を通して空気を塔内に直接吸引させることにより、圧縮機５２に負荷を与えることなく行うことができる。また、吸着塔Ａ内が大気圧付近まで上昇したら、あるいは、当初から吸着塔Ａ内が大気圧付近又はそれ以上の圧力の場合は、空気導入弁５５Ｖを閉じ、圧縮機５２で圧縮した原料空気を圧縮空気経路５６から入口経路６０を通して空気を塔内に導入することにより塔内の加圧が行われる。
【００４９】
吸着塔Ａ内が所定の圧力に達したら、図４（ｂ）に示すように、前記原料空気の導入を継続しつつ、均圧弁６１Ｖ及び製品戻弁５７Ｖを開として製品・原料同時加圧操作に切換える。製品・原料同時加圧操作では、製品ガス貯槽５１に貯留されている製品ガスの一部を、流量調節弁５７Ｆで流量調節して製品戻経路５７及び均圧経路６１を介して出口端から吸着塔Ａ内に導入し、吸着塔Ａの両端から加圧を実施する。
【００５０】
そして、吸着塔Ａの圧力が製品ガス貯槽５１の圧力を超えたとき、均圧弁６１Ｖ及び製品戻弁５７Ｖを閉じ、出口弁６２Ｖを開いて製品製出操作に切換える。この製品製出操作では、図４（ｃ）に示すように、入口端からの原料空気の導入が継続されることにより、吸着塔Ａから製品である酸素が押出され、製品出口経路６２を通って製品ガス貯槽５１に取出される。
【００５１】
さらに、製品製出操作を継続することにより、吸着塔Ａでは、酸素以外の成分（易吸着ガス）で飽和した吸着剤層が次第にガスの流れにおける下流側（図において上方）に進むので、製品酸素濃度が許容される範囲を超える直前で、出口弁６２Ｖを閉じて製品酸素の送出を停止する。これにより、吸着工程の各操作が終了する。
【００５２】
この吸着工程終了時点で、吸着塔Ａの入口弁６０Ｖを閉じ、吸着塔Ｂの入口弁７０Ｖを開くことにより、圧縮機５２からの圧縮空気を吸着塔Ｂ側の経路に流すことができるので、圧縮機の負荷のロスを無くすことができる。
【００５３】
次に、吸着塔Ａ内の圧力を連続的に下降させつつ吸着剤の吸着成分を脱着させる再生工程では、まず図２（ｄ）に示すように、吸着塔Ａの均圧弁６１Ｖと、吸着塔Ｂの均圧弁７１Ｖとを開き、吸着塔ＡのＭＴＺに保持された酸素分を、均圧弁６１Ｖ，均圧経路６１，７１及び均圧弁７１Ｖを経て吸着塔Ｂに回収する均圧操作を行う。
【００５４】
吸着塔Ａの圧力が大気圧以下になったら、両均圧弁６１Ｖ，７１Ｖを閉じて排気弁６３Ｖを開とし、図４（ｅ）から図４（ｆ）及び図４（ｇ）に示す排気操作に切換える。この排気操作では、排気経路６３の排気弁６３Ｖを開き、真空ポンプ５３により吸着塔Ａ内に残るガスを吸引して大気に排気する。
【００５５】
吸着塔Ａが所定の真空度に達したら、図４（ｈ）に示すパージ再生操作を行う。このパージ再生操作では、前記排気操作を続けつつ、両塔の均圧弁６１Ｖ，７１Ｖを開き、吸着塔Ｂからの均圧ガスを均圧弁７１Ｖ，均圧経路７１，６１及び均圧弁６１Ｖを経由して吸着塔Ａに回収する。
【００５６】
このパージ再生操作で吸着塔Ａが所定の圧力に達すると、両均圧弁６１Ｖ，７１Ｖが閉じられて入口弁６０Ｖが開き、図４（ａ）に示す加圧操作に戻り、上述のような吸着工程と再生工程とを繰返す。
【００５７】
なお、図４から明らかなように、吸着塔Ａが上記操作を行っている間、吸着塔Ｂは、排気操作（図４（ａ）〜（ｃ））、均圧操作（図４（ｄ））、吸着工程最初の加圧操作（図４（ｅ））、製品・原料同時加圧操作（図４（ｆ））、製品製出操作（図４（ｇ））、均圧操作（図４（ｈ））の各操作を行う。
【００５８】
このように、吸着塔Ａ，Ｂにおいて上述の吸着工程と再生工程とを交互に繰返して行うことにより、両吸着塔から交互に製品酸素を取出すことができ、製品ガス貯槽５１から製品送出弁５８Ｖ，製品送出経路５８を経て所定量の製品酸素を連続的に送出すことができる。
【００５９】
なお、入口弁６０Ｖ，７０Ｖや均圧弁６１Ｖ，７１Ｖを流量調節機能付きとし、これらの開閉及び流量調節を前記制御手段５４であらかじめ設定された所定の手順に基づいて行うことにより、均圧操作や排気操作におけるガスの流量を最適な条件に設定することができる。
【００６０】
また、２塔式における別のプロセス例として、吸着工程最初の吸着塔の加圧を原料空気で行わずに、製品の一部で加圧を行う製品加圧操作で行うようにしてもよい。すなわち、吸着塔入口側の入口弁６０Ｖ及び排気弁６３Ｖを閉じた状態で均圧弁６１Ｖ及び製品戻弁５７Ｖを開き、製品ガス貯槽５１の製品ガスの一部を吸着塔出口端から導入し、塔内を製品ガスで加圧するようにしてもよい。
【００６１】
吸着塔内が所定圧力になったら、製品加圧を継続しながら入口弁６０Ｖを開き、圧縮機５２で圧縮した原料空気を入口端から塔内に導入し、前記図４（ｂ）と同様の製品・原料同時加圧操作を行う。その後は、図４（ｃ）以下と同様の操作を行うことにより、前記同様にして製品酸素を得ることができる。
【００６２】
このような２塔式における運転操作条件としては、原料空気（混合ガス）の圧力は２０〜２００ｋＰａ、好ましくは３０〜５０ｋＰａ、サイクルタイムは３０〜９０秒、好ましくは５０〜７０秒、再生圧力は−８０〜−４０ｋＰａ、好ましくは−７５〜−６０ｋＰａが適当である。
【００６３】
上記両形態例に示すように、ＰＳＡ法プロセスにおいては、吸着工程の最後に、即ち製品ガスの導出停止直後に、吸着塔出口部分にいわゆる物質移動帯（ＭＴＺ）部分が残るので、この部分の製品ガス濃度の高いガスを均圧槽あるいは別の吸着塔に回収し、該回収したガスを、吸着工程の最終段階で吸着塔出口端、即ち製品導出側から吸着塔に供給しつつ吸着塔入口端、即ち原料供給側から排気すること、すなわち回収したガスによって吸着塔内をパージすることにより、ＭＴＺ部分のガスを効率良く利用することができ、製品ガスを使用した従来のパージ操作に比べて製品収率を大幅に向上させることができ、製品発生量に対する電力消費量を低減することができる。特に、回収したガスの供給量を吸着塔から放出する脱着ガスの放出量よりも多くすることが、より効果的である。また、吸着工程最初の加圧を原料の混合ガスでなく、製品ガスを使用することによっても製品採取時の初期純度安定という大きな効果が得られる。さらに、この加圧の段階で吸着塔内が負圧のときは、塔内外の圧力差で塔内に吸引させることにより、圧縮機動力のさらなる低減が図れる。
【００６４】
【実施例】
実施例１
前記図１及び図２に示した装置系統及びプロセスで、下記設備仕様にて空気から酸素を分離した。
【００６５】

【００６６】
その結果、純度９３％の酸素が回収率４０％で得られた。このときの剤当り発生量は５５Ｎｍ^３／ｈ／ｔｏｎである。従来の酸素回収率に比べて５〜１０％の向上が図れ、また、電力消費量においても従来より３〜５％の効率向上が得られた。
【００６７】
実施例２
前記図３及び図４に示した装置系統及びプロセスで、下記設備仕様にて空気から酸素を分離した。
【００６８】

【００６９】
その結果、純度９３％の酸素が回収率５５％で得られた。このときの剤当り発生量は１００Ｎｍ^３／ｈ／ｔｏｎとなった。従来の２塔式の酸素回収率に比べて５〜１０％の向上が図れ、また、電力消費量においても従来より３〜５％の効率向上が得られた。
【００７０】
【発明の効果】
以上説明したように、本発明によれば、簡単な装置構成で製品ガスの回収率の向上が図れるとともに、電力消費量の削減も図れる。
【図面の簡単な説明】
【図１】本発明のガス分離方法を説明するための１塔式ガス分離装置の一形態例を示す系統図である。
【図２】１塔式におけるプロセスの一例を示す説明図である。
【図３】２塔式ガス分離装置の一例を示す系統図である。
【図４】２塔式におけるプロセスの一例を示す説明図である。
【符号の説明】
Ａ，Ｂ…吸着塔、１１…製品ガス貯槽、１２…均圧槽、１３…圧縮機、１４…制御手段、２１…吸着塔入口経路、２２…吸着塔出口経路、３１…高圧経路、３１Ｖ…高圧弁、３２…低圧経路、３２Ｖ…低圧入口弁、３３…排気経路、３３Ｖ…排気弁、３４…原料空気導入経路、３４Ｖ…空気導入弁、３５…製品取出経路、３５Ｖ…製品取出弁、３６…製品戻経路、３６Ｖ…製品戻弁、３６Ｆ…流量調節弁、３７…均圧経路、３７Ｖ…均圧弁、３８…製品送出経路、３８Ｖ…製品送出弁、５１…製品ガス貯槽、５２…圧縮機、５３…真空ポンプ、５４…制御手段、５５…原料空気導入経路、５５Ｖ…空気導入弁、５６…圧縮空気経路、５７…製品戻経路、５７Ｖ…製品戻弁、５７Ｆ…流量調節弁、５８…製品送出経路、５８Ｖ…製品送出弁、６０，７０…入口経路、６０Ｖ，７０Ｖ…入口弁、６１，７１…均圧経路、６１Ｖ，７１Ｖ…均圧弁、６２，７２…製品出口経路、６２Ｖ，７２Ｖ…出口弁、６３，７３…排気経路、６３Ｖ，７３Ｖ…排気弁[0001]
BACKGROUND OF THE INVENTION
The present invention is a gas separation method. To the law More specifically, the method of separating the hardly adsorbed gas by selectively adsorbing the easily adsorbed gas in the gas mixture to the adsorbent by the pressure fluctuation adsorption type gas separation method. To the law Gas separation method particularly suitable for a method for separating and producing oxygen from air To the law It is related.
[0002]
[Prior art and problems to be solved by the invention]
In the pressure fluctuation adsorption type gas separation method (hereinafter referred to as PSA method), a method for producing oxygen by separating oxygen and nitrogen in air is already widely performed using zeolite as an adsorbent. When an adsorbent such as zeolite is used, oxygen, which is a hard-to-adsorb material, can be separated from air due to high selective adsorptivity to nitrogen, which is a material easily adsorbed on zeolite. However, since zeolite has substantially the same adsorption performance with respect to about 21% oxygen and about 0.9% argon in the air, oxygen and argon cannot be separated. Therefore, since oxygen separated by zeolite contains argon, the maximum concentration of oxygen by the PSA method has to be approximately 95%.
[0003]
As for the use of 95% oxygen, there are steel making using an electric furnace, etc. However, as an application where the oxygen concentration must be about 99.5% or more, high cutting speed and smooth cutting surface are required. There are metal cutting and medical oxygen used in hospitals. Medical oxygen is specified by the Pharmaceutical Affairs Law as requiring an oxygen concentration of 99.5% or higher.
[0004]
However, in reality, it is sufficient for most oxygen applications to have an oxygen concentration of around 90%, and the oxygen gas produced by the PSA method satisfies this required concentration, so that it is currently industrially used. Widely used. For this reason, various improvements have been made to oxygen production methods and apparatuses by the PSA method so that oxygen can be supplied more efficiently to users who need oxygen with a concentration of around 90%.
[0005]
One of the improvements is an attempt to reduce equipment costs by simplifying the equipment configuration. For example, Japanese Patent Application Laid-Open No. 49-36579 discloses an oxygen generation method and apparatus using a single bed PSA method. In the present invention, it is proposed not only to have one adsorption tower (one tower type), but also to use a compressor that compresses the raw air as a vacuum pump in the regeneration process to improve the regeneration efficiency.
[0006]
Japanese Patent Application Laid-Open No. 60-110318 discloses that a product tank for storing generated gas is provided in a single tower type PSA process. Further, a repressurization method is shown in which the raw material air pressurization and the product pressurization are simultaneously advanced using the product tank.
[0007]
However, since the pressure equalization operation generally used as a means for improving performance in a multi-column system cannot be performed in the single-column system, the oxygen recovery rate from the air is a multi-column system using a plurality of adsorption towers. As a result, there is a problem that the power consumption relative to the oxygen generation amount is large.
[0008]
As an improvement measure, in order to perform the pressure equalization operation in a single tower type, a container (equal pressure equalization tank) that stores the pressure equalization gas for performing the pressure equalization operation similar to the multiple tower type is provided. Easy to think. In this case, the recovery of the pressure equalizing gas to the pressure equalizing tank is performed by stopping the derivation of the gas as the product gas before the product concentration starts to drop below the determined product quality at the end of the adsorption process. Switching to the tank is performed by collecting the gas corresponding to the MTZ (mass transfer zone) remaining in the adsorption tower in the pressure equalizing tank. The gas recovered in the pressure equalization tank can be used as a regeneration purge gas when the adsorption tower is performing a regeneration process, or as a repressurization gas when the regeneration process is completed. Yes.
[0009]
For example, Japanese Patent Laid-Open No. 7-96128 discloses an example in which a gas recovered in a pressure equalizing tank is used for repressurization. Japanese Patent Laid-Open No. 49-64569 discloses that gas recovery from the adsorption tower to the pressure equalizing tank is performed in two stages, the first recovered gas is for repressurization, and the second recovered gas is for purge regeneration. An example for use in is disclosed. Further, Japanese Patent Laid-Open No. 9-150028 discloses an example in which the gas is recovered into the pressure equalizing tank once, but the recovered gas is used for purge regeneration and subsequent repressurization.
[0010]
Note that the process used in the single tower type can be easily applied to a process using a plurality of adsorption towers, and Japanese Patent Application Laid-Open No. 8-309139 discloses the above-mentioned special features for the single tower type and the two tower type. An example of the use of a pressure equalized recovery gas similar to that disclosed in Kaihei 9-150028 is disclosed.
[0011]
As described above, in these conventional techniques, in order to improve the yield of the product gas of each of the single tower type and the multi-column type, the combination of each process and the method of effective use such as the pressure equalizing gas are searched. However, it was still not enough.
[0012]
That is, in the PSA method in which a hardly adsorbed gas such as oxygen is separated from a gas mixture such as air to obtain a product, a pressure equalizing operation is usually performed. In the conventional example as described above in the case of applying to a tower type process, it is said that a method for performing pressure equalization and a method for efficiently using pressure equalization gas obtained by performing the pressure equalization method for regeneration are not established. There's a problem. Further, it cannot be said that the problem of improving the oxygen recovery rate and reducing the power consumption is solved.
[0013]
Therefore, the present invention can effectively perform the pressure equalization operation in the single-column PSA method, can improve the oxygen recovery rate and reduce the power consumption, and can be applied to the multi-column PSA method. How to separate The law It is intended to provide.
[0014]
[Means for Solving the Problems]
In order to achieve the above object, the gas separation method of the present invention uses one adsorption tower filled with an adsorbent, a product gas storage tank, and a pressure equalization tank, and the adsorption tower is relatively high pressure. By switching between an adsorption step and a relatively low pressure regeneration step, a pressure fluctuation adsorption type gas separation that separates the hardly adsorbed gas from a gas mixture containing the hardly adsorbed gas and the easily adsorbed gas with respect to the adsorbent. In the method, in the adsorption step, a pressure operation for supplying the gas mixture into the tower from the inlet end of the adsorption tower with the outlet end closed, and a difficulty from the product gas storage tank while continuing the pressure operation. Simultaneously pressurizes the product and raw material to supply the adsorption gas from the outlet end of the adsorption tower into the tower, and supplies the gas mixture from the inlet end to the tower, while supplying the difficult adsorption gas from the outlet end of the adsorption tower to the product gas storage tank. The product production operation to be taken out In the process, a pressure equalizing operation for recovering the hardly adsorbed gas remaining in the adsorption tower after completing the product production operation from the outlet end of the adsorption tower to the pressure equalizing tank, and the inside of the adsorption tower after completing the pressure equalizing operation. The exhaust operation for desorbing the gas and releasing it from the inlet end of the adsorption tower and the gas recovered in the pressure equalization tank by the pressure equalization operation are supplied from the pressure equalization tank into the tower through the outlet end of the adsorption tower. In addition, the purge regeneration operation for continuing the exhaust operation is performed, and the supply amount of the recovered gas supplied from the pressure equalization tank to the adsorption tower in the purge regeneration operation in the regeneration step is The amount of desorption gas released from the adsorption tower is larger than that of the adsorption tower.
[0015]
Further, the method for separating a gas mixture of the present invention uses at least two adsorption towers filled with an adsorbent and a product gas storage tank, and the plurality of adsorption towers are compared with a relatively high pressure adsorption process, In the pressure fluctuation adsorption type gas separation method for separating the hardly adsorbed gas from the gas mixture containing the hardly adsorbed gas and the easily adsorbed gas with respect to the adsorbent by sequentially switching to a low pressure regeneration step, In the adsorption step, a pressurizing operation for supplying the gas mixture into the tower from the inlet end of the adsorption tower with the outlet end closed, and the hardly adsorbed gas from the product gas storage tank while the pressurizing operation is continued. Simultaneously pressurizing the product and raw material to be supplied into the tower from the outlet end of the adsorption tower, and supplying the gas mixture from the inlet end into the tower, while causing difficult adsorption gas to enter the product gas storage tank from the outlet end of the adsorption tower. The product production operation to take out, In the regeneration step, a pressure equalizing operation for recovering the hardly adsorbed gas remaining in the adsorption tower after the product production operation from the outlet end of the adsorption tower to an adsorption tower different from the adsorption tower; An exhaust operation for desorbing the gas in the adsorption tower that has finished the pressure operation and releasing it from the inlet end of the adsorption tower to the outside of the system, and a separate adsorption tower in which the hardly adsorbed gas component was recovered by the pressure equalization operation And performing a purge regeneration operation for continuing the exhaust operation while recovering the remaining difficultly adsorbed gas as a pressure equalizing gas from the outlet end of the adsorption tower into the tower, and purging in the regeneration step The supply amount of the pressure equalizing gas supplied to the adsorption tower in the regeneration operation is larger than the discharge amount of the desorption gas released from the adsorption tower in the exhaust operation.
[0016]
Further, in place of each of the above operations, the adsorption step is a product pressurizing operation for introducing a hardly adsorbed gas from the product gas storage tank into the tower from the outlet end of the adsorption tower whose inlet end is closed; A product / raw material simultaneous pressurizing operation for supplying the gas mixture from the inlet end of the adsorption tower into the tower while continuing the pressure operation, and supplying the gas mixture into the tower from the inlet end to the hardly adsorbed gas Can be carried out by a product production operation for taking out the product from the outlet end of the adsorption tower into a product gas storage tank.
[0017]
The method of the present invention is particularly effective when the gas mixture is air and the hardly adsorbed gas is oxygen. In this case, in the pressurizing operation in the adsorption step, when the inside of the adsorption tower has a negative pressure, The atmospheric air is directly sucked from the inlet end of the adsorption tower into the tower, and when the inside of the adsorption tower is at or near atmospheric pressure, the air is compressed by a compressor and the adsorption is performed. By supplying into the tower from the inlet end of the tower, the power cost of the compressor can be reduced.
[0020]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 illustrates the present invention. To explain the gas separation method It is a systematic diagram which shows one example of a gas separation apparatus. This gas separation device is provided in one adsorption tower A, a product gas storage tank 11 and a pressure equalizing tank 12 connected thereto, a compressor 13 that also functions as a vacuum pump, a path connecting these, and each path And a control means 14 for controlling the opening and closing of the valve.
[0021]
An adsorption tower inlet passage 21 communicating with the inside of the tower is provided at the inlet end (lower end in FIG. 1) of the adsorption tower A, and the high pressure inlet valve 31V on the discharge side of the compressor 13 is connected to the adsorption tower inlet passage 21. Are connected to the suction side of the compressor 13 via a low-pressure inlet valve 32V. An exhaust passage 33 having an exhaust valve 33V is provided between the high pressure inlet valve 31V of the high pressure passage 31 and the compressor 13, and an air is introduced between the low pressure inlet valve 32V of the low pressure passage 32 and the compressor 13. Raw material air introduction paths 34 having valves 34V are connected to each other.
[0022]
Further, an adsorption tower outlet path 22 communicating with the inside of the tower is provided at the outlet end (upper end in FIG. 1) of the adsorption tower A, and between the adsorption tower outlet path 22 and the product gas storage tank 11 is provided. There are provided two paths, a product extraction path 35 having a product extraction valve 35V and a product return path 36 having a product return valve 36V and a flow rate adjustment valve 36F, and the adsorption tower outlet path 22 and the pressure equalizing tank 12 A pressure equalizing path 37 having a pressure equalizing valve 37V is provided between them. Further, the product gas storage tank 11 is provided with a product delivery path 38 having a product delivery valve 38V.
[0023]
Among the valves, the high-pressure inlet valve 31V, the low-pressure inlet valve 32V, and the pressure equalizing valve 37V are valves having a flow rate adjusting function. The opening / closing and flow rate adjustment (opening degree adjustment) of these valves are as follows. This is performed by the control unit 14. Similar to the product return valve 36V and the flow rate adjustment valve 36F, these valves may be formed by combining a normal on-off valve and a flow rate adjustment valve, and a flow rate adjustment mechanism is added to the product return valve 36V. May be.
[0024]
The adsorption tower A is filled with an adsorbent suitable for separating a gas mixture. For example, when air is used as a raw material and oxygen is produced as a product, zeolite is filled as a main adsorbent for gas separation. Examples of the zeolite include so-called A-type zeolite (trade name Molecular Sieves 5A), X-type zeolite (trade name Molecular Sieve 13X), mordenite, and agents obtained by introducing various metal ions into X-type zeolite, such as Ca-X type zeolite, Li-X zeolite and the like are suitable.
[0025]
When the gas mixture is air, the air contains water vapor, so that the inlet end side of the adsorption tower A is filled with activated alumina, silica gel, or zeolite suitable for moisture adsorption. When the water vapor is removed in advance using a refrigeration dehumidifier provided in the middle of the raw material supply line, it is not necessary to fill these adsorbents for water vapor removal. Of course, this does not deny the combined use of water removal by an adsorbent and other removal means.
[0026]
Next, a process for separating oxygen from air by the present embodiment apparatus will be described with reference to a process explanatory diagram shown in FIG.
[0027]
First, in the first stage of the adsorption process, as shown in FIG. 2 (a), with all the

valves

35V, 36V, and 37V on the adsorption tower outlet side closed, the raw material air enters the tower from the adsorption tower inlet path 21. Pressurizing operation to introduce. At this time, if the inside of the adsorption tower A is negative pressure, the raw material air to the inside of the tower can be loaded without applying a load to the compressor 13 by opening the

valves

31V, 32V, 33V, 34V on the inlet side of the adsorption tower. Can be introduced. When the inside of the adsorption tower A is near atmospheric pressure or higher, the raw material air introduction valve 34V and the high pressure inlet valve 31V are opened with the low pressure inlet valve 32V and the exhaust valve 33V closed, and the raw material air introduction valve is opened. The raw material air sucked from 34V is compressed to a predetermined pressure by the compressor 13 and introduced into the tower through the high-pressure inlet valve 31V. Thus, when the inside of the adsorption tower A is negative at the time of entering the pressurizing operation, the compressor 13 during this time is directly sucked into the tower with a pressure difference in the initial stage of the pressurizing operation. The power cost can be saved.
[0028]
When the inside of the adsorption tower A reaches a predetermined pressure by the pressurizing operation, as shown in FIG. 2B, the product return path is continued while continuing the introduction of the raw material air compressed by the compressor 13 into the tower. 36, the product return valve 36V is opened, and the product / raw material simultaneous pressurizing operation for introducing a part of the product gas in the product gas storage tank 11 into the tower through the product return path 36 from the outlet end while adjusting the flow rate by the flow rate adjusting valve 36F. I do. By this product / raw material simultaneous pressurization operation, the inside of the adsorption tower A is pressurized by the raw material air introduced from the inlet end and the product gas introduced from the outlet end.
[0029]
When the pressure in the adsorption tower A exceeds the pressure in the product gas storage tank 11 by the above-mentioned simultaneous product / raw material pressurization operation, the product return valve 36V is closed and the product take-off valve 35V is opened, and the product / raw material simultaneous pressurization operation is performed. To product production operation. In this product production operation, the gas in the tower is extruded from the outlet end by the raw air introduced from the inlet end. Thereby, the product oxygen gas which is a hardly adsorbed gas is led out from the adsorption tower A and taken out from the adsorption tower outlet path 22 to the product gas storage tank 11 through the product take-off valve 35V and the product take-out path 35. A predetermined amount of product gas (oxygen gas) in the product gas storage tank 11 is sent from the product delivery path 38 via the product delivery valve 38V.
[0030]
By continuing the introduction of the raw material air into the adsorption tower A in this product production operation, the adsorbent layer saturated with the easily adsorbed gas (nitrogen) gradually becomes downstream in the gas flow (this embodiment). In the example, proceeding to the upper part of the adsorption tower), and reaching a certain position, the purity of the product gas derived from the adsorption tower A decreases. Therefore, immediately before the product gas purity falls outside the allowable range, the product take-off valve 35V is closed, and the take-out of the product gas is terminated. At the same time, the high pressure inlet valve 31V on the adsorption tower inlet side is closed and the exhaust valve 33V is opened, and the gas passing through the compressor 13 is discharged from the raw air introduction valve 34V to the atmosphere from the exhaust valve 33V. Thereby, the load of the compressor 13 can be eliminated and the power cost can be reduced.
[0031]
A series of adsorption steps are completed by each of these operations, and then a regeneration step for desorbing the easily adsorbed gas adsorbed on the adsorbent in the adsorption tower A is started. This regeneration step is a step of desorbing the easily adsorbed gas from the adsorbent by continuously lowering the pressure in the tower.
[0032]
At the end of the adsorption process, the adsorption tower A has a so-called mass transfer zone (MTZ) at the exit part of the adsorption tower, where oxygen, which is a poorly adsorbed gas which is lower than the product quality but concentrated from the atmospheric concentration, is present. Therefore, as shown in FIG. 2D, a pressure equalizing operation is performed in which the pressure equalizing valve 37V is opened and the gas in the MTZ portion of the adsorption tower A is recovered from the pressure equalizing path 37 to the pressure equalizing tank 12.
[0033]
This pressure equalizing operation is performed until the pressure in the adsorption tower A and the pressure equalizing tank 12 becomes a predetermined pressure, usually substantially the same pressure, and the pressure equalizing valve 37V is closed. Next, the low pressure inlet valve 32V on the adsorption tower inlet side is opened, the raw material air introduction valve 34V is closed, and the exhaust operation shown in FIG. 2 (e) is performed (the exhaust valve 33V is kept open). At this time, the compressor 13 functions as a vacuum pump, and the gas in the adsorption tower A (desorption gas composed of easily adsorbed gas) is sucked into the compressor 13 from the adsorption tower inlet path 21 via the low pressure path 32, and the exhaust path. 33 is released into the atmosphere.
[0034]
In the initial stage of the exhaust operation, while the pressure in the adsorption tower A is higher than the atmospheric pressure, the raw material air introduction valve 34V is kept open, and the high pressure inlet valve 31V is opened to adsorb. The gas in the tower A can be discharged from the low pressure passage 32 through the raw material air introduction passage 34 and from the high pressure passage 31 through the exhaust passage 33, thereby reducing the load of the compressor 13 as a vacuum pump. it can.
[0035]
As described above, in this embodiment, the compressor 13 is also used as a vacuum pump, and is used for the compression of the raw material air and the vacuum exhaust in the tower. However, the compressor and the vacuum pump are separately prepared, It is also possible to provide an air supply system and a vacuum exhaust system separately.
[0036]
At the end of the regeneration step, as shown in FIG. 2 (f), a purge regeneration operation is performed in which the pressure equalizing valve 37V is opened and the gas recovered in the pressure equalizing tank 12 is introduced into the tower through the pressure equalizing path 37 from the outlet end of the adsorption tower. is there. At this time, the vacuum evacuation in the tower by the compressor 13 of the exhaust operation is continued as it is.
[0037]
The gas introduced into the adsorption tower A by the purge regeneration operation is a gas containing a considerably concentrated product gas component remaining in the MTZ portion of the adsorption tower A by the pressure equalization operation. Is not only desorbed by the pressure drop of the adsorption tower A and pushing the easily adsorbed gas around the adsorbent to the exhaust side, but also reduces the partial pressure of the easily adsorbed gas around the adsorbent to remove the adsorbent from the adsorbent. This has the effect of promoting the desorption of the easily adsorbed gas. Moreover, conventionally, purge regeneration using product gas is not a product, but since it is performed with a gas having an oxygen concentration close to the product concentration, the amount of product gas collected corresponding to the amount used for purge regeneration is increased. Expected.
[0038]
The purge regeneration operation can be performed while continuously increasing the pressure in the adsorption tower A according to the gas supply speed from the pressure equalizing tank 12 to the adsorption tower A and the capacity of the compressor 13, It can also be carried out while continuously reducing the pressure in the column A. In addition, this can be easily performed by using the flow rate adjusting function in the high pressure inlet valve 31V, the low pressure inlet valve 32V, and the pressure equalizing valve 37V, and controlling the respective flow rates in association with the opening / closing operation and the flow rate. it can. At this time, if the pressure in the adsorption tower A is increased, the power of exhaust by the compressor 13 can be reduced, and if the pressure is decreased, the regeneration can be performed more completely, and the amount of product generated relative to the amount of adsorbent is increased. It becomes possible.
[0039]
The adsorption tower A that has completed the purge regeneration operation in this manner returns to the first pressurization operation of the adsorption process, and repeats the operations of the adsorption process and the regeneration process in succession, so that oxygen is extracted from the air by the so-called PSA method. To separate.
[0040]
The product gas from the adsorption tower A is taken out only during the product production operation in the adsorption process. However, the product gas from the product gas storage tank 11 is sent out by the product gas stored in the product gas storage tank 11. Can be continuously performed by sending the product while limiting the flow rate with the product delivery valve 38V.
[0041]
The operating conditions in the single-column gas separation apparatus having such a configuration can be appropriately set according to the kind and amount of the mixed gas as the raw material or the gas as the product. In the case of separation, as general operating conditions, the pressure of the raw material air is 20 to 200 kPa, preferably 30 to 50 kPa, the cycle time is 30 to 90 seconds, preferably 50 to 70 seconds, and the regeneration pressure is −80 to It can be −30 kPa, preferably −50 to −40 kPa.
[0042]
Further, as another process of the embodiment apparatus, the adsorption step can be performed as follows. That is, instead of the pressurizing operation with the raw material air in the adsorption step, a product pressurizing operation for pressurizing the inside of the tower using a part of the product gas in the product gas storage tank 11 can be performed. In this product pressurization operation, the product return valve 36V is opened with the high pressure inlet valve 31V and the low pressure inlet valve 32V on the adsorption tower inlet side closed, and the product gas whose flow rate is adjusted by the flow rate adjusting valve 36F is returned to the product return path 36. To the adsorption tower A through the adsorption tower outlet path 22.
[0043]
When the inside of the adsorption tower A reaches a predetermined pressure by the product pressurizing operation, the high pressure inlet valve 31V and the raw material air introduction valve 34V are opened while the product pressurization is continued, and the raw material air compressed by the compressor 13 is taken into the adsorption tower. By introducing into the tower from the inlet end and performing a product / raw material simultaneous pressurization step, and further closing the product return valve 36V and opening the product withdrawal valve 35V when the inside of the adsorption tower A reaches the product removal pressure, The product / raw material simultaneous pressurizing operation is shifted to the product producing operation, and the product gas led out from the adsorption tower A is taken out to the product gas storage tank 11 through the product taking out path 35.
[0044]
Thus, by performing the first operation of the adsorption process by the product pressurizing operation instead of the pressurizing operation by the raw material air, compared with the method of pressurizing with air from the beginning, the initial operation of the product production operation Product concentration can be increased quickly.
[0045]
Next, an example of a process using a plurality of adsorption towers will be described based on the system diagram shown in FIG. 3 and the process explanatory diagram shown in FIG. First, in the case of using a plurality of adsorption towers, a pressure equalizing tank for storing recovered gas for use in a pressure equalizing operation in a single tower type becomes unnecessary. When a plurality of adsorption towers are used, a compressor for supplying raw air and a vacuum pump for exhausting the inside of the adsorption tower are prepared separately.
[0046]
That is, as shown in FIG. 3, in the case of a two-column type, two adsorption towers A and B and a product gas storage tank 51, a compressor 52 for supplying raw material air, and an exhaust for exhausting the inside of the adsorption tower. The vacuum pump 53 is formed by a path connecting them, a valve provided in each path, and a control means 54 for controlling opening and closing of the valve.
[0047]
Here, this embodiment process will be described with reference to the process explanatory diagram shown in FIG. In FIG. 3, common devices are numbered in the 50s, routes and valves attached to the adsorption tower A are numbered 60, and routes and valves attached to the adsorption tower B are numbered 70. The first digit is attached in common, and in the following description, the description will be given from the time when the adsorption tower A starts the adsorption process until the completion of the regeneration process. What is necessary is just to replace the code | symbol of a stand with the code | symbol of the 70s. Further, the gas mixture is air, and the hardly adsorbed gas (product) is oxygen, as described above, and the first stage is the stage where the adsorption tower A has entered the adsorption process. Furthermore, valves that are not described for opening are in principle closed.
[0048]
The adsorption step is performed from a pressurizing operation for introducing the raw material air into the adsorption tower A as shown in FIG. This pressurization operation is performed by opening the inlet valve 60V. When the pressure in the adsorption tower A is negative in the initial stage, the air introduction valve 55V is opened and air is supplied from the raw material air introduction path 55 through the inlet path 60. It can carry out without giving a load to the compressor 52 by making it suck | suck directly in a tower | column. Further, when the inside of the adsorption tower A rises to near atmospheric pressure, or when the inside of the adsorption tower A is at or near atmospheric pressure from the beginning, the air introduction valve 55V is closed and the raw material air compressed by the compressor 52 is used. Is introduced into the tower from the compressed air passage 56 through the inlet passage 60 to pressurize the tower.
[0049]
When the inside of the adsorption tower A reaches a predetermined pressure, as shown in FIG. 4 (b), while continuing the introduction of the raw material air, the pressure equalizing valve 61V and the product return valve 57V are opened to simultaneously press the product and the raw material. Switch to. In the product / raw material simultaneous pressurization operation, part of the product gas stored in the product gas storage tank 51 is adsorbed from the outlet end through the product return path 57 and the pressure equalization path 61 by adjusting the flow rate by the flow rate control valve 57F. It introduce | transduces in the tower A and pressurizes from the both ends of the adsorption tower A. FIG.
[0050]
When the pressure in the adsorption tower A exceeds the pressure in the product gas storage tank 51, the pressure equalizing valve 61V and the product return valve 57V are closed, and the outlet valve 62V is opened to switch to the product production operation. In this product production operation, as shown in FIG. 4C, by continuing the introduction of the raw material air from the inlet end, the product oxygen is extruded from the adsorption tower A and passes through the product outlet path 62. To the product gas storage tank 51.
[0051]
Furthermore, by continuing the product production operation, in the adsorption tower A, the adsorbent layer saturated with components other than oxygen (easily adsorbed gas) gradually proceeds downstream (upward in the figure) in the gas flow. Immediately before the oxygen concentration exceeds the allowable range, the outlet valve 62V is closed to stop the delivery of product oxygen. Thereby, each operation of the adsorption process is completed.
[0052]
By closing the inlet valve 60V of the adsorption tower A and opening the inlet valve 70V of the adsorption tower B at the end of this adsorption process, the compressed air from the compressor 52 can flow through the path on the adsorption tower B side. Loss of compressor load can be eliminated.
[0053]
Next, in the regeneration step of desorbing the adsorbent components while continuously reducing the pressure in the adsorption tower A, first, as shown in FIG. 2 (d), the pressure equalizing valve 61V of the adsorption tower A and the adsorption tower The pressure equalizing valve 71V of B is opened, and the pressure equalizing operation for collecting the oxygen content held in the MTZ of the adsorption tower A to the adsorption tower B through the pressure equalizing valve 61V, the

pressure equalizing paths

61, 71 and the pressure equalizing valve 71V is performed.
[0054]
When the pressure in the adsorption tower A becomes equal to or lower than the atmospheric pressure, the pressure equalizing valves 61V and 71V are closed and the exhaust valve 63V is opened, and the exhaust operation shown in FIGS. 4 (e) to 4 (f) and 4 (g) is performed. Switch to. In this exhaust operation, the exhaust valve 63V of the exhaust path 63 is opened, and the gas remaining in the adsorption tower A is sucked by the vacuum pump 53 and exhausted to the atmosphere.
[0055]
When the adsorption tower A reaches a predetermined degree of vacuum, a purge regeneration operation shown in FIG. In this purge regeneration operation, the pressure equalization valves 61V and 71V of both towers are opened while continuing the exhaust operation, and the pressure equalization gas from the adsorption tower B passes through the pressure equalization valve 71V, the

pressure equalization paths

71 and 61, and the pressure equalization valve 61V. And recovered in the adsorption tower A.
[0056]
When the adsorption tower A reaches a predetermined pressure by this purge regeneration operation, both the pressure equalizing valves 61V and 71V are closed and the inlet valve 60V is opened, and the operation returns to the pressurizing operation shown in FIG. The process and the regeneration process are repeated.
[0057]
As is apparent from FIG. 4, while the adsorption tower A is performing the above operation, the adsorption tower B is evacuated (FIGS. 4 (a) to (c)) and pressure equalized (FIG. 4 (d)). ), First pressurization operation of the adsorption process (FIG. 4 (e)), product / raw material simultaneous pressurization operation (FIG. 4 (f)), product production operation (FIG. 4 (g)), pressure equalization operation (FIG. 4). Each operation of (h)) is performed.
[0058]
As described above, by alternately repeating the adsorption step and the regeneration step described above in the adsorption towers A and B, the product oxygen can be alternately taken out from both adsorption towers, and the product delivery valve 58V can be obtained from the product gas storage tank 51. , A predetermined amount of product oxygen can be continuously delivered via the product delivery path 58.
[0059]
The inlet valves 60V and 70V and the pressure equalizing valves 61V and 71V are provided with a flow rate adjustment function, and these opening / closing and flow rate adjustment are performed based on a predetermined procedure set in advance by the control means 54. The gas flow rate in the exhaust operation can be set to an optimum condition.
[0060]
As another example of the process in the two-column system, the first adsorption tower may be pressurized by a product pressurizing operation in which a part of the product is pressurized without being pressurized with the raw material air. That is, with the inlet valve 60V and the exhaust valve 63V on the adsorption tower inlet side closed, the pressure equalizing valve 61V and the product return valve 57V are opened, a part of the product gas in the product gas storage tank 51 is introduced from the adsorption tower outlet end, The inside may be pressurized with product gas.
[0061]
When the inside of the adsorption tower reaches a predetermined pressure, the inlet valve 60V is opened while continuing the product pressurization, and the raw material air compressed by the compressor 52 is introduced into the tower from the inlet end, and the same as in FIG. Perform simultaneous pressurizing operation for products and raw materials. Thereafter, product oxygen can be obtained in the same manner as described above by performing the same operation as in FIG.
[0062]
As operating conditions in such a two-column system, the pressure of the raw air (mixed gas) is 20 to 200 kPa, preferably 30 to 50 kPa, the cycle time is 30 to 90 seconds, preferably 50 to 70 seconds, and the regeneration pressure is -80 to -40 kPa, preferably -75 to -60 kPa is suitable.
[0063]
As shown in the above two embodiments, in the PSA method process, a so-called mass transfer zone (MTZ) portion remains at the exit of the adsorption tower at the end of the adsorption step, that is, immediately after the stoppage of the product gas. A gas having a high product gas concentration is collected in a pressure equalization tank or another adsorption tower, and the collected gas is supplied to the adsorption tower outlet end, that is, from the product outlet side to the adsorption tower at the final stage of the adsorption process. By exhausting from the end, that is, from the raw material supply side, that is, by purging the inside of the adsorption tower with the recovered gas, the gas in the MTZ portion can be used efficiently, compared with the conventional purge operation using the product gas. Product yield can be greatly improved, and power consumption relative to the amount of product generated can be reduced. In particular, it is more effective to increase the supply amount of the recovered gas than the desorption gas released from the adsorption tower. Further, the use of a product gas instead of a raw material mixed gas for the initial pressurization step can provide a great effect of stabilizing the initial purity at the time of product collection. Further, when the inside of the adsorption tower is negative at this pressurization stage, the compressor power can be further reduced by suctioning the inside of the tower with a pressure difference between inside and outside the tower.
[0064]
【Example】
Example 1
In the apparatus system and process shown in FIGS. 1 and 2, oxygen was separated from air with the following equipment specifications.
[0065]

[0066]
As a result, oxygen having a purity of 93% was obtained at a recovery rate of 40%. The amount generated per agent at this time is 55 Nm ³ / H / ton. Compared to the conventional oxygen recovery rate, an improvement of 5 to 10% was achieved, and an efficiency improvement of 3 to 5% was also obtained in the power consumption.
[0067]
Example 2
3 and FIG. 4, oxygen was separated from air with the following equipment specifications.
[0068]

[0069]
As a result, oxygen with a purity of 93% was obtained at a recovery rate of 55%. The amount generated per agent at this time is 100 Nm ³ / H / ton. Compared to the conventional two-column oxygen recovery rate, it was improved by 5 to 10%, and the power consumption was improved by 3 to 5% compared to the conventional method.
[0070]
【The invention's effect】
As described above, according to the present invention, the recovery rate of the product gas can be improved with a simple apparatus configuration, and the power consumption can be reduced.
[Brief description of the drawings]
FIG. 1 of the present invention To explain the gas separation method It is a systematic diagram which shows one example of a 1-column type gas separation apparatus.
FIG. 2 is an explanatory diagram showing an example of a process in a single tower type.
FIG. 3 is a system diagram showing an example of a two-column gas separation device.
FIG. 4 is an explanatory diagram showing an example of a process in a two-column system.
[Explanation of symbols]
A, B ... adsorption tower, 11 ... product gas storage tank, 12 ... pressure equalization tank, 13 ... compressor, 14 ... control means, 21 ... adsorption tower inlet path, 22 ... adsorption tower outlet path, 31 ... high pressure path, 31V ... High pressure valve, 32 ... Low pressure path, 32V ... Low pressure inlet valve, 33 ... Exhaust path, 33V ... Exhaust valve, 34 ... Raw material air introduction path, 34V ... Air introduction valve, 35 ... Product extraction path, 35V ... Product extraction valve, 36 Product return path, 36V ... Product return valve, 36F ... Flow control valve, 37 ... Pressure equalization path, 37V ... Pressure equalization valve, 38 ... Product delivery path, 38V ... Product delivery valve, 51 ... Product gas storage tank, 52 ... Compressor 53 ... Vacuum pump, 54 ... Control means, 55 ... Raw material air introduction path, 55V ... Air introduction valve, 56 ... Compressed air path, 57 ... Product return path, 57V ... Product return valve, 57F ... Flow control valve, 58 ... Product delivery path, 58V ... Product delivery valve, 6 , 70 ... Inlet path, 60V, 70V ... Inlet valve, 61, 71 ... Pressure equalizing path, 61V, 71V ... Pressure equalizing valve, 62, 72 ... Product outlet path, 62V, 72V ... Outlet valve, 63, 73 ... Exhaust path, 63V, 73V ... exhaust valve

Claims

One adsorption tower filled with an adsorbent, a product gas storage tank, and a pressure equalization tank are used, and the adsorption tower is switched between a relatively high pressure adsorption process and a relatively low pressure regeneration process. In the pressure fluctuation adsorption type gas separation method for separating the hardly adsorbed gas from the gas mixture containing the hardly adsorbed gas and the easily adsorbed gas with respect to the adsorbent,
In the adsorption step,
Pressurization operation for supplying the gas mixture into the tower from the inlet end of the adsorption tower with the outlet end closed;
While continuing the pressurizing operation, a product / raw material simultaneous pressurizing operation for supplying the hardly adsorbed gas from the product gas storage tank into the tower from the outlet end of the adsorption tower;
While supplying the gas mixture from the inlet end into the tower, the product production operation is performed to extract the hardly adsorbed gas from the outlet end of the adsorption tower to the product gas storage tank,
In the regeneration step,
A pressure equalizing operation for recovering the hardly adsorbed gas remaining in the adsorption tower after the product production operation from the outlet end of the adsorption tower to the pressure equalizing tank;
An exhaust operation for desorbing the gas in the adsorption tower after the pressure equalizing operation and releasing it from the inlet end of the adsorption tower;
A gas separation characterized by performing a purge regeneration operation to continue the exhaust operation while supplying the gas recovered in the pressure equalization tank by the pressure equalization operation from the pressure equalization tank through the outlet end of the adsorption tower into the tower. Method.

The supply amount of the recovered gas supplied from the pressure equalizing tank to the adsorption tower in the purge regeneration operation in the regeneration step is larger than the release amount of the desorbed gas released from the adsorption tower in the exhaust operation. The gas separation method according to 1.

Using at least two adsorption towers filled with an adsorbent and a product gas storage tank, the plurality of adsorption towers are sequentially switched to a relatively high pressure adsorption process and a relatively low pressure regeneration process. In the pressure fluctuation adsorption type gas separation method for separating the hardly adsorbed gas from the gas mixture containing the hardly adsorbed gas and the easily adsorbed gas with respect to the adsorbent,
In the adsorption step,
A pressurizing operation for supplying the gas mixture into the tower from the inlet end of the adsorption tower with the outlet end closed;
A product / raw material simultaneous pressurization operation for supplying the hardly adsorbed gas from the product gas storage tank into the tower from the outlet end of the adsorption tower while continuing the pressurization operation;
While supplying the gas mixture from the inlet end into the tower, the product production operation for taking out the hardly adsorbed gas from the outlet end of the adsorption tower to the product gas storage tank is performed,
In the regeneration step,
A pressure equalizing operation for recovering the hardly adsorbed gas remaining in the adsorption tower after the product production operation from the outlet end of the adsorption tower to an adsorption tower different from the adsorption tower;
An exhaust operation for desorbing the gas in the adsorption tower that has finished the pressure equalization operation and releasing it from the inlet end of the adsorption tower;
The exhaust operation is continued while recovering the hardly adsorbed gas remaining in the separate adsorption tower from which the hardly adsorbed gas has been recovered by the pressure equalizing operation from the outlet end of the adsorption tower into the tower as a pressure equalizing gas. Performing a purge regeneration operation.

The supply amount of the pressure equalizing gas supplied to the adsorption tower in the purge regeneration operation in the regeneration step is larger than the release amount of the desorption gas released from the adsorption tower in the exhaust operation. Gas separation method.

In place of the above operations, the adsorption step,
A product pressurizing operation for introducing the hardly adsorbed gas from the product gas storage tank into the tower from the outlet end of the adsorption tower with the inlet end closed;
A product / raw material simultaneous pressurization operation for supplying the gas mixture from the inlet end of the adsorption tower into the tower while continuing the product pressurization operation;
A product production operation for taking out the hardly adsorbed gas from the outlet end of the adsorption tower to the product gas storage tank while supplying the gas mixture into the tower from the inlet end;
The gas separation method according to claim 1, wherein the gas separation method is performed.

The gas separation method according to claim 1 or 3, wherein the gas mixture is air and the hardly adsorbed gas is oxygen.

In the pressurizing operation in the adsorption step, when the inside of the adsorption tower has a negative pressure, air in the atmosphere is directly sucked into the tower from the inlet end of the adsorption tower, and the inside of the adsorption tower is at atmospheric pressure. 7. The gas separation method according to claim 6, wherein when the pressure is near or above, the air is compressed by a compressor and is supplied into the tower from the inlet end of the adsorption tower.