CN1076818C - 从低温空气分离设备进行超高纯氧气的生产 - Google Patents

从低温空气分离设备进行超高纯氧气的生产 Download PDF

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CN1076818C
CN1076818C CN96119808A CN96119808A CN1076818C CN 1076818 C CN1076818 C CN 1076818C CN 96119808 A CN96119808 A CN 96119808A CN 96119808 A CN96119808 A CN 96119808A CN 1076818 C CN1076818 C CN 1076818C
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R·阿格拉华尔
D·M·荷尔伦
T·R·怀特
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Abstract

本发明涉及制备超高纯氧气产品、氮气和/或工业纯氧气产品的低温空气分离方法的改进。特别是,本发明的改进的特征在于从在接近含氧气侧馏分流导出处的蒸馏区导出一部分在蒸馏塔系统中下行的液体。

Description

从低温空气分离设备进行超高纯氧气的生产
本发明涉及制备氮气和/或工业纯氧气和少量超高纯氧气的空气或氧气/氮气混合物的低温蒸馏方法。
在本领域已知有众多利用低温蒸馏来制备超高纯氧气产品流的方法,其中包括下列方法:
美国专利5049173公开了从制备氮气和/或工业纯氧气产品的低温空气分离过程制备超高纯氧气的改进方法。具体地说,这种改进包括从单塔或多塔低温空气分离设备上移出或制备出一贫(无)重污染物的含氧气流,并将所述的移出或制出的含氧气流在分级分馏器再汽提而生产出超高纯氧气(即污染物浓度<10vppm)。
美国专利3363427公开了从一般含约99.5-99.8%(体积)的氧气、少量作为轻杂质的氩气和少量包括各种烃(主要为甲烷)、氪和氙的较重杂质的工业纯氧气流制备超高纯氧气的方法。在该方法中,烃既可在催化室中通过燃烧除去也可作为清洗液从辅助蒸馏塔除去。当没有使用催化燃烧单元时,多个蒸馏塔和多个热交换器和重沸器/冷凝器一起使用来实现分离。在这种操作模式中,系统的致冷作用由输入外源的液氮来产生,或通过使用来自空气分离单元的氮流产生,该氮流被循环回空气分离单元,这样就将致冷作用从一处传到另一处。这种催化燃烧选择需要一另外的压缩器和热交换器。美国专利4560397公开了通过空气的低温蒸馏来生产超高纯氧气和高压氮气的方法。在该方法中,原料空气在高压塔中分馏,生产出从高压塔顶部移除的氮气产品流和从高压塔的底部移除的粗制液态氧气流。这种粗制液态氧气流含所有在原料空气中所含的重杂质,也含有在原料空气中所含的大多数氩气。这种粗制液态氧气流的一部分在较低压的副塔上蒸馏而生产出所滑的超高纯氧气。因为所有的重杂质均和氧气一起在副塔中往下流动,因此不可能直接从该塔中制备出只含痕量杂质的液氮产品。为克服这个问题,在位于该副塔的重沸器/冷凝器上方至少一平衡级的一处移出气态氧气产品。但是,因为这种气流和带高浓度重杂质的液流是处于平衡的,因此不可能将重杂质的浓度降至所需水平。例如,参照该专利引用的结果,在所谓的超高纯氧气中的甲烷浓度是8vppm、氪浓度是1.3vppm。按照电子工业具体所需的超高纯氧气标准,这种浓度是高浓度;电子工业上一般超高纯氧气中的烃浓度小于1vppm。
美国专利4755202公开了从使用双塔连环的空气分离装置制备超高纯氧气的方法。在该方法中,富氧气流(氧气浓度为90.0-99.9%)从低压塔的底部导出并送到逆流吸收塔中。在吸收塔中,上升的富氧气流被下行的液流洗去较重组分。贫烃的富氧气流从吸收塔的顶部移出并随后被冷凝。这种经冷凝的贫烃流的一部分作为回流循环回吸收塔,而另一部分则被送到汽提塔。在汽提塔中,下行的贫烃液流被汽提走轻组分如氩而在底部制备出超高纯液氧产品。一部分超高纯液氮被重沸用来提供汽提塔的气流。该气流从汽提塔的顶部移走,回收作为副产物。该方法基本上有两个不合需要的特点。第一是依靠使用被轻重两类杂质污染的来自低压塔底部的原料氧气流,需要二蒸馏塔进行分离(吸收塔和汽提塔)。第二是该方法在汽提塔的顶部产生了提高了氩浓度的含氧气流;降低了氧气含量的副氧气产品流通常是不受欢迎的。
美国专利4869741公开了一种制备超高纯氧气的方法。在该方法中,一种含重和轻污染物的液态氧被用作原料流。在该方法中,使用了两个蒸馏塔、三个重沸器/冷凝器和一个再循环氮流的压缩器和主热交换器来完成所述分离。
本发明涉及通过使用包括至少一蒸馏塔的低温蒸馏塔系统的低温蒸馏来进行的空气分馏方法,其中原料空气流被压缩、冷却到接近其露点并被送到蒸馏塔系统中精馏,从而制备出含氮顶部馏分和粗制液氧底部馏分;其中一基本上不含包括烃、二氧化碳、氙和氪等较重污染物的含氧气侧馏分流从蒸馏塔移出并在辅助汽提塔中汽提而在辅助汽提塔的底部产生超高纯氧气产品;其中所述含氧气流从主要分离氧气和氮气的蒸馏塔系统的一处移除,其氧气浓度在1-35%之间。
本发明改善之处的特征在于将一部分在蒸馏塔系统下行的液体从蒸馏塔系统的蒸馏区排出,而排出的位置位于或接近(最好是位于)送到辅助汽提塔的含氧气侧馏分流导出的位置,从而降低了在位于含氧气侧馏分流被导出处和含绝大多数重杂质的原料被导入之间的蒸馏区的液/气比。被称为支路流的所移除的液体部分被用于该过程内的其它地方;最好这种所移除的液体部分在接近含绝大多数重杂质的原料被导入处的一处导入到蒸馏塔系统中。所降低的气液比明显抑制了氧气-氮气分离,这反过来又提高了含氧侧馏分流的氧气含量,从而提高了来自辅助汽提塔的氧产生量。
在本发明中,所移去的待汽提的含氧气侧馏分流既可以液流导出也可以气流导出。
在本发明中,在辅助汽提塔中提供再沸的热负荷可通过低温冷却至少一部分来自低温蒸馏塔系统的蒸馏塔的粗制液氧底部馏分来提供,或通过至少部分冷凝一部分来自低温蒸馏塔系统的蒸馏塔的氮气顶部馏分来提供,或可通过冷凝器冷却任何适合的工作流体来提供。
本发明的改进成果可应用于包括高压蒸馏塔和低压蒸馏塔的低温蒸馏系统中,其中原料空气流被压缩,冷却到接近其露点并送到高压蒸馏塔系统精馏,从而产生含氮顶部馏分和粗制液氮底部馏分,其中粗制液氧底部馏分被减压,送到低压蒸馏塔进一步分馏,从而产生低压氮气顶部馏分。所移除的含氧侧馏分流可从低压塔或高压塔移除。
本发明的改进之处也可应用到由单(氮气发生器)蒸馏塔组成的低温蒸馏塔系统中,其中所述辅助汽提塔用基本上不含包括烃、二氧化碳、氙和氪等较重组分的来自蒸馏塔的液流回流。
图1是详述美国专利5049173方法的关键特征的设备示意图。
图2是详述本发明改进特征设备的示意图。
图3-5是本发明方法一些可选用实施方案的流程示意图。
本发明是用于制备大量超高纯氧气的、具有包括主蒸馏塔系统和辅助汽提塔的蒸馏塔系统的常规空气分离方法的改进方法,其中含氧气侧馏分流(液态或气态)从主蒸馏塔系统的一处导出,它基本不含比氧气重的组分的烃类、二氧化碳、氙和氪,随后含氧气侧馏分流在辅助汽提塔中汽提而产出超高纯氧气产品。所述主蒸馏塔系统可包括一个或多个蒸馏塔。本发明改进之处的特征在于在蒸馏塔系统中下行液体的一部分在或接近(最好是在)将被送到辅助汽提塔的含氧气侧馏分流被导出之处从蒸馏系统的蒸馏区移离,从而降低了在含氧气侧馏分流被导出处和含大多数重组分的原料被导入处之间的蒸馏区中的液/气比。被称为支路流的所移除液体部分被用于该过程的其它地方。所降低的气液比显著抑制了氧气-氮气分离,这反过来又提高了含氧气侧馏分流的氧气含量,从而提高到辅助汽提塔的氧气产生量。
要更好地理解本发明的改进之处,先注意说明美国专利5049173的关键特征的图1。在图1中,液体下行,气体在主蒸馏塔1中上升,二者组成随主蒸馏塔中蒸馏的进行而改变。基本上不含重组分的氧气侧馏分流(液体或气体)通过管线4从主蒸馏塔1导出并送到辅助汽提塔2进行分离而形成在管线5的超高纯氧气产品流和在管线6的含轻杂质的顶部馏分流。
现在转看说明本发明改正之处的图2。在图2中,也是液体下行,气体在主蒸馏塔中上升,两者组成相应于在主蒸馏塔中蒸馏的进行而改变。基本上不含重组分的含氧气侧馏分流(液体或气体)经管线4从主蒸馏塔1导出并送到辅助汽提塔2的顶部实施分离而形成在管线5的超高纯氧气产品流和在管线6的含轻杂质的顶部馏分流。但是沿主蒸馏塔下行的一部分液体在基本上和经管线4导出的含氧侧馏分流的导出点同样的位置上作为支流物经管线7导出。在含氧气侧馏分流作为液体经管线4导出的情况下,管线7的支流液将作为管线4的含氧气侧馏分流的一部分导走。
当本发明被应用到通过从空气分离装置中分离氮气和氧气的分馏塔的一处导出含一些氧气但不含或极贫含重组分诸如二氧化碳、氪、氙和轻烃类的侧馏分流来制备超高纯氧气产品的常规工艺中时,最好理解本发明的改进之处。所导出的侧馏分流可作为液体导出也可作为气体导出。这种导出位置对单塔或双塔系统的高压塔来说一般是离空气原料输入处上方几个级,对二塔或三塔系统的低压塔,则离粗制液氧原料输入处上方几个级之处。这种导出的无重杂质的含氧气侧馏分流随后在辅助蒸馏中通过汽提分离而在这种塔的底部生产出超高纯氧气产品。通过管线7将部分支流液移走并通过管线8将它重新导入,将正常提供处于管线3的进料和管线4的侧馏分流之间的主蒸馏塔1的蒸馏区的回流的这部分导出液绕出了主体区。这样,在主体区的液/气比被降低,从而提高了在管线4的含氧气侧馏分流的氧气浓度,同时仍能保证含氧气侧馏分流不含重组分。
借助下面由图3-5中的流程图说明的三种变化方案的讨论,本发明的改进之处可得到最好的了解。这些流程图可分成二个亚类。第一亚类从双塔系统的高压和/或低压塔导出不含重组分的含氧液流进行分离用于回收超高纯氧。第二亚类从高压和/或低压塔导出不含重组分的含氧气流进行分离用于回收超高纯氧。导出液体的第一亚类将先于导出气体的亚类加以讨论。在图3-5中共有的流和设备采用同样的编号。
图3显示了基于从单塔空气分离单元的高压塔导出液态侧馏分的流程图。参照图3,原料空气流经管线10送到主空气压缩器(MAC)12。压缩后原料空气流通常在空气冷却器或水冷却器中后冷却,然后在单元16处理以去除在低温下会冷凝的杂质即水和二氧化碳。去除水和二氧化碳的处理可用任何已知的方法进行,诸如吸附分子筛床。然后将经压缩、不含水和二氧化碳的空气经管线18送到主热交换器20,在那将其冷却至接近露点。然后将以冷却的原料空气流以管线21送到精馏塔22的底部而将原料空气分离成氮塔顶气流和粗制液氧底部馏分。
氮塔顶气流经管线24从精馏塔22的顶部导出然后被分成二股分流。第一股分流经管线26送到重沸器/冷凝器28,在那里被液化,然后经管线30返回到精馏塔22的顶部,为精馏塔提供回流。第二股分流经管线32从精馏塔22导出,在主热交换器20加温以产生致冷作用并作为气体氮气产品流经管线34从该过程中外排。
含氧气液态侧馏分流通过管线100从精馏塔22的中间区域导出。该中间区域要选择在一处使作为精馏塔22下行液体一部分的含氧侧馏分流具有小于35%的氧气浓度并且基本上不含较重组分如烃类、二氧化碳、氪和氙的地方。然后将含氧气侧馏分流通过一阀减压并送到分馏塔102进行汽提,依此生产出汽提塔顶部气流和超高纯氧气底液。用汽提塔顶部气流作为废流经管线104排除并在热交换器20中加暖以回收致冷作用。
除了经管线100从精馏塔22的中间区导出的含氧气液态侧馏分流外,另一部分精馏塔22的下行液体作为支流液经管线300导出,并在和管线21的空气原料导入处的同样塔高上重新导入到精馏塔22中。必须指出,尽管图中未画出,但实际在管线100的含氧气液态侧馏分流和在管线300的支路流可一起从精馏塔22导出然后再分开来履行其各自的功能。同样,在管线300的支路流可以加到以管线38排高精馏塔22底部的粗制液氧底液中。
至少一部分超高纯氧气底液通过在重沸器286中间接热交换而气化,从而提供汽提塔102的再沸。重沸分馏塔102的热负荷通过低温冷却一部分粗制液氧底部馏分来提供。一部分在管线38的粗制液氧底部馏分通过管线288送到位于汽提塔102底部的重沸器286。在重沸器286中,该部分被低温冷却,从而提供重沸汽提塔102所需的热负荷,随后被减压,并通过管线290和在管线38中的其余部分的粗制液氧底部馏分混合。
超高纯氧气产品从汽提塔102的底部导出。该产品可作为气体产品经管线112导出和/或作为液体产品经管线114导出。
粗制液氧流通过管线38从精馏塔22的底部导出,减压后送到重沸器/冷凝器28周围的罐中,在重沸器/冷凝器28中被气化,从而将管线26的氮气顶部馏分冷凝。经气化的流或废物流通过管线40从重沸器/冷凝器28周围的废物区的顶部排出。
然后将气化的废物流处理以回收该流本身产生的致冷作用。为平衡该废物流本身对该过程所产生致冷作用,流40被分成二部分。第一部分经管线44被送到主热交换器20;在那里它被加温以回收致冷作用。第二部分通过管线42和在管线44中的经加温的第一部分混合而形成管线46。然后将在管线46的重混合的流分成两部分,再去平衡该过程对致冷作用的需要。在管线50中的第一部分在膨胀机52中膨胀后和在管线48中的在其经一阀减压后第二部分再相混合而形成在管线54中的经膨胀的废物流。然后将这经膨胀的废物流送到主热交换器20中加温用以产生致冷作用,然后作为废物经管线56从该过程排掉。为限制通过热交换器20的流的数目,在管线104中的汽提塔废物流可和在管线54的来自精馏塔22的膨胀后的废物流混合。
最后,少量清洗流经管线60从重沸器/冷凝器28周围的罐导出,用以防止在该罐液体中烃类的积累。如果需要,液氮产品也可作为经冷凝的氮流的一部分回收。
图4显示了基于从高压或低压塔导出的气态侧馏分流的流程图。该气流中重组分极贫但含有氧气。对该气流进行了分离以生产超高纯氧气。该图将如下进一步详细讨论。
在图4中,气体侧馏分流经管线500从低压塔200导出。该气流在最高的含重组分的原料被导入低压塔200的位置高几个塔板的地方被导出,也就是说,该气流在比来自高压塔22的底部的粗制液氧底部馏分经管线38送到低压塔200的入口处高几个塔板的地方导出。如果膨胀后的原料空气在粗制液氧底部馏分原料的上方输入,那么送到塔402的气体原料将需要在塔200的经膨胀的空气原料的上方几个塔板处导出。这样选择导出的位置可以使沿低压塔200下行的无重组分的液体回流具有足够的塔板以汽提在低压塔200上行气体中的污染的重组分。塔402的底部通过管线108的来自高压塔顶部的气态氮流来重沸。或者,可将一部分原料空气流用于此目的。同样在图4中,一富氩流经管线460从塔402导出并送到低压塔200中。该步是可选的,用于降低超高纯氧气中的氩含量。
最后,一部分在低压塔200中下行的液体被导出并在和管线38中的粗制液氮底部馏分原料同样塔高的地方再导入到精馏塔200中。
当需要少量超高纯氧气时,图5是另一可能是特别有用的实施方案。和图4相类似,极贫含重组分的含氧气态侧馏分流经管线600从高压塔22导出,用于提供塔102的再沸。在管线602中的经冷凝的原料流被减压后送到塔102的顶部。从塔102的顶部经管线104导出的气体被送到在低压塔的合适位置。如果液态超高纯氧气流114要被产生,那么需要一另外的液体原料流。不含重组分的该流作为侧馏分流通过管线500从低压塔200导出并送到塔102的顶部。在这种情况下,一沿低压塔200下行的液流作为支流通过管线300从和在管线500的不含重组分的侧馏分液的同一位置导出并在粗制液氧底部馏分经管线38被输入的位置返回到低压塔200中。
尽管没有在图5中画出,一液态支路流可以和图3类似的方式从塔22从和在管线600中的流的同样位置导出,并和在管线38中的粗制液氧底部馏分相混合。
在气流从高压塔或低压塔导出并送到辅助汽提塔而用于制备超高纯氧气的情况下(图4至5),在这种气流中氧气的浓度将低于20%。最可能的氧气浓度范围为3%到15%。低于1%的氧气浓度将由于其超高纯氧气的极低生产率而不合乎需要。
                    实施例
为证明本发明的功效,用计算机模拟了本公开的图3说明的处理实施方案和美国专利5049173的图1所示的处理实施方案的比较。正象从两个图的比较中可看出的,其唯一的不同是本公开的图3中包含在管线300的部分支路流。比较的基础如下:
■主塔22中,在侧馏分上方含77个理论塔板,在其下方含13个理论塔板。该塔的操作压力在顶部是965.3kPa(140psia)。氮产品纯度是含0.1vppb氧气。侧馏分流量是每100摩尔原料8.1摩尔。支路流量为每100摩尔塔原料2至6摩尔。
■在管线300的支路流和在管线100的侧馏分流源于精馏塔22中的同一处,因此,两流具相同的组成。
■辅助汽提塔103含80块理论塔板。其操作压力在顶部为113.8kPa(16.5psia)。超高纯氧气纯度是含0.1vppb氩气和少于2vppb的甲烷(原料空气纯度为1.5vppm)。
模拟比较的结果显示在表1中。
                           表1
描述               模拟基础
支路流300  5,049,173              本发明
流量:摩尔/100摩尔原料     0     2     4     6
氧气浓度:摩尔%     18.0     20.1     21.8     23.1
甲烷浓度:vppt     39     64     107     182
氮流24
流量:摩尔/100摩尔原料     36.5     36.3     36.2     36.1
氧气浓度:摩尔%     0.1     0.1     0.1     0.1
氧气流112和114
流量:摩尔/100摩尔原料    0.76    0.80    0.83     0.85
氩浓度:vppb     0.1     0.1     0.1     0.1
甲烷浓度:vppb     0.3     0.5     0.9     1.4
上述结果表明如果分支流量设定在侧馏分流量的75%,氧产品可提高约10%。带支流操作的唯一缺点是氮气生产稍受损害。超高纯氧气产品的烃含量也稍有提高。但这可通过在主塔的底部增加二至三个理论塔板来克服。重要的是要指出增加的塔板对管线100的侧馏分流的氧气含量基本没有影响,因为氮气-氧气蒸馏受液/气比限制,因此蒸馏本已是板数过多的。
人们也会注意到在表1中在管线114中的超高纯氧气流的烃含量是和在管线100中的侧馏分流的烃含量成正比的。因此,增加精馏塔22的底部区的理论级数用来降低支路流和侧馏分流的烃含量也会降低在超高纯氧气中的烃含量。
支路流和侧馏分流的烃含量很容易通过增加主塔底蒸馏区的理论级数来降低的理论由表2所述模拟中的所示结果所证实。
                                表2
描述                     模拟基础
支路流300  5,049,173              Pre本发明
流量:摩尔/100摩尔原料     0     2     4     6
甲烷浓度:vppt
在底部分中13级     39     64     107     182
在底部分中16级     3.2     6.1     11.6     22.2
在底部分中19级     0.3     0.6     1.3     2.7
因为甲烷是最轻的烃,所以因为甲烷易通过增加级数来降低,所以所有其它烃也被消除。
本发明优于最接近的先有技术(美国专利5049173)的另一同样重要的优点是所述支路让人们可控制侧馏分的组成。当处理装置原料混乱时,侧馏分的组成可能起很大的变化。但是,正如表1所示,人们也可改变支路流量(甚至在恒定的侧馏分流量下)来显著影响在侧馏分流中的氧气含量。因此,人们可通过改变支路装置来减轻装置错孔的影响,从而保持侧馏分流的恒定氧气浓度而使输入辅助汽提塔的原料不受干扰。这种控制是特别重要的,因为和塔的原料流量相比超高纯氧气流量是如此之小以致原料流的小变化都会导致超高纯氧气产品组成的较大变化。
在本发明主题内的支路液体流动的技术可在任何使用不含重组分的侧馏分的时候有利地应用。
按照其几个实施例已对本发明进行了描述。这些实施例不应被看作是对本发明的限制,本发明的范围由本申请的权利要求书来确定。

Claims (15)

1.通过使用包括至少一蒸馏塔的低温蒸馏塔系统的低温蒸馏进行的空气分馏方法,其中原料空气流被压缩、冷却到接近其露点并送到蒸馏塔系统中精馏,从而制备出含氮顶部馏分和粗制液氧底部馏分;其中基本上不含包括烃、二氧化碳、氙和氪等较重污染物的含氧气侧馏分流从蒸馏塔导出并在辅助汽提塔中汽提而在汽提塔的底部产生超高纯氧气产品;其中所述含氧气侧馏分流从主要分离氧气和氮气的蒸馏塔系统的一处导出,其氧气浓度在1-35%之间,其特征在于:一部分在蒸馏塔系统中下行的液体在接近将送到辅助汽提塔的含氧气侧馏分流的导出之处从蒸馏塔系统的蒸馏区导出,从而降低了在含氧气侧馏分流被导出处和含绝大多数重组分的原料被导入处之间的蒸馏区的液气比。
2.按照权利要求1的方法,其中所导出的液体部分在接近含绝大多数重组分的原料被导入之处导入到蒸馏塔系统中。
3.按照权利要求1的方法,其中将被汽提的所导出的含氧气侧馏分流作为液流导出。
4.按照权利要求1的方法,其中将被汽提的所导出的含氧气侧馏分流作为气流导出。
5.按照权利要求1的方法,其中将辅助汽提塔再沸所需的热负荷通过将至少一部分来自低温蒸馏塔系统的蒸馏塔的粗制液氧底部馏分低温冷却来提供。
6.按照权利要求1的方法,其中将辅助汽提塔再沸所需的热负荷通过至少部人地将一部分来自低温蒸馏塔系统的蒸馏塔的氮气塔顶馏分冷凝来提供。
7.按照权利要求1的方法,其中所述低温蒸馏塔系统包括高压蒸馏塔和低压蒸馏塔,其中原料空气流压缩、冷却至接近其露点并送到高蒸馏塔系统精馏,从而产生含氮气塔顶馏分和粗制液氧底部馏分,其中粗制液氧被减压、送到低压蒸馏塔中进一步分馏,从而产生低压氮气塔顶馏分。
8.按照权利要求7的方法,其中将被汽提的所导出的含氧气侧馏分流作为液流导出。
9.按照权利要求7的方法,其中将被汽提的所导出的含氧气侧馏分流作为气流导出。
10.按照权利要求7的方法,其中将被汽提的所导出的含氧气侧馏分流从低压塔导出。
11.按照权利要求7的方法,其中将被汽提的所导出含氧气侧馏分流从高压塔导出。
12.按照权利要求1的方法,其中低温蒸馏塔系统包括一单(氮气发生器)蒸馏塔,其中所述辅助汽提塔用来自蒸馏塔的、基本不含包括烃、二氧化碳、氙和氪等较重组分的液流回流。
13.按照权利要求12的方法,其中将被汽提的所导出含氧气侧馏分流作为液流导出。
14.按照权利要求12的方法,其中将被汽提的所导出含氧气侧馏分流作为气流导出。
15.按照权利要求12的方法,其中将辅助汽提塔再沸的热负荷通过在精馏前将至少一部分含氧气侧馏分流冷凝来提供。
CN96119808A 1995-08-29 1996-08-27 从低温空气分离设备进行超高纯氧气的生产 Expired - Fee Related CN1076818C (zh)

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