CN112005068B - 用于从中压低温空气分离单元实现氮和氩的高回收率的系统和方法 - Google Patents

用于从中压低温空气分离单元实现氮和氩的高回收率的系统和方法 Download PDF

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CN112005068B
CN112005068B CN201980026691.3A CN201980026691A CN112005068B CN 112005068 B CN112005068 B CN 112005068B CN 201980026691 A CN201980026691 A CN 201980026691A CN 112005068 B CN112005068 B CN 112005068B
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stream
oxygen
argon
column
rich
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CN112005068A (zh
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N·M·普罗塞
J·R·汉德利
B·R·克罗默
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Praxair Technology Inc
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Praxair Technology Inc
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    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
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    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
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    • F25J3/04—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream for air
    • F25J3/04006—Providing pressurised feed air or process streams within or from the air fractionation unit
    • F25J3/04012—Providing pressurised feed air or process streams within or from the air fractionation unit by compression of warm gaseous streams; details of intake or interstage cooling
    • F25J3/04018—Providing pressurised feed air or process streams within or from the air fractionation unit by compression of warm gaseous streams; details of intake or interstage cooling of main feed air
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    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
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    • F25J3/04078—Providing pressurised feed air or process streams within or from the air fractionation unit providing pressurized products by liquid compression and vaporisation with cold recovery, i.e. so-called internal compression
    • F25J3/0409—Providing pressurised feed air or process streams within or from the air fractionation unit providing pressurized products by liquid compression and vaporisation with cold recovery, i.e. so-called internal compression of oxygen
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Abstract

本发明公开了一种中压空气分离单元和空气分离循环，该中压空气分离单元和空气分离循环提供最多至约96％的氩回收率和98％或更大的总氮回收率。该空气分离被构造为产生高纯度富氧流，该高纯度富氧流用作制冷剂以在氩冷凝器中冷凝氩，并且所得气化的氧流用于再生变温吸附预纯化器单元。使用氩超级塔来促进氩回收。

Description

用于从中压低温空气分离单元实现氮和氩的高回收率的系统 和方法
技术领域
本发明涉及从中压低温空气分离单元回收产物，并且更具体地涉及用于从中压低温空气分离单元实现氩和氮的高回收率的系统和方法。
背景技术
以生产氮为目标并在中压(即，高于常规空气分离单元压力的压力)下操作的空气分离设备已存在一段时间。在常规空气分离单元中，如果中压下的氮是期望的，则可在高于常规空气分离单元的压力下操作低压塔。然而，这种操作通常会导致氩回收率的显著降低，因为很多氩会在富氧流或富氮流中损失而不是传递至氩塔。
为了在此类中压制氮空气分离单元中增加氩回收率，在20世纪80年代晚期和20世纪90年代早期开发了改进的空气分离循环。参见例如技术出版物Cheung，中压低温空气分离过程、气体分离和纯化(Moderate Pressure Cryogenic Air Separation Process,Gas Separation&Purification)，第5卷，1991年3月和美国专利号4,822,395(Cheung)。在这些现有技术文献中，公开了氩回收率略高的制氮和氩的空气分离设备。改进的空气分离循环涉及在优选地介于约80至150psia之间的标称压力下操作高压塔，而低压塔优选地在约20至45psia的标称压力下操作，并且氩塔也将优选地在约20至45psia的标称压力下操作。约20至45psia的中压下的高纯度氮(即，>99.98％纯度)的回收率大约为94％。97.3％纯度和约20至45psia之间的压力下的高氩回收率一般高于90％但上限为约93％。
在上述现有技术中压空气分离循环中，来自低压塔的贮槽的高纯度液氧用作氩冷凝器中的制冷剂而不是釜液体。然而，当使用来自低压塔的贮槽的高纯度液氧时，氩塔需要在比常规氩塔更高的压力下操作以便实现氩冷凝器中的所需温度差。氩塔的压力增加需要低压塔和高压塔也在高于常规空气分离单元的压力下操作。
氩冷凝器中使用高纯度液氧也意味着避免了通常进给低压塔的较大釜蒸气流，这使得回收率显著提高。因此，该中压空气分离循环可能实现氮和氩的高回收率，即使与常规空气分离循环相比，升高的压力原本会不利于回收率。空气分离单元的中压操作一般有利于氮生产，因为这意味着氮压缩不太耗能并且氮压缩机往往比常规系统的氮压缩机更便宜。
需要进一步提高氩回收率并增强总氮回收率的改进的中压空气分离单元和中压空气分离循环。
发明内容
本发明可被表征为空气分离单元，该空气分离单元被配置为产生一种或多种高纯度氮产物并且具有98％或更大的氮回收率。本发明空气分离单元包括(i)主空气压缩系统，该主空气压缩系统被配置用于接收进入的进料空气流并且产生经压缩的空气流；(ii)基于吸附的预纯化器单元，该基于吸附的预纯化器单元被配置用于从经压缩的空气流去除水蒸气、二氧化碳、一氧化二氮和烃类并且产生经压缩并且纯化的空气流，其中经压缩并且纯化的空气流被分成至少经压缩并且纯化的空气流的第一部分和经压缩并且纯化的空气流的第二部分；(iii)主换热系统，该主换热系统被配置为冷却经压缩并且纯化的空气流的第一部分以产生蒸气空气流并且部分地冷却经压缩并且纯化的空气流的第二部分；(iv)涡轮膨胀机布置，该涡轮膨胀机布置被配置为使经压缩并且纯化的空气流的经部分冷却的第二部分膨胀以形成排气流，从而向空气分离单元赋予制冷；(v)蒸馏塔系统，该蒸馏塔系统包括具有介于6.0巴和10.0巴之间的操作压力的高压塔和具有介于1.5巴和2.8巴之间的操作压力的低压塔，该高压塔和该低压塔经由冷凝器再沸器以热传递关系相连，其中蒸馏塔系统还包括与低压塔操作性地联接的氩塔布置，该氩塔布置具有至少一个氩塔和氩冷凝器。蒸馏塔系统被配置为在高压塔中接收蒸气空气流的全部或一部分并在低压塔或高压塔中接收排气流，并且产生来自低压塔的一个或多个富氧流和来自低压塔的氮塔顶馏出物流。氩塔被配置为从低压塔接收富氩-氧流并且产生返回到或释放到低压塔中的富氧塔底馏出物流以及被引导至氩冷凝器的富氩塔顶馏出物，该氩冷凝器被配置为依靠来自低压塔的过冷富氧流来冷凝富氩塔顶馏出物以产生粗制氩流或产物氩流、氩回流流、富氧废物流和液体富氧流。空气分离单元还包括过冷器布置，该过冷器布置与蒸馏塔系统操作性地联接并且被配置为经由与来自低压塔的氮塔顶馏出物流的间接换热来使来自高压塔的釜氧流和来自冷凝器-再沸器的氮流过冷。过冷器布置被进一步配置为经由与富氧废物流的间接换热来使来自低压塔的至少一个富氧流过冷。
另选地，本发明可被表征为在低温空气分离单元中通过98％或更大的氮回收率分离空气以产生一种或多种高纯度氮产物的方法。本发明方法包括以下步骤：(a)压缩进入的进料空气流以产生经压缩的空气流；(b)在基于吸附的预纯化单元中纯化经压缩的空气流，该基于吸附的预纯化单元被配置为从经压缩的空气流去除水蒸气、二氧化碳、一氧化二氮和烃类以产生经压缩并且纯化的空气流；(c)将经压缩并且纯化的空气流分成至少经压缩并且纯化的空气流的第一部分和经压缩并且纯化的空气流的第二部分；(d)在适用于在低温蒸馏系统中精馏的温度下将经压缩并且纯化的空气流的第一部分冷却为蒸气空气流，并且部分地冷却经压缩并且纯化的空气流的第二部分；(e)在涡轮中使经压缩并且纯化的空气流的经部分冷却的第二部分膨胀以形成排气流；(f)在低温蒸馏塔系统中精馏空气流和排气流，该低温蒸馏塔系统包括具有介于6.0巴和10.0巴之间的操作压力的高压塔和具有介于1.5巴和2.8巴之间的操作压力的低压塔，该高压塔和该低压塔经由冷凝器再沸器以热传递关系相连，其中精馏步骤产生来自低压塔的一个或多个富氧流、来自低压塔的氮塔顶馏出物流和来自冷凝器-再沸器的经冷凝的氮流；(g)在过冷器单元中经由与富氧废物流的间接换热来使来自低压塔的一个或多个富氧流中的至少一个富氧流过冷；(h)经由与来自低压塔的氮塔顶馏出物流的间接换热来使来自高压塔的釜氧流和来自冷凝器-再沸器的经冷凝的氮流过冷；(i)在氩塔布置中精馏从低压塔提取的富氧-氩流，该氩塔布置具有至少一个氩塔和氩冷凝器，并且其中氩塔被配置为产生富氧塔底馏出物流和富氩塔顶馏出物；(j)使富氧塔底馏出物流从氩塔返回至低压塔；(k)将富氩塔顶馏出物从氩塔引导至氩冷凝器；(l)在氩冷凝器中依靠来自低压塔的过冷富氧流来冷凝富氩塔顶馏出物以产生粗制氩流、氩回流流、富氧废物流和液体富氧流；以及(m)在主换热器中加热来自低压塔的氮塔顶馏出物流以产生气态氮产物，并且从冷凝器-再沸器取出经冷凝的氮流的一部分作为液体氮产物。
在本发明系统和方法中，基于吸附的预纯化器单元优选地是被配置为纯化经压缩的空气流的多床变温吸附单元，该多床变温吸附单元被配置为使得每个床在在线操作阶段与离线操作阶段之间交替，该在线操作阶段从经压缩的空气流吸附水蒸气、二氧化碳和烃类，并且在该离线操作阶段中，使用优选地具有大于90％氧含量且最多至约99.5％氧的富氧废物流来再生或吹扫该床。基于吸附的预纯化器单元优选地还包括蒸汽加热器、电加热器或其他非燃烧式加热器，其被配置为将富氧废物流加热至小于或等于约450℉、优选地小于约400℉的温度以用于再生变温吸附单元中的吸附床。
在本发明系统和方法的一些实施方案中，来自低压塔的富氧流是如下任一种：(1)从富氧液体塔底馏出物所在的贮槽取出并且具有大于99.5％的氧浓度的高纯度富氧流；或(2)从富氧液体塔底馏出物所在的贮槽上方的若干级取出并且具有介于约93％和99.7％之间的氧浓度的低纯度富氧流。
优选的氩塔布置被配置为在介于约1.3巴和2.8巴之间的压力下操作，并且可被配置为具有介于180和260个之间的分离级的超级塔(superstaged column)及高比率塔。另选地，氩塔布置可被配置为具有介于185和270个之间的分离级的极超级塔(ultra-superstaged column)。任选地，被配置为精制粗制氩流以产生高纯度氩产物流的氩精制系统可设置在氩冷凝器的下游，氩精制系统。在此类实施方案中，氩精制系统可为基于氩液体吸附的系统、基于氩气相吸附的系统或基于催化脱氧的系统。
附图说明
虽然本发明系统和方法的以下描述结束于清楚地指出申请人视为其发明内容的主题的权利要求书，但据信本发明系统和方法在结合附图考虑时将被更好地理解，其中图1和图2是根据本发明系统的所选择的实施方案的空气分离单元的示意性过程流程图。
具体实施方式
本发明所公开的系统和方法提供了具有氮的极高回收率和氩的高回收率的低温空气分离。所公开的蒸馏塔系统的低压塔中产生的高纯度富氧流首先用作氩冷凝器中的冷凝介质以冷凝富氩流，然后来自氩冷凝器的富氧汽化气体用作吹扫气体以再生基于吸附的预纯化器单元中的吸附床。使用氩超级塔和高比率塔或具有巴氏灭菌区段且没有与之操作性地联接的高比率塔的氩超级塔来促进氩回收。在随后的段落中提供本发明系统和方法的细节。
中压下氮产物的高回收率
转到图1，示出了空气分离单元10的简化示意图。从广义上讲，所描绘的空气分离单元包括主进料空气压缩机组或系统20、涡轮空气回路30、初级换热器系统50以及蒸馏塔系统70。如本文所用，主进料空气压缩机组、涡轮空气回路和增压器空气回路共同构成“热端”空气压缩回路。类似地，主换热器或初级换热器、基于涡轮的制冷回路的部分和蒸馏塔系统的部分被称为通常容纳在绝缘冷箱中的“冷端”系统/设备。
在图中所示的主进料压缩机组中，进入的进料空气22通常被抽吸穿过空气吸滤器外壳(ASFH)并且在多级中间冷却的主空气压缩机布置24中被压缩至可介于约6.5巴(a)至约11巴(a)之间的压力。该主空气压缩机布置24可包括串联或并联布置的整体齿轮式压缩机级或直接驱动压缩机级。离开主空气压缩机布置24的经压缩的空气流26被进料至具有一体式除雾器的后冷却器(未示出)，以去除进入的进料空气流中的游离水分。通过用冷却塔水冷却经压缩进料空气，在后冷却器中将来自主空气压缩机布置24的最后压缩级的压缩的压缩热去除。来自该后冷却器以及主空气压缩布置24中的一些中间冷却器的冷凝物优选地输送到冷凝物罐，并且用于向空气分离设备的其他部分供应水。
然后将冷却且干燥的经压缩空气流26在预纯化单元28中纯化以从该冷却且干燥的经压缩空气进料中去除高沸点污染物。如本领域所熟知，预纯化单元28通常包含根据变温吸附循环操作的氧化铝和/或分子筛的两个床，在该变温吸附循环中水分及其他杂质(诸如二氧化碳、水蒸气和烃类)被吸附。这些床中的一个床用于预纯化该冷却且干燥的经压缩空气进料，而另一个床是优选地利用来自空气分离单元的废氮的一部分再生的。这两个床定期交换功用。在设置在预纯化单元28下游的粉尘过滤器中，从经压缩、预纯化的进料空气中去除颗粒以产生经压缩、纯化的空气流29。
经压缩并且纯化的空气流29在包括高压塔72、低压塔74和氩塔129的多个蒸馏塔中被分离为富氧馏分、富氮馏分和富氩馏分。然而，在这种蒸馏之前，通常将经压缩且预纯化的空气流29分成多个进料空气流，该多个进料空气流可包括锅炉空气流42和涡轮空气流32。可将锅炉空气流42在增压压缩机布置44中进一步压缩，随后在后冷却器45中冷却以形成增压空气流46，然后在主换热器52中将该增压空气流进一步冷却至精馏所需的温度。优选地通过与加热流(包括来自蒸馏塔系统70的氧流197、386以及氮流195)的间接换热来在主换热器52中完成对空气流的冷却或部分冷却，以产生经冷却的进料空气流38和47。
使经部分冷却的进料空气流38在涡轮35中膨胀，以产生被引导至低压塔74的排气流64。空气分离单元10的制冷也通常由涡轮35和其他相关的冷的和/或热的涡轮布置生成，该涡轮布置诸如为如本领域中所公知的闭环加热制冷回路。将经完全冷却的空气流47引入高压塔72中。
主换热器52优选地为钎焊铝制板翅式换热器。此类换热器是有利的，因为它们具有紧凑设计、高传热速率，而且它们能够处理多个流。它们被制造为完全钎焊和焊接的压力容器。对于小型空气分离单元而言，具有单个芯的换热器可能已足够。对于处理较高流量的较大空气分离单元而言，换热器可由必须并联或串联连接的若干芯构造而成。
基于涡轮的制冷回路通常被称为下塔涡轮(LCT)布置或上塔涡轮(UCT)布置，其用于向双塔或三塔低温空气蒸馏塔系统提供制冷。在图中所示的UCT布置中，经压缩、冷却的涡轮空气流32优选地在约6巴(a)至约10.7巴(a)之间的范围内的压力下。将经压缩、冷却的涡轮空气流32引导至或引入主换热器或初级换热器52中，在其中将该经压缩、冷却的涡轮空气流部分冷却至约140开尔文至约220开尔文之间的范围内的温度以形成经部分冷却、压缩的涡轮空气流38，该经部分冷却、压缩的涡轮空气流被引入涡轮35中以产生冷排气流64，该冷排气流随后被引入蒸馏塔系统70的低压塔74中。由该流38的膨胀而产生的补充制冷由此被直接施加到低压塔72，从而减轻了主换热器52的一些冷却负荷。在一些实施方案中，涡轮35可与用于直接或通过适当的齿轮装置进一步压缩涡轮空气流32的增压压缩机34联接。
虽然图中所示的基于涡轮的制冷回路被示出为上塔涡轮(UCT)回路(其中涡轮排气流被引导至低压塔)，但可设想到基于涡轮的制冷回路另选地可为下塔涡轮(LCT)回路或部分下塔涡轮(PLCT)(其中膨胀的排气流被进料至蒸馏塔系统70的高压塔72)。更进一步地，基于涡轮的制冷回路可为本领域技术人员众所周知的LCT布置、UCT布置和/或热再循环涡轮(WRT)布置的某种变型或组合。
在包括高压塔72、低压塔74、超级氩塔129、冷凝器-再沸器75和氩冷凝器78的蒸馏塔系统70内分离进入的进料空气流的上述组分(即，氧、氮和氩)。高压塔72通常在约6巴(a)至约10巴(a)之间的范围内操作，而低压塔74在约1.5巴(a)至约2.8巴(a)之间的压力下操作。高压塔72和低压塔74优选地以热传递关系相连，使得在位于低压塔74的基部中的冷凝器-再沸器75内依靠位于低压塔的塔底中的富氧液体塔底馏出物77来冷凝从接近高压塔72的顶部提取为流73的富氮蒸气塔顶馏出物的全部或一部分。富氧液体塔底馏出物77的沸腾引发在低压塔74内形成上升气相。该冷凝产生液体含氮流81，该液体含氮流被分成干净搁板回流流83和富氮流85，该干净搁板回流流可用于回流低压塔74以引发这种低压塔74中下降液相的形成，并且该富氮流回流高压塔72。
经冷却的进料空气流47优选地是略高于其露点的蒸气空气流，但其可处于或略低于其露点，该经冷却的进料空气流被进料至高压塔中，从而因多个传质接触元件(被示出为塔盘71)内发生上升气相与回流流85所引发的下降液相之间的传质而实现精馏。这产生了粗液氧塔底馏出物86(也称为釜液体，其作为流88取出)和富氮塔顶馏出物89(作为干净搁板液体流83取出)。
在低压塔中，上升气相包括来自冷凝器-再沸器的汽化气体以及来自涡轮35的排气流64，该排气流在过冷单元99B中过冷并且作为蒸气流引入在低压塔72的中间位置处。下降液体由氮回流流83引发，该氮回流流被送至过冷单元99A，其在此处过冷并且随后先在阀96中膨胀，再在接近低压塔的顶部的位置处引入至低压塔74。如果需要，可经由阀101取出过冷氮回流流83的小部分作为液体氮产物98。
低压塔74还设置有多个传质接触元件，这些接触元件可以是塔盘或规整填料或散堆填料或低温空气分离领域中的其他已知元件。低压塔74中的这些接触元件被示出为规整填料79。
如图1的实施方案中所示，在低压塔74内发生的分离产生被提取为氧浓度大于96％的富氧液体流90的富氧液体塔底馏出物77和被提取为气态氮产物流95的富氮蒸气塔顶馏出物91。将富氧液体流90优选地经由泵180来泵送，然后经由与富氧废物流196的间接换热来在过冷单元99B中过冷，之后传递至氩冷凝器78，其在此用于冷凝从氩塔129的塔顶馏出物123取出的富氩流126。
从氩冷凝器78汽化的气化的氧流是在过冷器99B内加热的富氧废物流196。将经加热的富氧废物流197引导至主换热器或初级换热器，然后用作吹扫气体以再生基于吸附的预纯化器单元28。另外，可从低压塔提取废物氮流93以控制气态氮产物流95的纯度。优选地将废物氮流93与过冷器99B上游的富氧废物流196合并。另外，在一些情况下，在可供使用的氧多于操作氩冷凝器78所需的氧时，最可能在氩产量减少时，可需要蒸气废物氧流97。
从氩冷凝器容器120抽出液体流130，使该液体流穿过凝胶捕集器370并且返回至低压塔74的基部或基部附近。凝胶捕集器370用于去除原本可能积聚在系统中的二氧化碳、一氧化二氮和某些重质污染物。另选地，可经由流130来抽出小流量作为来自系统的排放流，使得凝胶捕集器140被消除(未示出)。
优选地，图中所示的氩冷凝器是降流氩冷凝器。降流构型使得冷凝流与沸腾流之间的有效温差(ΔT)更小。如上所指示，更小的ΔT可引起氩塔、低压塔和高压塔内降低的操作压力，这转换成产生各种产物流所需的功率减少以及氩回收率提高。降流氩冷凝器的使用还实现了塔级数量的潜在减少，特别是对于氩塔而言。从资本的角度来看，氩降流冷凝器的使用也是有利的，部分原因是本发明公开的空气分离循环中已经要求泵180。另外，由于液体流130已经提供离开氩冷凝器壳体的连续液体流，该液体流还提供再沸表面的必要润湿以防止氩冷凝器‘蒸干’。
使氮产物流95穿过过冷单元99A以经由间接换热来使氮回流流83和釜液体流88过冷。如上所指示，使过冷氮回流流83在阀96中膨胀并且引入至低压塔的最上位置中，同时使过冷釜液体流88在阀107中膨胀并且引入至低压塔74的中间位置。在穿过过冷单元99A之后，经加热的氮流195在主换热器或初级换热器52内进一步加热以产生经加热的气态氮产物流295。
转到图2所示的实施方案，在低压塔74内发生的分离还产生被提取为氧浓度大于99.5％的富氧液体流380的富氧液体塔底馏出物77。低压塔还产生低纯度富氧液体流398，该低纯度富氧液体流优选地在比提取第一富氧液体流380的点高一些级的位置处从低压塔74取出。低纯度富氧液体流398将具有介于约93％和99.7％之间的氧浓度。蒸馏塔布置还产生被提取为气态氮产物流95的富氮蒸气塔顶馏出物91。
在泵385中泵送高纯度富氧液体流380，并且将所得泵送的氧流386引导至主换热器52，在此加热该氧流以产生高纯度气态氧产物流390。将低纯度富氧液体流398经由泵180来泵送，然后优选地经由与富氧废物流196的间接换热来在过冷单元99B中过冷，之后传递至氩冷凝器78，其在此用于冷凝从氩塔129的塔顶馏出物123取出的富氩流126。如图2所示，高纯度富氧液体流380的一部分可作为液氧产物395取出。
流392在泵385之后优选地穿过凝胶捕集器370。然后其返回至低压塔74的基部或基部附近。从氩冷凝器容器120抽出液体流130并且使该液体流在流398的抽吸位置正下方返回至低压塔。凝胶捕集器370用于去除原本可能积聚在系统中的二氧化碳、一氧化二氮和某些重质烃。另选地，可经由流392来抽出小流量作为来自系统的排放流，使得凝胶捕集器370被消除(未示出)。可在泵385之前抽出排放流。在这种情况下，流395可表示排放流，或除排放流之外还表示液体氧产物流。
任选地，不在涡轮进料流38中抽出涡轮空气回路30中流动的小部分空气。在换热器52的冷端处抽出任选的增压流48，使该增压流完全或部分冷凝，在阀49中降低压力，并且在离塔底若干级处进料至高压塔72。仅在所泵送的氧流386的大小足够高时利用流48。
氩回收和精制
上述实施方案中采用的氩塔布置可被配置为优选地具有与之操作性地联接的高比率氩塔的氩超级塔。再次转到图1，超级氩塔129从低压塔74接收含氩和氧的蒸气进料121，并且从位于超级氩塔129上方的氩冷凝器78接收降流富氩回流122。超级氩塔129具有约180与260之间的分离级，并且用于通过以下方式精馏含氩和氧的蒸气：将氩与氧分离成富氩塔顶馏出物蒸气126和富氧液体塔底馏出物，该富氧液体塔底馏出物作为流124返回至低压塔。超级氩塔129内的优选传质接触元件125优选地为规整填料。优选地将所得富氩蒸气塔顶馏出物126的全部或一部分引导至氩冷凝器78，在此依靠来自低压塔74的过冷富氧流来冷凝所得富氩蒸气塔顶馏出物的全部或一部分。所得冷凝物是从氩冷凝器78取出的粗液体氩流，该粗液体氩流大部分作为氩回流流122返回至超级氩塔129。
高比率氩塔160还接收作为流162离开氩冷凝器78的粗液体氩流的一部分，流162在阀164中进行压力调节并且引入在高比率氩塔160的中间位置处。在高比率塔160内精馏粗氩以形成液体氩塔底馏出物166和含氮高比率塔顶馏出物168。从高比率氩塔160的液体氩塔底馏出物166取出高纯度液体氩产物流165。
还将从接近高压塔72的顶部提取的富氮塔顶馏出物的一部分作为流163转移到设置在高比率氩塔160的底部处的高比率塔再沸器170，在此冷凝该流以形成液体氮流172。然后将液体氮流172引导或转移到高比率塔冷凝器175，其在此提供制冷负荷以冷凝或部分冷凝富氮高比率塔顶馏出物168。将离开高比率塔冷凝器175的气化的氮流174引导至过冷单元99A并且与该过冷单元上游的氮产物流95混合。
从高比率塔160的顶部附近的位置取出富氮高比率塔顶馏出物168，随后在高比率塔冷凝器175中冷凝或部分冷凝该富氮高比率塔顶馏出物。将所得流176送至分相器177，该分相器被配置为排放气化的部分178，同时使液体部分179作为回流返回至高比率氩塔160。使用该布置，可从空气分离设备获得高达96％的氩回收率。
在另选构型中，消除高比率氩塔并且直接从超级塔产生产物纯度氩。在这种情况下，在超级塔的顶部处包括另一个蒸馏区段。在该附加蒸馏区段(通常称为巴氏灭菌区)中，可去除少量氮以确保可靠的产物氩纯度。从塔129的顶部排放更富氮的小流，并且在巴氏灭菌区下方抽出产物氩。需要低压塔中的蒸气抽吸流121正上方的更高蒸馏区段以使得更少氮进入超级塔129。美国专利号5,133,790中描述了该另选形式。
可在另选氩精制系统或布置(诸如基于液体吸附的氩纯化/精制系统、基于气相吸附的氩纯化/精制系统或基于催化脱氧的氩纯化/精制系统)中回收或纯化从氩塔布置抽出的粗富氩流。
使用富氧废物流作为基于吸附的预纯化器的再生气体
当使用基于吸附的预纯化单元时，期望让经压缩、干燥、预纯化且冷却的空气流的连续流进入空气分离单元的蒸馏塔系统。优选地通过使用多个吸附床(优选地被布置为双床变温吸附单元)来进行预纯化。在优选的双床变温吸附预纯化器中，一个床处于吸附进入的进料空气中的杂质的在线操作阶段，而另一个床处于离线操作阶段，在该阶段中使用高纯度废物氧流的全部或一部分来再生该床。在许多双床吸附循环中，当一个床从在线操作阶段切换到离线操作阶段并且另一个床从离线操作阶段切换到在线操作阶段时，可存在两个床均处于在线操作阶段的短重叠时间段。
如本领域所熟知，在在线阶段中操作的吸附床可仅保持在线，直到其达到其吸附杂质的容量并且将可能发生杂质穿透。杂质穿透点一般由污染物(例如，水蒸气和二氧化碳)在出口处达到不可接受的水平(表明吸附床被污染物饱和)所需的时间定义。一旦接近穿透点，就使在线吸附床变为离线并且使先前再生的床恢复在线以吸附进料空气中的杂质。
优选的变温吸附单元是复合吸附布置，该复合吸附布置包括下方的至少一层氧化铝284和至少一层分子筛286。氧化铝用于去除大部分水蒸气，而分子筛用于从进入的进料空气去除水蒸气、二氧化碳、一氧化二氮和烃污染物。复合床通常被设计为在床的底部具有足够的氧化铝以从经压缩的空气进料流去除大部分水，并且由其上方的筛层去除剩余的水。复合床通常具有更低的吹扫或再生气体流需求并且需要比全筛床少大约30％的再生能量，因为它们可在更低温度下再生。
变温吸附预纯化器优选地以在约6与12小时之间范围内的“在线”吸附的循环时间操作。由于这些长循环时间，变温吸附预纯化器可在比变压吸附单元更长的时间跨度内减压和再加压，从而使得空气分离单元的塔操作更稳定。更短的循环时间有助于保持初始资本成本较低，因为竖直和水平取向的床中需要更少吸附剂和更矮的吸附剂高度。然而，更长的循环时间会因泄料和再生能量的寄生损失减少而产生减少的操作成本。进入变温吸附预纯化器的经压缩的空气或进料空气温度可在37℉至高达75℉的范围内，并且通常优选地将进入的经压缩的空气流冷却到约40℉至60℉之间。用于冷却经压缩的空气流的两种常见形式的进料空气冷却器包括双级后冷却器和直接接触式后冷却器(未示出)。
变温吸附预纯化器还需要介于进料空气或进入的经压缩的空气流的约5％和30％之间的吹扫或再生气体流，并且更优选地需要等于进入的经压缩的进料空气流的约10％的流。吹扫气体流以与进料空气流呈逆流的方式穿过该床。吹扫气体流将再生热携带到该床中，其在此引起污染物从吸附剂脱附，从该床去除脱附的污染物，并且在再生循环结束时冷却该床。在再生循环开始时，加热吹扫气体以进行热吹扫。稍后在该循环中，不加热吹扫气体，并且这是冷吹扫。
再生加热器的尺寸必须被设定为使得其可将吹扫气体流从其初始温度加热到期望的再生温度。再生加热器的尺寸设定的重要考虑因素是吹扫或再生气体的初始温度、期望的吹扫或再生气体流量、加热器与吸附床之间的热损失以及加热器效率。当再生或吹扫气体是富氧流时，出于安全原因，加热器出口温度应小于约400℉。在选择特殊材料的情况下，加热器出口温度可安全地达到450℉之高。另外，当再生或吹扫气体是富氧流时，仅应使用蒸汽加热器、电加热器或其他非燃烧式加热器。
吹扫/进料(P/F)比率是吹扫或再生气体流与进料空气流的比率。所需的P/F比率取决于若干变量，包括吸附剂类型、再生温度、循环时间和热吹扫比率，但优选地在约0.05与0.40之间的范围内。更高的再生温度会降低所需的P/F比率。更长的循环时间需要略微更低的P/F比率。热吹扫比率是热吹扫时间与总吹扫时间(即，热吹扫时间加冷吹扫时间)的比率。约0.40的热吹扫比率通常用于变温吸附预纯化器以确保足够的冷吹扫时间可用于有效地冷却吸附床，但一些空气分离单元可在更高的热吹扫比率下操作。更小的热吹扫比率产生更高的P/F比率，因为必须在更短的时间量内将相同量的热量携带到吸附床中。
再生鼓风机297优选地用于升高废物流290的压力，使之足以穿过基于吸附的预纯化单元以实现再生目的。离开再生鼓风机297后，废物流290的压力升高以使得其将穿过再生加热器、预纯化器容器及其相关联的吸附床和相关联的阀，进而排放到大气。再生鼓风机297优选地被配置为使离开主换热器的废物流290的压力升高约0.1巴(a)至0.3巴(a)。
虽然再生鼓风机的使用是任选的，但在没有再生鼓风机的情况下操作空气分离单元需要蒸馏塔系统在足够高的压力下运行，使得离开主换热器的废物流可穿过预纯化单元。换言之，再生鼓风机的使用允许氩塔和低压塔的操作压力降低约0.15巴(a)至0.5巴(a)并且高压塔的压力降低约0.35巴(a)至2.0巴(a)。
所公开的空气分离循环中的再生鼓风机的主要有益效果主要与氩生产相关。在没有再生鼓风机的情况下，高氩回收率是可行的，但氩塔中的更高压力仍会使得需要氩塔中的许多分离级和低压塔中的潜在附加级。氩回收的设计和操作灵敏度也较大。在使用再生鼓风机的情况下，蒸馏塔压力的伴随降低往往使氩回收更容易。氩回收率将提高，尤其是在目标氩回收率更低并且还减少氩塔和低压塔的分级需求的场景或实施方案中。
返回参见附图，示出了具有变温吸附预纯化器28的空气分离单元10的示意图。在变温吸附过程中，一般存在每个吸附床进行的多个不同步骤，即：共混；吸附；共混、减压；热吹扫；冷吹扫；和再加压。下表1示出了两个吸附床内的步骤的执行的相关性。
步骤编号 吸附床#1状态 持续时间(min) 吸附床#2状态 持续时间(min)
1 共混 20 共混 20
2 减压 10 吸附 450
3 热吹扫 170
4 冷吹扫 250
5 再加压 20
6 共混 20 共混 20
7 吸附 450 减压 10
8 热吹扫 170
9 冷吹扫 250
10 再加压 20
表1：双床变温吸附循环和时间的示例
在上述示例中，在“共混”步骤期间，两个吸附床均“在线”并且阀262、264、266和268打开，而阀304、306、314和316关闭。进料空气流在该步骤期间在两个床之间均匀分流且该系统中没有吹扫或再生气体。当“在线”时，吸附床281和282吸附水蒸气和其他污染物，诸如二氧化碳。该共混步骤的目的是稀释在再生期间留在吸附床中的余热量，因此防止受热的流往回进给到容纳蒸馏塔的冷箱。
在“共混”步骤后，一个吸附床281经受再生过程并且变为“离线”，而另一个吸附床282接收完全的进料流并且经历吸附步骤，在该步骤中继续吸附水蒸气、二氧化碳和烃类。此类再生过程通过四个不同步骤完成，这四个不同步骤包括：减压；热吹扫、冷吹扫；和再加压。本领域技术人员应当理解，还可包括其他步骤。在减压步骤期间，吸附床281从进料压力减压到更低压力，通常减压到接近大气压力。这通过关闭阀262和266并且打开阀314来完成。该更低压力是再生压力并且该步骤持续约10分钟，但时间长度可根据设备约束或工艺限制而变化。一旦减压，热吹扫步骤就开始，其中使用加热器299来加热再生富氧废物流290以将富氧废物流的温度增加到高于进料空气的温度并且通常高于300℉且低于380℉的温度，具体取决于工艺和吸附材料约束。可容许高达400℉的操作。在特殊材料选择的情况下，该操作可高达450℉。在该时间期间，阀304打开并且允许富氧废物流穿过吸附床281。在一定时间段过去之后，在该示例中在170分钟之后，富氧废物流绕过加热器299或该加热器(如果为电加热器的话)被关断，从而将废物流气体温度降低到接近环境条件(通常但不总是介于约40℉与100℉之间)。关断电加热器或绕过加热器会启动冷吹扫步骤，该冷吹扫步骤继续用富氧废物流吹扫吸附床，但不加热，这降低了吸附床的温度以及将热前沿推进穿过吸附床。在该示例中，该冷吹扫步骤持续约250分钟。
通过关闭阀314和304并且打开阀262来引发吸附床281的再加压步骤。这允许经压缩的空气流26的一部分将容器从接近环境压力加压到升高的进料压力。一旦加压到进料压力，吸附床281和282就进入共混步骤，因此阀266打开，从而允许进料流在吸附床281和282之间均匀分流。在共混步骤中的一定时间量之后，吸附床切换，并且现在吸附床281在吸附步骤中为在线的且吸附床282经历再生步骤。
如上所提及，根据本发明进行的空气分离过程优选地使用高纯度氧废物流作为变温吸附预纯化单元的再生气体来进行。使用纯度大于90％的氧流对吸附床的此类再生尚未在现有技术空气分离设备中使用。然而，本发明允许仅使用高纯度氧作为再生气体，其中再生气体的温度限于450℉或更优选地400℉，因此允许从空气分离设备得到总体更高的氮回收率。更高的氮回收率在更低资本成本和更低操作成本两方面改善了制氮空气分离设备的成本效率。例如，尺寸被设定为在中压下产生3000mcfh高纯度氮并且具有98.0％氮回收率的本发明制氮空气分离设备将需要必须被压缩、预纯化、冷却和精馏的3925mcfh进料空气。另一方面，如美国专利号4,822,395所述的尺寸被设定为在中压下产生3000mcfh TPD高纯度氮并且具有94.6％氮回收率的现有技术制氮空气分离设备将需要必须被压缩、预纯化、冷却和精馏的4066mcfh进料空气。操作现有技术制氮空气分离设备的增加的成本可包括压缩体积流量增加的进入的进料空气的附加功率、预纯化更高流量的进入的进料空气所需的附加吸附材料，以及处理体积增加的进入的进料空气可能需要的涡轮机械、换热器、后冷却器、预纯化器、塔内部等的可能增加的资本设备成本。
此处应当注意，尽管本文讨论了水蒸气和二氧化碳去除，但是应当理解，也将通过一种或多种吸附剂来去除其他杂质，例如一氧化二氮、乙炔和其他痕量烃类。然而，水蒸气和二氧化碳以比此类其他杂质高得多的浓度存在，因此将对所需的吸附剂量具有最大影响。另外，虽然上述讨论适合变温吸附预纯化器，但本发明的教导内容和范围也可适用于一些混合预纯化器布置。
尽管已通过参照一个或多个优选实施方案以及相关联的方法讨论了用于从空气分离单元回收氩和氮的本发明系统，但是本领域的技术人员应当想到，在不脱离所附权利要求书描述的本发明的实质和范围的情况下，可对其进行多种改变和省略。

Claims (15)

1.一种空气分离单元，所述空气分离单元包括：
主空气压缩系统，所述主空气压缩系统被配置用于接收进入的进料空气流并且产生经压缩的空气流；
基于吸附的预纯化器单元，所述基于吸附的预纯化器单元被配置用于从所述经压缩的空气流去除水蒸气、二氧化碳、一氧化二氮和烃类并且产生经压缩并且纯化的空气流，其中所述经压缩并且纯化的空气流被分成至少所述经压缩并且纯化的空气流的第一部分和所述经压缩并且纯化的空气流的第二部分；
主换热系统，所述主换热系统被配置为冷却所述经压缩并且纯化的空气流的第一部分以产生蒸气空气流并且部分地冷却所述经压缩并且纯化的空气流的第二部分；
涡轮膨胀机布置，所述涡轮膨胀机布置被配置为使所述经压缩并且纯化的空气流的经部分冷却的第二部分膨胀以形成排气流，所述排气流向所述空气分离单元赋予制冷；
蒸馏塔系统，所述蒸馏塔系统包括具有介于6.0巴和10.0巴之间的操作压力的高压塔和具有介于1.5巴和2.8巴之间的操作压力的低压塔，所述高压塔和所述低压塔经由冷凝器再沸器以热传递关系相连；
所述蒸馏塔系统还包括与所述低压塔操作性地联接的氩塔布置，所述氩塔布置具有至少一个氩塔和氩冷凝器；
所述蒸馏塔系统被配置为在所述高压塔中接收所述蒸气空气流的全部或一部分并在所述低压塔或所述高压塔中接收所述排气流，并且产生来自所述低压塔的一个或多个富氧流和来自所述低压塔的氮塔顶馏出物流；
其中所述氩塔被配置为从所述低压塔接收富氩-氧流并且产生返回到或释放到所述低压塔中的富氧塔底馏出物流以及被引导至所述氩冷凝器的富氩塔顶馏出物；
过冷器布置，所述过冷器布置与所述蒸馏塔系统操作性地联接并且被配置为经由与来自所述低压塔的所述氮塔顶馏出物流的间接换热来使来自所述高压塔的釜氧流和来自所述冷凝器-再沸器的氮流过冷；
其中所述过冷器布置被进一步配置为经由与所述富氧废物流的间接换热来使从所述低压塔提取的富氧流过冷以产生过冷富氧流；
其中所述氩冷凝器被配置为依靠从所述低压塔提取的所述过冷富氧流来冷凝所述富氩塔顶馏出物以产生粗制氩流或产物氩流、氩回流流、富氧废物流和液体富氧流；并且
其中所述空气分离单元被配置为产生一种或多种高纯度氮产物并且具有98％或更大的氮回收率。
2.根据权利要求1所述的空气分离单元，其中所述基于吸附的预纯化器单元是被配置用于纯化所述经压缩的空气流的多床变温吸附单元，所述多床变温吸附单元被进一步配置为使得每个床在在线操作阶段与离线操作阶段之间交替，所述在线操作阶段从所述经压缩的空气流吸附水蒸气、二氧化碳和烃类，在所述离线操作阶段中，使用从所述空气分离单元取出并且具有大于90.0％氧含量的吹扫气体来再生所述床。
3.根据权利要求2所述的空气分离单元，其中所述吹扫气体是所述富氧废物流。
4.根据权利要求3所述的空气分离单元，其中所述基于吸附的预纯化器单元还包括蒸汽加热器、电加热器或其他非燃烧式加热器，所述加热器被配置为将所述富氧废物流加热至小于或等于450℉的温度以用于再生所述变温吸附单元中的所述吸附床。
5.根据权利要求1所述的空气分离单元，其中从所述低压塔提取的所述富氧流是从所述富氧液体塔底馏出物所在的贮槽取出并且具有大于99.5％的氧浓度的高纯度富氧流。
6.根据权利要求1所述的空气分离单元，其中从所述低压塔提取的所述富氧流是从所述富氧液体塔底馏出物所在的贮槽上方的若干级取出并且具有介于93％和99.7％之间的氧浓度的低纯度富氧流。
7.根据权利要求1所述的空气分离单元，所述空气分离单元还包括增压压缩机，所述增压压缩机被配置为进一步压缩所述经压缩并且纯化的空气流的第二部分，并且其中将经纯化的空气流的经进一步压缩的第二部分的一部分在主换热器中完全或部分冷凝并且进料至所述高压塔的中间位置。
8.根据权利要求7所述的空气分离单元，其中所述涡轮膨胀机布置还包括增压器负载涡轮，所述增压器负载涡轮被配置为使所述经压缩并且纯化的空气流的经进一步压缩、部分冷却的第二部分膨胀以形成所述排气流，并且所述增压器负载涡轮被操作性地联接以驱动所述增压压缩机。
9.根据权利要求7所述的空气分离单元，其中所述过冷器布置被进一步配置为经由与所述富氧废物流的间接换热来使所述排气流过冷。
10.根据权利要求1所述的空气分离单元，其中所述氩塔被配置为在介于1.3巴和2.8巴之间的压力下操作。
11.一种在低温空气分离单元中通过98％或更大的氮回收率分离空气以产生一种或多种高纯度氮产物的方法，所述方法包括以下步骤：
压缩进入的进料空气流以产生经压缩的空气流；
在基于吸附的预纯化单元中纯化所述经压缩的空气流，所述基于吸附的预纯化单元被配置为从所述经压缩的空气流去除水蒸气、二氧化碳、一氧化二氮和烃类以产生经压缩并且纯化的空气流；
将所述经压缩并且纯化的空气流分成至少所述经压缩并且纯化的空气流的第一部分和所述经压缩并且纯化的空气流的第二部分；
在适用于在低温蒸馏系统中精馏的温度下将所述经压缩并且纯化的空气流的第一部分冷却为蒸气空气流，并且部分地冷却所述经压缩并且纯化的空气流的第二部分；
在涡轮中使所述经压缩并且纯化的空气流的经部分冷却的第二部分膨胀以形成排气流；
在低温蒸馏塔系统中精馏所述空气流和所述排气流，所述低温蒸馏塔系统包括具有介于6.0巴和10.0巴之间的操作压力的高压塔和具有介于1.5巴和2.8巴之间的操作压力的低压塔，所述高压塔和所述低压塔经由冷凝器再沸器以热传递关系相连，其中所述精馏步骤产生来自所述低压塔的一个或多个富氧流、来自所述低压塔的氮塔顶馏出物流和来自所述冷凝器-再沸器的经冷凝的氮流；
在过冷器单元中经由与富氧废物流的间接换热来使从所述低压塔提取的富氧流过冷以产生过冷富氧流；
经由与来自所述低压塔的所述氮塔顶馏出物流的间接换热来使来自所述高压塔的釜氧流和来自所述冷凝器-再沸器的所述经冷凝的氮流过冷；
在氩塔布置中精馏从所述低压塔提取的所述富氧-氩流，所述氩塔布置具有至少一个氩塔和氩冷凝器，并且其中所述氩塔被配置为产生富氧塔底馏出物流和富氩塔顶馏出物；
使所述富氧塔底馏出物流从所述氩塔返回至所述低压塔；
将所述富氩塔顶馏出物从所述氩塔引导至所述氩冷凝器；
在所述氩冷凝器中依靠所述过冷富氧流来冷凝所述富氩塔顶馏出物以产生粗制氩流、氩回流流、所述富氧废物流和液体富氧流；以及
在主换热器中加热来自所述低压塔的所述氮塔顶馏出物流以产生气态氮产物，并且从所述冷凝器-再沸器取出所述经冷凝的氮流的一部分作为液体氮产物，并且其中所述低温空气分离单元具有98％或更大的氮回收率；
其中所述基于吸附的预纯化器单元是被配置为纯化所述经压缩的空气流的多床变温吸附单元，所述多床变温吸附单元被配置为使得每个床在在线操作阶段与离线操作阶段之间交替，所述在线操作阶段从所述经压缩的空气流吸附水蒸气、二氧化碳和烃类，在所述离线操作阶段中，使用具有大于90％氧含量的所述富氧废物流来再生所述床。
12.根据权利要求11所述的方法，所述方法还包括将所述富氧废物流加热至小于或等于450℉的温度以用于再生所述吸附床的步骤。
13.根据权利要求11所述的方法，其中从所述低压塔提取的所述富氧流是从所述富氧液体塔底馏出物所在的贮槽取出并且具有大于99.5％的氧浓度的高纯度富氧流。
14.根据权利要求11所述的方法，其中从所述低压塔提取的所述富氧流是从所述富氧液体塔底馏出物所在的贮槽上方的若干级取出并且具有介于93％和99.7％之间的氧浓度的低纯度富氧流。
15.根据权利要求11所述的方法，其中所述氩塔布置还包括被配置为超级氩塔的第一氩塔和被配置为高比率氩塔的第二氩塔。
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