CN1077276C - 分段进料空气冷凝的低温精馏系统 - Google Patents

分段进料空气冷凝的低温精馏系统 Download PDF

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CN1077276C
CN1077276C CN97104520A CN97104520A CN1077276C CN 1077276 C CN1077276 C CN 1077276C CN 97104520 A CN97104520 A CN 97104520A CN 97104520 A CN97104520 A CN 97104520A CN 1077276 C CN1077276 C CN 1077276C
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CN1164635A (zh
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D·P·博纳奎斯特
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Abstract

用于生产低纯氧的双塔低温精馏系统，其中进料空气的一较少部分在进行精馏前在低压塔内的两个垂直定位的段上连续冷凝。

Description

分段进料空气冷凝的低温精馏系统
一般地讲，本发明涉及低温精馏，更具体地说，涉及低纯氧的生产。
通过低温精馏空气来生产氧和氮是已经很成熟的工业方法。一般进料空气在双塔系统中得到分离，其中来自高压塔的氮架(nitrogen shelf)或顶部蒸汽用来再沸低压塔中的氧底部液体。
在诸如玻璃制造、炼钢和能源生产的应用中对低纯氧的需求不断增加。对于生产氧的纯度不高于97％(摩尔)的低纯氧而言，需要比一般通过双塔操作产生较少的低压塔汽提段的蒸汽蒸出以及在低压塔的富集段中较少的液体回流。
因此，一般通过低温精馏系统来大量生产低纯氧，其中，处于高压塔压力的进料空气用来再沸低压塔底部液体，然后送入高压塔中。使用空气代替氮气来蒸发低压塔底部降低了对空气进料压力的要求，并且使得通过将空气的适宜部分送入低压塔再沸器或将总进料空气的较多部分冷凝来产生低压塔汽提段上只有所需的蒸出。
虽然常规空气沸腾低温精馏系统已经有效地用于低纯氧的生产，但其产生回流以供给低压塔顶部的能力是有限的。这是由于进料空气的部分冷凝减少了高压塔用以产生氮回流适合的蒸汽。由于产生回流的能力降低而导致氧回收率的减少，因此消耗更多的动力。
因此，本发明的一个目的是提供用于生产低纯氧的低温精馏系统，它使用双塔设备，并可比常规系统在降低的动力要求下操作。
本领域技术人员在阅读以下公开内容后，本发明所达到的上述及其它目的将显而易见。其一方面的内容是：
一种通过在具有高压塔和低压塔的双塔中进料空气的低温精馏来生产低纯氧的方法，包括：
(A)将进料空气的第一部分送入高压塔中，并通过低温精馏将该第一进料空气部分分离成富氧和富氮液；
(B)将来自高压塔的富氧并和富氮液送入低压塔中；
(C)通过与低压塔内液体进行间接热交换而部分地冷凝进料空气的第二部分以产生第一液体空气部分和第一蒸汽空气部分；
(D)通过与低压塔内液体在步骤(C)进行的位置上方进行间接热交换而至少部分地冷凝第一蒸汽空气部分以产生第二液体空气部分；
(E)将第一液体空气部分和第二液体空气部分各自在步骤(C)进行的位置上方送入低压塔中；
(F)通过低温精馏将送入低压塔内的液体分离成富氮液和富氧液；和
(G)将富氧液作为产品低纯氧回收。
本发明的另一方面的内容是：
生产低纯氧的设备，包括：
(A)具有第一塔和第二塔的双塔；
(B)将进料空气的第一部分送入第一塔中的装置；
(C)将来自第一塔的液体送入第二塔中的装置；
(D)在第二塔内的第一换热器以及将进料空气的第二部分送入第一换热器中的装置；
(E)在第二塔内位于第一换热器上方的第二换热器，以及将来自第一换热器的蒸汽送入第二换热器中的装置；
(F)将来自第一换热器的液体和来自第二换热器的液体各自在第一换热器上方送入第二塔中的装置；和
(G)将来自第二塔的产品低纯氧回收的装置。
此处所用的术语“低纯氧”指氧浓度不超过97％(摩尔)的液体。
此处所用的术语“进料空气”指主要包括氮气和氧气如环境空气的混合物。
此处所用的术语“汽轮膨胀”和“汽轮骤冷器”分别指用于高压气体流经汽轮机以减少压力及气体的温度因而产生制冷作用的方法和设备。
此处所用的术语“塔”指蒸馏或分馏塔或区，即接触塔或区，在其中液相和气相逆流接触以实现流体混合物的分离，例如通过气相和液相在塔内一系列垂直放置的塔盘或塔板和/或在填料单元(可以是结构填料和/或不规则的填料单元)上接触。对于蒸馏塔的进一步讨论，参见《化学工程师手册》第五版，R.H.Perry和C.H.Chilton编，纽约McGraw-Hill Book Company出版，第13章，“连续蒸馏法”。
气液接触分离法依赖于各组分蒸气压的差异。高蒸气压(或易挥发或低沸点)组分易于浓缩于气相而低蒸气压(或难挥发或高沸点)组分易于浓缩于液相，部分冷凝是利用蒸汽混合物的冷却来浓缩气相中的挥发组分从而难挥发组分在液相中藉以分离的方法。精馏或连续蒸馏是通过气液相的逆流处理获得连续部分蒸发和冷凝的分离方法。气液相的逆流接触是绝热的，并可包括相间积分或微分接触。利用精馏的原理来分离混合物的分离法设备通常可互换地称为精馏塔、蒸馏塔或分馏塔。低温精馏是至少部分在温度不超过150°K下进行的精馏方法。
此处所用的术语“间接热交换”指在流体相互之间没有任何物理接触或混合的情况下将两种液流导入热交换关系中。
此处所用的术语“塔盘”指接触段(不必是一平衡段)，也可指其它接触设备例如分离能力相当于一个塔盘的填料。
此处所用的术语“平衡段”指气-液接触段，在其中离开该段的蒸气和液体达到传质平衡，如具有100％效率的塔盘或一填料单元高度相当于一理论塔板(HETP)。
此处所用的术语“在塔内”当涉及热交换时指在机能上相当于在该塔内，即位置在塔内或邻近该塔，液体从该塔出来被送到热交换装置中。液体可以全部或部分被蒸发，产物气或气-液混合物返回到塔中。最好液体部分被蒸发，产物气-液混合物从与液体自塔中导出的相同高度的位置返回塔中。
图1是本发明低温精馏系统一个优选实施方案的流程示意图。
图2是本发明低温精馏系统的另一个优选实施方案的流程示意图。
图3代表在本发明实践中优选的热交换设备，其中所定义的塔内热交换在塔体外进行。
本发明用于近乎消除在双塔系统的低压塔的低温蒸馏中的不可逆性。比起可能的常规实践来，它将系统能源需求较大程度地减少。通过在低压塔中迎着部分再沸腾的塔液体而部分冷凝中间换热器中的低压进料空气流，塔的该段操作线更接近平衡线，因而减少了系统的能源需求。部分冷凝的低压进料空气的相分离为低压塔中第二中间换热器在较高位置的参与提供了机会。在该第二中间换热器中，换热器的分离的蒸汽最好迎着部分再沸腾的塔液体全部冷凝。离开中间换热器的液体不与蒸发侧进入的液体相混合。在中间换热器每一段产生的液体被送到塔的合适高度，因此补充了正常可用的回流。使用热交换的第二中间段进一步减少了塔中的不可逆性，因此减少了对系统的能源需求。对系统制冷作用的需求可通过将送入到一设备的空气的一部分汽轮膨胀来得到满足，所述设备已被增压，其压力大于用于中间换热器部分冷凝所用的压力。通过增加位于塔中较高位置、以和第一对中间换热器几乎相同操作方式的第二对中间换热器还可进一步减少能源需求。该第二对中间换热器用来自初级换热器的接近饱和的低压空气进料。第一对中间换热器用接近饱和的、压力稍微高于第二对的空气进料。对循环的制冷作用通过将送入到已被增压、压力大于中间换热器的第一对的设备中的空气的一部分汽轮膨胀而得到平衡。
本发明将参照附图更详尽地描述。现参照图1，进料空气100通过基础负荷(base load)压缩机31而被压缩至一般在1.37788×105-3.4447×105帕(20-50磅/平方英寸)绝对压力(psia)的范围内，所得进料空气流60通过净化器50而被清除高沸点杂质如水蒸汽和二化碳。已得到净化并被压缩的进料空气61的部分63一般含大约20-50％的进料空气100，从该进料空气中导出用于中间换热器，这将在后面更详加描述。剩下的进料空气流62通过增压压缩机32而被压缩至压力在2.75576×105-6.8894×105帕(40-100psia)的范围内，所得进料空气流79被送入主换热器1中，在其中它通过与返回流进行间接热交换而被冷却。
一般含大约5-15％进料空气的进料空气流79的部分80在部分横过主换热器1后导出，通过汽轮骤冷器30而被汽轮膨胀以产生致冷作用，并作为流81送入低压塔11中。最好含有进料空气的主要部分并一般含大约35-75％进料空气100的剩下进料空气流64从主换热器1出来，送入产品锅炉23，在此它通过与沸腾的产品氧进行间接热交换而至少部分得到冷凝。所得进料空气流65作为第一进料空气部分送入第一或高压塔10中。
第一塔10是双塔系统(也包括第二或低压塔11)的高压塔。高压塔10在2.75576×105-6.8894×105帕(40-100psia)的压力范围内操作。在高压塔10内第一进料空气部分通过低温精馏分离为富氮蒸汽和富氧液体。富氮蒸汽作为流82从塔10中导出并送入主冷凝器20，在此处它通过与沸腾的低压塔底液体进行间接热交换而被冷凝。所得富氮液体83被分成作为回流返回高压塔10的流84和通过换热器101而被冷却并作为回流通过阀87进入低压塔11的流85。富氧液作为流71从高压塔10中导出，通过换热器102而被冷却并经阀73进入低压塔11中。在示于图1的实施方案中，流71与来自第一交换的流68汇合，而该汇合流75被送入低压塔。第二或低压塔11在压力小于高压塔10的条件下操作，其压力在1.03341×105-2.06682×105帕(15-30psia)的范围内。
进料空气流63通过主换热器1与返回流进行间接热交换而被冷却。所得冷却的低压进料空气流66作为第二进料空气部分送入第一中间换热器21中，所述中间换热器21位于低压塔11内一般在底部再沸器20热交换的大约2-15个平衡级上方。在第一中间换热器21中，第二进料空气部分66通过与蒸发着的、最好是部分蒸发着的沿塔11流下的液体进行间接换热交换而被部分冷凝，藉以为塔11产生上向流蒸汽和在来自中间换热器21进入相分离器40的两相流67中生成第一液体空气部分和第一蒸汽空气部分。
氮气浓度超过流66的第一蒸汽空气部分99从相分离器40中出来进入第二中间换热器22中，该第二中间换热器22位于低压塔11内第一中间换热器21上方一般大约1-10个平衡级的位置。在第二中间换热器22内，第一蒸汽空气部分99通过与蒸发着的、最好是部分蒸发着的沿塔11流下的液体进行间接热交换而至少部分最好是全部被冷凝，藉以为塔11产生附加的上向流蒸汽并生成第一液体空气部分。
氧气浓度超过流66的第一液体空气部分68从相分离器40中出来，经阀69在第二中间换热器22上方一般在10个平衡级的位置或其上进入低压塔11。如先前提及的，图1示意了流68与流71汇合形成流75然后进入塔11的一个实施方案。氮气浓度超过流66的第二液体空气部分76从第二中间换热器22中出来，经阀77在第二中间换热器22一般5-20个平衡级的上方进入低压塔11中。第一和第二液体空气部分起着提供附加的回流液体进入低压塔11以提高塔内的低温分离的作用。
在第二或低压塔11中进入该塔的各流体通过低温精馏被分离成富氮流体和富氧流体。富氮流体作为蒸气流89从塔11中导出，经过换热器101、102和1时被加热并作为可以作氮气产品全部或部分回收的氮气流1离开系统。富氧流体从塔11中导出，并作为产品低纯氧全部或部分回收。在示于图1的实施方案中，富氧流体作为液体流92从塔11中导出，液流92进入产品蒸煮器23在其中通过与冷凝第一进料空气部分64进行间接热交换而得到蒸发。所得富氧蒸气流93经过主换热器1时被加热，并作为产品低纯氧流94被回收。如需要，流92的部分可以作为产品低纯液氧直接回收。
图2示意了本发明在低压塔内使用第二对中间换热器的另一个实施方案。图2对普通单元的数字相对应于图1的数字，而且这些普通单元不再详细加以描述。
现参照图2，一般含大约5-20％进料空气100的进料空气流61的第三部分103从流61中抽取出来在第二对中间换热器中加以处理。然后在如示于图1的实施方案所述进行处理前通过压缩机33被压缩至较高的压力。进料空气流103通过主换热器1时被加热，所得流104在位于低压塔11内第二中间换热器22上方一般约1-10个平衡级的位置的第三中间换热器24中得到部分冷凝。在第三中间换热器24内，进料空气流104通过与蒸发着的、最好是部分蒸发着的沿塔11流下的液体进行间接热交换而部分得到冷凝，藉以为塔11产生上向流蒸汽并生成第三液体空气部分和在两相流105中从第三中间换热器24出来进入相分离器41的另一蒸汽空气部分。氮气浓度超过流103的另一蒸汽空气部分106从相分离器41中出来进入低压塔11内第三中间换热器24上方一般约1-10个平衡级位置的第四中间换热器25。在第四中间换热器25中，另一蒸汽空气部分106通过与蒸发着的沿塔11流下的液体进行间接热交换而至少部分、最好是全部被冷凝。
氧气浓度超过流103的第三液体空气部分107经阀108并与流68汇合形成流109，然后与流71汇合形成流75并按如上所述处理。氮气浓度超过流103的第四流体空气部分110从第四中间换热器25中出来，经阀111并与如上述处理的流77汇合。
虽然图1和2示意的与换热器21、22、24和25相关的热交换位置在塔体内发生，但这仅是为了简化本发明方法的说明。在许多情况下可以预料一个或多个这种换热器将在位置上处于塔体内，即在功能上相当于在塔内。图3示意了一种这样功能上相当于位于塔内的换热器的广义形式的设备。
现参照图3，塔200内下行液体被收集并作为流204从塔中导出。用于液体回收和导出的装置对于蒸馏设备设计领域的技术人员来说是公知的。液流204导入换热器201(可以是黄铜铝质换热器)内。当液体204横过换热器201时，通过与至少部分被冷凝的流体202进行间接热交换而至少部分被蒸发。流体202代表流入换热器的蒸汽，如图1的流66或流99。流202和204在换热器201内以逆流形式流动。部分被蒸发的液体205从换热器201中出来，送回塔200中。最好该部分被蒸发的液体以下述方式返回塔中：蒸汽部分206可与塔内从液体204原先被导出的位置下方上升的蒸汽209混合。当两相流被导入进塔内的中间位置时，在蒸馏塔设计中常采用这些装置以完成上述目的。流205的液体部分207从蒸汽部分释放出来并最好分布给传质单元如紧挨着液体204原先被导出位置的下方的填料或塔盘。所述用于从蒸汽中释放液体和用于分布液体的装置常被用于蒸馏塔的设计中。虽然从实用的角度最好使用所有塔中下行液体用于流204，但在一些设计情况下可能会指令仅用部分这种下行液体用于此目的。如已提到的是，流202在换热器201内通过热交换而至少部分地冷凝。流203的流体被送入塔中。流203相当于例如图1的流67或流76。
虽然本发明已参照特定的优选实施方案作了详细的描述，但本领域技术人员将会认可在权利要求书的精神和范围内本发明的其它实施方案。

Claims (8)

1.一种通过在具有高压塔和低压塔的双塔中进料空气的低温精馏来生产低纯氧的方法，包括：
(A)将进料空气的第一部分送入高压塔和通过低温精馏在高压塔内将该第一进料空气部分分离成富氧和富氮液；
(B)将来自高压塔的富氧和富氮液送入低压塔中；
(C)通过与低压塔内液体进行间接热交换来部分地冷凝进料空气的第二部分以产生第一液体空气部分和第一蒸汽空气部分；
(D)通过与低压塔内液体在步骤(C)进行的位置上方进行间接热交换来至少部分地冷凝第一蒸汽空气部分以产生第二液体空气部分；
(E)将第一液体空气部分和第二液体空气部分各自在步骤(C)进行的位置上方送入低压塔中；
(F)通过低温精馏将进入低压塔的各种液体分离成富氮液和富氧液；和
(G)将富氧液作为产品低纯氧回收。
2.权利要求1的方法，还包括：
(H)通过与低压塔内液体进行间接热交换来部分地冷凝进料空气的第三部分以产生第三液体空气部分和另外的蒸汽空气部分；
(I)通过与低压塔内液体在步骤(H)进行的位置上方进行间接热交换至少部分地冷凝所述另外的蒸汽空气部分以产生第四液体空气部分；和
(J)将第三液体空气部分和第四液体空气部分分别在步骤(H)进行的位置上方送入低压塔中。
3.权利要求1的方法，其中富氧液作为液体从低压塔中导出，并在回收前通过与进料空气进行间接热交换而得到蒸发。
4.权利要求1的方法，还包括将富氮液作为产品氮回收。
5.生产低纯氧的设备，包括：
(A)具有第一塔和第二塔的双塔；
(B)将进料空气的第一部分送入第一塔中的装置；
(C)将来自第一塔的液体送入第二塔中的装置；
(D)在第二塔内的第一换热器和将进料空气的第二部分送入第一换热器中的装置；
(E)第二塔内在第一换热器位置上方的第二换热器，以及将来自第一换热器的蒸汽送入第二换热器中的装置；
(F)将来自第一换热器的液体和来自第二换热器的液体各自在第一换热器上方送入第二塔中的装置；和
(G)将来自第二塔的产品低纯氧回收的装置。
6.权利要求5的设备，还包括第二塔内的第三换热器，将进料空气的第三部分送入第三换热器的装置，第二塔内在第三换热器上方的第四换热器，将来自第三换热器的蒸汽送入第四换热器的装置，以及将来自第三换热器的液体和来自第四换热器的液体各自在第三换热器上方送入第二塔中的装置。
7.权利要求5的设备，还包括一产品蒸煮器，其中将进料空气的第一部分送入第一塔中的装置和将来自第二塔的产品低纯氧回收的装置都包括该产品蒸煮器。
8.权利要求5的设备，还包括将来自第二塔的产品氮回收的装置。
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CA2200249C (en) 2000-01-25
EP0797062A3 (en) 1998-05-20
KR100289877B1 (ko) 2001-05-15
ID16454A (id) 1997-10-02
CA2200249A1 (en) 1997-09-19
JPH09257365A (ja) 1997-10-03
KR970066478A (ko) 1997-10-13
EP0797062A2 (en) 1997-09-24
CN1164635A (zh) 1997-11-12
AR006264A1 (es) 1999-08-11
BR9701323A (pt) 1998-10-27
MX9702046A (es) 1998-03-31
US5666824A (en) 1997-09-16

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