CN1236884A - 空气分离 - Google Patents

空气分离 Download PDF

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CN1236884A
CN1236884A CN99106020A CN99106020A CN1236884A CN 1236884 A CN1236884 A CN 1236884A CN 99106020 A CN99106020 A CN 99106020A CN 99106020 A CN99106020 A CN 99106020A CN 1236884 A CN1236884 A CN 1236884A
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C·J·海内
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Abstract

用精馏法分离空气。将空气在主压缩机2中压缩至第一压力。压缩空气的第一流不作进一步压缩而在主热交换器6中冷却至适合于用精馏分离的温度。将该流引入双精馏塔14的高压塔16,双精馏塔还包括低压塔18,在低压塔的底部形成浓度为50—98.5(通常为50—96)摩尔百分数的氧;和使高压塔16与低压塔18形成热交换关系的冷凝—再沸器20。使压缩空气的第二流在膨胀透平32中膨胀并对外作功,在此上游不对压缩空气的第二流作进一步压缩。将膨胀后的第二流引入低压塔18。不纯氧产品从所述底部取出。对外作功用于发电,因此透平32与发电机34相连。

Description

空气分离
本发明涉及一种空气分离的方法和装置。
用精馏分离空气已被人们所熟知。精馏的方法是在下降液流和上升蒸汽流之间发生传质，使上升蒸汽流中富含要分离混合物的易挥发组分(氮)，下降液流中富含不易挥发的组分(氧)。
已知的空气分离是在双精馏塔中进行，精馏塔包括一个高压精馏塔和一个低压精馏塔，高压塔接收经净化、压缩后的温度适合于用精馏分离的汽化空气，低压塔接收来自高压塔用于分离的富氧液态空气流，它通过冷凝-再沸器与高压塔形成热交换关系，其中冷凝器提供用于分离的液氮回流，再沸器提供在低压精馏塔中的氮蒸汽的上升流动。
双精馏塔可用来在低压塔的底部生产氧馏分，在低压塔的顶部生产氮馏分。氧可以是含小于0.5％体积杂质的纯氧，也可以是含达到50％体积杂质的不纯氧。
对提供给空气分离设备的制冷有一个基本要求。这种要求的至少一部分起因于低温双精馏塔的运行。特别是当没有任何空气分离的产品是以液态形式提取时，这种制冷要求通常是这样满足的：将部分空气的压力提高到高于高压塔顶部运行压力至少2bar，使该空气在膨胀透平中膨胀并对外作功，透平排气进入低压塔。透平通常与增压压缩机相连，该压缩机将空气压力升高到高于高压塔顶部的压力。
空气分离设备通常消耗大量的能源，因此其结构应使得能量消耗最少而又不过分增加费用。为了减少能量消耗，本领域目前的方法是运行具有两个再沸器的低压精馏塔。一个在高温下运行，由被分离的空气流加热，另一个在低温下运行，由在高压塔中分离后的氮流加热。这类工厂的缺点是需要第二个再沸器，增加了基本建设费用。
US-A-5337570提供了另一种空气分离设备的例子。第一冷凝-再沸器用于冷凝在高压塔中分离后的部分顶部的氮。冷凝是通过与高压塔底部富氧液体形成间接热交换而进行的。底部的富氧液体流因此被部分再沸腾。所得的蒸汽和剩余的液体供给低压塔。该设备使用带一个发电机的膨胀透平，其排气进入低压塔。要分离的空气在多级主压缩机中被压缩。供给高压精馏塔的主空气从低压级中取走，该压力低于供给膨胀透平的压力。
本发明的目的是提供一种用精馏分离空气的方法和装置，它们能在合适的能量消耗下运行而不使得设备具有不可接受的高价格，并且不需要有两个再沸器与低压精馏塔相连。
本发明提供了一种用精馏分离空气的方法，包括：将空气压缩至第一压力；不进一步压缩，而使压缩空气的第一流在主热交换器中冷却至适合于用精馏分离的温度，将该第一流引入双精馏塔的高压塔，除了高压塔外，双精馏塔还包括低压塔，在低压塔底部形成浓度为50-98.5摩尔百分数(通常是50-96摩尔百分数)的氧；使压缩空气的第二流膨胀并对外作功，将膨胀后的第二流引入低压塔，从所述的底部组分中取出不纯的氧产品，其中对外作功用于发电，其特征在于，双精馏塔还包括使高压塔与低压塔形成热交换关系的冷凝-再沸器，在将压缩空气的第二流进行膨胀时不对第二流的上游作进一步的压缩。
本发明还提供一种用精馏分离空气的装置，该装置具有双精馏塔，包括一个高压精馏塔和一个低压精馏塔；至少一个空气压缩机，用于将空气压缩至第一压力；一个主热交换器，用于将压缩空气的第一流冷却至适合用精馏分离的温度；用于第一流进入高压塔的进口；一个膨胀透平，用于使压缩空气的第二流膨胀并对外作功，透平具有使压缩空气的第二流进入的进口和与低压塔相连的出口，膨胀透平带动一个发电机；和用于浓度为50-98.5(通常为50-96)摩尔百分数的不纯氧产品从低压塔底部流出的出口，其特征在于，没有另外的压缩装置用来将所述的压缩的所述第一流和第二流空气流的压力提高到高于第一压力，双精馏塔还包括一个使高压塔与低压塔形成热交换关系的冷凝-再沸器。
根据本发明的方法和装置具有很多优点。首先，能使较大比例的膨胀空气对外作功并将其引入低压塔，这使得能在相对高的效率下运行低压塔，同时具有比膨胀空气引入处低的蒸汽传输线。另外，减少了冷凝-再沸器的负荷。低压塔下部的有效直径可以减少，因此可以减少液体-蒸汽接触表面的总面积。冷凝-再沸器的尺寸也可以减少。尽管以这种方式进行的本发明方法和装置的运行可以使主热交换器的冷却流和加热流之间的温差加大，但该缺点早已由低压塔的高效运行所补偿，特别是由于在主热交换器中的大温差允许压降或单位体积的换热面积减少，或者是两个优点均可获得。第三，省去了与膨胀透平相连的普通增压压缩机。第四，本发明的方法和装置能用于产出大量的电力，因此减少了净能量消耗。
通常氧产品从低压精馏塔中排出时是液态，经过加压，再与压缩空气的第三流进行间接热交换而蒸发，压缩空气的第三流处于第二压力，它高于第一压力。这种热交换可以在主热交换器中进行，也可以在另外的热交换器中进行。根据本发明方法和装置的实例特别适合于生产氧浓度为70-90摩尔百分数的氧，最好是75-85摩尔百分数的氧。在优选的实例中，较好的是要分离空气体积流量的至少22％形成膨胀后的第二流体，最好的范围是23％-30％。在这些实例中，压缩空气的第一流通常是小于要分离的总空气体积流量的45％。
另外氧产品可以从低压塔中以蒸汽形式排出，如果需要，在主热交换器中加热至非低温后将其压缩至所需的传送压力。在这种情况下，不需要冷凝压缩空气的第三流。这样有可能使压缩空气的第二流占据总的要压缩空气流的较大比例。例如如果氧产品浓度为70-90摩尔百分数，通常有要分离空气总流量的至少40％能形成压缩空气的第二流。
膨胀透平的进出口压力比最好是2.5∶1-3.5∶1。
本发明的方法特别适合于没有分离的液态产品取出或液态产品总生产量小于10％的空气分离，较好是氧产品总生产量小于5％，最好是小于2％。
较好的情况是，压缩空气的第一流通常是在主热交换器中而不是在其上游与第二流中分开。在任何情况下，第一和第二流从所述的空气压缩机中以相同的压力排出。
压缩空气最好在主热交换器的上游被净化。
高压塔和低压塔两者均可以由一个或多个容器构成，其中液相和气相逆流接触进行空气分离，可以是例如使气液相在填料元件上或者在安装于容器中的成组的竖向间隔的塔盘或板片上接触。
下面将参照附图通过实施例对本发明的方法和装置加以描述，其中：
图1是本发明第一空气分离装置的流程图，图2是本发明第二空气分离装置的流程图。图中相同的部件标以相同的符号。参照图1，空气流在主空气压缩机2中被压缩，在与主空气压缩机2相连的后冷却器(未示出)中将所得的压缩空气中的压缩热量抽走。这样压缩后的空气流在吸附装置4中被净化。净化包括从空气流中去除较高沸点的不纯物，特别是水蒸气和二氧化碳，否则的话，它们会在装置的低温区冻结。装置4可通过压力变化吸附或温度变化吸附。装置4还可包括一层或多层催化剂用于去除一氧化碳和氢杂质。这种对一氧化碳和氢杂质的去除已在EP-A-438282中描述。吸附式净化元件的结构和运行已被人们所知，此处不进一步叙述。
在净化装置4下游，压缩空气流从热端8流进主热交换器6，在主热交换器6的中间区，压缩空气流被分成第一和第二流。第一流继续穿过主热交换器6，在或接近其露点温度时从冷端10流出，这也是适合用精馏分离的温度。压缩空气的第一流从主热交换器6的冷端10流出后通过进口12进入双精馏塔14的高压塔16的下部，双精馏塔还包括低压塔18和(单个的)冷凝-再沸器20。(这里没有另外的冷凝-再沸器使高压塔16中低压塔18形成间接热交换关系。)
在运行中，空气在高压塔16中分离成底部富氧液体馏分和顶部氮蒸汽馏分，富氧液体流通过出口22从高压塔16的底部流出，富氧液体空气流在进一步的热交换器24中被过冷，通过或焦耳-汤姆逊阀，或节流阀26，经进口27流入低压塔18选定的中间区。
从高压塔16顶部流出的氮蒸汽进入冷凝-再沸器20，在那里经与低压塔18底部的沸腾不纯液态氧进行间接热交换而被冷凝。所得的部分液氮冷凝液作为回流返回塔16，剩余的冷凝液流经热交换器24被过冷，然后流经节流阀或焦耳-汤姆逊阀28，通过进口30作为回流进入低压塔18的顶部。
从高压塔16的出口22流出的富氧液态空气形成要在低压塔中进行分离的空气的一部分。另一部分空气是在主热交换器6的中间区与压缩空气的第一流分流的压缩空气的第二流。压缩空气的第二流从主热交换器6中间区流出，在膨胀透平(有时称之为涡轮膨胀器)32中膨胀并对外作功。该功使与透平32相连的发电机34运行。所得的膨胀后气体在接近低压塔18压力时离开透平32，并由进口38引入低压塔中间区。在低压塔18中该空气流被分离成顶部的氮蒸汽和底部的通常含70-90摩尔百分数的液态氧。冷凝-再沸器20通过与冷凝氮的间接热交换使底部的不纯液态氧再蒸发。所得的部分氧蒸汽升至塔18，在那里与下降液流接触。其余的不纯氧蒸汽通过出口40从低压塔18流出，经从冷端10至热端8流过主热交换器6而被加热至非低温温度，即稍低于大气的温度。所得的加热后氧产品在氧压缩机42中被压缩至需要的传输压力。压缩后的氧产品流至氧输送管线44。
图2所示的设备与图1所示的基本相似，区别在于，通过出口40从低压塔18流出的氧产品是液体并在液体泵54中加压至所需的传输压力。部分净化后的空气从净化元件4中取出，在增压压缩机46中进一步压缩。所得的进一步压缩后空气流从热端8至冷端10流过主热交换器6，被冷却至液化温度。所得的冷却后的进一步压缩空气流在冷凝-蒸发器48中通过与加压后的不纯液态氧产品流进行间接热交换而冷凝，不纯液态氧产品流因此蒸发。流经冷凝-蒸发器48的空气通常是完全冷凝。所得的冷凝液流经节流阀50，通过进口52进入高压塔16。进口52的位置高于进口12。在冷凝-蒸发器48中形成的氧蒸汽从冷端10至热端8流经主热交换器6，然后以所需的压力流至产品氧输送管线44。通常，具有大致与空气相同组分的液体流从高压塔16的中间出口56排出，通过热交换器24被过冷，然后通过节流阀或焦耳-汤姆逊阀58由进口60引入低压塔18。另外，冷凝液态空气流也可以在阀50的上游分流，该流的一部分经节流阀或焦耳-汤姆逊阀(未示出)进入低压塔18。
在图2所示装置运行的典型例子中，经出口40从低压塔18流出的氧产品含80摩尔百分数的氧，可在泵54中提升至约4.3bar的压力。透平32的进口压力约3.8bar，出口压力约1.25bar。约有空气总体积流量的40％通过进口12引入高压塔16，约占总体积流量的25％通过进口16进入低压塔18，其余的通过进口52进入高压塔16。
在图1和图2所示的装置中，主空气压缩机2设定透平32的进口压力和高压塔16的进口12压力。在透平32进口处的空气压力比空气压缩机2出口的压力略低一些，这是由于流过净化装置4和主热交换器6时的压降所致。同理，高压塔16的进口12处的压力比主空气压缩机2出口的压力略低几分之一巴也是由于流经主热交换器6和净化装置4的压降所致。另外，用在图1图2所示装置中的膨胀透平32是单独的膨胀透平。

Claims (10)

1．一种用精馏分离空气的方法，包括：将空气压缩至第一压力；不进一步压缩，而使压缩空气的第一流在主热交换器中冷却至适合于用精馏分离的温度，将该流引入双精馏塔的高压塔，双精馏塔还包括低压塔，在低压塔底部形成浓度为50-98.5摩尔百分数的氧：使压缩空气的第二流膨胀并对外作功，将膨胀后的第二流体引入低压塔，从所述的底部组分中取出不纯的氧产品，其中对外作功用于发电，其特征在于，双精馏塔还包括使高压塔与低压塔形成热交换关系的冷凝一再沸器，在将压缩空气的第二流进行膨胀时不对第二流的上游作进一步压缩。
2．如权利要求1所述的方法，其中氧产品是以液态从低压塔流出的，经过压缩，在与压缩空气的第三流的间接热交换中蒸发，压缩空气的第三流的压力处于第二压力，它高于第一压力。
3．如权利要求2所述的方法，其中氧产品的浓度范围是50-96摩尔百分数。
4．如权利要求3所述的方法，其中氧产品的浓度范围是75-85摩尔百分数，要分离空气体积流量的至少22％形成膨胀后的第二流。
5．如权利要求4所述的方法，其中要分离空气体积流量的23％-30％形成膨胀后的第二流。
6．如前述任一权利要求所述的方法，其中膨胀透平进出口压力的比是2.5∶1-3.5∶1。
7．如前述任一权利要求所述的方法，其中没有分离的液体产品被取出。
8．如前述任一权利要求所述的方法，其中压缩空气的第一流在主热交换器中与第二流体分开。
9．一种用精馏分离空气的装置，该装置具有双精馏塔，包括一个高压精馏塔和一个低压精馏塔；至少一个空气压缩机，用于将空气压缩至第一压力；一个主热交换器，用于将压缩空气的第一流冷却至适合用精馏分离的温度；用于第一流体进入高压塔的进口；一个膨胀透平，用于使压缩空气的第二流膨胀并对外作功，透平具有使压缩空气流的第二进入的进口和与低压塔相连的出口，透平带动一个发电机；和用于浓度为50-98.5摩尔百分数的不纯氧产品从低压塔底部流出的出口，其特征在于，没有另外的压缩装置用来将所述的压缩空气的第一或第二流的压力提高到高于第一压力，双精馏塔还包括一个使高压塔与低压塔形成直接热交换关系的冷凝一再沸器。
10．如权利要求9所述的装置，还包括一个泵，用于从低压塔中排出液态氧产品并提高其压力；一个热交换器，用于使加压后的氧产品与压缩空气的第三流进行间接热交换而蒸发；和一个进一步的压缩机，用于使压缩空气的第三流在与蒸发氧产品发生热交换的上游将其压力提高。
CN99106020A 1998-04-09 1999-04-09 空气分离 Pending CN1236884A (zh)

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