CN1089427C - 用于生产低纯度氧的低温精馏系统 - Google Patents

用于生产低纯度氧的低温精馏系统 Download PDF

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CN1089427C
CN1089427C CN94107970A CN94107970A CN1089427C CN 1089427 C CN1089427 C CN 1089427C CN 94107970 A CN94107970 A CN 94107970A CN 94107970 A CN94107970 A CN 94107970A CN 1089427 C CN1089427 C CN 1089427C
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N·M·普罗泽
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Abstract

一种用于生产低纯氧的低温精馏系统，其中使用高压进料空气流使低压塔塔底物再沸，并且低压进料空气流直接加入高压塔。

Description

用于生产低纯度氧的低温精馏系统
一般地说，本发明涉及低温精馏，而更具体地说涉及低纯度氧的生产。
空气经低温精馏生产氧和氮是一种十分成熟的工业方法。典型地说，将进料空气置于一个双塔系统里进行分离，其中来自高压塔的氮基本馏份或塔顶蒸汽被用来使低压塔塔底氧液再沸。
目前，对于低纯氧的需求在诸如玻璃制造、炼钢以及能源生产等领域正日益增长。与双塔系统运转典型地产生的数量相比，低压塔的提馏段蒸汽蒸出量较少，且低压塔增浓段回流液量较少，这对于生产氧纯度小于98.5％(分子)的低纯氧是必须的。
因此，一般用于大量生产低纯度氧的低温精馏系统的情况是，其中处于高压塔压力的进料空气用于使低压塔塔底液再沸，然后再送入高压塔。使用空气代替氮来汽化低压塔底液降低了进料空气的压力要求，并使之可能产生恰好为低压塔提馏段所必要蒸出量，这样做的方法可以是向低压塔再沸器加入适宜量的空气，也可以借部分冷凝将全部进料空气的大部分冷凝。
虽然传统空气煮沸低温精馏系统已被用于有效地生产低纯度氧，但它的产生供给低压塔顶液氮回流的能力受到限制。造成这种情况的原因是，在类似于主空气进料压力的高压塔操作压力下组分相对挥发度较低。由于生成液氮回流能力降低而导致氧回收率降低，故耗能较高。
因此，本发明的一个目的是提供一种生产低纯度氧的低温精馏系统，其中低压塔的塔底液是借助与进料空气间接换热而再沸的，该系统与传统的空气煮沸系统相比以较低能量需求运转。
上述以及其他目的对于读过本公开的熟悉此项技术的人来说将变得很清楚，这些目的可以通过本发明而达到，其一个方面是：
一种生产低纯度氧的低温精馏方法，包括：
(A)提供一种低温精装置，它包括一个带塔顶冷凝器的第一塔和一个带有塔底再沸器的第二塔，所述第一塔操作压力超过第二塔的压力；
(B)提供第一进料空气流，其压力在39至100磅/平方英寸，绝压，(psia)，并使所述进料空气流通过上述塔底再沸器；
(C)将进料空气从塔底再沸器送至所述第一和第二塔中至少一个塔；
(D)提供压力低于第一进料空气流的第二进料空气流，并将所述第二进料空气流送入第一塔；
(E)从第二塔抽出低纯度氧并通过与上述第一进料空气流以及与上述第二进料空气流进行间接换热而提高上述所抽出的低纯度氧的温度；以及
(F)将生成的、温度提高后的低纯度氧做为产品回收。
本发明的另一方面是：
用于生产低纯氧的低温精馏设备，它包括：
(A)带塔顶冷凝器的第一塔和带塔底再沸器的第二塔；
(B)一台主换热器，以及用于将第一进料流送至主换热器以及由主换热器送到塔底再沸器的机构；
(C)用于将流体从塔底再沸器送至上述第一和第二塔中至少一塔的机构；
(D)用于将压力低于第一进料流的第二进料流送至主换热器，并从主换热器送至第一塔的机构；
(E)用于将产品流体从第二塔送至主换热器的机构；以及
(F)用于从主换热器回收产品流体的机构。
这里所用术语“低纯氧”意指一种含氧浓度为98.5％(分子)以及更低的流体。
这里所用术语“进料空气”意指一种主要含有氮和氧的混合物，例如空气。
这里所用术语“透平膨胀”和“透平膨胀机”分别指一种方法和设备，其作用是让高压气体流经一台透平以降低该气体的压力和温度并借此产生冷冻量。
这里所用的术语“塔”意指一种蒸馏或分馏塔或区，即一种接触塔或区，在其中液、汽两相逆流接触以实现流体混合物的分离，例如借助汽、液两相在一系列沿塔内纵向间隔安装的塔盘或塔板上，和/或在有规码放和/或无规堆放的填料元件上进行接触。关于蒸馏塔的进一步讨论，请参见“Chemical Engineer′s Handbook fifth edition”(《化学工程师手册·第五版》)，由R.H.Perry和C.H.Chilton编，McGraw-Hill Book Company出版，New York，Section 13，“连续蒸馏过程”。
汽、液接触分离过程依赖于各组分在蒸汽压方面的差别。高蒸汽压(易挥发或低沸点)组分将趋于在汽相中浓集，而低蒸汽压(难挥发或高沸点)组分将趋于在液相中浓集。部分冷凝是一种分离过程，其中通过蒸汽混合物的冷却达到在汽相中浓集易挥发组分，并从而在液相中具有较少的易挥发组分。精馏或连续蒸馏是一种分离过程，如同在借助对汽液相施以逆流处理而达到的那样，该过程把连续的部分蒸发与冷凝结合一体。汽、液相的逆流接触是绝热的且可包括相间的整体或微分接触。应用精馏原理分离混合物的分离过程的设备常常用几个互相通用的术语来称呼：精馏(rectification)塔、蒸馏(Distillation)塔、或分馏(Fractionation)塔。低温精馏是一种精馏过程，其至少一部分在150°K或更低温度下进行。
这里所使用的术语“间接换热”意指让两种流体流处于一种换热关系且不存在流体间互相的任何物理接触或掺混。
这里所用的术语“塔顶冷凝器”系指一种热交换装置，它由塔顶蒸汽产生沿塔下流液流。
这里所用术语“塔底再沸器”系指一种热交换装置，它由塔底液产生沿塔上升蒸汽。
图1是本发明一个较好具体实施方案的示意图，其中，低纯氧液用泵加至一个较高压力并在主换热器里蒸发。
图2是本发明另一较好具体实施方案的示意图，其中，低纯氧液用泵压至一个较高压力并在产品锅炉内蒸发。
图3是本发明又一个较好具体实施方案的示意图，其中，低纯氧蒸汽被从低压塔抽出并回收。
图4是本发明另外一个较好具体实施方案的示意图，其中，进料流在进透平膨胀之前被进一步压缩以便产生冷量。
本发明是一个改进的低温精馏系统，它使得可能在生产低纯氧时保持较传统系统低的进料压缩要求而同时仍旧维持高产率。本发明对于生产具有氧浓度在从70至98％(分子)的低纯氧尤为有利，但对于生产具有氧浓度从50至98.5％(分子)的低纯氧场合也非常有用。
下面结合附图详细说明本发明。现在参看图1，将进料空气1送入压缩机55进行压缩。从压缩机55抽出一股第一进料流2，其压力处于39-100磅/平方英寸·绝压(psia)范围之内。从压缩机55最终压缩机级上游抽出第二进料空气流5，这样就使得流5的压力低于流2且一般地在35至75psia之间。另一种可选择的方法是，采用两台单独压缩机把进料空气压缩到两种不同的压力。将两股流(流2和流5)进行冷却以除去压缩热并通过净化器56以除去高沸点杂质，例如水汽、二氧化碳和某些烃类。
随后将第一空气流通过第二塔60塔底再沸器63。一般地，通过塔底再沸器的第一进料空气流占总进料空气的10-50％。图1所示实施方案中，第一进料空气流4的部分流7，一般地占总进料空气的20-36％，通过压缩机57进一步压缩，再冷却以除去压缩热，继而通过主换热器58，在其中它借助与返回流间接换热至少部分地冷凝。生成的流16经阀76减压，并以流17送入相分离器69。从相分离器69出来的液流21被送入管经19，从相分离器69出来的蒸汽20被送入管线11，后面将对此进一步说明。
第一进料空气流4通过主换热器58，在其中，它通过与返回流间接换热而冷却。在图1所示的实施方案中，第一进料空气流4的部分流13，一般含有总进料空气量的5-30％，在仅仅部分地穿过主换热58之后被抽出，然后经透平膨胀机65进行透平膨胀以产生冷量，并通过发电机66产生电能。生成的流43随后被送入第二塔60，其操作压力在15-26psia范围。虽然通常较好地从第一进料空气流4抽出部分流用于透平膨胀，然而在一些情况下从第二进料空气流6或者从进一步压缩过的流8中抽取部分流送去透平膨胀可能是较好的。
第一进料空气流从主换热器58出来做为流10。在图1所示实例中，部分流33一般含有总进料空气的1-5％，将之送入换热器64，在其中通过与返回流间接换热而冷却，然后送入第二塔60。是否使用该股流是任选的。
第一进料空气的剩余流11与流20汇合，生成的合并流12被送去通过第二塔60的塔底再沸器63。在塔底再沸器内，至少有一些送入塔底再沸器的进料空气借助与第二塔塔底液间接换热而冷凝。一般地，通入塔底再沸器的进料空气全部靠这种间接换热而冷凝。
从塔底再沸器63出来的进料空气即流19与流21合并生成合并流22。出自塔底再沸器的进料空气的部分流23通过阀72并做为流24进入第一塔59，该塔操作压力超过第二塔60的压力，通常在35至75psia范围之内。出自塔底再沸器的进料空气的另一股部分流25在换热器64内部与流33合并生成合并流34，然后从换热器64出来变成流41，经阀73变成流42进入第二塔60。
第二进料空气流包含总进料空气的25-55％。净化第二进料空气流6通过主换热器58，在其中借助与返回流间接换热而冷却，随后以流14送入第一塔59。在图示实例中，主换热器表示成单台。应当理解，主换热器也可以包括多台。
在第一塔59内部，进料空气借助低温精馏被分离成富氮塔顶汽和富氧塔底液。富氮塔顶汽62进入第一塔59的塔顶冷凝器61，在其中，正如下面将更充分说明的，它与和一塔底物呈逆流而冷凝。如果需要的话，富氮塔顶汽62的部分流32可以通过主换热器58并做为含有氮浓度一般地在95-99.999％(分子)的氮产品52而加以回收。冷凝的富氮流80返回第一塔59做为回流。富氮流的部分流31部分地通过换热器64并以流37出来。如果需要的话，流37的部分流40可以做为产品液氮回收。剩余流38通过阀74并做为流39进入第二塔60做为回流。
富氧塔底液以流28从第一塔59抽出，部分地通过换热器64，并以流29出来。然后将该流通过阀75并以流30进入第一塔59的塔顶冷凝器61。在塔顶冷凝器61内富氧塔底液借助与上述冷凝的富氮汽间接换热而部分蒸发。产生的富氧汽和剩余的富氧液分别做为流35和36从塔顶冷凝器61进入第二塔60。
在第二塔60内，送入塔的流体借深冷精馏分离成氮塔顶汽和低纯氧。氮塔顶汽从第二塔60做为流45抽出，流经换热器64和58，然后从该系统中排出，如果需要的话，可作为流53回收，其氮浓度一般地在96-99.7％(分子)范围内。
低纯氧从第二塔抽出，借助与第一、第二进料空气间接换热而变暖(例如使之流经主换热器)并做为产品低纯氧回收。在图1所示实例中，低纯氧是做为液流4 7从第二塔60抽出的，而需要时，可取部分流51回收，产品为流51中的液态低纯氧。经由液体泵70将剩余部分48升至高压并将所得加压液流49蒸发，方法是将其流经主换热器58使之与上述进料空气流间接换热。部分流48的升压可以采用任何其他适当手段，例如通过重力头，从而不再需要液泵70。生成的汽流54做为低纯氧产品回收。
图2、3、和4表示本发明的其他较好实例。对于共同元件，图2、3和4中的数码与图1中的相对应，对于这些就不再详述。
在图2所示的实例中，将加压进料空气流16送入产品锅炉67，在其中借助与加压低纯氧液间接换热而至少部分地冷凝。生成的进料空气流81通过换热器77被冷却，再通过阀76，变为流17，送入相分离器69。在该实例中，所有液流47均通过液体泵70(若采用液体泵70)。生成的加压流49流经换热器7 7而变暖，并在产品锅炉67内部分地蒸发。从产品锅炉67排出蒸汽即流5 0，将之通过主换热器58借助与各进料流间接换热而变暖。从主换热器58回收产品低纯氧蒸汽54。液态低纯氧是从产品锅炉67做为流82回收的。
在图3所示的实例中，没有采用进一步加压的进料空气流。第一进料空气流11不经进一步添加而进入塔底再沸器63，并且在进料空气流19进入塔之前没有进一步的向其添加。由第二塔60抽出的液态低纯氧流47全部做为液体产品回收。低纯氧生产的大多数从第二塔60以蒸汽流83抽出，借助与诸进料空气流在主换热器58内间接换热变暖，并在流84中做为产品低纯氧回收。
在图4所示的实例中，另一股进料空气流90通过流经压缩机91被压缩，而该压缩机直接同透平膨胀机65相联结。该进一步压缩的流部分地流经主换热器58，然后流经透平膨胀机65透平膨胀，从而产生冷量并且也驱动压缩机91。经透平膨胀后形成的流88借流经换热器71而冷却，而后以流44送入第二塔60。从第二塔60抽出低纯氧蒸汽流83，流经换热器71而变暖，然后做为流86通过主换热器58，在其中通过与诸进料空气流间接换热而变暖。生成的蒸汽流87做为低纯氧产品被回收。
实施了根据图1所示实例的本发明计算机模拟，其结果载于表I，只是不包括液态产品回收亦没有从第一塔回收气态氮。给出这个例子的目的在于说得更清楚而绝不对本发明构成任何限制。表I中物料流编号与图1中是对应的。
                   表I
流号         标准化的流量         压力       组成
           (总空气流量＝100)     (PSIA)
14              37.5              43.4       空气
10              24.2              58.8       空气
16              25.8              188.3      空气
13              12.4              57.8       空气
12              23.3              58.8       空气
31              27.5              42.4   N2，含2.4％O2
45              78.9              18.1   N2，含1.2％O2
54              21.1              70.0   95％ 0，3％Ar，2％ N2在表I所报告的实例中，在可比氧回收率条件下，生产低纯氧时与传统空气沸腾低温精馏体系相比，单位能耗有所改进。
表II给出了本发明与先有技术单位功率比较，后者的例子取自美国专利号4,410,343和4,704,148所公开的循环，它们都被认为迄今低温低纯氧循环代表当前水平的好范例。表II中第一行代表图1所示发明的实例单位功率和氧回收率，第二行列出了图4所示本发明实例的这些数据，第三行为对应于美国专利4,704,148，第四行对应于美国专利4,410,343所公开的循环。此外还列出了以′343专利为基准每种循环单位功率降低百分率。
              表II
         单位功率         差别    氧回收率
    (千瓦·时/磅分子)     (％)     (％)
1         3.101           -7.5     95.49
2         3.167           -5.6     97.40
3         3.251           -3.0     95.95
4         3.353            0.0     98.30
正如可以从表II所载数据看到的，图1所示本发明实例与所有其他循环相比虽然氧回收率较低，但具有相当大的单位功耗的改进。正如熟悉此项技术的人所知晓的，当所有其他条件相同时，氧回收率高导致单位功耗降低，这是因为一定氧产品流量所需空气流量方面相应的减少所致。本发明功耗方面的改进是由于空气压缩机排量要求减少，而且尽管氧回收率较低情况仍然如此。低回收率是由于精馏塔内传质推动力(回流比)较低，而在这种情况下正标志是一个低纯氧生产的较合理工艺，因为低推动力被有效地转换为节省功耗。图4所示本发明实例具有比图1所示实例高的功耗，因为它不采用液氧泵送。由于其有回收率提高的特征，故该实例具有较高氧回收率。
一般地，在实施本发明时，第一进料空气流的压力会超过第二进料空气流至少5psia，尽管对于十分低的氧纯度来说这种压差将是较小的。由于采用双压力进料空气流，第一和第二塔被有效地解耦，从而使每只塔能够产生足够的回流和蒸出量而不至引起任何一座塔运行在高于必要的压力下。这就减小了总体进料压缩要求并有可能产生适量冷量而在较大设备参数范围及装置产品要求内不致危及产率。
尽管已结合某些较好实例对本发明做了详述，熟悉此项技术的人会认识到，在本权利要求之精神和范围内尚有其他实例。

Claims (10)

1.一种用于生产低纯氧的低温精馏方法，它包括：
(A)提供一种低温精馏装置，它包括一个带塔顶冷凝器的第一塔和一个带有塔底再沸器的第二塔，所述第一塔操作压力超过第二塔的压力；
(B)提供第一进料空气流，其压力在39至100磅/平方英寸，绝压，(psia)，并使所述进料空气流通过上述塔底再沸器；
(C)将进料空气从塔底再沸器送至所述第一和第二塔中至少一个塔；
(D)提供压力低于第一进料空气流的第二进料空气流，并将所述第二进料空气流送入第一塔；
(E)从第二塔抽出低纯度氧并通过与上述第一进料空气流以及与上述第二进料空气流进行间接换热而提高上述所抽出的低纯度氧的温度；以及
(F)将生成的、温度提高后的低纯度氧做为产品回收。
(G)在第一塔内生产富氮汽及富氧液，借助在塔顶冷凝器内与富氧液间接换热使富氮汽冷凝，将冷凝的富氮流体做为第一和第二塔中至少一塔的回流，并且将生成的富氧汽从塔顶冷凝器送至第二塔，其中所述生成的富氧汽并不通过一个减压步骤。
2.权利要求1的方法，其中低纯氧从第二塔以液体形式抽出、增加压力并蒸发再回收。
3.权利要求1的方法，其中低纯氧从第二塔以蒸汽形式抽出，且进一步包括从第二塔以液态抽出额外的低纯氧并将所抽出的液体做为附加低纯氧产品回收。
4.权利要求1的方法，进一步包括使具有高于第一进料空气流压力的另外一股进料空气流与来自第二塔的液态低纯氧间接换热。
5.权利要求1的方法，进一步包括从低温精馏装置回收含氮流体，该流体具有氮浓度超过95％(分子)。
6.权利要求1的方法，进一步包括将一股进料空气流透平膨胀以产生冷冻量并且将透平膨胀后的进料空气流送至第二塔。
7.一种用于生产低纯氧的低温精馏装置，它包括：
(A)一个带塔顶冷凝器的第一塔和一个带有塔底再沸器的第二塔；
(B)一台主换热器以及用于把第一进料流送入主换热器，并从主换热器送至塔底再沸器的机构；
(C)用于将流体从塔底再沸器送至第一和第二塔中至少一个的机构；
(D)用于将压力低于第一进料流的第二进料流送至主换热器并从主换热器送至第一塔的机构；
(E)用于把产品流体从第二塔送至主换热器的机构；以及
(F)用于从主换热器回收产品流体的机构。
(G)用于将流体从第一塔的上部送至塔顶冷凝器的机构，用于将流体从第一塔下部送至塔顶冷凝器的机构，用于将流体从塔顶冷凝器送入第一和第二塔中至少一个的机构以及将蒸汽从塔顶冷凝器送至第二塔而无需通过一个减压步骤的机构。
8.权利要求7的装置，其中用于将产品流体从第二塔送至主换热器的机构还包括一台液泵。
9.权利要求7的装置，进一步包括一台压缩机、用于将另外一股进料流送至主换热器并从主换热器送到第二塔的机构。
10.权利要求7的装置，进一步包括一台透平膨胀机、用于将一股液流送至透平膨胀机的机构以及将一股液流从透平膨胀机送至第二塔的机构。
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CA2128582A1 (en) 1995-01-23
JPH07305953A (ja) 1995-11-21
BR9402897A (pt) 1995-04-11
CN1102473A (zh) 1995-05-10
KR950003774A (ko) 1995-02-17
CA2128582C (en) 1998-08-25
DE69405829D1 (de) 1997-10-30
EP0635690A1 (en) 1995-01-25
EP0635690B1 (en) 1997-09-24
KR100225681B1 (ko) 1999-10-15
US5337570A (en) 1994-08-16
DE69405829T2 (de) 1998-04-09
ES2107720T3 (es) 1997-12-01

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