CN1112669A - 带混合产品蒸发器的低温精馏系统 - Google Patents

带混合产品蒸发器的低温精馏系统 Download PDF

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CN1112669A
CN1112669A CN95101920.1A CN95101920A CN1112669A CN 1112669 A CN1112669 A CN 1112669A CN 95101920 A CN95101920 A CN 95101920A CN 1112669 A CN1112669 A CN 1112669A
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tower
product
oxygen
equipment
evaporimeter
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C·S·拉福斯
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Praxair Technology Inc
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Abstract

一种低温空气分离系统，其中液体氧的气化是和 进料空气、氮的冷凝同步实现的，其中氮取自高压塔， 冷凝后又回流到高压塔顶部，因此供给添加回流液用 于空气分离，使得塔系统的运行有着较高的灵活性和 较低的能源消耗。

Description

本发明一般地涉及含氮、氧混合物如空气的低温精馏，且特别适用于通过低温精馏生产高压气体成品。
由于高压氧气在能源生产中煤的气化、氢的生产和炼钢等部分氧化过程中的广泛使用，使得高压氧气的需求在增加。氮气也常常用于这些过程中。
市售氧气的大量生产一般采用空气的低温精馏。生产高压氧气的一种途径是将低温精馏车间生产的成品氧气压缩。但这时的成品氧压缩机的投资费用和启动成品氧压缩机的运行费用都很高。生产高压氧气的另一种途径是让低温精馏车间在高压条件下运行，使所生产的氧气有着较高的初始压力，以降低或消除以后过程中的压缩要求。不幸的是，在高压条件下运行低温精馏车间会降低生产过程的效率。因为组份分离取决于各组份间的相对挥发性，它将随压力增加而降低。特别是在高压氮气也是低温精馏车间的所要产品时，因为从高压蒸馏塔中除去了作为产品的氮气，使得可以用作回流液的数量减少，从而降低了氧的回收。
为了解决这一问题，已经开发了用泵送或者水压方法压缩液态氧，然后使液态氧边气化、边与空气流进行热交换，使空气部分或全部冷凝的空气分离工艺。这时由于氧气成品压力的提高，使得压缩所需成本明显降低。
这种系统的一个问题是，空气分离车间高压塔的冷凝空气进口在塔底附近。这与空气作为气体进入高压塔底相比，冷凝空气实际上没有经历任何蒸馏作用。其结果是不能从液态空气中分离出氮，不象所有空气都作为气体进入高压塔的情况那样可以分离出氮并通常把它用作运行高压塔和低压塔时的液态氮回流液。由于高压塔的回流比例是固定的，取决于从塔顶收回的回流液纯度和塔中现有的平衡级数，在操作塔的上部时产生的回流液比较少，致使产品减少。
来自塔系统的氮气可以代替进料空气用于气化液态氧。然而这种安排常常导致所产生的回流液多个塔系统运行所需要的量，因而浪费了能源。再者，如果氮气取自低压塔，则为了得到具有产品蒸发所需压力的氮气，将导致相当高的能源和投资费用。
为此，本发明的目的是提供一种低温精馏系统，使得生产成品气体的效率，要比传统体系所能达到的结果有所提高，特别是在提高成本压力的场合。
本发明的另一个目的是提供一种低温精馏系统，其中所产生的回流液数量是可以调节至系统性能最优化，从而使生产气体的效率有所改进。
对于读过本材料的本领域的技术人员来说本发明显然能够达到以上目的和其他一些目的。其一方面是：一种使用包括第一塔和第二塔的塔系统，使进料空气经低温精馏生产氧气的方法，它包括：
（A）将进料空气经过渡冷却后通入第一塔中，使之在60～450磅/平方英寸的绝对压力范围内运行;
（B）通过低温精馏将第一塔中的进料空气分离成富氮蒸气和富氧液体;
（C）将富氧液体通入第二塔中并在低于第一塔的压力条件下运行;
（D）将富氮蒸气经过渡冷却后，将至少部分生成的富氮流体通入第一塔顶部;
（E）利用低温精馏将通入第二塔的流体分离成为富氮蒸气和富氧液体;
（F）将富氧液体和随后经过渡温热加压的富氧液体加压，通过与进料空气和富氮蒸气间接热交换，以实现步骤（A）和（D）中的过渡冷却并产生氧气;
（G）回收氧气作为产品。
本发明的另一方面是：一种用低温精馏分离进料空气的装置，包括：
（A）包括第一塔和第二塔的塔系统;
（B）产品蒸发器，将进料空气通入产品蒸发器以及从产品蒸发器通入第一塔的设备;
（C）将流体从第一塔通入产品蒸发器以及从产品蒸发器通入第一塔顶部的设备;
（D）从第二塔回收流体的设备和回收流体的加压设备;
（E）将上面所说的加压流体通入产品蒸发器的设备;以及
（F）从产品蒸发器回收气体成品的设备。
这里所说的“进料空气”，指主要含氮和氧的混合物，例如空气。
这里所说的“压缩机”，指增加气体压力的装置。
这里所说的“膨胀机”，指用于压缩气体因减压膨胀做功的装置。
这里所说的“塔”，指蒸馏或分馏塔或区，即液相和气相在其中逆流接触以便有效分离流体混合物的接触塔或区，例如，在塔内一系列垂直间隔安装的塔盘或塔板上，和/或在可以是结构填充的元件和/或自由填充元件上，蒸汽和液相的接触。对蒸馏塔的进一步讨论，可参阅R.H.Perry和C.H.Chilton主编的《化学工程师手册》（第5版，McGraw-Hill Book Company，New York）第13章，“连续蒸馏过程”，术语“双塔”指其上端与低压塔的下端有换热关系的高压塔。对双塔的进一步讨论，可参阅Ruheman的《气体分离》（Qxford University Press，1949）第7章，“市售空气分离”。
气液接触分离过程取决于各组份的蒸汽压的差别。高蒸气压（或高挥发性、低沸点）组份趋向于在气相中浓集，而低蒸气压（或低挥发性、高沸点）组份将趋向于在液相中浓集，部分冷凝是依靠气相混合物的冷却来使挥发性高的组份在气相中浓集，因而挥发性差的组份在液相中浓集的分离过程。精馏，或者连续蒸馏，是指利用气相和液相的逆流处理，将部分汽化和部分冷凝相继地结合在一起的分离过程。气相和液相的逆流接触是在绝热条件下进行的，且包括了两相之间的整体接触和微分接触。利用精馏原理分离混合物的分离过程的装置常常可互换名称为精馏塔、蒸馏塔或分馏塔。低温精馏要求精馏过程至少有一部分在绝对温度150°K或其以下运行。
这里所说的“间接热交换”，是指两种液体彼此没有任何物理接触或混合而实现的热交换。
这里所说的“氩塔”，是指处理含氩物料且得到的产品氩浓度高于料液氩浓度的塔，它还可以包括一个热交换器或者在塔上部的上方冷凝器。
这里所说的“液氧”，是指氧浓度至少是90%摩尔百分数的液体。
这里所说的“液氮”，是指氮浓度至少是99%摩尔百分数的液体。
这里所说的“过渡温热”，是指温热流体致使其中的液态汽化成气态，或者是在高于其临界压力的条件下流体的温热。
这里所说的“过渡冷却”，是指冷却流体致使其中的气态冷凝成液态，或者是在高于其临界压力的条件下流体的冷却。
这里所说的“塔系统”，是指进料空气在其中经低温精馏而分离的设施，它至少包括一个塔和一些辅助联接设备如泵、管道、阀门和热交换器。
这里所说的“低温冷却”，是指冷却到气液平衡温度以下。
这里所说的“上部”和“下部”，是分别指塔的中点以上和以下部分。
唯一草图是专门推荐用于将本发明中的低温精馏系统具体化的图示，进料空气、富氮气体和富氧气体在产品蒸发器中进行热交换之前先在该系统中分别加压。
本发明能够生产处于较高压力下的氧气，同时又避免或减少了成品气体的压缩程度，还对氮回流液的生成进行调节以改进系统的分离性能。
将参考示图详细描述本发明，现参考该图，进料空气100在通过空气主压缩机1加压至60～450磅/平方英寸，最好加至60～100磅/平方英寸的绝对压力。加压后的进料空气101随后被通入预纯化系统2中，以除去水蒸汽、二氧化碳、烃之类的高沸点杂质，得到清洁的进料空气102。其中一部分清洁的进料空气175通过空气增压压缩机3，加压至100～200磅/平方英寸，最好加压至120～180磅/平方英寸的绝对压力，得到的压缩空气流103随后依次在主热交换器的温热区7和冷却区8冷却，一般来说，空气流103将包含最终进入塔系统的进料空气100总量的大约5～30%。
压缩空气流103通入产品蒸发器12中，在那里和过渡温热的液态氧通过间接热交换实现了自身的过渡冷却，详见以后的讨论。由此得到的冷凝空气流124通过低温冷却器13实现低温冷却，低温空气流126通过节流阀20的节流之后作为物流127进入第一塔15的下部，在实施本发明时，低温冷却器13的使用属于任选范围。第一塔15是比塔系统中具有较高压力的塔，在60～450磅/平方英寸，最好在60～100磅/平方英寸的绝对压力范围内运行。
另一部分清洁的进料空气176通过空气增压压缩机4加压，得到压缩空气流105，随后在主热交换器的温热区7冷却，由此得到的空气流106通过膨胀机5的膨胀，形成膨胀气流107进入第二塔14。第二塔14是双塔系统中的低压塔，可在低于高压塔15的压力条件下运行，一般在12～125磅/平方英寸的绝对压力范围。建议如图所示，将膨胀机5直接和空气增压压缩机4相连或配对，使得通过膨胀机5膨胀空气物料释放的能量可用来直接驱动空气压缩机4。
第三部分进料空气流104，通过主热交换器的温热区7和冷却区8的冷却，形成物流109进入第一塔15。在第一塔15中进料空气因低温精馏而分离成富氮蒸气和富氧液体。将富氧液体从第一塔15的下部收回为物流112，在热交换器10中低温冷却，并作为物流113通入第二塔14。富氮蒸气作为物流177通入主冷凝器16，在其中和沸腾塔14底部液体进行间接热交换而被冷凝。得到的富氮冷凝液178随后回到第一塔15中作为回流液。富氮液体的一部分151通过热交换器11得到低温冷却，所产生的低温物流115进入第二塔的上部作为回流液。
富氮蒸气的一部分114来自第一塔15的上部，它通过热交换器7和8，温热到周围环境温度。由此得到的富氮蒸气流139通过压缩机6，通常压缩到100～2000磅/平方英寸的绝对压力，形成的压缩物流140再通过热交换器7和8冷却，然后作为物流138通入产品蒸发器12。在产品蒸发器中，通过与过渡温热的液氧进行间接热交换，富氮蒸气被过渡冷却。由此形成的富氮液体123可任选地通过热交换器13得到低温冷却，冷却物流125经节流阀19节流后作为物流128进入第一塔15的顶部用作回流液。所谓“第一塔的顶部”是指来自主冷凝器16的冷凝液流178进入第一塔的位置或其以上位置。附图所示的实施方案中所示，物流128和物流178相通，共同形成回流液进入第一塔15和第二塔14。控制通入产品蒸发器中的富氮蒸气量，就能调节所生成的回流液体量，使得精馏系统的运行性能达到最优化。
如果需要，可以从产品蒸发器的上游物流138中取出一部分富氮蒸气129，在热交换器9中和回流液流发生间接热交换将其冷凝。由此生成的物流130随后通过阀门18进入塔系统，例如随物流128进入即可。如果需要，也可从物流128中取出一部分成为物流179，以便回收为液态氮成品。
进入第二塔14的液体在其中经低温精馏分离成富氮蒸气和富氧液体。从第二塔14中作为物流117提取出富氮蒸气，并在热交换器11、10、9、8和7中因间接热交换而被温热，作为物流143离开系统，它可以作为氮气产品全部地或部分地回收，其纯度至少是99%（摩尔）。废液流118从塔14中在回流液流115的入口以下位置处收回，经热交换器11、10、9、8和7，作为物流142从系统中除去，以达到调节目的。
富氧液体即液态氧，从第二塔14的下部收回，成为物流119，优选可以通过例如液体泵17，使物流119加压到20～1000磅/平方英寸的绝对压力范围。加压的富氧液体流120通过热交换器13加温大致达到它的饱和温度，成为物流121进入产品蒸发器12。如果生产低压氧，从效率的观点来看，热交换器13并不重要，可以取消。在产品蒸发器12中，富氧液体通过和进料空气以及富氮蒸气的间接热交换得到以过渡温热，同时使这两种流体过渡冷却。在产品蒸发器12中因气化生成的氧气产物作为物流122从产品蒸发器12中收回，通过热交换器7和8而被温热，尤其是也使进来的进料空气得以冷却，随后全部或部分地作为氧气产品回收形成物流141，它的氧浓度至少是90%（摩尔），且压力最高可达1000磅/平方英寸的绝对压力水平。
本发明实施时可以在塔系统中包括一氩塔。这种系统在图中以简化的形式加以说明。使用氩塔时，来自第二塔14的物流180主要包含氧和氩，作为料液进入氩塔22，该氩塔包括一个顶部冷凝器21。料液在氩塔22中因低温精馏分离成高富氩蒸气和高富氧液体。高富氧液体作为物流181返回入第二塔14，使用氩塔时，富氧液体流113不如图上所示那样直接进入第二塔14，而是进入氩塔顶部的冷凝器21，在其中部分气化，随后分别作为蒸气流182和液体流183进入塔14。富氧液体在顶部冷凝器21中通过和富氩蒸气的间接热交换而被部分气化，而富氩蒸气被冷凝并用于氩塔22作为回流液。高富氩流体以气体或液体形式从塔22中回收成分物流184，它是含氩浓度至少是95%（摩尔）的粗氩产品。
在此，本发明采用了混合产品蒸发器装置，富氧流体在其中气化的同时也使来自高压塔的富氮蒸气和进料空气实现过渡冷却，这和传统的低温精馏车间中相对于一种或多种操作物流液态氧的气化相比，低温精馏车间运行的回收效率有所改进，特别是本发明比那些利用进料空气和来自低压塔的氮使氧气化或过渡温热的系统有利。因为从低压塔取氮就相当于在产品蒸发器和温度范围过高的低压塔顶部之间运行着一个加热泵。与之相反，实施本发明时，氮取自高温塔，并将过渡冷却了的氮通入高压塔顶部，产生足够的两个塔使用的回流液，这在降低能源消耗方面取得良好结果。
虽然在详细描述本发明时，参考了特别优选的实施方案，但本领域的技术人员会认识到，只要按此精神和遵照权利要求中的范围，本发明也存在其他实施方案。例如，热变换器9，10和11可以合成一个热变换器，热变换器7和8也可以合为一个单元。为了简化各种各样的主热变换器的音路分配，也可以利用隔离芯将有些物流相互隔开。再如缩机3和6也可以合成一个机器。

Claims (7)

1、一种使用包括第一塔和第二塔的塔系统，使进料空气经低温精馏生产氧气的方法，它包括：
(A)将进料空气经过渡冷却后通入第一塔中，使之在60～450磅/平方英寸的绝对压力范围内运行；
(B)通过低温精馏将第一塔中的进料空气分离成富氮蒸气和富氧液体；
(C)将富氧液体通入第二塔中并在低于第一塔的压力条件下运行；
(D)将富氮蒸气经过渡冷却后，将至少部分生成的富氮流体通入第一塔顶部；
(E)利用低温精馏将通入第二塔的流体分离成为富氮蒸气和富氧液体；
(F)将富氧液体和随后经过渡温热加压的富氧液体加压，通过与进料空气和富氮蒸气间接热交换，以实现步骤(A)和(D)中的过渡冷却并产生氧气；
(G)回收氧气作为产品。
2、按照权利要求1的方法，其中进料空气在步骤（A）中实现过滤冷却之前要先加压。
3、按照权利要求1的方法，其中富氮蒸气在步骤（D）中实现过渡冷却之前要先加压。
4、一种用低温精馏分离进料空气的装置，包括：
（A）包括第一塔和第二塔的塔系统;
（B）产品蒸发器，将进料空气通入产品蒸发器以及从产品蒸发器通入第一塔的设备;
（C）将流体从第一塔通入产品蒸发器以及从产品蒸发器通入第一塔顶部的设备;
（D）从第二塔回收流体的设备和回收流体的加压设备;
（E）将来自第二塔的流体通入产品蒸发器的设备;
（F）从产品蒸发器中回收气体成品的设备。
5、按照权利要求4的装置，其中将进料空气通入产品蒸发器的设备包括一个压缩机。
6、按照权利要求4的装置，其中将取自第一塔的流体通入产品蒸发器的设备包括一个压缩机。
7、按照权利要求4的装置，其中使用液体泵作为加压设备。
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