CN1162675C - 低温精馏塔的操作方法 - Google Patents

低温精馏塔的操作方法 Download PDF

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CN1162675C
CN1162675C CNB011049448A CN01104944A CN1162675C CN 1162675 C CN1162675 C CN 1162675C CN B011049448 A CNB011049448 A CN B011049448A CN 01104944 A CN01104944 A CN 01104944A CN 1162675 C CN1162675 C CN 1162675C
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J・F・比林哈姆
J·F·比林哈姆
赛勒尔
D·M·赛勒尔
洛克特
M·J·洛克特
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Abstract

一种操作低温精馏塔以通过低温精馏分离空气各组分的方法,其中,向上流过塔的蒸汽以通过每英尺高度的填料所产生的塔内压降至少为0.7英寸水柱的流速,流经具有规定结构的填料板,所述结构的底部结构与中部结构不同,而与顶部结构相同。该塔可以在其设计负荷之上操作,且不发生液泛。

Description

低温精馏塔的操作方法
本发明一般涉及将空气分离为各种组分的空气低温精馏,并且特别适用于以更好的性能对低温精馏塔进行精馏操作。
在超出设计的能力下运行空分装置以从中生产额外的产品是很理想的,只要这种超负荷运行能经济地进行。
空分装置的大部分单元可以被设计或改造来接受提高了的流量,例如:上游鼓风机能够被用于提高压缩机的能力;只要换热器能承受提高了的压降,换热器就可以在增加了的流量下运行;只要能避免吸附剂颗粒的流态化,空气预净化器的能力也能通过在升高的压差下操作而得以提高。但是,更为困难的是提高空分装置精馏塔的能力,因为精馏塔的能力受制于液泛现象。加工设备里存在垂直逆向的双相流,只要流体的流速超过了设备的能力时,设备中就随时发生液泛。在填料塔和塔板塔中达到液泛的特征都是压降的急速提高、分离能力的丧失以及操作的不稳定。当试图将空分装置的能力提高至超过设计的能力时,精馏塔内液泡的发生是通常所遇到的限制瓶颈。
一般来说,业已非常明确证实的一点是,精馏塔的能力可以通过改变塔压而被提高。升高精馏塔的压力能提高蒸汽的密度从而使蒸汽的质量流速提高。但是,升高其压力,使相对挥发度降低,结果使精馏分离更加困难。蒸汽质量流速能力的提高,对填料塔和塔板塔分别是塔操作压力的0.4和0.5次方。
这种解决液泛问题方法的缺点是,塔操作压力的提高基本上转化成为主空气压缩机的出口压力升高以及用电成本的升高。对于双塔装置的前塔,即低压塔,升高压力的方法特别不利,由于氧气和氮气两者蒸汽压/温度关系的差别,在通常的情况下,压力升高传到冷凝器和再沸器时,一定会是塔压升高的三倍。
解决此问题的办法是提高通过塔的流速,使其尽量超过设计值,但绝不能达到液泛点。典型的填料塔是按液泛点的80%左右设计的。但不幸的是,采用传统结构的填料塔时,流速只能提高到比设计值稍高一点之处,因为压降波动会如此之大,导致塔的操作变得不稳定。
因此,本发明的一个目的是提供用于低温精馏塔,以进行空气组分分离的方法,该方法在避免液泛的同时,可使其操作能力提高。
此公开内容一经本领域的技术人员阅读,本发明要达到的上述目的和其他的目的即显而易见,本发明是一种操作低温精馏塔的方法,该方法包括:
(A)使含有一种较易挥发空气组分与一种较难挥发空气组分的混合物通入一个塔,该塔包括具有底部、中部和顶部的填料板的一定高度的填料,该填料板每块在底部的结构与中部的结构不同,而和顶部的结构相同;
(B)在该塔中进行低温精馏,其中,蒸汽向上流过一定高度的填料板,液体向下流过该高度的填料板,由此,该较易挥发组分浓缩在向上流动的蒸汽里,该较难挥发组分浓缩在向下流动的液体里;
(C)使向上流过该填料高度的气体在塔里以一定的流速通过,以便在塔内达到每英尺(30.48cm)的填料高度有至少0.7英寸(1.78cm)水柱的压降;
(D)将较易挥发的组分从塔的上部抽出,同时将较难挥发的组分从塔的下部抽出。
在此所用的名称“塔”,是指一种蒸馏或分馏塔或蒸馏或分馏区,即液相和汽相在其中逆流接触以实现流体混合物分离的接触塔或接触区,例如,将液相和汽相在填料单元上接触。对蒸馏塔的进一步讨论,请参由纽约McGraw-Hill Book Company公司出版,由R.H.Perry和C.H.Chilton编辑的化学工程师手册第五版,由B.D.Smith等撰写的第13部分第13-3页“连续蒸馏方法”。汽液接触分离的工艺方法依靠的是各组分蒸汽压的不同。蒸汽压高的组分(即较易挥发或低沸点的组分)将倾向于浓缩在汽相,而蒸汽压低的组分(即较难挥发或高沸点的组分)将倾向于浓缩在液相。蒸馏就是采用加热液体混合物,使较易挥发组分浓缩在汽相,较难挥发组分浓缩在液相的分离方法。部分冷凝就是采用冷却蒸汽混合物,使较易挥发组分浓缩在汽相,较难挥发组分浓缩在液相的分离方法。而精馏或连续蒸馏则是通过汽液相逆流处理,将所获的连续的部分气化和部分冷凝相结合的分离方法。该蒸汽和液体两相逆流接触可以是绝热的或非绝热的,而且可以包括相之间的积分式(分段的)或微分式(连续的)的接触。采用精馏原理分离混合物的分离工艺装置,常可被互换地称为精馏塔、蒸馏塔或分馏塔等。低温精馏是至少有一部分在低于150°K的温度下进行的精馏过程。
本发明所用的术语“填料”,是指任何预先被确定了结构、尺寸和形状的实心或空心物体,该物体被用作塔的内部元件,以向液体提供两相逆流时在汽液界面能进行传质的表面。
本发明所用的术语“结构填料”,是指沿对角线走向的横向波纹填料,该填料中的各单元之间及每个单元与塔的轴线之间有特定的取向。
本发明所用的名称“塔的上部”和“塔的下部”,分别是指塔的中点以上和以下的部分。
图1是可能被用来实施本发明的低温精馏装置的流程示意图。
图2A和2B分别描绘了可用于实施本发明结构填料板的一个实施方案的透视图和侧面图,其中填料板底部和顶部的波纹皱褶高度被降至零。
图3A和3B分别描绘了可用于实施本发明时结构填料板实施方案的结构透视图和侧面图,其中填料板底部和顶部的波纹皱褶高度与中部的波纹皱褶高度相比有所降低,但不等于零。
图4A和4B分别描绘了另一种实施本发明时可用的结构填料板实施方案结构的透视图和侧面图,其中填料板底部和顶部的波纹比中部的波纹按更陡的角度形成皱褶。
人们已经知道,通过使填料板底部板间气或汽流阻力小于较高部位板间气的阻力,横向波纹结构填料的水力学能力可以被提高。本发明包括一种发现,即在塔中采用其底部结构与中部结构不同而和顶部结构相同的结构填料板时,同时使该塔在压降为每英尺(30.48cm)高填料超过0.7英寸(1.78cm)水柱的条件下运行,该塔就可以在高于设计点的负荷操作,此时,塔的传质性能得到了改进,并且操作稳定同时避免液泛。
依据附图本发明进行详细叙述。图1描述了一种可在其中实施本发明的低温精馏装置实施方案。所述的该特定装置包括一个双塔系统和一个氩侧塔。
参照图1,物流1即主要包含氮、氧和氩的空气进料,通常在压缩机2中被压缩,其压缩热通过冷却器3被冷却。压缩过的进料空气再通过净化器4,除去水蒸汽、二氧化碳和烃类等高沸点杂质,该净化器通常是变温或变压吸附型的净化器。然后,干净的压缩进料空气5在主换热器6中与返回的物流间接换热而被冷却。在图1所描述的实施方案中,进料空气5的第一部分7通过增压压缩机8被进一步压缩,进料空气的第二部分9通过增压压缩机10被进一步压缩,所得的被进一步压缩的两个部分11和12及其余的压缩进料空气50,再通过主换热器6冷却以产生被压缩的干净和冷却的进料空气,该进料空气分别为51、52和53三股。为了产生下游低温精馏所需的冷冻量,物流52通过透平膨胀机55透平膨胀形成流体54,然后通入低压塔24。而进料空气51和53均通入高压塔21。
在高压塔21中,进料空气经低温精馏被分离成富氮的蒸汽和富氧的液体。富氮的蒸汽流22通入主冷凝器23,在此通过与低压塔24塔底液间接换热被冷凝形成富氮液25。部分的富氮液25以流体26返回到高压塔21作为回流,富氮液25的另一部分以流体27在换热器6中过冷后通入低压塔24作为回流。从高压塔21下部流出的是富氧液28,其中分出的一股物流56进氩塔塔顶冷凝器29经与富氩蒸汽间接换热后汽化,然后形成的富氧流体30,如图所示,从顶部冷凝器29出来进入低压塔24。另一股富氧液57直接流入低压塔24。
一股包含氧和氩的流体31从低压塔24流出进入氩塔32,在此经低温精馏被分成富氩蒸汽和富氧液,富氧流体33返回到低压塔24,富氩蒸汽34进入塔顶冷凝器29,在此经与前述的汽化富氧液体之间的间接换热而被冷凝下来。所得富氩液体35返回氩塔32作为其回流。从氩塔32的上部出来的富氩流体36,以蒸汽和/或液体混合物的形式,作为产品被回收。
低压塔24在低于高压塔21的压力下操作,在低压塔24中各种原料进塔后经低温精馏被分离成富氮流体和富氧流体。富氮流体从低压塔24上部以汽流37抽出,流经主换热器6加热后被回收,成为氮产品38。从低压塔24上部抽出的一股废料58,通过换热器6加热后成为流体59从系统中排出。富氧流体从低压塔24的下部以汽态和/或液态抽出。如果以液态抽出,则富氧液体可以用泵加至高压后汽化,汽化既可在分离产品蒸发器中进行也可在主换热器6中进行,然后作为高压氧产品回收。在图1所描述的实施方案中,富氧流体39是从低压塔24抽出的液流,经液体泵60加到高压,再通过主换热器6汽化,然后作为产品40被回收。一部分液氧61可以在液态下被回收。
至少有一个塔包含垂直堆放的多个结构填料层或填料方块。每一层或每一方块都包含垂直取向的结构填料板,其波纹与垂直轴线成一定角度。安放填料板时要使一片板的波纹和与其相邻的另一片的波纹方向相反。各填料层的高度通常为6到12英寸(15.24-30.48cm)。为了加强混合作用,相邻的填料层围绕着垂直轴线交替地排列。塔的全部填料床包含多个填料层,填料层数取决于实现分离所要求的填料总高度。填料波纹的特征在于其皱褶的高度。波纹的形状可以是尖的(锯齿),也可以是圆的(正弦)。填料板在波纹的高峰和低谷处的接触点上相互接触。
一个或多个塔包含一定高度的填料,其高度至少要贯穿部分塔高,优选的是,要贯穿全部塔高,在此,每块填料板的底部结构都与其中部的结构不同,而与上部的结构相同。图2、图3和图4描述了这种填料的三个实施例。在本发明的实施中,底部结构占填料板高度下部最高达40%,但典型的是,底部结构占填料板高度下部的10%,更典型的是,底部结构占填料板高度下部的5%。在本发明的实施中,顶部结构占填料板高度上部最高达40%,但典型的是,顶部结构占填料板高度上部的10%,更典型的是,顶部结构占填料板高度上部的5%。在本发明的实施中,如图2、图3和图4所示,最优选的是,填料板底部的尺寸与其顶部的尺寸一样,以使填料板以其垂直中点为对称。也就是说,在本发明的实施中,最优选的是,填料板的上部是其下部的镜象。这样的安排有以下的优点:因为其顶部与底部是对等的,填料块可以颠倒放置,而塔的能力不会受损失。这就消除了在填料安装时搞错方向的可能性。
在塔内填料板是垂直放置的,并以横跨塔直径的方向互相连接,形成填料方块或填料层。另一方块或另一层这样的填料放在第一层的顶上,以此方式,一直放到用填料将塔填满为止。在本发明的实施中,最优选的是,每个方块填料的顶边都处于同一水平面上,使得每方块填料具有一个平坦的顶部。
在实验过程中,已注意到传统的填料在比正常的压降设计点0.7英寸(1.78cm)水柱高的压降下操作时,运行不稳定,在此时,任何汽流速率的波动及塔压降的波动,都会引起塔的液泛趋势。此时塔的操作非常困难,需要特别精心以避免液泛。与此相反,应当相信,采用本发明,在每英尺(30.48cm)高度填料0.7英寸(1.78cm)水柱压降下操作是稳定的。小的汽流速率波动对塔的操作没有影响,而且该塔有可能在高达每英尺(30.48cm)高度填料3英寸(7.62cm)水柱的压降下进行操作;而采用传统的填料,即使非常精心,也不可能在超过每英尺(30.48cm)高度填料2英寸(5.08cm)水柱的压降下操作。
低温空气分离的特点在于如氧-氩体系的低相对挥发度和接近最低回流比下的操作。为了避免浓度恒定区域的出现和分离效果的下降,必须始终将L和V的比值,即液体和蒸汽摩尔流速之比,保持在设计值。为了保持每一阶段的L/V比例,蒸汽流速的波动必须要用等量的液体流速变化与之协调。但是当蒸汽流速变化引起液体滞流量剧烈变化时,在每一阶段要建立新的液体流速时会有滞后现象发生,因为液体的下行量中一定会有一部分用于升高或降低每一段的液体滞留量。于是L/V比会变得偏离设计值,结果使分离效果变差。预期,传统填料的液体滞留量随蒸汽流速变化而产生的变化要比本发明填料的相应变化大得多。故此,装有本发明类型填料的塔的操作会更加稳定,并易于控制。
在空气分离装置的蒸馏塔中,各段与段之间,甚至在某段的全部区域内,蒸汽流速(以及液体流速)都会不同。其结果是,即使在负荷最高的一个或多个方块填料上压降超过了每英尺(30.48cm)高度填料0.7英寸(1.78cm)水柱的压降,塔的总压降或某段填料的压降还可能低于此值。也就是说,是局部的压降而不是总压降在决定着塔的稳定性,这一点在本发明中是重要的。
现在,通过实施本发明,人们就可以在高于设计点的条件下操作低温精馏塔,以分离空气的各组分,而同时避免液泛。虽然,已用一些优选的实施方案为参考,对本发明进行了详述,但是本领域的技术人员应意识到,还会有其他的实施方案仍包括在本发明权利要求的精神实质和范围之中。

Claims (10)

1.一种操作低温精馏塔的方法,该方法包括:
(A)将一种含有一个较易挥发的空气组分与一个较难挥发的空气组分的混合物通入一个塔,该塔内装有一定高度的填料,该填料包括具有底部、中部和顶部的填料板,每块填料板在底部的结构与填料板在中部的结构不同,而和填料板在顶部的结构相同;
(B)在该塔中进行低温精馏,其中,蒸汽向上流过该高度的填料板,同时,液体向下流过该高度的填料板,由此,该较易挥发组分浓缩在向上流动的蒸汽里,该较难挥发组分浓缩在向下流动的液体里;
(C)使向上流过填料的蒸汽在塔内以一定的流速通过,以便在塔内达到每30.48cm高度填料有至少1.78cm水柱的压降;和
(D)将较易挥发的组分从塔的上部抽出,将较难挥发的组分从塔的下部抽出。
2.权利要求1的方法,其中的较易挥发的组分是氮,而较难挥发的组分是氧。
3.权利要求1的方法,其中的较易挥发的组分是氩,而较难挥发的组分是氧。
4.权利要求1方法,其中所述的结构差别包括每块填料板底部和顶部的波纹皱褶高度比每块填料板中部的波纹皱褶高度低。
5.权利要求4方法,其中每块填料板底部和顶部的波纹皱褶高度等于零。
6.权利要求1的方法,其中所述的结构差别包括每块填料板底部和顶部的波纹与每块填料板中部的波纹相比具有一个更陡的角度。
7.权利要求1的方法,其中每块板的底部占每块板高度下部最高达40%。
8.权利要求1的方法,其中每块板的顶部占每块板高度上部最高达40%。
9.权利要求1的方法,其中每块板的底部的尺寸与其顶部的尺寸一样,以使填料板以其垂直中点为对称。
10.权利要求的1方法,其中的填料板排列在一起组成一个或多个方块,以形成一种填料高度,而且,其中每一方块填料板中各填料块的顶边都处于同一水平面上,使得每块填料具有一个平坦的顶部。
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BR0100833A (pt) 2001-10-30
EP1128144B1 (en) 2006-07-12
EP1128144A1 (en) 2001-08-29
US6212907B1 (en) 2001-04-10
DE60121379T2 (de) 2007-07-12
CN1322933A (zh) 2001-11-21
DE60121379D1 (de) 2006-08-24
CA2338641C (en) 2004-01-06
CA2338641A1 (en) 2001-08-23

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