文献翻译-分批冲孔模板精馏塔的操控

英文翻译 Chinese J of Chem Eng ， 9(2)141144(2001) Operation of a Batch Stripping Distillation Column xu Songlin(许松林 ) ， Jose Espinosab， Hector E Salomoneb and Oscar A Iribarrenb a National Engineering Research Center for Distillation Technology， Tianjin University, Tianjin 300072， China b Institute for Development and Design INGAR , Conicet， Santa Fe， Argentina Abstract A stripping batch distillation column is preferred when the amount of the light component in the feed is small and the products are to be recovered at high purity The operation modes of a batch stripping are believed to be the same as those of a rectifier However the control system of a stripper is different In this paper， we explore three different control methods with Hysys(Hyprotech Ltd 1997)for a batch stripper The main difference is the control scheme for reboiler liquid level： (a)controlled by reflux flow； (b)controlled by reboiler heat duty； (c)controlled by bottom product flow The main characteristics of operating a batch stripper with different control scheme are presented in this paper Guidelines axe provided for the startup of a batch stripper， the effects of some control tuning parameters on the column performance are discussed Key words batch stripper control Operation 1 INTRODUCTON Batch process is becoming more popular as chemical process industries move toward manufacturing fine and specialty chemicals， where flexibility is a key issue due to the frequent change of product demand Batch distillation columns are inherently flexible， as a single 1column call separate many different components from a multicomponent feed Thus the use of batch distillation is becoming more important for the seperation and purification of highvalue chemicalsin many chemical ,food， and pharmaceutical industries Traditionally the most popular kind of batch distillation column is the so-caled rectilying column which has a large reboiler， to which al the feed is charged an different products are removed from the top There are three ways to operate a rectifying column2 They are： (1)constant reflux and variable distillate composition， (2)variable reflux an d constant distillate composition of key component， (3)optimal reflux policy which trades of(1)and(2)and is based on the most profitable operation Batch stripping column is opposed to a batch rectifier It has its storage vessel at the top and the products leave the column at the bottom A stripping batch distilation column is preferred when the amount of the light component in the feed is small and the products are to be recovered at high purity4,5 The operation modes of a batch stripping are believed to be the same as those of a rectifier However the control system of a stripper is different In this paper， we explore three different control methods with Hysys(Hyprotech Ltd 1997)for a batch stripper The control schemes are shown in Fig 1 The main difference is the control scheme for reboiler liquid level： (a)controlled by reflux flow， (b)controlled by reboiler heat duty， (c)controled by bottom product flow The main characterics of operating a batch stripper with different control scheme are presented in this paper Guidlines are provided for the startup and the effect of so e control turning parameters on the column performance are discussed. 2 EXPERIMENTAL APPARTUS FOR THE SIMULATIONS The experimental apparatus in the simulations is the same for the three control schemes The stripping column has a reboiler， a condenser and 15 trays The volumes of the reboiler and the condenser are 2m3 and 5m3， respectively The diameter of the column is 0.5 m The feed is the mixture of methanol(0.05)and ethanol (0 95)(mole fraction) The liquid percent level set point for the reboiler is 50 and the mixture takes 80 of the whole volume of the condenser At the beginning， the trays are dry startup， but the reboiler is charged with the same mixture to the liquid level set point The specification of bottom product ethanol is 0 999 All the simulated experimental procedures are that the stripper is started up till the specification of the heavy key composition is reached， then the bottom product valve is opened so that the product leavesthe column， the product valve is shut down when the product composition declines to the specification 3 RESULTS AND DISCUSSION 3 1 Control reboiler Hquid level by reflux flow In this control scheme【 Fig 1(a)】 ， the reboiler liquid percent level is controlled autom atically by reflux flow， the reboiler heat input and bottom product flow are controled manualy At the beginning， the reboiler heat in put is set fixed The reboiler liquid level declines as the light com ponent is vaporized Which will cause reflux flow down the reboiler automatically The control of the reboiler liquid level is reversible So when the reboiler liquid level is higher， there wil be less reflux flow an d vice versa. When the composition of heavy key component gets to its specification， the bottom product flow valve is opened； once it declines to the specification， the bottom product flow valve is shut down manualy In this case， when ethan ol corn -position reaches 0 999， the bottom product flow valve is opened ， when ethan l is less than 0 999 the bottom product flow valve is shut down The dynamic process of this operation mode is shown in Fig 2 There is a time lag between the reboiler liquid level an d reflux flow ， especially when the number of stages is large In order to get a stable reboiler liquid level control during the whole operation， two aspects should be considered carefully 0ne is to use an appropriate reflux valve If the reflux valve is oversized， the reboiler liquid level controller wil get more reflux flow to the reboiler than the set point when the liquid level declines Then the reflux flow valve will be closed This makes the reboiler liquid level fluctuate frequently One case is shown in Fig 3 In this situation the heavy key component composition in the bottom is unstable The other aspect is that the tuning parameter of the reboiler liquid level should be chosen appropriately when a proportional only bottom level controler is employed The proportional gain of the controler should be between PK4 0and 8 0 If is too small， it is difficult to get a stable reboiler liquid level PKcontro1 Fig 4 shows the relation between reboiler liquid percent level and for the same PKreboiler duty From Fig 4 it is obvious that if is less than 4 0 the liqui d percent level in PKthe reboiler is far away from the set point level 50 If is between 4 0 and 8 0， the Pliquid level in the reboiler is near the set point 3 2 Control reboiler liquid level by reboiler heat input In this control scheme Fig 1(b)】 ， the reboiler liquid level is controlled by reboiler duty automatically,reflux and bottom products flow are controlled manually At the beginning， the reflux flow valve is opened to a fixed value Reboiler liquid level increases， which will cause heat input to the reboiler The action of the reboiler liquid level controler is direct， which means that the higher the reboiler liquid level， the more the heat input to the reboiler and vice versa When the com position of the heavy key component in the reboiler gets to its specification the bottom product flow valve is opened manuly When the heavy key component com position decreases to 0 999， the valves for bottom product an d reflux flow are shut down manually Fig 5 shows the dynamic process of this operation mode It is obvious that the boil up mass flow and the liquid levels of condenser and reboiler are fluxed at the startup of the operation This is due to the dynamic responsiveness of reboiler heat input to the liquid level controller 3 3 Control reboiler Hquid level by bottom product flow The reboiler liquid level is controled by bottom product flow in this control schemeFig 1(c)】 This scheme is similar to the third control mode for a rectifier in which the reboil ratio is variable In order to get the bottom product specification， a total reboil process should be established at the beginning of the operation The action of the reboiler liquid level controller is direct， which means that the higher the liquid level， the more the bottom product flow and vice versa Figure 6(b)shows that at the startup of this operation， the liquid levels in both reboiler and condenser are oscillated， since it is difficult to meet the requirement for the total reboil at the beginning of the operation， for the reflux flow and reboiler heat input are operated manually 4 CONCLUSION The dynamic simulation with Hysys for the operation of a batch stripping distillation column indicates the main characterics of this kind of column， in which three different control schemes are employed In the first scheme， reboil ratio is constant with variable bottom product com position； in the second scheme， reboil ratio is variable and the heavy key component composition in the bottom product is nearly constant， and the third is an optim al operation which could obtain more profit Among these three control modes， the third is the most difficult to operate， since both controllers for reflux flow and reboiler heat input are operated manually This work demonstrates the operation of a batch stripping column， provides some practical guidlines for the startup and operation of the column， shows how the column can be run under different operating modes， and clarifies the effect of some key control tuning on the column performance However， this work is a dynamic simulation The practical operation of a batch stripping distillation column still needs to be investigated in detail REFERENCES 1 Salomone， H E ， Chiotti， O J ， Iribarren， O A ， “Short cut design procedure for batch distillation”， Ind Eng Chen Res ， 36 (1)， 13 一 136(1997) 2 Sundaram， S ， Evans， L B ， “Shortcut procedure for simulating batch distillation operations”， Ind EI en Res ， 32(3)， 511 518(1993) 3 Yang， zh C ， Yu， G C (K T )， Mo， zh M ， e a ， t “Study on optimal strategies and microcomputer control of batch distillation( )Batch distillation column and its microcomputer control”， J (Chem Ind Eng (China， 40(3)， 28 一 286(1989) (in Chinese) 4 Lotter， S P ， Diwekar， U M ， “Shortcut models and feas ibility consideration for emerging batch distillation columns”， Ind Eng Chem Res ， 36(4)， 760767(1997) 5 Scrensen， E ， Skogestad， S ， “Comparison of regular and inverted batch distillation”， Chem Eng Sci ， 51 (22)， 4949一 4962 of 1996) 分批冲孔模板精馏塔的操控 许松林， Jose Espinosab， Hector E Salomoneb， Oscar A Iribarrenb a 中国 ，天津， 300072，天津大学，国家精馏工程技术研究中心 b 阿根廷，桑塔费，康尼赛特， INGAR发展与设计学院 摘要 当大量的轻的成分在流量中很少和高纯度产品回收时分批冲孔模板精馏很重要，批量精馏塔的操控与镇流器的作用是相同的。然而，冲孔模板的控制系统是不同的。在这篇论文里，我们探索冲孔模板三种不同的控制方法： Hysys(Hyprotech Ltd 1997)，最主要的不同之处是重沸器液相控制图；（ a）以回流量控制 ;（ b)以重沸器热负载控制；（ c）以底部产品流量控制。在此论文里阐述分批冲孔模板精馏塔的操控最主要的特征是不同的控制流程图，分批冲孔模板控制开始时提供了准则，将要讨论一些柱面上的控制调谐参数。 图 1 分批冲孔模板的控制流程 1-塔体； 2-重沸器； 3-冷却机； 4-整流器； LC-液面控制器； PC-压力控制器 关键词 分批冲孔模板 控制 操作 1 简介 随着化工工厂向着大规模精细生产和专业化工产品方向发展，批量生产变得比较流行，这样简易方法对于产品需求的频繁变化起关键作用。批量精馏塔是固有简易特性的，正如一个柱可以由一个多组分供给分成许多不同的组份，这样批量精馏的用途对于一些化学，食品和药物公司的高价值的化工产品的分离和提纯变得越来越重要。 传统的，最流行的批量精馏方法被称为整流柱，它有一个大的重沸器，对它所有的供给都是变化的，并且不同产品从顶部分离开。操作整流塔有三种方法：（ 1）回流量为恒量并且精馏组份为变量， （ 2）回流量为变量并且精馏的主要组份为恒量， （ 3）最佳回流量协调了（ 1）和（ 2）并且建立在最经济的试验。 批量冲孔模板与批量整流是相反的。在它的顶端有它的储存容器并且产品从塔的底部分离出。当大量的轻的成分在流量中很少和高纯度产品回收时分批冲孔模板精馏很重要。 批量精馏塔的操控与镇流器的作用是相同的。然而，冲孔模板的控制系统是不同的。在论文中，我们探索 Hysys(Hyprotech Ltd 1997)的批量冲孔模板三种不同的控制方法，图表 1给出了控制图。最主要的不同之处是重沸器液相控制图；（ a）以回流量控制 ;（ b)以重沸器热负载控制；（ c）以底部产品流量控制。 （ a）底部产品的组分 （ b）塔体中的温度 （ c）质量流量 （ d）顶部和底部的流量 在此论文里阐述分批冲孔模板精馏塔的操控最主要的特征是不同的控制流程图，分批冲孔模板控制开始时提供了准则，将要讨论一些柱面上的控制调谐参数。 2 模拟实验仪器 模拟实验仪器和三种控制图是相同的，脱模塔有个重沸器和 2 m 3和 5 m 3的冷凝器，他的直径是 0.5m.供给成分是甲醇（ 0.05）和乙醇（ 0.95） （馏分）的混合物。占冷凝器容量的 80%，开始时，板是干启动的，但是重沸器是由相同的混合液的液相点控制的。底部产品乙醇的规范是 0.999.所有的仿真实验程序是从冲模开始直到关键的组份达到规范，然后底部产品阀开启使产品分离，当产品组份低于规范时产品阀关闭。 3 结果和讨论 3.1 通过回流量控制重沸器液面 在控制图中【图表 1（ a） 】 ,重沸器液相百分比是由回流量自动控制的，重沸器的热输出和底部产品的流量是手动控制的。开始时，重沸器的热输出是设定的，重沸器的液面随着轻成分的蒸发而降低，这将导致回流自动地流向重沸器。重沸器的液面控制是可逆的，所以当重沸器的液面较高时，回流量将较少。当关键组份是成分达到其规范时，底部的阀开启，一旦它低于规范，底部产品流出阀就手动关闭，这样的话，当乙醇成分达到0.999，底部产品流出阀开启，当乙醇成分低于 0.999，底部产品流出阀关闭。 图表 3重沸器液面的波动 图表 2表示了此操作模式的动态过程。在重沸器液面和回流之间存在时间滞后，尤其是当阶段数目很大时。为了在整个控制中达到一个稳定的重沸器的液面。必须仔细考虑两个方面。如果回流阀过大，当液面降低时，重沸器的液面控制器将从重沸器得到比预设多的回流量。然后回流阀将会关闭。这使重沸器液面频繁波动。图表 3展现出了一种情况，在这种情况底部关键成分的组成是不稳定的，另一方面是重沸器的液相参数应该合理选择尽当底部控制器的比例试用时。控制器的比例增益 Kp应该在 4.0和 8.0之间。如果 Kp值太小，就很难使重沸器液面控制达到稳定。图表 4展示了重沸器液相百分比与相同的重沸器的 Kp值之间的关系。从图表 4中，很明显的看出如果 Kp值低于 4.0时重沸器的液相百分比将低于预设值的 50%。如果 Kp值在 4.0和 8.0之间，重沸器的液面会处在预设值的附近。 图表 4 Kp值对重沸器液面的影响 3.2 通过重沸器的热输出控制重沸器的液面 在控制图中【图表 1（ b） 】中，重沸器的液面是由重沸器的负载自动控制的，回流和底部产品的流出是手动控制的。开始时，回流阀须有一个特定值。重沸器的液面增加将导致对重沸器的热输入。重沸器的液面控制器的功能是直接的，这意味着重沸器液面越高，重沸器的热输入越多。当关键组份是成分达到其规范时，底部的产品流出阀手动关闭。当关键组份是成分降至 0.999时，底部产品流出阀和回流阀也手动关闭。图表 5表示了此操作模式的动态过程。很明显的看出煮沸的大量流量和冷凝器的液面