应用化学专业文献原文及翻译

Operation of plate rectification tower

WU Chang-xiang

(Harbin Gasification Plant,Harbin 154864,China)

Abstract:The influencing factors,abnoimal phenomenon and rectification process were analyzed to direct actual operation

Key words: rectification tower,recification,reboiler,operation

Distillation column is a multi-stage partial vaporization and partial condensation according to the different components in the mixture volatility in each floor tower board to achieve the separation of a mixture of various components of the tower gas-liquid contact device, also known as distillation. A plate column and packed column types. According to mode of operation are divided into continuous distillation and batch distillation. Steam from the bottom of the column entry, and the decline in liquid countercurrent contact with the two in contact, the drop in the volatile liquid (low boiling point) components is continuously transferred to the steam. The difficulty of steam volatile (high boiling) component continued to decline in the transfer of liquid, steam the closer the top of the tower, the higher the concentration of its volatile components, while the decline in the closer tower bottom liquid, its hard to be more volatile components rich set, to achieve component separation. Steam rising from the top of the tower into the condenser, the liquid part of the condensate as reflux liquid to return into the distillation tower, the rest is removed as distillate. Tower bottom outflow of liquid, some of which into the reboiler, thermal evaporation, the steam back to tower, and the other part of the liquid as residua release.

Compared with other chemical unit operations,distillation unit,although relatively simple,single production run that often appear in a variety of problems affecting the operation of the distillation unit,leading to tower top orbottom of product failure,severe constraints of production equipmentthe operation resulting in product loss.

1.Regular changes in process conditions of distillation column 1.1 Reboiler temperature

Under the same operating pressure,raising the temperature of the reboiler,the volatile components in the tower liquid to reduce,at the same time,the rising vapor velocity increases,and help to improve the efficiency of mass transfer.If products from the top of the tower,the tower reactor discharge of difficult volatiles volatile components to reduce and reduce losses.If the tower reactor effluents for the product,it can improve product quality tower discharge of volatile components

entrained difficult nolatile components increased,thereby increasing the losses.In balanced operation,the reactor temperature is suddenly increased,and it too late to adjust the pressure and temperature will inevitably lead to the reboiler fluid is steam-air, the pressure increased.At this time,the tower gas,liquid composition changes,the restructuring were likely to be steamed to the top of the tower,so that the failure of top product.

1.2 Operating pressure

In the case of certain operating temperature,increasing the operating pressure can increase the productive capacity of the tower,so that stable operation,but the content of volatile group in the tower reactor products.In distillation,often provides for the adjustment range of the operating pressure.When the fallout of the operating pressure by extmrnal factors,were destroyed,the normal operation of the tower will be completely destroyed.

1.3 Feeding temperature

1.3.1Condensate feed,the feed temperature is lower than the temperature of the feeding board,and added if all the material into the stripper segment,stripping segment load increases,the reboiler consumption increase in the amount of steam,and the top of the tower is difficult volatile group were lower.

1.3.2Saturated steam feed,the feed material temperature is higher than the temperature of feed board,all the material of the feed into the rectifying section and stripping section of the load reduction,and increased load of the rectifying section,make the top product quality reduce.

1.4 Feeding quantity and composition changes

Changes in the feedstock of a direct impact on the change of the amount of steam,the latter increase will produce entrained,even flooding.The feedstock is too low,the operation is not good to maintain the balance of the tower,the steam velocity decreases,the plate is prone to leakage,the rectification efficiency is low.Inthe low-load operation,may be appropriate to increase the reflux ratio,the tower operating in a load lower limit above normal and stable operation in order to maintain the tower.Feeding component of the changes directly affect the product quality.Increased restructuring concentration increase in the rectifying section load separation is not good,the results of restructuring were brought to the top of tower,causing the top of the tower of inferior quality.Product from the reboiler,the top of the tower losses increase.If the concentration of the volatile group in the feeding group were

increased,and the stripping section of the load increases,may be poor due to the separation caused by the tower reactor products of inferior quality,which entrained volatile components increased.Feeding restructuring concentration increased,the feeding mouth move down and vice versa,then move up.The same time,operating temperature,back flow and operating pressure must be adjusted accordingly in order to ensure the stability of the distillation operation.

Distillation,increasing the reflux ratio,can improve the quality of the product,but the reflux ratio is too large,the inner loop of the tower increased,increasing energy consumption.Reduction of the reflux ratio,the tower gas-liquid contact is not good,the balance to damaged and therefore the mass transfer efficiency decreased.The same time,the operating pressure drop,difficult volatile components easily brought to the top of the tower,resulting in a substandard product.

2 Anomalies in the distillation column during operation

2.1 Plate capacity

Rectifying section tray downcomer overflow liquid transportation,however,that the tower upper part of the beginning of flooding,a phenomenon known as downcomer obstruction or liquid flooding.Its causes is to block the liquid leaving the tower board level rise in the downcomer plate between mist entrained excessive leaving the tray efficiency to reduce entrainment of this phenomenon is known as the excessive fog or steam flooding,the reason is the relativein the gas while the tower board bubbling area is too small.

2.2 Plate fouling

Sediment cumulative to the board of board of the tower is an important issue,trays of dirt will tower premature flooding will reduce the plate efficiency.Plate scaling phenomenon:(1)The reflux ratio is not high on liquid pan;(2)The pressure drop increase between the tray;(3)Increase the reflux ratio on the bottom of the column temperature,flow or reboiler load does not have any impact,if the reflux ratio to the heat balance and material balance of 20% to 30%,while the tower did not change significantly,then the tower must be completely full of liquid.The amount of returning tower direct stream gas pipeline through the top of the tower back to the reflux tank.

2.3 Slug flows in the riser

Slug flow in the riser is a distillation column running unstable,may be caused due to an unstable gas-liquid mixture flow in the vertical pipeline.Reflux tank is elevated

at the of the condenser by the condenser discharge logistics is that part of the pipeline between the gas-liquid two-phase mixture,the condenser and reflux tank is called the riser.Generate a liquid column in the riser flow rate is too low will result in two-phase separation,the distillation column to produce a back pressure,this liquid column intermittently be introduced after the riser,back pressure will weaken,then the risergradually being filled with liquid,such slug flow will cause the tower pressureperiodic pulse of change.

Abnormal factors cause distillation column plate was washed away,condenser corrosion,clogged caondenser,not condensable gas influence condenser.

3.Reboiler

Reboiler in the distillation column occupies a very important position,it used to bebottom after the vaporization of the liquid part of the back to the distillation column,two phases of the tower gas-liquid contact and mass transfer to proceed.Which used the vertical thermal siphon reboiler,which is a vertical placement of the shell and tube heat exchanger.Partial vaporization of liquid in the bottom-up tube passes through the heat exchanger,heating the heat carrier in the shell.Vertical thermal siphon reboiler features:(1)cycle driving force:the density of the reactor liquid and the heat exchanger tube gas-liquid mixture;(2)compact,small footprint,high heat transfer coefficient;(3)of the shell can not be mechanically cleaned,not suitable for hightower reactor,heat transfer medium viscosity,or dirty;(4)provide the space and buffer zones of the gas-liquid separator.

Factors that determine the distillation column capacity restricted,find the reboiler failure is the most laborious,the distillation column by steam reboiler.

(1)gas-barrier drain valve failure;(2)steam condensate collected indoor pressure is too large;(3)the condensate liquid seal failure.

Hydrophobic failure caused by hydrophobic failure factors:

3.1 Thermosiphon rebiler failure

Reboiler liquid inlet pipe and outlet pipe cold liquid mixture exists between the density difference is the density difference driving the process of processing liquid flow through the reboiler.When tower humoral bit elevated to the reboiler back to the liquid nozzle height,siphon circulation will be impeded.The circulation rate reduction will result in the reduction of heat transfer,thus the cover back to the fluid nozzle is clearly an important reason for fluctuations in the reboiler duties.

3.2 Non-condensable gas in the water vapor

Steam reboiler to run the process,water vapor may be non-condensable gases,or the reboiler leak,the hydrocarbon vapor or other non-condensable gas into the reboiler,the non-condensable gas into the reboiler pipingthereby reducing the heat transfer capacity of the reboiler with the distillation column within a circulating fluid,thus causing the reboiler heat transfer efficiency decreased.

4 Conclusion

In view of these problems often appear in a production run affect the operation of the distillion unit,leading ton the top of the tower or the bottom of product failure,seriously restricting the production device to run resulting in product loss.In order to avoid such things from bappening,the operator should do the following:

4.1 storage and transportation of materials

Plate column distillation process must be set in place a number of different volume raw material storage tanks,pumps and all kinds of heat exchanger has been temporarily stored,transported and preheating(cooling)of materials used,in order to protect the device can be a continuous and stable operation.

4.2 Necessary means of detection

In order to facilitate the resolution of the problem in the operation shall be the appropriate place in the process to set the necessary instrumentation,as well as to obtain the pressure,temperature and other parameters.In addition,often set in a particular place manholes and hand holes,so that regular testing and maintenance. 4.3 Adjustment device

State parameters are not in the actual production value should be placed in the appropriate location of a certain number of the valve to be adjusted to achieve the production requirements,can be a double adjustment,that is both automatic and manual adjustment coexist,and at any timeswitch.

板式精馏塔的操作

吴昌祥

（哈尔滨气化厂，黑龙江哈尔滨154864）摘要：本文通过对影响精馏塔因素的分析及异常现象剖析，分析精馏过程从而指导实际操作。

关键词：精馏塔，精馏，再沸器，操作

中国分类号：TB657.6 文献标识码：A

精馏塔是根据混合物中各组分挥发度的不同，在每层塔板上进行多级部分汽化和部分冷凝，从而达到使混合物各组分分离的一种塔式气液接触装置，又称蒸馏塔。有板式塔和填料塔两种类型。根据操作方式又分为连续精馏塔与间歇精馏塔。蒸汽从塔底进入，与下降液进行逆流接触，两相接触中，下降液中的易挥发（低沸点）组分不断地向蒸汽中转移，蒸汽中的难挥发（高沸点）组分不断地向下降液中转移。蒸汽愈接近塔顶，其易挥发组分浓度愈高，而下降液愈接近塔底，其难挥发组分愈富集，达到组分分离的目的。由塔顶上升的蒸汽进入冷凝器，冷凝的一部分作为回流液返回塔顶进入精馏塔中，其余的部分则作为馏出液取出。塔底流出的液体，其中的一部分送入再沸器，热蒸发后，蒸汽返回塔中，另一部分液体作为釜残液放出。

与其它化工单元操作相比，精馏装置虽然比较简单，但生产运行中经常出现各种各样的问题而影响精馏装置的操作，从而导致塔顶或塔底产品不合格，严重制约生产装置的运行从而造成产品损失。

1精馏塔的常规工艺条件变化

1.1塔釜温度

在操作压力不变的情况下，提高塔釜温度，则使塔内液相中易挥发的组分减少，同时，使上升蒸气的速度增大，有利于提高传质效率。如果由塔顶得到产品，则塔釜排出难挥发物中易挥发组分减少，减少损失。如果塔釜排出物为产品，则可提高产品质量，但塔顶排出的易挥发组分中夹带的难挥发组分增多，从而增大损失。在平衡操作中，釜温突然升高，来不及调整相应的压力和温度时，必然导致塔釜液被蒸空，压力升高。这时，塔内气、液相组成变化很大，重组份容易被蒸到塔顶，使塔顶产品不合格。

1.2操作压力

在操作温度一定的情况下，提高操作压力，可以提高塔的生产能力，使操作稳定，但在塔釜产品中易挥发组份含量增加。在精馏操作中，常常规定了操作压力的调节范围。当受到外界因素的影响而使操作压力受到破坏时，塔的正常操作

就会完全破坏。

1.3加料温度

1.3.1冷凝进料，则进料温度低于可加料板上的温度，则加入的物料全部进入提馏段，使提馏段负荷增加，塔釜消耗蒸汽量增加，塔顶难挥发组份降低。

1.3.2饱和蒸汽进料，则进料温度高于加料板上的温度，所进物料全部进入精馏段，提馏段的负荷减少，精馏段的负荷增加，会使塔顶产品质量降低。

1.4加料量及组份的变化

加料量的变化直接影响蒸汽量的改变，后者的增大会产生夹带，甚至液泛。加料量过低，塔的平衡操作不好维持，蒸汽速度减小，塔板容易漏液，精馏效率较低。在低负荷操作时，可适当增大回流比，使塔在负荷下限之上操作，以维持塔的操作正常稳定。加料组分的变化直接影响到产品质量。重组份浓度增高使精馏段负荷增加，分离效果不好，结果重组份被带到塔顶，造成塔顶质量不合格。若从塔釜得到产品，则塔顶损失增加。如果加料组份中易挥发组份浓度增加，使提馏段的负荷增加，可能因分离不好而造成塔釜产品质量不合格，其中夹带的易挥发组份增多。加料中重组份浓度增高时，加料口往下移，反之，则向上移动。同时，操作温度、回流量和操作压力都须相应地调整，才能保证精馏操作的稳定性。

在精馏操作中，提高回流比，可以提高产品的质量，但回流比过大，塔内的内循环量增加，增加能耗。回流比减少时，塔内气液接触不好，使平衡受到破坏，因而传质效率下降。同时，操作压力下降，难挥发组份易被带到塔顶，导致产品质量不合格。

2 精馏塔操作过程中的异常情况

2.1塔板能力

精馏段塔板降液管输送不过来溢流液，亦即塔上部开始液泛，这种现象称为降液管阻塞或液体液泛。其产生的原因在于液体阻滞在降液管内而使塔板上液位升高，塔板间雾夹带过量而使塔板效率降低，此现象称为过量雾夹带或蒸气液泛，其原因是相对于较大的气量而塔板上鼓泡区过小。

2.2塔板结垢

沉积物在塔板上的累积是个重要问题，塔板上的污垢会使塔过早地发生液泛，也会降低板效率。塔板结垢的直观现象：（1）回流比不高时就发生液泛；（2）塔盘间的压力降增大；（3）加大回流比后，对塔底温度、流量或再沸器负荷不产生任何影响，如果把回流比提高到20%~30%而塔的热平衡和物料平衡没有明显变化，那么塔顶一定是被液体完全充满。回流的塔量通过塔顶的气相管路又直接流回到回流罐。

2.3提升管中的团状流动

提升管中的团状流动是精馏塔运行不稳定的问题，可能是由于垂直管线中不平稳的气液混合流引起的。回流罐被高架于冷凝器的上方，由冷凝器排出的物流是气液两相混合物，冷凝器与回流罐之间的那段管线被称为提升管。如果提升管中的流速太低将导致两相分离，同时生成一段液柱，对蒸馏塔产生一个背压，这段液柱间歇地被推出提升管后，背压也就减弱，接着提升管又渐渐地被液体充满，这类团状流动会引起塔压周期性脉动变化。

引起精馏塔的不正常因素还有塔板被冲垮，冷凝器腐蚀，冷凝器堵塞，不凝气影响冷凝器等。

3.再沸器

再沸器在精馏塔中占有很重要的位置，它用以将塔底液体部分汽化后送回精馏塔，是塔内气液两相间接触传质得以进行。其中常用到的立式热虹吸式再沸器，它是一种垂直放置的管壳式换热器。液体在自下而上通过换热器管程时部分汽化，由在壳程内的载热体供热。立式热虹吸式再沸器的特点有：（1）循环推动力：釜液和换热器传热管气液混合物的密度差；（2）结构紧凑、占地面积小、传热系数高；（3）壳程不能机械清洗，不适宜高粘度、或脏的传热介质；（4）塔釜提供气液分离空间和缓冲区。

在确定精馏塔生产能力受限制的因素中，查找再沸器故障是最费力的问题，精馏塔大多数都采用水蒸气进行再沸。

a.阻气排水阀故障；

b.蒸气冷凝液收集室内压力过大；

c.冷凝液液封失效。

疏水故障引起的疏水故障的因素主要有：

3.1热虹吸再沸器故障

再沸器入口管路的液体与出口管路中的冷液混合物之间存在着密度差，正是这个密度差在驱使着过程所加工的液体流过再沸器。当塔体液位升高到再沸器回液管口高度时，虹吸循环便受到阻碍。循环量降低会导致热传递的减少，因而盖住回液管口显然是再沸器负荷波动的一个重要原因。

3.2水蒸汽中的不凝气

在蒸气再沸器运行过程中，水蒸汽可能会有不凝气体，或再沸器发生泄漏，使烃类蒸气或其它不凝气体进入再沸器，由于不凝气体进入再沸器管路中从而降低了再沸器与精馏塔内循环液体的换热能力，因此引起再沸器传热效率下降。

4结论

鉴于这些在生产运行中经常出现的各种问题而影响精馏装置的操作，从而导致塔顶或塔底产品不合格，严重制约生产装置的运行从而造成产品损失。为避免此类事情的发生，操作人员应该做到以下几点：

4.1物料的储存和运输

板式塔精馏过程必须在适当的位置设置一定数量不同容积的原料储罐、泵和各种换热器，已暂时储存，运输和预热（冷却）所用原料，从而保障装置能连续稳定的运行。

4.2必要的检测手段

为了方便解决操作中的问题，须在流程中适当位置设置必要的仪表，以及时获取压力、温度等各项参数。另外，常在特定地方设置人孔和手孔，以便定期的检测维修。

4.3调节装置

由于实际生产中各状态参数都不是定值，应在适当的位置放置一定数量的阀门进行调节，以保证达到生产要求，可设双调节，即自动和手动两种调节方式并存，且随时进行切换。