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1、外文原文： Basic knowledge of distillation operation The principle of rectification The liquid mixture of times and partial vaporization, multiple partial condensation of the steam produced again at the same time, separate the mixture process called distillation for the operation of the required

2、components For a vaporization, condensation, due to the boiling point of liquid mixture contained components are different, when partial vaporization under a certain temperature, due to the low boiling point is easy to gasification, so it is in the liquid phase in the gas phase concentration

3、 is high, and the concentration of the liquid high boiling point material is the gas phase. It's changed the composition of gas liquid two phase. When condensation for the steam from partial vaporization parts, due to the high boiling point material easy to condensate, to make the concentration of h

4、igh boiling point material, the condensate gas phase is high, and for condensate gas of low boiling point matter concentration is higher than in the condensate. So after a part vaporization and condensation, make the change of mixture concentration of components in a preliminary separation. If multi

5、ple go on like this, will eventually left in the liquid phase is basically high boiling components, in the gas phase is basically a low boiling point components. Thus, multiple partial vaporization and partial condensation simultaneously for many times, can separate the mixture of pure or relatively

6、 pure components. Rectification tower is composed of a number of plate, the upper is called the top of the tower, the bottom is called the tower of the tower kettle. Tower a tray is only a part vaporization and condensation, tray number, the more the more the number of parts vaporization an

7、d condensation, separation effect is better. Through the distillation process, the final high purity of volatile components are obtained by the tower, tower kettle is basically difficult volatile components. entrainment Entrainment is refers to the gas entrainment from the lower plate belt t

8、o the upper plate of liquid droplets. In mass transfer process, a large number of smuggled with foam fog makes should not be on the top of a restructuring reached into products, so as to reduce the quality of the products, at the same time can reduce the concentration difference in the process of ma

9、ss transfer, is only plate efficiency decline. For a given tower, the maximum allowable amount of smuggled with foam fog will restrict the rising velocity of the gas. There are many factors which can influence the entrainment entrainment quantity, such as plate spacing, superficial velocity, hig

10、h weir, the flow velocity and material physical and chemical properties, etc. At the same time, you have to point out that smuggled with foam fog and capture device structure also has a lot to do. Although many factors affect the amount of smuggled with foam fog, but the main influence factor is the

11、 superficial velocity and gas liquid separation space between the two pieces of plate. For fixed tower, entrainment entrainment quantity increases with the increase of superficial velocity and mainly. If, however, increase the distance between the plate and enlarge the separation space, the correspo

12、nding improve superficial velocity. The structure of the float valve tray Float valve tower is widely used in the past ten years in our country a new enterprise mass transfer equipment. Now it is widely used in petrochemical industry, and have achieved satisfactory results. Float valve t

13、ower structure is simple, the main structure of the tray, downcomer, overflow weir, the float valve and plate. The advantages and disadvantages of float valve tray The performance of the float valve tray with blister tray and the advantages of porous plate, and improved their shortcomings. B

14、ubble column plate because of the opening of the slot is fixed, so its to adapt to the bad performance of steam load change. Steam speed hours, gas-liquid contact is bad, when the gas velocity is big, and easy to make steam liquid. Although the perforated plate structure is simple, processing capaci

15、ty is big, but smaller, elasticity of operation for float valve tower, steam valve opening, along with the speed. Low gas velocity, the valve plate under the action of gravity automatic fall, in order to reduce leakage. So, float valve tower of high efficiency, large elasticity of operation, can bet

16、ter adapt to the change of feed rate, with the experimental results show that the minimum load and maximum load ratio can reach about 7 ~ 9. Float valve tower structure is simple, free cross-sectional area is larger, than bubble column 12 ~ 15% lower cost, higher than that of bubble column plate pro

17、cessing capacity about 20 ~ 40%. Because the float valve tray is the level of the steam blowing into the liquid layer, therefore, better gas liquid agitation, entrainment placing small, contact Float valve tray are the main disadvantages of steam rising along the hole of the surrounding, there i

18、s still a liquid back, thus reduces the mass transfer efficiency. In addition, the valve is easy to get stuck, rusty, or stick to open. The influence factors of distillation operation In addition to equipment problems, the influence factors of distillation operation process basically has th

19、e following several aspects: temperature and pressure of the tower (including the tower, tower kettle, and some have a special meaning of plate). Feeding status; Feed rate. Feed composition; Feed temperature; The tower rises steam evaporation speed and kettle and heat; Back to the traffic; The tower

20、 cold dose; The amount and bottom at the top of the column can withdrawl. The operation of the tower is composed of overhead and bottom products in accordance with the requirements for this a few factors. Distillation column pressure changes on the effect of distillation operation Design and op

21、eration of the tower are based on certain pressure, thus the general rectification column, I always want to maintain a constant pressure. Tower pressure fluctuations will produce the following effect to the operation of the tower 1 ring the quality of the products change operating pressure and

22、material balance, will lead to gas-liquid phase balance on each plate of change. Pressure, the gas phase of restructuring, the corresponding improved the concentration of light component in the gas phase; Light component content in liquid phase, but also change the weight of the gas liquid ratio, in

23、crease the amount of liquid phase, reduce gas phasor. Concentration of light component in the overall result is: the overhead fraction increased, but the number is less; Reactor, such as concentration of light component in the increase, reactor fluid volume increases. By the same token, the pressure

24、 is reduced, the number of overhead fractions increase, concentration of light component; Still reduced the volume of liquid, concentration of light component. Should maintain a constant pressure in the normal operation, but if the operation is not normal, the cause of the overhead product restructu

25、ring concentration increases, the higher can adopt appropriate operating pressure, make the product quality qualified, but the loss of light components in the liquid phase increase at this time. 2 variable components increase the relative volatility between pressure, relative volatility between

26、components is reduced, the separation efficiency decreases, and vice versa. 3 change tower pressure increases, the capacity of components of the severe increase, increase processing capacity of the tower. 4 column pressure fluctuation which will cause temperature and composition of the corre

27、sponding relationship between chaos. We often with temperature in the operation as the indirect measure of the quality of the product, but it only in the tower under the condition of constant pressure is correct. When the pressure changes, the mixture of dew point and bubble point change, change cau

28、sed the temperature distribution of the tower, the corresponding relation of temperature and product quality will also change. From the above analysis, change the operating pressure, will change the working conditions of the tower, so should maintain a constant pressure in the normal operation,

29、only in the normal operation of the tower is damaged, can according to the above analysis, the technical index, to the extent permitted to appropriate adjust pressure of the tower. It should be pointed out that in the process of distillation operation, the feed rate and feed composition and the

30、change of feed temperature, column reactor heating steam change, back flow, reflux temperature, tower cold dose of change and clogging of plate, are likely to cause tower pressure fluctuations, at this time we should analyze the reason of pressure fluctuation, timely processing, make the operation b

31、ack to normal. The influence of the installation of the tower of distillation operation Different materials and different process, the tower equipment demands are different. But generally always hope the separation ability of high tower equipment, large production capacity, stable operation. For

32、a tower of finalize the design of the equipment, because there is something wrong with the installation, you will probably could not reach the requirements of the above. Such as the tower, tower board, the overflow mouth, if do not conform to the requirements when installation, are likely to impact

33、on distillation operation. 1) the tower the tower for vertical, generally of no more than one over one thousand, otherwise it will cause dead zone in the plate, for small diameter of column, if the installation is first section plate, and then to assemble, is not vertical tower will directly affe

34、ct the whole tower all the levelness of the plate, reduce the efficiency of the tower 2) plate plate requirements, its levelness level determination for no more than plus or minus 2 mm. If the plate is not level, will cause the liquid on the surface layer height, the tower rising steam easily fr

35、om the liquid layer height through smaller, thus reducing the efficiency of the plate. (3) the overflow mouth overflow mouth and the distance of the lower plate, use according to the production capacity and lower on the height of the overflow weir plate. But must meet the overflow mouth insert th

36、e tray in the liquid, to seal up steam. If the overflow mouth and the lower plate too close to the distance, may cause the upper plate back cannot smoothly into the lower plate, make higher liquid layer of the upper plate, the lower the pressure plate, serious when cause flooding. The overflow mouth

37、 is too high, more than the height of the overflow weir, rising steam "short circuit", straight from the overflow tube to the upper plate, no liquid seal effect, influence the plate efficiency. When installation, for all kinds of concrete plate type has different levels of demand, if not required

38、to install, may make the production efficiency of the tower. The operation of the rectifying column should grasp the three balance (1) the material balance embodies the production capacity of the tower, it mainly depends on the feed rate and storage overhead, bottom to adjust. When the operatio

39、n of the tower does not conform to the overall material balance, this can see from tower on the change of pressure difference, into more, get less, the differential pressure rise. For a fixed rectification tower, the tower pressure difference should be within a certain range. Tower pressure differen

40、ce is too big, that the tower rising steam too fast, entrainment entrainment is serious, even causing flooding and damage the normal operation of the tower; Tower pressure difference is too small, which indicates that the tower of the vapor rising speed is too small, the gas and liquid on the plate

41、of the turbulent level is too low, the mass transfer effect is poor, make the plate produces leakage, reduce the plate efficiency. If the column is not in conformity with the material balance the components of a certain type, there will be two kinds of performance: If the column is not in conform

42、ity with the material balance the components of a certain type, there will be two kinds of performance: Another case is the restructuring of the recovery of more than the amount of material balance, the material composition of the tower will be as for the operation gradually became light, the tow

43、er temperature drop, especially kettle temperature decreased obviously, still increased the concentration of light component in the liquid Thus, material balance master is bad, will make the whole operation of the tower is in chaos, can not reach the expected goal. In addition, if the material

44、balance of the normal, so, gas-liquid phase balance and can not meet the expected effect, also need to adjust the resulting heat balance. So the material balance is a key link of tower operation. (2) the gas-liquid balance mainly reflected the quality of the product and damage. It is by adjusting

45、 operating conditions (pressure, temperature) of the tower and tower plate gas-liquid contact to achieve. Because, only in the fixed temperature, pressure, in order to determine the gas-liquid equilibrium composition. Operating temperature and pressure of rectification tower is according to the sepa

46、ration of the tower task (that is, the key components of the separation and concentration). When the temperature and pressure changes, the composition of gas liquid equilibrium determined by the changes, the quality of the product or loss situation has changed. However, the composition of gas-liquid

47、 phase balance and depend on each plate of gas and liquid contact each other for mass transfer and heat transfer. That is to say, is closely related to the gas-liquid phase balance and material balance. Material balance control of good, the tower of the vapor rising speed, good gas-liquid contact, h

48、igh mass transfer efficiency, every board composition of gas and liquid is close to balance, is often said that plate of high efficiency, and vice versa. Of course, temperature, (3) the heat balance is the basis of material balance and gas liquid equilibrium are realized. No vapor rising column r

49、eactor heating, no, no overhead condensing backflow, the whole distillation process is unable to realize. The heat balance is attached to the material balance of gas and liquid phase equilibrium. Feed rate or composition changed, for example, column reactor heat consumption and the top of the tower

50、cold dose should be correspondingly changed. Operating pressure, temperature of the tower has changed (that is, the gas-liquid equilibrium composition changes), the gas phase on every board of condensing heat and liquid absorbs heat of gasification will also change. Heating kettle heating is not eno

51、ugh, for example, can cause the tower kettle temperature can not meet the specified value, that: (1) material balance, kettle liquid discharge increases, the tower distillate volume reduction, for the tower to get product process, production capacity of the tower fell; (2) the gas-liquid balance, th

52、e tower rises reduced the volume of steam, gas and liquid contact, mass transfer efficiency drops, restructuring of the gas content at the same time Known from the analysis of the above: grasp the material balance, gas-liquid balance, heat balance is the key to distillation operation. The three b

53、alance is to be able to influence each other, restrict each other, the operation is usually given priority to with the change of material balance, accordingly adjusting the heat balance to achieve the goal of gas-liquid phase balance. 譯文： 精餾操作基本知識 精餾的原理 把液體混合物進行多次部分汽化，同時又把產(chǎn)生的蒸汽多次部分冷凝，使混合

54、物分離為所要求組分的操作過程稱為精餾。 對于一次汽化，冷凝來說，由于液體混合物中所含的組分的沸點不同，當其在一定溫度下部分汽化時，因低沸點物易于氣化，故它在氣相中的濃度較液相高，而液相中高沸點物的濃度較氣相高。這就改變了氣液兩相的組成。當對部分汽化所得蒸汽進行部分冷凝時，因高沸點物易于冷凝，使冷凝液中高沸點物的濃度較氣相高，而為冷凝氣中低沸點物的濃度比冷凝液中要高。這樣經(jīng)過一次部分汽化和部分冷凝，使混合液通過各組分濃度的改變得到了初步分離。如果多次的這樣進行下去，將最終在液相中留下的基本上是高沸點的組分，在氣相中留下的基本上是低沸點的組分。由此可見，多次部分汽化和多次部分冷凝同時進行，就可以

55、將混合物分離為純或比較純的組分。 液體氣化要吸收熱量，氣體冷凝要放出熱量。為了合理的利用熱量，我們可以把氣體冷凝時放出的熱量供給液體氣化時使用，也就是使氣液兩相直接接觸，在傳熱同時進行傳質(zhì)。為了滿足這一要求，在實踐中，這種多次部分汽化伴隨多次部分冷凝的過程是逆流作用的板式設備中進行的。所謂逆流，就是因液體受熱而產(chǎn)生的溫度較高的氣體，自下而上地同塔頂因冷凝而產(chǎn)生的溫度較低的回流液體（富含低沸點組分）作逆向流動。塔內(nèi)所發(fā)生的傳熱傳質(zhì)過程如下1）氣液兩相進行熱的交換，利用部分汽化所得氣體混合物中的熱來加熱部分冷凝所得的液體混合物；2）氣液兩相在熱交換的同時進行質(zhì)的交換。溫度較低的液體混合物被溫度較

56、高的氣體混合物加熱二部分汽化。此時，因揮發(fā)能力的差異（低沸點物揮發(fā)能力強，高沸點物揮發(fā)能力差），低沸點物比高沸點物揮發(fā)多，結(jié)果表現(xiàn)為低沸點組分從液相轉(zhuǎn)為氣相，氣相中易揮發(fā)組分增濃；同理，溫度較高的氣相混合物，因加熱了溫度較低的液體混合物，而使自己部分冷凝，同樣因為揮發(fā)能力的差異，使高沸點組分從氣相轉(zhuǎn)為液相，液相中難揮發(fā)組分增濃。 精餾塔是由若干塔板組成的，塔的最上部稱為塔頂，塔的最下部稱為塔釜。塔內(nèi)的一塊塔盤只進行一次部分汽化和部分冷凝，塔盤數(shù)愈多，部分汽化和部分冷凝的次數(shù)愈多，分離效果愈好。 通過整個精餾過程，最終由塔頂?shù)玫礁呒兌鹊囊讚]發(fā)組分，塔釜得到的基本上是難揮發(fā)的組分。

57、 浮閥塔板的結(jié)構(gòu) 浮閥塔是我國近十余年來廣為使用的一種新型企業(yè)傳質(zhì)設備。目前它廣泛應用在石油化工中，并取得了令人滿意的效果。浮閥塔的結(jié)構(gòu)較為簡單，主要結(jié)構(gòu)有受液盤，降液管，溢流堰，浮閥和塔板。 浮閥塔板的優(yōu)缺點 浮閥塔板的性能兼有泡罩塔板與多孔塔板的優(yōu)點，并改進了它們的缺點。泡罩塔板由于齒縫開度是固定的，因此其對蒸汽負荷變動的適應性能不好。汽速小時，氣液接觸不好，氣速大時，又易使蒸汽吹開液體。多孔塔板雖然結(jié)構(gòu)簡單，處理能力大，但操作彈性比較小，對于浮閥塔來說，閥片的開度則隨汽速而變。低氣速時，閥片在重力作用下自動落下，以減少泄漏。所以，

58、浮閥塔的效率較高，操作彈性大，能較好的適應進料量的變化，有實驗表明，其最大負荷與最小負荷的比可達到7～9左右。浮閥塔結(jié)構(gòu)簡單，自由截面積較大，造價比泡罩塔降低12～15%，處理能力比泡罩塔板提高20～40%左右。由于浮閥塔板的蒸汽是水平吹入液層，因此，氣液攪動較好，霧沫夾帶小，接觸時間長，傳質(zhì)效果好，其效率比泡罩塔板藥膏15%。 浮閥塔板的主要缺點是蒸汽沿上升蒸汽氣孔的周邊噴出，仍然有液體的逆向混合，因而會降低傳質(zhì)效率。另外，閥片容易被卡住、銹住或粘住，影響開啟。 精餾操作的影響因素 除了設備問題以外，精餾操作過程的影響因素主要有以下幾個方面：塔的溫度和壓力（

59、包括塔頂、塔釜和某些有特殊意義的塔板）；進料狀態(tài)；進料量；進料組成；進料溫度；塔內(nèi)上升蒸汽速度和蒸發(fā)釜的加熱量；回流量；塔頂冷劑量；塔頂采出量和塔底采出量。塔的操作就是按照塔頂和塔底產(chǎn)品的組成要求來對這幾個影響因素進行調(diào)節(jié)。 精餾塔操作壓力的變化對精餾操作的影響 塔的設計和操作都是基于一定的壓力下進行的，因此一般的精餾塔總是先要保持壓力的恒定。塔壓波動對塔的操作將產(chǎn)生如下的影響。 1 響產(chǎn)品質(zhì)量和物料平衡 改變操作壓力，將使每塊塔板上的氣液相平衡的組成發(fā)生改變。壓力升高，則氣相中的重組份減少，相應的提高了氣相中的輕組分的濃度；液相中的輕組分含量增加，同時也改變

60、了氣液相的重量比，使液相量增加，氣相量減少?？偟慕Y(jié)果是：塔頂餾分中的輕組分濃度增加，但數(shù)量卻相對減少；釜液中的輕組分濃度增加，釜液量增加。同理，壓力降低，塔頂餾份的數(shù)量增加，輕組分濃度降低；釜液量減少，輕組分濃度減少。正常操作中應保持恒定的壓力，但若操作不正常，引起塔頂產(chǎn)品中重組分濃度增加時，則可采用適當升高操作壓力的辦法，使產(chǎn)品質(zhì)量合格，但此時液相中輕組分的損失增加。 2 變組分間的相對揮發(fā)度 壓力增加，組分間的相對揮發(fā)度降低，分離效率下降，反之亦然。 3 改變塔的生產(chǎn)能力 壓力增加，組分的重度增大，塔的處理能力增大。 4 塔壓的波動 這將引起溫度和組成間對

61、應關(guān)系的混亂。我們在操作中經(jīng)常以溫度作為衡量產(chǎn)品質(zhì)量的間接標準，但這只有在塔壓恒定的情況下才是正確的。當塔壓改變時，混合物的露點、泡點發(fā)生改變，引起全塔的溫度分布發(fā)生改變，溫度和產(chǎn)品質(zhì)量的對應關(guān)系也將發(fā)生改變。 從以上分析來看，改變操作壓力，將改變整個塔的工作狀況，因此在正常操作中應維持恒定的壓力，只有在塔的正常操作受到破壞時，才可以根據(jù)上述分析，在工藝指標允許的范圍內(nèi)，對塔的壓力進行適當?shù)恼{(diào)整。 應當指出，在精餾操作過程中，進料量、進料組成和進料溫度的改變，塔釜加熱蒸汽量的改變、回流量、回流溫度、塔頂冷劑量的改變以及塔板的堵塞等，都有可能引起塔壓的波動，此時我們應先分析塔壓波動的原因，及

62、時處理，使操作恢復正常。 塔的安裝對精餾操作的影響 不同的物料和不同的工藝過程，對塔設備提出的要求是不同的。但是，一般總希望塔設備的分離能力高，生產(chǎn)能力大，操作穩(wěn)定。對于一個定型的塔設備來說，由于安裝上有問題，就可能會達不到以上的要求。如塔身、塔板、溢流口等，在安裝時若不符合要求，都有可能對精餾操作帶來影響。 （1）塔身 塔身要求垂直，一般的傾斜度不能超過千分之一，否則將會在塔板上造成死區(qū)，對于小直徑的精餾塔來說，如果塔板的安裝是先分節(jié)安裝，然后再組裝的話，則塔身的不垂直將直接影響全塔的所有塔板的水平度，使塔的效率降低。 （2）塔板 塔板要求水平，其水平度用水平

63、儀測定不能超過±2毫米。如果塔板不水平，將造成板面上的液層高度不均，塔內(nèi)上升蒸汽易從液層高度較小的淺處穿過，從而降低塔板的效率。 （3）溢流口 溢流口與下層塔板的距離，用根據(jù)生產(chǎn)能力和下層塔板的溢流堰的高度而定。但必須滿足溢流口插入受液盤的液體中，以封住上升蒸汽。如果溢流口與下層塔板的距離太近，則可能造成上層塔板的回流也不能順利流入下層塔板，使上層塔板的液層增高，下層塔板的壓力增大，嚴重時造成液泛。溢流口過高，超過溢流堰的高度時，上升的蒸汽“走短路”，從溢流管直接上升到上層塔板，起不到液封作用，影響塔板效率。 安裝時，對于各種具體的塔板類型都有不同程度的要求，如果不按要求去安裝，將可能使

64、塔的生產(chǎn)效率大大下降。 精餾塔的操作應該掌握好三個平衡 （1）物料平衡體現(xiàn)了塔的生產(chǎn)能力，它主要是靠進料量和塔頂、塔底采儲量來調(diào)節(jié)。當塔的操作不符合總的物料平衡式時，這可以從塔壓差的變化上看出，進得多，取得少，則塔壓差上升。對于一個固定的精餾塔來說，塔壓差應該在一定范圍內(nèi)。塔壓差過大，說明塔內(nèi)上升的蒸汽速度過快，霧沫夾帶嚴重，甚至發(fā)生液泛，破壞塔的正常操作；塔壓差過小，表明塔內(nèi)上升蒸汽的速度過小，塔板上的氣液湍動的程度過低、傳質(zhì)效果差，使塔板產(chǎn)生漏液，降低塔板效率。 如果精餾塔不符合對某組分的物料平衡式時，將有兩種表現(xiàn)： A、輕組分的采出量超過了物料平衡的量，在這種情況下，

65、將使塔內(nèi)的物料組成變重，全塔的溫度逐步升高，塔頂餾分中重組份的濃度增加，以致使質(zhì)量不合格。 B、另一種情況是重組份的采出量超過了物料平衡的量，全塔的物料組成將隨著操作的進行而逐漸變輕，塔身溫度下降，特別是釜溫明顯下降，釜液中輕組分的濃度增加。 由此可見，物料平衡掌握不好，將使整個塔的操作處于混亂狀況，達不到預期的目的。另外，如果正常的物料平衡受到破壞，那么，氣液相平衡也達不到預想的效果，隨之而來的熱量平衡也得重新調(diào)整。所以物料平衡是塔操作中的一個關(guān)鍵環(huán)節(jié)。 （2）氣液平衡主要體現(xiàn)了產(chǎn)品的質(zhì)量和損失情況。它是靠調(diào)節(jié)塔的操作條件（溫度、壓力）及塔板上氣液接觸的情況來達到的。因為，只有在溫度、

66、壓力固定時，才能確定氣液平衡組成。精餾塔的操作溫度和壓力是根據(jù)塔的分離任務（即關(guān)鍵組分的分離濃度）決定的。當溫度、壓力發(fā)生變化時，氣液平衡所決定的組成就發(fā)生了變化，產(chǎn)品的質(zhì)量或損失情況也發(fā)生了變化。但是，氣液相平衡的組成又是靠在每塊塔板上的氣液互相接觸進行傳質(zhì)和傳熱而實現(xiàn)的。這就是說，氣液相平衡和物料平衡密切相關(guān)。物料平衡掌握的好，塔內(nèi)上升蒸汽的速度合適，氣液接觸好，則傳質(zhì)效率高，每塊板上的氣液組成就愈接近于平衡組成，也就是常說的板效率高，反之亦然。當然，溫度、壓力也會隨著物料平衡的改變而變化?？傊浩胶獾慕M成與物料平衡有著密不可分的關(guān)系。反過來，溫度、壓力的改變又可造成塔板上氣相和液相相對量的改變，從而破壞原來的物料平衡。例如，釜溫低于規(guī)定值，會使塔板上的液相量增加，蒸汽量減少，釜液量增加，頂部產(chǎn)物量減少；當頂溫高于規(guī)定值時，就會使塔板上的氣相量增加，液相量減少，頂部產(chǎn)物量增加，釜液量減少。這些都會破壞原來的物料平衡。 （3）熱量平衡是物料平衡和氣液相平衡得以實現(xiàn)的基礎(chǔ)。沒有塔釜供熱就沒有上升蒸汽，沒有塔頂冷凝就沒有回流液，整個精餾過程就無法實現(xiàn)。而熱量平衡又是依附于物料平衡和