传质与分离工程优秀PPT.ppt

《传质与分离工程优秀PPT.ppt》由会员分享，可在线阅读，更多相关《传质与分离工程优秀PPT.ppt（23页珍藏版）》请在淘文阁 - 分享文档赚钱的网站上搜索。

1、传质与分离工程1第1页，本讲稿共23页Fig.21.332第2页，本讲稿共23页Triangle acd represents the ideal plate and triangle abe the actual plate.The actual plate,instead of enriching the vapor from yn+1 to y*n,accomplished a lesser enrichment yn-yn+1.3第3页，本讲稿共23页To apply a known Murphree efficiency to an entire column,it is neces

2、sary only to replace the true equilibrium curve ye versus xe by an effective equilibrium curve ye versus xe,whose ordinates are calculated from the equation(21.70).4第4页，本讲稿共23页How to plot the effective equilibrium curve?Giving xGiving xn n,find y*n n from equilibrium curve and y from equilibrium cur

3、ve and yn+1 from from operating line,calculate yoperating line,calculate yn n from equation(21.70),then plot from equation(21.70),then plot point(xpoint(xn n,y,yn n)How to determine the number of actual plates?How to determine the number of actual plates?The reboiler is not subject to a discount for

4、 plate efficiency,and the true equilibrium curve is used for the last,and the true equilibrium curve is used for the last step in the stripping section.step in the stripping section.5第5页，本讲稿共23页How many actual plates are needed in the left construction?6第6页，本讲稿共23页How many actual plates are needed i

5、n the left construction?No fractional actual plate,then7第7页，本讲稿共23页Murphree efficiency can be different from individual plates,and this is more accurate to calculate the number of actual plates than by overall efficiency of a column全塔效率全塔效率.8第8页，本讲稿共23页3.BATCH DISTILLATION（间歇精馏间歇精馏间歇精馏间歇精馏 ）pp.700-7

6、031)Simple Distillation简单蒸馏简单蒸馏(自学自学)(1)Flow diagram(Refer to Fig.21.37)Batch FeedBatch Feed间歇进料间歇进料间歇进料间歇进料CondenserCondenserCooling waterCooling waterProduct Product receiverreceiverStillStill9第9页，本讲稿共23页 There are many cases where There are many cases where batch distillationbatch distillation间歇精

7、馏间歇精馏间歇精馏间歇精馏 is preferred,particularly in the food and pharmaceutical food and pharmaceutical industries.industries.Batch distillationBatch distillation is used when is used when small amounts of small amounts of productproduct are made in a pilot plant to provide samples for product sampling or te

8、sting.Features:1)Unsteady state;2)Without reflux;3)One-Features:1)Unsteady state;2)Without reflux;3)One-stage partial vaporization process.stage partial vaporization process.The vapor leaving the The vapor leaving the still at any time is in equilibrium with the liquid in the still.still at any time

9、 is in equilibrium with the liquid in the still.y y is in equilibrium with is in equilibrium with x.10第10页，本讲稿共23页Batch FeedBatch FeedCondenserCondenserCooling waterCooling waterProduct Product receiverreceiver11第11页，本讲稿共23页(2)Rayleigh equation（瑞利方程）（瑞利方程）（瑞利方程）（瑞利方程）HeaterEq.(21.83)is known as the

10、Rayleigh equation.Eq.(21.83)is known as the Rayleigh equation.dx/(y-x)dx/(y-x)can be can be integrated graphically or numerically using equilibrium integrated graphically or numerically using equilibrium data(data(yxyx equilibrium relationship).equilibrium relationship).12第12页，本讲稿共23页(3)For an ideal

11、 mixture,That is,Becauseor13第13页，本讲稿共23页After integration between limits14第14页，本讲稿共23页Number of moles of product:DEXAMPLE 21.9.Average concentration of product:15第15页，本讲稿共23页Advantages.The advantages of batch distillation are that several products can be made from a single unit,and can effectively h

12、andle sludges and solids.Disadvantages.For a given product rate,the equipment is larger.It requires more operator attention,uses more energy,and because it is a dynamic process,is harder to control and model.16第16页，本讲稿共23页2)Batch Distillation with reflux间歇精馏间歇精馏/有回流的间有回流的间歇蒸馏歇蒸馏 pp.702-703In many ca

13、ses,a rectifying column with reflux is used to improve the performance of the batch still.Flow diagram.Features:Features:Unsteady state;Only rectifying section in the Only rectifying section in the column.column.Product concentration differs from different Product concentration differs from differen

14、t operations.operations.17第17页，本讲稿共23页Two basic operation methods:(a).Keep the top composition(xD)constant by increasing the reflux ratio as the composition of the liquid in the reboiler changes.(b).Fix the reflux ratio and let the overhead product purity vary with time,stopping the distillation whe

15、n the amount of product or the average concentration in the total product reaches a certain(某个某个某个某个)value.18第18页，本讲稿共23页Calculation and analysis for the operation of a distillation column.The plate column has been established,and the following data are given:Equilibrium relationship;xF;q;N and M(Na

16、ctual).In order to obtain overhead and bottom products with required mole fractions of xD and xB,the reflux ratio RD and the feed plate position must be determined.Calculation method:Trial and error（反复试验）（反复试验）（反复试验）（反复试验）.19第19页，本讲稿共23页Attentions of Operation analysis of distillation column:(a)Suit

17、able feed plate position;(b)Keep material balance:If D and B changed,xD D and xB B will be changed too.will be changed too.(c)(c)Reflux ratio is the key measure of controlling product quality.For example,if N is given,RD Dx xD,xB B .(d)If x(d)If xF F changed,feed plate position should be changed too

18、.changed,feed plate position should be changed too.20第20页，本讲稿共23页4.AZEOTROPIC AND EXTRACTIVE DISTILLATION pp.131（恒沸精馏和萃取精馏恒沸精馏和萃取精馏恒沸精馏和萃取精馏恒沸精馏和萃取精馏）When When relative volatilityrelative volatility（相对挥发度）（相对挥发度）（相对挥发度）（相对挥发度）near or equal to unity,the separation of components is difficult by conven

19、tional the separation of components is difficult by conventional distillation,or impossible because of distillation,or impossible because of azeotropeazeotrope恒沸混合物恒沸混合物恒沸混合物恒沸混合物 formation.formation.Basic principles of azeotropic and extractive distillationBasic principles of azeotropic and extract

20、ive distillation:Adding a third component(Adding a third component(solventsolvent)to)to increase the relative increase the relative volatilityvolatility of the original components,so that the mixtures with relative volatility near or equal to unity can be separated by conventional distillation.21第21

21、页，本讲稿共23页(1)(1)Azeotropic distillationAzeotropic distillation恒沸精馏恒沸精馏 Materials called Materials called entrainersentrainers(夹带剂夹带剂夹带剂夹带剂)(third component)are(third component)are added to the original mixture,and usually a new added to the original mixture,and usually a new azeotrope with lowest-boi

22、ling pointsazeotrope with lowest-boiling points有最低恒沸点的恒沸有最低恒沸点的恒沸有最低恒沸点的恒沸有最低恒沸点的恒沸物物物物 is formed.The new azeotrope will of course contain one or more of the feed components,and leaving behind component(s)which may be recovered in the pure state.Example:Recovery and purification of ethanol and water

23、.Flow diagram Selection of Selection of entrainers.entrainers.22第22页，本讲稿共23页(2)(2)Extractive distillationExtractive distillation萃取精馏萃取精馏萃取精馏萃取精馏 A solvent is added to the distillation tower to increase A solvent is added to the distillation tower to increase relative volatility of key components in

24、the feed relative volatility of key components in the feed mixture.The effective mixture.The effective extractive solvent萃取剂萃取剂萃取剂萃取剂will will selectively interact with one(or more)of the components,selectively interact with one(or more)of the components,thereby increasing relative volatilities.ther

25、eby increasing relative volatilities.Example:Use of Example:Use of furfuralfurfural糠醛糠醛糠醛糠醛 to permit the separation of to permit the separation of butadienebutadiene丁二烯丁二烯丁二烯丁二烯 from a mixture containing butanebutane丁丁丁丁烷烷烷烷 and and butenesbutenes丁烯丁烯丁烯丁烯.Flow diagram.Flow diagram Selection of Selection of extractive solventssolvents.23第23页，本讲稿共23页