传质与分离工程精选PPT.ppt

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1、传质与分离工程1第1页，此课件共23页哦Fig.21.332第2页，此课件共23页哦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，此课件共23页哦To apply a known Murphree efficiency to an entire column,it is ne

2、cessary 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，此课件共23页哦How to plot the effective equilibrium curve?Giving xGiving xn n,find y*,find y*n n from equilibrium curve and y from equ

3、ilibrium curve and yn+1n+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

4、 a discount for plate efficiencyThe reboiler is not subject to a discount for plate efficiency,and the true equilibrium curve is used for the last step in the and the true equilibrium curve is used for the last step in the stripping section.stripping section.5第5页，此课件共23页哦How many actual plates are n

5、eeded in the left construction?6第6页，此课件共23页哦How many actual plates are needed in the left construction?No fractional actual plate,then7第7页，此课件共23页哦Murphree efficiency can be different from individual plates,and this is more accurate to calculate the number of actual plates than by overall efficiency

6、 of a column全塔效率全塔效率.8第8页，此课件共23页哦3.BATCH DISTILLATION（间歇精馏间歇精馏间歇精馏间歇精馏 ）pp.700-7031)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，此课件共23页哦There are ma

7、ny cases where There are many cases where batch distillationbatch distillation间歇精馏间歇精馏间歇精馏间歇精馏 is preferred,particularly in the is preferred,particularly in the food and pharmaceutical food and pharmaceutical industries.industries.Batch distillationBatch distillation is used when is used when small

8、amounts of small amounts of productproduct are made in a pilot plant to provide samples for are made in a pilot plant to provide samples for product sampling or testing.product sampling or testing.Features:1)Unsteady state;2)Without reflux;3)One-stage Features:1)Unsteady state;2)Without reflux;3)One

9、-stage partial vaporization process.partial vaporization process.The vapor leaving the still at any The vapor leaving the still at any time is in equilibrium with the liquid in the still.time is in equilibrium with the liquid in the still.y y is in is in equilibrium with equilibrium with x x.10第10页，

10、此课件共23页哦Batch FeedBatch FeedCondenserCondenserCooling waterCooling waterProduct Product receiverreceiver11第11页，此课件共23页哦(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 Rayleigh equation.Eq.(21.83)is known as the Rayleigh equation.dx/(y-x)dx/(y-x)can be integrated graphical

11、ly or numerically using can be integrated graphically or numerically using equilibrium data(equilibrium data(yxyx equilibrium relationship).equilibrium relationship).12第12页，此课件共23页哦(3)For an ideal mixture,That is,Becauseor13第13页，此课件共23页哦After integration between limits14第14页，此课件共23页哦Number of moles

12、of product:DEXAMPLE 21.9.Average concentration of product:15第15页，此课件共23页哦Advantages.The advantages of batch distillation are that several products can be made from a single unit,and can effectively handle sludges and solids.Disadvantages.For a given product rate,the equipment is larger.It requires m

13、ore operator attention,uses more energy,and because it is a dynamic process,is harder to control and model.16第16页，此课件共23页哦2)Batch Distillation with reflux间歇精馏间歇精馏/有回流的有回流的间歇蒸馏间歇蒸馏 pp.702-703In many cases,a rectifying column with reflux is used to improve the performance of the batch still.Flow diagr

14、am.Features:Features:Unsteady state;Unsteady state;Only rectifying section in the Only rectifying section in the column.column.Product concentration differs from different Product concentration differs from different operations.operations.17第17页，此课件共23页哦Two basic operation methods:(a).Keep the top c

15、omposition(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 when the amount of product or the average concentration in the total product reaches a

16、certain(某个某个某个某个)value.18第18页，此课件共23页哦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(Nactual).In order to obtain overhead and bottom products with required mole fractions

17、 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，此课件共23页哦 Attentions of Operation analysis of distillation column:Attentions of Operation analysis of distillation column:(a)Suitable feed plate position;

18、(a)Suitable feed plate position;(b)Keep material balance:If D and B changed,x(b)Keep material balance:If D and B changed,xD D and x and xB B will will be changed too.be changed too.(c)(c)Reflux ratio is the key measure of controlling product Reflux ratio is the key measure of controlling product qua

19、lity.quality.For example,if N is given,R For example,if N is given,RD Dx xD D ,x,xB B .(d)If x(d)If xF F changed,feed plate position should be changed too.changed,feed plate position should be changed too.20第20页，此课件共23页哦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

20、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 unitynear or equal to unity,the,the separation of components is difficult by conventional separation of components is difficult by conventional distillation,or impossible because of distillation,or impo

21、ssible because of azeotropeazeotrope恒沸混恒沸混恒沸混恒沸混合物合物合物合物 formation.formation.Basic principles of azeotropic and extractive distillationBasic principles of azeotropic and extractive distillation:Adding a third component(Adding a third component(solventsolvent)to)to increase the increase the relative

22、volatilityrelative volatility of the original components,so that of the original components,so that the mixtures with relative volatility near or equal to the mixtures with relative volatility near or equal to unity can be separated by conventional distillation.unity can be separated by conventional

23、 distillation.21第21页，此课件共23页哦(1)(1)Azeotropic distillationAzeotropic distillation恒沸精馏恒沸精馏恒沸精馏恒沸精馏 Materials called Materials called entrainersentrainers(夹带剂夹带剂夹带剂夹带剂)(third component)(third component)are added to the original mixture,and usually a new are added to the original mixture,and usually a

24、new azeotrope with lowest-boiling pointsazeotrope with lowest-boiling points有最低恒沸点的恒沸物有最低恒沸点的恒沸物有最低恒沸点的恒沸物有最低恒沸点的恒沸物 is formed.The new azeotrope will of course contain is formed.The new azeotrope will of course contain one or more of the feed components,and leaving one or more of the feed components

25、,and leaving behind component(s)which may be recovered in the behind component(s)which may be recovered in the pure state.pure state.Example:Recovery and purification of ethanol and water.Example:Recovery and purification of ethanol and water.Flow diagramFlow diagram Selection of Selection of entrai

26、ners.entrainers.22第22页，此课件共23页哦(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 the feed relative volatility of key components

27、 in the feed mixture.The effective mixture.The effective extractive solventextractive solvent萃取剂萃取剂萃取剂萃取剂will will selectively interact with one(or more)of the selectively interact with one(or more)of the components,thereby increasing relative ponents,thereby increasing relative volatilities.Example

28、: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 from a mixture containing butanebutane丁烷丁烷丁烷丁烷 and and butenesbutenes丁烯丁烯丁烯丁烯.Flow diagram.Flow diagram Selection of Selection of extractiveextractive solventssolvents.23第23页，此课件共23页哦