CBE 417 Unit Operations Lecture 3 7 Sep

CBE 417 “Unit Operations” Lecture: 3 7 Sep 2012 1

Overview • Introduction • UO course overview • Equilibrium Stage separations • What are “Unit Operations” • Brief thermodynamics review • Binary flash with energy balance • Multicomponent flash 2

Vapor Liquid Equilibrium (VLE) Vapor phase: good; liquid phase: good for HC or moderate – high pressures (compressible liquid phase) Typically used for liquid phase fugacity calculations Used for special cases (like gases dissolving into liquid phase) Typical simplifications: Ideal vapor phase Ideal liquid phase Raoult’s Law 3

Phase Equilibrium (Alternate Form VLE) Historically, when estimates were done by hand: • Seader & Henley (2006) 4

Phase Equilibrium (Recommendations) 5

Phase Equilibrium (Alternate Form VLE) Historically, when estimates were done by hand: Sometimes the K values are nearly composition independent “hand” techniques of design/solution have used De. Priester Charts (hydrocarbons): 6

De. Priester Chart P = 2 bar T = 100 o. C Isobutane others…. 7

De. Priester (equation fit) 8

Vapor Liquid Equilibrium (VLE) Vapor phase: good; liquid phase: good for HC or moderate – high pressures (compressible liquid phase) Typically used for liquid phase fugacity calculations Used for special cases (like gases dissolving into liquid phase) Equations of state models Activity coefficient models 9

Equations of State Models 10

Phase Equilibrium (Recommendations) 11

Activity Coefficient Models 12

Activity Coefficient Models 13

Activity Coefficient Models 14

Activity Coefficient Models 15

CBE 417 “Unit Operations” Lecture: 4 10 Sep 2012 16

Overview • Introduction • UO course overview • Equilibrium Stage separations • What are “Unit Operations” • Brief thermodynamics review • Binary flash with energy balance • Multicomponent flash 17

Activity Coefficient Models 18

Phase Equilibrium (Recommendations) Mixtures to model: • • Me. OH – water Et. OH – water propanol – water n-butane – n-pentane benzene – toluene acetic acid – propionic acid CO 2 – toluene (high P) 19

Other Equilibrium Diagrams: P – T diagram 20

PT Equilibrium Diagram: http: //www. dlr. de/vt/en/Portaldata/29/Resources/dokumente/CO 2 Gasphase. Diagrams_Goos_Riedel_Zhao_Blum 2010_GHGT_webnew. pdf 21

Other Equilibrium Diagrams: P = 1. 013 bar T = various o. C Benzene - Toluene Y vs X diagram T vs X or Temp vs Composition 22

Other Equilibrium Diagrams: 23

Y vs X Diagram (LLE) 24

Effect of Pressure: 25

Effect of Pressure: • Seader & Henley (2006) 26

Other Equilibrium Diagrams: 27

Overview • Brief thermodynamics review • Binary Flash with energy balance • Sequential solution • Simultaneous solution • Multicomponent Flash 28

Binary Flash Overall mole balance on a mole balance on b equilibrium eqn for a mole balance on a 29

Binary Flash separation: Specify: a = n-pentane b = n-hexane Find: Vfrac P functi on Xa Xb Ya Yb 0. 471 V/F 3. 000 bar -1. 89 E -08 0. 394 0. 606 0. 619 0. 381 30

Binary Flash Overall mole balance on a mole balance on b equilibrium eqn for a mole balance on a 31

Binary Flash separation: Specify: Find: a = n-pentane b = n-hexane 32

Binary Flash Graphical Solution: mole balance on a solve for ya “Operating Line” 33

Binary Flash Graphical: 1 Equilibrium curve 0. 9 y=x 0. 8 0. 7 Solution! Ya 0. 6 0. 5 0. 4 What if f is unknown, but T is known? Za 0. 3 0. 2 0. 1 0 0 0. 1 0. 2 0. 3 0. 4 0. 5 0. 6 0. 7 0. 8 0. 9 Xa 1 Limits: f =0 f =1 34

Binary Flash Energy Balance EB on CV: 35

Other Equilibrium Diagrams: 36

Alternative Thermodynamics Older (hand methods): Raoult’s law Relative Volatility (VLE): Aside (couple with MB) 37

Separation Factor or Relative Volatility 38

Effect of Pressure: • Seader & Henley (2006) 39

Constant Relative Volatility? 1 0. 9 0. 8 Y Me. OH 0. 7 0. 6 0. 5 0. 4 0. 3 0. 2 0. 1 0 0 0. 2 0. 4 0. 6 0. 8 1 X Me. OH 40

Alternative Thermodynamics Ki with multicomponent flash: Into MB: Sequential solution: suggestions p 35 -37 (Rachford-Rice Eqn) Simultaneous solution technique: suggestions p 40 -43 41

Sizing Flash Drums 42

Simulators Flash input: Sensitivity Analysis: Design Spec: 43

Questions? 44