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Equilibrium-Based Methods for Multicomponent Absorption, Stripping, Distillation, and Extraction

Chapter7. Equilibrium-Based Methods for Multicomponent Absorption, Stripping, Distillation, and Extraction. Purpose and Requirements: Know Equilibrium-Based Methods for Multicomponent Learn to use ASPEN PLUS, ChemCAD, HYSIM, PRO/II. Key and Difficult Points: Key Points

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Equilibrium-Based Methods for Multicomponent Absorption, Stripping, Distillation, and Extraction

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  1. Chapter7 Equilibrium-Based Methods for Multicomponent Absorption, Stripping, Distillation, and Extraction

  2. Purpose and Requirements: • Know Equilibrium-Based Methods for Multicomponent • Learn to use ASPEN PLUS, ChemCAD, HYSIM, PRO/II Key and Difficult Points: Key Points • Theoretical Model for an Equilibrium Stage • General Strategy of Mathematical Solution Difficult Points • Equation-Tearing Procedures • Simultaneous Correction Procedures • Inside-Out Method

  3. Outline 7.1 THEORETICAL MODEL FOR AN EQUILIBRIUM STAGE 7.2 GENERAL STRATEGY OF MATHEMATICAL SOLUTION 7.3 EQUATION-TEARING PROCEDURES 7.4 SIMULTANEOUS CORRECTION PROCEDURES 7.5 INSIDE-OUT METHOD

  4. Absorption (Gas Absorption/Gas Scrubbing/Gas Washing吸收) • Gas Mixture (Solutes or Absorbate) • Liquid (Solvent or Absorbent) • Separate Gas Mixtures • Remove Impurities, Contaminants, Pollutants, or Catalyst Poisons from a Gas(H2S/Natural Gas) • Recover Valuable Chemicals

  5. Physical Absorption • Chemical Absorption (Reactive Absorption) Figure 6.1 Typical Absorption Process

  6. Absorption Factor(A吸收因子) • A = L/KV Component A = L/KV K-value Water 1.7 0.031 Acetone 1.38 2.0 Oxygen 0.00006 45,000 Nitrogen 0.00003 90,000 Argon 0.00008 35,000 • Larger the value of A，Fewer the number of stages required • 1.25 to 2.0 ，1.4 being a frequently recommended value

  7. Stripping(Desorption解吸) • Stripping • Distillation • Stripping Factor(S解吸因子) • S = 1/ A= KV/L High temperature Low pressure is desirable Optimum stripping factor ：1.4.

  8. 7.1 EQUIPMENT trayed tower packed column bubble column spray tower centrifugal contactor Figure 6.2 Industrial Equipment for Absorption and Stripping

  9. Trayed Tower(Plate Clolumns板式塔) Figure7.3 Details of a contacting tray in a trayed tower

  10. (a) perforation (b) valve cap (c) bubble cap (d) Tray with valve caps Figure 7.4 Three types of tray openings for passage of vapor up into liquid

  11. (a) Spray(b) Froth(c) Emulsion(d) Bubble(e)Cellular Foam Liquid carries no vapor bubbles to the tray below Vapor carries no liquid droplets to the tray above No weeping of liquid through the openings of the tray Equilibrium between the exiting vapor and liquid phases is approached on each tray. Figure 7.5 Possible vapor-liquid flow regimes for a contacting tray

  12. Packed Columns Figure 7.6 Details of internals used in a packed column

  13. More surface area for mass transfer • Higher flow capacity • Lower pressure drop Packing Materails (a) Random Packing Materials (b) Structured Packing Materials • Expensive • Far less pressure drop • Higher efficiency and capacity Figure 7.7 Typical materials used in a packed column

  14. 7.2 ABSORBER/STRIPPER DESIGN • 7.2.1 General Design Considerations • 7.2.2 Trayed Towers • 7.2.2.1 Graphical Equilibrium-Stage • 7.2.2.2 Algebraic Method for Determining the Number of Equilibrium • 7.2.2.3 Stage Efficiency • 7.2.3 Packed Columns • 6.2.3.1 Rate-based Method • 6.2.3.2 Packed Column Efficiency, Capacity, and Pressure Drop

  15. 7.2.1 General Design Considerations Design or analysis of an absorber (or stripper) requires consideration of a number of factors, including: 1.Entering gas (liquid) flow rate, composition, temperature, and pressure 2. Desired degree of recovery of one or more solutes 3. Choice of absorbent (stripping agent) 4. Operating pressure and temperature, and allowable gas pressure drop 5. Minimum absorbent (stripping agent) flow rate and actual absorbent (stripping agent) flow rate as a multiple of the minimum rate needed to make the separation 6. Number of equilibrium stages 7. Heat effects and need for cooling (heating) 8. Type of absorber (stripper) equipment 9. Height of absorber (stripper) 10. Diameter of absorber (stripper)

  16. SUMMARY • 1. Rigorous methods are readily available for computer-solution of equilibrium-based models for multicomponent, multistage absorption, stripping, distillation, and liquid-liquid extraction. • 2. The equilibrium-based model for a countercurrent-flow cascade provides for multiple feeds, vapor side streams, liquid side streams, and intermediate heat exchangers. Thus, the model can handle almost any type of column configuration. • 3. The model equations include component material balances, total material balances, phase equilibria relations, and energy balances. • 4. Some or all of the model equations can usually he grouped so as to obtain tridiagonal matrix equations, for which an efficient solution algorithm is available. • 5. Widely used methods for iteratively solving all of the model equations are the bubble-point (BP) method, the sum-rales (SR) method, the simultaneous correction (SO method, and the inside-out method.

  17. 6. The BP method is generally restricted to distillation problems involving narrow-boiling feed mixtures. • 7. The SR method is generally restricted to absorption and stripping problems involving wide-boiling feed mixtures or in the ISR form to extraction problems. • 8. The SC and inside-out methods are designed to solve any type of column configuration for any type of feed mixture. Because of its computational efficiency, the inside-oi method is often the method of choice; however, it may fail to converge when highly! nonideal liquid mixtures are involved, in which case the slower SC method should j be tried. Both methods permit considerable flexibility in specifications. • 9. When both the SC and inside-out methods fail, resort can be made to the much slower relaxation and continuation methods.

  18. REFERENCES • 1. Wang. J.C.. and G.E. Hcnkc, Hydrocarbon Processing 45(8). 155-163 (1966). • 2. Myers. A.L.. and W.D. Seider. Introduction to Chemical Engi­neering and Computer Calculations, Prentice-Hall, Englewood Cliffs. NJ. 4X4-507 (1976). • 3. Lewis. W.K.. and G.L. Matheson, Ind. Eng. Chem. 24, 496-498 (1932). • 4. Thiele, E.W.. and R.L. Geddes. Ind. Eng. Chem. 25, 290 (1933). • 5. Holland. C.D.. Mullicomponent Distillation. Prentice-Hall. En­glewood Cliffs. NJ (1963). • 6. Amundson. N.R.. and A.J. Pontinen. Ind. Eng. Chem. 50, 730-736 (1958). • 7. Friday. J.R.. and B.D. Smith. AlChE J. 10, 698-707 (1964). • 8. Boston. J.K. and S.L. Sullivan. Jr., Can. J. Chem. Eng. 52,52-63 (1974).

  19. 16. Shinohara, T.. P.J. Johansen. and J.D. Seader, Stagewise Compu­lations—Computer Programs for Chemical Engineering Education, J. Christensen, Ed.. Aztec Publishing, Austin, TX pp. 390-428, A-17 (1972). • 17. Tsuboka. T.. and T. Katayama. J. Chem. Eng. Japan 9, 40-45 (1976). • 18. Hala, E.. I. Wiehterle. J. Polak. and T. Bouhlik. Vapor-Liquid Equilibrium Data at Normal Pressures. Pergamon. Oxford p. .108 ! (1968). • 19. Steih. V.H.../. Praki. Chem. 4, Reihe. Bd. 28. 252-280 (1965). • 20. Cohen, G.. and H. Renon. Can.J. Chem. Eng. 48, 241-2% j (1970). • 21. Goldstein, R.P.. and R.B. Stanlield, Ind. Eng. Chem., from' De.s. Develop. 9, 78-84 (1970). • 22. Naphtali, L.M.. "The distillation column as a large system." paper presented at the AIChE56th National Meeting. San Francisco.May 16-19. 1965.

  20. 23. Naphtali. L.M.. and P.P. Sandholm. AlChE J. 17, 14S-I53 (1971). • 24. Fredenslund. A.. J. GmehJing, and P. Rasmussen. Vapor-Liquid; Equilibria Using UNIFAC, A Group Contribution Method. Elscvicr, ; Amsterdam (1977). • 25. Beveridge, G.S.G., and R.S. Schechter. Optimization: Theory and Practice, McGraw-Hill, New York pp. 180-189 (1970). ; • 26. Block, U.. and B. Hegner, AIChE .I. 22, 582-589 (1976). • 27. Hofeling, B.. and J.D. Seader. AlChE J. 24, 1 131-1134 (1978). , • 28. Boston, J.F., and S.L. Sullivan. Jr., Can. .J. Chem. Engr. 52,52-63(1974). • 29. Boston. J.F., and H.I. Britt. Comput. Chem. Engng. 2, 109-122 (1978). • 30. Boston, J.F.. ACS Symp. Ser, No. 124. 135-151 (1980).

  21. 31. Russell, R.A., Chem. Eng. 90(20), 53-59 (1983). • 32. Trevino-Lo/ano. R.A.. T.P. Kisala, and J.F. Boston. Comput. Chem. Engng. 8, 105-115 (1984). • 33. Jelinek. J., Comput. Chem. Engng. 12, 195-198 (1988). • 34. Venkataraman. S.. W.K. Than, and J.F. Boston. Chem. % Prog. 86(8), 45-54 (1990). • 35. Robinson. C.S., and E.R. Gilliland, Elements of Fractional Dis­tillation, 4th edition, pp. 232-236. McGraw-Hill. New York (1950). • 36. Broyden, C.G.. Math Comp. 19, 577-593 (1965). • 37. Kister, H. Z.. "Distillation Design". McGraw-Hill, Inc., NY (1992)

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