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

1
Equilibrium-Based Methods for Multicomponent
Absorption, Stripping, Distillation, and
Extraction
Chapter10
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

• 10.1 THEORETICAL MODEL FOR AN EQUILIBRIUM STAGE
• 10.2 GENERAL STRATEGY OF MATHEMATICAL SOLUTION
• 10.3 EQUATION-TEARING PROCEDURES
• 10.4 SIMULTANEOUS CORRECTION PROCEDURES
• 10.5 INSIDE-OUT METHOD

4
Absorption (Gas Absorption/Gas Scrubbing/Gas
Washing??)

• 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????)

• 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??)

• Stripping
• Distillation
• Stripping Factor(S????)
• S 1/ A KV/L

High temperature Low pressure is
desirable Optimum stripping factor 1.4.
8
6.1 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???)
Figure 6.3 Details of a contacting tray in a
trayed tower
10
(b) valve cap
(c) bubble cap
(a) perforation
(d) Tray with valve caps

Figure 6.4 Three types of tray openings for
passage of vapor up into liquid
11
Froth
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.
(a) Spray(b) Froth(c) Emulsion(d)
Bubble(e)Cellular Foam
Figure 6.5 Possible vapor-liquid flow regimes for
a contacting tray
12
Packed Columns
Figure 6.6 Details of internals
used in a packed column
13
Packing Materails

• More surface area for mass transfer
• Higher flow capacity
• Lower pressure drop

(a) Random Packing Materials
(b) Structured Packing Materials

• Expensive
• Far less pressure drop
• Higher efficiency and capacity

Figure 6.7 Typical materials used in a packed
column
14
6.2 ABSORBER/STRIPPER DESIGN

• 6.2.1 General Design Considerations
• 6.2.2 Trayed Towers
• 6.2.2.1 Graphical Equilibrium-Stage
• 6.2.2.2 Algebraic Method for Determining
• the Number of Equilibrium
• 6.2.2.3 Stage Efficiency
• 6.2.3 Packed Columns
• 6.2.3.1 Rate-based Method
• 6.2.3.2 Packed Column Efficiency, Capacity,
• and Pressure Drop

15
6.2.1 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 CompulationsComputer 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

• 9. Boston. J.F.. and S.L. Sullivan. Jr.. Can. J.
  Chem. Eng. 50, 663-669 (1972).
• 10. Johanson, P.J., and J.D. Seader, Stagewi.se
  Computations-Computer Programs for Chemical
  Engineering Education (ed. by J.Christensen).
  A/tee Publishing, Austin. TX pp. 349-389,
  A-16(1972).
• 11. Lapidus, L.. Digital Computation for Chemical
  Engineers, McGraw-Hill. New York pp. 308-309
  (1962).
• 12. Orbach. ().. and C.M. Crowe, Can. J. Chem.
  Eng. 49, 509-513(1971).
• 13. Scheibel. E.G.. Ind. Eng. Chem 38,397-399
  (1946).
• 14. Sujata. A.D.. Hydrocarbon Processing 40(12).
  137-140 (1961).
• 15. Burningham, D.W., and F.D. Otto, Hydrocarbon
  Processing 46(10). 163-170 (1967)

21

• 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).

22

• 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)

23
(No Transcript)