Transcript Chapter9

Chapter9
Approximate Methods for
Multicomponent,
Multistage Separations
Purpose and Requirements:
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Learn Fenske-Underwood-Giliiland Method
Learn Kremser Group Method
Key and Difficult Points:
Key Points
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Fenske-Underwood-Giliiland Method for Multicomponent,
Multistage Separations
Kremser Group Method for Multicomponent, Multistage
Separations
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Difficult Points
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Kremser Group Method for Multicomponent, Multistage
Separations
Outline
9.1 FENSKE-UNDERWOOD-GILLILAND
METHOD
9.2 KREMSER GROUP METHOD
Absorption
(Gas Absorption/Gas Scrubbing/Gas Washing吸收)
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Gas Mixture (Solutes or Absorbate)
Liquid (Solvent or Absorbent)
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Separate Gas Mixtures
Remove Impurities, Contaminants, Pollutants, or
Catalyst Poisons from a Gas(H2S/Natural Gas)
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Recover Valuable Chemicals
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Physical Absorption
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Chemical Absorption
(Reactive Absorption)
Figure 6.1 Typical Absorption Process
Absorption Factor
(A吸收因子)
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A = L/KV
Component
Water
Acetone
Oxygen
Nitrogen
Argon
A = L/KV
1.7
1.38
0.00006
0.00003
0.00008
K-value
0.031
2.0
45,000
90,000
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
Stripping
(Desorption解吸)
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Stripping
Distillation
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Stripping Factor
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(S解吸因子)
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S = 1/ A= KV/L
High temperature
Low pressure is desirable
Optimum stripping factor ：1.4.
6.1 EQUIPMENT
trayed tower
packed column
bubble column
spray tower
centrifugal contactor
Figure 6.2 Industrial Equipment for Absorption and Stripping
Trayed Tower
(Plate Clolumns板式塔)
Figure 6.3 Details of a contacting tray in a trayed tower
(a) perforation
(b) valve cap (c) bubble cap
(d) Tray with valve caps
Figure 6.4 Three types of tray openings for
passage of vapor up into liquid
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
(a) Spray(b) Froth(c) Emulsion(d) Bubble(e)Cellular Foam
Equilibrium between the exiting
vapor and liquid phases
is approached on each tray.
Figure 6.5 Possible vapor-liquid flow regimes for a contacting tray
Packed Columns
Figure 6.6 Details of internals
used in a packed column
Packing Materails
•More surface area for mass transfer
•Higher flow capacity
•Lower pressure drop
(a)
(b) Random
Structured
Packing
Packing
Materials
Materials
•Expensive
•Far less pressure drop
•Higher efficiency and capacity
Figure 6.7 Typical materials used in a packed column
6.2 ABSORBER/STRIPPER DESIGN
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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
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,
6. Number
of equilibrium
stages
temperature,
and pressure
7. Heat effects and need for cooling (heating)
2. Desired degree of recovery of one or more solutes
8. Type of absorber (stripper) equipment
3.
of absorber
absorbent
(stripping agent)
9. Choice
Height of
(stripper)
4.
and(stripper)
temperature, and allowable
10.Operating
Diameter pressure
of absorber
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
SUMMARY
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1. The Fenske-Underwood-Gilliland (FUG) method for simple
distillation of ideal and nearly ideal multicomponent mixtures is
useful for making preliminary estimates, of stage and reflux
requirements.
2. Based on a specified split of two key components in the feed,
mixture, the theoretical1, Fenske equation is used to determine
the minimum number of equilibrium stages at total reflux. The
theoretical Underwood equations are used to determine the
minimum reflux ratio for an infinite number of stages. The
empirical Gilliland correlation relates the minimum stages and
minimum reflux ratio to the actual reflux ratio and the actual
number of equilibrium stages.
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3. Estimates of the distribution of nonkey
components and the feed-stage location can be
made with the Fenske and Kirkbride equations,
respectively.
4. The Underwood equations are more restrictive
than the Fenske equation and must be used with
care and caution!
5 The Kremser group method can be applied to
simple strippers and liquid-liquid, extractors to make
approximate estimates of component recoveries for
specified values of entering flow rates and number of
equilibrium stages.
REFERENCES
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1. Kremser. A.. Nail. Petroleum News, 22(21), 43-49 (1930).
2. Edmister. W.C.. AIChE J., 3, 165-171 (1957).
3. Kobe, K.A.. and J.J. McKetta. Jr., Eds, Advances in
Petroleum Chemistry and Refining, Vol. 2, Interscience, New
York, 315-355 (1959).
4. Bachelor. J.B., Petroleum Refiner, 36(6), 161-170 (1957).
5, Fenske, M.R., Ind. Eng. Chem., 24, 482-485 (1932).
6. Shiras.R.N., D.N. Hanson, and C.H. Gibson, Ind. Eng.
Chem.,42,871-876(1950).
7. Underwood, A.J.V.. Trans. Inst. Chem. Eng., 10,112-158
(1932).
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. Gilliland. E.R., Ind. Eng. Chem., 32, 1101-1106 (1940).
9. Underwood. A.J.V., Inst. Petrol, 32, 614-626 (1946).
10.Barnes, F.J., D.N. Hanson, and C.J. King. Ind. Eng.
Chem.,Process Des. Dev., 11, 136-140 (1972).
11.Tavana, M, and D.N. Hanson, Ind. Eng. Chem., Process Des.
Dev., 18, 154-156 (1979).
12. Fair, J.R.. and W.L. Bolles. Chem. Eng., 75(9). 156-178
(1%8).
13. Gilliland. E.R., Ind. Eng. Chem., 32, 1220-1223 (1940).
14. Robinson, C.S., and E.R. Gilliland. Elements of Fractional
Distillation, 4th ed., McGraw-Hill, New York, pp. 347-350 (1950).
15. Brown, G.G., and H.Z. Martin, Trims. AIChE, 35, 679708(1939).
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Van Winkle, M., and W.G. Todd. Chem. Eng., 78(21). 136148(1971).
17.Molokanov, Y.K., T.P. Korablina. N.I. Mazurina. and G.A.
Nikiforov. Int. Chem. Eng., 12(2). 209-212 (1972).
18. Guerreri, G., Hydrocarbon Processing, 48(8), 137-142
(1969).
19. Donnell, J.W., and C.M. Cooper. Chem. Eng., 57, 121-124
(1950).
20. Oliver, E.D., Diffusional Separation Processes: Theory,
Design, and Evaluation, John Wiley and Sons, New York. pp.
104-105 (1966).
21. Strangio, V.A., and R.E. Treybal, Ind. Eng. Chem., Process
Des. Dev., 13, 279-285 (1974).
22. Kirkbride, C.G., Petroleum Refiner, 23(9), 87-102 (1944).
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. Stupin, W.J., and FJ. Lockhart, "The Distribution of Non-Key
Components in Multicomponent Distillation," presented at the
61st Annual Meeting of the AIChE, Los Angeles, CA, December
1-5, 1968.
24. Souders, M., and G.G. Brown, Ind. Eng. Chem., 24,519522(1932).
25. Horton, G., and W.B. Franklin. Ind. Eng. Chem., 32, 13841388 (1940).
26. Edmister, W.C., Ind. Eng. Chem., 35, 837-839 (1943).
27. Smith, B.D., and W.K. Brinkley, AIChE J., 6, 446-450 (I960).