Unit Operations Lecture 22 (continued) 1 16 Nov 2012
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Trayed Columns (Diameter) 2 Chap 6 (10,p 314, Wankat) Fairs
Procedure o Considers entrainment flooding (most freq.) o Downcomer
flooding (sometimes) need different procedure o Downcomer flooding
rare if (1- ) 10% Used in AspenPlus James R. Fair (1920 -2010)
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Trayed Columns (Diameter) 3 Plate spacing (selected for
maintenance, performance). Typ: o 12 16 for Dia < 5 o 24 larger
columns Calc Dia & round up to nearest foot (USA) o 2.5 minimum
dia. o If < 2.5 consider packed tower Figure 6.23
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In-Class Exercise 4 Data: Let: Estimate the tower diameter in
meters. Pause video and do exercise. When done, resume the
video.
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In-Class Exercise 5 Data: Let: Estimate the tower diameter in
meters. G =7920kg/hr2.2kg/s L =2883kg/hr0.801kg/s roe V1.92kg/cum
roe L986kg/cum Flv =0.016 Csb,f =0.39ft/s surf ten70dyne/cm u flood
=11.34ft/s Ad/A =0.1 f =0.8 Dt =0.766m
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6 Tower Diameter
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AspenPlus In-Class Exercise 7 Estimate the tower diameter in
meters. (by hand and by AspenPlus) Benzene Toluene Separation F =
100 kmole/hr X BZ = 0.6 saturated liquid Use sieve trays
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AspenPlus PFD 8
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Column Internals 9 Base method: NRTL
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Column Internals 10 Not optimized by DSTWU N feed = 15 P col =
1.013 bar (constant)
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Column Internals 11
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Column Internals 12
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Column Internals 13
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Column Internals 14
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Column Internals 15
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Column Internals 16
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Column Internals 17
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Column Internals 18
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AspenPlus In-Class Exercise 19 Estimate the tower diameter in
meters. (by hand and by AspenPlus) Benzene Toluene Separation F =
100 kmole/hr X BZ = 0.6 saturated liquid Use sieve trays G
=30757.9kg/hr8.544kg/s L =34443.9kg/hr9.568kg/s roe V2.92kg/cum roe
L780.68kg/cum Flv =0.06849 Csb,f =0.375ft/s surf ten18.18dyne/cm u
flood =6.00448ft/s Ad/A =0.1 f =0.8 Dt =1.68m
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Column Internals 20
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Column Internals 21
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Column Internals 22
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Column Internals 23
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Overview 30 Questions from last week?? Review rigorous methods
/ RADFRAC Multicomponent systems: o Residue curves o DSTWU /
RADFRAC o Rules of thumb Complex (Enhanced) distillation Column
internals Batch distillation
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Batch (Rayleigh) Distillation 31 Seader & Henley (2006)
Usually for small capacity systems 1 column handle multi- campaigns
Produce sample new products Batch upstream processes Feed contains
solids/foulants Material Balance: leads to Rayleigh Equation
where:
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Batch (Rayleigh) Distillation 32 a) P = constant; K = f(T) only
b) Binary with = constant c) y = K x ; but K = f(T,x) Solve
graphically or numerically
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Multistage Batch Distillation 33 Modes of operation: Constant
reflux rate or ratio x D varies with time easily implemented (flow
sensors) Relatively simple and cost effective Constant distillate
composition R or D varies with time Requires fast response
composition sensors Sensors might not be available or only
justified for larger batch systems Optimal control mode x D and R
varied with time Designed to: Minimize operation time Maximize
amount of distillate Maximize profit More complex control scheme
Seader & Henley (2006)
