Distillation Design

1
Distillation Design

• Perform stage-by-stage material balances in a
  distillation column.
• Determine total number of stages needed for a
  column.
• Determine the location of the feed stage.
• Understand minimum reflux ratio.

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F D B xFF xDD xBB
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Balance Above Feed Stage
Condenser
V1 y1
D xD
L xD
1
L1 x1
V2 y2
2
V3 y3
L2 x2
4
Stage 1 Material Balance
Condenser
V1 y1
D xD
L xD
1
L1 x1
V2 y2
2
V3 y3
L2 x2
5
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6
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8
x1
y2
9
x2
y3
10
x3
y4
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Balance Below Feed Stage
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13
yB
xB
14
yN
xN
15
yN-1
xN-1
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Balance At Feed Stage
L xf-2
V yf-1
f-1
L xf-1
V yf
F xF
f
L xf
V yf1
f1
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Intersection of Upper/Lower Operating Lines
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Feed is 100 Vaporq 0
19
Feed is 100 Liquidq 1
xD
xF
xB
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Feed is 100 Vaporq 0
21
Feed is 100 Liquidq 1
xD
xF
xB
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Next Assignment

1. Design a shortcut column to separate methanol
   from ethanol where the feed is a liquid at its
   saturation temperature at 1 bar100 kg/hr
   methanol200 kg/hr ethanol
2. The target is to recover 90 of the methanol with
   only 5 of the ethanol in that stream
3. Use the stages and the location of the feed
   stage on a Tower model.
4. After converging the Tower model, vary the
   reflux ratio and note how this affects the purity
   and the recovery of methanol in the distillate,
   along with the amount of energy expended in the
   reboiler.

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Next Assignment

1. For a given reflux ratio of your choosing, see
   how the position of the feed stage affects the
   methanol product purity and methanol recovery.
2. Vary the feed vapor fraction and determine the
   product purity and methanol recovery.