Separacion

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Textbooks Chemical Engineering Separations 5
Lecture 1 – column profiles for ideal mixtures in simple columns John Christy • Douglas - Conceptual Design of Chemical Processes (especially chapter 7)• King - Separation Processes • Rose - Distillation Design in Practice • Doherty - Conceptual design of Distillation Systems • Biegler - Systematic Methods of Chemical Process Design

Column Profiles:binary, ideal
1.0 A xA B A Tray number B 1 Feed S C

McCabe-Thiele Diagrams
1.0 A yA B Upper op line A 0 Feed xA 1.0

• Good profile:
– zones A - rapid separation between feed and ends – zoneB - slower, but still reasonable, separation near feed

• “Good” column

Column Profiles: binary, ideal
1.0 xA

McCabe-Thiele Diagrams
1.0

yA

Tray number B 1 Feed S C 0 Feed xA 1.0

•Feed pinch, reflux too low

• Feed pinch: reflux too low

1

Column Profiles: binary, ideal
1.0 xA

McCabe-Thiele Diagrams
1.0

yA

Tray number B 1 Feed S C 0 Feed xA 1.0

•Insufficient plates: good separation not achieved

• Not enough plates

Column Profiles: binary, ideal
1.0 xA

McCabe-Thiele Diagrams
1.0

yA

Tray number B 1 Feed S C 0 Feed xA 1.0

• No effectof feed: reflux too high

• Reflux too high – op line slope ≈ 1

Column Profiles: binary, ideal
1.0 xA

McCabe-Thiele Diagrams
1.0

yA

Tray number B 1 Feed S C 0 Feed xA 1.0

• Feed toolow: upper feed pinch

• Feed too low: i.e. inserted below optimum stage

2

Column Profiles: binary, ideal
1.0 xA

Component distribution: multicomponent, ideal

Tray number B 1 Feed S C• “Out of mass balance”: distillate flow too high

multicomponent, ideal

Non-key plateaux
• Heavy non-keys (HNKs)
– From feed to bottoms in liquid – also a little in vapour, especially nearbase of column (T highest) – assume y → 0 up the column towards feed – then L′xn+1 = Vyn + BxB so x = BxB n+1 L′ if yn = 0. But xn+1 not less than BxB L′

• Key peaks: (A) mass balance effect...
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