Separacion
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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