distillation4 [compatibility mode]
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Gas liquid contact column
design
Distillation
AbsorptionStripping
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Equipment Design
1. Chemical Eng Design
2.
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Chemical Eng Design
Process selection Type of equipment
, Unit Internals
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Mechanical design
Material selection Thickness calculation - P, T
- Supports for the unit
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Data Distillation column design
1. ,2. Product specifications
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Calculation1. Optimum reflux ratio
2. ; Height
3. Column diameter
4. Column Efficiency
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Determination of the numberof stages required
For a binary mixturea) Sorels method (1893)
b) (1921/22)
c) Lewis method (1922) CMO
d) Mc-Cabe and Theile method (1925) CMO
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Determination of the numberof stages required
For a multi-component mixturea) Fenske, Underwood and Gilliland
,1948)
b) Lewis and Matheson method (1932)
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Number of equilibrium stages required,Feed tray location, L and G rates arekn wn f r v l l i n .
Actual number of trays depends on the
tray efficiency
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Unknowns;1. Column diameter
2. Tray type size, down comer, weir
size, hole size etc.
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Practical problems
Foaming Expansion of a liquid when aerated.
since it increases the interfacial contactarea.
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Priming (excessive foaming) Foam build up high enough to enter the
the tray- reduces the efficiency.
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Priming (excessive foaming)
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Entrainment The liquid carried away with the vapour
.carries liquid of lower volatility to theplate above and hence decreases the
efficiency and the distillate iscontaminated.
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Flooding Excessive entrainment or liquid backup in the
down comer. Sharp increase in the pressure
separation.
In commercial columns- 80-85% flooding ismaintained.
If foaming is expected 50-60% flooding isrecommended.
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http://www.emersonprocess.com/rosemount/document/notes/3051S_ASP_Distillation_Column_Flooding.pdf
Normal flooding
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Weeping When gas rate is low in perforated
columns.
When the liquid head on a plate is equalto the pressure holding it on the platethe liquid starts flowing through theperforations- This is weeping
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Weeping
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Dumping Excessive weeping- affectsthe operation seriously.
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Dumping
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Coning when the liquid rate is low the gasrising through the opening of the tray maypush the liquid away- gas liquid contact is
poor.
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Bubble cap tray
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Ideal column
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Video
This is an example of flooding andweeping in a distillation column. It is
h li i n in l w
enough to allow the previous tray'sliquid level to cover the opening andthe vapor goes up the tube instead of
the cap causing a pressure difference.