Distillation4 [Compatibility Mode]

8/10/2019 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.

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Distillation4 [Compatibility Mode]