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Shortcut Methods - Coggle Diagram
Shortcut Methods
Key parameters for designing a column
Plates/packing
No. stages/packing height
Column diameter
Reflux ratio
R=L/D :star:
Tells you the operating cost
High reflux ratio
:!!:
More liquid and vapour in the column
Higher duties on the condenser and rebiller
The more you feedback, more contact - initially more liquid then there will be more vapour
More energy needed to boil the increased liquid at the bottom
More condenser energy needed at the top too
Minimum reflux ratio
Rmin given for a degree of separation
Infinite number of stages required at Rmin
When R goes up, no. stages decreases :!!:
More energy needed also
Operating cost increases
Correlations
Difficult to calculate R and no, stages for MCS
Empirical methods
Gililand State reflux- correlation
Relates no. stages (n) and reflux ratio (R) to min no. stages (nm) and min reflux ratio (Rm)
Linear scale or Log scale
Erbar-maddox correlation
More accurate than Gilliland
Also need n,nm,R or Rm
Nm
Fenske Equation of total reflux :!:
Min no. theoretical stages :pen:
ONLY AT TOTAL REFLUX
Rm
Min reflux ratio :pen:
Underwood equation :!:
Infinite no. stages
N
Number of theoretical stages :pen:
Erbar-maddox correlation :!:
Allow us to determine R + no. stages based on bottom and top product specifications
Assumptions/Specifications :!!:
Have data for K values
alpha(LK)/alpha(HK)>= 1.05
There are no reactions
Temp and pressures in normal operating range
The order
1) Nm
Fenske eqn
2) Rm
Underwood eqn
3) Theoretical stages
Erbar-maddox correlation
4) Location of feed point
Kirkbride eqn