1. COMSATS Institute of Information Technology
Defence Road, Off Raiwind Road, Lahore, Pakistan

2. Continuous Distillation Columns
Characteristics at different operating
conditions

3. Group Members
• Group #7
Hafiz Annus Mahmood SP10-BEC-015
Mohammad Abubakar SP10-BEC-022
Noaman Ahmed SP10-BEC-037
Saim Khan SP10-BEC-044

4. What is Reflux ?
• In simple terms, it is the stream returning to
the distillation column after being condensed
from the condenser and after being re-boiled
from the re-boiler
• It is employed to increase purity of required
product

5. Total Reflux
• A condition at which no distillate and no
bottom product leaves the distillate column
• The vapors leaving the column are condensed
and the liquid leaving the column is vaporized
and re-circulated back to the column
• There is sufficient vapor and liquid content for
steady state operation

7. Material Balance on a Distillation
Column
• General material balance on a distillation
column
F = D + B
– Where, F, D, and B are either mass or mass flow
rate of feed, distillate, and bottom
product, respectively

8. Operating conditions based on Total
Reflux
• Four types of ‘Total Reflux’ conditions exist
1. Type 1: Total Reflux in Continuous Columns:
, F = D + B, when D and B are finite
2. Type 2: Total Reflux in both column sections:
D = 0, B = 0, F = 0 (the conventional total reflux)

9. Operating conditions based on Total
Reflux (contd.)
• Type 3: Total Reflux in Rectifying Section
D = 0, B = F
• Type 4: Total Reflux in Stripping Section
D = F, B = 0

10. Type 1
• Total reflux is achieved by approaching total
reflux conditions in both rectifying and
stripping sections
• Operating condition is reached when reflux
ratio is increased indefinitely at fixed feed rate
and non-zero product rates

11. Type 1 (contd.): The Θ method of
convergence
• Following specifications are made on the
column
1. Feed rate and its composition (Xi)
2. Distillate rate, D
3. Column Pressure
4. Number of Stages, N
5. Type of condenser (partial or total)

12. Type 1 (contd.): The Θ method of
convergence
• Reflux ratio, Lj / Vj+1 = 1 (as Vj+1 approaches
infinity)
• No need for energy balance on each stage (no
latent heat and sensible heat calculations
required to bring feed to boiling temperature)

13. Type 1 (contd.): The Θ method of
convergence
• Supposition: Both liquid and vapor phases
form Ideal Solutions throughout the column
• Method proposed by Fenske

14. The Θ method of convergence
for Type 1
(Mathematics and Example)

18. 34.68

19. The Newton Raphson Method for
Type 1
(Example)

21. What’s the difference then ?
• The Θ method of convergence is
comparatively faster than Newton-Raphson
method
• The calculated D values using the Θ method
have more accurate values with increasing
number of iterations compared to Newton-
Raphson method

22. Operating Characteristics at wide
ranges of distillate and reflux rates

23. THANK YOU FOR YOUR TIME