This document discusses different operating conditions of continuous distillation columns under total reflux, including four types of total reflux. It describes total reflux, where no distillate or bottom products leave the column. It also discusses the material balance equation and introduces the Θ method and Newton Raphson method for determining column specifications under Type 1 total reflux conditions, where distillate and bottom rates are finite as reflux ratio approaches infinity. The document provides an example application of the Θ method and compares it to the Newton Raphson method.

1. COMSATS Institute of Information Technology
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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

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