Date post: | 19-Jan-2015 |
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COMSATS Institute of Information TechnologyDefence Road, Off Raiwind Road, Lahore, Pakistan
Continuous Distillation Columns
Characteristics at different operating conditions
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
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
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
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
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)
Operating conditions based on Total Reflux (contd.)
• Type 3: Total Reflux in Rectifying SectionD = 0, B = F
• Type 4: Total Reflux in Stripping SectionD = F, B = 0
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
Type 1 (contd.): The Θ method of convergence
• Following specifications are made on the column1. Feed rate and its composition (Xi)
2. Distillate rate, D3. Column Pressure4. Number of Stages, N5. Type of condenser (partial or total)
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)
Type 1 (contd.): The Θ method of convergence
• Supposition: Both liquid and vapor phases form Ideal Solutions throughout the column
• Method proposed by Fenske
The Θ method of convergence for Type 1
(Mathematics and Example)
34.68
The Newton Raphson Method for Type 1(Example)
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
Operating Characteristics at wide ranges of distillate and reflux rates
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