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Continuous distillation columns - Characteristics at different operating conditions

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Continuous distillation columns - Characteristics at different operating conditions

  1. 1. COMSATS Institute of Information Technology Defence Road, Off Raiwind Road, Lahore, Pakistan
  2. 2. Continuous Distillation Columns Characteristics at different operating conditions
  3. 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. 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. 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
  6. 6. 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
  7. 7. 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)
  8. 8. 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
  9. 9. 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
  10. 10. 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)
  11. 11. 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)
  12. 12. Type 1 (contd.): The Θ method of convergence • Supposition: Both liquid and vapor phases form Ideal Solutions throughout the column • Method proposed by Fenske
  13. 13. The Θ method of convergence for Type 1 (Mathematics and Example)
  14. 14. 34.68
  15. 15. The Newton Raphson Method for Type 1 (Example)
  16. 16. 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
  17. 17. Operating Characteristics at wide ranges of distillate and reflux rates
  18. 18. THANK YOU FOR YOUR TIME

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