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Unit Operations Lecture 22 (continued)

Unit Operations Lecture 22 (continued). 16 Nov 2012. Trayed Columns (Diameter). Chap 6 (10 ,p 314, Wankat ) “Fair’s Procedure” Considers entrainment flooding (most freq.) Downcomer flooding (sometimes) – need different procedure Downcomer flooding rare if (1- h ) ≥ 10%

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Unit Operations Lecture 22 (continued)

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  1. Unit Operations Lecture 22 (continued) 16 Nov 2012

  2. Trayed Columns (Diameter) • Chap 6 (10 ,p 314, Wankat) “Fair’s Procedure” • Considers entrainment flooding (most freq.) • Downcomer flooding (sometimes) – need different procedure • Downcomer flooding rare if (1- h) ≥ 10% • Used in AspenPlus James R. Fair (1920 -2010)

  3. Trayed Columns (Diameter) • Plate spacing (selected for maintenance, performance). Typ: • 12 – 16” for Dia < 5’ • 24” larger columns • Calc Dia & round up to nearest ½ foot (USA) • 2.5’ minimum dia. • If < 2.5’ consider packed tower Figure 6.23

  4. In-Class Exercise Data: Let: Estimate the tower diameter in meters. Pause video and do exercise. When done, resume the video.

  5. In-Class Exercise Data: Let: Estimate the tower diameter in meters.

  6. Tower Diameter

  7. AspenPlus In-Class Exercise Benzene – Toluene Separation Estimate the tower diameter in meters. (by hand and by AspenPlus) F = 100 kmole/hr XBZ = 0.6 saturated liquid Use sieve trays

  8. AspenPlus PFD

  9. Column Internals Base method: NRTL

  10. Column Internals Not optimized by DSTWU Nfeed = 15 Pcol = 1.013 bar (constant)

  11. Column Internals

  12. Column Internals

  13. Column Internals

  14. Column Internals

  15. Column Internals

  16. Column Internals

  17. Column Internals

  18. Column Internals

  19. AspenPlus In-Class Exercise Benzene – Toluene Separation Estimate the tower diameter in meters. (by hand and by AspenPlus) F = 100 kmole/hr XBZ = 0.6 saturated liquid Use sieve trays

  20. Column Internals

  21. Column Internals

  22. Column Internals

  23. Column Internals

  24. Overview • Questions from last week?? • Review rigorous methods / RADFRAC • Multicomponent systems: • Residue curves • DSTWU / RADFRAC • Rules of thumb • Complex (Enhanced) distillation • Column internals • Batch distillation

  25. Batch (Rayleigh) Distillation • Usually for small capacity systems • 1 column handle multi-”campaigns” • Produce sample new products • Batch upstream processes • Feed contains solids/foulants Material Balance: leads to Rayleigh Equation Seader & Henley (2006) where:

  26. Batch (Rayleigh) Distillation a) P = constant; K = f(T) only b) Binary with  = constant Solve graphically or numerically c) y = K x ; but K = f(T,x)

  27. Multistage Batch Distillation • Modes of operation: • Constant reflux rate or ratio • xD varies with time • easily implemented (flow sensors) • Relatively simple and cost effective • Constant distillate composition • R or D varies with time • Requires fast response composition sensors • Sensors might not be available or only justified for larger batch systems • Optimal control mode • xD and R varied with time • Designed to: • Minimize operation time • Maximize amount of distillate • Maximize profit • More complex control scheme Seader & Henley (2006)

  28. Multistage Batch Distillation Removing volatile impurities. Flexible, multi-purpose system Seader & Henley (2006)

  29. Questions?

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