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Unit Operations Lecture 22 (continued)

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## Unit Operations Lecture 22 (continued)

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**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% • Used in AspenPlus James R. Fair (1920 -2010)**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**In-Class Exercise**Data: Let: Estimate the tower diameter in meters. Pause video and do exercise. When done, resume the video.**In-Class Exercise**Data: Let: Estimate the tower diameter in meters.**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**Column Internals**Base method: NRTL**Column Internals**Not optimized by DSTWU Nfeed = 15 Pcol = 1.013 bar (constant)**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**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**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:**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)**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)**Multistage Batch Distillation**Removing volatile impurities. Flexible, multi-purpose system Seader & Henley (2006)