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class 11 - Class 11 Separation Tower Design Typical Design...

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Class 11 Separation Tower Design

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Typical Design Parameters Operating Pressures: Typically, 1 – 415 psia For Temperature Sensitive Materials: Vacuum Distillation (P > 5 mm Hg) Condensers: Typically Total Condenser (unless low-boiling components)
Algorithm to determine column pressure and condenser type estimate distillate & bottoms comps bubble pt. pressure of distillate @ 120 ºF dew pt. pressure of distillate @ 120 ºF choose refrigerant for partial condenser @ 415 psia estimate bottoms pressure D P 215 psia < D P 215 psia use total condenser if P D < 30 psia, set P D =30 D P 365 psia < use partial condenser D P 365 psia bubble pt. temperature of bottoms @ P B T B < bottoms decomposition or critical temp start finish T B unacceptably high lower P D rule of thumb: add 10 psia to P D

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Combined Manual/Simulator Design Method Estimate the distillate and bottoms compositions and flow rates via a hand material balance and recognizing light and heavy key components Use the graphical algorithm in figure 8.9 (page 216 of text) to establish column pressure and condenser type Using Distillate Composition a) use HYSYS to help calculate the estimated bubble point pressure of the distillate, P D , at 120 o F (the idea is to use cooling water which typically exits at 120 o F). b) If this calculated bubble point P D < 215 psia, use a total condenser; however , if the bubble point P D < 30 psia, set the condenser outlet pressure at 20 < P D < 30 psia to avoid vacuum operation. c) However, if bubble point P D > 215 psia, calculate the distillate dew point pressure at 120 o F; if that dew point pressure is < 365 psia, use a partial condenser; if the dew point pressure is > 365 psia, select a refrigerant that gives a minimum approach temperature of 5 to 10 o F (select this in place of cooling water) for the partial condenser such that the distillate dew point pressure < 415 psia. Up to this point, the tower operating P has been determined by the estimated composition of the distillate. Checking Bottoms Composition d) Using the determined condenser outlet pressure from (a) to (c), assume a condenser P of 0 to 2 psia; assume a tower pressure drop of from 5 to 10 psia; hence, a P at the bottom of the column, P B , will be 5 to 12 psia greater than the condenser outlet pressure (almost all reboilers are partial reboilers that produce a bottoms product at or close to the bubble point).
Algorithm for Establishing Column P and Condenser Type Figure 8.9

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class 11 - Class 11 Separation Tower Design Typical Design...

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