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Unformatted text preview: ays. Any improvement in the separation by
changing other parameters.
Analysis: The Chemsep methods was applied with the Extractive Distillation option. For
physical properties necessary to size the column diameter and compute mass-transfer coefficients
and interfacial area, the following default options were chosen except that binary liquid
diffusivities were estimated from the Wilke-Chang method.
Used automatic initialization with Newton's method, but max. change of liquid or vapor flow rate
of only 5% and max. temperature change of only 2oC. The problem was difficult to converge.
The separation achieved is:
2 Feeds Distillate
0.8321 Exercise 12.16 (continued)
The above separation that was achieved for the problem specifications indicates that the
separation between n-heptane and toluene is not sharp. Also, it is desirable to try to reduce the
amount of phenol in the distillate. The average back-calculated Murphree vapor tray efficiencies
Constantly changing over a wide range from negative to 65%
To reduce the amount of phenol in the distillate, might lower the entrainer feed entry from tray 5
to 6. This reduced the phenol rate in the distillate from 1.22 to 0.78 kmol/h, but the toluene in the
distillate increased. The separation could not be significantly improved by changing the entrainer
and feed tray entries.
To improve the separation, might increase the number of trays and/or the reflux ratio. When the
number of trays was doubled to 60 (62 stages), with the entrainer fed to stage 13 and the feed to
stage 35, the separation was improved, but not dramatically, to the following: Component
Total: 2 Feeds
960.00 Increasing the reflux ratio from 5 to 6 had a negligible effect on the separation.
Increasing the entrainer flow rate by 20% had a negligible effect on the separation.
Thus, a sharp separation is difficult to achieve and is best accomplished by using a large number
of trays. Exercise 12.17
Subject: Absorption of light hydrocarbons in a rich gas with an absorber oil in a bubble-cap
column, using both equilibrium-stage and rate-based methods.
Given: Temperature, pressure, and component flow rates of the rich gas and absorber oil.
Find: (a) Number of equilibrium stages and splits of all components for 40% absorption of
(b) Actual number of trays, the splits, and Murphree vapor tray efficiencies, with a ratebased method
(c) Comparison and discussion.
Analysis: The ChemSep program was applied to both cases,...
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