Modelling and Performance Evaluation of a Distillation Column for Ethanol-Water Separation

Author : Caraig, Rogelio T.
Major Adviser : Acda, Reynaldo I.; Olea, Mariano B.
Committee Members :
Year : 1992
Month : April
Type : Thesis
Degree: BS
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A computer program (ALCO-H2O) that can be used to describe and evaluate the distillation column behavior/performance for the separation of ethanol and water at specified conditions was written. The algorithm used in the computer program was developed on the basis of non-equimolal overflow model which incorporated both mass and energy balances, and phase equilibria. The algorithm was encoded (into the ALCO-H2O computer program) using the TURBOPascal (Version 5.5) language. Desk-top testing of the program using literature and previously computed design/operating data was carried out.

Laboratory column performance data for the separation of ethanol and water were gathered in an attempt to validate the model using experimental data. In this study, a feed containing 19.98 mass percent ethanol was desired to separate into a distillate and bottoms having an ethanol concentration of 85.66 and 2.52 mass percent ethanol, respectively, by setting the reflux ratio at 1.48 in a column containing 11-bubble cap trays equipped with a total condenser and a partial reboiler.

The tray temperatures predicted by the model were lower than those recorded in the experiment, indicating that the desired degree of separation was not achieved. However, the trend in temperature variation of the different trays was predicted well. The deviations were attributed to the fact the two vital assumptions in the model did not hold, namely, negligible heat losses and theoretical stages. The difficulty of controlling the flowrate of the different streams could have also led to the observed differences. Based on the performance evaluation of the existing column, the following are recommended: equipment must be insulated to prevent heat losses; use of high precision valves and flowrates to facilitate better control; and installation of stream trap to maximize heat transfer (in the reboiler). The overall column efficiency was found to be 36.4%.

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