Application of NLP Based Techniques in Batch Distillation

Logsdon and Biegler (1993) considered a binary separation of cyclohexane-toluene mixture in a conventional batch distillation column. Maximum distillate problem was considered to maximise the amount of distillate with cyclohexane purity of 0.998 molefraction. The input data for the problem is given in Table 5.7. 

Note using a holdup model, Logsdon and Biegler also reported an optimal reflux ratio profile for the same example but it was significantly different than that obtained by using no holdup model. Refer to the original reference for further details. 

Mujtaba (1989) considered the minimum time problem with a separation task (D = 1.16 kmol, x D= 0.906). The task is same as those reported for ideal case in Table 4.8 (Chapter 4). The simulation used 4 reflux ratio levels including an initial total reflux operation. Mujtaba also used 4 reflux ratio levels to compare the simulation results. The lower and upper bounds on the reflux ratio are (0.3 and 1.0). 

The simulation results reported in Table 4.8 used 2.54 hr of initial total reflux operation (also used in the experimental column by Nad and Spiegel, 1987) before any product was withdrawn from the column. Here, the aim was also to find out- 

It is clear from Table 5.9 that the results obtained are in very good agreement with the objectives set for each individual optimisation problem. Table 5.9 also deary shows the advantages of optimal reflux policies over the conventional constant reflux operation. Table 5.9 shows that the time optimal control policy (variable reflux) saves about 63% of the operation time compared to that required in the simulation (Table 4.6). Even the time optimal constant reflux policy saves about 33% of the operation time compared to the original simulation 

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