Total Reflux Operation

This operation is the best suited for binary mixtures, whose components should be recovered at a relatively high degree of purity. The feed charge Hf is split between the reflux drum (HD kmol) and the reboiler (HB kmol), and the column is operated at total reflux for the whole duration of the batch. Under the assumptions of quasi-steady-state operation and constant relative volatility, the operation can be analysed easily. For a given pair of product specifications, the minimum number Nmin of theoretical stages necessary in order to achieve the desired separation can be determined from the Fenske equation:

Figure 8 Binary batch distillation at total reflux (three-ideal-stage column).

If the operation is feasible in the available column, the requested top and bottom hold-ups are calculated immediately by eqns [4] and [5], with xB = xBpec and

At any time t, the operating line is parallel to the diagonal line in a McCabe-Thiele diagram (Figure 8), and moves towards the diagonal as time progresses according to the following dynamics:

Since, at time t, the following material balance holds true:

the reflux drum and reboiler compositions at the same time instant can be determined by using the auxiliary line FQ, where the abscissa aQ of the auxiliary point Q on the x-axis is such that:

The segment BD is drawn, where B is on the diagonal line with aB = xB, and D is on the auxiliary line FQ with aD = xD. The product compositions at time t are correct if the segment BD, is parallel to the x-axis.

The total amount of heat to be supplied to the reboiler is given by:

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Solar Panel Basics

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