Figure 2.2. Middle Vessel Batch Distillation Column (MVC)
Figure 2.3. Multivessel Batch Distillation Column (MultiBD) 2.2.4. Continuous Column for Batch Distillation
Attarwala and Abrams (1974) considered the batch separation task operating in a single continuous column sequentially. The essential features of this type of column (Figure 2.4) are:
i) The feed is supplied to a suitable location in the middle of the column from a feed tank continuously (as in continuous distillation). The reboiler and condenser holdups are kept to a minimum.
ii) The column operates in a continuous mode and separate one component each pass as distillate and collect the residual in a storage tank.
iii) The storage tank from the previous pass is used as a feed tank for the next pass and the process from step (ii) is continued. This process is continued until the final binary mixture is separated.
This type of operation is known as Single Pass Sequential Steady State (SPSSS) operation. Each pass is operated using one reflux ratio and the overhead or bottom composition remains constant (may have different values for different passes) throughout the operation (until the feed tank is empty). Also this operation mode allows use of an already built continuous distillation column (with little extra arrangements for feeding the column by alternate changing of the feed tank) as batch distillation and the single column can be used for separating all the mixtures sequentially as in the case of conventional batch distillation. However, in each pass the column will operate in continuous mode for a finite time depending on the total feed in the feed tank and on the feed flow rate (Mujtaba, 1997).
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