Page 175 - Design of Simple and Robust Process Plants

160 Chapter 5 Process Simplification and Intensification Techniques
improvement realized was to integrate the mixing vessel in the separator (Figure
5.15), and the introduction of an extraction column to realize more extraction stages
and thus higher extraction efficiencies. These improvements are currently included
in the application of several extractions in one column (Figure 5.16), an example of
coupled functions. The reduction of equipment of the wash section (see Figure 5.14)
to the integrated wash column of Figure 5.16 was that six vessels were replaced by
one column, while a total of two pumps (plus their installed spares) could be
removed, assuming that the feed pumps would be needed in both situations
The functions avoided are intensive mixing and pumping, while extraction func-
tions are combined with higher extraction efficiencies due to more stages being
installed. The elements behind the avoidance can be analyzed. It is noted that the
ªdo-undo-redoº activities (or, in this example, mixing-settling-mixing) were the
opportunities for elimination. The design improvements realized were less capital
and greater extraction efficiencies, the last point resulting in less solvent circulation
with smaller purification equipment. Although the techniques described above are
not new, it is their implementation which is still lacking behind, and which deserves
to be considered under ªsimplificationº.

Effluent Neutralizer Wash water

Raw product Washed product

Fig. 5.14. Two sequential extraction wash steps consisting out
of respectively two and one stage(s).

Light phase Heavy phase

Fig. 5.15. Mixer settler in one cylindrical containment.