Page 126 - Design of Simple and Robust Process Plants

4.2 The Methodology of Process Synthesis 111

Extraction
Extracted
Solvent product Lights
Product P

Recovered
solvent
Feed
stream
Product A
Product B
Extract

Fig. 4.23. Intermediate solution.

Lights
Extraction Cooling
solvent
Product A

Product P

Feed
stream Recovered
solvent
Product A
Extract
Product B

Fig. 4.24. Low cost extraction concept.

component A between the extract stream and the raffinate stream. Product P was
now to be separated after the extractor from the solvent, lights and product A. The
separation was achieved in a divided wall column. As the lights were closer boiling
to A compared to product P, the previous solution of a vent at the reflux drum was
not suitable. Therefore, a dephlegmator was installed in the overhead stream of this
column. The final solution (Figure 4.24) was much cheaper in capital and energy,
particularly as the solvent flow was reduced by a factor of 3, as were the sizes of the
extractor and the solvent recovery tower. The dephlegmator was combined with the