Project ForgeThree distillation schemes for separating an equimolar ABC mixture (relative volatilities αA:αB:αC=8:2:1) into nearly-pure components are all designed for minimum total reboiler duty: I (direct sequence: split A off first, then split BC into B,C), II (indirect sequence: split C off first, then split AB into A,B), III (a prefractionator arrangement producing AB and BC streams that feed two further columns). The ascending order of total reboiler duty is
- AI, II, III
- III, I, II
- CII, I, III
- DIII, II, I
Explanation
A thermally-coupled/prefractionator arrangement (III) avoids the internal composition "remixing" penalty of sequential simple columns and generally has the lowest total reboiler duty. Between the two simple sequences, performing the EASIER split first while the feed flow is largest is more efficient: the A-vs-BC split (effective α=8/2=4) in scheme I is easier than the AB-vs-C split (effective α=2/1=2) in scheme II, so I requires less duty than II. Ascending order: III, I, II.
Source: GATE CH 2019 (2019)
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