Distillation is the primary separation method in the petroleum refining,
petrochemicals and gas separation industries. Distillation is well known to
be energy intensive and inefficient. For separation of three or more components,
two or more columns are usually cascaded. However, fully thermally coupled
distillation (Petlyuk distillation) is one scheme for three or more products
that can save significant amounts of energy by reducing thermodynamic losses.
The divided-wall column is one mechanical implementation of fully thermally
coupled distillation that is increasingly finding applications.
After decades since its conception, divided-wall distillation recently reached
commercial acceptance. It is estimated over 35 columns are in service. Divided-wall
columns are used commercially so far in niche applications in fine chemicals,
petrochemical, gas separation and refining industries. The divided-wall column
is applicable to some ternary separations where the mid boiling component
is desired in high purity along with high purity lighter and heavier boiling
products. One divided-wall column can replace two or more conventional columns.
The divided-wall column offers capital, energy and plot area savings compared
to the conventional column configurations.
Not all ternary separations are good candidates for fully thermally coupled
or divided-wall distillation. Also, for suitable separations, a real or perceived
price of the energy and capital savings may render a specific application
impractical. We present some guidelines for the selection of the divided-wall
column and for preliminary column design.
By Richard H. Nielsen
