Page 198 - Design of Simple and Robust Process Plants

5.6 Overall Process Simplification 183
. consider a vent condenser to increase condenser temperature;
. consider using a direct heat pump between top and bottom;
. use high-flux tubes;
. consider the number of trays or height of packing;
. consider feed preheating; and
. to use a multi (two- to three-) stage distillation.
For a sequence of distillation columns (Figure 5.31), the potential energy saving
options are:

. Alternative sequence.
. Three-component distillation, thermally coupled.
. Energy integration (top on bottom or side).
. Partial condenser with vapor feed to next column.
. Side reboilers/condensers.

Energy saving opportunities

Alternative sequence

Three components distillation,
thermally coupled
Energy integration (top on
bottom or side)

Partial condenser with vapor
feed to next column
Side reboilers / condensers

Fig. 5.31. Opportunities to realize energy savings for two
sequential distillation columns.

Special attention is required for those temperatures which are higher than the con-
densation temperature of the high-pressure steam grid.
An exergy-efficient supply of energy at this level is not always easy to obtain.
These temperature levels for process heating can be generated in furnaces, but the
furnaces have to be provided with a power generator or another high-temperature
process demand to achieve a reasonable exergy efficiency. Therefore, opportunities
of avoiding these temperature levels must be explored first. The potential energy
improvement of a fired re-boiler (Figures 4.36 and 37 in Chapter 4) include:
. lower pressure operation;
. allow more lights in the bottom;
. install side reboiler with electric heater in the bottom;