Page 203 - Design of Simple and Robust Process Plants

188 Chapter 5 Process Simplification and Intensification Techniques
± Do-undo-redo activities result in additional equipment that might be subject
to removal.
± Multiple trains and spare installed equipment offer major opportunities for
avoidance, and should receive close attention.
. The combination of process functions offers major possibilities for simplifi-
cation.
± The combination of reaction and separation opens opportunities to increase
conversion by shifting the equilibrium and increasing selectivity, at lower
investment. Reactive separation examples include: reactive distillation, reac-
tive extrusion, reactive extraction, reactive absorption, reactive adsorption.
± The combination of distillation separations offers advantages through more
extensive application of dephlegmators, side streams, and divided wall col-
umns; this results in fewer separation columns.
± The direct coupling of distillation columns can also be exploited around reac-
tor system where the conversion is limited.
± The combination of different separations such as: extraction where more
extractions can be executed in one column as neutralization and washing;
absorption and stripping; devolatilization and evaporation; stripping and
blending extrusion.
. Integration of equipment is another level of simplification. The benefits of
this are often less than derived from the integration of functions, but they
might be substantial on equipment costs and piping. Several examples are
given for the integration of reactor systems. The integration of distillation
equipment also receives wider application, resulting in lower capital costs;
similar opportunities are also exploitable with other units.
. Intensification of process functions; progress made in this area can be
divided into three categories:
± Building more compact units by installing more area per unit volume. Com-
pact heat exchangers are well known in this area. Also, mass exchangers
based on separation membranes (e.g., reverse-osmosis and ultrafiltration), as
well as gas absorption through membranes are being developed.
± Increase heat, mass and impulse transport. In many heterogeneous reactions
the conversion rate is limited by mass and/or heat transport. In these situations,
intensification is highly beneficial. Different techniques are applied to enhance
transport, such as intensive mixing and re-mixing of liquid/liquid reaction me-
dium, intensified mixing of gas/liquid, application of pulsing flow techniques
to create large surface area, and surface renewal in trickle flow reactors.
± Benefits from centrifugal fields (ªHigeeº). The exploration of centrifugal
forces to improve phase separation and allow for higher processing velocities
was initially not successful, the development time being much longer than
expected. However, industrial applications of ªHigeeº technology are increas-
ing, and include: de-aeration (devolatilization) of liquid streams; rotational
particle separation for sizes >0.1 lm in dust and mist streams; reactive strip-
ping in a rotating packed bed; polymer de-volatilization and pelletization in
rotating packed beds.