Page 211 - Design of Simple and Robust Process Plants

196 Chapter 5 Process Simplification and Intensification Techniques
Liquid phase-controlled reactions
These include:

1. Bubble column
2. STR with jet mixer
3. STR with agitator with gas dispersion in the liquid
4. Multi-tray bubble column (the liquid is the continuous phase)
5. Tray column (the gas is the continuous phase)
6. Membrane gas absorption; this technique is ranked at the bottom of the list,
but it might develop into a recognized separation system as an increasing
number of industrial applications are installed.

Interfacial-controlled reactions
These include:
1. Spray column
2. Packed column

5.7.1.5 Heterogeneous; G/L/S
These types of reactors are mainly applied where gas liquid reactions are supported by
a solid catalyst, as in hydrogenations. From a transfer-reaction perspective, the choice
must be made between a small catalyst particle and catalyst pellets or extrudates.
The small catalyst particles (<1 mm), as applied in slurry reactors, require an
expensive recovery system and therefore are not considered high priority here. In
the case of high heat releases, this approach may be more favorable over multi-tu-
bular reactors when the reaction temperature is controlled by evaporation.
The priorities are ranked as:

1. Trickle flow, packed bed reactors
2. Packed spray columns
3. Packed bubble column
4. Slurry reactor
5. Multi-tubular reactor
Heat transfer may dominate the final design. The preferred technique always sup-
ports adiabatic operation before any external heat transfer device with the reactor is
considered The preferred options are as mentioned previously:
. Increased flow of unconverted reactants or solvent.
. Decreased inlet temperature or application of distributed cold injection of
feed.
. Evaporation of reaction medium.
. Heat exchange within the reactor.