Evaporators offer a
multiplicity of choices -
Short
residence time for temperature sensitive materials, re-circulation for
materials with a tendency towards scaling, falling film for large flow
rates at high efficiency, rising films for high concentration
differential.
Unlike commonly believed,
the choice of the number of effects need not be a straight trade-off
between operating cost against investment cost. For temperature
sensitive materials, for instance, it makes sense to operate at low
steam pressure, and use the high pressure steam for re-compressing the
vent vapors. Again, where low pressure steam is required by the
process, it makes sense to put a single effect operating with high
pressure steam, and recover the low pressure steam to avoid multiple
effects altogether.
