The process of
flash-crystallization aims at producing small
(L50,3 = 20–90 mm) and pure crystals from a solution of well soluble
substances [1–4]. In conventional evaporation or cooling crystallization
processes, such substances are crystallized to a considerably
coarser product (L50,3 = 150–1000 mm) at low supersaturations [5].
Production of such
fine particles requires high nucleation rates.
This is realized by atomizing the undersaturated feed solution,
which is superheated with respect to the operating pressure pC of
the
flash-crystallizer; see Fig. 1 left side. Only a fraction of the
solvent is evaporated and, according to the operating conditions, a
solids content of z = 10–30% by weight is achieved in the
suspension. The suspension of crystals produced is collected in
the bottom of the crystallizer (sump) to allow for depletion of the
residual supersaturation of the droplets. Impurities remain
dissolved in the mother liquor and are separated from the crystals
by conventional solid–liquid separation, i.e., centrifugation or
filtration.