Influence of crystallization conditions on the mechanism and rate of crystal growth of potassium sulphate

Abstract

Growth rate of potassium sulfate crystals was studied in a fluidized bed crystallizer. Higher growth rates were observed at larger bed heights. Larger crystals grow faster than smaller size crystals due to the changed fluid dynamics. The growth rate was found to be very sensitive to the pH value of the solution. The growth rate increases with increasing the pH value and the increase of growth in the acidic medium is faster than in the basic medium. The presence of small amounts of Cr 3+ ions reduces the growth rate of potassium sulfate dramatically. The presence of Cr 3+ ions lowers the saturation temperature and increases the width of the metastable zone, i.e. shifts the metastability of the solution to be at lower level of supersaturation.

CFD simulation and comparison of industrial crystallizers

“…Oslo-Krystal Evaporative Crystallizer ( Figure 2C) [5] The operation is similar to that of APV Kestner or Swenson evaporative crystallizers, where the feed (1) passes through a pump (2) and a heat exchanger (3). The flow enters in an upward direction at position (4) of the crystallizer (5) below the liquid level (6).…”

“…The Figure 2I-K are examples of stirred tank crystallizers. Figure 2I shows a typical batch adiabatic crystallizer, which consists of a tank (1), propeller (2) and baffles (3). Vacuum (4) is applied at the top facilitating the vaporization of the solvent and results into evaporative cooling of solution.…”

“…Swenson Walker Crystallizer ( Figure 2H) [5] It consists of a trough (1) with internal agitation provided by a helical impeller (2) and a cooling jacket (3). The shape of the trough is semi-cylindrical.…”

“…The crystal growth process takes place within the metastable zone and the growth rate is controlled by the fluid dynamic conditions around the growing crystals. [3] Further, crystallization gives product of high purity at low energy costs. [4] There are three main characteristics of crystal product: mean size, CSD, and morphology.…”

Influence of Trivalent Metal Ions on the Metastable Zone Width of Ammonium Sulfate

“…The solubility and supersolubility enclose the metastable zone, which is a very important parameter for crystallization processes because therein all crystallization processes take place. It was already shown that trivalent metal ions can affect both, solubility [3,8] and supersolubility [6,9] and, therefore, the width of the metastable zone (MZW).…”