Transient Behavior of Silver Bromide Precipitation in a Continuous Suspension Crystallizer

ABSTRACT

Transient Behavior of Silver Bromide Precipitation in a Continuous Suspension Crystallizer (CSTR)

The behavior of AgBr precipitation in a continuous suspension crystallizer (CSTR-crystallizer) prior to the establishment of steady state was investigated. A dynamic mass balance and an attenuation model for crystal number were used to describe the transient behavior prior to the renucleation point. Renucleation occurred when the growth rate (or the supersaturation level) exceeded a critical value, which was affected by the precipitation conditions, and was independent of the initial content (reaction volume) of the reaction vessel. The time to reach the renucleation point varied from about 2.5 to 6.5 residence times, depending on both the precipitation conditions and the initial seeding conditions. After the onset of renucleation, at least four additional residence times were needed for continuous precipitation systems to achieve a steady state of crystal population.

This translates that only at ten to twelve residence times from the beginning of the crystallization are necessary to obtain steady state for the establishment of a steady-state crystal population.