Crystallization kinetics of potassium chloride in continuous and batch cooling crystallizers: Effect of magnesium and sulfate ions.

摘要

Extensive experimental investigation in continuous and batch cooling crystallizers into the kinetics of cooling crystallizations of KCl in water were carried out. The experiments were conducted in a continuous cooling Mixed Suspension Mixed Product Removal (MSMPR) crystallizer in the presence and absence of added impurities; and in a batch crystallizer for a pure solution of KCl in water.;The impurities selected for investigation were chosen from those naturally associated with KCl in the potash industry and were magnesium (Mg;The design of the elaborate experimental scheme of continuous experiments was factorial. The statistical tool of incomplete balanced block design was utilized to reduce the number of experiments by thirty-six per cent while reducing the quality of information collected by a mere six per cent.;As against prior findings that impurity effects are unpredictable and specific, the results unveiled that there appears to be a systematic phenomenon at work. The results exhibited that magnesium ion did not have any significant influence on crystallizations of KCl while sulfate ion enhanced the growth rate. The effect of the ions upon growth rate was independent of supersaturation. The nucleation rate was unaffected by the presence of impurities. The enhancement in growth rates in presence of sulfate ion were ascribed to an increase in aggegation kinetics. The measurements of equimolar impurity adsorption by growing crystals and lack of influence of impurities upon nucleation rates corroborated the proposition that the augmentation of growth rate could be attributed to aggregation.;It was demonstrated that the growth rate of small crystals were unchanged with or without the presence of added impurities. Based on this result it was ascertained and put forward as an original hypothesis the existence of two types of crystal growth rates differing by two orders of magnitude. The first, which is applicable to tiny crystals less than 50 ;In the case of batch crystallization a novel rigorous technique of iterative parameter estimation employing sensitivity analysis was adapted for extracting crystallization kinetics. An experimental scheme with simplicity in operation as the design goal and eliminating the need to measure transient supersaturation was developed. The only experimental measurements necessary were the time varying CSD which was carried out off-line and the initial solute concentration which was also measured off-line. An optimization performance index was developed with the squared deviations between the experimentally measured and the simulated CSD in engineering units. (Abstract shorteneed by UMI.).