SEARCH

SEARCH BY CITATION

Abstract

Hydraulic wash columns are well suited for solid–liquid separation and ultrapurification in melt-suspension crystallization. For steady operation of a hydraulic wash column and proper purification, the length of the crystal bed and position of the wash front should stay within safe limits, which requires a well-defined control system. To understand the interactions between slurry properties, column dimensions, and process conditions, a dynamic model was developed. The model was validated with help of experiments in a pilot-plant wash column, fed from a continuous crystallizer. P-Xylene was used as the model compound. It satisfactorily predicted the trends in the length of the crystal bed and the wash front height, and the interactions in the wash column are largely understood. With the help of the model a feedback control system with two control loops was designed and simulated. For a wide range of crystal fractions (0.05 to 0.3 v/v) in the feed stream, both the length of the bed and the wash front were kept at the desired setpoint values, indicating the flexibility of a controlled wash column.