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Abstract

Mathematical modelling and simulation of a continuous column crystallizer is carried out under dynamic conditions compared to the usual steady state modelling. The column used is of the Schildknecht type using an Archimedean transportation screw within a polished stainless steel jacket.

The process of column crystallization is considered as a multistage separation process similar to a distillation column. In this investigation the column is considered as a single piece of equipment, containing freezing and melting sections at either end of the column and a long purification section in between. Crystals formed in the freezing section are transported along a screw, through the purification section towards the melting section, where they are melted and some of the melt is allowed to flow countercurrently thus washing adhered impurities by reflux. Most of the melt is removed as pure product while impure product is removed from the opposite end.

The processes involved are those of mass transfer, heat transfer, mixing, transfer of impurities due to countercurrent contacting of pure and impure liquids and diffusion due to concentration gradient of the impurity. The purification section is considered to be theoretically divided into a number of stages involving temperature and purity gradients, similar to the theoretical places of a distillation column. The column was tested for
desalination purposes.

Mathematical models were developed into simulation models for each of the three sections. The freezing section was developed first, and on successful operation the other two simulation models were joined to form the entire column. The programme was written in FORTRAN IV and was simulated on a CDC 7600 computer. It is possible that a fuller understanding of the mechanism of the column could lead to large scale desalination plants of the column crystallizer type.

Publication Type:	Thesis (Doctoral)
Subjects:	Q Science > QA Mathematics > QA75 Electronic computers. Computer science Q Science > QD Chemistry
Departments:	School of Science & Technology > School of Science & Technology Doctoral Theses Doctoral Theses

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