ANALYSIS AND MODELLING OF STARCH DEWATERING

摘要

In industrial pressure filtration applications it is common to filter the suspension at constant pressure,and then to consolidate the formed filter cake at another,usually higher,constant pressure.The filtration phase can be described by the well-known classical filtration equation.The theories for expression have not been tested to the same degree and the determination of the point where the filtration stage ends and the dewatering stage begins is especially unclear.This paper shows four methods for the determination of this transition point.The methods are tested with filter cycle data from filtration tests with different starches.The theories of expression are also tested in order to find an easy and proper way to model the dewatering of starches in filter presses,and thus to reduce the experimental work required.The starch slurries were filtered in a piston press filter (78.5 cm~2) and in a small-scale pressure filter (0.1 m~2).The consolidation periods were modelled using Terzaghi's consolidation model,a simplified version of Terzaghi-Voigt's consolidation model with two parameters,the Terzaghi-Voigt consolidation model with three parameters and Shirato's consolidation model.The results suggest that the Terzaghi model is adequate for the prediction of starch dewatering,and the Terzaghi-Voigt model with three parameters can be used for the prediction of longer starch dewatering periods.In addition,Shirato's model can be used for the rapid prediction of starch filter cake consolidation.