Date of Award

1991

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

First Advisor

Andreze K. Wojtanowicz

Abstract

Dewaterability of a compressible suspension can be characterized by two fundamental properties of viscoelastic networks: permeability and bulk modulus of elasticity. Time required for dewatering can be obtained from the former, while the latter can furnish the data required for predicting ultimate compaction. A method has been derived and an apparatus constructed for measurement of these two properties in a centrifugal field. The method was applied to a variety of drilling fluids and mineral suspensions. A floor-mounted laboratory centrifuge was used in this investigation. The methods developed have merit for evaluating pre-treatments prior to centrifugal dewatering. A method for quantifying the density distribution from top to bottom of a sedimented cake less than 2 cm in height is reported. In one experiment, this density variation was less than 13%. The feasibility of replacing chemical pre-treatments by applying an alternating current electric field (electrocoagulation) was investigated. Several fluids were electrically treated before centrifuging. Upon centrifuging, only certain suspensions exhibited a cake while others did not. In those instances where a cake could be collected, its moisture content was measured. In the most effective electrical treatment, a salt/polymer drilling fluid containing 6% by weight solids (94% moisture) before treatment and centrifuging yielded a cake with a moisture content of 91%. This compares with a moisture content of 65% if the suspension had been chemically pre-treated. This meant that in the most optimum treatment, an unacceptably high moisture content was obtained. Thus, in view of this study, electrical treatments are unable to replace chemical pre-treatments to enhance centrifugal solid/liquid separation. Two mechanisms of electrocoagulation, ionization and electrostriction, are presented. The consistent increase in conductivity is more easily explained by the ionization mechanism. Thus, it is the favored mechanism to explain electrocoagulation.

Pages

192

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