(44d) On-Line Measurement of the Settling Behaviour of Concentrated 2-Phase Solid/Liquid Mixtures

Two-phase dispersions occur in a wide range of products such as paints, pharmaceuticals, foodstuffs (particularly dairy products) as well as in chemical processes involving crystallisation, minerals processing and waste water treatment. Accordingly understanding and modelling the effects of the various factors governing the stability of such systems is vital since it influences the process design of the appropriate chemical reactors, their subsequent downstream processing, storage and transportation. Central to this is the ability to make direct measurement of the sedimentation kinetics of such dispersions in an on-line manner.

This presentation will describe design and development of a novel vibrating reed technique for on-line measurement of the sedimentation kinetics of two-phase dispersions is described. The feasibility of operation of the analyser has been successfully verified in conjunction with a variety of model and industrially relevant systems. The former include mono and polydisperse glass ballotini / water mixtures with solids particle size and concentration ranges 55 - 200 ?Ým and 1.75 - 2.81 % v/v respectively. Measured settling velocities are in good accord with those obtained from direct visual observation of suspension-clear liquid interfaces. The industrially relevant systems include agglomerated kaolin/water suspensions with solids concentrations as high as 20 % v/v and oil / water emulsions with light phase concentrations in the range 30 - 50 % v/v.The technique has been tested in conjunction with a variety of solid/liquid and liquid/liquid dispersions with dense phase concentrations in the range 0 - 50 % v/v. Typical output include settling velocities, solids flux profiles as well as solids throughputs. Additionally, the performance of a number of sedimentation kinetics models proposed for dilute systems (0 - 2.81 % v/v) are evaluated by comparison with data obtained using the device. It is found that the correlations proposed by Richardson and Zaki (1954) as well as Garside and Al-Dibouni (1977) provide better agreement compared with those proposed by Reed and Anderson (1980) and Batchelor (1972).