MODELING OF PARTICLE SETTLING IN HIGH VISCOSITY LIQUID

The formation of insoluble phases in glass is an important problem of the vitrification of high-level waste (HLW). Spinel particles precipitated from molten glass below the liquidus temperature settle on the bottom of the melting space and may block the discharge chamber. To reduce the risk of melter failure due to spinel settling, the requirement has been imposed on HLW glass that its liquidus temperature is below the minimum temperature of the glass melter (estimated as 1050 °C). This restriction substantially increases the process and disposal cost due to the limited waste fraction loaded to the glass. One possibility for reducing the cost of HLW vitrification is to increase waste loading to an extent, at which the amount of accumulated spinel phase does not interfere with melter operation. An assessment of spinel accumulation during melter operation demands detailed knowledge of spinel behavior in glass including thermodynamics, kinetic, hydrodynamics and rheology of the spinel-glass system. The rate of spinel settling and accumulation on the melter bottom can be estimated using mathematical modeling. The experimental results by LaMont and Hrma [1] have shown that spinel crystals behave as a swarm rather than individual particles. The description of settling by the Stokes law appears inadequate. The aim of this work is to formulate a two-dimensional mathematical model of insoluble particle settling in high-viscosity liquid and to verify this model with laboratory experiments. EXPERIMENTAL PART