Investigation into the relationship between scale growth rate and flow velocity for a supersaturated caustic - Aluminate solution

Scale formation in pipe work and process equipment is inherent to the operation of many chemical processing industries. It results in reduced equipment availability; lost

production and is costly to remove. In the Bayer process, where alumina is chemically extracted from bauxite ore, the specific process step used to recover the alumina from

supersaturated caustic-aluminate solution, referred to as Precipitation, results in significant scale formation on tank walls, process piping and process equipment in contact with the fluid. Operational experience has shown that the rate at which the scaling occurs is, in part, a function of the fluid velocity.

This thesis presents and discusses the experimental observations of an investigation into scale growth rate and fluid velocity not previously conducted at the Queensland Alumina Limited (QAL) process plant. The experimental results have identified that gibbsite scale growth is a non-linear function of the flow velocity and viscous sub -layer conditions, and that the rate of deposition, with time, is also exponential.