In the pre-desilication of Bayer bauxite slurries, the first step is to heat the slurry to ~100°C. Direct steam injection adds unwanted dilution that has to be removed by additional evaporation, resulting in capital and operating cost impacts, and production losses.
With indirect heating, the nature of thick, viscous slurries can lead to accelerated scaling on tube walls and rapid reduction in heat transfer resulting in short operating cycles. Blockages and/or excess scale also create high heater cleaning maintenance. Often these fundamental issues render indirect heating uneconomic against direct steam injection.
This paper describes a new technology developed and patented by Hatch for Indirect Heating of Thick Slurry, which overcomes all of the issues above. This technology has been successfully trialled using a full size pilot plant and the first commercial scale project is in operation with a second commercial scale project in progress. The safety, technical, operational and cost advantages are discussed.