Abstract
Flash vessels in pressure hydrometallurgy are used to dissipate the energy of the slurry as it transitions from autoclave conditions to an atmospheric state and to separate the flashed steam from the slurry stream. The energy dissipation is realized through a slurry pool and impingement block that protect the vessel. The pool penetration and energy exerted on the impingement block vary with flow with the most punitive conditions often at reduced flows and not at the maximum flows. The best selection of the pool depth therefore requires flow considerations over a wide operational range. Historically, steam rise velocity has been primarily used to optimize separation in flash vessels. Simplistically, the lower the rise velocity, the better the separation and the lower the slurry droplet carryover. While the impact of carryover varies from plant to plant, it is always undesirable. The Souders-Brown equation compensates for gas densities at various conditions but does not capture all the relevant physics influencing carryover. Caldera Engineering has been performing CFD modeling of flash vessels to optimize flash tank designs and to facilitate troubleshooting in existing operations. During this investigation, it has become apparent there are more factors besides rise velocity that influence carryover. This paper presents the outcome of the modeling and the effect on pool size/depth, as well as how rise velocity, disengagement height, blast tube design, and pool flow dynamics influence carryover.