Mitigation of scale formation in unbaffled stirred tanks-experimental assessment and quantification

A qualitative and quantitative investigation on the formation of scale in mixing tanks was conducted. The fabrication of a purpose-built tank that could be disassembled into nine segments (including a base, four walls, and four baffles or four blanking pieces) allowed the measurement of scale thickness in critical regions such as the impeller zone. The scale grown on the walls of the tank was physically scanned using a coordinate measuring machine (CMM). The CMM readings were then used to plot 3-D graphs of scale thickness and distribution on the walls of the tank. Experiments conducted under unbaffled and baffled conditions showed that the bottom region of the reactor was almost free of scale while the top region near the liquid surface had noticeable scale formation under both configurations. The scale thickness and distribution were lower in the unbaffled tank compared to the baffled tank, which, in line with CFD simulations, can be attributed to the increased tangential liquid flow velocity near the tank wall under unbaffled condition. (C) 2019 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.