(39a) Use of Acoustic Backscatter Systems to Characterise Concentrated Dispersions

The chemicals industry is increasingly looking for modern instrumentation for process monitoring and control. For the production of particulate suspensions and colloids (from high value products such as paint, to minerals processing and water treatment) the complexity of these multiphase systems significantly limits the applicability of many types of online measurement equipment. One technique with wide potential application however is pulse-echo ultrasonics. This presentation is focused in particular, on understanding the use of acoustic backscatter systems (ABS) as a cost effective in situ/online technique for measuring dispersion dynamics in real time, including solid-liquid separation and mixing operations. Critically, backscatter transducers offer a flexible solution capable of remote operation, and can measure suspensions at high concentrations. They operate by recieving the backscatter voltage response of a high frequency (1 – 5 MHz) echo pulse, where the scattering and attenuation of particles can quantify important system parameters such as concentration and particle size. Here we develop a new calibration method to gain attenuation and scattering constants for any arbitrary particle type from large micron size to just within the colloidal range. By enabling the measurement of these constants, we are able to use a range of fully resolved and semi-empirical theories of acoustic scatter to characterize different systems. Additionally, the effect of particle aggregation, especially in the measurement of mineral wastes, has been analyzed in detail, with comparison to the fractal dimension of aggregates. This technique enables real time measurement of a range of important suspension process systems, including wet-milling, batch-scale solid-liquid separation, large-scale clarifier trials and liquid jet mixers, as part of nuclear waste processing operations (e.g. Bux et al. AIChE Journal, 63(7), p2618–2629 (2017)).