Ultrasound imaging of liquid fraction in foam

Abstract

Flotation is an important process in liquid-solid and solid-solid separation, whereby desired solids in suspensions are recovered by their attachment to gas bubbles. Monitoring the process is essential for an increased grade and reduced water consumption. However, in situ measurements of the froth’s phases (liquid, air, particles) and / or volume flow that would be easily integrable in industrial processes are not available. The constant alternation of phases remains challenging for measurement instrumentations. In this paper, we report on pilot tests of novel instrumentation that allows for measurement of low liquid fraction based on electrodes and ultrasound transducers measurements. It offers high milliscale spatial and temporal resolution in the low liquid fraction range of foam (≤ 0.83∙10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-2</sup> ). Improving the accuracy of prospective volume flow estimations, a high penetration depth of 9.2 cm was achieved. The measurement system was calibrated using homogeneous, steady foam and an integral conductivity measurement. A backscatter model was applied to reduce the effect of ultrasound shadowing and enhance quantitative liquid fraction estimates. Additionally, six cases of inhomogeneous and dynamic liquid fraction distributions were investigated qualitatively. The quantitative and qualitative validation was conducted with a reference neutron radiography measurement, showing good correspondence. This investigation distinguished between two of the three froth phases within the analyzed range. Whereby a first step towards in situ monitoring of foam parameters in industrial applications was achieved, which is especially relevant to widely used froth flotation processes.