Effect of salt and particles on the hydrodynamics of foam flows in relation to foam static characteristics

Foam flows containing particles are present in many applications including mining, wastewater treatment, environmental remediation of contaminants such as PFAS using foam fractionation, dewatering of gas wells and particle cleanout in pipelines. These applications usually involve dissolved salts and solid particulates, which may have a positive or adverse impact on the foam flow and its performance depending on the application, the system’s constituents (e.g., type and concentration of salt/particles) and the operating condition (e.g., gas and liquid flowrates). This work aims to investigate the effect of salts (primarily NaCl) up to 0.2 M salt and solid particulates (mainly clay) up to 25 g/L particles on the dynamic behaviour of 200 ppm sodium dodecylbenzene sulfonate (SDBS) foam flows, frictional and hydrostatic pressure gradient, foam holdup and flow regimes in a vertical column. Flow regimes are analysed through power spectral density (PSD) and the probability density function of differential pressure data. The results show that salt and particles affect the foaming performance of SDBS solutions, thus influencing the transition of flow regimes. Our static tests show a 1.2-to-2.2-fold increase in the effect of salts and particles on the foamability of the SDBS solutions, whereas the foam flow dynamic data show a strong dependence on the hydrodynamics of the system. For example, the pressure gradient of the foam flow experienced a 16% reduction with the addition of salt and particles at low gas superficial velocity (Vsg of 0.48–2.4 m/s and fixed Vsl of 0.02 m/s) due to the domination of gravitational dP/dz while it increased up to 22% at high Vsg of up to 11.2 m/s due to the domination of frictional forces. Our results demonstrate that the foam static properties such as foamability, foam stability and wetness are useful to understand the stabilising mechanisms of foams. However, they cannot represent and explain the foam behaviour in dynamic systems.