Experimental study of aqueous foam generation and transport in a horizontal pipe for deliquification purposes

This work presents and analyses the results of experimental activities aimed at a preliminary characterization of foamy flows for pipeline dewatering, in order to assess whether the addition of surfactants may effectively reduce the liquid holdup in horizontal pipelines. Static tests were run to compare the foam cycle (generation and decay) for three commercial surfactants and to choose the most suitable one. Dynamic tests with the selected product were performed in a 20 m long, 60 mm i.d. Plexiglas® pipe, where a 0.3% wt. solution of surfactant in tap water was pumped after mixing with an air flow at nearly atmospheric pressure and temperature. Superficial velocities ranged between 0.03 m/s and 0.05 m/s for water and between 1.5 m/s and 11.5 m/s for air, which would determine stratified/stratified wavy flows in the case of pure water-air flow, i.e. the benchmark case. Due to the presence of the surfactant, foam formed in the mixing section, which implied a significant change in the flow patterns that were photographically recorded and classified into three main types: plug, stratified wavy and stratified with foam entrainment, as far as the air superficial velocity was increased at constant water superficial velocity. The associated pressure drop, linearly distributed along the pipeline, resulted greater than the benchmark value in all the operating conditions, with a dramatic increase (even more than 100%) for plug flows. On the other hand, the percentage relative difference was found to lower with increasing the air superficial velocity, apart for stratified wavy flows where it seemed to keep constant at about 3.3%. Finally, a theoretical model for stratified flows was used to relate the pressure drop to the void fraction in order to get at least an approximate indication of the liquid load reduction due to the surfactant addition, which ranged between 6% and 39%.