Impact of plenum conditions and gas-liquid distributor on bubble column hydrodynamics

•Fluids flowrates and surfactant level affect free surface stability in the plenum.•Bubble cap dampens fluctuations from the plenum.•Size of bubbles in the plenum negligibly affect gas holdup above the bubble cap.•Bubble cap produces larger bubbles than perforated plate.•Bubble sizes above distributors correlated to energy dissipation rate and gas-liquid ratio. In an LC-FiningTM hydroprocessor, the orientation of the free surface in the plenum chamber and the efficiency of the internal gas-liquid separator impact the amounts of the gas and the liquid passing through individual bubble cap risers in the grid. Various gas and liquid flowrates were thus passed through a single bubble cap riser to determine resulting bubble properties. Bubble sizes correlated well with energy dissipation rate and gas-to-liquid velocity ratio to the power of −0.4 and 0.6, respectively, in agreement with theory on the turbulent breakup of dense dispersions. Bubbles were also influenced by the gas-liquid distributor geometry, where the bubble cap produced larger bubbles than a perforated plate. Finally, the size of bubbles sparged in the plenum marginally affected overall gas holdup, suggesting that a bubble cap distributor redesign should be prioritized over upstream gas introduction equipment to optimize the performance of the hydroprocessor.