Mass transfer and hydrodynamic characteristics of a high aspect ratio self-ingesting reactor for gas–liquid operations

Method for Intensive Gas–Liquid Dispersion in a Stirred Tank

This article presents the results of hydrodynamics and mass exchange in a stirred tank upon the introduction of gas from an open gas vortex cavity into local liquid regions with reduced pressure. It establishes conditions for the intensive dispersion of gas. Velocity fields and liquid pressure behind the stirrer paddles are determined by numerical simulation in OpenFOAM. The gas content value, gas bubble diameters, and phase surface are determined experimentally. The stirrer power criterion is calculated by taking into account the gas content and power input. The experimental mass transfer data based on the absorption of atmospheric oxygen into water during the dispersion of gas from the open vortex cavity in the local liquid regions behind the rotating stirrer paddles are presented. In this case, the energy dissipation from the rotating stirrer reaches 25 W/kg, with a phase surface of 1000 m−1 and a surface mass transfer coefficient of up to 0.3·10−3 m/s. These parameters are obviously higher than the data obtained in the apparatus for mass exchange through surface vorticity. The advantage of the given method for gas dispersion in a liquid is the functional stability of the apparatus regardless of how deep the stirrer is immersed in the liquid or the temperature or pressure of the gas. Apparatuses based on the intensive gas dispersion method allow for varying the mass transfer coefficient and gas content across a broad range of values. This allows establishing a dependency between the experimentally obtained mass transfer coefficient, energy dissipation, and phase surface values. An equation for calculating the mass transfer coefficient is formulated by taking into account the geometric parameters of the stirrer apparatus based on the stirring power and phase surface values.

Effects of geometric parameters on volumetric mass transfer coefficient of non-Newtonian fluids in stirred tanks

Scaling up stirred tanks is a significant challenge because of the research gaps between laboratory and industrial-scale setups. It is necessary to understand the effects of scale-up on the mass transfer in stirred tanks, and this requires meticulous experimental analysis. The present study investigates the effects of tank size and aspect ratio ( H L T ${H}_{L}}{T}$ ) on the volumetric mass transfer coefficients of shear-thinning fluids. The experiments were conducted in three stirred tanks of different sizes (laboratory and pilot scale) and geometries (standard and nonstandard). H L T ${H}_{L}}{T}$ was 1 for the standard tanks and 3.5 for the nonstandard stirred tanks. Three sizes of stirred tanks were used: 11 L with H L T ${H}_{L}}{T}$ of 1, 40 L with H L T ${H}_{L}}{T}$ of 3.5, and 47 L with H L T ${H}_{L}}{T}$ of 1. Impeller stirring speeds and gas flow rates were in the range of 800–900 rev min−1 and 8–10 L min−1, respectively. The volumetric mass transfer coefficient was estimated based on the dissolved oxygen concentration in the fluids, and the effects of rheology and operating conditions on the volumetric mass transfer coefficient were observed. The volumetric mass transfer coefficient decreased as tank size increased and increased with an increase in operating conditions, but these effects were also clearly influenced by fluid rheology. The impacts of scale-up and operating conditions on the volumetric mass transfer coefficient decreased as liquid viscosity increased.