Experimental analysis of the hydrodynamics of a three-phase system in a vessel with two impellers

Results of experimental analysis concerning gas hold-up and average residence time of gas bubbles in a three-phase gas-solid-liquid system produced in a baffled, double-impeller vessel are presented. Measurements were carried out in a vessel with the internal diameter of 0.288 m. Two different double-impeller configurations were used for agitation: Rushton turbine (lower) — A 315 (upper) and Rushton turbine (lower) — HE 3 (upper). Upper impellers differed in the fluid pumping mode. Coalescing and non-coalescing systems were tested. Liquid phases were distilled water (coalescing system) and aqueous solutions of NaCl (non-coalescing systems). The ability of gas bubbles to coalesce in the liquid was described using parameter Y. Dispersed phases were air and particles of sea sand. The experiments were conducted at seven different gas flow rates and two particle loadings. Effects of the ability of gas bubbles to coalesce (liquid phase properties), operating parameters (superficial gas velocity, impeller speed, solids loadings), and of the type of the impeller configuration on the investigated parameters were determined. The results were approximated mathematically. For both impeller configurations tested, significantly higher gas hold-up values were obtained in the non-coalescing gas-solid-liquid systems compared to the coalescing one. Out of the tested impeller systems, the RT-A 315 configuration proved to have better performance ensuring good gas dispersion in the liquid in the three-phase systems.