Gas—Liquid Contacting With Impeller Mixers

Authors:

J.Y. Oldshue

G.L. Connelley

This article explores the fundamentals and experimental studies of gas-liquid contacting using impeller mixers, focusing on both mass transfer and physical dispersion in chemical processes. It analyzes the effects of impeller size, sparge ring design, gas flow rates, and mixer power on absorption efficiency, fluid shear, and surface phenomena such as foaming and geysering. The study provides practical guidelines for optimizing mixing equipment design and operation, balancing mass transfer requirements with mechanical performance and flow pattern control.

Key Learnings

• Gas-liquid contacting efficiency depends on both mass transfer rates and physical dispersion, which are influenced by impeller and sparge ring design.
• Impeller diameter, speed, and power relative to gas flow determine whether the system is gas-controlled or mixer-controlled, affecting overall mixing performance.
• Sparge ring size and configuration significantly impact mass transfer efficiency, with an optimal diameter typically 0.8–0.9 times the impeller diameter.
• Different impeller types and sizes perform variably at low versus high gas rates and horsepower levels, highlighting the importance of matching equipment to process conditions.
• Surface phenomena such as foaming, geyser height, and bubble dispersion provide visual cues for evaluating flow patterns and mixer effectiveness.
• Mass transfer requirements and physical effects of gas dispersion should both be considered when selecting and operating mixing equipment.
• The K factor (ratio of gassed to ungassed impeller horsepower) is useful for predicting mixer performance under varying gas flow conditions.
• Operational decisions should balance efficiency, power consumption, and practical considerations such as foaming, flotation, and mechanical constraints.
• Visual observations, including swell diameter and geyser height, can help determine the transition point between gas-controlled and mixer-controlled flow patterns.
• Experimental evaluation of process performance under actual operating conditions is essential for accurate equipment design and selection.