Fermentation Mixing Scale-up Techniques

Author:

J.Y. Oldshue - Technical Director

Mixing Equipment Co., Inc.

This document explores the scale-up of fermentation mixing processes, detailing how pilot-scale data can be applied to design full-scale industrial systems. It examines key factors such as gas-liquid mass transfer, fluid shear rates, impeller and tank geometry, blending, and solid suspension, emphasizing how each affects overall process efficiency. The paper provides methods for estimating mixer size, power requirements, and process parameters to achieve consistent results across different scales.

Key Learnings

• Successful scale-up of fermentation mixing requires breaking the process into individual but interrelated steps, such as gas-liquid mass transfer, fluid shear, blending, and solid suspension.
• Impeller size, tank geometry, and mixer power must be carefully selected and balanced to maintain effective mass transfer and appropriate shear rates in full-scale systems.
• Fluid shear rates and turbulence intensity impact living biological solids, making accurate measurement and control critical for fermentation processes.
• Gas flow rate, viscosity, and impeller-to-tank diameter ratio (D/T) significantly influence gas absorption efficiency and overall mixing performance.
• Pilot-scale experiments provide essential data for predicting full-scale performance, including mass transfer rates, energy dissipation, and blending efficiency.
• Maintaining similar power per unit volume across scales helps achieve consistent process outcomes, though adjustments may be needed for non-geometric scale-up.
• Hot-wire velocity measurements and flow pattern analysis are useful tools for understanding mixing dynamics and optimizing impeller placement.
• Solid suspension is generally less problematic in fermentation due to low settling velocities, but pseudoplastic properties of fluids must be considered.
• Process design, mechanical design, and power characteristics must all be integrated to achieve efficient and reliable mixing at industrial scales.