Efficiency of Static Mixers as Gas / Liquid Contactors

Author:

John W. Weston

This thesis investigates the efficiency of three specific static mixers—the Koch CY, Kenics, and Ross LLPD—functioning as gas-liquid contactors by measuring their mass transfer coefficients and interfacial areas. Through experimental analysis of carbon dioxide absorption catalyzed by arsenite, the study determines that the Koch CY mixer provides superior performance in producing interfacial area per unit of power dissipated compared to its counterparts. The research further correlates liquid holdup and pressure drop data to offer a comprehensive evaluation of how these stationary baffle units compare to traditional industrial contacting devices.

Key Learnings

• Comparative Performance: The Koch CY mixer was found to be the most efficient of the three types tested, providing superior interfacial area per unit of dissipated power and remaining competitive with traditional industrial gas-liquid contactors.
• Mass Transfer Characteristics: Experimental results showed that the liquid-side mass transfer coefficient (kL) remained relatively constant at approximately 1.84 X 10⁻⁴ m/s across the various flow conditions studied.
• Operational Advantages: Static mixers offer significant benefits over dynamic mixers, including lower capital costs, negligible maintenance due to the absence of moving parts, and the ability to handle a wide range of fluid viscosities and explosive gases safely.
• Energy and Efficiency: The efficiency of these devices is defined by the amount of surface area created per unit of reaction volume relative to the power input required to overcome pressure drop.
• Hydrodynamic Correlations: The study successfully correlated liquid holdup and pressure drop across the mixers, providing a mathematical basis for predicting performance based on gas and liquid velocities.
• Methodological Utility: The use of chemically enhanced absorption (specifically CO₂ into a buffered arsenite solution) proved to be an effective method for simultaneously measuring interfacial area and mass transfer coefficients using a Danckwerts plot.