Gas-liquid mass transfer for coalescent system in a hot-sparged triple-impeller stirred reactor

Abstract

BACKGROUND: Industrial processes are often operated in hot-sparged agitated reactors and the volumetric mass transfer coefficient (k L a) is one of the most important parameters for design and scale-up of stirred tank reactors. In this work, the power consumption and volumetric mass transfer coefficient were studied under hot-sparged conditions. RESULTS: The relative power demand (RPD) increases remarkably with temperature according to a power law with an exponent of 0.44. k L a increases significantly with power consumption and superficial gas velocity according to power laws with exponents 0.56 and 0.28, respectively. However, the temperature has little influence on k L a, with a power law exponent of only 0.13 for a coalescent system, much smaller than the exponent of 1.64 for a non-coalescent system stirred by a similar triple-impeller. CONCLUSIONS: In a hot-sparged coalescent system, an increase in temperature cannot enhance the mass transfer rate as it does in a non-coalescent system. As a practical guide to industrial applications, it is more effective to enhance the gas-liquid mass transfer by increasing the power consumption than by increasing the gas flow rate, especially when the gas flow rate is already very high. The empirical relationships between power consumption and k L a obtained in this work can provide helpful guidance for industrial design and operation of hot-sparged stirred reactors.