Gas-liquid bubble column reactors are met in several industrial plants in the chemical and oil industry fields. The understanding of the global hydrodynamics, the local flow phenomena and the bubble properties are of fundamental importance in the comprehension of the flow dynamics as well as the mass transfer phenomena. This paper describes the experimental results obtained in a counter-current circular column of 240 mm in terms of the fluid dynamic behavior. The counter-current flow studied concerns an upward flow of air and a downward flow of liquid at ambient temperature and pressure. Air is introduced by means of a spider sparger distributor. Different liquids have been used as working fluids: water, water with NaCl (at different concentrations) and mixtures of water and ethanol. The following range of operating conditions was analyzed: superficial air velocities up to 20 cm/s and superficial liquid velocities up to - 11 cm/s, corresponding to a global air volume fraction (the holdup) up to 26%. The experimental investigations concerns (i) flow visualization, (ii) local data from a double fiber optical probe and (iii) holdup measurements. The images obtained from an optical camera were used to observe the general flow patterns and obtain information concerning the bubble shape. The data obtained from the double fibre optical probe were used to study the local flow characteristics at different radial position for different operating conditions. In particular, the local void fractions, the bubble velocities, the bubble mean diameters and the bubble diameter distributions and are presented and discussed. The bed expansion technique was used to obtain the gas holdup measurements for every operating condition. The gas holdup measurements are discussed, compared with existing correlations and used for investigating the flow regime transitions. Finally, the gas holdup and the local void fraction measurements data are compared and used for understanding the local hydrodynamics.
Holdup and local flow properties in a counter-current bubble column
BESAGNI, GIORGIO;INZOLI, FABIO
2014-01-01
Abstract
Gas-liquid bubble column reactors are met in several industrial plants in the chemical and oil industry fields. The understanding of the global hydrodynamics, the local flow phenomena and the bubble properties are of fundamental importance in the comprehension of the flow dynamics as well as the mass transfer phenomena. This paper describes the experimental results obtained in a counter-current circular column of 240 mm in terms of the fluid dynamic behavior. The counter-current flow studied concerns an upward flow of air and a downward flow of liquid at ambient temperature and pressure. Air is introduced by means of a spider sparger distributor. Different liquids have been used as working fluids: water, water with NaCl (at different concentrations) and mixtures of water and ethanol. The following range of operating conditions was analyzed: superficial air velocities up to 20 cm/s and superficial liquid velocities up to - 11 cm/s, corresponding to a global air volume fraction (the holdup) up to 26%. The experimental investigations concerns (i) flow visualization, (ii) local data from a double fiber optical probe and (iii) holdup measurements. The images obtained from an optical camera were used to observe the general flow patterns and obtain information concerning the bubble shape. The data obtained from the double fibre optical probe were used to study the local flow characteristics at different radial position for different operating conditions. In particular, the local void fractions, the bubble velocities, the bubble mean diameters and the bubble diameter distributions and are presented and discussed. The bed expansion technique was used to obtain the gas holdup measurements for every operating condition. The gas holdup measurements are discussed, compared with existing correlations and used for investigating the flow regime transitions. Finally, the gas holdup and the local void fraction measurements data are compared and used for understanding the local hydrodynamics.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
