Holdup in bubble columns

Krishna, R. Wilkinson, P.M. Van Dierendonck, L.L. A model for gas holdup in bubble columns incorporating the influence of gas density on flow regime transitions. Chem. Eng. Sci. 1991, 46, 2491. 

Zahradnik J. et al., The effect of electrolytes on bubble coalescence and gas holdup in bubble column reactors, Trans IChemE 73 (1995), Part A,... 

Bubble reactors do not contain any packing and are fed by gas and liquid streams that may be cocurrent or countercurrent. The gas holdup in bubble columns has been measured by Van Dierendonck [55], who obtained the following correlation ... 

Fransolet, E., Crine, M., Marchot, P, and Toye, D. (2005), Analysis of gas holdup in bubble columns with non-Newtonian fluid using electrical resistance tomography and dynamic gas disengagement technique, Chemical Engineering Science, 60 6118-6123. 

Kojima, H., Sawai, J., and Suzuki, H. (1997), Effect of pressure on volumetric mass transfer coefficient and gas holdup in bubble column, Chemical Engineering Science, 52(21-22) 4111-4116. 

Krishna, R., and EUenberger, J. (1996), Gas holdup in bubble column reactors operating in the churn-turbulent flow regime, AIChE Journal, 42(9) 2627-2634. 

Wilkinson PM, van Dierendonck LL. (1990) Pressnre and gas density effects on bnbble breaknp and gas holdup in bubble columns. Chem. Eng. Sci., 45 2309-2315. 

Kawase et al. developed a model for the gas holdup in bubble columns with non-Newtonian fluids [41]. In the model, the liquid circulation caused by the introduction of a gas is considered as the buoyancy-induced circulation. The resulting equation is written as... 

Ghosh [83] 145 CMC solutions 0.92-0.96. 044-0.126 Liquid-solid mass transfer and gas holdup in bubble columns. 

The gas holdup in bubble columns has been measured by van Dierendonck [1970], who obtained the following correlation... 

Bubble columns. Tracers are used in bubble columns and gas-sparged slurry reactors mainly to determine the backmixing parameters of the liquid phase and/or gas-liquid or liquid-solid mass transfer parameters. They can be used for evaluation of holdup along the lines reviewed in the previous Section 6.2.1. However, there are simpler means of evaluating holdup in bubble columns, e.g. monitoring the difference in liquid level with gas and without gas flow. Numerous liquid phase tracer studies of backmixing have been conducted (132-149). Steady-state or continuous tracer inputs (132,134,140,142) as well as transient studies with pulse inputs (136,141,142,146) were used. Salts such as KC Jl or NaCil, sulfuric acid and dyes were employed as tracers. Electroconductivity detectors and spectrophotometers were used for tracer detection. The interpretation of results relied on the axial dispersion model. Various correlations for the dispersion... 

Gas Holdup (e) in Bubble Columns With coalescing systems, holdup may be estimated from a correlation by Hughmark [Ind. Eng... 

Information on gas holdup and axial dispersion in bubble-columns containing suspended solid particles is scarce reference will therefore also be made to significant studies of bubble-columns with no particles present, results obtained for these systems being probably of some relevance to the understanding of bubble-column slurry operations. 

Akita, K. and F. Yoshida, Gas Holdup and Volumetric Mass Transfer Coefficient in Bubble Column," l EC Proc. Des. Dev. 12 (1973) 76-80. 

Radial distributions of gas-phase characteristics were measured from the wall to the center of the column in 1/4-inch increments. For gas-liquid flows, steady-state operation was achieved in 10 minutes, whereas for gas-liquid-solid flows, measurements were not performed until one hour after flow conditions were established. At the end of each run, average gas holdup was measured by quick closure of the feed stream valve. The sampling rate for the conductivity probes was 0.5 millisecond per point, and the total sample time for each local measurement was 60 seconds. These sampling conditions are comparable to those of another investigator of gas-phase characteristics in bubble columns (11). 

Gas Holdup (e) in Bubble Columns With coalescing systems, holdup may be estimated from a correlation by Hughmark [Ind. Eng Chem. Process Des. Dev., 6,218-220 (1967)] reproduced here as Fig. (14-104). For noncoalescing systems, with considerably smaller buB-... 

Physical measurements can be made of gas holdup a, bubble size, and specific surface area a in gas-liquid dispersions, as usually encountered in bubble columns, plate columns, mechanically agitated tanks, and spray towers. Any two of these interfacial parameters are sufiicient to define all three, since they are interrelated ... 

A systematic study of mass transfer in bubble columns by Mashelkar and Sharma (M8, M9, S23) is summarized in Fig. 23. Increasing the superficial gas velocity increases the gas holdup a, the volumetric mass-transfer coefficients, and the interfacial area per unit volume of dispersion, but not the true mass-transfer coefficients. Correlations proposed for ki, seem too specific to be extended to practical systems (H13, FI, A3). Sharma and Mashelkar (S21) found good agreement between their experimental values of and the values from Geddes stagnant sphere model equation (G3) ... 

In bubble columns and gas-liquid stirred reactors, the estimation of parameters is more difficult than in gas-solid or liquid-solid fluidized beds. Solid particles are rigid, and hence the fluid-solid interface is nonde-formable, whereas the gas-liquid interface is deformable. In addition, the effect of surface-active agents is much more pronounced in the case of gas-liquid interfaces. This leads to uncertainties in the prediction of all major parameters, such as the terminal bubble rise velocity, the bubble diameter, the gas holdup, and the relation between the bubble diameter and the terminal bubble raise velocity. 

In bubble columns, since the gas bubbles are dispersed in the continuous liquid phase, fractional gas holdup (Eg) is an important design parameter, affecting column performance. The most direct and obvious effect is on the column volume, since a significant fraction of the volume is occupied by the gas. The indirect influences are also important. For instance, the possible spatial variation of Eg gives rise to pressure variation, which results in intense liquid phase motion. These secondary motions govern the rates of mixing plus heat and mass transfer. 

In general, the gas holdups and kLa for suspensions in bubbling gas-liquid reactors decrease substantially with increasing concentrations of solid particles, possibly because the coalescence of bubbles is promoted by presence of particles, which in turn results in a larger bubble size and hence a smaller gas-liquid interfacial area. Various empirical correlations have been proposed for the kLa and gas holdup in slurry bubble columns. Equation 7.46 [24], which is dimensionless and based on data for suspensions with four bubble columns, 10-30 cm in diameter, over a range of particle concentrations from 0 to 200 kg m 3 and particle diameter of 50-200 pm, can be used to predict the ratio r of the ordinary kLo values in bubble columns. This can, in turn, be predicted for example by Equation 7.41, to the kLa values with suspensions. 

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