Gas-liquid as well as gas-liquid-solid bubble column reactors are extensively used in the chemical industry. This review evaluates the present state of the art for the estimation of "nonadjustable" parameters in bubble column reactors. All the pertinent literature concerning these parameters is discussed and the discussion is followed by re1evant.recommendations for their predictions. Literature on the modified bubble columns has beem incorporated. Finally, the inadequacies of the data in some areas of practical importance have been pointed out and the recommendations for future work are outlined. Y. T. SHAH SCOPEIt is well known that bubble column reactors have a wide range of applications such as absorption, catalytic slurry reactions, bioreactions, coal liquefaction etc. These reactors are preferred because of simplicity of operation, low operating costs, and ease with which liquid residence time can be varied. The vast literature makes it impossible to cover all the aspects of bubble column reactors in one review; therefore, we limit ourselves in this review to the parametric estimations in bubble column reactors. The only unified review on bubble columns was published by Mashelkar (1970). Since then, many articles have been published on different aspects of bubble columns, except for the estimations of non-adjustable parameters. This paper attempts to bring about a more complete and up-to-date review of this subject matter.In the introduction, a comprehensive list of processes in which bubble columns are used is presented. Bubble dynamics and flow regimes indirectly influence the scaleup and design of bubble column reactors; and hence, these aspects are discussed initially along with relevant recommendations. Nonadjustable parameters like phase holdup, gas-liquid interfacial area, interfacial mass transfer coefficients, dispersion coefficients and heat transfer coefficients have a direct bearing on the problems associated with the design of the bubble column reactors. A critical analysis of the available literature on each of these parameters is presented in conjunction with the recommendations for their estimation. Wherever possible, the literature on modified bubble columns pertaining to these parameters, is also outlined. Finally, suggestions for the future work on bubble columns are offered. CONCLUSIONS AND SIGNIFICANCEOver the past two decades, an extensive effort has been directed to the scaleup of bubble column reactors. Though easy to use, bubble columns are difficult to design because of the complexity of flow characteristics, and their unknown behavior under different sets of design parameters such as diameter, height, etc. The present review indicates that there are numerous methods available to evaluate the non-adjustable parameters; few of which are based on extensive collection of data.For water-like less viscous fluids, flow regime characteristics can be depicted with help of Richardson and Zaki's (1954) correlation. Unfortunately, no systematic effort has been made to study the effect of flu...

Hydrodynam cs and Mass Transfer in NonNewtonian Solutions in a Bubble ColumnUntil now the oxygen transfer in viscous nowNewtonian solutions has been studied only in bubble columns of about 0.14-m diameter. Recently Godbole et al. (1982) reported much smaller gas holdups in Carboxy Methyl Cellulose solutions (CMC) for a large-diameter column. Therefore, the gas holdups, volumetric mass transfer coefficients, and specific gas-liquid interfacial areas are measured in CMC solutions using a bubble column of diameter 0.305 m and height 3.4 m. The transition from churn-turbulent to slug flalw regime occured at higher viscosities and the gas holdups and volumetric mass transfer coefficients were lower in both flow regimes than reported for smaller column diameters. Empirical correlations are presented for the gas holdup, volumetric mass transfer coefficient, and specific gas-liquid interfacial area which would be suitable for the design of fermentors. SCOPEBubble column reactors are becoming increasingly popular in the biotechnological and pharmaceutical industry. The rheological behavior of microbiological cultures in a fermentation tower can be fairly well simulated by ithe solutions of carboxymethyl cellulose (CMC). All the literature data for the hydrodynamics and mass transfer in CMC solutions were taken in columns of up to 0.14-m diameter. Recently for viscous CMC solutions, Godbole et al. (1982) reported a strong decrease in the gas holdup with an increase in the column diameter. The strong dependency of the gas holdup on column diameter suggests a similar dependency for the volumetric mass transfer coefficient, i.e., the previous investigations in columns of 0.14-m diameter are insufficient for scale-up purposes. The correlation of Nakanoh and Yoshida (1980) even suggests an increase in volumetric mass transfer coefficient with increasing column diameter. Therefore, in this work oxygen mass transfer in CMC solution was studied in a 0.305-m diameter column.Volumetric mass transfer coefficients are measured by the dynamic method. Specific interfacial areas are determined by the sulfite oxidation technique used by . The kinetics of the cobalt catalyzed reaction is not affected by addition of CMC (Wesselingh and van? Hoog, 1970);Onken and Schalk, 1978;Poggemann, 1982) and the deviation of the chemically effective interfacial area from the geometrical one is small because of the small gas-phase conversion (Schumpe and Deckwer, 1980a,b). The gas holdups are measured using a hydrostatic head technique and fractional gas holdups are measured using the dynamic gas disengagement technique (Sriram and Mann, 1976). To study the influence of the added salt, volumetric mass transfer coefficients are determined in CMC/sodium sulfate solutions and compared with the kLa values obtained in pure CMC solutions. Fermentation media might be more complex than the model media used and hence the effect of surfactant (Triton X-114) on the hydrodynamics and mass transfer in CMC solutions is studied. The gas holdup, volumetric mass transfe...

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Thermally eftlcient production of natural gas can be accomplished by the use of hot brine to dissociate solid gas hydrate deposits in the earth, The advantages of brine stimulation over steam or hot-water injection are lower energy requirements for reservoir heating and hydrate dissociation, reduced heat losses, higher gas production, and improved thermal eftlciency. In addition, the problems of blockage of rock pores and wellbore because of reformation of hydrates during gas producdon can be avoided.A mathematical model for a hot-brine stimulation technique was developed to compute gas recovery and the energy4ficiency ratio (i.e., the ratio of energj content of produced gas to heat injected) for a reservoir coutaitdng gas hydrates. The effects of variations in reservoir porosity, hydrate-zone thickness, depth, safinity of brine, brine temperature, and brine injection rate on the energy-efticieniy ratio and" gas production were determined. A comparison of brine and steam injection cases for the smie heat inje+ion rate shows bigber gas production and ener~eftlciency ratio for the brine case.

Gas holdup and axial dispersion coefficient data for dilute aqueous alcohol solutions and two different diameter columns at larger gas and liquid velocities compared to those of Schiigerl et al. (1977) are presented. Data for cocurrent and batch systems are qualitatively explained using Zuber and Findlay's theory (1965) and bubble structure, and quantified further using a dynamic gas disengagement technique. Unified empirical correlations for the gas holdup and axial dispersion coefficients are presented.Applications of bubble columns as bioreactors and for the process of coal liquefaction are relatively recent. Characteristics of the liquid-phase media in these two reactors can be fairly well represented by dilute alcohol solutions. The only work reported on this subject is by Schugerl et al. (1977) for relatively lower gas and liquid throughputs. They propose an empirical correlation for gas holdup involving the bubble diameter which is more difficult to estimate than the gas holdup. They do not propose any correlation for determining the axial dispersion coefficient.The experimental studies were carried out in two different diameter columns using cocurrent and batch systems. Five aliphatic alcohols (methanol, ethanol, n-propanol, i-propanol, and butanol) were investigated with concentration varying from 0.5 wt % to 2.4 wt %. The gas holdup was measured using a hydrostatic head technique. The axial dispersion coefficient was measured using heat as a tracer, and was based on the dispersion model. A dynamic gas disengagement method is applied to quantify the bubble-size distribution and bubble-rise velocities. This method involves a measurement of a decline in liquid height as a function of time, after gas flow is suddenly stopped. The experimental data are explained both qualitatively and quantitatively. Empirical correlations for gas holdup and the axial dispersion coefficient, applicable over a wide range of gas and liquid throughputs are presented.This infers that the dispersion coefficient and the gas holdup are interrelated.