Bubble columns behavior

Bubble columns in series have been used to establish the same effective mix of plug-flow and back-mixing behavior required for Hquid-phase oxidation of cyclohexane, as obtained with staged reactors in series. WeU-mixed behavior has been established with both Hquid and air recycle. The choice of one bubble column reactor was motivated by the need to minimize sticky by-products that accumulated on the walls (93). Here, high air rate also increased conversion by eliminating reaction water from the reactor, thus illustrating that the choice of a reactor system need not always be based on compromise, and solutions to production and maintenance problems are complementary. Unlike the Hquid in most bubble columns, Hquid in this reactor was intentionally weU mixed. 

The difference between the curves for pure water and seawater again illustrates the significance of small concentrations of solute with respecl to bubble behavior. In commercial bubble columns and agitated vessels coalescence and breakup are so rapid and violent that the rise velocity of a single bubble is meaningless. The average rise velocity can, however, be readily calculated from holdup correlations that will be given later. 

GL 1] [R 1] [R 3] [P le] The falling film micro reactor has a better selectivity-conversion performance than the two micro bubble columns tested (Figure 5.18) (3, 38]. The micro bubble column with narrow channels has a better behavior at large conversion than the version with wide channels. The behavior of the falling film micro reactor and the micro bubble column with narrow channels is characterized by a nearly constant selectivity with increasing conversion, while the bubble column with wide channels shows notably decreasing selectivity with conversion (similar to the laboratory bubble column). 

The computation performed in this study is based on the model equations developed in this study as presented in Sections II.A, III.A, III.B, and III.C These equations are incorporated into a 3-D hydrodynamic solver, CFDLIB, developed by the Los Alamos National Laboratory (Kashiwa et al., 1994). In what follows, simple cases including a single air bubble rising in water, and bubble formation from a single nozzle in bubble columns are first simulated. To verify the accuracy of the model, experiments are also conducted for these cases and the experimental results are compared with the simulation results. Simulations are performed to account for the bubble-rise phenomena in liquid solid suspensions with single nozzles. Finally, the interactive behavior between bubbles and solid particles is examined. The bubble formation and rise from multiple nozzles is simulated, and the limitation of the applicability of the models is discussed. 

In order to verify the simulation results, experiments on bubble behavior in bubble columns are carried out under conditions similar to the simulations. A 3-D rectangular bubble column with the dimension of 8 x 8 x 20 cm3 is used for the experiments. Four nozzles with 0.4 cm I.D. and a displacement of 2.4 cm are designed in the experiments. For single-nozzle experiments, air is injected into the liquid bed through one of the orifices while the others are shut off. The outlet air velocity from the nozzle is approximated using the measured bubbling... 

In system 1, the 3-D dynamic bubbling phenomena in a gas liquid bubble column and a gas liquid solid fluidized bed are simulated using the level-set method coupled with an SGS model for liquid turbulence. The computational scheme in this study captures the complex topological changes related to the bubble deformation, coalescence, and breakup in bubbling flows. In system 2, the hydrodynamics and heat-transfer phenomena of liquid droplets impacting upon a hot flat surface and particle are analyzed based on 3-D level-set method and IBM with consideration of the film-boiling behavior. The heat transfers in... 

In small lab-scale STRs almost complete mixing of the gas-phase can also be assumed whereas plug-flow or mixed behavior can be generally assumed for the gas phase in bubble columns (Marinas et. al., 1993 Stockinger, 1995 Huang et al., 1998) and packed towers (Lin and Peng, 1997). 

Pfleger D, Becker S. Modelling and simulation of the dynamic flow behavior in a bubble column. Chem Eng Sci 2001 56 1737-1747. 

Dense-phase fluidized beds with bubbles represent the majority of the operating interests although the beds may also be operated without bubbles. The bubbling dense-phase fluidized bed behavior is fluidlike. The analogy between the bubble behavior in gas-solid fluidized beds and that in gas-liquid bubble columns is often applied. Dense-phase fluidized beds generally possess the following characteristics, which promote their use in reactor applications ... 

Hydrodynamic behaviors in bubble and slurry bubble columns... 

Gas-liquid bubble columns and gas-liquid-solid slurry bubble columns are widely used in the chemical and petrochemical industries for processes such as methanol synthesis, coal liquefaction, Fischer-Tropsch synthesis and separation methods such as solvent extraction and particle/gas flotation. The hydrodynamic behavior of gas-liquid bubble columns and gas-liquid-solid slurry bubble columns are of great importance for the design and scale-up of reactors. Although the hydrodynamics of the bubble and slurry bubble columns has been a subject of intensive research through experiments and computations, the flow structure quantification of complex multi-phase flows are still not well understood, especially in the three-dimensional region. In bubble and slurry bubble columns, the presence of gas bubbles plays an important role to induce appreciable liquid/solids mixing as well as mass transfer. The flows within these systems are divided into two... 

Example 38 Mass transfer in the G/L system in bubble columns with injectors as gas distributors. The effects of coalescence behavior of the material system... 

The sorption characteristics of an industrial-sized slot injector were measured in a bubble column of technical size (30 x 8 m), as dependenent on the common salt (NaCl) content, this influencing the coalescence behavior of the material system, see Fig. 74. The results demonstrate that already small amounts of cooking salt (5 g/1 4 0.5 %) suffice to increase the absorption rate by ca. 30 %. The following correlations were found ... 

Example 35 Steady-state heat transfer in bubble columns 149 Example 36 Time course of temperature equalization in a liquid with temperature-dependent viscosity in the case of free convection 153 Example 37 Mass transfer in stirring vessels in the G/L system (bulk aeration) Effects of coalescence behavior of the material system 156 Example 38 Mass transfer in the G/L system in bubble columns with injectors as gas distributors. The effects of coalescence behavior of the material system 160... 

Bubble Behavior in a Slurry Bubble Column Reactor Model... 

In this paper we present a generalized procedure for the calculation of bed-wall heat transfer coefficient in bubble columns on the basis of their hydrodynamic behavior. It has been shown that the high values of heat transfer coefficient obtained in bubble columns, as compared to the single phase pipe flow, can be explained on the basis of the enhanced local liquid velocities in the presence of gas phase. A comparison between the predicted and experimental values of heat transfer coefficient is presented over a wide range of design and operating variables. 

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