Gas-liquid-solid fluidization

The expression gas-liquid fluidization, as defined in Section III,B,3, is used for operations in which momentum is transferred to suspended solid particles by cocurrent gas and liquid flow. It may be noted that the expression gas-liquid-solid fluidization has been used for bubble-column slurry reactors (K3) with zero net liquid flow (of the type described in Sections III,B,1 and 1II,V,C). The expression gas-liquid fluidization has also been used for dispersed gas-liquid systems with no solid particles present. 

Recent research development of hydrodynamics and heat and mass transfer in inverse and circulating three-phase fluidized beds for waste water treatment is summarized. The three-phase (gas-liquid-solid) fluidized bed can be utilized for catalytic and photo-catalytic gas-liquid reactions such as chemical, biochemical, biofilm and electrode reactions. For the more effective treatment of wastewater, recently, new processing modes such as the inverse and circulation fluidization have been developed and adopted to circumvent the conventional three-phase fluidized bed reactors [1-6]. 

L. S. Fan, Gas-Liquid-Solid Fluidization Engineering, Butterworth, Boston, MA(1989) 368. 

Bavarian and Fan [3, 4] reported a similar phenomenon occurring in a three-phase fluidized bed. In their case, the hydraulic transport of a packed bed occurred at the start-up of a gas-liquid-solid fluidized bed. Although the cause was different from the case reported in the present study, similar phenomena were observed in both cases. 

Fan, L. S., Hwang, S. J., and Matsuura, A., Some Remarks on Hydrodynamic Behavior of a Draft Tube Gas-Liquid-Solid Fluidized Bed, AIChE Symp. Ser., 80(234) 91 (1984)... 

Fan, L. S., Fujie, K., Long, T. R., and Tang, W. T., Characteristics of Draft Tube Gas-Liquid-Solid Fluidized-Bed Bioreactor with Immobilized Living Cells for Phenol Degradation, Biotechnol. Bioeng., 30 498 (1987b)... 

III. System 1 Flow Dynamics of Gas-Liquid-Solid Fluidized Beds... 

C. Modeling the Motion and Collision Dynamics of Solid Particles in Gas-Liquid-Solid Fluidization... 

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... 

Fan, L. S., Gas-Liquid-Solids Fluidization Engineering . Butterworths, Stoneham, MA (1989). Fan, L. -S., and Tsuchiya, K., Bubble Wake Dynamics in Liquid and Liquid-Solid Suspensions . Butterworth-Heinemann, Stoneham, MA (1990). 

Reactors, 14 89. See also Autoclaves airlift, 15 708-709, 713-714 boiling water, 17 578-582 bubble column, 15 708-709 deep shaft, 15 713, 714 draft-tube sparged concentric draft-tube airlift, 15 712-713 fast-breeder, 17 585-588 gas-liquid-solid fluidized bed,... 

S. Heinrich, L. Mori, Description of the temperature, humidity and concentration distribution in gas-liquid-solid fluidized beds, Chem. 

Fluidized Gas-Liquid-Solid Reactors In a gas-liquid-solid fluidized bed reactor, only the fluid mixture leaves the vessel. Gas and liquid enter at the bottom. Liquid is continuous, gas is dispersed. Particles are larger than in bubble columns, 0.2 to 1.0 mm (0.008 to 0.04 in). Bed expansion can be small. Bed temperatures are uniform within 2°C (3.6°F) in medium-size beds, and heat transfer to embedded surfaces is excellent. Catalyst may be bled off and replenished continuously, or reactivated continuously. 

The cocurrent gas-liquid-solid fluidized beds considered are those in which the liquid supports and completely wets the solid. The gas flow thus constitutes a perturbation of a liquid fluidized bed. Unlike a gas-solid or a liquid-solid fluidized bed, a gas-liquid-solid fluidized bed may either contract or expand when gas bubbles are introduced into the bottom of the bed. Considerable work has been done on deriving the criteria for the bed contraction and expansion. The most up-to-date work on this subject is by Epstein.28 He derived the criterion for initial contraction and expansion of three-phase fluidized beds. He suggested that if the quantity... 

Narayanan et al.88 correlated gas holdup to the superficial gas velocity empirically and found hG oc U0G for U0G < 6.7 cm s 1 and hG oc UoG 8 for 6.7 cm s-1 < Uoc < 21.34 cm s"1. Hovmand and Davidson43 proposed a slug-flow model to correlate the gas holdup in gas-liquid-solid fluidized beds at superficial gas velocities in excess of that required for the incipient fluidization of solids. They correlated the gas holdup and superficial gas velocity by the equation... 

The results showed that the heat-transfer coefficient increased with the superficial gas velocity for all liquid flow rates and particle sizes. For a given particle size, the heat-transfer coefficient showed a maximum with respect to the bed porosity. For three particle sizes, namely 1 mm, 3 mm, and 5 mm, the effect of total gas plus liquid holdup on the heat-transfer coefficient obtained in this study is illustrated in Fig. 9-31. The results show a close resemblance between the trends for the two-phase (liquid-solid) and three-phase (gas liquid-solid) fluidized beds. In general, the maxima in the curves of Fig. 9-31 shifted to lower porosities with increasing particle size. 

PIV has also been applied to gas-liquid systems (Reese and Fan, 1994 Lin et al, 1996) to study the flow structure in bubble columns. A specific complication here is caused by the presence of the gas bubbles. On the basis of a prior knowledge of the size distribution of the tracer particles and the gas bubbles it is possible to discriminate bubbles from particles and thus phase-specific postprocessing of the images can be undertaken whereby both the flow pattern of the bubbles and the liquid in principle can be obtained. Particle image velocimetry has also been applied (Chen and Fan, 1992) to study the flow structure in 3D gas-liquid-solid fluidized beds. 

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