Fluidized bed stabilization

The Hydrodynamic Theory of fluidized bed stability was proposed by Foscolo and Gibilaro who adapted the stability principle of Wallis. They postulated that a fluidized bed is composed of two interpenetrating fluids. One fluid is the gas phase, and the solids phase is also considered as a continuous fluid phase. In this theory, voidage disturbances in the bed propagate as dynamic and kinetic waves. The stability of the fluidized bed depends upon the relative velocities of these two waves. The velocities of the kinetic wave (ue) and the dynamic wave (nj are ... 

The development of processing strategies in which the interaction between fluid motion and microstructural conformation can be used for (a) the development of microstructured materials with desired macroscopic properties and (b) active control of the flow itself, as in drag reduction and fluidized bed stabilization. 

A solid phase internal energy is related, again through a caloric equation-of-state, to the temperature. The solid phase pressure is defined as a function of the solid volume fraction where the functional relationship (cf., M) is based upon the fluidized bed stability measurements of Rietma and his coworkers ( ). 

Anderson, T.B. Jackson, R.A. Fluid mechanical description of fluidized beds stability of the state of uniform fluidization. I EC Fundam. 1968, 7,12. Verloop, J. Heertjes, P.M. Shock waves as a criterion for the transition from homogeneous to heterogeneous fluidization. Chem. Eng. Sci. 1970, 25, 825. 

Anderson, T.B., and Jackson, R. (1968). Fluid Mechanical Description of Fluidized Beds Stability of the State of Uniform Fluidization, I EC Fund. 7, pp. 12-21, February. 

The first parameter appears as a result of quasi-viscous stresses in the dispersed phase affecting the development of initial plane waves. In fact, this parameter characterizes an influence on fluidized bed stability caused by dispersed phase viscosity. The occurrence of the second parameter is due to the restriction imposed from below on permissible wave numbers for these plane waves. Actually, the second parameter descibes a so-called scaling effect of the bed dimensions on bed stability. The curves in Figure 4 correspond to the Carnahan-Starling model, save for the dotted ones which have been drawn when using Equation 4.8 to represent the osmotic pressure correction function and the Enskog factor. 

Anderson, T. B. and Jackson, R. A fluid mechanical description of fluidized beds. Stability of the state of uniform fluidization. Ind. Engng Chem. Fund. 7, 12-21 (1968). 

This discussion and calculations of fluidized bed flocculators are based on a parallel-sided tank. Hopper (inverted pyramid) and conical shapes are quite common and the values of GCt, and fluidized bed stability, involve... 

Eqn (8.36) is the statement of the general Wallis (1962, 1969) criterion for fluidized bed stability. The specific forms for the dynamic- and kinematic-wave velocities arising from the model formulation, eqns (8.19) and (8.30), yield the closed form of this criterion, which was derived indirectly in Chapter 6, and expressed in eqn (6.10). 

Anderson TB, Jackson R Fluid mechanical description of fluidized beds stability of state of uniform fluidization, Ind Eng Chem Fundam 7 12-21, 1968. http //dx.doi.org/10.1021/ il60025a003. 

Dry dense medium (pneumatic fluidized-bed) separation has been used, but has not received wide attention by the industry. An area of promise for future development is the use of magnetically stabilized dense medium beds by using ferro or magnetic fluids (2,10). Laboratory and pilot-scale units such as Magstream are available. In this unit, material is fed into a rotating column of water-based magnetic fluid. Particles experience centtifugal forces and... 

Commercially, stabilization is accomplished by controlled heating in air at temperatures of 200—300°C. A variety of equipment has been proposed for continuous stabilization. One basic approach is to pass a fiber tow through heated chambers for sufficient time to oxidize the fiber. Both Mitsubishi and Toho patents (23,24) describe similar continuous processes wherein the fiber can pass through multiple ovens to increase temperature and reaction rate as the thermal stabiUty of the fiber is increased. Alternatively, patents have described processes where the fiber passes over hot roUs (25) and through fluidized beds (26) to provide more effective heat transfer and control of fiber bundle temperature. 

Rietema, K., and Piepers, H. W., The Effect of Interparticle Forces on the Stability of Gas-fluidized Beds--I. Experimental Evidence, Chem Eng. Sci., 45 1627 (1990)... 

Hydrody namical ly, fluidized beds are considered to be stable when they are not bubbling and unstable when they are bubbling. Several researchers (Knowlton, 1977 Hoffman and Yates, 1986 Guedes de Carvalho et al., 1978) have reported that fluidized beds become smoother at elevated pressures (i.e., have smaller bubbles) and, therefore, are more stable at high pressures. There are generally two approaches as to what causes instability in fluidized beds. Rietema and co-workers (Rietema et al. 1993) forwarded the theory that the stability of the bed depends on the level of interparticle forces in the bed. However, Foscolo and Gibilaro (1984) have proposed that hydrodynamics determines whether a fluidized bed is stable. 

In this theory, increasing pressure causes gas to be absorbed onto the surface of the particles. This results in an increase in Mp and, by Eq. (7), an increase in the stability of the fluidized bed. 

New applications and novel reactor configurations or operational modes for three-phase systems are continually being reported. These include the operation of a three-phase fluidized bed in a circulatory mode (Liang et al., 1995), similar to the commonly applied gas-solid circulating fluidized bed the application of a three-phase fluidized bed electrode that can be used as a fuel cell (Tanaka et al., 1990) magnetically stabilized three-phase fluidized beds centrifugal three-phase reactors and airlift reactors. 

Several areas are receiving much of the research attention. Approaches that integrate product recovery with the fermentation in a three-phase fluidized bed bioreactor reflect general research trends in biochemical engineering (Yabannavar and Wang, 1991 Davison and Thompson, 1992). The successful use of three-phase biofluidization has also been demonstrated for recombinant protein systems, where it may have some benefit in improving plasmid stability (Shu and Yang, 1996). 

Bramble, J. L., Graves, D. J., and Brodelius, P., Plant Cell Culture Using a Novel Bioreactor The Magnetically Stabilized Fluidized Bed, Biotechnol. Prog.,... 

Federici, F., Petruccioli, M., and Miller, M. W., Enhancement and Stabilization of the Production of Glucoamylase by Immobilized Cells ofAureobasidium pullulans in a Fluidized-Bed Reactor, Appl. Microbiol. Biotechnol., 33 407... 

Siegell, J. H., Liquid-Fluidized Magnetically Stabilized Beds, Powder Tech., 52 139 (1987)... 

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