Chum-turbulent flow

Figure 5.3-8. Details of the chum-turbulent flow regime of BSCR according to Inga [1], (db)0-gas bubble size at atmospheric conditions in the absence of solid particles, (d, )ps- bubble size at the operating pressure and catalyst concentration. Column height = 2.8 m, internal diameter = 0.316 m. P < 8 bars. Organic media, catalyst diameter < 100 pm.

Recommendations for p range from 1 to 1.5 and for q from 0 to 2. Rice et al. [62] concluded that this was due to the different regimes and recommended q values of 2, 1, 1/3 and 0 for chain bubbling, bubbling flow, chum-turbulent flow and slug flow, respectively. 

Bubble columns Loop reactors Stirred tanks Hydrocyclones Reasonable Reasonable Reasonable Reasonable Modeling of chum-turbulent flow regime Modeling of chum-turbulent flow regime Improved geometrical representation of impeller and baffles Improved geometrical representation of system... 

Methods are given for the bubbly and chum-turbulent flow regimes within the vessel. The criterion for safe use to take account of disengagement is, GAh vJ Vv,(l-a,) - However, when disengagement is not accounted for, then = 1.0, and the above equation is not required. 

Three-phase fluidized beds and slurry reactors (see Figs. 30g-l) in which the solid catalyst is suspended in the liquid usually operate under conditions of homogeneous bubbly flow or chum turbulent flow (see regime map in Fig. 33). The presence of solids alters the bubble hydrodynamics to a significant extent. In recent years there has been considerable research effort on the study of the hydrodynamics of such systems (see, e.g., Fan, 1989). However, the scale-up aspects of such reactors are still a mater of some uncertainty, especially for systems with high solids concentration and operations at increased pressures it is for this reason that the Shell Middle Distillate Synthesis process adopts the multi-tubular trickle bed reactor concept (cf. Fig. 30e). The even distribution of liquid to thousands of tubes packed with catalyst, however poses problems of a different engineering nature. 

The optical impression of a bubble flow system is characterized by a great number of finely dispersed small bubbles, while in the case of the chum turbulent flow a growing bubble size is observed on its way to the liquid surface. 

Calculation of the characteristic dimensionless velocity at the liquid surface for chum turbulent flow Wg a according to Eq. (10.13) gives... 

In these balance equations all terms should be described at the same level of accuracy. It certainly does not pay to have the finest description of one term in the balance equations if the others can only be very crudely described. Current demands for increased selectivity and volumetric productivity require more precise reactor models, and also force reactor operation to chum turbulent flow which to a great extent is uncharted territory. An improvement in accuracy and a more detailed description of the molecular scale events describing the rate of generation terms in the heat- and mass balance equations has in turn pushed forward a need for a more detailed description of the transport terms (i.e., in the convection/advection and dispersion/conduction terms in the basic mass- and heat balances). 

Antal SP, Lahey Jr RT, Al-Dahhan MH (2004) Simulating Chum-Turbulent flows in a bubble column using a three field, two-fluid model. Paper presented at the 5th international conference on multiphase flow, ICMF 04, Yokohama, Japan, 30 May-4 June, p 182... 

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