Pulsed fluidization

Erlenmeyer flask shaked at 135 rpm and 25°C Continuous degradation in an air-pulsed fluidized bed bioreactor... 

The pulsed fluidized bed gives better mixing than a conventional fluidized bed, allows use of a wider range of particle sizes, and provides better solid-gas contacting. Instead of using an independent pulsator, the feed itself can be introduced through a pulse pump. In the use of this reactor, caution must be exercised in the use of proper range of pulsation parameters, and suitable baffles should be provided in the reactor. 

Gawrzynski, Z. and Glaser, R., Drying in a pulsed fluidized bed with relocated gas stream. Drying Technol, 14(9), 1121— 1172,1996. 

Reyes, A., Campos, C., and Vega, R., Drying of turnip seeds with microwaves in fixed and pulsed fluidized beds. Drying Technol, 24,1469-1480, 2006. 

Reyes, A., Vega, R.V., and Bruna, R.D., Effect of operating conditions in atmospheric freeze drying of carrot particles in a pulsed fluidized bed. Drying TechnoL, 28,1185-1192,2010. 

Reduced pressure drop (by 7%-12%) due to the lower minimum pulsed fluidization velocity and larger opening area of the supporting grid Lower minimum fluidization velocity (by 8%-25%) Improved bed structure (no channeling, better particle mixing)... 

Gawrzynski, Z. 1987. Sugar cooling in a pulsed fluidized bed with cyclically transferred airflow. Zuckerind, 112(10) 875-882 (in German). 

The pulsed fluidization can be further altered with some advantage if one uses periodic relocation of the gas stream that is, when the fluidizing gas is supplied sequentially to different sections of the bed. In fact, the idea of relocation of a supplementary gas to eliminate channeling in a fluidized bed of fine particles originated over 40 years ago (Belik, 1960), but it was not followed up. A similar principle of the gas-jet relocation has been proposed to fluidize particulate material by sequential relocation of the spouting gas... 

Basic hydrodynamic parameters of the rotation-pulsed fluidized bed can be calculated from the following relationships (Elenkov and Djurkov, 1992 Djurkov, 1998) ... 

Lower operating velocity (on average by 8%-25%) because both the minimum and the maximum pulsed fluidization velocities are shifted toward lower values... 

It should be noted that the term fluidization does not adequately reflect the bed behavior as particles in the PFB are vibrated rather than fluidized. Thus, at incipient pulsed fluidization (also called the lower pulsed fluidization velocity) and above, the bed performs as the vibrated or vibro-fluidized bed with frequency and amplitude depending on air velocity, static bed height, and frequency of the air stream relocation (GawrzynsM and Glaser, 1996 Blacha-Jurkiewicz, 1987). With increasing air velocity, more air bubbles and isolated spouts appear in the bed this velocity is called the upper (developed) pulsed fluidization velocity. Above this velocity, the bed turns into a classical... 

Drying kinetics in a pulsed fluidized bed (Figure 6.5) are similar to those for convective drying in a system with perfect gas-solid contact which conforms to the thin-layer drying conditions. The following equations are given as examples ... 

Incipient pulsed fluidization velocity, m/s (if cp and e are not known) Developed/incipient pulsed fluidization velocities ratio... 

Djurkov TG. Modehng of bed pressure drops in rotation-pulsed fluidized bed dryer. In Akritidis CB, Marinos-Kouris D, Saravacos GD, eds. Proc. 11 Inti. Drying Symposium (IDS 98), Halkidiki, Greece, 1998, pp 160-167. 

Elenkov VR, Diurkov TG. Rotating pulsed fluidized bed dryer for high moisture content bioproducts. In Mujumdar AS, ed. Drying 92. Amsterdam Elsevier Science Publishers, 1992, pp 1636—1641. 

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