Fluidized bed freeze drying

Tomova, R, Behns, W., Haida, H., Ihlow, M., and Mori, L., Experimental analysis of fluidized bed freeze drying, in Proceedings of the 14th International Drying Symposium, Silva, M.A. et al., Eds., UNICAMP, Sao Paulo, BrazU, 2004, pp. 526-532. 

We suggest a new process, i.e., a combined attnospheric spray and fluidized-bed freeze drying (ASFBFD) process. 

All these studies show that the atmospheric spray and fluidized-bed freeze drying combination is a viable new technology which requires further R D. Finally, a summary of comparison among four drying operations, i.e., SD, SFD, FD, and ASFBFD, are given in Table 9.10. 

Ordinary freeze-drying is carried out in vaeuum. Over the years, new developments showed that freezedrying can be carried out at atmospheric pressure and as well as in a fluidized bed (e.g.. Refs. [71-73]). Here the drying rate is very slow. Wolff and Gibert [74] showed that fluidized bed freeze-drying at... 

We suggest a new process, i.e., a combined atmospheric spray and fluidized-bed freeze drying (ASFBFD) process. The proposed schematic flow diagram is shown in Figure 10.52. It basically consists of a drying or freezing chamber, an internal bag filter, an internal fluidized bed, a liquid nitrogen cooler, a fan, nozzles, a pump, valves, pipes, etc. 

The hydration state of risedronate sodium was monitored continuously in a fluidized bed dryer and correlated to data on the physical stability of tablets made from the monitored material [275]. The final granulation moisture was found to affect the solid-state form, which in turn dictated the drug s physical stability over time. The process of freeze-drying mannitol was monitored continuously with in-line Raman and at-line NIR spectroscopies [276]. The thin polymer solvent coatings, such as poly(vinyl acetate) with toluene, methanol, benzene, and combinations of the solvents, were monitored as they dried to generate concentra-tion/time profiles [277]. 

In addition to the vertical mixing of solids, a degree of horizontal mixing occurs and this is especially important in long, shallow plug flow beds of the type used in fluidized bed drying or freezing (see Chapter 3). 

Other applications of liquid-solid fluidized beds that have been suggested or put into practice include the leaching of vegetable oils from seeds (Epsfein, 2003), fhe freeze concentration of solutions (Rios et al., 1985) and osmotic drying (Marouze et al., 2001). Fluidization is also the basis of fhe hydraulic fransport of vegetables (McKay et al., 1987). Three-phase fluidized beds have been employed for the fermentation of cocoa beans (Jacquef et al, 1981 Rios et al, 1985). 

Boeh-Ocansey O., Freeze-drying in a fluidized-bed atmospheric dryer and in a vacuum dryer evaluation of external transfer coefficients, /. Food Eng., 7 (1988) 127-146. 

Sublimation temperatures are in the range of —10 to —40°C and corresponding vapor pressures of water are 2.6-0.13 mbar. Cabinet tray dryers are the most commonly used type. The trays are lifted out of contact with hot surfaces so the heat transfer is entirely by radiation. Loading of 2.5 lb/sqft is usual for foodstuffs. Drying capacity of shelf-type freeze dryers is 0.1-1.0kg/(hr)(m2 exposed surface). Another estimate is 0.5-1.61b/(hr)(sqft). The ice surface has been found to recede at the rate of 1 mm/hr. Freeze drying also is carried out to a limited extent in vacuum pans, vibrating conveyors, and fluidized beds. Condensers operate as low as —70°C. 

Continuous hoi air driers are used to prepare most of the high quality, dried, piece-furm fruits and vegetables produced in the United States. Liquids and pastes arc commonly dried in spray, drum, or feeze dryers. Particulate foods can be dried in batch or continuous air-fluidized beds or freeze dryers. Many agricultural commodities are sun-dried when weather conditions at harvest provide low humidity, warm temperatures, and good air circulation. 

The solvent may be eliminated without chemical transformation by drying. Many different processes may be applied to this end such as drying in an oven, fluidized bed drying, spray drying, freeze drying. 

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