Fluidized bed freezing

Fluidized bed freezing was first introduced in the early 1960s (Holdsworth, 1983) for the freezing of peas (Persson and Londahl, 1993) and peas are now used as a reference product in the specification of production rates in commercial freezing equipment (De Michelis and 

Persson (1967) suggesfed that optimum operation is a balance between capacity and power consumption. Freezing capacity, expressed 

Dafa comparing the operation of fluidized beds wifh ofher types of freezing planf are also scarce. The models developed by Reynoso and Calvelo (1985), which are based on Plank s equation for fhe prediction of freezing fime, compare the production rate of peas in a fluidized bed freezer wifh that in a fixed bed confinuous freezer of fhe same dimensions. Af air velocities of 1.2 and 0.8 in fhe fluidized and 

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Figure 3.1 Optimum bed depth for fluidized bed freezing production rate per imit bed width for fixed and fluidized beds at an inlet bed temperature of -30°C (solid line = bed length 6 m, broken line=bed length 4m). Reprinted from Reynoso, R.O. and Calvelo, A., Comparison between fixed and fluidized bed continuous pea freezers, Int.. Refrig., 8 (1985) 109-115, with permission from Elsevier.

Figure 3.6 Experimental heat transfer coefficients in fluidized bed freezing. From Vazquez and Calvelo (1983a), by permission of the Institute of Food Technologists, USA.

Table 3.6 Reported freezing times in fluidized bed freezing.

Air below freezing point of liquid being removed (fluidized bed freeze dryers)... 

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. 

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