Components of a Freeze-drying Plant

This process is of special interest if a product has to be frozen more quickly than is possible on belts or in trays A pellet of 2 mm diameter is cooled from 0 °C to -50 °C in approx. 10 s, or at a rate of approx. 300 °C/min. The advantages are minimum freeze concentration, free-flow product, small ice crystals (which are acceptable in this case of small transport distances for energy and water vapor). It is likely that some pellets (those too large or too small) will need to be removed by sieving. 

Yokota [2.1] sprays the liquid to be frozen in to a film of cold n-hexane, which flows down the inner wall of a conical vessel. The frozen particles are sieved off. With this method, two problems need to be solved (i) The droplet size cannot be influenced, product parts can be extracted, and the product and n-hexane must to be completely separated, and (ii) the process must be sterile. 

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