Dryer selection has long been practiced as an art rather than science depending more on prior experience and vendors’ recommendations. As drying technologies have evolved and become more diverse and complex, this has become an increasingly difficult and demanding task for the non-expert not conversant with the numerous types of equipment, their pros and cons, etc.
Further, the task is exasperated by the need to meet stricter quality specifications, higher production rates, higher energy costs and stringent environmental regulations. Many of the food products are low valued products and use of expensive techniques such as freeze drying is not recommended although the product quality can be superior.
Hence it is necessary to critically evaluate the steps involved in classification and selection of dryers for food products. There have been tremendous efforts in the development of novel drying techniques which are compared with conventional drying techniques in this chapter. It should be noted that over 80 percent of major chemical companies in Europe – each using over 1000 dryers in their production facilities – made errors in selecting dryers in the past year alone (Mujumdar 2008).
What is optimal choice in one location at one point in time may be a wrong choice for another geographic location some years later. It should also be noted that the pre-drying as well as post-drying stages have important bearing on the selection of appropriate dryer types for a given application; this is very important in case of food products as it decides the quality as well as the drying time.
Selection of Dryers
Indeed, for an optimal selection of process, one must examine the overall flowsheet as well as the “drying system.” This chapter will be confined, however, only to the classification and selection of dryers. In addition, few case studies will be discussed such as milk powder and some fruits and the detailed stepwise procedure will be given for selection of dryer for the these products.
Another important point to note is that several dryer types (or drying systems) may be equally suited (technically and economically) for a given food product. A careful evaluation of as many of the possible factors affecting the selection will help reduce.
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