Dryer selection

Parker, N. H. (1963a) Chem. Eng., NY 70 (June 24th) 115. Aids to dryer selection. 

Parker, N.H. Aids to Dryer Selection, Chemical Engineering, June 24, 1963, p. 115. 

The maximum temperature at which the drying material may be held is controlled by the thermal sensitivity of the product and this varies inversely with the time of retention. Where lengthy drying times are employed, as for example in a batch shelf dryer, it is necessary to operate under vacuum in order to maintain evaporative temperatures at acceptable levels. In most continuous dryers, the retention time is very low, however, and operation at atmospheric pressure is usually satisfactory. As noted previously, dryer selection is considered in some detail in Volume 6. 

A listing of key information relating to dryer selection and design is in Table 9.5. Questionnaires of manufacturers of several kinds of dryers are in Appendix C. 

Initial selection of dryers. Select those dryers which appear best suited to handling the wet material and the dry product, which fit into the continuity of the process as a whole, and which will produce a product of the desired physical properties. This preliminary selection can be made with the aid of Table 12-9, which classifies the various types of dryers on the basis of the materials handled. 

EQUIPMENT SELECTION, SPECIFICATION AND DESIGN Table 10.7. Dryer selection... 

Dryer Selection Considerations Dryer selection is a challenging task and rarely clear-cut. For 500-pm particles, there m be several different dryer types which are likely to handle the task well, at similar cost. For 5-pm particles, there may be no dryers that are fully suitable, and the task is to find the least bad ... 

A detailed methodology for dryer selection, including the use of a rule-based expert system, has been described by Kemp [Drying Tech-nol. 13(5-7) 1563-1578 (1995) and 17(7 and 8) 1667-1680 (1999)]. A simpler step-by-step procedure is given here. 

If no cost data are available for the specific dryer selected, a good estimate can be obtained by using the logarithmic relationship known as the six-tenths-factors rule. A price for a similar one, but having different capacity, is the sole requirement. 

The purpose of this chapter is to review various forms of solids dryers and auxiliary components. It is intended to be a practical guide to dryer selection (as opposed to the theory of (hying, which is addressed in various technical manuals referenced in the bibliography). From a microscopic viewpoint, the process is simple water or solvent basically evaporates leaving the solid behind. When viewed macroscopically, it is apparent that the drying process is extremely complicated with many interdependent forces that combine in various dryers to achieve the end result. The information in this article can also help the reader become more familiar with the drying process from beginning to end. 

Due to the tacky nature of the product, one should begin the dryer selection process with a mechanically agitated style and proceed to test various types from there. If the material were free-flowing, a batch fluid bed dryer with an operating volume of 6.25 fl would be ideal. 

Baker (1997) has presented a structural approach for dryer selection that is iterative. It includes the following steps ... 

In Table 23.10, Kemp (1998) gives resnlts that were obtained from the proprietary dryer selection algorithm developed by Separation Processes Service (SPS) of AEA Technology, Harwell, United Kingdom. Althongh only one choice is reported here, it shonld be noted that, in most cases, alternate dryers can also be recommended with nearly equal performance. If local cost of equipment and energy are factored in along with the valne of the dried product itself, the results may be different as well. 

Table 23.11 lists some key recommendations on dryer selection based on specihc properties of the material. It is not all-inclnsive, nor does it cover all special physical and/or chemical... 

Key Recommendations on Dryer Selection Based on Specific Properties of the Materials... 

Baker, C.GJ. 1997. Dryer selection. In Industrial Drying of Foods, ed. C.G.J. Baker, 242-271. London Blackie Academic Professional. 

Kemp, l.C. 1998. Progress in dryer selection techniques. In Drying 98. Proceedings of the 11th International Drying Symposium Halkidiki, Greece, eds. C. Akritidis, D. Marinos-Kouris, G. Saravacos, and A.S. Mujumdar, 668-675. 

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