Wyeth Laboratories, Paoli, PA


Drying problems include air pollution by solvents, product degradation and packaging difficulties due to lumping. Extensive evaluation of different types of dryers narrowed to two contenders: a rotary vacuum unit operating at about 28 to 29 in/Hg and a TURBO-DRYER®. Both recovered solvents satisfactorily and produced an acceptable dried product (0.5% or less volatiles). the TURBO-DRYER® operating cost was less because its chilled-water refrigeration system for condensing solvents cost less than 75% of the cost of the direct-expansion' "Freon" system required for the rotary vacuum unit. The two closed-circuit TURBO-DRYER® purchased are steam heated, stainless steel interior construction, 9.5 ft dia. Large unit is 10 ft high, 18 trays. Smaller unit, 6 ft high, 12 trays. The drying medium is nitrogen at a slight positive internal pressure; make-up rate is 5 scfm max. Oxygen levels are less than 5% by volume. The large unit reduces 30% volatiles to 0.5% at 300 Ib/hr. The smaller unit is used for smaller batches and different grades and reduces 25% volatiles to 0.5% at 150 Ibs/hr. Dried material is free-flowing and non-lumpy. No solvent odors can be detected by operating per-sonnel.


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