Importance

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Abstract

An improved, high efficiency rotary drum dryer and method is disclosed which achieves outstanding thermal efficiencies by provision of a multiple-pass rotary dryer designed so that the product to be dried is first conveyed through an outermost drum of relatively large cross-sectional area and then through succeeding internal drums of progressively smaller cross-sectional areas. In this way, the velocity of induced air currents traveling through the dryer increases from pass to pass, with the result that the net velocity of product through successive passes also increases. The preferred dryer also includes housing structure in surrounding relationship to the innermost drum permitting introduction of relatively low humidity ambient-derived air into the central drum so as to lower the partial pressure of moisture in the drying atmosphere, thus promoting the final stage of drying. The preferred dryer also includes an assembly for selective introduction of a liquid or solid product treating agent into the final central drum. The dryer of the invention is capable of drying a greater volume of material with a shorter dryer and increased efficiencies are obtained because of increased airflow without attendant settling out of larger particles and possible dryer plugging.

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First Claim