Cyclone dryer: A pneumatic dryer with increased solid residence time

Pneumatic dryers, in which the moist solid is carried and transported by the drying air while being dried, are very cost-efficient dryers where short-time drying is sufficient. Their basic and most widely used form is the flash dryer. Most drying tasks requiring a longer drying time, however, could so far not be solved by pneumatic dryers. Long-time dryers like fluidized bed dryers or rotary drum dryers had to be used. In this paper, the cyclone dryer, a pneumatic dryer with significantly increased solid residence time, is described. Combined with a flash dryer as pre-dryer, it offers a straightforward and cost-efficient solution for many drying problems otherwise solved using fluidized bed or rotary drum dryers. The paper gives a brief description of design and working principles of the cyclone dryer and recalls the basic principles of parallel flow pneumatic drying. The dimensioning of flash dryer - cyclone dryer units for changing products in day-to-day practice is largely experimental due to the different and hardly predictable drying characteristics of the solids. A choice of products successfully dried on flash dryer cyclone dryer units is presented.