Column Dryer

The Column Dryer is well suited to process Polymers, Organic Chemicals, and Inorganics. However the feed to the Column Dryer must be non-sticky and in the form of free-flowing crumbs, granules, beads, pellets, or powder.

The Column Dryer is an economical way to provide heat and long residence time for slow diffusion-controlled drying. More often it is employed as a second stage dryer, following a first stage rotary, fluid bed, or indirect dryer.

The Column Dryer is a vertical vessel having a square cross sectional area with rounded corners. A feed distributor is located below the feed inlet nozzle at the top of the column. Similarly, a sweep gas distributor is employed at the bottom of the column, above a vibrating discharge device. Internal heating elements containing heat transfer fluid (steam, hot water, hot oil) are located in the upper section of the column. Vertical baffles are installed in the vessel below the heating plates and above the sweep gas distributor.

Free-flowing solids are metered into the top of the column dryer and move downward by gravity as a bed of solids in plug flow. As the solids pass the internal heating elements, conductive heat transfer increases the product temperature. Since the diffusion rate normally doubles for every 10°C rise in product temperature, it is advantageous to heat up the solids prior to diffusion drying. By employing a conductive heat transfer mechanism, the quantity of stripping gas is minimized - - - now determined not by heating requirements but by partial pressure differential driving force and gas/solids contact effectiveness. Once the feed solids have been preheated, the lower baffled section of the column dryer provides sufficient residence time and contact with the stripping gas for diffusion rate-controlled drying to occur.