Effect of feed concentration on the production of pregelatinized starch in a double drum dryer

Abstract

An industrial-scale double drum dryer is operated for producing pregelatinized maize starches using feed starch slurries of different solids content. Steam pressure, the level of pool between the drums and speed of drums rotation are varied together with the feed solids content in a practical range of values. The response of the dryer is registered by measuring several output variables, i.e. external drum temperature, product moisture content, mass flow rate and specific load (equivalent to product's film thickness). Experiments are also conducted with a different steam pressure in each drum and by preheating the feed slurry. The measurements of this work demonstrate for the first time that the concentration-dependent rheological and transport properties of the drying material dominate the drying process over and above the thermal condition of the drums. This information combined with the notion of thick momentum boundary layers surrounding the drums at the region of the gap are employed to explain the material application as a thin film over the drums. © 2002 Elsevier Science Ltd. All rights reserved.