feedoperations Troubleshooting the drier Each product and process has its own unique drying characteristics. These 15 simple rules will serve as guidelines to the science behind drying by Paul D. McKeithan The two main ingredients required to achieve convective drying are heat and air. Heat is required to energize the water in the product. This energy is responsible for the phase change from liquid to vapor. The air carries the heat to the product and water vapor away from the product. No textbook will give you the formula for how fast a specific product will dry under certain conditions, so with each new product it is necessary to establish a drying curve to serve as a baseline. A drying curve plots the rate of moisture reduction in a controlled drying environment, typically in a lab setting. Five product-related characteristics to know: * Inlet product moisture - Take a sample immediately at the entrance of the drier. Just a small increase of 1% to 2% (wet weight basis) on the inlet moisture could increase the amount of water to be evaporated by 10% to 25%. Be careful in this measurement since many "wet" products will yield errors in the moisture readings if not allowed to cool in a sealed container before analyzing. * Discharge product moisture - If the drier has to work harder to over-dry the product, you could lose capacity and energy. It is important that you periodically perform a detailed moisture uniformity check. Take samples across the width and height of the product bed BEFORE the product discharges. You should have good pelletto-pellet moisture uniformity. If not, the drier may have some internal airflow short circuits or design flaws. * Product bulk density - Since most products are stacked and not dried in mono-layers, the bulk density will affect the amount of resistance that the product will impose on the airflow system. If there is a major increase in bulk density, it could reduce the amount of airflow and therefore reduce the drying rate. Aeroglide 2-pass feed drier. 44 July 2005 / World Grain / www.World-Grain.comhttp://www.World-Grain.com