Operation Principle of Cabinet Dryers
In a cabinet dryer, the feed is loaded onto trays that, depending on the required quantity of material to be processed and hence dryer size, are loaded onto trolleys or inserted into the drying chamber. The door is closed, sealing the system. The trays may have a solid or perforated bottom, depending on the feed particle size distribution. The carrier (typically, air) is drawn in through an inlet duct or recycle channel into the heating compartment. The air is heated to the required temperature in this region, then distributed from side-to-side (cross-flow) or bottom-to-top (through-the-bed flow) in a circular motion, according to specific drying requirements.
The motive force for the air movement typically is a plug-type fan that acts as both an induced draft and forced draft machine. The fan sucks the air through the heating chamber and blows it across the trays, which act as channels or ducts to direct the air. The fresh air inlet is located on the suction side and the exhaust is located on the pressure side. The inlet and typically exhaust will have dampers on them, enabling the percentage of recycled air to be controlled. This recycle improves the efficiency of the unit operation, conserving energy in the gas stream.
Cabinet dryers come in various sizes and may have multiple fans on larger units. Carninet Dryers also may be more than one heating compartment. Units can be electrically heated, have gas or LFO heat sources, or use indirect heat sources such as steam or thermal oil.
Cabinet dryers can dry all types of feeds from liquids and slurries to granules, agglomerates and solids (objects). Next month, I will look at dryer loading and unloading, residence time, ancillary systems and potential operating drawbacks.
