Flash dryer is a pneumatic system, which is primarily used to dry products requiring the removal of free moisture. Drying takes place in a matter of seconds. Wet material is dispersed into a stream of heated air (or gas), which conveys it through a drying duct. Using the heat from the air stream, the material dries as it is conveyed. Product is separated using cyclones, and/or bag filters. Typically, cyclones are followed by scrubbers or bag filters for final cleaning of the exhaust gases to meet current emission requirements. Elevated drying temperatures can be used with many products since the flashing off of surface moisture instantly cools the drying gas without appreciably increasing the product temperature. A single operation provides mixing; heat transfer, and mass transfer to dry a solid. Residence time within the dryer is very short, usually less than three seconds, producing almost immediate surface drying.