Used Dryers

A dryer is any processing plant machine which removes moisture to produce a dry, solid product. Dryers come in a variety of shapes and sizes, many different types of materials of construction, can be batch type or continuous, rated for high temperature, low temperature, operate under vacuum, direct fired, indirect fired, etc.

Dryers are normally located in a process line near the end of process where the finished product is a dry powder. Many times in chemical or pharmaceutical plants the dryer is after the centrifuges or filters which remove most of the water before the product goes into the dryer.

Products dry much faster under vacuum than they do in atmospheric conditions and many times the products needs to be dried under a nitrogen blanket. These products need to be dried in a closed environment so you will see dryers rated for internal pressure and vacuum and will have a heating jacket.

Other products can be dried in something as simple as a large hot air oven.

Accessories for certain dryers include dust collectors, vacuum pump systems, heating systems, and condenser to condense any vapors created during the drying cycle.

Types of dryers:

• Air Dryers: used with compressors to remove the moisture from the compressed air. These can be desiccant type or refrigerated. Measured by CFM.
• Conveyor Dryers: These are continuous dryers that have a trough with a screw conveyor or paddle conveyor inside the trough. Typically the trough and the screw are heated. They may or may not have a cover that so you can dry under a vacuum. Measured by the width and length of the trough and number of conveyor screws.
• Drum Dryers: These have a heated drum or set of 2 drums where the product is distributed on the outside of the drum and dries as it rotates slowly toward a scraping blade which scrapes the dry product off the outside of the drum. These are good for milk drying, and cereals. Same as drum flakers which are cooled. Measured by the diameter and length of the drum.
• Fluid Bed Dryers: Can be batch or continuous. The product flows across a perforated bed in the dryer. Hot air is blown up through the perforated bed causing the product to flow in the air stream. Continuous beds vibrate to move the product through the dryer. Batch type have agitator to keep the product moving through the air stream. Found mostly in pharmaceutical plants. Measured by the Kg/Hr.
• Flash Dryers: Also called a pneumatic conveyor dryer, where the product is conveyed through a heat source and pulverizers before it is discharge through some type of air classifier. Measured by the CFM of the air flow though the dryer.
• Flakers or Belt Dryers: The product is distributed on a long continuous belt which passes through a heated chamber long enough to dry the product during it travel time though the chamber. Belt flakers are a solid belt which is cooled so the product dries or hardens and flakes off the belt at the end of the flaker. Measured by the diameter and length of the belt.
• Freeze Dryers (Lyophilizers): This is a low temperature batch dryer that has a vacuum rated housing with heated or cooled shelves inside. The product is spread onto trays that are inserted onto the shelves. Once the shelves are full the door to the dryer is closed until the drying process is complete. The identical to a shelf dryer except the product is processed under low temperatures. Many times vials filled with a pharmaceutical injectable medicine and a stopper on top are process in this dryer. When the process is complete the shelves compress to press the stoppers into to vials to completely seal them before leaving the dryer for sanitary reasons. Measured by the Square Foot of the shelves.
• Oven Dryers: Heated boxes that are either hot air or steam heated. Can be atmospheric pressure. Measured by the internal dimensions of the chamber.
• Porcupine Dryers: Special type of conveyor dryer with a trough and a special designed internal screw conveyor. Can be jacketed, and rated for internal pressure. Measured by the model number.
• Rotary Dryers: Rotary dryers are large long cylindrical tubes that rotate on external tires and trunnions, and hot air or direct flame is fired though the inside of the tube to dry the product as it tumbles its way through the rotating tube. Measured by diameter and length.
• Steam Tube Dryers: Same as a rotary dryers, except this dryer has internal steam heated tubes to dry the product as it tumbles through the rotating dryer housing tumbling over the outside of the steam heated tubes. Measured by the diameter and length.
• Shelf: This is a batch dryer with a square vacuum rated housing with internal heated shelves. Product is spread onto trays which are loading into the dryer on the shelves. Similar to a Lyophilize except this dryer is rated for heating only and does not have movable shelves. These are measured by the Square Foot Surface area of the shelves.
• Spray Dryers: This type of dryer has a large vertical chamber, measured by the diameter of the chamber, with either a co-current or counter current hot air flow through the chamber. A liquid product is fed into the top of the dryer chamber by a fast spinning wheel that atomizes the liquid into a fine spray. As the spray floats down though the hot air stream it dries into fine partials. Typical applications include Instant milk, instant tea, and powdered pigments.
• Vacuum Dryers: These are batch dryers that come in many different sizes an shapes. This category includes, double cone, twin shell, rotary vacuum, pan dryers, etc. They all are filled with some type of wet product, and move the product around the dryer under vacuum until dry. The product is either tumbled, agitated with a ribbon or paddle agitator, moved around a pan.
• Wyssmont Dryers: This is a continuous dryer with a cylindrical housing that is normally not pressure rated. Inside is a stack of trays that rotate with hot air blowing through the housing. Product is fed onto the top tray and is scraped onto the next tray each time a rotation is complete. The product continues to be scrapped from tray to tray until it reaches the bottom tray where dry product exits the dryer.