Generally speaking, the term “industrial dryers” applies to any machine that removes liquid or moisture from bulk materials. Usually, industrial dryers work through evaporation, or the process by which a liquid is converted into a gas and diffused into the atmosphere.
Sometimes, dryers also engage in sublimation, which is when a solid changes directly into a gas. The most common types of industrial dryers include fluidized bed dryers, rolling bed dryers, rotary dryers, conduction dryers, convection dryers, suspension/paste dryers, and dispersion dryers.
All of these dryers perform drying action using one of three methods: air drying, spray drying, and infrared drying.?
Of these, air drying is the most common. It works simply, by bringing materials being dried into direct contact with cold or hot air. Examples of air dryers include fluidized bed dryers, rotary dryers, flash dryers, and freeze dryers.
Fluidized bed dryers, also known as fluid bed dryers, dry using the power of intensive heat/mass exchange. To work, the substances or materials to be dried are set on a permeable surface inside the dryer. Here, they are struck with heated gas or air until the particles inside begin to vibrate slightly, indicating that the force generated by the air is slightly greater than the pull of gravity.
Once this happens, users may rest assured that even, thermodynamic drying has taken place. Fluidized bed dryers can be used to dry powders, pharmaceuticals and foods that are mostly uniform in size, like cereal. Read More…
Rotary dryers, which are sometimes called drum dryers, are composed of large, rotating cylindrical tubes. To dry products, operators place products and materials inside the dryer, where they will pass through one or more chambers. Inside these chambers, products come in contact with hot air as they tumble.
Moisture particles may encounter the hot air directly as they pass through a compartment, or they may encounter it indirectly, as it radiates from a separate chamber. Rotary dryers are useful in the drying of a number of substances, most notable powders such as industrial chemicals, laundry detergent and metal powders.
Flash dryers are pneumatic machines that dry moisture particles suspended in material or air streams within minutes. They work quite simply; a short burst of high heat comes forth as materials pass through the drying duct.
Freeze dryers work by first dropping air temperature so low that the substances become so cold that all moisture within them freezes. Then, they heat up the now-ice just enough so that it turns into vapor without ever turning back into a liquid. This transition, called sublimation, leaves the substances completely dry. Freeze dryers are used to preserve sensitive materials like penicillin and blood plasma, as well as to produce instant coffee.
Next, somewhat counterintuitively, spray dryers use hot steam to achieve dryness. To work, substances are first directed into the dryer, where any present solids are separated out. Then, the remaining substance is sent into the stream of hot steam, which evaporates moisture. After the moisture is vaporized, any remaining dry solids can be collected and disposed of or recycled.
This spray can be maintained as a constant stream, or it can be turned on in batches. Used with continuous dryers and conveyor dryers, spray dryers mostly service applications in the food processing, pharmaceutical, and pollution control industries. They are used to dry food flavorings, salts, pigments and more.
Finally, infrared dryers use the energy produced by infrared wavelengths to dry target materials and products from the inside out without overheating them. Infrared dryers are able to do this because, instead of being absorbed by the air, infrared radiation is absorbed by solid matter, where it matches its characteristics.
They may be produced as quartz tube types, short wave lamp types or perforated panel types. Infrared dryers are used in paper production, apparel, ink-drying, textiles, paint baking, and adhesive curing, among other processes.
In addition to these dryer types, there are some dryers out there that are designed for very specific purposes. Sludge dryers, for example, exist solely to dry solid matter and evaporate water inside sludge and slurry as much as possible, in order to reduce their volume and weight. Closely related to these are biosolids dryers, which dry sewage waste so it can be treated, recycled and used as fertilizer.
Other types of industrial dryers include tray dryers and steam tube dryers. The former, also called vacuum dryers or vacuum tray dryers, are industrial dryers that are used routinely for pharmaceutical purposes. Specifically, they are used to dry high-grade, temperature and oxygen-sensitive products, as well as hygroscopic substances and lumpy, glutinous products with low pomposity.
Steam tube dryers are a variation on the rotary dryer; they tumble materials inside a rotating cylinder that is attached to a series of small internal tubes that effectively increase heat transfer area.
The uses and capabilities of industrial dryers grow every day; they are increasingly essential to markets around the world.