Drying is an essential unit operation in a variety of chemical process industries (CPI) sectors. Food, pharmaceuticals, chemicals, plastics, timber, paper and other industries use drying equipment to eliminate moisture during product processing. Most dryers are classified as direct dryers, where hot air (at near atmospheric pressure) is used to supply the heat to evaporate water or other solvents from the product. Another important dryer category, vacuum dryers, involves the use of a reduced-pressure atmosphere to surround the product. Drying is among the most energy-intensive unit operations, due to the high latent heat of vaporization of water and the inherent inefficiency of using hot air as the (most common) drying medium. Depending on the specific product attributes required, different industry sectors require different types of drying technology. Drying high-value products that are likely to be heat-sensitive, such as food, pharmaceuticals and biological products, demands special attention. When dried by convection at higher temperatures, these heat-sensitive products degrade, change color and appearance and have lower vitamin or nutrient content. Vacuum dryers offer an alternate path.
Drying involves two distinct drying periods, known as the constant drying period and the falling drying period . Drying occurs when liquid is vaporized by supplying heat to the wet feedstock. The liquid removed by the drying process could be either free moisture (unbound) or bound within the structure of the solid. The unbound moisture, normally present as a liquid film on the surface of a solid particle, is easily evaporated, while the bound moisture could be found within the solid material, trapped in the micro structure of the solid. In this case, the moisture must travel to the surface to be evaporated. When a solid product is subjected to drying, removal of unbound and bound moisture depend on the rates at which these two processes proceed. Removal of unbound moisture depends on external conditions of air or gas temperature, flow, humidity, area of exposed surface and pressure. The movement of bound moisture depends on the nature of the product being dried and the extent of moisture within the product. Unbound moisture normally is removed by evaporation and vaporization. Raising the temperature facilitates the evaporation and air draws the moisture away. If the product being dried is heat-sensitive, then the temperature at which evaporation occurs (at the boiling point of water or other solvent) can be reduced by lowering the pressure with a vacuum.
Vacuum drying is a viable technology that has been used successfully for many years in the pharmaceutical, food, plastics and textile industries, among others in the CPI.A major advantage to vacuum drying is its energy conservation — less energy is needed for drying, cutting down on the economic and environmental costs associated with drying a product for storage, sale or other purposes. Vacuum-drying processes also tend to work faster than other drying methods, cutting down on processing times, which can be important in some facilities where products are being moved through quickly. Another advantage of drying materials in this way is a less damaging drying process. Some materials can experience problems at high temperatures, such as developing hard, leathery crusts from heat exposure during the drying process. Vacuum drying tends to retain the integrity of the original item without damaging it with heat. For foods and pharmaceuticals, this can be valuable, as other drying processes can degrade quality and make the food less appealing or affect potency of heat-sensitive drug product. Using vacuum-drying equipment also reduces risks to workers. With other types of drying equipment, there are vented fumes and particles that can make people sick or that force people to wear protective garments. With a vacuum dryer, ventilation does not occur, and personnel working near the dryer are safer. It is also possible to recover the precipitated moisture collected during the drying for further use.
Structure of vacuum dryer
The vacuum dryer is consist of vacuum chamber, tray,heating system, vacuum system, recycle system, electrical control system.
Specification of vacuum dryer
Inner chamber size
Heating by electric
From Room temperature to 250℃
From Room temperature to 125℃
Steam pressure in tube
PID automatic control temperature,pressure transmitter automatic vacuum degree.
Optional by buyer
Solvent Recovery Unit, filtrator, PLC human-computer interface,vacuum pump