Vacuum Drying

Vacuum drying is the process of removing bulk moisture from a wet solid by exposing the mixture to vacuum. Drying is an essential operation in many different processes and is found in the food processing, pharmaceuticals, agriculture, powders and textiles industries. Vacuum blending and mixing use similar principles as in vacuum drying, so Wintek often sells process vacuum systems in these markets as well.

How Vacuum Dryers Work

Traditional dryers use two main driving forces to remove moisture: elevated temperatures and stripping gasses to saturate and remove vapors. Adding vacuum as a third force to the process greatly increases the overall efficiency of a dryer. A vacuum system lowers the pressure inside a large drying vessel. As the pressure within the vessel lowers to the vapor pressure of the liquid, the moisture will vaporize, leaving a dry product. Heaters installed on the vacuum dryer increase the temperature of the vessel. This increase in temperature coupled with the decrease in pressure allows for very high evaporation rates to occur. Once in vapor form, the vacuum system removes the moisture from the dryer. Depending on the customer’s desires, a heat exchanger condenses and a receiver tank collects the solvent.

vacuum drying, condenser liquid ring vacuum system with a transfer pump — Wintek SN 18016: Vacuum Drying, Vapors Removed: 2,000 kg wet cake, 70% moisture (water), Operating Vacuum Level: ~250 Torr Peak, ~75 Torr Final

double-drum-vacuum-dryer — Wintek SN 050317: Handles 1,500 lb/hr water and 35 lb/hr air at 25-30 Torr for a vacuum drying application.

Why Use Vacuum for Drying Applications

Vacuum drying is the fastest and most efficient way of achieving the driest possible product when compared to heat drying. Batch times can be decreased for drying processes using vacuum because vaporization occurs more readily and effectively under lower absolute conditions. When handling temperature sensitive products, such as in the pharmaceutical or polymer industries, vacuum drying is the most cost-effective solution. In the food industry, freeze drying maintains and preserves important flavors and vitamins consistently.

Wintek has extensive experience in the vacuum drying industry and works closely with many of the dryer manufacturers. Our process vacuum systems are custom-built to cater to any application that requires vacuum. Generally, Wintek recommends liquid ring vacuum systems for dryer applications because they are more rugged and can handle liquid and solid process carryover better than other types of vacuum pumps. While most dryers use filtration to prevent their solid product from leaving the vessel, the filter does not capture everything. Wintek’s process vacuum systems are ideal in these scenarios. Liquid ring vacuum pumps still operate if small amount of process carryover are present. However, in the case the dryer does not use filtration, Wintek provides systems with knockout pot filtration vessels in the system package to protect the system from process carryover.