A flash dryer is the simplest and most ideal solution for easy-to-dry products requiring only surface moisture removal. Flash drying is applicable to most powders, pastes, cakes, or slurries including fine, sticky, and heat-sensitive materials. This wide variety of applications is credited to the flash dryer's the versatility on temperature profiles, feed conditioning, and dispersion into the drying airstream.
Flash dryers are pneumatic systems combining simultaneous air conveying and drying, where solids are introduced at the feed point and dry in a 1-pass arrangement before full discharge to the product collection system. With a short residence time of only a few seconds, the solids are in contact with a relatively low heat environment for a short period. As a result of its simplicity, versatility, and short drying time, flash dryers produce high-quality final products with uniform moisture content throughout and consistent particle size distribution.
Open-Circuit (OC) Configuration
A flash dryer in OC configuration operates at the lowest temperature for a given application and ensures the highest quality product. Using ambient fresh air in a once-through arrangement, the product always remains in contact with a clean, unadulterated, low-humidity drying medium to prevent risk of contamination or changes to the product's desired state. Additionally, an indirect heat source like steam-heating or electric heating, avoids product-contact with combustion products. Alternatively, system integration with alternate heat sources, such as gas turbines, can help to improve the overall plant operations efficiency.
Partial Gas Recycle (PGR) Configuration
Flash dryers can also be designed with a Partial Gas Recycle (PGR) configuration to access energy-recovery for improved efficiency. PGR recirculates the majority of the dryer exhaust stream back to the air heater as a preheated drying medium. Since the bleed-off stream contains high-humidity, a Gas Heated Evaporator (GHE) may be integrated to recover the energy for liquid concentration of a separate stream in the plant's operations. Dedert's GHE is designed for particulate-removal and stream saturation to maximize the evaporator's performance, while also eliminating the need for a wet scrubber for the dryer bleed-off stream and reducing the RTO size for a smaller vent stream.
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