Flash dryers are used for drying a wide range of products. It can be used to dry both organic and inorganic chemicals. Flash Dryers are characterized by short residence time of few seconds. Hence, great care needs to be taken in dispersion of the feed in the drying air, which is generally in the form of cake so that true surface water gets evaporated form the feed . Otherwise, the larger particles in the feed material may require longer drying time than the smaller ones in order to reach the desired moisture content.
Flash Dryers :
- Extended Residence Time Flash Dryer
- Flash Dryer
- Agitated Flash Dryer
- Multiple-Stage Drying Systems
- Spin Flash Dryers
- Chemical Dryers
Due to the very rapid drying process, flash dryers are not suitable for diffusion-controlled drying processes. Figure 1 shows a typical drying curve as obtained in a fixed or fluidized bed; the constant drying-rate area where surface moisture is removed is ideal for the flash-drying operation. The process is strictly controlled by the heat input without a residence-time requirement; the drying occurs "in a flash".
Flash drying systems are designed based on feed and product characteristics, available or permissible heating source, and operational safety requirements. Such systems can be designed in a closed-cycle arrangement suitable for evaporation of organic solvents rather than water. The drying gas is inert (typically nitrogen), and the solvent evaporated in the flash dryer is subsequently condensed.
Flash dryer feed can be :Moist, powdery, granular, or crystallized ,Wet solids discharged from centrifuges, rotary filters, and filter presses , Small in particle size ,Reasonably dry, friable, and not sticky.
- Low residence time-minimum exposure to save original product quality.
- Produces free flowing powders in agglomerated or granulated form.
- Produces powders having a very low content of small particles (dustless).
- Ideal for heat sensitive products as particle temperatures are kept low throughout the drying process.
- Drying is completed at low outlet drying temperatures, giving high energy utilization efficiencies.
- High drying efficiency and low energy costs.
- Direct drying with no initial diluting.
- Continuous processing with short drying time.
- Low operator overheads and minimum maintenance costs.
- Pressure shock-resistant chamber for safe drying of organic products.
- Continuous producation machine without human touch.
- Ideal replacement for tray drying of wet cakes.
- Extramely sticky/pasty wet cake can be handled .
- Particle size as fine as 500 mesh is achievable.
- On line particle size reduction-eliminating need of separate pulverizer.
- Fully automatic - needs little running attention.
- Negligible material dusting.
- High volume processing
- Large filtering area of bag filter-reduced pressure drop -large savings in power consumption of blower.
- Relatively simple in operation
- Take little space
- Generally require lower capital investment than other types of dryers
- Excellent choice for processing heat-sensitive or easily oxidized feed materials
- Product inventory in the flash-drying system is very low
- Easy to change product or product grade with minimum downtime
- Control of the flash-drying process is very simple
- Control system responds very quickly to operational changes
- Food and feed products
- Organic chemicals
- Pigments and dyestuffs
- Pigments and dyestuffs
- Waste products