Drying spin flash

Performance, Size, and Cost Comparison of Spray Dryer with Spin-Flash Dryer for Drying Yellow Iron Oxide... 

A modification of the vortex dryer in the vertical arrangement that improves the performance of the weU-known spin-flash dryers is the spin-stream dryer. Designed basically for drying liquids, slurries, and suspensions, the spin-stream... 

Kudra, T., Pallai, E., Bartczak, Z., and Peter, M. 1989. Drying of paste-like materials in screw-type spouted bed and spin-flash dryers. Drying TechnoL, 7(3) 583-597. 

For the first group the following types of dryers are generally used convective (tray, band, fluid bed, flash dryers, and their modifications) or contact (vacuum dryers such as double-cone dryer-blender, conical dryer with rotating helical mixer, paddle dryer). Pastelike materials are dried in tray dryers, band dryers equipped with extruding devices, and spin-flash dryers. Finally, thin pastes can be dried in spray dryers or on fluid beds or spouted beds of inert particles. Small amounts of solutions and suspensions are generally freeze-dried, especially if the product is thermolabile. 

The principle of separation of wet and dry particles is applied in the design of a spin-flash dryer for sticky and pastelike materials (Figure 33.7). In the bottom of a cylindrical chamber a high-speed impeller disintegrates the wet feed in a rapid stream of the tangentially introduced heated gas stream. The swirling gas carries away dry particles, which are then separated in a cyclone. Partially dried particles fall back into the impeller zone and are disintegrated. This type of dryer is especially suitable for thick pastes as it can handle them without dilution. 

FIGURE 52.12 Spin flash-dryer feed system. (1) Feed vat, (2) agitator, (3) feed screw, (4) feed pump, (5) rotor, (6) air heater, (7) drying chamber, (A) product inlet, (B) heating, (C) air inlet, (D) product outlet. (From APV Crepaco Inc., New York.)... 

One of the innovative technologies for atomizing viscous liquids and thin pasty materials in a gas is the use of shock waves. This method could be used in spray drying to disperse the liquid feed (see Chapter 14) and thus eliminate the conventional atomizer from the system. This wiii avoid probiems with erosion in disk atomizers and clogging of singie- or two-stream spray nozzies. Potentiai applications of this idea in other types of dryers for dispersed materials include pneumatic, ring, spin-flash, and vortex dryers, in which the momentum of shock waves can enhance the hydrodynamic impact of a conventional gas-carrier. 

Efficient heat and mass transfer in dispersed systems and low temperatures required for drying heat-sensitive materials justify the application of a heat-pump system in conjunction with pneumatic, fluid bed, vibrated bed, conveyor, spin-flash, and similar convection dryers. A simplified layout of a heat-pump fluid bed dryer developed at the Norwegian Institute of Technology (NTNU) and thoroughly tested for various products (Jonassen et al., 1994 Strpmmen and Jonasen, 1996 Alves-FiUio and Str0mmen, 1996) is shown in... 

Spin-Flash Drying. This process is in essence fluidized-bed drying. Filter cake is introduced into the chamber by a screw feeder and drops to the bottom. A stirrer breaks up the particles until they are small enough to be carried up by hot air to a cyclone via a central constriction of variable diameter which acts as a classifier. The dried powder does not have the good flow properties required for automatic pressing. 

FIGURE 16.4 Spin-flash dryer. (From Devahastin, S. (Ed.), Mujumdar s Practical Guide To Industrial Drying—Principles, Equipment And New Developments, Exergex Corporation, Montreal, Canada, 2000. With permission.)... 

Neither flash nor spin-drying produces highly uniform particles and, even though the bulk of the particles remain at or near the wet bulb temperature, small particles are often over-dried and overheated. Particles of uniform size can be formed by spray drying, however, although it is then necessary that the feed should be in the form of a pumpable liquid which can be atomised so that the particles are evenly exposed to the hot air. 

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