Size Enlargement Solids Fluidization

Related topic dryers, Section 5.6 and reactors. Section 6.30. 

For spouted bed with feed diameter 1 mm gives product diameter of 3 to 

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Liquid and solids Size enlargement High shear mixer granulator, fluidized granulator (bubbling bed, spouted bed)... 

Agglomerates from finely divided solids are generally advantageous in all those cases where both a large surface area and a coarse particle size are required. Therefore, size enlargement by agglomeration is used increasingly for catalysts and adsorbents as well as for intermediate products that ultimately are reacted in fluidized beds, shaft furnaces, or rotary kilns. 

Fluidized bed use if slimes or line particles in feed. Use superficial velocities of 8 to 14 L/m s. Feed contacts bed for 30 min or 0.8 bed volumes/h. Related topics include reactors (Section 16.11.6.27), heat transfer (Section 16.11.3.8), drying (Section 16.11.5.5), size enlargement (Section 16.11.9.5), and mixing liquid-solid (Section 16.11.7.5). 

Spray (indirect convection) residence time 3 to 30 s gas velocity 0.2 m/s thermal efficiency 50% adiabatic efficiency 100% solid temperatnre = adiabatic satnration temperatnre volnmetric heat transfer coefficient 0.13 to 0.18 kW/m K 1.8 to 2.7 kg steam/kg water evaporated. Ap = 1.5 to 5 kPa. See size redaction sprays, Section 16.11.8.2 spray reactor, Section 16.11.6.12 heat exchange. Section 16.11.3.12 and size enlargement. Section 16.11.9.4. Flash/transported (indirect convection) 175 to 630°C, gas velocity 3 to 30 m/s or 2.5 to 3 times the terminal velocity of the particles gas reqnirement 1 to 5 Nm /kg solid or 1 to 10 kg air/kg solid exit air temperatnre 20°C greater than exit dry solid temperatnre 4000 to 10,000 kJ/kg water evaporated. See transported slnrry, transfer Une reactors. Section 16.11.6.9. Heat transfer coefficient for gas drying h = 0.2 kW/m -K. Flnidized bed (indirect convection) residence time 30 to 60 s for surface fluid vaporization 15 to 30 min for internal diffnsion 3500 to 4500 kJ/kg water evaporated. See fluidized bed reactors. Section 16.11.6.27 heat transfer. Sections 16.11.3.4 and 16.11.3.8 size enlargement. Section 16.11.9.5 and mixing. Section 16.11.7.1. Tray/gas flow through the bed 0.24 to 3.3 g water evaporated/s m tray area. Residence time 2 to 8.5 h superficial air velocity 0.2 to 1 m/s steam 2 to 6.8 kg steam/kg water evaporated. Fan power 1.6 to... 

Suspended Particle Techniques. In these methods of size enlargement, granular solids are produced direcdy from a liquid or semiliquid phase by dispersion in a gas to allow solidification through heat and/or mass transfer. The feed liquid, which may be a solution, gel, paste, emulsion, slurry, or melt, must be pumpable and dispersible. Equipment used includes spray dryers, prilling towers, spouted and fluidized beds, and pneumatic conveying dryers, all of which are amenable to continuous, automated, large-scale operation. Because attrition and fines carryover are common problems with this technique, provision must be made for recovery and recycling. 

Fluidized bed (indirect convection), residence time 30-60 s for surface fluid vaporization 15-30 min for internal diffusion 3500 to 4500 kj/kg water evaporated. Allow 1-2 m for disengagement. The dewpoint of the exit gas should be at least 10 °C less than the exit solids temperature of the bed. Gas and particles leave the bed at the same temperature. Partide-gas heat transfer coeffident U = 0.01-0.06 kW/m K. Surface area 20000-100000 m /m bed. For solids with medium sensitivity, such as organics, grains, PVC. Inlet temp about 80-150 °C AT = 50-100 °C. Bed volume 10-60 m /kg water evap/s soUds residence or drying time, 400-1800 s. Mass air/mass water evaporated = 40-100 MJ/kg water evaporated = 2-10 evaporation rate = 0.002-0.5 kg water evaporated/s m. Solids holdup 100-500 kg solids/m See fluidized bed reactors Section 6.30, heat transfer Section 3.4, size enlargement Section 9.4. 

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