Designing of the dryer section of nutritional yeast production plant – Industrial sector review – Part 20
Wednesday, February 29th, 2012 6:04:01 by Ahmed Tariq
Designing of the dryer section of nutritional yeast production plant – Industrial sector review – Part 20
Spray-air contact
Mixing and flow is an important factor in the design of spray drier. The product and air flow into the dryer can be designed in co-current, counter-current or mixed flow patterns. Sine heat sensitive product is involved, the
counter current arrangements are not feasible as the hottest drying air comes to contact with the driest particles (Perry, 1997). Therefore the following arrangement is used in the dryer processing the cream (heat sensitive)
During the process, cream is sprayed by the atomizer at the rate of 1935.83 kg/hr and the droplet evaporation is rapid. In this type of arrangement, most of the evaporation takes place at low product temperature due to evaporative
cooling effect (the drying air cools as it reaches the bottom of the chamber). The final product temperature is limited by the air wet bulb temperature which is about 55°C (Appendix A6) until the drying process completes (Perry, 1997). The Air coming into
the dryer is at ? 300 °C with approximate humidity of 0.005 kg water/ kg dry air.
The manner of spray-air flow characterizes the droplet population throughout the chamber and bears important relation to the evaporation rate of the spray, the optimum residence time of droplets in the chamber and the extent
of wall deposit formation.
Each droplet in the resulting spray is ejected at a velocity greater than the air velocities in the chamber. The droplet kinetic energy is soon dissipated to surrounding by air friction. For this reason, the direct penetration
of the droplets towards the walls (wall deposits) of the chamber cannot occur unless the atomization has been incomplete.
Continued in part 21
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Posted by Ahmed Tariq
on Feb 29 2012. Filed under Business.
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