APV Dryer Handbook - Umbc

66
variations, some plants utilize an inlet air dehumidification system.
The ambient air is drawn into the plant through filters to remove dust and airborne
contaminants which could foul the equipment, then across a chilling coil. This coil
is cooled to around 33°F (0.5°C) by a recirculated stream of water and glycol.
The cold coil surface, with the extended fins, cools the air and causes the
ambient moisture to condense on the coil surface. This condensation runs down
the surface of the coils and is collected in a trough at the base from which it runs
to a building drain. The air velocity across the face of the coil is important. Too
high a velocity will prevent the water droplets from clinging to the coil surface,
producing a mist, that will pass downstream to the fan. To reduce the danger
of this, most systems are followed by a demister, comprising either chevrons or
a coarse polymer demisting pad.
OUTLET TEMPERATURE
The spray dryer outlet temperature is controlled by adjusting the feed rate to the
atomizer. This, in turn, is accomplished by adjusting the speed of the feed pump
through a variable frequency drive. As more feed is atomized into the dryer
chamber, it cools the air in the chamber and the outlet temperature goes down. It
is important to note that unless the feed is adequately atomized, the outlet
PRODUCTION RATE
(Kg/hr)
9,000
5,000
2,500
(lbs/hr)
20,000
15,000
10,000
5,000
0
1 3 5 7 9 11
MONTH
20
18
16
14
12
10
8
6
4
2
0
INLET AIR
ABSOLUTE HUMIDITY
(g/kg)
PRODUCT 1
PRODUCT 2
PRODUCT 3
PRODUCT 4
PRODUCT 5
PRODUCT 6
ABS. HUMIDITY
Figure 32. Seasonal capacity changes when spray drying hygroscopic products