Page 309 - Chemical Process Equipment - Selection and Design

9.10. SPRAY DRYERS
EXAMPLE 9.9-(continued) When drying is entirely in the falling rate period with rate equation
Adiabatic saturation line:
dW k(H,-H,)
__= w, w 5 w,,
d0 wc
the drying time will be
Vapor pressure:

P' = exp111.9176 - 7173.9/(T, C 389.5)]. (6)

Saturation humidity: where H,, Hg, and W are final conditions. When the final W is
small, 0.01 in the present numerical example, the single stage drying
time will be prohibitive. In such cases, multistaging, batch drying,
(7) or some other kind of drying equipment must be resorted to.

Eliminate T3 between Eqs. (4) and (5):
0.36(T4 - 100) + 261
350 --
%

Procedure: Fror a specified value of R =A/$, solve Eqs. (6),
(7), and (8) simultaneously.

R TI rs %l 4 0 (min)
5 145.14 119.84 0.0730 0.0803 0.662
6 178.11 119.74 0.0633 0.0800 0.289
8 220.09 119.60 0.0513 0.0797 0.170
10 245.72 119.52 0.0440 0.0795 0.136
12 262.98 119.47 0.0392 0.0794 0.120
Take

R = 10 lb air/lb solid,
A = lO(100) := 1000 lb/hr,
0 = 0.136 min.

Cross section!:
A/Gf = 1000/34.34 = 29.12 sqft, 6.09 ft dia.

Avg density:
f(1/20.96 -+ 1./19.03) = 0.0501 lb/cuft.

Linear velocity:
34.34
u=Gf= = 24.62 fpm.
~~(60) 0.0501(0.464)(60)
Bed depth:
L=uB=24.62(0.156)=3.35ft.

Note: In a completely mixed fluidized bed, the drying time is
determined by the final moisture contents of the air and solid.