Page 308 - Chemical Process Equipment - Selection and Design

272 DRYERS AND COOLING TOWERS
TABLE S.l+(continued)
(d) Data of Rosin Engineering Ltd.
Sodium Weed
Perborate Killer PVC Coal Sand
Method of feed screw vibrator screw vibrator vibrator
Material size 30-200 5-1 mm 60-1 20 3 mesh- 30-1 20
mesh flake mesh zero mesh
Product rate (Ib product/hr) 1 1,400 5100 10,075 440,000 11 2,000
Initial moisture (% w/w basis) 3.5 14 2.0 8 8
Final moisture (% w/w basis) 0.0 0.2 0.2 1 0.2
Residence time (min) 1.5 11 30 0.3 0.45
Drier bed size (ft x ft) 22.5 X 5.5 18 X 4.5 23 X 6 16 x 6.6 12.5 x 3.2
Fluid bed height (in.) 4 3 18 5 6
Air inlet temperature (“F) 176 212 167 932 1202
104 150 122 180 221
Air outlet temperature (OF)
Air quantity (ft3/min std) 6600 14,200 5400 67,330 8000
104 205 122 180 212
Material exit temperature (OF)
Evaporation (Ib/hr) 400 720 183 33,440 9750
Method of heating steam steam steam coke-oven oil
gas
Heat consumption (Btu/lb water evaporated) 21 00 3060 4640 1970 2200
Fan installed HP 33 40 34 600 70
(Williams-Gardner, 1971 ),

EXAMPLE 9.9 - 688(0.00787)1’83[0. 048(150 - 0. 048)]0.94
-
Sizing a Fluidized Bed Dryer (0.023)o.88
A wet solid at 100°F contains W = 0.3 lb water/lb dry and is to be = 17.17 lb/(hr)(sqft).
dried to W = 0.01. Its feed rate is 100 lb/hr dry. The air is at 350°F
and has H,,=O.O151b water/lb dry. The rate of drying is
represented by the equation Let Gf = 2Gmf = 34.34 lb/(hr)(sqft).
Expanded bed ratio
dW- 60(Hs - H,), (Ib/lb)/min. @/Lo) = (Gf /Gmf)o.” = 2O.’’ = 1.16.
de
Take voidage at minimum fluidization as
The solid has a heat capacity 0.35 Btu/(lb)(“F), density 150 lb/cuft,
and average particle size 0.2pm (0.00787in.). The air has a = 0.40,
viscosity of 0.023 CP and a density of 0.048 lb/cuft. The fluidized
bed may be taken as a uniform mixture. A suitable air rate and :. ef = 0.464.
dimensions of the bed will be found:
Drying time:

e= Wo - W 0.3 - 0.01
60(Hs - H,) = 60(Hs - H,) ’

Since complete mixing is assumed, H, and H, are exit
conditions of the fluidized bed.
I -
Humidity balance:
A(H, - H,,) = s(W0 - W),
A I H, = 0.015 + 0.29SIA.
I
HgO = 0.015 (H,) w = 0.01 Average heat capacity:
T, (T,)
Tgo = 350 F (T,)
C, = i(C,, + C,) = 0.24 + 0.45[(0.015 + H,)/2]
Symbols used in the computer program are in parentheses. = 0.2434 + 0.225H6. (3)
Minimum fluidizing rate by Leva’s formula: Heat balance:

6880~83[0.048(150 - 0.048)]0.94
Gmf =
Yo.88