Page 298 - Chemical Process Equipment - Selection and Design

262 DRYERS AND COOLING TOWERS
TABLE 9.12. Performance of Drum Dryers
(a) Single, Double drum and Vacuum Drums

Moisture Content,
(% Wet Basis) Steam Drum Feed Capacity
Method Pressure, Speed Temp. [Ib product/ Vacuum
Material of Feed Feed Product (Ib/sq in.) (rpm) (“F) (hr)(sq R)] (in. Hg)
Double-drum dryer
Sodium sulfonate trough 53.6 6.4 63 8; 164 7.75
Sodium sulfate trough 76.0 0.06 56 7 150 3.08
Sodium phosphate trough 57.0 0.9 90 9 180 8.23
Sodium acetate trough 39.5 0.44 70 3 205 1.51
Sodium acetate trough 40.5 10.03 67 8 200 5.16
Sodium acetate trough 63.5 9.53 67 8 170 3.26
Single-drum dryer
Chromium sulfate spray film 48.5 5.47 50 5 - 3.69
Chromium sulfate dip 48.0 8.06 50 4 - 1.30
Chromium sulfate pan 59.5 5.26 24 2; 158 1.53
Chromium sulfate splash 59.5 4.93 55 1; 150 2.31
Chromium sulfate splash 59.5 5.35 53 4; 154 3.76
Chromium sulfate dip 59.5 4.57 53 5; 153 3.36
Vegetable glue pan 60-70 10-12 20-30 6-7 - 1-1.6
Calcium arsenate slurry 75-77 0.5-1.0 45-50 3-4 - 2-3
Calcium carbonate slurry 70 0.5 45 2-3 - 1.5-3
Twin-drum dryer
Sodium sulfate dip 76 0.85 55 7 110 3.54
Sodium sulfate top 69 0.14 60 9; 162 4.27
Sodium sulfate top 69 5.47 32 9; 116 3.56
Sodium sulfate splash 71 0.10 60 6 130 4.30
Sodium sulfate splash 71.5 0.17 60 12 140 5.35
Sodium sulfate splash 71.5 0.09 60 10 145 5.33
Sodium phosphate splash 52.5 0.59 58 5; 208 8.69
Sodium phosphate dip 55 0.77 60 54 200 6.05
Sodium sulfonate top 53.5 8-10 63 8; 172 10.43
Vacuum single-drum dryer
Extract pan 59 7.75 35 8 - 4.76 27.9
Extract Pan 59 2.76 35 6 - 1.92 27.9
Extract Pan 59 2.09 36 4 - 1.01 atmos.
Extract pan 56.5 1.95 35 74 - 3.19 22.7
Extract pan 56.5 1.16 50 22 - 0.75 atmos.
Skim milk pan 65 2-3 10-12 4-5 - 2.5-3.2
Malted milk Pan 60 2 30-35 4-5 - 2.6
Coffee pan 65 2-3 5-10 1-1; - 1.6-2.1
Malt extract spray film 65 3-4 3-5 0.5-1.0 - 1.3-1.6
Tanning extract pan 50-55 8-10 30-35 8-10 - 5.3-6.4
Veoetable alue oan 60-70 10-12 15-30 5-7 - 2-4
(Perrys Chemical Engineers Handbook, McGraw-Hill, 1950 edition).

calculation of residence time when assumptions are made about collecting fines, and a heater and blower for the gaseous drying
terminal temperatures. medium.
Much ingenuity has been applied to the design of fluidized bed
9.9. FLUIDIZED BED DRYERS drying. Many different arrangements of equipment are illustrated
and described in the comprehensive book of Kro11 (1978) for
Free flowing granular materials that require relatively short drying instance. Figure 9.13(a) depicts the basic kind of unit and the other
times are particularly suited to fluidized bed drying. When longer items are a few of the many variants. Tables 9.14 and 9.15 are
drying times are necessary, multistaging, recirculation or batch selected performance data.
operation of fluidized beds still may have advantages over other Shallow beds are easier to maintain in stable fluidization and of
modes. course exert a smaller load on the air blower. Pressure drop in the
A fluidized bed is made up of a mass of particles buoyed up out air distributor is approximately 1 psi and that through the bed
of permanent contact with each other by a flowing fluid. Turbulent equals the weight of the bed per unit cross section. Some pressure
activity in such a bed promotes high rates of heat and mass transfer drop data are shown in Table 9.14. The cross section is determined
and uniformity of temperature and composition throughout. The by the gas velocity needed for fluidization as will be described. It is
basic system includes a solids feeding device, the fluidizing chamber usual to allow 3-6 ft of clear height between the top of the bed and
with a perforated distributing plate for the gas, an overflow duct for the air exhaust duct. Fines that are entrained are collected in a
removal of the dry product, a cyclone and other equipment for cyclone and blended with the main stream since they are very dry