Page 287 - Chemical Process Equipment - Selection and Design

254 DRYERS AND COOLING TOWERS
/Friction seal
Girth aear

4

assembly Drive
assembly Discharae

--__)_wI) -
U
Recycle conveyor
Filter
n Elevator
Vent gas
Air
lock
Air heater Feeder
Entering' ~wmw
air f Recycle -
mixer
Feeder
Steam tube dryer
Product discharge
(b) (C)

Figure 9.9. Rotary dryer assemblies. (a) Parts of the shell of a direct fired rotary dryer (C.E. Raymond Bartlett Snow Co.). (b) Assembly of a
rotary dryer with pneumatic recycle of fines (Standard Steel Corp.). (c) Steam tube dryer with mechanical conveyor for partial recycle of
product for conditioning of the feed.

thermally sensitive materials and, of course, may generate dust if data of Table 9.10(a) are represented roughly by
the gas rate through the open dryer is high.
In the Roto-Louvre design of Figure 9.10(b) the gas enters at P = 5 + O.llDL, (9.19)
the wall, flows first through the bed of particles and subsequently
through the shower of particles. Performance data are in Tables where P is in HP and the diameter D and length L are in feet.
9.10(b) and (c).
A formula for the power required to rotate the shell is given by
Wentz and Thygeson (1979):
9.7. DRUM DRYERS FOR SOLUTIONS AND SLURRIES
P = O.45Wtu, + O.l2BDNf, (9.18)
Solutions, slurries and pastes may be spread as thin films and dried
where P is in watts, W, is the weight (kg) of the rotating parts, u, is on steam heated rotating drums. Some of the usual arrangements
the peripheral speed of the carrying rollers (m/sec), B is the holdup are shown on Figure 9.11. Twin drums commonly rotate in opposite
of solids (kg), D is diameter of the shell (m), N is rpm, and f is the directions inward to nip the feed, but when lumps are present that
number of flights along the periphery of the shell. Information could damage the drums, rotations are in the same direction. Top
about weights may be obtained from manufacturers catalogs or may feed with an axial travelling distributor is most common. Dip feed is
be estimated by the usual methods for sizing vessels. Fan and driver shown in Figure 9.11(d) where an agitator also is provided to keep
horsepower are stated for the examples of Tables g.lO(a)-(c). The solids in suspension. When undesirable boiling of the slurry in the