Page 110 - Chemical Process Equipment - Selection and Design
P. 110
82 TRANSFER OF SOLIDS
TABLE 5.!j-(continued) particularly suited to a process. Capacity and power data for bucket
machines are given in Table 5.6. Flight and apron conveyors are
illustrated in Figure 5.11.
(c) Power to Drive Empty Conveyor
CONTINUOUS FLOW CONVEYOR ELEVATORS
One design of a drag-type of machine is the Redler shown on Figure
5.12. They function because the friction against the flight is greater
than that against the wall. Clearly they are versatile in being able to
transfer material in any direction and have the often important
merit of being entirely covered. Circular cross sections are available
but usually they are square, from 3 to 30 in. on a side, and operate
at speeds of 30-250 ft/min, depending on the material handled and
the construction. Some data are shown in Table 5.7. Most dry
granular materials such as wood chips, sugar, salt, and soda ash are
handled very well in this kind of conveyor. More difficult to handle
are very fine materials such as cement or those that tend to pack
such as hot grains or abrasive materials such as sand or crushed
stone. Power requirement is dependent on the coefficient of sliding
friction. Factors for power calculations of a few substances are
shown in Table 5.7.
The closed-belt (zipper) conveyor of Figure 5.13 is a carrier
that is not limited by fineness or packing properties or abrasiveness.
Of course, it goes in any direction. It is made in a nominal 4-in.
size, with a capacity rating by the manufacturer of O.O7cuft/ft of
travel. The power requirement compares favorably with that of
open belt conveyors, so that it is appreciably less than that of other
types. The formula is
Hp = 0.001[(L1/30 + 5)u + (LJ16 + 2L,)T], (5.26)
where
u = ft/min,
T = tons/hr,
L, = total belt length (ft),
Lz = length of loaded horizontal section (ft),
L, = length of loaded vertical section (ft).
Speeds of 200ft/min or more are attainable. Example 5.5 shows
0 400 800 1200 1600 2000 2400 that the power requirement is much less than that of the Redler
Length of Conveyor in Feet
conveyor.
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DRIVE-END
Figure 5.9. Some arrangements of belt conveyors (Stephens-Adamson Co.) and types of idlers
(FMC Corp.). (a) Horizontal conveyor with discharge at an intermediate point as well as at the
end. (b) Inclined conveyor, satisfactory up to 20" with some materials. (c) Inclined or retarding
conveyor for lowering materials gently down slopes. (d) A flat belt idler, rubber cushion type. (e)
Troughed belt idler for high loadings; usually available in 20°, 35", and 45" side inclinations.
