Page 105 - Chemical Process Equipment - Selection and Design

5.3. MECHANICAL CONVEYORS AND ELEVATORS 77

EXAMPLE 5.2 = [(45.4),/64.4][5.9 + (4.5/D)](4.91D2)
Size and Power Requirement of a Pneumatic Transfer Line = 157.1D2(5.9 + 4.5/D)
A pneumatic firansfer line has 300 ft of straight pipe, two long radius
elbows, and a lift of 50ft. A two-stage cyclone is at the receiving For the solid, take the coefficient of sliding friction to be f, = 1.
end. Solid with a density of 125 Ib/cuft lis at the rate of 10 tons/hr Power loss is made up of four contributions. Assume no slip
and the free air is at 5000ft/min. Inlet condition is 27psia and velocity;
100°F. Investigate the relation btween line diameter and power
requirement. w, = w, + w, + w4+ w,
On a first pass, the effect of pressure loss on the density of the
air will be neglected. = [u2/2g + A2 +f,L + 2(Q.0488)f,u2]mj
Mass flow rate of solid: = 5.56[45.4'/64.4 + 50 + 300 + 2(0.0488)45.42]
= 3242.5ft lbf/sec.
rnd = 20,0800/3600 = 5.56 lb/sec.
Total friction power:
Mass flow rate of air:
wf = 3242.5 + 157.1D2(5.9 + 4.5/D).
50061 n
m;=--- (0.075)D2 = 4.91D2 lb/sec.
60 4 Pressure drop:
Density of air:
(3
p, = 0.075 ~ = 0.138 lb/cuft. Fan power at q = 0.5:

Density of mixture: . WC+Y 2e!!.f~~p/tp~,
P= 550(0.5)(10) - 2750
5000( x/4) D2
saturation = 20,000/60 = 11.780, SCFM/(lb/min).
- (rn; + 5.56)
-
rn:/0.138 + 5.56/125
IPS ~(ft) rn; pm w, w,
Linear velocity of air at inlet: 3 0.2557 0.3210 2.4808 6362 3484
4 0.3356 0.5530 1.5087 10,959 3584
5 0.4206 0.8686 1.0142 17,214 3704
6 0.5054 1.2542 0.7461 24,855 3837
AP SCFIVI/
Assume air and solid velocities equal. Elbow radius = 120. 1 PS (psi) HP/TPH Ib/min
Elbow equivalent length, 3 10.2 3.58 0.77
4 6.1 5.29 I .33
Le = 1.6(n/2)(12D) = 30.20 5 4.1 7.60 2.08
6 2.9 70.44 3.55
Power for compression from 14.7 psia and 560 R to 27 psia,
From Table 5.1, data for pebble Iime are
k/(k - 1) = 3.5,
w, = 3.5RT1[(P,/P,)O 2857 - 111.: sat = 1.7 SCFM/(lb/min)
= 3.5(53.3)(560)[(27/14.7)0.a57 - 1]4.91D2 power = 3.0 HP/TPH
= 973050, ft Ib€/sec. and for soda ash:
sat = 1.9 SCFM/(lb/min)
Frictional! contribution of air
power = 3.4 HP/TPH.
uL The calculated values for a 4in. line are closest to the recom-
w - - + (O.O15/D)(300 + 2(30.2:1D]rnA
['i
1-2g mendations of the table.

services. A related design is the apron conveyor with overlapping For bulk materials, belts are troughed at angles of 20-45". Loading
pans of various shapes and sizes (Fig. 5.8), used primarily for short of a belt may be accomplished by shovelling or directly from
travel at elevated temperatures. With pivoted deep pans they are overhead storage or by one of the methods shown on Figure 5.9.
also effective elevators. Discharge is by throwing over the end of the run or at intermediate
Flat belts are used chiefly for moving large objects and cartons. points with plows.