Page 487 - Chemical process engineering design and economics

464 Chapter 8

g c Ap 32.2 (144) (5)
= ——— = ——————— = 1 1 .56 ft ( 3.52 m)
(AH) E
g p 32.2 (62.3)
(AH)' F = 3.25 + 1 1.56 + 0.299 = 15.1 1 ft ( 4.61 m)

(AH) V = (0.33 / 0.67) (15.11) = 7.442 ft ( 2.26 m)
Pump Size

Next, calculate the total head.

AH = 49 + 1 15.0 + 3.25 + 1 1.56 + 7.442 - (7 + 34.0 - 0.29) = 145.5 ft (44.3 m)

3
The point at 100 gal/min (0.379 m /min) and 145.5 ft (44.3 m) in Figure
8.4.2 is slightly above the characteristic curve for the 6 in (1.52 cm) impeller di-
ameter. Select the pump with a 6 1/2 in (16.5 cm) impeller diameter. Pump casings
can be fitted with several impeller diameters. Thus, in the future the pump size can
be expanded from the 6 V4 in (16.5 cm) to the 7 in (17.8 cm) impeller diameter.

Valve Size

Now, calculate the actual pressure drop across the control valve. From Fig-
1
ure 8.4.2 and at 100 gal/min for the 6 A in impeller, the total available head is 173
ft (52.7 m). Therefore,
AH = 49+115.0 + 3.25 + H.56 + (AH)v - (7 + 34.0- 0.29)= 173.0 (52.7m)

(AH) V = 34.90 ft (10.6m)

gp(AH) v 32.2 (62.3) (34.90)
2
(Ap) v = ————— = —————————— = 15.10 lb F/in (1.04 bar)
32.2 (144)
g c
Size the valve for a flow rate greater than the anticipated operating flow rate
to allow for some flexibility.
3
Q (design) = 1.3 (100) = 130 gal/min (0.492 m /min)

For incompressible flow, the valve size (Cv) is given by
172
1/2
C v = Q [ r) / (Ap) v ] = 130 (1.0 / 15.10) = 33.45 gal/min-(psi) 1/2
Round off C v to 33.

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