Page 110 - APPLIED PROCESS DESIGN FOR CHEMICAL AND PETROCHEMICAL PLANTS, Volume 1, 3rd Edition

94 Applied Process Design for Chemical and Petrochemical Plants

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10 20 30 40 60 BO 1 00 200 300 400 600 BOO 1 000 2000 4000 8000
OOWTHERM FLOW - GPM AT AVERAGE TEMPERATURE
Figure 2-25. Pressure drop for Dowtherm® liquid in schedule 40 pipe. By permission, Struthers Wells Corp. Bull. 4-45, 1956.

Then, incorporating the requirements of A, B, and C Assume, Q.1v1 = 120% ofQ
above, the estimated overall control valve drop is:
QM/Qo = 1.2
Required L'>Pc = 0.05 Ps + 1.1 [(QM/Qo)2 - I] Use cage type valve, B = 4
F 0 + B, psi (2-66)
From Equation 2-59,

B = base pressure drop for control valve with valve in wide- Available L'>Pc = (Ps - Pc) - Fo
open posit.ion, psi. (see list above). = (Ps - 37) - 96 = P5 - 133

From Equation 2-66,
Example 2-4: Using Figure 2-26, Determine Control
Valve Pressure Drop and System Start Pressure (See Required L'>P = 0.05Ps + 1.1 [QM/Qo)2 - l] F 0 + B
Example 2-3) = 0.05 (Pc) + 1.1 [(1.2) 2 - I] (96) + 4
= 0.05 Ps + 46.5 + 4 = 0.05Ps + 50
To determine Ps, the value of t!P through the control
valve must be known. Substituting:

Ps - 133 = 0.05Ps + 50
Pe= 37 psi 0.95Ps = 183
F 0 = 96 psi (all except control valve), psi Ps = 192 psi, start pressure at the pump