Page 282 - Chemical process engineering design and economics

Compressors, Pumps, and Turbines 261

quires knowing the final motor size. With some loss in accuracy, we will use the
power calculated above. Thus, the motor efficiency is 91.9 %, and electric-motor
power,

P P= 341.2 / 0.919 = 371.3 hp (276.9 kw)

From Table 5.10, select a standard 400 hp (298 kW) motor, which results in
a safety factor of 7.73 %. The next size motor is 450 hp (336 kW) resulting in a
safety factor of 21.2 %. Based on his past experience, the process engineer would
have to decide what safety factor to chose.

NOMENCLATURE

English
CP heat capacity at constant pressure
or condensing-pressure efficiency correction factor for a multistage steam
turbine
c s superheat efficiency correction factor for a single stage
or multistage steam-turbine

E friction losses

E D friction losses on the discharge side of a pump
ES friction losses on the suction side of a pump
g acceleration of gravity
gc conversion factor
h enthalpy
k ratio of the heat capacity at constant pressure to the heat capacity at constant
volume

L length
m mass flow rate
M molecular weight
n number of moles or polytropic exponent
N number of compression stages for cooling
p pressure

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