Page 244 - Chemical process engineering design and economics

Compressors, Pumps, and Turbines 225

To determine the compressibility factor at the compressor inlet, z b first
calculate the reduced temperature and pressure.

TI 278.2
TRI=—- = ——— = 0.7517
370.1
T c
P! 1.4
PRI= —= —— = 0.03290
PC 42.55

From Figure 5.14, z\ = 0.97.
At the compressor inlet, the specific volume of the gas (Equation 5.7.24),

z,RT! 0.970.08314 bar-m 3 1 278.2 K

P! 1 1 kgmol-K 1.4 bar 1

3
= 16.03 nrVkgmol (257 ft /lbmol)
At the inlet conditions, the volumetric flow rate of the gas from Equation
5.7.9,

16.03 m 3 1090.0 kgmol
3
4
Vi = —————— ——————— = 1.747x10 m /h
1 kgmol 1 h
or

4
1.747xl0 m 3 1 h 35.31ft 3
3
V,= —————— ———— ———— =1.028x10" ft /min
1 h 60 min 1 m 3
From Figure 5.15 at Vi the polytropic or hydraulic efficiency, r\ f = 0.73. There-
fore, from Equation 5.7.7,

n-1 ( k - l ) / k (1.131-1)/1.13
——— = —————— = ————————— = 0.1587
n t|p 0.73

Assume one stage of compression, and calculate the polytropic work of
compression given by Equation 5.7.1. Because the discharge temperature is un-

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