Page 235 - Chemical process engineering design and economics

216 Chapter 5

After calculating the isentropic work, then calculate the shaft work, brake
work, or compressor work, i.e, the work that is delivered to the shaft of the com-
pressor. The compressor work,

(5.21)
T!S TIB r) c

If the polytropic work is calculated, then the compressor work,

W P
(5.22)
T| G

where W c is called the compressor, shaft, or brake work.
Using either method, the compressor work should be approximately the
same. Finally, the compressor horsepower,

niW r
Pc = - (5.23)
550

If the compressor driver is an electric motor, then divide the compressor
power by an electric-motor efficiency to size the electric motor.

Table 5.6 Compressor Gear, Bearing, and Seal Efficiencies

Component Efficiency

Gears 0.95 to 0.98
Bearings 0.95 to 0.99
Mechanical Seals 3 0.98 to 0.995

a) For seal power losses from 5 kW to 25kW

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