Page 206 - Chemical process engineering design and economics

Compressors, Pumps, and Turbines

Compressors are required to transfer gases from one process unit to another and
to compress them to carry out chemical reactions, separations, and to liquefy
gases. Compressors cover the range from vacuum to high pressure and are called
vacuum pumps, fans, blowers and compressors, according to their operating
pressure range. Roughly vacuum pumps compress gases from about 0.00133 to
1.01 bar (0.0193 to 14.7 psia) [3], fans from 1.01 to 1.15 bar (14.7 to 16.7 psia)
[1], blowers from 1.15 to 1.70 bar (16.7 to 24.7 psia) [1], and compressors above
1.70 bar (24.7 psia) [1]. These regions of application are not distinct, and may
overlap. The word pump is usually reserved for transferring liquids, but in the
vacuum region the compressor is called a vacuum pump.

Compressors are divided into two main classes, positive displacement and
dynamic. Positive-displacement compressors compress essentially the same vol-
ume of gas in a chamber regardless of the discharge pressure. In a dynamic com-
pressor, a gas is first accelerated to a high velocity to increase its kinetic energy.
Then, the compressor converts kinetic energy into pressure by reducing the gas
velocity, according to the macroscopic energy balance.

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