Page 36 - Reciprocating Compressors Operation Maintenance

Reciprocating Compressors and Their Applications 213

complex question to which designers must give thorough consideration,
A problem of this nature is occasionally solved by increasing the number
of compression stages.
Figure 1-13 shows the theoretical effect of two- and three-staging on
the discharge temperature per stage.

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,2OO f ' .THEORETICAL ANABATIC DISCHARGE .
Li. 4! - . TEMPERATURE FOR AW WITH ?O*F .
- INTAKE TEMPERATURE.
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1 1 1,
o 106 200 901 0 400 SCO 60
AIR DISCHARGE PRESSURE—PSIA
FIGURE f-13. Theoretical adiabatic discharge temperature for air with 70°F
intake temperature.

Figure 1-14 shows the effect of staging on power requirements.
In both figures, the compressors are handling normal air at 14.7 psia
suction pressure. The data are theoretical, with intercooling to suction
temperature between stages (perfect intercooling) and equal ratios for all
stages, and are based on 70°F suction temperature.
Power savings are obvious. Percentages are shown in Figure 1-14. The
importance to be placed upon power savings in unit selection will depend
to a large degree upon load factor (percentage of total time a unit actually
operates) and the size of the compressor. In actual practice, when com-
pression stages exceed four, power savings are frequently slight through
adding an extra stage, because of the greater gas friction losses through
valves, piping, and coolers. There are often other practical advantages,
however.