Page 227 - Reciprocating Compressors Operation Maintenance

212 Reciprocating Compressors: Operation and Maintenance

or stream is used and it is normally quite cold. Although this cold water
provides the greatest possible amount of cooling, it is often necessary to
restrict the water flow so as not to drop the cylinder operating tempera-
ture too much. Excessively low water temperatures can prove bother-
some when handling partially or completely saturated gases.
As discussed earlier, inlet passages colder than the incoming gas can
cause condensation and liquid knockout, which may result in serious dam-
age. Occasionally, attempts to prevent condensation by restricting water
flow may cause an appreciable water temperature rise across the cylinder
and, if the water is hard, scale deposits begin to form. These deposits
always build up most at the hot spots in the cylinder where the greatest
heat transfer is usually desired. Thus, frequent descaling operations are
required in an effort to curtail performance and maintenance drawbacks,

Thermostatic and Thermosyphon Systems

These systems may be used where a small amount of cooling is advis-
able but the expense of a system involving a pump does not seem justi-
fied. They make use of the natural thermal circulation that results when
the cooling water is heated in the cylinder. In these systems, the jackets
are filled with water, oil, or ethylene glycol, and the heat of the cylinder
is distributed by convection currents. The thermosyphon system is used
with gases having a "k" value of 1.26 and below and with cylinder dis-
charge temperatures over 210°F and up to 250°K

Closed Water System

The most common form of compressor cooling water system involves
a closed, soft or treated water arrangement. The water coming from the
compressor cylinder or cylinders is cooled by either an air radiator sys-
tem, a cooling tower, or by a water-to-water heat exchanger. Figure 3-63
shows a schematic arrangement of a closed cooling system using a water-
to-water heat exchanger.
Figure 3-64 shows piping schematics for thermostatic, thermosyphon
and forced cooling systems.

COOLING WATER RECOMMENDATIONS

Cooling water recommendations have been developed for intercoolers,
cylinder jackets, and aftercoolers of typical air compressors:
In general, the following guidelines should be considered: