Compressed air at gage pressures of 550 to 1000 kPa (80 to 150 psig) is
commonly used in industrial facilities to perform a wide variety of tasks
such as cleaning, operating pneumatic equipment, and even refrigeration. It
is often referred to as the fourth utilityafter electricity, water, and natural gas
or oil. In production facilities, there is a widespread waste of energy associ-
ated with compressed-air systems and a general lack of awareness about the
opportunities to conserve energy. A considerable portion of the energy waste
associated with compressed-air systems can be avoided by following some
commonsense measures. In this section we discuss the energy losses associ-
ated with compressed-air systems and their costs to manufacturers. We also
show how to reduce the cost of compressed air in existing facilities by mak-
ing some modifications with attractive payback periods. With the exception
of a few compressors that are driven by natural gas engines, all compressors
are driven by electric motors (Fig. 7–71).
Some primitive methods of producing an air blastto keep the fire in fur-
naces alive, such as air-threading bags and the Chinese wind box, date back
at least to 2000 BC. The water trompethat compresses air by the fall of water
in a tube to blow forges (metal heat shops) is believed to have been in use by
150 BC. In 1650, Otto van Guericke made great improvements in both the
compressor and vacuum pump. In 1683, Papin proposed using compressed air
to transmit powerover long distances. In 1829, William Mann received a
patent for multistage compression of air. In 1830, Thilorier was recognized
for compressing gases to high pressures in stages. In 1890, Edward Rix trans-
mitted power with air several miles to operate lifting machines in the North
Star mine near Grass Valley, California, by using a compressor driven by Pel-
ton wheels. In 1872,coolingwas adapted to increase efficiency by spraying
water directly into the cylinder through the air inlet valves. This “wet com-
pression” was abandoned later because of the problems it caused. The cooling
then was accomplished externally by water jacketingthe cylinders. The first
large-scale compressor used in the United States was a four-cylinder unit built
in 1866 for use in the Hoosac tunnel. The cooling was first accomplished by
water injection into the cylinder, and later by running a stream of water over
the cylinder. Major advances in recent compressor technology are due to
Burleigh, Ingersoll, Sergeant, Rand, and Clayton, among others.
The compressors used range from a few horsepower to more than 10,000
hp in size, and they are among the major energy-consuming equipment in
most manufacturing facilities. Manufacturers are quick to identify energy
(and thus money) losses from hot surfacesand to insulate those surfaces.
However, somehow they are not so sensitive when it comes to saving com-
pressed airsince they view air as being free, and the only time the air leaks
and dirty air filters get some attention is when the air and pressure losses
interfere with the normal operation of the plant. However, paying attention
to the compressed-air system and practicing some simple conservation mea-
sures can result in considerable energy and cost savings for the plants.Chapter 7 | 391TOPIC OF SPECIAL INTEREST* Reducing the Cost of Compressed Air
*This section can be skipped without a loss in continuity.
FIGURE 7–71
A 1250-hp compressor assembly.
Courtesy of Dresser Rand Company, Painted
Post, NY.