Page 102 - Air and gas Drilling Field Guide 3rd Edition

CHAPTER

Compressors and Nitrogen

Generators 5

There are a variety of air and gas compressor designs in use throughout industry.
These designs vary greatly in the volume amounts of air or gas moved and the
pressures attained. The largest usage of compressors is in the oil and gas produc-
tion and transportation industries and in the chemical industry. Information
regarding this technology will be used to develop an understanding of how com-
pressors can be used in air and gas drilling operations.
Air or gas compressors are very similar in basic design and operation to liquid
pumps. The basic difference is that compressors are movers of compressible
fluids; pumps are movers of incompressible fluids (i.e., liquids).

5.1 COMPRESSOR CLASSIFICATION
Similar to the classification of pumps, compressors are grouped in one of two general
classes: continuous flow (i.e., dynamic) and intermittent flow (i.e., positive displace-
ment)(see Figure 5-1)[1, 2]. Intermittent flow or positive displacement compressors
move the compressible fluid through the compressor in separate volume packages of
compressed fluid (these volume packages are separated by moving internal struc-
tures in the machine). The most important subclass examples of positive displace-
ment compressors are reciprocating and rotary compressors. Continuous flow or
dynamic compressors utilize the kinetic energy of the continuously moving com-
pressible fluid in combination with the internal geometry of the compressor to com-
press the fluid as it moves through the device. The most important subclass examples
of dynamic compressors are centrifugal and axial-flow compressors.
Each of the two general classes of compressors and their subclasses have cer-
tain advantages and disadvantages regarding their respective volumetric flow rate
capabilities and overall compression pressure ratios. Figure 5-2 shows the typical
application range in volumetric flow rates (actual cfm) and compression pressure
ratios for most important compressor classes and subclasses [2].
In general, positive displacement compressors are best suited for handling high
pressure ratios (i.e., up to approximately 200), but this can be accomplished with
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