OVERVIEW

Centrifugal compressors are mainly used as process compressors in petrochemical industries. Centrifugal compressors are used in other applications, such as the compressors in a gas turbine. In this chapter, we deal with the centrifugal compressors used in the process industry both onshore and offshore.

The centrifugal compressors used in the process industry can be divided into two major regions:

• Process compressors for compressed air in large plants

• Process compressors for compressing gasses to high pressures in a petrochemical facility, either onshore or offshore applications

AIR COMPRESSORS

Two of the fundamental factors in selecting the desired compressor are its capacity and its horsepower ranges. One has to select the compressor with the aid of its performance characteristics. For example, a reciprocating compressor can only handle an 18,000-psig requirement. On the other hand, a single 200,000 cfm, 35-psig compressor must be either centrifugal or axial type.

The majority of air compressors range around 125 psig or less, some even go as high as 500 psig. Various types such as reciprocating, vane, helical-lobe rotary, and dynamic types are used for this range. The choice is further limited by cfm. For example, normal capacity of a reciprocating unit is 10,500 cfm at 100 psig. The vane-type rotary compressor has a maximum cfm around 3600, and the helical rotary type can be used up to 20,000 cfm. The centrifugal type is used for a minimum of 5000 cfm, but larger size and high-speed designs are available even for tower capacities. Figure 1-2 serves...