Centrifugal compressors selection

Several other types of compressors are used in the process industries for a wide variety of special applications that may not fit the larger reciprocating or centrifugal compressor selections. One of the smaller compressors is a diaphragm compressor. Figures 12-116 and 12-117 and Table 12-10. 

Gas turbine driven centrifugal compressors are very efficient under the right operating conditions but require careful selection and demand higher levels of maintenance than reciprocating compressors. Compression facilities are generally the most expensive item in an upstream gas process facility. 

Compressor Configuration To propeny design a centrifugal compressor, one must know the operating conditions—the type of gas, its pressure, temperature, and molecular weight. One must also know the corrosive properties of the gas so that proper metallurgical selection can be made. Gas fluctuations due to process instabilities must be pinpointed so that the compressor can operate without surging. 

Historically, the most popular driver for the centrifugal compressor has been the steam turbine. Steam turbines can readily be speed matched to the compressor. Prior to the upsurge in energy costs, reliability, simplicity, and operational convenience were the primary factors in driver selection. The steam turbine, with its ability to operate over a relatively wide speed range, was ideal for the centrifugal compressor, which could be matched to the process load by speed modulation. 

The proper compressor selection for the application is probably the most important single factor to achieving long-term reliable operation. For all the factors that make the centrifugal one of the most reliable compressors, a misapplication will negate these most dramatically. 

Th chapter presents an overview of the types of compresL . ,. eratic i for selecting a type of compressor, a procedure for estimating hors iwer and number of stages, and some process considerations for both ciprocating and centrifugal compressors. Chapter 11 discusses... 

Selection of construction materials for rotors and casings is more limited than for centrifugal compressors. 

Selection Guide for Multistage Centrifugal Compressors, Elliott Co., Bui. P-26 15-194-FL, pub. date not available. 

Figure 14-14. Selection chart for centrifugal compressor drive. (Used by permission E-M Synchronizer, 200-SYN-52, 1958. Dresser-Rand Company.)...

Polytropic efficiencies are obtained from measurements of power consumption of test equipment. They are essentially independent of the nature of the gas. As the data of Figure 7.27 indicate, however, they are somewhat dependent on the suction volumetric rate, particularly at low values, and on the compression ratio. Polytropic efficiencies of some large centrifugal compressors are listed in Table 7.6. These data are used in Example 7.9 in the selection of a machine for a specified duty. 

The refrigeration compressor is usually the most expensive equipment of small-scale liquefaction plants. Smaller units may employ screw or reciprocating compressors, whereas centrifugal compressors always are used in larger units. Driver selection is a key decision point in project development, and can be either turbine, gas engine or electric motor. 

Selection of a Centrifugal Compressor A hydrocarbon mixture with molecular weight 44.23 is raised from 41°F and 20.1 psia to lOO.Spsia at the rate of 2400lbmol/hr. Its specific heat ratio is k = 1.135 and its inlet and outlet compressibilities are estimated as zj = 0.97 and Zj = 0.93. A size of compressor will be selected from Table 7.6 and its expected performance will be calculated ... 

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