Refrigeration centrifugal compressors

Figure 11-21A. Typical centrifugal compressor with economizer packaged refrigeration system. Note that screw-type or even reciprocating compressors can be used in such a system. (Used by permission Cat. 521-727, 1995. Carrier Corporation, a United Technologies Company.)...

Centrifugal machines can be built for industrial use with ammonia and other refrigerants, and these mayhave up to seven compression stages. With the high tip speeds in use, it is not practical to build a small machine, and the smallest available centrifugal compressor for refrigeration dutyhas a capacityof some 260 kW. Semi-hermetic compressors are made up to 7000 kW and open drive machines up to 21 000 kW capacity. 

Large systems working at temperatures above freezing may be able to use centrifugal compressors, but the pressure ratio is not favourable. Most heat pumps will have reciprocating or screw compressors. Refrigerants are those in general use. 

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. 

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