Centrifugal compressors may not be efficient for most plant installations but they are the only choice for 1,000+hp applications.
Unlike rotary screw compressors, piston compressors, and vane compressors, centrifugal compressors are not considered to be positive-displacement compressors. Centrifugal compressors are considered to be mass-flow compressors because they use the velocity of the incoming air to create pressure.
Centrifugal compressors consist of a spinning impeller and a stationary diffuser. The high-speed impeller (which sometimes spins at speeds as high as 50,000 rpm) increases the velocity of the air and sends it to the diffuser. The diffuser is a specially shaped chamber that increases the pressure of the fast-flowing air as it slows it down.
The capabilities of a single-stage centrifugal compressor are quite limited so they often come with 2-4 stages with a water-cooled intercooler between each stage. As the temperature of air increases, it becomes increasingly difficult to compress. By using intercoolers between stages, the overall efficiency of the compressor is increased.
The operating life of a centrifugal compressor is basically determined by the cleanliness of the air entering the compressor. The high-speed of the impeller makes it very sensitive to contaminants and liquid within the inlet air.
For high-volume (2,000 – 25,000 cfm), continuous-duty applications, centrifugal compressors are a good choice. In fact in the 1,000+ hp range, centrifugal compressors are the only choice.
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