Dry Screw Compressor Performance and Application Range

Screw compressors have the advantage of low mechanical vibration levels similar to those found in centrifugal compressors due their rotary motion. However, screw compressors are positive displacement machines with a working principle similar to reciprocating compressors, which gives screws some advantages compared to centrifugals, such as: • The suction volume flow and power consumption grow linearly with the compressor speed, at constant discharge pressure. • the suction volume flow is nearly constant for variation of pressure ratio or gas molecular weight with no surging limit. • The achievable pressure ratio per compressor stage does not depend on the gas molecular weight but is limited mostly by the allowable discharge temperature or by mechanical limits. • By using liquid injection for cooling, pressure ratios up to 10 and in some cases higher are possible in one compressor stage. The largest dry screw compressors built up to now have a suction volume flow of 45,300 acfm (77,000 m3/h). Driver power may reach 9 MW. Discharge pressures up to 747 psia (51.5 bar abs) have been realized.