Rotary Sliding Vane Compressor
Flooded Screw Compressor
Rotary Vane compressors manage ratios up to 7:1 in compression applications.
Ro-Flo’s have a MAWP of 200 psig (13.6 barg).
Flooded screws can manage pressure ratios up to 10:1 or greater.
Screws can achieve higher discharge pressures.
Rotary vanes require a small amount of oil which is continuously injected for lubrication purposes only.
Screws require a large amount of recirculating oil which removes the heat of compression. Contamination of recirculated oil can be a problem.
In some cases, a producer’s largest maintenance cost is for oil changes.
Ro-Flo’s can handle almost any gas imaginable, including acid, sour, hydrogen or heavy hydrocarbons.
In one case, a Ro-Flo was used to compress a 90% H2S gas stream.
Gas Composition Tolerance
Flooded screws are not tolerant to sour or heavy MW gases.
Rotary vanes have no minimum delta P.
Delta P Requirement
Screws typically require a minimum of 40 PSI delta P for adequate separation of oil and gas. Lower pressures promote oil dilution and loss of lubricity.
Vanes run from 100% RPM down to about 40% RPM either via VFD or by sheave changes on a lower cost belt drive.
Turn Down / Speed Variability
With screw compressors speed variation is limited. While the slide valve is sometimes used to control flow variations this is not very efficient.
Vanes are field repairable. Infrequent wear part replacement requires three hand tools and a few hours on site.
Maintenance / Ease of Repair
Screw compressors often require complete change out for maintenance or when problems occur.
Ro-Flo casings are ductile iron castings.
Screws come in cast and ductile iron with some availability of cast steel or stainless steel.
Vanes employ a water jacket with recirculation of coolant to maintain proper casing temperatures.
Screw compressors utilize a heat exchanger to cool the oil, which is typically the only cooling needed.
A rotary sliding vane compressor is the proper choice when compressing gas streams which are near their dew point (close to condensing to liquids) and/or gas streams containing corrosive or sour components.
Conclusion & Application
An oil flooded screw compressor is the proper selection for a high-pressure ratio application in a clean natural gas environment.