Are there other compressor principles besides the Oilfree-screw and the Centrifugal providing Oil-free Compressed air. The question often is raised, what about Scroll compressor, Water injected compressor, Oil-free industrial compressors and other innovations…?

 Oil-free Compressed Air can be obtained with other compressor principles but all of them have their application range.

The scroll compressor is mainly used at power levels of 2.2-5 kW. Some larger size are being developed to obtain 7,5 or even 15kW. However, the range for single units, will remain limited in capacity. The limit in pressure is to 10 bar single stage and 13 bar in two stage. For the piston compressor, a semi-industrial and the industrial piston compressor can be distinguished. The semi industrial compressors is without cross-head and is mainly in the capacity below 30kW. Reliable machines, efficient in energy consumption, exist. 

The industrial piston compressors, equipped with cross-head, have a large application range and used up to very high pressures and have very long lifetime. These industrial pistons compressors can be found in the oil and gas industry where the loads and conditions are extremely difficult. Derivatives from those applications exist for the Oil-free Air compression. Those machines have a very long lifetime, low maintenance and are very energy efficient. Disadvantage is the size of the machine which is somewhat bigger.

The Water injected screw compressor should look like the ideal solution for the air compression. The water lubricates and cools down the compressed air. One would expect an isothermal compression. The Water injected screw compressor is more energy efficient than the Oil-free screw compressor. However, the lifetime of the screw block is limited. Depending on the type of bearings and seals used, the corrosion or the water leakage can create increased maintenance needs. Due to the use of exotic materials like copper and ceramics, the competitiveness of its application range is below the 100kW-150HP.

The Tooth and Claw, is the type similar to the Oil-free screw. Below 75kW, the Oil-free screw efficiency becomes too low. The Tooth and Claw compressor has less compression chambers resulting in a better efficiency at those low flowrates .

 Also new innovative principles are being developed but in an early stage of development. One is the Carnot principle and another is the Blade compressor.

 In the range of Centrifugals, the High speed Turbo technology, based on High speed motor(s), are being released. The benefit of the High speed motors are the low mechanical losses and their ability to fast run down allowing to have a larger regulation capability beyong 25% without blowing off. The challenge of these designs is still the high cost and the bearing system. The two variants are the magnetic bearings and the air(foil)bearings. The magnetic bearing is a far more robust design, but introduces limitations on the rotor dynamics due to the longer shaft length.

 Is it difficult to choose ?