Many users of compressed air in segments which needs ISO 8753 class 1 air quality, are still considering Oil-flooded compressors instead of Oil-free compressors.
Injecting oil to compress air to seperate it again from the air, is an absurd idea. However, it is still a very common practice. The only reason is because the Oil-free compressed air is more EXPENSIVE.
Which are the drivers for the cost of Oil-free compressed air.
The first driver is the capital cost. The initial investment of an Oil-free compressor is higher than for an Oil-flooded compressor. Below 100kW, the price ratio can be 1:3.
As the size of the compressor increases, the ratio declines and equalize around 250kW.
As the number of provider of Oil-free compressors is substantially smaller than for Oil-flooded, the price increases much faster than for the Oil-flooded equivalent.
The second driver is the energy cost, representing 80% of the total cost. Below 250kW, the Oil-flooded screw compressor has a better energy efficiency than the Oil-free screw compressor. This will be off-set by the pressure drop over the filters. Centrifugals and Industrial Reciporcating compressors have a superior energy efficiency. The efficiency of the centrifugal drops fast as the flow reduces and becomes very inefficient when blowing off below 30% turndown.
Third driver is the cost of the aftermarket. The cost of the aftermarket should not be that high for both. Here the accesibiliy of genuine parts is making the difference. For the Oil-flooded screw compressor market, the availability of quality spare parts is much higher than for the Oil-free screw parts.
Above 350kW, the picture for the investment, energy and aftermarket changes in favor to the Centrifugals. The energy efficiency of the centrifugal becomes superior and the aftermarket is quite low. On top, the lifetime of the centrifugal is longer. For partial load, a good selection of a volumetric efficient Oil-free compressor is the better solution.
What would be the best volumetric Oil-free compressor for partial load to be combined with an efficient centrifugal as base load ?