Scroll compressors
A scroll compressor typically contains one or more 2.5, 5 or 7.5 kW modules. The advantages of scroll compressors include low price, good reliability, low noise, and affordable maintenance.
Their drawbacks are poor efficiency and low module service life. In other words, scroll compressors are a clear winner for applications requiring less than 30 kW of compressor output.
If an application requires some 15 kW of output during normal use, a four-module 30 kW compressor can be used, meaning there are four compressors inside one housing. In normal operation, two generate compressed air while the other two stand by. If one module fails, two can still generate air while one remains on standby.
Scroll compressors require relatively little regular maintenance compared to other technologies. In general, scroll compressor modules are ran to failure and then replaced. The price of a scroll module is typically a fraction of the price of a new screw element.
Water-lubricated screw compressors
If more than 30 kW of output is needed, the price of electricity starts to play a larger role, and the lower consumption of screw compressors beats out the advantages of scroll compressors. Typically, the next step is a water-lubricated screw compressor.
While water- and oil-lubricated screw compressors share some similarities, the obvious difference is their lubricant. The advantages of water-lubricated screw compressors are a good range of adjustment, low noise, and good efficiency. Their service life is mediocre.
The prices of water-lubricated screw compressors land somewhere between scroll and two-stage screw compressors. As a rule, water-lubricated compressors are a good choice for applications between 30 and 75 kW.
Oil-free two-stage screw compressors
For larger applications (> 55 kW), oil-free two-stage screw compressors are the right choice. On one hand, they are often pricy, loud, and less adjustable, but on the other, they offer a long service life and reliable operation. Their efficiency may be very high, depending on the technology used, even higher than oil-lubricated screw compressors.
In recent years, twin-motor compressors with excellent adjustment ranges have entered the market. The maintenance costs of two-stage oil-free screw compressors are roughly on par with oil-lubricated screw compressors, but the initial investment and replacement elements are pricier, of course. However, you should always remember to weigh the risk of oil contaminating the network whenever you price your investments.
Turbocompressors
For very large (> 250 kW) applications, turbocompressors may be the right choice. The advantages of turbocompressors include the best efficiency on the market, extremely reliable technology, and a very long service life.
Typically, turbocompressors have an adjustment range between 30 and 40 per cent, so for a consumption of 50 m3/min, the turbocompressor can adjust by up to 20 m3/min. Turbocompressors are not base load machines, even though many treat them as such.
The initial investment is often expensive with turbocompressors, but increasing a turbocompressor’s capacity from 400 to 600 kW, for example, will not add much to the final price. For comparison, buying two 300 kW two-stage screw compressors is already a more expensive solution than just buying one 600 kW turbocompressor. Once we add the efficiency, lower maintenance costs, and longer service life, it is as clear as day that turbocompressors are the top choice for these capacities.
Turbocompressors must be dimensioned carefully, as there are multiple things to consider. For example, they include intake air temperature, pressure requirements, cooling water temperature, and the needed adjustment range. All of the above affect the compressor’s efficiency, maximum power, number of stages, etc.
