Why does two-stage compression screw air compressors save energy?

We know that the **standard** for judging whether a screw air compressor is energy-efficient is "specific power", which refers to the energy consumption required to produce one cubic meter of compressed air per unit time, commonly expressed in units of kw/m3/min. Therefore, the energy-saving of a two-stage compression screw air compressor is mainly reflected in technological innovations aimed at reducing specific power.

Let's focus on understanding its energy-saving principle and briefly explain how to reduce specific power compared to a single-stage screw compressor for your reference.

Taking the commonly used 8bar machine as an example:

Analysis of the pressure ratio of a single-stage compressor: The inlet pressure at the inlet end is approximately 1 bar, which is the conventional atmospheric pressure (taking 0 altitude as an example). After being compressed by the rotor, the pressure reaches 8 bar at the outlet (the rotor's exhaust end). The compression ratio of this compression process is 8:1 = 8, indicating that the compression ratio of the single-stage compressor (with an outlet pressure of 8 bar) is 8.

Analysis of the pressure ratio of a two-stage compressor: The inlet pressure at the inlet end is approximately 1 bar, which is conventional atmospheric pressure (taking 0 altitude as an example). It is compressed by the first-stage rotor to an outlet pressure (at the exhaust end of the first-stage rotor) of 3.15 bar (this pressure is the inlet pressure of the second-stage rotor). The compressed air compressed by the first-stage rotor then enters the second-stage rotor to increase the pressure to the required outlet pressure of 8 bar (the exhaust pressure at the end of the second-stage rotor). The compression ratio of the first-stage low-pressure rotor is: 3.15:1 = 3.15; the compression ratio at the end of the second-stage high-pressure rotor is: 8:3.15 ≌ 2.54, which means the compression ratio at the second-stage end (with an outlet pressure of 8 bar) is approximately 2.54. The **compression ratio of the two-stage compression rotor system (taking an 8 bar machine as an example) is 3.15

It is not difficult to see that, compared to a single-stage compression screw machine, a two-stage compression screw machine with the same outlet pressure of 8 bar has a compression ratio less than 50% of that of the single-stage compression screw machine.

Like other fluids, compressed air naturally flows back from the high-pressure end to the low-pressure end, a phenomenon we refer to as "backflow leakage". It is not difficult to understand that the higher the compression ratio, the greater the backflow leakage. Compared to single-stage compression screw machines with the same power and exhaust pressure, two-stage compression screw machines have a lower compression ratio, which ensures a significant reduction in backflow leakage and greatly increases exhaust flow, meaning an improvement in efficiency, that is, a decrease in specific power. This is the core of the energy-saving principle of two-stage compression screw machines.

In summary, under the same installed power and exhaust pressure conditions, compared to single-stage compression screw compressors, the conservative energy-saving ratio of two-stage compression screw compressors is around 7% to 13%, indicating an energy saving of over 7%. When customers choose energy-saving air compressors, two-stage compression screw air compressors have become a key focus, and their energy-saving effect has been verified by users both domestically and internationally.

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