Why do two-stage compressed air compressors save energy?

Screw air compressors are the mainstream compressed air compressor products in the market, and there are single-stage air compressors and double-stage air compressors. So why are the two-stage air compressors in the market so energy-saving and power-saving? How much energy can a two-stage air compressor save compared to a single-stage air compressor? The editor of JOY Machinery will summarize for you:

We know that the criterion for judging whether a screw air compressor is energy-saving is "specific power", that is, the energy consumption required to produce one cubic meter of compressed air per unit time, and the commonly used unit is: kw/m3/min. Therefore, the main energy-saving principle of the two-stage compression screw air compressor is also to carry out technical innovation on how to reduce the specific power.

Then we focus on the principle of energy saving. Compared with the single-stage screw compressor, we will briefly explain how to reduce the specific power for your reference.

Take the 8bar single-stage compressed air compressor commonly used by users as an example:

Single-stage compressor pressure ratio analysis: The intake pressure at the intake end is about 1 bar at the normal atmospheric pressure (take 0 altitude as an example), and it is compressed by the rotor to the outlet pressure (the exhaust end of the rotor) 8 bar. The compression ratio of the compression process is: 8:1 = 8; that is, the compression ratio of the single-stage compressor (the outlet pressure is 8bar) is 8 for the machine.

Analysis of the pressure ratio of the two-stage compressor: the intake pressure at the intake end is the normal atmospheric pressure (take 0 altitude as an example) about 1bar, and is compressed by the first-stage rotor to the outlet pressure (the exhaust end of the first-stage rotor) 3.15bar (the pressure is inlet pressure of the secondary rotor). The compressed air compressed by the primary rotor then enters the secondary rotor to increase the pressure to the required outlet pressure of 8 bar (the exhaust pressure at the secondary rotor end). The compression ratio of the first-stage low-pressure rotor is: 3.15:1 = 3.15; the compression ratio of the second-stage high-pressure rotor end is: 8:3.15 ≌ 2.54, that is, the compression ratio of the second-stage end (the outlet pressure is 8bar) is about 2.54. The maximum compression ratio for a two-stage compression rotor system (for an 8bar machine as an example) is 3.15. 

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

Like other fluids, compressed air follows the natural return flow from the high pressure end to the low pressure end, which we call "return leakage". It is not difficult to understand that the higher the compression ratio, the greater the return leakage. Compared with the single-stage compression screw machine with the same power and the same exhaust pressure, the compression ratio of the double-stage compression screw machine is lower, which ensures that the amount of reflux leakage is greatly reduced, and the exhaust flow rate is greatly improved, which means that the efficiency is improved, that is, the ratio of power reduction. This is the core of the energy-saving principle of the two-stage compression screw machine.

In short, in the case of the same installed power and the same exhaust pressure, compared with the single-stage compression screw machine, the conservative energy-saving ratio of the double-stage compression screw machine is about 7%~13%, that is, the energy saving of the double-stage air compressor is generally above 7%. The two-stage compressor has been used and verified by many domestic users.

JOY Machinery (Shanghai) Co., Ltd. has a professional design team with rich experience and welcomes customization. Diversified products can meet most applications and meet your one-stop shopping needs. The air compressor series includes power frequency screw air compressors, variable frequency screw air compressors, permanent magnet variable frequency screw air compressors, two-stage compression screw air compressors, integrated screw air compressors, laser cutting air compressors, medium and high pressure air compressors Air compressors, oil-free water-lubricated screw air compressors (special oil-free screw air compressors for the medical industry), diesel-moving screw air compressors, electric-moving screw air compressors and other products.

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