Air compressors, fans and pumps belong to the same kind of fluid machinery with constant torque. According to industry experience data, a 75 kW asynchronous frequency converter can save 20% - 30% energy than a power frequency air compressor, and a permanent magnet synchronous frequency converter can save 30% - 40% energy. (except for full load).
A rough analysis is made of the power consumption cost of a 75 kW air compressor running continuously for one year: 75 kW/h *8760 hours/year *0.7 yuan/kW = 460,000 yuan.
If the pneumatic compressor applies the frequency conversion control technology of permanent magnet motor, the power cost can be saved by 460,000 yuan * 35% = 160,000 yuan. Of course, this is a common usage situation, specifically based on professional field analysis.
Why is there such a huge difference in the cost of electricity? As we all know, there is no breakthrough in the homogenization of compressor technology, asynchronous motor has a history of several hundred years, frequency converter is not a fresh product, the key is the following principle
According to the simplest formula of hydrodynamics, P power =Q (flow) * P (pressure).
The flow rate is proportional to the rotational speed in the first order, the pressure is proportional to the rotational speed in the second order, and the shaft power is proportional to the rotational speed in the third order.
Generally, compressors, fans and pumps are selected according to the requirement of full-load operation. In practice, they are not always in full-load state. So as long as the speed is slightly reduced, the load power will drop quickly, thus achieving energy-saving effect.
The axle power is 0.95 x 0.95 x 0.95 = 0.857 at 95% speed, and the axle power is 0.729 at 90% speed, 0.512 at 80% speed, 0.343 at 70% speed, 0.125 at 50% speed, 0.064 at 40% speed and 0.027 at 30% speed.
That is to say, when the gas consumption is 30%, the shaft power required by a low speed motor is only 2.7%.
In fact, it is affected by the comprehensive control of the main engine, motor and control.
The conventional motor control of air compressor consists of three kinds.
One is on/off, on the highest efficiency full load work, off zero power outage, which is the most ideal energy-saving control mode! According to the national standard 20 kilowatts above asynchronous motor start and stop for an hour can not exceed 6 times, can not frequent start and stop. But now a kind of ultra-efficient permanent magnet motor with ultra-low starting current suitable for any frequent start-up and shutdown has come out, and it is estimated that it will play an energy-saving role for the society in the near future.
The other is unloading idling, which is to realize light-load operation by closing the intake valve. Generally, it consumes about 60% of the shaft power at full load. This kind of control is not economical and suitable for the control of asynchronous motors above 20 kW which can not start and stop frequently.
So in general, the variable frequency driven air compressor is the choice to save energy and trade-off.
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