- Michael Xu
- Issue Time
How to choose a frequency conversion screw air compressor?
Appropriate selection is beneficial to both the user and the air compressor equipment. Excessive selection is wasteful, and too small selection may cause the air compressor to be in a fully loaded state for a long time or insufficient air or pressure can not reach the disadvantages. Therefore, the selection is extremely important. When the configuration capacity is larger than the actual air volume, the air consumption is unstable, and the air pressure is stable, the variable frequency screw compressor can be selected.
The steps of model selection: first determine the working pressure, then determine the corresponding exhaust volume, and finally the motor power:
1. Exhaust pressure:
The sum of the customer's operating pressure, pipeline resistance loss and the pressure drop of the supporting equipment is set as the lower limit Pmin of the rated discharge pressure of the selected compressor, and the selected working pressure is Pmin+0.5bar.
Assuming that the customer’s minimum gas pressure is Pmin=6bar, then the working pressure only needs to be 6.5bar instead of 8bar.
Because the air pressure of the frequency conversion screw machine is stable: because the frequency conversion screw machine uses the stepless speed regulation characteristics of the frequency converter, the pressure can be quickly adjusted and controlled through the controller or the internal PID regulator of the frequency converter, and the pressure can be kept at a constant State. There is no need to consider the upper and lower limit pressure difference as the power frequency screw machine.
Under normal circumstances, it is recommended that customers choose a larger diameter of the gas pipeline to reduce resistance loss and achieve the purpose of long-term operation and reduce energy consumption. The higher the discharge pressure of the compressor, the more energy it consumes, so do not choose a compressor with a too high discharge pressure; choose a compressor with a too high discharge pressure,
Then the pressure is reduced through the pressure regulating valve, which is absolutely wasteful.
2. Exhaust volume:
A, the choice of maximum displacement:
① First understand the volumetric flow rate of all gas-consuming equipment, and multiply the total flow rate by 1.2 (that is, enlarge the margin by 20%);
② The new project can be selected according to the flow value provided by the design institute;
③ Learn about the volumetric flow parameters of the gas-consuming equipment from the gas-consuming equipment supplier for selection;
④ The air compressor station can be selected with reference to the original parameter value and the actual air consumption situation for the renovation of the air compressor station;
B. Selection of long-term gas consumption
The air consumption on site should be 60%~~85% of the air compressor's exhaust volume, that is, the whole machine should be operated at 30HZ~45HZ most of the time.
C. When selecting the exhaust volume, pay attention not to be too large or too small
★ When the exhaust volume is too large (the customer's air volume has been lower than 30% of the rated exhaust volume for a long time)
⑴ The motor runs at a low frequency for a long time and is prone to high temperatures.
⑵ The purchase cost of a large displacement compressor is higher.
★ The selected exhaust volume is too small (the customer's gas consumption is longer than 90% of the rated exhaust volume for a long time)
⑴ Customers will respond that the exhaust volume is not enough
⑵ If the motor runs at full load for a long time, the inverter frequency conversion effect is not good, and the motor is prone to high temperature
In this case, power frequency screw compressor can be used
3, the choice of motor power
According to the selected working pressure and exhaust volume, select the matching motor power
4. Treatment plan under special circumstances:
★ When the customer’s air consumption during the day is close to the maximum displacement, and the air consumption is relatively stable, but the air consumption at night is relatively small, choose a variable frequency air compressor.
Suggestion: The frequency conversion screw compressors introduced by the company will all have dual industrial-variable systems. Customers can be advised to use power frequency during the day and frequency conversion at night. Reason: When running at 50HZ, the frequency conversion air compressor consumes more power than the industrial frequency air compressor, and the motor is prone to heat.
★ When the customer's gas consumption is very uneven, it will be very large at one time, and then very small at the other time.
Suggestions: a. Increase the acceleration time and decrease the ascent rate.
B, increase the gas tank
C, increase the upper limit pressure value
You should be considerate before purchasing, so as to avoid the troubles that are only discovered when you use it.