Is it necessary to use frequency conversion motors for screw air compressors?
Analysis on the necessity of application of variable frequency motor in screw air compressor
1. Technical principles and core advantages of inverter motor
Inverter motors achieve speed adjustment by changing the power supply frequency. Their application in screw air compressors can bring the following improvements:
- dynamic response capability: The frequency conversion system can adjust the motor speed in real time according to gas demand, and control the pressure fluctuation range within ±0.02MPa, which is significantly better than ±0.1MPa for fixed-frequency units.
- Energy efficiency optimization mechanism: Under part-load conditions, the inverter unit reduces energy consumption by reducing the speed. Experimental data shows that when the air consumption is reduced to 60% of the rated flow, the energy consumption of the frequency conversion unit is 28%-35% lower than that of the fixed frequency unit.
- Device protection functions: The soft starting feature reduces the peak starting current of the motor from 6 times the rated current of the fixed-frequency unit to less than 2 times, effectively extending the service life of the motor, bearings and transmission components.
2. Economic assessment of applicable scenarios
- Scenarios where inverter motors must be used
- Gas consumption fluctuates greatly: For example, in an automobile welding workshop, the gas consumption frequently fluctuates between 20% and 100% of the rated flow, and the annual electricity saving of the inverter unit can reach 80,000 – 120,000 kW·h (taking the 110kW unit as an example).
- Multiple units parallel system: In the central gas supply system, the frequency conversion unit can be used as the main unit to automatically adjust the output according to the main pipe pressure, so that the fixed-frequency standby unit always operates in an efficient area.
- special technological requirements: For example, for air splices in the textile industry, the pressure needs to be stabilized at 0.65±0.01MPa. The frequency conversion unit can avoid the decline in splicing quality caused by pressure fluctuations in the fixed frequency unit.
- Scenes with selectable frequency motors
- constant load condition: For continuous gas supply in chemical processes, the gas consumption is maintained at 80%-100% of the rated flow for a long time, and the energy-saving advantages of the inverter unit are not obvious.
- Short-term investment sensitive projects: The initial investment cost of fixed-frequency units is 15%-20% lower, which can be used as a transition plan when the budget is strictly limited.
3. Comparison of full life cycle costs
Taking the 110kW screw air compressor as an example, compare the full life cycle costs (10-year cycle) of frequency conversion and fixed frequency units:
| cost category | Inverter unit (ten thousand yuan) | Fixed frequency unit (10,000 yuan) | variance rate |
|---|---|---|---|
| initial investment | 28 | 24 | +16.7% |
| energy costs | 320 | 410 | -22.0% |
| maintenance costs | 45 | 60 | -25.0% |
| total cost | 393 | 494 | -20.4% |
Note: The energy consumption cost is calculated based on 0.8 yuan/kW·h and 6000 hours of annual operation; the difference in maintenance costs is due to the extended bearing life of the inverter unit and the reduced frequency of spare parts replacement.
4. Selection decision model
Enterprises can evaluate the economics of frequency conversion transformation through the following formula:
Payback period (years)=(premium of inverter unit)/(annual electricity saving × electricity price + annual maintenance saving)
When the calculation result is less than 3 years, it is recommended to use a frequency converter unit. For example, if a 110kW unit has a premium of 40,000 yuan, an annual electricity saving of 90,000 kW·h, an electricity price of 0.8 yuan/kW·h, and an annual maintenance saving of 15,000 yuan, then the payback period =4/(9×0.8+1.5)=0.4 years (about 5 months).
V. Technological development trends
- Permanent magnet synchronous frequency conversion technology: Motor efficiency can reach 96%(3%-5% higher than asynchronous variable frequency motors) and has been widely used in high-end models.
- intelligent IoT control: Through the linkage of pressure sensors, temperature sensors and frequency converters, predictive maintenance and energy efficiency optimization are achieved.
- system integration scheme: The frequency conversion unit, gas storage tank, dryer, and filter form a smart gas supply unit, improving the overall energy efficiency by 15%-20%.
conclusion
For scenarios with large fluctuations in gas consumption, high energy efficiency requirements or process sensitivity, the use of variable frequency motors for screw air compressors has significant economic and technical advantages. Enterprises should combine load characteristics, electricity price policies and equipment utilization rates to make decisions through full life cycle cost analysis. In the context of the “double carbon” goal, frequency conversion technology has become the mainstream direction of energy-saving renovation of air compressors. It is recommended to give priority to frequency conversion units for new projects. Existing equipment renovations need to evaluate the payback period, and transformation projects that can usually recover costs within 3 years are feasible.