air compressor is a kind of equipment which uses motor to compress gas in compression chamber and make the compressed gas have a certain pressure. It mainly has four main processes: inhalation, compression, work transportation and exhaust. It has been used for hundreds of years, and the mechanical structure has developed for 100 years. The principle is mature, but the start-up and discharge of large-capacity air compressor with load in the working process has always been a difficult problem. There are piston, screw, centrifugal and scroll air compressors in structure. It can be widely used in metallurgy, machinery manufacturing, mining, electric power, textile, petrochemical and other industries, and is an essential equipment for various factories, road construction, mining and construction industries. Air compressors account for 15% of the power consumption of large industrial equipment (fans, pumps, boilers, air compressors, etc.).
After investigation, most air compressors have the following shortcomings:
1. When the output pressure is greater than a certain value, the unloading valve is automatically opened to make the asynchronous motor idle, which is uneconomical operation and causes serious energy waste. 2. The asynchronous motor is easy to start and stop frequently, which affects the service life of the motor. 3. The working conditions are harsh, and the noise is extremely high when it is automatically emptied and deflated, causing environmental pollution. 4. The degree of automation is low, and the adjustment of output pressure is realized by the opening of the artificial regulating valve, which is slow, unstable and low in accuracy. 5. The power frequency starting current of the air compressor is large, which has a great impact on the power grid, great wear of motor bearings and a large amount of equipment maintenance. 6. The upper and lower pressure is not easy to adjust. If the pressure is adjusted too small, it is easy to cause continuous start-stop and burn the motor and electromagnetic switch; Too large adjustment will easily lead to high pressure, high transmission loss, air leakage and pipeline rupture, and the pressure range is too large to meet the requirements of modern technology. To sum up, the current air compressor system can be reformed by frequency converter to establish a constant pressure air supply system, so as to save electricity, reduce noise, reduce equipment wear and tear, reduce power grid impact, improve power factor and stabilize product quality. In recent years, the speed of the motor of the air compressor is changed by frequency conversion speed regulation technology, and the air supply flow of the air compressor can be adjusted by itself with the change of the gas consumption flow, so as to achieve a real balance between supply and demand, and at the same time, the whole system can achieve the best working efficiency, and the frequency conversion air compressor has become the development trend of the air compressor market.
Introduction to the principle of frequency conversion transformation of air compressor (taking screw machine as an example)
Frequency conversion speed regulation technology has developed rapidly in recent years and played an important role in many fields. Because many screw air compressors operate in loading and unloading modes. When the load is reduced, the motor idles, so the energy is wasted, and the motor speed itself cannot be changed, so the speed can only be adjusted by changing the motor frequency. Frequency conversion control is to control the air output of air compressor per unit time by changing the speed of motor, so as to control the pressure of pipeline. The principle is as follows: the pressure value of pipe network measured by pressure transmitter is compared with the set value of pressure to get the deviation, and the frequency value of frequency converter acting on asynchronous motor is calculated by PID regulator. Alternating current with corresponding frequency and amplitude output by frequency converter makes the motor get corresponding speed. Then the air compressor outputs the corresponding compressed air to the air storage tank to make the pressure change until the pipe network pressure is the same as the given pressure value.
Benefit after frequency conversion transformation of air compressor
1.Save energy. Compared with the compressor controlled by frequency converter, the energy saving is the most practical significance, and the compressor working condition supplied according to the air demand is the economic operation condition. 2. The operating cost is reduced. The operation cost of traditional compressor consists of three items: initial purchase cost, maintenance cost and energy cost. Among them, the energy cost accounts for about 77% of the compressor operating cost. By reducing the energy cost by 44.3%, and the impact on the equipment is reduced after frequency conversion starting, the maintenance and repair amount are also reduced, so the operation cost will be greatly reduced. 3. Improve the accuracy of pressure control. Frequency conversion control system has accurate pressure control ability. Make the air pressure output of the compressor match the air volume required by the user's air system. The output gas volume of variable frequency control compressor changes with the change of motor speed. Because the accuracy of frequency conversion control motor speed is improved, it can keep the system pressure change of pipe network within the range of 3pisg, that is, within the range of 0.2bar, which effectively improves the quality of working conditions. 4. Extend the service life of the compressor. The inverter starts the compressor from 0HZ, and its starting acceleration time can be adjusted, thus reducing the impact on the electrical and mechanical parts of the compressor during starting, enhancing the reliability of the system and prolonging the service life of the compressor. In addition, frequency conversion control can reduce the current fluctuation when the unit starts, which will affect the power consumption of power grid and other equipment, and the frequency converter can effectively reduce the peak value of starting current to a minimum. 5. Reduce the noise of the air compressor. According to the working requirements of the compressor, after the transformation of frequency conversion speed regulation, the running speed of the motor is obviously slowed down, so the noise of the air compressor during operation is effectively reduced.
To sum up, because the air compressor can run at the lowest pressure required to ensure production, the input power of the motor is greatly reduced. With the help of closed-loop pressure control, the dynamic matching between the air supply pressure and the rotating speed of the air compressor is realized, the actual input power of the motor is reduced, and the purpose of energy saving is achieved. That is, the rotation speed of the motor is controlled by the air supply pressure, and the motor outputs as much power as the compressor needs, without doing useless work, thus achieving good energy-saving effect. The second aspect of energy-saving is that the air compressor stops idling and the motor does not run under light load, which is considerable. Other corresponding benefits are: the air supply pressure is stable, the air compressor can be kept working at the set pressure value through the pressure regulator, the pressure stability and reliability are high, and the pressure can be set steplessly and adjusted at any time. The service life and maintenance cycle of the compressor will be greatly prolonged if the motor realizes soft start. The air displacement of the air compressor is controlled by the rotating speed of the air compressor, the air valve plate in the cylinder is not opened and closed repeatedly, the working conditions such as valve seat and spring are greatly improved, the rapid flow and impact of high temperature and high pressure gas are avoided, and the maintenance workload is reduced.