An air compressor is a device that uses a motor to compress gas in a compression chamber and make the compressed gas have a certain pressure. There are four main processes: suction, compression, work delivery, and exhaust.
I. Overview
An air compressor is a device that uses a motor to compress gas in a compression chamber and make the compressed gas have a certain pressure. There are four main processes: suction, compression, work delivery, and exhaust. It has been applied for hundreds of years, and it has been developed for 100 years in terms of mechanical structure. The principle is mature, but the starting and discharging of large-capacity air compressors in the working process has always been a problem. There are piston type, screw type, and centrifugal type in structure. It has a wide range of uses and can be used in various industries such as metallurgy, machinery manufacturing, mining, power, textile, petrochemical, etc. Air compressors account for 15% of the power consumption of large industrial equipment (fans, pumps, boilers, air compressors, etc.).
2. Working principle
Common large and medium air compressors are screw or piston compressors. When working, a motor drives the screw or piston to inflate the gas tank. When the pressure of the gas tank rises to the set maximum pressure, the clutch plate acts, the motor is automatically unloaded, the motor is idling, and the screw or piston stops compressed air. This working method of the compressor brings the following problems:
1) Defects of the current air compressor control system
The operation mode of the main motor of the air compressor is star-shaped to triangular pressure reduction, and then it is operated at full pressure. The control mode of air supply for loading and unloading is the control mode of the intake valve switch, that is, the valve is closed when the pressure reaches the upper limit, and the compressor runs without load; The valve opens when the pressure reaches the lower limit, and the compressor is loaded and running. If the system pressure rises to the upper pressure limit, the controller closes the intake valve, and the compressor runs without load until the system pressure drops to the lower pressure limit, the controller reopens the intake valve, the exhaust valve closes, and compresses The machine is turned on, the compressor is running at full load, and the above process is repeated continuously. The displacement and pressure of the air compressor are not constant during operation, and the air consumption is often changed due to the change of working conditions. Therefore, the air compressor always repeats the full-load-unload work mode when working. The operating current at full load is close to the rated current of the motor. The idle current at unloading is about 30-50% of the rated current of the motor. This part of the current is not doing useful work, but the idle loss of the machine at the rated speed.
a waste of a lot of energy, resulting in increased production costs.
b The current at the moment of starting is very large, which has a huge impact on the stability of the power grid and other electrical equipment. In severe cases, it may even cause the same power grid equipment to fail to operate normally.
c There is also a huge impact on the equipment machinery when starting, the subsequent maintenance workload is large, and the maintenance cost is high. Restricting the production efficiency.
d. The method of frequent unloading and loading to adjust. This makes the pressure of the entire air network change frequently, can not maintain a constant supply pressure, and also affects the service life of the compressor.
f Because the air pressure cannot be constant and the fluctuation range is large, it indirectly affects the production quality of the product to a certain extent. It is particularly obvious in some occasions that have strict requirements on the air pressure of the gas source.
g Low degree of automation, poor system stability, not conducive to maintenance, requiring special personnel to stop or start the unit to adjust the demanded gas volume, but it still cannot be effectively adjusted to a reasonable range. Since there is no fault alarm system, the source of the fault cannot be quickly and effectively found and eliminated malfunction
3. System configuration
This system can choose 6100-3037G inverter, which has excellent performance, high reliability, built-in PID regulator, various parameters can be flexibly set, and can well meet the control requirements. (The pressure sensor can use the MSP-300-016-B-S-W type made in the United States. This type of sensor is easy to install, has good linearity and high signal transmission accuracy.) The control principle diagram is as follows:
1. System function description
The system takes pressure as the control object, and the pressure value is set by the inverter keyboard potentiometer. It can be set freely within the maximum allowable working pressure of the air compressor according to the actual needs of the gas-consuming equipment, and the adjustment is convenient. The pressure sensor detects the pressure of the gas supply network in real time, and converts it through the transmitter, outputs a standard 4-20mA signal, sends it to the inverter for feedback, PID closed-loop control in the inverter, and real-time adjustment according to the system air consumption requirements The output of the inverter can adjust the speed of the compressor motor in real time to ensure the constant pressure of the pipe network.
4. Revenue from transformation
After the system is modified, the air supply of the compressor unit is dynamically matched with the required amount of the system. The compressor motor speed will be adjusted according to the different air consumption of the system, avoiding the energy caused by the motor idling and frequent loading and unloading Loss, the input power of the motor is greatly reduced, and the power saving effect is significant. For the air machine, the air supply quantity Q is proportional to the speed N, the air pressure F is proportional to the square power of the speed N, and the shaft power is proportional to the cube of the speed N, see the table below:
Generally speaking, for the air compressor system with continuous gas consumption, the operating frequency of the motor is dynamically adjusted between 25-50HZ with the change of gas consumption, and the power saving rate of the system can reach about 20%.
In addition, the indirect benefits brought by the system transformation should not be underestimated. First, the compressor motor achieves soft start and stop, soft acceleration and deceleration, and the impact on the power grid is greatly reduced; secondly, the air valve in the compressor cylinder no longer repeatedly opens and closes, increasing the life of the equipment and reducing the system maintenance time; Again, the air pressure of the system pipe network is stable, which improves the efficiency of pneumatic equipment.
After transformation of the air compressor unit, the following results have been achieved through actual measurement
1: Save electricity:
After the constant pressure gas supply system is put into operation, the air pressure of the gas storage tank can be kept within the range of 2.5% of the set value, and the energy lost by automatic emptying can be saved. After actual measurement, the power saving rate reaches about 40%. The power factor is increased to COSф>0.95, reducing the reactive power loss.
2: Reduce noise and environmental pollution:
Since the constant pressure gas supply system realizes frequency conversion control, it basically eliminates the situation of evacuation and deflation, thereby improving the pollution of noise to the environment.
3: Extend the service life of mechanical parts:
After using the JBJ air compressor power saving system, most of the time the air compressor runs below the power frequency, it can be clear
Significantly reduce the wear of mechanical parts, extend machine life, reduce maintenance costs and shorten maintenance time.
4: A soft start is achieved:
Reduce the impact of the unit's starting current on the power grid, while flexibly repeating multiple starts, avoiding the shortcomings of self-coupling buck starting in this regard.
5: Realize constant pressure gas supply:
After the system is put into operation, it improves the reliability of gas supply and the ability to adjust load changes, ensuring a constant gas supply pressure and further ensuring the stability of product quality.
6: Reliable operation, the failure rate is almost zero:
The system is equipped with overload, loss of pressure, undervoltage, overcurrent, lack of equal protection function, reliable operation.
7: Simple operation, failure does not affect production:
After the economizer fails, it can automatically shut down and send out a fault signal. At the same time, it can be switched to the commercial power to make the air compressor run normally without affecting production.