1. This paper introduces the application of frequency converter in vacuum pump, and briefly describes the principle of energy saving and the parameter setting of frequency converter.
In the production industry, the cost of electricity has become the third largest expenditure after the cost of raw materials and labor; in today’s power shortage, saving electricity has become a major consideration for business operators; and the liquid ring vacuum system is widely used in various industries of production, becoming one of the important equipment in production, as well as one of the main power consumption equipment. According to the requirements of the production process, our company has a vacuum system composed of three liquid ring vacuum pumps. In use, there are two vacuum pumps that are fixed at the maximum speed for a long time, and the other one is standby. In the actual production conditions, the actual mechanical effective pumping rate of the vacuum system is much higher than the effective pumping rate of the designed container in most of the time; in the case of fixed rotation speed, the actual vacuum degree is far greater than the vacuum degree required by the production, which results in a serious waste of power consumption of the vacuum pump motor, so it has a certain reality to carry out the automatic control transformation of frequency conversion and energy saving for the liquid ring vacuum pump Significance.
2. liquid ring vacuum pump analysis of operating conditions
2.1 liquid ring vacuum pump basic principle
When the working wheel of the liquid ring pump rotates in the vacuum pump body, a liquid ring and a working chamber are formed. The extracted gas enters the suction chamber through the air inlet pipe and the air inlet. The rotor rotates further so that the gas is compressed and discharged through the exhaust port and exhaust pipe. The discharged gas and water drop enter the water tank through the exhaust pipe. At this time, the gas is separated from the water. The gas is discharged into the atmosphere through the pipe, and the water enters the vacuum pump from the water tank or into the drainage equipment through the pipe.
Liquid ring pump is mainly used in the process of coarse vacuum and large air extraction.
2.2 liquid ring vacuum pump energy saving principle
It can be seen from the pumping rate formula (1) of the crude pumping pump that when Q1 of the vacuum system is constant, s and P1 are in inverse proportion. The smaller P1 is, the larger the effective pumping rate of the mechanical pump is needed; if P1 is greater than the actual value, there will be excess vacuum, resulting in the waste of the effective pumping rate of the mechanical pump. At the same time, the value of Q1 will also be a variable when the production industry changes. S is proportional to Q1, and the effective pumping rate of mechanical pump is proportional to the air leakage rate and the pre vacuum required to be achieved;
If the air leakage rate is too large and exceeds the effective pumping rate of the mechanical pump used in advance, a new mechanical pump must be put into use to meet the vacuum degree; air leakage is caused in the production and use process, which is controllable and small, so it causes more waste of excess vacuum.
According to formula (1), formula (2) can be obtained. From formula (2), we can see that the vacuum P1 needed for production can be used as the regulating quantity. As the regulating quantity, there is a SV value which is a constant value. The difference between the actual detected vacuum degree PV and SV, MV, is used as the regulating value of the effective pumping rate of the mechanical pump. Through the frequency converter, the effective pumping rate of the mechanical pump can be adjusted to save energy Reduce consumption.
P1 = Q1 / S (bracket)…… (2)
S – effective pumping speed of mechanical pump
Q1 – air leakage rate of vacuum system (Torr · L / s)
P1 – required pre vacuum (Torr)
3. Energy saving analysis of automatic control of vacuum system
3.1 operation status
The vacuum system used by our company is a vacuum system composed of three liquid ring vacuum pumps (rated power of 75kW), which is mainly used in the crimping process of spinning workshop. Each production line has 24 suction nozzles for suction tow. A vacuum pump can achieve the vacuum degree required by production without using suction nozzle or using less than 3 suction nozzles. When the number of suction nozzles is more than 3, two vacuum pumps must be started to maintain the required vacuum. However, in the long-term working condition, there are less than 3 suction nozzles (only one suction nozzle is used when repairing the plate), but in order to prevent the sudden stop accident of 24 spinning pumps, two vacuum pumps have been used all the time, and the other one is standby, which results in the energy waste of one vacuum pump.
3.2 feasibility analysis
According to the operation status, the energy consumption of vacuum system should be reduced under the condition of meeting the production emergency demand. The control system used by our company is Y – △ startup control mode, so we maintain the original y of a vacuum pump-
△ control system to meet the vacuum degree requirements of the vacuum system; another vacuum pump is transformed into a inverter controlled vacuum pump, and its mechanical effective pumping rate is controlled by the vacuum pressure degree signal.
The working condition of the vacuum pump system is analyzed, which shows that the maximum energy-saving effect can be achieved after the application of the frequency converter. After the system is put into operation, the operation is stable. The application of the analog quantity of the frequency converter to regulate the operation of the frequency converter not only saves a lot of energy, but also effectively meets the requirements of the vacuum degree at any time during the emergency production, reduces the impact of the start and stop process on the mechanical part of the vacuum pump, prolongs the service life, and improves the working efficiency of the system with perfect monitoring and reliability measures.