Frequency conversion speed regulation technology used in reciprocating scroll compressor
Frequency conversion speed regulation technology is a kind of motor drive speed regulation and energy saving and consumption reducing technology developed rapidly in the 1980s. It has been widely used in water pumps, fans, elevators, etc. It has the characteristics of improving control level and significant energy saving effect. Various gas compressors or blowers are widely used in the gas and heat industry.
Generally, the machine is always selected and configured according to the large demand of Z, while in actual operation, the user's requirements often change due to various reasons. How to make it not only meet the requirements of users, but also achieve economic and energy-saving, safe use and simple operation has always been the goal of people.
With the specification of production, it is required to increase the pressure, large flow and stable gas supply, and reciprocating gas compressor must be used. However, it is difficult to completely balance the gas supply and the compressor discharge, and it is difficult to manually adjust the return flow to ensure the stability of the demand pressure and flow, which makes the following disadvantages of the system obvious: the gas supply is not large, making the gas repeatedly compressed, low operating efficiency, consuming a large amount of electricity, increasing costs, manually adjusting the gas supply using bypass valves, large workload, difficult to control the gas supply pressure, poor gas supply quality, and poor system safety.
Therefore, frequency conversion speed regulation technology is adopted for the reciprocating compressor system. 2 Energy saving principle and technical scheme of frequency conversion speed regulation When the air supply needs to change within the rated air discharge of a single compressor, certain measures must be taken to adjust the air discharge of the compressor to balance the supply and demand of air and the balanced operation of the transmission and distribution system. For reciprocating compressor, there are many methods to adjust the discharge capacity, but the method to change the speed is economical and practical.
The suction capacity can not be changed by using reflux regulation, so the compressor will always operate at full load, which can not save energy. Changing the speed will change the suction capacity of the compressor, and its power consumption will also change.
Variable frequency speed regulation technology is adopted to make it possible for the compressor to realize variable speed regulation, and the compressor speed is changed by changing the compressor motor speed, so as to finally achieve the purpose of energy saving.
According to the production situation, during the transformation, two compressors will be changed into one power frequency and one frequency conversion, one for use and one for standby.
In terms of electrical control circuit design, considering the special requirements of reciprocating compressor for lubrication and cooling, all the control circuits of the original system for process interlocking and emergency shutdown are retained and added to the frequency conversion electrical system to ensure the safe and stable operation of the compressor. Since the compressor is equipped with a 10 pole 280 kW asynchronous motor, its supporting large frequency converter has no domestic capacity.
Thus, the outlet pressure can be adjusted to automatically track the set pressure, and the automatic constant pressure control can be realized to ensure the system stability and gas supply quality.
The frequency conversion speed regulation technology is adopted, so the machinery, pipelines and other parts in the original system do not need to be changed, only the step-down starting cabinet of one unit in the power supply circuit needs to be replaced with a frequency converter cabinet, and the interlocking of the frequency conversion power frequency of two units in the main circuit can be completed, so the workload of the transformation process is not large.
During the system commissioning, it is worth noting that the compressor load belongs to the category of constant torque load. When the motor speed is too low and the load is large (that is, the pipe network pressure is high), the motor output will be insufficient, the motor will lock up, and equipment accidents will easily occur. Therefore, through many tests, it is found that the lower limit frequency can be set to 15 Hz for stable operation.
In addition, in order to ensure the safety of the pipe network system, the pipe network return valve should be properly opened to ensure that the pipe network pressure will not become too high when the gas consumption suddenly decreases.
3 Economic Indicators of System Energy Saving Effect The system has been used for more than a year with a total investment of 350000 yuan. According to the user's needs, the company first tests the gas supply at 30 kPa, 70 kPa, 100 kPa and other different pressure conditions, and the work is very stable. Then the air supply pressure of 100 kPa has been working for one year, and the frequency can be guaranteed to be below 18 Hz, which not only meets the pressure and air supply requirements, but also fully reflects the energy-saving effect.
Practice has proved that the smaller the gas supply, the more obvious the power saving effect. According to the current working condition, the no-load current of the system under power frequency operation is about 400 A, which has obvious energy-saving effect.
(1) The variable frequency governor can realize the wide range stepless speed regulation of the motor by simply setting parameters, make it operate stably at 15~50 Hz, realize the soft start of the motor, and improve the power factor.
(2) The closed-loop control of frequency conversion speed regulation can make the output power of the compressor motor change according to the shaft power required by the compressor, with obvious energy-saving effect.
(3) After variable frequency speed regulation, the compressor usually runs at a speed lower than the rated speed (the current working speed is only 1/3 of the rated speed). Therefore, by reducing the compressor discharge, the pressure loss through the air valve and pipeline is reduced, and the cooling effect of the gas in the cylinder is strengthened, so that the power consumption is reduced.
(4) The reduction of rotating speed reduces the mechanical friction, reduces the friction power consumption, extends the service life of the equipment, reduces the noise, and improves the working environment.
(5) Fully automatic control of pressure and flow is realized, which makes the system control simple and reliable. It not only greatly improves the gas supply quality and the operation safety of the pipe network, but also makes the operation extremely simple, reducing the labor intensity of the operators. (6) Because the speed is controlled by the closed loop programmable controller, the control accuracy can reach ± 1, the reliability of safe and stable operation is greatly enhanced, and it is more convenient to settle the cost with users.