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Frequency Conversion Constant Pressure Control of Air Compressor
Time:2019.01.03 15:14  View:  Anthor:admin

First, the air compressor system application industry

In industrial and agricultural production, compressed air of a certain pressure is often required. Such as electronics, plastics, hardware, chemicals, wood, textiles, pharmaceuticals, paper and a large number of systems that require pneumatics, so these industries have installed air compressors. Power ranges from 7.5 kW to 280 kW. This equipment consumes a large amount of electric energy during operation, which increases the production cost, and the noise is huge. Equipment maintenance is often required. Therefore, the power saving reform of the compressor is imperative.

Second, the working principle of the screw-type air compressor system

The screw type single-stage compression air compressor works by rotating a pair of mutually parallel male and female rotors (or screws) in the cylinder, so that the air between the rotor slots continuously generates periodic volume changes. Then it is transported from the suction side to the extrusion side along the rotor axis to realize the whole process of suction, compression and exhaust of the screw air compressor. The air inlet and the air outlet of the air compressor are respectively located at two ends of the casing, and the female rotor and the male rotor are driven to rotate by the main motor.

Generally, the starting mode of the air compressor adopts the full-pressure operation after the star-delta step-down start. After the step-down start, the air compressor starts to load and the system pressure rises from 0 kg. If the system pressure rises to the unloading pressure (typically 8 kg), the controller closes the intake valve, deflates the oil separator, and operates the compressor at no load; until the system pressure is lower than the loading pressure (typically 6 kg), the control The intake valve is opened, the oil and gas separator bleed valve is closed, and the compressor is loaded and circulated. As shown below:

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Third, Unreasonable analysis of the operation of traditional air compressors

1, serious waste of electricity

a. Power consumption during loading

After the pressure reaches the required working pressure, the traditional control method determines that the pressure will continue to rise by about 10% until the unloading pressure (usually 8 kg). During the pressurization process, more heat and noise are generated, resulting in loss of electrical energy. On the other hand, before the high-pressure gas enters the pneumatic component, its pressure needs to be depressurized by the pressure reducing valve, which is also energy-consuming.

b. Power consumption during unloading

When the unloading pressure is reached, the air compressor automatically opens the unloading valve, causing the motor to idle, causing serious energy waste. When the air compressor is unloaded, the power consumption is about 30% to 50% at full load. It can be seen that the traditional air compressor has obvious energy saving space.

2, power frequency start surge current is large

Although the main motor adopts the star-delta step-down starting, the starting current is still very large, which has a large impact on the power grid, which may cause instability of the power grid and threaten the operation safety of other electrical equipment. For self-generating plants, several times the rated current surge may cause other equipment to be abnormal.

3, the pressure is unstable, the degree of automation

The traditional air compressor has a low degree of automation, and the output pressure is adjusted by the control of the loading and unloading valve and the regulating valve. The adjustment speed is slow, the fluctuation is large, the precision is low, and the output pressure is unstable.

4, large equipment maintenance

The air compressor has a large starting current of up to 5-8 times of rated current. The working mode determines the repetitive action of the loading and unloading valve, the components are easy to aging, the power frequency is running at high speed, the bearing wear is large, and the equipment maintenance is large.

5, loud noise

Continuous power frequency high-speed operation, additional pressure exceeding the required working pressure, repeated loading and unloading, directly lead to high noise in the power frequency operation.

Fourth, air compressor power saving transformation plan

a. Special inverter for air compressor, built-in PID controller, integrated air compressor control logic, with LCD display, perfect inverter air compressor control, advanced functions such as multi-computer network monitoring, easy maintenance, It realizes automatic switching of frequency conversion and power frequency, and can provide users with uninterrupted air supply capability when the air compressor has a single failure.

b. Use a separate inverter control cabinet, built-in frequency conversion transformation of most components, including inverters, operating panels, AC contactors, control buttons and so on. When the air compressor is modified, it is only necessary to connect the main circuit and control circuit signal of the user's original air compressor system to the corresponding control terminal, and connect the 0-10V remote pressure gauge or 4-20 mA pressure sensor. Complete the frequency conversion transformation project of the air compressor. The process does not need to change too much or even change the internal structure of the original air compressor, and has the advantages of simple transformation, convenient implementation, no change of user habits, and preservation of the original interface, and also facilitates future maintenance and repair.

c. After the conversion of constant voltage and power saving, three aspects of power saving space can be obtained.

1. Since the pneumatic equipment can work at 5 Kw, we can set the pneumatic pressure of 6.5-7 kg on the gas storage tank to fully satisfy the use and avoid the high pressure gas supplied to the system by the main engine (7- 8 kg) large load loss was incurred.

2. After the constant pressure transformation, the pressure on the gas storage tank is stable. When the gas consumption is reduced, the gas supply is reduced by reducing the rotation speed of the variable frequency drive. The smaller the gas consumption is, the smaller the rotation speed of the variable frequency drive is. The greater the electrical effect.

3. When the air compressor system is not modified, the air supply pressure is within the range of 6-8 kg. It will be stabilized at a certain pressure value according to the amount of gas used. It will not be unloaded and will be operated under the condition of constant loading. Since the supply is usually larger than the required air volume during design, it is usually stabilized at a pressure of 7-7.9 kg, which is commonly referred to as full load operation. If the constant voltage and power saving transformation is carried out, a minimum pressure stability value can be set according to the pneumatic equipment, and in the case of ensuring the use of the pneumatic equipment, the loss of the high pressure gas generated by the main engine to the gas storage tank for a long time is avoided.

Fifth, the advantages of air compressors after switching to frequency conversion power saver

1. Reduced operating costs

The operating cost of a conventional compressor consists of three items: procurement cost, maintenance cost, and energy cost. Among them, the energy cost accounts for about 77% of the compressor operating cost, and the energy cost is reduced by 44.3%. In addition, the impact on the equipment after the frequency conversion starts is reduced, and the maintenance and repair volume is also reduced, so the comprehensive cost will be greatly reduced.

2, improve the accuracy of pressure control

The frequency control system has specific and precise pressure control capabilities. Match the air pressure output of the compressor to the amount of air required by the user's air system. The output air volume of the variable frequency control compressor changes with the change of the motor speed. Because the accuracy of the speed control motor speed is improved, it can keep the system pressure variation of the pipe network within 0.2 bar, which effectively improves the quality of the working condition.

3. Extend the service life of the compressor

The inverter starts the compressor from OHz, and its starting acceleration time can be adjusted, thereby reducing the impact on the electrical components and mechanical components of the compressor during starting, enhancing the reliability of the system and prolonging the service life of the compressor. In addition, the variable frequency control can reduce the current fluctuation when the unit starts. This fluctuation current will affect the power consumption of the power grid and other equipment. The frequency converter can effectively reduce the peak value of the starting current to a minimum.

4, reduce the noise of the air compressor

According to the working condition of the compressor, after the frequency conversion speed regulation is reformed, the motor rotation speed is obviously slowed down, so the noise during the operation of the air compressor is effectively reduced. The on-site measurement shows that the noise is reduced by about 3 to 7 decibels compared with the original system. .

Benefit Analysis of Energy Saving Device for 22KW Air Compressor

1. Determination of power saving

Power saving degree = power frequency state 24 hours power consumption - the difference between 24 hours of power consumption in the energy saving state.

Power saving rate = (24-hour power consumption in power frequency state, 24 hours power consumption in energy-saving state) 投资 Power frequency state 24-hour power consumption energy-saving equipment investment benefit analysis

2. The air compressor motor power is: A= 22KW

Daily power consumption (B) is calculated as 70% load ratio: B = A * 0.7 * 24 = 22 * 0.7 * 24 = 369.6 degrees

The electricity bill is 0.8 yuan / kWh, and the daily electricity bill (C) is C = B * 0.8 = 369 6 * 0.8 = 295.6 yuan

After the transformation, the minimum power saving rate is calculated at 20%.

Monthly electricity savings (D) is: D = C * 20% * 30 = 295.6 * 20% * 30 = 1774.2 yuan

Annual electricity saving (G) is: G=D*12=1774.2*12=21290.10

Seven, summary

Intuitive power saving effect

The main components of the system are all imported, the service life of the system is 8-l0 years (calculated according to the minimum service life of -8 years), and the annual system maintenance cost is 10%. This energy-saving technology transformation brings H=( GG*10%)*8=( 21290-21290*10%)*8=153288 yuan.



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