Application of Hekang Frequency Conversion in Energy Saving Reconstruction of Air Compressor
one. introduction
The screw air compressor is a device that provides compressed air. The motor has a large capacity and runs continuously for many years. Generally, the cost of electricity for the air compressor accounts for more than 70% of the cost of use. Because of changes in production conditions, the alternation of workers, the uncertainty of gas consumption, air compressors are prone to frequent loading and unloading, resulting in waste of energy. When the inverter and the air compressor are used together, the air supply pressure of the air compressor will be more stable, reducing the unloading time and saving production costs.
two. Operation before air compressor reform
At the invitation of the energy-saving renovation customer, Hekang Inverter will carry out energy-saving renovation of the air compressor pipe network composed of four air compressors of Henan Yanai Group Co., Ltd. The company is the largest supplier of refractory products in the steel industry in China. The air compressor station of this transformation consists of four air compressors, one 250kW Ingersoll Rand and three 110kW Sullage screw air. press.
Before the equipment was rebuilt, all four air compressors were working at the power frequency. The pressure adopts two-point control (upper and lower limit control), that is, when the pressure in the cylinder of the air compressor reaches the upper limit of the set value, the air compressor closes the intake valve by its own oil pressure, when the pressure drops to the lower limit of the set value. The air compressor opens the intake valve. This results in frequent unloading and loading of the air compressor, which is often used in night shifts, while the air compressor runs at full speed, at which point this portion of the electrical energy is wasted. Therefore, it is very necessary to modify the screw air compressor to save energy, improve equipment stability, reduce maintenance costs and reduce noise pollution.
three. Design requirements for frequency conversion energy-saving retrofit plan
According to the problems existing in the original working conditions and combined with the requirements of the production process, the system needs to meet the following requirements after the air compressor is modified:
1. It can adjust the gas production volume of the air compressor according to the actual gas consumption, which can meet the production requirements and reduce the energy consumption.
2. The system has two sets of control loops of frequency conversion and power frequency, and can effectively control the oil leakage problem of the air compressor when the air compressor fails.
3. After the original system adopts the frequency converter for speed regulation, the original main circuit of the air compressor and the control mode of the secondary circuit cannot be changed.
4. Reduce operating noise, especially at start-up and full load operation, the noise is significantly reduced.
four. Air compressor frequency conversion transformation implementation plan
The main motor of the air compressor is a 250kW motor with a rated current of 450A. According to the actual situation of the site, Hekang inverter technicians provide a HID600A series high-performance inverter to control the air compressor, and feedback the gas tank through the remote pressure gauge. When the feedback pressure is higher than the production demand pressure, the inverter runs down to the set lower limit frequency. When the lower limit frequency continues to run for 300S, the inverter sleeps; when the feedback pressure is lower than the demand pressure, the inverter frequency increases. The air compressor is loaded and running. The electrical system adopts the industrial frequency conversion bypass design. When the inverter is faulty, it can be switched to the original power frequency operation through the rotary power frequency conversion bypass switch to improve the stability of the system.
The main motor before the transformation has been running at full speed. During the operation, the air pressure has been rising all the time (even if the production process does not require such a large pressure), when the pressure of the gas tank has risen to the upper limit pressure, the air compressor will stop. load. Usually when setting the value of this parameter, generally consider the equipment usage rate and the needs of the production process. The upper limit value will generally set the pressure 2bar larger than the actual required value as the upper limit. The increase of the exhaust pressure will result in power consumption. Impact, the power consumption increases by about 6% for every 1 bar of pressure increase.
After adopting the inverter PID constant pressure control system, the variable frequency speed control system takes the pipe network pressure as the control object, and the pressure transmitter installed in the gas storage tank converts the pressure of the gas storage tank into an electrical signal and transmits it to the PID inside the controller. The regulator compares with the pressure set value, and performs operation according to the predetermined PID control mode according to the magnitude of the difference, generates a control signal to control the output voltage and the inverter frequency of the frequency converter, and adjusts the rotational speed of the motor, thereby making the actual pressure Always maintain the set pressure to achieve a constant air pressure.
For the impact of current and equipment on the start of the main motor, Hekang Inverter uses the optimized SPWM algorithm to make the motor start smoothly, increase the starting torque, and reduce the interference of the inrush current to other equipment. The advanced process is adopted in the acceleration process. The multi-point acceleration curve reduces the wear of the bearing and the main screw of the head due to the quick start, which can greatly increase the service life of the equipment and the maintenance period of the mechanical equipment. In addition, if the inverter fails, the production process does not allow the air compressor to stop. Therefore, the system sets the power frequency and frequency conversion function, so that when the inverter fails, the power supply directly supplies power through the power frequency contactor, so that the air pressure The function works as usual.
Fives. energy saving effect
The 250kW ordinary unit runs 8759 hours a year, with a loading time of 2442 hours, an unloading time of 6317 hours, and an electricity fee of 0.7 yuan/kWh.
1, no-load loss:
Unloading time × no-load current loss (1.732 × 0.38 × 175 × 0.85) × 6317 hours / year = 618442 kWh; but considering that the screw air compressor can ensure lubrication without leakage at low frequencies, it is generally required The frequency limit of the frequency conversion is set to 30 Hz, and the power consumption of the frequency conversion is 618442×40%=247377 degrees.
2, differential pressure loss:
Loading time × loss due to 1 bar pressure difference 0.6 × 7% × 250 kW × 2442 hours / year = 25641 degrees.
In summary, the frequency conversion unit is 247377+25641=273018 kWh than the ordinary unit.
The annual electricity saving fee is 273,018 × 0.7 yuan / kWh = 191,111 yuan.
six. Problems that should be paid attention to during system transformation
1. The screw unit can't run in reverse direction. When changing, you must pay attention to the running direction of the motor.
2. Adjust the loading pressure to be equal to the set pressure (because the inverter has a lower limit frequency), thus preventing the inverter from accelerating in the unloaded state.
3, need to pay attention to the heat dissipation problem of the motor, the motor uses frequency conversion to adjust the speed, the speed is reduced, and the heat dissipation effect of the motor fan is also reduced.
4. Pay attention to the lubrication problem of the air compressor. The lower the speed of the air compressor, the smaller the consumption of the lubricating oil, and the worse the lubrication effect.
5, system pressure setting problem Under the requirements of the production process, the lower the pressure setting, the better, because the higher the exhaust pressure of the air compressor, the greater the motor shaft power required, the more power the motor consumes. .
Seven. summary
Hekang HID600A series high-performance vector frequency converter works well in energy-saving retrofit of air compressors, effectively reducing the power consumption of air compressor operation, improving system stability and reducing maintenance costs. As a compression equipment that provides long-term production power source, screw air compressor has a promising market for frequency conversion energy-saving transformation. The energy-saving transformation of Hekang inverter on air compressor is worthy of widespread promotion and use.
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