1 Introduction
Frequency conversion speed control technology has been widely used due to its remarkable power saving effect, convenient speed control mode, wide speed range, reliable operation, and perfect protection functions. A chemical factory is a large-scale enterprise that produces sulfuric acid, and its annual electricity consumption is huge. How to save energy has become an important measure for the plant to reduce costs.
2 Blower Frequency Conversion Modification
2.1 Before the transformation
The air supply system uses a 350kW 380V fan and adjusts the amount of air supply by adjusting the air baffle to adapt to changes in production load. Due to the large selection of wind turbines at the time of construction, a “big horse-drawn vehicle†situation occurs, and most of the electric energy is consumed on the air damper, which results in a drop in the efficiency of the wind turbine.
There are still other problems with this system during its operation:
(1) The air damper moves slowly. When the manual operation is performed, the operation of the personnel is inflexible, which easily causes vibration of the fan and it is difficult to satisfy the best adjustment quality.
(2) The fan damper actuator has more malfunctions.
(3) At the start of the blower, although an auto-buck start method is used, the starting current is still large, and the mechanical and electrical impact on the motor is large, and the rotor cage breaks often occur.
In order to solve the above problems, it is decided to reform the air blower control system, use the motor frequency conversion speed control method to achieve the air flow control, motor soft start, to achieve energy conservation and achieve stable control.
2.2 Introduction to Transformation Project
A frequency conversion device is added between the original motor and the switch, and the original power frequency loop is left as a bypass.
The frequency converter uses Alpha frequency converter, which is the core of the system. The output voltage of the inverter is 0-380V, and the output frequency is 0-400Hz. In actual use, the frequency converter upper limit frequency is set to 50Hz. It is controlled by a high-performance digital processor DSP. The power components use IGBT modules, which have the advantages of good input and output waveforms and small harmonics. Inverter has complete protection functions, including overvoltage, overcurrent, undervoltage, phase loss, short circuit, overheating, instantaneous power failure protection, etc. It can effectively protect the motor and its own device, and can query the records of changes of various parameters during faults. Simplified maintenance workload.
The frequency changer adopts the high-accuracy regulating potentiometer to give the output frequency, and adjusts the speed according to the required air volume in the field. The potentiometer is connected to the inverter controller through a shielded wire and a low-pass filter is set to improve the control accuracy. The output frequency signal of the Y1 port is used as on-site monitoring. Due to the use of electrical interlocking devices, the system will not cause accidents such as misoperation.
Due to the large capacity of the inverter, in order to reduce the dv/dt and di/dt interference to the system, a DC reactor was added on the DC side of the inverter. And in the cabinet ventilation and heat dissipation also took a lot of measures, by increasing the inlet and outlet outlet area and other methods, so that the temperature of the inverter reduced to a small extent, thus ensuring the reliable operation of the variable frequency speed control system.
3 blower frequency conversion efficiency analysis
The power consumed by the motor is proportional to the cube of the motor speed, and the air volume of the fan is proportional to the speed. When the rotation speed decreases, the power consumed by the fan decreases in the third power ratio. In the case of adopting a damper to adjust the air volume, the power consumed by the motor is about 90% of the rated power, and the actual utilization is small. A considerable part of the energy is consumed on the air damper and the energy loss is serious.
4 The effect of inverter transformation
The system fan motor 350kW, rated current 629A, 2 pole. In the original power frequency operation, the average operating current is 530 to 590A. Take 550A to calculate, and the power consumption is about 317kWh per hour (active). After the inverter system is put into operation, the average power consumption is 207kWh per hour (active) at the input side of the inverter ( Power end) test, the voltage is still 380V, the operating current is 280-320A, take 300A calculation; the power factor of the frequency conversion system takes 0.93; the electricity price is 0.5 yuan / kWh.
(1) Saving electricity per hour
According to the active calculation, the result of the above equation is multiplied by the above power factor 0.93
40%×0.93≈37%
Saving electricity per hour: 317-207=110 (kWh)
(2) Annual benefits
The fan runs for 365 days without stopping operation, so the annual electricity saving benefit is:
365×24×0.9×110×0.5≈43.4 (ten thousand yuan)
(3) Years of investment recovery
The system has a total investment of more than 200,000 yuan and annual revenue of 434,000 yuan. Therefore, the investment recovery period of the project is only six months; at the same time, the production efficiency is improved, the production cost is reduced, and the benefits are significant. The system has been stable to use so far and has never had any problems.
5 Concluding remarks
The greatest significance of this project is energy conservation. Compared with the original power frequency driving method, the fan efficiency is stable within the ideal range, and the motor energy consumption is greatly reduced. Especially when the unit is running at low load, the effect is more significant. At the same time, it improves reliability and extends the life of the motor. In addition, because the damper is fully open, the vibration and wear of the air duct are reduced, and the mechanical life is improved. In short, the frequency conversion device has good energy-saving effect, advanced speed regulation, mature use, and reliable performance, and is an ideal energy-saving project.