Electrical control Yan Guangqi, etc.: Frequency conversion energy-saving transformation of air compressors, frequency conversion energy-saving transformation of air compressors Yan Guangqi, Yan Wei, Wang Wolin, Li Ke, Cheng Xiaodong, Shen Jianjun, Wan Peng, Gao Guofu U Kenan Building Materials Research and Design Institute of limited liability company, Zhengzhou 450002, China) 1 Air compressor operating characteristics and energy saving space analysis Air compressor is a kind of equipment that uses electric motor to compress gas in the compression chamber and has constant pressure of compressed gas. It is produced in cement enterprises. It also has a wide range of applications. In recent years, more screw-type air compressors have been used in cement companies. The screw air compressor is rotated in a cylinder by a pair of male and female rotors (or screws) which are mutually engaged with each other, so that the air between the rotor slots continuously generates a periodic volume change, and the air is transported by the suction side along the rotor axis. To the output side, the whole process of suction, compression and exhaust of the screw air compressor is realized. The air inlet and the air outlet of the air compressor are respectively located at two ends of the casing, and the slots of the female rotor and the teeth of the male rotor are driven to rotate under the driving of the main motor. In the selection of air compressors, in order to ensure that the production requirements can be met under any circumstances, the rated gas supply capacity is selected to be about 1.1 to 1.2 times the maximum production gas consumption. In the actual production process, due to seasonal and time fluctuations in the actual demand of the factory, in most cases, only 50% to 60% of the rated gas supply can be used, or even lower. Therefore, the air compressor is not fully loaded for most of the time and has a large energy saving space. In order to reduce the waste of electric energy of the air compressor while maintaining the balance between the air supply amount and the gas consumption amount, whether it is a piston type or a screw type compressor, a more common control method is to provide an adding and unloading mechanism therein. When loading, the air compressor supplies compressed gas to the gas storage tank; when unloading, the air compressor does not supply compressed gas to the gas storage tank, and is in an "idle" state rather than a shutdown state. The reason why it is idling and not entering the stop state is because the no-load starting current of the air compressor is about 3~5 times of the rated current (the air compressor motor is like the star/delta starting mode), and the idling avoids the loading start. Powerful current surges and mechanical shocks, as well as impacts on other electrical equipment in the grid, while reducing the life of the air compressor. However, the process of adding and unloading is alternated. During the loading period, the pressure of the gas storage tank is rising, and during the unloading, the pressure of the gas storage tank is decreasing. Generally, the pressure curve of the gas storage tank is "sawed" (see). In order to ensure the normal production, the minimum pressure (P) must meet the requirements; at the end of the loading process to the unloading state, the pressure of the gas tank is the largest, expressed by Pmax, called the maximum pressure. In general, the relationship between Pmax and Pmax can be expressed by the following formula: That is to say, there is 15% to 30% waste on the air pressure. Shortening the addition and unloading time can reduce 8 and reduce waste; however, the number of additions and uninstallations per unit time must increase. The mechanical shock during frequent loading and unloading will seriously shorten the life of the equipment, and the frequent opening/closing of the bleed valve will accelerate the wear of the intake valve, greatly shorten the life of the bleed valve, and increase the maintenance and maintenance costs; The process of frequent addition and unloading is bound to increase the consumption of electric energy. The energy that is wasted and unloaded by the gas supply control method is mainly in the following aspects. (1) Power consumption at the time of loading. When the air pressure in the gas storage tank reaches Pmm, the supply and unloading control modes must continue to increase the pressure until it reaches. This process requires the power supply to continue to supply energy to the compressor, which is a loss of energy. (3) Consumption of electric energy during unloading. When the pressure reaches the maximum value, the air compressor depressurizes the unloading by closing the intake valve to make the motor idling. This adjustment method causes a great waste of energy, and it is estimated that When the press is unloaded, the energy consumption accounts for about 10% and 35% of the air compressor's full load operation. Obviously, under the load and unloading air supply control mode, the air compressor motor has a large energy saving space. 2 Energy-saving measures of air compressors With the development of power electronics technology, Yan Guangqi of air compressors, etc.: The best energy-saving measures for the air-conversion energy-saving retrofit of air compressors are to implement variable frequency speed regulation. When the frequency conversion speed control is adopted, the pipe network pressure is taken as the control object, and the pressure of the gas storage tank is detected to realize the closed-loop pressure control of the system, and the rotation speed of the air compressor and the running number of the air compressor are automatically adjusted. The modified air compressor is started by the frequency converter to realize the working mode of soft start and soft stop with load, avoiding the impact current and the mechanical shock caused by starting the air compressor, and achieving continuous adjustment of the air supply volume. To ensure the stability of the manifold pressure. The running curve in the inverter control mode is as shown. The air compressor motor parameters of an enterprise are as follows: the power is 160kW, the speed is 1 480r/min, the rated current is 294A, and the power factor is 0.89. In the traditional method of adding and unloading gas supply, the normal production situation, the pressure needs to be maintained at In the range of 0.600.72 MPa, the air intake valve switch of the air compressor has a certain regularity, that is, the valve open loading time is about 125s, and the closing and unloading time is about 90s (that is, the loading time accounts for 58% of the total time, and the unloading time accounts for about 42%); The motor current during loading is about 256A, and the motor current of the closing valve is about %. After the constant voltage control is used, the normal pressure is maintained at a relatively stable value of 0.60MPa*0.02MPa. The inverter displays 36Hz. The motor current is maintained at around 193A and the fluctuations are small. In this way, the annual energy saving is about 278.9x103kWh. According to the current average industrial electricity price of 0.615 yuan/kWh, the annual production cost can be saved by about 172,000 yuan. The energy consumption running curve of the air compressor before and after the transformation *å© inverter control mode and the addition and unloading air supply control mode) is as shown. Among them, the ordinary air compressor and the variable frequency air compressor all operate near the rated power when starting up or starting after hibernation. Therefore, the variable frequency air compressor can ensure the rapidity of inflation. After the air compressor is modified by frequency conversion, it has the following system advantages: (1) The change of the air pressure amplitude is small, and the measured pressure change amplitude is about *0.03MPa, which has good gas supply quality and high production efficiency; (3 average noise reduction of 37dB ( A), improved working environment; (3) easy to operate; (4) air-compressed variable frequency air compressor Zhang Yanbin using frequency conversion speed regulation and low speed operation. Beijing: Mechanical Industry Press, 2000 . 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