Key factors for energy conservation in screw air compressors

Thread Content

The rotor profile of screw air compressors has a certain impact on energy efficiency; before the year 2000, screw air compressors were still in their developmental stage, and reliability was the main concern. At that time, the development of the rotor profile for screw air compressors focused on reliability as the main goal. 　　After the 21st century, an energy crisis has enveloped the world, and the development of rotor profiles for screw air compressors aims to create energy-efficient compressors, with reliability being a key consideration in this process. The SKK-type wire is one of the excellent energy-saving wires developed under this broader context. The SKK type uses surface-to-surface internal sealing; under the same clearance, its sealing performance between the male and female rotors is far superior to that of traditional types that employ linear sealing. 　　Nosepiece manufacturing – The gaps between the male and female rotors, as well as between the rotors and the cylinder and cylinder head, have a significant impact on the energy consumption of screw air compressors. Improving the machining accuracy and surface finish of the rotor is an effective way to reduce the gaps between various components of the head. The SKK type wire uses grinding as its means of implementation. Therefore, surface grinding must be used for processing. The surface grinders produced by British Precision Machinery Ltd., which feature real-time monitoring and automatic grinding wheel compensation, have raised the precision of rotor processing to an unprecedented level. 　　The grinding machine provided by UK Precision Machinery Ltd. for the processing of SKK-type wires is the latest generation of machine tools introduced after 2006. Its processing capability has been enhanced to handle wires with a diameter of up to 370 mm; the processing accuracy reaches 2 microns, and the surface finish level is 10. Previously, for rotors of screw compressors of this size, milling machines were the only option; the maximum machining precision achieved was 40 micrometers, with a surface finish of grade 6. 　　Screw compressor configuration: The speed of the male rotor is the most important parameter for assessing the energy efficiency, lifespan, and reliability of screw air compressors. The belt drive results in a power loss of 5%, while gear transmissions cause a power loss of 3%. For screw air compressors to be energy-efficient, it is necessary that the speed of the male rotor be equal to the speed of the motor’s main shaft; at a frequency of 50 Hz, this means the male rotor should rotate at 1485 revolutions per minute or 2985 revolutions per minute. 　　The lifespan of a screw air compressor is inversely proportional to the speed of the male rotor. 　　Efficiency: When idling, a screw air compressor consumes 30% to 40% of the motor’s rated power; its efficiency drops by about 5% under certain operating conditions. All screw compressors are designed for a specific operating condition; when operated under those design conditions, they are the most energy-efficient. 　　When the air production volume of the screw air compressor continuously equals the air consumption of the pipeline network, the screw air compressor is in its most energy-efficient state. 　　Energy-saving analysis of variable-frequency air compressors: 1. The inverter itself consumes 3% of the power; the efficiency of the motor decreases significantly when it operates away from its rated power and speed. In screw air compressors, when the speed deviates from the rated value, the optimal mixture ratio of oil and gas is disrupted, resulting in a significant drop in efficiency as well. Therefore, although using a variable-frequency screw air compressor ensures that the air production rate remains equal to the consumption rate of the pipeline network, the power consumed to produce each cubic meter of compressed air increases. In other words, under continuous loading conditions, variable-frequency screw air compressors do not save energy. 　　2. In most applications involving screw air compressors, the air consumption in the pipeline network is constantly changing. Therefore, the air output generated by the compressor cannot always be equal to the air consumption in the pipeline network. When the pipeline pressure reaches the set value, the screw air compressor enters an unloaded state. During this unloaded operation, it consumes 30%–40% of its rated motor power; hence, the efficiency of a screw air compressor in such a state is extremely low. Reducing idling time or preventing screw air compressors from entering an idling state can achieve certain energy-saving effects. 　　3. Variable-frequency screw air compressors can effectively reduce idling time or prevent the compressor from entering an idling state; therefore, when the rated gas production of the compressor is greater than the gas consumption of the pipeline network, such compressors offer certain energy-saving benefits. 　　4. Variable-frequency screw air compressors are very effective at maintaining stable pressure in the pipeline network, enabling the pressure to remain within the range of ±0.01 MPa – a level that is difficult to achieve with other flow control methods. 　　Air compressor station configuration The principles for configuring energy-efficient air compressor stations are as follows: 1. The gas production volume should always be equal to the gas consumption of the pipeline network ； 　　2. A single air compressor is either operating at its rated conditions or is shut down. 　　Based on the results of statistical analysis, the gas consumption of the pipeline network is distributed among multiple air compressors, with a larger compressor providing a constant portion of the required gas supply ； Several smaller air compressors are used to start or stop operating according to changes in air demand, while an inverter-driven air compressor is employed to make further fine adjustments to the air supply volume. 　　The waste heat from screw air compressors holds great value for utilization, and energy-efficient air compression stations should give full consideration to waste heat recovery and utilization.