Application of Frequency Conversion Technology of Compressed Air System Based on System Performance Analysis Qin Hongbo Hu Shougen Shanghai Energy Conservation Service Center Ding Yongqing frequency technology has a very large energy saving space in China, but should be based on comprehensive testing of the performance of compressed air system.
i Introduction Compressed air has been widely used in various industrial fields due to its advantages of clear, transparent, harmless, non-polluting, and dangerous. It is even called the first energy source. However, compressed air is also a very expensive theory. It only accounts for the entire life cycle cost, while energy costs account for 75 Zuo Shi 121. According to the US Department of Energy's 2002 global survey results, the global air compressor average load rate is 79, while the Chinese air compressor average load rate It is 66, which is 13% lower than the average load rate of the global air compressor, and has a lot of energy saving space. According to the data, many compressed air systems can achieve the above energy-saving effects through energy-saving retrofits, such as the application of pipe network optimization technology, variable frequency technology, pressure control technology and central control technology. Of course, each compressed air system is different, and the applicable energy-saving technologies are also different. The application of the technology should be based on a comprehensive analysis of the dynamic characteristics of the system. 3. It is difficult to achieve the expected energy-saving effect by blindly implementing inappropriate energy-saving technologies. .
2 screw air compressor control method and efficiency comparison The most widely used compressors in the industry are screw compressor reciprocating compressors and centrifugal compressors. Among them, screw compressors are simple, safe, reliable and easy to maintain. The advantages are the most widely used in industry. In view of this, this paper focuses on the comparative analysis of different control methods of screw air compressors.
2.1 Loading and unloading control The loading and unloading control is the earliest control scheme of the screw compressor. The pressure control range is from 0.070.3. The compressor will run at full capacity until the measured system pressure reaches the pressure switch intake valve and is released. The pressure of some or all of the lubricating oil separator tanks. By closing the intake valve, the compressor can be operated at no load. When the system pressure drops to the lowest pressure set point, a signal is sent to reopen the intake valve while the compressor is again operating at full load. If the compressed air system has the correct compressed air storage capacity, this control can fully meet the system requirements. There is not enough gas storage capacity in the system. The loading and unloading control will result in higher energy consumption than expected, and the system pressure fluctuates frequently. Reduce the service life of the equipment. Load and unload control air compressor load power comparison curve 1.
When multiple air compressors are operated in parallel, the number of air compressors will be limited by the maximum allowable system pressure fluctuation range. Since each loaded no-load machine has a differential pressure of at least 0.143 with the nearest compressor at the maximum and minimum pressure set points, the classification is performed in this way, and the originally designed system operating between 6.9 and 7.5 bar is increasing. After the compressor, the system pressure fluctuation range will increase, resulting in an increase in the average supply pressure of the system, and the operating power of the air compressor will also increase.
2.2 Constant pressure regulation control mode The system pressure fluctuation range of loading no-load control is about 73. This pressure fluctuation is unfavorable in most occasions, because the efficiency of air equipment will vary between l and 1.4 for each 0.07 bar supply pressure. Change between. In applications with a small amount of storage capacity, loading no-load control can result in frequent pressure fluctuations and excessive intake valve wear. The air compressor with constant pressure regulation control solves these two aspects by ensuring the stability of the system air supply pressure through the minimum valve movement. When the system pressure rises, the air compressor intake valve is closed, the air compressor flow is reduced, and the compression ratio is increased. The power required to adjust the load operation of the compressor is relatively large, and the efficiency is significantly reduced. In multi-air compressor applications, regulating compressor operation is subject to the same limitations as the number of machines loaded with no-load compressors. The operation of multiple air compressors below the full load at the same time makes the system pressure very stable, but the use efficiency is very low. Constant pressure control air compressor load power comparison curve 2.
2.3 Variable Frequency Control The variable frequency control air compressor can match the air supply of the compressed air with the gas phase by changing the speed of the compressor main engine. This type of control is very effective when designing and matching is reasonable by using small changes in gas pressure and keeping the inlet pressure constant. Due to some inherent losses in the variable speed drive process, special care must be taken when selecting a variable speed drive compressor. The variable speed drive control mode works best in a single compressor application where the load changes relatively large and is rarely in full load. In multi-stage compressor applications, the variable speed control compressor should only be used as a regulating compressor. This type of control is most efficient at partial loads, but when the compressor is in continuous full load operation, the internal losses of the drive reduce the energy efficiency of the control mode. Variable frequency control air compressor load power comparison curve 3.
Produce the expected energy savings. Screw compressors operate very efficiently at specific speed ranges. Rotating the compressor host too quickly or too slowly can damage the efficiency of the compressor. If the existing compressor is operating near the edge of the efficiency curve, actually reducing the compressor speed may require more power than less.
3 System Test Analysis The flow and pressure dynamics of compressed air systems vary very rapidly. In many systems, hundreds of air loads are randomly operated, often resulting in an imbalance between the supply side and the demand side of the compressed air system. In addition, the variable frequency control compressor has a certain control range, and only the system flow fluctuation is within its control range, and the frequency conversion control can better play the role of energy saving and stable system supply pressure. The best way to understand the range of system load fluctuations is to use a professional compressed air system test recorder to conduct a comprehensive test analysis of the system, and record the parameters of the system air compressor power and system pressure, and analyze the system load in a complete cycle. The process of load change within. On this basis, a reliable frequency conversion control scheme can be proposed, and the system flow test is 4.
Change, the instrument world April 2006 system application 4 frequency conversion control case 4.1 system operation overview Shanghai a factory compressed air system consists of 5 Ingersoll Rand screw air compressors, divided into two systems independently.
System 1 consists of two Ingersoll Rand 200 air compressors. Each unit's rated gas production 2 system is equipped with a refrigerating and adsorption dryer and a 313 gas storage tank. The system operation mode is open, and the constant pressure control mode operates, mainly supplying gas for production in the filter rod workshop.
System 2 consists of 3 Ingersoll Rand air compressors, 2 sets of 100 and 1 set of EP100S, and the rated gas production of the unit is respectively. 9m3min and 10, the system is equipped with a refrigerating dryer and a dry and wet gas storage tank. The capacity is 1.5 and 1 respectively. The system is operated in two modes, which are operated by loading and unloading control mode, mainly for the production of gas in the carton workshop and packaging workshop. .
4.2 System test analysis system 1 According to the test results, the system output pressure fluctuation range of the system is 0.63 beyond the normal pressure fluctuation range of the constant voltage control mode. Due to system configuration reasons, the compressor cannot be placed in the loading and unloading control mode before the compressor 0. In addition, the output flow range of the air compressor fluctuates between 060, the average flow rate is about 9.5 system 2 according to the test results, the system manifold pressure fluctuation range is 0. The servant 3 compressor output flow fluctuates between 0100, the average flow rate About 3.7 out of 3 claws.
4.3 System Optimization and Effect Based on the system test analysis, the following transformation plan was adopted to optimize the system piping system to carry out grid-connected operation of two independent pipeline systems. According to the system flow test results, in normal production, the station 20 is empty. The press can meet its peak load demand; the high-efficiency frequency conversion control system is installed to control the air compressor of the 200 air compressor, which not only reduces the number of units that can be turned on, but also improves the efficiency of the operation of the air compressor.
5 Conclusion The dynamic characteristics of the compressed air system are different. The comprehensive diagnosis of the compressed air system is the basis for the correct evaluation of the energy-saving space of the compressed air system. The energy-saving measures of the compressed air system should be formulated according to the specific conditions of the system, not every energy-saving measure. Applicable in any system, the system optimization plan should not only consider the high efficiency of the current system, but also consider the future development of the system, and the system efficiency is still efficient.
Qin Hongbo's main research direction for 1977 male doctoral students is the performance testing technology and optimization potential analysis of compressed air systems.
Zhang Xuanzheng male electrical automation senior engineer has long been engaged in inverter engineering application projects, and is now technically supported by Shanghai Jialing Electric Co., Ltd.
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