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Compressed air system has been gradually expanded in the field of industrial automation since the 1970s due to its low cost of components and easy maintenance of the system. It has been in steel, oil, natural gas, food, textile, semiconductor, liquid crystal, medicine, Medical, analytical instruments, cleaning and other industries play an increasingly important role. Compressed air is used in almost every factory, from small machine shops to large chemical companies with compressed air systems.
However, the consequent energy consumption of compressed air systems has become one of the major energy consuming systems in modern industry. In the United States and other countries, the energy consumption of the compressed air system accounts for about 9% of the total industrial power consumption in the country, while the European air compressor consumes about 10% of the total electricity consumption of the industry. In China, the compression in 2010 The power consumption of the machine is as high as 270 billion kWh, accounting for 8.7% of the total industrial electricity consumption in the country. Today, the problems of low efficiency and serious waste in the compressed air system have attracted people's attention. Both research institutions and user companies are paying more attention to energy-saving work in compressed air systems.
This paper analyzes the basic potential of energy saving by introducing the main energy consumption forms of compressed air. Then it introduces the energy saving status of compressed air systems at home and abroad. At the same time, it proposes four major targets for the current problems of energy saving in compressed air systems. Energy-saving measures, and pointed out the prospects of energy-saving in China's compressed air system.
1 Basic energy saving potential The composition of a typical compressed air system at an industrial site is as shown. The working process is as follows: the air compressor compresses the air under atmospheric pressure and compresses it and outputs it at a higher pressure; the output compressed air is buffered by the gas storage tank, and after initial water removal and degreasing, the teaching is input to the dryer and the like. research work.
The air purification equipment performs further water removal, degreasing and the like purification; then the clean compressed air is piped to the end gas equipment, such as a spray gun, a cylinder, etc. Therefore, the entire compressed air system can be roughly divided into three parts: (1) Manufacture of compressed air; (2) delivery of compressed air; (3) use of compressed air.
Compared with gas and natural gas, which have the cost to be used after purchase, users generally have compressed air from the atmosphere, which is inexhaustible. The production and use of compressed air is a misunderstanding of the cost. There are few studies on the energy-saving operation of compressed air systems by experts and scholars at home and abroad. As a result, a large amount of waste of compressed air energy in the production work is caused. With reference to the composition of the compressed air system, the energy waste is mainly manifested as: the operating load of the air compressor (group) does not match the air compressor system design or equipment selection. Both follow the principle of maximum load conditions (ie 100%% load). However, in actual use, the working conditions will not be running at full capacity. Therefore, the actual gas production of the air compressor needs to match the load air flow to meet the operating conditions of the industrial production site.
Unreasonable configuration and management of the pipeline network mainly includes leakage and unreasonable supply pressure.
In the case of leakage, the leakage in the factory usually accounts for 1030% of the gas supply, and the poorly managed factory may even be as high as 50%. Sometimes there are 20,000 leak points in a car assembly shop, of which 90 More than % of the parts from the use of the equipment are aged or broken.
Because the pipeline pressure loss is uncertain, the equipment starts to have a peak flow, etc., the supply pressure of the compressor is sometimes 0.2~0.3 MPa higher than the required pressure on the site, and the waste is very serious.
Low-efficiency air guns such as air gun nozzles are widely used in the process of finishing and machining of manufacturing and processing. The gas consumption reaches 50% of the total gas supply in some industrial fields. Usually, the air gun is in use. There are problems such as excessive supply of gas pipes, high supply pressure, and nozzles made of straight copper tubes.
2 Energy-saving status of compressed air systems at home and abroad In order to reduce the energy consumption of compressed air systems and improve their working efficiency, countries around the world have set up special research projects, such as the CAC (Compressed AirChallenge) project in the United States, the EEAP project in Australia, and the CAS (Compressed Air System) in New Zealand. Optimize running projects, etc. Among them, the CAC project in the United States is the most well-known. The project was initiated by the US Department of Energy in October 1997. It is supported by major financial and human resources from the compressed air system hardware suppliers. Its main purpose is to provide education for factory engineers. A training framework for energy saving in compressed air systems. The CAC project is only for compressed air systems, based on user investment, it integrates information on the design, operation and evaluation of compressed air systems, providing comprehensive theoretical guidance and recommendations for companies to improve the efficiency of compressed air systems, saving annually in the United States. The electricity consumption is about 3 billion degrees. However, due to the lack of specific technical means and equipment achievements, the project has limited promotion benefits.
China's "Tenth Five-Year Plan" ten key energy-saving projects include the energy-saving project of the motor system. In addition, the China Taiwan Foundation Corporation researched the energy-saving technology of the compressed air system and pointed out the main problems of the system, such as insufficient pressure. The pressure fluctuation is too large, the compressed air leaks, the air compressor unloading time is long, the pipeline is arbitrarily extended, etc. The diagnosis method is proposed, and a simple monitoring system of the compressed air pipe network is developed. Due to the lack of energy evaluation standards for compressed air systems and advanced control methods, the research results lack sufficient theoretical basis, control energy saving effect is limited, and the energy saving effect on the entire compressed air system is limited.
Japan is at the forefront of the world in the research and implementation of energy saving in compressed air systems. Since the signing of the Kyoto Protocol to prevent the global warming effect in 1997, Japan has launched a massive energy-saving campaign, including energy-saving activities for compressed air systems. According to a survey conducted by the Japan Fluid Power Industry Association in 2002, after energy-saving by various companies, the aerodynamic energy consumption has been reduced by 10% and 30%. If the total electricity consumption of the Japanese compressed air system is calculated based on 40 billion kWh, it can be saved. Electricity is 40 to 12 billion degrees.
3 The current problem of energy saving in compressed air system For a long time, China's manufacturing industry is mainly based on extensive development mode. In most production enterprises, the efficiency of compressed air system is low, and there is widespread waste. Therefore, in order to improve corporate profits and reduce energy consumption, many companies have carried out simple energy-saving activities, such as pipeline plugging and air compressor installation of frequency conversion devices. However, due to the lack of systematic and comprehensive energy-saving measures and technical support, the effect of energy-saving activities is very limited. At present, the domestic energy consumption of compressed air system is mainly unreasonable in energy consumption evaluation, the operation of air compressor station is unscientific, the energy supply management is to be optimized, and the end equipment is to be improved. The energy consumption index of compressed air system commonly used in industrial sites is Air consumption. The air consumption does not have energy units, and the energy consumption of each equipment cannot be expressed independently of the whole system. Therefore, the energy loss of the intermediate part of the gas source output end to the equipment use end cannot be quantified by using the evaluation system, and the inside of the compressed air system cannot be clearly defined. The problem of energy loss and low efficiency of the compressed air system will not be solved. In addition, there is no uniform scientific standard for the evaluation and measurement of energy consumption in compressed air systems in the world, which makes it impossible to guide users to preferentially use compressed air components and equipment with high energy efficiency.
Reasonable configuration and reasonable operation of unscientific compressors in air compressor stations are very important for energy conservation. Usually, many industrial field compressors use an inhalation valve adjustment method to ensure that the output pressure is stable. However, this way, the compressor still consumes 3070% of the rated power without the supply of gas, and the waste is serious. To this end, in order to reduce energy waste, the more effective measures at present are variable frequency speed control and compressor group number control. These are basically ignored in the actual production of the factory, ensuring that pressure has become the only requirement for compressor management in most factories. A new evaluation index for compressed air energy consumption: pneumatic power. This index analyzes the relationship between the change of compressed air state and the external mechanical energy, based on the change of enthalpy and entropy, considers the influence at different temperatures, and uses it to express the function of air relative to the atmospheric environment. This indicator can directly quantify the energy consumption of pneumatic equipment. Its representation and measurement method was adopted by the Japanese Fluid Power Association in 2008 as the industry standard FPS2018:2008, which has been used in Japanese companies and was adopted by Chinese countries in December 2011. The Standards Committee decided to establish the project as GB national standard project.
The energy evaluation index can reveal the energy loss of each link of the compressed air system, and lays a theoretical foundation for the energy-saving diagnosis of the compressed air system, especially the calculation of the energy-saving rate, and provides a calculation basis for selecting high-efficiency pneumatic components and equipment.
4.2 Air compressor group operation optimization management The problem of air compressor group system control of air compressor station is roughly divided into pressure control and flow control according to the existing control technology. The following is a brief introduction.
At present, the world's major air compressor manufacturers have developed different air compressor group control systems. However, by reducing the operating pressure difference of the air compressor system and reducing the operating pressure of the system, only a few air compressor manufacturers have introduced related products, but their application range is limited, for some occasions where the amount of compressed air varies greatly. The system pressure difference is still large, can not effectively reduce the operating pressure of the system, and most of the controllers only play the role of automatic control or sequential control, on page 3 on how to make the entire compressed air system run efficiently and reliably, There is very little research on air compressor manufacturers.
At the end of the year, the air compressor group energy-saving controller ES+ was introduced. The controller collects the pressure of the rear compressed air tank and communicates with the air compressor through Profibus or hard-wire connection. According to the principle of traditional logic selection, the pressure changes. Rotate to start or stop the air compressor.
Into the control system X81 system, the hard wire is connected with the air compressor, and the control technology of starting, loading, unloading and stopping of the air compressor is controlled in turn by collecting the pressure of the compressed air at the rear.
Kaiser, Germany, introduced the Sigma Air System Controller based on ProfibusDP communication in 2001. Its main function is to sequentially control the operation and stop of the air compressor by monitoring the change of the rear pressure. The controller follows the first-in, first-out control principle, and configures air compressors of different sizes in the air compressor system. The high-power air compressor is used as the base load, and the low-power air compressor is used as the peak-load air compressor. To adjust the change in gas consumption. This allows the highest efficiency of the high-power air compressor to achieve the highest efficiency.
The controller has achieved good results in the EU and North America.
The controller used is SmartAir8, which can communicate with the air compressor by RS485. By monitoring the change of the rear pressure, it can rotate or start the air compressor in the system. The controller implements rotation start and control, and its main purpose is automatic control and operation.
曰本本立 (HITACHI has developed a number controller (MultirollerEX. This controller controls the operation of the air compressor to realize the start and stop control of the number of air compressors. The number of controllers calculates the current maximum at regular intervals) The number of running units is compared with the actual number of running units, and the number of operating units of the air compressor is increased or decreased. The principle of calculating the optimal number of operating units in the compressed air system is to judge the running time of the air compressor in the unloading operation of the air compressor group. When the unloading operation time exceeds the set value, the number controller thinks that there is not much air compressor running in the compressed air system, so it stops. When the pressure of the air supply pipe network is detected to decrease, the pressure drop is calculated. At the arrival point of the speed and predicted pressure, before the pressure drops to the lower limit, the air compressor is started in advance to control the pressure drop. The start and stop of the air compressor can be realized by the corresponding digital ON/OFF of the PLC.
Compared with the air compressor group control system with pressure matching as the control target, a flow control group-based air compressor group control method is proposed, which is based on the pressure required by the industrial field production. The operation combination of the fleet and the distribution of the gas load of the fourth page of each air compressor to improve the operating efficiency of the air compressor group and reduce the energy consumption of the operation.
Beijing Aishe Times 03COSO) adopted the minute-level prediction method for the future gas flow rate for the control demand of the screw air compressor, and calculated the pressure fluctuation rate of the air storage tank of the air compressor station; the control of the centrifugal air compressor Demand, for the future gas flow using the support vector machine algorithm for hourly forecasting.
Aiming at the problem that the unloading pressure constant setting of each screw air compressor can not adapt to the flow change, the optimal unloading pressure line control method is proposed, that is, the air compressor unloading pressure setting value is dynamically adjusted, when the set value is low. Frequent loading and unloading and finding a balance point between the increase in energy consumption when the set value is high; and based on the predicted value of gas consumption, comprehensive consideration of factors such as air compressor power, gas production efficiency, and running time, etc. Expert decision-making, the establishment of air compressor group loading and unloading sequence.
4.3 Energy-saving monitoring and management of gas supply links The positioning of compressed air leakage points is an important technology in the field of energy saving in pneumatic systems. When gas leaks into the atmosphere through small holes, the turbulence generated by the gas will generate ultrasonic waves at the small holes, and the ultrasonic waves will propagate along the straight line. With good directivity, the leak signal can be quickly located by detecting the ultrasonic signal generated by the compressed air leak position.
In addition, a parallel access gas leakage measurement method based on reference flow is proposed. By introducing the reference flow, the influence of the unknown volume can be eliminated, and the leakage of the pipeline equipment can be measured under the condition that the volume of the measured object is unknown.
The compressed air supercharging technology adopts the local supercharging method, and reducing the output pressure of the air compressor is an important part of the energy-saving technical system of the compressed air system, and has an important energy-saving effect. At present, the common compressed air boosting technology limits its popularization and application in industrial sites due to its small output flow and low efficiency. In order to improve the output flow and efficiency of the compressed air local supercharging technology and the device to meet the needs of the industrial site, an efficient, high-flow compressed air boosting technology is proposed, which utilizes the expansion energy of the compressed air in the driving cavity and effectively improves the efficiency. The output flowmeter efficiency of the supercharger can meet the needs of industrial sites and has a good promotion prospect.
Control of pressure and flow The reasonable and accurate pressure and flow supply to the workshop is an important means to ensure efficient production and reduce waste in the workshop. The pipeline gas supply and energy saving management unit can automatically collect the gas supply pressure and overflow flow of the high and low pressure pipelines, and timely and effectively carry out pressure regulation and flow regulation between the high and low pressure gas supply pipeline networks, and stabilize the high pressure side or low pressure side tubes. The pressure of the net ensures the effective distribution and utilization of compressed air between the various pressure pipe networks, reduces the pressure fluctuation of the gas supply pipe network and the waste caused by the gas supply surplus, and carries out comprehensive energy conservation management on the gas supply pipe network.
4.4 End energy-saving gas equipment Pneumatic nozzles are widely used in industrial automation fields, especially in the machining industry. Today, energy issues are becoming more and more prominent, and the energy saving of pneumatic nozzles is of great significance. Conventional nozzles are equipped with a pressure reducing valve to reduce the nozzle supply pressure and reduce the flow rate, but this method has a large amount of energy loss. In order to improve the efficiency of the nozzle and reduce the consumption of compressed air, a device for converting a continuous gas flow into a flow of a discontinuous flow such as a rectangular shape has been proposed. The device can reduce the pressure caused by the pressure reducing valve portion without using a pressure reducing valve. Energy loss, enhance the blowing effect and reduce air consumption. In addition, based on the Coanda principle, energy-saving and efficiency-enhancing nozzles, energy-saving air curtains, etc. can replace the traditional nozzles and nozzles to achieve a larger solar efficiency.
Prospects for energy saving in compressed air systems in China The energy consumption of compressed air systems in modern industrial sites cannot be ignored. Energy-saving retrofits and improved operational efficiency will become an important task in industrial energy conservation. At present, most enterprises in China still have problems such as low efficiency, serious waste, and lack of experience in implementing energy-saving systems. Whether it is a factory enterprise or an expert or scholar, it is constantly exploring effective energy-saving technologies. Beijing Aishe Times 汩COSO) adopts energy-saving diagnostic transformation service from source to end. In the application of more than 20 enterprises, it has achieved energy-saving effect of more than 20% energy saving and 50 million kWh of electricity per year. It is worth learning. .
At present, the power consumption of air compressors in China is close to 300 billion kWh. The promotion of energy-saving work in the compressed air system can save about 60 billion kWh of electricity per year in the country, equivalent to 21.6 million tons of standard coal, and reduce carbon dioxide emissions by 57 million tons, which has enormous economic and social benefits. This will have a direct contribution to China's industrial energy conservation business.
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