Compressed air has a wide range of applications in the industrial sector, mainly for pneumatic equipment, pneumatic tools, pneumatic conveying and purging. Compressed air is provided by air compressor stations that are centrally located in the plant or dispersed in each plant. The energy consumption of compressed air systems accounts for about 10% to 35% of the total energy consumption of industrial production, and 96% of the energy consumption of compressed air is the power consumption of air compressors.
Because the screw air compressor has the advantages of large span of gas supply range and small fluctuation of gas supply pressure, the air compressor of the factory is mainly screw air compressor, so the analysis of this paper takes the screw air compressor as an example. The useful part of the input energy of the air compressor is the increase of the compressive air potential energy, which accounts for about 15% of the input power; the unused work is the thermal energy generated by the mechanical work, which accounts for about 85% of the input power. Part of the input power is 3%5%), which is the heat dissipation of the casing. This part of the heat cannot be recycled. Most of the converted heat energy accounts for 80% of the input power. 82%) The cooling system of the air compressor is cooled or cooled by water cooling. Go to the surrounding environment to ensure the normal operation of the air compressor. The heat in this part is called waste heat and can be recycled. According to the above analysis, waste heat utilization can significantly improve energy utilization efficiency, reduce energy consumption and production costs. The author is the first: Fan Yawei, born in 1984, male, from Fan County, Henan Province, graduated from Harbin Institute of Technology in 2008, majoring in gas, ventilation and air conditioning engineering, master's degree, engineer.
Combine with your own design experience, talk about several commonly used air compressor waste heat recovery and utilization systems, and analyze the characteristics of various systems and matters needing attention in the design.
1The direct cooling of the hot air The cooling system of the air-cooled air compressor is composed of an air cooler built in the air cooler, a gas cooler, and an exhaust fan. The cooling air cools the oil and gas by forced convection to ensure the normal operation of the air compressor. Due to the heat dissipation of the unit, the cooling exhaust air temperature is usually 10 ° C higher than the inlet air temperature by 15 ° C. When the air compressor station is designed, the air compressor cooling hot air is usually connected to the outside through the air duct, and the hot air is directly sent to the air duct through the air duct. The place to be heated is a common way of directly recycling waste heat.
1.1 Hot air is used for winter auxiliary heating in the workshop. When the air compressor station is attached to the plant construction, the cooling hot air of the air compressor can be directly discharged into the workshop for the auxiliary heating in the workshop. See the schematic diagram of the connection of the hot air duct of the air compressor.
In summer, when the workshop does not need heating, open the air inlet louver A, exhaust louver A, close the air inlet louver B, exhaust air louver B, air compressor station cooling air intake from the outdoor, cooling heat exhaust air to the outside, ensure empty The pressure unit is in normal operation, and no residual heat is utilized at this time. In winter, open air inlet louver B, exhaust louver B, close air inlet louver A, exhaust louver A, air compressor station cooling air intake from the factory, cooling hot exhaust air discharged into the workshop, supplemental heating of the workshop.
The waste heat utilization mode has the following characteristics: simple construction or transformation, and small investment; the utilization of waste heat is seasonal. This kind of waste heat utilization mode is especially suitable for the central region, such as Jiangsu and Zhejiang provinces. The winter workshop does not heat, but the temperature is relatively low. For example, Zhejiang Haining Aijia Furniture Factory has significantly improved the temperature in the workshop after the air-cooling system of the air compressor station was rebuilt. This type of waste heat utilization should pay attention to the influence of noise on the workshop during use.
1.2 Hot air is used for process heating in special rooms. There are places in the industrial field that need to be heated all year round, such as paint room and drying room in the post-processing workshop, and the use time is synchronized with the start and stop of the air compressor station. Cooling hot air is directed to the room to be heated. At this time, the utilization efficiency of waste heat is high, and there is no seasonality. It should be noted that at this time, the exhaust air duct is generally long, and an induced draft fan is required to conduct the air intake, and should be implemented simultaneously during the construction of the plant.
2 Indirect recovery of heat Indirect recovery of heat refers to the modification of the cooling system inside the air compressor, and the waste heat is recovered by heat exchange. Compared with direct recovery of hot air, indirect recycling has a wider range of applications and better utilization. It can be used not only for air-cooled air compressors but also for water-cooled air compressors.
The working process of the oil-injected screw air compressor is as follows. The dust after filtering and removing impurities enters the compressor, and is mixed with the injected cooling oil during the compression process, and the compressed mixed gas is discharged from the compression chamber. It is separated into high temperature and high pressure oil and gas by oil and gas separator. In order to ensure the normal operation of the machine, the high temperature and high pressure oil and gas must enter the respective cooling system for cooling, wherein the compressed air enters the use system after passing through the cooler and the filter; the high temperature and high pressure lubricating oil is cooled by the cooler and returned to the oil circuit for reuse. . The temperature of the high temperature and high pressure lubricating oil is between 80 °C and 100 * C, which carries most of the heat of the residual heat. The oil circuit system is modified, and the heat is recycled through the heat exchange equipment, which is the indirect heat of the air compressor. recycle and re-use. According to engineering experience, the heat recoverable by the lubricating oil road system accounts for about 60% of the waste heat. 0. The newly added chemical equipment and its ancillary facilities are called heat recovery units in the project, and now all air compressor manufacturers can provide this product.
In the project, the waste heat is usually used as the heat source of the shower thermal system in the factory.
The waste heat utilization system has a wide range of applications in the factory, especially in the textile, chemical fiber and other industries where the gas consumption is large, and the residual heat of the air compressor can fully satisfy the shower heat of the workers in the entire plant. For example, Hangzhou Huaxin Textile Factory has five screw compressors with a rated power of 250kW in the air compressor station. After energy-saving renovation, it can meet the heat problem of showers for about 2,000 workers in the factory.
In the engineering application of the air compressor waste heat utilization process, the application of the system requires the addition of a thermal energy return unit and appropriate modification of the original shower thermal system. Therefore, the heat indirect recycling system has the following characteristics: increasing equipment investment and renovation costs; requiring equipment to occupy the site; waste heat utilization can be used all year round; waste heat recovery and utilization efficiency is high, and economic benefits are significant. It should be noted that the configuration of the waste heat system needs to be modified to the internal pipeline of the air compressor. Therefore, the waste heat recovery unit should generally be configured by the supplier of the air compressor, or it should be modified by the organic group, otherwise it will easily become empty. Disputes on press warranty.
3 Conclusion The use of residual heat in air compressors has significant energy-saving effects; for production enterprises, it has significant economic benefits; it must be given enough attention in engineering design and citation. In the actual project, different waste heat recovery and utilization systems should be selected according to the specific conditions.
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