Thread Content
This post was last edited by Bao’s Purification on 2021-11-24 at 16:07. At present, most enterprises in China that use compressed air systems do not pay much attention to energy savings in these systems; they believe that it is sufficient for the compressors to operate stably and reliably, with energy efficiency being a secondary concern. However, issues such as mismatched configurations and operation of air compressors (with the sole aim of maintaining a proper supply pressure), large fluctuations in the supplied pressure, high leakage rates, faulty air gun nozzles, and improper use of air by end devices are common, which creates significant opportunities for improving the energy efficiency of these air compressor systems. I. Typical on-site compressed air systems: A conventional compressed air system consists of components such as air compressor units, compressed air buffer tanks, pre-filters for compressed air, refrigerated dryer units (desiccant dryers), post-filters (for removing dust, water, and oil), and control systems. The air compressor compresses the air, which first enters a buffer air storage tank. The compressed air is then purified using a pre-filter, and moisture is removed from it through a cold dryer. An adsorption dryer is used to further remove any remaining moisture from the compressed air. Finally, a post-filter ensures that the compressed air is finely filtered, and once it meets the required standards, it is sent to the devices that require it. Working process of the air compressor: Air passes through the intake filter to remove dust or large particles from the atmosphere, and then enters the compressor unit via the intake control valve. When the air is compressed to the specified pressure, the minimum pressure valve opens, allowing the compressed air to be discharged to a cooler (either water-cooled or air-cooled) for cooling, after which it is sent to the subsequent buffer tank equipment. The compressed air buffer tank has the following main functions: (1) It acts as a buffer; firstly, it helps to stabilize the flow rate of the gas being discharged, thereby extending the service life of the subsequent purification equipment. Secondly, air storage tanks are used to stabilize system pressure and reduce the frequent loading and unloading of air compressors. (2) It serves to cool down and remove water. The temperature of the compressed air drops rapidly in the storage tank, causing a large amount of water vapor to liquefy; this eliminates a significant amount of moisture and oil, thereby reducing the workload on the subsequent purification equipment. Pre-filter: Its function is to remove large impurity particles as well as some oil and contaminants, thereby preventing damage to the cold dryer. Cold dryer: Its function is to cool compressed air, condense the moisture contained in it, and remove this moisture through an automatic drain valve, thereby producing air that is relatively dry. Adsorption dryer: Since freeze-dryers cannot completely remove water vapor from the air, in applications where strict requirements are placed on the quality of air, an adsorption dryer is needed to keep the moisture content within the specified limits. An adsorption dryer uses adsorbents to remove moisture from compressed air under high temperature and pressure, thereby achieving drying. Post-filter: Its filtration precision is higher than that of the pre-filter, and it generally consists of 3 types of filters: an oil removal filter, a water removal filter, and a dust removal filter. Primarily, it filters out impurities, oil, moisture, and solid particles from the air. II. Energy-saving directions and measures for compressed air systems. Based on the production process of compressed air and the characteristics of the equipment used, as well as the requirements for subsequent air supply, the energy-saving directions and measures for compressed air production include: selecting appropriate compression technologies, properly configuring and optimizing the operation of compression unit clusters, choosing appropriate equipment for purifying compressed air, and using heat recovery systems. (1) Selection of air compression technology: During the operation of the entire system, electrical energy consumption is primarily concentrated in the air compressor. The energy conversion efficiency of the air compressor itself is also one of the important factors to consider. Currently, piston air compressors, screw air compressors, and centrifugal air compressors are widely used in the manufacturing industry. The operating principles, characteristics, and structural design of reciprocating air compressors give rise to their drawbacks: the periodic reciprocating motion of the pistons generates significant vibration and noise. Additionally, due to the presence of numerous transmission components and vulnerable parts, they require extensive maintenance. As a result, they have gradually been replaced by screw air compressors and centrifugal compressors. Centrifugal air compressors are mainly suitable for applications that require high flow rates and stable air supply. In such operating conditions, their energy conversion efficiency is significantly higher compared to other types of air compressors. However, it is not suitable for working environments with low air consumption and large pressure fluctuations. In addition, centrifugal air compressors are noisy and have poor adjustability; moreover, changes in the volume of air discharged can cause the compressor to experience surge, which in turn affects the efficiency of air production. Screw air compressors are easy to use, produce a steady flow of air, and require simple maintenance; they are widely used in applications with moderate exhaust volumes. In particular, variable-frequency control is even more convenient. With the use of variable frequency technology, air compressors can operate at a minimal unloaded load; by reducing the motor speed, the volume of air produced by the compressor is decreased, thereby achieving the minimum pressure required by the air distribution network. The energy efficiency of variable frequency screw air compressors still needs to be improved, both under full-load and partial-load conditions. (2) Rational configuration and optimal operation of air compressor arrays: The demand for air supply among existing enterprises fluctuates. Based on calculations derived from these fluctuations, an optimal air compressor array can be formed by combining standard-frequency compressors with variable-frequency units. In this setup, centrifugal standard-frequency compressors or screw air compressors operating at a fixed speed run at full load, thereby achieving maximum efficiency. The variable-frequency screw air compressor unit paired with it operates in variable frequency mode, providing the highest efficiency for regulating partial loads as well. To control an air compression unit cluster, a centralized controller is required. This controller adjusts the operating status of the compression units autonomously based on the varying demands for air volume and pressure from downstream systems, thereby helping to reduce operating costs. (3) Post-treatment equipment for compressed air purification. The main drying devices for compressed air are refrigeration dryers and adsorption dryers. When selecting such drying devices, it is necessary not only to meet the quality requirements for compressed air but also to minimize the pressure loss in the drying equipment, thereby reducing the energy consumption of compressed air. At the same time, for adsorption dryers, it is necessary to choose units with low regeneration air consumption in order to avoid waste of compressed air and resulting energy losses. In some applications, strict requirements are placed on the oil content in compressed air. To ensure the desired quality of this air, it is possible to achieve high efficiency and energy savings through proper configuration; this can be accomplished by using efficient oil removal filters in combination with suitable energy-saving air compressors, thereby reducing energy consumption costs. (4) Integrated heat recovery device: During the compression of air, 80%-50% of the electrical energy consumed by the compressor is converted into heat energy; currently, only 10%-20% of the electrical energy is converted into useful energy. A heat recovery device recovers the heat generated during air compression through means such as energy exchangers. These energies are reused as recyclable energy sources to improve the operating efficiency of air compressors. III. Compressed air transportation and energy-saving measures The energy-saving measures for compressed air transportation mainly include the following aspects: rational design of the transportation pipeline system, leakage prevention in the pipelines, and local pressure enhancement techniques. (1) Rational design of the conveying pipeline system: A rational design of the compressed air conveying pipeline system can **reduce the resistance losses in the pipelines. To meet the air demand of subsequent processes, air compressors often have their outlet pressure increased by 0.1–0.2 MPa; for every 0.1 MPa increase in the exhaust pressure of an air compressor, its energy consumption increases by 3%–10%. Therefore, reducing the pressure loss in compressed air delivery pipelines is crucial. The main energy-saving measures for conveying pipeline systems are as follows: First, select a reasonable and economical pipe diameter based on empirical values for the pipeline, thereby avoiding waste associated with using overly large diameters. In theory, smaller diameters result in higher pipeline resistance and greater energy losses. Second, reduce the pressure drop in the pipeline network by minimizing the resistance caused by air compressors and pipelines leading to areas where air is used. Third, decreasing the number of pipe bends, using valves with low pressure drops, and employing a looped design for air pipelines can all help reduce pressure drop in the network and minimize energy losses. (2) Leak sealing in delivery pipelines: In factories, leaks from compressed air in various equipment, as well as leaks at valves, connections, flanges, and threaded joints, typically account for 10%-30% of the total air supply. Such leaks result in energy losses. Therefore, the main measures for sealing leaks in delivery pipelines are: first, to minimize the number of welds, valves, flanges, and threaded connections, thereby reducing the number of potential leak points; second, to use specialized monitoring equipment to detect leaks in the compressed gas delivery pipelines and equipment, thus preventing leaks in the compressed air delivery system. (3) Local pressure boosting technology: In an entire gas utilization system, there are often a few devices that require high-pressure gas supply. A common approach is to increase the pressure supplied by the air compressors; this leads to an increased load on the air compressor units and higher energy consumption. Additionally, raising the pressure throughout the pipeline network increases the likelihood of leaks in the pipes. To meet the local need for high-pressure compressed air, local pressure enhancement can be employed. Currently, there are two methods: A) Electric pressure enhancement technology, which uses electricity to boost the pressure of compressed air through mechanical devices. Such electric boosters are developed from improved compressors; they feature a high output flow rate and pressure, with an energy conversion efficiency of up to 80%. However, these devices lack proper control mechanisms, making them prone to causing disturbances in the plant’s power and gas networks, as well as resulting in significant damage to the equipment itself. B. Pneumatic boosting technology. By using compressed air and a piston to compress the air, pressure can be increased. Such boosters are powered by compressed air, do not require an electrical power source; they are simple in design, compact in size, and easy to use. They are widely used in situations where a small amount of high-pressure air is needed locally. However, the energy conversion efficiency of such devices is only 20%. An efficient compression air boosting technology with high flow rates can also be employed to meet the demands for large-scale local pressure enhancement in industrial applications. In summary, the purpose of energy conservation is to improve the effective utilization rate of compressed air systems. A series of measures, including equipment selection, transportation of compressed air, and local pressure boosting, are all aimed at providing end-users with high-quality compressed air to meet their needs in precision processing and manufacturing.