How air compressor systems can save energy, which can result in significant cost savings

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As one of the power sources in manufacturing enterprises, compressed air needs to operate continuously in order to maintain a stable pressure level; this is a fundamental requirement for the smooth operation of such enterprises. The air compression units, which are the main equipment used for production, serve as the key devices for fulfilling this task, and they must operate continuously and reliably to ensure fault-free and stable performance. Since it is a operating device, it needs power to function, and high electricity consumption is the main factor contributing to increased costs. At the same time, during continuous air supply, it is important to check whether there are any leaks or inefficient usage within the company’s entire air supply network system; otherwise, the compressed air produced will be wasted through leaks, which represents another major factor contributing to increased costs. To effectively reduce the operating costs of air compressor units, the author explains from the following aspects. 1. In the technological upgrading of equipment, attention should be paid to high-efficiency units; for example, replacing piston compressors with screw compressors is a trend in equipment development. Although the industry has been in the era of screw compressors for nearly twenty years, many domestic users are still using piston compressors. Compared to traditional piston compressors, screw air compressors offer advantages such as a simpler structure, smaller size, higher reliability, better stability, and easier maintenance. The market share of screw air compressors is increasing year by year. In particular, in recent years there has been an emergence of energy-efficient screw compressors, with various companies competing to launch products that meet higher energy efficiency standards; it is important to pay attention to this aspect in every equipment upgrade. ⒉Leak control for the entire pipeline network system during compressed air use. The average leakage rate of compressed air in factories is as high as 20–30%, so the top priority for energy savings is to address these leaks. For all pneumatic tools, hoses, connectors, and valves, a small hole of 1 square millimeter can result in losses of around 4,000 yuan per year at a pressure of 7 bar. It is urgent to check for leaks in the air compressor pipelines and optimize their design. It is a great shame that the compressed air that leaks away is not utilized effectively; it represents an energy source that could be generated through power consumption, electricity, and water, only to be wasted as a result of these leaks. I hope that business managers will pay close attention to this issue. 3. Compressed air loses pressure after passing through each device; as a result, the pressure at the air source decreases. It is necessary to address this pressure drop by installing pressure gauges along various sections of the pipeline. Generally, from the air compressor outlet to the point of use in the factory, the pressure drop should not exceed 1 bar; more strictly, it should not exceed 10%, or 0.7 bar. The pressure drop in the cold dry filtration section is generally 0.2 bar; check the pressure drop in each section in detail, and carry out maintenance promptly if any issues are found. (An increase of 1 kilogram in pressure results in a 7%-10% increase in energy consumption). When selecting compressed air equipment and evaluating the pressure requirements of the devices that use air, it is necessary to take into account both the supply pressure and the supply volume; it is not advisable to blindly increase the supply pressure and total power of the equipment. While ensuring production, the exhaust pressure of the air compressor should be reduced as much as possible; the cylinders of many equipment that use air require only 3–4 bar, with only a few robotic arms needing more than 6 bar. (For every 1 bar decrease in pressure, energy savings of about 7–10% are achieved). For industrial gas equipment, it is sufficient to ensure production operations by meeting the equipment’s gas consumption and pressure requirements. 4. For equipment selection, high-efficiency compressors should be used. Taking into account the enterprise’s gas consumption patterns, it is necessary to consider usage levels during peak and off-peak periods; variable-speed operation can be employed, and high-efficiency permanent-magnet variable-frequency screw air compressors help save energy. Currently, the leading high-efficiency permanent-magnet variable-frequency screw air compressors in China feature permanent-magnet motors that save more than 10% energy compared to conventional motors. They provide constant pressure air, eliminating waste due to pressure differences; they supply exactly the amount of air needed, and there is no need for loading or unloading mechanisms. It saves more than 30% energy compared to ordinary air compressors. Gas used for variable-frequency production is particularly suitable for modern manufacturing; units with high gas consumption can also employ centrifugal units, which offer high efficiency and large flow rates to address the issue of insufficient gas supply during peak periods. 5. In the era of Internet big data, centralized control of multiple devices is an excellent way to improve modern enterprise management practices. Centralized coordinated control of multiple air compressors can prevent a stepwise increase in exhaust pressure that occurs when setting parameters for these compressors, thereby avoiding waste of the compressed air energy produced. The coordinated control of multiple air compressor units, as well as the synchronized operation of post-treatment equipment, along with monitoring of the flow rate in the gas supply system, the pressure of the gas supply, and the temperature of the gas supply, can effectively prevent various problems that may arise during equipment operation and enhance the reliability of its performance. 6. Reduce the inlet temperature of the air compressor. It is generally appropriate to place the air compressor in an indoor environment; usually, the temperature inside an air compression station is higher than that outside, so taking in air from the outside can be considered. Proper maintenance and cleaning of equipment, improving the cooling efficiency of air compressors, enhancing the performance of heat exchangers such as water-cooled and air-cooled types, and maintaining the quality of oil – all these measures can help reduce energy consumption. According to the operating principle of air compressors, they draw in air from the environment, process it through multiple stages, and compress it step by step to produce high-pressure, clean air that is then supplied to other devices. Throughout this entire process, the air in nature is continuously compressed, and most of the heat energy converted from electrical energy is absorbed; as a result, the temperature of the compressed air rises. Such high temperatures are detrimental to the proper operation of the equipment, so it is necessary to keep the equipment cooled down. At the same time, introducing more natural air helps to lower the temperature of the incoming air, and increasing the volume of air supplied is an ideal situation. 7. Waste heat recovery during compression. Heat recovery from air compressors generally involves the use of efficient heat recovery equipment to absorb the waste heat generated by the compressors and use it to heat cold water, with no additional energy consumption. It primarily addresses issues such as employees’ living needs and hot water for industrial use, helping companies save a significant amount of energy and thereby **reducing their operational costs**. Schematic diagram of waste heat recovery – Compressor waste heat recovery unit: (1) The compressor waste heat recovery unit is an energy-saving device that makes use of the thermal energy from the hot oil and gas produced by compressors, utilizing heat exchange to fully exploit this thermal energy. It collects the heat generated during the operation of the air compressor through energy exchange and energy-saving control, while also improving the operating conditions of the air compressor; it is an energy-saving device that offers relatively efficient utilization of waste heat and operates at zero cost. (2) The source of heat can be an oil-injected screw air compressor, an oil-injected screw compressor used in central air conditioning systems, or the waste heat from energy centers or other equipment in a facility. Hot water can be used for domestic purposes, hot air drying, heating supply, constant temperature and humidity control systems, as make-up water for boilers, and for cleaning equipment. (A 75kW air compressor; the heat recovered from waste heat over one day is sufficient to provide hot water for about 500 people.) (3) The thermal energy of the high-temperature oil and gas during compression is transferred to normal-temperature water through heat exchange, thereby enabling the utilization of this thermal energy. The electric motor drives the screw compressor to rotate; air is drawn into the screw compressor through a filter and compressed into high-pressure air. This air then mixes with the circulating oil to form a high-pressure, high-temperature gas-oil mixture, which enters the gas-oil separator. After the oil-gas mixture is separated into oil and gas on one hand and air on the other, the compressed air is cooled by an aftercooler before being supplied to the user. The circulating oil and gas, on the other hand, are separated in the oil-gas separator; once they have condensed into a liquid state, they pass through an precooler for cooling and a filter before returning to the compressor, thus completing one cycle. A compressor-based heat water generator introduces high-temperature circulating oil (and high-temperature compressed gas) into the heat water generator; the heat generated during the operation of the air compressor is fully absorbed by the heat water generator, thereby cooling the compressor. (4) During the long-term continuous operation of screw air compressors, electrical energy is converted into mechanical energy, which is then converted into heat energy. In this process of conversion from mechanical energy to heat energy, the air is compressed at high pressure, causing its temperature to rise sharply; this is a phenomenon of mechanical energy conversion as described in basic physics. The high-speed rotation of the mechanical screw generates frictional heat; this heat is mixed with the lubricating oil in the air compressor to form oil/gas vapor, which is then expelled from the machine. The heat contained in this hot oil/gas stream accounts for about 1/4 of the power input by the air compressor, and its temperature typically ranges from 80°C (in winter) to 100°C (in summer and autumn). All of this thermal energy is needlessly wasted and discharged into the atmosphere due to the temperature requirements for machine operation; it is the air compressor’s cooling system that ensures these temperature requirements are met. In summary, improving the efficiency of compressed air usage is one of the key measures for enterprises to reduce energy consumption and emissions. It requires attention from managers, users, and operators, as well as the implementation of effective measures to increase the utilization rate of air compressors, thereby ensuring production continuity while reducing operating costs.