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1. Introduction to air compressors Currently, there are mainly three types of air compressors in use: centrifugal air compressors, screw air compressors, and reciprocating piston air compressors. 1.1 Centrifugal air compressors: Centrifugal air compressors use an impeller to drive gas to rotate at high speed, creating centrifugal forces. As the air passes through the impeller, its velocity and pressure increase, thereby enabling continuous production of compressed air. The characteristics of centrifugal air compressors are: ① The equipment operates smoothly with a high operating rate; it is reliable in operation, has no friction components, and requires minimal maintenance costs later on. ②Centrifugal compressors can achieve completely oil-free compression. ③The equipment has a high gas output, compact structure, light weight, and occupies little space. Centrifugal compressors are not suitable for applications requiring low gas volumes, nor can the pressure ratio be too high. ⑤The stable operating range of centrifugal compressors is relatively narrow, and the regulation of gas flow is uneconomical. 1.2 Screw air compressors: The core component of a screw air compressor’s head is a pair of intermeshing male and female rotors; each pair rotates in opposite directions to achieve air compression. The features of screw air compressors are: The features of screw air compressors are: ① Simple operation. Screw compressors feature a high degree of automation; they have low requirements for operators and can easily be operated remotely or in an unattended manner. ②Operates reliably. Screw air compressors have few components, are simple to maintain, lack vulnerable parts, operate reliably, and have a long service life. ③High applicability. Screw air compressors force air to flow, so their volumetric flow rate is not affected by the discharge pressure; this allows them to operate in a wide range of conditions while maintaining high efficiency. ④It has good dynamic balance. Screw air compressors have no unbalanced inertial forces, allowing them to operate smoothly at high speeds, with low requirements regarding the foundation on which they are installed. 1.3 Piston compressors The core components of piston compressors consist of the cylinder, the intake and exhaust valves, and the piston that moves back and forth within the cylinder. The rotation of the crankshaft drives the piston to move back and forth within the cylinder, completing the processes of intake, compression, and exhaust. Advantages of piston compressors: ① Wide range of applicable pressures – piston compressors can be designed to operate at various pressures, and they are irreplaceable by other compressors, especially in high or ultra-high pressure ranges. ②It has a high compression efficiency; the process of compressing gas in a piston compressor takes place within a closed system, which results in high compression efficiency. ③They have strong adaptability; piston compressors offer a wide range of discharge capacities, and the impact of gas density on compressor performance is not as significant as in rotary compressors. Piston compressors of the same specification can often be adapted to compress other gas substances with only minor modifications. ④The gas contains oil contamination, which is particularly evident in cases where oil is used for lubrication. ⑤The exhaust is discontinuous, and the gas pressure fluctuates, which may lead to flow pulsation resonance. ⑥There are many vulnerable components, resulting in high maintenance costs. 2. Analysis of compressed air requirements: The demand for compressed air is influenced by various factors. To meet production needs efficiently and effectively, this analysis focuses on aspects such as flow rate, pressure, and humidity. 2.1 Flow rate: Under ideal operating conditions, production and consumption are in balance; the amount of compressed air used meets the requirements without any waste. However, in actual operation, to accommodate fluctuations in production demands, the compressor flow rate becomes too high; the user cannot make use of this excess compressed air. As a result, the equipment operates at reduced load, and at such times it is either idle or running at partial load, with energy being wasted in doing unnecessary work. 2.2 Pressure: A change of 0.1 MPa in the exhaust pressure of an air compressor results in a 6% increase or decrease in energy consumption. To this end, the exhaust pressure must be selected appropriately based on actual needs, without leaving too much margin for pressure loss. Furthermore, the compressed air consumption of pneumatic equipment is directly proportional to the pressure level; reducing the pressure appropriately can minimize unnecessary compressed air usage. 2.3 Humidity: Since most devices have requirements regarding the water content in compressed air, it is generally dried to remove condensation water. The degree of dryness of compressed air is usually measured by the pressure dew point temperature; the lower this temperature, the drier the compressed air, although it also requires more energy. The pressure dew point temperature of a freeze-dryer is generally between 2°C and 5°C, and its energy consumption is about 1.5% of that of an air compressor. The pressure dew point temperature of adsorption dryers can reach -50°C, and the energy consumption is correspondingly as high as 10% to 15% of that of air compressors. 2.4 Lubrication: During operation, air compressors can be classified into two main categories based on whether air is mixed with lubricating oil: oil-type and oil-free types. The use of lubricating oil significantly improves the volumetric efficiency of air compressors. Therefore, from an energy-saving perspective, the energy efficiency of oil-based air compressors is **higher than that of oil-free air compressors. More importantly, the overall price of oil-free machines is twice that of oil-lubricated equipment. For applications with special requirements such as deoxygenation presses, compressors equipped with oil lubrication systems should be selected, along with appropriate post-treatment equipment, to meet the needs of gas supply users. In fact, if one wants to use oil-free compressed air while also saving energy, it is possible to achieve both energy savings and oil-free operation by using an oil-lubricated energy-saving air compressor in combination with a reliable catalytic oil removal device. 3. Selection of air compressors and post-treatment equipment 3.1 Selection of compressor types For the production of low-pressure compressed air (below 1.6 MPa): When the demand for compressed air is stable and ≥100 m3/min, it is recommended to use centrifugal compressors; whereas when the supply of compressed air is not continuous or the amount of compressed air required