Air compressor classification, working principle and air compressor selection

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Air compressor classification, working principle and air compressor selection

The air compressor is the main body of the air source device. It is a device that converts the mechanical energy of the prime mover (usually an electric motor) into gas pressure energy, and is a pressure generating device for compressed air. There are many types of air compressors, which can be divided into positive displacement compressors and speed compressors according to their working principles.

The working principle of a positive displacement compressor is to compress the volume of gas, increasing the density of gas molecules per unit volume to increase the pressure of the compressed air; the working principle of a speed compressor is to increase the movement speed of gas molecules, so that the gas molecules have kinetic energy The pressure energy is converted into gas, thereby increasing the pressure of compressed air. Commonly used gas compressors include centrifugal gas compressors and reciprocating gas compressors. Over the years, my country's compressor manufacturing industry has overcome many difficulties and made major breakthroughs on the basis of introducing foreign technology, digestion and absorption, and independent development. For example, the main fans and rich gas compressors used in catalytic cracking units, the circulating hydrogen compressors used in hydrogenation units, the new hydrogen compressors, the three major compressors for ethylene, and the four major compressor units for fertilizers have been widely used in petrochemical production. Among them, the manufacturing technology of horizontally split centrifugal compressors and axial compressors has approached or reached the international advanced level of similar products, and the reciprocating piston compressors have reached the international level of similar products.

2. Working principle of piston air compressor In pneumatic transmission, a positive displacement piston air compressor is usually used. Two typical structures are introduced here to help understand the working principle of air compressors. Figure 3.33 (animation) and Figure 3.34 (animation) respectively show the working principle diagrams of vertical and horizontal air compressors. The cylinder center line of the vertical air compressor is perpendicular to the ground, and the cylinder center line of the horizontal air compressor is parallel to the ground. The rotary motion of the prime mover (electric motor or internal combustion engine) is converted into the reciprocating linear motion of the piston by the crank connecting rod mechanism. The air intake and exhaust process in an air compressor is similar to the oil suction and pressure process of a hydraulic pump, so I won't repeat them here.

3. The choice of air compressor The choice of air compressor is mainly based on the working pressure and flow rate of the pneumatic system. The working pressure of the gas source should be about 20% higher than the maximum working pressure in the pneumatic system, because the loss along the way and the local loss of the gas supply pipeline should be considered. If the working pressure requirements in some parts of the system are low, a pressure reducing valve can be used to supply air. The rated discharge pressure of the air compressor is divided into low pressure (0.7~1.0MPa), medium pressure (1.0~10MPa), high pressure (10~100MPa) and ultra high pressure (above 100MPa), which can be selected according to actual needs.

4. Calculation process of air compressor selection The air supply volume of air compressor can be calculated according to the following empirical formula:

1MPa (megapascals) = 1000kPa (kilopascals) = 1000000Pa (Pascals)

 1bar (bar) = 0.1MPa  

 1atm (standard atmospheric pressure=0.1013MPa=1.013bar=760mmHg=10.33mH2O

  1kgf/cm2 (engineering kilogram force)=0.981bar=0.0981Mpa

  1psi (Lb/in2 )=0.07031kgf/cm2=0.06893kpa bar= bar

1MPa=145psi  Psi (lb/in2 ) pounds

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In the formula, qz-air compressor supply (m3/s); ψ-pneumatic equipment utilization factor K1-leakage coefficient, generally K1 = 1.15 ~ 1.5; K2-spare coefficient, generally 1.3 ~ 1.6; qj- The average free air consumption of a single device (m3/s). One point: The air flow involved in formula (3.36) refers to the air flow in the uncompressed free state. The conversion relationship between the actual compressed air flow and free air flow through each pneumatic device is

refrigeration compressor,compressor,Mitsubishi Compressor,Bristol Compressor,HITACHI Compressor,Danfoss compressor to solve the problem

In the formula, qj—free air flow rate (m3/s); qy—compressed air flow rate (m3/s); py—compressed air absolute pressure (MPa); pz—free air pressure (MPa); Tz—free air absolute Temperature (K); T—The thermodynamic temperature of compressed air (K). According to the above calculation and actual situation, you can select the air compressor of the corresponding model and specification from the product sample. Of course, when choosing an air compressor, the origin, quality, and service of the air compressor must also be considered.