Compression purpose and method of compressed air theory

Compression purpose and method of compressed air theory

The basic purpose of gas compression is to deliver gas at a pressure higher than the original pressure. The original pressure level may vary from a very low absolute pressure (a few thousandths of a kilogram) to several thousand kilograms; the pressure ranges from a few grams to several thousand kilograms; and the transmitted air volume ranges from a few cubic meters per minute to hundreds of thousands. Cubic meters per minute.

　　 There are various specific purposes for compression:

　　 　　 1. Transfer power in the compressed air system that drives the pneumatic tool;

　　 　　 2. Provide air for combustion;

　　 　　3. Transport and distribute gas in natural gas pipelines and city gas distribution systems;

　　 　　 4. Make the gas circulate through a process or system;

　　 　　 5. Create a more active condition for chemical reactions;

　　 　　6. ​​To create and maintain a higher pressure level than the original for various purposes, the method is to exhaust the gas leaking into or flowing into the system or the originally existing impurities out of the system.

　　 compression method

　　 　　 There are 4 ways to compress gas: 2 are the discontinuous airflow method, and the other 2 are the continuous airflow method (this is an explanatory terminology, not thermodynamic or functional classification). These methods should:

　　 　　 1. A certain amount of continuous gas is trapped in a certain container, its volume is reduced to increase the pressure, and then the compressed gas is pushed out of the container.

　　 　　 2. To trap a certain amount of continuous gas in a certain container, bring the gas to the exhaust port without changing its volume, compress the gas through the reverse flow of the exhaust system, and then push the compressed air out of the container.

　　 　　 3. The gas is compressed by the mechanical movement of the rapidly rotating rotor. The rotor transfers speed and pressure to the flowing gas (the speed is further converted into pressure on a fixed diffuser or baffle).

　　 　　4. Feed the gas into the high-speed nozzle of the same or another gas (usually, but not necessarily steam), and convert the high velocity of the mixed gas into pressure on the diffuser.

Compressors using methods 1 and 2 belong to the intermittent airflow category and are called variable-capacity compressors; those using method 3 are called speed compressors; those using method 4 are called jet compressors, whose intake pressure is generally lower than the atmosphere pressure.

　　 Types and characteristics of compressors

　　 　　The main types of compressors are listed in Figure 1A, and the definitions of various compressors are as follows. Compressors such as cam type, diaphragm type and diffusion pump are not included because of their special purpose and relatively small size.

　　 　　 positive displacement compressor-is to restrict a certain amount of continuous air flow in a closed space to increase the pressure.

　　 　　 reciprocating compressor-is a positive displacement compressor, its compression element is a piston, reciprocating in the cylinder.

　　 　　 rotary compressor-is a positive displacement compressor, compression is achieved by the forced movement of the rotating element.

　　 　　 sliding vane compressor-is a rotary variable capacity compressor, the axial sliding vane slides radially on a rotor eccentric to the cylinder block. The air trapped between the sliding plates is compressed and discharged.

　　 　　 Liquid-piston compressor-is a rotary positive displacement compressor in which water or other liquid acts as a piston to compress gas and then discharge the gas.

　　 Roots double-rotor compressor-a rotary positive displacement compressor, in which two Roots rotors mesh with each other to intercept the gas and send it from the inlet to the outlet. There is no internal compression.

　　 　　 Screw compressor-is a rotary positive displacement compressor in which two rotors with helical gears mesh with each other to compress and discharge gas.

　　 　　Speed ​​type compressor-is a rotary continuous flow compressor, in which high-speed rotating blades accelerate the gas passing through it, thereby converting speed energy into pressure. This conversion occurs partly on the rotating blades and partly on the fixed diffuser or reflux baffle.

　　 　　 Centrifugal compressor-a speed compressor, in which there are one or more rotating impellers (blade usually on the side) to accelerate the gas. The main air flow is radial.

　　 　　 Axial compressor-a speed compressor in which gas is accelerated by a rotor equipped with blades. The main air flow is axial.

　　 　　 Mixed flow compressor-also a speed compressor, the shape of its rotor combines some of the characteristics of both centrifugal and axial flow.

　　 　　 Jet compressor--Using high-speed gas or steam jets to take away the inhaled gas, and then convert the speed of the mixed gas into pressure on the diffuser.