The principle and characteristics of screw air compressor and ordinary air compressor

The main compressor is divided into piston, screw and centrifugal. Pistons are rarely used now, old machines. Use a screw with a small amount of gas and centrifuge with a large amount of gas.

Structure and working principle
1. Piston oil-free lubricated Air compressor
Piston oil-free lubricated Air Compressor is composed of compressor main unit, cooling system, regulating system, lubrication system, safety valve, motor and control equipment. The compressor and the motor are fastened to the base with bolts, and the base is fixed to the foundation with anchor bolts. When working, the motor directly drives the crankshaft through the coupling, drives the connecting rod, the crosshead and the piston rod, and makes the piston reciprocate in the compressor cylinder to complete the suction, compression, and discharge processes. The machine is a double-acting compressor, that is, the piston moves upwards and downwards, all have air suction, compression and discharge.
2. Screw air compressor
Screw air compressor is composed of screw head, motor, oil and gas separation barrel, cooling system, air conditioning system, lubrication system, safety valve and control system. The whole machine is installed in a box, which is self-contained and can be placed directly on the flat concrete floor without fixing it with anchor bolts. The screw head is a kind of dual-shaft displacement rotary compressor head. A pair of high-precision main (male) and auxiliary (female) rotors are installed horizontally and parallel inside the casing. The main (male) rotor has 5 teeth and the auxiliary (female) rotor has 6 teeth. The main rotor has a large diameter and the auxiliary rotor has a small diameter. The teeth form a spiral shape, and the two mesh with each other. Both ends of the main and auxiliary rotors are respectively supported and positioned by bearings. During operation, the motor directly brings the main rotor through the coupling (or belt). Since the two rotors mesh with each other, the main rotor directly drives the auxiliary rotor to rotate together. The cooling liquid is directly sprayed into the rotor meshing part by the nozzle in the lower part of the compressor casing, and is mixed with the air to take away the heat generated by the compression to achieve the cooling effect. At the same time, a liquid film is formed to prevent direct metal-to-metal contact between the rotors and to close the gap between the rotors and the casing. The injected coolant can also reduce the noise generated by high-speed compression.
The main components of the screw air compressor are the screw head and the oil-gas separation barrel. The screw head sucks air through the suction filter and the intake control valve, while oil is injected into the air compression chamber to cool and seal the head and lubricate the screw and bearings. The compression chamber generates compressed air. The compressed oil-gas mixture gas is discharged into the oil-gas separation barrel. Due to the mechanical centrifugal force and gravity, most of the oil is separated from the oil-gas mixture. Air passes through the oil and gas separation cylinder core made of boron silicate glass fiber, and almost all the oil mist is separated. The oil separated from the oil-gas separation cylinder core returns to the screw head through the oil return pipe. An oil filter is installed on the oil return pipe. After the oil return is filtered by the oil filter, the clean oil flows back into the screw head. When the oil is separated, the compressed air leaves the oil and gas cylinder through the minimum pressure control valve and enters the aftercooler. The after-cooler cools the compressed air and discharges it to the air storage tank for use by each air-consuming unit. The condensed water is concentrated in the air storage tank and discharged through an automatic drain or manually.
Features
1. Piston oil-free lubricated air compressor
The piston ring in the cylinder of the oil-free lubricated air compressor and the packing in the packing device are filled with self-lubricating polytetrafluoroethylene as the sealing element. Therefore, the cylinder and the packing device do not need to be lubricated with lubricating oil. Under normal circumstances, the compressed gas is basically pure and free of oil pollution, and there is no need to add an oil removal device. The shortcomings of this machine are that the motor power is too large, the exhaust pressure is not stable enough, the exhaust temperature is high, the noise is too large, the maintenance workload is large, and the maintenance cost is too high.
2. Screw air compressor
The precise cooperation between the male and female rotors of the screw air compressor and the rotor and the casing of the body reduces the gas return leakage and improves the efficiency; only the inter-rotation of the rotors and the reciprocating movement of the cylinders reduce the source of vibration and noise. The unique lubrication method has the following advantages. With the pressure difference generated by itself, it continuously injects cooling fluid into the compression chamber and bearings, which simplifies the complex mechanical structure; the injection of cooling fluid can form a liquid film between the rotors, and the auxiliary rotor can be directly The main rotor is driven without the help of high-precision synchronous gears; the injected coolant can increase the effect of air tightness, reduce the noise caused by high-frequency compression, and also absorb a large amount of compression heat. Therefore, the single-stage compression ratio is even Up to 16 can also prevent the exhaust temperature from being too high, and there will be no friction between the rotor and the casing due to different thermal expansion coefficients. Therefore, the screw air compressor has the advantages of low vibration, no need to be anchored on the foundation, low motor power, low noise, high efficiency, stable exhaust pressure, and no wearing parts. The shortcoming of this machine is that the compressed air contains oil, and its oil content is 1 ~ 3 × 10-6. For the process with strict requirements on the oil content of compressed gas, an oil removal device needs to be added. The plant's compressed air system has added a two-stage oil removal device. Because the compressed air in the ADC process directly contacts the product ADC foaming agent, the quality of the air is more demanding, and the gas used in the ADC process has a three-stage oil removal device. See Table 1 for the comparison of compressor performance parameters.
Major failure
1. Piston oil-free lubricated air compressor
The piston ring and packing device of this machine do not need oil injection and lubrication. Under normal circumstances, the compressed gas is basically pure and does not contain oil, but because the oil scraping ring often scrapes the oil incompletely and the seal is not good, oil often runs on the packing device or even the piston ring, so that the compressed gas contains oil. In addition, the exhaust temperature is high, sometimes as high as 200 ℃; the cooler is clogged, so that the cooling effect is not good; the piston ring is stained with oil, and it is particularly easy to wear; the valve racket leaks; the cylinder liner wears etc.
2. Screw air compressor
The screw air compressor has few failures, as long as it regularly maintains the oil and gas separator, air and oil filter, etc., it can ensure its normal operation. The maintenance of the two 10m3 screw machines used for maintenance is clogged sewage pipes and control panel failures. The host system has been operating normally for 2 years.
Conclusion
From the use effect, the screw air compressor has the unparalleled advantages of the piston air compressor, which not only reduces the labor intensity of the operator, but also does not need to be equipped with a maintenance worker, which greatly reduces the maintenance cost. On the other hand, when the piston machine is used, the exhaust pressure is occasionally too low, which causes the ionic membrane control system to alarm. After switching to the screw machine, the exhaust pressure is set at 0.58MPa, the pressure remains stable, and there has not been any exhaust. The pressure is too low to cause the alarm of the ion membrane control system, thus ensuring the safe production of the ion membrane system.