The differences between oil-injected and oil-free screw air compressors

The rotor of the oil-free screw air compressor does not directly touch each other, and there is a certain gap between them. The outer rotor drives the inner rotor to rotate through a synchronous gear, ensuring the gap between the rotors during power transmission. The term "oil-free" means that the gas is not in contact with oil during the compression process, but the bearings and synchronous gears of the compressor still require lubricating oil, but only between these lubrication components and the compression chamber. An effective sealing system is used to isolate the oil-injected screw compressor. A large amount of lubricating oil is injected into the compressed gas medium for lubrication, sealing, cooling, and noise reduction. The oil-injected screw compressor has no synchronous gear. The anode rotor directly drives the rotation of the cathode rotor. The lubricating oil not only reduces the exhaust temperature but also provides lubrication for bearings, mechanical seals, sliding valves, etc.

Since the rotors of the oil-free screw air compressor do not come into contact with each other, the medium gas and lubricating oil are separated by the shaft seal, so there is no direct contact. Therefore, the oil-free screw air compressor has been widely applied in waste gas recovery. Coke oven gas recovery, coal seam gas boosting,变压吸附 and other medium gases contain dust and liquids， and the gas composition changes greatly. The oil-free screw compressor can meet the long-term continuous operation requirements of industrial production, and the continuous uninterrupted operation time is 24，000 hours. The volumetric efficiency of the oil-free screw air compressor is lower than that of the oil-filled screw air compressor. Generally speaking， the single-stage pressure ratio does not exceed 10.

The rotor of the oil-injected screw compressor directly meshes and transmits, resulting in high volumetric efficiency. The single-stage pressure ratio can reach over 10. However, due to the direct contact between the lubricating oil and the process medium, the medium gas should be relatively clean and should not contain a large amount of impurities and water; otherwise, it will affect the lubricating oil. Additionally, it is necessary to select lubricating oil that does not react with the medium gas during the selection process. Usually, this is a special synthetic oil. Therefore, oil-filled screw air compressors are typically used for medium-pressure gases in single working conditions, such as air compressors and refrigeration compressors, etc.