1. Lubrication of the air compressor

Air compressors can be divided into the following three categories according to the lubrication method: oil-free compressors, the compressed air does not contact the lubricating oil; oil-lubricated compressors.the moving parts in the compression chamber are lubricated with oil, and the lubricating oil is lubricated by a special oiler or by supply of other parts of the compressor; oil-injected rotary compressor, a large amount of lubricating oil is injected into the compression chamber, the lubricating oil not only lubricates the moving parts, but also helps to seal and absorb the heat of compression.

Use of lubricating oil

Generally, the brand and grade of lubricating oil recommended by the air compressor manufacturer should be used. If other lubricating oils are used, the air compressor manufacturer should be consulted. Oxidation of oil can form acetaldehyde, which has a low autoignition temperature, and is therefore potentially dangerous. The classification of lubricating oil and its typical application in air compressors are in accordance with the provisions of GB/T 7631.9. The high temperature safety switch of the oil-injected air compressor should be set to no higher than the maximum exhaust temperature +10°C, and the industry generally believes that the regulation should not exceed 120°C. For oil-lubricated air compressors operating in the open air or in a non-hot machine room, at the lowest possible ambient temperature, the calculated viscosity of the lubricating oil should not exceed 2000mm2/s, and the freezing point should be about 5°C lower than the lowest ambient temperature.

If the ambient temperature is particularly high, lubricating oil with a high viscosity grade must be used. Special care is required to ensure that the lubricant is non-toxic where air may be drawn in. The oil supplier shall provide information to enable the user to assess any health hazards associated with the intended use of the compressed air. The limit value of oil mist in air is usually set at 5mg/m3. The lubricating oil that meets the lubrication requirements and has the lowest viscosity should be selected, and the lubricating oil must be suitable for start-up at the lowest ambient temperature and operation at the highest ambient temperature. In special cases, lubricating oils of different viscosity grades can be used according to different seasons of the year.

2. The mechanism of spontaneous combustion of carbon deposits and the cause of oil explosion

The oil and compressed air are prone to oxidation reaction, and the speed of oxidation reaction increases with the increase of temperature, partial pressure of oxygen, and particles of iron or iron oxide that act as catalysts. The oxidation reaction will increase the viscosity of the oil, and if the oil stays in the hot zone for sufficient time, carbon deposits may form in the air compressor exhaust system. These carbon deposits continue to be oxidized, and the oxidation reaction produces exothermic phenomena, so there is a necessary condition for spontaneous combustion.

In fact, on the one hand, the heat generated by the oxidation reaction is cooled and taken away by the compressed air flow above the carbon deposit layer, and at the same time, it is transferred to the metal wall where it is located through the carbon deposit layer. When the heat generated by the oxidation reaction cannot be taken away in time, the temperature of the soot layer will rise. In special cases, it will reach the temperature of the spontaneous combustion of the soot layer, and generate enough heat to weaken or soften the metal on the wall of the pressure system. . Although no actual explosion occurs, such a sudden rupture of the vessel wall can be mistaken for an explosion.

3. Fire and explosion of pressure system

(1). Oil lubricated compressor

Generally, fire accidents in the pressure system of oil-lubricated air compressors are caused by carbon deposits. When selecting lubricants, the air compressor and pressure system should be clean and free of carbon deposits, which will reduce fire accidents. For pressure systems that produce carbon deposits, the grade of the oil is more important, as is regular cleaning of the pressure system.

(2). Oil-injected rotary compressor (special precaution)

Experience has proven that good design, lubrication and maintenance can prevent oil-injected rotary air compressors from catching fire. However, due to the abnormal temperature rise caused by the oil filter core, the oxidation of the oil is accelerated, and there is also a risk of fire.