Application of pressure dew point in compressed air system

Application of pressure dew point in compressed air system

The air that is reduced in volume and increased in pressure by the mechanical movement of the air compressor is called compressed air. Compressed air is an important power source and is widely used in many industrial fields such as machinery, metallurgy, electronics, electric power, medicine, packaging, chemicals, food, mining, textiles, and transportation. However, compressed air contains water, oil mist, impurities and solid particles, so the compressed air must be filtered and purified to produce dry, dust-free, and oil-free compressed air. The filter can eliminate oil and dust, but the moisture must be processed by a dryer.

　　 Dew point temperature (Td)

　　 refers to the temperature at which water vapor saturated with water in the air begins to condense, that is, the temperature at which condensation occurs. At 100% relative humidity, the ambient temperature is equal to the dew point temperature. The lower the dew point temperature is than the ambient temperature, the smaller the possibility of condensation and the drier the air. The dew point is not affected by temperature, but by pressure.

　　 Moisture in compressed air

　　As the compressor compresses the air, the dew point of the gas rises. At some point, the water in the gas is saturated and condensation begins. Therefore, water treatment must be considered. For example, a 30-kilowatt compressor can produce about 20 liters of liquid during 8 hours of working time when compressing air at 20°C and 60% RH.

　　 The moisture in the compressed air will have an adverse effect on the production process, not only affecting the quality of the final product but also causing harm to the compressed air system. Moisture can cause many hazards, such as adhesion of moisture-absorbing products (such as the sugar industry); foaming in the coating process (such as "fish eyes" in the spray painting process).

　　Most compressed air systems use steel or non-galvanized steel. When they come in contact with compressed air containing more water, they will corrode. The dust and peeling rust in the pipeline will blow into the sensitive equipment along the gas path, causing system failure. If part of the system is installed outdoors, excessive moisture will cause freezing in winter.

　　 Dew point measurement can save energy better:

　　Reliable dew point measurement can accurately control whether the dryer is working within the technical indicators. For adsorption dryers, the regeneration interval can be controlled by measuring the dew point and save a lot of energy for users. Unlike the traditional timer method, as long as the compressed air is dry within the range required by the user, the system will not start the regeneration function. Dew point control can save users up to 80% of energy costs.

　　 Typical compressed air dryer working environment:

　　1. Dew point (Td):

　　Refrigeration dryer +3℃/7℃/10℃

　　 desiccant dryer -20℃/-40℃/ -70℃

　　2, output pressure 7bar, maximum 10bar

　　3, T output up to +40℃