Dew point is the critical temperature at which air is cooled to vapor saturation and liquid droplets begin to precipitate under constant pressure. The air separation industry generally uses dew point to represent the air moisture content, rather than the relative humidity and moisture ppm value, which mainly meets the operation requirements of air separation low-temperature process. The specific reasons are as follows.
First, the dew point can accurately reflect the absolute moisture content of the air, and the value is not affected by the ambient temperature. The relative humidity will fluctuate with the change of gas temperature. The relative humidity of the same wet air will increase significantly after cooling, so it is impossible to directly judge the real total moisture. When the total amount of air moisture is constant, the dew point value is always constant, and the measurement results are accurate and stable, which is suitable for continuous industrial monitoring.
Secondly, the dew point index is highly consistent with the low temperature condition of air separation. The air separation equipment relies on low-temperature rectification to separate oxygen and nitrogen. The water in the raw air is very easy to freeze in the low-temperature pipeline, heat exchanger and rectification tower, blocking the flow channel and damaging the equipment. The dew point directly corresponds to the critical temperature of moisture condensation and icing. The operation and maintenance personnel can directly predict the icing risk through the dew point value, quickly judge whether the pre dryer and molecular sieve adsorber are invalid, and control the bottom line of safe operation of the equipment.
Finally, the dew point measurement is convenient and the benchmarking industry standard is unified. Compared with the complex conversion process of PPM value of trace moisture, the dew point reading is intuitive and easy to understand, and the high and low values directly correspond to the moisture content: the lower the dew point, the drier the air. At the same time, the dew point is taken as the water content index in the domestic air separation industry, and the measurement standard is unified to facilitate equipment commissioning, daily inspection and troubleshooting.
