A question for a beginner, related to air dew point!
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Generally, the dew point of the instrument air supplied by instrument air compressors ranges from -40 to -50. When this air is used as a sealing gas for liquid oxygen pumps and liquid nitrogen pumps, the operating environment temperature is even lower; could water precipitate in such conditions? Similarly, the pressure dew point of the air after passing through the molecular sieve is below -65, but the temperature inside the distillation tower is around 200 degrees Celsius; at such conditions, water should also precipitate!
Sure! Nitrogen is the best for the sealing gas of oxygen-nitrogen pumps! Requirements for purification gasifiers: below -70! It works better to perform a thorough heating cycle every time you drive the car!
Yes, nitrogen is generally used for sealing
Then why is instrument air still used for sealing in designs these days? What to do with the moisture that precipitates from the air entering the tower?
The sealing with nitrogen was modified by the users themselves; when designing the Air Liquide and Hangyang Oxygen equipment, instrument air was used for sealing. Don’t they know that water can precipitate?
It can’t be called precipitation; it’s more like freezing. The dew point of the instrument air is not within the specified range. When used as sealing gas for oxygen and argon pumps, freezing may cause blockages in the instrument air pipelines, so thorough heating and purging are necessary during shutdown!
Manufacturers generally require that the dew point of the sealing gas be below –60 degrees Celsius; the air at the instrument station is clearly not up to standard. It is recommended to use air that has passed through a molecular sieve – it’s no longer a problem related to water condensation, as crystallization occurs even at normal conditions. However, this level is still within the acceptable range for air separation units, which is why these units need to be thoroughly heated every two years~~
The instrument air supplied by the instrument air compressor station generally has a dew point of -40 to -50. Except in a very few extremely cold areas, where the use of molecular sieves can reduce the dew point to -90, the temperature inside the tower is still around -200; as a result, moisture will eventually crystallize. It is therefore appropriate to carry out heating operations every two years. In that case, there is no need to use instrument air as the sealing gas for the oxygen-nitrogen pump; even instrument air after passing through a molecular sieve would work fine. Using the product nitrogen directly is better – it contains no water, and even contaminated nitrogen will do!