What is good for the gas used in heating and purging the expander?
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We use molecular sieves in the gas chamber of our expander for heating and blowing out air. However, no matter how effective the molecular sieve treatment is, the output air still contains trace amounts of moisture, carbon dioxide, hydrocarbons, and even impurities such as molecular sieve powder. This air then enters the distillation tower; the amount of such impurities is very small. Is it necessary to replace it with clean nitrogen? Thank you
No need to change. The dew point of the high-purity nitrogen exiting the column after purification by the purifier is also -60, which is the same
It’s more or less the same; ours also goes through a molecular sieve, and as long as attention is paid to the pressure during evacuation, there are no issues.
Generally, there is a concern that what comes after the molecular sieve may contain a small amount of moisture or molecular sieve powder; nitrogen is better as it is cleaner
You can choose to use nitrogen; since the molecular sieve isn’t effective, why not check the molecular sieve adsorber? Problems need to be addressed early; if a large amount of molecular sieve powder accumulates in the heat exchanger plates, things will become even more problematic! It’s important to detect and address it as early as possible! ! !
No matter what the gas is, as long as the main dew point is below -65°C, that’s fine! Of course, it cannot contain dust
Either gas is acceptable; reheat with pressure after the molecular sieve is faster, and this helps prevent overpressure in cases of low-pressure expanders or operations with liquid present after the compressor.
It is recommended to use contaminated nitrogen – the gas that comes out of the cryogenic tank; if there is anything present, it’s basically all remaining inside the tank, haha. Not much gas is needed for the expander regeneration; it accounts for only a very small portion of the nitrogen waste gas. The gas after passing through the molecular sieve has several drawbacks: 1. It affects the volume of gas entering the tower, especially in small air separation units. 2. There may be impurities such as dust, which can more or less affect the expander. This is just my personal opinion for reference only
No need to change. The air after passing through the molecular sieve is suitable; the temperature inside the expander gradually increases, so even trace amounts of water and carbon dioxide are not a problem. Using dirty nitrogen results in low pressure and slow flow rate. The temperature is slightly lower than that of air. If the molecular sieve is not good, it should be replaced.
Instrument air can also be used; it should work fine after passing through a filter following the molecular sieve.
There is a filter before entering the expander. Our heating process involves reverse blowing, but the air still passes through a filter; there’s no need to worry. Even if dust is present, it gets blown out through the outlet