Fluctuations in the liquid-air level of the lower column liquid in the air separation tower
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Recently, the liquid air level in the lower column of the air separation tower at my company has been experiencing periodic fluctuations (the target value is 800 mm; the fluctuation cycle is 1 hour, with the level dropping suddenly from 810 mm to 750 mm before rising slowly back to the normal value over 10 minutes). These fluctuations cause the liquid level control valve to respond to the level switch, thereby leading to process instability. I would be extremely grateful if experts could help identify the reasons behind these periodic fluctuations in the liquid air level
The main issue in such cases lies in the proper distribution of the primary cryogenic liquid nitrogen; the amount of liquid nitrogen sent to the upper column should be reduced slightly to stabilize the reflux liquid in the lower column. Such issues are discussed in great detail at Air Separation Home or in the Air Separation Home group (36792049).
Check whether it is due to these reasons: 1) The pressure control valve in the upper tower becomes stuck, which causes the tower pressure to drop when dirty nitrogen gas is used for regeneration, thereby leading to periodic fluctuations; 2) The pressure control valve in the lower tower experiences periodic \"valve surging\"; 3) An excessive amount of expanded air enters the upper tower, causing fluctuations.
First of all, I want to state that I’m not an expert. 1. Check the operating condition of the level control valve, its sensitivity, and whether it can keep up with fluctuations in the liquid level. 2. Check for any abnormalities in the regeneration system. 3. Check whether the process operations are correct. Whether it is in a liquid suspension.