When the output of the air separation unit drops suddenly, the failure of the molecular sieve purifier is the core inducement of high frequency. It needs to be determined quickly and accurately and dealt with decisively to avoid more serious accidents caused by the freezing and blocking of the cold box.
First look at the core online indicators for judging the molecular sieve failure: the carbon dioxide content at the outlet of the purifier continues to be higher than 1ppm and does not fall back after switching, and the moisture dew point rises to above -65 ℃, basically confirming the adsorption penetration. Secondly, the regeneration curve was observed. The cold blowing peak value fell from above 120 ℃ to below 80 ℃ and the platform period was shortened, indicating that the adsorption capacity of molecular sieve decreased sharply and the analysis was not complete. Looking at the chain reaction at the back end, the temperature difference at the hot end of the main heat exchanger is increased, the resistance between the upper and lower towers is gradually increased, the liquid level of the main cooling is difficult to maintain, and the oxygen production and purity are simultaneously decreased, which are the secondary characteristics of molecular sieve failure.
It is necessary to strictly distinguish between true and false failures: the internal leakage of the program control valve, the failure of the regeneration heater, the excessive water in the air cooling tower, and the distortion of the instrument probe are all false failures. The molecular sieve itself is intact, and the valve and heating system can be recovered by troubleshooting; However, oil poisoning caused by air compressor oil leakage, long-term water hardening and pulverization, and expiration of service life are permanent failures, and the molecular sieve must be stopped and replaced.
Once the penetration failure is confirmed, the load shall be immediately reduced for operation, and the shutdown heating scheme shall be formulated simultaneously to thoroughly blow out the frozen water and carbon dioxide in the cold box, so as to prevent the sand removal maintenance caused by the complete blockage of the flow channel. It is necessary to strictly control the outlet water temperature and oil content of the air cooling tower, regularly detect the adsorption capacity of molecular sieve, and ensure the stable operation of the purification system from the source.
