Regeneration Principle of Molecular Sieve in PSA Air Separation Plant
For the PSA molecular sieve air separation plant, the molecular sieve is undoubtedly the core component of the system; only the clean compressed air is continuously adsorbed and regenerated through the molecular sieve, in order to continuously produce the nitrogen or oxygen we need.
Regeneration can be understood as the reverse process of adsorption; because after the molecular sieve completes a saturated adsorption, it cannot continue to adsorb gas, and it needs to “recover” its adsorption capacity, which is what we call “regeneration”.
Molecular sieve regeneration can help the molecular sieve to last as long as possible and maintain good working performance. Correctly regenerated molecular sieves have very low attenuation and aging of adsorption properties and mechanical properties. There are two methods for molecular sieve regeneration.
1. Change the temperature of PSA molecular sieve
It heats the molecular sieve, removes metal ions and combined water in the molecular sieve with low electricity price and large ionic radius, and restores it to the cavity state; in industrial production, it will be heated with preheated regeneration gas , to purge the molecular sieve and take away the desorbed adsorbate. Generally speaking, the regeneration temperature of molecular sieve is recommended to be 200-250 degrees. If the temperature is too high, the pores of the molecular sieve will be permanently blocked, and the molecular sieve will fail.
2. Change the relative pressure of PSA molecular sieve
Generally used in gas phase adsorption process. The basic method is to keep the temperature of the adsorbent constant, and remove the adsorbate by reducing the pressure and backflushing with inert gas.
Regeneration is usually carried out in reverse with adsorption. Most of the adsorbate contained at the inlet of the adsorption bed does not need to pass through the entire bed, which effectively reduces the contact between the molecular sieve and the hot and humid gas, and improves the service life of the PSA molecular sieve. Of course, the regeneration gas should be as dry as possible, otherwise it will affect the adsorption efficiency.
As for whether the regeneration is qualified or not, the usual way to judge is to look at the instrument. The regeneration time and temperature curve of the same tower recorded by the instrument remain normal, and the fluctuation value is stable; and the gas concentration (purity) of the sampled product when the same tower is put into adsorption again is all within the qualified range. Within the range, and the range of change is very small, it means that the regeneration is complete.
